CA1104881A - Process for producing microcapsules having secondary capsule walls and microcapsules produced thereby - Google Patents
Process for producing microcapsules having secondary capsule walls and microcapsules produced therebyInfo
- Publication number
- CA1104881A CA1104881A CA302,327A CA302327A CA1104881A CA 1104881 A CA1104881 A CA 1104881A CA 302327 A CA302327 A CA 302327A CA 1104881 A CA1104881 A CA 1104881A
- Authority
- CA
- Canada
- Prior art keywords
- microcapsules
- capsule wall
- aqueous dispersion
- aldehyde
- condensation polymer
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
- B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
- B41M5/00—Duplicating or marking methods; Sheet materials for use therein
- B41M5/124—Duplicating or marking methods; Sheet materials for use therein using pressure to make a masked colour visible, e.g. to make a coloured support visible, to create an opaque or transparent pattern, or to form colour by uniting colour-forming components
- B41M5/165—Duplicating or marking methods; Sheet materials for use therein using pressure to make a masked colour visible, e.g. to make a coloured support visible, to create an opaque or transparent pattern, or to form colour by uniting colour-forming components characterised by the use of microcapsules; Special solvents for incorporating the ingredients
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
- B01J13/02—Making microcapsules or microballoons
- B01J13/06—Making microcapsules or microballoons by phase separation
- B01J13/14—Polymerisation; cross-linking
- B01J13/18—In situ polymerisation with all reactants being present in the same phase
Abstract
Abstract of the Disclosure This invention relates to filterable microcapsules and to a process for preparing such microcapsules which are advan-tageous in the preparation of hot melt coating compositions for pressure-sensitive carbonless copy papers in that the micro-capsules are produced in an aqueous continuous phase and the microcapsules can be easily removed by the aqueous dispersion by vacuum filtering. The process comprises preparing an aqueous dispersion of microcapsules containing an oil solution of a chromogenic material, the chromogenic material being an electron donor type color precursor, and the microcapsules having a primary capsule wall comprising a reaction product of hydroxy-propylcellulose and at least one oil soluble cross-linking agent for hydroxypropylcellulose. The cross-linking agent is selected from the group consisting of the polyfunctional isocyanates, acyl chlorides, phosphoryl chlorides, sulfonyl chlorides, alkylene bischloroformates and mixtures thereof, the primary capsule wall being substantially oil and water impermeable.
There is then added and mixed into the aqueous dispersion of microcapsules a phenol and an aldehyde, the aldehyde being selected from the group consisting of acetaldehyde, formaldehyde, glyoxal, glutaraldehyde, fu?fural and mixtures thereof. The mixing is maintained while the phenol and the aldehyde react together to form a condensation polymer, the condensation polymer being insoluble in the aqueous dispersion of micro-capsules thereby precipitating the condensation polymer on the primary capsule wall as a secondary capsule wall.
There is then added and mixed into the aqueous dispersion of microcapsules a phenol and an aldehyde, the aldehyde being selected from the group consisting of acetaldehyde, formaldehyde, glyoxal, glutaraldehyde, fu?fural and mixtures thereof. The mixing is maintained while the phenol and the aldehyde react together to form a condensation polymer, the condensation polymer being insoluble in the aqueous dispersion of micro-capsules thereby precipitating the condensation polymer on the primary capsule wall as a secondary capsule wall.
Description
~(kcJrouncJ oF_the Invel!tion Fielcl oF tr!a Irlventioll:
This invention relates to the pro~uc-tion o-f microcapsules contain-ing an oil an~ having a prilnary capsule wall oF a reac-tion product o~ hydroY~y-propylcellulose ancl a cross l-inking a~ent and a secondary capsule wall forme~
by the reaction of a phenol and an aldehyde. The microcapsules produce~ by the process o-F this invention are particularly adaptable For use in preparing pressure-sensitive carbonless trans~er papers.
Prior Art:
A process for the production oF microcapsules containing oils using coacervation is disclosed in U.S. Patent 2,800,457 (1957) to Green et al. The process described therein involves the coating of oil droplets with a liquid wall of gelatin-gum arabic colloidal material produced by coacervation. The liquid wall is hardened by treatment with formaldehyde. Microcapsules made by the process oF Green et al have had wide commercial acceptance, particular--ly in the fiëld of pressure-sensitive carbonless copy papers.
Since that time, microcapsules have been made using many types of wall-forming materials, wall-forming processes and wall structures. The microcap-; sules produced have been suggested For many uses, including the encapsulation of aromas, per'umes, flavoring agents, adhesives, reactants, color reactants, pharmaceuticals, pigmenis and as opacifyin~ agents. The nature of the ma~er-ial to be encapsulated and ultirnate use o-F the microcapsules many times dic-tated the materials, structure and process of making them.
Dual-walled microcapsules having inner ~primary) walls and outer (sec-ondary) walls oF difFerent wall-Forming materials are kno~n From the Following:
;~ U. S. Patent 2,9O9,331 (1961) Brynko et al U. S. Patent 3,551~3~6 (1970) Breen et al U. S. Patent 3,578,605 (1971) Baxter , , ~ .
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It -is also known from tile follo~ ti-~at sin(Jl~ (l m-icrocapsules could be m~de in ~Ihich -the ~Jall-forming material -is a contlensation polyrner o-f resorcinol and an aldehycle:
U. S. Patent 3,755,190 (1973) to l-lart et al.
U. S. Pa-tent 3,816,331 (1974) to ~rown, Jr. et al Canadian Patent 879,043 (1971) to Bayless Additionally, the following pa-tents disclose processes for producing an aqueous dispersion of microcapsules containing an oil. The microcapsules have hydrophilic (water-swellable) polymeric capsule walls which are ir;lpre~-nated with or otherwise contain resorcinol which is then reacted.with Pormal-dehyde.
U. S. Patent 3,576,660 (1971) to Bayless et al U. S. Patent 3,726,803 (1973) to Bayless et al U. S. Patent 3,803,046 ~197~ to Matsukawa et al 1~ Carbonless copy paper, briefly stated, is a standard type of paper wherein during manufacture the backside of the paper substrate is coated with what is reFerred to as a CB or transfer coating, the CB coating containing ~. .
--- one or more chromogenic materials, generally in capsular form. At the same time the -front side of the paper substrate is coated during manu-facture~with what is referred to as a ~F coating, which contains ane or more chromogenic material. Both the chromogenic materials remain in the coatings on the re-spective back surfaces of the paper in substantially colorless -Form. This is true until the CB and CF coatings are brought into o~erlying relationship and ~: - sufficient pressure~ as by a typewriter, is applied to rupture the ce coating to release the encapsulated chromogenic material. At this time the chromo-genic material contacts the CF coatin~ and reacts with the chromogenic mater-~ ial therein to form a colored image. Carbonless copy paper has proved to be .~ an.exceptionally valuable image transfer media for a variety of reasons7 only one of which is the fact that until a CB coating is placed next to a CF
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coa-ting both the CB antl t~le CF coat-ings are in an inactive sta-te as the co-reactive elernents are not -in coiltact ~`I-ith one another until pressure is appliecl Patents relating -to carbonless copy paper pro~ucts are:
U. S. Paten-t 2,~50,456 (1951) to Green et ai U. S. Patent ~,712,507 (1955) to Green U. S. Pa-ten-t 2,730,456 (1956) to Green e-t al U. S. Patent 3,016,308 (1962) to Macaulay U. S. Patent 3,170,809 (1965) to Barbour U. S. Patent 3,455,721 (1969) to Phillips et al U. S. Patent 3,466,184 (1369) to Bowler et al U. S. Patent 3,672,935 (1972) to Miller et al U. S. Patent 3,955,025 (197~) to Matsukawa et al U. S. Patent 3,981,523 (1976) to ~aalouf A disadvan-tage oF coated paper products such as carbonless transfer papers stems from the necessity of applying a liquid coating composition containing the color forming ingredients during the manufacturing process.
In the application of such coatings, volatile organic solvents are sometimes r used which then in turn requires evaporation of excess ~olvent to dry the coating thus producing volatile solvent vapors. An alternate method of coating involves the application of the color forming ingredients in an aque-ous slurry, again requiring removal of excess ~Jater by drying. Both methods suffer from serious disadvantages. In particular the organic solvent coating method necessarily involves the production of generally volatile solvent va-pors, crea-ting ~oth a health and a ~ire hazard in the surrounding environment.
When using an aqueous solvent system the water must be evaporated which in-volves~the expenditure of significant amounts o-F energy.~ Further, the neces-:`
sity of a drying step requires the use of complex and expensive appara-tus to - continuously dry a substra-te which has been coated with an aqueous coating compound. The applicatlon of heat not only is expensive~ making the total :
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~aper manufacturing operation less effective, but also is potenti-ally damaging to the encapsulated chromogenic materials which are generally coated onto the paper substrate during manufacture. High degrees of temperature in the drying step :require specific formulation of coating compositions which permit the use of excess heat. The problems encountered in the actual coating step are generally attributable to the necessity for a heated drying step following the coating operation.
In an attempt to overcome the difficulties associated with the coating and drying of microcapsular compositions as noted above, attempts have been made as disclosed in the prior art to use liquid coatings containing substantially no volatile solvent.
Notable among these attempts are the use o~ hot melt coating compositions as disclosed in the following patents:
U.S. Patent 3,016,308 (1962) to Macaulay U.S. Patent 3,079,351 (1963) to Staneslow et al U.S. Patent 3,864,549 (.1972) to Shank The use of hot melt coatings containing microcapsules for CB transfer coatings is disclosed in both Staneslow et al and Macaulay. Macaulay also discloses preparation of hot melt CB
coating compositions using spray dried microcapsules. Improved ; coating compositions containing microcapsules having improved dispersion of the microcapsules within the hot melt suspending media are disclosed in U.S. patent no. 4,143,890 issued on March 13, 1979.
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The process of the present invention provides a novel method by which novel dual-walled microcapsules can be produced.
Use of these micxocapsules is particularly advantageous in the preparation of hot melt coating compositions for pressure-sensitive ~; carbonless copy papers. The microcapsules are produced in an aqueous continuous phase and the microcapsules can be easily removed from the a~ueous dispersion by vacuum filtering. The still wet microcapsules can be easiIy incorporated into a hot melt in a : .
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disclosecl ill the above-c-e-,~e~linc~-~t~ ic-atiol~. Acldit-ional advanta~es of the micrucaps-lles are h-igh stren~th and their capability o-F being rnore eFfic-iently usecl-than nlost prior ar-t n~icrocapsules in the produc-tion oF cetransfer coatings. Reductions in microcapsular coat we-ights are thus S possible.
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Sta-tement of the Invention This invention relates to a process for preparing filterable microcapsules comprising the followiny steps: There is prepared an aqeuous dispersion of microcapsules containing an oil solution of a chromogenic material, said chromogenic material being an electron donor type color precursor. The microcapsules have a primary capsule wall comprising a reaction product of hydroxypropylcellulose and at least one cross-linking agent for hydroxypropylcellulose. This cross-linking agent is selected from the group consisting of the polyfunc-tional isocyanates, acyl chlorides, phosphoryl chloride~, sulfonyl chlorides, alkylene bischloroformates and mixtures thereof. The primary capsule wall is substantially oil and water impermeable. A phenol and an aldehyde is added and mixed into the a~ueous dispersion of microcapsules. The aldehyde is selected from the group consisting of acetaldehyde, formal-dehyde, glyoxal, glutaraldehyde, furfural and mixtuxe~ thereof.
Mixing is maintained while t~e phenol and the aldehyde react together to form a condensation polymer. The condensation polymer is inlsoluble in the aqueous dispersion of microcapsules whereby the condensation polymer is precipitated on the primary capsule wall as a secondary capsule'wall. A binder can be 'added to the microcapsules and the coating composition can be' applied to a substrate.
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The invention ~urther relates to microcapsules containing an oil solution of a chromogenic material, said chromogenic material being an electron donor type color precursor. The microcapsules ha~e a primary capsule wall and a secondary capsule wall which surrounds and adheres to the primary capsule wall. The primary capsule wall comprises a reac-tion product ~; of hydroxypropylcellulose and at least one cross-linking agent for hydroxypropylcellulose. This crcss-linking agent is' selected from the group consisting of the polyfunctional isocyanates, acyl chlorides, phosphoryl chlorides, sulfonyl 7 ~
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chlorides, a].kylene bischloroformates and mixtures -thereof.
The primary capsule wall is substantially impermeable to oil and water. The secondary capsule wall comprises a conden-sation polymer of a phenol and an aldehyde. The aldehyde is selected from the group consistiny of acetaldehyde, formal-dehyde, glyoxal, glutaraldehyde, furfural and mixtures thereof.
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.; ' , i~ta e~ Descri~t-ion of_ he Invent~0~1 The process o~ this in~ention is concerne~ with a further treatment ; of known microcapsules having substantially impermeable ~lalls comprisiny the reaction product of hydroxypropylcellulose and at least one oil soluble cross-linking agent for hydroxypropylcellulose. The treatment involves adding to an aqueous dispersion of microcapsules,as defined above,a phenol and an aldehyde.
The phenol and aldehyde react with each other to Form a condensation polymer.
The condensation polyrner, beins insoluble in the aqueous continous phase oF thedispersion, precipitates on the primary walls of -the microcapsules as secondarywalls. Microcapsules produced by the process of this invention are effective-ly dual walled in that a secondary capsule wall oF precipitated condensation polymer deposits on the primary cross-linked hydroxypropylcellulose wall.
In a pre~erred embodiment oF this invention, microcapsules having a primary capsule wall are produced according to the process disclosed in U.S.
l~ Patent ~,025,455 issued May 24, 1977 to Dale Richard Shackle and assigned to The Mead Corporation o-F Dayton, Ohio. Microcapsules as disclosed in U. S
Patent 4,025,455 have a cross-linked hydroxypropylcellulose primary wall formed by the re.action oF hydroxypropylcellulose in an aqueous continuous phase with at least one cross~linking agent -For hydroxypropylcellulose in a dispersed oil phase. The microcapsules m y contain a chromoyenic material dissolved in the oil phase. The resultant primary wall is substantially impermeable to the microencapsu1ated oil and the water in the aqueous contin-uous~ phase. The hydroxypropylcellulose, hereinaFter sometimes referred to as HPC,is a fil~ orlning cellulosic ether polymer soluble in cold water, but insoluble in hot water. The commercially available polymers have a molar substitution (M.S.) of about three to five hydroxypropyl units to each cell-ulose unit. A particular group o~ hydroxypropylcelluloses are manu-Factured by Hercules~ Inc. and sold~by them under the trade ~m~ of~hvei~. These ~; polymers precipitate out of a ~Yater so1ution at a temperature of about 45 C
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an~I pre-Ferably At from about ~5 (` to a~out 52 C zs a finel~ cli~i~ed suIi~
precipitate. The polymers are ava-iIabIe in a var-iety of viscosity -types.
The lo~Ier viscosity types, G, J, L an~ E are preFerred for use in this in vention. OF these, Type L haYiny a molecule ~Ieight of ~pproximacely 75,000 and an M.S. of approximately three has been found -to be par-ticularly useful.
The aqueous phase, con-taining ~IPC, can be prepared by dissolv-iny the HPC in water at a temperature below 40 C, preferably at frorn about 10 C -30 C. To facilitate the preparation, the HPC can be dispersed in the water at 45 C or above prior to lowering the ternperature of the dispersion to below 4G C to dissolve the HPC. The concentration of the HPC is not critical~ but would clepend on the ratio of aqueous phase to the material to be encapsula~ed~
the size of the desired oil solu-tion droplets and the desired thickness of the microcapsular ~Jalls. Aqueous solutions containiny from about 0.2% to about 6%, preferably 1.5% to ~%, of HPC are used in the preparation of the aqueous phase.
The oil phase is prepared by combining an oil soluble cross-linking agent for the HPC wall-forming compound with an oil. The oil solution can be prepared by adding and stirring the oil soluble cross-linking agent to the oil while the mixture is cool, preferably below 15 C. The choice of oil depends largely on the final utiliza-tion o-F the microcapsules. If, for example~ the microcapsules are to be used in preparing pressure~sensitive paper~ the oil should be a carrier oil for a chromogenic~aterial. Such carrier oils are preferably monoisopropylbiphenyl (MIPB), ch70rinated biphenyls,~alkylnaphtha~
Ienes, kerosene, petroleum naphtha or mixtures thereo~.
The oil soluble cross-linking agents used in this embodiment for form ing the oil phase are those conta;niny more than one group capable of reacting with hydroxyl groups thus providing the desired cross-linkage with the HPC
wall-forming compound. The cross-linking agents must be soluble in the oil phase and not: reactable with the oil: or interfere with the desired func-; 30 tion o~ any omponent of the oil phase~ For example, if an oil solution o~
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color precur~or is clesire~ to be encapsuldt~d and coated on p~-per, the cross-linking agerl-t should Ilot interfere ~Ii-th the color producing func~ion o-F the resultan-t paper. In general poly-Functional isocyanates, acyl chlor-ides, sulfonyl chlorides, alkylene bischloroformates or mixtures thereof can be ùsed. If microcapsules -for use in the preparation oF pressure-sensitive papers are desired, the polyfunctional isocyanates or prepolyrners conta-ining more than one reactive isocyanate group are preferred. The concen-tration of the oil so~uble cross-linking agent in the oil phase is no-t critical. The degree of cross-linking desired is dependent on the encl utilization of the microcapsules. For example, if the microcapsules are to be incorpora-ted into an aqueous coating composition, sufficient reactive groups must be present to react ~lith available hydroxyl groups of the wall-forming compound to render the wall-forming compound water insoluble. It has, however, been shown that the superior microcapsules Formed by the process oF this invention are a pro-duct o-F the use of HPC and not the particular oil soluble cross-linking agent.
In particular9 any of the cross-linking agents exhibiting the above reci~ed characteristics can be used in combination with HPC to produce the desired microcapsules.
EmulsiFication of $he oil phase in the aqueous phase can be accomplished by adding the oil phase to the aqueous phase with vigorous mixing. Mixing may be by stirring, shaking or millIng. During the mixing operation, the tempera-ture of the mixture must be kept below the temperature at which the HPC wall :
forming compound precipitates. A small amount oF an emulsifier, such as about .25% by weight Turkey Red Oil (sulfonated castor oil) can be added to the aqueous phase prior to mixing. However, the hydroxypropylcellulose acts as an emulsifier and an acceptable dispersion oF drople-ts can be obtained in the absence~of an additional emulsifier. Droplet sizes of about 1 micron to about 100 mlcrons can be produced.
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AFter th~ clesire~ cI ropl e t si 7.e i s obta-ined, tiI~ mixe(I ernuision is heated ~)ith mild ayita-tion to a teIrlperatur~ abo~e -the prec-ipitation temperature of the HPC wall-forrning compound. lhe wall formin~ compound precipi-tates nn the droplets to form rnicrocapsule walls. The ternperature increase promotes cross-linking of the ~IPC wall Formin~ compoun~ ~Iith the oil solu-ble cross-linking agent. The -temperature can be main-tained ~Iith continued - agitation o-F the mixture For a sustained perio~ of -time, pre-Ferably more than about 1 hour, and most pre-Ferable 3 to 16 hours, if microcapsules of low oil and water permeability are desired. However, longer periods do not appear to be detrimental. The exact temperature is not critical so long as the precipi-tation temperature of the HPC wall forming compound is reaohed. Satisfactory microcapsules may be made using a hydroxypropylcellulose where a temperature of at least 45 C, pre-Ferably 45 C to 52 C, can be maintained for a period of1 to 16 hours.
The preferred phenols For use in this invention are, for example, resorcinol, hydroquinone, catechol, o-cresol, m-cresol, p-cresnl, Bisphenol A, naphthalenediols, ~all;c acid, phloroglucinol, pyrogallol, guaiacol, digallic acid, tannic acid, the chlorophenols, the xyleno1s, eugenol, the hydroxybi-phenols and the naphthols. Mixtures of these phenolic materials may also be used. The phenol most pre-Ferred is resorcinol.
The preferred aldehydes are, for example~ acetaldehyde9 ~ormaidehyde, glyoxal, glutaraldehyde, and furFural. Mixtures of these aldehydes may also be used. The aldehyde most preferred is formaldehyde which is preferably used in its commercial form as an aqueous solution o-F 37% formaldehyde.
~25 ~ If resorcinol is used, the weight ratio of resorc~inol to dry microcap-sules can be from about 0.015 to about 0.15. The pre~erred range is ~rom abou~
~ ; 0.02 to about 0.10 and the most preferred range is about 0.03 to about 0.07.
; ~ The ratio of formaldehyde to resorcinol can be fro~ about 0.2 to about 2~0.
The preFerred range is ~rom about 0.4 to about 1.5, and the most preferred range is from about 0.6 to about 1.3.
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The phenols an~ alclehydes m3~ be ad~ecl to -the aqueous dispersion of microcapsules in any ~anner wh;ch provides thorough mixing of the added ingredien-ts with the aqueous clispersion. A pre~erre~ manner of adding them is in the Form of aqueous solutions. An aqueous phenol solution is preferably added and mixed into the aqueous dispersion prior to adding and mixing in an aqueous aldehyde solution. An atlueous solution of urea may be added, if de-sired. At this point, the phenol and aldehyde react toge-ther to Form a condensa-tion polymer. The condensation polymer is insoluble in the agueous dispersion o~ microcapsules and precipitates out on the primary capsule walls to form a secondary capsule wall. Conditions which promo-te the formation o~
acceptable secondary walls are as follows:
The pH of the aqueous dispersion containing the phenol and aldehyde is pre~erably below about 6. A most preferred pH range ;s from about 2 to about 4. The reaction temperature can be between about Z5 C and about 70 C. The preferred range is about 35 C to about 55 C~ and the most preferred range is about 45 C to about 50 C. Under these cond;tions, the condensation polymer can be substantially completely formed in about 1 hour to about 16 hours and under pre~erred conditions from about 2 hours to about 5 hours.
Although the addition oF the phenol may bring the pH of the aqueous dispersion below a pH oF 6, it is desirable in most cases to add a small amount of dilute acetic acid to -the aqueous dispersion to bring the pH into the preFerred or most preferred range. Sulfuric acid or ylacial acetlc acid may also be used instead oF dilute acetic acid.
The reaction of the phenol and aldehyde to form a condensation polymer .
is also accompanied by an interaction o-f the phenol and/or aldehyde with the ingredients in the primary wall to provide a tight bond between the primary and secondary walls oF the microcapsule. The secondary wall surrounds and adheres tightly to the primary capsule wall.
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A~ter the phenol/al~ehy~le rcaction is substant-ially complete, the p~l of the aqueous clispersion o-f microcapsules can be raise~ to above about 7 by the addition of a base such as sodium hyclrox-i~e. At th-is point, the microcapsules can be Filterecl, such as by vacuum fil-tration, and air dried, if desired, to a microcapsular powder. The microcapsular po~der can, For example, be dispersed in a liquid (melted) hot melt suspen~ing medium to form a hot melt coating composition by the process disclo~ed in U.S.-Ap~
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e~t~ e~ Z~ mentioned supra. The coating composition can be applied to a substrate, and allowed to cool to a solid coating. The hot melt medium binds the microcapsules to the substrate. A?ternatively, the aqueous dispersion of microcapsules, perferably containing additionally a water dis-persible binder, such as a latex or starch, can be formed into an aqueous coating composit;on. This composition can be coated onto a substrate and air dried. The substrate can be paper, plastic film or fabric. A preferred substrate for both the hot mel-t composition and aqueous composition is paper.
; Stilt material may be added, if desired, to prevent premature breakage of the m;crocapsules. The coating compositions can be set to a solid coating by - coolin~ or by drying.
In a preferred embodiment of this invention, the microcapsules can contain an oil solution of a chromogenic material, such as a color precursor ; ~ color former or color developer. Chromogenic materials most useful for this purpose are the electron donor type color precursors. Microcapsules coated papers containing oil solutions of these chromo~enic materials can be used a pressure-sensitive carbonless copy papers. Microscopic examination of the microcapsules has shown the presence of significant amounts of polynuclear ~
microcapsule particles in the resultant dispersion. This phenomenon is appar-ently due to the aggregation (clustering~ of the smaller microcapsules having ;~ a primary ~qall prior to formation oF the secondary wall. The secon~ary wall envelopes the whole cluster causing the formation of the polynuclear microcap-sule ~articles. The larg~r microcapsules were not observed to cluster. The , ~ :
ra-tio o-F po1ynllclear m-icrocapsule p~rt-icles to nlononuclear microcapsules particl~s can ~e controlled by the reactants, the reaction temperature an~
pH value. Higher temperatures, lower prl, ancl larger arno~lnts of reactants, for example, resorcinol, during the condensation step Favor clustering and therefore, increase the Formation of the polynuclear microcapsule part-icles.
The process o-F this invention can substantially eliminate the smaller micro-capsules particles and thus can con-trol the particle size of the microcap-sules to a narrow range. For coating on a paper substrate, the particle size distribution is preferable between about 3 microns to about 25 microns, ~ith the average particle size being preferably between 7 to 12 microns.
A comparison of microcapsules containing chromogenic material before and after treatment by the process oF this invention demonstrates ~he advan-tages obtained by this practice of this invention. Microcapsule which were treated according to the process of this invention showed an improvement in typewri-ter intensity of a microcapsular coated fibrous substrate for a given microcapsular coat weight over that of the untreated (prior artl microcapsules.
This improvement apparently is due to the clustering effect oF the treatment - process which promotes the aggregation oF the smaller microcapsules during the formation of the secondary wall. In the case o-F the untreated (prior art) microcapsules~. these smaller microc-apsules appear to be small enough to pene-~ trate the sur'ace of a paper substrate, lodging in the interstices between ; ,-- the paper fibers, adn do not rupture under ordinary writing or typinq pressure.
In contrast to this, the clustered polynuclear microcapsule particles do not penetrate the paper surFace and are thus available for rupturing durin~ pres-25 - sure imaging. Addlt1onally, the -treated microcapsules are easily filtered using a vacuum filter whereas the untreated microcapsules cannot be filtered.
The treated microcapsules are also skronger and more heat resistant. Thus7 -.
`~ they can be used ~or a variety of uses. A preferred use in the production oF
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hot melt coatings for pressure-sensitive paper.
The following exarilples illustra-te the profluction of these filterable microcapsules an~ pressure-sens-itive carbonless copy papers made usin~ the filterable microcapsules. The eY~amples fur-ther descr-ibe but do not lirnit the scope of the invention.
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Example 1 A carrier oil solution of color precursors was prepared by dissolving 7 grams of crystal violet lactone, 0.9 grams of 3,3-bis(l'-ethyl-2'methylindol-3-yl) phthalide, 1.8 grams of 3-N,N-diethyl-amino-7-(N,N-dibenzyl~amino) fluoran, and 2.9 grams of 3-N,N-diethylamino-6,8-dimethyl-fluoran in 150 ml. of monoiso-propylbiphenyl (MIPB) at 90C. This oil solution was then cooled to 15C. To this carrier oil solution was added 2.5 grams of a liquid biuret reaction product of hexamethylene diisocyanate and water in 3 ~o 1 molar ratio made and sold by Mobay Chemical Co.
under the trade mark DESMODUR N-100, 2.5 grams o~ a trifunctional aromatic polyurethane prepolymer having a free isocyanate content of 32.5% made and sold by Union Carbide under the trade mark NIAX
SF-50, and 1 drop of dibutyl tin laurate as a catalyst for the hydroxypropylcellulose-polyisocyanate reaction. An aqueous solution of hydroxypropylcellulose was prepared by dissolving 5 grams of hydroxypropylcellulose(KLUCEL L - ~lercules, Inc.) in 215 ml. of distilled water at room temperture.
The aqueous solution of hydroxyproplycellulose was charged into a Sunbeam blender and the speed was set at 8. The carrier oil solution was slowly added to the blender and stirred thereafter for about 1 minute. The emulsion formed in the blender ` was transferred to a 600 ml. metal beaker and the beaker was put in a 50C water bath. The emulsion was stirred with paddle stirrer for about 1 hour during which time the microcapsules were formed.
The aqueous dispersion of microcapsules was treated as follows:
A solution of 0.7 grams of urea and 2.7 grams of resorcinol in 50 ml. of water was warmed to 50C and charged to an addition funnel. A solution of 5.4 ml. of 37% aqueous formalde-hyde was dissolved in 10.8 ml. of water at room temperature andcharged to a second addition fun~el. The urea-resorcinol solution was slowly dripped into the aqueous dispersion of microcapsules while stirring over a period of about 25 minutes. The reaction .
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mixture was kept at ~5-50C. The formaldehyde solution was then slowly dripped into the reaction mixture and the reaction mixture was maintained at ~5~50C with stirring for 3.5 hours.
The resulting dispersion of microcapsules was coated on a paper substrate and dried, and the dried coated paper performed well as the CB part of a carbonless form using a phenolic (novolac) resin coated paper as the CF part.
Example 2 The procedure of Example 1 was repeated except that the pH of the reaction mixture was adjusted to 2.5 with 0.5 ml. of 10%
sulfuric acid prior to the addition of the formaldehyde solution.
After a 3.5 hour reaction time, the pH of the reaction mixture was readjusted to 9.6 with sodium hydroxide thus stoppin~ the reaction.
About half of the reaction mixture was vacuum filtered at about 30 mm. Hg absolute pressure and the resultant filter cake was washed twice with 100 ml. of distilled water. A light gray filter cake of microcapsules was obtained. 40 grams of methoxy poly-ethylene glycol marketed under the trade mark CARBOWAX 5000 by Union Carbide was melted on a hot plate and 12 grams of the still wet capsules were added to the melted CARBOWAX while stirring. The mel-ted CARBOWAX containing the microcapsules was coated onto a 34.5 pound per 3300 square foot paper substrate using a hot glass rod.
The resulting coated paper substrate was cooled and the coated paper substrate performed well as the CB part of a carbonless form using a phenolic (no~oP~c ~ esin coated paper às the CF part.
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Example 3 ~;~ All amounts are in parts by weight. A carrier oil solution of color precurso:rs was prepared by dissolving 53.2 parts of crystal ~iolet lactone, 6.9 parts of 3,3~bis~ ethyl-2'methylindol-3-yl) phthalide, 13.5 parts of 3-N,N-diethylamino-7-(N,N-dibenzylamino) fluoran, and 16.1 parts of 3-N,N-diethylamino-6,8-dimethylfluoran ~` in 1142 parts of monoisopropylbiphenyl~ PB)~. . . . . . . ~ . . .
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; - I7 -at 90 ( -rhi~ o-i'1 so'lution ~ac. ki~ rl coo'1~(1 to '1'1 C. To this carrier oil D~s~a~
~- ~ solution ~135 ~dc1e(1 5n par-ts of ~51flO~t1-f i`1-'100, l~ parts o~ ~1XAX SF 50 and 0.05 par-ts of d-ibutyl tin dila11r~te cata'1yst An aqueous so'lut-ion o-f hy('roxy-propycellulose was prepared by dissolvin~ 50 parts of hydroxypropylcellu'1Ose in 2082 parts of ~Jater a-t roo1n temperature.
The carrier oil solution was emulsi-fied into the aqueous solution of hydroxypropylcell~lose For abou-t ~5 minutes. The resultant emulsion ~1as heatedto 47 ~ while stirring and the temperature was maintained be-tween 47 C and 50 C for a period of 2 hours to form the microcapsules. At this point 160, parts of the aqueous dispersion oF microcapsules was removed frorn the process and designated "Comparative Sample A". The remainin~ aqùeous dispersion of microcapsules was treated as follows: A solution oF 7.~ parts oF resorcinol in 37 parts of water was added to the aqueous emulsion in a period of 3 minutes.
A solution of 7 parts o-f glacial acetic acid in 3~ parts oF water was added in a period of 4 minutes. A solution of 18.3 parts of 37% aqueous formaldehyde in 24.~ pa;r~s o~ water were added in a period oF 3 minutes. The reaction mixture was maintained at 46.8 to 48.2 C with stirring for 2 hol1rs. A solution oF
5 parts o-f sodium hydroxide in l~.~ parts of water was added ~o the reaction ! mixture to bring the reaction mixture to a pH of 7~8 and stop the resorcinol-formaldehyde reaction. The aqueous dispersion of treated microcapsules ~Jas ' designated "Treated Sample B".
Particle size determina-tions were made on Samples A and B by means of a Coulter Counter (a commerically available e1ec-tronic particle size counter made and sold b~ Coulter Electronics, Inc., Hialeah, Fla.j. The results were as ~ollows:
Percent by Particle ~ n Mîcrons) Weigh-t Comparative Sample A Treated S_mple B
' ~ 25 9.l and above 12.3 and above 6~6 and above 9.7 and above ~ 4.7 and above 7.7 and above 100 ~l.3 and above 3.1 and above .
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sh()~ irl the aL~ove Lc~ e the 5 i~t~ uf the 111iCrOCapsUle5 incre2s*d ~luring trea~;mellt o-F the aqueolls clispersiorl of microcallsu'lec with resorcirlol ancl formald~hyde. ~icroscopic exanlination n-f Samp'les ~ an~ B sho~,/e~ an aggregation (c'lustering) o~ the smaller microcaps~'les in Treated Sample whereas in Comparat-ive Sample A substantia'l'ly no clustering was observed.
Examele 4 The procedure of Example 3 ~las repeated except tha-t -the resorcinol was reduced to 6 parts instead of 7.~ parts as in Example 3. Samples of the aqueousdispersion o-F microcapsules before and af-ter treatment with resorcinol and ~ormaldehyde were obtained. These samples were designated respectively "Com-parative Sample C" and "Treated Sample D". A coating composition was prepared using each of Samples C and D using the following general formulation at 39.7%
solids in water. The amounts are given in parts on a dry ~eight basis ; Amount Microcapsules 51 Cooked Starch Binder 18 Uncooked Starch Binder 31 , . .
Each coating composition was applied to the back side o-f a 34 pound per 3300 square ~oot commerical CF paper. The CF paper contained a coating o~ a zinc modified phenol-Formaldehyde novolac resin o~ the front side. Typewriter intensity determinations o-f papers coated with several different weights of .
microcapsules were~as ~ollows: ' -Coating Composition MicrocapsuleCoat Weight Typewriter Contains _ (Pounds per 3300_square ft.) Intensity ~ 25 Comparative Sample C 1.84 66 " " " ' 1.9~ 63 ~ " " 2.26 , 60 Treated Sample D 1.48 65 : : " '' " 1.~6 ' ~ 6~
~: 30 The above test results showed that for a given microcapsule coat weight ; ' the coating composition containing the Treated Sample D performed bet-ter than the coating composition containing the Comparative (untreated) Sample C.
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Exall~inlt-i()ns of the coate(l pclpers re~Jelle~ thll siglli-ricant alnollnts oF
clus-tered (polynllclear) microcapsules were present in tl~e papers coated ~-iththe compos-itio1-s containiny Trea-te(l Sanlple D and -that such clustered micro-capsules were subs-tantially absent ir- the papers coated with the compositions 3 containing Compara-tive Sample C.
As used herein -the typewriter in-tensity is a contrast ra-tio and is equal to lG0 times the ratio -For the reflectance of a printed character divid ed by the background reflectance. A typewriter intensity value oF 100 incli-cates a not discernible print and a lower value indicates a more intense print.
Specifically the backside of the papers made in Example 4 and a CF sheet coa-ted with a phenolformaldehyde novolac resin were placed with the coated sides together and a series of close-spaced characters were typed on the test paper. Reflectance readings were then taken of the background and also the printed chracters transferred to the reactant sheet and the contrast ratio was 15 calculated.
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This invention relates to the pro~uc-tion o-f microcapsules contain-ing an oil an~ having a prilnary capsule wall oF a reac-tion product o~ hydroY~y-propylcellulose ancl a cross l-inking a~ent and a secondary capsule wall forme~
by the reaction of a phenol and an aldehyde. The microcapsules produce~ by the process o-F this invention are particularly adaptable For use in preparing pressure-sensitive carbonless trans~er papers.
Prior Art:
A process for the production oF microcapsules containing oils using coacervation is disclosed in U.S. Patent 2,800,457 (1957) to Green et al. The process described therein involves the coating of oil droplets with a liquid wall of gelatin-gum arabic colloidal material produced by coacervation. The liquid wall is hardened by treatment with formaldehyde. Microcapsules made by the process oF Green et al have had wide commercial acceptance, particular--ly in the fiëld of pressure-sensitive carbonless copy papers.
Since that time, microcapsules have been made using many types of wall-forming materials, wall-forming processes and wall structures. The microcap-; sules produced have been suggested For many uses, including the encapsulation of aromas, per'umes, flavoring agents, adhesives, reactants, color reactants, pharmaceuticals, pigmenis and as opacifyin~ agents. The nature of the ma~er-ial to be encapsulated and ultirnate use o-F the microcapsules many times dic-tated the materials, structure and process of making them.
Dual-walled microcapsules having inner ~primary) walls and outer (sec-ondary) walls oF difFerent wall-Forming materials are kno~n From the Following:
;~ U. S. Patent 2,9O9,331 (1961) Brynko et al U. S. Patent 3,551~3~6 (1970) Breen et al U. S. Patent 3,578,605 (1971) Baxter , , ~ .
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It -is also known from tile follo~ ti-~at sin(Jl~ (l m-icrocapsules could be m~de in ~Ihich -the ~Jall-forming material -is a contlensation polyrner o-f resorcinol and an aldehycle:
U. S. Patent 3,755,190 (1973) to l-lart et al.
U. S. Pa-tent 3,816,331 (1974) to ~rown, Jr. et al Canadian Patent 879,043 (1971) to Bayless Additionally, the following pa-tents disclose processes for producing an aqueous dispersion of microcapsules containing an oil. The microcapsules have hydrophilic (water-swellable) polymeric capsule walls which are ir;lpre~-nated with or otherwise contain resorcinol which is then reacted.with Pormal-dehyde.
U. S. Patent 3,576,660 (1971) to Bayless et al U. S. Patent 3,726,803 (1973) to Bayless et al U. S. Patent 3,803,046 ~197~ to Matsukawa et al 1~ Carbonless copy paper, briefly stated, is a standard type of paper wherein during manufacture the backside of the paper substrate is coated with what is reFerred to as a CB or transfer coating, the CB coating containing ~. .
--- one or more chromogenic materials, generally in capsular form. At the same time the -front side of the paper substrate is coated during manu-facture~with what is referred to as a ~F coating, which contains ane or more chromogenic material. Both the chromogenic materials remain in the coatings on the re-spective back surfaces of the paper in substantially colorless -Form. This is true until the CB and CF coatings are brought into o~erlying relationship and ~: - sufficient pressure~ as by a typewriter, is applied to rupture the ce coating to release the encapsulated chromogenic material. At this time the chromo-genic material contacts the CF coatin~ and reacts with the chromogenic mater-~ ial therein to form a colored image. Carbonless copy paper has proved to be .~ an.exceptionally valuable image transfer media for a variety of reasons7 only one of which is the fact that until a CB coating is placed next to a CF
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coa-ting both the CB antl t~le CF coat-ings are in an inactive sta-te as the co-reactive elernents are not -in coiltact ~`I-ith one another until pressure is appliecl Patents relating -to carbonless copy paper pro~ucts are:
U. S. Paten-t 2,~50,456 (1951) to Green et ai U. S. Patent ~,712,507 (1955) to Green U. S. Pa-ten-t 2,730,456 (1956) to Green e-t al U. S. Patent 3,016,308 (1962) to Macaulay U. S. Patent 3,170,809 (1965) to Barbour U. S. Patent 3,455,721 (1969) to Phillips et al U. S. Patent 3,466,184 (1369) to Bowler et al U. S. Patent 3,672,935 (1972) to Miller et al U. S. Patent 3,955,025 (197~) to Matsukawa et al U. S. Patent 3,981,523 (1976) to ~aalouf A disadvan-tage oF coated paper products such as carbonless transfer papers stems from the necessity of applying a liquid coating composition containing the color forming ingredients during the manufacturing process.
In the application of such coatings, volatile organic solvents are sometimes r used which then in turn requires evaporation of excess ~olvent to dry the coating thus producing volatile solvent vapors. An alternate method of coating involves the application of the color forming ingredients in an aque-ous slurry, again requiring removal of excess ~Jater by drying. Both methods suffer from serious disadvantages. In particular the organic solvent coating method necessarily involves the production of generally volatile solvent va-pors, crea-ting ~oth a health and a ~ire hazard in the surrounding environment.
When using an aqueous solvent system the water must be evaporated which in-volves~the expenditure of significant amounts o-F energy.~ Further, the neces-:`
sity of a drying step requires the use of complex and expensive appara-tus to - continuously dry a substra-te which has been coated with an aqueous coating compound. The applicatlon of heat not only is expensive~ making the total :
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~aper manufacturing operation less effective, but also is potenti-ally damaging to the encapsulated chromogenic materials which are generally coated onto the paper substrate during manufacture. High degrees of temperature in the drying step :require specific formulation of coating compositions which permit the use of excess heat. The problems encountered in the actual coating step are generally attributable to the necessity for a heated drying step following the coating operation.
In an attempt to overcome the difficulties associated with the coating and drying of microcapsular compositions as noted above, attempts have been made as disclosed in the prior art to use liquid coatings containing substantially no volatile solvent.
Notable among these attempts are the use o~ hot melt coating compositions as disclosed in the following patents:
U.S. Patent 3,016,308 (1962) to Macaulay U.S. Patent 3,079,351 (1963) to Staneslow et al U.S. Patent 3,864,549 (.1972) to Shank The use of hot melt coatings containing microcapsules for CB transfer coatings is disclosed in both Staneslow et al and Macaulay. Macaulay also discloses preparation of hot melt CB
coating compositions using spray dried microcapsules. Improved ; coating compositions containing microcapsules having improved dispersion of the microcapsules within the hot melt suspending media are disclosed in U.S. patent no. 4,143,890 issued on March 13, 1979.
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The process of the present invention provides a novel method by which novel dual-walled microcapsules can be produced.
Use of these micxocapsules is particularly advantageous in the preparation of hot melt coating compositions for pressure-sensitive ~; carbonless copy papers. The microcapsules are produced in an aqueous continuous phase and the microcapsules can be easily removed from the a~ueous dispersion by vacuum filtering. The still wet microcapsules can be easiIy incorporated into a hot melt in a : .
manner c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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disclosecl ill the above-c-e-,~e~linc~-~t~ ic-atiol~. Acldit-ional advanta~es of the micrucaps-lles are h-igh stren~th and their capability o-F being rnore eFfic-iently usecl-than nlost prior ar-t n~icrocapsules in the produc-tion oF cetransfer coatings. Reductions in microcapsular coat we-ights are thus S possible.
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Sta-tement of the Invention This invention relates to a process for preparing filterable microcapsules comprising the followiny steps: There is prepared an aqeuous dispersion of microcapsules containing an oil solution of a chromogenic material, said chromogenic material being an electron donor type color precursor. The microcapsules have a primary capsule wall comprising a reaction product of hydroxypropylcellulose and at least one cross-linking agent for hydroxypropylcellulose. This cross-linking agent is selected from the group consisting of the polyfunc-tional isocyanates, acyl chlorides, phosphoryl chloride~, sulfonyl chlorides, alkylene bischloroformates and mixtures thereof. The primary capsule wall is substantially oil and water impermeable. A phenol and an aldehyde is added and mixed into the a~ueous dispersion of microcapsules. The aldehyde is selected from the group consisting of acetaldehyde, formal-dehyde, glyoxal, glutaraldehyde, furfural and mixtuxe~ thereof.
Mixing is maintained while t~e phenol and the aldehyde react together to form a condensation polymer. The condensation polymer is inlsoluble in the aqueous dispersion of microcapsules whereby the condensation polymer is precipitated on the primary capsule wall as a secondary capsule'wall. A binder can be 'added to the microcapsules and the coating composition can be' applied to a substrate.
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The invention ~urther relates to microcapsules containing an oil solution of a chromogenic material, said chromogenic material being an electron donor type color precursor. The microcapsules ha~e a primary capsule wall and a secondary capsule wall which surrounds and adheres to the primary capsule wall. The primary capsule wall comprises a reac-tion product ~; of hydroxypropylcellulose and at least one cross-linking agent for hydroxypropylcellulose. This crcss-linking agent is' selected from the group consisting of the polyfunctional isocyanates, acyl chlorides, phosphoryl chlorides, sulfonyl 7 ~
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chlorides, a].kylene bischloroformates and mixtures -thereof.
The primary capsule wall is substantially impermeable to oil and water. The secondary capsule wall comprises a conden-sation polymer of a phenol and an aldehyde. The aldehyde is selected from the group consistiny of acetaldehyde, formal-dehyde, glyoxal, glutaraldehyde, furfural and mixtures thereof.
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.; ' , i~ta e~ Descri~t-ion of_ he Invent~0~1 The process o~ this in~ention is concerne~ with a further treatment ; of known microcapsules having substantially impermeable ~lalls comprisiny the reaction product of hydroxypropylcellulose and at least one oil soluble cross-linking agent for hydroxypropylcellulose. The treatment involves adding to an aqueous dispersion of microcapsules,as defined above,a phenol and an aldehyde.
The phenol and aldehyde react with each other to Form a condensation polymer.
The condensation polyrner, beins insoluble in the aqueous continous phase oF thedispersion, precipitates on the primary walls of -the microcapsules as secondarywalls. Microcapsules produced by the process of this invention are effective-ly dual walled in that a secondary capsule wall oF precipitated condensation polymer deposits on the primary cross-linked hydroxypropylcellulose wall.
In a pre~erred embodiment oF this invention, microcapsules having a primary capsule wall are produced according to the process disclosed in U.S.
l~ Patent ~,025,455 issued May 24, 1977 to Dale Richard Shackle and assigned to The Mead Corporation o-F Dayton, Ohio. Microcapsules as disclosed in U. S
Patent 4,025,455 have a cross-linked hydroxypropylcellulose primary wall formed by the re.action oF hydroxypropylcellulose in an aqueous continuous phase with at least one cross~linking agent -For hydroxypropylcellulose in a dispersed oil phase. The microcapsules m y contain a chromoyenic material dissolved in the oil phase. The resultant primary wall is substantially impermeable to the microencapsu1ated oil and the water in the aqueous contin-uous~ phase. The hydroxypropylcellulose, hereinaFter sometimes referred to as HPC,is a fil~ orlning cellulosic ether polymer soluble in cold water, but insoluble in hot water. The commercially available polymers have a molar substitution (M.S.) of about three to five hydroxypropyl units to each cell-ulose unit. A particular group o~ hydroxypropylcelluloses are manu-Factured by Hercules~ Inc. and sold~by them under the trade ~m~ of~hvei~. These ~; polymers precipitate out of a ~Yater so1ution at a temperature of about 45 C
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an~I pre-Ferably At from about ~5 (` to a~out 52 C zs a finel~ cli~i~ed suIi~
precipitate. The polymers are ava-iIabIe in a var-iety of viscosity -types.
The lo~Ier viscosity types, G, J, L an~ E are preFerred for use in this in vention. OF these, Type L haYiny a molecule ~Ieight of ~pproximacely 75,000 and an M.S. of approximately three has been found -to be par-ticularly useful.
The aqueous phase, con-taining ~IPC, can be prepared by dissolv-iny the HPC in water at a temperature below 40 C, preferably at frorn about 10 C -30 C. To facilitate the preparation, the HPC can be dispersed in the water at 45 C or above prior to lowering the ternperature of the dispersion to below 4G C to dissolve the HPC. The concentration of the HPC is not critical~ but would clepend on the ratio of aqueous phase to the material to be encapsula~ed~
the size of the desired oil solu-tion droplets and the desired thickness of the microcapsular ~Jalls. Aqueous solutions containiny from about 0.2% to about 6%, preferably 1.5% to ~%, of HPC are used in the preparation of the aqueous phase.
The oil phase is prepared by combining an oil soluble cross-linking agent for the HPC wall-forming compound with an oil. The oil solution can be prepared by adding and stirring the oil soluble cross-linking agent to the oil while the mixture is cool, preferably below 15 C. The choice of oil depends largely on the final utiliza-tion o-F the microcapsules. If, for example~ the microcapsules are to be used in preparing pressure~sensitive paper~ the oil should be a carrier oil for a chromogenic~aterial. Such carrier oils are preferably monoisopropylbiphenyl (MIPB), ch70rinated biphenyls,~alkylnaphtha~
Ienes, kerosene, petroleum naphtha or mixtures thereo~.
The oil soluble cross-linking agents used in this embodiment for form ing the oil phase are those conta;niny more than one group capable of reacting with hydroxyl groups thus providing the desired cross-linkage with the HPC
wall-forming compound. The cross-linking agents must be soluble in the oil phase and not: reactable with the oil: or interfere with the desired func-; 30 tion o~ any omponent of the oil phase~ For example, if an oil solution o~
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color precur~or is clesire~ to be encapsuldt~d and coated on p~-per, the cross-linking agerl-t should Ilot interfere ~Ii-th the color producing func~ion o-F the resultan-t paper. In general poly-Functional isocyanates, acyl chlor-ides, sulfonyl chlorides, alkylene bischloroformates or mixtures thereof can be ùsed. If microcapsules -for use in the preparation oF pressure-sensitive papers are desired, the polyfunctional isocyanates or prepolyrners conta-ining more than one reactive isocyanate group are preferred. The concen-tration of the oil so~uble cross-linking agent in the oil phase is no-t critical. The degree of cross-linking desired is dependent on the encl utilization of the microcapsules. For example, if the microcapsules are to be incorpora-ted into an aqueous coating composition, sufficient reactive groups must be present to react ~lith available hydroxyl groups of the wall-forming compound to render the wall-forming compound water insoluble. It has, however, been shown that the superior microcapsules Formed by the process oF this invention are a pro-duct o-F the use of HPC and not the particular oil soluble cross-linking agent.
In particular9 any of the cross-linking agents exhibiting the above reci~ed characteristics can be used in combination with HPC to produce the desired microcapsules.
EmulsiFication of $he oil phase in the aqueous phase can be accomplished by adding the oil phase to the aqueous phase with vigorous mixing. Mixing may be by stirring, shaking or millIng. During the mixing operation, the tempera-ture of the mixture must be kept below the temperature at which the HPC wall :
forming compound precipitates. A small amount oF an emulsifier, such as about .25% by weight Turkey Red Oil (sulfonated castor oil) can be added to the aqueous phase prior to mixing. However, the hydroxypropylcellulose acts as an emulsifier and an acceptable dispersion oF drople-ts can be obtained in the absence~of an additional emulsifier. Droplet sizes of about 1 micron to about 100 mlcrons can be produced.
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AFter th~ clesire~ cI ropl e t si 7.e i s obta-ined, tiI~ mixe(I ernuision is heated ~)ith mild ayita-tion to a teIrlperatur~ abo~e -the prec-ipitation temperature of the HPC wall-forrning compound. lhe wall formin~ compound precipi-tates nn the droplets to form rnicrocapsule walls. The ternperature increase promotes cross-linking of the ~IPC wall Formin~ compoun~ ~Iith the oil solu-ble cross-linking agent. The -temperature can be main-tained ~Iith continued - agitation o-F the mixture For a sustained perio~ of -time, pre-Ferably more than about 1 hour, and most pre-Ferable 3 to 16 hours, if microcapsules of low oil and water permeability are desired. However, longer periods do not appear to be detrimental. The exact temperature is not critical so long as the precipi-tation temperature of the HPC wall forming compound is reaohed. Satisfactory microcapsules may be made using a hydroxypropylcellulose where a temperature of at least 45 C, pre-Ferably 45 C to 52 C, can be maintained for a period of1 to 16 hours.
The preferred phenols For use in this invention are, for example, resorcinol, hydroquinone, catechol, o-cresol, m-cresol, p-cresnl, Bisphenol A, naphthalenediols, ~all;c acid, phloroglucinol, pyrogallol, guaiacol, digallic acid, tannic acid, the chlorophenols, the xyleno1s, eugenol, the hydroxybi-phenols and the naphthols. Mixtures of these phenolic materials may also be used. The phenol most pre-Ferred is resorcinol.
The preferred aldehydes are, for example~ acetaldehyde9 ~ormaidehyde, glyoxal, glutaraldehyde, and furFural. Mixtures of these aldehydes may also be used. The aldehyde most preferred is formaldehyde which is preferably used in its commercial form as an aqueous solution o-F 37% formaldehyde.
~25 ~ If resorcinol is used, the weight ratio of resorc~inol to dry microcap-sules can be from about 0.015 to about 0.15. The pre~erred range is ~rom abou~
~ ; 0.02 to about 0.10 and the most preferred range is about 0.03 to about 0.07.
; ~ The ratio of formaldehyde to resorcinol can be fro~ about 0.2 to about 2~0.
The preFerred range is ~rom about 0.4 to about 1.5, and the most preferred range is from about 0.6 to about 1.3.
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The phenols an~ alclehydes m3~ be ad~ecl to -the aqueous dispersion of microcapsules in any ~anner wh;ch provides thorough mixing of the added ingredien-ts with the aqueous clispersion. A pre~erre~ manner of adding them is in the Form of aqueous solutions. An aqueous phenol solution is preferably added and mixed into the aqueous dispersion prior to adding and mixing in an aqueous aldehyde solution. An atlueous solution of urea may be added, if de-sired. At this point, the phenol and aldehyde react toge-ther to Form a condensa-tion polymer. The condensation polymer is insoluble in the agueous dispersion o~ microcapsules and precipitates out on the primary capsule walls to form a secondary capsule wall. Conditions which promo-te the formation o~
acceptable secondary walls are as follows:
The pH of the aqueous dispersion containing the phenol and aldehyde is pre~erably below about 6. A most preferred pH range ;s from about 2 to about 4. The reaction temperature can be between about Z5 C and about 70 C. The preferred range is about 35 C to about 55 C~ and the most preferred range is about 45 C to about 50 C. Under these cond;tions, the condensation polymer can be substantially completely formed in about 1 hour to about 16 hours and under pre~erred conditions from about 2 hours to about 5 hours.
Although the addition oF the phenol may bring the pH of the aqueous dispersion below a pH oF 6, it is desirable in most cases to add a small amount of dilute acetic acid to -the aqueous dispersion to bring the pH into the preFerred or most preferred range. Sulfuric acid or ylacial acetlc acid may also be used instead oF dilute acetic acid.
The reaction of the phenol and aldehyde to form a condensation polymer .
is also accompanied by an interaction o-f the phenol and/or aldehyde with the ingredients in the primary wall to provide a tight bond between the primary and secondary walls oF the microcapsule. The secondary wall surrounds and adheres tightly to the primary capsule wall.
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A~ter the phenol/al~ehy~le rcaction is substant-ially complete, the p~l of the aqueous clispersion o-f microcapsules can be raise~ to above about 7 by the addition of a base such as sodium hyclrox-i~e. At th-is point, the microcapsules can be Filterecl, such as by vacuum fil-tration, and air dried, if desired, to a microcapsular powder. The microcapsular po~der can, For example, be dispersed in a liquid (melted) hot melt suspen~ing medium to form a hot melt coating composition by the process disclo~ed in U.S.-Ap~
c~t~YD~ D
e~t~ e~ Z~ mentioned supra. The coating composition can be applied to a substrate, and allowed to cool to a solid coating. The hot melt medium binds the microcapsules to the substrate. A?ternatively, the aqueous dispersion of microcapsules, perferably containing additionally a water dis-persible binder, such as a latex or starch, can be formed into an aqueous coating composit;on. This composition can be coated onto a substrate and air dried. The substrate can be paper, plastic film or fabric. A preferred substrate for both the hot mel-t composition and aqueous composition is paper.
; Stilt material may be added, if desired, to prevent premature breakage of the m;crocapsules. The coating compositions can be set to a solid coating by - coolin~ or by drying.
In a preferred embodiment of this invention, the microcapsules can contain an oil solution of a chromogenic material, such as a color precursor ; ~ color former or color developer. Chromogenic materials most useful for this purpose are the electron donor type color precursors. Microcapsules coated papers containing oil solutions of these chromo~enic materials can be used a pressure-sensitive carbonless copy papers. Microscopic examination of the microcapsules has shown the presence of significant amounts of polynuclear ~
microcapsule particles in the resultant dispersion. This phenomenon is appar-ently due to the aggregation (clustering~ of the smaller microcapsules having ;~ a primary ~qall prior to formation oF the secondary wall. The secon~ary wall envelopes the whole cluster causing the formation of the polynuclear microcap-sule ~articles. The larg~r microcapsules were not observed to cluster. The , ~ :
ra-tio o-F po1ynllclear m-icrocapsule p~rt-icles to nlononuclear microcapsules particl~s can ~e controlled by the reactants, the reaction temperature an~
pH value. Higher temperatures, lower prl, ancl larger arno~lnts of reactants, for example, resorcinol, during the condensation step Favor clustering and therefore, increase the Formation of the polynuclear microcapsule part-icles.
The process o-F this invention can substantially eliminate the smaller micro-capsules particles and thus can con-trol the particle size of the microcap-sules to a narrow range. For coating on a paper substrate, the particle size distribution is preferable between about 3 microns to about 25 microns, ~ith the average particle size being preferably between 7 to 12 microns.
A comparison of microcapsules containing chromogenic material before and after treatment by the process oF this invention demonstrates ~he advan-tages obtained by this practice of this invention. Microcapsule which were treated according to the process of this invention showed an improvement in typewri-ter intensity of a microcapsular coated fibrous substrate for a given microcapsular coat weight over that of the untreated (prior artl microcapsules.
This improvement apparently is due to the clustering effect oF the treatment - process which promotes the aggregation oF the smaller microcapsules during the formation of the secondary wall. In the case o-F the untreated (prior art) microcapsules~. these smaller microc-apsules appear to be small enough to pene-~ trate the sur'ace of a paper substrate, lodging in the interstices between ; ,-- the paper fibers, adn do not rupture under ordinary writing or typinq pressure.
In contrast to this, the clustered polynuclear microcapsule particles do not penetrate the paper surFace and are thus available for rupturing durin~ pres-25 - sure imaging. Addlt1onally, the -treated microcapsules are easily filtered using a vacuum filter whereas the untreated microcapsules cannot be filtered.
The treated microcapsules are also skronger and more heat resistant. Thus7 -.
`~ they can be used ~or a variety of uses. A preferred use in the production oF
~ ~ .
hot melt coatings for pressure-sensitive paper.
The following exarilples illustra-te the profluction of these filterable microcapsules an~ pressure-sens-itive carbonless copy papers made usin~ the filterable microcapsules. The eY~amples fur-ther descr-ibe but do not lirnit the scope of the invention.
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Example 1 A carrier oil solution of color precursors was prepared by dissolving 7 grams of crystal violet lactone, 0.9 grams of 3,3-bis(l'-ethyl-2'methylindol-3-yl) phthalide, 1.8 grams of 3-N,N-diethyl-amino-7-(N,N-dibenzyl~amino) fluoran, and 2.9 grams of 3-N,N-diethylamino-6,8-dimethyl-fluoran in 150 ml. of monoiso-propylbiphenyl (MIPB) at 90C. This oil solution was then cooled to 15C. To this carrier oil solution was added 2.5 grams of a liquid biuret reaction product of hexamethylene diisocyanate and water in 3 ~o 1 molar ratio made and sold by Mobay Chemical Co.
under the trade mark DESMODUR N-100, 2.5 grams o~ a trifunctional aromatic polyurethane prepolymer having a free isocyanate content of 32.5% made and sold by Union Carbide under the trade mark NIAX
SF-50, and 1 drop of dibutyl tin laurate as a catalyst for the hydroxypropylcellulose-polyisocyanate reaction. An aqueous solution of hydroxypropylcellulose was prepared by dissolving 5 grams of hydroxypropylcellulose(KLUCEL L - ~lercules, Inc.) in 215 ml. of distilled water at room temperture.
The aqueous solution of hydroxyproplycellulose was charged into a Sunbeam blender and the speed was set at 8. The carrier oil solution was slowly added to the blender and stirred thereafter for about 1 minute. The emulsion formed in the blender ` was transferred to a 600 ml. metal beaker and the beaker was put in a 50C water bath. The emulsion was stirred with paddle stirrer for about 1 hour during which time the microcapsules were formed.
The aqueous dispersion of microcapsules was treated as follows:
A solution of 0.7 grams of urea and 2.7 grams of resorcinol in 50 ml. of water was warmed to 50C and charged to an addition funnel. A solution of 5.4 ml. of 37% aqueous formalde-hyde was dissolved in 10.8 ml. of water at room temperature andcharged to a second addition fun~el. The urea-resorcinol solution was slowly dripped into the aqueous dispersion of microcapsules while stirring over a period of about 25 minutes. The reaction .
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81~
mixture was kept at ~5-50C. The formaldehyde solution was then slowly dripped into the reaction mixture and the reaction mixture was maintained at ~5~50C with stirring for 3.5 hours.
The resulting dispersion of microcapsules was coated on a paper substrate and dried, and the dried coated paper performed well as the CB part of a carbonless form using a phenolic (novolac) resin coated paper as the CF part.
Example 2 The procedure of Example 1 was repeated except that the pH of the reaction mixture was adjusted to 2.5 with 0.5 ml. of 10%
sulfuric acid prior to the addition of the formaldehyde solution.
After a 3.5 hour reaction time, the pH of the reaction mixture was readjusted to 9.6 with sodium hydroxide thus stoppin~ the reaction.
About half of the reaction mixture was vacuum filtered at about 30 mm. Hg absolute pressure and the resultant filter cake was washed twice with 100 ml. of distilled water. A light gray filter cake of microcapsules was obtained. 40 grams of methoxy poly-ethylene glycol marketed under the trade mark CARBOWAX 5000 by Union Carbide was melted on a hot plate and 12 grams of the still wet capsules were added to the melted CARBOWAX while stirring. The mel-ted CARBOWAX containing the microcapsules was coated onto a 34.5 pound per 3300 square foot paper substrate using a hot glass rod.
The resulting coated paper substrate was cooled and the coated paper substrate performed well as the CB part of a carbonless form using a phenolic (no~oP~c ~ esin coated paper às the CF part.
: ~:
Example 3 ~;~ All amounts are in parts by weight. A carrier oil solution of color precurso:rs was prepared by dissolving 53.2 parts of crystal ~iolet lactone, 6.9 parts of 3,3~bis~ ethyl-2'methylindol-3-yl) phthalide, 13.5 parts of 3-N,N-diethylamino-7-(N,N-dibenzylamino) fluoran, and 16.1 parts of 3-N,N-diethylamino-6,8-dimethylfluoran ~` in 1142 parts of monoisopropylbiphenyl~ PB)~. . . . . . . ~ . . .
.:~ ~ : :
:, :
~:
; - I7 -at 90 ( -rhi~ o-i'1 so'lution ~ac. ki~ rl coo'1~(1 to '1'1 C. To this carrier oil D~s~a~
~- ~ solution ~135 ~dc1e(1 5n par-ts of ~51flO~t1-f i`1-'100, l~ parts o~ ~1XAX SF 50 and 0.05 par-ts of d-ibutyl tin dila11r~te cata'1yst An aqueous so'lut-ion o-f hy('roxy-propycellulose was prepared by dissolvin~ 50 parts of hydroxypropylcellu'1Ose in 2082 parts of ~Jater a-t roo1n temperature.
The carrier oil solution was emulsi-fied into the aqueous solution of hydroxypropylcell~lose For abou-t ~5 minutes. The resultant emulsion ~1as heatedto 47 ~ while stirring and the temperature was maintained be-tween 47 C and 50 C for a period of 2 hours to form the microcapsules. At this point 160, parts of the aqueous dispersion oF microcapsules was removed frorn the process and designated "Comparative Sample A". The remainin~ aqùeous dispersion of microcapsules was treated as follows: A solution oF 7.~ parts oF resorcinol in 37 parts of water was added to the aqueous emulsion in a period of 3 minutes.
A solution of 7 parts o-f glacial acetic acid in 3~ parts oF water was added in a period of 4 minutes. A solution of 18.3 parts of 37% aqueous formaldehyde in 24.~ pa;r~s o~ water were added in a period oF 3 minutes. The reaction mixture was maintained at 46.8 to 48.2 C with stirring for 2 hol1rs. A solution oF
5 parts o-f sodium hydroxide in l~.~ parts of water was added ~o the reaction ! mixture to bring the reaction mixture to a pH of 7~8 and stop the resorcinol-formaldehyde reaction. The aqueous dispersion of treated microcapsules ~Jas ' designated "Treated Sample B".
Particle size determina-tions were made on Samples A and B by means of a Coulter Counter (a commerically available e1ec-tronic particle size counter made and sold b~ Coulter Electronics, Inc., Hialeah, Fla.j. The results were as ~ollows:
Percent by Particle ~ n Mîcrons) Weigh-t Comparative Sample A Treated S_mple B
' ~ 25 9.l and above 12.3 and above 6~6 and above 9.7 and above ~ 4.7 and above 7.7 and above 100 ~l.3 and above 3.1 and above .
:
.
. . .. . .. . .. .. ., .. ......... ~.. .~..... ~
. . .
sh()~ irl the aL~ove Lc~ e the 5 i~t~ uf the 111iCrOCapsUle5 incre2s*d ~luring trea~;mellt o-F the aqueolls clispersiorl of microcallsu'lec with resorcirlol ancl formald~hyde. ~icroscopic exanlination n-f Samp'les ~ an~ B sho~,/e~ an aggregation (c'lustering) o~ the smaller microcaps~'les in Treated Sample whereas in Comparat-ive Sample A substantia'l'ly no clustering was observed.
Examele 4 The procedure of Example 3 ~las repeated except tha-t -the resorcinol was reduced to 6 parts instead of 7.~ parts as in Example 3. Samples of the aqueousdispersion o-F microcapsules before and af-ter treatment with resorcinol and ~ormaldehyde were obtained. These samples were designated respectively "Com-parative Sample C" and "Treated Sample D". A coating composition was prepared using each of Samples C and D using the following general formulation at 39.7%
solids in water. The amounts are given in parts on a dry ~eight basis ; Amount Microcapsules 51 Cooked Starch Binder 18 Uncooked Starch Binder 31 , . .
Each coating composition was applied to the back side o-f a 34 pound per 3300 square ~oot commerical CF paper. The CF paper contained a coating o~ a zinc modified phenol-Formaldehyde novolac resin o~ the front side. Typewriter intensity determinations o-f papers coated with several different weights of .
microcapsules were~as ~ollows: ' -Coating Composition MicrocapsuleCoat Weight Typewriter Contains _ (Pounds per 3300_square ft.) Intensity ~ 25 Comparative Sample C 1.84 66 " " " ' 1.9~ 63 ~ " " 2.26 , 60 Treated Sample D 1.48 65 : : " '' " 1.~6 ' ~ 6~
~: 30 The above test results showed that for a given microcapsule coat weight ; ' the coating composition containing the Treated Sample D performed bet-ter than the coating composition containing the Comparative (untreated) Sample C.
; - 19 --, - '~ . ' . .
Exall~inlt-i()ns of the coate(l pclpers re~Jelle~ thll siglli-ricant alnollnts oF
clus-tered (polynllclear) microcapsules were present in tl~e papers coated ~-iththe compos-itio1-s containiny Trea-te(l Sanlple D and -that such clustered micro-capsules were subs-tantially absent ir- the papers coated with the compositions 3 containing Compara-tive Sample C.
As used herein -the typewriter in-tensity is a contrast ra-tio and is equal to lG0 times the ratio -For the reflectance of a printed character divid ed by the background reflectance. A typewriter intensity value oF 100 incli-cates a not discernible print and a lower value indicates a more intense print.
Specifically the backside of the papers made in Example 4 and a CF sheet coa-ted with a phenolformaldehyde novolac resin were placed with the coated sides together and a series of close-spaced characters were typed on the test paper. Reflectance readings were then taken of the background and also the printed chracters transferred to the reactant sheet and the contrast ratio was 15 calculated.
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Claims (13)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for preparing filterable microcapsules comprising the steps of:
(a) preparing an aqueous dispersion of microcapsules containing an oil solution of a chromogenic material, said chromogenic material being an electron donor type color precursor, said microcapsules having a primary capsule wall comprising a reaction product of hydroxypropylcellulose and at least one oil soluble cross-linking agent for hydroxypropylcellu-lose, said cross-linking agent being selected from the group consisting of the polyfunctional isocyanates, acyl chlorides, phosphoryl chlorides, sulfonyl chlorides, alkylene bischloroformates and mixtures thereof, said primary capsule wall being substantially oil and water impermeable;
(b) adding and mixing into said aqueous dispersion of micro-capsules a phenol and an aldehyde, said aldehyde being selected from the group consisting of acetaldehyde, formaldehyde, glyoxal, glutaraldehyde, furfural and mixtures thereof; and (c) maintaining said mixing while said phenol and said aldehyde react together to form a condensation polymer, said condensation polymer being insoluble in said aqueous dispersion of microcapsules thereby precipitating said condensation polymer on said primary capsule wall as a secondary capsule wall.
(a) preparing an aqueous dispersion of microcapsules containing an oil solution of a chromogenic material, said chromogenic material being an electron donor type color precursor, said microcapsules having a primary capsule wall comprising a reaction product of hydroxypropylcellulose and at least one oil soluble cross-linking agent for hydroxypropylcellu-lose, said cross-linking agent being selected from the group consisting of the polyfunctional isocyanates, acyl chlorides, phosphoryl chlorides, sulfonyl chlorides, alkylene bischloroformates and mixtures thereof, said primary capsule wall being substantially oil and water impermeable;
(b) adding and mixing into said aqueous dispersion of micro-capsules a phenol and an aldehyde, said aldehyde being selected from the group consisting of acetaldehyde, formaldehyde, glyoxal, glutaraldehyde, furfural and mixtures thereof; and (c) maintaining said mixing while said phenol and said aldehyde react together to form a condensation polymer, said condensation polymer being insoluble in said aqueous dispersion of microcapsules thereby precipitating said condensation polymer on said primary capsule wall as a secondary capsule wall.
2. The process of claim 1 wherein said phenol is selected from the group consisting of resorcinol, hydroquinone, catechol, o-cresol, m-cresol/ p-cresol, Bisphenol A, naphthalenediols, gallic acid, phloroglucinol, pyrogallol, guaiacol, digallic acid, tannic acid, chlorophenols, xylenols, eugenol, hydroxy-biphenols, naphthols and mixtures thereof.
3. A process for preparing filterable microcapsules suitable for use in pressure-sensitive carbonless transfer papers comprising the steps of:
(a) preparing an aqueous dispersion of microcapsules containing a chromogenic material in a carrier oil, said chromogenic material being an electron donor type color precursor, said microcapsules having a primary capsule wall comprising a reaction product of hydroxypropylcellulose and at least one polyisocyanate, said primary capsule wall being sub-stantially impermeable to said carrier oil and water;
(b) adding and mixing into said dispersion of microcapsules (1) a phenol, said phenol being selected from the group consisting of resorcinol, hydroquinone, catechol, o-cresol, m-cresol, p-cresol, Bisphenol A, naphtha-lenediols, gallic acid, phloroglucinol, pyrogallol, guaiacol, digallic acid, tannic acid, chlorophenols, xylenols, eugenol, hydroxybiphenols, naphthols and mixtures thereof, (2) an aldehyde, said aldehyde being selected from the group consisting of acetaldehyde, formaldehyde, glyoxal, glutaraldehyde, furfural and mixtures thereof, and (3) sufficient acid to bring said aqueous dispersion of microcapsules to a pH of below about 6, said phenol, said aldehyde and said acid each being in the form of aqueous solutions; and (c) maintaining said mixing while said phenol and said aldehyde react together to form a condensation polymer, said condensation polymer being insoluble in said aqueous dispersion thereby precipitating said condensation polymer on said primary capsule wall as a secondary capsule wall.
(a) preparing an aqueous dispersion of microcapsules containing a chromogenic material in a carrier oil, said chromogenic material being an electron donor type color precursor, said microcapsules having a primary capsule wall comprising a reaction product of hydroxypropylcellulose and at least one polyisocyanate, said primary capsule wall being sub-stantially impermeable to said carrier oil and water;
(b) adding and mixing into said dispersion of microcapsules (1) a phenol, said phenol being selected from the group consisting of resorcinol, hydroquinone, catechol, o-cresol, m-cresol, p-cresol, Bisphenol A, naphtha-lenediols, gallic acid, phloroglucinol, pyrogallol, guaiacol, digallic acid, tannic acid, chlorophenols, xylenols, eugenol, hydroxybiphenols, naphthols and mixtures thereof, (2) an aldehyde, said aldehyde being selected from the group consisting of acetaldehyde, formaldehyde, glyoxal, glutaraldehyde, furfural and mixtures thereof, and (3) sufficient acid to bring said aqueous dispersion of microcapsules to a pH of below about 6, said phenol, said aldehyde and said acid each being in the form of aqueous solutions; and (c) maintaining said mixing while said phenol and said aldehyde react together to form a condensation polymer, said condensation polymer being insoluble in said aqueous dispersion thereby precipitating said condensation polymer on said primary capsule wall as a secondary capsule wall.
4. The process of claim 3 wherein said phenol is resorcinol, said resorcinol being present in said aqeous dispersion of said microcapsules in a ratio of about 0.015 parts to about 0.15 parts of said resorcinol to 1 part, dry weight, of said microcapsules having a primary capsule wall.
5. The process of claim 4 wherein said aldehyde is formaldehyde, said formaldehyde is present in said aqueous dispersion of said microcapsules in a ratio of about 0.2 parts to about 2.0 parts of said formaldehyde to 1 part, by weight, of said resorcinol.
6. A process for preparing filterable microcapsules suitable for use in pressure-sensitive carbonless transfer papers comprising the steps of:
(a) preparing an aqueous dispersion of microcapsules containing a chromogenic material in a carrier oil, said chromogenic material being an electron donor type color precursor, said microcapsules having a primary capsule wall comprising a reaction product of hydroxypropylcellulose and at least one polyisocyanate, said primary capsule wall being sub-stantially impermeable to said carrier oil and water;
(b) adding to said aqueous dispersion of microcapsules with mixing, resorcinol, formaldehyde and acid to a pH of below about 6, said resorcinol, said formaldehyde and said acid each being added in the form of an aqueous solution, said resorcinol being present in a ratio of about 0.015 parts to about 0.15 parts by weight of resorcinol to 1 part, dry weight, of microcapsules, said formaldehyde being present in a ratio of about 0.2 parts to about 2.0 parts of said formaldehyde to 1 part, by weight, of said resorcinol;
(c) heating, with mixing, said aqueous dispersion of micro-capsules to a temperature of from about 25° C to about 70° C
for a period of about 1 hour to about 16 hours while said resorcinol and said formaldehyde react together to form a condensation polymer, said condensation polymer being insoluble in said aqueous dispersion thereby precipitating said condensation polymer on said primary capsule wall as a secondary capsule wall; and (d) adjusting the pH of said aqueous dispersion of micro-capsules to a pH of above about 7.
(a) preparing an aqueous dispersion of microcapsules containing a chromogenic material in a carrier oil, said chromogenic material being an electron donor type color precursor, said microcapsules having a primary capsule wall comprising a reaction product of hydroxypropylcellulose and at least one polyisocyanate, said primary capsule wall being sub-stantially impermeable to said carrier oil and water;
(b) adding to said aqueous dispersion of microcapsules with mixing, resorcinol, formaldehyde and acid to a pH of below about 6, said resorcinol, said formaldehyde and said acid each being added in the form of an aqueous solution, said resorcinol being present in a ratio of about 0.015 parts to about 0.15 parts by weight of resorcinol to 1 part, dry weight, of microcapsules, said formaldehyde being present in a ratio of about 0.2 parts to about 2.0 parts of said formaldehyde to 1 part, by weight, of said resorcinol;
(c) heating, with mixing, said aqueous dispersion of micro-capsules to a temperature of from about 25° C to about 70° C
for a period of about 1 hour to about 16 hours while said resorcinol and said formaldehyde react together to form a condensation polymer, said condensation polymer being insoluble in said aqueous dispersion thereby precipitating said condensation polymer on said primary capsule wall as a secondary capsule wall; and (d) adjusting the pH of said aqueous dispersion of micro-capsules to a pH of above about 7.
7. A process for the production of a pressure-sensitive carbonless transfer sheet comprising the steps of;
(a) preparing an aqueous dispersion of microcapsules containing a chromogenic material in a carrier oil, said chromogenic material being an electron donor type color precursor, said microcapsules having a primary capsule wall comprising a reaction product of hydroxypropylcellulose and at least one polyisocyanate, said primary capsule wall being substantially impermeable to said carrier oil and water;
(b) adding and mixing into said aqueous dispersion of said microcapsules a phenol and an aldehyde, said aldehyde being selected from the group consisting of acetaldehyde, formaldehyde, glyoxal, glutaraldehyde, furfural and mixtures thereof;
(c) maintaining said mixing while said phenol and said aldehyde react together to form a condensation polymer, said condensation polymer being insoluble in said aqueous dispersion thereby precipitating said condensation polymer on said primary capsule wall as a secondary capsule wall;
(d) adding a binder to said microcapsules containing said secondary capsule wall to form a coating composition;
(e) applying said coating composition to a substrate; and (f) setting said coating composition to a solid coating.
(a) preparing an aqueous dispersion of microcapsules containing a chromogenic material in a carrier oil, said chromogenic material being an electron donor type color precursor, said microcapsules having a primary capsule wall comprising a reaction product of hydroxypropylcellulose and at least one polyisocyanate, said primary capsule wall being substantially impermeable to said carrier oil and water;
(b) adding and mixing into said aqueous dispersion of said microcapsules a phenol and an aldehyde, said aldehyde being selected from the group consisting of acetaldehyde, formaldehyde, glyoxal, glutaraldehyde, furfural and mixtures thereof;
(c) maintaining said mixing while said phenol and said aldehyde react together to form a condensation polymer, said condensation polymer being insoluble in said aqueous dispersion thereby precipitating said condensation polymer on said primary capsule wall as a secondary capsule wall;
(d) adding a binder to said microcapsules containing said secondary capsule wall to form a coating composition;
(e) applying said coating composition to a substrate; and (f) setting said coating composition to a solid coating.
8. A process for the production of pressure-sensitive carbonless transfer paper comprising the steps of:
(a) preparing an aqueous dispersion of microcapsules containing a chromogenic material in a carrier oil, said chromogenic material being an electron donor type color precursor, said microcapsules having a primary capsule wall comprising a reaction product of hydroxypropylcellulose and at least one polyisocyanate, said primary capsule wall being substantially impermeable to said carrier oil and water;
(b) adding and mixing into said aqueous dispersion of said microcapsules a phenol and an aldehyde, said aldehyde being selected from the group consisting of acetaldehyde, formaldehyde, glyoxal, glutaraldehyde, furfural and mixtures thereof;
(c) maintaining said mixing while said phenol and said alde-hyde react together to form a condensation polymer, said condensation polymer being insoluble in said aqueous dispersion thereby precipitating said condensation polymer on said primary capsule wall as a secondary capsule wall;
(d) adding a binder to said aqueous dispersion of said micro-capsules containing said secondary capsule wall to form an aqeuous coating composition;
(e) applying said aqueous coating composition to a paper substrate; and (f) drying said aqueous composition to a solid coating.
(a) preparing an aqueous dispersion of microcapsules containing a chromogenic material in a carrier oil, said chromogenic material being an electron donor type color precursor, said microcapsules having a primary capsule wall comprising a reaction product of hydroxypropylcellulose and at least one polyisocyanate, said primary capsule wall being substantially impermeable to said carrier oil and water;
(b) adding and mixing into said aqueous dispersion of said microcapsules a phenol and an aldehyde, said aldehyde being selected from the group consisting of acetaldehyde, formaldehyde, glyoxal, glutaraldehyde, furfural and mixtures thereof;
(c) maintaining said mixing while said phenol and said alde-hyde react together to form a condensation polymer, said condensation polymer being insoluble in said aqueous dispersion thereby precipitating said condensation polymer on said primary capsule wall as a secondary capsule wall;
(d) adding a binder to said aqueous dispersion of said micro-capsules containing said secondary capsule wall to form an aqeuous coating composition;
(e) applying said aqueous coating composition to a paper substrate; and (f) drying said aqueous composition to a solid coating.
9. A process for the production of a pressure-sensitive carbonless transfer paper comprising the steps of:
(a) preparing an aqueous dispersion of microcapsules containing a chromogenic material in a carrier oil, said chromogenic material being an electron donor type color precursor, said microcapsules having a primary capsule wall comprising a reaction product of hydroxypropylcellulose and at least one polyisocyanate, said primary capsule wall being substantially impermeable to said carrier oil and water;
(b) adding and mixing into said aqueous dispersion of said microcapsules a phenol and an aldehyde, said aldehyde being selected from the group consisting of acetaldehyde, formaldehyde, glyoxal, glutaraldehyde, furfural and mixtures thereof;
(c) maintaining said mixing while said phenol and said aldehyde react together to form a condensation polymer, said condensation polymer being insoluble in said aqueous dispersion thereby precipitating said condensation polymer on said primary capsule wall as a secondary capsule wall;
(d) filtering said aqueous dispersion of said microcapsules to obtain said microcapsules;
(e) dispersing said microcapsules in a liquid hot melt sus-pending medium to form a hot melt coating composition;
(f) apply said coating composition to a paper substrate; and (g) cooling said hot melt suspending medium to a solid coating.
(a) preparing an aqueous dispersion of microcapsules containing a chromogenic material in a carrier oil, said chromogenic material being an electron donor type color precursor, said microcapsules having a primary capsule wall comprising a reaction product of hydroxypropylcellulose and at least one polyisocyanate, said primary capsule wall being substantially impermeable to said carrier oil and water;
(b) adding and mixing into said aqueous dispersion of said microcapsules a phenol and an aldehyde, said aldehyde being selected from the group consisting of acetaldehyde, formaldehyde, glyoxal, glutaraldehyde, furfural and mixtures thereof;
(c) maintaining said mixing while said phenol and said aldehyde react together to form a condensation polymer, said condensation polymer being insoluble in said aqueous dispersion thereby precipitating said condensation polymer on said primary capsule wall as a secondary capsule wall;
(d) filtering said aqueous dispersion of said microcapsules to obtain said microcapsules;
(e) dispersing said microcapsules in a liquid hot melt sus-pending medium to form a hot melt coating composition;
(f) apply said coating composition to a paper substrate; and (g) cooling said hot melt suspending medium to a solid coating.
10. Microcapsules containing an oil solution of a chromogenic material, said chromogenic material being an electron donor type color precursor, said microcapsules having a primary capsule wall and a secondary capsule wall, said secondary wall surrounding and adhering to said primary capsule wall, said primary capsule wall comprising a reaction product of hydroxy-propylcellulose and at least one oil soluble cross-linking agent for hydroxypropylcellulose, said cross-linking agent being selected from the group consisting of the polyfunctional isocyanates, acyl chlorides, phosphoryl chlorides, sulfonyl chlorides, alkylene bischloroformates and mixtures thereof, said primary capsule wall being substantially impermeable to oil and water, said secondary capsule wall comprising a condensation polymer of a phenol and an aldehyde, said aldehyde being selected from the group consisting of acetaldehyde, formaldehyde, glyoxal, glutaraldehyde, furfural and mixtures thereof.
11. The microcapsules of claim 10 wherein said phenol is selected from the group consisting of resorcinol, hydroquinone, catechol, o-cresol, m-cresol, p-cresol, Bisphenol A, naphtha-lenediols, gallic acid, phloroglucinol, guaiacol, digallic acid, tannic acid, chlorophenols, xylenols, eugenol, hydro-xybiphenols, naphthols and mixtures thereof.
12. Microcapsules containing an oil solution of a chromogenic material, said chromogenic material being an electron donor type color precursor, said microcapsules having a primary capsule wall and a secondary capsule wall, said secondary wall surrounding and adhering to said primary capsule wall, said primary wall comprising a reaction product of hydroxypropyl-cellulose and at least one polyisocyanate, said primary capsule wall being substantially impermeable to oil and water, said secondary capsule wall comprising a condensation polymer of resorcinol and formaldehyde, said microcapsules having significant amounts of polynuclear microcapsule particles present, said polynuclear microcapsule particles being a cluster of smaller microcapsules enveloped by said secondary capsule wall.
13. A pressure-sensitive carbonless transfer paper comprising the microcapsules of claim 12 coated on a paper substrate.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US80952177A | 1977-06-24 | 1977-06-24 | |
| US809,521 | 1977-06-24 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1104881A true CA1104881A (en) | 1981-07-14 |
Family
ID=25201522
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA302,327A Expired CA1104881A (en) | 1977-06-24 | 1978-05-01 | Process for producing microcapsules having secondary capsule walls and microcapsules produced thereby |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPS5417377A (en) |
| CA (1) | CA1104881A (en) |
| DE (1) | DE2826939A1 (en) |
| GB (1) | GB1603448A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5346931A (en) * | 1991-02-09 | 1994-09-13 | Basf Aktiengesellschaft | Color former preparations |
| US9056948B2 (en) | 2010-03-12 | 2015-06-16 | Follmann & Co. Gesellschaft Fuer Chemie-Werkstoffe Und Verfahrenstechnik Mbh & Co. Kg | Microcapsules and production thereof |
| CN113453794A (en) * | 2018-12-18 | 2021-09-28 | 国际香料和香精公司 | Hydroxyethyl cellulose microcapsules |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3044113A1 (en) | 1980-11-24 | 1982-07-15 | Basf Ag, 6700 Ludwigshafen | GROCES CONTAINING MICROCAPSULES |
| PT78129B (en) * | 1983-08-18 | 1986-05-19 | Moore Business Forms Inc | Microcapsules with reduced permeability |
| JPS60149489A (en) * | 1984-01-17 | 1985-08-06 | Kureha Chem Ind Co Ltd | Partial pressure sensitive paper |
| US4601863A (en) * | 1984-02-09 | 1986-07-22 | Kanzaki Paper Manufacturing Co., Ltd. | Process for producing powder of microcapsules |
| DE19852928C1 (en) * | 1998-11-17 | 2000-08-03 | Steffen Panzner | Structures in the form of hollow spheres |
| DE102009012455A1 (en) * | 2009-03-12 | 2010-09-23 | Follmann & Co. Gesellschaft Für Chemie-Werkstoffe Und -Verfahrenstechnik Mbh & Co. Kg | Improved microcapsules and their preparation |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5030030A (en) * | 1973-07-19 | 1975-03-26 | ||
| CA1040018A (en) * | 1974-06-19 | 1978-10-10 | Dale R. Shackle | Cross-linked hydroxypropylcellulose microcapsules and process for making |
-
1978
- 1978-05-01 CA CA302,327A patent/CA1104881A/en not_active Expired
- 1978-05-23 JP JP6157078A patent/JPS5417377A/en active Pending
- 1978-05-31 GB GB2487678A patent/GB1603448A/en not_active Expired
- 1978-06-20 DE DE19782826939 patent/DE2826939A1/en not_active Withdrawn
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5346931A (en) * | 1991-02-09 | 1994-09-13 | Basf Aktiengesellschaft | Color former preparations |
| US9056948B2 (en) | 2010-03-12 | 2015-06-16 | Follmann & Co. Gesellschaft Fuer Chemie-Werkstoffe Und Verfahrenstechnik Mbh & Co. Kg | Microcapsules and production thereof |
| CN113453794A (en) * | 2018-12-18 | 2021-09-28 | 国际香料和香精公司 | Hydroxyethyl cellulose microcapsules |
| CN113453794B (en) * | 2018-12-18 | 2023-06-27 | 国际香料和香精公司 | Hydroxyethyl cellulose microcapsules |
Also Published As
| Publication number | Publication date |
|---|---|
| DE2826939A1 (en) | 1979-01-18 |
| GB1603448A (en) | 1981-11-25 |
| JPS5417377A (en) | 1979-02-08 |
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