US3437481A - Resin compositions - Google Patents

Description

United States Patent O Int. Cl. G03g /04 US. Cl. 961.8 12 ClalmS ABSTRACT OF THE DISCLOSURE Resin compositions, useful as binders for photoconductive coatings in electrostatic copying processes, are obtained by blending an alkyd resin having an acid number of less than and a hydroxyl number of less than 100, said resin being soluble in hydrocarbon solvents, and composed of (1) about 25 to 70% by weight of a monobasic acid of 4 to 26 carbon atoms, (2) about to 60% by weight of a polycarboxylic acid, and (3) about 15 to 45% by weight of a polyhydric alcohol; and (4) from 5 to 40% by weight of the blend of a polymer of a vinyl monomer having the general formula CH =CR R where R is selected from the group consisting of hydrogen, chlorine, and methyl radicals, and R is selected from the group consisting of phenyl, chlorine, fluorine,

o O--i JRa and radicals in which R is a lower alkyl group of 1 to 4 carbon atoms, said blend having an acid number of less than 10 and a hydroxyl number of less than 100.

The present invention relates to novel resin compositions and, more particularly, to resin compositions which are useful in the electro-photographic art.

Direct electrostatic processes employ a substrate, normally paper, containing a coating of a p'hotoconductor, such as zinc oxide, uniformly dispersed in a binder. Direct electrostatic processes are described in detail in US. Patent 3,052,539 and US. Patent 3,121,006. In the electrostatic process the Zinc oxide coated paper is first made sensitive to light by giving it a blanket negative electrostatic charge in the substantial absence of any ultra-violet or visible radiation. One convenient means of giving the zinc oxide layer on electrostatic negative charge is by means of ion transfer from a corona discharge. The zinc oxide photoconductive layer can then be exposed to a photographic image in the usual manner, portions of the zinc oxide or other photoconductor which receive light or ultra-violet radiation losing wholly, or in part (depending upon extent of exposure), the negative electrostatic charge, while the unexposed portions of the photoconductive layer retain their negative electrostatic charge. The resulting latent image can then be developed by means of a pigmented powder which has a charge opposite to the negative charge of the unexposed areas of the photoconductive layer. The pigmented powder is thus firmly attached or attracted to the negatively charged areas. The pigmented resin powder can then be affixed to the photoconductive layer by simply melting the resinous vehicle at a temperature below the charting temperature of the paper so that the resinous powder becomes fused to the surface of the original photoconductive layer.

Various means of developing the latent image in the photoconductive layer to a visible image. have been described in the prior art. A particularly useful means of developing the latent electrophotographic image comprises use of a magnetic brush. This magnetic brush development makes use of a ferromagnetic powder such as iron filings,

3,437,481 Patented Apr. 8, 1969 which have been intimately admixed wtih pigmented resin or sulfur. Agitation of the ferromagnetic powder and pigmented resin results in a triboelectric effect wherein the pigmented resin acquires an electric charge depending upon the relative position of the resin to the ferromagnetic powder in the triboelectric series. That is, ordinary iron powder is below most resins in the triboelectric series and admixture with a resin higher in the series results in the deposition of a positive electrostatic charge on the resin. The resulting mixture can then be picked up by a magnet on which the iron particles or other ferromagnetic powder particles arrange themselves in the conventional pattern so that the long chains of filings resemble an ordinary brush. On contacting the magnetic brush with the photoconductive material which has residual negative charge thereon, the electrostatic attraction between the charged pigmented resin particles and the oppositely charged image areas in the photoconductive material is greater than the attraction between these particles and the ferromagnetic powder, so that the pigmented resin is deposited on the surface of the photoconductive material, roughly in proportion to the residual charge on the surface of the photoconductive coating. Other methods of developing the latent image include the use of pigment dispersions in organic solvents and resin solutions.

The resin employed in combination with the photoconductor to form the photoconductive coating is of extreme importance in the success of the process. Thus, the resin must be an extremely good insulator which prevents decay of the electrostatic charge before the photoconductive coating is exposed to the image. In order to have the photoconductor accept a maximum electrostatic charge, it is necessary that as many of the individual photoconductor particles are separately encapsulated by the resin. The resin must therefore be capable of properly wetting the p-hotoconductor and keep it in place in the photoconductive matrix. Additionally, the resin should not interfere in the discharge of the electrostatic charge when the coating is exposed to the image to be copied. It will be apparent that the binder resin employed should cause good adhesion to the support. Furthermore, the resin should not exhibit color or decompose on aging. The resin should bond readily to the pigmented developer and give rise to good printing quality.

It is therefore an object of the present invention to prowide novel alkyd resin compositions. It is another object of the present invention to provide novel alkyd resin compositions which are particularly suitable for photoconductive coatings. Still another object of the present invention is to provide improved photoconductive coatings. Other objects will become apparent hereinafter.

The novel compositions of the present invention comprise blends of (a) alkyd resins which are soluble in hydrocarbon solvents and have acid numbers of less than 10 and hydroxyl numbers of less than with (b) 5 to 40% by weight of the composition of a polymer of a vinyl monomer having the general formula R2 where R is hydrogen, chlorine, or a methyl group, and R is selected from the group consisting of phenyl, chlorine, fluorine,

in which R is a lower alkyl group of 1 to 4 carbon atoms and preferably methyl or ethyl. When such a blend is employed as a binder in photoconductive compositions, the blend exhibits synergistically improved insulating and electrical properties as compared to the components of the blend. By acid number is meant the milliequivalents of KOH required to neutralize the acid in one gram of polymer and by hydroxyl number is meant the milliequivalents of KOl-I required to saponify the hydroxyl groups in one gram of resin on esterification with an acid anhydride. The details of these standard tests are known in the art.

Although alkyd resins have heretofore been employed as binders for photoconductors, such compositions have shown serious deficiencies with respect to their ability to retain an electrostatic charge in the absence of light and the degree to which such compositions can be charged. This deficiency of alkyd resins is in part ascribed to the wide molecular weight distribution of hydrocarbon soluble alkyd resins, and their high acid and hydroxyl numbers. Thus alkyd resins in order to be soluble in hydrocarbon solvents and when prepared by standard prior art methods, contain a high number of acid and hydroxyl groups which interfere in the dielectric properties desired in binders of photoconductors, Alkyd resins prepared by these techniques apparently retain, even on curing, a sufficiently high percentage of polar groups which interferes in the desired electrical properties of the coating. Standard polymerization techniques to decrease the acid numbers and the hydroxyl number result in hydrocarbon insoluble alkyd resins which cannot be employed to properly disperse the photoconductors to obtain a uniform distribution and individual particle insulation of such conductors in the coating.

More recently, however, a novel method for preparing alkyd resins has been discovered which involves a solution polymerization of the alkyd resin components to a more uniform and narrower molecular weight distribution allowing the formation of an alkyd resin of higher molecular weight which has the required low acid and hydroxyl number and yet is soluble in hydrocarbon solvents.

(The alkyd resins employed in the compositions of the present invention are preferably prepared by reacting the alkyd resin components to form an alkyd resin if a high acid number which is soluble, refluxing a solution of the acidic alkyd resin in a hydrocarbon solvent having a boiling point in the range of about 150 to about 420 F., the solvent being employed in a concentration of 30 to 70% of the total mixture, while removing any water of reaction and continuing the reaction until the desired acid number below is obtained. The alkyd resins are of the fast or air drying type which contain generally from about 25 to 70% by weight of the resin of a monobasic acid selected from the class consisting of aliphatic, alicyclic, and aromatic acids having from 4 to 26 carbon atoms, which can also be defined by the general formula RCOOH wherein R is a hydrocarbyl radical of 3 to 25 carbon atoms, about to about 60% by weight of the total composition of a polybasic acid containing two or more carboxylic acid groups, such as phthalic anhydride, phthalic acid, isophthalic acid, terephthalic acid, maleic anhydride, fumaric acid, adipic acid, and succinic acid, and from about 15 to 45% by weight of a polyhydric alcohol containing two or more hydroxyl groups such as trimethylol ethane, trimethylol propane, glycerol, pentaerythritol, sorbitol, ethylene glycol, propylene glycol, neopentyl glycol, hexane triol, and butylene glycol. The preferred monobasic acids employed in the alkyd resin compositions are the unsaturated fatty acids, having from 12 to 24 carbon atoms, such as are derived from soya, linseed, safilower, tung, cocoanut, walnut, rape seed, perilla, sunflower, castor, cottonseed, tuna, sardine, menhaden, and tallow oil. Other monobasic acids which can be employed in the alkyd resins either by themselves or in combination with the fatty acids include benzoic acid, p-tertbutyl benzoic acid, rosin acids, cyclohexane carboxylic acid, abietic acid, pelargonic acid and the like. The saturated acids can be used to control the viscosity of the resin and increase its thermoplasticity. Preferably saturated monobasic acids are employed in a concentration not exceeding 50% of the total concentration of monobasic acids. It is to be understood, however, that the composition of the alkyd resin employed in the present invention is not critical as long as the resin is soluble in a hydrocarbon solvent and has the required acid and hydroxyl number. The preparation of alkyd resins meeting these requirements is more fully disclosed in copending application SN. 1249 filed J an. 8, 1960* now abandoned.

As indicated hereinabove, the second component of the blends of the present invention comprises a polymer of a vinyl monomer containing substituents of the type defined. Particularly suitable polymers are the acrylic ester polymers and copolymers, vinyl halide polymers and c0- polymers, polystyrene, poly(alpha-methylstyrene) styrene acrylate copolymers and vinyl ester polymers. The acrylic esters of these polymers comprise in general esters of acrylic and methacrylic acid in which the ester radical contains from one to four carbon atoms and more particularly such acrylic esters as methyl methacrylate, ethyl acrylate, n-butyl acrylate, and isobutyl acrylate. The vinyl halide polymers employed are principally poymers of vinyl chloride and vinylidene chloride. The vinyl ester polymers employed are normally vinyl acetate polymers although polymers of vinyl esters having from four to six carbon atoms are operable. These vinyl polymers may be homopolymers or may be copolymers of each other and of other ethylenically unsaturated monomers. If copolymers of the described vinyl monomers are employed, the described vinyl monomers must constitute the major component of the vinyl resin, i.e., the concentration of the vinyl monomers or combination of the vinyl monomers must be greater than 50%. If a copolymer of these vinyl monomers with an unsaturated acid or unsaturated alcohol is employed, the concentration of the acid or alcohol in the vinyl resin must be such that the total acid concentration and hydroxyl concentration in the blend does not exceed the required acid and hydroxyl limitations. Thus, although it is feasible to employ for example a copolymer of ethyl acrylate and acrylic acid, which contains ethyl acrylate as the major component, or a similarly constituted copolymer of vinyl acetate and vinyl alcohol, which contains vinyl acetate as the major component, the concentration of the acid or alcohol comonomer should not be such that, when it is employed in the blend with the alkyd resin, the acid number of the blend exceeds ten or the hydroxyl number of the blend exceeds 100. Since, however, the vinyl resin can be employed in a concentration of 5 to 40% it will be apparent that the composition of the vinyl polymer can be substantially varied. Vinyl polymers which do not contain either acid or hydroxyl groups are, however, preferred blending agents for the binder compositions of the present invention.

The vinyl polymer is employed in a concentration of 5 to 40% and preferably in a concentration of 7 to 15% by weight of the total composition. More than one vinyl polymer can be employed. It will be recognized that in view of the properties required of good binders, the concentration of the vinyl polymer in the blend should be such that a compatible blend with the alkyd resin is formed, and hence the upper concentration of a particular vinyl polymer component in a particular blend may be limited by its compatibility with the alkyl resin.

The photoconductive compositions of the present composition are prepared using methods heretofore developed, such as described in US. Patents 3,128,179 and 3,121,006. In general the vinyl polymer is added to the alkyl resin solution to which is then added the photoconductor and such other additives as photosensitive dyes and similar materials. The ratio of the photoconductor, such as zinc oxide, to the binder can be varied over a wide range. Sufiicient binder, however, should be employed to insulate each of the photoconductive particles from the surrounding particles in the composition. The most useful or optimum quantity of zinc oxide to resin binder for a particular photoconductive composition can be readily determined by making a series of test coatings wherein the quantity and relative amounts of the photoconductor to the binder resin are employed. In general the ranges will be from 10 to 90% by weight of the total composition.

The present invention is further illustrated by the following examples, which, however, are not to be construed as limitative of the scope of this invention. Unless otherwise stated, all quantitative units are by weight.

Example 1 An alkyd resin was prepared by employing 725 parts of soya fatty acid, 332 parts of glycerol, 196 parts of pentaerythritol, and 932 parts of phthalic anhydride. The components were admixed and cooked in the conventional manner until an acid value of about 40-50 was reached, at which time the reaction mixture was diluted with 4,000 parts of xylene, and the reaction continued at reflux until a resin solution was obtained having an acid number of 6-10. The acid number was determined in accordance with the standard procedure and constitutes the number of milliequivalents of potassium hydroxide which are required to neutralize the acid in one gram of resin. At a non-volatile solids content of 50% this resin was found to have a viscosity of 15 to 25 stokes.

To 1620 parts of a 50% solution of this resin in xylene was added 200 parts of a 45% solution of a 50/50 n-butyl/ isobutyl methacrylate copolymer in V. M. P. naphtha, commercially available as Acryloid B-67. To this solution of the blend was added 3600 parts of zinc oxide and the resulting mixture was mixed for a period of approximately one hour. The composition was then applied to ordinary bond paper and a coating of about 2 grams per square foot was obtained on air drying. The resulting paper was charged under a corona discharge and thereafter exposed. The coating was found to accept a maximum voltage of 825 volts, showed a 20 second dark decay voltage of 760 volts, a one second exposure voltage of 410 volts, a residual voltage of 75 volts after an exposure time of 1.3 seconds. The print quality of the coating was extremely good. Particularly unexpected was the improvement in maximum voltage and residual voltage since the acrylate copolymer by itself has a maximum voltage of 400 to 500 volts while the alkyl resin by itself has a maximum voltage of 5 to 600 volts.

Example 2 The procedure of Example 1 was repeated employing instead of the acrylate copolymer a vinyl acetate copolymer commercially available as VAGD. The same electrical properties as obtained in Example 1 were obtained with this resin blend.

Example 3 The procedure of Example 1 was repeated using instead of the acrylate copolymer a copolymer of vinylidene chloride and vinyl chloride. Substantially the same electrical properties were obtained on the resulting coating as in Example 1.

Example 4 An alkyd resin was prepared by employing 638 parts soya fatty acid, 45.4 parts of p-tert-butyl benzoic acid, 299 parts of trimethylol propane and 635 parts of phthalic anhydride. The components were admixed and refluxed with 5% xylene at 400 F. until an acid number of 25 to 30 was attained. Xylene was then added until a non-volatile content of 50% was reached and the reflux was continued at 465 to 480 F. until a resin solution was obtained in which the resin had an acid number of 6 to 10, a hydroxyl number of 70 to 80, and a viscosity of 5 to 10 stokes at a non-volatile solids content of 50%. Photoconductive compositions were prepared following the procedure of Example 1. The electrical properties of coatings prepared from the photoconductive composition were the same as those shown in Example 1.

The foregoing examples have illustrated the preparation of the resin blends of the present invention, their use in the preparation of photoconductive elements and the outstanding electrical properties obtained as a result of using the resin blend of the present invention. Particularly noteworthy is the synergistic improvement in maximum voltage resulting from the use of the above specified resin components. It is to be recognized that substantially the same results are also obtained when using other alkyd resins so long as such alkyd resins have acid numbers below 10, hydroxyl numbers below 100, and so long as such resins are soluble in hydrocarbon solvents. The utility of the resin blends of the present invention is however not limited to the use of such resin blends in the preparation of photoconductive compositions. The resin blends of the present invention, in view of their ability to be air dried, have utility as coatings per se in a wide variety of applications.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

What is claimed is:

1. A photoconductive composition comprising a blend of (a) an alkyd resin having an acid number of less than 10 and a hydroxyl number of less than 100, said resin being soluble in hydrocarbon solvents, and composed of (1) about 25 to 70% by weight of monobasic acid of 4 to 26 carbon atoms, (2) about 15 to 60% by weight of a polycarboxylic acid, and (3) about 15 to 45 by weight of a polyhydric alcohol having more than two hydroxyl groups; and (b) from 5 to 40% by weight of the blend of a polymer of a vinyl monomer having the general formula where R is selected from the group consisting of hydrogen, chlorine, and methyl radicals, and R is selected from the group consisting of phenyl, chlorine, fluorine,

radicals in which R is a lower alkyl group of 1 to 4 carbon atoms, said polymer consisting essentially of said monomer, said blend having an acid number of less than 10 and a hydroxyl number of less than 100 and containing uniformly dispersed therein from 10 to by weight of the photoconductive composition of a photoco'nductor.

2. The photoconductive composition of claim 1 wherein at least 50% of the monobasic acid is unsaturated and has 12 to 24 carbon atoms.

3. The photoconductive composition of claim 1 wherein the polycarboxylic acid is phthalic anhydride, isophthalic acid, or mixtures thereof.

4. The photoconductive composition of claim 1 wherein the polyhydric alcohol is selected from the class consisting of pentaerythritol, trimethylol ethane, triethylol propane, and glycerol.

5. The photoconductive composition of claim 1 where'- in the monocarboxylic acid is a soya fatty acid.

6. A photoconductive composition comprising a blend of (a) an alkyd resin having an acid number of less than 10, a hydroxyl number of less than 100, said resin being soluble in hydrocarbon solvents and composed of (1) about 25 to 70% by Weight of an unsaturated fatty acid having from 12 to 24 carbon atoms, (2) about 15 to 60% by weight of a polycarboxylic acid selected from the class consisting of phthalic acid, isophthalic acid, adipic acid, fumaric acid, maleic acid, and anhydrides thereof, and (3) about 15 to 45 by weight of a polyhydric alcohol selected from the class consisting of glycerol, trimethylol ethane, triethylol propane, and pentaerythritol and (b) from to 40% by weight of the blend of a polymer of a vinyl monomer having the general formula where R is selected from the group consisting of hydrogen, chlorine, and methyl radicals, and R is selected from the group consisting of phenyl, chlorine, fluorine,

radicals in which R is a lower alkyl group of 1 to 4 carbon atoms, said polymer consisting essentially of said vinyl monomer, said blend having an acid number of less than and a hydroxyl number of less than 100 and containing uniformly dispersed therein from 10 to 90% by weight of the photoconductive composition of a photoconductor.

7. The photoconductive composition of claim 6 wherein the monomer of the vinyl polymer is an ester of acrylic acids, an ester of methacrylic acid, or a mixture thereof.

8. The photoconductive composition of claim 6 wherein the monomer of the vinyl polymer is vinyl acetate, vinyl chloride, vinylidene chloride, vinyl alcohol, or mixtures thereof.

9. The photoconductive composition of claim 7 wherein the monomer of the vinyl polymer is n-butyl acrylate, n-butyl methacrylate, or methyl methacrylate.

10. The photoconductive composition of claim 6 wherein the monomer of the vinyl polymer is vinyl chloride.

11. A photoconductive composition comprising a compatible blend of (a) an alkyd resin having an acid number of less than 10 and a hydroxyl number of less than 100 and (b) from 5 to 40% by weight of the blend of a polymer of a vinyl monomer having the general formula /R1 CHz=G where R is selected from the group consisting of hydrogen, chlorine, and methyl radicals, and R is selected from the group consisting of phenyl, chlorine, fluorine,

-ICIOR3 and OfiRa o o radicals in which R is a lower alkyl group of 1 to 4 carbon atoms, said polymer consisting essentially of said vinyl monomer, said blend having an acid number of less than 10 and a hydroxyl number of less than 100, and containing uniformly dispersed therein from 10 to by weight of the photoconductive composition of a photoconductor.

12. The photoconductive composition of claim 11 wherein the photoeonductor is zinc oxide.

References Cited UNITED STATES PATENTS 2,767,151 10/1956 Dunlap. 3,121,006 2/1964 Middleton 96-1.8 3,080,331 3/ 1963 Thielking 260-20 3,149,087 9/ 1964 Anagnostopoulos et al. 260-873 3,281,498 10/1966 Watkins et a1. 260873 FOREIGN PATENTS 236,675 12/1961 Australia.

r DONALD E. CZAIA, Primary Examiner. a W. E. PARKER, Assistant Examiner.

US. Cl. X.R.