CA1306566C - Aqueous coating agent, a process for its preparation, and its use for coating of cans - Google Patents
Aqueous coating agent, a process for its preparation, and its use for coating of cansInfo
- Publication number
- CA1306566C CA1306566C CA000544527A CA544527A CA1306566C CA 1306566 C CA1306566 C CA 1306566C CA 000544527 A CA000544527 A CA 000544527A CA 544527 A CA544527 A CA 544527A CA 1306566 C CA1306566 C CA 1306566C
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- Prior art keywords
- weight
- coating agent
- cans
- coating
- monomers
- 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.)
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F283/00—Macromolecular compounds obtained by polymerising monomers on to polymers provided for in subclass C08G
- C08F283/10—Macromolecular compounds obtained by polymerising monomers on to polymers provided for in subclass C08G on to polymers containing more than one epoxy radical per molecule
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
- C09D4/00—Coating compositions, e.g. paints, varnishes or lacquers, based on organic non-macromolecular compounds having at least one polymerisable carbon-to-carbon unsaturated bond ; Coating compositions, based on monomers of macromolecular compounds of groups C09D183/00 - C09D183/16
- C09D4/06—Organic non-macromolecular compounds having at least one polymerisable carbon-to-carbon unsaturated bond in combination with a macromolecular compound other than an unsaturated polymer of groups C09D159/00 - C09D187/00
Abstract
June 22, 1987 Aqueous coating agent, a process for its preparation, and its use for coating of cans Abstract of the disclosure The invention relates to an aqueous coating agent, obtained from an epoxy resin, ethylenically unsaturated monomers, some of which contain carboxyl groups, a peroxide ini-tiator in a proportion of at least 2% by weight, rela-tive to the total weight of the monomers, a crosslinking agent, a neutralizing agent, organic solvents, and, if ap-propriate, further conventional additives, such as plas-ticizers, stabilizers, wetting agents, dispersion auxi-liaries, catalysts and pigments. The coating agent is based on a binder a) which is obtainable from A) 20 to 80% by weight of an epoxy resin having an average of more than one epoxy group Per molecule and having an average molecular weight of at least 500, B) 1 to 60% by weight of polyester polycarboxylic acids having an average molecular weight of 500 to 5,000 and having an acid number of 30 to 150, and C) 10 to 50% by weight of ethylenically unsaturated monomers, 10 to 50% by weight of the monomers containing carboxyl groups, where the sum of A), 33 and C) is 100% by weight, June 22, 1987 Aqueous coating agent, a process for its preparation, and its use for coating of cans Abstract of the disclosure The invention relates to an aqueous coating agent, obtained from an epoxy resin, ethylenically unsaturated monomers, some of which contain carboxyl groups, a peroxide ini-tiator in a proportion of at least 2% by weight, rela-tive to the total weight of the monomers, a crosslinking agent, a neutralizing agent, organic solvents, and, if ap-propriate, further conventional additives, such as plas-ticizers, stabilizers, wetting agents, dispersion auxi-liaries, catalysts and pigments. The coating agent is based on a binder a) which is obtainable from A) 20 to 80% by weight of an epoxy resin having an average of more than one epoxy group per molecule and having an average molecular weight of at least 500, B) 1 to 60% by weight of polyester polycarboxylic acids having an average molecular weight of 500 to 5,000 and having an acid number of 30 to 150, and C) 10 to 50% by weight of ethylenically unsaturated monomers, 10 to 50% by weight of the monomers containing carboxyl groups, where the sum of A), B) and C) is 100% by weight,
Description
~3~i5i~
P~T 86 094 June 22, 1987 9ASF Lacke ~ Farben Aktiengesellschaft, Munster s Aqueous coating agent, process for its preparation, and ;ts use for coating cans The invention relates to an aqueous coating agent ob-1~ tained from an epoxy resin, ethylenically unsatura-ted monomers, some of which contain carboxyL groups, a peroxide initiator, a crosslinking agent, a neutralizing agent, organic solvents, and, ;f appropriate, further conventional additives, such as ptasticizers, stabilizers, wetting agents, dispersion auxiliaries, catalysts and pigments.
H;gh-molecular-weight epoxy resins are suitable, in par-ticular, for internal protective lacquers for tinplate packaging. The crosslinking agents used are, for example, phenol-formaldehyde, melamine and urea resins. Due to the prespecified application viscos;ty, such coating agents based on solvents have a solvent content which is usually between 70 and 60g. If - as in the coating of two-part drink cans - ;t is necessary to carry out the application of the coat;ng by spraying, a turther in-crease in the solvent content usually results~ which has the consequence of great pollution through solvent emis-sions.
3~
In contrast to this, the advantages of aqueous coating systems are to be seen in a markedly reduced solvent emis-sion. In th;s connection, the application of aqueous synthetic resin dispersions by means of electrocoating is particularly advantageous, since a v;rtually 100~ coat-ing yield and a further reduced emission of solvents can be achieved using this method. In addition, it is poss-ible to coat a very ~ide variety of can geometries using electrophoretic coating through the effect of the thro~-ing power of electrodeposition coatings, a uniform coatingthickness, and thus also good edge coverage, being achieved, in contrast to coating application by spraying. In addi-tion, the electrocoating process offers the best prerequi-sites for process automation, this process additionally of-fering the opportunity for savings besides the reduced ma-terial requirement.
As is kno~n, electrocoating can be smployed both for an-ionic and for cationic binder systems. However, in the case of coneact with foodstuffs, for example for interna!
coatings of cans, it must be remembered that internal protective coatings must meet strict legal requirements regarding foodstuffs. In addition, such coatings must be stable on storage in contact with the contents, Z5 which are mainly acidic to neutral. Taking into account these requirements, anodic electrocoating is, in prin-ciple, more advantageous than the cathodic version since cathodically deposited films usually contain amine groups and can thus give rise to stability weaknesses on contact - 3 - 13~,~6~6 with acidic contents.
Solvent containing internal protective coatings for cans which are based on combinations of epoxy resins and phenol-formaldehyde resins or amino resins and which have good properties have long been known for coating cans.
In particular, epoxy resins which are based on bisphenol A and have average molecular weights of more than 3,000 g~mol give rise to very resistant coatings, whereas phenol-formaldehyde resins make a decisive contribution to stab-ility against acidic and sulfur-producing contents.
In order to use such systems in an aqueous medium, the epoxy resin must be modified by incorporation of solubi-lizing groups in a fashion such that a water-soluble or water-dispersible system is produced. Cationic, aqueous systems can be obtained in a known fashion by reaction of epoxy resins with amines. For the preparation of anionically dissolved synthetic resins, a carboxyl func-tionality is usually introduced. To this purpose, theepoxy resin, as described, for example, in US Patent 3,862,914, is converted into a carboxyl-functional poly-mer by means of a reaction with polycarboxylic anhydrides.
Such systems, in which polycarboxylic acids are bound to polymers via monoester functions, are however extremely susceptible to hydrolysis, which causes the storage sta-bility of the corresponding aqueous dispersions of such polymers to be too low tE.T. Turpi-n, J. Paint Technol., Vol. 47, No. 602, page 40, 1975). Hydrolysis-stable 13(~
attachment of the carboxyl functionality to the epoxy resin can be achieved according to US Patent 3,960,795 by reacting the epoxy functions with parahydro~ybenzoates with formation of an ether bond, followed by hydrolysis of the benzoate with liberation of the carboxyl function-ality. The disadvantage of this method is that, in par-ticular, the high-molecular-weight epoxy resins which are requ;red for internal protective coatings for cans cannot be functionalized with carboxyl groups by this route to the extent necessary for an aqueous dispersion, as a consequence of their low content of epoxy groups.
US Patent 4,247,439 and European Patents 6334 and 6336 disclose hydrolysis-stable aqueous internal protective coatings for cans, which coatings are obtained from products of the esterification of epoxy resins using carboxyl-functional polyacrylate resins. In addition, hydrolysis-stable, aqueous internal protective coatings for cans have been disclosed by US Patent 4,21Z,781 and US Patent 4,308,185.
The genus-forming US Patent 4,21Z,781 discloses resin mix-tures which are dispersible in an aqueous, basic medium and which are obtained by copolymerization of ethyleni-cally unsaturated monomers, some of which contain carboxyl groups, in the ?resence of an aliphatic or aromatic 1,2-diepoxy resin using at least 3~ by weight, relative to the ~eight of the monomer, of benzyl peroxide or equi-valent initiators. The resin mixtures disclosed by US
5 13~f ~S~6 Patent 4,21Z,781 can be crosslinked using amino resins.
They are suitable, in particuLar, for spray coating of drink cans.
S German Offenlegungsschrift 3,446,178 discloses water-dilutable compositions for coating of metal cans, the poly-mer present in the composition comprising a product of the reac~ion of acrylic monomers, a high-molecular-weight epoxy resin, a phenol-formaldehyde resin and a free-radical initiator.
The aqueous systems known from the prior art are employedmainly for spray coating of two-part aluminum drink cans.
They have the disadvantage that they offer inadequate surface protection on difficult substrates, such as, for example, drawn and ironed drink cans made from tinplate.
The object of the present invention was to provide an aqueous coating agent for coating metal cans, where uni-versal applicability of the coating agents is to be gua-ranteed, ie. the coating agents must be suitable for coat-ing cans made from aluminum, tinplate and other specifi-cally surface-pretreated steel. In particular, the coat-ing of two-part drink cans ;s considered, but, in addition, also the coating of food cans, which need to be stable to a wide range of contents, even under sterilization ron-ditions. The new coating systems are also intended to offer adequate surface protection on difficult substrates.
Substrates which are regarded as difficult here are, for ~3~
example, drawn and ironed tinplate cans which have a thin tin coat;ng and whose surface, as is known, comprises iron, a little free tin and various iron-tin alloys. In particular, the aqueous dispersions are intended to be storage-stable, and they should allow themselves to be readily pigmented. Coating agents prepared therefrom shouLd allow themselves to be applied without flaws by spray coating and also by anodic electrocoating. In the case of electrocoat;ng, the binders must coagulate at the can, connected as the anode, under the influence of the electrode reactions to form a closed coating fiLm ~Jhich has the highest possible film resistance. In this pro-cess, all coating agent components, such as crosslinking agents, auxiliaries and, if appropriate, pigments must be deposited in the amount ratio in which they are also present in the dispersion. In most systems of the prior art, the problem occurs that the neutral crosslinking agent is not deposited to the e~tent that it ;s present in the aqueous dispersion.
A further requirement of the coating agents to be prepar-ed is that the electrodeposition coatings should make possible coat;ng times of between about 0.5 and 30 se-conds, taking into account the c;rcumstances in industrial can manufacture. Under these conditions, it must be poss-ible to produce film thicknesses of between about 4 and 10 ~m which are typical for tinplate packaging. To accom-plish this, the wet-film resistance must be at least 10~ Q 1cm 1. The throwing power of the electrodeposition 5~
coating should be so well developed that it is possible to coat even complicated can geometries with an imperme-able coating film of constant coating thickness. Fur-thermore, the current strength/voltage character;stics of S the electrocoating materials must be matched to elec-trode geometries which can be used in practice.
The wet depos;ted films should be sufficiently hydropho-bic to make it possible to rinse the cans with common rinsing media, such as distilled water, drinking water, ultrafiltrate, and to exclude redissolution in the elec-trocoating material.
The baked coating films should at least reach the property levels of convent;onal internal protective coatings for cans with respect to freedom from pores, stability towards the contents, adhesion to the metal, hardness, elasticity and flavor neutrality, or should surpass these levels. To this purpose, the residual monomer contents ;n the binders must, if appropriat~, be kept as small as possible by suitable preparation processes. for first assessment of the con-tents stability in the form of short tests, the pasteur-i7ation or sterilization stability of baked coating films towards various test solutions - in the simPlest case towards water - is important here.
The object of the present invention is achieved by the aqueous coating agent of the type mentioned initially, wherein the coating agent is based on a binder a) which ~3~5~;
is obtainable from A) 20 to 80X by weight of an epoxy resin having an aver-age of more than one epo~y group per molecule and hav-ing an average molecular weight of at least 500, 5 9) 1 to 60% by weight of polyester polycarboxylic acids having an average molecular ~eight of 500 to 5,000 and having an acid number of 30 to 150, and C) 10 to 50~ by weight of ethylenically unsaturated mono-mers, 10 to 50% by weight of the monomers containing carboxyl groups, where the sum of A), B) and C) is 100~ by weight, the peroxide initiator is employed in a proportion of at least 2% by weight, relative to the total weight of the monomers C), the binder a) has an acid number of 20 to 150, and the crosslinking agents b) used are phenolic and/or amino resins, with the proviso that the coating agent contains a) 30 to 70% by we;ght of the binder a), b) 2 to 30% by weight, preferably 5 to 16% by weight, of the phenolic and/or am;no resin b), c) 1 to ~X by weight, preferably 2 to 5~ by weight, of ammonia and/or amine as neutralizing agent, and d) 20 to 60% by w~ight of organic solvents, where the sum of a), b), c) and d) is 100X by weight.
As component A), polyglycidyl ethers of bisphenol A hav ing an average molecular weight of 500 to 20,000 are pre-ferably employed. Examples of suitable epoxy resins are glycidyl polyethers, which are marketed, for example, V~ 5~
under the tradenames Epikote 10~1, 1004, 1007 and 1009.
The epoxy resins (component A) advantageously have an average molecular weight of at least 3,000 g/mol.
The polyester polycarboxylic acids employed as component ~) are prepared under the conditions known to those skilled in the art for polyester;f;cat;on reactions. These com-pounds are known polycondensates made from aromatic and/
or aliphatic d;carboxylic acids, aromatic dicarboxylic anhydrides, aromatic tricarboxylic anhydrides, aromatic tetracarboxylic anhydrides and dianhydrides, and aliphatic and cycloaliphatic mono-, di- and triols. Preferred starting compounds for the polyester polycarboxylic acids are tereph-thalic acid, isophtha~ic acid, trimellitic acid, trimellitic anhydride, adipic acid, sebacic acid, aliphatic monools having 4 to 20 carbon atoms, 2,2-dimethyl-1,3-propanediol, ethylene glycol, diethylene glycol, trimethylol propane, glycerol and pentaerythritol.
The polyester polycarboxylic acids 8) preferably have an average molecular weight of 1,000 to 3,000 and an acid number of 50 to lU0.
A preferred embodiment of the polyester polycarboxylic acid component 8) comprises using ester diols and/or gly-cidyl esters of monocarboxylic acids as the polyol com-ponent for the preparation of the polyester polycarboxy-lic acids. Neopentyl glycol hydroxypivalate may be men-tioned as an example of a suitable ester diol. A suitable - 10 ~
commercially available glycidyl ester of monocarboxylic acids is the glycidyl ester of versatic acid, a branched monocarboxylic acid.
The polyester polycarboxylic acids prepared using ester diols and/or glycidyl esters of monocarboxylic acids have acid numbers in the range ~rom 100 to 130.
10 to 50% by ~eight of the ethylenically unsaturated mono-mers employed as component C) are monomers containing carboxyl groups. Examples which should be mentioned of monomers containing carboxyl groups are acrylic acid and methacrylic acid. In addition, nonfunctionali~ed mono-mers, such as, for example, styrene, vinyltoluene and r~-methylstyrene~ may be employed as monomers.
(Meth)acrylates having 1 to 20 carbon atoms in the alco-hol radical are preferably used as the third class of monomers, it also being possible to employ hydroxy-func-tional monomers. Examples of these are ethyl acrylate,propyl acrylate, isopropyl acrylate, butyl acrylate, iso-butyl acrylate, t-butyl acrylate, pentyl acrylate, decyl acrylate, lauryl acrylate, methyl methacrylate, butyl methacrylate, isobutyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, nonyl meth-acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxyethyl methacrylate, hydroxy-propyl methacrylate and hydroxybutyl methacrylate.
13~S~
The ethylenicalLy unsaturated monomers of component C~
preferably co~prise ~) 10 to S0% by weight, preferably 20 to 40% by weight, of monomers rontaining carboxyl groups, 5 y) 0 to 50% by weight, preferably 20 to 40~ by weight, of nonfunctionalized monomers, and z) S to 60X by weight, preferably 10 to 50% by weight, of (meth)acrylates, having 1 to 20 carbon atoms in the alcohol radical, and, if appropriate, being hydroxy-functional,where the sum of x), y) and z) is 100X by weight.
Component C) has an acid number in the range from 30 to 150, preferably in the range from 50 to 100.
The binder a) is preferably obtained from 35 to 60~ by weight of A), 10 to 35% by weight of 8) and 15 to 30~ by weight of C), where the sum of A), B) and C) is 100% by weight.
It is preferred that at least 2.6~ by weight, parti-cularly preferably at least 3~ by weight, relative to the total weight of the ethylenically unsaturated monomers, of peroxide initiators are enployed.
According to the present invention, any phenolic resin can be used so long as it has the methylol functionality which is necessary for the reactivity. Preferred phenolic resins are products, prepared under alkaline conditions, - 12 - 13~S~
of the reaction of phenol, substituted phenols and bis-phenol A with formaldehyde. Under such conditions, the methylol group is linked to the aromatic ring either in the ortho or in the para position.
s Phenolic resins of the resol type ~hich are based on bis-phenol A and contain more than one methylol group per phenyl ring are preferably employed.
Typical amino resins are melamine, benzoguanamine and urea-formaldehyde resins. These are preferably used in the form which has been etherified with lower alcohols, usually butanol. Suitable amino resins are commercially ;`' ~rqde~
" ~available, for example, under the tr~e~4 Cymel. A
suitable amino resin is, for example, hexamethoxymethyl-melamine.
Of course, besides condensation products with formalde-hyde, those with other aldehydes can also be used.
According to the invention, the coating agent contains 1 to 7~ by weight, preferably 2 to S% by weight, of ammonia and/or amines as neutralizing agents. The coating agent becomes dispersible in water through neutralization with component c). Triethylamine and/or dimethylethanolamine are preferably employed as neutralizing agents.
The aqueous coating agents according to the inven~ion furthermore contain 20 to 60% by weight of organic 13U~5~6 solvents. When the aqueous coating agents are used as anodic electrodeposition coatings, it must be ensured that the organic solvents positively influence the effec-tiveness of the anodic deposition and the flow of the coating film. In a preferred fashion, nonvolatile cosol-vents are employed, such as monoalcohols having 4 to 18 carbon atoms, glycol ethers, such as, for example, ethy-lene glycol monoethyl ether and its higher homologs hav-ing 5 to 20 carbon atoms, or corresponding ethers of 1,2-and 1,3-propanediol.
The coating agents according to the invention and describ-ed above are prepared in a process wherein the epoxy re-sin A) is initially reacted with the polyester polycar-boxylic acid component 8) at 80 to 200C, preferably at120 to 180C, with the use of catalysts, so that at least 80% of the oxirane rings initially present are opened, component C) is subsequently subjected to free-radical polymer;zation, in the presence of the reaction product obtained in the first process step, at 100 to 160C, pre-ferably 120 to 140C, with the use of at least 2% by weight, relati~e to the weight of the ethylenically unsaturated monomers, of peroxidic initiators preferably ones which generate benzoyloxy and/or phenyl free radicals, the pro-duct obtained is neutralized in a third process step usingcomponent c), and the organic solvent d), the crosslinking agent b) and, if appropriate, further conventional addi-tives are added and mixed, and the coating agent is dis-persed in uater.
- 14 ~3~6S~
The reaction of the epoxy resin with polyester polycar-boxylic acids taking place in the first process step is cata~yzed by amines, preferably tertiary amines. The re-action is carried out in a fashion such that at least 80%
S of the oxirane rings are converted into ~-hydroxyester groups.
In the second process step, the ethylenically unsaturated monomers, some of wh;ch conta;n carboxyl g,oups, of com-ponent c) are subjected to a free-radical polymerization reaction in the presence of the B-hYdroxYester produced in the first process step. The free-radical polymeriza-tion is initiated by at least 2X by weight, relative to the total weight of the monomers, of peroxidic initiators, preferably ones which generate benzoyloxy and/or phenyl free rad;cals. In this reaction, at least 2.6~ by ~eight of initiators are preferably used, particularly prefer-ably at least 3~ by weight. Of course, good results are also achieved when high proportions, for example 8 to 10%
by weight, of initiators are employed, but this is not recommended for economic reasons. If the polymerization is carried out in the presence of relatively low initiator concentrations, for example with less than 3X by weight, relative to the monomer weight, a higher degreee of neu-tralization is necessary in order to obtain a stable dis-persion (cf. Example 3 from Table 1).
Primarily, peroxidic initiators are employed which decom-pose to produce benzoyloxy and/or phenyl free radicals.
, 5 13 U ~;i 5ir^i ~
Of course, it is also possible to use other initiators so long as these lead to equivalent free-radical condi-tions.
S Preferred initiators are dibenzoyl peroxide and/or tert.
butyl perbenzoate. Further possible initiators which should be ment;oned are tert. butyl peroctoate, cumene hydroperoxide and methyl ethyl ketone peroxide.
1û The proportion of residual monomers is advantageously kept to less than 0.2~, relative to the sum of a) to d), by adding further initiator and/or by extending the ini-ator feed time.
After the free-radical polymeri2ation, the polymer ob-tained is neutralized in a third process step in order to make the coating agent water-dispersible. The nonvola-tile cosolvent d) necessary for production of a readily flowing, anodically deposited film, the phenolic resins 2û or a0ino resins b) used as crossl;nking agents, and fur-ther addit;ves uhich are conventional, for example, in electrocoating are added and mixed with the system. Fin-ally, the system is dispersed in water.
A preferred embodiment of the process according to the invention co~prises carrying out a precondensation with the crossl;nking agent b) after the free-radical polymer-ization. In this fashion, the crosslinking agent b) is also deposited during electrocoating to the same extent 3.3~
as it is present in the aqueous coating agent.
The mixture obtained before dispersal in ~ater can be used as a compensation coating by not preparing the aque-S ous dispersion until the binder is incorporated into theelectrodeposition coating.
A preferred embodiment of the process according to the invention comprises already using the organic solvent d) as a solvent in the esterification, occurring as the first process step, of the epoxy resin A~ and the polyester polycarboxylic acids B).
The aqueous coating agents according to the invention are advantageously used for anodic electrocoating of cans and can halves. Of course, they can also be employed for spray coating of cans. In anodic electrocoating, the cans are dipped in an aqueous bath based on the coating agent according to the invention described above and are 2û connected as the anode.
By means of direct current, a film is deposited on the cans, the substrate is removed from the bath, and the film is hardened by baking.
~oth in spray coating and in electrodeposition, the final hardening of the coating film is carried out by baking.
The aqueous coating agents according to the invention are ~3~
suitable for coating of cans which can comprise d;fferent materials and which can have a very wide variety of can geometr;es. Thus, cans made from aluminum and those made ~rom tinplate, for example drawn ancl ironed, two-part S drink cans, can be coated equally well using the coating agints according to the invention. In addition, cans made from surface-Pretreated steel sheeting can be coated e%cel~ently.
The aqueous coat;ng agents described above are likewise highly suitable for coating foodstuff cans which have been drawn and ironed or deep-drawn in another fashion and which are subjected to sterilization for preservation of the contents.
The can halves discussed are bodies and lids which are used for the manufacture of foodstuff cans. Anodic coating of the can halves has proven particularly advantageous when the bodies are welded and the lids are pull-tab lids.
2û
The advantages of the process according to the invention are that there is a wide variety of possible ways of con-trolling the acid number by varying the polyester or the polymer. In this ~ash;on, applicational properties and adhesion properties can be optimized for specific metal surfaces. The compatibility of the components with one another and the safety with respect to residual monomers are ensured by the polymerization process.
SI~
The aqueous coa~ing agents according to the invention are storage-stable and can be applied without flaws by means of anodic electrocoating. The baked coating films ob-tained have a good property level with respect to freedom S from pores, stability towards the contents, adhesion to the metal, hardness, elasticity and flavor neutrality.
In addition, the binder combinations employed enable good pigment wetting.
The invention is described in greater detail below ~ith reference to illustrative embodiments:
1. Preparation of a polyester polycarboxylic acid 15 1.1 1,330 9 of isophthalic acid, 145 9 of adipic acid, 780 9 of 2,2-dimethyl-1,3-propanediol, 268 9 of tri-methylolpropane and 200 9 of isodecanol are weighed out into a four-neck flask fitted with stirrer, thermometer and water separator, and the mixture is condensed at 220C to an acid number of less than 5 mg of KOH/g. 500 9 of trimellitic anhydride are added at 110C, and the batch is kept at this tem-perature until the viscosity becomes constant. Fin-ally, the polyester resin melt is dissolved in butyl glycol to give a 70X strength solution. The acid number is 85 mg of KOH/g.
1.2 1,200 9 of the glycidyl ester of versatic acid, 900 9 of 2-butanone, 900 9 of trimellitic anhdyride and :13(~65~i _ 19 _ 5 9 of N,N-dimethylbenzylamine are warmed to 90C in a four-neck flask fitted with stirrer thermometer and reflux condenser. When the viscosity (measured at 23C) has increased to 1.5 Pas the batch is cooled and discharged.
2. Preparation of epoxy ester resins 2.1 Prepara~ion of an epoxy ester resin based on the 1û polyester polycarboxylic acid prepared under 1.1.
A mixture of 1 050 9 of an epoxy resin based on bis-phenol A and having an epoxy equivalent weight of 3,400 700 9 of butyl glycol 3S0 9 of 1-phenoxy-2-propanol Z g of N N-di1ethylbenzylamine and 1 000 g of the polyester polycarboxylic acid prepared un-der 1.1 is warmed to 160C in a four-neck flask fitted with stirrer,.thermometer and reflux conden-ser until the acid number has fallen to 20 mg of KOH/g. In a 30X strength solution in butyl glycol, the epoxy ester thus prepared has a viscosity of 370 mPa.s at 23C.
2.2 Preparation of an epoxy ester based on the polyester carboxylic acid prepared under 1.2 A solution of 1,050 9 of an epoxy resin based on bisphenol A and having an epoxy equivalent ueight of 3 400, in 1 000 g of butyl glycol and 440 9 of ~3~t~
propylene glycol monophenyl ether is heated to 140C
in a four-neck flask fitted with stirrer, thermome-ter and distillation attachment. After 2 g of N,N-dimethylbenzyla~ine are added, 950 9 of the potyes-ter polycarboxylic acid prepared under 1~2 are run in and the solvent (2-butanone) is simultaneously distilled off. The batch is kept at 160C for a further 3 hours. The acid number is then 37 mg of KOH/g and the viscosity (of a 30~ strength sotution in butyl glycol at Z3C) is 380 mPa.s.
3. Preparation of binder solutions from the epoxy ester resins prepared under 2.
3.1 Preparation using the epoxy ester resin prepared un-der 2.1 Example 1 2,400 9 of the epoxy ester prepared under 2.1 are placed in a four-neck flask fitted ~ith stirrer, thermometer, reflux condenser and tuo supply con-tainers. At 140C, a mixture of 130 9 of acrylic acid, 160 9 of styrene and 200 9 of butyl acrylate is added to this from the first supply container and a solution of 30 9 of tert. butyl perbenzoate in 40 9 of butyl glycol is simultaneously added from the second supply container. The monomers are added over 2 hours and the initiator over 3 hours. When - 21 - ~3~6~
the polymerization is complete, 190 9 of a highly methylolated bisphenol A-formaldehyde resin are pre-condensed w;th the batch at 90C for 2 hours~
A 58~ strength b;nder solution is produced which, after addition of basic neutralizing agents, can be employed directLy as a compensation coating for anodic electrocoating~
Example 2 Z,400 9 of the epoxy ester prepared under 2.1 are placed in a four-neck flask fitted with stirrer, thermometer, reflux condenser and two supply con-tainers. At 140C, a mixture of 130 9 of acrylic acid, 160 9 of styrene and 200 9 of butyl acrylate is added to this from the first supply container and a solution of 30 9 of tert. butyl perbenzoate in 40 9 of butyl gLycol is added simultaneously from 2û the second supply container. The monomers are add-ed over 2 hours, and the initiator over 3 hours.
~hen the polymerization is complete, 190 9 of a butylated melamine-formaldehyde resin are added.
A 58~ strength binder solution is produced which, after addition of a basic neutralizing agent, can be employed directly as a compensation coating for anodic electrocoating.
13~'~S~
ExampLe 3 2,352 9 of the epoxy ester prepared under 2.1 are placed in a four neck flask fitted with stirrer, thermometer, ref~ux condenser and t~o supply con-tainers. At 140C, a mixture of 130 9 of acry~ic ac;d, 160 9 of styrene and 190 9 of butyl acrylate is added to this from the first supply container and a solution of 13.4 9 of tert. butyl perbenzoate in 4û 9 of butyl glycol is added simultaneously from the second supply container. The monomers are add-ed over 2 hours, and the initiator over 3 hours.
hhen the polymerization is complete, 19û 9 of a h;ghly methylolated bisphenol A-formaldehyde resin are precondensed with the batch at 90C for 2 hours.
A 57% strength binder solution is produced which, after addition of bas;c neutralizing agents, can be employed directly as a compensation coating for anodic electrocoating.
3.2 Preparation using the epoxy ester resin prepared under 2.2 Example 4 2,100 9 of the epoxy ester prepared under 2.2 and 300 9 of butyl glycol are placed in a four-neck flask fitted with stirrer, thermometer, reflux condenser and two supply containers. At 140C, a mixture of 130 9 of acryLic acid, 160 9 of styrene and 200 g of butyl acrylate is added to this from the first supply container and a solution of 30 9 S of tert. butyL perbenzoate in 40 9 of butyl glycol is added simultaneously from the second supply con-tainer The monomers are added over 2 hours, and the initiator over 3 hours. When the polymerization is complete, 190 9 of a highly methylolated bisphenol A-formaldehyde resin are precondensed with the batch at 90C for 2 hours.
A 56X strength binder solution is produced which, after addition of basic neutralizing agents, can be employed directly as a compensation coating for anodic electrocoating.
3.3 Comparison Examples Comparison Example 1 Modification of an epoxy resin using trimellitic anhydride In order to prepare a comparison batch wi~hout addi-tion polymer, the high-molecular-weight epoxy resin employed under 2. is reacted with trimellitic anhyd-ride after esterification of the glycidyl radicals using a monocarboxylic acid.
13~65~i To this purpose, 41.8 par~s of a high-molecular-weight epoxy resin based on bisphenol A and having an epoxy equivalent weight of 3,400 are dissolved in 41.C parts of ethylene glycol monobutyl ether and S reacted at 130C with 1.94 parts of isononanoic acid and O.û6 parts of N,N-dimethylbenzylamine until the acid number has fallen to below 3 mg of KOH/g.
7.7 parts of trimellitic anhydride are added, and the temperature is maintained until an acid number of 80 mg of KOHtg is reached. After cooling to 90C, 3.5 parts of a phenol-formaldehyde resin (resol tyDe based on bisphenol A) are added, and the batch is stirred at 90C for 2 hours. The solids content is then 55~.
Comparison ~xample 2 Preparation of an acrylic-epoxy graft polymer In order to prepare a comparison ba~ch, a monomer mixture is polymerized in the presence of a high-molecular-weight epoxy resin, but in the absence of a polyester component.
To this purpose, 1,120 9 of a high-molecular-weight epoxy resin based on bisphenol A and having an epoxy equivalent weight of 3,400 are dissolved in 570 9 of butyl glycol and 850 9 of n-butanol and reacted at 140C with 44 9 of dimethylolpropanoic acid and 130~,S~i ;f~, 1.5 9 of N,N-dimethylbenzylamine until the acid num-ber has fallen to below 3 mg of KOH/g. A mixture of 175 9 of methacrylic acid, 130 9 of styrene, S g of 2-ethylhexyl methacrylat~ and 28 9 of benzoyl perox-ide (75Z strength~ is added to this at 120C with-in 2 hours. When the polymerization is complete, 160 9 of a highly methylolated bisphenol A-form-aldehyde resin are precondensed with the batch at 90C for 2 hours. A 50% strength binder solution hav;ng a viscosity (30~ strength in solution in butyl glycol) of 0.8 Pa.s and an acid number of 90 mg of KOH/g is produced.
P~T 86 094 June 22, 1987 9ASF Lacke ~ Farben Aktiengesellschaft, Munster s Aqueous coating agent, process for its preparation, and ;ts use for coating cans The invention relates to an aqueous coating agent ob-1~ tained from an epoxy resin, ethylenically unsatura-ted monomers, some of which contain carboxyL groups, a peroxide initiator, a crosslinking agent, a neutralizing agent, organic solvents, and, ;f appropriate, further conventional additives, such as ptasticizers, stabilizers, wetting agents, dispersion auxiliaries, catalysts and pigments.
H;gh-molecular-weight epoxy resins are suitable, in par-ticular, for internal protective lacquers for tinplate packaging. The crosslinking agents used are, for example, phenol-formaldehyde, melamine and urea resins. Due to the prespecified application viscos;ty, such coating agents based on solvents have a solvent content which is usually between 70 and 60g. If - as in the coating of two-part drink cans - ;t is necessary to carry out the application of the coat;ng by spraying, a turther in-crease in the solvent content usually results~ which has the consequence of great pollution through solvent emis-sions.
3~
In contrast to this, the advantages of aqueous coating systems are to be seen in a markedly reduced solvent emis-sion. In th;s connection, the application of aqueous synthetic resin dispersions by means of electrocoating is particularly advantageous, since a v;rtually 100~ coat-ing yield and a further reduced emission of solvents can be achieved using this method. In addition, it is poss-ible to coat a very ~ide variety of can geometries using electrophoretic coating through the effect of the thro~-ing power of electrodeposition coatings, a uniform coatingthickness, and thus also good edge coverage, being achieved, in contrast to coating application by spraying. In addi-tion, the electrocoating process offers the best prerequi-sites for process automation, this process additionally of-fering the opportunity for savings besides the reduced ma-terial requirement.
As is kno~n, electrocoating can be smployed both for an-ionic and for cationic binder systems. However, in the case of coneact with foodstuffs, for example for interna!
coatings of cans, it must be remembered that internal protective coatings must meet strict legal requirements regarding foodstuffs. In addition, such coatings must be stable on storage in contact with the contents, Z5 which are mainly acidic to neutral. Taking into account these requirements, anodic electrocoating is, in prin-ciple, more advantageous than the cathodic version since cathodically deposited films usually contain amine groups and can thus give rise to stability weaknesses on contact - 3 - 13~,~6~6 with acidic contents.
Solvent containing internal protective coatings for cans which are based on combinations of epoxy resins and phenol-formaldehyde resins or amino resins and which have good properties have long been known for coating cans.
In particular, epoxy resins which are based on bisphenol A and have average molecular weights of more than 3,000 g~mol give rise to very resistant coatings, whereas phenol-formaldehyde resins make a decisive contribution to stab-ility against acidic and sulfur-producing contents.
In order to use such systems in an aqueous medium, the epoxy resin must be modified by incorporation of solubi-lizing groups in a fashion such that a water-soluble or water-dispersible system is produced. Cationic, aqueous systems can be obtained in a known fashion by reaction of epoxy resins with amines. For the preparation of anionically dissolved synthetic resins, a carboxyl func-tionality is usually introduced. To this purpose, theepoxy resin, as described, for example, in US Patent 3,862,914, is converted into a carboxyl-functional poly-mer by means of a reaction with polycarboxylic anhydrides.
Such systems, in which polycarboxylic acids are bound to polymers via monoester functions, are however extremely susceptible to hydrolysis, which causes the storage sta-bility of the corresponding aqueous dispersions of such polymers to be too low tE.T. Turpi-n, J. Paint Technol., Vol. 47, No. 602, page 40, 1975). Hydrolysis-stable 13(~
attachment of the carboxyl functionality to the epoxy resin can be achieved according to US Patent 3,960,795 by reacting the epoxy functions with parahydro~ybenzoates with formation of an ether bond, followed by hydrolysis of the benzoate with liberation of the carboxyl function-ality. The disadvantage of this method is that, in par-ticular, the high-molecular-weight epoxy resins which are requ;red for internal protective coatings for cans cannot be functionalized with carboxyl groups by this route to the extent necessary for an aqueous dispersion, as a consequence of their low content of epoxy groups.
US Patent 4,247,439 and European Patents 6334 and 6336 disclose hydrolysis-stable aqueous internal protective coatings for cans, which coatings are obtained from products of the esterification of epoxy resins using carboxyl-functional polyacrylate resins. In addition, hydrolysis-stable, aqueous internal protective coatings for cans have been disclosed by US Patent 4,21Z,781 and US Patent 4,308,185.
The genus-forming US Patent 4,21Z,781 discloses resin mix-tures which are dispersible in an aqueous, basic medium and which are obtained by copolymerization of ethyleni-cally unsaturated monomers, some of which contain carboxyl groups, in the ?resence of an aliphatic or aromatic 1,2-diepoxy resin using at least 3~ by weight, relative to the ~eight of the monomer, of benzyl peroxide or equi-valent initiators. The resin mixtures disclosed by US
5 13~f ~S~6 Patent 4,21Z,781 can be crosslinked using amino resins.
They are suitable, in particuLar, for spray coating of drink cans.
S German Offenlegungsschrift 3,446,178 discloses water-dilutable compositions for coating of metal cans, the poly-mer present in the composition comprising a product of the reac~ion of acrylic monomers, a high-molecular-weight epoxy resin, a phenol-formaldehyde resin and a free-radical initiator.
The aqueous systems known from the prior art are employedmainly for spray coating of two-part aluminum drink cans.
They have the disadvantage that they offer inadequate surface protection on difficult substrates, such as, for example, drawn and ironed drink cans made from tinplate.
The object of the present invention was to provide an aqueous coating agent for coating metal cans, where uni-versal applicability of the coating agents is to be gua-ranteed, ie. the coating agents must be suitable for coat-ing cans made from aluminum, tinplate and other specifi-cally surface-pretreated steel. In particular, the coat-ing of two-part drink cans ;s considered, but, in addition, also the coating of food cans, which need to be stable to a wide range of contents, even under sterilization ron-ditions. The new coating systems are also intended to offer adequate surface protection on difficult substrates.
Substrates which are regarded as difficult here are, for ~3~
example, drawn and ironed tinplate cans which have a thin tin coat;ng and whose surface, as is known, comprises iron, a little free tin and various iron-tin alloys. In particular, the aqueous dispersions are intended to be storage-stable, and they should allow themselves to be readily pigmented. Coating agents prepared therefrom shouLd allow themselves to be applied without flaws by spray coating and also by anodic electrocoating. In the case of electrocoat;ng, the binders must coagulate at the can, connected as the anode, under the influence of the electrode reactions to form a closed coating fiLm ~Jhich has the highest possible film resistance. In this pro-cess, all coating agent components, such as crosslinking agents, auxiliaries and, if appropriate, pigments must be deposited in the amount ratio in which they are also present in the dispersion. In most systems of the prior art, the problem occurs that the neutral crosslinking agent is not deposited to the e~tent that it ;s present in the aqueous dispersion.
A further requirement of the coating agents to be prepar-ed is that the electrodeposition coatings should make possible coat;ng times of between about 0.5 and 30 se-conds, taking into account the c;rcumstances in industrial can manufacture. Under these conditions, it must be poss-ible to produce film thicknesses of between about 4 and 10 ~m which are typical for tinplate packaging. To accom-plish this, the wet-film resistance must be at least 10~ Q 1cm 1. The throwing power of the electrodeposition 5~
coating should be so well developed that it is possible to coat even complicated can geometries with an imperme-able coating film of constant coating thickness. Fur-thermore, the current strength/voltage character;stics of S the electrocoating materials must be matched to elec-trode geometries which can be used in practice.
The wet depos;ted films should be sufficiently hydropho-bic to make it possible to rinse the cans with common rinsing media, such as distilled water, drinking water, ultrafiltrate, and to exclude redissolution in the elec-trocoating material.
The baked coating films should at least reach the property levels of convent;onal internal protective coatings for cans with respect to freedom from pores, stability towards the contents, adhesion to the metal, hardness, elasticity and flavor neutrality, or should surpass these levels. To this purpose, the residual monomer contents ;n the binders must, if appropriat~, be kept as small as possible by suitable preparation processes. for first assessment of the con-tents stability in the form of short tests, the pasteur-i7ation or sterilization stability of baked coating films towards various test solutions - in the simPlest case towards water - is important here.
The object of the present invention is achieved by the aqueous coating agent of the type mentioned initially, wherein the coating agent is based on a binder a) which ~3~5~;
is obtainable from A) 20 to 80X by weight of an epoxy resin having an aver-age of more than one epo~y group per molecule and hav-ing an average molecular weight of at least 500, 5 9) 1 to 60% by weight of polyester polycarboxylic acids having an average molecular ~eight of 500 to 5,000 and having an acid number of 30 to 150, and C) 10 to 50~ by weight of ethylenically unsaturated mono-mers, 10 to 50% by weight of the monomers containing carboxyl groups, where the sum of A), B) and C) is 100~ by weight, the peroxide initiator is employed in a proportion of at least 2% by weight, relative to the total weight of the monomers C), the binder a) has an acid number of 20 to 150, and the crosslinking agents b) used are phenolic and/or amino resins, with the proviso that the coating agent contains a) 30 to 70% by we;ght of the binder a), b) 2 to 30% by weight, preferably 5 to 16% by weight, of the phenolic and/or am;no resin b), c) 1 to ~X by weight, preferably 2 to 5~ by weight, of ammonia and/or amine as neutralizing agent, and d) 20 to 60% by w~ight of organic solvents, where the sum of a), b), c) and d) is 100X by weight.
As component A), polyglycidyl ethers of bisphenol A hav ing an average molecular weight of 500 to 20,000 are pre-ferably employed. Examples of suitable epoxy resins are glycidyl polyethers, which are marketed, for example, V~ 5~
under the tradenames Epikote 10~1, 1004, 1007 and 1009.
The epoxy resins (component A) advantageously have an average molecular weight of at least 3,000 g/mol.
The polyester polycarboxylic acids employed as component ~) are prepared under the conditions known to those skilled in the art for polyester;f;cat;on reactions. These com-pounds are known polycondensates made from aromatic and/
or aliphatic d;carboxylic acids, aromatic dicarboxylic anhydrides, aromatic tricarboxylic anhydrides, aromatic tetracarboxylic anhydrides and dianhydrides, and aliphatic and cycloaliphatic mono-, di- and triols. Preferred starting compounds for the polyester polycarboxylic acids are tereph-thalic acid, isophtha~ic acid, trimellitic acid, trimellitic anhydride, adipic acid, sebacic acid, aliphatic monools having 4 to 20 carbon atoms, 2,2-dimethyl-1,3-propanediol, ethylene glycol, diethylene glycol, trimethylol propane, glycerol and pentaerythritol.
The polyester polycarboxylic acids 8) preferably have an average molecular weight of 1,000 to 3,000 and an acid number of 50 to lU0.
A preferred embodiment of the polyester polycarboxylic acid component 8) comprises using ester diols and/or gly-cidyl esters of monocarboxylic acids as the polyol com-ponent for the preparation of the polyester polycarboxy-lic acids. Neopentyl glycol hydroxypivalate may be men-tioned as an example of a suitable ester diol. A suitable - 10 ~
commercially available glycidyl ester of monocarboxylic acids is the glycidyl ester of versatic acid, a branched monocarboxylic acid.
The polyester polycarboxylic acids prepared using ester diols and/or glycidyl esters of monocarboxylic acids have acid numbers in the range ~rom 100 to 130.
10 to 50% by ~eight of the ethylenically unsaturated mono-mers employed as component C) are monomers containing carboxyl groups. Examples which should be mentioned of monomers containing carboxyl groups are acrylic acid and methacrylic acid. In addition, nonfunctionali~ed mono-mers, such as, for example, styrene, vinyltoluene and r~-methylstyrene~ may be employed as monomers.
(Meth)acrylates having 1 to 20 carbon atoms in the alco-hol radical are preferably used as the third class of monomers, it also being possible to employ hydroxy-func-tional monomers. Examples of these are ethyl acrylate,propyl acrylate, isopropyl acrylate, butyl acrylate, iso-butyl acrylate, t-butyl acrylate, pentyl acrylate, decyl acrylate, lauryl acrylate, methyl methacrylate, butyl methacrylate, isobutyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, nonyl meth-acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxyethyl methacrylate, hydroxy-propyl methacrylate and hydroxybutyl methacrylate.
13~S~
The ethylenicalLy unsaturated monomers of component C~
preferably co~prise ~) 10 to S0% by weight, preferably 20 to 40% by weight, of monomers rontaining carboxyl groups, 5 y) 0 to 50% by weight, preferably 20 to 40~ by weight, of nonfunctionalized monomers, and z) S to 60X by weight, preferably 10 to 50% by weight, of (meth)acrylates, having 1 to 20 carbon atoms in the alcohol radical, and, if appropriate, being hydroxy-functional,where the sum of x), y) and z) is 100X by weight.
Component C) has an acid number in the range from 30 to 150, preferably in the range from 50 to 100.
The binder a) is preferably obtained from 35 to 60~ by weight of A), 10 to 35% by weight of 8) and 15 to 30~ by weight of C), where the sum of A), B) and C) is 100% by weight.
It is preferred that at least 2.6~ by weight, parti-cularly preferably at least 3~ by weight, relative to the total weight of the ethylenically unsaturated monomers, of peroxide initiators are enployed.
According to the present invention, any phenolic resin can be used so long as it has the methylol functionality which is necessary for the reactivity. Preferred phenolic resins are products, prepared under alkaline conditions, - 12 - 13~S~
of the reaction of phenol, substituted phenols and bis-phenol A with formaldehyde. Under such conditions, the methylol group is linked to the aromatic ring either in the ortho or in the para position.
s Phenolic resins of the resol type ~hich are based on bis-phenol A and contain more than one methylol group per phenyl ring are preferably employed.
Typical amino resins are melamine, benzoguanamine and urea-formaldehyde resins. These are preferably used in the form which has been etherified with lower alcohols, usually butanol. Suitable amino resins are commercially ;`' ~rqde~
" ~available, for example, under the tr~e~4 Cymel. A
suitable amino resin is, for example, hexamethoxymethyl-melamine.
Of course, besides condensation products with formalde-hyde, those with other aldehydes can also be used.
According to the invention, the coating agent contains 1 to 7~ by weight, preferably 2 to S% by weight, of ammonia and/or amines as neutralizing agents. The coating agent becomes dispersible in water through neutralization with component c). Triethylamine and/or dimethylethanolamine are preferably employed as neutralizing agents.
The aqueous coating agents according to the inven~ion furthermore contain 20 to 60% by weight of organic 13U~5~6 solvents. When the aqueous coating agents are used as anodic electrodeposition coatings, it must be ensured that the organic solvents positively influence the effec-tiveness of the anodic deposition and the flow of the coating film. In a preferred fashion, nonvolatile cosol-vents are employed, such as monoalcohols having 4 to 18 carbon atoms, glycol ethers, such as, for example, ethy-lene glycol monoethyl ether and its higher homologs hav-ing 5 to 20 carbon atoms, or corresponding ethers of 1,2-and 1,3-propanediol.
The coating agents according to the invention and describ-ed above are prepared in a process wherein the epoxy re-sin A) is initially reacted with the polyester polycar-boxylic acid component 8) at 80 to 200C, preferably at120 to 180C, with the use of catalysts, so that at least 80% of the oxirane rings initially present are opened, component C) is subsequently subjected to free-radical polymer;zation, in the presence of the reaction product obtained in the first process step, at 100 to 160C, pre-ferably 120 to 140C, with the use of at least 2% by weight, relati~e to the weight of the ethylenically unsaturated monomers, of peroxidic initiators preferably ones which generate benzoyloxy and/or phenyl free radicals, the pro-duct obtained is neutralized in a third process step usingcomponent c), and the organic solvent d), the crosslinking agent b) and, if appropriate, further conventional addi-tives are added and mixed, and the coating agent is dis-persed in uater.
- 14 ~3~6S~
The reaction of the epoxy resin with polyester polycar-boxylic acids taking place in the first process step is cata~yzed by amines, preferably tertiary amines. The re-action is carried out in a fashion such that at least 80%
S of the oxirane rings are converted into ~-hydroxyester groups.
In the second process step, the ethylenically unsaturated monomers, some of wh;ch conta;n carboxyl g,oups, of com-ponent c) are subjected to a free-radical polymerization reaction in the presence of the B-hYdroxYester produced in the first process step. The free-radical polymeriza-tion is initiated by at least 2X by weight, relative to the total weight of the monomers, of peroxidic initiators, preferably ones which generate benzoyloxy and/or phenyl free rad;cals. In this reaction, at least 2.6~ by ~eight of initiators are preferably used, particularly prefer-ably at least 3~ by weight. Of course, good results are also achieved when high proportions, for example 8 to 10%
by weight, of initiators are employed, but this is not recommended for economic reasons. If the polymerization is carried out in the presence of relatively low initiator concentrations, for example with less than 3X by weight, relative to the monomer weight, a higher degreee of neu-tralization is necessary in order to obtain a stable dis-persion (cf. Example 3 from Table 1).
Primarily, peroxidic initiators are employed which decom-pose to produce benzoyloxy and/or phenyl free radicals.
, 5 13 U ~;i 5ir^i ~
Of course, it is also possible to use other initiators so long as these lead to equivalent free-radical condi-tions.
S Preferred initiators are dibenzoyl peroxide and/or tert.
butyl perbenzoate. Further possible initiators which should be ment;oned are tert. butyl peroctoate, cumene hydroperoxide and methyl ethyl ketone peroxide.
1û The proportion of residual monomers is advantageously kept to less than 0.2~, relative to the sum of a) to d), by adding further initiator and/or by extending the ini-ator feed time.
After the free-radical polymeri2ation, the polymer ob-tained is neutralized in a third process step in order to make the coating agent water-dispersible. The nonvola-tile cosolvent d) necessary for production of a readily flowing, anodically deposited film, the phenolic resins 2û or a0ino resins b) used as crossl;nking agents, and fur-ther addit;ves uhich are conventional, for example, in electrocoating are added and mixed with the system. Fin-ally, the system is dispersed in water.
A preferred embodiment of the process according to the invention co~prises carrying out a precondensation with the crossl;nking agent b) after the free-radical polymer-ization. In this fashion, the crosslinking agent b) is also deposited during electrocoating to the same extent 3.3~
as it is present in the aqueous coating agent.
The mixture obtained before dispersal in ~ater can be used as a compensation coating by not preparing the aque-S ous dispersion until the binder is incorporated into theelectrodeposition coating.
A preferred embodiment of the process according to the invention comprises already using the organic solvent d) as a solvent in the esterification, occurring as the first process step, of the epoxy resin A~ and the polyester polycarboxylic acids B).
The aqueous coating agents according to the invention are advantageously used for anodic electrocoating of cans and can halves. Of course, they can also be employed for spray coating of cans. In anodic electrocoating, the cans are dipped in an aqueous bath based on the coating agent according to the invention described above and are 2û connected as the anode.
By means of direct current, a film is deposited on the cans, the substrate is removed from the bath, and the film is hardened by baking.
~oth in spray coating and in electrodeposition, the final hardening of the coating film is carried out by baking.
The aqueous coating agents according to the invention are ~3~
suitable for coating of cans which can comprise d;fferent materials and which can have a very wide variety of can geometr;es. Thus, cans made from aluminum and those made ~rom tinplate, for example drawn ancl ironed, two-part S drink cans, can be coated equally well using the coating agints according to the invention. In addition, cans made from surface-Pretreated steel sheeting can be coated e%cel~ently.
The aqueous coat;ng agents described above are likewise highly suitable for coating foodstuff cans which have been drawn and ironed or deep-drawn in another fashion and which are subjected to sterilization for preservation of the contents.
The can halves discussed are bodies and lids which are used for the manufacture of foodstuff cans. Anodic coating of the can halves has proven particularly advantageous when the bodies are welded and the lids are pull-tab lids.
2û
The advantages of the process according to the invention are that there is a wide variety of possible ways of con-trolling the acid number by varying the polyester or the polymer. In this ~ash;on, applicational properties and adhesion properties can be optimized for specific metal surfaces. The compatibility of the components with one another and the safety with respect to residual monomers are ensured by the polymerization process.
SI~
The aqueous coa~ing agents according to the invention are storage-stable and can be applied without flaws by means of anodic electrocoating. The baked coating films ob-tained have a good property level with respect to freedom S from pores, stability towards the contents, adhesion to the metal, hardness, elasticity and flavor neutrality.
In addition, the binder combinations employed enable good pigment wetting.
The invention is described in greater detail below ~ith reference to illustrative embodiments:
1. Preparation of a polyester polycarboxylic acid 15 1.1 1,330 9 of isophthalic acid, 145 9 of adipic acid, 780 9 of 2,2-dimethyl-1,3-propanediol, 268 9 of tri-methylolpropane and 200 9 of isodecanol are weighed out into a four-neck flask fitted with stirrer, thermometer and water separator, and the mixture is condensed at 220C to an acid number of less than 5 mg of KOH/g. 500 9 of trimellitic anhydride are added at 110C, and the batch is kept at this tem-perature until the viscosity becomes constant. Fin-ally, the polyester resin melt is dissolved in butyl glycol to give a 70X strength solution. The acid number is 85 mg of KOH/g.
1.2 1,200 9 of the glycidyl ester of versatic acid, 900 9 of 2-butanone, 900 9 of trimellitic anhdyride and :13(~65~i _ 19 _ 5 9 of N,N-dimethylbenzylamine are warmed to 90C in a four-neck flask fitted with stirrer thermometer and reflux condenser. When the viscosity (measured at 23C) has increased to 1.5 Pas the batch is cooled and discharged.
2. Preparation of epoxy ester resins 2.1 Prepara~ion of an epoxy ester resin based on the 1û polyester polycarboxylic acid prepared under 1.1.
A mixture of 1 050 9 of an epoxy resin based on bis-phenol A and having an epoxy equivalent weight of 3,400 700 9 of butyl glycol 3S0 9 of 1-phenoxy-2-propanol Z g of N N-di1ethylbenzylamine and 1 000 g of the polyester polycarboxylic acid prepared un-der 1.1 is warmed to 160C in a four-neck flask fitted with stirrer,.thermometer and reflux conden-ser until the acid number has fallen to 20 mg of KOH/g. In a 30X strength solution in butyl glycol, the epoxy ester thus prepared has a viscosity of 370 mPa.s at 23C.
2.2 Preparation of an epoxy ester based on the polyester carboxylic acid prepared under 1.2 A solution of 1,050 9 of an epoxy resin based on bisphenol A and having an epoxy equivalent ueight of 3 400, in 1 000 g of butyl glycol and 440 9 of ~3~t~
propylene glycol monophenyl ether is heated to 140C
in a four-neck flask fitted with stirrer, thermome-ter and distillation attachment. After 2 g of N,N-dimethylbenzyla~ine are added, 950 9 of the potyes-ter polycarboxylic acid prepared under 1~2 are run in and the solvent (2-butanone) is simultaneously distilled off. The batch is kept at 160C for a further 3 hours. The acid number is then 37 mg of KOH/g and the viscosity (of a 30~ strength sotution in butyl glycol at Z3C) is 380 mPa.s.
3. Preparation of binder solutions from the epoxy ester resins prepared under 2.
3.1 Preparation using the epoxy ester resin prepared un-der 2.1 Example 1 2,400 9 of the epoxy ester prepared under 2.1 are placed in a four-neck flask fitted ~ith stirrer, thermometer, reflux condenser and tuo supply con-tainers. At 140C, a mixture of 130 9 of acrylic acid, 160 9 of styrene and 200 9 of butyl acrylate is added to this from the first supply container and a solution of 30 9 of tert. butyl perbenzoate in 40 9 of butyl glycol is simultaneously added from the second supply container. The monomers are added over 2 hours and the initiator over 3 hours. When - 21 - ~3~6~
the polymerization is complete, 190 9 of a highly methylolated bisphenol A-formaldehyde resin are pre-condensed w;th the batch at 90C for 2 hours~
A 58~ strength b;nder solution is produced which, after addition of basic neutralizing agents, can be employed directLy as a compensation coating for anodic electrocoating~
Example 2 Z,400 9 of the epoxy ester prepared under 2.1 are placed in a four-neck flask fitted with stirrer, thermometer, reflux condenser and two supply con-tainers. At 140C, a mixture of 130 9 of acrylic acid, 160 9 of styrene and 200 9 of butyl acrylate is added to this from the first supply container and a solution of 30 9 of tert. butyl perbenzoate in 40 9 of butyl gLycol is added simultaneously from 2û the second supply container. The monomers are add-ed over 2 hours, and the initiator over 3 hours.
~hen the polymerization is complete, 190 9 of a butylated melamine-formaldehyde resin are added.
A 58~ strength binder solution is produced which, after addition of a basic neutralizing agent, can be employed directly as a compensation coating for anodic electrocoating.
13~'~S~
ExampLe 3 2,352 9 of the epoxy ester prepared under 2.1 are placed in a four neck flask fitted with stirrer, thermometer, ref~ux condenser and t~o supply con-tainers. At 140C, a mixture of 130 9 of acry~ic ac;d, 160 9 of styrene and 190 9 of butyl acrylate is added to this from the first supply container and a solution of 13.4 9 of tert. butyl perbenzoate in 4û 9 of butyl glycol is added simultaneously from the second supply container. The monomers are add-ed over 2 hours, and the initiator over 3 hours.
hhen the polymerization is complete, 19û 9 of a h;ghly methylolated bisphenol A-formaldehyde resin are precondensed with the batch at 90C for 2 hours.
A 57% strength binder solution is produced which, after addition of bas;c neutralizing agents, can be employed directly as a compensation coating for anodic electrocoating.
3.2 Preparation using the epoxy ester resin prepared under 2.2 Example 4 2,100 9 of the epoxy ester prepared under 2.2 and 300 9 of butyl glycol are placed in a four-neck flask fitted with stirrer, thermometer, reflux condenser and two supply containers. At 140C, a mixture of 130 9 of acryLic acid, 160 9 of styrene and 200 g of butyl acrylate is added to this from the first supply container and a solution of 30 9 S of tert. butyL perbenzoate in 40 9 of butyl glycol is added simultaneously from the second supply con-tainer The monomers are added over 2 hours, and the initiator over 3 hours. When the polymerization is complete, 190 9 of a highly methylolated bisphenol A-formaldehyde resin are precondensed with the batch at 90C for 2 hours.
A 56X strength binder solution is produced which, after addition of basic neutralizing agents, can be employed directly as a compensation coating for anodic electrocoating.
3.3 Comparison Examples Comparison Example 1 Modification of an epoxy resin using trimellitic anhydride In order to prepare a comparison batch wi~hout addi-tion polymer, the high-molecular-weight epoxy resin employed under 2. is reacted with trimellitic anhyd-ride after esterification of the glycidyl radicals using a monocarboxylic acid.
13~65~i To this purpose, 41.8 par~s of a high-molecular-weight epoxy resin based on bisphenol A and having an epoxy equivalent weight of 3,400 are dissolved in 41.C parts of ethylene glycol monobutyl ether and S reacted at 130C with 1.94 parts of isononanoic acid and O.û6 parts of N,N-dimethylbenzylamine until the acid number has fallen to below 3 mg of KOH/g.
7.7 parts of trimellitic anhydride are added, and the temperature is maintained until an acid number of 80 mg of KOHtg is reached. After cooling to 90C, 3.5 parts of a phenol-formaldehyde resin (resol tyDe based on bisphenol A) are added, and the batch is stirred at 90C for 2 hours. The solids content is then 55~.
Comparison ~xample 2 Preparation of an acrylic-epoxy graft polymer In order to prepare a comparison ba~ch, a monomer mixture is polymerized in the presence of a high-molecular-weight epoxy resin, but in the absence of a polyester component.
To this purpose, 1,120 9 of a high-molecular-weight epoxy resin based on bisphenol A and having an epoxy equivalent weight of 3,400 are dissolved in 570 9 of butyl glycol and 850 9 of n-butanol and reacted at 140C with 44 9 of dimethylolpropanoic acid and 130~,S~i ;f~, 1.5 9 of N,N-dimethylbenzylamine until the acid num-ber has fallen to below 3 mg of KOH/g. A mixture of 175 9 of methacrylic acid, 130 9 of styrene, S g of 2-ethylhexyl methacrylat~ and 28 9 of benzoyl perox-ide (75Z strength~ is added to this at 120C with-in 2 hours. When the polymerization is complete, 160 9 of a highly methylolated bisphenol A-form-aldehyde resin are precondensed with the batch at 90C for 2 hours. A 50% strength binder solution hav;ng a viscosity (30~ strength in solution in butyl glycol) of 0.8 Pa.s and an acid number of 90 mg of KOH/g is produced.
4. Preparation of binder dispersions from the binders of Examples 1, 2, 3 and 4 and Comparison Exa~ples 1 and 2 The binder solutions of Examples 1, 2, 3 and 4 and Comparison Examples 1 and 2 are neutralized with amine according to the figures in Table 1, dispersed slo~Ly in demineralized water with vigorous stirring and adjusted to a solids content of 1Z~. The pro-perties and characteristic numbers of the resulting dispersions are collated in Table 1 8inder dispersion E is not adequately stable on stor-age at room temperature. After one month, the bin-der has substantially coagulated and the dispersion is destroyed. In contrast, the dispersions A, B, C, ;~3~
D and F are free of sediment even after storage for 6 months at room temperatlJre.
Table 1:
s Dispersion A _ El C _ D E F
El;nder Examp~e 1 Example 2 Example 3 ExampLe 4 Comparison Comparison Example 1 Example 2 Amine N,N-dime- N,N-dime- N,N-dime- N,N-dime- Tr;ethyl- Triethyl-thyletha- thyletha- thyletha- thyletha- amine amine nolamine nolamine nolamine nolamine Degree of ne~trali-zation 80% 80X 98X 80X 53X 49X
SSorage stability of the dispersion (20C) >6 mon. >6 mon. >6 mon. >6 mon. <1 mon. >6 mon.
pH 8.2 8.2 8.3 7.8 8.5 7.2 Conductiv-;ty ~S/cm) Z000 2200 2540 2700 2000 1750 27 - 6 ~ ~ ~
D and F are free of sediment even after storage for 6 months at room temperatlJre.
Table 1:
s Dispersion A _ El C _ D E F
El;nder Examp~e 1 Example 2 Example 3 ExampLe 4 Comparison Comparison Example 1 Example 2 Amine N,N-dime- N,N-dime- N,N-dime- N,N-dime- Tr;ethyl- Triethyl-thyletha- thyletha- thyletha- thyletha- amine amine nolamine nolamine nolamine nolamine Degree of ne~trali-zation 80% 80X 98X 80X 53X 49X
SSorage stability of the dispersion (20C) >6 mon. >6 mon. >6 mon. >6 mon. <1 mon. >6 mon.
pH 8.2 8.2 8.3 7.8 8.5 7.2 Conductiv-;ty ~S/cm) Z000 2200 2540 2700 2000 1750 27 - 6 ~ ~ ~
5. Coating of drink cans with binder dispersions A, 8, C~ ~, E and F from Table I
5.1 Coating of a drink can with binder dispersion A
Example 5 . _ An uncoated, two-part drink can made from tinplate is he~d at the flange using an electroconductive clip, filled with binder dispersion A and submerged in a conductive vessel which has a diameter of 20 cm, is insulated against earth and has previously like-wise been filled with the electrodeposition coating.
The positive Pole of a direct current voltage source is connected to the can and the negative pole is connected to the external vessel. The coating is carried out using an auxiliary cathode in the can interior. After rinsing with demineralized water, the coating is baked for 5 minutes at 21ûC in a circulation oven. The can is fully coated internally Z0 and externally with a thin, clear, impermeable coating film. Measurement results, cf. Table 2.
5.2 Coating of a drink can with binder dispersion Example 6 The coating is carried out analogously to the pro-cedure under 5.1. The can is fully coated internally ~3a~
- 28 ~
and externall~ ~with a thin, impermeable, clear coat-;ng -fiCm. Measurement results, cf. Table 2 Table 2:
Example 5 Example 6 Example 7 Example 8 Example 9 Comparison Comparison Example 3 Example 4 _ _ _ _ _ Solids content 12% 12% 1Z,5% 10X 12% 12% 12%
pH 8.2 7.8 8.2 8.3 7.8 8.5 7.2 Conductivity 2000 2700 2200 2540 2700 2000 1750 ~uS/cm 3ath tempera -ture Z7C 27C 27C 27C 27C 27C 27C
Deposition time 20 s 20 s 20 s 20 s 20 s 20 s 20 s ~epositicn Voltage SO V 60 V 60 V 50 V 60 V 160 V 90 V
Coatingtcan 480 mg 490 mg 900 mg 500 mg 490 mg 450 mg 460 mg Surface glossy glossy glossy glossy glossy matt matt Poros;ty, mA
(enamel rater~ 0.1 0.1 0.3 1 0.1 10 5 Coa t i ng adhes i on 2 0 ( c ros s-hat c h test) Gt O Gt O Gt O Gt O Gt O Gt 1 Gt 1 Steril1zation water water with water, absorption absorption 30 min/121C OK OK OK OK OK (blushing) (blushing) S~ 66 5.3 Coating a drink can with pigmented binder dispersion Example 7 s The binder from Example 2 is pigmented with titanium dîoxide (binder:pigment = 1:1) and adjusted to a solids content of 12.5~ using demineralized water.
The coating is carried out analogously to 5.1 and 5.2. The can is coated completely with a white coat-ing fiLm. Measurement results, cf. Table 2.
5.4 Coating of a drink can with binder dispersion C
Example 8 -The coating is carried out analogously to 5.1 and 5.2. The can is fully coated internally and exter-nally with a thin, impermeable, clear coating film.
Measurement results, cf. Table 2.
5.5 Coating of a drink can with binder dispersion D
Example 9 Coating is carried out analogously to 5.1 and 5.2.
The can is fully coated internally and externally with a thin, impermeable, clear coating film.
~3~J~5'~
-- ~o --Measurement results, cf. Table 2.
5.6 coating of a drink can with binder dispersion E
Comparison Example 3 . . _ The coating ;s carried out analogously to Example 4 - 9. The can is coated internally and externally with a clear, matt coating film wh;ch is not impermeable and has surface defects. Measurement results, cf. Table 2.
5.7 Coating of a drink can with binder dispersion F
Comparison Example 4 The coat;ng is carried out as described above. The can is coated internally and externally with a clear, matt coating film which is not impermeable and which ZO has surface defects. Measurement results, cf. Table 2.
The deposited and baked coating films in all examples exhibit no odor, flavor or color impairment of water as the contents. Similar results are achieved when a drink can made from aluminum is used in place of a two-part drink can made from tinplate.
5.1 Coating of a drink can with binder dispersion A
Example 5 . _ An uncoated, two-part drink can made from tinplate is he~d at the flange using an electroconductive clip, filled with binder dispersion A and submerged in a conductive vessel which has a diameter of 20 cm, is insulated against earth and has previously like-wise been filled with the electrodeposition coating.
The positive Pole of a direct current voltage source is connected to the can and the negative pole is connected to the external vessel. The coating is carried out using an auxiliary cathode in the can interior. After rinsing with demineralized water, the coating is baked for 5 minutes at 21ûC in a circulation oven. The can is fully coated internally Z0 and externally with a thin, clear, impermeable coating film. Measurement results, cf. Table 2.
5.2 Coating of a drink can with binder dispersion Example 6 The coating is carried out analogously to the pro-cedure under 5.1. The can is fully coated internally ~3a~
- 28 ~
and externall~ ~with a thin, impermeable, clear coat-;ng -fiCm. Measurement results, cf. Table 2 Table 2:
Example 5 Example 6 Example 7 Example 8 Example 9 Comparison Comparison Example 3 Example 4 _ _ _ _ _ Solids content 12% 12% 1Z,5% 10X 12% 12% 12%
pH 8.2 7.8 8.2 8.3 7.8 8.5 7.2 Conductivity 2000 2700 2200 2540 2700 2000 1750 ~uS/cm 3ath tempera -ture Z7C 27C 27C 27C 27C 27C 27C
Deposition time 20 s 20 s 20 s 20 s 20 s 20 s 20 s ~epositicn Voltage SO V 60 V 60 V 50 V 60 V 160 V 90 V
Coatingtcan 480 mg 490 mg 900 mg 500 mg 490 mg 450 mg 460 mg Surface glossy glossy glossy glossy glossy matt matt Poros;ty, mA
(enamel rater~ 0.1 0.1 0.3 1 0.1 10 5 Coa t i ng adhes i on 2 0 ( c ros s-hat c h test) Gt O Gt O Gt O Gt O Gt O Gt 1 Gt 1 Steril1zation water water with water, absorption absorption 30 min/121C OK OK OK OK OK (blushing) (blushing) S~ 66 5.3 Coating a drink can with pigmented binder dispersion Example 7 s The binder from Example 2 is pigmented with titanium dîoxide (binder:pigment = 1:1) and adjusted to a solids content of 12.5~ using demineralized water.
The coating is carried out analogously to 5.1 and 5.2. The can is coated completely with a white coat-ing fiLm. Measurement results, cf. Table 2.
5.4 Coating of a drink can with binder dispersion C
Example 8 -The coating is carried out analogously to 5.1 and 5.2. The can is fully coated internally and exter-nally with a thin, impermeable, clear coating film.
Measurement results, cf. Table 2.
5.5 Coating of a drink can with binder dispersion D
Example 9 Coating is carried out analogously to 5.1 and 5.2.
The can is fully coated internally and externally with a thin, impermeable, clear coating film.
~3~J~5'~
-- ~o --Measurement results, cf. Table 2.
5.6 coating of a drink can with binder dispersion E
Comparison Example 3 . . _ The coating ;s carried out analogously to Example 4 - 9. The can is coated internally and externally with a clear, matt coating film wh;ch is not impermeable and has surface defects. Measurement results, cf. Table 2.
5.7 Coating of a drink can with binder dispersion F
Comparison Example 4 The coat;ng is carried out as described above. The can is coated internally and externally with a clear, matt coating film which is not impermeable and which ZO has surface defects. Measurement results, cf. Table 2.
The deposited and baked coating films in all examples exhibit no odor, flavor or color impairment of water as the contents. Similar results are achieved when a drink can made from aluminum is used in place of a two-part drink can made from tinplate.
6~ Coating of a drink can by means of spray coating 1 3~J ~ 6 using binder dispersion A
The inter;or of a two-~art drink can made from tin-plate is sPray-coated with anionic binder dispersion A. 65 bar is selected as the spraying pressure.
The coating is baked for 2 minutes at 210C in a circulation oven. An applied coating layer ot 220 mg dry/0.33 l can is produced. The coating film is clear and glossy and has a porosity (enamel rater) 1Q of 0.8 mA. The other coating proper~ies (adhesion and sterili~ation stability) correspond to those of Examp(es S to 9 from Table 2.
The inter;or of a two-~art drink can made from tin-plate is sPray-coated with anionic binder dispersion A. 65 bar is selected as the spraying pressure.
The coating is baked for 2 minutes at 210C in a circulation oven. An applied coating layer ot 220 mg dry/0.33 l can is produced. The coating film is clear and glossy and has a porosity (enamel rater) 1Q of 0.8 mA. The other coating proper~ies (adhesion and sterili~ation stability) correspond to those of Examp(es S to 9 from Table 2.
Claims (29)
1. An aqueous coating agent, obtained from an epoxy resin, ethylenically unsaturated monomers, some of which contain carboxyl groups, a peroxide initiator, a crosslinking agent, a neutralizing agent, organic solvents, wherein the coating agent is based on a binder a) which is obtainable from A) 20 to 80% by weight of an epoxy resin having an average of more than one epoxy group per molecule and having an average molecular weight of at least 500, B) 1 to 60% by weight of polyester polycarboxylic acids having an average molecular weight of 500 to 5,000 and having an acid number of 30 to 150, and C) 10 to 50% by weight of ethylenically unsaturated mono-mers, 10 to 50% by weight of the monomers containing carboxyl groups, where the sum of A), B) and C) is 100% by weight, the peroxide initiator is employed in a proportion of at least 2% by weight, relative to the total weight of the monomers, the binder a) has an acid number of 20 to 150, and the crosslinking agents b) used are phenolic or amino resins, with the proviso that the coating agent contains a) 30 to 70% by weight of the binder a), b) 2 to 30% by weight of the phenolic or amino resin b), c) 1 to 7% by weight of ammonia or amine as neutralizing agent, and d) 20 to 60% by weight of organic solvent, where the sum of a), b), c) and d) is 100% by weight.
2. A coating agent as claimed in claim 1, wherein at least 2.6% by weight relative to the total weight of the ethylenically unsaturated monomers, of peroxide initiators are employed.
3. A coating agent as claimed in claim 1, wherein the epoxy resin A) is based on bisphenol A.
4. A coating agent as claimed in claim 1, 2 or 3, wherein the epoxy resin A) has an average molecular weight of at least 3,000.
5. A coating agent as claimed in claim 1, 2 or 3, wherein the polyester polycarboxylic acids B) have an average molecular weight of 1,000 to 3,000 and an acid number of 50 to 100.
6. A coating agent as claimed in claim 1, 2 or 3, wherein the alcohol component used for the preparation of the polyester polycarboxylic acids B) is an ester diol or a glycidyl ester of a monocarboxylic acid.
7. A coating agent as claimed in claim 1, 2 or 3, wherein the ethylenically unsaturated monomers C) comprise x) 10 to 50%
by weight of monomers containing carboxyl groups, y) 0 to 50%
by weight of nonfunctionalized monomers, and z) 5 to 60% by weight of (meth)acrylates having 1 to 20 carbon atoms in the alcohol radical where the sum of x), y) and z) is 100% by weight.
by weight of monomers containing carboxyl groups, y) 0 to 50%
by weight of nonfunctionalized monomers, and z) 5 to 60% by weight of (meth)acrylates having 1 to 20 carbon atoms in the alcohol radical where the sum of x), y) and z) is 100% by weight.
8. A coating agent as claimed in claim 1, 2 or 3, wherein the ethylenically unsaturated monomers C) comprises x) 20 to 40 by weight of monomers containing carboxyl groups, y) 20 to 40%
by weight of nonfunctionalized monomers, and z) 10 to 50% by weight of (meth)acrylates having l to 20 carbon atoms in the alcohol radical and which are hydroxy-functional, where the sum of x), y) and z) is 100% by weight.
by weight of nonfunctionalized monomers, and z) 10 to 50% by weight of (meth)acrylates having l to 20 carbon atoms in the alcohol radical and which are hydroxy-functional, where the sum of x), y) and z) is 100% by weight.
9. A coating agent as claimed in claim 1, 2 or 3, wherein the binder a) is obtainable from 35 to 60% by weight of A), 10 to 35% by weight of B) and 15 to 30% by weight of C).
10. A coating agent as claimed in claim l, 2 or 3, wherein the phenolic resin used is of the resol type, is based on bisphenol A and contains more than one methylol group per phenyl ring.
11. A coating agent as claimed in claim 1, 2 or 3, wherein the neutralizing agent c) is triethylamine or dimethylethanolamine.
12. A coating agent as claimed in claim l, 2 or 3, wherein the coating agent contains 5 to 16% by weight of the phenolic or amino resin b).
13. A coating agent as claimed in claim 1, 2 or 3 wherein the coating agent contains 2 to 5% by weight of ammonia or amine as neutralizing agent.
14. A coating agent as claimed in claim 1, 2 or 3, wherein at least 3% by weight relative to the total weight of the ethyleni-cally unsaturated monomers of peroxide initiators are employed.
15. A coating agent as claimed in claim 1, 2 or 3 which further comprises one or more members selected from the group con-sisting of plasticizers, stabilizers, wetting agents, dispersion auxiliaries, catalysts and pigments.
16. A process for the preparation of the coating agent as claimed in claim 1, wherein the epoxy resin A) is initially reacted with the polyester polycarboxylic acid component s) at 80 to 200°C, with the use of a catalyst, so that at least 80% of the oxirane rings initially present are opened, component C) is subse-quently polymerized in the presence of the reaction product obtained in the first process step, at 100 to 160°C, with the use of at least 2% by weight, relative to the weight of the ethyleni-cally unsaturated monomers, of a peroxidic initiator, the product obtained is neutralized in a third process step using component c), the organic solvent d) and the crosslinking agent b) are added and mixed, and the coating agent is dispersed in water.
17. The process as claimed in claim 16, wherein the epoxy resin A) is initially reacted with the polyester polycarboxylic acid component B) at 120 to 180°C, with the use of a catalyst, so that at least 80% of the oxirane rings initially present are opened, component C) is subsequently polymerized in the presence of the reaction product obtained in the first process step, at 120 to 140°C, with the use of at least 2% by weight, relative to the weight of the ethylenically unsaturated monomers, of a per-oxidic initiator which generates benzoyloxy or phenyl free radicals, the product obtained is precondensed in a third process step with the crosslinking agent b), the neutralization using component c) is subsequently carried out, and the organic solvent d) are added and mixed, and the coating agent is dispersed in water.
18. The process as claimed in claim 16, wherein less than 0.2% by weight, relative to the sum of a) to d), of residual mono-mers are present after the free-radical polymerization.
19. The process as claimed in claim 16, 17 or 18, wherein the initiator used is dibenzoyl peroxide or tert.butyl perbenzoate.
20. The process as claimed in claim 16, 17 or 18, wherein component d) is used as solvent in the esterification, occurring as the first process step, of components A) and B).
21. A process for anodic electrocoating or spray coating of cans or can parts, wherein the coating agent is an aqueous coating agent as claimed in claim 1.
22. A process as claimed in claim 21, wherein the cans or can parts are manufactured from tinplate.
23. A process as claimed in claim 21, wherein the cans or can parts comprise aluminum.
24. A process as claimed in claim 21, wherein the cans com-prise surface-pretreated steel sheeting.
25. A process as claimed in claim 21, 22 or 23, wherein the cans or can parts are drawn and ironed, two-part drink cans or parts thereof.
26. A process as claimed in claim 21, 22 or 23, wherein the cans or can parts are foodstuff cans or parts thereof which have been drawn and ironed or deep-drawn and which are subjected to sterilization for preservation of the contents.
27. A process as claimed in claim 21, 22 or 23, wherein the can parts are bodies and lids which are used for the manufacture of foodstuff cans.
28. A process as claimed in claim 21, 22 or 23, wherein the can parts are bodies and lids which are used for the manufacture of foodstuff cans, the bodies being welded and the lids being pull-tab lids.
29. A can or can part coated which has been coated with an aqueous coating composition as claimed in claim 1, 2 or 3.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19863627860 DE3627860A1 (en) | 1986-08-16 | 1986-08-16 | AQUEOUS COATING AGENT, METHOD FOR THE PRODUCTION THEREOF AND ITS USE FOR COATING CAN |
| DEP3627860.2-43 | 1986-08-16 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1306566C true CA1306566C (en) | 1992-08-18 |
Family
ID=6307558
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000544527A Expired - Lifetime CA1306566C (en) | 1986-08-16 | 1987-08-14 | Aqueous coating agent, a process for its preparation, and its use for coating of cans |
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| Country | Link |
|---|---|
| US (2) | US4997865A (en) |
| EP (2) | EP0324741A1 (en) |
| JP (1) | JP2536889B2 (en) |
| CN (1) | CN1012069B (en) |
| AT (1) | ATE58389T1 (en) |
| AU (1) | AU607934B2 (en) |
| BR (1) | BR8707772A (en) |
| CA (1) | CA1306566C (en) |
| DE (2) | DE3627860A1 (en) |
| DK (1) | DK172740B1 (en) |
| ES (1) | ES2018670B3 (en) |
| FI (1) | FI97065C (en) |
| GR (1) | GR3002551T3 (en) |
| IE (1) | IE60579B1 (en) |
| LT (1) | LT3311B (en) |
| LV (1) | LV10473B (en) |
| MD (1) | MD940049A (en) |
| NO (1) | NO300811B1 (en) |
| NZ (1) | NZ221445A (en) |
| PT (1) | PT85541B (en) |
| RU (1) | RU2074210C1 (en) |
| WO (1) | WO1988001287A1 (en) |
| ZA (1) | ZA876028B (en) |
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| CN102140299B (en) * | 2011-04-08 | 2013-04-17 | 广州慧谷化学有限公司 | Pop-top can cap coating with self-lubricating function and suitable for high-speed punching |
| US9752044B2 (en) * | 2013-08-16 | 2017-09-05 | Ppg Industries Ohio, Inc. | Aqueous-based coating composition containing an oleoresinous component |
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| CN102977338B (en) * | 2012-11-08 | 2015-08-26 | 西安交通大学 | A kind of aqueous epoxy resins and preparation method thereof and prepare the method for varnish |
| JP6191221B2 (en) * | 2013-04-25 | 2017-09-06 | 凸版印刷株式会社 | Water-based coating agent and gas barrier film |
| US20150017359A1 (en) * | 2013-07-11 | 2015-01-15 | Ppg Industries Ohio, Inc. | Coating compositions with improved adhesion to containers |
| EP3242907B1 (en) | 2015-01-05 | 2020-12-02 | Rhodia Operations | Amine-imino dialcohol neutralizing agents for low volatile compound aqueous organic coating compositions and methods for using same |
| JP7232022B2 (en) * | 2018-04-13 | 2023-03-02 | 東洋インキＳｃホールディングス株式会社 | Aqueous paint composition, can member, and can |
| CN111971353B (en) * | 2018-04-13 | 2022-03-29 | 东洋油墨Sc控股株式会社 | Water-based coating composition, can member, and can |
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| US3862914A (en) | 1972-11-01 | 1975-01-28 | Mobil Oil Corp | Water-based coatings from polyepoxides and polycarboxylic acid monoanhydrides |
| US4247439A (en) * | 1973-11-06 | 1981-01-27 | E. I. Du Pont De Nemours And Company | Water-borne coating composition made from epoxy resin, polymeric acid and tertiary amine |
| US3960795A (en) | 1974-08-13 | 1976-06-01 | Ppg Industries, Inc. | Hydrolyzed reaction product of a polyepoxide with a phenolic compound having a group hydrolyzable to carboxyl |
| DE2608901A1 (en) * | 1976-03-04 | 1977-09-08 | Hoechst Ag | Process for the preparation of hardenable, liquid, graft copolymers containing epoxy groups |
| DE2608869A1 (en) * | 1976-03-04 | 1977-09-08 | Hoechst Ag | Process for the preparation of hardenable, liquid, graft copolymers containing epoxy groups |
| US4308185A (en) | 1976-05-11 | 1981-12-29 | Scm Corporation | Graft polymer compositions of terminated epoxy resin, processes for making and using same, and substrates coated therewith |
| US4212781A (en) | 1977-04-18 | 1980-07-15 | Scm Corporation | Modified epoxy resins, processes for making and using same and substrates coated therewith |
| JPS54102399A (en) * | 1978-01-30 | 1979-08-11 | Hitachi Chem Co Ltd | Preparation of water-thinnable resin |
| CA1183641A (en) | 1978-06-12 | 1985-03-05 | George L. Brown | Production of self-emulsifiable epoxy ester copolymer mixtures |
| CA1186846A (en) | 1978-06-12 | 1985-05-07 | George L. Brown | Aqueous emulsion coatings composition comprising self-emulsifiable epoxy ester copolymer mixture |
| US4302373A (en) * | 1980-08-05 | 1981-11-24 | E. I. Du Pont De Nemours And Company | Water-borne coating composition made from modified epoxy resin, polymeric acid and tertiary amine |
| JPS58180521A (en) * | 1982-04-16 | 1983-10-22 | Asahi Chem Ind Co Ltd | Production of flexible epoxy resin |
| US4423165A (en) * | 1982-04-16 | 1983-12-27 | E. I. Du Pont De Nemours And Company | Water-borne coating composition made from epoxy resin, first polymeric acid, tertiary amine and second polymeric acid |
| JPS5951909A (en) * | 1982-09-20 | 1984-03-26 | Toyo Ink Mfg Co Ltd | Aqueous resin dispersion composition |
| US4476262A (en) * | 1982-12-30 | 1984-10-09 | Mobil Oil Corporation | Aqueous coatings comprising ionic polymer ester and diluent polymer with reduced monomer residue and method of preparation |
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| FR2557116B1 (en) | 1983-12-21 | 1988-07-22 | Inmont Corp | WATER-SOLUBLE ACRYLATE EPOXYPHENOLIC COATING COMPOSITIONS |
-
1986
- 1986-08-16 DE DE19863627860 patent/DE3627860A1/en not_active Withdrawn
-
1987
- 1987-08-13 AU AU77888/87A patent/AU607934B2/en not_active Ceased
- 1987-08-13 WO PCT/EP1987/000445 patent/WO1988001287A1/en active IP Right Grant
- 1987-08-13 US US07/327,964 patent/US4997865A/en not_active Expired - Fee Related
- 1987-08-13 DE DE8787111720T patent/DE3766187D1/en not_active Expired - Lifetime
- 1987-08-13 EP EP87905209A patent/EP0324741A1/en not_active Withdrawn
- 1987-08-13 AT AT87111720T patent/ATE58389T1/en not_active IP Right Cessation
- 1987-08-13 BR BR8707772A patent/BR8707772A/en not_active IP Right Cessation
- 1987-08-13 JP JP62504771A patent/JP2536889B2/en not_active Expired - Lifetime
- 1987-08-13 RU SU874613521A patent/RU2074210C1/en active
- 1987-08-13 EP EP87111720A patent/EP0256521B1/en not_active Expired - Lifetime
- 1987-08-13 NZ NZ221445A patent/NZ221445A/en unknown
- 1987-08-13 ES ES87111720T patent/ES2018670B3/en not_active Expired - Lifetime
- 1987-08-14 PT PT85541A patent/PT85541B/en unknown
- 1987-08-14 IE IE218287A patent/IE60579B1/en not_active IP Right Cessation
- 1987-08-14 ZA ZA876028A patent/ZA876028B/en unknown
- 1987-08-14 CA CA000544527A patent/CA1306566C/en not_active Expired - Lifetime
- 1987-08-15 CN CN87106405A patent/CN1012069B/en not_active Expired
-
1988
- 1988-04-13 NO NO881601A patent/NO300811B1/en unknown
- 1988-04-14 DK DK198802046A patent/DK172740B1/en not_active IP Right Cessation
-
1989
- 1989-02-15 FI FI890718A patent/FI97065C/en not_active IP Right Cessation
-
1990
- 1990-12-21 GR GR90401123T patent/GR3002551T3/en unknown
-
1991
- 1991-01-08 US US07/642,243 patent/US5114993A/en not_active Expired - Fee Related
-
1993
- 1993-05-06 LT LTIP527A patent/LT3311B/en not_active IP Right Cessation
- 1993-05-27 LV LVP-93-431A patent/LV10473B/en unknown
- 1993-12-22 MD MD94-0049A patent/MD940049A/en not_active Application Discontinuation
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