JPS6213384B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to aqueous coating compositions based on epoxy ester copolymers containing residual unsaturation to enable oxidative curing. These coatings are dried in air at room temperature and cured, or aminoplast or phenoplast resins are added to provide aqueous coatings that cure at relatively low temperatures since part of the cure is an oxidative cure mechanism.

In accordance with the present invention, a resinous polyepoxide, and preferably a bisphenol-based polyepoxide having a 1,2-epoxy equivalent weight of 1.4 to 2.0, is reacted with two different ethylenically unsaturated monocarboxylic acids to substantially eliminate this epoxy functionality. Consume.
One of the monocarboxylic acids contains conjugated ethylenic unsaturation and the other monocarboxylic acid contains non-terminal non-conjugated ethylenic unsaturation. The polyepoxide can be reacted with the acid separately or with a mixture of acids. The unsaturated epoxy ester thus formed contains two different types of unsaturated side chains, and the epoxy ester preferably contains terminal ethylenic unsaturation and carboxyl functionality in solution in a water-miscible organic solvent. Copolymerizes with monoethylenically unsaturated monomers containing monomers. It forms a normally solid, non-gelling, organic solvent soluble copolymer with conjugated unsaturation in the epoxy ester, while containing carboxyl groups such that it is dispersible in water by at least partial neutralization with a volatile base. The non-terminal non-conjugated unsaturation remains unconsumed in the copolymer to form the aqueous coating solution. This provides an aqueous coating that dries in air and cures at room temperature. When some of the monomers mentioned above provide primary hydroxyl groups, and when an aminoplast or phenoplast resin is dispersed in the coating composition, a coating is provided that heat cures at very low temperatures.

The remaining unsaturation in the copolymer has the ability to bind atmospheric oxygen, so that the deposited coating cures at room temperature. When the copolymer with retained unsaturation contains a monomer that provides primary hydroxyl groups, curing occurs by reaction of the methylol groups in the aminoplast or phenoplast resin with the primary hydroxyl groups in the copolymer, as well as by the reaction of the primary hydroxyl groups in the copolymer with the aminoplast or phenoplast resin. This occurs by oxidative hardening promoted by the mild heat used for plasto or phenoplast reactions. This air drying allows the clear coating to air cure at room temperature for 3 days to pass the 500 hour 5% salt spray test, which is not normal in the absence of baking and the presence of anti-corrosion pigments to avoid corrosion. Air-cured, water-based coatings are noteworthy. Aminoplast curing of hydroxy-functional resins to produce a good corrosion-resistant cure
This low temperature curing aqueous coating is also noteworthy as it typically requires curing temperatures of 325 to 400°C. In contrast, curing of the present invention only requires firing temperatures in the range of 240 to 290°C. Since the calcination temperature varies depending on whether the aminoplast or phenoplast is used and the intended purpose of the product, the temperatures required in the present invention are generally consistently lowered by at least about 50°.

It is also possible to replace this unsaturated monocarboxylic acid with the corresponding monoalcohol and to proceed by etherification instead of esterification. However, unsaturated acids are more available and the esterification reaction proceeds more efficiently, so unsaturated acids are preferred over the corresponding unsaturated alcohols.

Suitable starting materials are diepoxides or include diepoxides mixed with monoepoxides. The epoxy esters of the present invention are derivatives of diepoxide components and have the following formula: (wherein R ₁ is the residue of a fatty acid containing conjugated unsaturation, R ₂ is the residue of a fatty acid containing non-terminal non-conjugated unsaturation, and Z is the residue of an organic diepoxide). The fatty acids usually contain 8-22 carbon atoms, preferably 10-18 carbon atoms in the molecule. It will be appreciated that mixtures are formed that include the species represented by the formula. Some or all of the hydroxyl groups can be esterified with fatty acids, but this is not shown in the formula.

When the epoxy esters are copolymerized with monoethylenically unsaturated monomers having terminal unsaturation and containing hydroxy-functional as well as carboxyl-functional monomers in a water-miscible organic solvent solution, Most of the non-conjugated unsaturation of is retained in the carboxyl group-containing copolymer and also a copolymer having primary hydroxyl groups is formed. The acidic unsaturated resinous copolymers thus obtained are non-gelling and organic solvent soluble and can be dispersed in water with the aid of a base and a water-miscible organic solvent.

Oxidative curing by atmospheric oxygen is aided by the presence of a desiccant, and desiccants such as cobalt naphthenate, zirconium naphthenate, calcium naphthenate, or similar desiccant metal fatty acid salts can be used and are useful, however. , these are not necessary. This desiccant is based on the weight of the copolymer, approximately
It is used in amounts of 0.3 to about 2%.

A preferred starting material is a resinous polyepoxide. Bisphenol-based diepoxides are particularly suitable. Their average molecular weight is about 350 to about
4000 and the epoxy functionality is preferably within the range 1.4-2.0, optimally 1.8-2.0. Higher functional polyepoxides may also be used, but care must be taken to limit the proportion of conjugated unsaturation to no more than 1.2 moles of conjugated fatty acid per mole of polyepoxide to avoid gelation during copolymerization. These molecular weights are obtained by calculating from the epoxide equivalent weight.

Particular preference is given to using diglycidyl ethers of bisphenol A with an average molecular weight of 800 to 3000 and an epoxide equivalent of 900.
The diglycidyl ether of bisphenol A with an average molecular weight of 1800 is used as an example.

As described above, the starting diepoxide is reacted with two different types of fatty acids. First, fatty acids containing conjugated unsaturation are relied upon to enable copolymerization with terminal unsaturation in monoethylenically unsaturated monomers. These fatty acids are commercially available fatty acid mixtures containing conjugated unsaturation at the 9 and 11 positions.
-11 is exemplified here as castor fatty acid. Eleostearic acid, found in tung oil, and ricanic acid, found in oticica oil, further illustrate contemplated conjugated fatty acids.

As can be seen, conjugated unsaturation is highly reactive, and monoethylenically monomers containing CH ₂ =C groups (terminal unsaturation) copolymerize with conjugated unsaturation in organic solvent solutions, while Leave most of the non-terminal non-conjugated unsaturation intact.

It is desirable for the copolymerization to leave the epoxy ester in non-gelling organic solvent soluble conditions, and this means that the number of conjugated groups per molecule is limited to avoid cross-linking that causes premature gelation.
For this reason, the conjugated fatty acids are used in amounts providing from 0.2 (preferably at least 0.5) to 2.0 moles per equivalent of epoxy in the polyepoxide. A preferred ratio is 0.8 to 1.5 moles of conjugated fatty acid per equivalent of epoxy in the polyepoxide.

Substantially the entire balance of epoxy functionality is achieved by reaction with non-terminal, non-conjugated unsaturated fatty acids. However, by esters with saturated fatty acids (lauric acid or myristic acid are used)
or one can choose to consume some of the epoxy groups by etherification with a saturated alcohol (lauryl alcohol is an example) and leave enough in the final copolymer so that significant oxidative curing can occur. This can be done as long as at least 0.5 mole (preferably at least 0.8 mole) of non-terminal non-conjugated unsaturated fatty acid is used per mole of polyepoxide so as to provide sufficient residual unsaturation.

Fatty acids containing non-conjugated ethylenic unsaturation are well known and include tall oil fatty acids. Other useful acids are oleic acid, linoleic acid, linolenic acid and erucic acid.

A typical ratio is diepoxide reacted with 2 molar portions of conjugated fatty acids and 2 molar portions of non-terminal non-conjugated unsaturated fatty acids, with a molar excess of not more than 50% of either type of fatty acid over the other. exemplified by the use of All of the epoxy groups are esterified, and preferably at least some of the hydroxyl groups are esterified. The acid number of the epoxy ester product should be below 40, preferably below 20, to minimize the proportion of free fatty acids.

The reaction of fatty acids with polyepoxides is a conventional process assisted by the presence of small amounts of basic catalysts. The formation of epoxy esters and the production of soluble copolymers therefrom is shown in US Pat. No. 2,877,195.

The monoethylenically unsaturated monomer constitutes 15 to 150%, preferably 50 to 90%, based on the weight of the epoxy ester. These monomers contain terminal unsaturation as described above and are preferably composed of a mixture of carboxyl-functional monomers, optionally monomers having primary hydroxyl groups, and non-reactive monomers. Ru. As is commonly known, non-reactive monomers do not react under the intended conditions of polymerization and curing. This usually means that a single ethylenic group is the only functional group present. When air drying is intended, the proportion of monomers is preferably less than 100%, based on the weight of the epoxy ester;
Most preferably it is between 25 and 75%.

Carboxyl functional monomers must be selected for their solubility and ability to copolymerize. Suitable acids are acrylic acid, methacrylic acid, fumaric acid and maleic acid. The number of carboxyl groups is not critical, but one is preferred, as in acrylic acid. Sufficient acid should be used to enable dispersion in water after neutralization, which is based on the copolymer.
to 20% carboxyl functional monomer. A preferred practice uses 5 to 12% carboxyl functional monomer, based on the weight of the copolymer.

Hydroxy-functional monomers are exemplified by hydroxyethyl acrylate or methacrylate or allyl alcohol, which provide primary hydroxyl groups for curing with aminoplast resins. From 1 to 15%, preferably from 2 to 8% by weight of the copolymer should constitute hydroxyl monomer. Although the epoxy esters themselves have hydroxyl groups, these are secondary hydroxyl groups that do not provide the low temperature cure desired here.

The non-reactive monomer is best exemplified by styrene, but vinyltoluene can be used instead. Less desirably, methyl methacrylate, acrylonitrile, vinyl acetate, ethyl acrylate, butyl acrylate, etc. may be used alone or in admixture with others. Styrene or vinyltoluene constitutes the bulk of the non-reactive monomers since they provide transparent homogeneous copolymers which are difficult to obtain when using other non-reactive monomers.

Solution copolymerization is itself entirely conventional and is carried out in a solvent medium using thermal and free radical polymerization catalysts, usually a combination of peroxides, such as ditertiary butyl peroxide and cumene hydroperoxide. A reaction occurs. Preferably, the solution polymerization does not consume all of the unsaturation and has a residual iodine number of at least about 40 in the copolymer.

The solvent used must be selected to be minimal and miscible with water in the amounts used. 2
-Ether alcohols such as butoxyethanol exhibit good water miscibility, and ketones such as methyl ethyl ketone are also very good. However, solvents with limited miscibility in water, such as small amounts of butanol, are also useful. The types of organic solvents that can be present when acidic resins are dispersed in water with the aid of a base are well known, and although not a feature of the invention, alcoholic solvents are suitable.

The base used to neutralize copolymer acidity is subject to wide variation, but sodium hydroxide is useful. Volatile nitrogen-containing bases are preferred and are well known for the purpose of solubilizing acidic resins to provide aqueous coatings. Amines or ammonia are particularly useful, with tertiary amines being the best. Although dimethylethanolamine is used to illustrate the invention, this choice of base is not a feature of the invention.

Neutralization of copolymer acidity may be partial or complete depending on the need for dispersion in water. Complete (100%) neutralization is preferred here, but typically 50-
100% neutralization is suitable.

Dilute the initial solvent solution of neutralized resin with water until it is predominately water. Depending on the desired coating thickness and acceptable viscosity for the application, the final resin solids content ranges up to about 20%. Although flow coating constitutes a preferred application technique in the present invention, the invention is not limited thereto. Typical coatings are applied at 30-60% resin solids, and may be pigmented or unpigmented as desired. Corrosion resistant pigments can be used, such as conventional chromate pigments such as strontium chromate and lead chromate. Resin solids contents in the range of 2-20%, preferably 5-15% are used for electrocoatings.

When this coating is dried in air at room temperature and cured, oxidative curing by atmospheric oxygen gradually removes the solvent sensitivity of the film and is complete in about 3 days. Whether curing is at room temperature or above, desiccants such as cobalt naphthenate, zirconium naphthenate or calcium naphthenate can be used in amounts of 0.3 to 2% based on the weight of the copolymer.

The aminoplast and phenoplast resins useful herein may be of any character so long as they can be dissolved or stably dispersed in water containing the dissolved acidic copolymer. These resins provide methylol groups that are particularly reactive with primary hydroxyl groups and contain 5-40%, preferably 10%, based on the total amount of resin.
-Used in an amount of 35%. Typical aminoplast resins, all of which are formaldehyde condensates, are urea-formaldehyde, water-dispersible transethers with hexamethoxymethylmelamine and ethanol or other lower alcohols, benzoguanamine formaldehyde, etc., in which the carboxyl groups are dissolved in an aqueous alkaline medium. Contains acidic derivatives that aid solubilization. Also useful are water-soluble or dispersible phenolic resins (phenoplasts), exemplified by the well-known non-gelling alkaline condensates of phenol with excess formaldehyde, known as "A" stage resols. Any of these formaldehyde condensates can be used alone or in any desired mixture. Although phenolic resins offer the most outstanding corrosion and detergent resistance, they introduce color problems that limit their use in primers coated with opaque topcoats. Although this phenolic resin also requires higher firing temperatures than aminoplast resins, the present invention still serves to reduce the required temperature.

The invention is illustrated in the examples below. All parts herein are by weight unless otherwise specified.

Example 1 Charge Composition (g) 936 A Dean Stark trap with diglycidyl ether of bisphenol A 528 conjugated 9-11 castor fatty acid 528 tall oil fatty acid xylol with an epoxide equivalent weight of 936 900 is set up. Heat to 150°C to melt. Then add: 60 Xylol 3 Trimethylamine Heat to 220°C and maintain an acid number of 20-23. Cool and add the following solvents: 480 2-butoxyethanol 360 Butanol Premix the following monomers and catalyst and 120-
Add over 3 hours at 125°C. Hold for 1 hour.

600 Styrene 90 Acrylic Acid 10 Ditertiary Butyl Peroxide 27 Cumene Hydroperoxide 12 Cumene Hydroperoxide, add and hold for 1 hour.

12 Add cumene hydroperoxide and hold for 2 hours.

Add the solvents listed below and then cool.

50 2-Butoxyethanol 50 Butanol 180 Methyl Ethyl Ketone This product has a Gardner-Holdt viscosity of Z ₃ - Z ₄ , a Gardner color of 4, an acid number of 38.8, and
It is an organic solvent solution with a non-volatile solids content of 67.9%. The product is water soluble when enough dimethylethanolamine is added to neutralize 100% of the acidity.

This aqueous solution at 40% solids is coated onto a substrate, such as a zinc phosphate steel panel, to provide a coating thickness of 1 mil. The deposited film is dried in air for 1 hour to provide a handleable, tack-free coating. The coating is then cured in air for three days to develop resistance to solvent attack and corrosion. The fully air cured film resists 5% salt spray for 500 hours, which is exceptional for water applied, air cured unpigmented coatings. It is known that even pigmented air-dried coatings have difficulty passing this test, and no commercially available products are able to pass this rigorous corrosion test in the absence of calcination.

Example 2 Charge composition (g) 820 Diglycidyl ether of bisphenol A with epoxide equivalent weight of 900 310 Conjugated 9-11 castor fatty acid 310 A Dean Stark trap is set with tall oil fatty acid xylol. Heat to 150°C to melt. Then add: 60 xylol 3 triethylamine Heat to 225°C and maintain acid number 15-17. 125
Cool to 1200 °C and add the following solvents: 1200 2-butoxyethanol Premix the following monomers and catalyst and 120 -
Add over 3 hours at 125°C.

900 Styrene 170 Acrylic acid 60 Hydroxyethyl acrylate 15 Ditert-butyl peroxide 45 Cumene hydroperoxide 20 Tertiary butyl mercaptan 350 2-Butoxyethanol Keep at 120℃ for 1 hour.

10 Cumene Hydroperoxide - Add and hold for 1 hour 10 Cumene Hydroperoxide - Add and hold for 2 hours Add the following solvents and then cool.

100 2-Butoxyethanol This product has a Gardner-Holdt viscosity of Z ₃ , 3
Gardner Color, an organic solvent solution with an acid number of 55.4 and a non-volatile solids content of 58.3%. The product is water soluble when enough dimethylethanolamine is added to neutralize 100% of the acidity.

The aqueous solution of this example contains 25% by weight (based on total resin) of a liquid thermoset benzoguanamine-formaldehyde condensate (American Cyanamid Product XM).
-1123 (trade name)) and neutralize the acidity to 100% with dimethylethanolamine. This neutralized solution is colored with rutile titanium dioxide at a pigment to binder ratio of 0.2:1 and deionized water is added to provide an aqueous solution with the desired total solids content. In this case, the solution at 40% total solids was flow coated onto the substrate (zinc phosphate treated steel panel).
Provides a coating thickness of 0.5 mil. Baking the deposited film at 250° C. for 20 minutes provided a cured coating having a 4H pencil hardness and passing 60 inch pounds of reverse impact. It also showed good resistance to solvent attack and corrosion.

The same pigmented aqueous solution diluted to 10% solids was
Depositing a film having a thickness of 0.6 mils by anodic electrodeposition at 110 volts, it was found that the film could be cured at temperatures 50° below that normally required. Thus, the cure was 375° for 20 minutes instead of 425-450° as would normally be required for the same degree of cure.
Despite the reduced cure temperature, the cured coating had a pencil hardness of 4H and passed nearly 80 inch pounds of reverse impact. The higher firing temperatures used for electrocoated panels are based on the fact that greater corrosion resistance is emphasized for this type of product.

Claims (1)

[Scope of Claims] 1. A resinous polyepoxide having an epoxy functionality in the range of 1.4 to 2.0, an ethylenically unsaturated monocarboxy fatty acid containing at least 0.2 mole of conjugated ethylenically unsaturation per epoxy equivalent in the epoxide, and the epoxide. a copolymer of an epoxy ester with an ethylenically unsaturated monocarboxy fatty acid containing at least 0.5 moles of non-terminal, non-conjugated ethylenically unsaturation per epoxy equivalent in the epoxy ester, the epoxy ester having substantially no epoxy functionality; copolymerized in an organic solvent solution with a monoethylenically unsaturated monomer containing 15 to 150% terminal ethylenic unsaturation based on the weight of the epoxy ester to make it compatible with oxidative curing. A non-gelling, solvent-soluble copolymer containing ethylenic unsaturation is formed, where the monomers contain 3 to 20%, based on the weight of the copolymer, of acrylic acid, methacrylic acid, The copolymer is composed of carboxy-functional monomers selected from fumaric acid and maleic acid, and is dispersed in water with the aid of a volatile base and a water-miscible organic solvent, in which the aminoplast is further dispersed. A low temperature curable aqueous coating composition containing an epoxy ester copolymer, which contains a resin and a phenolplast resin dispersed therein. 2. The composition of claim 1, wherein said carboxy-functional monomer is present in an amount of 5 to 12% of the weight of the copolymer. 3 The polyepoxide has an average molecular weight of 800 to 3000
and an epoxy functionality of from 1.8 to 2.0. 4. The composition of claim 3, wherein the epoxy ester contains 0.8 to 1.5 moles of the conjugated fatty acid per epoxy equivalent in the polyepoxide. 5. The composition of claim 1, wherein the monocarboxy fatty acid contains 8 to 22 carbon atoms. 6 The polyepoxide has an average molecular weight of 350 to 4000
2. The composition of claim 1, wherein the composition is a bisphenol-based diepoxide having an epoxy functionality of from 1.8 to 2.0, and the non-reactive monomer is selected from styrene and vinyltoluene. 7. The composition of claim 6, wherein the epoxy ester contains 2.0 moles or less of the conjugated fatty acid per epoxy equivalent in the polyepoxide. 8. The composition of claim 1, wherein the monoethylenically unsaturated monomer is used in an amount of 25 to 70% based on the weight of the epoxy ester. 9. The composition of claim 1, wherein said copolymer has an iodine number of at least 40. 10 The monomer further comprises 1 to 1 of the copolymer weight
2. A composition according to claim 1, comprising a monomer providing primary hydroxyl groups in an amount of 15%. 11. Claim 10, wherein said carboxy-functional monomer is present in an amount of 5 to 12% of the weight of the copolymer.
Compositions as described in Section. 12. The composition of claim 11, wherein the monocarboxy fatty acid has 10 to 18 carbon atoms. 13 The polyepoxide has an average molecular weight of 800~
3000 and a diglycidyl ether of bisphenol A with an epoxy functionality ranging from 1.8 to 2.0;
12. A composition according to claim 11, wherein the non-reactive monomer is selected from styrene and vinyltoluene. 14. The composition of claim 13, wherein a desiccant for promoting oxidative curing of the copolymer is present in an amount of 0.3 to 2% based on the weight of the copolymer. 15. The composition of claim 11, wherein said epoxy ester contains 0.8 to 1.5 moles of said conjugated fatty acid per equivalent of epoxy in said polyepoxide. 16 The monoethylenically unsaturated monomer is used in an amount of 50 to 90% based on the weight of the epoxy ester, and the hydroxy monomer is used in an amount of 2% of the weight of the copolymer.
12. The composition of claim 11, wherein the composition is present in an amount of ~8%. 17. The composition of claim 11, wherein the acidity of the copolymer is provided by acrylic acid. 18. The composition of claim 11, wherein said copolymer has an iodine number of at least 40. 19. The composition according to claim 11, wherein the hydroxy monomer is hydroxyethyl acrylate. 20. The composition of claim 11, wherein the copolymer is neutralized with an amine and the aminoplast resin is benzoguanamine/formaldehyde. 21. The composition according to claim 11, wherein the proportion of the aminoplast resin is 5 to 40% based on the total resin.