WO1997043340A1

WO1997043340A1 - Low volatile organic compound content waterborne coating composition

Info

Publication number: WO1997043340A1
Application number: PCT/US1997/007932
Authority: WO
Inventors: John O. Bayer
Original assignee: Ameron International Corporation
Priority date: 1996-05-13
Filing date: 1997-05-12
Publication date: 1997-11-20
Also published as: AU3002797A

Abstract

Waterborne coating compositions are prepared by combining, in a first embodiment, an epoxy resin, phenolic resin ingredient with, an amino resin, a polysiloxane resin, and emulsifying agent, one or more solvent(s), and water. A second embodiment is prepared by combining each of the above-mentioned ingredients except for the epoxy resin. A desired epoxy resin has an epoxide equivalent weight in the range of from about 400 to 3,800 and has a weight average molecular weight in the range of from about 900 to 20,000. A desired phenolic resin is selected from the group consisting of phenolic resoles. A desired amino resin is selected from the group consisting of melamine and urea formaldehyde resins having a weight average molecular weight in the range of from about 200 to 1,000. A desired polysiloxane resin includes hydroxy-functional polysiloxane resins having a hydroxy functionality in the range of from 1 to 10 percent. The ingredients are added together to form an oil-in-water emulsion having low VOC content. The oil-in-water emulsion compositions is applied to a substrate and subjected to elevated temperature conditions to effect cross-linking between the resin ingredients, forming a protective coating.

Description

LOW VOLATILE ORGANIC COMPOUND CONTENT WATERBORNE COATING COMPOSITION

Field of the Invention

The present invention relates generally to waterbome coating compositions and, more particularly, to a low volatile organic compound content waterbome coating composition comprising an emulsion of an organic component suspended in water.

Background of the Invention

Chemical compositions that are currently being used for coating metal substrates, and more particularly, the interior surfaces of steel storage containers, such as steel drums and the like, typically comprise a large proportion of organic solvent to dilute the effective organic polymer for purposes of achieving a desired film thickness during application. Such conventional chemical compositions necessarily have a high volatile organic compound (VOC) content which, under recent environmental legislation, can no longer be used.

In response to such legislation, substitute low VOC compound content chemical compositions have been developed for such applications. An example of such substitute chemical compositions include those that can be applied without the use of a solvent, such as powder coated chemical coatings. However, powder coated compositions do not perform as well as the high VOC content coating compositions that they replace because of their inability to completely wet the applied substrate surface. For example, when used for coating the inside surface of steel drums, powder coated compositions do not adequately wet the seam portions of the drum surface, causing the seam areas to remain exposed.

Another example of such substitute chemical compositions are so-called waterbome compositions that comprise an emulsion of effective organic polymer in water which depend, to some extent, on the use of one or more emulsifying agent(s). In order to provide coating protection similar to that provide by the high VOC content compositions that they replace, such waterbome coating compositions comprise a high level of solids. However, such high-solids coating compositions require the use of an organic solvent to lower the viscosity of the composition for low film thickness applications, such as when used to coat the inside surface of steel drums and the like. Accordingly, when such water-borne coating compositions are applied, the VOC content is greater than that indicated in a packaged state, which may be greater than that allowed by current law. Also, due to the high solids content, such waterbome coating compositions do not allow for water cleanup, further requiring use of organic solvents and creating a potential fire hazard.

It is, therefore, desirable that a coating composition be prepared that has a low VOC content, which satisfies current limits set by law. It is desirable that such coating composition be waterbome and facilitate low film thickness application and clean up without the use of organic solvents. It is also desirable that such composition be formulated to provide a coating that is equal to or better than high VOC content coating compositions that it replaces.

Summary of the Invention:

There is, therefore, provided in practice of this invention waterbome coating compositions that are prepared by combining, in a first embodiment, an epoxy resin, a phenolic resin ingredient, an amino resin, a polysiloxane resin, emulsifying agents, one or more solvent(s), and water. A second embodiment is prepared by combining each of the above-mentioned ingredients except for the epoxy resin.

A desired epoxy resin has an epoxide equivalent weight in the range of from about 400 to 3,800, and has a weight average molecular weight in the range of from about 900 to 20,000. The first composition embodiment comprises in the range of from about 50 to 80 percent by weight epoxy resin based on the total weight of the composition. A desired phenolic resin is selected from the group consisting of phenolic resoles. A first composition embodiment comprises in the range of from 10 to 40 percent by weight, and a second composition embodiment comprises in the range of from 40 to 80 percent by weight phenolic resin based on the total weight ofthe composition. A desired amino resin is selected from the group consisting of melamine and urea formaldehyde resins having a weight average molecular weight in the range of from about 200 to 1 ,000. A first composition embodiment comprises in the range of from 5 to 25 percent by weight, and a second composition embodiment comprises in the range of from 10 to 40 percent by weight amino resin based on the total weight of the composition. A desired polysiloxane resin includes hydroxy-functional polysiloxane resins having hydroxy functionality in the range of from about 0.5 to 15 percent. A first composition embodiment comprises in the range of from

0.5 to 5 percent by weight, and a second composition emboc:rnent comprises in the range of from 0.5 to 15 percent by weight polysiloxane resin based on th* total weight ofthe composition.

A desired emulsifying agent is an acrylic resin having an acid number in the range of from about 50 to 200. First and second composition embodiments each comprise in the range of from 0.5 to 10 percent by weight acrylic resin based on the total weight ofthe composition. A desired solvent is a blend of hydrophobic and hydrophilic solvents, of which in the range of from 10 to 100 percent by weight is hydrophobic. First and second composition embodiments each comprise in the range of from 1 to 20 percent by weight ofthe solvent blend based on the total weight of the composition. Water is present in the first and second composition embodiments in the range of from about 2 to 30 percent by weight ofthe total composition.

The waterbome coating compositions are prepared by combining the emulsifying agent with a hydrophobic solvent to form a first mixture and partially neutralizing the first mixture with an amine compound to obtain a desired degree of water solubility. A cross-linking mixture is formed by adding the epoxy resin, phenolic resin, polysiloxane resin, and the amino resin under agitation to the first mixture. In the second composition embodiment, the epoxy resin is not added to the first mixture. A water-in-oil emulsion is formed by adding sufficient water to the cross-linking mixture under conditions of high shear. The water-in-oil emulsion is then inverted to form an oil-in-water emulsion by adding sufficient water to the water-in-oil emulsion.

The resulting oil-in-water emulsion has a low VOC content, can be further diluted with water if desired for a particular application technique, and can be cleaned up using water. After application, the composition is cured under conditions of elevated temperature for a period of time sufficient to effect and complete cross linking reactions between the resin ingredients, forming a coating having desired properties of hardness, flexibility, and chemical resistance.

Detailed Description:

Low VOC content waterbome coating compositions are prepared according to principles of this invention by combining a phenolic resin with, an amino resin, a polysiloxane resin, an emulsifying agent, one or more solvents), and water. In one embodiment, a waterbome coating composition is prepared by combining, in addition to the above-identified chemical ingredients, an epoxy resin. Waterbome coating compositions prepared using the above-identified ingredients produce an oil-in-water emulsion having a VOC content well below four pounds per gallon, that is reducible with water to facilitate both low film thickness application and cleanup. A first embodiment waterbome coating composition is prepared, accordingly to principles of this invention by combining a phenolic resin with, an epoxy resin, an amino resin, a polysiloxane resin, an emulsifying agent, one or more solvent(s), and water.

With respect to the epoxy resin ingredient, suitable epoxy resins include, but are not limited to, those derived from the reaction of bisphenol-A or bisphenol-F and epichlorohydrin that result in a resin having both epoxide and hydroxyl functionality. Use ofthe epoxy resin is desired because it contributes to the coating composition by providing exceptional chemical resistance and enhanced flexibility.

It is desired that the epoxy resin have an epoxide equivalent weight in the range of from about 400 to 3,800, and have a weight average molecular weight in the range of from about 900 to 20,000. An epoxy resin having an epoxide equivalent weight of less than about 400, or having a weight average molecular weight of less than about 900, may not possess a sufficient degree of hydroxy functionality for cross linking during baking to provide a desired cross link density, thereby producing a finally-cured coating that may have reduced chemical resistance. An epoxy resin having an epoxide equivalent weight greater than about 3,800, or having a weight average molecular weight greater than about 20,000, may require use of a large amount of solvent to put the polymer in solution, thereby causing any dispersal made from it to be instable.

Preferred bisphenol-A derived epoxy resins include those having the general formula

where R, is selected from the group consisting of alkyl groups and hydrogen, wherein each R, can be the same or different, and where n, is an integer having an average number value in the range of from about 2 to 30.

Preferred bisphenol-A derived epoxy resins include those having an emulsifier built into the polymer and which are provided as an emulsion in water; those produced by Shell Chemical of Houston, Texas under the product designations 1001 , 1007, 1009 and the emulsion 3540 w 55; those produced by Ciba Specialty Chemicals of Hawthorne, New York under the product designations 7071 , 6097, 7097 and the emulsion PZ 3907; and those produced by Dow Coming Corp., of Midland, Michigan under the product designations 661, 667 and 550. Preferred bisphenol-F derived epoxy resins include those that are commercially available from, for example, Shell Chemical under the product designations EPON 862; Dow Coming Corp., under the product designations DER 354 and DER 354LV; and Ciba Specialty Chemicals under the product designations GY 281, GY 282, GY 285, and PY 302-2.

It is desired that the percent by weight of the epoxy resin, to other constituents of the composition used to prepare the composition, be in the range of from about 50 to 80 percent, with an optimum range of from about 60 to 75 percent. Levels of epoxy resin greater than about 80 percent be weight may produce coating films that do not fully cure during baking, while levels of epoxy resin less than about 50 percent by weight may produce coating films that are too brittle for the intended application, and that do not display good resistance to substances that are alkaline or basic in nature.

With respect to the phenolic resin, suitable phenolic resins include those classified as phenolic resole resins, i.e., phenolic resins that are formed by condensation reaction between phenol and formaldehyde in the presence of an alkali catalyst. It is desired that the phenolic resole be esterified at the methylol group sites on the resin with an alcohol, such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tertbutanol and the like. Etherified phenolic resole resins are preferred over non-etherified phenolic resole resins because they are more compatible with other ingredients ofthe compositions, have lower odor, and are easier to emulsify than the non-etherified versions. The phenolic resole resin serves primarily as a cross linker for the epoxy resin through condensation with the hydroxy functionality of the epoxy resin, but also serves to enhance the chemical resistance ofthe finally-cured coating.

Preferred etherified phenolic resole resins include those produced by Ciba Specialty Chemicals under the product designation HZ 365; by Shell under the product designation Epikure DX-200-N-60; and by Georgia Pacific under the product designations GPRI 7550 and GPRI 7597. The weight percent ofthe phenolic resin, to other constituents ofthe composition, used to prepare coating compositions of this invention is in the range of from about 10 to 40 percent, with an optimum weight percent being in the range of from about 15 to 35 percent. Levels ofthe phenolic resin below about ten percent by weight may produce coating films that do not fully cure during baking, while levels greater than about 40 percent by weight may produce coating films that are too brittle for the intended application, and that contain a necessarily reduced amount ofthe epoxy resin which can provide poor chemical resistance.

With respect to the amino resin ingredient, suitable amino resins can be selected from the group consisting of melamine formaldehyde resins and urea formaldehyde resins. The amino resin ingredient serves as a additional cross linker to the phenolic resin, serves to ensure compatibility between the remaining resins in the composition, and serves to reduce raw material costs for the composition. The amino resin can be etherified with such alcohols as methanol, butanol, or combinations thereof.

Preferred melamine formaldehyde resins include those having the general formula

where R₃ is selected from the group consisting of alkyl, aryl, and alkoxy groups and ether, wherein each R₃ can be the same or different, and wherein n₃ is an integer having an average number value providing a weight average molecular weight in the range of from about 200 to 1 ,000, and a specific weight in the range of from about 350 to 550.

A melamine formaldehyde resin having a weight average molecular weight less than about 200, or having a specific weight less than about 350, may possess a low degree of functionality, making it extractable from the film and degrading the chemical resistance of the cured composition. A melamine formaldehyde resin having a weight average molecular weight greater than about 1,000, or having a specific weight greater than about 550, may not possess a sufficient number of reactive sites to provide a cross link density needed for good chemical resistance and would require higher levels of solvent to form a solution.

Preferred urea formaldehyde resins include those having the general formula

where R, is selected from the group consisting of alkyl, and alkoxy groups, hydrogen and ether, wherein each R, can be the same or different, and wherein n₄ is an integer having an average number value providing a weight average molecular weight in the range of from about 350 to 550. A particularly preferred urea formaldehyde resin is butylated urea formaldehyde.

Preferred amino resin ingredients include those produced by Monsanto Co., of Saint Louis, Missouri under the product designations Resimene 747 and 757; and by American Cyanamid Co., of Wayne, New Jersey under the product designations Cymel 303 and 1 130. The weight percent ofthe amino resin ingredient, to other constituents ofthe composition used to prepare coating compositions of this invention, is in the range of from about 5 to 25 percent, with an optimum weight percent being in the range of from about 5 to 10 percent. Levels of the amino resin below about five percent by weight may produce coating films having increased raw material costs, while levels above about 25 percent by weight may produce a finally-cured coating having reduced chemical resistance.

With respect to the polysiloxane resin ingredient, suitable polysiloxane resins include those that are selected from the group consisting of hydroxy-functional polysiloxane resins. The polysiloxane resin contributes water resistance, i.e., hydrophobicity, to the finally-cured coating. It is desired that the hydroxy-functional polysiloxane resin be either methyl or methyl-phenyl based, and have a hydroxy functionality in the range of from about 0.5 to 15 percent because the hydroxy functionality allows the polysiloxane resin to become a part of the cross-linked film during the bake and must be in the range to prevent adverse effects on chemical resistance. It is also desired that the specific hydroxy content ofthe hydroxy-functional polysiloxane be in the range of from about one to five percent by weight because at this level it provides cross linking of the polysiloxane into the film, compatibility with other constituents, and water resistance without adversely affecting the chemical resistance ofthe film.

Preferred polysiloxane resins include those having the general formula

where R₅ is selected from the group consisting of alkyl, aryl and alkoxy groups, where R₆ is selected from the group consisting of alkyl, aryl, alkoxy groups and hydroxy groups, where R₇ is selected from the group consisting of alkyl groups, aryl groups and hydrogen, where each R can be the same or different, and where n₅ is an integer having an average number value providing a weight average molecular weight in the range of from about 200 to 5,000.

Preferred polysiloxane resins include those produced by Wacker of Adrian, Michigan under the product designation Silres SY 409; and by Dow Coming Corp., under the product designation DC-6018. The weight percent of the polysiloxane resin, to other constituents of the composition used to prepare coating compositions of this invention, is in the range of from about 0.5 to 5 percent, with an optimum weight percent being in the range of from about 0.5 to 2 percent. Levels of the polysiloxane resin below about 0.5 percent by weight may produce coating films having a reduced degree of water resistance, while levels above about five percent by weight may lead to instability of the liquid resin composition prior to emulsification as described in detail below.

With respect to the emulsifying agent, suitable emulsifying agents are acrylic resins and include those having a sufficient acid number to permit water solubility when neutralized. Preferred acrylic resins are those having an acid number in the range of from about 50 to 200, and optimally those having an acid number in the range of from about 75 to 125. It is desired that the acrylic resin emulsifying agent have hydroxy functionality for cross linking and for forming part of the final resin polymer. The acrylic resin serves as an emulsifier to allow the final resin composition to be emulsified in water, as discussed below, and is preferred over other surfactants and the like because of its ability to form part ofthe final resin polymer. To facilitate use in forming the coating composition it is desired that the acrylic resin ingredient be provided in the form of a solution to permit free movement in the composition during the emulsion process so that it can migrate to the water-oil interface. Preferred acrylic resins useful as an emulsifying agent include those having the general formula

where R_g is an alkyl group, where Ro is selected from the group consisting of alkyl, aryl, and alkoxy groups, hydroxy groups, carboxy groups, hydrogen and ester, where each R₈ and each R, can be the same or different, and where n₆ is an integer having an average number value providing a weight average molecular weight in the range of from about 200 to 5,000.

Preferred acrylic resins include those produced by Cook Composites and Polymers of Kansas City, Missouri under the product designation A2678, and any of the Tallicin line of acrylic products available from Pflaumer Brothers. The weight percent of the acrylic resin, to other constituents ofthe composition useful for preparing coating compositions of this invention, is in the range of from about 0.5 to 10 percent, with an optimum weight percent being in the range of from about 0.5 to 3 percent. Levels of the acrylic resin below about 0.5 percent by weight may produce coating films having reduced emulsion stability, while levels above about ten percent by weight may produce coating compositions having reduced chemical resistance when finally cured and that may adversely effect film formation in spray applications.

With respect to the solvent ingredient, it is desired that the solvent be a blend of hydrophobic and hydrophilic solvents, of which in the range of from about 10 to 100 percent by weight is hydrophobic, and optimally is in the range of from about 70 to 100 percent hydrophobic. Suitable hydrophobic solvents include those selected from the group including acetate, xylene, toluene, VM&P, SC-100, SC-150 and the like manufactured by Ashland Chemical of Columbus, Ohio; Eastman Kodak Co., of Rochester, New York; Shell Chemical Co., and others. Suitable hydrophilic solvents include those selected from the group including alcohols, glycol ethers, ketones, and the like. The solvent blend acts as a carrier for the above- identified resins, which constitutes the film-forming part ofthe composition.

The weight percent ofthe solvent blend, to other constituents ofthe composition, used to prepare coating compositions of this invention is in the range of from about 1 to 20 percent, with an optimum weight percent being in the range of from about one to ten percent. Levels of the solvent blend below about one percent by weight may produce a composition having a high viscosity that can make processing difficult, while levels above about 20 percent by weight may not cause harmful effects to the film or emulsion but can negate the benefit of using an emulsion system which has low solvent emissions. It is preferred that the weight percent of the solvent blend be as low as possible. During the emulsification process, as discussed below, the weight percent ofthe solvent blend can be within the above-mentioned range, but can be removed by stripping the solvent from the emulsion under vacuum after the process is complete.

With respect to the water ingredient, water serves as a carrier for the emulsion suspension. The weight percent of water, to other constituents of the composition, used to prepare coating compositions of this invention is in the range of from about 2 to 30 percent, depending on the final desired viscosity ofthe emulsion.

A second embodiment of a waterbome coating composition is prepared in a manner similar to the first embodiment, by combining each of the same above-described ingredients except for the epoxy resin. Accordingly, the second embodiment is an epoxy-resin free waterbome coating composition that relies primarily on the phenolic resin as the primary resin in the composition, functioning primarily through self condensation in combination with the amino resin ingredient.

In the second embodiment, the weight percent ofthe phenolic resin ingredient, to other constituents ofthe composition used to prepare coating compositions of this invention is in the range of from about 40 to 80 percent, with an optimum range of from about 55 to 60 percent. The weight percent ofthe amino resin ingredient, to other constituents ofthe second embodiment composition, is in the range of from about 10 to 40 percent, with an optimum range of from about 25 to 35 percent. The weight percent of the polysiloxane resin ingredient to other constituents of the second embodiment composition is in the range of from about 0.5 to 15 percent, with an optimum range of from about 1 to 7.5 percent. The weight percent ofthe acrylic resin ingredient, the solvent blend, and the water to other constituents ofthe second embodiment composition is the same as that described for the first composition embodiment. Levels ofthe ingredients outside of these ranges produces the same undesirable effects discussed above for each respective ingredient in the first composition embodiment.

Coating compositions of this invention may also optionally comprise fillers. Conventional fillers can be used in the coatings, such as silica powder, talc (magnesium silicate), clays such as china clay (aluminum silicate), wollastonite (calcium silicate), calcium carbonate, barites (barium sulfate, barium metaborate), aluminum trihydrate, graphite, zinc, aluminum, copper and the like. Barium metaborate is a preferred filler when the resistance to acids is desired because it has been found that coating compositions containing barium metaborate exhibit improved resistance to attack by acid. While the first and second embodiments of the coating composition as described above cure to form a clear coating, colored coating compositions can also be prepared according to principles of this invention by using pigments such as iron oxide, aluminum oxide, and titanium dioxide. Pigments containing lead should be avoided because of toxicity. Organic pigments such as hansa yellow, phthalo green, and phthalo blue may also be used to color the product.

Other materials commonly used in coating compositions may also be included. For example, the coating composition may include plasticizers for the binder such as esters or silicone oils. Phthalates work well as plasticizers. Flow control additives, wetting agents for pigment dispersion, and thixotropic agents such as fumed silica may also be included.

The coating composition is an oil-in-water emulsion comprising a cross-linking suspension made up of epoxy, phenolic, amino, polysiloxane, and acrylic resins in the first embodiment, and phenolic, amino, polysiloxane, and acrylic resins in the second embodiment in the oil phase. It is believed that the acrylic resin is at the interface with the water phase.

Coating compositions of this invention are prepared by first mixing the acrylic resin (emulsifying agent) in solution form with the solvent mixture. The acrylic solution/solvent mixture is partially neutralized with an amine compound to obtain a desired degree of water solubility. In preferred composition embodiments, the acrylic solution/solvent mixture is neutralized by approximately 75 percent using dimethylaminoethanol. The epoxy resin, phenolic resin, polysiloxane resin and amino resin ingredients in the first embodiment, and the phenolic resin, polysiloxane resin and amino resin ingredients in the second embodiment are, added to the neutralized acrylic solution/solvent mixture in the above-described proportions under agitation to form a cross-linking mixture. The resulting mixture is placed under conditions of high shear, and water is added in a step-wise fashion until a water-in-oil emulsion is formed. At this stage the weight ratio of hydrophobic solvent to hydrophilic solvent is greater than about 1: 1. Water is further added under conditions of high shear until the emulsion is inverted into an oil-in-water emulsion.

The coating composition can be packaged in lined or plastic containers with a shelf life of about six months. Coating compositions of this invention can be sold as a single component system, and can be applied by conventional application techniques, such as by spray, roll or brush method. In applications where the waterbome coating composition is being used as a protective coating for the inside of steel drums, cans, tanks and the like, the coating is applied by spray application using an airless spray application technique.

Once applied, the resin ingredients ofthe waterbome coating compositions undergo both homo and heteropolycondensation cure reactions, resulting in the formation of a highly cross- linked film. Coating compositions of this invention are cured via a bake process at temperatures in the range of from about 400 to 450°F for in the range of from about 7 to 15 minutes. It is to be understood that the cure conditions may vary depending on the such variables as the substrate thickness, the coating film thickness, and environmental factors such as relative humidity and the like. While not wishing to be bound by any particular theory or mechanism, it is believed that both the phenolic resin and the amino resin undergo homopolycondensation to form extended respective polymers. Such homopolycondensation reactions are facilitated by the presence of hydroxyl-functional polysiloxane resins. During these homopolycondensation reactions, the newly-formed extended polymers also undergo heteropolycondensation reactions with the polysiloxane and acrylic resins, to form a highly cross-linked film. In the first embodiment, the epoxy resin ingredient forms the primary backbone ofthe cross-linked film, while in the second embodiment, the phenolic resins forms the primary backbone ofthe cross-linked film.

The fully-cured coatings develop a pencil hardness of better than about 4H, display no loss of hardness after a ten minute soak in MEK solvent, display no loss in hardness when soaked for four hours in 150°F, 10 percent sodium hydroxide, and have less that 1/8 inch creep from a scribe cut in the film prior to immersion and resistance to acid stripper at 80 °F for better than 8 minutes when immersed.

Although low VOC waterbome coating compositions ofthe present invention have been described with considerable detail with reference to certain preferred variations thereof, other variations are possible. Therefore, the spirit and scope ofthe appended claims should not be limited to the preferred variations described herein.

Claims

What is Claimed is:

1. An oil-in-water coating composition emulsion prepared by combining: a phenolic resin; an amino resin; a polysiloxane resin; an acrylic resin emulsifier; a blend of hydrophobic and hydrophilic solvent; and water.

2. A coating composition as recited in claim 1 wherein the phenolic resin is selected from the group consisting of phenolic resole resins.

3. A coating composition as recited in claim 1 comprising in the range of from 40 to 80 percent by weight ofthe phenolic resin.

4. A coating composition as recited in claim 1 wherein the amino resin is selected from the group consisting of melamine formaldehyde resins and urea formaldehyde resins.

5. A coating composition as recited in claim 1 wherein the polysiloxane resin has a hydroxy functionality in the range of from 0.5 to 15 percent.

6. A coating composition as recited in claim 1 wherein the acrylic resin emulsifier has an acid number in the range of from 10 to 200.

7. A coating composition as recited in claim 1 comprising in the range of from 40 to 80 percent by weight phenolic resin, 10 to 40 percent by weight amino resin, 1 to 15 percent by weight polysiloxane resin, and 0.5 to 10 percent by weight acrylic resin.

8. A coating composition as recited in claim 1 further comprising an epoxy resin

9. A coating composition as recited in claim 8 wherein the epoxy resin is derived from the reaction of bisphenol-A or bisphenol-F and epichlorohydrin and has a weight average molecular weight in the range from 900 to 20,000.

10. A coating composition as recited in claim 8 comprising in the range of from 50 to 80 percent by weight ofthe epoxy resin.

11. An oil-in-water emulsion coating composition comprising: a major proportion of phenolic resin; an amino resin selected from the group consisting of melamine formaldehyde and urea formaldehyde resins; o a polysiloxane resin; an acrylic resin emulsifier having an acid number in the range of from 10 to 200; a blend of hydrophobic and hydrophilic solvent; and water.

5 12. A coating composition as recited in claim 11 comprising in the range of from 5 to 40 percent by weight ofthe amino resin.

13. A coating composition as recited in claim 11 wherein the polysiloxane resin has a hydroxy functionality in the range of from 0.5 to 15 percent. 0

14. A coating composition as recited in claim 13 comprising in the range of from 0.5 to 15 percent by weight ofthe polysiloxane resin.

15. A coating composition as recited in claim 11 comprising in the range of from 0.5 5 to 10 percent by weight ofthe acrylic resin.

16. An oil-in-water emulsion coating composition comprising: a major proportion of epoxy resin; a phenolic resole resin; 0 an amino resin selected from the group consisting of melamine formaldehyde and urea formaldehyde resins; a polysiloxane resin; an acrylic resin emulsifier having an acid number in the range of from 10 to 200; and a blend of hydrophobic and hydrophilic solvent; and 5 water.

17. A coating composition as recited in claim 16 wherein the epoxy resin is derived from the reaction of bisphenol-A or bisphenol-F and epichlorohydrin, has an epoxide equivalent weight in the range of from 400 and 3800, and has a weight average molecular weight in the range of from 900 to 20,000.

18. A coating composition as recited in claim 17 comprising in the range of from 50 to 80 percent by weight ofthe epoxy resin.

19. A coating composition as recited in claim 16 comprising in the range of from 10 to 40 percent by weight ofthe phenolic resin.

20. A coating composition as recited in claim 16 wherein the polysiloxane resin has a hydroxy functionality in the range of from 0.5 to 15 percent.

21. A coating composition as recited in claim 20 comprising in the range of from 0.5 to 5 percent by weight ofthe polysiloxane resin.

22. A coating composition as recited in claim 16 comprising in the range of from 0.5 to 10 percent by weight ofthe acrylic resin.

23. A method for preparing an oil-in-water emulsion coating composition comprising the steps of: forming a first mixture by combining an acrylic resin solution with a solvent mixture; partially neutralizing the first mixture with an amine compound to obtain a desired degree of water solubility; forming a cross-linking mixture by adding a phenolic resin, a polysiloxane resin, and an amino resin under agitation to the first mixture; forming a water-in-oil emulsion by adding sufficient water to the cross-linking mixture under high shear; and inverting the emulsion to form an oil-in-water emulsion by adding sufficient water to the water-in-oil emulsion

24. A method as recited in claim 23 wherein the step of forming a first mixture comprises using a sufficient amount of hydrophobic solvent to allow the mixture to be higher in hydrophobic solvent than hydrophilic solvent.

25. A method as recited in claim 23 wherein the step of forming a water-in-oil emulsion comprises adding water to the cross-linking mixture so that the weight ratio of hydrophobic solvent to hydrophilic solvent is greater than 1 :1.

26. A method as recited in claim 23 wherein the step of inverting the water-in-oil emulsion comprises adding water until the oil-in-water emulsion is formed.

27. A method as recited in claim 26 wherein the step of partially neutralizing the first mixture comprises neutralizing the acrylic first mixture by approximately 75 percent.

28. A method as recited in claim 26 wherein the step of forming a cross-linking mixture further comprises adding an epoxy resin.