GB2113231A

GB2113231A - Polymer coating compositions

Info

Publication number: GB2113231A
Application number: GB08300601A
Authority: GB
Inventors: Morris Robert Olson
Original assignee: Cargill Inc
Current assignee: Cargill Inc
Priority date: 1982-01-15
Filing date: 1983-01-11
Publication date: 1983-08-03
Also published as: DE3301135A1; IT8347544A0; JPS58122970A; IT1203645B; CA1238442A; GB8300601D0; GB2113231B

Abstract

A coating solution comprising a polyester having a hydroxyl value of at least 150; and organic solvent which has a water solubility in the range from 5% by weight to complete miscibility in water; water comprising at least 2% by weight of the coating solution; and a cross linking agent miscible with the polyester, the organic solvent, and the water.

Description

SPECIFICATION Polyester coating compositions This invention relates to polyester compositions. More particularly, this invention relates to water as a solvent in high solid polyester coating compositions to reduce organic emissions.

Environmental concern has become increasingly important in recent years. This concern not only extends to preservation of the environment for its own sake, but extends to safety for the public as to both living and working conditions. Volatile organic emissions resulting from coating compositions which are applied and used by industry and by the consuming public are often not only unpleasant, but contribute to photochemical smog. Governments may or have established regulations setting forth guidelines relating to volatile organic compounds (VOCs) which may be released to the atmosphere. The United States Environmental Protection Agency (EPA) has established guidelines relating to the amount of VOCs released to the atmosphere, such guidelines being scheduled for adoption by the states of the United States.Guidelines relating to VOCs, such as those of the EPA, and environmental concerns are particularly pertinent to the paint and industrial coating industry which uses organic solvents which are emitted into the atmosphere.

With respect to coating compounds, and in response to environmental concem, organic resins which are high in solids content have been developed and are known to reduce organic emissions with the use of resinous coatings. The higher the solid content, the less solvent available to emit into the atmosphere. Higher solid content is almost always a goal, but generally some solvent is required to apply coating resins. It is an object of this invention to provide a solvent system which is compatible with a baking high solid polyester coating composition which will provide reduced organic emissions into the atmosphere.

It has been discovered that water in conjunction with an organic solvent or solvent mixture, which is soluble in water at 250C. in the range from about 5% by weight to complete miscibility in water; a polyester having a hydroxyl value of 1 50 or greater; and one or more cross linking agents which are miscible with such polyester/solvent/water combination reduces the emission of volatile organic compounds from that which would be experienced with the use of organic solvents without water as a cosolvent.

Surprisingly, high solids polyesters having hydroxyl values of 1 50 or greater have been discovered to have an affinity for water. The amount of water which can be added to a polyester baking system increases with increasing hydroxyl value and decreasing molecular weight. Hence, in the invention the amount of water used is a function of the hydroxyl value of the polyester in the coating composition.

High solids polyesters with a hydroxyl value of 1 50 or greater may be prepared from the reaction of a dibasic acid and an organic polyoi having at least two hydroxyl groups. The resulting high solids polyesters may be mixed with an organic solvent which has a water solubility in the range from about 5% by weight to complete miscibility in water, water, and an amino resin cross linking agent to form a coating composition with reduced volatile organic emissions. To be effective in reducing VOCs, water must comprise at least about 2% by weight of the coating system, and the organic solvent may comprise up to about 30% by weight of the coating composition with the preferred range of the ratio of water to organic solvent being from about 20/80 to about 60/40.Cellosolve acetate or z-ethoxyethyl acetate, normal butanol, isobutanol, n-propoxypropanol and butyl cellosolve or z-butoxyethanol are representative solvents which may be used in the coating composition with butyl cellosolve a preferred solvent. Methylated melamine, methylated urea, and hexamethoxymethyl melamine are representative amino resin cross linking agents with hexamethoxymethyl melamine, commercially available as Cymel 303 from American Cyanamid Co. and being a preferred cross linking agent. The invention is not appropriate with cross linking agents such as urethanes which react with water.

The polyester/solvent/water compositions of the invention are blended by mechanically mixing the ingredients. Preferably, as it is made, the polyester will have sufficient organic solvent to reduce its viscosity to Z6 or less. Preferably the cross linking agent such as Cymei 303 then is added to such polyester organic solvent mixture. Preferably, thereafter, the remaining desired organic solvent is added and then the desired water is added. The addition of too much water before the addition of sufficient organic solvent may result in poor mixing. Preferably all of the aforedescribed mixing is done between room temperature to about 500C.

High Solids Polyesters The preferred polyesters for use with the water and organic cosolvent combination have hydroxyl values of at least about 1 50 to about 350 and number average molecular weights in the range from about 300 to about 1100. Generally, they are made from the reaction of dibasic acids or acid an hydrides such as isophthalic acid, adipic acid, phthalic anhydride and terephthalic acid with polyols such as propylene glycol, neopentyl glycol, and trimethylol propane. Optionally, a solvent of the type specified in this invention may be added during or immediately after production of the resin for ease in handling the resin. Further pigments may be optionally added to the polyester resin.These pigments include metallic oxides such as titanium dioxide and iron oxide, metallic flakes such as bronze or nickel flakes, metallic powders, phthalocyanine pigments, monastral pigments, molybdate pigments such as molybdate organge; quinacridone pigments, sulfate pigments, carbonate pigments, carbon black pigments, silica pigments, and other organic and inorganic pigments known in the art. The pigment to binder ratio is usually in the ratio from about 0 (for clear coatings) to about 2 to 1. The solids content of the resulting polyester resin normally is in the range from about 85% to about 100% by weight.

The following examples of polyesters are provided to illustrate polyesters which can be used in the invention; however, they should not be construed as limiting the scope of the invention.

EXAMPLE I 41.00 grams of propylene glycol, 29.82 grams of phthalic anhydride, and 29.40 grams of adipic acid are charged into a reactor and are heated under an inert gas to about 4600 F. for about 2 hours.

After the 2 hours, the reaction is cooled to 2500F. and 10.00 grams of cellosoive acetate is added. The resulting mixture is cooled and yields a polyester having about 90% solids by weight, a hydroxy value of about 160, a viscosity in the range of about Z3 to about Z5 and a weight per gallon of about 9.8 pounds.

EXAMPLE II 44.90 grams of neopentyl glycol (90% in water), 5.77 grams of trimethylol propane, 23.39 grams of adipic acid, and 26.58 grams of isophthalic acid are charged into a reactor and are slowly heated to 4600 F. under an inert gas until an acid value of about not more than 10 is reached. The reaction mixture is cooled to 2500F., whereupon, 15.00 grams of cellosolve acetate is added to the reaction mixture. The resulting mixture is a polyester having a number average molecular weight of about 750, about 85% solids by weight, a hydroxyl value of about 175, a viscosity of about Z4 to about Z6, and a weight per gallon of about 9.3 pounds.

EXAMPLE Ill 47.06 grams of propylene giycol, 28.96 grams of adipic acid, 32.96 grams of isophthalic acid, and 0.05 grams of Fascat 4100 whcih is hydrated monobutyltin oxide and a product of MST Chemical Co.

are slowly heated to 3800 F. and then to 4200 F. until the resin clears and an acid number of about 9 (90% in cellosolve acetate) is reached. The reaction mixture is cooled to 2750F. and 5 grams of cellosolve acetate is added. The resulting mixture is a polyester having a number average molecular weight of about 450, about 90% solids by weight, a hydroxyl value of about 240 to about 250, a viscosity of about Z5 to about Z6, and a weight per gallon of about 9.8 pounds.

EXAMPLE IV A high solids baking alkyd for use in the invention may be prepared by charging 400 grams of soya acids, 193 grams of trimethylol propane, 20 grams of xylol, 6 grams of triphenyl phosphate, and 490 grams of propylene glycol into a reactor and heating the reactants to about 2000F. 748 grams of isophthalic acid, and 100 grams of terephthalic acid then are added to the reaction mixture which is slowly heated to 4500 F. for abut 1 5 hours when the mixture clears and an acid value of about 9 to 10 is reached. the mixture then is cooled to about 2400 F. and 325 grams of butyl cellosolve is added to the resulting alkyd resin. The resin has a number average molecular weight of about 750, a weight per gallon of about 8.95 pounds, a hydroxyí value of about 1 50, and a viscosity of about Z2 (85% in cellosolve acetate). A suitable alkyd may also be obtained by substituting tall oil acids for the soya acids in the above formulation.

Finally, polyesters which are suitable for use in the invention may be obtained by mixing the reactants in the ratios shown in Table I according to the general procedure of Example I, except that the cooks may be done at about 400"F. to about 4200 F. and Fascat is used in all cooks.

TABLE I Suitable Polyesters for Use in the Invention Moles Moles Moles Moles Propylene Neopentyl Trimethylol Isophthalic RESIN Glycol Glycol Propane Acid 1 3.0 0.3 2 3.3 1.0 3 2.7 0.3 4 2.85 0.15 1.0 5 3.0 1.0 6 3.3 1.0 7 3.3 8 2.85 0.15 9 2.1 0.1 Moles Poly Moles Moles ethylene Phthalic Adipic Tereph- OH Acid RESIN Anhydride Acid thalate Value Value Viscosity 1 1.0 1.0 329 9.4 Z3-Z4 2 1.0 310 9.2 Z5 3 1.0 1.0 238 8.2 Z4-Z5 4 1.0 224 7,5 Z4 5 1.0 211 7.9 Z4 6 1.0 262 9.6 Z5 7 1.0 1.0 262 8.6 Z5 8 1.0 1.0 224 7.3 Z3 9 1.0 0.9 243 7.9 Z3 Cosolvent Polyester Amino Resin Formulations According to the invention, the previously described high solids polyesters may be combined with up to about 30% by weight an organic solvent or solvent mixture which has a water solubility in the range from about 5% by weight to complete miscibility in water; at least 2% by weight water based upon the weight of the coating composition; and one or more cross linking resins which are miscible with such polyester/solvent/water combination. The latter combination forms a coating composition which will reduce the emission of conventional vplatile organic compounds as opposed to using a composition with a neat organic solvent. The preferred cross linker resins are amino resins such as methylated melamine, methylated urea, or hexamethyoxymethyl melamine which form from about 20 to about 35 percent by weight of the coating compositions.Table II illustrates various formulations which result in the reduction of VOCs by using water as a solvent in the coating composition. Table II also includes the amount of solids (NV), and the amount of volatile organic compounds per 1000 grams of coating composition for systems using cellosolve acetate (CA) as solvent, butyl cellosolve (BC) as solvent, and a butyl cellosolve-water solvent. In each case the polyester or alkyd resin was combined with hexamethyoxymethyl melamine commercially known as Cymel 303 (Cy 303).

TABLE II Reduction of VOCs Using Water Cosolvent RESIN OH Value Resin/Cy 303 % VOC Solvent Example Il 175 75/25 28-CA Example Il 175 75/25 30-BC Example II 175 75/25 24.0-BC Resin 4, Table I 220 73/27 25-CA Resin 4, Table 1 220 73/27 27-BC Resin 4, Table 1 220 73/27 19.3-BC Example Ill 245 70/30 23-CA Example Ill 245 70/30 25-BC Example Ill 245 70/30 23-CA Resin 6, Table 1 260 73/27 22-CA Resin 6, Table 1 260 73/27 24-BC Resin 6, Table I 260 73/27 3-CA, 14-BC Resin 1, Table 1 320 70/30 20-CA Resin 1, Table I 320 70/30 22-BC Resin 1, Table I 320 70/30 2.7-CA, 7.6BC Example IV 150 75/25 30-CA Example IV 150 75/25 31.5-BC Example IV 150 75/25 25.8-BC Resin 6, Table I 260 73/27 13.7-BC Resin 1, Table I 320 70/30 8.3-BC RESIN %Water % NV VOC Gms.100 Film Example II 72 480 Example II 80 (524) Example II 8.0 68 440 Resin 4, Table I 75 430 Resin 4, Table I 73 (468) Resin 4, Table I 9.9 70.8 373 Example III - 77 404 Example III - 75 (440) Example lil 12.0 75.7 250 Resin 6, Table I 78 375 Resin 6,Table I 76 (410) Resin 6, Table i 10.0 73 322 Resin 1, Table I 80 351 Resin 1, Table I 78 (387) Resin 1,Table I 13.7 76 228 Example IV 70 524 Example IV 68.5 (557) Example IV 6.7 67.5 475 Resin 6, Table I 9.2 77 263 Resin 1,Table I 11.5 80 193 H20-BC vs CA% VOC RESIN reduced (%) Example II Example II Example II 8.3% Resin 4, Table I Resin 4, Table I Resin 4, Table I 13.2% Example Ill Example III Example III 38.1% Resin 6, Table I Resin 6, Table I * Resin 6, Table I 14.15/o Resin 1, Table I Resin 1, Table I * Resin 1, Table I 35.0% Example IV Example IV Example IV 9.3% Resin 6, Table 1 29.9% Resin 1, Table I 45.0% * Can be increased with all BC ( ) BC systems listed in parentheses because they were not used in the "VOC reduced %" calculation.

Table Ill shows formulations of various high solids polyesters and alkyds with Cymel 303 and different organic solvent water combinations.

TABLE Ill Polyester/Cymel 303/Solvent Systems RESIN OH Value Resin/Cy 303 % VOC Solvent Example lil 245 70/30 23-CA Example III 245 70/30 18.4-CA Example III 245 70/30 2.8-CA, 10-BC Example Ill 245 70/30 3.0-CA, 8-n-BuOH Example III 245 70/30 12.0-BC Example II 175 .75/25 28-CA Example II 175 75/25 24.5-CA Example II 175 75/25 24.0-BC Example I 160 75/25 18.7-CA Resin 4, Table I 220 73/27 20-CA Resin 4, Table 1 220 73/27 1 9.3-BC Resin 6, Table I 260 73/27 18-CA Resin 6, Table I 260 73/27 3-CA, 14-BC Resin 1 ,Table I 320 70/30 18-CA Resin 1, Table I 320 70/30 2.7-CA, 7.6-BC Example IV 150 75/25 30-CA Example IV 150 75/25 31.5-BC Example IV 150 75/25 25.8-BC RESIN % Water % NV VOC gms/1 000 Film Example lil 77 404 Example 111 4.6 77 337 Example lil 10.7 76.5 260 Example 111 11.0 78 233 Example lil 12.0 75.7 250 Example II 72 480 Example II 3.5 72 430 Example II 8.0 68 440 Example I 6.0 75 355 Resin 4, Table I 6.0 75 378 Resin 4, Table I 9.9 70.8 373 Resin 6, Table í 6.0 75 348 Resin 6, Table I 10.0 73 322 Resin 1 Table I 9.0 75 333 Resin 1,Table I 13.7 76 228 Example IV 70 524 Example IV 68.5 557 Example IV 6.7 67.5 475 The hydroxyl value, polyester cross linker ration, percent water, percent solids, and grams of VOCs for each formulation are all illustrated in Table Ill, and show a general reduction of VOCs with a water/organic solvent combination.

The amount of water that can be added to the polyester and amino resin cross linking agent is closely related to the hydroxyl content of the polyester or alkyd. Under maximum conditions for water solubility with butyl cellosolve as the sole cosolvent and a low melamine level, the hydroxyl number is approximately equal to the pounds of water that can be added to 1,000 pounds of the polyester portion of the system formulation. Generally, the degree of water acceptance decreases if the amino resin cross linking agent content is increased or if there is much cellosolve acetate in the system. Generally, however, it can be stated that the resin, solvent, and cross linker are selected such that (OH#R) (X)R + (0H#s) (us) + (OH) (XC) 105 where OH#.s.c represent the hydroxyl values of the resin, the solvent and the cross linking agent; XR,S,C represent the proportions by weight of the latter ingredients; and XR + X5 + XC = 1.

It should be understood that while certain preferred embodiments of the present invention have been illustrated and described, various modifications thereof will become apparent to those skilled in the art.

Claims

1. A coating solution comprising a polyester having a hydroxyl value of at least about 1 50; an organic solvent which has a water solubility in the range from about 5% by weight to complete miscibility in water; water comprising at least about 2% by weight of the coating solution; and a cross linking agent miscible with the polyester, the organic solvent, and the water.

2. A coating solution as claimed in claim 1 wherein the cross-linking agent is an amino resin.

3. A coating solution as claimed in claim 2 wherein the amino resin cross linking agent is methylated melamine, hexamethyloxymethyl melamine, methylated urea, or a mixture thereof.

4. A coating solution as claimed in any one of the preceding claims wherein the coating composition further comprises a pigment.

5. A coating solution as claimed in any one of the preceding claims wherein the organic solvent is cellosolve acetate, butyl cellosolve, n-butyl alcohol, isobutanol, n-propoxypropanol or a mixture thereof.

6. A coating solution as claimed in any one of the preceding claims wherein the water to organic solvent ratio is in the range of from about 20/80 to about 60/40.

7. A method for preparing a polyester coating solution comprising: mixing water in an amount of at least 2% by weight of the polyester coating solution into a polyester composition which comprises a polyester having a hydroxyl value of at least about 1 50; an organic solvent which has a water solubility in the range from about 5% by weight to complete miscibility in water, the organic solvent comprising less than about 30% by weight of the coating solution; and a cross linking agent miscible with the polyester, the organic solvent, and the water.

8. A method as claimed in claim 7 wherein the cross linking agent is an amino resin.

9. A method as claimed in claim 8 wherein the amino resin cross linking agent is methylated melamine, hexamethyoxymethyl melamine, methylated urea, or a mixture thereof.

10. A method as claimed in any one of claims 7 to 9 wherein the polyester includes a pigment.

11. A method as claimed in any one of claims 7 to 10 wherein the organic solvent is cellosolve acetate, butyl cellosolve, n-butyl alcohol, isobutanol, n-propoxypropanol or a mixture thereof.

12. A method as claimed in any one of claims 7 to 11 wherein the water to organic solvent ratio is in the range of from about 20/80 to about 60/40.

13. A coating solution produced by reacting an organic dibasic acid or acid anhydride with an organic polyol having at least two hydroxyl groups to form a polyester having a hydroxyl value of at least 150; mixing the polyester with an organic solvent, water, and a cross linking agent miscible with the polyester, the organic solvent and the water; the organic solvent having a water solubility in the range from about 5% by weight to complete miscibility in water, and comprising less than about 30% by weight of the coating composition; and the water comprising at least about 2% by weight of the coating composition.

14. A coating solution as claimed in claim 13 wherein the cross linking agent is an amino resin.

1 5. A coating solution as claimed in claim 14 wherein the amino resin cross linking agent is methylated melamine, hexamethyloxymethyl melamine, methylated urea; or a mixture thereof.

1 6. A coating solution as claimed in any one of claims 13 to 1 5 wherein the organic solvent is cellosolve acetate, butyl cellosolve, n-butyl alcohol, isobutanol, n-propoxypropanol or a mixture thereof.

17. A coating solution as claimed in any one of claims 13 to 1 6 wherein the water to organic solvent ratio is in the range of from about 20/80 to about 60/40.

1 8. A coating solution comprising a polyester having a hydroxyl value in the range of about 1 50 to about 350 and a number average molecular weight in the range of about 300 to about 1100; an organic solvent which has a water solubility in the range from about 5% by weight to complete miscibility in water; water comprising at least about 2% by weight of the coating solution; and a cross linking agent miscible with the polyester, the organic solvent, and the water.

1 9. A coating solution as claimed in claim 1 8 wherein the polyester is the reaction product of a dibasic acid or acid anhydride thereof with a polyol.

20. A coating solution as claimed in claim 19 wherein the dibasic acid or anhydride thereof is isophthalic acid, adipic acid, phthalic acid, terephthalic acid or anhydrides thereof, or a mixture thereof, and wherein the polyol is propylene glycol, neopentyl glycol, trimethylol propane or a mixture thereof.

21. A coating solution as claimed in any one of claims 1 8 to 20 wherein said cross linking agent is methylated melamine, hexamethoxymethyl melamine, methylated urea or a mixture thereof.

22. A coating solution as claimed in any one of claims 18 to 21 wherein the organic solvent is cellosolve acetate, butyl cellosolve, n-butyl alcohol, isobutanol, n-propoxypropanol or a mixture thereof.

23. A method for preparing a polyester coating solution comprising: mixing water in an amount of at least 2% by weight of the polyester coating solution into a polyester composition which comprises a polyester having a hydroxyl value in the range from about 1 50 to about 350 and a number average molecular weight in the range of about 300 to about 1100; an organic solvent which has a water solubility in the range from about 5% by weight to complete miscibility in water, the organic solvent comprising less than about 30% by weight of the coating solution; and a cross linking agent miscible with the polyester, the organic solvent, and the water.

24. A method as claimed in claim 23 wherein the polyester is the reaction product of a dibasic acid or anhydride thereof with a polyol.

25. A method as claimed in claim 24 wherein the dibasic acid or anhydride thereof is isophthalic acid, adipic acid, phthalic acid, terephthalic acid or anhydrides thereof, or a mixture thereof, and wherein the polyol is propyiene glycol, neopentyl glycol, trimethylol propane or a mixture thereof.

26. A method as claimed in any one of claims 23 to 25 wherein the cross linking agent is methylated melamine, hexamethyoxymethyl melamine, methylated urea, or a mixture thereof.

27. A method as claimed in any one of claims 23 to 26 wherein the organic solvent is cellosolve acetate, butyl cellosolve, n-butyl alcohol, isobutanol, n-propoxypropanoi or a mixture thereof.

28. A coating solution substantially as hereinbefore described in any one of the Examples.

29. A method for preparing a coating solution substantially as hereinbefore described in any one of the Examples.