GB2125405A

GB2125405A - A coating composition curable above 50 c containing a hydrolyzed epoxy resin

Info

Publication number: GB2125405A
Application number: GB08322028A
Authority: GB
Inventors: Michael Brent Cavitt
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1982-08-16
Filing date: 1983-08-16
Publication date: 1984-03-07
Also published as: GB8322028D0; IT8322516A0; WO1984000769A1; IT1163888B

Abstract

Coating compositions curable at temperatures above 50oC. Properties such as solvent resistance are improved by hydrolyzing at least a portion of the epoxy groups present in the epoxy resin. The compositions contain (1) a hydrolyzed epoxy resin such as the polyglycidyl ether of either a polyhydric aromatic or polyhydric aliphatic compound; (2) a curing amount of a curing agent selected from (a) triazine-aldehydes, (b) urea-aldehydes, (c) compounds having an average of more than one NCO or NCS group per molecule, or (d) mixtures thereof; and (3) a sufficient quantity but less than 55 percent by weight of a suitable solvent system so as to provide a suitable application viscosity.

Description

SPECIFICATION A coating composition curable above 500C containing a hydrolyzed epoxy resin The present invention relates to a coating composition curable at temperatures above 500C that contain hydrolyzed epoxy resins.

Walker in U.S. 3,632,836 and U.S. 3,787,508 discloses the use of hydrolyzed epoxy resins in epoxy resin coatings up to an amount of 20 percent by weight to improve the reactivity of the epoxy resin and to improve pigment dispersability in the epoxy resin coating composition.

Irwin in U.S. 3,891,525 and U.S. 3,991,028 discloses the use of hydrolyzed epoxy resins in water dispersed electrodepositable coating compositions employing an interpolymer of a hydroxyalkyl ester of an unsaturated acid and an amine-aldehyde resin.

Irwin et al in U.S. 4,145,234 disclose coating formulations of (1) an oil in water emulsion of a solution of a hydrolyzed diglycidyl ether of a bisphenol, a nonionic surfactant and a curing agent; or (2) a solution of a hydrolyzed diglycidyl ether of a bisphenol and a curing agent in alkoxyethanol or a mixture of alkoxyethanol with alcohols, ketones, carbitols or their acetates and, optionally, liquid aromatic hydrocarbon solvents. Such solution coating compositions are stated to have solid (nonvolatile) content of from 15 to about 35 weight percent.

It has now been discovered that one or more of the properties of elevated temperature coatings prepared from glycidyl ethers of aromatic dihydric compounds or aliphatic dihydric compounds can be improved by hydrolyzing at least a portion of the epoxy groups.

The present invention concerns coating compositions curable at temperatures above 500 C, preferably above 1000C, which comprises (1) a hydrolyzed epoxy resin; (2) a curing amount of a curing agent selected from (a) triazine-aldehyde curing agents, (b) urea-aldehyde curing agents, (c) compounds having an average of more than one NCO or NCS group per molecule or (d) mixtures thereof; and (3) a sufficient quantity, but less than 55 percent by weight of said coating composition, of a suitable solvent system so as to provide a suitable application viscosity; characterized in that component (1) is at least one of a polyglycidyl ether of a polyhydric aromatic compound or a polyglycidyl ether of a polyhydric aliphatic compound, even such glycidyl ether having an average epoxide equivalent weight, before hydrolysis, of from 1 70 to 2000, preferably from 1 75 to 1 000, and from 5 to 1 00, preferably from 5 to 50, percent of the total epoxy groups have been hydrolyzed.

Any epoxy resin which is a glycidyl ether of a polyhydric aromatic or aliphatic compound when at least partially hydrolyzed can be employed in the present invention. Suitable polyglycidyl ethers of polyhydric phenols, before hydrolysis, which can be employed herein include, for example, polygylcidyl ethers of resorcinol, catechol, hydroquinone, bisphenols, triphenols, and novolac resins.

Suitable polyglycidyl ethers of aliphatic polyhydric compounds, before hydrolysis, include, for example, dipropylene glycol, tripropylene glycol, glycerine, neopentyl glycol, and dibromoneopentyl glycol. Also suitable are the polyglycidyl ethers of alkylene oxide adducts of such aliphatic polyhydric compounds as glycerine, propylene glycol, trimethylol propane, pentaerythritol, neopentyl glycol, and dibromoneopentyl glycol. These and other suitable such epoxy resins, before hydrolysis are disclosed, for example, in Handbook of Epoxy Resins by Lee and Neville, McGraw-Hill, 1967.

Any process can be employed to hydrolyze the epoxy resins employed in the present invention such as those methods disclosed by Walker in U.S. 3,632,836; U.S. 3,405,093; U.S. 3,787,508; and by Davis and Cavitt in U.S. 4,340,713.

A particularly suitable process for hydrolyzing the epoxy resins employed in the present invention comprises reacting the epoxy resin with water in the absence of substantial quantities of an organic solvent in the presence of catalytic quantities of a combination catalyst comprising (1) at least one dicarboxylic acid and (2) a phosphonium compound wherein components (1) and (2) are present in a molar ratio of from 1:1 to 20:1, preferably from 3:1 to 10:1, most preferably from 5:1 to 7:1, respectively.

Suitable dicarboxylic acids which can be employed herein include those having from 2 to 10, preferably from 2 to 6, most preferably from 2 to 4, carbon atoms, such as, for example, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, and mixtures thereof. Also suitable are the hydrates of the aforementioned acids.

Suitable phosphonium catalysts which can be employed with the oxalic acid for hydrolyzing epoxy resins include, for example, those disclosed by Perry in U.S. 3,948,855 or by Dante in U.S.

3,477,990. Particularly suitable phosphonium catalysts include, for example, ethyltriphenylphosphonium chloride, ethyltriphenylphosphonium bromide, ethyltriphenylphosphonium iodide, ethyltriphenylphosphonium acetate, ethyltriphenylphosphonium diacetate (ethyltriphenylphosphonium acetate acetic acid complex), tetrabutylphosphonium chloride, tetrabutylphosphonium bromide, tetrabutylphosphonium iodide, tetrabutylphosphonium acetate and tetrabutylphosphonium diacetate (tetrabutylphosphonium acetate acetic acid complex). The total quantity of catalyst varies depending upon the conditions employed, but is usualiy from 0.001 to 0.01, preferably from 0.003 to 0.008 mole of total catalyst per epoxide equivalent contained in the resin or resins to be hydrolyzed. Higher quantities can be employed, but no beneficial results are obtained.

The hydrolysis process is conducted at temperatures of from 500C to 2000 C, preferably from 11 OOC to 1 500C for a period of time to reach the desired degree of hydrolysis.

The amount of water employed is dependent upon the desired degree of hydrolysis, but usually from 0 to 100, preferably from 0 to 30, most preferably from 0 to 5 percent in excess of the theoretical amount of water required for hydrolysis is employed.

Suitable curing agents are the urea-formaldehyde resins, triazine-formaldehyde resins, polyisocyanates or polyisothiocyanates, and mixtures thereof. Particularly suitable triazine-aldehyde curing agents which can be employed herein include, for example, hexamethoxymethylmelamine and methylated melamineformaldehyde.

Suitable polyisocyahates which can be employed herein as curing agents include, for example, 2,4-toluene-diisocyanate, 2,6-toluenediisocyanate, p,p'-diphenylmethanediisocyanate, p-phenylenediisocyanate, naphthalenediisocyanate, polymethylene polyphenylisocyanates; polyisothiocyanates such as the thioanalogs of the above mentioned polyisocyanates and mixtures thereof.

Most of these and other curing agents are described in the aforementioned Handbook of epoxy Resins.

Suitable solvents which can be employed herein include, for example, ketones such as acetone and methyl ethyl ketone; glycol ethers such as butylene glycol methyl ether, diethylene glycol n-butyl ether, diethylene glycol ethyl ether, diethylene glycol methyl ether, dipropylene glycol methyl ether, ethylene glycol n-butyl ether, ethylene glycol methyl ether, ethylene glycol phenyl ether, propylene glycol methyl ether, and tripropylene glycol methyl ether; glycol esters such as ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, and ethylene glycol monomethyl ether acetate; and mixtures of the above with aromatic hydrocarbons such as toluene and xylene.

The following examples are illustrative of the invention, but are not to be construed as to limiting the scope thereof in any manner.

The following components were employed in the examples.

CATALYST A is a 70 weight percent solution of ethyftriphenyl phosphonium acetate acetic acid complex in methanol.

CATALYST B is oxalic acid 2H20.

EPOXY RESIN A is a diglycidyl ether of bisphenol A having an average EEW of 191.

EPOXY RESIN B is a diglycidyl ether of bisphenol A having an average EEW of 358.

EPOXY RESIN C is a diglycidyl ether of bisphenol A having an average EEW of 488.

EPOXY RESIN D is a diglycidyl ether of bisphenol A having an average EEW of 187.

EPOXY RESIN E is a diglycidyl ether of a polyoxypropyleneglycol having an average EEW of 194.

CURING AGENT A is a hexamethoxymethylmelamine curing agent commercially available from American Cyanamid Company under the trade name of CYMEL 303.

CURING AGENT B is a methylated melamine-formaldehyde curing agent commercially available from American Cyanamid Company under the trade name of CYMEL 325.

The following components were employed to evaluate coating performance on cold rolled steel panels using the resin examples.

COATING FORMULATION A was prepared by adding enough solvent to the test resin to obtain a Gardner dip viscosity between 29.4 to 37.3 seconds at room temperature. The size of the Gardner dip viscosity cup was a Zahn Type 2. The solvent was 38 parts methyl ethyl ketone, 31 parts toluene, 1 8 parts xylene and 1 3 parts 2-ethoxyethyl acetate. To 100 parts of resin was added 1 5 parts of curing agent A and then added 10 parts of a 10 percent nonvolatiles (N.V.) isopropanol solution of p-toluene sulfonic acid. A coating was made of this formulation and cured at 2800F (1 490C) for 30 minutes (1 800 s) to obtain MEK double rub results. See gravelometer test for its cure conditions.

COATING FORMULATION B was composed of 100 parts of a resin solution as described in Coating Formulation A, 1 5 parts curing agent A, 10 parts of a 10 percent N.V. isopropanol solution of p-toluene sulfonic acid, 9.2 parts iron oxide, 9.2 parts of titanium dioxide, 9.2 parts ASP-400 clay filler and 90 parts barium sulfate. These components were mixed in a metal container with steel balls (1/8 in. in diameter) for 0*5 hour (1800 s) on a paint shaker. The steel balls were removed and the paint was ready for use.

Coatings made from the epoxy resins were evaluated by the following tests.

MEK double rubs To the ball end of a 2 Ib. (0.9 kg) ball pein hammer was attached a pad of cheese cloth composed of 8 plys. The pad was saturated with methyl ethyl ketone (MEK) and then rubbed across a coated substrate. A constant back and forth motion is used allowing only the weight of the hammer to apply force on the coating. A back and forth movement counts as one double rub. This motion is continued until the coating is mared and/or begins to be removed by the solvent effect.

Gravelometer test This procedure is from the Society of Automotive Engineers, Inc. 1 968 Technical Report No.

J 400. Coating formulation B was used for this test. The paints were aged for 16 hours at 1 400F (600 C) before using.

Hydrolyzed epoxy resin A A 2 liter pressure reactor was charged in order, with 829.9 g (4.349 epoxy equivalents) of epoxy resin A, 170.1 g (1.492 moles) of bisphenol A, 1.69 g (0.003 mole) of catalyst A, 7.1 5 g (0.397 mole) of water and 2 g (0.016 mole) of catalyst B. The reactor was sealed, purged with nitrogen and left with a 20 psig (137.9 kPa gage pressure) of nitrogen. The contents were heated to 1300C in 0.63 hour (2268 s) and maintained at 1 360C for 1.05 hour (3780 s). The reactor was then heated to 1 900C and the temperature maintained at 1 850C under a vacuum for 0.83 hour (2988 s). The resultant product had 1 6 percent of the epoxy groups hydrolyzed.

Hydrolyzed epoxy resin B A 2 liter pressure reactor was charged in order, with 829.9 g (4.349 epoxy equivalents) of epoxy resin A, 170.1 g (1.492 mole) of bisphenol A, 1.69 g (0.003 mole) of catalyst A, 28 g (1.556 mole) of water and 4 g (0.032 mole) of catalyst B. The reactor was sealed, purged with nitrogen and left with a 20 psig (137.9 kPa gage pressure) of nitrogen. The contents were heated to 1 320C in 0.83 hour (2988 s) and maintained at 1 350C for 4 hours (14,400 s). The reactor was then heated to 2250C and the temperature maintained at 1 900C under a vacuum for 1 hour (3600 s). The resultant product had 58 percent of the epoxy groups hydrolyzed.

Hydrolyzed epoxy resin C A 2 liter pressure reactor was charged in order, with 829.9 g (4.349 epoxy equivalents) of epoxy resin A, 170.1 g (1.492 moles) of bisphenol A, 1.69 g (0.003 mole) of catalyst A, 56 g (3.111 mole) of water and 4 g (0.032 mole) of catalyst B. The reactor was sealed, purged with nitrogen and left with a 20 psig (137.9 kPa gage pressure) of nitrogen. The contents were heated to 1 350C in 0.85 hour (3060 s) and maintained at 1 380C for 3.78 hour (13,608 s). The reactor was then heated to 1 830C and the temperature maintained at 1 850C under a vacuum for 1 hour (3600 s). The resultant product had 100 percent of the epoxy groups hydrolyzed.

Hydrolyzed epoxy resin D A 2 liter pressure reactor was charged in order, with 700 g (3.668 epoxy equivalents) of epoxy resin A, 210.58 g (1.847 moles) of bisphenol A, 1.7 g (0.003 mole) of catalyst A, 4.92 g (0.273 mole) of water and 2 g (0.016 mole) of catalyst B. The reactor was sealed, purged with nitrogen and left with a 20 psig (137.9 kPa gage pressure) of nitrogen. The contents were heated to 1250C in 0.67 hour (2412 s) and maintained at 1 270C for 1 hour (3600s). The The reactor was then heated to 2050C and the temperature maintained at 1 880C under a vacuum for 1 hour (3600 s). The resultant product had 17 percent of the epoxy groups hydrolyzed.

Hydrolyzed epoxy resin E A 2 liter pressure reactor was charged in order, with 700 g (3.668 epoxy equivalents) of epoxy resin A, 210.58 g (1.847 moles) of bisphenol A, 1.7 g (0.003 mole) of catalyst A, 32.22 g (1.79 mole) of water and 2 g (0.01 6 mole) of catalyst B. The reactor was sealed, purged with nitrogen and left with a 30 psig (206.9 kPa gage pressure) of nitrogen. The contents were heated to 1 250C in 0.7 hour (2520 s) and maintained at 1 350C for 1.52 hour (5472 s). The reactor was then heated to 1 700C and the temperature maintained at 1 870C under a vacuum for 1.07 hour (3852 s). The resultant product had 50 percent of the epoxy groups hydrolyzed.

Hydrolyzed epoxy resin F A 2 liter pressure reactor was charged in order, with 700 g (3.668 epoxy equivalents) of epoxy resin A, 210.58 g (1.847 moles) of bisphenol A, 1.7 g (0.003 mole) of catalyst A, 35 g (1.944 mole) of water and 4 g (0.032 mole) of catalyst B. The reactor was sealed, purged with nitrogen and left with a 20 psig (137.9 kPa gage pressure) of nitrogen. The contents were heated to 1 380C in 0.67 hour (2412 s) and maintained at 1 350C for 4 hours (14,400 s). The reactor was then heated to 1 900C and the temperature maintained at 1 800C under a vacuum for 1 hour (3600 s). The resultant product had 100 percent of the epoxy groups hydrolyzed.

Hydrolyzed epoxy resin G A 2 liter pressure reactor was charged in order, with 660.63 g (3.353 epoxy equivalents) of epoxy resin D, 165.16g (0.85 epoxy equivalents ofepoxy E, 174.21 g (1.528 moles) of bisphenol A, 1.71 g (0.003 mole) of catalyst A, 9.5 g (0.528 mole) of water and 2.02 g (0.016 mole) of catalyst B. The reactor was sealed, purged with nitrogen and left with a 20 psig (137.9 kPa gage pressure) of nitrogen.

The contents were heated to 131 0C in 0.73 hour (2628 s) and maintained at 1 360C for 1 hour (3600 s). The reactor was then heated to 1 880C and the temperature maintained at 1 900C under a vacuum for 0.5 hour (1800s). The resultant product had 20 percent of the epoxy groups hydrolyzed.

Hydrolyzed epoxy resin H A 2 liter pressure reactor was charged in order, with 660.63 g (3.535 epoxy equivalents) of epoxy resin D, 165.16 g (0.85 epoxy equivalents) of epoxy E, 174.21 g (1.528 moles) of bisphenol A, 1.71 g (0.003 mole) of catalyst A, 14.3 g (0.794 mole) of water and 2.02 g (0.01 6 mole) of catalyst B. The reactor was sealed, purged with nitrogen and left with a 20 psig (137.9 kPa gage pressure) of nitrogen.

The contents were heated to 1 350C in 0.62 hour (2232 s) and maintained at 1 400C for 1 hour (3600 s). The reactor was then heated to 21 00C and the temperature maintained at 1 920C under a vacuum for 1.03 hour (3708 s). The resultant product had 30 percent of the epoxy groups hydrolyzed.

Coatings were prepared from hydrolyzed epoxy resins and unhydrolyzed epoxy resins. The formulations and test results are given in the following Table I and Table II.

Table I Comp. Comp.

Ex. Ex. Ex. Expt. Ex. Ex. Ex. Expt.

1 2 3 A 4 5 6 B Epoxy resin B - - B - - - C Hydrolyzed epoxy resin A B C - D E F Formulation A A A A A A A A Non volatiles, % 57.9 51.8 47.2 59.2 52.6 48.2 47.2 53.4 Viscosity', seconds 32.4 33.5 37.3 29.4 37.3 35.9 35.2 35.9 MEKdoublerubs 35 > 100 > 100 10 65 > 100 > 100 50 'Viscosity was determined at 259C using a No. 2 Zahn cup.

Table II Comp.

Example Expt. Example Example 7 C 8 9 Epoxy resin - B - Hydrolyzed epoxy resin A - G H Formulation B B B B Gravelometertest 61 61 6' 71 82 72 82 82 Cured at 2750F (1 350C) for 30 min. (1800 seconds).

2 Cured at 325 OF (1 62.8 OC) for 30 min. (1800 seconds).

Claims

1. A coating composition curable at temperatures above 500C which comprises (1) a hydrolyzed epoxy resin; (2) a curing amount of a curing agent selected from (a) triazine-aldehyde curing agents, (b) urea-aldehyde curing agents, (c) compounds having an average of more than one NCO or NCS group per molecule, or (d) mixtures thereof; and (3) a sufficient quantity, but less than 55 percent by weight of said coating composition of a suitable solvent system so as to provide a suitable application viscosity; characterized in that component (1) is at least one of a polyglycidyl ether of a polyhydric aromatic compound or a polyglycidyl ether of a polyhydric aliphatic compound, each such glycidyl ether having an average epoxide equivalent weight, before hydrolysis, of from 170 to 2000 and from 5 to 100 percent of the total epoxy groups have been hydrolyzed.

2. The coating composition of Claim 1 characterized in that component (1) is a diglycidyl ether of bisphenol A having an epoxide equivalent weight, before hydrolysis, of from 1 75 to 1000 and from 5 to 50 percent of its epoxy groups have been hydrolyzed.

3. A composition as claimed in Claim 1, wherein the average epoxide equivalent weight, before hydrolysis, is from 175 to 1000.

4. A composition as claimed in Claim 1 or Claim 2, wherein 5 to 50 percent of the total epoxy groups have been hydrolyzed.

5. A composition as claimed in any one of Claims 1,3 and 4, wherein the polyglycidyl ether, before hydrolysis, is selected from polyglycidyl ethers of resorcinol, catechol, hydroquinone, bisphenols, triphenols, and novolac resins.

6. A composition as claimed in Claim 5, wherein the polyglycidyl ether is a diglycidyl ether of bisphenol A.

7. A composition as claimed in any one of Claims 1,3 and 4 wherein the polyglycidyl ether, before hydrolysis, is selected from polyglycidyl ethers of dipropylene glycol, tripropylene glycol, glycerine, neopentyl glycol and dibromoneopentyl glycol.

8. A composition as claimed in any one of Claims 1,3 and 4, wherein the polyglycidyl ether, before hydrolysis, is a polyglycidyl ether of an alkylene oxide adduct of an aliphatic polyhydric compound.

9. A composition as claimed in Claim 8, wherein the aliphatic polyhydric compound is selected from glycerine, propylene glycol, trimethylol propane, pentaerythritol, neopentyl glycol and dibromoneopentyl glycol.

10. A composition as claimed in any one of the preceding claims, wherein the epoxy resin has been hydrolyzed by reaction with water in the absence of organic solvent in the presence of a combination catalyst comprising (1) at least one dicarboxylic acid and (2) a phosphonium compound, the components (1) and (2) being present in a molar ratio of from 1:1 to 20:1.

11. A composition as claimed in Claim 1 and substantially as described in any one of Examples 1 to 9.