Liquid coating composition having a reactive catalyst

Abstract

A thermosetting coating composition having a binder of a film forming polymer having reactive hydroxyl groups, epoxy groups or methylol groups and a melamine, benzoguanamine or urea crosslinking agent and about 0.1-10% by weight of reactive catalyst which is a solid at 30.degree. C. in which the catalyst has one of the following structures: ##STR1## or mixtures of the above; where R is an alkyl group or a hydroxy alkyl group having 1-18 carbon atoms; the catalyst is prepared by reacting in a 1:1 molar ratio trimellitic anhydride and an aliphatic monohydric alcohol or an aliphatic diol.

Description

BACKGROUND OF THE INVENTION

This invention related to coating compositions having a reactive catalyst.

Crosslinking agents for powder coating compositions of trimellitic anhydride and an aliphatic diol containing 2-10 carbon atoms in a molar ratio of anhydride to diol of 2/l to 1.5/l are known as shown in Thomas et al. U.S. Pat. No. 4,024,111. These crosslinking agents do not work well in high solids coating compositions. There is a need for a catalyst for liquid high solids coating compositions that will remain unreactive in the composition but after the composition is applied, the catalyst will react during baking of the composition. The catalyst not only catalyzes the crosslinking reaction but reacts with the film forming constituents of the composition to form a durable, crosslinked finish.

SUMMARY OF THE INVENTION

A thermosetting coating composition having a binder of a film forming polymer having reactive hydroxyl groups, epoxy groups or methylol groups and a melamine, benzoguanamine or urea crosslinking agent and about 0.1-10%, by weight, based on the weight of the coating composition, of reactive catalyst which is a solid at 30.degree. C. and has a structure selected from the following group: ##STR2## or mixtures of the above; wherein R is an alkyl group or a hydroxy alkyl group having 1-18 carbon atoms in the alkyl group or hydroxy alkyl group. The process for making the catalyst comprises reacting in a 1:1 molar ratio trimellitic anhydride and an aliphatic monohydric alcohol or an aliphatic diol each having 1-18 carbon atoms at about 125.degree.-250.degree. C. for about 10 minutes-2 hours.

DETAILED DESCRIPTION OF THE INVENTION

The reactive catalyst is a solid at 30.degree. C. and does not react with film-forming constituents of high solids coating compositions under temperatures of conventional storage conditions and under usual application conditions and temperatures. When the composition is baked after application, the catalyst not only catalyzes the crosslinking reaction but reacts with the film forming constituents of the composition to form a durable, crosslinked finish.

In the process for preparing the reactive catalyst, trimellitic anhydride is reacted with an aliphatic monohydric alcohol or an aliphatic diol in a molar ratio of trimellitic anhydride to alcohol or diol of about 1:1. The catalyst is prepared by reacting the above constituents at about 125.degree.-250.degree. C. for about 10 minutes to 2 hours. The resulting catalyst is then cooled to room temperature and if a solid, divided for example, by grinding.

Typical aliphatic monohydric alcohols and diols that can be used have 1-18 carbon atoms and are as follows: methyl alcohol, butyl alcohol, ethyl alcohol, propyl alcohol, ethylene glycol, propylene glycol, hexyl alcohol, 1,4-hexanediol, 1,6-hexanediol, heptyl alcohol 2-ethyl 1,3-hexanediol, 2-ethylhexyl alcohol, nonyl alcohol, decyl alcohol, lauryl alcohol, stearyl alcohol and the like.

The alcohol or diol is chosen to form a catalyst which will melt and or dissolve at a desired temperature to catalyze and react with the film forming constituents of a coating composition.

Preferred reactive catalysts that are used in a variety of coating compositions are as follows:

monoester of trimellitic anhydride and lauryl alcohol and monoester of trimellitic anhydride and 2-ethyl 1,3-hexanediol.

About 1.0-10% by weight, based on the weight of a coating composition, of catalyst is added to a coating composition. Under some circumstances it may be desirable to add a greater amount of catalyst.

Typical coating compositions in which the catalyst can be used are as follows:

thermosetting acrylic enamels containing a reactive acrylic constituent and a crosslinking agent such as melamine formaldehyde resin, alkylated melamine formaldehyde resin, urea formaldehyde resin, or benzoguanamine formaldehyde resin; thermosetting polyester or alkyd enamels containing a reactive polyester or alkyd resin and one of the aforementioned crosslinking agents; thermosetting epoxy resin compositions containing an epoxy resin and one of the aforementioned crosslinking agents; thermosetting epoxy ester resin composition containing an epoxy ester resin and one of the aforementioned crosslinking agents.

One useful coating composition comprises a blend of polyester resins, an acrylic resin, an epoxy ester resin, hexamethoxy methylmelamine with about 1 to 5% by weight, based on the weight of the composition, of a catalyst of the mono ester of trimellitic anhydride and 2-ethyl 1,3-hexanediol.

Coating compositions containing the reactive catalyst can be applied by conventional techniques such as spraying, electrostatic spraying, roller coating, flow coating, dip coating, electrocoating, brushing and the like and baked at a temperature sufficiently high that will activate the catalyst usually at about 95.degree.-225.degree. C. for about 10 minutes to 2 hours.

With the reactive catalyst in a coating composition, the composition can be baked at lower temperatures than compositions without the catalyst and still form a fully crosslinked finish. Also, finishes of compositions containing the catalyst generally are smoother, harder, have improved adhesion to the substrate and improved gloss in comparison to finishes of composition that do not contain the reactive catalyst.

The following examples illustrate the invention. All parts and percentages are on a weight basis unless otherwise indicated.

EXAMPLE 1

Catalyst I is prepared as follows:

______________________________________ Parts by Weight______________________________________Trimellitic anhydride 384Neodecanol 405Total 789______________________________________

The above constituents are charged into a reaction vessel and heated to 185.degree. C. and held at this temperature for about five minutes. The vessel is cooled to room temperature and a waxy solid is formed. A 50% dispersion is formed by blending 50 parts of catalyst I with 50 parts methyl ethyl ketone.

Catalyst II is prepared as follows:

______________________________________ Parts by Weight______________________________________Trimellitic anhydride 7682-ethyl 1,3-hexanediol 584Total 1352______________________________________

The above constituents are charged into a reaction vessel and over a 10 minutes period slowly heated to 175.degree. C. and then the heat source is removed. A waxy liquid is formed which is a solid at 30.degree. C. A 70% solids dispersion is formed by adding butyl acetate.

About 5% by weight, based on the total weight of a coating composition, of Catalyst I dispersion is added to the following set coating compositions: a conventional thermosetting acrylic enamel of an acrylic resin and a methylated melamine formaldehyde resin; a polyester/methylated melamine formaldehyde resin; an epoxy/urea formaldehyde resin, an epoxy/benzoguanamine resin and an oligomeric polyester/methylated melamine formaldehyde resin. Similarly Catalyst II dispersion in the same amount was added to another set of the above coating compositions.

Each of the above prepared sets of coating composition are sprayed onto separate phosphatized steel panels and baked to form a finish. An identical set of finished panels is prepared from the above coating compositions that did not contain a catalyst. In each case, the finishes of the coating compositions that contained catalysts have improved hardness and gloss and can be baked at lower temperatures for a shorter time period in comparison to the compositions that did not contain a catalyst. Also, the compositions containing the catalyst had an acceptable shelf life at room temperature and at an elevated temperature.

EXAMPLE 2

A coating composition is prepared by first forming the following mill bases and then blending these mill bases with resin solutions and a reactive catalyst.

______________________________________ Parts byWhite Mill Base Weight______________________________________Amyl acetate 30.98Polyester solution I (83% 114.04solids of a polyester ofneopentyl glycol/monoesterof neopentyl glycol and hydroxy-pivalic acid/isophthalic acid/adipic acid/phthalic anhydridehaving an acid number below 8and Gardner Holdt viscositymeasured at 25.degree. C. and at the abovesolids of Z.sub.2 -Z.sub.4 in a solventblend of xylene, 2-ethyl hexanoland amyl acetate)Polymeric dispersant (50% 9.71solids of a polymer of methylmethacrylate/2-ethyl hexylacrylate having blocked isocyanategroups in a solvent blend oftoluene, methyl ethyl ketone andmethyl isobutyl ketone)Titanium dioxide pigment 311.90Total 466.63______________________________________

The above constituents are blended together and ground in a conventional sand mill to form a mill base.

______________________________________ Parts byColloidal Silica Mill Base Weight______________________________________Polyester solution II (90% solids 46.03of a polyester of 2,2,4-trimethylpentane-1,3-diol and isophthalicacid having an acid number lessthan 9 and a hydroxyl number of200-260 and a Gardner Holdtviscosity measured at 25.degree. C. at theabove solids of Z-Z.sub.4 in toluene)Polyester Solution III (100% solids 24.79of a polyester of 2,2,4-trimethylpentane-1,3-diol and mixed methylesters of succinic acid/glutaricacid/adipic acid a weight ratioof 1:2:1 and having a GardnerHoldt viscosity at 25.degree. C. of R-Uand a hydroxyl No. 220-270)Butyl acetate 19.85Hexamethoxymethyl melamine 75.42Colloidal silica 8.34Total 174.43______________________________________

The above constituents are blended together and charged into a conventional sand mill and ground to form a mill base.

______________________________________ Parts byCarbon Black Mill Base Weight______________________________________Polymeric dispersant (described 0.61above)Amyl acetate 0.79Polyester solution III (described 1.79above)Polyester solution II (described 4.02above)Carbon Black Pigment (furnace 0.59type carbon black)Polyester solution III (described above) 0.16Amyl acetate 0.16Total 8.12______________________________________

The above constituents are added to a mixing vessel in the order as listed above and mixed together and the resulting mixture is charged into a conventional sand mill and ground to form a mill base.

______________________________________ Parts byYellow Mill Base Weight______________________________________Polyester solution II (described above) 11.32Polyester solution III (described above) 5.50Polymeric dispersant (described above) 1.72Amyl acetate 1.61Ferrite yellow orange pigment 16.49Total 36.65______________________________________

The above constituents are blended together and charged into a conventional sand mill and ground to form a mill base.

A catalyst dispersion is prepared as follows:

______________________________________ Parts by Weight______________________________________Portion 12-Ethyl 1,3-hexanediol 290.18Portion 2Trimellitic anhydride 381.60Portion 3Ethylene glycol monoethyl ether 288.22acetateTotal 960.00______________________________________

Portion 1 is charged into a reaction vessel and heated to about 82.degree. C. and then portion 2 is added and heated to about 105.degree. C. and heat is turned off and the temperature increases to about 175.degree. C. and held at this temperature for about 5 minutes, portion 3 is added and the resulting dispersion is cooled to room temperature.

A coating composition is prepared by thoroughly blending together the following constituents:

______________________________________ Parts by Weight______________________________________Portion 1White Mill Base (prepared above) 411.2Colloidal Silica Mill Base 153.7(prepared above)Portion 2Polyester resin solution II (des- 16.9cribed above)Toluene 1.3Aromatic controlled VM&P Naphtha 0.6Portion 3Polyester solution I (described 56.6above)Xylene 3.1Amyl acetate 3.12-Ethyl hexanol (plasticizer 2.3grade)Portion 4Hexamethoxymethyl melamine 80.7Portion 5Epoxy resin dehydrated 34.3castor oil esterHydrocarbon solvent (boiling 41.9point 182-192.degree. C. aniline point280.degree. C.)Portion 6Acrylic resin solution (60% solids 29.4of a styrene/butyl acrylate/hydroxy ethyl acrylate/acrylicacid polymer weight ratio 50/38/8/4,having an acid No. 28-32, and aGardner Holdt viscosity measuredat 25.degree. C. at the above solids U-X)Petroleum Naphtha 6.1Ethylene glycol monoethyl ether 11.3acetateN--Butyl alcohol 2.2Portion 7N--Butyl alcohol 16.2Microcrystalline wax 94-102.degree. C. 3.2melting pointN--butyl alcohol 13.0Portion 8Catalyst dispersion (prepared 29.5above)Ethylene glycol monoethyl ether 12.6acetatePortion 9Disulfonic Acid Solution (40% 0.4solids in isobutanol)Isobutanol 0.6Portion 10N,N--dimethyl ethanol amine 0.1Portion 11Amorphous silica having an 30.4average particle size of about9 micronsPortion 12Carbon Black Mill Base (prepared 7.2above)Portion 13Yellow Mill Base (prepared above) 32.2Total 1000.2______________________________________

Portions 2, 3 and 5-9 are premixed and then portions 1-13 are charged into a mixing vessel in the order shown and thoroughly mixed after each addition to form a coating composition. The resulting coating composition contains 32.75% by weight pigment, 48.69% by weight binder and has a weight solids content of 81.43%.

The coating composition is applied by spraying under standard conditions to a phosphatized steel substrate and baked for 20 minutes at 163.degree. C. to form a film 1.2 mils thick that has the following properties: 4H pencil hardness, resistant to 50 rubs with methyl ethyl ketone, gloss measured at 60.degree. of 60 (semigloss product), excellent adhesion, impact resistance at 40 inch pounds--no cracks in finish, salt spray resistance--exposure 500 hours--0 to 1/16 inch creep from scored line in finish, humidity resistance--no blisters after 1000 hours exposure in humidity cabinet.

Claims

1. A thermosetting coating composition comprising a binder of a film forming acrylic polymer or polyester polymer having reactive hydroxyl groups, carboxyl groups or methylol groups and a crosslinking agent selected from the group consisting of melamine formaldehyde resin, alkylated melamine formaldehyde resin, urea formaldehyde resin or benzoguanamine formaldehyde resin and about 0.1-10% by weight, based on the weight of the coating composition, of reactive catalyst which is a solid at 30.degree. C. and comprises a structure selected from the group of ##STR3## and mixtures thereof; wherein R is the residue of neodecanol or 2-ethyl 1,3-hexanediol.

2. The thermosetting coating composition of claim 1 which the R group of the reactive catalyst is the residue of 2-ethyl 1,3-hexanediol.

3. The thermosetting coating composition of claim 1 in which the R group of the reactive catalyst is the residue of neodecanol.

4. The thermosetting coating composition of claim 1 in which the binder is an acrylic polymer having reactive hydroxyl groups, carboxyl groups or mixtures thereof and an alkylated melamine formaldehyde resin crosslinking agent.

5. The thermosetting coating composition of claim 1 in which the binder is a polyester having reactive hydroxyl or carboxyl groups and an alkylated melamine formaldehyde crosslinking agent.