JPH0125786B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to high solids film-forming compositions of low molecular weight polyester and epoxy resins or esters of the resins and monocarboxylic acids with controlled hydroxyl functionality, wherein the polyesters and epoxy resins are formed by an aminoplast resin. It is cross-linked during curing. Conventional polyester-based coating compositions, often containing one or more hydroxy-functional components that co-react with suitable hardeners to form polymeric paint films, are well known in the finishing art. be. For example, US Patent No.
No. 3,994,851 discloses certain polyester polyols cured with amine-aldehyde condensation products. However, research into related finishing techniques clearly shows that in the polyester coating field, enhancing one property often requires sacrificing another desirable property. For example, it is often difficult to obtain coating compositions that are not only applicable at high solids levels but also tough, flexible, and durable. Also, coating compositions that are curable at lower temperatures are often not hard enough for industrial use. Therefore, with regard to modern concerns regarding the reduction of solvent generation, it is desirable to be able to not only apply low solvent levels but also cure at industrially acceptable temperatures to provide durable, flexible, but weather and stain resistant materials. There is a continuing need for coating compositions that are capable of producing a transparent film. In accordance with the present invention, the blend comprises a film-forming blend and a solvent for the blend, the blend comprising at least 50% by weight of the combined weight of the blend and solvent, and consisting essentially of (a) 30% by weight by weight of the blend; ~70% by weight of (1) pentaerythritol and at least one branched chain glycol in a glycol/pentaerythritol molar ratio of 2:1 to 6:1; (2) having not more than 18 carbon atoms; aromatic or aliphatic monocarboxylic acids or mixtures thereof, and (3) an aromatic acid/aliphatic acid molar ratio of 2:1 to
a polyester polyol having a hydroxy content of 5 to 9% by weight, which is the reaction product of a 6:1 mixture of aromatic acids and aliphatic dicarboxylic acids; (b) 4 to 35% by weight of epichlorohydrin, based on the weight of the blend; - A coating composition is provided consisting of a bisphenol A epoxy resin, an esterification product of said resin with a monocarboxylic acid, or a mixture thereof, and (c) 25 to 35% by weight aminoplast resin, based on the weight of the blend. . The polyester coating compositions of this invention, which are very useful as finishes for tools, general industrial applications, or automobiles, consist primarily of a film-forming blend and a solvent for the blend. However, it can also contain pigments, reaction catalysts for shortening the curing time and any of the various additives advantageously used in coating compositions for industrial or automotive finishes. The film-forming blend consists essentially of a polyester polyol, an epoxy resin or an epoxy resin/acid ester, and an aminoplast hardener or crosslinker. The film-forming blend contains at least 50% of the combined weight of blend and solvent, preferably 60%.
Make up ~90%. The polyester polyol used in the present invention comprises 30-70% by weight of the film-forming blend;
Preferably 50-70% by weight and most preferably 60
Constituting ~65% by weight. This polyol is a condensation reaction product of pentaerythritol, glycols, monocarboxylic acids, and aromatic and aliphatic dicarboxylic acids. The first set of reaction components necessary to produce the polyester polyols useful in this invention are pentaerythritol and at least one branched-chain type of glycol. It has been found that the inclusion of such glycols and pentaerythritol into the polyester imparts the desired hardness to the final cured film. All branched chain glycols can be used in the polyester formulation, but it is preferred that these glycols contain no more than 8 carbon atoms. Neopentyl glycol and picol are examples of preferred branched chain glycols. Particularly useful polyols are formed when the molar ratio of glycol to pentaerythritol is from about 2:1 to about 6:1. A ratio of 3:1 to 4.5:1 is preferred. The monocarboxylic acid component of the polyester polyol is primarily present to prevent an increase in the molecular weight of the polyol. It has been discovered that for this purpose any aromatic or aliphatic monocarboxylic acid having 18 or fewer carbon atoms or mixtures thereof may be used. Typically, this acid is used in an acid/pentaerythritol molar ratio of about 1:1 to 2.5:1. Examples of preferred aromatic monocarboxylic acids are benzoic acid, P-tert-butylbenzoic acid, triethylbenzoic acid, toluic acid, phenyl acetic acid, and others.
Examples of preferred aliphatic acids are acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid or unsaturated homologs thereof. Branched aliphatic monocarboxylic acids may also be used. Most preferred are benzoic acid, lauric acid and pelargonic acid. Dicarboxylic acids useful in the formulation of polyester polyols have the general formula , where R is aliphatic or aromatic.
The most useful of the aliphatic acids are those in which R is alkylene, vinylene or cycloaliphatic. Preferred acids when R is alkylene are those in which R contains 2 to 10 carbon atoms. Most preferred among these are succinic acid, glutaric acid, adipic acid and pimelic acid. When R is monounsaturated aliphatic, the most useful acids are those in which R has 2 to 8 carbon atoms, the preferred acids being maleic acid and itaconic acid.
Preferred aromatic dicarboxylic acids are phthalic acid, isophthalic acid, terephthalic acid, and uvitic acid.
acid) and cumidic acid. When R is cycloaliphatic, preference is given to cyclohexane or cyclohexenedicarboxylic acid, but other such dicarboxylic acids may also be used. Mixtures of these aromatic and aliphatic dicarboxylic acids may also be used. Regardless of whether a mixture of various acids or only one of the various acids is used, the molar ratio of aromatic diacids to aliphatic diacids is about 2:1 to 6. : should have a range of 1. A ratio of about 4:1 is preferred. Additionally, lower alkyl mono- or diesters of these acids and anhydrides of these acids when available can also be used in place of the acids themselves;
And corresponding results are obtained. When said esters are used, the alkyl group preferably has no more than 5 carbon atoms. Polyester polyols can typically be produced by charging the reaction components, a suitable solvent, and optionally a reaction catalyst to a reaction vessel, usually equipped with a condenser and a stirrer. However, as mentioned above, the monocarboxylic acid is primarily present to inhibit molecular weight increase by reducing the functionality of pentaerythritol. Therefore, instead of reacting all the polyol components together, it is possible to first form the prepolymer by reaction of acid and pentaerythritol in the molar ratios mentioned. This prepolymer is then reacted with the other components of the polyol, namely the branched glycol and dicarboxylic acid. Solvents useful in the preparation of polyols are, for example, xylene, toluene and other substituted benzenes, naphthalenes and substituted naphthalenes. Reaction catalysts can be present in conventional amounts, such as one of dibutyltin oxide, dibutyltin dilaurate, sulfuric acid or sulfonic acid. This reaction mixture is heated to its reflux temperature (usually 100-300
°C) and hold there for 1-8 hours. During this time esterification by-products are removed. The reaction product polyester polyol should have a number average molecular weight (determined on polystyrene standards by gel permeation chromatography) of 150 to 1000, preferably 250 to 450. The reactants should be selected such that the polyester polyol has a hydroxy content of 5 to 9% by weight, preferably about 7 to 8% by weight. The film-forming blends of the present invention also contain epoxy resins or epoxy resin/acid esters, which are esterification products of epoxy resins and monocarboxylic acids. The ester is present at 4-35% by weight of the film-forming blend, preferably 4-15% and most preferably 5-10%.
form. The epoxy resin itself is the reaction product of dipichlorohydrin and bisphenol A, which has the general formula , where n is large enough to produce an epoxy resin having an epoxide equivalent weight of 450 to 2000, preferably 850 to 1050. The epoxide equivalent weight is the unit weight of epoxy resin containing one unit equivalent of epoxide. Esters that can be used in place of or in admixture with epoxy resins are produced by reacting said epoxy resins with monocarboxylic acids. Although the choice of acid is not critical, the most preferred are benzoic acid, p-tert-butylbenzoic acid and higher fatty acids containing from 8 to 18 carbon atoms. These fatty acids are often found in fatty oils in the form of their glycerides. This can be reacted directly with an epoxy resin to produce the desired acid ester. Examples are coconut oil, castor oil, cottonseed oil, peanut oil, tung oil, linseed oil and soybean oil. The ester can be prepared by reacting the acid or the corresponding oil and the epoxy resin together in a closed vessel equipped with a stirrer, thermocouple and condenser. Increase the temperature by gradually applying heat to about 230-270 over 1-2 hours
℃, but as soon as the epoxy resin melts, start stirring. This temperature is maintained until the resulting ester achieves the desired functionality. This can be determined by taking samples intermittently and measuring the acid value of the ester. At this point the reaction mixture can be cooled and diluted with a suitable solvent. Aminoplast resins are well known as crosslinkers or hardeners. Particularly useful are the alkylated products of aminoplast resins, which themselves contain at least one aldehyde such as urea, N,N
- produced by condensation with at least one of ethylene urea, dicyandiamide and aminotriazine such as melamine and guanamine.
Among the suitable aldehydes are formaldehyde, its reversible polymers such as paraformaldehyde, acetaldehyde, crotonaldehyde and acrolein. Preferred is formaldehyde and its revertable polymers.
Aminoplast resins can be alkylated with at least one and up to _{six C 1-6 alkanol} molecules. Alkanols can be linear, branched, cyclic or mixtures thereof. Preferred are aminoplast resins alkylated with methanol, butanol or mixtures of the two. Most preferred are methylated melamine-formaldehyde resins such as hexamethoxymethylmelamine. In the coating composition, the aminoplast resin is used in a film-forming blend of 25 to
It is 35% by weight. The polyester polyol and the epoxy resin or epoxy resin/acid ester are each typically in solution after their manufacture, and they are blended with each other and with a curing agent to form the coating composition of the present invention. Suitable for direct use. The final composition is 50~
90% by weight film-forming blend and 10-15
% by weight of blending solvent, these percentages are based on the combined weight of blend and solvent.
One of the useful aspects of the present invention is that it can be spray applied even at these high solids levels. The solvent of the final composition can be a mixture of organic solvents, each of which forms a component of the film-forming blend. The compositions of the present invention may contain from about 0.01 to 2% by weight curing catalyst, based on the weight of the film-forming blend. Particularly useful are acid catalysts such as organic sulfonic acids, acid phosphates such as methyl and butyl acid phosphates, acid pyrophosphates such as dimethyl acid pyrophosphate, and organic acid sulfate esters.
Preferred are sulfonic acids such as p-toluenesulfonic acid and dinonylnaphthalenedisulfonic acid. Sulfonic acids can be neutralized with amines, preferably tertiary amines. The coating compositions of this invention may be pigmented to include pigments in an amount having a pigment/film former weight ratio of about 0.005/1 to 100/1. Useful pigments are, for example, metal oxides such as titanium dioxide or zinc oxide, metal hydroxides, metal flakes,
Sulfides, sulfates, carbonates, carbon black, silica, talc, china clay and organic dyes. The pigment can be introduced into the coating composition by first forming a mill base with the polyester polyol. The mill base can be prepared, for example, by conventional sand sanding or ball milling techniques, and then blended with the other ingredients of the coating composition by simply stirring or mixing. The coating composition may further optionally contain UV stabilizers, antioxidants, or both as durability enhancers. The UV stabilizer may be present in an amount of 1 to 20% by weight based on the weight of the film-forming blend. The antioxidant can be present in an amount of 0.1 to 5% by weight based on the weight of the film-forming blend. Typical UV stabilizers are benzophenones, triazoles, triazines, benzotriazoles, benzoates, lower alkylthiomethylene-containing phenols, substituted benzenes, organophosphorus sulfides and substituted methylene malonitriles. Particularly useful are sterically hindered amines and nickel compounds, which are shown in US Pat. No. 4,061,616. Typical antioxidants are tetrakisalkylene(dialkylhydroxyaryl)alkyl ester alkanes, the reaction product of p-aminodiphenylamine and glycidyl methacrylate, and nitrogen of heterocyclic nuclei containing imidodicarbonyl or imidodithiocarbonyl groups. An alkylhydroxyphenyl group attached to an atom by a carbalkoxy bond. One preferred combination of UV stabilizer and antioxidant is 2-hydroxy-4-dodecyloxybenzophenone or substituted 2(2'-hydroxyphenyl)benzotriazole and tetrakismethylene 3(3',5'- Dibutyl-4'-hydroxyphenyl) propionate methane. The coating composition can be applied to a variety of substrates by any conventional application method such as spraying, dipping, brushing or flow coating. Substrates which can advantageously be coated with the compositions of the invention are, for example, metal, steel, wood, glass or plastics, such as polypropylene, polystyrene, styrene copolymers and the like. This coating is particularly suitable for application on subbed or unsubbed metal or steel. Typical uses are for coating zinc phosphate or iron phosphate treated steel, metal substrates precoated with conventional alkyd or epoxy primers and galvanized steel. This composition can be cured by heating to 120-200°C for 10-30 minutes. Particularly preferred compositions cure in 15 minutes at 150°C or 30 minutes at 135°C to provide a hard, durable, scratch and stain resistant, and chemical reagent resistant film. The compositions are suitable, for example, for the coating of motor vehicle or truck bodies, railway equipment, tools and all industrial equipment. In other embodiments, the coating composition of the invention is a two-coat system in which a first pigmented coat is applied onto a substrate and then a second non-pigmented coat is overlaid as described above. It is possible to apply it as This gives the finish an improved gloss or appearance than would be achievable if a single coat system were used. This is particularly desirable when the composition is used as an automotive coating. If such a two-coat system is used, however, the first coat should be cured to the point of being tack-free before applying the second coat. This usually prevents the solvent in the second coat from attacking the first coat. This attack or strike-in can cause the film formers of the two coats to bond at the interface and offset the gloss or appearance improvement. The following example illustrates the best mode of the invention. Example The following ingredients are prepared as follows. (1) Parts by weight of prepolymer solution Pentaerythritol 435.2 Benzoic acid 780.8 Dibutyltin oxide 1.2 Xylene 85.0 The reaction components are charged into a reaction vessel equipped with a stirrer and a steam condenser and gradually heated to reflux. The mixture is then held until the reaction is complete as measured by tracking the flow of water from the condenser. After the mixture is allowed to cool, it is approximately
It has a solids content of 91%. (2) Polyester polyol solution 1st part by weight Neopentyl glycol 1331.2 Component 1 (91% solids by weight) 1210.8 Isophthalic acid 664.0 Phthalic anhydride 592.0 Adipic acid 252.0 Dibutyltin oxide 3.9 Xylene 75.0 2nd part by weight 2-ethyl Hexanol 180.0 Amylacetate 105.0 Xylene 80.0 Charge the first portion to a reaction vessel equipped with a stirrer and steam condenser and slowly heat to reflux. This reflux condition is maintained until the reaction is complete as determined by tracking the flow of water from the condenser. The total amount of water collected is approximately 303 parts by weight.
Cool the mixture to 80°C and add the second portion. The mixture is then stirred for 1 hour and then filtered. The resulting reaction product polyester polyol has a hydroxyl content of about 7.7% by weight (based on product solids weight) and a number average molecular weight (gel permeation chromatography) of 340. This solution has a Gardnerholt viscosity of Z-8 and a solids content of 87% by weight. (3) Mill base

[Table] Polymer
TiO ₂ white pigment 300.0
Add these ingredients to a mixing vessel and mix for 1 hour. This mixture is then placed in a sand mill and ground at a temperature of approximately 35°C. A coating composition is then prepared using the following ingredients.

Table: Charge the first portion into a stainless steel container and mix for 15 minutes, then add the second portion and continue mixing for an additional 5 minutes. The third portion is then incorporated into the container, and the film-forming blend (polyester polyol, epoxy resin/acid ester and hexamethoxymethyl melamine) is approximately 70% of the combined weight of the film-forming blend and solvent.
A coating composition is produced. Inclusion of pigment gives the composition approximately 83% solids by weight. This composition was sprayed (DeVilbis air gun using a pressure of 70 pounds per square inch) onto a "Bonderlite 1000" panel (cold rolled steel with a layer of iron phosphate) and the thus coated panel Bake at 135℃ for 30 minutes. The cured coating has a thickness of approximately 1.4 mils. When then tested, this coating had a pencil hardness of 5H, 20.3 at 25°C and 70°C.
It has a two-con hardness of 4.4. Several coated panels are scored down to the metal using nails and placed in a salt spray cabinet where they are exposed to a mist of an aqueous NaCl (5% by weight) solution. After 300 hours, the creep of the coating from the score line is 3 mm. The coating on such panels is resistant to contamination from common substances such as mustard, lipstick and orange dye, and is insensitive to attack by common solvents such as toluene, xylene and methyl ethyl ketone. It has been found that

Claims (1)

Claims: 1. A film-forming blend comprising a film-forming blend and a solvent for the blend, wherein the blend is at least 50% by weight of the combined weight of the blend and solvent, and essentially comprises: (a) 30 to 70% by weight, based on the weight of the blend, consisting of (1) pentaerythritol and a branched chain glycol selected from neopentyl glycol, pinacol and mixtures thereof, with a glycol/pentaerythritol molar ratio of 2: (2) aromatic or aliphatic monocarboxylic acids having not more than 18 carbon atoms in such an amount that the monocarboxylic acid/pentaerythritol molar ratio is from 1:1 to 2.5:1; or a mixture thereof, and (3) an aromatic acid/aliphatic acid molar ratio of from 2:1 to
(b) a polyester polyol having a hydroxyl content of 5 to 9% by weight, which is the reaction product of a 6:1 mixture of aromatic and aliphatic dicarboxylic acids; (b) epichlorohydrin, of 4 to 35% by weight, based on the weight of the blend; - a bisphenol A epoxy resin, an esterification product of said resin with a monocarboxylic acid, or a mixture thereof, and (c) 25 to 35% by weight, based on the weight of the blend, of an aminoplast resin. A coating composition. 2. A coating according to claim 1, wherein 50-70% by weight of (a), 4-15% by weight of (b) are present, and (b) is the esterification product. Composition. 3. The coating of claim 2, wherein the branched glycol is neopentyl glycol and the monocarboxylic acid of the polyester polyol is selected from the group consisting of benzoic acid, lauric acid, pelargonic acid and mixtures thereof. Composition. 4. The aromatic dicarboxylic acid is selected from the group consisting of phthalic acid, isophthalic acid, terephthalic acid and mixtures thereof, and the aliphatic dicarboxylic acid is selected from the group consisting of succinic acid, glutaric acid, adipic acid, pimelic acid and mixtures thereof. A coating composition according to claim 3, which is selected. 5. The coating composition of claim 4, wherein the polyester polyol is a reaction product of benzoic acid, pentaerythritol, neopentyl glycol, isophthalic acid, phthalic acid and adipic acid. 6 The monocarboxylic acid of the esterification product is 8
6. The coating composition of claim 5, wherein the coating composition is a fatty acid containing ~18 carbon atoms. 7. The coating composition of claim 6, wherein the aminoplast resin is hexamethoxymethylmelamine. 8. The coating composition according to any one of claims 1 to 7, further comprising a pigment. 9. A coating composition according to any one of claims 1 to 7, further comprising a UV stabilizer, an antioxidant, or both.