HK1196388A - Branched polyester polymers comprising isophthalic acid and coatings comprising the same - Google Patents

Description

Branched polyester polymers comprising isophthalic acid and coatings comprising the same

Technical Field

The present invention relates to branched polyesters prepared from isophthalic acid. The invention further relates to a coating comprising said polyester and to a substrate to which said coating is applied.

Background

Conventional linear and branched polyester resins prepared by polycondensation of various combinations of polyols and polyacids have been widely used in the coatings industry. They are used to coat many metallic and non-metallic substrates used in many different industries. Particularly suitable examples include substrates for certain industrial and automotive coatings. Depending on the substrate and end use, these coatings typically require a specific combination of properties, including surface properties such as smoothness, gloss, and distinctness of image ("DOI") and performance properties such as chemical resistance, scratch resistance, and weatherability.

Summary of The Invention

The present invention relates to a branched polyester polymer comprising the reaction product of reactants comprising: a) a polyacid comprising at least 90 mole% isophthalic acid, including esters and/or anhydrides thereof; and b) a polyol comprising a tri-or higher functional polyol. Coatings, including clear coatings, comprising the branched polyester polymers, as well as substrates at least partially coated with the coatings are also within the scope of the present invention.

Detailed Description

For the purposes of the following detailed description, it is to be understood that the invention may assume various alternative variations and step sequences, except where expressly specified to the contrary. Moreover, other than in any operating examples or where otherwise indicated, all numbers expressing, for example, quantities of ingredients used in the specification and claims are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

Moreover, it should be recognized that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of "1 to 10" is intended to include all sub-ranges between (and inclusive of) the recited minimum value of 1 and the recited maximum value of 10, i.e., all sub-ranges having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10.

In this application, the use of the singular includes the plural and plural encompasses singular, unless specifically stated otherwise. In addition, in this application, the use of "or" means "and/or" unless explicitly stated otherwise, even though "and/or" may be explicitly used in certain instances. Also, in this application, the use of "a" means "at least one" unless otherwise indicated.

As previously mentioned, the present invention relates to a branched polyester polymer comprising the reaction product of reactants comprising: a) a polyacid comprising at least 90 mole% isophthalic acid, including esters and/or anhydrides thereof; and b) a polyol comprising a tri-or higher functional polyol. The branched polyester may be dissolved or dispersed in a solvent. Coatings comprising the branched polyester polymers, including clear or tinted coatings, and substrates at least partially coated with the coatings, with or without an underlying base coating, are also within the scope of the invention.

As noted above, the branched polyester polymer may be prepared from a polybasic acid. As used herein, "polyacid" and similar terms refer to compounds having two or more acid groups and include esters and/or anhydrides of the acids.

In certain embodiments, the polyacid used comprises at least 90 mole%, such as at least 95 mole%, and in other embodiments greater than 95 mole%, such as 100 mole%, of isophthalic acid, including esters and/or anhydrides thereof.

In certain embodiments, one or more additional acids may also be used. Such acids may include, for example, other polybasic acids, monobasic acids, fatty acids, esters and/or anhydrides of any of these acids, and/or combinations thereof. It will be understood by those skilled in the art that the polyacid has two or more carboxylic acid functional groups, or residues thereof (e.g., anhydride groups). Suitable polybasic acids include, but are not limited to, saturated polybasic acids such as adipic acid, azelaic acid, sebacic acid, succinic acid, glutaric acid, decanedioic acid, dodecanedioic acid, cyclohexanedicarboxylic acid, hydrogenated C36 dimer fatty acids, and esters and anhydrides thereof. Suitable monobasic acids include, but are not limited to, cycloaliphatic carboxylic acids including cyclohexane carboxylic acid, tricyclodecane carboxylic acid, camphoric acid, and aromatic monobasic carboxylic acids including benzoic acid and tert-butylbenzoic acid; C1-C18 aliphatic carboxylic acids, such as acetic acid, propionic acid, butyric acid, caproic acid, oleic acid, linoleic acid, pelargonic acid, undecanoic acid, lauric acid, isononanoic acid, other fatty acids, and those derived from hydrogenated fatty acids of naturally occurring oils, such as coconut fatty acid; and/or esters and/or anhydrides of any of these. The additional acid constitutes at most less than 10 mole%, for example no more than 5 mole%, of the total amount of the acid and the polyacid used to form the branched polyester polymer.

As used herein, "monoacid" and similar terms refer to a compound having one acid group and include esters and/or anhydrides of the acid.

In certain other embodiments, the additional monobasic acid comprises benzoic acid, esters thereof and/or anhydrides thereof. In certain of these embodiments, the benzoic acid, ester thereof, and/or anhydride thereof comprises up to 25 weight percent of the total weight of the branched polyester polymer. In certain of these embodiments, the benzoic acid, ester thereof, and/or anhydride thereof comprises 5 to 15 weight percent of the total weight of the branched polyester polymer. In certain of these embodiments, the benzoic acid, ester thereof, and/or anhydride thereof comprises 10 to 15 weight percent, such as 15 weight percent, of the total weight of the branched polyester polymer.

As noted above, the branched polyester polymer may also be prepared from a polyol. As used herein, "polyol" and similar terms refer to compounds having two or more hydroxyl groups. The polyol may also be selected to provide stiffness to the branched polyester polymer. Suitable polyols for use in the present invention may be any polyol known for use in the preparation of polyesters. Examples include, but are not limited to, alkylene glycols such as ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, hexylene glycol, polyethylene glycol, polypropylene glycol, and neopentyl glycol; hydrogenated bisphenol a; cyclohexanediol; propylene glycol includes 1, 2-propylene glycol, 1, 3-propylene glycol, butylethylpropylene glycol, 2-methyl-1, 3-propylene glycol, and 2-ethyl-2-butyl-1, 3-propylene glycol; the butanediol includes 1, 4-butanediol, 1, 3-butanediol, and 2-ethyl-1, 4-butanediol; the pentanediol comprises trimethyl pentanediol and 2-methyl pentanediol; 2,2, 4-trimethyl-1, 3-pentanediol, cyclohexanedimethanol; hexylene glycols include 1, 6-hexanediol; 2-ethyl-1, 3-hexanediol, caprolactone diol (e.g., the reaction product of epsilon-caprolactone and ethylene glycol); a hydroxyalkylated bisphenol; polyether glycols such as poly (oxytetramethylene) glycol; trimethylolpropane, ditrimethylolpropane, pentaerythritol, dipentaerythritol, trimethylolethane, trimethylolbutane, dimethylolcyclohexane, glycerol, tris (2-hydroxyethyl) isocyanurate, and the like.

The branched polyesters of the present invention may be dissolved or dispersed in a single solvent or a mixture of solvents during and/or after their formation. Any solvent typically used during polyester formation can be used and these are well known to those skilled in the art. Typical examples include water, organic solvents, and/or mixtures thereof. Suitable organic solvents include, but are not limited to, glycols, glycol ether alcohols, ketones, such as: methyl ethyl ketone, methyl isobutyl ketone, and mixtures thereof; aromatic hydrocarbons such as xylene and toluene, and those available from Exxon-Mobil Chemical Company under the SOLVESSO trade name; acetates including glycol ether acetates, ethyl acetate, n-butyl acetate, n-hexyl acetate, and mixtures thereof; mineral essential oils, naphtha and/or mixtures thereof. "acetates" include glycol ether acetates. In certain embodiments, the solvent is a non-aqueous solvent. By "non-aqueous solvent" and like terms, it is meant that less than 50% of the solvent is water. For example, less than 10%, or even less than 5% or 2% of the solvent may be water. It will be understood that mixtures of solvents, including or excluding water in amounts below 50%, may constitute "non-aqueous solvents".

In certain embodiments, the solvent added to disperse or dissolve the branched polyester is in an amount such that the branched polyester is about 30 to 80 weight percent based on resin solids (i.e., wherein the solvent is 20 to 70 percent of the total weight of the branched polyester and the solvent). In certain embodiments, the amount of solvent added to disperse or dissolve the branched polyester is such that the branched polyester is about 50 to 70 weight percent, for example 60 weight percent, based on resin solids.

In certain embodiments, the branched polyesters of the present invention have a weight average molecular weight M_WCan be as low as 600, or can have a M of greater than 1000, e.g., greater than 5000, greater than 10,000, greater than 15,000, greater than 25,000, or greater than 50,000_WAs determined by gel permeation chromatography using polystyrene standards. The weight average molecular weight of 2,000-6,000 is in some embodimentsAre particularly suitable.

In addition to the above molecular weights, the branched polyesters of the present invention may also have relatively high functionality; in some cases, the functionality is higher than that typically found in conventional polyesters having such molecular weights. The average functionality of the polyester may be 2.0 or higher, such as 2.5 or higher, 3.0 or higher, or even higher. As used herein, "average functionality" refers to the average number of functional groups on the branched polyester. The functionality of the branched polyester is measured by the number of hydroxyl groups remaining unreacted on the branched polyester, rather than by the unreacted unsaturation. In certain embodiments, the hydroxyl number of the branched polyester of the present invention may be from 10 to 500mg KOH/gm, such as from 30 to 250mg KOH/gm.

In certain embodiments, the branched polyester comprises the reaction product of reactants comprising, based on the total weight of the polyester, 5 to 50 weight percent 2-methyl-1, 3-propanediol, 5 to 60 weight percent neopentyl glycol, 5 to 70 weight percent isophthalic acid, and 5 to 40 weight percent trimethylolpropane, wherein the mole percent ratio of diol to diol components is greater than 51 percent and the mole ratio of alcohol equivalents to carboxyl equivalents is 1.03 to 1.15. The weight average molecular weight as determined by gel permeation chromatography using polystyrene standards is preferably about 2,000-6,000. In certain of these embodiments, the branched polyester is reduced to 30 to 80% resin solids (i.e., 20 to 70% by weight solvent based on the total weight of the branched polyester) by adding a solvent or mixture of solvents.

In certain embodiments, the branched polyester comprises the reaction product of reactants comprising, based on the total weight of the reactants: (a)5 to 70 weight percent dicarboxylic acid, wherein at least 90 mole percent of the dicarboxylic acid comprises isophthalic acid; and (b)5 to 50 weight percent of a polyol, wherein 1 to 99 weight percent of the polyol comprises an asymmetric diol and wherein the remainder of the polyol comprises a tri-or higher functional polyol. In certain of these embodiments, the branched polyester is reduced to 30-80% resin solids by the addition of a solvent or mixture of solvents.

In certain embodiments, the branched polyester comprises the reaction product of reactants comprising, based on the total weight of the reactants: (a)5-70% dicarboxylic acid, wherein at least 90 mole% of the dicarboxylic acid comprises isophthalic acid; (b)5-50% of a polyol, wherein 1-99% of the polyol comprises an asymmetric diol, and wherein the remainder of the polyol comprises a tri-or higher functional polyol; and (c)1-30% of monobasic acid. In certain related embodiments, the monobasic acid comprises benzoic acid. In certain of these embodiments, the branched polyester is reduced to 30 to 80 weight percent of the total weight of the branched polyester by adding a solvent or mixture of solvents (i.e., wherein the solvent and/or mixture of solvents comprises 20 to 70 weight percent of the total weight of the polyester and solvent).

Since the branched polyester of the present invention includes functionality, it is suitable for use in coating formulations in which the hydroxyl groups (and/or other functionality) are crosslinked with other resins and/or crosslinkers typically used in coating formulations. The present invention therefore further relates to coatings comprising a branched polyester according to the invention and a crosslinker. The crosslinking agent, or crosslinking resin or agent, may be any suitable crosslinking agent or crosslinking resin known in the art and will be selected to be reactive with the functional groups or groups on the polyester. It will be appreciated that the coatings of the present invention cure by reaction of the hydroxyl and/or other functionality with the crosslinker, rather than through the double bonds of the polyacid/anhydride/ester moieties, even if any such unsaturation is present in the branched polyester.

Non-limiting examples of suitable crosslinking agents include phenolic resins, amino resins, epoxy resins, isocyanate resins, beta-hydroxy (alkyl) amide resins, alkylated urethane resins, polyacids, anhydrides, organometallic acid-functional materials, polyamines, polyamides, aminoplasts, and mixtures thereof. In certain embodiments, the crosslinking agent is a phenolic resin, including alkylated phenol/formaldehyde resins with a functionality >3, and difunctional ortho-cresol/formaldehyde resins. Such cross-linking agents are commercially available from Hexion as BAKELITE6520LB and BAKELITE7081 LB.

Suitable isocyanates include polyfunctional isocyanates. Examples of the polyfunctional polyisocyanate include aliphatic diisocyanates such as hexamethylene diisocyanate and isophorone diisocyanate, and aromatic diisocyanates such as toluene diisocyanate and 4,4' -diphenylmethane diisocyanate. The polyisocyanate may be blocked or unblocked. Examples of other suitable polyisocyanates include isocyanurate trimers, allophanate esters, and uretdiones of diisocyanates and polycarbodiimides, such as those in U.S. patent application serial No. 12/056,304 filed 3.27.2008, incorporated herein by reference in its relevant part. Suitable polyisocyanates are well known in the art and are widely commercially available. For example, suitable polyisocyanates are disclosed in U.S. Pat. No.6,316,119 at column 6, lines 19-36, which is incorporated herein by reference. Examples of commercially available polyisocyanates include DESMODURVP2078 and DESMODUR N3390 sold by Bayer Corporation, and TOLONATE HDT90 sold by Perstorp.

Suitable aminoplasts include condensates of amines and/or amides with aldehydes. For example, condensates of melamine with formaldehyde are suitable aminoplasts. Suitable aminoplasts are well known in the art. Suitable aminoplasts are disclosed, for example, in U.S. Pat. No.6,316,119 at column 5, lines 45-55, which is incorporated herein by reference.

In preparing the coatings of the present invention, the branched polyester and the crosslinking agent may be dissolved or dispersed in a single solvent or a mixture of solvents. Any solvent capable of being formulated for coating onto a substrate may be used, as is well known to those skilled in the art. Suitable organic solvents include, but are not limited to, glycols, glycol ether alcohols, ketones such as: methyl ethyl ketone, methyl isobutyl ketone, and mixtures thereof; aromatic hydrocarbons such as xylene and toluene, and those available from Exxon-Mobil Chemical Company under the trade name SOLVESSO; acetates including glycol ether acetates, ethyl acetate, n-butyl acetate, n-hexyl acetate, and mixtures thereof; mineral essential oils, naphtha and/or mixtures thereof. "acetates" include glycol ether acetates. In certain embodiments, the solvent is a non-aqueous solvent. By "non-aqueous solvent" and like terms, it is meant that less than 50% of the solvent based on the total weight of the solvent is water. For example, less than 10%, or even less than 5% or 2% of the solvent may be water. It will be understood that mixtures of solvents, including or excluding water in an amount of less than 50% based on the total weight of the solvent, may constitute "non-aqueous solvents".

In certain embodiments, the coating of the present invention further comprises a curing catalyst. Any curing catalyst typically used for catalyzing a crosslinking reaction between a polyester resin and a crosslinking agent such as a phenol resin may be used, and the catalyst is not particularly limited. Examples of such curing catalysts include phosphorus-containing acids, alkaryl sulfonic acids, dodecylbenzene sulfonic acid, dinonylnaphthalene sulfonic acid, and dinonylnaphthalene disulfonic acid.

The coating composition can include other optional materials well known in the art of formulating surface coatings, such as colorants, plasticizers, abrasion resistant particles, antioxidants, hindered amine light stabilizers, ultraviolet light absorbers and stabilizers, surfactants, flow control agents, thixotropic agents, fillers, organic cosolvents, reactive diluents, catalysts, millbases, and other conventional adjuvants, if desired.

It will be appreciated that the polyester and crosslinker of the invention may thus form all or part of the film-forming resin of the coating. In certain embodiments, one or more additional film-forming resins are also used in the coating. For example, the coating composition may comprise any of a variety of thermoplastic and/or thermosetting compositions known in the art. The coating composition may be a water-based or solvent-based liquid composition or, alternatively, may also be in the form of solid particles, i.e. a powder coating.

Thermosetting or curable coating compositions may also include additional film-forming polymers or resins having functional groups that are reactive with themselves or with the crosslinking agent. The additional film-forming resin may be selected from, for example, acrylic polymers, polyester polymers, polyurethane polymers, polyamide polymers, polyether polymers, polysiloxane polymers, copolymers thereof, and mixtures thereof. In general, these polymers may be any of these types of polymers prepared by any method known to those skilled in the art. Such polymers may be solvent-borne or water-dispersible, emulsifiable, or have limited water solubility. The functional groups on the film-forming resin can be selected from any of a variety of reactive functional groups including, for example, carboxylic acid groups, amine groups, epoxide groups, hydroxyl groups, thiol groups, carbamate groups, amide groups, urea groups, isocyanate groups (including blocked isocyanate groups), mercapto groups, and combinations thereof. Suitable mixtures of film-forming resins may also be used to prepare the coating compositions of the present invention. In certain embodiments, wherein the film-forming resin comprises an acrylic polymer, such as an acrylic polyol polymer, the amount of acrylic polyol polymer may be less than 55 weight percent of the total solids weight of the coating composition.

The coating composition may optionally contain additional polyol polymers or oligomers other than the additional film-forming polymers or resins described in the preceding paragraph. In certain embodiments, wherein the film-forming resin comprises an acrylic polymer, such as an acrylic polyol polymer and an additional polyol polymer different from the acrylic polyol polymer, the total amount of the acrylic polyol polymer and the additional polyol polymer may be from about 1 to about 70% by weight, based on the total solids weight of the coating composition.

The acrylic polymer is a copolymer of one or more alkyl esters of acrylic or methacrylic acid, optionally with one or more other polymerizable ethylenically unsaturated monomers. Suitable alkyl esters of acrylic or methacrylic acid include aliphatic alkyl esters having 1 to 30, preferably 4 to 18, carbon atoms in the alkyl group. Examples include methyl methacrylate, ethyl methacrylate, butyl methacrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate and 2-ethylhexyl methacrylate. Suitable other copolymerizable ethylenically unsaturated monomers include vinyl aromatic compounds such as styrene (which is preferred) and vinyl toluene; nitrites such as acrylonitrile and methacrylonitrile; vinyl and vinylidene halides, such as vinyl chloride and vinylidene fluoride, and vinyl esters, such as vinyl acetate.

Hydroxyl functionality is most often added to polymers by using functional monomers such as: hydroxyalkyl acrylates and methacrylates having 2 to 4 carbon atoms in the hydroxyalkyl group including hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate, and the like. And also hydroxy-functional adducts of caprolactone with hydroxyalkyl acrylates and methacrylates. Mixtures of these hydroxyalkyl-functional monomers may also be used. The acrylic polyol polymer may be prepared by solution polymerization techniques. During the reaction, the monomers are heated, typically in the presence of a village radical initiator and optionally a chain transfer agent, in an organic solvent compatible with the ingredients and the resulting polymer product. Typically, the organic solvent is added to the reaction vessel and heated to reflux, optionally under an inert atmosphere. Monomers and other free radical initiators were slowly added to the refluxing reaction mixture. After the addition is complete, some additional initiator may be added and the reaction mixture maintained at an elevated temperature to complete the reaction.

The weight average molecular weight of the acrylic polymer used in the film-forming composition is typically from about 2,000 to about 25,000, preferably 3,000 and 10,000, as determined by gel permeation chromatography using polystyrene standards. The hydroxyl equivalent weight of the polymer generally deviates from about 200 to about 800, preferably from about 300 to about 500.

Thermosetting coating compositions typically include a crosslinker, which may be selected from any of the crosslinkers described above. In certain embodiments, the coating of the present invention comprises a thermosetting film-forming polymer or resin and a crosslinker therefor, which may be the same or different from the crosslinker used to crosslink the polyester. In certain other embodiments, thermosetting film-forming polymers or resins having functional groups capable of reacting with themselves are used; in this case, the thermosetting coating is self-crosslinking.

The coating of the present invention may comprise from 1 to 100 wt%, for example from 10 to 90 wt% or from 20 to 80 wt% of the polyester of the present invention, the wt% based on the total solids weight of the coating composition. The coating composition of the present invention may further comprise 0 to 90 wt%, such as 5 to 60 wt% or 10 to 40 wt% of a crosslinker for the branched polyester, the wt% based on the total solids weight of the coating composition. If used, additional components may comprise 1 wt%, up to 70 wt% or more, the wt% based on the total solids weight of the coating composition.

In certain embodiments, a coating composition comprises: (1)55 to 85 weight percent of a polyester comprising the reaction product of reactants comprising: (a) a polyacid comprising at least 90 mole% isophthalic acid, including esters and/or anhydrides thereof; (b) a polyol comprising at least one tri-or higher functional polyol; and (c) a solvent; and (2)15 to 45 weight percent of a co-reactive aminoplast or isocyanate crosslinker suitable for crosslinking with a polyester, wherein the weight percentages are based on the total solids weight of the coating composition.

In certain embodiments, the coating composition includes a thermosetting binder comprising 60% to 95%, such as 80% to 95%, by weight of the branched polyester polymer in combination with 40% to 5%, such as 20% to 5%, by weight of a co-reactive aminoplast or isocyanate crosslinker suitable for crosslinking with a polyester, wherein the weight percentages are based on the total solids weight of the coating composition.

The coatings of the present invention can be applied to any substrate known in the art, such as automotive substrates, industrial substrates, packaging substrates, wood flooring and furniture, clothing, electronic equipment, including household and circuit boards, glass and transparencies, sporting equipment including golf balls, and the like. These substrates may be metallic or non-metallic, for example. Metallic substrates include tin, steel, tinplated steel sheet, chromium passivated steel, aluminum foil. Non-metallic substrates include polymeric, plastics, polyesters, polyolefins, polyamides, cellulosics, polystyrenes, polyacrylics, poly (vinyl naphthalene), polypropylene, polyethylene, nylon, EVOH, polylactic acid, other "green" polymeric substrates, poly (ethylene terephthalate) ("PET"), polycarbonate acryl or butadiene styrene ("PC/ABS"), polyamides, wood, plywood, wood composites, particle board, medium density fiberboard, ceramics, stone, glass, paper, cardboard, fabric, synthetic and natural leather, and the like. The substrate may be one that has been treated in some way, for example to impart a visual and/or color effect thereto.

The coatings of the present invention can be applied by any standard method known in the art, such as electrocoating, spraying, electrostatic spraying, dipping, roll coating, brushing, and the like.

The coating may be applied to a dry film thickness of 0.04 mils to 4 mils, such as 0.3 to 2 or 0.7 to 1.3 mils. In other embodiments, the coating may be applied at a dry film thickness of 0.1 mils or greater, 0.5 mils or greater, 1.0 mils or greater, 2.0 mils or greater, 5.0 mils or greater, or even greater. The coating of the present invention may be used alone or in combination with one or more other coatings. For example, the coatings of the present invention may or may not include a colorant and may be used as a primer, a base coating and/or a topcoat. For substrates coated with multiple coatings, one or more of these coatings may be coated as described herein. The coatings of the present invention may also be used as packaging "size" coatings, wash-resistant coatings, spray coatings, finish coatings, and the like.

It is appreciated that the coating described in the present invention may be one component ("1K") or a combination of components, for example two components ("2K") or more. A 1K composition will be understood to mean a composition in which all coating components remain in the same container after manufacture, during storage, etc. The 1K coating may be applied to the substrate by any conventional means and cured, such as by heat, forced air, and the like. The coating of the invention may also be a multi-component coating, which is to be understood as a coating in which the different components are kept separately before application. As noted above, the coatings of the present invention may be thermoplastic or thermosetting.

In certain embodiments, the coating is a clear coating. A clear coating is to be understood as a coating which is substantially transparent. The clear coat may thus have a certain degree of color, provided that it does not opacify the varnish or otherwise affect the ability to see the underlying substrate to any significant degree. The varnish of the invention can be used, for example, with a pigmented base coat. The clear coat may be formulated as known in the art of coatings.

Examples

Part A-preparation of polyester for evaluation

Example 1

The polyester is prepared by the following method: a total of 104 grams of trimethylolpropane, 231 grams of neopentyl glycol, 231 grams of 2-methyl-1, 3-propanediol, 784 grams of isophthalic acid, 0.7 grams of dibutyltin oxide, and 1.4 grams of triphenyl phosphite are added to a suitable reaction vessel equipped with a stirrer, a temperature probe, a glycol recovery distillation apparatus (packed column with empty column above and distillation head connected to a water cooled condenser), and a nitrogen purge. The contents of the reactor were gradually heated to 230 ℃. The reaction started to produce water at about 206 ℃. The temperature of the reaction mixture was maintained at 230 ℃ until about 154 grams of water was collected and the acid value of the reaction mixture was 5.4mg KOH/g of sample. The contents of the reactor were cooled to 123 ℃ and then diluted to 65% theoretical solids with 510 g of Solvesso100 (available from Exxon) and then 128 g of 2-butoxyethanol and the mixture was poured off. The final resin solution had a measured solids (110 deg.C/1 hour) of about 65.6%, a Gardner-Holt viscosity of Z, an acid number of 3.4mg KOH/g of sample, and a hydroxyl number of 108.1mg KOH/g of sample. Gel permeation chromatography was performed using tetrahydrofuran solvent and polystyrene standards to determine a weight average molecular weight of 4907.

Example 2

The polyester is prepared by the following method: a total of 360 grams of trimethylolpropane, 360 grams of neopentyl glycol, 360 grams of 2-methyl-1, 3-propanediol, 1319 grams of isophthalic acid, 402 grams of benzoic acid, 1.4 grams of dibutyltin oxide, and 2.8 grams of triphenyl phosphite are added to a suitable reaction vessel equipped with a stirrer, a temperature probe, a glycol recovery distillation apparatus (packed column with empty column above and distillation head connected to a water cooled condenser), and a nitrogen purge. The contents of the reactor were gradually heated to 230 ℃. The reaction started to produce water at about 195 ℃. The temperature of the reaction mixture was maintained at 230 ℃ until about 297 grams of water was collected and the acid value of the reaction mixture was 8.6mg KOH/g of sample. The contents of the reactor were cooled to 148 ℃ and then diluted to 65% theoretical solids with 929 grams of Solvesso100 (available from Exxon) and then 398 grams of Dowanol PM acetate and the mixture poured off. The measured solids (110 deg.C/1 hour) of the final resin solution was about 64.0%, the Gardner-Holt viscosity was U-V, the acid number was 5.6mg KOH/g of sample, and the hydroxyl number was 56.5mg KOH/g of sample. Gel permeation chromatography was performed using tetrahydrofuran solvent and polystyrene standards to determine a weight average molecular weight of 3331.

Example 3

The polyester is prepared by the following method: a total of 102 grams of neopentyl glycol, 390 grams of 2-methyl-1, 3-propanediol, 678 grams of isophthalic acid, 130 grams of adipic acid, and 0.46 grams of butylstannoic acid were added to a suitable reaction vessel equipped with a stirrer, a temperature probe, a glycol recovery distillation apparatus (packed column with empty column above and distillation head connected to a water cooled condenser), and a nitrogen purge. The contents of the reactor were gradually heated to 210 ℃. The reaction started to produce water at about 180 ℃. The temperature of the reaction mixture was maintained at 210 ℃ until about 158 grams of water was collected and the acid value of the reaction mixture was 7.8mg KOH/g of sample. The contents of the reactor were cooled to 108 ℃ and then diluted to 62% theoretical solids with 517 grams of Solvesso150 (available from Exxon) and then 172 grams of Dowanol PM acetate and the mixture poured off. The measured solids (110 deg.C/1 hour) of the final resin solution was about 61.5%, the Gardner-Holt viscosity was X-Y, the acid number was 4.3mg KOH/g of sample, and the hydroxyl number was 22.3mg KOH/g of sample. Gel permeation chromatography was performed using tetrahydrofuran solvent and polystyrene standards to determine a weight average molecular weight of 6751.

Example 4

The polyester is prepared by the following method: a total of 207 grams of trimethylolpropane, 452 grams of neopentyl glycol, 452 grams of 2-methyl-1, 3-propanediol, 1223 grams of isophthalic acid, 366 grams of adipic acid, 1.4 grams of dibutyltin oxide, and 2.7 grams of triphenyl phosphite were added to a suitable reaction vessel equipped with a stirrer, a temperature probe, a glycol recovery distillation apparatus (packed column with empty column above and distillation head connected to a water cooled condenser), and a nitrogen purge apparatus. The contents of the reactor were gradually heated to 230 ℃. The reaction started to produce water at about 167 ℃. The temperature of the reaction mixture was maintained at 230 ℃ until about 348mL of water was collected and the acid value of the reaction mixture was 10.8mg KOH/g of sample. The contents of the reactor were cooled to 148 ℃, then diluted to 65% theoretical solids with 1015 grams of Solvesso150 (available from Exxon) and 254 grams of butyl cellosolve (available from Dow Chemical Co.) and the mixture was poured out. The final resin solution had a measured solids (110 ℃/1 hour) of about 64.6%, a Gardner-Holt viscosity of Z2+, an acid number of 6.2mg KOH/g sample, and a hydroxyl number of 85.3mg KOH/g sample gel permeation chromatography using tetrahydrofuran solvent and polystyrene standards to determine a weight average molecular weight of 11,509.

Part B-preparation of clear coating for evaluation

Next, clear coating compositions were prepared with the polyesters from part a as shown in table 1 below:

TABLE 1

¹US 138-methylolated Melamine, commercially available from Cytec Industries

²DDBSA-sulfonic acid catalyst for melamine, commercially available from Cytec Industries

Available from Dow Chemical Company

Available from Exxon Corporation

⁴Poly (butyl acrylate) flow additive, available from DuPont

⁶Solvent, commercially available from Degussa Corp

⁷Cymel202 is a melamine composition available from Cytec Industries

⁸Acrylic polyols are described in U.S. patent No.5,965,670, appendix 1, example a, containing hydroxyl groups derived from hydroxyethyl methacrylate and an adduct of acrylic acid and glycidyl neodecanoate.

The above clear coat is prepared by first mixing all solvents in a suitably sized vessel and then adding the polyester, melamine, catalyst and then Modaflow sequentially with gentle stirring.

Example 9 an acrylic polymer blend was added to a clear coating composition. The formulation in example 9 was slightly adjusted to suggest different viscosities of the raw materials.

Part C-evaluation of clear coats in Multi-layer coating systems

The clear coat composition from part B was then evaluated in a multilayer coating system applied to a steel substrate material. The results are summarized in table 2 below.

The clear coat was sprayed using a SPRAYMATION machine onto a 4 inch x 12 inch steel panel coated with a cured electrocoat (ED6060)/PPG HP77224ER primer, available from ACTTest board, inc. A water-based black coating (HWH-9517), available from PPG Industries, was spray applied to the electrocoated panels to a total dry ester film thickness of 0.5 mils, and the clearcoat was applied. The water-based black coating was dehydrated at 176 ° F for 10 minutes before applying the clear coating. After application of the clearcoat and 10 minutes of room temperature flash off, the entire stack was baked at 285 ° F for 30 minutes.

Dry film thickness was measured using a fish separator delta, which was measured by fish cutter co log, inc.

GLOSS was measured using a NOVO GLOSS statistical 20 ℃ GLOSS meter, available from Paul N.Gardner Company, Inc.Pompono Beach, Florida.

Microhardness was measured using a microhardness tester, available from Helmut Fischer GMBH & Company, Sindelfingen, Germany. A 400 microliter drop of 38% sulfuric acid was placed on each plate for three days and the resulting damage was recorded. The grade of the score is as follows: 0= OK/1= mild ring/2 = ring/3 = mild whitish and/or blistering/4 = white & swollen, matt, intense blistering/5 = complete destruction.

The acid test was performed using the GM Opel (GM60409) test, where 400 microliter drops of 38% sulfuric acid were placed on each plate for three days and the resulting damage was recorded. The grade of the score is as follows: 0= OK/1= mild ring/2 = ring/3 = mild whitish and/or blistering/4 = white & swollen, matt, intense blistering/5 = complete destruction.

Scratch tests were performed using an Atlas AATCC CM-5 (electric) scratch tester, available from Atlas electric Devices Co., 4114N. ravenswood Ave., Chicago, IL 60613. A9 micron wet or dry abrasive sandpaper (available from 3M Corp (3M enter Bldg., 251-2A-08, St. Paul, MN55144-1000, Phone (800) 533-. Percent retention is expressed as the percentage of 20 ° gloss retained after the surface was scratched with a scratch tester.

Scratch resistance = (scratch gloss/original gloss) x 100.

TABLE 2

¹Microhardness apparatus available from Helmut Fischer GMBH&Company, Sindelfingen, Germany.

²The Opel test method is GM engineering Standard test method GME 60409.

³WOM is recorded as% gloss retention.

⁴Shaft bending test ASTM D522-93a (method A), Standard test method for shaft bending test of adhered organic coatings.

⁵Gloss readings were recorded on a black water-based base coating-HWH 9517.

⁶Atlas scratch test-9 μ, 3M paper.

⁷Auto Europa Clear is a standard acrylic automotive Clear coat.

⁸At 2000 hours, the coating retained 0% of its original gloss.

⁹At 2000 hours, the coating retained 0% of its original gloss.

¹⁰The test results are based on a WOM of 3500 hours.

Table 6 demonstrates that the multilayer coating system with the clear coat formed according to example 5 (using the polyester formed in example 1) exhibits excellent gloss retention and acid resistance (GMOpel etch test).

Table 6 also demonstrates that the multilayer coating system having a clearcoat formed according to example 6 (using the benzoic acid formed in example 2) has a high Fischer microhardness value. These coatings form acceptable coatings that exhibit excellent initial gloss, gloss retention, and etch resistance.

Table 6 demonstrates that the multilayer coating system with the clear coat formed according to example 7 (using the linear polyester formed in example 3) exhibits good initial gloss, acceptable gloss retention and scratch resistance, but that the coating is unacceptably poor in chemical resistance (as shown in the Opel etch test and MEK double scratch). These clearcoats have a reduced crosslink density and, therefore, poor ultimate chemical resistance. Coatings exhibiting poor acid etch, poor MEK resistance or solvent resistance are known in the art to be poorly water stained and to be splashed with gasoline during refueling, as well as to show bird droppings, sap and associated damage in field tests. Automotive manufactures used the acid etch test cited above, and the MEK or gasoline resistant litmus test for field performance. Coatings that do not have sufficient chemical resistance are not acceptable for use in the field.

Table 6 also demonstrates that a multilayer coating system having a clearcoat formed according to example 8 (using the polyester formed in example 4), which includes an acid other than isophthalic acid (here adipic acid) and therefore has a lower isophthalic acid content, exhibits a softer film (low Fischer microhardness value). From the poor etch test, chemical resistance is also compromised. Furthermore, the clear coat plate showed very poor performance in accelerated UV testing (WOM results as described above). Moreover, the film was poorly stained with water, making it impossible to measure the gloss retention, which was independently confirmed in the following Florida exposed plate.

Table 6 also demonstrates that inclusion of acrylic in the clearcoat to modify the clearcoat of example 5 (as shown in example 9) exhibits high Fischer microhardness values, excellent initial gloss, good gloss retention, and good etch resistance, similar to the panel of example 5.

Finally, examples of acrylic coatings used by several european automotive manufacturers are shown in table 6, example 10. This coating is the benchmark for automotive clearcoats, a coating with poor UV durability or poor chemical resistance, which is not suitable for use as an automotive clearcoat.

While specific embodiments of the invention have been described for purposes of illustration, it will be apparent to those skilled in the art that numerous variations of the details of the invention may be made without departing from the invention as defined in the appended claims.

Claims (20)

1. A branched polyester polymer comprising the reaction product of reactants comprising:

a) a polyacid comprising at least 90 mole% isophthalic acid, including esters and/or anhydrides thereof; and

b) polyols including tri-or higher functional polyols.

2. The branched polyester polymer of claim 1, wherein the reactants further comprise (c) a monoacid.

3. The branched polyester polymer of claim 1, wherein said monoacid (c) comprises benzoic acid.

4. The branched polyester polymer of claim 1, wherein said polyol (b) further comprises an asymmetric diol.

5. The branched polyester polymer of claim 4, wherein the asymmetric diol comprises 2-methyl-1, 3-propanediol and/or neopentyl glycol.

6. The branched polyester polymer of claim 5, wherein said tri-or higher functional polyol comprises trimethylolpropane.

7. The branched polyester polymer of claim 1, wherein said polyacid comprises 5 to 70 weight percent and said polyol comprises 5 to 50 weight percent, based on the total weight of said reactants.

8. The branched polyester polymer of claim 2, wherein said polybasic acid comprises 5 to 70 weight percent, said polyhydric alcohol comprises 5 to 50 weight percent, and said monobasic acid comprises 1 to 30 weight percent, based on the total weight of said reactants.

9. The branched polyester polymer of claim 1, wherein M of the branched polyester polymer_W2,000 and 6,000.

10. A coating composition comprising the branched polyester polymer of claim 1 and a crosslinker.

11. A substrate at least partially coated with the coating composition of claim 10.

12. The substrate of claim 11, wherein the coating comprises a clear coat.

13. A coating composition comprising:

(a) a crosslinking agent; and

(b) a branched polyester polymer comprising the reaction product of reactants comprising: (1) a polyacid comprising at least 90 mole% isophthalic acid, including esters and/or anhydrides thereof; and (2) a polyol comprising at least one tri-or higher functional polyol.

14. The coating composition of claim 13, wherein the reactant further comprises (3) a monoacid.

15. The coating composition of claim 14, wherein the monobasic acid comprises benzoic acid.

16. The coating composition of claim 13, wherein the polyol (2) further comprises an asymmetric diol.

17. The coating composition of claim 13, further comprising (c) an acrylic polymer.

18. A multilayer coated substrate comprising:

a substrate;

a base coat applied to the substrate; and

a clear coat applied to the base coat, the clear coat deposited from a coating composition comprising:

(a) a crosslinking agent; and

(b) a branched polyester polymer comprising the reaction product of reactants comprising: (1) a polyacid comprising at least 90 mole% isophthalic acid, including esters and/or anhydrides thereof; and (2) a polyol comprising at least one tri-or higher functional polyol.

19. The multilayer coated substrate of claim 18, wherein the reactant further comprises (3) benzoic acid.

20. The multilayer coated substrate of claim 19 wherein the coating composition further comprises (c) an acrylic polymer.