NO308956B1 - Processes for the preparation of a multilayer coating and a water-based substrate mixture, as well as for coating a vehicle substrate - Google Patents

Description

Multilayer systems have for many years been used to coat cars, but in the early development of these systems, organic solvents were used. When environmental regulations became more stringent, and the costs of organic solvents rose, organic-based substrate systems were less desirable. Recent research in the area of multilayer systems, especially underlay systems, has emphasized the development of water-based systems for multilayer coatings.

Switching from organic solvents to water for dispersion and using resins in multilayer systems solved many of the environmental and cost problems associated with the use of organic solvents. Water-based systems, on the other hand, have resulted in other problems.

Application of a multi-layer coating to an automotive surface, for example, would be facilitated by the use of a system that provides rapid drying of the solvent during and after application of a coating. The Eask drying characteristics provide a wide range of applications and allow minimal control of relative humidity and temperature in the spray zone, resulting in lower energy costs. By facilitating drying, the time between coatings will be shorter, resulting in higher manufacturing efficiency and lower energy costs. In addition, there would be no need for a cooling zone after drying which would also increase manufacturing efficiency. Low boiling point organic solvents were originally used in multi-layer coatings to take advantage of their quick drying characteristics. With the introduction of aqueous based multilayer systems, drying of water from a given resin coating after use became a problem. It was desirable to produce a substrate composition that could be dried in a time period short enough to maintain manufacturing efficiency.

The present invention is directed to a method for producing a multi-layer coating, characterized in that it includes: a) application of a water-borne base layer mixture comprising: (i) an anionic polyurethane resin consisting of

the reaction product of:

(1) a polyester resin component prepared by the reaction of a carboxylic acid component with at least 50 wt-# of at least one long-chain carboxylic acid with between 18 and 60 carbon atoms and at most 50 wt-# of a short-chain dicarboxylic acid and an alcohol with at least 2 hydroxyl groups; and (2) a mixture of at least one multifunctional compound with at least 1 active hydrogen group and at least one carboxylic acid functionality, at least one compound with at least two active hydrogen groups and a polyisocyanate, the said carboxylic acid groups being neutralized with an amine; (ii) a cross-linking agent;

(iii.) a rheological control agent;

(iv) optionally, a branched chain polyester resin

consisting of the reaction product of:

(1) a carboxylic acid component comprising at least 50 wt-# of a long-chain carboxylic acid with between 18 and 60 carbon atoms, not more than 48 wt-# of a short-chain dicarboxylic acid and between 2 and 25 wt-# of a polyfunctional carboxylic acid or acid anhydride with at least 3 carboxylic acid groups; and (2) an alcoholic compound with an average alcohol functionality of at least 2;

(v) a pigment; and

(b) applying a clear top coating composition to overcoat said base composition.

The present invention also relates to a method for producing a water-based substrate mixture for use in a multi-layer coating, characterized in that it includes the following sequential steps;

a) adding cross-linking agent in solution to a rheological control agent in solution and then

mix this thoroughly:

b) adding an anionic polyurethane resin dispersion consisting of the reaction product of: (i) a polyester resin component prepared by the reaction of a carboxylic acid component consisting of at least 50% by weight of a long-chain acid having between 18 and 60 carbon atoms and not more than 50$ of a short-chain dicarboxylic acid and an alcohol having at least 2 hydroxyl groups; and (ii) a mixture of a multifunctional compound having at least one active hydrogen functionality and at least one carboxylic acid functionality and at least one compound having at least two active hydrogen groups and a polyisocyanate, and wherein said carboxylic acid group is neutralized with an amine to the mixture in step (a) while stirring and thoroughly mixing; (c) adding a premixed mass consisting of: a mass prepared by premixing a branched chain polyester resin dispersion consisting of the reaction product of: 1) a carboxylic acid component consisting of at least 50 wt. % of a long-chain carboxylic acid having between 18 and 60 carbon atoms, and not more than 48 wt-# of a short-chain dicarboxylic acid and between 2 and 25 wt-# of a polyfunctional carboxylic acid having at least 3 carboxylic acid groups; and 2) an alcohol component having an average functionality of at least 2

3) water and

4) an amine-containing compound to the mixture provided according to step (c); d) stirring the mixture provided from step (b) with the mixture from step (c); and e) adding pigment paste to the mixture obtained from step (d) under thorough mixing, f) adjusting the pH and viscosity of the mixture obtained from step (e).

Furthermore, the present invention also relates to a method for coating a car substrate with a multi-layer coating, characterized in that it includes: a) applying to a primed substrate a first layer of a water-based coating mixture consisting of: i) a polyurethane resin obtained from the reaction product of:

KJ

1) a polyester resin component produced by the reaction of a carboxylic acid component consisting of at least 50% by weight of a long-chain carboxylic acid having between 18 and 60 carbon atoms and at most 50$ of a short-chain dicarboxylic acid with an alcohol having at least 2 hydroxyl groups; and 2) a mixture of a multifunctional compound having at least one active hydrogen functionality and at least one carboxylic acid functionality, and at least one compound having at least two active hydrogen groups, and polyisocyanate, wherein said carboxylic acid groups are neutralized with an amine;

ii) a cross-linking agent;

iii) a rheological control agent; and

iv) a pigment paste;

v) a branched polyester resin,

b) drying by evaporation of said first layer at a temperature of between room temperature and 63° C between

30 seconds and 10 minutes; and

c) applying at least one layer of a clear topcoat to said substrate; and d) curing said substrate and topcoat to a hard, durable film.

Polyurethane resins described above may be formulated as a water-dispersed base resin together with an abrasive resin, a cross-linking agent, thixotropic or rheological control agents, thickeners, pigments, aluminum and/or mica particles, base forming agents, water, fillers, surfactants, stabilizing agents, plasticizers, wetting agents , dispersants, adhesion promoters, defoamers, catalysts and additional polymers, such as a branched polyester among other ingredients.

After formulation, the substrate composition can be sprayed or electrostatically deposited on the car surface, preferably in one or two coats. Usually two even coats of the substrate are applied with a one minute evaporation between coats. After depositing the substrate, before using a clear coat with a high solids content, it is generally preferable to evaporate approximately 90% of the water from the substrate to provide optimum appearance and to eliminate water boiling in the clear coat.

A preparation of water-dispersible anionic resin can be a polyurethane product in which polyurethane is prepared with a mixture of an excess of diisocyanate, a multi-functional compound having at least one active hydrogen functionality and at least one carboxylic acid functionality, and a hydroxy-terminated polyester resin. This mixture produces a urethane-containing resin intermediate having one or two free isocyanate groups per polymer chain. In particularly preferred embodiments, the free isocyanate groups are then covered with an excess of an alcohol with a hydroxy functionality of at least one and preferably two or more.

The polyester compound is produced from an alcohol component that has at least 2 hydroxy groups per molecule (polyol) and a carboxylic acid component. The carboxylic acid component consists of at least 50 wt-# of a long-chain carboxylic acid-containing compound having between 18 and 60 carbon atoms in the chain. This long-chain carboxylic acid component is an alkyl, alkylene, aralkyl, aralkylene or a compound of similar hydrophobicity containing 18 and 60 carbon atoms in the chain. The polyester chain may be branched, but it is preferred that chain branching is kept to a minimum. It has been discovered that the low temperature evaporation and fast drying characteristics of the substrate compositions according to the present invention are a result of containing a high percentage of strongly hydrophobic groups in the polyester resin. C18 to C60 carboxylic acids account for a number of compounds that have suitable hydrophobicity. This long chain carboxylic acid can be a dicarboxylic acid such as a C35 dicarboxylic acid known as a dimer acid. The remaining carboxylic acid component consists of a short-chain dicarboxylic acid. The short-chain dicarboxylic acid may preferably be a short-chain alkyl or alkali dicarboxylic acid, for example, azelaic acid, adipic acid, or an equivalent aliphatic dicarboxylic acid or an aromatic dicarboxylic acid. The aromatic dicarboxylic acid is preferably isophthalic acid. It should be noted that a large number of short chain carboxylic acid compounds can be used, but the main objective is to maintain the hydrophobic, fast evaporation characteristics of the polyester resin.

The polyresins described above are useful on almost any elastomeric substrate and are particularly useful when formulated into polyurethane coatings and used in substrate formulations for deposition on metal or plastic substrates, particularly automotive surfaces. The polyurethane resins prepared from the above-described polyesters exhibit fast drying, low temperature evaporation characteristics. These polyurethane resins are, of course, useful in the manufactures where fast drying, low temperature evaporation characteristics are necessary. These resins have been found to be particularly useful as a substrate in a multi-layer undercoat/clear coat automotive coating system.

The composition of the carboxylic acid component and the polyol component used to prepare the polyester resins is such that it provides an excess of polyol and over the total number of equivalents of acid present in the composition. In other words, the reactants should be selected and the stoichiometric proportions of the respective acid and polyol components adjusted to provide hydroxy-terminated polyester molecules each theoretically having a hydroxyl functionality of two or more.

As mentioned above, the acid mixture used to prepare the polyester intermediate may contain a C35 dicarboxylic acid product known as dimer acid. Methods for the preparation of this acid are well known and form the basis of many US patents including numbers 2,482,761, 2,793,220, 2,793,221 and 2,995,121 or alternatively dimer fatty acids can be purchased from a chemical company (Empol 1010, from Emery Chemical Co.).

The C35dimer fatty acid fraction consists essentially of dimers (C35dicarboxylic acids) together with amounts of up to approximately 20-22% C54trimers. Those skilled in the art refer to this dimertrimer mixture as "dimer", and this is also used in the following. The preferred grade contains 97% dimer and 3% trimer. These polymerization reaction products may be used as recovered from the polymerization unit, or they may be given a partial or complete hydrogenation treatment to reduce unsaturation prior to reaction with the polyol compound to produce polyesters. Polyesters produced in this way can then be used to produce a polyurethane resin that can be used in substrate formulations that exhibit low temperature evaporation, quick drying characteristics.

The polyurethanes according to the present invention remain stable during storage and are, of course, water dispersible. The water dispersibility of the resins is controlled by the amount of free carboxylic acid that is in the final resin particles, and the number of salt groups that are formed from the free acid groups.

The coating compositions prepared using the polyurethane resins described herein have exhibited low temperature evaporation and rapid drying characteristics which are surprising for a water dispersible resin.

A production of polyurethane resins can be the formation of a urethane product in which the polyurethane resin intermediate product described above has free isocyanate groups at the terminal positions of the polyurethane resin. The isocyanate groups were then covered with an excess of a polyfunctional alcohol with at least two alcohol groups, and preferably at least three alcohol groups.

The specific characteristics of polyurethane resins are determined by the components of the polyester resin. It has unexpectedly been discovered that polyester resins prepared from a carboxylic acid component consisting of at least 50 wt-# of a long-chain fatty acid or dicarboxylic acid having between 18 and 60 carbon atoms can be formulated into water-dispersible polyurethane coating resins which exhibit particularly advantageous low-temperature evaporating and quick-drying properties for water-based underlay resins.

The acid component of polyesters is, of course, critical in the invention and consists of a mixture of at least 50 wt-# of a long-chain carboxylic acid component having between 18 and 60 carbon atoms, and at most 50 wt-# of a short-chain dicarboxylic acid. The long-chain carboxylic acid can be a dicarboxylic acid can be a dicarboxylic acid such as e.g. can be a C3£dimeric dicarboxylic acid or dimer acid.

The higher the percentage of long chain carboxylic acid, the better the quick drying or evaporation characteristics of the final polyurethane resin. The beneficial evaporation characteristics must be balanced with the effect that change in carboxylic acid component has on the metallic effects, durability and other characteristics of the resin, including, in the case of abrasive resins, the ability to adapt pigment.

The short-chain carboxylic acid component according to the invention is a dicarboxylic acid. Such dicarboxylic acid components include, for example, adipine, azelein and other aliphatic dicarboxylic acids. Aromatic dicarboxylic acids are also preferred. A particularly preferred aromatic dicarboxylic acid is isophthalic acid. Alkylene and aralkylene carboxylic acid can also be used. When branched chains in polyesters are desired, a carboxylic acid containing three or more carboxylic acid groups, for example citric acid, is used. A preferred acid of this type is trimellitic anhydride.

The polyester resins are produced from the carboxylic acid component described above and an excess of a polyol component. An excess of polyol is used so that the polyester resin preferably contains terminal hydroxyl groups. Polyol compounds have an average hydroxy functionality of at least 2.

The polyester resin contains one or more polyols, preferably a diol. Up to 25% by weight of the polyol component may be a polyol having three or more hydroxy groups per molecule. In those cases where polyols having three or more hydroxy groups are chosen, the result is a branched polyester.

It is not always desirable to have a triol or higher multi-functional alcohol present because of the tendency to form a branched chain polyester, some branching may be desirable. The polyester resin should not be highly branched. A small amount of monoalcohol should also be present, in the polyol component, especially if large proportions of higher functional alcohols are used. These monoalcohols act as chain terminators. In some cases, for example, where certain high molecular weight polyols are used, the polyols may be made mainly or entirely of components with functionality higher than two.

Diols commonly used to prepare polyester resin include alkylene glycols, such as ethylene glycol, propylene glycol, butylene glycol and neopentyl glycol, 1,6 hexanediol and other glycols such as hydrogenated bisphenol A, cyclohexanedimethanol, caprolactonediol (ie, the reaction product of caprolactone and ethylene glycol), hydroxyalkylated bisphenols, and such. Other diols of various types, and as indicated, polyols with higher functionality may also be used. Such higher functional alcohols may include, for example, trimethylolpropane, trimethylolethane, pentaerythritol, and the like, and also higher molecular weight polyols.

Low molecular weight diols which are preferred in the present invention are known in the art. They have hydroxy values of 200 or more, usually in the range of 200 to 2000. Such materials include aliphatic diols, especially alkylene polyols containing from 2 to 18 carbon atoms. Examples include ethylene glycol, 1,4-butanediol, cycloaliphatic diols such as 1,2-cyclohexanediol and cyclohexanedimethanol. A particularly preferred diol is 1,6 hexanediol.

The resulting polyester resin is preferably prepared with dimer fatty acid as the long-chain carboxylic acid, isophthalic acid as the short-chain carboxylic acid component of which there is less and an excess of 1,6 hexanediol so that the resulting polyester polyol varies in size between approximately 200 and 2000 grams per equivalent of hydroxyl. The polyester resin preferably has a range of between 700 and 800 grams per equivalent hydroxyl and most preferably, is about 750 grams per equivalent hydroxyl.

To prepare the polyurethane resins useful in base compositions, the polyester polyol described above is reacted with a mixture of a polyisocyanate, a multifunctional compound having at least one active hydrogen group and at least one carboxylic acid group, and a compound containing a chemical compound having at least two active hydrogen groups , but no carboxylic acid group.

Polyester, polyisocyanate and multifunctional compound can also be reacted in the same batch, or react sequentially, depending on the desired results. Sequential reaction produces resin that is more ordered in structure. Both polyesters and the multifunctional compound can act as chain extenders to build up the polyurethane backbone through reaction of the hydroxyl groups with the isocyanate groups. To act as a chain extender, the multifunctional compound must have at least two active hydrogen groups. In those cases where the multifunctional compound has only one active hydrogen group, the result is chain termination. Several chain extenders having at least two active hydrogen groups but no carboxylic acid groups can be added to increase the chain length or to change the chemical characteristics of the polyurethane resin. Generally, an excess of polyisocyanate is used so that a polyurethane resin intermediate can be prepared with free isocyanate groups at the terminal ends. The free isocyanate groups can then preferably be covered with trimethylolpropane or dimethanolamine.

Organic polyisocyanate which is reacted with the polyhydric material as described is essentially any polyisocyanate and is preferably a diisocyanate, e.g. hydrocarbon diisocyanates or substituted hydrocarbon diisocyanates. Many such organic diisocyanates are known in the art, including p-phenylene diisocyanate, biphenyl 4,4' diisocyanate, toluene diisocyanate, 3,3'-dimethyl-4,4 biphenylene diisocyanate, 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 2,2 ,4-trimethylhexane-1,6 diisocyanate, methylene bis(phenyl isocyanate), 1,5 naphthalenedi diisocyanate, bis (isocyanatoethyl fumarate), isophorone diisocyanate (IPDI) and methylene bis-(4-cyclohexyl isocyanate). It is also possible to use isocyanate-terminated additives of polyols, such as ethylene glycol, or 1,4-butylene glycol trimethylolpropane, etc. These are produced by reacting more than one mole. of a diisocyanate, such as those mentioned, with a mol. of a polyol to form a longer chain diisocyanate. Alternatively, polyol can be added together with diisocyanate.

Diisocyanates and other multifunctional isocyanates can be used. Examples are 1,2,4-benzenetriisocyanate and polymethylene polyphenyl isocyanate.

An aliphatic diisocyanate can be used, since it has been discovered that these provide better color stability in the final coating. Examples include 1,6-hexamethylene diisocyanate, 1,4-butylene diisocyanate, methylene bis(4-cyclohexyl isocyanate) and isophorone diisocyanate. Mixtures of diisocyanates can also be used.

The proportions of diisocyanate, polyester, and multi-functional compound are selected to provide an isocyanate-terminated polyurethane resin intermediate. This can be achieved by using a stoichiometric excess of polyisocyanate, ie, more than one isocyanate group per nucleophilic proportion (which reacts with isocyanate) in the other components.

In order to promote water solubility, it is important to incorporate acid groups into the polyurethane. For example, the presence of acid groups makes the composition water-dilutable.

The acids that are used to provide free acid groups in the polyurethane resins are readily available. They contain at least one active hydrogen group and at least one carboxylic acid functionality. The active hydrogen group may include a thiol, a hydroxyl or an amine, with primary amines having an active hydrogen group. Examples of such compounds include hydroxyl carboxylic acids, amino acids, thiolic acids, aminothiolic acids, alkanolamino acids and hydroxythiolic acids.

Compounds containing at least 2 hydroxyl groups and at least one carboxylic acid are preferred. They can be prepared from an aldehyde containing at least two hydrogens in the alpha position. Such aldehydes are reacted in the presence of a base catalyst with two equivalents of formaldehyde to form a 2,2-hydroxymethylaldehyde. The aldehyde is then carefully oxidized to the acid using known methods. The acids used in the invention can be represented in simplified form by formula I:

in which R stands for hydroxymethyl, hydrogen or alkyl of up to 20 carbon atoms and preferably up to 8 carbon atoms.

Specific illustrative examples of such acids which are used in the invention include 2,2-di(hydroxymethyl) acetic acid, 2,2,2-tri(hydroxymethyl) acetic acid, 2,2-di(hydroxymethyl) propionic acid, 2,2-di( hydroxymethyl)butyric acid, 2,2-di(hydroxymethyl)pentanoic acid, and the like. The preferred acid is 2,2-di(hydroxymethyl) propionic acid.

Long-chain polyurethane resins are obtained by chain extension of the polyurethane chain with a compound or mixture of compounds containing at least two active hydrogen groups that have no carboxylic acid groups, for example diols, dithiols, diamines, or compounds that have a mixture of hydroxyl, thiol, and amine groups, for example , alkanolamines, aminoalkyl mercaptans, and hydroxy-alkyl mercaptans, among others. Because of this, both primary and secondary amine groups are considered to have an active hydrogen. Alkanolamines, for example, ethanolamine or diethanolamine, are preferably used as chain extenders, but most preferred is a diol. Examples of preferred diols used as polyurethane chain extenders include 1,6 hexanediol, cyclohexanedimethylol, and 1,4-butanediol. A particularly preferred diol is neopentyl glycol. The same diols that are used to prepare the polyester component of the polyurethane resins can be used here as well. While polyhydroxy compounds containing at least three hydroxyl groups can be used as chain extenders, use of these compounds forms branched polyurethane resins. According to the present invention, it is preferred to minimize the amount of branching in the polyurethane resin. Therefore, if polyhydroxy compounds are used, they are preferably limited to a very small component of the polyurethane-making composition. These higher functional polyhydroxy compounds include, for example, trimethylolpropane, trimethylolethane, pentaerythritol, among other compounds.

Polyurethane resin can be chain extended in any manner using these compounds having at least two active hydrogen groups. These compounds can thus be added to the mixture of polyisocyanate, polyester and multi-functional compound, or alternatively, can be reacted in an intermediate stage, to bind two free isocyanate groups present at the terminal ends of a polyurethane resin intermediate.

It is generally preferred that a polyurethane resin intermediate produced by reacting the polyester resin and the mixture of polyisocyanate, multifunctional compound containing at least 2 hydroxyl groups and 1 carboxylic acid group, and chain extender is terminated with free isocyanate groups. To provide this, an excess of the polyisocyanate component is used. The molar ratio of the other components will be adjusted according to the desired characteristics of the intermediate and final polyurethane resins. The polyester component comprises no more than 80% by weight of the reaction mixture and the polyester component may comprise from 20% to 70% by weight of reactants in the mixture.

In a particularly desirable embodiment of the invention, a multifunctional alcohol is used to terminate the reaction (cover the free isocyanate groups) at the desired stage (determined by the viscosity and the isocyanate groups present), also thereby providing remaining hydroxyl groups. Particularly desirable for such purposes are amino alcohols, such as ethanolamine, diethanolamine and the like, since amino groups preferably react with isocyanate groups present. Multi-functional alcohols, such as ethylene glycol, trimethylolpropane and hydroxyl-terminated polyesters, can also be used in this way.

Since the ratio of the components of the polyester, multi-functional isocyanate and the terminating agent can be varied, one skilled in the art will note that the amounts should be chosen to prevent gelation and to produce a non-gelling urethane reaction product containing hydroxyl groups. The hydroxyl value of the urethane reaction product should be at least 5 and preferably 20 to 200.

The amount of polyisocyanate used in the mixture is preferably between 20% and 30% by weight of the reactants in the mixture, but will vary depending on the polyesters used, the acid number of the final polyurethane resin, and the desired molecular weight of the final polyurethane resin. The amount of polyisocyanate also varies depending on whether it is desired to terminate the polyurethane intermediate with free isocyanate groups or with hydroxyl groups. In those cases where it is preferred to terminate the polyurethane resin intermediates with free isocyanates for coating with trimethylolpropane or diethanolamine, an excess of polyisocyanate can be used. Where the polyurethane resin intermediate is terminated with hydroxyl groups, a stoichiometric deficit of polyisocyanate may be used.

The amount of multi-functional component having at least one active hydrogen group and at least one carboxylic acid group can also vary depending on the desired acid number of the final polyurethane resin. The final polyurethane resin has an acid number of at least 10, and the amount of this multi-functional component includes between 1% and 25% by weight of the reactants of the polyurethane manufacturing reaction mixture (polyisocyanate, polyester, multi-functional compound, and optionally other chain extenders, such as compounds having two active hydrogens but no carboxyl groups). It is preferred that the acid number is higher, because as the acid number increases, the water dispersibility of the polyurethane resin is potentially increased. The practical upper limit of the acid number is that which adversely affects the low temperature evaporation or rapid drying characteristics and physical properties of the final resin. The upper limit of the acid number will of course vary depending on the chemical composition of the final polyurethane resin, but an acid number at the upper limit of 100 is, in general, the practical limit of the polyurethane resins.

The amount of chain extender to prepare polyurethane resin varies between 2 and 25 wt-# of the reactants. The amount will depend on the amount of chain extension desired and the desired size of a polyurethane molecule.

After polyurethane resin has been produced, the free carboxylic acid groups are neutralized with base to form salt groups. The base is an amino-containing compound. Tertiary amines are generally preferred over primary and secondary amines because of the tendency of the primary and secondary amines to react with aminoplast cross-linking agents. Preferred tertiary amines include trialkylamines, for example, trimethyl and triethylamine. Also preferred is triethanolamine. Particularly preferred is dimethylethanolamine.

Polyurethane resins are formulated, along with other compounds, into water-dispersible substrate compositions that can be sprayed or electrostatically deposited onto metal, plastic substrates, for example, automobiles. Generally, a polyurethane resin is formulated as described herein, and mixed with an aminoplast resin, pigments, an abrasive resin, water, a portion of an organic solvent, aluminum and/or mica particles, and a rheological control agent. Other agents can also be added, for example, various fillers, surfactants, plasticizers, stabilizers, wetting agents, dispersing agents, antifoams, adhesion promoters and catalysts in smaller amounts.

As indicated, an aqueous dispersion of polyurethane resin is used as the principal or principal component resin. Generally, the principal or main component resin comprises between 20 and 80% by weight of the total amount of solids present in the substrate composition. The preferred polyurethane resin is a resin prepared from a polyester prepared from dimer fatty acid, isophthalic acid and 1,6 hexanediol. The resulting polyester is then reacted with a diisocyanate of isophorne, dimethylolpropionic acid and a diol, for example, neopentyl glycol. The resulting polyurethane intermediate having free isocyanate groups is then reacted with trimethylolpropane to cap these groups.

The polyurethane reaction product described above is mixed with an aminoplast resin. Aminoplast resins are aldehyde condensation products of melamine, urea, and similar compounds. Products obtained from the reaction between formaldehyde and melamine, urea and benzoguanamine are best known and are preferred herein. Condensation products of other amines and amides, on the other hand, can also be used, for example aldehyde condensates of triazines, diazines, triazoles, guanidines, guanamines and alkyl and aryl substituted derivatives of such compounds, including alkyl and aryl substituted urea and alkyl and aryl substituted melamines. Some examples of such compounds are N,N'-dimethylurea, benzourea, dicyandiamide, formoguanamine acetoguanamine, ammelin, 2-chloro-4,6-diamino-1,3,5-triazine, 6-methyl-2,4-diamino,1 ,3,5-triazine, 3,5-diaminotriazole, triaminopyrimidine, 2-mercapto-4,6-diaminopyrimidine, 2,4,6-triethyltriamino-1,3,5-triazine and the like.

Since the aldehyde used most often is formaldehyde, other similar condensation products can be prepared from other aldehydes, for example, acetaldehyde, crotonaldehyde-acrolein, benzaldehyde, furfural and others.

The amine-aldehyde condensation products contain methylol or similar alkylol groups, and in most cases at least a portion of these alkylol groups are esterified by reaction with an alcohol to provide organic solvent-soluble resins. Any monohydric alcohol can be used for this, including such alcohols as methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol and others, as well as benzyl alcohol and other aromatic alcohols, cyclic alcohols, for example, cyclohexanol, monoethers or glycols such as Cellosolves and Carbitols (Union Carbide), and halogen-substituted or other substituted alcohols, such as 3-chloropropanol. The preferred amine-aldehyde resins are esterified with methanol or butanol.

An abrasive resin is also used in the substrate mixtures. While pigment resin may consist of a large number of water-soluble polyurethane resins, it is preferred that the abrasive resin has a chemical character similar to the major or principal component resin, i.e., contains a polyester resin component consisting of a carboxylic acid component consisting of at least 50 wt-# of a C18 to C60 carboxylic acid, preferably a dicarboxylic acid. The abrasive resin may vary in the range between 2 and 75 wt-# of the total solids in the coating composition and will vary depending on the desired color and preferably contains 5-40 wt-# of the base composition.

A preferred anionic polyurethane resin for use as an abrasive resin in compositions according to the present invention is prepared from a polyester polyol which is prepared from dimer fatty acid, adipic acid and 1,6-hexanediol. The resulting polyester diol is reacted with isophorone diisocyanate, dimethylol propionic acid and neopentyl glycol to produce a polyurethane intermediate which is capped with diethanolamine.

Pigments may be incorporated into the substrate to provide the desired cosmetic characteristics. This is carried out by mixing pigments with the pigment resin described above and possibly with other additives to form a pigment paste. Any standard pigments known in the art can be used with the resins according to the present invention if these pigments can be formulated without affecting the desired low temperature evaporation and fast drying characteristics.

Specific examples of the dyes or pigments may be inorganic or organic, for example, graphite, carbon black, zinc chromate, strontium chromate, barium chromate, lead chromate, lead cyanide, titanium dioxide, zinc oxide, cadmium sulfide, iron oxide, aluminum flakes, mica flakes, zinc sulfide, phthalo-cyanine complexes, naphthol red, quinacridones and halogenated thioindigo pigments, among others.

The preferred metallic pigments are metal powders preferably mixed with aluminum metal flakes. Preferred aluminum flake pigments are available from Silberline Corp, Lansford, Pennsylvania or from Eckart Werke, Guenterstahl, West Germany. The aluminum flake pigments add a reinforced "metallic cover" to the coating. In a preferred embodiment of the present invention, standard quality aluminum is stabilized with phosphate ester. Other metallic flakes, such as silver, can also be used, but these are usually very expensive and have a poorer appearance. The metallic pigments can also be mixed with non-metallic pigments, but these should be chosen carefully so as not to reduce the desired metallic effect.

The resins used in the substrate are dispersed in deionized water. The deionized water has a conductance reading of less than 13 microohms-<1>and preferably less than 5 microohms-<1>to prevent gassing caused by the reaction between aluminum and water. Deionized water is also chosen to prevent salts that naturally occur in tap water. Other solvents can also be used with deionized water. A particularly preferred solvent is Butyl Cellosolve which promotes mixing, formulation and dispersion of the pigments in the substrate composition. Other solvents can also be used, for example, low-boiling mono- and polyhydric alcohols, ethers, esters, ketones and other organic substances.

The organic solvent, comprising a maximum of 80% of the substrate composition, and preferably comprising 10 to 20% by weight of the substrate composition (including water) may be selected to promote the dispersibility of individual components of the final substrate composition (with emollient characteristics) and for volatile character - the tart traits.

A rheological control agent is also preferably incorporated into the substrate composition. The rheological control agent controls the viscosity of the resulting composition and is incorporated in amounts that will prevent drift or creep after a substrate has been sprayed onto a vertical surface such as the surface of an automobile. The direct result of incorporating a rheology control agent is to provide control of flow, shape and sprayability. Other beneficial results of adding a rheological control agent are to enhance the flip effect of the metallic flake pigments, and to deposit a thickening coating and to provide complete coverage of a substrate. The sprayed coatings containing these agents also provide better orientation of the metallic flake pigments on the coated substrate. Rheological control agents which can be used in the preparations according to the present invention include the fume-stained silicon oxide compounds and bentonite clay. Preferred fumed silica compounds are the hydrophobic silica compounds, such as Aerosil R972, which is available from DeGussa Corporation, (Frankfurt, West Germany. Another rheological control agent that may be used, and in certain substrate compositions, is a synthetic sodium lithium magnesium silicate hectorite clay. An example of such a clay is Lapinite RD, which is available from Laporte, Inc (Saddlebrook, New Jersey). In certain preferred formulations, rheology control agents are mixed in. The rheology control agent, when added, includes 0.1 to 20 wt.# of the substrate composition and preferably includes between 1 and 5 wt-# of the final substrate composition.

The particle size of the rheological control agent affects the entire thixotropic properties of these resins. Rheological control agents in the preparations according to the present invention are suspended in the material. One can assume that the rheological control agents are suspended and act, at least in part, through coulombic or electrostatic interactions.

Particle sizes can range from less than 0.1 micrometer to over 200 micrometers. These sizes can be used to provide the rheological properties that are desirable. In appropriate cases, the particle sizes may be from 0.01 to 10 micrometers.

In addition to the essential resin or main component resin and an abrasive resin, preferred substrate compositions also consist of at least 5% by weight of the resinous component of a branched polyester resin. Branched-chain polyesters are added to improve their use and to improve their physical properties (caused by increased cross-link density). In general, the branched-chain polyesters are made from the same components as the polyester component, with the exception that in addition to the long and short-chain carboxylic acid components, a small percentage of trifunctional acid or acid anhydride is also used. The carboxylic acid component of the branched-chain polyester may consist of at least 50 wt-# of a long-chain fatty acid, for example C36 dimer fatty acid and no more than 50 wt-# of a combination of a dicarboxylic acid such as isophthalic acid and a small percentage of a trifunctional carboxylic acid such as trimetallic anhydride. In one preparation, the branched chain polyester can be prepared from dimer fatty acid, isophthalic acid and 1,6-hexanediol. A small percentage, 5-20% trimetallic anhydride is also added to the polyesterification reaction to branch polyesters. Branched chain polyester is boiled to a final acid number of 10-50, and preferably 20-40. In general, the branched polyester contains about 20% resinous constituents, but it can be less depending on the color.

Additives that are used, for example, surfactants, fillers, stabilizers, wetting agents, dispersing agents, adhesion promoters, etc. can be incorporated into the substrate composition. The agents are well known according to previous methods, and the amount used must be carefully controlled to prevent a negative influence on the coating and quick-drying properties.

When formulating the substrate mixtures, the order of addition of the individual components is very important. As a rule, the cross-linking agent in a solvent is added to the rheological control agent in the solution and mixed well. Next, the main component resin dispersion (neutralized with amine) is added to the rheological control solution with stirring. If desired, a mixture of aluminum metal flakes and/or mica particles (mica particles are used alone in cases where an aluminum metallic appearance is not desired) in Butyl Cellosolve is mixed with a premixed mixture of a branched-chain polyester resin and dimethylethanolamine. This aluminum mixture is then stirred with the mixture containing resinous component, cross-linking agent, and rheological control agent. Pigment pastes containing polyurethane resin, pigment, filler, stabilizers, plasticizers and other additives are then mixed with stirring with the above resulting mixture. Pigment paste particles are then prepared in a sand mill, attritor or other common grinding device before use.

The pigment pastes can be produced by mixing amimoplast resin with approximately 1/4 of the total polyurethane resin to be added to the pigment paste. Pigment is added to this mass with stirring for about 1/2 hour. The rest of the polyurethane resin is then added and the resulting paste is mixed for another half hour. The pH and viscosity of the paste is investigated and adjustments are made by adding deionized water and/or tertiary amine. The weight ratio between pigment and binder is usually in the range between 0.15-5.0. The amount of pigment varies between 6 and 60% of the total weight of pigment and binder. Other well-known methods for formulating pre-paint pastes can also be used.

The final substrate composition is adjusted to a pH of 7.6-7.8 with a tertiary amine, for example N-ethylmorpholine. Viscosity can be adjusted using deionized water. Final substrate compositions are composed of the following components in the indicated weight ratios.

Table I

Amount (weight-$ of solid

substances in final Ingredient substrate composition)

Polyurethane resin 20-80$

Melamine 5-50$

Rheology control agent 0-20$

Branched chain polyester 0-35$

Pigment 2-65$

The substrate compositions described above may be deposited on a metal or plastic substrate in one or two coats using, for example, an air atomizer (Binks Model 60 spray gun, available from Binks Manufacturing Corporation, Franklin Park, Illinois), or using other conventional spraying methods. The substrate compositions can also be applied electrostatically. The substrate compositions are preferably sprayed at 50-80 psi, and a relative humidity of between 50 and 90$ (optimally at 60-80$ relative humidity) and a temperature of 21-32°C.

After deposition, the substrate compositions are dried by evaporation within a temperature range of room temperature to 63°C for between 30 seconds and 10 minutes using hot air flowing at a relative humidity of 5-40%. The evaporation temperature is 49° C and is preferably carried out in between 1 and 5 minutes. The evaporation conditions described herein result in approximately 90-95$ of the solvents

(water plus organic substances) is evaporated from the substrate during this short period of time.

After the first layer is deposited, another layer can be deposited over the first without drying (evaporation), or alternatively a clear coating can be deposited over the evaporated layer. Any of the known clear coat compositions can be used. Any non-pigmented or other transparently pigmented coating agents are in principle suitable for use as a clear coat. A typical topcoat composition contains 30-70% film-forming resin and 30-70% volatile organic solvent.

After the clear coat is coated on the base layer, the multi-layer coating is baked to cross-link the polymeric component and to remove the small amounts of residual water and organic solvents from the multi-layer polymer composition. Baking steps include heating the coated substrate for a period of 10-60 minutes at a temperature of between 66°C and 149°C. The baking step hardens the coating into a hard, durable film.

The invention will further be described in connection with several examples that follow below. These examples are shown to illustrate the invention. All parts and percentages in the examples are by weight unless otherwise indicated.

Polyurethane example 1

Preparation of a polyurethane resin

A polyester polyol resin is prepared by charging a reaction vessel (bottle with a fractionating column) with 551.9 g (15.8$ polyester resin) isophthalic acid, 1923 g (54.9$) Empol 1010 (dimer fatty acid from Emery Chemical Co.), and 1025.1 g (29.3$) of 1,6-hexanediol and 100 g of toluene. More toluene can be added to fill the column. The mixture was heated under nitrogen and the water of condensation was removed. During this heating, 235.7 g of water was distilled out. Heating is continued at approximately 200°C until the acid number is less than or 8. Remaining toluene is then removed by vacuum at 200°C to prepare a polyester resin for use in the polyurethane resin.

At this time, 697.9 g of the above-prepared polyester resin, 43.0 g of dimethylolpropionic acid, 16.1 g of neopentyl glycol, 243.0 g of isophorone diisocyanate and 300 g of methyl isobutyl ketone are charged to a reactor and heated at reflux (about 128°C). until a constant isocyanate value is provided. 36.8 g of trimethylolpropane is then added to the reactor and this mixture is refluxed for another hour. At this point, the nitrogen is turned off and the mixture is cooled to 95°C. 28.6 g of dimethylethanolamine and 45.4 kg of water are then added with a portion of the water being used for rinsing. The mixture is then allowed to stand until homogenous (about 5 minutes) and then 2048.71 g of water is added over a period of 20 minutes with vigorous stirring.

At the end of this addition, the mixture is distilled at high heat with vigorous stirring to remove the water and methyl isobutyl ketone. The water is again returned to the mixture and the approximately 300 grams of methyl isobutyl ketone that was distilled out is discarded. 238 g of n-butanol are added and the mixture is kept at 80°C for 30 min. The mixture is then submerged and filtered through a 10 micron filter to provide a polyester-urethane component for use in the substrate composition. The resulting dispersion has a solids content of 30% and a Gardner viscosity of Z2.

Polyurethane dispersion 2

Manufacture of polyester resin

1995 g of adipic acid, 1995 g of dimer acid, and 2450 g of 1,6-hexanediol, and 136 g of toluene are added to a reaction vessel. The mixture is heated under nitrogen to 209°C, with removal of water until an acid number of less than 8 is obtained. Residual toluene is removed by vacuum to produce a polyester resin having a solids content of greater than 98%.

Polyurethane dispersion manufacturing

857.4 g of the above polyester is mixed with 14.6 g of neopentyl glycol, 53.1 g of dimethylol propionic acid, 306.5 g of isophorone diisocyanate, 97.1 g of methyl ethyl ketone, and 235.0 g of methyl amyl ketone is refluxed until a constant isocyanate value is provided. Then 24.8 g of diethanolamine are added and the mixture is left to stand for 30 minutes. Then 24.8 g of dimethylethanolamine and 116.8 g of deionized water and 118.2 g of isopropyl alcohol are added and mixed for 15 minutes. 3123.2 g of deionized water is added over a period of 20 minutes with vigorous stirring. The resulting dispersion has a solids content of 26% and an appropriate Gardner viscosity.

Polyurethane dispersion 3

Manufacture of polyester

770 g of dimer acid, 230 g of 1,6-hexanediol and 25 g of toluene are added and the resulting mixture is heated to 200°C. Heating is continued, with removal of water until an acid number of less than 10 is achieved. The remaining toluene is then removed under vacuum.

Polyurethane

700 g of the above polyesters, 12.6 g of neopentyl glycol, 43 g of dimethylol propionic acid, 244 g of isophorone diisocyanate, 77.8 g of methyl ethyl ketone, and 195.3 g of methyl amyl ketone are reacted using Polyurethane Dispersion Method 2. The resulting dispersion has a solids content of 26% and a Gardner viscosity of Zl.

Branched polyester 1

2594 g of dimer acid, 2564 g of 1,6-hexanediol and 744 g of isophthalic acid are added and the mixture heated to 195°C under

nitrogen with stirring until an acid number of 10 or less is reached. The mixture is then cooled to 150°C and 1000 g trimellitic anhydride is slowly added and refluxed until an acid number of 30-32 is reached. After cooling to 150°C or less, 729 g of butyl Cellosolve and 1459 g of n-butanol are added. The resulting polyester has a solids content of 70% and a Gardner viscosity of U-V.

Branched polyster 2

1230 g of dimer acid and 769.5 g of 1,6-hexanediol are added and heated to 195°C under nitrogen with stirring. Heating is continued until an acid number of less than 10 is provided. The mixture is then cooled to 150°C and 420.1 g of trimellitic anhydride is slowly added and heated until the acid number falls below 30. Then 335 g of butyl glycol and 670 g of n-butanol are added with stirring. The resulting polyester solution has a solids content of 70% and a Gardner viscosity of Zl.

Branched polyester 3

868.7 g of 1,6 hexanediol, 1346.2 g of dimer acid and 386 g of isophthalic acid are heated at 195°C until an acid number less than 8 is obtained. 206.6 g trimellitic anhydride is then slowly added with stirring and heat is applied until an acid number of less than 30 is obtained. A 2:1 mixture of n-butanol and butyl glycol is then added until 70% solids are obtained. The resulting polyester resin has a Gardner viscosity of U.

MANUFACTURE OF COATING AGENTS

The composition of the coating agents is shown in table 2, where the numbers denote parts by weight. The following notes refer to the components listed therein: Thickener 1: Paste of Aerosil R972 (Degussa) hydrophobic fume-stained silica sand ground with appropriate polyurethane abrasive resin and melamine in water, 11$ strength organic solvent mixture.

Thickener 2: Paste of synthetic sodium lithium magnesium silicate hectorite clay, Laponite RD (Laporte), 2$ strength in deionized water; the paste is prepared by stirring with Cowles leaf in water for an hour.

Thickener 3: Paste from Laponite RD 3$ strength in deionized water. Prepare as thickener 2.

Titanium dioxide pigment paste: 41$ concentration of DuPont R-960 titanium dioxide sand ground with appropriate polyurethane abrasive resin and melamine.

Melamine resin: Commercially available methanol esterified melamine/formaldehyde resin, solids content 90 wt-$ in n-butanol.

Aluminum Pigment I: Silberline SS-5251 AR post treated with 4.5$ Vircopet 40 (phosphate ester commercially available from Albright & Wilson, Richmond, Va.)

Aluminum pigment II: Stapa Hydrolac WH-R607 from Eckhart Werke.

Aluminum pigment III: Stapa Hydrolac WH-8487 from Eckart Werke.

123456789 Thickener 2 40 37 37 38

Thickens 3 25 13 13

Melamine resin 444487412 ButylCellosolve 111112 1

Polyurethane 1 40 40 18

($30NW)

Polyurethane 2 44 42 38 17

($26NW)

Polyurethane 3 44 38

($26NW)

Aluminum 16 6 6 6

($54NW)

Aluminum II 5

($65NW)

Aluminum III 5 6

($65NW)

Butyl Cellosolve 111 4 2 1

Polyester 1 ($70) 6 6 3 Polyester 2 ($70) 6 6

Polyester 3 ($70) 6

Dimethylethanolamine 22221661

5$ strength in water

Thickener 1 27 27 17 17 Titanium dioxide paste 48 49 Deionized water 12 4 12 12

Examples 1 to 4

Melamine resin and Butyl Cellosolve are premixed and added to the thickener while stirring. The polyurethane dispersion is then added to this mixture with stirring. An aluminum mass is provided by first mixing aluminum pigment and butyl cellosolve, then adding polyester resin, and then finally preneutralizing this mass with a 5% DMEA solution. The aluminum mass is then added to the polyurethane/thickener/melamine mixture while stirring.

Example 5

Half of the melamine resin and butyl Cellosolve are premixed and added to the thickener while stirring. The polyurethane dispersion is then added. An aluminum mass is separately produced by mixing aluminum pigment, remaining butyl Cellosolve and melamine resin. The aluminum mass is then added while stirring to the rest of the paint. The pH is adjusted with 5% dimethylethanolamine in water.

Example 6

An aluminum mass is produced with aluminum pigment, melamine resin, and Butyl Cellosolve while stirring. The polyurethane dispersion is added to the aluminum mass. Thickeners are then added with stirring. The pH is adjusted with 5% DMEA and the viscosity is adjusted with deionized water.

Example 7

The polyurethane dispersion, melamine resin and Butyl Cellosolve are mixed with stirring. An aluminum mass is prepared as in examples 1 to 5 and added to the first mixture while stirring. The thickener is added while stirring. The viscosity is adjusted with deionized water.

Examples 8 and 9

Melamine resin and Butyl Cellosolve are pre-mixed and added while stirring to thicken 3. The polyurethane dispersion is then added while stirring. In Example 8, polyester resin is preneutralized with 5% DMEA and added with stirring. Thickener 1 (R972 paste) is added and then titanium dioxide paste is added, both while stirring.

Claims (3)

1. Method for the production of a multi-layer coating, characterized in that it includes: a) application of a water-borne base layer mixture comprising: (i) an anionic polyurethane resin consisting of the reaction product of: (1) a polyester resin component produced by the reaction of a carboxylic acid component with at least 50% by weight of at least one long-chain carboxylic acid with between 18 and 60 carbon atoms and at most 50% by weight of a short-chain dicarboxylic acid and an alcohol with at least 2 hydroxyl groups; and (2) a mixture of at least one multifunctional compound with at least 1 active hydrogen group and at least one carboxylic acid functionality, at least one compound with at least two active hydrogen groups and a polyisocyanate, the said carboxylic acid groups being neutralized with an amine; (ii) a cross-linking agent; (iii) a rheological control agent; (iv) optionally, a branched chain polyester resin consisting of the reaction product of: (1) a carboxylic acid component comprising at least 50 wt% of a long chain carboxylic acid with between 18 and 60 carbon atoms, not more than 48 wt% of a short chain dicarboxylic acid and between 2 and 25 wt-$ of a polyfunctional carboxylic acid or acid anhydride with at least 3 carboxylic acid groups; and (2) an alcoholic compound with an average alcohol functionality of at least 2; (v) a pigment; and (b) applying a clear top coating composition to overcoat said base composition. 2. Method for producing a water-based substrate mixture for use in a multi-layer coating, characterized in that it includes the following sequential steps; a) addition of crosslinking agent in solution to a rheology control agent in solution and then thoroughly mixing this: b) addition of an anionic polyurethane resin dispersion consisting of the reaction product of: (i) a polyester resin component prepared by the reaction of a carboxylic acid component consisting of at least 50 wt-# of a long-chain acid having between 18 and 60 carbon atoms and at most 50% of a short-chain dicarboxylic acid and an alcohol having at least 2 hydroxyl groups; and (ii) a mixture of a multifunctional compound having at least one active hydrogen functionality and at least one carboxylic acid functionality and at least one compound having at least two active hydrogen groups and a polyisocyanate, and wherein said carboxylic acid group is neutralized with an amine to the mixture in step (a) while stirring and thoroughly mixing; (c) adding a premixed mass consisting of: a mass prepared by premixing a branched chain polyester resin dispersion consisting of the reaction product of: 1) a carboxylic acid component consisting of at least 50 wt. % of a long-chain carboxylic acid having between 18 and 60 carbon atoms, and not more than 48 wt-# of a short-chain dicarboxylic acid and between 2 and 25 wt-$ of a polyfunctional carboxylic acid having at least 3 carboxylic acid groups; and 2) an alcohol component having an average functionality of at least 2 3) water and 4) an amine-containing compound to the mixture provided according to step (c); d) stirring the mixture provided from step (b) with the mixture from step (c); and e) adding pigment paste to the mixture obtained from step (d) under thorough mixing, f) adjusting the pH and viscosity of the mixture obtained from step (e). 3. Process for coating a car substrate with a multi-layer coating, characterized in that it includes: a) applying to a primed substrate a first layer of a water-based coating mixture consisting of: i) a polyurethane resin obtained from the reaction product of: 1) a polyester resin component produced by the reaction of a carboxylic acid component consisting of at least 50% by weight of a long-chain carboxylic acid having between 18 and 60 carbon atoms and at most 50% of a short-chain dicarboxylic acid and an alcohol having at least 2 hydroxyl groups; and 2) a mixture of a multifunctional compound which has at least one active hydrogen functionality and at least one carboxylic acid functionality, and at least one compound which has at least two active hydrogen groups, and polyisocyanate, where said carboxylic acid groups are neutralized with an amine; ii) a cross-linking agent; iii) a rheological control agent; and iv) a pigment paste; v) a branched polyester resin^b) drying by evaporation of said first layer at a temperature of between room temperature and 63° C. for between 30 seconds and 10 minutes; and c) applying at least one layer of a clear topcoat to said substrate; and d) curing said substrate and topcoat to a hard, durable film.