NO307259B1 - Multilayered metal or plastic substrate - Google Patents

Description

The present invention relates to a multi-coated metal or plastic substrate.

Multi-layer systems have been used to coat cars for a number of years, but the early development of these systems necessarily used organic solvents. As environmental regulations became more stringent and the costs of organic solvents rose, organically based systems became less desirable. The later research effort in the area of multilayer systems, especially base coating systems, has been focused on the development of waterborne systems for multilayer coatings.

A shift from organic solvents to water for dispersing and applying resins in a multilayer system solved many of the environmental and cost problems associated with the use of organic solvents. However, waterborne systems have brought other problems.

A solution to these problems has been the development of anionic polyurethane resins as described for example in US 4,179,168. These resins exhibit superior coating characteristics in many base/clear coat multi-layer systems. However, in certain cases these resins may not be compatible with highly acid catalyzed high solids melamine clear coatings due to the tendency to show some curling and further loss of DI (image distinctness), especially when light colored pigments (white, light blue, yellow and so on ) is used.

The present application is separated from NO-C 175.064.

This patent concerns a non-ionic, laterally, stabilized polyurethane resin which is characterized in that it comprises the reaction product of: a) one or more polyester polyols, possibly in a mixture with one or more organic compounds with two or

several reactive hydrogen functionalities;

b) a non-ionic stabilizer produced by reacting:

i) a monofunctional polyether with a single active

hydrogen functionality with a first polyisocyanate compound to give a partially end-capped isocyanate intermediate; and

ii) a compound with at least one active amine hydrogen and at least two active hydroxyl groups; and

c) at least one second isocyanate-containing compound,

d) as well as possibly a masking agent.

Reference should also be made to NO-C 178.108 which relates to a terminally stabilized polyurethane resin comprising the reaction product of: a) at least one organic compound with at least two reactive hydrogen functionalities;

b) a polyether containing at least one active hydrogen; and

c) a polyisocyanate.

The polyurethane resins described in these patents can

however, are used in the above-described melamine-containing systems without the negative characteristics shown by anionic resins. Thus, a combination of non-ionic polyurethane-based coatings with strongly acid catalyzed clear coatings allows a lower composite volatile organic content (VOC) than with anionic polyurethane-based coatings.

The resins have excellent water dispersibility properties, a surprising result considering the absence of salt-forming groups. It is particularly surprising that these resins retain their water dispersibility even when formulated as principal resins in base coat compositions. It is also a surprising result, considering the water dispersibility of these resins, that according to the resin the resins coalesce and stick to a vertical plate.

The resins can be formulated into ground-up resins for use in basecoats. However, aqueous dispersions of non-ionic polyurethanes are known in the literature and have been used to produce films and coatings. In general, polymer dispersions are unsuitable for use in ground-up pigments. It is rather surprising that the aqueous dispersions of the non-ionic polyurethanes as described in the above-mentioned applications are effective grinding resins for a wide range of pigments.

The present invention relates to a multi-coated metal or plastic substrate and this is characterized by the fact that it comprises the substrate coated with:

a) at least one waterborne base coating preparation comprising:

i) 20 to 80% by weight, calculated on the final solids in the base coating composition, of a linear polyurethane composition obtained by reacting: 1) at least one polyester polyol; 2) at least one low molecular weight alcoholic compound with at least two alcohol functionalities; 3) a non-ionic stabilizer prepared by reacting: a) a monofunctional polyether with a first polyisocyanate compound to obtain a

partially uncovered isocyanate intermediate;

and

b) a compound with at least one active amine hydrogen and at least two active hydroxyl groups; and 4) at least one second isocyanate-containing compound;

ii) 5 to 50 wt-# of a cross-linking agent selected

among aminoplast resin and polyisocyanate;

iii) optionally up to 20% of a rheology control agent selected from fumed silica components, bentonite clays and hectorite clays;

iv) 5 to 65% of a pigment paste;

as the base coating preparation is flash-dried before that

is coated with

b) a clear top coat, the base coat and top coat being cured to a hard durable film.

The above-mentioned patents describe two types of polyether-containing polyurethane resins. These two types are called laterally stabilized and terminally stabilized resins.

In particular, a laterally stabilized polyurethane coating preparation is described consisting of: 1) at least one organic compound with at least two reactive hydrogen atoms; 2) a nonionic stabilizer prepared by reacting: i) a monofunctional polyether with a first polyisocyanate-containing compound to produce a partially terminated isocyanate intermediate; and

ii) a compound with at least one active hydrogen and at least two active hydroxyl groups; and

3) at least one second polyisocyanate-containing compound.

The organic compound comprises a polyester polyol, a low molecular weight diol/triol or mixtures thereof. Optionally, a masking agent can be used to cover any remaining free isocyanate parts.

In addition, terminally stabilized polyurethane preparations are described consisting of: 1) at least one organic compound with at least two reactive hydrogen atoms;

2) a monofunctional polyether; and

3) a polyisocyanate.

The organic compound of the thermally stabilized polyurethane preparations preferably comprises a polyester polyol, a low molecular weight diol and/or triol or mixtures thereof. Optionally, a separate trifunctional hydroxyl-containing monomer is used for use in the polyurethane resin. Optionally, a covering agent is used to cover any free isocyanate parts.

In the laterally stabilized polyurethane resins, incorporation of polyether groups causes chain extension of the polyurethane resin. The polyurethane resins can be formulated as water-dispersed base coating preparations which, in addition to one of the resins described above, contain a grinding resin, a cross-linking resin, a thixotropy or rheology control agent, thickening agents, pigments, aluminum and/or mica particles, basifying agents, water, fillers, surfactants, stabilizers, plasticizers, wetting agents, dispersing agents, adhesion promoters, defoamers, catalysts and additional polymers.

In preferred embodiments of base coating preparations, the laterally stabilized polyurethane resin is used as paint-up resin.

After formulation, the base coating preparation can be sprayed or deposited on a car body, preferably in one or two coats. In general, two equal coats of base coat are applied with a few minute flash between coats. After depositing the base coat before applying a high-solids clear coat, it is generally preferred to flash off approx. 90% of the water from the base coat for optimal appearance and to eliminate water damage in the clear coat.

In both the linear and branched polyurethane resins, a polyester polyol resin is preferably a major component.

The polyester polyol resins described above are in themselves usable on virtually any elastomeric substrate, but they are particularly useful when formulated in polyurethane coatings and used in base coating formulations for deposition on metal or plastic substrates, especially car bodies. The polyester component can be of any type, for example branched or straight, and is formed by reacting at least one dicarboxylic acid component and at least one alcohol component in which the alcohol has at least two hydroxyl groups.

So to speak, any carboxylic acid-containing compound with two or more carboxylic acid moieties or equivalents which can be used when synthesizing polyester compounds are usable according to the invention.

The carboxylic acid component can of course consist of short-chain dicarboxylic acid compounds, long-chain dicarboxylic acid compounds or mixtures thereof.

Short-chain dicarboxylic acids mean compounds with at least two carboxylic acid groups and fewer than 18 carbon atoms in the chain. These dicarboxylic acids can be alkyl, alkylene, aralkyl, aralkylene or arylene, among others. In the polyester resins, the carboxylic acid-containing compound can be polyfunctional with two or more carboxyl groups. A preferred carboxylic compound for use in branched polyester resins is trimellitic anhydride. Short chain alkyl or aryldicarboxylic acid compounds such as azelaic acid, adipic acid or an equivalent aliphatic or aromatic acid are preferred. A preferred aromatic dicarboxylic acid is isophthalic acid.

The carboxylic acid component can also consist of a long-chain dicarboxylic acid component. This long-chain dicarboxylic acid-containing compound can be an alkyl, alkylene, aralkyl, aralkylene or equivalent compound, but it must be pointed out that virtually any long-chain dicarboxylic acid-containing compound can be used. A particularly preferred long-chain carboxylic acid-containing compound is the C36 dicarboxylic acid known as dimer acid. A discussion of dimer acid can be found in US 4,179,168. As with short chain dicarboxylic acid containing compounds, linear dicarboxylic acid containing compounds are preferred for use in linear polyurethane resins and linear or branched dicarboxylic acid containing compounds may be preferred and used in branched chain polyurethane resins.

In addition to the carboxylic acid-containing compound, the polyester resin also consists of one or more low molecular weight diols or triols. Here, any compound with more than one alcohol group is called a polyol. The polyols can be diols (dialcohol-containing), triols (trialcohol-containing) or higher alcohol-functional compounds in the case of branched-chain polyurethanes, as the amount and type of triol-containing compounds can be varied to increase the branching effect. A preferred trialcohol-containing compound for use in branched chain polyesters is trimethylolpropane.

The polyester resin or mixture of polyester resins used to synthesize the polyurethane resins is preferably hydroxyl terminated. This is accomplished by synthesizing the polyester using an excess of a diol- or triol-containing compound. The relative weight proportions of the carboxylic acid component and the alcoholic compound depend on the desired chain length in the polyester compound used. The result of this synthesis is a polyester with two or more free hydroxyl groups (polyesterdiol or polyol).

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

Monocarboxylic acids and monoalcohols can also be used in polyester synthesis, but these are generally used for chain termination of a polyester resin. As a general rule and where they are used, the monocarboxylic acids and/or monoalcohols comprise a very small percentage by weight of the final polyester resin.

As a general rule, the polyester diol component comprises between 20 and 80% by weight of the final polyurethane resin. Preferably, the polyester diol comprises between approx. 50 and 70 wt-# of the polyurethane resin and most preferably the polyester diol comprises between 55 and 65 wt-#.

While it is recognized that virtually any chain length of polyester polyol can be used, it is preferred to use a polyester diol within the molecular weight range of 500 and 5,000. Preferably, the molecular weight of the polyester diol component is between 1,000 and 3,500.

In addition to the polyester diol, the polyurethane resins also consist of additional organic compounds with at least two reactive hydrogen atoms. This component is preferably a low molecular weight diol or triol compound but may contain alcohol groups, thiols and/or amines or mixtures of these functionalities. The same alcohol-containing compounds used to synthesize the polyester-containing compound can be used as a separate component here. Thus, one each di- or trialcohol-containing compound can be used, for example neopentyl glycol and 1,6 hexanediol. High molecular weight diols and triols are not preferred, where the hydrophobicity of their molecular chains has an impact on the water dispersibility of the finished polyurethane resins. The purpose of this alcohol-containing component is to provide chain extension and/or branching via the isocyanate-containing compounds. Depending on the desired amount of chain extension and/or branching which is desirable in the finished polyurethane resins, different weight # proportions and types of diols and/or triols can thus be used. Where linear polyurethane resins are desired, the ratio of diol-containing compounds:triol-containing compounds can be higher than when branched chain polyurethane compounds are desired.

The amount of low molecular weight diol and/or triols used in the polyurethane resins can vary up to 20% by weight of the polyurethane resin. Preferably, this low molecular weight alcohol component comprises between up to 10% of the polyurethane resin and most preferably it is between 1 and 6% by weight of the polyurethane resin.

The polyurethane resins further comprise a polyisocyanate, preferably a diisocyanate. In general, the diisocyanate comprises between 5 and 40% by weight of the final polyurethane resin. Preferably, the diisocyanate comprises between approx. 10 and 30 wt-# of the final resin and most preferably the value lies between approx. 10 and 20 wt-# of the polyurethane resin.

A polyether-containing compound provides polyurethane resins with the preferred water dispersibility properties. These are attributed to the polyurethane resins according to the invention without the need to incorporate salt-forming groups in the resin. The absence of salt-forming groups enables the polyurethane resins to be incorporated into base coating preparations that can be used in combination with strongly acid-catalyzed high-solids melamine-containing clear coatings. This results in a lower VOC composite coating that does not exhibit the same curling, loss of DI (tanning) effects exhibited by cationic polyurethane resins.

The approach to synthesizing a laterally stabilized polyurethane utilizes a polyether diol prepared by reacting a monofunctional polyether with a diisocyanate to give a polyether half-capped diisocyanate. This half-covered diisocyanate is then reacted with a compound with one active amine hydrogen and at least two active hydroxyl groups to thereby give a non-ionic stabilizer (polyetherdiol) with a polyether chain, a urea moiety, a urethane moiety and two free hydroxyl groups.

Once synthesized, the non-ionic stabilizer is then added to a reaction mixture consisting of at least one organic compound with two or more reactive hydrogen functionalities, and an excess of a polyisocyanate-containing compound (in addition to that which is incorporated into the non-ionic stabilizer). Preferably, a polyester polyol is also added to obtain the polyurethane. Optionally, a capping agent such as trimethylolpropane or diethanolamine can be used to cover any remaining free isocyanate group. The resulting laterally stabilized polyurethane resin can be formulated into a base coating preparation and preferably used as a grinding resin. The laterally stabilized polyurethane resin can also be formulated as a principal resin.

The polyether component which gives water dispersible characteristics to the laterally stabilized branched chain polyurethane resin is a polyether with a functional group, for example methoxy polyethylene glycol among others. The polyether components are generally formed by using a monoalcohol-initiated polymerization of ethylene oxide, propylene oxide or mixtures thereof. The functional group on the polyether compound can be any group that is reactive with isocyanates to thereby form a stable product. Thus, the polyether compound may contain free hydroxyl, thiol or amine, but hydroxyl functionalities are preferred to minimize the possibility of salt formation.

In the laterally stabilized polyurethane resin, the monofunctional polyether compound as described earlier is reacted with a polyisocyanate-containing compound to give a semi-uncovered isocyanate. This half-capped isocyanate is then reacted with a compound containing an amino-active hydrogen and at least two free hydroxyl groups (or equivalent functionalities). This resulting product, called the nonionic stabilizer, is then incorporated into the polyurethane resin by reaction with the other components.

The monofunctional polyether compound is reacted with a mixture consisting of at least one polyester polyol, a polyisocyanate and, in addition, possibly a short chain low molecular weight diol or a higher functional polyol, or mixtures of diols and polyols. Optionally, a masking agent, for example trimethylolpropane or diethanolamine, can be used.

Preferably, the polyisocyanate in the laterally stabilized polyurethanes is a diisocyanate comprising between approx. 10 and 30$ and preferably between 10 and 20 weight-# polyurethane.

In laterally stabilized polyurethane resins, the polyether component can be multifunctional (the functional groups are hydroxyls, thiols or amines where the hydroxyl groups are preferred) and is preferably a mono- or difunctional polyether with monofunctional polyethers being particularly preferred. In general, water-soluble polyether-containing compounds are useful. Polyethers which are formed from the mono-alcohol initiated polymerization of ethylene oxide, propylene oxide or mixtures thereof are preferred. Of course, smaller amounts of butylene oxide ethers and other longer chain ethers can be incorporated into the polyether chain without adversely affecting the water dispersibility of the resins. Most preferably, the ethylene oxide polymers comprise 100% of the polyether component. In general, the polyether-containing component comprises between 20 and 40% by weight of the polyurethane, preferably between 8 and 30 and most preferably between 10 and 25% by weight of the final polyurethane resin.

The molecular weight of the polyether-containing compounds is generally within the range of 500 to 7,000, preferably 1,000 to 4,000 and preferably 1,200 to 3,000.

The polyurethanes are preferably storable and are, of course, water dispersible. The water dispersibility of the resins is controlled by the amount of polyether character contained in the final resin particles and the hydrophobicity of the non-polyether components.

The polyester component is not particularly critical, but it is necessary that the polyester component is compatible with the desired water dispersibility characteristics for the resins described here.

Thus, the carboxylic acid component in the polyester can consist of long-chain dicarboxylic acids, short-chain dicarboxylic acids, mixtures thereof or carboxylic acid equivalents such as anhydrides, lactones and polycarbonates, among others. Long-chain monocarboxylic acids can also be used, but these are generally used to chain-terminate the polyester resin.

The shorter chain carboxylic acid component can, if used, consist of a mono-, di- or higher functionality carboxylic acid or a mixture of such carboxylic acids with carbon chains of 18 or fewer carbon units. Monocarboxylic acids cause termination of a polyester chain and are chosen for this purpose. It is preferred that the short-chain carboxylic acid component is a dicarboxylic acid. Such preferred dicarboxylic acid compounds are, for example, adipic, azelaic and other aliphatic dicarboxylic acids, however, any dicarboxylic acid-containing compound which is compatible with the objective of maximizing water dispersibility can be used. Aromatic dicarboxylic acids can also be used. A particularly preferred aromatic dicarboxylic acid is isophthalic acid. Alkylene and aralkylene carboxylic acids can also be used. Where branched chains in the polyester are desirable, the carboxylic acid contains three or more carboxylic acid groups, for example citric acid. A preferred carboxylic acid-containing compound of this type is trimellitic anhydride. The polyester resins are synthesized 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. The polyol compounds preferably have an average hydroxy functionality of at least 2.

In most cases, the polyester resins consist of one or more polyols, preferably a diol. Up to approx. 25% by weight of the polyol component can be a polyol with three or more hydroxy groups per molecule. Where polyols with three or more hydroxy groups are chosen, the result is a branched polyester. As a general rule, the laterally stabilized polyurethane resin consists of a polyester with no more than approx. 15% by weight of the alcohol-containing component of a polyol with three or more alcohol functionalities.

While it is not always desirable to have a triol or higher multifunctional alcohol present due to the tendency to form a branched chain polyester, some branching may be desirable, especially in the case where the polyester is to be incorporated into a branched polyurethane. A small amount of monoalcohol may also be present in the polyol component, especially when larger proportions of higher functional alcohols are used. These monoalcohols serve as chain terminators.

The diols commonly used in the manufacture of the polyester resins include alkylene glycols such as ethylene glycol, propylene glycol, butylene glycol, neopentyl glycol, 1,6-dihexane diol and other glycols such as hydrogenated bisphenol A, cyclohexane dimethanol, caprolactone diol (that is, the reaction product of caprolactone and ethylene glycol) , hydroxyalkylated bisphenols and the like. However, other diols of various types, and, as indicated, polyols of higher functionality, may also be used. Such higher functionality alcohols may include, for example, trimethylpropane, trimethylolethane, pentaerythritol and the like, as well as higher molecular weight polyols.

The low molecular weight diolenes which are preferred are well known in the art. They have hydroxy values of 200 or more, usually in the range of approx. 1,500 to 2,000. Such substances include aliphatic diols and especially alkylene polyols containing from 2 to 18 carbon atoms. Examples are ethylene glycol, 1,4-butanediol, cycloaliphatic diols such as 1,2 cyclohexanediol and cyclohexanedimethanol. A particularly preferred diol is 1,6 hexanediol.

To produce the laterally stabilized polyurethane resins that can be used in base coating preparations, the polyester polyol described above is reacted with a mixture of a polyisocyanate, possibly a low molecular weight diol and/or triol and a non-ionic stabilizer consisting partly of a polyether-containing compound. Two general synthesis approaches are used to synthesize the polyurethane resins. A first approach is to react all products in a flask using an excess of hydroxy equivalents when synthesizing the polyurethane resin (capping occurs simultaneously with synthesis of the polyurethane resin). Alternatively, an excess of isocyanate can be used to give a polyurethane intermediate which is then covered with a capping agent such as trimethylolpropane, diethanolamine, diols or mixtures of diols, triols and so on.

The polyester polyol, the polyisocyanate, the low molecular weight diols and/or triols and the nonionic stabilizer may be reacted in the same flask or may be reacted sequentially depending on the desired results. Sequential conversion produces resins that are more ordered in structure. Both polyester and triol-containing compounds can serve as chain extenders to build up the polyurethane backbone by reaction between hydroxyl groups and isocyanate groups. Additional chain extenders with at least two active hydroxyl groups (diols, thiols, amines or mixtures of these functional groups) can be added to increase the chain length or to change the chemical characteristics of the polyurethane resin. An excess of the polyisocyanate is preferably used so that a polyurethane resin intermediate product with free isocyanate groups at the ends can be produced. The free isocyanate groups can then preferably be covered with trimethylolpropane or dimethanolamine. The low molecular weight diols/triols/higher functional alcohols used as a separate component in synthesizing the polyurethane resins include alkylene glycols, for example ethylene glycol, propylene glycol, butylene glycol and neopentyl glycol among others. Additional alkylene glycols include cyclohexanedimethylol and caprolactonediol. Examples of higher functional alcohols are trimethylolpropane, trimethylolethane and pentaerythritol.

The organic polyisocyanate which is reacted with the polyester polyol and the low molecular weight diol and/or triol as described is essentially any polyisocyanate, that is to say a compound which contains at least two isocyanate groups and is preferably an isocyanate, for example hydrocarbon diisocyanates or substituted hydrocarbon bon 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 (isocyanate ethyl fumarate), isoporone diisocyanate (IPDI) and methylene bis-(4-cyclohexyl isocyanate). Isocyanate-terminated adducts of diols such as ethylene glycol or 1,4-butylene glycol can also be used. These are obtained by reacting more than 1 mole of a diisocyanate such as those mentioned, with 1 mole of a diol to give a longer chain diisocyanate. Alternatively, the diol can be added together with the diisocyanate. When the diisocyanates are preferred, other multifunctional diisocyanates can be used. Examples are 1,2,4-benzene triisocyanate and polymethylene polyphenyl isocyanate.

It is preferred to use an aliphatic diisocyanate as it has been found that these provide better color stability in the finished coating. Examples include 1,6-hexamethylene diisocyanate, 1,4-butylene diisocyanate, methylene bis(4-cyclohexyl isocyanate) and isoporone diisocyanate. 2,4-toluene diisocyanates are also preferred. Mixtures of diisocyanates can also be used.

The proportions of diisocyanate, polyester, diol and/or triol component and non-ionic stabilizer or monofunctional polyether are selected to obtain an isocyanate-terminated polyurethane resin intermediate. This can be achieved by using a stoichiometric excess of polyisocyanate, i.e. more than one isocyanate group per nucleophilic part (reactive with isocyanate) in the other components. The free isocyanates that remain after the reaction can be covered with a covering agent, for example trimethylolpropane.

Longer-chain polyurethane resins can be obtained by chain extension of the polyurethane chain with diol- and/or triol-containing compounds. In addition, although not preferred, further chain extender compounds with at least two active hydrogen groups, for example diols, dithiols, diamines, or compounds with a mixture of hydroxyl, thiol and amine groups, for example alkanolamines, aminoalkyl mercaptans and hydroxyalkyl mercaptans can be used . For the purposes of this aspect of the invention, both primary and secondary amine groups are considered to have an active hydrogen. Alkanolamines, for example ethanolamine or diethanolamine, can be used as chain extenders and most preferably a diol is used.

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. Polyhydroxy compounds containing at least three hydroxyl groups can also be used as chain extenders; the use of these compounds gives branched polyurethane resins. For the purpose of the invention and if it is preferred to minimize the amount of branching in the polyurethane resin, these polyhydroxy compounds should be limited to a very small component of the polyurethane manufacturing mixture. These higher functionality polyhydroxy compounds include, for example, trimethylolpropane, trimethylolethane, pentaerythritol among other compounds.

The polyurethane resin can be chain extended in any way by using these diol- and triol-containing compounds or alternative compounds with at least two active hydrogen groups. Thus, these compounds can be added to the mixture of polyisocyanate, polyester and polyether-containing compound (non-ionic stabilizer or monofunctional polyether compound) or alternatively reacted in an intermediate step to connect two free isocyanate groups present at the terminal ends of the polyurethane resin intermediate.

The polyether-containing compounds as described above are preferably mono- or difunctional polyethers with monofunctional polyethers being preferred. The monofunctional polyethers are preferably formed from monoalcohol-initiated polymerization of ethylene oxide, propylene oxide and mixtures thereof. A polyether compound consisting of 100% ethylene oxide units is particularly preferred. In the most preferred embodiment, the monofunctional polyether comprises between 10 and 25% by weight of the finished polyurethane resin and has a molecular weight of between 1,200 and 3,000.

It is generally preferred that the polyurethane resin intermediate produced by reaction of the polyester resin and the mixture of polyisocyanate, diol/triol mixture and polyether-containing compound is terminated with free isocyanate groups. To achieve this, an excess of the polyisocyanate compound is used. Thus, diols/triols, polyether component and polyester diol will all react with the isocyanate parts to thereby give polyurethane resins with at least some free isocyanate groups. Of course, the molar ratio between the other components will be adjusted according to the desired characteristics of the intermediate and final polyurethane resins.

In a particularly preferred embodiment, a multifunctional alcohol, for example trimethylolpropane, is used to terminate the reactions (cover the free isocyanate group) at the desired stage (determined by the viscosity and isocyanate groups present) and thereby also contribute residual hydroxyl groups. Particularly desirable for such purposes are amino alcohols such as ethanolamine, diethanolamine and the like because the amino groups preferably react with the isocyanate groups present. These masking agents are particularly preferred for use in the grinding resin aspect according to the invention. Multifunctional alcohols such as ethylene glycol, trimethylolpropane and hydroxyl-terminated polyesters can also be used in this way.

While the ratios between the components polyester, multifunctional isocyanate, diol triol mixture, polyether-containing compounds and the masking agent can be varied, the person skilled in the art will have noticed that the amounts should be chosen so as to avoid gel formation in order to thereby produce a non-gelled urethane reaction product containing hydroxyl groups. The hydroxyl number of the final polyurethane reaction product will be at least 5 and preferably between 20 and approx. 200.

The amount of polyisocyanate used in the mixture is preferably between 10 and 30% by weight of the reactants in the mixture and is most preferably between approx. 10 and 20$ but will vary depending on the polyester used and the desired molecular weight for the final polyurethane resin. The amount of polyisocyanate will also vary depending on whether it is desirable to have the polyurethane intermediate terminated with free isocyanate groups or with hydroxyl groups. Where it is thus preferred to terminate the polyurethane resin intermediate with free isocyanates for capping with trimethylolpropane or diethanolamine, an excess of polyisocyanate can be used. Where the polyurethane resin intermediate is to be terminated with hydroxyl groups, a stoichiometric deficit of polyisocyanate can be used.

The polyurethane resins are formulated together with other components into water-dispersible base coating preparations which are sprayed or electrostatically deposited on metal or plastic substrates, for example car bodies. In general, a polyurethane resin, formulated as described above, is mixed with an aminoplast resin, a polyisocyanate cross-linking agent, a grinding resin, water, a portion of an organic solvent, pigments and a rheology controlling agent. Other agents can be incorporated, for example various fillers, surfactants, plasticizers, stabilizers, wetting agents, dispersants, defoamers, adhesion promoters and catalysts in smaller amounts. In one embodiment, a branched chain polyester component can also be added to the base coating composition.

As indicated, an aqueous dispersion of the polyurethane resin is used as principal or mainly carrier resin. In general, the principal or main carrier resin comprises between 20-80% by weight of the total solids present in the base coating composition. An acceptable polyurethane resin for use as a primary resin is a resin prepared from a polyester synthesized from dimer fatty acid, isophthalic acid and 1,6 hexanediol. The resulting polyester is then reacted with a diisocyanate of isoporone, a triol and a polyether monoalcohol and a diol, for example neopentyl glycol. The resulting polyurethane intermediate with free isocyanate groups is then reacted with trimethylolpropane to cover these groups.

The polyurethane reaction product is mixed as described above with an aminoplast resin or a polyisocyanate cross-linking agent. The aminoplast resin is the aldehyde condensation product from melamine, urea and similar compounds. Products obtained from the reaction of formaldehyde with melamine, urea or benzoguanamine are most common and are preferred here. However, condensation products of other amines and amides 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 ureas 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-diamino-triazole, triamine pyrimidine, 2-mercapto-4,6-diamino-pyrimidine, 2,4,6-triethyl triamino-1,3,5-triazine and the like.

While the most frequently used aldehyde is formaldehyde, other similar condensation products can be produced from other aldehydes, for example acetaldehyde, crotonaldehyde acrolein, benzaldehyde, furfural and others.

The amine aldehyde condensation products may contain methylol or corresponding alkylol groups and in most cases at least a proportion of these alkylol groups are etherified by reaction with an alcohol to give organic solvent soluble resins. Any monohydroxy alcohol can be used for this purpose including such alcohols as methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, as well as benzyl alcohol and aromatic alcohol, cyclic alcohols, for example cyclohexanol, monoethers of glycols such as "Cellosolves" and "Carbitol ", and halogen-substituted or other substituted alcohols such as 3-chloropropanol. The preferred amine aldehyde resins are etherified with methanol or butanol.

Alternatively, isocyanate-containing compounds such as those previously described can be used as cross-linking agents. When polyisocyanates are used, they generally make up between 5 and 50$ of the base coating preparation. Preferably, a fully blocked polyisocyanate is used as crosslinking agent.

In the production of the blocked organic polyisocyanate, any suitable organic polyisocyanate can be used.

Examples are aliphatic compounds such as trimethylene, tetramethylene, hexamethylene, 1,2-propylene, 1,2-butylene, 2,3-butylene, 1,3-butylene, ethylidine and butylidine diisocyanates; cycloalkylene compounds such as 1,2-cyclopentane, 1,4-cyclohexane and 1,2-cyclohexane diisocyanates, aromatic compounds such as phenylene, p-phenylene, 4,4'-diphenyl, 1,5-naphthalene and 1,4-naphthalene diisocyanates, aliphatic -aromatic compounds such as 4,4' diphenylmethane, 2,4- or 2,6-tolylene or mixtures thereof, 4,4' soluidine and 1,4-xylylene diisocyanates: nuclear substituted aromatic compounds such as dianisidine diisocyanate, 4,4' -diphenyl ether diisocyanate and chlorodiphenylene diisocyanate, triisocyanates such as triphenylmethane-4,4',4"-triisocyanate, 1,3,5-triisocyanatebenzene and 2,4,6-triisocyanates such as 4,4'-diphenyl-dimethylmethane 2,2 ', 5,5'-tetraisocyanate; polymerized isocyanates such as tolylene diisocyanate dimers and trimers and the like.

Any suitable aliphatic, cycloaliphatic, aromatic alkyl monoalcohol and phenolic compound can be used as blocking agent, for example lower aliphatic alcohols such as methyl, ethyl, chloroethyl, propyl, butyl, cyclohexyl, heptyl, octyl, nonyl 3,3,5 -trimethylhexanol, decyl and lauryl alcohols and the like, aromatic alkyl alcohols such as phenylcarbinol, methylphenylcarbinol, ethyl glycol monoethyl ether, ethyl glycol monobutyl ether and the like; phenolic compounds such as phenol itself, substituted phenols where the substituents do not adversely affect the coating. Examples are cresol, xylenol, nitrophenol, chlorophenol, ethylphenol, 1-butylphenol and 2,5-di-t-butyl-4-hydroxy toluene. Smaller amounts of higher molecular weight, relatively non-volatile monoalcohols can also be used.

Additional blocking agents include tertiary hydroxylamines such as diethylethanolamine and oximes such as methyl ethyl ketone oxime, acetone oxime and cyclohexanone oxime. The use of oximes and phenols are particularly useful because specific polyisocyanates blocked with these agents are revealed at relatively low temperatures without the need for externally added urethane-forming catalysts such as those described below.

The organic polyisocyanate blocking agent adduct is formed by reacting a sufficient amount of blocking agent with the organic polyisocyanate to ensure that no free isocyanate groups are present.

Pigments can be incorporated into the base coating preparation to provide the desired cosmetic characteristics. This takes place by mixing pigments with the above-described grinding resin and, in addition, any aminoplast resin to thereby produce a pigment paste according to the invention. In a preferred embodiment, the methodology for producing a pigment paste with the non-ionic polyurethane resins according to the invention is simplified compared to that used to produce pigment paste with anionic polyurethane resins. In this method, a non-ionic polyurethane resin is simply mixed with the pigment. Aminoplast crosslinking agents can also be added, but such an addition is not preferred.

The final pigment paste comprises 3 to 65 wt-# of pigment and 5 to 65 wt-# of laterally terminated stabilized polyurethane resin and optionally up to 50 wt-# of a cross-linking agent.

Any standard pigment known in the art can be used with the resins as long as the pigments can be formulated without affecting the desired characteristics of the resin. Specific examples of dyes or pigments may be inorganic or organic, for example graphite, carbon black, zinc chromate, strontium chromate, barium chromate, lead chromates, lead cyamide, titanium dioxide, zinc oxide, cadmium sulphide, iron oxide, aluminum flakes, zinc sulphide, phthalcyamine complexes, naphthol red, quinine -dons and halogenated thioindigo pigments among others.

Preferred aluminum flake pigments are available commercially from various sources. The aluminum flake pigments give the coating an improved "metallic varnish". In a preferred embodiment of the invention, standard-quality aluminum stabilized with phosphate ester is used. Other metal flake pigments such as silver can also be used. The metallic pigments can also be mixed with non-metallic pigments, but these must be carefully selected so as not to reduce the desired "metallic" effect. The resinous dispersions of the base coating in the preparations are dispersed in deionized water. It is preferred that the deionized water has conductance values of less than 13 jjfl-<1> and preferably less than approx. 5uf?-<1> to prevent gas formation caused by the reaction between aluminum and water. Deionized water is also chosen to avoid the salts that naturally occur in tap water. Other solvents can also be used together with deionized water. A particularly preferred solvent is "Butyl Cellosolve" which supports the mixing, formulation and dispersion of pigment in the base coating preparation. Other solvents can also be used, for example low-boiling mono- and polyhydroxyalcohols, ethers, esters, ketones and other organic substances. The organic solvent which makes up no more than 80% of the base coating preparation and preferably makes up approx. 10 to 20 wt# of this (including water) may be selected to promote the dispersibility of individual components in the final basecoat formulation (plasticizer characteristics) and because of its low volatility characteristics.

A rheology control agent is also preferably incorporated into the base coat preparation. The rheology control agent controls the viscosity of the resulting formulation and is incorporated in amounts that prevent seepage or creep after a base coat is sprayed onto a vertical surface such as a car body. The direct result of incorporating a rheology control agent is to provide flow control, sprayability and the like. Another beneficial result of adding rheology control agents is to allow the deposition of a heavier coating, also to allow more total coverage of a substrate. Sprayed-on coatings containing these agents also show a greater orientation of the flake pigments on the ready-coated substrate. Rheology control agents that can be used in embodiments of the invention include fumed silica compounds and bentonite clays. Preferred silica compounds are hydrophobic silica compounds such as available "Aerosil" R972. Other rheology control agents which may be used and in certain base coating preparations may be preferred, is a synthetic sodium lithium magnesium silicate hectorite clay. An example of such a clay is the commercially available "Laponite" RD. In certain preferred embodiments, rheology control agents are mixed. Rheology control agents make up, if incorporated, up to 20% by weight of the base coating preparation and preferably between 1 and 5% of the final base coating composition.

In general, the particle size of the rheology control agent plays a role in the overall thixotropic properties of these resins. Rheology control agents in embodiments according to the invention are suspended in the material. It can be suggested that the suspended rheology control agent acts at least in part via coulombic or electrostatic interactions.

In general, particle size can be from less than 0.01 pm to over approx. 200 p.m. These sizes can be adapted to partially develop the desired rheological properties. Under special circumstances, the particle sizes can be from approx. 1 to 10 p.m.

Other additional agents are used, for example surfactants, fillers, stabilizers, wetting agents, dispersants, adhesion promoters and so on and these can be incorporated into the base coating preparation. While the agents are well known in the art, the amount used must be carefully regulated to avoid adversely affecting the coating and quick drying properties.

The finished base coating mixture is adjusted to a pH value of between 6 and 8. The viscosity can be adjusted by using deionized water. Finished base coating preparations consist of the following components in the indicated weight ratios.

The base coating compositions described above can be applied to a metal or plastic substrate in one or two coats using, for example, a commercial type air atomizer "Binks" model 60 spray gun or by using other commercial spray devices. The base coating preparations are preferably sprayed on at a pressure of 3.5-5.6 kg/cm^ and a relative humidity of between 50 and 90% (optimal at 60-80$ relative humidity) and a temperature of 21-32°C.

After deposition, the base coating preparations are flash dried within a temperature range from approx. room temperature and up to 63° C. The preferred flash temperature is approx. 50°C. The flash conditions described here result in approx. 90% of the solvents (water + organic substances) are flashed from the base coating within a short time.

After the first base coat has been deposited, a second base coat can be deposited over the first without drying (flash off); Alternatively, a clear coat can be deposited over the flashed base coat. It is a surprising result of the use of the non-ionic resins that when direct shade (non-metallic) or metallic pigments are used, a coating of base coating can be used to provide excellent cosmetic characteristics. Any number of clear coat compositions known in the art may be used. Any non-pigmented or other transparent pigmented coating agent is in principle suitable for use as a top coating. A typical topcoat formulation contains 30 to b0% film-forming resin and 40 to 70% volatile organic solvent.

After the clear coat is coated on the base coat layer, the multilayer coating is fired to cross-link the polymer carrier and drive the small amount of residual water and organic solvent out of the multilayer polymer preparation. A preferred firing step involves heating the coated substrate for a period of 10 to 60 minutes at temperatures between 150 and 300°F. This step hardens the coating into a hard, durable film.

This final multi-layer coated substrate according to the invention comprises: a) a waterborne base coating preparation comprising 20 to 80% by weight of the base coating preparation of a polyurethane mixture; b) 5 to 50 wt% of a cross-linking agent; c) optionally up to 20 weight-$ of a rheology control agent;

d) 5 to 65% by weight of a pigment paste; and

e) a clear top coating.

The invention shall be further described in connection with

the examples that follow below. These examples are shown by way of illustration of the invention. All parts and percentages in the examples are by weight unless otherwise stated.

Example 1: Production of polyester resin A

A polyester polyol resin is prepared by charging a reaction flask equipped with a fractionating column with 551.9 g or 15.8$ of the polyester resin of isophthalic acid, 1923 g or 54.9$ of "Empol 1010" (dimer fatty acid) and 1025.1 g or 29.3 $ 1,6-hexanediol and 100 g of toluene. Additional toluene can be added to fill the trap. The mixture was heated under nitrogen and water of condensation was removed. During this heating, 235.7 g of water was distilled. The heating was continued at approx. 200°C until the acid number is less than or equal to 8. The remaining toluene is then vacuum stripped at 200°C to thereby give a polyester resin for use in the polyurethane resin.

Example 2: Production of polyester B

A reaction container is charged with 960.0 g corresponding to 43.5 wt-$ neopentyl glycol, 664.6 g corresponding to 30.1 wt-$ isophthalic acid, 84.7 g corresponding to 26.5 wt-$ adipic acid and 50 g toluene. The mixture is heated under nitrogen to 240°C until an acid number of 3.5 is achieved.

Example 3a: Production of laterally stabilized polyurethane resins

Linear non-ionic PE/PU "main resin" Preparation of a methoxypolyetherdiol.

A carbowax diol is prepared by charging a flask with 4538 g of methoxypolyethylene glycol 2000 and 1015 g of toluene. The mixture is heated to reflux to remove water present in the carbon wax. When all the water has been removed, the temperature is reduced to 50°C and 4.5 g of benzoyl chloride is added and allowed to mix for 10 minutes. At this point, 394.7 g of toluene diisocyanate is added to the flask and the whole is heated to 70°C and held until the suitable isocyanate numbers are reached. The heat is turned off and 249 g of diethanolamine is added to the flask. When the exotherm is complete, the batch is held for 10 minutes. Then a vacuum stripping is started to remove all the toluene. When all the toluene is removed, the diol is ready for use in polyurethane production .

Preparation of a polyurethane resin.

A flask is charged with 600 g of polyester A (example = 1), 100 g of carbowax diol, 50.2 g of neopentyl glycol, 249.8 g of isophorone diisocyanate and 205 g of propylene glycol monomethyl ether acetate. The mixture is heated to 125°C and converted to a constant isocyanate value. 44.8 g of trimethylolpropane are then added and the whole is reacted for 1 hour at 125°C. The batch is then cooled to 110°C and 362.2 g of ethylene glycol monobutyl ether is added. Then, 1632.2 g of deionized water is added with high stirring to thereby give a dispersion.

Example 3B: Grinding resin - Laterally stabilized non-ionic PE/ PV

Preparation of a carbowax diol

A carbowax diol is prepared by charging a flask with 4538 g of methoxy polyethylene glycol 2000 and 1015 g of toluene. The mixture is heated to reflux to remove water present in the carbon wax. When all the water has been removed, the temperature is reduced to 50°C and 4.5 benzoyl chloride is added and the whole mixture is allowed to mix for 10 minutes. At this point, 394.76 g of toluene diisocyanate are added to the flask and the whole is heated to 70°C and held there until the suitable isocyanate number is achieved. The heat is turned off and 249 g of diethanolamine is added to the flask. When the exotherm is finished, the whole thing is held for 10 minutes. A vacuum stripping is then started to remove all the toluene. When all the toluene has been removed, the diol is ready for use in polyurethane production.

Preparation of a polyurethane resin

A flask is charged with 600 g of polyester A (example = 1), 100 g of carbowax diol, 50.2 g of neophentyl glycol, 249.8 g of isophorone diisocyanate and 205 g of propylene glycol monomethyl ether acetate. The mixture is heated to 125°C and converted to a constant isocyanate number. The whole is then cooled to 110°C and 35 g of diethanolamine is added. 1632.2 g of deionized water are then added with high stirring to thereby give a dispersion.

Example 4: Production of a silver metallic base coating using laterally stabilized non-ionic resin

The polyurethane resin from Example 5 was slowly added to 2$ "Laponite" paste with vigorous stirring. In a separate container, the aluminum slurry is prepared by mixing aluminum paste, phosphate ester solution and melamine while stirring. The aluminum slurry was slowly added to the resin mixture with high agitation. Deionized water is added to reduce the viscosity of the paint to 14 seconds (No. 2 FISHER CUP). The pH value in the paint is 6.7.

Example 5: Comparative example: Preparation of a silver metallic base coating using terminal-stabilized non-ionic resin

The paint is produced according to example 8 except that the terminally stabilized polyurethane resin from example 4 is used. The paint has a viscosity of 14 seconds (no. 2

FISHER CUP).

Comparison study: Lateral stabilization versus terminal stabilization silver metallic base coating

The silver metallic basecoats from Examples 4 and 5 were sprayed side by side using an automatic siphon spray gun. Both paints were sprayed at 65 psi over primed steel plates at 28°C and 44% relative humidity. The plate was heat treated at 122°C for 30 minutes and the metallic effect was judged by comparison with a series of five standard silver metallic plates (1 = best). The results were as follows:

The silver metallic basecoats from Examples 4 and 5 were sprayed again at 20°C and 80% relative humidity to test the seepage resistance of the paint. After heat treatment of the plates for 30 minutes at 122°C, a relative seepage resistance value was given to each plate (1 = best, no seepage; 5 = worst, strong seepage). The results are as follows:

The following examples of pigment build-up pastes and direct shade paints can be used on both types of urethanes [that is, both lateral stabilization and terminal stabilization].

Example 6: Preparation of a TiOaPigment paste

Dispersion of Ti02

The non-ionic urethane dispersions were used to paint up, for example, T102 of commercial type and more specifically using the type R960HGHG as in the example below:

The urethane dispersion is placed in an 8 l container equipped with a propeller-type agitator. This dry TiO 2 is added to the ground dispersion. Deionized water is used to maintain a fluid paste. After the pigment has been added, the slurry is stirred for 30 minutes. The viscosity is adjusted to 75 to 95 Krebs units (700-1500 cP) with water. Stirring is continued for 15 minutes. The paste is fed through a commercial-type gravity-fed sand mill, charged with ceramic or glass media. Particle sizes of 0 to 6.5 pm are reached with one or two passes.

Example 7: Preparation of a blue pigment paste disperse. ion of phthalocyanine blue pigments

The non-ionic urethane dispersions are used to paint up phthalocyanine pigments, for example the commercially available X3485 as in the example below

The urethane dispersion is placed in an 8 l container equipped with a propeller-type agitator. The dry pigment is added to the stirred dispersion. After adding the pigment, the slurry is stirred for 30 minutes. Deionized water can be added if necessary to achieve a viscosity of 60 to 85 Krebs units (500 - 1000 cP). The stirring is then continued for 15 minutes. The paste is then fed through a gravity-fed sand mill as described above until the particle size is 0 - 12 µm.

Example 8: Production of a perylene pigment paste-disperse. lon of perylene pigments

The non-ionic urethane dispersions are used to paint up perylene pigments of commercial type, more particularly R6424:

The urethane dispersion is placed in an 8 l container with a propeller-type agitator. The dry pigment is added to the stirred dispersion. Stirring is continued for 30 minutes after the pigment has been added. Deionized water can be added if necessary to achieve a viscosity of 50 - 85 Krebs units

(200 - 1000 cP). The slurry is then fed to a commercial type attritor, charged with stainless steel elements. After 4-8 hours the particle size is 6.5 pm.

Example 9: Preparation of a soot pigment paste disper-s. ion of soot pigments

The non-ionic urethane dispersions were used to paint up commercial type soot pigments, more specifically Cabot Black Pearls 1300 in the example below:

The urethane dispersion is placed in an 8 l container with a propeller-type agitator. The dry pigment is added to the dispersion. Stirring is continued for 30 minutes after the pigment has been added. If necessary, deionized water is added to achieve a viscosity of 50 - 85 Krebs units (200 -1000 cP). The slurry is then fed to a commercial type attritor, charged with stainless steel elements. After 4-8 hours the particle size is 6-12 pm.

Example 10: Preparation of a non-ionic white base coating

Part A is mixed under high stirring for two hours. Part B is added slowly with stirring followed by part C.

Part D is ground separately in a mill and this and parts E and F are added while stirring. Final adjustments in viscosity are carried out with deionised water. The pH value in the base coating is 6.0 to 8.0.

Claims (1)

Multi-coated metal or plastic substrate, characterized in that it comprises the substrate coated with: a) at least one water-borne base coating preparation comprising: i) 20 to 80 weight-$, calculated on the final solids in the base coating preparation, of a linear polyurethane preparation obtained by reacting: 1) at least one polyester polyol; 2) at least one low molecular weight alcoholic compound with at least two alcohol functionalities; 3) a nonionic stabilizer prepared by reacting: a) a monofunctional polyether with a first polyisocyanate compound to obtain a partially uncovered isocyanate intermediate; and b) a compound with at least one active amine hydrogen and at least two active hydroxyl groups; and 4) at least one second isocyanate-containing compound; ii) 5 to 50 wt-$ of a cross-linking agent selected among aminoplast resin and polyisocyanate; lii) possibly up to 20% of a rheology control agent selected from fumed silica components, bentonite clays and hectorite clays; iv) $5 to $65 of a pigment paste; in that the base coating preparation is flash-dried before it is coated with b) a clear top coating, in that the base coating and the top coating are hardened to a hard, durable film.