CS244671B2 - Coating material - Google Patents

Abstract

A coating composition comprising a liquid diluent and film-forming components A/ and B/ in a weight ratio A:B ranging from 95:5 to 85:15, where A/ represents a film-forming polymer and B/ microparticles of a crosslinked adduct polymer, which can be prepared by polymerizing a mixture of ethylenically unsaturated monomers in a dispersion in a liquid aliphatic hydrocarbon. In the presence of a steric dispersion stabilizer, which is a graft copolymer comprising a main chain of an acrylic polymer that is unsolvable in the liquid hydrocarbon and a plurality of side chains that are solvable in the liquid hydrocarbon formed by residues of poly/12-hydroxystearic acid/, attached to the main polymer chain, which graft copolymer is contained in the liquid hydrocarbon.

Description

The invention relates to coating compositions containing polymer microparticles.

The preparation of polymer particles and their addition to coating compositions containing a film-forming polymer has been described, for example, in BP No. 967,051, 1,242,051, 1,451,948 and 1,538,151, in USP No. 4,025,474, in DT-OS 2,818,093, 2,818,094, 2,818,095, 2,818,100, 2,818,102 and in European patent applications No. 78,300,095 and 78,300,419. In some of these publications, the particles are referred to as microgel particles. In such a case, the polymer from which the particles are formed is crosslinked to a greater or lesser extent, which makes it insoluble in all inert liquid diluents used as carriers for the film-forming polymer of the coating composition. However, the microgel particles may be swollen by this diluent. In other cases, the microparticles may be uncrosslinked and yet retain their identity in the coating compositions because the polymer from which they are formed is insoluble in the diluent used.

Such microparticles are typically prepared by dispersion polymerization of monomers in suitable liquids in the presence of polymeric stabilizers to stabilize the dispersion of the resulting polymer particles. The microparticles may then be sterically stabilized against flocculation or aggregation as described in Dispersion Polymerization in Organic Media, ed.

K. E. J. Barrett (John Wiley, 1975) and in many patent publications, such as BP No. 934,038,

941,305, 1,052,241, 1,122,397, 1,143,404 and 1,231,614.

Two types of such dispersion polymerization processes can be distinguished. In the first case, which is described in the above-mentioned BP No. 1,451,948, microgel particles are formed as a by-product of the dispersion polymerization of ethylenically unsaturated monomers in the presence of so-called polyfunctional stabilizers. These stabilizers have characteristic features in terms of the structure of their molecules that are common to all sterically stabilizing substances, i.e. they contain a polymer component of the molecule that is solvated by the continuous phase of the dispersion and another component that is associated with the dispersed phase. In addition, however, they contain a larger number of groups that are capable of copolymerizing with the monomers polymerized in the dispersion.

The main result of using such a stabilizer (which is more generally described in BP No. 1,231,614) is that the stabilizer is covalently bound to the dispersion polymer. However, there is a side effect that while the greater part of the polymer formed as the dispersion phase is uncrosslinked, a small part is crosslinked. The crosslinking of this small part of the polymer occurs by the action of the copolymerizable groups of the stabilizer. When a sufficient amount of an effective solvent of the uncrosslinked dispersion polymer is added to the dispersion thus obtained, a solution-type coating composition can be produced in which the uncrosslinked polymer forms the main film-forming substance, but in which the crosslinked microgel remains in the form of insoluble, separate and sterically stabilized particles. However, in this method, it is difficult to control the mutual ratio of the amount of microgel to the uncrosslinked polymer formed, and it is also difficult to control the molecular weight of the uncrosslinked polymer without adversely affecting the yield of the microgel. In doing so, control of the molecular weight of the uncrosslinked polymer may be desirable to optimize its film-forming properties.

Furthermore, it is of course inevitable that the microgel produced in this way has essentially the same monomer composition as the uncrosslinked polymer.

In the second method of producing microparticles, which is described in BP No. 1,538,151 and in the DT-OS and European patent applications cited above, the particles are produced essentially as a single dispersant. Here, crosslinking is achieved by the presence in the polymerized monomer feed of pairs of comonomers carrying mutually chemically reactive groups (except for copolymerizable groups). The reaction of these groups can result in covalent crosslinks between the polymer chains. Various combinations of mutually reactive groups have been proposed, for example epoxy group - carboxy group, amino group - carboxy group, epoxy group - carboxylic acid anhydride group, amino group, - carboxylic acid anhydride group, hydroxy group - carboxylic acid anhydride group, amino group - carboxylic acid chloride group, alkylamino group - carboxy group and organoalkoxysilane group - carboxy group.

Since the microparticles produced by this process are not accompanied by large amounts of other polymer products, they can easily be added in any amount to coating compositions based on film-forming resins of any type.

One class of coating materials to which polymer microparticles can be advantageously added are those based on solutions of thermosetting acrylic resins. These coating materials are of particular importance for the painting of car bodies and other metal objects which may be subjected to relatively high firing temperatures after application of the materials. During firing, the coating material is converted into a hard insoluble coating by the reaction of the resin with a crosslinker, such as melamine formaldehyde resin, into a hard insoluble coating. Up to 40% by weight of styrene is usually added to the monomer charge for the production of these thermosetting acrylic resins. This is done for two main reasons. The first reason is that polystyrene has a significantly higher refractive index compared to the refractive index of most unmodified acrylic or methacrylic acid ester polymers (1.59 compared to 1.46 to 1.49). The introduction of styrene increases the reflectivity of light at the air-polymer interface and thus increases the gloss of the coating.

The second reason is that copolymers containing a certain amount of styrene show improved flow properties during firing compared to methyl methacrylate copolymers. On the other hand, there is a practical upper limit to the amount of styrene, which is about 50% by weight, based on all monomers. This upper limit is due to the high absorption of ultraviolet light by polystyrene, which has an adverse effect on the durability of outdoor coatings.

When adding polymer microparticles to a coating composition, it must be taken into account that if the refractive index of the polymer from which the microparticles are made does not match the refractive index of the main film-forming resin quite accurately, light scattering will occur at the interface between the two polymer phases and the coating film will appear cloudy. This is of course indifferent in coating compositions containing light-scattering pigments, such as titanium dioxide, but in compositions colored to deep shades with light-absorbing pigments, especially in colored metallics containing a small proportion of aluminum components and especially in completely unpigmented compositions intended for the production of clear coatings, this can be a serious defect. In the case where the thermosetting copolymer contains a substantial amount of styrene, the addition of microparticles consisting essentially of polymethyl methacrylate will have this undesirable consequence, and moreover this problem is exacerbated by the fact that melamine-formaldehyde resins, which are most often used as crosslinkers in these systems, themselves have a relatively high refractive index (around 1.52).

When the microgel particles are produced by the first of the two dispersion polymerization methods mentioned above, it is obvious that the microgel polymer will always have approximately the same monomer composition as the main film-forming polymer produced with it, so that the above-mentioned refractive index problem does not arise. A disadvantage of this method, in addition to the disadvantages already mentioned, is that the very polymers which are usefully used as the main film-forming components in a number of coating compositions intended for clear coatings and compositions with a high solids content cannot be easily prepared by dispersion polymerization in a non-aqueous medium. For various reasons, such polymerization is most conveniently carried out in organic liquids of low polarity, especially in aliphatic hydrocarbons. While polymers based exclusively or predominantly on methyl methacrylate are practically insoluble in these liquids, copolymers containing a significant amount of other monomers, such as styrene, can be significantly dissolved in them. This can cause difficulties in obtaining stable dispersions of the copolymers.

The above discussion has considered the problems that arise when the main film-forming polymer is of the addition type, i.e., when it is a polymer made from ethylenically unsaturated monomers. However, the same need to ensure that the refractive index of the microgel particles matches that of the film-forming agent may also arise when certain alkyd or polyester resins are used as film-forming agents, especially alkyd resins which are derived in part from aromatic starting materials such as phthalic anhydride and which consequently have a relatively high refractive index.

Melamine formaldehyde resins, which also have a high refractive index, can also be used as crosslinkers here.

The obvious way to overcome these difficulties in the second of the above two dispersion polymerization methods, whatever the nature of the film-forming polymer to which the microgel particles are added, is to produce a microgel polymer which contains a substantial amount of styrene. However, as has already been shown, dispersion polymerization of styrene in aliphatic hydrocarbons using radical initiators presents some additional problems: the polymerization proceeds slowly and the polymer formed swells strongly in the hydrocarbons at the temperatures usually used, so that a coarse-grained dispersion is formed (see Dispersion Polymerization in Organic Media, ed. K. E. J. Barrett: John Wiley, London, 1975: pp. 213-214).

These problems are also encountered in processes using monomer mixtures containing substantial amounts of styrene, for example amounts above 20% by weight.

It has now been found in connection with the invention that the dispersion polymerization of such monomer mixtures can be carried out without these difficulties if the monomer mixture contains, in addition to styrene, a specific derivative of maleic acid or fumaric acid.

The subject of the invention is a coating composition, which is characterized in that it contains a liquid diluent and film-forming components A/ and B/ in a weight ratio A:B ranging from 95:5 to 85:15, where it represents

A/ film-forming polymer and

B/ microparticles of cross-linked addition polymer, transportable by polymerizing a mixture of ethylenically unsaturated monomers, consisting of:

1/ 10 to 40% by weight of styrene or its homologue or their chlorine-substituted derivatives,

2/ 2 to 30% by weight of a derivative of maleic acid or fumaric acid which is soluble in a liquid hydrocarbon at the polymerization temperature and

3/ 30 to 88% by weight of one or more other ethylenically unsaturated monomers selected from the group consisting of acrylic acid, methacrylic acid and alkyl esters of these acids, wherein these other ethylenically unsaturated monomers contain either a/ 0.2 to 10% by weight, based on the entire monomer mixture, of a pair of monomers containing both epoxy groups and carboxyl groups, or b/ 1 to 20% by weight, based on the entire monomer mixture, of a monomer containing a hydroxy group and 1 to 5% by weight, based on the entire monomer mixture, of a monomer containing a carboxy group, wherein in the case of alternative b/, the polymerization of the monomer mixture is carried out in the presence of 0.5 to 20% by weight, based on the entire monomer mixture, of an alkylated melamine-formaldehyde condensate, the total amount of monomer is 100% and the polymerization is carried out in the presence of a steric dispersion stabilizer, with which the grafted a copolymer comprising a liquid hydrocarbon-unsolvable main chain of an acrylic polymer and a plurality of liquid hydrocarbon-solvable side chains formed by poly(12-hydroxystearic acid) residues attached to the main polymer chain, said graft copolymer being contained in the liquid hydrocarbon.

Any derivative of maleic or fumaric acid that is soluble in a liquid aliphatic hydrocarbon can be used in the production of microparticles. This solubility requirement excludes the possibility of using maleic and fumaric acids alone, as well as maleic anhydride, but various compounds derived from these substances, for example by reacting carboxy groups, can be used.

A preferred type of derivative is one containing at least one aromatic group in the molecule, since the presence of an aromatic nucleus results in an increase in the refractive index of the microparticles in addition to the increase achieved by copolymerizing styrene or a derivative thereof.

One class of maleic or fumaric acid derivatives which contain at least one aromatic nucleus and which are particularly suitable for this purpose is the class of N-aryl substituted maleimides of the general formula

CH-CO “ N-Ar

CH-CO' where

Ar represents an aromatic radical which may contain one benzene nucleus or two or more fused or condensed benzene nuclei and which optionally carries other substituents,

Such compounds are usually soluble in aliphatic hydrocarbons. Examples of substances falling into this class of compounds include

N-phenylmaleimide,

N-o-tolylmaleimide,

N-m-tolyl-naphthaleneimide,

N-p-tolylmaleimide,

N-o-biphenylylmaleimide,

N-p-biphenylylmaleimide,

N-p-(tert.butyl)phenylmaleimide,

N-p-dodecylphenylmaleimide,

N-α-naphthylmelainimide,

N-β-naphthylmaleimide,

N-o-chlorophenylmaleimide,

N-m-chlorophenylmaleimide,

N-p-chlorophenylmaleimide,

N-p-methoxyphenylmaleimide,

N-2-methyl-4-chlorophenylmaleimide,

N-2-methoxy-5-chlorophenylmaleimide,

N-4-phenoxyphenylmaleimide,

N-4-phenylcarboxyphenylmaleimide,

N-4-(o-chlorophenyl)phenylmaleimide,

N-2,5-dichlorophenylmaleimide,

N-2,5-dimethoxyphenylmaleimide a

N-2,4,5-Trichlorophenylmaleimide.

Any of the above substances can be prepared by the method described in BP 1,040,907 and 1,041,027.

Another class of maleic or fumaric acid derivatives containing at least one aromatic nucleus which are soluble in aliphatic hydrocarbons and suitable for use according to the invention is the class of maleic or fumaric acid diesters of the general formula

CH.CO.OX or

CH.CO.OX

CH.CO.OY

YO.CO.CH where one of the substituents

X and Y or both of these substituents represent aromatic radicals which may contain one benzene nucleus or two or more fused or condensed benzene nuclei and which optionally carry further substituents.

Examples of substances falling within this class include diphenylmaleate, methylphenylmaleate, dibenzylmaleate, di-(o-chlorobenzyl)maleate, di(p-chlorobenzyl)maleate, benzylmethylmaleate, dinaphthylmaleate, bis(diphenylyl)maleate, diphenylfumarate, methylphenylfumarate and other fumaric acid esters corresponding to the above maleic acid esters.

Yet another class of suitable derivatives of maleic or fumaric acid, which are soluble in aliphatic hydrocarbons, are the diesters of these acids of the general formula

CH.COOR or CH.COOR

CH.COOR ¹ R ¹ O.CO.CH where each of the symbols

R and R, which are the same or different, represent an alkyl radical containing two or more carbon atoms.

Examples of substances falling into this group include diethyl maleate, diethyl fumarate, dibutyl maleate, dibutyl fumarate, dioctyl maleate, dioctyl fumarate, diisooctyl maleate, diisooctyl fumarate, dicyclohexyl maleate and dicyclohexyl fumarate.

Of the maleic and fumaric acid derivatives described above, the most preferred are N-aryl substituted maleimides, especially N-p-chlorophenylmaleimide.

As styrene derivatives which can be used instead of styrene or simultaneously with it, o-methylstyrene, o-, m-, and p-vinyltoluenes, p-tert-butylstyrene and o-, m-, and p-chlorostyrenes are considered.

According to the above definition, microparticles of addition polymers are insoluble in a liquid aliphatic hydrocarbon and therefore precipitate from it when formed during dispersion polymerization. The particles remain in a state of stable dispersion due to the presence of a steric stabilizer. The insolubility of microparticles can be achieved in one of two ways. In the first t

In this case, the monomers from which the polymer of the microparticles is formed can be selected such that the polymer is insoluble in the liquid hydrocarbon. In this case, the monomer mixture used for the polymerization usually contains one or more ethylenically unsaturated monomers, in addition to the monomers mentioned above, more particularly alkyl esters of acrylic acid or methacrylic acid, such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, lauryl methacrylate, ethyl acrylate, butyl acrylate, hexyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, lauryl acrylate and cetostearyl acrylate.

In the latter case, the insolubility of the microparticle can be achieved by providing a sufficient degree of crosslinking to a polymer which would be soluble in the aliphatic hydrocarbon in the uncrosslinked state. Crosslinking can be achieved by adding to the polymerized monomer mixture pairs of monomers containing functional groups which can react together by condensation. Examples of such monomer pairs include monomers containing epoxy groups and monomers containing carboxy groups, such as the glycidyl acrylate-acrylic acid pairs, monomers containing hydroxymethylamino or alkoxymethylamino groups and monomers containing carboxy groups, as described in British Patent Application No. 7,921,615.

According to an alternative process, the crosslinking can be carried out by polymerizing the monomers in the presence of a reactive amino resin which is insoluble in a liquid aliphatic hydrocarbon. The monomer mixture in this case contains at least one monomer which carries a group capable of reacting with the amino resin, such as a hydroxyl or carboxyl group. The latter process is described in the co-pending British patent application of the same applicant No. 7,922,061.

In the case where the insolubility of the microparticles is achieved by crosslinking, by whatever method, the degree of crosslinking should preferably not be higher than that required to render the polymer insoluble. As in the case of uncrosslinked microparticles, the polymerized monomer mixture may also contain one or more ethylenically unsaturated monomers which do not carry functional groups, such as acrylic monomers or other monomers.

Liquid aliphatic hydrocarbons suitable for use in the process of the invention include hexane, heptane and commercially available gasoline fractions of various boiling ranges. These gasoline fractions may also contain minor amounts of aromatic hydrocarbons.

The spherical stabilizer used in the production of microparticles is an amphipathic tissue-type substance, such as those commonly used in polymerisation processes carried out in non-aqueous dispersion (see Dispersion Polymerisation in Organic Media, ed. K. E. J. Berrett, John Wiley and Sons, 1975). The preferred type of stabiliser is a graft copolymer in which the main chain is formed by a chain of an acrylic polymer derived predominantly from methyl methacrylate and the pendant chains are formed by poly(12-hydroxystearic acid) residues which are readily solvated by aliphatic hydrocarbon media. These copolymers can be prepared, for example, by first reacting poly(12-hydroxystearic acid) with glycidyl acrylate or glycidyl methacrylate, then converting the terminal carboxy group in the polymeric acid to an ester containing a polymerizable unsaturated group, and copolymerizing the resulting derivative with methyl methacrylate, optionally in the presence of minor amounts of other copolymerizable comonomers.

When acrylic acid or methacrylic acid are used as these additional comonomers, carboxyl groups can be introduced into the main chain of the graft copolymer. This has a beneficial effect, since the main chain is then more polar than if it were composed exclusively of methyl methacrylate units. The increased polarity makes the main chain even less solvable by non-polar diluents such as aliphatic hydrocarbons, and as a result, the strength with which it is anchored to the microparticles is increased.

Further details regarding suitable stabilizing agents and dispersion polymerization in general are given in the above-cited publications and in the patent literature, for example in British Patents Nos. 941,305, 1,052,241, 1,122,397 and 1,231,614.

The addition of the above-defined maleic or fumaric acid derivative to the polymerized mixture has two advantageous consequences. First, it increases the polymerization rate compared to monomer mixtures containing styrene but not containing any of these derivatives.

This will increase the quality of the polymer dispersion obtained. Secondly, as already mentioned, in those cases where the derivatives themselves contain one or more aromatic nuclei in the molecule, this fact leads to a further increase in the refractive index of the dispersion polymer beyond the values obtained as a result of the use of styrene.

Therefore, the amount of styrene required to achieve a certain refractive index value can be reduced.

The polymer microparticles produced in the above-described manner can be added to any coating composition based on a film-forming polymer or resin.

Any film-forming resin commonly used in coating compositions may be used. The resin may be of either the sieving or non-sieving type, i.e. the coating composition may be either thermosetting or thermoplastic.

One class of coating materials of interest is thermosetting acrylic resins, such as those useful in coating materials for automotive applications. Such resins are typically derived from one or more esters of acrylic or methacrylic acid, such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate, which are used in conjunction with other monomers containing functional groups through which the resin can be further crosslinked by reaction with an amino resin.

Such homomonomers are acrylic acid, methacrylic acid, hydroxyethyl acrylic acid, hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, N-(alkoxymethyl) acrylamides and N-(alkoxymethyl) methacrylamides (where the alkoxy group may be, for example, butoxy), glycidyl acrylate and glycidyl methacrylate. Such functional monomers typically constitute 5 to 30% by weight of the total acrylic resin. The acrylic resin may also contain minor amounts of other copolymerizable monomers such as vinyl acetate, vinyl propionate and acrylonitrile. According to common practice, resins intended for the automotive industry in particular also contain 5 to 40% by weight, based on the total resin, of styrene. The invention is particularly valuable in these circumstances, since it is possible to increase the refractive index of the microparticles to the level of the refractive index of the film-forming resin, which is high due to the presence of styrene. Thermosetting acrylic resins can be crosslinked in a conventional manner with a crosslinking amino resin also present in the composition. The crosslinking amino resin can be any substance of this type, i.e. of the type of condensate of formaldehyde with a nitrogenous compound such as melamine, urea or benzoguanamine or of such a condensate in which a substantial part of the methylol groups present are etherified by reaction with a lower alcohol, especially butanol. The amount of crosslinking agent is typically in the range of 20 to 50% by weight, based on the total thermosetting acrylic resin.

Instead of thermosetting acrylic resins, thermoplastic acrylic resins derived from any of the monomers listed above, excluding monomers containing functional groups, can be used as film formers in the coating compositions.

According to another alternative, the film-forming substance may be an alkyd resin produced in a conventional manner by condensation of one or more polycarboxylic acids with one or more polyhydric alcohols, the reaction mixture also containing fatty acid residues of drying or semi-drying oils. In this case, the resin is cured by an autoxidative polymerization mechanism. However, polyesters derived from similar polyfunctional starting materials, which do not contain any autoxidizable residues, may also be used. In such a case, the curing of the resin is achieved by reaction of the remaining hydroxyl and/or carboxyl groups contained in the condensation product with a crosslinking amino resin.

The stability of the polymer microparticles after their addition to the coating composition can in some cases be increased by further associating the above-described microparticles before addition to the coating composition with another substantially uncrosslinked polymer which is soluble in the liquid forming the continuous phase or diluent of the coating composition and which is also compatible with the film-forming polymer contained in this composition. This uncrosslinked polymer, which can be referred to as an auxiliary polymer, is most conveniently combined with the microparticles by carrying out, after completion of the monomer conversion and possible crosslinking, the polymerization of another monomer from which the auxiliary polymer is to be prepared directly in the reaction mixture. This is done in the original aliphatic hydrocarbon environment and in the presence of the original dispersion stabilizer, although an additional stabilizer may optionally be added.

The monomers used for the preparation of the auxiliary polymer may be acrylic monomers or other neutral monomers, as mentioned above in connection with the preparation of the microparticles themselves, but of course no crosslinking monomers are used. It is clear to those skilled in the art which monomers may be used to obtain an uncrosslinked polymer having the desired solubility.

The amount of polymer microparticles added to the coating composition can lie within wide limits depending on the type of microparticles and the type of main film-forming polymer and on the effect to be achieved. In a particular case, it may therefore be appropriate to use different amounts depending on whether the microparticles are added in order to modify the rheological properties of the coating composition, i.e. in order to influence its flow properties after application to the substrate or in order to modify the mechanical properties of the coating film after application.

The coating composition may optionally contain a suitable catalyst for the crosslinking reaction between the film-forming substance and the sulfiding agent, for example an acidic reacting compound such as acid butyl maleate, acid butyl phosphate or p-toluenesulfonic acid.

Alternatively, the catalytic effect can be achieved by introducing free acid groups into the film-forming substance, for example by using acrylic or methacrylic acid as a comonomer in the preparation of a sulfurizable acrylic polymer.

The coating composition may contain one or more pigments. As already mentioned, the invention is of particular interest in coating compositions containing pigments of the light-absorbing type (as opposed to those which scatter light), including those compositions which additionally contain aluminium flakes and are intended for the production of so-called metallic finishes on car bodies.

However, the greatest benefit of the invention is with unpigmented clear coating compositions which are normally applied over lightly pigmented metallic type basecoats.

In such a case, the ability to match the refractive index of the polymer microparticles exactly to the refractive index of the film-forming resin, which the invention provides, is a significant advantage, since this preserves the high clarity of the unmodified resin.

The selection of the precise composition of the monomer mixture to be used in the production of the polymer microparticles of the invention in order to achieve the refractive index of the particular film-forming resin used is a matter of simple experimentation that can be readily performed by one skilled in the art of coating polymers.

The invention is further illustrated in the following examples. The examples are for illustrative purposes only and do not limit the scope of the invention in any way. All parts, percentages and ratios given in the examples are by weight.

Examples 1 to 5 and Comparative Examples A to C

The following is placed in a flask equipped with a stirrer, thermometer, reflux condenser and a device for dosing the liquid feed into the returned condensate:

Parts aliphatic hydrocarbon (boiling range 170 to 210 °C, aromatic hydrocarbon content 5%) 10.355 hexane 2.536 heptane 13.561

The flask and the charge are flushed with inert gas and then the mixture is heated to reflux temperature (100 °C). Over a short period of time, a pre-formed mixture of the following composition is added to the boiling mixture:

Parts methyl methacrylate 0.833 methacrylic acid 0.017 azodiisobutyronitrile 0.066 graft copolymer as stabilizer (33% solution described below) 0.310

The contents of the flask are then heated to reflux for 30 minutes to form a seed dispersion. A pre-formed mixture of the following composition is then added to the hydrocarbon returning from the reflux condenser at a uniform rate over a period of 3 hours:

Parts monomer mixture prepared in detail below 16.145 azodiisobutyronitrile 0.212 graft copolymer as stabilizer (33% solution described below) 3.330 dimethylaminoethanol 0.031

After the addition of monomers is complete, the reaction mixture is refluxed for 3 hours. ¹

The monomer mixtures used for dosing in Examples 1 to 5 and Comparative Examples A to C have the compositions shown in Table I. The first number in each case indicates the amount in parts by weight and the second number (in parentheses) indicates the percentage of monomer in the entire monomer mixture used for dosing (in % by weight).

In all cases, a fine, stable dispersion of crosslinked polymer microparticles is obtained. The dispersions have a solids content in the range of 38 to 40% (determined by evaporation at 150°C for 1 hour) and an undissolved gel content in the range of 21 to 31%. In all cases, the volume median size of the microparticles produced is also measured based on Brownian motion and laser light autocorrelation. The sizes determined are also listed in Table I. Before cooling from the reaction temperature, each dispersion is diluted with 12.549 parts of xylene.

The graft copolymer solution used as a stabilizer in the above examples is prepared as follows:

12-Hydroxystearic acid is autocondensed until an acid number of about 31 to 34 mg KOH/g is reached (corresponding to a molecular weight of 1,650 to 1,800) and then the product is reacted with an equivalent amount of glycidyl methacrylate. The resulting unsaturated ester is copolymerized in a 2:1 weight ratio with a 95:5 weight ratio mixture of methyl methacrylate and acrylic acid. The copolymer is used as a 33% solution in a 74:14:12 weight ratio mixture of aliphatic hydrocarbon, toluene and ethyl acetate.

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The particle size determination results shown in Table I illustrate the fact that the use of styrene as a conionomer in the absence of the maleic or fumaric acid derivative required by the invention results in relatively coarse particles in the dispersion, which cause the dispersion to settle rapidly during storage. In contrast, when the method of the invention is used, dispersions are obtained whose particles are of a similar size to those produced using only acrylic monomers (i.e., without styrene).

Example 6a comparative examples D to G

Thermosetting acrylic coating materials are produced by mixing melamine formaldehyde resin with an acrylic solution polymer of the following composition: styrene 42.5%, butyl methacrylate 21.25%, butyl acrylate 21.25%, hydroxyethyl methacrylate 14.0% and acrylic acid

ΜΙ %. In all but one case, insoluble microparticles prepared as described in Examples 1 to 5 and Comparative Examples A to C above were also added. Details relating to the specific microparticles used and the amounts of the three components used are given in Table II. The amounts are in all cases in parts by weight, based on 100% non-volatiles. Each mixture was then diluted with a 1:1 mixture of butyl acetate and xylene to a spray viscosity of 50 to 60 seconds (measured in a B3 cup at 25°C according to the British Standard) and sprayed onto glass plates which were then baked for 30 minutes at 127°C. The appearance of the resulting film was recorded. The results of this testing are also given in Table II.

Table II

Example number 6 D E F G Melamine formaldehyde resin 30 30 30 30 30 acrylic polymer 60 60 60 60 70 microparticles from the example- I am 4 10 - - - - comparative example A - 10 - - - comparative example B - - 10 - < comparison example C - — - 10 - Film appearance clear very slightly clear clear clear cloudy cloudy The results shown show that the clearness of the hardened acrylic film (compare- the example G) is lost, when they join microparticles that do not have matching index quarry i.e. microparticles containing zero or less what proportion of styrene (comparative examples D and E) .

The clarity of the film is maintained when the microparticles contain a high proportion of styrene (Comparative Example F), but this is achieved, as is evident from the results given in the previous group of examples, at the expense of the coarseness of the microparticles, which then tend to sediment in the dispersion. In contrast, the use of styrene in conjunction with a maleic or fumaric acid derivative according to the invention (Example 6) maintains the clarity of the film without the attendant disadvantages.

Examples 7 to 8a comparative ^example H

a) In a flask equipped with a stirrer, thermometer, reflux condenser and Dean-Stark separator, add

Parts of an aliphatic hydrocarbon with a boiling range

140 to 156 °C, which does not contain aromatic components 25.735 methyl methacrylate 1.341 methacrylic acid 0.026 azodiisobutyronitrile 0.107 graft copolymer as stabilizer (33% solution, described below) 0.497

The flask and charge are flushed with inert gas and then the mixture is heated to reflux temperature (100 °C).

The contents of the flask are then heated to reflux for 30 minutes to form a seed dispersion. A pre-formed mixture of the following composition is then added to the flask at 100 °C with constant stirring over a period of 3 hours:

Parts monomer, described in detail below 19.877 hydroxyethyl acrylate 1.130 hexamethoxymethylmelamine 1.130 methacrylic acid 0.451 azodiisobutyronitrile 0.140 graft copolymer as stabilizer (33% solution described below) 4.664 aliphatic hydrocarbon (described above) 11.320

The reaction mixture is then maintained at 100°C for a further 30 minutes and then the temperature is increased to 140-145°C when the distillate is recycled. These conditions are maintained for 2 hours during which time 1.2 parts of water are separated in the separator. The contents of the flask are then cooled. A fine dispersion of crosslinked microparticles is obtained. The dispersions have a solids content in the range of 38-39% and an insoluble gel content in the range of 31-32%.

The graft copolymer solution used as a stabilizer in the above examples is prepared as follows:

a) 12-hydroxystearic acid is autocondensed until an acid number of 31 to 34 mg KOH/g is reached (corresponding to a molecular weight of 1,650 to 1,800) and then the product is reacted with an equivalent amount of glycidyl methacrylate. The resulting unsaturated ester is copolymerized in a weight ratio of 49:46:5 with methyl methacrylate and glycidyl methacrylate and the copolymer thus obtained is finally reacted with methacrylic acid and p-nitrobenzoic acid in the presence of a tertiary amine as catalyst at a ratio of 0.070 parts of methacrylic acid and 0.019 parts of p-nitrobenzoic acid per 100 parts of copolymer.

b) Into a flask equipped as described in step a), but equipped with a device for introducing a liquid charge into the recycled distillate, 66.418 parts of the dispersion obtained in step a) are introduced. The dispersion is heated to 145 °C, i.e. the reflux temperature, and a previously prepared mixture of the following composition is introduced into the flask at a constant rate through the recycled distillate over a period of 3 hours:

Parts reaction product of poly(12-hydroxystearic acid) and glycidyl methacrylate, (50% solution in an aliphatic hydrocarbon with a boiling range of 136 to 165 °C 14.982 hydroxyethyl acrylate 1.972 methacrylic acid 0.394 styrene 5.913 methyl methacrylate 3.943 di-tert.butyl peroxide 0.394 graft copolymer as stabilizer (33% solution, described in paragraph a) 5)984

When the addition is complete, the reaction mixture is refluxed for an additional 3 hours. The resulting dispersion of crosslinked microparticles modified with the uncrosslinked auxiliary polymer has a solids content in the range of 47 to 48% and an undissolved gel content in the range of 29 to 30°C.

The monomer used for dosing in step a) of the process in these examples and the comparative example has the composition shown in Table III. The first number in each case represents the amount of each monomer in parts by weight and the second number (in parentheses) represents the percentage of the monomer in the total monomer mixture used in dosing in step a).

Table III

Example number 7

methyl methacrylate 16,283 (72.0) 15,085 (66.8) 19,877 (88.0) N-o-chloro- -phenylmaleimide 2,396 (10.6) 2,396 (10.6) - styrene 1,198 (5.3) 2,396 (10.6) -

Examples 9 to 10 and Comparative Example J

An air-drying alkyd coating composition was prepared by mixing 90 parts of an alkyd resin of pentaerythritol, p-tert-butylbenzoic acid, benzoic acid and phthalic anhydride modified with 52% tall oil with 10 parts of insoluble microparticles prepared according to any of Examples 7 to 8 or Comparative Example H. Each mixture was diluted to a viscosity of 24 seconds (measured in a B3 cup at 25°C according to the British Standard) with a solvent consisting of an aliphatic hydrocarbon boiling at 138 to 165°C (95 parts), nonanol (5 parts) and a mixture of terpenic alcohols (1 part). The mixtures were sprayed onto glass plates and the coatings were allowed to dry overnight and then the film appearance was evaluated. The specific microparticles used and the film appearance are given in Table IV.

Claims (3)

SUBJECT OF THE INVENTION CLAIMS 1. Coating composition comprising liquid diluent and film forming components A / and B / in a weight ratio of A: B in the range of from 95: 5 to 85:15, wherein: A / film forming polymer a B / microparticles of crosslinked addition polymer, obtainable by polymerizing a mixture of ethylenically unsaturated monomers in a dispersion in a liquid aliphatic hydrocarbon consisting of 1/10 to 40% by weight of styrene or its homologs or their substituted halides, 2/2 to 30% by weight of a maleic acid or fumaric acid derivative which is soluble in a liquid hydrocarbon at the polymerization temperature; and 3/30 to 88% by weight of one or more other ethylenically unsaturated monomers selected from the group consisting of acrylic acid, methacrylic acid and alkyl esters thereof, wherein the other ethylenically unsaturated monomers comprise either a / 0.2 to 10% by weight, based on the total a monomer mixture, a pair of monomers containing both epoxy and carboxy groups, or b / 1 to 20% by weight, based on the total monomer mixture, a monomer containing hydroxy and 1 to 5% by weight, based on the total monomer mixture, of alternative b), the polymerization of the monomer mixture is carried out in the presence of 0.5 to 20% by weight, based on the total monomer mixture, of the alkylated melamine-formaldehyde condensate, the total amount of monomer being 100% and polymerization carried out in the presence of a sterile dispersion stabilizer. comprising a non-solvable acrylic polymer backbone in the liquid hydrocarbon and a plurality of polyhydric (12-hydroxystearic) acid-side-chain side-chain hydrocarbon side-chain hydrocarbon side chains attached to the polymer backbone, which graft copolymer is contained in the liquid hydrocarbon. 2. The coating composition according to claim 1, wherein the polymer particles are associated with a substantially uncrosslinked polymer which is soluble in the liquid diluent of the coating composition and which is compatible and film-forming polymer prior to addition to the composition.