Multi-layer coating process involving use of aqueous basecoat composition containing crosslinked polymer microparticles and having a pseudoplastic or thixotropic character.

Method for forming a multilayer protective and / or decorative coating on the surface of a substrate and primer composition used in the method

The present invention relates to a method for forming a multilayer protective and / or decorative coating on the surface of a substrate, in particular on the surfaces of car bodies, and to a priming composition used in the method.

It is well known, especially in the automotive industry, to use coating compositions containing metal pigments; these are so-called metallic finishes, whereby different light reflection effects are achieved depending on the viewing angle. To maximize this flickering color tone effect, careful formulation of the coating composition with respect to both the film-forming resin and the liquid medium is required. Difficulties may be associated with the preparation of a single composition that both meets this requirement and at the same time gives a strong shine to the final coating, which is usually desirable in the automotive industry. For this reason, one method proposed for forming metallic finishes is a double coating process, in which a primer containing a metallic pigment and having a composition such as to obtain the highest possible effect is first applied by spraying on the substrate, and then a non-pigmented topcoat is also applied. which gives the desired gloss by altering in any way the properties of the primer.

An essential condition for a successful double coat / metal finishing system of this primer / topcoat type is that the primer film must be able to withstand the effects of the solvents in the clear topcoat test when applied to prevent damage to the metal pigment and without compromising the Small effect; moreover, it is very advantageous if the primer has this property without the need for a long intermediate drying or intermediate curing.

In known primer / topcoat systems, where both primer and topcoat layer compositions are based on organic solvents, this requirement is met in most cases by the use of an additive capable of imparting a gel-like character to the freshly prepared primer film; the main additive used is cellulose acetate butyrate. The transition between the relatively low viscosity required of the spray device from the primer composition and this gel-like nature is aided by ensuring that the liquid diluent of the composition contains volatile components which are preferably removed by evaporation as it moves from the spray device to the substrate.

In order to prevent air pollution, there has been considerable interest recently in coating compositions using water as a diluent instead of organic solvents. Numerous such compositions have been proposed for use in the automotive industry. To date, however, it has not been possible to use water-based compositions satisfactorily as a primer component for primer / clear layer systems. One of the factors that makes this difficult is the difficulty in ensuring that the diluent is selectively removed from the primer composition by evaporation between the spray device and the substrate, except for the very expensive control of ambient humidity in the spray zone. However, we have now found that a satisfactory aqueous primer composition can be based on an aqueous dispersion of a crosslinked polymeric microgel.

The method according to the invention for forming a multilayer protective and / or decorative coating on a substrate comprises the following steps:

(1) applying to the surface a primer composition comprising (a) a film-forming material, (b) a volatile liquid medium for said material, and (c) a pigment moiety dispersed in said liquid medium;

(2) forming a polymer film on the surface of the substrate from the composition of step (1):

(3) applying to the undercoat film thus obtained a transparent coating composition comprising (d) a film-forming polymer and (e) a volatile carrier liquid for said polymer; and (4) forming a second polymer film on the primer film from the composition of step (3). The process is characterized in that the components (a) and (b) of the primer composition are obtained by dispersing crosslinked polymer microparticles in the range of 0.01 to 10 micrometers in diameter which are insoluble in said aqueous medium and do not form flocculants in an aqueous medium, wherein the dispersion has a pseudoplastic or thixotropic nature.

A priming composition according to the invention suitable for use in the method according to the invention comprises

(a) film-forming material

(b) a volatile liquid medium for said material; and

c) pigment particles dispersed in said liquid medium. The primer composition is characterized in that components a) and b) are obtained from a dispersion of crosslinked polymeric microparticles having a diameter of 0.01 to 10 μm in an aqueous medium, the polymer particles being insoluble in said aqueous medium and stable to flocculation, and wherein flocculation is stable, and

Crosslinked polymeric microparticles can be formed from different types of polymers. Of particular interest for this purpose are acrylic acid addition polymers derived from one or more alkyl esters of acrylic acid or methacrylic acid, if desired together with other ethylenically unsaturated monomers. Suitable esters of acrylic acid or methacrylic acid include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, ethyl acrylate, butyl acrylate and 2-ethylhexyl acrylate. Other suitable copolymerizable monomers include vinyl acetate, vinyl propionate, acrylonitrile, styrene and vinyl toluene. Since the polymer must be crosslinked, a small proportion of the monomer polyfunctional with respect to the polymerization reaction, for example ethylene glycol dimethacrylate, allyl methacrylate or divinylbenzene, may be added to the monomers from which the polymers are derived, alternatively react with each other either during or after polymerization, such as epoxy and carbonyl (such as glycidyl methacrylate and methacrylic acid), anhydride and hydroxyl or isocyanate and hydroxyl group pairs.

The chemical composition and degree of crosslinking of the polymer microparticles may be such that its Tg (transition temperature from glassy to rubbery) is below room temperature, in which case the microparticles are rubbery in nature; alternatively, it may be such that the Tg value is above room temperature, m.p. the particles are hard and vitreous.

As mentioned above, it is necessary that the polymeric microparticles be dispersed in the primer composition in a state where no flocculation occurs, i.e. a state in which, even at low solids contents, the dispersion contains little or no aggregates formed by several parts of the yarn; however, this does not exclude the possibility of a low degree of flocculation, especially at high solids concentrations. This state can be achieved, for example, by steric stabilization, whereby a protective layer of different polymer chains is formed around the particles, which is solvated by the aqueous medium of the composition and is thus a long chain-like structure. In this context, the term solvation means that the polymer chains in question, if they were independent molecules, would dissolve in said aqueous medium, since the chains are in fact attached to the microparticles at one or more points along their length, the microparticles retaining steric hindrance permanently. Polymeric microparticles which are sterically stabilized in this way can be conveniently prepared by dispersion polymerization of the appropriate monomers in an aqueous medium in the presence of a steric stabilizer. The stabilizer is amphipathic in nature, meaning that it contains two actual polymer moieties of a different nature in its molecule; the second polymer moiety is a polymer chain that is solvated by an aqueous medium and the other moiety is a polymer chain that is not solvated by an aqueous medium and therefore adheres to polymeric microparticles which are by definition insoluble in an aqueous medium. Suitable dispersion polymerization processes are disclosed in our GB patent application 7,940,088 (now published as Application No. 20 39 497 A). The aqueous medium in which the polymerization is carried out consists of water mixed with a volatile organic co-solvent, the mixture as a whole being able to dissolve the monomers, most or all of which may be substantially insoluble in water alone. An additional requirement of these processes is that the polymerization is carried out at a temperature at least 10 ° C higher than the glass transition temperature of the polymer to be formed and in such a way that no separate monomer is ever present. The steric stabilizer of the amphipaths may be added to the polymerization mixture as a preformed material or may be formed in situ during polymerization from a polymer that is soluble in an aqueous medium and copolymerizable with a monomer to be polymerized or grafted to that monomer upon separation of hydrogen. The sterically stabilized microparticle dispersions obtained by these methods are very suitable for preparing the primer compositions used in accordance with this invention because it is possible to remove the organic co-solvent therefrom by distillation without compromising the dispersed phase stability and a product in which the continuous phase consists of water alone.

Alternatively, the dispersion of polymeric microparticles can be obtained by emulsion polymerization of appropriate monomers in water, in which case the ability to inhibit the formation of beneficial ones is due to the presence of electrically charged species obtained from a water-soluble ionized surfactant and / or a water-soluble ionizable polymerization inhibitor. These polymerization methods have been extensively described in the literature.

Polymeric microparticles can be further prepared by an anhydrous dispersion polymerization process of monomers, followed by transfer of the resulting polymer to an aqueous medium. Such a procedure is disclosed in our GB patent application 42457/77 (now published as Application No. 2,006,229 A). The method comprises, as a first step, forming a sterically stabilized dispersion in an anhydrous liquid from a polymer insoluble in both anhydrous liquid and water using a method well known in the art to prepare such a dispersion, then in a second step polymerizing in the presence of an ethereal stabilizer the resulting dispersion may form one or more monomers. polymer, which as such is soluble in the desired aqueous medium at a suitable pH; and finally transferring the obtained composite polymer microparticles from the anhydrous medium to the aqueous medium.

Such a treatment has been associated with the case where the crosslinked polymeric microparticles consist of an addition polymer, which is the most suitable type of polymer for this purpose. However, it is possible that the microparticles alternatively consist of a condensation polymer, for example a polyester made of a polyhydric alcohol and a polycarboxylic acid. Suitable polyhydric alcohols include ethylene glycol, propylene glycol, butylene glycol, 1,6-hexylene glycol, neopentyl glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, glycerol, trimethylolpropane, trimethylolethane, pentaerythritol, dipentaerythritol, tripentaerythritol, hexanetriol, styrene, and allyl alcohol oligomers (for example that sold by Monsanto Chemical Company under the designation RJ 100), condensation products of trimethylolpropane with ethylene oxide or propylene oxide (such as products known commercially as Niax triols; Niax is a registered trade name). Suitable polycarboxylic acids include succinic acid (or anhydride thereof), adipic acid, azelaic acid, sebacic acid, maleic acid (or anhydride thereof), fumaric acid, muconic acid, trituric acid, phthalic acid, phthalic acid, or phthalic acid (or its anhydride), its anhydride). These polymers are crosslinked by adding materials with greater than two functionalities to the starting composition, although in this case, due to the characteristic wide distribution of molecular species formed in condensation polymerization compared to addition polymerization, it can be difficult to guarantee that all of these species are actually crosslinked.

It should be noted that the methods mentioned above for the preparation of polymeric microparticles by polymerizing addition-type monomers in an aqueous medium are generally not suitable for condensation-type monomers due to the water-blocking effect on the condensation reaction. However, microparticles of condensation polymer can be readily prepared by dispersion polymerization in an anhydrous medium according to the method disclosed in our GB Patents 1,373,531; 1,403,794 and 1,419,199 and methods for obtaining crosslinked microparticles are disclosed in these patents. These microparticles can then be subjected, in dispersion in an anhydrous medium, to a second polymerization step according to GB Patent Application 42457/77 (published as Application No. 2,006,229 A) referred to above, after which they are transferred to the desired aqueous medium.

The term aqueous medium as used herein means either water alone or water mixed with a water-miscible organic liquid such as methanol; the aqueous medium may also contain water-soluble substances added against adjusting the pH of the primer composition, as described in more detail below.

The size of the pigment particles dispersed in the aqueous medium of the primer composition can range from 1 to 50 micrometers and can be any of the pigments commonly used in surface coating compositions, including inorganic pigments such as thian dioxide, iron oxide and carbonic acid, chromium oxide, lead oxide, lead chromium carbazole violet, anthropyrimidine yellow, flavantron yellow, isoindoline yellow, indatron blue, quinacridone violet and perylene red. For this purpose, the term pigment is also meant to include conventional fillers and extenders such as talc and kaolin.

The method according to the invention is very suitable for cases where primer compositions are used which contain metal flake pigments and which are intended for the formation of metallic coatings mainly on the surfaces of car bodies. Suitable metal pigments are in particular aluminum flakes and copper-bronze flakes. However, the invention also offers advantages in producing rich color finishes as described below. In general, pigments of all kinds can be added to primer compositions in amounts of 2-100% based on the total weight of the composition. When metal pigmentation is used, its amount is preferably 5-30% based on the above-mentioned total weight.

These pigments, metallic or otherwise, can be added to primer compositions using known pigment dispersants suitable for use in aqueous systems.

The use of crosslinked polymer microparticles in the primer composition gives the film formed from the latter the advantageous ability to withstand application of the finishing composition without damaging the film or pigmentation, especially the metal pigmentation it contains and without which a successful primer / finishing system cannot be implemented.

In addition to this essential property, it is also required that the dispersion nature of the insoluble microparticles be pseudoplastic or thixotropic. By this is meant that the apparent viscosity of the dispersion differs according to the shear force applied to the dispersion and, more specifically, that the apparent viscosity at high shear force is higher than at high shear force. The change in viscosity due to the applied shear force may be sudden or require a certain time interval, which, however, is within the time scale of the viscosity measurement. The reason for requiring this property for the dispersion on which the primer composition is based is most obvious in cases where this composition contains metal flake pigments. In this case, it is desirable that the total content of solids used be relatively low in order to obtain a significant shrinkage of the primer film after its application to the substrate and during drying, thus ensuring the correct orientation of the metal flakes and thus the optimal Low effect. However, if the primer composition is applied to the substrate by spraying, it is necessary that the viscosity of the composition is low enough for effective spraying in the sprayer and upon arrival on the substrate its viscosity must be high enough to prevent film runoff and run or to prevent metal flakes from overlapping (uneven) where the removal of water and other solvents by evaporation between the sprayer and the substrate is only small (due to high ambient humidity).

The presence of these pseudoplastic properties is often expressed by reporting_a~ values ​​(apparent viscosity, off) at selected D-values ​​(cutting speed sec ^). In the case of the metal pigmented base paint compositions used according to the invention, the? sec \ Even more advantageous primer composition ·⁷} should be less than 0.25 poise ^a -1

With a D value of 10,000 sec and greater than 40 poise with a D value of 1.0 sec \ In the case of solid base color compositions using non-metallic flakes, it is recommended that at a solids content of less than 30%,^z7The value of J, is less than

-1 ^a poise with a D value of 10,000 sec and greater than 5 poise

With a D value of 1.0 sec; more preferably, the value is less than -1^aHowever, the nature of the pseudoplastic or thixotropic behavior is such that it cannot be accurately determined by a few viscosity / shear force values; much depends on the method actually used in the viscosity measurements. Thus, the above values ​​are not intended to be considered as absolute limits to be maintained in order to achieve the advantages of the invention;

There are several ways in which pseudoplasticity or thixotropy can be obtained in a primer composition. No special measures are required in certain cases. This may be the case, for example, when the microparticles have been prepared according to the method of GB Patent Application 42457/77 (published as Application No. 2,006,229 A) set forth above. This process primarily uses the preparation of suitable polymeric microparticles by anhydrous dispersion polymerization of the appropriate monomers, followed by polymerization of the other monomers to obtain a second polymer that is substantially non-crosslinked and hydrophilic in nature so as to dissolve in an aqueous medium. . However, the second polymer is not completely soluble in the aqueous medium when the product of the two anhydrous polymerization steps is transferred to it. A substantial portion of the second polymer remains associated with the polymeric microparticles and the microparticles are thus stabilized in dispersion in an aqueous medium; at the same time, however, this associated polymer can impart pseudoplastic or thixotropic properties to the aqueous dispersion. Monomers suitable for use in the second polymerization step include, for example, a hydroxyalkyl ester of acrylic acid or methacrylic acid, a monoacrylic or methacrylic ester of a polyglycol such as polyethylene glycol, butyrate of this polyglycol monovinyl ether or vinylate, e.g.

Alternatively or in addition, the required solubility in the aqueous medium can be obtained by using as the main monomer an acrylic acid ester containing basic groups, for example dimethylaminoethyl methacrylate or diethylaminoethyl methacrylate, these groups being converted into salt groups by reaction with a suitable acid, e.g. lactic acid. In this case, the second polymer can also be derived from comonomers containing a considerable proportion of a polymerizable carboxylic acid, such as acrylic acid or methacrylic acid, and is then able to dissolve in an aqueous medium containing a dissolved base, for example dimethylaminoethanol. In this case, in general, the second polymer can be non-ionic, anionic or cationic in nature.

If the polymeric microparticles are prepared by aqueous emulsion polymerization, as is well known in the art, another polymer of a water-soluble nature can be produced by further polymerizing in the same aqueous medium and in the presence of microparticles monomers that form acidic salt-forming groups. Thus, suitable monomers include polymerizable carboxylic acids such as

68985 acrylic acid or methacrylic acid, if desired together with small amounts of non-hydrophilic monomers such as methyl methacrylate and also with water-insoluble homopolymers such as hydroxyethyl methacrylate and hydroxypropyl methacrylate.

If the polymeric microparticles are prepared by dispersion polymerization in an aqueous medium, as disclosed in GB Patent Application 7,940,088 (published as Patent Application No. 2,039,497A), another water-soluble polymer can be conveniently prepared by further polymerizing in the same medium suitable monomers such as those mentioned above and also such as dimethylaminoethyl methacrylate, when water-soluble salt derivatives can be formed.

Not all water-soluble polymers formed in situ in the presence of microparticles by any of the above methods are capable of imparting the desired pseudoplastic properties to a primer composition, but suitable polymer compositions can be obtained by a simple test procedure such as measuring viscosity at selected shear rates or actually applied.

Instead of forming a suitable water-soluble polymer in situ or in connection therewith, such a polymer may be added as a preformed separate ingredient to the aqueous dispersion of microparticles. Suitable polymers are those which, when dissolved in an aqueous medium, even at low concentrations, significantly improve the viscosity of the composition. For example, one or more thickeners well known for use in coating compositions based on aqueous polymer latices may be added. However, not all of these thickeners are suitable for this purpose because some thickeners are unable to impart the necessary pseudoplastic properties to the composition to which they are added. On the other hand, certain thickeners dissolved alone in an aqueous medium do not have such properties, but may obtain these properties in the dispersion of microparticles due to their interaction with the microparticles (e.g. due to the interaction of hydrogen bonds or polar groups). One commercially available thickener that has been found to be very suitable is Acrysol ASE60, manufactured by Rohm. & Haas (Acrysol is a trade name).

Although it follows that any inherently water-soluble polymer incorporated into the polymeric microparticles or added to the dispersion of microparticles to impart washing-doped or thixotropic properties to the dispersion must be non-crosslinked in nature, these polymers may be of the crosslinkable type. This means that they may contain chemically reactive groups, so that they can be crosslinked, if desired by means of an added crosslinking agent, after application of the primer composition and preferably also after application of the topcoat to the substrate. Thus, as already mentioned, the polymer may contain hydroxyl or carboxyl groups derived from monomers containing these groups and can then be crosslinked with an amino resin, for example a methylated melamine-formaldehyde condensate, which is soluble in an aqueous medium.

From the above presentation, it can be seen that the primer composition can consist solely of polymeric microparticles, pigment particles, an aqueous medium in which both subgroups are dispersed, and an inherently water-soluble polymer that imparts pseudoplastic properties to it. However, it is much more preferred if the composition further comprises a film-forming polymer that is soluble in the aqueous medium to ensure that after application of the primer to the substrate and evaporation of the aqueous medium it contains a substance that can bond together to fill the microparticle gaps. in the film method step (2). This requirement may indeed be met by the proportion of inherently water-soluble polymer in the composition to impart pseudoplastic or thixotropic properties to it, but due to the small proportion of such polymer generally required for this purpose, it may be advantageous to supplement the composition with one or more water-soluble film-forming materials. which may, if desired, react chemically with ingredients already present. Thus, the composition may contain oligomeric substances that can be converted to high molecular weight products after application of the composition, but which themselves do not significantly affect the viscosity of the composition prior to application.

In this context, mention should be made of low-volatility diols, such as 2-ethyl-1,3-hexanediol, low-molecular-weight polypropylene glycols, low-molecular-weight ethylene oxide by-products with dihydric or trihydric alcohols, glycol alpha-glycol, hydroxyalkylamides such as M, N, N^Z,OF^Z-tetrakis (β-hydroxyethyl) -adipamide and cyclic amides and esters such as ε-caprolactam and ε-caprolactone. Although these materials are not significantly soluble in pure water, they must be dissolved in an aqueous medium containing water together with a water-miscible organic liquid. Each of these oligomeric substances can be converted to a high molecular weight polymer after application of the primer layer to the substrate by coupling them via their hydroxyl groups or other reactive groups also with the polyfunctional reactant present in the composition. Particularly useful for this purpose are amino resins which are soluble in the aqueous medium of the composition, especially melamine / formaldehyde condensates such as hexa (alkoxymethyl) melamines and their low molecular weight condensates.

Alternatively, instead of the ingredients that form the film-forming polymer after application to the substrate, the primer layer may contain a preformed water-soluble acrylic polymer that does not impart pseudoplastic properties to it, or may contain non-crosslinked polymer particles in a dispersion stabilized in the same manner as Each of these alternative ingredients may, if desired, contain functional groups, such as hydroxyl groups, which may cause them to crosslink after application of the composition to the support with a crosslinking agent such as an amino resin.

The relative proportions of the various components of the primer composition can vary widely and the most preferred proportions in each particular system are often best determined experimentally, but some general principles can be found. In particular, if the proportion of polymeric microparticles is too large compared to the second film-forming material in the composition, the latter material is not sufficient to fill the gaps between the microparticles; as a result, when the clear topcoat is then applied, there may be a tendency for this composition to sink into the primer layer, resulting in a loss of gloss. On the other hand, if the proportion of microparticles is too small, it will not give the primer layer the desired protective effect with respect to the solvent in the clear topcoat composition; to a certain extent, a smaller amount of microparticles can be replaced in this respect by allowing the primer film to cure or dry for a longer period of time before applying the clear coating, but this impairs one of the main advantages of the present invention. In general, a sufficient amount of microparticles is in the range of 5-80% by weight of the total amount of non-volatile components in the primer composition. However, the most preferred amount depends to some extent on whether the pigments in the primer composition are metal or non-metal. The recommended concentration of microparticles for metallic compositions is 40-75% by weight, calculated as described above. For compositions of uniform color, since they generally require a higher pigment content to achieve sufficient opacity with relatively thin films, the recommended concentration range of microparticles is relatively small, namely 10-50% by weight as calculated. The reduced proportion of microparticles avoids an excessive proportion of the dispersed material in the total volume, which could cause the porous primer film and thus the topcoat film to sink into it, as well as poor gloss.

Again, it can be generally stated / that the proportion of thickener or second polymer imparting pseudoplastic properties used in the composition may be in the range of 0.3-50% of the total weight of the non-volatiles; the proportion of the second film-forming material may be in the range of 0 to 30% by weight, and if a crosslinking agent such as an amino resin is used, it may be present in an amount of up to 30% by weight of the total non-volatile content of the primer composition. The primer composition may further contain a catalyst for the crosslinking reaction desired after application of the composition to the substrate. This may be a water-soluble acidic compound such as p-toluenesulfonic acid, orthophosphoric acid, maleic acid or another strong carboxylic acid such as tetrachlorophthalic acid; alternatively, it may be a heat-sensitive salt of such an acid with a volatile amine.

The nature of the film-forming polymer used as a component of the coating layer composition in step (3) is by no means critical. In general, any suitable film-forming polymer may be used, which may be of either the thermosetting or thermosetting type. A suitable class of polymers consists of those derived from one or more ethylenically unsaturated monomers. Particularly useful members of this class are acrylic addition polymers, which are well known in the manufacture of coatings in the automotive industry; these are polymers or copolymers of one or more alkyl esters of acrylic acid or methacrylic acid, other ethylenically unsaturated monomers being used if desired. Suitable acrylic esters include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, ethyl acrylate, butyl acrylate and 2-ethyl acrylate. Suitable other copolymerizable monomers include vinyl acetate, vinyl propionate, acrylonitrile, styrene and vinyl toluene. If the acrylic polymer is desired to be of the thermosetting, crosslinking type, suitable functional monomers to be used in addition to the latter include acrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, N-butyl acrylamide, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 2-hydroxypropyl methacrylate, N- (alk. and glycidyl methacrylate. The coating layer composition in this case may also contain a crosslinking agent such as a diisocyanate, diepoxide or especially a nitrogen resin, i.e. a condensate of formaldehyde with a nitrogen-containing compound such as urea, thiourea, melanin or benzoguanamine or a lower alkyl ether of such a condensate. Particularly suitable crosslinking agents are melamine / formaldehyde condensates in which a considerable proportion of the methylol groups have been etherified by reaction with butanol.

The coating composition may contain a suitable catalyst for the crosslinking reaction between the acrylic polymer and the crosslinking agent, for example an acid-reactive compound such as acid butyl maleate, acid butyl phosphate or p-toluenesulfonic acid. Alternatively, the catalytic effect can be obtained by adding free acid groups to the acrylic polymer, for example by using acrylic acid or methacrylic acid as a comonomer in the preparation of the polymer.

The topcoat polymer may be either a solution or a dispersion in the volatile carrier liquid of the topcoat composition, i.e., the carrier liquid may be either a solvent or a non-solvent for the topcoat polymer. If the liquid is a solvent, it may be an organic liquid or mixture of organic liquids suitably used as solvents for polymers in coating compositions, for example an aliphatic hydrocarbon such as hexane or heptane, an aromatic hydrocarbon such as toluene or xylene, and variable boiling hydrocarbons which are predominantly aliphatic. but with a significant aromatic content, esters such as butyl acetate, ethylene glycol diacetate and 2-ethoxyethyl acetate, ketones such as acetone and methyl isobutyl ketone, and alcohols such as butyl alcohol. The liquid or liquid mixture selected as the carrier liquid depends on the nature of the coating layer polymer according to principles well known in the coating technique, so that the polymer is soluble in the liquid.

If the carrier liquid is an organic non-solvent, it has a relatively low polarity compared to the above and may consist of one or more aliphatic hydrocarbons such as hexane, heptane or low aromatic petroleum fractions if desired mixed with the high polarity liquids mentioned above to achieve it. that the total liquid mixture is not a solvent with respect to the topsheet polymer. In this case, the topcoat composition is an anhydrous polymer dispersion and is generally a sterically stabilized dispersion in which the polymer particles are stabilized by a block or graft polymer, wherein one polymer component is not solvated by liquid and is associated with the dispersed polymer. The well-known principles according to which such dispersions can be prepared have been thoroughly set forth in patents and other literature, for example in GB patent publication.

941 305; 1,052,241; 1,122,397 and 1,231,614 and in Disperision Polymerization in Organic Media, edited by KEJ Berret (John Wiley and Sons, 1975).

Alternatively, the topcoat composition, like the substrate paint composition, may be water-based, and in this case, the topcoat composition may also be either as a solution or as a stable dispersion in an aqueous medium. In the case of a dispersion, it may be sterically stabilized, such as prepared by dispersion polymerization by the procedure set forth in GB Patent Application No. 7,940,088 (published as Patent Application No. 2,039,497A), or charge stabilized, such as prepared by well known aqueous emulsion polymerization methods. Unlike the polymeric microparticles of the primer composition, the topsheet polymer can always be of the thermosetting type and thus be able to crosslink after application to the substrate, if desired by means of a crosslinking agent.

Generally, the topcoat composition is substantially colorless so that the pigmentation effect of the primer is not significantly altered, but in some cases it may be advantageous, most commonly if the primer contains metal pigments, to form a transparent tint to the topcoat composition.

In the first step of the method of the invention, the primer composition is applied to the surface of the substrate, which may be pre-primed or otherwise treated in a manner conventional in the art. The substrates of major interest according to the invention are metals such as steel or aluminum, which are commonly used in the manufacture of car bodies, but other materials such as glass, ceramic, wood or even plastic may be used provided they can withstand the temperature at which the multilayer coating is finally cured. . After application of the primer composition, it forms a polymer film on the surface of the substrate. If desired, this can be achieved by applying heating to the substrate and applied coating to remove water and any organic liquid diluents by evaporation, and it is within the scope of the invention to use a heating temperature sufficient to crosslink the primer layer where the composition contains a thermosetting film-forming material. However, a particular advantage of the invention is that it is sufficient to use only a short drying time to achieve that the topcoat composition can be applied to the primer without the tendency for the former to mix or dissolve in the latter in a manner that may interfere with proper orientation of the metal pigmentation. Suitable drying conditions in each individual case depend, inter alia, on the ambient humidity, but generally a drying time of 1 to 5 minutes at 15 to 80 ° C is sufficient to prevent mixing of the two coating layers. At the same time, the topcoat composition suitably wets the primer layer so as to achieve satisfactory interlayer adhesion.

After application of the topcoat composition to the primer layer, the coated substrate may be subjected to a heating or curing treatment to remove volatile carrier fluid from the topcoat and possibly crosslink the film-forming material of the topcoat and / or primer layer with crosslinking agent (s). This heating or curing treatment is usually performed at a temperature in the range of 100-140 ° C, but if desired, this lower temperature may be used provided it is high enough to initiate the required crosslinking mechanism.

When using the method of the invention, the primer and topcoat composition can be applied to the substrate by any conventional method such as brushing, spraying, dipping or draining, but it is recommended to use spray application for best results in pigmentation control, especially metal pigment orientation. Any known spraying method can be applied, for example, compressed air spraying, electrostatic spraying, hot spraying and airless spraying, and either manual or automatic methods are suitable.

The thickness of the applied primer layer is preferably 12.5 to 37.5 micrometers and the topcoat layer 25 to 75 micrometers (in each case the thickness of the dry layer).

As can be seen from the above description, the invention has the advantage, when considering metallic finishes, of providing a primer / clear coat system that eliminates or significantly reduces the disadvantages of air pollution by using a water-based primer composition without compromising good control of metal pigmentation orientation. In the case of full-color finishes, pigment orientation control is of course no longer a significant factor, but the advantage remains that the primer film is not damaged by applying the topcoat composition to it and it has also been found that the primer film is much less susceptible to inside polymeric microparticles.

The invention is illustrated by the following examples, in which parts and percentages are by weight. In these examples, the viscosity values ​​of the primer compositions were measured using two different devices. Täl^a The 1 impact values ​​at a shear rate of 10,000 sec were measured using an ICI Cone and Plate Viscometer as a variation designed to cover a viscosity value of 0-2.0 poise at that shear rate. This measuring device is described in an article by CH Monk in the Journal of the Oil and Color Chemists Association, July 1966, and is manufactured by Research Equipment (London) Limited.

Values ​​ey at a cutting speed of 1.0 sec were measured cl using a Rheomat 30 concentric cylindrical viscometer with ‘A’ cup and weight; each sample was subjected to 660 sec^X until a constant shear force reading was obtained, after which the shear rate was immediately changed to 1.0 sec 1 and the shear force was measured and the viscosity was calculated from these values. Rheomat 30 devices are manufactured by Contraves AG, Zurich; Rheomat is a registered trade name.

Example 1

A. Preparation of a dispersion from polymeric microparticles to an aliphatic hydrocarbon.

A reactor equipped with a stirrer, thermometer, reflux condenser and means for adding monomer to the reflux distillate was charged with 35.429 parts of heptane. This was heated to reflux (95-96 ° C) and then the following premixed ingredients were added:

methyl methacrylate

5.425 parts of absodiisobutyronitrile graft copolymer stabilizer (33% of the following solution)

0.420 parts

1,984 parts

The contents of the reactor were maintained at reflux for 30 minutes to form a seed dispersion of the polymer, after which the following premixed ingredients were fed to the reflux distillate over 3 hours:

<td>methyl methacrylate</td><td> 25,000</td><td>part</td>

<td>allyl methacrylate</td><td> 0,775</td><td>part</td>

<td>azodiisobutyronitrile</td><td> 0,338</td><td>part</td>

<td>graft copolymer stabilizer (33% of the following solution)</td><td> 5,316</td><td>part</td>

At the end of the feed, the reactor components were kept at reflux temperature for a further 1 hour, after which 12.874 parts of heptane were added and the reflux heating was restarted. The following premixed ingredients were then fed to the reactor with the returned distillate at a constant rate over 1 hour:

<td>methyl methacrylate</td><td> 3,883</td><td>part</td>

<td>butyl acrylate</td><td> 3,066</td><td>part</td>

<td>hydroxyethyl acrylate</td><td> 2,044</td><td>part</td>

<td>acrylic acid</td><td> 1,226</td><td>part</td>

<td>azodiisobutyronitrile</td><td> 0,071</td><td>part</td>

graft copolymer stabilizer (33% of the following solution)

2,149 parts

At the end of the feed, the reaction mixture was heated to reflux for 1 hour. A stable dispersion of crosslinked polymer microparticles was obtained with a total non-volatile solids content of 43.5-44.5% and a non-volatile solids content (i.e., gel content) insoluble in any polar solvent.

The graft copolymer stabilizer used in the above procedure was obtained as follows. 12-Hydroxystearic acid was self-condensed to an acid number of about 31-34 mg KOH / g (corresponding to a molecular weight of 1650-1800) and then reacted with an equivalent amount of glycidyl methacrylate. The resulting unsaturated ester was copolymerized in a weight ratio of 2: 1 with a mixture of methyl methacrylate and acrylic acid in a ratio of 95: 5. The copolymer was used as a 33% solution in a mixture of ethyl acetate 11.60%, toluene 14.44%, aliphatic alcohol, b.p. 98-122 ° C, 61.29% and aliphatic hydrocarbon, b.p. 138-165 ° C, 12.67%.

B. Transfer of polymer microparticles to a dispersion in an aqueous medium.

The reactor, equipped with a stirrer, a thermometer and means for removing volatile solvent by distillation, was charged with:

demineralized water 72,308 parts butoxyethanol 10,332 parts dimethylaminoethanol 0.529 parts

The contents of the reactor were heated to 100 ° C and 46.497 parts of the microparticle dispersion from step A was fed at such a rate that the heptane contained in the dispersion was distilled off without forming a significant concentration in the reactor contents. The time required for this was about 2 hours and the amount of distillate, which consisted mainly of heptane and a small amount of water, was 29-30 parts.

The product was a stable aqueous dispersion of polymer microparticles with a non-volatile solids content of 20-22% and a pH of 7.2-7.5.

C. Manufacture of aluminum pigment concentrate

The mixed mixing vessel was charged with: aluminum paste (metal content 65%) 5.8 parts butoxyethanol 2.9 parts

These ingredients were mixed together for 15 minutes and then an additional 2.9 parts of butoxyethanol was added at a constant rate over 30 minutes, after which the mixture was further stirred for 1 hour. 4.84 parts of hexamethoxymethylmelamine were then added thereto, and stirring was continued for 1 hour; finally, an additional 1.93 parts of hexamethoxymethylmelamine and 0.97 parts of butoxyethanol were added and the mixture was stirred for a further 1 hour.

D. Preparation of Primer Composition

The following ingredients:

aluminum concentrate from step C microparticle dispersion from step B hexamethoxymethylmelamine

19.34 parts

79.61 parts

0.46 parts of dimethylaminoethanol salt of p-toluenesulphonic acid, 10% solution in demineralized water

3.57 parts were mixed together for 1 hour. The properties of the primer composition thus obtained were as follows:

solids content: 27.2% apparent viscosity ^; 35 poise cutting-1 '^a at D = 1 s

E. Preparation of Acrylic Polymer for Clear Coating Composition

The reactor, equipped with a stirrer, thermometer and reflux condenser, was charged with:

xylene 22,260 parts of aromatic hydrocarbon (b.p. 190-210 ° C) 10.00 parts

The mixture was heated to reflux (142-146 ° C) and the following premixed ingredients were added at a constant rate over 3 hours:

<td>styrene</td><td> 21,49</td><td>part</td>

<td>ethyl acrylate</td><td> 4,51</td><td>part</td>

<td>2-ethylhexyl acrylate</td><td> 13,75</td><td>part</td>

<td>hydroxyethyl acrylate</td><td> 10,05</td><td>part</td>

<td>acrylic acid</td><td> 0,49</td><td>part</td>

<td>kumeen ihydroperoks idia</td><td> 1,41</td><td>part</td>

<td colspan="3">The reactants were kept at reflux temperature</td>

<td>for 2 hours, after which the following were added:</td><td></td><td></td>

<td>isobutyl alcohol</td><td> 12,72</td><td>part</td>

<td>xylene</td><td> 3,32</td><td>part</td>

The solids content of the clear polymer solution thus obtained was 50%.

F. Preparation of Solvent-Based Clear Coating Composition

The following ingredients were mixed together:

<td>a polymer solution from step E</td><td> 53,3</td><td>part</td>

<td>butylated melamine / formaldehyde resin, a 67% solution of</td><td></td><td></td>

<td>tanolissa</td><td> 26,5</td><td>part</td>

<td>dipentene</td><td> 5,0</td><td>part</td>

<td>A flow-promoting polymer, 10% solution in xylene</td><td> 0,1</td><td>part</td>

<td>isobutyl alcohol</td><td> 2,0</td><td>part</td>

<td>xylene</td><td> 13,1</td><td>part</td>

A clear solution with a solids content of 44.4% was obtained. Its viscosity was 40 sec. (BS B4 cup at 25 ° C).

G. Applying a primer coat and a clear top coat to the substrate.

The metal plate was treated with a primer and a topcoat, then two coats of the metal primer composition from step D were applied by spraying and diluting at 22 ° C and 39% relative humidity. A drying time of two minutes was allowed between layers; the paint flow rate from the sprayer was 400 ml / min.

After application of the second primer layer, the board was blown with air at 25 ° C and then the clear coating of step F was applied in two layers, the clear layer composition being pre-diluted with xylene to a viscosity of 45 sec (BS B3 cup at 25 ° C). The two coats were applied wet to wet using a drying time of two minutes between coats. After a final drying time of three minutes, the plate was kept in an oven at 125-130 ° C for 30 minutes.

The resulting silver-colored metal coating Väike was excellent and showed no displacements and corresponded in appearance to the highest quality glitter finish obtained from the solvent-based paint system alone. The gloss and adhesion between coats were good and there was no indentation of the clear coat in the primer coat.

Example 2

The metal sheet was primed and treated with an abrasive paint, then applied by spraying two coats of the metal primer composition shown in Example 1, Step D without dilution at 25 ° C and 58% relative humidity. Layers spread29

68985 a drying time of two minutes was allowed between the paint flow rate from the paint sprayer was 400 ml / min.

After application of the second primer layer, the board was dried at 35-42 ° C for 10 minutes and then applied with two coats of the clear coating composition of Example 1, Step F, the clear coating composition pre-diluted to a viscosity of xylene for 45 seconds (BS B3 cup at 25 ° C). The two coats were applied wet to wet using a drying time of two minutes between coats. After a final drying time of three minutes, the plate was kept in an oven at 125-130 ° C for 30 minutes.

The properties of the coating thus obtained were as excellent as those shown in Example 1.

Example 3

A, Preparation of an aqueous dispersion of polymer microparticles

<td></td><td>The following premixes were prepared:</td><td></td><td></td>

<td>(i)</td><td>Monomer mixture</td><td></td><td></td>

<td></td><td>methyl methacrylate</td><td> 18,350</td><td>part</td>

<td></td><td>alllyl methacrylate</td><td> 1,340</td><td>part</td>

<td></td><td>styrene</td><td> 4,700</td><td>part</td>

<td></td><td>butyl acrylate</td><td> 18,800</td><td>part</td>

<td></td><td>methacrylic acid</td><td> 1,410</td><td>part</td>

<td></td><td>prim.-octyl mercaptan</td><td> 0,159</td><td>part</td>

<td></td><td>(nonylphenol + 5 moles of ethyl</td><td></td><td></td>

<td></td><td>lene oxide) sulphate ammonium</td><td></td><td></td>

<td></td><td>salt</td><td> 0,185</td><td>part</td>

<td>(ii)</td><td>Initiator solution</td><td></td><td></td>

<td></td><td>ammonium persulfate</td><td> 0,130</td><td>part</td>

<td></td><td>demineralized water</td><td> 4,010</td><td>part</td>

(iii) Surfactant solution methyl methacrylate (nonylphenol + 5 moles of ethylene oxide) sulfate ammo20.00 parts of sodium salt

20,000 parts

The reactor, equipped with a stirrer, thermometer, reflux and means for the controlled addition of two separate liquid feeds, was charged with:

demineralized water

47,641 parts of surfactant solution

<td>(iii)</td><td>0.100 parts</td>

<td>Input</td><td>heated to 80-85 ° C, then added</td>

<td>was set at 2.00</td><td>part of the monomer mixture (i) and the mixture</td>

maintained at 80-85 ° C for 15 minutes. Then, 1.068 part of the initiator solution (ii) was added thereto, and the reaction mixture was kept at the same temperature for 20 minutes. The following premixed ingredients were then added at a constant rate over 5 hours: monomer mixture (i) 42.944 parts of hydroxyisopropyl methacrylate 2.350 parts Over the same 5 hours, 3.672 parts of initiator solution (ii) were fed separately at a constant rate. The reaction mixture was then maintained at 80-85 ° C for 1 hour and then cooled to room temperature to give a stable aqueous dispersion of crosslinked polymer microparticles. The total solids content of the dispersion was 46.6% and the content of non-volatile solids insoluble in any organic solvent was 44.5%.

B. Preparation of the primer composition

Premix (iv)

2.563 parts of a commercial thickener known as Acrysol ASE 60 (Acrysol is a registered trade name, manufactured by Rohm &amp; Haas Company) was mixed with a sufficient amount of a 25% solution of dimethylaminoethanol in demineralized water to bring the pH to 7.65. Demineralized water was then added until the total was 23,956 parts.

Premix (v)

The pH of the mixture containing 29.299 parts of the microparticle dispersion obtained from step A above and 18.614 parts of demineralized water was adjusted to 7.65 by adding a sufficient 25% solution of dimethylaminoethanol in demineralized water. Then, 23.956 parts of premix (iv) prepared as described above was added with stirring.

The mixing device was charged with stirring: aluminum paste (metal content 65%) 5.133 parts 2-butoxyethanol 15.193 parts

The batch was stirred for 15 minutes and then the following was added:

hexamethoxymethylmelamine 3.66 parts of polypropylene glycol (average molecular weight 400) 2.464 parts and stirring was continued for another 1 hour.

Then the following was added:

premix (v) 71.869 parts of demineralized water 1.623 parts and stirring was continued for another 1 hour. The properties of the primer composition thus obtained were as follows:

solids content: 20.5% apparent viscosity34.6 poise at cutting speed D = 1 s ¹

0.42 poy with a D value of 10,000 s

C. Preparation of Acrylic Polymer for Clear Coating

A reactor equipped with a stirrer, thermometer and reflux condenser was charged with 42.20 parts of isopropanol. This was heated to reflux (84 ° C) and the following premixed ingredients were added at a constant rate over 3 hours:

<td>methyl methacrylate</td><td> 19,85</td><td>part</td>

<td>butyl acrylate</td><td> 24,80</td><td>part</td>

<td>hydroxyethyl methacrylate</td><td> 2,48</td><td>part</td>

<td>acrylic acid</td><td> 2,48</td><td>part</td>

<td>isopropanol</td><td> 7,45</td><td>part</td>

<td>benzoyl peroxide (60%</td><td></td><td></td>

<td>paste in dimethyl phthalate)</td><td> 0,74</td><td>part</td>

The reactants were kept at reflux for a further 2 hours. A polymer solution with a solids content of 50% was obtained. From this, 28.87 parts of isopropanol were removed directly by distillation, and 1.86 parts of dimethylaminoethanol and then 80.35 parts of demineralized water were added to the residue with stirring. The distillation of the azeotropic mixture of isopropanol and water was then continued to 96-98 ° C, demineralized water was added again to replace the distillate. The total amount of distillate was 118.83 parts and the amount of demineralized water added was 114.65 parts. An aqueous solution of the acrylic polymer with a solids content of 33.5% was obtained.

D. Preparation of a water-based clear topcoat composition

The following ingredients were mixed together: polymer solution from step C above 71.16 parts hexamethoxymethylmelamine 6.29 parts butoxyethanol 12.26 parts

<td>demineralized water p-toluenesulfonic acid dimethylaminoethyl salt (pH 7.6)</td><td>5.50 parts 0.79 parts</td>

The clear top layer composition thus obtained had a solids content of 31.5% and a viscosity of 0.5

E. Applying a primer coat and a clear top coat to the substrate.

The metal sheet was primed and treated with an abrasive lacquer paint, then applied by spraying three coats of the metal primer composition of step B undiluted at 25 ° C and 51% relative humidity. A one minute drying step was allowed between coats; the paint flow rate from the paint sprayer was 400 ml / min.

After applying the third primer layer, the board was dried for 10 minutes at 35-42 ° C and then three coats of the clear topcoat composition obtained from step D were applied. The three layers were applied wet to wet using a drying time of two minutes between application of the layers and finally a drying time of 3 minutes. The plate was then preheated to 70 ° C and then kept in an oven at 150 ° C for 30 minutes

The coating thus obtained Väike was excellent and showed no displacements and its appearance corresponded to the best obtained with fully solvent-based paint systems. The gloss and adhesion between coats were good and the clear top coat had not sunk into the primer coat.

Example 4

A. Preparation of an aqueous dispersion of polymer microparticles

A reactor equipped with a stirrer thermometer, a reflux condenser and means for adding two separate liquid feeds was charged with 29.030 parts of demineralized water and then a premixed mixture containing 0.029 parts of methyl methacrylate was added. ° C with stirring and the following premixed ingredients were added:

butyl acrylate 0.069 parts methyl methacrylate 0.069 parts

The reaction mixture was kept at 80-85 ° C for 15 minutes, after which a mixture containing:

demineralized water 0.67 parts grace iumper sulfate 0.021 parts

After maintaining the reactor contents at 80-85 ° C for an additional 20 minutes, the following premixed ingredients were added to the reactor at a constant rate over 3 hours:

<td>butyl acrylate</td><td> 10,758</td><td>part</td>

<td>methyl methacrylate</td><td> 10,189</td><td>part</td>

<td>allyl methacrylate</td><td> 0,686</td><td>part</td>

<td>(nonylphenol + 5 moles of ethylene</td><td></td><td></td>

<td>ammonium) sulphate ammonium salt</td><td> 0,081</td><td>part</td>

and at the same time a solution containing was fed to the reactor at a constant rate over the same period of 3 hours

0.037 parts of ammonium persulfate in 4.985 parts of demineralized water.

After completion of the above feeds, the contents of the reactor were maintained at 80-85 ° C for 1 hour. 34.716 parts of demineralized water were then added and the temperature was raised back to 80-85 ° C, then the following premixed ingredients were added at a constant rate over 1 hour:

methacrylic acid 0.950 parts butyl acrylate 2.035 parts hydroxyethyl acrylate 1.357 parts methyl methacrylate 0.950 parts (nonylphenol + 5 moles of ethylene oxide) sulfate ammonium salt 0.901 parts After the completion of both feeds, the temperature of the reaction mixture was maintained at 80-85 ° C for 1 hour, after which it was rapidly cooled to obtain a stable aqueous dispersion of polymer microparticles. The total non-volatile solids content of the dispersion was 30% and the content of non-volatile solids insoluble in organic solvents was 27%.

B. Preparation of the primer composition

The pH of the dispersion from step A was adjusted to 8.0 by the addition of dimethylaminoethanol and 54.15 parts by weight were charged to the stirrer. The following ingredients were then added in that order:

demineralized water 18.91 parts butoxyethanol 8.12 parts aluminum pigment concentrate (shown in Example 1 (C). 18.02 parts

The mixture was stirred for 1 hour to obtain a primer composition having the following properties:

solids content: 25.8% apparent viscosity'Q: 20 poise 1 window speed D = 1 s ~ l

0.2 poise at a cutting speed of D = 10,000 s¹

C. Applying a primer coat and a clear top coat to the substrate

Two layers of the metal primer composition obtained from step B were applied undiluted to a primed and abrasive coated metal sheet at 22 ° C and 39% relative humidity. The clear topcoat composition that was then applied was the same as shown in Example 1, Step F, and the procedure for applying both the primer layer and the clear topcoat was otherwise the same as that set forth in Example 1, Step G.

The results obtained were similar to those shown in Example G, Example.

Comparative Example A

A. Preparation of a silver metallic primer composition without microparticles.

The following was added to the mixer with stirring:

6.0 parts of aluminum paste (metal content 65%)

18.7 parts of 2-butoxyethanol

The batch was stirred for 30 minutes and then the following ingredients were added:

hexamethoxymethylmelamine 4.3 parts polypropylene glycol (average molecular weight 400) 2.9 parts and stirring was continued for another 1 hour. Then, with stirring, 51.2 parts of an aqueous solution of the acrylic polymer shown in Example 5 (C) containing 33.5% solids and then 16.9 parts of demineralized water were added over 30 minutes.

The pigment-binder ratio of the primer composition thus obtained was the same, the ratio of hexamethoxymethylmelamine to the total amount of nonvolatile matter was the same, and the value of the apparent viscosity (0.3 poise) at D was 10,000 sec. ^X was almost the same as the values ​​shown in Example 1 for the primer composition of the invention. The apparent viscosity value of the composition free of polymer microparticles indicated that it was suitable for application by spraying to a substrate; but I see such viscosity at low cutting speeds, i. D = 1 sec^Z, was found to have only about 1 poise, indicating that the composition had only minor pseudoplastic or thixotropic properties.

The primer composition was applied to the substrate and covered with a clear acrylic coating composition as shown in Example 1 (G), wherein the clear coating composition used was the same as in Example 1 (E) and (F). The small amount of the silver-metal coating thus obtained was very weak and showed transition streaks. It was also prone to crackling when heated in the oven.

Examples 1-4 illustrate the invention applied to the manufacture of metallic coatings. The following example illustrates its application to the production of full-color coatings.

Example 5

A. Preparation of paint base from white pigment

The following ingredients were ground together in a ball mill for 16 hours:

titanium dioxide pigment

2-butoxyethanol demineralized water dimethylaminoethanol hexamethoxymethylmelamine

31.3 parts

18.9 parts

18.9 parts

0.2 parts

7.7 parts

The obtained paint base with a particle size of less than 0.5 micrometers was then diluted with 11.6 parts

2-butoxyethanol and 11.6 parts of demineralized water.

B. Preparation of paint base from blue pigment

The following ingredients were ground together in a ball mill for 16 hours:

<td></td><td>phthalocyanine blue pigment</td><td colspan="2">12.9 parts</td>

<td></td><td>2, butoxyethanol</td><td colspan="2">23.8 parts</td>

<td></td><td>demineralized water</td><td colspan="2">23.8 parts</td>

<td></td><td>dimethylaminoethanol</td><td colspan="2">0.2 parts</td>

<td></td><td>hexamethoxymethyl-imylamine</td><td colspan="2">9.7 parts</td>

<td colspan="2">Obtained paint base with a smaller particle size</td><td>than</td><td></td>

<td> 0,</td><td colspan="2">5 micrometers, then diluted with 14.8 aliquots of 2-</td><td></td>

<td colspan="3">butoxyethanol and 14.8 parts of demineralized water</td><td>ί.</td>

<td>C.</td><td>Preparation of an aqueous solution of acrylic polymer</td><td></td><td></td>

<td></td><td colspan="2">The following ingredients were mixed together:</td><td></td>

<td></td><td>methyl methacrylate</td><td> 19,9</td><td>part</td>

<td></td><td>butyl acrylate</td><td> 24,8</td><td>part</td>

<td></td><td>hydroxyethyl methacrylate</td><td> 2,5</td><td>part</td>

<td></td><td>acrylic acid</td><td> 2,5</td><td>part</td>

<td></td><td>isopropanol</td><td> 7,4</td><td>part</td>

<td></td><td>benzoyl peroxide</td><td> 0,7</td><td>part</td>

A mixture of 15.0 parts of the above mixture and 42.2 parts of isopropanol was charged to a vessel equipped with a stirrer, thermometer, reflux condenser and means to increase the liquid supply at a controlled rate. The contents of the vessel were heated to reflux (84 ° C) and the remainder of the above mixture (42.8 parts) was added at a constant rate over 3 hours. The reaction mixture was heated under reflux for an additional 2 hours to give a polymer solution with a solids content of 51.0%. To this solution was then added 1.8 parts of dimethylaminoethanol, the mixture was reheated to reflux, and a total of 33.0 parts of distillate were removed over 10 hours using a condenser while adding 85.0 parts of demineralized water. The aqueous solution of the acrylic polymer finally obtained had a solids content of 33.5%.

D. Preparation of Blue Undercoat Composition

The following ingredients were mixed together in this order:

a white paint base according to (A), a blue paint base according to (B), a microparticle dispersion according to Example 1 (B), an acrylic polymer solution according to (C), a 10% aqueous solution of p-toluenesulfonic acid, adjusted to pH 7.6 by adding dimethylaminoethanol

52.25 parts

8.39 parts

14.62 parts

24.33 parts

0.41 parts

The resulting primer composition had a viscosity of 16.0 poise at a shear rate of 1 sec and 0.53 poise at a shear rate of 10,000 sec.

E. Application of primer and clear top coat to substrate.

The metal sheet was treated with a primer and a topcoat, then applied by spraying two coats of the blue primer composition of step (D) without dilution at 22 ° C and 39% relative humidity. A drying time of two minutes was allowed between coats. After applying the second primer layer, the sheet was blown with air at 25 ° C and then two coats of the clear coating composition of Example 1 (F) were applied, the clear coating composition being pre-diluted with xylene to a viscosity of 45 seconds as measured by BS cup B3 at 25 ° C. The two top coats were applied wet to wet using a two minute drying time between coats. After a final drying time of three minutes, the plate was placed in an oven at 125-130 ° C for 30 minutes.

The opacity and gloss of the obtained coating were good and there was no indentation of the clear coating layer in the primer.

Comparative Example B

A. Preparation of a Blue Substrate Composition Without Polymer Microparticles.

The following ingredients were mixed together in the order given:

white paint according to Example 5 (A) blue paint according to Example 5 (B) hexamethoxymethylmelamine acrylic polymer solution according to Example 5 (C) 10% aqueous solution of p-toluenesulphonic acid brought to pH 7.6 by adding dimethylaminoethanol

54.9 parts

8.8 parts

0.3 parts

35.7 parts

0.4 parts

The resulting primer composition had a viscosity of 1.0 poise at a shear rate of 1 sec and 0.83 poise at a shear rate of 10,000 sec; this means that its pseudoplastic or tistropic properties were highly HeiB. Applying a primer and a clear coating to the substrate.

The procedure of Example 5 (E) was repeated except that the primer composition of Example 5 (D) was replaced with the primer composition of (A). In this case, a significant spatter of the primer was observed, i.e. air trapped in the primer layer was removed by bubbling, breaking the surface of the film and damaging its uniform appearance. In addition, a drying time of more than three minutes was required between the application of the second primer layer and the first clear top coat, otherwise the clear top coat adversely affected the substrate layer and the final appearance of the board.