Method of manufacturing multilayer decorative and/or protective coatings on substrate surface

The invention relates to the application of protective and decorative coatings to surfaces, in particular to the surface of automobile bodies.

Especially in the automotive industry, it is well known to use coatings containing metal pigments. These so-called "metallic paints" show different light reflectance depending on the viewing angle. In order to achieve the highest degree of this effect, the so-called "flip", great attention must be paid to the composition of the coating himota, both the film-forming resin and the liquid medium. It may be difficult to design a single mass that meets the above requirement and at the same time exhibits a high degree of gloss after finishing, as is typically required for automobiles. For this reason, a process involving the application of two coatings has been proposed as one of the processes proposed for the production of inetallic coating.

The first coating to be applied by spraying onto the surface of the substrate is a metallic pigment containing primer. This coating is formulated to achieve an optimal flip. A non-pigmented topcoat is again sprayed over the base coat to achieve the desired gloss level without modifying the base coat characteristics in any way.

The basic criterion for a successful two-layer metallic system consisting of a base layer and a clear coating is that the base film coating must be able to withstand the solvents contained in the mass of the clear coating film when applying the coating. This is important to avoid damaging the metal pigment and thereby aggravating the flip. Moreover, it is highly desirable that the base coat has this property without having to undergo long intermediate drying or curing.

In the known base coat / clear coat systems, in which both the base coat and the solvent-based cover coat, this requirement is achieved in most cases by the use of an additive capable of imparting a gelatinous character to the freshly formed base film. Cellulose acetobutyrate was used predominantly as this additive. The transition between the relatively low viscosity that the primer in the spray gun must have and this gelatinous. by nature it is aided that the liquid diluent contained in this mass contains volatile components which preferably evaporate during the journey from the spray gun to the substrate.

In an effort to prevent atmospheric pollution, recent interest has been focused on coating compositions in which water is used as a diluent instead of organic solvents. A large number of such compositions have been suggested for use in the automobile industry. Until now, however, it has not been possible to successfully use aqueous compositions based on primers / clear coat systems as a primer. One of the factors that tends to hinder the successful achievement of this goal is that it is extremely difficult to selectively vaporize the diluent from the primer between the spray gun and the substrate in a controlled manner, except for the very costly humidity control in the spraying environment. Surprisingly, it has now been found that satisfactory aqueous-based coating compositions based on an aqueous dispersion of cross-linked polymeric micro-gel can be obtained.

It is an object of the present invention to provide a multi-layered protective and / or decorative coating on a substrate surface by

1. apply to the surface a matrix comprising a) a film-forming substance, b) a volatile liquid medium for the substance and c) pigment particles dispersed in the liquid medium,

2. the material applied in step 1 forms a polymer film on the surface,

3. a transparent topcoat comprising d) a film-forming polymer and e) a volatile carrier liquid therefor is applied to the base film thus obtained;

4. of the mass applied in step 3. forming a second polymeric film on the base film, characterized in that a dispersion of crosslinked polymeric microparticles in an aqueous medium is formed as components a) and b) of the base coat and are formed from acrylic-addition polymers derived predominantly from at least one alkyl acrylate; methacrylic and having a diameter of 0,01 to 10 μΐη, insoluble in the aqueous medium used and stable to coarse flocculation, the dispersion having a pseudoplastic or thixotropic character.

Suitable crosslinked polymeric microparticles are acrylic addition polymers derived from one or more alkyl esters of acrylic or methacrylic acid or mixtures thereof with other ethylenically unsaturated monomers. Suitable esters of acrylic or methacrylic acid are 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 vinyltoluene. Since the polymer is to be crosslinked, minor amounts of monomer that are polyfunctional to the polymerization reaction, such as ethylene glycol dimethacrylate, allyl methacrylate or divinylbenzene, may be added to the monomers from which the polymer is prepared. Alternatively, minor amounts of two additional monomers bearing pairs of chemical groups may be added to these monomers, which may be reacted together either during or after the polymerization. Examples of such pairs of mutually reactive groups include an epoxy group and a carboxy group (for example, a glycidyl methacrylate-methacrylic acid system), an anhydride group and a hydroxy group or an isocyanate group and a hydroxy group.

The chemical composition and degree of crosslinking of the microparticulate polymer may be such that the polymer has a glass transition temperature Tg of either below room temperature, in which case the particles have a rubbery character, or- higher than room temperature then hard and glassy particles.

As already mentioned, the polymer microparticles need to be dispersed in the matrix in a state that is stable to coarse flocculation, i.e. in a state where, even at low solids content, the dispersion contains few aggregates of a larger number of particles, if at all contains some such aggregates. However, this does not exclude the possibility of a slight degree of flocculation of the particles, especially at higher solids content. This can be achieved, for example, by spherical stabilization, i. by forming a wall of chains of another polymer around the particles that are solvated by the aqueous coating composition. Therefore, these strings have an advanced configuration. The term "solvated" in this context means that these polymer chains would actually be soluble in said aqueous medium if they formed independent molecules. However, since these chains are attached to the microparticles at one or more sites, the spherical barrier remains permanently attached to the microparticles. The spherically stabilized polymer microparticles may conveniently be prepared by a process of dispersed polymerization of the respective monomers in an aqueous medium in the presence of a spherical stabilizer. The stabilizer is amphipathic in nature; it contains two basic polymeric components with different properties in the molecule: one component is a polymer chain which is solvated by an aqueous medium and the other a polymer chain which is not solvated by this medium and consequently anchors on polymeric microparticles which by definition are insoluble in aquatic environment. Suitable dispersion polymerization processes are described in British Patent Application Publication No. 2,039,497A. The aqueous medium in which the polymerization is carried out consists of water mixed with a volatile organic co-solvent. The mixture of water and co-solvent is capable of dissolving monomers, most or all of which would be substantially insoluble in water alone. These procedures include the additional requirement that the polymerization be carried out at a temperature which is at least 10 ° C higher than the glass temperature of the polymer to be formed, and the requirement that no separate monomer phase be present in the system at any time. . The amphipathic steric stabilizer may be added to the polymerization mixture as a 'preformed substance' or may be formed in situ during polymerization from an aqueous-soluble polymer that is capable of copolymerizing with any of the polymerized monomers, or after hydrogen cleavage, it may undergo copolymerization with one of the polymerized monomers. The sterically stabilized dispersions of microparticles obtained by these processes are very suitable for the production of the base materials used according to the invention, since the organic co-solvent can be separated therefrom by distillation without compromising the stability of the dispersed phase to form a product in which a continuous phase consisting entirely of water.

Alternatively, the dispersion of polymeric microparticles can be obtained by aqueous emulsion polymerization of suitable monomers. In this case it achieves stability to flocculation by the presence on the particles of electrically charged substances derived from a water-soluble ionogenic surfactant and / or a water-soluble ionizable surfactant.¹ polymerization initiator. Such polymerization processes are extensively described in the literature.

Polymeric microparticles can further be produced by a non-aqueous dispersion monomer polymerization process after which the resulting polymer is transferred to an aqueous medium. Such a procedure is described in British Patent Application Publication No. ICI No. 2,006,229A. In a first step of this process, a sterically stabilized dispersion in a non-aqueous liquid forms a polymer which is insoluble in both the non-aqueous liquid and water using any of the processes known for making such dispersions. the dispersion thus obtained is polymerized in the presence of a spherical stabilizer one or more monomers from which a second polymer may be formed, which itself is soluble in the desired aqueous medium at a suitable pH and finally the resulting composite polymer microparticles are transferred from the non-aqueous medium to the aqueous medium.

The above discussion is focused on the case where the crosslinked polymer microparticles consist of addition polymers, which are the most suitable type of polymers for this purpose. However, it is also possible for the microparticles to be formed from a condensation type polymer, for example a polyester prepared from a polyhydric alcohol and a polybasic acid. Suitable polyhydric alcohols are propylene glycol, butylene glycol, 1,6-hexylene glycol neopentyl glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, glycerol, trimethylolpropane, tri-methylolethane. pentaerythritol, dipentaerythritol, tripentuerythritol, hexanetriol, styrene and allylalcohol oligomers (for example, the product of Monsanto Chemical Compound "RJ 100"), condensation products of trimethylolpropane with ethylene oxide or propylene oxide (such as commercially available products such as triacetols). Suitable polycarboxylic acids are succinic acid (or anhydride), adipic acid, agelaic acid, sebacic acid, maleic acid (or anhydride), furnaric acid, muconic acid, itonic acid, phthalic acid [or its anhydride, isophthalic acid, terephthalic acid] , trimellitic acid (or anhydride thereof) and pyromellitic acid (or anhydride thereof). Enhancement of polycondensates is achieved by adding substances of greater functionality than 2 to the initial reaction mixture, although in this case it may be difficult to ensure that all molecules are actually crosslinked. This is because the polycondensation molecules are characterized by a broad molecular weight distribution compared to the addition polymer molecules.

The methods outlined above for making polymeric microparticles by polymerizing addition type monomers in an aqueous medium are generally not applicable to condensation type monomers because water has an inhibitory effect on the condensation reaction. However, microparticles of condensation polymers can easily be produced by non-aqueous dispersion polymerization according to the procedures described in British Patent Nos. 1,373,531, 1,440,794 and 1,419,199. These microparticles can then be subjected to a second polymerization stage in a non-aqueous medium dispersion as described above. in British Patent Application Publication No. 2,006,229A cited above, after which the microparticles are transferred to a selected aqueous medium.

The term "aqueous medium" is used herein to refer to either water alone or water mixed with a water-miscible organic liquid such as methianol. The aqueous medium may also contain water-soluble substances added to adjust the pH of the matrix, as detailed below¹ described below.

The pigment particles which, by definition, are dispersed in the aqueous medium of the matrix may have a size in the range of 1 dd 50 and may be any of the pigments commonly used in coating compositions for¹ surface treatment of substrates such as inorganic pigments, for example titanium dioxide, gelatinous oxide, chiromoxide, lead chromate and carbon black, organic pigments; for example, phthalocyanine blue and phthalocyariin green, carbazole violet, anthrapyrimidine yellow, flavathutran yellow, iso-dihydrate yellow, indan thronium, quinacridone violet and perylene red. For the purposes of the invention, the term pigment also includes conventional fillers and extenders such as talc or kaolin.

The process according to the invention is of particular importance in the case of primers containing metallic flakes as pigment, which are used for the production of bright metallic coatings, the so-called metallic paints, mainly on the surface of car bodies. Particularly suitable metal pigments are aluminum flakes and copper bronze flakes. However, the invention also offers advantages in permanent shade painting, as detailed below. Generally, pigments of any kind can be added to the matrix in an amount of from 2 to 100%, based on the total mass of the mass. When metal pigments are used, their amount is preferably in the range of 5 to 30 percent by weight based on the total weight of the mass.

These pigments, whether metallic or otherwise, can be blended into the matrix using known pigment dispersants suitable for use in aqueous systems.

The presence of the crosslinked polymeric microparticles in the coating composition confers the desired filmmaking capability to withstand the subsequent application of the coating coating without disturbing the film or pigmentation, especially pigmentation with metallic pigments. Without the use of these microparticles, a satisfactory matrix / clear coating system cannot be produced.

In addition to this essential property, it is also desirable that the dispersion of insoluble microparticles be of a pseudoplastic or thixotropic nature. It is to be understood that the apparent viscosity of the dispersion varies according to the degree of shear to which the dispersion is exposed, in particular that the apparent viscosity under conditions of low shear is higher than at high shear. The change in viscosity that occurs when the shear applied is changed may be immediate or may require a finite time interval, but is within the viscosity measurement time range. The reason why the dispersion on which the matrix is ​​based is required to have this character is most evident in the case where the matrix contains metallic flakes as pigment. In such a case, it is desirable that the total concentration of non-volatile solids present be relatively small. Thus, after application to the substrate and during drying, a substantial shrinkage of the base film can be achieved, resulting in the correct orientation of the metal flakes and an optimum flip effect. However, when the primer is to be applied to the substrate by spraying, it needs to have a sufficiently low viscosity to ensure efficient spraying in the spray gun. However, as soon as the mass hits the substrate, its viscosity should be bravely high in order to prevent it from flowing, creating curtains or uneven distribution and uneven orientation of the metal flakes, even though water and other solvents are evaporated by evaporation between the spray gun and the substrate. low (due to high ambient humidity).

These pseudoplastic properties are often documented by reporting the apparent viscosity values ​​of 7j in Pa. s at the selected shear rate D [s¹]. In the case of the metallic pigment base materials used according to the invention, this value ηa should be below 30% by weight, preferably less than 0.05 Pa, at a non-volatile solids content. s at shear rate D = 10 000 s¹ and more than 2 Pa. s at D = 1 s^_1. More preferably, the matrix has a r-value of less than 0.025 Pa. s at D = 10,000 s^_1 and more than 4 Pa. s at D = 1.0 s¹. In the case of primers dyed to permanent shades with pigments other than metal flakes, the preferred value of ya, again with a solids content below 30%, is less than 0.1 Pa. s at D = 10,000 s¹ and more than 0.5 Pa. s at D = 1.0 s¹. Preferably, the γ i is less than 0.07 Pa. s at D = 10000 s¹and greater than 1.0 Pa. s at D = 1,0 s'¹. However, it is in the nature of pseudoplastic- or thioxotropic behavior that they cannot be fully and accurately defined by several selected viscosity / shear stress data. Much depends on the viscosity measurement method actually used. Therefore, the above values ​​cannot be considered as strict limits to be observed in order to achieve the advantageous effects of the invention. Rather, this is an approximate guide and one of ordinary skill in the art can readily determine, by simple practical tests, whether a particular dispersion or a matrix formed therefrom has a sufficient degree of pseudoplasticity or thioxotropy.

There are various ways in which the base dispersion can be given a pseudoplastic or thloxotropic nature. In some cases, no special measures are required. Thus, for example, the microparticles may have been prepared as described above¹ according to the procedure described in British Patent Application Publication No. 2,006,229A. In this process, the polymer (microparticles) is first produced by dispersing polymerization of suitable monomers in a non-aqueous medium and then polymerizing other monomers to produce a second substantially non-crosslinked polymer having hydrophilic character, which means that it is inherently soluble at a suitable pH. in an aqueous medium in which the resulting dispersion is to be formed. In fact, not all of the second polymer dissolves in the aqueous medium when the product obtained by the two-step polymerization in the non-aqueous medium is transferred to the aqueous medium. Much of the second polymer remains associated with the polymeric microparticles, and the microparticles are thereby stabilized in dispersion in an aqueous medium. The associated polymer can simultaneously impart pseudoplastic or thioxotropic properties to the aqueous dispersion. Other monomers suitable for the second polymerization step are, for example, hydroxyalkyl esters of acrylic or methacrylic acid, monoesters of acrylic or methacrylic acid and polyglycol such as polyethylene glycol, monovinyl ether of such polyglycol, or vinylpyrrolidone, optionally in admixture with minor amounts of nonhydrophilic monomers methyl methacrylate, butyl acrylate, vinyl acetate or styrene.

Alternatively or additionally, the desired aqueous solubility may be achieved by using an acrylic-type ester containing basic groups as the major monomer component, for example, dimethylsulfonyl, e.g. Ethyl methacrylate or diethyl ammonium methacrylate. These groups are then converted to salt groups by reaction with a suitable acid, for example lactic acid, dissolved in an aqueous medium. The second polymer may further be derived from comonomers containing a substantial amount of a polymerizable carboxylic acid, such as acrylic acid or methacrylic acid, in which case the polymer may be soluble in an aqueous medium containing a dissolved base such as dimethylaminoethanol. Thus, generally, the second polymer may be nonionic, anionic or cationic in nature.

If the polymeric microparticles have been produced by a known aqueous emulsion polymerization process, the second inherently water-permeable polymer can be produced by further polymerization in the same aqueous medium and in the presence of microparticles. The monomers used are monomers capable of providing a polymer which contains acidic salt groups which can impart water solubility to the polymer. Thus, suitable monomers are polymerizable carboxylic acids such as acrylic or methacrylic acid, optionally together with minor proportions of non-hydrophilic monomers, such as methyl methacrylate, as well as hydrophilic monomers, which provide water-insoluble homopolymers such as hydroxyethyl methacrylate and hydroxypropyl methacrylate.

If the polymeric microparticles have been produced by the aqueous dispersion polymerization process described in the above-cited British Patent Application No. 2,039,497A, the second water-soluble polymer can conveniently be formed by further polymerization in the same medium. Suitable monomers are those mentioned in the preceding paragraph and also basic monomers, such as dimethylaminoethyl methium crystals, from which water-soluble salts can be formed.

Not all water-soluble polymers produced in situ in the presence of microparticles by any of the methods described above can impart the desired pseudoplastic properties to the primer. A suitable polymer composition can be obtained by simple testing, for example by measuring the viscosity at selected shear rates, or by actually applying the compositions to the substrate.

Instead of preparing a suitable water-soluble polymer in situ, the polymer may be added as a preformed separate component to the aqueous dispersion of microparticles. Suitable polymers are those which, when dissolved in an aqueous medium even at low concentrations, cause a significant increase in the viscosity of the mass. For example, one or more thickeners which are well known and used in aqueous polymer latex based coatings may be added. However, not all thickeners are suitable for this purpose, since some of them are unable to impart the necessary pseudoplastic properties to the materials to which they are added. On the other hand, some thickeners which, when dissolved by themselves in an aqueous medium, do not possess these properties, can impart these properties to the dispersion of the microparticles through interactions between them and the microparticles (for example via hydrogen bridges or polar group interactions). One of the commercially available thickeners that has proven very advantageous is "Acrysol" ASE60 (Rohm and Haas).

It follows from the foregoing that any inherently water-soluble polymer which is associated with polymer particles or which is added to the microparticle dispersion to impart pseudoplastic or thioxotropic properties to the dispersion must be non-crosslinked in nature; however, such a polymer may, if desired, be a polymer of the crosslinkable type. That is, it may contain chemically reactive groups by means of which it can be crosslinked after application of the primer and preferably also the coating coatings. Optionally, the crosslinking may be carried out with the aid of an added crosslinker. Thus, the polymer may contain, as already shown, hydroxyl or carboxyl groups derived from monomers bearing these groups and these groups can be used for subsequent crosslinking using an amino resin, for example methylated methoformaldehyde; condensate which is soluble in an aqueous medium.

It follows from the foregoing description that the primer coating composition may consist solely of polymeric microparticles, pigment particles, an aqueous medium in which both groups of particles are dispersed and an inherently water-soluble polymer which imparts pseudoplastic properties to the mass. This is true, but much more preferred if the composition also comprises a film-forming polymer which is soluble in an aqueous medium. The presence of the film-forming polymer ensures that upon application of the matrix to the substrate and evaporation of the aqueous medium, a substance is present on the substrate that can coalesce and fill the voids between the microparticles to form a coherent sufficiently integrated film in the second step of the process. In fact, part of the inherently water-soluble polymer that is present in the mass to impart pseudoplastic or thioxotropic properties can fulfill this function. Since the amount of such polymer required for this purpose is usually low, it may be appropriate to supplement it with one or more other water-soluble film forming agents which are added to the mass. These substances may optionally be chemically reactive with the components already present. Thus, the composition may contain oligomeric substances which, upon application of the composition, may be converted to high molecular weight products, but which in themselves do not significantly contribute to the viscosity of the composition prior to application. Examples of these are low volatility diols such as 2-ethyl-1,3-hexanediol, low molecular weight propylene glycols, low molecular weight adducts of ethylene oxide with divalent or trivalent alcohols such as neopentyl glycol, bisphenol A, cyclohexanedimethanol, glycerol and trimethyl β-hydroxyalkylamides such as HHN1NM.traks- (3-hydroxyethyl) adipamide and cyclic amides and esters such as ε-caprolactam and ε-capro-lactone. If these substances are not sufficiently soluble in pure water, they should be soluble in an aqueous medium containing water together with an organic liquid which is miscible with water. Each of these oligomeric materials can be converted to a high molecular weight polymer upon application of the matrix to the substrate by utilizing their hydroxyl groups or other reactive groups to form linkages using a polyfunctional reagent which is also present in matter. Particularly suitable for this purpose are amino-resins soluble in the aqueous medium of the mass, in particular melamine-formaldehyde condensates such as hexa-alkoxymethyl-melamine and their low molecular weight condensates.

Instead of containing the constituents of the film-forming polymer when applied to the substrate, the primer may comprise a preformed water-soluble acrylic polymer that does not impart pseudoplastic properties to the mass, or may contain dispersed particles of non-crosslinked polymer that are stabilized similar; in a manner such as the cross-linked microparticles present. Each of these alternative components may optionally contain functional groups, such as hydroxy groups, through which it can be crosslinked after application of the mass to the substrate using a crosslinking agent, for example an amino resin.

The relative proportions of the amounts of the various constituents of the matrix may vary within wide limits, and the optimum ratios of each individual system are often best determined experimentally, but some general principles may serve as a guide. Particular consideration should be given to the fact that when the amount of polymeric microparticles is too high in relation to the other film-forming substances present in the mass, the mass does not contain sufficient material to fill the gaps between the microparticles. In this case, after the application of the clear coating, the coating has a tendency to decrease (sow into the gaps of the base film, resulting in a loss of gloss. On the other hand, if the microparticle content is too low, the particles may not give the base film the desired degree of resistance against attack by the solvent contained in the clear coating material. To a certain extent, a lower amount of microparticles can be compensated in this direction by allowing the base film to dry for a longer time before applying the clear coating, but thereby reducing one of the main advantages to be obtained in the process of the invention. The satisfactory microparticle content is usually in the range of 5 to 80% by weight based on the total non-volatile content of the matrix. However, the optimum microparticle content depends to some extent on whether the pigment present in the matrix is ​​metallic or non-metallic. For compositions containing metal pigments, the preferred microparticle content range is 40 to 75% by weight based on the above base. Using conventional color fast pigments, the preferred range of microparticle content is somewhat lower, i. 10 up to 50% by weight, based on the aforementioned base, since higher amounts of these pigments are usually required to achieve suitable opacity at a sufficiently low film thickness. By reducing the amount of microparticles, an excessively high volume fraction of the total amount of dispersed substances that could result in the formation of a porous base film can be avoided. Applying the opaque coating to such a porous filament could leak (infiltrate) the opaque coating composition into the base coat, resulting in poor gloss of the opaque film.

As regards the thickener or second polymer which imparts pseudoplastic properties to the mass, it can generally be stated as a guide that their amount in the matrix may vary from 0.3 to 50% by weight, based on the total non-volatile content of the matter. The amount of other film-forming substances present in the mass may be in the range of 0 to 30% by weight, and when a crosslinker such as an amino-resin is present, the amount may also be up to 30% by weight based on the total non-volatile content of the base material. In addition, the matrix may optionally contain a crosslinking catalyst to be carried out after application of the matrix to the substrate. The catalyst may be a water-soluble acidic compound, such as p-toluenesulfonic acid, orthophosphoric acid, maleic acid or another strong carboxylic acid, such as tetrachloroththalic acid. Instead of the acid, the thermally volatile salts of such an acid with a volatile amine can also be used.

The nature of the film-forming polymer in the topcoat used in step 3 of the process of the invention is not critical. In general, any suitable film-forming polymer may be used, which may be of the thermosetting or thermoplastic type. One suitable class of polymers consists of polymers derived from one or more ethylenically unsaturated monomers. Particularly suitable representatives of this class of materials are acrylic addition polymers, which are well established in the automotive coating industry. These are polymers or copolymers of one or more alkyl esters of acrylic or methacrylic acid, optionally together with other ethylenically unsaturated monomers. Suitable acrylic esters are methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, ethyl acrylate, butyl acrylate and 2-ethylhexyl acrylate Suitable other copolymerizable monomers are vinyl acetate, vinyl propionate, acrylonitrile, styrene and vinyltoluene. In the event that the acrylic polymer is to be thermosetting, i. functional monomers such as acrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, N- (alkoxymethyl) acrylamide and N- (alkoxymethyl) methacrylamides, wherein the alkoxy groups may be, for example, butoxy, glycidyl acrylate and glycidyl methacrylate. The topcoat may in this case also contain a crosslinker such as a diisocyanate, diepoxide or preferably a nitrogenous resin, i.e. a formaldehyde condensate with a nitrogen compound, such as urea, thiourea, melamine or benzoguanamine or a lower alkyl ether of such a condensate in which Alkyl groups containing 1 to 4 carbon atoms. Particularly suitable crosslinkers are the melaiminoformaldehyde condensates in which a substantial proportion of the methylol groups have been etherified by reaction with butanol.

The topcoat may contain a suitable crosslinking catalyst between the acrylic polymer and the crosslinker, for example an acid-reacting compound such as acid butyl maleate, acid butyl phosphate or p-toluenesulfonic acid. Alternatively, the acidic substances may be added to the mass via the free acid groups of the acrylic monomers, for example when acrylic acid or methacrylic acid is used as the comonomer in the preparation of the polymer.

The coating polymer may be present in the coating coating composition either in the form of a solution or in the form of a constant dispersion in the volatile carrier liquid, in other words, the carrier liquid may be a solvent or a non-solvent for the coating polymer. When the liquid is to be a solvent, it may be any organic liquid or a mixture of organic liquids commonly used as solvents for polymers in coating compositions, for example aliphatic hydrocarbons such as hexane and heptane aromatic hydrocarbons such as · Toluene and xylene, petroleum fractions of varying boiling points, which are predominantly aliphatic but contain enough flavoring substances, esters such as butyl acetate, ethylene glycol diacetate and 2-ethoxy-ethyl acetate, ketones such as acetone and methyl isobutyl ketone; and alcohols such as butyl alcohol. The particular choice of liquid or mixture of liquids as the carrier liquid depends on the kind of polymer of the coating and is made according to principles well known in the art of coating so that the polymer is soluble in the selected liquid.

If the carrier liquid is to be an organic non-solvent, substances with a slightly lower polarity than those mentioned above are suitable. One or more aliphatic hydrocarbons such as hexane, heptane or low aromatic compound petroleum fractions may be used, optionally in admixture with liquids having a high polarity, such as the above liquids. However, the resulting mixture must be a non-solvent for the coating polymer. Thus, in this case, the coating is a non-aqueous polymer dispersion and is usually a sterically stabilized dispersion in which the polymer particles are stabilized by a block or graft copolymer, one polymer component of which is unsolvable by the liquid used and associated with the dispersion polymer. The well-known bases according to which such dispersions are prepared are widely described in patents and other literature, for example in British Pat. 941 305, 1 052 241, 1 122 397 and 1 231 614 and in the publication "Dispersion Polymerization in Organic Media" red. KFJ Barrett (John Wiley and Sons, 1975)

Alternatively, the topcoat, like the base, may be aqueous based, and in this case the topcoat polymer may be present either in solution or in the form of a stable dispersion in an aqueous medium. If it is a dispersion, the dispersion can be sterically stabilized, such as when the dispersion has been prepared by aqueous dispersion polymerization, as described in the published UK patent application. C. 2 039 497A, or may be stabilized by electric charges, such as in the case of dispersions prepared by well known aqueous emulsion polymerization processes.

In contrast to the polymeric microparticles contained in the primer, the coating polymer is always a thermosetting type polymer, i.e. a polymer that can be crosslinked after application to the substrate, optionally with the aid of a crosslinker.

The topcoat is usually substantially colorless in order not to substantially alter the effect of the pigment contained in the base film, but in some cases - more often when primers containing metal pigments have been used - a transparent coloring of the topcoat is desirable. mass.

In the first step of the process according to the invention, the primer is applied to a surface of a substrate which may have previously been coated with a primer or otherwise treated in a conventional manner. The process according to the invention is of particular interest for coating metal surfaces, such as steel or aluminum surfaces, which are commonly used in the manufacture of automobile bodies, but can also be used on other substrates such as glass, ceramics, wood or plastics, provided They are capable of withstanding temperatures at which the final curing of the multilayer coating is carried out. Upon application of the primer, a polymer film is formed from the substrate on the substrate surface. This may optionally be achieved by heating the coated substrate to evaporate the water and any organic liquid diluents contained in the coating. It is also within the scope of the invention to use temperatures sufficient to crosslink the base film in those cases where the coating composition comprises a thermosetting type film forming agent. However, the main merit of the invention is that for drying to ensure that the coating can be applied to the base film without any tendency to mix the coating with the base film or dissolve the base film to such an extent that it would result in disruption of the correct orientation of the metallic pigment to achieve the optimal flip effect, and only a short period of time is sufficient. Suitable drying conditions in each individual case depend, inter alia, on the drying conditions. The mixing of the two coatings is usually avoided when the base coat is dried for 1 to 5 minutes at 15 to 80 ° C. At the same time, the base film is sufficiently wetted by the topcoat to provide satisfactory adhesion between coatings.

After application of the overcoat to the base film, the coated substrate may be heated or cured, the volatile carrier liquid being removed from the overcoat and optionally crosslinking the film former in the overcoat and / or base layer with the aid of the crosslinker or crosslinkers present. Heating or curing is generally carried out at a temperature in the range of from 100 to 140 ° C, but may also be operated at a lower temperature as needed, provided that this temperature is sufficient for^and activation of the necessary networking mechanism.

In carrying out the process of the invention, the base and topcoat can be applied to the substrate by any conventional technique, such as brushing, spraying, dipping, or pouring. However, spraying is preferably used, as this will give the best results both in terms of pigment distribution and in particular the orientation of the metal pigment and in terms of gloss. Any spraying process can be used, such as compressed air spraying, electrostatic spraying, hot spraying and air-free spraying, both manual and automatic.

The dry film thickness of the base film is preferably 12.7 to 38.1 fzm. and the coating film thickness is 25.4 to 76.2 µm.

As can be seen from the above description, the advantage of the invention with respect to so-called metallics is that the proposed system of primer / clear coating avoids or greatly reduces atmospheric pollution by using a water-based primer. without sacrificing good control and orientation of pigmentation with metallic pigments. In the case of conventional pigments, the regulation of the orientation of the pigment is of course not a significant factor, but there is still the advantage that the base film is not disturbed by further application of the coating material. The matrix film of the present invention also has a much less blistering tendency than water-based coatings that do not contain polymeric microparticles.

The invention is illustrated by the following examples in which parts and percentages are always intended to be parts and percentages by weight. The examples are illustrative only, but do not limit the scope of the invention in any way. The apparent viscosity values ​​of the matrixes were determined in the examples using two different instruments. Values ​​of y_and at a shear rate of 10,000 were measured using a cone-shaped viscometer modified to allow viscosity measurements in the range of 0 to 0.2 Pa. s at the specified shear rate. This apparatus is described in the Journal of the Oil and Chemicals Association, July, 1966, in an article by CH Monek and manufactured by Research Equipment (London) Limited.

Ra values ​​at a shear rate of 1.0 s^_1 were measured using a concentric cylinder viscometer, "Rheomat 30" with an "A" cup and a weight. Each sample was subjected to a shear rate of 660 s^_1until a constant shear stress was reached and immediately thereafter the shear rate was changed to 1.0 sec.¹, the shear stress was measured and the viscosity was calculated from these data. The Rheomat 30 is manufactured by Oontraves AG in Zurich.

Example 1

A. Preparation of a dispersion of polymeric microparticles in an aliphatic hydrocarbon

A reactor equipped with a stirrer, a thermometer, a reflux condenser and a monomer feed device for the returned distillate was charged with 35.429 parts of heptane. The heptane was heated to reflux (95-96 ° C) and a mixture of the following ingredients was added:

<td>methyl methacrylate</td><td> 5,425</td><td>part</td>

<td>azodiisobutyronitrile</td><td> 0,420</td><td>part</td>

<td>graft copolymer as ·</td><td></td><td></td>

<td>stabilizer (33% r</td><td></td><td></td>

<td>described below)</td><td> 1,984</td><td>part</td>

<td>The reactor contents were 30 minutes</td><td>keeps</td><td>at</td>

at the reflux temperature to form a &amp; quot; batch &amp; quot; polymer dispersion and then the following mixture of ingredients is added to the returning distillate. The mixture was added at a constant rate for 3 hours.

<td>methylimetbacrylate</td><td> 25,000</td><td>part</td>

<td>allylmethacrylate</td><td> 0,775</td><td>part</td>

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

<td>a graft copolymer such as</td><td></td><td></td>

<td>stabilizer (33% solution</td><td></td><td></td>

<td>described below)</td><td> 5,316</td><td>part</td>

<td>After dosing is finished</td><td colspan="2">content of the reaction-</td>

The mixture was maintained at reflux for an additional hour, 12.874 parts of heptane were added and the mixture was again heated to reflux. A preformed mixture of the following composition is introduced into the returning distillate for 1 hour at a constant rate:

methyl methacrylate butyl acrylate hydroxyethyl acrylate acrylic acid azodiisobutyronitrile graft copolymer stabilizer (33% solution described below)

3,883 part

3,066 díl

2,044 díl

1,226 part

0.071 díl

2,149 díl

After the entire amount of this mixture was added, the reaction mixture was kept at reflux temperature for 1 hour. A stable dispersion of cross-linked polymeric microparticles having a total non-volatile solids content is obtained

43.5 to 44.5% and a non-volatile solids insoluble in any polar solvent [so-called. gel content) 34.5 to 35 percent.

The graft copolymer stabilizer used in the above process was prepared as follows: 12-hydroxystearic acid was autocondensed to an acid value of about 31-34 mg KOH / g (corresponding to a molecular weight of 1850 to 1800) and then reacted with an equivalent amount of glycidyl methacrylate. The resulting unsaturated ester is copolymerized in a weight ratio of 2: 1 with a mixture of methyl methacrylate and acrylic acid in a weight ratio of 95: 5. The copolymer was used as a 33% solution in a mixture of ethyl acetate (11.60%), toluene [14.44%], an aliphatic hydrocarbon boiling point of 98-122 ° C (61.29%) and an aliphatic hydrocarbon boiling point of 138 to 138 ° C. 165 ^CC (12.67%).

B. Conversion of polymeric microparticles into an aqueous dispersion

To a reactor equipped with a stirrer, a thermometer, and a volatile solvent removal apparatus by distillation was charged demineralized water 72.308 parts butoxyethanol 10.332 parts dimethylaminoethanol 0.529 parts

The reactor contents are heated to 100 ^CC and 46.497 parts of the dispersion of microparticles from step A were introduced into the reactor at a rate such that the heptane contained in the dispersion was removed by distillation without significantly concentrating in the reactor. The time required for this operation is about. 2 hours. 29 to 30 parts of a distillate consisting mainly of heptane and some water are separated.

The product obtained is a stable aqueous dispersion of polymeric microparticles having a nonvolatile solids content of 20-22% and a pH of 7.2-7.5.

C. Preparation of Aluminum Pigment Concentrate

An aluminum paste (metal content 65%) of 5.8 parts of butoxyethanol of 2.9 parts was introduced into the stirred mixing vessel

The ingredients were mixed together for 15 minutes, then 2.9 parts of buioxyethanol was added at a constant rate for 30 minutes, and the mixture was further stirred for 1 hour. Then, 4.84 parts of hexamethoxymethylmelam was added₍stirring was continued for an additional hour, 1.93 parts of hexamethoxymethylmelamine and 0.97 parts of butoxyethanol were added and stirring was continued for 1 hour.

D. Preparation of the base coat

The following ingredients are mixed together for 1 hour:

the aluminum concentrate of step C of the microparticle dispersion of step B of hexamethoxymethylmethylamine dimethylaminoethanol salt of p-toluenesulfonic acid,

10% solution in demineralised water

19,34 part

79,61 part

0.46 part

3.57 part

The base material thus obtained has the following characteristics:

Solids content: 27.2%

Viscosity · · 0,35 Pa. s at shear rate D = = 1 s ~ - 0.006 Pa. s · at shear rate D = 10,000 si

E. Preparation of the acrylic polymer with a clear coating

To a reactor equipped with a stirrer, a thermometer and a reflux condenser was charged xylene 22.260 parts aromatic hydrocarbon boiling point 190 to 210 ° C 10,000 parts

The mixture was heated to reflux (142-146 ° C) and a pre-formed mixture of the following composition was added over 3 hours:

styrene ethyl acrylate

2-ethylhexyl acrylate hydroxyethyl acrylate acrylic acid cumene hydroperoxide

21,49 díl

4.51 part

13.75 part

10.05 part

0.49 part

1.41 parts

The reactants were maintained at reflux for an additional 2 hours and then isobutyl alcohol xylene was added

12.72 parts

3.32 parts

A clear polymer solution is obtained having a solids content of 50%.

F. Preparation of a Clear Solvent-Based Coating Material

The following components shall be mixed together:

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

<td>butylovainá melarninformalde-</td><td></td><td></td>

<td>poultry resin in the form of</td><td></td><td></td>

<td>67% solution in butanol</td><td> 26,5</td><td>part</td>

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

<td>flow enhancing polymer</td><td></td><td></td>

<td>Properties in the form of 10%</td><td></td><td></td>

<td>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 is obtained with a solids content of 44.4%. Its viscosity is 40 s (British standard cup B4 at 25 ° C).

G. Applying a primer coating form and a clear coating composition to a substrate

The metal plate is provided with a primer layer (primer), then with a leveling coating, then sprayed with two primer coatings containing the metallic pigment described in step D (the materials are used without further dilution) at 22 ° C and relative humidity 39%. Between the two coatings, allow the first coat to dry for 2 minutes. The feed rate to the spray gun is 400 ml / min.

After applying the second coating, the board is blown at 25 ° C with air and then two clear coatings described in step F are applied. (The clear coating is diluted with xylene to a viscosity of 45 s according to the British standard using a cup before application. B 3 at 25 ^QC). The second coating is applied to the wet first coating; between the two coatings, the first coat is allowed to dry for only 2 minutes. After a final three-minute drying time, the plate is baked at 125 to 130 ° C for 30 minutes.

The resulting silvery metallic look has an excellent flip, pigment orientation is good, and the look is comparable to those with the highest degree of flip made using fully solvent-based coating systems. The gloss and adhesion between coatings is good and there is no leakage of the clear coating composition into the base coat.

Example 2

The metal plate is coated with a primer, then a leveling coat, then sprayed with two primer coatings containing the metallic pigment described in step D of Example 1 (the material is used without further dilution) at 25 ° C. ^CC and a relative humidity of 58 ·%. A first coating is left between the two coatings

/ ...

<img file="CS226427B2_D0001.tif" />

minutes to dry. The feed rate to the spray gun is 400 ml / min.

After applying the second base coat, the board is dried at 35 to 42 ° C for 10 minutes, and then two clear coatings described in step F of Example 1 are applied. (Clear coat, dilute to viscosity 45 with xylene before application). s according to British standard using cup B 3 at 25 ° C.) The second topcoat is applied to the wet first coat; between the two coatings, the first coat is allowed to dry only for 2 minutes. · After the final three minutes of drying, the plate is baked at 125 to 130 ° C for 30 minutes.

The coating thus obtained has the same excellent properties as the coating described in Example 1.

Example 3

A. Preparation of an aqueous dispersion of polymeric microparticles

The following mixtures of substances are prepared:

(1) monomer mixture

<td>methyl methacrylate allyl methacrylate styrene butylacrylate methacrylic acid primary octyl caplan ammonium salt of nonylphenol adduct sulfate and 5 moles of ethylene oxide</td><td>18,350 díl 1,340 díl 4,700 díl 18,800 part 1,410 díl 0,159 díl 0,185 díl</td>

<td>(2) initiator solution</td><td></td>

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

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

<td>(3) surfactant solution</td><td>substances</td>

<td>methyl methacrylate</td><td>20,000 part</td>

<td>ammonium salt of adduct sulfate</td><td></td>

<td>nonylphenol and 5 moles</td><td></td>

<td>ethylene oxide</td><td>20,000 part</td>

<td colspan="2">To a reactor equipped with a stirrer,</td>

<td>meter, reflux condenser</td><td>and equipment</td>

<td>for regulated introduction of two</td><td>separate</td>

<td>of liquid charges shall be stated:</td><td></td>

<td>demineralized water</td><td>- '7 6 6 ^ -H part</td>

<td>surfactant solution</td><td></td>

<td>fabrics (3)</td><td>0.100 part</td>

The batch is heated to 80 to 85 ° C, then 2000 parts of monomer mixture (1) are added and the resulting mixture is maintained at 80 to 85 ° C for 15 minutes. Then, 1.068 parts of the initiator solution (2) is added and the reaction mixture is kept at the same temperature for 20 minutes. Then a monomer mixture (1) of 42.944 parts hydroxisopropyl methacrylate 2.500 parts was added at a constant rate over 5 hours.

During the same five-hour period, 3.672 parts of the initiator solution were fed separately into the reactor at a constant rate. The reaction mixture is kept at 80-85 ° C for 1 hour and then cooled to room temperature. A stable aqueous dispersion of crosslinked polymeric microparticles is obtained. The dispersion contains 49.6% solids and the content of non-volatile solids insoluble in any organic solvent is 44.5%.

B. Preparation of the primer

Mixture (4)

2,563 parts of a commercially available thickener known as Aorysol ASS 60 (Rohm &amp; amp; Haas Co.) are mixed with sufficient. with a 25% solution of dimethylaminoethanol in demineralized water to adjust the pH to 7.65. Additional demineralized water was then added to give a total weight of 23.956 parts.

Mixture (5)

The mixture of 29.299 parts of the microparticle dispersion from step A and 18.614 parts of demineralized water is adjusted to pH 7.65 by adding a sufficient amount of a 25% solution of dimethylaminoethanol in demineralized water. Then 23.956 parts of the mixture (4) prepared in the manner described above are mixed into the resulting mixture.

· Running into the mixer shall aluminum pa sta

<td>(metal content 65%)</td><td> 5,133</td><td>part</td>

<td>2-butoxyethanol</td><td> 15,193</td><td>part</td>

<td>The batch is stirred for 15 minutes</td><td>minutes,</td><td>then</td>

<td>is added:</td><td></td><td></td>

<td>hexamethoxymethylmelamine</td><td> 3,696</td><td>part</td>

<td>polypropylene glycol (medium</td><td></td><td></td>

<td>molecular weight 400)</td><td> 2,464</td><td>part</td>

<td>and stirring is continued</td><td>hour.</td><td>Then</td>

<td>is added</td><td></td><td></td>

<td>mixture (5)</td><td> 71,869</td><td>part</td>

<td>demineralized water</td><td> 1,623</td><td>part</td>

and the mixture was stirred for an additional hour. The base material thus obtained has the following characteristics:

solids content: 20.5%

Apparent viscosity y_and: 3.46 Pa. s at shear rate D = 1 s^_1

0,042 Pa. with

D = 10000 s4

C. Preparation of Acrylic Polymer for Clear Coating

A reactor equipped with a stirrer, a thermometer, and a reflux condenser was charged with 42.20 parts of isopropyl alcohol. Isopropyl alcohol is heated to reflux (84 ° C) and then the following mixture of substances is added at a constant rate over 3 hours:

methyl methacrylate 19.85 parts butyl acrylate 24.80 parts hydroxyethyl methacrylate 2.48 parts acrylic acid 2.48 parts isopropyl alcohol 7.45 parts benzoyl peroxide (60% paste in dimethyl phthalate) 0.74 parts

The reactants were kept at reflux for a further 2 hours. A polymer solution was obtained containing 50% solids. 28.87 parts of isopropanol were removed from the solution by direct distillation and 1.86 parts of dimethylaminoethanol were added to the residue with stirring, followed by 80.35 parts of de-mineralized water. The distillation of the azeotropic mixture of isopropyl alcohol and water is then continued until a temperature of 96-98 ° C is reached and the distillate is collected. it is replaced by the addition of demineralized water.

The total amount of separated distillate is 118.83 parts and the total amount of additionally added demineralized water is 114.65 parts. An aqueous acrylic polymer solution was obtained containing 33.5% solids.

D. Preparation of a clear water-based coating material

The following substances are mixed together:

polymer solution from above

<td>of that¹ degree · C</td><td> 75,16</td><td>part</td>

<td>hexamethoxymethymethylamine</td><td> 6,29</td><td>part</td>

<td>butoxyethanol</td><td> 12,26</td><td>part</td>

<td>demineralized water</td><td> 5,50</td><td>part</td>

<td>dimethylaminoethane salt</td><td></td><td></td>

<td>p-toluenesultonic acid</td><td></td><td></td>

<td>(PH 7,6)</td><td> 0,79</td><td>part</td>

The clear coating thus obtained contains 31.5% solids and has a viscosity of 0.05 Pa. with.

E. Applying a primer and a clear coating to a substrate

The metal plate is prepared with a primer, then a leveling coat is applied and then three coatings of the metallic pigment primer described in step B are sprayed. The coatings are used without further dilution and sprayed at 25 ° C. ^QC and relative humidity 51%. The second coating is applied 1 minute after the first coating has been applied, the feed rate to the sift gun being 400 rpm / min.

After the third coating is applied, the board is dried at 35 to 42 ° C for 10 minutes. Three coatings of the clear coating composition described in step D are then applied. The coatings are applied without intermediate drying to the wet previous coating, since there is a 2 minute delay between the individual coatings and a 3 minute delay after the third coat. Then the plate is first heated to 70 ° C and finally baked at 150 ° C for 30 minutes.

The resulting coating has an excellent &amp; quot; tear &amp; quot ;, the pigment orientation is good, and the coating is visually equivalent to coatings with the highest degree of tear produced using fully solvent-based coating systems. The gloss and adhesion between coatings is good and there is no leakage of the clear coating composition into the base coat.

Example 4

A. Preparation of an aqueous dispersion of polymeric microparticles

To a reactor equipped with a stirrer, a thermometer, a reflux condenser and a device for the controlled introduction of two separate liquid charges are charged with demineralized water

29.030 parts and then a premix containing the methyl methacrylate ammonium salt of the adduct sulphate and · 5 moles of ethylene oxide

0,029 díl

0,029 díl

The contents of the reactor are heated to 85 ° C with stirring and a pre-prepared mixture of the following components is added:

butylacrylate 0.069 parts methyl methacrylate 0.069 parts

The reaction mixture is held at 80-85 ° C for 15 minutes and then a mixture of demineralized water of 0.67 part ammonium persulfate 0.021 part is added.

The contents of the reactor are kept at 80-85 ° C for a further 20 minutes and then cooled. a preformed mixture of methyl methacrylate butylacrylate, allyl methacrylate, ammonium salt of nonyltenol sulfate adduct and 5 moles of ethylene oxide is introduced into the reactor at a constant rate for 3 hours

10,758 díl

10,189 díl

0,686 part

0,081 díl

During the same three-hour period, a solution of 0.037 parts of ammonium persulfate in 4.985 parts of demineralized water was simultaneously introduced into the reactor at a constant rate.

After the addition of the above two batches, the reactor contents were maintained at 80-85 for 1 hour ^CC. Then add 34.716 parts of demineralized water, bring the temperature back to 80-85 ° C and add the following pre-prepared mixture to the mixture at a constant rate over 1 hour:

<td>methacrylic acid</td><td> 0,950</td><td>part</td>

<td>butyl acrylate</td><td> 2.035</td><td>part</td>

<td>hydroxyethyl acrylate</td><td> 1,357</td><td>part</td>

<td>methyl methacrylate</td><td> 0,950</td><td>part</td>

<td>ammonium sulphate adduct</td><td></td><td></td>

<td>nonylphenol and 5 moles</td><td></td><td></td>

<td>ethylene oxide</td><td> 0,02«</td><td>part</td>

During the same one-hour period, a solution of 0.019 parts of ammonium persulfate and 0.016 parts of sodium borate in 0.59 parts of demineralized water was simultaneously introduced into the reactor at a constant rate.

After addition of the above two batches, the temperature of the reaction mixture was maintained at 80-85 ° C for an additional hour. The mixture was then cooled rapidly. A stable aqueous dispersion of polymeric microparticles is obtained. The dispersion has a total non-volatile solids content of 30 why, and the non-volatile solids content insoluble in organic solvents is 27%.

B. Preparation of the primer

The pH of the dispersion obtained in Step A was adjusted to 8.0 by addition of dimethylaminoethanol and 54.15 parts of this dispersion were introduced into a mixer. The following substances are then added to the blender in the following order:

demineralized water 18.91 parts butoxyethanol 8.12 parts aluminum pigment concentrate described in Example IC) 18.02 parts

The mixture was stirred for 1 hour. A primer is obtained with the following properties:

Solids content: 25.8 ° / o

Apparent viscosity η_η: 0.20 Pa. s at spraying speed D = = 1 s ”¹

0,02 Pa. s at the spraying speed

D = 10,000 sec. "¹

C. Application of primer and clear coat to substrate

Prepared underlay on metal plate. Two primers containing the metallic pigment described in step В (without further dilution) at 22 ° C and a relative humidity of 39 ° / o are sprayed onto the primer (primerein) and the leveling coating. The procedure for applying both the primer and the clear coating is otherwise identical to that described in Example 1, step G.

The results obtained are similar to those obtained in Example 1, step G.

Comparative example

A. Preparation of a silvery metal base without microparticles

The blender is mixed with stirring:

aluminum paste (metal content 65%) 6.0 parts

2-butoxyethanol 18.7 parts

The batch is stirred for 30 minutes, then hexamethoxymethylmelainin (4.3 parts) of polypiropylene glycol (average molecular weight 400) of 2.9 parts is added and the mixture is further stirred for 1 hour. % of an aqueous acrylic polymer dispersion having a solids content of 33.5%, prepared as described in Example 5C below, and then 16.9 parts of demineralized water.

In this way, a matrix is ​​obtained which has the same ratio of pigment to binder, the same ratio of hexamethoxymethylmelamine to total non-volatile content, and a very similar apparent viscosity at D = 10,000 sec.^-1 (0.03 Pa.s), such as; The apparent viscosity of the microparticle-free coating composition at high shear rate indicates that the composition is suitable for spray application to a substrate. Its apparent viscosity at low shear rate D = 1 s¹ however, it is only about 0.1 Pa.s, indicating that the mass has weak pseudo-plastic or thioxotropic properties.

The primer is not applied to the board and a clear acrylic overcoat is applied to the primer, as described in Example 1G. The composition of the clear opaque coating corresponds to that of Examples EE and F. The silvery metallic coating thus obtained has a very low "flip" and shows traces of inhomogeneous pigment distribution and orientation. In addition, blisters form on the coating during firing.

Examples 1-4 illustrate the application of the process of the invention in the production of metallic coatings. The following example illustrates its application to coatings pigmented with conventional colourfast pigments.

Example 5

A. Preparation of a white pigment base

In a ball mill, the following ingredients are ground for 16 hours:

titanium dioxide, as a pigment of 31.3 parts

2-butoxyethanol 18.9 parts demineralized water 18.9 parts dimethylaminoethanol 0.2 parts hexamothoxyinmethyimelamine 7.7 parts

The resulting friction base having a particle size below 0.5 µm is then diluted with 11.6 parts of 2-butoxyethanol and 11.6 parts of demineralized water.

B. Preparation of the blue pigment friction base

<td>In the ball mill for · time</td><td>14 h</td><td>odin</td>

<td>together they grind the following ingredients:</td><td></td><td></td>

<td>Italocyanine blue pigment</td><td> 12,9</td><td>part</td>

<td>2-butoxyethanol</td><td> 23,8</td><td>part</td>

<td>demineralized water</td><td> 23,8</td><td>part</td>

<td>dimethyla minoethanol</td><td> 0,2</td><td>part</td>

<td>hexamethoxymethylmelami n</td><td> 9,7</td><td>part</td>

The resulting friction base having a particle size below 0.5 μηι is then diluted with 14.8 parts of 2-butoxyethanol and 14.8 parts of demineralized water.

C. Preparation of an aqueous acrylic polymer solution

The following ingredients are mixed together:

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

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

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

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

<td>isopropyl alcohol</td><td> 7,4</td><td>part</td>

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

Mixtures 15.0 parts of the above mixture and 42.2 parts are_andThe pellopiaacobol was introduced into a flask equipped with a stirrer, thermometer, reflux condenser, and a rate-controlled liquid feed addition apparatus. The contents of the flask were heated to reflux (84 ° C) and the remainder of the above mixture (42.8 parts) was introduced into the flask at a constant rate over 3 hours. The reaction mixture was refluxed for a further 2 hours to give a polymer solution containing 51.0% solids. 1.8 parts of dimethylaminoethanol are then added to the solution, the mixture is again heated to reflux, the reflux condenser is brought to a descending temperature, and a total of 33 parts of distillate are distilled off over 10 hours and 85.0 parts of demlneralized water are added. The aqueous acrylic polymer solution finally obtained contains 33.5% solids.

D. Preparation of blue primer

The following components are mixed in the following order:

white pigment fraction described in paragraph A 52.25 parts blue pigment fraction described in paragraph B 8.39 parts microparticle dispersion described in Example 1 B 14.62 parts acrylic polymer solution described in paragraph C 24.33 parts

10% aqueous solution of p-toluenesulfonic acid, neutralized to pH 7.6 by addition of dimethylaminoethanol 0.41 parts

The resulting primer has a viscosity of 1.6 Pa. s · at a shear rate of 1 s¹ and 0.053 Pa .. · S at shear rate of 10 · 000 s “1.

E. Application of the primer and clearcoat to the substrate

The metal plate is provided with a primer primer, a leveling material coating and two coats of the blue primer described in paragraph D. The blue coating material used without further dilution is sprayed onto the surface at a temperature of 22 ° C and a relative humidity of 39%, The deposition time is 2 minutes. After application of the second primer, the board is leached with air at a temperature of 25 ° C and then two coats of the clearcoat described in Example 1F are applied. The clear coat is diluted with xylene · 45 sec viscosity, measured according to British standard, in cup B · 3 at 25 ° C prior to spraying. The second coat is applied to the still wet first coat, since the delay between the first and second application is 2 minutes · After the second coat is applied, the coating is allowed to dry for 3 minutes and then the plate is baked for 30 minutes at 125 to 130 Deň: 32 ° C.

The resulting coating has good opacity and gloss, and no clear coating material flows into the base film.

Comparative example

A. Preparation of a blue primer without polymeric microparticles

The following components are mixed together, in that order:

the white pigment friction base described in Example 5A the blue pigment friction base described in Example 5B hexamethoxymiethylmelamine acrylic polymer solution described in Example 5C

10% aqueous solution of p-toluenesulfonic acid neutralized to pH 7.6 by addition of dimethylaminoethanol

54.8 part

B. Application of a primer and a clear coating to a substrate

8,8

0.3 part part

35.7 part

0.4 parts viscosity

The resulting matrix has

0.1 Pa. s at shear rate of 1 s'¹ and 0.083 Pa. s at a shear rate of 10,000 s¹, ie it has a very weak pseudoplastic or thioxotropic character.

The procedure described in Example 5E is repeated except that the primer described in the above paragraph is used instead of the primer described in Example 5D. А. In this case, considerable blistering of the base coat is observed, i.e. air entrained in the base coat is separated in the form of bubbles that deform the film surface and damage its smooth appearance. In addition, a delay of more than 3 minutes must be used between the application of the second coat of primer and the first coat of clearcoat, since otherwise the clear coating material disrupts the base film, which has a detrimental effect on the resulting board appearance.