Coating process

The present invention relates to protective and / or decorative coatings for automobiles.

The use, especially in the automotive industry, of coating compositions containing metallic pigments is known _; these are the so-called metallic finishes through which a differential effect of light reflection is obtained depending on the angle of view.

In order to maximize this reflection tone effect, a careful formulation of the coating composition is required with regard to both the resin forming the film and the liquid medium. Difficulties can be encountered when formulating a single composition that pursues this objective and, at the same time, produces a high degree of brightness of the final layer, as is usually desirable in the automotive field.

For this reason, one of the methods that have been proposed for the production of metallic finish is the application of two layers, by first applying, by splashing, a base layer containing the metallic pigment and formulated in such a way as to give the optimum effect. of reflection and then on the base layer is applied, by spraying, an unpigmented top layer that will give the desired degree of gloss, without modifying in any way the characteristics of the base layer.

For a successful metallic finishing system in two layers of this type of base layer / final layer, an essential criterion is the fact that ¹⁰ the base layer film must be able to withstand the attack of the solvents in the final layer composition, when the latter is subsequently applied to prevent pigment disturbance¹⁵ of metal tones and, thus, the reduction of the reflection effect, too, it is desirable for the base layer film to exhibit this property without the need for a prolonged operation by us²⁰ which or intermediate cure.

In the known systems of base layer / final layer, in which both the base layer compositions as well as the layer layers 25 are based on an organic solvent, this need has appeared, in most cases, when using a suitable additive. to confer a similar character ³⁰ with the gel of the base film for81966

LAW PRICE 45.55

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Fresh Imat; the additive that has been predominantly used is cellulose acetate butyrate.

The liquid diluent of the composition must contain volatile components which, preferably, are lost by evaporation during the passage from the spray gun to the substrate.

In order to avoid air pollution, coating compositions using water as a diluent instead of organic solvents were used. A number of such compositions have been proposed for use in the automotive dc industry. However, until now it has not been possible to use water based compositions satisfactorily as a base layer component in a base / final layer system.

One of the factors that tends to inhibit the achievement of such an objective is the extreme difficulty of arranging a selective loss, controlled by the diluent from the composition of the base layer by evaporation between the spray gun and the substrate, except for a very expensive regulation of ambient humidity. in the spray area.

However, it has been found that a satisfactory composition of the base layer containing water can be based on an aqueous dispersion of a cross-linked polymer microgel.

The present invention removes the above disadvantages, in that the protective and / or decorative coating is constituted by a base layer consisting of a composition containing as a film material a dispersion of: (a) cross-linked particles of an addition or condensation polymer derived from acrylic or methacrylic acid esters having a diameter between 0.01 and 10 μm; and (b) the aqueous dispersion medium containing metallic or non-metallic pigment particles, the respective dispersion having pseudoplastic or thixotropic properties, with an apparent viscosity below 1 P for a shear rate of 10,000 s^_1 and over 5 poise for a shear rate of 1 s ~¹ and a solids content of less than 30%, the second layer or surface layer being formed of a transparent composition, which contains as a film-forming material an addition polymer of acrylic or methacrylic acid esters in a dispersion medium consisting of: a volatile liquid.

Following are examples of embodiments of the invention.

Example 1 A) Preparation of a dispersion of polymer particles in aliphatic hydrocarbons in a reactor, provided with a stirrer, thermometer, reflux condenser and device for adding monomer to the distillate in return, 35,429 parts of heptane are introduced and the latter is heated to reflux of 95 ... 96 ° C, then adding the following pre-mixed ingredients: methyl methacrylate 5,425 parts, azodiisobutyronitrile 0.420 parts, graft copolymer stabilizer (33% solution as described below) 1,984 parts.

The contents of the reactor are kept at reflux temperature for 30 minutes, thus forming a polymer dispersion seed, after which the following pre-mixed ingredients are introduced at a constant rate for 3 hours: 25,000 parts methyl methacrylate, allyl methacrylate 0.775 parts, azodiisobutyronitrile 0.338 parts, graft copolymer stabilizer (33% solution as described below) 5.316 parts.

After the feed is complete, the contents of the reactor are kept at reflux for one hour, then 12,874 parts of heptane are added and the reflux is resumed. The following premixed ingredients are introduced into the reactor by means of a constant rate of one hour distillate: methyl methacrylate 3,883 parts, butyl acrylate, 3,066 parts, hexamethoxymethylamine 0.46 parts, acrylic acid 1,226 parts, azodiisobutironitrile 0.071 parts, graft copolymer stabilizer (solution 32 »/₀ described below) 2,149 parts.

After completion of this feeding, the reaction mixture is kept at reflux temperature for one hour. A stable dispersion of polymer microparticles is obtained, cross-linked with a total non-volatile solids content of 43.5 ... 44.6% and a non-volatile solids content insoluble in a polar solvent (ie gel content) of 34, 5 ... 35%.

The graft copolymer stabilizer used in the above method was obtained as follows: 12-hydroxystearic acid self-condenses to an acidity value of about 31 ... 34 mg KOH / g (corresponding to a molecular weight of 1 650 ... 1 800) and then allowed to react with an equivalent amount of glycidyl methacrylate.

The resulting unsaturated ester is copolymerized at a weight ratio of 2: 1 with a mixture of methyl methacrylate and acrylic acid in a ratio of 95: 5. The copolymer is used as a 33% solution in a mixture of 11.60% acetate. ethyl, 14.44% toluene, 61.29% aliphatic hydrocarbons with boiling point 98 ... 122 ° C and 12.67% aliphatic hydrocarbons boiling point 138 ... 165 ° C.

13. The passage of the polymers in the form from the microparticles to the dispersion in the aqueous medium in a reactor provided with a stirrer, thermometer and device for removing the volatile solvent by distillation, introduces: demineralized water 72,308 parts, butoxyethanol 10,332 parts; dimethylaminoethanol 0.529 parts.

The contents of the reactor are heated to 100 ° C and 46,497 parts of the Phase A microparticle dispersion are then introduced at such a rate that the heptane contained in the dispersion is removed by distillation, without a somewhat important concentration in the content of the reactor. The time required for this is about 2 hours and the distillate consisting mainly of heptane with some water rises to 29 ... 30 parts. The product is a stable aqueous dispersion of polymer microparticles with a non-volatile solids content of 20 ... 22¼ and a pH of 7.2 ... 7.5.

C. Preparation of aluminum pigment concentrate

In a mixing bowl, stir with: aluminum paste (metal content 65¼) 5.8 parts, butoxyethanol

2.9 parts.

These ingredients are stirred together for 15 minutes and then added at a constant rate, for a further 30 minutes,

2.9 parts butoxyethanol, after which the mixture is stirred for an additional hour. Then 4.84 parts hexamethoxymethylmelamine are added and stirring is continued for one hour; at the end, add another 1.93 parts hexamethoxymethylmelriinine and 0.97 parts butoxyethanol and the mixture is stirred for an additional hour.

D. Preparation of the base layer composition

The following ingredients are stirred together for one hour: aluminum concentrate of phase C. 19.34 parts, dispersion of microparticles of phase B 79.61 parts, hexamethoxymethylamine 0.46 parts salt of p-toluenesulfonic acid dimethylaminomethanol. in demineralized water 3.57 parts.

The basic layer composition thus obtained has the following characteristics: solids content 27.27%, apparent viscosity: 35P at shear rate D = ls^-1; 0.06 P approximately at the shear rate D = 10,000â^-1.

E. Preparation of acrylic polymer for clear layer composition in a reactor provided with stirrer, thermometer and reflux condenser, insert: xylene 22,260 parts, boiling point aromatic hydrocarbons

19o ... 21o^rC, 10,000 parts.

The mixture is heated to reflux temperature of 142 ... 146 ° C and, at a constant rate for 3 hours, the following pre-mixed ingredients are added: styrene 21.49 parts, ethyl acrylate 4.51 parts, acrylate 2 -ethylhexyl 13.75 parts, hydroxyethyl acrylate 10.05 parts, acrylic acid 0.49 parts, cumene hydroperoxide 1.41 parts.

The reactants are kept at reflux temperature for a further 2 hours, followed by the addition: isobutyl alcohol 12.72 parts, xylene 3.32 parts.

This results in a clear polymer solution with a solids content of 50¼.

F. Preparation of the solvent-based clear layer composition

The following ingredients are mixed together: E 53.3-part polymer solution, butylated melamine resin and formaldehyde, butanol 67¼ solution

26.5 parts, 5.0 parts dipentane, polymer favoring flow, 10¼ solution in xylene 0.1 parts, isobutyl alcohol 2.0 parts, xylene 13.1 parts.

A clear solution with 44,4¼ solids and a viscosity of 40 s is obtained (BS ring B4 at 25Ό).

But. Applying the base layer and the clear layer on a substrate

A metal plate is prepared by priming and rubbing the surface, after which, without undiluted spraying, two layers of the metallic base layer composition, described in phase D, are applied at a temperature of 22 ° C and a relative humidity of 39¼. . between layers is allowed a period of time of 2 min; The output speed of the paint to the spray gun is 400 ml / min.

After applying the second base dc layer, the plate is blown with air at 25 ° C and two layers of clear layer composition are applied, as described in phase F, the clear layer composition being further diluted with xylene to a viscosity of 45 s (BS ring B3 at 25 ° C). The two layers are applied wet to wet, with a time period of 2 minutes between layers. After a final rest of 3 minutes, the plate is allowed to stand for 30 minutes at

125 ... 130 ° C.

The metallic coating as the resulting silver has a very good reflection and lacks shear and is equivalent in appearance with finishes of the highest degree of reflection obtained from a complete solvent based paint system. The gloss and adhesion between the layers are good and the clear layer is not penetrated into the base layer.

Example 2. Prepare a metal plate with primer and abrasion on the face above 81966, after which, without further dilution, apply two layers of the metal-based layer composition, described in step D in example 1, namely, by spraying at a temperature. of 25 ° C and relative humidity of 58¼. Between layers it is left for a period of time of 2 min; the paint flow rate to the spray gun is 400 ml / min.

After applying the second base layer, the plate is dried at 35 ... 42 C for 10 minutes and then two layers of the clear layer composition described in step F of Example 1 are applied, the clear layer being diluted beforehand. with xylene at a viscosity of 45 s (BS ring B3 at 25 ° C).

The two layers are applied wet to wet with a time period of 2 minutes between layers. After a final period of 3 minutes, the plate is kept for 30 minutes at

125 ... 130 ° C. The coating thus obtained has the same characteristics as those described in Example 1.

Example 3. A) Preparation of an aqueous dispersion of polymer microparticles

The following premixtures are prepared.

I) Monomer premix: 18,350 parts methyl methacrylate, 1,340 parts allyl methacrylate, 4,700 parts styrene, 18,600 parts butyl acrylate, 1,410 parts methacrylic acid, 1,410 parts, 0.159 parts first-octyl mercaptan, ammonium sulphate salt (nonylphenol plus 5 mol of ethylene) 0.185 parts.

II) Initiator solution: ammonium persulfate 0.130 parts, demineralized water 4.010 parts.

III) Surfactant agent solution: 20,000 parts methyl methacrylate, ammonium sulfate salt (nonylphenol plus 5 mol ethylene oxide) 20,000 parts.

In a reactor provided with a stirrer, thermometer, reflux condenser and device for controlled introduction of two separate liquid substances, 47,641 parts demineralized water, 0.100 parts surfactant solution (III) are introduced.

The country is heated to 8O ... 85 ° C, then se. add 2,000 parts monomer premix (I) and the mixture is kept at 8O ... 85 ° C for 15 minutes, then 1.068 parts initiator solution (II) is added and the reaction mixture is kept at the same temperature for 20 minutes. Thereafter, at a rate of 5 hours, the following premixed ingredients are introduced: 42,944 parts monomer (I) premix, hydroxyisopropyl methacrylate 2,350 parts.

During the same 5 h period, at a constant rate, 3,672 parts initiator solution (II) are introduced separately. Afterwards the reaction mixture is kept at 80 ... 85 ° Ο for one hour

S and then cooled to room temperature, giving a stable aqueous dispersion of cross-linked polymer microparticles. The dispersion has a total solids content of 46.6¼ and a non-volatile solids content insoluble in any kind of organic solvent of 44.5¼.

B. Preparation of the base layer composition

Preamestec (IV)

2,563 parts of the commercially available thickening agent known as "Acrysol" ASE 60 ("Acrysol) are stirred with sufficient 25¼ solution of dimethylaminoethanol in demineralized water to bring the pH to 7.65. Then added demineralized water to a total of 23,956 parts.

Preamestec (V)

A mixture of 29,299 parts of the above A-phase microparticle dispersion and 18,614 parts of demineralized water is brought to a pH of 7.65 by addition of sufficient 25¼ dimethylaminoethanol solution in demineralized water. Then mix into 23,956 parts premix (IV) prepared as above. In a mixer stir with: aluminum paste (metal content 65¼) 5,133 parts, 2-butoxyethanol 15,193 parts.

The batch is stirred for 15 min, then the following is added: hexamethoxymethylmelamine 3,696 parts, polypropylene glycol (average molecular weight 400) 2,464 parts and stirring is continued for about 1 hour, followed by the addition: premix (V) 71,869 parts, water demineralized 1,623 parts and stirring continued for another hour. The basic layer composition thus obtained has the following characteristics: solids content 20,5¼. apparent viscosity η 3 1.6 P at the shear rate D- 1_:

11.42 P at D = 10,000 s ~ \

C. Preparation of acrylic polymer for clear layer composition

42.20 parts isopropanol is introduced into a reactor equipped with a stirrer, thermometer and reflux condenser. Heat to reflux temperature of 84 ° C and the ingredients below premixed, then add at a constant rate for 3 hours, methyl methacrylate 19.85 parts, butyl acrylate 24.80 parts, hydroxyethyl methacrylate 2, 48 parts, acrylic acid 2.48 parts, isopropanol 7.45 parts, benzoyl peroxide (60% paste in dimethyl phthalate) 0.74 parts.

The reactants are maintained at reflux temperature for a further 2 hours, obtaining a 50% solids polymer solution. From this, 28.87 parts isopropanol are removed by direct distillation and 1.86 parts dimethylaminoethanol are added to the residue with stirring, followed by 80.35 parts demineralized water. Then, the distillation of the azeotropyol of isopropanol and water is continued at a temperature of 96 ... 98 C, to replace the distillate by adding further demineralized water.

The total amount of distillate removed is 118.83 parts and the total amount of demineralized water added is 114.65 parts. An aqueous acrylic polymer solution with a solids content of 33.5 % dc is thus obtained .

D. Preparation of a clear layer composition based on water

The following ingredients are mixed together: the above C phase polymer solution 75.16 parts, hexamethoxymethylmelamine 6.29 parts, butoxyethanol 12.26 parts, demineralized water 5.50 parts, p-toluenesulfonic acid dimethylaminoethanol salt (pH = 7 , 6) 0.79 parts.

The clear layer composition thus obtained has a solids content of 31.5% and a viscosity of 0.5 P.

E. Applying the base layer and the clear layer on a substrate

Prepare a metal plate by priming and rubbing the surface and then apply three layers of the metallic base layer composition described in step B above, by spraying, without further dilution, at a temperature of 25 ° C and a relative humidity of 51%. between layers, leave a period of dc for 1 min; the dc flow rate at the spray gun is dc 4P0 ml / min.

After applying the third base layer, the plate is dried at 35 ... 42 ° C for 10 minutes and then three layers of the clear layer composition described in step D above are applied. The three layers are applied wet on wet with a time of 2 minutes between layers and a final time of 3 minutes. Then the plate is preheated to 70 ° C, then kept for 30 minutes at 150 ° C.

The coating thus obtained has a very good reflection and is free from shearing and is equivalent in appearance with the best complete solvent-based metal paint system. The gloss and adhesion between the layers are good and no clear layer penetrates into the base layer.

Example 4

A) The preparation of an aqueous dispersion of polymer microparticles in a reactor provided with a stirrer, thermometer, reflux condenser and device for controlled introduction of two separate liquid materials is introduced; demineralized water 29,030 parts, followed by a premix10 mixture of: methyl methacrylate 0.029 parts, ammonium sulphate salt (nonphenol plus 5 mol ethylene oxide) 0.029 parts.

The contents of the reactor are heated to 8O ... 85 ° C with stirring and the following premixed ingredients are added: 0.069 parts butyl acrylate, methyl methacrylate0.069 parts.

The reaction mixture is kept at 80 ... ... 85 ° C for 15 minutes, followed by a mixture of: 0.67 parts demineralized water, 0.021 parts ammonium persulfate.

After the contents of the reactor were kept at 80 ... 85 C for a further 20 minutes, the following pre-mixed ingredients are introduced into the reactor at a constant rate for 3 hours: butyl acrylate 10,758 parts, methyl methacrylate 10,189 parts, allyl methacrylate 0,686 parts, ammonium sulphate salt of (nonphenol plus 5 mol ethylene oxide) 0.081 parts and simultaneously in the reactor at a constant rate over time 3 h, a solution of 0.037 parts ammonium persulfate is introduced into 4,985 parts demineralized water.

After completion of the above addition, the contents of the reactor are kept at 80 ... 85C ° for one hour, after which 34,716 parts of demineralized water are added and the temperature is restored to 8O ... 85 ° C. Then, at a constant rate for one hour, add the following pre-mixed ingredients: 0.950 parts methacrylic acid, 2.035 parts butyl acrylate, 1.35 parts hydroxyethyl acrylate, 0.950 parts methyl methacrylate, ammonium sulphate salt of ( non-phenphenol plus 5 mol ethylene oxide) 0.028 parts and at a constant rate for one hour, a solution of 0.019 parts ammonium persulfate and 0.016 parts sodium borate in 0.596 parts demineralized water is introduced into the reactor.

After the completion of the two feedings, the temperature of the reaction mixture is kept at 80 ... 85 ° C for one hour, then cooled rapidly to obtain a stable aqueous dispersion of polymer microparticles. The dispersion has a total non-volatile solids content of 30% and a non-volatile solids content insoluble in organic solvents 27%.

B. Preparation of the base layer composition

The dispersion obtained from phase A brings to a pH = 8.0, by the addition of dimethylaminoethanol, and 54.15 parts thereof are introduced into a mixer, after which the following ingredients are added: in demineralized water 18, 91 parts, butoxyethanol 8.12 parts, aluminum pigment concentrate (as described in Example 1 C) 18.02 parts.

The mixture is stirred hourly to obtain a basic layer composition with the following characteristics: solids content 25.8%, apparent viscosity 20 P at shear rate D = = 1 s^-'; 0.2 P at the shear rate D = = .10 000 s-¹.

C. Applying a base layer and a clear layer on a substrate

On a metal plate, prepared by priming and rubbing the surface, two layers of the metallic base layer composition described in step B above, at a temperature of 22 ° C and a humidity, are applied by spraying without further dilution. relative to 39¼. The clear layer composition is the same as that described in phase G of example 1, the results being similar.

Comparative Example IA Preparation of a metallic base layer such as silver without microparticles

In a mixer, stir with: aluminum paste (metal content 65¼) 6.0 parts, 2-butoxyethanol 18.7 parts.

The batch is stirred for 30 minutes, then the following are added: 4.3 parts hexamethoxymethylmelamine, polypropylene glycol (400 molecular weight average) 2.9 parts and stirring is continued for an additional hour, followed by stirring over time. of 30 min, 51.2 parts of a 33.5¼ aqueous acrylic polymer solution, as described in Example 5 C below, followed by the addition of 16.9 parts demineralized water.

This results in a base layer composition having the same pigment / binder ratio, the same ratio of hexamethoxymethylmelamine to total non-volatile matter and a very similar value (0.3 P) of apparent viscosity η at D = 10,000 s^-1, as shown in "Example 1 for a base layer composition according to the present invention.

Apparent viscosity The high shear rate of the composition that does not contain polymer microparticles shows that it is suitable for application by spraying on a substrate, but its apparent viscosity at low shear rate, ie D = ls.^-', is found to be only 1.0 P, which means that the composition has only weak pseudoplastic or thixotropic properties.

The base layer composition is applied to a plate and covered with a clear acrylic layer composition as described in Example 1G, the clear layer composition used being that described in Example 1E and F. The meta12 coating as smooth as the silver thus obtained shows very poor reflection and shear portions. It is also exposed to flowering during the storage operation.

Examples 1 ... 4 illustrate the present invention as it is applied for the production of "metallic charming finishes". The following example shows its application on "solid color" finishes.

Example 5

A. Preparation of a white pigment fracture in a ball mill for 16 hours, the following ingredients are ground: 31.3 parts titanium dioxide pigment, 18.9 parts 2-butoxyethanol, demineralized water

18.9 parts, dimethylaminoethanol 0.2 parts, hexamethoxymethylmelamine 7.7 parts.

The resulting milled mixture, which has a granulation of less than 0.5 μ, is then diluted with 11.6 parts 2-butoxyethanol and 11.6 parts demineralized water.

B. Preparation of a ground mixture of blue pigment in a ball mill for 16 hours, the following ingredients are milled together: 12.9 parts phthalocyanine blue pigment, 23.8 parts 2-butoxyethanol, 23.8 demineralized water parts, dimethylaminoethanol 0.2 parts, hexamethoxymethylmelamine 9.7 parts.

The milled mixture, with a granulation of less than 0.5 μ, is then diluted with

14.8 parts 2-butoxyethanol and 14.8 parts demineralized water.

C. Preparation of an aqueous acrylic polymer solution

The following ingredients are mixed: 19.9 parts methyl methacrylate, 24.8 parts butyl acrylic, 2.5 parts hydroxyethyl methacrylate, 2.5 parts acrylic acid, 7.4 parts isopropanol, 0.7 parts benzoyl peroxide.

A mixture of 15.6 parts of the above mixture and 42.2 parts isopropanol is introduced into a flask fitted with a stirrer, thermometer, reflux condenser and a device for adding liquid material at a controlled rate. The contents of the flask are heated to a reflux temperature of 84 ° C and the rest of the mixture above

42.8 parts are added at a constant rate for 3 hours.

The reaction mixture was heated with reflux for a further 2 h, to obtain a polymer solution with a solids content of 51.0¼. To the solution is then added 1.8 parts dimethylaminoethanol, the mixture is reheated to reflux temperature and, after installing the condenser, a total of 33.0 parts is removed by distillation, 85.0 parts demineralized water is added, for 10 b The aqueous solution resulting from acrylic polymer has a solids content of 33.5%.

D. Preparation of a blue base layer composition in the order determined, the following ingredients are mixed: the white mixture as

52.25 parts, blue mixture 8.39 parts, microparticle dispersion as in Example 1 B 14.62 parts, acrylic polymer solution, obtained as above, 24.33 parts, 10% aqueous solution of p-toluenesulfonic acid at pH = 7.6 by addition of 0.41 parts of dimethylaminoethanol.

The resulting base layer composition exhibits a viscosity of 16.0 P at a shear rate of 1 s ~¹ and 0.53 P at a shear rate of 10,000 s^-1.

E. Applying a base layer and a clear layer on a substrate

Prepare a metal plate by priming and rubbing the surface, then, by spraying, without dilution, at a temperature of 22C and a relative humidity of 39%, apply two layers of the basic layer composition described above.

between layers is allowed a period of time of 2 min. After applying the second base layer, the plate is blown with air at 25 ° C and two layers of the clear layer composition are applied, as described in example 1 F, the clear layer composition being previously diluted with xylene at a viscosity of 45 s determined in a BS ring B3 at 25 C.

The two upper final layers are applied wet to wet with a period of time of 2 minutes between layers. After a final time of 3 minutes, the plate is stored at 125., 130'C for 30 minutes. The resulting coating presents a good opacity and gloss and the clear layer is not penetrated into the base layer.

Comparative example II.

A) Preparation of a composition of blue basic ointment without polymeric microparticles in the established order, the following ingredients are mixed: white mixture as in example 5 A 54.8 parts, blue mixture as in example 5 B 8.8 parts, hexamethoxymethylmelamine 0.3 parts acrylic polymer solution as in Example 5 C 35.7 parts, 10% aqueous solution of p-toluenesulfonic acid brought to pH = 7.6 by addition of 0.4 parts dimethylaminoethanol.

The resulting base layer composition has a viscosity of dc 1.0 P at a shear rate of 1 s ~ 'and 0.83 P at a

Shear rate of 10,000 s^-', ie it has a very pseudoplasmic or thixotropic character.

B) Applying a base layer and a clear layer on a substrate

Repeat the working method from Example 5E, but replacing the base layer composition described in Example 5D with the base layer described above.

In this case, a flowering of the base layer is observed, ie in the base layer it has penetrated air separated by bubbles, deforming the surface of the film and degrading its smooth appearance. Also, between the application of the second base layer and the first clear layer, a longer period of time must be allowed than 3 minutes, thus, the base layer is degraded by the clear layer with an adverse effect on the final appearance. of the plate.

According to the present invention, a process has been developed for producing a protective and / or decorative coating in several layers on a substrate surface comprising the phases of:

1. Surface application of a basic layer composition comprising: a) a film-forming material_; b) a volatile liquid environment for this material; c) pigment particles dispersed in this liquid medium.

2. Formation of a polymer film on the surface of the composition applied in phase 1).

3. The application on the base layer film thus obtained of a transparent final layer composition comprising: d) a film-forming polymer, e) a volatile liquid carrier material for this polymer.

4. Formation of a second polymer film on the base layer film of the composition applied in step 3).

Constituents a) and b) from the base layer composition are formed by dispersion in an aqueous medium of cross-linked polymer microparticles with a diameter in the range between 0.01 and 10 μ, are insoluble in this aqueous medium and are stable with respect to intense flocculation, the dispersion having a pseudoplastic or thixotropic character,

The cross-linked polymer microparticles can be composed of different types of polymer. Of particular interest for this purpose is the addition acrylic polymers, derived from one mu several alkyl esters of acrylic acid with other ethylenically unsaturated monomers. Suitable acrylic or methacrylic esters comprise methyl methacrylate, methacrylate or methacrylic acid, optionally together ethyl, propyl methacrylate, butyl methacrylate, ethyl acrylate, butyl acrylate and dc 2-ethylhexyl acrylate.

Other suitable copolymerizable monomers include vinyl acetate, vinyl propionate, acrylonitrile, styrene and vinyltoluene. Because the polymer needs to be crosslinked, a small proportion of a monomer which is polyfunctional with respect to the polymerization reaction, for example, ethylene glycol dimethylacrylate, allyl methacrylate, or divinylbenzene may be included in the monomers from which the polymer is derived. alternatively, in these monomers a smaller proportion of two other monomers may be included which comprises pairs of chemical groups which can be reacted with another group, either during or after the polymerization reaction with epoxy and carboxyl (as , for example, in glycidyl methacrylate and methacrylic acid), anhydride and hydroxyl or isocyanate and hydroxyl.

The chemical composition and degree of cross-linking of the polymer into microparticles may be such that it may exhibit a Tg (glass transition temperature of rubber) below room temperature, in which case the microparticles will be rubber in nature. _; Alternatively, they may be so Tg that they are above room temperature, that is, the particles are strong and glassy.

As mentioned, it is necessary for the polymer microparticles to be dispersed in the base layer composition in a stable state as opposed to intense flocculation, that is, a state where, even at low solids content, the dispersion may possibly contain few aggregates. of several particles ·, however, this does not exclude the possibility of a reduced degree of particle flocculation, especially at higher solids content.

This state can be obtained, for example, by spherical stabilization, that is, by creating around a particle a chain barrier of a different polymer that is solvated by the aqueous medium of the composition and thus presenting itself in a chain configuration. extended.

In this context, the term solvated means that the polymer chains, if they are independent molecules, will be slightly soluble in this aqueous environment. _; but, because the chains are, in fact, attached by the microparticles at one or more points along their length, the spherical barrier is always attached by the microparticles. The polymer microparticles, which are sterically stabilized in this way, can conveniently be produced by a polymerization process of dispersing the corresponding monomers in the aqueous environment, in the presence of a steric stabilizer.

The stabilizer is amphipathic in nature, ie it contains two important polymer components in the molecule with different characteristics: one component is a polymer chain that is solvated by the aqueous medium and the other component is a polymer chain that is not solvated by this medium and, consequently, it binds to the polymer particles, which, by definition, are insoluble in the aqueous environment.

Suitable dispersion polymerization processes are known. The aqueous medium in which the polymerization is performed consists of water mixed with a volatile organic cosolvent, the mixture as a whole being able to dissolve the monomers, most or all of them being especially insoluble in water.

The polymerization is carried out at a temperature which is at least 10 ° C higher than the vitrifying temperature of the polymer to be formed and thus, so that at no time there is no separate phase of the monomer.

The amphipathic steric stabilizer may be added to the mixture by polymerization with a preformed substance or it may be formed in situ during polymerization of a polymer that is soluble in the aqueous medium and is capable of copolymerizing with / or by hydrogen separation, by grafting from the monomer to be polymerized. The dispersions of sterically stabilized microparticles obtained by these methods are very suitable for formulating the base layer compositions to be used according to the present invention, because it is possible to remove the organic co-solvent from them by distillation, without reducing the stability of the dispersed phase, giving a product in which the continuous phase consists only of water.

The dispersion of polymer microparticles can be obtained by the aqueous emulsion polymerization of the corresponding monomers, in which case, the stability against the flocculation is conferred by the presence on the particles of electrically charged species derived from a water soluble ionizing surfactant and / or an initiator. of water-soluble ionizable polymerization. Such polymerization processes are known.

Similarly, the polymer microparticles can be prepared by a polymerization process of non-aqueous dispersion of monomers, followed by the passage of the resulting polymer into the aqueous medium. It comprises, in a first phase, the formation of a sterically stabilized dispersion in a non-aqueous liquid of a polymer which is insoluble both in the non-aqueous liquid and in water, using r

any of the well known methods for preparing such dispersions; then, in a second phase, the polymerization in the dispersion thus obtained, in the presence of a steric stabilizer, of one or more monomers which may cause the formation of a second polymer which is inherently soluble in the desired aqueous medium at a corresponding pH and, Finally, the passage of the polymer microparticles resulted in composition from aqueous to aqueous.

The above discussion referred to the case when microparticles of crosslinked polymers are composed of an addition polymer, this being the most appropriate type of polymer for the present purpose.

The microparticles may be composed, on the other hand, of a condensing polymer, for example, a polyester prepared from a polyhydric alcohol and a polycarboxylic acid. Polyhydric alcohols suitable! they comprise ethylene glycol, propylene glycol, butylene glycol, 1,6-hexiylene glycol, neopentyl glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, glycerine, trimethylolpropene, trimethylethane, pentaerythritol, dipentaerythritol, tripentaerythritol, hexenterylthylene, product ethylene or propylene oxide.

Suitable polycarboxylic acids include succinic acid (or its anhydride), adipic acid, alzaic acid, sebacic acid, maleic acid, (or its anhydride), fumaric acid, muconic acid, itaconic acid, italic acid (or its anhydride), isophthalic acid, terephthalic acid, trimethyl acid (or its anhydride) and pyromellitic acid (or its anhydride).

These polymers result from crosslinking by incorporating materials with increased functionality in the initial composition, although due to the large distribution of the molecular species formed in a condensation polymerization as compared to that of an addition polymerization, it may be difficult to achieve it ensures that all of these species are indeed cross-linked.

It will be taken into account that the methods mentioned above for the preparation of polymer microparticles by polymerization of addition type monomers in an aqueous environment are not generally applicable to condensation type displays, because of the effect of condensation. inhibition of water on the condensation reaction.

However, condensation polymer microparticles can be easily prepared by dispersion polymerization in non-aqueous media, as well as obtaining cross-linked microparticles. These microparticles can then, in dispersion in the non-aqueous environment, be subjected to the second polymerization phase.

The aqueous medium means either single water or water mixed with an organic liquid miscible with water such as methanol _; the aqueous medium may also contain water-soluble substances introduced in order to match the pH of the base layer composition, as shown in more detail below.

The pigment particles which, as already shown, are dispersed in the aqueous medium of the base layer composition, may vary in size in the range from 1 to 50 μ and may be any of the pigments commonly used in surface coating compositions, comprising inorganic pigments such as titanium dioxide, iron oxide, chromium oxide, lead chromate and carbon black, and organic pigments, such as ftaiocyanin blue and ftaiocyanine green, carbazole purple, anthrapyrimidine yellow, flavantrona yellow, isoindoline yellow, indantron blue, quinacridone violet and perylene red.

For the purposes herein, the term "pigment" is understood to also include ordinary fillers and diluents, such as talc or kaolin.

The process, according to the present invention, relates in particular to the case of basic layer compositions containing metallic pigments in flakes intended for the production of metal and face finishes, especially on the surface of the car bodies, as shown above, suitable metal pigments comprising, in particular, aluminum powder and copper bronze powder.

The present invention also has advantages for producing solid color finishes, as shown below. In general, pigments of any kind can be incorporated into the base layer compositions in an amount of between 2 and 100% of the total weight of the composition.

If metallic pigments are used, they will preferably be in the amount of 5 to 30¼ by weight of the total weight mentioned above.

Such pigments, metallic or otherwise, may be incorporated into the base layer compositions by means of known pigment dispersants, suitable for use in aqueous systems.

The presence of cross-linked polymer microparticles in the base layer composition gives the latter film the desired ability to withstand subsequent application of the higher composition without adverse influence of the film or pigmentation, especially metallic pigmentation, and without which it does not. an advantageous base / final layer system can be obtained.

In addition to this essential feature, it is also necessary, as shown above, for the dispersion of insoluble microparticles to have a pseudoplastic or thixotropic character. By this, it is understood that the apparent viscosity of the dispersion will differ with the degree of shear, to which the dispersion is subjected and especially that the apparent viscosity at reduced shear is higher than it is at strong shear.

The variation of the viscosity following the variation of the shear applied may be instantaneous or may require a finite time interval, which, however, is found in the viscosity measurement time period.

The reason which requires this character in the dispersion on which the base layer composition is based is best shown if this composition contains a pigment in the form of metallic powder. Then I assign that the total concentration of existing non-volatile solids should be relatively low, in order to obtain * an important shrinkage of the base layer film after application on the substrate and during the drying operation * and thus to ensure the correct orientation of the metal powder. * and thus the optimal reflection effect.

It is, however, necessary that when the dc * base layer composition should be applied to a spray substrate, the composition must present * a low enough viscosity for efficient atomization of the spray gun and, once it has reached the substrate, the viscosity it must be large enough to prevent deformation or bending of the film or the development of uneven (distribution and uneven orientation) of the metal powder, even if the loss of water and other solvents by evaporation between the spray gun and the substrate is only reduced (due to high ambient humidity).

The presentation of such pseudoplastic properties is often expressed when scoring -q values_of (apparent viscosity in Poise) at values ​​chosen for D (shear rate in s^_1). In the case of base coat compositions with metallic pigments, used according to the present invention, the value, at a solids content less than 30% by weight of non-volatile materials, will preferably be less than 0.5 P at a shear rate of D of 10,000 s^_1 and greater than 20 P at a value of D of 1.0 s ~ '. Preferably, the base layer composition has an r value_takes less than 0.25 P at a value of D of 10,000 s^—1 and more than 40 P at a value of D of 1.0 s^_1.

In the case of basic layer compositions of "solid color containing pigments, other than metallic powder, it is preferable as η_α , also in solids content below 3O »/₀, be less than 1 P at D 1 000 s¹ and greater than 5 P at D — l, 0s ~ \ preferably is that ηα is less than 0.7 P at D = 10,000 s^_1 and greater than 10 P at D = 1, 0 s ~¹.

It is, however, in the nature of pseudoplastic or thixotropic behavior that it cannot be perfectly and precisely defined by a few chosen viscosity / shear data; much depends on the precise method of measuring the viscosity. Therefore, the values ​​noted above are not intended to be considered as rigid limits that must be reached in order to obtain the advantages of the present invention; they are given only as an approximate guide and the specialist in the subject can easily determine, by simple practical tests, whether the special dispersion or the base layer composition derived therefrom has the necessary degree of pseudoplasticity or thixotropic.

There are different ways by which a pseudoplastic or thixotropic character can be conferred to the dispersion of the base layer. In some cases, no special measures are required.

This method consists in producing the microparticles of polymers of certain dimensions by a process of polymerization in non-aqueous dispersion of the corresponding monomers, followed by the polymerization of other monomers to produce a second polymer which is non-crosslinked and has a hydrophilic character, so that it is capable of dissolving in the aqueous environment, in which the final dispersion is to be formed, at an appropriate pH.

Not all of this second polymer is dissolved, but in fact, in the aqueous environment at the transfer or the product of these two non-aqueous polymerization phases. An important part of the second polymer remains associated with the polymer microparticles and these microparticles are thus stabilized in dispersion in the aqueous environment; At the same time, however, this associated polymer may appear in aqueous dispersion, having pseudoplastic or thixotropic properties.

Other monomers which are suitable for use in the second phase of polyβ 96β mercury are, for example, a hydroxyalkyl ester of acrylic acid or methacrylic acid, a monoacrylic or monomethacrylic ester of a polyglycol such as polyethylene glycol, a monovin-like ether. polyglycol or vinylpyrrolidone, possibly in combination with smaller portions of non-hydrophilic monomers, such as methyl methacrylate, butyl acrylate, vinyl acetate or styrene.

The required solubility in the aqueous medium can be obtained by using, as a major monomer constituent, an acrylic ester containing basic groups, for example, dimethylaminoethyl methacrylate or diethylaminoethyl methacrylate, these groups being then converted to salt groups by reaction with a suitable acid, for example, yiacic acid, dissolved in aqueous medium.

Similarly, the second polymer can be derived from comonomers containing a significant proportion of a carboxylic acid polymerizable as acrylic acid or methacrylic acid, and is then able to dissolve in an aqueous medium containing a base dissolved as dimethylaminoethanol. In general, therefore, the second polymer may be nonionic, anionic or cationic.

If the polymer microparticles were prepared by a process of aqueous emulsion polymerization, as is well known in the art, a second polymer, inherently soluble in water, may be produced by another polymerization, in the same aqueous medium and in the presence of the microparticles, of monomers, giving rise to a polymer containing acidic salt producing groups which can confer water solubility.

Thus, suitable monomers are polymerizable carboxylic acids, such as acrylic acid or methacrylic acid, or their mixing with smaller amounts of non-hydrophilic monomers such as methyl methacrylate and also of hydrophilic monomers which give rise to water-insoluble, e.g. hydroxyethyl methacrylate and hydroxypropyl methacrylate.

If the polymer microparticles were prepared by a dispersion polymerization process in an aqueous medium, the second water soluble product may conveniently be produced by further polymerization in the same medium of suitable monomers, as mentioned in the preceding paragraph, and also basic monomers such as dimethylaminoethyl methacrylate, from which water soluble salt derivatives can be obtained.

Not all water soluble polymers generated in situ in the presence of microparticles by one of the methods described above will be able to confer the desired pseudoplastic properties to the base layer composition, but suitable poly 22 compositions can be obtained by a simple experimentation process, comprising, for example, viscosity measurements at different shear rates, chosen as described above, or the precise application of the compositions on a substrate.

Instead of in situ generation of a suitable water soluble polymer or as an addition thereto, such a polymer, as a separate preformed ingredient, may be added to the aqueous dispersion of microparticles.

Suitable polymers are those which, when dissolved in the aqueous environment even at low concentrations, cause a significant improvement in the viscosity of the composition. For example, one or more of the thickening agents known to be used in coating compositions based on aqueous polymer compositions may be added. However, not all such thickening agents are suitable for the present purpose, as some thickening agents are not able to confer the pseudoplastic properties necessary for the composition to which they are added.

On the other hand, certain thickening agents, which, if dissolved alone in the aqueous environment, do not exhibit such properties, may confer these properties on the dispersion of microparticles by interactions between them and microparticles (for example, by hydrogen bonding or by hydrogen bonding). polar groups).

A commercially available thickener that has been found to be very suitable is 'Acrysol ·' ASE 60.

While it turns out that any kind of inherently water soluble polymer, which is associated with the polymer microparticles or is added to the dispersion of microparticles, in order to confer pseudoplastic or thixotropic properties to the dispersion, it must, in its nature, be non-crosslinked, however, such a polymer may, at will, be of a crosslinkable type. That is, it may contain chemically reactive groups, which can be done, possibly with the aid of an added crosslinking agent, to become crosslinked after applying the base layer composition and preferably also the final composition on the substrate.

Thus, the polymer may contain, as already mentioned, hydroxyl or carboxyl groups derived from monomers having these groups and can then be cross-linked using an amino resin, for example, a methylated melamine condensate and formaldehyde, which is soluble in aqueous medium. .

The base layer composition may consist exclusively of the polymer microparticles, the pigment particles, the aqueous medium in which fine groups of particles are dispersed, and the inherently water soluble polymer conferring pseudoplastic properties.

However, it is preferable for the composition to also comprise a film-forming polymer which is soluble in the aqueous medium to ensure that, after applying the base layer to a substrate and evaporating the aqueous medium, there is a material which can thus fuse to fill the gaps between the microparticles and thus produce a suitable coherent film integrated in phase 2 of the process.

This function may indeed be performed, on the one hand, from an inherently water-soluble polymer found in the composition, as described above, for the purpose of conferring its pseudoplastic or thixotropic properties, but taking into account by the generally reduced proportions of such a polymer required for this purpose, it may be desirable to be supplemented by one or more other water-soluble film-forming materials introduced into the compositions which may possibly be chemically reactive to existing constituents.

Thus, the composition may contain oligomeric substances which can be converted to high molecular weight products after application of the composition, but which do not greatly contribute to the viscosity of the composition prior to application.

In this connection, low volatility diols such as 2-ethyl-1, 3hexanediol, low molecular weight polypropylene glycols, low molecular weight ethylene oxide adducts may be mentioned with dihydric or trihydric alcohols such as neopenOlglycol, bisphenyl A, cyclohexane, trimethylolpropane, befa-hydroxyalkyl, amides such as N, N, Ni, Ni-tefra-cbis (foie-hydroxyethyl) adipamide and cyclic amides and esters such as ε -caprolactam and ε-eaprolactone.

If such materials are not well soluble in pure water, they may be soluble in the aqueous environment consisting of water together with the water-miscible organic liquid, as described above.

Any of these oligomeric substances can be converted to a high molecular weight polymer, after applying the base layer composition to the substrate, by fixing it by its hydroxyl or other reactive groups with the aid of a polyfunctional reactant also present in the composition.

Particularly useful for this purpose are amino soluble resins in the aqueous medium of the composition, especially condensates of melamine and formaldehyde such as hex (alkoxymethylmelamines and their low molecular weight condensates.

As an alternative to that containing constituents of a film-forming polymer, upon application to the substrate, the base layer composition may contain a water-soluble, preformed acrylic polymer that does not confer pseudoplastic properties or may contain non-crosslinked polymer particles. which are stabilized in a similar manner to the present cross-linked microparticles.

Each of these alternative constituents may, as desired, contain functional groups such as hydroxyl groups, which may become cross-linked, after applying the composition to the substrate, with the aid of a cross-linking agent, for example, an amino resin.

The relative proportions of the different constituents of the layer-based composition can vary to a great extent and the optimum proportions in any separate system are often best determined by testing, but some guiding principles can generally be established.

Particularly, if the proportion of polymer microparticles is too high compared to the other film-forming material present in the composition, as described above, it will not be sufficient for this material to fill the gaps between the microparticles, · consequently, upon subsequent application of final layer composition (clear layer), there will be a tendency for its composition to penetrate the base layer film resulting in the loss of gloss; if, on the other hand, the proportion of microparticles is too low, it cannot confer the desired degree of protection against the attack by the solvent found in the final layer composition to the base layer composition; To a certain extent, a lower level of microparticles may be compensated for by allowing, for a longer period of time, for the base layer film to evaporate or dry before applying the final layer, but this diminishes one of the main advantages obtained by the present invention.

In general, a satisfactory level of microparticles will be in the range of 5 to 80% by weight of the total non-volatile content of base layer composition. The optimum level, however, depends to some extent on whether the pigment found in the base layer composition of metallic or non-metallic nature.

For metallic compositions, the preferred range of microparticle content is 40 ... 75% by weight. For solid color compositions, as a result of the proportions, in genes8196 &

2.5 ral, larger pigment required to obtain a Late opaque suitable for fairly small film thicknesses, the preferred range for microparticle content is quite small, namely

10 ... 50o / "by weight on the same basis, as above.

The reduced proportion of microparticles avoids an excessively large fraction of the total volume of dispersed material, which could give a porous base layer film and, thus, the immersion of the upper final film and the low gloss itself.

Also, in general terms it can be established that the proportions used in the composition of a thickening agent or of a second polymer conferring pseudoplastic properties can vary between 0.3 and 50% by weight of the total non-volatile content; the amount present of other film-forming material may range from 0 to 30% by weight and, if a cross-linking agent is found as an angiosin resin, it may amount to up to 30% by weight of the total non-volatile matter content of the composition. base layer.

This base layer composition may, if desired, additionally contain a catalyst for a crosslinking reaction that is required to occur after the composition is applied to the substrate. This may be a water-soluble acid compound such as p-toluenesulfonic acid, or / o-phosphoric acid, maleic acid or other strong carboxylic acid, as tetrachlorphthalic acid_; Alternatively, it may be a different acid-soluble salt with a volatile amine.

The nature of the film-forming polymer constituent of the final layer composition used in phase 3, from the process according to the present invention, is in no way critical. In general, any suitable film-forming polymer can be used, which may be of thermoset or thermoplastic type.

A suitable class of polymers consists of those derived from one or more ethylenically unsaturated monomers. Particularly useful members of this class are the addition acrylic polymers, which are well recommended for the production of coatings in the automotive industry, ie polymers or copolymers of one or more alkyl esters of acrylic acid or methacrylic acid, possibly together with other ethylene monomers. unsaturated.

Suitable acrylic esters include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, ethyl acrylate, butyl acrylate and

2-ethylhexyl. Other suitable copolymerizable monomers include vinyl acetate, vinyl pionate pro26, acrylonitrile, styrene and vinyltoluene.

When the acrylic polymer needs to be of the type of thermoset crosslinking, the functional monomers suitable for use, in addition to the latter, comprise acrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate N- (alkomethyl) acrylamide and M- (alkoxymethyl) methacrylamide, when the alkoxy groups may be, for example, a butoxy, glycidyl acrylate and glycidyl methacrylate.

The upper final composition may, in such a case, also contain a crosslinking agent such as a diisocyanate, a diosoxide or, in particular, a nitrogenous resin, i.e. a formaldehyde condensate with a nitrogenous compound such as urea, thiourea , melamine or benzoguanamine or a lower alkyl ether of such a condensate wherein the alkyl group contains from 1 to 4 carbon atoms.

Particularly suitable cross-linking agents are condensed with melamine and formaldehyde, in which a significant proportion of the methylol groups was etherified by reaction with butanol.

The upper final composition may have incorporated a catalyst suitable for the cross-linking reaction between the acrylic polymer and the cross-linking agent, for example, an acid reaction compound such as butyl acid maleate, butyl acid phosphate or p-toluenesulfonic acid. Alternatively, the catalytic action may be aided by the incorporation of free acid groups into the acrylic polymer, for example, by using acrylic acid or methacrylic acid as a comonomer in the preparation of the polymer.

The upper end polymer can be found either in solution or in stable dispersion in the volatile support liquid of the upper end layer composition, in other words, the support liquid can be a solvent or an insolvent for the upper end layer polymer.

If the liquid will be a solvent, it can be any of the organic liquids or mixtures of organic liquids that are typically used as polymer solvents in coating compositions, for example, aliphatic hydrocarbons such as hexane and heptane, aromatic hydrocarbons such as toluene and xylene and oil fractions with different boiling ranges that are predominantly aliphatic, but have an important content of aromatics, esters, such as butyl acetate, ethylene glycol diacetate and 2-ethoxyethyl acetate, ketones, as acetone and methylisobutyl ketone and alcohols, as butyl alcohol.

The liquid or mixture of liquids, chosen as the carrier liquid, will depend on the nature of the upper-end polymer in accordance with well-known coating principles, taking into account that the polymer will need to be soluble in the liquid.

If the carrier liquid is an organic insolvent, it will be considered to have a rather low polarity compared to those mentioned above and may consist of one or more aliphatic hydrocarbons such as hexane, heptane or petroleum fractions with low content of aromatics, possibly in mixing with liquids with high polarity as already shown above, but only that the total mixture be an insolvent for the upper final layer polymer.

In such a case, the upper final layer composition will be a non-aqueous polymer dispersion and this will generally be a sterically stabilized dispersion, in which the polymer particles are stabilized by means of a block or graft copolymer, of which one constituent polymer is insoluble by this liquid and associated with the dispersed polymer.

Well-known principles, according to which such dispersions can be prepared, are known.

Alternatively, the upper final layer composition may be prepared from water, as well as the base layer composition, and in this case also the upper final layer polymer may be in solution or in a state of stable dispersion in an aqueous medium, · in the case of a dispersion, it may be sterically stabilized, for example, if it has been prepared by a known aqueous dispersion polymerization method or stabilized in the charge, such as, if prepared by the well-known methods of aqueous emulsion polymerization.

Unlike the subsequent microparticles in the base layer composition, the upper final layer polymer will always be of the thermosetting type and thus capable of becoming cross-linked after application to the substrate, possibly with the aid of a cross-linking agent.

Usually, the composition of the upper final layer will be particularly colorless, so that the pigmentation effect, due to the base layer, is not much modified, but it may be desirable, in some cases, if the base layer contains a metallic pigment provides for a transparent coloring of the upper final layer composition.

In the first working phase of the process, according to the present invention, the base layer composition is applied to the surface of the substrate which may be previously painted or otherwise treated as usual in the subject.

The substrates that are of primary interest, in the context of the present invention, are metallic in nature, such as steel or aluminum, which are currently used for the manufacture of car bodies, but other materials, such as glass, materials can be used. ceramics, wood and even plastics, only if they are able to withstand the temperatures at which the final hardening of the multilayer coating can be performed.

After applying the base layer composition, a polymer film forms on the surface of the substrate. At will, this can be done by subjecting the substrate and the heat applied layer to volatilize the water and the organic liquid diluent therefrom, and it is within the scope of the present invention to use a sufficient heating temperature to cross-link the base layer film to those cases, in which the composition contains a film-forming material of the thermosetting lip.

According to the invention, it is sufficient to allow only a short drying period to ensure that the upper final layer composition can be applied to the base layer film, without the tendency for the first to mix and / or dissolve the base layer. basis for obtaining the optimum 'reflection' effect.

Drying conditions, suitable in any separate case, will depend, inter alia, on the ambient humidity, but in general, a drying time between 1 and 5 minutes at a temperature between 15 and 80 ° C will be appropriate to ensure preventing the mixing of the two layers. at the same time, the base layer film is adequately moistened by the upper final layer composition, so that satisfactory adhesion of the layers is obtained.

After applying the upper final layer composition to the base layer film, the coated substrate may be subjected to a heating or curing operation, in which the volatile support liquid of the final layer is removed and, possibly, in the film material of the final layer and / or that of the base layer is cross-linked using the present cross-linking agent (s).

This heating or curing operation is usually performed at a temperature in the range of 100 to 140 ° C, but at a lower temperature than this can be used only if it is sufficient to operate the required mechanism. crosslinking.

In executing the process, according to the present invention, the compositions of the base layer and of the upper final layer can be applied to the substrate by any of the usual methods such as brushing, spraying, plunging or flowing, but it is preferable to use application by spray, because this is how the best results are obtained both in terms of pigment control, in particular the orientation of the metallic pigment, and the gloss.

Any of the spray methods known as compressed air spray, electrostatic spray, hot spray and airless spray can be adopted, any kind of manual or automatic methods being suitable.

The thickness of the applied base layer film is preferably 0.5 ... 1.5 millimeters and that of the upper final layer ₂₅is 1 ... 3 thousandths (in each case, the thickness of the dry film).

As is apparent from the description, the advantage of the present invention, in terms of "charming metal finishes", is the use of a base / clear layer system, in which damage due to air pollution or greatly reduced by using a base layer composition is eliminated. with water, without leaving a good control of the orientation of the metal pigmentation.

When it comes to solid color finishes, controlling the pigment orientation is not, of course, an important factor, but the advantage as ⁴⁰the base layer film is not disturbed by the subsequent application of the upper final layer composition and it was also found that the base layer film is much less effective ⁴⁵known as "flowering than a water-based coating that does not contain polymer microparticles.

In these examples, the apparent viscosity & values, noted of the base layer compositions, were determined using two different devices. Its values ​​at 10,000 s ~¹ shear rate were determined using the viscometer with _Mcone and plate ICI in the modification foreseen to cover the viscosity range of 0 ... 2.0 P at the rate of forfeiture30 in question. This apparatus is described in the Journal of the Oii and Color Chemists Association, 1966, in an article by CH Monk and is provided by Research Equipment (London) Limited.

The values ​​of vja at 1.0 s "¹ The shear rate was determined using a concentric cylinder viscometer "Rheomat 30 with ring and disc" A; each sample was subjected to a shear rate of 660 s^_1, until a constant shear record was obtained, after which the shear rate changed immediately to 1.0 s ”¹, the shear stress was determined and the viscosity of these data was calculated.

The present invention has the advantage of obtaining a multilayer coating with increased strength.