JPS6224519B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a matte electrodeposition coating method, and more specifically, the present invention relates to a matte electrodeposition coating method, and more specifically, the present invention relates to a matte electrodeposition coating method, and more specifically, by electrodeposition coating an object in an anionic electrodeposition paint bath consisting of an acrylic copolymer containing an alkoxysilane group and an amino resin, The present invention relates to a matte electrodeposition coating method that forms a stable and uniform matte coating even during production. Since the electrodeposition coating method uses water as a solvent, there is no risk of fire or explosion, and the process can be automated and large quantities can be coated continuously over a long period of time. It has been widely used since it has many advantages such as easy control. However, the coatings obtained by electrodeposition are generally glossy, and as long as they are used as an undercoat, the presence or absence of gloss is of little concern; In fields where single-coat finishes are used, the diversification of user needs has led to a lack of metallic luster, and there is now a strong demand for matte coatings that create a calm atmosphere. However, various methods have been proposed in the past to make the surface of an electrodeposition coating matte. For example, an inorganic transparent pigment having a matting effect is contained in an electrocoating paint bath, and the inorganic pigment is precipitated together with the organic resin component of the paint during electrocoating to obtain a matte effect. A method of immersion treatment in an acidic treatment solution before baking hardening,
Furthermore, as a method for forming a coating film having a desired gloss from high gloss to low gloss in the same electrodeposition paint bath, amino resin-cured anionic electrodeposition paints have sulfonic acid groups or sulfuric acid esters in the molecule. Various methods have been proposed for electrodeposition coating in an electrodeposition paint bath containing a specific amount of a specific organic compound having a group (JP-A-52-137444, JP-A No. 52-137445).
No. 52-137446, No. 56-106977). However, in the method of adding an inorganic transparent pigment in the method described above, since the inorganic transparent pigment that is usually available has a specific gravity of 2.5 or more, the pigment sedimentation rate in the electrocoating paint bath is high, and in order to prevent pigment sedimentation, it is necessary to It is essential that the bath be vigorously stirred at all times. Furthermore, even if the electrodeposition paint bath is sufficiently stirred, the gloss will vary depending on the part of the object to be coated, and in particular, the upper surface of the object will have a low gloss and the lower surface will have a high gloss. I can't avoid it. In addition, in a method in which the object to be coated is immersed in an acidic treatment solution before baking and hardening, the acidic substance causes a crosslinking reaction of the electrodeposited coating, thereby suppressing the smoothing of the coating due to melting during baking. As a result, coating film defects such as pinholes tend to remain, making it difficult to obtain a coating film with excellent performance. In addition, in the method of adding an organic compound having a sulfonic acid group or a sulfuric acid ester group to the electrodeposition paint, the electrophoretic speed of the base resin for the electrodeposition paint (-COOH type) and the organic compound containing a sulfonic acid group used as a curing catalyst , because the deposition characteristics are different, the amount of the organic compound deposited in the coating film will vary due to slight differences in voltage, current density, etc. As a result, the degree of gloss will vary, making it impossible to obtain a stable matte coating film. There is a drawback. Therefore, the present inventors have developed a method for obtaining a matte coating film without the above-mentioned drawbacks by adding an inorganic transparent pigment or a curing catalyst, or by immersing the object to be coated in an acidic treatment liquid before curing by baking. As a result of intensive research with the aim of obtaining a stable matte coating film with little variation in gloss and regardless of the shape of the object to be coated, without any special precautions, we have developed an alkoxysilane-based electrodeposition coating. The present inventors have discovered that the above object can be achieved by using an anionic electrodeposition coating material comprising a water-soluble or water-dispersible acrylic copolymer having in the side chain and an amino resin, and have completed the present invention. Thus, according to the present invention, the object to be coated is electrodeposited in an anionic electrodeposition paint bath consisting of a water-soluble or water-dispersible acrylic copolymer having an alkoxysilane group in its side chain and an amino resin, There is provided a matte electrodeposition coating method characterized in that the electrodeposition coating film is then washed with water and then cured by baking. Usually, the coating film obtained by electrodeposition has a dense surface, forming a fine rough surface and a matte state.
When this is baked and cured, it melts and flows, creating a smooth surface and a glossy coating. However, in the method of the present invention, the acrylic copolymer used as the base resin of the electrodeposition paint has an alkoxysilane group in the side chain, so this neutralizes the acrylic copolymer and makes it water-soluble by adding water. (or water dispersion), hydrolyzes to produce silanol (-Si-OH), and condensation of the silanols produces -Si.
-O-Si- bonds are formed to form fine dispersion particles with an intraparticle gel structure.
The coating film obtained by electrodeposition of this material forms a fine rough surface, and even if it is baked and cured, the coating film does not completely melt and flow and maintains the rough surface. It becomes matted. The matte coating film thus obtained exhibits an aesthetically pleasing, transparent, uniform matte finish, and since the acrylic copolymer has Si--O bonds, the coating film has high hardness and excellent adhesion to the substrate. In addition, the formation of the intraparticle gel structure of electrocoating paint occurs quickly after the particles are uniformly dispersed, so the dispersed particles become stable in a short time and do not settle over time, resulting in a glossy finish. No unevenness occurs. Furthermore, there is almost no change in the particle size of the dispersed particles or the state of the electrodeposited coating over time, so even if continuous coating is performed, there is little change in gloss, coating deposition amount, coating performance, etc., resulting in a stable matte coating. It is possible to obtain The electrodeposition paint that can be used in the present invention is an anionic electrodeposition paint consisting of a water-soluble or water-dispersible acrylic copolymer having an alkoxysilane group in its side chain and an amino resin, and the acrylic copolymer forms The monomer components are (1) an unsaturated monomer containing a polymerizable unsaturated double bond and an alkoxysilane group in the molecule, (2) an α,β-ethylenically unsaturated carboxylic acid, and (3) an acrylic monomer containing a hydroxyl group. and (4) other radically polymerizable unsaturated monomers other than those mentioned above. The unsaturated monomer containing a polymerizable unsaturated double bond and an alkoxysilane group in (1) above is a monomer component that introduces an alkoxysilane group into the copolymer, and examples thereof include:

【table】

[Table] (or alkoxyalkoxy)silane compound. Among these, unsaturated trialkoxysilane compounds are preferred. The alkoxysilane compound as component (1) is contained in an amount of 1 to 10% by weight, preferably 2 to 7% by weight, based on the total amount of all monomers used. If the amount used is less than 1% by weight, a matte coating film cannot be obtained;
If it exceeds 10% by weight, the dispersed particles will become coarser, causing sedimentation or uneven coating. Examples of the α,β-ethylenically unsaturated carboxylic acids mentioned in (2) above include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, fumaric acid, crotonic acid, and itaconic acid. A carboxyl group is introduced into the copolymer to make the copolymer water-soluble or water-dispersible. The amount of α,β-ethylenically unsaturated carboxylic acid used is such that the acid value of the copolymer is 20 to 150, preferably 30.
It is best to use a ratio of ~100. If the acid value of the copolymer is less than 30, water solubility or water dispersibility will be somewhat insufficient;
If it exceeds 100, the water resistance of the resulting coating film may decrease. Examples of the hydroxyl group-containing acrylic monomer in (3) above include 2-hydroxyethyl acrylate, hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, and hydroxypropyl methacrylate. A hydroxyl group is introduced into the resin and reacts with the amino resin to perform a crosslinking reaction. The amount of the hydroxyl group-containing acrylic monomer to be used is preferably one with a hydroxyl value of 30 to 200.
Used in proportions such as 50-150. If the hydroxyl value of the copolymer is less than 30, the coating film performance will be poor, while if the hydroxyl value exceeds 200, the water resistance of the coating film will be poor. In addition, other radically polymerizable unsaturated monomers mentioned in (4) above are the remaining components constituting the acrylic copolymer, such as methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, and acrylic acid. Butyl, hexyl acrylate, octyl acrylate, lauryl acrylate, cyclohexyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, hexyl methacrylate, octyl methacrylate, lauryl methacrylate, etc. Alkyl ( _C1-18 ) esters of acrylic acid or methacrylic acid; Vinyl aromatic monomers such as styrene, α-methylstyrene, and vinyltoluene; Amide compounds of acrylic acid or methacrylic acid; Usually acrylic resins such as acrylonitrile and methacrylonitrile Known monomers used in the synthesis of can be used. These unsaturated monomers (1) to (4) are appropriately selected depending on the desired physical properties, and each may be used alone.
Alternatively, two or more types can be used in combination. The above unsaturated monomers (1) to (4) are copolymerized according to methods known per se for producing acrylic copolymers, such as solution polymerization, emulsion polymerization, suspension polymerization, etc. It can be done using Advantageously,
It is preferable to carry out the polymerization according to a solution polymerization method, in which the above two components are mixed in a suitable inert solvent in the presence of a polymerization catalyst, usually at about 0 to about 180°C, preferably at about 40 to about
The reaction can be carried out by continuing the reaction at a reaction temperature of 170°C for about 1 to 20 hours, preferably about 4 to about 10 hours. As the solvent used, it is desirable to use a solvent that can dissolve the copolymer to be produced and is miscible with water so that gelation does not occur during the copolymerization reaction. Examples of such solvents include cellosolve solvents, carbitol solvents, glyme solvents, cellosolve acetate solvents, and alcohol solvents. Further, as the polymerization catalyst, for example, azo compounds, peroxide compounds, sulfides, sulfin compounds, diazo compounds, nitroso compounds, etc. can be used. The acrylic copolymer thus obtained has a molecular weight of 20 to
It has an acid value of 150, a hydroxyl value of 30 to 200, and about
It has a number average molecular weight ranging from 10,000 to 100,000, preferably from about 20,000 to about 60,000. molecular weight
If the molecular weight is less than 10,000, it will not necessarily give a coating film that is fully satisfactory in terms of durability, and if the molecular weight is less than 100,000,
If it exceeds 100%, the viscosity of the resin becomes high and it becomes difficult to form uniform fine particles when dispersing in water. Water solubilization or water dispersion of the above acrylic copolymer can be carried out according to a conventional method. , 0.5 for the carboxyl group
Treatment with ~1.0 equivalent of an amine compound, such as aliphatic amines such as monoethylamine, diethylamine, and triethylamine, alkanolamines such as diethanolamine and triethanolamine, cyclic amines such as pyridine and piperidine, and ammonia. This can be done by Furthermore, in the present invention, examples of the amino resin used as a crosslinking agent for the acrylic copolymer include conventionally known melamine resins, benzoguanamine resins, urea resins, etc. Among them, alkoxymethylated melamine resins are preferred. It is a methyl etherified type or a mixed etherified type with an alcohol having 4 or less carbon atoms. The electrodeposition paint bath is prepared by blending the above acrylic copolymer and amino resin in a solid content weight ratio of 9:1 to 3:7, and adding the above-mentioned neutralizing agent and auxiliary solvent (for example, alcohol-based This is done by adding a solvent (such as a cellosolve solvent) and diluting it with water. In addition to pigments, dyes or other colorants, various commonly used additives may be used in the electrodeposition paint bath, if necessary. When carrying out the electrodeposition coating according to the present invention, the solid content concentration of the electrodeposition paint bath is suitably 4 to 15% by weight. If it is less than 4% by weight, the coating voltage will be too high, and if it is more than 15% by weight, the loss to the outside of the coating system will be large, making it uneconomical. Electrodeposition coating is usually carried out under the conditions of an electrocoat bath temperature of 15 to 35°C, a coating voltage of 80 to 350V, and a treatment time of 1 to 5 minutes. The electrodeposited object is washed with water and then heated to 150 ml.
Heat cured at ~200°C for 15-60 minutes. If the electrodeposited object is not washed with water before heating and curing, the unelectrodeposited paint adhering to the surface of the electrodeposited object will be heated and hardened, smoothing out the rough electrodeposited surface. A matte coating film is formed and an initial matte electrodeposition coating film cannot be obtained. In this way, an electrodeposited coating having the desired matte effect is formed. The object to be coated that can be applied to the matte electrodeposition coating method of the present invention is not particularly limited as long as it has conductivity, but when aluminum or aluminum alloy is used as the object to be coated, performance such as smoothness may be affected. The method of the present invention is particularly suitable because it provides an excellent uniform matte coating film and can form a coating film that has properties equivalent to those of glossy clear coatings in terms of alkali resistance, acid resistance, and weather resistance. Next, the present invention will be further explained by examples.
In the examples, "parts" and "%" mean "parts by weight" and "% by weight." Acrylic copolymer production example 1 55 parts of isopropyl alcohol was charged into a reaction vessel and maintained at 80°C, and 15 parts of styrene, 31 parts of methyl methacrylate, and 19 parts of n-butyl acrylate were added.
parts, 10 parts of ethyl acrylate, 15 parts of hydroxyethyl acrylate, 7 parts of acrylic acid, 3 parts of α-methacryloxypropyltrimethoxysilane (trade name: KBM-503, manufactured by Shin-Etsu Chemical Co., Ltd.), and 1.0 parts of azobisdimethylvaleronitrile. The mixture was added dropwise over a period of 3 hours, kept at this temperature for 1 hour after the addition, and then added with 1 liter of azobisdimethylvaleronitrile.
1 part and 13 parts of butyl cellosolve were added dropwise and further heated to 80°C.
The reaction was continued for 4 hours. After the reaction was completed, the solid content was adjusted to 53% with benzyl alcohol to obtain an acrylic copolymer varnish with a polymerization rate of 100%, a number average molecular weight of about 30,000, an acid value of 53, and a hydroxyl value of 72. Acrylic copolymer production examples 2 to 4 Acrylic copolymer varnishes were produced in the same manner as in Production Example 1 above based on the monomer formulations shown in Table 1 below.

[Table] Example 1 Acrylic copolymer varnish obtained in Production Example 1
0.8 to 100 parts per carboxyl group of the copolymer
Equivalent amounts of triethylamine and 47 parts of Cymel 303 (melamine resin manufactured by Mitsui Toatsu Co., Ltd.) were added and mixed uniformly. Deionized water was added to the electrodeposition coating composition thus obtained to give a solid content of 12%, and the composition was subjected to electrodeposition coating. This electrodeposition coating composition was placed in an electrodeposition coating test device, and a 6063S aluminum alloy plate subjected to alumite treatment (alumite film thickness 9μ) was used as the object to be coated (anode). Power was applied for a minute. In addition, three coated plates were prepared when electricity was applied for 3 minutes at voltages of 150V, 180V, and 210V, respectively. After electrodeposition, these coated plates were washed with water and heated at 180℃.
Bake hardened for 30 minutes. The performance test results of the electrodeposited coating film obtained are shown in Table 2 below.

【table】

[Table] Examples 2 to 4 Electrodeposition coating compositions were prepared in the same manner as in Example 1 based on the formulations shown in Table 3 below, and the voltage was changed.
An electrodeposited coating film was prepared in the same manner as in Example 1 at 150V. The performance test results of the electrodeposited coatings obtained are shown in the table below.
4.

[Table] Manufactured by Sanwa Chemical Co., Ltd.

【table】

Claims (1)

[Claims] 1 The object to be coated is electrodeposited in an anionic electrodeposition paint bath consisting of a water-soluble or water-dispersible acrylic copolymer having an alkoxysilane group in the side chain and an amino resin, and then the electrodeposition coating is washed with water. A matte electrodeposition coating method, which is characterized by the following steps: