JPH07166102A - Aqueous emusion-based coating - Google Patents

Abstract

PURPOSE:To obtain an emulsion-based coating consisting essentially of a carboxyl group-containing resin latex and a carboxylic acid group-crosslinkable crosslinking agent and capable of providing a coating film having good water resistance and suitable as an undercoating for automobiles. CONSTITUTION:This coating contains a carboxyl group-containing latex and a carboxyl group-crosslinkable crosslinking agent as main components or this coating contains a methylol group-containing resin latex as a main component. Besides, the resin component is perferably a partially crosslinked resin having 10-90wt.% toluene-insoluble content. Further, a curing accelerator such as diethyltriamine is preferably used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aqueous emulsion paint suitable as an undercoat paint for automobiles.

[0002]

2. Description of the Related Art Conventionally, an undercoat paint has been used as a chipping-resistant paint applied to automobile tire houses, under floors, front aprons, etc. to prevent damage to the vehicle due to flying stones. Since such undercoat paints come into contact with water in particular, such as when traveling in the rain or in a water pool, water resistance is one of the important performances, and it is necessary to form a coating film in a thick film.
Therefore, polyvinyl chloride plastisols have been widely used in the past, but in many cases when the automobile is scrapped and the steel sheet is regenerated, the coating film is removed by incineration. But,
Polyvinyl chloride resin is problematic in terms of environment because it generates hydrogen chloride when incinerated.

For this reason, paints replacing polyvinyl chloride plastisols have been demanded, and water-based emulsion paints using water as a dispersion medium have been attracting attention as paints in line with this.

However, the water-based emulsion-based paint has a problem that the water resistance of the coating film generally obtained is not sufficient, and there is a demand for a water-based emulsion-based paint which is excellent in water resistance and gives a suitable coating film for undercoating. It was

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an aqueous emulsion coating composition which gives a coating film having good water resistance.

[0006]

Means for Solving the Problems The present inventors have conducted extensive studies to achieve the above-mentioned object, and as a result, use of a carboxyl group-containing resin latex and a carboxyl group-crosslinking crosslinking agent, or a methylol group It has been found that it is effective to use the contained resin latex, in which case the resin component is a partially crosslinked resin having a toluene insoluble content of 10 to 90% by weight.

That is, the latex in which the carboxyl group is introduced into the polymer is excellent in the adhesiveness not only to the electrodeposition coated plate but also to the substrate such as a metal steel plate, and therefore the latex from the interface portion between the formed undercoat film and the substrate is excellent. Water can be prevented from entering, and in this respect, the initial water resistance is excellent. However, on the other hand,
Since the carboxyl group remaining after forming the coating film is hydrophilic, it has a function of attracting water, and thus long-term water resistance is deteriorated, but it reacts with the carboxyl group remaining during heating and drying. By adding a cross-linking agent that changes this to non-hydrophilicity, it is possible to eliminate the remaining carboxyl groups and significantly improve water resistance.In addition to this, cross-linking increases the areal density, resulting in water permeation. It has been found that the water resistance is improved by decreasing the rate and increasing the resistance to the intrusion of water from the outside of the coating film.

Further, the latex having a methylol group introduced into the polymer has a so-called self-crosslinking property because the methylol groups are condensed and crosslinked by the heat during heating and drying.
It has been found that the hydrophilic methylol group disappears and the areal density increases, and the same effect as described above can be obtained.

Further, the resin is cross-linked at the time of production of the latex, and the partially cross-linked resin latex having a toluene insoluble content (gel fraction) of 10 to 90% by weight has a higher degree of cross-linking, a lower elongation and a higher tensile strength. It was found that the water resistance and weather resistance are further improved by the above, and the present invention has been completed.

Accordingly, the present invention is characterized in that the main component is a carboxyl group-containing resin latex and a carboxyl group crosslinkable crosslinking agent, and the main component is a methylol group-containing resin latex. And an aqueous emulsion paint as described above, wherein the resin component is a partially crosslinked resin having a toluene insoluble content of 10 to 90% by weight.

The present invention will be described in more detail below. The aqueous emulsion coating composition according to the first invention of the present invention uses the carboxyl group-containing resin latex and the crosslinking agent as described above.

Examples of the base resin for introducing such a carboxyl group include acrylic resins and styrene-butadiene copolymer resins. For example, unsaturated carboxylic acids such as acrylic acid and methacrylic acid. A latex obtained by emulsion polymerization in which is copolymerized as the third component can be used. In this case, the concentration of the carboxyl group is preferably about 0.5 to 5% by weight. In the present invention, such a carboxyl group-containing resin latex may be used in combination with an ordinary polyurethane resin latex, styrene-butadiene copolymer resin latex, acrylic resin latex, etc. within a range that does not impair the effects of the present invention. You can

On the other hand, the cross-linking agent is a compound which reacts and cross-links with a carboxyl group by heat during heating and drying, and specifically, a compound having a hydroxyl group (methylol group) such as urea resin, melamine resin, phenol resin and glycols. Examples thereof include compounds having an epoxy group such as epoxy resin, compounds having an imine group, compounds having an amine group, and metal oxides such as zinc white and sodium aluminate. Methylated melamine resin, water dispersibility A thermosetting resin such as a blocked isocyanate is preferable, whereby the pot life as one liquid can be secured, and the water resistance and solvent resistance can be improved without losing the flexibility of the coating film. Examples of commercially available blocked isocyanates include FX manufactured by Nippon Carbide Industry Co., Ltd.
-977 can be mentioned.

The amount of such a cross-linking agent blended is such that the resin component 1
0.1 to 10 parts with respect to 00 parts (weight part, the same applies hereinafter),
The range of 0.5 to 5 parts is more preferable, and the amount may be appropriately changed depending on the carboxyl group content of the resin. If the amount of the cross-linking agent is less than 0.1 part, the compounding effect may not be exhibited. On the other hand, if the amount of the cross-linking agent is more than 10 parts, the storage stability becomes poor and the degree of resin cross-linking increases to bake dry. The coating may be hardened and the elasticity of the coating may be lost.

When a cross-linking agent is blended, a curing accelerator may be used in combination, and examples of the curing accelerator include organic amine-based ones such as diethylenetriamine and alicyclic polyamine salts. The blending amount is preferably about 1/10 of the crosslinking agent.

On the other hand, the emulsion coating composition according to the second aspect of the present invention uses a self-crosslinking methylol group-containing resin latex.

Examples of the base resin into which such a methylol group is introduced include acrylic resins and styrene-butadiene copolymer resins, such as 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate. , N-methylol acrylamide or the like is added as a third component, and an emulsion-polymerized resin can be used. In this case, the concentration of the methylol group is preferably about 0.5 to 5% by weight. The self-crosslinking resin latex can be used in combination with an ordinary latex as long as the effect of the present invention is not impaired.

A partially crosslinked resin latex is preferably used as the carboxyl group- or methylol group-containing resin latex. As a result, not only the water resistance and weather resistance are further improved, but the viscosity of the latex is lowered and a high solid content can be obtained, and the tackiness during drying during coating film formation is low, so that the surface The skinning phenomenon is relatively delayed, and the occurrence of swelling during drying can be prevented, which is effective for forming a thick film.

In this case, the value of partial cross-linking can be given by the gel fraction insoluble in toluene, and this gel fraction is preferably 10 to 90%, particularly 30 to 80%. If the gel fraction is lower than 10%, the above-mentioned effect due to the partial cross-linking may not be exhibited, while the gel fraction is 90% or less.
If it exceeds%, the degree of cross-linking may be too high, and it may be difficult to form a coating film.

In the case of producing such a partially crosslinked resin latex, for example, during emulsion polymerization of the latex, a third component such as divinylbenzene, diallyl phthalate, polyoxyethylene di (meth) acrylate, trimethylolpropane triacrylate or allyl acrylate. A method of causing partial crosslinking by addition can be adopted.

If desired, the aqueous emulsion paint of the present invention may contain a filler, a defoaming agent, a thickener, a dispersant, a wetting agent and the like.

As the filler, for example, calcium carbonate,
Talc, clay, silica, diatomaceous earth, zeolite, magnesium carbonate, mica and the like can be mentioned, but if the shape of the particles of the filler is flat, it tends to hinder the evaporation of water, so among these, the shape of the particles is Non-planar calcium carbonate and diatomaceous earth are preferred. The average particle size of the filler is 1
About 20 μm is preferable.

The amount of the filler compounded is 50 to 300 parts, especially 150 parts, relative to 100 parts of the resin component in the latex.
A range of ˜250 parts is preferred. If the blending amount is less than 50 parts, proper thixotropy can not be obtained even in combination with a thickener, and the swelling tends to occur and the cost may increase. On the other hand, if the amount exceeds 300 parts, it becomes difficult for the resin to sufficiently wet the filler, and the chipping resistance may not be satisfied due to performance deterioration, and cracks may easily occur.

The defoaming agent is blended for the purpose of reducing the occurrence of bubbles and facilitating the elimination of bubbles once they are formed, because low viscosity emulsions and emulsion mixtures are likely to cause bubbles by stirring.

The thickener is used for helping the dispersion of the pigment to prevent sedimentation, improve the stability of the coating material, finish the viscosity adjustment to an appropriate level, and obtain the balance of both sprayability and thixotropy. In addition to methylcellulose, hydroxyethylcellulose, carboxymethylcellulose, protein, polyvinyl alcohol, sodium polyacrylate, etc., carboxyl-modified ones can be thickened with an alkali such as amine or ammonia. A combination of two or more species can be used at a regular dose.

The dispersant is for helping the filler and the like to be dispersed in water, and examples thereof include various sodium polyphosphates and surfactants such as polyoxyethylene nonylphenyl ether. , Can be used in normal doses.

The aqueous emulsion paint of the present invention can be prepared by mixing the above components according to a general method. For example, after latex, filler, dispersant, wetting agent, defoaming agent, etc. are kneaded, thickener, cross-linking agent, etc. are added to disperse, then defoaming agent, etc. is added to defoam, and finally The aqueous emulsion paint of the present invention can be prepared by filtration. In this case, a high-speed disperser is suitable as the disperser, and the kneading and the subsequent viscosity adjustment can be simultaneously performed, so that the production efficiency can be higher than that of other machines.

The water-based emulsion paint of the present invention can be used as a paint for parts such as automobile tire houses, under floors and front aprons that require chipping resistance, and also as a sealing material for seal joints. is there.

In this case, a general high-pressure pump can be used for coating by a spray gun coating method or the like, and the coating amount is 150 to 40 in terms of the thickness of the dried coating material.
It can be about 100 μm.

The drying conditions are, for example, 10 to 6 at room temperature.
After leaving it for 0 minutes, it is dried in a calcining furnace at about 110 ° C. for about 8 to 12 minutes, then at 120 to 150 ° C. for 20 to 30 minutes in an intermediate coating furnace, and finally in a top coating furnace at 120 to 150 ° C. for 2 minutes.
Conditions for drying for 0 to 30 minutes can be adopted.

[0031]

The water-based emulsion paint of the present invention can provide a coating film having good water resistance.

[0032]

EXAMPLES Hereinafter, the present invention will be specifically shown by showing Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[Examples 1 to 3 and Comparative Examples 1 and 2] Aqueous emulsion coatings were prepared with the formulations shown in Table 1, and the adhesion, water resistance and storage stability were tested by the following methods. The results are also shown in Table 1. <Adhesion> The sample was applied on a steel plate that had been subjected to electrodeposition coating so that the film thickness after drying was 500 μm, and the temperature was 10 at room temperature.
After being left for a minute, preliminary drying was performed at 90 ° C. for 10 minutes, and then main baking was performed at 130 ° C. for 20 minutes. The above baked sample was cut with a cutter knife and peeled from the end portion with a nail, and the quality of the adhesion was determined by the degree of peeling. <Water resistance> A sample was applied on a steel plate that had been electrodeposited so that the film thickness after drying was 500 μm, and the temperature was 10 at room temperature.
After being left for a minute, preliminary drying was performed at 90 ° C. for 10 minutes, and then main baking was performed at 130 ° C. for 20 minutes.

The above-mentioned baked sample was set at an angle of 45 ° from the horizontal with the coated surface facing upward, and the lower end of a vinyl chloride pipe having an inner diameter of 20 mm and a length of 2 m, which was erected perpendicularly to this coated surface, was applied to this coated surface. The M-4 nut specified in JIS was dropped from the upper end through the pipe, and the total weight of the nut until the base material was exposed was measured to determine the initial chipping resistance.

Next, after the baked sample was treated with warm water at 40 ° C. for 10 days, the above test was conducted on the sample left at room temperature for 2 hours, the chipping resistance after water resistance was determined, and the rate of reduction from the initial value was evaluated. <Storage stability> The prepared coating material was evaluated by the increase in viscosity after the coating material was treated at 35 ° C for 240 hours.

[0036]

[Table 1] (Note) Carboxylated styrene-butadiene copolymer resin
Oil latex (1) Resin content 50% by weight, carboxyl group content 2% by weight, methylol group-containing styrene-butadiene copolymer resin la
Tex (2) Resin content 50% by weight, Methylol group content 2% by weight, Styrene-butadiene copolymer resin latex (3) Resin content 50% by weight Melamine resin (4)

From the results shown in Table 1, the aqueous paints containing the carboxyl group-introduced SBR latex and the crosslinking agent (Examples 1 and 2) were the same as those using the SBR latex containing no carboxyl group (Comparative Example 2). It is recognized that the adhesiveness is good as compared with each other, and the water resistance is very good as compared with the case where the crosslinking agent is not added (Comparative Example 1).
It is also recognized that the water-based paint using the self-crosslinking SBR latex (Example 3) also has good water resistance.

Claims (3)

[Claims] 1. A water-based emulsion-based coating material comprising a carboxyl group-containing resin latex and a carboxyl group-crosslinking crosslinking agent as main components. 2. A water-based emulsion coating material comprising a resin latex containing a methylol group as a main component. 3. The aqueous emulsion paint according to claim 1, wherein the resin component is a partially crosslinked resin having a toluene insoluble content of 10 to 90% by weight.