JPH078968B2 - Aqueous coating composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to a water-based coating composition, and more particularly to a water-based coating composition that exhibits excellent corrosion resistance when coated on a steel sheet or the like. The water-based paint composition of the present invention is useful as an undercoat paint for underbody parts of automobiles, casting parts, forged parts and the like.

[Prior Art] The underbody parts of automobiles and the like have been conventionally coated with an electrodeposition coating, and the formed electrodeposition coating film imparts corrosion resistance. However, for cast parts or forged parts, rust-preventive paints other than electrodeposition paints are used because it is difficult to apply electrodeposition coating. Above all, it was discovered that a coating film formed from a water-based paint using a vinylidene chloride resin-based emulsion as a base resin has a great barrier function of suppressing permeation of water, oxygen, ions, etc. and has excellent corrosion resistance. Therefore, it is being studied intensively for use.

For example, JP-A-63-105073 discloses a vinylidene chloride-based emulsion emulsion-polymerized from vinylidene chloride, a monomer such as an acrylic ester, and a vinyl-based unsaturated carboxylic acid such as acrylic acid, and a tannin substance. Mixed anticorrosion coating compositions are disclosed. This coating composition exhibits excellent rust prevention performance due to the synergistic effect of the barrier action of vinylidene chloride and the chelate reaction of tannin with iron.

[Problems to be Solved by the Invention] An aqueous paint containing a tannin substance is suitable as a rust preventive paint because it forms a chelate compound with iron and stabilizes. However, studies conducted by the present inventors have revealed that an aqueous coating material containing a tannin substance undergoes a change during storage to gradually reduce the effect of tannin. In addition, a coating film formed from a water-based paint using a conventional vinylidene chloride resin-based emulsion as a base resin does not have sufficient corrosion resistance under severe test conditions, and has even better corrosion resistance. It has been desired to develop a paint capable of forming a coating film.

The present invention has been made in view of such circumstances,
It is an object of the present invention to improve the composition of a coating composition using a vinylidene chloride resin-based emulsion as a base resin without using a tannin substance so as to have more excellent corrosion resistance.

[Means for Solving the Problems] The aqueous coating composition of the present invention comprises vinylidene chloride 40 to 80% by weight, vinyl chloride 10 to 60% by weight, vinyl monomer 5 to 49.9% by weight, and vinyl unsaturated carboxylic acid 0.1 to 5%. A vinylidene chloride resin emulsion containing 40 to 70% by weight of chlorine atoms in the resin skeleton, which is formed by emulsion polymerization of a monomer component consisting of 10% by weight and 100 parts by weight in terms of solid content, and has a particle size of 0.2 to 5 μm. Within the range, the average particle size is 1 to 5 μm
20-90 parts by weight of the first powder and 20-250 parts by weight of a powdery filler composed of 10-80% by weight of the second powder having a particle size in the range of 5-50 μm and an average particle size of 8-15 μm. It is characterized by containing.

In the monomer composition of the resin constituting the vinylidene chloride resin-based emulsion contained in the aqueous coating composition of the present invention, vinylidene chloride is 40 to 8 when the total amount is 100% by weight.
It is set to 0% by weight. 40% by weight of vinylidene chloride
If the amount is less than the above range, the above-mentioned barrier action is deteriorated and sufficient corrosion resistance cannot be obtained. On the other hand, if it exceeds 80% by weight, the resulting emulsion tends to crystallize and the film-forming property tends to be poor. In addition, heat resistance may be defective.

Vinyl chloride is added in an amount of 10 to 60% by weight. If the blending amount of vinyl chloride is less than 10% by weight, the corrosion resistance is lowered, and if it is more than 60% by weight, the amount of vinylidene chloride is insufficient and the corrosion resistance is inferior. A range of 10-30% by weight is particularly preferred.

The content of chlorine atoms in the resin skeleton is 40 to 70% by weight. When the content of chlorine atoms is less than 40% by weight, the barrier action is small and the corrosion resistance becomes poor, and when it exceeds 70% by weight, the adhesiveness of the coating film decreases. When the content of vinylidene chloride and vinyl chloride is within the above range, the content of chlorine atoms is usually within this range.

As another monomer, 5 to 49.9% by weight of a vinyl monomer is blended. If the blending amount of the vinyl monomer is less than 5% by weight, the adhesion will be insufficient, and if it is more than 49.9% by weight, the blending amount of vinylidene chloride and vinyl chloride will be relatively decreased and the corrosion resistance will be deteriorated. This vinyl monomer can be selected from one or more conventionally known monomers such as various acrylic acid esters, various methacrylic acid esters, vinyl acetate, and styrene.

The water-based coating composition of the present invention contains 0.1 to 5% by weight of vinyl unsaturated carboxylic acid. If the content is less than 0.1% by weight, the film-forming property is poor, and if it exceeds 5% by weight, the stability of emulsion particles during the polymerization reaction becomes insufficient. Acrylic acid or methacrylic acid is typically used as the vinyl unsaturated carboxylic acid.

The vinylidene chloride resin-based emulsion, which is one of the constituents of the aqueous coating composition of the present invention, can be obtained by mixing the above-mentioned respective monomers in the above-mentioned range, and adding an emulsifier to carry out emulsion polymerization. This emulsion polymerization can be performed in a conventional manner.

The greatest feature of the aqueous coating composition of the present invention is that it contains a powdery filler having a specific particle size distribution. This powdery filler has a particle size in the range of 0.2 to 5 μm and an average particle size of 1 to 5 μm, 20 to 90% by weight of the first powder, and a particle size of 5 to 50%.
Second powder with average particle size of 8-15 μm in the range of μm
It consists of 80% by weight. By using a powdery filler having a particle size distribution in this range, the powdery filler is packed close to the closest packing in the coating film, and as it aids the barrier action of the vinylidene chloride resin, it exhibits excellent corrosion resistance. become.

The content of the powdery filler is 10 to 250 parts by weight based on 100 parts by weight of the vinylidene chloride resin emulsion solid content. If the content of the powdery filler is less than 10 parts by weight, the effect of improving the corrosion resistance is not sufficient, and if it is more than 250 parts by weight, the physical properties such as the coating strength are lowered due to the relative decrease of the resin component, On the contrary, the corrosion resistance also decreases. The first powder and the second powder may be of different types or may be of the same type.

As the powdery filler, extrinsic pigments such as talc, calcium carbonate, barium sulfate, clay, and diatomaceous earth are mainly used, but other inorganic pigments such as titanium oxide, iron oxide, mica, and lead chromate, and azo-based pigments. , A phthalocyanine-based organic pigment, carbon black and the like can be used in combination.

The aqueous coating composition of the present invention preferably further contains a rust preventive pigment. By using a rust preventive pigment together with the vinylidene chloride resin emulsion, the rust preventive performance can be further improved. This rust preventive pigment is 5 parts by weight per 100 parts by weight in terms of solid content of vinylidene chloride resin emulsion.
~ 50 parts by weight is recommended. If the amount is less than 5 parts by weight, the effect of inclusion cannot be seen. Even if the amount is more than 50 parts by weight, the effect is saturated, and the physical properties such as coating strength and corrosion resistance decrease due to the relative decrease of the resin component. Occurs. As this rust preventive pigment, known rust preventive pigments such as zinc chromate, red lead, calcium leadate, alizanine and zinc phosphate can be used. Of these, non-toxic zinc phosphate and the like are preferably used.

The aqueous coating composition of the present invention may contain various coating additives such as an anti-sagging agent, a defoaming agent, a film-forming aid, and a coupling agent in addition to the above-mentioned composition.

The water-based coating composition of the present invention is coated on the surface of the article to be coated by a known coating method such as air spraying, and is formed by holding at room temperature or under heating for a predetermined time to form a coating film having excellent corrosion resistance. It

[Operation and Effect of the Invention] The aqueous coating composition of the present invention comprises 20 to 90% by weight of the first powder having a particle size in the range of 0.2 to 5 μm and an average particle size of 1 to 5 μm.
And the particle size is in the range of 5 to 50 μm and the average particle size is 8 to 15 μm.
m of the second powder of 10 to 80% by weight. By using a powdery filler having a particle size distribution in this range, the powdery filler is packed close to the closest packing in the coating film, preventing water and ions from reaching the material, and Since it assists the barrier action, it comes to exhibit excellent corrosion resistance.

Therefore, according to the water-based coating composition of the present invention, a coating film having excellent corrosion resistance comparable to that of conventional cationic electrodeposition coating films can be obtained, and thus cast parts, forged parts, etc., which have been difficult to perform by conventional electrodeposition coating, etc. Can be painted on to improve corrosion resistance.

[Examples] Hereinafter, specific examples will be described. All parts below mean parts by weight.

(Synthesis of vinylidene chloride resin emulsion) 95 parts deionized water, 14 parts vinylidene chloride, 4 vinyl chloride
Parts, 0.1 part of sodium alkyldiphenyl ether disulfonate and 0.2 part of sodium persulfate are put into a pressure resistant reaction vessel and kept at 50 ° C. for 4 hours while stirring. Next, sodium alkyl diphenyl ether disulfonate 0.1
56 parts of vinylidene chloride and 16 parts of vinyl chloride are continuously added over 10 hours with stirring while maintaining the temperature at 50 ° C. Thereafter, 8 parts of ethyl acrylate, 2 parts of acrylic acid and 0.04 part of sodium sulfite are further added, and the mixture is maintained at 50 ° C. for 10 hours while stirring. As a result, a vinylidene chloride resin-based emulsion having a solid content of 60% by weight was obtained.

(Example 1) As shown in Table 1, 100 parts by weight of the vinylidene chloride resin emulsion synthesized above was converted into 1 part by weight of carbon black, 1 part of carbon black, 0.5 to 50 μm in particle size, and 8 to 8 in average particle size. Add 12 parts of talc A of 12 μm, 25 parts of particle size 0.2 to 10 μm and average particle size of 3 to 5 μm talc B, 10 parts of zinc phosphate as an anticorrosive pigment, 1 part of paint additive and 200 parts of pure water, and stir-disperse. The aqueous coating composition of Example 1 was prepared. When talc A and talc B are mixed in the above ratio, the particle size is in the range of 0.2 to 5 μm and the average particle size is 1 to 1.
The composition is such that the first powder of 5 μm is 40% by weight, the particle size is in the range of 5 to 50 μm, and the second powder of 8 to 15 μm is 60% by weight.

This water-based coating composition was applied to the surface of the steel sheet by air spraying so that the dry film thickness was 40 μm, and the temperature was kept at room temperature (20 ° C, humidity 50
%) For 24 hours to form a test plate. Then, the adhesion of the coating film was evaluated by a cross-cut test. In addition, a cross cut is carved on the coating film, and a salt spray test of spraying 5% salt solution at 35 ° C and a water resistance test of dipping in warm water at 40 ° C are performed. The shorter one of the test time until the occurrence of blister and the test time until the occurrence of blisters on the coated surface was measured. The results are shown in Table 1. The test was terminated after 240 hours.

(Example 2) A coating material was prepared in the same manner as in Example 1 except that talc A was 10 parts and talc B was 40 parts, and the same coating and test were conducted. The results are shown in Table 1. In this case, as the whole talc, 64% by weight of the first powder having a particle size of 0.2 to 5 μm and an average particle size of 1 to 5 μm, and having a particle size of 5 to 50 μm and an average particle size of 8 36% by weight of second powder of ~ 15μm
This is the configuration.

(Comparative Example 1) A coating material was prepared in the same manner as in Example 1 except that 50 parts of talc A was used and talc B was not used, and coating and testing were performed in the same manner, and the results are shown in Table 1.

(Comparative Example 2) A coating material was prepared in the same manner as in Example 1 except that 50 parts of talc B was used and talc A was not used, and coating and testing were conducted in the same manner, and the results are shown in Table 1.

(Evaluation) From the test results of Table 1, the test plate formed in the comparative example is the result of 72 to 120 hours in the salt spray test, but the test plate formed in the example is 192-240 in the salt spray test. It has excellent corrosion resistance over time. Also in water resistance, blister was generated in 120 hours in the comparative example, but no abnormality was observed in the test plate of the example even after 240 hours. It is clear that these results are based on the particle size distribution of talc used in the examples.

Claims (1)

[Claims] 1. Vinylidene chloride 40 to 80% by weight and vinyl chloride
It is formed by emulsion polymerization of a monomer component consisting of 10 to 60% by weight, 5 to 49.9% by weight of vinyl monomer, and 0.1 to 5% by weight of vinyl unsaturated carboxylic acid.
The vinylidene chloride resin-based emulsion containing 100% by weight is 100 parts by weight in terms of solid content, and the particle size is in the range of 0.2 to 5 μm and the average particle size is 1 to 5 μm.
20 to 90 parts by weight of the first powder and 20 to 250 parts by weight of a powdery filler composed of 10 to 80% by weight of the second powder having a particle size of 5 to 50 μm and an average particle size of 8 to 15 μm. A water-based coating composition comprising: