JPH04213370A - Coating composition and coated steel sheet - Google Patents

Abstract

PURPOSE:To improve water resistance and chem. resistance by incorporating specified aq. film-forming resin, crosslinking agent and finely powdered silica. CONSTITUTION:A mixture of an aq. film-forming resin having a functional group reactive with a crosslinking agent (e.g. an aq. acrylic resin emulsion) with a crosslinking agent (e.g. a melamine resin) in a ratio of the solid content of 50:50-95:5 is blended with 0.1-10wt.% finely powdered silica with a DBA value of 100 or smaller as a matting agent.

Description

[Detailed description of the invention]

BACKGROUND OF THE INVENTION AND PROBLEMS From the standpoint of resource conservation and environmental protection, reducing the amount of organic solvents used that volatilize into the atmosphere is a current challenge in the paint industry. For this reason, water-based paints have come to be used in place of solvent-based paints in many fields. In that case, depending on the application, a matte finish may be required. For example, a water-based baking paint applied to steel furniture, etc., consists of a water-based film-forming resin that has a functional group that can react with a crosslinking agent, and a water-based film-forming resin that has a functional group that can react with a crosslinking agent. Finely powdered silica is added to the system containing the crosslinking agent in an amount to provide the desired level of matteness.

However, such baked water-based paints containing finely powdered silica have inferior water resistance and chemical resistance of the coating film compared to full-gloss water-based paints that do not contain silica. In addition, water-based paints are generally inferior to solvent-based paints in terms of workability such as sagging and sagging, and when conventional silica is added to create a matte finish, compared to full-gloss paints that do not contain silica, Wrinkling level (limit of dry coating thickness that does not cause wrinkling)
A decrease in Therefore, there is a drawback that it is not possible to add the necessary amount of silica to obtain the desired matting effect, or the necessary film thickness cannot be obtained. Therefore, it is an object of the present invention to overcome such drawbacks.

[0003] Since the finely powdered silica conventionally used in matte paints is hydrophilic, the paint film becomes hydrophilic, resulting in lower water resistance and chemical resistance than full gloss paints that do not contain it. Conceivable. Therefore, by adding hydrophobic fine powder silica instead of hydrophilic fine powder silica, it was possible to obtain a matte paint comparable to full gloss paint in terms of water and chemical resistance. In addition, this hydrophobic fine powder silica is estimated to have an antifoaming function against the micro bubbles that exist in the paint film before baking, and by adding it, the underarm level will be lower than that of the full gloss paint before it is added. I was also able to improve it.

[0004] The above-mentioned problem is solved by using (A) an aqueous film-forming resin having a functional group capable of reacting with a cross-linking agent, (B) a cross-linking agent for the film-forming resin, and (C) finely powdered silica as a matting agent in an aqueous medium. The problem is solved by the present invention, which is a water-based baking paint composition comprising: , wherein the fine powder silica (C) is a hydrophobic silica having a DBA value of 100 or less.

Preferred Embodiment The silica conventionally used for the above purpose is a hydrophilic silica having a large number of silanol groups on its surface. The silica used in the present invention is made hydrophobic by chemically treating such hydrophilic silica to block the silanol groups.

The degree of hydrophobicity of silica is determined by the DBA value (mmo
l/Kg). DBA value is mmol of dibutylamine required to neutralize 1 kg of silica.
The silanol group on the silica surface easily reacts with dibutylamine, so it can be measured by titration. The DBA value of the silica used so far is generally 200 or more, but the DBA value of the silica used in the present invention is 100 or less, preferably 50 or less. Silicas with such low DBA values can be prepared by reacting silicas with high DBA values with dimethyldichlorosilane at high temperatures, for example in an atmosphere of inert gas and water vapor, to block some of the silanol groups on the silica surface. can be obtained by Alternatively, it can be obtained by reacting silica and polysiloxane under heat and pressure in the presence of amines and water, and similarly blocking a portion of the silanol groups on the silica surface. When added to matte paints, silica treated in this way does not make the paint film hydrophilic and therefore does not reduce its water and chemical resistance. It is also presumed to have an antifoaming function against the microbubbles that exist in the paint film before baking, and by adding this, the underfill level can be improved compared to the full gloss paint before addition.

The coating composition of the present invention has a DBA value of 100.
The composition may be the same as that of conventional baking water-based paints, except that it contains the following silica. Such a coating composition (
It contains A) an aqueous film-forming resin having a functional group capable of reacting with a crosslinking agent, and (B) a crosslinking agent.

Aqueous film-forming resins having functional groups capable of reacting with crosslinking agents are well known in the coatings field;
Water-based acrylic resin emulsion, water-based alkyd resin,
including water-soluble acrylic resins, and mixtures thereof.

[0009] The aqueous acrylic resin emulsion contains acrylic monomers containing a hydroxyl group or a carboxyl group as a functional group capable of reacting with a crosslinking agent, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, acrylic acid and Obtained by emulsion polymerization using a conventional method of a monomer mixture containing methacrylic acid, etc., and an alkyl (meth)acrylate such as methyl (meth)acrylate, n-butyl (meth)acrylate, or 2-ethylhexyl (meth)acrylate. It will be done.

Water-soluble alkyd resins include ethylene glycol, diethylene glycol, neopentyl glycol,
It is obtained by condensing a polyol component such as glycerin or trimethylolpropane, a polyhydric carboxylic acid component such as phthalic acid, isophthalic acid, or trimethic acid, and an oil such as dehydrated castor oil or its fatty acid.

The water-soluble acrylic resin is composed of a carboxyl group-containing monomer such as alrylic acid or methacrylic acid, a hydroxy group-containing monomer such as 2-hydroxy (meth)acrylate, and an alkyl group-containing monomer such as methyl (meth)acrylate. It is obtained by solution polymerizing a monomer mixture containing (meth)acrylate by a conventional method.

The water-soluble alkyd resin and water-soluble acrylic resin are used in the form of a solution in an aqueous medium containing a neutralizing amount of amines.

A typical example of a crosslinking agent is melamine resin. Melamine resins include condensates of formaldehyde and aminotriazine compounds such as melamine, acetoguanamine, and benzoguanamine, as well as those obtained by etherifying at least a portion of the methylol groups of the condensates with lower alkanols such as methanol and butanol.

[0014] The ratio of the aqueous film-forming resin to the crosslinking agent is 50:50 to 95:5, preferably 60:40 to 90 in terms of solid content.
: The range is 10.

[0015] Silica having a DBA value of 100 or less can be used in an amount of 0.1 to 0.1 to 0.1 by weight of the coating composition, depending on the degree of the desired matting effect.
It is added in an amount of 10%, preferably 0.5-5%. 0.1%
If it is less than 10%, there will be no matting effect, and if it exceeds 10%, the coating film will become brittle and the film performance will deteriorate.

The coating composition contains coloring pigments such as titanium dioxide, carbon black, and quinacridone, and extender pigments such as clay, mica, and talc, in PVC (pigment volume concentration).
It can contain less than 50%. It goes without saying that it may also contain small amounts, for example 0.1 to 1.0%, of conventional surface conditioners, antifoaming agents, and the like.

The paint of the present invention is used for coil coating,
It is useful as a matte coating for various pre-coating applications and other general industrial use, and is especially used for manufacturing matte coated steel plates by baking coating on steel plates such as cold-rolled steel sheets, galvanized steel sheets, and aluminum-galvanized steel sheets using conventional methods. can do.

The invention will now be illustrated by examples and comparative examples. In these terms, "parts" and "%" are based on weight unless otherwise specified.

Reference Example 1 a) Emulsion resin formulation example #1 Deionized water
120 copies
Levenol WZ (manufactured by Kao Atlas Co., Ltd.)
9 parts #2 Ammonium persulfate
0.9 parts deionized water

20 parts #3 Styrene

30 parts n-butyl acrylate
33.5 copies
2-hydroxyethyl acrylate
13 parts methacrylic acid
3.5 parts N,n-butoxymethylacrylamide 6 parts #4
Methyl methacrylate
Part 19
methacrylic acid
Part 1 b) Example of emulsion resin production After heating the emulsifier aqueous solution of #1 to 80°C in a Kolben equipped with a stirrer and a condenser, 80% by weight of #2 was added, and after stirring at 80°C for 10 minutes, #1 was heated to 80°C. The mixed monomer solution of step 3 was added dropwise and stirred for 150 minutes. 30 minutes after completion of dripping
After stirring at 80° C. for minutes, 20% by weight of #2 is added. 1
After stirring for 0 minutes, mixed monomer solution #4 is added dropwise and stirred for 30 minutes. After the dropwise addition was completed, stirring was continued for 120 minutes at 80°C to obtain an emulsion with an average particle size of 0.17μ.

Examples 1 and 2 and Comparative Examples 1 to 3 Reference Example 1
A paint was made using the acrylic resin emulsion synthesized in the following formulation. emulsion
74 copies
Water-soluble acrylic resin (50% non-volatile content)
4 parts (acid value 60, number average molecular weight = 8,
000) Cymail 303 (non-volatile content 10
0%) 4 parts (Water-soluble melamine resin manufactured by Mitsui Toatsu Chemical Co., Ltd.) Taipei
R-930
20 parts (Titanium dioxide pigment manufactured by Ishihara Sangyo Co., Ltd.) Finely powdered silica was mixed with the above full-gloss paint according to the formulation shown in Table 1 to prepare paints for Examples and Comparative Examples. Coat SP-DIF PO1 Primer, an epoxy-based undercoat paint, with a bar coater to a dry film thickness of 5 μm, bake at 200°C for 60 seconds, and then coat each of the above paints with a bar coater to a dry film thickness of 12 μm.
It was applied and baked at 200°C for 60 seconds.

[Table 1] The coating film performance is shown in Table 2.

[Table 2]

Reference Example 2 Raw materials having the following composition were charged into a container equipped with a stirrer, a temperature control device, and a decanter, and heated while stirring. isophthalic acid
28 parts Trimellitic anhydride 10 parts Hartol FA-1 (Note 1)
22 parts trimethylolpropane
Part 8 Neopentyl glycol 20
Part RJ-100 (Note 2)
Part 9 xylene

Part 2 Dibutyltin oxide
0.2 parts (Note 1) Tall oil fatty acid (Note 2) Styrene/allyl alcohol copolymer, molecular weight approximately 1,600 Water generated as the reaction progresses is removed by azeotroping with xylene, acid value 40, hydroxyl value Heating was continued until the temperature reached 80°C to complete the reaction. The obtained resin was mixed with isopropanol/butyl cellosolve/butyl diglycol = 1/1/ so that the nonvolatile content was 70%.
1 was diluted with a mixed solvent to obtain an alkyd resin varnish (A). This varnish had a Gardner viscosity of X to Y, and a solubility parameter measured by the duct method of 9.60. Theoretically, this alkyd resin varnish (A) is
The varnish was neutralized to 0.00%, and the nonvolatile content was adjusted to 40% with deionized water to obtain a water-soluble varnish (B).

Examples 3 and 4 and Comparative Examples 4 to 6 Reference Example 2
A paint was made using the water-soluble varnish (B) prepared in the following formulation. Water-soluble varnish (B)
128 copies
Sumimaru M-50W (100% nonvolatile)
17 parts (methanol-modified melamine resin manufactured by Sumitomo Chemical Co., Ltd.) Typeke R-9
30 1
00 parts (Titanium dioxide pigment manufactured by Ishihara Sangyo Co., Ltd.)
Finely powdered silica was mixed with the above full-gloss paint in the formulation shown in Table 3 to prepare paints for Examples and Comparative Examples. These paints were diluted with deionized water, adjusted to a viscosity of NK#2 cup for 60 seconds, sprayed onto a 0.8 mm zinc phosphate treated steel plate to a dry film thickness of 25 μm, and allowed to set for 10 minutes.
It was baked at 140°C for 20 minutes. Table 4 shows the coating film performance.

[Table 3]

[Table 4]

Reference Example 3 76 parts of ethylene glycol monobutyl ether was charged into a 1-liter reaction vessel equipped with a stirrer, a temperature controller, and a cooling tube, and 159 parts of styrene, 66 parts of lauryl methacrylate, and 49 parts of 2-hydroxyethyl methacrylate were added.
1 part, 27 parts of methacrylic acid, and 61 parts of a monomer solution consisting of 3 parts of azobisbutyronitrile, and the temperature was lowered to 1 part with stirring.
The temperature was set to 20°C. Further, 245 parts of the above monomer solution was added dropwise over 3 hours, and stirring was continued for 1 hour. Furthermore, 28 parts of dimethylethanolamine and 200 parts of deionized water were added to obtain an acrylic resin varnish with a volatile content of 50% and a resin number average molecular weight of 6,000. This resin had an OH value of 70, an acid value of 58, and an SP value of 10.5.

Examples 5 and 6 and Comparative Examples 7 to 9 Reference Example 3
A paint was made using the acrylic resin varnish obtained in the following formulation. acrylic resin varnish
102 copies
Sumimaru M-50W (100% non-volatile content)
17 parts (methanol-modified melamine resin manufactured by Sumitomo Chemical Co., Ltd.) Typeke R-9
30 1
00 parts (Titanium dioxide pigment manufactured by Ishihara Sangyo Co., Ltd.)
Finely powdered silica was mixed with the above full-gloss paint in the formulation shown in Table 5 to prepare paints for Examples and Comparative Examples. These paints were diluted with deionized water, adjusted to a viscosity of NK#2 cup for 60 seconds, and applied to a 0.8 mm zinc phosphate treated steel plate with a dry film thickness of 2.
After spray painting 5μ and setting for 10 minutes,
Baked at 40°C for 20 minutes. The coating film performance is shown in Table 6.

[Table 5]

[Table 6]

Claims (4)

[Claims] 1. In an aqueous medium, (A) an aqueous film-forming resin having a functional group capable of reacting with a crosslinking agent, (B) a crosslinking agent for the film-forming resin, and (C) containing finely powdered silica as a matting agent. 1. A water-based baking paint composition, wherein the fine powder silica (C) is hydrophobic silica having a DBA value of 100 or less. 2. Claim 1, wherein the aqueous film-forming resin (A) is an aqueous acrylic resin emulsion, a water-soluble alkyd resin, a water-soluble acrylic resin, or a mixture thereof, and the crosslinking agent (B) is a melamine resin. Baking water-based paint composition. 3. The ratio of the aqueous film-forming resin (A) to the crosslinking is from 50:50 to 95:5 in solid weight ratio,
3. The aqueous baking paint composition according to claim 1, wherein the fine powder silica (C) is contained in the paint composition in an amount of 0.1 to 10% by weight. 4. A coated steel sheet obtained by baking the aqueous baking paint composition according to any one of claims 1 to 3.