JPH0636904B2 - Method for forming white coating film with excellent weather resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a method for forming a white coating film using a titanium dioxide pigment, which is excellent in weather resistance and less in gloss reduction.

<Prior Art> Conventionally, fluororesin-based paints have been known as weather-resistant paints, but in recent years, organic solvent-soluble fluorocopolymers have been developed and are being used in automobiles, bridges, tanks, building materials, electrical products, etc. In a wide range of fields, paints containing the fluorine-containing copolymer as a binder have been widely applied.

There are various types of paints using a fluorine-containing copolymer as a binder, such as metallic paints, enamel paints and clear paints.
In most of these paints, the long-term durability and long-term weather resistance, which are the original characteristics of fluororesins, are utilized, and the coating film life is greatly extended compared to conventional paints.

<Problems to be Solved by the Invention> However, a typical white paint of an enamel paint, that is, a paint containing a fluorine-containing copolymer using a titanium dioxide pigment as a binder (hereinafter referred to as a white fluorine-containing copolymer paint) is
There is a problem that the gloss of the coating film is reduced outdoors.

Normally, in acrylic resin-based paints and polyester resin-based paints, the surface of the coating film caused chalking, resulting in a decrease in gloss, but in white fluorine-containing copolymer paints, the gloss did not occur even though chalking did not occur. There was a phenomenon that it decreased. Then, when the surface of the coating film was observed with an electron microscope to elucidate the cause of the decrease in gloss, it was found that many fine holes were formed on the surface of the coating film, which caused the decrease in gloss.

Such a phenomenon in which fine holes are generated on the surface of the coating film is a phenomenon that has not been observed in ordinary acrylic resin-based paints, polyester resin-based paints, or colored fluorine-containing copolymer paints other than white. The reason why many fine holes are generated on the surface of the coating film is not clear, but it is considered to be probably due to the following reasons. That is, the fluorine-containing copolymer has a large light transmittance as compared with other general synthetic resins for coating materials, and the amount of light energy that reaches the surface of the titanium dioxide pigment increases even though it passes through the coating film in the short wavelength region.

On the other hand, in the titanium dioxide pigment, radicals are generated on the surface of the pigment due to the absorbed light energy, which decomposes the fluorocopolymer, and as a result, holes are formed around the pigment distributed near the surface layer of the coating film. It is considered that the pores become larger and the pigment comes off from the surface of the coating film as it progresses.

Therefore, the present inventors generated many fine holes on the coating surface,
As a result, it was considered to form a clear coating film containing no pigment on the coating film formed by the white fluorine-containing copolymer coating as a means for preventing the decrease in gloss of the coating film. When a film is applied, the formation of holes can be prevented, but the color of the resin itself, which is the binder used for the clear coating, interferes, and the original white color of the white coating without the clear coating is slightly hindered. , There was a problem that the commercial value was reduced.

As a result of diligent studies in view of such a current situation, the present inventors,
The present invention has found a method for forming a coating film which makes good use of the long-term durability and weather resistance of the fluorocopolymer and has little deterioration in gloss, and which does not impair the original color of the white coating film. Is.

<Means for Solving the Problems> That is, according to the present invention, the substrate surface contains (1) 20 to 70% by weight of a titanium dioxide pigment and 20 to 80% by weight of a binder in a coating solid content, and The courageous solvent-soluble fluorocopolymer in the binder is 65-100.
Apply white paint containing 5% by weight, and then (2) 5-20% by weight of titanium dioxide pigment in the solid content of the paint.
And a white coating material containing 70 to 95% by weight of a binder and 65 to 100% by weight of a courageous solvent-soluble fluorocopolymer in the binder, and a white coating film having excellent weather resistance is obtained. The present invention relates to a forming method.

The method of the present invention uses a titanium dioxide pigment as an overcoating white paint in an amount that does not affect gloss reduction even if some holes are formed on the surface of the coating film, and does not impair the original white appearance of the lower white coating film. Use a blended amount of about,
The above-mentioned problems are solved by applying it over a white coating film.

Hereinafter, the present invention will be described in detail.

The white paint forming the lower coating film used in the present invention is an organic solvent-soluble fluorine-containing copolymer, a titanium dioxide pigment and an organic solvent as a main component, further modified resin, curing agent, extender pigment, UV It is composed of a mixture of various additives such as an absorber, a dispersant and a flow control agent, and a minute amount of coloring dyes and pigments can be blended if necessary.

The fluorine-containing copolymer serving as the binder is not particularly limited as long as it is soluble in an organic solvent usually used for coating materials, and conventionally known fluorine-containing copolymers can be used, and they are hardeners. A lacquer type that cures without use, a self-crosslinking type, a room temperature curing type that is used in combination with a curing agent, a bake curing type, and the like can be used without particular limitation.

Specifically, for example, JP-A-57-34107 and JP-A-5-34107
9-78270, JP-A-59-102961,
JP-A-59-120661 and JP-A-59-19747
1, JP-A-60-28458, JP-A-61-127.
60, JP-A-61-43667, JP-A-61-57.
609, JP-A-61-115967, and JP-A-61-161.
No. 200145, JP-A-61-247727, JP-A-61-258852, JP-A-62-84137, and the like, fluorine-containing copolymers, modified products of the copolymers, or copolymers and acrylics. Typical fluorine-containing copolymers include, but are not limited to, mixtures with other synthetic resins such as resins.

A specific example of the copolymer is fluoroolefin,
A vinyl ether having a functional group, a vinyl ether not having a functional group, and / or a vinyl carboxylate ester and another comonomer as constituent components are 40 to 60 mol% and 0 to 0, respectively.
It is a copolymer containing 25 mol%, 5-60 mol% and / or 5-60 mol%, 0-30 mol%.
As commercially available products, Lumiflon LF100, L manufactured by Asahi Glass Co., Ltd.
Representative examples include F200, LF210, LF300, LF400; K-700 and K-701 manufactured by Dainippon Ink and Chemicals, Inc.

The titanium dioxide pigment that is usually used for paints can be used as it is, and is also called titanium white.

The organic solvent may be aromatic hydrocarbons such as xylene and toluene, alcohols such as n-butanol, esters such as butyl acetate, ketones such as methyl ibutyl ketone, ethyl cellosolve, which are commonly used for dyes. Typical examples are glycol ethers such as those mentioned above, and various commercially available Nancy can also be used.

The curing agent is not necessarily used as long as the fluorine-containing copolymer can be cured at room temperature or by baking without using a curing agent, but usually the fluorine-containing copolymer has a functional group, It is desirable to use a curing agent that reacts with the functional group.

As the curing agent, in the case of a room temperature curing type, a polyvalent isocyanate having two or more isocyanate groups in one molecule is suitable.

Examples of the polyvalent isocyanates include aliphatic or alicyclic diisocyanates such as hexamethylene diisocyanate, tetramethylene diisocyanate, isophorone diisocyanate, hydrogenated diphenylene diisocyanate, hydrogenated xylene diisocyanate, etc. or burettes, dimers, trimers or Typical examples are reaction products of an excess of these isocyanate compounds with a low molecular weight polyol such as ethylene glycol, glycerin, trimethylolpropane, and pentaerythritol. Needless to say, in the case of the room temperature curing type, the curing agent is a two-pack type coating composition which is mixed with the fluorine-containing copolymer solution as the main component immediately before coating.

In the case of the bake-curable type, the polyisocyanate described above is masked with a masking agent such as phenols, alcohols, oximes, lactams, amines or amides; melamine, urea, bezoguanamine, acetoguanamine, etc. A typical example thereof is a condensation product of the amino compound and the aldehyde compound or a curing agent such as an aminoplast resin obtained by etherifying the condensation product with an alcohol such as butanol.

The white paint forming the lower coating film used in the present invention has the above-described components as the main components, but the amount of each component is the gradient of titanium dioxide pigment in consideration of the coloring power or hiding power of the coating film obtained. A solid content of 20 to 70% by weight is suitable.

In the conventional white paint, the titanium dioxide pigment is generally contained in an amount of 20 to 50% by weight in the solid content of the dye. However, in the present invention, the overcoating is further performed. It is possible to blend in.

The fluorine-containing copolymer or the binder containing it as a main component is 20 to 80% by weight in the solid content of the coating material. The amount of the fluorinated copolymer in the binder is 65 to 100% by weight. It is suitable to add other extender pigments and additives in an amount of about 0 to 20% by weight and 0.5 to 4% by weight, respectively, in the solid content of the coating material.

The amount of the organic solvent varies depending on the coating means and the like, but generally 30 to 60% by weight in the coating is suitable.

Next, as the white paint for forming the upper coating film used in the present invention, the same paint as that for forming the lower coating film can be used as a constituent component of the coating material, and the mixing ratio thereof is changed.

That is, 5 to 20% by weight of titanium dioxide pigment in the coating solid content and 70 to 95% by weight of binder in the coating solid content are blended. The amount of the fluorinated copolymer in the binder is 65 to 100% by weight.

If the amount of the titanium dioxide pigment added is more than the above range, the amount of titanium dioxide pigment distributed in the surface layer of the overcoat film will increase accordingly, and as a result, the decrease in gloss will be noticeable due to the holes generated on the surface of the coating film. On the contrary, when the amount is less than the above range, the color of the fluorine-containing copolymer itself as the binder becomes conspicuous in the overcoat film, and as a result, the original white color of the lower white film becomes hindered, which is preferable. Absent. In addition,
The white coating film in the present invention refers to a coating film having a white color due to a titanium dioxide pigment, and includes a slightly turbid white coating film containing a trace amount of a dye pigment.

Next, the coating method of the present invention will be described.

As the substrate applied in the present invention, of course, various metal materials such as steel plate, stainless plate, aluminum plate,
Typical examples include mortar, concrete, inorganic materials such as glass, plastics, wood and the like, and these substrates may be those which have been subjected to surface treatment, primer or the like as necessary.

As a painting method, air spray, airless spray,
Electrostatic spray, shower coat, dipping paint, brush coating,
Conventional methods that are generally used, such as roll coating, can be used as they are.

In the present invention, first, the white paint for forming a lower layer coating film is applied on the surface of a substrate. Although the film thickness can be arbitrarily set according to the type of the object to be coated, for example, in the case of a metal material, it is suitable to apply the coating so that the dry film thickness is 15 to 50 μm.

Next, the white paint forming the upper coating film is overcoated. It is suitable to apply the coating so that the film thickness is 5 to 30 μm. When the film thickness is thicker than the above range, the original white color of the lower white coating film is likely to be impaired, and conversely when the film thickness is thinner than the above range, the effect of applying the top coating film tends to decrease.

In the process of applying the white paint that forms the lower layer coating film, and then the white paint that forms the upper layer coating film, in the latter coating process, the lower layer coating film formed in the former coating process is cured at room temperature or by baking and drying. When it becomes a coating film,
Alternatively, a white pigment that forms the upper coating film can be overcoated even when the lower coating film is uncured.

<Effect of the Invention> With the method for forming a white coating film of the present invention, a unique phenomenon that occurs due to the use of a fluorocopolymer as a binder, that is, a decrease in gloss due to the generation of fine holes on the coating surface, It is possible to prevent the white color of the original white coating film without hindering it, and therefore, it is possible to solve the problems of the white paint which is used very often, and the technical value is great.

The present invention will be described below with reference to examples. In the examples, "parts" and "%" are shown by weight.

Example 1 52 parts of chlorotrifluoroethylene, 4-hydroxy-
A monomer consisting of 21 parts of n-butyl vinyl ether, 17 parts of cyclohexyl vinyl ether and 10 parts of ethyl vinyl ether was used as a fluorine-containing copolymer (number average molecular weight 6800, hydroxyl value 100) of 60 according to the method described in JP-A-57-4107. % Xylol solution was obtained. To 100 parts of this solution, 50 parts of titanium dioxide pigment was added and dispersed, and 2 parts of additives such as a surface modifier and a polymerization catalyst and a buret solution of hexamethylene diisocyanate ["Sumijour N-75" (manufactured by Sumitomo Bayer Urethane Co., Ltd.). Product name),
Solid content of 75%] 23 parts was added to prepare a two-component curing type fluororesin white dye for the lower layer.

On an alumite-treated aluminum plate with a plate thickness of 0.8 mm,
Butyl acetate / xylol / cellosolve acetate = 40
Viscosity of 20 seconds with a diluted solvent of / 40/20 (FC # 4/20
The fluororesin-based white coating material (amount of titanium dioxide pigment in the coating solid content of 39%) adjusted to (° C.) was air-spray coated so that the dry film thickness was 40 μ, and dried at 80 ° C. for 20 minutes.

Next, in the lower layer two-component curable fluororesin white paint, the upper layer two-component curable fluororesin white paint having the same composition except that 50 parts of titanium dioxide pigment is replaced by 9 parts (titanium dioxide pigment in the solid content of the paint) 10% amount) viscosity 2
After adjusting to 0 seconds, it was applied by air spray so as to have a dry film thickness of 20 μm and dried at 80 ° C. for 20 minutes to form a white coating film.

Comparative Example 1 The same as Example 1 except that an upper layer two-component curable fluororesin type clear coating material obtained by removing the titanium dioxide pigment from the coating material was used in place of the upper layer two-component curing type fluororesin type white coating material of Comparative Example 1. Then, a white coating film consisting of two layers was formed.

Example 2 A monomer comprising 55 parts of chlorotrifluoroethylene, 18 parts of cyclohexyl vinyl ether, 17 parts of ethyl vinyl ether and 10 parts of hydroxybutyl vinyl ether was reacted in the same manner as in Example 1 to obtain a fluorinated copolymer. Furthermore, 0.9 part of succinic anhydride was added to the copolymer,
After reacting at 150 ° C. for 1 hour, the illustrated varnish containing fluorine (solid content 50%, hydroxyl value 47, acid value 5, number average molecular weight 2000)
0) was obtained. To 85 parts of this varnish, 90 parts of titanium dioxide pigment were added and dispersed, and 15 parts of a butyl etherified melamine resin solution [“Melan 21A” (trade name, manufactured by Hitachi Chemical Co., Ltd., solid content 60%)] was added to the baking layer for the lower layer. A fluorinated resin-based white paint was prepared. A white paint (a titanium dioxide pigment amount of 64% in the solid content of the paint) whose viscosity was adjusted to 18 seconds with the same diluting solvent as in Example 1 was air-spray coated to a dry film thickness of 25 μm, and the temperature was set to 150 ° C. for 3 days. Baked for minutes.

Next, in the above lower layer baking type fluororesin white paint, the upper layer baking type fluororesin white paint having the same composition except that 90 parts of titanium dioxide pigment is replaced with 3 parts (titanium dioxide pigment amount in the paint solid content is 6%) Was adjusted to have a viscosity of 18 seconds, then applied repeatedly with an air spray so as to have a dry film thickness of 10 μm, and baked at 150 ° C. for 30 minutes to form a white coating film.

Comparative Example 2 Baking type fluororesin white paint for lower layer having the same composition except that 90 parts of titanium dioxide pigment was replaced with 28 parts in the baking type fluororesin type white paint for lower layer of Example 2 (dioxide in solid paint) After adjusting the viscosity of the titanium pigment (35%) to 18 seconds, air spray coating was performed to a dry film thickness of 25 μm, and baking was performed at 150 ° C. for 30 minutes.

Next, the same coating material was applied again so that the dry film thickness was 10 μm, and baked at 150 ° C. for 30 minutes to form a white coating film.

Example 3 A monomer comprising 30 parts of chlorotrifluoroethylene, 25 parts of tetrafluoroethylene, 10 parts of 4-hydroxy-n-butyl vinyl ether, 18 parts of cyclohexyl vinyl ether, and 17 parts of ethyl vinyl ether was used.
4 of the fluorine-containing copolymer (number average molecular weight 45,000, hydroxyl value 52) according to the method described in JP-A-7-34107.
A 0% cyclohexanone solution was obtained. To 100 parts of this solution, 30 parts of titanium dioxide pigment was added and dispersed, and further 7 parts of 80% methyl ethyl ketone solution of blocked polyisocyanate (NCO equivalent 359) in which hexamethylene diisocyanate trimer was blocked with methyl ethyl ketone oxime, γ-aminopropyltrimer 1 part of ethoxysilane, 1 part of ultraviolet absorber, and 1 part of surface conditioner were added to prepare a baking type fluororesin-based white coating material for the lower layer (amount of titanium dioxide pigment in the coating solid content of 38%). Degreased stainless steel plate with 0.8 mm thickness (SUS # 304 hairline finish)
Then, the above fluororesin-based white paint whose viscosity was adjusted to 120 seconds with Solvent # 150 / isophorone = 80/20 diluted solvent was coated with a reverse roll coater to a dry film thickness of 15 μ, and the plate temperature was heated for 60 seconds. It was baked at 230 ° C.

Next, in the above-mentioned lower layer baking type fluororesin white paint, the upper layer baking type fluororesin white paint having the same composition except that 30 parts of titanium dioxide pigment is replaced by 6 parts (the amount of titanium dioxide pigment in the paint solids is 11%. Was adjusted to a viscosity of 120 seconds, and the coating was repeatedly applied with a reverse roll coater to a dry film thickness of 10 μm, and baked for 60 seconds to a plate temperature of 240 ° C. to form a white coating film.

Comparative Example 3 Baking-type fluororesin-based white coating material for lower layer whose viscosity was adjusted to 120 seconds in Example 3 (titanium dioxide pigment content 3 in coating material solid content 3
A white coating film was formed in the same manner as in Example 3 except that 8%) was applied to give a dry film thickness of 25 μm. (However, the baking type fluororesin-based white paint for the upper layer was not applied over again.) Example 4 30 parts of chlorotrifluoroethylene, 25 parts of tetrafluoroethylene, 10 parts of 4-hydroxy-n-butyl vinyl ether, 18 parts of cyclohexyl vinyl ether. Part, and a monomer consisting of 17 parts of ethyl vinyl ether are disclosed in
4 of the fluorine-containing copolymer (number average molecular weight 45,000, hydroxyl value 52) according to the method described in JP-A-7-34107.
A 0% cyclohexanone solution was obtained.

On the other hand, 44 parts of ethyl acrylate, 43 parts of isobutyl methacrylate, 12 parts of hydroxyethyl methacrylate,
0.8 parts of methacrylic acid and 0.2 parts of polymerization catalyst were dropped into a solvent consisting of 50 parts of xylol and 50 parts of butyl acetate, and solution polymerization was carried out by a usual method to obtain an acrylic resin having a nonvolatile content of 50% (glass transition temperature). A solution of 14 ° C., hydroxyl value 52, acid value 5) was obtained.

20 parts of this acrylic resin solution and 100 parts of the cyclohexanone solution of the fluorine-containing copolymer were added to titanium dioxide pigment 26.
Parts and 0.5 parts of carbon black were added and dispersed, and the blocked polyisocyanate solution 1 used in Example 3 was further dispersed.
4 parts, 2 parts of γ-aminopropyltriethoxysilane, 2 parts of an ultraviolet absorber, and 1.5 parts of a surface conditioner were added, and a lower layer baking type off-white paint (amount of titanium dioxide pigment in the paint solid content of 28%) was added. Prepared.

Mirror-finished stainless steel plate with a plate thickness of 0.6 mm (SUS # 3
04-BA), xylol / cellosolve acetate =
The off-white paint, whose viscosity was adjusted to 70 seconds with an 80/20 diluted solvent, was applied by a flow coater so that the dry film thickness was 15 μm.

Then, 26 parts of titanium dioxide pigment and 0.
An upper layer baking type off-white paint (a titanium dioxide pigment amount of 11% in the coating solid content) for the upper layer having the same composition except that 5 parts was replaced with 0.15 parts was adjusted to a viscosity of 70 seconds, and then a dry film thickness was 10 μm. The coating was repeated using a flow coater and baked for 60 seconds to a plate temperature of 220 ° C. to form an off-white coating film.

Comparative Example 4 Baking-type off-white color paint for lower layer whose viscosity was adjusted to 70 seconds of Example 4 (titanium dioxide pigment amount in the paint solids was 28
%) Was coated with a flow coater to a dry film thickness of 25 μm, and baked for 60 seconds to a plate temperature of 220 ° C. to form an off-white coating film. (However, the upper layer bake type paint was not applied over again.) Appearance of the coated plates obtained in Examples 1 to 4 and Comparative Examples 1 to 4,
The 60 ° specular gloss and the color difference after the accelerated test by the sunshine weatherometer and the Okinawa outdoor exposure test were measured, and the results are shown in Table 1.

As is clear from Table 1, the coating film obtained by the method of the present invention maintained the original white color and had a small decrease in gloss.

On the other hand, the coating film of Comparative Example 1 in which the clear coating material was applied repeatedly as the upper layer coating material had a good gloss retention rate, but the color of the binder itself used in the clear coating film appeared and had a yellowish color, which was originally the lower coating film. The white color was hindered and the commercial value was low.

Further, both the coating film of Comparative Example 2 in which the titanium dioxide pigment was excessively applied as the upper layer coating material and the coating films of Comparative Examples 3 and 4 in which the upper layer coating material containing a small amount of titanium dioxide pigment was not applied were glossy. Markedly decreased.

Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location B05D 7/24 303 B 8720-4D

Claims (1)

[Claims] 1. A substrate surface comprising (1) 20 to 70% by weight of a titanium dioxide pigment and 20 to 80% by weight of a binder in a coating solid content, and an organic solvent-soluble fluorine-containing copolymer in the binder. 65 to 100 polymer
Apply white paint containing 5% by weight, and then (2) 5-20% by weight of titanium dioxide pigment in the solid content of the paint.
And a white coating material containing 70 to 95% by weight of a binder and 65 to 100% by weight of an organic solvent-soluble fluorocopolymer in the binder, the white coating film having excellent weather resistance. Forming method.