JPH07247464A - Coating composition for stainless steel - Google Patents

Abstract

PURPOSE:To obtain a coating composition containing a water-soluble polymer obtained by the hydrolytic condensation of a silane compound in the presence of a surfactant, having excellent chemical, weather stain and heat-resistances, etc., in aqueous system and giving a coating film having high hardness and excellent flexibility. CONSTITUTION:This coating composition contains (A) a water-soluble polymer obtained by the hydrolytic condensation of a silane compound of the formula (R<2> is H, a lower alkyl, etc.; R<2> is H, an acyl, etc.; (m) is 0-2; (n) is 2-4; m+n=4) (preferably tetramethoxysilane, etc.) in the presence of a surfactant (preferably a dodecylbenzenesulfonate-type surfactant) in water and (B) an aqueous dispersion of a polymer produced by the emulsion polymerization of a radically polymerizable monomer in water at a solid weight ratio (A/B) of 0.1-5. The component B is preferably composed of 0.1-30 pts. of a polymerizable monomer having phosphoric acid group or carboxyl, group such as 2-(meth) acryloyloxyethyl acid phosphate and 70-99.9 pts. of other polymerizable monomer.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention forms a flexible film which is excellent in water resistance, chemical resistance, weather resistance, stain resistance, heat resistance, workability, high hardness and flexibility. The present invention relates to the obtained coating composition for stainless steel.

[0002]

2. Description of the Related Art Stainless steel sheets are used not only in kitchen appliances but also in chemical machinery and industrial machinery fields because of their excellent corrosion resistance, durability and beautiful appearance. It is also used for the exterior of vehicles. Similar to other metallic materials, stainless steel sheets are also subjected to surface treatment such as plating and enamel processing for the purpose of improving various surface properties, and coated steel sheets made of organic materials are also known. Since stainless steel sheets have poor adhesion to paint, butyral-based or epoxy-resin-based primer treatment or chemical conversion treatment is performed as a pretreatment, and then urethane- or acrylic-based organic solvent-based paint is applied to the coated steel sheet. However, since these primers and paints are based on organic solvents, they are environmentally problematic.

In the field of paints, water-based paints are becoming more and more water-based from the viewpoints of environmental pollution and safety and hygiene, and water-based emulsion paints are now widely used in place of conventional organic solvent-based paints. However, emulsion paints produced by general emulsion polymerization are inferior in water resistance and chemical resistance, so that they have not been applied to stainless steel sheets so far.

[0004]

Therefore, in the present invention, in water system, water resistance, chemical resistance, weather resistance, stain resistance, heat resistance,
An object of the present invention is to provide a coating composition for stainless steel, which has excellent workability and flexibility, and which can form a coating film having high hardness and good flexibility.

[0005]

According to the present invention, a coating composition for stainless steel comprises a silane compound (I) R ¹ _m Si (OR ² ) _n (I) (wherein R ¹ May be the same or different and each represents a hydrogen atom, a lower alkyl group, an aryl group or an unsaturated aliphatic residue, R ² represents a hydrogen atom, a lower alkyl group or an acyl group, and m represents 0, 1 or 2 , N is 2, 3 or 4
And m + n is 4), a water-soluble polymer (A) obtained by hydrolytically condensing in water in the presence of a surfactant,
The water-dispersible polymer (B) obtained by emulsion-polymerizing a radically polymerizable polymerizable monomer in water is converted into the water-soluble polymer (A) / the water-dispersible polymer (B) (solid content weight ratio). )But,
The gist is that it is contained so as to be 0.1 to 5.

The water-dispersed polymer (B) contains 0.1 to 30.0 parts by weight of a radical-polymerizable polymerizable monomer (B-1) having a phosphoric acid group or a carboxyl group, and other radical polymerization. Possible polymerizable monomer (B-2) 70.0-9
9.9 parts by weight (however, (B-1) + (B-2) is 10
(0 parts by weight) is emulsion-polymerized in water to improve storage stability as a composition, film-forming property, film adhesion, and other physical properties of the coating film. is there.

[0007]

The function of the present inventors is as follows:
We focused on polysiloxane that forms a film that is dense and has excellent weather resistance, chemical resistance, and water resistance. In addition to flexibility such as flexibility and poor film formation, the alkoxysilane that is a raw material monomer Since there is a problem that polymerization stability and storage stability are inferior in an aqueous system, since a class of compounds reacts with water to cause hydrolysis and condensation in the first place, a thorough study was conducted, and in combination with an aqueous dispersion polymer, high hardness and The inventors of the present invention have found that a flexible film can be formed and that hydrolysis condensation of a silane compound can be controlled by adding a surfactant, and thus the present invention has been achieved. The present invention will be described in detail below.

The silane compound (I) used as a starting material for the water-soluble polymer (A) in the present invention is not limited as long as it satisfies the following formula, and one or more thereof can be used. R ¹ _m Si (OR ² ) _n (I) (In the formula, R ¹ may be the same or different and represents a hydrogen atom, a lower alkyl group, an aryl group or an unsaturated aliphatic residue, and R ² is Represents a hydrogen atom, a lower alkyl group or an acyl group, m is 0, 1 or 2, n is 2, 3 or 4
, And m + n is 4.) Here, the lower alkyl group refers to a linear or branched alkyl group having 6 or less carbon atoms.

Specific examples of these silane compounds (I) include tetramethoxysilane, tetraethoxysilane,
Tetrapropoxysilane, tetrabutoxysilane, methyltrimethoxysilane, methyltriethoxysilane, methyltripropoxysilane, methyltributoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxy Silane, i-propyltrimethoxysilane, i-propyltriethoxysilane, γ-chloropropyltrimethoxysilane, γ-chloropropyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, γ-glycidoxypropyltrimethoxy Silane, γ-glycidoxypropyltriethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-
Mercaptotriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, 3,4-epoxycyclohexylethyltrimethoxysilane, 3,4-
Examples thereof include epoxycyclohexylethyltriethoxysilane, and one or more of these can be used. From the viewpoint of versatility and storage stability, tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane and methyltriethoxysilane are preferable.

The composition of the present invention comprises a water-soluble polymer (A) obtained by previously hydrolyzing and condensing one or more compounds selected from the above-exemplified silane compounds (I).
After obtaining the above, it is mixed with the below-mentioned water dispersion polymer (B). Here, the hydrolytic condensation of the silane compound (I) is an essential requirement to be carried out in water in the presence of a surfactant. This is because the surfactant has a function of suppressing a rapid reaction of the silane compound (I) during hydrolysis and condensation and preventing gelation.

As the surfactant, anionic, nonionic, a combination of anion and nonionic, cationic,
A surfactant such as amphoteric can be used. As the anionic surfactant, for example, higher alcohol sulfuric acid ester sodium salt, alkylbenzene sulfonic acid sodium salt,
Succinic acid dialkyl ester sulfonic acid sodium salt,
Examples thereof include alkyl diphenyl ether disulfonic acid, and examples of the nonionic surfactant include polyoxyethylene alkyl allyl ether. As the cationic surfactant, for example, alkylpyridinyl chloride, alkylammonium chloride and the like are used, and as the double-sided surfactant, for example, lauryl betaine and the like can be used. It is also possible to use a reactive surfactant. From the viewpoint of the stability of the hydrolyzed condensate of the silane compound, an anionic surfactant can be preferably used, and a dodecylbenzene sulfonic acid type surfactant is particularly preferable.

The amount of these surfactants used is 0.001-1 with respect to 100 parts by weight of the silane compound (I).
0 parts by weight. It is more preferably 0.01 to 5 parts by weight.
When the amount of the surfactant is less than 0.001 part by weight, the storage stability of the water-soluble polymer (A), which is a hydrolysis-condensation product, is poor,
If it exceeds 10 parts by weight, the water resistance of the coating film may deteriorate, which is not preferable. No hydrolysis condensation reaction
It can be easily carried out by stirring in water under a temperature condition of ~ 200 ° C. A small amount of an aqueous solvent such as alcohol may be added.

The hydrolysis-condensation reaction can be represented by the following formula, for example, when tetraethoxysilane is used as the silane compound (I). Si (OC ₂ H ₅ ) ₄ + 4H ₂ O → Si (OH) ₄ + 4C ₂ H ₅ OH Si (OH) ₄ → SiO ₂ + 2H ₂ O After that, the silane compound undergoes condensation polymerization to become three-dimensional. As the water-soluble polymer (A), one having a molecular weight of about 100 to 5,000 in terms of polystyrene is useful in terms of film-forming property and coating film performance. This water-soluble polymer (A) further causes a three-dimensional reaction by heating during the subsequent coating film formation.

The water-dispersed polymer (B) which is another component of the composition of the present invention is obtained by emulsion-polymerizing a radically polymerizable polymerizable monomer in water. The water-dispersed polymer (B) not only improves the film-forming property of the composition of the present invention, but also functions to improve the flexibility and other physical properties of the coating film. As the radically polymerizable polymerizable monomer (hereinafter simply referred to as a polymerizable monomer), a water-soluble polymer (A)
Is a polymerizable monomer having either a phosphoric acid group or a carboxyl group, which is a functional group capable of acting as a catalyst for the above-mentioned hydrolysis reaction, so that a three-dimensional curing reaction can be further caused during the subsequent coating film formation. It is preferable to include (B-1),
The water-dispersed polymer (B) may be formed only from the other polymerizable monomer (B-2).

As the polymerizable monomer (B-1), 2- (meth) acryloyloxyethyl acid phosphate having a phosphoric acid group, acid phosphooxypolyoxypropylene glycol mono (meth) acrylate, acid phosphooxypolyoxy. Ethylene glycol mono (meth) acrylate, methacryloyloxyethyl acid phosphate monoethanolamine half salt, etc .;
(Meth) acrylic acid having a carboxyl group, 2- (meth) acryloxyethylsuccinic acid, 2- (meth) acryloxyethylphthalic acid, 2- (meth) acryloyloxyethylhexahydrophthalic acid, etc. Alternatively, they can be used as a mixture.

As the polymerizable monomer (B-2), methyl (meth) acrylate, ethyl (meth) acrylate,
Butyl (meth) acrylate, cyclohexyl (meth)
Acrylate, 4-t-butylcyclohexyl (meth)
Acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, ethylene glycol di (meth) acrylate, diethylene glycol (Meth) acrylic acid esters such as di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate; Aromatic vinyl compounds such as styrene, α-methylstyrene, divinylbenzene and their nuclear substitution derivatives; hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth A hydroxyl group-containing compound such as acrylate, 2-hydroxybutyl (meth) acrylate, glycerol mono (meth) acrylate, 2- (meth) acryloyloxyethyl-2-hydroxyethylphthalic acid; glycidyl (meth) acrylates having a glycidyl group; Γ- (meth) acryloxypropyltrimethoxysilane having an alkoxysilyl group, γ- (meth)
Acryloxypropyltriethoxysilane; acrylonitrile, acrylamide, etc., among which 1
Use more than one seed.

The polymerizable monomer (B-1) is 0.1 to 30.
0 parts by weight, the polymerizable monomer (B-2) is 70.0 to 99.
It is preferable to configure the water-dispersed polymer (B) as 9 parts by weight (however, (B-1) + (B-2) is 100 parts by weight). The polymerizable monomer (B-1) acts as a catalyst for the three-dimensional reaction of the water-soluble polymer (A) and also improves the adhesion with the stainless steel plate. However, when the polymerizable monomer (B-1) exceeds 30.0 parts by weight, the water resistance of the coating film may be deteriorated. A more preferable amount of the polymerizable monomer (B-1) used is 1.0 to 20.0 parts by weight,
More preferably, it is 5.0 to 15.0 parts by weight.

The polymerizable monomers (B-1) and (B-2) are selected so that the glass transition temperature (Tg) of the water-dispersed polymer (B) is -50 to 150 ° C. It is preferable. If the Tg of the water-dispersed polymer (B) is too low, the resulting coating film may have tackiness. Preferred Tg
Has a lower limit of -30 ° C, more preferably 0 ° C. Also,
If Tg is too high, the flexibility of the coating film deteriorates.
The preferred upper limit of Tg is 100 ° C, more preferably 60 ° C.
Is. The Tg may be designed by calculating from the Tg when the selected polymerizable monomer is a homopolymer and the amount used.

The water-dispersed polymer (B) can be obtained by ordinary emulsion polymerization. For example, the above-mentioned polymerizable monomer and emulsifier, a polymerization initiator, a chain transfer agent if necessary, and a pH adjuster in an aqueous medium. The formulation may be added and polymerization may be carried out at 20 to 100 ° C. for about 0.5 to 30 hours. As the emulsifier used here, the surfactant used when the silane compound (I) is hydrolyzed and condensed can be exemplified. The amount used is preferably 0.001 to 10 parts by weight based on 100 parts by weight of the total amount of polymerizable monomers. If it is less than 0.001 part by weight, the stability of micelles during polymerization is poor, and 1
If it is more than 0 parts by weight, the water resistance of the coating film may be poor.

As the polymerization initiator, a water-soluble persulfate,
Hydrogen peroxide or the like can be used, and if necessary, it can be used in combination with a reducing agent. Further, an oil-soluble polymerization initiator such as 2,2′-azobisisobutyronitrile or 2,2′-azobis (4-methoxy-2,4)
It is also possible to use an azo-based polymerization initiator such as dimethylvaleronitrile) or an organic peroxide polymerization initiator such as benzoyl peroxide or butyl peroxide. The amount of the polymerization initiator used is 0.01 with respect to 100 parts by weight of the total amount of the polymerizable monomers.
-5 parts by weight is preferred.

The coating composition of the present invention contains the water-soluble polymer (A) / water-dispersed polymer (B) in a solid content weight ratio of 0.1 to 5. This time,
The water-soluble polymer is R ¹ _m —SiO _{(4-m) / 2,} and is calculated as solid content in an absolutely dry state. A more preferable compounding ratio is (A) /
(B) is 0.5 to 3. When it is more than 5, the flexibility such as flexibility of the coating film is poor, and when it is less than 0.1, the chemical resistance and hardness are lowered.

An organic solvent may be added to the composition of the present invention in order to improve film-forming property and wettability.
Specific examples of the organic solvent used here include alcohols such as methanol, ethanol, 2-propanol, 1-butanol, ethylene glycol, diethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether; acetone, methyl ethyl ketone, etc. In addition to the above ketones, methyl acetate, tetrahydrofuran and the like can be mentioned, and one or more of these can be mixed and used. Of these, alcohols are preferably used. The amount of these organic solvents used is less than 35 parts by weight, preferably less than 30 parts by weight, and more preferably less than 10 parts by weight in the total solvent of the composition. If it exceeds 35 parts by weight, it is against the object of the present invention to provide an aqueous coating composition.

The composition of the present invention needs various inorganic and organic additives such as a curing agent, a wettability improver, a plasticizer, a defoaming agent, and a thickening agent within a range that does not impair the effects of the present invention. It can also be added according to. Known water-soluble, water-insoluble or water-dispersible additives may be added as coating additives. Examples of water-soluble additives include water-soluble polymers such as polyvinyl alcohol. Examples of water-insoluble or water-dispersible additives include water-dispersible silica, alcohol-dispersible silica, talc, diatomaceous earth, calcium carbonate,
Examples thereof include clay, titanium dioxide, aluminum silicate, aluminum phosphate, alumina sol, magnesia sol, titania sol, zirconia sol and the like.

The method of coating the stainless steel sheet with the coating composition of the present invention is not particularly limited, and a roll coating method, a dip coating method, a bar coating method, a nozzle coating method or a combination thereof is adopted. Note that a known stainless steel plate surface treatment can be performed before the coating.

After coating, the coating film is cured and dried. It can be cured and dried at room temperature, but if it is to be cured and dried quickly, it will be at room temperature to 300 ° C, preferably 50 to 250.
It is good to heat dry at ℃. The thickness of the coating film is not particularly limited, but 0.001 to 100 μm, more preferably 0.01 to 40 μm is suitable after drying. When the thickness is less than 0.001 μm, the coating film is not uniform and pinholes are easily generated, and when the thickness is more than 100 μm, cracks are easily generated in the coating film, which is not preferable.

[0026]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples. Example 1 Methyltrimethoxysilane 7.4 g, tetraethoxysilane 6.3 g, Hitenol N08 (Daiichi Kogyo Seiyaku Co., Ltd. surfactant) 0.3 g, and water 36.5 g were mixed and stirred at 50 ° C. for 1 hour. A transparent water-soluble polymer (component A) having a solid content of 10.8% was obtained. Next, a four-necked flask was equipped with a stirrer and a thermometer, and 119.0 g of water and Hitenol N08 were added.
Charge 0.6 g and ammonium persulfate 0.34 g,
After purging with nitrogen gas and heating to 80 ° C., 46.5 g of butyl acrylate, 41.8 g of methyl methacrylate, 11.7 g of methacrylic acid, 30.1 g of water, Hitenol N08
A mixture of 0.7 g was continuously added dropwise over 3 hours. After completion of the dropping, the mixture was heated at 80 ° C. for 1 hour, cooled, and filtered through a 200-mesh wire net to obtain an aqueous dispersion polymer (component B) having a solid content of 40% by weight. The glass transition temperature (Tg) of the obtained water-dispersed polymer was 40.1 ° C. and the average particle size was 94.5.
was nm.

Coating composition 1 was obtained by mixing 50.4 g of the water-soluble polymer and 27.2 g of the water-dispersed polymer while stirring. This coating composition 1 was applied to a stainless steel plate (SUS304) using a bar coater so that the thickness after drying would be 2.0 μm, and dried at 200 ° C. for 30 seconds. The resulting coating film was transparent. The results of the physical property test of this coating film are shown in Table 1.

Examples 2 to 9 The same operations as in Example 1 were carried out to prepare coating compositions 2 to 2.
Got 9. The results of physical property tests are also shown in Tables 1 and 2. The solid content of the water-soluble polymer is 10.8% by weight.
In addition, the solid content concentration of the water-dispersed polymer was adjusted to 40% by weight.

Example 10 The high tenol N08 of Example 1 was used as Neoperex No. 2
A coating composition 10 was obtained in place of 5 (manufactured by Kao Corporation).
The physical property test results are also shown in Table 2. Example 11 The same operation as in Example 1 was performed except that SUS302 was used instead of the stainless steel plate. The physical property test results are also shown in Table 2. Example 12 The same operation as in Example 1 was performed except that the stainless steel plate was replaced with SUS430. The physical property test results are also shown in Table 2.

Comparative Example 1 Only the water-dispersed polymer obtained in Example 1 was applied to a stainless steel plate (SUS304) using a bar coater so that the thickness after drying would be 2.0 μm, and at 200 ° C. It was dried for 30 seconds. The resulting coating film was transparent. The coating has a cross-section test of 10, a chemical resistance of ×, and a pencil hardness of 6
B, Gobang eyes Eriksen was 10. The storage stability was good.

Comparative Example 2 Only the water-soluble polymer obtained in Example 1 was applied to a stainless steel plate (SUS304) with a bar coater to give a thickness of 2.0.
It was applied so as to have a thickness of μm and dried at 200 ° C. for 30 seconds.
The resulting coating film was transparent. This coating film had a goggles eye test of 0, a chemical resistance of ◯, a pencil hardness of 4H, and a gougins eye Erichsen of 0. The storage stability was x.

Physical property evaluation method Gobang eye test: A paint film coated on a stainless steel plate is carved with a cutter knife into 100 * 100 mm intervals, and a cellophane tape is pressure-bonded and then peeled off. It was evaluated by. 10 points (good) → 0 points (poor) Chemical resistance: A coating film coated on a stainless steel plate was subjected to a rubbing test 100 times with ethanol. ◯: No change in coating film ×: Whitening of coating film, dissolution of coating film Pencil hardness: Coating film coated on stainless steel plate,
It was performed according to JIS-K5400. Gobin eye Eriksen: A stainless steel plate coated with a cutter knife at 1 mm intervals of 100 x 100
mm scoring, extruded 5 mm Erichsen, pressed with cellophane tape and then peeled off, and the degree of peeling of the coating film was evaluated by a 10-point method. 10 points (good) → 0 points (poor) Storage stability: The coating composition was stored at 21 ° C. for 3
Observe the condition after months ○: No change ×: Aggregation, gelation

Abbreviations BA: Butyl acrylate MMA: Methyl methacrylate HEMA: 2-Hydroxyethyl methacrylate St: Styrene GMA: Glycidyl methacrylate MAA: Methacrylic acid AA: Acrylic acid MTMOS: Methyltrimethoxysilane ES: Tetraethoxysilane nPTMOS: n-propyltrimethoxysilane t-GPTMOS: t-glycidoxypropyltrimethoxysilane

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

The coating composition for stainless steel of the present invention comprises a silane-based water-soluble polymer having excellent chemical resistance and hardness, and an aqueous dispersion polymer having excellent film-forming properties and forming a flexible film. Since it is a new water-based coating composition for stainless steel plates that is effectively combined, there is no concern about environmental pollution, and water resistance, chemical resistance, weather resistance, stain resistance, heat resistance, workability It was possible to provide a coating composition capable of forming a flexible film having excellent hardness, high hardness and excellent flexibility.

Claims (2)

[Claims] 1. A silane compound (I) R ¹ _m Si (OR ² ) _n ... (I) represented by the following general formula (wherein R ^{1 s} may be the same or different, and is a hydrogen atom or a lower alkyl group). , An aryl group or an unsaturated aliphatic residue, R ² represents a hydrogen atom, a lower alkyl group or an acyl group, m is 0, 1 or 2, n is 2, 3 or 4
, And m + n is 4), and a water-soluble polymer (A) obtained by hydrolyzing and condensing in water in the presence of a surfactant, and a radically polymerizable polymerizable monomer in water. The water-dispersed polymer (B) thus obtained is contained so that the water-soluble polymer (A) / the water-dispersed polymer (B) (solid content weight ratio) is 0.1 to 5. A coating composition for stainless steel, characterized in that 2. The water-dispersed polymer (B) according to claim 1.
Is 0.1 to 30.0 parts by weight of a radically polymerizable polymerizable monomer (B-1) having a phosphoric acid group or a carboxyl group, and another radically polymerizable polymerizable monomer (B-
2) 70.0 to 99.9 parts by weight (however, (B-1) +
The coating composition for stainless steel according to claim 1, which is obtained by emulsion-polymerizing (B-2) is 100 parts by weight in water.