JP2001064569A - Coating composition and surface-coating material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water-based coating composition useful for applying to a steel plate or the like and a surface-coating material, obtained by backing the composition, having a high hardness and good stain resistance and excellent in lubricating properties at ordinary temperatures and higher temperatures. SOLUTION: The objective coating composition comprises an aqueous emulsion, obtained by copolymerizing vinyl-polymerizable self-crosslinkabel monomers; an N-hydroxyanlkyl (meth)acrylamide, an N-methoyalkyl (meth) acrylamide or glycidyl (meth)acrylate, and, incorporated therein, 2-10 wt.%, based on the solids content of the aqueous emulsion, of a lubricating compound selected from the group consisting of silicon-containing compounds, fluorine- containing compounds and polyethylene compounds. Another objective surface- coating material is coated with a film which is obtained by baking the composition at 60-300 deg.C and has a pencil hardness of at least 6H, good resistance to stain, and a dynamic coefficient of friction of not higher than 0.15 at 25 deg.C and a dynamic coefficient of friction, at 120 deg.C, of less than 1.2 times that at 25 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-based coating composition comprising a self-crosslinking water-based acrylic emulsion mixed with a lubricating compound selected from the group consisting of a silicon compound, a fluorine compound and a polyethylene compound. And a surface coating material obtained by baking the composition at 60 to 300 ° C. and having excellent hardness, good stain resistance, and excellent lubricity at room temperature and high temperature.

[0002]

2. Description of the Related Art A liquid medium dispersion of fine particles called an emulsion, a suspension, a latex, etc. has been conventionally used in aqueous paints, adhesives, paper coating agents, leather base conditioners,
It is widely used as an admixture for cement, a lubricant for films, a binder for fibers, and the like. When a water-based paint is applied to a steel plate or resin plate to form a coating film, the coating film must meet the requirements of scratch resistance, stain resistance, weather resistance, non-adhesion between steel plates and resin plates, and good appearance. In addition, recently, lubrication is required in order to omit oiling during machining. Further, depending on the application, solvent resistance and alkali elution resistance are also required.

[0003] In order to satisfy these requirements, the coating film must be hard and have high lubricity, but it is difficult to harden the coating film using a conventional aqueous emulsion. In addition, it is easy to think of mixing a lubricant with an aqueous emulsion in order to enhance lubricity, but the generally used lubricant and the aqueous emulsion have poor mixing properties, and may aggregate for several days or instantly. Many. In addition, when machining is performed continuously, the dies of the processing machine are heated to a high temperature, but without the high-temperature lubricity of the coating film, there arises a problem such as galling and a need to change machining conditions. .

For this reason, at present, an organic solvent-based paint having a crosslinkable component such as melamine, epoxy, urethane or the like is used at 200 ° C.
Alternatively, by baking at a high temperature of 300 ° C., a hard and good lubricating coating film is obtained, but a large-scale furnace is required to recover the volatile organic solvent and obtain a high temperature.
Although the invention disclosed in Japanese Patent Application Laid-Open No. H11-80485 discloses a self-crosslinking aqueous emulsion, the self-crosslinking monomer in the invention has low reactivity, so that the baking property at low temperatures is inferior and the lubricity is low. Does not disclose anything.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to overcome the above-mentioned disadvantages of the prior art, and to achieve high hardness, good stain resistance and appearance even when baked at a low temperature in a completely aqueous system, at normal and high temperatures. An object of the present invention is to provide a coating composition capable of forming a film having excellent lubricating performance and a surface coating material coated with the film.

[0006]

In order to solve the above problems, the present invention has the following arrangement.

That is, the present invention provides an acrylic copolymer obtained by copolymerizing 2 to 30% by weight of a vinyl polymerizable self-crosslinkable monomer and another copolymerizable monomer in the presence of a non-polymerizable emulsifier. Coating composition comprising, as essential components, a combined aqueous emulsion and a lubricating compound selected from the group consisting of a silicon compound, a fluorine compound and a polyethylene compound in an amount of 2 to 10% by weight based on the solid content of the aqueous emulsion. It is.
Further, the composition may contain one or more acidic compounds selected from the group consisting of a phosphoric acid compound, sulfuric acid, nitric acid, and hydrochloric acid in an amount of 0.5 to 10% by weight based on the solid content of the aqueous emulsion. It is recommended that the crosslinkable monomer be selected from the group consisting of N-hydroxyalkyl (meth) acrylamide, N-methoxyalkyl (meth) acrylamide, and glycidyl (meth) acrylate.

[0008] The present invention also relates to such a composition.
Pencil hardness of more than 6H, good stain resistance, kinetic coefficient of friction at 25 ° C of 0.15 or less and 120, baked at 0 ° C
Also encompasses surface coating materials coated with a coating having a coefficient of kinetic friction at 25 ° C. less than 1.2 times that at 25 ° C.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, self-crosslinkable monomers include N-hydroxyalkyl (meth) acrylamide, N-methoxyalkyl (meth) acrylamide,
Those selected from the group of glycidyl (meth) acrylates are preferred. The self-crosslinkable monomer referred to in the present invention has a functional group such as a hydroxyalkylamide group, a methoxyalkylamide group, or an epoxy group, and is employed together with the functional group or with the functional group in the copolymerization of the present application. The compound reacts with a carboxyl group of (meth) acrylic acid or a hydroxyl group of a hydroxyl group-containing monomer which is another copolymerizable monomer, and the above-mentioned compound group is representative. Specifically, N-hydroxymethyl (meth) acrylamide, N
-Hydroxyethyl (meth) acrylamide, N-hydroxypropyl (meth) acrylamide, N-hydroxybutyl (meth) acrylamide, N-methoxymethyl (meth) acrylamide, N-methoxyethyl (meth)
Acrylamide, N-methoxypropyl (meth) acrylamide, N-methoxybutyl (meth) acrylamide and the like, that is, alkyls include C1 to C4.
These self-crosslinking monomers may be used alone or as a mixture of two or more. In addition, what is described as (meth) acryl- refers to methacryl or acryl (the same applies hereinafter).

The self-crosslinkable monomer is used in an amount of 2 to 30% by weight based on the total amount of the monomers forming the emulsion. If the amount is less than 2% by weight, the pencil hardness, stain resistance and lubricating properties at room temperature and high temperature are deteriorated. If the amount is more than 30% by weight, the stability as an aqueous emulsion is impaired and cannot be adopted.

The other copolymerizable monomer is not particularly limited as long as it copolymerizes with the above-mentioned self-crosslinking monomer, but is not particularly limited. It is preferable to use one or more monomers selected from (meth) acrylic acid and a hydroxyl group-containing monomer. Needless to say, the total amount of these other copolymerizable monomers is the amount excluding the self-crosslinking monomer, and is 70 to 98% by weight.

Examples of the (meth) acrylate include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, and n- (meth) acrylate. Butyl,
C1 such as isobutyl (meth) acrylate, secondary butyl (meth) acrylate, tertiary butyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate
And C8 alkyl esters and cyclohexyl (meth) acrylate. These monomers may be used alone or as a mixture of two or more.

The above-mentioned hydroxyl group-containing monomer is (meth)
It refers to those having one or more hydroxyl groups in the alkyl chain of the acrylic acid alkyl ester. Examples of such hydroxyl group-containing monomers include 2-hydroxyethyl (meth) acrylate,
2-hydroxypropyl (meth) acrylate, (meth)
4-hydroxybutyl acrylate and the like. These hydroxyl group-containing monomers may be used alone or as a mixture of two or more.

The (meth) acrylic acid ester monomer, styrene, (meth) acrylic acid, and the hydroxyl group-containing monomer are used in an amount of 70 to 98% by weight as described above. If the amount is less than 70% by weight, the stability of the aqueous emulsion becomes poor,
If it exceeds 98% by weight, the resulting film has poor pencil hardness, stain resistance, solvent resistance, alkali elution resistance, and lubricity at high temperatures, and cannot be used.

The emulsion of the present invention in which such a monomer mixture is copolymerized in an aqueous system employs a non-polymerizable emulsifier during polymerization. The non-polymerizable emulsifier has a relatively high molecular weight by itself, has a functional group having good compatibility with water, and does not have an addition-polymerizable functional group such as a vinyl group. It is characterized in that it is not incorporated into the polymerized main chain formed by polymerization. The presence of this non-polymerizable emulsifier is effective for the stability of the composition of the present invention as described below.

Examples of the non-polymerizable emulsifier include sodium dodecylbenzenesulfonate, an anionic surfactant such as polyoxyethylene having a molecular weight of about 20,000, a nonionic surfactant, and polyvinyl alcohol, polyacrylic acid, and polymethacrylic acid. And water-soluble protective colloids such as polyacrylamide, and products synthesized by polymerizing monomers having a hydroxyl group, a sulfonic acid group, and a carboxyl group. These non-polymerizable emulsifiers may be used in combination. When a non-polymerizable emulsifier was not used, aggregates were generated in the acrylic emulsion during the polymerization step, resulting in poor stability, or with a silicon-based compound, a fluorine-based compound, and a polyethylene-based compound mixed with an aqueous emulsion. The use of such an emulsifier is indispensable because the mixing stability of the compound may deteriorate. The amount used depends on the polymerization conditions, but is generally about 1 to 5 parts per 100 parts by weight of the monomer mixture.

The lubricating compound (hereinafter also referred to as a lubricant) to be added to such an aqueous emulsion is selected from a silicon compound, a fluorine compound and a polyethylene compound, and these may be used in combination. Absent.
Examples of these include Paintad 51, a silicon-based compound (manufactured by Dow Corning Asia Co., Ltd.), and KM-86.
2 (manufactured by Shin-Etsu Silicon Co., Ltd.), Chemipearl W700, a polyethylene compound (manufactured by Mitsui Chemicals, Inc.), K
SL-240A (manufactured by Futaba Fine Chemical Co., Ltd.),
Maycatex HP-50 (manufactured by Meisei Chemical Industry Co., Ltd.),
Sunleaf CLA-3 (manufactured by Sanyo Chemical Industry Co., Ltd.), Fluon AD-1 which is a fluorine compound (Asahi IC Co., Ltd.)
Manufactured), Polyflon LDW40 (manufactured by Daikin Industries, Ltd.)
Etc. The form of the lubricant when added to the aqueous emulsion is preferably a wet state with a particle diameter of 10 μm or less, and it is recommended to add the lubricant little by little while stirring the aqueous emulsion.

It is necessary that such a lubricant be contained in an amount of 2 to 10% by weight based on the solid content of the aqueous emulsion. 2
If the amount is less than 10% by weight, lubricity is poor at both normal temperature and high temperature. If the amount is more than 10% by weight, agglomerates are generated in the aqueous emulsion in the composition, resulting in poor stability of the composition itself. Note that lubricants other than those recommended by the present invention,
For example, when a linear alkyl acid compound such as a stearic acid compound is used as a lubricant, even when the amount of addition is 2 to 10% by weight, when mixed with the aqueous emulsion of the present invention,
The composition will aggregate in a few days. The coating composition of the present invention contains the above-described aqueous emulsion and a lubricant having a solid content of 2 to 10% as essential components.
As other components, a rust inhibitor, a thickener, an acidic compound described below, and the like may be added.

The crosslinking reaction of the self-crosslinkable monomer is promoted by adding 0.5 to 10% by weight of the acidic compound with respect to the solid content of the above-mentioned aqueous emulsion.
Even when baked at a relatively low temperature, a surface coating material having good solvent resistance and alkali elution resistance can be obtained. When the amount is less than 0.5% by weight, the effect as an accelerator is weak, and as a result, the solvent resistance and the alkali elution resistance of the surface coating material when baked at a low temperature are poor. This significantly lowers the pH of the composition for use, resulting in a lack of operational safety.

The acidic compound is selected from the group consisting of a phosphoric acid compound, sulfuric acid, nitric acid and hydrochloric acid, and preferably has a dissociable hydrogen ion. Examples of the phosphate compound include ammonium dihydrogen phosphate, sodium dihydrogen phosphate, sodium monohydrogen phosphate, trisodium phosphate, sodium pyrophosphate,
Examples thereof include sodium polyphosphate, sodium metaphosphate, magnesium dihydrogen phosphate, aluminum monophosphate, hypophosphorous acid, orthophosphoric acid, and polyphosphoric acid. These acidic compounds may be used alone or as a mixture of two or more.

The method for producing the coating composition described above comprises:
Although not limited, an example is as follows. That is, a predetermined amount of a non-polymerizable emulsifier and deionized water are put into a reaction tank, and the liquid temperature is raised to 70 ° C. A mixture of the oil-soluble polymerization initiator dissolved in a predetermined amount of the monomer mixture, or a predetermined amount of the monomer mixture, an aqueous solution of ammonium persulfate, and an aqueous solution of sodium acid sulfite were stirred simultaneously and in two hours so as to end. After that, the mixture was continuously added at 70 ° C for 2 hours.
The polymerization reaction is carried out while stirring for an hour to obtain an aqueous emulsion. Next, a method of adding the wet lubricant little by little to the above-mentioned aqueous emulsion under stirring at 10 to 50 ° C. and about 100 rpm to obtain a composition is given. In addition, when adding an acidic compound, 10 to 50 ° C., about 10
A method of adding to the above composition under stirring at 0 rpm may be mentioned.

The baking temperature of the coating of the composition of the present invention on the material to be coated is preferably from 60 to 300 ° C.
If the baking temperature is lower than 60 ° C., it is difficult to remove water as a solvent, and the cross-linking of the self-crosslinkable monomer portion in the copolymer is insufficient, and the pencil hardness of the coating and the coating If the appearance, lubricity at room temperature and high temperature are poor and the temperature exceeds 300 ° C, the decomposition of the film will gradually start and burn, the equipment for heating will be large, and the processing material will be forcibly cooled. This is undesirable because more equipment is required. The film obtained from the composition of the present invention thus obtained has a pencil hardness of 6H or more, good stain resistance, and a kinetic friction coefficient of 0.15 or less at 25 ° C and a kinetic friction coefficient at 120 ° C of 25 ° C. Excellent physical properties with less than 2 times. Note that, depending on the use of the surface coating material, solvent resistance or alkali elution resistance is required. In order to meet such a requirement, when a coating composition of the present invention containing no acidic compound is used, a baking temperature of 120 ° C. or higher is required. Even at a baking temperature of 60 ° C. to 120 ° C., a film having excellent solvent resistance (grade 4 or higher according to the evaluation method described later) and alkali elution resistance (10% or less according to the evaluation method described below) can be obtained.

Examples of materials to be coated with the composition of the present invention include cold-rolled steel sheets, aluminum sheets, aluminum alloy-plated steel sheets, zinc sheets, galvanized steel sheets, zinc alloy-plated steel sheets, ABS resin sheets, and the like. In this case, since the above-described film has good lubricity through low and high temperatures, the film has a large endurance effect in continuous press working and the like.

[0024]

The present invention will be described in more detail with reference to the following examples. In addition, each evaluation in an Example measured and judged by the following method.

1. Composition stability About 30 ml of a composition mainly composed of an aqueous emulsion was placed in a 50 ml glass bottle, sealed, and allowed to stand at 50 ° C. for one month. The state of the emulsion one month later was visually determined. : Good without aggregation, thickening, sedimentation and separation.・
・ Pass △: Aggregate and / or sediment are generated. ...
Failed ×: Gelation. ··· failure

2. Lubricity (Coefficient of Dynamic Friction) After roll-coating a composition mainly composed of an aqueous emulsion on a base material such as a steel plate, the composition is left standing in a hot-air dryer until a predetermined temperature is reached, and the coating film is baked. A constant speed (1) in a room adjusted to 25 ° C. on a coating film cooled to room temperature.
(0 cm / min), slide the weight, and measure the load generated by the friction at that time. The dynamic friction coefficient was calculated by the following equation. In addition,
Regarding the lubricity at high temperature, an electric heater was installed under the substrate, the coating film was heated to 120 ° C. in advance, and the dynamic friction coefficient at that time was measured by the above method. (JIS K-7125) Dynamic friction coefficient = weight of weight (g) / load generated by friction (g)
f)

3. Stain resistance After roll-coating a composition mainly composed of an aqueous emulsion on a substrate such as a steel sheet, the composition is allowed to stand in a hot-air dryer until a predetermined temperature is reached, and the coating film is baked. 2 ml of a 10% aqueous solution of carbon black is dropped on one portion of the coating film cooled to room temperature and left in a hot air drier at 80 ° C. for 24 hours.
The sample was taken out, and the portion where the carbon black was dropped was rubbed with a rag or the like under running pure water, and the state of adhesion of the carbon black on the coating film was visually determined. ◎: Not adhered ・ ・ ・ Passed ○: Adhered to such a degree that it could be seen faintly ・ ・ ・
Pass △: Adhering to the degree of conspicuousness ・ ・ ・ Fail ×: Clearly adhering ・ ・ ・ Failure XX: Clearly adhering and spreading to the surroundings ・ ・ ・
failure

4. Pencil hardness After roll-coating a composition mainly composed of an aqueous emulsion on a substrate such as a steel plate, the composition is allowed to stand in a hot air dryer until a predetermined temperature is reached, and the coating film is baked. The coated film cooled to room temperature was scratched with a pencil having a different hardness, and the hardness of the pencil which did not damage the coated film was read.

5. Solvent resistance After the composition mainly composed of an aqueous emulsion is roll-coated on a base material such as a steel plate, the composition is allowed to stand in a hot air dryer until a predetermined temperature is reached, and the coating film is baked. The coating film cooled to room temperature is rubbed 5 times with a load of about 1 kg with ethyl alcohol impregnated in a waste cloth or the like. Thereafter, the appearance change on the coating film was visually determined. 5 (grade): no change in appearance 4 (grade): change is observed depending on the viewing angle 3 (grade): slightly changed 2 (grade): clearly changed 1 (grade): coating Peeled

6. Alkali elution resistance Measure the weight of the substrate in advance, after roll coating the composition mainly composed of an aqueous emulsion on the substrate such as a steel plate,
It is allowed to stand in a hot air dryer until a predetermined temperature is reached, and the coating film is baked. The weight of the coating film including the substrate cooled to room temperature is measured to determine the coating film weight A. Thereafter, an alkaline aqueous solution of Surf Cleaner SD280MZ (manufactured by Nippon Paint Co., Ltd.) adjusted to 2% by weight in advance is kept at 43 ° C., and the coating film including the base material is immersed therein for 2 minutes. After 2 minutes, take out and wash gently with water, and dry in a hot air dryer at 50 ° C. until there is no more water. Thereafter, the weight of the coating film including the substrate is measured again, and the coating film weight B remaining on the substrate even after the alkali treatment is measured.
And the alkali dissolution rate (%) shown in the following equation is determined. Alkali elution rate (%) = {1- (B / A)} × 100

7. Coating appearance After a composition mainly composed of an aqueous emulsion is roll-coated on a base material such as a steel plate, the composition is left standing in a hot-air dryer until a predetermined temperature is reached, and the coating film is baked. The appearance of the surface of the coating film cooled to room temperature was visually judged. ：: no discoloration Δ: slightly discolored ×: clearly discolored

Example 1 (Synthesis of non-polymerizable emulsifier) 893 parts (parts by weight; the same applies hereinafter) of deionized water, monomer 1 having the composition shown in the composition column of Table 1
00 parts, ammonium persulfate 3 parts, acid sodium sulfite 4
The liquid temperature is increased to 70 ° C. while stirring the part in a reaction vessel. Subsequently, a polymerization reaction was carried out with stirring at 70 ° C. for 12 hours to synthesize non-polymerizable emulsifiers ac satisfying the present invention. Table 1 also shows commercially available surfactants d to f that can be employed as the non-polymerizable emulsifier of the present invention.

[0033]

[Table 1]

* MAA: methacrylic acid * VSS: sodium vinyl sulfonic acid * HEA: 2-hydroxyethyl acrylate * SPSS: sodium p-styrene sulfonic acid

Example 2 (Synthesis of an aqueous emulsion) 495 parts (parts by weight; the same applies hereinafter) of deionized water and 5 parts of a non-polymerizable emulsifier shown in Table 2 were put into a reaction vessel and the liquid temperature was raised to 70 ° C. . Table 2
In 300 parts of a monomer mixture having the composition shown in the column of other copolymerizable monomer composition, 3 parts of ammonium persulfate dissolved in 97 parts of deionized water, and 4 parts of sodium acid sulfite in 96 parts of deionized water The solution was added dropwise with stirring so as to complete the reaction in 2 hours at the same time, and then the polymerization reaction was carried out with stirring at 70 ° C. for 2 hours to obtain an aqueous emulsion No. 1 satisfying the present invention. AP were synthesized.

As a comparative example, an aqueous emulsion No. 1 deviating from the present invention was used. Q to V were similarly synthesized at the monomer copolymerization ratios shown in Table 2. "Emulsion stability" in Table 2 is a result of visually evaluating a water-based emulsion placed in a closed container and allowed to stand at 50 ° C. for one month, and ○ indicates aggregation, thickening, sedimentation, Those that are good without separation, those that generate aggregates and / or sediments,
× represents a gelled substance.

[0037]

[Table 2]

* MMA: methyl methacrylate * n-BA: n-butyl acrylate * i-BMA: isobutyl methacrylate * 2EHMA: 2-ethylhexyl methacrylate * CHMA: cyclohexyl methacrylate * St: styrene * MAA: methacrylic acid * HEA: 2-hydroxyethyl acrylate * N-MAM: N-methylolacrylamide * N-MMAM: N-methoxymethylacrylamide * GMA: Glycidyl methacrylate * DvB: Divinylbenzene

From Table 2, it is understood that the aqueous emulsions A to P satisfying the requirements of the present invention are excellent in both polymerization and the stability of the emulsion formed smoothly. On the other hand, R, which has an excessively large amount of self-crosslinkable monomer, and V, which does not employ a non-polymerizable emulsifier, already lack stability in the emulsion itself.
Q and S having too few self-crosslinkable monomers, T using SPSS which is a polymerizable emulsifier, and U using DvB which is not a self-crosslinkable monomer have no problem with the stability of the aqueous emulsion itself, As shown below, a composition containing a lubricant reveals defects.

Examples 3 to 7 and Comparative Examples 1 to 3 Using the aqueous emulsion C shown in Table 2, four kinds of lubricants shown in Table 3 were added to the solid content of the aqueous emulsion.
A coating composition (hereinafter also simply referred to as “composition”) was prepared by mixing the respective amounts shown in (1) and (2), and the composition was roll-coated on an aluminum plate so that the film after baking had a thickness of 3 μm. Was heated to 130 ° C. to obtain a surface-coated steel sheet coated with a film of the coating composition. Table 3 shows the results of evaluating the stability of the composition and other surface properties of the steel sheet.

[0041]

[Table 3]

From Table 3, it is understood that Examples 3 to 7, which satisfy the requirements of the present invention, have good paintability, pencil hardness and stain resistance, and also have excellent lubricating properties due to the kinetic friction coefficients at normal temperature and high temperature. It also has excellent solvent resistance and alkali elution resistance.
On the other hand, Comparative Example 2 in which the mixing amount of the lubricant was too large, and Comparative Example 3 in which the lubricant of the stearic acid compound was used, lacked the stability of the composition itself and could not be coated on a steel sheet. In Comparative Example 1 in which the amount of the lubricant mixed was too small, there was no problem in the stability of the composition itself, but the lubricity at room temperature and high temperature was lacking.

Examples 8 to 22 and Comparative Examples 4 to 8 Using the aqueous emulsions shown in Table 2, a coating composition was prepared by mixing 5 parts by weight of Paintad 51 (silicon compound) with respect to the solid content of the aqueous emulsion. Then, after baking the composition on steel plates of various materials shown in Table 4,
After roll coating to a thickness of μm, baking was performed so that the ultimate temperature was 130 ° C. to obtain a surface-coated steel sheet coated with a film of the coating composition. Table 4 shows the results of evaluating the stability of the composition and other surface properties of the steel sheet.

[0044]

[Table 4]

* Material 1: Aluminum plate * Material 2: Electrogalvanized steel plate

From Table 4, it can be understood that Examples 8 to 22 satisfying the requirements of the present invention have good paintability, pencil hardness and stain resistance, and also have excellent lubricating properties due to the kinetic friction coefficients at ordinary temperature and high temperature. Also, except for Examples 20 and 22, solvent resistance,
Excellent alkali elution resistance. Examples 20 and 22 are inferior in alkali elution resistance. This is considered to be due to the high content of MAA as a copolymer component. However, it is excellent in other performances and is sufficiently practical for uses not requiring alkali elution resistance. On the other hand, Comparative Examples 4 and 5 in which the amount of the self-crosslinkable monomer was too small, and Comparative Example 6 in which DvB which is not a self-crosslinkable monomer were used, had no problem with the stability of the composition itself, but the stain resistance was low. Comparative Examples 7 and 8, which did not use a non-polymerizable emulsifier, lacked pencil hardness and high-temperature lubricity, and lacked the stability of the composition mixed with the lubricant.

Examples 23 to 32 and Comparative Examples 9 to 11 Using the aqueous emulsion C shown in Table 2, 5 parts by weight of paintad 51 (silicone compound) based on the solid content of the aqueous emulsion and various acidic substances shown in Table 5 A coating composition containing the compound was prepared, roll-coated on an aluminum plate so that the film after baking had a thickness of 3 μm, and then baked to reach the ultimate temperature shown in Table 5 to obtain a coating composition. To obtain a surface-coated steel sheet coated with the above film. Table 5 shows the results of evaluating the stability of the composition and the surface properties of the other steel sheets.

[0048]

[Table 5]

From Table 5, it is understood that Examples 23 to 32 satisfying the requirements of the present invention have good paintability, pencil hardness and stain resistance, and also have excellent lubricating properties due to their dynamic friction coefficients at normal temperature and high temperature. Example 4 in which the baking temperature was 120 ° C. or more,
Nos. 31 and 32 are excellent in solvent resistance and alkali elution resistance. In Examples 26 to 30 in which an acidic compound was mixed, good solvent resistance and alkali elution resistance were obtained even at a relatively low baking temperature of 80 ° C. Is possible. In addition,
Examples 23 to 25 are slightly inferior in solvent resistance and alkali elution resistance, but are excellent in other performances, and are sufficiently practical for applications not requiring solvent resistance and alkali elution resistance. It is. Comparative Example 9 where the baking temperature is too low
No satisfactory film hardness can be obtained, and the stain resistance is poor. In Comparative Example 10 in which the baking temperature was excessively high, the surface coating material and the lubricant were decomposed, and the evaluation of the coating film was not completed. In Comparative Example 11 in which the mixing amount of the acidic compound was too large, the appearance of the coating after baking was inferior, and the pH of the composition was significantly lowered, so that the safety of operation was significantly lacking.

[0050]

INDUSTRIAL APPLICABILITY According to the present invention, a coating composition based on a water-based emulsion excellent in safety and environment, which provides a film having high hardness and stable lubricity from low to high temperatures, and a coating composition coated with the coating. A surface coating material is provided.
When the present composition is applied to, for example, a steel sheet or the like, the steel sheet can be subjected to continuous punching, which was conventionally impossible due to a decrease in lubricity at high temperatures.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C09D 183/04 C09D 183/04

Claims (4)

[Claims] 1. A vinyl polymerizable self-crosslinkable monomer (2 to 3)
A water-based emulsion of an acrylic copolymer obtained by copolymerizing 0% by weight and another copolymerizable monomer in the presence of a non-polymerizable emulsifier;
10% by weight of a lubricating compound selected from the group consisting of a silicon compound, a fluorine compound and a polyethylene compound,
A coating composition as an essential component. 2. The self-crosslinking monomer is selected from the group consisting of N-hydroxyalkyl (meth) acrylamide, N-methoxyalkyl (meth) acrylamide and glycidyl (meth) acrylate. Item 6. A coating composition according to Item 1. 3. The aqueous emulsion according to claim 1, wherein at least one acidic compound selected from the group consisting of a phosphoric acid compound, sulfuric acid, nitric acid and hydrochloric acid is contained in an amount of 0.5 to 10% by weight based on the solid content of the aqueous emulsion. 3. The coating composition according to item 2. 4. The composition according to claim 1, which is baked at 60 to 300 ° C., having a pencil hardness of 6H or more, good stain resistance, and a coefficient of kinetic friction at 25 ° C. of 0.15.
A surface coating material coated with a coating having a dynamic friction coefficient at 120 ° C. less than 1.2 times that at 25 ° C.