JPH09241582A - Coating composition for precoat metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating compsn. for a precoat metal which possesses stain resistance and is usable as an excellent outdoor architactural material. SOLUTION: This coating compsn. for a precoat metal comprises: a hydroxyl- contg. film forming resin (A) having a hydroxyl value of 5 to 100; a first curing agent (B), in an amount on a solid basis of 0.5 to 10 pts.wt. based on 100 pts.wt. film forming resin (A), the solubility parameter of the first curing agent being not less than 0.5 lower than that of the film forming resin (A); a second curing agent (C), in an amount on a solid basis of 10 to 50 pts.wt. based on 100 pts.wt. film forming resin (A), the solubility parameter of the second curing agent being larger than or less than 0.5 lower than that of the film forming resin (A); an organosilica sol (D) in an amt. on a solid basis of 30 to 100 pts.wt. based on 100 pts.wt. resin (A); an acid catalyst, (E) for promoting a crosslinking reaction between the resin (A) and the first curing agent (B), in an amt. on a solid basis of 0.1 to 2.0 pts.wt. based on 100 pts.wt. resin (A); and a volatile amine compd. (F) in excess of neutral equivalent of the acid catalyst, the volatile amine compd. having a b.p. of 40 deg.C to the baking temp. of the compsn.

Description

Detailed Description of the Invention

[0001] BACKGROUND The present invention relates to a pre-coat metal coating composition to be used in home appliances and building materials.

Pre-coated metal is widely used in home appliances and building materials. It is desired that the precoat metal coating has excellent weatherability and stain resistance, especially in building materials used outdoors, in addition to the contradictory properties of workability and hardness. For example, in the case of pre-coated metal (PCM) used outdoors, traces of rainwater containing dust make the appearance unsightly. In addition, since the effects of acid rain and acid exhaust gas have increased in recent years, it is necessary to take measures for pre-coated metal used for roofing materials, road materials, tunnel interior materials, and the like. In addition, the coating film is damaged by dust in the atmosphere (hard dust such as sand, earth and sand, dust, etc.), and contaminants are apt to enter. Also, for siding materials and tunnel interior materials, use a brush etc. to wash and remove the contamination. Therefore, scratch resistance (high hardness) is required.

However, the conventional coating materials for precoat metal have not satisfied all the requirements described above. For example, Kanai et al., “Materials and Processes” VO
L. No. 6 (1993), 1494-1497 is a precoated metal prepared by blending a polyester resin having a hydroxyl value (OHV) of 8 to 40 and a melamine resin at a solid content weight ratio of 7/3, and thermally curing using a sulfonic acid-based catalyst. It is reported that stain resistance is satisfactory and processability is maintained only when a fully alkylated melamine resin is used as a melamine resin and a sulfonic acid-based acid catalyst is blocked with an amine compound. doing. The mechanism is that a concentration gradient of melamine resin occurs in the thickness direction of the coating film,
Explain that while the melamine concentration is high only near the surface of the coating film and the stain resistance is improved, the melamine concentration inside the coating film is conversely low, so that the flexibility required for workability is maintained as a whole coating film Have been. However, the stain resistance studied here is for oil-based magic ink, and not for raindrops or exhaust gas containing contaminants. Tests have shown that this system is not effective enough for raindrop contamination that is different from oily soils. Further, there is a disadvantage that the coating film shrinks because the vicinity of the surface having a high melamine concentration starts to cure earlier than the inside of the coating film.

Topcoat paints for automobiles aiming at improvement of acid rain resistance, scratch resistance, weather resistance and the like are disclosed in, for example, JP-A-3-172368 and 5-320562.
6-41496, 4-36365, 7-2
No. 07223, etc., none of them simultaneously satisfy all of the performances required for the PCM paint used outdoors, especially the resistance to rain dripping contamination. JP-A-6-166846 discloses a coating composition using a lactone-modified acrylic resin for automotive top coating or PCM, but does not satisfy the resistance to rain dripping even if the workability can be satisfied. JP-A-4-173882, JP-A-4-173883, JP-A-4-21482 and the like aiming at improving the coating film hardness do not satisfy workability and resistance to rain dripping contamination. .

Therefore, an object of the present invention is to improve workability, raindrop contamination resistance, acid resistance, and hardness of PC.
A coating composition for M is provided.

SUMMARY OF THE INVENTION The present invention provides (A) a hydroxyl group-containing film-forming resin having a hydroxyl value of 5 to 100, and (B) a solid content of 0.5 per 100 weight of the film-forming resin (A).
10 parts by weight of a first curing agent having a solubility parameter value smaller than that of the film-forming resin (A) by 0.5 or more,
(C) The film-forming resin (A) 10 as a solid content
10 to 50 parts by weight per 0 parts by weight of a second curing agent having a solubility parameter value larger than that of the film-forming resin (A) or smaller than 0.5, and (D) the film-forming property as a solid content. 30 per 100 parts by weight of resin (A)
To 100 parts by weight of the organosilica sol, and (E) 0.1 to 2.0 parts by weight of the film-forming resin (A) and the first as a solid content per 100 parts by weight of the film-forming resin (A). Acid catalyst that accelerates the reaction with the curing agent (B), and (F) a volatile amine compound that is in excess of the neutralization equivalent of the acid catalyst (E) and has a boiling point of 40 ° C. or higher and a baking temperature of the composition or lower. Provided is a coating composition for a precoat metal, which contains as an essential component.

The principle by which the coating composition of the present invention satisfies the above-mentioned performance required for a coating for pre-coated metal, particularly for outdoor building materials, particularly raindrop contamination resistance is considered as follows. That is, since the first curing agent (B) has a lower compatibility with the film-forming resin (A) than the second curing agent (C), it floats on the surface of the coating film when it is baked, The catalyst (E) is used as an excess amine (F) having a relatively low boiling point.
By blocking with, the volatilization during baking helps the surface concentration of the acid catalyst (E), thereby increasing the crosslink density of the coating film surface portion and suppressing the penetration of contaminants into the interior. On the other hand, the second curing agent (C) having a high compatibility with the film-forming resin (A) stays inside the coating film, and (1) the coating film is harder than the system using only the first curing agent (B). (2) The second hardener C is hardly self-condensed to suppress the excessive hardening inside and is designed to have a slightly lower crosslink density. It is also considered that the shrinkage of the coating film is suppressed. Further, the added organosilica sol (D) is uniformly dispersed in the coating film, and the silica sol imparts high hardness to the coating film without impairing processability. In addition, the use of the fine particle silica sol keeps the appearance of the coating film normal.

Detailed Description of Preferred Embodiments (A) Film Forming Resin: Resins which are crosslinked with an external crosslinking agent such as a melamine resin or a blocked polyisocyanate to form a cured coating film are well known in the paint field.
Typical examples of these resins are hydroxyl group-containing acrylic resins and polyester resins.

The hydroxyl group-containing acrylic resin can be obtained by copolymerizing a hydroxyl group-containing acrylic monomer and another ethylenically unsaturated monomer by a conventional method. Examples of hydroxyl group-containing acrylic monomers are 2
-Hydroxyalkyl (meth) such as hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate and 4-hydroxybutyl methacrylate
Although it is an acrylate, it imparts flexibility to the coating film and
Containing a soft segment in order to improve the processability of the polymer, for example, PCL-F from Daicel Chemical Industries, Ltd.
2-hydroxyethyl (meth) acrylate / ε-capron adduct marketed as A and FM series,
Polyalkylene glycol mono (meth) acrylate can be used in combination.

Monomers copolymerizable with the hydroxyl group-containing acrylate include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate and t. -Butyl acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate and other alkyl (meth) acrylates, styrene, vinyltoluene, acrylonitrile, vinyl acetate, glycidyl (meth) acrylate, acrylic acid, methacrylic acid and the like.

As is well known, a polyester resin is a polycondensation product of an acid component mainly composed of polycarboxylic acid and an alcohol component mainly composed of polyhydric alcohol.

As the acid component, terephthalic acid, isophthalic acid, phthalic acid or anhydride thereof, aromatic dicarboxylic acid such as 2,6-naphthalenedicarboxylic acid or 2,7-naphthalenedicarboxylic acid and anhydride thereof, and succinic acid. And aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid. Further, lactones such as γ-butyrolactone and ε-caprolactone and corresponding hydroxycarboxylic acids, and aromatic oxymonocarboxylic acids such as p-oxyethoxybenzoic acid and p-oxybenzoic acid, trimellitic acid, trimedic acid, and pyromellitic acid. A small proportion of trivalent or higher polycarboxylic acids such as acids can be included.

Alcohol components include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, triethylene glycol and 1,4-cyclohexane. In addition to diols, 1,4-cyclohexanedimethanol, bisphenol A alkylene oxide adducts, bisphenol S alkylene oxide adducts, 1,2-propanediol, neopentyl glycol, 1,2-butanediol, 1,3-butanediol , 2,3-butanediol, 1,2-pentanediol, 2,3-pentanediol, 1,4-pentanediol, 1,4-hexanediol, 2,5-hexanediol, 3-methyl-1,5 -Pentanediol, 1,2-dode Njioru, there is an aliphatic glycol having a side chain such as 1,2-octadecanediol.
The alcohol component may also include a small proportion of trihydric or higher polyhydric alcohols such as trimethylolpropane, glycerin, pentaerythritol and the like. As another component, a monoepoxy compound such as Cardura E may be contained.

The physical properties required for the film-forming resin (A) are a hydroxyl number of 5 to 100, preferably 10 to 60.
Is within the range. Within this range, both curability and workability are compatible. Generally, if the hydroxyl value is less than 5, curing will be poor, and if it exceeds 100, workability will be deteriorated, which is not preferable. Naturally, the other physical properties must be in the range that should be provided as a film forming resin for PCM paints, for example, an acid value of 0 to 50, a Tg of -20 to 60 ° C, and a number average molecular weight of 1800 to 20,000. It is desirable to be within. The SP value is the S of resin (A)
Since it must be selected based on the difference from the P value,
It is desirably in the range of 9.5 to 12, preferably 10.4 to 12, most preferably 11 to 12. When two or more resins are blended and used as the resin (A), the SP value means its weighted average value.

Here, the SP value (solubility parameter) is a measure of solubility and is measured as follows. References SUH, CLARKE [J. P. S. A
Measurement temperature: 20 ° C. Sample: 0.5 g of resin is weighed into a 100 ml beaker, 10 ml of a good solvent is added by using a whole pipette, and dissolved by a magnetic stirrer. ・ Measurement of turbidity point Using a 50 ml burette, a poor solvent is dropped, and the point at which turbidity occurs is defined as the dropping amount.・ Calculation The SP value δ of the resin is given by the following equation.

Δ = (V _ml ^1/2 δ _ml + V _mh ^1/2 δ _mh ) /
^{_{(V ml 1/2 + V mh 1/2}} ) V m = V 1 V 2 / (φ 1 V 2 + φ 2 V 1) δ m = φ 1 δ 1 + φ 2 δ 2 V i: solvent molecular volume (ml / Mol) φ _i : volume fraction of each solvent at the cloud point δ _i : SP value of the solvent ml: low SP poor solvent mixed system mh: high SP poor solvent mixed system

(B) First curing agent: The physical properties that the first curing agent should have are such that the SP value is the film-forming resin (A).
Is smaller than the SP value by 0.5 or more. When the SP value is out of this range, since the compatibility with the film-forming resin (A) is large, the SP value stays inside the coating film during baking and does not float on the surface. Therefore, stain resistance and workability are reduced. The first curing agent can be chosen from amino resins, especially melamine resins. However, since this type of curing agent must not self-condense before rising to the surface in the coating, a difference in SP value of more than 0.5 with the film-forming resin (A) and a self-condensation In consideration of the properties, a melamine resin which is etherified with an i-butyl group or an n-butyl group alone or with a butyl group and a methyl group is preferred.

Commercially available melamine resins satisfying the above conditions include the following.

Alkoxy group, mol% SP value Product name Methoxy 60 / i-butoxy 40 10.5 Cymel 238 (Mitsui Cytec) Methoxy 60 / Butoxy 40 10.5 Cymel 235 (same as above) Methoxy 65 / Butoxy 35 10.4 Cymel 232 (same as above) Methoxy 40 / Butoxy 60 10.1 Cymel 236 (same as above) Methoxy 70 / Butoxy 30 10.6 Cymel 266 (same as above) Same as above 10.6 Cymel 267 (same as above) Butoxy 100 9.5 Mycoat 506 (same as above) Same as above 10.0 Yuban 20SE (Mitsui Toatsu) Same as above 10.5 Uban 20N- 60 (same as above)

In addition to the above melamine resins, other amino resins satisfying the above-mentioned conditions, for example, benzoguanamine resins may be used.

(C) Second curing agent: The physical property that the second curing agent should have is that the SP value is greater than, equal to, or less than 0.5 less than that of the film-forming resin (A).
Accordingly, the SP value of the film-forming resin (A) may be less than 0.5, equal to or less than 0.5. When the SP value is out of this range, the initial effect is not exhibited due to low compatibility with the film-forming resin (A). Since the compatibility with the film-forming resin (A) is larger than that of the first curing agent (B), the resin stays inside the film at the time of baking, and works in a direction to make the crosslinking density uniform over the entire coating film.

Non-limiting examples of the second hardener (C) are etherified melamine resins and blocked isocyanate compounds.

As the etherified melamine resin, for example, Sumimar M40S (Sumitomo Chemical) has an SP value of 12.9, and the second curing agent is used in combination with the film-forming resin (A) having an SP value of 9.5 to 12. It can be used as (C).

Examples of the polyisocyanate compound include aliphatic diisocyanates such as hexamethylene diisocyanate (HMDI) and trimethylhexamethylene diisocyanate, alicyclic diisocyanates such as isophorone diisocyanate (IPDI), and fragrances such as xylylene diisocyanate (XDI). Aliphatic diisocyanates, tolylene diisocyanate (TDI), 4,4'-
Examples include aromatic diisocyanates such as diphenylmethane diisocyanate (MDI), dimers and trimers of these diisocyanate compounds, adducts with polyhydric alcohols such as trimethylolpropane, and water.

As the blocking agent, oximes such as methyl ethyl ketoxime, acetoxime, cyclohexanone oxime, acetophenone oxime and benzophenone oxime, phenols such as m-cresol and xylenol, methanol, ethanol, butanol, 2-
Alcohols such as ethylhexanol, cyclohexanol, ethylene glycol monoethyl ether, ε-
Lactams such as caprolactam, diethyl malonate,
There are diketones such as acetoacetate and mercaptans such as thiophenol.

The reaction initiation temperature of the blocked isocyanate is determined by the deblocking temperature of the blocking agent and is generally 1
It is preferably 50 ° C. or lower. Such blocking agents include methyl ethyl ketoxime (MEK oxime) and β-diketones. The use of the polyisocyanate compound blocked with these blocking agents accelerates the curing of the inside of the coating film, and contributes to the improvement of stain resistance.

According to a particularly preferred embodiment of the invention,
The combination of the first and second curing agents is such that the second curing agent (C) has a lower reaction initiation temperature than the first curing agent. As a result, the compatibility with the film-forming resin (A) is large, and the second curing agent (C) causes the interior of the coating film to start to cure before the surface due to dust, which causes Hard to happen. The reaction initiation temperature here is an inflection point of a curve obtained by plotting Er (relative dynamic elastic modulus) against temperature at a temperature rising rate of 3 ° C./min by DSA (dynamic, spring, analysis method). It means what was measured by reading.

(D) Organosilica sol: Organosilica sol is a colloidal solution in which isolated colloidal particles of amorphous silica are dispersed in an organic solvent. The sol generally contains 50% by weight or less of silica and has a particle size of up to 300 nm, but those usable in the present invention have a particle size of 100 nm or less, particularly 10 to 100 nm. These are available on the market.

(E) Acid catalyst: A known acid catalyst used when a polyester resin or a hydroxyl group-containing acrylic resin is crosslinked and cured with a melamine resin can be used.
Examples thereof include aromatic sulfonic acids such as dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid and p-toluenesulfonic acid, and aminotri (methylenephosphonic acid), 1-hydroxyethylidene-1,1-diphosphonic acid, ethylenediaminetetra (methylene). Phosphonic acid),
An organic phosphonic acid such as diethylenetriamine penta (methylenephosphonic acid).

(F) Amine compound: Since the acid catalyst (E) accelerates the crosslinking reaction even at room temperature, it is generally used in the form of ammonium salt or amine salt which dissociates at the baking temperature in the one-component coating composition. Is normal. In the present invention, in addition to selecting a curing agent that is difficult to be compatible with the film-forming resin as the first curing agent for floating the first curing agent (B) onto the coating film surface, the acid catalyst is neutralized. Or requires help by volatilization of blocking amines. Therefore, the amine compound that can be used must have a boiling point of 40 ° C. or higher and a baking temperature of the coating film or lower. Examples include b. p. 40-230 ° C, preferably b. p. 50
It is in the range of up to 150 ° C. When the boiling point of the amine compound is 40 ° C. or less, the acid catalyst (E) is volatilized before baking when the surface is thickened, so that the cross-linking density of the coating film surface portion cannot be increased and the staining property is deteriorated. . If the coating temperature is higher than the baking temperature, it will not volatilize and will remain in the coating film, thus similarly deteriorating the staining property.

As a specific example, propylamine (b.
p. 48 ° C.), diethylamine (bp 56 ° C.), diisopropylamine (bp 84 ° C.), triethylamine (bp 90 ° C.), 2- (dimethylamino) ethanol (bp 135 ° C.) , Cyclohexylamine (bp 135 ° C.), 2- (diethylamino) ethanol (bp 162 ° C.), butylamine (bp 7)
7 ° C.), aniline (bp 185 ° C.), N, N-dimethylaniline (bp 193 ° C.) and the like.

One of the features of the present invention in terms of blending the coating material is that 0.5 to 10 parts by weight of the first curing agent (B), preferably 100 parts by weight of the film-forming resin (A) as solid matter, is preferable. 2 to 7 parts by weight, and 10 to 50 parts by weight of the second curing agent (C),
Preferably, the amount is 20 to 40 parts by weight. In other words, the curing agent (C) is the main, and the curing agent (B) is the auxiliary curing agent. If this ratio is reversed, it becomes difficult to achieve a balance between stain resistance and hardness and workability.

The amount of the organosilica sol (D) compounded is 30 to 100 parts by weight per 100 parts by weight of the film-forming resin (A) as a solid content. This significantly improves hardness and chemical resistance (acid and alkali). However, if the amount is too large, the processability is reduced, so that it should be avoided. If the amount is too small, there is no effect of improving the hardness.

The amount of the acid catalyst (E) may be a usual amount, and may be 0.10 per 100 parts by weight of the solid content of the film-forming resin (A).
1 to 2.0 parts by weight, preferably 0.5 to 1.5 parts by weight. If it is less than 0.1 part by weight, the reaction of the first curing agent (B) does not proceed sufficiently and the stain resistance is lowered. Also 2.0
If it exceeds the amount by weight, the appearance of the coating film is abnormal (shrinkage) and the chemical resistance is deteriorated.

Another feature of the present invention in terms of compounding is the first
That is, the amine compound (F) is used in excess of the neutralization equivalent of the acid catalyst as an aid for floating the curing agent (B) onto the surface. Generally 5 to 20 times the neutralization equivalent, preferably 10 to 1.
5 times is blended. If it is less than 5 times, the surface concentration of the acid catalyst (E) will not be sufficient and the stain resistance will decrease. If it exceeds 20 times, the chemical resistance is lowered.

Coating Method and Coating Method When a blocked polyisocyanate compound is used as the second curing agent (B), it goes without saying that a tin-based catalyst such as dibutyltin oxide or dibutyltin dilaurate can be added.

The coating composition of the present invention is generally used in the form of being dissolved in an organic solvent. Examples of the organic solvent include toluene, xylene, Solvesso 100, Solvesso 15
0, ethyl acetate, butyl acetate, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, butanol, octanol, diacetone alcohol, carbitol acetate, methoxybutyl acetate, etc. can be selected in consideration of solubility and evaporation rate.

Depending on the purpose and use, titanium dioxide, carbon black, iron oxide, various baked pigments, coloring pigments such as cyanine green and cyanine blue, extender pigments such as calcium carbonate, clay and barium sulfate, aluminum powder, etc. It may contain conventional additives such as metal powder, delustering agent such as silica and alumina, defoaming agent, leveling agent, anti-sagging agent, ultraviolet absorber, surface modifier, dispersant, viscosity modifier, wax and the like. .

The pigment is dispersed with a dispersion resin to form a dispersion paste, to which a main resin, a curing agent, an amine, a catalyst, various additives and a solvent are added, and a machine such as a roller mill, a paint shaker, a pot mill, a disper or a bead mill. Is made into a paint.

The material is a galvanized steel plate, an alloyed galvanized steel plate, a zinc / aluminum plated steel plate, an aluminum plated steel plate, an aluminum plate, a stainless steel plate, a cold rolled steel plate and the like. It can be directly applied to the material, but after surface treatment such as zinc phosphate treatment or coating type chromate, especially for applications requiring corrosion resistance, epoxy resin primer, polyurethane modified epoxy resin primer, polyester resin primer etc. It is preferable to apply a primer in advance and apply the coating composition of the present invention in a two-coat, two-bake system.

For coating, a roll coater, an airless spray, an electrostatic spray, a curtain flow coater and other general coating methods can be used, but a roll coater is generally used. The baking temperature is the ultimate plate temperature of 190 ° C to 2
The temperature is generally 30 ° C., and the time is generally 30 to 70 seconds.

The PCM board using the coating composition of the present invention can be used for other purposes, of course, but it is also contaminated by the roof materials of buildings, wall materials, highway girder covers, tunnel interior materials, etc. It is particularly suitable for building materials used in outdoor environments where severe pollution by acid rain, exhaust gas, etc.).

In the following Production Examples and Examples, "parts" and "%" are based on weight unless otherwise specified.

Production Example 1 Production of Acrylic Resin A reactor equipped with a heating device, a stirrer and a reflux condenser was charged with 49 parts of xylene and 10 parts of cyclohexanone, heated to 115 ° C. with stirring, and held. A mixture of 100 parts of the indicated monomer and 4.5 parts of t-butylperoxy-2-ethylhexanoate was added dropwise from the dropping funnel over 3 hours. Keep at 115 ° C for 30 minutes after completion of dropping,
Subsequently, 0.5 part of t-butylperoxy-2-ethylhexanoate was added. After the addition, the mixture was further stirred at 115 ° C. for 2 hours to complete the reaction.

Monomer parts by weight Methyl methacrylate 36.7 Ethyl methacrylate 31.4 PCL FM-2 (Note) 31.9 Polymer properties Nonvolatile content (%) 64 OH value (mgKOH / g) 50 SP value 11. 5 Mn 5000 (Note) 2-hydroxyethyl methacrylate / ε-caprolactone (1: 2) added, manufactured by Daicel Chemical Industries, Ltd.

Production Example 2 Neopentyl glycol 20 was placed in a reactor equipped with a heating device, a stirrer, a reflux device, a water separator, a rectification column and a thermometer.
, 15 parts of 1,6-hexanediol, 6.5 parts of trimethylolpropane and 26 parts of ε-caprolactone were charged and heated to 100 ° C. After the raw materials were melted and allowed to be stirred, 0.02 parts of dibutyltin oxide and 57 parts of isophthalic acid were charged and the temperature was raised to 230 ° C.
However, the temperature was raised at a constant rate over 3 hours from 180 to 230 ° C. The generated condensed water was distilled out of the system. 23
After keeping the temperature at 0 ° C. for 1 hour, 5 parts of xylene was gradually added, and the reaction was switched to the reaction in the presence of a solvent. When the acid value of the resin reached 7.0, the reaction was terminated.
50 45 parts and xylene 23 parts were added to obtain a polyester resin. Non-volatile content 60%, SP value 10.7, OH value 5
0, number average molecular weight 4,000

Examples 1 to 4 Preparation Method of Paint 130 parts of titanium dioxide and 50 parts of resin (A) (as solid) were dispersed together with glass beads in an SG mill at 30 ° C. for 1.5 hours. The degree of dispersion was measured with a grain gauge and found to be 5 microns or less. Further, the remaining resin (A) 50
Parts and the rest of the components (B) to (F) were sequentially added in the amounts shown in Table 1, and after stirring with a disper, 3 parts of an antifoaming agent,
3 parts of wax was added, and the mixture was stirred again with a disper. In a system containing a blocked polyisocyanate, 0.2 parts of dibutyltin dilaurate was added.

Method for producing coated plate (1) Material: Zinc-plated steel plate having a thickness of 0.4 mm and treated with zinc phosphate (2) Primer: Polyester resin-based primer (Flexcoat P600 primer: Nippon Paint Co., Ltd.) dried Coating with a bar coater to a film thickness of 5 microns,
It was baked (achieved plate temperature 220 ° C., time 1 min). (3) Overcoating: The composition prepared above was applied and baked with a bar coater (attained plate temperature of 220 ° C., time of 1 min) to a dry film thickness of 20 μm.

Appearance of the coated plate according to the following test method,
Curability, hardness, workability, chemical resistance and stain resistance were tested and the results shown in Table 3 were obtained.

Comparative Examples 1 to 3 Paints were prepared in the same manner as in Examples 1 to 4 except that the formulation was changed as shown in Table 2, coated plates were prepared, and the same tests were conducted.
The results are shown in Table 3.

Test method Appearance: The presence or absence of shrinkage of the coating film and the smoothness were visually determined. ◎ Very good: ○ Good: × Poor Hardness: Pencil hardness according to JIS S-6006. Curability: Gauze impregnated with xylene is rubbed by reciprocating 100 times on a coated plate under a load of 1 kg, and the state of the coating film is examined. ○ No change: △ Partially dissolved: × Substrate exposed Workability: The coated plate was bent 180 °, and the minimum T number that did not cause cracks in the bent portion was recorded. For example, 2T means that two steel plates having the same thickness are sandwiched during bending. Chemical resistance: Acid resistance: The test piece is placed in a hydrochloric acid aqueous solution with a concentration of 5% at 20 ° C for 24
The coated surface after immersion for hours was visually evaluated. ○ No abnormalities: × blistering generated Alkali resistance: The coated surface after immersing the test piece in a 5% aqueous sodium hydroxide solution at 20 ° C. for 24 hours was visually evaluated. ○ No abnormality: × blister generated Contamination resistance: Magic ink: Draw a line on the coated plate with oil-based magic ink (red) using a felt-tip pen, dry at room temperature for 24 hours, and wipe with a pad soaked with ethanol to remove traces. Examined. ○ No trace: △ Slight trace: × Trace large Carbon: 10% carbon black aqueous dispersion about 2 on coated plate
The mixture is dried at 80 ° C. for 24 hours, wiped off with a pad soaked with water, and measured for color difference ΔE between a non-stained area and a stained area after wiping using a color difference meter. Dust: Yoshizawa et al., After contaminating the coating for 15 minutes by the accelerated A method described in Academic Lectures, 1995, pp. 203-206 of the Japan Society for Architectural Finishing, washed with water, and measured the color difference ΔE from the initial value. Natural raindrop: The coating film was exposed to natural rainfall for three months, contaminated, rinsed with water, and the color difference change ΔE from the initial value was measured.

[0052]

[Table 1]

[0053]

[Table 2]

[0054]

[Table 3]

(Note 1) Type of component (B) Cymel 238: Methoxy / isobutoxy = 60/40 alkyl etherified melamine resin manufactured by Mitsui Cytec Co., Ltd. Cymel 232: Methoxy / butoxy = 65/35 alkyl ether manufactured by Mitsui Cytec. Melamine resin Uvan 20SE: Mitsui Toatsu's butyl etherified melamine resin (Note 2) (C) Component type Desmodur TPL2062: Sumitomo Bayer Urethane's diethyl malonate block HMDI cyanurate Sumimar M40S: Sumitomo Chemical's alkyl etherification Melamine resin (Note 3) (E) Component type Catalyst 6000: Dodecyl benzene sulfonic acid type catalyst manufactured by Mitsui Toatsu

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication C09D 161/32 PHK C09D 161/32 PHK 167/02 PLB 167/02 PLB 175/04 PHM 175/04 PHM

Claims (12)

[Claims] 1. (A) a hydroxyl group-containing film-forming resin having a hydroxyl value of 5 to 100; and (B) a film-forming resin (A) 10 as a solid content.
0.5-10 parts by weight per 0 parts by weight of a first curing agent having a solubility parameter value smaller than that of the film-forming resin (A) by 0.5 or more; and (C) a solid content of the film-forming resin (A). ) 10
10 to 50 parts by weight per 0 parts by weight of a second curing agent having a solubility parameter value greater than or equal to or less than 0.5 than the film-forming resin (A), and (D) the film as solid content. Formable resin (A) 10
30 to 100 parts by weight of organosilica sol per 0 parts by weight, and (E) the film-forming resin (A) 10 as a solid content.
0.1 to 2.0 parts by weight per 0 parts by weight of an acid catalyst that promotes the reaction between the film-forming resin (A) and the first curing agent (B), and (F) the acid catalyst ( A coating composition for a precoated metal, which contains as an essential component a volatile amine compound having a boiling point of 40 ° C. or higher and a baking temperature of the composition or lower, which is in excess of the neutralization equivalent of E). 2. The organosilica sol has a particle size of 10 to 10.
The coating composition according to claim 1, which has a thickness of 100 nm. 3. The coating composition according to claim 1, wherein the film-forming resin (A) has a hydroxyl value of 10 to 60. 4. The coating composition according to claim 1, wherein the film-forming resin (A) is a hydroxyl group-containing acrylic resin or polyester resin. 5. The solubility parameter value of the acrylic resin or polyester resin is 9.5 to 12.
Coating composition. 6. The coating composition according to claim 1, wherein the first curing agent (B) is an alkyl etherified amino resin. 7. The alkyl etherified amino resin is n-
The coating composition according to claim 6, which is a melamine resin etherified with a butyl group or an i-butyl group alone or with an n-butyl group or an i-butyl group and a methyl group. 8. The coating composition according to claim 1, wherein the second curing agent (C) has a lower reaction initiation temperature than the first curing agent. 9. The coating composition according to claim 8, wherein the second curing agent (C) is a blocked polyisocyanate compound or an etherified melamine resin. 10. The coating composition according to claim 1, wherein the acid catalyst (E) is an aromatic sulfonic acid or an organic phosphonic acid. 11. The coating composition according to claim 1, wherein the amine (F) is present in an amount of 5 to 20 times the neutralization equivalent of the acid catalyst (E). 12. A precoated metal steel sheet obtained by applying the coating composition according to any one of claims 1 to 11 to a steel sheet and baking and curing it.