JPH10292148A - Chipping-resistant coating composition, and formation of coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a chipping-resistant coating composition capable of forming chipping-resistant primer layers good in coating appearance and chipping resistance, and excellent in water-resistant secondary adhesivity. SOLUTION: This chipping resistant coating composition contains 80-10 pts.wt. of a polyolefin-modified resin having a hydroxyl group value of 10-200 and a number-average mol.wt. of 10,000-100,000, 20-90 pts.wt. of a curing agent, an epoxy resin in an amount of 1-35 pts.wt. per 100 pts.wt. of the total amount of the polyolefin-modified resin and the curing agent, and a pigment in an amount of 1-50 wt.% based on PWC, wherein PWC is a concentration expressed by the formula: [pigment(g) ÷ (pigment(g) + resin solid content(g) × 100]%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a chipping-resistant coating composition and a method for forming a coating film using the coating composition.

[0002]

2. Description of the Related Art When a vehicle is running, a small stone or the like collides with a coating film applied to an outer panel of an automobile body, causing cracks or peeling of the coating film. It is known that a phenomenon called chipping occurs. When such chipping occurs, water or the like enters from this portion, and rust is generated on the outer surface of the vehicle body outer panel.

[0003] Particularly, in a cold region, a large amount of salt and sand is sprayed on a road surface for melting snow in winter.
There is a demand for a coating film having excellent chipping resistance because pebbles and the like easily collide with the coating film of an automobile outer panel.

As a method for imparting chipping resistance to a coating film, a method of forming a chipping-resistant primer layer is known. In general, a chemical conversion treatment is applied to the surface of the outer panel of an automobile body, an electrodeposition coating is formed thereon as an undercoat, a chipping-resistant primer layer is formed, and an intermediate coat and a top coat are sequentially applied thereon. doing.

[0005] Generally, chipping often occurs due to peeling of the coating film between the intermediate coating layer and the electrodeposition coating film. Therefore, as a chipping resistant primer,
Those having adhesiveness to the electrodeposition coating film and the intermediate coating layer and having elasticity are preferred. From such a viewpoint, a modified polyolefin-based resin such as a chlorinated polyolefin-based resin has been conventionally used as a chipping-resistant primer. However, the modified polyolefin-based resin has a problem that the solvent solubility is poor and therefore a large amount of solvent must be used. Also, because of poor solvent solubility,
There is also a problem that dust tends to be generated at the time of coating and the appearance of the coating film is not good. Furthermore, because of poor solvent solubility,
There was a problem with the cleanability of the pipes and painting machines in the painting line.

As an alternative to such a modified polyolefin-based chipping-resistant primer, Japanese Patent Publication No.
36995 and the like propose a coating composition containing a polyhydroxy compound and a blocked isocyanate as main components. Although these coating compositions give a good appearance of the coating film, the chipping resistance is insufficient, and the intermediate coating layer is applied thereon without curing the chipping-resistant primer layer to form a primer layer. There has been a problem in the coating workability in a so-called wet-on-wet system in which the intermediate coating layer is simultaneously cured.

[0007] Further, it has been conventionally required that a chipping-resistant primer be capable of forming a coating film having good adhesion after immersion of the coating film in warm water, that is, a so-called water-resistant secondary adhesion.

An object of the present invention is to provide a chipping-resistant coating composition capable of forming a coating film having good coating appearance and chipping resistance and excellent water-resistant secondary adhesion, and a method for using the coating composition. To provide a coating film forming method.

[0009]

The chipping-resistant coating composition of the present invention comprises 20 to 99% by weight of a polyolefin macromer having an ethylenically unsaturated bond (A) and 80 to 1% by weight of an unsaturated compound (B). % Of the grafted hydroxyl value of 10 to 200, the number average molecular weight of 10,000 to 100,
80 to 10 parts by weight of the polyolefin-modified resin (I), 20 to 90 parts by weight of the curing agent (II), and 1 to 35 parts by weight based on 100 parts by weight of the total of the polyolefin-modified resin (I) and the curing agent (II) (1) epoxy resin (III) and 1 to 50% by weight of pigment (IV) as PWC.

Hereinafter, each component contained in the present invention will be described in detail. [Polyolefin-modified resin (I)] Hydroxyl value (OHV) of polyolefin-modified resin (I) used in the present invention
Is 10 to 200, preferably 20 to 100. If the hydroxyl value is too low, chipping resistance tends to be poor, and if the hydroxyl value is too high, water resistance tends to be poor. The number average molecular weight (Mn) is 10,000
0-100,000, preferably 20,000-
60,000. If the number average molecular weight is too low, the appearance of the coating film tends to be poor, and if the number average molecular weight is too high, the solvent solubility tends to be poor.

The acid value (AV) of the polyolefin-modified resin (I) is preferably from 0 to 100, more preferably from 0 to 70. If the acid value is too high, the water resistance tends to be poor.

The polyolefin-modified resin (I) used in the present invention contains 20 to 99% by weight, preferably 30 to 70% by weight, of the polyolefin-based macromer (A) having an ethylenically unsaturated bond, and the unsaturated compound (B). 80 ~
It is a resin to which 1% by weight, preferably 70 to 30% by weight is grafted. Polyolefin macromer (A)
Is too small, the chipping resistance and appearance deteriorate. On the other hand, if the content of the polyolefin-based macromer (A) is too large, the thermal cycling resistance tends to decrease.

Polyolefin Macromer (A) The polyolefin macromer (A) is, for example, a macromer obtained by reacting an ethylenically unsaturated group-containing monomer (b) with a hydroxyl group of a polyolefin (a) having hydroxyl groups at both ends. Can be mentioned.

As the polyolefin (a), for example,
Polyolefin resins such as polybutadiene, hydrogenated polybutadiene, polyisoprene, hydrogenated polyisoprene, and EPDM, and resins having hydroxyl groups at both ends can be given. The number average molecular weight (Mn) is 200
~ 5000, more preferably 500 ~ 40.
00.

Commercially available products of the above-mentioned hydroxyl group-containing polyolefins include the following. -Trade name "G-1000" (manufactured by Nippon Soda Co., Ltd.) .... alpha.,. Omega.-polybutadiene glycol Mn = about 1500-Trade name "G-2000" (manufactured by Nippon Soda Co., Ltd.) .... alpha.,. Omega.-polybutadiene glycol Mn = Approximately 2000-Trade name "G-3000" (manufactured by Nippon Soda Co., Ltd.) .... alpha.,. Omega.-polybutadiene glycol Mn = about 2900-Trade name "GI-1000" (manufactured by Nippon Soda Co., Ltd.) .... alpha.,. Omega.-hydrogenated Polybutadiene glycol Mn = about 1500-Trade name "GI-2000" (manufactured by Nippon Soda Co., Ltd.) .... alpha.,. Omega.-hydrogenated polybutadiene glycol Mn = about 2100-Trade name "GI-3000" (manufactured by Nippon Soda Co., Ltd.) ... α, ω-hydrogenated polybutadiene glycol Mn = about 3000 ・ Product name “R-15HT” (manufactured by Idemitsu Petrochemical Co., Ltd.)... α, ω-polybutadiene glycol Mn = about 12 0-Trade name "R-45HT" (made by Idemitsu Petrochemical Co., Ltd.) .... alpha.,. Omega.-polybutadiene glycol Mn = about 2800-Trade name "LIR-506" (made by Kuraray Co., Ltd.) ... polyisoprene pentaol Mn = about 25000 Examples of the ethylenically unsaturated group-containing monomer (b) include an acid anhydride containing an ethylenically unsaturated group. Such an acid anhydride reacts with the hydroxyl group of the polyolefin (a) by opening the acid anhydride ring.

The acid anhydride may be any compound having an ethylenically unsaturated bond at the same time, and examples thereof include maleic anhydride, itaconic anhydride and succinic anhydride. Of these, maleic anhydride is particularly preferred. Further, the reaction ratio between the polyolefin (a) having a hydroxyl group at both terminal groups and the acid anhydride is preferably polyolefin / anhydride = 5/5 to 8/2,
More preferably, it is 5/5 to 6/4.

Other examples of the ethylenically unsaturated group-containing monomer (b) include compounds having an ethylenically unsaturated group and a hydroxyl group. This compound can be reacted with the hydroxyl group of the polyolefin (a) via the diisocyanate compound (c). Examples of the monomer having an ethylenically unsaturated group and a hydroxyl group include a hydroxyl group-containing acrylic monomer.

The hydroxyl group-containing acrylic monomer is a monomer having a hydroxyl group and an acrylic group or a methacryl group, such as hydroxyethyl methacrylate (HEM).
A), hydroxyethyl acrylate (HEA), hydroxypropyl methacrylate (HPMA), hydroxypropyl acrylate (HPA), hydroxybutyl acrylate (HBA) and the like can be used. These can be used alone or in combination of two or more. Among these hydroxyl group-containing acrylic monomers,
Particularly preferably, hydroxyethyl (meth) acrylate is used.

As the diisocyanate compound (c),
The diisocyanate compounds listed in the curing agent (II) described below can be used. Of these diisocyanate compounds, isophorone diisocyanate is particularly preferred.

As described above, the polyolefin-based macromer (A) can be obtained, for example, by reacting the polyolefin (a), the diisocyanate compound (c), and the hydroxyl group-containing acrylic monomer (b). The order in which they are performed is not particularly limited. Preferably, the polyolefin (a) and the diisocyanate compound (c) are mixed and heated to react, and then the hydroxyl group-containing acrylic monomer (b) is mixed and heated to react.

The mixing ratio a / c of the polyolefin (a) and the diisocyanate compound (c) is -O expressed by a molar ratio.
H / -NCO is preferably from 8/2 to 4/6, more preferably from 7/3 to 4/6, and even more preferably about 5/5.
/ 5.

The mixing ratio c / b of the diisocyanate compound (c) and the hydroxyl group-containing acrylic monomer (b) is preferably from 6/4 to 2/8, more preferably from the molar ratio of -NCO / -OH. It is 6/4 to 3/7, and more preferably about 5/5.

Unsaturated Compound (B) The unsaturated compound (B) is selected from ethylenically unsaturated monomers (b-1), unsaturated acrylic resins (b-2), and unsaturated polyester resins (b-3). At least one compound selected from the group consisting of:

Examples of the ethylenically unsaturated monomer (b-1) include acrylic monomers.
Specifically, general acrylic monomers such as methyl acrylate, methyl methacrylate, acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, n-butyl acrylate, and n-butyl methacrylate can be used. These acrylic monomers may be used alone or as a mixture of two or more. Further, other monomers copolymerizable with these acrylic monomers such as styrene and vinyl acetate may be used in combination.

As the unsaturated acrylic resin (b-2),
Acid value (AV) is 0 to 200, more preferably 0 to 15
0, a hydroxyl value (OHV) of 10 to 300, more preferably 10 to 200, and a number average molecular weight (Mn).
Is from 1,000 to 50,000, more preferably from 2,000 to 50,000
5,000 and an iodine value of 0.5 to 100, more preferably 0.5 to 70.

These unsaturated acrylic resins (b-2)
Can be obtained by introducing an unsaturated bond into the acrylic resin. For example, by adding glycidyl methacrylate to a carboxylic acid group of an acrylic resin, by adding an acid anhydride having an unsaturated bond to a hydroxyl group of an acrylic resin, or a carboxylic acid having an unsaturated bond to an oxirane group of an acrylic resin. Can be obtained by adding

The unsaturated polyester resin (b-3) has an acid value (AV) of 0 to 200, more preferably 0 to 200.
And a hydroxyl value (OHV) of 10 to 300, more preferably 10 to 200, and a number average molecular weight (M
n) is from 1000 to 50,000, more preferably 100
It is preferably from 0 to 4000, and the iodine value is preferably from 0.5 to 100, more preferably from 0.5 to 70.

The unsaturated polyester resin (b-
3) can be obtained by a general method, for example,
It can be obtained by reacting a polyol compound with a polybasic acid compound having an unsaturated group.

[Curing Agent (II)] The curing agent (II) used in the present invention is not particularly limited as long as it is a compound capable of curing the polyolefin-modified resin (I). Isocyanates are used.

The isocyanate preferably has a number average molecular weight (Mn) of from 170 to 3,000, more preferably from 170 to 2,500. If the number average molecular weight is too high, the compatibility with the resin tends to be poor. The NCO equivalent is preferably from 50 to 750, more preferably from 50 to 600. If the NCO equivalent is too low, the chipping resistance tends to be poor, and if the NCO equivalent is too high, the curability tends to be poor.

The isocyanate may be a polyisocyanate such as an adduct type, a burette type or a nurate type of diisocyanate.
It is preferable that the CO group is blocked by a sealing agent such as alcohols, phenols, lactams, and oximes.

Examples of the diisocyanate compound include isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HMDI), tolylene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), and lysine diisocyanate. (LDI),
Hydrogenated MDI, hydrogenated TDI (HTDI), hydrogenated XD
I, diisocyanate compounds such as tetramethylene diisocyanate (TMDI) and dimer acid diisocyanate (DDI). These can be used alone or in combination of two or more.

Further, as a polyisocyanate compound,
Examples include a reaction product of hexamethylene diisocyanate and water, an adduct of xylylene diisocyanate and trimethylolpropane, and an adduct of tolylene diisocyanate and hexamethylene diisocyanate.

Examples of the blocked isocyanate compound include (i) a polyisocyanate such as hexamethylene diisocyanate, and (ii) a low molecular weight polyol such as ethylene glycol, propylene glycol, 1,3 butylene glycol, neopentyl glycol, and trimethylolpropane. The active isocyanate group of the polyisocyanate obtained by the addition reaction of the above is blocked with alcohols, oximes, lactams and the like. Specifically, polyhexamethylene diisocyanate obtained by blocking MEK oxime or ε-caprolactam, or polyhexamethylene diisocyanate / buret type polyisocyanate
Examples include those blocked with EK oxime or ε-caprolactam.

The mixing ratio of the polyolefin-modified resin (I) and the curing agent (II) is 8/2 to 1/9,
That is, the curing agent (II) is 20 to 90 parts by weight based on 80 to 10 parts by weight of the polyolefin-modified resin (I). More preferably, the mixing ratio is in the range of 7/3 to 2/8, that is, 30 to 80 parts by weight of the curing agent (II) to 70 to 20 parts by weight of the polyolefin-modified resin (I). If the blending ratio of the polyolefin-modified resin (I) is too large, the curability tends to decrease, and if the blending ratio of the polyolefin-modified resin (I) is too small, the appearance of the coating film tends to decrease.

[Epoxy Resin (III)] The epoxy resin used in the present invention is not particularly limited as long as it is a resin or compound having two or more epoxy groups in one molecule. For example, a phenol compound and epichlorohydrin Reaction product of polyhydric alcohol and epichlorohydrin, a reaction product of organic acid and epichlorohydrin, and a copolymer of glycidyl methacrylate and an unsaturated compound.

Particularly preferred epoxy resins include the following compounds synthesized from epichlorohydrin and bisphenol A.

[0038]

Embedded image

In the above structural formula, n represents the average degree of polymerization of the epoxy resin, and is preferably from 0 to 20, more preferably from 0 to 12, and even more preferably from 0.5 to 5. When the average degree of polymerization n exceeds 20, the adhesiveness tends to decrease.

The epoxy equivalent of the epoxy resin is 1
It is preferably from 50 to 6000, more preferably from 150 to 6000.
3500. If the epoxy equivalent is too large, the adhesion tends to decrease.

The mixing ratio of the epoxy resin (III) in the present invention is 1 to 35 parts by weight, preferably 1 to 30 parts by weight, based on 100 parts by weight of the total of the polyolefin-modified resin (I) and the curing agent (II). Parts by weight, more preferably 1 to 20 parts by weight, even more preferably 2 to 10 parts by weight. If the mixing ratio of the epoxy resin is too small, the adhesion tends to decrease, and if the mixing ratio is too high, the curability tends to decrease.

[Pigment (IV)] The pigment used in the present invention is not particularly limited, and pigments such as color pigments, extender pigments, flat pigments, brilliant materials, and mica can be used. Among them, as a general pigment used for the chipping primer layer, carbon black, titanium oxide or the like as a coloring pigment is particularly preferable, and an extender pigment can be added as necessary. The concentration of the pigment is preferably 1 to 50% by weight in PWC, more preferably 3 to 30% by weight. Here, the PWC is [pigment (g) ÷ (pigment (g) + resin solid content (g)) × 10
0] (%).

[Method for forming a coating film] The method for forming a coating film of the present invention is a method for forming a coating film using the above-mentioned chipping-resistant coating composition of the present invention for forming a primer layer. Forming a primer layer comprising the chipping-resistant coating composition of the present invention on the undercoat layer, and forming an intermediate coating layer thereon without curing the primer layer, The primer layer and the intermediate coating layer are simultaneously cured to form a primer layer having a tensile strength of 30 to 4
The method includes a step of forming a cured coating film having a thickness of 00 kg / cm ² and an elongation of 30 to 400%, and a step of forming and curing an overcoat layer on the intermediate coat layer.

Hereinafter, the coating film forming method of the present invention will be described in detail. Formation of primer layer in a coating film forming method of the primer layer present invention,
The above-mentioned chipping-resistant coating composition of the present invention is used. The coating of the primer layer can be performed by diluting with a solvent such that the coating composition of the present invention has an appropriate viscosity, and then spraying, coating or the like. Paint viscosity at the time of painting, for example,
It can be adjusted using a Ford cup.

As the coating machine, an air spray coating machine,
An airless spray coating machine and an atomization type coating machine such as an air atomization type or a rotary electrostatic coating machine can be used.

For example, the coating composition of the primer layer was prepared by using an arbitrary solvent to have a viscosity of 1 in a No. 3 Ford cup.
After diluting for 0 to 60 seconds, preferably 12 to 30 seconds, the film thickness after drying is 1 to 50 μm, preferably 4 to 50 μm.
Coating is performed so as to be in a range of 25 μm. The coating film of this primer layer, moderate time to be judged to have been dried by touch,
For example, after drying for about 1 minute or more, an intermediate coating film is applied in a usual process, and is applied at 60 to 200 ° C., preferably 80 to 160 ° C.
By baking together with the intermediate coating film at 5 ° C. for 5 to 60 minutes, preferably 10 to 40 minutes, a composite coating film can be formed.

Undercoat Layer In the method of forming a coating film of the present invention, the undercoat layer formed on the object to be coated is not particularly limited. To form an electrodeposition coating film. As the electrodeposition paint, any of an anionic resin and a cationic resin can be used.

The resin which is the main component of the electrodeposition paint can be roughly classified according to its structure. (1) Dry rubber or liquid rubber such as polybutadiene, and those having an epoxidized resin as a skeleton, for example, maleated (2) those having a fatty acid ester of a resinous polyol as a main skeleton, such as oil resin, maleated polybutadiene resin and amine epoxidized polybutadiene resin, and modified derivatives thereof, such as epoxy resin and esterified resin, and (3) alkyd resin And (4) a resin having an acrylic resin as a main skeleton.

When the resin for the electrodeposition coating material is an acidic resin, it is preferable to neutralize the resin with a base such as ammonia, an amine or an inorganic alkali and to dissolve or disperse the resin in water. In the case of a basic resin, it is preferable that the resin is neutralized with an acid such as acetic acid, lactic acid, boric acid, phosphoric acid or the like and dissolved or dispersed in water.

In the electrodeposition coating material, additives such as a crosslinking agent such as a melamine resin and a blocked isocyanate, a pigment, and a solvent can be appropriately compounded. Usually, the electrodeposition coating film is preferably formed such that the film thickness after baking is 10 to 40 μm. Before the electrodeposition coating, it is preferable to perform a normal chemical conversion treatment.

Intermediate layer As the intermediate coat used for the intermediate layer of the coating film forming method of the present invention, an alkyd resin-based, polyester resin-based, or acrylic resin-based paint can be used. The coating of the intermediate coating layer can be performed by a usual method, for example, an electrostatic coating method. The thickness of the intermediate coating film is from 20 to 6
About 0 μm is preferable.

In the method for forming a coating film of the present invention, an intermediate coating layer is formed on the primer layer without curing the primer layer.
The intermediate coating layer is formed by a so-called wet-on-wet method. Therefore, after drying to remove the solvent in the primer layer, an intermediate coating layer is formed on the primer layer. After forming the intermediate coating layer, the primer layer and the intermediate coating layer are simultaneously cured. Therefore, in the coating film forming method of the present invention, so-called two-coat one-bake coating is performed.

In the method for forming a coating film of the present invention, the primer layer and the intermediate coating layer are simultaneously cured by such two-coat / one-bake coating, and the primer layer has a tensile strength of 30 to 400 kg / cm ² , preferably 40 kg / cm ² . ~ 300k
g / cm ² , elongation 30 to 400, preferably 40 to 3
A cured coating film of 00% results. If the tensile strength is lower than this, the strength of the formed coating film decreases, and if it is higher than this, the bending resistance and flexibility decrease. On the other hand, when the elongation percentage is lower than this, the chipping property is lowered, and when it is higher than this, a problem occurs in the cooling / heating cycle resistance.

[0054] In the method of forming a coating film overcoat layer present invention, further forming an overcoat layer was cured on the coating layer in the above. A paint such as an acrylic resin-based paint, a polyester resin-based paint, or a fluororesin-based paint can be used for coating the overcoat layer. These resins may be any of an organic solvent type, an aqueous type, and a powder type.

[0055]

BEST MODE FOR CARRYING OUT THE INVENTION

Production Example 1 [Production of polyolefin-based macromer (A)] A 2-liter reaction vessel equipped with a thermometer, stirrer, cooling pipe, nitrogen introduction pipe, and dropping funnel has hydroxyl groups at both ends as shown in Table 1. Table 1 shows polyolefin and toluene.
The solution containing isophorone diisocyanate (IPDI) and toluene in the amounts shown in Table 1 was added dropwise over 1 hour, and the mixture was kept at 50 ° C. for 1 hour. Next, the temperature was raised to 85 ° C., and a solution containing the hydroxyethyl methacrylate (HEMA) and toluene in the amounts shown in Table 1 was added dropwise over 1 hour. Macromers (Ai) to (A-iii) were obtained.

[0056]

[Table 1]

Production Example 2 [Grafting of Polyolefin Macromer (A) and Acrylic Monomer] Obtained in Production Example 1 in a 300 ml reaction vessel equipped with a thermometer, a stirrer, a cooling pipe, a nitrogen introduction pipe, and a dropping funnel. The polyolefin-based macromers (Ai) to (A-iii) and toluene were charged in the amounts shown in Table 2, and the temperature was increased to 110 ° C.
A solution containing the other monomers shown in Table 2 in the amounts shown in Table 2 and containing 1.50 parts of t-butylperoxy-2-ethylhexanoate as an initiator was added dropwise over 3 hours. , 110 ° C for 30 minutes. Next, t-
Butyl peroxy-2-ethylhexanoate 0.5
And 5.0 parts of toluene were added dropwise over 30 minutes. 9 more
After continuing stirring for 0 minutes, the mixture was cooled, and polyolefin-modified acrylic resins (A-1) to (A-) obtained by grafting a polyolefin-based macromer (A) and an acrylic monomer.
4) was obtained.

[0058]

[Table 2]

Production Example 3 [Production of Blocked Isocyanate] 200 m equipped with a thermometer, a stirrer, a cooling pipe and a nitrogen introduction pipe
l, a polyisocyanate, a blocking agent, D
BTL was charged and heated and mixed at 110 ° C. for 2 hours to obtain a blocked isocyanate.

As the polyisocyanate, trade name “Sumidur N3500” (manufactured by Sumitomo Bayer Urethane Co., Ltd.)
In Table 3, it is simply referred to as "N-3500").
As a blocking agent, MEK oxime (indicated by “MEK” in Table 3) was used. The compounding amount was such that the blocking agent was about 1.2 times equivalent to the polyisocyanate. Specifically, "Sumijur N3500" 4
9.5 parts was reacted with 26.6 parts of MEK oxime. Dibutyltin dilaurate (DBTL)
0.60 parts were used.

Epoxy resin As the epoxy resin, trade name "Araldite GY-2"
50 "(manufactured by Ciba Geigy, n = 0, epoxy equivalent 18)
0-190 g / eq), trade name “Epotote YD-01
1 "(manufactured by Toto Kasei Co., Ltd., n = 2, epoxy equivalent 450 to 5)
00g / eq) and the trade name “Epotote YD-01
9 "(manufactured by Toto Kasei, n = 12, epoxy equivalent 2400
-3300 g / eq).

Examples 1 to 8 and Comparative Examples 1 and 2 (Preparation of paint) To 4.83 parts of carbon black (manufactured by Mitsubishi Chemical Corporation, trade name "MA-100") were added a polyolefin-modified acrylic resin (Table 3). I) 52.0 parts of toluene and 12.6 parts of toluene were mixed using a desktop SG mill, and carbon black as the pigment (IV) was dispersed to obtain a pigment-dispersed paste. Based on the obtained pigment dispersion paste, each of the polyolefin-modified acrylic resin (I) and the curing agent (II) shown in Table 3 so as to have a compounding ratio shown in Table 3
And epoxy resin (III) while stirring, and if necessary, a surface conditioner (trade name “DISPARON KS-273”)
N ", manufactured by Kusumoto Kasei Co., Ltd.) and crosslinked resin particles as a viscosity controlling agent,
2 was obtained.

(Formation of Coating Film) A cationic electrodeposition paint (trade name “Power Top U-50” manufactured by Nippon Paint Co., Ltd.) was applied to a 0.8 mm-thick dull steel sheet treated with zinc phosphate to a dry film thickness of about 0.8 mm. Electrodeposited so as to have a thickness of 25 μm.
Bake for 0 minutes. On the obtained electrodeposition coating film, apply the coating materials of Examples 1 to 8 and Comparative Examples 1 and 2 to a dry film thickness of 5 μm.
After spray-coating and setting for about 4 minutes, an intermediate coating (Nippon Paint Co., Ltd., trade name “Olga P-2”) is spray-coated so that the dry film thickness is about 40 μm, After setting for 140 minutes,
It was baked for 0 minutes to obtain an intermediate coated board.

After cooling, a top coat was applied on the intermediate coated board. As the overcoat paint, a metallic paint (manufactured by Nippon Paint Co., Ltd., trade name "Super Rack M-15")
5 Silver ”) to a dry film thickness of about 15 μm, and then wet-on-wet to form a clear paint (trade name“ Super Rack O-15 ”manufactured by Nippon Paint Co., Ltd.).
0 clear ") was applied to a dry film thickness of about 40 μm. After setting for about 7 minutes,
For a minute to obtain a laminated coating film. In order to evaluate the chipping resistance, the laminated coating film obtained as described above is further subjected to water polishing with a # 1000 sandpaper, followed by drying and wiping with petroleum benzene to form an overcoat. This was repeated twice, and a laminated coated plate on which three coating films were formed as a top coat (base / clear) was subjected to evaluation.

FIG. 1 is a sectional view showing the laminated coating film formed as described above. As shown in FIG. 1, an electrodeposition coating film 2 is formed on a steel sheet 1 on which a chemical conversion film as an object to be coated is formed, and a chipping-resistant primer layer 3 is formed on the electrodeposition coating film 2. Are formed. An intermediate coating layer 4 and an upper coating layer 5 are sequentially formed on the chipping-resistant primer layer 3.

About the obtained coating film, chipping resistance,
The appearance, the thermal cycle, and the water-resistant secondary adhesion were evaluated. The evaluation method is as follows. For the primer layer, the tensile strength and elongation of the cured coating film were measured.
The evaluation method is as follows.

(Evaluation Method) Using a chipping resistance gravure tester (manufactured by Suga Test Instruments Co., Ltd.), a test was performed under the following conditions. Size of stone: No. 7 crushed stone Quantity of stone: 50 g Distance: 35 cm Air pressure: 4.0 kg / cm ² Angle: 45 ° Test temperature: -20 ° C

The results of the chipping resistance test were visually evaluated in four stages as follows. A: No peeling after stepping stone test. ：: Peeling is slightly observed after the stepping stone test (peeling area is minute). Δ: Peeling occurs after the stepping stone test. X: A substance that remarkably peels off after a stepping stone test (a substance having a maximum peeling area).

The appearance was visually evaluated as follows. ：: No abnormality is observed in appearance (gloss, surface roughness). ：: The appearance (gloss, surface roughness) is slightly reduced, but no abnormality is observed after the top coat. Δ: The appearance (gloss, surface roughness) is reduced, and the appearance is reduced even after overcoating. ×: Appearance (gloss, surface roughness) is remarkably reduced, and appearance is remarkably reduced even after overcoating.

The change of the environmental temperature under the condition of the cooling and heating cycle was defined as one cycle, and after repeating this for at least 10 cycles, cracks on the surface of the coating film were visually observed and evaluated according to the following criteria. (−30 ° C. × 1 hour → room temperature × 30 minutes → 80 ° C. × 1 hour → room temperature × 30 minutes) = 1 cycle ：: No crack occurs at the end of the cooling / heating cycle. ×: Cracks occur at the end of the cooling / heating cycle.

The water-resistant secondary adhesion test piece was immersed in warm water at 40 ° C., left for 10 days, taken out, and subjected to an adhesion test within one hour.

The adhesion test was performed as follows.
First, holding the cutting edge of the cutter (NT cutter S type, A type or equivalent) at about 30 degrees with respect to the coating surface of the test piece, draw 11 parallel lines at 2 mm intervals to reach the substrate, and further, Eleven parallel lines at 2 mm intervals perpendicularly intersecting those parallel lines were drawn to form a grid on the coating film. An adhesive tape (Nichiban industrial cellophane tape) is uniformly pressed on the grid with a fingertip so as not to leave air bubbles, and immediately, one end of the adhesive tape is immediately held at about 45 degrees with respect to the painted surface. The tape was peeled off from the test piece by suddenly pulling at an angle of, and the coating film was peeled off.

Tensile strength and elongation of the primer layer A primer coating is applied to a polypropylene plate having a thickness of 3 mm so as to have a dry film thickness of 40 to 60 μm, set for about 20 minutes, and baked at 140 ° C. for 25 minutes. Dried. The effective part of the obtained coating film is 5cm in length x 1c in width.
m and cut off from a polypropylene plate to obtain a free film. This free film is pulled by a tensile tester (Toyo Baldwin Co., Ltd.
The elongation and tensile strength (tensile strength) were measured at a tensile speed of 10 mm / min in an environment of 20 ° C. under “Tensilon”. The above evaluation results are also shown in Table 3.

[0074]

[Table 3]

[0075] As the binder resin used in Comparative Example 3-6 Comparative Example 3-6 were prepared binder resin shown in Table 4 below. In addition, as shown in Table 4, the binder resins (A-6) and (A-8)
Ai and GI-1000, respectively, were used without grafting.

[0076]

[Table 4]

Using the binder resins (A-5) to (A-8) obtained as described above, a curing agent (II) and an epoxy resin (III) were mixed in the composition shown in Table 5, A paint for the primer layer was prepared in the same manner as in the above example. Using the obtained paint, on a tall steel plate as in the above example,
An electrodeposition coating film is formed, and a primer layer, an intermediate coating layer,
And the laminated coating film obtained by forming an overcoat layer was evaluated. Also for the obtained primer layer, the tensile strength and the elongation were measured in the same manner as in the above example. Table 5 shows the obtained results.

[0078]

[Table 5]

As is clear from Tables 3 and 5, Examples 1 to 8 using the chipping-resistant coating composition according to the present invention.
It can be seen that the coating film of Example 1 is excellent in chipping resistance and also excellent in appearance, cooling cycle, and secondary adhesion to water.

As is clear from Table 4, Comparative Example 5 is a comparative example using a binder resin (A-7) having a large amount of an acrylic resin component obtained by polymerizing a large amount of an unsaturated monomer with respect to a macromer. Using the same binder resin for the primer layer as in Comparative Example 5, a so-called two-coat two-bake coating was used to form a primer layer and an intermediate coating layer. That is,
After the primer layer was applied, baking was performed at 140 ° C. for 30 minutes, and then an intermediate coating was applied and set in the same manner as in the above example, and then baked at 140 ° C. for 30 minutes. As a result, the appearance was evaluated as ○. As is clear from this, the conventional acrylic resin-based primer layer does not provide a good coating appearance with two coats and one bake, whereas according to the present invention, two coats and one bake do not. A coating film having a good appearance can be obtained.

In the above-described embodiment, a so-called two-coat one-bake coating film in which a clear layer is formed on a base coat layer by a wet-on-wet method as an overcoat layer has been described, but the present invention is not limited to this. Instead, a one-coat / one-bake coating film that forms a solid coating film may be used.

[0082]

As described above, by using the chipping-resistant coating composition of the present invention, a chipping-resistant primer layer having good coating appearance and excellent chipping resistance can be formed.

Further, since the binder resin of the primer layer has excellent solvent solubility, the particle size of dust at the time of coating is reduced, the dust concealing property is improved, and the compatibility with the resin of the intermediate coating layer is improved to some extent. By suppressing, familiarization can be prevented. Thereby, wet-on-wet workability is improved.

Furthermore, the chipping-resistant coating composition of the present invention has an improved adhesive force by containing an epoxy resin, and therefore can form a chipping-resistant primer layer having excellent water-resistant secondary adhesion. it can.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a laminated coating film provided with a chipping-resistant primer layer in an example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Coated object 2 ... Electrodeposition coating film 3 ... Chipping resistant primer layer 4 ... Intercoat layer 5 ... Top coat layer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08F 299/00 C08F 299/00 C08G 18/63 C08G 18/63

Claims (7)

[Claims] 1. A hydroxyl value obtained by grafting 20 to 99% by weight of a polyolefin macromer having an ethylenically unsaturated bond (A) and 80 to 1% by weight of an unsaturated compound (B), and a number average molecular weight of 10 to 200. 10,000-100,
80 to 10 parts by weight of the polyolefin-modified resin (I), 20 to 90 parts by weight of the curing agent (II), and 1 to 35 parts by weight based on 100 parts by weight of the total of the polyolefin-modified resin (I) and the curing agent (II) A chipping-resistant coating composition, comprising: an epoxy resin (III), and 1 to 50% by weight of a pigment (IV) as a PWC. 2. The polyolefin-based macromer (A)
Is a macromer obtained by reacting an ethylenically unsaturated group-containing monomer (b) with a hydroxyl group of a polyolefin having hydroxyl groups at both ends (a). The chipping-resistant coating composition according to claim 1. 3. The chipping-resistant coating composition according to claim 2, wherein the ethylenically unsaturated group-containing monomer (b) is an acid anhydride containing an ethylenically unsaturated group. 4. The monomer (b) having an ethylenically unsaturated group and having an ethylenically unsaturated group and a hydroxyl group, and reacting with a hydroxyl group of the polyolefin (a) via a diisocyanate compound (c). The chipping-resistant coating composition according to claim 2. 5. The method according to claim 1, wherein the unsaturated compound (B) is at least one compound selected from the group consisting of ethylenically unsaturated monomers, unsaturated acrylic resins, and unsaturated polyester resins. The chipping-resistant coating composition according to claim 1. 6. The polyolefin-modified resin (I),
The chipping-resistant coating composition according to any one of claims 1 to 5, which is a polyolefin-modified acrylic resin. 7. A step of forming an undercoat layer on an object to be coated, and forming a primer layer comprising the chipping-resistant coating composition according to claim 1 on the undercoat layer. Performing a step of forming an intermediate coating layer thereon without curing the primer layer; simultaneously curing the primer layer and the intermediate coating layer to form a primer layer having a tensile strength of 30 to 400 kg /
A method for forming a coating film comprising: a step of forming a cured coating film having a cm ² and an elongation of 30 to 400%; and a step of forming and curing an overcoat layer on the intermediate coating layer.