JPH04320468A - Base coating resin composition - Google Patents

Abstract

PURPOSE:To obtain the title composition improved in adhesion to a recoated film of a clear coating material without detriment to the film properties of an acrylic coating material by mixing a specified acrylic copolymer with a curing agent. CONSTITUTION:A monomer having a prim. hydroxyl group and a sec. hydroxyl group is copolymerized with a monomer copolymerizable therewith in the presence of a polymerization initiator and optionally a chain transfer agent to obtain an acrylic copolymer (A) having a hydroxyl value of 30-100kOHmg/g, a ratio of the prim, hydroxyl groups to the sec. hydroxyl groups of (80-20)/(20-80) (in terms of a ratio between hydroxyl values), an acid value of 3-25kOHmg/g, a number-average molecular weight of 5000-20000 and a glass transition temperature of -20 to 50 deg.C. 50-95wt.% component A is mixed with 5-50wt.% curing agent selected from among an amino resin, an isocyanate prepolymer, a blocked polyisocyanate, a silane coupling agent and an aluminum chelate curing agent, and a resin, a coloring agent, a surfactant, a flow controlling agent, etc., are optionally added to the obtained mixture.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to coating compositions for automobiles, which require cosmetic properties and long-term weather resistance. More specifically, when forming a paint film using a two-coat, one-bake method using a base coat paint containing colorants such as metallic powder and colored pigments and a clear paint,
The present invention relates to a paint resin composition for base coats that is suitable for use as a base coat paint and has excellent recoat adhesion with clear paints.

0002

BACKGROUND OF THE INVENTION Acrylic paint compositions are used for painting automobile bodies because of their excellent physical properties, particularly gloss, weather resistance, chemical resistance, and stain resistance.

0003

[Problems to be Solved by the Invention] However, conventional acrylic coating compositions have the following problems, and improvement thereof has been desired. That is, when completely repairing paint film defects that occur when painting a new car, there is a problem in that recoat adhesion with clear paint is poor. The present invention was completed as a result of intensive studies to solve these conventional problems, and an object of the present invention is to provide a clear paint composition without losing the original good film performance of the acrylic paint composition. An object of the present invention is to provide a base coat paint with improved recoat adhesion to the base coat paint.

0004

[Means for Solving the Problems] That is, the present invention provides a base coat paint for use in a coating system in which a base coat paint containing a colorant is applied, a clear paint is then overcoated, and the coating film is obtained by heating and curing the base coat paint. The base coat paint has a hydroxyl value of 30 to 100 KOHmg/g, and the ratio of primary hydroxyl groups to secondary hydroxyl groups is 80/20 to 20/80 in terms of hydroxyl value ratio, and has an acid value of 3 to 25 K.
Acrylic copolymer (A) with OHmg/g 50-9
5% by weight of the curing agent (B) and 5 to 50% by weight of the curing agent (B).

In the acrylic copolymer (A) used in the base coat coating composition of the present invention, among the monomers having a hydroxyl group, examples of monomers having a primary hydroxyl group include 2-hydroxyethyl (meth)acrylate. , 3-hydroxypropyl (meth)acrylate,
4-hydroxybutyl (meth)acrylate, adduct of ε-caprolactone and 2-hydroxyethyl (meth)acrylate (Plaxel F series; trade name manufactured by Daicel Chemical Industries, Ltd.), adduct of ethylene oxide and methacrylic acid ( Examples include the Blenmar PE series (trade name, manufactured by Nippon Oil & Fats Co., Ltd.). Note that, for example, 2-hydroxyethyl (meth)acrylate refers to 2-hydroxyethyl methacrylate and 2-hydroxyethyl acrylate. As a monomer having a secondary hydroxyl group, 2
Examples include -hydroxypropyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and adducts of propylene glycol and methacrylic acid (Blenmar PP series; trade name, manufactured by NOF Corporation). In addition, 1
The monomers having primary and secondary hydroxyl groups are
More than one species can be used. In the present invention, preferred examples of monomers having acid groups used in the acrylic copolymer (a) include acrylic acid and methacrylic acid, and further examples include maleic acid, maleic anhydride, itaconic acid, and their like. Examples include monoesterified products, and one or more of these can be used.

Examples of copolymerizable monomers include:
Methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate,
tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, stearyl (meth)acrylate, tridecyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, phenyl (meth)acrylate, dimethylaminoethyl Acrylic acid and methacrylic acid esters such as (meth)acrylate and diethylaminoethyl (meth)acrylate can be used. Other copolymerizable monomers include, for example, styrene, α-methylstyrene, vinyltoluene, acrylonitrile, methacrylnitrile, vinyl acetate, vinyl propionate, acrylamide, methacrylamide, methylolacrylamide, methylolmethacrylamide, vinyl chloride, propylene , ethylene, C4 to C20 α-olefins, and the like.

The hydroxyl group-containing monomer has a hydroxyl value of 30 to 100 KOHmg/acrylic copolymer (a).
Adjust the amount to be used within the range of g. Hydroxyl value is 3
When the acid value is less than 0 KOHmg/g, the curability is insufficient and solvent resistance is poor, and when the acid value exceeds 100 KOHmg/g, the water resistance of the coating film decreases. In addition, the hydroxyl value is resin 1
It is expressed in mg of KOH required to neutralize g, and the unit is KOHmg/g. In addition, in the monomers having hydroxyl groups, the usage ratio of the monomers having primary hydroxyl groups to the monomers having secondary hydroxyl groups is adjusted so that the ratio of the hydroxyl values is in the range of 80/20 to 20/80. Prepare. If the hydroxyl value ratio of primary hydroxyl groups exceeds 80, recoat adhesion with the clear paint will be poor, and if the ratio is less than 20, curing properties will be insufficient and solvent resistance will be poor. The amount of the monomer having an acid group is adjusted so that the acid value of the acrylic copolymer (a) is in the range of 3 to 25 KOHmg/g. When the acid value is less than 3KOHmg/g, curing properties are insufficient and solvent resistance is poor;
If it exceeds g, the water resistance of the coating film will decrease.

Acrylic copolymer (a) can be synthesized by conventional methods, such as solution polymerization method, suspension polymerization method,
It can be produced by any known polymerization method such as bulk polymerization or emulsion polymerization. At that time, as a polymerization initiator,
For example, azobisisobutyronitrile, 4,4'-azobis(4-cyanopentaic acid), benzoyl peroxide, t-butylperoxy-2-ethylhexanoate,
Cumene hydroperoxide, potassium persulfate, hydrogen peroxide, 2,2'-azobis[2-methyl-
N-(2-hydroxyethyl)propioamide], etc. can be used, and if necessary, as a chain transfer agent,
Dodecyl mercaptan, mercaptoethanol, α-methylstyrene dimer, etc. can be used. In the present invention, the number average molecular weight of the acrylic copolymer (a) is preferably in the range of 5,000 to 20,000, and the glass transition temperature is preferably in the range of -20°C to 50°C. The base coat paint of the present invention contains a curing agent (B) in order to satisfy the above-mentioned quality performance in automotive paints and the like, which are the main uses of the present invention.

As the curing agent (B), for example, amino resins, isocyanate prepolymers, blocked polyisocyanates, silane coupling agents, and aluminum chelate curing agents can be used. The amount of curing agent (B) used is
It is 5 to 50% by weight. If the amount of curing agent used is less than 5% by weight, the weather resistance, solvent resistance, water resistance, etc. of the coating film will be insufficient, and if it exceeds 50% by weight, the glossiness, metallic feel, physical performance, etc. of the coating film will be deteriorated. Poor overall chemical performance and undesirable. The amino resin is a resin synthesized from at least one of melamine, urea, benzoguanamine, glycoluril, etc., and formaldehyde. A part or all of which is alkyl etherified is used. When using an amino resin as a curing agent, an external catalyst such as paratoluenesulfonic acid, dodecylbenzenesulfonic acid, naphthalenesulfonic acid, or their amine neutralized products can be added to the base coating composition. .

[0010] The isocyanate prepolymer referred to in the present invention is a compound containing two or more free or blocked isocyanate groups in one molecule, and specifically,
Aliphatic isocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate and trimethylhexane diisocyanate, alicyclic diisocyanates such as isophorone diisocyanate and 4,4'-methylenebis(cyclohexyl isocyanate), aromatic compounds such as xylene diisocyanate and tolylene diisocyanate. Diisocyanates, polyhydric alcohol adducts such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, etc. to other isocyanates, adducts of low molecular weight polyester resins having functional groups that react with isocyanate groups, or water, etc. Examples include burettes, polymers of diisocyanates, and compounds in which the isocyanate groups of these compounds are blocked with known blocking agents such as lower monohydric alcohols and methyl ethyl ketoxime. Even when using isocyanate prepolymers, external catalysts such as dibutyltin dilaurate, triethylamine, etc. can be added. The base coating composition of the present invention basically consists of the above-mentioned acrylic copolymer (A) and curing agent (B), but in addition to these, it also includes the following: Resins other than acrylic resins, such as polyester resins, epoxy resins, and cellulose resins, can be included within a range that does not impair properties. Metallic and colored pigments used in base coat paints include, for example, aluminum flakes, copper bronze flakes, and mica. Coloring pigments include, for example, inorganic pigments, especially titanium dioxide, iron oxide, chromium oxide,
Examples of organic pigments include lead chromate and carbon black, and examples of organic pigments include phthalocyanine blue and phthalocyanine green. Further, the base coat coating composition can further contain conventional additives such as surfactants, flow control agents, thixotropic agents, microgels, ultraviolet absorbers, catalysts, and the like.

[0011] The base coat paint resin composition of the present invention includes:
It is manufactured by blending the above-mentioned components using a common blending method. When using it as a base paint, use various diluting solvents to make Food Cup No. by 4, 2
The viscosity at 0°C is adjusted to within the range of 10 to 20 seconds, and this is applied to the base material to a dry film thickness of 10 to 30 seconds.
Either apply directly to the base material so that the dry film thickness is 10 μm, or apply the primer coat on the base material in advance to a dry film thickness of 10 μm.
Paint so that the thickness is ~30 μm. Next, after being left at room temperature for several minutes, for example, an acrylic resin/amino resin or an acrylic resin/isocyanate prepolymer is used as a vehicle, and if necessary, an ultraviolet absorber, a light stabilizer,
A clear paint containing auxiliary additives such as anti-sagging agents is mixed with Ford Cup No. 1 using a diluting solvent. 20 by 4
The viscosity at °C was adjusted to be within the range of 13 to 40 seconds, and this was applied onto the base coating film to a dry film thickness of 20 to 50 seconds.
Apply multiple coats to a thickness of μm and leave at room temperature for several minutes. After that, when an amino resin is used as a curing agent, it is cured in a temperature range of 60°C to 180°C, and when an isocyanate prepolymer is used, it is cured in a temperature range of room temperature to 140°C for 10 to 40 minutes. let The base coat paint and clear paint may be applied using conventional methods such as brush painting, spray painting, dipping painting, or dipping, but spray painting gives an excellent appearance to the paint film. This is the preferred method. Examples of the spray coating method include an air atomization method, a bell atomization method, and the like.

0012

[Examples] In order to explain the present invention more specifically, Examples and Comparative Examples will be given below, but the present invention is not limited to these Examples. In addition, during the explanation "
Parts and percentages are by weight unless otherwise specified.

Reference Example 1 [Preparation of acrylic copolymers (a-1 to a-11)] After purging nitrogen into a four-necked flask equipped with a stirrer, thermometer, reflux condenser, and nitrogen inlet tube, the flask was 85 parts of xylene and 15 parts of n-butanol were added to 100
The temperature was raised to ℃. The raw materials shown in Table 1 were added dropwise thereto over 5 hours, and then held at 100°C for 6 hours to prepare an acrylic copolymer (a) having an acid group with a solid content of about 50% by weight. -1) to (a-11) were obtained.

[0014]

[Table 1]

Reference Example 2 [Adjustment of base coat paint] (2-1. Adjustment of metallic base coat paint) Table-1
180 parts of acrylic resin obtained in Yuban 20SE-
60 (butylated melamine resin, manufactured by Mitsui Toatsu Chemical Co., Ltd., solid content 60%) and 16.8 parts of aluminum paste 7160N (manufactured by Toyo Aluminum Co., Ltd.) were stirred and mixed using a stirrer. The base coat paint composition obtained above was diluted with the following mixed solvent and applied in a Ford Cup #4 for 13 seconds/25.
The viscosity was adjusted to ℃ to obtain a metallic base coat paint. Ethyl acetate
1
Part 5 Toluene

40 parts Solvesso #100 (manufactured by Esso)
35 copies
cell solve acetate
10 parts (2-2. Preparation of solid color base coat paint) A solid color base coat paint was blended as follows. Acrylic resin synthesized in Table 1 (solid content 50%)
60.7 parts Titanium oxide CR-90 (manufactured by Ishihara Sangyo Co., Ltd.)
52 parts Using the above formulation, use a paint shaker.
The pigment was dispersed for 1 hour. Furthermore, Yuban 20SE-60
21.7 parts of was added, diluted with the following mixed solvent, and the viscosity was adjusted to 13 seconds/25° C. using a Ford cup #4 to obtain a solid color base coat paint. toluene

60 parts Solvesso #100 (manufactured by Esso)
30 copies n-
butanol
10 copies

[0016]
Reference Example 3 (Preparation of clear coat paint) After purging nitrogen into a four-necked flask equipped with a stirrer, thermometer, reflux condenser, and nitrogen inlet tube, Solvesso #100 (manufactured by Esso, aromatic hydrocarbon, Boiling point 150-177℃)8
5 parts and 15 parts of n-butanol were added and heated to 100°C. Here, 30 parts of styrene, 24 parts of n-butyl methacrylate, 7 parts of 2-ethylhexyl methacrylate, 15 parts of 2-ethylhexyl acrylate, 21 parts of 2-hydroxyethyl methacrylate, 3 parts of methacrylic acid, and the polymerization initiator azobisisobutyronitrile. 3 parts were added dropwise over 5 hours and then maintained at 100° C. for 6 hours to obtain an acrylic resin with a solid content of about 50% by weight. 140 parts of this acrylic resin, Yuban 20SE-60 (
Butylated melamine resin; manufactured by Mitsui Toatsu Chemical Co., Ltd., solid content 60
%) 50 parts, and 0.2% by weight based on the resin solid content of Remix RL-4 (leveling agent, manufactured by Mitsui Toatsu Chemical Co., Ltd.)
Add Solvesso #100, 50 and stir with a stirrer.
diluted with a mixed solvent consisting of 50 parts of Solvesso #150 (manufactured by Esso) and 3 parts in a food cup #4.
The viscosity was adjusted to 0 seconds/25°C to obtain a clear coat paint.

Example 1 A metallic base coat paint was prepared using the acrylic copolymer (a-1) according to the method of Reference Example 2-1. Apply the above metallic base coat paint to a steel plate for automobile bodies that has been cationically electrodeposited and coated with intermediate paint and sanded. After setting for 3 minutes after painting, apply the clear coat paint of Reference Example 3 wet.・After on-wet painting and setting for 10 minutes, 140
A test plate was obtained by heating at ℃ for 20 minutes. The coating performance is shown in Table-2.
Shown below.

Example 2 A solid color base coat paint was prepared using the acrylic copolymer (a-2) by the method of Reference Example 2-2. Hereinafter, test plates were obtained using the same method as in Example 1. The coating performance is shown in Table-2.

Examples 3 and 4, Comparative Examples 1 to 6 Acrylic copolymers (a-3), (a-4), (a-6), (a-
A test plate was obtained in the same manner as in Example 1, except that 11) was changed. The coating performance is shown in Table-2.

Example 5, Comparative Example 7 Test plates were obtained in the same manner as in Example 2, except that the acrylic copolymers were changed to (a-5) and (a-8). The coating performance is shown in Table-2.

[0021] Performance evaluation was performed as follows. 1) Visual Appearance Those with excellent coating film appearance were rated ◎, and those with poor appearance were rated ×. 2) The coating surface was rubbed back and forth 50 times with gauze impregnated with solvent-resistant xylene, and then observed. Those with no traces were evaluated as ◎, those with some traces as ○, and those with traces as ×. 3) Water resistance The coating film was immersed in warm water at 50° C. for 48 hours and then observed. Those with no abnormality were evaluated as ◎, those with slight whitening were evaluated as ○, and those with significant whitening and blisters were evaluated as ×. 4) Recoat adhesion Apply base coat paint and clear paint wet-on-wet, set for 10 minutes, and heat at 140℃ for 2 hours.
On the coating film cured by heating for 0 minutes, the same base coat paint and clear coat paint were applied again in the same manner and cured by heating. After that, make 100 goblin stitches at 1mm intervals.
After cutting with a piece cutter, adhesiveness between the layers was evaluated by peeling off with cellophane tape. The number of closely adhered gobbles after the tape was peeled off was displayed.

[0022]

[Table 2]

[0023]

[Table 3]

[0024]

Effects of the Invention The coating film formed by the two-coat one-bake method using the base coat paint resin composition of the present invention has excellent visual appearance, solvent resistance, water resistance, and recoat adhesion. It is clear from Table-2.

Claims (4)

[Claims] Claim 1: A base coat paint used in a coating system in which a base coat paint containing a coloring agent is applied, a clear paint is then overcoated, and a paint film is obtained by heating and curing the base coat paint, wherein the base coat paint has a hydroxyl value of 30 to 30. 100
An acrylic copolymer ( A) 50-95% by weight and a curing agent (B)
A paint resin composition for base coat comprising 5 to 50% by weight. 2. The base coat coating resin composition according to claim 1, wherein the acrylic copolymer (A) has a number average molecular weight in the range of 5,000 to 20,000. 3. The paint resin composition for base coat according to claim 1, wherein the acrylic copolymer (A) has a glass transition temperature in the range of -20°C to 50°C. 4. The base coat coating resin composition according to claim 1, wherein the curing agent (B) is an amino resin, an isocyanate prepolymer, a blocked polyisocyanate, a silane coupling agent, or an aluminum chelate curing agent.