JPH078974B2 - Thermosetting solvent type coating composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to a clear coating composition for top coating, which is applied on a base coat by a wet-on-wet system.

More specifically, in the coating of automobile bodies, a clear coating composition in a coating system in which a base coat containing a coloring pigment and a metallic pigment is coated, and a clear top coat is coated on the base coat by a wet-on-wet method, and simultaneously baked. The present invention relates to a thermosetting solvent-based coating composition which is suitable for use in, and has excellent acid resistance, solvent resistance, water resistance, gas hole resistance, and coating film appearance.

[Conventional technology and its problems]

Strong demand for automotive paints includes high appearance quality and high durability.

In recent years, in order to satisfy these requirements, a two-coat system in which a clear coat is applied on a base coat containing a pigment is widely used. As a conventional clear coat paint,
Acrylic melamine-based thermosetting solvent-based paints are often used. However, acrylic melamine-based paints have not reached a sufficient level to meet the requirements for appearance quality mainly of gloss. In addition, resistance to acid rain is insufficient, rain spots are generated, and durability is also insufficient.

The urethane-based clear coat used in some parts has high appearance quality, but it is inconvenient to handle because it is a two-component type that requires a curing agent to be mixed immediately before use, and resistance to acid rain. It also has the drawback of lacking in terms of sex.

Acrylic powder samples that employ the curing reaction of acid groups and epoxy groups have also been tried, but they have drawbacks such as poor appearance quality and high baking temperature of 160 ° C or higher. There is.

Further, as disclosed in JP-A-56-24074, acrylic powder coatings use dicarboxylic acid as a curing agent component, but these have poor solvent solubility, and as solvent-based coatings, precipitates are present in the coating. There is a problem with the stability such as occurrence of, and it cannot be applied.

[Means for solving problems]

The present inventors have been keen on the fact that a clear coating composition for top coating applied on a base coat by a wet-on-wet method has not reached a sufficient level in terms of appearance quality and durability in the prior art. As a result of research, a thermosetting solvent-based coating composition using an acrylic copolymer having an acid group, an acrylic copolymer having an epoxy group and an amino resin has excellent appearance quality and excellent acid resistance and is acidic. Generation of rain stains due to rain is reduced, and durability such as scratches due to car wash brush is less likely to occur, solvent resistance, water resistance, resistance to gas holes, which is gasoline containing a small amount of methanol used as fuel, They have found that they are also excellent in weather resistance and various physical properties, and have reached the present invention.

That is, the present invention comprises the following components (a), (b) and (c), wherein the equivalent ratio of the acid group of (a) to the epoxy group of (b) is 1 / 0.5 to 0.5 / 1. And the amount of (c) relative to the total of (a), (b) and (c) is 1 to 20% by weight, which is a thermosetting solvent-based coating composition.

Component (a): α, β-monoethylenic monomer having an acid group, α, β-monoethylenic monomer having a hydroxyl group, and other copolymerizable α, β-monoethylenic monomer It has an acid value of 30 to 150 mg-KOH / g and a hydroxyl value of 5
An acrylic copolymer having 130 mg-KOH / g and a number average molecular weight of 3500 or more.

Component (b): composed of an α, β-monoethylenic monomer having an epoxy group and another copolymerizable α, β-monoethylenic monomer and having an epoxy equivalent of 200 to 1000 g / eq,
And an acrylic copolymer having a number average molecular weight of 5000 or less.

Component (c): amino resin.

In the present invention, as the α, β-monoethylenic monomer having an acid group used for the acrylic copolymer (a), acrylic acid and methacrylic acid can be exemplified as preferable ones,
Further, maleic acid, maleic anhydride, itaconic acid and monoesters thereof can be mentioned, and one or more of them can be used.

Further, as the α, β-monoethylenic monomer having a hydroxyl group, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, ε-caprolactone adduct of hydroxyethyl (meth) acrylate, Examples thereof include ethylene and propylene adducts of hydroxyethyl (meth) acrylate, and one or more of these may be used.

As the copolymerizable α, β-monoethylenic monomer,
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 ( Esters of acrylic acid and methacrylic acid such as (meth) acrylate and diethylaminoethyl (meth) acrylate can be used. Note that, for example, methyl (meth) acrylate means methyl methacrylate and methyl acrylate. Other copolymerizable α, β
-As the monoethylenic monomer, styrene, α-methylstyrene, vinyltoluene, acrylonitrile, methacrylnitrile, vinyl acetate, vinyl propionate, acrylamide, methacrylamide, methylol acrylamide, methylol methacrylamide, vinyl chloride, propylene, ethylene. , C _{4 to} C ₂₀ α-olefins, and the like.

In the present invention, a copolymer containing an α, β-monoethylenic monomer is referred to as an acrylic copolymer.

The use amount of the α, β-monoethylenic monomer having an acid group is limited so that the acrylic copolymer (a) has an acid value of 30 to 150. When the acid value is less than 30, the curability is insufficient and the solvent resistance is poor, and when the acid value is more than 150, the solubility in the solvent is poor and the stability of the paint such as a precipitate in the paint is poor, Not practical as a mold paint. The preferred acid value range is 50 to 120, more preferably 70 to 100. The acid value is the mg of KOH required to neutralize 1 g of resin.
It is expressed as a number and the unit is KOH mg / g.

The hydroxyl value of the acrylic copolymer (a) needs to be 5 or more. If the hydroxyl value is less than 5, the cross-linking reaction between the acrylic resin and the amino resin will be insufficient and the gasohol resistance of the coating film will be poor. The preferred hydroxyl value range is 5 to 130,
It is more preferably 5 to 100.

The number average molecular weight is measured by using GPC with polystyrene as a standard. The number average molecular weight needs to be 3500 or more, and if it is less than 3500, the solvent resistance is poor, and it is easy to get scratches with a brush when washing a car,
Also, the water resistance is poor, and the durability for maintaining good coating quality is poor. In addition, in wet-on-wet coating with the base coat, the base coat and the clear coat are mixed with each other, resulting in glossiness and inferior appearance of the coating film. A preferred number average molecular weight is more than 5000 and up to 20000, more preferably 5500.
The range is over 20,000.

The glass transition temperature of the acrylic copolymer (a) is preferably 50 ° C or lower, more preferably -20 ° C to 40 ° C.

The copolymer having an acid group needs to be an acrylic copolymer, and when another polymer such as a polyester resin having an acid group is used instead of the acrylic copolymer (a), However, it has poor acid resistance and is not practical because it causes rain stains due to acid rain.

The acrylic copolymer (a) can be synthesized by a conventional method and can be produced by any known polymerization method such as a solution polymerization method, a suspension polymerization method, a bulk polymerization method and an emulsion polymerization method. . At that time, as the polymerization initiator, azobisisobutyronitrile, 4,4′-azobis (4-cyanopentanoic acid), benzoyl peroxide, t-butylperoxy-2-
Ethyl hexanoate, cumene hydroperoxide, potassium persulfate, hydrogen peroxide, 2,2'-
Azobis [2-methyl-N- (2-hydroxyethyl)
Pyropioamide] and the like, and if necessary, dodecyl mercaptan, mercaptoethanol, α-methylstyrene dimer and the like can be used as a chain transfer agent.

Examples of the α, β-monoethylenic monomer having an epoxy group used in the acrylic copolymer (b) in the present invention include glycidyl methacrylate, glycidyl acrylate, methylglycidyl methacrylate, methylglycidyl acrylate, and allylglycidyl ether. . One or more of these may be used.

As the copolymerizable α, β-monoethylenic monomer, all of those exemplified as the copolymerizable α, β-monoethylenic monomer described in the section of the acrylic copolymer (a) are used. be able to. In addition, acrylic copolymer (b)
Can be synthesized by a conventional method in the same manner as the acrylic copolymer (a), and is produced by using the polymerization method described in the acrylic copolymer (a), a polymerization initiator, and, if necessary, a chain transfer agent. be able to.

The α, β-monoethylenic monomer having an epoxy group is
The amount used is limited so that the epoxy equivalent of the acrylic copolymer (b) is 200 to 100. If the epoxy equivalent exceeds 1000, the curability is insufficient and the solvent resistance is poor. If the epoxy equivalent is less than 200, the surface of the coating film will not be smooth,
The desired coating quality cannot be obtained. The epoxy equivalent is represented by the number of grams of resin per gram equivalent of epoxy group. The unit is g / eq.

The number average molecular weight of the acrylic copolymer (b) needs to be 5,000 or less. If it exceeds 5,000, the reaction does not proceed sufficiently during the curing reaction with the acrylic copolymer (a) during baking, resulting in poor solvent resistance. This is considered to be because the present invention uses an interpolymer crosslinking reaction composed of the acrylic copolymer (a) and the acrylic copolymer (b), that is, the acrylic copolymer (b). Has a number average molecular weight of 5000
It is presumed that when the value exceeds the above range, the viscosity of the uncured coating material increases remarkably in the initial stage of the crosslinking reaction, and the collision reaction frequency of the acid group and the epoxy group decreases in the subsequent crosslinking reaction. It is desirable that the number average molecular weight of the acrylic copolymer (b) is lower than that of the acrylic copolymer (a). The acrylic copolymer (b) is the acrylic copolymer (a)
Acts as a curing agent for.

The glass transition temperature of the acrylic copolymer (b) is preferably 50 ° C or lower, and more preferably -20 ° C to 40 ° C.

In the present invention, the crosslinking reaction at the time of baking the paint is mainly the reaction between the acid group of the acrylic copolymer (a) and the epoxy group of the acrylic copolymer (b), but the amino resin also undergoes the crosslinking reaction. Share That is, it is a curing agent component that reacts with the hydroxyl groups contained in the acrylic copolymer (a) and the hydroxyl groups generated by the reaction between the acid groups and the epoxy groups. Further speaking, a coating film having a high cross-linking density is formed mainly by the reaction from the early stage of the curing reaction with the hydroxyl group contained in the acrylic copolymer (a), and the resistance to low molecular substances such as gas holes is increased. It is presumed to act as an enhancing co-curing agent.

As the amino resin (c) in the present invention, melamine,
A resin synthesized from at least one of urea, benzoguanamine, glycoluril, etc. and formaldehyde, in which one or all of the methylol groups are alkyl etherified with a lower alcohol such as methanol, ethanol, prapanol, isopropanol, butanol, isobutanol. What is done is used.

In the present invention, the amino resin needs to be 1 to 20% by weight based on the total of the acrylic copolymer (a), the acrylic copolymer (b) and the amino resin (c). If it is less than 1% by weight, the cross-linking density of the cured coating film is not sufficient and the gas hole resistance is poor. If it exceeds 20% by weight, the acid resistance is poor.

It is necessary to prepare the paint so that the equivalent ratio of the acid groups of the acrylic copolymer (a) and the epoxy groups of the acrylic copolymer (b) is 1 / 0.5 to 0.5 / 1. In the range other than this, the coating film has poor solvent resistance and water resistance.

Examples of the solvent that can be used in the thermosetting solvent-based coating composition of the present invention include hexane, aliphatic hydrocarbons such as heptane, aromatic hydrocarbons such as toluene or xylene, and mainly aliphatic hydrocarbons. Petroleum fraction with various boiling points containing aromatic hydrocarbons, butyl acetate,
Ethylene glycol diacetator, esters such as 2-ethoxyethyl acetate, ketones such as acetone and methyl isobutyl ketone, and alcohols such as butyl alcohol can also be used. It is preferable that the amount of aliphatic hydrocarbons and aromatic hydrocarbons is 50% by weight or more.

The coating composition of the present invention was prepared by using an amino resin having an equivalent ratio of acid groups in the acrylic copolymer (a) to epoxy groups in the acrylic copolymer (b) of 1: 0.5 to 0.5: 1. It may be added by a conventional method so that (c) is 1 to 20% by weight of the total of (a), (b) and (c). In addition to the above acrylic copolymer (a) and acrylic copolymer (b) components, other conventional components such as organic montmorillonite, microgel, polyamide, and polyethylene wax may be used for viscosity modification, if necessary. Agents, silicones, surface preparation agents of acrylic organic polymers, ultraviolet absorbers, melamine resins, blocked isocyanate resins and the like may be added.
Furthermore, a small amount of pigment may be added to the clear coat to color it to the extent that the complete hiding property is not exhibited. The obtained clear coat composition is adjusted to have a predetermined viscosity by using an appropriate solvent as a diluent thinner. At that time, it is preferable to use 50% or more of aromatic and aliphatic hydrocarbon solvents.

As the coating composition for the base coat, all that can be used in automobile coating can be used. The base coat coating composition contains a resin and a pigment that is a colorant, and useful resin compositions include acrylic-melamine-based, polyester (alkyd) -melamine-based, water-soluble acrylic-melamine-based and acrylic polyols and polyester polyols-polyethers. Valent isocyanate type, acrylic emulsion,
Examples include acrylic lacquer. Moreover, you may use the resin for clear coats of this invention as a resin composition for base coats.

Examples of the metallic pigments and coloring pigments used in the base coat coating composition include aluminum flakes, copper bronze flakes, and mica. Coloring pigments include, for example, inorganic pigments, especially titanium dioxide, iron oxide, chromium oxide, lead chromate and carbon black, and organic pigments include phthalocyanine blue and phthalocyanine green.

Further, the base coat coating composition may further contain usual additives such as a surfactant, a flow control agent, a thixotropic agent, a microgel, an ultraviolet absorber and a catalyst. Further, a cellulosic resin may be blended.

Typical examples of the method of using the coating composition of the present invention as a clear coat include the following methods.

After applying the base coat to the substrate, a flash time is set and a clear coat is applied. Since the flash time is left at room temperature for 1 to 10 minutes, an appropriate heating step at about 80 ° C. may be added. After the base coat and clear coat are applied to the object to be coated, the setting time of about 5 to 20 minutes is taken, and then the object to be coated is about 10 to 10 at about 100 to 180 ° C.
Bake for 60 minutes. The thickness of a general clear film is 20 to 60 μm.

As a method for applying the clear coat composition, a usual method such as brush coating, spray coating, dip coating and the like may be used, but spray coating is preferable because it gives an excellent coating film appearance. Examples of the spray coating method include an air atomization method and a bell atomization method.

〔Example〕

The following Reference Examples, Examples and Comparative Examples are for explaining the present invention, and in the description, "part" and "%" are based on weight.

Reference Example 1 (Preparation of Acrylic Copolymer (a) Having Acid Group) After purging nitrogen into a four-necked flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen inlet tube, Solvesso 100 ( Made by Esso, aromatic hydrocarbon, boiling point 150
(-177 ° C) 85 parts and n-butanol 15 parts were charged and heated to 100 ° C. The raw materials shown in Table 1 were added dropwise over 5 hours and then held at 100 ° C. for 6 hours to obtain an acrylic copolymer (a-1) having an acid group with a solid content of about 50%.
~ (A-8) were obtained.

Reference Example 2 (Preparation of Acrylic Copolymer (b) Having Epoxy Group) After purging nitrogen into the same reaction apparatus as used in Reference Example 1, Solvesso # 100 (manufactured by Esso, aromatic hydrocarbon) was placed in a flask. , Boiling point 150 to 177 ° C.), and heated to 140 ° C. The raw materials shown in Table 2 were added dropwise over 5 hours, and then held at 100 ° C for 6 hours. Then, 50 parts of Solvesso # 100 was heated under reduced pressure (0 to 30 mmHg) and distilled off. Then, acrylic copolymers (b-1) to (b-7) having an epoxy group with a solid content of about 50% were obtained.

Reference Example 3 (3-1. Preparation of Base Coat Paint) (3-1-1. Preparation of Metallic Base Coat Paint) 100 parts of xylene was charged in a 4-necked flask equipped with a stirrer, a thermometer, and a condenser, and the temperature was raised to 100 ° C. The temperature was raised by heating. A raw material consisting of 10 parts of styrene, 10 parts of methyl methacrylate, 30 parts of butyl acrylate, 35 parts of isobutyl acrylate, 12 parts of 2-hydroxymethacrylate, 3 parts of methacrylic acid and 2 parts of azobisbutyronitrile was mixed and mixed in 4 hours. The mixture was added dropwise over a period of time, and then the temperature was kept at the same temperature for 6 hours to obtain an acrylic resin having a solid content of about 50%. 180 parts of this acrylic resin, 37.5 parts of Uban 20SE-60 (butylated melamine resin, manufactured by Mitsui Toatsu Chemicals, Inc., solid content 60%), and 16.8 parts of aluminum paste 7160N (manufactured by Toyo Aluminum Co., Ltd.) were mixed by stirring with a stirrer. .

(3-1-2. Preparation of Metallic Base Coat Coating) A metallic base coat was blended as follows and stirred and mixed with a stirrer to obtain a base coat coating composition.

Acrylic copolymer (a-3) 107 produced in Reference Example 1
Part Acrylic copolymer (b-1) produced in Reference Example 2 30 parts U-Van 20SE-60 9.3 parts Aluminum paste 7160N (manufactured by Toyo Aluminum Co., Ltd.) 10.3
Parts The base coat coating composition obtained in (3-1-1) or (3-1-2) above was diluted with the following mixed solvent to Ford Cup # 4.
The viscosity was adjusted to 13 seconds / 25 ° C. to obtain a metallic base coat paint.

Ethyl acetate 15 parts Toluene 40 parts Soleveso # 100 (manufactured by Esso) 35 parts Cellosolve acetate 10 parts (3-2. Preparation of solid color base coating composition) Solid color base coating compositions were blended as follows.

For the base synthesized in (3-1-1) (acrylic resin (solid content 50%) 60.7 parts Titanium oxide CR-90 (manufactured by Ishihara Sangyo Co., Ltd.) 52 parts A pigment was dispersed for 1 hour by a paint shaker with the above composition. Further, 21.7 parts of U-Van 20SE-60 was added, diluted with the following mixed solvent and the viscosity was adjusted to 13 seconds / 25 ° C. with Ford Cup # 4 to obtain a solid color base coat paint.

Toluene 60 parts Solvesso # 100 (manufactured by Esso) 30 parts n-Butanol 10 parts Reference example (Preparation of clear coat paint) Clear coat paint was blended in the ratio shown in Table-3, and further 0.2% based on the resin solid content. REGIMIX RL-4 (manufactured by Mitsui Toatsu Kagaku Co., Ltd.) is added and stirred with a stirrer,
Dilute with a mixed solvent consisting of 50 parts of Solvesso # 100 and 50 parts of Solvesso # 150 (manufactured by Esso) and use Ford Cup # 4.
The viscosity was adjusted to 30 seconds / 25 ° C to obtain a clear coat paint.

Example 1 Acrylic copolymer (a-1), acrylic copolymer (b-1) and amino resin (c) (Uvan 20N-6
0) was blended in the proportions shown in Table 3, and a clear coat paint was prepared by the method shown in Reference Example 4.

The metallic base coat paint prepared in (3-1-1) of Reference Example 3 was applied to a steel plate of an automobile body by a cationic electrodeposition paint, and the baked object was set by air spraying for 3 minutes after setting, and then the above-mentioned clear. Wet-on-wet coating and set for 10 minutes, then 140
A test plate was obtained by heating at 0 ° C for 20 minutes. Table 4 shows the clear film thickness and coating film performance.

Example 2, Example 5, Example 6, and Comparative Examples 1 to 4 In the same manner as in Example 1, coating materials were prepared in the proportions shown in Table 3, and test plates were obtained by the same method.

Example 3 In the same manner as in Example 1, a clear coat paint was prepared in the proportions shown in Table-3.

The solid color base coat paint prepared in (3-2) of Reference Example 3 was applied to the same object as in Example 1 by air spraying, and after setting for 3 minutes, the above clear coat paint was wet-on-wet coated. After setting for 10 minutes, it was heated at 140 ° C. for 20 minutes to obtain a test plate. Table 4 shows the clear film thickness and coating film performance.

Example 4 In the same manner as in Example 1, a clear coat paint was prepared in the proportions shown in Table-3.

The same coating material as in Example 1 was coated with the metallic base coat paint prepared in (3-1-2) of Reference Example 3 in the same manner as in Example 3, and then the clear paint was applied by the same method and baked to give a test plate. Obtained. The clear film thickness and coating performance are shown in Table-
4 shows.

The performance evaluation was performed as follows.

1) Visual Appearance The excellent appearance of the coating film was marked with ⊚, and the poor appearance was marked with x.

2) Acid resistant 40 vol% H ₂ SO ₄ was dropped on the coating film, left standing at 50 ° C. for 5 hours, and wiped and observed. Those with no trace were evaluated as ⊚, and those with a trace were evaluated as x.

3) Solvent resistance The surface of the coating film was rubbed 50 times with gauze impregnated with xylene and then observed. Those with no traces were evaluated as ⊚, those with some traces as ○, and those with traces as ×.

4) Gas hole resistance Gasoline containing 50 vol% methanol is coated at room temperature for 2 days.
The coating film after being immersed for a period of time was observed. The case where the coating film had no abnormality was marked with ⊚, and the case where the coating film was swollen and cracked was marked with x.

5) Scratch resistance The coating film surface was reciprocated 1000 times with a car wash brush, and the coating film after cleaning was observed. Those with no trace were evaluated as ⊚, those with some traces were evaluated as Δ, and those with traces were evaluated as x.

6) Weather resistance After being tested for 3000 hours with a sunshine weather meter, the retention rate of gloss was displayed.

Claims (1)

[Claims] 1. A composition comprising the following components (a), (b) and (c), wherein the equivalent ratio of the acid group of (a) to the epoxy group of (b) is 1 / 0.5 to 0.5 / 1, And the thermosetting solvent type coating composition, wherein the amount of (c) is 1 to 20% by weight based on the total of (a), (b) and (c). Component (a): α, β-monoethylenic monomer having an acid group, α, β-monoethylenic monomer having a hydroxyl group, and other copolymerizable α, β-monoethylenic monomer It has an acid value of 30 to 150 mg-KOH / g and a hydroxyl value of 5
An acrylic copolymer having 130 mg-KOH / g and a number average molecular weight of 3500 or more. Component (b): composed of an α, β-monoethylenic monomer having an epoxy group and another copolymerizable α, β-monoethylenic monomer and having an epoxy equivalent of 200 to 1000 g / eq,
And an acrylic copolymer having a number average molecular weight of 5000 or less. Component (c): amino resin.