JPH07188587A - Impact-resistant powder coating composition - Google Patents

Abstract

PURPOSE:To obtain a powder coating composition having excellent impact resistance, weather resistance, acid resistance, solvent resistance and hardness of coating film, containing an acrylic copolymer prepared by the polymerization of an epoxy group-containing monomer, a polyfunctional carboxylic acid and a specific graft copolymer. CONSTITUTION:This composition contains (A) an acrylic copolymer prepared by polymerizing an epoxy group-containing monomer (e.g. glycidyl methacrylate) and/or a copolymerizable monomer [e.g. methyl (meth)acrylate], (B) a polyfunctional carboxylic acid (e.g. adipic acid or dodecanedioic acid) and (C) a graft copolymer comprising a synthetic rubber obtained by polymerizing a diene monomer (e.g. butadiene or isoprene) and/or an unsaturated monomer (e.g. 2-ethylhexyl acrylate) as a core component and a vinyl polymer [e.g. a (co)polymer of hydroxyethyl (meth)acrylate, (meth)acrylic acid or styrene] as a shell component.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermosetting powder coating composition having excellent impact resistance and weather resistance.

[0002]

2. Description of the Related Art Recently, powder paints, which are non-dangerous and do not contain solvents due to organic solvent discharge during paint baking and work environment problems, and which are resource-saving features, are used in a wide range of fields. . As the above powder coating material, epoxy resin and polyester resin powder coating materials mainly containing bisphenol A have been put to practical use, but they have weather resistance and resistance to acid rain which has been a problem in recent years. Since it was inferior, there was a problem in outdoor use.

An acrylic powder coating (Japanese Patent Publication No. Sho 48-38617) has been proposed as a powder coating that overcomes the drawbacks. However, a problem with this powder coating is that it is not possible to obtain impact resistance equivalent to that of conventional polyester resin powder coatings.

[0004]

SUMMARY OF THE INVENTION The present invention is intended to solve such conventional problems as described above. That is, it is an object of the present invention to improve the weather resistance, which is a drawback of epoxy resin powder coatings and polyester powder coatings, and to provide an acrylic powder coating having impact resistance comparable to that of polyester powder coatings.

[0005]

Means for Solving the Problems As a result of intensive studies to solve the conventional drawbacks, the present inventors have found that a combination of an acrylic copolymer having an epoxy group and a polyvalent carboxylic acid has a core / shell structure. The inventors have found that the object can be achieved by modifying a graft copolymer having a structure, and arrived at the present invention. That is, the present invention is as follows. (A) An acrylic copolymer obtained by polymerizing a monomer having an epoxy group and / or a copolymerizable monomer, (b)
A synthetic rubber obtained by polymerizing a polycarboxylic acid, (c) a diene monomer and / or an unsaturated monomer is used as a core component,
A graft copolymer having a vinyl polymer as a shell component,
An impact resistant powder coating composition comprising:

Further, the present invention is a graft copolymer (c) comprising a rubber obtained by polymerizing a diene monomer and / or an unsaturated monomer as a core component and a vinyl polymer as a shell component. Content of the epoxy group-containing monomer and /
Alternatively, the impact resistant powder is 2 to 50 parts by weight based on 100 parts by weight of the total amount of the acrylic copolymer (a) obtained by polymerizing a copolymerizable monomer and the polyvalent carboxylic acid (b). It is a body coating composition.

In the present invention, examples of the epoxy group-containing monomer used in the acrylic copolymer (a) include glycidyl methacrylate, glycidyl acrylate, methylglycidyl methacrylate and methylglycidyl. Examples thereof include acrylate and acrylic glycidyl ether, and one or more of them can be used.

Other copolymerizable monomers include methyl (meth) acrylate and 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, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, 1,4-butanediol mono (meth) acrylate
, Acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid and their monoesters, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, and other acrylic acids and methacrylic acid Can be used.
In the above compounds, for example, methyl (meth) acrylate means methyl methacrylate and methyl acrylate. Other copolymerizable monomers include, for example, styrene, α-methylstyrene, vinyltoluene, acrylonitrile, methacrylonitrile,
Also included are vinyl acetate, vinyl propionate, acrylamide, methacrylamide, methylol acrylamide, methylol methacrylamide, vinyl chloride, ethylene, propylene, C ₄ -C ₂₀ α-olefins and the like.

From the problem that the low temperature curability at the time of baking the paint is not achieved and the curability is insufficient and the solvent resistance is lowered, and also the surface of the coating film is not smooth and it is difficult to obtain a preferable coating film appearance, The monomer having an epoxy group has an epoxy equivalent of the acrylic copolymer (a) of 200 to 1,000 g /
It is appropriate to limit the amount used so that it becomes eq. More preferable epoxy equivalent is 300 to 800 g /
eq. The above-mentioned epoxy equivalent is represented by the weight g of the resin per 1 g equivalent of the epoxy group. The unit is g / eq.

The effect of the storage stability of the paint on practicality,
Alternatively, the number average molecular weight of the acrylic copolymer (a) is 1,00 from the viewpoint of the influence on the smoothness of the coating film and the appearance quality due to the deterioration of the fluidity of the coating upon baking the coating.
Suitably it is between 0 and 10,000. The number average molecular weight of the acrylic copolymer was obtained by using GPC and using polystyrene as a standard.

From the same viewpoint, the glass transition point of the acrylic copolymer (a) is suitably 20 to 120 ° C., more preferably 40 to 110 ° C. The glass transition point of the acrylic copolymer can be obtained by the Fox equation.

The acrylic copolymer (a) can be synthesized by a conventional method and can be produced by any known polymerization method such as solution polymerization method, suspension polymerization method, bulk polymerization method and emulsion polymerization method. be able to.

Polycarboxylic acid (b) used in the present invention
Is a curing agent component for reacting with the epoxy group contained in the acrylic copolymer (a). Examples of the polycarboxylic acid include aliphatic dibasic acids such as adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecane diacid, dodecane diacid, tridecane diacid, tetradecane diacid, pentadecane diacid, and hexadecane. Examples thereof include diacid, octadecane diacid, eicosane diacid, docosane diacid, tetracosane diacid, and the like, and aromatic polyvalent carboxylic acids include isophthalic acid, trimellitic acid and the like, and alicyclic dibasic acid. Examples include hexahydrophthalic acid and tetrahydrophthalic acid. From the viewpoint of reducing the solvent resistance of the coating film, the amount of the polycarboxylic acid (b) used is 0.5: 1 to the equivalent ratio of the epoxy group and the acid group of the acrylic copolymer (a).
A ratio of 1: 0.5 is suitable.

The diene monomer used in the present invention includes
Butadiene and isoprene are typical. The unsaturated monomers used in the present invention include (1) alkyl acrylates such as 2-ethylhexyl acrylate, butyl acrylate, ethyl acrylate and methyl acrylate, and / or alkyl methacrylates such as methyl methacrylate and n-butyl methacrylate. Acrylates, (2) vinyl esters such as vinyl acetate, (3) vinyl halides and / or vinylidene halides such as vinyl chloride and vinylidene chloride, (4) unsaturated monomers such as acrylonitrile and acrylamide, (5) hydroxyethyl acrylate And hydroxymethacrylate, methylolacrylamide, methylolmethacrylamide and other hydroxyl group-containing unsaturated monomers, (6) acrylic acid, methacrylic acid, maleic anhydride, itaconic acid and other carboxylic acid group-containing unsaturated monomers (7) styrene, alpha-methyl styrene, and aromatic unsaturated monomers such as vinyl toluene. These unsaturated monomers may be used alone or in combination of two or more. As typical examples of synthetic rubbers obtained from these, polybutadiene, polyisoprene, polyacrylate rubber, polyvinyl chloride, styrene-butadiene copolymer, styrene-butadiene-styrene block copolymer, styrene-isoprene- Examples thereof include styrene copolymers and styrene-ethylene / butylene-styrene copolymers. Above all, polybutadiene, polyisoprene, styrene-butadiene copolymer, and polyacrylate rubber are preferable.

The core component and the shell component referred to in the present invention are
The core component is the name of the component forming the inner part, and the shell component is the name of the component forming the outer part, which are the respective components constituting the polymer having a so-called core-shell type morphology.

The vinyl polymer of the present invention is a polymer obtained by polymerizing one and / or two or more vinyl monomers. Vinyl-based monomers include (1) alkyl acrylates such as 2-ethylhexyl acrylate, butyl acrylate, ethyl acrylate, and methyl acrylate, and / or alkyl methacrylates such as methyl methacrylate and n-butyl methacrylate, and (2) acetic acid. Vinyl esters such as vinyl, (3) vinyl halides and / or vinylidene halides such as vinyl chloride and vinylidene chloride, (4) unsaturated monomers such as acrylonitrile and acrylamide, (5) hydroxyethyl acrylate and hydroxymethacrylate, methylol Hydroxyl group-containing unsaturated monomers such as acrylamide and methylol methacrylamide, (6) Carboxylic acid group-containing unsaturated monomers such as acrylic acid, methacrylic acid, maleic anhydride and itaconic acid, (7) Styrene, α- Methylstyrene, aromatic unsaturated monomers such as vinyl toluene and the like. Among these, particularly preferred are the above-mentioned (1) alkyl acrylate, alkyl methacrylate, (5) hydroxyl group-containing unsaturated monomer, (6) carboxylic acid group-containing unsaturated monomer, and (7) It is a homopolymer of an aromatic unsaturated monomer or a copolymer composed of a combination thereof.

The method for producing the graft copolymer (c) composed of the synthetic rubber and the vinyl polymer used in the present invention is not particularly limited and may be carried out by a conventional method. For example, there is a so-called emulsion polymerization method in which a synthetic rubber emulsion is preliminarily charged in a kettle and a vinyl monomer and a radical polymerization initiator are added thereto to perform polymerization.

From the viewpoint of impact resistance, hardness, and heat resistance deterioration, a synthetic rubber obtained by polymerizing a diene monomer and / or an unsaturated monomer is used as a core component, and a vinyl polymer is used as a shell component. The content of the graft copolymer (c) is
2 to 100 parts by weight of the total amount of the acrylic copolymer (a) obtained by polymerizing a monomer having an epoxy group and / or a copolymerizable monomer and the polyvalent carboxylic acid (b) 5
0 parts by weight is suitable. It is preferably 5 to 30 parts by weight.

To the thermosetting powder coating composition of the present invention, various resins such as epoxy resins, polyester resins, polyamides and other synthetic resins, or fibrin derivatives are blended to such an extent that the object of the present invention is not impaired. May be, in addition to the pigment,
Flow additives, antiblocking agents, ultraviolet absorbers, benzoin, antistatic agents, antioxidants and other commonly used coating additives may be added. Further, when used as a clear coat, a small amount of pigment may be added so that the pigment is colored to such an extent that the hiding property is not fully expressed.

Any known method can be used for producing the powder coating, but usually the above-mentioned acrylic copolymer (a), polyvalent carboxylic acid (b), diene monomer and A synthetic rubber obtained by polymerizing an unsaturated monomer is used as a core component and a graft copolymer (c) having a vinyl polymer as a shell component is mixed. Then, this may be sufficiently melt-mixed with a melt-kneader such as a heating roll or an extruder, cooled, and then pulverized into a powder coating material. Regarding the coating method, an object to be coated can be coated by a coating method such as an electrostatic coating method or a fluidized-bed method, and this can be baked in a baking oven to obtain a coating film.

[0021]

EXAMPLES The present invention will be described below with reference to Examples and Comparative Examples for more specific description, but the present invention is not limited to these Examples. In the description, "part" and "%" are by weight unless otherwise specified.

Production Examples 1 and 2 (Production of Acrylic Copolymer) 66.7 parts of xylene was placed in a 4-necked flask equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen introducing tube, and the temperature was raised to the reflux temperature. Warmed. Here, the monomers shown in Table 1 and N, N'- as a polymerization initiator
Azobisisobutyronitrile was added dropwise over 5 hours,
After that, the temperature was kept at 100 ° C. for 5 hours. An acrylic copolymer (Production Example 1 and Production Example 2) was obtained by removing the solvent of the obtained polymerization solution.

[0023]

[Table 1]

(Production of Graft Copolymer) Production Example 3 First, a polyacrylate rubber as a core component was prepared as follows. In the flask, 44.2 parts of water and 0.1 part of a surfactant (trade name Perex SS-L, manufactured by Kao),
A polymerization initiator, 0.2 parts of potassium persulfate, is charged. The temperature is maintained at 75 ° C under a nitrogen stream. Butyl acrylate 2
2.5 parts, acrylonitrile 15.8 parts, methacrylic acid 1.2 parts and a surfactant (trade name Perex SS-L,
A liquid previously emulsified with 0.3 part of Kao Corporation) and 15.7 parts of water was continuously added dropwise to the flask kept at 75 ° C. for 4 hours under a nitrogen stream to react. After that, the remaining monomer was polymerized for 3 hours, and the reaction solution was cooled to room temperature.
The resulting polyacrylic ester rubber had a solid content of 40% and a viscosity of 22 cps. Then, using this, the shell component was reacted as follows to prepare a graft copolymer. Latex 3 of polyacrylate rubber obtained above
A flask was charged with 8.0 parts of water, 32.0 parts of water and 0.2 part of a polymerization initiator potassium persulfate, and the temperature was adjusted to 7 under a nitrogen stream.
It was kept at 5 ° C. Next, with 8.0 parts of methyl methacrylate, 5.5 parts of styrene, 1.5 parts of acrylic acid, 0.3 part of a surfactant (trade name Perex SS-L, manufactured by Kao) and 14.5 parts of water. Pre-emulsified liquid in a nitrogen stream at 75 ° C
The reaction mixture was continuously added dropwise to the flask kept for 6 hours over 6 hours. After that, the remaining monomer is polymerized for 2 hours,
The reaction was cooled to room temperature. The resulting graft copolymer latex was coagulated, precipitated, filtered, dried, and dried to give a powder.

Examples 1 and 2 Acrylic copolymers (Production Examples 1 and 2), dodecane diacid, graft copolymers (Production Example 3) and titanium oxide are shown in Table 2.
It was compounded in the ratio shown in. This is melt-kneaded with a hot roll at 90 ° C., cooled, and then finely pulverized with a pulverizer to obtain
The sections that passed through the mesh screen were collected to obtain a powder coating. The powder coating thus obtained is applied onto a phosphoric acid treated steel plate by electrostatic spraying 60
After coating so as to have a film thickness of ˜70 μm, it was heated at 130 ° C. for 30 minutes to obtain a test plate. The performance evaluation results of the coating film are shown in Table-3.
Shown in.

Comparative Example 1 74.1 parts of a main component (ER-8105, manufactured by Unitika Ltd.) of a polyester powder coating, 5.9 parts of triglycidyl isocyanurate as a curing agent and 20.0 parts of titanium oxide were blended. . This was made into a powder coating material by the same method as in Example 1, coated on a phosphoric acid-treated steel plate by electrostatic spraying to a film thickness of 60 to 70 μm, and then heated at 200 ° C. for 20 minutes to obtain a test plate. The results of performance evaluation of the coating film are shown in Table 3.

Comparative Example 2 A test plate was obtained in the same manner as in Example 1 except that the graft copolymer was not used. The results of performance evaluation of this coating film are shown in Table 3.

The performance evaluation was carried out as follows. 1) Impact resistance test DuPont impact resistance test (JIS K5400 6.13.
Same as 3. ). The weights used at this time were 500 g and 1 kg.
The display of the results was shown by the drop height at which the coating film cracked or peeled. 2) Weather resistance test A 1000 hour accelerated test was performed using a QUV tester, the glossiness of the coating film before and after the accelerated test was measured, and the residual gloss ratio (%) was determined. The residual gloss ratio was calculated by the following formula. 3) Acid resistance test 10 vol% of sulfuric acid was dropped on the surface of the coating film, left at room temperature for 1 day, and then wiped and observed. As a result, those without traces were indicated as ◯, and those with traces were indicated as x. 4) Visual appearance By observing the appearance of the coating film, those with particularly excellent smoothness are marked with ◎,
Good smoothness was rated as ◯, normal smoothness was rated as Δ, and poor smoothness was rated as x. 5) Solvent resistance The coating film was observed after rubbing the surface of the coating film 50 times back and forth with gauze impregnated with xylol. As a result, those without traces were indicated as ◯, and those with traces were indicated as x. 6) Coating hardness test It was carried out by a pencil scratching test (according to JIS K5400 6.14). The indication is shown by the hardness symbol of the pencil.

[0029]

[Table 2]

[0030]

[Table 3]

[0031]

EFFECTS OF THE INVENTION Although conventional polyester powder coatings are excellent in impact resistance and the like, they have a problem in weather resistance. On the other hand, an acrylic powder coating was used to improve the weather resistance, but on the contrary, it had the drawback of poor impact resistance. The present invention solves these problems all at once, and as can be seen from the results of Examples 1 and 2, the impact resistance test shows a value equal to or higher than that of the comparative example, and the weather resistance. In the test and the acid resistance test, the value is superior to that of the polyester powder coating material (Comparative Example 1). In addition, since Examples 1 and 2 show data with no problems in visual appearance, solvent resistance test, and coating film hardness test, they also have practical normal physical properties as paints.

Claims (2)

[Claims] 1. (a) Epoxy group-containing monomer and /
Alternatively, an acrylic copolymer obtained by polymerizing a copolymerizable monomer, (b) a polycarboxylic acid, and (c) a synthesis obtained by polymerizing a diene monomer and / or an unsaturated monomer An impact resistant powder coating composition comprising a graft copolymer having rubber as a core component and a vinyl polymer as a shell component. 2. The content of the graft copolymer (c) comprising a rubber obtained by polymerizing a diene monomer and / or an unsaturated monomer as a core component and a vinyl polymer as a shell component, A total of 100 parts by weight of the acrylic copolymer (a) obtained by polymerizing a monomer having an epoxy group and / or a copolymerizable monomer and the polyvalent carboxylic acid (b).
The impact-resistant powder coating composition according to claim 1, which is about 50 parts by weight.