JP2018131606A - Powder coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a main agent for a powder coating capable of providing a coating film excellent in smoothness, glossiness, and flexibility.SOLUTION: There are provided: a main agent for a powder coating which contains a copolymer comprising a (meth)acrylate having an epoxy group and an alkyl (C12-33 alkyl group) (meth)acrylate as constituent monomers, the copolymer having an epoxy group concentration of 1.5-6.5 mol/kg; and a powder coating composition which contains the main agent for a powder coating and a polycarboxylic acid (anhydride), the polycarboxylic acid being at least one selected from the group consisting of an acrylic resin having a carboxyl group and a polyvalent carboxylic acid (anhydride).SELECTED DRAWING: None

Description

  The present invention relates to a powder coating composition.

Powder coatings are used in a wide range of fields because they have many characteristics such as being pollution-free compared to solvent-based coatings and being easy to collect and recycle.
In addition, a powder coating having a better coating film appearance is desired, and a composition comprising a glycidyl group-containing copolymer and a polyvalent carboxylic acid has been proposed (for example, Patent Document 1).
However, even the above-mentioned technique is not satisfactory with respect to the appearance of the coating film, and the development of a more excellent powder coating is desired.

Japanese Patent Laid-Open No. 2003-321641

  An object of this invention is to provide the main ingredient for powder coatings which can obtain the coating film excellent in smoothness, glossiness, and a softness | flexibility.

  The inventors of the present invention have reached the present invention as a result of studies to achieve the above object. That is, the present invention relates to a copolymer (A) containing (meth) acrylate (a1) having an epoxy group and alkyl (alkyl group having 12 to 33 carbon atoms) (meth) acrylate (a22) as constituent monomers. ), And the main component for powder coating (X) having an epoxy group concentration of (A) of 1.5 to 6.5 mol / kg.

The main component (X) for powder coating of the present invention has the following effects.
(1) It imparts excellent smoothness and gloss to the coating film of the powder coating composition.
(2) Excellent flexibility of the coating film.

<(Meth) acrylate having epoxy group (a1)>
Examples of the (meth) acrylate (a1) having an epoxy group in the present invention include glycidyl (meth) acrylate and 4-hydroxybutyl acrylate glycidyl ether. Of the above (a1), preferred is glycidyl methacrylate.

<Alkyl (alkyl group having 12 to 33 carbon atoms) (meth) acrylate (a22)>
Examples of the (meth) acrylate (a22) in the present invention include a linear alkyl (meth) acrylate (a221) having a linear alkyl group, and a branched alkyl (meth) acrylate (a222) having a branched structure in the alkyl group. Can be mentioned.

Examples of the linear alkyl (meth) acrylate (a221) include n-dodecyl (meth) acrylate, n-hexadecyl (meth) acrylate, n-octadecyl (meth) acrylate, n-tetracosyl (meth) acrylate, n- Dotriacontyl (meth) acrylate is mentioned.
Examples of the branched alkyl (meth) acrylate (a222) include 2-methylpentadecyl (meth) acrylate, 2-hexyldecyl (meth) acrylate, 2-octyldecyl (meth) acrylate, 2-hexyldecyl ( (Meth) acrylate, 2-methylheptadecyl (meth) acrylate, 2-octyldodecyl (meth) acrylate, 2-decyltetradecyl (meth) acrylate, 2-dodecylhexadecyl (meth) acrylate, 2-tetradecyloctadecyl (meta) ) Acrylates.
Of the above (a22), from the viewpoint of the flexibility of the coating film described later, (a222) is preferable, and more preferable is carbon number of the alkyl group [may be abbreviated as C] 24-32 (a222) It is.
The above (a22) may be used alone or in combination of two or more. Moreover, each structural monomer in this invention may be used individually by 1 type, or may use 2 or more types together.

<Copolymer (A)>
The copolymer (A) in the present invention contains (a1) and (a22) as constituent monomers.
The weight ratio [(a1) / (a22)] of (a1) and (a22) is preferably 10/90 to 99/1 from the viewpoint of the flexibility of the coating film and the blocking resistance of the powder coating material, The ratio is preferably 30/70 to 97/3, particularly preferably 50/50 to 95/5.

The number average molecular weight (Mn) of the copolymer (A) is preferably 1,000 to 10, from the viewpoint of the smoothness of the coating film, the glossiness, and the blocking resistance of the powder coating material main agent (X). 000, more preferably 1,200 to 7,000, particularly preferably 1500 to 5,000.
The number average molecular weight is measured under the following conditions using gel permeation chromatography (GPC) with (A) dissolved in tetrahydrofuran (THF) as a sample solution.
-Equipment: HLC-8120 manufactured by Tosoh Corporation
・ Column: TSK GEL GMH6 2 [manufactured by Tosoh Corporation]
・ Measurement temperature: 40 ℃
Sample solution: 0.25 wt% THF solution Solution injection amount: 100 μL
-Detection device: Refractive index detector-Reference material: TOSOH standard polystyrene [TSK standard POLYSTYRENE] 12 points (molecular weight: 500, 1050, 2800, 5970, 9100, 18100, 37900, 96400, 190000, 355000, 1090000, 2890000)

The copolymer (A) has an epoxy group concentration (mol / kg) of 1.5 to 6.5 mol / kg, preferably 2.0 to 6.0 mol / kg, more preferably 2.5 to 5. .5 mol / kg. When the epoxy concentration is less than 1.5 mol / kg, the flexibility of the coating film is insufficient, and when it exceeds 6.5 mol / kg, the smoothness of the coating film becomes insufficient.
Moreover, as a constituent monomer of the copolymer (A), in addition to the (a1) and (a22), styrene (a3) and alkyl (alkyl group having 1 to 11 carbon atoms) (meth) acrylate ( At least one selected from the group consisting of a21) may be used as a constituent monomer.

<Styrene (a3)>
Examples of styrene (a3) in the present invention include styrene.
Based on the total weight of (a1) and (a22), the weight of (a3) is preferably 1 to 150% by weight, more preferably 5 to 100, from the viewpoint of the smoothness, gloss and physical properties of the coating film. % By weight, particularly preferably 10 to 70% by weight.

<Alkyl (alkyl group having 1 to 11 carbon atoms) (meth) acrylate (a21)>
Examples of (a21) in the present invention include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, and tert-butyl (meth). An acrylate is mentioned.
Among the above (a21), methyl (meth) acrylate, ethyl (meth) acrylate, and n-propyl are preferable from the viewpoint of blocking resistance of the main component for powder coating (X) and the powder coating composition (Y). (Meth) acrylate and n-butyl (meth) acrylate.

  Further, based on the total weight of (a1) and (a22), the weight of (a21) is preferably 1 to 150% by weight, more preferably 5 from the viewpoint of the smoothness, gloss and physical properties of the coating film. -100% by weight, particularly preferably 10-70% by weight.

As the monomer constituting (A), in addition to the above (a1), (a22), (a21), and (a3), other monomers (a4) include, for example, (meth) acrylamide and vinyl acetate. Can be mentioned.
The (a4) is preferably 10% by weight or less, more preferably 5% by weight or less, based on the total weight of (a1) and (a22).
The copolymer (A) in the present invention is obtained by polymerizing the constituent monomers by a known method.

<Main agent for powder coating (X)>
The main component (X) for powder coating of the present invention comprises the copolymer (A). The (X) may contain a phosphoric acid ester (C) described later, if necessary.
The main component for powder coating (X) can be suitably used as a main component for a powder coating composition (Y) described later.

<Phosphate ester (C)>
Examples of the phosphoric acid ester (C) in the present invention include phosphoric acid monoesters and phosphoric acid diesters [hereinafter sometimes abbreviated as phosphoric acid (di) esters].
Examples of (C) include (di) butyl phosphate, (di) hexyl phosphate, (di) octyl phosphate, (di) (2-ethylhexyl) phosphate, (di) lauryl phosphate, and phosphoric acid. (Di) cetyl, phosphoric acid (di) stearyl, and phosphoric acid (di) phenyl.
Among these (C), from the viewpoint of pigment dispersibility, phosphoric acid (di) lauryl, phosphoric acid (di) cetyl, and phosphoric acid (di) stearyl are preferable.
The weight ratio [(A) / (C)] of (A) and (C) is from the viewpoint of pigment dispersibility and prevention of gelation at the time of preparation of powder coating main agent (X) and coating. Preferably, it is 20-2000, More preferably, it is 50-1000, Most preferably, it is 100-500.

<Powder coating composition (Y)>
The powder coating composition (Y) of the present invention comprises the main component (X) for powder coating and a polycarboxylic acid (anhydride) (B) described later.
The equivalent ratio [(A) / (B)] of the epoxy group of (A) and the carboxylic acid (anhydride) of (B) is preferably from the viewpoint of curability and flexibility of the coating film. It is 5-1.5, More preferably, it is 0.6-1.4, Most preferably, it is 0.7-1.3.
In addition, in the said equivalent ratio, when (B) has a carboxylic acid an acid-free group, the one is counted as two carboxylic acid groups (carboxyl group).

<Polycarboxylic acid (anhydride) (B)>
Examples of the polycarboxylic acid (anhydride) (B) in the present invention include an acrylic resin (B1) having a carboxyl group and a polyvalent carboxylic acid (anhydride) (B2). The (B) preferably has no epoxy group.

Examples of the acrylic resin (B1) having a carboxyl group include (co) polymers containing (meth) acrylic acid (b1) as a constituent monomer. Examples of (b1) include acrylic acid and methacrylic acid.
In addition to (b1), the (co) polymer may further be a copolymer having (a21), (a22), (a3), and (a4) as constituent monomers.
The number average molecular weight of (B1) is preferably 200 to 20,000, and the amount of carboxyl group of (B1) is preferably 0.5 to 5.0 mol / kg.

  Examples of the polyvalent carboxylic acid (anhydride) (B2) include aliphatic polycarboxylic acids (such as dodecanedioic acid), aromatic polyvalent carboxylic acids (such as phthalic acid and terephthalic acid), and anhydrides thereof. It is done.

Among the above (B), (B2) is preferable from the viewpoint of physical properties and smoothness of the coating film.
Further, the carboxyl group concentration of (B) is preferably 0.3 to 20 mol / kg, more preferably 0.4 to 15 mol / kg, particularly preferably 0. 0 from the viewpoint of the physical properties and smoothness of the coating film. 5 to 10 mol / kg. As in the case of the equivalence ratio, when (B) has a carboxylic acid non-acidic group, one of them is counted as two carboxylic acid groups (carboxyl groups).

In addition to the (X) and (B), the powder coating composition (Y) may contain a known additive (D) as long as the effects of the present invention are not impaired.
Examples of (D) include a filler (D1), a leveling agent (D2), and an antifoaming agent (D3).

  Examples of (D1) include colorants (such as titanium dioxide), sodium carbonate, and silica. The weight of (D1) is preferably 0.1 to 35% by weight, more preferably 0.5 to 30% by weight, based on the total weight of (X) and (B).

  Examples of (D2) include those having a number average molecular weight of 100 to 1,000, polyolefin resins [polyethylene, polypropylene, etc.], olefin- (meth) acrylic acid copolymers [ethylene- (meth) acrylic acid copolymers Etc.], polyvinylpyrrolidone and the like. The weight of (D2) is preferably 0.1 to 6% by weight, more preferably 0.5 to 3% by weight, based on the total weight of (X) and (B).

Examples of (D3) include mineral oil, silicone oil, and benzoin.
The weight of (D3) is preferably 0.1 to 6% by weight, more preferably 0.5 to 3% by weight, based on the total weight of (X) and (B).

  The powder coating composition (Y) can be produced, for example, by adding (X), (Y), and (D) if necessary, and mixing, melt-kneading, pulverizing, and classifying each component.

  The volume average particle size of (Y) is preferably 5 to 60 μm, more preferably 15 to 40 μm, from the viewpoint of the smoothness, glossiness and workability of the coating film. The volume average particle diameter in the examples is a value measured using a particle size distribution measuring instrument using a laser diffraction scattering method [trade name “Microtrack MT3000II particle size analyzer”, manufactured by Nikkiso Co., Ltd.] Unit: μm).

<Coating film>
The coating film of the present invention is obtained by curing the powder coating composition (Y). That is, (Y) is applied and cured.
Examples of the method of applying the (Y) to the base material include a method of spray coating, electrostatic powder coating, fluidized dip coating, etc. on the object to be coated. From the viewpoint, electrostatic powder coating is preferable.

The coated object is preferably 100 to 230 ° C., more preferably 140 to 200 ° C. from the viewpoint of coating film curability and industrial, and preferably from 60 to 60 minutes from the same viewpoint. More preferably, the coating film can be formed with a curing time of 8 to 30 minutes, particularly preferably 10 to 20 minutes.
The film thickness after curing is preferably 10 to 150 μm, more preferably 20 to 100 μm, from the viewpoint of coating effect and industrial viewpoint.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, this invention is not limited to this. In the following description, “parts” represents parts by weight and “%” represents% by weight.

Production Example 1
<Phosphate ester (C)>
A reaction vessel equipped with a thermometer, a stirrer and a nitrogen inlet was charged with 90 parts of octadecyl alcohol (c1-1) and 0.05 part of diphosphorous acid, and the temperature was raised to 70 ° C. Next, 4 parts of phosphoric anhydride was added and reacted at 70 ° C. for 60 minutes, and then 6 parts of phosphoric anhydride was further added. It heated up to 120 degreeC and reacted for 3 hours, and phosphoric acid ester (C-1) which is phosphoric acid (di) ester was obtained.

<Examples 1-7, Comparative Examples 1-3>
66.7 parts of xylene was charged into a pressure-resistant reaction vessel equipped with a thermometer, a stirrer, a reflux condenser, and a nitrogen inlet, and the air in the reaction vessel was replaced with nitrogen gas with stirring, followed by heating to reflux.
Next, after heating and refluxing, the container was hermetically sealed and heated up to 160 ° C. Then, according to the blending composition (part) in Table 1, each monomer, a polymerization initiator, and a chain transfer agent were mixed. It dripped over time and superposed | polymerized. Furthermore, the reaction was continued for 1 hour at the same temperature.
Furthermore, the solvent was removed under reduced pressure, and the mixture was taken out from the reaction vessel to obtain each powder coating main agent (X) containing the copolymer (A).
In Example 7, after removing the solvent, (C) was added to obtain a powder coating main agent (X-7). The results are shown in Table 1.

The raw materials used in the examples and their symbols are as follows.
(Meth) acrylate having an epoxy group (a1):
(A1-1): Glycidyl methacrylate

Alkyl (alkyl group having 12 to 33 carbon atoms) (meth) acrylate (a22):
(A22-1): dodecyl methacrylate (a22-2): octadecyl methacrylate (a22-3): 2-decyl-1-tetradecyl methacrylate (a22-4): 2-tetradecyl-1-octadecyl methacrylate

Alkyl (alkyl group having 1 to 11 carbon atoms) (meth) acrylate (a21):
(A21-1): Methyl methacrylate (a21-2): Butyl acrylate

<Examples 11 to 17, Comparative Examples 4 to 6>
In accordance with the composition (parts) in Table 2, the powder coating main component (X), the polycarboxylic acid (anhydride) (B), and the additive (D) were charged, and the melt kneader KONDER [made by Buss Co., Ltd.] ] And kneaded at 120 ° C.
Next, the obtained kneaded material was coarsely pulverized and then pulverized using a pulverizer atomizer [manufactured by Fuji Powder Co., Ltd.]. The obtained pulverized product (sample) was classified with a 325 mesh Tyler standard sieve [aperture 44 μm], and fine particles were removed using an airflow classifier DS-2 type [manufactured by Nippon Pneumatic Industry Co., Ltd.]. As a result, a powder coating composition (Y) was obtained.
The obtained powder coating composition (Y) was evaluated according to the following evaluation methods (1) to (3). The results are shown in Table 2.

<Evaluation method>
(1) Smoothness of coating film (1-1) Evaluation of smoothness by pellet flow Pellets (diameter 13 mm, thickness 5 mm) prepared using 0.8 g of powder coating material are defined as test steel plates [JIS G3141. A surface of a cold rolled steel sheet (SPCC-SD) of 0.5 mm × 80 mm × 150 mm was degreased with methanol] and heated at 180 ° C. for 20 minutes using a circulation oven. The length of the melt-flowed pellet was measured.

(1-2) Evaluation of visual smoothness Obtained on test steel plate [0.5 mm × 80 mm × 150 mm cold rolled steel plate (SPCC-SD) surface degreased with methanol defined in JIS G3141]. The powder coating was applied using a corona charging type coating gun [“GX116”, manufactured by Parker Rising Co., Ltd.) with the coating amount adjusted to a cured film thickness of 60 μm.
Next, the coated object to be coated was baked at 180 ° C. for 20 minutes to obtain a test strip with a coating film. The smoothness of the coating film of this test rope was evaluated according to the following evaluation criteria.
<Evaluation criteria>
◎: Very good ○: Good △: Slightly inferior ×: Poor

(2) Gloss of coating film (60 degree specular gloss)
About the coating film, the reflectance (%) was measured by the method prescribed | regulated to JISK5600-4-7, when an incident angle and a light-receiving angle were each 60 degree | times.

(3) Flexibility of coating film (Eriksen test)
About the coating film, the depth (mm) of the pusher which the crack of a coating film and the peeling of a coating film from a steel plate start was measured by the method prescribed | regulated to JISK5600-5-2.

The raw materials used in the examples and their symbols are as follows.
Polycarboxylic acid (anhydride) (B)
(B-1): Dodecanedioic acid additive (D)
Pigment (D1):
(D1-1): Titanium dioxide
[Product name "Taipeke CR-90", manufactured by Ishihara Sangyo Co., Ltd.]
Leveling agent (D2):
(D2-1): Leveling agent (acrylic polymer)
[Product name "Acronal 4F", manufactured by BASF]
Antifoam (D3):
(D3-2): Benzoin

  From the results of Tables 1 and 2, it is clear that the main component for powder coating of the present invention imparts excellent smoothness and gloss to the coating film of the powder coating composition as compared with the comparative one. . Moreover, the coating film is excellent in flexibility.

  The main component for powder coatings of the present invention provides a powder coating composition capable of obtaining a coating film excellent in smoothness, glossiness and flexibility, and in particular, coatings for civil engineering, buildings, home appliances, etc. It can be suitably used for applications and is extremely useful.

Claims (7)

  It contains a copolymer (A) containing (meth) acrylate (a1) having an epoxy group and alkyl (alkyl group having 12 to 33 carbon atoms) (meth) acrylate (a22) as constituent monomers. The main component for powder coating (X), wherein the epoxy group concentration of (A) is 1.5 to 6.5 mol / kg.   The main ingredient for powder coating material according to claim 1, wherein the weight ratio [(a1) / (a22)] of (a1) to (a22) is 10/90 to 99/1.   The copolymer (A) further contains, as a constituent monomer, at least one selected from the group consisting of styrene (a3) and alkyl (alkyl group having 1 to 11 carbon atoms) (meth) acrylate (a21). The main ingredient for powder coatings according to claim 1 or 2.   Furthermore, the base agent for powder coatings in any one of Claims 1-3 containing phosphoric ester (C).   An acrylic resin having a carboxyl group (B) comprising the main component for powder coating (X) according to any one of claims 1 to 4 and a polycarboxylic acid (anhydride) (B). A powder coating composition (Y) which is at least one selected from the group consisting of B1) and a polyvalent carboxylic acid (anhydride) (B2).   The powder according to claim 5, wherein the equivalent ratio [(A) / (B)] of the epoxy group (A) to the carboxylic acid (anhydride) group (B) is 0.5 to 1.5. Paint composition.   A coating film obtained by curing the powder coating composition (Y) according to claim 5 or 6.