CN115996964A

CN115996964A - Multistage copolymer for powder coating, process for producing the same, and powder coating composition

Info

Publication number: CN115996964A
Application number: CN202180045900.6A
Authority: CN
Inventors: 宫井章吾; 近藤徹
Original assignee: Mitsubishi Chemical Corp
Current assignee: Mitsubishi Chemical Corp
Priority date: 2020-06-29
Filing date: 2021-06-29
Publication date: 2023-04-21
Also published as: WO2022004689A1; JPWO2022004689A1

Abstract

A multistage copolymer for powder coating comprising at least 3 polymer components of a first stage polymer (A), a second stage polymer (B) and a third stage polymer (C). The glass transition temperature of the polymer (A) is-15 ℃ or higher, the glass transition temperature of the polymer (B) is-20 ℃ or lower, the glass transition temperature of the polymer (C) is 60 ℃ or higher, and the polymer (A) is contained in an amount of 1 to 30 mass% inclusive, based on 100 mass% of the total amount of the multistage copolymer for powder coating.

Description

Multistage copolymer for powder coating, process for producing the same, and powder coating composition

Technical Field

The present invention relates to a multistage copolymer (multistage copolymer) for powder coating and a method for producing the same, and a powder coating composition containing the multistage copolymer for powder coating.

The present application claims priority based on 29 th month 2020 in japanese patent application No. 2020-111778, the contents of which are incorporated herein by reference.

Background

In recent years, since powder coatings do not generate organic solvents or contain organic solvents during baking of coating films, they are excellent in working environment, are non-hazardous materials, and are resource-saving, and are used in a wide range of fields.

Compared with solvent type paint, the powder paint has the characteristic that besides no solvent, the powder paint can be coated into a thick film of 30-100 mu m by one-time coating. On the other hand, powder coating materials have problems such as reduced processability of the coating film due to the thickening of the coating film obtained by coating. Conventionally, polyester powder coatings are widely used for outdoor applications such as road materials and building materials. In recent years, from the viewpoint of maintenance-free, further studies have been made on polyester powder coatings having high weather resistance. For polyester powder coatings having such high weather resistance, there is an increasing demand for improving the toughness of the resulting coating film.

For example, patent document 1 discloses an example in which a multilayer polymer obtained by graft polymerizing a vinyl monomer onto a rubbery polymer is applied to a powder coating material. Patent document 1 discloses that a multistage copolymer having a polymer layer with a glass transition temperature of 20 ℃ or lower and a polymer layer with a glass transition temperature of 60 ℃ or higher is dispersed in a powder coating material, whereby the processability and impact resistance of a coating film can be improved. However, it is desired to develop a powder coating capable of further improving the toughness of the coating film.

In addition, it has been known that a thermoplastic resin is blended with a multilayered polymer particle (multistage polymer) to improve impact resistance. Patent documents 2 to 4 disclose examples in which multilayered polymer particles are used as impact modifiers. Specifically, patent documents 2 to 4 disclose techniques for improving the temperature dependence of impact resistance and haze, the impact whitening resistance, and the like by adding a multistage polymer having a three-layer structure of hard/soft/hard as a basic structure to a hard resin such as a methacrylic resin. However, since the technology described relates to application in a resin material facing a molding member, in the case of applying the above technology to a powder coating material, dispersibility of a multistage polymer in a thermoplastic resin is insufficient. In addition, the melt viscosity of the powder coating composition containing the multistage polymer tends to increase, and thus the appearance and toughness of a coating film obtained from the powder coating composition are insufficient.

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open No. 2000-1633

Patent document 2: japanese patent laid-open No. 48-55233

Patent document 3: japanese patent laid-open No. 10-338723

Patent document 4: international publication No. 2005/095480

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made in view of the above circumstances, and an object thereof is to provide a multistage copolymer for powder coating capable of obtaining a coating film excellent in toughness and good in appearance, a method for producing the same, and a powder coating composition containing the multistage copolymer for powder coating.

Technical proposal for solving the problems

The invention comprises the following scheme:

[1] a multistage copolymer for powder coating comprising at least 3 polymer components of a first stage polymer (A), a second stage polymer (B) and a third stage polymer (C), wherein,

the glass transition temperature of the polymer (A) is-15 ℃ or higher, the glass transition temperature of the polymer (B) is-20 ℃ or lower, the glass transition temperature of the polymer (C) is 60 ℃ or higher, and the polymer (A) is contained in an amount of 1 to 30 mass% inclusive, based on 100 mass% of the total amount of the multistage copolymer for powder coating.

[2] A multistage copolymer for powder coating comprising at least an inner layer, an intermediate layer and an outer layer, wherein,

the inner layer comprises a polymer (A) having a glass transition temperature of-15 ℃ or higher,

the intermediate layer comprises a polymer (B) having a glass transition temperature of-20 ℃ or lower,

the outer layer contains a polymer (C) having a glass transition temperature of 60 ℃ or higher.

[3] The multistage copolymer for powder coating according to [1] or [2], which contains: the polymer (B) obtained by polymerizing a monomer mixture in the presence of the polymer (A), and the polymer (C) obtained by polymerizing a monomer mixture in the presence of a polymer containing the polymer (A) and the polymer (B).

[4] A multistage copolymer for powder coating comprising at least 3 polymer components of polymer (A), polymer (B) and polymer (C), wherein,

in the temperature dispersion measurement of the multistage copolymer for powder coating with dynamic viscoelasticity, at least two peaks exist in the tan delta curve between-60 ℃ and 140 ℃.

[5] The multistage copolymer for powder coating according to any one of [1] to [4], wherein the polymer (A) contains 35 to 99.5 mass% of methyl methacrylate units and 0.5 to 5 mass% of a polyfunctional monomer, based on 100 mass% of the total monomer units in the polymer (A).

[6] The multistage copolymer for powder coating according to any one of [1] to [5], wherein the polymer (B) contains 70 to 99.5 mass% of a (meth) acrylic acid alkyl ester unit having 4 to 8 carbon atoms in the alkyl group and 0.5 to 5 mass% of a polyfunctional monomer, based on 100 mass% of the total monomer units in the polymer (B).

[7] The multistage copolymer for powder coating material according to any one of [1] to [6], wherein the polymer (C) contains 70 mass% or more and 100 mass% or less of methyl methacrylate units, based on 100 mass% of the total monomer units in the polymer (C).

[8] The multistage copolymer for powder coating material according to any one of [1] to [7], wherein the primary particles have a volume average particle diameter of 0.1 μm or more and 10 μm or less.

[9] The multistage copolymer for powder coating material according to any one of [1] to [8], wherein the volume average particle diameter of the secondary particles is 1 μm or more and 500 μm or less.

[10] The multistage copolymer for powder coating material according to any one of [1] to [9], wherein the total of the polymer (A), the polymer (B) and the polymer (C) is 100% by mass, and the polymer (A) is 1% by mass or more and 30% by mass or less, the polymer (B) is 31% by mass or more and 94% by mass or less, and the polymer (C) is 5% by mass or more and 39% by mass or less.

[11] A method for producing the multistage copolymer for powder coating according to any one of [1] to [10], comprising the steps of:

a step (1) of polymerizing a first monomer mixture for constituting a polymer (A) to obtain a first dispersion containing the polymer (A), then adding a second monomer mixture for constituting a polymer (B) dropwise to the first dispersion to polymerize the second monomer mixture to obtain a second dispersion containing the polymer (A) and the polymer (B), and then adding a third monomer mixture for constituting a polymer (C) dropwise to the second dispersion to polymerize the third monomer mixture to obtain a third dispersion containing a multistage copolymer containing the polymer (A), the polymer (B) and the polymer (C);

and (2) a step of spray-drying the third dispersion to obtain a multistage copolymer-containing powder.

[12] A powder coating composition comprising the multistage copolymer for powder coating according to any one of [1] to [10], and a thermoplastic resin.

[13] The powder coating composition according to [12], wherein the thermoplastic resin is a polyester.

[14] The powder coating composition according to [12] or [13], wherein the multistage copolymer for powder coating is contained in an amount of 1 mass% or more and 20 mass% or less, based on 100 mass% of the total amount of the powder coating composition.

Effects of the invention

According to the present invention, it is possible to provide a multistage copolymer for powder coating capable of obtaining a coating film having good appearance and excellent toughness, a method for producing the same, and a powder coating composition containing the multistage copolymer for powder coating.

Drawings

FIG. 1 is a graph showing tan delta between-60℃and 140℃calculated by dynamic viscoelasticity temperature dispersion measurement for multistage copolymers in example 1.

Detailed Description

Next, embodiments of the multistage copolymer for powder coating and the method for producing the same according to the present invention will be described.

[ multistage copolymer for powder coating Material ]

The multistage copolymer for powder coating according to the embodiment of the present invention (hereinafter referred to as "the present embodiment") comprises at least 3 polymer components of the first stage polymer (a), the second stage polymer (B) and the third stage polymer (C), wherein the glass transition temperature of the polymer (a) is at least-15 ℃, the glass transition temperature of the polymer (B) is at most-20 ℃, the glass transition temperature of the polymer (C) is at least 60 ℃, and the polymer (a) is contained in an amount of 1 to 30 mass% based on 100 mass% of the total amount of the multistage copolymer for powder coating.

The glass transition temperature (hereinafter also referred to as "Tg") is a value obtained from the FOX formula (1)) described below. In this specification, tg is in ". Degree.C". Specifically, in the case of a polymer (homopolymer) composed of only single monomers, the analysis value of the standard described in "Polymer data Manual" or the like by the society of high molecular weight can be used, and in the case of a copolymer obtained by polymerizing n (n is a natural number of 2 or more) monomers, the Tg of the homopolymer of each monomer can be calculated by the following formula (1). Table 1 shows Tg literature values for representative homopolymers.

1/(273+Tg)＝∑(Wn/(273+Tgn)) (1)

Wherein Wn represents the mass fraction of monomer n, tgn represents the glass transition temperature (. Degree. C.) of the homopolymer of monomer n. Here, the mass fraction is the ratio of the amount of monomer n charged to the total amount of all the monomers charged.

TABLE 1

	Tg[℃]
		MMA	105
EMA	66
		n-BMA	20
i-BMA	53
		t-BMA	107
n-HMA	-5
		2-EHMA	-10
MA	10
		EA	-22
n-BA	-54
		n-HA	-57
2-EHA	-50
		MAA	228
2-HEMA	85

The abbreviations in Table 1 represent the following monomers.

"MMA": methyl methacrylate

"EMA": methacrylic acid ethyl ester

"n-BMA": n-butyl methacrylate

"i-BMA": isobutyl methacrylate

"t-BMA": methacrylic acid tert-butyl ester

"n-HMA": n-hexyl methacrylate

"2-EHMA": 2-ethylhexyl methacrylate

"MA": acrylic acid methyl ester

"EA": acrylic acid ethyl ester

"n-BA": acrylic acid n-butyl ester

"n-HA": n-hexyl acrylate

"2-EHA": 2-ethylhexyl acrylate

"MAA": methacrylic acid

"2-HEMA": methacrylic acid 2-hydroxyethyl ester

The homopolymer whose glass transition temperature is not described in the literature can be obtained by measurement. In this case, tg may be measured for the homopolymer by a known method such as differential scanning calorimetry, thermomechanical analysis, dynamic viscoelasticity measurement, or the like. In the multistage copolymer or the resin composition containing the multistage copolymer, even when Tg cannot be calculated by the above formula (1), tg may be measured by the above method.

The Tg of the polymer (A) is-15℃or higher, preferably 0℃or higher. If the Tg of the polymer (A) is-15 ℃ or higher, a multistage copolymer can be obtained, which can provide a powder coating composition that can form a coating film excellent in toughness and appearance.

The Tg of the polymer (B) is-20℃or lower, preferably-40℃or lower. If the Tg of the polymer (B) is-20 ℃ or lower, a block copolymer can be obtained, which can provide a powder coating composition that can form a coating film excellent in toughness.

The Tg of the polymer (C) is 60℃or higher, preferably 80℃or higher. If the Tg of the polymer (C) is 60℃or higher, the dispersion of the multistage copolymer with respect to the thermoplastic resin becomes good, and therefore a multistage copolymer can be obtained which can provide a powder coating composition capable of forming a coating film excellent in appearance.

The multistage copolymer for powder coating of the present invention comprises at least 3 polymer components, namely, polymer (A), polymer (B) and polymer (C), and at least two peaks exist in the tan delta curve between-60 ℃ and 140 ℃ in the temperature dispersion measurement with dynamic viscoelasticity in the multistage copolymer for powder coating. When at least two peaks exist in the tan delta curve, a multistage copolymer for powder coating can be obtained, which can provide a powder coating composition that can form a coating film excellent in toughness and appearance.

Of the peaks present in at least two of the tan delta curves, the peak at the low temperature side is preferably present at-60℃to 15 ℃, more preferably present at-60℃to 5 ℃, and even more preferably present at-60℃to-5 ℃. The peak at the high temperature side is preferably present at 60℃to 140℃and more preferably present at 70℃to 140℃and even more preferably present at 80℃to 140 ℃. When at least two peaks present in the tan delta curve are present in the above range, a multistage copolymer for powder coating can be obtained, which can provide a powder coating composition that can form a coating film excellent in toughness and appearance.

The dynamic viscoelasticity of the multistage copolymer for powder coating can be measured by a known method. In this embodiment, a film-like test piece of a multistage copolymer for powder coating was produced by press molding with a press molding machine at 180℃and 3MPa for 10 minutes using a viscoelasticity measuring apparatus DMA6100 (manufactured by Hitachi high technology, inc.), and the film-like test piece was measured in a bending mode at a frequency ranging from 1Hz to-100℃to 150℃to calculate a tan delta curve.

"composition of Polymer (A), polymer (B) and Polymer (C)".

The compositions of the polymer (a), the polymer (B) and the polymer (C) constituting the multistage copolymer for powder coating of the present embodiment are as follows.

When the total amount of monomer units constituting the polymer (a) is set to 100 mass%, the polymer (a) preferably contains 35 mass% or more and 99.5 mass% or less of methyl methacrylate units, 0.5 mass% or more and 5 mass% or less of polyfunctional monomer units, more preferably 40 mass% or more and 99.5 mass% or less of methyl methacrylate units, 0.5 mass% or more and 5 mass% or less of polyfunctional monomer units, and still more preferably 45 mass% or more and 99.5 mass% or less of methyl methacrylate units, and 0.5 mass% or more and 5 mass% or less of polyfunctional monomer units.

The polymer (a) contains methyl methacrylate units in an amount of 35 to 99.5 mass%, whereby a multistage copolymer which can provide a powder coating composition capable of forming a coating film excellent in toughness and appearance can be obtained.

Since the polymer (a) contains 0.5 mass% or more of the polyfunctional monomer unit, the multistage copolymer is well dispersed in the thermoplastic resin, and thus a multistage copolymer can be obtained, which can provide a powder coating composition capable of forming a coating film excellent in appearance. The polymer (a) contains 5 mass% or less of a polyfunctional monomer unit, whereby a multistage copolymer which can provide a powder coating composition capable of forming a coating film excellent in toughness can be obtained.

The monomer forming the polyfunctional monomer unit is a monomer having at least two or more polymerizable groups in a molecule, and examples thereof include: unsaturated carboxylic acid allyl esters such as allyl acrylate, allyl methacrylate, diallyl maleate, diallyl fumarate, diallyl itaconate, ethylene glycol dimethacrylate, propylene glycol dimethacrylate, 1, 3-butylene glycol dimethacrylate, 1, 4-butylene glycol dimethacrylate, divinylbenzene, and the like. These monomers may be used singly or in combination of two or more.

When the total amount of monomer units constituting the polymer (B) is 100% by mass, the polymer (B) preferably contains 70% by mass or more and 99.5% by mass or less of a (meth) acrylic acid alkyl ester unit having 4 to 8 carbon atoms in an alkyl group, 0.5% by mass or more and 5% by mass or less of a polyfunctional monomer unit, more preferably contains 85% by mass or more and 99.5% by mass or less of a (meth) acrylic acid alkyl ester unit having 4 to 8 carbon atoms in an alkyl group, and 0.5% by mass or more and 5% by mass or less of a polyfunctional monomer unit.

The polymer (B) contains 70 mass% or more and 99.5 mass% or less of alkyl (meth) acrylate units having 4 to 8 carbon atoms in the alkyl group, whereby a multistage copolymer can be obtained, which can provide a powder coating composition capable of forming a coating film excellent in toughness.

Since the polymer (B) contains 0.5 mass% or more of the polyfunctional monomer unit, the multistage copolymer can be well dispersed in the thermoplastic resin, and thus a multistage copolymer can be obtained, which can provide a powder coating composition capable of forming a coating film excellent in appearance. The polymer (B) contains 5 mass% or less of a polyfunctional monomer unit, whereby a multistage copolymer which can provide a powder coating composition capable of forming a coating film excellent in toughness can be obtained.

Examples of the monomer forming the alkyl (meth) acrylate unit having 4 to 8 carbon atoms in the alkyl group include: (meth) acrylic esters such as n-butyl (meth) acrylate, sec-butyl (meth) acrylate, isobutyl (meth) acrylate, tert-butyl (meth) acrylate, hexyl (meth) acrylate, cyclohexyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate. These (meth) acrylates may be used singly or in combination of two or more.

The "(meth) acrylate" is a generic term for acrylate and methacrylate, and the "(meth) acrylic acid" is a generic term for acrylic acid and methacrylic acid.

The monomer forming the polyfunctional monomer unit in the polymer (B) includes the monomer forming the polyfunctional monomer unit in the polymer (a) described above.

When the total amount of monomer units constituting the polymer (C) is 100% by mass, the polymer (C) preferably contains 70% by mass or more and 100% by mass or less of methyl methacrylate units, and more preferably contains 70% by mass or more and 99.5% by mass or less.

Since the polymer (C) contains 70 mass% or more and 100 mass% or less of methyl methacrylate units, the multistage copolymer can be well dispersed in the thermoplastic resin, and thus a multistage copolymer can be obtained, which can provide a powder coating composition capable of forming a coating film excellent in appearance.

Since the dispersion of the multistage copolymer in the thermoplastic resin is good, the multistage copolymer can be obtained, which can provide a powder coating composition that can form a coating film excellent in appearance, and therefore, it is preferable that the polymer (C) contains a polyfunctional monomer unit. Examples of the polyfunctional monomer unit include monomers forming a polyfunctional monomer unit in the polymer (a).

The polymer (C) may contain a monomer unit containing a reactive group. The monomer forming the reactive group-containing monomer unit is a polymerizable monomer having a functional group capable of reacting with a thermoplastic resin or a curing agent constituting the powder coating composition in its molecule. Examples of the functional group include: hydroxyl, carboxyl, epoxy, and the like. Examples of the polymerizable monomer having a hydroxyl group include: 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, and the like. Examples of the polymerizable monomer having a carboxyl group include: methacrylic acid, acrylic acid, and the like. Examples of the polymerizable monomer having an epoxy group include: glycidyl (meth) acrylate, and the like. Since the polymer (C) contains a reactive group-containing monomer unit, the multistage copolymer is well dispersed in the thermoplastic resin, and thus a multistage copolymer can be obtained, which can provide a powder coating composition capable of forming a coating film excellent in appearance. Further, since the polymer (C) contains a monomer unit containing a reactive group, it can react with a thermoplastic resin or a curing agent constituting the powder coating composition, and thus a multistage copolymer can be obtained, which can provide a powder coating composition capable of forming a coating film excellent in toughness. The reactive group-containing monomer unit is preferably a monomer unit formed from a polymerizable monomer having at least one of a hydroxyl group, a carboxyl group, and an epoxy group.

When the total amount of monomer units constituting the polymer (C) is set to 100 mass%, the polymer (C) preferably contains 70 mass% or more and 100 mass% or less of methyl methacrylate units, more preferably 70 mass% or more and 99.5 mass% or less of methyl methacrylate units and 0.5 mass% or more and 5 mass% or less of polyfunctional monomer units.

Since the polymer (C) contains 0.5 mass% or more of the polyfunctional monomer unit, the multistage copolymer is well dispersed in the thermoplastic resin, and thus a multistage copolymer can be obtained, which can provide a powder coating composition capable of forming a coating film excellent in appearance. By containing 5 mass% or less of the polyfunctional monomer unit in the polymer (C), a multistage copolymer can be obtained, which can provide a powder coating composition capable of forming a coating film excellent in toughness.

The polymer (A), the polymer (B) and the polymer (C) may contain monomer units other than the above monomer units. The monomer forming the monomer unit other than the monomer unit (hereinafter also referred to as "other monomer") is not particularly limited as long as it can undergo radical polymerization, and examples thereof include: and (meth) acrylate compounds, aromatic vinyl compounds, vinyl cyanide compounds, and the like, other than the monomers forming the methyl methacrylate and the reactive group-containing monomer units. Examples of the aromatic vinyl compound include: styrene, alpha-methylstyrene, p-methylstyrene, and the like. Examples of the vinyl cyanide compound include: acrylonitrile, methacrylonitrile, and the like. These other monomers may be used singly or in combination of two or more.

Volume average particle diameter of primary particles "

In the multistage copolymer for powder coating material of the present embodiment, the volume average particle diameter of the primary particles is preferably 0.1 μm or more and 10 μm or less, more preferably 0.3 μm or more and 3 μm or less, and still more preferably 0.4 μm or more and 1 μm or less.

The primary particles herein refer to polymer particles constituting the smallest unit of powder of a multistage copolymer containing the multistage copolymer recovered as a powder. When the volume average particle diameter of the primary particles is 0.1 μm or more, the increase in viscosity at the time of melting of the powder coating composition can be suppressed, and a multistage copolymer can be obtained, which can provide a powder coating composition capable of forming a coating film excellent in appearance. When the volume average particle diameter of the primary particles is 10 μm or less, a multistage copolymer can be obtained, which can provide a powder coating composition capable of forming a coating film excellent in toughness.

The volume average particle diameter of the primary particles of the multistage copolymer can be measured by a known method, for example, a laser diffraction method (laser diffraction/scattering method). In the present embodiment, the volume average particle diameter of the primary particles is obtained by measuring the primary particle diameter of a multistage polymer (dispersed particles) in a dispersion containing a multistage copolymer using a laser diffraction/scattering particle diameter distribution measuring apparatus (product name: LA-960, manufactured by horiba, inc.), and taking the average value.

Volume average particle diameter of secondary particles "

In the multistage copolymer for powder coating material of the present embodiment, the volume average particle diameter of the secondary particles is preferably 1 μm or more and 500 μm or less, more preferably 1 μm or more and 300 μm or less, and still more preferably 1 μm or more and 100 μm or less.

The secondary particles herein refer to a multistage copolymer-containing powder that will contain the multistage copolymer recovered as a powder. When the volume average particle diameter of the secondary particles is 1 μm or more, dust or the like can be suppressed, and thus the operability as a powder is good. When the volume average particle diameter of the secondary particles is 500 μm or less, the dispersibility with the constituent powder coating compound becomes good, and a multistage copolymer can be obtained, which can provide a powder coating composition capable of forming a coating film excellent in appearance.

The volume average particle diameter of the secondary particles of the multistage copolymer can be measured by a known method, for example, a laser diffraction method (laser diffraction/scattering method), as in the case of the volume average particle diameter of the primary particles. In the present embodiment, the volume average particle diameter of the secondary particles is obtained by measuring the secondary particle diameter of the multistage polymer (dispersed particles) in the multistage copolymer-containing dispersion by using a laser diffraction/scattering particle diameter distribution measuring apparatus (product name: LA-960, manufactured by horiba, inc.), and taking the average value.

Multistage copolymer for powder coating "

The multistage copolymer for powder coating of the present embodiment preferably contains: a polymer (B) obtained by polymerizing a monomer mixture in the presence of a polymer (A), and a polymer (C) obtained by polymerizing a monomer mixture in the presence of a polymer containing a polymer (A) and a polymer (B). Thus, a multistage copolymer can be obtained, which can provide a powder coating composition that can form a coating film excellent in appearance and toughness.

The monomers mentioned above can be used as the monomer units constituting the polymer (A), the polymer (B) and the polymer (C), respectively.

The multistage copolymer for powder coating of the present embodiment preferably contains 1 to 30 mass% of the polymer (a), 31 to 94 mass% of the polymer (B), and 5 to 39 mass% of the polymer (C), based on 100 mass% of the total of the polymer (a), the polymer (B), and the polymer (C).

If the content of the polymer (a) is in the range of 1 mass% or more and 30 mass% or less, a multistage copolymer can be obtained, which can provide a powder coating composition that can form a coating film excellent in toughness and appearance.

If the content of the polymer (B) is 31 mass% or more and 94 mass% or less, a multistage copolymer can be obtained, which can provide a powder coating composition that can form a coating film excellent in toughness.

If the content of the polymer (C) is 5 mass% or more, the dispersion of the multistage copolymer with respect to the thermoplastic resin becomes good, and therefore a multistage copolymer can be obtained which can provide a powder coating composition capable of forming a coating film excellent in appearance. If the content of the polymer (C) is 39 mass% or less, a multistage copolymer can be obtained, which can provide a powder coating composition that can form a coating film excellent in toughness.

From the viewpoint of satisfying both the toughness and the appearance of the coating film, the multistage copolymer for powder coating of the present embodiment more preferably contains 2 to 20 mass% of the polymer (a), 45 to 93 mass% of the polymer (B), 5 to 35 mass% of the polymer (C), and further preferably contains 3 to 15 mass% of the polymer (a), 50 to 93 mass% of the polymer (B), and 5 to 35 mass% of the polymer (C).

The multistage copolymer for powder coating according to another embodiment of the present invention is a multistage copolymer for powder coating comprising at least an inner layer, an intermediate layer and an outer layer, wherein the inner layer comprises a polymer (a) having a glass transition temperature of-15 ℃ or higher, the intermediate layer comprises a polymer (B) having a glass transition temperature of-20 ℃ or lower, and the outer layer comprises a polymer (C) having a glass transition temperature of 60 ℃ or higher. An intermediate layer is present on the outside of the inner layer and an outer layer is present on the outside of the intermediate layer. The polymer constituting the multistage copolymer may contain a polymer other than the polymer (a), the polymer (B) and the polymer (C) (hereinafter also referred to as "other polymer"). In this case, the other polymer may be present at a position inside the polymer (a), at a position inside the polymer (B), at a position outside the polymer (B), or at a position outside the polymer (C).

Other polymers may be used within a range that does not impair the function of the multistage copolymer for powder coating of the present embodiment. When the total polymer content of the multistage copolymer for powder coating of the present embodiment is 100 mass%, the content of the other polymer is preferably 20 mass% or less.

According to the multistage copolymer for powder coating of the present embodiment, since the multistage copolymer for powder coating is composed of at least 3 polymer components of the first stage polymer (a), the second stage polymer (B) and the third stage polymer (C), the glass transition temperature of the polymer (a) is-15 ℃ or higher, the glass transition temperature of the polymer (B) is-20 ℃ or lower, and the glass transition temperature of the polymer (C) is 60 ℃ or higher, the multistage copolymer for powder coating contains 1 to 30 mass% of the polymer (a) when the total amount of the multistage copolymer for powder coating is 100 mass%, and therefore, a multistage copolymer can be provided which can form a powder coating composition having a good appearance and excellent toughness. If the order of the first, second, and third stages is maintained, other polymer components may be formed before and after the first stage, after the second stage, and after the third stage.

The description of the powder coating composition according to the present embodiment described above in the present specification is also applicable to the powder coating composition according to the other embodiments of the present invention described above.

[ method for producing multistage copolymer for powder coating Material ]

The method for producing a multistage copolymer for powder coating according to the present embodiment is a method for producing a multistage copolymer for powder coating according to the present embodiment, and comprises the steps of: a step (1) of polymerizing a first monomer mixture for constituting a polymer (A) to obtain a first dispersion containing the polymer (A), then adding a second monomer mixture for constituting a polymer (B) dropwise to the first dispersion to polymerize the second monomer mixture, to obtain a second dispersion containing the polymer (A) and the polymer (B), and then adding a third monomer mixture for constituting a polymer (C) dropwise to the second dispersion to polymerize the third monomer mixture, to obtain a third dispersion containing a multistage copolymer containing the polymer (A), the polymer (B) and the polymer (C); and (2) a step of spray-drying the third dispersion to obtain a multistage copolymer-containing powder.

The multistage copolymer for powder coating according to the present embodiment can be produced by a known emulsion polymerization method or the like, for example. Hereinafter, a preferable example is shown as a method for producing the multistage copolymer for powder coating material of the present embodiment, but the method for producing the multistage copolymer for powder coating material of the present embodiment is not limited thereto. An example of using the emulsion polymerization method in the step (1) is shown here.

The step (1) includes: a step (1-1) of polymerizing a first monomer mixture for constituting the polymer (A) to obtain a first dispersion liquid containing the polymer (A); a step (1-2) of adding dropwise a second monomer mixture for constituting the polymer (B) to the first dispersion liquid to polymerize the second monomer mixture, thereby obtaining a second dispersion liquid containing the polymer (A) and the polymer (B); and (1-3) dropwise adding a third monomer mixture for constituting the polymer (C) to the second dispersion to polymerize the third monomer mixture, thereby obtaining a third dispersion containing a multistage copolymer containing the polymer (A), the polymer (B) and the polymer (C).

(Process (1-1))

In the step (1-1), deionized water and, if necessary, an emulsifier are added to a reaction vessel, and then a first monomer mixture containing a monomer for constituting the polymer (a) is added, and the first monomer mixture is polymerized to obtain a first latex (first dispersion) containing first dispersed particles composed of the polymer (a).

(Process (1-2))

In the step (1-2), a second monomer mixture containing a monomer for constituting the polymer (B) is added dropwise to the first latex (first dispersion) to polymerize the second monomer mixture, thereby obtaining a second latex (second dispersion) containing second dispersed particles composed of the polymer (a) and the polymer (B). The second dispersible granule is a polymer with a two-layer structure, wherein the first section (inner layer) is composed of a polymer (A), and the second section (outer layer) is composed of a polymer (B).

(Process (1-3))

In the step (1-3), a third monomer mixture containing a monomer for constituting the polymer (C) is added dropwise to the second latex (second dispersion) to polymerize the third monomer mixture, thereby obtaining a third latex (third dispersion) containing a multistage copolymer (third dispersion particles) containing the polymer (A), the polymer (B) and the polymer (C). The multistage copolymer is a polymer having a three-layer structure in which the first stage (inner layer) is composed of the polymer (a), the second stage (intermediate layer) is composed of the polymer (B), and the third stage (outer layer) is composed of the polymer (C).

A radical polymerization initiator and an emulsifier are used in the emulsion polymerization.

The radical polymerization initiator is not particularly limited, but examples thereof include: peroxides, azo initiators, redox initiators formed by combining an oxidizing agent and a reducing agent, and the like.

The emulsifier is not particularly limited, but various carboxylic acid salts such as sodium sulfonate, sodium sarcosinate, potassium fatty acid, sodium fatty acid, dipotassium alkenylsuccinate, and rosin acid soap are preferable because the latex during radical polymerization is excellent in stability and the polymerization rate can be improved.

The polymerization temperature in emulsion polymerization varies depending on the kind and amount of the radical polymerization initiator, but is preferably 40℃or more and 120℃or less, more preferably 60℃or more and 95℃or less. As a method of adding the radical polymerization initiator, a method of adding to at least one of the aqueous phase and the monomer phase can be used.

(step (2))

The multistage copolymer obtained by emulsion polymerization is usually in the form of a latex. Thus, in the step (2), the multistage copolymer is recovered from the latex of the multistage copolymer (third latex) obtained in the step (1).

In the step (2), examples of a method for recovering a multistage copolymer from a latex of the multistage copolymer include: a wet method in which a latex of a multistage copolymer is coagulated in a slurry state by adding the latex to hot water in which a coagulant is dissolved; and a spray drying method in which a latex of the multistage copolymer is sprayed in a heating atmosphere to recover a powder containing the multistage copolymer. Since the aggregated particles obtained by the spray drying method have a poor bond between primary particles, it is difficult to form a high-order particle structure, and the aggregated particles can be uniformly dispersed as primary particles and can be directly recovered, and thus, as a recovery method, a spray drying method is preferable.

The method for producing a multistage copolymer for powder coating according to the present embodiment has the steps (1) and (2), and thus can provide a multistage copolymer which can provide a powder coating composition capable of forming a coating film having a good appearance and excellent toughness.

[ powder coating composition ]

The powder coating composition of the present embodiment contains the multistage copolymer for powder coating and the thermoplastic resin.

Examples of the thermoplastic resin include: polyesters, epoxy resins, acrylic resins, and the like. Among these, polyester is preferable from the viewpoints of toughness, appearance, light resistance, and cost of the powder coating composition containing the thermoplastic resin.

The powder coating composition of the present embodiment, when containing a polyester as a thermoplastic resin, forms a polyester-based powder coating. In addition, the powder coating composition of the present embodiment, when containing a polyester and an epoxy resin as essential components, forms a polyester-epoxy hybrid powder coating. In addition, the powder coating composition of the present embodiment forms an acrylic powder coating when it contains an acrylic resin as a basic component. In addition, the powder coating composition of the present embodiment forms an epoxy powder coating when it contains an epoxy resin as a basic component.

The polyester is not particularly limited as long as it is used as a polyester-based powder coating material in the field of the art. For example, a polyester resin having two or more hydroxyl groups or acid groups in one molecule and having a softening point in the range of 60℃to 150℃is generally used as the thermoplastic resin.

The epoxy resin is not particularly limited as long as it is used as an epoxy powder coating material by those skilled in the art. Epoxy resins having an average of about 2 or more epoxy groups in one molecule are generally used, and examples thereof include: bisphenol a epoxy resin, bisphenol B epoxy resin, bisphenol F epoxy resin, novolac epoxy resin, brominated epoxy resin, alicyclic epoxy resin, and the like.

The acrylic resin is not particularly limited as long as it is used as an acrylic powder coating material by those skilled in the art. For example, a (meth) acrylate copolymer having a softening point in the range of 60 to 150 ℃ synthesized by copolymerizing a (meth) acrylate monomer with a (meth) acrylate monomer having a glycidyl group in the molecule is generally used as the thermoplastic resin.

The powder coating composition of the present embodiment preferably has a multistage copolymer content of 1 to 20 mass%, more preferably 1 to 15 mass%, and still more preferably 1 to 10 mass%, based on 100 mass% of the total powder coating composition.

If the content of the multistage copolymer for powder coating is 1 mass% or more, a powder coating composition capable of forming a good coating film excellent in toughness can be provided. If the content of the multistage copolymer for powder coating is 20 mass% or less, an increase in melt viscosity of the powder coating composition can be suppressed, and a powder coating composition capable of forming a smooth coating film can be provided.

The powder coating composition of the present embodiment may contain a curing agent, a pigment, and other various additives in addition to the multistage copolymer for powder coating and the thermoplastic resin.

The powder coating composition of the present embodiment is generally produced by a known method. That is, the powder coating composition of the present embodiment can be produced by dry-mixing the multistage copolymer for powder coating, the thermoplastic resin, and, if necessary, a curing agent, a pigment, and other additives, melt-kneading the mixture at a temperature equal to or higher than the softening point of the thermoplastic resin, and then, if necessary, pulverizing and classifying the mixture.

Examples of the other additives include: known additives used in usual powder coating compositions such as surface conditioner, ultraviolet absorber, antioxidant and antifoaming agent.

Examples of the dry mixing of the powder coating composition include a henschel mixer, a banbury mixer, a high-speed mixer, and a noda mixer.

Examples of the apparatus used for melt kneading a powder coating composition include: a heated roll machine, a heated kneader, an extruder, etc.

Examples of the pulverizer for pulverizing the powder coating composition after melt-kneading include: impact mills such as hammer mills and pin mills.

Examples of the classifier for classifying the pulverized powder coating composition include: vibrating screens, and the like.

The powder coating composition of the present embodiment can be applied to an object by a usual coating method such as an electrostatic coating method or a flow dipping method, and then heated and cured to form a coating film.

The heating temperature (baking temperature) and time at the time of forming the coating film can be appropriately set. For example, the heating temperature is usually not lower than the melting point of the thermoplastic resin.

Examples of the object to be coated by applying the powder coating composition of the present embodiment include: the metal such as iron, zinc, tin, stainless steel, copper, aluminum, and the like, and the inorganic substance such as glass, and the base material composed of these metals or inorganic substances are optionally subjected to sand blast treatment, primer coating, intermediate coating, and the like.

The film thickness of the coating film formed from the powder coating composition of the present embodiment is not particularly limited, but is preferably 15 μm or more and 1mm or less.

Before forming a coating film using the powder coating composition of the present embodiment, a primer coating film may be formed on the coated surface (surface coated with the powder coating composition) of the object using a known primer coating.

According to the powder coating composition of the present embodiment, since the multistage copolymer for powder coating and the thermoplastic resin are contained, a powder coating composition capable of forming a coating film having good appearance and excellent toughness can be provided.

Examples

The present invention will be specifically described below with reference to examples. The present invention is not limited to these examples. Hereinafter, "parts" means "parts by mass".

Various measurement and evaluation methods are described below.

[ measurement of the volume average particle diameter of primary particles of multistage copolymer ]

The volume average particle diameter of the primary particles of the multistage copolymer was measured by the following method.

The primary particle diameter of the dispersed particles in the dispersion containing the multistage copolymer was measured using a laser diffraction/scattering particle diameter distribution measuring apparatus (product name: LA-960, manufactured by horiba, inc.). The average value of the primary particle diameter is defined as the volume average particle diameter of the primary particles. The relative refractive index of the resin particles and the dispersion medium was all 1.12. As the dispersion medium, ion-exchanged water was used.

[ measurement of volume average particle diameter of secondary particles of multistage copolymer ]

The volume average particle diameter of the secondary particles of the multistage copolymer was measured by the following method.

The secondary particle diameter of the dispersed particles in the dispersion containing the multistage copolymer was measured using a laser diffraction/scattering particle diameter distribution measuring apparatus (product name: LA-960, manufactured by horiba, inc.). The average value of the secondary particle diameter is taken as the volume average particle diameter of the secondary particles. The relative refractive index of the resin particles and the dispersion medium was all 1.12. As the dispersion medium, ion-exchanged water was used.

[ evaluation of appearance of coating film ]

The appearance of the coating film obtained by applying the powder coating composition and curing was evaluated by leveling property of the coating film. Leveling property of the coating film was evaluated by the following method.

A powder coating composition was sprayed onto a metal substrate (test piece: Q-panQD 46, thickness: 0.5 mm) and cured at 200℃for 10 minutes to form a coating film having a film thickness of 100. Mu.m.

Then, the Long Wavelength (LW) of the reflected light irradiated to the coating light was measured using a micro orange peel detector AW-4824 (manufactured by BYK Co.).

The leveling property of the coating film was determined based on the obtained measured values according to the following criteria. If LW is less than 50, leveling is good.

LW50 or more: x-ray;

LW40 or more and less than 50: and (2);

LW is less than 40: and (3) excellent.

[ evaluation of coating film toughness ]

The toughness of the coating film obtained by applying the powder coating composition and curing was evaluated by the anti-cupping property of the coating film. The cupping resistance of the coating film was evaluated by the following method.

A powder coating composition was sprayed onto a metal substrate (test piece: Q-panQD 46, thickness: 0.5 mm) and cured at 200℃for 10 minutes to form a coating film having a film thickness of 40. Mu.m.

Then, the depth of penetration of the coating film was measured using a PCE-CPT manual cupping tester and according to ISO 1520.

Based on the obtained measurement value, the cupping resistance was determined according to the following criteria. If the press-in depth is 2.5mm or more, the cupping resistance is good.

The pressing depth is less than 2.5mm: x-ray;

the pressing depth is more than 2.5mm and less than 4.0mm: and (2);

the pressing depth is more than 4.0mm: and (3) excellent.

[ evaluation of impact resistance of coating film ]

The toughness of the coating film obtained by applying the powder coating composition and curing the composition was evaluated by the impact resistance of the coating film. The impact resistance of the coating film was evaluated by the following method.

Then, a ball drop test was performed on the side of the coating film according to ASTM D-2794, and the impact resistance of the coating film was measured as inch-English (in-lbn).

Impact resistance was determined based on the obtained measurement values according to the following criteria. If the inch-English ratio is 100 or more, the impact resistance is good.

Less than 100in-lbn: x-ray;

100in-lbn and less than 140in-lbn: and (2);

140in-lbn or more: and (3) excellent.

Example 1 ]

[ procedure (1-1) ]

Into a 5 liter separable flask having a capacity of a thermometer, a nitrogen inlet pipe, a stirring rod, a dropping funnel and a cooling pipe, 63.8 parts of deionized water was charged, and nitrogen gas was introduced for 30 minutes to replace dissolved oxygen in the deionized water.

Then, the nitrogen gas was stopped and the temperature was raised to 80℃while stirring at 200 rpm.

Then, 2.96 parts of methyl methacrylate, 1.97 parts of n-butyl acrylate, 0.19 parts of allyl methacrylate and 0.03 parts of 1, 3-butanediol dimethacrylate were added together at a point in time when the temperature in the separable flask reached 80 ℃, and further, 0.05 parts of potassium persulfate and 2.38 parts of deionized water were added and the mixture was kept for 60 minutes, thereby obtaining a latex containing polymer (a) particles.

[ procedure (1-2) ]

To the latex obtained in the step (1-1), 0.04 part of PELEX OT-P, 0.05 part of potassium persulfate, 4 parts of deionized water were added, and 75.1 parts of n-butyl acrylate, 2.85 parts of allyl methacrylate, 1.52 parts of 1, 3-butanediol dimethacrylate, 0.75 parts of PELEX OT-P, and 51.6 parts of deionized water were added dropwise over 180 minutes.

Then, the polymerization was completed after holding for 1 hour, and a latex containing particles obtained by polymerizing the polymer (B) around the polymer (a) was obtained.

[ procedure (1-3) ]

To the latex obtained in the step (1-2), 17.7 parts of methyl methacrylate, 0.35 parts of ethyl acrylate, 1.9 parts of 2-hydroxyethyl methacrylate, 0.20 parts of 1, 3-butanediol dimethacrylate, 0.20 parts of PELEX OT-P and 15 parts of deionized water were dropwise added over 140 minutes.

Then, the polymerization was completed by holding for 2 hours, and a latex containing a multistage copolymer in which the polymer (C) was polymerized around the particles composed of the polymer (A) and the polymer (B) was obtained.

[ step (2) ]

The latex obtained in the step (1-3) was spray-dried using a spray dryer (product name: type L-8i, manufactured by Dain chemical Co., ltd.) under the conditions of inlet temperature/outlet temperature=120℃at 60℃and rotational speed of the turntable at 20000rpm, to obtain a multistage copolymer (P-1).

The volume average particle diameter of the primary particles of the multistage copolymer was 0.70. Mu.m. The results are shown in Table 2.

The tan delta curve of the multistage copolymer between-60℃and 140℃calculated by the temperature dispersion measurement of dynamic viscoelasticity is shown in FIG. 1.

The Tg of each of the polymer (a), the polymer (B) and the polymer (C) is calculated from the Tg of the homopolymer described in table 1 corresponding to the monomer unit constituting each polymer and using the formula (1).

Example 2 ]

A multistage copolymer (P-2) was obtained in the same manner as in example 1, except that the monomers constituting the monomer units of the polymer (A), the polymer (B) and the polymer (C) were each formulated into a mass ratio shown in Table 2. The results are shown in Table 2.

Example 3 ]

A multistage copolymer (P-3) was obtained in the same manner as in example 1, except that the monomers constituting the monomer units of the polymer (A), the polymer (B) and the polymer (C) were each composed in the mass ratio shown in Table 2. The results are shown in Table 2.

Example 4 ]

A multistage copolymer (P-4) was obtained in the same manner as in example 1, except that the monomers constituting the monomer units of the polymer (A), the polymer (B) and the polymer (C) were each composed in the mass ratio shown in Table 2. The results are shown in Table 2.

Example 5 ]

A multistage copolymer (P-5) was obtained in the same manner as in example 1, except that the monomers constituting the monomer units of polymer (A), polymer (B) and polymer (C) were each formulated into the mass ratio shown in Table 2. The results are shown in Table 2.

Example 6 ]

A multistage copolymer (P-6) was obtained in the same manner as in example 1, except that the monomers constituting the monomer units of the polymer (A), the polymer (B) and the polymer (C) were each composed in the mass ratio shown in Table 2. The results are shown in Table 2.

Example 7 ]

[ procedure (1-1) ]

Then, at the time point when the temperature in the separable flask reached 80 ℃, 6.00 parts of methyl methacrylate, 4.00 parts of n-butyl acrylate, 0.39 parts of allyl methacrylate, and half of the monomer mixed solution of 0.05 parts of 1, 3-butanediol dimethacrylate were added together, and further 0.05 parts of potassium persulfate and 2.38 parts of deionized water were added thereto for 60 minutes.

Then, the remaining half of the monomer mixture solution was added dropwise over 30 minutes.

Then, the polymerization was completed by holding for 30 minutes, and a latex containing polymer (A) particles was obtained.

[ procedure (1-2) ]

To the latex obtained in the step (1-1), 0.04 part of PELEX OT-P, 0.05 part of potassium persulfate, 4 parts of deionized water were added, and 70.0 parts of n-butyl acrylate, 2.66 parts of allyl methacrylate, 1.42 parts of 1, 3-butanediol dimethacrylate, 0.70 parts of PELEX OT-P, 48.1 parts of deionized water were added dropwise over 180 minutes.

[ procedure (1-3) ]

[ step (2) ]

The latex obtained in the step (1-3) was spray-dried in the same manner as in example 1 to obtain a multistage copolymer (P-8). The results are shown in Table 2.

Comparative example 1 ]

A multistage copolymer (P-8) was obtained in the same manner as in example 1, except that the monomers constituting the monomer units of polymer (A), polymer (B) and polymer (C) were each formulated into the mass ratio shown in Table 2. The results are shown in Table 2.

TABLE 2

The compounds in table 2 represent the following compounds:

"MMA": methyl methacrylate (Mitsubishi chemical Co., ltd.)

"n-BA": n-butyl acrylate (Mitsubishi chemical Co., ltd.)

"AMA": allyl methacrylate (Mitsubishi chemical Co., ltd.)

"BDMA":1, 3-butanediol dimethacrylate (Mitsubishi chemical Co., ltd.)

"EA": ethyl acrylate (Mitsubishi chemical Co., ltd.)

"2-HEMA": 2-hydroxyethyl methacrylate (Mitsubishi chemical Co., ltd.)

"MAA": methacrylic acid (Mitsubishi chemical Co., ltd.)

Example 8 ]

The constituent components of the powder coating composition are as follows:

polyester resin: SP-6400 (manufactured by Sun polymer international Co., ltd.)

Curing agent: triglycidyl isocyanurate (TGIC) (manufactured by Aalchem Co., ltd.)

Leveling agent: resiffow P-67 (Estron chemical Co., ltd.)

Deaerating agent: benzonin (manufactured by Estron chemical company)

Pigment: tiPure R960 (manufactured by Venator Co., ltd.)

Toughening agent: multistage copolymer (P-1)

61.4 parts of SP-6400, 4.6 parts of TGIC, 1 part of Resiffow P-67, 0.5 part of Benzon, 30 parts of TiPure R960, 2.5 parts of multistage copolymer (P-1) were premixed with a Vitamix mixer for 8 seconds.

The obtained product after the preliminary kneading was melt-kneaded by using a twin-screw extruder APV 19mm (set at 100 ℃, screw rotation speed 500rpm, and cooling roll 18 rpm).

Next, the melt-kneaded product was pulverized by a linear mill (strand mill) and then sieved with a 140-mesh sieve, thereby obtaining a powder coating composition.

A coating film was formed from the obtained powder coating composition, and the leveling property, the cupping resistance and the impact resistance of the coating film were evaluated. The results are shown in Table 3.

Example 9 ]

A powder coating composition was obtained in the same manner as in example 8, except that the multistage copolymer (P-2) was used in place of the multistage copolymer (P-1).

Example 10 ]

A powder coating composition was obtained in the same manner as in example 8, except that the multistage copolymer (P-3) was used in place of the multistage copolymer (P-1).

Example 11 ]

A powder coating composition was obtained in the same manner as in example 8, except that the multistage copolymer (P-4) was used in place of the multistage copolymer (P-1).

Example 12 ]

A powder coating composition was obtained in the same manner as in example 8, except that the multistage copolymer (P-5) was used in place of the multistage copolymer (P-1).

Example 13 ]

A powder coating composition was obtained in the same manner as in example 8, except that the multistage copolymer (P-6) was used in place of the multistage copolymer (P-1).

Example 14 ]

A powder coating composition was obtained in the same manner as in example 8, except that the multistage copolymer (P-7) was used in place of the multistage copolymer (P-1).

Comparative example 2 ]

A powder coating composition was obtained in the same manner as in example 2, except that the multistage copolymer (P-8) was used in place of the multistage copolymer (P-1).

Comparative example 3]

63.7 parts of SP-6400, 4.8 parts of TGIC, 1 part of Resiffow P-67, 0.5 part of Benzon, 30 parts of TiPure R960 were premixed for 8 seconds with a Vitamix mixer.

Then, the obtained melt-kneaded product was pulverized by a linear mill and then sieved by a 140-mesh sieve, thereby obtaining a powder coating composition.

TABLE 3

Industrial applicability

The multistage copolymer for powder coating of the present invention can provide a powder coating composition which can form a coating film having good appearance and excellent toughness, and thus can be suitably used for outdoor applications such as road materials and building materials.

Claims

1. A multistage copolymer for powder coating comprising at least 3 polymer components of a first stage polymer A, a second stage polymer B and a third stage polymer C, wherein,

the glass transition temperature of the polymer A is-15 ℃ or higher, the glass transition temperature of the polymer B is-20 ℃ or lower, the glass transition temperature of the polymer C is 60 ℃ or higher, and the polymer A is contained in an amount of 1 to 30 mass% inclusive, based on 100 mass% of the total amount of the multistage copolymer for powder coating.

2. A multistage copolymer for powder coating comprising at least an inner layer, an intermediate layer and an outer layer, wherein,

the inner layer comprises a polymer A having a glass transition temperature of-15 ℃ or higher,

the interlayer comprises a polymer B having a glass transition temperature of-20 ℃ or lower,

the outer layer comprises a polymer C having a glass transition temperature of 60 ℃ or higher.

3. The multistage copolymer for powder coating according to claim 1 or 2, which contains: the polymer B obtained by polymerizing a monomer mixture in the presence of the polymer A, and the polymer C obtained by polymerizing a monomer mixture in the presence of a polymer containing the polymer A and the polymer B.

4. A multistage copolymer for powder coating comprising at least 3 polymer components of polymer A, polymer B and polymer C, wherein,

5. The multistage copolymer for powder coating according to any one of claims 1 to 4, wherein the polymer a contains 35 to 99.5 mass% of methyl methacrylate units and 0.5 to 5 mass% of a polyfunctional monomer, based on 100 mass% of the total monomer units in the polymer a.

6. The multistage copolymer for powder coating according to any one of claims 1 to 5, wherein the polymer B contains 70 to 99.5 mass% of the alkyl (meth) acrylate unit having 4 to 8 carbon atoms and 0.5 to 5 mass% of the polyfunctional monomer, based on 100 mass% of the total monomer units in the polymer B.

7. The multistage copolymer for powder coating according to any one of claims 1 to 6, wherein the polymer C contains 70 to 100 mass% of methyl methacrylate units, based on 100 mass% of the total amount of monomer units in the polymer C.

8. The multistage copolymer for powder coating according to any one of claims 1 to 7, wherein the primary particles have a volume average particle diameter of 0.1 μm or more and 10 μm or less.

9. The multistage copolymer for powder coating according to any one of claims 1 to 8, wherein the volume average particle diameter of the secondary particles is 1 μm or more and 500 μm or less.

10. The multistage copolymer for powder coating according to any one of claims 1 to 9, wherein the total of the polymer a, the polymer B, and the polymer C is 100 mass%, and the polymer a is 1 mass% or more and 30 mass% or less, the polymer B is 31 mass% or more and 94 mass% or less, and the polymer C is 5 mass% or more and 39 mass% or less.

11. A method for producing the multistage copolymer for powder coating according to any one of claims 1 to 10, comprising the steps of:

a step (1) of polymerizing a first monomer mixture for constituting a polymer a to obtain a first dispersion liquid containing the polymer a, then adding dropwise a second monomer mixture for constituting a polymer B to the first dispersion liquid to polymerize the second monomer mixture to obtain a second dispersion liquid containing the polymer a and the polymer B, and then adding dropwise a third monomer mixture for constituting a polymer C to the second dispersion liquid to polymerize the third monomer mixture to obtain a third dispersion liquid containing a multistage copolymer containing the polymer a, the polymer B and the polymer C;

12. A powder coating composition comprising the multistage copolymer for powder coating according to any one of claims 1 to 10 and a thermoplastic resin.

13. The powder coating composition of claim 12, wherein the thermoplastic resin is a polyester.

14. The powder coating composition according to claim 12 or 13, wherein the multistage copolymer for powder coating is contained in an amount of 1 mass% or more and 20 mass% or less, based on 100 mass% of the total amount of the powder coating composition.