JP7484107B2 - Graft copolymer, thermoplastic resin composition and molded article thereof - Google Patents

Description

The present invention relates to a graft copolymer that provides a thermoplastic resin composition that is excellent in molded appearance and impact resistance as well as in flowability, and to a thermoplastic resin composition containing this graft copolymer and a molded article thereof.

Improving the impact resistance of resin materials is extremely useful industrially, not only expanding the applications of resin materials but also enabling the creation of thinner and larger molded products. Various methods have been proposed to improve the impact resistance of resin materials. Of these, a method of combining a rubber polymer with a hard resin material to increase impact resistance while retaining the properties of the hard resin material has already been commercialized. One such material is acrylonitrile-butadiene-styrene (ABS) resin.

However, although ABS resin has excellent impact resistance and molded appearance, the polybutadiene rubber component has poor weather resistance, making it difficult to use without applying decoration such as paint or film.

To solve these problems with ABS resin, acrylonitrile-styrene-acrylic acid ester (ASA) resin, which uses acrylic rubber as the rubber component, has been developed and commercialized.

For example, Patent Document 1 discloses a method in which an acrylonitrile-styrene (AS) resin is used as a hard resin material and an ASA resin is added thereto.
However, ASA resin has a problem that the appearance of the molded product is poor when molded at a low injection speed because of the large difference in refractive index between the acrylic rubber and the acrylonitrile-styrene (AS) resin, which is the hard resin component, and the appearance of the molded product is further deteriorated when molded at a high injection speed.

Patent Documents 2 and 3 disclose a method of adding a polybutadiene/acrylic rubber composite having a structure in which the outside of polybutadiene particles is covered with acrylic rubber to an AS resin.
This method reduces the difference in refractive index between the rubber component and the AS resin by compounding polybutadiene, resulting in a good molded appearance, but the compounding of polybutadiene causes a problem of reduced weather resistance.

Patent Document 4 discloses a method for increasing the refractive index of acrylic rubber by copolymerizing butyl acrylate and styrene.
However, the method described in Patent Document 4 significantly reduces impact resistance. In addition, the appearance during molding is good at a low injection speed, but the appearance deteriorates at a high injection speed, that is, the appearance is highly injection speed dependent.

In the graft polymer such as ASA resin, the crosslink density of rubber particles such as acrylic rubber has a large effect on the physical properties of the molded product. In general, the higher the crosslink density, the better the molded appearance of the molded product tends to be. In order to increase the crosslink density, a method is generally used in which, when producing acrylic rubber, a multifunctional compound having two or more functional groups such as (meth)acryloyl groups, vinyl groups, allyl groups, etc. in the molecule is copolymerized with an acrylic acid ester to increase the amount of the multifunctional compound added.
However, in a region where the crosslink density of the acrylic rubber is high, the impact resistance tends to decrease.
In other words, there is a trade-off between the impact resistance and the appearance of a molded article, and it has been difficult to achieve both the impact resistance and the appearance of a molded article by adjusting the crosslink density of rubber particles.

JP 2017-71660 A JP 2007-204763 A JP 2009-242595 A JP 2017-88774 A

The present invention aims to provide a graft copolymer that can achieve both impact resistance and molded appearance of a molded article, and a thermoplastic resin composition that uses this graft copolymer to obtain a molded article that is excellent in flowability, impact resistance, molded appearance, and even the injection speed dependency of the molded appearance.

The inventors of the present invention have conducted extensive research to solve the above problems, and as a result, have found that a thermoplastic resin composition having excellent molded appearance, impact resistance, and flowability can be obtained by using rubber particles having a low crosslink density inside and a high crosslink density outside, specifically, rubber particles of a graft copolymer, in which the core part is copolymer (A) obtained by polymerizing a vinyl monomer mixture (m1) containing a (meth)acrylic acid ester (Aa) and a hydrophobic substance (Ab) having a hydrocarbon group selected from an alkyl group, an alkenyl group, and a cycloalkyl group having 12 or more carbon atoms, and the shell part is copolymer (B) obtained by polymerizing a vinyl monomer mixture (m2) containing a (meth)acrylic acid ester (Ba), in which the swelling degree of the copolymer (A) in the core part is 7 to 15 times that of the core-shell type particle (C), and the swelling degree of the core-shell type particle (C) is 5 to 12 times that of the core-shell type particle (C).

That is, the gist of the present invention is as follows:

[1] A graft copolymer (D) obtained by polymerizing a vinyl monomer mixture (m3) in the presence of a core-shell type particle (C) having a core portion made of a copolymer (A) obtained by polymerizing a vinyl monomer mixture (m1) containing a (meth)acrylic acid ester (Aa) and a hydrophobic substance (Ab) having a hydrocarbon group selected from an alkyl group, an alkenyl group, and a cycloalkyl group having 12 or more carbon atoms, and a shell portion made of a copolymer (B) obtained by polymerizing a vinyl monomer mixture (m2) containing a (meth)acrylic acid ester (Ba), the graft copolymer (D) being characterized in that the swelling degree of the copolymer (A) is 7 to 15 times, the swelling degree of the core-shell type particle (C) is 5 to 12 times, and the swelling degree of the copolymer (A) is greater than the swelling degree of the core-shell type particle (C).

[2] In [1], the hydrophobic substance (Ab) is a hydrophobic substance having a logarithm [logP] value of the partition coefficient [P] expressed as the ratio [c1/c2] of the concentration [c1] in 1-octanol to the concentration [c2] in water of 6 or more. [2] In the graft copolymer (D),

[3] In the graft copolymer (D) of [1] or [2], the content of the copolymer (A) is 60 to 96 mass% and the content of the copolymer (B) is 4 to 40 mass% in 100 mass% of the core-shell type particles (C).

[4] In any one of [1] to [3], the copolymer (A) is a graft copolymer (D) containing a (meth)acrylic acid ester (Aa) unit and a unit derived from a crosslinking agent and/or a unit derived from a graft crosslinking agent.

[5] In [4], the graft copolymer (D) has a ratio of units derived from a crosslinking agent and/or a graft crosslinking agent in the copolymer (A) of 0.05 to 0.3 mass% in a total of 100 mass% of (meth)acrylic acid ester (Aa) units and units derived from a crosslinking agent and/or units derived from a graft crosslinking agent.

[6] In [4] or [5], the vinyl monomer mixture (m1) contains 0.1 to 10 parts by mass of the hydrophobic substance (Ab) per 100 parts by mass of the (meth)acrylic acid ester (Aa) and the crosslinking agent and/or graft crosslinking agent in the graft copolymer (D).

[7] In any one of [1] to [6], the copolymer (B) is a graft copolymer (D) containing a (meth)acrylic acid ester (Ba) unit and a unit derived from a crosslinking agent and/or a unit derived from a graft crosslinking agent.

[8] In [7], the graft copolymer (D) has a ratio of units derived from a crosslinking agent and/or a graft crosslinking agent in the copolymer (B) of 0.03 to 0.3 mass% in a total of 100 mass% of (meth)acrylic acid ester (Ba) units and units derived from a crosslinking agent.

[9] In any one of [1] to [8], the graft copolymer (D) has a volume average particle diameter of 50 to 800 nm and the core-shell type particles (C) have a volume average particle diameter of 60 to 820 nm.

[10] In any one of [1] to [9], the vinyl monomer mixture (m3) contains an aromatic vinyl monomer and a vinyl cyanide monomer, and the content of the aromatic vinyl monomer contained in the vinyl monomer mixture (m3) is 40 to 90 mass %, and the content of the vinyl cyanide monomer is 10 to 60 mass %. Graft copolymer (D).

[11] In any one of [1] to [10], the ratio of the core-shell type particles (C) to the total of the core-shell type particles (C) and the vinyl monomer mixture (m3) is 50 to 80 mass%, the ratio of the vinyl monomer mixture (m3) is 20 to 50 mass%, and the graft ratio is 25 to 100%.

[12] A thermoplastic resin composition containing the graft copolymer (D) described in any one of [1] to [11].

[13] In [12], a thermoplastic resin composition comprising the graft copolymer (D) and a copolymer (E) obtained by polymerizing a vinyl monomer mixture (m4).

[14] In the thermoplastic resin composition of [13], the vinyl monomer mixture (m3) contains an aromatic vinyl monomer and a vinyl cyanide monomer, and the vinyl monomer mixture (m4) contains an aromatic vinyl monomer having the same structure as the aromatic vinyl monomer contained in the vinyl monomer mixture (m3) and a vinyl cyanide monomer having the same structure as the vinyl cyanide monomer contained in the vinyl monomer mixture (m3).

[15] In the thermoplastic resin composition of [13] or [14], the graft copolymer (D) is present in an amount of 10 to 50% by mass, and the copolymer (E) is present in an amount of 50 to 90% by mass, with the total amount of the graft copolymer (D) and the copolymer (E) being 100% by mass.

[16] A molded article obtained by molding a thermoplastic resin composition according to any one of [12] to [15].

The present invention provides a thermoplastic resin composition and molded products thereof that are excellent in molded appearance and impact resistance, and also in fluidity and the injection speed dependency of molded appearance.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the preferred embodiments.
In the present invention, "(meth)acrylic acid" means one or both of "acrylic acid" and "methacrylic acid", and the same applies to "(meth)acrylate".
Further, the term "unit" refers to a structural portion contained in a polymer and derived from a compound (monomer) before polymerization, for example, "(meth)acrylic acid ester (Aa) unit" refers to "a structural portion derived from (meth)acrylic acid ester (Aa) and contained in copolymer (A) which is the core portion of core-shell type particle (C)." The content ratio of each monomer unit in a polymer corresponds to the content ratio of the monomer in the monomer mixture used in the production of the polymer.

[Graft Copolymer (D)]
The graft copolymer (D) of the present invention is a core-shell type particle (C) having a core portion made of a copolymer (A) obtained by polymerizing a vinyl-based monomer mixture (m1) containing a (meth)acrylic acid ester (Aa) and a hydrophobic substance (Ab) having a hydrocarbon group selected from an alkyl group, an alkenyl group, and a cycloalkyl group having 12 or more carbon atoms, and a shell portion made of a copolymer (B) obtained by polymerizing a vinyl-based monomer mixture (m2) containing a (meth)acrylic acid ester (Ba), and is obtained by polymerizing a vinyl-based monomer mixture (m3) in the presence of a core-shell type particle (C) (hereinafter sometimes referred to as "the core-shell type particle (C) of the present invention") in which the swelling degree of the copolymer (A) is 7 to 15 times, the swelling degree of the core-shell type particle (C) is 5 to 12 times, and the swelling degree of the copolymer (A) is greater than that of the core-shell type particle (C).

<Mechanism>
The graft copolymer (D) of the present invention is characterized in that it uses specific core-shell type particles (C) as rubber particles. In particular, the degree of swelling of the copolymer (A) constituting the core of the core-shell type particles (C) is greater than the degree of swelling of the core-shell type particles (C), so that the impact resistance and the appearance of the molded article can be compatible.
That is, by forming a distribution of crosslink density inside the rubber particle, when an external force is applied to the thermoplastic resin composition, stress is concentrated on the copolymer (A) which is the core part and has a low crosslink density in the rubber particle, and the deformation of the copolymer (A) absorbs the impact. At this time, the swelling degree of the core-shell type particle (C) is smaller than that of the copolymer (A) which is the core part, that is, the crosslink density of the copolymer (B) which is the shell part is higher than that of the copolymer (A), so that stress is less likely to be concentrated on the shell part, and this shell part contributes to suppression of large deformation of the core-shell type particle (C). Suppression of large deformation of the core-shell type particle (C) is important for improving the appearance of the molded product.
If the core-shell particle (C) has a lower swelling degree than the copolymer (A), that is, if the shell portion of the copolymer (B) has a lower crosslink density than the core portion of the copolymer (A), stress is concentrated in the shell portion, making it impossible to suppress large deformation of the core-shell particle.
Therefore, in order to achieve both impact resistance and good molded appearance, it is important that the degree of swelling of the copolymer (A) is greater than the degree of swelling of the core-shell particles (C).

<Core-shell type particles (C)>
In the core-shell type particle (C) of the present invention, a copolymer (A) obtained by polymerizing a vinyl-based monomer mixture (m1) containing a (meth)acrylic acid ester (Aa) and a hydrophobic substance (Ab) having a hydrocarbon group selected from an alkyl group, an alkenyl group, and a cycloalkyl group having 12 or more carbon atoms constitutes a core portion, and a copolymer (B) obtained by polymerizing a vinyl-based monomer mixture (m2) containing a (meth)acrylic acid ester (Ba) constitutes a shell portion.

(Copolymer (A))
The copolymer (A) is obtained by polymerizing a vinyl monomer mixture (m1) containing a (meth)acrylic acid ester (Aa) and a hydrophobic substance (Ab) having a hydrocarbon group selected from an alkyl group, an alkenyl group, and a cycloalkyl group having 12 or more carbon atoms.

As the (meth)acrylic acid ester (Aa), a (meth)acrylic acid alkyl ester in which the alkyl group has 1 to 12 carbon atoms is preferred. Among these, n-butyl acrylate, 2-ethylhexyl acrylate, and ethyl acrylate are particularly preferred because the resulting thermoplastic resin composition has excellent impact resistance. The (meth)acrylic acid ester (Aa) can be used alone or in combination of two or more kinds.

The copolymer (A) is preferably a copolymer having, in addition to the (meth)acrylic acid ester (Aa), either or both of units derived from a crosslinking agent and units derived from a graft crosslinking agent. When the copolymer (A) contains units derived from a graft crosslinking agent and/or a crosslinking agent, the molded appearance and impact resistance of the resulting thermoplastic resin composition are further improved.

Graft crosslinking agents include allyl compounds, specifically allyl methacrylate, triallyl cyanurate, triallyl isocyanurate, etc. These may be used alone or in combination of two or more.

The crosslinking agent may be a dimethacrylate compound, specific examples of which include ethylene glycol dimethacrylate, propylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, and 1,4-butylene glycol dimethacrylate. These may be used alone or in combination of two or more.

When a crosslinking agent and/or a graft crosslinking agent is used, the proportion of units derived from the crosslinking agent and/or the graft crosslinking agent in the copolymer (A) is preferably 0.05 to 0.3 mass%, more preferably 0.08 to 0.24 mass%, based on 100 mass% of the total of the (meth)acrylic acid ester (Aa) units and the units derived from the crosslinking agent and/or the units derived from the graft crosslinking agent, since the resulting thermoplastic resin composition has excellent molded appearance and impact resistance.

The copolymer (A) may contain other monomer units other than the (meth)acrylic acid ester (Aa) units and the units derived from the crosslinking agent and/or graft crosslinking agent used as necessary, within the scope of the present invention. Examples of other monomer units that may be contained in the copolymer (A) include one or more vinyl monomer units other than the (meth)acrylic acid ester (Aa) contained in the vinyl monomer mixture (m3) described below. In order to effectively obtain the effects of the present invention, it is preferable that the content of these other vinyl monomer units is 20% by mass or less, particularly 10% by mass or less, based on 100% by mass of the copolymer (A).

The method for producing the copolymer (A) is preferably a method of emulsion polymerization or mini-emulsion polymerization of a vinyl monomer mixture (m1) containing a (meth)acrylic acid ester (Aa) and a specific hydrophobic substance (Ab), and optionally a crosslinking agent and/or a graft crosslinking agent, and the mini-emulsion polymerization method is particularly preferred because the resulting thermoplastic resin composition has excellent physical properties.

The mini-emulsion polymerization for producing the copolymer (A) can include, but is not limited to, for example, a process of mixing a (meth)acrylic acid ester (Aa), a crosslinking agent and/or a graft crosslinking agent, a specific hydrophobic substance (Ab), and an initiator, adding water and an emulsifier to the resulting mixture, and applying shear force to prepare a pre-emulsion (mini-emulsion), as well as a process of heating the mixture to a polymerization initiation temperature to polymerize it.

In the mini-emulsion process, for example, a shearing process is carried out by ultrasonic irradiation, whereby the monomer is torn off by the shearing force, and monomer micro-oil droplets covered with emulsifier are formed. The monomer micro-oil droplets are then polymerized as they are by heating to the polymerization initiation temperature of the initiator, and polymer microparticles are obtained. Any known method can be used to apply shear force to form a mini-emulsion, and examples of high shear devices capable of forming a mini-emulsion include, but are not limited to, an emulsification device consisting of a high-pressure pump and an interaction chamber, and a device that forms a mini-emulsion using ultrasonic energy or high frequency. Examples of emulsification devices consisting of a high-pressure pump and an interaction chamber include the "Pressure Homogenizer" manufactured by SPX Corporation APV and the "Microfluidizer" manufactured by Powrex Corporation, and examples of devices that form mini-emulsions using ultrasonic energy or high frequency include the "Sonic Dismembrator" manufactured by Fisher Scientific and the "ULTRASONIC HOMOGENIZER" manufactured by Nippon Seiki Seisakusho Co., Ltd., but are not limited to these.

From the viewpoints of workability, stability, manufacturability, etc., the amount of water solvent used during mini-emulsion is preferably about 100 to 500 parts by mass per 100 parts by mass of the mixture other than water, so that the solids concentration of the reaction system after polymerization is about 5 to 50% by mass.

In the present invention, a hydrophobic substance (Ab) having a hydrocarbon group selected from an alkyl group, an alkenyl group, and a cycloalkyl group having 12 or more carbon atoms is an essential component. By using the hydrophobic substance (Ab) having this specific hydrophobic hydrocarbon group, the production stability of the mini-emulsion can be improved. In addition, by using the hydrophobic substance (Ab), it becomes possible to easily control the particle size of the copolymer (A), and by selecting a particle size that has an advantageous effect on impact resistance, the impact resistance of the resulting thermoplastic resin composition can be improved.

The degree of hydrophobicity of the hydrophobic substance (Ab) used in the present invention can be expressed by the logarithm [logP] value of the partition coefficient [P], which is expressed as the ratio [c1/c2] of the concentration [c1] in 1-octanol to the concentration [c2] in water, and it is preferable that the logarithm [logP] value of the partition coefficient [P] of the hydrophobic substance (Ab) used in the present invention is 6.0 or more.

Examples of hydrophobic substances having a logarithm [logP] value of the partition coefficient [P] of 6 or more include non-polymerizable hydrophobic compounds such as hydrocarbons having 12 or more carbon atoms and alcohols having 12 or more carbon atoms, and hydrophobic monomers such as vinyl esters of alcohols having 14 to 30 carbon atoms, vinyl ethers of alcohols having 14 to 30 carbon atoms, vinyl esters of carboxylic acids having 15 to 30 carbon atoms (preferably 15 to 22 carbon atoms), p-alkylstyrenes having 20 to 40 carbon atoms, and hydrophobic chain transfer agents. These may be used alone or in combination of two or more.

Specific examples of the hydrophobic substance (Ab) used in the present invention include tetradecane (log P: 6.3), pentadecane (log P: 7.7), hexadecane (log P: 8.3), heptadecane (log P: 8.8), octadecane (log P: 9.3), icosane (log P: 10.4), liquid paraffin (log P > 6.0), liquid isoparaffin (log P > 6.0), paraffin wax (log P > 6.0), polyethylene wax (log P > 6.0), olive oil (log P > 6.0), cetyl alcohol (log P: 6.7), stearyl alcohol (log P: 8.2), stearyl acrylate (log P: 7.7), stearyl methacrylate (log P: 9.6), etc.

By using these hydrophobic substances (Ab), it is possible to suppress the increase in particle size non-uniformity caused by Ostwald ripening and synthesize a monodisperse copolymer (A). Using core-shell type particles (C) containing this copolymer (A), it is possible to obtain a graft copolymer (D) that is effective in improving the impact resistance of a thermoplastic resin composition.

From the viewpoint of particle size control of the copolymer (A), it is preferable to use 0.1 to 10 parts by mass, and more preferably 0.5 to 3 parts by mass, of the hydrophobic substance (Ab) per 100 parts by mass of the (meth)acrylic acid ester (Aa) and the crosslinking agent and/or graft crosslinking agent combined.

The emulsifier used in producing the copolymer (A) may be a carboxylic acid-based emulsifier, such as an alkali metal salt of oleic acid, palmitic acid, stearic acid, or rosin acid, or an alkali metal salt of alkenyl succinic acid, or an anionic emulsifier selected from alkyl sulfates, sodium alkylbenzene sulfonates, sodium alkyl sulfosuccinates, sodium polyoxyethylene nonylphenyl ether sulfates, or the like. Known emulsifiers may be used alone or in combination of two or more.

The amount of emulsifier added is preferably 0.01 to 3.0 parts by mass, and more preferably 0.05 to 1.5 parts by mass, per 100 parts by mass of the (meth)acrylic acid ester (Aa) and the crosslinking agent and/or graft crosslinking agent in terms of particle size control of the copolymer (A).

The initiator used in the production of copolymer (A) is a radical polymerization initiator for radical polymerization. There are no particular limitations on the type, but examples include azo polymerization initiators, photopolymerization initiators, inorganic peroxides, organic peroxides, and redox initiators that combine organic peroxides with transition metals and reducing agents. Of these, azo polymerization initiators, inorganic peroxides, organic peroxides, and redox initiators that can initiate polymerization by heating are preferred. These may be used alone or in combination of two or more.

Examples of azo polymerization initiators include 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), 1-[(1-cyano-1-methylethyl)azo]formamide, 4,4'-azobis(4-cyanovaleric acid), dimethyl 2,2'-azobis( 2-methylpropionate), dimethyl 1,1'-azobis(1-cyclohexanecarboxylate), 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide], 2,2'-azobis(N-butyl-2-methylpropionamide), 2,2'-azobis(N-cyclohexyl-2-methylpropionamide), 2,2'-azobis[2-(2-imidazolin-2-yl)propane], 2,2'-azobis(2,4,4-trimethylpentane), etc.

Examples of inorganic peroxides include potassium persulfate, sodium persulfate, ammonium persulfate, and hydrogen peroxide.

Examples of organic peroxides include peroxyester compounds, and specific examples thereof include α,α'-bis(neodecanoylperoxy)diisopropylbenzene, cumyl peroxyneodecanoate, 1,1,3,3-tetramethylbutyl peroxyneodecanoate, 1-cyclohexyl-1-methylethyl peroxyneodecanoate, t-hexyl peroxyneodecanoate, t-butyl peroxyneodecanoate, t-hexyl peroxypivalate, t-butyl peroxypivalate, 1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate, 2,5-dimethyl-2,5-bis(2-ethylhexanoylperoxy)hexane, 1-cyclohexyl-1-methylethyl peroxy-2-ethylhexanoate, ester, t-hexylperoxy 2-hexylhexanoate, t-butylperoxy 2-hexylhexanoate, t-butylperoxy isobutyrate, t-hexylperoxy isopropyl monocarbonate, t-butylperoxy maleic acid, t-butylperoxy 3,5,5-trimethylhexanoate, t-butylperoxy laurate, 2,5-dimethyl-2,5-bis(m-toluoylperoxy)hexane, t-butylperoxy isopropyl monocarbonate, t-butylperoxy 2-ethylhexyl monocarbonate, t-hexylperoxybenzoate, 2,5-dimethyl-2,5-bis(benzoylperoxy)hexane, t-butylperoxy acetate, t-butylperoxy-m-toluoylbenzoate benzoate, t-butylperoxybenzoate, bis(t-butylperoxy)isophthalate, 1,1-bis(t-hexylperoxy)3,3,5-trimethylcyclohexane, 1,1-bis(t-hexylperoxy)cyclohexane, 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, 1,1-bis(t-butylperoxy)cyclododecane, 2,2-bis(t-butylperoxy)butane, n-butyl 4,4-bis(t-butylperoxy)valerate, 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, α,α'-bis(t-butylperoxy)diisopropylbenzene, dicumyl peroxide, 2,5-dimethyl Examples of such peroxy compounds include 2,5-bis(t-butylperoxy)hexane, t-butylcumyl peroxide, di-t-butyl peroxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, dilauroyl peroxide, diisononanoyl peroxide, t-butyl hydroperoxide, benzoyl peroxide, lauroyl peroxide, dimethylbis(t-butylperoxy)-3-hexyne, bis(t-butylperoxyisopropyl)benzene, bis(t-butylperoxy)trimethylcyclohexane, butyl-bis(t-butylperoxy)valerate, 2-ethylhexaneperoxy acid t-butyl, dibenzoyl peroxide, paramenthane hydroperoxide, and t-butyl peroxybenzoate.

Redox initiators that are preferred are those that combine an organic peroxide with ferrous sulfate, a chelating agent, and a reducing agent. Examples include those that consist of cumene hydroperoxide, ferrous sulfate, sodium pyrophosphate, and dextrose, and those that combine t-butyl hydroperoxide, sodium formaldehyde sulfoxylate (Rongalit), ferrous sulfate, and disodium ethylenediaminetetraacetate.

Of these, organic peroxides are particularly preferred as initiators.

The amount of initiator added is usually 5 parts by mass or less, preferably 3 parts by mass or less, for example 0.001 to 3 parts by mass, per 100 parts by mass of the (meth)acrylic acid ester (Aa) and the crosslinking agent and/or graft crosslinking agent combined.

The process for preparing the above pre-emulsion is usually carried out at room temperature (approximately 10 to 50°C), and the mini-emulsion polymerization process is carried out at 40 to 100°C for approximately 30 to 600 minutes.

The average particle size of the copolymer (A) dispersed in the aqueous dispersion is preferably from 50 to 800 nm, more preferably from 100 to 600 nm, and even more preferably from 250 to 450 nm, in order to provide excellent physical properties for the resulting molded article.
The method for controlling the average particle size of the copolymer (A) is not particularly limited, but includes a method of adjusting the type or amount of an emulsifier used.
The average particle size of the copolymer (A) and the average particle size of the core-shell type particles (C) described below are volume average particle sizes measured by the method described in the Examples section below.

In the present invention, the swelling degree of the copolymer (A) is from 7 to 15 times, preferably from 7.5 to 12 times, in order that the impact resistance and molded appearance of the resulting thermoplastic resin composition are excellent.
If the swelling degree of the copolymer (A) is less than 7 times, the impact resistance of the resulting thermoplastic resin composition will be poor, whereas if it exceeds 15 times, the appearance of the molded product will be poor.
The swelling degree of copolymer (A) can be adjusted by the amount of crosslinking agent and/or graft crosslinking agent used in producing copolymer (A). By increasing the amount of crosslinking agent and/or graft crosslinking agent used, the crosslink density can be increased and the swelling degree can be decreased, whereas by decreasing the amount of crosslinking agent and/or graft crosslinking agent used, the crosslink density can be decreased and the swelling degree can be increased.
The swelling degree of the copolymer (A) and the swelling degree of the core-shell type particles (C) described later are measured by the method described in the Examples section below.

(Copolymer (B))
The copolymer (B) is a copolymer obtained by polymerizing a vinyl monomer mixture (m2) containing a (meth)acrylic acid ester (Ba). The copolymer (B) constitutes a shell portion as an outer shell encapsulating a core portion made of the copolymer (A) obtained by polymerizing a vinyl monomer mixture (m1) containing a (meth)acrylic acid ester (Aa) and the above-mentioned hydrophobic substance (Ab). Therefore, for example, by polymerizing the vinyl monomer mixture (m2) in the presence of the copolymer (A), the core-shell type particle (C) of the present invention in which the core portion is the copolymer (A) and the shell portion is the copolymer (B) can be obtained.

As the (meth)acrylic acid ester (Ba) contained in the vinyl monomer mixture (m2), a (meth)acrylic acid alkyl ester having an alkyl group with 1 to 12 carbon atoms is preferred. Among these, n-butyl acrylate, 2-ethylhexyl acrylate, and ethyl acrylate are particularly preferred because the resulting thermoplastic resin composition has excellent impact resistance. The (meth)acrylic acid ester (Ba) can be used alone or in combination of two or more.

The copolymer (B) is preferably a copolymer having, in addition to the (meth)acrylic acid ester (Ba), either or both of units derived from a crosslinking agent and units derived from a graft crosslinking agent. When the copolymer (B) contains units derived from a graft crosslinking agent and/or a crosslinking agent, the molded appearance and impact resistance of the resulting thermoplastic resin composition are further improved.

As the graft crosslinking agent and crosslinking agent, those exemplified as the graft crosslinking agent and crosslinking agent used in copolymer (A) can be used.

When a crosslinking agent and/or a graft crosslinking agent is used, the ratio of units derived from the crosslinking agent and/or the graft crosslinking agent in the copolymer (B) is preferably 0.03 to 0.3 mass%, more preferably 0.05 to 0.25 mass%, based on 100 mass% of the total of the (meth)acrylic acid ester (Ba) units and the units derived from the crosslinking agent and/or the units derived from the graft crosslinking agent, since the resulting thermoplastic resin composition has excellent molded appearance and impact resistance.

The copolymer (B) may contain other monomer units other than the (meth)acrylic acid ester (Ba) units and the units derived from the crosslinking agent and/or graft crosslinking agent used as necessary, within the scope of the present invention. Examples of other monomer units that may be contained in the copolymer (B) include one or more vinyl monomer units other than the (meth)acrylic acid ester (Ba) contained in the vinyl monomer mixture (m3) described below. In order to effectively obtain the effects of the present invention, it is preferable that the content of these other vinyl monomer units is 20% by mass or less, particularly 10% by mass or less, based on 100% by mass of the copolymer (B).

(Core-shell type particles (C))
The method for producing the core-shell type particles (C) is not particularly limited. When the copolymer (A) is produced by mini-emulsion polymerization, it is preferable to produce the core-shell type particles (C) by emulsion polymerization using a vinyl monomer mixture (m2).

As a method of emulsion polymerization, a method of radical polymerization in which a vinyl monomer mixture (m2) is added all at once, continuously, or intermittently in the presence of an emulsion of copolymer (A) can be mentioned. In addition, when polymerizing copolymer (B), a chain transfer agent may be used for the purpose of adjusting the molecular weight or graft ratio of copolymer (B), or a known inorganic electrolyte may be used for the purpose of adjusting the viscosity or pH of the latex. In addition, various emulsifiers and radical initiators can be used in emulsion polymerization as necessary.

There are no particular limitations on the type or amount of emulsifier and radical initiator. Examples of emulsifiers and radical initiators include the emulsifiers and radical initiators exemplified above in the description of copolymer (A).

In order to obtain a thermoplastic resin composition having excellent impact resistance and molded appearance, the proportion of the copolymer (B) in 100% by mass of the core-shell type particles (C) is preferably from 4 to 40% by mass, and more preferably from 10 to 30% by mass.
In addition, since the obtained thermoplastic resin composition has excellent impact resistance and molded appearance, the content of the copolymer (A) in 100% by mass of the core-shell type particles (C) is preferably 60 to 96% by mass, more preferably 50 to 95% by mass, and more preferably 70 to 90% by mass.

The average particle size of the core-shell particles (C) dispersed in the aqueous dispersion is preferably from 60 to 820 nm, more preferably from 110 to 620 nm, and even more preferably from 260 to 470 nm, in order to provide excellent physical properties for the resulting molded article.
The method for controlling the average particle size of the core-shell particles (C) is not particularly limited, but mainly includes a method of adjusting the type or amount of an emulsifier used during the production of the copolymer (A).

The swelling degree of the core-shell type particles (C) is 5 to 12 times, and preferably 5.5 to 11 times, because the thermoplastic resin composition obtained has excellent impact resistance and molded appearance. If the swelling degree of the core-shell type particles (C) is less than 5 times, the thermoplastic resin composition obtained has poor impact resistance, and if it exceeds 12 times, the molded appearance is poor.

In addition, the present invention is characterized in that the swelling degree of the copolymer (A) is greater than that of the core-shell type particles (C), and by having the swelling degree of the copolymer (A) greater than that of the core-shell type particles (C), both impact resistance and molded appearance of the molded article can be achieved.
As described above, the swelling degree can be adjusted by the amount of the crosslinking agent and/or the graft crosslinking agent used. Therefore, in the present invention, the amount of the crosslinking agent and/or the graft crosslinking agent used in producing the copolymer (B) is made larger than the amount of the crosslinking agent and/or the graft crosslinking agent used in producing the copolymer (A) to increase the crosslink density of the copolymer (B) to be higher than the crosslink density of the copolymer (A), thereby making it possible to obtain the core-shell type particles (C) in which the swelling degree of the copolymer (A) is larger than the swelling degree of the core-shell type particles (C).

There is no particular restriction on the difference between the swelling degree of the copolymer (A) and the swelling degree of the core-shell type particles (C), but the difference between the swelling degrees of the two is preferably 0.9 or more, and particularly preferably about 1 to 3. If this difference is too small, the effect of adjusting the swelling degree between the copolymer (A) and the core-shell type particles (C) as in the present invention cannot be fully obtained, and making this difference too large reduces the impact resistance of the resulting thermoplastic resin composition.

<Graft Copolymer (D)>
The graft copolymer (D) can be obtained by graft polymerizing a vinyl monomer mixture (m3) in the presence of the core-shell particles (C) of the present invention.

The vinyl monomer mixture (m3) preferably contains an aromatic vinyl monomer and a vinyl cyanide monomer, since the thermoplastic resin composition obtained by blending the resulting graft copolymer (D) has excellent physical properties.

Examples of aromatic vinyl monomers contained in the vinyl monomer mixture (m3) include styrene, α-methylstyrene, o-, m- or p-methylstyrene, vinylxylene, p-t-butylstyrene, ethylstyrene, etc., which may be used alone or in combination of two or more. There are no particular restrictions on the structure of the aromatic vinyl monomer, but it is preferable that the aromatic vinyl monomer has the same structure as the aromatic vinyl monomer contained in the vinyl monomer mixture (m4) described below in terms of the impact resistance and molded appearance of the thermoplastic resin composition and its molded article.

The content of aromatic vinyl monomers in the vinyl monomer mixture (m3) is preferably 40 to 90% by mass from the viewpoints of the impact resistance and molded appearance of the thermoplastic resin composition containing the resulting graft copolymer (D) and its molded article, and is more preferably 60 to 80% by mass.

Examples of the vinyl cyanide monomer contained in the vinyl monomer mixture (m3) include acrylonitrile and methacrylonitrile, and one or more of these can be used. There are no particular restrictions on the structure of the vinyl cyanide monomer, but it is preferable that the structure be the same as that of the vinyl cyanide monomer contained in the vinyl monomer mixture (m4) described below in terms of the impact resistance and molded appearance of the resulting thermoplastic resin composition and its molded article.

The content of the vinyl cyanide monomer in the vinyl monomer mixture (m3) is preferably 10 to 60% by mass from the viewpoints of the impact resistance and molded appearance of the thermoplastic resin composition containing the resulting graft copolymer (D) and its molded article, and is more preferably 20 to 40% by mass.

The vinyl monomer mixture (m3) may contain the above-mentioned aromatic vinyl monomer and vinyl cyanide monomer, as well as other vinyl monomers copolymerizable therewith.
The content of other copolymerizable vinyl monomers in the vinyl monomer mixture (m3) is preferably 20% by mass or less, particularly preferably 10% by mass or less.

Other vinyl monomers include, for example, methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, amyl methacrylate, isoamyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, decyl methacrylate, lauryl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, and phenyl methacrylate, as well as N-methylmaleimide, N-ethylmaleimide, and the like. Examples of the maleimide-based compounds include N-cycloalkylmaleimides such as N-n-propylmaleimide, N-i-propylmaleimide, N-n-butylmaleimide, N-i-butylmaleimide, N-tert-butylmaleimide, and N-cyclohexylmaleimide; N-arylmaleimides such as N-phenylmaleimide, N-alkyl-substituted phenylmaleimide, and N-chlorophenylmaleimide; and acrylic esters such as methyl acrylate, ethyl acrylate, propyl acrylate, and butyl acrylate. These may be used alone or in combination of two or more.

The graft copolymer (D) is formed by graft polymerizing a vinyl monomer mixture (m3) onto the core-shell type particles (C).
The thermoplastic resin composition containing the obtained graft copolymer (D) has excellent impact resistance and molded appearance, and in particular, the injection speed dependency of the molded appearance can be reduced. Therefore, the core-shell type particles (C) and the vinyl monomer mixture (m3) used in the production of the graft copolymer (D) preferably contain 50 to 80 mass% of the core-shell type particles (C) and 20 to 50 mass% of the vinyl monomer mixture (m3) in 100 mass% of the graft copolymer (D).

The graft copolymer (D) preferably has a graft ratio of 25 to 100%, since the thermoplastic resin composition containing the graft copolymer (D) has excellent impact resistance and molded appearance. The graft ratio of the graft copolymer (D) is measured by the method described in the Examples section below.

The graft copolymer (D) is produced by known methods such as bulk polymerization, solution polymerization, bulk suspension polymerization, suspension polymerization, emulsion polymerization, and mini-emulsion polymerization. The emulsion polymerization method is preferred because the thermoplastic resin composition containing the resulting graft copolymer (D) has good impact resistance.

The emulsion graft polymerization method may include a method in which the vinyl monomer mixture (m3) is added all at once, continuously, or intermittently in the presence of an emulsion of the core-shell type particles (C) to carry out radical polymerization. In addition, during the graft polymerization, a chain transfer agent may be used for the purpose of adjusting the molecular weight of the graft copolymer (D) or controlling the graft rate, or a known inorganic electrolyte may be used for the purpose of adjusting the viscosity or pH of the latex. In addition, in the emulsion graft polymerization, various emulsifiers and radical initiators may be used as necessary.
The type and amount of the emulsifier and radical initiator are not particularly limited. Examples of the emulsifier and radical initiator include the emulsifiers and radical initiators exemplified above in the description of the copolymer (A).

Methods for recovering graft copolymer (D) from its aqueous dispersion include (i) a method in which the aqueous dispersion of graft copolymer (D) is poured into hot water in which a coagulant has been dissolved, and the graft copolymer (D) is recovered by coagulating into a slurry state (wet method), and (ii) a method in which the aqueous dispersion of graft copolymer (D) is sprayed into a heated atmosphere to recover graft copolymer (D) semi-directly (spray dry method).

Examples of coagulants include inorganic acids such as sulfuric acid, hydrochloric acid, phosphoric acid, and nitric acid, and metal salts such as calcium chloride, calcium acetate, and aluminum sulfate. The coagulant is selected according to the emulsifier used in the polymerization. In other words, when only carboxylic acid soaps such as fatty acid soaps and rosin acid soaps are used, any coagulant may be used. When an emulsifier that exhibits stable emulsifying power even in the acidic range, such as sodium dodecylbenzenesulfonate, is included, a metal salt must be used.

Methods for obtaining a dry graft copolymer (D) from a slurry of graft copolymer (D) include (i) a method in which the emulsifier residue remaining in the slurry is dissolved in water by washing, and then the slurry is dehydrated in a centrifugal dehydrator or press dehydrator and further dried in an air flow dryer or the like, and (ii) a method in which dehydration and drying are simultaneously performed in a squeeze dehydrator, extruder, or the like. After drying, the graft copolymer (D) is obtained in the form of powder or particles. The graft copolymer (D) discharged from the squeeze dehydrator or extruder can also be sent directly to an extruder or molding machine for producing a thermoplastic resin composition.

[Copolymer (E)]
The copolymer (E) is obtained by polymerizing a vinyl monomer mixture (m4).

The vinyl monomer mixture (m4) preferably has the same composition as the vinyl monomer mixture (m3) described above, since the thermoplastic resin composition obtained by blending the copolymer (E) has excellent physical properties, and preferably contains an aromatic vinyl monomer and a vinyl cyanide monomer.

Examples of aromatic vinyl monomers contained in the vinyl monomer mixture (m4) include styrene, α-methylstyrene, o-, m- or p-methylstyrene, vinylxylene, p-t-butylstyrene, ethylstyrene, etc., which may be used alone or in combination of two or more. There are no particular restrictions on the structure of the aromatic vinyl monomer, but it is preferable that the aromatic vinyl monomer has the same structure as the aromatic vinyl monomer contained in the vinyl monomer mixture (m3) described above in terms of the impact resistance and molded appearance of the resulting thermoplastic resin composition and its molded article.

From the viewpoints of the impact resistance and molded appearance of the resulting thermoplastic resin composition and its molded article, the content of aromatic vinyl monomer contained in the vinyl monomer mixture (m4) is preferably 40 to 90 mass%, and more preferably 60 to 80 mass%.

Examples of the vinyl cyanide monomer contained in the vinyl monomer mixture (m4) include acrylonitrile and methacrylonitrile, and one or more of these can be used. There are no particular restrictions on the structure of the vinyl cyanide monomer, but it is preferable that the structure is the same as that of the vinyl cyanide monomer contained in the vinyl monomer mixture (m3) described above in terms of the impact resistance and molded appearance of the resulting thermoplastic resin composition and its molded article.

From the viewpoints of the impact resistance and molded appearance of the resulting thermoplastic resin composition and its molded article, the content of the vinyl cyanide monomer contained in the vinyl monomer mixture (m4) is preferably 10 to 60 mass%, and more preferably 20 to 40 mass%.

The vinyl monomer mixture (m4) may contain the above-mentioned aromatic vinyl monomer and vinyl cyanide monomer, as well as other vinyl monomers copolymerizable therewith.
The content of other copolymerizable vinyl monomers in the vinyl monomer mixture (m4) is preferably 20% by mass or less, particularly preferably 10% by mass or less.
Examples of the other vinyl-based monomer include those exemplified as the other vinyl-based monomers that may be contained in the vinyl-based monomer mixture (m3), and these other vinyl-based monomers may be used alone or in combination of two or more.

The mass average molecular weight of the copolymer (E) is not particularly limited, but is preferably in the range of 10,000 to 300,000, and particularly preferably in the range of 50,000 to 200,000. When the mass average molecular weight of the copolymer (E) is within the above range, the resulting thermoplastic resin composition has excellent fluidity and impact resistance.
The mass average molecular weight of the copolymer (E) is measured by the method described later in the Examples section.

The method for producing the copolymer (E) is not particularly limited, and includes known methods such as emulsion polymerization, suspension polymerization, bulk polymerization, and solution polymerization. From the viewpoint of the heat resistance of the resulting thermoplastic resin composition, suspension polymerization and bulk polymerization are preferred.

There are no particular limitations on the polymerization initiator used in producing copolymer (E), but examples include organic peroxides.

When producing copolymer (E), a chain transfer agent can be used to adjust the molecular weight of copolymer (E). There are no particular limitations on the chain transfer agent, but examples include mercaptans, α-methylstyrene dimer, terpenes, etc.

[Thermoplastic resin composition]
The thermoplastic resin composition of the present invention contains the above-mentioned graft copolymer (D) of the present invention, and preferably contains the graft copolymer (D) of the present invention and the above-mentioned copolymer (E).

The content of the graft polymer (D) of the present invention in the thermoplastic resin composition of the present invention is preferably 10 to 50 mass%, and the content of the copolymer (E) is preferably 50 to 90 mass%, assuming that the total of the graft copolymer (D) and the copolymer (E) is 100 mass%. When the contents of the graft polymer (D) and the copolymer (E) are within the above ranges, the thermoplastic resin composition and its molded article have excellent impact resistance and molded appearance.

The thermoplastic resin composition of the present invention may contain other thermoplastic resins as necessary. There are no particular limitations on the other thermoplastic resins, and examples thereof include polycarbonate resin, polybutylene terephthalate (PBT resin), polyethylene terephthalate (PET resin), polyvinyl chloride, polystyrene, polyacetal resin, modified polyphenylene ether (modified PPE resin), ethylene-vinyl acetate copolymer, polyarylate, liquid crystal polyester resin, polyethylene resin, polypropylene resin, fluororesin, and polyamide resin (nylon). These may be used alone or in combination of two or more.

The thermoplastic resin composition of the present invention may contain other commonly used additives, such as lubricants, pigments, dyes, fillers (carbon black, silica, titanium oxide, etc.), heat resistance agents, antioxidants for oxidation degradation, weather resistance agents, release agents, plasticizers, antistatic agents, etc., during production (mixing) and molding of the thermoplastic resin composition, to the extent that the physical properties of the thermoplastic resin composition and the molded product thereof are not impaired.

The thermoplastic resin composition of the present invention can be produced by a known method using known equipment. For example, a common method is a melt mixing method, and examples of equipment used in this method include an extruder, a Banbury mixer, a roller, and a kneader. Either a batch method or a continuous method may be used for mixing. There are also no particular limitations on the order in which the components are mixed, as long as all the components are mixed uniformly.

[Molding]
The molded article of the present invention is a product obtained by molding the thermoplastic resin composition of the present invention. Examples of the molding method include injection molding, injection compression molding, extrusion, blow molding, vacuum molding, pressure molding, calendar molding, and inflation molding. Among these, injection molding and injection compression molding are preferred because they are excellent in mass productivity and can produce molded articles with high dimensional accuracy.

[Application]
There are no particular limitations on the applications of the thermoplastic resin composition of the present invention and molded articles thereof, but the thermoplastic resin composition of the present invention and molded articles thereof are excellent in impact resistance, molded appearance, and flowability, and are therefore useful in a wide range of fields, including office equipment and home appliances, vehicles and ships, housing-related fields such as furniture and building materials, sanitary products, miscellaneous goods, stationery, toys, and sporting goods.

The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited to the following examples in any way as long as the gist of the present invention is not exceeded.
In the following description, "parts" means "parts by mass" and "%" means "% by mass".

The various measurement and evaluation methods used in the following examples and comparative examples are as follows:

<Volume Average Particle Diameter of Copolymer (A) and Core-Shell Particles (C)>
The volume average particle size of the copolymer (A) or the core-shell type particles (C) dispersed in the aqueous dispersion was measured using a Microtrac (Nanotrac 150 manufactured by Nikkiso Co., Ltd.) and ion-exchanged water as a measurement solvent.

<Swelling Degree of Copolymer (A) and Core-Shell Particles (C)>
The aqueous dispersion of the copolymer (A) or the core-shell type particle (C) was dried at 80° C. for 24 hours, and then vacuum-dried at 80° C. for 24 hours to prepare a film-like dried product of the copolymer (A) or the core-shell type particle (C). The weight of the obtained dried product was designated as W1. 1 g of this dried product was immersed in 80 mL of acetone, and the acetone was refluxed at 65 to 70° C. for 3 hours. Next, the obtained acetone suspension solution was centrifuged at 14,000 rpm for 30 minutes using a centrifuge (Hitachi Koki Co., Ltd. "CR21E") to separate the precipitated component (acetone insoluble component). The weight of the acetone insoluble component was designated as W2. Then, the acetone insoluble component was vacuum-dried at room temperature for 24 hours. The weight of the acetone insoluble component after vacuum drying was designated as W3. The swelling degree of the copolymer (A) and the core-shell type particle (C) was calculated by the following formula (1).
Swelling degree (%) = (W2 / W3) × 100 ... (1)
The degree of swelling serves as a measure of crosslink density, and it is generally known that the higher the degree of swelling, the lower the crosslink density, and vice versa.

<Graft ratio of graft copolymer (D)>
1 g of the graft copolymer (D) was added to 80 mL of acetone, and the mixture was heated to reflux at 65 to 70° C. for 3 hours. The resulting acetone suspension was centrifuged at 14,000 rpm for 30 minutes using a centrifuge (Hitachi Koki Co., Ltd., “CR21E”) to separate the precipitate (acetone insoluble component) and the acetone solution (acetone soluble component). The precipitate (acetone insoluble component) was then dried to measure its mass (Y(g)), and the graft ratio was calculated using the following formula (2). In the formula (2), Y is the mass (g) of the acetone insoluble component of the graft copolymer (D), X is the total mass (g) of the graft copolymer (D) used to determine Y, and the rubber fraction is the solids concentration in the aqueous dispersion of the core-shell type particles (C) used to produce the graft copolymer (D).
Graft ratio (mass%)={(Y−X×rubber fraction)/X×rubber fraction}
× 100 ... (2)

<Weight average molecular weight of copolymer (E)>
The mass average molecular weight of the copolymer (E) was determined by dissolving the copolymer in tetrahydrofuran (THF) and measuring the molecular weight by gel permeation chromatography (GPC), and converting the molecular weight into that of standard polystyrene (PS).

[Production Example 1: Production of Core-Shell Particles (C-1)]
<Production of Copolymer (A-1)>
First, a copolymer (A-1) was produced according to the following composition.

[Composition]
n-Butyl acrylate (BA) 40 parts Allyl methacrylate 0.16 parts Liquid paraffin (LP) 0.5 parts Dipotassium alkenyl succinate (ASK) 0.24 parts Dilauroyl peroxide 0.24 parts Ion-exchanged water 140 parts

A reactor equipped with a reagent injection vessel, a cooling tube, a jacket heater, and a stirrer was charged with n-butyl acrylate, liquid paraffin, allyl methacrylate, dilauroyl peroxide, ion-exchanged water, and dipotassium alkenylsuccinate, and a pre-emulsion was obtained by ultrasonic treatment at room temperature for 20 minutes at an amplitude of 35 μm using an ULTRASONIC HOMOGENIZER US-600 manufactured by Nippon Seiki Seisakusho Co., Ltd. The volume average particle size of the obtained latex was 350 nm.
The pre-emulsion was heated to 60° C. to initiate radical polymerization. Due to the polymerization, the liquid temperature rose to 78° C. The temperature was maintained at 75° C. for 30 minutes to complete the polymerization, thereby obtaining a copolymer (A-1) dispersed in an aqueous dispersion.

<Production of Core-Shell Particles (C-1)>
After producing the copolymer (A-1), an aqueous solution consisting of 0.0001 parts of ferrous sulfate, 0.0003 parts of disodium ethylenediaminetetraacetate, 0.2 parts of Rongalit, and 5 parts of ion-exchanged water was added while maintaining the internal temperature of the reactor at 75° C., and then 0.06 parts of dipotassium alkenylsuccinate was added. Thereafter, a mixed solution consisting of 10 parts of n-butyl acrylate, 0.25 parts of allyl methacrylate, and 0.02 parts of t-butyl hydroperoxide was added dropwise at a rate of 0.26 parts/min to polymerize the copolymer (B-1), thereby obtaining an aqueous dispersion of core-shell type particles (C-1).

[Production Examples 2 to 20, 23: Production of Core-Shell Particles (C-2) to (C-20), and (C-23)]
Core-shell particles (C-2) to (C-20) and (C-23) dispersed in an aqueous dispersion were obtained in the same manner as for the core-shell particles (C-1), except that the amounts of n-butyl acrylate, allyl methacrylate, dipotassium alkenyl succinate, dilauroyl peroxide and liquid paraffin used in producing copolymer (A-1) and the amounts of n-butyl acrylate, dipotassium alkenyl succinate, allyl methacrylate and t-butyl hydroperoxide used in producing copolymer (B) were changed as shown in Tables 1 and 2.

[Production Examples 21 and 22: Production of Rubber Particles (C-21) and (C-22)]
The amounts of n-butyl acrylate, allyl methacrylate, dipotassium alkenylsuccinate, and dilauroyl peroxide used in producing copolymer (A-1) were changed as shown in Table 2, and aqueous dispersions of non-core-shell type rubber particles (C-21) and (C-22) consisting only of copolymers (A-21) and (A-22) were obtained in the same manner as in the production of copolymer (A-1).

The volume average particle size and swelling degree of the copolymers (A-1) to (A-23) dispersed in the aqueous dispersions obtained in Production Examples 1 to 23, and the volume average particle size and swelling degree of the core-shell type particles or rubber particles (C-1) to (C-23) dispersed in the aqueous dispersions are shown in Tables 1 and 2.

[Example I-1: Production of Graft Copolymer (D-1)]
After producing the core-shell particles (C-1), an aqueous solution consisting of 0.001 part of ferrous sulfate, 0.003 part of disodium salt of ethylenediaminetetraacetic acid, 0.3 part of Rongalit, and 5 parts of ion-exchanged water was added to 50 parts of the core-shell particles (C-1) (as solid content) while maintaining the internal temperature of the reactor at 75° C., and then 0.1 part of dipotassium alkenylsuccinate was added. Thereafter, a mixed liquid consisting of 14 parts of acrylonitrile, 36 parts of styrene, and 0.17 parts of t-butyl hydroperoxide was added dropwise over 1 hour and 40 minutes to carry out graft polymerization.

After the dropwise addition was completed, the internal temperature was kept at 75°C for 10 minutes and then cooled. When the internal temperature reached 60°C, an aqueous solution of 0.2 parts of dipotassium alkenyl succinate dissolved in 5 parts of ion-exchanged water was added. The aqueous dispersion of the reaction product was then coagulated with an aqueous sulfuric acid solution, washed with water, and dried to obtain graft copolymer (D-1).

[Examples I-2 to I-14 and Comparative Examples I-1 to I-9: Production of Graft Copolymers (D-2) to (D-23)]
Graft copolymers (D-2) to (D-23) were obtained in the same manner as for graft copolymer (D-1), except that the type of core-shell particles or rubber particles (C) used was changed as shown in Tables 3 and 4.

The graft ratios of the graft copolymers (D-1) to (D-23) obtained in Examples I-1 to I-14 and Comparative Examples I-1 to I-9 are shown in Tables 3 and 4.

[Production of copolymer (E-1)]
In a pressure-resistant reaction vessel, 150 parts of ion-exchanged water, a mixture of 34 parts of acrylonitrile and 66 parts of styrene as a vinyl monomer mixture (m4), 0.2 parts of 2,2'-azobis(isobutyronitrile), 0.45 parts of n-octyl mercaptan, 0.47 parts of calcium hydroxyapatite, and 0.003 parts of potassium alkenyl succinate were charged, and the internal temperature was raised to 75°C and reacted for 3 hours. Thereafter, the temperature was raised to 90°C and maintained for 60 minutes to complete the reaction. The contents were washed and dehydrated repeatedly with a centrifugal dehydrator, and dried to obtain a copolymer (E-1) having a mass average molecular weight of 95,000.

[Examples II-1 to 14 and Comparative Examples II-1 to 9: Production and Evaluation of Thermoplastic Resin Compositions]
The components were mixed in the compositions (parts by mass) shown in Tables 5 and 6, and 0.8 parts of carbon black was further mixed therein. The mixture was melt-kneaded at 240°C using a 30 mmφ vacuum vented twin-screw extruder (Ikegai Corporation's "PCM30") to obtain a pellet-shaped thermoplastic resin composition. The melt volume rate of the obtained thermoplastic resin composition was evaluated by the following method. The molded product obtained by injection molding the obtained thermoplastic resin composition was evaluated for mold appearance and impact resistance by the following methods.
The evaluation results are shown in Tables 5 and 6.

[Each evaluation method]
<Melt Volume Rate (MVR) Measurement>
The MVR of the thermoplastic resin composition at 220° C. was measured under a load of 98 N (10 kg) in accordance with ISO 1133:1997. The MVR is an indicator of the fluidity of the thermoplastic resin composition, with a higher value indicating better fluidity.

<Injection molding 1>
The pellets of the thermoplastic resin composition obtained by melt kneading were molded into a molded article having a length of 80 mm, a width of 10 mm and a thickness of 4 mm using an injection molding machine (manufactured by Toshiba Machine Co., Ltd., "IS55FP-1.5A") under conditions of a cylinder temperature of 200 to 270°C and a mold temperature of 60°C, and the molded article was used as a molded article for a Charpy impact test (molded article (Ma1)).

<Injection molding 2>
The pellets of the thermoplastic resin composition obtained by melt kneading were molded into a molded article having a length of 100 mm, a width of 100 mm and a thickness of 3 mm using an injection molding machine (manufactured by Toshiba Machine Co., Ltd., "IS55FP-1.5A") under conditions of a cylinder temperature of 200 to 270°C, a mold temperature of 60°C and an injection rate of 7 g/sec. This was used as a molded article for appearance evaluation (molded article (Ma2)).

<Injection molding 3>
The pellets of the thermoplastic resin composition obtained by melt kneading were molded into a molded article having a length of 100 mm, a width of 100 mm and a thickness of 3 mm using an injection molding machine (manufactured by Toshiba Machine Co., Ltd., "IS55FP-1.5A") under conditions of a cylinder temperature of 200 to 270°C, a mold temperature of 60°C and an injection rate of 128 g/sec. This was used as a molded article for appearance evaluation (molded article (Ma3)).

<Appearance Evaluation (1)>
The lightness L ^* of the molded product (Ma2) was measured by the SCE method using a spectrophotometer (Konica Minolta Optips Co., Ltd. "CM-3500d"). The L ^* thus measured is called "L ^* (ma)". The lower the L ^* , the blacker the color and the better the appearance.

<Appearance Evaluation (2)>
The lightness L ^* of the molded product (Ma3) was measured by the SCE method using a spectrophotometer (Konica Minolta Optips Co., Ltd. "CM-3500d"). The L ^* thus measured is referred to as "L ^* (mb)". The lower the L ^* , the blacker the color and the better the appearance.
When molding is performed under conditions of high injection speed, the rubber components in the resin become oriented, causing whitening and bronzing, and increasing L ^* . Therefore, the appearance of the molded product under conditions of high injection speed is important.

<Appearance Evaluation (3) (Evaluation of Dependence of Appearance on Injection Speed)>
ΔL ^* was calculated from formula ² : ΔL ^* = (L ^* (mb) - L ^* (ma)). The smaller ΔL ^* is, the less injection speed dependency of the appearance. Generally, in molded products such as vehicle parts, the injection speed differs depending on the part location. Therefore, with a resin that is highly injection speed dependent, color unevenness occurs on the surface of the part during molding, resulting in poor appearance.

<Impact resistance evaluation: Charpy impact test>
The Charpy impact strength (impact direction: edgewise) of the molded article (Ma1) was measured at a test temperature of 23° C. or −20° C. (Type B1, notched: Shape A single notch) in accordance with ISO 179-1:2013 edition. The higher the Charpy impact strength, the better the impact resistance.

As shown in Examples II-1 to 14 in Table 5, each example produced a thermoplastic resin composition and molded product with excellent impact resistance, fluidity, and appearance.

On the other hand, in Comparative Example II-1, the swelling degree of the copolymer (A) and the core-shell type particles (C) was low, and in Comparative Example II-2, the swelling degree of the core-shell type particles (C) was low, so that the impact resistance was low and the fluidity was also low. In Comparative Example II-3, the swelling degree of the copolymer (A) was lower than that of the core-shell type particles (C), so that the molded appearance was poor. In Comparative Example II-4, the swelling degree of the core-shell type particles (C), in Comparative Example II-5, the swelling degrees of the copolymer (A) and the core-shell type particles (C), and in Comparative Example II-6, the swelling degree of the copolymer (A) were high, so that the molded appearance was poor.
In Comparative Example II-7, the rubber portion is not a core-shell type particle, and therefore the molded appearance is poor. When the swelling degree is reduced in an attempt to improve the molded appearance of Comparative Example II-7, the impact resistance is deteriorated as in Comparative Example II-8.
In Comparative Example II-9, since the vinyl monomer mixture (m1) did not contain the hydrophobic substance (Ab), it was difficult to control the particle size of the copolymer (A), and the obtained graft copolymer (D-23) had poor impact resistance.

Claims (14)

A graft copolymer (D) obtained by polymerizing a vinyl monomer mixture (m3) in the presence of core-shell type particles (C) having a core portion made of a copolymer (A) obtained by polymerizing a vinyl monomer mixture (m1) containing a (meth)acrylic acid ester (Aa) and a hydrophobic substance (Ab) having a hydrocarbon group selected from an alkyl group, an alkenyl group and a cycloalkyl group having 12 or more carbon atoms, and a shell portion made of a copolymer (B) obtained by polymerizing a vinyl monomer mixture (m2) containing a (meth)acrylic acid ester (Ba),
a graft copolymer (D) in which the swelling degree of the copolymer (A) is 7 to 15 times, the swelling degree of the core-shell type particles (C) is 5 to 12 times, and the swelling degree of the copolymer (A) is greater than the swelling degree of the core-shell type particles (C);
the hydrophobic substance (Ab) is a hydrophobic substance having a logarithm [log P] value of a partition coefficient [P] represented by the ratio [c1/c2] of a concentration [c1] in 1-octanol to a concentration [c2] in water of 6 or more;
The hydrophobic substance (Ab) is one or more of liquid paraffin, liquid isoparaffin, and paraffin wax ;
The vinyl monomer mixture (m3) contains an aromatic vinyl monomer and a vinyl cyanide monomer, and the content of the aromatic vinyl monomer contained in the vinyl monomer mixture (m3) is 40 to 90 mass %, and the content of the vinyl cyanide monomer is 10 to 60 mass %. The graft copolymer (D) according to claim 1 , wherein the content of the copolymer (A) is 60 to 96 mass% and the content of the copolymer (B) is 4 to 40 mass% in 100 mass% of the core-shell type particles (C). The graft copolymer (D) according to claim 1 or 2 , wherein the copolymer (A) contains a (meth)acrylic acid ester (Aa) unit and a unit derived from a crosslinking agent and/or a unit derived from a graft crosslinking agent. The graft copolymer (D) according to claim 3 , wherein the ratio of the units derived from the crosslinking agent and/or the graft crosslinking agent in the copolymer (A) is 0.05 to 0.3 mass% in a total of 100 mass% of the (meth)acrylic acid ester (Aa) units and the units derived from the crosslinking agent and/or the units derived from the graft crosslinking agent. The graft copolymer (D) according to claim 3 or 4 , wherein the vinyl-based monomer mixture (m1) contains the hydrophobic substance (Ab) in an amount of 0.1 to 10 parts by mass per 100 parts by mass of the (meth)acrylic acid ester (Aa) and the crosslinking agent and/or the graft crosslinking agent in total. The graft copolymer (D) according to any one of claims 1 to 5 , wherein the copolymer (B) contains a (meth)acrylic acid ester (Ba) unit and a unit derived from a crosslinking agent and/or a unit derived from a graft crosslinking agent. The graft copolymer (D) according to claim 6 , wherein the ratio of the units derived from the crosslinking agent and/or the graft crosslinking agent in the copolymer (B) is 0.03 to 0.3 mass% in a total of 100 mass% of the (meth)acrylic acid ester (Ba) units and the units derived from the crosslinking agent and/or the units derived from the graft crosslinking agent. The graft copolymer (D) according to any one of claims 1 to 7 , wherein the volume average particle diameter of the copolymer (A) is 50 to 800 nm, and the volume average particle diameter of the core-shell particles (C) is 60 to 820 nm. The graft copolymer (D) according to any one of claims 1 to 8 , wherein a ratio of the core-shell particles (C) to a total of 100% by mass of the core-shell particles (C) and the vinyl-based monomer mixture (m3) is 50 to 80% by mass, a ratio of the vinyl-based monomer mixture (m3) is 20 to 50% by mass, and a graft ratio is 25 to 100%. A thermoplastic resin composition comprising the graft copolymer (D) according to any one of claims 1 to 9 . The thermoplastic resin composition according to claim 10 , comprising the graft copolymer (D) and a copolymer (E) obtained by polymerizing a vinyl monomer mixture (m4). The thermoplastic resin composition according to claim 11 , wherein the vinyl-based monomer mixture (m4) contains an aromatic vinyl-based monomer having the same structure as the aromatic vinyl-based monomer contained in the vinyl-based monomer mixture (m3), and a cyanide vinyl-based monomer having the same structure as the cyanide vinyl-based monomer contained in the vinyl-based monomer mixture (m3). The thermoplastic resin composition according to claim 11 or 12 , comprising 10 to 50 mass% of the graft copolymer (D) and 50 to 90 mass% of the copolymer (E) in a total of 100 mass% of the graft copolymer (D) and the copolymer (E). A molded article obtained by molding the thermoplastic resin composition according to any one of claims 10 to 13 .