JP2006298977A - Thermoplastic resin composition and molded article - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermoplastic resin composition having characteristics which a polyacetal resin has originally, particularly capable of providing a molded article improved in mechanical properties and suppressed in decomposition of polyacetal resin and to provide the molded article. <P>SOLUTION: The thermoplastic resin composition comprises (A) a graft copolymer obtained by carrying out graft polymerization of a rubber-like polymer (R) obtained by polymerizing a monomer constituting a rubber-like polymer in the presence of α-methylstyrene dimer with a vinyl-based monomer and (B) a polyacetal resin. The molded article is obtained by molding the resin composition. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a thermoplastic resin composition containing a polyacetal resin and a molded article formed by molding the same.

  Polyacetal resin is an engineering plastic with excellent mechanical strength, fatigue resistance, slidability, chemical resistance, etc., made of resin in OA equipment, information equipment, home appliances, automobiles, clothing, stationery, sundries, building materials, etc. Widely used as materials for gears, mechanical parts, etc. In particular, in addition to the above characteristics, it can be mass-produced at low cost, etc., so that it is used as a material for buttons, clips, and gears that require the above characteristics.

When polyacetal resin is used as a material for buttons, clips, and gears, performance such as high impact resistance, low noise, low wear, and high accuracy is required. In particular, it is important to have excellent impact resistance.
As a means for improving the impact resistance of a molded article made of polyacetal resin, a reinforcing filler such as an inorganic filler such as glass fiber, carbon fiber, potassium titanate whisker, calcium carbonate, or talc is added to polyacetal resin. It is possible. However, since the reinforcing filler is usually harder than the polyacetal resin, the reinforcing filler may scrape the polyacetal resin during sliding to increase the amount of wear.

In addition, homopolymers and copolymers exist in polyacetal resins, and homopolymers tend to have higher impact resistance than copolymers. However, the homopolymer has a large post-shrinkage accompanying the progress of crystallization, and therefore has poor dimensional stability and is not suitable for the exemplified applications.
In addition, in consideration of plating applications, clip characteristics, and the like, Patent Document 1 and Examples in which a core-shell polymer having a rubber-like polymer core and a glass-like polymer shell is blended with a polyacetal resin to improve impact resistance are disclosed. 2 is proposed. However, the impact resistance is still insufficient, and further improvement in impact resistance is required. Further, there is a problem that the polyacetal resin is easily decomposed during melt-kneading and molding of the core-shell polymer and the polyacetal resin.
JP-A-2-129266 JP-A-6-1000075

  An object of the present invention is to provide a thermoplastic resin composition having inherent properties of a polyacetal resin, particularly capable of obtaining a molded article having improved mechanical properties such as impact resistance, and in which decomposition of the polyacetal resin is suppressed, and An object of the present invention is to provide a molded article having the original characteristics of polyacetal resin and having improved mechanical properties such as impact resistance.

The thermoplastic resin composition of the present invention comprises a graft copolymer (A) obtained by graft polymerization of a vinyl monomer to a rubbery polymer (R), and a polyacetal resin (B), and the rubbery polymer The polymer (R) is obtained by polymerizing a monomer constituting the rubber polymer in the presence of α-methylstyrene dimer.
The molded article of the present invention is formed by molding the thermoplastic resin composition of the present invention.

According to the thermoplastic resin composition of the present invention, it is possible to obtain a molded product having the original characteristics of a polyacetal resin, in particular, improved mechanical properties such as impact resistance, and the decomposition of the polyacetal resin is suppressed.
The molded article of the present invention has the original characteristics of polyacetal resin, and particularly has improved mechanical properties such as impact resistance.

<Rubber polymer (R)>
The rubber polymer (R) is a rubber polymer obtained by polymerizing monomers constituting the rubber polymer in the presence of α-methylstyrene dimer.
Usually, at the time of production of a rubbery polymer, in order to ensure the impact resistance of the obtained molded product, the degree of rubber crosslinking is controlled using a chain transfer agent. For example, when a chain transfer agent is not used, the degree of rubber cross-linking of the rubbery polymer is increased, which may lead to a reduction in impact resistance of the resulting molded product. Mercaptan compounds are used.

  In the present invention, α-methylstyrene dimer is used as a chain transfer agent. By using α-methylstyrene dimer, the thermal stability and decomposition resistance of the polyacetal resin (B) can be improved as compared with the case of using a conventional mercaptan-based compound or the like. In addition, about chain transfer agents other than alpha methyl styrene dimer, you may use in the range which does not exceed the usage-amount of alpha methyl styrene dimer on a mass basis.

  The amount of α-methylstyrene dimer used is preferably 0.01 to 20% by mass, more preferably 0.05 to 10% by mass, and more preferably 0.1 to 5% by mass in 100% by mass of the rubber polymer (R). Is particularly preferred. When the amount of α-methylstyrene dimer used is less than 0.01% by mass, the effect of chain transfer is not sufficiently exhibited, and the mechanical properties of the obtained molded product may be insufficient. If the amount of α-methylstyrene dimer used exceeds 20% by mass, the impact resistance of the molded product may be reduced.

Examples of the rubber polymer (R) include the following.
(1) A diene rubber (R1) obtained by polymerizing a monomer containing a diene monomer in the presence of α-methylstyrene dimer.
(2) Polyalkyl (meth) acrylate obtained by polymerizing a monomer containing (meth) acrylic acid ester in the presence of α-methylstyrene dimer and containing two or more kinds of acrylic rubber components having different glass transition temperatures -Based composite rubber (R2).
(3) A silicone / acrylic composite rubber (R3) obtained by polymerizing a monomer containing (meth) acrylic acid ester in the presence of polyorganosiloxane and α-methylstyrene dimer.
In the present invention, “(meth) acrylic acid ester” means acrylic acid ester and / or methacrylic acid ester, and “alkyl (meth) acrylate” means alkyl acrylate and / or alkyl methacrylate.
Of these rubber polymers (R), the diene rubber (R1) is suitable as the rubber polymer (R) produced using a chain transfer agent.
Hereinafter, these rubber-like polymers (R) will be described.

(Diene rubber (R1))
The diene rubber is preferably a 1,3-butadiene homopolymer or copolymer (hereinafter referred to as a butadiene rubber polymer). The butadiene rubber polymer is obtained by polymerizing 1,3-butadiene, if necessary, a crosslinkable monomer and a vinyl monomer copolymerizable with 1,3-butadiene.

  Examples of the crosslinkable monomer include aromatic polyfunctional vinyl compounds such as divinylbenzene and divinyltoluene; dicarboxylic acid esters of polyhydric alcohols such as ethylene glycol dimethacrylate and 1,3-butanediol diacrylate; trimethacrylic acid Examples include esters; triacrylic acid esters; carboxylic acid allyl esters such as allyl acrylate and allyl methacrylate; di- or triallyl compounds such as diallyl phthalate, diallyl sebacate, and triallyl triazine. A crosslinkable monomer may be used individually by 1 type, and may use 2 or more types together.

  Examples of vinyl monomers that can be copolymerized with 1,3-butadiene (excluding crosslinkable monomers; the same shall apply hereinafter) include aromatic vinyl compounds such as styrene and α-methylstyrene; methyl methacrylate, Alkyl methacrylates such as ethyl methacrylate; alkyl acrylates such as ethyl acrylate and n-butyl acrylate; unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; vinyl ethers such as methyl vinyl ether and butyl vinyl ether; halogenation such as vinyl chloride and vinyl bromide Vinyl: vinylidene halides such as vinylidene chloride and vinylidene bromide; glycidyl group-containing vinyl monomers such as glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, and ethylene glycol glycidyl ether It is. A vinyl monomer may be used individually by 1 type, and may use 2 or more types together.

  The proportion of each monomer is 65 to 100% by mass of 1,3-butadiene and 0 to 10% of the crosslinkable monomer when the total amount of monomers used for the polymerization of the butadiene rubber polymer is 100% by mass. It is preferable to use a vinyl monomer that can be copolymerized with 1,3-butadiene. By making 1,3-butadiene 65 mass% or more, a good impact resistance imparting effect can be obtained. The crosslinkable monomer is preferably 10% by mass or less from the viewpoint of impact resistance imparting effect.

  As a method for producing a butadiene rubber polymer, an emulsion polymerization method is preferred. In the emulsion polymerization, various known emulsifiers can be appropriately used. As the emulsifier, a sulfonic acid salt compound and / or a sulfate salt compound is preferable. Although superposition | polymerization temperature is based also on the kind of polymerization initiator, it is about 40-80 degreeC normally. Further, before starting the polymerization, for example, a seed latex containing styrene or the like may be charged in advance.

  As the emulsion polymerization method, a multistage emulsion polymerization method is preferred. Specifically, a method in which a part of the monomer is charged in the reaction system in advance and the remaining monomer is added all at once, dividedly, or continuously after the polymerization is started is particularly preferable. In the multistage emulsion polymerization method, the composition of the monomer charged in the initial stage and the composition of the monomer added later may be the same or different. By adopting a multistage emulsion polymerization method, good polymerization stability can be obtained, and a latex of a butadiene rubber polymer having a desired particle size and particle size distribution can be stably obtained. In addition, by using a butadiene rubber polymer obtained by a multistage emulsion polymerization method, a molded product having very excellent impact resistance, fluidity, and molded appearance can be obtained.

  The mass average particle diameter (dw) of the butadiene rubber polymer is preferably 80 to 800 nm, more preferably 85 to 400 nm, and particularly preferably 90 to 250 nm. If the mass average particle diameter (dw) is less than 80 nm, the impact resistance imparting effect may be reduced. If the mass average particle diameter (dw) exceeds 800 nm, the impact resistance of the molded product may be reduced.

As for the particle size distribution of the butadiene rubber polymer, a high level of impact strength is obtained when the ratio (dw / dn) of the mass average particle size (dw) to the number average particle size (dn) is 2 or less. It is preferable for this purpose. If dw / dn of the butadiene rubber polymer exceeds 2, the impact resistance imparting effect may be reduced.
The mass average particle diameter (dw) and dw / dn of the butadiene rubber polymer can be measured by a known method. For example, it can be measured using a commercially available capillary particle size distribution meter.

(Polyalkyl (meth) acrylate composite rubber (R2))
Examples of the polyalkyl (meth) acrylate composite rubber (R2) include (meth) acrylic acid esters of alcohol having branched side chains, (meth) acrylic acid esters of alcohols having an alkyl group having 13 or more carbon atoms, and ethoxyethoxy. An acrylic rubber component (1) containing at least one selected from the group consisting of ethyl acrylate and 4-hydroxybutyl acrylate as a constituent unit, and an acrylic rubber component (2) containing n-butyl acrylate as a constituent unit. And the composite rubber whose glass transition temperature (Tg1) derived from an acrylic rubber component (1) is lower than the glass transition temperature (Tg2) derived from an acrylic rubber component (2) is preferable. The composite rubber containing the acrylic rubber component (1) and the acrylic rubber component (2) has an excellent impact resistance imparting effect. A composite rubber having a Tg1 lower than Tg2 is excellent in impact resistance imparting effect at low temperatures.

The acrylic rubber component (1) is a (meth) acrylic ester of an alcohol having a branched side chain, an (meth) acrylic ester of an alcohol having an alkyl group having 13 or more carbon atoms, ethoxyethoxyethyl acrylate, and 4-hydroxybutyl. It contains at least one selected from the group consisting of acrylate as a structural unit.
Examples of the (meth) acrylic ester of alcohol having a branched side chain include 2-ethylhexyl acrylate, methoxytripropylene glycol acrylate, isobutyl acrylate, and 3-methoxybutyl acrylate. Examples of the (meth) acrylic acid ester of an alcohol having an alkyl group having 13 or more carbon atoms include lauryl methacrylate, tridecyl methacrylate, stearyl methacrylate and the like.

  Among these, when at least one of 2-ethylhexyl acrylate, ethoxyethoxyethyl acrylate, methoxytripropylene glycol acrylate, 4-hydroxybutyl acrylate, lauryl methacrylate, and stearyl methacrylate is included as a constituent unit, impact resistance imparting effect When at least one of 2-ethylhexyl acrylate, lauryl methacrylate, and stearyl methacrylate is included as a structural unit, the impact resistance imparting effect at low temperatures is particularly excellent.

The acrylic rubber component (1) may contain structural units composed of other monomers as necessary. Examples of other monomers include other vinyl monomers and monomers having two or more polymerizable double bonds (hereinafter referred to as polyfunctional monomers).
Other vinyl monomers include (meth) acrylic acid esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate and n-butyl acrylate; aromatic vinyl compounds such as styrene, α-methyl styrene and vinyl toluene; Examples thereof include unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; methacrylic acid-modified silicones, fluorine-containing vinyl compounds and the like. These other vinyl monomers may be used alone or in combination of two or more. The structural unit which consists of another vinyl monomer is 30 mass% or less in an acrylic rubber component (1) (100 mass%).

  The polyfunctional monomer has a role as a crosslinking agent or a graft crossing agent. Examples of the crosslinking agent include ethylene glycol dimethacrylate, propylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,4-butylene glycol dimethacrylate, divinylbenzene, and polyfunctional methacrylic group-modified silicone. Examples of the graft crossing agent include allyl methacrylate, triallyl cyanurate, triallyl isocyanurate and the like. Allyl methacrylate can also be used as a crosslinking agent. These polyfunctional monomers may be used individually by 1 type, and may use 2 or more types together. The structural unit consisting of a polyfunctional monomer is 20% by mass or less, preferably 0.1 to 18% by mass, in the acrylic rubber component (1) (100% by mass).

  The acrylic rubber component (2) contains n-butyl acrylate as a structural unit. The acrylic rubber component (2) may contain structural units composed of other monomers as necessary. Examples of other monomers include other vinyl monomers and polyfunctional monomers.

  Other vinyl monomers include methyl acrylate, ethyl acrylate, n-propyl acrylate, 2-ethylhexyl acrylate, ethoxyethoxyethyl acrylate, methoxytripropylene glycol acrylate, 4-hydroxybutyl acrylate, lauryl methacrylate, stearyl methacrylate, etc. (Meth) acrylic acid esters; aromatic vinyl compounds such as styrene, α-methylstyrene and vinyltoluene; unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; methacrylic acid-modified silicones and fluorine-containing vinyl compounds. These other vinyl monomers may be used alone or in combination of two or more. The structural unit which consists of another vinyl-type monomer is 30 mass% or less in an acrylic rubber component (2) (100 mass%).

  Examples of the polyfunctional monomer include the above-described crosslinking agents and graft crossing agents. These polyfunctional monomers may be used individually by 1 type, and may use 2 or more types together. The structural unit consisting of a polyfunctional monomer is 20% by mass or less, preferably 0.1 to 18% by mass, in the acrylic rubber component (2) (100% by mass).

  The polyalkyl (meth) acrylate composite rubber (R2) has a glass transition temperature (Tg1) derived from the acrylic rubber component (1) lower than a glass transition temperature (Tg2) derived from the acrylic rubber component (2). From the viewpoint of impact resistance, Tg1 and Tg2 are preferably 10 ° C. or lower.

  The glass transition temperature of the polyalkyl (meth) acrylate composite rubber (R2) is measured as a transition point of a Tan δ curve measured by a dynamic mechanical property analyzer (hereinafter referred to as DMA). A polymer obtained by polymerizing a vinyl monomer has a unique glass transition temperature, and is a homopolymer obtained by polymerizing a single vinyl monomer or a plurality of vinyl monomers. In the random copolymer obtained by polymerizing the monomer, one transition point is observed. On the other hand, in a mixture of several types of polymers or a polymer in which several types of polymers are complexed, a plurality of transition points derived from the respective polymer components are observed. For example, in the case of the rubbery polymer (A) containing at least the acrylic rubber component (1) and the acrylic rubber component (2), at least two transition points (Tg1 and Tg2) are observed in the Tan δ curve. In the Tan δ curve measured by DMA, when the composition ratio is uneven or when the transition temperature is close, the peak derived from each polymer may approach and may be observed as a peak having a shoulder portion. However, it can be distinguished from the simple one-peak curve found in the case of a homopolymer or a random copolymer. That is, the glass transition temperature (Tg1) derived from the acrylic rubber component (1) is observed to be lower than the glass transition temperature (Tg2) derived from the acrylic rubber component (2).

  The production method of the polyalkyl (meth) acrylate composite rubber (R2) includes (meth) acrylate ester of alcohol having a branched side chain, and (meth) acrylate ester of alcohol having an alkyl group having 13 or more carbon atoms. A monomer mixture containing at least one of ethoxyethoxyethyl acrylate and 4-hydroxybutyl acrylate is polymerized by an emulsion polymerization method or the like to obtain latex of acrylic rubber component (1), and then acrylic rubber component Examples include a method in which a monomer mixture containing n-butyl acrylate is added to and impregnated in the latex of (1) and then polymerized in the presence of a radical polymerization initiator. As the polymerization proceeds, a latex of a polyalkyl (meth) acrylate composite rubber (R2) in which two acrylic rubber components are combined is obtained. As another method, a method in which a monomer mixture containing n-butyl acrylate is suitably polymerized in the latex of the acrylic rubber component (1) (appropriate polymerization method) can be mentioned. Moreover, you may enlarge the compounded rubber | gum with an acid or a salt.

The method for producing the acrylic rubber component (1) is preferably an emulsion polymerization method, and 2-ethyl acrylate, lauryl methacrylate, and stearyl methacrylate are poor in water solubility, and therefore a forced emulsion polymerization method is more preferable. When stearyl methacrylate or the like having crystallinity near room temperature is used, it is preferably used by mixing it with a monomer that dissolves it.
Examples of the emulsifier and dispersion stabilizer include known surfactants such as anionic, nonionic, and cationic. When these mixtures are used, it is preferable to use a combination of an emulsifier having a large micelle-forming ability and an emulsifier having a small micelle-forming ability.

The mass average particle diameter (dw) of the polyalkyl (meth) acrylate composite rubber (R2) is preferably 100 to 800 nm in consideration of the impact resistance and the molded appearance of the obtained molded product. When the mass average particle diameter (dw) is less than 100 nm, the impact resistance of the molded product may be reduced. If the mass average particle diameter (dw) exceeds 800 nm, the impact resistance of the molded product may be reduced and the molded appearance may be deteriorated.
The mass average particle diameter (dw) is determined by measuring the mass distribution. The “mass distribution” is a distribution in which the mass ratio of particles within a minute interval between a certain particle diameter dp and dp + Δdp is expressed as a percentage. The mass average particle diameter of the polyalkyl (meth) acrylate composite rubber (R2) can be measured in the same manner as in the above butadiene rubber polymer.

(Silicone / acrylic composite rubber (R3))
The silicone / acrylic composite rubber (R3) has a structure in which 1 to 99% by mass of the polyorganosiloxane component and 99 to 1% by mass of the polyalkyl (meth) acrylate rubber component are intertwined so as not to be separated, and The total amount of the polyorganosiloxane component and the polyalkyl (meth) acrylate rubber component is preferably 100% by mass.

  As the polyorganosiloxane, a polyorganosiloxane containing a vinyl polymerizable functional group is preferable. The polyorganosiloxane is obtained by polymerizing a siloxane mixture containing a diorganosiloxane, a vinyl polymerizable functional group-containing siloxane, and, if necessary, a siloxane crosslinking agent.

  Examples of the diorganosiloxane include 3-membered or more diorganosiloxane-based cyclic bodies, and those having 3 to 7-membered rings are particularly preferable. Specific examples include hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, and dodecamethylcyclohexasiloxane. These may be used alone or in combination of two or more.

  Any vinyl polymerizable functional group-containing siloxane may be used as long as it contains a vinyl polymerizable functional group and can be bonded to a diorganosiloxane via a siloxane bond. Various alkoxysilane compounds containing a functional functional group are preferred. Specifically, β-methacryloyloxyethyldimethoxymethylsilane, γ-methacryloyloxypropyldimethoxymethylsilane, γ-methacryloyloxypropylmethoxydimethylsilane, γ-methacryloyloxypropyltrimethoxysilane, γ-methacryloyloxypropylethoxydiethylsilane, methacryloyloxysilane such as γ-methacryloyloxypropylethoxydiethoxymethylsilane, δ-methacryloyloxybutyldiethoxymethylsilane; vinylsiloxane such as tetramethyltetravinylcyclotetrasiloxane; vinylphenylsilane such as p-vinylphenyldimethoxymethylsilane Mercaptosyl such as γ-mercaptopropyldimethoxymethylsilane, γ-mercaptopropyltrimethoxysilane, etc. Acid and the like. A vinyl polymerizable functional group containing siloxane may be used individually by 1 type, and may use 2 or more types together.

  Examples of the siloxane crosslinking agent include trifunctional or tetrafunctional silane crosslinking agents such as trimethoxymethylsilane, triethoxyphenylsilane, tetramethoxysilane, tetraethoxysilane, and tetrabutoxysilane.

  Polyorganosiloxane can be produced, for example, by rotating a latex obtained by emulsifying a siloxane mixture containing diorganosiloxane, vinyl polymerizable functional group-containing siloxane and, if necessary, a siloxane-based crosslinking agent with an emulsifier and water at high speed. After making the particles fine using a homomixer that makes fine particles by the shearing force of a high pressure generator, a homogenizer that makes fine particles by the jet output of a high-pressure generator, etc., polymerize at high temperature using an acid catalyst, and then neutralize the acid catalyst with an alkaline substance This can be done.

  Examples of the method for adding an acid catalyst include (i) a method of mixing with a siloxane mixture, an emulsifier and water; (ii) a method of dropping a latex in which a siloxane mixture is atomized into a high-temperature acid aqueous solution at a constant rate. . Considering the ease of control of the particle diameter of the polyorganosiloxane, the method (ii) is preferable. Moreover, as a method of mixing a siloxane mixture, an emulsifier, water, and / or an acid catalyst, the method of mixing by high speed stirring, the method of mixing using high pressure emulsifiers, such as a homogenizer, etc. are mentioned. Among these, the method of mixing using a homogenizer is preferable because the particle size distribution of the polyorganosiloxane latex can be reduced.

  Examples of the emulsifier include anionic surfactants such as sodium alkylbenzene sulfonate, sodium lauryl sulfate, and sodium polyoxyethylene nonylphenyl ether sulfate. Of these, sodium alkylbenzene sulfonate and sodium lauryl sulfate are particularly preferred.

  Examples of the acid catalyst include sulfonic acids such as aliphatic sulfonic acid, aliphatic substituted benzenesulfonic acid, and aliphatic substituted naphthalenesulfonic acid; and mineral acids such as sulfuric acid, hydrochloric acid, and nitric acid. These acid catalysts may be used alone or in combination of two or more. Of these, aliphatic substituted benzenesulfonic acid is preferable, and n-dodecylbenzenesulfonic acid is particularly preferable in that it is excellent in the stabilizing effect of the polyorganosiloxane latex. In addition, when n-dodecylbenzenesulfonic acid and a mineral acid such as sulfuric acid are used in combination, the appearance defect of the molded product due to the emulsifier component of the polyorganosiloxane latex can be reduced, which is preferable.

  The polymerization of the siloxane mixture can be stopped by cooling the reaction solution and further neutralizing the acid catalyst with an alkaline substance such as sodium hydroxide, potassium hydroxide or sodium carbonate.

The silicone / acrylic composite rubber (R3) can be produced by adding a (meth) acrylic acid ester to a polyorganosiloxane latex and polymerizing with a known radical polymerization initiator.
As a method for adding the (meth) acrylic acid ester, there are a method of mixing with a polyorganosiloxane latex at a time, a method of dropping at a constant rate into the polyorganosiloxane latex, and the like. However, considering the impact resistance of the resulting resin composition, the former method is preferred.

  Examples of (meth) acrylic acid esters include alkyl acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate; hexyl methacrylate, 2-ethylhexyl methacrylate, and n-lauryl methacrylate. Examples thereof include alkyl methacrylate. Among these, n-butyl acrylate is particularly preferable in consideration of the impact resistance and molding gloss of the molded product.

Examples of (meth) acrylic acid esters include allyl methacrylate, ethylene glycol dimethacrylate, propylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,4-butylene glycol dimethacrylate, triallyl cyanurate, Polyfunctional (meth) acrylates such as allyl isocyanurate may be used.
One (meth) acrylic acid ester may be used alone, or two or more may be used in combination.

  Examples of radical polymerization initiators include peroxides, azo initiators, redox initiators combined with oxidizing agents and reducing agents, and the like. Among these, a redox initiator is preferable, and a redox initiator combined with ferrous sulfate, ethylenediaminetetraacetic acid disodium salt, longalite, and hydroperoxide is particularly preferable.

  The mass average particle diameter (dw) of the silicone / acrylic composite rubber (R3) is preferably 100 to 800 nm in consideration of the impact resistance and molded appearance of the molded product. When the mass average particle diameter (dw) is less than 100 nm, the impact resistance of the molded product may be lowered. When the mass average particle diameter (dw) exceeds 800 nm, the impact resistance of the molded product is lowered and the molded appearance may be deteriorated.

<Graft copolymer (A)>
The graft copolymer (A) is obtained by graft-polymerizing a vinyl monomer to the rubber polymer (R), and is added to the polyacetal resin (B) as an impact strength modifier. Examples of the graft copolymer (A) include the following.
(1) Graft copolymer (A1) obtained by graft-polymerizing vinyl monomer to diene rubber (R1).
(2) A graft copolymer (A2) obtained by graft-polymerizing a vinyl monomer to a polyalkyl (meth) acrylate composite rubber (R2).
(3) Graft copolymer (A3) obtained by graft-polymerizing a vinyl monomer to silicone / acrylic composite rubber (R3).
Hereinafter, these graft copolymers (A) will be described.

(Graft copolymer (A1))
The graft copolymer (A1) has a mass average particle diameter (dw) of 80 to 800 nm and a ratio (dw / dn) of the mass average particle diameter (dw) to the number average particle diameter (dn) of 2. In the presence of a latex containing 50 to 85% by mass of the following butadiene-based rubber polymer, a total of 80 to 100% by mass of a methacrylic acid ester and an aromatic vinyl compound, and other vinyl-based monomers copolymerizable therewith A graft copolymer obtained by polymerizing 0 to 20% by mass of the polymer (provided that the total amount of these monomers is 100% by mass) is preferred.

  The content of the butadiene rubber polymer in the latex (100% by mass) is preferably 50 to 85% by mass. When the content of the butadiene rubber polymer is less than 50% by mass, the impact resistance of the molded product may be insufficient. When the content of the butadiene-based rubber polymer exceeds 85% by mass, the dispersibility of the graft copolymer (A1) in the polyacetal resin (B) which is a matrix resin is reduced, and the butadiene-based rubber polymer After graft polymerization of the vinyl monomer, it may be difficult to recover the graft copolymer (A1) as a powder.

  The graft copolymer (A1) is a total of 80 to 100% by mass of a methacrylic ester and an aromatic vinyl compound in the presence of a latex of a butadiene rubber polymer, and other vinyl monomers that can be copolymerized therewith. It is obtained by polymerizing 0 to 20 parts by mass of the body (however, the total amount of these vinyl monomers is 100% by mass), and then recovering as a powder by spray drying or salting out.

  As the graft polymerization method, single-stage polymerization or multistage polymerization of two or more stages can be applied. When employing multistage polymerization, it is particularly preferable to prepare a part of the monomer used for the polymerization in the reaction system in advance and then add the remaining monomers all at once, divided addition or continuous addition after the start of the polymerization. By adopting such a polymerization method, it is possible to obtain a latex of the graft copolymer (A1) having good polymerization stability and having a desired particle size distribution.

The vinyl monomer contains at least a methacrylic acid ester, and if necessary, an aromatic vinyl compound and, if necessary, other vinyl monomers copolymerizable with these. .
As the methacrylic acid ester, the affinity with the polyacetal resin (B) which is a matrix resin is enhanced, and after graft polymerization of a vinyl monomer to a butadiene rubber polymer, the graft copolymer (A1) Alkyl methacrylate is preferable because it is recovered as a good powder. Examples of the alkyl methacrylate include methyl methacrylate and ethyl methacrylate.
Examples of the aromatic vinyl compound include styrene, α-methylstyrene, halogen, and alkyl-substituted styrene.

Examples of other vinyl monomers include alkyl acrylates such as ethyl acrylate and n-butyl acrylate; unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; glycidyl group-containing vinyl systems such as glycidyl acrylate, glycidyl methacrylate, and allyl glycidyl ether. And monomers. Moreover, you may use together the crosslinkable monomer used for manufacture of a butadiene-type rubber polymer.
These vinyl monomers may be used alone or in combination of two or more.

  When the total amount of the vinyl monomer is 100% by mass, the methacrylic acid ester is 10 to 100% by mass, the aromatic vinyl compound is 0 to 70% by mass, and the other vinyl monomer is 0 to 20% by mass. preferable.

  The ratio of the butadiene rubber polymer and the vinyl monomer is 50 to 85 mass butadiene rubber polymer when the total of the butadiene rubber polymer (solid content) and the vinyl monomer is 100 mass%. %, And the vinyl monomer is preferably 15 to 50% by mass. If the ratio of a vinyl-type monomer is 50 mass% or less, it is preferable at points, such as the impact resistance of a molded article. If the ratio of the vinyl monomer is 15% by mass or more, a lump is hardly generated at the time of graft polymerization, which is preferable in terms of moldability.

  In the graft polymerization, various radical polymerization initiators may be used as necessary. Examples of the radical polymerization initiator include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate; t-butyl hydroperoxide, cumene hydroperoxide, benzoyl peroxide, lauroyl peroxide, diisopropylbenzene hydroperoxide Organic peroxides such as: azo-based initiators such as azobisisobutyronitrile and azobisisovaleronitrile; the above compounds and sulfites, bisulfites, thiosulfates, first metal salts, sodium formaldehyde sulfone And redox initiators combined with xylate, dextrose, and the like.

(Graft copolymer (A2))
Examples of vinyl monomers to be graft-polymerized on the polyalkyl (meth) acrylate composite rubber (R2) include aromatic vinyl compounds such as styrene, α-methylstyrene and vinyltoluene; methacryl such as methyl methacrylate and 2-ethylhexyl methacrylate. Examples include acid esters; acrylic acid esters such as methyl acrylate, ethyl acrylate, and n-butyl acrylate; unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile. These may be used alone or in combination of two or more.

  For vinyl monomers, ethylene glycol dimethacrylate, propylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,4-butylene glycol having two or more unsaturated bonds in the molecule, if necessary. Crosslinking agents such as dimethacrylate, divinylbenzene, polyfunctional methacrylic group-modified silicones; grafting agents such as allyl methacrylate, triallyl cyanurate and triallyl isocyanurate may be added within a range of 20% by mass or less.

  The ratio of the polyalkyl (meth) acrylate composite rubber (R2) and the vinyl monomer is 60 to 99.9% by mass of the polyalkyl (meth) acrylate composite rubber (R2), and the vinyl monomer 40 to 40%. 0.1% by mass is preferable; polyalkyl (meth) acrylate composite rubber (R2) 70 to 99.9% by mass, vinyl monomer 30 to 0.1% by mass is more preferable; polyalkyl (meth) acrylate -Based composite rubber (R2) 80-99.9% by weight, vinyl-based monomer 20-0.1% by weight is more preferable; polyalkyl (meth) acrylate-based composite rubber (R2) 85-95% by weight, vinyl-based The monomer content is particularly preferably 15 to 5% by mass.

  When the vinyl monomer is less than 0.1% by mass, the dispersibility of the obtained graft copolymer (A2) in the polyacetal resin (B) is lowered, and the resin composition obtained by blending it is processed. May decrease. If the vinyl monomer exceeds 40% by mass, the impact strength imparting effect of the graft copolymer (A2) may be reduced.

(Graft copolymer (A3))
The graft copolymer (A3) can be obtained by polymerizing a vinyl monomer in the presence of the silicone / acrylic composite rubber (R3). For example, it can be produced by adding a vinyl monomer to a latex of silicone / acrylic composite rubber (R3) and polymerizing the vinyl monomer in one or more stages. When multi-stage polymerization is used, a part of the vinyl monomer used for polymerization is charged in the reaction system in advance, and after the start of polymerization, the remaining vinyl monomer is added all at once, dividedly or continuously. Is preferred. By employing such a polymerization method, good polymerization stability can be obtained, and a latex of the graft copolymer (A3) having a desired particle size and particle size distribution can be stably obtained.

  Examples of vinyl monomers include aromatic vinyl compounds such as styrene, α-methylstyrene, and vinyl toluene; methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, and 2-ethylhexyl methacrylate; methyl acrylate, ethyl acrylate, butyl acrylate, and the like. Acrylic acid esters; unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile. These vinyl monomers may be used alone or in combination of two or more.

  As the radical polymerization initiator, those exemplified in the production of silicone / acrylic composite rubber (R3) (reaction between polyorganosiloxane and (meth) acrylic acid ester) can be used.

  The content of the polyorganosiloxane in the graft copolymer (A3) (100% by mass) is preferably 8 to 70% by mass. If the content of the polyorganosiloxane is less than 8% by mass, sufficient impact resistance imparting effect may not be obtained. When content of polyorganosiloxane exceeds 70 mass%, there exists a possibility that the other outstanding characteristic of a polyacetal resin (B) may be impaired.

  The content of the silicone / acrylic composite rubber (R3) in the graft copolymer (A3) (100% by mass) is preferably 65 to 90% by mass. If the content of the silicone / acrylic composite rubber (R3) is less than 65% by mass, sufficient impact resistance imparting effect may not be obtained. If the content of the silicone / acrylic composite rubber (R3) exceeds 90% by mass, other excellent characteristics of the polyacetal resin (B) may be impaired.

When the graft copolymer (A) is recovered as a powder, a coagulant is used in the case of a product obtained by emulsion polymerization.
As the coagulant, a calcium salt is particularly preferable. When the calcium salt is used, the stability of the polyacetal resin (B) can be increased. Examples of calcium salts include calcium chloride and calcium acetate.

  0.1-20 mass parts is preferable with respect to 100 mass parts (solid content) of a graft copolymer (A), and, as for the usage-amount of a calcium salt, 0.2-10 mass parts is more preferable, 0.5- 8 parts by mass is particularly preferred. If the amount of calcium salt used is less than 0.1 parts by mass, powder recovery may be difficult, and the stability of the polyacetal resin (B) may not be maintained. When the usage-amount of calcium salt exceeds 20 mass parts, there exists a possibility that the mechanical physical property of a molded article may fall.

<Polyacetal resin (B)>
The polyacetal resin (B) is preferably a polyoxymethylene copolymer having an oxymethylene group as a main repeating unit and an oxyalkylene group unit having 2 or more carbon atoms.

The polyacetal resin (B) preferably has a content of oxyalkylene group units having 2 or more carbon atoms of 0.5 to 3.0% by mass, more preferably 0.6 to 2.0% by mass, The thing of 0.7-1.6 mass% is especially preferable. If the content of oxyalkylene group units having 2 or more carbon atoms is too small, the stability of the polyacetal resin (B) to heat and chemicals will be insufficient, and the long-term durability of various properties such as strength and accuracy of the molded product will be reduced. There is a risk. When the content of the oxyalkylene group unit having 2 or more carbon atoms is too large, the strength and rigidity of the molded product tend to decrease.
A polyacetal resin (B) may be used individually by 1 type, and may use 2 or more types together.

  The polyacetal resin (B) has, as a main monomer, formaldehyde or trioxane which is a cyclic oligomer thereof, ethylene oxide, propylene oxide, 1,3-dioxolane, 1,3,5-trioxepane, 1,4-butanediol formal, diethylene glycol formal, etc. These are obtained by copolymerizing at least one selected from the group consisting of cyclic ethers having at least one carbon-carbon bond and cyclic acetals in the presence of a cationic catalyst. As the comonomer, 1,3-dioxolane and / or 1,3,5-trioxepane that does not cause chain transfer in the polymer is preferable because of its good dispersibility.

The polyacetal resin (B) can be produced by the same apparatus and method as the known trioxane copolymerization method.
In the production of the polyacetal resin (B), any of batch-type and continuous-type production methods may be employed, and any polymerization method such as melt polymerization or solution bulk polymerization may be employed. In consideration of industrial productivity, a continuous bulk polymerization method using a liquid monomer as a raw material and obtaining a solid powdery bulk polymer as the polymerization proceeds in the presence of an inert liquid catalyst as necessary is preferable.

  During the polymerization, a chain transfer agent may be added to adjust the molecular weight of the polyacetal resin (B). Examples of the chain transfer agent include methylal, ethylal, and butyral. These may be used alone or in combination of two or more. The addition amount of the chain transfer agent is appropriately adjusted within the range of 0 to 1000 ppm depending on the molecular weight of the polyacetal resin (B).

  Examples of the polymerization catalyst include known cationically active catalysts. Cationic active catalysts include Lewis acids (borides such as boron, tin, titanium, phosphorus, arsenic and antimony, such as boron trifluoride, tin tetrachloride, titanium tetrachloride, phosphorus pentachloride, phosphorus pentafluoride, Arsenic fluoride, antimony pentafluoride, complex compounds or salts thereof), protonic acid (eg, trifluoromethanesulfonic acid, perchloric acid), ester of protonic acid (ester of perchloric acid and lower aliphatic alcohol, eg, perchlor Acid tertiary butyl ester), protonic acid anhydrides (mixed anhydrides of perchloric acid and lower aliphatic carboxylic acids, eg acetyl perchlorite), isopolyacids, heteropolyacids (eg phosphomolybdic acid), triethyl Oxonium hexafluorophosphate, triphenylmethyl hexafluoroarzena DOO, acetyl hexafluoro borate and the like. Among these, boron trifluoride or a coordination compound of boron trifluoride and an organic compound (for example, ethers) is preferable. These polymerization catalysts may be used individually by 1 type, and may use 2 or more types together. The addition amount of the polymerization catalyst is usually 10 to 300 ppm with respect to the total amount of the main monomer and the comonomer.

Examples of the polymerization apparatus include a continuous polymerization apparatus for trioxane such as a kneader, a twin screw continuous extrusion mixer, and a twin screw paddle type continuous mixer. The apparatus may be divided into two or more stages as long as it is a closed system. The thing provided with the grinding | pulverization function in which the solid polymer produced | generated by a polymerization reaction is obtained with a fine form is preferable.
The polymerization temperature is usually 64 to 120 ° C., and a relatively low temperature is suitable within this range. The preferred range of the polymerization time varies depending on the amount of the catalyst, and is usually 0.5 to 100 minutes.

  It is preferable to deactivate the polymerization catalyst by immediately mixing a deactivator with the crude polymer discharged from the polymerization apparatus. Examples of the deactivator include a solution in which an amine such as triethylamine or triethanolamine is mixed with an inorganic alkaline substance such as sodium fluoride or potassium fluoride. The quenching agent is preferably an aqueous solution.

  The polyacetal resin (B), after deactivating the polymerization catalyst, is subjected to washing, separation and recovery of unreacted monomers, drying, etc., if necessary, and terminal stabilization such as decomposition and removal of unstable terminal parts as necessary. And, if necessary, additives such as various stabilizers and processability improvers are added, and then melt-kneaded pellets are produced.

Examples of the additive include an antioxidant, a nitrogen-containing compound, a heat resistance stabilizer, an ultraviolet absorber, a light stabilizer, a lubricant, and a plasticizer.
Antioxidants include 2,2′-methylenebis (4-methyl-6-tert-butylphenol), 1,6-hexanediol-bis [3- (3,5-di-tert-butyl-4-hydroxyphenyl). ) Propionate], pentaerythritol tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol bis [3- (3-t-butyl-5-methyl-4-hydroxy) Phenyl) propionate], 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) benzene, n-octadecyl-3- (4′-hydroxy-) 3 ', 5'-di-t-butylphenyl) propionate, 4,4'-methylenebis (2,6-di-t-butylphenol), 4,4'-butylidenebi -(6-t-butyl-3-methylphenol), 3,9-bis {2- [3- (3-t-butyl-4-hydroxy-5-methylphenyl) propionyloxy] -1,1-dimethyl Ethyl} 2,4,8,10-tetraoxaspiro [5,5] undecane, di-stearyl-3,5-di-t-butyl-4-hydroxybenzylphosphonate, 2-t-butyl-6- (3 -T-butyl-5-methyl-2-hydroxybenzyl) -4-methylphenyl acrylate, N, N'-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide), etc. Hindered phenols and the like.

Examples of the nitrogen-containing compound include polyamides such as nylon 6 · 10, nylon 6 · 66 · 610, and polyacrylamide; polycondensates of melamine, dicyandiamide, and the like with formaldehyde.
Examples of the heat stabilizer include metal-containing compounds such as sodium salts, potassium salts, magnesium salts, calcium salts, and barium salts of higher fatty acids such as stearic acid or substituted higher fatty acids having a substituent such as a hydroxyl group.
Examples of the ultraviolet absorber include benzotriazoles such as 2- [2-hydroxy-3,5-bis- (α, α′-dimethylbenzyl) phenyl] benzotriazole, and benzophenones such as 2-hydroxy-4-methoxybenzophenone. Etc.
Examples of the light stabilizer include hindered amines such as 4-acetoxy-2,2,6,6-tetramethylpiperidine and bis (2,2,6,6-tetramethyl-4-piperidyl) adipate.
Examples of the lubricant include higher fatty acid esters such as glycerin monostearate and pentaerythritol tristearate; higher fatty acid amides such as ethylenebis (stearylamide).
Examples of the plasticizer include polyethylene glycol and polyoxyethylene polypropylene copolymer.

Antioxidants include pentaerythritol tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], triethylene glycol bis [3- (3,5-di-tert-butyl-4). -Hydroxyphenyl) propionate], 3,9-bis- {2- [3- (3-t-butyl-4-hydroxy-5-methylphenyl) propionyloxy-] 1,1-dimethylethyl} -2,4 Hindered phenols such as 8,10-tetraoxaspiro [5,5] undecane are preferred.
As the nitrogen-containing compound, polycondensation of melamine, dicyandiamide or the like with formaldehyde is preferable.
As the metal-containing compound, magnesium salts and calcium salts of higher fatty acids or substituted higher fatty acids are preferable.

<Thermoplastic resin composition>
The thermoplastic resin composition of the present invention contains a graft copolymer (A) and a polyacetal resin (B).
The blending ratio of the graft copolymer (A) to the polyacetal resin (B) is preferably 1 to 50% by mass of the graft copolymer (A) and 99 to 50% by mass of the polyacetal resin (B). A) 5 to 40% by mass, polyacetal resin (B) 95 to 60% by mass is more preferable, graft copolymer (A) 7 to 35% by mass, and polyacetal resin (B) 93 to 65% by mass are particularly preferable (however, The total of the graft copolymer (A) and the polyacetal resin (B) is 100% by mass). If the graft copolymer (A) is less than 1% by mass, a molded article having desired impact resistance may not be obtained. When the graft copolymer (A) exceeds 50% by mass, the mechanical properties of the obtained molded product may be impaired.

  The thermoplastic resin composition of the present invention may be prepared by any method that can blend a predetermined amount of the graft copolymer (A) with respect to the polyacetal resin (B). For example, the polyacetal resin (B) and the graft copolymer (A) are mixed directly or in advance, and then kneaded with a single or twin screw extruder or the like, and pelletized to prepare a thermoplastic resin composition. be able to. In preparing the thermoplastic resin composition, it is preferable to pulverize part or all of the polyacetal resin (B) in advance in order to improve the dispersibility of other components to be blended therein.

In the thermoplastic resin composition of the present invention, the following thermoplastic resins may be blended as long as the original physical properties are not impaired.
Thermoplastic resins include vinyl chloride resin (PVC), chlorinated polyethylene resin, chlorinated vinyl chloride resin, vinylidene chloride resin and other hard, semi-rigid and soft chlorine-containing resins; polypropylene (PP), polyethylene (PE) Olefin resins such as: polystyrene (PS), high impact polystyrene (HIPS), (meth) acrylate-styrene copolymer (MS), styrene-acrylonitrile copolymer (SAN), styrene-maleic anhydride copolymer ( Styrenic resins (St resin) such as SMA), acrylonitrile-butadiene-styrene resin (ABS), acrylate-styrene-acrylonitrile resin (ASA), acrylonitrile-ethylenepropylene rubber-styrene resin (AES); polymethyl methacrylate (PMMA) ) Etc. Ryl resin (Ac resin); Polycarbonate resin (PC resin); Polyamide resin (PA resin); Polyester resin (PEs resin) such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT); Polylactic acid resin, thermoplastic polyvinyl alcohol resin, polybutylene succinate, other biodegradable natural raw materials, environmentally friendly resins derived from petroleum raw materials (biodegradable resins); (modified) polyphenylene ether resins (PPE resins) , Polyoxymethylene resin (POM resin), polysulfone resin (PSO resin), polyarylate resin (PAr resin), polyphenylene resin (PPS resin), thermoplastic polyurethane resin (PU resin) ) Engineering plastics; styrene-based elastomer -Thermoplastic elastomers (TPE) such as olefin elastomers, vinyl chloride elastomers, urethane elastomers, polyester elastomers, polyamide elastomers, fluorine elastomers, 1,2-polybutadiene, trans 1,4-polyisoprene; PC / PC resin such as ABS / St resin resin alloy, PVC resin such as PVC / ABS / St resin resin alloy, PA resin such as PA / ABS / St resin resin alloy, PA resin / TPE alloy, PA / Alloys between PA resins such as PP / polyolefin resins, PBT resins / TPE, PC resins such as PC / PBT / PEs resins, polyolefin resins / TPE, olefin resins such as PP / PE, P such as PPE / HIPS, PPE / PBT, PPE / PA Examples thereof include polymer alloys such as PE resin alloys, PVC resins such as PVC / PMMA / Ac resin alloys, and the like.

<Molded product>
The molded article of the present invention is formed by molding the thermoplastic resin composition of the present invention.
As a forming method, a method of forming pellets prepared to have a desired composition; after preparing a plurality of types of pellets having different compositions, these are mixed (diluted) at a predetermined ratio and used for forming; A method of obtaining a desired composition can be employed.
Examples of the molded article of the present invention include resin gears and mechanical parts in OA equipment, information equipment, home appliances, automobiles, clothing, stationery, sundries, building materials, and the like.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, “parts” and “%” in the examples represent “parts by mass” and “mass%”, respectively.

The mass average particle size and particle size distribution of the polymer in the latex in the production example were measured as follows.
Using the obtained latex diluted with distilled water as a sample, a mass average particle size and a particle size distribution were measured using a CHDF2000 type particle size distribution meter manufactured by MATEC USA. The measurement conditions were standard conditions recommended by MATEC. Specifically, using a dedicated capillary cartridge for particle separation and a carrier liquid, the liquidity is neutral, the flow rate is 1.4 mL / min, the pressure is 28 MPa, and the temperature is 35 ° C., and the concentration is 3%. This was measured using 0.1 mL of diluted latex sample. As the standard particle size substance, a total of 12 monodisperse polystyrenes having a known particle size manufactured by DUKE Co., Ltd. in the United States were used in the range of 0.03 μm to 0.8 μm.

(Production of graft copolymer (A))
[Production Example 1]
(1) Production of butadiene rubber polymer (R1-1) latex:
As an emulsifier, 0.1 part of sodium alkyldiphenyl ether disulfonate, as a first monomer, 19.0 parts of 1,3-butadiene, 1.0 part of styrene, 0.1 part of α-methylstyrene dimer, After adding 0.3 parts of diisopropylbenzene hydroperoxide and 146.67 parts of deionized water as peroxides to a 70 L autoclave, the temperature was raised to 50 ° C., and as a redox initiator, sulfuric acid was used. Polymerization was initiated by adding 0.003 parts of ferrous iron, 0.3 parts of sodium formaldehyde sulfoxylate, and 4 parts of deionized water. Thereafter, the temperature was further raised to 60 ° C.
Six hours after the start of the polymerization, 0.36 parts of diisopropylbenzene hydroperoxide as an initiator, 76.0 parts of 1,3-butadiene, 4.0 parts of styrene, α-methylstyrene dimer, 0.002 parts as a second monomer. As an emulsifier, 4 parts of sodium alkyldiphenyl ether disulfonate 1.1 parts and 24.7 parts of deionized water were continuously added dropwise over 6 hours.
After 21 hours from the start of polymerization, a butadiene rubber polymer (R1-1) latex was obtained. The mass average particle diameter (dw) of the butadiene rubber polymer (R1-1) in the latex was 165 nm, and dw / dn = 1.2. Further, the conversion of the butadiene rubber polymer in the latex was 97.6%.

(2) Production of graft copolymer (A1-1):
A flask substituted with 77.5 parts (solid content) of butadiene rubber polymer (R1-1) latex and 0.3 part of sodium formaldehyde sulfoxylate was charged with nitrogen, and the internal temperature was maintained at 75 ° C.
Next, in the flask, 19.7 parts of methyl methacrylate, 0.1 part of styrene, 2.7 parts of ethyl acrylate, cumene hydroxy peroxide (amount to be 0.3 parts with respect to 100 parts of vinyl monomer) The mixture was added dropwise over 1 hour and then held for 2 hours.
After the completion of the polymerization reaction, a latex of graft copolymer (A1-1) was obtained. To this latex, 5.0 parts of calcium acetate is added with respect to 100 parts of latex solids, and the graft copolymer (A1-1) in the latex is coagulated and dried at 65 ° C. for 12 hours to obtain a powder. A graft copolymer (A1-1) was obtained.

[Production Example 2]
(1) Production of butadiene rubber polymer (R1-2) latex:
A butadiene-based rubber polymer (R1-2) latex was obtained in the same manner as in Production Example 1 (1) except that α-methylstyrene dimer was not used. The mass average particle diameter (dw) of the butadiene rubber polymer (R1-2) in the latex was 160 nm, and dw / dn = 1.25.
(2) Production of graft copolymer (A1-2):
A graft polymer (A1-2) is obtained in the same manner as in Production Example 1 (2) except that the butadiene rubber polymer (R1-2) is used instead of the butadiene rubber polymer (R1-1). It was.

[Production Example 3]
(1) Production of butadiene rubber polymer (R1-3) latex:
A butadiene-based rubber polymer (R1-3) latex was obtained in the same manner as in (1) of Production Example 1 except that normal octyl mercaptan was used instead of α-methylstyrene dimer. The mass average particle diameter (dw) of the butadiene rubber polymer (R1-3) in the latex was 155 nm, and dw / dn = 1.2.
(2) Production of graft copolymer (A1-3):
A graft polymer (A1-3) is obtained in the same manner as in (2) of Production Example 1 except that the butadiene rubber polymer (R1-3) is used instead of the butadiene rubber polymer (R1-1). It was.

[Production Example 4]
A mixture of trioxane and a small amount of 1,3-dioxolane (comonomer) is polymerized in the presence of boron trifluoride etherate (catalyst) to obtain a polyacetal resin (B-1) containing 1.50% oxyethylene groups. After being obtained, the catalyst was deactivated with triethylamine (deactivator), and further pelletized through a terminal stabilization step.

[Example 1, Comparative Examples 1-2]
In the proportion shown in Table 1, the graft copolymer (A) is blended with the polyacetal resin (B-1), pelletized with a TEM35B type twin screw extruder manufactured by Toshiba Machine Co., Ltd., and a thermoplastic resin composition is obtained. Obtained.
Subsequently, in order to perform various evaluation tests, the obtained thermoplastic resin composition was injection-molded under normal conditions with a SAV60 type injection molding machine manufactured by Sanjo Kikai, and a test piece was produced.

The following evaluation tests were performed on the thermoplastic resin composition and the test piece.
(1) Evaluation of degradation resistance of polyacetal resin:
The thermoplastic resin composition pellets were weighed and charged for 5 minutes to a 2.1 mm diameter die mounted on a Techno Seven melt indexer heated to 210 ° C., and then loaded for 10 minutes. The mass (MI) flowing out in 30 seconds was measured for the amount of strands extruded thereby. Similarly, MI was measured after holding for 30 minutes. The ΔMI obtained by subtracting the MI when held for 5 minutes from the MI when held for 30 minutes was used as a criterion for determination of decomposition resistance. A positive value or a negative value as small as possible was judged as good.
At the same time, the coloring and odor of the strands when held for 30 minutes were evaluated. It shows that it is so favorable that there is no coloring and there are few smells.

(2) Izod impact strength:
The Izod impact strength of the specimen was measured at 23 ° C. according to ASTM D256. A 1/8 inch thick, notched specimen was used.

(3) Tensile test:
The elongation at break and elastic modulus of the dumbbell specimen were measured at 23 ° C. according to ASTM D638. The thickness of the test piece was 1/8 inch.

  As shown in Table 1, in the examples, the polyacetal resin has good decomposition resistance (stability) and excellent mechanical properties of the molded product. On the other hand, the comparative example 1 which did not use a chain transfer agent was inferior to the mechanical property of a molded article. Comparative Example 2 using a mercapto chain transfer agent was inferior in the decomposition resistance of the polyacetal resin.

The thermoplastic resin composition of the present invention is excellent in stability and has excellent mechanical properties of a molded product to be obtained. Therefore, it is used for OA equipment, information equipment, home appliances, automobiles, clothing, stationery, miscellaneous goods, building materials, etc. It is suitably used for resin gears, mechanical parts, and the like.

Claims (2)

A graft copolymer (A) obtained by graft-polymerizing a vinyl monomer to the rubber polymer (R);
Containing a polyacetal resin (B),
A thermoplastic resin composition, wherein the rubber polymer (R) is obtained by polymerizing monomers constituting the rubber polymer in the presence of α-methylstyrene dimer. A molded article formed by molding the thermoplastic resin composition according to claim 1.