Rubber-modified styrenic resin composition and molded article

Abstract

To provide a rubber-modified styrenic resin composition from which a molded article that is excellent in flexural elastic modulus and extremely excellent in Charpy impact strength can be obtained, and a molded article using the rubber-modified styrenic resin composition.SOLUTION: A rubber-modified styrenic resin composition contains a styrenic resin forming a matrix phase and rubbery polymer particles dispersed in the matrix phase, wherein a gel content is 26.0 to 30.0 mass%, and a difference between an 85% diameter of an integrated value and a 15% diameter of the integrated value in a volume cumulative distribution curve of a particle diameter of the rubbery polymer particles is 5.1 to 6.9 μm.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a rubber-modified styrenic resin composition and a molded article. [Background technology]

[0002] Rubber-modified styrene resin compositions have excellent rigidity and impact resistance and are therefore used in applications such as food containers such as food trays, lunch boxes, and cups, packaging, office automation equipment, home appliance parts, and miscellaneous goods.

[0003] For example, Patent Document 1 discloses a rubber-modified styrene-based resin composition that has an excellent balance between rigidity and impact resistance, has little thickness deviation due to molding, and is less susceptible to reductions in buckling strength and drop strength due to the complex shape and weight reduction of containers. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-222751 Summary of the Invention [Problem to be solved by the invention]

[0005] However, depending on the application and usage environment, further improvement may be required, particularly in Charpy impact strength, which is a physical property related to impact resistance, and the Charpy impact strength of previous rubber-modified styrene-based resins has sometimes been insufficient.

[0006] The present invention has been made in view of the above problems, and provides a rubber-modified styrene-based resin composition from which molded articles having excellent flexural modulus and extremely excellent Charpy impact strength can be obtained, and a molded article using the rubber-modified styrene-based resin composition. [Means for solving the problem]

[0007] According to the present invention, there is provided a rubber-modified styrene-based resin composition comprising a styrene-based resin forming a matrix phase and rubber-like polymer particles dispersed in the matrix phase, the composition having a gel content of 26.0 to 30.0 mass %, and the difference between the 85% diameter and the 15% diameter of the integrated value in a volume-integrated particle size distribution curve of the rubber-like polymer particles being 5.1 to 6.9 μm.

[0008] As a result of extensive research, the present inventors have found that a rubber-modified styrene-based resin composition having excellent flexural modulus and extremely excellent Charpy impact strength can be obtained by controlling the difference between the 85% volume cumulative diameter and the 15% volume cumulative diameter of the rubber particle diameter and the gel content within a specific range, and have thus completed the present invention.

[0009] Various embodiments of the present invention will be described below as examples, and the embodiments shown below can be combined with each other.

[0010] [1] A rubber-modified styrene-based resin composition comprising a styrene-based resin forming a matrix phase and rubber-like polymer particles dispersed in the matrix phase, wherein the gel content is 26.0 to 30.0 mass %, and the difference between the 85% diameter and the 15% diameter of the integrated value in a volume-integrated particle diameter distribution curve of the rubber-like polymer particles is 5.1 to 6.9 μm. [2] The rubber-modified styrene-based resin composition according to [1], which has a melt mass flow rate of 3.5 g / 10 min or less as measured at 200°C and 49 N. [3] The rubber-modified styrene-based resin composition according to [1] or [2], having a rubber content of more than 11% by mass. [4] A molded article obtained by molding the rubber-modified styrene-based resin composition according to any one of [1] to [3]. [Brief explanation of the drawings]

[0011] [Figure 1] Fig. 1 shows an example of a volume-integrated distribution curve of rubber-like polymer particles, which shows the volume median particle diameter of the rubber-like polymer particles and the difference between the 85% diameter and the 15% diameter of the integrated value of the volume-integrated distribution curve. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described. Various features shown in the following embodiments can be combined with each other. Furthermore, each feature can be an invention independently. In this specification, when A to B is written, it means A or more and B or less.

[0013] 1. Rubber-modified styrene resin composition A rubber-modified styrene-based resin composition according to one embodiment of the present invention is a composition containing a styrene-based resin that forms a matrix phase and rubbery polymer particles dispersed in the matrix phase.

[0014] The styrene-based resin forming the matrix phase contains a styrene-based monomer unit as a monomer unit constituting the copolymer. Examples of the styrene-based monomer from which the styrene-based monomer unit is derived include styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, and the like, either alone or in mixture, with styrene being particularly preferred. Other vinyl-based monomers copolymerizable with the styrene-based monomer include acrylic acid monomers such as acrylic acid and methacrylic acid, vinyl cyanide monomers such as acrylonitrile and methacrylonitrile, acrylic monomers such as butyl acrylate and methyl methacrylate, α,β-ethylenically unsaturated carboxylic acids such as maleic anhydride and fumaric acid, and imide-based monomers such as phenylmaleimide and cyclohexylmaleimide, which can be copolymerized within a range that does not impair the effects of the present invention.

[0015] The rubbery polymer particles dispersed in the matrix phase are formed by graft polymerizing a styrene-based monomer onto a rubbery polymer. The styrene-based monomer graft polymerized onto the rubbery polymer may be the same as or different from the styrene-based monomer from which the styrene-based monomer units constituting the styrene-based resin forming the matrix phase are derived. Examples of the rubbery polymer include homopolymers of diene monomers such as polybutadiene, low-cis polybutadiene, high-cis polybutadiene, and high-cis high-vinyl polybutadiene; styrene-butadiene copolymers; styrene-butadiene block copolymers; hydrogenated (partially hydrogenated) polybutadiene; hydrogenated (partially hydrogenated) styrene-butadiene copolymers; hydrogenated (partially hydrogenated) styrene-butadiene block copolymers; ethylene-propylene copolymers; ethylene-propylene-non-conjugated diene terpolymers; isoprene polymers; and styrene-isoprene copolymers. Among these, homopolymers of diene monomers are preferred. Furthermore, the rubbery polymer particles preferably encapsulate styrene-based polymer particles and have a sea-island structure. The rubber-like polymers and rubber-like polymer particles may be used singly or in combination of two or more. A rubber-modified styrenic resin composition according to one embodiment of the present invention preferably contains two or more types of rubber-like polymers and rubber-like polymer particles. A rubber-modified styrenic resin composition according to one embodiment of the present invention may contain two types of rubber-like polymers and rubber-like polymer particles. The two or more types of rubber-like polymers and rubber-like polymer particles may differ in at least one of the monomer units constituting the rubber-like polymer, their composition, molecular weight, and particle size of the rubber-like polymer particles (85% diameter of integrated value, 15% diameter of integrated value, volume median particle size). For example, the two types of rubber-like polymers and rubber-like polymer particles may differ in at least the particle size of the rubber-like polymer particles (85% diameter of integrated value, 15% diameter of integrated value, volume median particle size).

[0016] <Gel content> The gel fraction of the rubber-modified styrene-based resin composition is 26.0 to 30.0% by mass, preferably 26.5 to 29.0% by mass. This range of values ​​results in extremely excellent Charpy impact strength. Methods for adjusting the gel fraction include adjusting the rubber content or initiator amount during the polymerization process of the rubber-modified styrene-based resin composition, as well as blending with a styrene homopolymer after polymerization. Specific examples of the gel fraction are 26.0, 26.5, 27.0, 27.5, 28.0, 28.5, 29.0, 29.5, and 30.0% by mass, and may be within a range between any two of the values ​​exemplified here.

[0017] The gel content is the proportion of rubber-like polymer particles in the rubber-modified styrene-based resin composition. 1.00 g of the rubber-modified styrene-based resin composition was precisely weighed (W), dissolved in 35 ml of a 50% methyl ethyl ketone / 50% acetone mixed solution, and the resulting solution was centrifuged at 10,000 rpm for 30 minutes in a centrifuge (H-2000B (rotor: H) manufactured by Kokusan Co., Ltd.) to precipitate the insoluble matter. The supernatant was removed by decantation to obtain the insoluble matter, which was then pre-dried in a safety oven at 90°C for 2 hours, further dried under reduced pressure in a vacuum dryer at 125°C for 1 hour, cooled in a desiccator for 20 minutes, and then the mass G of the dried insoluble matter was measured and the gel content was determined as follows: Gel content (amount of dispersed rubber particles) (mass%) = (G / W) x 100

[0018] <Rubber> The rubber content of the rubber-modified polystyrene and rubber-modified styrene-based resin composition according to one embodiment of the present invention can be more than 11% by mass, and preferably more than 12% by mass. By being in this range, the Charpy impact strength is further improved. The rubber content is, for example, 11.1, 11.2, 11.3, 11.4, 11.5, 11.6, 11.7, 11.8, 11.9, 12.0, 12.1, 12.2, 12.3, 12.4, 12.5, 12.6, 12.7, 12.8, 12.9, 13.0, 13.1, 13.2, 13.3, 13.4, 13.5, 13.6, 13.7, 13.8, 13.9, 14.0, 14.1, 14.2, 14.3, 14.4, 14.5, 14.6, 14.7, 14.8, 14.9, or 15.0% by mass, and may be within a range between any two of the values ​​exemplified here.

[0019] The rubber content can be calculated from the amount of iodine monochloride added by dissolving rubber-modified polystyrene (or rubber-modified styrene-based resin composition) in chloroform, adding a certain amount of iodine monochloride / carbon tetrachloride solution, leaving the mixture in a dark place for about 1 hour, adding potassium iodide solution, and titrating the excess iodine monochloride with 0.1 N sodium thiosulfate / ethanol aqueous solution.

[0020] <Swelling degree> The swelling degree of the rubber-modified polystyrene and rubber-modified styrene-based resin composition according to one embodiment of the present invention can be 10.0 to 17.0. The swelling degree is, for example, 10.0, 10.5, 11.0, 11.5, 12.0, 12.5, 13.0, 13.5, 14.0, 14.5, 15.0, 15.5, 16.0, 16.5, or 17.0, and may be within a range between any two of the numerical values ​​exemplified here.

[0021] The degree of swelling can be calculated based on the following formula: 1 g of rubber-modified polystyrene (or rubber-modified styrene-based resin composition) is weighed out, 30 mL of toluene is added to dissolve the resultant solution, and the solution is centrifuged at 14,000 rpm for 30 minutes in a centrifuge (H-2000B (rotor: H) manufactured by Kokusan Co., Ltd.) to precipitate the insoluble matter. The supernatant is removed by decantation, and the mass (S) of the insoluble matter swollen with toluene is measured. The insoluble matter swollen with toluene is then pre-dried in a safety oven at 90°C for 2 hours, and then vacuum-dried in a vacuum dryer at 125°C for 1 hour. The resultant is cooled in a desiccator for 20 minutes, and the dry mass (D) of the insoluble matter is measured. Swelling ratio = S / D

[0022] <Grafting rate> The graft ratio of the rubber-modified polystyrene and rubber-modified styrene-based resin composition according to one embodiment of the present invention may be 1.0 to 2.0, for example, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2.0, and may be within a range between any two of the values ​​exemplified here.

[0023] The graft ratio can be calculated from the gel content (mass %) and the rubber content (mass %) according to the following formula: Graft ratio = (gel content - rubber content) / rubber content

[0024] <Methanol solubles> The methanol soluble content of the rubber-modified polystyrene and rubber-modified styrene-based resin composition according to one embodiment of the present invention may be 1.5 to 3.0 mass %. The methanol soluble content is, for example, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, or 3.0 mass %, and may be within a range between any two of the values ​​exemplified here.

[0025] The methanol-soluble content of rubber-modified polystyrene and rubber-modified styrene-based resin compositions can be measured as follows: 1.00 g of rubber-modified polystyrene (or rubber-modified styrene-based resin composition) was precisely weighed (P), dissolved in 40 ml of methyl ethyl ketone, and 400 ml of methanol was added rapidly to separate and precipitate the methanol-insoluble content (resin component). After allowing to stand for approximately 10 minutes, the mixture was slowly filtered through a glass filter to separate the methanol-soluble content, which was then dried under reduced pressure at 120°C for 2 hours in a vacuum dryer and allowed to cool in a desiccator for 25 minutes. The mass N of the dried methanol-insoluble content was measured, and the mass N was calculated using the following formula: Methanol soluble matter (mass%) = (PN) / P × 100

[0026] In addition, when the rubber-modified styrene-based resin composition is obtained by mixing multiple rubber-modified polystyrenes, parameters of the rubber-modified styrene-based resin composition such as the rubber content, gel content, and methanol-soluble content can also be calculated from the parameters of the rubber content, gel content, and methanol-soluble content of each of the multiple rubber-modified polystyrenes contained in the rubber-modified styrene-based resin composition and the mixing mass ratio.

[0027] The difference between the 85% diameter and the 15% diameter of the integrated value in the volume integral distribution curve of the particle diameter of the rubber-like polymer particles (rubber particle diameter difference) is 5.1 to 6.9 μm, preferably 5.5 to 6.5 μm. Being in this range of values ​​results in excellent flexural modulus and extremely excellent Charpy impact strength. The difference between the 85% diameter and the 15% diameter of the integrated value is specifically, for example, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, or 6.9 μm, and may be within a range between any two of the values ​​exemplified here.

[0028] The volume median particle diameter of the rubber-like polymer particles contained in the rubber-modified styrene-based resin composition is preferably 4.5 to 8.0 μm, more preferably 6.0 to 7.0 μm. Being within this range of values ​​results in a superior flexural modulus. Specific examples of this volume median particle diameter include 4.5, 5.0, 5.5, 6.0, 6.1, 6.3, 6.5, 6.7, 7.0, 7.5, and 8.0 μm, and may be within a range between any two of the values ​​exemplified here.

[0029] The volume median particle size, 85% diameter of the integrated value in the volume integral distribution curve, and 15% diameter of the integrated value in the volume integral distribution curve of the rubber-like polymer particles can be calculated based on the 50% diameter, 85% diameter, and 15% diameter of the volume integral distribution curve of particle size (volume-based particle size distribution curve) as shown in Figure 1. The volume integral distribution curve can be obtained as a graph as shown in Figure 1 by dissolving the rubber-modified styrene-based resin composition in dimethylformamide and measuring it with a laser diffraction / scattering particle size distribution analyzer (LA-960, manufactured by Horiba, Ltd., relative refractive index 120A000I). Methods for adjusting the particle size include adjusting the stirring speed in the phase inversion region of the rubber particles in the polymerization process, adjusting the amount of chain transfer agent in the raw material liquid, mixing two or more rubber-modified polystyrenes containing rubber-like polymer particles with different particle sizes, and using two or more different rubber-like polymers as raw materials for producing the rubber-modified styrene-based resin composition.

[0030] The melt mass flow rate (MFR) of the rubber-modified styrene-based resin composition measured at 200°C under a load of 49 N is preferably 3.5 g / 10 min or less, and more preferably 3.3 g / 10 min or less. A value within this range ensures good flowability during molding and practical strength. The MFR can be measured according to JIS K-7210. Specific examples of the MFR are 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, and 3.0 g / 10 min, and may be within a range between any two of the values ​​exemplified here.

[0031] The Vicat softening temperature of the rubber-modified styrene-based resin composition measured under a load of 50 N is preferably 90°C or higher, and more preferably 90 to 94°C. Being in this range provides excellent heat resistance and moldability. The Vicat softening temperature was measured in accordance with JIS K-7206 at a temperature rise rate of 50°C / hr and a test load of 50 N. Specific examples of the Vicat softening temperature are 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, and 100°C, and may be within a range between any two of the values ​​exemplified here.

[0032] The Charpy impact strength of the molded article of the rubber-modified styrene-based resin composition is preferably 18.0 kJ / m 2 More preferably, 19.0 kJ / m or more. 2 The Charpy impact strength is, for example, 18.0, 19.0, 20.0, 21.0, 22.0, 23.0, 24.0, 25.0 kJ / m or more. 2 and may be within a range between any two of the numerical values ​​exemplified here. The Charpy impact strength was determined by preparing a test piece using an injection molding machine and measuring it in accordance with JIS K-7111-1.

[0033] The flexural modulus of a molded article of the rubber-modified styrene-based resin composition is preferably 1800 MPa or more, more preferably 1850 MPa or more. The flexural modulus may be, for example, 1800, 1850, 1900, 1950, 2000, 2050, 2100, 2150, or 2200 MPa, and may be within a range between any two of the values ​​exemplified here. The flexural modulus was determined by preparing a test piece using an injection molding machine and measuring it in accordance with JIS K-7171.

[0034] The rubber-modified styrene-based resin composition may contain additives such as phosphorus-based, phenol-based, and amine-based antioxidants; higher fatty acids such as stearic acid, zinc stearate, calcium stearate, and magnesium stearate, and salts thereof; lubricants such as ethylene bisstearylamide; plasticizers such as liquid paraffin; inorganic fillers such as talc and calcium carbonate; ultraviolet absorbers, antistatic agents, silicone oil, flame retardants, colorants, pigments, deodorizers, and antibacterial agents, provided that the effects of the present invention are not impaired.

[0035] <Method of producing rubber-modified styrene-based resin composition> A method for producing a rubber-modified styrenic resin composition according to one embodiment of the present invention may include a step of synthesizing a rubber-modified polystyrene by graft polymerizing a styrenic monomer in the presence of a rubbery polymer. The graft polymerization may be carried out by a known method, such as bulk polymerization, suspension polymerization, two-stage bulk / suspension polymerization, or solution polymerization. Solvents that can be used include alkylbenzenes such as benzene, toluene, ethylbenzene, and xylene; ketones such as acetone and methyl ethyl ketone; and aliphatic hydrocarbons such as hexane and cyclohexane. Reactor types include complete mixing reactors, plug flow reactors, and loop reactors in which a portion of the polymerization liquid is withdrawn as the polymerization proceeds. A so-called continuous polymerization method, which combines these with a devolatilization step to remove unreacted monomers, may also be used.

[0036] Examples of the rubbery polymer include the rubbery polymers described above. In the graft polymerization step according to one embodiment of the present invention, a styrene-based monomer can be graft polymerized in the presence of two or more types of rubbery polymers to synthesize a rubber-modified polystyrene. The two or more types of rubbery polymers can differ in at least one of the monomer units constituting the rubbery polymer, their composition, and molecular weight.

[0037] In the step of synthesizing rubber-modified polystyrene, a polymerization solvent, a polymerization initiator such as an organic peroxide, or a chain transfer agent such as an aliphatic mercaptan can be used as needed from the viewpoint of controlling the polymerization reaction.

[0038] The polymerization initiator is preferably a radical polymerization initiator, for example, peroxyketals such as 1,1-di(t-butylperoxy)cyclohexane, 2,2-di(t-butylperoxy)butane, 2,2-di(4,4-di-t-butylperoxycyclohexyl)propane, 1,1-di(t-amylperoxy)cyclohexane, etc.; hydroperoxides such as cumene hydroperoxide, t-butyl hydroperoxide, etc.; alkyl peroxides such as t-butyl peroxyacetate, t-amylperoxyisononanoate, etc.; t-butylcumyl peroxide, di-t-butyl peroxide, dicumyl peroxide, di-t-hexyl peroxide, etc. peroxyesters such as t-butylperoxyacetate, t-butylperoxybenzoate, and t-butylperoxyisopropyl monocarbonate; peroxycarbonates such as t-butylperoxyisopropyl carbonate and polyethertetrakis(t-butylperoxycarbonate); N,N'-azobis(cyclohexane-1-carbonitrile), N,N'-azobis(2-methylbutyronitrile), N,N'-azobis(2,4-dimethylvaleronitrile), and N,N'-azobis[2-(hydroxymethyl)propionitrile]; and the like, and these can be used alone or in combination of two or more.

[0039] The chain transfer agent may be a monofunctional chain transfer agent having one chain transfer group, or a polyfunctional chain transfer agent having multiple chain transfer groups. Examples of monofunctional chain transfer agents include aliphatic mercaptans, aromatic mercaptans, pentaphenylethane, α-methylstyrene dimer, and terpinolene. Examples of polyfunctional chain transfer agents include polyfunctional mercaptans obtained by esterifying the hydroxyl group of a polyhydric alcohol such as ethylene glycol, tetraethylene glycol, neopentyl glycol, trimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol, or sorbitol with thioglycolic acid or mercaptopropionic acid. These may be used alone or in combination of two or more.

[0040] A method for producing a rubber-modified styrene-based resin composition according to one embodiment of the present invention preferably includes a step of mixing two or more rubber-modified polystyrenes. The two or more rubber-modified polystyrenes may have rubber-like polymers and rubber-like polymer particles that differ in at least one of the monomer units constituting the rubber-like polymers, their compositions, molecular weights, and particle sizes of the rubber-like polymers (85% diameter of integrated value, 15% diameter of integrated value, volume median particle size), and may have rubber-like polymers and rubber-like polymer particles that differ in at least particle sizes (85% diameter of integrated value, 15% diameter of integrated value, volume median particle size).

[0041] A method for producing a rubber-modified styrenic resin composition according to one embodiment of the present invention may include a step of mixing a styrenic resin and a rubber-modified polystyrene. The rubber-modified styrenic resin composition may contain other resins, such as thermoplastic resins other than the styrenic resin and rubber-modified polystyrene, or rubber reinforcing resins, to the extent that the physical properties of the rubber-modified styrenic resin composition are not impaired.

[0042] The method for producing a rubber-modified styrene-based resin composition may include a step of polymerizing a styrene-based monomer to synthesize a styrene-based resin. The step of synthesizing the styrene-based resin may further include a step of synthesizing a multifunctional vinyl copolymer that serves as a cross-linking agent. The step of synthesizing the styrene-based resin may also include a step of polymerizing the styrene-based monomer in the presence of a polymerization initiator, a solvent, and, if necessary, a necessary cross-linking agent.

[0043] There are no particular limitations on the method for mixing two or more types of rubber-modified polystyrene, or the method for mixing a styrene resin and a rubber-modified polystyrene. Examples include a method in which multiple resins are melt-kneaded and re-granulated using an extruder, or a method in which the mixture of multiple resins is dry-blended using a Henschel mixer, ribbon blender, super mixer, V blender, or the like.

[0044] 2. Molded products The molded article according to one embodiment of the present invention is a molded article characterized by comprising the above-mentioned rubber-modified styrene-based resin composition of the present invention, and may be a molded article of any shape or application. However, since the molded article according to one embodiment of the present invention has excellent impact resistance and rigidity, examples of the molded article include parts such as housings and chassis of large home appliances such as televisions and air conditioners, household electrical appliances such as refrigerator interiors, office automation equipment such as copiers, printers, facsimiles, and personal computers, and office equipment.

[0045] <Method of manufacturing molded products> The method for obtaining a molded product is not particularly limited, and known molding methods such as extrusion molding, injection molding, injection blow molding, and foam molding can be applied, and molding methods combining various molding techniques are also acceptable. Furthermore, methods of molding into sheets or films using a T-die sheet extruder, a biaxial stretching processing device, or an inflation processing device can also be applied, but injection molding is preferred as a method for obtaining a molded product. [Example]

[0046] The present invention will be described in more detail below based on examples, but the present invention should not be construed as being limited to these examples.

[0047] [Rubber-modified polystyrene] The methods for producing resins A to D, which are rubber-modified polystyrenes, will now be described.

[0048] <Resin A> A 25 L volume completely mixed reactor equipped with an agitator was used as the first reactor, a 40 L volume plug flow reactor equipped with an agitator was used as the second reactor, a 50 L volume plug flow reactor equipped with an agitator was used as the third reactor, and a 50 L volume static mixer type plug flow reactor was used as the fourth reactor, and these reactors were connected in series to constitute the polymerization process. A raw material solution consisting of 77.3 parts by mass of styrene monomer, 13.6 parts by mass of ethylbenzene, 9.1 parts by mass of polybutadiene "Asaprene 730AX" manufactured by Japan Elastomer Co., Ltd. as a rubber-like polymer, 0.010 parts by mass of 1,1-di(t-butylperoxy)cyclohexane, and 0.020 parts by mass of t-dodecyl mercaptan was continuously supplied to the reactors at a supply rate of 22 L / hr, and polymerization was carried out at a temperature of 120°C and a stirring rate of 100 rpm in the first reactor, and at a temperature of 125 to 128°C and a stirring rate of 140 rpm in the second reactor. To the polymerization solution from the outlet of the third reactor, 0.025 parts by mass of t-dodecyl mercaptan was added, and polymerization was carried out at a temperature of 130 to 130°C, a stirring speed of 30 rpm, and a temperature of 130 to 140°C in the fourth reactor. The resulting mixture was then introduced into a two-stage preheater-equipped vacuum devolatilizer tank in series. After separating unreacted styrene and ethylbenzene, liquid paraffin (Kaneda Co., Ltd., "Hicol K-350") and silicone oil (Dow Chemical Co., Ltd., "DOWSIL SH200 100 cSt") were added and mixed to a concentration of 1.0% by mass relative to Resin A, respectively. The resulting mixture was extruded into a strand, cooled, and then cut into pellets. The resin temperature in the first devolatilizer tank was set to 190°C, the pressure in the vacuum devolatilizer tank was 67 kPa, and the resin temperature in the second devolatilizer tank was set to 230°C, and the pressure in the vacuum devolatilizer tank was 1.3 kPa. The properties of the obtained resin A are shown in Table 1.

[0049] <Resin B> A 25 L volume completely mixed reactor equipped with an agitator was used as the first reactor, a 40 L volume plug flow reactor equipped with an agitator was used as the second reactor, a 50 L volume plug flow reactor equipped with an agitator was used as the third reactor, and a 50 L volume static mixer type plug flow reactor was used as the fourth reactor, and these reactors were connected in series to constitute the polymerization process. A raw material solution consisting of 77.6 parts by mass of styrene monomer, 13.7 parts by mass of ethylbenzene, 8.7 parts by mass of polybutadiene "BR-15HB" manufactured by Ube Industries as a rubber-like polymer, and 0.025 parts by mass of t-dodecyl mercaptan was continuously fed into the reactor at a feed rate of 22 L / hr, and polymerization was carried out at a temperature of 125 ° C. in the first reactor, stirring speed of 100 rpm, a temperature of 128 to 130 ° C. in the second reactor, stirring speed of 40 rpm, a temperature of 130 to 130 ° C. in the third reactor, stirring speed of 30 rpm, and a temperature of 135 to 160 ° C. in the fourth reactor. The mixture was then introduced into a vacuum devolatilizer tank equipped with a preheater, which was configured in series with two stages. After separating unreacted styrene and ethylbenzene, liquid paraffin ("Hicol K-350" manufactured by Kaneda Co., Ltd.) was added / mixed to a concentration of 1.4 mass% relative to resin B, extruded into a strand, cooled, and cut into pellets. The resin temperature in the first devolatilization tank was set to 190°C, the pressure in the vacuum devolatilization tank was 60 kPa, and the resin temperature in the second devolatilization tank was set to 230°C, the pressure in the vacuum devolatilization tank was 1.3 kPa. The properties of the obtained Resin B are shown in Table 1.

[0050] <Resin C> The polymerization process was carried out using a 25 L volume, impeller-equipped complete mixing reactor as the first reactor, a 40 L volume, impeller-equipped plug flow reactor as the second reactor, a 50 L volume, impeller-equipped plug flow reactor as the third reactor, and a 50 L volume, static mixer-type plug flow reactor as the fourth reactor, all connected in series. A raw material solution consisting of 80.9 parts by mass of styrene monomer, 14.3 parts by mass of ethylbenzene, and 4.8 parts by mass of Asahi Kasei Corporation's polybutadiene "Diene 55AE" as a rubber polymer was continuously fed to the reactors at a feed rate of 20 L / hr. The temperature of the first reactor was 125 °C, the stirring rate was 100 rpm, and the temperature of the second reactor was 128-130 °C, the stirring rate was 80 rpm. After polymerization, 0.03% t-butylcumyl peroxide was added to the polymerization solution from the outlet of the second reactor. Eight parts by mass of ethylene glycol stearate (EPO) was added, and polymerization was carried out at a temperature of 128-128°C in the third reactor, agitation speed of 30 rpm, and a temperature of 125-140°C in the fourth reactor. The resulting mixture was then introduced into a two-stage preheater-equipped vacuum devolatilizer tank. Unreacted styrene and ethylbenzene were separated, and then liquid paraffin (Kaneda Co., Ltd., "Hicol K-350") was added and mixed to a concentration of 2.0% by mass relative to Resin C. The resulting mixture was extruded into strands, cooled, and then cut into pellets. The resin temperature in the first devolatilizer tank was set to 190°C, the pressure in the vacuum devolatilizer tank was 67 kPa, and the resin temperature in the second devolatilizer tank was set to 230°C, the pressure in the vacuum devolatilizer tank was 1.3 kPa. The properties of the resulting Resin C are shown in Table 1.

[0051] <Resin D> The polymerization process was carried out in series using a 25 L volume impeller-equipped complete mixing reactor as the first reactor, a 40 L volume impeller-equipped plug flow reactor as the second reactor, a 50 L volume impeller-equipped plug flow reactor as the third reactor, and a 50 L volume impeller-equipped static mixer plug flow reactor as the fourth reactor. A raw material solution consisting of 77.4 parts by mass of styrene monomer, 13.6 parts by mass of ethylbenzene, 9.0 parts by mass of Ube Industries polybutadiene "BR-15HB" as a rubber polymer, and 0.025 parts by mass of t-dodecyl mercaptan was continuously fed into the reactors at a feed rate of 20 L / hr. The temperature of the first reactor was 120 °C, the stirring rate was 100 rpm, and the temperature of the second reactor was 122-123 °C, the stirring rate was 100 rpm. After polymerization, the polymerization solution from the outlet of the second reactor was treated with t-butylcumyl mercaptan. 0.009 parts by mass of peroxide was added, and polymerization was carried out at a temperature of 126-127°C in the third reactor, agitation speed of 30 rpm, and a temperature of 130-135°C in the fourth reactor. The resulting mixture was then introduced into a two-stage, serially connected vacuum devolatilizer with a preheater. Unreacted styrene and ethylbenzene were separated, and then liquid paraffin (Kaneda Co., Ltd., "Hicol K-350") was added and mixed to a concentration of 1.0% by mass relative to Resin D. The mixture was extruded into strands, cooled, and then cut into pellets. The resin temperature in the first devolatilizer was set to 190°C, the pressure in the vacuum devolatilizer was 60 kPa, and the resin temperature in the second devolatilizer was set to 230°C, the pressure in the vacuum devolatilizer was 1.3 kPa. The properties of the resulting Resin D are shown in Table 1.

[0052] <Melt mass flow rate> The melt mass flow rate of the rubber-modified polystyrene was measured under conditions of 200°C and a load of 49 N in accordance with JIS K-7210.

[0053] <Vicat softening temperature> The Vicat softening temperature of the rubber-modified polystyrene was measured under conditions of a load of 50 N and a heating rate of 50°C / hr in accordance with JIS K-7206.

[0054] <Rubber> The rubber content of rubber-modified polystyrene was calculated by dissolving the rubber-modified polystyrene in chloroform, adding a certain amount of iodine monochloride / carbon tetrachloride solution, leaving it in a dark place for about 1 hour, adding potassium iodide solution, and titrating the excess iodine monochloride with 0.1N sodium thiosulfate / ethanol aqueous solution.

[0055] <Rubber particle size (volume median particle size)> The measurement was carried out in the same manner as the rubber particle diameter (volume median particle diameter) in the rubber-modified styrene-based resin composition described below.

[0056] <Gel content> The gel content was measured in the same manner as in the rubber-modified styrene-based resin composition described below.

[0057] <Grafting rate> The graft ratio was calculated from the gel content (mass %) of the rubber-modified polystyrene and the rubber content (mass %) of the rubber-modified polystyrene according to the following formula. Graft ratio = (gel content - rubber content) / rubber content

[0058] <Methanol solubles> The methanol-soluble content of rubber-modified polystyrene was measured as follows: 1.00 g of rubber-modified polystyrene was precisely weighed (P), dissolved in 40 ml of methyl ethyl ketone, and 400 ml of methanol was added rapidly to separate and precipitate the methanol-insoluble content (resin component). After allowing to stand for approximately 10 minutes, the mixture was slowly filtered through a glass filter to separate the methanol-soluble content, which was then dried under reduced pressure at 120°C for 2 hours in a vacuum dryer and then allowed to cool in a desiccator for 25 minutes. The mass N of the dried methanol-insoluble content was measured and calculated using the following formula: Methanol soluble matter (mass%) = (PN) / P × 100

[0059] <Swelling degree> The degree of swelling was determined by precisely weighing 1 g of rubber-modified polystyrene, adding 30 mL of toluene to dissolve it, centrifuging the solution at 14,000 rpm for 30 minutes in a centrifuge (H-2000B (rotor: H) manufactured by Kokusan Co., Ltd.) to precipitate the insoluble matter, removing the supernatant by decantation, and measuring the mass S of the insoluble matter swollen with toluene. The insoluble matter swollen with toluene was then pre-dried in a safety oven at 90°C for 2 hours, and then vacuum-dried in a vacuum dryer at 125°C for 1 hour. After cooling in a desiccator for 20 minutes, the dry mass D of the insoluble matter was measured and calculated based on the following formula. Swelling ratio = S / D

[0060] [Table 1]

[0061] [Examples 1 to 2, Comparative Examples 1 to 6] The rubber-modified polystyrenes (resins A to D) produced by the above methods were premixed in the ratios shown in Table 2 and melt-kneaded in a single-screw extruder (Ikegai, PMS40-28V) set at 180 to 220° C. The resin properties of the resulting rubber-modified styrene-based resin composition are shown in Table 2.

[0062] <Melt mass flow rate> The melt mass flow rate of the rubber-modified styrene-based resin composition was measured at 200°C under a load of 49N in accordance with JIS K-7210.

[0063] <Vicat softening temperature> The Vicat softening temperature of the rubber-modified styrene-based resin composition was measured in accordance with JIS K-7206 under conditions of a load of 50 N and a temperature rise rate of 50° C. / hr.

[0064] <Gel content> The gel content of the rubber-modified styrene-based resin composition was measured as follows: 1.00 g of the rubber-modified styrene-based resin composition was precisely weighed (W), dissolved in 35 mL of a 50% methyl ethyl ketone / 50% acetone mixed solution, and the resulting solution was centrifuged at 10,000 rpm for 30 minutes in a centrifuge (H-2000B (rotor: H) manufactured by Kokusan Co., Ltd.) to precipitate the insoluble matter. The supernatant was removed by decantation to obtain the insoluble matter, which was pre-dried in a safety oven at 90°C for 2 hours, further dried under reduced pressure at 125°C for 1 hour in a vacuum dryer, and cooled in a desiccator for 20 minutes. The mass G of the dried insoluble matter was measured and calculated according to the following formula: Gel content (amount of dispersed rubber particles) (mass%) = (G / W) x 100

[0065] <Rubber particle diameter (volume median particle diameter) and rubber particle diameter difference (volume 85% diameter - volume 15% diameter)> The volume median particle diameter, 85% diameter of the integrated value in the volume integral distribution curve, and 15% diameter of the integrated value in the volume integral distribution curve were calculated based on the 50% diameter, 85% diameter, and 15% diameter of the volume integral distribution curve. The volume integral distribution curve was obtained by dissolving the rubber-modified styrene-based resin composition in dimethylformamide and measuring it with a laser diffraction / scattering particle size distribution analyzer (LA-960, manufactured by Horiba, Ltd., relative refractive index 120A000I).

[0066] <Charpy impact strength> Using an injection molding machine (manufactured by The Japan Steel Works, Ltd., J100E-P), A-type test pieces (dumbbells) according to JIS K-7139 were molded at a cylinder temperature of 220°C and a mold temperature of 45°C. Test pieces were cut out from the center of the dumbbell pieces, and a notch (type A, r = 0.25 mm) was made by cutting, and measurements were performed in accordance with JIS K-7111-1.

[0067] <Flexural modulus> Using an injection molding machine (manufactured by The Japan Steel Works, Ltd., J100E-P), A-type test pieces (dumbbells) according to JIS K-7139 were molded at a cylinder temperature of 220°C and a mold temperature of 45°C. Test pieces cut out from the center of the dumbbells were used for measurements in accordance with JIS K-7171.

[0068] [Table 2]

Claims

1. The composition comprises a styrene-based resin that forms a matrix phase and rubber-like polymer particles dispersed in the matrix phase, The gel content is 26.0 to 30.0% by mass, The rubber-modified styrene resin composition has a particle diameter of the rubber-like polymer particles, the difference between the 85% diameter of the integrated value and the 15% diameter of the integrated value in a volume-integrated distribution curve of the particle diameter of the rubber-like polymer particles being 5.1 to 6.9 μm.

2. 2. The rubber-modified styrene-based resin composition according to claim 1, which has a melt mass flow rate measured at 200°C and 49 N of 3.5 g / 10 min or less.

3. The rubber-modified styrene-based resin composition according to claim 1 or claim 2, wherein the rubber content is more than 11% by mass.

4. A molded article obtained by molding the rubber-modified styrene-based resin composition according to claim 1 or 2.

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