TWI880081B - Transparent rubber modified styrene resin composition - Google Patents

Abstract

A rubber-modified styrene resin composition having excellent transparency and surface impact strength is provided. According to the present invention, a rubber-modified styrene resin composition is provided, which has a continuous phase containing a styrene copolymer and dispersed particles containing a rubber-like polymer, wherein the styrene copolymer has a styrene monomer unit and one or more (meth)acrylate monomer units, the grafting rate of the rubber-modified styrene resin composition is 2.12-2.40, and the hydrogenation rate of the rubber-like polymer is less than 7 mol%.

Description

Transparent rubber modified styrene resin composition

The present invention relates to a rubber-modified styrene-based resin composition having a continuous phase containing a styrene-based copolymer and dispersed particles containing a rubbery polymer.

High impact polystyrene (HIPS) is a rubber-modified styrene resin composition with excellent impact resistance. It is obtained by graft copolymerizing styrene monomers in the presence of polybutadiene, but it is opaque due to the difference in refractive index between the continuous phase polystyrene and the dispersed particles containing polybutadiene. In order to reconcile the refractive index of the continuous phase and the dispersed particles, a styrene-butadiene rubber obtained by copolymerizing (meth)acrylate monomer units in the continuous phase and styrene in the dispersed particles is used to obtain a transparent rubber-modified styrene resin composition. It has various properties such as transparency, impact resistance, and rigidity, and is therefore widely used in various fields. Due to its excellent moldability, it is mostly manufactured into molded bodies by injection molding, but there are still problems with the surface impact strength related to practical strength. [Prior art literature] [Patent literature]

[Patent Document 1] Japanese Patent No. 4663107 [Patent Document 2] Japanese Patent No. 4386772 [Patent Document 3] Japanese Patent No. 3618876 [Patent Document 4] Japanese Patent No. 3151481 [Patent Document 5] Japanese Patent Publication No. 2004-520459

[Problem to be solved by the invention] The subject of the present invention is to provide a rubber-modified styrene resin composition having excellent transparency, surface impact strength and Charpy impact strength. [Means for solving the problem]

According to the present invention, a rubber-modified styrene resin composition is provided, which has a continuous phase containing a styrene copolymer and dispersed particles containing a rubber-like polymer, wherein the styrene copolymer has a styrene monomer unit and one or more (meth)acrylate monomer units, the grafting rate of the rubber-modified styrene resin composition is 2.12-2.40, and the hydrogenation rate of the rubber-like polymer is less than 7 mol%.

Various embodiments of the present invention are exemplified below. The embodiments shown below can be combined with each other. (1) A rubber-modified styrene resin composition, which has a continuous phase containing a styrene copolymer and dispersed particles containing a rubber-like polymer, wherein the styrene copolymer has a styrene monomer unit and one or more (meth)acrylate monomer units, the grafting rate of the rubber-modified styrene resin composition is 2.12 to 2.40, and the hydrogenation rate of the rubber-like polymer is less than 7 mol%. (2) The rubber-modified styrene resin composition as described in (1), wherein the haze of the 2 mm thick molded body is 5% or less. (3) The rubber-modified styrene resin composition as described in (1) or (2), wherein the rubber-like polymer is a styrene-butadiene rubber copolymer. (4) A rubber-modified styrene resin composition as described in (3), wherein the content of styrene monomer units in the styrene-butadiene rubber copolymer is 10 to 50% by mass. (5) A rubber-modified styrene resin composition as described in any one of (1) to (4), wherein the refractive index is 1.53 to 1.57. (6) A rubber-modified styrene resin composition as described in any one of (1) to (5), wherein the styrene copolymer has 35 to 75% by mass of the styrene monomer units and 25 to 65% by mass of the (meth)acrylate monomer units. [Effect of the invention]

The rubber-modified styrene resin composition of the present invention has excellent transparency, surface impact strength and Charpy impact strength, so a molded product with high appearance and use strength can be obtained. In addition, due to its excellent fluidity, it is particularly suitable for injection molding.

<Terminology> In this manual, for example, "A~B" means A or more and B or less.

The implementation of the present invention is described in detail below.

The resin composition of the present invention is a transparent rubber-modified styrene resin composition having a continuous phase containing a styrene copolymer and dispersed particles containing a rubbery polymer, wherein the styrene copolymer has a styrene monomer unit and one or more (meth)acrylate monomer units.

The styrene monomer unit is a unit derived from a styrene monomer used for polymerization. The styrene monomers include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, ethylstyrene, p-tert-butylstyrene, α-methylstyrene, α-methyl-p-methylstyrene, etc. Among them, styrene is preferred. The styrene monomer unit may be used alone or in combination of two or more.

The (meth)acrylate monomer unit is a unit derived from a (meth)acrylate monomer used for polymerization. The (meth)acrylate monomers include (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; a mixture of one or more of methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-methylhexyl acrylate, 2-ethylhexyl acrylate, and decyl acrylate. From the viewpoint of excellent hue and heat resistance, methyl methacrylate is preferably used as the main component. In addition, in one embodiment, as the (meth)acrylate monomer unit, it is preferred to contain methyl methacrylate and n-butyl acrylate.

The styrene copolymer constituting the continuous phase has a styrene monomer unit and one or more (meth)acrylate monomer units. The styrene copolymer has a styrene monomer unit as a main component and contains one or more (meth)acrylate monomer units, preferably two or more (meth)acrylate monomer units. By using a component with excellent heat resistance and a component with excellent fluidity, the fluidity of the rubber modified resin composition can be improved. For example, there is a styrene-methyl methacrylate-butyl acrylate copolymer.

The rubber-like polymer shows the properties of rubber at room temperature, for example, a polymer having a butadiene component such as polybutadiene, styrene-butadiene rubber copolymer, preferably a styrene-butadiene rubber copolymer having a styrene monomer unit and a butadiene monomer unit such as styrene-butadiene rubber or styrene-butadiene block rubber (block copolymer). The content of the styrene monomer unit of the styrene-butadiene rubber copolymer is preferably 10 to 50% by mass, more preferably 30 to 45% by mass. The content of the styrene monomer unit of the styrene-butadiene rubber copolymer is specifically, for example, 10, 15, 20, 25, 30, 35, 40, 45, 50% by mass, and may also be in the range between any two values exemplified here. In addition, a part of the unsaturated units such as butadiene monomer units contained in the rubber-like polymer may be hydrogenated, and the ratio of hydrogenated units in the unsaturated units contained (hydrogenation rate) is less than 7 mol %, preferably less than 5 mol %, and more preferably less than 1 mol %.

The rubber-modified styrene resin composition can be obtained by graft copolymerizing styrene monomers and (meth)acrylate monomers in the presence of a rubbery polymer. The graft copolymerization method can be used in the production of high impact polystyrene (HIPS). The production of HIPS is mostly carried out by a continuous polymerization method, for example, a rubbery polymer is dissolved in a styrene monomer, a (meth)acrylate monomer, and a polymerization solvent to prepare a raw material solution, which is then continuously supplied to a reactor for graft copolymerization. As the polymerization proceeds, dispersed particles are formed and a phase inversion occurs, and then a polymerization reaction is further performed. The polymerization solution exiting the reactor is supplied to a stripping step to remove unreacted monomers and the polymerization solvent, and at the same time, crosslinking of the rubbery polymer constituting the dispersed particles is performed. Examples of the reactor type include a complete mixing tank reactor, a tower reactor with plug flow, and a circulation reactor that extracts part of the polymerization solution while performing polymerization. There is no particular restriction on the arrangement order of these reactors. The devolatization step is composed of a vacuum devolatization tank with a heater or a devolatization extruder with pores. The resin in a molten state after the devolatization step is transferred to the granulation step. In the granulation step, the molten resin is extruded from a porous die in a linear shape and processed into a granular shape by cold cutting, air hot cutting, or underwater hot cutting. More than one polymerization reactor can be arranged in series. When there is one, it can be used alone. When there are more than two, at least two can be arranged in series.

In order to control the polymerization reaction, a polymerization solvent, a polymerization initiator, and a chain transfer agent can be used. The polymerization solvent is used to adjust the polymerization rate, adjust the molecular weight, and reduce the viscosity of the polymerization solution. For example, alkylbenzenes such as benzene, toluene, ethylbenzene, and xylene; ketones such as acetone or methyl ethyl ketone; aliphatic hydrocarbons such as hexane or cyclohexane, etc. can be used. The amount of the polymerization solvent used is not particularly limited. Generally, as a composition in the polymerization reactor, it is preferably in the range of 1 to 50 mass%, and more preferably in the range of 3 to 25 mass%. When it exceeds 50 mass%, sometimes the productivity is significantly reduced, and the molecular weight of the rubber-modified styrene resin composition is excessively reduced.

The polymerization initiator is preferably a free radical polymerization initiator. Examples of the known and commonly used initiators include peroxyacetals such as 1,1-di(tert-butylperoxy)cyclohexane, 2,2-di(tert-butylperoxy)butane, 2,2-di(4,4-di-tert-butylperoxycyclohexyl)propane, and 1,1-di(tert-amylperoxy)cyclohexane, hydroperoxides such as isopropylbenzene hydroperoxide and tert-butyl hydroperoxide, alkyl peroxides such as tert-butyl peroxyacetate and tert-amyl peroxybenzoate, tert-butyl cumyl peroxide, di-tert-butyl peroxide, diisopropyl peroxide, and di-tert-butyl peroxide. Dialkyl peroxides such as hexyl peroxide, peroxide esters such as tert-butyl peroxyacetate, tert-butyl peroxybenzoate, tert-butyl peroxyisopropyl monocarbonate, peroxycarbonates such as tert-butyl peroxyisopropyl carbonate and polyether tetrakis (tert-butyl peroxycarbonate), N,N'-azobis(cyclohexane-1-carbonitrile), N,N'-azobis(2-methylbutyronitrile), N,N'-azobis(2,4-dimethylvaleronitrile), N,N'-azobis[2-(hydroxymethyl)propionitrile], etc., can be used alone or in combination of two or more. Examples of the chain transfer agent include aliphatic thiols, aromatic thiols, pentaphenylethane, -methylstyrene dimer, and terpinolene.

The grafting rate of the rubber modified styrene resin composition is 2.12 to 2.40, preferably 2.15 to 2.35. When the grafting rate is less than 2.12, the surface impact strength and transparency may be deteriorated, and when it is greater than 2.40, the Charpy impact strength may be reduced. Specifically, the grafting rate is, for example, 2.12, 2.13, 2.14, 2.15, 2.16, 2.17, 2.18, 2.19, 2.20, 2.25, 2.30, 2.35, 2.40, and may be within the range between any two of the values exemplified here. The grafting rate is calculated from the gel component and the rubber component by grafting rate = (gel component - rubber component) / rubber component, and represents the ratio of components other than rubber per unit rubber component. Components other than rubber refer to components such as styrene bonded to the rubber, grafted styrene copolymers, encapsulated styrene copolymers, etc. The grafting rate can be adjusted by adjusting the composition of the rubber-like polymer used, the content of 1,2-vinyl bonds, the type and amount of the polymerization initiator added initially, the form of the reactor for forming rubber particles, etc. In addition, it can also be adjusted by adjusting the type and amount of the polymerization initiator added to the polymerization solution after phase inversion.

The gel component represents the content of dispersed particles. 1g of rubber-modified styrene resin composition (mass W) is accurately weighed, and 35ml of a 50% methyl ethyl ketone/50% acetone mixed solution is added and dissolved. The solution is centrifuged at 14000rpm for 30 minutes using a centrifuge (H-2000B (rotor: H) manufactured by KOKUSAN) to precipitate the insoluble components. The supernatant is removed by decantation to obtain the insoluble components. The components are pre-dried at 90℃ for 2 hours in a safety oven, and then vacuum dried at 120℃ for 1 hour in a vacuum dryer. After cooling in the dryer for 20 minutes, the mass G of the dried insoluble components is measured and can be obtained as follows. Gel component (mass %) = (G/W) × 100 It should be noted that the supernatant obtained by decanting and separation was added to 300 ml of baked cake, and 250 ml of methanol was quickly added to reprecipitate the polymer component. The precipitated polymer component was filtered by a screening process, and the polymer on the screening process was vacuum dried in a vacuum dryer for more than 1.5 hours to measure the monomer unit and weight average molecular weight of the styrene resin constituting the continuous phase described later.

For the rubber component, when the rubber-like polymer is a polymer containing a butadiene monomer unit, it can be calculated as a butadiene component (butadiene monomer unit). The rubber-modified styrene resin composition is dissolved in chloroform, and a certain amount of iodine monochloride/carbon tetrachloride solution is added. After standing in a dark place for about 1 hour, a potassium iodide solution is added, and the excess iodine monochloride is titrated with a 0.1N sodium thiosulfate/ethanol aqueous solution. The content of the butadiene component can be calculated based on the amount of iodine monochloride added.

The solubility expansion ratio SR of the rubber-modified styrene resin composition is preferably 8 to 12. The solubility expansion ratio indicates the degree of crosslinking of dispersed particles. If it is less than 8, the impact resistance may be reduced, and if it exceeds 12, the appearance may be deteriorated. The swelling ratio SR can be obtained as follows: accurately weigh 1g of rubber-modified styrene resin, add 30ml of toluene to dissolve it, centrifuge the solution at 14000rpm for 30 minutes using a centrifuge (H-2000B (rotor: H) manufactured by KOKUSAN) to precipitate the insoluble components, remove the supernatant by decanting, and measure the mass S of the insoluble components after swelling with toluene. Then, pre-dry the insoluble components after swelling with toluene in a safety oven at 90℃ for 2 hours, and then vacuum dry them at 120℃ for 1 hour in a vacuum dryer. After cooling in the dryer for 20 minutes, measure the dry mass D of the insoluble components and obtain the swelling ratio SR as follows. Swelling ratio SR = S/D

The particle size of the dispersed particles containing the rubbery polymer is preferably 0.2 to 2.0 μm, more preferably 0.4 to 1.5 μm. If the particle size is less than 0.2 μm, the impact resistance may be reduced, and if it is greater than 2.0 μm, the appearance such as transparency may be deteriorated. The particle size is a value calculated as follows: ultrathin sections are cut from particles of the rubber-modified styrene resin composition, observed using a transmission electron microscope (TEM), and the particles dispersed in the continuous phase are analyzed by image analysis to measure the equivalent circular diameter Di of about 2,000 particles, and calculated using the following formula. Particle size = Σni･ Di ⁴ /Σni･Di3 The particle size can be adjusted by adjusting the composition of the rubbery polymer used or the content of 1,2-vinyl bonds, the stirring rate of the reactor during phase inversion to form dispersed particles, and the type and amount of polymerization initiator and chain transfer agent added before phase inversion.

The monomer units of the styrene copolymer constituting the continuous phase are preferably 35-75% by mass of styrene monomer units and 25-65% by mass of (meth)acrylate monomers, and more preferably 45-70% by mass of styrene monomer units and 30-55% by mass of (meth)acrylate monomers. If the constituent units are within the above range, the obtained rubber-modified styrene resin composition has excellent balance in physical properties such as transparency, impact resistance, and fluidity. The constituent units constituting the continuous phase are the values obtained by measuring the reprecipitate of the supernatant other than the gel component obtained in the measurement of the gel component using 13C-NMR. The monomer units of the styrene resin constituting the continuous phase can be adjusted by adjusting the composition of the raw materials used for polymerization.

The weight average molecular weight of the styrene copolymer constituting the continuous phase is preferably 80,000 to 220,000, and more preferably 120,000 to 180,000, from the viewpoint of the strength and moldability of the rubber-modified styrene resin composition. The weight average molecular weight is a value converted to polystyrene measured in THF solvent using gel permeation chromatography (GPC), and is measured under the following conditions using the reprecipitate of the supernatant other than the gel component obtained in the measurement of the gel component. Device name: SYSTEM-21 Shodex (Showa Denko Co., Ltd.) Column: 3 PL gel MIXED-B in series Temperature: 40°C Detection: Differential refractive index Solvent: Tetrahydrofuran Concentration: 2 mass % Standard curve: Plotted using standard polystyrene (PS) (PL Co., Ltd.)

The haze of a 2 mm thick molded article of a rubber-modified styrene resin composition is preferably 5% or less, more preferably 2% or less. The haze can be obtained by the following method: using an injection molding machine (IS-50EP manufactured by Toshiba Machine Co., Ltd.), a mirror panel with a length of 90 mm, a width of 55 mm, and a thickness of 2 mm is molded under molding conditions of a barrel temperature of 230°C and a mold temperature of 60°C, and the haze is measured using a haze meter (NDH-1001DP manufactured by Nippon Denshoku Industries Co., Ltd.) according to ASTM D1003.

The refractive index of the rubber-modified styrene resin composition is preferably 1.53 to 1.57, and more preferably 1.54 to 1.56. If the refractive index is within the above range, the obtained rubber-modified styrene resin composition has an excellent balance of physical properties such as transparency, impact resistance, and fluidity. The refractive index of a molded product with a thickness of 2 mm can be measured using an Abbe refractometer.

The rubber modified styrene resin composition can be added with dyes such as blueing agent, plasticizers, hindered phenol antioxidants, phosphorus antioxidants, UV absorbers, hindered amine stabilizers, antistatic agents, internal lubricants such as stearic acid, external lubricants such as ethylene distearylamide, MS resins, MBS resins, emulsified graft copolymers, etc. within the range that does not damage the transparency.

The rubber-modified styrene resin composition can be made into a molded body by a known molding method. Due to its excellent fluidity, it is particularly preferably used for injection molding. [Example]

The following examples are used to illustrate the details, but the present invention is not limited to the following examples.

(Examples 1 to 5, Comparative Examples 1 to 3) The first reactor and the second reactor, which are complete mixing type stirring tanks, and the third reactor, which is a tower type plug flow reactor with stirring blades, are connected in series to form a polymerization step. The capacity of each reactor is 5L for the first reactor, 15L for the second reactor, and 40L for the third reactor. The raw material solution is prepared according to the raw material composition listed in Table 1, and the raw material solution is continuously supplied to the first reactor at the flow rate listed in Table 1. The rubber-like polymer used is ASAPRENE 670A manufactured by Asahi Kasei Corporation (styrene-butadiene block rubber, styrene content of 40% by mass, 5% by mass styrene solution viscosity at 25°C of 32mPa･s, 1,2-vinyl bond ratio of 13.5 mol%, hydrogenation rate of 0 mol%). The polymerization initiator and the chain transfer agent were added to the raw material solution so that the inlet of the first reactor and the third reactor became the addition concentration (concentration based on the mass of the raw material supply flow rate) listed in Table 1, and the mixture was uniformly mixed. In Table 1, the polymerization initiator-1 was 1,1-bis(tert-butylperoxide)-cyclohexane (PERHEXA C manufactured by NOF Corporation), the polymerization initiator-2 was tert-butyl peroxide isopropylbenzene (PERBUTYL C manufactured by NOF Corporation), and the chain transfer agent was n-dodecyl mercaptan. For the reaction temperature adjustment, the temperature in the tank was adjusted to the temperature listed in Table 1, and in the third reactor, a gradient was set so that the inlet temperature was 130°C and the outlet temperature was 165°C. Then, the polymerization solution was continuously taken out from the third reactor and introduced into a vacuum degassing tank with a preheater. The temperature of the preheater was adjusted so that the resin temperature became 230°C, and the pressure in the degassing tank was adjusted to 1 kPa. After the unreacted styrene and ethylbenzene (EB) were separated, they were extruded from a porous die in a linear shape. The strands were cooled and cut by cold cutting to obtain a granulated rubber-modified styrene-based resin composition. The measurement and evaluation of the obtained rubber-modified styrene-based resin composition and the styrene-based copolymer contained therein are shown in Table 2.

(Rubber component) The content of butadiene component (mass %) is calculated as rubber component. The rubber-modified styrene resin composition is dissolved in chloroform, and a certain amount of iodine monochloride/carbon tetrachloride solution is added. After being placed in a dark place for about 1 hour, potassium iodide solution is added, and the excess iodine monochloride is titrated with 0.1N sodium thiosulfate/ethanol aqueous solution, and the content is calculated based on the amount of iodine monochloride added.

(Gel component) Accurately weigh 1g of rubber-modified styrene resin composition (mass W), add 35ml of 50% methyl ethyl ketone/50% acetone mixed solution and dissolve. Centrifuge the solution at 14000rpm for 30 minutes in a centrifuge (H-2000B (rotor: H) manufactured by KOKUSAN) to precipitate the insoluble components, and remove the supernatant by decanting to obtain the insoluble components. Pre-dry the insoluble components at 90℃ for 2 hours in a safety oven, and then vacuum dry them at 120℃ for 1 hour in a vacuum dryer. After cooling in the dryer for 20 minutes, measure the mass G of the dried insoluble components. Calculate the gel component using G and W based on the following formula. Gel component (mass %) = (G/W) × 100

(Grafting rate) The grafting rate is calculated based on the following formula. Grafting rate = (gel component - rubber component) / rubber component

(Swelling ratio SR) The swelling ratio SR is calculated as follows: 1g of rubber-modified styrene resin is accurately weighed, 30ml of toluene is added and dissolved, the solution is centrifuged at 14000rpm for 30 minutes using a centrifuge (H-2000B (rotor: H) manufactured by KOKUSAN Co., Ltd.) to precipitate the insoluble components, the supernatant is removed by decanting, the mass S of the insoluble components after swelling with toluene is measured, and then the insoluble components also after swelling with toluene are pre-dried at 90°C for 2 hours using a safety oven, and then vacuum dried at 120°C for 1 hour using a vacuum dryer, and after cooling in the dryer for 20 minutes, the dry mass D of the insoluble components is measured and calculated based on the following formula. Swelling ratio SR = S/D

(Rubber Particle Size) The particle size is calculated as follows: Ultrathin sections are cut from particles of a rubber-modified styrene resin composition, observed using a transmission electron microscope (TEM), and the particles dispersed in the continuous phase are analyzed by image analysis. The equivalent circular diameter Di of approximately 2,000 particles is measured and calculated based on the following formula. Particle size = Σni･ Di ⁴ /Σni･Di ³

(Refractive index) The refractive index was measured using an Abbe refractometer based on JIS K 7142 by producing a molded product with a thickness of 2 mm.

(Weight average molecular weight) The weight average molecular weight of the styrene copolymer constituting the continuous phase was measured as a polystyrene-converted value in THF solvent using gel permeation chromatography (GPC) under the following conditions using the reprecipitate of the supernatant obtained in the measurement of the gel component excluding the gel component. Apparatus name: SYSTEM-21 Shodex (manufactured by Showa Denko Co., Ltd.) Column: 3 PL gel MIXED-B in series Temperature: 40°C Detection: Differential refractive index Solvent: Tetrahydrofuran Concentration: 2 mass % Standard curve: drawn using standard polystyrene (PS) (manufactured by PL Co., Ltd.)

The reprecipitate used was obtained in the following manner: in the above-mentioned determination of the gel component, the supernatant separated by decanting was added to a 300 ml beaker, 250 ml of methanol was quickly added to reprecipitate the polymer component, the precipitated polymer component was filtered by a screening process, and the polymer on the screening process was vacuum dried in a vacuum dryer for more than 1.5 hours.

(Styrene content and MMA content) The content of styrene monomer units (styrene content) and methyl methacrylate monomer units (MMA content) as constituent units of the styrene copolymer constituting the continuous phase were measured by 13C-NMR using the reprecipitate of the supernatant excluding the gel component obtained in the measurement of the gel component. The reprecipitate is the same as the reprecipitate in (weight average molecular weight). It should be noted that the constituent units of the styrene copolymer contain n-butyl acrylate (n-BA) as a (meth)acrylate monomer unit, and the content of the n-butyl acrylate is the amount obtained by subtracting the styrene content and the MMA content from 100% by mass.

[Table 1]

(Melt flow rate) The melt flow rate is measured at 200°C and 49N load based on JIS K7210.

(Haze) Using an injection molding machine (IS-50EP manufactured by Toshiba Machinery Co., Ltd.), a mirror panel with a length of 90 mm, a width of 55 mm, and a thickness of 2 mm was molded under the molding conditions of a barrel temperature of 230°C and a mold temperature of 60°C. The haze was measured using a haze meter (NDH-1001DP manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with ASTM D1003.

(Charpy impact strength) Charpy impact strength is based on JIS K7111-1, using a notched test piece and striking along the edge. The measuring machine used is a digital display impact tester manufactured by Toyo Seiki Seisaku-sho Co., Ltd.

(Surface impact strength) The injection molding machine (IS-55EPN manufactured by Toshiba Machinery Co., Ltd.) was used to mold a test piece (film gate) with a length of 90 mm, a width of 90 mm, and a thickness of 2 mm under the molding conditions of a barrel temperature of 230°C, a mold temperature of 60°C, and an injection speed of 70%. The test piece was used to perform a surface impact test using a high-speed puncture impact tester (HITS-PX) manufactured by Shimadzu Corporation. At 23°C, a striker diameter of 12.7 mm (ASTM D3763), and a piston speed of 5 m/sec, the center of the test piece fixed to the fixture was impacted and destroyed, and the energy absorbed before reaching the maximum impact point was used as the surface impact strength.

(Flexural modulus) Flexural modulus is measured at a bending speed of 2 mm/min based on JIS K7171.

[Table 2]

From the results in Table 2, it can be seen that the rubber-modified styrene resin composition of the embodiment has excellent transparency, surface impact strength and Charpy impact strength. [Industrial Applicability]

The rubber-modified styrene resin composition of the present invention can be used to obtain a transparent molded body with excellent impact resistance. In addition, due to its excellent fluidity, it is particularly suitable for injection molding purposes, and due to its excellent surface impact strength, it is suitable for use in the frame of home appliances, etc.

Claims (6)

A rubber-modified styrene resin composition, which has a continuous phase containing a styrene copolymer and dispersed particles containing a rubber-like polymer, The rubber-like polymer is a styrene-butadiene rubber copolymer, The styrene copolymer has a styrene monomer unit and one or more (meth)acrylate monomer units, The styrene copolymer has 35-75% by mass of the styrene monomer unit and 25-65% by mass of the (meth)acrylate monomer unit, The grafting rate of the rubber-modified styrene resin composition is 2.12-2.40, The grafting rate is calculated by the following formula: Grafting rate = (gel component - rubber component) / rubber component, The rubber component is the content of the butadiene component, and the gel component is the content of the dispersed particles, The hydrogenation rate of the rubbery polymer is less than 7 mol %. The rubber-modified styrene resin composition as described in claim 1 has a haze of 2 mm thick molded body of 5% or less. The rubber-modified styrene resin composition as described in claim 1, wherein the styrene monomer unit includes a unit derived from styrene, and the (meth)acrylate monomer unit includes a unit derived from methyl (meth)acrylate. The rubber-modified styrene resin composition as described in claim 3, wherein the content of styrene monomer units in the styrene-butadiene rubber copolymer is 10 to 50 mass %. The rubber-modified styrene resin composition as described in claim 1 has a refractive index of 1.53 to 1.57. The rubber-modified styrene resin composition as described in any one of claims 1 to 5, wherein the styrene monomer units include units derived from styrene, and the (meth)acrylate monomer units include units derived from methyl (meth)acrylate and units derived from n-butyl acrylate.