Rubber-modified styrene resin composition, sheet, lighting cover and molded product

Abstract

To provide a rubber-modified styrene resin composition having an excellent balance of total light transmittance, diffused light transmittance, and whitening resistance, by optimizing reinforcing rubber particles dispersed in the rubber-modified styrene resin composition.SOLUTION: The rubber-modified styrene resin composition of the present invention contains a styrene polymer forming a matrix and rubber-like polymer particles dispersed as islands in the matrix. The rubber-like polymer particles include styrene-based polymer particles and have a sea-island structure, containing 99.0 to 94.0% by mass of the styrene-based polymer and 1.0 to 6.0% by mass of the rubber-like polymer. The rubber-like polymer particles are a polybutadiene rubber and / or a styrene-butadiene copolymer. The particle size of the rubber-like polymer particles is 2.0 to 5.5 μm, and a content of methyl ethyl ketone insoluble gel in the rubber-modified styrene resin composition is 2.0 to 15.0% by mass.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a rubber-modified styrene-based resin composition having excellent light diffusibility, light transmittance, and whitening resistance, a sheet containing the resin composition, and a molded article such as a lighting cover obtained from the sheet. [Background technology]

[0002] In recent years, LEDs, which have stronger directionality, have been used as the light source for lighting, replacing the fluorescent lamps that were previously used. As a result, lighting covers are required to have stronger light diffusion properties to prevent the light source from being seen through, while still ensuring sufficient light transmittance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 60-21662 [Patent Document 2] Japanese Patent Application Publication No. 139758 / 1983 [Patent Document 3] Patent No. 2512544 [Patent Document 4] Japanese Patent Application Publication No. 11-60966 [Patent Document 5] JP 2004-50607 A [Patent Document 6] Japanese Patent Application Publication No. 08-198976 [Patent Document 7] JP 2000-296581 A [Patent Document 8] JP 2004-90626 A Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, conventionally, such lighting covers have achieved both light diffusibility and light transmittance by adding a large amount of a light diffusing agent to a transparent resin such as an acrylic resin or a styrene resin.

[0005] Specifically, as a method for imparting light diffusion to a transparent resin, a method of blending fine particles with different refractive indexes into the transparent resin has been disclosed for a long time. For example, a technique of blending fine particles of 1 to 10 μm (Patent Document 1), a technique of blending fine particles of 10 to 50 μm (Patent Document 2), a technique of using silicone resin fine particles of 1 to 6 μm in combination with inorganic powder of 1 to 7 μm (Patent Document 3), a technique of using crosslinked resin fine particles of less than 5 μm in combination with crosslinked resin fine particles of 5 to 10 μm (Patent Document 4), a technique of blending a light diffusing agent of 1 to 20 μm (Patent Document 5), etc. can be mentioned. However, whether organic or inorganic, these fine particles have low affinity with resin, and when added in large amounts, there is a problem that impact resistance decreases.

[0006] Furthermore, a technique of adding an acrylic multilayer polymer for the purpose of improving impact resistance has been disclosed (Patent Documents 6 to 8), but the particle size of the multilayer polymer produced by emulsion polymerization is usually smaller than 0.5 μm and light on the short wavelength side is easily absorbed, which is undesirable as it increases the yellowness of the transmitted color.

[0007] Furthermore, as a styrene resin having impact resistance, there is a rubber-modified styrene resin (impact-resistant polystyrene), but the conventional rubber-modified styrene resin has a problem that the transmitted color is highly yellow, and furthermore, the light diffusion and light transmittance are poor. Patent Document 9 discloses that the rubber-modified styrene resin has excellent light transparency and light diffusion properties by setting the diameter of the particles dispersed in the rubber-modified styrene resin and the cumulative volume ratio of these particles within a specific range. However, although this technology improves the diffuse light transmittance, there is a problem that white scratches occur when the product is lightly pressed with a fingernail, and when the light is turned on, a shadow appears as a black spot.

[0008] Therefore, an object of the present invention is to provide a rubber-modified styrene-based resin composition having an excellent balance of total light transmittance, diffuse light transmittance, and whitening resistance by optimizing the reinforcing rubber particles dispersed in the rubber-modified styrene-based resin composition, a sheet containing the resin composition, and a molded article such as a lighting cover obtained from the sheet. [Means for solving the problem]

[0009] In view of the current situation, the present inventors have conducted detailed studies on the structure and content of reinforcing rubber particles contained in a rubber-modified styrene-based resin composition, and as a result, have found that a rubber-modified styrene-based resin composition having an excellent balance of diffuse light transmittance and whitening resistance, which is suitable for use in lighting covers, can be obtained by using a specific amount of rubbery polymer and rubber particle structure, thereby completing the present invention.

[0010] That is, the present invention provides [1] A rubber-modified styrene-based resin composition comprising a styrene-based polymer forming a matrix and rubber-like polymer particles dispersed in the matrix in the form of islands, the rubber-like polymer particles containing the styrene-based polymer particles and having a sea-island structure, The styrene-based polymer and the rubber-like polymer constituting the rubber-like polymer particles are mixed in an amount of 99.0 to 94.0% by mass, and 1.0 to 6.0% by mass of the rubber-like polymer, relative to 100% by mass in total of the styrene-based polymer and the rubber-like polymer constituting the rubber-like polymer particles; The rubber-like polymer is polybutadiene rubber and / or styrene-butadiene copolymer, The rubber-like polymer particles have a particle size of 2.0 to 5.5 μm, 2. A rubber-modified styrene-based resin composition, wherein the rubber-modified styrene-based resin composition has a methyl ethyl ketone-insoluble gel content of 2.0 to 15.0% by mass. [2] The rubber-modified styrene-based resin composition according to the above [1], wherein the toluene-insoluble matter of the rubber-modified styrene-based resin composition has a swelling index in toluene of 10 to 14. [3] A sheet obtained by extrusion molding the rubber-modified styrene-based resin composition described in [1] or [2] above. [4] A molded product obtained by thermoforming the sheet described in [3] above. [5] A lighting cover obtained by thermoforming the sheet described in [3] above. Effect of the Invention

[0011] According to the present invention, it is possible to provide a rubber-modified styrene-based resin composition having an excellent balance of total light transmittance, diffuse light transmittance, and whitening resistance, a sheet containing the resin composition, and a molded article such as a lighting cover obtained from the sheet. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention (hereinafter, referred to as "the present embodiment") will be described in detail, but the present invention is not limited to the present embodiment.

[0013] The rubber-modified styrene-based resin composition of the present embodiment comprises a styrene-based polymer forming a matrix and rubber-like polymer particles dispersed in the matrix in the form of islands, and the rubber-like polymer particles encapsulate the styrene-based polymer particles and have a sea-island structure. Here, examples of the styrene monomer forming the styrene polymer in the rubber-modified styrene resin composition in this embodiment include styrene, α-methylstyrene, p-methylstyrene, pt-butylstyrene, etc., which may be used alone or in combination of two or more. Among these, styrene is preferred. If necessary, other monomers copolymerizable with the styrene monomer may be used within the scope of the present invention. Examples of other copolymerizable monomers that can be used here include cyan vinyl monomers such as acrylonitrile and methacrylonitrile, (meth)acrylic acid ester monomers such as methyl (meth)acrylate, ethyl (meth)acrylate, and butyl (meth)acrylate, anhydride group-containing monomers such as maleic anhydride and itaconic anhydride, dicarboxylic acid imide-containing monomers such as maleimide, N-methylmaleimide, N-phenylmaleimide, and N-cyclohexylmaleimide, and carboxyl group-containing monomers such as acrylic acid, methacrylic acid, maleic acid, and itaconic acid. The amount of other monomers copolymerizable with the styrene monomer is preferably 25% by mass or less, more preferably 10% by mass or less, as monomers constituting the matrix.

[0014] The rubber-modified styrene-based resin composition in this embodiment has an island-in-a-sea structure, in which the styrene-based polymer forms a matrix and the rubber-like polymer particles are dispersed in the matrix in the form of islands. The rubber-like polymer particles in the rubber-modified styrene-based resin composition contain styrene-based polymer (particles) in the rubber-like polymer particles. In the rubber-modified styrene-based resin composition in this embodiment, it is preferable that the styrene-based polymer particles contained in the rubber-like polymer particles have an extremely small and uniform particle size.

[0015] The rubbery polymer forming the rubbery polymer particles in this embodiment is polybutadiene rubber (low-cis polybutadiene, high-cis polybutadiene) and / or styrene-butadiene copolymer (random and block styrene-butadiene copolymer (SBR)), with polybutadiene rubber being preferred, and high-cis polybutadiene being particularly preferred. When a styrene-butadiene copolymer is used as the rubbery polymer, the content of the styrene polymer in the copolymer is preferably 25% by mass or less, more preferably 10% by mass or less. When the content of the styrene polymer in the styrene-butadiene copolymer increases, the refractive index difference with the matrix becomes closer, and the diffusivity tends to decrease.

[0016] The rubber-modified styrene-based resin composition of the present embodiment contains 1.0 to 6.0% by mass of the rubber-like polymer and 99.0 to 94.0% by mass of the styrene-based polymer and rubber-like polymer in total 100% by mass. Also, preferably, the rubber polymer is contained in the range of 1.5 to 5.0% by mass and the styrene-based polymer is contained in the range of 98.5 to 95.0% by mass, and more preferably, the rubber polymer is contained in the range of 2.0 to 4.5% by mass and the styrene-based polymer is contained in the range of 98.0 to 95.5% by mass. If the rubber-like polymer is less than 1.0% by mass, the light diffusion property and impact resistance are reduced, and if it exceeds 6.0% by mass, the light transmittance and rigidity are reduced, and whitening scratches are likely to occur.

[0017] The particle size of the dispersed particles of the rubber-like polymer in the rubber-modified styrene-based resin composition is 2.0 to 5.5 μm, preferably 2.5 to 5.0 μm, and more preferably 3.0 to 4.5 μm. If the particle size is less than 2.0 μm, the diffusibility is reduced, and when used for light diffusing purposes such as lighting covers, the light source is easily seen through, the yellowness of the transmitted color increases, and the impact resistance is poor. On the other hand, if the particle size exceeds 5.5 μm, a large amount of rubber-like polymer particles must be added to satisfy high light diffusibility, and adding too many rubber-like polymer particles is undesirable because it reduces rigidity and makes it easy for whitening scratches to occur.

[0018] The methyl ethyl ketone insoluble gel content of the rubber-modified styrene-based resin composition is in the range of 2.0 to 15.0 mass%, preferably 4.0 to 13.0 mass%, more preferably 5.0 to 12.0 mass%. As the methyl ethyl ketone insoluble gel content decreases, the impact strength and light diffusibility tend to decrease, while as the content increases, whitening scratches tend to occur more easily and light transmittance tends to decrease.

[0019] The content of the methyl ethyl ketone insoluble gel fraction of the rubber-modified styrene-based resin composition is measured by dissolving the resin in a solvent, separating the soluble fraction from the insoluble fraction, which is the dispersed phase, by decantation after centrifugation, and then drying the insoluble fraction. Generally, toluene is used as the solvent. However, in a rubber-modified styrene-based resin composition in which the diameter of the dispersed particles is small or the degree of crosslinking of the rubber-like polymer is low, if toluene is used, the affinity between toluene and the gel fraction is good, so that the gel fraction may flow out during decantation during measurement, and the content of the dispersed phase may be lower than the true value. Therefore, in the present invention, methyl ethyl ketone is used as the solvent. By using methyl ethyl ketone, the gel fraction does not flow out during decantation, and the content of the dispersed phase can be measured.

[0020] The swelling index of the toluene insoluble matter of the rubber-modified styrene-based resin composition in toluene is 10 to 14, preferably 10 to 13, and more preferably 11 to 13. The swelling index indicates the crosslink density of the rubber-like polymer, and the smaller the value, the higher the crosslink density, and the larger the value, the lower the crosslink density. As the swelling index decreases, the strength of the rubber-modified styrene-based resin composition tends to decrease. On the other hand, as the swelling index increases, the dispersed particles tend to be easily deformed due to orientation during molding, and the strength in the direction perpendicular to the orientation direction decreases, and the diffusibility tends to decrease.

[0021] An example of a method for producing the rubber-modified styrene-based resin composition of the present embodiment will be described below. In a typical embodiment, the rubber-modified styrene-based resin composition can be produced by a method including polymerizing a styrene-based monomer in the presence of a rubber-like polymer to form an island structure in which the rubber-like polymer is dispersed in the styrene-based polymer. There is no particular restriction on the polymerization method of the styrene-based monomer, and a solution in which rubber is dissolved in the styrene-based monomer can be used to carry out normal bulk polymerization, solution polymerization, suspension polymerization, etc. In addition, it is preferable to appropriately select and use a solvent and a chain transfer agent in order to adjust the melt flow rate. As the solvent, toluene, ethylbenzene, xylene, etc. can be used. The amount of the solvent used is not particularly limited, but is preferably in the range of 0 to 50 mass% with respect to the total amount of the polymerization raw material liquid (100 mass%). As the chain transfer agent, n-dodecyl mercaptan, t-dodecyl mercaptan, α-methylstyrene dimer, etc. are used, and α-methylstyrene dimer is preferred. The amount of the chain transfer agent used is preferably 0.01 to 2% by mass, more preferably 0.03 to 1% by mass, and even more preferably 0.05 to 0.2% by mass, based on 100% by mass of the total amount of the polymerization raw material liquid. The polymerization reaction temperature is preferably 80 to 200°C, and even more preferably 90 to 180°C. If the reaction temperature is 80°C or higher, the productivity is good and it is industrially appropriate, while if it is 200°C or lower, it is preferable because it is possible to avoid the production of a large amount of low molecular weight polymer. If the target molecular weight of the styrene-based polymer cannot be adjusted only by the polymerization temperature, it may be controlled by the amount of initiator, the amount of solvent, the amount of chain transfer agent, and the like. The reaction time is generally 0.5 to 20 hours, and preferably 2 to 10 hours. If the reaction time is 0.5 hours or more, the reaction proceeds well, while if it is 20 hours or less, the productivity is good and it is industrially appropriate.

[0022] In the above-mentioned production method, the particle size of the dispersed particles of the rubber-like polymer in the rubber-modified styrene-based resin composition can be controlled by the rotation speed of the stirrer in the reactor, the amount of the methyl ethyl ketone-insoluble gel fraction can be controlled by the amount of the initiator, and the swelling index of the toluene-insoluble fraction with respect to toluene can be controlled by the temperature of the extruder in the recovery system.

[0023] The amount of the rubber-like polymer in the rubber-modified styrene-based resin can be controlled by adjusting the content or polymerization rate of the rubber-like polymer in the raw material so as to obtain a target content. The rubber-modified styrene-based resin of the present invention can be produced by the above-mentioned production method. As another method, it can also be produced by mixing and diluting the rubber-modified styrene-based resin composition obtained by the above-mentioned production method with a styrene-based resin such as polystyrene resin that does not contain a rubber-like polymer. When the rubber-modified styrene-based resin composition is produced by the above-mentioned production method, the amount of the rubber-like polymer in the rubber-modified styrene-based resin composition is preferably 1 to 6 mass%, more preferably 1.5 to 5 mass%, and even more preferably 2 to 4.5 mass%.

[0024] Examples of the organic peroxide used as a polymerization initiator include peroxyketals, dialkyl peroxides, diacyl peroxides, peroxydicarbonates, peroxyesters, ketone peroxides, and hydroperoxides.

[0025] As the polymerization solvent, ethylbenzene, toluene, xylene, etc. can be used.

[0026] In the present embodiment, at any stage before or after the recovery step in producing the rubber-modified styrene-based resin composition, or at the stage of extruding or molding the rubber-modified styrene-based resin composition, various additives, for example, ultraviolet absorbers, light stabilizers, hindered phenol-, phosphorus-, sulfur-based and other antioxidants, lubricants, plasticizers such as liquid paraffin, antistatic agents, flame retardants, various dyes and pigments, fluorescent brightening agents, light diffusing agents, and selective wavelength absorbers may be added as necessary within a range that does not impair the object of the present invention.

[0027] Here, an ultraviolet absorber and a light stabilizer can be added to the rubber-modified styrene-based resin composition of the present embodiment in order to prevent coloring due to ultraviolet light generated from a light source lamp. Examples of ultraviolet absorbers include benzotriazole-based ultraviolet absorbers such as 2-(5-methyl-2-hydroxyphenyl)benzotriazole, 2-[2-hydroxy-3,5-bis(α,α'dimethylbenzyl)phenyl]benzotriazole, and 2-(3,5-di-t-amyl-2-hydroxyphenyl)benzotriazole, benzophenone-based ultraviolet absorbers such as 2-hydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone, and 2-hydroxy-4-n-octoxybenzophenone, salicylic acid-based ultraviolet absorbers such as phenyl salicylate and 4-t-butylphenyl salicylate, 2-(1-arylalkidene)malonic acid ester-based ultraviolet absorbers, and oxalanilide-based ultraviolet absorbers. Examples of light stabilizers include hindered amine-based light stabilizers. Examples of the hindered amine-based light stabilizer include bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate and N,N'-bis(3-aminopropyl)ethylenediamine·2,4-bis[N-butyl-N-(1,2,2,6,6-pentamethyl-4-piperidyl)amino]-6-chloro-1,3,5-triazine condensate. The ultraviolet absorber and the light stabilizer can be used alone or in combination, and the amount of the ultraviolet absorber and the light stabilizer added is preferably 0.02 to 2.0 parts by mass in total relative to 100 parts by mass of the rubber-modified styrene-based resin composition. More preferably, it is 0.1 to 1.5 parts by mass.

[0028] Furthermore, in the rubber-modified styrene-based resin composition of the present embodiment, a masking agent such as a fluorescent whitening agent or a bluing agent can be optionally used as necessary. The method of adding the additives to the rubber-modified styrene-based resin of the present embodiment can be selected from known methods. For example, the rubber-modified styrene-based resin composition, additives, and optionally a styrene-based resin not containing a rubber-like polymer are mixed in a Henschel mixer or a tumbler, and then melt-kneaded using a single-screw or twin-screw extruder or various kneaders to obtain a composition molded into pellets, plates, or the like.

[0029] In this embodiment, a sheet can be produced from the rubber-modified styrene-based resin composition by extrusion molding, and various molded products can be produced from the rubber-modified styrene-based resin composition or the sheet by extrusion molding, injection molding, compression molding, etc. These sheets and molded products can be suitably used for lighting fixtures, illuminated signs, liquid crystal displays, liquid crystal televisions, etc. In particular, the rubber-modified styrene-based resin composition of this embodiment is suitably used as a lighting cover obtained by thermoforming the sheet. EXAMPLES

[0030] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0031] <How to prepare Resin 1> A polymerization solution obtained by mixing and dissolving 78.2 parts by mass of styrene as a styrene monomer, 9.8 parts by mass of polybutadiene rubber (BR15HB manufactured by Ube Industries, Ltd.) as a rubber-like polymer, 12 parts by mass of ethylbenzene as a solvent, 0.003 parts by mass of 1,1-bis(t-butylperoxy)cyclohexane as a polymerization initiator, 0.10 parts by mass of α-methylstyrene dimer as a chain transfer agent, and 0.15 parts by mass of Irganox 1076 (manufactured by BASF Japan, Ltd.) as an antioxidant, was continuously charged at 3.2 L / Hr into a 6.2 L laminar flow reactor-1 equipped with a stirrer and capable of temperature control in three zones, and the temperature was adjusted to 117 ° C. / 123 ° C. / 129 ° C. The rotation speed of the stirrer was set to 120 revolutions per minute.

[0032] The reaction liquid in the laminar flow reactor-1 was then sent to a 6.2-liter laminar flow reactor-2 equipped with an agitator and capable of temperature control in three zones, which was connected in series with the laminar flow reactor-1. The agitator rotation speed was set to 15 rpm, and the temperature was set to 136°C / 138°C / 140°C. The reaction liquid in the laminar flow reactor-2 was then sent to a 6.2-liter laminar flow reactor-3 equipped with an agitator and capable of temperature control in three zones. The agitator rotation speed was set to 10 rpm, and the temperature was set to 147°C / 156°C / 159°C.

[0033] The polymer solution continuously discharged from the polymerization reactor (laminar flow reactor-3) was introduced into an extruder equipped with a vacuum vent, and after devolatilization under a reduced pressure of 10 torr, the solution was pelletized. The temperature of the extruder was set at 230°C. The properties of the obtained Resin 1 are shown in Table 1.

[0034] <How to prepare resin 2> Resin 2 was produced in the same manner as Resin 1, except that the amount of the polymerization initiator was changed as shown in Table 1. The properties of the obtained Resin 2 are shown in Table 1.

[0035] <How to prepare resins 3 and 4> Resins 3 and 4 were produced in the same manner as Resin 1, except that the temperature of the extruder in the recovery system was changed as shown in Table 1. The properties of the resulting resins 3 and 4 are shown in Table 1.

[0036] <How to prepare resins 5 to 7> Resins 5 to 7 were produced in the same manner as Resin 1, except that the rotation speed of the stirrer in the laminar flow reactor-1 was changed as shown in Table 1. The properties of the obtained Resins 5 to 7 are shown in Table 1.

[0037] <How to prepare resin 8> Resin 8 was produced in the same manner as Resin 1, except that the raw material composition and the rotation speed of the agitator in the laminar flow reactor-1 were changed as shown in Table 1. The raw liquid paraffin used was CP-68N manufactured by Idemitsu Kosan Co., Ltd. The properties of the obtained Resin 8 are shown in Table 1.

[0038] <How to prepare Resin 9> Resin 9 was produced in the same manner as Resin 1, except that the raw material composition, the rotation speed of the agitator in the laminar flow reactor-1, and the extruder temperature in the recovery system were changed as shown in Table 1. The properties of the obtained Resin 9 are shown in Table 1.

[0039] [Table 1]

[0040] The analysis and evaluation methods are described below. (1) Rubber-like polymer content 0.4g of the rubber-modified styrene-based resin composition was weighed out precisely in a 100ml measuring flask (W). After adding 75ml of chloroform and dispersing well, 20ml of a solution in which 18g of iodine monochloride was dissolved in 1000ml of carbon tetrachloride was added and stored in a cool, dark place. After 8 hours, the mixture was adjusted to the mark with chloroform. 25ml of this was taken, and 60ml of a solution in which 10g of potassium iodide was dissolved in a mixture of 800ml of water and 200ml of ethanol was added, and titrated with a solution (molar concentration x) in which 10g of sodium thiosulfate was dissolved in 1000ml of water. The main test volume was Aml, and the blank test volume was Bml. The rubber-like polymer content (mass%) was calculated by the following formula. Rubber polymer content (mass%) = 10.8 x x (BA) / W

[0041] (2) Particle size of rubber-like polymer particles Using a COULTER MULTISIZER III (trade name) manufactured by Beckman Coulter, Inc. equipped with a 30 μm aperture tube, 2 to 5 pellets of the rubber-modified styrene-based resin composition were placed in about 5 ml of dimethylformamide and left for about 2 to 5 minutes. Next, the dimethylformamide soluble content was measured as an appropriate particle concentration, and the volume-based median diameter was calculated.

[0042] (3) Methyl ethyl ketone insoluble matter (gel matter) 1 g of the rubber-modified styrene-based resin composition was precisely weighed (W1), 20 ml of a methyl ethyl ketone / methanol mixed solvent (mixture mass ratio 90 / 10) was added, and the mixture was shaken at 23°C for 2 hours, and then centrifuged at 10°C or less and 20,000 rpm for 60 minutes in a centrifuge (himac (trade name) CR-20 (rotor: R20A2) manufactured by Hitachi, Ltd.). The supernatant was removed by decantation to obtain an insoluble matter. The mixture was then vacuum-dried for 60 minutes at 160°C or less under conditions of 20 mmHg or less, and cooled to room temperature in a desiccator, after which the mass of the insoluble matter was precisely weighed (W2). The methyl ethyl ketone insoluble matter (gel matter) was calculated by the following formula. Methyl ethyl ketone insoluble matter (mass%) = (W2 / W1) x 100

[0043] (4) Swelling index for toluene 1 g of the rubber-modified styrene-based resin composition was weighed out (W3), 20 ml of toluene was added, and the mixture was shaken at 23°C for 2 hours, and then centrifuged at 10°C or less and 20,000 rpm for 60 minutes using a centrifuge (Hitachi, Ltd., himac (product name) CR-20 (rotor: R20A2)). The supernatant was removed by decantation, and the mass of the insoluble matter containing toluene was weighed out (W4). Subsequently, the mixture was vacuum-dried for 60 minutes under conditions of 160°C and 20 mmHg or less, and then cooled to room temperature in a desiccator, and the mass of the insoluble matter was weighed out (W5). The swelling index for toluene was calculated using the following formula. Swelling index for toluene = W4 / W5

[0044] (5) Whitening test The rubber-modified styrene-based resin composition was injection-molded at 220° C. to prepare a 1 mm-thick plate. The plate was placed on a Dupont impact tester equipped with a 30.5 mm support, a 12.7 mmΦ impact core was placed on it, and the weight of the weight was gently increased in 100 g increments to measure the load at which whitening scratches occurred.

[0045] (6) Total light transmittance, diffuse light transmittance, haze, yellowness index The rubber-modified styrene-based resin composition was injection molded at 220°C to prepare a 1 mm thick plate. The total light transmittance, diffuse light transmittance, haze, and yellow index were measured using a chromaticity and turbidity meter COH300A (product name) manufactured by Nippon Denshoku Industries Co., Ltd., using a C light source / 2-degree visual field and a 12 mmΦ area as transmitted light.

[0046] (7) Charpy impact test Test pieces were prepared by injection molding at a resin temperature of 220°C and a mold temperature of 45°C, and the notched Charpy impact strength was measured in accordance with ISO 179.

[0047] (8)Melt mass flow rate Measurements were carried out at 200°C and 49N in accordance with ISO 1133.

[0048] (9) Amount of liquid paraffin 2 g of the rubber-modified styrene-based resin composition was precisely weighed, 40 ml of methyl ethyl ketone was added, and the mixture was shaken at 23°C for 40 minutes, dropped into 200 ml of methanol, heated at 60°C for 10 minutes, cooled to 23°C, and filtered through a membrane filter with a hole diameter of 0.45 μm. The filtrate was concentrated by vacuum distillation, dried at 80°C for 30 minutes, cooled to 23°C, and dissolved in normal hexane to obtain a 10 ml sample. The liquid paraffin content (mass%) of the obtained sample was quantified by liquid chromatography under the following conditions.

[0049] Equipment: High-performance liquid chromatograph (Shimadzu Corporation, product name: LC-10A) Column: Fully porous silica gel with an average particle size of 5 μm, inner diameter 4.6 mm, length 250 mm Solvent: normal hexane Temperature: 23℃ Solvent flow rate: 2g / min Injection amount: 200μm

[0050] [Examples 1 to 9] In Examples 1 to 8, rubber-modified styrene-based resin compositions were prepared by mixing either Resin 1, Resin 2 or Resin 5 with Resin 9 in the ratios shown in Table 2 and melt-kneading. Resin 8 was used in Example 9. The obtained rubber-modified styrene-based resin compositions were evaluated as described above, and the results are shown in Table 2. The rubber-modified styrene-based resin compositions of Examples 1 to 9 all had a high load at which whitening scratches occurred, and a good balance between total light transmittance and haze, resulting in high diffuse light transmittance and high light diffusivity.

[0051] [Comparative Example 1] In Comparative Example 1, Resin 1 and Resin 9 were mixed in the ratio shown in Table 2. The resulting rubber-modified styrene-based resin composition was evaluated as described above, and the results are shown in Table 2. The rubber-modified styrene-based resin composition of Comparative Example 1 has a small amount of rubber and a small gel content, and therefore has a high total light transmittance, but has a low haze and therefore a low diffuse light transmittance and low impact strength.

[0052] [Comparative Example 2] In Comparative Example 2, Resin 1 and Resin 9 were mixed in the ratio shown in Table 2. The resulting rubber-modified styrene-based resin composition was evaluated as described above, and the results are shown in Table 2. The rubber-modified styrene-based resin composition of Comparative Example 2 has a large amount of rubber and a large gel content, so the load at which whitening scratches occur is low. The total light transmittance is low, so the diffuse light transmittance is low. The yellowness index is also high.

[0053] [Comparative Example 3] In Comparative Example 3, Resin 2 and Resin 9 were mixed in the ratio shown in Table 2. The resulting rubber-modified styrene-based resin composition was evaluated as described above, and the results are shown in Table 2. The rubber-modified styrene-based resin composition of Comparative Example 3 has a high gel content, so the load at which whitening scratches occur is low, and the total light transmittance is low, so the diffuse light transmittance is low. The yellowness index is also high.

[0054] [Comparative Example 4] In Comparative Example 4, Resin 6 and Resin 9 were mixed in the ratio shown in Table 2. The resulting rubber-modified styrene-based resin composition was evaluated as described above, and the results are shown in Table 2. In the rubber-modified styrene-based resin composition of Comparative Example 4, the rubber particle diameter is small, so that the yellowness of the transmitted light increases.

[0055] [Comparative Example 5] In Comparative Example 5, Resin 7 and Resin 9 were mixed in the ratio shown in Table 2. The resulting rubber-modified styrene-based resin composition was evaluated as described above, and the results are shown in Table 2. The rubber-modified styrene-based resin composition of Comparative Example 5 has a large rubber particle diameter, and therefore has low light diffusibility (haze).

[0056] [Comparative Example 6] In Comparative Example 6, Resin 3 and Resin 9 were mixed in the ratio shown in Table 2. The resulting rubber-modified styrene-based resin composition was evaluated as described above, and the results are shown in Table 2. The rubber-modified styrene-based resin composition of Comparative Example 6 has a low swelling index and therefore a low impact strength.

[0057] [Comparative Example 7] In Comparative Example 7, Resin 4 and Resin 9 were mixed in the ratio shown in Table 2. The resulting rubber-modified styrene-based resin composition was evaluated as described above, and the results are shown in Table 2. The rubber-modified styrene-based resin composition of Comparative Example 7 has a high swelling index, and therefore the light diffusibility is reduced, resulting in a low diffuse light transmittance.

[0058] [Table 2] [Industrial Applicability]

[0059] According to the present invention, by optimizing the reinforcing rubber particles dispersed in the rubber-modified styrene-based resin composition, it is possible to provide a rubber-modified styrene-based resin composition having an excellent balance between diffuse light transmittance and whitening resistance, a sheet containing the resin composition, and a molded article such as a lighting cover obtained from the sheet. The rubber-modified styrene-based resin composition of the present invention is also suitable for use in applications requiring light transmission and light diffusion properties, such as lighting covers.

Claims

[Claim 1] A rubber-modified styrene-based resin composition comprising a styrene-based polymer forming a matrix and rubber-like polymer particles dispersed in the matrix in the form of islands, the rubber-like polymer particles containing the styrene-based polymer particles and having an island-in-sea structure, The styrene-based polymer and the rubber-like polymer constituting the rubber-like polymer particles are mixed in an amount of 99.0 to 94.0% by mass, and the rubber-like polymer is mixed in an amount of 1.0 to 6.0% by mass, based on a total of 100% by mass of the styrene-based polymer and the rubber-like polymer constituting the rubber-like polymer particles. the rubber-like polymer is polybutadiene rubber and / or styrene-butadiene copolymer, The rubber polymer particles have a particle size of 2.0 to 5.5 μm, The rubber-modified styrene-based resin composition has a methyl ethyl ketone-insoluble gel content of 2.0 to 15.0 mass %.

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