Styrenic resin composition and molded article thereof

Abstract

Provided is a styrene-based resin composition that has excellent hue and transparency.　The styrene-based resin composition according to the present invention contains a styrene-based resin (A) and a component (B). The styrene-based resin (A) is a copolymer including a styrene-based monomer unit (a1) and a (meth)acrylic acid-based monomer unit (a2). The component (B) includes 4-methoxyphenol or hydroquinone. A specific amount of the component (B) is included.

Description

[Technical Field]

[0001] The present invention relates to a styrene-based resin composition and a molded article thereof. [Background technology]

[0002] Styrenic resin compositions are used in a variety of applications and environments, such as optical components and containers (Patent Document 1, etc.). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-170186 Summary of the Invention [Problem to be solved by the invention]

[0004] However, there remains a problem in controlling the hue, etc. The present invention has been made in view of such problems, and provides a styrene-based resin composition excellent in hue, and a molded article thereof. [Means for solving the problem]

[0005] According to the present invention, there is provided a styrene-based resin composition comprising a styrene-based resin (A) and a component (B), wherein the styrene-based resin (A) is a copolymer comprising a styrene-based monomer unit (a1) and a (meth)acrylic acid-based monomer unit (a2), and the component (B) comprises 4-methoxyphenol or hydroquinone, and the content of the component (B) is 1 μg or more and less than 16 μg per 1 g of the styrene-based resin (A).

[0006] As a result of extensive research, the present inventors have found that an excellent hue can be achieved by adjusting the content of 4-methoxyphenol and / or hydroquinone contained in a styrene-based resin composition within a predetermined range, and have thus completed the present invention.

[0007] Various embodiments of the present invention will be described below as examples, and the embodiments shown below can be combined with each other. Preferably, the copolymer contains a styrene-based monomer unit (a1) and a (meth)acrylic acid-based monomer unit (a2), and when the total content of the styrene-based monomer unit (a1) and the (meth)acrylic acid-based monomer unit (a2) is taken as 100 mass%, the content of the styrene-based monomer unit (a1) is 99.9 to 40 mass%, and the content of the (meth)acrylic acid-based monomer unit (a2) is 0.1 to 60 mass%. Preferably, the (meth)acrylic acid-based monomer unit (a2) is a methacrylic acid monomer unit. Preferably, a molded article made of the styrene-based resin composition. Preferably, the light guide is made of the above molded article. Preferably, a film made of the above styrene-based resin composition. Preferably, a foamed sheet made of the above styrene-based resin composition. Preferably, a container made of the foam sheet. DETAILED DESCRIPTION OF THE INVENTION

[0008] The following describes embodiments of the present invention. The various features shown in the following embodiments can be combined with each other. Furthermore, each feature can be an invention independently.

[0009] 1. Styrene-based resin composition A styrene-based resin composition according to one embodiment of the present invention contains a styrene-based resin (A) and a component (B).

[0010] <Styrene-based resin (A)> The styrene-based resin (A) is a copolymer containing styrene-based monomer units (a1) and (meth)acrylic acid-based monomer units (a2), i.e., a copolymer obtained by copolymerizing monomers containing a styrene-based monomer and a (meth)acrylic acid-based monomer.

[0011] The styrene-based monomer unit (a1) is a unit constituting the styrene-based resin (A) and is a monomer unit derived from these styrene-based monomers. The styrene-based monomer is a monocyclic or polycyclic aromatic vinyl monomer, such as styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene, 3,4-dimethylstyrene, 3,5-dimethylstyrene, p-ethylstyrene, m-ethylstyrene, o-ethylstyrene, p-tert-butylstyrene, 1-vinylnaphthalene, 2-vinylnaphthalene, 1,1-diphenylethylene, isopropenylbenzene (α-methylstyrene), isopropenyltoluene, isopropenylethylbenzene, isopropenyl isopropenylpropylbenzene, isopropenylbutylbenzene, isopropenylpentylbenzene, isopropenylhexylbenzene, isopropenyloctylbenzene, etc., either alone or in a mixture of two or more thereof, preferably styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene, 3,4-dimethylstyrene, 3,5-dimethylstyrene, p-ethylstyrene, m-ethylstyrene, o-ethylstyrene, p-tert-butylstyrene, either alone or in a mixture of two or more thereof, more preferably styrene.

[0012] The (meth)acrylic acid monomer is, for example, one or both of acrylic acid and methacrylic acid, preferably methacrylic acid. The (meth)acrylic acid monomer unit (a2) is a unit constituting the styrene-based resin (A) and is a monomer unit derived from these (meth)acrylic acid monomers, preferably a monomer unit derived from methacrylic acid (methacrylic acid monomer unit).

[0013] The monomer mixture used for copolymerization of the copolymer may contain other monomers copolymerizable with the styrene-based monomer and the (meth)acrylic acid-based monomer, provided that the effects of the present invention are not impaired. That is, the copolymer may contain monomer units derived from other monomers. Examples of such other monomers include vinyl cyanide monomers such as acrylonitrile and methacrylonitrile; acrylic monomers such as butyl acrylate, ethyl acrylate, methyl acrylate, and methyl methacrylate; α,β-ethylenically unsaturated carboxylic acids such as maleic anhydride and fumaric acid; and imide monomers such as phenylmaleimide and cyclohexylmaleimide. The copolymer preferably contains substantially only styrene-based monomers and (meth)acrylic acid-based monomers, more preferably only styrene-based monomers and (meth)acrylic acid-based monomers.

[0014] When the total content of the styrene-based monomer units (a1) and the (meth)acrylic acid-based monomer units (a2) is taken as 100% by mass, the content of the styrene-based monomer units (a1) in the styrene-based resin (A) is preferably 99.9 to 40% by mass, and more preferably 85 to 99% by mass. By setting the content within such a range, excellent moldability and foamability as well as hue and transparency can be achieved. Specific examples of the content of the styrene-based monomer units (a1) include 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 88, 90, 92, 95, 96, 99, and 99.9% by mass, and may be within a range between any two of the values ​​exemplified here.

[0015] When the total content of the styrene-based monomer units (a1) and the (meth)acrylic acid-based monomer units (a2) is taken as 100% by mass, the content of the (meth)acrylic acid-based monomer units (a2) in the styrene-based resin (A) is preferably 0.1 to 60.0% by mass, more preferably 1 to 20% by mass. By setting the content within this range, excellent moldability and foamability as well as hue and transparency can be achieved. Specifically, the content of the (meth)acrylic acid-based monomer units (a2) is, for example, 0.1, 1, 4, 5, 8, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, or 60% by mass, and may be within a range between any two of the values ​​exemplified here.

[0016] The content of (meth)acrylic acid monomer units in the styrene-based resin (A) is measured at room temperature. 0.5 g of styrene-(meth)acrylic acid copolymer resin is weighed and dissolved in a mixed solution of toluene / ethanol = 8 / 2 (volume ratio), followed by neutralization titration with 0.1 mol / L potassium hydroxide ethanol solution. The endpoint is detected, and the mass-based content of (meth)acrylic acid units is calculated from the amount of potassium hydroxide ethanol solution used. An automatic potentiometric titrator, such as the AT-510 manufactured by Kyoto Electronics Manufacturing Co., Ltd., can be used for the measurement.

[0017] The weight-average molecular weight of the styrene-based resin (A) is preferably 50,000 to 400,000, specifically, for example, 50,000, 100,000, 150,000, 200,000, 250,000, 300,000, 350,000, or 400,000, and may be within a range between any two of the numerical values ​​exemplified here. By setting it within such a range, the properties and moldability of a molded product will be improved. The weight-average molecular weight of the styrene-based resin (A) can be controlled by the reaction temperature and residence time in the polymerization step, the type and amount of polymerization initiator added, the type and amount of chain transfer agent added, the type and amount of solvent used during polymerization, etc. The weight average molecular weight was measured using gel permeation chromatography (GPC) under the following conditions. GPC model: Showa Denko Shodex GPC-101 Column: Polymer Laboratories PLgel 10 μm MIXED-B Mobile phase: tetrahydrofuran Sample concentration: 0.2% by mass Temperature: Oven 40℃, injection port 35℃, detector 35℃ Detector: differential refractometer The molecular weight in the present invention is calculated as a polystyrene-equivalent molecular weight by calculating the molecular weight at each elution time from the elution curve of monodisperse polystyrene.

[0018] Examples of polymerization methods for styrene-based resins include known styrene polymerization methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. From the viewpoints of quality and productivity, bulk polymerization and solution polymerization are preferred, and continuous polymerization is preferable. Examples of 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.

[0019] When polymerizing the styrene resin, a polymerization initiator and a chain transfer agent can be used as necessary. As the polymerization initiator, a radical polymerization initiator is preferred, and examples of the known and commonly used initiators include peroxyketals such as 1,1-di(t-butylperoxy)cyclohexane, 2,2-di(t-butylperoxy)butane, 2,2-di(4,4-di-t-butylperoxycyclohexyl)propane, and 1,1-di(t-amylperoxy)cyclohexane, hydroperoxides such as cumene hydroperoxide and t-butyl hydroperoxide, alkyl peroxides such as t-butyl peroxyacetate and t-amyl peroxyisononanoate, t-butylcumyl peroxide, di-t-butyl peroxide, dicumyl peroxide, and di-t-hexyl peroxide. Examples of suitable peroxides include dialkyl peroxides such as t-butyl peroxyacetate, t-butyl peroxybenzoate, and t-butylperoxyisopropyl monocarbonate; peroxyesters such as t-butylperoxyisopropyl carbonate and polyether tetrakis(t-butylperoxycarbonate); and peroxycarbonates such as N,N'-azobis(cyclohexane-1-carbonitrile), N,N'-azobis(2-methylbutyronitrile), N,N'-azobis(2,4-dimethylvaleronitrile), and N,N'-azobis[2-(hydroxymethyl)propionitrile]. These may be used alone or in combination. Examples of suitable chain transfer agents include aliphatic mercaptans, aromatic mercaptans, pentaphenylethane, α-methylstyrene dimer, and terpinolene.

[0020] In the case of continuous polymerization, first, in the polymerization step, a known complete mixing tank type agitator tank or tower reactor is used, and the polymerization reaction is controlled by adjusting the polymerization temperature, etc., so as to achieve the target molecular weight, molecular weight distribution, and reaction conversion rate. The polymerization solution containing the polymer that has left the polymerization step is transferred to the devolatilization step, where unreacted monomers and polymerization solvent are removed. The devolatilization step is composed of a vacuum devolatilization tank equipped with a heater or a devolatilization extruder equipped with a vent. The molten polymer that has left the devolatilization step is transferred to the granulation step. In the granulation step, the molten resin is extruded in the form of strands through a multi-hole die and processed into pellets using the cold cut method, the in-air hot cut method, or the underwater hot cut method.

[0021] <Ingredient (B)> Component (B) contains 4-methoxyphenol or hydroquinone. The content of component (B) is 1 μg or more and less than 16 μg per gram of styrene-based resin (A). By setting the content within this range, excellent transparency and color can be achieved. The content of component (B) per gram of styrene-based resin (A) is, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or 15.9 μg, and may be within a range between any two of the values ​​exemplified here.

[0022] Component (B) may be added during polymerization, or may be removed by known methods such as distillation or adsorption removal, specifically the method described in JP-A-8-310979.

[0023] The content of component (B) was measured by the following method. After the pellets were thoroughly dissolved in 20 ml of methyl ethyl ketone, 5 ml of methanol was added dropwise and the mixture was stirred for approximately 20 minutes. The supernatant separated by centrifugation was measured by gas chromatography (GC). The concentration was determined using a calibration curve prepared in advance for each antioxidant. GC measurement conditions: GC device: Shimadzu GC-2010 Column: DB-1 (0.25 mm id x 30 m) Liquid phase thickness 0.10mm Column temperature: 240°C (hold for 1 min) (10°C / min temperature increase) → 320°C (held for 5 min) Total 14 min Inlet temperature: 320°C Injection method: Split method (split ratio 1:5) Sample volume: 1 μl

[0024] Various additives can be blended into the styrene-based resin (A) as needed, provided that the properties of the present invention are not impaired. The types of additives are not particularly limited as long as they are those commonly used in plastics, and examples thereof include antioxidants, flame retardants, lubricants, processing aids, antiblocking agents, antistatic agents, deodorizers, antibacterial agents, antifogging agents, light resistance improvers, softeners, plasticizers, inorganic reinforcing agents, crosslinking agents, pigments, dyes, and others, as well as mixtures thereof.

[0025] 2. Molded products In one embodiment of the present invention, a molded article is obtained from the styrene-based resin composition. Examples of molded articles include electrical appliances, household products, food packaging containers, etc., processed or molded by extrusion molding, injection molding, blow molding, sheet molding, foam molding, etc. Optical applications include light guides such as light guide plates and light diffusion plates, films, etc. Foam sheets, etc., are also used for microwave-safe containers, etc. [Example]

[0026] The present invention will be described in more detail below with reference to examples, but these examples are merely illustrative and are not intended to limit the scope of the present invention.

[0027] [Example 1] (Preparation of styrene-based resin composition) Pellets of a styrene-based resin composition containing a styrene-methacrylic acid copolymer were obtained by the following steps.

[0028] The polymerization process was configured by connecting in series the first reactor, a complete mixing type agitation tank with an internal volume of 39 L, and the second reactor, also a complete mixing type agitation tank with an internal volume of 39 L. A raw material solution consisting of a mixed solution of 76 mass% styrene, 6 mass% methacrylic acid (4-methoxyphenol concentration 50 μg / g), and 18 mass% ethylbenzene was prepared.

[0029] This raw material solution was continuously supplied to the first reactor at a rate of 13.2 kg per hour, and each reactor was filled with the solution. At the inlet of the first reactor, 250 ppm by mass of 1,1-bis(t-butylperoxy)cyclohexane (Perhexa C, manufactured by NOF Corporation) was mixed with the raw material solution relative to the total amount of styrene and methacrylic acid. The reaction temperatures in each reactor were adjusted to 130°C in the first reactor and 140°C in the second reactor.

[0030] Next, the solution containing the copolymer resin continuously removed from the second reactor was introduced into a two-stage series of preheater-equipped vacuum devolatilizer tanks. After separating the unreacted monomer and ethylbenzene, the solution was extruded into strands, cooled, and then cut into pellets to obtain a styrene-based resin composition. For the first preheater-equipped vacuum devolatilizer tank, the preheater temperature was set to 175°C, the vacuum devolatilizer tank pressure to 500 mmHg, and the vacuum devolatilizer tank jacket temperature to 185°C. For the second preheater-equipped vacuum devolatilizer tank, the preheater temperature was set to 240°C, the vacuum devolatilizer tank pressure to 8 mmHg, and the vacuum devolatilizer tank jacket temperature to 240°C. The resin temperature in the first vacuum devolatilizer tank was 168°C, and the resin temperature in the second vacuum devolatilizer tank was 231°C. The 4-methoxyphenol concentration in the resulting styrene-based resin composition was 1.2 μg / g.

[0031] (Transmittance YI) The pellets were injection molded at a cylinder temperature of 230°C and a mold temperature of 50°C to form a plate-shaped molded product measuring 127 x 127 x 3 mm thick. The sample for evaluating long-term durability (the sample after the long-term durability test) was stored in an oven at 80°C for 1000 hours. Next, test pieces measuring 115 x 85 x 3 mm were cut out from the plate-shaped molded products of the initial sample and the sample after the long-term durability test. The obtained plate-shaped molded product was cut and polished to 115 × 127 × 3 mm using a gate processing machine GCPB-500 manufactured by Megaro Technica Co., Ltd., to obtain a plate-shaped molded product with a mirror-finished end surface. The obtained plate-shaped molded product was measured for spectral transmittance at wavelengths of 350 nm to 800 nm using a UV-visible spectrophotometer V-670 manufactured by JASCO Corporation, with dimensions of 20 × 1.6 mm and incident light with a divergence angle of 0°, at an optical path length of 115 mm, and the YI value at a 2° field of view using a C light source was calculated according to JIS K7105. The obtained value is the YI. The transmittance represents the average transmittance at wavelengths of 380 nm to 780 nm for the molded product before long-term durability testing. ΔYI represents the difference between the YI of the molded product before the long-term durability test and the YI of the molded product after the long-term durability test (Equation 1). ΔYI = (YI of molded product after long-term durability test) - (YI of molded product before long-term durability test) (Equation 1)

[0032] [Example 2] A styrene-based resin composition was obtained in the same manner as in Example 1, except that the 4-methoxyphenol content in the methacrylic acid used was 100 μg / g. The concentration of 4-methoxyphenol in the obtained styrene-based resin composition was 2.8 μg / g. [Example 3] A styrene-based resin composition was obtained in the same manner as in Example 1, except that the 4-methoxyphenol content in the methacrylic acid used was 140 μg / g. The 4-methoxyphenol concentration in the obtained styrene-based resin composition was 3.8 μg / g. [Example 4] A styrene-based resin composition was obtained in the same manner as in Example 1, except that the 4-methoxyphenol content in the methacrylic acid used was 230 μg / g. The 4-methoxyphenol concentration in the obtained styrene-based resin composition was 8.3 μg / g. [Example 5] A styrene-based resin composition was obtained in the same manner as in Example 1, except that the 4-methoxyphenol content in the methacrylic acid used was 280 μg / g. The 4-methoxyphenol concentration in the obtained styrene-based resin composition was 11.8 μg / g. [Example 6] A styrene-based resin composition was obtained in the same manner as in Example 1, except that a raw material solution consisting of a mixed solution of 76 mass% of styrene, 7 mass% of methacrylic acid (4-methoxyphenol concentration 50 μg / g), and 17 mass% of ethylbenzene was prepared. The concentration of 4-methoxyphenol in the obtained styrene-based resin composition was 1.8 μg / g. [Example 7] A styrene-based resin composition was obtained in the same manner as in Example 1, except that a raw material solution consisting of a mixed solution of 74 mass% of styrene, 9 mass% of methacrylic acid (4-methoxyphenol concentration 50 μg / g), and 17 mass% of ethylbenzene was prepared. The concentration of 4-methoxyphenol in the obtained styrene-based resin composition was 2.5 μg / g. [Example 8] A styrene-based resin composition was obtained in the same manner as in Example 1, except that a raw material solution consisting of a mixed solution of 74 mass% of styrene, 9 mass% of methacrylic acid (4-methoxyphenol concentration 50 μg / g), and 17 mass% of ethylbenzene was prepared. The concentration of 4-methoxyphenol in the obtained styrene-based resin composition was 1.3 μg / g. [Example 9] A styrene-based resin composition was obtained in the same manner as in Example 1, except that a raw material solution consisting of a mixed solution of 33 mass% of styrene, 50 mass% of methacrylic acid (4-methoxyphenol concentration 50 μg / g), and 17 mass% of ethylbenzene was prepared. The concentration of 4-methoxyphenol in the obtained styrene-based resin composition was 7.9 μg / g. [Example 10] A styrene-based resin composition was obtained in the same manner as in Example 1, except that a raw material solution consisting of a mixed solution of 71 mass % of styrene, 12 mass % of methacrylic acid (hydroquinone concentration 50 μg / g), and 17 mass % of ethylbenzene was prepared. The hydroquinone concentration in the obtained styrene-based resin composition was 3.8 μg / g. [Comparative Example 1] A styrene-based resin composition was obtained in the same manner as in Example 1, except that the 4-methoxyphenol content in the methacrylic acid used was 330 μg / g. The 4-methoxyphenol concentration in the obtained styrene-based resin composition was 12.1 μg / g. Comparative Example 2 A styrene-based resin composition was obtained in the same manner as in Example 9, except that the 4-methoxyphenol content in the methacrylic acid used was 500 μg / g. The concentration of 4-methoxyphenol in the obtained styrene-based resin composition was 18.4 μg / g. Comparative Example 3 A styrene-based resin composition was obtained in the same manner as in Example 9, except that the 4-methoxyphenol content in the methacrylic acid used was 200 μg / g. The concentration of 4-methoxyphenol in the obtained styrene-based resin composition was 21.1 μg / g. Comparative Example 4 A styrene-based resin composition was obtained in the same manner as in Example 1, except that a raw material solution consisting of a mixed solution of 76 mass % of styrene, 6 mass % of methacrylic acid (hydroquinone concentration 330 μg / g), and 18 mass % of ethylbenzene was prepared. The hydroquinone concentration in the obtained styrene-based resin composition was 18.0 μg / g.

[0033] [Table 1]

[0034] [Table 2]

[0035] As can be seen from Tables 1 and 2, when component (B) was within the specified range, the transparency and hue were excellent (Examples 1 to 10). On the other hand, when component (B) was outside the specified range, the transparency and hue, especially the hue, were significantly deteriorated.

Claims

1. A styrene-based resin composition comprising a styrene-based resin (A) and a component (B), The styrene-based resin (A) is a copolymer containing a styrene-based monomer unit (a1) and a (meth)acrylic acid-based monomer unit (a2), the content of the component (B) in the styrene-based resin composition is 1.2 μg / g or more and 8.3 μg / g or less, the content of the (meth)acrylic acid-based monomer units (a2) is 4 to 60 mass%, when the total content of the styrene-based monomer units (a1) and the (meth)acrylic acid-based monomer units (a2) is 100 mass%, The component (B) is 4-methoxyphenol and / or hydroquinone, The content of the component (B) is 1 μg or more and 8 μg or less per 1 g of the styrene-based resin (A). Styrenic resin composition.

2. The styrene-based resin composition according to claim 1, wherein the (meth)acrylic acid-based monomer unit (a2) is a methacrylic acid monomer unit.

3. A molded article made of the styrene-based resin composition according to claim 1 or 2.

4. A light guide comprising the molded article according to claim 3.

5. A film comprising the styrene-based resin composition according to claim 1 or 2.

6. A foamed sheet comprising the styrene-based resin composition according to claim 1 or 2.

7. A container comprising the foamed sheet according to claim 6.

8. A method for producing the styrene-based resin composition according to claim 1 or claim 2, comprising: The production method includes a step of copolymerizing a styrene-based monomer and a (meth)acrylic acid-based monomer in which the content of the component (B) is 50 to 230 μg / g to obtain the styrene-based resin (A). A method for producing a styrene-based resin composition.

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