Styrene-based 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 product.BACKGROUND ART

[0002] A styrene-based resin composition is used in various applications such as optical members and containers, and in various environments (Patent Literature 1).CITATION LIST PATENT LITERATURE

[0003] Patent Literature 1 JP-A-2013-170186SUMMARY OF INVENTION TECHNICAL PROBLEM

[0004] However, there was a problem in controlling hue and the like. The present invention has been made in view of such problems and provides a styrene-based resin composition and a molded product thereof, which are excellent in hue.SOLUTION TO PROBLEM

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

[0006] The present inventors have made intensive studies and found that the hue is excellent by setting the content of 4-methoxyphenol and / or hydroquinone contained in the styrene-based resin composition within a predetermined range, completing the present invention.

[0007] The following are examples of various embodiments of the present invention. The embodiments shown below can be combined with each other.Preferably, the styrene-based resin (A) contains a styrene monomer unit (a1) and a (meth)acrylic acid monomer unit (a2), when a total content of the styrene-based monomer unit (a1) and the (meth)acrylic acid-based monomer unit (a2) is 100% by mass, a content of the styrene-based monomer unit (a1) is 99.9 to 40% by mass and a content of the (meth)acrylic acid-based monomer unit (a2) is 0.1 to 60% by mass.Preferably, the (meth)acrylic acid-based monomer unit (a2) is a methacrylicacid-based monomer unit.Preferably, a molded product comprising the styrene-based resin composition.Preferably, a light guide body comprising the molded product.Preferably, a film comprising the styrene-based resin composition.Preferably, a foamed sheet comprising the styrene-based resin composition. Preferably, a container comprising the foamed sheet.DESCRIPTION OF EMBODIMENTS

[0008] The following is an explanation of the embodiments of the present invention. The various features shown in the following embodiments can be combined with each other. In addition, the invention is independently established for each property.

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

[0010] <Styrene-based Resin (A)>The styrene-based resin (A) is a copolymer containing a styrene-based monomer unit (a1) and a (meth)acrylic acid-based monomer unit (a2). That is, it is 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 styrene-based monomers, such as the following styrene-based monomers. The styrene-based monomers are monocyclic or polycyclic aromatic vinyl monomers 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 (a-methylstyrene), isopropenyltoluene, isopropenylethylbenzene, isopropenylpropylbenzene, isopropenylbutylbenzene, isopropenylpentylbenzene, isopropenylhexylbenzene, isopropenyloctylbenzene and the like or 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, and p-tert-butylstyrene may be used singly or as a mixture of two or more thereof, and styrene is more preferable.

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

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

[0014] When the total content of the styrene-based monomer unit (a1) and the (meth)acrylic acid-based monomer unit (a2) is 100% by mass, a content of the styrene-based monomer unit (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 as such a range, in addition to hue and transparency, moldability and foamability are also excellent. Specifically, the content of the styrene-based monomer unit (a1) is, for example, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 88, 90, 92, 95, 96, 99, 99.9% by mass, and may be in the range between the two values exemplified herein.

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

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

[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, 400,000 and may be in the range between the two values exemplified herein. By setting the weight average molecular weight as such a range, the characteristics and moldability as a molded product are improved. The weight average molecular weight of the styrene-based resin (A) can be controlled by adjusting the reaction temperature, residence time, kind and amount of polymerization initiator, kind and amount of chain transfer agent, kind and amount of solvent used in polymerization, and the like. The weight average molecular weight was measured using gel permeation chromatography (GPC) under the following conditions.GPC model: Shodex GPC-101 manufactured by Showa Denko K.K.Column: PLgel 10 pm MIXED-B manufactured by Polymer Laboratories Ltd.Mobile phase: TetrahydrofuranSample concentration: 0.2% by massTemperature: oven 40°C, inlet 35°C, detector 35°CDetector: Differential refractometerThe molecular weight of the present invention is obtained by calculating the molecular weight at each elution time from the elution curve of monodisperse polystyrene and calculating the molecular weight in terms of polystyrene.

[0018] A method for polymerizing the styrene-based resin includes known styrene polymerization methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. In terms of quality and productivity, bulk polymerization and solution polymerization are preferable, and continuous polymerization is preferable. Examples of the solvent that can be used include benzene, alkylbenzenes such as toluene, ethylbenzene, and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane.

[0019] During polymerization of the styrene-based resin, polymerization initiators and chain transfer agents can be used as needed. Regarding the polymerization initiator, radical polymerization initiator is preferable, and commonly known radical polymerization initiator such as peroxy ketals such as 1,1-di(t-butylperoxy)cyclohexane, 2,2-di(t-butyl peroxy)butane, 2,2-di(4,4-di-t-butyl peroxy cyclohexyl)propane, 1,1-di(t-amyl peroxy)cyclohexane and the like, hydroperoxides such as cumene hydroperoxide, t-butyl hydroperoxide and the like, alkyl peroxides such as t-butyl peroxyacetate, t-amyl peroxyisononanoate and the like, dialkyl peroxides such as t-butylcumyl peroxide, di-t-butyl peroxide, di-cumyl peroxide, di-t-hexyl peroxide and the like, peroxy esters such as t-butyl peroxyacetate, t-butyl peroxybenzoate, t-butyl peroxy isopropyl monocarbonate and the like, peroxycarbonates such as t-butyl peroxy isopropyl carbonate, polyether tetrakis(t-butyl peroxycarbonate) and the like,N,N'-azobis(cyclohexane-1-carbonitrile), N,N'-azobis(2-methyl butyronitrile), N,N'-azobis(2,4-dimethyl valeronitrile), N,N'-azobis[2-(hydroxymethyl)propionitrile] and the like can be mentioned for example. These radical polymerization initiators can be used alone, or two or more of these can be used in combination. As the chain transfer agent, aliphatic mercaptans, aromatic mercaptans, pentaphenylethane, a-methyl styrene dimer, terpinolenes and the like can be mentioned.

[0020] In the case of continuous polymerization, firstly, in the polymerization step, target molecular weight, molecular weight distribution, and reaction conversion rate are achieved by using a known continuous stirred tank reactor or plug flow reactor and by adjusting polymerization temperature and the like to control the polymerization reaction. The polymerization solution containing the polymer which went through the polymerization step is transferred to the devolatilization step to remove unreacted monomer and the polymerization solvent. The devolatilization step is constituted with a vacuum devolatilization tank equipped with a heater, a devolatilization extruder equipped with a vent, and the like. The molten polymer which went through the devolatilization step is transferred to the pelletizing step. In the pelletizing step, the molten resin is extruded into strands from a porous die, and processed into pellets by cold cut method, air-cooled hot cutting method, or underwater hot cutting method.

[0021] <Component (B)>The component (B) contains 4-methoxyphenol or hydroquinone. A contentof component (B) is 1 p,g or more and less than 16 μg with respect to 1 g of the styrene-based resin (A). By setting the content as such a range, transparency and hue are excellent. The content of the component (B) with respect to 1 g of the styrene-based resin (A) is specifically, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 15.9 μg, may be in the range between the two values exemplified herein.

[0022] The component (B) may be added during polymerization or may be removed by a known method such as distillation or adsorption removal. Specifically, the method is described in JP-A-H8-310979.

[0023] The content of the component (B) was measured by the following method. After the pellets were sufficiently dissolved in 20 ml of methyl ethyl ketone, 5 ml of methanol was added dropwise to the solution, and the mixture was stirred for about 20 minutes. A supernatant separated by centrifugation was measured with gas chromatography (GC). A calibration curve prepared in advance was used to determine the concentration of each antioxidant.GC measurement conditions:GC device: SHIMADZU CORPORATION GC-2010 Column: DB-1 (0.25mm i.d. x 30m)Liquid phase thickness 0.10 mmColumn temperature: 240°C (held for 1 minute) (temperature rising rate 10°C / min) 320°C (held for 5 minutes) 14 minutestotalInlet temperature: 320°CInjection method: Split method (split ratio 1:5)Sample amount: 1 μl

[0024] Various additives can be added to the styrene-based resin (A) as necessary as long as the characteristic of the present invention is not impaired. The kind of additive is not particularly limited as long as it is commonly used in plastics. Examples of the additive include antioxidants, flame retardants, lubricants, processing aids, antiblocking agents, antistatic agents, deodorants, antibacterial agents, antifog agents, lightfastness improvers, softeners, plasticizers, inorganic reinforcing agents, crosslinkers, pigments, dyes, others or mixtures thereof.

[0025] 2. Molded ProductIn one embodiment of the present invention, a molded product comprising the styrene-based resin composition is obtained. Examples of the molded product include electrical appliances, household products, food packaging containers, and the like, which are processed and molded by extrusion molding, injection molding, blow molding, sheet molding, foam molding, and the like. Optical applications include light guide bodies such as light guide plates and light diffusion plates, films, and the like. Foam sheets and the like are also used as microwavable containers.EXAMPLES

[0026] The present invention will be described in more detail with reference to the following examples. Moreover, these are all examples, and do not limit the content of the present invention.

[0027] [Example 1](Preparation of Styrene-based Resin Composition)Through the following steps, pellets were obtained from a styrene-based resin composition containing a styrene-methacrylic acid-based copolymer.

[0028] The polymerization step comprises a first reactor, which is a continuous stirred tank reactor with an internal volume of 39 liters, and a second reactor, which is a continuous stirred tank reactor with an internal volume of 39 liters, and they are connected in series. A raw material solution was prepared from a mixed solution of 76% by mass of styrene, 6% by mass of methacrylic acid (concentration of 4-methoxyphenol: 50 μg / g), and 18% by mass of ethylbenzene.

[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 circulated in a fully liquid state. At the inlet of the first reactor, 250 ppm by mass of 1,1-bis(t-butylperoxy) cyclohexane (PERHEXA C manufactured by NOF CORPORATION) with respect to the total amount of styrene and methacrylic acid in the raw material solution was added and the solution was mixed. The reaction temperature of each reactor was adjusted to 130°C in the first reactor and 140°C in the second reactor.

[0030] Subsequently, the solution containing the copolymer resin continuously taken out from the second reactor was introduced into two stage vacuum devolatilization tanks, which were installed in series and had a preheater, and unreacted monomers and ethylbenzene were separated. By extruding into strands, cooling them, and then cutting them into pellets, a styrene-based resin composition was obtained. In the first-stage vacuum devolatilization tank with a preheater, the temperature of the preheater was set at 175°C, the pressure of the vacuum devolatilization tank was set at 500 mmHg, and the jacket temperature of the vacuum devolatilization tank was set at 185°C. In the second-stage vacuum devolatilization tank with a preheater, the temperature of the preheater was set at 240°C, the pressure of the vacuum devolatilization tank was set at 8 mmHg, and the jacket temperature of the vacuum devolatilization tank was set at 240°C. The resin temperature in the first-stage vacuum devolatilization tank was 168°C, and the resin temperature in the second-stage vacuum devolatilization tank was 231°C. The concentration of 4-methoxyphenol in the obtained styrene-based resin composition was 1.2 μg / g.

[0031] (Transmittance / YI)Using the obtained pellets, injection molding was performed at a cylinder temperature of 230°C and a mold temperature of 50°C to form a plate-shaped molded product with a size of 127 x 127 x 3 mm thickness. The sample for evaluating long-term durability (samples after the long-term durability test) was stored in an oven at 80°C for 1000 hours.Next, a test piece with a size of 115 x 85 x 3 mm thickness was cut from each of the plate-shaped molded products of initial sample and the sample after the long-term durability test.The obtained plate-shaped molded product was cut into a size of 115 x 127 x 3 mm thickness using a gate processing machine GCPB-500 manufactured by MEGAROTECHNICA CO.,LTD. and it was polished to obtain a plate-shaped molded product having mirror surfaces on the end faces.The spectral transmittance of the obtained plate-shaped molded product at awavelength of 350 nm to 800 nm at an optical path length of 115 mm was measured using an ultraviolet-visible spectrophotometer V-670 manufactured by JASCO Corporation, with incident light with a size of 20 x 1.6 mm and a spread angle of 0°. YI value at a field of view of 2° under the C light source was calculated according to JIS K7105. The resulting value is YI. Further, the transmittance represents the average transmittance at wavelengths of 380 nm to 780 nm for the molded product before the long-term durability test.AYI 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 (Formula 1).ΔYI = (YI of molded product after long-term durability test) - (YI of moldedproduct before long-term durability test) (Formula 1)

[0032] [Example 2]A styrene-based resin composition was obtained in the same manner as in Example 1, except that the concentration of 4-methoxyphenol in the methacrylic acid used was 100 p,g / g. The concentration of 4-methoxyphenol in the obtainedstyrene-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 concentration of 4-methoxyphenol in the methacrylic acid used was 140 p,g / g. The concentration of 4-methoxyphenol in the obtainedstyrene-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 concentration of 4-methoxyphenol in the methacrylic acid used was 230 p,g / g. The concentration of 4-methoxyphenol in the obtainedstyrene-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 concentration of 4-methoxyphenol in the methacrylic acid used was 280 p,g / g. The concentration of 4-methoxyphenol in the obtainedstyrene-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 was prepared from a mixed solution of 76% by mass of styrene, 7% by mass of methacrylic acid (concentration of 4-methoxyphenol: 50 μg / g), and 17% by mass of ethylbenzene.The concentration of 4-methoxyphenol in the obtained styrene-based resin composition was 1.8 μg / g.[Example 7]A styrene-based solution was prepared in the same manner as in Example 1, except that a raw material solution was prepared from a mixed solution of 74% by mass of styrene, 9% by mass of methacrylic acid (concentration of 4-methoxyphenol: 50 μg / g), and 17% by 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 solution was prepared in the same manner as in Example 1, except that a raw material solution was prepared from a mixed solution of 74% by mass of styrene, 9% by mass of methacrylic acid (4-methoxyphenol concentration 50 μg / g), and 17% by mass of ethylbenzene. The concentration of 4-methoxyphenol in the obtained styrene-based resin composition was 1.3 μg / g.[Example 9]A styrene-based solution was prepared in the same manner as in Example 1, except that a raw material solution was prepared from a mixed solution of 33% by mass of styrene, 50% by mass of methacrylic acid (4-methoxyphenol concentration 50 μg / g), and 17% by mass of ethylbenzene. The concentration of 4-methoxyphenol in the obtained styrene-based resin composition was 7.9 μg / g. [Example 10]A styrene-based solution was prepared in the same manner as in Example 1, except that a raw material solution was prepared from a mixed solution of 71% by mass of styrene, 12% by mass of methacrylic acid (hydroquinone concentration of 50 μg / g), and 17% by mass of ethylbenzene. The concentration of hydroquinone 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 concentration of 4-methoxyphenol in the methacrylic acid used was 330 μg / g. The concentration of 4-methoxyphenol 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 concentration of 4-methoxyphenol 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 concentration of 4-methoxyphenol 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 prepared in the same manner as in Example 1, except that a raw material solution was prepared from a mixed solution of 76% by mass of styrene, 6% by mass of methacrylic acid (concentration of hydroquinone: 330 μg / g), and 18% by mass of ethylbenzene. The concentration of hydroquinone 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 the component (B) is within the predetermined range, the transparency and hue are excellent (Examples 1 to 10). On the other hand, when the component (B) was outside the predetermined range, the transparency and hue, especially the hue, were greatly deteriorated.

Claims

1. A styrene-based resin composition comprising a styrene-based resin (A) and a component (B), wherein 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 component (B) contains 4-methoxyphenol or hydroquinone; and a content of the component (B) is 1 μg or more and less than 16 μg with respect to 1 g of the styrene-based resin (A).

2. The styrene-based resin composition of Claim 1, wherein the styrene-based resin (A) contains the styrene monomer unit (a1) and the (meth)acrylic acid monomer unit (a2), when a total content of the styrene-based monomer unit (a1) and the (meth)acrylic acid-based monomer unit (a2) is 100% by mass, a content of the styrene-based monomer unit (a1) is 99.9 to 40% by mass and a content of the (meth)acrylic acid-based monomer unit (a2) is 0.1 to 60% by mass.

3. The styrene-based resin composition of Claim 1 or 2, wherein the (meth)acrylic acid-based monomer unit (a2) is a methacrylic acid-based monomer unit.

4. A molded product comprising the styrene-based resin composition of any one of Claims 1 to 3.

5. A light guide body comprising the molded product of Claim 4.

6. A film comprising the styrene-based resin composition of any one of Claims 1 to 3.

7. A foamed sheet comprising the styrene-based resin composition of any one of Claims 1 to 3.

8. A container comprising the foamed sheet of Claim 7.