JP4480342B2 - Styrenic resin composition for foam molding, foam sheet and container - Google Patents

Description

【００４９】
実施例１〜６
表２に示すように参考例に記載したスチレン系樹脂組成物（ＰＳ−１〜ＰＳ−５、ＰＳ−１０）に対し、造核剤としてタルクをスチレン系樹脂組成物に対して０．３質量％添加し、押出機内で２５０℃に溶融しながら混合し、これに発泡剤としてｎ−ブタンとｉ−ブタンの混合物（ｎ−ブタン５０％）を注入しながら、サーキュラーダイより押し出し、厚さ２ｍｍの発泡シートを得た。得られたシートの物性及びシートを成形して得られた容器の物性を表２に示す。
【００５０】
実施例７
参考例３で得られたスチレン系樹脂組成物（ＰＳ−３）に、さらに共役ジエン系重合体としてスチレン−ブタジエン共重合体（日本ゼオン（株）製 Ｎｉｐｏｌ ＮＳ−３１２Ｓ）を２質量％添加した以外は、実施例１〜６と同様にして発泡シート及び容器を得た。得られたシート及び容器の物性を表２に示す。
【００５１】
【表２】

【００５２】
比較例１〜５
表３に示すように参考例に記載したスチレン系樹脂組成物（ＰＳ−６〜ＰＳ−９、ＰＳ−１１）を使用し、以降実施例と同様の方法にて、発泡シート及び容器を得た。得られたシート及び容器の物性を表３に示す。
【００５３】
【表３】

【００５４】
表１〜表３より、共役ジエン系重合体を添加していない、または添加量が少ないものは、樹脂の熱分解が起きやすく、結果的に、分子量の低下が大きく、またスチレン２量体及びスチレン３量体の生成量が多くなっていることがわかる。そしてこれらの発泡成形品においては、外観が不良であったり、強度が不足していること、ｎ−ヘプタンへのスチレン２量体、３量体の溶出量が著しく増加していることがわかる。また、比較例２より、共役ジエン重合体の添加量が多すぎると、ｎ−ヘプタンへのスチレン２量体、３量体の溶出量が著しく増加し、かつ発泡体の外観も悪くなっていることが分かる。一方、実施例７より、発泡成形時にさらに共役ジエン系重合体を添加することにより、分子量の低下、またスチレン２量体及びスチレン３量体の生成が抑えられているのがわかる。
【００５５】
【発明の効果】
以上の通り、本発明の発泡成形用スチレン系樹脂組成物は発泡成形性に優れており、かつ成形した発泡体は表面状態、強度に優れると共に、食品容器とした場合、スチレン２量体及びスチレン３量体の溶出量が極めて低い特徴を有している。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a styrene-based resin composition suitable for foam molding and a foamed molded product thereof, which is extremely low in molecular weight reduction due to thermal deterioration during molding processing, and has very little production of styrene dimers and styrene trimers.
[0002]
[Prior art]
Styrenic resins generally have high rigidity, are excellent in processing characteristics such as sheet processability, foaming characteristics, and vacuum moldability, and can be easily produced in large quantities. Therefore, packaging materials, sundries, food containers, etc. It is used for various purposes. In addition, styrene resin foams have characteristics such as surface gloss, light weight, thermal barrier properties, and buffering properties, and the fields of use differ depending on the density and thickness of the foam. A sheet of styrene resin foam with a foaming ratio of about 10 times and a thickness of about 3 mm or less is called polystyrene paper (PSP). It is widely used for bags, cups, trays, etc., taking advantage of its characteristics such as sex.
[0003]
Generally, these styrenic resins for foam molding are produced by radical polymerization. In particular, a styrene resin produced by a continuous bulk radical polymerization method is suitably used because it has a small variation in physical properties between production lots, has few impurities, and is inexpensive. By the way, it is generally known that in the radical polymerization method, a styrene dimer or a styrene trimer is by-produced when a styrene resin is produced. In particular, the bulk radical polymerization process is performed at 80 to 180 ° C., and then the polymer is recovered by heating and devolatilizing the solvent and unreacted monomer contained therein. It is known that the body is produced as a by-product in this polymerization process, and also by thermal decomposition of a styrene resin exposed to high temperature in the heat devolatilization process. Similarly, it is known that styrene dimers and styrene trimers are generated by thermal decomposition of a styrene resin when exposed to a high temperature during molding of a styrene resin.
[0004]
When such a styrene resin having a relatively large amount of styrene dimer or styrene trimer is used for foam molding, there is a risk of causing problems such as adhesion to a mold or a molded product. Recently, when these foam-molded products are put into practical use as food packaging containers, a problem has been pointed out that styrene dimers and styrene trimers migrate to food. Although research results showing these safety have already been published, there is still a social need to control the amount of elution into food soup.
[0005]
Also, when molding styrenic resin, it is exposed to high temperature and thermally decomposed, so that not only the production of styrene dimer and styrene trimer, but also the molecular weight of the resin is reduced at the same time, especially the high molecular weight component is reduced. It is a problem to do. As a result, the melt tension of the resin is lowered, and as a result, the bubble cells of the foamed molded product are easily broken, and the heat insulation performance and strength of the foam may be lowered.
[0006]
The method for reducing the production of styrene dimers and styrene trimers in the polymerization step can be achieved to some extent by controlling the polymerization conditions such as the polymerization temperature and the addition of a polymerization initiator. However, in order to suppress thermal decomposition of the polystyrene resin during the heat devolatilization process and molding process, the temperature of the polystyrene resin during the devolatilization process and process is set low, or the shear of resin mixing is reduced. It is necessary to make the conditions mild, for example, to suppress them, and these measures cause a decrease in productivity and a decrease in moldability.
[0007]
As a method for suppressing the thermal decomposition of a polystyrene resin, it is generally known to use an antioxidant. For example, as a method for reducing the production of styrene dimer and trimer, JP-A-5-170825 and JP-A-5-170825 are disclosed. 2002-121215 proposes a method for reducing the content of styrene dimers and styrene trimers in the styrene resin by adding an antioxidant to the polymerization step and the devolatilization step of the styrene resin. . Japanese Patent Application Laid-Open No. 2000-158507 proposes a styrene-based resin foam having a small content of styrene dimer or styrene trimer, to which an antioxidant is added and subjected to extrusion foaming. However, these antioxidants are generally very expensive compared to styrene resins, and the addition of a small amount increases the cost.
[0008]
Also, it is already known to add a conjugated diene polymer to a polystyrene resin, but the addition amount of the conjugated diene polymer, suppression of thermal decomposition, suppression of increase in styrene dimer and styrene trimer. The relationship between effects has never been reported so far, and it has not been possible to easily analogize these effects.
[0009]
[Problems to be solved by the invention]
The present invention has few styrene dimers and styrene trimers and is excellent in thermal stability during molding, production of styrene dimers and styrene trimers, molecular weight reduction is extremely low, and excellent strength, Further, the present invention intends to propose a styrene resin composition for foam molding that can be produced at low cost, a foam sheet formed by molding the resin composition, and a food container formed by molding the sheet.
[0010]
[Means for Solving the Problems]
As a result of intensive studies to solve the above-mentioned problems, the present inventors have added a specific amount of a conjugated diene polymer to a styrene resin, and contain the styrene dimer and styrene trimer in the resin composition. By making the amount below a certain amount, it was found that a styrenic resin composition for foam molding having excellent properties, which could not be expected so far, was obtained, and the present invention was completed.
[0011]
That is, the present invention is a styrene resin composition obtained by adding 10 to 0.1 parts by mass of (B) conjugated diene polymer to 100 parts by mass of (A) styrene resin, The total content of styrene dimer and styrene trimer is 1500 ppm or less, a styrene resin composition for foam molding, a method for producing the same, and foaming obtained by molding the resin composition Is the body.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below. The styrene resin composition for foam molding of the present invention is obtained by adding a conjugated diene polymer to a styrene resin. The styrene resin is obtained by radical polymerization of a styrene monomer. As the styrene monomer, known monomers such as styrene, α-methyl styrene, o-methyl styrene, m-methyl styrene, and p-methyl styrene can be used, and styrene is preferable. In addition, monomers other than styrenic monomers such as acrylonitrile, (meth) acrylic acid, (meth) acrylic acid ester and the like that can be copolymerized with these styrenic monomers also improve the performance of the styrenic resin composition. It may be added and polymerized as long as it is not impaired, that is, 5 parts by mass or less with respect to 100 parts by mass of the styrene monomer. Further, in the present invention, a crosslinking agent such as divinylbenzene may be polymerized by adding less than 1 part by mass to 100 parts by mass of the styrene monomer.
[0013]
Conjugated diene polymers constituting the present invention include polybutadiene, styrene-butadiene random or block copolymers, polyisoprene, polychloroprene, styrene-isoprene random, block or graft copolymers, ethylene-propylene copolymer. Polymers, ethylene-propylene-butadiene copolymers, styrene-methyl methacrylate grafted butadiene copolymers, and the like. Random, block or graft copolymers of polybutadiene and styrene-butadiene are preferable, and styrene-based is particularly preferable. Random, block or graft copolymers of styrene-butadiene that are compatible with the resin. Also included is so-called high impact polystyrene, which is a mixture of particulate styrene graft polybutadiene and styrene resin. These may be partially hydrogenated. Further, these shapes are not particularly limited and can be used, such as a crumb shape, a powder shape, a latex shape, and a liquid shape.
[0014]
The method for producing the styrene resin is not particularly limited, but a radical polymerization method using an organic polymerization initiator is preferable, and a continuous bulk polymerization method is more preferable from the viewpoint of cost. Specifically, the styrenic monomer is continuously polymerized in the polymerization step, then unreacted substances and / or solvents are removed from the reaction product after the polymerization reaction in the devolatilization step, and the styrenic resin is removed. The manufacturing method is preferred. Although there is no restriction | limiting in particular about the apparatus used in a superposition | polymerization process here. For example, in the case of bulk radical polymerization, a polymerization apparatus comprising a first reactor, a second reactor, and a third reactor can be used.
[0015]
Further, the polymerization is advanced until the unreacted styrene monomer is finally 40% by weight or less, and devolatilization is performed by a known method in order to remove volatile components such as the styrene monomer. . This devolatilization step is for removing unreacted substances and / or solvent from the reaction product after the polymerization reaction. For the devolatilization treatment, for example, a flash drum, a twin-screw devolatilizer, a thin film evaporator, An extruder or the like can be used. In addition, the temperature of devolatilization processing is about 200-280 degreeC normally, and the pressure of devolatilization processing is 1-400 torr normally, Preferably it is 1-100 torr. As the devolatilization method, for example, it is desirable to remove by passing through a method of removing under reduced pressure under heating or an extruder designed for the purpose of removing volatile matter.
[0016]
The organic polymerization initiator used for the polymerization of the styrene resin is not particularly limited, but is preferably an organic peroxide having a one-hour half-life temperature of 90 to 130 ° C, more preferably 105 to 115 ° C. The product polymerization initiator is preferably used in an amount of 500 to 1500 ppm, more preferably 800 to 1200 ppm based on the styrene monomer. Examples of these organic peroxide polymerization initiators include 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane and 1,1-bis (t-butylperoxy) -cyclohexane. 1,1-bis (t-amylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis (t-amylperoxy) -cyclohexane, 1,1-bis (t-hexylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis (t-hexylperoxy) -cyclohexane, 2,2-bis (4,4-di-butylperoxycyclohexyl) propane, t-hexylperoxyisopropyl Examples thereof include monocarbonate and t-amyl peroxyisononanoate. These may be used alone or in combination of two or more. In some cases, a chain transfer agent such as t-dodecyl mercaptan, n-dodecyl mercaptan, α-methylstyrene dimer, terpinolene, etc. may be used. If desired, a solvent, a heat stabilizer such as a general antioxidant, a plasticizer, or the like may be added as long as the performance of the styrene resin composition is not impaired.
[0017]
Examples of the solvent used as desired include aromatic hydrocarbons such as toluene, xylene, and ethylbenzene, which may be used alone or in combination of two or more. Furthermore, other solvents such as aliphatic hydrocarbons and dialkyl ketones can be mixed with aromatic hydrocarbons within a range that does not lower the solubility of the polymerization product. This solvent is preferably used in an amount not exceeding 25% by weight based on the monomer. When the solvent exceeds 25% by weight, the polymerization rate is remarkably reduced, and the impact strength of the resulting resin is greatly reduced. Moreover, since a large amount of energy is required for the recovery of the solvent, the economy is inferior. The solvent may be added after the polymerization proceeds and becomes relatively high in viscosity, or may be added before the polymerization, but is added at a rate of 5 to 15% by weight before the polymerization. However, it is easier to make the quality uniform, and this is preferable from the viewpoint of controlling the polymerization temperature.
[0018]
In the production of the styrene-based resin composition of the present invention, it is preferable to add the conjugated diene polymer constituting the present invention in the polymerization step or the devolatilization step. That is, in this case, the conjugated diene polymer constituting the present invention is added to a reactor or an extruder used for the polymerization reaction. Moreover, it is more preferable to add after the end of the polymerization step (preferably immediately after) and before the devolatilization step. In this case, at the outlet of the reactor used for the polymerization reaction, the conjugated diene polymer is Will be added.
[0019]
In the styrene resin composition of the present invention, the addition amount of the conjugated diene polymer needs to be 0.1 to 10 parts by mass, preferably 0.2 to 5, with respect to 100 parts by mass of the styrene resin. More preferably, it is 0.5-2 mass parts. When the addition amount is less than 0.1 parts by mass, the effect of suppressing thermal decomposition of the styrene-based resin composition in the devolatilization step and the molding step becomes insufficient, resulting in a decrease in molecular weight and styrene dimer and This leads to a significant increase in trimers. On the other hand, when the amount exceeds 10 parts by mass, the foamed molded product, which can be roughened by foam molding, has a poor appearance. In addition, in a food container obtained by foam molding, the elution amount of styrene dimer and styrene trimer is remarkably increased, which is not preferable.
[0020]
In the styrene resin composition of the present invention, a mixture of a conjugated diene polymer and a styrene resin, a conjugated diene copolymer having a relatively low conjugated diene component in the conjugated diene polymer, or the like is added. However, the content of the conjugated diene component in the styrenic resin composition after addition is preferably 0.05 to 5% by mass, more preferably 0.2 to 3% by mass, and particularly preferably. 0.4-2 mass%.
[0021]
It is also preferable to add a conjugated diene polymer to a styrene resin pellet using a mechanical device such as an extruder or a Banbury mixer in order to suppress thermal decomposition during molding. In this case, a conjugated diene polymer may be newly added to a styrene resin pellet to which no conjugated diene polymer is added, or a styrene-based polymer that already contains a conjugated diene polymer. A method of adding additional resin composition pellets at the time of molding may also be used.
[0022]
The styrene resin of the present invention produced by newly adding a conjugated diene polymer to a styrene resin pellet to which no conjugated diene polymer has been added at the time of molding is 15 minutes at 230 ° C. under a nitrogen atmosphere. The rate of decrease in z-average molecular weight upon melt-kneading is preferably 20%. The rate of decrease in the z-average molecular weight was determined by the following formula from the z-average molecular weight before and after kneading, using a “Plasticcoder PL2000” manufactured by Brabender Co., Ltd. in a nitrogen atmosphere and melt-kneading the resin pellets at 230 ° C. for 15 minutes. Calculated with z average molecular weight reduction rate (%) = [{(z average molecular weight of resin pellets before kneading) − (z average molecular weight of resin pellets after kneading)} / (z average molecular weight of resin pellets before kneading)] × 100
[0023]
The total content of the styrene dimer and the styrene trimer in the styrene resin composition of the present invention needs to be 1500 ppm or less. When the total content of the styrene dimer and the styrene trimer exceeds 1500 ppm, the appearance of the obtained foamed molded product is deteriorated, and the styrene dimer and the styrene 3 amount in the food container obtained by foam molding. The amount of elution of the body increases significantly, which is not preferable.
[0024]
In the present invention, the styrene dimer refers to 1,3-diphenylpropane, 2,4-diphenyl-1-butene, and 1,2-diphenylcyclobutane. The styrene trimer refers to 1-phenyl-4- (1′-phenylethyl) tetralin and 2,4,6-triphenyl-1-hexene.
[0025]
The styrenic resin composition of the present invention may contain known additives such as higher fatty acids, higher fatty acid salts, higher fatty acid amides, mineral oils, antioxidants, anti-fungal agents, antistatic agents, flame retardants, and sliding agents as required. It may be added.
[0026]
The foam molding method of the styrene resin composition of the present invention is not particularly limited, and can be foam molded by a known method. For example, add a nucleating agent such as talc or calcium carbonate to a styrene resin, melt and mix using an extruder, press the foaming agent, adjust to the optimum foaming temperature, and foam from a circular die to form a sheet By making it, a foam sheet can be manufactured. The thickness of the foam sheet is preferably 0.5 to 5 mm, more preferably 1 mm to 3 m. Moreover, a foaming container is obtained by secondary-molding this foaming sheet by a well-known method. The molding method is not particularly limited, and vacuum molding, pressure molding, or the like can be employed.
[0027]
As the blowing agent to be used, any blowing agent such as lower hydrocarbons such as propane, butane, pentane and hexane, halogenated hydrocarbons such as trichloromonofluoromethane and methyl chloride, inorganic gases such as carbon dioxide and water is used alone. Or it can mix and use.
[0028]
In addition, in the same way as the foam sheet, add a flame retardant to the styrene resin, add a flame retardant, melt and mix using an extruder, press the foaming agent, and foam from the slit die. A flame retardant foam board can also be obtained. As the flame retardant to be added, known flame retardants can be used. For example, among halogen flame retardants, brominated flame retardants are preferable from the viewpoint of flame retardancy, and hexabromo is particularly preferred from the viewpoint of compatibility with styrene resins. Cyclododecane is preferred.
[0029]
The thickness of the foam of the flame retardant foam board is not particularly limited, and is appropriately selected depending on the application. For example, in the case of a heat insulating material used for applications such as building materials, the thickness is preferably 10 to 150 mm, more preferably 20 to 100 mm in order to impart preferable heat insulating properties, bending strength and compressive strength.
[0030]
The foamed molded sheet of the present invention may have a multilayer sheet structure in which a layer made of a thermoplastic resin is laminated on one side of the foamed sheet as necessary. The layer made of the thermoplastic resin to be laminated may have a multilayer structure including an adhesive layer. Moreover, although it may be a foam or a film, it is preferably a film, and a film having a thickness of 10 to 1000 μm is particularly preferable. Lamination of a thermoplastic resin film is effective in improving scratch resistance, rigidity, etc., as well as improving appearance, printability, and impact resistance. Examples of the thermoplastic resin to be laminated include a non-foamed styrene resin and an olefin resin, but a polystyrene resin that can be easily laminated without an adhesive is preferable, and impact-resistant polystyrene having excellent impact strength is particularly preferable. It can be preferably used. In the case of a multilayer sheet, it is preferable to form a container so that the styrene resin foam layer is inside the container.
[0031]
【Example】
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these Examples. First, the evaluation method in the present invention will be described below.
[0032]
(1) Measurement of styrene dimer and styrene trimer in resin
200 mg of the resin is dissolved in 2 mL of 1,2-dichloromethane, 2 mL of methanol is added to precipitate the styrene-based resin, and the mixture is allowed to stand, and then the supernatant is used with a gas chromatography HP-5890 manufactured by Hewlett-Packard Company. It was measured. Detailed conditions are described below.
(A) Column: DB-1 (ht) 0.25 mm × 30 m Film thickness 0.1 μm
(B) Injection temperature: 250 ° C
(C) Column temperature: 100 to 300 ° C
(2) Detector temperature: 300 ° C
(E) Split ratio: 50/1
(F) Internal standard substance: n-eicosane
[0033]
(2) Measurement of elution amount of styrene dimer and styrene trimer into n-heptane
The foam sheet was heated in an oven at 170 ° C. for 25 seconds to form a bowl-shaped container having a diameter of 110 mm and a depth of 121 mm. At this time, it was molded so that the styrene resin was inside. 550 mL of n-heptane was put into the molded foam container, and the solution eluted at 60C for 25 minutes was measured by GC / MS-SIM. Detailed conditions are described below.
(A) Column: DB-5 0.25 mm × 30 m, film thickness 0.25 μm
(B) Injection temperature: 250 ° C
(C) Column temperature: 120 ° C. (5 minutes) → 10 ° C./minute→250° C. (12 minutes)
(2) Interface: 200 ° C
(E) Ionization voltage: 70 eV
(F) Split ratio: 30
[0034]
(3) Weight average molecular weight and z average molecular weight
It measured on the following conditions using the Tosoh company make and HLC-802A type | mold gel permeation chromatography (GPC).
(B) Column: Tosoh Corporation Column
(B) Mobile phase: tetrahydrofuran
(C) Sample concentration: 0.3% by weight
(D) Measurement temperature: 38 ° C
(E) Detector: Differential refractometer
[0035]
▲ 4 ▼ Appearance
The rough surface of the foam surface was evaluated by visual observation.
○: The surface is beautiful and smooth.
Δ: Some rough skin is observed.
X: Rough skin is recognized as a whole.
[0036]
▲ 5 ▼ Container strength
The container obtained in (2) was compressed from the bottom using a Tensilon measuring machine at a speed of 400 mm / min and indicated by the strength when the container was buckled.
[0037]
Reference example 1
A fully mixed reactor with a stirring blade with a volume of 25 L is used as a first reactor, a fully mixed reactor with a stirring blade with a volume of 40 L is used as a second reactor, and a static mixer type plug flow reactor with a volume of 50 L is used as a third reactor. A polymerization reactor was configured by connecting the reactors in series. The number of stirring in the first reactor is 110 rpm, the reaction temperature is 101 ° C., the number of stirring in the second reactor is 110 rpm, the reaction temperature is 103 ° C., and the third reactor is a temperature gradient of 107 ° C. to 116 ° C. in the flow direction. It was adjusted so that
Feed rate of 23 L / hr of raw material solution prepared by adding 0.08 parts by mass of 1,1-bis (t-butylperoxy) cyclohexane as a polymerization initiator to 80 parts by mass of styrene monomer and 20 parts by mass of ethylbenzene The polymer was continuously fed to the first reactor and polymerized, and then polymerized continuously in the second reactor and the third reactor, and the polymerization was allowed to proceed until the polymerization conversion rate was 92%. Immediately after the completion of the polymerization step, that is, at the outlet of the third reactor, a styrene-butadiene copolymer (Nipol NS-312S manufactured by Nippon Zeon Co., Ltd., butadiene content 60 mass%) is used as a conjugated diene polymer. It added so that it might become 2% with respect to resin obtained from the 3rd reactor. Next, while performing heat treatment at 230 ° C. in a 3-vent twin screw extruder, volatile components such as unreacted styrene and the solvent ethylbenzene are removed under reduced pressure, and then cooled and cut to form a pellet-shaped styrene resin. A composition (PS-1) was obtained. Table 1 shows the physical properties of the obtained styrene-based resin composition.
[0038]
Reference example 2
A styrene resin composition (PS-2) was obtained in the same manner as in Reference Example 1 except that the addition amount of the styrene-butadiene copolymer as the conjugated diene polymer was 5%. Table 1 shows the physical properties of the obtained styrene-based resin composition.
[0039]
Reference example 3
A styrene resin composition (PS-3) was obtained in the same manner as in Reference Example 1 except that the addition amount of the styrene-butadiene copolymer as the conjugated diene polymer was 0.2%. Table 1 shows the physical properties of the obtained styrene-based resin composition.
[0040]
Reference example 4
In the same manner as in Reference Example 1, except that 2% of a styrene-butadiene copolymer (Denka STR1250 manufactured by Denki Kagaku Kogyo Co., Ltd., butadiene content 60% by mass) was added as a conjugated diene polymer, a styrene-based polymer was used. A resin composition (PS-4) was obtained. Table 1 shows the physical properties of the obtained styrene-based resin composition.
[0041]
Reference Example 5
As a mixture of a conjugated diene polymer and a styrene resin, styrene was prepared in the same manner as in Reference Example 1, except that 5% of high impact polystyrene (Toyostyrene E785 (butadiene content 7.5%) manufactured by Toyo Styrene Co., Ltd.) was added. Table 1 shows the physical properties of the resulting styrene-based resin composition.
[0042]
Reference Example 6
A styrene resin composition (PS-6) was obtained in the same manner as in Reference Example 1 except that the amount of styrene-butadiene copolymer added as the conjugated diene polymer was 0.08%. Table 1 shows the physical properties of the obtained styrene-based resin composition.
[0043]
Reference Example 7
A styrene resin composition (PS-7) was obtained in the same manner as in Reference Example 1 except that the amount of styrene-butadiene copolymer added as a conjugated diene polymer was 13%. Table 1 shows the physical properties of the obtained styrene-based resin composition.
[0044]
Reference Example 8
A styrene resin composition (PS-8) was obtained in the same manner as in Reference Example 1 except that the conjugated diene polymer was not added. Table 1 shows the physical properties of the obtained styrene-based resin composition.
[0045]
Reference Example 9
Using the same polymerization apparatus as in Reference Example 1, the reaction temperature of the first reactor was 118 ° C., the reaction temperature of the second reactor was 124 ° C., and the third reactor was a temperature gradient of 131 ° C. to 136 ° C. in the flow direction. In the same manner as in Reference Example 1, except that the amount of 1,1-bis (t-butylperoxy) cyclohexane added was 0.02 parts by mass, the styrene resin composition ( PS-9) was obtained. Table 1 shows the physical properties of the obtained styrene-based resin composition.
[0046]
Reference Example 10
100 kg of pure water, 400 g of tribasic calcium phosphate and 10 g of sodium dodecylbenzenesulfonate were added to an autoclave with an internal volume of 200 L and a stirrer, and stirred at 130 rpm. Subsequently, 80 kg of styrene and 104 g of 1,1-bis (t-butylperoxy) cyclohexane were charged, the autoclave was sealed, the temperature was raised to 115 ° C. for 3 hours, and further raised to 135 ° C. and held for 2 hours. Polymerization was completed. The conversion rate at the end of the polymerization was 99.9%. The obtained beads were washed, dehydrated and dried to obtain a styrene resin. The styrene resin had a weight average molecular weight of 37.4 million, a z average molecular weight of 7660,000, and the total content of styrene dimer and styrene trimer in the resin was 860 ppm.
Subsequently, 2% of a styrene-butadiene copolymer (Nipol NS-312S manufactured by Nippon Zeon Co., Ltd.) was added as a conjugated diene polymer to the styrene resin, and the temperature was 210 ° C. using a single screw extruder. Extrusion was carried out while degassing with a styrene resin composition (PS-10) in the form of pellets. Table 1 shows the physical properties of the obtained styrene-based resin composition.
[0047]
Reference Example 11
A styrene resin composition (PS-11) was obtained in the same manner as in Reference Example 9 except that the conjugated diene polymer was not added. Table 1 shows the physical properties of the obtained styrene-based resin composition.
[0048]
[Table 1]

[0049]
Examples 1-6
As shown in Table 2, with respect to the styrene resin composition (PS-1 to PS-5, PS-10) described in the reference example, talc as a nucleating agent was 0.3 mass relative to the styrene resin composition. %, And mixed while melting at 250 ° C. in an extruder. While being injected with a mixture of n-butane and i-butane (50% of n-butane) as a blowing agent, this was extruded from a circular die and had a thickness of 2 mm. The foam sheet was obtained. Table 2 shows the physical properties of the obtained sheet and the physical properties of the container obtained by molding the sheet.
[0050]
Example 7
2% by mass of a styrene-butadiene copolymer (Nipol NS-312S manufactured by Nippon Zeon Co., Ltd.) was further added as a conjugated diene polymer to the styrene resin composition (PS-3) obtained in Reference Example 3. Except for the above, foamed sheets and containers were obtained in the same manner as in Examples 1-6. Table 2 shows the physical properties of the obtained sheet and container.
[0051]
[Table 2]

[0052]
Comparative Examples 1-5
Using the styrenic resin compositions (PS-6 to PS-9, PS-11) described in the reference examples as shown in Table 3, foam sheets and containers were obtained in the same manner as in the following examples. . Table 3 shows the physical properties of the obtained sheets and containers.
[0053]
[Table 3]

[0054]
From Tables 1 to 3, when the conjugated diene polymer is not added or the addition amount is small, the resin is likely to be thermally decomposed, resulting in a large decrease in molecular weight, and the styrene dimer and It can be seen that the amount of styrene trimer produced is increased. And in these foam-molded articles, it can be seen that the appearance is poor, the strength is insufficient, and the elution amount of styrene dimer and trimer into n-heptane is remarkably increased. From Comparative Example 2, when the amount of the conjugated diene polymer added is too large, the amount of styrene dimer and trimer eluted into n-heptane is remarkably increased, and the appearance of the foam is also deteriorated. I understand that. On the other hand, it can be seen from Example 7 that the addition of a conjugated diene polymer during foam molding suppresses the decrease in molecular weight and the generation of styrene dimers and styrene trimers.
[0055]
【The invention's effect】
As described above, the styrene resin composition for foam molding of the present invention is excellent in foam moldability, and the molded foam is excellent in surface condition and strength, and when used as a food container, styrene dimer and styrene. The trimer has a very low elution amount.

Claims (5)

(A) A styrene resin composition obtained by adding 10 to 0.1 parts by mass of a conjugated diene polymer to 100 parts by mass of a styrene resin.
The total content of styrene dimer and styrene trimer in the resin composition is 1500 ppm or less, and a styrene resin composition for foam molding,   In the method of continuously polymerizing a styrenic monomer in a polymerization step and then removing unreacted substances and / or solvent from the reaction product after the polymerization reaction in a devolatilization step to produce a styrene resin, The styrene resin composition for foam molding according to claim 1, wherein the styrene resin composition for foam molding is produced by adding a conjugated diene polymer in the polymerization step or the devolatilization step, and after the polymerization step and before the devolatilization step. object 3. The styrenic resin composition for foam molding according to claim 1 or 2 , wherein the reduction rate of the z-average molecular weight when melt-kneaded for 15 minutes in a nitrogen atmosphere at 230 ° C. is within 20%. A foam sheet having a thickness of 0.5 to 5 mm, which is obtained by foam-molding the resin composition according to any one of claims 1 to 3.   A container formed by molding the foamed sheet according to claim 4