JP2009149054A - Biaxially stretched foamed sheet made of polystyrene resin, its manufacturing method, and molded article made from the sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biaxially stretched foamed sheet made of polystyrene resin, which is less apt to suffer cracking, breakage, etc. during handling and can be reduced in thickness and weight and be repeatedly used since the sheet has moderate rigidity and is excellent in strengths (impact strength, tear strength, and folding endurance), and which can be cleaned, reutilized, and thermoformed since the sheet is excellent in shape reproducibility and long-lasting antistatic properties, its manufacturing method, and a molded article made from the sheet. <P>SOLUTION: The biaxially stretched foamed sheet made of the polystyrene resin is characterized in that at least one foamed layer and at least one unfoamed layer or foamed layer are laminated. The manufacturing method of the biaxially stretched foamed sheet made of the polystyrene resin, and the molded article made from the sheet are provided. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention is not only a one-way food or non-food molding material but also a multilayer for food or non-food paper substitutes that are difficult to crack, tear, etc. during handling or can be used repeatedly. The present invention relates to a foamed biaxially stretched sheet made of polystyrene resin having a structure, a method for producing the same, and a molded product produced using this sheet as a raw material.

  Conventionally, a polystyrene-based non-foamed resin sheet (particularly, a high-impact polystyrene sheet (hereinafter sometimes referred to as “HIPS”)) and a polystyrene-based foamed resin sheet (particularly, a foamed polystyrene sheet (hereinafter referred to as “PSP”). )) Is widely used as a production material for various food containers such as sugar beet containers because of its excellent thermoformability. The former is further excellent in rigidity and dimensional stability of the secondary molded product, and the latter is excellent in heat insulation, buffering, and weight reduction. When considering safety during handling, it is difficult to provide cushioning and flexibility in the former, and in the latter, if heat insulation and cushioning are emphasized, the sheet has a highly foamed structure, and rigidity and dimensional stability Will decline. Therefore, the thickness is increased to cover the decrease in mechanical strength, resulting in an increase in storage space and transportation cost. Therefore, it is desired to develop a sheet that has an intermediate performance between the two, can be reduced in thickness and weight, and is excellent in cost.

  In recent years, from the viewpoints of environmental protection, effective use of resources, cost reduction, and the like, molding materials such as PSP have begun to be reused after being washed and ground. On the other hand, food and non-food papers are also being replaced by plastics, and there is an increasing demand for cleaning and reuse.

  In Patent Document 1, the rubber content is 20% or less, the expansion ratio is 1.5 to 7.0, the thickness is 0.3 to 1.0 mm, the number of bubble films in the thickness direction is 5 to 20, and the residual gas amount is 0.3 mol. An extruded expanded polystyrene sheet for heat molding of a thin-walled molded product of / kg or less is disclosed. This sheet is at a practical level in the case of a 0.5 mm-thick tray (Example 4 of Patent Document 1) when a large number of rib structures are used (there is no specific numerical value for strength). When it is necessary to make it, cracks and tears are likely to occur, which is not sufficient.

  On the other hand, in Patent Document 2, a chemical foaming agent is blended, biaxially stretched so that the expansion ratio is 1.07 to 2.1 times, and the thickness is 0.1 to 1 mm, and the bending strength is 10 or more. A styrene resin sheet is disclosed. Here, it is described that the toughness and formability of PSP are improved by biaxial stretching, but when the expansion ratio is 1.24 times or more, the bending strength is 30 times or less (patent) Table 1 of Document 2), which is insufficient to prevent cracking and tearing during handling.

Japanese Examined Patent Publication No. 61-003820 Japanese Patent Publication No. 64-006014

This invention is made | formed in view of the said background art, and the subject of this invention is the following (1) and / or (2) and / or (3).
(1) Since it has excellent moderate rigidity and strength (impact strength, tear strength, folding strength), it is difficult to crack and break during handling, and it is made of polystyrene resin that is thin and lightweight and can be used repeatedly. To provide a sheet, a manufacturing method thereof, and a molded product made of the sheet.
(2) To provide a moldable reproducible polystyrene resin foam biaxially stretched sheet, a method for producing the same, and a molded article made of this sheet because of excellent mold reproducibility.
(3) To provide a foamed biaxially stretched sheet made of polystyrene resin that can be washed and reused, and a method for producing the same, and a molded product made of this sheet, because it has excellent persistent antistatic properties.

  As a result of intensive studies to solve the above-mentioned problems, the present inventor has solved the above-mentioned drawbacks and has achieved the above-mentioned problems. The finished product was completed.

  That is, the present invention provides a polystyrene resin foamed biaxially stretched sheet, wherein at least one foamed layer and at least one non-foamed layer or foamed layer are laminated.

  In the present invention, the polystyrene-based resin is characterized in that the non-foamed layer / foamed layer / non-foamed layer are laminated in this order, and the total thickness of both non-foamed layers is 1 to 70% of the total thickness. A foamed biaxially stretched sheet is provided.

  In the present invention, the foamed biaxial polystyrene resin is characterized in that the foamed layer / non-foamed layer / foamed layer are laminated in this order, and the thickness of the non-foamed layer is 5 to 95% of the total thickness. A stretched sheet is provided.

  Further, the present invention is the above-mentioned polystyrene resin foam biaxial stretching, wherein the foamed layer / foamed layer / foamed layer are laminated in this order, and the thickness of each foamed layer is 1 to 99% of the total thickness. A sheet is provided.

  In addition, the present invention provides a molded product characterized by being manufactured by a thermoforming method using the above polystyrene resin foamed biaxially stretched sheet as a raw material.

  Further, the present invention forms a sheet by melt-kneading a polystyrene resin composition containing a foaming agent and a polystyrene resin composition not containing a foaming agent in separate extruders and coextruding from one die, The polystyrene-based biaxial foam made of the above-mentioned polystyrene resin, wherein the sheet is reheated after being cooled and co-stretched in the biaxial direction to laminate at least one non-foamed layer and at least one foamed layer A method for producing a stretched sheet is provided.

  Further, the present invention provides a polystyrene-based resin composition containing a foaming agent, which is separately melt-kneaded with at least two extruders and coextruded from a single die to form a sheet. The present invention provides a method for producing the above-mentioned polystyrene resin foamed biaxially stretched sheet, wherein only two or more foamed layers are laminated by heating and co-stretching in the biaxial direction.

According to the present invention, the following (1), (2), (3) and / or (4) can be achieved.
(1) The polystyrene resin foamed biaxially stretched sheet according to the present invention has excellent strength (impact strength, tear strength, folding strength), so that it is possible to reduce the thickness and weight of the molded product obtained by thermoforming. Thus, a larger number of molded products can be produced from the raw materials per unit mass.
(2) Since the polystyrene resin foam biaxially stretched sheet according to the present invention is excellent in mold reproducibility, it is excellent in thermoformability.
(3) Since the polystyrene resin foamed biaxially stretched sheet according to the present invention has both moderate rigidity and flexibility and buffering properties, it is difficult to crack and break during handling, and can be used safely.
(4) Since the polystyrene resin foamed biaxially stretched sheet according to the present invention has little reduction in antistatic property due to repeated use including washing, it has not only a cost advantage as a substitute for paper discarded every time, but also naturally It also leads to protection.
(5) By blending a large amount of antistatic agent only in the outer layer or in the outer layer, the surface resistance value can be lowered without increasing the production raw material cost.

  Hereinafter, the present invention will be described. However, the present invention is not limited to the following embodiments, and can be arbitrarily modified and implemented.

  The polystyrene resin composition in the present invention is (A) alone, (B) alone, or (B) a polystyrene resin containing a rubber component. , (A) and a mixture of (B).

  Typical examples of (A) include polystyrene such as general-purpose polystyrene (hereinafter sometimes referred to as “GPPS”), and further styrene and alkylstyrene (for example, o-, m-, p-). Homopolymers of aromatic vinyl compounds such as methyl styrene, p-ethyl styrene, pt-butyl styrene), α-alkyl styrene (eg, α-methyl styrene, α-ethyl styrene), and combinations of these monomers And styrene- (meth) acrylic acid ester copolymers (for example, styrene-butyl acrylate copolymers), styrene- (meth) acrylic acid copolymers, and the like. Here, (meth) acrylic acid means acrylic acid or methacrylic acid. These (A) can be used individually or in combination of 2 or more types.

  (A) is preferably GPPS. (A) other than the above-described GPPS is preferably used alone or in combination of two or more in a range having compatibility with GPPS.

  Among GPPS, GPPS having a melt flow rate of 0.5 to 20 g / 10 minutes at a temperature of 200 ° C. and a load of 5 kg is preferable, and GPPS having a range of 2 to 10 g / 10 minutes is particularly preferable. By using such GPPS, melt kneading and extrusion foaming at a relatively low temperature are possible, and dispersibility of the kneading type antistatic agent described later is improved.

  Examples of (B) include HIPS, which is representative of graft copolymers, and styrene-butadiene-styrene block copolymers (hereinafter, “SBS”), which are representative of ABA type block copolymers. And styrene-isoprene-styrene block copolymer (hereinafter sometimes referred to as “SIS”). “HIPS” includes a blend type HIPS obtained by blending this graft type HIPS and GPPS in addition to a graft type HIPS alone in which at least a styrene monomer is graft-polymerized to a rubber component (however, blended GPPS). Are classified as (A)).

  The polystyrene resin having the rubber component (B) may be a hydrogenated product as long as it has compatibility.

  Examples of the rubber used in the production of (B) include non-styrene rubbers such as butadiene rubber, isoprene rubber, acrylic rubber, and butadiene-isoprene rubber; and styrene rubbers such as styrene-butadiene rubber and styrene-isoprene rubber. Can be mentioned. Among them, butadiene rubber is preferable, and among butadiene rubbers, a high cis type having a high content of cis-1,4 structure is preferable from the viewpoint of thermal stability than a low cis type having a low content.

  The “rubber component” in the present invention refers to a component having a low elastic modulus that is bonded to a polystyrene-based resin, for example, the rubber described above.

  “Rubber component content” is determined by measuring the diene content by potentiometric titration using iodine monochloride, potassium iodide and sodium thiosulfate standard solution, and calculating the diene content as “rubber component content”. To do. Analytical methods include, for example, the Japan Analytical Chemical Society, Polymer Analysis Research Roundtable, “New Edition Polymer Analysis Handbook”, Kinokuniya (1995 version), P.A. 659 “(3) Rubber content”, measured by this method and defined as the value so measured. The “sheet rubber component content” for the entire sheet, which will be described later, is also measured in the same manner, and is defined as a value measured as such.

  Therefore, the “content of rubber component” in (B) is preferably 3 to 50% by mass, more preferably 5 to 40% by mass, and particularly preferably 7 to 30% by mass with respect to the whole (B).

  (B) is preferably HIPS or SIS in which the melt flow rate at a temperature of 200 ° C. and a load of 5 kg is in the range of 0.5 to 20 g / 10 minutes, and particularly preferably HIPS or SIS in the range of 2 to 10 g / 10 minutes. . (B) can be used singly or in combination of two or more.

  By using such a polystyrene resin, melt kneading and extrusion foaming at a relatively low temperature are possible, and dispersibility of the kneading type antistatic agent described later is improved.

  Examples of the foaming agent in the present invention include volatile foaming agents such as propane, butane, pentane, and hexane; ammonium carbonate, ammonium bicarbonate, sodium bicarbonate, sodium citrate, azo compounds (azobisisobutyronitrile, azodicarbonamide , Diazoaminobenzene, etc.), sulfonyl hydrazide compounds (benzenesulfonyl hydrazide, p-toluenesulfonyl hydrazide, diphenyloxy-4,4′-bissulfonyl hydrazide, etc.), nitroso compounds (N, N′-dinitrosopentamethylenetriamine, etc.) Chemical foaming agents (decomposable foaming agents) such as carbon dioxide, nitrogen gas and other gases; water and the like. These foaming agents may be used in combination.

  The foam molding method includes (1) a method of extruding by adding a chemical foaming agent, (2) a method of extruding while injecting a foaming gas raw material, and (3) a liquid foaming gas raw material into the resin composition. A method of extruding the impregnated material or the like can be applied. Of these, the method (1) is preferable from the viewpoint of handling properties of the foaming agent, stability during biaxial stretching, and foaming ratio, and a polystyrene-based masterbatch (for example, manufactured by Eiwa Kasei Kogyo Co., Ltd.) Polyslen ES series, Sankyo Kasei Co., Ltd. Cell Microphone MB6000 series) can be suitably used. In addition, for food use, a product registered by the Sanitation Council such as polyolefin can be selectively used from the above.

  Content of a foaming agent is 0.1-5 mass parts normally with respect to 100 mass parts of said polystyrene-type resins, Preferably it is 0.3-3 mass parts. If the amount of the foaming agent is too small, not only the flexibility and buffering properties are not obtained, but also the sheet surface appearance may be inferior. On the other hand, if the amount is too large, not only the sheet surface appearance deteriorates but also the strength (impact Strength, tear strength, and bending strength) may be reduced, and mold reproducibility during thermoforming and appearance of a molded product may be deteriorated.

  Moreover, fillers (for example, talc, silica, kaolin, mica, calcium carbonate, magnesium carbonate, etc.) and bubble regulators (for example, polyvalent carboxylic acids, etc.) for improving followability to the die such as T-die and surface appearance. Or a reaction mixture of a polyvalent carboxylic acid and sodium carbonate or sodium bicarbonate, or the like, or a master batch as well as a foaming agent may be used. The ratio of these fillers and bubble regulators is usually 0.01 to 2 parts by mass with respect to 100 parts by mass of the polystyrene resin composition.

The polystyrene resin foamed biaxially stretched sheet of the present invention has a continuous antistatic property, and specifically, the sheet surface resistance value measured according to JIS K6911 is 10 ⁷ to 10 ¹³ Ω. preferable.

  The polystyrene resin composition preferably contains an antistatic agent. The antistatic agent is not particularly limited, and examples thereof include a low molecular weight type antistatic agent such as a surfactant, and a polymer type antistatic agent. Surfactants are roughly classified into cationic, anionic, zwitterionic, and nonionic, and the most commonly used is anionic with a good balance between effect and economic efficiency. 1) fatty acid salts, 2) higher alcohol sulfates, 3) liquid fatty oil sulfates, 4) sulfates of aliphatic amines and amides, 5) aliphatic alcohol phosphates, 6) dibasic Examples thereof include fatty acid ester salts, 7) fatty acid amide sulfonates, 8) alkylaryl sulfonates, 9) formalin-condensed naphthalene sulfonates, and the like.

  Further, examples of the cationic system which is weak against heat and high in cost but has high antistatic properties include 1) aliphatic amine salts, 2) quaternary ammonium salts, and 3) alkylpyridinium salts. Furthermore, amphoteric ion systems with slightly improved heat resistance, which are weak points of anionic systems, include 1) imidazoline derivatives, 2) ammonium carboxylates, 3) ammonium sulfate esters, 4) ammonium phosphate esters, 5 ) Ammonium sulfonates and the like.

  As for these low molecular weight type antistatic agents such as surfactants, those in the form of a masterbatch may be used like the foaming agent. Moreover, it is preferable to selectively use a Sanitation Council registered product such as polyolefin from among the above for food use. [1]: Use of a kneading type antistatic agent, [2]: Use of a coating type antistatic agent, [3]: [1] and [2]. ] And the like.

  The ratio of the polystyrene resin to the “low molecular weight type antistatic agent such as a surfactant” (mass ratio, in the case of a multilayer sheet, the mass ratio per layer including the low molecular weight type antistatic agent) is the polystyrene resin. / Antistatic agent is preferably selected from the range of 80/20 to 99.5 / 0.5, particularly preferably 90/10 to 99/1. If the amount of the antistatic agent is too small, the antistatic property or the sustained antistatic property may be inferior. On the other hand, if the amount is too large, if there is no further effect, the contact material is caused by excessive bleeding out of the antistatic agent. May become contaminated.

  In the case of repeated use including cleaning, the use is not particularly limited, but a polymer type antistatic agent is preferable because it can prevent contamination of the contact material due to excessive bleeding out of the antistatic agent to the sheet surface. Specifically, nonionic polymer antistatic agents such as polyether ester polymer antistatic agents, potassium ionomers of ethylene / unsaturated carboxylic acid copolymers, polystyrene sulfonic acid polymer antistatic agents, etc. Cationic polymer antistatic agents such as anionic polymer antistatic agents and polyacrylic ester polymer antistatic agents are preferred. Of these, polyether ester polymer type antistatic agents and potassium ionomers of ethylene / unsaturated carboxylic acid copolymers are preferred from the viewpoint of excellent antistatic performance, and polyether ester amide polymer type antistatic agents and ethylene are preferred. -A potassium ionomer of a (meth) acrylic acid random copolymer is particularly preferred. Here, the potassium ionomer of the ethylene / (meth) acrylic acid random copolymer may contain glycerin or polyethylene glycol for the purpose of improving the antistatic performance. In addition, (meth) acrylic acid means acrylic acid or methacrylic acid.

  The ratio of the polystyrene resin to the polymer antistatic agent (mass ratio, in the case of a multilayer sheet, the mass ratio per layer including the polymer antistatic agent) is polystyrene resin / polymer antistatic agent = It is preferable to select from the range of 50/50 to 99.5 / 0.5, and more preferably 60/40 to 95/5.

  Antistatic agents such as the above surfactants and other low molecular weight antistatic agents; the above-described polyether ester polymer antistatic agents and polymer antistatic agents such as potassium ionomer; However, the amount of the antistatic agent used can be reduced without lowering the antistatic performance of the polystyrene resin foamed biaxially stretched sheet by blending only in the outer layer or more in the outer layer than in the inner layer. That is, the surface resistance value can be sufficiently lowered without increasing the manufacturing raw material cost. In particular, in the polystyrene resin foamed biaxially stretched sheet of the present invention laminated in the order of foamed layer / foamed layer / foamed layer, the effect of the laminated form is more exhibited for the reasons described above.

  In addition, the dispersant may be added together with the polymer type antistatic agent. Although it does not specifically limit as a dispersing agent, For example, the copolymer which has a nonpolar unit compatible with a polystyrene-type resin in a molecular chain, and a polar unit compatible with a polymer type antistatic agent is mentioned. Specific examples include acid-modified olefin resins. The ratio of the dispersing agent is usually 0.01 to 20 parts by mass, preferably 1 to 10 parts by mass with respect to 100 parts by mass in total of the polystyrene resin and the polymer antistatic agent.

  The polystyrene-based resin composition includes other fillers, other dispersants, internal lubricants, thermal stabilizers, antioxidants, ultraviolet absorbers, flame retardants, plasticizers, anti-proofing agents, as long as the object of the present invention is not impaired. Various additives such as a clouding agent, an antibacterial agent, a pigment, a dye, a fluidity improver, a thickener, carbon black, ketjen black, graphite, and a reinforcing material may be blended.

  The polystyrene-based resin composition can also contain other resins that do not impair the compatibility. Examples of other resins include polyphenylene ether (which preferably forms a completely compatible system with GPPS and / or HIPS). However, it is preferable that substantially no polyolefin-based resin, polyester-based resin or polyamide-based resin is contained (here, the polymer type antistatic agent is excluded). When these resins are substantially contained, the compatibility is low, or the compatibility is still insufficient even with the use of a compatibilizing agent, so biaxial stretching becomes difficult, and even when possible, the strength (particularly the tear strength) , Folding strength) may be reduced, and it may be difficult to develop a sheet having excellent cost. The “polyolefin resin” does not include the polystyrene resin.

The polystyrene resin foamed biaxially stretched sheet of the present invention is preferably in the following form (1), (2) or (3).
(1) The above-mentioned polystyrene resin foamed biaxially stretched sheet (2), which is laminated in the order of non-foamed layer / foamed layer / non-foamed layer, and the total thickness of both non-foamed layers is 1 to 70% of the total thickness. ) The above-mentioned polystyrene resin foamed biaxially stretched sheet (3) foamed layer / foamed layer, which is laminated in the order of foamed layer / non-foamed layer / foamed layer, and the thickness of the non-foamed layer is 5 to 95% of the total thickness. / The foamed biaxially stretched sheet made of the polystyrene resin, wherein the foamed layers are laminated in the order of the foamed layers, and the thickness of each foamed layer is 1 to 99% of the total thickness.

  About the manufacturing method of the polystyrene resin foam biaxially stretched sheet of the present invention, in the polystyrene resin foamed biaxially stretched sheet of (1) and (2), a polystyrene resin composition containing a foaming agent, and foaming are used. By melt-kneading a polystyrene-based resin composition not containing an agent in a separate extruder and co-extruding from one die to form a sheet, reheating the sheet after cooling, and co-stretching in a biaxial direction A production method in which at least one non-foamed layer and at least one foamed layer are laminated is preferable.

  In addition, for the polystyrene resin foamed biaxially stretched sheet of (3) above, a polystyrene resin composition containing a foaming agent is separately melt-kneaded by at least two extruders and coextruded from one die. A production method in which only a foam layer of at least two layers is laminated by forming a sheet, reheating the sheet after cooling, and co-stretching in a biaxial direction is preferable.

  Any polystyrene resin foamed biaxially stretched sheet of (1), (2) or (3) above is melt-kneaded with a separate extruder and coextruded from a single die to form a sheet. The sheet is preferably reheated after cooling and co-stretched in the biaxial direction, but it is particularly preferable to produce the sheet as follows. However, the present invention is not limited to the following specific scope and can be modified within the scope of the idea of the present invention.

  For example, melt-kneading in a twin screw extruder while measuring a predetermined amount of “the above (B) such as HIPS” and / or “the above (A) such as GPPS”, an antistatic agent, and various other additives as required. And pelletizing to prepare an antistatic agent-containing masterbatch. Depending on the type of the antistatic agent, a commercially available master batch can be used, or a commercially available product can be used as it is.

  Next, at least two extruders are prepared. On the other hand, HIPS, GPPS, or an antistatic agent-containing master batch is weighed, stirred by a blender or tumbler, charged as a dry blend (polystyrene resin composition containing no foaming agent), and melt-kneaded. On the other hand, HIPS, GPPS or antistatic agent-containing masterbatch and foaming agent masterbatch are weighed, stirred with a blender or tumbler, charged as a dry blend (polystyrene resin composition containing a foaming agent), and melted. Knead.

  Next, a set of feed blocks and feed block dies connected to these extruders or a multi-manifold die (these dies may be collectively referred to as “T-die”) are joined and stacked to be continuous. Co-extrusion is performed while extruding and foaming, and the product is quenched with a cooling roll. Next, the foam raw sheet in which at least one foamed layer and “at least one non-foamed layer or foamed layer” are laminated is re-heated with a heating roll, and longitudinally stretched by a roll stretching method. Transverse stretching is performed by the tenter method, and continuous co-stretching (sequential biaxial stretching) is performed. Finally, a method of winding in a roll with a winder is preferable.

  Here, the polystyrene resin foamed biaxially stretched sheet of the present invention must have a configuration in which at least one foamed layer and “at least one non-foamed layer or foamed layer” are laminated. In this way, in the case of a configuration in which at least one foamed layer and at least one non-foamed layer are laminated, even if the foamed base material is biaxially stretched, breakage from the end during longitudinal stretching It is possible to suppress chuck detachment at the time of lateral stretching due to defective edges, and biaxial stretching stability is ensured, leading to an improvement in yield. At the same time, the strength of the polystyrene resin foamed biaxially stretched sheet itself and the molded product itself produced using the sheet as a raw material are also improved. That is, it is possible to reduce the thickness and weight, which is difficult only by ordinary extrusion foaming, by the biaxial stretching technique.

  On the other hand, in the case of a structure in which a foam layer and a foam layer are laminated, it is possible to reduce the total amount of use of the antistatic agent by blending the antistatic agent into a desired layer, and non-foaming It is possible to increase the flexibility and cushioning properties of the entire sheet from the structure in which the layers are laminated. However, the biaxial stretching stability of the sheet consisting only of the foamed layer tends to be lower than that of the structure in which the non-foamed layer is laminated. Since the foaming ratio is higher, the foamed laminated component can suppress the fluctuation of the foaming magnification in the thickness direction in one layer compared to the single-layer foamed component of the same thickness, It is possible to suppress sheet hole opening and breakage associated therewith. (2) By changing the expansion ratio / and / or rubber component content of each layer (for example, in a three-layer structure, the expansion ratio / and / or rubber component content of both outer layers is made lower than that of the intermediate layer, or vice versa. Therefore, it is possible to suppress breakage from the end during longitudinal stretching, sheet punching during longitudinal and lateral stretching, and breakage associated therewith, and improve biaxial stretching stability.

  As a specific layer structure, in the case of non-foamed layer / foamed layer / non-foamed layer, the total thickness of both non-foamed layers is preferably 1 to 70% of the total thickness. More preferably, it is 3-45%, More preferably, it is 5-20%. Here, if the total thickness of both non-foamed layers is less than 1%, biaxial stretching stability may not be maintained, or the sheet may have insufficient strength. On the contrary, if it is thicker than 70%, not only the rigidity of the sheet is increased, but also the flexibility and the buffering property may be lowered.

  As another specific layer configuration, in the case of foam layer / non-foam layer / foam layer, the thickness of the non-foam layer is preferably 5 to 95% of the total thickness. More preferably, it is 10 to 65%, and further preferably 15 to 35%. Here, if the thickness of the non-foamed layer is less than 5%, biaxial stretching stability may not be maintained, or the sheet may have insufficient strength. On the other hand, if it is thicker than 95%, not only the rigidity of the sheet will be increased, but also the flexibility and buffering properties will be reduced, and the foamed appearance (feel, unevenness, etc.) of the sheet may be lost.

  As another specific layer structure, in the case of foam layer / foam layer / foam layer, the thickness of each foam layer is preferably 1 to 99% of the total thickness. More preferably, it is 5-95%, More preferably, it is 10-80%. Here, if the thickness of any of the foam layers is too thin, or conversely too thick, coextrusion itself is difficult, or even if possible, a thick layer breaks during biaxial stretching. As a result, a hole may be formed in the sheet and a break may occur. In addition, when the layer structure is asymmetric, the sheet may be warped or deformed during repeated use, and even when the layer structure is symmetric, the foamed appearance (feel, texture, etc.) of the sheet is lost. There is a case.

  The thickness of the polystyrene resin foamed biaxially stretched sheet according to the present invention is preferably 0.05 to 1 mm. From the viewpoint of reducing the thickness and weight, it is more preferably 0.08 to 0.5 mm, and still more preferably 0.1 to 0.3 mm. When the thickness of the sheet is less than 0.05 mm, the rigidity of the sheet itself and the molded product itself is insufficient, and when used repeatedly as a sheet, the sheet may be easily folded or wrinkled. In the case of a molded product (tray or the like) manufactured using the sheet as a raw material, it may be difficult to hold and store the stored food. On the other hand, when the thickness exceeds 1 mm, the bulk of the sheet or the molded product and the stack height increase, resulting in an increase in storage space and transportation cost, which is not preferable from the viewpoint of recycling and cost. The polystyrene resin foamed biaxially stretched sheet produced by the method of the present invention (polystyrene resin foamed biaxially stretched sheet of the present invention) can achieve the above-mentioned thickness while maintaining other physical properties in good condition. It is. In particular, it is possible to ensure the stability of biaxial stretching and the strength to prevent cracking and tearing even if the thickness and weight are reduced.

  The polystyrene-based foamed biaxially stretched sheet of the present invention preferably contains a rubber component substantially. The rubber component content of the polystyrene resin foamed biaxially stretched sheet of the present invention (hereinafter sometimes referred to as “the rubber component content of the sheet”) is more preferably 0.1 to 30% by mass. Especially preferably, it is 1.0-20 mass%, More preferably, it is 5.0-15 mass%. Here, the “rubber component content of the sheet” in the present invention is different from the “content of rubber component” for the whole resin such as HIPS, SIS, SBS, etc., and is a polystyrene resin foamed biaxially stretched sheet. It means the rubber component content relative to the whole. That is, it means not the content of the rubber component in each resin, but the content of the rubber component in the polystyrene resin foamed biaxially stretched sheet or a molded product produced from the sheet. This is the same as the case of “content of component”. If the rubber component is not substantially contained, or if the “rubber component content of the sheet” is less than 0.1% by mass, the impact of the produced biaxially stretched sheet and molded product (container, etc.) In some cases, the strength, tear strength, and folding strength are not improved, and are easily broken or easily broken. On the other hand, when the “rubber component content of the sheet” exceeds 30% by mass, not only the extrusion stability and the stretching stability during production are deteriorated, but also the rigidity of the produced biaxially stretched sheet and molded product is lowered. May end up.

  In order to make the “rubber component content of the sheet” within the above range, even if a small amount of (B) containing a large amount of the rubber component is used, A small amount (B) may be used in a large amount so as to fall within the range. Moreover, you may adjust with content of (A) which does not contain a rubber component. Further, the thickness of each layer may be adjusted so as to fall within the above range.

  The longitudinal direction (extrusion direction of the sheet, hereinafter sometimes referred to as “MD”) and lateral direction (direction perpendicular to the extrusion direction of the sheet, hereinafter “TD”) of the polystyrene resin foamed biaxially stretched sheet in the present invention. The average value of the heat shrinkage stress is preferably 0.10 to 2.0 MPa. More preferably, it is 0.20 to 1.0 MPa, and a more preferable range is 0.30 to 0.7 MPa. If this average value is less than 0.10 MPa, the sheet itself and the molded product itself formed from this sheet may be easily broken or easily broken. Also, during thermoforming, particularly hot plate heating type air pressure molding, there may be a case where a molding failure occurs due to tearing at the back portion of the outer periphery of the mold. Conversely, if the average value is higher than 2.0 MPa, the mold reproducibility during thermoforming (the ability of the sheet to faithfully reproduce the mold cavity shape) may be poor. Further, even when not for thermoforming, the rigidity of the sheet becomes too high, which may not be preferable in terms of flexibility and buffering properties.

  In the present invention, “thermal shrinkage stress” means that a polystyrene resin foamed biaxially stretched sheet is thermally shrunk using a “DN-type stress tester” manufactured by Nichi Kogyo Co., Ltd. according to ASTM D-1504. It means a numerical value (unit [MPa]) obtained by measuring the maximum load at the time and dividing the maximum load value by the cross-sectional area of the sheet before thermal shrinkage.

  The “stretching” of the polystyrene resin foamed biaxially stretched sheet of the present invention is not particularly limited with respect to the stretching ratio and the like as long as it has undergone a stretching process. The MD and TD stretch ratios of the polystyrene resin foamed biaxially stretched sheet of the present invention are preferably determined so that the average value of the thermal shrinkage stress of MD and TD falls within the above range. Preferably both MD and TD are 1.1 to 5.0 times, particularly preferably 2.0 to 3.0 times. Further, in order to achieve a surface state suitable for the application or for the purpose of shrinking at the time of secondary processing, the thermal shrinkage stress and the draw ratio may be greatly different between MD and TD to give anisotropy.

  The above draw ratio is the ratio of the length of the straight line written on the test piece of the polystyrene-based resin foamed biaxially stretched sheet before and after shrinkage. Specifically, the following formula, that is, the draw ratio = Y This means a value (unit [times]) calculated by / Z. In this formula, Y represents the length [mm] of a straight line drawn on MD and TD using a ruler and a writing instrument on a test piece of a polystyrene-based resin foamed biaxially stretched sheet, and Z is 140 ° C. The length [mm] of the straight line after the test piece is immersed and contracted in a silicone oil bath for 10 minutes is shown.

  The “foaming” in the polystyrene resin foamed biaxially stretched sheet of the present invention means a foaming ratio of 1.01 to 20 times and an average major axis of the cell of 10 μm to 5000 μm.

  The foaming ratio of the polystyrene resin foamed biaxially stretched sheet of the present invention is not particularly limited as long as it falls within the definition of “foaming” and can be selected according to the desired application, characteristics, etc. It is preferably 2.5 times. If it is less than 1.1 times, the sheet appearance, flexibility, cushioning, hand feeling, etc. will be reduced, and if it exceeds 2.5 times, the rigidity, appearance, surface uniformity, etc. of the sheet may be reduced. When the thickness is thin, the frequency of breakage from the sheet end increases, and continuous operation of biaxial stretching may become impossible. The expansion ratio is preferably 1.2 to 2.0 times, particularly preferably 1.3 to 1.7 times. The expansion ratio can be controlled by the type of foaming agent, particularly the blending amount, the resin temperature during foaming extrusion, the resin pressure, and the like.

  The expansion ratio (P) is the density (Q) of the foam sheet measured according to JIS K7222, and the density (R) of the foam material measured according to JIS K7112 D method (R). ), P = R / Q.

  Moreover, although it does not specifically limit about the size of a bubble cell, It is preferable to make an average major axis into 10-5000 micrometers, and it is especially preferable to set it as 100-3000 micrometers. The average aspect ratio (= average long diameter of bubbles / average short diameter of bubbles) is preferably 1 to 5, and particularly preferably 1 to 4.

  When there is a foam layer in the outermost layer or in the very vicinity of the surface, the average major axis may be set to 200 to 2000 μm, for example, for the purpose of obtaining a design-like surface appearance, surface uniformity, pearly luster and feel. The thickness is preferably 500 to 1000 μm. The average aspect ratio (= average long diameter of bubbles / average short diameter of bubbles) is preferably 1 to 4, and particularly preferably 1 to 2. The average major axis and the average aspect ratio are measured using photographs observed with an electron microscope from the direction perpendicular to the sheet surface. Therefore, the “average” in the “average major axis” and the “average aspect ratio” is a number average. When the expansion ratio, the average length of the bubble major axis, and the average aspect ratio are within the above ranges, good surface appearance, surface uniformity, pearly luster and feel can be obtained. In addition, it is possible to obtain a product having good mold reproducibility at the time of thermoforming and having a good appearance with no shading or bubble trace.

  On the other hand, when the foam layer is an inner layer, the average major axis and the average aspect ratio are measured using a photograph observed with an electron microscope with respect to a sheet cross section parallel to the sheet flow direction. In this case, the bubble cell has a flat shape due to stretching, and is different from the visual field shape described above. The size of the bubble cell is not particularly limited, but the average major axis is preferably 10 to 5000 μm, particularly preferably 100 to 3000 μm. The average aspect ratio (= average long diameter of bubbles / average short diameter of bubbles) is preferably 2 to 20, particularly preferably 2 to 10.

  Control of the size and shape of the bubble cell can be controlled by the type and blending amount of the foaming agent, particularly the resin temperature at the time of foaming extrusion, the resin pressure, particularly the MD, TD stretch ratio, and the like. Specifically, when the longitudinal draw ratio and / or the transverse draw ratio is increased, the average major axis is increased, and when the difference between the longitudinal draw ratio and the transverse stretch ratio is increased (anisotropy is increased), the average aspect is accordingly increased. The ratio also increases.

  The polystyrene resin foamed biaxially stretched sheet according to the present invention has a tensile elastic modulus measured according to JIS K7127 of 0.6 to 2.2 GPa, an impact strength of 200 kg · cm / cm or more, and tearing. The strength is preferably 2.5 N / mm or more, and the folding strength is preferably 200 times or more. By making all of the tensile modulus, impact strength, tear strength, and folding strength within the above ranges, even when thinning and lightening by biaxial stretching, the strength (impact strength, tear strength, bending strength) is also available. ). Therefore, cracking, tearing and the like are unlikely to occur during handling, and repeated use is possible. The tensile elastic modulus, impact strength, tear strength, and folding strength are defined by those measured by the methods of the examples.

  Particularly preferably, in terms of the above, the tensile modulus is 1.0 to 1.9 GPa, the impact strength is 300 kg · cm / cm or more, the tear strength is 3.0 N / mm or more, and / or the bending strength is 300. More than once.

In the polystyrene resin foamed biaxially stretched sheet according to the present invention, for example, for food use, a release agent may be applied before winding into a roll after biaxial stretching. The coating method is not particularly limited. For example, a dimethylsilicone emulsion containing a dimethylsilicone oil having a viscosity at 25 ° C. of 1,000 to 20,000 mm ² / s and an emulsifier, and a solid content concentration of about 0.1 to 5% by mass. A method in which the aqueous solution is coated with a spray coater, an air knife coater, a squeeze roll coater, a gravure roll coater, a knife coater or the like and dried with a hot air drier or the like is preferable. An antistatic agent may be mixed with the release agent, and the mixing ratio is preferably 30 to 80% by mass with respect to the total amount with the silicone oil (solid content).

  In the release agent, as long as the effect of the present invention is not impaired, an antistatic agent other than the above, an antiblocking agent, a viscosity modifier, an antifoaming agent, an ultraviolet absorber, an anti-coloring agent, Various additives such as antibacterial agents, pigments and dyes can be blended.

  The polystyrene resin foamed biaxially stretched sheet according to the present invention can be formed into a molded product such as a container or a tray by a thermoforming method. There is no limitation on the thermoforming method, and conventionally known methods such as a vacuum forming method, a pressure forming method, and a differential pressure forming method combining a vacuum forming method and a pressure forming method are exemplified. Among them, for example, the sheet is heated close to or in close contact with the hot plate by the compressed air pressure from the mold and the vacuum pressure from the hot plate side, and immediately after that, the compressed air pressure from the hot plate side and the mold side is used. A molded product with good mold reproducibility can be obtained by a hot plate heating type air pressure molding method in which a heated and softened sheet is pressed against a mold by the vacuum pressure.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to a following example, unless the summary is exceeded. As raw materials, commercially available products having the following properties are used, and the evaluation items of the polystyrene resin foamed biaxially stretched sheet and the molded product obtained from this sheet are as follows.

<Raw materials>
[(A) Polystyrene resin having no rubber component]
1. GPPS: Polystyrene for general use, manufactured by PS Japan Co., Ltd., trade name: HH102, temperature 200 ° C., load at 5 kg (hereinafter referred to as “MFR (200 ° C., 5 kg)”) is 3.5 g / 10 min. is there.
2. SC: Styrene-butyl acrylate copolymer PS Japan make, brand name: SC004, MFR (200 degreeC, 5 kg) is 6.5 g / 10min.

[(B) Polystyrene resin having a rubber component]
3. HIPS: high impact polystyrene manufactured by PS Japan, trade name: HT478, MFR (200 ° C., 5 kg) is 3.0 g / 10 min.
4). SIS: Styrene-isoprene-styrene block copolymer manufactured by Asahi Kasei Chemicals Corporation, trade name: AFX (R) i-350, MFR (200 ° C., 5 kg) is 8 g / 10 min.

[Antistatic agent]
5. Polymer type: polyether ester amide Sanyo Kasei Kogyo Co., Ltd., trade name: Pelestat NC6321, and the above HIPS at 15:85 (mass ratio), kneaded in a twin screw extruder and re-pelletized, 15% master It is a batch.
6). Surfactant: Alkylsulfonic acid salt type manufactured by Kao Corporation, trade name: Elest Master S-520, PS-based 20% by mass master batch type, registered product of Poly-Ekyo.
7). Polymer type: Potassium ion ionomer of ethylene / methacrylic acid copolymer, manufactured by Mitsui DuPont Polychemical Co., Ltd., trade name: ENTIRA MK400, registered by Poly-Ekyo.

[Foaming agent]
8). FA-1: Effervescent agent manufactured by Eiwa Kasei Kogyo Co., Ltd., trade name: Polyslen ES106, decomposition temperature 200 ° C., PS-based 10% by mass master batch type.
9. FA-2: Effervescent agent, manufactured by Eiwa Kasei Kogyo Co., Ltd., trade name: Polyslen ES405, decomposition temperature 155 ° C., PS-based 40% by mass master batch type, registered by Poly Sankyo.

<Evaluation items>
(1) Stretch stability When producing a polystyrene resin foamed biaxially stretched sheet having a multilayer structure under the conditions described in the Examples and Comparative Examples, the conditions such as the resin temperature become almost constant for 2 hours. Then, the sheet was visually observed for breakage.
○: No break once every 2 hours ×: One or more breaks during 2 hours

(2) Average value of heat shrinkage stress in longitudinal direction and transverse direction Test piece having a size of 10 mm × 100 mm from the foamed (or non-foamed) biaxially stretched (or unstretched) sheet obtained in Examples and Comparative Examples Were prepared for each sheet with 5 long sides of MD and 5 with long sides of TD. For these test pieces, the maximum load generated by heat shrinkage was measured at a set temperature of 180 ° C. using a “DN-type stress tester” made by Nichi Kogyo Co., Ltd. in accordance with ASTM D-1504. The value divided by the cross-sectional area was defined as the heat shrinkage stress (unit [MPa]). For MD and TD, the average value of 5 test pieces was determined, and the average value of heat shrinkage stress was determined from the average value of MD and TD.

(3) Tensile elastic modulus From the foamed (or non-foamed) biaxially stretched (or unstretched) sheet obtained in the examples and comparative examples, test piece type 2 (width 10 mm) is MD, TD in accordance with JIS K7127. Create 5 each, and use “Autograph DSS2000” manufactured by Toyo Seiki Co., Ltd. to obtain an average value by measuring at an initial clamp distance of 5 cm and a tensile speed of 10 mm / min. The tensile elastic modulus (unit [GPa]) was obtained.

(4) Impact strength Five test pieces having a size of 100 mm × 100 mm were prepared for each sheet from the foamed (or non-foamed) biaxially stretched (or unstretched) sheets obtained in the examples and comparative examples. The amount of energy (impact strength [kg · cm]) required to destroy the test piece was measured using a “puncture tester (the tip uses a 12.7 mm round spherical head)” manufactured by Toyo Seiki Co., Ltd. according to P8134. Read from the scale plate. The value obtained by dividing the amount of energy by the sheet thickness [cm] was used as the impact strength (puncture impact strength, unit [kg · cm / cm]), and the average value of the measured five test pieces was determined. When this value was 200 kg · cm / cm or more, the impact strength was determined to be good, and when it was less than 200 kg · cm / cm, it was determined to be inferior.
○: 200 kg · cm / cm or more ×: less than 200 kg · cm / cm

(5) Tear strength From the foamed (or non-foamed) biaxially stretched (or unstretched) sheets obtained in Examples and Comparative Examples, test pieces having a size of 50 mm × 64 mm were used, and the MD of each sheet was taken as the long side. Five were created with TD as the long side. An indication value when the test piece is torn using a “light load tear tester” manufactured by Toyo Seiki Co., Ltd., with a notch of 13 mm in length parallel to the long side from the center end on the short side (50 mm) side of these test pieces. The value obtained by dividing the indicated value by the thickness [mm] of the initial test piece was taken as the tear strength (unit [N / mm]). About MD and TD, the average value in five test pieces made into each long side was calculated | required, and the total average value was calculated | required from both average values. When this value was 2.5 N / mm or more, the tear strength was determined to be good, and when it was less than 2.5 N / mm, it was determined to be inferior.
○: 2.5 N / mm or more ×: less than 2.5 N / mm

(6) Folding strength From the foamed (or non-foamed) biaxially stretched (or unstretched) sheets obtained in the examples and comparative examples, test pieces having a size of 15 mm × 150 mm, and the MD of each sheet as the long side And 5 with TD as the long side. For these test pieces, using a “MIT weather resistance tester” manufactured by Toyo Seiki Co., Ltd. in accordance with JIS P-8115, bending until breaking occurs at a folding angle of ± 90 °, a bending speed of 175 rpm, and a load of 1 kg. The number of times was measured, and this number of times was defined as the bending strength (unit: times). For MD and TD, five average values were obtained, and the total average value was obtained from the average value of both. When this value was 200 times or more, the folding strength was determined to be good, and when it was less than 200 times, it was determined to be inferior.
○: 200 times or more ×: less than 200 times

(7) Surface resistance value From the foamed (or non-foamed) biaxially stretched (or unstretched) sheets obtained in Examples and Comparative Examples, five samples having a size of 100 mm × 100 mm were prepared, and the relative temperature was 23 ° C. Conditioned for 24 hours at 50% humidity. Next, in accordance with JIS K6911, the surface resistance value (unit: [Ω]) was used under the conditions of an applied voltage of 500 V and a measurement time of 60 seconds using “High Lester UP MCP-450 type (J box U type)” manufactured by Mitsubishi Chemical Corporation. ) Was measured and the average value was determined. In addition, these sheet samples were washed with running water at 60 ° C. for 3 minutes, wiped with clean paper, conditioned for 24 hours at 23 ° C. and 50% relative humidity, and then measured for surface resistance under the same conditions as before washing. The average value was obtained.

(8) Mold reproducibility MD, TD from three places (left end, center, right end) in the width direction of the foamed (or non-foamed) biaxially stretched (or unstretched) sheets obtained in Examples and Comparative Examples. A sheet sample was cut out so that the direction of the sheet was understood. These sheet samples were attached to a hot plate heating type pneumatic molding machine (“PK-450 type” manufactured by Kansai Automatic Molding Machine Co., Ltd.) with the following evaluation type, and the hot plate temperature was 128 ° C. when the sheet thickness was 0.11 mm. When 0.3 mm and 0.4 mm, 136 ° C., when 0.7 mm, 140 ° C., heating time 2.0 seconds (10 seconds when sheet thickness is 0.7 mm), heating pressure 1.0 kg / cm ² (≒ 0.10MPa), molding time 1.0 seconds, a molding pressure ^{3.0kg / cm 2 (≒ 0.29MPa)} , subjected to molding at a mold temperature of 60 ° C., to observe the sheet groove visually The maximum aperture ratio (unit: [none]) with good mold reproducibility was obtained. For each of MD and TD, the average value of the above three locations was determined, and the total average value was determined from the average value of both. When this value was 1.00 or more, the mold reproducibility was determined to be good, and when it was less than 1.00, it was determined to be inferior.
○: 1.00 or more ×: less than 1.00

[Evaluation type]
It is a drawing ratio evaluation mold having a rectangular shape, a long side (parallel to the sheet MD) of 200 mm, and a short side (parallel to the sheet TD) of 150 mm. A mold in which a number of grooves with different depths from 0.3 to 1.2 are provided in this rectangular plane with a drawing ratio (maximum depth of opening / width of opening) in increments of 0.1. The groove opening width is 10 mm, the groove length is 50 to 70 mm, and ten grooves are provided in each of MD and TD directions.

Example 1
<For non-food applications that do not mainly require antistatic properties>
After weighing out the resin composition and foaming agent master batch (hereinafter referred to as “(MB)”) in the proportions shown in Table 1 for both outer layers, and uniformly mixing with a ribbon blender to obtain a dry blend product And supplied to a tandem 115 mmφ extruder (manufactured by Ikekai Tekko Co., Ltd.) and melted at a cylinder temperature of about 190 ° C. On the other hand, for the inner layer, the resin composition in the ratio shown in Table 1 was weighed and uniformly mixed with a ribbon blender to obtain a dry blend, and then supplied to a vent type 65 mmφ extruder (manufactured by Plastic Giken Co., Ltd.). It melted at about 220 ° C.

  Sheets from the feed block & distribution block for 2 types and 3 layers (Pura Giken Co., Ltd.) and a 850 mm T-die (Pura Giken Co., Ltd .; coat hanger type) mounted on each of the extruders via a connecting conduit. And then rapidly cooled with a cooling roll set at 80 ° C. to obtain an unstretched foam sheet in which both outer layers are foam layers and the inner layer is a non-foam layer. The obtained unstretched foamed sheet was stretched about 2.5 times in the longitudinal direction and about 2.5 times in the transverse direction by a roll type longitudinal stretching machine and then a tenter transverse stretching machine, and the thickness was 0.11 mm and the width was 980 mm. The biaxially stretched foam sheet was wound into a roll. The stretching stability was good. The above (1) to (6) and (8) were evaluated, and the obtained results are shown in Table 1.

Example 2
<For non-food applications that mainly require antistatic properties>
The antistatic agent (MB) in the ratio shown in Table 1 for both outer layers was weighed and supplied to a vent type 65 mmφ extruder (manufactured by Plastic Giken Co., Ltd.), and melted at a cylinder temperature of about 220 ° C. On the other hand, for the inner layer, after weighing the resin composition and the foaming agent (MB) in the proportions shown in Table 1 and uniformly mixing them with a ribbon blender to obtain a dry blend product, the tandem 115 mmφ extruder (manufactured by Ikekai Tekko) The mixture was fed and melted at a cylinder temperature of about 190 ° C.

  A feed block and distribution block for two types and three layers (made by Pla Giken Co., Ltd .; a type having a different flow path from Example 1) and a T-die having a surface length of 850 mm (mounted on each of the extruders via a connecting conduit) Extruded into a sheet form from Plastic Giken Co., Ltd. (Coat Hanger Type) and quenched with a cooling roll set at 80 ° C. to obtain an unstretched foamed sheet in which both outer layers are non-foamed layers and inner layers are foamed layers. The obtained unstretched foamed sheet was stretched about 2.5 times in the longitudinal direction and about 2.5 times in the transverse direction by a roll-type longitudinal stretching machine and then a tenter transverse stretching machine, with a thickness of 0.3 mm and a width of 980 mm. The biaxially stretched foam sheet was wound into a roll. The stretching stability was good. The above (1) to (7) were evaluated, and the obtained results are shown in Table 1.

Example 3
<Mainly for food applications that do not require antistatic properties>
A biaxially stretched foam sheet was produced in the same procedure as in Example 2 except that the ratio of the resin composition and the foaming agent (MB) described in Table 1 were used (however, the cylinder temperature of the 65 mmφ extruder was about 200 ° C. did). The layer ratio was changed by changing the number of revolutions of the extruder. The stretching stability was good. Also, in order to impart releasability to the sheet, after transverse stretching, a 3% by weight aqueous solution of dimethyl silicone emulsion (“KM9738” manufactured by Shin-Etsu Chemical Co., Ltd.) is applied on one side with a spray coater and dried with hot air After drying with a machine, it was wound into a roll. The coating amount determined using a calibration curve prepared from a sheet with a known coating amount was 20 mg / m ² . About this roll, said (1)-(8) evaluation was performed and the obtained result was described in Table 1.

Example 4
<For food applications that mainly require antistatic properties>
A biaxially stretched foam sheet was produced in the same procedure as in Example 1 except that the resin composition, the antistatic agent (MB), and the foaming agent (MB) in the proportions shown in Table 1 were used. The stretching stability was good. In order to impart releasability to the sheet, the dimethyl silicone emulsion was applied in the same procedure as in Example 3, then dried and wound into a roll. The coating amount was 20 mg / m ² . About this roll, said (1)-(8) evaluation was performed and the obtained result was described in Table 1.

Example 5
For both outer layers, the resin composition in the proportions listed in Table 1, antistatic agent (potassium ionomer), and foaming agent (MB) were weighed and mixed uniformly with a ribbon blender to form a dry blend, and then the vent hole was blocked. It was supplied to a 65 mmφ extruder (manufactured by Plastic Giken Co., Ltd.) and melted at a cylinder temperature of about 190 ° C. On the other hand, for the inner layer, the composition and the foaming agent (MB) in the proportions shown in Table 1 were weighed and uniformly mixed with a ribbon blender to obtain a dry blend, and then the tandem 115 mmφ extruder (manufactured by Ikekai Tekko). The mixture was fed and melted at a cylinder temperature of about 190 ° C.

  Two types and three layers of feed block & distribution block (Pura Giken Co., Ltd.) of the same type as in Example 2 and a T-die (Pla Giken Co., Ltd.) with a surface length of 850 mm, mounted on each of the extruders via a connecting conduit. Made from a coat hanger type) and quenched with a cooling roll set at 80 ° C. to obtain an unstretched foamed sheet in which all layers consist of foamed layers. The obtained unstretched foamed sheet was stretched about 2.0 times in the longitudinal direction and about 2.3 times in the transverse direction by a roll type longitudinal stretching machine and then a tenter transverse stretching machine, and the thickness was 0.4 mm and the width was 980 mm. The biaxially stretched foam sheet was wound into a roll. The stretching stability was good. The above (1) to (7) were evaluated, and the obtained results are shown in Table 1.

Comparative Example 1
A biaxially stretched foam sheet composed of a foamed layer of all layers in the same procedure as in Example 5 except that the resin composition, antistatic agent (potassium ionomer), and foaming agent (MB) described in Table 2 were used. Manufactured. However, when the longitudinal magnification was increased to about 2.5 times while being stretched about 2.5 times in the transverse direction, sampling was stopped because a fracture occurred in the longitudinally stretched portion. The end of the sheet was torn at the longitudinally stretched portion. Therefore, evaluation was not carried out.

Comparative Example 2
A biaxially stretched foam sheet composed of an expanded foam layer in the same manner as in Comparative Example 1 except that the resin composition, antistatic agent (potassium ionomer), and foaming agent (MB) described in Table 2 were used. Manufactured. However, a biaxially stretched foamed sheet having a thickness of 0.4 mm and a width of 980 mm was wound in a roll shape with the draw ratio being about 2.0 times in the vertical direction and about 2.3 times in the horizontal direction. The stretching stability was good. The above (1) to (7) were evaluated, and the obtained results are shown in Table 2.

Comparative Example 3
Except for using the resin composition and the foaming agent (MB) in the ratios shown in Table 2, the same procedure as in Example 3 was applied, and both the outer layer was a non-foamed layer and the inner layer was a foamed layer. A stretched sheet was prepared and sampled as it was without performing biaxial stretching. However, a polystyrene resin not containing a rubber component was used, and the cylinder temperature of the 65 mmφ extruder was about 220 ° C., and that of the 115 mmφ extruder was about 190 ° C. The sheets (1) to (6) and (8) were evaluated for this sheet, and the results obtained are shown in Table 2. Note that (5) tear strength was not measurable because the evaluation method described above could not tear the sheet completely. In addition, (8) during evaluation of mold reproducibility (pressure forming), the sheet was torn at the mold part on the outer periphery of the mold, and molding defects occurred.

Comparative Example 4
In the same procedure as in Example 4, a 0.7 mm-thick foam unstretched sheet in which both outer layers were foamed layers and inner layers were non-foamed layers was sampled without performing biaxial stretching. This sheet was evaluated in the above (1) to (8), and the obtained results are shown in Table 2. Note that (5) tear strength was not measurable because the evaluation method described above could not tear the sheet completely.

Comparative Example 5
A biaxially stretched sheet composed of all non-foamed layers was produced in the same procedure as in Example 3 except that only the resin composition in the proportion described in Table 2 was used. However, the cylinder temperature was about 220 ° C. for both the 65 mmφ and 115 mmφ extruders, and a non-foamed biaxially stretched sheet having a sheet thickness of 0.11 mm was wound into a roll. The stretching stability was good. These rolls were evaluated in the above (1) to (6) and (8), and the results obtained are shown in Table 2.

表１中、「ＰＨＲ」は、per hundred resin、即ち樹脂組成１００質量部に対する発泡剤（マスターバッチ）の混合量（質量部）を表す。実施例２で用いた高分子型帯電防止剤には、前記したようにＨＩＰＳを含有する。

In Table 1, “PHR” represents a per hundred resin, that is, a mixing amount (parts by mass) of a foaming agent (master batch) with respect to 100 parts by mass of the resin composition. The polymer type antistatic agent used in Example 2 contains HIPS as described above.

From the above Tables 1 and 2, the following became clear.
(1) A polystyrene resin foamed biaxially stretched sheet having a laminated structure in which a non-foamed layer and a foamed layer were coextruded and costretched was excellent in stretching stability (see Examples 1 to 4). In addition, a polystyrene resin foamed biaxially stretched sheet having a laminated structure in which the foamed layer / foamed layer / foamed layer were coextruded and costretched was also excellent in stretching stability (see Example 5).
(2) A polystyrene-based resin foamed biaxially stretched sheet having a laminated structure in which the sheet thickness, the rubber component content, and the average value of the heat shrinkage stress in the longitudinal direction and the transverse direction all satisfy the requirements specified in claim 5 The strength (impact strength, tear strength, folding strength) was excellent at the same time as moderate rigidity (see Examples 1 to 5).
(3) Moreover, the polystyrene-type resin-made foam biaxially stretched sheet of the said laminated structure had favorable mold reproducibility, and was excellent in the thermoforming use (refer Example 1, 3, 4).
(4) Even in the “foamed layer / foamed layer / foamed layer”, if the rubber component content is 0.1% or more and the draw ratio is lowered (about 2.0 times in the longitudinal direction and about 2.3 in the transverse direction) Times), the stretching stability was good, and the surface resistance value was sufficiently small and excellent (see Example 5).
In contrast, when the rubber component content is 0% and the stretching ratio is in the normal range (about 2.5 times in the longitudinal direction and about 2.5 times in the transverse direction), the stretching stability is poor and the sheet cannot be formed. (See Comparative Example 1). Also, even if the rubber component content was 0%, if the draw ratio was lowered (about 2.0 times in the longitudinal direction and about 2.3 times in the transverse direction), the sheet had a good stretching stability. The physical properties were extremely poor (see Comparative Example 2).
(5) It has a laminated structure in which a non-foamed layer and a foamed layer are coextruded, and even if the thickness of the sheet is within the range of claim 5, a polystyrene-based resin foam unstretched sheet without co-stretching is: The average value of the heat shrinkage stress in the longitudinal direction and the transverse direction is less than 0.1 MPa, the folding strength and impact strength are inferior, or the folding strength is low even if the rubber component content is within the range of claim 5. Not only was it inferior, it was easy to break or torn, but it was difficult to use repeatedly. In addition, molding failure occurred during thermoforming, or sufficient mold reproducibility could not be obtained, making it unsuitable for molding applications (see Comparative Examples 3 and 4).
(6) Biaxial stretching made of polystyrene resin having no foamed layer even if the sheet thickness, rubber component content, and the average value of the heat shrinkage stress in the longitudinal and transverse directions are within the range of claim 5 Since the sheet has too high rigidity (tensile modulus) and lacks cushioning and flexibility, the safety during handling is reduced (see Comparative Example 5).
(7) Even if it is a polystyrene resin foamed biaxially stretched sheet having a laminated structure, if it does not contain an antistatic agent, the surface resistance value becomes higher than the order of 13th power, and an antistatic property is required. It was unsuitable for only (see Example 3).

  A polystyrene resin foamed biaxially stretched sheet having a laminated structure according to the present invention and a molded product produced from this sheet as a raw material have moderate rigidity and excellent strength (impact strength, tear strength, folding strength), Since it has flexibility and buffering properties, and has an excellent sheet appearance depending on the layer structure, it is suitable for food, non-food-use paper substitute sheets, or for repeated use including a washing process. Moreover, since the mold reproducibility is excellent, it can be suitably used for containers, trays, three-dimensionally shaped articles, etc. regardless of food use or non-food use.

Claims (9)

  A foamed biaxially oriented sheet made of polystyrene resin, wherein at least one foamed layer and at least one non-foamed layer or foamed layer are laminated.   2. The polystyrene-based resin foamed product according to claim 1, wherein the non-foamed layer / foamed layer / non-foamed layer are laminated in this order, and the total thickness of both non-foamed layers is 1 to 70% of the total thickness. Axial stretched sheet.   2. The polystyrene-based foamed biaxially stretched sheet made of polystyrene resin according to claim 1, wherein the foamed layer / non-foamed layer / foamed layer are laminated in this order, and the thickness of the non-foamed layer is 5 to 95% of the total thickness.   2. The polystyrene-based foamed biaxially stretched sheet made of polystyrene resin according to claim 1, wherein the foamed layer / the foamed layer / the foamed layer are laminated in this order, and the thickness of each foamed layer is 1 to 99% of the total thickness. 5. The polystyrene resin foamed biaxially stretched sheet according to any one of claims 1 to 4, wherein the following (1) to (7) are simultaneously satisfied.
(1) Sheet thickness is 0.05 to 1 mm
(2) The rubber component content of the sheet is 0.1 to 30% by mass.
(3) The average value of the heat shrinkage stress in the vertical and horizontal directions is 0.10 to 2.0 MPa.
(4) Tensile modulus measured according to JIS K7127 is 0.6 to 2.2 GPa
(5) Impact strength is 200 kg · cm / cm or more (6) Tear strength is 2.5 N / mm or more (7) Folding strength is 200 times or more The polystyrene-based foamed biaxially stretched sheet made of polystyrene resin according to any one of claims 1 to 5, wherein the surface resistance value measured in accordance with JIS K6911 is 10 ⁷ to 10 ¹³ Ω.   A molded article produced by a thermoforming method using the polystyrene resin foamed biaxially stretched sheet according to any one of claims 1 to 6 as a raw material.   A polystyrene resin composition containing a foaming agent and a polystyrene resin composition not containing a foaming agent are melt-kneaded in separate extruders and coextruded from a single die to form a sheet. 6. The method according to claim 1, wherein at least one non-foamed layer and at least one foamed layer are laminated by heating and co-stretching in a biaxial direction. A method for producing a polystyrene resin foamed biaxially stretched sheet according to any one of the preceding claims.   A polystyrene-based resin composition containing a foaming agent is melt-kneaded separately with at least two extruders and coextruded from one die to form a sheet, and the sheet is cooled and reheated to biaxially The foamed biaxial stretching made of polystyrene-based resin according to any one of claims 1 to 4, wherein only two or more foamed layers are laminated by co-stretching to each other. Sheet manufacturing method.