JP2005238614A - Transparent sheet excellent in vacuum formability and formed product using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transparent sheet excellent in transparency and vacuum formability using a rubber modified styrenic polymer excellent in transparency, impact strength, and formability, and a formed product using it. <P>SOLUTION: The transparent sheet is a multilayered sheet comprising multilayered constituent components and stretched in a multi-axial direction, and the surface layer has an orientation factor relaxing stress within a specified range. The surface layer comprises a styrenic polymer composed of a disperse phase using a rubbery elastomer if necessary and a continuous phase comprising a polymer containing a styrenic monomer unit and a (meth)acrylic ester monomer unit. An intermediate layer comprises a rubber modified styrenic polymer composed of a disperse phase comprising a rubbery elastomer and a continuous phase comprising a polymer containing a specific range of a styrenic monomer unit % and a (meth)acrylic ester monomer unit % and the rubbery elastomer is a styrenic polymer composed of 30-50 mass% of a styrenic monomer unit and 70-50 mass% of a butadiene monomer unit. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a sheet excellent in transparency and vacuum moldability, and a molded product thereof, using a rubber-modified styrene polymer excellent in transparency, impact strength, and moldability.

  As a material for a molded article for packaging, a vinyl chloride resin has been conventionally used that requires transparency. However, vinyl chloride resin is not only used for incinerator corrosion due to hydrogen chloride generated during incineration as waste, and for air pollution caused by hydrogen chloride released into the atmosphere, but also for dioxins generated in incinerators. It is considered as one of the causative substances, and due to such problems, a material replacing vinyl chloride resin has been demanded. As alternative materials that do not cause these problems, polycarbonate, transparent ABS, and the like have some results in the market, but both of them have the disadvantage of lacking practicality as alternative materials for high-priced and low-priced vinyl chloride resins. In addition, the material for the molded article for packaging electronic parts is required to have good rigidity and impact resistance, and a transparent, excellent impact strength, high rigidity, and low cost alternative material has been desired.

On the other hand, styrenic polymers exist as low-cost materials. Styrenic polymers have been widely used as molding materials for household goods, electrical products, packaging and the like because they are synthetic resins with excellent transparency, moldability, and rigidity. As the field of application expands, there has been a strong demand for improvement in impact strength of styrenic polymers.
In order to improve the impact strength of the styrene polymer, there is a styrene polymer containing a rubber-like elastic body as dispersed particles, that is, a rubber-modified styrene polymer, which is known as a transparent resin having an excellent balance. Also known is a technique for improving impact strength by blending polystyrene with a styrene-butadiene block copolymer. However, this styrenic polymer composition has the disadvantage that the styrene-butadiene block copolymer is cross-linked by the heat history during the molding process, so-called gel-like substance is generated, and the appearance of the molded product is deteriorated. . Furthermore, this styrenic polymer composition has a drawback that it is expensive. On the other hand, there are styrenic polymers containing rubbery elastic particles as dispersed particles, that is, rubber-modified styrenic polymers, which have been used in a wide range of fields due to their excellent stability under heat history and moldability. ing. These transparent resins are molded by various processing methods depending on the application, but when used for packaging materials such as electronic parts and foods, the resin material is made into a sheet in consideration of the economy and performance of the final product. There are many processing methods that become containers after thermoforming. In addition, these thermoforming processes are a process in which a pre-sheeted resin is shaped by heating and stretching, and there are several methods such as hot plate molding, pressure forming, and vacuum molding. For containers that require squeezing, plug-assisted vacuum forming, which is a combination of male action and vacuum forming, is often used.

  Of course, vacuum molded containers using transparent resins require molded products with good transparency, but even with rubber-modified styrenic polymers that satisfy the above performance balance, good molded products can be obtained. The problem is that the rubber particles in the molded product cause a sudden change in shape due to rapid stretching at the time, causing the surface of the molded product to become cloudy. A styrene-butadiene block copolymer having a specific lamellar structure is disposed on the surface layer. Although a multilayer sheet has been proposed, sufficient effects have not been obtained in terms of transparency reduction and thermal stability during recycling (see, for example, Patent Document 1).

JP-A-7-314611 (Claims 1 to 13)

  An object of the present invention is to provide a sheet and a molded product thereof that are transparent, excellent in impact strength, excellent in vacuum formability and excellent in vacuum formability, based on the above technical situation.

As a result of intensive studies to solve the above problems, the inventors of the present invention have excellent vacuum formability characterized in that the multilayer structure is a multilayer sheet composed of specific components and stretched in the multiaxial direction. The present inventors have found a transparent sheet and a molded product thereof and have completed the present invention.
That is, the present invention is a sheet characterized in that (1) a multilayer structure (A: surface layer, B: intermediate layer, C: surface layer) is composed of the following components, and is a multilayer sheet stretched in a multiaxial direction. And the sheet | seat characterized by the orientation relaxation stress of each surface layer (A, C) layer satisfy | filling the following relationship.
σM and σT are 1 MPa or less and 0.05 MPa or more, and the value of | σM−σT | ÷ | σM + σT | is 0.5 or less.
σM: longitudinal orientational relaxation stress (MPa) of surface layers (A, C)
σT: orientational relaxation stress (MPa) in the lateral direction of the surface layer (A, C)
In the surface layers (A, C), the dispersed phase composed of a rubber-like elastic body is 0 to 5 parts by mass, and 35 to 75% by mass of a styrene monomer unit and 65 to (meth) acrylic acid ester monomer unit. Styrenic polymer whose continuous phase which consists of a polymer containing 25 mass% is 100-95 mass parts (however, the sum total of a dispersion layer and a continuous layer is 100 mass parts).
In the intermediate layer (B), the dispersed phase composed of a rubber-like elastic body is 1 to 20 parts by mass, and 35 to 75% by mass of styrene monomer units and 65 to 25 (meth) acrylate monomer units. In a rubber-modified styrenic polymer having a continuous phase of 99 to 80 parts by mass composed of a polymer containing mass%, the rubber-like elastic body comprises 30 to 50 mass% of styrene monomer units and 70 to 70 mass parts of butadiene monomer units. (2) The refractive index of the transparent material used for the multilayer sheet at 25 ° C. is the refractive index of the material A = the refractive index of the material B ± 0.010, the refractive index of the material C = the material B (3) The sheet according to (1) or (2), wherein the multilayer sheet is stretched by a biaxial stretching method, (4) ) (1) ~ (3) any sheet (5) The molded product according to (4), wherein the molded product is a food packaging container, (6) The molded product is an electronic component packaging container ( 4) It is a molded article as described.

According to the present invention, it is possible to obtain a transparent sheet which is less deteriorated in appearance (transparency) even after being subjected to vacuum forming, excellent in sheet productivity and molding processability, and excellent in economic efficiency and recyclability.
The obtained transparent sheet excellent in vacuum formability is particularly suitable for food packaging containers and electronic component packaging containers.

The present invention is described in detail below.
The rubber-like elastic body used in the styrene polymer is a styrene-butadiene block copolymer. The rubber-modified styrenic polymer has good transparency and impact strength when the weight ratio of the styrene monomer unit to the butadiene monomer unit in the styrene-butadiene block copolymer is 30 to 50:70 to 50. Necessary for the balance. The styrene-butadiene block copolymer also needs to have a polystyrene part weight average molecular weight (Mw) in the range of 45,000 to 75,000. When Mw is less than 45,000 or exceeds 75,000, the rubber-modified styrenic polymer has poor transparency. Furthermore, the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is 1.20 to 1.80. Outside this range, the excellent transparency of the rubber-modified styrenic polymer cannot be obtained. In addition, the molecular weight of the polystyrene portion was determined using a styrene-butadiene block copolymer in the literature “RUBBERCHEMISTRY AND TECHNOLOGY”, Vol. 58, p. 16 (Y. Tanaka, et.al., 1985), polystyrene obtained by ozonolysis was measured by GPC, and the molecular weight corresponding to each peak was obtained from a calibration curve created using standard polystyrene. Calculated.

  A styrene-butadiene block copolymer is obtained by polymerizing a styrene monomer and a butadiene monomer under specific conditions in an organic solvent using an organic lithium compound as an initiator. Examples of organic solvents include aliphatic hydrocarbons such as butane, pentane, hexane, isopentane, heptane, octane, and isooctane, cycloaliphatic hydrocarbons such as cyclopentane, methylcyclopentane, cyclohexane, methylcyclohexane, and ethylcyclohexane, or benzene, toluene, Known organic solvents such as aromatic hydrocarbons such as ethylbenzene and xylene can be used. An organic lithium compound is a compound in which one or more lithium atoms are bonded in the molecule, such as ethyl lithium, n-propyl lithium, isopropyl lithium, n-butyl lithium, sec-butyl lithium, t-butyl lithium and the like. Can be used. And the weight average molecular weight (Mw) of the polystyrene part of a styrene-butadiene block copolymer is controlled by adjusting the addition amount ratio of the initiator with respect to the addition amount of a styrene monomer and a butadiene monomer. Further, the ratio (Mw / Mn) of the weight average molecular weight (Mw) of the polystyrene portion of the styrene-butadiene block copolymer to the number average molecular weight (Mn) is such as organic acids such as acetic acid and stearic acid, ethanol and butanol. It is controlled by adding a quenching agent such as alcohol or water while adjusting the amount used or the timing of addition during the polymerization.

  The rubber-like elastic body contained in the rubber-modified styrenic polymer is 1 to 15 parts by mass. If the rubber-like elastic body is less than 1 part by mass, an excellent impact strength cannot be obtained, and if it exceeds 15 parts by mass, the transparency and moldability deteriorate, which is not preferable.

  A styrene monomer that is a polymer unit that forms a continuous phase (hereinafter, a particle layer made of a rubber-like elastic body is called a dispersion layer, and a resin component that forms the other continuous layer is called a continuous layer) and ( The (meth) acrylic acid ester monomer will be described. Examples of the styrene monomer include styrene, α-methyl styrene, p-methyl styrene, pt-butyl styrene, and the like, preferably styrene. These styrenic monomers may be used alone or in combination of two or more. On the other hand, examples of the (meth) acrylic acid ester monomer include methyl methacrylate, ethyl methacrylate, methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-methylhexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, etc. Methyl methacrylate or n-butyl acrylate is preferable. These (meth) acrylic acid ester monomers may be used alone or in combination of two or more.

  The mass ratio of the styrene monomer unit forming the continuous phase of the rubber-modified styrene polymer and the (meth) acrylate monomer unit is 35 to 75:65 to 25, preferably 42 to 59. : 58-41. When the mass ratio of the styrene monomer unit to the (meth) acrylate monomer unit is outside the range of 35 to 75:65 to 25, the rubber-modified styrene polymer and the rubber-modified styrene resin composition are transparent. The transparency decreases when the recycled sheet is used.

  If necessary, a vinyl monomer copolymerizable with these monomers, for example, acrylic acid, methacrylic acid, acrylonitrile, N-phenylmaleimide, N-cyclohexylmaleimide and the like can be copolymerized. .

  As the rubber-modified styrene polymer, a bulk polymerization method, a solution polymerization method, a suspension polymerization method, an emulsion polymerization method and the like commonly used in the production of styrene polymers are used. In addition, either a batch polymerization method or a continuous polymerization method can be used. These polymerization methods include azo compounds such as azobisbutyronitrile and azobiscyclohexanecarbonitrile as polymerization initiators, benzoyl peroxide, t-butylperoxybenzoate, and t-butylperoxy-2-ethylhexanoate. Organic peroxides such as di-t-butyl peroxide, dicumyl peroxide, ethyl-3,3-di- (t-butylperoxy) butyrate can be used. In addition, t-dodecyl mercaptan, n-dodecyl mercaptan, 4-methyl-2,4-diphenylpentene-1 may be added as a molecular weight modifier, and butylbenzyl phthalate or the like may be added as a plasticizer, if necessary.

  Lubricants such as higher fatty acid metal salts and / or higher fatty acid esters and / or polyethylene wax can be added to the styrenic polymer as long as the performance is not impaired.

  It is possible to add other types of rubber-like elastic bodies to the styrene polymer as long as the transparency is not lowered. Examples of rubber-like elastic bodies with little decrease in transparency include styrene-butadiene-styrene copolymers (Tufprene 125: Asahi Kasei) and the like, which can be added without exceeding 10% by mass. If it exceeds 10% by mass, the rigidity of the material and the transparency will not be greatly reduced.

  The surface layer (A and C) of the multilayer sheet is 0 to 5 parts by mass of a dispersed phase composed of a rubber-like elastic body, 35 to 75% by mass of a styrene monomer unit, and a (meth) acrylate monomer unit. It is a styrenic polymer whose continuous phase consisting of a polymer containing 65 to 25% by mass is 100 to 5 parts by mass, preferably 0 to 4 parts by mass of the dispersed phase and 100 to 96 parts by mass of the continuous phase. Particularly preferably, the dispersed phase is 0 to 3 parts by mass and the continuous phase is 100 to 97 parts by mass. The resin compositions of the surface layers A and C may be the same or different as long as the surface layer conditions are satisfied.

  The method of processing into a sheet shape in the present invention is not particularly limited, and conventional methods such as a T-die method, a calender roll method, an inflation method, and a press molding method can be given. Also, the stretching method is not particularly limited, and the sheet is stretched by a plurality of processes including a biaxial stretching method such as a tenter method and a tubular method, a multiaxial stretching method such as blow molding, and further uniaxial stretching. Various conventional methods such as a method of making the direction multiaxial can be raised, but a biaxial stretching method is preferred.

  The multilayer structure referred to in the present invention is produced by superimposing different kinds of sheet materials, and the method for producing a sheet having a multilayer structure is not particularly limited, and a conventionally known multilayer sheet production method can be employed. . That is, the sheet of the present invention can be laminated with various resin molding apparatuses such as a sheet extruder having a feed block capable of simultaneously laminating and fusing with a calender apparatus or a T-die extruder, or a surface layer and an intermediate layer. Can be produced under ordinary sheeting conditions.

  In addition, the material of each constituent layer of the multilayer sheet molded body of the present invention includes an antioxidant, a weathering agent, a lubricant, a plasticizer, a colorant, an antistatic agent, in addition to the configuration that expresses the present invention described above. Or you may mix | blend additives, such as mineral oil, in the range which does not impair the performance of the rubber modified styrene resin composition of this invention. Regarding the timing of blending, any stage such as before the start of polymerization, during the polymerization reaction, after-treatment of the polymer, granulation of the polymer, molding, and processing can be appropriately selected.

  Various vacuum forming is suitably used for forming the packaging container in the present invention. Among them, in the deep drawing shape, a plug assist molding method capable of assisting shaping is often used. Examples of the molding method by plug assist include molding methods by plug assist forming, plug assist reverse draw forming, plug assist-air slip forming, and the like.

  At that time, the styrene polymer reinforced with rubber by the sea-island structure causes rapid elongation on the surface and whitening due to rapid cooling. If the dispersed phase composed of the rubber elastic bodies of the surface layers (A, C) exceeds 5 parts by weight, the molded product obtained for the above reasons is not preferable because it shows a significant decrease in transparency compared to the sheet molded product.

  In addition, scrap materials are generally returned in sheet production due to environmental friendliness, productivity and economy. In this case, in order to maintain the transparency of the final sheet, it is necessary to select materials having good compatibility with the transparent styrene resin (B) serving as the intermediate layer and having a refractive index close to the surface layers (A, C). . Actually, the continuous phase of the surface layer is a continuous layer composed of a polymer containing 35 to 75% by mass of styrene monomer units and 65 to 25% by mass of (meth) acrylate monomer units in the same manner as the intermediate layer. A styrenic polymer having a phase of 100 to 5 parts by mass is desirable.

In order to obtain a sheet excellent in vacuum formability and transparency, when the surface layers (A, C) are made by a biaxial stretching method, the orientation relaxation stresses of the surface layers (A, C) satisfy the following relationship: It is desirable to do.
σM and σT are 1 MPa or less and 0.05 MPa or more, and the value of | σM−σT | ÷ | σM + σT | is 0.5 or less.
σM: longitudinal orientational relaxation stress (MPa) of surface layers (A, C)
σT: orientational relaxation stress (MPa) in the lateral direction of the surface layer (A, C)

In order to suppress whitening after vacuum forming, the rubbery elastic body contained in the surface layers (A, C) is preferably 5 parts by mass or less, but at that time, the rubber is formed by orientation (biaxial stretching) at the sheet stage. A reinforcing effect that can be bent similarly to biaxially oriented polystyrene (OPS) or the like also appears on the surface layer with a small amount. These orientation relaxation stresses σM and σT are required to be 1 MPa or less and 0.05 MPa or more, but preferably 0.9 or less and 0.05 or more. When σM and σT are smaller than 0.05, the reinforcing effect by stretching is small. On the other hand, if σM and σT exceed 1, in the secondary processing (hot plate forming or the like) of the obtained sheet, the sheet shrinks greatly, which may cause problems in stable production.
Furthermore, the value of | σM−σT | ÷ | σM + σT | is 0.5 or less, but is preferably 0.3 or less. If this value is larger than 0.5, the anisotropy of the sheet is high and it is difficult to obtain a stable high strength.

  Further, different resin layers can be appropriately added to the intermediate layer of the multilayer sheet in the present invention as long as the required performance such as transparency and strength properties of the sheet is satisfied.

  The multilayer sheet excellent in vacuum formability and the molded product of the present invention are environmentally friendly because a transparent molded body can be obtained even if the surface layer and intermediate layer are recovered without being separated and recovered and melt molded. Used as a transparent sheet suitable for recycling.

  In addition, the molded product is suitably used in a wide variety of product fields in which vacuum forming is performed such as industrial parts such as IC magazines and carrier tapes, food packaging containers such as electronic parts packaging containers, ice creams, and cups for beverages.

  EXAMPLES Next, although an Example demonstrates this invention further, this invention is not limited to these examples. In the following description, “parts” and “%” mean “parts by mass” and “% by mass”, respectively.

  First, the production of styrenic polymers used in Examples and Comparative Examples will be described.

Styrene polymer-1
A monomer mixture of 58.5 parts of styrene, 36.0 parts of methyl methacrylate and 5.5 parts of n-butyl acrylate was added to a styrene-butadiene block copolymer A (styrene monomer unit content 40%, polystyrene part Mw 62,500). , Mw / Mn = 1.52) is dissolved, 0.04 part of benzoyl peroxide is added as a polymerization initiator, and 0.2 part of t-dodecyl mercaptan is added as a chain transfer agent. And heated for 8 hours, and then cooled to stop bulk polymerization. Subsequently, 0.2 part of dicumyl peroxide was newly added to the reaction mixture as a polymerization initiator. To 200 parts of pure water, 0.001 part of sodium dodecylbenzenesulfonate and 0.5 part of tricalcium phosphate were added as suspension stabilizers, and the mixed solution was dispersed while stirring. The mixture was subjected to heat polymerization at 100 ° C. for 2 hours, 115 ° C. for 3.5 hours, and 130 ° C. for 2.5 hours. After completion of the reaction, washing, dehydration and drying were performed to obtain a bead-like rubber-modified styrene polymer (copolymer-1). Next, the obtained bead polymer was extruded with a twin screw extruder (TEM-35B manufactured by Toshiba Machine Co., Ltd.) at a cylinder temperature of 220 ° C. to obtain a rubber-modified styrenic polymer (P-1). It was. The composition of P-1 is shown in Table 1. The material properties are shown in Table 2.

Styrene polymer-2
To a monomer mixture of 54 parts of styrene and 46.0 parts of methyl methacrylate, 0.04 part of benzoyl peroxide as a polymerization initiator and 0.2 part of t-dodecyl mercaptan as a chain transfer agent were added, and the mixture was stirred at 90 ° C. for 8 hours. After heating for a time, the bulk polymerization was stopped by cooling. Thereafter, the pellets were formed by extruding at a cylinder temperature of 220 ° C. using a bead-like modified styrenic polymer and a twin screw extruder (TEM-35B manufactured by Toshiba Machine Co., Ltd.) in the same manner as in the preparation of P-1. A rubber-modified styrenic polymer (P-2) was obtained. A styrene polymer (P-2) was obtained. The composition of the obtained P-2 is shown in Table 1, and the physical properties are shown in Table 2.

Styrene polymer-3
MS resin Denka TX polymer Trade name: TX-400-300L was used for the test as P-3. The composition of P-3 is shown in Table 1, and the physical properties are shown in Table 2.

Styrene polymer-4
39 parts of butadiene, 26 parts of styrene, 150 parts of pure water, 0.5 part of potassium oleate, 0.13 part of t-butyl hydroperoxide, 0.03 part of Rongalite, 0.002 part of ferrous sulfate, ethylenediaminetetraacetic acid Sodium salt 0.003 part Sodium pyrophosphate 0.1 part and t-dodecyl mercaptan 1.0 part were charged in an autoclave equipped with a stirrer and polymerized at a temperature of 45 ° C. for 17 hours. The number average particle diameter of the obtained styrene-butadiene rubber latex was 0.08 um. The latex was stabilized by adding 0.005 part of sodium sulfosuccinate. By adding a 0.2% aqueous solution of hydrogen chloride and a 2% aqueous solution of sodium hydroxide to the latex while stirring, the latex particles are coagulated and enlarged so as to maintain the pH of 8 to 9, and the number average particles A rubber latex having a diameter of 0.2 um was obtained. After adding 19.5 parts of styrene, 13.5 parts of MMA, 2 parts of n-butyl acrylate, 0.04 part of divinylbenzene, 0.5 part of t-butylphenol and 0.5 part of dilauryl thiopropionate to this latex. The copolymer was precipitated with hydrochloric acid, neutralized, washed, dehydrated and dried to obtain a powdery copolymer-2. Next, the copolymer 1 and the copolymer-2 are uniformly mixed at a ratio of 80/20 and extruded at a cylinder temperature of 220 ° C. with a twin-screw extruder (TEM-35B manufactured by Toshiba Machine Co., Ltd.). A modified rubber-modified styrenic polymer (P-4) was obtained. The composition of the obtained P-4 is shown in Table 1, and the physical properties are shown in Table 2.

Styrene polymer-5
Polystyrene resin (GPPS) Denkastyrol Trade name: MW-1-301 was used for the test as P-5. The composition of P-5 is shown in Table 1, and the physical properties are shown in Table 2.

Next, preparation of a multilayer stretched sheet will be described.
Using the above styrene resins (P-1 to P-5) as samples, a multilayer sheet having each configuration was prepared using a T-die type multilayer extrusion stretching machine. The multi-layer extruder consists of a single 65mmφ full-flight screw single screw extruder for the main core and one 40mmφ full-flight screw single screw extruder for the surface layer. A test extruder that was joined and multilayered was used. In addition, each cylinder temperature in sheeting was operated and molded at 230 ° C. In addition, the stretching conditions of the stretching (tenter method) were adjusted as needed so that the intended orientation state appeared, and film formation was performed.

Vacuum formed sheets were formed into the shape shown in FIG. 1 using a plug assist type vacuum forming machine manufactured by Asano. The sheet was attached to a vacuum forming machine so that the A layer side was on the plug side, and the forming conditions were that vacuum forming started when the sheet surface reached 120 ° C. by heating the sheet.

Recycling test Trial sheet was pulverized to a size that can be supplied to the extruder using a pulverizer, and a 65 mmφ full flight screw type extruder was operated as a single layer sheet at a cylinder temperature of 230 ° C. to obtain a 0.8 mm thick sheet. Created.
○: Good recyclability ×: Poor recyclability (white turbidity)

Each measurement method and judgment standard pellets were obtained by using, as a sample, a test piece obtained by injection molding at a cylinder temperature of 230 ° C. with an inline screw injection molding machine (IS-50EP manufactured by Toshiba Corporation). However, the above pellets were used for MFR. The measuring method of each composition value and each physical property value is as follows.
(1) Izod impact strength: Based on ASTM D256, a test piece having a thickness of 12.7 × 64 × 6.4 mm was provided with a notch having a depth of 2.54 mm and measured at an impact speed of 3.46 m / sec.
(2) MFR: Measured according to JIS K7210 at a temperature of 200 ° C. and a load of 5 kgf.
(3) Haze: measured in accordance with ASTM D1003 using a test piece of 30 × 90 × 2 mm thickness.
(4) Refractive index: Measured with a solid refractometer (RX-2000 manufactured by Atago Co., Ltd.) using a test piece having a thickness of 30 × 90 × 2 mm. (Measured at 25 ° C)
(5) Composition confirmation: The composition of the polymer was quantified for each component using a calibration curve prepared using a standard substance by pyrolysis gas chromatography.
(6) Wall thickness measurement: The total wall thickness was measured with a micrometer. Further, the thickness of each layer of the multilayer sheet was calculated by observing with an optical microscope after smoothing the cross section of the sheet with abrasive grains.
(7) Bending test: A sample sheet made by sheet extrusion was bent in two directions, the take-up direction and the anti-take-up direction, and the occurrence of cracks in the sheet was visually observed.
○: Good (no cracks)
X: Defect (with cracks)
(8) Container compression test: A vacuum-formed product was placed as shown in FIG. 2 and compressed from above to observe the occurrence of cracks.
○: Good (no cracks)
X: Defect (with cracks)
(9) Transparency of the cup-formed product: measured by visual observation.
○: Good (no cloudiness)
X: Defect (with surface haze)
(10) Amount of rubber-like elastic body of rubber-modified styrenic polymer: rubber-modified styrene-type obtained by infrared absorption spectrum method and weight ratio of styrene and butadiene of rubber-like elastic body previously obtained by infrared absorption spectrum method From the weight ratio of butadiene in the polymer, the amount of rubber-like elastic material in the rubber-modified styrene polymer was determined. The infrared absorption spectrum was measured using FTS-575C type manufactured by Nippon Bio-Rad Laboratories.
(11) The structural unit of the continuous phase in the rubber-modified styrene polymer and the rubber-free styrene polymer: The rubber-modified styrene polymer and the rubber-free styrene polymer are dissolved in toluene, and then centrifuged. The supernatant liquid was collected and methanol was added to precipitate a styrene- (meth) acrylic acid ester copolymer. This precipitate is dried, dissolved in deuterated chloroform, adjusted to a 2% solution and used as a measurement sample, ¹³ C is measured using FT-NMR (manufactured by JEOL, FX-90Q type), and styrene- (meta ) The structural unit of the continuous phase was determined from the peak area of the acrylate polymer.
(12) Measurement of orientation relaxation stress: According to ASTM D1504, σM and σT, which are the maximum values of orientation relaxation stress in the longitudinal (extrusion direction) and lateral direction of the sheet, were measured. A test piece cut out from a sheet to 20 × 135 mm was used.
In addition, the measurement of the orientational relaxation stress in the vertical and horizontal directions of the surface layer was evaluated by separately preparing a sheet with the same resin as that for forming the multilayer sheet with a single resin constituting the surface layer.

Examples 1 to 8
Using the materials of the styrene copolymers P-1 to P-4, sheets having the layer structure shown in Table 3 were prepared. Moreover, the obtained sheet | seat shape | molded the cup-shaped goods of FIG. 1 with the vacuum forming machine, and the evaluation result of these sheets and a molded article was shown in Table 3.

Comparative Examples 1-6
Sheets having the layer structure shown in Table 4 were prepared using materials of the styrene copolymers P-1, P-2, P-4, and P-5. The obtained sheets were molded into cup-shaped products shown in FIG. 1 using a vacuum forming machine, and the evaluation results of these sheets and molded products are shown in Table 4.

Sectional drawing of the molded article vacuum-formed is shown. The schematic of the compression test of the molded article vacuum-formed is shown.

Claims (6)

A multilayer structure (A: surface layer, B: intermediate layer, C: surface layer) is a multilayer sheet comprising the following components and stretched in a multiaxial direction, and each surface layer (A, A sheet characterized in that the orientation relaxation stress of C) satisfies the following relationship.
σM and σT are 1 MPa or less and 0.05 MPa or more, and the value of | σM−σT | ÷ | σM + σT | is 0.5 or less.
σM: longitudinal orientational relaxation stress (MPa) of surface layers (A, C)
σT: orientational relaxation stress (MPa) in the lateral direction of the surface layer (A, C)
In the surface layers (A, C), the dispersed phase composed of a rubber-like elastic body is 0 to 5 parts by mass, and 35 to 75% by mass of a styrene monomer unit and 65 to (meth) acrylic acid ester monomer unit. Styrenic polymer whose continuous phase which consists of a polymer containing 25 mass% is 100-95 mass parts (however, the sum total of a dispersion layer and a continuous layer is 100 mass parts).
In the intermediate layer (B), the dispersed phase composed of a rubber-like elastic body is 1 to 20 parts by mass, and 35 to 75% by mass of styrene monomer units and 65 to 25 (meth) acrylate monomer units. In a rubber-modified styrenic polymer having a continuous phase of 99 to 80 parts by mass composed of a polymer containing mass%, the rubber-like elastic body comprises 30 to 50 mass% of styrene monomer units and 70 to 70 mass parts of butadiene monomer units. A styrenic polymer comprising 50% by mass. The refractive index at 25 ° C. of the transparent material used for the multilayer sheet is that the refractive index of the material A = the refractive index of the material B ± 0.01 and the refractive index of the material C = the refractive index of the material B ± 0.010. The sheet according to claim 1. The sheet according to claim 1 or 2, wherein the multilayer sheet is stretched by a biaxial stretching method. A molded article obtained by using the sheet according to any one of claims 1 to 3. The molded article according to claim 4, wherein the molded article is a food packaging container. The molded article according to claim 4, wherein the molded article is an electronic component packaging container.

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