JP2005349591A - Polystyrenic biaxially stretched laminated sheet, molded product and container - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polystyrenic biaxially stretched laminated sheet excellent in film forming properties, transparency, oil resistance, heat resistance and appearance and well-balanced with strength, and a molded product. <P>SOLUTION: The polystyrenic biaxially stretched laminated sheet has a base material layer and the surface layer provided thereon. The resin composition of the surface layer is composed of a copolymer (A1), which comprises a styrenic monomer unit and a (meth)acrylic acid ester type monomer unit, and a copolymer (A2), which comprises the styrenic monomer unit and a carboxylic acid monomer unit and the base material layer comprises a copolymer which is composed of the styrenic monomer unit and the carboxylic acid monomer unit. The mass composition ratio other than the styrenic monomer unit in A1 and the mass composition ratio other than the styrenic monomer unit in A2 satisfy a specific condition and, in the Vicat softening point VA of the resin composition of the surface layer and the Vicat softening point VB of the copolymer of the base material layer, VB-VA is below 20°C. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

TECHNICAL FIELD The present invention relates to a polystyrene-based biaxially stretched laminated sheet and a molded article that are excellent in oil resistance, heat resistance, appearance, and balance in strength, and particularly relates to a sheet, molded article, and container useful for food packaging applications. Is.

Polystyrene biaxially stretched sheets are transparent, rigid and relatively inexpensive, and are therefore widely used as lightweight containers for food packaging. However, since these containers are inferior in heat resistance and oil resistance, they have not been used as a microwave heating application that has rapidly spread in recent years. As a means to solve this, a biaxially stretched styrene heat-resistant sheet using a copolymer comprising a styrene monomer unit and at least one monomer of acrylic acid, methacrylic acid, and maleic anhydride is proposed. However, when heated in a microwave oven in contact with food such as curry or yakiniku lunch in a molded container at a convenience store etc., there is a problem that the contact portion is whitened and deformed. However, it does not reach the level that satisfies the demands of the market in heat resistance and oil resistance.

Japanese Examined Patent Publication No. 3-67608

The present invention has been made in view of such circumstances, and has a film-forming property, transparency, oil resistance, heat resistance, excellent appearance, and a polystyrene-based biaxially stretched laminated sheet and molded body that are well balanced in strength. Is intended to provide.

２）下記の数５式の条件を満足することを特徴とする１）記載のポリスチレン系二軸延伸積層シート。

３）上記１）または２）記載のポリスチレン系二軸延伸積層シートにおいて、基材層を構成する共重合体（Ｂ）中のスチレン系単量体単位以外の成分が占める割合が３.５〜２０質量％であることを特徴とするポリスチレン系二軸延伸積層シート。
４）上記１）〜３）記載のポリスチレン系二軸延伸積層シートにおいて、その縦方向の配向緩和応力をσＭ、横方向の配向緩和応力をσＴとした場合、下記の数６式の条件を満足することを特徴とするポリスチレン系二軸延伸積層シート。

５）上記１）〜４）記載のポリスチレン系二軸延伸積層シートにおいて、総シート厚さに占める表層厚さの５％以上２５％以下であることを特徴とするポリスチレン系二軸延伸積層シート。
６）上記１）〜５）に記載のポリスチレン系二軸延伸積層シートを熱成形してなる成形品およびその食品包装容器。 As a result of intensive studies to solve the above-mentioned problems in the polystyrene-based biaxially stretched sheet, the present inventors have found a biaxially stretched laminated sheet characterized in that the laminated structure is composed of specific components, and a molded product thereof. The present invention has been completed. That is, the present invention is as follows.
1) Copolymer (A1) having a base material layer and a surface layer on at least one surface thereof, and the resin composition (A) of the surface layer comprising a styrene monomer unit and a (meth) acrylate monomer unit And a copolymer (A2) consisting of a styrene monomer unit and at least one monomer unit of acrylic acid, methacrylic acid, and maleic anhydride, and the base material layer is a styrene monomer unit And a copolymer (B) comprising at least one monomer unit of acrylic acid, methacrylic acid, and maleic anhydride, and a mass composition ratio (RA1) other than the styrenic monomer unit in A1 The mass composition ratio (RA2) other than the styrene monomer unit in A2 satisfies the condition of the following equation (4), and the Vicat softening point of the surface resin composition (A) is VA [° C.], the base material Vicat softening point of layer copolymer (B) If the B [° C.], polystyrene biaxially oriented laminated sheet characterized by VB-VA is less than 20 ° C..

2) The polystyrene-based biaxially stretched laminated sheet according to 1), which satisfies the following formula (5).

3) In the polystyrene-based biaxially stretched laminated sheet described in 1) or 2) above, the proportion of components other than the styrene-based monomer units in the copolymer (B) constituting the substrate layer is 3.5 to A polystyrene-based biaxially stretched laminated sheet characterized by being 20% by mass.
4) In the polystyrene-based biaxially stretched laminated sheet described in 1) to 3) above, when the longitudinal orientation relaxation stress is σM and the lateral orientation relaxation stress is σT, the following equation (6) is satisfied. A polystyrene-based biaxially stretched laminated sheet characterized by:

5) The polystyrene-based biaxially stretched laminated sheet described in 1) to 4) above, wherein the polystyrene-based biaxially stretched laminated sheet is 5% or more and 25% or less of the surface layer thickness in the total sheet thickness.
6) A molded product obtained by thermoforming the polystyrene-based biaxially stretched laminated sheet described in 1) to 5) above and a food packaging container thereof.

The present invention provides a styrene-based laminate sheet having a good balance between oil resistance, heat resistance, and excellent strength by combining a specific resin, a method for producing the same, and a container. The obtained container is particularly suitable for use as a lightweight container for food packaging.

The present invention is described in detail below.
The resin composition (A) of the present invention comprises a copolymer (A1) comprising a styrene monomer unit and a (meth) acrylate monomer unit, a styrene monomer unit, acrylic acid, methacrylic acid, And a copolymer (A2) comprising at least one monomer unit of maleic anhydride. Examples of the styrene monomer constituting the component (A1) include styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, ethylstyrene, p-t-butylstyrene, chlorostyrene, bromostyrene, and the like. However, styrene, α-methylstyrene, and particularly preferably styrene are preferable. These styrenic monomers may be used alone or in combination of two or more.

Examples of the (meth) acrylic acid ester monomer unit used in the present invention include methyl methacrylate, ethyl methacrylate, methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-methylhexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, and the like. Among them, methyl methacrylate is preferable. These (meth) acrylic acid ester monomers may be used alone or in combination of two or more.

Mass composition ratio (RA1) other than styrene monomer units in the copolymer (A1) constituting the resin composition (A) and mass composition other than styrene monomer units in the copolymer (A2) It is essential that the ratio (RA2) satisfies the condition of the following equation (1). The mass composition ratio referred to here is the mass expressed in mass% other than the styrene monomer units contained in the copolymer. If it is out of the range of the following formula 1, the compatibility of the copolymer (A1) and the copolymer (A2) is poor, the transparency is lowered, and the appearance is impaired. In the present invention, the mass composition ratios RA1 and RA2 are not particularly limited as long as the following Expression 7 is satisfied.

When the Vicat softening point of the resin composition (A) of the surface layer is VA [° C.] and the Vicat softening point of the copolymer (B) of the base material layer is VB [° C.], VB-VA is less than 20 ° C. However, preferably 3 ≦ VB−VA ≦ 15, more preferably 6 ≦ VB−VA ≦ 9. The mass ratio of (A1) / (A2) constituting the resin composition (A) is not particularly limited, but is preferably 10/90 to 90/10. Here, the Vicat softening point refers to the softening temperature of the resin measured according to JIS-K7206. The mechanism for expressing the oil resistance of the laminated sheet of the present invention is due to the fact that the laminated sheet is stretched at a stretching temperature suitable for the resin of the base material layer having a high Vicat softening point, so that the surface layer is not distorted. That is, the base material layer is oriented to express the strength as a sheet, and the surface layer contributes to oil resistance because no distortion occurs. Therefore, if 0 ≦ VB−VA <3, the difference between VB and VA is too small, and the surface layer may be distorted, and sufficient oil resistance may not be obtained. On the other hand, if VB-VA is 20 or more, oil resistance is exhibited, but the viscosity of the surface layer becomes lower than that of the base material layer, so that trouble may be caused particularly in the longitudinal stretching step of the production process. Specifically, when the film is formed at an appropriate temperature of the base material layer, the surface layer adheres to the roll, resulting in difficulty in film formation, or a striped pattern is formed on the sheet so that the appearance is too soft and adheres to the roll. The appearance of the sheet is inferior. On the other hand, if the film is formed at an appropriate temperature of the surface layer, the base material layer is too hard and the sheet breaks. Even if a sheet is obtained, when it is formed by hot platen molding, it is likely to be fused to the hot platen, or unevenness on the water droplets called rain drop is likely to occur. In addition, in this invention, VB-VA is less than 20 by adjusting a copolymer composition to a surface layer resin composition and a base material layer, and can satisfy 3 <= VB-VA <= 15 of a preferable range.

The proportion of components other than the styrene monomer units in the copolymer (B) constituting the base material layer is 3.5 to 20% by mass, and a preferable range is 6.0 to 15% by mass, and more preferable. A range is 8.0-12 mass%. If this value is low, the heat resistance level required in the market cannot be satisfied, and if it is high, the extrusion processability is significantly reduced, and acrylic acid and methacrylic acid cause a dehydration reaction in the extruder, causing gelation. Is generated in a large amount, deteriorating the appearance of the obtained sheet.

In the polystyrene-based biaxially stretched laminated sheet, when the orientation relaxation stress in the longitudinal direction is σM and the orientation relaxation stress in the transverse direction is σT, | σM−σT | ≦ 0.2 [MPa] must be satisfied, A preferable range is 0 ≦ | σM−σT | ≦ 0.1 [MPa], and a more preferable range is 0 ≦ | σM−σT | ≦ 0.02 [MPa]. The orientation relaxation stress here is measured using a test piece cut out from the sheet along the sheet extrusion direction (longitudinal direction) or the direction perpendicular to it (lateral direction), and can be measured according to ASTM D1504. When the difference between the orientation relaxation stresses in the vertical direction and the horizontal direction is large, there is a tendency that the strength against tearing in one direction tends to be weak because the directionality of the sheet exists strongly. This is thought to be because cracks tend to break up because they are low in strength, that is, concentrated in the direction of low orientation and grow easily.

The surface layer thickness in the total sheet thickness is desirably 5% or more and 25% or less, preferably 8% or more and 20% or less, and more preferably 10% or more and 15% or less. If the surface layer thickness is less than 5%, flow disturbance may occur at the resin interface, and the sheet appearance may be impaired. This is presumably because if the flow path of the surface layer resin in the mold is too narrow, the flow of the resin is not smooth, so that the interface is disturbed at the time of joining with the base layer resin. If the ratio of the surface layer thickness exceeds 25%, the surface layer that develops oil resistance is weak in terms of strength because of its low strain and no orientation, and transparent if the ratio of the surface layer thickness exceeds 25%. May decrease. As a result of intensive studies as described above, the ratio of the surface layer thickness to the total sheet thickness is preferably 5% or more and 25% or less. As a method for checking the layer ratio, for example, there is a method in which only the surface layer is colored, the laminated sheet after film formation is cut with a sharp blade such as a microtome, and the cross section is observed and measured with an optical microscope. For simplicity, the ratio of the discharge amounts of the base layer extruder and the surface layer extruder may be replaced with the layer ratio.

There is no restriction | limiting in particular about the manufacturing method of a polystyrene type biaxially stretched laminated sheet, The method currently used in manufacture of the conventional biaxially stretched laminated sheet is used. For example, a resin is melt-kneaded by an extruder, and a laminated sheet is produced by a multi-layer extrusion method using a multi-manifold die or a feed block, and then a sheet obtained by a stretching method such as a tenter method is longitudinally oriented. Then, the film is stretched in the transverse direction (biaxial stretching) and cooled. At this time, as a method for adjusting the temperature, there is a method in which water or oil refrigerant is circulated inside the roll and cooled by heat exchange during longitudinal stretching. It is preferable to use a sensor that automatically opens and closes a solenoid valve or the like depending on the difference from the set temperature when the temperature sensor senses the actual temperature. During transverse stretching, hot air heated by a heater is blown into the tenter to raise the ambient temperature, and by sensing the actual temperature of a temperature sensor such as a thermocouple, the heater is turned on / off depending on the difference from the set temperature. It is common to let them. The set temperature at the time of longitudinal stretching and transverse stretching is preferably set to a temperature at which the base layer resin can develop strength by orientation, specifically, a temperature 5-10 ° C. higher than the Vicat softening point VB of the base layer resin. At the same time, this temperature is a temperature at which it is difficult for the surface layer resin to be distorted, and oil resistance is also exhibited. Moreover, as a method for controlling the orientation relaxation stress, there is a method of changing the stretching set temperature or the line speed.

Polystyrene-based biaxially stretched laminated sheets can be used for antioxidants, lubricants, mold release agents, plasticizers, and pigments as necessary, so long as they do not impair the purpose of the present invention during melt kneading or raw material production. , Dyes, foaming agents, foam nucleating agents, inorganic fillers, antistatic agents, and other known additives can be contained.

As a method for obtaining a molded product from a polystyrene-based biaxially stretched laminated sheet, it can be obtained by using a commercially available general hot platen pressure forming machine. The molding machine to be used is preferably of a type that can set the time during which the sheet is pressed against the hot platen, the time for forming with pressure air, the time lag for switching from sheet pressure welding to pressure forming, the molding cycle, etc. It is described in Patent Document 1.

The Society of Polymer Science “Plastic Processing Technology Handbook”, Nikkan Kogyo Shimbun (1995)

Hereinafter, embodiments of the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples.

First, the manufacturing method of the resin compositions 1-16 used in the Example and the comparative example is shown.
Resin compositions 1-16
Henschel in the blending ratio shown in Table 1 from resin (A) -1 to copolymer composition (A1) -1-5 and copolymer (A2) -1-6 obtained from the following method After mixing with a mixer, pellets were obtained by melt-kneading using a twin-screw extruder (TEM 35B manufactured by Toshiba Machine Co., Ltd., cylinder temperature 230 ° C.) to obtain resin compositions 1-16. The Vicat softening points of the resin compositions 1 to 16 are shown in Table 1.

(1) Production of copolymer A1 Copolymer (A1-1)
After adding 70.4 kg of pure water and 300 g of tricalcium phosphate to a polymerization vessel having an internal volume of 200 liters and stirring, 76.0 kg of styrene, 4.0 kg of methyl methacrylate, and 267.2 g of benzoyl peroxide are added and sealed. The reaction was carried out for 6 hours at ° C. After cooling, it was neutralized, dehydrated and dried. As a result of analysis using pyrolysis gas chromatography, the methyl methacrylate mass composition ratio (RA1) was 5%.

Copolymer (A1-2)
  A copolymer was obtained in the same manner as in the copolymer (A1) -1, except that 64.0 kg of styrene and 16.0 kg of methyl methacrylate were used. As a result of carrying out the same analysis as above, the methyl methacrylate mass composition ratio (RA1) was 20%.

Copolymer (A1-3)
  A copolymer was obtained in the same manner as in the above copolymer (A1) -1, except that 44.0 kg of styrene and 36.0 kg of methyl methacrylate were used. As a result of conducting the same analysis as described above, the methyl methacrylate mass composition ratio (RA1) was 45%.

Copolymer (A1-4)
  A copolymer was obtained in the same manner as in the copolymer (A1) -1, except that styrene was 24.0 kg and methyl methacrylate was 56.0 kg. As a result of carrying out the same analysis as above, the methyl methacrylate mass composition ratio (RA1) was 70%.

Copolymer (A1-5)
A copolymer was obtained in the same manner as for the copolymer (A1) -1, except that 8.0 kg of styrene and 72.0 kg of methyl methacrylate were used. As a result of conducting the same analysis as described above, the methyl methacrylate mass composition ratio (RA1) was 90%.
(2) Production of copolymer (A2)

Copolymer (A2-1)
After adding 90.0 kg of pure water and 100 g of polyvinyl alcohol to a polymerization can having an internal volume of 210 liters and stirring, 49.0 kg of styrene, 1.0 kg of methacrylic acid, and t-butylperoxy-2-ethylhexa as a polymerization initiator. 55 g of noate, 10 g of ethyl-3,3-di (t-butylperoxy) butyrate and 45 g of α-methylstyrene dimer as a chain transfer agent were heated to 112 ° C. for 6 hours and then at 132 ° C. The polymerization was carried out while maintaining for 4.5 hours. The obtained beads were washed, dehydrated and dried, and then extruded to obtain a pellet-shaped resin. As a result of analyzing this using pyrolysis gas chromatography, the methacrylic acid mass composition ratio (RA2) was 2%.

Copolymer (A2-2)
A copolymer was obtained in the same manner as the copolymer (A2-1) except that the amount of styrene charged was 47 kg and the amount of methacrylic acid charged was 3 kg. As a result of conducting the same analysis as above, the methacrylic acid mass composition ratio (RA2) was 6%.

Copolymer (A2-3)
A copolymer was obtained in the same manner as the copolymer (A2-1) except that the amount of styrene charged was 45 kg and the amount of methacrylic acid was 5 kg. As a result of conducting the same analysis as described above, the methacrylic acid mass composition ratio (RA2) was 10%.

Copolymer (A2-4)
A copolymer was obtained in the same manner as the copolymer (A2-1) except that the amount of styrene charged was 42.5 kg and the amount of methacrylic acid charged was 7.5 kg. As a result of conducting the same analysis as above, the methacrylic acid mass composition ratio (RA2) was 15%.

Copolymer (A2-5)
A copolymer was obtained in the same manner as the copolymer (A2-1) except that the amount of styrene charged was 40.0 kg and the amount of methacrylic acid charged was 10.0 kg. As a result of carrying out the same analysis as described above, the methacrylic acid mass composition ratio (RA2) was 20%.

Copolymer (A2-6)
A copolymer was obtained in the same manner as the copolymer (A2-1) except that the amount of styrene charged was 37.5 kg and the amount of methacrylic acid was 12.5 kg. As a result of conducting the same analysis as described above, the methacrylic acid mass composition ratio (RA2) was 25%.

  Next, the manufacturing method of copolymer (B) -1-5 used in the Example and the comparative example is shown.

Copolymer (B) -1
A copolymer was obtained in the same manner as the copolymer (A2-1) except that the amount of styrene charged was 48.5 kg and the amount of methacrylic acid was 1.5 kg. As a result of conducting the same analysis as described above, the methacrylic acid mass composition ratio (RA2) was 3%.

Copolymer (B) -2
A copolymer was obtained in the same manner as for the copolymer (A2-1) except that the amount of styrene charged was 48.25 kg and that of methacrylic acid was 1.75 kg. As a result of carrying out the same analysis as described above, the methacrylic acid mass composition ratio (RA2) was 3.5%.

Copolymer (B) -3
A copolymer was obtained in the same manner as the copolymer (A2-1) except that the amount of styrene charged was 46.0 kg and the amount of methacrylic acid charged was 4.0 kg. As a result of carrying out the same analysis as described above, the methacrylic acid mass composition ratio (RA2) was 8%.

Copolymer (B) -4
A copolymer was obtained in the same manner as the copolymer (A2-1) except that the amount of styrene charged was 44.0 kg and the amount of methacrylic acid charged was 6.0 kg. As a result of carrying out the same analysis as described above, the methacrylic acid mass composition ratio (RA2) was 12%.

Copolymer (B) -5
A copolymer was obtained in the same manner as the copolymer (A2-1) except that the amount of styrene charged was 37.5 kg and the amount of methacrylic acid was 12.5 kg. As a result of conducting the same analysis as described above, the methacrylic acid mass composition ratio (RA2) was 25%.

Next, the measurement method and evaluation method in the present invention will be described below.

(1) Vicat softening point (Vicat softening point)
In accordance with JIS-K7206, each resin composition 1-16 and copolymer (B) -1-5 was used to mold an injection molded product having a thickness of 3.2 mm as a test piece, and then 23 ° C. × 50%. Left in a constant temperature and constant temperature room for 24 hours to adjust the condition, using a 5 kg weight, 50 ° C./hr. The temperature when the indenter entered 1 mm into the test piece was recorded. This was repeated three times and the average value was adopted.

(2) When forming a sheet from a T-die of a film-forming multi-layer extruder, it was possible to smoothly form a film where roll adhesion was extremely impossible, and the thickness accuracy of the obtained sheet was widened. Five points were measured at 10 cm intervals in the direction. Thickness accuracy (ratio between the difference between the maximum and minimum thickness values and the average thickness at each measurement point) exceeds 10% and is 30% or less. .

(3) Sheet Appearance The case where the corrugation phenomenon at the interface of the multilayer sheet obtained from the T-die of the multilayer extruder was remarkably poor was rated as x, the slightly inferior one as Δ, and the good one as ◯.

(4) Evaluation of transparency The haze of the sheet obtained in the examples described later is measured, the haze value is less than 1.5, and the haze value is 1.5 or more and less than 3.0. Zero or more was made x.

(5) Maximum orientation relaxation stress The maximum orientation relaxation stress in the sheet extrusion direction (longitudinal direction) and the direction perpendicular to it (transverse direction) according to ASTM D1504 using a biaxially stretched sheet of the copolymer of the examples described later. The value was measured.

(6) Evaluation of oil resistance Molding condition of fitting container for test evaluation A fitting container was obtained using a biaxially stretched sheet of a copolymer of Examples described later under the following conditions, such as a mold and molding conditions.
(I) Mold:
Top surface: 90 x 170 [mm]
Height: 50 [mm]
Mating surface: 120 × 200 [mm] (b) Molding conditions:
Molding machine: Manufactured by Kansai Automatic Molding Machine Co., Ltd. Pressurized vacuum molding machine Heater temperature: 145 [° C]
Mold temperature: 145 [° C]
Molding time: 15 [sec]
Pressure contact pressure delay: 0.8 [sec]
Pressure welding vacuum delay: 1.0 [sec]
Pressure welding time: 5.0 [sec]
Molding pressure time: 3.5 [sec]
As an evaluation of oil resistance, a 50 × 30 [mm] test piece was collected from the center of the top surface of the obtained container molded product and soaked in coconut oil at 90 ° C. (refined palm oil manufactured by Tsukishima Food Industry Co., Ltd.) for 5 minutes. And then visually observed for the presence or absence of cloudiness.
◎: Good ○: Slightly cloudy △: Cloudy ×: Large deformation and cracking

(5) Evaluation of heat resistance The container molded product obtained under the above molding conditions was visually observed for deformation of the container after being placed in a hot air dryer set at 110 ° C for 10 minutes.
○: Deformation is not known.
Δ: There is deformation, but the outer dimensions do not change much.
×: Deformated greatly and dimensions changed

(6) Evaluation of strength As an evaluation of strength, energy that drops a cone on the center of the top surface of the container molded product obtained under the above molding conditions and generates cracks ([J] = cone height [m] × cone weight) [Kg]) was measured, and this was taken as the drop drop strength. The portion of the cone that is in contact with the molded product is the same, and the mass can be changed. The tip of the cone is a hemisphere with a diameter of 15 mm. The height is increased in 1 cm increments until cracks occur, and a preliminary test is performed until the sheet breaks. When cracks occur in the sheet, the drop height is lowered by 1 cm, and when no cracks occur, the test of increasing the drop height by 1 cm is repeated. The average value measured 10 times was adopted as the measurement value.
◎: 50 [J] or more ○: 30 or more and less than 50 [J]
×: Less than 30 [J]

Example 1
The above-mentioned resin composition 2 is used for the surface layer and for the copolymer (B) -3 base material layer, and the resin co-extruded from the T-die of the multilayer extruder at 240 ° C., respectively, is set at a set temperature with a longitudinal stretching machine Multi-layer biaxial of each configuration of 2 types and 3 layers having a thickness of about 0.3 mm by stretching 2.2 times in the flow direction at 115 ° C. and then 2.2 times in the width direction at a set temperature of 115 ° C. with a horizontal stretching machine A stretched sheet was obtained. At this time, the discharge amounts of the base layer extruder and the surface layer extruder were adjusted so as to obtain a predetermined surface layer ratio. The difference between the orientation relaxation stress in the longitudinal direction and the orientation relaxation stress in the transverse direction of the obtained multilayer sheet | σM−σT |, the ratio of the surface layer thickness to the total sheet thickness, film forming property, sheet appearance, transparency, Table 2 shows the oil resistance, heat resistance, and falling strength of the container obtained by hot plate molding the obtained multilayer sheet at 135 ° C. It can be seen that the results are good and balanced for each evaluation item.

Examples 2 to 15 and Comparative Examples 1 to 9
It implemented similarly to Example 1 except having changed resin used for a surface layer and a base material layer.

Claims (7)

A substrate (A1) having a surface layer on at least one surface thereof and a resin composition (A) of the surface layer comprising a styrene monomer unit and a (meth) acrylate monomer unit; Consists of a copolymer (A2) comprising a styrene monomer unit and at least one monomer unit of acrylic acid, methacrylic acid, and maleic anhydride, and the base material layer is composed of a styrene monomer unit and acrylic. It consists of a copolymer (B) comprising at least one monomer unit of acid, methacrylic acid, and maleic anhydride, and in the mass composition ratio (RA1) other than the styrene monomer unit in A1 and in A2 The mass composition ratio (RA2) other than the styrene-based monomer unit satisfies the condition of the following formula 1, and the Vicat softening point of the resin composition (A) of the surface layer is VA [° C.] The Vicat softening point of the copolymer (B) is expressed as VB [ If a, polystyrene biaxially oriented laminated sheet characterized by VB-VA is less than 20 ° C..

The polystyrene-based biaxially stretched laminated sheet according to claim 1, wherein the following formula 2 is satisfied.

The ratio of the components other than the styrene monomer units in the copolymer (B) constituting the substrate layer is 3.5 to 20% by mass, according to claim 1 or 2, Biaxially stretched laminated sheet. In the polystyrene type biaxially stretched laminated sheet according to any one of claims 1 to 3, when the longitudinal relaxation stress is σM and the lateral relaxation stress is σT, A polystyrene-based biaxially stretched laminated sheet characterized by satisfying conditions.

5. The polystyrene-based biaxially stretched laminate sheet according to claim 1, wherein the surface layer thickness in the total sheet thickness is 5% to 25%. Laminated sheet. A molded product obtained by thermoforming the polystyrene-based biaxially stretched laminated sheet according to any one of claims 1 to 5. The food packaging container according to claim 6.