JP4979293B2 - Thermoplastic resin foam sheet and container made of this foam sheet - Google Patents

Description

The present invention relates to a foamed sheet made of thermoplastic resin and a container made of this foamed sheet. More specifically, not only the appearance is excellent, but also mechanical strength, heat resistance, and oil resistance are excellent, and trays, cups, bowls, dishes, boxes, and the like (hereinafter collectively referred to as containers). The present invention relates to a foamed sheet made of a thermoplastic resin suitable for the production of the above and a container made of this foamed sheet.

  Processed foods (lunch boxes, side dishes, frozen foods, etc.) marketed at supermarkets and convenience stores are usually sold in thermoplastic resin containers. Depending on the type of food, the purchaser may put the entire thermoplastic resin container stored in the microwave oven and cook it for cooking. Thermoplastic containers that contain food to be cooked have a beautiful appearance, heat resistance that does not deform when cooked by a microwave oven, and oil resistance that is not easily eroded by oils, seasonings, etc. Insulation is required to hold the container with bare hands even after being cooked in a microwave oven.

  Polystyrene resin containers with excellent moldability, mechanical strength, and manufacturing cost are inferior in heat resistance and oil resistance. Therefore, when food containing oil is stored and cooked in a microwave oven, the container deforms. There are drawbacks. For this reason, foamed sheets made from a resin obtained by copolymerizing styrene and methacrylic acid have been proposed (Patent Documents 1 and 2), but containers obtained from these foamed sheets have poor oil resistance. There is a disadvantage that the raw material cost increases.

On the other hand, containers made of polyolefin resin, particularly polypropylene resin, are excellent in heat resistance and oil resistance, but containers made of non-foamed sheets made of polyolefin resin are inferior in heat insulation, so holding the container with bare hands However, there is a disadvantage that burns may be caused by the stored items. For the purpose of eliminating this drawback, a polyolefin resin foam sheet having excellent heat insulation properties has been proposed (Patent Documents 3 to 5). However, these foamed sheets have larger bubbles than polystyrene-based resin foamed sheets, so the appearance is poor, and it is necessary to perform special treatment (such as electron beam crosslinking) when producing polypropylene resin foamed sheets. Therefore, there is a disadvantage that the manufacturing cost increases.
Japanese Patent Publication No. 5-79251 Japanese Patent Publication No. 6-89167 Japanese Patent Laid-Open No. 10-130412 Japanese Patent Laid-Open No. 11-5860 JP 2000-103893 A

In view of the above situation, the present inventors not only have excellent appearance but also have excellent mechanical strength, heat resistance, and oil resistance, eliminating the conventional drawbacks, and are made of a thermoplastic resin suitable for manufacturing containers. As a result of intensive studies aimed at providing a foam sheet and a container made of the foam sheet, the present invention has been completed. That is, the object of the present invention is as follows.
1. To provide a thermoplastic resin foam sheet having an excellent appearance.
2. To provide a thermoplastic resin foam sheet excellent in mechanical strength, heat resistance and oil resistance.
3. To provide a container made of the above-mentioned thermoplastic resin foam sheet and excellent in mechanical strength, heat resistance, oil resistance and the like.

In order to solve the above-mentioned problem, in the first invention, the total amount of two kinds of resin components of 50 to 95% by weight of a polystyrene resin (A) and 5 to 50% by weight of a polyolefin resin (B) is 100 parts by weight. In contrast, (c-1) styrene-butadiene-styrene block copolymer, (c-2) hydrogenated product of styrene-butadiene-styrene block copolymer, (c-3) styrene-isoprene-styrene block copolymer A compatibilizing agent selected from the group consisting of: (c-4) hydrogenated styrene-isoprene-styrene block copolymer; and (c-5) styrene-ethylene-propylene-styrene copolymer (C 3) to 30 parts by weight and a resin mixture in which 0.1 to 5.0 parts by weight of the nucleating agent (D) are blended, and (e-1) carbon dioxide, (e-2) nitrogen, and ( e 3) manufactured by tetrafluoroethane blowing agent selected from the group consisting of (E) extrusion molding in the presence of a, 1.1 to 2.5 times expansion ratio, thickness 0.3~1.5mm The tensile stress measured in accordance with JIS K7113 is 10 to 25 MPa in the MD direction, 7 to 15 MPa in the TD direction, and the tensile elastic modulus measured in accordance with ASTM-D790 is 400 in the MD direction. A foamed sheet made of a thermoplastic resin, which is a foamed sheet made of a thermoplastic resin having a viscosity of ˜900 MPa and 200 to 500 MPa in a TD direction, which satisfies the following requirements (1) and (2).
(1) A plurality of bubbles observed on a cut surface cut in a direction perpendicular to the foam sheet surface in parallel with the foam sheet extrusion direction (hereinafter referred to as MD direction),
(A) The ratio of the bubbles in which the longest part of the bubbles is in the range of 15 to 150 μm occupies 70% or more of all the bubbles that can be observed, and
(B) The ratio of the bubbles in which the shortest part of the bubbles is in the range of 15 to 75 μm accounts for 70% or more with respect to all the observed bubbles.
(2) A plurality of bubbles observed on a cut surface cut in a direction perpendicular to the MD direction (hereinafter referred to as TD direction) and perpendicular to the surface of the foam sheet,
(C) The ratio of the bubbles in which the longest part of the bubbles is in the range of 15 to 75 μm occupies 75% or more of all the observed bubbles, and
(D) The ratio of the bubbles in which the shortest part of the bubbles is in the range of 15 to 75 μm accounts for 75% or more with respect to all the observed bubbles.

In the second invention, there is provided a container made of a thermoplastic resin foam sheet, which is manufactured by a thermoforming method using the thermoplastic resin foam sheet according to the first invention as a raw material.

The present invention is as described in detail below, has the following particularly advantageous effects, and its industrial utility value is extremely great.
1. Since the foamed sheet made of a thermoplastic resin according to the first invention (hereinafter may be simply abbreviated as “foamed sheet”), the size distribution of the bubbles contained in the foamed sheet is in a specific narrow range. The shape of the bubbles is almost uniform and has a beautiful appearance.
2. Since the foamed sheet according to the first invention has a specific gravity smaller than that of the unfoamed sheet, the foamed sheet can be produced with less raw material than the unfoamed sheet, and the container formed from the foamed sheet is lightweight and easy to handle.
3. The foamed sheet according to the first invention is excellent in oil resistance and heat resistance because the resin mixture as a raw material combines the polystyrene resin (A) and the polyolefin resin (B) in a specific range.
4). The thermoplastic resin foam sheet container according to the second aspect of the invention (hereinafter sometimes simply referred to as “foam sheet container”) has a specific narrow range of distribution of the size of bubbles contained in the foam sheet container. Therefore, the gloss of the foam sheet container is not uneven and has a beautiful appearance.
5. Since the foam sheet container according to the second invention has a beautiful appearance and excellent heat resistance, it is suitable as a container for storing processed foods cooked with a microwave oven.

The foam sheet according to the first invention is made from a resin mixture containing a polystyrene resin (A), a polyolefin resin (B), a compatibilizing agent (C), and a nucleating agent (D), and the foaming agent is present. Thus, it is obtained by forming into a sheet by an extrusion method.

In the present invention, the polystyrene-based resin (A) refers to a polymer of a styrene-based monomer, a copolymer of a styrene-based monomer as a main component, and another monomer copolymerizable therewith. . Examples of the styrene monomer include alkyl-substituted styrenes such as styrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 4-ethylstyrene, 4-t-butylstyrene, 2,4-dimethylstyrene, Examples include α-alkyl-substituted styrenes such as α-methylstyrene and α-methyl-4-methylstyrene, and halogenated styrenes such as 2-chlorostyrene and 4-chlorostyrene. These styrenic monomers may be one kind or a mixture of two or more kinds.

Examples of the styrene monomer and other copolymerizable monomer, acrylic acid, methacrylic acid, acrylic acid _(C 1 ~C ₈₎ esters, methacrylic acid (C ₁ ~C ₈₎ esters, acrylonitrile, maleic anhydride Examples include acids, maleic acid, and derivatives thereof. Examples of acrylic acid (C ₁ -C ₈ ) esters include methyl acrylate, ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate. Examples of the methacrylic acid (C ₁ -C ₈ ) ester include methyl methacrylate, ethyl methacrylate, butyl methacrylate, and 2-ethylhexyl methacrylate. These other monomers may be one kind or a mixture of two or more kinds.

  The polystyrene resin (A) can be produced by a conventionally known production method. Examples thereof include a bulk polymerization method, a suspension polymerization method, an emulsion polymerization method, and a bulk-suspension polymerization method.

  The polystyrene resin (A) has a heat distortion temperature of 70 ° C. or higher, preferably 80 ° C. or higher, more preferably 85 ° C. or higher. Here, the heat distortion temperature refers to a value measured according to JIS K7207. The weight average molecular weight of the polystyrene resin (A) is preferably in the range of 200,000 to 400,000. Here, the weight average molecular weight refers to a molecular weight measured by gel permeation chromatography (GPC).

  In the present invention, the polyolefin-based resin (B) is an α-olefin homopolymer or other unsaturated monomer that can be copolymerized with the α-olefin (may be plural types) as a main component. Good) as a secondary component. Examples of the α-olefin include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene and the like. α-olefins are preferred, and propylene having 3 carbon atoms is particularly preferred. Examples of other unsaturated monomers that can be copolymerized include unsaturated organic acids such as (meth) acrylic acid, (meth) acrylic acid ester, maleic acid, or esters, anhydrides thereof, And unsaturated aliphatic cyclic olefins. Here, the copolymer may be a block copolymer, a random copolymer, a graft copolymer, or a composite thereof. These olefin polymers may be modified by chlorination, sulfonation, carbonylation or the like.

The polyolefin resin (B) preferably has a density of 0.90 to 0.96 g / cm ³ and a melt flow rate (MFR) measured in accordance with JIS K7210 of 0.5 to 20 g / 10 minutes. When the MFR is less than 0.5 g / 10 minutes, the fluidity is inferior and it is difficult to produce a foamed sheet. When the MFR exceeds 20 g / 10 minutes, when a foamed sheet container is produced from the foamed sheet by a thermoforming method, immediately before molding. Since the surface of the foamed sheet is melted by the heat treatment performed in (5) and the appearance of the obtained foamed sheet container is easily damaged, both are not preferable.

  The blending ratio of the polystyrene resin (A) and the polyolefin resin (B) is 50 to 95% by weight of the polystyrene resin (A) and 5 to 50% by weight of the polyolefin resin (B) (these two types). The total amount of the resin components is 100% by weight). When the proportion of the polystyrene resin (A) is less than 50% by weight, the distribution of the size of the bubbles cannot be controlled to a specific narrow range when producing the foamed sheet, and the appearance of the foamed sheet is inferior, 95% by weight. If it exceeds 1, the heat resistance and oil resistance will deteriorate, both of which are not preferred. Preferred in the above ranges are 60 to 85% by weight of polystyrene resin (A) and 15 to 40% by weight of polyolefin resin (B).

In the present invention, the compatibilizer (C) is a component for improving the mutual solubility of two types of resin components, that is, the incompatible polystyrene resin (A) and the polyolefin resin (B). Specific examples include the following. (C-1) Styrene-butadiene copolymer, hydrogenated product thereof, (C-2) Styrene-butadiene-styrene block copolymer, hydrogenated product thereof, (C-3) Styrene-isoprene-styrene block Copolymer, its hydrogenated product, (C-4) epoxy-modified styrene-butadiene copolymer, its hydrogenated product, (C-5) styrene-ethylene-propylene-styrene copolymer, (C-6) polypropylene -Graft-polystyrene copolymer, (C-7) styrene-maleic anhydride copolymer, (C-8) vinyl acetate / ethylene copolymer, (C-9) acrylic modified polytetrafluoroethylene, ( C-10) Polycarbonate-graft-polystyrene copolymer. Among these, (C-1) a styrene-budadiene copolymer, a hydrogenated product thereof, (C-2) a styrene-butadiene-styrene block copolymer, a hydrogenated product thereof, and the like are preferable.

The compounding amount of the compatibilizing agent (C) is in the range of 3 to 30 parts by weight with respect to 100 parts by weight of the total amount of the two types of resin components of the polystyrene resin (A) and the polyolefin resin (B). To do. When the blending amount is less than 3 parts by weight, the function as a compatibilizing agent is not exhibited. The above range is preferably 5 to 20 parts by weight, and particularly preferably 7 to 15 parts by weight.

In the present invention, the nucleating agent (D) is a component for creating a bubble start part and making it easy to control the size of bubbles in the foamed sheet within a predetermined range when the foamed sheet is produced from the molten resin. Examples of the nucleating agent (D) include silica, talc, a mixture of talc and titanium dioxide, citric acid, a mixture of citric acid and sodium bicarbonate, and the like. The nucleating agent (D) is preferably one having an average particle diameter of 1 to 10 μm, and the blending amount is the total amount of two types of resin components, that is, a polystyrene resin (A) and a polyolefin resin (B). It is set as the range of 0.1-5.0 weight part with respect to 100 weight part. When the blending amount is less than 0.1 parts by weight, the function as a nucleating agent is not exhibited. Neither is desirable because it tends to be a cause. The above range is preferably 0.2 to 4.5 parts by weight, and particularly preferably 0.3 to 3.0 parts by weight.

The nucleating agent (D) is preferably mixed with various resin additives to be described later, and then melt-kneaded and granulated, or dry blended with the obtained granular raw resin mixture. In the present invention, a master batch in which a large amount of the nucleating agent (D) is blended with a resin composition comprising a polystyrene resin (A) and / or a polyolefin resin (B) is prepared in advance. The compounding quantity of a nucleating agent (D) can be adjusted in the said range with the method of mix | blending with the resin composition which consists of a polystyrene-type resin (A) and a polyolefin-type resin (B).

When manufacturing the foam sheet which concerns on 1st invention, a foaming agent is made to exist in a raw material resin mixture. The foaming agent functions to generate bubbles in the obtained resin sheet and to control the expansion ratio according to the size of the bubbles, the density of the bubbles, and the like. The presence of the foaming agent in the raw material resin mixture depends on the form of the foaming agent at room temperature. (1) The foaming agent that is solid at room temperature is mixed with the above-mentioned various resins in the form of pellets, (2) The foaming agent that is liquid or gas at room temperature is injected into the molten raw material resin mixture, etc. Can exist.

Specific examples of the above-mentioned (1) foaming agent solid at room temperature include azodicarbonamide, P, P′-oxybis (benzenesulfonylhydrazide), N, N′-dinitrosopentamethylenetetramine, 5-phenyl-1, Organic foaming agents such as 2,3,4-tetrazole and organic acid metal salts, and inorganic foaming agents such as sodium hydrogen carbonate, a mixture of citric acid and sodium bicarbonate, and the like. Specific examples of the foaming agent (2) liquid or gas at room temperature include aliphatic hydrocarbons, alicyclic hydrocarbons, halogenated hydrocarbons, inorganic gas, water and the like. Examples of the aliphatic hydrocarbons include propane, butane, pentane, hexane, and heptane. Examples of the alicyclic hydrocarbons include cyclobutane, cyclopentane, and cyclohexane. Examples of the halogenated hydrocarbons include Chlorodifluoromethane, difluoromethane, trifluoromethane, trichlorofluoromethane, dichloromethane, dichlorofluoromethane, dichlorodifluoromethane, chloromethane, chloroethane, dichlorotrifluoroethane, dichloropentafluoroethane, tetrafluoroethane, difluoroethane, pentafluoroethane, trifluoro Ethane, dichlorotetrafluoroethane, trichlorotrifluoroethane, tetrachlorodifluoroethane, perfluorocyclobutane, etc. Te is carbon dioxide, nitrogen, such as air and the like. These foaming agents may be used alone or as a mixture of two or more. A solid foaming agent at room temperature and a liquid or gaseous foaming agent at room temperature can be used in combination. Among the above blowing agents, sodium hydrogen carbonate, a mixture of citric acid and sodium bicarbonate, butane, trichlorofluoromethane, dichlorofluoromethane, carbon dioxide, nitrogen and water are preferable.

The amount of foaming agent used varies depending on the type of foaming agent, the foaming ratio (foaming ratio) of the foamed sheet, etc., but the amount of the gas at normal temperature is 0.01 to 0.10 mol / l with respect to 1 kg of the resin mixture. It is preferable that the liquid or solid at room temperature is selected in the range of 0.5 to 5.0 parts by weight with respect to 100 parts by weight of the resin mixture. The higher the amount of foaming agent used, the higher the pressure in the bubbles and the combined effect of the lower bubble wall resistance against deformation due to the plasticizing action of the foaming agent. The magnification also increases.

The raw material resin mixture is filled with an antioxidant, a heat stabilizer, an ultraviolet absorber, a light stabilizer, a fluorescent brightener, a metal soap, a plasticizer, and a filler, as necessary, as long as the object of the present invention is not impaired. Various resin additives such as an agent, a reinforcing agent, a pigment, a dye, a flame retardant, and an antistatic agent can be blended.

A method for producing the foam sheet according to the first invention will be described. (1) When a foaming agent that is solid at room temperature is used, a mixture obtained by dry blending the above-mentioned various resins is melt-kneaded. When a liquid or gaseous foaming agent is used at room temperature, the raw material resin in a molten state is used. A step of injecting and kneading into the mixture to prepare a foamable mixture; (2) when the prepared foamable mixture is extruded from the die portion of the extruder into a sheet, a large number of fine closed cells inside the foamed sheet And a process of manufacturing a foam sheet. Any of the above steps can be performed using an extruder. The extruder may be either a single screw extruder or a twin screw extruder, and the die that can be attached to the tip of the extruder when extruding into a sheet shape may be any of a T die, a flat die, and a circular (circular) die.

In the case of a T die and a flat die, when passing through a water-cooled roll, in the case of a circular die, a thin film-like foam that is continuously extruded from a die lip when air is blown or a water-cooled ring is passed. It is preferable to quench the sheet. When the foamed sheet is not rapidly cooled, the bubbles contained in the foamed sheet are easily connected in a rosary shape, and a plurality of bubbles observed on the cut surface of the foamed sheet are unlikely to occupy a predetermined ratio within the above-described predetermined range. It is because it becomes easy to become a bad foam sheet. The surface temperature of the water-cooled roll or the water-cooled ring and the spraying temperature of the air are influenced by the take-up speed of the foamed sheet, but are preferably set to 20 to 30 ° C.

The foamed sheet produced by the above method has a foaming ratio of 1.1 to 2.5 times and a thickness of 0.3 to 1.5 mm.
It is preferable to be in the range. If the expansion ratio is less than 1.1 times, the heat insulation and impact resistance are inferior, and if the expansion ratio exceeds 2.5 times, the mechanical strength decreases and the size of a plurality of bubbles contained in the foam sheet. It is difficult to distribute the thickness in a specific narrow range, and the appearance is inferior. The foaming ratio preferable in the above range is 1.4 to 2.0 times. Further, when the thickness is less than 0.3 mm, the mechanical strength, impact resistance, heat insulation and the like are inferior, and when the thickness exceeds 1.5 mm, the size of the plurality of bubbles contained in the foam sheet is limited to a specific narrow range. In addition to being difficult to distribute, the use amount of the raw material resin mixture is increased and the production cost is increased. The preferred range is 0.4 to 1.2 mm.

According to the experiments by the present inventors, in order to achieve the object of the present invention, it is effective to adjust the size of the plurality of bubbles contained in the foamed sheet so as to be distributed in a specific narrow range. I found out. In addition, since it is difficult to accurately grasp all the sizes of the plurality of bubbles contained in the foam sheet, in the present invention, the foam sheet is parallel to the MD direction and perpendicular to the surface of the foam sheet. A method of observing a plurality of bubbles observed on two cut surfaces, that is, a cut surface parallel to the TD direction and a cut surface cut at right angles to the surface of the foam sheet, as described later. Adopted.

Since the shape of the bubbles contained in the foam sheet exhibits a three-dimensional shape, the shape (size) of the bubbles can be specified if the dimensions in the vertical direction, the horizontal direction, and the height direction can be grasped. However, from the cut surface cut in parallel with the MD direction, the dimensions of the plurality of bubbles in the vertical direction (MD direction) and the height direction (thickness direction of the foamed sheet) can be grasped. (Direction) dimensions cannot be grasped. In addition, from the cut surface cut in parallel with the TD direction, the dimensions of the bubbles in the horizontal direction (TD direction) and the height direction (thickness direction of the foam sheet) can be grasped, but the vertical direction (MD direction). The dimensions of cannot be grasped. Therefore, two cut surfaces cut in parallel with the MD direction and the TD direction were observed at different positions of the foam sheet. In addition, the cut surface cut | disconnected in parallel with the thickness direction of the foam sheet is not included in the method of observing the size of the bubbles. Including a cut surface cut in parallel to the thickness direction of the foam sheet is considered to be able to grasp the size of the bubbles more accurately, the foam sheet is usually a few mm thick, This is because it is difficult to cut parallel to the thickness direction.

The bubbles observed on the two cut surfaces vary widely. That is, there are one cut near the center of the bubble, one cut near the end of the bubble, etc., and the shape (size) of the bubble cross section changes depending on the cutting position. Further, in one bubble, it is practical to confirm the cut surface of the bubble by cutting the foam sheet parallel to the MD direction and observing the cut surface of the bubble, and then cutting the cut surface parallel to the TD direction. Impossible. Therefore, the present inventors measured a number of the longest and shortest portions of a plurality of bubbles observed on the cut surface obtained by cutting the foam sheet parallel to the MD direction and the TD direction and perpendicular to the foam sheet surface. Then, the distribution of the longest part and the shortest part of the bubbles was statistically processed from these measured values, and the sizes of the plurality of bubbles were estimated.

In order to achieve the object of the present invention, the foam sheet according to the first invention must satisfy the following requirements (1) and (2).
(1) A plurality of bubbles observed on a cut surface cut in a direction parallel to the MD direction and perpendicular to the surface of the foam sheet are: (a) a bubble whose longest portion is within a range of 15 to 150 μm. The ratio accounts for 70% or more with respect to all observable bubbles, and (b) the ratio of bubbles with the shortest portion of the bubbles within the range of 15 to 75 μm occupies 70% or more with respect to all the observed bubbles. .
(2) A plurality of bubbles observed on a cut surface cut in a direction parallel to the TD direction and perpendicular to the surface of the foam sheet, (c) a bubble whose longest portion is within a range of 15 to 75 μm The ratio accounts for 75% or more with respect to all the observed bubbles, and (d) the ratio of the bubbles whose shortest part of the bubbles is in the range of 15 to 75 μm is 75% or more with respect to all the observed bubbles. Occupy.

According to the experiments by the present inventors, the foam sheet according to the first invention has a plurality of bubbles observed on a cut surface cut in a direction parallel to the MD direction and perpendicular to the foam sheet surface. It was found that the bubbles having the longest portion in the range of 15 to 150 μm are required to occupy 70% or more of all the bubbles that can be observed {requirement (a) above}. In the foam sheet satisfying this requirement, since the longest part of the bubbles is concentrated and distributed in a narrow range of 15 to 150 μm, it seems that the bubbles are uniformly generated in an appropriate size when viewed from the whole foam sheet. Appears and has an excellent appearance. When the longest part of the bubbles is in the range of 15 to 150 μm and the amount of bubbles is less than 70% with respect to all the observable bubbles, the bubble size distribution becomes wide and the foam sheet is inferior in appearance. Moreover, when there are many air bubbles whose longest part is less than 15 micrometers, foaming of a foam sheet becomes inadequate and the heat insulation of a foam sheet does not improve. When there are many air bubbles whose longest part exceeds 150 μm, since there are many relatively large air bubbles, the appearance of the foam sheet is deteriorated, and thus the object of the present invention is not achieved.

The foam sheet according to the first aspect of the present invention has a plurality of bubbles observed on a cut surface parallel to the MD direction and perpendicular to the surface of the foam sheet, and the shortest part of the bubbles is in the range of 15 to 75 μm. It has been found that the ratio of the bubbles in the inside needs to occupy 70% or more with respect to all the observed bubbles {requirement (b) above}. In the foam sheet satisfying this requirement, since the shortest portion of the bubbles is concentrated and distributed in a narrow range of 15 to 75 μm, it seems that the bubbles are uniformly generated in an appropriate size when viewed in the whole foam sheet. Appears and has an excellent appearance. When the shortest part of the bubbles is in the range of 15 to 75 μm and the amount of the bubbles is less than 70% with respect to all the observable bubbles, the bubble size distribution becomes wide, so that the foam sheet is inferior in appearance. Moreover, when there are many air bubbles whose shortest part of a bubble is less than 15 micrometers, foaming of a foam sheet becomes inadequate and the heat insulation of a foam sheet does not improve. When there are many air bubbles in which the shortest portion of the air bubbles exceeds 75 μm, since there are many relatively large air bubbles, the appearance of the foam sheet is deteriorated and the object of the present invention is not achieved.

Further, in the foam sheet according to the first invention, a plurality of bubbles observed on a cut surface cut in a direction parallel to the TD direction and perpendicular to the surface of the foam sheet have a longest bubble range of 15 to 75 μm. It is necessary that the air bubbles inside account for 75% or more of all the air bubbles that can be observed {requirement (c) above}. In the foam sheet satisfying this requirement, since the longest part of the bubbles is concentrated and distributed in a narrow range of 15 to 75 μm, it seems that the bubbles are uniformly generated in an appropriate size when viewed from the whole foam sheet. Appears and has an excellent appearance. When the longest part of the bubbles is in the range of 15 to 75 μm and less than 75% of all the observable bubbles, the bubble size distribution is widened, so that the foam sheet is inferior in appearance. Moreover, when there are many air bubbles whose longest part is less than 15 micrometers, foaming of a foam sheet becomes inadequate and the heat insulation of a foam sheet does not improve. When there are many air bubbles whose longest part exceeds 75 micrometers, since there are many relatively large air bubbles, since the external appearance of a foam sheet worsens, the said objective of this invention is not achieved.

Furthermore, the foam sheet according to the first invention has a plurality of bubbles observed on a cut surface cut in a direction parallel to the TD direction and perpendicular to the surface of the foam sheet, and the shortest part of the bubbles is 15 to 75 μm. It is necessary that the ratio of bubbles in the range occupy 75% or more of all the observed bubbles {requirement (d) above}. In the foam sheet satisfying this requirement, since the shortest portion of the bubbles is concentrated and distributed in a narrow range of 15 to 75 μm, it seems that the bubbles are uniformly generated in an appropriate size when viewed in the whole foam sheet. Appears and has an excellent appearance. When the shortest part of the bubbles is in the range of 15 to 75 μm and the amount of the bubbles is less than 75% with respect to all the bubbles that can be observed, the bubble size distribution becomes wide, so that the foam sheet is inferior in appearance. Moreover, when there are many air bubbles whose shortest part of a bubble is less than 15 micrometers, foaming of a foam sheet becomes inadequate and the heat insulation of a foam sheet does not improve. When there are many air bubbles in which the shortest portion of the air bubbles exceeds 75 μm, since there are many relatively large air bubbles, the appearance of the foam sheet is deteriorated and the object of the present invention is not achieved. In the requirement (1) and the requirement (2), the range of the longest part of the bubbles and the ratio of the bubbles are different in order to achieve the object of the present invention. It is the result examined based on various experiments conducted.

A method for observing a plurality of bubbles contained in the foam sheet according to the first invention and a method for measuring / calculating the lengths of the maximum and shortest portions of the bubbles are as follows.
(I) In the case of (1), the procedure is as follows.
(I) The foamed sheet according to the first invention is cut as thin as possible in parallel with the MD direction and at a right angle to the surface of the foamed sheet from an arbitrary place using a sharp blade.
(Ii) An enlarged photograph is taken of the cut surface generated by the cutting with a scanning electron microscope (SEM). The magnification to enlarge is preferably such that 50 to 200 bubble cross sections can be observed from the enlarged photograph.
(Iii) The center of each elliptical bubble cross section that can be observed from this enlarged photograph is visually determined, and the longest and shortest portions of the line connecting the two points on the periphery of the bubble are measured with calipers. Then, the longest part and the shortest part are calculated by dividing the measured value by the magnification of the enlarged photograph.
(Iv) The position of cutting in the MD direction is changed, the above operations (i) to (iii) are repeated three times, and an average value thereof is calculated (unit: μm).

(II) In the case of (2), the procedure is as follows.
(V) The foamed sheet according to the first invention is cut as thinly as possible in parallel with the TD direction and at a right angle to the surface of the foamed sheet from an arbitrary place using a sharp blade.
(Vi) An enlarged photograph of the cut surface generated by cutting is taken with an SEM. The magnification to enlarge is preferably such that 50 to 200 bubble cross sections can be observed from the enlarged photograph.
(Vii) The center of each of the elliptical bubble cross sections that can be observed from this enlarged photograph is determined visually, and the longest and shortest portions of the line connecting the two points on the periphery of the bubble are measured with calipers. Then, the longest part and the shortest part are calculated by dividing the measured value by the magnification of the enlarged photograph.
(Viii) The above-mentioned operations (v) to (vii) are repeated three times by changing the cutting position in the TD direction, and the average value thereof is calculated (unit: μm).

In the above (iii) and (vii), an enlarged photograph of the cut surface is obtained by using an image processing apparatus in which image processing software (for example, product name: Image-Pro PLUS manufactured by Nippon Roper) is installed. The part and the shortest part can be measured and calculated. The ratio of bubbles was measured in (ii) and (vi) above with respect to the number of bubbles in which the longest and shortest portions of the bubbles calculated in (iv) and (viii) were within the predetermined range. It can be calculated by dividing by the number of bubbles in which the outline of the bubble cross section is all shown in the enlarged photograph (unit:%).

In the foam sheet according to the first invention, it is preferable that the size of the bubbles near the surface layer portion is concentrated and distributed in a predetermined range. That is, the following requirements (3) and (4) are satisfied.
(3) Among a plurality of bubbles observed on a cut surface cut in a direction parallel to the MD direction and perpendicular to the surface of the foam sheet, the foam is foamed from both surface layer portions of the foam sheet toward the center of the foam sheet. A plurality of bubbles observed up to a portion within 25% of the total thickness of the sheet, (e) the proportion of bubbles in which the longest portion of the bubbles is in the range of 15 to 150 μm More than 85%, and
(4) Among a plurality of bubbles that can be observed on a cut surface cut in a direction parallel to the TD direction and perpendicular to the surface of the foam sheet, the foam sheet from both surface layers of the foam sheet toward the center of the foam sheet A plurality of bubbles observed up to a portion within 25% of the total thickness of (f) The ratio of bubbles whose longest portion of the bubbles is in the range of 15 to 75 μm It accounts for over 85%.

According to the experiments by the present inventors, further, bubbles observed up to 25% or less of the total thickness of the foamed sheet from both surface layer parts of the foamed sheet toward the central part of the foamed sheet, It has been found that the appearance of the foam sheet is particularly affected. Therefore, when satisfying the requirements of the above (3) and (4), the bubbles contained in the visible foam sheet appear to be more uniform in an appropriate size. Appearance.

In the foam sheet according to the first invention, the bubble density in the plurality of bubbles observed on the cut surface of (1) is 80 / mm ² or more, and is observed on the cut surface of (2). The bubble density in the plurality of bubbles is preferably 170 / mm ² or more. A foam sheet having a cell density that satisfies the above range is further excellent in heat insulation and appearance. The bubble density can be calculated by dividing the bubble density from the number of bubbles in which the outline of the bubble can be observed by the actual area of the foamed sheet photographed in the magnified photograph (unit: pieces / mm ² ).

The foamed sheet according to the first invention is such that the distribution of the size of the bubbles is distributed in a narrow range as described above, and thus has excellent mechanical strength. The foamed sheet according to the first invention preferably has a tensile stress (unit: MPa) measured in accordance with JIS K7113 in the range of 10 to 15 MPa in the MD direction and in the range of 7 to 15 MPa in the TD direction. When the tensile stress in the MD direction is less than 10 MPa (or the tensile stress in the TD direction is 7 MPa), the foamed sheet itself and a molded product obtained by molding the foamed sheet are easily broken. On the other hand, if the tensile stress in the MD direction is higher than 25 MPa (or the tensile stress in the TD direction is 15 MPa), the moldability deteriorates, which is not preferable. More preferable ranges of the tensile stress are 12 to 20 MPa in the MD direction and 8 to 10 MPa in the TD direction.

The foamed sheet according to the first invention has a tensile modulus (unit: MPa) measured according to ASTM-D790 in the range of 400 to 900 MPa in the MD direction and in the range of 200 to 500 MPa in the TD direction. preferable. If the tensile modulus in the MD direction is less than 400 MPa (or the tensile modulus in the TD direction is 200 MPa), the foamed sheet itself and a molded product obtained by thermoforming the foamed sheet are liable to break. On the other hand, when the tensile elastic modulus in the MD direction is higher than 900 MPa (or the tensile elastic modulus in the TD direction is 500 MPa), the moldability deteriorates, which is not preferable. More preferable ranges of the tensile modulus are 400 to 700 MPa in the MD direction and 250 to 400 MPa in the TD direction.

A non-foamed film made of a thermoplastic resin can be laminated on at least one surface of the foamed sheet according to the first invention. When a non-foamed film made of a thermoplastic resin is laminated, mechanical strength, thermoformability, printability, appearance, oil resistance, and the like can be improved. The thermoplastic resin that is the raw material of the non-foamed film to be laminated includes polyolefin resin, polyester resin, polystyrene resin, modified polyphenylene ether resin, polyamide resin, polylactic acid resin, acrylic resin, polyvinyl chloride resin Examples thereof include resins and polycarbonate resins. The non-foamed film made of thermoplastic resin may be unstretched, uniaxially stretched or biaxially stretched, and may be subjected to secondary processing such as printing. The laminated film may be a single layer or a plurality of layers. The method of laminating the non-foamed film made of thermoplastic resin on the foamed sheet according to the first invention may be a conventionally known method. For example, (a) after the foamed sheet is produced, a separately prepared thermoplastic resin Examples thereof include a method of laminating a non-foamed film through a heating method or an adhesive, and (a) a method of extruding and laminating a non-foamed film made of a thermoplastic resin from a T-die directly on the surface of a foamed sheet. . The thickness of the non-foamed film made of thermoplastic resin is preferably 5 to 100 μm. If the thickness is less than 5 μm, the film formability tends to be impaired when molded into a foam sheet container to be described later, and the appearance is impaired. On the other hand, if the thickness exceeds 100 μm, the raw material cost increases. A more preferable thickness is 10 to 60 μm.

  The foamed sheet container according to the second invention can obtain the foamed sheet according to the first invention by a thermoforming method. Thermoforming methods include vacuum forming methods (matched mold forming method, straight forming method, drape forming method, plug assist forming method, plug assist / reverse draw forming method, etc.), pressure forming method (air slip forming method, snapback) Molding method, reverse draw molding method, plug-and-ridge molding method, ridge molding method, etc.).

EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to the following description examples. In the following description examples, the raw material resin, the resin for the surface layer film, the characteristics of the foamed sheet, and the evaluation method of the foamed sheet container are as described below. In the present invention, the density is a value measured according to JIS K6767, and the MFR is a value measured according to JIS K7210.

<Raw resin>
(1) GPPS: General-purpose polystyrene (manufactured by PS Japan, brand name: HH102, density 1.05 g / cm ³ , MFR 2.9 g / 10 min).
(2) PP-1: Polypropylene (manufactured by Nippon Polypro Co., Ltd., brand name: FY6C, density 0.90 g / cm ³ , MFR 2.4 g / 10 min).
(3) Compatibilizer: Hydrogenated styrene-based thermoplastic elastomer (manufactured by Asahi Kasei Co., Ltd., trade name: Tuftec H1052).
(4) Nucleating agent: Baking soda-citric acid (manufactured by Eiwa Kasei Co., Ltd., brand name: EE275).

<Resin for surface film>
(5) PP-2: polypropylene (manufactured by Nippon Polypro Co., Ltd., brand name: MA3, density 0.90 g / cm ³ , MFR 11 g / 10 min).
(6) HIPS: high impact polystyrene (manufactured by Toyo Styrene Co., Ltd., brand name: H350, density 1.05 g / cm ³ , MFR 8.3 g / 10 min).

<Characteristics of foam sheet>
(A) Thickness of foam sheet: Measured according to JIS K7130 using a dial gauge. In addition, the foam sheet of Example 4-Example 7 measured the thickness including a surface layer film.
(B) Foaming ratio of the foam sheet: Test pieces having a size of 50 mm × 50 mm were punched from the foam sheet with a cutting blade so as to be almost uniform in the width direction of the foam sheet, and three pieces were prepared for each foam sheet. Each cut specimen was measured for the specific gravity of the foamed sheet using an electronic hydrometer (Mirage Trading Co., Ltd., model: ED-120T), and the average value of the three specimens was calculated. It calculated by dividing by the above average value from the value of specific gravity when the obtained foamed sheet was not foamed (unit: times).
(C) Thickness of the surface layer film: Foamed sheet with an unused razor blade (made by Feather Safety Razor Co., Ltd., trade name: Feather High / Stainless Steel Double Blade, the same shall apply hereinafter) from any location in parallel with the TD direction, And it cut | disconnected as thinly as possible at right angles with respect to the foam sheet surface, and the cut surface produced by the cutting | disconnection was expanded 100 times using SEM (NEC Corporation, model: JSM-5200, the same hereafter). An enlarged photograph of the cut surface was taken, and the thickness of the surface film portion was measured with a caliper. This operation was performed three times while changing the position in the MD direction, and the three measured values were averaged and calculated according to the magnification of the enlarged photograph (unit: μm).

(d) Ratio of bubbles: A foam sheet is cut as thinly as possible in parallel with the MD direction (or TD direction) from an arbitrary position with an unused razor blade and perpendicular to the foam sheet surface. Then, an enlarged photograph of the cut surface, which was magnified 100 times, was taken using an SEM of the cut surface generated by cutting. For the enlarged photograph of the cut surface, after counting the number of bubbles that can completely observe the outline of the bubble cross section, the enlarged image of the cut surface is recognized by the image processing device, and the software installed in the image processing device ( The longest part and the shortest part of the bubbles were measured by Nippon Roper Co., Ltd. (trade name: Image-Pro PLUS). In the enlarged photograph of the cut surface, the longest and shortest portions of each bubble are within the range of 15 to 75 μm (15 to 150 μm for the largest portion of bubbles in the MD direction) with respect to the number of bubbles that can completely observe the outline of the bubble cross section. The ratio of bubbles in the air was calculated. This operation was performed three times while changing the position in the TD direction (or MD direction) for cutting, and the results of the three times were averaged (unit:%).

(E) Ratio of air bubbles in the surface layer portion: The foamed sheet is cut as thinly as possible in parallel with the MD direction from an arbitrary place using an unused razor blade and perpendicular to the surface of the foam sheet. The photograph which expanded the cut surface produced by the cutting | disconnection 100 times with SEM was image | photographed. Draw a line that divides the foam sheet cut surface shown in this enlarged photograph into four equal parts in the thickness direction, and in the foam sheet cut surface divided into four parts by the thickness direction, two places in the center Black paper was affixed on the top so that the cut surface of the foam sheet could not be seen. After that, it was carried out according to the above method (d) (unit:%).

(F) Bubble density: The foamed sheet is cut as thinly as possible from an arbitrary position in parallel with the MD direction (or TD direction) and at right angles to the surface of the foamed sheet using an unused razor blade. Using the SEM, an enlarged photograph of the cut surface, which was magnified 100 times, was taken using the SEM. With respect to the enlarged photograph of the cut surface, the number of bubbles that can completely observe the outline of the bubble cross section was counted and converted into the actual area of the cut surface of the foam sheet in the enlarged photo. This operation was repeated three times while changing the position in the TD direction (or MD direction) for cutting, and the average value of the three times was defined as the bubble density (unit: pieces / mm ² ).

(G) Tensile stress: The foamed sheet was measured according to JIS K7113. The test piece was a No. 2 type test piece. It can be determined that the tensile stress in the MD direction is 12 to 20 MPa and the tensile stress in the TD direction is 9 to 12 MPa, and the tensile stress in the MD direction is 10 to 12 MPa, or 20 to 25 MPa, and the tensile stress in the TD direction. Of 7 to 9 MPa or 12 to 15 MPa can be determined to be excellent, and the tensile stress in the MD direction or TD direction can be determined to be inferior in other ranges.

(H) Tensile modulus: The foamed sheet was measured according to JIS K7113. It can be determined that the tensile elastic modulus in the MD direction is 500 to 800 MPa and the tensile elastic modulus in the TD direction is 300 to 400 MPa, and the tensile elastic modulus in the MD direction is 400 to 500 MPa, or 800 to 900 MPa, TD direction. It can be determined that the tensile elastic modulus of 200 to 300 MPa or 400 to 500 MPa is excellent, and the tensile elastic modulus in the MD direction or TD direction is inferior to those in other ranges.
* In Comparative Example 4, the thickness of the foam sheet was not uniform, so the tensile stress and the tensile modulus could not be measured.

<Method for evaluating foam sheet container>
(I) Appearance: When the foam sheet container is visually observed, the surface is smooth and glossy, the surface is rough and the surface is poor, and the surface is rough and the surface is not glossy. Judged.
(J) Heat resistance: After holding the foam sheet container in glycerin heated to 110 ° C. for 15 seconds, the degree of deformation of the container is visually confirmed. Those that can withstand use as containers were evaluated as Δ, and those that could not function as a container because of large deformation were determined as ×.

(K) Oil resistance: Three test pieces each having a size of 50 mm in the MD direction and 10 mm in the TD direction were punched out with a cutting blade so as to be substantially uniform in the TD direction of the foam sheet. 0.02 g of edible oil (trade name: Coconut RK, manufactured by Kao Co., Ltd.) was uniformly applied to one surface of each of the cut test pieces excluding the portion from both ends in the MD direction to 20 mm. One end of the test piece in the MD direction was fixed, and a tensile load of 100 gf was applied to the other end. After leaving in this state for 8 hours, the test piece was visually checked, and all of the three test pieces were not cut or cracked. Each was judged.

[Manufacture of foam sheet]
<Example 1 to Example 3, Comparative Example 1 to Comparative Example 4>
The GPPS, PP-1, compatibilizer, and nucleating agent were weighed at the ratios shown in Tables 1 and 2, and uniformly mixed with a ribbon blender to obtain a thermoplastic resin mixture. This resin mixture was applied to a hopper of a 40 mmφ twin-screw extruder (model: RT-40-S2-36-L, L / D = 36, the same shall apply hereinafter) with a cylinder temperature set to 210 ° C. The mixture was melted and kneaded under the conditions of a screw speed of 60 rpm. Carbon dioxide was used as a foaming agent for the resin mixture in the molten state, injected and mixed from the middle of the extruder cylinder, and extruded under atmospheric pressure from a T die attached to the tip of the twin screw extruder. The thin-film thermoplastic resin foam sheet continuously extruded passes through a water-cooled roll (diameter 60 mm, surface length 600 mm, the same applies hereinafter) adjusted to 25 ° C., thereby rapidly cooling the foam sheet. The foamed sheet was taken up under the condition of 5 m / min and wound up into a roll. In addition, the surface temperature of the foam sheet just before a winding part was 40 degreeC.

<Example 4 to Example 7>
The GPPS, PP-1, compatibilizer, and nucleating agent were weighed in the proportions shown in Table 1, and uniformly mixed with a ribbon blender to obtain a thermoplastic resin mixture. Then, as a surface layer extruder, two 40 mmφ single-screw extruders (manufactured by GM Engineering, model: VGM40-25, L / D = 25), and as a core layer extruder, 40 mmφ twin screw One extruder was prepared, and the tips of these extruders were mounted on a two-kind three-layer feed block (model: Clawlene three-layer FGII feed block), and a T-die was mounted on the feed block. Next, the PP-2 single pellet was placed in one surface single screw extruder at a cylinder temperature of 230 ° C, and the HIPS single pellet was placed in the other surface single screw extruder at a cylinder temperature of 200 ° C. The resin mixture is supplied to each hopper in a twin-screw extruder for core layer at a cylinder temperature of 210 ° C. and melted. Further, carbon dioxide is used as a blowing agent for the resin mixture in the molten state. The mixture was injected and mixed from the middle of the cylinder, the extrusion amount of each extruder was adjusted so as to have the thickness shown in Table 1, and extruded into a sheet under atmospheric pressure. The foamed sheet made of two layers and three layers of thermoplastic resin extruded continuously is passed through a water-cooled roll adjusted to 25 ° C., thereby rapidly cooling the foamed sheet under the condition of a speed of 3.5 m / min. The foamed sheet which was taken up and wound up into a roll was obtained. In addition, the surface temperature of the foam sheet just before a winding part was 40 degreeC.

<Comparative Example 5>
The above GPPS, PP-1, compatibilizing agent and nucleating agent were weighed in the proportions shown in Table 2, and these were tandem extruder {first extruder (Plastics Engineering Laboratory Co., Ltd., model: RT-40-S2). -36-L, L / D = 36), second extruder (manufactured by Plastics Engineering Laboratory Co., Ltd., model: PG50-28, L / D = 28), and so on. The mixture was melt-kneaded under the conditions of a screw rotation speed of 96 rpm and a second extruder screw rotation speed of 47 rpm. A circular die attached to the tip of a tandem extruder by injecting and mixing from the middle of the first extruder cylinder using butane as a blowing agent for the above-mentioned polystyrene resin composition in the molten state and setting the cylinder temperature to 230 ° C. Extruded from (75mmφ) under atmospheric pressure, drawn into a mandrel at a speed of 3.5m / min, and blown at 25 ° C at 0.15m ³ / min. A foam sheet was obtained by cutting a sheet with a cutter. In addition, the surface temperature of the foam sheet just before a winding part was 40 degreeC.

<Comparative Example 6>
The PP-1 and the nucleating agent were weighed at the ratio shown in Table 2, and uniformly mixed with a ribbon blender to obtain a thermoplastic resin mixture. This resin mixture was supplied to a hopper of a 40 mmφ twin screw extruder having a cylinder temperature set to 230 ° C., and melt kneaded under the condition of a screw rotation speed of 60 rpm. Carbon dioxide is used as a blowing agent in the molten resin mixture, injected and mixed from the middle of the extruder cylinder, and extruded under the atmospheric pressure from a circular die (75 mmφ) attached to the tip of the twin-screw extruder. While taking up the mandrel at a condition of .5 m / min, blowing air at 30 ° C. at 0.15 m ³ / min to the inside of the mandrel, stretching and cooling to obtain a cylindrical foam sheet, which is foamed by cutting it with a cutter A sheet was obtained. In addition, the surface temperature of the foam sheet just before a winding part was 40 degreeC.

<Comparative Example 7>
GPPS and talc masterbatch (manufactured by Dainichi Seika Co., Ltd., brand name: 0815N) are supplied to the hopper of the tandem extruder and melt kneaded under the conditions of the first extruder screw rotation speed of 96 rpm and the second extruder screw rotation speed of 47 rpm. I let you. In addition, the compounding quantity of the nucleating agent was 1 part by weight with respect to 100 parts by weight of GPPS including GPPS included in the talc masterbatch. A circular die attached to the tip of a tandem extruder by injecting and mixing from the middle of the first extruder cylinder using butane as a blowing agent for the above-mentioned polystyrene resin composition in the molten state and setting the cylinder temperature to 230 ° C. Extruded from (75mmφ) under atmospheric pressure, drawn into a mandrel at a speed of 3.5m / min, and blown at 25 ° C at 0.15m ³ / min. A foam sheet was obtained by cutting a sheet with a cutter. In addition, the surface temperature of the foam sheet just before a winding part was 40 degreeC.

[Manufacture of foam sheet containers]
The foamed sheets obtained in Examples 1 to 7 and Comparative Examples 1 to 7 were used in a batch type differential pressure molding machine (manufactured by Kansai Automatic Molding Machine Co., Ltd., model: PK450V), and 50 cm × 50 cm. It is fixed with a clamp of the size of, and heated from the top and bottom of the foam sheet for 15 seconds with a heater set at a set temperature of 300 ° C. It shape | molded by the pressure forming method (method to reduce pressure from the male die side).

From the above Tables 1 and 2, the following becomes clear.
(1) When the blending ratio of the raw material resin and the longest and shortest parts of the bubbles contained in the foamed sheet satisfy the requirements specified in claim 1, the appearance of the foamed sheet is beautiful and has an appropriate mechanical strength. Moreover, the container made from a foam sheet obtained by thermoforming this foam sheet is excellent in oil resistance and heat resistance (see Examples 1 to 7).
(2) On the other hand, when the blending ratio of the polystyrene-based resin (A) and the polyolefin-based resin (B) does not satisfy the requirements specified in claim 1, the size of the bubbles varies greatly. Mechanical strength and appearance are inferior compared to those of Comparative Example 1 (see Comparative Example 1, Comparative Example 6 to Comparative Example 7)
(3) Further, when the blending ratio of the compatibilizing agent (C) does not satisfy the requirement defined in claim 1, the size of the bubbles is greatly varied. Compared to the examples, the mechanical strength and Appearance is poor (see Comparative Example 2).
(4) In addition, when the blending ratio of the nucleating agent (D) does not satisfy the requirements specified in claim 1, the size of the bubbles is greatly varied, and mechanical strength and appearance are compared with those of the examples. Is inferior (see Comparative Example 3).
(5) If the mixing ratio of the raw material resin satisfies the requirements specified in claim 1, but the distribution of the size of the bubbles contained in the foamed sheet does not satisfy the requirements specified in claim 1, The mechanical strength and appearance are inferior (see Comparative Example 5).

  The thermoplastic resin foam sheet according to the present invention is not only lightweight and excellent in appearance, but also excellent in mechanical strength, heat resistance, and oil resistance. Therefore, thermoforming such as vacuum forming method and pressure forming method. Various secondary molded products such as containers, trays, cups, bowls, dishes and boxes can be obtained by the method. Further, the foam sheet container obtained by the thermoplastic resin foam sheet according to the present invention by a thermoforming method such as vacuum forming method, pressure forming method, etc. is not only lightweight and excellent in appearance, but also mechanical strength, Excellent heat and oil resistance, suitable for containers for processed foods (such as bento, side dishes, and frozen foods) that contain pre-cooked food and are cooked by a microwave oven when eating. It is.

Claims (4)

(C-1) Styrene-butadiene-styrene with respect to 100 parts by weight of the total amount of two types of resin components of polystyrene resin (A) 50 to 95% by weight and polyolefin resin (B) 5 to 50% by weight. Block copolymer, (c-2) hydrogenated product of styrene-butadiene-styrene block copolymer, (c-3) styrene-isoprene-styrene block copolymer, (c-4) styrene-isoprene-styrene block A hydrogenated copolymer, and (c-5) a compatibilizer (C) selected from the group consisting of a styrene-ethylene-propylene-styrene copolymer, 3 to 30 parts by weight, and a nucleating agent (D) 0 the resin mixture .1～5.0 parts, which are formulated as a raw material, (e-1) carbon dioxide, (e-2) nitrogen, and, from the group consisting of (e-3) tetrafluoroethane Manufactured by Barre blowing agent (E) extrusion molding in the presence of a, 1.1 to 2.5 times expansion ratio, has a thickness of 0.3 to 1.5 mm, measured in accordance with JIS K7113 The tensile stress is 10 to 25 MPa in the MD direction, 7 to 15 MPa in the TD direction, and the tensile modulus measured according to ASTM-D790 is 400 to 900 MPa in the MD direction and 200 to 500 MPa in the TD direction. A foamed sheet made of a thermoplastic resin, which satisfies the following requirements (1) and (2):
(1) A plurality of bubbles observed on a cut surface cut in a direction perpendicular to the foam sheet surface in parallel with the foam sheet extrusion direction (hereinafter referred to as MD direction),
(A) The ratio of the bubbles in which the longest part of the bubbles is in the range of 15 to 150 μm occupies 70% or more of all the bubbles that can be observed, and
(B) The ratio of the bubbles in which the shortest part of the bubbles is in the range of 15 to 75 μm accounts for 70% or more with respect to all the observed bubbles.
(2) A plurality of bubbles observed on a cut surface cut in a direction perpendicular to the MD direction (hereinafter referred to as TD direction) and perpendicular to the surface of the foam sheet,
(C) The ratio of the bubbles in which the longest part of the bubbles is in the range of 15 to 75 μm occupies 75% or more of all the observed bubbles, and
(D) The ratio of the bubbles in which the shortest part of the bubbles is in the range of 15 to 75 μm accounts for 75% or more with respect to all the observed bubbles. The thermoplastic resin foam sheet according to claim 1, which satisfies the following requirements (3) and (4).
(3) Of the plurality of bubbles observed on the cut surface of (1) above, a portion within 25% of the total thickness of the foam sheet from both surface layer parts of the foam sheet toward the center of the foam sheet Among the plurality of bubbles observed so far, (e) the ratio of the bubbles having the longest portion of the bubbles in the range of 15 to 150 μm occupies 85% or more with respect to all the observed bubbles.
(4) Of the plurality of bubbles that can be observed on the cut surface in (2) above, from both surface layer portions of the foam sheet to the portion within 25% of the total thickness of the foam sheet toward the center portion of the foam sheet (F) The ratio of the bubbles in which the longest part of the bubbles is in the range of 15 to 75 μm occupies 85% or more of all the observed bubbles. A thermoplastic resin foam sheet comprising a thermoplastic resin non-foam film laminated on at least one surface of the thermoplastic resin foam sheet according to claim 1 . A container made of a foamed sheet made of thermoplastic resin, which is manufactured by a thermoforming method using the thermoplastic resin foamed sheet according to any one of claims 1 to 3 as a raw material.