JP7470468B1 - Laminated Sheets and Thermoformed Products - Google Patents

Abstract

[Problem] To provide a laminated sheet having a small amount of drawdown and good moldability. [Solution] A laminated sheet (1) is formed by laminating a foamed layer (10) formed of a mixed resin of a polystyrene-based resin and a polyolefin-based resin, and at least one non-foamed layer (20) formed of a polystyrene-based resin or a polyolefin-based resin, and the foamed layer (10) contains at least one of biomass polyethylene and biomass polypropylene as a polyolefin-based resin. [Selected Figure] Figure 1

Description

The present invention relates to a laminated sheet and a thermoformed product.

Plastic containers such as packaging containers are generally manufactured by thermoforming plastic sheets. When a sheet is heated, thermal deformation causes the sheet to sag in the direction of gravity (a phenomenon known as drawdown). It is known that if the amount of drawdown (the amount by which the sheet sags in the direction of gravity due to thermal deformation) is large, the sheet is more likely to become wavy during molding, which can lead to defects in the appearance of the molded product, such as wrinkles.

Various methods for reducing the amount of drawdown have been studied. For example, Patent Document 1 discloses that for a laminated foam sheet having a polystyrene-based resin foam sheet layer and a high-impact polystyrene resin sheet layer, the maximum heat shrinkage load of these sheets is adjusted. It also discloses that the polystyrene-based resin foam sheet contains a polyphenylene ether resin.

Patent Document 2 also discloses that a laminated foam sheet is formed by laminating a biaxially stretched polypropylene resin film on a polypropylene resin foam sheet, and the heat shrinkage rate of the polypropylene resin film is adjusted.

Furthermore, Patent Document 3 discloses a method for manufacturing a vacuum molded body in which a thermoplastic resin sheet having an infrared reflective material or a line drawn with an infrared reflective ink is placed at the boundary between a thermoplastic resin sheet and a substrate adjacent to the thermoplastic resin sheet during molding.

JP 2012-035496 A JP 2002-086646 A JP 2011-189620 A

The techniques described in Patent Documents 1 and 2 require the use of a sheet with a specified heat shrinkage load or heat shrinkage rate, which limits the freedom of choice of sheet material. The method described in Patent Document 3 requires the installation of a member for reflecting infrared rays, which complicates the thermoforming process.

One aspect of the present invention aims to provide a laminated sheet or the like that has a wide range of material options, can be easily thermoformed, has a small amount of drawdown, and has good formability.

The laminated sheet according to aspect 1 of the present invention is a laminate of a foamed layer formed from a mixed resin of a polystyrene-based resin and a polyolefin-based resin, and at least one non-foamed layer formed from a polystyrene-based resin or a polyolefin-based resin, and the foamed layer contains at least one of biomass polyethylene and biomass polypropylene as the polyolefin-based resin.

The inventors discovered that in a laminate sheet, it is important to keep the bonding strength between the foamed layer and the non-foamed layer within an appropriate range in order to reduce the amount of drawdown, and from this perspective, they investigated the configuration of the laminate sheet, leading to the invention of a laminate sheet having the above-mentioned configuration.

In other words, the laminated sheet having the above-mentioned configuration has a foamed layer and a non-foamed layer laminated therein, and the non-foamed layer is formed of a resin of the same type as at least one of the polystyrene-based resin and the polyolefin-based resin contained in the foamed layer. In addition, a part of the resin forming the foamed layer is a resin different from that of the non-foamed layer. With this configuration, the bond strength between the foamed layer and the non-foamed layer is in an appropriate range where the amount of drawdown is not large. Therefore, with this laminated sheet, molding defects caused by drawdown can be reduced.

In addition, laminate sheets that achieve such small drawdown amounts can be formed using common polystyrene-based resins and polyolefin-based resins. This allows for a high degree of freedom in the selection of materials for the laminate sheets.

In addition, if the foam layer contains at least one of biomass polyethylene and biomass polypropylene as a polyolefin resin, this contributes to reducing carbon emissions throughout the entire product cycle of the laminate sheet.

In the laminate sheet according to aspect 2 of the present invention, in the above-mentioned aspect 1, the foam layer may contain biomass polyethylene as the polyolefin resin.

The laminate sheet according to aspect 3 of the present invention may be the same as that according to aspect 1 or 2, in which a first non-foamed layer formed of a polystyrene resin is laminated on a first surface of the foamed layer, and a second non-foamed layer formed of a polyolefin resin is laminated on a second surface of the foamed layer, which is different from the first surface.

In this configuration in which non-foamed layers are laminated on both sides of the foamed layer, regardless of the content of polystyrene-based resin and polypropylene-based resin in the foamed layer, at least one of the first non-foamed layer and the second non-foamed layer does not have an excessively strong bond with the foamed layer. This allows for a high degree of freedom in selecting the material for the foamed layer to reduce the amount of drawdown in the laminated sheet.

In the laminate sheet according to aspect 4 of the present invention, in the above aspect 3, the foam layer may have a polystyrene resin content of 30% by weight or more and 75% by weight or less.

According to the above configuration, the bond strength between the foamed layer and the first non-foamed layer can be set within an appropriate range for reducing the amount of drawdown. As a result, the amount of drawdown of the laminated sheet is reduced, and good moldability is obtained.

In the laminate sheet according to aspect 5 of the present invention, in aspect 3 or 4, the foam layer may have a polyolefin resin content of 15% by weight or more and less than 60% by weight.

According to the above configuration, the bond strength between the foamed layer and the second non-foamed layer can be set within an appropriate range for reducing the amount of drawdown. As a result, the amount of drawdown of the laminated sheet is reduced, and good moldability is obtained.

In the laminate sheet according to aspect 6 of the present invention, in any one of aspects 2 to 5, at least one of the first non-foamed layer and the second non-foamed layer may be peelable from the foamed layer by a 180° peel test method.

With this configuration, the bond strength between the foam layer and at least one of the first non-foamed layer and the second non-foamed layer is within a range appropriate for reducing the amount of drawdown. As a result, the amount of drawdown of the laminated sheet is reduced, and good moldability is obtained.

The thermoformed product according to aspect 7 of the present invention is a thermoformed product of the laminated sheet according to any one of aspects 1 to 6.

According to one aspect of the present invention, it is possible to provide a laminate sheet or the like that has a wide range of material options, a simple structure, a small amount of drawdown, and good moldability.

1 is a cross-sectional view showing a schematic layer structure of a laminate sheet according to one embodiment of the present invention.

One embodiment of the present invention will be described below. The laminate sheet according to this embodiment is made of a resin material, and has excellent formability in thermoforming due to its small drawdown amount. Thermoforming is a method of heating a laminate sheet and molding the laminate sheet in a state in which the resin material has been softened by heat. Examples of thermoforming methods include press molding and differential pressure molding. Examples of differential pressure molding methods include vacuum molding and pressure molding.

The laminate sheet according to this embodiment has a small amount of drawdown and good moldability. FIG. 1 is a cross-sectional view that shows a schematic layer structure of the laminate sheet 1 according to this embodiment. The cross section shown in FIG. 1 is a cross section in a direction perpendicular to the stretch direction of the laminate sheet 1. The stretch direction of the laminate sheet 1 is intended to be the MD (machine direction) direction, but is not limited to this, and may be, for example, the TD (transverse direction) direction, or any direction on the same plane as a virtual plane including the MD and TD directions.

As shown in FIG. 1, the laminate sheet 1 according to this embodiment is formed by laminating a foamed layer 10 and at least one non-foamed layer 20. The laminate sheet 1 has a first non-foamed layer 21 and a second non-foamed layer 22 as the non-foamed layer 20. Hereinafter, when the term "non-foamed layer 20" is used, it is intended to refer collectively to all the non-foamed layers that the laminate sheet 1 has.

(Foam layer)
The foam layer 10 is a sheet member formed from a mixed resin of a polystyrene resin and a polyolefin resin.

The polystyrene resin contained in the mixed resin may be a polymer of a styrene monomer, a copolymer mainly composed of a styrene monomer and other monomers copolymerizable with the styrene monomer, or the like. Examples of styrene monomers include styrene, alkyl-substituted styrenes, α-alkyl-substituted styrenes, and halogenated styrenes. These styrene monomers may be one type or a mixture of two or more types. HIPS (high impact polystyrene) may also be used as the polystyrene resin.

Examples of other monomers that can be copolymerized with styrene-based monomers include acrylic acid, methacrylic acid, acrylic acid esters, methacrylic acid esters, acrylonitrile, maleic anhydride, and maleic acid, or derivatives thereof. These other monomers may be one type or a mixture of two or more types.

Other resins contained in polystyrene-based resins include, for example, a mixture of polyphenylene ether and polystyrene.

When the polystyrene resin is HIPS, the HIPS may contain a styrene component and a rubber component, and the styrene component may be 65% by weight or more and 98% by weight or less, and the rubber component may be 2% by weight or more and 35% by weight or less. Such HIPS may be, for example, a random copolymer resin, a block copolymer resin, or a graft copolymer resin consisting of a styrene component and a rubber component, or a mixture containing two or more of these copolymer resins.

The polystyrene resin may be any one of the above-mentioned examples, or may be a mixture of two or more.

The polyolefin resin contained in the mixed resin may be a resin mainly composed of polyolefin, such as polyethylene (PE), polypropylene (PP), biomass polyethylene, or biomass polypropylene. Examples of polyolefin resins include olefin homopolymers, olefin random copolymers mainly composed of polyolefin, olefin block copolymers, and olefin graft copolymers. When the polyolefin resin is polyethylene or biomass polyethylene, it may be low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), or high-density polyethylene (HDPE).

The polyolefin resin may be any one of the above-mentioned examples, or may be a mixture of two or more.

The foam layer 10 preferably contains a biomass-derived resin such as biomass polyethylene or biomass polypropylene as a polyolefin resin. This configuration contributes to reducing carbon emissions throughout the entire product cycle of the laminated sheet 1. This also contributes to achieving, for example, Goal 13 of the Sustainable Development Goals (SDGs) advocated by the United Nations, "Take urgent action to combat climate change."

The foam layer 10 may contain components other than the polystyrene resin and the polyolefin resin. Examples of such components include a compatibilizer, a foaming agent, a foam nucleating agent, and a coloring component. The compatibilizer is not particularly limited as long as it is a substance that enhances the compatibility between the polystyrene resin and the polyolefin resin.

In one embodiment of the present invention, the compatibilizer improves the mutual solubility of polystyrene resins and polyolefin resins. Specific examples include the following. That is, examples of the compatibilizer include styrene-butadiene copolymers or hydrogenated products thereof, styrene-butadiene-styrene block copolymers or hydrogenated products thereof, styrene-isoprene-styrene block copolymers or hydrogenated products thereof, styrene-ethylene-propylene-styrene copolymers, polypropylene-graft-polystyrene copolymers, styrene-maleic anhydride copolymers, and vinyl acetate-ethylene copolymers. Among these, styrene-butadiene copolymers or hydrogenated products thereof, and styrene-butadiene-styrene block copolymers or hydrogenated products thereof are particularly preferred.

The foam layer 10 is formed by foaming the mixed resin described above. The foam layer 10 may contain a foaming agent and a foam nucleating agent for foaming the mixed resin. The type of foam nucleating agent is not particularly limited, and may be a conventional foam nucleating agent, and may have the function of promoting foaming of the mixed resin by the foaming agent when a gas such as carbon dioxide is added as a foaming agent to the mixed resin. The foam layer 10 may be foamed by a method other than the addition of such a foaming agent and foam nucleating agent.

The thickness of the foamed layer 10 is not particularly limited, but is preferably greater than the thickness of the non-foamed layer 20. With such a configuration, a laminated sheet 1 having excellent strength and moldability is obtained. The thickness of the foamed layer 10 may be, for example, 0.30 mm or more and 1.50 mm or less, or 0.50 mm or more and 1.50 mm or less.

(Non-foamed layer)
The non-foamed layer 20 is a sheet member made of a polystyrene-based resin or a polyolefin-based resin.

When there are two non-foamed layers 20, a first non-foamed layer 21 and a second non-foamed layer 22, as in the laminated sheet 1, the first non-foamed layer 21 and the second non-foamed layer 22 may be formed from different resin materials. For example, the first non-foamed layer 21 may be formed from a polystyrene-based resin, and the second non-foamed layer 22 may be formed from a polyolefin-based resin. In addition, both the first non-foamed layer 21 and the second non-foamed layer 22 may be formed from a polystyrene-based resin, or may be formed from a polyolefin-based resin.

The laminate sheet 1 may also have only one non-foamed layer 20. When the laminate sheet 1 has a single non-foamed layer 20, the single non-foamed layer 20 may be formed from either a polystyrene-based resin or a polyolefin-based resin.

The polystyrene resin forming the first non-foamed layer 21 may be the polystyrene resin exemplified as the polystyrene resin contained in the mixed resin forming the foamed layer 10. In this case, the polystyrene resin forming the foamed layer 10 and the polystyrene resin forming the first non-foamed layer 21 may be the same resin, or different resins of the same family. As an example of different resins of the same family, the polystyrene resin contained in the mixed resin of the foamed layer 10 may be a polymer of a styrene monomer, and the polystyrene resin forming the first non-foamed layer 21 may be HIPS.

The polyolefin resin forming the second non-foamed layer 22 may be a polyolefin resin exemplified as the polyolefin resin contained in the mixed resin forming the foamed layer 10. In this case, the polyolefin resin forming the foamed layer 10 and the polyolefin resin forming the second non-foamed layer 22 may be the same resin, or different resins of the same family. As an example of different resins of the same family, the polyolefin resin contained in the mixed resin of the foamed layer 10 may be polyethylene, and the polyolefin resin forming the second non-foamed layer 22 may be polypropylene.

The non-foamed layer 20 may contain components other than polystyrene-based resin or polyolefin-based resin. Examples of such components include coloring components.

The thickness of the non-foamed layer 20 is not particularly limited, but is preferably smaller than the thickness of the foamed layer 10. In addition, the thickness of the first non-foamed layer 21 is preferably larger than the thickness of the second non-foamed layer 22. The polyolefin resin forming the second non-foamed layer 22 is a crystalline resin, unlike the polystyrene resin, and therefore has a relatively large temperature dependency of melt tension. When such a second non-foamed layer 22 is heated, the tensile strength decreases, and the effect of reducing the amount of drawdown tends to be lower than that of the first non-foamed layer 21. Therefore, if the thickness of the second non-foamed layer 22 is smaller than the thickness of the first non-foamed layer 21, it is easier to reduce the amount of drawdown of the laminated sheet 1.

The thickness of the non-foamed layer 20 may be, for example, 5 μm or more and 35 μm or less. Also, when the laminated sheet 1 has two non-foamed layers 20, the thickness of the first non-foamed layer 21 may be 15 μm or more and 35 μm or less, and the thickness of the second non-foamed layer 22 may be 10 μm or more and 25 μm or less.

(Other layers)
The laminate sheet 1 may further include a layer other than the foamed layer 10 and the non-foamed layer 20. For example, such a layer may be laminated adjacent to the non-foamed layer 20 on at least one surface of the laminate sheet 1 having the non-foamed layer 20. Examples of such a layer include a laminate film formed of the same resin as the adjacent non-foamed layer 20 or a different resin of the same type. Such a laminate film may be printed.

(Laminated structure)
The laminate sheet 1 may have a non-foamed layer 20 laminated on at least one side of the foamed layer 10. From the viewpoint of the strength and oil resistance of the laminate sheet 1, it is preferable that a non-foamed layer 20 be laminated on each of both sides of the foamed layer 10.

For ease of explanation, one side of the foam layer 10 is referred to as the first side 11, and the non-foamed layer 20 laminated to the first side 11 is referred to as the first non-foamed layer 21. The side of the foam layer 10 opposite the first side 11 is referred to as the second side 12, and the non-foamed layer 20 laminated to the second side 12 is referred to as the second non-foamed layer 22. The first side 11 and the second side 12 of the foam layer 10 respectively constitute the front and back surfaces of the foam layer 10. In this case, either the first side 11 or the second side 12 may be the front surface.

The bond strength between the foamed layer 10 and the non-foamed layer 20 laminated to the foamed layer 10 tends to be greater the more similar the resin material forming the foamed layer 10 is in chemical structure to the resin material forming the non-foamed layer 20. This is thought to be because the more similar the chemical structures of the two resin materials are, the greater the compatibility, and the more easily these resin materials will be compatible and bonded when the layers are laminated. For example, when the foamed layer 10 and the non-foamed layer 20 are both formed from polystyrene-based resins, or both are formed from polyolefin-based resins, the bond strength between the two layers tends to be strong.

The inventors have found that the amount of drawdown of the laminated sheet 1 is affected by the bond strength between the foamed layer 10 and the non-foamed layer 20. Specifically, the inventors have found that if the bond strength between the foamed layer 10 and at least one non-foamed layer 20 is within an appropriate range, the amount of drawdown of the laminated sheet 1 formed by stacking these layers can be reduced, and have completed the present invention. A bond strength within an appropriate range may be, for example, a bond strength that results in a drawdown amount within a range in which molding defects of the laminated sheet 1 caused by drawdown do not occur with a problematic frequency.

The polystyrene resin content of the foam layer 10 may be 30% by weight or more and 75% by weight or less, preferably 35% by weight or more and 70% by weight or less, more preferably 40% by weight or more and 65% by weight or less, and more preferably 50% by weight or more and 65% by weight or less. Here, the polystyrene resin content in the foam layer 10 may be the content when the total amount of the resin material contained in the foam layer 10 is taken as 100% by weight. The resin material here includes polystyrene resin, polyolefin resin, and compatibilizer, but does not include auxiliary agents such as foaming agents or foam nucleating agents, the amount of which may be calculated as an additional number.

If the content of the polystyrene resin in the foam layer 10 is within this range, the bond strength between the foam layer 10 and the non-foam layer 20 will be within the appropriate range when the non-foam layer 20 is formed of a polystyrene resin. Also, even if the non-foam layer 20 is formed of a polyolefin resin, the bond strength between the foam layer 10 and the non-foam layer 20 is likely to be within the appropriate range. The foam layer 10 contains a polystyrene resin and a polyolefin resin. Therefore, if the content of the polystyrene resin in the foam layer 10 is within the above range, the content of the polyolefin resin is also likely to be within the range in which the bond strength with the non-foam layer 20 formed of a polyolefin resin is within the appropriate range.

The foam layer 10 may have a polyolefin resin content of 15% by weight or more and less than 60% by weight, preferably 20% by weight or more and 55% by weight or less, more preferably 25% by weight or more and 50% by weight or less, and even more preferably 30% by weight or more and 45% by weight or less.

If the content of the polyolefin-based resin in the foamed layer 10 is within this range, the bond strength between the foamed layer 10 and the non-foamed layer 20 will be within an appropriate range when the non-foamed layer 20 is formed from a polyolefin-based resin. Also, even when the non-foamed layer 20 is formed from a polystyrene-based resin, the bond strength between the foamed layer 10 and the non-foamed layer 20 is likely to be within an appropriate range.

In addition, when the laminate sheet 1 has a first non-foamed layer 21 formed of a polystyrene resin and a second non-foamed layer 22 formed of a polyolefin resin, the bond strength between at least one of the non-foamed layers 20 and the foamed layer 10 is within an appropriate range. Therefore, with this configuration, it is possible to ensure a high degree of freedom in the selection of the mixed resin material that forms the foamed layer 10. Therefore, it is possible to manufacture various laminate sheets 1 that have properties such as rigidity, oil resistance, heat resistance, or cold resistance with high selectivity.

The bond strength between the foamed layer 10 and the non-foamed layer 20 can be evaluated by a 180° peel test method. The 180° peel test method is performed by cutting a test piece (25 mm x 190 mm) from the laminated sheet 1 so that it is parallel to the MD direction. As a test machine, for example, a Tensilon (registered trademark) universal testing machine RTF-1210 (manufactured by Orientec Co., Ltd.) can be used. The test speed is 200 mm/min, the peel distance is up to 80 mm, and the integrated average load in the peel distance section from 20 mm to 60 mm is calculated. This can be performed multiple times for the same sample, and the average value can be used as the peel strength.

It is preferable that at least one of the first non-foamed layer 21 and the second non-foamed layer 22 of the laminated sheet 1 can be peeled from the foamed layer 10 by such a 180° peel test method. With such a configuration, the laminated sheet 1 has a bond strength between the foamed layer 10 and the non-foamed layer 20 within an appropriate range, and the amount of drawdown is small. Here, if the 180° peel test method is completed and the peel strength can be calculated, it can be evaluated as "peelable". Also, even if peeling is confirmed by the 180° peel test method, but the non-foamed layer 20 breaks before the peel distance reaches 60 mm, and the integrated average weight for the peel distance range from 20 mm to 60 mm cannot be calculated, it may be evaluated as "peelable".

(Method of manufacturing laminated sheet)
The laminate sheet 1 may be manufactured by a general manufacturing method for manufacturing a resin laminate sheet. For example, the laminate sheet 1 can be manufactured by multi-layer extrusion molding using coextrusion, but is not limited thereto.

(Thermoformed products)
One embodiment of the present invention also includes a thermoformed product of the laminate sheet 1 obtained by thermoforming the laminate sheet 1. The thermoforming method for thermoforming the laminate sheet 1 has already been described, and therefore will not be described here. Examples of such thermoformed products include packaging containers such as trays for storing food or other items.

If such thermoformed products are formed using the laminated sheet 1, the occurrence of molding defects such as wrinkles during manufacturing can be reduced, which leads to a reduction in raw material waste. This effect also contributes to the achievement of Goal 12 "Responsible Consumption and Production" and Goal 14 "Conserve and sustainably use the oceans and seas" of the Sustainable Development Goals (SDGs) advocated by the United Nations.

[Additional Notes]
The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

One embodiment of the present invention will be described below. However, the present invention is not limited to the embodiments described below.

〔Test method〕
A laminate sheet according to one embodiment of the present invention was produced, and packaging containers were molded as thermoformed products of the obtained laminate sheet (Tests No. 1 to 15). The foamed layer and non-foamed layer in each test were formed from the raw materials shown in Table 1 below.

SHE150 (manufactured by Braskem) shown in Table 1 is a high-density polyethylene (biomass polyethylene) produced from biomass raw materials. In Table 1, "Kraton", "POLYTHLENE" and "Novatec" are registered trademarks.

The manufacturing method and thermoforming method for the laminated sheet are shown below.

(Method of manufacturing laminated sheet)
The laminated sheets under each test condition were manufactured by extrusion molding as follows. As an extruder for the foamed layer, one 40 mmφ twin-screw extruder (manufactured by Plastics Engineering Research Institute, model: RT-40-S2-36-L, L/D=36) was prepared. As an extruder for the non-foamed layer, two 40 mmφ single-screw extruders (manufactured by GM Engineering, model: VGM40-25, L/D=25) were prepared. The two extruders correspond to the extrusion of the non-foamed layer (first non-foamed layer) formed of polystyrene resin and the non-foamed layer (second non-foamed layer) formed of polyolefin resin, respectively. The tips of these extruders were attached to a three-kind three-layer feed block, and a T-die was attached to this feed block.

The cylinder temperature of the twin-screw extruder for the foamed layer was set to 160-245°C, and the cylinder temperature of the single-screw extruder for the non-foamed layer was set to 230°C. The resin material and, if necessary, a foaming nucleating agent were fed into the hopper of each extruder and melted. Carbon dioxide (liquefied carbon dioxide gas) was injected as a foaming agent into the cylinder of the twin-screw extruder for the foamed layer, and further kneaded.

Two-layer or three-layer sheet-like materials were extruded by coextrusion under atmospheric pressure. The sheets were quenched by passing them through water-cooled rolls adjusted to 25°C to obtain laminated sheets for each test condition.

(Thermoforming method)
The obtained laminated sheet was fixed to a molding machine (Model FVS-500, manufactured by Wakisaka Engineering Co., Ltd.) with a 50 x 40 cm clamp, heated from above and below with heaters set at a temperature of 310 to 460°C for about 25 seconds, and then a thermoformed product measuring 176 x 147 x 33 mm was obtained by a differential pressure molding method. At this time, thermoforming was performed so that the non-foamed layer (first non-foamed layer) formed by the polystyrene resin was on the outside of the container, and the non-foamed layer (second non-foamed layer) formed by the polyolefin resin was on the inside of the container.

〔Evaluation methods〕
(thickness)
The thickness of the laminate sheet under each test condition was measured with a vernier caliper at three points at approximately equal intervals in the width direction of the laminate sheet, and the average value was taken as the thickness of the laminate sheet.

For the thickness of the non-foamed layer, a test piece (10 mm x 50 mm) was cut so that its long side was parallel to the MD direction of the laminated sheet. A cross section of the short side of the test piece was cut out, and the cut cross section was photographed using a stereomicroscope (ZEISS, model: SteREO Discovery.V20, magnification 150x). In the photographed image, the distance from the surface of the laminated sheet to the boundary between the non-foamed layer (the outer layer) and the foamed layer was measured at three random locations, and the average value was taken as the thickness of the non-foamed layer.

(specific gravity)
A test piece (40 mm×40 mm) was cut out from the laminate sheet of each test condition, and the specific gravity of the laminate sheet was measured by the underwater displacement method using an electronic specific gravity meter (manufactured by Mirage Trading Co., Ltd., model: ED-120T).

(deflection amount)
The deflection of the laminated sheet was measured under the following conditions as an index of the amount of drawdown. The deflection was measured by cutting a test piece (30 mm x 150 mm) so that its long side was parallel to the TD direction of the laminated sheet. The obtained test piece was evenly sandwiched between two U-shaped metal frames (outer dimensions 150 mm x 150 mm, inner dimensions 100 mm x 100 mm, thickness 3 mm) at both ends of the longitudinal direction of the test piece. Then, the test piece sandwiched between the metal frames was heated to the test temperature (120 ° C). The amount of movement of the center part of the test piece from before the temperature of the test piece was raised to 60 seconds after the start of the temperature rise was measured as the deflection.

If the deflection amount is 10 mm or less, the occurrence rate of molding defects due to drawdown can be reduced. Also, if the deflection amount is 6 mm or less, the laminated sheet can be evaluated as having a particularly small amount of drawdown.

(Peel Strength)
The possibility of peeling the non-foamed layer from the foamed layer and the peel strength were determined by cutting a test piece (25 mm x 190 mm) so that its long side was parallel to the MD direction of the laminated sheet, and performing a 180° peel test. A Tensilon universal testing machine RTF-1210 (manufactured by Orientec Co., Ltd.) was used, the test speed was 200 mm/min, the peel distance was up to 80 mm, and the integrated average load was calculated for the peel distance section from 20 mm to 60 mm. This was performed five times for the same sample, and the average value was taken as the peel strength.

When the peel strength could be calculated, it was rated as peelable. Note that the non-foamed layer formed from polystyrene resin is highly brittle due to its material properties. Therefore, although peeling was confirmed using the 180° peel test method, there were cases where the non-foamed layer broke before the peel distance reached 60 mm. Even in such cases, if peeling was confirmed halfway using the 180° peel test method, it was rated as △ (peelable).

(Moldability)
Using the method described above under "thermoforming method," thermoforming was performed three times for each laminated sheet under each test condition, and thermoformed products with crimps were rated as "x" (not suitable), those with minor crimps were rated as "△" (passable), and those with no crimps were rated as "○" (suitable, but not eligible for evaluation). In addition, cases in which the crimps were minor and the problem of the present invention was solved, but the heating time for thermoforming was long, or there was a problem with the roughness of the laminated sheet surface, were rated as "-" (suitable, but not eligible for evaluation). Note that "crimps" refers to poor appearance due to wrinkles or uneven thickness on the surface of the thermoformed product.

(Oil resistance)
Test pieces measuring 50 mm in MD × 10 mm in TD were punched out from the laminated sheets under each test condition with a cutting blade so that they were almost uniform in the TD direction of the laminated sheets, and three pieces were prepared for each laminated sheet. 0.02 g of edible oil (manufactured by Kao Corporation, brand name: Coconard (registered trademark) RK) was evenly applied to one side of each cut test piece, excluding the portion within 20 mm from both ends in the MD direction.

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 it in this state for 8 hours, the test pieces were visually inspected, and those in which no cuts or cracks were found were rated as ○ (satisfactory), and those in which cuts or cracks were found in any of the test pieces were rated as × (unsuitable).

(Heat-resistant)
The laminated sheets under each test condition were thermoformed, and the thermoformed products obtained were kept in salad oil heated to 110° C. for 30 seconds, after which the degree of deformation of the thermoformed products was visually confirmed. Thermoformed products with no observed deformation were rated as ○ (suitable), those that were deformed but could withstand use as a thermoformed product were rated as △ (passable), and those with significant deformation and unable to function as a thermoformed product were rated as × (unsuitable).

〔Evaluation results〕
The component compositions and evaluation results for the laminate sheets under each test condition are summarized in Tables 2 to 5 below. Tables 2 and 3 show the component compositions and evaluation results for laminate sheets having two non-foamed layers, a first non-foamed layer and a second non-foamed layer (Test Nos. 1 to 9). Table 4 shows the component compositions and evaluation results for laminate sheets having one non-foamed layer formed of a polystyrene-based resin (Test Nos. 10 to 13). Table 5 shows the component compositions and evaluation results for laminate sheets having one non-foamed layer formed of a polyolefin-based resin (Test Nos. 14 and 15).

Under all test conditions, a laminate sheet with a deflection of 10 mm or less was obtained. It was also shown that when the polystyrene resin content in the foam layer was 30% by weight or more and 75% by weight or less, a laminate sheet with smaller deflection and better moldability was obtained.

REFERENCE SIGNS LIST 1 Laminated sheet 10 Foamed layer 11 First surface 12 Second surface 20 Non-foamed layer 21 First non-foamed layer 22 Second non-foamed layer

Claims (6)

a foam layer containing a mixed resin of a polystyrene-based resin and a polyolefin-based resin;
a first non-foamed layer formed of a polystyrene-based resin and laminated on a first surface of the foamed layer;
a second non-foamed layer formed of a polyolefin resin and laminated on a second surface of the foamed layer, the second surface being different from the first surface;
The foam layer comprises at least one of biomass polyethylene and biomass polypropylene as the polyolefin resin. The laminate sheet according to claim 1, wherein the foam layer contains biomass polyethylene as the polyolefin resin. 2. The laminate sheet according to claim 1 , wherein the foam layer has a polystyrene resin content of 30% by weight or more and 75% by weight or less. The laminate sheet according to claim 1 , wherein the foam layer has a polyolefin resin content of 15% by weight or more and less than 60% by weight. The laminate sheet according to claim 1 , wherein at least one of the first non-foamed layer and the second non-foamed layer is peelable from the foamed layer by a 180° peel test method. A thermoformed product of the laminate sheet according to claim 1.

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