Laminate sheet and heat molded article

Abstract

To provide a laminate sheet and the like easy to treat a residue, and excellent in production cost while containing a filler.SOLUTION: A laminae sheet (1) includes: at least one non-foamed layer (20) formed by a polyolefin resin containing a cellulose nanofiber; and a foamed layer (10) formed by a mixed resin including a polystyrene resin and a polyolefin resin for being laminated with the at least one non-foamed layer (20).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a laminated sheet and a thermoformed product.

Background Art

[0002] Resin containers such as packaging containers are generally manufactured by thermoforming a resin sheet. It is known that physical properties such as strength and heat resistance of such resin containers are greatly influenced by the component composition of the resin sheet.

[0003] In order to improve physical properties such as strength and heat resistance, materials other than resin may be used as fillers in the resin sheet. Patent Document 1 discloses a thermoforming resin sheet containing high-density polyethylene, block polypropylene, homopolypropylene, and an inorganic filler. Patent Document 2 also discloses a sheet material including an epidermal layer made of cellulose nanofibers and a resin layer that contacts the epidermal layer from the inside.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Since the thermoforming resin sheet described in Patent Document 1 uses an inorganic filler, the residue treatment cost during waste treatment increases. Since the sheet material described in Patent Document 2 forms the epidermal layer with cellulose nanofibers, the manufacturing cost increases.

[0006] An aspect of the present invention aims to provide a laminated sheet or the like that is easy to treat residues while containing a filler and is also excellent in manufacturing cost.

Means for Solving the Problem

[0007] The laminated sheet according to Aspect 1 of the present invention includes at least one non-foamed layer formed of a polyolefin resin containing cellulose nanofibers, and a foamed layer formed of a mixed resin containing a polystyrene resin and a polyolefin resin, to which at least one of the non-foamed layers is laminated.

[0008] According to the above configuration, since the laminated sheet contains cellulose nanofibers, the strength and heat resistance of the laminated sheet can be improved. In addition, since the specific gravity of cellulose nanofibers is smaller than that of inorganic fillers such as talc, the product weight can be reduced while ensuring strength and heat resistance equal to or higher than those in the case of using inorganic fillers. Further, although inorganic fillers such as talc are costly for residue treatment during the disposal of the laminated sheet or its molded product, cellulose nanofibers, for example, do not leave ash or the like after incineration, and residue treatment is easy.

[0009] In addition, since the laminated sheet contains cellulose nanofibers, the content of bio-derived materials increases, so the environmental load can be reduced. Furthermore, by including cellulose nanofibers in the non-foamed layer rather than the foamed layer, the influence of the inclusion of cellulose nanofibers on the impact resistance of the laminated sheet can be minimized.

[0010] The laminated sheet according to Aspect 2 of the present invention may have two non-foamed layers in the above Aspect 1, and the foamed layer may be laminated between the two non-foamed layers.

[0011] According to the above configuration, while maintaining good impact resistance of the laminated sheet by the foamed layer, the strength and heat resistance of the laminated sheet can be effectively improved by the two non-foamed layers.

[0012] The laminated sheet according to Aspect 3 of the present invention may have a cellulose nanofiber content of 1 wt% or more and 50 wt% or less in the non-foamed layer in the above Aspect 1 or 2.

[0013] According to the above configuration, the effect of improving the strength and heat resistance by the cellulose nanofibers can be obtained. Further, since the content of the cellulose nanofibers does not become excessive, an increase in the manufacturing cost of the product can be reduced and oil resistance can be ensured.

[0014] In the laminated sheet according to Embodiment 4 of the present invention, in any of the above Embodiments 1 to 3, the foamed layer may have a polystyrene-based resin content of 25% by weight or more and 80% by weight or less.

[0015] In the laminated sheet according to Embodiment 5 of the present invention, in any of the above Embodiments 1 to 4, the foamed layer may have a polyolefin-based resin content of 10% by weight or more and less than 65% by weight.

[0016] According to each of the configurations according to the above Embodiments 4 and 5, for the foamed layer, a content of a polystyrene-based resin effective for improving impact resistance can be ensured. Therefore, the impact resistance of the laminated sheet becomes good. Further, the bonding strength between the foamed layer and the non-foamed layer containing the polyolefin-based resin does not become too strong, and the draw-down amount of the laminated sheet can be reduced. Therefore, the manufacturing efficiency of the laminated sheet can be improved.

[0017] The thermoformed article according to Embodiment 6 of the present invention is a thermoformed article of the laminated sheet according to any of the above Embodiments 1 to 5.

Effects of the Invention

[0018] According to one aspect of the present invention, it is possible to provide a laminated sheet or the like that is easy to process residues while containing a filler and is also excellent in manufacturing cost.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0020] Hereinafter, an embodiment of the present invention will be described. FIG. 1 is a cross-sectional view schematically showing the layer structure of the laminated sheet 1 according to this embodiment. FIG. 1 is only a schematic diagram and does not limit the ratio of the thickness of each layer in the laminated sheet 1.

[0021] The cross-section shown in FIG. 1 is a cross-section in a direction orthogonal to the stretching direction of the laminated sheet 1. The stretching direction of the laminated sheet 1 is intended to be the MD (Machine direction) direction, but is not limited thereto. For example, it may be the TD (Transverse Direction) direction, or may be any direction on the same plane as a virtual plane including the MD direction and the TD direction.

[0022] As shown in FIG. 1, the laminated sheet 1 according to this embodiment is laminated with a foamed layer 10 and two non-foamed layers 20.

[0023] (Foamed layer) The foamed layer 10 is a sheet member formed of a mixed resin containing a polystyrene-based resin and a polyolefin-based resin.

[0024] The polystyrene resin contained in the mixed resin forming the foamed layer 10 may be a polymer of a styrene monomer, or may be a copolymer etc. having a styrene monomer as a main component and other monomers copolymerizable with the styrene monomer. Examples of the styrene monomer include styrene, alkyl-substituted styrenes, α-alkyl-substituted styrenes, and halogenated styrenes. These styrene monomers may be of one kind or a mixture of two or more kinds. Also, HIPS (high impact polystyrene) may be used as the polystyrene resin.

[0025] Examples of other monomers copolymerizable with the styrene monomer include acrylic acid, methacrylic acid, acrylic esters, methacrylic esters, acrylonitrile, maleic anhydride, and maleic acid, or derivatives thereof. These other monomers may be of one kind or a mixture of two or more kinds.

[0026] Also, examples of other resins contained in the polystyrene resin include a mixture of polyphenylene ether and polystyrene.

[0027] When the polystyrene resin is HIPS, the HIPS contains 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 composed of a styrene component and a rubber component, or a mixture containing two or more of these copolymer resins.

[0028] The polystyrene resin may be a resin composed of any one of the above examples, or may be a mixture of two or more kinds.

[0029] The polyolefin resin contained in the mixed resin may be a resin mainly composed of polyolefins such as polyethylene (PE), polypropylene (PP), biomass polyethylene or biomass polypropylene. Examples of the polyolefin resin include olefin homopolymers, olefin random copolymers mainly composed of polyolefins, 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).

[0030] The polyolefin resin may be a resin composed of any one of the above examples, or a mixture of two or more kinds.

[0031] The foamed layer 10 preferably contains a biomass-derived resin such as biomass polyethylene or biomass polypropylene as the polyolefin resin. According to such a configuration, it contributes to reducing the carbon emissions of the entire product cycle of the laminated sheet 1. This also contributes to the achievement of, for example, Goal 13, "Take urgent action to combat climate change", of the Sustainable Development Goals (SDGs) proposed by the United Nations.

[0032] The foamed layer 10 may contain components other than the polystyrene resin and the polyolefin resin. Examples of such components include compatibilizers, foaming agents, foaming nucleating agents, and coloring components. 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.

[0033] In one embodiment of the present invention, the compatibilizer improves the mutual solubility between the polystyrene-based resin and the polyolefin-based resin. Specifically, the following are examples. That is, as the compatibilizer, for example, styrene-butadiene copolymer or its hydrogenated product, styrene-butadiene-styrene block copolymer or its hydrogenated product, styrene-isoprene-styrene block copolymer or its hydrogenated product, styrene-ethylene-propylene-styrene copolymer, polypropylene-graft-polystyrene copolymer, styrene-maleic anhydride copolymer, vinyl acetate-ethylene copolymer, and styrene-ethylene-propylene-styrene copolymer can be mentioned. Among these, styrene-butadiene copolymer or its hydrogenated product, styrene-butadiene-styrene block copolymer or its hydrogenated product are particularly preferred.

[0034] The foam layer 10 is formed by foaming the above-mentioned mixed resin. The foam layer 10 may contain a foaming agent and a foaming nucleating agent for foaming the mixed resin. The type of the foaming nucleating agent is not particularly limited and may be a conventionally common foaming nucleating agent. The foaming nucleating agent may have a function of promoting the foaming of the mixed resin by the foaming agent when a gas such as carbon dioxide is added as the foaming agent to the mixed resin. In addition, the foam layer 10 may be foamed by a method other than the addition of such a foaming agent and foaming nucleating agent.

[0035] The thickness of the foam layer 10 is not particularly limited, but it is preferably larger than the thickness of the non-foam layer 20. According to such a configuration, the laminated sheet 1 excellent in strength and moldability can be obtained. The thickness of the foam layer 10 may be, for example, 0.30 mm or more and 1.50 mm or less, or may be 0.50 mm or more and 1.50 mm or less.

[0036] (Non-foam layer) The non-foam layer 20 is a sheet member formed of a polyolefin-based resin containing cellulose nanofibers.

[0037] Cellulose nanofibers are components in which cellulose fibers are fibrillated into nano units. The cellulose nanofibers improve physical properties typified by the strength and heat resistance of the non-foamed layer 20 as an organic filler for the polyolefin resin forming the non-foamed layer 20.

[0038] Conventionally, inorganic fillers such as talc have been used to improve the physical properties of the non-foamed layer 20. However, such inorganic fillers increase the weight of the laminated sheet 1 because of their large specific gravity. In addition, conventional laminated sheets containing inorganic fillers or their thermoformed products incur residue treatment costs during disposal. For example, when the conventional laminated sheet is incinerated, the inorganic filler remains as ash, resulting in ash treatment costs.

[0039] If cellulose nanofibers are used as the filler, the problems of the inorganic filler can be solved while obtaining an effect of improving the physical properties of the non-foamed layer 20 equal to or better than that of the inorganic filler. For example, since cellulose nanofibers have a smaller specific gravity than inorganic fillers such as talc, the laminated sheet 1 can be lightened. In addition, since cellulose nanofibers do not leave residues such as ash even when incinerated, for example, residue treatment is easy.

[0040] Furthermore, cellulose nanofibers are manufactured from cellulose, which is a biomass material. By including such cellulose nanofibers in the laminated sheet 1, the content rate of the biomass material in the laminated sheet 1 increases, so that the environmental load can be reduced. Also, if the polyolefin resin forming the non-foamed layer 20 is a resin derived from biomass such as biomass polyethylene or biomass polypropylene, it is possible to form substantially the entire non-foamed layer 20 from the biomass material. According to such a configuration, it is effective in reducing the carbon emissions throughout the product cycle of the laminated sheet 1.

[0041] Note that resins containing cellulose nanofibers generally tend to become brittle as their strength increases, and it is known that their impact resistance at low temperatures is more likely to decrease than when they do not contain cellulose nanofibers. Low temperatures refer to, for example, temperatures below 0 degrees, such as the temperature inside a freezer or a deep freezer.

[0042] The laminated sheet 1 contains cellulose nanofibers in the non-foamed layer 20. The foamed layer 10 has good impact resistance due to being foamed and further contains a polystyrene-based resin effective for ensuring impact resistance, thus improving the impact resistance of the laminated sheet 1. In this regard, the cellulose nanofibers contained in the non-foamed layer 20 are less likely to affect the impact resistance of the foamed layer 10. Therefore, according to the above configuration, in the laminated sheet 1, it is possible to realize improvements in physical properties such as strength and heat resistance due to the inclusion of cellulose nanofibers while maintaining the impact resistance at low temperatures.

[0043] Cellulose nanofibers include cellulose fibers with a fiber diameter of 1000 nm or less of nano size. Also, cellulose nanofibers may contain cellulose fibers of micro size exceeding 1000 nm. The content of such micro-sized cellulose fibers is not particularly limited as long as it does not inhibit advantageous effects such as the effect of improving physical properties achieved by the inclusion of cellulose nanofibers.

[0044] The fiber diameter of the cellulose fibers contained in the cellulose nanofibers is not particularly limited, but for example, it is preferably 5 nm or more and 1000 nm or less in terms of the average fiber diameter, and more preferably 30 nm or more and 300 nm or less. According to such cellulose nanofibers with such a configuration, it is easy to improve the physical properties of the non-foamed layer 20. When the cellulose nanofibers contain cellulose fibers with a fiber diameter exceeding 1000 nm, the fiber diameter of the cellulose fibers is preferably 5000 nm or less.

[0045] The fiber length of the cellulose fibers contained in the cellulose nanofibers is not particularly limited, and for example, the average fiber length may be 100 μm or less. With cellulose nanofibers having such a configuration, they are easily dispersed in the polyolefin resin. For example, when the non-foamed layer 20 is formed by extrusion molding, the occurrence of poor dispersion of the cellulose nanofibers can be effectively reduced. Therefore, the effect of improving the physical properties of the non-foamed layer 20 can be obtained uniformly. In addition, it is possible to reduce the deterioration of the appearance of the non-foamed layer 20 caused by the aggregation of the cellulose nanofibers, and the occurrence of defects such as tearing or perforation due to thermoforming.

[0046] In addition to cellulose fibers, the cellulose nanofibers may contain components derived from plants (especially trees) such as lignin and hemicellulose. According to such a configuration, cellulose nanofibers can be easily produced from trees and the like.

[0047] The cellulose nanofibers are preferably subjected to a hydrophobization treatment in order to improve the dispersibility in the polyolefin resin. According to such a configuration, the amount of the dispersant used to disperse the cellulose nanofibers in the polyolefin resin can be reduced or omitted.

[0048] The cellulose nanofibers may be produced by defibrating cellulose fibers by a mechanical fibrillation method or the like, or commercially available products may be used. Suitable cellulose nanofibers for inclusion in the polyolefin resin can be produced, for example, by the method described in Japanese Patent No. 6699014.

[0049] The content of the cellulose nanofibers in the non-foamed layer 20 is preferably 1% by weight or more, and may be 2% by weight or more, or may be 5% by weight or more. With such a content, the effect of improving the physical properties of the non-foamed layer 20 by the cellulose nanofibers can be obtained.

[0050] On the other hand, cellulose nanofibers tend to have high raw material costs. Further, when the thermoformed product of the laminated sheet 1 comes into contact with foodstuffs such as a packaging container, it is preferable that the non-foamed layer 20 coming into contact with the foodstuffs has oil resistance. If the non-foamed layer 20 contains an excessive amount of cellulose nanofibers, for example, it is considered that microcracks are likely to occur along with an improvement in the strength of the non-foamed layer 20. Since there is a risk that the oil component of the foodstuff may enter through such microcracks and erode the foamed layer 10, excessive addition of cellulose nanofibers may reduce the oil resistance of the laminated sheet 1.

[0051] Therefore, the content of cellulose nanofibers in the non-foamed layer 20 is preferably 50% by weight or less, and may be 40% by weight or less, 30% by weight or less, 20% by weight or less, 15% by weight or less, 10% by weight or less, or 5% by weight or less. With such a content, the oil resistance of the non-foamed layer 20 can be ensured well, and an increase in manufacturing cost can also be reduced.

[0052] The polyolefin resin contained in the non-foamed layer 20 may be the polyolefin resin exemplified as the polyolefin resin contained in the mixed resin forming the foamed layer 10. The polyolefin resin forming the foamed layer 10 and the polyolefin resin forming the non-foamed layer 20 may be the same resin or different resins of the same series.

[0053] Also, the resins forming the two non-foamed layers 20 may be the same resin or different resins from each other. For example, the polyolefin resins contained in the two non-foamed layers 20 may be different resins of the same series. Further, in the two non-foamed layers 20, the contents of cellulose nanofibers and / or polyolefin resins may be different from each other.

[0054] The non-foamed layer 20 may contain components other than the polyolefin resin containing cellulose nanofibers. Examples of such components include a dispersant, a resin additive, or a coloring component. The dispersant may contain a component that promotes the dispersion of cellulose nanofibers in the polyolefin resin.

[0055] The method for producing the polyolefin resin containing cellulose nanofibers is not particularly limited. For example, the polyolefin resin and cellulose nanofibers may be mixed. In this mixing, components such as a dispersant may be further included. It is preferable that the cellulose nanofibers are uniformly dispersed in the polyolefin resin. Therefore, the polyolefin resin containing cellulose nanofibers is preferably produced using a dispersant.

[0056] Also, as the polyolefin resin containing cellulose nanofibers, a commercially available masterbatch in which cellulose nanofibers are dispersed in the polyolefin resin may be used.

[0057] The thickness of the non-foamed layer 20 is not particularly limited, but it is preferably smaller than the thickness of the foamed layer 10. The thickness of the non-foamed layer 20 may be, for example, 5 μm or more and 50 μm or less, may be 10 μm or more and 45 μm or less, or may be 15 μm or more and 40 μm or less. The two non-foamed layers 20 may have the same thickness or may have different thicknesses from each other.

[0058] (Other Layers) The laminated sheet 1 may further have a layer other than the foamed layer 10 and the non-foamed layer 20 laminated thereon. Such a layer may be laminated, for example, adjacent to the non-foamed layer 20 on at least one surface of the laminated sheet 1. Examples of such a layer include a laminate film formed of the same resin or a different resin of the same series as the adjacent non-foamed layer 20. Such a laminate film may be printed.

[0059] (Laminated Structure) The laminated sheet 1 is formed by laminating a foam layer 10 between two non-foam layers 20. For convenience of explanation, one surface of the foam layer 10 is defined as the first surface 11, and the other surface is defined as the second surface 12. The first surface 11 and the second surface 12 of the foam layer 10 respectively constitute the front and back surfaces of the foam layer 10. At this time, either the first surface 11 or the second surface 12 may be the surface.

[0060] The non-foam layers 20 are laminated adjacent to both the first surface 11 and the second surface 12 of the foam layer 10 respectively. The bonding strength between the foam layer 10 and the non-foam layer 20 laminated on the foam layer 10 tends to increase as the resin material forming the foam layer 10 has a more similar chemical structure to the resin material forming the non-foam layer 20. This is presumably because the more similar the chemical structures between the two resin materials, the greater the compatibility, and the contact portions between these resin materials are more likely to be compatible and bond easily when each layer is laminated.

[0061] Both the foam layer 10 and the non-foam layer 20 contain polyolefin-based resins. Therefore, the bonding strength between the foam layer 10 and the non-foam layer 20 tends to be strong. On the other hand, when the bonding strength between the foam layer 10 and the non-foam layer 20 is excessively strong, the drawdown amount of the laminated sheet 1 increases, and the moldability of the laminated sheet 1 may deteriorate. "The moldability deteriorates" means, for example, in the thermoforming of the laminated sheet 1, an increase in the molding defect rate due to the generation of wrinkles on the surface or the like.

[0062] In this regard, the foam layer 10 is formed of a mixed resin containing not only polyolefin-based resin but also polystyrene-based resin. Therefore, by adjusting the contents of the polystyrene-based resin and the polyolefin-based resin in the mixed resin, the bonding strength between the foam layer 10 and the non-foam layer 20 can be easily adjusted.

[0063] The foamed layer 10 may have a polyolefin resin content of 10% by weight or more and less than 65% by weight. Further, the content may be 15% by weight or more and less than 60% by weight, may be 20% by weight or more and 55% by weight or less, may be 20% by weight or more and 50% by weight or less, or may be 20% by weight or more and 45% by weight or less. If the content of the polyolefin resin in the foamed layer 10 is within such a range, the bonding strength between the foamed layer 10 and the non-foamed layer 20 will be within an appropriate range.

[0064] Further, the foamed layer 10 may have a polystyrene resin content of 25% by weight or more and 80% by weight or less. Further, the content may be 30% by weight or more and 75% by weight or less, may be 35% by weight or more and 70% by weight or less, may be 40% by weight or more and 65% by weight or less, or may be 50% by weight or more and 65% by weight or less. If the content of the polystyrene resin in the foamed layer 10 is within such a range, for the foamed layer 10, the content of the polystyrene resin effective for improving impact resistance can be ensured. Therefore, the impact resistance of the laminated sheet 1 becomes good.

[0065] Here, the content of each of the polyolefin resin and the polystyrene resin in the foamed layer 10 may be the content when the total amount of the resin materials contained in the foamed layer 10 is 100% by weight. The resin materials referred to here include polystyrene resins, polyolefin resins, and compatibilizers, but do not include auxiliaries such as foaming agents or foaming nucleating agents whose addition amounts may be calculated as external numbers.

[0066] (Manufacturing method of laminated sheet) The laminated sheet 1 may be manufactured by a general manufacturing method for manufacturing a resin laminated sheet. The laminated sheet 1 can be manufactured, for example, by multi-layer extrusion molding by co-extrusion, but is not limited thereto.

[0067] (Thermoformed product) The thermoformed product of the laminated sheet 1 obtained by thermoforming the laminated sheet 1 is also included in one embodiment of the present invention. Thermoforming is a method of heating the laminated sheet 1 and molding the laminated sheet 1 in a state where the resin material is softened by heat. Examples of the thermoforming method for obtaining the laminated sheet 1 include a press molding method and a differential pressure molding method. Examples of the differential pressure molding method include a vacuum molding method and a pressure air molding method. Examples of such thermoformed products include packaging containers such as trays for accommodating articles to be accommodated such as food products.

[0068] 〔Modification example〕 Various modification examples are assumed for the laminated sheet 1 according to the present embodiment. For example, as shown in FIG. 2, the laminated sheet 1a according to the modification example of the present embodiment may be in a mode having only one non-foamed layer 20. In the laminated sheet 1a, the non-foamed layer 20 is laminated on the first surface 11 of the foamed layer 10. The non-foamed layer 20 may be laminated on the second surface 12 instead of the first surface 11 of the foamed layer 10.

[0069] Regarding such a laminated sheet 1a as well, similar to the laminated sheet 1, the effect of improving the strength and heat resistance by the non-foamed layer 20 containing cellulose nanofibers can be obtained, and excellent impact resistance by the foamed layer 10 can be obtained. Further, since the laminated sheet 1 has only one non-foamed layer 20, it is possible to realize a laminated sheet 1a having these strengths, heat resistance and impact resistance while reducing the amount of cellulose nanofibers with high raw material costs.

[0070] When the thermoformed product of the laminated sheet 1a comes into contact with a food product such as a packaging container, it is preferable that the non-foamed layer 20 is laminated on the surface of the laminated sheet 1a that comes into contact with the food product. Further, the other layers described above may be laminated on the surface of the foamed layer 10 opposite to the surface on which the non-foamed layer 20 is laminated.

[0071] 〔Supplementary matters〕 The present invention is not limited to the above-mentioned embodiments, and various modifications are possible within the scope of the claims. The technical scope of the present invention also includes embodiments obtained by appropriately combining the technical means disclosed in the different embodiments. [Examples]

[0072] An example of the present invention will be described below. However, the present invention is not limited to the examples shown below.

[0073] [Test Method] A laminate sheet according to an example of the present invention or a laminate sheet according to a comparative example was manufactured, and a packaging container was molded as a thermoformed product of the obtained laminate sheet. The foamed layer and the non-foamed layer in the laminate sheets of the examples and the comparative examples were formed from the raw materials shown below.

[0074] (Foam Layer) In all of the Examples and Comparative Examples, the foam layer was formed using the following raw materials. As the polystyrene (PS) resin, polystyrene (PS Japan Co., Ltd., PSJ-Polystyrene 685 K27 7, MI (Melt Flow Index): 1.7 to 2.7) was used. As the polyolefin (PO) resin, polypropylene (Prime Polymer Co., Ltd., Prime Polypro E702G, MI: 0.8 to 1.1) was used.

[0075] In addition, a compatibilizer (Kraton DX408, manufactured by Kraton Polymer Japan Co., Ltd. JOP, MI: 3.5-6.0) and a foaming nucleating agent (Polysurene EE275F, manufactured by Eiwa Kasei Kogyo Co., Ltd.) were used.

[0076] (Non-foamed layer) As polyolefin resins for the non-foamed layer, Resins A-1, A-2, A-3, B-1, B-2, and C were used. Resin A-1 is a PP masterbatch (manufactured by Kowa Kasei Kogyosho Co., Ltd., PP-CNFC-40) containing polypropylene and cellulose nanofibers (CNF, manufactured by Mori Machinery Co., Ltd., lignocellulose nanofibers). Resin A-2 is a PP masterbatch (manufactured by Kowa Kasei Kogyosho Co., Ltd., PP-CNFC-20-CSTM) containing polypropylene and the above-mentioned cellulose nanofibers. Resin A-3 is a PP masterbatch (manufactured by Kowa Kasei Kogyosho Co., Ltd., PP-CNFC-T-2) containing polypropylene, the above-mentioned cellulose nanofibers, and 5 wt% maleic anhydride-modified polyolefin as a dispersant. The cellulose nanofibers contained in Resins A-1, A-2, and A-3 contain 35 wt% lignin, 15 wt% hemicellulose, and 50 wt% cellulose.

[0077] Resin B-1 is a random polymer of polypropylene (manufactured by Japan Polypropylene Corporation, Novatec PP MA3, MI: 11). Resin B-2 is a random polymer of polypropylene (manufactured by Prime Polymer Co., Ltd., Prime Polypro F-724NPC). Resin C is a PP masterbatch (manufactured by Takehara Chemical Industry Co., Ltd., MAX2080T-3) containing polypropylene and talc, an inorganic filler.

[0078] Note that "Prime Polypro", "Clayton", "POLYTHLENE", and "Novatec" are registered trademarks.

[0079] 〔Manufacturing Method〕 The manufacturing method of the laminated sheet and the thermoforming method are shown below.

[0080] (Manufacturing Method of Laminated Sheet) The laminated sheets of each example and comparative example were manufactured by extrusion molding as follows. As an extruder for the foam layer, one 40-mm φ twin-screw extruder (manufactured by Plastic Engineering Laboratory, model: RT-40-S2-36-L, L / D = 36) was prepared. As extruders for the non-foam layer, two 40-mm φ single-screw extruders (manufactured by G.M.Engineering, model: VGM40-25, L / D = 25) were prepared.

[0081] The tips of these extruders were attached to a two-component three-layer feed block, and a T-die was attached to this feed block.

[0082] The cylinder temperature of the twin-screw extruder for the foam layer was set to 190 to 240°C, and the cylinder temperature of the single-screw extruder for the non-foam layer was set to 195 to 210°C. Resin materials were supplied to the hoppers of the respective extruders and melted. Carbon dioxide (liquefied carbon dioxide) was injected into the cylinder of the twin-screw extruder for the foam layer and further kneaded.

[0083] Under atmospheric pressure, a three-layer sheet-like material was extruded by a coextrusion method. This three-layer sheet-like material was passed through a water-cooled roll adjusted to 25°C and rapidly cooled to obtain a laminated sheet.

[0084] (Thermoforming method) The obtained laminated sheet was fixed to a molding machine (manufactured by Wakizaka Engineering Co., Ltd., model: FVS-500 type) with a 50×40 cm clamp, heated from above and below with a heater at a set temperature of 295 to 450°C for about 20 to 28 seconds, and then a thermoformed product with a size of 176×147×33 mm was obtained by a differential pressure forming method.

[0085] 〔Evaluation method〕 (Thickness) Regarding the thickness of the laminated sheet, three points were measured with a vernier caliper at substantially equal intervals in the width direction of the laminated sheet, and the average value was taken as the thickness of the laminated sheet.

[0086] Regarding the thickness of the non-foamed layer, a test piece (10 mm × 50 mm) was cut out such that its long side was parallel to the MD direction of the laminated sheet, and a cross-section on the short side of the test piece was cut out. The cut-out cross-section was photographed with a stereomicroscope (manufactured by ZEISS, model: SteREO Discovery.V20, photographing magnification 150 times). In the photographed image, the distance from the surface of the laminated sheet to the boundary between the surface layer (non-foamed layer) and the foamed layer was measured at three arbitrary points, and the average value was taken as the thickness of the non-foamed layer.

[0087] (Specific gravity) A test piece (40 mm × 40 mm) was cut out from the laminated sheet, and the specific gravity of the laminated sheet was measured by the water displacement method using an electronic specific gravity meter (manufactured by Mirage Trading Co., Ltd., model: ED-120T).

[0088] (Strength) For a packaging container, which is a thermoformed product of the laminated sheet, a jig (length of the part fixing the edge: 25 mm) was abutted against the central part of each of the opposite edge parts, and the packaging container was fixed. One of the jigs was moved inward of the packaging container at a test speed of 100 mm / min. The maximum value of the load value (N) detected at this time was evaluated as the strength of the packaging container. This test was carried out for the directions corresponding to the MD direction and the TD direction of the laminated sheet in the packaging container, respectively. Regarding the strength shown in Tables 1 to 4, "MD" is the result of measurement with each edge part in the direction corresponding to the MD direction fixed, and "TD" is the result of measurement with each edge part in the direction corresponding to the TD direction fixed. For the measurement of strength, a testing machine: Tensilon universal testing machine RTF-1210 manufactured by A&D was used.

[0089] (Appearance) Regarding the surface of the packaging container, when spot-like contamination was visually observed, the appearance was evaluated as "defective", and when no spot-like bumps were visually observed, the appearance was evaluated as "good".

[0090] (Heat-resistant temperature) The packaging container was placed on a heat-resistant plate and heated and held for 1 hour in a forced-air thermostatic chamber (Yamato Scientific Co., Ltd. DKN612) heated to a predetermined temperature. After heating, the packaging container together with the heat-resistant plate was taken out and naturally cooled at room temperature for 30 minutes. After cooling, the deformation of the packaging container was observed. The highest temperature at which no deformation was observed in the packaging container was defined as the heat resistance temperature of the packaging container.

[0091] (Impact resistance) Water (200 mL) was put into the packaging container and it was left to freeze in a freezer set at -40°C for 24 hours. The frozen packaging container was freely dropped from a position where the height from the floor surface to the bottom surface of the packaging container was 80 cm with the bottom surface of the packaging container being substantially parallel to the floor surface.

[0092] The number of tests for the impact resistance test was set to 3 times. When none of the packaging containers were cracked, the impact resistance was evaluated as "good", and when any of the packaging containers were cracked, the impact resistance was evaluated as "poor".

[0093] 〔Evaluation results〕 For the laminated sheets of each example and comparative example, the component compositions and evaluation results are shown in Tables 1 to 4 below. "%" in Tables 1 to 4 all indicate weight %. Tables 1 to 4 respectively show the component compositions and evaluation results of the laminated sheets in each test carried out by changing the component compositions of the foamed layer and / or non-foamed layer.

[0094] Figures 3 and 4 are diagrams showing the correlation between the strength increase rate of the thermoformed product (Figure 3: MD direction, Figure 4: TD direction) and the cellulose nanofiber content of the non-foamed layer of the example between the corresponding example and comparative example in Examples 4 to 17 and Comparative Examples 4 to 7. The strength increase rate is a value calculated by comparing an example and a comparative example in which the composition of the foamed layer is the same and the presence or absence of cellulose nanofibers in the non-foamed layer is different, and shows the value calculated by the following formula (1). Strength increase rate (%) = (Strength of example - Strength of comparative example) / Strength of comparative example (1)

[0095] In FIGS. 3 and 4, the vertical axis represents the strength increase rate, and the horizontal axis represents the content of cellulose nanofibers in the examples. For the combinations of the examples and comparative examples to be compared, they were classified as follows for each composition of the foam layer. · 75 wt% polystyrene resin / 14 wt% polyolefin resin (PS75 / PO14): combination of Examples 4 - 5 and Comparative Example 4 · 65 wt% polystyrene resin / 24 wt% polyolefin resin (PS65 / PO24): combination of Examples 6 - 10 and Comparative Example 5 · 45 wt% polystyrene resin / 44 wt% polyolefin resin (PS45 / PO44): combination of Examples 11 - 12 and Comparative Example 6 · 29 wt% polystyrene resin / 60 wt% polyolefin resin (PS29 / PO60): combination of Examples 13 - 17 and Comparative Example 7

[0096]

Table 1

[0097]

Table 2

[0098]

Table 3

[0099]

Table 4

[0100] As shown in Table 1, the laminated sheet of Example 1 containing cellulose nanofibers in the non-foamed layer had better strength and heat resistance than the laminated sheet of Comparative Example 1 containing no filler. Also, the laminated sheet of Example 1 had better strength and heat resistance even when compared with the laminated sheet of Comparative Example 2 containing talc instead of cellulose nanofibers. Furthermore, the laminated sheet of Example 1 had good impact resistance equivalent to that of the laminated sheets of Comparative Examples 1 and 2.

[0101] Also, as shown in Table 2, the laminated sheets of Examples 2 and 3 containing cellulose nanofibers in the non-foamed layer had good heat resistance temperature compared with the laminated sheet of Comparative Example 3 containing no filler, and were equal to or higher in strength. Also, the laminated sheets of Examples 2 and 3 had good impact resistance equivalent to that of the laminated sheet of Comparative Example 3.

[0102] Also, as shown in Table 3, Table 4, FIG. 3 and FIG. 4, it was shown that the higher the content of the polyolefin resin in the foamed layer, the higher the strength of the thermoformed product. That is, it was suggested that the higher the content of the polyolefin resin in the foamed layer, the more likely the effect of the cellulose nanofibers contained in the non-foamed layer is to be exerted.

[0103] Also, it was shown that the strength and heat resistance temperature of the thermoformed product improved as the content of cellulose nanofibers in the non-foamed layer increased. This tendency was remarkable when the content of cellulose nanofibers was 5% by weight or less. In Examples 4 to 17, it is considered that the non-foamed layer contains a dispersant, so that even if the content of cellulose nanofibers is small, it is easily dispersed uniformly. It was suggested that such a dispersant makes it easy to improve the physical properties of the thermoformed product while reducing the content of cellulose nanofibers.

[0104] Note that when the content of cellulose nanofibers in the non-foamed layer exceeds 5% by weight, a tendency was observed that the increasing rate of the strength and heat resistance temperature of the thermoformed product with respect to the increase in the content of cellulose nanofibers becomes small.

[0105] Also, when Examples 15 to 17 and Comparative Example 6, where the strength of the thermoformed products is comparable, were compared, it was also shown that the addition of cellulose nanofibers to the non-foamed layer improved the heat resistance temperature (by 12°C).

Explanation of Signs

[0106] 1, 1a Laminated sheet 10 Foamed layer 11 First surface 12 Second surface 20 Non-foamed layer

Claims

1. At least one non-foamed layer formed of a polyolefin resin containing cellulose nanofibers; and a foamed layer formed of a mixed resin containing a polystyrene-based resin and a polyolefin-based resin, on which the at least one non-foamed layer is laminated.

2. The non-foamed layer is provided. The laminate sheet of claim 1 , wherein the foamed layer is laminated between two of the non-foamed layers.

3. The laminate sheet according to claim 1 , wherein the non-foamed layer has a cellulose nanofiber content of 1% by weight or more and 50% by weight or less.

4. 2. The laminate sheet according to claim 1, wherein the foam layer contains a polystyrene resin in an amount of 25% by weight or more and 80% by weight or less.

5. The laminate sheet according to claim 1 , wherein the foam layer has a polyolefin resin content of 10% by weight or more and less than 65% by weight.

6. A thermoformed product of the laminate sheet according to any one of claims 1 to 5.

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