JP7520996B2 - Multilayer resin sheet and molded container - Google Patents

Description

The present invention relates to a multilayer resin sheet containing polylactic acid resin and a molded container comprising the same.

In recent years, there has been an increasing demand for biodegradable resins in order to reduce the burden on the environment. Polylactic acid resin, a type of biodegradable resin, is inexpensive and has excellent rigidity and high transparency. For this reason, polylactic acid resin is expected to be used as a material for molded containers such as packs, cups, and trays for beverages, foods, cosmetics, home appliances, and other daily necessities, and technical improvements are being made to the material.

Patent Document 1 (JP Patent Publication No. 2007-130895) describes how combining polylactic acid with a specific plasticizer (succinic acid esters) and a crystal nucleating agent (organic crystal nucleating agent) promotes crystallization during thermoforming while maintaining transparency, resulting in a molded product with excellent heat resistance, etc.

Patent Document 2 (JP 2014-51646 A) describes that in thermoforming of a polylactic acid resin composition, differences in phase difference (phase difference due to birefringence that occurs when light passes through a sheet, so-called retardation) in a thermoforming sheet significantly affects thermoformability, and that thermoformability can be greatly improved by forming the sheet so that the phase difference remains within a specific range by adjusting various conditions in the sheeting process.

On the other hand, polybutylene succinate resin is known as a biodegradable resin other than polylactic acid resin. Taking advantage of the excellent tensile strength and tensile elongation of polybutylene succinate resin, various technical improvements are being made. For example, Patent Document 3 (JP 2003-253105 A) describes coloring polybutylene succinate resin for the purposes of decorative effects, control of light transmission, and prevention of plastic deterioration. Patent Document 4 (JP 2006-168375 A) describes a resin sheet in which heat resistance, impact resistance, and moldability are improved by blending polylactic acid resin and polybutylene succinate resin.

JP 2007-130895 A JP 2014-51646 A JP 2003-253105 A JP 2006-168375 A

However, since polylactic acid resin has high fluidity, there is a problem that drawdown is likely to occur during sheet formation, making it difficult to achieve a desired surface appearance. In addition, while polylactic acid resin has a high tensile modulus, it has poor impact resistance. For this reason, there is also a problem that the formed sheet is prone to cracking when wound up. The same problem occurs when polylactic acid resin sheets are subjected to secondary molding processes such as container processing. On the other hand, polybutylene succinate resin does not have the problem of cracking during sheet winding, but has the problem of poor punching processability, and cannot be used as a substitute for polylactic acid resin. Furthermore, both polylactic acid resin and polybutylene succinate resin have the problem of poor oxygen barrier properties, and even if the two are blended, it is difficult to say that the performance required for a high-performance resin sheet is fully met.

The present invention was created in consideration of the above circumstances, and in one embodiment, it is an object of the present invention to provide a resin sheet containing polylactic acid resin, which has excellent environmental performance, is capable of suppressing the occurrence of cracks during winding, and further has excellent punching workability and oxygen barrier properties. In another embodiment, it is an object of the present invention to provide a molded container including such a resin sheet.

The inventors conducted intensive research to solve the above problems and discovered that by laminating an oxygen barrier layer via an adhesive layer to a substrate layer containing a resin composition in which polylactic acid resin and polybutylene succinate resin are blended in a specified ratio, a highly functional resin sheet can be obtained while still having a high proportion of biodegradable resin, leading to the invention illustrated below.

[1]
A multilayer resin sheet including a base layer and an oxygen barrier layer laminated on one surface of the base layer via an adhesive layer,
the base layer contains polylactic acid resin and polybutylene succinate resin in a mass ratio of polylactic acid resin:polybutylene succinate resin=2:8 to 8:2;
The ratio of biodegradable resin in the multilayer resin sheet is 90% by mass or more.
Multi-layer resin sheet.
[2]
The multilayer resin sheet according to [1], wherein the adhesive layer between the substrate layer and the oxygen barrier layer contains a biodegradable resin adhesive.
[3]
The multilayer resin sheet according to [2], wherein the adhesive layer between the base material layer and the oxygen barrier layer contains a biodegradable acid-modified polyester resin as a biodegradable resin-based adhesive.
[4]
The multilayer resin sheet according to any one of [1] to [3], wherein the oxygen barrier layer contains a biodegradable oxygen barrier resin.
[5]
The multilayer resin sheet according to [4], wherein the oxygen barrier layer contains a biodegradable vinyl alcohol-butenediol copolymer as the biodegradable oxygen barrier resin.
[6]
The multilayer resin sheet according to any one of [1] to [5], further comprising a surface layer laminated via an adhesive layer on a surface of the oxygen barrier layer opposite to a surface having the base layer, the surface layer containing a biodegradable resin.
[7]
The multilayer resin sheet according to [6], wherein the adhesive layer between the surface layer and the oxygen barrier layer contains a biodegradable acid-modified polyester resin.
[8]
The multilayer resin sheet according to [6] or [7], wherein the surface layer contains a polylactic acid resin and a polybutylene succinate resin.
[9]
The multilayer resin sheet according to [8], wherein the surface layer contains polylactic acid resin and polybutylene succinate resin in a mass ratio of polylactic acid resin:polybutylene succinate resin=2:8 to 8:2.
[10]
The multilayer resin sheet according to any one of [1] to [9], further comprising an underskin layer laminated on a surface of the base layer opposite to a surface having the oxygen barrier layer, the underskin layer comprising a biodegradable resin.
[11]
The multilayer resin sheet according to [10], wherein the underlayer contains a polylactic acid resin and a polybutylene succinate resin.
[12]
The multilayer resin sheet according to [11], wherein the underlayer contains polylactic acid resin and polybutylene succinate resin in a mass ratio of polylactic acid resin:polybutylene succinate resin = 2:8 to 8:2.
[13]
The multilayer resin sheet according to any one of [1] to [12], wherein the substrate layer contains a crystal nucleating agent.
[14]
an oxygen barrier layer laminated on one surface of a base layer via an adhesive layer;
a surface layer laminated via an adhesive layer on a surface of the oxygen barrier layer opposite to the surface having the base layer;
a subskin layer laminated on a surface of the base layer opposite to a surface having the oxygen barrier layer;
[14] The multilayer resin sheet according to any one of [1] to [13], wherein at least one of the substrate layer, the skin layer, and the underskin layer contains a crystal nucleating agent.
[15]
The multilayer resin sheet according to any one of [1] to [14], wherein the multilayer resin sheet has a total thickness of 200 to 1300 μm, and the oxygen barrier layer has a thickness of 1 to 50 μm.
[16]
The multilayer resin sheet according to any one of [1] to [15], having a DuPont impact strength measured in accordance with JIS K7211-1:2006 of 1.0 J or more.
[17]
The multilayer resin sheet according to any one of [1] to [16], wherein the tensile modulus measured in accordance with JIS K7161:2014 is 1100 MPa or more in the TD direction and 1100 MPa or more in the MD direction.
[18]
The multilayer resin sheet according to any one of [1] to [17], wherein a peel strength between the oxygen barrier layer and the base layer, measured in a 180° peel test in accordance with GB8808-1988, is 7 N/15 mm or more when peeled in the TD direction, and 7 N/15 mm or more when peeled in the MD direction.
[19]
A molded container comprising the multilayer resin sheet according to any one of [1] to [18].
[20]
The molded container according to [19], wherein a notch is formed in the multilayer resin sheet.

The multilayer resin sheet according to one embodiment of the present invention has high environmental performance because the proportion of biodegradable resin is 90% by mass or more, while it is possible to suppress the occurrence of cracks during winding and it also has excellent punching processability and oxygen barrier properties. Therefore, by using this resin sheet, it is possible to mold various molded products that combine environmental performance and practicality, such as molded containers such as packs and trays for beverages, foods, cosmetics, home appliances, and other daily necessities.

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

<1. Multilayer resin sheet>
According to one embodiment of the present invention, a multilayer resin sheet is provided that includes a base layer and an oxygen barrier layer laminated on one side of the base layer via an adhesive layer. Since the ratio of biodegradable resin in the multilayer resin sheet is 90% by mass or more, the multilayer resin sheet has excellent environmental performance. Here, the biodegradable resin in this specification refers to a resin that is completely consumed by microorganisms and produces only natural by-products (carbon dioxide, methane, water, biomass, etc.). Preferably, the biodegradable resin has a biodegradability of 60% or more within one year in aerobic compost soil as defined in JIS K6953-1 (2011). In addition, the base layer is composed of a resin composition containing polylactic acid resin and polybutylene succinate resin in a mass ratio of polylactic acid resin:polybutylene succinate resin = 2:8 to 8:2, thereby making it possible to suppress the occurrence of cracks during winding and to achieve both punching processability. Furthermore, the multilayer resin sheet has an oxygen barrier layer, thereby ensuring oxygen barrier properties that cannot be achieved by the base layer alone.

1 shows a multilayer resin sheet 10 according to one embodiment of the present invention. The multilayer resin sheet 10 has a base layer 14, an oxygen barrier layer 13 laminated on one side of the base layer 14 via an adhesive layer 12b, a surface layer 11 laminated on the surface of the oxygen barrier layer 13 opposite to the surface having the base layer 14 via an adhesive layer 12a, and an underskin layer 15 laminated on the surface of the base layer 14 opposite to the surface having the oxygen barrier layer 13. That is, the multilayer resin sheet 10 has a layered structure in which the surface layer 11/adhesive layer 12a/oxygen barrier layer 13/adhesive layer 12b/base layer 14/underskin layer 15 are laminated in this order from the top to the bottom of the paper. In this embodiment, the oxygen barrier layer 13 is laminated on the surface layer 11 and the base layer 14 via the adhesive layers 12a and 12b, while the base layer 14 and the underskin layer 15 are directly laminated. Hereinafter, the embodiment of each layer will be described.

(a. Substrate Layer)
The multilayer resin sheet 10 according to this embodiment has a base layer 14 composed of a resin composition containing polylactic acid resin and polybutylene succinate resin in a mass ratio of polylactic acid resin:polybutylene succinate resin = 2:8 to 8:2, preferably a mass ratio of 3:7 to 7:3, and more preferably a mass ratio of 4:6 to 6:4.

Polylactic acid resin can be produced from plants such as corn, sugar cane, and sugar radish, without using petroleum as a raw material, and is also completely biodegradable into water and carbon dioxide by microorganisms in the soil, making it highly environmentally friendly. Examples of polylactic acid resin include homopolymers such as poly(L-lactic acid) and poly(D-lactic acid), copolymers having structural units of both L-lactic acid and D-lactic acid (DL-lactic acid), and mixtures of these.

Polylactic acid resins that are composed only of the L-form have the disadvantage of being brittle and difficult to process, so copolymers containing approximately 0.1 to 8 mol% of the D-form (DL-lactic acid) are preferred, and copolymers containing approximately 0.1 to 4 mol% of the D-form (DL-lactic acid) are even more preferred.

The polylactic acid resin preferably has an MFR of 2 to 12 g/10 min at 190°C and 2.16 kg, measured in accordance with JIS K7210-1:2014. The lower limit of the MFR is preferably 2 g/10 min or more, more preferably 3 g/10 min or more, and even more preferably 4 g/10 min or more, which provides the advantage that the molten resin easily spreads in the sheet width direction. The upper limit of the MFR is preferably 12 g/10 min or less, more preferably 10 g/10 min or less, and even more preferably 8 g/10 min or less, which provides the advantage that the flow of the molten resin to both ends in the sheet width direction is moderately suppressed.

Polylactic acid resin can be polymerized by known methods such as condensation polymerization and ring-opening polymerization. For example, in the condensation polymerization method, L-lactic acid, D-lactic acid, or a mixture thereof can be directly dehydrated and condensed to obtain a polylactic acid resin having any composition. During polymerization, various additives may be added within a range that does not impair the effects of the present invention. For example, non-aliphatic dicarboxylic acids such as terephthalic acid and non-aliphatic diols such as ethylene oxide adducts of bisphenol A can be appropriately added to improve heat resistance. In addition, chain extenders such as diisocyanate compounds, epoxy compounds, and acid anhydrides can be appropriately added to increase the molecular weight.

Polybutylene succinate resin can also be produced using plants such as sugar cane, cassava and corn as raw materials. It can be completely biodegraded into water and carbon dioxide by microorganisms in the soil. Polybutylene succinate resin can be produced by known polymerization methods, for example, it can be synthesized by esterifying 1,4-butanediol and succinic acid through condensation polymerization. During polymerization, various additives may be added within a range that does not impair the effects of the present invention. For example, known catalysts and binders can be added as appropriate for the purpose of increasing the molecular weight.

Among polybutylene succinate resins, those that use succinic acid derived from plants such as corn as a raw material are preferred from the perspective of environmental impact.

The polybutylene succinate resin preferably has an MFR of 2 to 12 g/10 min at 190°C and 2.16 kg, measured in accordance with JIS K7210-1:2014. The lower limit of the MFR is preferably 2 g/10 min or more, more preferably 3 g/10 min or more, and even more preferably 4 g/10 min or more, which provides the advantage that the molten resin easily spreads in the sheet width direction. In addition, the upper limit of the MFR is preferably 12 g/10 min or less, more preferably 10 g/min or less, and even more preferably 8 g/10 min or less, which provides the advantage that the flow of the molten resin to both ends in the sheet width direction is appropriately suppressed.

The base layer 14 may contain a crystal nucleating agent. By incorporating a crystal nucleating agent, the crystallization of the polylactic acid resin is promoted when the resin sheet is formed, thereby improving the heat resistance. The crystal nucleating agent is preferably selected from, but not limited to, natural or synthetic silicate compounds, metal salts such as titanium oxide, barium sulfate, tricalcium phosphate, calcium carbonate, and sodium phosphate, inorganic compounds such as kaolinite, halloysite, talc, smectite, vermiculite, and mica, metal phthalocyanine complexes such as phthalocyanine iron, organic metal salts such as organic phosphonate compounds such as phenylphosphonic acid metal salts, amide compounds having a ring structure, organic hydrazide compounds, organic sulfonate compounds, phthalocyanine compounds and melamine compounds, and organic compounds such as alkylene oxides. The content of the crystal nucleating agent in the base layer 14 can be, for example, 3 phr to 15 phr, and preferably 5 phr to 10 phr, based on the total mass of the polylactic acid resin and the polybutylene succinate resin.

In addition, when performing printing processing on the multilayer resin sheet or its molded product by laser irradiation or the like, it is preferable that the base layer 14 contains a white pigment in an amount of 1 phr or more and 5 phr or less. Furthermore, it is more preferable that the white pigment contained in the base layer 14 is 1.5 phr or more and 4 phr or less. The unit phr used here refers to the mass parts of the white pigment per 100 mass parts of the total resin components in the base layer 14. By containing 1 phr or more of white pigment in the base layer 14, concealment properties can be obtained, and when performing printing processing on the multilayer resin sheet or its molded product, the print color can be improved, and further, light blocking properties can be obtained, and discoloration and deterioration of the contents due to light irradiation from the outside of the molded product can be suppressed. In addition, by making the white pigment in the base layer 14 5 phr or less, aggregation of the white pigment can be suppressed, and poor appearance due to aggregates of the multilayer resin sheet or its molded product can be suppressed. In addition, in terms of cost, it is preferable to have a small amount of white pigment.

The white pigments include titanium oxide (titanium white), zinc oxide (zinc white), lithopone, white lead, etc., of which titanium oxide is preferred. The white pigments may be used alone or in combination of two or more.

In the base layer 14, other resins may be mixed, and various additives other than the resin components may be added, as long as the effects of the present invention are not impaired. Examples of such additives include the above-mentioned crystal nucleating agent and white pigment, as well as compatibilizers that make different components compatible, other pigments, colorants such as dyes, release agents such as silicone oil and alkyl esters, fibrous reinforcing agents such as glass fibers, granular lubricants such as talc, clay, and silica, antistatic agents such as salt compounds of sulfonic acid and alkali metals, polyalkylene glycols, ultraviolet absorbers, and additives such as antibacterial agents. In addition, scrap resin generated in the manufacturing process of the multilayer resin sheet or molded container according to one embodiment of the present invention can be mixed.

However, generally, the total content of polylactic acid resin and polybutylene succinate resin in the base layer 14 is 80% by mass or more, typically 90% by mass or more, more typically 95% by mass or more, and can even be 100% by mass.

The thickness of the base layer 14 is preferably 100 to 800 μm, and more preferably 150 to 500 μm. Making the thickness of the base layer 14 100 μm or more is advantageous in that it ensures the strength of the molded product obtained by molding the multilayer resin sheet. Making the thickness of the base layer 14 800 μm or less is advantageous in that it reduces the cost of the multilayer resin sheet and its molded products, such as thermoformed containers.

(b. Oxygen Barrier Layer)
The multilayer resin sheet 10 according to the present embodiment has an oxygen barrier layer 13 laminated on one surface of a base layer 14 via an adhesive layer 12b. Oxygen barrier properties can be imparted to the multilayer resin sheet by providing the oxygen barrier layer 13. In particular, since polylactic acid resin and polybutylene succinate resin have low oxygen barrier properties, when a resin sheet is used as a material for packaging containers for products that are susceptible to deterioration in the presence of oxygen, such as beverages and foods, it is useful to provide them as a laminate having an oxygen barrier layer and a base layer.

The oxygen barrier layer 13 may be made of a known oxygen barrier resin, and is not particularly limited. In a preferred embodiment, the oxygen barrier layer 13 contains a biodegradable oxygen barrier resin. Representative examples of the biodegradable oxygen barrier resin include, but are not limited to, biodegradable polyamide and biodegradable polyvinyl alcohol. In addition to currently known biodegradable oxygen barrier resins, those that will be developed in the future as technological development progresses can be used. The oxygen barrier resin may be used alone or in combination of two or more types.

As a biodegradable oxygen barrier resin, a biodegradable vinyl alcohol-butenediol copolymer is particularly preferred in terms of extrusion moldability and peel strength. In order to provide the biodegradable vinyl alcohol-butenediol copolymer with oxygen barrier properties and extrusion moldability, it is preferable that the saponification degree is 90 mol% or more, preferably 95 mol% or more. The saponification degree is measured in accordance with JIS K6726:1994.

The lower limit of the butenediol content in the vinyl alcohol-butenediol copolymer is preferably 10% by mass or more, and more preferably 20% by mass or more, from the viewpoint of enhancing biodegradability. The upper limit of the butenediol content in the vinyl alcohol-butenediol copolymer is preferably 40% by mass or less, and more preferably 30% by mass or less, from the viewpoint of exhibiting sufficient oxygen barrier properties. The butenediol content refers to the ratio of the mass of butenediol units to the total mass of vinyl alcohol units and butenediol units that constitute the vinyl alcohol-butenediol copolymer.

Examples of biodegradable polyamides include nylon 4 and nylon 2/nylon 6 copolymer.

The oxygen barrier resin preferably has an MFR of 0.50 to 10.0 g/10 min at 190°C and 2.16 kg, measured in accordance with JIS K7210-1:2014. The lower limit of the MFR is preferably 0.50 g/10 min or more, more preferably 0.80 g/10 min or more, and even more preferably 1.00 g/10 min or more, which provides the advantage that the molten resin easily spreads in the sheet width direction. The upper limit of the MFR is preferably 10.0 g/10 min or less, more preferably 8.0 g/10 min or less, and even more preferably 6.0 g/10 min or less, which provides the advantage that the flow of the molten resin to both ends in the sheet width direction is moderately suppressed.

The oxygen barrier layer 13 may contain resins other than the oxygen barrier resin, and various additives other than the resin components may be added, as long as the effect of the present invention is not impaired. Examples of such additives include colorants such as pigments and dyes, release agents such as silicone oils and alkyl esters, fibrous reinforcing agents such as glass fibers, granular lubricants such as talc, clay, and silica, antistatic agents such as salt compounds of sulfonic acid and alkali metals, polyalkylene glycols, and additives such as ultraviolet absorbers and antibacterial agents. However, in general, the content of the biodegradable oxygen barrier resin in the oxygen barrier layer 13 is 80% by mass or more, typically 90% by mass or more, more typically 95% by mass or more, and can be 100% by mass. In a preferred embodiment, the content of the vinyl alcohol-butenediol copolymer in the oxygen barrier layer 13 is 80% by mass or more, typically 90% by mass or more, more typically 95% by mass or more, and can be 100% by mass.

The thickness of the oxygen barrier layer 13 is preferably 1 to 50 μm, and more preferably 5 to 30 μm. Making the oxygen barrier layer 13 1 μm or more thick is advantageous in terms of enhancing the oxygen barrier properties of the multilayer resin sheet 10. Making the oxygen barrier layer 13 50 μm or less thick makes it easier for the oxygen barrier layer 13 to be thermally stretched when the multilayer resin sheet 10 is molded into a container or the like, ensuring a smoother thickness for the molded product, and enabling the production of a molded product with a better appearance.

(c. Epidermis Layer)
The multilayer resin sheet 10 according to the present embodiment has a skin layer 11 laminated via an adhesive layer 12a on the surface of the oxygen barrier layer 13 opposite to the surface having the base layer 14. The skin layer 11 is not necessarily provided, but is preferably provided. Specifically, if the oxygen barrier layer 13 constitutes the outermost layer of the multilayer resin sheet 10, the oxygen barrier layer 13 tends to have high adhesion, which may cause a problem that the layer sticks to the rolls during the cooling process during the production of the laminate, making it difficult to obtain a good surface appearance. However, by forming the surface of the multilayer resin sheet 10 by covering the oxygen barrier layer 13 with the skin layer 11, such a problem can be eliminated.

The skin layer 11 can be made of a resin that is basically the same as or similar to the base layer 14. Therefore, in one embodiment, the skin layer 11 can contain polylactic acid resin and polybutylene succinate resin, and the polylactic acid resin and the polybutylene succinate resin are preferably contained in a mass ratio of polylactic acid resin:polybutylene succinate resin = 2:8 to 8:2, more preferably in a mass ratio of 3:7 to 7:3, and even more preferably in a mass ratio of 4:6 to 6:4. Other embodiments of the skin layer 11, including preferred embodiments, are basically the same as the base layer 14, so duplicated explanations will be omitted. Below, the differences between the skin layer 11 and the base layer 14 will be explained.

It is desirable that the skin layer 11 does not contain scrap resin in order to improve the appearance of the multilayer resin sheet 10.

The thickness of the skin layer 11 is preferably 10 to 300 μm, and more preferably 30 to 200 μm. By making the thickness of the skin layer 11 10 μm or more, the skin layer 11 is stretched when the multilayer resin sheet 10 is thermoformed, and an excellent molded container can be obtained without tearing. By making the thickness of the skin layer 11 300 μm or less, the notch blade can reach the oxygen barrier layer 13 sufficiently when notching during thermoforming, and the layer can be successfully ruptured.

(d. Hypodermis Layer)
The multilayer resin sheet 10 according to the present embodiment has an underskin layer 15 laminated on the surface of the substrate layer 14 opposite to the surface having the oxygen barrier layer 13. The underskin layer 15 may not be provided, but may be provided for the reason of improving the appearance of the multilayer resin sheet 10. For example, even if the substrate layer 14 has defects in appearance due to the inclusion of scrap resin, such defects in appearance do not appear on the surface of the multilayer resin sheet 10, and a multilayer resin sheet 10 with a better appearance can be obtained. The underskin layer 15 can be basically composed of the same or similar resin as the substrate layer 14. Thus, in one embodiment, the underskin layer 15 can contain a polylactic acid resin and a polybutylene succinate resin, and the polylactic acid resin and the polybutylene succinate resin are preferably contained in a mass ratio of polylactic acid resin:polybutylene succinate resin=2:8 to 8:2, more preferably in a mass ratio of 3:7 to 7:3, and even more preferably in a mass ratio of 4:6 to 6:4. Other than that, the embodiments of the underskin layer 15, including the preferred embodiments, are basically the same as those of the base material layer 14, and therefore a duplicated description will be omitted. Below, the differences between the underskin layer 15 and the base material layer 14 will be described.

In view of the objective of improving the appearance of the multilayer resin sheet 10, it is desirable that the undercoat layer 15 does not contain scrap resin.

The thickness of the underskin layer 15 is preferably 5 to 100 μm, more preferably 10 to 60 μm. By making the thickness of the underskin layer 15 5 μm or more, it is more effective at concealing defects in appearance caused by the base material layer 14. By making the thickness of the underskin layer 15 100 μm or less, it is possible to increase the utilization rate of scrap resin in the multilayer resin sheet and reduce manufacturing costs.

In order to perform printing processing on the multilayer resin sheet and its molded products by laser irradiation, etc., the underskin layer 15 preferably contains 0.04 phr to 0.50 phr of a pigment suitable for printing by laser marking. Furthermore, it is more preferable that the pigment contained in the underskin layer 15 is 0.07 phr or more and 0.15 phr or less. The unit phr used here refers to the parts by mass of pigment per 100 parts by mass of all resin components in the underskin layer 15. The underskin layer 15 containing 0.04 phr or more of pigment is advantageous for expressing laser printability, and containing 0.50 phr or less can reduce the cost of the multilayer resin sheet and its molded products such as thermoformed containers.

Pigments suitable for marking by laser processing include mica, titanium oxide, antimony oxide, metal salts such as copper phosphates and sulfates, and black pigments such as carbon black, of which antimony oxide is preferred because it can enhance the contrast of markings made by laser processing. The above pigments may be used alone or in combination of two or more.

(e. Adhesive Layer)
A known adhesive can be used for the adhesive layers 12a and 12b, and there is no particular restriction on this, but in a preferred embodiment, the adhesive layers 12a and 12b contain a biodegradable resin adhesive. As the biodegradable resin adhesive, a polyester adhesive containing a biodegradable acid-modified polyester resin is preferred from the viewpoint of achieving both excellent environmental performance and high interlayer adhesive strength, although this is not a limitation. The biodegradable resin adhesive may be used alone or in combination of two or more types.

Examples of polyester-based adhesives containing acid-modified polyester resins include, but are not limited to, acid-modified polyesters obtained by condensation polymerization of dicarboxylic acids and diol compounds, and acid-modified polyester-polyether copolymers. Polyesters include polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), and polybutylene naphthalate (PBN), which are obtained by dehydration condensation of polyalcohol resins and polycarboxylic acids. Polyester-polyether copolymers include polyester elastomers with polyester as the hard segment and polyether polyol as the soft segment, and a specific example is polybutylene terephthalate-polytetramethylene ether glycol copolymer. Examples of the acid modification method include a method of acid modification under graft reaction conditions using unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, tetrahydrophthalic acid, etc., or derivatives thereof such as acid halides, amides, imides, anhydrides, esters, etc., specifically malenyl chloride, maleimide, maleic anhydride, citraconic anhydride, monomethyl maleate, dimethyl maleate, glycidyl maleate, etc. In order to enhance biodegradability, it is preferable to introduce a hydroxyl group into the side chain of the acid-modified polyester resin.

As an acid-modified polyester resin, it is preferable to use an acid-modified polybutylene terephthalate-polytetramethylene ether glycol copolymer because it is biodegradable and has high interlayer adhesion.

The adhesive layers 12a and 12b preferably have an MFR of 2 to 12 g/10 min at 230°C and 2.16 kg, measured in accordance with JIS K7210-1:2014. The lower limit of the MFR is preferably 2 g/10 min or more, more preferably 4 g/10 min or more, which provides the advantage that the molten resin easily spreads in the sheet width direction. The upper limit of the MFR is preferably 12 g/10 min or less, more preferably 10 g/10 min or less, which provides the advantage that the flow of the molten resin to both ends in the sheet width direction is appropriately suppressed.

The thickness of each of the adhesive layers 12a and 12b is preferably 2 to 30 μm, and more preferably 5 to 20 μm. By making the thickness of the adhesive layers 12a and 12b 2 μm or more, sufficient interlayer adhesive strength can be obtained in the multilayer resin sheet, and by making the thickness 30 μm or less, the problem of poor appearance called whisker burrs that occurs during punching of containers and the like performed after molding can be suppressed.

It is permissible to add various additives to the adhesive layers 12a and 12b as long as they do not impair the effects of the present invention. Examples of such additives include colorants such as pigments and dyes, release agents such as silicone oils and alkyl esters, fibrous reinforcing agents such as glass fibers, granular lubricants such as talc, clay, and silica, antistatic agents such as salt compounds of sulfonic acid and alkali metals and polyalkylene glycols, and additives such as ultraviolet absorbers and antibacterial agents. However, in general, the content of the biodegradable resin adhesive in the adhesive layers 12a and 12b is 80% by mass or more, typically 90% by mass or more, more typically 95% by mass or more, and can be 100% by mass. In a preferred embodiment, the content of the biodegradable acid-modified polyester resin in the adhesive layers 12a and 12b is 80% by mass or more, typically 90% by mass or more, more typically 95% by mass or more, and can be 100% by mass.

(f. Nucleating Agent)
From the viewpoint of improving heat resistance, it is preferable that at least one of the base layer 14, the skin layer 11, and the underskin layer 15 constituting the multilayer resin sheet 10 contains a crystal nucleating agent, it is preferable that two or more layers contain a crystal nucleating agent, and it is more preferable that all layers contain a crystal nucleating agent. Specific examples of the crystal nucleating agent are as described above. The content of the crystal nucleating agent in the base layer 14, the skin layer 11, and the underskin layer 15 can be, for example, 3 phr to 15 phr, and preferably 5 phr to 10 phr, based on the total mass of the polylactic acid resin and the polybutylene succinate resin.

(g. Properties of the Multilayer Resin Sheet)
The thickness of the multilayer resin sheet 10 is preferably 200 to 1300 μm. By making the thickness of the multilayer resin sheet 10 200 μm or more, the strength of the molded product obtained by molding the multilayer resin sheet 10 can be ensured. For example, the side or bottom of the container obtained by thermoforming can be made sufficiently thick, thereby obtaining sufficient container strength. By making the thickness of the multilayer resin sheet 10 1300 μm or less, the cost of the multilayer resin sheet 10 and molded products such as thermoformed containers can be reduced.

The multilayer resin sheet 10 preferably has a DuPont impact strength of 1.0 J or more measured in accordance with JIS K7211-1:2006. The lower limit of the DuPont impact strength is preferably 1.0 J or more, more preferably 1.4 J or more, which provides the advantage of sufficient impact resistance as a molding container and being less likely to break when dropped. There is no particular limit to the upper limit of the DuPont impact strength, but it can be, for example, 4.0 J or less, typically 3.5 J or less. Therefore, in one embodiment, the multilayer resin sheet 10 has a DuPont impact strength of 1.0 to 4.0 J measured in accordance with JIS K7211-1:2006. Here, the DuPont impact strength refers to the 50% breaking energy E50 (J) when a DuPont impact test is performed under a drop load of 500 g and a measurement environment of 23°C x 50% R.H.

The multilayer resin sheet 10 preferably has a tensile modulus of elasticity measured in accordance with JIS K7161:2014 of 1100 MPa or more in the TD direction and 1100 MPa or more in the MD direction. The lower limit of the tensile modulus in the MD direction and the TD direction is preferably 1100 MPa or more, more preferably 1500 MPa or more, which provides the advantage of sufficient rigidity as a molded container and making it difficult to crush. There is no particular limit to the upper limit of the tensile modulus in the MD direction and the TD direction, but it can be, for example, 2500 MPa or less, typically 2100 MPa or less. Therefore, in one embodiment, the multilayer resin sheet 10 has a tensile modulus of elasticity measured in accordance with JIS K7161:2014 of 1100 to 2500 MPa in the TD direction and 1100 to 2500 MPa in the MD direction. Here, the tensile modulus is measured in a measurement environment of 23°C x 50% R.H. The measurement is performed under the conditions of a chuck distance of 100 mm and a tensile speed of 50 mm/min.

In the multilayer resin sheet 10, the peel strength when a 180° peel test is performed between the oxygen barrier layer 13 and the base layer 14 measured in accordance with GB8808-1988 is preferably 7 N/15 mm or more when peeled in the TD direction and 7 N/15 mm or more when peeled in the MD direction. The lower limit of the peel strength in the MD direction and the TD direction is preferably 7 N/15 mm or more, more preferably 10 N/15 mm or more, and this provides the advantage that when the molded container is used as a package, delamination due to interlayer peeling of the molded container is unlikely to occur when the heat-sealed lid material is peeled off. There is no particular limit to the upper limit of the peel strength in the MD direction and the TD direction, but it can be, for example, 30 N/15 mm or less, typically 25 N/15 mm or less. Therefore, in one embodiment, the multilayer resin sheet 10 has a peel strength of 7 to 30 N/15 mm when peeled in the TD direction and 7 to 30 N/15 mm when peeled in the MD direction when a 180° peel test is carried out between the oxygen barrier layer 13 and the base layer 14 measured in accordance with GB8808-1988. Here, the peel strength is measured under the conditions of a measurement environment of 23° C.×50% RH, a chuck distance of 100 mm, and a tensile speed of 300 mm/min.

The layer structure of the multilayer resin sheet according to one embodiment of the present invention is not limited to the laminated structure shown in FIG. 1. For example, each layer may be configured to have two or more layers. In addition, a new layer may be provided in which scrap generated in the process of manufacturing a multilayer resin sheet or molded product such as a molded container is finely crushed and returned instead of being discarded, or a new layer may be provided in which recycled material that has been repelletized after thermal melting is returned to the multilayer resin sheet structure.

(h. Method for producing multi-layer resin sheet)
The method for producing the multilayer resin sheet is not particularly limited, and a general method can be used. For example, the multilayer resin sheet can be produced by a melt co-extrusion molding method in which a plurality of resins are bonded and laminated in a molten state using a plurality of extruders. More specifically, the multilayer resin sheet can be produced by melt-extruding the raw materials of each layer using five or more single-screw or twin-screw extruders, and obtaining the multilayer resin sheet using a feed block and a T-die equipped with a selector plug, or by using a multi-manifold die.

From the viewpoint of reducing the burden on the environment, it is preferable that the proportion of biodegradable resin in the multilayer resin sheet is 90% by mass or more, more preferably 95% by mass or more, and even more preferably 100% by mass.

<2. Molded container>
The multilayer resin sheet according to the present invention is thermoformable. Therefore, according to one embodiment of the present invention, a molded product including the multilayer resin sheet according to the present invention is provided. The type of molded product is not particularly limited, and examples include molded containers such as packs, cups, and trays for beverages, foods (including seasonings), cosmetics, home appliances, and other daily necessities. The multilayer resin sheet according to the present invention can constitute a part or all of the molded container. Among molded containers, a food packaging container is a preferred embodiment. Some food packaging containers have a connecting portion that connects multiple container bodies, and a notch (hereinafter referred to as a "notch") is formed in the connecting portion to separate each container body. In addition, there is also a so-called distribution package in which a notch is formed in the lid body to discharge the food packaged inside the packaging container to the outside of the packaging container. The distribution package is a small food packaging container that can easily extract liquid, paste, granular, or powder-like contents such as cosmetics, medicines, and other foods such as seasonings and beverages by pinching and folding with fingers.

The multilayer resin sheet constituting the molded container according to one embodiment of the present invention may have a notch. The notch may be formed on either the surface layer or the underskin layer of the multilayer resin sheet, but it is preferable that the notch at least partially cuts the oxygen barrier layer in order to improve crack propagation, and more preferably completely cuts it. This is because the oxygen barrier layer tends to stretch easily. Normally, the base layer of a multilayer resin sheet tends to be thick, so when comparing the distance from the surface layer side to the oxygen barrier layer and the distance from the underskin layer side to the oxygen barrier layer, the former is generally shorter. For this reason, in order to make it easier for the notch blade to reach the oxygen barrier layer when forming the notch, it is preferable to form the notch on the surface layer side of the multilayer resin sheet. The notch formed in the molded product of the multilayer resin sheet improves crack propagation due to the rigidity of the polylactic acid resin contained in the multilayer resin sheet, so that it can be imparted with excellent notch folding properties that allow it to be stably folded by hand.

When the multilayer resin sheet shown in FIG. 1 is used as a material for a molded container, it is preferable to construct a part or all of the molded container so that the skin layer 11 is located on the inner surface side of the molded container and the underskin layer 15 is located on the outer surface side of the molded container. For example, a distribution package generally comprises a lid body made of a hard material having a folding line with a notch called a "half cut part" in the center of the surface and a protrusion for facilitating extraction of the contents, and a container body made of a flexible material having a peripheral part fixed to the back surface of the lid body and forming pockets on both sides of the folding line. For example, the multilayer resin sheet according to the present invention can be molded into the lid body of the distribution package. In this case, it is preferable to manufacture the distribution package so that the skin layer 11 is located on the back surface side (the side that contacts the food) of the lid body and the underskin layer 15 is located on the front surface side of the lid body.

Methods for thermoforming multilayer resin sheets include, but are not limited to, typical vacuum forming and pressure forming, as well as applications of these, such as the plug-assist method in which a plug is brought into contact with one side of a multilayer resin sheet to perform thermoforming, and the so-called match mold forming method in which a pair of male and female molds are brought into contact with both sides of a multilayer resin sheet to perform thermoforming. In addition, known sheet heating methods, such as radiative heating using an infrared heater or the like, which is a non-contact heating method, can be used to heat and soften the multilayer resin sheet before thermoforming.

The multilayer resin sheet according to the present invention has excellent punching processability. For this reason, the multilayer resin sheet according to the present invention can be suitably used for so-called form-fill-seal (FFS) packaging, which involves an integrated process of thermoforming, filling with contents, heat-sealing a cover film as a lid material, and then punching out the packaging container to produce the finished product.

The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to the contents of the examples.

<1. Preparation of resin sheet>
The raw materials used in the examples and comparative examples are as follows.
(1) Surface layer, base layer, and underskin layer Polylactic acid resin: Product name "4032D" (Nature Works), density: 1.24 g/cm ³ , MFR: 4.0 g/10 min. (190° C., 2.16 kg), optical purity: D-form ratio <2 mol%, (This polylactic acid resin was used for the surface layer, base layer, and underskin layer to which a crystal nucleating agent was added.)
Polylactic acid resin: Product name "LX175" (Corbion), density: 1.24 g/cm ³ , MFR: 3.0 g/10 min. (190° C., 2.16 kg), optical purity: D-form ratio 4 mol % (This polylactic acid resin was used for the skin layer, base layer and underskin layer to which no crystal nucleating agent was added.)
Polybutylene succinate resin: trade name "BioPBS ^TM /FZ91PM" (Mitsubishi Chemical Corporation), density: 1.26 g/cm ³ , MFR: 5.0 g/10 min. (190° C., 2.16 kg)
Nucleating agent (containing at least one selected from the group consisting of organic phosphonate compounds, amide compounds having a ring structure, organic hydrazide compounds, organic sulfonate compounds, phthalocyanine compounds, and melamine compounds): Trade name "S-920MB" (Dai-ichi Kogyo Seiyaku Co., Ltd.), density: 1.24 g/cm ³ , MFR: 4.0 g/10 min. (190° C., 2.16 kg)
(2) Adhesive layer: Acid-modified polyolefin resin: "MODIC ^™ /F502C" (non-biodegradable resin adhesive) (Mitsubishi Chemical Corporation), MFR: 1.3 g/10 min. (190°C, 2.16 kg), main chain is polyolefin resin, and has a chemical structure in which maleic anhydride is attached to the side chain by graft reaction.
Acid-modified polyester resin (biodegradable resin adhesive): "BTR8002P" (Mitsubishi Chemical Corporation), MFR: 9.4 g/10 min. (230°C, 2.16 kg), main chain is polybutylene terephthalate-polytetramethylene ether glycol copolymer, and has a chemical structure in which unsaturated carboxylic acid or its anhydride and hydroxyl group are attached to the side chain by graft reaction.
(3) Oxygen Barrier Layer Ethylene-vinyl alcohol copolymer resin (non-biodegradable oxygen barrier resin): "EVAL ^™ /J171B" (Kuraray Co., Ltd.), MFR: 1.7 g/10 min. (190°C, 2.16 kg), ethylene content: 32 mol%, saponification degree: 95 mol% or more Vinyl alcohol-butenediol copolymer resin (biodegradable oxygen barrier resin): "Nichigo G-Polymer ^™ /BVE8049P" (Mitsubishi Chemical Corporation), MFR: 4.3 g/10 min. (190°C, 2.16 kg), saponification degree: 95 mol% or more

(Comparative Examples 1 to 7)
Using a φ105 mm single screw extruder, each raw material of the base material layer shown in Tables 1 and 2 corresponding to the test number was melt extruded by the T-die method, cooled and solidified by a cooling roll, transported by a take-up machine, and wound into a roll by a winding machine. As a result, a single layer resin sheet 10 m in the machine direction (MD direction) and 640 mm in the width direction (TD direction) was obtained.

(Examples 1 to 6, Comparative Examples 8 to 12)
Using one φ105 mm single screw extruder (for substrate layer), one φ60 mm single screw extruder (for skin layer), and three φ45 mm single screw extruders (for oxygen barrier layer, adhesive layer, and underskin layer, respectively), the raw materials of each layer shown in Tables 1 and 2 corresponding to the test number were melt-extruded by the feed block method, cooled and solidified by a cooling roll, transported by a take-up machine, and wound into a roll by a winding machine. As a result, a multilayer resin sheet having the laminate structure shown in Tables 1 and 2 and measuring 10 m in the machine direction (MD direction) and 640 mm in the width direction (TD direction) was obtained.

2. Characterization
The resin sheets obtained according to the examples and comparative examples were evaluated in various ways by the following methods.
(A) Thickness of each layer Test pieces were cut out at five equally spaced positions throughout the entire transverse direction (TD), which is a direction perpendicular to the machine direction (MD), of the resin sheet, and the cross-sections of the test pieces were exposed using a single-edged knife, and the thickness of each layer was measured using an electron microscope. The results are shown in Tables 1 and 2.
The thickness value of each layer was determined as the average value of the thicknesses of each layer at five points in the width direction of the multilayer resin sheet.
Measuring equipment: Electron microscope KH7700 (Hirox)
(B) Surface Appearance of Sheet The entire rolled resin sheet was unwound, and the appearance of the sheet was visually confirmed. The evaluation criteria were as follows. The results are shown in Tables 1 and 2.
1) ◎: Overall it was very glossy and smooth. When a fluorescent light was held up to it, the outline of the fluorescent light was clearly visible.
2) Good: Overall glossy and smooth. However, when viewed through a fluorescent light, the outline of the fluorescent light was blurred.
3) Δ: There was no gloss in parts, resin pool patterns were partially observed, and smoothness was partially lost.
4) ×: There was no gloss overall, resin pool patterns were observed overall, and smoothness was lost overall.
(C) Occurrence of cracks during sheet winding The entire resin sheet wound into a roll was unwound, and it was visually confirmed whether or not cracks occurred on both sides of the sheet. The evaluation criteria were "absent" when no cracks were observed, and "present" when cracks were observed. The results are shown in Tables 1 and 2.
(D) DuPont impact strength A test piece measuring 300 mm long x 640 mm wide was prepared from the resin sheet, and the 50% fracture energy E50 (J) of this test piece was measured using a DuPont impact tester (Model No. 517, manufactured by Yasuda Seiki Seisakusho Co., Ltd.) in accordance with JIS K7211-1:2006. The weight was collided with the lower skin layer, and the drop load was 500 g, and the measurement was performed under an environment of 23°C x 50% R.H. The results are shown in Tables 1 and 2.
(E) Tensile modulus A test piece measuring 150 mm in length and 10 mm in width was prepared from the resin sheet, and the test piece was pulled in the longitudinal direction using a tensile tester (Shimadzu Corporation, model AGS-J) in accordance with JIS K7161:2014. The tensile modulus (MPa) was measured under a measurement environment of 23°C x 50% R.H., a chuck distance of 100 mm, and a tensile speed of 50 mm/min. The tensile modulus was measured in both the MD and TD directions. The results are shown in Tables 1 and 2.
(F) Interlayer adhesive strength (peel strength)
A test piece measuring 150 mm in length and 15 mm in width was prepared from the resin sheet, and pulled in the longitudinal direction using a tensile tester (Shimadzu Corporation, model AGS-J) in accordance with GB8808-1988. A 180° peel test between the oxygen barrier layer and the base material layer was performed under the conditions of a measurement environment of 23°C x 50% RH, a chuck distance of 100 mm, and a pulling speed of 300 mm/min, to measure the peel strength. The peel strength was measured in both the MD and TD directions. The results are shown in Tables 1 and 2.
(G) Punching Processability A cup-shaped molded container having an opening diameter of 50 mm, a bottom diameter of 50 mm, a height of 50 mm, a side thickness of 10% to 30% of the total sheet thickness, and a bottom thickness of 25% to 40% of the total sheet thickness was molded from the resin sheet by a single-shot vacuum molding machine (manufactured by Asano Laboratory Co., Ltd.). The hot plate temperature was 600°C (non-contact heating with the distance between the upper and lower hot plates and the sheet set to 90 mm and 120 mm, respectively), and the molding time was 24 seconds. Next, the molded container was punched out with a Thomson blade and removed, and the punching processability was evaluated according to the following criteria. The results are shown in Tables 1 and 2.
1) ◎: All were punched out, and no burrs were observed. 2) ◯: All were punched out, but burrs were observed. 3) △: Partially not punched out. 4) ×: Not punched out at all. (H) Heat Resistance The molded containers prepared in the above punching workability test were immersed in 80°C or 90°C hot water for 15 seconds, then removed and allowed to cool to room temperature. The shape and softening degree of the molded containers after cooling were confirmed by visual inspection and touch, and the heat resistance was evaluated according to the following criteria. In addition, for the resin sheets that could not be punched out in the punching workability test, the edges of the obtained cup-shaped molded product were cut with scissors to separate the molded containers, and the heat resistance was evaluated. The results are shown in Tables 1 and 2.
1) ◯: No deformation or softening was observed. 2) Δ: No deformation, but the sides were slightly softened. 3) ×: Deformation was observed. (I) Oxygen Barrier Property The oxygen permeability of the resin sheet was measured by the following method.
[Measurement method] Compliant with GB/T 1038 Equipment used: PERME W3/031 manufactured by LabThink
Measurement conditions: 23°C x 65% R.H.
Sample setting: In the case of multilayer resin sheets, in consideration of practical use after container molding, the samples were set in a direction such that oxygen permeated from the lower skin layer side of the resin sheet sample. The results are shown in Tables 1 and 2. When the oxygen permeability is 5.0 cc/( ^m2 ·24h·atm) or less, it can be determined that the oxygen barrier property is good.
(J) Bending Resistance A test piece (15 mm x 100 mm) was cut out at an arbitrary position from the resin sheet, and both ends of the test piece in the longitudinal direction were chucked and a folding endurance test was performed using a folding endurance tester.
Folding endurance tester: FPC folding endurance tester (Model MY-FPC-01, manufactured by Shenzhen Mingyu Instrument and Equipment Co., Ltd.)
Measurement conditions: The test piece was bent at a bending angle (135°) and a bending speed (135 rpm) under a load (1600 g), and the number of times it was bent until the resin sheet broke (meaning it broke in two) was measured. Note that the bending resistance of the resin sheet before thermoforming was evaluated here, but it has been found that the bending resistance of the resin sheet before thermoforming tends to be the same as the ease of breaking of a thermoformed product equipped with a resin sheet. The results are shown in Tables 1 and 2.
The bending resistance was evaluated according to the following four levels.
1) ◎: The number of bending times is less than 400 times. 2) ◯: The number of bending times is 400 times or more and less than 700 times. 3) △: The number of bending times is 700 times or more and 1000 times or less. 4) ×: The number of bending times is more than 1000 times.

<3. Discussion>
Although the single-layer resin sheets of Comparative Examples 1 to 7 have excellent environmental performance, they have poor oxygen barrier properties because they do not have an oxygen barrier layer. However, the results of Comparative Examples 1 to 7 show that the balance of mechanical properties is improved by appropriately adjusting the compounding ratio of the polylactic acid resin and the polybutylene succinate resin in the base layer, the occurrence of cracks during winding of the resin sheet can be suppressed, and the punching processability of the resin sheet is also improved.
The multilayer resin sheets of Examples 1 to 6 have an appropriate laminate structure and resin composition of each layer, and therefore have excellent environmental performance, can suppress cracking during winding, and have excellent punching processability and oxygen barrier properties. Furthermore, the sheets have excellent surface appearance, excellent foldability, high impact resistance, high tensile modulus, and excellent heat resistance.
Comparing the multilayer resin sheets of Example 2 and Example 3, the adhesive strength between the oxygen barrier layer and the base layer is higher in Example 2. This is presumably because the acid-modified polyester resin used in the adhesive layer in Example 2 has good compatibility with the polylactic acid resin and polybutylene succinate resin constituting the base layer.
Comparing the multilayer resin sheets of Example 1 and Example 2, the adhesive strength between the oxygen barrier layer and the base layer is higher in Example 1. This is presumably because the vinyl alcohol-butenediol copolymer resin used in the oxygen barrier layer in Example 1 has many polar groups, resulting in strong interaction with the adhesive layer.
The multilayer resin sheet of Comparative Example 8 had an oxygen barrier layer and an adhesive layer made of non-biodegradable resin, and also contained a non-biodegradable crystal nucleating agent, so that the proportion of biodegradable resin in the multilayer resin sheet was less than 90% by mass, and the environmental performance was insufficient.
The multilayer resin sheets of Comparative Examples 9 to 13 did not use polybutylene succinate resin in the surface layer, the base layer, and the underskin layer, and therefore the surface appearance of the sheet was deteriorated. In addition, cracks occurred during the sheet winding, and the heat resistance was also deteriorated.

10 Multilayer resin sheet 11 Surface layer 12a, 12b Adhesive layer 13 Oxygen barrier layer 14 Base layer 15 Underlayer

Claims (21)

A multilayer resin sheet including a base layer and an oxygen barrier layer laminated on one surface of the base layer via an adhesive layer,
the base layer contains polylactic acid resin and polybutylene succinate resin in a mass ratio of polylactic acid resin:polybutylene succinate resin=2:8 to 6:4;
The total content of the polylactic acid resin and the polybutylene succinate resin in the base layer is 95 % by mass or more,
The ratio of biodegradable resin in the multilayer resin sheet is 90% by mass or more.
Multi-layer resin sheet. The multilayer resin sheet according to claim 1, wherein the substrate layer contains polylactic acid resin and polybutylene succinate resin in a mass ratio of polylactic acid resin:polybutylene succinate resin = 4:6 to 6:4. The multilayer resin sheet according to claim 1 or 2, wherein the adhesive layer between the substrate layer and the oxygen barrier layer contains a biodegradable resin adhesive. The multilayer resin sheet according to claim 3, wherein the adhesive layer between the substrate layer and the oxygen barrier layer contains a biodegradable acid-modified polyester resin as a biodegradable resin adhesive. The multilayer resin sheet according to any one of claims 1 to 4, wherein the oxygen barrier layer contains a biodegradable oxygen barrier resin. The multilayer resin sheet according to claim 5, wherein the oxygen barrier layer contains a biodegradable vinyl alcohol-butenediol copolymer as the biodegradable oxygen barrier resin. The multilayer resin sheet according to any one of claims 1 to 6, which has a surface layer laminated via an adhesive layer on the surface of the oxygen barrier layer opposite to the surface having the substrate layer, and the surface layer contains a biodegradable resin. The multilayer resin sheet according to claim 7, wherein the adhesive layer between the skin layer and the oxygen barrier layer contains a biodegradable acid-modified polyester resin. The multilayer resin sheet according to claim 7 or 8, wherein the surface layer contains polylactic acid resin and polybutylene succinate resin. The multilayer resin sheet according to claim 9, wherein the surface layer contains polylactic acid resin and polybutylene succinate resin in a mass ratio of polylactic acid resin:polybutylene succinate resin = 2:8 to 8:2. The multilayer resin sheet according to any one of claims 1 to 10, which has an underskin layer laminated on the surface of the substrate layer opposite to the surface having the oxygen barrier layer, and the underskin layer contains a biodegradable resin. The multilayer resin sheet according to claim 11, wherein the undercoat layer contains polylactic acid resin and polybutylene succinate resin. The multilayer resin sheet according to claim 12, wherein the undercoat layer contains polylactic acid resin and polybutylene succinate resin in a mass ratio of polylactic acid resin:polybutylene succinate resin = 2:8 to 8:2. The multilayer resin sheet according to any one of claims 1 to 13, wherein the substrate layer contains a crystal nucleating agent. an oxygen barrier layer laminated on one surface of a base layer via an adhesive layer;
a surface layer laminated via an adhesive layer on a surface of the oxygen barrier layer opposite to the surface having the base layer;
a subskin layer laminated on a surface of the base layer opposite to a surface having the oxygen barrier layer,
The multilayer resin sheet according to any one of claims 1 to 14, wherein at least one of the substrate layer, the surface layer, and the underskin layer contains a crystal nucleating agent. The multilayer resin sheet according to any one of claims 1 to 15, wherein the overall thickness of the multilayer resin sheet is 200 to 1300 μm, and the thickness of the oxygen barrier layer is 1 to 50 μm. The multilayer resin sheet according to any one of claims 1 to 16, which has a DuPont impact strength of 1.0 J or more as measured in accordance with JIS K7211-1:2006. The multilayer resin sheet according to any one of claims 1 to 17, wherein the tensile modulus measured in accordance with JIS K7161:2014 is 1100 MPa or more in the TD direction and 1100 MPa or more in the MD direction. The multilayer resin sheet according to any one of claims 1 to 18, wherein the peel strength between the oxygen barrier layer and the base layer in a 180° peel test measured in accordance with GB8808-1988 is 7N/15mm or more when peeled in the TD direction and 7N/15mm or more when peeled in the MD direction. A molded container comprising the multilayer resin sheet according to any one of claims 1 to 19. The molded container according to claim 20, wherein the multilayer resin sheet has a notch formed therein.

Images