JP7794061B2 - Multilayer foam sheet and molded product thereof - Google Patents

Description

The present invention relates to a multilayer foam sheet comprising a laminate of a non-foamed layer (X) containing a specific propylene polymer (A) and a foamed layer (Y), and to a molded article obtained by thermoforming the multilayer foam sheet. More specifically, the present invention relates to a multilayer foam sheet having a favorable foamed state in the foamed layer (Y) and excellent cold impact resistance, and to a molded article obtained by thermoforming the multilayer foam sheet.

From the perspective of reducing the weight of materials and the environmental impact, foam sheets made from thermoplastic resins such as polystyrene, polyethylene, and polypropylene have traditionally been used in industrial materials and household goods, and are particularly popular as thermoforming materials for producing various food and beverage containers and trays.

In recent years, demand for refrigerated and frozen foods has increased due to the ease of cooking, wide variety, and improvements in price and taste. Non-foamed sheets made from polypropylene resins, which have excellent cold and impact resistance, heat resistance, and oil resistance, are ideal materials for containers that are also suitable for microwave cooking, but there is a demand for them to be lighter.

For example, Patent Document 1 proposes a foam molded product that uses a specific polypropylene resin to reduce rupture of the bubbles (hereinafter sometimes referred to as "cells") that form the foam (low open cell ratio). Furthermore, Patent Document 2 proposes a polypropylene surface layer to improve the appearance of the foam molded product, but makes no mention of cold impact resistance.

Meanwhile, Patent Document 3 proposes a foam formed from a mixed resin of polypropylene and ethylene-α-olefin copolymer as a material that satisfies cold impact resistance requirements, and Patent Document 4 proposes a laminated foam in which a biaxially oriented polypropylene film is further laminated to this. However, mixing in an ethylene-α-olefin copolymer inhibits the foaming of the polypropylene, increasing the open cell ratio of the foam and resulting in reduced strength and poor appearance of the molded product. Therefore, depending on the molding method, particularly when molding foam sheets using a T-die, it has been difficult to obtain foam sheets and thermoformed products that have sufficient cold impact resistance and good foamability.

JP 2013-100491 A Japanese Patent Application Laid-Open No. 2019-65235 Japanese Patent Application Publication No. 8-259721 Japanese Patent Application Laid-Open No. 2002-11838

In light of the current state of the art, the problem that the present invention aims to solve is to provide a multi-layer foamed sheet having a foam layer with a good foaming state and good cold impact resistance, as well as a molded article obtained by thermoforming the multi-layer foamed sheet.

As a result of extensive research to solve the above-mentioned problems, the inventors discovered that a multilayer foamed sheet characterized by laminating a non-foamed layer (X) containing a specific propylene polymer (A) and a foamed layer (Y), as well as a molded article obtained by thermoforming the multilayer sheet, can solve the above-mentioned problems. Based on these findings, the present invention was completed.

That is, according to the first aspect of the present invention, there is provided a multilayer foamed sheet (Z) comprising a laminate of a foamed layer (Y) and a non-foamed layer (X) containing a propylene polymer (A) that satisfies the following requirements (A-i) to (A-ii), wherein the thickness of the non-foamed layer (X) in the sheet is 0.05 mm or more and accounts for 7 to 40% of the total thickness of the sheet {= (thickness of the non-foamed layer (X) ÷ total thickness of the sheet) × 100%):
Requirement (A-i): In differential scanning calorimetry (DSC), the sample is heated from 23°C to 200°C at a rate of 10°C/min, held at 200°C for 5 minutes, cooled to 40°C at a rate of 10°C/min, held at 40°C for 1 minute, and then heated to 200°C at a rate of 10°C/min. The peak melting temperature (Tm) observed during the second heating is 130 to 165°C, and the total heat of fusion (ΔH) observed during the heating from 40°C to 200°C is 60 to 100 J/g.
Requirement (A-ii): The melt flow rate (230°C, 2.16 kg load) (MFR(A)) is 2 to 20 g/10 min, and the foamable resin composition (D) used in the foam layer (Y)
The ratio of the melt flow rate (230°C, 2.16 kg load) (MFR(D)) of the copolymer to the melt flow rate (230°C, 2.16 kg load) (MFR(D)) is 0.2 to 2.0 (=MFR(A)÷MFR(D)).

The second aspect of the present invention provides the multi-layer foamed sheet (Z) of the first aspect of the present invention, characterized in that the non-foamed layer (X) contains 10 to 200 parts by weight of an ethylene polymer (B) satisfying the following requirement (Bi) per 100 parts by weight of the propylene polymer (A):
Requirement (Bi): Melt flow rate (230°C, 2.16 kg load) (MFR(B))
is 0.5 to 20 g/10 min, and the ratio of MFR(B) to the MFR(A) of the propylene polymer (A) is 0.05 to 1.5 (=MFR(B)÷MFR(A)).

According to the third aspect of the present invention, in the first or second aspect of the present invention, the non-foamed layer (X)
and the non-foamed layer (X) contains 10 to 200 parts by weight of a thermoplastic elastomer (C) that satisfies the following requirement (C-i) based on 100 parts by weight of the propylene-based polymer (A).
Requirement (C-i): The melt flow rate (230°C, 2.16 kg load) (MFR(C)) is 0.5 to 20 g/10 min, and the ratio of the MFR(C) to the MFR(A) of the propylene polymer (A) is 0.05 to 1.5 (=MFR(C)/MFR(A)).

The fourth aspect of the present invention provides a molded article obtained by thermoforming the multilayer foamed sheet (Z) described in any one of the first to third aspects of the present invention.

The multilayer foam sheet of the present invention has excellent appearance, moldability, light weight, rigidity, heat resistance, thermal insulation, and oil resistance, as well as a good foaming state in the foam layer and excellent cold impact resistance. Therefore, the multilayer foam sheet can be cut or thermoformed into food containers such as trays, plates, and cups, vehicle interior materials such as automobile door trim and automobile trunk mats, packaging, stationery, and building materials.

The present invention relates to a multilayer foamed sheet (Z) in which a non-foamed layer (X) containing a specific propylene-based polymer (A) and a foamed layer (Y) are laminated to a specific thickness, and a molded article obtained by thermoforming the multilayer sheet.
Each component used in the present invention and its molded body will be described in detail below.

1. Propylene-based polymer (A)
The propylene polymer (A) used in the present invention satisfies the following requirements (Ai) to (A-ii).
Requirement (A-i): In differential scanning calorimetry (DSC), the sample is heated from 23°C to 200°C at a rate of 10°C/min, held at 200°C for 5 minutes, cooled to 40°C at a rate of 10°C/min, held at 40°C for 1 minute, and then heated to 200°C at a rate of 10°C/min. The peak melting temperature (Tm) observed during the second heating is 130 to 165°C, and the total heat of fusion (ΔH) observed during the heating from 40°C to 200°C is 60 to 100 J/g.
Requirement (A-ii): The melt flow rate (230°C, 2.16 kg load) (MFR(A)) is 2 to 20 g/10 min, and the ratio of the melt flow rate (230°C, 2.16 kg load) (MFR(D)) of the foamable resin composition (D) used in the foam layer (Y) to the melt flow rate (230°C, 2.16 kg load) (MFR(A)) is 0.2 to 2.0 (=MFR(A)/MFR(D)).
Each of these will be explained in detail below.

Requirements (A-i):
The propylene polymer (A) used in the present invention has a melting peak temperature (Tm) of 130 to 165°C, preferably 140 to 163°C, and more preferably 150 to 162°C, as measured by differential scanning calorimetry (DSC) during a second heating cycle in which the polymer is heated from 23°C to 200°C at a rate of 10°C/min, maintained at 200°C for 5 minutes, cooled to 40°C at a rate of 10°C/min, maintained at 40°C for 1 minute, and then heated to 200°C at a rate of 10°C/min. The total heat of fusion (ΔH) observed during the heating cycle from 40°C to 200°C is 60 to 100 J/g, preferably 70 to 98 J/g, and more preferably 80 to 95 J/g.
A peak melting temperature (Tm) of 130°C or higher or a total heat of fusion (ΔH) of 60 J/g or higher is preferred because the multilayer foam sheet (Z) and its molded article have sufficient rigidity and heat resistance. A peak melting temperature (Tm) of 165°C or lower or a total heat of fusion (ΔH) of 100 J/g or lower is preferred because the multilayer foam sheet and its molded article have sufficient cold impact resistance.

Requirement (A-ii):
The melt flow rate (hereinafter sometimes abbreviated as MFR) (230°C, 2.16 kg load) of the propylene polymer (A) used in the present invention is a value measured in accordance with Method A, Condition M (230°C, 2.16 kg load) of JIS K7210:1999 "Plastics - Test methods for melt mass-flow rate (MFR) and melt volume-flow rate (MVR) of thermoplastics."

MFR is the most fundamental factor in the molding and processing of polypropylene, and therefore, the MFR of the propylene polymer (A) used in the present invention is in the range of 2 to 20 g/10 min, preferably 5 to 15 g/10 min, and more preferably 8 to 12 g/10 min.
The ratio of the melt flow rate (230°C, 2.16 kg load) (MFR(D)) of the foamable resin composition (D) used in the foam layer (Y) to the melt flow rate (230°C, 2.16 kg load) (MFR(D)) is 0.2 to 2.0 (=MFR(A)/MFR(D)), preferably 0.4 to 1.5, and more preferably 0.6 to 1.3.
Here, MFR(A) represents the MFR of the propylene polymer (A). However, when two or more types of polymers are mixed and used as the propylene polymer (A), MFR(A) represents the MFR of the blend after mixing.
When the MFR and MFR ratio are within the above ranges, the cells of the foamed layer are less likely to break when the non-foamed layer (X) and the foamed layer (Y) are laminated together, and the open cell ratio is less likely to become high.

The propylene polymer (A) used in the present invention is not particularly limited as long as it satisfies the above-mentioned requirements (A-i) to (A-ii), and examples thereof include a propylene-α-olefin block copolymer and a propylene-α-olefin random copolymer. These can also be used in combination of two or more types. The α-olefin used in the copolymerization can be an α-olefin having 2 to 20 carbon atoms other than propylene, such as ethylene, 1-butene, 1-hexene, and 1-octene. One or more types of α-olefins can be used as copolymers with propylene. Among these, ethylene and 1-butene are preferred, and ethylene is more preferred.
Furthermore, if necessary, a propylene homopolymer may be mixed within a range that does not significantly impair the effects of the present invention.

Method for Producing Propylene Polymer (A) Hereinafter, a method for producing the propylene polymer (A) used in the resin composition for a thermoformable sheet of the present invention will be described.
First, a method for producing a propylene-α-olefin block copolymer will be described.

(i) Method for Producing Propylene-α-Olefin Block Copolymer When the propylene-based polymer (A) used in the present invention is a propylene-α-olefin block copolymer, the propylene-α-olefin block copolymer is preferably produced by a polymerization method using a highly stereoregular catalyst. The propylene-α-olefin block copolymer is a reaction mixture of a propylene homopolymer (component (A-1)) and a propylene-α-olefin copolymer (component (A-2)). This is obtained by a multi-stage polymerization method comprising the steps of polymerizing the propylene homopolymer (component (A-1)), which is the crystalline propylene polymer portion, (first stage) and subsequently polymerizing the propylene-α-olefin copolymer (component (A-2)) (second stage).
Furthermore, it is also possible to produce a propylene homopolymer by following the method for producing the propylene homopolymer (component (A-1)) described above.

The catalyst used in the polymerization is not particularly limited as long as it is a highly stereoregular catalyst, and as described above, known catalysts can be used. For example, a so-called Ziegler-Natta catalyst, which is a combination of a titanium compound and an organoaluminum compound (described, for example, in Polypropylene Handbook (first edition, first printing published May 15, 1998)), or a metallocene catalyst (see, for example, JP-A-5-295022) can be used.
Ziegler-Natta catalysts include those obtained by treating titanium trichloride or titanium trichloride compositions obtained by reduction with an organoaluminum compound or the like as a titanium compound with an electron donor compound to further activate them (see, for example, JP-A Nos. 47-34478, 58-23806, and 63-146906), and so-called supported catalysts obtained by supporting titanium tetrachloride on a carrier such as magnesium chloride (see, for example, JP-A Nos. 58-157808, 58-83006, 58-5310, and 61-218606).

Examples of organoaluminum compounds used as promoters include trialkylaluminums such as trimethylaluminum, triethylaluminum, and triisobutylaluminum, alkylaluminum halides such as diethylaluminum chloride and diisobutylaluminum chloride, alkylaluminum hydrides such as diethylaluminum hydride, alkylaluminum alkoxides such as diethylaluminum ethoxide, alumoxanes such as methylalumoxane and tetrabutylalumoxane, and composite organoaluminum compounds such as dibutyl methylboronate and lithium aluminum tetraethyl. Mixtures of two or more of these compounds may also be used.
The catalysts described above can also contain various polymerization additives for the purposes of improving stereoregularity, controlling particle properties, controlling soluble components, controlling molecular weight distribution, etc. Examples of such additives include electron-donating compounds such as organosilicon compounds such as diphenyldimethoxysilane and tert-butylmethyldimethoxysilane, esters such as ethyl acetate, butyl benzoate, methyl p-toluate and dibutyl phthalate, ketones such as acetone and methyl isobutyl ketone, ethers such as diethyl ether, organic acids such as benzoic acid and propionic acid, and alcohols such as ethanol and butanol.

The polymerization method is as described above, but possible methods include slurry polymerization using an inert hydrocarbon such as hexane, heptane, octane, benzene, or toluene as the polymerization solvent, bulk polymerization using propylene itself as the polymerization solvent, and gas-phase polymerization in which the raw material propylene is polymerized in a gas-phase state. It is also possible to combine any of these polymerization methods. Examples include a method in which a propylene homopolymer (component (A-1)) is polymerized by bulk polymerization and a propylene-α-olefin copolymer (component (A-2)) is polymerized by gas-phase polymerization, and a method in which a propylene homopolymer (component (A-1)) is polymerized by bulk polymerization and then gas-phase polymerization, and a method in which a propylene-α-olefin copolymer (component (A-2)) is polymerized by gas-phase polymerization.
The polymerization may be carried out in a batch, continuous or semi-batch manner, and if desired, a multi-stage continuous polymerization method such as two-stage or three-stage may be used.
Furthermore, the polymerization reactor may be of any shape or structure, and examples thereof include a tank equipped with a stirrer, which is generally used in a slurry polymerization method or a bulk polymerization method, a tubular reactor, a fluidized bed reactor, which is generally used in a gas-phase polymerization method, and a horizontal reactor equipped with a stirring blade.

In gas-phase polymerization, the polymerization process for propylene homopolymer (component (A-1)) is carried out in the presence of the catalyst by supplying propylene and hydrogen as a chain transfer agent at a temperature of 0 to 100°C, preferably 30 to 90°C, and particularly preferably 40 to 80°C, a propylene partial pressure of 0.6 to 4.2 MPa, preferably 1.0 to 3.5 MPa, and particularly preferably 1.5 to 3.0 MPa, and a residence time of 0.5 to 10 hours. The propylene homopolymer (component (A-1)) may be copolymerized with an α-olefin other than propylene, for example, less than 0.5% by weight of ethylene when the α-olefin is ethylene, as long as the effects of the present invention are not impaired.

The MFR (230°C, 2.16 kg load) of the propylene homopolymer (component (A-1)) of the propylene-α-olefin block copolymer used in the present invention is usually in the range of 0.1 to 50 g/10 min. In order to make the propylene homopolymer (component (A-1)) of the propylene-α-olefin block copolymer in this range, it is possible to adjust the MFR to the desired value by using hydrogen as a chain transfer agent in a hydrogen/propylene molar ratio range of 5 x 10 ^-3 to 0.2, although this depends on the type of catalyst.

When producing a propylene-α-olefin block copolymer, subsequently, that is, in the presence of the propylene homopolymer (component (A-1)) produced in the first polymerization step, in the second polymerization step, propylene, an α-olefin, and hydrogen are supplied and copolymerization of propylene and an α-olefin is carried out in the presence of the catalyst (the catalyst used in the production of the propylene homopolymer (component (A-1))) at 0 to 100°C, preferably 30 to 90°C, and particularly preferably 40 to 80°C, with partial pressures of propylene and α-olefin each of 0.1 to 2.0 MPa, preferably 0.1 to 1.5 MPa, for a residence time of 0.5 to 10 hours, to produce a propylene-α-olefin copolymer (component (A-2)), and a propylene-α-olefin block copolymer is obtained as the final product.
The propylene-α-olefin copolymer (component (A-2)) may be copolymerized with propylene and two or more types of α-olefins, as long as the effects of the present invention are not impaired.

When the propylene polymer (A) used in the present invention is a propylene-α-olefin block copolymer, in order to set the MFR of the propylene-α-olefin block copolymer in the range of 2 to 20 g/10 min, since the MFR of the propylene homopolymer (component (A-1)) is usually in the range of 0.1 to 50 g/10 min as described above, the MFR (230°C, 2.16 kg load) of the propylene-α-olefin copolymer (component (A-2)) is preferably set to 1 × 10 ^-4 to 10 g/10 min.
When the MFR of the propylene-α-olefin copolymer (component (A-2)) is controlled to 1×10 ⁻⁴ to 10 g/10 min, it is possible to adjust the MFR to the desired value by adjusting the hydrogen/(propylene + α-olefin) molar ratio within the range of 1×10 ⁻⁵ to 0.8, although this will depend on the type of catalyst.
In order to maintain the α-olefin content in the propylene-α-olefin copolymer (component (A-2)) within a specific range, the α-olefin concentration relative to the propylene concentration in the subsequent step may be adjusted.

Furthermore, in order to suppress gel formation and stickiness, it is desirable to add an alcohol such as ethanol during or before the reaction of the propylene-α-olefin copolymer (component (A-2)). Specifically, the reaction can be carried out under conditions where the molar ratio of alcohol to organoaluminum compound is 0.5 to 3.0. Furthermore, the proportion of the propylene-α-olefin copolymer (component (A-2)) in the propylene-α-olefin block copolymer can also be controlled by the amount of alcohol added.
Furthermore, since various companies have put various types of such propylene-α-olefin block copolymers on the market, it is also possible to measure the physical properties of these commercially available products and use the desired one.

(ii) Method for Producing Propylene-α-olefin Random Copolymer When the propylene polymer (A) used in the present invention is a propylene-α-olefin random copolymer, the method for producing the propylene-α-olefin random copolymer may be carried out in accordance with the method for producing a propylene homopolymer (component (A-1)) among the methods for producing a propylene-α-olefin block copolymer described above, in which a method is used in which the propylene homopolymer (component (A-1)) is copolymerized with an α-olefin other than propylene, preferably ethylene or 1-butene as the α-olefin, more preferably ethylene.
Furthermore, since various companies have put various types of such propylene-α-olefin random copolymers on the market, it is also possible to measure the physical properties of these commercially available products and use the desired one.

2. Ethylene-based polymer (B)
The non-foamed layer (X) of the present invention may contain, in addition to the propylene polymer (A), an ethylene polymer (B) satisfying the following requirement (Bi):
Requirement (Bi): The melt flow rate (230°C, 2.16 kg load) (MFR(B)) is 0.5 to 20 g/10 min, and the ratio of the MFR(B) to the MFR(A) of the propylene polymer (A) is 0.05 to 1.5 (=MFR(B)/MFR(A)).

From the viewpoint of improving the appearance and cold impact resistance of the multi-layer foamed sheet and the molded article thereof, the ethylene polymer (B) used in the present invention preferably has an MFR of 0.5 to 20 g/10 min, more preferably 5 to 15 g/10 min, and even more preferably 8 to 12 g/10 min, and the ratio of the MFR to the MFR (A) of the propylene polymer (A) is preferably 0.05 to 1.5 (= MFR(B)/MFR(A)), more preferably 0.5 to 1.3, and even more preferably 0.8 to 1.2.
When the ethylene polymer (B) has an MFR of 0.5 g/10 min or more, or when the ratio of the MFR to the propylene polymer (A) (= MFR(B)÷MFR(A)) is 0.05 or more, the ethylene polymer (B) is well dispersed when the ethylene polymer (B) is contained in the propylene polymer (A), and the multi-layer foam sheet and its molded article are less likely to have surface irregularities and poor appearance. Furthermore, when the ethylene polymer (B) has an MFR of 20 g/10 min or less, or when the ratio of the MFR to the propylene polymer (A) (= MFR(B)÷MFR(A)) is 1.5 or less, the multi-layer foam sheet and its molded article can have sufficient cold impact resistance, which is preferred.

Examples of the ethylene polymer (B) include high-density polyethylene, linear low-density polyethylene, and branched low-density polyethylene. Among these, from the viewpoint of improving the impact resistance of the multi-layer foamed sheet and its molded article, it is preferable to use linear low-density polyethylene and branched low-density polyethylene, which are highly effective in this regard. Furthermore, when oil resistance is required for the multi-layer foamed sheet and its molded article, it is preferable to use high-density polyethylene. These polymers may be used alone or in combination of two or more.
Various products of these ethylene polymers are commercially available from many companies, and ethylene obtained from fossil fuels or ethylene derived from biomass may be used as a raw material, and a desired product can be purchased and used from among them. In particular, biomass-derived ethylene polymers are carbon-neutral materials, and therefore the environmental impact of producing the multilayer foamed sheet can be reduced. A specific example is I'm green ^™ Polyethylene, available from Braskem.

Blending Proportion of Ethylene-Based Polymer (B) The non-foamed layer (X) of the present invention may contain preferably 10 to 200 parts by weight, more preferably 20 to 100 parts by weight, and even more preferably 30 to 70 parts by weight of the ethylene-based polymer (B) per 100 parts by weight of the propylene-based polymer (A).
When the amount of the ethylene polymer (B) is 10 parts by weight or more, the multi-layer foamed sheet and its molded article can have sufficient cold impact resistance, while when the amount is 200 parts by weight or less, the rigidity and oil resistance of the multi-layer foamed sheet and its molded article are less likely to decrease.

3. Thermoplastic elastomer (C)
The non-foamed layer (X) of the present invention may contain, in addition to the propylene polymer (A), a thermoplastic elastomer (C) satisfying the following requirement (Ci):
The non-foamed layer (X) of the present invention may contain, in addition to the propylene polymer (A) and the ethylene polymer (B), a thermoplastic elastomer (C) satisfying the following requirement (C-i):
Requirement (C-i): The melt flow rate (230°C, 2.16 kg load) (MFR(C)) is 0.5 to 20 g/10 min, and the ratio of the MFR(C) to the MFR(A) of the propylene polymer (A) is 0.05 to 1.5 (=MFR(C)/MFR(A)).

From the viewpoint of improving the appearance and cold impact resistance of the multi-layer foamed sheet and the molded article thereof, the thermoplastic elastomer (C) used in the present invention preferably has an MFR of 0.5 to 20 g/10 min, more preferably 5 to 15 g/10 min, and even more preferably 8 to 12 g/10 min, and the ratio to the MFR of the propylene polymer (A) (= MFR(C)/MFR(A)) is preferably 0.05 to 1.5, more preferably 0.5 to 1.3, and even more preferably 0.8 to 1.2.
When the thermoplastic elastomer (C) has an MFR of 0.5 g/10 min or more, or when the ratio to the MFR of the propylene polymer (A) (= MFR(C)÷MFR(A)) is 0.05 or more, the thermoplastic elastomer (C) disperses well when the propylene polymer (A) contains the thermoplastic elastomer (C), and the multi-layer foam sheet and its molded article are less likely to have surface irregularities and have poor appearance. Furthermore, when the thermoplastic elastomer (C) has an MFR of 20 g/10 min or less, or when the ratio to the MFR of the propylene polymer (A) (= MFR(C)÷MFR(A)) is 1.5 or less, the multi-layer foam sheet and its molded article can have sufficient cold impact resistance, which is preferred.

The thermoplastic elastomer (C) is, for example, at least one selected from the group consisting of olefin-based elastomers and styrene-based elastomers.
Examples of olefin-based elastomers include ethylene-α-olefin copolymer elastomers such as ethylene-propylene copolymer elastomer (EPR), ethylene-butene copolymer elastomer (EBR), ethylene-hexene copolymer elastomer (EHR), and ethylene-octene copolymer elastomer (EOR); and ethylene-α-olefin-diene terpolymer elastomers such as ethylene-propylene-ethylidenenorbornene copolymer, ethylene-propylene-butadiene copolymer, and ethylene-propylene-isoprene copolymer. Specific examples include those commercially available under the trade name DYNARON (registered trademark) from JSR Corporation, under the trade name TAFUMER (registered trademark) from Mitsui Chemicals, Inc., under the trade name ENGAGE (registered trademark), AFFINITY (registered trademark), and VERSIFY (registered trademark) from The Dow Chemical Company, Ltd., under the trade name KERNEL from Japan Polyethylene Corporation, and under the trade name Vistamaxx (registered trademark) from ExxonMobil Chemical Corporation.

Examples of styrene elastomers include styrene-butadiene-styrene triblock copolymer elastomer (SBS), styrene-isoprene-styrene triblock copolymer elastomer (SIS), styrene-ethylene-butylene copolymer elastomer (SEB), styrene-ethylene-propylene copolymer elastomer (SEP), styrene-ethylene-butylene-styrene copolymer elastomer (SEBS), styrene-ethylene-butylene-ethylene copolymer elastomer (SEBC), hydrogenated styrene-butadiene elastomer (HSBR), styrene Examples of the elastomer include styrene-based elastomers such as ethylene-propylene-styrene copolymer elastomer (SEPS), styrene-ethylene-ethylene-propylene-styrene copolymer elastomer (SEEPS), styrene-butadiene-butylene-styrene copolymer elastomer (SBBS), partially hydrogenated styrene-isoprene-styrene copolymer elastomer, and partially hydrogenated styrene-isoprene-butadiene-styrene copolymer elastomer, as well as hydrogenated polymer-based elastomers such as ethylene-ethylene-butylene-ethylene copolymer elastomer (CEBC).
Specific examples include those commercially available under the trade names Dynalon (registered trademark) and JSR SIS (registered trademark) from JSR Corporation, Hybler (registered trademark) and Septon (registered trademark) from Kuraray Co., Ltd., Tuftec (registered trademark) from Asahi Kasei Corporation, Shibstar (registered trademark) from Kaneka Corporation, and Kraton (registered trademark) and Kraton D (registered trademark) from Shell Corporation.
These may be used alone or in combination of two or more. A variety of thermoplastic elastomers (C) are commercially available from many companies, and a desired product can be purchased and used.

The non-foamed layer (X) of the present invention may contain preferably 10 to 200 parts by weight, more preferably 20 to 100 parts by weight, and even more preferably 30 to 70 parts by weight of the thermoplastic elastomer (C) per 100 parts by weight of the propylene polymer (A).
When the amount of the thermoplastic elastomer (C) is 10 parts by weight or more, the multi-layer foamed sheet and its molded article can have sufficient cold impact resistance, while when the amount is 200 parts by weight or less, the rigidity and oil resistance of the multi-layer foamed sheet and its molded article are not likely to decrease.

In addition to the propylene polymer (A) to thermoplastic elastomer (C), the non-foamed layer (X) of the present invention may further contain optional additive components, if necessary, to further improve the effects of the present invention or to impart other effects, within a range that does not significantly impair the effects of the present invention.

Specific examples of the additive include colorants such as pigments, light stabilizers such as hindered amines, ultraviolet absorbers such as benzotriazoles, nucleating agents such as sorbitols, antioxidants such as phenols and phosphorus-based antioxidants, nonionic antistatic agents, β-crystal nucleating agents such as amide compounds, neutralizing agents such as inorganic compounds, antibacterial and antifungal agents such as thiazoles, flame retardants such as halogen compounds, plasticizers, dispersants such as organic metal salts, lubricants such as fatty acid amides, metal deactivators such as nitrogen compounds, nonionic surfactants, and thermoplastic resins such as polyolefin resins, polyamide resins, and polyester resins other than the propylene polymer (A) and the ethylene polymer (B).
Two or more of these optional additive components may be used in combination, may be added to the composition, or may be added to the propylene-based polymer (A), the ethylene-based polymer (B), or the like. Two or more of each component may also be used in combination.

As the colorant, for example, inorganic or organic pigments are effective in imparting or improving the colored appearance, appearance, texture, commercial value, weather resistance, durability, etc. of the multilayer foamed sheet (Z) and its molded article.
Specific examples of inorganic pigments include carbon blacks such as furnace carbon and ketjen carbon; titanium oxide; iron oxides (e.g., red iron oxide); chromic acid (e.g., lead chrome); molybdic acid; selenide sulfides; and ferrocyanides. Specific examples of organic pigments include azo pigments such as sparingly soluble azo lakes, soluble azo lakes, insoluble azo chelates, condensed azo chelates, and other azo chelates; phthalocyanine pigments such as phthalocyanine blue and phthalocyanine green; anthraquinones, perinones, perylenes, and threne pigments such as thioindigo; dye lakes; quinacridones; dioxazines; and isoindolinones. To achieve metallic or pearlescent finishes, aluminum flakes or pearl pigments can be added. Dyes can also be added.

As the light stabilizer or ultraviolet absorber, for example, a hindered amine compound, a benzotriazole-based compound, a benzophenone-based compound, or a salicylate-based compound is effective in imparting or improving the weather resistance, durability, etc. of the multilayer foamed sheet (Z) and its molded article, and is effective in further improving the weather discoloration resistance.
Specific examples of the hindered amine compound include a condensation product of dimethyl succinate and 1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethylpiperidine; poly[[6-(1,1,3,3-tetramethylbutyl)imino-1,3,5-triazine-2,4-diyl][(2,2,6,6-tetramethyl-4-piperidyl)imino]hexamethylene[(2,2,6,6-tetramethyl-4-piperidyl)imino]]; tetrakis(2,2,6,6-tetramethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate; tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate; bis(1,2,2,6,6-pentamethyi) 2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl)-5-chlorobenzotriazole;2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl)-5-chlorobenzotriazole; benzophenones such as 2-hydroxy-4-methoxybenzophenone and 2-hydroxy-4-n-octoxybenzophenone; and salicylate compounds such as 4-t-butylphenyl salicylate and 2,4-di-t-butylphenyl-3',5'-di-t-butyl-4'-hydroxybenzoate.
Here, the method of using the light stabilizer and the ultraviolet absorber in combination is preferable because it has a significant effect of improving weather resistance, durability, weather discoloration resistance, and the like.

As the antioxidant, for example, a phenol-based, phosphorus-based or sulfur-based antioxidant is effective in imparting or improving the heat resistance, processing stability, heat aging resistance, etc. of the multi-layer foamed sheet (Z) and its molded article.
Furthermore, as an antistatic agent, for example, a nonionic or cationic antistatic agent is effective in imparting or improving the antistatic properties of the multilayer foamed sheet (Z) and its molded article.

The β-crystal nucleating agent is not particularly limited as long as it is a crystallization nucleating agent that selectively forms β-crystals when added to a polypropylene resin. However, various pigment-based compounds (e.g., quinacridone) and amide-based compounds can be preferably used, and amide-based compounds are particularly preferred for achieving high β-crystal formation ability.
Here, the method of using a pre-β crystal nucleating agent in combination is effective in improving the thermoformability by lowering the softening temperature of the sheet.

5. Manufacturing Method of Non-Foamed Layer (X) The non-foamed layer (X) of the present invention can be manufactured by mixing and/or melt-kneading the specific propylene-based polymer (A) and, if necessary, the ethylene-based polymer (B), the thermoplastic elastomer (C), and any optional additional components in the above-mentioned blending ratios by a conventionally known method, and then extruding the mixture into a sheet.

Mixing is typically carried out using mixing equipment such as a tumbler, V-blender, or ribbon blender, and melt-kneading can typically be carried out using kneading equipment such as a single-screw extruder, twin-screw extruder, Banbury mixer, roll mixer, Brabender plastograph, or kneader, followed by melt-kneading and granulation. However, melt-kneading is not required.

The extrusion sheet molding method is not particularly limited, and the sheet can be obtained by a conventionally known extrusion sheet molding method. Representative extrusion sheet molding methods include a T-die (rectangular die) extrusion sheet molding method and a circular die (round die) extrusion sheet molding method.
The extruder used in the above-mentioned typical extrusion foam sheet molding methods may be a single-screw or twin-screw extruder.

6. Foam layer (Y)
The foam layer (Y) of the present invention is not particularly limited and can be produced by a conventionally known method.
Each of these will be explained in detail below.

(1) Foamable resin composition (D)
The foam layer (Y) of the present invention can be obtained by extrusion molding a mixture of the foamable resin composition (D) and a foaming agent into a foam sheet.
As the foamable resin composition (D), a conventionally known one can be used, and examples of the resin component include polystyrene, polypropylene, polyethylene, etc. Among these, in the present invention, it is preferable to use polypropylene, which has excellent melt adhesion to the non-foamed layer (X).
When the foamable resin composition (D) contains polypropylene, for example, propylene-based resin compositions exhibiting specific curability as described in Patent Document 1 (JP 2013-100491 A) and Patent Document 2 (JP 2019-65235 A) can be suitably used, but other conventionally known foamable resin compositions (D) can also be used within a range that does not impair the effects of the present invention.

(2) Foaming Agent There are no particular limitations on the type of foaming agent, and any known foaming agent used in plastics, rubber, etc. may be used. Any foaming agent used in various foam molding processes may also be used, including, for example, physical foaming agents, decomposable foaming agents (chemical foaming agents), and microcapsules containing a thermal expansion agent.
Specific examples of physical blowing agents include aliphatic hydrocarbons such as propane, butane, pentane, and hexane, alicyclic hydrocarbons such as cyclopentane and cyclohexane, halogenated hydrocarbons such as chlorodifluoromethane, difluoromethane, trifluoromethane, trichlorofluoromethane, dichlorodifluoromethane, chloromethane, dichloromethane, chloroethane, dichlorotrifluoroethane, dichlorofluoroethane, chlorodifluoroethane, dichloropentafluoroethane, tetrafluoroethane, difluoroethane, pentafluoroethane, trifluoroethane, trichlorotrifluoroethane, dichlorotetrafluoroethane, chloropentafluoroethane, and perfluorocyclobutane, and inorganic gases such as water, carbon dioxide, and nitrogen. These compounds may be used alone or in combination.
Among these, aliphatic hydrocarbons such as propane, butane, and pentane, and carbon dioxide gas are preferred because they are inexpensive and have high solubility in polypropylene-based resins. In particular, when carbon dioxide gas is used, it is more preferred to use it under supercritical conditions of 7.4 MPa or more and 31°C or more, since this results in a state in which it is highly diffusible and soluble in the polymer.
When a physical foaming agent is used, a foam regulator can be used as necessary. Examples of foam regulators include inorganic decomposable foaming agents such as ammonium carbonate, sodium bicarbonate (sodium bicarbonate), ammonium bicarbonate, and ammonium nitrite; azo compounds such as azodicarbonamide, azobisisobutyronitrile, and diazoaminobenzene; nitroso compounds such as N,N'-dinitrosopentanemethylenetetramine and N,N'-dimethyl-N,N'-dinitrosoterephthalamide; organic decomposable foaming agents such as benzenesulfonyl hydrazide, p-toluenesulfonyl hydrazide, p,p'-oxybisbenzenesulfonylsemicarbazide, p-toluenesulfonylsemicarbazide, trihydrazinotriazine, and barium azodicarboxylate; inorganic powders (inorganic powders) such as talc and silica; acid salts of polycarboxylic acids; and reaction mixtures of polycarboxylic acids with sodium carbonate or sodium bicarbonate. These foam regulators may be used alone or in combination.
When a cell regulator is used, the compounding amount of the cell regulator is preferably in the range of 0.01 to 5 parts by weight in pure form per 100 parts by weight of the foamable resin composition.
Specific examples of decomposable foaming agents (chemical foaming agents) include mixtures of sodium bicarbonate and organic acids such as citric acid, azo-based foaming agents such as azodicarbonamide and barium azodicarboxylate, nitroso-based foaming agents such as N,N'-dinitrosopentamethylenetetramine and N,N'-dimethyl-N,N'-dinitrosoterephthalamide, sulfohydrazide-based foaming agents such as p,p'-oxybisbenzenesulfonylhydrazide and p-toluenesulfonylsemicarbazide, and trihydrazinotriazine.
The amount of the foaming agent to be added is preferably in the range of 0.05 to 6.0 parts by weight, more preferably 0.05 to 3.0 parts by weight, even more preferably 0.5 to 2.5 parts by weight, and particularly preferably 1.0 to 2.0 parts by weight, relative to 100 parts by weight of the foamable resin composition.

In addition to the foamable resin composition and foaming agent, the foam layer (Y) may further contain the optional additives described above, as well as an ethylene polymer (B) and a thermoplastic elastomer (C), as needed, within a range that does not significantly impair the effects of the present invention, for example, to further improve the effects of the present invention or to impart other effects.

(3) Method for Producing Foam Layer (Y) There are no particular limitations on the method for producing the foam layer (Y) of the present invention, and the foam layer (Y) can be obtained by a conventionally known extrusion foam sheet molding method. Typical extrusion foam sheet molding methods include a T-die (rectangular die) extrusion foam sheet molding method and a circular die (round die) extrusion foam sheet molding method.
The extruder used in the above-mentioned typical extrusion foam sheet molding methods may be a single-screw or twin-screw extruder.

7. Production of Multilayer Foamed Sheet (Z) The multilayer foamed sheet (Z) of the present invention is a sheet obtained by laminating a non-foamed layer (X) and a foamed layer (Y), and a conventionally known lamination method can be used. Typical lamination methods include extrusion lamination, dry lamination, and co-extrusion. Among these, co-extrusion is preferred from the viewpoints of cost and environment.

Regarding the layer structure of the multilayer foamed sheet (Z) of the present invention, the thickness of the non-foamed layer (X) in the sheet is 0.05 mm or more, preferably 0.10 mm or more, more preferably 0.15 mm or more, and accounts for 7 to 40% of the total layer thickness of the sheet {thickness of the non-foamed layer (X) ÷ total layer thickness of the sheet × 100%}, preferably 10 to 30%, more preferably 12 to 20%.
When the thickness of the non-foamed layer (X) is 0.05 mm or more, or 7% or more of the total thickness of the sheet, sufficient cold impact resistance is obtained. On the other hand, when the thickness of the non-foamed layer (X) is 40% or less of the total thickness of the sheet, the density of the multilayer foamed sheet (Z) is reduced, thereby achieving a sufficient weight reduction effect.
The non-foamed layer (X) and the foamed layer (Y) may each be laminated in one layer or in two or more layers, and examples thereof include a two-layer structure in which the non-foamed layer (X)/foamed layer (Y) are laminated in this order, a three-layer structure in which the non-foamed layer (X)/foamed layer (Y)/non-foamed layer (X) or foamed layer (Y)/non-foamed layer (X)/foamed layer (Y) are laminated in this order, and in such a case, the thicknesses of the non-foamed layers (X) may be equal or unequal, and the thicknesses of the foamed layers (Y) may also be equal or unequal. When cold impact resistance is required on both sides of the multilayer foamed sheet (Z), it is preferable to laminate the non-foamed layers (X) in the same thickness and the foamed layers (Y) in the same thickness.

The layer structure of the multilayer foam sheet (Z) of the present invention may further include, in addition to the non-foamed layer (X) and foamed layer (Y), known gas barrier resin layers, adhesive resin layers, recycled resin layers, decorative resin layers, filler-containing resin layers, etc., as needed, within the scope of not significantly impairing the effects of the present invention, for example, to further improve the effects of the present invention or to impart other effects.

The gas barrier resin layer can be made of known barrier resins, such as polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyamides such as nylon 6, nylon 66 and MXD nylon (metaxylylene adipamide polyamide), ethylene-vinyl alcohol copolymers, polyvinylidene chloride, etc. These can be used in a single layer using one type, or in a mixture of two or more types, or in a laminate of two or more layers of gas barrier resins.

The adhesive resin layer may be provided between the non-foamed layer (X) and the foamed layer (Y), or between a known gas barrier resin layer, a recycled resin layer, a decorative resin layer, a filler-containing resin layer, or the like, from the viewpoint of further improving the adhesive strength of the laminated surfaces.
Examples of adhesive resins include polypropylene graft-modified with an ethylenically or propylenically unsaturated carboxylic acid such as maleic anhydride, acrylic acid, or methacrylic acid, or an anhydride thereof, a propylene-α-olefin copolymer, a propylene-α-olefin random copolymer, an ethylenically based polymer, a thermoplastic elastomer, and a petroleum resin, and two or more types of resins can be mixed and used.
In particular, when an ethylene-vinyl alcohol copolymer layer or a metaxylylene adipamide-based polyamide resin is used as the gas barrier resin, it is preferable to use a maleic anhydride-grafted polypropylene or a propylene-α-olefin copolymer as the adhesive resin, from the viewpoint of further improving the adhesive strength of the laminated surface.

From the viewpoint of recycling, the recycled resin layer may be a layer containing both end materials, commonly called ears, which are generally trimmed in the sheet molding method, and the remaining part, commonly called skeleton, which is removed from the molded body in the thermoforming method, crushed and kneaded into pellets, or may be laminated in one layer or two or more layers.
Furthermore, since the non-foamed layer (X) of the present invention contains polypropylene, it is preferable to use a resin containing polypropylene as the recycled resin layer.

As the decorative resin layer, from the viewpoint of improving the design of the multilayer foamed sheet (Z) of the present invention and its molded article, one or more layers of at least one kind of decorative resin layer selected from the group consisting of a decorative resin layer decorated by a conventionally known technique, for example, a decorative resin layer formed by pressing with a roll having a textured pattern such as a matte finish, animal hide finish, hairline finish, or carbon finish to transfer the textured pattern onto the surface, and a decorative resin layer containing a scaly luster pigment or an organic coloring pigment such as interference alumina flakes, interference mica flakes, glass flakes, interference silica flakes, and/or interference talc flakes, may be laminated.
Furthermore, since the non-foamed layer (X) of the present invention contains polypropylene, it is preferable to use a resin containing polypropylene as the decorative resin layer.

As the filler-containing resin layer, one or more filler-containing resin layers may be laminated from the viewpoint of improving the rigidity of the multilayer foamed sheet (Z) of the present invention and the molded article thereof.
The filler is not particularly limited, but at least one selected from the group consisting of inorganic fillers and organic fillers can be used.
Examples of inorganic fillers include oxides such as silica, diatomaceous earth, barium ferrite, beryllium oxide, pumice, and pumice balloons; hydroxides such as aluminum hydroxide, magnesium hydroxide, and basic magnesium carbonate; carbonates such as calcium carbonate, magnesium carbonate, dolomite, and dawsonite; sulfates or sulfites such as calcium sulfate, barium sulfate, ammonium sulfate, and calcium sulfite; talc, clay, mica, glass fiber, carbon fiber, glass balloons, glass beads, calcium silicate, silicates such as wollastonite, montmorillonite, and bentonite; molybdenum sulfide, boron fiber, zinc borate, barium metaborate, calcium borate, sodium borate, basic magnesium sulfate fiber, potassium titanate fiber, aluminum borate fiber, calcium silicate fiber, and calcium carbonate fiber.
On the other hand, examples of organic fillers include husk fibers such as rice husks, wood flour, cotton, jute, paper shreds, cellophane pieces, aromatic polyamide fibers, cellulose fibers, nylon fibers, polyester fibers, various organic fibers, and thermosetting resin powders.

Furthermore, the surface of the multilayer foam sheet (Z) of the present invention may be subjected to a surface treatment such as corona discharge treatment, flame treatment, or plasma treatment in order to improve printability and paintability.

8. Thermoforming Method for Molded Article The molded article of the present invention can be obtained by subjecting the multilayer foamed sheet (Z) produced by the above-described method to a known thermoforming method such as vacuum forming, vacuum pressure forming, or plug-assisted vacuum pressure forming. Examples of heating methods used in such thermoforming methods include indirect heating, hot plate heating, and hot roll heating.

The multilayer foamed sheet of the present invention and the molded article obtained by thermoforming the multilayer foamed sheet have a good foaming state in the foam layer and excellent cold impact resistance, and therefore can be suitably used for food containers such as trays, plates, and cups, vehicle interior materials such as automobile door trims and automobile trunk mats, packaging, stationery, building materials, etc.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.
The evaluation methods, analysis methods and materials used in the examples are as follows.

1. Evaluation and Analysis Methods (1) MFR (unit: g/10 min)
The MFR (230°C, 2.16 kg load) of the propylene polymer (A), the ethylene polymer (B), and the thermoplastic elastomer (C) was measured in accordance with JIS-K7210, in units of g/10 min.
(2) Propylene homopolymer (component (A-1)) in propylene polymer (A)
and propylene-α-olefin copolymer (component (A-2)), the α-olefin content was determined by a combination of the cross-fractionation method and the FT-IR method described in JP 2017-031359 A.
(3) Melting peak temperature (Tm), total amount of heat of fusion (ΔH)
In differential scanning calorimetry (DSC), the sample was heated from 23°C to 200°C at a rate of 10°C/min, held at 200°C for 5 minutes, cooled to 40°C at a rate of 10°C/min, held at 40°C for 1 minute, and then heated to 200°C at a rate of 10°C/min. The endothermic peak top temperature observed during the second heating was defined as the melting peak temperature (Tm), and the total heat of fusion (ΔH) of the melting peak was calculated from the area of the endothermic peak observed during the heating from 40°C to 200°C in accordance with JIS K7122 (1987).
(4) Flexural modulus (unit: MPa), flexural stress (unit: MPa)
Using injection-molded test pieces having a thickness of 4.0 mm, a width of 10.0 mm and a length of 80 mm, measurements were made in accordance with JIS K7171 at an ambient temperature of 23°C (unit: MPa).
The test specimens were molded using an injection molding machine IS80G manufactured by Toshiba Corporation under conditions of a molding temperature of 200°C and a mold temperature of 40°C.
(5) Charpy impact strength (23°C, -20°C)
Measurements were made in accordance with ISO 179 (notched) at an ambient temperature of 23° C. (unit: kJ/m ² ) using injection-molded test pieces with a thickness of 4.0 mm, a width of 10.0 mm and a length of 80 mm and a notch (notch radius: 0.25 mm).
The test pieces were molded in the same manner as in the bending modulus.
(6) Deflection temperature under load (0.46 MPa)
Using injection-molded test pieces having a thickness of 4.0 mm, a width of 10.0 mm and a length of 80 mm, measurements were carried out in accordance with JIS K7191-1, 2 under a load of 0.46 MPa.
The test pieces were molded in the same manner as in the bending modulus.
(7) Layer Thickness The thicknesses of the foamed layer and the multi-layer foamed sheet were calculated by cutting out test pieces from the multi-layer foamed sheets obtained in Examples and Comparative Examples, and enlarging and projecting the cross section of the multi-layer foamed sheet using a stereomicroscope (Nikon Corporation: Model SMZ-1000-2). Furthermore, the thickness of the layer consisting of the non-foamed layer (X) was calculated using the following formula:
Thickness of the layer consisting of the non-foamed layer (X) = Thickness of the multi-layer foamed sheet (Z) - Thickness of the foamed layer (Y) (8) Apparent density,
Test pieces were cut out from the multilayer foamed sheets obtained in the Examples and Comparative Examples, and the foam density was determined by dividing the weight (g) of the test piece by the volume (cm ³ ) determined from the outer dimensions of the test piece. Measurement was carried out in accordance with JIS K7222 to determine the density of the foam.
(9) Open Cell Ratio Test pieces were cut out from the multilayer foamed sheets obtained in the Examples and Comparative Examples, and the open cell ratio was measured using an Air Pycnometer (manufactured by Tokyo Science Co., Ltd.) in accordance with the method described in ASTM D2856.
(10) Appearance The appearance of the multi-layer foamed sheets obtained in each of the Examples and Comparative Examples was evaluated according to the following criteria.
◯: The multilayer foam sheet has a uniform thickness and is beautiful with no defects in appearance such as wrinkles or blisters on the surface.
△: The thickness of the multilayer foam sheet is uniform, but there is poor appearance due to wrinkles or blisters on part of the surface.
x: The thickness of the multilayer foam sheet is uneven, and there is poor appearance due to wrinkles or blisters on the entire surface.
(11) DuPont impact strength (23°C, -20°C)
Test specimens cut from the multilayer foam sheets obtained in Examples and Comparative Examples were conditioned for 30 minutes in a room set at a measurement temperature (23°C or -20°C), and then placed on the core holder of a DuPont impact tester (core holder inner diameter 3/2 inch, core tip R 1/4 inch) described in JIS K5600-5-3, and a 200 g (measurement temperature 23°C) or 100 g (measurement temperature -20°C) weight was dropped on the test specimen. The 50% fracture energy (E) was then calculated from the fracture state of the test specimen using the following formula, and this was used as the DuPont impact test value.
E={HS(T/100-1/2)}×W
E: DuPont impact test value (unit: J)
H: Height at the time of complete destruction (unit: cm)
S: Height interval at which the weight is dropped (unit: cm)
T: Sum of destruction percentage (no destruction to total destruction) (unit: %)
W: Weight of the weight (unit: kg)
(12) Bending Test Test pieces measuring 100 mm in length and 100 mm in width were cut out from the multilayer foamed sheets obtained in the Examples and Comparative Examples and conditioned for 30 minutes in a room set at a measurement temperature (23°C or -20°C). Thereafter, in the same room, both ends of the test piece were held and the center of the test piece was pressed vertically against a metal plate 140 mm in height, 30 mm in width, and 3 mm in thickness from above, folding the test piece in half, and the condition of the bent part was evaluated according to the following criteria.
○: The bent portion is not cracked.
△: Part of the bent portion is cracked and the test piece does not separate into two pieces.
×: The bent portion broke and separated into two test pieces.
(13) Oil resistance test (100°C, 130°C)
A test piece measuring 100 mm in length and 100 mm in width was cut out from the multilayer foamed sheet obtained in each of the Examples and Comparative Examples. Edible rapeseed oil (Canola oil manufactured by Showa Sangyo Co., Ltd.) and a polyethylene terephthalate (hereinafter abbreviated as PET) film were placed on the test piece in this order, and the test piece was placed in a thermostatic chamber set at a measurement temperature (100°C or 130°C) for 30 minutes.
Thereafter, the PET film was removed, and the specimen was washed with water and dishwashing detergent (CHARMY Magica, manufactured by Lion Corporation). The specimen was then placed on a flat surface in a room at 23°C, and the highest value of the height of the target corner from the flat surface when one of the four corners of the specimen was pressed was measured as the warpage. In addition, the oil resistance was evaluated based on the change in surface gloss of the surface to which edible rapeseed oil was applied, according to the following criteria.
◯: The warpage of the test piece is less than 10 mm, and there is no change in the surface gloss.
△: The warpage of the test piece is 10 mm or more, and there is no change in the surface gloss.
×: The warpage of the test piece is less than 10 mm, and the surface gloss is increased.
XX: The warpage of the test piece is 10 mm or more, and the surface gloss is increased.

2. Materials Used 2-1. Propylene Polymer (A)
The following propylene polymers, Components A1 to A5, were prepared. The properties of these resins are summarized in Table 1. (All of the following are pellets to which antioxidants and neutralizing agents have been added.)
Component A1: A grade of "Novatec PP" manufactured by Japan Polypropylene Corporation and having the following composition was used.
The material is a propylene-α-olefin block copolymer polymerized with a Ziegler-Natta catalyst, where the α-olefin is ethylene. The MFR (230°C, 2.16 kg load) of the entire copolymer is 8.5 g/10 min, the content of propylene homopolymer (component (A-1)) is 84 wt%, the content of propylene-α-olefin copolymer (component (A-2))) is 16 wt%, and the content of α-olefin in the propylene-α-olefin block copolymer is 8 wt%.
Component A2: A grade of "Novatec PP" manufactured by Japan Polypropylene Corporation and having the following composition was used.
The material is a propylene-α-olefin block copolymer polymerized with a Ziegler-Natta catalyst, where the α-olefin is ethylene. The MFR (230°C, 2.16 kg load) of the entire copolymer is 0.5 g/10 min, the content of propylene homopolymer (component (A-1)) is 86 wt%, the content of propylene-α-olefin copolymer (component (A-2))) is 14 wt%, and the content of α-olefin in the propylene-α-olefin block copolymer is 6 wt%.
Component A3: A grade of "Novatec PP" manufactured by Japan Polypropylene Corporation and having the following composition was used.
The material is a propylene-α-olefin block copolymer polymerized with a Ziegler-Natta catalyst, in which the α-olefin is ethylene. The MFR (230°C, 2.16 kg load) of the entire copolymer is 3.0 g/10 min, the content of propylene homopolymer (component (A-1)) is 83 wt%, the content of propylene-α-olefin copolymer (component (A-2))) is 17 wt%, and the content of α-olefin in the propylene-α-olefin block copolymer is 5 wt%.
Component A4: A grade of "Novatec PP" manufactured by Japan Polypropylene Corporation and having the following composition was used.
The material is a propylene-α-olefin block copolymer polymerized with a Ziegler-Natta catalyst, where the α-olefin is ethylene. The MFR (230°C, 2.16 kg load) of the entire copolymer is 13.0 g/10 min, the content of propylene homopolymer (component (A-1)) is 98 wt%, the content of propylene-α-olefin copolymer (component (A-2))) is 2 wt%, and the content of α-olefin in the propylene-α-olefin block copolymer is 1 wt%.
Component A5: A grade of "Novatec PP" manufactured by Japan Polypropylene Corporation and having the following composition was used.
The material is a propylene homopolymer polymerized with a Ziegler-Natta catalyst, and has an MFR (230° C., 2.16 kg load) of 60.0 g/10 min.

2-2. Ethylene polymer (B)
The following commercially available ethylene polymer, Component B1, was prepared.
Component B1: Trade name "Novatec LD LF640MA" manufactured by Japan Polyethylene Co., Ltd. The MFR (230°C, 2.16 kg load) of this material is 10.0 g/10 min, and the density is 0.924 g/cm ³ .
Component B2: Trade name "Novatec HD HJ360" manufactured by Japan Polyethylene Co., Ltd. The MFR (230°C, 2.16 kg load) of this material is 11.0 g/10 min and the density is 0.951 g/cm ³ .
Component B3: Trade name "Novatec UJ960" manufactured by Japan Polyethylene Co., Ltd. The MFR (230°C, 2.16 kg load) of this material is 10.0 g/10 min, and the density is 0.935 g/cm ³ .

2-3. Thermoplastic elastomer (C)
Component C1: trade name "Tafmer PN2070" manufactured by Mitsui Chemicals, Inc. The MFR (230°C, 2.16 kg load) of this material is 7.0 g/10 min and the density is 0.867 g/cm ³ .
Component C2: Trade name "Kraton G1657" manufactured by Kraton Polymer Japan Co., Ltd. The MFR (230°C, 2.16 kg load) of this material is 8.0 g/10 min, and the density is 0.890 g/cm ³ .
Component C3: Trade name "Kernel KC452T" manufactured by Japan Polyethylene Co., Ltd. The MFR (230°C, 2.16 kg load) of this material is 13.0 g/10 min and the density is 0.888 g/ ^cm3 .
Component C4: Trade name "Kernel KF380" manufactured by Japan Polyethylene Co., Ltd. The MFR (230°C, 2.16 kg load) of this material is 8.0 g/10 min and the density is 0.918 g/ ^cm3 .
Component C5: trade name "TAFMER DF110" manufactured by Mitsui Chemicals, Inc. The MFR (230°C, 2.16 kg load) of this material is 2.2 g/10 min, and the density is 0.905 g/ ^cm3 .
Component C6: Trade name "Engage 8450" manufactured by Dow Chemical Japan Co., Ltd. The MFR (230°C, 2.16 kg load) of this material is 6.0 g/10 min and the density is 0.902 g/cm ³ .

3. Examples and Comparative Examples [Examples 1 to 21 and Comparative Examples 1 to 8]
The propylene polymer (A), ethylene polymer (B), and thermoplastic elastomer (C) used in the non-foamed layer (X) described in Examples 1 to 21 and Comparative Examples 1 to 3 and 5 to 8 were uniformly mixed by stirring using a ribbon blender in the ratios shown in Tables 2 and 3. The foamable resin composition (D) and chemical foaming agent (trade name: Hydrocellol CF40E-J, manufactured by Clariant Japan KK) used in the foamed layer (Y) described in Examples 1 to 21 and Comparative Examples 1 to 8 were uniformly mixed by stirring using a ribbon blender in the ratios shown in Tables 2 and 3.

3-2. Production of Multilayer Foam Sheet A mixture of the foamable resin composition (D) and chemical foaming agent used for the foam layer (Y) described in Examples 1 to 21 and Comparative Examples 1 to 8 was fed into a single-screw extruder with a screw diameter of 65 mm and a barrel hole for injecting a physical foaming agent. The cylinder temperature in the upstream section of the extruder was set to 240°C, and the foamable resin composition (D) was heated and melted to plasticize it while decomposing the foaming agent. While this was happening, 0.70 parts by weight of liquefied carbon dioxide was injected into 100 parts by weight of the foamable resin composition (D) using a high-pressure pump and mixed. The cylinder temperature in the downstream section of the extruder was then set to 185°C, and the mixture was rapidly cooled. The mixture was then extruded through a feed block and a T-die with a width of 1,180 mm and a lip width of 0.4 mm.
At this time, the mixture used for the non-foamed layer (X) described in Examples 1 to 21 and Comparative Examples 1 to 3 and 5 to 8 was charged into a single-screw extruder with a screw diameter of 40 mmΦ, heated and melted by setting the cylinder temperature of the front stage of the extruder to 230°C and the cylinder temperature of the rear stage of the extruder to 180°C, and laminated as non-foamed layers (X) on both sides of the foamed layer (Y) via a feed block to obtain a multi-layer foamed sheet having a two-kind three-layer structure in which the non-foamed layer (X)/foamed layer (Y)/non-foamed layer (X) were laminated in this order, but only in Comparative Example 1, the non-foamed layer (X) could not be extruded, and the desired sheet was not obtained. Furthermore, in Comparative Example 4, the non-foamed layer (X) was not laminated, and a single layer of non-foamed layer (X) was obtained.
The extruded multi-layer foamed sheet was first cooled on one side by a roll having a diameter of 110 mm installed immediately adjacent to the die, and then cooled on both sides by three rolls having a diameter of 110 mm installed thereafter, and was taken up at a constant speed by a pinch roll so that the thickness of the multi-layer foamed sheet became about 1.5 mm.

The obtained multilayer foamed sheets were molded into test specimens for evaluation according to the methods described above, and the performance of the sheets was evaluated. The results are shown in Tables 2 to 4.

From the results shown in Tables 2 and 3, it can be seen that in Examples 1 to 21, which satisfy the specific features of the multi-layer foamed sheet of the present invention, the multi-layer foamed sheet had a DuPont impact value of 0.1 J or more at −20° C., and no cracks were observed at the bent portion in the bending test at −20° C., indicating good cold impact resistance.
On the other hand, the results shown in Table 4 show that Comparative Examples 1 to 8, which do not satisfy the specific features of the present invention, are inferior due to poor balance of these performances. For example, Comparative Examples 1 and 3 to 4, which do not contain the propylene polymer (A) that satisfies the requirements (A-i) to (A-ii), have DuPont impact values at −20° C. of less than 0.1 J and break at the bent portion in the bending test at −20° C., resulting in inferior cold impact resistance.

The multilayer foam sheet of the present invention has excellent cold impact resistance, and can be cut or thermoformed to be suitable for use in food containers such as trays, plates, and cups, vehicle interior materials such as automobile door trim and trunk mats, packaging, stationery, and building materials.

Claims (4)

The multilayer foamed sheet (Z) is a sheet obtained by laminating a foamed layer (Y) and a non-foamed layer (X) containing a propylene-based polymer (A) that satisfies the following requirements (A-i) to (A-ii), and is characterized in that the thickness of the non-foamed layer (X) in the sheet is 0.05 mm or more and accounts for 7 to 40% of the total thickness of the sheet {= (thickness of the non-foamed layer (X) ÷ total thickness of the sheet) × 100%):
Requirement (A-i): In differential scanning calorimetry (DSC), the sample is heated from 23°C to 200°C at a rate of 10°C/min, held at 200°C for 5 minutes, cooled to 40°C at a rate of 10°C/min, held at 40°C for 1 minute, and then heated to 200°C at a rate of 10°C/min. The peak melting temperature (Tm) observed during the second heating is 130 to 165°C, and the total heat of fusion (ΔH) observed during the heating from 40°C to 200°C is 60 to 100 J/g.
Requirement (A-ii): The melt flow rate (230°C, 2.16 kg load) (MFR(A)) is 2 to 20 g/10 min, and the ratio of the melt flow rate (230°C, 2.16 kg load) (MFR(D)) of the foamable resin composition (D) used in the foam layer (Y) to the melt flow rate (230°C, 2.16 kg load) (MFR(A)) is 0.2 to 2.0 (=MFR(A)/MFR(D)). The multilayer foamed sheet (Z) according to claim 1, wherein the non-foamed layer (X) contains 10 to 200 parts by weight of an ethylene polymer (B) satisfying the following requirement (Bi) per 100 parts by weight of the propylene polymer (A):
Requirement (Bi): The melt flow rate (230°C, 2.16 kg load) (MFR(B)) is 0.5 to 20 g/10 min, and the ratio of the MFR(B) to the MFR(A) of the propylene polymer (A) is 0.05 to 1.5 (=MFR(B)/MFR(A)). The multilayer foamed sheet (Z) according to claim 2, wherein the non-foamed layer (X) contains 10 to 200 parts by weight of a thermoplastic elastomer (C) satisfying the following requirement (C-i) per 100 parts by weight of the propylene-based polymer (A):
Requirement (C-i): The melt flow rate (230°C, 2.16 kg load) (MFR(C)) is 0.5 to 20 g/10 min, and the ratio of the MFR(C) to the MFR(A) of the propylene polymer (A) is 0.05 to 1.5 (=MFR(C)/MFR(A)). A molded article obtained by thermoforming the multilayer foam sheet (Z) according to any one of claims 1 to 3.