Polyolefin resin foam sheet and laminate

Abstract

The present invention provides a polyolefin resin foam sheet and a laminate having exceptional flexibility and moldability. This polyolefin resin foam sheet has, as a substrate resin, a resin mixture containing 0-30 mass% (inclusive) of a polyethylene resin, 30-80 mass% (inclusive) of a polypropylene resin, and 20-40 mass% (inclusive) of a polyolefin elastomer, and moreover is such that the rate of change in dimensions upon heating when the polyolefin resin foam sheet is heated from a maximum melting point, which is the highest melting peak in DSC measurement, to a temperature 20°C higher over the course of ten minutes is -35 to 0% (inclusive).

Description

[Technical Field]

[0001] The present invention relates to a polyolefin resin foam sheet and a laminate having excellent flexibility and moldability. [Background technology]

[0002] Crosslinked foam sheets using polyolefin resins as a base resin have been used for automobile interior materials such as ceilings, door panels, instrument panels, etc., because of their excellent flexibility, heat resistance, mechanical strength, etc. In these applications, there is an increasing demand for foams with enhanced flexibility, with the objectives of imparting a luxurious feel through appropriate flexibility and imparting functionality to reduce the burden on areas such as armrests that come into contact with people.

[0003] The polyolefin resin foam sheet contains 15 to 75 parts by mass of an olefin block copolymer having a melting point of 115°C or higher and a melt index of 0.1 g / 10 min to 40 g / 10 min (at 190°C), and 25 to 85 parts by mass of a polypropylene resin having a melt index of 0.1 g / 10 min to 25 g / 10 min (at 230°C), and has a gel fraction of 20% to 75% and a density of 25 kg / m 3 More than 250kg / m 3 A polyolefin resin foam sheet has been proposed (see, for example, Patent Document 1) that is characterized by the following:

[0004] Furthermore, a laminate and an automobile interior material have been proposed that are made using a polyolefin resin foam, which is a laminate of a polyolefin resin foam and a skin body, characterized in that the polyolefin resin foam contains 30% by mass to 60% by mass of a polypropylene resin, 1% by mass to 20% by mass of a polyethylene resin, and 30% by mass or more of a thermoplastic elastomer resin, relative to 100% by mass of the polyolefin resin that constitutes the polyolefin resin foam (see, for example, Patent Document 2).

[0005] The methods for producing the polyolefin resin foam sheet and polyolefin resin foam are not particularly limited, but can be broadly divided into the following steps: forming a resin composition into a sheet to obtain a foamable sheet; crosslinking the foamable sheet; and heating and foaming the crosslinked foamable sheet to obtain a foamed sheet. In consideration of productivity, the foamed sheet-producing step often involves continuously supplying a roll of the crosslinked foamable sheet to a heat medium to foam it, and then winding it up into a roll of foamed sheet. In this process, the MD stretch ratio (the winding speed divided by the unwinding speed) is generally greater than 3.0, depending on the degree of foaming. To prevent sagging and wrinkling during foaming, increasing the MD stretch ratio during foaming improves production efficiency. In particular, when a polyolefin elastomer resin is contained, the sheet is typically produced at a high stretch ratio due to the risk of sticking to rolls, etc. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-187232 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-155344 Summary of the Invention [Problem to be solved by the invention]

[0007] The polyolefin resin foam sheets and laminates using polyolefin resin foams disclosed in Patent Documents 1 and 2 have excellent flexibility, but there is a problem in that moldability is insufficient because sufficient consideration has not been given to moldability such as dimensional defects due to heat shrinkage during molding and poor appearance due to wrinkles.

[0008] Therefore, an object of the present invention is to provide a polyolefin resin foam sheet and a laminate thereof having excellent flexibility and moldability. [Means for solving the problem]

[0009] As a result of extensive investigations to achieve the above object, the present inventors have found that a polyolefin resin foam sheet has excellent flexibility and moldability, the polyolefin resin foam sheet having a base resin mixture containing 0% to 30% by mass of polyethylene resin, 30% to 80% by mass of polypropylene resin, and 20% to 40% by mass of polyolefin elastomer, and having a thermal dimensional change of -35% to 0% when heated for 10 minutes at a temperature 20°C higher than the maximum melting point, which is the highest melting peak in DSC measurement.

[0010] Also, the 25% compressive stress (kPa) is used to calculate the density (kg / m 3 ) is 2.5 or less, and the thermal dimensional change rate when heated for 10 minutes at a temperature 20°C higher than the maximum melting point, which is the highest melting peak in DSC measurement, is -35% or more and 0% or less, also has excellent flexibility and moldability, and the present invention has been completed based on this finding. The present invention relates to the following (1) to (12). (1) A polyolefin-based resin foam sheet having a resin mixture containing 0% by mass or more and 30% by mass or less of a polyethylene-based resin, 30% by mass or more and 80% by mass or less of a polypropylene-based resin, and 20% by mass or more and 40% by mass or less of a polyolefin-based elastomer as a base resin, in which the thermal dimensional change rate in the MD and TD directions when heated for 10 minutes at a temperature 20°C higher than the maximum melting point, which is the highest melting peak in DSC measurement, is -35% or more and 0% or less. (2) 25% compressive stress (kPa) vs. density (kg / m 3 ) is 2.5 or less, and the thermal dimensional change rates in the MD and TD directions when heated for 10 minutes at a temperature 20°C higher than the maximum melting point, which is the highest melting peak in DSC measurement, are -35% or more and 0% or less. (3) Thickness is 1 mm or more and 5 mm or less, and density is 40 kg / m 3 More than 100kg / m 3 The polyolefin resin foam sheet according to (1) or (2), wherein the gel fraction is 30% or more and 60% or less.

[0011] (4) The polyolefin resin foam sheet according to any one of (1) to (3), wherein the MD / TD ratio of thermal dimensional change when heated for 10 minutes at a temperature 20°C higher than the maximum melting point, which is the highest melting peak in DSC measurement, is 0.5 or more and 1.5 or less. (5) The polyolefin resin foam sheet according to any one of (1) to (4), wherein the thermal dimensional change in the MD and TD directions when heated for 10 minutes at a temperature 20°C lower than the maximum melting point, which is the highest melting peak in DSC measurement, is -5% or more and 0% or less. (6) Average bubble diameter in MD direction (BD) MD is the average bubble diameter in the TD direction, and TD Average bubble diameter ratio BD MD / BD TD The polyolefin resin foam sheet according to any one of (1) to (5), wherein the value is 0.7 or more and 1.3 or less. (7) The polyolefin resin foam sheet according to any one of (1) to (6), wherein the tensile strength ratio in MD direction / TD direction at 23° C. is 0.7 or more and 1.3 or less. (8) The polyolefin resin foam sheet according to any one of (1) to (7), wherein the curl height when heated for 10 minutes at a temperature 20°C higher than the maximum melting point, which is the highest melting peak in DSC measurement, is from the foam sheet thickness to 15 mm or less. (9) When the polyolefin resin foam sheet is divided into 5 equal parts in the thickness direction and the layers are divided into 1 to 5 in the thickness direction, the larger gel fraction value of the 1st layer and the 5th layer is designated as GF. A , the smaller value is GF B Then, GF A / GF B 9. The polyolefin resin foam sheet according to any one of (1) to (8), wherein the gel fraction ratio of the surface layer calculated by the following formula is 1.0 or more and 1.2 or less. (10) When the polyolefin resin foam sheet is divided into 5 equal parts in the thickness direction and the layers are divided into 1 to 5 in the thickness direction, the larger value of the average cell diameter BD of the 1st layer and the 5th layer is used as BD. A , the smaller value is BD B Then, BD A / BD B10. The polyolefin resin foam sheet according to any one of (1) to (9), wherein the average cell diameter ratio of the surface layer calculated by the formula (1) is 1.0 or more and 1.2 or less. (11) The average cell diameter of the polyolefin resin foamed sheet before heating is measured in both the MD and TD directions. BF The average cell diameter of the foamed sheet heated for 10 minutes at a temperature 20°C higher than the maximum melting point, which is the highest melting peak in the DSC measurement, is BD. AF When BD BF / BD AF The polyolefin resin foam sheet according to any one of (1) to (10), wherein the average cell diameter ratio before and after heating, calculated by the formula: is 1.0 or more and 1.5 or less. (12) A laminate obtained by laminating one or more skin materials selected from the group consisting of sheets, films, cloth, nonwoven fabrics, and leathers with the polyolefin resin foam sheet according to any one of (1) to (11). [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a polyolefin resin foam sheet and a laminate thereof that have both excellent flexibility and moldability. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram illustrating the measurement of the average cell diameter of the polyolefin resin foam sheet according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] The polyolefin resin foam sheet according to the present invention has a resin mixture as a base resin containing 0% by mass or more and 30% by mass or less of a polyethylene resin, 30% by mass or more and 80% by mass or less of a polypropylene resin, and 20% by mass or more and 40% by mass or less of a polyolefin elastomer.

[0015] <Base resin> The polyethylene resin used in the present invention is a resin primarily containing polyethylene, such as high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), ethylene-ethyl acrylate copolymer (EEA), and ethylene-butyl acrylate copolymer (EBA). Furthermore, copolymers of ethylene monomers with other copolymerizable monomers can also be used as needed. These polyethylene resins may be used alone or in blends of two or more. The polymerization method for these polyethylene resins is not particularly limited, and may be any of a high-pressure method, a slurry method, a solution method, or a gas-phase method. The polymerization catalyst may also be a Ziegler catalyst, a metallocene catalyst, or the like, but is not particularly limited.

[0016] The polyethylene resin is not particularly limited, but preferably has a density of 890 kg / m 3 More than 950kg / m 3 In the following, those having an MFR (190°C) in the range of 1 g / 10 min to 15 g / 10 min are preferably used, and among these, those having a density of 920 kg / m 3 More than 940kg / m 3 Ethylene-α-olefin copolymers having an MFR (190° C.) of 2 g / 10 min or more and 10 g / 10 min or less and a melting point of 100° C. or more and 130° C. or less are particularly preferably used. The proportion of the polyethylene resin in the base resin is from 0% to 30% by mass. By setting the polyethylene resin content to from 0% to 30% by mass, excellent flexibility and moldability can be imparted. If the polyethylene resin content exceeds 30% by mass, shrinkage during molding becomes significant, resulting in defects such as sizing defects. The proportion of the polyethylene resin in the base resin is preferably from 0% to 25% by mass, more preferably from 0% to 20% by mass, and even more preferably from 0% to 15% by mass.

[0017] The polypropylene-based resin used in the present invention is a resin primarily containing polypropylene, such as homopolypropylene, ethylene-propylene random copolymer, or ethylene-propylene block copolymer. If necessary, a copolymer of a propylene monomer with another copolymerizable monomer can also be used. The polyolefin-based resin foam sheet may contain one type of polypropylene-based resin, or a blend of two or more types of polypropylene-based resin. The polymerization method for these polypropylene-based resins is not particularly limited, and may be any of a high-pressure method, a slurry method, a solution method, or a gas-phase method. The polymerization catalyst may also be a Ziegler catalyst, a metallocene catalyst, or the like, but is not particularly limited.

[0018] The polypropylene resin is not particularly limited, but particularly preferred are random polypropylenes having an ethylene content of 5% by mass or more and 15% by mass or less in 100% by mass of the polypropylene resin, a melting point of 135°C or more and 160°C or less, and an MFR (230°C) of 0.5 g / 10 min or more and 5.0 g / 10 min or less, or block polypropylenes having an ethylene content of 100% by mass of the polypropylene resin from 1% by mass or more and 5% by mass or less, a melting point of 150°C or more and 170°C or less, and an MFR (230°C) of 1.0 g / 10 min or more and 7.0 g / 10 min or less. The proportion of polypropylene resin in the base resin is 30% by mass or more and 80% by mass or less. By making the polypropylene resin 30% by mass or more and 80% by mass or less, excellent flexibility and moldability can be imparted. If the polypropylene resin is less than 30% by mass, shrinkage during molding becomes significant, resulting in defects such as sizing defects. If the polypropylene resin is more than 80% by mass, sufficient flexibility cannot be imparted. The proportion of polypropylene resin in the base resin is preferably 30% by mass or more and 70% by mass or less, more preferably 30% by mass or more and 60% by mass or less, and even more preferably 30% by mass or more and 50% by mass or less.

[0019] The polyolefin elastomers used in the present invention are often composed of soft and hard segments. Copolymers of ethylene and propylene monomers with other copolymerizable monomers can also be used as needed. These polyolefin elastomers can be used alone or in a blend of two or more types. The polymerization method is not particularly limited, and high-pressure, slurry, solution, or gas-phase methods are acceptable. The polymerization catalyst is not particularly limited, and includes Ziegler catalysts, metallocene catalysts, and other methods. Furthermore, two or more types of polymers that form hard segments and soft segments can be physically mixed to form a polymer alloy. Elastomers such as polystyrene elastomers (SBC, TPS), polyvinyl chloride elastomers (TPVC), polyurethane elastomers (TPU), polyester elastomers (TPEE, TPC), polyamide elastomers (TPAE, TPA), and polybutadiene elastomers may also be included, provided that they do not impair the effects of the present invention.

[0020] The polyolefin elastomer is not particularly limited, but is preferably a polyolefin elastomer having a melting point of 120°C or more and 160°C or less, an MFR (230°C) of 0.1g / 10min or more and 40.0g / 10min or less, and a glass transition temperature of -40°C or less. The proportion of polyolefin elastomer in the base resin is 20% by mass or more and 40% by mass or less. By adjusting the polyolefin elastomer content to 20% by mass or more and 40% by mass or less, excellent flexibility and moldability can be imparted. If the polyolefin elastomer content is less than 20% by mass, sufficient flexibility cannot be imparted. If the polyolefin elastomer content exceeds 40% by mass, shrinkage during molding becomes significant, resulting in defects such as sizing defects. The proportion of polyolefin elastomer in the base resin is preferably 20% by mass or more and 35% by mass or less, more preferably 25% by mass or more and 35% by mass or less, and even more preferably 30% by mass or more and 35% by mass or less.

[0021] <Foaming agent> The polyolefin resin foam sheet of the present invention is produced by mixing a foaming agent capable of generating gas with a base resin. Examples of production methods include the atmospheric foaming method in which a thermally decomposable chemical foaming agent is added to the base resin as a foaming agent, melt-kneaded, and foamed by heating under atmospheric pressure, the extrusion foaming method in which a thermally decomposable chemical foaming agent is thermally decomposed in an extruder and foamed while being extruded under high pressure, the press foaming method in which a thermally decomposable chemical foaming agent is thermally decomposed in a press mold and foamed while being reduced in pressure, and the extrusion foaming method in which a gas or vaporizable solvent is melt-mixed in an extruder and foamed while being extruded under high pressure.

[0022] The thermally decomposable chemical foaming agent used herein is a chemical foaming agent that decomposes upon application of heat and releases gas, and examples thereof include organic foaming agents such as azodicarbonamide, N,N'-dinitrosopentamethylenetetramine, and P,P'-oxybenzenesulfonylhydrazide, and inorganic foaming agents such as sodium bicarbonate, ammonium carbonate, ammonium bicarbonate, and calcium azide. The foaming agents can be used alone or in combination of two or more. In order to obtain a high-expansion foam that is flexible, highly moldable, and has a smooth surface, the atmospheric foaming method using azodicarbonamide as the foaming agent is preferably used.

[0023] <Crosslinking aid> The polyolefin resin foam sheet of the present invention can be either a crosslinked resin foam (referred to as a crosslinked foam) or a non-crosslinked resin foam (referred to as a non-crosslinked foam), and the appropriate resin foam can be selected depending on the application. A crosslinked resin foam is preferred for the polyolefin resin foam sheet because the resin foam has a smooth surface, resulting in an excellent laminate appearance, and because it is less likely to tear during molding, allowing for design flexibility. There are no particular limitations on the method for producing a crosslinked foam. Examples of methods for producing a crosslinked foam include a chemical crosslinking method in which a crosslinking agent having a chemical structure such as a silane group, peroxide, hydroxyl group, amide group, or ester group is added to the raw materials to chemically crosslink the foam; and a radiation crosslinking method in which a polyolefin resin is irradiated with electron beams, α-rays, β-rays, γ-rays, or ultraviolet rays to crosslink the foam. When it is difficult to achieve a crosslinked structure using electron beam irradiation alone, a crosslinked foam can be obtained by adding a crosslinking aid to the base resin used to produce the polyolefin resin foam sheet. The crosslinking aid is not particularly limited, but a polyfunctional monomer is preferably used. Examples of polyfunctional monomers that can be used include divinylbenzene, trimethylolpropane trimethacrylate, 1,6-hexanediol dimethacrylate, 1,9-nonanediol dimethacrylate, 1,10-decanediol dimethacrylate, trimellitic acid triallyl ester, triallyl isocyanurate, ethylvinylbenzene, etc. These polyfunctional monomers may be used alone or in combination of two or more.

[0024] <Other additives> The base resin and the polyolefin resin foam sheet may contain, as needed, an antioxidant, a heat stabilizer, a colorant, a flame retardant, an antistatic agent, and the like.

[0025] <Mixing ratio> The polyolefin resin foam sheet according to the present invention contains 100% by mass of the base resin, and contains from 0% by mass to 30% by mass of polyethylene resin, from 30% by mass to 80% by mass of polypropylene resin, and from 20% by mass to 40% by mass of polyolefin elastomer.

[0026] <Polyolefin resin foam sheet> The polyolefin resin foam sheet according to the present invention preferably has a closed-cell structure. In the case of a foam having a closed-cell structure, the structure allows for sufficient air to be removed by vacuum forming, making it possible to mold the foam into complex shapes. In addition, it is preferable that the cells are fine and uniform, since this results in a smooth surface for the foam and for the molded product obtained by molding the foam.

[0027] When the polyolefin resin foam sheet according to the present invention is used as an automobile interior material, the thickness of the polyolefin resin foam sheet is preferably 1.0 mm or more and 5.0 mm or less. If the thickness is less than 1.0 mm, bottoming out may occur. If the thickness exceeds 5.0 mm, the lightweight properties of the component deteriorate. The thickness is more preferably 1.0 mm or more and 4.0 mm or less, and even more preferably 2.0 mm or more and 4.0 mm or less. The apparent density of the polyolefin resin foam sheet according to the present invention is 40 kg / m 3 More than 100kg / m 3 It is preferable that the apparent density is 40 kg / m or less. 3 If it is less than this, bottoming out may occur, and the load should be 100 kg / m 3 If the density exceeds 50 kg / m, sufficient flexibility cannot be imparted. 3 More than 100kg / m 3 Less than 50 kg / m is more preferable. 3 More than 80kg / m 3 The following is even more preferred:

[0028] The gel fraction in the present invention refers to the proportion of crosslinked and polymerized resin in the base resin, i.e., the proportion of the portion that does not plasticize at normal molding temperatures. Generally, a higher proportion of this portion improves heat resistance but reduces moldability. Therefore, this proportion is selected arbitrarily depending on the molding method. The gel fraction of the polyolefin resin foam sheet according to the present invention is preferably 30% or more and 60% or less. If the gel fraction is less than 30%, the heat resistance decreases, causing the foam sheet to deteriorate during molding, making molding difficult. Furthermore, if the gel fraction exceeds 60%, flexibility may be impaired. The gel fraction of the polyolefin resin foam sheet is more preferably 30% or more and 55% or less, and even more preferably 30% or more and 50% or less. In addition, when the polyolefin resin foam sheet of the present invention is divided into 5 equal parts in the thickness direction and the layers are divided into 1 to 5 in the thickness direction, the larger gel fraction value of the 1st layer and the 5th layer is designated as GF. A , the smaller value is GF B Then, GF A / GF B The gel fraction ratio of the surface layer calculated by the formula (2) is preferably 1.0 or more and 1.2 or less. By setting the gel fraction ratio of the surface layer to 1.0 or more and 1.2 or less, excellent moldability can be achieved. If the gel fraction ratio of the surface layer exceeds 1.2, the foam will curl significantly, resulting in molding defects such as poor appearance due to missing dimensions and wrinkles. The gel fraction ratio of the surface layer is more preferably 1.0 or more and 1.1 or less.

[0029] The 25% compressive strength of the polyolefin resin foam sheet according to the present invention is preferably 250 kPa or less. If the 25% compressive strength exceeds 250 kPa, it becomes difficult to impart sufficient flexibility. The 25% compressive strength is more preferably 200 kPa or less, and even more preferably 150 kPa or less. In the polyolefin resin foam sheet according to the present invention, the 25% compressive strength (kPa) is 3 The value obtained by dividing the 25% compressive strength (kPa) by the density (kg / m 3 If the value obtained by dividing the 25% compressive strength (kPa) by the density (kg / m3 ) is more preferably 2.3 or less, further preferably 2.1 or less, and particularly preferably 1.9 or less.

[0030] The tensile strength (MD, TD) of the polyolefin resin foam sheet according to the present invention at 23°C is preferably 500 kPa or more. If the tensile strength (MD, TD) at 23°C is less than 500 kPa, breakage may occur during molding, making it difficult to obtain a good molded product. The tensile strength (MD, TD) at 23°C is more preferably 700 kPa or more, and even more preferably 900 kPa or more. In the polyolefin resin foam sheet according to the present invention, the tensile strength ratio, obtained by dividing the tensile strength in the MD direction by the tensile strength in the TD direction at 23°C, is preferably 0.7 to 1.3. If the tensile strength ratio is less than 0.7 or more than 1.3, shrinkage due to heating during molding processing becomes significant, which may cause sizing defects and make it impossible to obtain a molded product. The tensile strength ratio is more preferably 0.8 to 1.3, even more preferably 0.8 to 1.2, and particularly preferably 0.9 to 1.1.

[0031] The tensile strength (MD, TD) of the polyolefin resin foam sheet according to the present invention at -35°C is preferably 500 kPa or more. If the tensile strength (MD, TD) at -35°C is less than 500 kPa, breakage may occur during molding, making it impossible to obtain a good molded product. The tensile strength (MD, TD) at -35°C is more preferably 700 kPa or more, and even more preferably 900 kPa or more. The tensile elongation (MD, TD) of the polyolefin resin foam sheet according to the present invention at 23°C is preferably 200% or more. If the tensile elongation (MD, TD) at 23°C is less than 200%, tearing may occur during molding, making it impossible to obtain a good molded product. The tensile elongation (MD, TD) at 23°C is more preferably 250% or more, and even more preferably 300% or more.

[0032] The tensile elongation (MD, TD) of the polyolefin resin foam sheet according to the present invention at -35°C is preferably 30% or more. If the tensile elongation (MD, TD) at -35°C is less than 30%, tearing may occur during molding, making it impossible to obtain a good molded product. The tensile elongation (MD, TD) at -35°C is more preferably 40% or more, and even more preferably 50% or more. The polyolefin resin foam sheet according to the present invention preferably has a tear strength (MD and TD) of 50 N / cm or more at 23°C. If the tear strength (MD and TD) at 23°C is less than 50 N / cm, the sheet may break during molding, making it difficult to obtain a satisfactory molded product. The tear strength (MD and TD) at 23°C is preferably 60 N / cm or more, more preferably 70 N / cm or more.

[0033] In the polyolefin resin foam sheet according to the present invention, the tear strength ratio, calculated by dividing the MD tear strength by the TD tear strength at 23°C, is preferably 0.7 or more and 1.3 or less. If the tensile strength ratio is less than 0.7 or more and more than 1.3, shrinkage due to heating during molding processing increases, which may cause defects and make it impossible to obtain a molded product. The tear strength ratio is more preferably 0.8 or more and 1.3 or less, even more preferably 0.8 or more and 1.2 or less, and particularly preferably 0.9 or more and 1.1 or less. The polyolefin resin foam sheet according to the present invention preferably has a thermal dimensional change (MD and TD) of -5% or more and 0% or less when heated at 120°C for 1 hour. When the thermal dimensional change is within this range, shrinkage during thermoforming is suppressed, and a good molded product can be obtained. The thermal dimensional change in the MD and TD is more preferably -4% or more and 0% or less, and even more preferably -3% or more and 0% or less.

[0034] The polyolefin resin foam sheet according to the present invention preferably exhibits a thermal dimensional change (MD and TD) of -5% to 0% when heated for 10 minutes at a temperature 20°C lower than the maximum melting point, which is the highest melting peak in DSC measurement. By controlling the thermal dimensional change to -5% to 0%, shrinkage during thermoforming can be suppressed, preventing molding defects such as missing dimensions. The thermal dimensional change at a temperature 20°C lower than the maximum melting point in the MD and TD is more preferably -4% to 0%, and even more preferably -3% to 0%. In the polyolefin resin foam sheet according to the present invention, the thermal dimensional change rate (DC) in the MD direction when heated for 10 minutes at a temperature 20°C lower than the maximum melting point, which is the highest melting peak in DSC measurement, is MD is the rate of dimensional change in the TD direction TD The ratio of dimensional change rate due to heating, DC, divided by MD / DC TD The ratio of the thermal dimensional change rate DC at a temperature 20°C lower than the maximum melting point is preferably 0.5 or more and 1.5 or less. MD / DC TD If the ratio is within this range, shrinkage anisotropy during thermoforming can be reduced and good molded products can be obtained. MD / DC TD is more preferably 0.7 or more and 1.5 or less, further preferably 0.7 or more and 1.4 or less, and particularly preferably 0.8 or more and 1.3 or less.

[0035] The polyolefin resin foam sheet according to the present invention exhibits a thermal dimensional change (MD and TD) of -35% or more and 0% or less when heated for 10 minutes at a temperature 20°C higher than the maximum melting point, which is the highest melting peak in DSC measurement. By controlling the thermal dimensional change to -35% or more and 0% or less, shrinkage during thermoforming can be suppressed, preventing molding defects such as missing dimensions. The thermal dimensional change at a temperature 20°C higher than the maximum melting point is preferably -33% or more, more preferably -31% or more, and even more preferably -30% or more. In the polyolefin resin foam sheet according to the present invention, the thermal dimensional change rate (DC) in the MD direction when heated for 10 minutes at a temperature 20°C higher than the maximum melting point, which is the highest melting peak in DSC measurement, is MD is the rate of dimensional change in the TD direction TD The ratio of dimensional change rate due to heating, DC, divided by MD / DC TD The ratio of the thermal dimensional change rate DC at a temperature 20°C higher than the maximum melting point is preferably 0.5 or more and 1.5 or less. MD / DC TD When the ratio is within this range, shrinkage anisotropy during thermoforming can be reduced and good molded products can be obtained. MD / DC TD is more preferably 0.6 or more and 1.4 or less, and further preferably 0.7 or more and 1.3 or less.

[0036] The polyolefin resin foam sheet according to the present invention preferably exhibits a curl height of at least the foam sheet thickness but not more than 15 mm when heated for 10 minutes at a temperature 20°C higher than the maximum melting point, which is the highest melting peak in DSC measurement. By controlling the curl height to at least the foam sheet thickness but not more than 15 mm, excellent moldability can be achieved. A curl height exceeding 15 mm can result in molding defects such as poor appearance due to missing dimensions or wrinkles. A lower curl height is preferable, but the thickness of the foam sheet is the substantial lower limit. The curl height of the polyolefin resin foam sheet is more preferably at least the foam sheet thickness but not more than 14 mm, even more preferably at least the foam sheet thickness but not more than 13 mm, and particularly preferably at least the foam sheet thickness but not more than 12 mm. The curl height of a polyolefin resin foam sheet can be reduced by reducing the gel fraction ratio of the surface layer of the polyolefin resin foam sheet. The gel fraction ratio of the surface layer is determined by dividing the polyolefin resin foam sheet into five equal layers in the thickness direction, and dividing them into layers 1 to 5 in the thickness direction. The larger gel fraction of the first and fifth surface layers is designated as the GF. A , the smaller value is GF B Then, GF A / GF B This is the value calculated as follows. The curl height of the polyolefin resin foam sheet can be reduced by reducing the average cell diameter ratio of the surface layer of the polyolefin resin foam sheet. The average cell diameter ratio of the surface layer is determined by selecting the larger value of the average cell diameters of the first and fifth layers. A , the smaller value is BD B Then, BD A / BD B This is the value calculated as follows. Furthermore, reducing the proportion of polyethylene-based resin or polyolefin-based resin in the base resin, within a range that does not impair flexibility, is also effective in reducing curl height. Curl height can be reduced by adjusting one or more of the resin composition, the gel fraction ratio of the surface layer, and the average cell diameter ratio of the surface layer, and it is preferable to adjust multiple factors.

[0037] The average cell diameter (MD and TD) of the polyolefin resin foam sheet according to the present invention is preferably 50 μm or more and 500 μm or less. If the average cell diameter is less than 50 μm, heat resistance may decrease. If the average cell diameter is more than 500 μm, the surface may lose smoothness, and dents may occur during molding. The average cell diameter of the polyolefin resin foam sheet is more preferably 100 μm or more and 500 μm or less, and even more preferably 200 μm or more and 500 μm or less. The average cell diameter BD in the MD direction of the polyolefin resin foam sheet according to the present invention MD is the average bubble diameter in the TD direction, BD TD Average bubble diameter ratio BD divided by MD / BD TD The average cell diameter ratio BD of the polyolefin resin foam sheet is preferably 0.7 or more and 1.3 or less. If the average cell diameter ratio is less than 0.7 or more than 1.3, shrinkage due to heating during molding processing becomes large, which may cause insufficient dimensions and make it impossible to obtain a molded product. MD / BD TDis more preferably 0.8 or more and 1.3 or less, even more preferably 0.8 or more and 1.2 or less, and particularly preferably 0.9 or more and 1.1 or less. When stretching stress acts in the MD direction during the production process, residual stress remains, causing flat cells to form in the MD direction. Furthermore, when heated during the foaming process, the cells formed by decomposition of the foaming agent tend to become round, but when stress is applied, the cells become flat. The degree of flattening of the cells can be used to determine the strength of the stretching stress during production, so the average cell diameter ratio BD MD / BD TD A foam with a small value shrinks less in size when heated and has excellent moldability. The average cell diameter ratio of the surface layer of the polyolefin resin foam sheet according to the present invention is preferably 1.0 or more and 1.2 or less. When the polyolefin resin foam sheet is divided into 5 equal layers in the thickness direction and the layers are divided into 1 to 5 layers in the thickness direction, the average cell diameter BD of the first layer and the fifth layer is determined as the larger value of BD. A , the smaller value is BD B Then, BD A / BD B The average bubble diameter ratio of the surface layer, BD, is calculated as follows: A / BD B By setting the average cell diameter ratio BD of the surface layer to 1.0 or more and 1.2 or less, curling of the foam can be reduced and molding defects such as poor appearance due to missing dimensions and wrinkles can be prevented. A / BD B is more preferably 1.0 or more and 1.1 or less, and is even more preferably 1.0.

[0038] In the polyolefin resin foam sheet according to the present invention, the average cell diameter BD before heating BF and the average bubble diameter BD after heating for 10 minutes at a temperature 20°C higher than the maximum melting point, which is the highest melting peak in DSC measurement. AF Ratio of BD BF / BD AF The average cell diameter ratio BD before and after heating (MD direction, TD direction) is preferably 1.0 or more and 1.5 or less. BF / BD AF By setting the ratio BD between 1.0 and 1.5, excellent moldability can be achieved.BF / BD AF If the ratio exceeds 1.5, molding defects such as missing dimensions may occur. BF / BD AF is more preferably 1.0 or more and 1.4 or less, further preferably 1.0 or more and 1.3 or less, and particularly preferably 1.0 or more and 1.2 or less.

[0039] <Laminate> The laminate of the present invention is formed by laminating the polyolefin resin foam sheet described above with one or more skin materials selected from sheets, films, cloth, leather, etc. Laminating a skin material to the polyolefin resin foam sheet of the present invention allows for a high-quality appearance due to its excellent design. The material of the skin material is not particularly limited, but examples include sheets or films of thermoplastic polyolefin elastomers (TPO) containing elastomer components such as polyethylene, polypropylene, ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer (EEA), ethylene-butyl acrylate copolymer (EBA), and ethylene-propylene rubber; sheets or films of vinyl resins such as polyvinyl chloride and polyvinylidene chloride, polyurethane resins, polystyrene resins, polyether resins, and polyamide resins; and copolymers composed of monomers copolymerizable with these resins, cloth, nonwoven fabric, or leather. These skin materials may be used alone or in combination.

[0040] <Method of manufacturing polyolefin resin foam sheet> The polyolefin resin foam sheet of the present invention can be produced by the steps of: forming a base resin into a sheet to obtain a foamable sheet; crosslinking the foamable sheet; and heating and foaming the crosslinked foamable sheet to obtain a foamed sheet. Hereinafter, the method for producing the polyolefin resin foam sheet of the present invention will be described taking as an example a normal pressure foaming method using a thermal decomposition type foaming agent as the foaming agent.

[0041] To obtain a foamable sheet, a base resin, such as a polyethylene resin, a polypropylene resin, or an olefin elastomer, and a thermally decomposable foaming agent are uniformly mixed using a mixing device such as a Henschel mixer or a tumbler. The mixture is then uniformly melt-kneaded using a melt-kneading device such as an extruder or a pressure kneader at a temperature below the decomposition temperature of the thermally decomposable foaming agent, and then molded into a sheet using a T-shaped die. When molding into a sheet, it is preferable to reduce the draw-down ratio, i.e., mold under reduced stretching stress. The draw-down ratio is calculated as the ratio of the sheet thickness to the gap at the tip of the die; a smaller value indicates a less stretched foamable sheet extruded from the die. Reducing the draw-down ratio reduces the MD distortion of the foamable sheet and also reduces residual distortion in the foamed sheet, thereby reducing shrinkage during molding and heating, i.e., preventing undercutting and improving moldability. Typically, the foaming temperature in the foam sheet production process is higher than the molding temperature in the foam sheet production process. Therefore, if the drawdown ratio is high and significant distortion remains in the foam sheet, the distortion is relaxed and the foam sheet shrinks in the MD direction during the initial expansion process. The MD stretch ratio is calculated by dividing the take-up speed by the unwinding speed. However, due to this shrinkage, the actual unwinding speed becomes slower, resulting in a more stretched state in the MD direction. In addition, if the MD shrinkage due to strain relaxation is large, the foam state becomes unstable, making it difficult to reduce the set MD stretch ratio. Furthermore, the so-called air gap, which indicates the distance between the die and the first nip roll that forms the sheet discharged from the die, varies depending on the amount of resin discharged and the thickness and width of the sheet, but it is preferable to widen it. Widening the air gap allows for the relaxation of the resin orientation after the die. Therefore, by providing a sufficient distance within the range in which drawdown and neck-in are acceptable, distortion of the foam sheet can be reduced, thereby reducing the shrinkage of the foam sheet. Furthermore, it is preferable to set the temperature when molding the sheet higher, as long as the thermally decomposable foaming agent does not decompose, since this reduces distortion. It is preferable that the temperature of the base resin extruded from the die be in the range of 165°C or higher and 190°C or lower.Furthermore, it is important to reduce the tension when winding the formed sheet to a level that does not cause the sheet to collapse. When mixing the base resin and the thermally decomposable foaming agent, an antioxidant, a heat stabilizer, a crosslinking aid, etc. may be added as needed.

[0042] In the step of crosslinking the foamable sheet, the formed foamable sheet is irradiated with ionizing radiation to crosslink the foamable sheet. Examples of ionizing radiation include electron beams, α-rays, β-rays, γ-rays, and X-rays, and electron beams are preferably used in consideration of productivity.

[0043] The step of obtaining a foam sheet involves heating and foaming the crosslinked foamable sheet to obtain a polyolefin resin foam sheet. Specifically, the base resin is softened by heating, and the temperature is raised to or above the decomposition temperature of the thermally decomposable foaming agent. The base resin is then expanded by the gas generated by the decomposition of the thermally decomposable foaming agent, thereby obtaining the polyolefin resin foam sheet of the present invention. Examples of heating methods include floating the sheet on a salt bath as a heat medium or immersing the sheet in an atmosphere such as hot air. The floating method on a salt bath is preferred because it minimizes stress applied during foaming and suppresses distortion, thereby improving the thermal shrinkage during thermoforming of the polyolefin resin foam sheet, i.e., moldability. The crosslinked foam sheet may also be stretched in the MD and / or TD. Considering productivity, a roll of the crosslinked foam sheet may be continuously fed into a high-temperature salt bath and wound into a roll product. In this case, the MD stretch ratio, calculated by dividing the winding speed by the unwinding speed, is preferably 2.0 to 3.0. If the MD stretch ratio is less than 2.0, the sheet may meander during the foaming process, potentially preventing the production of a satisfactory foamed sheet. On the other hand, if the MD stretch ratio exceeds 3.0, the stress applied to the foamed sheet increases, leaving distortion in the foamed sheet, which may result in significant dimensional shrinkage during heating during molding, i.e., insufficient dimensions, making molding impossible. The MD stretch ratio is preferably 2.2 to 2.8, more preferably 2.2 to 2.7, and even more preferably 2.3 to 2.7. To reduce distortion in the crosslinked foamable sheet and stabilize the foamed state, preheating is preferably performed before heating to a temperature equal to or higher than the decomposition temperature of the foaming agent. The preheating temperature is preferably equal to or lower than the highest melting peak temperature and 30°C lower than the lowest melting peak temperature obtained in DSC measurement of a resin mixture containing a polyethylene resin, a polypropylene resin, and a polyolefin elastomer. Preheating the foamable sheet within this temperature range reduces sheet distortion and allows the MD stretch ratio to be reduced during the foaming process.Furthermore, since the heating temperature during foaming can reduce the MD stretch ratio by slowing down the foaming, it is preferable to provide a temperature difference between the first and second half of foaming rather than keeping a constant temperature. From the viewpoint of reducing the MD shrinkage of the foam, it is preferable to reduce the MD stretch ratio by reducing the rotational resistance of the transport rolls used to cool the foam and then take it up during the foaming step. The TD stretch ratio, calculated by dividing the TD length of the resin foam sheet by the TD length of the resin foam sheet before foaming, is preferably equal to the MD stretch ratio.

[0044] <Method of manufacturing laminate> The method for laminating a skin material onto a polyolefin resin foam sheet to form a laminate is not particularly limited, and examples thereof include extrusion lamination, adhesive lamination, thermal lamination, and hot melt lamination.

[0045] <Molding of polyolefin resin foam sheet or laminate> The method for molding the polyolefin resin foam sheet or laminate of the present invention is not particularly limited, and examples thereof include known methods such as extrusion molding, vacuum molding, stamping molding, blow molding, etc. Molded products obtained by these methods may be subjected to secondary processing into desired shapes by heat welding, vibration welding, ultrasonic welding, laser welding, etc. [Example]

[0046] <Physical property evaluation> Various physical properties of polyolefin resin foam sheets aged for at least 4 days after foaming under conditions of a temperature of 23°C and a humidity of 50% were measured according to the following methods. Note that MD refers to the longitudinal direction, and TD refers to the width direction. When it is impossible to distinguish between MD and TD, the direction with the longest cell diameter is taken as MD, and the direction perpendicular to this is taken as TD. Regarding the range of physical properties of the present invention, unless there is a description limiting it to either the MD or TD direction, it is necessary for both the MD and TD directions to satisfy the range conditions. Furthermore, regarding the physical property values, the obtained values ​​are rounded off and judged using the significant figures described in the specification.

[0047] (1) Thickness (mm) The thickness of the polyolefin resin foam sheet was measured in accordance with ISO 1923:1981 "Foam plastics and rubber - Measurement of linear dimensions." Specifically, the resin foam sheet was placed on a flat table and measured at a 10 cm 2 A dial gauge with a circular probe having an area of ​​10g / 10cm was placed on the surface of a resin foam sheet. 2 The measurement was carried out by contacting the sample with a constant pressure of 1000 kJ / cm. (2) Apparent density (kg / m 3 ) The apparent density of the polyolefin resin foam sheet was measured in accordance with JIS K6767:1999 "Foam plastics - Polyethylene - Testing method." Specifically, the thickness and mass of a 10 cm square test piece (polyolefin resin foam sheet) were measured and calculated using the following formula. Density (kg / m 3 ) = mass of test piece (kg) / [test piece area 0.0001 (m 2 ) × thickness of test piece (m)]

[0048] (3) Foaming ratio (cm 3 / g) The expansion ratio of the polyolefin resin foam sheet was measured in accordance with JIS K6767:1999 "Foamed plastics - Polyethylene - Testing methods," and the reciprocal of the apparent density was taken as the expansion ratio. (4) Gel fraction, surface gel fraction ratio (%) A polyolefin resin foam sheet was cut into approximately 0.5 mm squares, and approximately 100 mg of the cut polyolefin resin foam sheet was weighed to the nearest 0.1 mg. The weighed polyolefin resin foam sheet was immersed in 200 ml of tetralin at 130°C for 3 hours, then naturally filtered through a 100-mesh stainless steel wire mesh. The insoluble matter on the wire mesh was dried in a hot air oven at 120°C for 1 hour. The sheet was then cooled for 10 minutes in a desiccator containing dried silica gel. The mass of the insoluble matter was weighed to the nearest 0.1 mg, and the gel fraction was calculated as a percentage according to the following formula: Gel fraction (%) = [mass of insoluble matter (mg) / mass of weighed foam (mg)] × 100 The gel fraction of the surface layer was calculated as follows. The polyolefin resin foam sheet was divided into 5 equal parts in the thickness direction using a slicer (NP-120RS manufactured by Nippi Machinery Co., Ltd.), and layers 1 to 5 were obtained in the thickness direction. The gel fractions of the foams of the 1st and 5th layers were determined in the same manner as in the measurement of the gel fraction described above, and the larger value was used as the GF. A , the smaller value is GF B Then, GF A / GF B The value calculated by the above formula was taken as the gel fraction ratio of the surface layer.

[0049] (5) 25% compressive stress (kPa) The 25% compressive stress of the polyolefin-based resin foam sheet was measured in accordance with JIS K6767:1999 "Foamed Plastics - Polyethylene - Test Method." Specifically, the polyolefin-based resin foam sheet was cut into 50 mm x 50 mm pieces, and the cut polyolefin-based resin foam sheets were stacked to a thickness of 20 mm to 30 mm, and the initial thickness was measured. The stacked sample was placed on a flat plate and compressed to 25% of the initial thickness at a rate of 10 mm / min. The compression was stopped, and the load after 20 seconds was measured and calculated using the following formula. 25% compression stress (kPa) = Load after 20 seconds after 25% compression (N) / 0.0025 (m 2 ) / 1000

[0050] (6) Tensile strength (kPa) · Tensile elongation (%) The tensile strength and tensile elongation of the polyolefin resin foam sheet were measured in accordance with JIS K6767:1999 "Foam plastics - Polyethylene - Test method." The polyolefin resin foam sheet was punched into a dumbbell shape so that the machine direction and the transverse direction were the longitudinal directions, respectively, to prepare test pieces. The test piece was left to stand in a thermostatic chamber adjusted to 23°C for 5 minutes, and then a uniaxial tensile test was carried out in a 23°C environment. The maximum strength value at this time was the 23°C tensile strength, and the elongation at which it broke was the 23°C tensile elongation. MD tensile strength TS MD is the tensile strength in the TD direction, TS TD The value divided by is the tensile strength ratio TS MD / TSTD , tensile elongation in MD direction TE MD is the tensile elongation in the TD direction TE TD The value divided by this is the tensile elongation ratio TE MD / TE TD It was decided. In addition, the test piece was left to stand in a thermostatic chamber adjusted to -35°C for 5 minutes, and then a uniaxial tensile test was performed in an environment of -35°C. The maximum strength value at this time was recorded as the -35°C tensile strength, and the elongation at which the test piece broke was recorded as the -35°C tensile elongation.

[0051] (7) Tear strength (N / cm) The tear strength of the polyolefin resin foam sheet was measured in accordance with JIS K6767:1999 "Foam plastics - Polyethylene - Test method." Test specimens were prepared by punching the polyolefin resin foam sheet with a die so that the MD and TD directions were the longitudinal directions. Here, the MD direction refers to the machine direction and the TD direction refers to the width direction. The test specimens were left to stand in a thermostatic chamber adjusted to 23°C for 5 minutes, and then a tear test was carried out in a 23°C environment. The maximum load at the time of breaking was taken as the tear strength. MD tear strength TeS MD is the tear strength in the TD direction TeS TD The value divided by is the tear strength ratio TeS MD / TeS TD It was decided.

[0052] (8) Dimensional change rate due to heating (%) The thermal dimensional change of polyolefin-based resin foam sheets was measured according to JIS K7133:1999, "Plastics - Films and Sheets - Measurement of Thermal Dimensional Change." Specifically, a 120 x 120 mm square specimen was punched out of the polyolefin-based resin foam sheet at the center of the TD direction, with two sides parallel to the MD direction. Marked lines were drawn in the MD and TD directions of the specimen, and their lengths were measured to the nearest 0.1 mm using a vernier caliper. Next, a metal container containing a kaolin bed was placed in a 120°C oven to adjust the temperature of the kaolin bed. Kaolin was sprinkled on the specimen, and the specimen was placed flat on the kaolin bed and heated at 120°C for 1 hour. After heating, the specimen was cooled for at least 30 minutes at 23°C and 50% humidity. After the test, the lengths of the markings in the MD and TD directions were measured to the nearest 0.1 mm using a vernier caliper. The thermal dimensional shrinkage in the MD and TD directions was calculated using the following formula: MD heating dimensional change rate (DC MD ) = [(MD gauge length after heating) - (MD gauge length before heating)] / (MD gauge length before heating) × 100 TD heating dimensional change rate (DC TD ) = [(TD gauge length after heating) - (TD gauge length before heating)] / (TD gauge length before heating) × 100 The same measurements were taken for the "temperature 20°C higher than the maximum melting point" and "temperature 20°C lower than the maximum melting point," except that the heating temperature and heating time were changed from 1 hour to 10 minutes. MD is the rate of dimensional change in the TD direction TD The value divided by is the thermal dimensional change ratio DC MD / DC TD It was decided.

[0053] (9) Average bubble diameter (μm), average bubble diameter ratio, average bubble diameter ratio of the surface layer, average bubble diameter ratio before and after heating The average cell diameter of the polyolefin resin foam sheet was calculated by measuring the length in both the MD and TD directions. To measure the average cell diameter, the polyolefin resin foam sheet was first cut with a razor to create a surface with open cell cross sections parallel to the MD. The cross section was then photographed at an arbitrary magnification using a scanning electron microscope (S-3000N, manufactured by Hitachi High-Technologies Corporation). The resulting image was printed on A4 paper. Figure 1 illustrates the measurement of the average cell diameter of the polyolefin resin foam sheet. As shown in Figure 1, a line was drawn at the center of the thickness direction, connecting 20 or more cells in the MD. The average chord length was calculated from the length of the line and the number of cells touching this line using the following formula. The line was designed to pass through the cells rather than through the junctions between adjacent cells whenever possible. When the line passed through a junction between cells, the number of cells on the line was counted as two. Average chord length (μm) = length of straight line (μm) / number of bubbles (pcs) From the calculated average chord length, the average bubble diameter BD in the MD direction is calculated using the following formula: MD was calculated. Average bubble diameter (μm) = average chord length (μm) / 0.62 In the TD direction, the average bubble diameter BD TD was calculated. Average bubble diameter in MD direction BD MD is the average bubble diameter in the TD direction, BD TD The value divided by the average cell diameter ratio BD MD / BD TD It was decided.

[0054] The average cell diameter ratio of the surface layer of the polyolefin resin foam sheet was calculated as follows. The polyolefin resin foam sheet was divided into 5 equal parts in the thickness direction using a slicer, and layers 1 to 5 were obtained in the thickness direction. For the foam of the first layer, a straight line was drawn at the center of the thickness direction, and the average cell diameters in the MD and TD directions were calculated in the same manner as in the measurement of the average cell diameter described above, and the average value was used as the average cell diameter of the first layer. For the foam of the fifth layer, the average cell diameters in the MD and TD directions were calculated in the same manner as in the measurement of the average cell diameter described above, and the average value was used as the average cell diameter of the fifth layer. The larger of the average cell diameters of the first and fifth layers was used as the BD. A , the smaller value is BD B When BD A / BD B The value calculated by the above formula was taken as the average bubble diameter ratio of the surface layer. The average cell diameter ratio before and after heating was calculated as follows. A metal container containing a kaolin bed was placed in an oven at a temperature 20°C higher than the maximum melting point, which is the highest melting peak in DSC measurement, to adjust the temperature. Kaolin was sprinkled on a polyolefin resin foam sheet that had been aged at a temperature of 23°C and a humidity of 50% for at least 4 days after foaming, and the sheet was placed flat on the kaolin bed and heated for 10 minutes at a temperature 20°C higher than the maximum melting point, which is the highest melting peak in DSC measurement. After heating, the polyolefin resin foam sheet was cooled for 30 minutes or more in an environment of 23°C and 50% humidity. A straight line was drawn through the center of the thickness direction of the obtained polyolefin resin foam sheet in each of the MD and TD directions in the same manner as in the measurement of the average cell diameter described above, to determine the average cell diameter. This was used as the average cell diameter after heating BD. AF The average bubble diameter before heating was calculated for both the MD and TD directions. BF , the average bubble diameter after heating is BD AF When BD BF / BD AF The value calculated by the above is the average bubble diameter ratio BD before and after heating. BF / BD AF It was decided.

[0055] (10) Maximum melting point (℃) Measurement was performed using a differential scanning calorimeter (DSC, RDC220-Robot DSC manufactured by Seiko Instruments Inc.). 5 mg of a polyolefin resin foam sheet was heated from room temperature to 200°C at a rate of 10°C / min in a nitrogen atmosphere, and then held at 200°C for 5 minutes (1 st Then, the temperature was increased again to 200°C at a rate of 10°C / min after cooling to 0°C at a rate of 10°C / min (2 nd run). 2 nd The top value of the melting peak (endothermic peak) on the highest temperature side of the run was read and taken as the maximum melting point.

[0056] (11) Curl height (mm) The length was measured using a test piece after measuring the dimensional change rate upon heating at a temperature 20°C higher than the maximum melting point. The test piece was placed on the metal plate so that the contact area between the foam test piece and the metal plate was maximized. The height of the foam sheet in the direction perpendicular to the metal plate surface was measured with a vernier caliper, and the highest point was taken as the curl height.

[0057] (12) Molding evaluation Polyolefin resin foam sheets were cut parallel to the MD or TD directions to prepare 200 mm square test pieces. Each of the two edges parallel to the MD direction was clamped evenly within 10 mm of the edge. The foam sheets were heated with an infrared heater for 50 to 70 seconds until the surface temperature reached 20°C higher than the maximum melting point (the highest melting peak in DSC measurement). The sheets were then vacuum molded in a 150 mm square metal mold with a 20 mm deep vacuum hole. The metal mold was positioned so that it was centered on the surface of the foam sheet, and its position was adjusted so that the edges of the foam sheet and the metal mold were parallel. Test pieces clamped along the two edges parallel to the TD direction were molded in the same manner. The molding evaluation was visually evaluated on a 5-point scale according to the following criteria. A higher molding evaluation score indicated better moldability, with a molding evaluation score of 3 to 5 being considered acceptable. The following evaluation criteria had to be met in both the MD and TD directions. Molding evaluation 1: There are sizing defects, and the foam sheet has folds and wrinkles at the edges, resulting in a poor appearance. Molding evaluation 2: There are sizing defects, and the foam sheet has folds and wrinkles at the edges, resulting in poor appearance. Molding evaluation 3: No missing dimensions, folds and slight wrinkles on the edges of the foam sheet can be seen Forming rating 4: No missing dimensions, slight wrinkles can be seen Molding rating 5: No defects and good appearance

[0058] <Resins and additives used> In the examples and comparative examples, the following resins and additives were used. Polyethylene resin: Made by Nippon Polyethylene, product name "Novatec (registered trademark) UJ960 (MFR: 5 g / 10 min, density: 935 kg / m 3 )" Polypropylene resin: Sanaromer, product name "PB222A" (MFR 0.75g / 10min, density: 900kg / m 3 )" Polyolefin elastomer: Infuse (registered trademark) 9107 (MFR: 1 g / 10 min, density: 866 kg / m) manufactured by DOW 3 )" Foaming agent: Azodicarbonamide (manufactured by Eiwa Chemical Industry Co., Ltd., product name "Vinihall (registered trademark) AC♯R") Crosslinking agent: 55% divinylbenzene (Wako Pure Chemical Industries, Ltd.) Antioxidant: BASF, trade name "IRGANOX (registered trademark) 1010"

[0059] <Examples 1 to 10, Comparative Examples 1, 4 to 6> A mixture of 100 parts by mass of a base resin prepared by mixing a polyethylene resin, a polypropylene resin, and a polyolefin elastomer in the proportions shown in Table 1, to which a foaming agent, a crosslinking aid, and an antioxidant were added in the amounts shown in Table 1, was charged into a Henschel mixer and pulverized and mixed. The resulting mixture was fed into a twin-screw extruder and melt-kneaded at a resin temperature of 160°C to 180°C, and then molded into a sheet having a thickness of 1.4 mm using a T-die at a drawdown ratio of 1.4, and wound into a roll to obtain a foamable sheet. However, in order to adjust the thickness of the foam, the thickness of the foamable sheet was set to 2.0 mm in Example 3, 1.3 mm in Example 4, and 1.6 mm in Example 5. The resulting foamable sheet was irradiated from one side with an electron beam at an accelerating voltage of 800 kV and a dose of 90 kGy to obtain a crosslinked foamable sheet, except that the dose was set to 60 kGy in Example 6 and 140 kGy in Example 7 in order to adjust the gel fraction of the foam. A roll of crosslinked foamable sheet was preheated in hot water at 80°C to 95°C, then floated on a salt bath heated continuously (first at 220°C to 229°C and second at 230°C to 235°C) while also being heated from above with an infrared heater to obtain a polyolefin resin foam sheet. The MD stretch ratio, calculated by dividing the take-up speed at which the sheet was removed from the salt bath after foaming was completed by the unwinding speed at which the sheet was fed into the salt bath, was adjusted to 2.7. However, to adjust the foam thickness, the MD stretch ratio was set to 3.0 in Example 4 and 2.3 in Example 5. The resulting foam sheet was cooled and washed in 50°C water, and then dried with warm air. The physical properties of the obtained polyolefin resin foam sheet are shown in Tables 1 to 3.

[0060] Example 11 Except for changing the drawdown ratio to 1.6, the same procedure as in Example 1 was followed to produce the polyolefin resin foam sheet. Table 2 shows the physical properties of the resulting polyolefin resin foam sheet. Example 12 A mixture of 100 parts by mass of a base resin prepared by mixing a polyethylene resin, a polypropylene resin, and a polyolefin elastomer in the proportions shown in Table 1, to which a foaming agent, a crosslinking aid, and an antioxidant were added in the amounts shown in Table 1, was charged into a Henschel mixer and pulverized and mixed. The obtained mixture was fed into a twin-screw extruder and melt-kneaded at a resin temperature of 160°C or higher and 180°C or lower. After that, it was formed into a sheet having a thickness of 1.4 mm using a T-die at a drawing rate of 1.4, and then wound into a roll to obtain a foamable sheet. The resulting expandable sheet was irradiated from one side with an electron beam at an accelerating voltage of 800 kV and an exposure dose of 90 kGy to obtain a crosslinked expandable sheet. The roll-shaped crosslinked foamable sheet was cut into a 10 cm square, and heated by floating it on a salt bath adjusted to 230 to 240°C while a salt heat transfer medium at the same temperature was poured in from above to heat both sides, thereby obtaining a polyolefin resin foamed sheet. The obtained foamed sheet was cooled and washed with water at 50°C, and then dried with hot air. The physical properties of the obtained polyolefin resin foam sheet are shown in Table 2.

[0061] Example 13 The polyolefin resin foam sheet was produced in the same manner as in Example 1, except that the drawdown ratio was 1.0, the foam sheet thickness was 1.2 mm, and the MD stretch ratio was adjusted to 2.0. The physical properties of the resulting polyolefin resin foam sheet are shown in Table 2. Example 14 The polyolefin resin foam sheet was produced in the same manner as in Example 1, except that the drawdown ratio was 1.0, the foam sheet thickness was 1.6 mm, and the MD stretch ratio was adjusted to 3.1. The physical properties of the resulting polyolefin resin foam sheet are shown in Table 2. Example 15 The polyolefin resin foam sheet was produced in the same manner as in Example 1, except that the drawdown ratio was 1.6, the foam sheet thickness was 1.2 mm, and the MD stretch ratio was adjusted to 2.0. The physical properties of the resulting polyolefin resin foam sheet are shown in Table 2. Example 16 A foam was produced according to Example 6 described in JP-A 2015-187232, except that the drawdown ratio was adjusted to 1.0 and the MD stretch ratio was adjusted to 2.7. The physical properties of the obtained polyolefin resin foam sheet are shown in Table 2. A base resin (100 parts by weight) was prepared by blending 33 parts by weight of an olefin-based elastomer resin (DOW, product name "Infuse® 9107 (MFR: 1.0 g / 10 min)") and 67 parts by weight of a polypropylene-based resin (Sunoco Chemicals, product name "TR3020F (MFR: 2.1 g / 10 min)") with 6.5 parts by weight of a foaming agent (Eiwa Chemical Industries, product name "Vinihall® AC#R"), 1 part by weight of an antioxidant (BASF, product name "IRGANOX® 1010"), and 4 parts by weight of a cross-linking coagent (Wako Pure Chemical Industries, 80% divinylbenzene). The mixture was melt-extruded using a Henschel mixer at a drawdown rate of 1.0 and a temperature of 160°C, and then extruded into a 1.3 mm-thick polyolefin-based resin sheet (expandable sheet) using a T-die. The obtained polyolefin resin sheet was continuously irradiated on one side with an electron beam under conditions of an acceleration voltage of 700 kV, a current of 65 mA, and an irradiation speed of 14.4 m / min to obtain a crosslinked expandable sheet. The roll-shaped crosslinked foamable sheet was floated on a salt bath at 220°C and heated from above with an infrared heater to expand at a MD stretch ratio of 2.7. The sheet was cooled in water at 60°C to obtain a polyolefin resin foamed sheet. Example 17 A foam was produced in accordance with Example 6 of JP-A 2015-187232, except that the drawdown ratio was adjusted to 1.0. The physical properties of the obtained polyolefin resin foam sheet are shown in Table 2. The film was produced in the same manner as in Example 16, except that the MD stretching ratio was adjusted to 3.1. Example 18 A foam was produced according to Example 7 of JP 2015-187232 A, except that the MD stretch ratio was adjusted to 2.7. The physical properties of the obtained polyolefin resin foam sheet are shown in Table 2. This was produced in the same manner as in Example 16, except that the blending ratio of the base resin was changed to 40 parts by mass of olefin-based elastomer resin and 60 parts by mass of polypropylene-based resin, and the withdrawal ratio was adjusted to 1.6.

[0062] <Comparative Examples 2 and 3> Except for adjusting the thickness of the foamable sheet to 1.6 mm and the MD stretch ratio to 3.1, the foamable sheet was produced in the same manner as in Example 1. The physical properties of the obtained polyolefin resin foamed sheet are shown in Table 3. <Comparative Example 7> The polyolefin resin foam sheet was produced in the same manner as in Example 1, except that the drawdown ratio was 1.6, the foam sheet thickness was 1.6 mm, and the MD stretch ratio was adjusted to 3.1. The physical properties of the resulting polyolefin resin foam sheet are shown in Table 3. <Comparative Example 8> The foamed sheet was produced in the same manner as in Example 1, except that the acceleration voltage was 1000 kV, the foamed sheet thickness was 1.6 mm, and the MD stretch ratio was adjusted to 3.1. The physical properties of the resulting polyolefin resin foamed sheet are shown in Table 3.

[0063] <Comparative Example 9> A foam was produced according to Example 6 described in JP 2015-187232 A. The physical properties of the obtained polyolefin resin foam sheet are shown in Table 3. A base resin (100 parts by weight) was prepared by blending 33 parts by weight of an olefin-based elastomer resin (DOW, product name "Infuse® 9107 (MFR: 1.0 g / 10 min)") and 67 parts by weight of a polypropylene-based resin (Sunoco Chemicals, product name "TR3020F (MFR: 2.1 g / 10 min)") with 6.5 parts by weight of a foaming agent (Eiwa Chemical Industries, product name "Vinihall® AC#R"), 1 part by weight of an antioxidant (BASF, product name "IRGANOX® 1010"), and 4 parts by weight of a cross-linking coagent (Wako Pure Chemical Industries, 80% divinylbenzene). The mixture was melt-extruded using a Henschel mixer at a drawdown rate of 1.6 and a temperature of 160°C, and then extruded into a 1.3 mm-thick polyolefin-based resin sheet (expandable sheet) using a T-die. The obtained polyolefin resin sheet was continuously irradiated on one side with an electron beam under conditions of an acceleration voltage of 700 kV, a current of 65 mA, and an irradiation speed of 14.4 m / min to obtain a crosslinked expandable sheet. The roll-shaped crosslinked foamable sheet was floated on a salt bath at 220°C and heated from above with an infrared heater to foam the sheet at a MD stretch ratio of 3.1. The sheet was cooled in water at 60°C to obtain a polyolefin resin foamed sheet. The heat shrinkage of the obtained polyolefin resin foam sheet was measured by the method described in JP 2015-187232 A, and was found to be 6.9% at 140°C.

[0064] <Comparative Example 10> A foam was produced according to Example 7 described in JP 2015-187232 A. The physical properties of the obtained polyolefin resin foam sheet are shown in Table 3. The same procedure as in Comparative Example 9 was repeated except that the blending ratio of the base resins was changed to 40 parts by mass of the olefin elastomer resin and 60 parts by mass of the polypropylene resin. The heat shrinkage of the obtained polyolefin resin foam sheet was measured by the method described in JP 2015-187232 A, and was found to be 8.3% at 140°C.

[0065] <Comparative Example 11> A foam was produced according to Example 4 described in JP 2016-155344 A. The physical properties of the obtained polyolefin resin foam sheet are shown in Table 3. To 100 parts by mass of a base resin prepared by mixing 30 parts by mass of an olefin-based elastomer resin (manufactured by Mitsui Chemicals, trade name "Tafmer (registered trademark) PN-3560" (MFR: 6.0 g / 10 min)), 50 parts by mass of a polypropylene-based resin (manufactured by Prime Polymer, trade name "Prime Polypro (registered trademark) J452HP" (MFR: 3.5 g / 10 min)), and 20 parts by mass of a polyethylene-based resin (manufactured by Japan Polyethylene, trade name "Novatec (registered trademark) LL UJ960" (MFR: 5.0 g / 10 min)), 6.7 parts by mass of a foaming agent (manufactured by Eiwa Chemical Industry, trade name: "Vinihall (registered trademark) AC#R"), 1.2 parts by mass of an antioxidant (manufactured by BASF, trade name: "IRGANOX (registered trademark) 1010"), and 4.4 parts by mass of a cross-linking coagent (manufactured by Wako Pure Chemical Industries, Ltd., 55% divinylbenzene) were added and mixed using a Henschel mixer. The mixture was melt-extruded in an extruder at a drawdown rate of 1.4 and a temperature of 170°C, and a polyolefin resin sheet (expandable sheet) having a thickness of 1.5 mm was produced using a T-die. The obtained polyolefin resin sheet was continuously irradiated on one side with an electron beam under conditions of an acceleration voltage of 800 kV and an exposure dose of 60 kGy to obtain a crosslinked expandable sheet. The roll-shaped crosslinked foamable sheet was floated on a salt bath at 220°C and heated from above with an infrared heater to foam at a MD stretch ratio of 3.2. The sheet was cooled with water at 60°C, the foam surface was washed with water, and then dried to obtain a polyolefin resin foam sheet.

[0066] <Comparative Example 12> A foam was produced according to Example 5 described in JP 2016-155344 A. The physical properties of the obtained polyolefin resin foam sheet are shown in Table 3. The same procedure as in Comparative Example 11 was repeated except that the blending ratio of the base resins was changed to 60 parts by mass of polypropylene resin and 10 parts by mass of polyethylene resin. <Comparative Example 13> The polyolefin resin foam sheet was produced in the same manner as in Example 1, except that the drawdown ratio was 1.0, the sheet thickness was 1.8 mm, and the MD stretch ratio was adjusted to 3.5. The physical properties of the obtained polyolefin resin foam sheet are shown in Table 3. <Comparative Example 14> The polyolefin resin foam sheet was produced in the same manner as in Example 1, except that the drawdown ratio was 1.6, the sheet thickness was 1.8 mm, and the MD stretch ratio was adjusted to 3.5. The physical properties of the obtained polyolefin resin foam sheet are shown in Table 3.

[0067] [Table 1]

[0068] [Table 2]

[0069] [Table 3]

[0070] From the results of the Examples in Table 1, it was confirmed that "the polyolefin resin foam sheets of Examples 1 to 18, which use as the base resin a resin mixture containing 0% by mass or more and 30% by mass or less of polyethylene resin, 30% by mass or more and 80% by mass or less of polypropylene resin, and 20% by mass or more and 40% by mass or less of polyolefin elastomer, and which have a thermal dimensional change of -35% or more and 0% or less when heated for 10 minutes at a temperature 20°C higher than the maximum melting point, which is the highest melting peak in DSC measurement" have excellent flexibility and moldability. 3 ) is 2.5 or less, and the thermal dimensional change rate when heated for 10 minutes at 20°C above the maximum melting point, which is the highest melting peak in DSC measurement, is -35% or more and 0% or less, and good results were obtained with no sizing defects.

Claims

1. The polyolefin-based resin foam sheet has as its base resin a resin mixture containing 0% by mass or more and 30% by mass or less of a polyethylene-based resin, 30% by mass or more and 80% by mass or less of a polypropylene-based resin, and 20% by mass or more and 40% by mass or less of a polyolefin-based elastomer, and exhibits thermal dimensional changes of -28.9% or more and 0% or less in the MD and TD directions when heated for 10 minutes at a temperature 20°C higher than the maximum melting point, which is the highest melting peak in DSC measurement.

2. A resin mixture containing 0% to 30% by mass of polyethylene resin, 30% to 80% by mass of polypropylene resin, and 20% or more by mass of polyolefin elastomer is used as the base resin, and the 25% compressive stress (kPa) is used as the density (kg / m 3 ) is 2.5 or less, and the thermal dimensional changes in the MD and TD directions when heated for 10 minutes at a temperature 20°C higher than the maximum melting point, which is the highest melting peak in DSC measurement, are -28.9% or more and 0% or less.

3. Thickness: 1mm to 5mm, density: 40kg / m 3 More than 100kg / m 3 3. The polyolefin resin foam sheet according to claim 1, wherein the gel fraction is 30% or more and 60% or less.

4. The polyolefin resin foam sheet according to any one of claims 1 to 3, wherein the MD / TD ratio of thermal dimensional change when heated for 10 minutes at a temperature 20°C higher than the maximum melting point, which is the highest melting peak in DSC measurement, is 0.5 or more and 1.5 or less.

5. 5. The polyolefin resin foam sheet according to claim 1, wherein the dimensional changes due to heating in the MD and TD directions when heated for 10 minutes at a temperature 20°C lower than the maximum melting point, which is the highest melting peak in DSC measurement, are -5% or more and 0% or less.

6. Average bubble diameter in MD direction BD MD The average bubble diameter in the TD direction is TD Average bubble diameter ratio BD divided by MD / BD TD The polyolefin resin foam sheet according to any one of claims 1 to 5, wherein the σ is 0.7 or more and 1.3 or less.

7. 7. The polyolefin resin foam sheet according to claim 1, wherein the tensile strength ratio in MD direction / TD direction at 23° C. is 0.7 or more and 1.3 or less.

8. 8. The polyolefin resin foam sheet according to claim 1, wherein the height of curl when heated for 10 minutes at a temperature 20°C higher than the maximum melting point, which is the highest melting peak in a DSC measurement, is equal to or greater than the thickness of the foam sheet and is 15 mm or less.

9. The polyolefin resin foam sheet is divided into five equal parts in the thickness direction, and the first to fifth layers are formed in that order. The larger gel fraction value between the first layer and the fifth layer is designated as GF. A , the smaller value is GF B Then, GF A / GF B 9. The polyolefin resin foam sheet according to claim 1, wherein the gel fraction ratio of the surface layer calculated by the following formula is 1.0 or more and 1.2 or less.

10. The polyolefin resin foam sheet is divided into five equal parts in the thickness direction, and the first to fifth layers are arranged in the thickness direction. The larger value of the average cell diameter BD of the first layer and the fifth layer is designated as BD. A , the smaller value is BD B Then, BD A / BD B 10. The polyolefin resin foam sheet according to claim 1, wherein the average cell diameter ratio of the surface layer calculated by the formula (2) is 1.0 or more and 1.2 or less.

11. The average cell diameter of the polyolefin resin foamed sheet before heating was determined in both the MD and TD directions. BF The average cell diameter of the foamed sheet heated for 10 minutes at a temperature 20°C higher than the maximum melting point, which is the highest melting peak in the DSC measurement, is BD. AF When this is done, BD BF / BD AF 11. The polyolefin resin foam sheet according to claim 1, wherein the average cell diameter ratio before and after heating, calculated by the following formula, is 1.0 or more and 1.5 or less.

12. A laminate obtained by laminating one or more skin materials selected from the group consisting of sheets, films, cloth, nonwoven fabrics and leathers and the polyolefin resin foam sheet according to any one of claims 1 to 11.

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