JP2024094957A - Laminate and vehicle interior material including same - Google Patents

Abstract

The present invention provides a laminate having a surface layer with high cleavability and excellent airbag deployment and formability, and a vehicle interior material including the laminate.
[Solution] The present invention relates to a laminate comprising a crosslinked resin foam and a polyolefin-based resin skin layer disposed on a first surface of the crosslinked resin foam, wherein the polyolefin-based resin skin layer is melted by first heating from 40°C to 200°C at a heating rate of 10°C/min by DSC, and then crystallized by cooling from 200°C to 40°C at a heating rate of 10°C/min, and then heated a second time from 40°C to 200°C at a heating rate of 10°C/min, and in a DSC curve obtained during the second heating, the DSC curve has a first peak whose peak temperature is in the range of 110 to 135°C and the heat of fusion of the first peak is 40.0 J/g or less, and the polyolefin-based resin skin layer has a sea-island structure, and the area ratio of island regions in the sea-island structure is 50.0% or more.
[Selected Figure] Figure 1

Description

The present invention relates to a laminate that can be suitably used for vehicle interior materials, and a vehicle interior material that includes the laminate.

Laminates in which a resin skin layer is laminated on the surface of a crosslinked resin foam are widely used as skin materials in the interiors of vehicles such as automobiles. For example, in the instrument panel of an automobile, such laminates are disposed on and integrated with the surface of a resin substrate housing an airbag.
On the other hand, an incision (a so-called tear line for tearing) is provided on the back side of an instrument panel of an automobile so that an airbag can be deployed in the event of an impact or the like. In recent years, an incision has been provided only in the base material housing the airbag, and no incision has been provided in the laminate disposed on the surface of the base material, thereby improving tearability. For example, Patent Document 1 describes that in a laminate comprising a crosslinked polyolefin foam and a skin layer, the peel strength at -30°C, the elongation at 160°C of the crosslinked polyolefin foam, and the 25% compression hardness are set within a predetermined range in order to facilitate tearing.

JP 2020-163753 A

However, in the laminate described in Patent Document 1, the surface layer may have poor cleavability. In addition, when the laminate is used for vehicle interior materials, it needs to be processed into a predetermined shape by molding such as vacuum forming.

The present invention provides a laminate having a highly cleavable surface layer and excellent airbag deployment and moldability, and a vehicle interior material containing the laminate.

The present invention relates to a laminate comprising a crosslinked resin foam and a polyolefin-based resin skin layer disposed on a first surface of the crosslinked resin foam, the polyolefin-based resin skin layer being melted by first heating from 40°C to 200°C at a heating rate of 10°C/min, then crystallized by cooling from 200°C to 40°C at a heating rate of 10°C/min, and then heated a second time from 40°C to 200°C at a heating rate of 10°C/min, as measured by differential scanning calorimetry (DSC). In the DSC curve obtained during the second heating, the DSC curve has a first peak at a peak temperature in the range of 110 to 135°C, and the heat of fusion of the first peak is 40.0 J/g or less, the polyolefin-based resin skin layer has a sea-island structure consisting of a sea region of a continuous phase and island regions of a dispersed phase dispersed in the continuous phase, and the area ratio of the island regions in the sea-island structure is 50.0% or more.

The present invention also relates to a vehicle interior material that includes the laminate.

The present invention can provide a laminate having a highly cleavable surface layer and excellent airbag deployment and moldability, and a vehicle interior material containing the laminate.

1 is an image of a surface layer in the laminate of Example 4 observed with a transmission electron microscope. 1 is an image of a surface layer in the laminate of Comparative Example 4 observed with a transmission electron microscope.

The inventors of the present invention conducted extensive research to solve the above problems. As a result, they discovered that by using a polyolefin resin skin layer that exhibits predetermined DSC characteristics and has a sea-island structure with an island area ratio of 50.0% or more, the skin layer has high cleavability, and the airbag deployment of a laminate in which the skin layer is disposed on one surface (first surface) of a crosslinked resin foam is improved and moldability is also good.

In this specification, when a numerical range is indicated with "~", the numerical range includes both end values (upper and lower limits). For example, a numerical range of "A to B" is a range that includes both end values A and B. In addition, when multiple numerical ranges are stated in this specification, they are considered to include numerical ranges that appropriately combine the upper and lower limits of different numerical ranges.

(Polyolefin resin skin layer)
The polyolefin-based resin skin layer (hereinafter also simply referred to as "skin layer") may be made of a polyolefin-based resin and may have a sea-island structure consisting of a sea region of a continuous phase (hereinafter also referred to as the sea phase) and island regions of a dispersed phase dispersed in the continuous phase (hereinafter also referred to as the island phase). From the viewpoint of facilitating the formation of a sea-island structure, the skin layer preferably contains an olefin-based thermoplastic elastomer, a polypropylene-based resin, and a polyethylene-based resin. The skin layer may be in the form of a sheet.

The polypropylene resin may be a homopolymer of propylene or a copolymer of propylene and another α-olefin. The polypropylene copolymer may contain 70 to 99.5% by mass of propylene and 0.5 to 30% by mass of another α-olefin. Examples of the other α-olefin include ethylene, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, cyclopentene, and cyclohexene. The polypropylene copolymer may be a random copolymer or a block copolymer. One type of polypropylene resin may be used alone, or two or more types may be used in combination.

The melt flow rate (hereinafter also referred to as MFR) of the polypropylene-based resin is not particularly limited, but is preferably 0.3 to 30.0 g/10 min, more preferably 0.5 to 20.0 g/10 min, and even more preferably 0.5 to 10.0 g/10 min, from the viewpoint of the processability of the skin layer sheet and the dispersibility of the polypropylene-based resin during processing of the skin layer sheet. In this specification, the MFR of the polypropylene-based resin can be measured in accordance with JIS K 6921-2 under conditions of a temperature of 230°C and a load of 2.16 kg (21.18 N).

The melting point of the polypropylene resin is not particularly limited, but from the viewpoint of easily maintaining the melt tension during secondary processing such as vacuum molding, it is preferably 140 to 170°C, more preferably 142 to 165°C, and even more preferably 145 to 163°C.

The polyethylene resin may be a homopolymer of ethylene or a copolymer of ethylene and other monomers. The polyethylene copolymer may contain 70.0 to 99.0% by mass of ethylene and 1.0 to 30.0% by mass of other monomers. Examples of the other monomers include α-olefins having 4 or more carbon atoms, such as 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, cyclopentene, and cyclohexene. The polyethylene copolymer may be a random copolymer or a block copolymer. More specifically, examples of the polyethylene resin include high-density polyethylene, low-density polyethylene, linear low-density polyethylene (hereinafter also referred to as LLDPE), and ethylene-butene copolymers. The polyethylene resin may be used alone or in combination of two or more types.

The MFR of the polyethylene resin is not particularly limited, but from the viewpoint of dispersibility during sheet processing, it is preferably 1.0 to 15.0 g/10 min, more preferably 1.0 to 10.0 g/10 min, and even more preferably 1.0 to 8.0 g/10 min. In this specification, the MFR of the polyethylene resin can be measured in accordance with JIS K 6922-2 under conditions of a temperature of 190°C and a load of 2.16 kg (21.18 N).

The melting point of the polyethylene resin is not particularly limited, but from the viewpoint of easily adjusting the tensile strength during vacuum molding, it is preferably 100 to 135°C, more preferably 110 to 130°C, and even more preferably 115 to 125°C.

The olefin-based thermoplastic elastomer may be any of a blend type, a polymerization type (also called reactor TPO), and a dynamic crosslinking type (also called TPV). From the viewpoint of increasing the cleavability of the skin layer, it is preferable that the olefin-based thermoplastic elastomer includes a dynamic crosslinking type. The dynamic crosslinking type may be partially crosslinked or completely crosslinked.

Specifically, the olefin-based thermoplastic elastomer may include hard segments such as polypropylene and polyethylene, and soft segments (also called rubber components) such as ethylene-propylene copolymer (EPM) and ethylene-propylene-diene copolymer (EPDM). The rubber components such as EPM and EPDM may be uncrosslinked or dynamically crosslinked. The dynamic crosslinking may be partial crosslinking or complete crosslinking.

The MFR of the olefin-based thermoplastic elastomer is not particularly limited, but from the viewpoint of, for example, sheet processability for the skin layer and making the skin layer easier to break, it is preferably 1.0 to 50.0 g/10 min, more preferably 2.0 to 40.0 g/10 min, and even more preferably 3.0 to 35.0 g/10 min. In this specification, the MFR of the olefin-based thermoplastic elastomer can be measured specifically in accordance with ISO 1130 under conditions of a temperature of 230°C and a load of 98 N or 49 N.

The olefin-based thermoplastic elastomer is not particularly limited, but from the viewpoint of the grain transferability and moldability during vacuum molding, for example, in differential scanning calorimetry, the elastomer is first heated from 40°C to 200°C at a heating rate of 10°C/min to melt, then cooled from 200°C to 40°C at a heating rate of 10°C/min to crystallize, and then heated from 40°C to 200°C at a heating rate of 10°C/min for a second time. In the DSC curve obtained at the second heating, the elastomer has two peaks, the temperature of the low-temperature peak (also referred to as the low-temperature melting point) is 110 to 135°C, and the temperature of the high-temperature peak (hereinafter also referred to as the high-temperature melting point) is preferably 140 to 170°C. Examples of such olefin-based thermoplastic elastomers include commercially available products such as the Esporex (registered trademark) TPE series from Sumitomo Chemical Co., Ltd. and the Trexplain TPV series from Mitsubishi Chemical Corporation.

The Shore A hardness of the olefin-based thermoplastic elastomer is not particularly limited, but from the viewpoint of the feel and cushioning when the surface layer is pressed, it is preferably 40 to 90, more preferably 50 to 80, and even more preferably 55 to 70. In this specification, the Shore A hardness can be measured specifically as described in the Examples.

In the sea-island structure of the skin layer, the area ratio of the island region is 50.0% or more. This makes it easier to cleave the sea phase and the interface between the sea phase and the island phase, which is presumably why the cleavability of the skin layer is improved. In addition, the improved cleavability of the skin layer also improves the airbag deployment of the laminate including the skin layer. In addition, since the area ratio of the sea phase is less than 50%, the moldability of the laminate including the skin layer, such as vacuum moldability, is also improved. The area ratio of the island region is preferably 50.5% or more, and more preferably 51.0% or more. In addition, for example, from the viewpoint of further improving the vacuum moldability, the area ratio of the island region in the sea-island structure is preferably 90% or less, and more preferably 80% or less. The morphology of the skin layer can be observed with a transmission electron microscope. In this specification, the sea-island structure can be confirmed and the area ratio of the island region can be measured as described in the examples.

In differential scanning calorimetry (DSC), the skin layer is melted by first heating from 40°C to 200°C at a heating rate of 10°C/min, then crystallized by cooling from 200°C to 40°C at a heating rate of 10°C/min, and then heated a second time from 40°C to 200°C at a heating rate of 10°C/min. In the DSC curve obtained at the second heating, the peak temperature has a first peak in the range of 110 to 135°C, and the heat of fusion of the first peak (hereinafter also referred to simply as the first heat of fusion) is 40.0 J/g or less. This improves the cleavability of the skin layer. The reason for this is that, although it is only a guess, the resin is more likely to break in the low temperature range, making it easier to form a sea-island structure. In addition, the improved cleavability of the skin layer also improves the airbag deployment of the laminate including the skin layer. In addition, when the first heat of fusion of the skin layer is within the above-mentioned range, the elongation and flexibility of the skin layer are maintained even if the surface temperature is lowered during vacuum forming, and the moldability, such as vacuum formability, of the laminate including the skin layer is also improved. The first heat of fusion of the skin layer is preferably 39.5 J/g or less, more preferably 39.0 J/g or less, and even more preferably 38.5 J/g or less. The lower limit of the first heat of fusion of the skin layer is not particularly limited, but for example, from the viewpoint of improving the grain transferability and heat resistance during vacuum forming, it is preferably 7.5 J/g or more, more preferably 8.0 J/g or more, and even more preferably 8.5 J/g or more. Specifically, the first heat of fusion of the skin layer is measured as described in the examples.

The surface layer is melted by first heating from 40°C to 200°C at a heating rate of 10°C/min using DSC, then crystallized by cooling from 200°C to 40°C at a heating rate of 10°C/min, and then heated a second time from 40°C to 200°C at a heating rate of 10°C/min. In the DSC curve obtained at the second heating, the peak temperature has a second peak in the range of 140 to 170°C, and the heat of fusion of the second peak is preferably 2.0 to 15.2 J/g. This results in a sheet with a better appearance and also improves vacuum formability.

When the skin layer contains an olefin-based thermoplastic elastomer, a polypropylene-based resin, and a polyethylene-based resin, the polypropylene-based resin constitutes the sea region of the continuous phase, and the olefin-based thermoplastic elastomer and polyethylene constitute the island region of the dispersed phase. From the viewpoint that the morphology of the skin layer is likely to satisfy the above-mentioned conditions, when the total mass of the olefin-based thermoplastic elastomer, the polypropylene-based resin, and the polyethylene-based resin is taken as 100 parts by mass, it is preferable that the olefin-based thermoplastic elastomer is 55 to 90 parts by mass, the polypropylene-based resin is 5 to 40 parts by mass, and the polyethylene-based resin is 5 to 40 parts by mass, and more preferably that the olefin-based thermoplastic elastomer is 60 to 85 parts by mass, the polypropylene-based resin is 5 to 35 parts by mass, and the polyethylene-based resin is 5 to 35 parts by mass.

When the skin layer contains an olefin-based thermoplastic elastomer, a polypropylene-based resin, and a polyethylene-based resin, in the DSC curve at the second heating described above, the first peak is derived from the polyethylene-based resin, and the second peak is derived from the polypropylene-based resin. From the viewpoint that the DSC curve at the second heating of the skin layer easily satisfies the above-mentioned conditions, when the total mass of the olefin-based thermoplastic elastomer, the polypropylene-based resin, and the polyethylene-based resin is 100 parts by mass, it is preferable that the olefin-based thermoplastic elastomer is 55 to 90 parts by mass, the polypropylene-based resin is 5 to 40 parts by mass, and the polyethylene-based resin is 5 to 40 parts by mass, and more preferably that the olefin-based thermoplastic elastomer is 60 to 85 parts by mass, the polypropylene-based resin is 5 to 35 parts by mass, and the polyethylene-based resin is 5 to 35 parts by mass.

The surface layer is not particularly limited, but may contain additives such as antioxidants, antistatic agents, flame retardants, UV absorbers, light stabilizers, colorants, and inorganic fillers, as necessary, within the range that does not impair the effects of the present invention. The additives may be used alone or in combination of two or more. The additives may be used in an amount of 0.5 parts by mass or less, or 0.5 to 10.0 parts by mass, per 100 parts by mass of the total of the olefin-based thermoplastic elastomer, the polypropylene-based resin, and the polyethylene-based resin.

The tensile strength of the skin layer is not particularly limited, but for example, from the viewpoint of further increasing the cleavability of the skin layer, the -35°C tensile strength is preferably 18 to 40 MPa, and more preferably 20 to 35 MPa, in both the flow direction (also called machine direction, hereinafter also referred to as MD) of the skin layer (skin layer sheet) and the transverse direction perpendicular to the flow direction of the skin layer (skin layer sheet) (hereinafter also referred to as TD). In this specification, the -35°C tensile strength of the skin layer can be specifically measured as described in the Examples.

The tensile elongation of the skin layer is not particularly limited, but from the viewpoint of further increasing the cleavability of the skin layer, the -35°C tensile elongation is preferably 150 to 400%, and more preferably 200 to 350%, in both MD and TD. In this specification, the -35°C tensile elongation of the skin layer can be specifically measured as described in the examples.

The tear strength of the skin layer is not particularly limited, but for example, from the viewpoint of further increasing the cleavability of the skin layer, the -35°C tear strength is preferably 850 to 1850 N/cm in both MD and TD, and more preferably 900 to 1800 N/cm. In this specification, the -35°C tear strength of the skin layer can be specifically measured as described in the examples.

The thickness of the skin layer is not particularly limited, but from the viewpoint of achieving both abrasion resistance and tearability, it is preferably 0.4 to 1.3 mm, more preferably 0.5 to 1.2 mm, and even more preferably 0.5 to 1.0 mm.

The Shore A hardness of the surface layer is not particularly limited, but from the viewpoint of achieving both abrasion resistance and cleavability, it is preferably 60 to 100, more preferably 70 to 95, and even more preferably 80 to 90. In this specification, the Shore A hardness of the surface layer can be measured specifically as described in the examples.

The oil resistance of the surface layer is not particularly limited, but is preferably 110 to 200%, more preferably 115 to 180%, and even more preferably 120 to 160%, from the viewpoint of easily suppressing poor appearance due to adhesion of suntan oil, grease oil, etc. In this specification, the oil resistance can be specifically measured as described in the examples.

(Crosslinked resin foam)
The crosslinked resin foam is not particularly limited, and any known foam may be used. From the viewpoints of cushioning, heat resistance, and surface smoothness, it is preferable to use a crosslinked olefin-based resin foam. The crosslinked resin foam may be in the form of a sheet.

The crosslinked polyolefin resin foam is not particularly limited, and may be one which is crosslinked by a conventionally known method and then foamed. The polyolefin resin is not particularly limited, and may be an olefin thermoplastic elastomer, polypropylene resin, polyethylene resin, or the like described in the skin layer. The method for forming the crosslinked structure is not particularly limited, and examples thereof include a method of irradiating with ionizing radiation such as α-rays, β-rays, γ-rays, and electron beams, a method of irradiating with ultraviolet rays, and a method using a crosslinking agent such as an organic peroxide or a silane compound. The foaming method is not particularly limited, and examples thereof include extrusion foaming, in-mold foaming, atmospheric foaming, and chemical reaction foaming. Examples of the foaming agent that can be used include inorganic gases, hydrocarbons or halogenated hydrocarbons having a boiling point of -50 to 120°C, water, and thermal decomposition type foaming agents.

The crosslinked resin foam is not particularly limited, but from the viewpoint of further improving moldability, the degree of crosslinking may be, for example, 30 to 65%, or 35 to 55%. In this specification, the degree of crosslinking of the crosslinked resin foam can be measured, for example, as described in the Examples.

The cross-linked resin foam is not particularly limited, but from the viewpoint of flexibility and cushioning, the foaming ratio may be, for example, 5 to 40 times. Specifically, the foaming ratio of the cross-linked resin foam can be measured as described in the examples.

The crosslinked resin foam may contain additives such as foaming aids, softeners, lubricants, antioxidants, antistatic agents, flame retardants, UV absorbers, light stabilizers, colorants, and inorganic fillers, as necessary, but are not limited thereto, so long as the effects of the present invention are not impaired.

The thickness of the cross-linked resin foam is not particularly limited, but may be, for example, 0.5 to 5.0 mm or less, 1.0 to 4.5 mm, or 1.5 to 4.0 mm from the viewpoint of elasticity.

The Shore C hardness of the crosslinked resin foam is not particularly limited, but from the viewpoint of the feel when pressed with the hand and the cushioning feeling, it is preferably 55 to 100, more preferably 60 to 90, and even more preferably 65 to 80. In this specification, the Shore C hardness can be measured specifically as described in the examples.

The 25% compression hardness of the crosslinked resin foam is not particularly limited, but from the viewpoint of excellent elasticity, it is preferably 230N or less, more preferably 200N or less, and even more preferably 180N or less. Furthermore, from the viewpoint of bottoming out when pressed by hand and shock absorption, the 25% compression hardness of the crosslinked resin foam is preferably 100N or more, more preferably 110N or more, and even more preferably 120N or more. In this specification, the 25% compression hardness can be measured specifically as described in the examples.

(Laminate)
The laminate includes a crosslinked resin foam and a polyolefin resin skin layer disposed on one surface (first surface) of the crosslinked resin foam. The laminate may be in the form of a sheet, and may be molded into a predetermined three-dimensional shape according to the shape of a vehicle interior material, as described later.

In the laminate, although there are no particular limitations, for example, from the viewpoint of further enhancing the airbag deployment property, the -35°C peel strength between the polyolefin-based resin skin layer and the crosslinked resin foam is preferably 28 N/25 mm or more, more preferably 30 N/25 mm or more, and even more preferably 32 N/25 mm or more. In addition, from the viewpoint of bonding the skin material and the crosslinked resin foam by heating, the -35°C peel strength between the polyolefin-based resin skin layer and the crosslinked resin foam is preferably 60 N/25 mm or less, more preferably 58 N/25 mm or less, and even more preferably 55 N/25 mm or less. In this specification, the -35°C peel strength between the polyolefin-based resin skin layer and the crosslinked resin foam can be measured as described in the examples.

The Shore A hardness of the laminate is not particularly limited, but from the viewpoint of abrasion resistance, for example, when the polyolefin resin skin layer is used as the measurement surface, it is preferably 30 to 85, more preferably 35 to 80, and even more preferably 40 to 80.

From the viewpoint of excellent airbag deployment properties, in a high-speed punching test (also called a puncture impact test) at -35°C in accordance with JIS K 7211-2, if the maximum test force is greater than 500 N, the breaking energy is preferably 1.0 to 2.0 J, and if the maximum test force is 500 N or less, the breaking energy is preferably 3.0 J or less, more preferably 2.0 J or less, and it is particularly preferable that the maximum test force is 100 to 400 N.

The tensile strength of the laminate is not particularly limited, but for example, from the viewpoint of further improving the airbag deployment performance, the -35°C tensile strength is preferably 3.0 to 6.5 MPa in both MD and TD, and more preferably 3.5 to 6.0 MPa. In this specification, the -35°C tensile strength of the laminate can be specifically measured as described in the examples.

The tensile elongation of the laminate is not particularly limited, but for example, from the viewpoint of further improving the airbag deployment property, the -35°C tensile elongation is preferably 30 to 120% in both MD and TD, and more preferably 40 to 90%. In this specification, the -35°C tensile elongation of the laminate can be specifically measured as described in the examples.

The tear strength of the laminate is not particularly limited, but from the viewpoint of further improving the airbag deployment performance, the -35°C tear strength is preferably 180 to 420 N/cm in both MD and TD, and more preferably 190 to 400 N/cm. In this specification, the -35°C tear strength of the laminate can be measured specifically as described in the examples.

The laminate can be produced by preparing a skin layer sheet using a polyolefin resin or a polyolefin resin composition containing a polyolefin resin and an additive, and then placing and laminating the obtained skin layer sheet on the first surface of the crosslinked resin foam. The skin layer sheet may be formed by calendar molding or extrusion molding. For example, the skin layer sheet may be obtained by melt-kneading a polyolefin resin or a polyolefin resin composition containing a polyolefin resin and an additive in the range of 185 to 210 ° C, and then calendar molding with a two-roll machine. The skin layer sheet and the crosslinked resin foam may be laminated directly by heating to a temperature above the melting point of the constituent resin, or may be laminated via an adhesive. When the cross-linked resin foam is a cross-linked polyolefin-based resin foam, for example, the skin layer sheet and the cross-linked resin foam may be laminated together by overlapping them, and then using a heat press machine to apply pressure to 80 to 95% of the total thickness of the skin layer sheet and the cross-linked resin foam when overlapped, at a temperature range of 165 to 185°C, to heat seal the skin layer sheet and the cross-linked resin foam.

The laminate may include a surface treatment layer disposed on the surface opposite to the side where the crosslinked resin foam of the polyolefin resin skin layer is disposed, as necessary, within the scope of not impairing the effects of the present invention. The surface treatment agent constituting the surface treatment layer is not particularly limited, and may include, for example, a water-based polyurethane dispersion (also called water-based urethane paint), a solvent-based polyurethane dispersion (also called solvent-based urethane paint), etc., and may include silicon, silicon beads, urethane beads, etc. The surface treatment layer may be composed of only a top layer, or may be composed of a top layer and a primer layer. The top layer may be composed of, for example, a surface treatment agent for the top. The surface treatment agent for the primer layer is not particularly limited, and may include, for example, a water-based industrial material adhesive or a solvent-based industrial material adhesive, and the primer layer may be composed of a surface treatment agent for the primer that may include, for example, polyurethane, vinyl chloride, acrylic, vinyl acetate, etc.

The laminate is not particularly limited, but can be used, for example, as a skin material for vehicle interior substrates, and can be suitably used as a skin material for vehicle interior substrates such as instrument panels, door trims, trunk trims, seats, pillar covers, ceiling materials, rear trays, console boxes, airbag covers, arm rests, head rests, meter covers, and crash pads for vehicles such as automobiles, and can be particularly suitably used as a skin material for vehicle interior substrates in which airbags are housed.

The vehicle interior material may include a laminate as a skin material. When the laminate is a skin material for a vehicle interior base material, the laminate can be molded to match the shape of the vehicle interior material. The vehicle interior material can be obtained by placing the laminate on one surface of the vehicle interior base material and molding it into a predetermined shape by vacuum molding or the like. Examples of vehicle interior materials include base materials such as instrument panels, door trims, trunk trims, seats, pillar covers, ceiling materials, rear trays, console boxes, airbag covers, armrests, headrests, meter covers, and crash pads for vehicles such as automobiles.

The present invention will be described in more detail below using examples. Note that the present invention is not limited to the following examples.

The measurement and evaluation methods used in the examples and comparative examples are as follows:

(DSC: Differential Scanning Calorimetry)
In accordance with JIS K7122 (1987), using a "Differential Scanning Calorimeter DSC-60Plus" manufactured by Shimadzu Corporation, 8 g of a sample was melted by heating from 40°C to 200°C at a heating rate of 10°C/min (first heating), then crystallized by cooling from 200°C to 40°C at a heating rate of 10°C/min, and then heated from 40°C to 200°C at a heating rate of 10°C/min (second heating) to obtain a DSC curve, and the melting peak and heat of fusion in the DSC curve obtained by the second heating were measured.

(thickness)
According to the measurement method of JIS K 7130 (1999), the thickness was determined as the average value of five measurements taken using a "micrometer CLM1-15QMX" manufactured by Mitutoyo Corporation.

(Shore A hardness)
In accordance with JIS K 7215, an "Asker Rubber Hardness Tester Type A" manufactured by Kobunshi Keiki Co., Ltd. was used, and the scale was read immediately after the indenter was brought into contact with the sample three times, and the average value was taken as the Shore A hardness.

(Shore C hardness)
In accordance with JIS K 7215, an "Asker Rubber Hardness Tester Type C" manufactured by Kobunshi Keiki Co., Ltd. was used, and the scale was read immediately after contact with the semicircular indenter three times, and the average value was taken as the Shore C hardness.

(Morphological condition evaluation)
According to JIS K 0132 (1997) Scanning Electron Microscope Test Method General Rules, an epoxy resin was applied to the surface of the sheet for surface layer, cooled to -60°C, and surface-finished with a microtome, and then dyed in steam of a 1% _RuO4 aqueous solution at 60°C for 90 minutes. The dyed sheet sample for surface layer was cooled to -60°C, surface-finished with a microtome, and coated with Pt-Pd to a thickness of about 2 mm using Hitachi High-Tech's "Ion Sputter Sample Pretreatment Device E-1010" to prepare a sample for observing the state of morphology. Three points were observed using Hitachi High-Tech's "Transmission Electron Microscope H-7650" at an accelerating voltage of 100 Kv, a magnification of 5000 times, and in the observation direction TD (width direction). The parts that turned black by dyeing were morphological island phases, and the island phases were judged to have a spherical shape and a different color tone from the surroundings. When the island phase could be identified, it was judged to have an island-sea structure, and when the island phase could not be identified, it was judged not to have an island-sea structure, i.e., to be in an interconnected state.

(Morphological area ratio evaluation)
An arbitrarily selected image of about ¹⁰⁰ μm2 from the images taken during morphology observation was imported into a Keyence VHX7000. Using the automatic area measurement software built into the instrument, the black parts were regarded as island phases of the morphology and the white parts as sea phases, and the areas were converted to measure the area ratios of the island phase and sea phase, thereby obtaining the island area ratio and sea area ratio, respectively.

(Expansion Ratio)
The expansion ratio was calculated from the density of the crosslinked resin foam measured in accordance with JIS K 6767 using an "electronic specific gravity meter MDS-300" manufactured by Alphatech Co., Ltd.

(Degree of cross-linking)
The foam was cut into pieces of 0.3 to 0.5 mm in the thickness direction, and approximately 100 mg was weighed to an accuracy of 0.1 mg. The weighed sample was placed in a 100-mesh stainless steel wire net and immersed in 200 ml of tetralin solution heated to 140°C for 3 hours, after which the insoluble portion in the wire net was dried for 1 hour in a hot air oven kept at 120°C. The sample was then cooled for 30 minutes in a desiccator containing silica gel, the mass of the insoluble portion was weighed, and the degree of crosslinking was calculated according to the following formula.
Degree of crosslinking (%)={mass of insoluble matter (mg)/weighted foam mass (mg)]×100

(25% compression hardness)
In accordance with JIS K 6767 (ISO7214), a sample of a crosslinked resin foam with a width of 50 mm, a length of 50 mm and a thickness of 25 mm or more was compressed by 25% from the original thickness at a speed of 10 mm/min using a "desktop testing machine: EZ-LX" manufactured by Shimadzu Corporation, and the load after stopping for 20 seconds was measured to calculate the compression hardness (= load/area). The average value of three measurements was defined as the 25% compression hardness.

(-35°C tensile strength and -35°C tensile elongation)
In accordance with JIS K 7128-3 (1998), a sample punched out with a dumbbell No. 3 was held at -35°C for 3 minutes using Shimadzu Corporation's "Autograph: AGS-X" and then subjected to a tensile test at a speed of 200 mm/min, and the average values of the maximum breaking strength and breaking elongation measured three times were taken as the -35°C tensile strength and -35°C tensile elongation, respectively. The measurements were performed in the MD direction (machine direction, also called the flow direction of the sheet) and the TD direction (the transverse direction perpendicular to the flow direction of the sheet).

(-35°C tear strength)
According to JIS K 7128-3 (1998), a sample punched out with a tear dumbbell was held at -35°C for 3 minutes and then subjected to a tear test at a speed of 200 mm/min using Shimadzu Corporation's "Autograph: AGS-X," and the average of the maximum breaking strengths measured three times was taken as the -35°C tear strength. The measurements were performed in the MD and TD directions.

(Oil resistance)
A sample of the epidermis layer sheet measuring 50 mm × 50 mm was placed in a 200 mL bottle with a lid, and at least about 50 mL of "liquid paraffin" manufactured by Kanto Chemical Co., Ltd. was added until the sample was immersed. The weight change rate (%) after immersion in liquid paraffin for 24 hours in an environment of 80°C was recorded as the oil resistance.
Weight change rate (%)=weight (g) of the sample of the skin layer sheet after immersion−weight (g) of the sample of the skin layer sheet before immersion/weight (g) of the sample of the skin layer sheet before immersion×100

(-35°C peel strength between skin layer and foam)
In each of the MD and TD directions of the laminate, test pieces cut to 150 mm x 25 mm were attached to a holding plate (a 3 mm thick polypropylene resin plate) using the adhesive "Aron Alpha (registered trademark) EXTRA (registered trademark) Fast-acting multi-purpose" manufactured by Toagosei Co., Ltd., and after the adhesive had hardened, the test pieces were held at -35°C for 3 minutes using an "Autograph: AGS-X" manufactured by Shimadzu Corporation, and then the average peel strength was determined when measured at a speed of 200 mm/min, a peel angle of 180°, and a peel distance of 80 mm. The average value of the average peel strengths in the MD and TD directions was taken as the -35°C peel strength between the skin layer and the foam.

(High speed punching test)
In accordance with JIS K 7211-2, a laminate was placed so that the skin layer side faced the striker using a "Hydroshot: HITS-P10" manufactured by Shimadzu Corporation, and after holding at -35°C for 3 minutes, the average value of three impact forces measured under conditions of striker diameter: ½ inch, speed: 5 m/s, and holding jig Φ40 mm was defined as the maximum test force (N), and the total energy at break was defined as the break energy (J).

(How the skin layer sheet breaks during high-speed punching test)
The cutting state of the surface layer sheet in the samples punched in the high-speed punching test was evaluated according to the following criteria.
A: The punched shape is quite good. The skin material punched by the striker is clamped vertically with vernier calipers, and the length of the fragments of the skin material generated during punching is measured. The length is 1.0 mm or more and 2.0 mm or less, and the punched shape is a beautiful circle. B: The punched shape is good. The skin material punched by the striker is clamped vertically with vernier calipers, and the length of the fragments of the skin material generated during punching is measured. The length is more than 2.0 mm and 5.0 mm or less, and the punched shape is a circle or ellipse. C: The punched shape is poor. The skin material punched by the striker is clamped vertically with vernier calipers, and the length of the fragments of the skin material generated during punching is measured. The length is more than 5.0 mm and 10.0 mm or less, and the punched shape is a circle or ellipse. D: The punched shape is quite poor. The skin material punched out by the striker is clamped vertically with a vernier caliper, and the length of the fragments of the skin material generated during punching is measured. The length exceeds 10.0 mm, and the shape of the punched out piece is circular or oval.

(How laminate samples are cut during high-speed punching tests)
The condition of the samples punched in the high-speed punching test was judged according to the following criteria. A score of 3 or more was judged to be good.
5: The skin layer side is broken in a circular shape of 2/3 or more, or the entire circumference, and there are no cracks. 4: The skin layer side is broken in a circular shape of 2/3 or more, or the entire circumference, and cracks can be seen. 3: The skin layer side is broken in a circular shape of 1/2 to less than 2/3, and there are no cracks. 2: The skin layer side is broken in a circular shape of 1/2 to less than 2/3, and cracks can be seen. 1: The skin layer side is broken in a circular shape of less than 1/2, or there is no circular break.

(Airbag deployment)
Based on the test force and breaking energy measured in the high-speed punch test, the test was judged according to the following criteria: A rating of 4 or more was deemed to indicate good airbag deployment.
5: Maximum test force is 100 to 400 N and breaking energy is 1.0 to 2.0 J
4: The maximum test force is 100 to 400 N, and the breaking energy is greater than 2.0 J and less than or equal to 3.0 J; or
The maximum test force is greater than 400N and less than 500N, and the breaking energy is 1.0 to 2.0J.
3: The maximum test force is 100 to 400 N, and the breaking energy is greater than 3.0 J;
The maximum test force is greater than 400 N and less than or equal to 500 N, and the breaking energy is greater than 2.0 J and less than or equal to 3.0 J; or
The maximum test force is greater than 500N and the breaking energy is 1.0 to 2.0J.
2: The maximum test force is greater than 400 N and less than or equal to 500 N, and the breaking energy is 3.1 J or more; or
The maximum test force is greater than 500 N, and the breaking energy is greater than 2.0 J and less than or equal to 3.0 J. 1: The maximum test force is greater than 500 N, and the breaking energy is greater than 3.1 J.

(Moldability)
Using a test vacuum forming machine, both sides of the laminated sheet were heated to 180°C to 230°C, and then the laminated sheet was vacuum formed into a box shape with a length of 150 mm, a width of 100 mm, and a depth of 50 mm, and the part with an expansion rate of 220% was judged according to the following criteria. A score of 3 or more was judged to have good moldability.
5: The appearance, box shape, and grain shape are all quite good.
4: The appearance, box shape, and grain shape are all good, and either the appearance and box shape or the grain shape is quite good.
3: The appearance, box shape, and grain shape are all good.
2: There is a defect in the appearance and either the box shape or the grain shape.
1: Poor appearance and shape due to breakage.

The polyolefin resins used in the examples and comparative examples are shown in Tables 1 and 2 below.

Example 1
<Preparation of Sheet for Epidermal Layer>
Polyolefin resins having the blending ratios shown in Table 3 below were melt-kneaded for 5 to 8 minutes at a temperature range of 185°C to 195°C using a test roll (two rolls) to prepare a uniform skin layer sheet having a thickness of about 0.5 mm, and cut to a size of 360 mm x 360 mm.
<Preparation of Laminate>
The skin layer sheet prepared in the preparation of the skin layer sheet was superimposed on one surface of a cross-linked resin foam (cross-linked olefin-based resin foam, manufactured by Toray Industries, Inc., product name "AH1F-15025") cut to a size of 350 mm x 350 mm, and the skin layer and the cross-linked foam layer were heat-fused at a clearance of 90% of the total thickness when superimposed using a heat press machine at a temperature of 160°C to 175°C to prepare a laminate.

Example 2
A sheet for a surface layer and a laminate were produced in the same manner as in Example 1, except that a crosslinked olefin-based resin foam (manufactured by Toray Industries, Inc., product name "AHSF-15025") was used as the crosslinked resin foam.

(Examples 3 to 8)
A skin layer sheet and a laminate were produced in the same manner as in Example 1, except that the composition of the polyolefin resin and the thickness of the skin layer sheet were as shown in Table 3 or Table 4 below.

(Example 9)
A skin layer sheet and a laminate were produced in the same manner as in Example 1, except that the formulation of the polyolefin resin and the thickness of the skin layer sheet were as shown in Table 4 below, and a cross-linked olefin resin foam (manufactured by Sekisui Chemical Co., Ltd., product name "NVF-15040") was used as the cross-linked resin foam.

(Examples 10 to 14)
A skin layer sheet and a laminate were produced in the same manner as in Example 1, except that the composition of the polyolefin resin and the thickness of the skin layer sheet were as shown in Table 4 below.

(Comparative Examples 1, 3 to 5, 7 to 13)
A skin layer sheet and a laminate were produced in the same manner as in Example 1, except that the composition of the polyolefin resin and the thickness of the skin layer sheet were as shown in Table 5 below.

(Comparative Examples 2 and 6)
A skin layer sheet and a laminate were produced in the same manner as in Example 1, except that the formulation of the polyolefin resin and the thickness of the skin layer sheet were as shown in Table 5 or Table 6 below, and a cross-linked olefin resin foam (manufactured by Toray Industries, Inc., product name "AHSF-15025") was used as the cross-linked resin foam.

In the examples and comparative examples, the differential scanning calorimetry of the skin layer sheets, the thickness and Shore A strength measurements, the morphology state and area observations, the -35°C tensile strength, -35°C tensile elongation and -35°C tear strength measurements, and the oil resistance evaluation were performed as described above. The results are shown in Tables 3 to 6 below. The skin layer may be separated by slicing the laminate, and the separated skin layer may be used as the measurement sample. In Tables 3 to 6, the notation "-" in the first and second heats of fusion means that they are heats of fusion.

In the examples and comparative examples, the peel strength between the skin layer and the foam in the laminate, the -35°C tensile strength, -35°C tensile elongation and -35°C tear strength of the laminate, the maximum test force in a -35°C high-speed punching test and the breaking energy in a -35°C high-speed punching test were measured. The results are shown in Tables 7 to 10 below. The expansion ratio, thickness, Shore C hardness and 25% compression hardness of the crosslinked resin foam were measured as described above, and the results are shown in Tables 7 to 10.

Images of the skin layers of the laminates of Example 4 and Comparative Example 4 observed with a transmission electron microscope are shown in Figures 1 and 2, respectively. From Figure 1, it can be seen that in Example 4, the skin layer has a sea-island structure. From Figure 2, it can be seen that in Comparative Example 4, the skin layer does not have a sea-island structure, and the components are interconnected.

As can be seen from Tables 3, 4, 7 and 8 above, in the examples, the skin layer was easily cut, the cleavability was high, and the airbag deployment and moldability of the laminate were also good.

On the other hand, as can be seen from Tables 5, 6, 9, and 10, in Comparative Examples 3, 5 to 7, and 11 that do not have an island-sea structure, Comparative Examples 1, 2, 4, 9, 10, 12, and 13 in which the area ratio of the island regions in the island-sea structure is less than 50.0%, and Comparative Examples 8, 9, and 11 in which the heat of fusion of the first peak exceeds 40.0 J/g, the skin layer was poorly cut and the cleavability was poor. In Comparative Examples 1 to 7 and 9 to 13, the airbag deployment of the laminate was poor. In Comparative Examples 3, 6, 8, 10, and 11, the moldability of the laminate was poor.

Claims (11)

A crosslinked resin foam and a polyolefin-based resin skin layer disposed on a first surface of the crosslinked resin foam,
The polyolefin resin surface layer is melted by first heating from 40°C to 200°C at a heating rate of 10°C/min, then crystallized by cooling from 200°C to 40°C at a heating rate of 10°C/min, and then heated a second time from 40°C to 200°C at a heating rate of 10°C/min, as measured by differential scanning calorimetry (DSC). In the DSC curve obtained during the second heating, the polyolefin resin surface layer has a first peak whose temperature is in the range of 110 to 135°C, and the heat of fusion of the first peak is 40.0 J/g or less.
the polyolefin-based resin surface layer has a sea-island structure consisting of a sea region of a continuous phase and island regions of a dispersed phase dispersed in the continuous phase, and the area ratio of the island regions in the sea-island structure is 50.0% or more. The laminate according to claim 1, wherein the heat of fusion of the first peak is 7.5 J/g or more. The laminate according to claim 1, wherein the polyolefin resin surface layer is melted by first heating from 40°C to 200°C at a heating rate of 10°C/min, then crystallized by cooling from 200°C to 40°C at a heating rate of 10°C/min, and then heated a second time from 40°C to 200°C at a heating rate of 10°C/min, in a DSC curve obtained by the second heating, the DSC curve has a second peak in the range of 140 to 170°C, and the heat of fusion of the second peak is 2.0 to 15.2 J/g. 2. The laminate according to claim 1, wherein the average area of each island in the sea-island structure of the polyolefin-based resin skin layer is 0.70 to 2.5 ^μm2 . The laminate according to claim 1, wherein the polyolefin-based resin skin layer contains an olefin-based thermoplastic elastomer, a polypropylene-based resin, and a polyolefin-based resin. The laminate according to claim 1, wherein the polyolefin resin skin layer has a thickness of 0.4 to 1.3 mm. The laminate according to claim 1, wherein the polyolefin resin skin layer has a Shore A hardness of 70 to 100. The laminate according to claim 1, wherein the crosslinked resin foam is a polyolefin-based resin foam. The laminate according to claim 1, which is for use in vehicle interior materials. A vehicle interior material comprising the laminate according to any one of claims 1 to 9. The vehicle interior material according to claim 10, which is an automobile interior instrument panel.