JPH07224182A - Production of polyolefin cross-linked foamed material - Google Patents

Abstract

PURPOSE:To provide a method for production of a polyolefin-based cross-linked resin foamed material excellent in skin strength and capable of being laminated to a skin material to form a laminate excellent in fabrication quality. CONSTITUTION:This is a method for producing a polyolefin cross-linked foamed material by forming a foamable composition composed of a polyolefin-based resin and an organic heat decomposition type foaming agent at a temperature below the decomposition point of the foaming agent, irradiating the obtained formed material with ionizing radiation to conduct cross-linking reactions and conducting a foaming reaction of the resultant cross-linked formed material in a high-temperature atmosphere enough to decompose the forming agent. In this production method, the cross-linking reactions are composed of the first cross-linking reaction conducted by irradiating one or both of the surfaces of the formed material with ionizing radiation under a low-concentration oxygen so that the degree (b) of cross-linking in the layer from the surface of the foamed material to 300mum depth may be within a range of (b)/(a)X100+ or -25 based on the degree (a) of cross-linking in the whole foamed material and the second cross-linking reaction by the subsequent irradiation with ionizing radiation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polyolefin crosslinked foam having excellent skin strength and good secondary processability.

[0002]

2. Description of the Related Art Polyolefin resin foams are generally excellent in flexibility and heat insulation and have been conventionally used as vehicle interior materials such as ceilings, doors and instrument panels. These interior materials are mainly polyolefin resin foam, laminated with vinyl chloride resin sheet, thermoplastic elastomer sheet, cloth-like material, and skin material such as leather, and subjected to secondary processing such as vacuum molding and compression molding. Is molded into a predetermined shape.

In the interior material molded in this way, the foam often breaks when the strength of the surface layer of the foam is insufficient, and when the degree of crosslinking of the surface layer of the foam is low, the foam and the skin In many cases, delamination occurs between the material and the interior material, and the resulting interior material swells and wrinkles.

[0004]

In order to improve the strength of the surface layer portion of the foam with respect to such a problem, a foam body in which the density of the surface layer portion of the surface to be laminated with the skin material is reduced has been proposed (Japanese Patent Laid-Open No. Hei 10 (1999) -135242). No. 1-222937), and a foam having a higher degree of cross-linking in the surface layer has been proposed (Japanese Patent Publication No. Sho 5).
7-26207). However, neither of them has completely solved the defect that delamination occurs between the foam and the skin material during the secondary processing of the laminate in which the foam and the skin material are laminated.

The present invention solves the above points and provides a method for producing a polyolefin crosslinked foam which is excellent in skin strength and has good secondary workability when laminated with a skin material.

[0006]

The invention according to claim 1 is
A foaming composition prepared by blending a polyolefin-based resin with an organic pyrolyzable foaming agent is molded in a temperature range in which the foaming agent does not decompose, and the molded body is irradiated with ionizing radiation to carry out a crosslinking reaction. In the method for producing a polyolefin crosslinked foam by performing a foaming reaction in a high temperature atmosphere sufficient for decomposing the foaming agent, the crosslinked molded body is treated from the surface of the foamed body after foaming. One is performed on one side or both sides of the molded body so that the degree of crosslinking (b) in the range of 300 μm is (b) / (a) × 100 ± 25 with respect to the degree of crosslinking (a) of the entire foam. A method for producing a cross-linked polyolefin foam, which comprises a cross-linking reaction by irradiation of ionizing radiation under a low oxygen concentration for the second time and a cross-linking reaction by subsequent irradiation of ionizing radiation.

The method for producing a polyolefin crosslinked foam according to claim 2 is the same as the method for producing a polyolefin crosslinked foam according to claim 1, wherein the following formulas (1) to
The compound represented by (3) is contained. (CH ₂ = CH-CH ₂ -O-CO-) _n R ₁ …………………… (1) (CH ₂ = CH−) _n R ₂ …………………………………… (2) (CH ₂ = CR ₄ -CO-O-) _n R ₃ …………………… (3) In the formula, R ₁ , R ₂ and R ₃ are hydrocarbon groups. , R ₄ represents hydrogen or a methyl group, and n is an integer of 1 to 4.

The method for producing a polyolefin crosslinked foam according to claim 3 is the same as the method for producing a polyolefin crosslinked foam according to claim 1 or 2, wherein the polyolefin resin is 40 to 90% by weight of a polypropylene resin and a polyolefin resin. It is characterized by comprising 60 to 10% by weight.

The polypropylene resin is a propylene homopolymer or a copolymer containing propylene as a main component,
Examples thereof include polypropylene, a propylene-ethylene copolymer containing propylene as a main component, and an α-olefin copolymer other than propylene-propylene containing propylene as a main component. As α-olefins other than propylene, 1-butene, 1-pentene, 1-hexene, 4-
Methyl-1-pentene, 1-heptene, 1-octene and the like can be mentioned.

The polyethylene resin is a homopolymer of ethylene or a copolymer containing ethylene as a main component. For example, polyethylene or ethylene containing ethylene as a main component is used.
It is a copolymer with an α-olefin copolymer, ethylene- (meth) acrylic acid, lower alkyl esters of (meth) acrylic acid, vinyl acetate and the like. As the α-olefin, propylene, 1-butene, 1-pentene, 1
-Hexene, 4-methyl-1-pentene, 1-heptene, 1-octene and the like can be mentioned.

Examples of the organic thermal decomposition type foaming agent include, for example,
Examples thereof include azodicarbonamide, benzenesulfonyl hydrazide, dinitropentamethylene tetramine, toluenesulfonyl human azide and 4,4-oxybis (benzenesulfonyl hydrazide). These foams may be used alone or in combination. The amount of the heat-decomposable foaming agent added is determined in consideration of the expansion ratio of the resulting foam, and is not particularly limited, but is usually 1 with respect to 100 parts by weight of the total amount of the polyolefin resin.
˜50 parts by weight.

As the cross-linking aid, the above formulas (1) to
It is necessary to use at least one kind of the polyfunctional monomer represented by (3), and it is possible to use it together with other crosslinking aids, for example, a radical generator such as benzoyl peroxide. The amount of the crosslinking aid added is not particularly limited, but is usually 0.1 to 10 parts by weight based on 100 parts by weight of the total amount of the polyolefin resin. This is because if the amount is less than 0.1 parts by weight or exceeds 10 parts by weight, the foamability of the resulting foam will deteriorate.

The polyfunctional monomer represented by the above formula (1) includes 1,2,4-benzenetricarboxylic acid triallyl ester (trimellitic acid triallyl ester),
Examples include 1,3,5-benzenetricarboxylic acid triallyl ester and diallyl phthalate.

Examples of the polyfunctional monomer represented by the above formula (2) include divinylbenzene, 1,9-nonanediol di (meth) acrylate, styrene and ethyl-vinylbenzene.

The polyfunctional monomer represented by the above formula (3) is trimethylolpropane tri (meth).
Examples thereof include acrylate and 1,6-hexanediol di (meth) acrylate. These cross-linking aids are particularly useful for promoting the cross-linking reaction when the olefin resin contains a polypropylene resin.

The polyolefin resin may be a phenol resin, a phosphorus resin, or a polyolefin resin as long as the characteristics of the resulting foam are not impaired.
Amine-based and sulfur-based antioxidants, metal damage inhibitors, flame retardants, fillers, antistatic agents, pigments and the like can be added.

In the present invention, the foamable composition is molded into a predetermined shape such as a plate, a sheet, or a tube at a temperature at which the foaming agent does not decompose. The molding method may be extrusion molding or other methods. A molding method can be used. Examples of the kneading / molding apparatus for the resin composition include a single-screw extruder, a twin-screw extruder, a Banbury mixer, and a roll.

In the present invention, the unfoamed molded article is irradiated with ionizing radiation to cause a crosslinking reaction. Examples of the ionizing radiation include α-ray, β-ray, γ-ray and electron beam. Can be given. The irradiation dose of this ionizing radiation is usually preferably 1 to 20 Mrad. More preferably, it is 1 to 6 Mrad. When the irradiation dose is less than 1 Mrad, the degree of cross-linking is too low and the strength is insufficient, so that a foam having a sufficient expansion ratio cannot be obtained. On the contrary, a foam obtained at a high dose exceeding 20 Mrad is obtained. Is harder than necessary and loses flexibility.

In the present invention, the irradiation of ionizing radiation is performed twice or more, but the first irradiation of ionizing radiation needs to be performed at a low oxygen concentration. Then, by the irradiation, the degree of cross-linking (b) in the range of 300 μm from the surface of the foam after foaming becomes (b) / (a) × 100 ± 25 with respect to the degree of cross-linking (a) of the entire foam. To be The range of (b) / (a) × 100 ± 20 is more preferable. The surface to be irradiated is a surface to be laminated with a skin material or the like.

In the present invention, "under low oxygen concentration" means that the volume occupied by oxygen is about 5% or less in the volume of the irradiation atmosphere. It is preferably 3% or less, more preferably 1
% Or less. As a method of embodying such a low oxygen concentration, specifically, an atmosphere in which an inert gas such as nitrogen, argon, or helium is substituted is used, or a vacuum condition is set. When a large amount of oxygen under a high oxygen concentration of 5% or more is present, ozone is generated by irradiation with ionizing radiation, and this ozone is a carbon-carbon double bond of a polyfunctional monomer having a high electron density. So-called ozonolysis, which is the cleavage of two carbonyl compounds by the reaction with, is lost as a result of the activity as a cross-linking aid. This is because the degree of crosslinking is insufficient.

The first irradiation of ionizing radiation is preferably performed at a low acceleration voltage. When the accelerating voltage is set to a low value, the surface layer portion can be crosslinked without the ionizing radiation penetrating the surface of the molded article. Specifically, when a polyolefin sheet having a thickness of about 0.5 to 3.0 mm is crosslinked, the acceleration voltage for the first irradiation is preferably set to about 50 to 400 keV, and the acceleration voltage for the subsequent irradiation is preferably set. Is preferably 200 to 1200 keV.

The degree of crosslinking is represented by the gel fraction (%) of the foam, which can be obtained by determining the xylene extraction residue value at 120 ° C. The gel fraction of the whole foam is usually 20 to 60%. The xylene extraction residue value at 120 ° C. of the obtained foam was 0.
About 1 g was weighed, the air bubbles were crushed, and the mixture was kept in 50 ml of xylene at a temperature of 120 ° C. for 24 hours.
Dry weight (g) of the residue passed through a 0 mesh wire mesh
It is calculated by the following formula. Crosslinking degree (gel fraction) = [dry weight of residue (g) / weighing weight (g)] × 100

The degree of cross-linking (gel fraction) of the surface layer portion is calculated and calculated in the same manner as above for the foamed sheet obtained by slicing the surface layer portion irradiated surface of the foamed sheet up to a depth of 300 μm.

In order to carry out the foaming reaction in a high temperature atmosphere sufficient for the foaming agent to decompose the cross-linked molded body, a method of supplying the molded body to a foaming furnace to heat and foam the molded body, a molded body with a heating roll A method for foaming under normal pressure, such as a method for heating and foaming, is used, a method for supplying a molded product to a mold and heating for foaming in a batch system, and the like.

As the skin material laminated on the foam obtained by the method of the present invention, a skin material that has been conventionally used, for example, a vinyl chloride resin sheet, a thermoplastic elastomer,
Cloth, leather, etc. are used. These skin materials are adhered to the foam by an adhesive or heat-sealed by thermal lamination to be laminated. At this time, the surface of the foam can be subjected to conventional surface treatment such as corona discharge treatment to improve the adhesiveness.

[0026]

[Function] When a polyolefin resin molded product is cross-linked by irradiation with ionizing radiation using a polyfunctional monomer as a cross-linking aid, the polyfunctional monomer has a high electron density in the double bond, and therefore has reactivity with ozone. And reacts with ozone changed from oxygen by irradiation of ionizing radiation in air,
So-called ozonolysis, which is the cleavage of two carbonyl compounds by reacting with the carbon-carbon double bond of the polyfunctional monomer, is performed, and the activity as a crosslinking aid is lost. As a result, in the surface portion of the molded body, the ozone decomposition rate occurs faster than the crosslinking reaction rate, and the degree of crosslinking of this surface portion is insufficient, but in the present invention, irradiation with ionizing radiation under a low oxygen concentration causes Since the cross-linking reaction is performed so that the degree of cross-linking is as described above, there is little ozone change in oxygen, so-called ozonolysis is suppressed, and the performance of the polyfunctional monomer as a cross-linking auxiliary agent is fully expressed, forming The cross-linking reaction of the surface portion of the body is reliably performed.

As a result, the foam has good flexibility and elongation properties, and the surface portion thereof is sufficiently crosslinked, and when laminated with the skin material, it is subjected to a large shearing force even in vacuum molding or compression molding. It is possible to process a molded product having a complicated and deep shape and a good appearance without causing any problems such as swelling on the surface or peeling of the skin material.

[0028]

Embodiments of the present invention will be described below. Less than,
Parts by weight are simply called parts. (Example 1) Polyethylene as a polyolefin resin (density 0.920 g / cm ³ , melt index 4 g
/ 10 min) 100 parts, azodicarbonamide 10 parts as a foaming agent, 2,6-di-t-butyl-p-cresol and dilaurylthiopropionate 0.3 parts as antioxidants, respectively, metal damage The foamable composition to which 0.5 part of methylbenzotriazole was added as an inhibitor was extruded at a temperature of 150 ° C. using a twin-screw extruder (PCM87, manufactured by Ikegai Iron Works) to obtain a sheet having a thickness of 1.3 mm. It was

This sheet was irradiated with an electron beam of 9.0 Mrad at an accelerating voltage of 200 keV in a nitrogen atmosphere (oxygen concentration of 1.0%) to perform the first electron beam irradiation. Next, under the air, the electron beam was irradiated with an electron beam of 8.0 Mrad at an acceleration voltage of 700 keV to perform the second electron beam irradiation. The crosslinked sheet thus obtained by two times of electron beam irradiation was placed in an oven at 250 ° C. and allowed to freely foam for 5 minutes without applying a load to obtain a foamed sheet having a thickness of about 3 mm. The gel fraction (overall average, surface layer portion) and apparent density of this foamed sheet were measured. The results are shown in Table 1.

The surface of the obtained foamed sheet was subjected to corona discharge treatment, and the surface-treated surface was treated with vinyl chloride resin A
A commercially available impact-resistant type resin sheet (having a thickness of 0.65 mm) prepared by blending a BS resin was attached using a two-component curing type polyester adhesive to obtain a laminate.

With respect to this laminate, the peel strength was measured, and vacuum forming was performed to evaluate the vacuum formability and appearance.
The results are shown in Table 1. The peel strength was measured by cutting the laminated body into a test piece by cutting it into a width of 25 mm and a length of 100 mm, and controlling the temperature at 150 ° C. for 5 minutes, using Tensilon (type UCT-500) manufactured by Orientec Co., Ltd.
The strength (g / 25 mm) when peeled at 50 ° C. was measured, and this was taken as the peel strength. The appearance of the vacuum-molded product was evaluated as × when blemishes, blisters, dents, surface roughness, etc. were visually observed, and ◯ when none were found. Also, the vacuum moldability is such that the surface temperature of the foam of the laminate is 150 to 160 ° C. with a far infrared heater
It is heated so that it becomes a cylindrical depression (diameter: 100
mm, depth: 10 mm to 150 mm in 10 mm increments, vacuum forming is performed to find the maximum depth Hmm without breaking, and the ratio to the diameter D (100 mm) (H
/ D) was determined. The larger the H / D value, the better the vacuum formability.

Example 2 The same foamable composition as in Example 1 was used, except that 3.0 parts of trimethylolpropane trimethacrylate and 12 parts of azodicarbonamide were added as crosslinking aids. It was similarly extruded to obtain a sheet having a thickness of 1.1 mm.

This sheet was irradiated with an electron beam of 7.0 Mrad at an accelerating voltage of 150 keV in a nitrogen atmosphere (oxygen concentration of 2.0%) to perform the first electron beam irradiation. Then, under the air, the electron beam was irradiated with an electron beam of 6.0 Mrad at an acceleration voltage of 600 keV to perform the second electron beam irradiation. The crosslinked sheet thus obtained by electron beam irradiation twice was foamed in the same manner as in Example 1 to give a thickness of about 2.5 m.
A foamed sheet of m was obtained. Example 1 was applied to the obtained foamed sheet.
A resin sheet was laminated in the same manner as above to obtain a laminate. The gel fraction, the apparent density, and the elongation of the obtained foam were measured, the peel strength of the obtained laminate was measured, and its appearance and vacuum formability were evaluated in the same manner as in Example 1. The results are shown in Table 1.

Example 3 As polyolefin resin, 60 parts of ethylene-propylene random copolymer of polypropylene resin (ethylene content 4.0% by weight, melt index 1.5 g / 10 minutes) and polyethylene resin Linear low density polyethylene (density 0.920,
Melt index 17 g / 10 minutes) 40 parts,
To this, 3.5 parts of divinylbenzene as a crosslinking aid,
The same foamable composition as in Example 1 except that 12 parts of azodicarbonamide was added was extruded in the same manner as in Example 1 to obtain a sheet having a thickness of 1.5 mm.

This sheet was placed under vacuum (oxygen concentration: 1000
ppm) at an accelerating voltage of 180 keV and an electron beam of 8.
The first electron beam irradiation was performed by irradiating 0 Mrad.
Then, under air, with an accelerating voltage of 800 keV, an electron beam 6.
The second electron beam irradiation was performed by irradiating 0 Mrad.
The crosslinked sheet thus obtained by the twice electron beam irradiation was foamed in the same manner as in Example 1 to obtain a foamed sheet having a thickness of about 3 mm. A resin sheet was laminated on the obtained foamed sheet in the same manner as in Example 1 to obtain a laminate. The gel fraction, the apparent density, and the elongation of the obtained foam were measured, the peel strength of the obtained laminate was measured, and its appearance and vacuum formability were evaluated in the same manner as in Example 1. The results are shown in Table 1.

Example 4 As a polyolefin resin, 70 parts of an ethylene-propylene random copolymer of polypropylene resin (ethylene content 4.0% by weight, melt index 0.5 g / 10 minutes) and polyethylene resin Linear low density polyethylene (density 0.920,
Melt index 10 g / 10 minutes) 30 parts,
The same foamable composition as in Example 1 was extruded in the same manner as in Example 1 except that 2.5 parts of trimellitic acid triallyl ester and 13 parts of azodicarbonamide were added thereto as a crosslinking aid, A 1.8 mm thick sheet was obtained.

An electron beam 1 was applied to this sheet in a nitrogen atmosphere (oxygen concentration 0.5%) at an acceleration voltage of 200 keV.
Irradiation with 2.0 Mrad was performed for the first electron beam irradiation. Next, under air, an electron beam of 7.5 Mrad was irradiated with an accelerating voltage of 800 keV, and a second electron beam irradiation was performed. The crosslinked sheet thus obtained by electron beam irradiation twice was foamed in the same manner as in Example 1 to give a thickness of about 3.5 m.
A foamed sheet of m was obtained. Example 1 was applied to the obtained foamed sheet.
A resin sheet was laminated in the same manner as above to obtain a laminate. The gel fraction, the apparent density, and the elongation of the obtained foam were measured, the peel strength of the obtained laminate was measured, and its appearance and vacuum formability were evaluated in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 1 Azodicarbonamide was added to 12
The same foamable composition as in Example 1 except that the parts were added,
Extrusion was performed in the same manner as in Example 1 to obtain a sheet having a thickness of 1.3 mm.

On this sheet, under air (oxygen concentration 20%)
At an acceleration voltage of 700 keV and an electron beam of 8.5 Mra
d. The crosslinked sheet obtained by this electron beam irradiation was foamed in the same manner as in Example 1 to obtain a foamed sheet having a thickness of about 3 mm. A resin sheet was laminated on the obtained foamed sheet in the same manner as in Example 1 to obtain a laminate. The gel fraction, the apparent density, and the elongation of the obtained foam were measured, the peel strength of the obtained laminate was measured, and its appearance and vacuum formability were evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 2) As a polyolefin resin, 70 parts of ethylene-propylene random copolymer of polypropylene resin (ethylene content 4.0% by weight, melt index 0.5 g / 10 minutes) and polyethylene resin Linear low density polyethylene (density 0.920,
Melt index 10 g / 10 minutes) 30 parts,
The same foamable composition as in Example 1 was extruded in the same manner as in Example 1 except that 2.5 parts of trimellitic acid triallyl ester and 13 parts of azodicarbonamide were added thereto as a crosslinking aid, A sheet having a size of 1.5 mm was obtained.

On this sheet, under air (oxygen concentration 20%)
At an acceleration voltage of 800 keV, an electron beam of 6.0 Mra
d. The crosslinked sheet obtained by this electron beam irradiation was foamed in the same manner as in Example 1 to obtain a foamed sheet having a thickness of about 3 mm. A resin sheet was laminated on the obtained foamed sheet in the same manner as in Example 1 to obtain a laminate. The gel fraction, the apparent density, and the elongation of the obtained foam were measured, the peel strength of the obtained laminate was measured, and its appearance and vacuum formability were evaluated in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 3 The same foaming composition as in Example 1 was used, except that 3.0 parts of trimethylolpropane trimethacrylate and 12 parts of azodicarbonamide were added as crosslinking aids. Extruded into a thickness of 1.1
A sheet of mm was obtained.

This sheet was irradiated with an electron beam of 1.5 Mrad at an acceleration voltage of 150 keV in a nitrogen atmosphere (oxygen concentration of 2.0%) to perform the first electron beam irradiation. Then, the electron beam was irradiated with 7.0 Mrad at an accelerating voltage of 600 keV under air to perform the second electron beam irradiation. The crosslinked sheet thus obtained by electron beam irradiation twice was foamed in the same manner as in Example 1 to give a thickness of about 2.5 m.
A foamed sheet of m was obtained. Example 1 was applied to the obtained foamed sheet.
A resin sheet was laminated in the same manner as above to obtain a laminate. The gel fraction, the apparent density, and the elongation of the obtained foam were measured, the peel strength of the obtained laminate was measured, and its appearance and vacuum formability were evaluated in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 4 As a polyolefin resin, 60 parts of an ethylene-propylene random copolymer of polypropylene resin (ethylene content 4.0% by weight, melt index 1.5 g / 10 minutes) and polyethylene resin Linear low density polyethylene (density 0.920,
Melt index 17 g / 10 minutes) 40 parts,
The same foamable composition as in Example 1 was extruded in the same manner as in Example 1 except that 3.5 parts of divinylbenzene and 8 parts of azodicarbonamide were added as a crosslinking aid thereto,
A sheet having a thickness of 1.5 mm was obtained.

This sheet was placed under vacuum (oxygen concentration 1000
electron beam 3 at an acceleration voltage of 250 keV
Irradiation with 0.0 Mrad was performed, and the first electron beam irradiation was performed. Then, under air, an electron beam of 5.0 Mrad was irradiated at an accelerating voltage of 800 keV to perform a second electron beam irradiation. The crosslinked sheet thus obtained by the twice electron beam irradiation was foamed in the same manner as in Example 1 to obtain a foamed sheet having a thickness of about 3 mm. A resin sheet was laminated on the obtained foamed sheet in the same manner as in Example 1 to obtain a laminate. The gel fraction, the apparent density, and the elongation of the obtained foam were measured, the peel strength of the obtained laminate was measured, and its appearance and vacuum formability were evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 5) As a polyolefin resin, 60 parts of ethylene-propylene random copolymer of polypropylene resin (ethylene content 4.0% by weight, melt index 1.5 g / 10 minutes) and polyethylene resin Linear low density polyethylene (density 0.920,
Melt index 17 g / 10 minutes) 40 parts,
The same foamable composition as in Example 1 was extruded in the same manner as in Example 1 except that 3.5 parts of divinylbenzene and 8 parts of azodicarbonamide were added as a crosslinking aid thereto,
A sheet having a thickness of 1.5 mm was obtained.

On this sheet, under air (oxygen concentration 20%)
At an acceleration voltage of 180 keV, an electron beam of 8.0 Mra
Then, the first electron beam irradiation was performed. Then
An electron beam of 6.0 Mra at an acceleration voltage of 800 keV under air
Then, the second irradiation with electron beam was performed. The crosslinked sheet thus obtained by the twice electron beam irradiation was foamed in the same manner as in Example 1 to obtain a foamed sheet having a thickness of about 3 mm. A resin sheet was laminated on the obtained foamed sheet in the same manner as in Example 1 to obtain a laminate. The gel fraction, the apparent density, and the elongation of the obtained foam were measured, the peel strength of the obtained laminate was measured, and its appearance and vacuum formability were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0048]

[Table 1]

As is clear from Table 1, the laminates using the foams obtained in Examples 1 to 4 have a peel strength of 37.
g / 25 mm or more and H / D (vacuum formability) of 0.8 or more, whereas the foams of Comparative Examples 1 to 4 have a peel strength of 1
Inferior to 9 g / 25 mm or less, and inferior to H / D (vacuum formability) of 0.7 or less, and in both cases, the appearance was poor.

[0050]

According to the method for producing a foam of the present invention,
The obtained foam has excellent elongation, good adhesion to the skin material, and excellent secondary workability such as vacuum formability.
It is easy to obtain a secondary processed product with good appearance without blurring, blistering, dents, and surface roughness.

Claims (3)

[Claims] 1. A foamable composition comprising a polyolefin resin and an organic pyrolyzable foaming agent mixed therein is molded in a temperature range in which the foaming agent does not decompose, and the molded body thus formed is irradiated with ionizing radiation. In the method for producing a polyolefin crosslinked foamed product by performing a foaming reaction in a high temperature atmosphere sufficient for decomposing the foaming agent, a crosslinking reaction is performed after foaming. One side or both sides of the molded body so that the degree of crosslinking (b) in the range of 300 μm from the surface of the foam is (b) / (a) × 100 ± 25 with respect to the degree of crosslinking (a) of the entire foam. The method for producing a cross-linked polyolefin foam, which comprises the first cross-linking reaction by irradiation with ionizing radiation under a low oxygen concentration and the subsequent cross-linking reaction by irradiation with ionizing radiation. 2. The method for producing a crosslinked polyolefin foam according to claim 1, wherein the foamable composition contains a compound represented by the following formulas (1) to (3) as a crosslinking aid. . (CH ₂ = CH-CH ₂ -O-CO-) _n R ₁ …………………… (1) (CH ₂ = CH−) _n R ₂ …………………………………… (2) (CH ₂ = CR ₄ -CO-O-) _n R ₃ …………………… (3) In the formula, R ₁ , R ₂ and R ₃ are hydrocarbon groups. , R ₄ represents hydrogen or a methyl group, and n is an integer of 1 to 4. 3. The polyolefin resin comprises 40 to 90% by weight of polypropylene resin and 60 to 60 of polyolefin resin.
The method for producing a crosslinked polyolefin foam according to claim 1 or 2, characterized in that it comprises 10% by weight.