JPH09150473A - Crosslinked polyolefin foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide crosslinked polyolefin foam excellent in thermal moldability such as vacuum moldability, good in heat resistance and excellent in the thermal adhesiveness with a base material such as a skin material or a core material. SOLUTION: This crosslinked polyolefin foam has a heat-sensitive adhesive layer formed to at least the single surface thereof. The heat-sensitive adhesive layer consists of 40-70wt.% of an ethylene/ethyl acrylate/maleic anhydride copolymer with a melt flow rate of 2-15g/10min and an m.p. of 100-120 deg.C and 60-30wt.% of an ethylene/ethyl acrylate/maleic anhydride copolymer with a melt flow rate of 15-23g/10min and an m.p. of 60-85 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crosslinked polyolefin foam having excellent thermal adhesiveness, and more particularly to a crosslinked polyolefin foam having excellent thermal adhesiveness to a wood-based substrate obtained by hardening wood chips with a phenolic resin. Regarding the body

[0002]

Crosslinked polyolefin foams are heat insulating materials,
It is used in a wide range of fields such as cushioning materials. Especially,
In automobile applications, it is used as a heat insulating cushioning material for ceilings, door inner surface materials, instrument panels and the like.

In this type of application, generally, a foamed sheet with a skin material is formed by laminating a plastic sheet such as a soft vinyl chloride resin sheet or a skin material on one surface of a crosslinked polyolefin foam sheet to form a foam sheet with a skin material. And the like are integrally formed with the base material (core material). As the base material, a wood-based base material obtained by hardening wood chips with a phenol-based resin or a resin-based base material such as polypropylene is used.

When the skin material is attached to the foam sheet or when the foam sheet with the skin material is integrally molded with the base material,
Each material may be bonded by heat fusion without using an adhesive, but various adhesives are often used in order to enhance the adhesive strength.

When the above materials are bonded by an adhesive, a heat-sensitive adhesive (hot melt adhesive) is used in place of the solvent-based adhesive from the viewpoint of safety and hygiene, and the foamed sheet from the viewpoint of adhesive workability. Has been proposed an adhesive foam sheet in which a heat-sensitive adhesive layer made of a copolymer such as ethylene-vinyl acetate copolymer is previously formed on at least one surface (see, for example, JP-B-4-17784). .

[0006]

However, a conventional ethylene-based foam is formed on at least one surface of the crosslinked polyolefin foam.
Those with a heat-sensitive adhesive layer made of a copolymer such as vinyl acetate copolymer do not have sufficient adhesiveness especially to a wood-based substrate obtained by hardening wood chips with a phenol-based resin. There is a problem.

That is, when the above-mentioned crosslinked polyolefin foam is integrally molded with the above-mentioned wood-based substrate by a vacuum forming method or the like, if the temperature of the crosslinked polyolefin foam becomes too high, the air bubbles are crushed. ~ 15
It must be integrally molded at a temperature of about 0 ° C. However, at such a temperature, sufficient adhesive force cannot be obtained, heat resistance is particularly insufficient, and the adhesiveness decreases in a high temperature environment.
There is a problem in automotive applications where heat resistant adhesion is required.

The present invention solves the above problems, and its object is to have excellent thermoformability such as vacuum formability, good heat resistance, and a base material such as a skin material or a core material. It is intended to provide a crosslinked polyolefin foam excellent in heat adhesion.

[0009]

The crosslinked polyolefin foam of the present invention comprises a crosslinked polyolefin foam having a heat-sensitive adhesive layer formed on at least one side thereof, and the heat-sensitive adhesive layer has a melt flow rate of 2 to 2. 15g / 10 minutes,
Ethylene-ethyl acrylate-maleic anhydride copolymer having a melting point of 100 to 120 ° C. 40 to 70% by weight, melt flow rate of 15 to 23 g / 10 min, and melting point of 60 to 85 ° C. ethylene-ethyl acrylate-maleic anhydride copolymer. It is characterized by comprising 60 to 30% by weight, whereby the above object can be achieved.

The crosslinked polyolefin foam used in the present invention is obtained by blending a polyolefin resin with a thermal decomposition type foaming agent and, if necessary, a crosslinking aid, an organic peroxide and other additives, and extruding the resin blend. Make a foamable sheet by melting and kneading at a temperature at which the foaming agent does not decompose using a machine or roll,
It can be produced by a method in which the resin is crosslinked by irradiating it with ionizing radiation or by decomposing an organic peroxide preliminarily blended, and heating and foaming the resin.

Here, as the polyolefin resin, a polyethylene resin, a polypropylene resin, or a mixed resin of a polyethylene resin and a polypropylene resin is preferably used. In particular, a polyolefin resin containing a polypropylene-based resin as a main component is preferable because the foamed sheet has good heat resistance and rigidity at high temperatures and good thermoformability.

As the polyethylene resin, a homopolymer of ethylene (low density, medium density, high density) or a copolymer containing ethylene as a main component is used. Examples of the copolymer containing ethylene as a main component include, for example, an ethylene-α-olefin copolymer containing 80% by weight or more of an ethylene component,
Examples thereof include ethylene-vinyl acetate copolymer.

As the polypropylene resin, a homopolymer of propylene or a copolymer containing propylene as a main component is used. Examples of the propylene-based copolymer include a propylene-α-olefin random copolymer or a block copolymer containing 50% by weight or more of a propylene component.

As the thermal decomposition type foaming agent, one having a decomposition temperature of about 180 to 270 ° C. is generally used.
Examples thereof include azodicarbonamide, N, N'-dinitrosopentamethylenetetramine, p-toluenesulfonyl semicarbazide, p, p'-oxybis (benzenesulfonyl semicarbazide) and the like. The blending amount of the thermal decomposition type foaming agent is generally 5 to 30 parts by weight with respect to 100 parts by weight of the polyolefin resin, and is set according to a desired expansion ratio.

When a crosslinking aid is used, for example, divinylbenzene, trimethylolpropane trimethacrylate, 1,2,4-triallyl trimellitate, 1,9-
Nonanediol dimethacrylate or the like is used. The amount of the crosslinking aid compounded is generally 0.3 to 10 parts by weight with respect to 100 parts by weight of the polyolefin resin, and is set according to the desired degree of crosslinking.

When an organic peroxide is used, for example, dicumyl peroxide, di-t-butyl peroxide, methyl ethyl ketone peroxide, etc. are used. The amount of the organic peroxide compounded is generally 0.3 to 5 parts by weight with respect to 100 parts by weight of the polyolefin resin, and is set according to the desired degree of crosslinking.

Other additives include decomposition accelerators for foaming agents, cell nucleus control agents, antioxidants, heat stabilizers, light stabilizers, flame retardants, antistatic agents, inorganic fillers, colorants, etc. Is used.

In order to produce the crosslinked polyolefin foam used in the present invention, first, the above-mentioned resin composition is used in a general kneading machine such as an extruder or a roll at a temperature at which the thermal decomposition type foaming agent does not decompose, for example, 160. The mixture is melt-kneaded at a temperature of about 180 ° C. and molded into a sheet to prepare a foamable sheet.

Then, the resin is crosslinked by irradiating the foamable sheet with ionizing radiation or by decomposing an organic peroxide which has been previously mixed. As the ionizing radiation, electron rays, α rays, β rays, γ rays and the like are used. The irradiation dose is generally from 1 to 20 Mrad, and the dose is set according to the desired degree of crosslinking.

The foamable sheet in which the resin is cross-linked can be formed, for example, by hot air, infrared rays, a metal bath, an oil bath, or the like.
The resin is foamed by the decomposition gas of the foaming agent by heating to a temperature not lower than the decomposition temperature of the thermal decomposition type foaming agent and not lower than the melting point of the resin, for example, 190 to 290 ° C.

When the apparent density of the foam becomes low, the high temperature elongation is insufficient and the thermoformability such as vacuum moldability is deteriorated, and the foam becomes soft and the cushioning property is impaired. In general, 0.03 ~
It is set to 0.1 g / cm ³ . The thickness of the foam is generally 1-10 mm. In this way, a sheet-shaped crosslinked polyolefin foam is obtained.

In the present invention, the heat-sensitive adhesive layer formed on at least one surface of the cross-linked polypropylene foam has a melt flow rate of 2 to 15 g / 10 minutes and a melting point of 10.
Ethylene-ethyl acrylate-maleic anhydride copolymer 40-70% by weight of 0-120 ° C, melt flow rate 15-23g / 10 minutes, melting point 60-85 ° C ethylene-ethyl acrylate-maleic anhydride copolymer 60 ~
30% by weight.

In any of the above ethylene-ethyl acrylate-maleic anhydride copolymers, the ethylene component is 92 to 70% by weight, the ethyl acrylate component is 3 to 20% by weight, and the maleic anhydride component is 1 to
10% by weight is preferably used. Further, the thickness of the heat-sensitive adhesive layer is preferably 5 to 50 μm.

Here, the melt flow rate of the above copolymer is measured by using an extrusion type plastometer according to JIS K72.
The test temperature is 190 ° C. and the test load is 2.16 kgf. The melting point is the temperature of the melting peak measured by a differential scanning calorimeter (DSC) according to JIS K7121.

In the above heat-sensitive adhesive layer, when the ethylene-ethyl acrylate-maleic anhydride copolymer having a melt flow rate of 2 to 15 g / 10 minutes and a melting point of 100 to 120 ° C. is more than 70% by weight, it is particularly woody. Adhesiveness to the base material is reduced, conversely melt flow rate 15-23g
When the content of the ethylene-ethyl acrylate-maleic anhydride copolymer having a melting point of 60 to 85 ° C. for 10 minutes is more than 60% by weight, the heat-resistant adhesive property decreases.

In the present invention, in order to form a heat-sensitive adhesive layer on at least one surface of the crosslinked polyolefin foam, as described in the above-mentioned Japanese Patent Publication No. 4-17784, a resin-crosslinked foam is formed. A method in which a heat-sensitive adhesive having the above composition is melt-extruded on at least one side of the heat-resistant sheet, and this is heat-foamed is preferably adopted. In addition, a method in which a crosslinked polyolefin foam is prepared in advance and the heat-sensitive adhesive having the above composition is melt-extruded on at least one surface of the foam can also be used.

(Function) The crosslinked polyolefin foam of the present invention has a good heat insulating cushion and, in addition, since the resin is crosslinked, it has good heat resistance and excellent thermoformability such as vacuum formability.
Further, the heat-sensitive adhesive adheres well to the cross-linked polyolefin foam, and at a temperature at which bubbles of the foam do not collapse, for example, at a relatively high temperature of about 130 to 150 ° C. It has good adhesiveness (peeling adhesive strength at room temperature) and heat-resistant adhesiveness (creep adhesive strength at 80 ° C.) to the wood-based base material hardened by.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples and comparative examples of the present invention will be described below. Examples and Comparative Examples 70 parts by weight of polypropylene resin (MI1.8, propylene-ethylene random copolymer having ethylene content of 3.6% by weight) and polyethylene resin (MI1.9,
30 parts by weight of linear low density polyethylene having a density of 0.920 g / cm ³ ) was mixed to prepare a polyolefin resin. To 100 parts by weight of this polyolefin resin, 10 parts by weight of azodicarbonamide as a thermal decomposition type foaming agent,
2.5 parts by weight of 1,2,4-triallyl trimellitate as a crosslinking aid, and a phenolic antioxidant (2,5-
1 part by weight of di-t-butyl-p-cresol) was blended to prepare a resin blend.

This resin composition was melt-kneaded using an extruder at a temperature not higher than the decomposition temperature of the foaming agent and extruded into a sheet,
A foamable sheet having a thickness of about 1.1 mm was obtained. This foamable sheet was irradiated with an electron beam (accelerating voltage 800 kV) of 2 Mrad to crosslink the resin, and ethylene-ethyl acrylate-maleic anhydride as shown in Table 1 was formed on one side of the crosslinked foamable sheet. A heat-sensitive adhesive made of a copolymer (Nos. 3 to 6 are examples of this invention, No. 1
2, 7 to 9 are comparative examples of the present invention)
m was melt extruded, and this was heated in a hot air type vertical foaming furnace at 240 ° C. to foam.

The above ethylene-ethyl acrylate-maleic anhydride copolymer has a melt flow rate of 5
g / 10 min, melting point 101 ° C. ethylene-ethyl acrylate-maleic anhydride copolymer (trade name Bondine LX
4110: manufactured by Sumitomo Chemical Co., Ltd.) and melt flow rate 2
Ethylene-ethyl acrylate-maleic anhydride copolymer having a melting point of 80 ° C. (trade name: Bondine HX8141:
Sumitomo Chemical Co., Ltd.) was used.

Each of the crosslinked polyolefin foam sheets thus obtained had an apparent density of 0.04 g / cm ³ ,
The total thickness was about 2.3 mm and the thickness of the heat-sensitive adhesive layer was about 23 μm. The crosslinked polyolefin foam sheet was evaluated for adhesiveness to a wood-based substrate (adhesive strength at room temperature and heat resistant adhesiveness) by the following method. Table 1 shows the results.

<Adhesion at Room Temperature> A heat-sensitive adhesive layer of the above crosslinked polyolefin foam sheet is heated to 130 ° C., and this is heated to 90 ° C. A plate-shaped wood-based base material composed of a wood chip and a phenol resin ( It was vacuum-bonded to a particle board) and integrally molded, and the resulting molded body was peeled with fingers to evaluate the peeling adhesive strength at room temperature. Here, the case where material destruction occurs in the foamed sheet itself is indicated by ◯, and the case where the heat-sensitive adhesive layer is peeled from the wood-based substrate is indicated by x.

<Heat-resistant Adhesion> The heat-sensitive adhesive layer of the above crosslinked polyolefin foam sheet is heated to 130 ° C., and this is heated to 90 ° C. A plate-shaped wood-based base material composed of wood chips and a phenol resin ( Particle board) is vacuum-bonded and integrally molded, and the obtained molded body is cut into a width of 25 mm to prepare a strip-shaped test piece. The test piece is erected vertically, and is projected in advance on the upper end of the base material. Bend the above foamed sheet downward and attach a weight of 100 g to it.
The peel length after standing at 24 ° C. for 24 hours was measured to evaluate the creep adhesive strength at 80 ° C. Here, the peeling length is 5c
When it was less than m, it was evaluated as ○, and when it was 5 cm or more, it was evaluated as x.

[0034]

[Table 1]

[0035]

As described above, the crosslinked polyolefin resin foam of the present invention has a thermosensitive adhesive layer formed on at least one side of the crosslinked polyolefin foam, and the thermosensitive adhesive layer has a melt flow rate of 2 ~ 15g / 10
40 to 70% by weight of ethylene-ethyl acrylate-maleic anhydride copolymer having a melting point of 100 to 120 ° C., a melt flow rate of 15 to 23 g / 10 minutes, and a melting point of 60 to 85.
Since it comprises 60 to 30% by weight of ethylene-ethyl acrylate-maleic anhydride copolymer at 0 ° C., it has excellent thermoformability such as vacuum formability, good heat resistance, and excellent compatibility with base materials such as skin materials and core materials. Excellent heat adhesion.

In particular, the heat-sensitive adhesive layer adheres well to the cross-linked polyolefin foam, and at the temperature such that the bubbles of the foam do not collapse, for example, at a temperature of about 130 to 150 ° C., especially wood chips. It has good adhesiveness (peeling adhesive strength at room temperature) and heat resistant adhesiveness (creep adhesive strength at 80 ° C.) to a wood-based base material hardened with a phenolic resin.

Therefore, the crosslinked polyolefin resin foam of the present invention is particularly required to have heat resistant adhesiveness, and is used for automobiles in which a wood-based base material obtained by hardening wood chips with a phenol-based resin is used as a core material for ceilings and doors. Inner surface material,
It can be suitably used as a heat insulating cushioning material for instrument panels and the like.

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Claims (1)

[Claims] 1. A heat-sensitive adhesive layer is formed on at least one surface of a crosslinked polyolefin foam, and the heat-sensitive adhesive layer has a melt flow rate of 2 to 15 g / 10 minutes and a melting point of 100 to 120 ° C. ethylene. Ethyl acrylate-
It is characterized by comprising 40 to 70% by weight of maleic anhydride copolymer, 60 to 30% by weight of ethylene-ethyl acrylate-maleic anhydride copolymer having a melt flow rate of 15 to 23 g / 10 minutes and a melting point of 60 to 85 ° C. And a crosslinked polyolefin foam.