JPH05247247A - Crosslinked polyolefin resin foam - Google Patents

Abstract

PURPOSE:To provide the title foam having high skin strengths, excellent mechanical properties such as tensile strength, elongation and compressive strength, and a beautiful surface. CONSTITUTION:The title foam is one prepared by crosslinking and foaming a foamable resin composition comprising a polyolefin resin and a heat- decomposable blowing agent. The polyolefin resin comprises 10-40 pts.wt. linear low-density polyethylene prepared by copolymerizing ethylene with a 4 C alpha- olefin, 10-40 pts.wt. linear low-density polyethylene prepared by copolymerizing ethylene with a 6C alpha-olefin, and 20-80 pts.wt. other polyolefin resins.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyolefin resin crosslinked foam, and more particularly to a polyolefin resin crosslinked foam having excellent mechanical properties such as skin strength, tensile strength, elongation and compressive strength and having a beautiful surface. .. INDUSTRIAL APPLICABILITY The polyolefin resin cross-linked foam of the present invention is suitable for automobile interior moldings, folded plate heat insulating materials, tape bases and the like.

[0002]

2. Description of the Related Art Conventionally, polyolefin resin crosslinked foams have been used in a wide range of fields as heat insulating materials, cushioning materials and the like. In particular, in automotive applications, it is used as a heat insulating material and an interior material for ceilings, doors, instrument panels, cooler covers and the like.

[0003] In automobile interior moldings and the like, polyolefin resin crosslinked foams are usually obtained by laminating a skin material such as a soft polyvinyl chloride sheet on the surface thereof by an adhesive method or an extruder to obtain a composite material. The composite sheet is set on an aggregate such as a polypropylene resin sheet which is heated by an infrared heater or the like to be in a molten state and is pressed to obtain a molded product. Therefore, the polyolefin resin crosslinked foam is required to have high skin strength, mechanical strength, thermoformability and the like.

Further, the polyolefin resin crosslinked foam is required to have good heat insulating properties and cushioning properties. Therefore, it is preferable that the foaming ratio is relatively high. However, if the expansion ratio of the skin layer is too high, the skin strength is lowered and air bubbles are generated by the breakage of air bubbles in the skin layer during laminating, causing so-called "blister".

Therefore, the skin strength of the polyolefin resin crosslinked foam is generally required to be 1.0 kg / 25 mm or more. When the skin strength is lower than this value, as described above, the air bubbles in the skin layer are broken and "blister" occurs when the film is attached to the skin material. In order to set the skin strength of the polyolefin resin cross-linked foam to 1.0 kg / 25 mm or more, if the expansion ratio is lowered, the heat insulating property is impaired.

Conventionally, a method of improving mechanical properties by blending a linear low density polyethylene with a polyolefin resin has been proposed (Japanese Patent Publication No. 2-57576).
No., Japanese Patent Publication No. 2-57577, etc.). However, 1.0
In order to obtain a skin strength of kg / 25 mm or more, 70 parts by weight of a linear low density polyethylene (hereinafter abbreviated as C ₄ -LLDPE) obtained by copolymerizing ethylene with an α-olefin having 4 carbon atoms is used. It is necessary to mix the above proportions. In addition, linear low-density polyethylene obtained by copolymerizing ethylene with an α-olefin having 6 carbon atoms (hereinafter referred to as C ₆ -LLD
When PE is used, it is necessary to mix it in a proportion of 40 parts by weight or more.

However, a polyolefin resin composition containing such a high proportion of linear low-density polyethylene generates a large amount of heat during kneading, and therefore a thermal decomposition type foaming agent and a foaming auxiliary agent are added for foaming properties. Primary foaming occurs at the stage of preparing a foamable sheet before foaming using a resin composition. If the foaming aid is not added, the decomposition temperature of the thermal decomposition type foaming agent cannot be lowered, so a large amount of heat must be added when the foamable sheet is heated and foamed. The surface is so rough that a beautiful foam cannot be obtained.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a polyolefin resin crosslinked foam which has a high skin strength, excellent mechanical properties such as tensile strength, elongation and compressive strength and has a beautiful surface. As a result of diligent research, the present inventors have combined C ₄ -LLDPE and C ₆ -LLDPE in a specific ratio and blended them into a polyolefin resin, so that the skin strength is 1.0 kg / 25 mm or more even at a high expansion ratio. It has been found that a foam having a high cost and capable of adding a foaming auxiliary agent and having a beautiful surface can be obtained, and based on this finding, the present invention has been completed.

[0009]

According to the present invention, there is provided a polyolefin resin crosslinked foam obtained by crosslinking and foaming a foamable resin composition containing a polyolefin resin and a thermal decomposition type foaming agent. Resin is (A)
10 to 40 parts by weight of linear low-density polyethylene obtained by copolymerizing ethylene with an α-olefin having 4 carbon atoms, and (B) linear low-density polyethylene 10-40 obtained by copolymerizing ethylene with an α-olefin having 6 carbon atoms A polyolefin-based resin crosslinked foam comprising 20 parts by weight of (C) and 20 to 80 parts by weight of another polyolefin resin is provided.

The present invention will be described in detail below. For polyolefin resins such as low density polyethylene, C ₆ -LL
By incorporating DPE, a crosslinked foam having improved mechanical properties can be obtained. However, if a large amount of C ₆ -LLDPE is blended in order to increase the skin strength, the amount of heat generated during molding of the foamable sheet increases, and when a foaming aid is added, primary foaming occurs. Therefore, C ₆ -LLDPE
The compounding ratio is kept as low as 10 to 40 parts by weight, and the heat generation during kneading is suppressed while the mechanical properties are improved to some extent.

If the proportion of C ₆ -LLDPE is small,
Although the effect of improving the skin strength and other mechanical properties is small, C ₄ -LLDPE is added in an amount of 10 to 40 parts by weight in order to supplement the effect. When C ₄ -LLDPE is blended in a large amount, heat generation during kneading becomes large, but when a small amount is blended, heat generation is smaller than that of C ₆ -LLDPE.

As a result, even if the expansion ratio is increased to about 30 times, a polyolefin resin crosslinked foam having a skin strength of 1.0 kg / 25 mm or more and other excellent mechanical properties can be obtained. Since the polyolefin resin composition having such a composition generates a relatively small amount of heat during kneading, even if a foaming auxiliary agent that acts to lower the decomposition temperature of the heat-decomposable foaming agent is added, the foamable sheet is molded. No primary foaming. Further, since a foaming aid can be added to lower the heating temperature at the time of heat foaming, a crosslinked foam having a beautiful surface can be obtained. Furthermore, C ₄ -L with high density
Since it contains LDPE, it has a feeling of rigidity and is easy to handle during molding.

Examples of α-olefins having 4 carbon atoms include 1-butene and 2-butene, and examples of α-olefins having 6 carbon atoms include 1-hexene and 4-methyl-1-pentene. In addition, C ₄ -LLDPE and C ₆ -L
A commercially available product can be used as the LDPE.

Other polyolefin resins include
For example, low density polyethylene (LDPE), medium to high density polyethylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl chloride copolymer, ethylene-acrylate copolymer, polypropylene, butene-propylene. Examples thereof include copolymers.

As the foaming agent, a generally used thermal decomposition type foaming agent can be used. The thermal decomposition type foaming agent is one that generates a decomposition gas by heating, and specifically, azodicarbonamide, benzenesulfonyl hydrazide, dinitrosopentamethylenetetramine, azobisisobutyronitrile, barium azodicarboxylate,
Examples include toluenesulfonyl hydrazide and 4,4-oxybis (benzenesulfonyl hydrazide). These may be used alone or in combination of two or more. The blending amount of these thermal decomposition type foaming agents is usually 1 to 50 parts by weight, preferably 5 to 25 parts by weight with respect to 100 parts by weight of the total amount of the resin components, and depending on the desired expansion ratio,
The blending amount can be appropriately selected.

In the present invention, since the heat generation during kneading can be suppressed to a relatively low level, it is possible to add a foaming auxiliary which can lower the decomposition temperature of the thermal decomposition type foaming agent to 180 ° C. or lower. Examples of the foaming aid include calcium stearate, zinc stearate, zinc oxide, urea compounds, lead compounds and the like. Addition of these foaming aids enables foaming at a relatively low temperature, resulting in fine bubbles.
A foam with a beautiful surface is obtained.

As the crosslinking aid, for example, a polyfunctional monomer represented by divinylbenzene, trimethylolpropane triacrylate, ethylene glycol dimethacrylate, a polymer having an unsaturated double bond represented by 1.4-polybutadiene, etc. May be added. The mixing ratio of these crosslinking aids is about 1 to 20 parts by weight with respect to 100 parts by weight of the resin component.

The expandable resin composition of the present invention may further contain an antioxidant, an antioxidant, a UV absorber, and
Antistatic agents, pigments and the like can be added.

The polyolefin resin foamable resin composition of the present invention is prepared by pyrolyzing each component by using a general-purpose kneading device such as a single screw extruder, a twin screw extruder, a Banbury mixer, a kneader mixer and a roll. It is usually melt-kneaded at a temperature lower than the decomposition temperature of the agent to form a sheet. The obtained foamable sheet is irradiated with ionizing radiation such as α-rays, β-rays, γ-rays and electron rays to be crosslinked. The irradiation dose of ionizing radiation is
Usually 0.1 to 50 Mrad, preferably 0.5 to 20 M
It is rad. Next, the crosslinked foamable sheet is heated to a temperature equal to or higher than the decomposition temperature of the thermal decomposition type foaming agent to foam.

Incidentally, an organic peroxide may be added to the foamable resin composition to chemically crosslink. In this case, usually
When the foamable sheet is heated and foamed in a foaming furnace, the organic peroxide is decomposed and crosslinked.

[0021]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

The methods for measuring the physical properties of the foams obtained in Examples and Comparative Examples are as follows. <Expansion Ratio> A foam was cut into a 10 cm square, the weight and the thickness thereof were measured, and the volume was calculated from the thickness, and the volume / weight was calculated. <Tensile strength, Elongation> After leaving the foam for 5 minutes in a heat insulation box set at 20 ° C or 120 ° C, J
It was measured according to IS K-6767. MD: vertical direction, TD: horizontal direction. <Compressive strength, etc.> According to JIS K-6767. ZD:
Thickness direction. <Episode strength> A cloth tape having a width of 25 mm was attached to the surface of the foam, and a 4 kg roll was reciprocated twice on the tape, and the tape and the epidermis were peeled off by a tensile tester, and the strength at that time was measured. <Bending rigidity> Using a taper type stiffener tester,
The initial stiffness was measured. <Heat dimensional change> The dimensional change rate (%) after standing for 22 hours at 100 ° C was measured. <Vacuum forming maximum drawing ratio> The foam is heated with a far-infrared heater, vacuum forming is performed using a cylindrical female die, and the ratio (H / D) of the depth (H) and the diameter (D) at the time of forming is formed. Displayed in D). The larger this value is, the better the moldability is.

[Example 1, Comparative Examples 1 to 3] Density 0.92
40 parts by weight of low density polyethylene (LDPE) of 0, C ₄
-LLDPE 30 parts by weight, C ₆ -LLDPE 30 parts by weight, azodicarbonamide 12 parts by weight as a foaming agent, and calcium stearate (Ca-S as a foaming aid).
t) is blended and the thickness is 1.0 mm and the width is 400 mm with an extruder.
Was extruded. The obtained foamable sheet was irradiated with an electron beam irradiator at a dose of 3.8 Mrad to be crosslinked, and then continuously passed through a hot air oven at 200 ° C. to foam (Example 1).

For comparison, crosslinked foams were obtained in the same manner as in Example 1 except that the formulation and irradiation dose shown in Table 1 were used (Comparative Examples 1 to 3). The results are collectively shown in Table 3.

Further, in order to see the effect of the foaming aid, Table 2
As shown in, the foaming sheet was extruded in the same manner as in Example 1 and Comparative Examples 1 to 3 without changing the type of foaming aid or adding it, and the presence or absence of air bubbles (primary foaming) at that time was confirmed. The results are shown in Table 2.

[0026]

[Table 1]

[0027]

[Table 2] (Footnote) Zn-St: Zinc stearate Ca-St: Calcium stearate ◯: No primary foaming, ×: Primary foaming.

[0028]

[Table 3]

As can be seen from Table 2, the foamable resin composition of the present invention has a primary foaming property at the time of molding the foamable sheet even when the foaming auxiliary agent is added to lower the foaming temperature of the thermal decomposition type foaming agent. As a result, a crosslinked foam having fine bubbles and a beautiful surface can be obtained. Further, it can be seen from Table 3 that the crosslinked foamed product of the present invention has a skin strength of 1.0 kg / 25 mm or more and is excellent in other mechanical properties and moldability.

[0030]

According to the present invention, it is possible to provide a crosslinked foam having a high skin strength, excellent mechanical properties, fine cells, and a beautiful surface. Furthermore, dense C ₄
Since -LLDPE is blended, the crosslinked foam of the present invention has a rigidity and is easy to handle during processing.

Claims (1)

[Claims] 1. A polyolefin resin crosslinked foam obtained by crosslinking and foaming a foamable resin composition containing a polyolefin resin and a thermal decomposition type foaming agent, wherein the polyolefin resin comprises (A) ethylene and a carbon number. Linear low-density polyethylene 10 to 40 copolymerized with α-olefin of 4
Parts by weight, (B) 10 to 40 parts by weight of linear low density polyethylene obtained by copolymerizing ethylene with an α-olefin having 6 carbon atoms, and (C) other polyolefin resin 20 to 80
A polyolefin resin crosslinked foam comprising a part by weight.