JPH05214144A - Polypropylene-based resin crosslinked foam - Google Patents

Abstract

PURPOSE:To obtain the subject foam having improved elongation and tensile force in a high temperature range, excellent moldability and processability by crosslinking and foaming an expandable resin composition comprising a specific polyolefin-based resin, a thermal decomposition type blowing agent and a crosslinking auxiliary. CONSTITUTION:A fomable resin composition comprising (A) 100 pts.wt. total amount of a polypropylene-based resin composed of (i) 10-60 pts.wt. polypropylene-based resin (e.g. ethylene-propylene block copolymer having two or more total peaks of one peak in 100-135 deg.C and one peak in 135-175 deg.C prepared by polymerization using a stereoregular catalyst, (ii) 10-80 pts.wt. ethylene- propylenebutene random copolymer having 1-10wt.% ethylene content and 125-160 deg.C melting point prepared by polymerization using a stereoregular catalyst and (iii) 10-80 pts.wt. polyethylene-based resin (preferably linear low-density polyethylene), (B) a thermal decomposition type blowing agent and (C) a crosslinking agent is crosslinked and expanded to give the objective foam.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyolefin resin cross-linked foam, and more specifically, it has improved elongation and tensile strength in the high temperature range and is excellent in moldability even for complex and deep shapes. It relates to a resin crosslinked foam.

[0002]

2. Description of the Related Art A polypropylene-based resin is added with a thermal decomposition type foaming agent and a crosslinking aid such as divinylbenzene or ethylene glycol dimethacrylate, which is crosslinked by being irradiated with an organic peroxide or ionizing radiation, and heated. It is a known technique to obtain a crosslinked foam by firing (Japanese Patent Publication No. 46-38716, Japanese Patent Publication No. 59-191107, Japanese Patent Publication No. 60-28552, Japanese Patent Publication No. 1-272641, etc.).

Polypropylene resin crosslinked foam has a high melting point among polyolefin resin crosslinked foams,
Since it has excellent elongation at 110 to 120 ° C, it is widely used in various fields including vehicle-related products. However, the conventional polypropylene-based resin crosslinked foam has
There is a problem that elongation rapidly decreases in a high temperature range of 0 to 160 ° C, and shape retention is poor when molding at a high temperature. Further, the polypropylene-based resin crosslinked foam has a high tensile strength at high temperature, and has a problem that a bridge (gap) occurs when it is molded into a complicated shape.

In the recent field of foam molding, for example, vehicle interior materials are required to be processed into complicated shapes such as doors, instrument panels and console boxes, and deep drawing is required. Further, due to rapid heating for improving productivity and accompanying increase in processing temperature, extensibility (elongation) particularly at 140 to 160 ° C. is required.
However, the conventional polypropylene-based resin cross-linked foam has a large temperature dependency and is insufficient in these required properties.

[0005]

The object of the present invention is to improve the extensibility at high temperature, particularly the extensibility at 140 to 160 ° C., the temperature dependency is small, and the polyolefin resin is excellent in deep drawability. To provide a crosslinked foam.

As a result of intensive studies, the inventors of the present invention used a blend of two kinds of polypropylene-based resin polymerized using a stereoregular catalyst and a polyethylene-based resin as a resin component, and cross-linked them by a conventional method. It was found that the above-mentioned object can be achieved by firing, and the present invention has been completed based on the findings.

[0007]

According to the present invention, a polyolefin resin crosslinked foam obtained by crosslinking and foaming a foamable resin composition containing a polyolefin resin, a thermal decomposition type foaming agent and a crosslinking aid, The polyolefin resin is
(1) Polymerized with a stereoregular catalyst to obtain at least 1
One between 00 ℃ and less than 135 ℃, and 135 ℃ or more 1
10 to 60 parts by weight of a polypropylene resin having a total of two or more melting point peaks at 75 ° C. or lower, (2) polymerized using a stereoregular catalyst, and having an ethylene content of 1 to 1
10% by weight and 10 to 80 parts by weight of ethylene-propylene random copolymer having a melting point of 125 to 160 ° C., and (3) 10 to 80 parts by weight of polyethylene resin (total 100 parts by weight). A cross-linked foamed polyolefin resin is provided.

The present invention will be described in detail below. The polypropylene resin (1) used in the present invention is polymerized by a gas phase method, a bulk polymerization method or the like using a stereoregular catalyst, and at least one resin is present between 100 ° C. and 135 ° C. and 135 ° C. or higher and 175 ° C. It is a polypropylene resin having a total of two or more melting point peaks between the following:
This melting point peak is 1 by a differential scanning calorimeter (DSC).
It is an endothermic peak obtained when the temperature is raised at a rate of 0 ° C./min.

The polypropylene resin (1) is a resin represented by an ethylene-propylene block copolymer, and has two kinds of melting point peaks of an ethylene block portion and a propylene block portion. Further, what is copolymerized with propylene is not limited to ethylene, butene,
Octene, 4-methylpentene, etc. may be used.

The comonomer component of the polypropylene resin (1) is usually 3 to 30% by weight, preferably 7 to 15% by weight. The lower melting point peak is preferably 120-
130 ° C., the higher melting point is preferably 150-
165 ° C. When the lower melting point is less than 100 ° C, the heat resistance of the foam becomes insufficient, and the higher melting point is 175
If the temperature exceeds ℃, extrusion moldability will be impaired, and the tensile strength of the foam at high temperature will be high, resulting in poor moldability. Polypropylene resin (1) melt index (M
I; ASTM D1238) is usually about 0.5 to 15.

The polypropylene resin (2) is an ethylene-propylene random copolymer which is polymerized by using a stereoregular catalyst and has an ethylene content of 1 to 10% by weight and a melting point of 125 to 160 ° C. The ethylene content is preferably 2 to 6% by weight, and the melting point is preferably 1
30 to 150. Polypropylene resin (2) M
I is usually about 0.5 to 15.

The polyethylene resin (3) is a low density polyethylene, a medium density polyethylene, a high density polyethylene,
There is no particular limitation as long as it is a polyethylene or ethylene-based copolymer such as linear low-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-butene copolymer and the like. Polyethylene resin (3) usually has a melting point of 105.
MI is about 0.5 to 15 at ˜135 ° C. Among these, density 0.910 to 0.925, melting point 118 to 1
23 ° C. linear low density polyethylene is preferred.

The resin (1) has a mixing ratio of 1 for each resin component.
0-60 parts by weight, preferably 20-50 parts by weight, resin (2) 10-80 parts by weight, preferably 20-50 parts by weight, resin (3) 10-80 parts by weight, preferably 30-
40 parts by weight (total 100 parts by weight). If even one of these resin components is lacking, the elongation at high temperature decreases, the tensile strength at high temperature increases, and the deep drawability deteriorates. Especially when heat resistance is required, resin (1) and resin (2)
It is preferable that the total amount thereof is 60 to 70% by weight.

A thermal decomposition type foaming agent, a crosslinking aid, and various additives as required are added to the above resin components to produce a crosslinked foam by a known method for producing a polyolefin resin crosslinked foam.

Specifically, a mixture containing a polypropylene resin, a thermal decomposition type foaming agent, a cross-linking aid and the like is molded into a predetermined shape such as a sheet and irradiated with ionizing radiation to cross-link, and then the foaming agent Method of heating above the decomposition temperature to fire,
Alternatively, a polypropylene resin, a pyrolytic foaming agent, an organic peroxide, a mixture containing a cross-linking aid, etc. is molded into a predetermined shape such as a sheet and heated to a temperature above the decomposition temperature of the organic peroxide and the foaming agent. Examples include a method of crosslinking and foaming. From the viewpoint of moldability, the irradiation crosslinking method using ionizing radiation is preferable.

As the thermal decomposition type foaming agent, for example, heating of azodicarbonamide (ADCA), oxybenzenesulfonyl hydrazide, azobisisobutyronitrile, barium azodicarboxylic acid, dinitrosopantamethylenetetramine, hydrazodicarbonamide, etc. A compound is used that decomposes to generate a gas when exposed. The addition ratio of the thermal decomposition type foaming agent can be appropriately determined according to the desired expansion ratio, but usually 100 parts by weight of the resin component,
It is 2 to 50 parts by weight, preferably 5 to 30 parts by weight.

As the crosslinking aid, for example, divinylbenzene (DVB), diallyl phthalate, ethylene glycol dimethacrylate, trimethylolpropane triacrylate (TMPT), 1,9-nonanediol dimethacrylate (1,9ND) and the like are used. Mention may be made of functional monomers. The addition ratio of these crosslinking aids is usually 1 to 10 parts by weight with respect to 100 parts by weight of the resin component.

If necessary, various additives such as, for example,
Antioxidants, anti-aging agents, pigments, UV absorbers, anti-aging agents and the like can be added.

The mixture is melted and kneaded at a temperature not higher than the decomposition temperature of the foaming agent with an extruder (single-screw, twin-screw), Banbury mixer, kneader, etc., and extruded into a foamable sheet.
The obtained foamable sheet is irradiated with ionizing radiation such as electron rays, α rays, β rays, and γ rays to be crosslinked, and further, this is treated with a foaming agent in a hot air circulation oven, a salt bath or a metal bath. A polypropylene resin crosslinked foam is obtained by foaming at a temperature equal to or higher than the decomposition temperature.

The ionizing radiation is preferably an electron beam, and the irradiation dose is usually 0.1 to 50 Mrad, preferably 0.5 to 20 Mrad. It is preferable to adjust the irradiation dose, the addition amount of the crosslinking aid, and the like such that the degree of crosslinking (gel fraction) of the obtained crosslinked foam is in the range of 20 to 70%. If the degree of crosslinking is too small, the heat resistance will decrease, and if it is too large, the flexibility such as elongation will decrease.

[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 method for measuring the physical properties of the foam is as follows. <Crosslinking degree> About 50 mg of foam is weighed, immersed in xylene at 120 ° C for 24 hours, taken out, dried for 8 hours, weighed, and divided by the weight of the first foam. Multiply by 100 and calculate.

<Elongation and tensile strength> After being left for 5 minutes in a heat-retaining box whose temperature condition was set at 140 ° C. or 160 ° C., it was measured by a tensile tester. Based on JIS K-6767. M
D: vertical direction, TD: horizontal direction.

<Deep drawability> The far infrared heater was used to set the surface temperature of the foam to 150 to 160 ° C., vacuum molding was performed using a cylindrical female die, and the depth (H ) And the diameter (D) (H / D). The larger this value is, the better the moldability is.

<PVC Peel Strength> The foam was corona-treated, laminated with PVC and an adhesive, and allowed to stand for 24 hours, then cut into 25 mm strips to prepare test pieces, and the peel strength was measured.

[Examples 1 to 3, Comparative Examples 1 to 3] Polypropylene resin (P
P1), polypropylene-based resin (PP2), and polyethylene-based resin (PE) were blended as shown in Table 1 and Table 2, respectively, and 0.5 parts by weight of a phenol-based antioxidant was added to 100 parts by weight of the resin component. Parts, sulfur antioxidant 1.0
Parts by weight, azodicarbonamide (ADC) as a foaming agent
A) 10 parts by weight, divinylbenzene (DV as a cross-linking agent
B) 6 parts by weight was added, and a resin sheet having a thickness of 1.0 mm was extruded at a resin temperature of 180 ° C. or lower with a 65 mmφ single screw extruder.

The obtained foamable sheet was irradiated with an electron beam irradiator at 3.0 Mrad to be crosslinked, and then was blown with hot air at 300 ° C. in a vertical foaming furnace to be foamed. A foam having a thickness of 04 g / cm ³ and a thickness of 2.5 mm was obtained.
The physical properties of the obtained foam were measured, and the results are shown in Tables 1 and 2. Elongation of Examples 1 to 3 (140 ° C, 160 ° C)
Was better than Comparative Examples 1 to 3, and the surface of the foam of Comparative Example 3 was rough.

[Examples 4 and 5, Comparative Examples 4 and 5] A polypropylene resin (P
P1), polypropylene resin (PP2), and polyethylene resin (PE) were blended as shown in Table 1 and Table 2, respectively, and 0.5 parts by weight of phenol antioxidant, sulfur antioxidant 1. 0 parts by weight, 10 parts by weight of ADCA, and 2.0 parts by weight of trimethylolpropane triacrylate (TMPT) as a cross-linking agent were added, and the resin temperature was set to 180 ° C. or less with a 120 mmφ co-rotating twin-screw extruder to a thickness of 1.0.
A mm foamable sheet was extruded.

The obtained foamable sheet was irradiated with 2.0 Mrad with an electron beam irradiator to be crosslinked, and then was blown with hot air at 300 ° C. in a vertical foaming furnace to be foamed. The density was 0.04 g. A foam having a thickness of / cm ³ and a thickness of 2.5 mm was obtained.
The physical properties of the obtained foam were measured, and the results are shown in Tables 1 and 2.

[Examples 6 to 8 and Comparative Examples 6 to 8] A polypropylene-based resin having the physical properties shown in Tables 1 and 2 (P
P1), polypropylene-based resin (PP2), and polyethylene-based resin (PE) were blended as shown in Table 1 and Table 2, respectively (however, in Comparative Examples 6 to 8 as PP1, homopolypropylene having a melting point of 163 ° C.). It was used.
As PE, low-density polyethylene was used in Example 6 and Comparative Example 6, high-density polyethylene in Example 7 and Comparative Example 7, and linear low-density polyethylene was used in Example 8 and Comparative Example 8. ).

0.5% phenolic antioxidant in the above formulation
Parts by weight, sulfur-based antioxidant 1.0 parts by weight, ADCA10
Parts by weight, 3 parts by weight of 1,9-nonanediol dimethacrylate (1,9ND) as a cross-linking agent, and a resin temperature of 180 ° C. or less with a 65 mmφ single-screw extruder to a thickness of 1.0 m.
m foamable sheet was extruded.

The obtained foamable sheet was irradiated with an electron beam irradiator at 2.7 Mrad to be crosslinked, and then foamed in a vertical foaming furnace to have a density of 0.04 g / cm ³ and a thickness of 2. A 5 mm foam was obtained. The physical properties of the obtained foam were measured, and the results are shown in Tables 1 and 2. The foams of Examples 6 to 8 were subjected to corona treatment, then laminated with PVC and an adhesive, left for 24 hours, and then cut into 25 mm strips to obtain test pieces, and the peel strength was measured. The foam is
The material was destroyed in all cases, but the peel strength was as shown in Table 1.

[0033]

[Table 1]

[0034]

[Table 2]

[0035]

According to the present invention, at high temperature (especially 140-
It is possible to provide a polyolefin-based foam having good deep drawability by improving the elongation at 160 ° C.) and temperature dependence. The foam of the present invention is particularly suitable as an interior material for vehicles.

Claims (1)

[Claims] 1. A polyolefin resin crosslinked foam obtained by crosslinking and foaming a foamable resin composition containing a polyolefin resin, a thermal decomposition type foaming agent and a crosslinking aid, wherein the polyolefin resin is (1) three-dimensional. Polymerized using a regular catalyst and at least 100 ° C. and less than 135 ° C.
And a polypropylene resin having a total of two or more melting point peaks between 135 ° C and 175 ° C.
60 parts by weight, (2) polymerized using a stereoregular catalyst,
Ethylene content is 1-10% by weight, melting point 125-1
60 ° C ethylene-propylene random copolymer 10
80 parts by weight, and (3) polyethylene resin 10-80
A polyolefin resin crosslinked foam comprising 100 parts by weight (total 100 parts by weight).