JPH05214143A - Polypropylene-based resin crosslinked foam - Google Patents

Abstract

PURPOSE:To obtain the subject foam having improved elongation at a high temperature, temperature dependence and bride during molding by crosslinking and expanding a fomable resin composition comprising a specific polypropylene- 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) 40-75 pts.wt. ethylene- propylene random copolymer having 3-7wt.% ethylene content and 130-145 deg.C melting point prepared by polymerization using a stereoregular catalyst, (ii) 5-40 pts.wt. ethylene-propylene-butene random copolymer having 1-7wt.% ethylene content, 1-7% butene content and 4-14wt.% total contents of ethylene and butene and 120-140 deg.C melting point prepared by polymerization using a stereoregular catalyst and (iii) 5-40 pts.wt. polyethylene-based resin having 105-135 deg.C melting point, (B) a thermal decomposition type blowing agent (e.g. azodicarbonamide) and (C) a crosslinking agent (e.g. divinylbenzene) 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 polypropylene-based resin crosslinked foam, and more specifically, it has improved elongation and tensile strength in the high temperature region 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 Examined Patent Publication No. 46-38716, Japanese Unexamined Patent Publication No. 59-191107, Japanese Examined Patent Publication No. 60-28552, Japanese Examined 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 elongation at high temperature, the temperature dependence, the bridge at the time of molding, and the polypropylene resin crosslinked foam which is excellent in the deep drawing moldability in the high temperature region. To provide.

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 polypropylene-based resin crosslinked foam obtained by crosslinking / foaming a foamable resin composition containing a polypropylene-based resin, a thermal decomposition type foaming agent and a crosslinking aid, The polypropylene resin is
(A) 40-75 parts by weight of an ethylene-propylene random copolymer polymerized using a stereoregular catalyst, having an ethylene content of 3-7% by weight and a melting point of 130-145 ° C.
(B) Polymerized using a stereoregular catalyst, the ethylene content is 1 to 7% by weight, and the butene content is 1 to 7% by weight.
And the total content of ethylene and butene is 4 to
14% by weight, 5 to 40 parts by weight of ethylene-propylene-butene random copolymer having a melting point of 120 to 140 ° C., and (c) 5 to 40 parts by weight of a polyethylene resin having a melting point of 105 to 135 ° C. (100 parts by weight in total) is provided, and a polypropylene resin crosslinked foam is provided.

One of the polypropylene resins used in the present invention, which will be described in detail below, is polymerized using a stereoregular catalyst and has an ethylene content of 3 to 7% by weight.
And is an ethylene-propylene random copolymer (resin a) having a melting point of 130 to 145 ° C. The preferable content of ethylene is 3.5 to 6% by weight. When the ethylene content is low and the melting point is too high, the elongation at high temperature is lowered, the deep drawability is deteriorated, and the tensile strength at high temperature is increased, so that a bridge is likely to be formed at the time of molding.

Another polypropylene resin used in the present invention is polymerized by using a stereoregular catalyst and has an ethylene content of 1 to 7% by weight and a butene content of 1 to 7%.
It is an ethylene-propylene-butene random copolymer (resin b) having a total content of ethylene and butene of 4 to 14% by weight and a melting point of 120 to 140 ° C. It is preferable that the content of ethylene is 2 to 5% by weight, the content of butene is 3 to 5% by weight, and the total content of ethylene and butene is 6 to 10% by weight.
If the content of ethylene and butene is low and the melting point is too high, the elongation at high temperature will decrease, the deep drawability will deteriorate, and the tensile strength at high temperature will increase, so bridges are likely to occur during molding. ..

The melt index (MI), molecular weight, molecular weight distribution and the like of the polypropylene resin (a) and the resin (b) are not particularly limited, but MI (AS
TM D1238) is usually 0.5 to 15, weight average molecular weight (Mw) is 180,000 to 290,000, and molecular weight distribution (Mw / M).
It is preferable that n) is 3.3 to 5.5.

In addition, in the resin (a) and the resin (b), the way ethylene or butene enters the polypropylene chain is preferably uniformly distributed in every portion, that is, a random copolymer. For example, if there are many ethylene blocks in the polypropylene chain, the melting point peaks will appear in two places, and as a result, the polypropylene molecular chain will become longer, and homopolypropylene with a partially higher melting point will be formed. It is not preferable because it will happen.

The polyethylene resin used in the present invention is
It is a polyethylene resin (resin c) having a melting point of 105 to 135 ° C., and examples thereof include low density polyethylene, medium density polyethylene, high density polyethylene, and linear low density polyethylene, but there is no particular limitation, but among these, Linear low density polyethylene is desirable.

The resin (a) has a mixing ratio of 4 for each resin component.
0-75 parts by weight, preferably 50-70 parts by weight, resin (b) 5-40 parts by weight, preferably 10-30 parts by weight, resin (c) 5-40 parts by weight, preferably 10-3.
0 parts by weight (total 100 parts by weight).

If even one of these resin components is lacking, the deep drawability deteriorates, and a bridge is likely to occur. If the amount of the resin (a) is too large, the impact resistance will be poor, if the amount of the resin (b) is too large, the heat resistance will be poor, and if the amount of the resin (c) is too large, the elongation at high temperature will be poor. 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 foaming by heating above the decomposition temperature,
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, azodicarbonamide (ADCA), oxybenzenesulfonyl hydrazide, azobisisobutyronitrile, barium azodicarboxylic acid, dinitrosopantamethylenetetramine, hydrazodicarbonamide, etc. can be heated. 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.

Examples of the crosslinking aid include polyfunctional monomers such as divinylbenzene (DVB), diallyl phthalate, ethylene glycol dimethacrylate, and trimethylolpropane triacrylate.
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. Further, various additives such as antioxidants, pigments, ultraviolet absorbers, and antioxidants can be added if necessary.

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.

[0020]

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 foam are as follows.

<Crosslinking degree> About 50 mg of foam is weighed and
After soaking in xylene at 20 ° C. for 24 hours, it is taken out, dried for 8 hours, weighed, and then the weight is divided by the weight of the original foam, multiplied by 100.

<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 drawing property> The far infrared heater was used to set the surface temperature of the foam to 150 to 160 ° C., and vacuum molding was performed using a cylindrical female die as shown in FIG.
Ratio (H / D) of depth (H) and diameter (D) at the time of molding
Displayed in. The larger this value is, the better the moldability is.

<Bridge Resistance> A pyramid mold (1) as shown in FIG. 2 was prepared and covered with a foam sheet, and the foam sheet was depressurized to bring the foam sheet into close contact with the mold. First, as shown in FIG. 3, a foam sheet (2) held by a clamp was heated from above and below by a heater (3), and then the mold was covered with the foam sheet as shown in FIG. .. Figure 5
As shown in Fig. 6, when voids (4) were generated in the corners, it was evaluated that the bridge resistance was poor, and when the foam sheet was in close contact with the mold as shown in Fig. 6, no voids were formed. It was evaluated that the bridge resistance was good. The evaluation was visually conducted in the following three stages. A: The foamed sheet was completely adhered to the mold. ◯: The foamed sheet was in close contact with the mold. X: Voids were generated in the corners.

Example 1 Polymerization with a stereoregular catalyst,
70% by weight of ethylene-propylene random copolymer (resin a) having an ethylene content of 3.6% and a melting point of 140 ° C., polymerized with a stereoregular catalyst, ethylene content of 3.0%, butene content of 4.0% , 10 parts by weight of ethylene-propylene-butene random copolymer (resin b) having a melting point of 126 ° C., and linear low-density polyethylene (LLDP) having a melting point of 120 ° C.
E: To 20 parts by weight of resin c), azodicarbonamide (A
65 mm by adding 10 parts by weight of DCA), 1 part by weight of antioxidant, and 3 parts by weight of divinylbenzene (DVB) as a cross-linking agent.
Melt-kneading was performed with a φ2 screw extruder to obtain a foamable sheet having a thickness of 1.0 mm. 2.0 Mrad on the resulting foamable sheet
After irradiating the electron beam of
Foamed at ℃, thickness 2.5mm, density 0.04g / cm
A foam of ³ was obtained.

Comparative Example 1 The same procedure as in Example 1 except that 70 parts by weight of the resin (a) and 30 parts by weight of the resin (c) of Example 1 were used as the resin components, and the thickness was 2.5 mm.
A foam having a density of 0.04 g / cm ³ was obtained. This foam did not have very good elongation at high temperature. Also, the bridge resistance was not good.

Example 2 50 parts by weight of a resin (a) having an ethylene content of 4.5% and a melting point of 138 ° C., an ethylene content of 3.0%, a butene content of 4.0% and a melting point of 129 ° C. ( b) The same procedure as in Example 1 except that 10 parts by weight of ADCA, 1 part by weight of antioxidant, and 3 parts by weight of DVB were added to 20 parts by weight of LLDPE (resin c) having a melting point of 122 ° C. and 30 parts by weight. 2.5 mm, density 0.04 g / cm ³
To obtain a foam. This foam was more excellent in deep drawability and bridge resistance than the foam of Example 1.

Example 3 As a resin component, 60 parts by weight of resin (a) having an ethylene content of 5.5% and a melting point of 143 ° C.,
Ethylene content 3.7%, butene content 4.4%, melting point 134 ° C. resin (b) 20 parts by weight, melting point 122 ° C. LL
The remains of using 20 parts by weight of DPE (resin c) were the same as in Example 1, and had a thickness of 2.5 mm and a density of 0.04.
A foam of g / cm ³ was obtained.

Example 4 Except for changing the compounding ratio of the resin components as shown in Table 1, the same procedure as in Example 1 was carried out.
A foam having a thickness of 2.5 mm and a density of 0.04 g / cm ³ was obtained. This foam was superior to the foam of Example 1 in bridge resistance.

[Comparative Example 2] The same procedure as in Example 1 was repeated except that the same resin as in Example 3 was used, the resin (b) was 40 parts by weight, and the resin (c) was not used. A foam having a thickness of 2.5 mm and a density of 0.04 g / cm ³ was obtained.
The foam had a soft feel to the touch and lacked flexibility.

[Example 5] The same resin as in Example 3 was used.
A foam having a thickness of 2.5 mm and a density of 0.04 g / cm ³ was obtained in the same manner as in Example 3 except that only the compounding ratio was changed as shown in Table 1. This foam was slightly inferior to the foam of Example 3 in bridging resistance and slightly inferior in elongation.

Example 6 Example 1 was repeated except that the cross-linking agent was 1 part by weight of trimethylolpropane triacrylate.
A sheet having a thickness of 1.0 mm was obtained in the same manner as in. After irradiating the obtained foamable sheet with an electron beam of 1.5 Mrad,
Foaming was performed at a temperature of 250 ° C. in a hot air circulation oven to obtain a foamed product having a thickness of 2.5 mm and a density of 0.04 g / cm ³ .

[Comparative Example 3] As a resin component, 50 parts by weight of a resin (a) having an ethylene content of 1.5% and a melting point of 149 ° C,
Except that 25 parts by weight of resin (b) having an ethylene content of 1.5%, butene content of 1.0%, a melting point of 148 ° C., and LLDPE (resin c) having a melting point of 120 ° C. were used,
Similar to Example 1, thickness 2.5 mm, density 0.04
A foam of g / cm ³ was obtained. This foam had a large difference between the elongation at 140 ° C. and the elongation at 160 ° C., and was also poor in bridge resistance.

COMPARATIVE EXAMPLE 4 Except that the same kind of resin as in Example 3 was used, except that the resin (a) was not used and 70 parts by weight of the resin (b) and 30 parts by weight of the resin (c) were used. In the same manner as in Example 1, the thickness was 2.5 mm and the density was 0.04 g / cm ^3.
To obtain a foam. This foam had a small temperature dependence at 140 to 160 ° C., but had a small absolute value and poor bridging resistance. The results are collectively shown in Table 1.

[0035]

[Table 1]

[0036]

EFFECTS OF THE INVENTION According to the present invention, there is provided a polypropylene resin crosslinked foam which is improved in elongation at high temperature, temperature dependency and bridge at the time of molding and is excellent in deep drawability in a high temperature region. .. The polypropylene resin crosslinked foam of the present invention is particularly suitable as a vehicle member.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a mold used for measuring the deep drawability of a foam.

FIG. 2 is a diagram illustrating a mold used for measuring the bridging resistance of a foam.

FIG. 3 is a diagram illustrating a method for heating a foamed sheet.

FIG. 4 is a diagram illustrating a method of covering a mold with a heated foam sheet.

FIG. 5 is a diagram illustrating a bridge generation state.

FIG. 6 is a diagram illustrating that the foam sheet is in close contact with the mold and has no bridge.

[Explanation of symbols]

 1 Pyramid-shaped mold 2 Foamed sheet 3 Heater 4 Gap (bridge)

Claims (1)

[Claims] 1. A polypropylene resin crosslinked foam obtained by crosslinking and foaming a foamable resin composition containing a polypropylene resin, a thermal decomposition type foaming agent, and a crosslinking aid, wherein the polypropylene resin is a solid (a) solid. Polymerized using an ordered catalyst, ethylene content is 3 to 7% by weight, and melting point is 1.
40-75 parts by weight of an ethylene-propylene random copolymer having a temperature of 30 to 145 ° C., (b) is polymerized using a stereoregular catalyst, the content of ethylene is 1 to 7% by weight, and the content of butene is 1 to 1. 7% by weight, the total content of ethylene and butene is 4 to 14% by weight, and the melting point is 120 to 1
5 to 40 parts by weight of an ethylene-propylene-butene random copolymer at 40 ° C, and (c) a melting point of 105 to 135 ° C.
The polypropylene-based resin crosslinked foam containing 5 to 40 parts by weight of the polyethylene resin (total 100 parts by weight).