JP2002332371A - Polyolefin resin foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyolefin resin foam having high flexibility, good heat resistance, excellent formability, excellent adhesion to a skinning material, and a beautiful appearance. SOLUTION: This foam is prepared by crosslinking and foaming a polyolefin resin composition comprising 100 pts.wt. resin matrix comprising 30-100 wt.% polypropylene resin comprising structural units derived from propylene and structural units derived from an α-olefin other than propylene and having a content of the α-olefin of 15-70%, a weight-average molecular weight/number- average molecular weight ratio of 2-8, and a melt index(MI) of 0.1-10 g/min and 0-70 wt.% polypropylene resin comprising structural units derived from propylene and structural units derived from an α-olefin other than propylene and having a content of the α-olefin of 1-15 wt.%, a weight-average molecular weight/number-average molecular weight ratio of 2-8, and a melt index(MI) of 0.1-10 g/min.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyolefin resin foam, and more particularly, to flexibility, heat resistance,
The present invention relates to a crosslinked polyolefin-based resin foam having excellent mechanical strength and capable of secondary processing of a complicated shape.

[0002]

2. Description of the Related Art Polyolefin resin foams are generally excellent in flexibility, light weight and heat insulation, and have been conventionally used as interior materials for vehicles such as ceilings, doors and instrument panels.

[0003] These interior materials are usually formed into a predetermined shape by subjecting a sheet-like polyolefin resin foam to secondary processing by vacuum molding, compression molding or the like. The polyolefin-based resin foam is generally used as a laminate in which a sheet of a polyvinyl chloride resin, a sheet of a thermoplastic elastomer, a natural or artificial cloth, and a skin material such as leather are bonded.

[0004] In recent compression molding such as vacuum molding and stamping molding of foams, a processing temperature is set to a high temperature of 120 to 200 ° C in order to improve productivity, and deep drawing molding is performed to form a complicated shape. Therefore, polyolefin resin foams are required to have good moldability at high temperatures.

[0005] In addition, the interior of automobiles is required to have a good touch and feel, and the flexibility of interior materials is strongly demanded in pursuit of safety.

[0006] Originally, a polyethylene resin foam is excellent in flexibility but insufficient in heat resistance, so that it is not suitable for molding at high temperatures. On the other hand, the polypropylene-based resin foam has heat resistance but is less flexible than the polyethylene-based resin.

Therefore, conventionally, efforts have been made to impart heat resistance and flexibility by crosslinking and foaming a polypropylene-based resin and a polyethylene-based resin, and to improve moldability at high temperatures.

[0008] However, when such a laminate is integrally molded with a high-pressure high-temperature resin such as compression molding, a problem is that the foam is extremely compressed in a portion where pressure is strongly applied. Because part of the foam melts into the base resin due to contact with the molten base resin, the flexibility originally possessed by the foam may be impaired, and the foam may become very hard. There were many.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a combination of high flexibility and good heat resistance, excellent secondary moldability, and excellent adhesion to the skin material as described above. An object of the present invention is to provide a beautiful polyolefin resin foam.

The present inventors have conducted intensive studies in order to solve the above-mentioned problems of the prior art. As a result, polypropylene having a specific melt index as a resin component, a specific amount of α-olefin other than propylene, and a specific amount of copolymerized polypropylene. It has been found that the above object can be achieved by crosslinking and foaming using a system resin, a polyfunctional monomer, and an organic pyrolytic foaming agent.

The resin composition containing the resin component, the polyfunctional monomer, and the organic pyrolytic foaming agent can be uniformly and efficiently cross-linked by irradiating ionizing radiation. . When the foam is heated and foamed, a polyolefin-based resin foam having excellent heat resistance, flexibility, secondary workability, and adhesion to a skin material and having a beautiful appearance can be obtained.

[0012]

According to the present invention, (1)
Propylene and an α-olefin other than propylene as a constituent unit, the α-olefin content is 15 to 70% by weight, the weight average molecular weight / number average molecular weight is 2 to 8,
Melt index (hereinafter abbreviated as “MI”: ASTM
D-1238) 0.1 g to 10 g / 1
30 to 100% by weight of polypropylene resin which is 0 minutes
And (2) propylene and an α-olefin other than propylene as constituent units, and the α-olefin content is 1 to 15
% By weight, and the weight average molecular weight / number average molecular weight is 2 to 8
And a melt index of 0.1 g to 10 g / 10
100 parts by weight of a resin matrix composed of 0 to 70% by weight of a polypropylene resin,
5 to 10 parts by weight and (4) an organic pyrolytic foaming agent 1 to 5
A polyolefin-based resin foam is provided, which is obtained by molding a polyolefin-based resin composition containing 0 parts by weight into a predetermined shape, followed by crosslinking and foaming.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The polypropylene resin used in the present invention is a copolymer of propylene and an α-olefin other than propylene.

Examples of the α-olefin as a copolymer component include ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene,
Octene and the like.

The foam of the present invention comprises an α-olefin of 15%.
Polypropylene resin alone containing up to 70% by weight or
It is characterized by containing two types of polypropylene resins having different α-olefin contents.

When two types of polypropylene resins are used, specifically, an α-olefin is used in an amount of 15 to 70%.
A polypropylene resin (A) containing 1% by weight and a polypropylene resin (B) containing 1 to 15% by weight of an α-olefin.

The content of the resin (A) is preferably at least 30%, more preferably at least 50%.
When the content of the resin (A) is less than 30% by weight, the obtained foam is insufficient in flexibility, which is not preferable.

The polypropylene resin used in the present invention must have an MI of 0.1 to 10 g / 10 minutes. If the MI is too small, the moldability during the production of the foam is reduced, and if it is too large, the resulting foam has poor elongation and heat resistance. MI is preferably 0.3 to 10 (g / 10 minutes), more preferably 0.5 to 10 (g / 10 minutes).
８8 (g / 10 minutes).

In the present invention, a polyfunctional monomer is used as a crosslinking assistant. Examples of the polyfunctional monomer include divinylbenzene, trimethylolpropane trimethacrylate, 1,9-nonanediol dimethacrylate,
10-decanediol dimethacrylate, triallylic acid triallyl ester, triallyl isocyanurate,
Ethyl vinyl benzene and the like can be used.

These polyfunctional monomers can be used alone or in combination of two or more. These polyfunctional monomers are added in an amount of about 0.5 to 10 parts by weight based on 100 parts by weight of the resin matrix.

The foam of the present invention is characterized by having both flexibility and heat resistance.

One of the indices indicating the flexibility of the foam in the present invention is the heat capacity of fusion. It is a well-known fact that the higher the crystallinity of a polymer, the higher the heat of fusion, but the higher the crystallinity, the higher the rigidity. In order to maintain the flexibility of the foam of the present invention, it is important that its heat of fusion is 90 mJ / mg or less. If it exceeds 90 mJ / mg, the flexibility of the foam is impaired as described above, As a result, the flexibility of the molded product is reduced, which is not preferable.

In general, the flexibility of a foam is higher as the expansion ratio is higher when the raw material composition is the same.
In a two-dimensional graph with 25% compression hardness on the vertical axis,
(25% compression hardness) = 3.17 × (density) −60 It is more preferable to be located in a region below the straight line represented by −60. Positioning above the region indicated by this straight line is not preferred because it tends to impair the flexibility of the molded product.

One of the indices indicating the heat resistance of the foam in the present invention is a dimensional change rate during heating, and more specifically, the dimensional change rate after being left in an oven at 120 ° C. for 60 minutes. It is important that the dimensional change rate is 5% or less. If the dimensional change rate exceeds 5%, it is not preferable because the shrinkage of the foam increases due to heating during molding.

Further, the gel fraction of the foam of the present invention is 30 to 70% in order to maintain heat resistance and moldability at high temperatures.
It is preferable that When the gel fraction is less than 30%, the heat resistance of the foam is reduced, and the moldability at high temperatures is significantly reduced, which is not preferable. When the gel fraction exceeds 70%, the elongation of the foam is reduced. However, it is not preferable because the moldability is reduced.

The expansion ratio of the foam of the present invention is preferably 5 to 50 times. If the expansion ratio is less than 5 times, the flexibility of the molded product is reduced. This is not preferable because the temperature and the moldability at high temperatures are significantly reduced.

Specific examples of the organic thermal decomposition type foaming agent used in the present invention include azodicarbonamide, benzenesulfonylhydrazide, dinitrosopentamethylenetetramine, toluenesulfonylhydrazide, azobisisobutyronitrile, azobisisobutyronitrile and azobisisobutyronitrile. And barium dicarboxylate. These may be used alone or in combination, and 1 to 50 parts by weight based on 100 parts by weight of the resin matrix.
Use in parts by weight.

If the amount of the organic thermal decomposition type foaming agent is too small, the foaming property of the resin composition is reduced. If the amount is too large, the strength and heat resistance of the obtained foam are reduced.
Therefore, the addition amount of the pyrolytic foaming agent is preferably 4 to
25 parts by weight.

In the present invention, other thermoplastic resins such as ultra-low-density polyethylene, low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, and the like, as long as the effects of the present invention are not impaired. High-density polyethylene, ultra-high-molecular-weight polyethylene, polypropylene, ethylene-propylene rubber, polyvinyl acetate, or polybutene can be added as a small component. In addition, phenol-based, phosphorus-based, amine-based, sulfur-based antioxidants, metal damage inhibitors, flame retardants, fillers, antistatic agents, heat stabilizers, pigments, and the like may be added.

In the present invention, the polyolefin resin foam composition obtained by blending the above components is molded into a predetermined shape, and then crosslinked and foamed to produce a polyolefin resin foam.

Specifically, for example, the following production method can be mentioned.

Using a kneading device such as a single-screw extruder, a twin-screw extruder, a Banbury mixer, a kneader mixer, or a mixing roll, a predetermined amount of the polyolefin resin composition is adjusted to a temperature lower than the decomposition temperature of the pyrolytic foaming agent. The mixture is uniformly melt-kneaded and formed into a sheet. Next, the obtained sheet is irradiated with a predetermined amount of ionizing radiation to crosslink the olefin-based resin, and the crosslinked sheet is foamed by heating it to a temperature equal to or higher than the decomposition temperature of the pyrolytic foaming agent. Instead of crosslinking by irradiation with ionizing radiation, crosslinking by peroxide or silane crosslinking may be performed.

As the ionizing radiation, α-ray, β-ray, γ
And electron beams. The irradiation dose of the ionizing radiation varies depending on the type of the polyfunctional monomer, the amount added, the desired degree of crosslinking, and the like, but is generally 1 to 500 kGy,
Preferably it is 5-300 kGy. When the irradiation dose is too small, the heat resistance of the obtained foam becomes insufficient, and when it is too large, the moldability of the obtained foam decreases.

The gel fraction referred to in the present invention is a value calculated by the following method.

About 50 mg of polyolefin resin foam
It is precisely weighed, immersed in 25 ml of xylene at 120 ° C. for 24 hours, and then filtered through a 200-mesh stainless steel wire gauze, and the insoluble portion of the wire gauze is vacuum-dried. Then, the weight of the insoluble portion was precisely weighed, and the gel fraction was calculated as a percentage according to the following equation.

Gel fraction (%) = ｛weight of insoluble matter (m
g) / weight of weighed polyolefin resin foam (m
g)｝ × 100 The differential scanning calorimetry in the present invention was performed by the following method. About 10 mg of a polyolefin-based resin foam previously pressed at room temperature is put in a platinum pan, and a differential scanning calorimeter (DSC: RDC220 manufactured by Seiko Instruments Inc.) is used.
-Robot DSC). The measurement conditions were such that the sample was melted once, cooled at a rate of 10 ° C./min to −50 ° C., and then heated at a rate of 5 ° C./min.

The heating dimensional change in the present invention was performed by the following method. 15 polyolefin resin foam
Cut accurately to a cm square and leave in an oven set at 120 ° C. for 60 minutes. After 60 minutes, remove from the oven and cool at room temperature for about 30-60 minutes. The dimensions of the sample were measured, and the dimensional change was calculated as a percentage based on the following equation.

Heating dimensional change (%) = [{Sample length before placing in oven-Sample length after removing from oven} / Sample length before placing in oven] × 100 The 25% compression hardness in the present invention is as follows. The following method was used. The foam was cut into 5 cm squares, four of which were stacked and measured with a compression tester (AF-200 manufactured by Kobunshi Keiki Co., Ltd.). The measuring method conforms to JIS K6767.

[0039]

EXAMPLES Next, examples of the present invention will be described, but the present invention is not limited to these examples. Hereinafter, “parts” means “parts by weight”. Example: MI obtained by random copolymerization of propylene with 50% by weight of ethylene was 5.0 g / 10 min, and the density was 0.880 kg / m3.
128 kg of polypropylene resin, 2.5 g of MI obtained by random copolymerization of propylene with 3.6% by weight of ethylene
32 kg of a / 10 minute polypropylene resin, 0.95 kg of "Irganox 1010" as a stabilizer, 7.4 kg of azodicarbonamide and 8.0 kg of divinylbenzene as a foaming agent were prepared, and a polypropylene resin, a polyethylene resin, a foaming agent, The stabilizer is put into a Henschel mixer, mixed at a low speed of 200 to 400 rpm for about 3 minutes, and then at a high speed of 800 to 1000 rpm,
Mix for 3 minutes to obtain a foaming resin composition.

The foaming resin composition is introduced into a vented extruder heated to a temperature at which the foaming agent is not decomposed, specifically, heated to 160 to 190 ° C., extruded from a T-die, and used for cross-linking foaming with a thickness of 1.5 mm. It was molded into a sheet. The sheet was irradiated with an electron beam of 320 kGy and crosslinked, then continuously introduced into a vertical hot-air foaming apparatus, heated and foamed, and wound up as a continuous sheet-like crosslinked foam.

The thickness of the foam thus obtained was 3.0 mm, the gel fraction was 55%, and the expansion ratio was 15 times.

Table 2 shows the properties of the polyolefin resin foam thus obtained. Comparative Example The same operation as in the example was performed using the polyethylene-based resin and the polypropylene-based resin shown in Table 1 to obtain a polyolefin-based resin foam having the properties shown in Table 2.

[0043]

[Table 1]

[0044]

[Table 2]

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4F074 AA24A AA25A AA26A AA98 AB01 AB03 AB05 BA13 BA14 BA15 BA16 BA17 BA18 BB25 BB27 BB28 CA29 CC04X CC04Y CC32X CC46Y DA02 DA04 DA23 DA35 4J002 BB14W BB14X BB15X BB15BB GN00

Claims (3)

[Claims] (1) propylene and an α-olefin other than propylene as a constituent unit, wherein the α-olefin content is 15 to
70% by weight, weight average molecular weight / number average molecular weight of 2 to 8, and melt index (MI) of 0.1 g
Polypropylene-based resin 30-1 having a viscosity of 10 to 10 g / 10 minutes
And propylene and an α-olefin other than propylene as constituent units, and the α-olefin content is 1 to 100% by weight.
15% by weight, weight average molecular weight / number average molecular weight is 2 to 8, and melt index (MI) is 0.1 g.
Polypropylene resin 0 to 70 which is 10 g / 10 min
% By weight of a polyolefin-based resin composition comprising 100 parts by weight of a resin matrix, and a foam having a heat capacity of fusion of 90 mJ / measured using a differential scanning calorimeter (DSC). mg or less, and the dimensional change after being left in an oven at 120 ° C. for 60 minutes is 5% or less. 2. The two-dimensional graph of the foam according to claim 1, wherein the horizontal axis represents density and the vertical axis represents 25% compression hardness, (25% compression hardness) = 3.17 × (density). A polyolefin-based resin foam, which is located in a region below a straight line represented by -60. 3. A gel fraction of 30 to 70% and an expansion ratio of 5
The polyolefin resin foam according to claim 1, wherein the ratio is up to 50 times.