JPH04248848A - Forming polyolefin-based resin composition - Google Patents

Abstract

PURPOSE:To obtain a foaming polyolefin-based resin composition having excellent moldability and resistance to thermoelasticity and suitable for producing a crosslinked polyolefinic resin foam, and a crosslinked foam in which the above-mentioned composition is crosslinked and foamed. CONSTITUTION:A foaming polyolefin-based resin composition containing 40-80 pts.wt. polypropylene having 0.5-12 melt index, 60-20 pts.wt. polyethylene having 15-45 melt index and 0.91-0.94 density (g/cm<2>), a thermally decomposable foaming agent and a crosslinking assistant, and a crosslinked polyolefin-based resin foam obtained by crosslinking and foaming the above-mentioned resin composition.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a foamable polyolefin resin composition, and more particularly to a foamable polyolefin suitable for producing a crosslinked polyolefin resin foam with excellent moldability and heat-resistant elasticity. based resin composition,
The present invention also relates to a crosslinked foam obtained by crosslinking and foaming the resin composition.

0002

BACKGROUND OF THE INVENTION Conventionally, crosslinked polypropylene resin foams have been used in a wide range of fields as heat insulating materials, cushioning materials, and the like. Particularly in automobile applications, it is used as a heat insulating material for ceilings, doors, instrument panels, etc., but there is a problem in that it is difficult to mold complex and deep shapes.

[0003] A crosslinked foam is obtained by adding a crosslinking aid such as divinylbenzene or diethylene glycol dimethacrylate to a polypropylene resin, crosslinking it by irradiating it with organic peroxide or ionizing radiation, and heating and foaming it. is a well-known technique (Special Publication No. 1973-38)
No. 716, JP-A-59-191107, etc.). This crosslinked polypropylene resin foam has the highest melting point among polyolefin resin foams, 110 to 120°C.
Because of its excellent extensibility, it is used in various fields, including vehicle-related fields. However, in the high temperature range of 140 to 160° C., crosslinked foams produced by conventional methods rapidly exhibit poor elongation and poor moldability. In the recent field of foam molding, it is required to be able to process foams into complex shapes and to perform deep drawing. Furthermore, rapid heating and an increase in processing temperature are required to improve productivity. However, conventional crosslinked polypropylene resin foams have not been able to meet these requirements. In addition, for example, in automotive applications, when the interior of a car is exposed to high temperatures during the summer, it must ensure sufficient performance as insulation and cushioning materials, and for this purpose, heat-resistant elasticity is essential. .

By the way, in order to improve moldability, there is a method of blending a large amount of polyethylene resin into the resin component, but in this case, due to the heat resistance requirements for conventional crosslinked polypropylene resin foam, As polyethylene resins, those having a relatively high molecular weight, that is, those having a melt index (MI) of 10 or less, have been mainly used. For example, JP-A No. 57-212236 proposes mixing polyethylene having an MI of about 3 to 9 with a specified polypropylene. In addition, JP-A-56
-112940 proposes a method of forming a crosslinked foam by mixing polyethylene with an MI of about 1 to 4, a polyolefin thermoplastic elastomer, and polyethylene with a molecular weight of 2,000 to 5,000. . However, these methods have the disadvantage that the heat-resistant elasticity of the foam is lost.

[0005] There is a demand for a crosslinked polypropylene resin foam that satisfies moldability and heat-resistant elasticity at the same time, but the reality is that the conventional techniques have not been able to adequately meet this demand.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a crosslinked polyolefin resin foam with excellent moldability and heat-resistant elasticity, and a foamable polyolefin resin composition suitable for producing the foam. Our goal is to provide the following.

[0007] As a result of intensive research in order to overcome the problems of the prior art, the present inventors have developed a polypropylene resin blended with a low molecular weight polyethylene resin having an MI of 15 to 45 as a resin component. By using
The inventors have discovered that the above object can be achieved, and have completed the present invention based on this knowledge.

[0008]

[Means for Solving the Problems] Thus, according to the present invention, (a) 40 to 80 parts by weight of a polypropylene resin having a melt index of 0.5 to 12; (b) a melt index of 15 to 45; Density (g/
cm3) is 0.91 to 0.94, and the total amount of resin components (a+b
) 100 parts by weight, (c) 1 to 50 parts by weight of a pyrolyzable blowing agent, and (d) 0.1 to 10 parts by weight of a crosslinking aid. things are provided.

Further, according to the present invention, there is provided a crosslinked polyolefin resin foam characterized by being formed by crosslinking and foaming the above-mentioned foamable polyolefin resin composition. The present invention will be explained in detail below.

The polypropylene resin used in the present invention is a propylene homopolymer or a copolymer containing propylene as a main component, and among these, what is generally called isotactic polypropylene is preferred. The copolymer is usually a copolymer with ethylene or other α-olefins if the content of the propylene component is 85% by weight or more, preferably 90% by weight or more. α-olefins include ethylene, 1-butene, 4-methyl-1-pentene, 1-octene, 1-hexene, 3,3-dimethyl-1
-Hexene, etc.

[0011] The polypropylene resin used in the present invention is
Its MI (measured according to ASTM D-1238) is from 0.5 to 12, preferably from 1 to 10, more preferably from 1 to 5. Moreover, the melting point (mp) is usually 135 to 155°C. If MI is less than 0.5, extrusion moldability will be difficult, and if it is greater than 12, foaming will be difficult.

[0012] The polyethylene resin used in the present invention is
It is an ethylene homopolymer or a copolymer mainly composed of ethylene, preferably linear low density polyethylene (
L-LDPE) is a copolymer of ethylene and α-olefin. α-olefins include propylene, 1-butene, 4-methyl-1-pentene, 1-
Examples include octene, 1-hexene, 3,3-dimethyl-1-hexene, and the like. Density of polyethylene resin (g/
cm3) ranges from 0.91 to 0.94. MI (ASTM D-1238) of polyethylene resin is
It ranges from 15 to 45. If the MI is less than 15 or the density is greater than 0.94, the secondary molding processability will be poor, and if the MI is greater than 45 or the density is less than 0.91, problems will occur in heat resistance, and the heat resistant elasticity will be poor. become weak.

[0013] The mixing ratio of polypropylene resin and polyethylene resin is 40:60 to 80:20 (weight ratio).
It is. If the proportion of polypropylene resin is more than 80% by weight, a problem will arise in secondary processability, and if the proportion of polyethylene resin is more than 60% by weight, a problem will arise in heat resistance elasticity.

A crosslinked foam can be obtained by adding a thermally decomposable blowing agent, a crosslinking aid, and various additives to the above polyolefin resin component and using a known method for producing a crosslinked polyolefin resin foam. Here, a general method for producing a crosslinked foam will be explained.

[0015] A method in which a mixture containing a polyolefin resin, a blowing agent, and a crosslinking aid is crosslinked with ionizing radiation, and then heated to a temperature higher than the decomposition temperature of the blowing agent to foam, or a method in which a mixture containing a polyolefin resin, a blowing agent, Examples include a method in which a mixture consisting of an organic peroxide, a crosslinking accelerator, and in some cases a crosslinking regulator is heated to a temperature higher than the decomposition temperature of the organic peroxide and a blowing agent to cause crosslinking and foaming. From the point of view, it is preferable to use a crosslinking method using ionizing radiation.

In the present invention, the blowing agent is a compound that decomposes to generate gas when heated, such as azodicarbonamide, oxybenzenesulfonyl hydrazide, azobisisobutyronitrile, barium azodicarboxylate,
A thermally decomposable blowing agent such as dinitrosopentamethylenetetramine or hydrazodicarbonamide is used. The addition ratio of the pyrolytic foaming agent can be determined as appropriate depending on the desired expansion ratio (2 to 100 times), but it is usually 2 to 50 parts by weight, preferably 5 parts by weight, per 100 parts by weight of the resin component. ~30
Parts by weight.

Examples of crosslinking aids include polyfunctional monomers represented by divinylbenzene, trimethylolpropane triacrylate, and ethylene glycol dimethacrylate, and unsaturated double bonds represented by 1,4 polybutadiene (PB). Examples include polymers that have The addition ratio of these crosslinking aids can be determined as appropriate depending on the desired degree of crosslinking, etc., but in the case of polyfunctional monomers, it is usually 1 to 100 parts by weight of the resin component.
10 parts by weight, and in the case of a polymer having unsaturated double bonds such as PB, a range of 4 to 20 parts by weight is preferred.

[0018] Furthermore, various additives such as antioxidants, anti-aging agents, ultraviolet absorbers, antistatic agents,
Pigments etc. can be added.

The above mixture, ie, polypropylene resin, polyethylene resin, thermally decomposable blowing agent, crosslinking aid, and optionally various additives, is mixed at a temperature below the temperature at which the blowing agent decomposes, for example, using a Banbury mixer or a single screw mixer. The mixture is melt-kneaded and molded into a desired shape using an extruder, multi-screw extruder, or the like. It is usually formed into a sheet.

The molded foamable resin composition is then cross-linked and foamed. When an organic peroxide is used, the cross-linking and foaming are carried out by heating above the decomposition temperature of the organic peroxide and the foaming agent. have them do it.

When the foamable composition is crosslinked by irradiation with ionizing radiation, α-rays, β-rays, and γ-rays are preferred as the ionizing radiation, but X-rays and ultraviolet rays may also be used. These radiation doses vary depending on the type of crosslinking accelerator and the desired crosslinking ratio, but are generally 0.1 to 5.
0 Mrad, preferably 0.5 to 20 Mrad. Foaming of the thus crosslinked resin composition is carried out by heating to a temperature equal to or higher than the decomposition temperature of the foaming agent. This heating and foaming is performed using, for example, a vertical foaming furnace, a horizontal foaming furnace, a salt bath, a metal bath, or the like.

Note that the gel fraction of the obtained crosslinked foam is 2
It is preferable to adjust the irradiation dose, the amount of crosslinking aid added, etc. so that it becomes 0 to 70%. If the gel fraction is too small,
Heat resistance cannot be obtained, and conversely, if it is too large, flexibility such as elongation rate will be lacking, so both are unfavorable.

The crosslinked polyolefin resin foam thus obtained has excellent heat resistance, moldability, and heat-resistant elasticity. This means that low molecular weight polyethylene resin with an MI of 15 to 45 is molded at a high temperature of 140 to 16
At 0°C, the viscosity of the foamable resin composition is reduced, and 2
It is presumed that this is to significantly improve the subsequent processability.

[0024]

[Examples] The present invention will be explained below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. [Examples 1 to 7, Comparative Examples 1 to 3] Using polypropylene resin (PP) and polyethylene resin (PE) shown in Table 1 as resin components, pyrolytic type 13 parts by weight of azodicarbonamide as a blowing agent, divinylbenzene (DVB) or trimethylolpropane triacrylate (TMPT) as a crosslinking aid in the amounts shown in Table 1, and 0.5 parts by weight of an antioxidant were mixed to form a 6 inch Roll at 170℃,
Mixing was carried out for 5 minutes at a speed of 20 revolutions/minute. The board you created is 1
It was formed into a 1 mm sheet at 80° C. and 100 kg/cm 2 and irradiated with an electron beam of 6 Mrad. After that, 250℃
The mixture was placed in an oven for 5 minutes to foam to obtain a foam.

The physical properties of the obtained foam were measured. The method for measuring each physical property is as follows.

<Vacuum formability> The crosslinked foam is heated with a far infrared heater until the surface temperature of the foam reaches 150-160°C.
℃, vacuum forming is performed using a cylindrical female mold, and the ratio of depth H to diameter D (H/D
). The larger this value is, the better the moldability is.

<Heat-resistant elasticity> 10 mm at 160°C
The evaluation was made based on the tensile strength at break when pulled at a speed of 1/min (unit: kg/cm2).

<Melting point Tm> Regarding Tm, the temperature was raised at 5° C./min using a DSC manufactured by Seiko Electronics, and the maximum endothermic peak temperature was determined. (unit: °C)

<Melt Index> MI is ASTM
Determined using D1238. (Unit is g/10mm)

0
<High temperature tensile strength at break> Tensile strength at break when a crosslinked foam was subjected to a tensile test at 160° C. at a speed of 10 mm/min. (The unit is kg
/cm2)

[0031]

[Table 1] The larger the value of H/D, the better the moldability; for ordinary door handles, etc., a value of 1.0 or more is required.
Therefore, the values of Examples 1 to 7 are all 1.0 or more, which is a satisfactory value. On the other hand, the values of Comparative Examples 1 to 3 are all less than 0.1, which is insufficient. Tensile strength at break is 0
．． 35 or more is required, but all of the examples have this value or more.

[0032]

[Effects of the Invention] According to the present invention, the low-molecular polyethylene resin functions to reduce the viscosity at 150 to 160°C, which is the temperature during molding, and a significant improvement in the secondary processability of the crosslinked foam has been achieved. . Further, it is possible to provide a crosslinked polyolefin foam with improved heat resistance and elasticity, and a foamable resin composition suitable for producing the foam.

Claims (2)

[Claims] Claim 1: (a) Melt index is 0.5~
40 to 80 parts by weight of polypropylene resin No. 12, and (b
) melt index is 15-45, density (g/cm
3) is 0.91 to 0.94 polyethylene resin 6
0 to 20 parts by weight, and the total amount of resin components (a + b) 1
00 parts by weight, (c) 1 to 50 parts by weight of a pyrolyzable foaming agent, and (d) 0.1 to 10 parts by weight of a crosslinking aid. . 2. A crosslinked polyolefin resin foam obtained by crosslinking and foaming the foamable polyolefin resin composition according to claim 1.