JP2002113733A - Polyolefinic resin foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture polyolefinic resin foam excellent in compression recovery capacity. SOLUTION: A mixture, which contains 100 pts.wt. of a polyolefinic resin, 5-30 pts.wt. of a thermally decomposable foaming agent and 1-5 pts. wt. of an alkoxysilane compound having an acryloyl or methacryloyl group in its molecule, is molded at temperature lower than the decomposition temperature of the foaming agent to obtain a molded article which is then irradiated with ionizing radiation. This molded article is heated to the decomposition temperature of the foaming agent and further immersed in a heating medium to manufacture the polyolefinic resin foam.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a polyolefin resin foam.

[0002]

2. Description of the Related Art Polyolefin resin foams having closed cells are widely used in various fields as heat insulating materials and cushioning materials because they are flexible and have excellent heat insulating properties and mechanical strength. In order to produce this kind of polyolefin-based resin foam, it is common to foam it after crosslinking using a chemical crosslinking agent or ionizing radiation (for example, electron beam). For example, JP-A-55-75432 discloses a method in which an alkoxysilane is graft-polymerized to a polyolefin resin in the presence of a radical generator, and then the graft resin is crosslinked and foamed. In this case, a)
First, an alkoxysilane is graft-bonded to a polyolefin resin having a radical generator, b) a foaming agent is kneaded and molded into the obtained graft resin, and c) an appropriate degree of crosslinking required for foaming is applied, followed by heating and foaming. Let it. This requires a complicated process. JP-A-3-221542 discloses a method in which an alkoxysilane and a foaming agent are added to a polyolefin resin, followed by crosslinking by ionizing radiation followed by foaming, but the compression recovery performance is not sufficient. Was.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a polyolefin resin foam having excellent compression recovery performance.

[0004]

SUMMARY OF THE INVENTION Polyolefin resin 1
A mixture containing 00 parts by weight, 5 to 30 parts by weight of a thermally decomposable blowing agent, and 1 to 5 parts by weight of an alkoxysilane compound having an acryloyl group or a methacryloyl group in a molecule is molded at a temperature not higher than the decomposition temperature of the blowing agent. A method for producing an olefin-based resin foam, which comprises irradiating the obtained molded product with an electron beam, heating the molded product to a temperature equal to or higher than the decomposition temperature of the foaming agent, and further immersing the molded product in a heat medium.

The polyolefin resins used in the present invention include low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, polypropylene, ethylene-propylene copolymer, ethylene and other monomers such as acetic acid. Copolymers with vinyl, acrylic acid, methacrylic acid, and the like can be given. These are used alone or as a mixture of two or more.

The alkoxysilane compound having an acryloyl group or a methacryloyl group used in the present invention is an alkoxysilane compound containing one or more acryloyl or methacryloyl groups in the molecule and one or more alkoxyl groups. It is not particularly limited. Specific examples of these compounds include, for example, (meth) acryloyloxyalkyltrimethoxysilane. The amount of the alkoxysilane compound to be added is 0.1 to 15 parts by weight, preferably 1 to 5 parts by weight, based on 100 parts by weight of the resin. If the amount is less than 0.1 part by weight, the crosslinking is insufficient and the recovery rate of the obtained foam is reduced. If the amount exceeds 15 parts by weight, the crosslinking proceeds too much to obtain a good foam.

As the thermal decomposition type foaming agent used in the present invention, a compound which generates a gas such as nitrogen upon heating is used. Specific examples thereof include, for example, azodicarbonamide, oxybenzenesulfonylamide, azobisisobutylene Nitrile, N, N-dinitrosopentamethylenetetramine and the like. The amount of the additive of the thermal decomposition type foaming agent is preferably 10 to 30 parts. If the amount is less than 10 parts by weight, foaming is insufficient and a good foam cannot be obtained. If the amount exceeds 30 parts by weight, foaming becomes uneven and a good foam cannot be obtained.

In the above-mentioned mixed raw material containing the polyolefin resin, the above-mentioned alkoxysilane, and the above-mentioned pyrolytic foaming agent, if necessary, ordinary additives such as a lubricant, a flame retardant and the like may be used as long as the present invention is not impaired. , Antioxidants, anti-aging agents, ultraviolet absorbers, antistatic agents, inorganic and organic fillers,
A coloring agent or the like may be added.

In the present invention, the mixed raw material is melt-kneaded using a Banbury mixer, a kneader mixer, or a single-screw or multi-screw extruder at a temperature lower than the decomposition temperature of the heat-decomposable foaming agent, and then molded. The molding may have any shape, but is desirably formed into a sheet.

Next, the obtained molded product is irradiated with ionizing radiation to cause a radical crosslinking reaction of the olefin resin, thereby performing a preliminary crosslinking reaction required for foaming. At this time, at the same time as the crosslinking, the alkoxysilane compound undergoes a graft reaction to the olefin-based resin to obtain a crosslinked graft molded product. Examples of the ionizing radiation include an α-ray, a β-ray, a γ-ray, and an electron beam. Of these, an electron beam is preferable.

The crosslinked graft molded product obtained above is foamed by heating it to a temperature not lower than the decomposition temperature of the thermolytic foaming agent. In the foaming step, a condensation crosslinking reaction with the alkoxysilane compound proceeds simultaneously with or after the foaming. This reaction is carried out by the heat required for the decomposition of the blowing agent and a trace amount of water in the atmosphere, for example, in the air.

Finally, the foam is passed through a heat medium to cause a complete condensation reaction of the alkoxysilane compound. Examples of the heat medium include hot air, hot water, an infrared heater, and the like. Preferably, a liquid, particularly hot water, is used as the heat medium. The temperature of the heating medium is preferably 80 to 90 degrees.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be specifically described based on embodiments.

[0014]

EXAMPLES (Example 1) Low density polyethylene (MI:
4.1, density: 0.924, melting point: 109 ° C.) Using a single-screw extruder, extrude the resin at a temperature of 130 ° C. before the mold, and obtain a
mm sheet was obtained. 3.0 Mrad on the obtained sheet
The sheet was then passed through a hot air oven at 240 ° C. to foam and crosslink. The expansion ratio and sheet thickness of the obtained foam were measured by the following methods.
The results are shown in Table 1. Next, the foam was impregnated with hot water adjusted to 85 ° C. for 15 minutes. After electron beam irradiation, after foaming, and after hot water treatment, the degree of crosslinking was measured by the following method.
The results are shown in Table 1.

[0015] The foam obtained above was subjected to a thickness compression recovery test. As shown in FIG. 1, a 20 kg weight was placed on a cylinder having a diameter of 20 mm for one week and released, and immediately after that, the thickness of the foam was measured. Table 1 shows the results.

Comparative Example 1 The procedure of Example 1 was repeated, except that hot water was not passed.

(Comparative Example 2) The procedure of Example 1 was repeated, except that 3-methacryloxypropyltrimethoxysilane was not used.

Comparative Example 3 The procedure of Example 1 was repeated except that 3-methacryloxypropyltrimethoxysilane was not used and the irradiation dose was 9 Mrad.

(Comparative Example 4) The procedure of Example 1 was repeated, except that 3-methacryloxypropyltrimethoxysilane was not used and the irradiation dose was 12 Mrad.

[Measurement method] (Gel fraction measurement method)
The sample was immersed in xylene at 0 ° C. for 24 hours, and the undissolved portion was dried and then weighed, and the ratio was determined as a ratio to the initial weight of the sample. (Measurement of Expansion Ratio) The apparent density was measured in accordance with JIS K6767, and the reciprocal thereof was defined as the expansion ratio.

[0021]

[Table 1]

[0022]

According to the method of the present invention, by irradiating the above molded product with ionizing radiation, radicals are generated in the polyolefin resin, crosslinks necessary for foaming are obtained, and the above alkoxysilane compound is converted into a polyolefin resin. It grafts to the system resin. The above-mentioned alkoxysilane compound is merely mixed at the time of molding, and does not hinder moldability. Furthermore, at the time of foaming, the alkoxysilane compound is crosslinked with foaming to obtain a foam, but the obtained foam is further passed through a heating medium so that the crosslinking with the silane compound proceeds completely, and the compression recovery property is improved. Excellent foam is obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a compression recovery measuring method.

[Explanation of symbols]

 1: Foam 2: Cylindrical body (20 mmφ) 3: Weight (25 kg)

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Claims (1)

[Claims] 1. A mixture comprising 100 parts by weight of a polyolefin resin, 5 to 30 parts by weight of a pyrolytic foaming agent, and 1 to 5 parts by weight of an alkoxysilane compound having an acryloyl group or a methacryloyl group in a molecule is foamed. Molding at a temperature not higher than the decomposition temperature of the agent, irradiating the obtained molded article with ionizing radiation, then heating it to a temperature higher than the decomposition temperature of the foaming agent, and further immersing it in a heating medium. How to make the body.