JPH0632929A - Production of olefinic resin foam - Google Patents

Abstract

(57) [Summary] [Objective] To provide a production method for obtaining a continuous long olefin resin foam by using a clean inorganic gas. [Structure] An olefin resin is modified by heating in the presence of a radical generator to a temperature at which free radicals are generated or higher, or by irradiating with ionizing radiation, and the weight average molecular weight thereof is 1.5 before modification. A method for producing an olefin-based resin foam, comprising injecting an inorganic gas in a molten state under pressure into a modified olefin-based resin that is 10 times larger, and then extruding it into a low-pressure region for foaming.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an olefin resin foam by extruding and foaming a polymerized olefin resin with an inorganic gas which is a clean foaming agent.

[0002]

2. Description of the Related Art Conventionally, as a method for producing a thermoplastic resin foam, a chemical foaming agent method in which a pyrolytic chemical foaming agent is kneaded into a resin and heated to a temperature above the decomposition temperature of the foaming agent to form a foam, A gas foaming method in which an organic gas or a volatile liquid having a boiling point below the melting point of a resin such as butane, pentane, dichlorodifluoromethane (CFC R-12) is pressed into a molten resin and then discharged into a low pressure region to foam. It has been known. By using the chemical foaming agent method, a foam having uniform and fine closed cells can be obtained, but since the decomposition residue of the foaming agent remains in the foam, discoloration of the foam, generation of odor, food It causes hygiene problems.

On the other hand, in the gas foaming method, when the foaming agent used is a low-boiling organic solvent such as butane or pentane, an explosive gas is generated during the production of the foam, which causes a danger of explosion. Also, when the blowing agent used is dichlorodifluoromethane (CFC R-12), there is little danger of explosion, the bubble film can be rapidly cooled and solidified by the latent heat of vaporization that accompanies vaporization during foaming, and gas permeation to the cell film Since it has low properties, it is easy to obtain a foam with a high expansion ratio, but due to environmental problems such as ozone layer depletion, CFC-based gas is being abolished.

In order to solve the above problems, carbon dioxide gas,
A method has been proposed in which an inorganic gas such as nitrogen gas or air or water is used as a foaming agent. These foaming agents are clean and do not cause the above problems, but it is difficult to stably obtain a foam having a high expansion ratio.

British Patent No. 899,389 discloses a method of foaming cross-linked polyethylene with nitrogen gas in a pressure resistant container. However, in order to obtain a foam having a high expansion ratio, a very high pressure is required. It is necessary, dangerous, expensive in equipment, and inefficient in work. Also, with this method, foam molding of a continuous long product is difficult.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to overcome the above-mentioned drawbacks of the prior art and to provide a production method for obtaining a continuous elongated foam using clean inorganic gas. The present inventors, as a result of intensive research to solve the above problems, heating the olefin resin to a temperature at which free radicals are generated in the presence of a radical generator, or higher,
Alternatively, when a modified olefin resin modified by irradiation with ionizing radiation and having a weight average molecular weight Mw of 1.5 to 10 times that before modification is used, a clean inorganic gas is used as a foaming agent by an extrusion foaming method. It has been found that continuous and continuous production of foams can be carried out easily and safely.
The present inventors have completed the present invention based on these findings.

[0007]

According to the present invention, an olefin resin is modified by heating it in the presence of a radical generator to a temperature at which free radicals are generated or by irradiating it with ionizing radiation. An olefin-based resin foam characterized in that a modified olefin-based resin having a weight-average molecular weight of 1.5 to 10 times that before modification is injected with an inorganic gas in a molten state and then extruded into a low-pressure region to foam. A method of manufacturing the same is provided.

The present invention will be described in detail below. Examples of the olefin resin used in the present invention include polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-ethyl acrylate copolymer, ethylene-propylene-diene copolymer, chlorinated polyethylene,
Polybutene and the like can be mentioned. These can be used alone or in 2
A mixture of two or more species can be used.

The olefin resin is modified by a radical generator or ionizing radiation. Although the radical generator is not particularly limited, for example, 1,1-bis (t-
Butylperoxy) cyclohexane, t-butylperoxymaleic acid, t-butylperoxy-3,5,5-
Trimethylhexane, cyclohexane peroxide,
t-butylperoxyallyl carbonate, t-butylperoxyisopropyl carbonate, 2,2-bis (t-butylperoxy) octane, t-butylperoxyacetate, 2,2-bis (t-butylperoxy) butane , T-butyl peroxybenzoate, n-
Butyl-4,4-bis (t-butylperoxy) berulate, di-t-butyldiperoxyisophthalate, dicumyl peroxide, t-butylcumyl peroxide, 2,5-dimethyl-2,5-di ( Organic peroxides such as t-butyl peroxide) hexane may be mentioned.

A compound having at least one carbon-carbon unsaturated bond may be added as a polymerizing aid together with the radical generator, if necessary. To modify the olefin resin with the radical generator, the olefin resin and the radical generator are charged into an extruder and extruded at a temperature not lower than the decomposition temperature of the radical generator to generate free radicals to crosslink the olefin resin. The modified resin may be pelletized and then charged into an extrusion foaming machine, or the extruder used for modification may be directly connected to the extrusion foaming machine.

When the olefin resin is irradiated with ionizing radiation to be modified, the olefin resin is molded into a sheet, and the sheet is irradiated with ionizing radiation such as an electron beam or γ-ray to be crosslinked. Then, after pelletizing, it is put into an extrusion foaming machine. By these methods, the olefin resin is modified to have a weight average molecular weight Mw of 1.5 to 0.5 before modification.
Make it 10 times. The Mw is a value measured by high temperature gel permeation chromatography (GPC).

When the increase ratio of Mw is less than 1.5 times, the viscosity during extrusion foaming is low, and only a foam having a low expansion ratio and a large number of open cells can be obtained. On the other hand, if it exceeds 10 times, the melt viscosity becomes too high to make extrusion impossible, or even if extrusion is possible, it is difficult to obtain a foam having a target shape having a smooth surface due to melt fracture. The preferable range of the increase ratio of Mw due to denaturation is 1.5 to 3.0.

By the way, even if an olefin resin having the same Mw as the weight average molecular weight Mw obtained by the above modification is used, a foam having a high expansion ratio cannot be obtained. The reason for this is not clear, but it is presumed that the modified resin has a longer branched chain than the unmodified resin.
That is, it is presumed that the longer the branched chain, the higher the extension viscosity at the time of foaming, the less likely the foam will break at the time of foaming, and that the foam having a high magnification can be obtained.

Examples of the inorganic gas used as the foaming agent in the present invention include air, nitrogen gas, carbon dioxide gas (carbon dioxide), argon, helium, neon, hydrogen, etc. These may be used alone or in combination of two or more. Can be used in combination. In order to obtain a foam having a high expansion ratio, carbon dioxide gas or a mixture of carbon dioxide gas and other inorganic gas is preferable. The amount of these inorganic gases used can be appropriately determined according to the desired expansion ratio.

In the present invention, a cell nucleating agent may be added if necessary. Such substances include calcium carbonate, talc, clay, magnesium oxide, zinc oxide,
Examples thereof include carbon black, silicon dioxide, titanium oxide, citric acid, sodium bicarbonate, orthoboric acid and talc, and alkaline earth metal salts of fatty acids. The particle size thereof is preferably 500 μm or less. The use of a bubble nucleating agent having a size of 500 μm or more is not preferable because the bubble diameter becomes large.

Further, in the present invention, if necessary,
Fillers, antioxidants, pigments, flame retardants and the like may be added.
In the present invention, a modified olefin resin is used to produce a foam by an extrusion foaming method. Specifically, a modified olefin resin is charged into an extruder provided with an inorganic gas injection hole, and an inorganic gas is pressed into the resin molten state through an injection port, and rod-shaped, pipe-shaped, sheet from the die. It is extruded into a low-pressure region and foamed into a desired shape such as a shape.

[0017]

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.

[Example 1] A low-density polyethylene (ZH-52, Mw = 71,300 manufactured by Mitsubishi Petrochemical Co., Ltd.) was molded into a sheet having a thickness of 2 mm, and both sides were irradiated with an electron beam having an irradiation voltage of 500 kev and an irradiation dose of 4 Mrad. After irradiating, the mixture was pelletized by a pelletizer. At this time, Mw by high temperature GPC
Had risen to 138,000.

A bubble nucleating agent (talc, average particle size 15 μm) 0.8 was added to 100 parts by weight of the modified low density polyethylene.
Dry blending 1 part by weight with 0.6 part by weight of antioxidant,
Vent type extruder set at 30 ° C (diameter 65m
m, L / D = 35). Carbon dioxide gas is injected at a pressure of 70 kg / cm ² from the vent, and 20 k
It was extruded and foamed into a rod shape from a die having a diameter of 2 mm set at 110 ° C. at a discharge rate of g / hr. The foam thus obtained was a foam having an expansion ratio of 25 and good surface properties of uniform fine cells.

Example 2 100 parts by weight of the same low-density polyethylene (ZH-52) as in Example 1 and 0.2 part by weight of dicumyl peroxide as an organic peroxide were charged into the hopper of the extruder, and 170 After extruding into a sheet at ℃,
Pelletized with a pelletizer. At this time, Mw by GPC had risen to 141,000.

A bubble nucleating agent (talc, average particle size 15 μm) 0.8 was added to 100 parts by weight of the modified low density polyethylene.
Dry blending 1 part by weight with 0.6 part by weight of antioxidant,
Vent type extruder set at 30 ° C (diameter 65m
m, L / D = 35). Carbon dioxide gas is injected at a pressure of 70 kg / cm ² from the vent, and 20 k
It was extruded and foamed into a rod shape from a die having a diameter of 2 mm set at 110 ° C. at a discharge rate of g / hr. The foam thus obtained had a foaming ratio of 24 times and was a foam having good surface properties of uniform fine cells.

Comparative Example 1 A foam was produced in the same manner as in Example 1 except that the low density polyethylene was not irradiated with an electron beam. The foam thus obtained was an open-cell foam with a low expansion ratio of 5 times.

[Comparative Example 2] In the same manner as in Example 1, the electron beam irradiation conditions were a voltage of 500 kev and a dose of 6 Mrad. At this time, however, the degree of crosslinking proceeded too much, and the molecular weight measurement by GPC was not possible. It was possible. Using this resin, a foam was produced in the same manner as in Example 1 with a cell nucleating agent and an antioxidant. The foam thus obtained had a high expansion ratio of 23 times, but did not become a predetermined rod-like shape due to melt fracture, and had a wavy shape.

Comparative Example 3 100 parts by weight of low-density polyethylene (ZC-30, manufactured by Mitsubishi Petrochemical Co., Ltd., Mw = 140,000) was added to a cell nucleating agent (talc, average particle size 15 μm).
0.8 part by weight and 0.6 part by weight of the antioxidant were dry-blended and fed to a hopper of a vent type extruder (diameter 65 mm, L / D = 35) set at 130 ° C. Carbon dioxide gas was injected at a pressure of 70 kg / cm ² from the vent,
Diameter 2 set at 110 ° C with a discharge rate of 20 kg / hr
It was extruded and foamed into a rod shape from a mm die. The foam thus obtained was a foam having an expansion ratio of 12 times.

[0025]

EFFECTS OF THE INVENTION According to the present invention, there can be provided a method for producing a continuous and long olefinic resin foam which is safer and has excellent workability and does not worry about environmental pollution because the blowing agent is an inorganic gas. . The foam according to the present invention comprises a heat insulating material, a cushioning material,
It is extremely useful because it can be applied to various fields such as sealing materials and float materials.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location B29K 105: 04 B29L 7:00 4F C08L 23:00

Claims (1)

[Claims] 1. An olefin resin is modified by heating in the presence of a radical generator to a temperature at which free radicals are generated or higher, or by irradiating with ionizing radiation, and the weight average molecular weight thereof is 1 before modification. A method for producing an olefin-based resin foam, comprising injecting an inorganic gas in a molten state into a modified olefin-based resin having a volume ratio of 5 to 10 times, and then extruding the gas into a low-pressure region for foaming.