JPH04224833A - Production of expanded polyolefin molding - Google Patents

Abstract

PURPOSE:To produce an expanded polyolefin molding of a high expansion ratio. CONSTITUTION:A process for extrusion-foaming a polyolefin resin, wherein a mixture of methanol or ethanol with at least one compound selected from the group consisting of diethyl ether, vinyl ethyl ether, acetone, n-pentane and isopentane is used as a blowing agent. Since the blowing agent is liquid, it can be supplied at high accuracy. A high-speed signal transmission cable provided with a highly expanded insulation layer of a degree of expansion of 75% or above can be produced in a nonpolluting manner.

Description

[Detailed description of the invention]

The present invention relates to a method for producing a foamed polyolefin molded article, and more particularly to a method for producing a foamed polyolefin molded article with a high expansion rate using a non-polluting blowing agent.

0002

2. Description of the Related Art Foam insulated wires, in which the outer periphery of a conductor is covered with an insulating layer of foam, are widely used as wires connecting computers, for example, in order to shorten signal propagation delay time as much as possible. One of the methods for manufacturing such a foam insulated wire is as follows.

That is, a polyolefin resin such as polyethylene is melt-kneaded in an extruder, a foaming agent is supplied from the middle of the extruder, and the outer periphery of the conductor is covered with foam while the polyolefin resin is foamed. This is the way to do it. Conventionally, the foaming agents used for this foam extrusion coating include:
Chlorofluorocarbon (commonly known as CFC), nitrogen gas,
Gases that are gases at room temperature and pressure, such as carbon dioxide, propane, and butane, and that do not react with polyolefin resins,
Low boiling point organic solvents such as n-pentane, n-hexane, methanol, and ethanol have been used. In particular, fluorocarbons have been widely used because they are easy to handle and have excellent effects as blowing agents.

Among these blowing agents, gases are supplied in a predetermined amount in the middle of the extruder using a gas flow meter or gas pressure regulator, and low boiling point organic solvents are It is supplied using a liquid injection pump etc. However, gases such as some chlorofluorocarbons, which are gases at room temperature and pressure but have a low vapor pressure, are sometimes supplied after being pressurized at a relatively low pressure and liquefied.

[0005]

[Problems to be Solved by the Invention] By the way, fluorocarbons, which have been the mainstream of conventional foaming agents, destroy the ozone layer. Therefore, the use of certain fluorocarbons, which have a particularly high ozone resolution, is expected to be completely abolished by the year 2000, and it is expected that other fluorocarbons will also be completely abolished in the coming years.

[0006] Therefore, for the production of foamed polyolefin molded articles, there is a strong demand for the development of a non-polluting blowing agent that can replace fluorocarbons. On the other hand, among the above-mentioned foamed insulated wires, those for high-speed signal transmission cables are becoming more foamed and smaller in diameter in recent years. However, as the diameter of the foamed insulator becomes smaller, the amount of blowing agent that must be supplied during foaming becomes smaller, and moreover, it becomes necessary to precisely control the amount of foaming agent supplied. This is because if the supply amount of the foaming agent is unstable, the thickness and electrical properties of the molded foamed insulator will also become unstable.

[0007] However, it is extremely difficult to supply the above-mentioned gases with high accuracy by adjusting the amount of the gases described above using the above-mentioned flowmeter or the like. In addition, if these gases are liquefied, it becomes possible to supply small quantities with high precision, but liquefaction requires an environment of ultra-high pressure or ultra-low temperature, which is very difficult to achieve industrially from a safety and economic perspective. This cannot be said to be a proper treatment. Therefore, as a blowing agent to replace chlorofluorocarbons, the above-mentioned low-boiling point organic solvents are considered to be suitable for supplying a small amount with high precision.

By the way, in the case of foam insulated wires for high-speed signal transmission cables, for example, it is preferable that the insulator is highly foamed, as described above. It is said that the foaming rate at this time is preferably 50% or more, particularly 75% or more. However, if each of the above-mentioned low-boiling organic solvents is used alone as a blowing agent, the pollution problems caused by using fluorocarbons can be solved, but on the other hand, it is difficult to produce a foamed polyolefin molded article with a high foaming rate. Have difficulty. In particular, it has been extremely difficult to manufacture products with a foaming rate of 75% or more.

The object of the present invention is to solve the above-mentioned problems and provide a method for producing a foamed polyolefin molded article having a foaming rate of 75% or more even when a low boiling point organic solvent is used.

0010

[Means for Solving the Problems] In order to achieve the above object, in the present invention, a polyolefin resin is melt-kneaded in an extruder, and then a foaming agent is injected from the middle of the extruder to form a foamed polyolefin. In the method of manufacturing a foaming agent, the blowing agent comprises methanol or ethanol;
diethyl ether, vinyl ethyl ether, acetone,
Provided is a method for producing a foamed polyolefin molded article, characterized in that the mixture is a mixture with at least one compound selected from the group of n-pentane and iso-pentane.

First, the polyolefin resin used in the method of the present invention includes, for example, polyethylene such as low density polyethylene, medium density polyethylene, high density polyethylene, and linear low density polyethylene; polypropylene; ethylene-acrylic acid copolymer; Examples include polyolefin copolymers such as ethylene-methacrylic acid copolymer, ethylene-ethyl acrylate copolymer, ethylene-vinyl acetate copolymer, and ethylene-propylene copolymer. Each of these may be used alone, or two or more types may be mixed as appropriate.

Next, the blowing agent used in the method of the present invention is a liquid mixture prepared by mixing an organic solvent described below. In that case, methanol (boiling point 64
．． 6°C), ethanol (boiling point 78.3°C), and the other organic solvent was diethyl ether (boiling point 34.5°C), vinyl ethyl ether (boiling point 35.7°C), acetone (boiling point 35.7°C). 56.1℃)
, n-pentane (boiling point: 36.1°C), and iso-pentane (boiling point: 27.9°C). One or more of them are selected, and both are mixed.

[0013] The mixing ratio at this time is not particularly limited, and may be any ratio. In the method of the present invention, when a polyolefin resin is melt-kneaded and extruded using an extruder, a predetermined amount of the above-mentioned blowing agent may be injected from the middle of the extruder. At this time, in addition to the above foaming agent,
A pyrolytic blowing agent that generates nitrogen gas, carbon dioxide gas, etc. by pyrolysis may be used in combination. Also, if necessary,
The polyolefin resin to be melt-kneaded may further contain a foaming nucleating agent, an anti-aging agent, a coloring agent, a crosslinking aid, and the like. Furthermore, even if the crosslinking treatment is performed, the effect of the blowing agent injection described above does not change.

[0014]

[Example] [Examples 1 to 10, Comparative Examples 1 to 13] Low density polyethylene (melt index 1.0 g/10 minutes)
A composition consisting of 100 parts by weight and 1.0 parts by weight of talc (foaming nucleating agent) was melt-kneaded in an extruder with a diameter of 30 mm,
Inject the blowing agent shown in Table 1 from the middle of the extruder,
A foamed insulated wire with a finished outer diameter of about 1.0 mm was produced by extrusion coating on a soft copper single wire with a diameter of 0.32 mm.

For each example, the maximum foaming rate (%) was measured when the injection amount of the foaming agent and the set temperature during melt-kneading were varied, and the value was taken as the foaming rate. Table 1 shows the above results.
It was shown to.

[0016]

[Table 1]

[0017]

As is clear from the above description, according to the method of the present invention, a foamed polyolefin molded article with a high expansion rate can be produced without using fluorocarbons. Since the foaming agent used is a non-polluting liquid, its supply amount can be adjusted with high precision, making it suitable for producing highly foamed and thin-diameter foamed insulated wires.

Claims (1)

[Claims] 1. A method for producing a foamed polyolefin molded article by melt-kneading a polyolefin resin in an extruder and then injecting a foaming agent from the middle of the extruder, comprising:
Foamed polyolefin molding, characterized in that the blowing agent is a mixture of methanol or ethanol and at least one compound selected from the group of diethyl ether, vinyl ethyl ether, acetone, n-pentane, and iso-pentane. How the body is manufactured.