JPH06298981A - Foam and its production - Google Patents

Abstract

PURPOSE:To obtain a foam, having a prescribed thickness, a prescribed average bubble diameter and a prescribed foaming degree, excellent in uniformity and insulating properties without causing the buckling, etc., and suitable as an insulating layer, etc., of a coaxial cable by carrying out the expansion with a physical foaming agent such as a rare gas and a chemical foaming agent. CONSTITUTION:The foam is obtained by carrying out the expansion with a physical foaming agent, composed of a rare gas such as argon gas or the rare gas and one or more of gaseous carbon dioxide and nitrogen and containing >=40vol.% content of the rare gas [used in an amount of preferably 0.001-10 pts.wt. based on 100 pts.wt. organic polymer to be foamed] and a chemical foaming agent such as azodicarbonamide [used in an amount of preferably 0.1-10 pts.wt. based on 100 pts.wt. organic polymer to be foamed]. This foam has >=1mm thickness, 200-500mum average cell diameter of >=80% cells present therein and 75-85% foaming degree.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a high degree of foaming of 75 to 85% obtained by using a rare gas, particularly argon as a physical foaming agent, and 80% of the bubbles existing in the foam. The above is the average bubble diameter of 200 to 500 μm.
The present invention relates to a foam having a very fine bubble diameter, and particularly to a foam suitable for an insulating layer of a coaxial cable.

[0002]

2. Description of the Related Art Conventionally, various freon gases have been used as a foaming agent in order to obtain a foam having a high degree of foaming.
Its use tends to be regulated for environmental protection because it causes destruction of the ozone layer.

[0003]

Under such circumstances, there is currently a demand for a foam which is obtained by using a physical foaming agent instead of Freon gas and which has a high degree of foaming and a fine and fine foam diameter. Has been. Insulated conductors such as foam insulated wires are required to have a high degree of insulation properties and may be subjected to considerably severe conditions when laid, so that the insulation foam layer may not buckle. Required.

[0004]

As a result of various studies aimed at solving the above problems, the present inventors have used a physical foaming agent containing a rare gas, particularly 40% or more of an argon gas, as a physical foaming agent. The thickness of the foam is 1
mm or more, the degree of foaming is 75 to 85%, and 80% or more of the bubbles present in the foam have an average bubble diameter of 200 to 500 μ.
The present invention has been completed by finding that such a foam having m and being sufficiently usable as an insulated conductor.

That is, the present invention comprises a rare gas or a rare gas and at least one of carbon dioxide and nitrogen,
A foam produced by using a physical foaming agent having an amount of a rare gas of 40% by volume or more, the foam having a thickness of 1 mm or more, and 80% or more of bubbles existing in the foam. It relates to a foam having an average foam diameter of 200 to 500 μm and a foaming degree of 75 to 85%.

The foam of the present invention has a thickness of at least 1 m.
It must be m. When the thickness of the foam is less than 1 mm, sufficient insulation cannot be obtained and electrical characteristics are not satisfied. Further, it is essential that the foaming degree of the foam is in the range of 75 to 85%. 8 of the bubbles that exist in the foam
It is essential that 0% or more of the average diameter is in the range of 200 to 500 μm. When the degree of foaming is higher than 85% and the average bubble diameter is larger than 500 μm, the width of the bubble diameter distribution becomes large and the number of continuous bubbles also increases, so that the buckling resistance is lowered and the VSWR characteristics are also increased. Also decreases. On the other hand, the average bubble diameter is 2
If it is attempted to make the particles finer than 00 μm, the degree of foaming will not increase.

In order to obtain such a foam, in the present invention, a rare gas of helium, neon, argon, krypton, xenon and radon, or a mixed gas of a rare gas and at least one selected from carbon dioxide and nitrogen. Is used as a physical foaming agent. Among the rare gases, particularly when argon is used, a foam having a high degree of foaming and having closed cells with a fine bubble diameter can be obtained. When a mixed gas of a rare gas and carbon dioxide gas and / or nitrogen is used as the physical foaming agent, the amount of the rare gas needs to be 40% by volume or more in the physical foaming agent, and further 50 to 70% by volume. Ranges are preferred. If the amount of the rare gas is less than 40% by volume, a sufficient degree of foaming cannot be obtained and the electrical properties of the cable cannot be satisfied. When carbon dioxide and nitrogen are used in addition to the rare gas, the ratio (volume ratio) of carbon dioxide and nitrogen is preferably 40:60 to 60:40.

The purity of the foaming agent is preferably 99.9% or more, more preferably 99.99% or more.

As the organic polymer to be foamed in the present invention, an olefin resin and a thermoplastic resin such as polystyrene are targeted, and among them, an olefin resin is preferable.
In particular, α-olefin resins such as polyethylene including high density polyethylene (HDPE) and low density polyethylene (LDPE), polypropylene, and ethylene / propylene copolymer are preferable. These may be used alone or as a mixture.

The organic polymer contains a chemical foaming agent. The chemical foaming agent plays a role of a foaming agent, but is believed to be able to play a role of a nucleating agent. Specific examples of such a chemical foaming agent include 4,
4'-oxybisbenzenesulfonyl hydrazide (OB
Examples thereof include organic foaming agents such as SH) and azodicarbonamide (ADCA), inorganic decomposable compounds such as sodium bicarbonate, and the like, which decompose to generate gas by heat. These may be used alone or as a mixture.
Among them, ADCA alone or ADCA and OBSH
The mixture (1) is preferable from the viewpoint that a particularly high degree of foaming can be obtained.

The amount of the chemical foaming agent varies depending on the type of the organic polymer or the chemical foaming agent to be used and cannot be generally stated. Generally, it is about 0.1 to 10 parts by weight per 100 parts by weight of the organic polymer. Parts, preferably 0.5 to 5 parts by weight, more preferably 1 to 3 parts by weight.

The organic polymer and the chemical foaming agent may further contain inorganic particles as a nucleating agent. As a specific example of such inorganic particles, silicon oxide (Si
O ₂ ), boron nitride (BN) and the like. The amount of the inorganic particles used is 0.01 with respect to 100 parts by weight of the organic polymer.
-10 parts by weight, particularly 0.1-1 part by weight is preferred.

The foam of the present invention can be obtained by injecting a physical foaming agent into a mixture obtained by melt-mixing an organic polymer with a chemical foaming agent and, if necessary, inorganic particles to foam the mixture. The addition amount of the physical foaming agent varies depending on the type of the organic polymer and the foaming agent to be used and is not unconditionally determined, but generally, it is 0.0
The amount is 01 to 10 parts by weight, preferably 0.01 to 1 part by weight.

If necessary, the foamable composition may be appropriately mixed with additives such as a copper damage inhibitor, an antioxidant and a coloring agent.

The foam of the present invention is preferably one obtained by foaming extrusion molding. Among them, the foamable composition is fed onto the conductor by an extrusion molding method to form an insulating layer on the conductor. However, the one obtained by a method of forming an insulating layer having a foamed structure simultaneously with molding is a particularly preferred embodiment.

For example, an organic polymer, a chemical foaming agent, and optionally inorganic particles are supplied to an extruder, and a physical foaming agent is pressed into a barrel of the extruder through a foaming agent injection hole formed separately. Then, the both are mixed to form a foamable composition, which is foamed and extruded on a conductor to form an insulated conductor having a foamed insulating layer. The foamed insulating layer thus formed may be further subjected to a subsequent treatment such as a crosslinking treatment or a post-foaming treatment. The method for injecting the physical foaming agent is not particularly limited, but it is preferable to inject it by injecting at a sonic velocity.

The temperature and pressure in the extruder are appropriately determined depending on the chemical foaming agent, organic polymer, etc. used. For example, when polyethylene is used, 130 to 170
It is preferable to adjust the temperature to 100 ° C. and 100 to 200 atm. Similarly to the above, the pressure at which the foaming agent is press-fitted cannot be determined unconditionally, but it is usually adjusted to 100 to 200 atm, preferably about 150 atm.

[0018]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

Example 1 Using a foam insulation cable production line, high density polyethylene as an organic polymer and ADCA as a chemical foaming agent
0.5 parts by weight of 100 parts by weight of the organic polymer are melt-mixed, and a mixture of argon and carbon dioxide (Ar: CO ₂ = 6: 4, volume ratio) is added as a physical foaming agent to the organic polymer 100 parts by weight. 0.2 parts by weight of each part was sonically injected and press-fitted. This is the foam insulation cable (9.6m) under the following extrusion conditions.
m) Extruded and foamed on top. Internal temperature of the first extruder (65 mm): 210 to 200 ° C. Internal temperature of the second extruder (90 mm): 160 to 150 ° C. The foamed insulation cable provided with the foamed layer discharged from the die is
To harden the surface, it was blown with cooling air and then rolled through a cooling water bath. The outer diameter of the obtained insulated cable was 22 mm. The obtained foamed layer had fine closed cells uniformly. The degree of foaming, the average diameter of the foam, the buckling resistance, the amount of attenuation, and the VSWR characteristics of the obtained foam layer were measured. Buckling resistance refers to the diameter of the mandrill when the obtained foam insulated cable (outer diameter: 22 mm) is wound around the mandrill and buckling occurs for the first time. The composition of the starting composition is shown in Table 1, and the physical properties of the foamed insulated cable obtained are shown in Table 2. In Table 1, the blending amount of the physical foaming agent, the chemical foaming agent and the inorganic particles is 100 parts by weight based on 100 parts by weight of the organic polymer, the component ratio when the physical foaming agent is used as a mixture is the volume ratio, and the organic polymer is The component ratio when used as is a weight ratio.

Example 2 0.3 parts by weight of ADCA as a chemical foaming agent was used per 100 parts by weight of an organic polymer, and SiO ₂ as inorganic particles was used at 0.2 parts by weight per 100 parts by weight of an organic polymer. A foam insulated cable was obtained in the same procedure as in Example 1 except for the above. The obtained foamed layer had fine closed cells uniformly. With respect to the obtained insulated cable, the same physical properties as in Example 1 were measured. The composition of the starting compound is shown in Table 1, and the physical properties of the foamed insulated cable obtained are shown in Table 2.

Example 3 As a physical blowing agent, a mixture of argon and nitrogen (Ar: N ₂
= 6: 4, capacity ratio) was used to obtain a foam insulated cable in the same procedure as in Example 1. The obtained foamed layer had fine closed cells uniformly. With respect to the obtained insulated cable, the same physical properties as in Example 1 were measured. The composition of the starting compound is shown in Table 1, and the physical properties of the foamed insulated cable obtained are shown in Table 2.

Example 4 Mixing Argon, Carbon Dioxide and Nitrogen as Physical Blowing Agent
Thing (Ar: CO₂: N ₂= 5: 3: 2, capacity ratio)
A foam insulated cable was prepared by the same procedure as in Example 1 except that
Obtained. The obtained foam layer has fine closed cells uniformly.
Was there. Regarding the obtained insulated cable, the same as in Example 1
Was measured. The formulation of the starting compounds is given in Table 1,
Table 2 shows the physical properties of the foamed insulated cable.

Example 5 A foam insulated cable was obtained in the same procedure as in Example 2 except that BN was used instead of SiO ₂ as the inorganic particles. The obtained foamed layer had fine closed cells uniformly. With respect to the obtained insulated cable, the same physical properties as in Example 1 were measured. The composition of the starting compound is shown in Table 1, and the physical properties of the foamed insulated cable obtained are shown in Table 2.

Example 6 A mixture of helium and carbon dioxide gas (He:
A foam insulated cable was obtained by the same procedure as in Example 1 except that CO ₂ = 6: 4, capacity ratio) was used. The obtained foamed layer had fine closed cells uniformly. With respect to the obtained insulated cable, the same physical properties as in Example 1 were measured. The composition of the starting compound is shown in Table 1, and the physical properties of the foamed insulated cable obtained are shown in Table 2.

Example 7 A foam insulated cable was obtained in the same procedure as in Example 1 except that a mixture of high-density polyethylene and low-density polyethylene (5: 5, weight ratio) was used as the organic polymer. The obtained foamed layer had fine closed cells uniformly. With respect to the obtained insulated cable, the same physical properties as in Example 1 were measured. The composition of the starting compound is shown in Table 1, and the physical properties of the foamed insulated cable obtained are shown in Table 2.

Example 8 A foam insulated cable was obtained by the same procedure as in Example 1 except that argon was used as the physical foaming agent. The obtained foamed layer had fine closed cells uniformly. With respect to the obtained insulated cable, the same physical properties as in Example 1 were measured. The composition of the starting compound is shown in Table 1, and the physical properties of the foamed insulated cable obtained are shown in Table 2.

Comparative Example 1 A foam insulated cable was obtained in the same procedure as in Example 1 except that ADCA was not used. Open cells were present in the obtained foam layer. Regarding the obtained insulated cable, Example 1
The same physical properties were measured.

Reference Example 1 A foam insulated cable was obtained by the same procedure as in Example 1 except that Freon 22 was used as a physical foaming agent in an amount of 0.2 part by weight based on 100 parts by weight of polyethylene. Open cells were present in the obtained foam layer. With respect to the obtained insulated cable, the same physical properties as in Example 1 were measured. Table 1 shows the composition of the starting compounds.
Table 2 shows the physical properties of the foamed insulated cable obtained.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

As described above, foaming is performed using the rare gas which is the foam of the present invention, or the physical foaming agent which comprises at least one of rare gas and carbon dioxide gas and nitrogen and whose rare gas content is 40% by volume or more. The foam, which has a thickness of 1 mm or more, and is 8 mm or less in the foam.
0% or more has an average foam diameter of 200 to 500 μm, and the degree of foaming is 75 to 85%. The foam has a high degree of foaming and at the same time the diameter of the bubbles in the foam is fine and uniform.
It is a foam having a dense foam structure. Therefore, when it is applied as a foam layer of an insulated conductor such as a foam insulated wire that requires particularly high insulation properties and may be subjected to considerably severe conditions during its laying, buckling does not occur. Can be an insulated conductor.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takuma Takai, 8 Nishinomachi, Higashimukaijima, Amagasaki City, Hyogo Prefecture Mitsubishi Electric Wire & Cable Co., Ltd. (72) Mutsumi Wada, 8th Nishinomachi, Higashimukaijima, Amagasaki City, Hyogo Wire Industry Co., Ltd. (72) Inventor Kanesharu Suga 4-3 Ikejiri, Itami City, Hyogo Prefecture Mitsubishi Cable Industries Itami Works

Claims (6)

[Claims] 1. A foam formed by using a rare gas or a physical foaming agent containing at least one of rare gas, carbon dioxide gas and nitrogen and having a rare gas content of 40% by volume or more, and a chemical foaming agent. , The foam has a thickness of 1 mm or more, and 80% or more of the bubbles present in the foam have an average bubble diameter of 2
A foam having a foaming degree of 75 to 85% and having a size of 00 to 500 μm. 2. The foam according to claim 1, wherein the rare gas is argon gas. 3. The foam according to claim 1, which is foamed using ADCA and / or OBSH as a chemical foaming agent. 4. The foam according to claim 1, 2 or 3, wherein the physical foaming agent is used in an amount of 0.001 to 10 parts by weight based on 100 parts by weight of the organic polymer to be foamed. 5. The foam according to claim 1, 2, 3 or 4, wherein the amount of the chemical foaming agent used is 0.1 to 10 parts by weight based on 100 parts by weight of the organic polymer to be foamed. body. 6. A physical foaming agent containing a rare gas or at least one kind of a rare gas, carbon dioxide gas and nitrogen and having a rare gas content of 40% by volume or more and a chemical foaming agent, and foamed to have a thickness of 1 mm or more. , 80% of the foam present in the foam
The average bubble diameter is 200 to 500 μm and the foaming degree is 75.
A method for producing a foam, which comprises obtaining a foam having a content of ˜85%.