JPH0290418A - Foamed insulating wire - Google Patents

Abstract

PURPOSE:To obtain one with good appearance by making a foamed insulating material with which the surface of a core conductor is covered into such a composition as prescribed. CONSTITUTION:The foamed insulating material of a foamed insulating wire made up of a core conductor and a formed insulating material provided thereon consists of tetrafluoroalkyl vinyl ether copolymer (PFA) whose melt flow rate(MFR) is 20-30g/10min. When an MFR value of PFA is 20-30g/10min. as above, the melt viscosity of PFA is small and the expansion speed of gas becomes fast, so that even in case the wall thickness of an insulating material is small, bubbles sufficiently grow before the insulating material cools and freezes with the result that even in case of a wire whose external diameter of an insulating wire is less than 0.3mm, it is possible to obtain a thin and greatly expanded one whose expansion ratio is 70% or more without deteriorating the appearance of the wire.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is particularly applicable to coaxial cables with low propagation delay time and low characteristics among high-speed signal transmission coaxial cables used, for example, for wiring between computer racks and inside racks. This invention relates to improvements in foam insulated wires used in coaxial cables that require impedance.

(Prior technology) Insulated wires used in coaxial cables for high-speed signal transmission are (
Three characteristics are required: a) high-speed signal transmission, (b) high flame retardancy, and (c) high heat resistance. In recent years, requirements for these characteristics have become stricter, and in particular, high-speed signal transmission characteristics and lower characteristic impedance have been proposed. One of the measures of signal transmission speed is the propagation delay time, which is given by the following equation (1), and the smaller it is, the faster the signal transmission speed is.

τ= εs/3x108 --- (1) Furthermore, in the above formula, ε
S is the dielectric constant of the insulator. Further, the characteristic impedance Zo is given by the following equation (2).

Zo= (138,1/εs)x Iogd2/d+
-(2) In the above formula, d□ is the outer diameter of the core conductor, and d2 is the outer diameter of the insulated wire.

From these equations (1) and (2), in order to achieve low propagation delay time and low characteristic impedance, it is necessary to reduce εS, d2/d, and reduce the thickness of the insulated wire. Further, the foaming rate F is given by the following equation (3), and a low propagation delay time can be obtained by a high foaming rate.

F=(2ts+εair)(εo−ε5)x 10
0/3εs (εo −εair)---1-(3
) In the above equation, 60 is the relative permittivity specific to the material, and εair is the relative permittivity of air (cape i, o).

In the prior art, general-purpose thermoplastic resins or fluororesins with relatively low dielectric constants, such as foamed polyethylene (PE) and foamed polypropylene (PP), have been used as the insulators of the foamed insulated wires.

(Problems to be Solved by the Invention) PE and PP can make insulators thin and highly foamable, but they have extremely poor flame retardancy, and even after crosslinking, the heat resistance is 120 to 135 at continuous use temperature. If the temperature is low, about 100°C, and the thickness is thinner and the foam is highly foamed, it will be easily deformed and there will be problems in terms of strength.

Fluororesins include low dielectric constant tetrafluoroethylene (PTFE), tetrafluoroethylene/hexafluoroethylene copolymer (FEP), tetrafluoroethylene/perfluoroalkyl vinyl ether copolymer (PFA), and tetrafluoroethylene/hexafluoroethylene copolymer (FEP). Ethylene copolymer (ETFE) is used. Among these, PTFE has an extremely high melt viscosity, so it cannot be subjected to normal extrusion molding. In order to obtain a foam insulated wire, it must be made into a porous tape and wrapped. However, the drawbacks were that productivity was low, the foaming rate (porosity) was unstable, long products could not be obtained, and material costs were high.

Furthermore, thermoplastic resins such as FEP, PFA, and ETFE can all be used to manufacture foamed insulated wires by extrusion molding, but FEP is weak in terms of strength, and when used for foamed insulated wires, the tensile strength is low. , the deformability becomes extremely poor. This tendency increases as the thickness of the insulator decreases.
Moreover, the larger the foaming rate is, the more noticeable it becomes.

On the other hand, ETFE has drawbacks such as a small decrease in strength even when foamed, and a low melting point and low heat resistance. That is, the melting point is approximately 260
FEP (7) softens and deforms due to the heat of molten solder (220-250°C) at °C, and the continuous use temperature is 150°C.
It is much lower than 2000C and 2606C of PFA.

As mentioned above, PFA has an extremely high melting point of 300 to 310'C at a continuous operating temperature of 260 degrees Celsius, and its strength decreases little when foaming, making it suitable for thin-walled, highly foamed insulated wires.
Better than EP and ETFE. However, the PFA that has been used for foam insulated wires is ASTM D33
Melt flow rate (MF
R) Value: 7 to 16 g Zlo min (temperature 372°C 1 load 5
kgf), but if the wall thickness of the insulator is 0.3 mm or less, it becomes difficult to increase the foaming rate, so in order to increase the foaming rate of the insulator, it is necessary to increase the amount of gas that is the foaming source or to mold the insulator. Controlling the temperature to encourage bubble growth had the disadvantage that the gas could break through the insulation, making the surface of the wire look unsightly.

An object of the present invention is to avoid the above-mentioned drawbacks and provide a foam insulated wire having a thin wall and a high foaming ratio insulator without deteriorating the appearance.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides a foam insulated wire consisting of a core conductor and a foam insulator provided thereon, in which the foam insulator has a melt flow rate. The present invention provides a foam insulated wire characterized in that it is made of a tetrafluoroethylene/perfluoroalkyl vinyl ether copolymer (PFA) containing 20 to 30 g of ZlO (MFR) or 20 to 30 g of ZlO.

[Effect]

In this way, PFA(7) MFR value is 20-30g710
If the insulator is cooled and solidified, bubbles will grow sufficiently even if the insulator is thin because the melt viscosity of PFA is low and the expansion rate of the gas is high. Therefore, even if the insulated wire has an outer diameter of 0.3 mm or less, a thin, highly foamed insulated wire with a foaming rate of 70% or more can be obtained without deteriorating the appearance of the wire.

〔Example〕

Next, the foam insulated wire of the present invention will be described in detail, and this foam insulated wire consists of a core conductor and a foam insulator provided thereon.

Foam insulation has a melt flow rate (MFR) of 20 to 3.
It consists of 0 g/lo of tetrafluoroethylene/perfluoroalkyl vinyl ether copolymer (PFA). Note that this MFR is specified by ASTM D3307, the temperature is 372° C., and the load is 5 kgf. Foaming sources such as chlorofluorocarbon gas, carbon dioxide gas, and nitrogen gas are added to PFA, and a core material such as fine ceramic powder is added, but additives such as pigments may also be added as necessary. Can be done.

PFA is foamed by the following mechanism. First, PFA to which a nucleating agent has been added is melt-kneaded in an extruder, and a gas serving as a foaming source is added. The gas is dispersed within the extruder, and immediately after being discharged from the die, the gas expands using the nucleating agent as a nucleus to form bubbles. As already mentioned, when the MFR value of PFA is 20 to 30 g/10 minutes, the melt viscosity of PFA is small and the gas expansion speed is high, so even if the insulator is thin, the insulator will cool and solidify. The bubbles have grown sufficiently before Therefore, even if the insulated wire has an outer diameter of 0.3 mm or less, it is possible to obtain a thin, highly foamed insulated wire with a foaming rate of 70% or more without deteriorating the appearance of the wire. If the MFR value is less than 20, the melt viscosity is high and the insulator cools and solidifies before the bubbles grow sufficiently, and if it exceeds 30, too many bubbles are generated, which is not preferable.

Next, some specific examples of the present invention will be explained together with comparative examples.

Using an extruder with an outer diameter of 30 mm, 0.5 parts by weight of a ceramic nucleating agent was added to 100 parts by weight of PFA from a hopper,
Inject chlorofluorocarbon gas (Freon 22),
A foam insulated wire was manufactured by covering a core conductor of a single mild steel wire with an outer diameter of 0.18 mm with a foam insulator. The foaming rate and deformation rate of the foamed insulated wire thus obtained were measured, and the surface condition of the wire was observed. The results are shown in Table 1.2 below. Table 1 shows three specific examples of the present invention, and Table 2 shows two comparative examples.

The foaming rate can be determined from equation (3) after measuring the capacitance per meter of wire and finding the dielectric constant εS of the foam insulated wire using equation (4).

εs = (Cx log d2/d+)/24.13-
-- (4) In the above formula, F is foaming rate (%) and C is capacitance (pF/m).

In addition, the appearance of the surface of the electric wire was judged by visual inspection and touch, and was rated as ``good'' and ``bad'' as 1.

Table 1 Example 1 Example 2 Example 3 Material PFA (MFR25) 100 Nucleating agent 0.5 0.5 0.5 Freon 22 Freon 22 Freon 22 Specifications Characteristics Finished outer diameter (mm) Wall thickness (m layer) Static Capacity (, F/m) Foaming rate (z) Surface appearance material PFA (Liver R14) System core Agent specification characteristics Finished outer diameter (m+*) Wall thickness (11 plates) Capacitance (PF/m) Foaming rate ( X) 0.60 0.21 58.6 70.1 Good comparison example 1 0.5 Freon 22 0.70 0.26 52.2 69.5 0.70 0.26 52.0 70.0 Good comparison Example 2 0.70 0.26 50.0 75.0 Good 0.5 Freon 22 0.70 0.26 Surface appearance Bad Very bad According to the embodiment of the present invention, especially 70
It can be seen that even the electric wires with a high foaming rate of 50% or more have a good surface appearance. In addition, in the above Examples and Comparative Examples, the foaming rate was set to 69.5 to 75 (%), but in general, in the present invention, even if the foaming rate is increased, the appearance of the surface of the product will not deteriorate, but in the Comparative Example However, if the foaming rate is increased, the appearance of the product's surface will deteriorate, and sometimes the foaming rate cannot be increased even if the foaming rate is increased. In particular, it should be noted that the present invention can provide a thin, highly foamed insulator with a wall thickness of 0.5 mm or less and a foaming rate of 75% or more with good surface appearance.

(Effects of the Invention) According to the present invention, as described above, the MFR value of PFA is 2.
Since it is 0 to 30 g and 710 minutes, there is a practical benefit in that a thin-walled and highly foamed insulated wire can be obtained without deteriorating the surface appearance.

Claims (1)

[Claims] In a foam insulated wire consisting of a core conductor and a foam insulator provided thereon, the foam insulator is a tetrafluoroethylene/perfluoroalkyl vinyl ether copolymer having a melt flow rate (MFR) of 20 to 30 g/10 min. A foam insulated wire characterized by being made of a composite material (PFA).