JP4694225B2 - Method for reducing water absorption of coaxial cable and method for reducing tan δ of coaxial cable - Google Patents

Description

The present invention relates to a method for reducing the amount of water absorption of a coaxial cable that has low hygroscopicity and improved dielectric characteristics, and a method for reducing tan δ of the coaxial cable .

  In recent years, the frequency band used for cables has expanded and has expanded to the GHz band. On the other hand, the higher the frequency used, the greater the loss (dielectric loss) of the cable insulator portion. Therefore, a low dielectric characteristic (for example, tan δ) that is a measure of the loss is required.

  Conventionally, as a method for reducing such dielectric characteristics, it is often performed to foam a base resin. There are two types of foaming methods. One is gas foaming by introducing gas (for example, gas such as chlorofluorocarbon, nitrogen, carbon dioxide, hydrocarbon) into the base resin, and the other is foaming agent such as organic compound in the base resin. It is chemical foaming that is foamed with a gas obtained when added and thermally decomposed.

  In the case of gas foaming, there is an advantage that a foam having a high foaming degree can be obtained as compared with chemical foaming. On the other hand, chemical foaming, like gas foaming, is difficult to achieve high foaming, but has an advantage that foamed cells (nuclei) can be formed finely and uniformly.

In such chemical foaming, a compound used as a foaming agent is usually selected as appropriate depending on the extrusion temperature and kneading temperature of the base resin. For example, in polyethylene, azodicarbonamide (ADCA, see, for example, Patent Documents 1 to 3) and 4,4′-oxybis (benzenesulfonylhydrazide) (OBSH) are mainly used. Further, if necessary, a foaming assistant is also added. Foaming assistants have been used conventionally because they have a function of lowering the decomposition temperature of the foaming agent and increasing the foaming processing temperature.
JP 05-002939 A JP 2000-225638 A JP 2001-191388 A

  However, in the case of chemical foaming, there is an advantage that the foamed cells are finely and uniformly formed. However, the foaming agent compound is thermally decomposed to generate a foaming gas, and at the same time, generally a secondary cell is formed. A reaction also occurs, and a by-product that becomes a foaming residue is generated. Since the foaming gas is mainly nitrogen gas, carbon dioxide gas, or carbon monoxide gas, a compound having a polar functional group is inevitably generated as a foaming residue, which deteriorates the dielectric properties of the foam. there were.

  On the other hand, when a foaming aid is used together with the foaming agent, as described above, the decomposition temperature of the foaming agent can be lowered and low-temperature foaming is possible. There is a problem.

  Under such circumstances, the present inventors conducted various tests and found the following points. First, as described above, a foaming residue is generated by thermal decomposition of the foaming agent, but the residue component also varies depending on the thermal decomposition temperature, and as a result, characteristics of the resulting foam (dielectric characteristics, hygroscopicity, etc.) ) Also inspired me.

  Therefore, while the foaming agent, especially azodicarbonamide (ADCA), is foamed at the thermal decomposition temperature, it was investigated how the properties of the foam depended on the presence of foaming aid (such as zinc oxide). As a result, it was found that a foam having good characteristics can be obtained when an appropriate amount of foaming aid is added as compared with the case where no foaming aid is added. In particular, it has also been found that good results can be obtained by adding a foaming aid and foaming the foaming agent in a high temperature region (200 to 240 ° C.). In this case, if the base resin polyethylene (PE) having specific characteristics is used, in addition to low dielectric characteristics (for example, tan δ) and hygroscopicity, the outer diameter fluctuation is small, and the foam is rich in uniformity. It turns out that a cell is obtained.

The present invention has been made in this respect. Basically, an appropriate amount of a foaming agent, that is, a foaming aid of ADCA and a zinc compound, is added to the PE resin of the base resin. An object of the present invention is to provide a method of reducing the water absorption of a coaxial cable excellent in tan δ and hygroscopicity by extruding and foaming at 0 ° C. and a method of reducing tan δ of the coaxial cable .

The present invention according to claim 1 is a foaming aid comprising 100 parts by mass of polyethylene resin and 0.4 to 0.8 parts by mass of azodicarbonamide as a foaming agent and 5 to 15% by mass of zinc oxide based on the foaming agent. In the method of reducing the water absorption amount of the coaxial cable, an appropriate amount is added and extruded and foamed at 200 to 240 ° C.

The present invention according to claim 2 is a foaming aid comprising 100 parts by mass of polyethylene resin and 0.4 to 0.8 parts by mass of azodicarbonamide as a foaming agent and 5 to 15% by mass of zinc oxide based on the foaming agent. A method for reducing tan δ of a coaxial cable, which is characterized by adding an appropriate amount as described above and extruding and foaming at 200 to 240 ° C.

According to the method of reducing the tanδ of the method and coaxial cable to reduce the water absorption of the coaxial cable made in claim 1 of the present invention, the blowing agent of 0.4 to 0.8 parts by weight of polyethylene resins to 100 parts by mass A suitable amount of zinc compound of 5 to 15% by mass with respect to ADCA and the foaming agent is added as a foaming aid and extruded and foamed at 200 to 240 ° C., so that dielectric properties, tan δ are small, and hygroscopicity is small. A coaxial cable with excellent characteristics can be obtained.
In other words, when the dielectric property of the coaxial cable is small, the use frequency band of the cable is expanded by that amount, and the loss of the cable insulation portion can be minimized in use up to the GHz band. . Also, if the hygroscopicity is small, it is difficult to be affected by humidity fluctuations due to seasonal changes, and stable cable performance can be obtained.

FIG. 1 shows an example of a coaxial cable according to the present invention. In the figure, 1 is a conductor (internal conductor) such as a stranded wire conductor, 2 is an insulator made of foam coated on the conductor 1 by the method for manufacturing a coaxial cable of the present invention, and 3 is a metal braid or corrugated copper pipe. 4 is a sheath made of lead-free PVC or the like. The outer diameter of the cable is not particularly limited, but is formed as about 1.6 mm. If necessary, a metal laminate tape, for example, an aluminum pet made of aluminum foil and PET (PET) resin, or a copper pet tape made of copper foil and PET resin may be inserted between the insulator 2 and the metal layer 3. it can.

  In the case of the insulator, although not particularly limited, a polyethylene (PE) -based resin is used as a base resin, and 100 parts by mass of the PE-based resin is 5 to 15% by mass of zinc with respect to the blowing agent ADCA and the blowing agent. It is formed by adding an appropriate amount of a compound as a foaming aid and extruding and foaming at 200 to 240 ° C. As a result, it is possible to obtain a foam having excellent characteristics with low dielectric characteristics, for example, tan δ and low hygroscopicity. That is, the coaxial cable of the present invention can be obtained by covering the conductor 1 with the insulator made of the foam, coating the outer conductor, and then covering the sheath.

  As the foaming agent used in the present invention, it is desirable to use an azo compound type, and examples thereof include the above-mentioned azodicarbonamide (ADCA). In particular, it is preferable to use a fine particle having an average particle size of 10 μm or less, more preferably an average particle size of 5 μm or less. The reason is that a finer light emitting cell is obtained as the particle size is smaller.

  And the addition amount of this ADCA will not be specifically limited if it is the range used normally, For example, when obtaining a foaming degree of about 50%, with respect to 100 mass parts of PE resin, it is 0.4- It is desirable to set it as 0.8 mass part. In this case, if the amount is less than 0.4 parts by mass, a sufficient foaming effect cannot be obtained. If the amount exceeds 0.8 parts by mass, it is difficult to control the degree of foaming, the foam cell diameter, and the outer diameter fluctuation. Because.

  Although it does not specifically limit as a foaming adjuvant used by this invention, Use of a zinc compound (ZnO) is desirable. And the addition amount is desirable to be 5-15 mass% with respect to a foaming agent. If the amount is less than 5% by mass, a sufficient tan δ or hygroscopic reduction effect cannot be obtained with respect to the obtained foam, and if it exceeds 5% by mass, a better tan δ or hygroscopic reduction effect can be obtained. This is because it is not obtained, and further increases the cost and tan δ and εr.

  The addition of such appropriate amounts of foaming agent and foaming aid to the PE resin and extrusion foaming at 200-240 ° C. is evident from the examples described below, at temperatures below 200 ° C., tan δ and moisture absorption. This is because the property cannot be sufficiently reduced. In addition, at temperatures exceeding 240 ° C., it is presumed that the higher the thermal decomposition temperature of the foaming agent, the smaller the decomposition residue of the composition that lowers the properties of the resulting foam, but at this high temperature, This is because there is a risk that various decomposition reactions are promoted while the resin is retained. Further, even in the PE-based resin to be used, as will be described later, there are many cases where the melt breaking tension and the melt breaking speed are out of the range suitable for foaming.

In the case of a PE-based resin to which such an appropriate amount of foaming agent and foaming aid are added, in order to suppress fluctuations in the outer diameter of the obtained foam and to make the foam cell uniform, It is desirable to use a material having a density of 0.935 g / cm ³ or more, a melt breaking tension at a temperature of 200 to 240 ° C. of 0.05 g or more, and a melt breaking rate of 50 m / min or more at a temperature of 200 to 240 ° C.

  Such characteristics (conditions) of the PE-based resin may be satisfied by a single resin, or may be satisfied by a combination of a plurality of resins. Commercially available products satisfying such characteristics include ZC023 (trade name, manufactured by Ube Maruzen Polyethylene), Cab658 (trade name, manufactured by Ube Industries), 2070 (trade name, manufactured by Ube Industries), Hz-5305E (product) Name, manufactured by Mitsui Chemicals, Inc.), a blended product of Cab658 and 2070, a blended product of 2070 and B028, and the like.

  The base resin other than the PE resin is a homopolymer of a polyolefin hydrocarbon monomer such as polypropylene (PP), butene-1, pentene-1, hexene-1 or heptene-1, or two or more of these. Copolymers of these monomers, such as ethylene-propylene copolymers, ethylene-butene-1 copolymers, etc., or copolymers of these olefinic hydrocarbon monomers with a small amount of vinyl ester monomers or acrylate monomers, Examples thereof include an ethylene-vinyl acetate copolymer (EVA) and an ethylene-ethyl acrylate copolymer (EEA). And it is also possible to use these alone or as a blended product (mixture) of two or more.

  If necessary, other additives such as antioxidants, copper damage inhibitors, crosslinking aids, dispersants, inorganic fillers and the like can be appropriately added to the base resin composition of the present invention.

<Test example>
First, master batches (MB1, MB2) having the composition shown in Table 1 were prepared by kneading with a roll at 130 ° C. The PE resin at this time is ZC023 (trade name, manufactured by Ube Maruzen Polyethylene). Its properties are 0.940 g / cm ³ or more of density, 0.05 to 0.09 g of melt fracture tension at a temperature of 200 to 240 ° C., and 85.5 to 113 of melt fracture rate at a temperature of 200 to 240 ° C. .8 m / min or more.

  Next, this MB1 and PE resin were kneaded at a rotational speed of 80 rpm and 150 ° C. using a single screw extruder with the formulation shown in Table 2 to prepare a foamed resin mixture. Subsequently, in the same manner, a resin blend containing a foaming aid and a resin blend without an aid were prepared by blending shown in Table 3. In addition, in the said Tables 1-3, a compounding numerical value represents a mass part number.

  About the resin blend containing the foaming aid and the resin blend without the aid obtained as described above, as shown in Table 4, the foaming temperature was changed (160 ° C. to 240 ° C.), and foamed. The resulting foam was evaluated for water absorption (hygroscopicity) and tan δ (dielectric properties).

  In the foaming, first, each resin mixture was extruded using a single screw extruder at a rotation speed of 3 rpm and a residence time of 10 minutes. Next, this extruded foamed resin was press degassed at 130 ° C. and then pelletized, and formed into a rod-like body having an outer diameter of 2 mm × height of about 100 mm at 140 ° C. Thereafter, the formed rod-shaped body was once dried by a vacuum dryer at 60 ° C. and 1 mmHg or less for 72 hours. Moisture absorption was performed by sealing in a desiccator (container) at 24 ° C. and 100% RH. The water absorption amount and tan δ (Δtan δ) were measured by the following method after drying and sealing the sample in a desiccator and then removing the sample rods every few hours.

<Measurement of Water Absorption> The measurement was performed by the Karl Fischer moisture measurement method. Sample heating temperature: 150 ° C., sample heating time: 15 min, moisture detection time: 10 min.
<Tan δ Measurement> The measurement was performed by a cavity resonance perturbation method. As described above, the sample rod-shaped body had an outer diameter of 2 mm and a height of around 100 mm. In this tan δ measurement, specifically, a Δ tan δ value was obtained.

  From Table 4, it can be seen that, in the case of a resin blend containing a foaming aid, the amount of water absorption and the tan δ value decrease as the temperature increases in each foaming temperature region, compared to the resin blend without an aid. . In the case of the resin mixture without an auxiliary agent, ADCA hardly hardly decomposes at a foaming temperature of 160 ° C. or 180 ° C., so the test was omitted.

  In Table 5, the amount of foaming agent and the amount of foaming aid of the resin admixture containing the foaming aid were changed (foaming agent amount 0.4 parts by weight, foaming aid amount 0.02 parts by weight, foaming agent amount 0.8 The water absorption amount and tan δ were evaluated in the same manner as in the case of Table 4 above. In addition, the addition amount of a foaming adjuvant is 5-15 mass% with respect to the addition amount of a foaming agent. From Table 5, even when the amount of foaming agent and the amount of foaming aid is small (lower limit value), on the contrary, when the amount of foaming agent and the amount of foaming aid is large (upper limit value), the practical water absorption amount, tan δ value It can be seen that

  In Tables 6 to 7, using other PE-based resins 1 to 6 other than ZC023, as in Tables 1 to 3, resin blends containing foaming assistants were prepared, and these resin blends were extruded. Each of the conductors (inner conductors) was extrusion coated with an insulator thickness of 0.51 mm and a foaming degree of 50% at a heating temperature of 200 ° C., 220 ° C., and 240 ° C. using a machine. Thereafter, an outer conductor and a sheath were applied to obtain a coaxial cable. The inner conductor is 7 bare soft copper stranded wires with a diameter of 0.203 mm.

A capillary rheometer (manufactured by Toyo Seiki Co., Ltd.) was used for evaluating the characteristics (melting rupture tension and melt rupture speed) in the table of the PE resins 1 to 6 used. In this measuring apparatus, measurement temperature: 190 ° C., piston speed: 10 mm / min, time scale: 10 min (time required to accelerate from the initial speed to the maximum speed of 200 m / min), acceleration: about 20 m / min ² {(maximum Speed−initial speed) / time scale}, capillary: outer diameter 2.095 mm × height 8.03 mm.

  In the coaxial cable covered with the above foamed insulator, the outer diameter fluctuation and the state of the foamed cell were evaluated, and comprehensive evaluation was performed.

  <Outer diameter fluctuation> The outer diameter fluctuation was evaluated according to the following criteria. “Small”: The fluctuation width of the outer diameter is less than 5% of the thickness of the foamed insulator. “Medium”: The outer diameter fluctuation width is 5% or more and less than 10% of the thickness of the foamed insulator. “Large”: The outer diameter fluctuation width is 10% or more of the thickness of the foamed insulator.

  <State of foamed cell> The state of the foamed cell was evaluated according to the following criteria. “◯”: No bubble (continuous foaming), average foamed cell diameter of 80 μm or less, and small variation in cell diameter. “X”: One having continuous bubbles, one having an average foamed cell diameter of more than 80 μm, or one having a large variation in cell diameter.

From Tables 6 to 7, the PE resin used in the present invention has a density of 0.935 g / cm ³ or more, a melt breaking tension of 0.05 g or more at the temperature of 200 to 240 ° C., The melt fracture rate at a temperature of 200 to 240 ° C. is 50 m / min or more (in the case of A, B, G, and H in the table), the fluctuation of the outer diameter is small, the state of the foam cell is uniform, and the foam cell Is also small.

1 is a longitudinal end view showing an example of a high-frequency coaxial cable according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Conductor (inner conductor), 2 ... Insulator, 3 ... Metal layer (outer conductor), 4 ... Sheath

Claims (2)

An appropriate amount of 0.4 to 0.8 parts by mass of azodicarbonamide as a foaming agent and 5 to 15% by mass of zinc oxide based on the foaming agent as a foaming aid is added to 100 parts by mass of polyethylene resin , and 200 to 240 ° C. A method for reducing the water absorption of a coaxial cable, characterized by being extruded and foamed underneath. An appropriate amount of 0.4 to 0.8 parts by mass of azodicarbonamide as a foaming agent and 5 to 15% by mass of zinc oxide based on the foaming agent as a foaming aid is added to 100 parts by mass of polyethylene resin , and 200 to 240 ° C. A method for reducing tan δ of a coaxial cable, characterized by being extruded and foamed under.

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