JP3605136B2 - High foam polyethylene coaxial cable manufacturing method - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a method for manufacturing a coaxial cable, and more particularly to a method for manufacturing a coaxial cable suitable for manufacturing a coaxial cable having a highly foamable insulator.
[0002]
[Prior art]
A coaxial cable that uses a foam material injected into polyethylene to form an insulator with a high degree of foaming and uses this insulator as the dielectric of the coaxial cable has a dielectric loss that is lower than that of a coaxial cable that uses ordinary polyethylene as the insulator. And the transmission characteristics are significantly improved.
[0003]
As a method of forming bubbles in polyethylene, there are known a method using a chemical foaming material that generates bubbles by a decomposition gas generated by decomposition of a foaming material, and a method using an inert gas. Such a foamed material has a high foaming material decomposition temperature, so that the resin is soft and the cell wall is continuous, so that a stable product cannot be obtained.
[0004]
Therefore, as the foaming material, chlorofluorocarbon (Fluoro Carbon), which is a compound of carbon, fluorine, hydrogen, and chlorine (CHClF ₂ ), which is currently usually called chlorofluorocarbon gas, is used. A high degree of foaming of about 70% is achieved.
By the way, the above chlorofluorocarbon gas is gasified at a low boiling point and becomes a colorless and odorless stable gas.When this gas is released into the atmosphere and reaches the stratosphere, when it is decomposed by ultraviolet rays, it generates chlorine atoms and destroys the ozone layer. Global environmental problems have arisen.
[0005]
[Problems to be solved by the invention]
Therefore, there is a demand for a technique for producing a coaxial cable having a foaming ratio of 70% or more using an inert gas injected into polyethylene instead of chlorofluorocarbon, but a general inert gas is polyethylene. Due to its low solubility compared to the above, it has not yet been established to manufacture a coaxial cable using a homogeneous insulator having a high foaming ratio of 70% or more.
[0006]
[Means for Solving the Problems]
The present invention has been made for the purpose of solving such problems,
In the method for manufacturing a high-foamed polyethylene coaxial cable in a high-foamed coaxial cable manufacturing apparatus, an inert gas obtained by mixing nitrogen gas and carbon dioxide, and a resin obtained by mixing high-density polyethylene and low-density polyethylene are supplied to an extruder and discharged from the extruder. The insulated wire having a foaming degree of at least 70% is formed by extruding the melted and foamed polyethylene around the central conductor through a gear pump, and a hot melt type adhesive is applied to the outer surface of the insulated wire. After the coating, the outer conductor and the sheath are covered, and the adhesive is melted by heating at the time of covering the sheath so that the outer conductor and the insulator are integrated to produce a coaxial cable. is there.
[0009]
[Action]
High-density polyethylene and low-density polyethylene are mixed at a predetermined ratio, and the mixed polyethylene is extruded in a molten state while injecting an inert gas as a foaming material, and a certain amount of polyethylene is rectified to the discharge port side. Since the gear pump for supplying to the crosshead is provided, the outer diameter of the foamed insulator covering the periphery of the conductor can be made uniform, and the bubbles in the foamed polyethylene can be generated in a uniform state. Will be possible.
[0010]
In addition, when a hot-melt type adhesive is thinly applied to the outer surface of the insulator covered by the above-described method, when the outer conductor constituting the coaxial cable and the insulator are later covered with a sheath for protecting the cable. , The rainwater leaking into the coaxial cable can be effectively prevented from causing running water, and the transmission characteristics of the cable can be prevented from deteriorating.
[0011]
【Example】
FIG. 1 is a perspective view showing the appearance of a cable manufactured by the method for manufacturing a high-foamed coaxial cable of the present invention, wherein 1 is a center conductor, and 2 is around the center conductor, which is covered by an extruder described later. 2 shows an insulator. The outer periphery of the insulator is covered with an external conductor 3 with aluminum or the like to form a coaxial cable.
Reference numeral 4 denotes a sheath for protecting the coaxial cable.
[0012]
The insulator 2 is formed by extruding polyethylene around the central conductor 1. In extruding the polyethylene, the inert gas is kneaded to form bubbles 5 so that the foaming property is increased. It forms an insulator.
[0013]
FIG. 2 is an enlarged (20-fold) cross section of the coaxial cable of the present invention in which nitrogen gas and carbon dioxide are mixed as an inert gas. In this embodiment, nitrogen gas 75%, carbon dioxide 25%, high The density of the polyethylene is 90% and the density of the low density polyethylene is 10%.
FIG. 3 shows the value of the solubility (solubility) of the inert gas into polyethylene (Henris Law). The carbon dioxide gas is 0.275 with respect to 0.435 (cc / g · atm) of Freon, and the nitrogen gas is Is 0.111.
When only nitrogen gas is used as the inert gas, for example, as shown in FIG. 4A, the bubbles 5 are small but the degree of foaming is low (65%). As shown in the cross section of FIG. 4 (b), the bubble 5 can be made very large. However, since carbon dioxide gas has a large compression / expansion ratio, the bubble is continuous and the insulator having a uniform bubble and outer shape is formed. Extrusion becomes difficult.
[0014]
According to the present invention, the mixing ratio of the insulator 2 having high foaming properties and relatively uniform bubbles obtained by mixing the two inert gases described above was confirmed by experiments. Could be obtained.
In this figure, the vertical axis indicates the degree of foaming, and the horizontal axis indicates the mixing ratio of nitrogen gas and carbon dioxide gas.
{N ₂ / (N ₂ + CO ₂ )} × 100%
Foaming degree W is for weight P ₀ per unit of extruded insulation only polyethylene, the weight P _M per unit of foamed insulation that is molded by injecting the extruder the mixture gas as blowing agent It is expressed as a ratio,
W = [1− (P _M / P _O )] × 100%, and the degree of nitrogen gas is 60% to 95% and the degree of foaming is as uniform as shown in the cross section of FIG. It has been established by experiment that an insulator with is extruded.
[0015]
In addition, the present invention improves the homogeneity of air bubbles by mixing high-density polyethylene and low-density polyethylene at a high proportion of high-density polyethylene as a polyethylene serving as the insulator and mixing an appropriate foam core material, Foamability can be increased. FIG. 6 is a graph showing the relationship between the mixing ratio of low-density polyethylene (0.910 to 0.929) and high-density polyethylene (0.945 or more) and the degree of foaming. From the experimental data, it was confirmed that when the ratio of the high-density polyethylene was 75% to 98%, the foamed cell could extrude an insulator having discontinuous closed cells.
[0016]
FIG. 7 shows an outline of an apparatus showing a method of manufacturing a coaxial cable according to the present invention from the top (a) and the side (b).
In this figure, reference numeral 10 denotes a dual supply for supplying the center conductor 1, and the drawn center conductor 1 is extruded by a precapstan 13 via a skin bath device 11 and a cleaning device 12 so as to have a constant linear velocity. Then, after being heated to a predetermined temperature by the preheater 14, it is supplied to the precoat extruder 15.
[0017]
The precoat extruder 15 coats the surface of the center conductor with polyethylene on the order of several tens of μm in advance so that the interface between the center conductor and the polyethylene has an adhesive property. Then, it is supplied to a foamed polyethylene extruder 17 via a trough 16.
[0018]
The foamed polyethylene extruder 17 is constituted by an L-type (dual) extruder as described later to form the above-described coaxial cable of the present invention. , Polyethylene is kneaded at a predetermined temperature, extruded in a molten state through the crosshead, around the central conductor 1 and pulled out from an opening having a predetermined die diameter to be insulated. become.
[0019]
The method for producing a high-foamed coaxial cable of the present invention is characterized in that, when supplying foamed polyethylene to the crosshead by the foamed polyethylene extruder 17 as described later, a fixed amount is always used by using a gear pump described later. The first characteristic is that the foamed polyethylene is discharged.
[0020]
Reference numeral 18 denotes a trough for gradually cooling the extruded insulated wire by a predetermined temperature control, and the insulated wire passing through the trough is taken up by a winding machine 21 via a dancer 20 and a take-up capstan 19.
[0021]
By the way, in the method of manufacturing a coaxial cable according to the present invention, before winding the cable covered with only the insulator with the winding machine 21, the cable passes through the take-up capstan 19, and then the adhesive is applied via the cable pulley 30. The second characteristic is that the hot melt type adhesive is applied to the outer surface of the insulator 2 by being sent to the device 31.
The hot-melt type adhesive is, for example, a modified olefin adhesive, and uses P-PET-1301S (Toa Gosei Chemical Co., Ltd.) or polyurethane emulsion F9105D (Daiichi Kogyo Seiyaku Co., Ltd.). Can be.
[0022]
The insulated wire coated with the hot-melt type adhesive is returned again via the pulley and is once wound up by the winder 21, but in the next step (not shown), the outer conductor is covered with aluminum or the like, and the sheath is removed. By bonding due to the heat generated when placing, the integration of the outer conductor and the insulator is promoted, and it is effective in preventing rainwater that has entered the cable from running through the cable and degrading the cable characteristics Role can be achieved.
Further, since the adhesive prevents the outer conductor and the insulator from shifting from each other, there is an advantage that the flexibility of the cable is improved, and the life cycle of the cable after being wired or laid can be lengthened.
[0023]
This hot-melt type adhesive can be applied by a simple device 31 such that the cable passes through the adhesive solution, and since it becomes an extremely thin film, the electrical characteristics of the cable are not impaired.
Reference numerals 22A and 22B denote accumulators constituting the wire storage device, and reference numeral 32 denotes a drying device for removing the solvent component of the hot melt type adhesive.
[0024]
FIG. 8 shows details of an extruder capable of achieving high foamability when producing the coaxial cable of the present invention.
In this figure, reference numeral 41 denotes a first extruder, which is supplied from a hopper 42 in which high-density polyethylene and low-density polyethylene are mixed at a predetermined ratio. Reference numeral 43 denotes a motor for rotating the first extruder 41. The low-density and high-density mixed polyethylene material supplied at a predetermined ratio from the hopper 42 is made into a fluidized state by a heating device (not shown) to form a spiral. It is extruded while being kneaded to the right by a screw.
[0025]
Reference numeral 44 denotes a cylinder of a mixed gas composed of the above-mentioned nitrogen gas and carbon dioxide gas. The cylinder 44 or the mixed gas obtained by individually mixing the carbon dioxide gas and the nitrogen gas at a predetermined ratio is supplied through a flow rate adjusting device 45 to the The extruder 41 is injected from an intermediate position.
46 is a second extruder, and 47 is its prime mover. The mixed gas and the polyethylene are kneaded by the first extruder 41, and the foamed material is further kneaded by the second extruder 46 to form a kneaded foamed polyethylene body downward in the drawing. It is extruded and controlled by a gear pump 48 provided on the outlet side so that the supply amount is constant.
Then, the foamed polyethylene is coated on the periphery of the center conductor 1 passing through the crosshead 50 described below.
[0026]
The gear pump 48 is extremely important in rectifying the moving pressure of the foamed polyethylene kneaded in the extrusion screw. By using the gear pump 48, the bubbles of the inert gas can be made uniform instead of CFC.
[0027]
Further, by providing a gear pump drive system 50 for controlling the number of rotations of the gear pump 48 in accordance with the feed speed of the center conductor, the discharge amount is accurately controlled, and the outer dimensions of the insulator attached by the crosshead 49 are provided. Can be finished within an appropriate error. Reference numeral 55 denotes a pressure gauge for monitoring the amount of pressing force of the gear pump 48.
[0028]
Reference numerals 51 and 53 denote resin pressure gauges for detecting pressures at outlets of the first and second extruders 41 and 46, and feed back the indicated values via the first and second control devices 52 and 54. Thus, the prime movers 43 and 47 and the rotation speed are controlled.
[0029]
FIG. 9 is a structural view of the gear pump 48, which is provided with two gears 48A and 48B that mesh with each other and rotate.
Since the foamed polyethylene supplied from the second extruder 46 is press-fitted while moving while the air bubbles and the polyethylene are kneaded, a fluctuating pressure is partially generated due to the waving phenomenon by the screw. The pulsating flow is rectified by the rotation of the gears 48A and 48B, and is discharged to the crosshead 49.
As a result, the bubbles in which the nitrogen gas and the carbon dioxide gas are mixed are also made uniform on the discharge port side, and as shown in FIG.
[0030]
FIG. 10 shows data showing the effect of the gear pump 48, in which the variation of the outer dimensions of the foamed insulator is shown with time on the horizontal axis, and the length of the orthogonal diameter of the insulator is measured in the X and Y directions. It is.
When chlorofluorocarbon is used as the foam material, chlorofluorocarbon gas easily dissolves in polyethylene, so the difference between the data A of the external dimensions when the gear pump is not used and the data B of the external dimensions when the gear pump is used is extremely small. The variation in (dimensions in the X and Y directions) is suppressed to 0.05 mm or less on average.
However, when the above-mentioned inert mixed gas in place of CFC is extruded with polyethylene without using a gear pump, the variation in external dimensions is reduced to about 0.2 mm as shown in data C showing the external dimensions. Become.
[0031]
In this case, as shown in the apparatus of the present invention, when the discharge amount of the foamed polyethylene is quantified using the gear pump 48 on the discharge side of the second extruder, the fluctuation width of the external dimensions can be seen in the data D. As shown in FIG. 11, the amount of attenuation per unit length of the coaxial cable becomes almost the same as that of the conventional cable, and the attenuation of the coaxial cable becomes almost the same as shown in FIG. Electrical and mechanical properties can be significantly improved.
[0032]
【The invention's effect】
The method of manufacturing a coaxial cable according to the present invention as described above uses an inert gas (nitrogen or carbon dioxide gas, argon) instead of chlorofluorocarbon, which has low solubility in polyethylene and is difficult to increase the foaming state with a normal device. In this case, a gear pump is used on the outlet side of the foamed polyethylene extruder to make the outer diameter uniform, so that the foaming state can be made almost the same as a coaxial cable using a chlorofluorocarbon foam material. There is.
[0033]
Further, since a hot-melt type adhesive is applied to the outer surface of the foamed insulator covered by the center conductor, the cable manufactured by the manufacturing method of the present invention is used when coating the outer conductor. The heat, or the heat applied in the step of coating the sheath provided on the outermost periphery, allows the integration of the outer conductor and the insulator to be naturally performed, and prevents water running of the cable, and this integration allows This has the advantage that a coaxial cable with excellent flexibility can be manufactured.
[Brief description of the drawings]
FIG. 1 is an external view of a coaxial cable manufactured by a manufacturing method of the present invention.
FIG. 2 is a sectional view of an insulator portion of the cable of FIG.
FIG. 3 is an explanatory graph showing the ease of gas dissolution into polyethylene.
FIG. 4 is a cross-sectional view showing bubbles of an insulator foamed by nitrogen gas or carbon dioxide gas.
FIG. 5 is experimental data showing the relationship between the mixing ratio of nitrogen gas and carbon dioxide gas and the degree of foaming.
FIG. 6 is experimental data showing the relationship between the mixing ratio of low-density polyethylene and high-density polyethylene, the degree of foaming, and the degree of foaming.
FIG. 7 is a schematic view of an apparatus showing a manufacturing method of the present invention.
FIG. 8 is a schematic view showing an outline of an extruder for foamed polyethylene.
FIG. 9 is an explanatory diagram showing the operation of the gear pump.
FIG. 10 is data showing a change in the outer diameter of the insulator formed by the manufacturing method of the present invention and a change in the outer dimension of the insulator made of freon gas as a foam material.
FIG. 11 is a view showing electrical characteristics of a cable manufactured by the manufacturing method of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Central conductor 2 Foam insulator 3 Outer conductor 4 Sheath 5 Bubble 10 Dual supply 14 Preheater 15 Precoat extruder 17 Polyethylene extruder 21 Winding machine 31 Adhesive coating device 48 Gear pump

Claims (1)

Is a mixture of high density polyethylene and low density polyethylene resin and the inert gas mixture injection, by extrusion in a certain direction while kneading by heating and melting an inert mixed gas of the polyethylene and the nitrogen gas and carbon dioxide A high foam coaxial cable comprising: an extruder for kneading and moving foamed polyethylene to a crosshead provided at a discharge port; and a gear pump for feeding a fixed amount of foamed polyethylene between the extruder and the crosshead. In the method for manufacturing a high-foam polyethylene coaxial cable in a manufacturing apparatus,
And the inert gas mixed with the nitrogen gas and carbon dioxide, the high-density polyethylene and low density polyethylene mixed resin was fed to the extruder,
By extruding the molten foamed polyethylene discharged from the extruder around the central conductor through a gear pump, an insulated wire having a foaming degree of at least 70% is formed,
After applying the adhesive hot melt type to the outer surface of the insulated wire, covering the outer conductor and the sheath, molten outer conductor and the insulator the adhesive by heating at the time of covering the sheath is integrated A method for manufacturing a high-foam polyethylene coaxial cable, wherein

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