JP3576590B2 - High foam coaxial cable manufacturing equipment - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a coaxial cable manufacturing apparatus, and more particularly to a high foam coaxial cable manufacturing apparatus 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]
At present, as the foaming material, chlorofluorocarbon (Fluoro Carbon), which is a compound of carbon and fluorine, hydrogen, and chlorine (CHClF ₂ ), is used. Has achieved a degree of foaming.
By the way, the above-mentioned CFCs gasify at a low boiling point and become a colorless, odorless and stable gas, but this gas is released into the atmosphere and reaches the stratosphere, and when it is decomposed by ultraviolet rays, it generates chlorine atoms and destroys the ozone layer. Global environmental problems have arisen.
[0004]
[Problems to be solved by the invention]
Therefore, various types of inert gas that can be injected into polyethylene instead of chlorofluorocarbon to obtain high foaming properties have been sought, but it is extremely difficult to obtain an inert gas having high solubility corresponding to fluorocarbon.
In addition, when foaming is performed using an inert gas having low solubility, it becomes difficult to perform sufficient kneading in an extruder that coats the insulator on the center conductor, and the insulator having uniform bubbles is formed. There is a problem that molding cannot be performed.
[0005]
[Means for Solving the Problems]
The present invention has been made for the purpose of solving such problems,
The polyethylene supplied from the hopper is heated and melted, and the polyethylene melted by the extrusion screw moving in a certain direction is supplied to the crosshead provided at the discharge port, and the center conductor surface is covered with an insulator by molding. In the foam coaxial cable manufacturing equipment,
The extruded screw is formed by a first extruder into which an inert mixed gas is injected together with the polyethylene, and a second extruder kneading and moving the foamed polyethylene extruded by the first extruder to the crosshead side. A gear pump is provided between the second extruder and the crosshead for feeding a fixed amount of foamed polyethylene.
[0006]
The mixed gas is composed of 60% to 95% of nitrogen gas and 5% to 40% of carbon dioxide, and the insulating material polyethylene is 75% to 98% of high density polyethylene and 2% to 25% of low density polyethylene. The degree of foaming was adjusted to 70% or more by supplying at a ratio.
[0007]
Further, the manufacturing apparatus of the present invention adds a step of thinly applying a hot-melt type adhesive to the outer peripheral portion of the insulator after extruding the insulator having a high foaming degree as described above with respect to the center conductor, The adhesive promotes the integration of the outer conductor and the center conductor by the heat generated when the sheath covers the cable sheath.
[0008]
[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 introducing an inert mixed gas as a foaming material, and a fixed amount is discharged to the discharge port side of the extruder. Since a gear pump that supplies polyethylene to the crosshead while rectifying it is provided, the degree of foaming of the foamed insulator covering the periphery of the conductor is improved, and bubbles in the foamed polyethylene are generated in a uniform state. In addition, it is possible to reduce the variation in the outer diameter of the extrusion.
[0009]
In addition, since an adhesive coating device for thinly applying a hot-melt type adhesive to the outer surface of the insulator covered by the above-described device is provided, the outer conductor and the insulator constituting the coaxial cable will be provided later. In order to protect the cable, it is bonded by the heat generated during the processing of the sheath to be covered, effectively preventing rainwater leaking into the coaxial cable from running water and preventing the transmission characteristics of the cable from deteriorating. Can be
[0010]
【Example】
FIG. 1 is a perspective view of the appearance of a cable manufactured by the coaxial cable manufacturing apparatus according to the present invention, wherein 1 is a center conductor, 2 is an insulation around the center conductor 1 covered by an extruder described later. Show body. An outer conductor 3 is coated on the outer periphery of the insulator 2 with aluminum or the like to form a coaxial cable.
Reference numeral 4 denotes a sheath for protecting the coaxial cable.
[0011]
The insulator 2 is formed by extruding polyethylene around the center conductor 1. When extruding the polyethylene, an inert mixed gas is kneaded to generate air bubbles 5 so that foam is formed. Is formed. Reference numeral 6 denotes a hot melt adhesive layer described later.
[0012]
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 is 75%, carbon dioxide is 25%, and high density is used. Polyethylene 90% and low-density polyethylene 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 CFC, and the nitrogen gas is nitrogen. The gas is 0.111.
When only nitrogen gas is used as the inert gas, for example, as shown in FIG. 4 (a), the bubbles 5 are small but the degree of foaming is low (65%). Since the compression / expansion ratio is extremely large, the degree of foaming can be increased. However, as shown in the cross section of FIG. 4B, the bubbles 5 become extremely large, and the bubbles may be continuous.
[0013]
According to the present invention, the mixing ratio at which the insulator 2 having high foaming properties and relatively uniform air bubbles was obtained by mixing the two inert gases described above was obtained by experiments. Data was obtained.
In this figure, the vertical axis indicates the degree of foaming, and the horizontal axis indicates the mixing ratio with nitrogen 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,
When defined as W = (1− (P _M / P _O ) × 100%, an insulator having a mixing ratio of 75% to 98% and a uniform degree of foaming as shown in the cross section of FIG. Extrusion was established by experiment.
[0014]
In addition, the present invention mixes high-density polyethylene and low-density polyethylene at a high proportion of high-density polyethylene as the polyethylene to be the foamed insulator, thereby improving the homogeneity of the bubbles and increasing the foamability. .
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. It was confirmed that when the percentage of polyethylene was 75% to 98%, the foam cell could extrude an insulator having discontinuous closed cells.
[0015]
FIG. 7 shows an outline of an apparatus for 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.
[0016]
The precoat extruder 15 coats the surface of the center conductor with polyethylene about 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.
[0017]
The foamed polyethylene extruder 17 is constituted by an L-type (dual) extruder as described later in order to form the above-mentioned coaxial cable of the present invention. Are kneaded at a predetermined temperature, extruded in a molten state around the central conductor passing through the crosshead, and pulled out from an opening having a predetermined die diameter to be insulated.
[0018]
The coaxial cable manufacturing apparatus of the present invention uses a gear pump to constantly discharge a fixed amount of foamed polyethylene when supplying foamed polyethylene to the crosshead by the foamed polyethylene extruder 17 as described later. Has the first feature.
[0019]
Reference numeral 18 denotes a trough for gradually cooling the extruded insulator by a predetermined temperature control. The insulated wire passing through the trough 18 is wound by a dual winder 21 via a dancer 20 and a take-up capstan 19.
[0020]
Note that the coaxial cable of the present invention passes through the take-off capstan 19 and is then sent to the adhesive application device 31 via the cable pulley 30 so that the hot melt type adhesive is applied to the outer surface of the insulator 2. Has a second feature.
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.
[0021]
The insulated wire coated with the hot melt type adhesive is once again wound up by the winder 21 via a pulley. Then, the cable wound by the winding machine 21 is coated with an outer conductor such as aluminum in the next step (not shown), and a sheath is covered to complete a coaxial cable. The bonding of the outer conductor and the insulator is promoted by bonding by the heat of the cable, and achieves an effective role in preventing rainwater that has entered the cable from running through the cable and deteriorating the characteristics of the cable. be able to.
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.
[0022]
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.
[0023]
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, and high-density polyethylene and low-density polyethylene are mixed and supplied at a predetermined ratio from a hopper. Reference numeral 43 denotes a motor for rotating the extrusion screw. The low-density and high-density mixed polyethylene materials supplied at a predetermined ratio from the hopper 42 are made to flow by a heating device (not shown), and are rotated rightward by the spiral screw. It is extruded while being kneaded.
[0024]
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.
[0025]
The gear pump 48 is extremely important in rectifying the moving pressure of the foamed polyethylene kneaded in the extrusion screw. The use of the gear pump 48 makes it possible to make the discharge amount uniform.
Further, by providing a gear pump drive system 50 for controlling the number of revolutions of the gear pump 48 in accordance with the feed speed of the center conductor, the outer dimensions of the insulator attached by the crosshead 49 can be finished within an appropriate error. Can be.
Reference numeral 55 denotes a pressure gauge that monitors the extrusion pressure of the gear pump 48.
[0026]
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.
[0027]
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 gas bubbles in which the nitrogen gas and the carbon dioxide gas are mixed are also made uniform on the discharge port side, and the discharge amount can be made uniform.
[0028]
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 measured by measuring the length of the orthogonal diameter of the insulator in the X and Y directions with the horizontal axis as time. is there.
When chlorofluorocarbon is used as a 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 the dimensions in the X and Y directions) is suppressed to 0.05 mm or less on average.
However, when the mixed gas is extruded together with the polyethylene without using the gear pump, the variation in the external dimensions is deteriorated to about 0.2 mm at the maximum as shown in the external dimension data C.
[0029]
In this case, as shown in the apparatus of the present invention, when the discharge amount of the foamed polyethylene is quantified by using the gear pump 48 on the discharge side of the second extruder, the fluctuation width as shown in the external dimension data D is obtained. Is almost the same as the fluctuation width when using CFC as the foam material, and as shown in FIG. 11, the attenuation per unit length of the coaxial cable is almost the same as that of the conventional cable, Electrical and mechanical properties can be significantly improved.
[0030]
【The invention's effect】
As described above, the coaxial cable manufacturing apparatus of the present invention is an extruder for foamed polyethylene even when an inert gas (nitrogen or carbon dioxide gas, argon) is substituted, which is difficult to raise the foaming state with a normal apparatus. Since a gear pump is arranged on the outlet side of the, so as to uniformize the bubbles, there is an effect that a foaming state almost similar to that of a coaxial cable using a chlorofluorocarbon gas as a foaming material can be produced.
[0031]
Further, since a device for applying a hot-melt type adhesive to the outer surface of the foamed insulator covered by the center conductor is provided, the cable manufactured by the manufacturing device of the present invention is used for coating the outer sheath. The outer conductor and the insulator are bonded by the heat of the heat or the subsequent heating of the step of coating the sheath of the cable provided on the outermost periphery, thereby preventing water running of the cable and improving the flexibility by this integration. This has the advantage that a coaxial cable 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 diagram 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 diagram showing electrical characteristics of the highly foamed coaxial cable of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Center conductor 2 Foam insulator 3 Outer conductor 4 Sheath 5 Bubble 10 Dual supply 14 Preheater 15 Precoat extruder 17 Extruder of foamed polyethylene 21 Winding machine 31 Adhesive coating device 48 Gear pump

Claims (7)

The polyethylene supplied from the hopper is heated and melted, but the polyethylene melted by the extrusion screw moving in a certain direction is supplied to the crosshead provided at the discharge port, and the center conductor surface is coated with an insulator. In coaxial cable manufacturing equipment,
The extruding screw comprises a first extruder into which an inert gas mixture is injected together with the polyethylene;
A second extruder for kneading and moving the foamed polyethylene extruded by the first extruder to the crosshead side;
A gear pump for delivering a certain amount of foamed polyethylene between the second extruder and the crosshead;
A highly foamed coaxial cable manufacturing apparatus, comprising: The high inertia coaxial cable manufacturing apparatus according to claim 1, wherein the inert gas is a mixed gas of a nitrogen gas and a carbon dioxide gas. 3. The high-foamed coaxial cable manufacturing apparatus according to claim 1, wherein the mixed gas has a nitrogen gas content of 60% to 95% and a carbon dioxide gas content of 5% to 40%. 3. The high-foamed coaxial cable according to claim 1, wherein the coaxial cable has a high-density polyethylene of 75% to 98% and a low-density polyethylene of 2% to 25% as an insulator. manufacturing device. Polyethylene supplied from a hopper is heated and melted, and the polyethylene melted by an extrusion screw that moves in a certain direction is supplied to a crosshead provided at the discharge port, and high insulation foaming is performed by coating the conductor surface with an insulator. In coaxial cable manufacturing equipment,
The extruding screw comprises a first extruder into which an inert gas mixture is injected together with the polyethylene;
A second extruder for kneading and moving the foamed polyethylene extruded by the first extruder to the crosshead side;
A gear pump for delivering a certain amount of foamed polyethylene between the second extruder and the crosshead;
An adhesive application device that applies a hot-melt type adhesive to the surface of the foamed insulator covered by the crosshead,
An apparatus for producing a high-foamed coaxial cable, wherein the hot-melt type adhesive is melt-bonded in a sheath coating step of the coaxial cable. The high-foamed coaxial cable manufacturing apparatus according to claim 5, wherein the mixed gas contains 60% to 95% of nitrogen gas and 5% to 40% of carbon dioxide gas. 7. The high-foamed coaxial cable according to claim 5, wherein the coaxial cable has a high-density polyethylene of 75% to 98% and a low-density polyethylene of 2% to 25% as an insulator. apparatus.

Images