JP4626014B2 - High-frequency signal transmission product and its manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high-frequency signal transmission product, such as a high-frequency signal transmission cable and a printed wiring board, which have low high-frequency dielectric loss and excellent end processability, and a method for manufacturing the same.
[0002]
[Prior art]
Dielectric loss always occurs in a cable that transmits a high-frequency signal, such as a coaxial cable or a LAN cable. Similarly, dielectric loss is an important factor for printed wiring boards used in various transmission devices that transmit high-frequency signals.
[0003]
The dielectric loss is a function of dielectric constant (ε) and dielectric loss tangent (tan δ), and it is preferable that both are small. In order to reduce dielectric loss, high-frequency cables using PTFE having excellent electrical characteristics as an insulating coating layer material have been proposed (Japanese Patent Laid-Open Nos. 11-31422 and 11-283448, JP 2000-21250 A).
[0004]
PTFE has different melting points, electrical characteristics, molding processability, etc. depending on the molecular weight, presence or absence of modification, and the melting point, dielectric constant, dielectric loss tangent, and mechanical strength change by heat treatment (firing treatment). For example, a high molecular weight PTFE having a high melting point of 340 ± 7 ° C. is superior in electrical characteristics to a low melting point PTFE having a high melting point, and has a dielectric constant (ε) of 1.8 and a dielectric loss tangent (tan δ) when unfired. Is as low as 0.3 × 10 ⁻⁴ (both measured at 12 GHz, the same applies hereinafter), but when incompletely fired (semi-fired), the melting point dropped to 327 ± 5 ° C. and the dielectric constant (ε) was 2.15. The dielectric loss tangent (tan δ) is as high as 0.7 × 10 ⁻⁴ . When completely fired, the melting point is further lowered to 323 ± 5 ° C., the dielectric constant (ε) is increased to 2.10, and the dielectric loss tangent (tan δ) is increased to 2.0 × 10 ⁻⁴ . Further, the mechanical strength is improved by firing.
[0005]
Therefore, from the viewpoint of dielectric loss, it is advantageous to use unfired or semi-fired PTFE having a high molecular weight and a high melting point.
[0006]
In view of this, the above publication proposes an insulating coating layer in which sintered PTFE, semi-fired PTFE, and unfired PTFE are combined to improve workability while maintaining electrical characteristics such as dielectric constant and dielectric loss tangent.
[0007]
Japanese Patent Application Laid-Open No. 11-31442 proposes a method of increasing the degree of firing on the outer surface side (grading the degree of firing of PTFE in the radial direction) as a method of firing the unfired PTFE insulating coating layer.
[0008]
In JP-A-11-283448, the insulating coating layer is basically unfired or semi-fired PTFE, and only the end portion to be processed (about 10 cm from the end) is made of completely fired PTFE (in the longitudinal direction of the core wire). Proposal for the grade of firing).
[0009]
Furthermore, in Japanese Patent Application Laid-Open No. 2000-21250, a porous layer of PTFE is used as an insulating coating layer, and the surface portion is further fired to increase the crystallization rate to 75 to 92% (the degree of firing in the radial direction). Slope).
[0010]
[Problems to be solved by the invention]
However, the end workability when processing the end of the cable is such that when the degree of firing in the radial direction is inclined, the end is peeled off with a nipper or the like, and when the end is peeled or cut, the unfired or semi-fired PTFE does not break cleanly and becomes a fiber. The thread is pulled.
[0011]
Therefore, it has been thought that the end processing cannot be performed neatly unless the completely calcined PTFE is used as in JP-A-11-283448.
[0012]
As described above, regarding PTFE for an insulating coating layer of a high-frequency cable, various studies have been made on the degree of firing and the degree of crystallization, but the melting point has not been studied. The present invention pays attention also to the melting point that has not been studied so far, considering that the low melting point PTFE is difficult to be fiberized, and further considering the degree of firing, not only the electrical characteristics but also the workability, particularly the end workability. Has also developed an excellent PTFE insulation coating material.
[0013]
An object of the present invention is to provide a high-frequency signal transmission product that can smoothly perform terminal processing of a high-frequency signal transmission product having PTFE as an insulating coating layer and that has a low dielectric loss, and a manufacturing method thereof.
[0014]
[Means for Solving the Problems]
That is, the present invention relates to a low melting point PTFE insulating layer having a maximum peak temperature of 338 ° C. or less on a crystal melting curve measured with a differential scanning calorimeter and a maximum endothermic curve on a crystal melting curve measured with a differential scanning calorimeter. The present invention relates to a high-frequency signal transmission product having a two-layer insulating layer with a high melting point PTFE insulating layer having a peak temperature of 342 ° C. or higher, such as a high-frequency signal transmitting cable or a printed wiring board.
[0015]
The low melting point PTFE insulating layer is preferably a fired layer, and the high melting point PTFE insulating layer is preferably a semi-fired or unfired layer.
[0016]
Furthermore, it is preferable that both or one of the low melting point PTFE and the high melting point PTFE is modified PTFE.
[0017]
The high-frequency signal transmission cable is a high-frequency signal transmission cable having a metal core and a fluororesin insulation layer, and the fluororesin insulation layer comprises an outer insulation layer of the low melting point PTFE and an inner insulation layer of the high melting point PTFE. A two-layer structure is particularly preferable.
[0018]
In such a high-frequency signal transmission cable, the low-melting point PTFE and the high-melting point PTFE are co-paste extruded onto the core wire so that the low-melting point PTFE is on the outside, and then substantially only the outer low-melting point PTFE layer is completely fired. Can be manufactured.
[0019]
Moreover, it becomes easy to control firing by performing firing by passing the co-paste extrudate through a molten salt bath.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
In the low melting point PTFE powder used in the present invention, the maximum peak temperature of the endothermic curve appearing on the crystal melting curve by the differential scanning calorimeter (hereinafter referred to as “maximum endothermic peak temperature”) is 338 ° C. or less , preferably 332 to 338 ° C. Of powder. One high melting point PTFE powder is a powder having a maximum endothermic peak temperature of 342 ° C. or higher, preferably 342 to 348 ° C.
[0021]
These PTFE powders may be homopolymers of TFE or modified PTFE modified with other monomers. Examples of the modifying monomer include perfluoro (alkyl vinyl ether) such as perfluoro (methyl vinyl ether) and perfluoro (propyl vinyl ether), and hexafluoropropylene. It is denatured by. Hereinafter, unless otherwise specified, modified PTFE is also referred to as PTFE.
[0022]
This low melting point PTFE is a powder produced by polymerization by an emulsion polymerization method, has the above-mentioned maximum endothermic peak temperature (crystal melting point), dielectric constant (ε) is 2.08 to 2.2, dielectric loss tangent ( tan δ) is 1.9 × 10 ^{−4 to} 4.0 × 10 ⁻⁴ . Examples of commercially available products include polyflon fine powders F201, F203, F205, F301, F302 manufactured by Daikin Industries, Ltd .; CD090, CD076 manufactured by Asahi Glass Industry Co., Ltd .; TF6C, TF62 manufactured by DuPont, TF40 etc. are mention | raise | lifted.
[0023]
One high melting point PTFE powder is also a powder produced by polymerization by an emulsion polymerization method, having the above-mentioned maximum endothermic peak temperature (crystal melting point), and a dielectric constant (ε) of 2.0 to 2.1, The dielectric loss tangent (tan δ) is generally as low as 1.6 × 10 ^{−4 to} 2.2 × 10 ⁻⁴ . Examples of commercially available products include Polyflon Fine Powder F104 manufactured by Daikin Industries, Ltd .; CD1, CD141, CD123 manufactured by Asahi Glass Industry Co., Ltd .; TF6, TF65 manufactured by DuPont, and the like.
[0024]
The average particle size of the powder obtained by secondary aggregation of both PTFE polymer particles is usually preferably 250 to 2000 μm. In particular, a granulated powder obtained by granulation using a solvent is preferable from the viewpoint of improving the fluidity at the time of filling a mold at the time of preforming.
[0025]
In order to improve dielectric properties, the two-layered insulating layer of the present invention may further contain a filler such as boron nitride in one or both of the insulating layers. In addition, carbon (carbon black, carbon fiber, etc.) may be blended in the low melting point PTFE insulating layer to change and adjust its dielectric characteristics.
[0026]
Examples of the two-layered insulating layer of the present invention include various parts of high-frequency signal transmission products or insulation coating layers. Examples of various parts for high-frequency signal transmission equipment include mobile phones, various computers, and communication equipment. Typical examples include printed wiring boards, casings, antenna connectors, and the like, but are not limited thereto. A flat molded product such as a printed wiring board can be produced by laminating the two types of PTFE powder of the present invention sequentially by a conventionally known molding method such as compression molding. The total thickness of the insulating layer and the ratio of the thickness of the low-melting point PTFE insulating layer to the high-melting point PTFE insulating layer vary depending on the intended frequency, application location, type of product or component, and the like. Usually, in the case of a flat plate shape, the total thickness is 0.1 to 3 mm, and the ratio of the thickness of the low melting point PTFE insulating layer to the high melting point PTFE insulating layer is about 1/10 to 4/1.
[0027]
Typical insulation layers for high-frequency signal transmission equipment include insulation coating layers for high-frequency signal transmission cables such as coaxial cables, LAN cables, and flat cables, and insulation layers such as printed wiring boards. It is not limited.
[0028]
As described above, the present invention further relates to a high-frequency signal transmission cable, particularly a coaxial cable, having the specific two-layered insulating layer of the present invention.
[0029]
The structure of the coaxial cable for high-frequency signal transmission according to the present invention is such that a high melting point PTFE insulating layer 2 is first provided around a metal core wire 1 and then a low melting point PTFE insulation as shown in FIG. The layer 3 is laminated, and a metal exterior 4 is provided as an outer skin on the outer side.
[0030]
Hereinafter, although the method of forming the insulation coating layer of a coaxial cable by the paste coextrusion method is demonstrated, it is not restricted to this manufacturing method.
[0031]
First, the low melting point PTFE powder is mixed with a known paste extrusion aid and compression preformed to form a cylindrical outer insulating layer preform. Separately, the high melting point PTFE powder is mixed with a known paste extrusion aid. Then, compression molding is performed to obtain a cylindrical preform for the inner insulating layer. The size is set so that the inner diameter of the outer insulating layer preform is slightly larger than the outer periphery of the inner insulating layer preform. Next, the preform for the inner insulating layer is put into the preform for the outer insulating layer, loaded in this form into a paste extruder, coextruded on the core wire, heated (150 to 250 ° C.), dried, and then fired. Is performed under the condition that only the low melting point PTFE of the outer insulating layer is completely fired. Thereafter, the outer skin is coated according to a conventional method.
[0032]
In the present invention, the unfired, semi-fired and (complete) fired states refer to the following states, respectively. The unfired state is a state where the maximum peak in the endothermic curve is at the same position as before firing and the crystal conversion is less than 20%, and the semi-fired state is the position where the maximum peak in the endothermic curve is the same as before firing. And the crystal conversion rate is 20% or more and less than 90%, and the complete firing state is a state in which the maximum peak in the endothermic curve is shifted to the low temperature side from before firing and the crystal conversion rate is 90% or more. It is.
[0033]
In the production method of the present invention, excellent processing characteristics are exhibited also in the paste coextrusion step and the firing step.
[0034]
That is, conventionally, an unfired high melting point PTFE powder was paste-extruded alone to form an insulating coating layer. However, since the unfired high melting point PTFE powder easily becomes a fiber, it is necessary to increase the extrusion pressure. In addition, the surface of the coating layer may sag. In the present invention, the low melting point PTFE powder paste that is not fiberized is simultaneously extruded on the outside, so that the extrusion pressure can be reduced and the fiberization at the time of extrusion molding can be suppressed, and the surface of the obtained insulating coating layer can be made smooth. Can do.
[0035]
In order to maintain the excellent electrical characteristics of the inner insulating layer made of high-melting point PTFE, the baking process needs to stop the high-melting point PTFE of the inner insulating layer in the unfired or semi-fired stage as much as possible. In the case of the melting point PTFE single extrusion method, characteristics related to high-frequency signal transmission such as dielectric constant and dielectric loss tangent are greatly affected by the firing temperature, and thus the firing temperature must be carefully controlled. However, in the two-layered insulating layer of the present invention, the low-melting point PTFE insulating layer that is originally inferior in high-frequency signal transmission characteristics is provided in the outer insulating layer, so the influence of the firing temperature on the high-melting point PTFE layer is mitigated. Even if the firing temperature fluctuates somewhat, relatively high frequency signal transmission characteristics can be obtained, so that the firing temperature can be easily managed and the yield can be improved.
[0036]
In the present invention, the crystallization rate is 10 to 90%, preferably 20 to 80% in total on the inside and outside.
[0037]
As described above, the heating conditions for firing are an important factor and affect the characteristics of the product. Therefore, a method capable of controlling the temperature as accurately and uniformly as possible is preferable. In the present invention, although not limited, a so-called molten salt method (a salt bath method) in which the molten salt is heated and fired through a cable after paste coextrusion is suitably employed. The molten salt used is preferably a 1/1 mixture of potassium nitrate and sodium nitrate.
[0038]
The thickness of the outer insulating layer in the high-frequency signal transmission cable of the present invention is usually 0.5 to 5 mm, preferably 1 to 3 mm, although it varies depending on the standard and application of the cable. Further, the thickness of the inner insulating layer varies depending on the cable standard, application, etc., but is usually 0.1 to 1 mm, preferably 0.2 to 0.5 mm. The thickness ratio between the outer insulating layer and the inner insulating layer is usually 1/9 to 9/1, preferably 3/7 to 7/3, on the outside / inside.
[0039]
The product for high-frequency signal transmission of the present invention such as a printed wiring board and a high-frequency signal transmission cable thus obtained causes the substrate and the insulating coating layer to be fiberized at the time of terminal processing or peeling due to the action of the outer insulating layer made of low melting point PTFE. It is difficult to improve workability on site.
[0040]
【Example】
Next, the present invention will be described with reference to examples and comparative examples, but the present invention is not limited to such examples.
[0041]
Example 1
(Manufacture of preforms for paste extrusion)
Low melting point PTFE particles obtained by emulsion polymerization (maximum endothermic peak temperature of 337 ° C., polyflon fine powder F201 manufactured by Daikin Industries, Ltd.) and an extrusion aid (petroleum solvent “Isopar E” manufactured by Exxon) ) 21 parts by weight was mixed and aged for 24 hours to prepare an outer insulating layer paste. Next, this paste is filled into a hollow space of a cylindrical mold (inner diameter: 38 mm, inner core: outer diameter: 28 mm), and pressed with a press machine at a surface pressure of 1.96 MPa (20 kgf / cm ² ), and the outer side has a length of 50 mm. Ten preforms for forming the insulating layer were produced.
[0042]
Separately, as a preform for forming the inner insulating layer, 100 parts by weight of high melting point PTFE particles obtained by emulsion polymerization (maximum endothermic peak temperature: 345 ° C., Polyflon Fine Powder F104 manufactured by Daikin Industries, Ltd.) and extrusion assistant 24 parts by weight of the agent (Isopar E) was mixed and aged for 24 hours to prepare an inner insulating layer paste. Next, this paste is filled in a hollow space of a cylindrical mold (inner diameter 27 mm, inner core outer diameter 16 mm), pressurized with a press machine at a surface pressure of 1.96 MPa (20 kgf / cm ² ), and a 50 mm long spare. Ten compacts were produced.
[0043]
The maximum endothermic peak temperature of the PTFE powder was determined by drawing a crystal melting curve with a differential scanning calorimeter (RDC220 manufactured by Seiko Denshi Co., Ltd.) at a temperature rising rate of 10 ° C./min.
[0044]
(Paste coextrusion and firing)
The preform for the inner insulating layer was put into the preform for the outer insulating layer, and this was stacked 10 times and used for the next paste coextrusion for covering the electric wire.
[0045]
A double cylindrical preform is loaded into a paste extruder (manufactured by Jennings, cylinder diameter 38 mm, mandrel diameter 16 mm, die orifice diameter 1.32 mm), and core wire (American wire gauge size 24: silver with a diameter of 0.127 mm) Coated by extruding the paste on 19 stranded copper wires with an apparent outer diameter of 0.65 mm at a winding speed of 15 m / min, an oven at 150 ° C. (passing time 10 seconds) and an oven at 250 ° C. (passing time) 10 seconds), the extrusion aid was removed by drying. The thickness of the outer insulating layer (low melting point PTFE) was 0.130 mm, and the thickness of the inner insulating layer (high melting point PTFE) was 0.115 mm.
[0046]
Subsequently, it was passed through a salt bath (potassium nitrate / sodium nitrate = 1/1) at 340 ° C. for 20 seconds and subjected to heat treatment (firing treatment) to produce a PTFE-coated cable having an insulating coating layer having an outer diameter of 1.15 mm.
[0047]
The surface of the obtained coated cable was smooth and no undulation was observed. Moreover, the ram pressure at the time of paste extrusion was as low as 54 MPa.
[0048]
The core wire was pulled out from this covered cable 20m, and when the crystal endothermic curve was examined with a differential scanning calorimeter every 2 m (11 points in total) under the above conditions, the maximum endothermic peak at 337 ° C. of the low melting point PTFE disappeared. A new post-baking endothermic peak appeared at 327 ° C. There was no change in the endothermic peak temperature of the high melting point PTFE.
[0049]
Moreover, the crystal conversion rate calculated from the change in heat of crystal fusion between the raw material PTFE powder and the obtained insulating coating layer was in the range of 0.60 to 0.62.
[0050]
From these endothermic peaks and changes in the crystal conversion rate, it can be seen that only the outer insulating layer (low melting point PTFE) is fired, and the inner insulating layer (high melting point PTFE) is almost unfired.
[0051]
Further, in order to examine the end processability, the coating was peeled off with a wire stripper. As a result, the insulating layer could be easily cut without forming fibers, and the cut surface was clean.
[0052]
Comparative Example 1
Except that a high-melting point PTFE was used alone in Example 1 to prepare an extrusion preform (outer diameter 38 mm, inner diameter 16 mm), paste extrusion was performed in the same manner to prepare a PTFE-coated cable. The ram pressure at the time of paste extrusion was 72 MPa.
[0053]
Further, when the endothermic peak was examined in the same manner as in Example 1, it had a peak at the same position as that of the high melting point PTFE powder of the raw material, but the amount of heat of crystal fusion was changed, and the crystal conversion calculated from that was 0. It was 20 to 0.23.
[0054]
Further, in order to examine the end processability, when the coating was peeled off with a wire stripper, fiberization occurred on the cut surface.
[0055]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the product for high frequency signal transmission which has the insulating layer of the 2 layer structure which is excellent in a moldability and is easy to carry out baking temperature control can be provided. The insulating layer of this high-frequency signal transmission device is excellent in high-frequency signal transmission characteristics such as a low dielectric constant and dielectric loss tangent, and has improved end processability.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of an embodiment of a high-frequency signal transmission cable of the present invention.
[Explanation of symbols]
1 Core wire 2 Inner insulating layer 3 Outer insulating layer 4 Exterior

Claims (10)

  Maximum peak temperature of the endothermic curve on the crystal melting curve measured with a low melting point polytetrafluoroethylene insulating layer with a differential melting calorimeter and a low melting point polytetrafluoroethylene insulating layer measured with a differential scanning calorimeter A high-frequency signal transmission product having an insulating layer having a two-layer structure with a high melting point polytetrafluoroethylene insulating layer having a temperature of 342 ° C. or higher.   The maximum peak temperature of the endothermic curve on the crystal melting curve measured with the differential scanning calorimeter of the low melting point polytetrafluoroethylene is 332 to 338 ° C., and the crystal measured with the differential scanning calorimeter of the high melting point polytetrafluoroethylene The product for high-frequency signal transmission according to claim 1, wherein the maximum peak temperature of the endothermic curve on the melting curve is 342 to 348 ° C.   The product for high-frequency signal transmission according to claim 1 or 2, wherein the low melting point polytetrafluoroethylene insulating layer is a fired layer, and the high melting point polytetrafluoroethylene insulating layer is a semi-fired or unfired layer.   The product for high-frequency signal transmission according to any one of claims 1 to 3, wherein one or both of the low melting point polytetrafluoroethylene and the high melting point polytetrafluoroethylene are modified polytetrafluoroethylene.   A high-frequency signal transmission cable having a metal core wire and a fluororesin insulating layer, wherein the fluororesin insulating layer has a low melting point with a maximum peak temperature of an endothermic curve on a crystal melting curve measured by a differential scanning calorimeter of 338 ° C. or lower. It has a two-layer structure consisting of a polytetrafluoroethylene outer insulating layer and a high melting point polytetrafluoroethylene inner insulating layer having a maximum peak temperature of the endothermic curve on the crystal melting curve measured with a differential scanning calorimeter of 342 ° C or higher. High-frequency signal transmission cable characterized by   The maximum peak temperature of the endothermic curve on the crystal melting curve measured with a differential scanning calorimeter of the low melting point polytetrafluoroethylene forming the outer insulating layer is 332 to 338 ° C., and the high melting point poly for forming the inner insulating layer The high-frequency signal transmission cable according to claim 5, wherein the maximum peak temperature of the endothermic curve on the crystal melting curve measured with a differential scanning calorimeter of tetrafluoroethylene is 342 to 348 ° C.   The high-frequency signal transmission cable according to claim 5 or 6, wherein the low-melting polytetrafluoroethylene outer insulating layer is a fired layer, and the high-melting polytetrafluoroethylene inner insulating layer is a semi-fired or unfired layer.   The cable for high-frequency signal transmission according to any one of claims 5 to 7, wherein one or both of the low melting point polytetrafluoroethylene and the high melting point polytetrafluoroethylene are modified polytetrafluoroethylene. The maximum peak temperature of the endothermic curve on the crystal melting curve measured with the differential scanning calorimeter is 342 ° C. or lower, and the maximum peak temperature of the endothermic curve on the crystal melting curve measured with the differential scanning calorimeter is 342. Co-paste extrusion of high melting point polytetrafluoroethylene at ℃ or higher so that the high melting point polytetrafluoroethylene is on the core wire and the low melting point polytetrafluoroethylene is outside the high melting point polytetrafluoroethylene. The method for producing a high-frequency signal transmission cable according to any one of claims 5 to 8, wherein only the outer low melting point polytetrafluoroethylene layer is completely fired.   The process according to claim 9, wherein the calcination is carried out by passing a co-paste extrudate through a molten salt bath.

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