WO2022181623A1 - 伝送線 - Google Patents
伝送線 Download PDFInfo
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- WO2022181623A1 WO2022181623A1 PCT/JP2022/007311 JP2022007311W WO2022181623A1 WO 2022181623 A1 WO2022181623 A1 WO 2022181623A1 JP 2022007311 W JP2022007311 W JP 2022007311W WO 2022181623 A1 WO2022181623 A1 WO 2022181623A1
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- acicular
- transmission line
- agent
- nucleating
- nucleating agent
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Images
Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B7/00—Insulated conductors or cables characterised by their form
- H01B7/02—Disposition of insulation
- H01B7/0208—Cables with several layers of insulating material
- H01B7/0216—Two layers
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
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- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
- H01B3/002—Inhomogeneous material in general
- H01B3/006—Other inhomogeneous material
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
- H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
- H01B3/30—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes
- H01B3/44—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins
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- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
- H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
- H01B3/30—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes
- H01B3/44—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins
- H01B3/443—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins from vinylhalogenides or other halogenoethylenic compounds
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- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
- H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
- H01B3/30—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes
- H01B3/44—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins
- H01B3/443—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins from vinylhalogenides or other halogenoethylenic compounds
- H01B3/445—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins from vinylhalogenides or other halogenoethylenic compounds from vinylfluorides or other fluoroethylenic compounds
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- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
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Definitions
- the present disclosure relates to transmission lines with dielectric layers. More particularly, it relates to a transmission line including a dielectric layer having bubbles and a conductor, the conductor serving as a transmission path for electrical signals.
- a foamed dielectric containing bubbles in a resin can realize a dielectric constant lower than the dielectric constant peculiar to the resin, and is therefore useful as a dielectric for transmission paths of high-frequency electrical signals.
- a foamed dielectric as an insulating layer formed between the central conductor and the outer conductor of a coaxial cable, it is possible to obtain a cable with small attenuation of electrical signals and excellent transmission characteristics.
- the cells in the foam are required to be fine and uniformly distributed. Additives called nucleating agents can be utilized in forming such foams.
- JP-A-2008-174752 discloses a resin composition containing a fluororesin and boron nitride, wherein the d99 of the boron nitride is 15 ⁇ m or less. It is assumed that this provides a foam in which fine cells are evenly distributed.
- the foam nucleating agent functions as a starting point for generating air bubbles during foam molding.
- Japanese Patent Application Laid-Open No. 2005-206745 discloses a foamable composition containing a fluororesin and an electrically insulating whisker, a foam obtained by foaming the same, and a coaxial insulated cable having a foam layer containing the fluororesin as an insulator. disclosed. It has been found that the use of whisker-like insulating whiskers enables the formation of fine cells with a high foaming rate.
- the present invention provides a transmission line with excellent transmission properties, comprising a foamed dielectric layer with excellent cell geometry.
- a transmission line comprising a conductor and a dielectric layer, the dielectric layer having a plurality of bubbles and a plurality of acicular nucleating agents, the plurality of needle-like structures observed in a cross-section of the dielectric layer. Based on the observed length of the nucleus agent, needle-like nucleus agent longer than the median length is classified into the long nucleus agent group, and needle-like nucleus agent shorter than the median length is classified into the short nucleus agent group. is 3.5 times or less of the average length of the acicular nucleus agent of the short nucleus agent group.
- FIG. 1 is an example of a cross-sectional view illustrating a transmission line 10 according to a first embodiment of the present disclosure
- FIG. 3 is a conceptual diagram for explaining details of a dielectric layer 30 of the transmission line 10
- FIG. 4 is a diagram conceptually explaining the action of a needle-like nucleating agent during bubble growth. It is an electron microscope image of a needle-like nucleating agent that crosses the bubble interface. It is a figure explaining the formation process of the acicular nucleating agent which cross
- the dielectric layer of the transmission line has a plurality of needle-like nucleating agents, and among those needle-like nucleating agents, the group consisting of long acicular nucleating agents, It is characterized in that the average length is suppressed as compared with the group consisting of acicular nucleating agents with small lengths.
- a transmission line comprising a conductor and a dielectric layer, the dielectric layer having a plurality of bubbles and a plurality of acicular nucleating agents, and the plurality of Based on the observed length of the needle-shaped nucleus agent, a group consisting of multiple needle-like nucleus agents longer than the median length is classified as a long-nucleus agent group, and a group consisting of multiple needle-like nucleus agents shorter than the median length is classified as a short-nucleus agent group.
- the average length of the acicular nucleus agent in the long nucleus agent group is 3.5 times or less that of the acicular nucleus agent in the short nucleus agent group.
- FIG. 1 is an example of a cross-sectional view illustrating a transmission line 10 according to the first embodiment of the present disclosure.
- the signal transmission direction of the transmission line shown in this drawing is perpendicular to the plane of the paper, that is, this drawing shows a cross section of the transmission line in a plane perpendicular to the longitudinal direction of the cable-like transmission line.
- the transmission line 10 comprises a core 40 including a central conductor 20 and a dielectric layer 30 formed around the central conductor 20 .
- the central conductor 20 for example, a thin metal wire containing a low-resistance metal such as silver or copper can be used.
- the dielectric layer 30 is made of an insulating material such as resin, and contains a large number of fine air bubbles (not shown) inside, so that it is configured as a layer with a low dielectric constant.
- Transmission line 10 may further include a coating layer formed around core 40 .
- the transmission line 10 has a coaxial cable structure including an outer conductor 50 formed around a core 40 and a jacket 60 formed around the outer conductor 50 .
- FIG. 2 is a conceptual diagram for explaining the details of the dielectric layer 30 of the transmission line 10.
- Dielectric layer 30 includes a plurality of bubbles 320 formed in resin layer 340 .
- the bubbles are shown as independent spheres and prolate spheres with circular cross-sections and elliptical cross-sections, respectively. , the shape may be distorted. From the viewpoint of mechanical properties, it is considered preferable that the cross-sectional shape of the cells is as close to circular as possible.
- the dielectric of the transmission line there is an advantage that the dielectric constant can be reduced by increasing the proportion of air bubbles in the dielectric layer. For this reason, the resin layer between a certain bubble and the adjacent bubble is stretched into a film, and the ratio of the bubbles is reduced until a plurality of regions with a substantially constant thickness and a planarly extending shape are generated. Larger is preferred.
- the dielectric layer 30 includes a plurality of acicular nucleating agents 330 .
- the acicular nucleating agent refers to fine needle-like substances made of an insulating material having an aspect ratio of 3 or more, preferably 6 or more.
- the aspect ratio is a value obtained by dividing the length in the direction in which the needle-like nucleus agent extends, that is, the length in the major axis direction, by the diameter (or width).
- the size in the extending direction of the agent can be measured as length, and the size in the direction perpendicular to the extending direction can be measured as diameter.
- the acicular nucleating agent used for the dielectric layer of the transmission line must be fine in order to suppress an increase in the dielectric constant of the dielectric layer.
- the diameter is preferably 0.1 ⁇ m or more and 10 ⁇ m or less, more preferably 0.1 ⁇ m or more and 3 ⁇ m or less, and particularly preferably 0.1 ⁇ m or more and 1 ⁇ m or less.
- an electrically insulating whisker disclosed in Patent Document 2 can be used as a material for such an acicular nucleating agent.
- the acicular nucleating agent 330 is uniformly dispersed in the resin layer 340 .
- the direction and distribution position of the acicular nucleating agent may not have clear regularity.
- the length distribution of the individual acicular nucleating agents of the transmission line 10 in this embodiment has the characteristics described later. That is, the length of the acicular nucleating agent observed in the cross section of the dielectric layer of the transmission line 10 is defined as the observation length, the acicular nucleating agent longer than the median value is the long nucleating agent group, and the acicular nucleating agent shorter than the median value is the short nucleating agent.
- the average length of the acicular core agent in the long core agent group is 3.5 times or less that of the acicular core agent in the short core agent group.
- the transmission line 10 having such characteristics makes it possible to obtain excellent transmission characteristics.
- this magnification that is, the average length of the needle-shaped nucleus agent of the long-nucleus agent group is set to the average length of the acicular nucleus agent of the short-nucleus agent group. It is more preferable to set the value divided by the length to 3 or less, and particularly preferably to 2.7 or less.
- the observation length is, for example, the length obtained by observing the cross section of the dielectric with a scanning electron microscope (SEM) or the like.
- it is the extension direction length on each image of a plurality of acicular nucleating agents measured in an electron microscope image of a cross section.
- the direction of observation and the actual extending direction of the needle-like nucleating agent are not necessarily perpendicular, and part of the entire length of the needle-like nucleating agent cannot be seen due to the shadow of the resin or other nucleating agent. Therefore, in most cases, the observed length is smaller than the actual length of the acicular nucleating agent.
- the median value is the value located in the center when the observed length values of each nucleating agent are arranged in order of size. If the number of data is even, the average value of the two middle values can be applied.
- the action of the acicular nucleating agent during the formation of bubbles in the dielectric layer was considered.
- the surface of the nucleating agent in the resin layer can be the starting point of bubble generation. Dispersion of the nucleating agent in the resin makes it possible to simultaneously generate starting points for bubble generation in the resin layer. can be obtained.
- the acicular nucleating agent having a large aspect ratio acts more effectively than the granular nucleating agent having an aspect ratio close to 1. That is, even if the weight of each nucleating agent is the same, the surface area of the nucleating agent can be increased, so that the region from which air bubbles are generated can be expanded.
- the nucleating agent with a high aspect ratio can increase the region in the resin layer that is adjacent to the nucleating agent.
- the application of a needle-shaped nucleating agent with a predetermined aspect ratio that can increase the area per unit weight of the additive and the range of existence is considered to be a great advantage. .
- FIG. 3 is a diagram conceptually explaining the action of the acicular nucleating agent during bubble growth.
- FIG. 3(a) shows the state immediately after the generation of bubbles
- FIG. 3(b) shows the state in which the bubbles have grown over a short period of time.
- the resin layer (340) is a resin layer that is in a molten state during the generation and growth of bubbles in the manufacturing process of the transmission line 10 (for example, the process of forming a foamed resin layer to be described later). When this is cooled and solidified, it becomes the resin layer 340 in the transmission line 10 .
- Bubbles 320 and acicular nucleating agents 330 are present in the molten resin layer (340). Aside from the needle-shaped nucleating agent 330 shown in the figure, there may be a needle-shaped nucleating agent that is the starting point of the bubble 320, but the illustration is omitted here. At the stage of FIG. 3( a ), the air bubble 320 and the needle-like nucleating agent 330 shown are separated to some extent, and the needle-like nucleating agent 330 does not greatly affect the growth of the air bubble 320 . As the bubble 320 grows over time, the bubble 320 eventually comes into contact with the acicular nucleating agent 330 either directly or via a thin resin film. As shown in FIG.
- the bubble 320 grows further with the rotation and movement of the acicular nucleating agent 330. Growth is suppressed as compared with the case without the acicular nucleating agent 330 . Since a bubble that grows and expands earlier than other bubbles has a higher probability of contact with the acicular nucleating agent, the growth of such a bubble that grows first is easily suppressed, and as a result, the bubble can reduce the difference in size between At this time, since the acicular nucleating agent exists over a longer distance than the granular nucleating agent, it is easy to increase the probability of contact with the air bubbles. It is thought that the effect of suppressing the growth of bubbles will also be significantly increased. In addition, especially when the acicular nucleating agent is arranged along the resin film between the cells, the mechanical strength of the resin film between the cells increases, so that coalescence of the cells due to film breakage is suppressed. Effectiveness is also expected.
- FIG. 4 is an electron microscope image of a needle-like nucleating agent intersecting the bubble interface.
- the needle-shaped nucleating agent is observed in the vicinity of the center of the image and extends in the vertical direction of the paper in a slightly inclined state. It can be seen that a part of the acicular nucleating agent located at the upper left of the paper surface is embedded in the resin layer, and the remaining part protrudes into the space inside the bubble.
- the region of the acicular nucleating agent that protrudes into the bubble greatly reduces the contribution to the aforementioned effect of suppressing the growth of bubbles. put away.
- the acicular nucleating agent in the region protruding into the bubble does not particularly contribute to the improvement of transmission characteristics and mechanical characteristics, but its presence increases the dielectric constant. Therefore, it is preferable to suppress the generation of the acicular nucleating agent that crosses the bubble interface. In examining this suppressing means, we considered in what form the intersection between the acicular nucleating agent and the bubble interface occurred.
- FIG. 5 is a diagram explaining the process of forming needle-like nucleating agents that intersect with bubble interfaces. Similar to FIG. 3, in the molten resin layer (340), a bubble 320 in the process of growing and a needle-like nucleating agent 330 are illustrated.
- FIG. 5(a) shows a state in which the air bubble 320 and the acicular nucleating agent 330 are separated from each other, and at the stage of FIG. state. It differs from FIG. 3 in that the length of the existing acicular nucleating agent 330 is long, and as a result of the growth of the bubble 320, the acicular nucleating agent intersects the bubble interface. As in FIG.
- the growing bubble tries to rotate or move the acicular nucleating agent after its interface comes into contact with the acicular nucleating agent.
- the longer the needle-shaped nucleating agent the stronger the fixation in the resin.
- the long acicular nucleating agent was thought to be likely to break through the resin film because the pressure of the air bubble would easily exceed the strength of the resin film at the contact point between the air bubble and the acicular nucleating agent.
- the unique effect of the needle-like nucleating agent to suppress the growth of pre-grown bubbles is obtained by the characteristic shape of the needle-like nucleating agent having a large longitudinal length (or aspect ratio).
- the length in the major axis direction becomes excessively large, the phenomenon that the needle-like nucleating agent breaks through the bubble interface is likely to occur, resulting in a decrease in the above-mentioned inherent effect.
- the length of the acicular nucleating agent is controlled so as to have a predetermined distribution. More specifically, the ratio of the average length in the group of short needle-like nuclei and the average length in the group of long needle-like nuclei is suppressed below a certain level.
- an acicular nucleating agent is prepared.
- the acicular nucleating agent is preferably composed of an insulating material that has little effect on the electrical characteristics of the transmission line.
- Such materials include metal compounds and ceramic materials.
- needle-like nucleating agents may be formed from granules of these materials in order to obtain needle-like nucleating agents having a predetermined length distribution, fibrous materials with high aspect ratios may be used. It is preferable to prepare and adjust to a predetermined length distribution by suitable processing.
- potassium titanate and aluminum borate are commercially available as fibrous or needle-like materials for use in reinforcing plastics or adjusting wear in brakes.
- fibrous materials that are also used to enhance these mechanical properties often contain large aspect ratios in order to increase the effect. Therefore, in order to obtain a length distribution of the acicular nucleating agent that can realize excellent properties in the dielectric layer of the transmission line, it is necessary to apply an appropriate mechanical stress to such a fibrous material. It is necessary to adjust the thickness distribution.
- machining such that shear stress is applied to the acicular nucleating agent can be applied.
- Processing by a stirrer, a Henschel mixer, a tumbler, a mill, etc. is exemplified.
- these means may be applied to deaggregate materials or improve dispersibility.
- Destruction of some nucleating agents, especially long nucleating agents may also change the length distribution.
- the aggregated nucleating agent was deaggregated to the extent that almost no aggregated nucleating agent was observed in electron microscopic observation, and the agent was in a uniformly dispersed state. It was very large compared to the average length of the drug group. This is because each of the above materials is fine and has high hardness, so it is a material that is difficult to break unless suitable machining energy is applied to the material, and each nucleating agent is a surface modification to suppress aggregation. This is thought to be due to the influence of this and other factors.
- a fibrous material having a certain aspect ratio is prepared.
- commercially available materials containing many fibrous materials having a diameter of less than 3 ⁇ m and a length of 10 ⁇ m or more are available. Many of these materials contain more than a certain amount of solids that are too long to be applied to the acicular nucleating agent of the dielectric layer of transmission cables. can be adjusted.
- the needle-like nucleating agents longer than the median length are classified into a group of long nucleating agents shorter than the median length.
- the value obtained by dividing the average length of the needle-shaped core agent in the long-nucleus agent group by the average length of the needle-shaped core agent in the short-nucleus agent group (hereinafter referred to as will be simply referred to as the average length ratio) within a specific range, it is necessary to consider the following.
- the average length ratio is also affected by the relationship between the strength of the fiber material and the mechanical stress for breaking, and the distribution of the mechanical stress.
- An example of the breaking method using a Henschel mixer and a tumbler will be described below.
- a Henschel mixer is a device that stores a material to be processed alone or together with other materials in a container equipped with a metal blade, and mixes and agitates the material by rotating the metal blade. In breaking the fibrous material, the rotating metal blade can directly collide with the fibrous material, so the fibrous material can be broken effectively. In particular, it is suitable when it is desired to surely destroy a high-strength fibrous material.
- a tumbler is a device that stores an object to be processed alone or together with other materials in a container, and mixes and agitates the object by changing the direction of the container (that is, the direction of gravity). When used to break fibrous materials, the collision with the container and other contents in the container becomes the breaking energy, so the mechanical strength is extremely high.
- Breaking of fibrous materials is more disadvantageous than the Henschel mixer, but moderate. It is expected that the breakage of the fibrous material with a length of is suppressed. It is suitable for fibrous materials with relatively low mechanical strength, and because it is easy to uniformly apply a breaking stress to the entire object in the container, it is also advantageous for increasing the batch size of processing. In this way, by setting appropriate processing conditions according to the strength of the fibrous material to be applied, the processing batch size, etc., it is possible to obtain a dielectric in which acicular nucleating agents having a desired average length ratio are distributed. can be done.
- the Henschel mixer not only destroys the fibrous material, but also deagglomerates the fibrous material, thereby obtaining the effect of reducing variations in the subsequent destruction of the fibrous material by the tumbler. Therefore, even when the fibrous material to be applied is significantly aggregated, it becomes easier to obtain a stable average length ratio.
- the adjustment of the length distribution of the nucleating agent is not limited to the above.
- needle-like nucleating agents longer than the median length are selected.
- the average length of the acicular-nucleus agents in the long-nucleus agent group and the acicular-nucleus in the short-nucleus agent group A transmission line with excellent transmission characteristics can be obtained by setting the adjustment conditions so that the ratio of the average lengths of the agents becomes a desired value.
- the average length of the acicular core agents in the group of long core agents is at least 1.5 times the average length of the acicular core agents in the group of short core agents. This is because if the fibrous material is destroyed until this ratio becomes 1.5 or less, the function of the nucleating agent becomes closer to that of the particulate nucleating agent, and there is a possibility that the original effect of the needle-like nucleating agent may be reduced. It's for.
- the nucleating agent whose length distribution is adjusted as described above is dispersed in the resin.
- the resin serving as the dispersion medium for the acicular nucleating agent may be the resin serving as the dielectric resin layer.
- fluororesin itself is a material with a low dielectric constant, it can form a dielectric layer of a transmission line with excellent transmission characteristics.
- Suitable fluorine resins include tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-alkyl vinyl ether copolymer such as tetrafluoroethylene-perfluoropropyl vinyl ether copolymer, ethylene-tetrafluoroethylene-perfluorobutyl
- Thermoplastic fluororesins such as ethylene copolymers, ethylene-chlorotrifluoroethylene copolymers, and polyvinylidene fluoride can be used.
- the melt flow rate (MFR) of these resins is preferably 10 g/10 min or more and 40 g/10 min or less, and particularly preferably 20 g/10 min or more and 30 g/10 min or less. Melt flow rate can be adjusted by grade selection of material resins or blending resins with appropriate grades.
- Dispersion of the needle-shaped nucleating agent in the resin can be carried out by kneading a mixture of the needle-shaped nucleating agent and the resin using a mixer or the like.
- a mixture of the kneaded needle-shaped nucleating agent and the resin is formed into resin pieces called pellets, thereby improving the storability and usability in downstream processes.
- the length distribution of the needle-like nucleating agent changes in this dispersing step, pelletizing step, or foamed resin layer forming step described later. Even in such a case, the stress applied to the nucleating agent in each step should be adjusted so that the observation length in the transmission line has a predetermined length distribution.
- it is preferable to adjust the needle-shaped nucleating agent so that it is in a state close to the required length distribution in the upstream steps as much as possible. preferable.
- a foamed resin layer is formed. Formation of the resin layer by extrusion is preferred when the transmission line is configured to include a central conductor and a foamed resin layer disposed therearound.
- the formed resin layer can be made into a foamed resin layer.
- a foaming substance that generates gas by chemical reaction or thermal decomposition may be mixed in the pellets or the resin obtained by melting the pellets, and foaming may be performed by the generated gas.
- the transmission line 10 of the present embodiment can be obtained through the above steps.
- the transmission line 10 is a coaxial cable
- formation of the outer conductor and formation of the jacket can be carried out.
- the outer conductor can be formed by winding a metal foil around the core or forming a braid of fine metal wires. Either one of the metal foil wound layer and the metal fine wire braided layer may be formed, or both may be formed.
- Example 2 Each transmission line having the configuration shown in Table 1 was produced, and the observed length of the acicular nucleating agent and the dielectric constant were measured. A copper single wire was applied as the central conductor.
- Comparative Example 1 a commercially available whisker made of aluminum borate (Albolex Y manufactured by Shikoku Kasei Co., Ltd.) was used as the raw material nucleating agent, in which a long nucleating agent is relatively likely to remain even after various steps. Pellets were prepared from the mixture with the fluororesin without controlling the length distribution, such as suppressing the average length of the long nucleating agent group, although the conditions were such that aggregation was sufficiently broken and dispersibility could be secured. .
- Examples 1, 2 and 3 are considered to have mechanical properties similar to those of the whiskers described above, but are commercially available whiskers (Otsuka Kagaku was applied. Such a nucleating agent having an average diameter of less than 1 ⁇ m is particularly suitable for the present embodiment because it is easy to control the length distribution. In Examples 1, 2 and 3, conditions were applied that not only deagglomerated and improved dispersibility, but also length distribution clearly changed. Although there is no extreme difference in the average length of the entire nucleating agent, a needle-like nucleating agent group is prepared in which the average length of the long nucleating agent group is suppressed compared to the comparative example, and is composed of a mixture of this and a fluororesin. A pellet was formed. A tetrafluoroethylene-hexafluoropropylene copolymer was used as the fluororesin.
- a dielectric layer was formed on the center conductor using each of the above pellets.
- the dielectric layer was formed by extruding a resin obtained by melting pellets through a discharge hole of an extrusion die and cooling the resin.
- a cable-shaped core was continuously formed by running a fine metal wire serving as a central conductor from the same ejection hole in the same direction as the ejection of the resin. Nitrogen gas is pressurized into the molten resin in the mold, and the pressure drop around the resin immediately after coming out of the injection hole is used to form a dielectric layer on the conductor and to form bubbles inside the dielectric layer. went at the same time.
- C is the capacitance per meter (pF)
- D is the outer diameter of the core (mm)
- d is the diameter of the central conductor (mm).
- a dielectric layer including a cross section to be an observation sample was prepared.
- the cross-section of the observation sample may be formed by general sample preparation means such as cutting and polishing or a microtome. A method of cleaving by mechanically breaking while cooling is preferred.
- the obtained cross section was observed using a desktop microscope (TM4000PLUS/manufactured by Hitachi High-Technologies Corporation). The observation magnification can be appropriately selected in the range of 500 times to 2500 times according to the state of the sample to be observed.
- a rectangular area was randomly set in the acquired electron microscopic image, and all acicular nucleating agents contained within the rectangular area were measured.
- the extremely small nucleating agents observed here may be granular nucleating agents generated in the adjustment stage of the length distribution, etc. Such granular nucleating agents include acicular nucleating agents. No inherent bubble control effect can be expected.
- the measurement error of the observation length may increase and the reproducibility may deteriorate.
- the distribution of acicular nucleating agents can be accurately grasped by excluding nucleating agents whose observed length in the longitudinal direction of each nucleating agent on the image is less than 1 ⁇ m from the calculation. .
- the number of observation length data for each level In order to understand the distribution, it is preferable to secure the number of observation length data for each level.
- the number of data used to calculate the median value and average length was 28 to 80 or more, depending on the level. If the variation in observation length becomes large, it is preferable to further increase the number of data. Accurate distribution can be grasped by securing at least 28 data, preferably 80 or more. If the distribution density of the nucleating agent is small and it is difficult to secure the necessary number of data, the observation area may be expanded or added.
- the median value, the average observation length of the long-nucleus agent group, and the average observation length of the short-nucleus agent group were calculated for each level, and the average observation length of the long-nucleus agent group was calculated.
- the average length ratio of the nucleus agent group at each level was obtained. This length ratio indicates the state of distribution of long needle-like nuclei agents in a plurality of needle-like nucleating agents. It can be judged that the drug is in a relatively large amount.
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Abstract
Description
このような用途において、発泡誘電体の発泡状態を制御することにより、伝送線の伝送特性を改善する試みがなされている。例えば、発泡体中の気泡には、微細であること、均一に分布していることなどが求められる。そのような発泡体の形成には、核剤と呼ばれる添加剤を利用することができる。
導体と誘電体層とを備えた伝送線であって、前記誘電体層は複数の気泡と複数の針状核剤とを有し、前記誘電体層の断面において観察される前記複数の針状核剤の観察長に基づき、長さの中央値より長い針状核剤を長核剤群、長さの中央値より短い針状核剤を短核剤群と分類したとき、長核剤群の針状核剤の平均長さは短核剤群の針状核剤の平均長さの3.5倍以下であることを特徴とする伝送線である。
本開示の第1の実施形態において、伝送線の誘電体層は複数の針状核剤を有しており、それらの針状核剤のうち長さが大きな針状核剤からなる群は、長さが小さな針状核剤からなる群にくらべ、平均長さが抑制されている点を特徴とする。
すなわち、導体と誘電体層とを備えた伝送線であって、前記誘電体層は複数の気泡と複数の針状核剤とを有し、前記誘電体層の断面において観察される前記複数の針状核剤の観察長に基づき、長さの中央値より長い複数の針状核剤からなる集団を長核剤群、長さの中央値より短い複数の針状核剤からなる集団を短核剤群と分類したとき、長核剤群の針状核剤の平均長さは短核剤群の針状核剤の平均長さの3.5倍以下である、との構成を備える。これにより、優れた伝送特性を有する伝送線を得る事ができる。
伝送線10は中心導体20と該中心導体20の周囲に形成された誘電体層30とを含むコア40を備える。中心導体20としては、例えば銀、銅などの低抵抗金属を含む金属細線を用いることができる。誘電体層30は樹脂などの絶縁材料からなり、内部に多数の微細な気泡(不図示)を含むことで、低誘電率の層として構成される。
伝送線10は、さらにコア40の周囲に形成された被覆層を備えていても良い。本図において、伝送線10は、コア40の周囲に形成された外部導体50と、前記外部導体50の周囲に形成された外被60とを備えた同軸ケーブル構造となっている。
誘電体層30は、樹脂層340中に形成された複数の気泡320を含む。簡略化のため、本図において気泡は断面円形および断面楕円形のそれぞれ独立した球状および長球状のものとして示されているが、一部が隣接する気泡と連結した形状であってもよく、または、いびつに変形した形状であっても良い。機械的な特性の観点からは、気泡の断面形状は円形に近いほど好ましいと考えられる。一方、伝送線の誘電体においては、誘電体層中における気泡の占める割合を大きくすることにより、誘電率を小さくできるとの利点がある。このため、ある気泡と隣接する気泡との間の樹脂層が膜状に引き伸ばされ、ほぼ一定の厚さで平面的に延在した形状の領域が複数個所で発生するまで、気泡の占める割合を大きくすることが好ましい。
すなわち、伝送線10の誘電体層の断面において観察される針状核剤の長さを観察長とし、その中央値より長い針状核剤を長核剤群、短い針状核剤を短核剤群と分類したとき、長核剤群の針状核剤の平均長さは短核剤群の針状核剤の平均長さの3.5倍以下である。
このような特徴を備えた伝送線10により、優れた伝送特性を得ることが可能となる。
また、さらに安定して優れた伝送特性を得られるとの観点から、この倍率、すなち、長核剤群の針状核剤の平均長さを短核剤群の針状核剤の平均長さでわった値を3以下とすることがさらに好ましく、2.7以下とすることが特に好ましい。
中央値とは各核剤の観察長の数値を大きさの順番に並べた時に、中央に位置する数値である。データ数が偶数の場合は、中央に位置する2つの数値の平均値を適用することができる。
本願発明者は、各種核剤及び樹脂などの材料、あるいは伝送線の製造条件等の条件を変化させた試作水準間の比較を実施した。これらの評価を通じ、針状核剤が優れた伝送特性を備える伝送線を提供できることを確認するとともに、針状核剤適用した伝送線同士の比較においても特に誘電率の小ささとその安定性に差があることを見出した。
単純に添加量を増加させると誘電率が悪化する伝送線において、添加剤の単位重量当たりの面積や存在範囲を大きくできる所定のアスペクト比を有する針状核剤の適用は大きな利点になると考えられる。
溶融樹脂層(340)中には、気泡320と針状核剤330とが存在している。図示された針状核剤330とは別に、気泡320の起点となった針状核剤があっても良いが、ここでは図示を省略している。図3(a)の段階では、気泡320と図示された針状核剤330とはある程度離間しており、気泡320の成長にこの針状核剤330は大きな影響を与えない。時間経過とともに気泡320が成長すると、やがて気泡320は、直接、または薄い樹脂膜を介して、この針状核剤330と接触する。図3(b)に示されるように、接触後も、この針状核剤330の回転や移動を伴いながら気泡320はさらに成長するが、針状核剤の移動を伴う必要があるために、針状核剤330が無い場合に比べ成長が抑制されることになる。他の気泡に比して成長が先行し拡大した気泡ほど針状核剤との接触確率が増大する形となるため、このような成長が先行した気泡の成長が抑制されやすく、結果的に気泡間の大きさの差を縮小することができる。このとき、針状核剤は、粒状核剤に比して長い距離にわたり存在するため、気泡との接触確率を大きくしやすく、さらに、接触後の回転、移動抵抗も大きくなるため、先行成長する気泡の成長抑制効果も各段に大きくなると考えられる。
また、特に気泡間の樹脂膜に沿って針状核剤が配置された状態になると気泡間樹脂膜の機械的な強度が大きくなることで、膜破壊に伴う気泡同士の合一も抑制される効果も期待される。
これに対して、本実施形態の伝送線は、針状核剤の長さが所定の分布を有するように制御されている。より具体的には、短い針状核剤群における平均長と、長い針状核剤群における平均長の比が一定以下に抑制されている。これにより、針状核剤固有の気泡制御効果を高い水準で実現しつつ、針状核剤の気泡界面交差による制御効果の低下の発生を相対的に小さくすることを可能とするものである。
なお、気泡界面と交差する針状核剤の発生が完全にゼロになっている必要は無く、界面に沿って延在する針状核剤と共存していても良い。特にフッ素樹脂のように核剤材料に対する濡れ性を確保しにくい樹脂においては発生を完全にゼロにすることは難しい。むしろ、そのように濡れ性が確保されにくいものはもともと界面交差が生じやすい状態にあると見なすことができ、針状核剤の長さ分布を制御する本構成により、界面交差する針状核剤の発生数を抑制することで大きな改善効果をえることができると理解される。
次に、本実施形態の伝送線の製造方法を説明する。まず、針状核剤を準備する。針状核剤としては、伝送線の電気特性への影響が小さな、絶縁性の材料から構成されることが好ましい。このような材料として、金属化合物やセラミック系の材料が挙げられる。所定の長さ分布を有する針状核剤を得るために、これらの材料からなる粒状物から針状の核剤を形成することが可能な場合もあるが、高アスペクト比の繊維状の材料を準備し、これに適当な加工を行うことにより、所定の長さ分布に調整する形が好ましい。例えばチタン酸カリウムやホウ酸アルミニウムは、プラスチックの補強や、ブレーキの摩耗調整用途として、繊維状あるいは針状の材料が市販されているため、このような市販材料の活用が検討される。しかし、これらの機械特性強化にも利用される繊維状材料はその効果を大きくするために、多くの場合アスペクト比が大きいものが多く含まれる。このため伝送線の誘電体層において優れた特性を実現可能な針状核剤の長さ分布を得るためには、このような繊維状材料に対して適切な機械ストレスを与えること等により、長さ分布の調整が必要となる。
なお、これらの手段は、材料の凝集を解いたり、分散性を向上させたりするために適用されることがあり、仮に繊維状または針状の核剤の凝集を解く手段として適用した場合に、一部の核剤、特に長さが大きな核剤が破壊されることで長さ分布も変化している可能性がある。しかし、所定の長さ分布を得るためには、単に凝集を解いたりする場合と比較して、大きな外部応力の印加が必要となる。例えば後述する比較例1は電子顕微鏡観察において、凝集した核剤がほとんど観察されない程度にまで凝集が解かれ、均一に分散された状態にあったが、長核剤群の平均長さは短核剤群の平均長さに比して非常に大きなものであった。これは、上記の各材料は微細かつ高硬度であるために材料に適した機械加工エネルギーを付与しないと破壊されにくい材料であること、また、それぞれの核剤は凝集を抑制するための表面修飾されていることも多く、この影響等も受けるためであると考えられる。
しかし、特に、誘電体層の断面において観察される前記複数の針状核剤の観察長に基づき、長さの中央値より長い針状核剤を長核剤群、長さの中央値より短い針状核剤を短核剤群と分類したとき、前記長核剤群の針状核剤の平均長さを、前記短核剤群の針状核剤の平均長さで割った値(以下では単に平均長さ比と記載する)を特定の範囲内に制御するためには以下を考慮する必要がある。
以下、ヘンシェルミキサーとタンブラーを用いて破壊方法の例を説明する。
ヘンシェルミキサーは、処理対象物を単独または他の材料と同時に、金属ブレードを備えた容器中に格納し、金属ブレードを回転させることで、混合、攪拌を行う装置である。繊維状材料の破壊においては、回転する金属ブレードを繊維状材料に直接衝突させることができるため、繊維状材料を効果的に破壊することができる。特に高強度の繊維状材料を確実に破壊したい場合などに好適である。
一方で、処理対象物全体の中において、ブレードと衝突する局所的な領域においてのみ大きなストレスを印加する形になるため、処理のバッチサイズが大きな場合などは、短時間処理では処理ムラが生じる虞がある。これに対して、単に処理時間を長くすると中程度の長さの繊維状材料の破壊も進む結果、平均長さ比が大きくなることがある。
タンブラーは処理対象物を単独で、または他の材料と共に容器中に格納し、容器の向き(すなわち重力の向き)を変化させることで、混合、攪拌を行う装置である。繊維状材料の破壊に用いた場合は、容器や容器内にある他の内容物との衝突が破壊エネルギーとなるため機械的強度が極めて高い繊維状材料の破壊はヘンシェルミキサーより不利だが、中程度の長さの繊維状材料の破壊が抑制されるメリットが期待される。機械的強度が相対的に低い繊維状材料に好適であり、容器内の対象物全体に均一に破壊ストレスを印加しやすいため、処理のバッチサイズの大型化にも有利である。
このように、適用する繊維状材料の強度、処理バッチサイズなどに応じて、適切な加工条件を設定することで、所望の平均長さ比を有する針状核剤が分布した誘電体を得ることができる。
なお、前記長核剤群の針状核剤の平均長さは、前記短核剤群の針状核剤の平均長さの1.5倍以上であることが好ましい。これは、この比が1.5以下になるまで繊維状材料を破壊した場合は、核剤の働きが粒子状核剤に近くなり、針状核剤本来の効果まで減少してしまう虞があるためである。
メルトフローレートは、材料樹脂のグレード選択または適切なグレードを備えた樹脂の混合により、調整することが可能となる。
この分散工程、ペレット化工程、あるいは後述する発泡樹脂層形成工程においても、針状核剤の長さ分布の変化が生じることが考えられる。このような場合であっても、伝送線における観察長さが所定の長さ分布となるように、各工程において核剤に印加される応力を調整すればよい。但し後の工程になるほど、直接的な長さ分布の制御が難しくなるため、できるだけ上流の工程において、針状核剤が、必要な長さ分布に近い状態になるように調整しておくことが好ましい。
表1に示す構成の各伝送線を作製し、針状核剤の観察長さと誘電率の測定を行った。中心導体としては銅の単線を適用した。原料核剤として比較例1は、各種工程を経ても長い核剤が相対的に残留しやすいホウ酸アルミニウムからなる市販ウィスカー(四国化成製のアルボレックスY)を適用した。十分に凝集が解かれ、分散性を確保できる条件ではあるが、長核剤群の平均長さの抑制等の長さ分布の制御は特に行うことなくフッ素樹脂との混合物からなるペレットを作成した。これに対して実施例1、2および3は、上記ウィスカーと同様の機械的特性を備えると考えられるが、径がやや細いことで相対的に長さ分布の制御が容易な市販ウィスカー(大塚化学製のティスモD)を適用した。このような平均径が1μmより小さな核剤は長さ分布の制御が行いやすいため、本実施形態に特に好適である。実施例1、2および3においては、凝集を解き、分散性を向上させるだけでなく、長さ分布が明確に変化する条件を適用した。核剤全体としての平均長さに極端な差はないものの、比較例に比べ長核剤群の平均長さが抑制された針状核剤群を準備し、これとフッ素樹脂との混合物からなるペレットを形成した。フッ素樹脂としてはテトラフルオロエチレン-ヘキサフルオロプロピレン共重合体を適用した。
このようにして得られたケーブル状のコアの静電容量を、キャパーシタンスモニタを用いて測定し、以下の式1に基づいて誘電率εを算出し、その値から比誘電率を求めた。
式1 ε=(C×log(D/d))/24.16
ここで、Cは1m当たりの静電容量(pF)、Dはコアの外径(mm)、dは中心導体の直径(mm)である。
上記コアの誘電体層を切り出した上で、観察試料となる断面を含む誘電体層を準備した。観察試料の断面形成は切削研磨やミクロトーム等の一般的な試料作製手段を用いても良いが、樹脂層の発泡状態の変化が小さいとの利点からは、切り出した誘電体層を液体窒素などで冷却しながら機械的に破壊することにより割断する方法が好適である。
得られた断面を卓上顕微鏡(TM4000PLUS/日立ハイテクノロジーズ製)を用いて観察した。観察倍率は観察対象の試料状態に応じて、500倍から2500倍の範囲で適宜選択できる。
この長さ比は、複数の針状核剤中における、長い針状核剤の分布状態を示すものであり、長さ比が大きな針状核剤においては、母集団中において、長い針状核剤が相対的に多い状態にあると判断できる。
Claims (10)
- 導体と誘電体層とを備えた伝送線であって、
前記誘電体層は複数の気泡と複数の針状核剤とを有し、
前記誘電体層の断面において観察される前記複数の針状核剤の観察長に基づき、長さの中央値より長い針状核剤を長核剤群、長さの中央値より短い針状核剤を短核剤群と分類したとき、前記長核剤群の針状核剤の平均長さは前記短核剤群の針状核剤の平均長さの3.5倍以下であることを特徴とする伝送線。 - 前記長核剤群の針状核剤の平均長さが、前記短核剤群の針状核剤の平均長さの3倍以下であることを特徴とする請求項1記載の伝送線。
- 前記長核剤群の針状核剤の平均長さが、前記短核剤群の針状核剤の平均長さの1.5倍以上であることを特徴とする請求項1記載の伝送線。
- さらに前記誘電体層の周囲に形成された外部導体と、前記外部導体の周囲に形成された外被とを備えていることを特徴とする請求項1に記載の伝送線。
- 前記誘電体層はフッ素樹脂を含むことを特徴とする請求項1に記載の伝送線。
- 前記針状核剤は金属化合物またはセラミック材料からなる絶縁体であることを特徴とする請求項1に記載の伝送線。
- 前記針状核剤の平均径は1μmより小さいことを特徴とする請求項1に記載の伝送線。
- 前記針状核剤はアスペクト比が3以上のものを含むことを特徴とする請求項1に記載の伝送線。
- 前記針状核剤はアスペクト比が6以上のものを含むことを特徴とする請求項1に記載の伝送線。
- 前記針状核剤は、アスペクト比が大きな原料核剤の破壊を行うことにより長さ分布の調整を行ったものであることを特徴とする請求項1に記載の伝送線。
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