JP2007238829A - Foamable resin composition, method for foaming the same and method for producing foamed insulated electric wire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a foamable resin composition using a fluorinated oil as a spreader. <P>SOLUTION: This foamable resin composition comprising a thermoplastic resin, such as FEP or PFA, being foamed by the addition of a foaming nucleating agent is characterized by adding a fluorinated oil, such as perfluoropropyl ether, having an average mol.wt. of 2,700 to 4,500 as a spreader in an amount of 0.05 to 0.2 mass% per 100 pts.mass of the thermoplastic resin to promote the dispersion of the foaming nucleating agent. The foaming nucleating agent, such as boron nitride, can uniformly be dispersed in the resin composition with the fluorinated oil. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a foamed resin composition using a fluorinated oil as a spreading agent, a foaming method thereof, and a method for producing a foam insulated wire.

In the case of insulated wires used in various electronic devices in recent years, for example, in a high-frequency coaxial cable, the used frequency band has reached the GHz order. In the GHz band, a cable characteristic having a smaller attenuation than that in the low frequency band is required. Therefore, foaming is performed on the insulator coated on the inner conductor (center conductor) (patent) Literatures 1-2).
Japanese Patent No. 3227091 Japanese Patent No. 2668198

  As the insulator, in addition to the polyethylene resin, a thermoplastic fluororesin such as tetrafluoroethylene-hexafluoropropylene which has a low dielectric constant and is excellent in lightness, heat resistance, nonflammability, smokelessness, etc. A polymer (FEP), a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), and the like are also used.

For foaming such insulators, chemical foaming is performed by filling the resin compound with a chemical substance that is foamed by heating during extrusion, or nitrogen gas or carbon dioxide gas is introduced into the resin compound from the outside during extrusion. The physical foaming method is used.
However, it is difficult to obtain a uniform and fine foam insulator with a high foaming degree only by these methods.

  For this reason, it has been proposed to add a substance that becomes the core of foaming to the resin compound, that is, a foaming nucleating agent in advance to promote foaming. For example, it is known to use boron nitride (BN) as a foam nucleating agent in the physical foaming method. In the case of boron nitride, advantages such as thermal stability, low reactivity and excellent dielectric properties are obtained in the vicinity of the extrusion temperature of the thermoplastic fluororesin.

  However, since it is quite difficult to uniformly disperse the foam nucleating agent such as boron nitride in the foamed resin composition, conventionally, a dispersing agent is added to achieve uniform dispersion of the foam nucleating agent. Alternatively, attempts have been made to modify the shape and surface characteristics of the foam nucleating agent, or to put a spreading agent on the pellet side of the base resin.

However, some dispersants may deteriorate the dielectric characteristics, and kneading of the dispersant may adversely affect the resin itself as a heat history. Moreover, even if the foam nucleating agent has good dielectric properties and is suitable for foaming, the surface is often inactive and difficult to modify, and further, when the shape and size are changed for modification In some cases, the characteristics were lost.
Even in the case of a spreading agent, it was not clear what specific characteristics it is desirable to use because of the relationship with the base resin used. Furthermore, when a thermoplastic fluororesin is used as the base resin, the processing temperature is close to the resin decomposition temperature, so when a dispersant or a spreading agent is added thereto, kneading cannot be performed smoothly, and heat generated by this kneading. There is also a problem that the original characteristics are easily lost due to deterioration of the resin due to the heat history.

  Under such circumstances, the present inventor desirably uses a spreading agent having any characteristic in foaming a foamed resin composition comprising a thermoplastic resin using a foaming nucleating agent such as boron nitride. As a result of various tests, it has been found that good results can be obtained when a fluorine-based oil having a certain characteristic is used.

That is, in the case of fluorinated oil, heat resistance is high (about 300 ° C.), and if the average molecular weight and kinematic viscosity are set within appropriate ranges, for example, from a normal temperature (20-25 ° C.) to a molding machine (extruder, etc.) It has been found that the following advantages can be obtained by selecting a material that does not easily volatilize in the vicinity of the hopper temperature and that easily vaporizes within the feed portion temperature and residence time of the molding machine.
(1) Fluorine-based oil spread on the base resin pellets is difficult to release until kneaded by a molding machine, that is, good oil spread can be obtained, and (2) because it volatilizes smoothly during foaming. (3) Since the oil flows smoothly in the molding machine, it does not cause seizure and does not remain in the foamed resin. It has been found that there is no concern of deteriorating the dielectric characteristics. It has also been found that it is particularly suitable in combination with thermoplastic fluororesins such as FEP and PFA.
In addition, even in the case of ordinary foamed resin molded products that do not require special characteristics such as the above coaxial cable, such as ordinary cable insulators, foam plates for heat insulation and sound insulation, and molded products for weight reduction. It has been found that it is useful to use a spreading agent for fluorine oil.

  The present invention has been made in view of this point of view, and provides a foamed resin composition using a fluorine-based oil as a spreading agent, a foaming method thereof, and a foamed insulated wire manufacturing method.

  The present invention according to claim 1 is a foamed resin composition comprising a thermoplastic resin foamed by addition of a foam nucleating agent, wherein a fluorine-based oil spreading agent is added to 100 parts by mass of the thermoplastic resin. In the foamed resin composition, 0.05 to 0.2% by mass is added to promote the dispersion of the foam nucleating agent.

  The present invention according to claim 2 resides in the foamed resin composition according to claim 1, wherein the fluorinated oil is polyperfluoropropyl ether.

  The present invention according to claim 3 is the foamed resin composition according to claim 2, wherein the polyperfluoropropyl ether has an average molecular weight of 2700 to 4500.

In the present invention according to claim 4, when the average molecular weight of the polyperfluoropropyl ether is 2700, the kinematic viscosity (20 ° C.) is 43 to 63 mm ² / s, and the volatile loss at 150 ° C. × 3 hours is 6% or less. It exists in the foamed resin composition of Claim 3 characterized by the above-mentioned.

  According to the fifth aspect of the present invention, when the average molecular weight of the polyperfluoropropyl ether is 2700, the kinematic viscosity (40 ° C.) is 58 to 72, and the volatilization loss at 200 ° C. × 3 hours is 2% or less. The foamed resin composition according to claim 3.

  The present invention according to claim 6 is the foamed resin composition according to any one of claims 1 to 5, wherein the thermoplastic resin is a tetrafluoroethylene-hexafluoropropylene copolymer, a tetrafluoroethylene-perfluoroalkyl. The foamed resin composition is a thermoplastic fluororesin of vinyl ether copolymer.

  The present invention according to claim 7 is the foamed resin composition according to any one of claims 1 to 6, wherein the foam nucleating agent is boron nitride, zeolite, silica, activated carbon, or silica gel. It is in the foamed resin composition.

  The present invention according to claim 8 is a foaming method using the foamed resin composition according to any one of claims 1 to 7, wherein a fluorine-based oil spreading agent is added to 100 parts by mass of the thermoplastic resin. After adding 0.05 to 0.2 mass% and adhering to the surface of the resin pellet, an appropriate amount of the foam nucleating agent is added thereto and extruded and foamed.

  The present invention according to claim 9 is a method for producing a foam insulated wire using the foamed resin composition according to any one of claims 1 to 7, wherein a fluorine-based oil is expanded with respect to 100 parts by mass of the thermoplastic resin. Add 0.05-0.2% by mass of the adhering agent and attach it to the surface of the resin pellet, then add an appropriate amount of the above-mentioned foaming nucleating agent, extrude and foam it, and extrude it as a foam insulator outside the conductor. It is in the manufacturing method of the foam insulated wire characterized by this.

  According to the foamed resin composition of the present invention, the foamed nucleating agent such as boron nitride easily adheres to the surface of the resin pellet because the fluorine resin is used as the spreading agent and spreads on the surface of the resin pellet. It can be uniformly dispersed in the product. That is, the wettability of the resin pellet surface is improved by the spreading agent. As a result, a good foamed state can be obtained, the amount of the foam nucleating agent used can be reduced, and the cost can be reduced.

  Also, in the kneading (mixing) of fluorinated oil itself, if the setting of the average molecular weight and kinematic viscosity is optimally selected according to the application, the base resin can be given comfortably, that is, it gives a large thermal history (heat stress). Can be done without. For example, addition and kneading of a spreading agent at room temperature (20 to 25 ° C.), addition and kneading under a slight heating (about 30 to 40 ° C.), and further adjustment of kneading time (long kneading) It is possible to cope with the problem by heating by the above. Furthermore, when thermoplastic fluororesins such as FEP and PFA are used as the base resin, the fluorocarbon oil has high heat resistance as well as this resin, so it does not decompose or deteriorate during molding and has good foaming properties. Is obtained. In particular, when this resin composition is used as a foamed insulator such as a coaxial cable, an insulator having a low dielectric constant and excellent in lightness, heat resistance, nonflammability, smokelessness and the like can be obtained. Of course, other foamed resin molded products can also be obtained.

  According to the method for molding a foamed resin composition of the present invention, after adding a fluorine-based oil spreading agent to a thermoplastic resin and adhering it to the surface of the resin pellet, an appropriate amount of a foam nucleating agent is added thereto and extruded. Since foaming is performed, the foam nucleating agent is added in a state where good wettability is ensured on the surface of the resin pellets, and uniform dispersion (mixing) of the foam nucleating agent is obtained. Thereby, a foamed resin molded article having a good foamed state is obtained.

  According to the method for producing a foam insulated wire of the present invention, after adding a fluorine-based oil spreading agent to a thermoplastic resin and adhering it to the surface of the resin pellet, an appropriate amount of a foam nucleating agent is added thereto and extruded and foamed. In order to coat the outside of the conductor as a foam insulation, the foam nucleating agent is added in a state where good wettability is secured on the surface of the resin pellets, and the foam nucleating agent is uniformly dispersed (mixed) Is obtained. Thereby, the foam insulation electric wire of a favorable foaming state is obtained.

  Although it does not specifically limit as a thermoplastic resin used for the foamed resin composition of this invention, For example, in the case of the insulator of a foam insulated wire, thermoplastic fluororesins, for example, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), Tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) or the like is used. As described above, the thermoplastic fluororesin has a low dielectric constant and is excellent in lightness, heat resistance, nonflammability, smokelessness, and the like, and thus is suitable as an insulator for a foam insulated wire. Among these, as the thermoplastic fluororesin having characteristics suitable for foaming, those having a melt flow ratio (MFR, 190 ° C., 2.16 Kgf) measured according to ASDTM-D1238-70 of 14 to 30 g / 10 min are preferable.

  In the case of these FEPs and PFAs, the usual ones have a problem in terms of dielectric properties due to the presence of terminal functional groups, and thus preferably stabilized by subjecting the terminal functional groups to fluorination treatment or the like. Use is desirable. As a commercial product of FEP subjected to such fluorination treatment, 5100J (trade name, MFR = 22) manufactured by Mitsui DuPont Fluorochemical Co., Ltd., and as a commercial product of PFA, 440HP-J manufactured by Mitsui DuPont Fluorochemical Co., Ltd. (Trade name, MFR = 15).

  As the foam nucleating agent added to these base resins, boron nitride (ceramics), zeolite, silica, activated carbon, silica gel, or the like can be used. When used as an insulator for electric wires, the size (particle diameter) of the median diameter (d50) is 1 to 10 μm, preferably 1 to 5 μm. The reason is that, when the submicron is less than 1 μm, secondary aggregation occurs and the number of particles that substantially contribute to foaming is reduced, so that finer foaming cannot be obtained. On the other hand, if the thickness exceeds 10 μm, the number of particles contributing to foaming in the unit volume decreases as in the case of secondary aggregation, and it is impossible to obtain finer foaming. And although it also depends on the specific surface area of the foam nucleating agent, the amount added to the base resin is preferably 0.1 to 1.5% by mass. Particularly in the case of boron nitride, the median diameter is preferably 1 to 10 μm and 0.1 to 1.0% by mass. Examples of such commercially available boron nitride include HP-P1 (trade name) manufactured by Mizushima Alloy Iron Company.

Moreover, it does not specifically limit as a fluorine-type oil of a spreading agent, What is necessary is just to select suitably with the target foamed resin insulator and foamed resin molded product. As the foam insulator for the high-frequency coaxial cable described above, it is desirable to use polyperfluoropropyl ether (common name, perfluoroether) having the following structure. And it is particularly preferable to use those having an average molecular weight of 2700 to 4500 as follows.
CF3- (CF2-CF2-CF2-O-) n-CF2-CF3) (1)

For example, (1) When the average molecular weight is 2700, the kinematic viscosity (20 ° C.) is 43 to 63 mm ² / s, and the volatile loss at 150 ° C. × 3 hours is 6% or less. It can be spread on the pellets at room temperature (20 to 25 ° C.), and is suitable as a spreading agent for a foamed insulation of a coaxial cable. As a commercially available product having this characteristic, there can be mentioned demnum S-20 (trade name) manufactured by Daikin Industries. (2) When the average molecular weight is 4500, the kinematic viscosity (40 ° C.) is 58 to 72, and the volatilization loss at 200 ° C. × 3 hours is 2% or less. Although it requires some heating, it is still suitable as a spreading agent for foamed insulation of coaxial cables. As a commercially available product having this characteristic, there can be mentioned demnum S-65 (trade name) manufactured by Daikin Industries.
Table 1 shows more detailed characteristic data of these demnum S-20 and S-65, and the same kind of fluorinated oils having different characteristics (Demkin S-100 and S-200 manufactured by Daikin Industries, Ltd.). In Table 1, the evaporation loss (volatilization loss) is a value measured by putting 15 to 25 g of sample oil in a heat-resistant petri dish having an inner diameter of about 90 mm and heating it in a hot air circulating electric furnace at the target temperature to obtain the weight loss. It is. As other physical properties of the oils in Table 1, the specific heat of each oil is 1.0 J / g (0.24 cal / g), and the dielectric breakdown voltage is (2.5 mm) 72 KV.

  When fluorine oil has the above characteristics, prior to foaming, this fluorine oil is added to the base resin pellets, kneaded and spread, and then supplied to a molding machine (such as an extruder). However, if the volatilization loss at a specific temperature is too large, excessive evaporation occurs at the supply port (such as a hopper) of the molding machine, and there is a problem that oil tends to adhere to the vicinity of the supply port. However, conversely, if the volatilization loss at a high temperature such as the forming temperature is too small, there is a possibility that it remains in the composition even after molding. .

  For example, as in demnum S-100 and S-200 in Table 1, when the average molecular weight increases (5600 to 8400), the kinematic viscosity naturally increases, and it is uniformly developed by addition to the base resin pellet and kneading. It becomes difficult to attach (attach), and the moldability (workability) by the molding machine also decreases. Further, even at high temperatures (250 ° C. and 300 ° C.), the volatilization loss is small, so that there is a possibility that it remains as a residual component in the composition even after molding. On the other hand, in the case of demnum S-20 in Table 1, since the average molecular weight is small and the kinematic viscosity is also low at room temperature, uniform spreading is possible by addition and kneading at room temperature. In addition, since the loss on volatilization is small (6% or less at 150 ° C. × 3 hours), it is difficult to volatilize near the hopper temperature and good usability can be obtained. In the case of demnum S-65, the average molecular weight and kinematic viscosity are slightly higher than demnum S-20, so it is necessary to heat it during kneading. There is almost no fear of giving large heat stress. Further, even at room temperature, the kneading time (mixing time) can be increased by heating a little (about several minutes). Basically, as with demnum S-20, good usability can be obtained. .

  In addition, the usable temperature of the fluorinated oil to be used needs to be in a temperature range corresponding to the molding temperature of the base resin to be used. In particular, when the base resin is a thermoplastic fluorine-based resin such as FEP or PFA, the heat resistance is high, the molding temperature is as high as about 300 ° C., and it is decomposed or altered in this temperature range as a spreading agent to be used. However, in the case of a fluorinated oil, the heat resistance is high, and it can sufficiently cope with this molding temperature environment. In other words, the desired spreading function can be obtained until the end without the oil being decomposed or altered during molding.

  The amount of the fluorine-based oil added is desirably 0.05 to 0.2% by mass with respect to 100 parts by mass of the base resin pellets. If it is less than 0.05% by mass, the desired spreading effect (insufficient wettability) cannot be obtained. Conversely, if it exceeds 0.2% by mass, the compression portion of the molding machine (such as an extruder) Even when (pressure part) is reached, the oil remains, causing problems such as poor adjustment of the degree of foaming, and large fluctuations in the outer diameter.

  If necessary, other additives such as antioxidants, copper damage inhibitors, flame retardants, dispersants, inorganic fillers, cross-linking agents, cross-linking aids, etc. may be added to the foamed resin composition as necessary. Can do.

  In molding a foamed resin composition having such a composition, as described above, preferably, fluorine-based oil is first added to the base resin pellets, mixed and spread. Thereby, fluorine-type oil adheres to the resin pellet surface, and desired wettability is acquired. A foam nucleating agent such as boron nitride is added to the resin pellets on which the oil has been spread, and is adhered to the spread layer of the oil. These operations should be performed in series. This mixing is performed using, for example, a shaker mixer or a Brabender mixer. In the case of gas foaming (physical foaming), a desired gas (inert gas such as nitrogen gas) is injected (injected) to cause foaming. In chemical foaming, foaming is performed with a chemical foaming agent added in advance. Both of these foaming methods can be used in combination.

  In the case of fluorinated oils, if you select ones with properties that meet your purposes, the desired wettability can be achieved by spreading the resin pellets sufficiently and easily within the molding temperature and molding time of a thermoplastic resin, such as thermoplastic fluororesin. Sex is obtained. Moreover, since mixing can be performed under normal temperature, 30-40 degreeC heating, or a long mixing time (about several minutes), the influence of the heat history by kneading | mixing can be suppressed to the minimum.

  The use of the foamed resin body obtained using such a fluorinated oil is not particularly limited. As described above, it can be used as a foam insulator of a foam insulated wire such as a coaxial cable. In the coaxial cable, the inner conductor (center conductor) is foamed and coated as an insulator. In particular, when a thermoplastic fluororesin such as ToFE or PFA is used as the base resin, a coaxial cable having a low dielectric constant and excellent in lightness, heat resistance, nonflammability, smokelessness, and the like can be obtained. Of course, this foamed resin body can also be used as a foamed insulator for ordinary electric wires and cables. Further, various general foamed resin molded articles, for example, foamed plate materials for heat insulation and sound insulation, and further molded articles for weight reduction can be obtained.

  FIG. 1 shows an example of a foam insulated wire using the foamed resin composition according to the present invention as a foam insulator. This foam insulated wire is a foam coaxial cable. In the figure, 1 is an internal conductor such as a stranded wire conductor, 2 is a foam insulator in which the foamed resin composition of the present invention is coated on the conductor 1 by extrusion molding. 3 is a metal layer (outer conductor) made of a metal braid or corrugated copper pipe, 4 is a sheath made of a polyolefin resin composition, 5a and 5b are applied as needed, and an inner skin layer and outer skin with a thickness of about 50 μm Is a layer. The outer diameter of the cable is not particularly limited, but is formed as about 3 to 50 mm. In addition, an aluminum tape etc. can also be put between the insulator 2 and the metal layer 3 as needed.

  FIG. 2 shows an example of an extrusion apparatus system for carrying out the method for manufacturing a foam insulated wire according to the present invention. An example of the extrusion apparatus system for enforcing the manufacturing method of the foaming coaxial cable which concerns on this invention is shown. 10 is a first extruder, 11 is a resin supply port of the first extruder, 12 is a crosshead of the first extruder, 20 is a cooling unit, 30 is a gas blowing agent supply unit to the first extruder, and 40 is an internal It is the 2nd extruder for skin layers.

  In this manufacturing method using an extrusion apparatus system, first, pellets of base resin, for example, thermoplastic fluorine-based resin pellets, to which fluorine-based oil is added, kneaded and spread from the resin supply port 11 of the first extruder 10, Then, a foam nucleating agent such as boron nitride and necessary additives are supplied, and the foamed insulator (foaming degree of about 50%) is coated on the inner conductor 1 by the crosshead 12. Prior to this, the inner skin layer 5a made of the same thermoplastic fluororesin as that of the foam layer is coated on the inner conductor 1 by the second extruder 40 for the inner skin layer. Here, the extrusion temperature of the first extruder 10 is set to about 300 ° C. The extrusion temperature of the second extruder is set to about 300 to 350 ° C. Nitrogen gas or the like is supplied as a gas foaming agent from the gas foaming agent supply unit 30 to the first extruder 10. As a result, the foam nucleating agent functions well and the foamed cells are made finer. The first extruder 10 may have a two-stage extruder structure in which another kneading extruder having a resin supply port and a gas foaming agent supply unit is connected.

  The foamed insulation covered with the cross head 12 of the first extruder 10 is cooled by the cooling unit 20. At this time, preferably, the extruded portion of a third extruder (not shown) is incorporated into the cross head 12, for example, and the outer skin layer 5b made of the same thermoplastic fluorine-based resin as the inner skin layer is made of a foamed insulator. Cover the outer periphery. The extrusion temperature of the third extruder is set to about 300 to 350 ° C. Thereafter, the above-described foamed coaxial cable is obtained by applying necessary external conductors and sheaths.

  These extrusion moldings can be performed by a normal extruder and can be performed with good productivity. The extrusion method may be performed in tandem (sequentially) for each coating layer, or may be simultaneous extrusion. Moreover, the extrusion temperature in each extruder is the measured resin temperature. As the gas as the foaming agent (physical foaming agent), in addition to nitrogen gas, as described above, for example, an inert gas such as argon gas, alternative chlorofluorocarbon gas, or carbon dioxide gas can be used. Further, the chemical foaming agent has a problem of generation of decomposition residues, but it can be added if it is in a very small amount and can be used in combination with the above gas foaming. Examples of such chemical foaming agents include bistetrazole-based ones such as bistetrazole / diammonium, bistetrazole / piperazine, and bistetrazole / diguanidine.

<Examples and comparative examples>
[Combination]
First, the material which consists of a mixture ratio shown in Table 2-Table 10 was prepared.
Base resin: PFA [440HP-J (trade name, manufactured by Mitsui DuPont Fluoro Chemical Co.)], FEP [5100J (trade name, manufactured by Mitsui DuPont Fluoro Chemical Co., Ltd.)], Spreading agent: Fluorine oil [DEMNUM S-20, S-65, S-100, S-200 (trade name, manufactured by Daikin Industries, Ltd.)], foaming nucleating agent: boron nitride [HP-P1 (trade name, manufactured by Mizushima Alloy Iron Company)]. In the compounding materials in the table, the amount of the base resin indicates the number of parts by mass, and the amount of the spreading agent indicates mass%.
First, 1 kg of base resin pellets and a spreading agent were introduced into a shaker mixer (capacity 1 L), and mixing was performed so that the surface of the resin pellets was uniformly wetted with the spreading agent. Thereafter, the foam nucleating agent was added and mixed again. In mixing, the foam nucleating agent remained in the container, so the remaining amount was measured and statistically fed back to the formulation. The mixing time was about 1 minute when the spreading agent was adhered to the pellet. In the case of spreading the foam nucleating agent, 5 minutes was used as a guide. The reason for this is that there was no change in extrudability and foaming even if it was carried out further. Moreover, about the heating (degreeC) at the time of mixing, several types, normal temperature (20-25 degreeC), 30-40 degreeC, 50-60 degreeC, 70-80 degreeC, were set and selected according to the spreading agent. .

〔processing〕
The resin pellets that had been spread with the above composition were put into a supply part (popper) of an extruder (molding machine), and extruded and foamed around the conductor using a nitriding gas as a gas foaming agent (physical foaming agent). Here, the conductor outer diameter was 1.0 mm, the foamed insulator diameter was 3 mm, and the foaming degree was 50%.

〔Evaluation methods〕
The “wetting property” of the spreading agent to the resin pellet was judged by measuring the amount of powder remaining in the container after spreading the foam nucleating agent. When the remaining amount of the powder was less than 10%, the wettability was evaluated as “good”. When the remaining amount of the powder was 10% or more, the wettability was evaluated as “bad”.

  “Extrudability” was determined by measuring the discharge amount and the resin pressure with respect to the screw rotation speed. And the case where spreading and extrusion foaming were performed satisfactorily was evaluated as “good”. Compared with the case of “good”, when the resin pressure and the discharge amount of the gas injection part were lower by 20% or more, they were evaluated as “bad”.

Since the “variation in the degree of foaming” appears as a variation in the outer diameter of the foamed insulator, the variation in the outer diameter was measured with an outer diameter measuring machine and a thickness gauge. If there is a variation in the outer diameter, the cable will cause a variation in impedance and become involved in the reflection of electrical signals, and the outer diameter variation will be an important factor in the cable characteristics. In the case of the above structure (conductor outer diameter 1.0 mm, foam insulator diameter 3 mm, foaming degree 50%), the tolerance of the outer diameter is about ± 30 μm. The tolerance of the foaming degree is 49 to 51%. Assuming that the variation in the outer diameter of the foamed insulator is caused only by the change in the discharge amount, the variation when extruded as a non-foamed insulator (solid) without foaming is about ± 20 μm. However, since it is actually about ± 10 μm, it can be seen that the variation in the outer diameter of the foamed insulator is caused by the variation in the degree of foaming.
Therefore, in the evaluation results, the outer diameter fluctuation tolerance is converted into the foaming degree fluctuation tolerance. When the outer diameter variation was within the tolerance range, it was evaluated as “tolerance range”. When the outside diameter fluctuation is outside the tolerance range and is large, it is set as “large fluctuation”. Here, the case where the fluctuation was particularly large, the foaming was sparse and dense, and the foaming degree was not uniform was defined as “bad”.

〔Evaluation results〕
Evaluation was performed as follows according to Tables 2 to 10 above.
(1) Spreading agent: When demnum S-20 is used When the amount of spreading agent is 0.05 to 0.2% by mass, the surface of the resin pellets is uniformly wet and foamed at a mixing time of about 1 minute at room temperature. It was found that the state was not uneven (Examples 1 to 3 and 10 to 12). If the amount of spreading agent is less than 0.05% by mass, the amount is insufficient to uniformly wet the surface of the resin pellet, and the foam nucleating agent falls off from the surface of the resin pellet in the hopper of the extruder and accumulates under the hopper. Was found to occur. As a result, it was found that fluctuations in the concentration of the foam nucleating agent (dispersion unevenness) occurred in the extruded foam insulation, and there were large fluctuations in the degree of foaming, the foamed cell diameter, and the outer diameter (Comparative columns 1 to 4). . Also, if the amount of spreading agent exceeds 0.2% by mass, oil will remain to some extent even if it reaches the compression part of the extruder, and there will be a problem in adjusting the foaming degree, so that the fluctuation of the outer diameter will increase. (Comparison columns 5 to 8).

(2) Spreading agent: When demnum S-65 is used Resin pellets are uniform in the amount of addition (Examples 1 to 3 and 10 to 12) in which good foamed insulation was obtained with demnum S-20 and mixing time (Comparative rows 9 to 12). In this case, if the resin pellets are heated to about 30 to 40 ° C. with a heater (such as an oven) and then mixed, the resin pellets can be spread well as in the case of demnum S-20, and can be extruded well. It turned out that it can foam (Examples 7-9, 16-18). Further, it was found that, even if the resin pellets are not heated, by extending the mixing time, the resulting heat is generated by the heat generated by the mixing, so that good spreading and extrusion foaming can be achieved (Examples 4 to 6). , 13-15). Also in this case, it was found that the applicable range where good spreading and extrusion foaming can be performed is the same as that of demnum S-20 (Examples 13 to 15). Of course, it was found that when the addition amount is small, the wettability is insufficient and the fluctuation of the foaming degree is also large (Comparative Examples 13 to 16).

(3) When using demnum S-100, 200 It was found that in this case as well, as with demnum S-65, good spreading cannot be achieved at room temperature. If the resin pellets are heated or the mixing time is increased, the resin pellets can be spread. However, as with the case where the amount of addition is increased with demnum S-20, the oil is less likely to volatilize. It was found that extrudability deteriorates due to sliding of the resin pellets or remains as an oil component in the foamed insulator, and adversely affects the foamed state (Comparative Rows 17 to 30).

  In addition, when thermoplastic foam resin is extruded and foamed at an extrusion temperature of about 300 ° C. using ordinary fluorine oil with low heat resistance, there is a risk of oil decomposition and risk of toxic decomposition gas generation. The same test was not conducted.

It is the vertical end view which showed an example of the foam insulated wire which used the foamed resin composition which concerns on this invention as the foam insulator. It is the schematic explanatory drawing which showed an example of the extrusion apparatus system for enforcing the manufacturing method of the foam insulated wire which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal conductor, 2 ... Foam insulator, 3 ... Metal layer (outer conductor), 4 ... Sheath, 5a ... Inner skin layer, 5b ... Outer skin layer, 10 * ..First extruder, 12 ... Cross head of first extruder, 20 ... Cooling unit, 30 ... Gas blowing agent supply unit, 40 ... Second extruder

Claims (9)

A foamed resin composition comprising a thermoplastic resin foamed by the addition of a foam nucleating agent, and 0.05 to 0.2% by mass of a fluorine-based oil spreading agent with respect to 100 parts by mass of the thermoplastic resin. Is added to promote dispersion of the foam nucleating agent. The foamed resin composition according to claim 1, wherein the fluorinated oil is polyperfluoropropyl ether. The foamed resin composition according to claim 2, wherein the polyperfluoropropyl ether has an average molecular weight of 2700 to 4500. When the average molecular weight of the polyperfluoropropyl ether is 2700, the kinematic viscosity (20 ° C) is 43 to 63 mm ² / s, and the volatile loss at 150 ° C x 3 hours is 6% or less. 3. The foamed resin composition according to 3. The kinematic viscosity (40 ° C) is 58 to 72 when the average molecular weight of the polyperfluoropropyl ether is 2700, and the volatilization loss at 200 ° C for 3 hours is 2% or less. Foamed resin composition. The foamed resin composition according to any one of claims 1 to 5, wherein the thermoplastic resin is a thermoplastic fluorine-based copolymer of a tetrafluoroethylene-hexafluoropropylene copolymer or a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer. A foamed resin composition, which is a resin. The foamed resin composition according to any one of claims 1 to 6, wherein the foam nucleating agent is boron nitride, zeolite, silica, activated carbon, or silica gel. A foaming method using the foamed resin composition according to any one of claims 1 to 7, wherein 0.05 to 0.2% by mass of a fluorine-based oil spreading agent is added to 100 parts by mass of the thermoplastic resin. A foaming method for a foamed resin composition, which comprises adding an appropriate amount of the foam nucleating agent to the resin pellet surface and then extruding and foaming. It is a manufacturing method of the foam insulated wire using the foamed resin composition in any one of the said Claims 1-7, Comprising: The spreading | diffusion agent of fluorine-type oil is 0.05-0.100 with respect to 100 mass parts of said thermoplastic resins. A foam insulated electric wire characterized by adding 2% by mass and adhering to the surface of the resin pellets, adding an appropriate amount of the foam nucleating agent to the resin pellets, extruding and foaming, and covering the outer side of the conductor as a foam insulation. Production method.

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