JPS63210145A - Porous polytetrafluoroethylene material, its production and directional resistor prepared therefrom - Google Patents

Abstract

PURPOSE:To obtain a porous material comprising a number of unidirectionally oriented long polytetrafluoroethylene long fibers and giving a directional resistor, by unidirectionally stretching a polytetrafluoroethylene molding obtained by a specified production process. CONSTITUTION:Polytetrafluoroethylene powders (hereinafter abbreviated as PTFE powders) are dispersed in a nonwetting liquid (e.g., methanol) to finely divide them. A liquid lubricant (e.g., polychlorotrifluoroethylene) is added to this dispersion to transfer the finely divided PTFE powders to the side of the liquid lubricant, and the nonwetting liquid is removed by an operation such as decantation. The mixture of the PTFE powders with the liquid lubricant is rolled, and the liquid lubricant is removed from the molding by an operation such as extraction or evaporation. This molding is unidirectionally stretched by roll stretching to obtain a porous PTFE material.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to polytetrafluoroethylene (PTF).
The present invention relates to a porous body (referred to as E) and a directional resistor using the porous body.

(Technology of Jubei) Porous material technology by stretching PTFE was developed, for example, in the
It is described in Japanese Patent Publication No. 2-13560, Japanese Patent Publication No. 18991-1980, etc.

The above stretching method involves forming a mixture of unfired PTFE powder and a liquid lubricant such as naphtha into a predetermined shape by extrusion or the like (so-called paste molding), evaporating the lubricant from the molded product, The lubricant can be removed by extraction or the like.@The lubricant can be removed during the next step of stretching (or it can be done after stretching), and then the molded product is stretched at a temperature lower than the melting point of PTFE to form a porous body. It is.

The microstructure of a porous body obtained by the conventional stretching method is disclosed in the above-mentioned Japanese Patent Publication No. 18991/1983. That is, as shown in FIG. 7, this porous body 1 consists of a large number of fibrils 2 and scattered nodules 3, and the fibrils 2 are oriented in one direction (in the case of uniaxial stretching, the fibrils 2 are oriented in the stretching direction). ) and the nodule 3 has its long axis along the fibril 2
direction perpendicular to the orientation direction (direction perpendicular to the stretching direction)
The tubercles are arranged along the same lines, and the nodules are connected by fibrils. Note that the microstructure of the porous body can also be observed using an electron microscope. Figure 8 shows an example,
It is a scanning electron micrograph (magnification: 500 times).

The expanded porous PTFE material having such a microstructure may be used as a constituent material of an electric conductor.
For example, as described in Japanese Unexamined Patent Publication No. 60-225750, it has been proposed to laminate a metal foil on the surface of the substrate via an adhesive layer and use it as a printed circuit board.

Naturally, the laminate of the expanded porous PTFE body and metal foil has approximately the same electrical resistance (isotropy) in two directions perpendicular to each other on the surface of the metal foil.

(Problems to be Solved by the Invention) Currently, directional resistors using a porous PTFE material, that is, articles with different electrical resistances in two orthogonal directions on a given surface (surface electrical resistance (objects exhibiting directivity) have not been obtained.

Of course, the above-mentioned Japanese Patent Publication No. 42-13560 discloses that carbon black can be used in producing a porous PTFE material by a stretching method. However, the electrical resistance of the surface of a porous body obtained by applying this method using a carbon blank is isotropic, not anisotropic.

(Another means to solve the problem) The inventors of the present invention, while considering improvements to the PTFE porous material technology,
We have developed a technology to produce porous bodies with a new microstructure that is different from porous bodies produced by conventional stretching methods. Further investigation led to the discovery that a directional resistor can be obtained by using the porous body with the novel microstructure described above, leading to the completion of the present invention.

It is characterized by its shape being maintained by the binding of long fibers together.

Further, 5 directional resistors according to other aspects of the present invention are as follows.

It is a porous body consisting of a large number of PTFE long fibers oriented in one direction and whose shape is maintained by binding of the long fibers, and the electrical resistance in the long fiber orientation direction on the surface of the porous body is , the electric resistance in the direction perpendicular to the long fiber orientation direction is smaller than that in the direction perpendicular to the long fiber orientation direction.

FIG. 1 shows the microstructure of the porous PTFE material according to the present invention. The porous PTFE body shown here is composed of a large number of long fibers 4 oriented along one direction, and the long fibers are bound together 5, and this binding provides shape retention ability. .

The long fibers may be bound to each other in a relatively short portion, such as 5a, or in a long portion, such as 5b.

The length of the bond can be any length, but most are about 0.
It seems to be more than 03μ poison. Furthermore, the diameter, porosity, and pore diameter of each long fiber are not limited at all, but are usually 0.02 to 3 μm, 5 to 95%, and 0.02 to 3 μm.
02-50μ poisonous.

The PTFE porous body according to the present invention has the above-mentioned microstructure, and as described above, the conventional PTFE porous body is dotted with nodules, and these dotted nodules are connected by a large number of small fibers. A notable difference is that there are virtually no nodules compared to those that have been removed.

Furthermore, the fibers constituting the conventional PTFE porous body are divided by knots, and therefore the length of the fibers is usually relatively short, about 5 to 500 μm. On the other hand, in the porous body according to the present invention, fiber division due to nodules did not occur.

The fibers become longer. Therefore, in the present invention, fibers that are one of the constituent elements of the porous body are named "long fibers".

The porous body of the present invention is expected to be applied to insulating coating materials, filters, sliding materials, artificial blood vessels, etc. in the same way as conventional products.

It has also been found that this porous material exhibits a property of selectively transmitting light in one direction, a so-called "polarization property." No conventional PTFE porous body is known to have polarizing properties, and the possession of polarizing properties is one of the characteristics of the porous body according to the present invention.

Next, an example of the PTFE porous packaging according to the present invention will be described. In this method, unfired PTFE powder is dispersed in a non-wetting liquid and stirred to make the powder fine.Secondly, a liquid lubricant is added to this dispersion to make the powder fine. transfer the PTFE powder to the liquid lubricant side, then remove the non-wetting liquid,
Next, after rolling the mixture of the powder and liquid lubricant,
The liquid lubricant is removed from the molded product, and then the molded product is stretched in the I) uniaxial direction by roll stretching.

In one method, the PTFE powder is treated prior to paste molding. This process consists of two steps: micronization of the PTFE powder and transfer of the micronized powder from the non-wetting liquid used for the micronization to a liquid lubricant.

Here, the refinement of PTFE powder will be explained. The PTFE powder used in the present invention is generally referred to as fine powder, and the commercially available fine powder is in the form of a mixture of primary particles of PTFE produced by a polymerization reaction and secondary particles formed by agglomerating a large number of charcoal particles. However, the content of secondary particles is much larger than that of primary particles. The particle size of these secondary particles is usually several tens of micrometers to several hundred micrometers.

In the distribution method, first, PTFE fine powder and a liquid that does not wet PTFEK (non-wetting liquid) are mixed, the powder is dispersed, and this dispersion is stirred. The mixing ratio of powder and non-wetting liquid at this time may vary depending on various conditions;
00 parts by weight of non-wetting liquid 1000-10000
Parts by weight.

This stirring is performed to release or reduce the agglomeration state of the secondary particles in the PTFE fine powder and to reduce the particle size of the secondary particles (refining the powder).
Particle size is about 10 μm or less, preferably about 0.04 to 0.2 μm
It is preferable to set the stirring speed and time so that the stirring speed is 100 m. In addition, stirring can be performed using a mixer, etc., and the result.

The volume of the PTFE fine powder is apparently increased by about 7 times or more.

Note that the above-mentioned "non-wetting liquid" is mainly a polar solvent and can be defined as one that is not compatible with the liquid lubricant described below, and specific examples of such liquids include methanol, ethanol, water, etc. Can be done.

After the PTFE fine powder has been pulverized in this manner, a liquid lubricant that is compatible with the non-wetting liquid is added to the dispersion. Although the amount of liquid lubricant added may vary depending on the type of the lubricant, it is usually 400 to 600 parts by weight per 1.00 y parts of PTF'E powder.

The above-mentioned liquid lubricant can be appropriately selected from among those conventionally used for PTFE paste molding, and has a high affinity for PTFE and no compatibility with non-wetting liquids. , polychlorotrifluoroethylene.

When a liquid lubricant is added to a dispersion containing finely divided PTFE fine powder, the non-wetting liquid and the liquid lubricant are not compatible and separate, while the PTFE fine powder is separated due to the difference in affinity for both liquids. Shift to liquid lubricant side. Therefore, the non-wetting liquid can be removed from the system by an operation such as decantation, and a mixture of PTFE fine powder and liquid lubricant, that is, a paste-like product is obtained. It consists of fine powder and liquid lubricant, and is similar to the paste-like material used in the conventional stretching method. However, since the secondary particles in the PTFE fine powder are fine and the content of liquid lubricant is high (the powder in the paste is 60% by volume or less), the paste used in the conventional stretching method is There is a big difference between things. Incidentally, the paste-like material used in the conventional stretching method is PTFE powder 100
Per weight part.

On the other hand, the liquid lubricant is about 15 to 100 parts by weight.

The present invention is made of PTFE powder 100 as described above.
The amount is 400 to 600 parts by weight.

In this method, after performing the above-mentioned pretreatment, the non-wetting liquid is further removed to obtain a paste-like material, which is then subjected to a rolling process. In rolling forming, a paste is placed on a rigid support material such as an aluminum plate, and pressure is applied in one direction to form the paste into a sheet.The pressure is then removed and the sheet is rolled in the same direction. It is best to fold the sheet in half or more and apply pressure again in the rolling direction (folding the sheet and then applying pressure again)
% 2 cycles or more may be performed).

In the above method, the liquid lubricant is removed from the sheet material obtained by such rolling.

Roll stretching is then performed.

The liquid lubricant can be removed by extraction, evaporation, or a combination thereof.

Further, roll stretching is a method in which a sheet-like material from which liquid lubricant has been removed is placed along the roll surface, and a tensile force (stretching force) is applied to it in the rolling direction.

This roll stretching method involves (a) placing a sheet-like material along the roll surface and stretching the sheet once, and (b) folding the sheet stretched as in (a) above in two or more. A method of folding and stacking, or cutting to a predetermined size and stacking (stretching direction of each stacked layer is the same direction), and roll stretching again (superimposing and subsequent roll stretching are one cycle, 2 cycles Any of the above methods may be used. (a)
Method (b) yields a porous body with longer binding parts than method (b), and method (b) tends to increase the diameter of long fibers as the number of cycles of overlapping and subsequent roll rolling increases. There is.

During the roll stretching, the rolls are maintained at a temperature lower than the melting point of PTFE, preferably about 150 to 300°C.

In addition, although the stretching rate is not particularly limited, (a)
When using the method, it is preferably about 500 to 1500%.

(b) in each cycle, approximately 150
It is preferable to set it to ~300%.

Furthermore, prior to the roll stretching, the sheet material is coated with PTFE.
Preliminary stretching can also be performed in one direction (the same direction as the roll stretching) at a temperature below the melting point of . The stretching ratio at this time is approximately 200
% or less, and by performing such preliminary stretching, stretching during roll stretching can be easily performed.

In addition, in the case of this method, it is preferable to maintain the stretched state of the porous body after roll stretching and heat treatment, and if the heating is performed at a temperature equal to or higher than the melting point of PTFE, a fired porous body can be obtained.

It is not yet clear why a porous PTFE material having the above-mentioned novel microstructure can be obtained by such a method. However, as shown in the Examples below, it was confirmed that the desired porous body could be obtained.

Next, a directional conductor according to another aspect of the present invention will be described. This conductor has the same microstructure as the above-described porous PTFE material, and its electrical resistance in the direction of orientation of the long fibers is smaller than that in the direction perpendicular to the direction of orientation of the long fibers.

Directivity can be imparted to the porous body having the novel microstructure by, for example, treating the porous body with an alkali metal.

This alkali metal treatment is easily and preferably carried out by immersing the porous body in a liquid ammonia solution containing an alkali metal such as sodium, potassium, or lithium, or in a tetrahydrofuran or dimethoxyethane solution of a naphthalene complex of an alkali metal. However, when one surface of a porous body is treated, methods such as coating and casting can also be applied.

As a commercially available alkali metal treatment solution, there is "Tetra Etch (manufactured by Junkosha)" which is a dimethoxyethane solution of a naphthalene complex of sodium metal.

The concentration of the alkali metal naphthalene complex in the solution used for this treatment is usually 0.03 to 0.5 mol/l, preferably 0.05 to 0.3 mol/l. If the complex concentration is too dilute, the treatment effect may not be obtained, and if it is too concentrated, the strength of the porous PTFE material may be significantly reduced.

When a porous PTFE material is treated with such a solution, the treatment effect varies depending on the concentration of the alkali metal naphthalene complex, the immersion time (usually 10 to 600 seconds), or the number of times of coating and casting. Therefore, by appropriately selecting these conditions, resistors with different degrees of directivity can be obtained.

Since alkali metal fluoride salts and carbonates adhere to the treated surface of the alkali metal-treated PTFE porous body, these salts are removed by tetrahydrofuran cleaning or ultrasonic cleaning.

The directional resistor thus obtained has a ratio of electrical resistance in the long fiber orientation direction on the treated surface to electrical resistance in a direction perpendicular to the orientation direction of 1=2 to 1:8. The electrical resistance in the long fiber orientation direction is approximately 10 OKΩ to 105 MΩ/
crn, and that in the direction orthogonal to this direction is approximately several hundred Ω to 10' MΩ/F.

Here, a phenomenon caused by alkali metal treatment of a porous PTFE material will be explained.

Figure 5 shows PT before and after alkali metal treatment (using a tetrahydrofuran solution of sodium naphthalene complex).
X-ray photoelectron spectroscopy (hereinafter referred to as ESC) on the surface of the FE porous sheet
A) spectrum is shown.

As can be seen from this figure, C1 of -CF2-
8 peak has disappeared, while the hydrocarbon C18 peak has become sharper. Furthermore, the F18 peak disappears due to the processing, and the 018 peak becomes sharper.

FIG. 6 shows infrared absorption spectra for three samples: the same two samples used for taking the ESCA spectra in FIG. 5, and a sample treated with an alkali metal and further treated with bromine.

As can be seen from this Figure 6, by sodium treatment,
Peaks at 1580 cm and 1390 cm appear. The former peak is attributed to C=C stretching vibration, and is similar to the normal isolated double bond peak 1640-16.
Compared to 80crrL, it has shifted considerably to the lower wavenumber side. This shows that the double bond represented by C=C is a conjugated system.

The latter peak is attributed to the CH0 in-plane bending vibration originating from the C=C double bond. and.

By bromine treatment, both of these peels disappeared, while 1
A new peak appears at 710cIIL. This peak was generated in the p-PTFE porous material by the alkali metal treatment, but became apparent by the bromine treatment.

That is, by alkali metal treatment, defluorination occurs on the treated surface of the porous PTFE material, and due to this defluorination, saturated or unsaturated hydrocarbon skeletons, carbonyl groups, and carboxy groups are generated, and the main chain is carbonized. Conjugated double bonds now exist in the hydrogen skeleton.

Incidentally, alkali metal treatment of a non-porous PTFE molded product is carried out, for example, in the production of an adhesive tape using a non-porous PTFE sheet as a support, in order to improve the anchoring ability of the adhesive to the support, and is well known. .

Then, E by alkali metal treatment of the PTFE porous body
The SCA spectrum and infrared absorption spectrum are the same as those obtained by conventionally known alkali metal treatment of non-porous PTFE molded articles.

However, when porous PTFE is treated with an alkali metal, it can be given directivity, whereas non-porous PTFE
Even if a molded article is treated in the same way, the above characteristics cannot be imparted.

From this, the details of the directionality of electrical resistance in the resistor according to the present invention are not yet clear, but A19.

It is inferred that this is due to the synergistic effect of the alkali metal treatment and the microstructure of the porous body subjected to the treatment. Next, another example of imparting directionality to the PTFE porous body will be described. Directivity can also be imparted to the porous PTFE body by adhering countless fine conductive metal particles such as gold, silver, copper, etc. to the surface of the porous body.

Adhesion of fine metal particles to the surface of a porous body can be achieved by 1, for example, vapor deposition,
This can be done by sputtering.

Therefore, it is not possible to visually distinguish each of the metal particles closely attached to the surface of the porous body, and the metal particles are visually recognized as if a thin metal film had been formed on the surface of the porous body.

However, when this is observed using an electronic microscope (magnification is approximately 5,000 to 10,000 times), individual metal particles can be seen. The size of the metal particles adhering to the surface of the porous body may vary depending on the method of adhesion, working conditions, etc., but is usually about 100 to 25 oX. The electrical resistance in the orientation direction (stretching direction) of the long fibers of the porous material is smaller than that in the direction perpendicular to the orientation direction. Although the ratio of electrical resistance in both directions is not particularly limited, it is usually about 1:2 to 1:100.

More specifically, the electric resistance in the orientation direction of the long fibers is approximately 0.1Ω to 100KΩ, and that in the direction orthogonal to this direction is approximately 1Ω to IOMΩ.

It is not clear why directivity can be imparted by the close contact of fine metal particles to the surface of the PTFE porous material as described above, but in any case, as shown in the following example, this It was confirmed that the resistor obtained by this method showed clear electrical directivity.

The resistor according to the present invention has 1 due to its electrical directivity.
Application to various fields can be expected.

An example of what seems to be an applicable RIJ function will be described. When a sheet-like directional resistor is wound into a roll with the direction of low electrical resistance facing the circumferential direction and a voltage is applied to it, it is difficult for current to flow in the axial direction (lengthwise direction) of the roll. At high frequencies, the state is the same as when a coil is wound around an iron core and a voltage is applied to it, producing an L component. Then, due to this L and the interelectrode capacitance, the rolled resistor becomes K so that it can function as an oscillating sheet.

By the way, in Japanese Patent Application No. 58-4548, the present applicant applied a voltage to an oscillating sheet to oscillate high-frequency radio waves, thereby separating two liquids from a mixed liquid that came into contact with the seed. He said he would get it.

Therefore, the directional resistor of the present invention may be used alone or in
- Composite the fluororesin molded article proposed in No. 4548 with an oscillating fluororesin molded article obtained as a base material.
Can be used as an oscillator.

(Example) Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 8 parts by weight of unfired PTFE fine powder (manufactured by Daikin Corporation, trade name F103) is dispersed in 100 parts by weight of methanol, and stirred for 10 minutes at a high speed of 9500 rpm using a high cutting power mixer. As a result of this stirring, the average particle size of the shibauder was refined from about 500 μm to about 10 μm, and the apparent volume expanded to about 7 times.

Next, 40 parts by weight of a low polymer of polychlorotrifluoroethylene (manufactured by Daikin Corporation, trade name: Daifloil #20), which is a liquid lubricant, is added to this dispersion. As a result of this addition, the liquid phase undergoes phase separation such that methanol is located at the top and Dyfloil is located at the bottom, and the PTFE powder moves to the Dyfloil side where it has a strong affinity and is dispersed.

Next, methanol is removed from the thread by decantation to obtain a paste consisting of PTFE fine powder and die 7° oil.

This paste-like material is placed on an aluminum plate and rolled with rolling rolls to a thickness of about 1 to 2 mm. This rolled product is folded into four pieces and stacked on top of each other, and the rolling rolls are run again to give a thickness of about 1 to 2 IIllI. Further, this stacking and subsequent rolling are repeated 10 cycles to obtain a sheet-like product with a thickness of about 1.

Next, this tunnel-like material is immersed in gold trichlorethylene to extract and remove the dichloroil.

Thereafter, the sheet-like material was placed along the surface of a quartz roll (temperature maintained at 260°C) and uniaxially stretched in the circumferential direction of the roll (stretching rate: 800%) to form a PTFE porous body with a thickness of 80 μm. Obtained.

The microstructure of the surface of this porous body was as shown in the scanning electron micrograph shown in FIG. 2 (magnification: 2000 times). In FIG. 2, numerals 4 are long fibers, each oriented in one direction (orientated along the stretching direction). Reference numeral 5 denotes a large number of bonds present in the porous body 1, which maintains the sheet shape of the porous body 1.

Example 2 The same sheet-like material used in Example 1 (from which Daifloyl was extracted and removed) was heated to 150°C.

Preliminary stretching is carried out in the uniaxial direction so that the stretching ratio becomes 150%.

Next, under the same conditions as in Example 1, the film was stretched in the same direction as the preliminary stretching direction to a stretching ratio of 300%.

Thereafter, this sheet is cut at the center in the stretching direction, overlapped so that the stretching direction is the same, and rolled stretched again in the same direction (temperature 290"C, stretching ratio 200%).Furthermore, this overlapping and Subsequent rolling was performed for 4 cycles to obtain a porous PTFE body with a thickness of 100 μm.

The microstructure of the surface and cross-section in the thickness direction of this porous body was as shown in the scanning electron micrographs shown in FIGS. 3 and 4 (both magnifications were 2000 times).

In FIGS. 3 and 4, long fibers 4 are oriented in one direction, and the long fibers are bound together 5 to maintain the sheet shape of the porous body.

Example 3 PTFE porous sheet fc3 obtained in Example 2
It was cut into c7rL squares, fixed to the glass tube wall, immersed in an alkali metal treatment solution, treated on one side, then washed with tetrahydrofuran, and further treated in the same solution for 30 minutes.
After ultrasonic cleaning for 0 minutes, air drying was performed to obtain a sheet-like directional resistor.

A tetrahydrofuran solution with a sodium-naphthalene complex concentration of 0.05 mol/l was used as the alkali metal treatment solution, and the immersion times were set to 10 seconds, 30 seconds, and 60 seconds.

In order to know the electrical resistance characteristics of the obtained directional resistor, two electrodes were arranged at a distance lα in the long fiber orientation direction (stretching direction) of the sheet, and two electrodes were similarly arranged in the direction perpendicular to this direction. electrodes were placed and the electrical resistance in both directions was measured. The results are shown in Table 1 below. The measurement was performed using a DC stabilized power supply (model 6120, manufactured by Takeda Riken Co., Ltd.) and an electrometer (model 8411, manufactured by Takeda Riken Co., Ltd.).

Table 1 Example 4 Silver was deposited on one side of the PTFE porous body obtained in Example 2 using a known resistance heating type deposition apparatus.

A predetermined amount of iron pieces is set on a tungsten board, and rough drawing and main drawing are carried out for 20 minutes and 30 minutes, and the deposition chamber is maintained at k I X 10-' Torr.

Next, a voltage of 75 V is rapidly applied to the tungsten board, and when melting of the iron piece is observed, the voltage application is rapidly stopped. This time is about 2 to 3 seconds.

A directional resistor was obtained by repeatedly applying and stopping voltage until the iron piece disappeared.

In addition, during vapor deposition, the porous body is cut into an appropriate size, and a cutout of 15 mm x 25 mm is formed on one side of the porous body.
, polyethylene terephthalate film (thickness 100μ
The edges of the porous body are fixed to the film with adhesive tape to prevent shrinkage due to heat during vapor deposition, and the portion exposed by the cutout (area 375 vtA) is silver was vapor-deposited.

In order to understand the electrical resistance characteristics of the obtained directional resistor, two electrodes were placed at a distance of 11 mm in the direction of orientation of the long fibers of the sheet.
Two electrodes were similarly arranged in a direction perpendicular to this direction, and the electrical resistance in both directions was measured. The results are shown in Table 2 below. The measurement was performed using a digital multimeter (3438A manufactured by Hulett Barakad).
This was done using

Table 2 (Effects of the Invention) According to the present invention, it is possible to provide a porous body having a new and unique microstructure different from conventional ones and a resistor having electrical directivity.

[Brief explanation of the drawing]

Figures 1 and 2 to 4 are schematic diagrams and scanning electron micrographs showing the microstructure of the porous PTFE material according to the present invention, and Figure 5 is an ESCA spectrum diagram of the porous material before and after alkali metal treatment. , the spectrogram, and FIGS. 7 and 8 are schematic diagrams and scanning electron micrographs showing the microstructure of conventional products. l... PTFE porous material 4... Long fiber 5...
conclusion

Claims (5)

[Claims] (1) A polytetrafluoroethylene porous body comprising a large number of polytetrafluoroethylene long fibers oriented in one direction, and retaining its shape by binding the long fibers together. (2) Polytetrafluoroethylene powder is dispersed in a non-wetting liquid and stirred to make the powder fine, and then a liquid lubricant is added to this dispersion to make the powder fine. The polytetrafluoroethylene powder is transferred to the liquid lubricant side, the non-wetting liquid is removed, and the mixture of the powder and the liquid lubricant is rolled and formed, and then the liquid lubricant is removed from the formed product. . A method for producing a polytetrafluoroethylene porous body, which comprises: then stretching the molded product in a uniaxial direction by roll stretching. (3) A porous body consisting of a large number of polytetrafluoroethylene long fibers oriented in one direction and whose shape is maintained by binding of the long fibers, and the long fiber orientation on the surface of the porous body. A directional resistor characterized in that an electric resistance in a direction is smaller than an electric resistance in a direction perpendicular to the long fiber orientation direction. (4) A directional resistor according to claim 3, wherein the porous body is treated with an alkali metal. (5) A directional resistance body according to claim 3, wherein countless fine metal particles are closely attached to at least one surface of a porous body.