JP2004255274A - Method and apparatus for manufacturing polytetrafluoroethylene porous membrane - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polytetrafluoroethylene (PTFE) porous membrane having not only excellently uniform pore size but also various excellent uniform characteristics. <P>SOLUTION: A PTFE sheet 1 is stretched/drawn in the sheet conveying direction by a supplying roll 12 and a take-up roll 13 which are arranged apart from each other while conveying the sheet 1 from the roll 12 to the roll 13. The sheet 1 is heated between the rolls 12 and 13 by irradiating it with the infrared rays from an infrared heater 5, for example. The sheet 1 between the rolls 12 and 13 is made to pass through at least one guide roll 17 or 18 which is arranged at the position parted from a drawing starting line 7 and close to the roll 13 and the diameter of which is made smaller than that of the roll 13. The sheet 1 is restrained from being necked and the pore size of this PTFE porous membrane 2 can be made uniform by using these rolls 17 and 18. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for producing a porous polytetrafluoroethylene (hereinafter abbreviated as “PTFE”) membrane.
[0002]
[Prior art]
The PTFE porous membrane is manufactured by blending various liquid lubricants with PTFE fine powder, extruding and rolling, removing the liquid lubricant, and then stretching. In the stretching step, sequential biaxial stretching is generally used. It is considered that the pore diameter of the porous membrane is usually determined by the length of the fibrils formed at the time of the first stretching performed in the rolling direction (Machine Direction, hereinafter abbreviated as “MD direction”). For this reason, the conditions at the time of stretching in the MD direction have a great effect on the properties of the obtained film. As a stretching method of the PTFE sheet, a zone stretching method and a hot roll stretching method are known.
[0003]
As shown in FIG. 5, in the zone stretching method, the PTFE sheet 51 is stretched while being exposed to a high-temperature atmosphere in an oven 66 and heated. The PTFE sheet 51 fed from the rolls 61 and 62 to the rolls 63 and 64 on the downstream side is gradually made porous in the stretching region 65 in the oven 66, and becomes the PTFE porous film 52. However, in this stretching method, since the length L ′ of the stretching region 65 is long, necking caused by stretching increases. For this reason, the stretching becomes non-uniform and the variation in the pore size increases, and as a result, the variation in the characteristics of the PTFE porous membrane such as the pressure loss also increases. In the zone stretching method, a hot-air circulation type electric heater, a gas burner, or the like is used as a heating source.
[0004]
Patent Document 1 discloses a method for producing a PTFE porous membrane in which stretching and firing are performed simultaneously. In this method, the PTFE sheet is stretched in a heating zone maintained at a temperature not lower than the melting point of PTFE (327 ° C.). Although the PTFE porous membrane obtained by firing at the same time as the stretching has high strength, the PTFE porous membrane in the width direction significantly changes, and the width of the product becomes small. The method described in Patent Document 1 does not solve the problem of the zone stretching method in which the variation in pore diameter is large.
[0005]
As shown in FIG. 6, in the hot roll stretching method, the PTFE sheet 51 is heated by the roll 72 held at a high temperature. In this method, the PTFE sheet 51 is stretched in a region 75 near the roll 72. The use of the hot roll stretching method eliminates the need for an oven, so that the space between the rolls 71 and 72 for feeding out the PTFE sheet 51 and the rolls 73 and 74 for winding up the PTFE porous film 52 can be shortened to reduce necking. However, in the hot roll stretching method, the stretching start position is liable to fluctuate, so that the stretching becomes uneven and the variation in the pore diameter increases.
[0006]
[Patent Document 1]
JP-B-58-25332 [0007]
[Problems to be solved by the invention]
PTFE porous membranes are used as filter media for air filters used in clean rooms of the semiconductor and chemical industries, as filter media for bag filters used for collecting valence powders and collecting dust from incinerators, and as electrical products. It is widely used as a film for preventing intrusion of moisture from the internal pressure adjusting hole. For example, in an air filter used in a clean room for semiconductor manufacturing, importance is attached to the uniformity of the air volume distribution of the air filter. If the air volume distribution is not uniform, the air flow in the clean room is disturbed and air pools are generated, and as a result, the gas concentration which causes a decrease in the yield of semiconductor manufacturing locally increases. For other uses, it is required to reduce the variation in the pore size of the porous PTFE membrane in order to make the properties in the membrane uniform.
[0008]
However, the conventional stretching method cannot sufficiently suppress the variation in the pore size of the PTFE porous membrane.
[0009]
[Means for Solving the Problems]
Therefore, in the present invention, the PTFE sheet is heated between a pair of rolls (a feeding roll and a take-up roll) to suppress the fluctuation of the stretching start position, and the PTFE sheet after the stretching is started is wound between these rolls. Necking was suppressed by passing through at least one guide roll having a smaller diameter than the take-up roll.
[0010]
In the method for producing a porous PTFE membrane of the present invention, the PTFE sheet is pulled in the transfer direction by the supply roll and the take-up roll while transferring the PTFE sheet from the supply roll arranged separately to the take-up roll. By stretching, when the PTFE sheet is continuously made porous, the PTFE sheet is heated between the payout roll and the winding roll, and the winding of the PTFE sheet is started from the position where the stretching of the PTFE sheet is started. The PTFE sheet is transferred via at least one guide roll that is arranged on the take-up roll side and has a smaller diameter than the take-up roll.
[0011]
The apparatus for manufacturing a porous PTFE membrane of the present invention includes a feeding roll and a winding roll that are separately arranged, and heating means for heating the PTFE sheet so that the PTFE sheet can be stretched. An apparatus for continuously making the PTFE sheet porous by pulling and stretching the PTFE sheet in the transfer direction with the take-up roll, wherein the heating means includes a feeding roll and a take-up roll. An infrared heater arranged so that the distance between the PTFE sheet and the PTFE sheet is 0.1 mm or more and 100 mm or less, and the diameter of the winding roll is smaller than that of the infrared heater. At least one guide roll through which the PTFE sheet passes is arranged. To.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
The PTFE sheet may be heated by irradiating infrared rays emitted from an infrared heater. If an infrared heater is used, the PTFE sheet can be locally and strongly heated. In the conventional zone stretching method, it was practically necessary to heat the PTFE sheet over about 500 mm or more. When stretching is performed while heating in a belt-shaped region having a limited length, for example, in the range of 1 to 100 mm in the transport direction of the PTFE sheet, the variation in the pore diameter of the porous PTFE membrane can be further suppressed.
[0013]
The wavelength at which the energy radiated from the infrared heater becomes maximum (maximum energy wavelength) is preferably 1 μm or more and 4 μm or less. This is because the heat absorption efficiency of the PTFE sheet is increased, and heating and stretching in a narrow region can be performed.
[0014]
As the guide roll, a roll whose diameter is smaller than that of the winding roll is used. The smaller the diameter of the guide roll is, the easier it is to arrange the guide roll in a narrow space. On the other hand, if the roll is too thin, the roll tends to be distorted, so that the diameter of the guide roll is preferably 5 mm or more.
[0015]
One guide roll may be used, but two or more guide rolls are preferable in order to suppress slippage of the PTFE sheet. However, when the number of guide rolls is large, the pass line of the PTFE sheet becomes long, so that the stretching unevenness is more likely to occur. The optimal number of guide rolls is two. The position of the guide roll is not particularly limited as long as it is between the position where the stretching of the PTFE sheet is started and the winding roll.
[0016]
The transfer direction of the PTFE sheet may be changed by 30 ° or more, preferably 45 ° or more by passing through any guide roll selected from at least one guide roll disposed between the rolls. As the so-called sheet holding angle is increased, the slip of the PTFE sheet on the guide roll can be suppressed.
[0017]
The take-up roll needs to securely hold the porous PTFE sheet so that the PTFE sheet can be pulled between the take-up roll and the take-out roll. In consideration of this, the diameter of the winding roll is preferably not smaller than 50 mm, for example, 70 to 200 mm. It is preferable that the diameter of the feeding roll is also in the above range for the same reason.
[0018]
The stretching ratio of the PTFE sheet is preferably 1.05 to 50 times, particularly preferably 1.2 to 50 times. However, if the stretching ratio is too high, the water resistance of the film may decrease. Therefore, in applications where water resistance is required, it is preferable to limit the stretching ratio to, for example, about 5 times or less.
[0019]
The PTFE sheet may be stretched while being heated to a temperature lower than the melting point of PTFE. When the PTFE sheet is fired, the stretched PTFE porous membrane may be further fed out, heated to a temperature equal to or higher than the melting point of PTFE, and fired continuously. The PTFE sheet may be stretched a plurality of times. In this case, the PTFE sheet is heated to a temperature lower than the melting point of PTFE at least between the first rolls, and if firing is required, the PTFE sheet is preferably heated to a temperature higher than the melting point of PTFE at least between the last rolls. .
[0020]
The PTFE sheet may be stretched while heating or cooling at least one of a feeding roll and a winding roll. This is for controlling the temperature of the PTFE sheet between the rolls, or for steepening the temperature distribution in the transport direction of the PTFE sheet and / or the stretched PTFE sheet (PTFE porous membrane). Heating and cooling may be used in combination. For example, the downstream roll may be cooled while the upstream roll is heated to preheat the PTFE sheet.
[0021]
The PTFE porous film stretched by applying the present invention may be a porous film formed by biaxial stretching (biaxially stretched film) or a porous film stretched only in one axis direction (uniaxially stretched film). . In the case of forming a biaxially stretched film, the film may be stretched by a stretching device using the guide roll, and then stretched in a direction perpendicular to the stretching direction. When firing a biaxially stretched film, the firing step should be performed after stretching biaxially.
[0022]
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In the stretching apparatus shown in FIGS. 1 and 2, the PTFE sheet 1 is continuously fed from the rolls 11 and 12, is heated by infrared rays emitted from the infrared heater 5, and is fed to the feeding roll 12 by a difference in roll rotation speed. It is stretched between the take-up roll 13 and made porous. The porous PTFE sheet is continuously wound by the rolls 13 and 14 as the PTFE porous film 2 via the guide rolls 17 and 18. The roll 12 on the payout side and the roll 13 on the winding side are drive rolls whose rotational speed can be controlled. The rolls 11 and 14 may be free rolls together with the guide rolls 17 and 18.
[0023]
In this apparatus, the transfer direction of the PTFE sheet 1 is changed twice or more by 90 ° or more between the feeding roll 12 and the winding roll 13 via the guide rolls 17 and 18. The stretched PTFE sheet is held by these guide rolls, and variation in stress in the width direction is suppressed. The positions of the guide rolls 17 and 18 are preferably closer to the region 6 heated by the infrared rays from the heater 5, but in reality, it is better to separate them from the heater 5 so that the temperature of the rolls does not become too high.
[0024]
The heater 5 is preferably arranged so that the distance D from the PTFE sheet 1 is 0.1 mm to 100 mm, particularly 0.1 mm to 10 mm. If strong heating is required, the distance D may be 5 mm or less. If the heater is too close to the membrane, it may come into contact with the PTFE sheet. Conversely, if it is too far, the temperature distribution of the sheet will be non-uniform, and stretching unevenness will easily occur. As the infrared heater, a medium-wavelength heater, a low-wavelength heater, a carbon heater, or the like can be used.
[0025]
As shown in FIG. 2, the PTFE sheet 1 fed from the upstream feed roll 12 to the downstream take-up roll 13 receives the PTFE sheet 1 while passing through the belt-shaped heating region 6 which crosses the direction of film advance. Infrared rays are emitted from a heater (not shown in FIG. 2) disposed on the region. The stretching of the PTFE sheet is started from a stretching start line 9 in this area 6. Distance PTFE sheet from stretching start line 9 until the winding roll 13 on the downstream side (more precisely, the roll 13 and the porous PTFE membrane 2 are in contact with the position) is transferred (transfer distance; pass line) L ₁ In order to suppress necking, it is appropriate that the thickness be 500 mm or less, particularly 300 mm or less, for example, 1 mm or more and 250 mm or less.
[0026]
Strain rate of the transfer distance L ₁ is a short sheet is increased. A high strain rate is preferable for making the pore diameter uniform, but if the strain rate is too high, it becomes difficult to obtain a PTFE porous membrane having a low pressure loss. Meanwhile, of simply took a large transport distances L _1, is impaired uniformity of pore size. However, heating by irradiation of infrared rays from the infrared heater between rolls, and for example, the PTFE sheet is stretched while held by the guide rolls while ensuring the transfer distance L ₁ of more than 100 mm, the average value of the pressure loss below 50Pa Even if it is lowered, it is possible to obtain a PTFE porous membrane having a uniform pore diameter and a small variation in characteristics (for example, a variation in pressure loss) in the membrane.
[0027]
Variations in pressure loss can be suppressed to a level where the fluctuation rate measured with 24 measurements is 2% or less so that the measurement locations do not overlap each other. An example of how to determine the measurement points is shown in the following examples. A porous PTFE membrane having a low pressure loss and a small fluctuation rate up to the above-mentioned level has been made possible only by applying the present invention, and constitutes one aspect of the present invention.
[0028]
Distance _{L 2} between the rolls 12 and 13 (transfer distance of the PTFE sheet between the case where there is no guide rolls roll) is usually about 50mm~500mm appropriate. However, the pressure loss of about the obtaining low porous PTFE membrane, the distance _{L 2} is may keep more than 100 mm.
[0029]
The temperature gradient between the heating area 6 and the non-heating area is preferably steep. Infrared rays, particularly infrared rays having a wavelength of 1 μm to 4 μm, and more preferably 1.5 μm to 3 μm, are excellent as PTFE absorption efficiency, and thus are suitable as radiation that enables the PTFE sheet to be locally stretched in a band-shaped region. I have. When it is desired to keep the temperature gradient steeper, at least one selected from the feeding roll 12 and the winding roll 13 may be cooled. When the PTFE sheet 1 does not reach the desired stretching temperature in the heating area 6, the PTFE sheet may be pre-heated using the feeding roll 12. For preheating, hot air or the like may be blown on the PTFE sheet 1 on the upstream side of the area 6.
[0030]
In the apparatus illustrated in FIG. 1, one heater crosses the PTFE sheet above the sheet so as to be orthogonal to the traveling direction of the PTFE sheet. This arrangement of the heater is an example of a preferable arrangement for uniformly heating the PTFE sheet in the width direction. However, the position, the number of heaters, and the angle with respect to the film traveling direction of the heater are not limited to those shown in FIG. A heater may be added below the sheet so that the PTFE sheet is heated from both sides, or a plurality of heaters may be arranged on the same side of the PTFE sheet. A heat ray reflection plate or the like may be provided around the heater in order to concentrate infrared rays on a predetermined area.
[0031]
If the stretching is started after heating by a roll as in the conventional hot roll stretching method, it is difficult to determine the stretching start position. However, as shown in FIGS. 1 and 2, when the region including the stretching start position is locally and strongly heated, the sheet can be stretched at a high strain rate while preventing the fluctuation of the stretching start position.
[0032]
The other conditions for stretching the PTFE sheet are not limited, and may be appropriately determined according to desired characteristics. Usually, the speed of the roll on the payout side is 0.1 to 15 m / min, and the stretching temperature is 50 ° C. to 50 ° C. 300 ° C. are respectively suitable.
[0033]
The PTFE porous membrane thus obtained may be used as it is as a uniaxially stretched membrane, but is further stretched in a direction orthogonal to the MD direction (Transverse Direction, hereinafter abbreviated as “TD direction”) to form a biaxially stretched membrane. Is also good. However, the stretching in the MD direction may be performed after the stretching in the TD direction. The stretching ratio of stretching in the TD direction is preferably 1.2 to 50 times, and the stretching temperature is preferably room temperature to 200 ° C. In the case of a uniaxially stretched film, it is preferable that the film has an air permeability of 3 to 100 seconds (measured value according to a method specified in JIS P8117) and an average pore diameter of 0.02 to 3.0 μm. When a biaxially stretched film is used, the pressure loss is preferably 10 to 1000 Pa and the average pore diameter is preferably 0.05 to 51.0 μm.
[0034]
The PTFE porous membrane 2 stretched by the apparatus shown in FIGS. 1 and 2 may be further fired. When high mechanical strength is required, it is preferable to stretch at a temperature lower than the melting point of PTFE and then to fire at a temperature higher than the melting point of PTFE, specifically, 327 ° C or higher, particularly 350 ° C or higher. The firing method is not particularly limited, but it is preferable to continuously fire the PTFE film 2 using the oven 8 as shown in FIG. As the oven 8, it is sufficient to use a hot air circulation type electric oven or a gas oven which has been conventionally used for stretching (or stretching and baking). However, the heating means is not limited to these ovens. The firing time (time for contact with the atmosphere maintained at the firing temperature) is usually 5 seconds or more, preferably 10 seconds or more, and more preferably 200 seconds or less.
[0035]
The rotation speed of the pay-out roll and the take-up roll at the time of firing may be appropriately adjusted according to the characteristics of the film to be obtained. Basically, the speed should be the same, but the film may be further stretched or shrunk to such an extent that the film does not sag. The fired PTFE porous membrane 7 provides higher strength than the PTFE porous membrane 2 before firing.
[0036]
The PTFE sheet to be stretched is not particularly limited, but preferably has a thickness of about 0.01 mm to 2 mm, particularly about 0.01 mm to 1 mm. As the PTFE sheet, a sheet obtained by a conventionally known method is sufficient. In general, a PTFE sheet is prepared by preforming a paste-like admixture obtained by adding a liquid lubricant to PTFE fine powder, extruding the preform into a paste, and rolling to form a sheet. The liquid lubricant is not particularly limited as long as it can wet the surface of the PTFE fine powder and can be removed by extraction or heating, and hydrocarbons such as liquid paraffin, naphtha, and white oil may be used. The appropriate amount of the liquid lubricant to be added is 5 to 50 parts by weight based on 100 parts by weight of the PTFE fine powder. The preforming may be performed at such a pressure that the liquid lubricant is not squeezed out. The liquid lubricant may be removed in advance from the PTFE sheet to be stretched, but may be removed after stretching.
[0037]
【Example】
(Example 1)
A paste-like mixture obtained by adding 20 parts by weight of a liquid lubricant (kerosene) to 100 parts by weight of PTFE fine powder was preformed, formed into a round bar by paste extrusion, and further rolled. The PTFE sheet (thickness: 0.2 mm) obtained by rolling was heated to 130 ° C. to evaporate and remove the liquid lubricant.
[0038]
The PTFE sheet thus obtained was stretched using the stretching apparatus shown in FIGS. In this stretching device, the upstream rolls 11 and 12 and the downstream rolls 13 and 14 are connected to roll driving means for arbitrarily controlling the rotation speed. The diameter of these rolls 11 to 14 was 120 mm. On the other hand, the diameter of the guide rolls (free rolls) 17 and 18 was 10 mm. As the heater 5, an infrared heater (width 3 cm, rated output 0.8 kW, maximum energy wavelength 2.6 μm) was used. The distance between the heater 5 and the PTFE sheet was adjusted to 2 mm. The interval between the rolls 12 and 13 (FIG. 2: L ₂ ) was 150 mm. As shown in FIG. 4, the temperature of the PTFE sheet at the time of stretching was measured using a radiation thermometer 10 (manufactured by CHINO, model number 1R-TAP) arranged close to the downstream side of the heater 5.
[0039]
The PTFE sheet was made porous by setting the feeding speed from the upstream roll to 0.6 m / min and the winding speed by the downstream roll to 6 m / min. The pass line (FIG. 2: L ₁ ) of the PTFE sheet from the stretching start line 7 to the take-up roll 13 was about 200 mm. The film temperature (stretching temperature) measured with a radiation thermometer was 173 ° C.
[0040]
A group of 2 points (TD direction) × 6 points (MD direction) were formed on the PTFE sheet at four locations along the MD direction. The point interval in the reference point group was 10 mm. The gauge interval after stretching was measured, and the average value and the fluctuation rate of the stretching ratio were calculated. The average value of the stretching ratio was 9.7 times, and the variation rate was 1.25%.
[0041]
(Example 2)
The uniaxially stretched film obtained in Example 1 was further stretched in the TD direction using a tenter stretching device to obtain a biaxially stretched film. In the stretching in the TD direction, the stretching ratio was 30 times, and the stretching temperature was room temperature. The pressure loss of the biaxially stretched PTFE porous membrane thus obtained was measured. The measurement was performed at a plurality of points arbitrarily selected so as not to overlap each other. When the measurement was performed at a total of 25 points of 1 point in the TD direction × 25 points in the MD direction, the average value of the pressure loss was 134 Pa, and the fluctuation rate was 1.96%. Furthermore, when the number of measurements was measured as 24 of 4 points in the TD direction × 6 points in the MD direction, the average value of the pressure loss was 135 Pa, and the fluctuation rate was 1.84%.
[0042]
The pressure loss was measured by a pressure gauge (manometer) when air was passed at a wind speed of 5.3 cm / sec with the PTFE porous membrane set in a circular holder having an effective area of 100 cm ² . The value was adopted.
[0043]
Note that the fluctuation rate can be calculated by the following equation.
Fluctuation rate (%) = (standard deviation / mean value) × 100
[0044]
(Comparative Example 1)
A PTFE sheet was stretched in the same manner as in Example 1 except that these rolls were not passed except for the guide rolls 17 and 18. The pass line of the PTFE sheet (FIG. 2: L ₁ ) was reduced to about 150 mm. However, the average value and the fluctuation rate of the stretching ratio measured in the same manner as in Example 1 were 9.8 times and 2.08%, respectively.
[0045]
(Comparative Example 2)
The uniaxially stretched film obtained in Comparative Example 1 was further stretched in the TD direction using a tenter stretching device to obtain a biaxially stretched film. Stretching in the TD direction was performed in the same manner as in Example 2. The pressure loss of the PTFE porous membrane thus obtained was measured in the same manner as in Example 2. When the measurement was performed at a total of 24 points (4 points in the TD direction × 6 points in the MD direction), the average value of the pressure loss was 120 Pa, and the fluctuation rate was 2.68%. When the measurement was performed at a total of 25 points (1 point in the TD direction × 25 points in the MD direction), the average value of the pressure loss was 128 Pa, and the fluctuation rate was 2.17%.
[0046]
【The invention's effect】
As described above, according to the present invention, it is possible to obtain a PTFE porous membrane with small variations in pore diameter and uniform properties. In particular, according to the present invention, it is possible to obtain a PTFE porous membrane having a low pressure loss and a small variation in the membrane.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing one embodiment of an apparatus for producing a porous PTFE membrane of the present invention.
FIG. 2 is a plan view of the manufacturing apparatus of FIG.
FIG. 3 is a cross-sectional view showing one embodiment of an apparatus for further firing a stretched PTFE porous membrane.
FIG. 4 is a plan view showing an arrangement of a thermometer in a stretching device used in Examples.
FIG. 5 is a cross-sectional view illustrating a conventional apparatus for producing a PTFE porous membrane by a zone stretching method.
FIG. 6 is a cross-sectional view showing a conventional apparatus for producing a porous PTFE membrane by a hot roll stretching method.
[Explanation of symbols]
1 PTFE sheet 2 Stretched PTFE sheet (PTFE porous membrane)
Reference Signs List 5 Infrared heater 6 Heating area 7 Fired PTFE porous film 8 Oven 9 Stretching start line 10 Radiation thermometer 11 to 14 Feeding roll, winding roll 17, 18 Guide roll

Claims (7)

By transferring the polytetrafluoroethylene sheet from the dispensing roll disposed at a distance to the take-up roll, the sheet is continuously stretched by stretching the sheet in the transport direction by the dispensing roll and the winding roll. A method for producing a polytetrafluoroethylene porous membrane to be porous,
Heating the sheet between the feeding roll and the winding roll,
The sheet is transported via at least one guide roll that is disposed closer to the take-up roll than a position where the stretching of the sheet is started and has a smaller diameter than the take-up roll. A method for producing a fluoroethylene porous membrane. The method for producing a polytetrafluoroethylene porous membrane according to claim 1, wherein the sheet transport direction is changed by 30 ° or more by passing through any one of the at least one guide roll. The method for producing a polytetrafluoroethylene porous membrane according to claim 1 or 2, wherein the sheet is heated by irradiating the sheet with infrared rays emitted from an infrared heater. The production of the polytetrafluoroethylene porous membrane according to claim 3, wherein the infrared heater is disposed such that a distance between the sheet and the sheet is 0.1 mm or more and 100 mm or less between the feeding roll and the winding roll. Method. A feeding roll and a take-up roll, which are spaced apart, and heating means for heating the sheet so that the polytetrafluoroethylene sheet can be stretched, and the sheet is transferred by the feeding roll and the take-up roll. An apparatus for producing a polytetrafluoroethylene porous membrane, wherein the sheet is continuously made porous by stretching by pulling in the direction,
As the heating unit, an infrared heater disposed between the feeding roll and the winding roll so that a distance between the sheet and the sheet is 0.1 mm or more and 100 mm or less,
A production of a porous polytetrafluoroethylene membrane, characterized in that at least one guide roll having a smaller diameter than the take-up roll and passing the sheet is arranged on the take-up roll side of the infrared heater. apparatus. The apparatus for producing a polytetrafluoroethylene porous membrane according to claim 5, wherein the sheet transport direction is changed by 30 ° or more by passing through any one of the at least one guide roll. The apparatus for producing a polytetrafluoroethylene porous membrane according to claim 5 or 6, wherein a wavelength at which energy radiated from the infrared heater is maximum is 1 µm or more and 4 µm or less.

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