JP5154784B2 - filter - Google Patents

Description

The present invention relates to a filter over, details, clogging hardly occurs while maintaining a high capture rate of ultrafine particles, moreover, excellent in flow permeability, is suitably used as the microfiltration filter.

  In addition to the high heat resistance, chemical stability, weather resistance, non-flammability, high strength, non-adhesiveness, low friction coefficient, etc. of PTFE itself, polytetrafluoroethylene (hereinafter referred to as PTFE) porous filter, It has characteristics such as flexibility, liquid permeability, particle trapping, low dielectric constant, etc. possessed by porous materials. Conventionally, liquid / gas microfiltration filters (membrane filters), wire coating materials, breathing valves (air vents) ) Is used in a wide range of fields.

In recent years, PTFE porous filters are frequently used as filtration filters for chemicals, gases, etc., particularly in semiconductor-related fields, liquid crystal-related fields, and food and medical-related fields due to their excellent characteristics such as high chemical stability.
In such fields, higher performance microfiltration filters are desired due to further technological innovation and increasing requirements. Specifically, in semiconductor manufacturing, the degree of integration is increasing year by year, and the photoresist is miniaturized to an area of 0.5 μm or less. Similarly, in liquid crystal production, fine processing using a photosensitive material is performed, and therefore a microfiltration filter capable of reliably capturing fine particles in a smaller area is required. These microfiltration filters are mainly used as cleanroom outdoor air treatment filters and chemical filter filters, and their performance affects the product yield.
Further, in the food / medical field, due to the recent increase in safety awareness, there is a strong demand for the completeness of filtration (absolute removability) for minute foreign substances.

However, if a filter with a small pore size is used to ensure high particle trapping properties, the permeability, that is, the processing speed of the chemical solution or air is reduced, and the productivity of the product is reduced. In the PTFE porous membrane having a pore having a pore diameter of 0.02 μm that is currently on the market, the IPA flow rate becomes 0.0005 ml / cm ² / min at a differential pressure of 0.95 kg / cm ² , and almost no permeability is obtained. .
Thus, with the conventional microfiltration filter, it is very difficult to balance the processing speed and the particle capture rate.

Various PTFE porous bodies have been proposed for the problems described above.
For example, in Japanese Patent Application Laid-Open No. 2003-80590 (Patent Document 1), the PTFE fine powder or its extrusion-molded product is irradiated with radiation before being stretched to have high filtration performance even with the same permeability. A porous material is proposed.
However, the porous body of Patent Document 1 has a problem that it is expensive and expensive because a process of irradiating radiation is essential.

JP-A-7-316327 (Patent Document 2) discloses that particles having a particle size of 0.109 μm can be removed with a particle removal rate of 90% or more, a porosity of 60 to 90%, and a differential pressure of 1 kg. A PTFE porous material having an IPA flow rate measured at / cm ² of 0.6 ml / cm ² / min or more is provided.
Although the PTFE porous material of Patent Document 2 is excellent in that a high particle removal rate is obtained, there is still room for improvement in permeability. That is, the IPA flow rate is 0.6 ml / cm ² / min or more, and even the best IPA flow rate among the examples in Patent Document 2 is 1.8 ml / cm ² / min. It takes a considerable amount of time.
It is difficult to obtain a filter having such a high particle removal rate and permeability.

JP 2003-80590 A JP 7-316327 A

The present invention has been made in view of the above problems, has high particle capture properties, and has an object to provide Hisage excellent filter permeability of gas and liquid.

In order to solve the above-mentioned problems, the present invention provides a molded body obtained by paste extrusion of a high molecular weight PTFE (polytetrafluoroethylene) unsintered powder having a molecular weight of 12 million or more and a liquid lubricant in the longitudinal direction of 10 times to 40 times. A filter obtained by biaxial stretching at a stretching ratio of 20 times to 60 times in the lateral direction and stretching after being stretched to 300 times or more in an area ratio to be a porous film and then sintered .
An average pore diameter of 0.01 to 0.20 μm, and
The value of the IPA flow rate (sec) (A) and IPA bubble point (kPa) represented by the measured value of (B) (A) / ( B) will provide a filter over which is characterized in that 0.08 or less ing.

The present inventors have result of intensive studies, the filter comprising a porous PTFE material, as well as using a PTFE unsintered powder of molecular weight of 12 million or more and a high molecular weight than the past, the draw ratio of the vertical and horizontal biaxial direction of the molded body It has been found that a porous filter having high permeability while having fine pores can be obtained by increasing the.
This is because, if high-molecular weight PTFE unsintered powder with a molecular weight of 12 million or more is used, even if stretching is performed at a higher magnification in the vertical and horizontal biaxial directions, one hole is excessively expanded or the film is torn. while preventing that the highly allowed to proceed fibrosis, nodular a mass of PTFE also substantially eliminated, it is possible to prepare a porous filter with dense microvoids to the fine fiber and backbone It depends on what you can do. Therefore, a high porosity and flow rate can be obtained while having a micropore diameter, and both an increase in the treatment flow rate and a high particle capture rate can be achieved.

PTFE unsintered powder at the end of the molecular weight is number-average molecular weight of 1 2 million. This is a particularly high molecular weight grade among the PTFE green powders currently on the market.
The number average molecular weight described above is obtained from the specific gravity of the molded product, but the molecular weight of PTFE varies depending on the measurement method, and accurate measurement is difficult. Therefore, depending on the measurement method, the above range may not be obtained. .
The upper limit of the number average molecular weight is preferably higher and is not particularly limited.

The draw ratio in the longitudinal direction of the filter of the present invention is 10 to 40 times, preferably 18 to 25 times. If the stretching ratio in the machine direction is less than 10 times, fine pores cannot be formed. On the other hand, if the draw ratio exceeds 40 times, fiber formation cannot be achieved and tearing may occur, resulting in large pores.
The transverse draw ratio is 20 to 60 times, preferably 30 to 38 times. If the stretching ratio in the transverse direction is less than 20 times, a lump of resin remains, the shape of the pores does not become round, and sufficient permeability cannot be obtained. On the contrary, if it exceeds 60 times, the fiber is torn. Since the hole diameter becomes too large in the lateral direction, it is not preferable.
The longitudinal and lateral stretch ratios are preferably 1: 1 to 1: 2.7, and 1: 2 to 1: 2 in order to make the fiber lengths in the longitudinal direction and the transverse direction equal and make a round hole shape. .2 is more preferable.

The stretching ratio is not less than 300 times in area ratio, is et to preferably 600 times or more, most preferably 800 times or more. The upper limit of the draw ratio (area ratio) is preferably 2400 times or less.
If the draw ratio is less than 300 times in terms of area ratio, fiberization cannot be advanced to a high degree. On the other hand, if it exceeds 2400 times, the film becomes too thin and the strength decreases.

The method for producing the filter of the present invention described above will be described in detail.
As a 1st process, a molded object is manufactured by the paste extrusion method of the PTFE green powder conventionally known.
In the paste extrusion method, the liquid lubricant is usually mixed at a ratio of 10 to 40 parts by mass, preferably 16 to 25 parts by mass with respect to 100 parts by mass of the PTFE resin, and extrusion molding is performed.

As the liquid lubricant, various lubricants conventionally used in paste extrusion methods can be used. For example, petroleum solvents such as solvent / naphtha and white oil, hydrocarbon oils such as undecane, aromatic hydrocarbons such as toluol and xylol, alcohols, ketones, esters, silicone oil, fluorochlorocarbon oil, etc. Examples thereof include a solution in which a polymer such as polyisobutylene or polyisoprene is dissolved in the above solvent, a mixture of two or more thereof, water or an aqueous solution containing a surfactant, and the like.
Since a single component can be uniformly mixed rather than a mixture, it is preferable.

Molding by paste extrusion is performed at a sintering temperature of PTFE, that is, 327 ° C. or lower, usually around room temperature. Prior to paste extrusion, preforming is usually performed. In the pre-molding, the mixture is compression-molded at a pressure of, for example, about 10 to 500 kPa to form blocks, rods, tubes, and sheets.
A molded body having a shape that can be stretched is produced by extruding the molded body obtained by the preliminary molding with a paste extruder, rolling with a calender roll or the like, or extruding and rolling.

Next, the liquid lubricant is removed from the molded body. The liquid lubricant may be removed before sintering and may be removed after stretching, but is preferably removed before stretching.
Removal of the liquid lubricant is performed by heating, extraction or dissolution, and is preferably performed by heating. The heating temperature in the case of heating is usually preferably 200 to 330 ° C. Further, when a liquid lubricant having a relatively high boiling point such as silicone oil or fluorocarbon is used, it is preferably removed by extraction.

In addition to the liquid lubricant, other substances may be included depending on the purpose.
For example, carbon black, graphite, silica powder, glass powder, glass fiber, silicates and carbonic acid for coloring pigments, improving wear resistance, preventing low temperature flow and facilitating pore formation. Inorganic fillers such as salts, metal powder, metal oxide powder, metal sulfide powder and the like can be added. In addition, in order to assist the formation of a porous structure, a substance that is removed or decomposed by heating, extraction, dissolution, etc., such as ammonium chloride, sodium chloride, other plastics, rubber, etc., is mixed in a powder or solution state. You can also.

Next, the molded body by paste extrusion thus obtained is stretched at a high magnification of 10 to 40 times in the longitudinal direction (conveying direction) and 20 to 60 times in the transverse direction (axial direction of the rolling roll). Film.
Stretching can be performed by mechanically stretching the sheet by an ordinary method. For example, when winding from one roll to another roll, make the winding speed larger than the feed speed and stretch it, or grab two opposite sides and stretch it to widen the gap Can be done. The stretching in the machine direction and the transverse direction may be sequential biaxial stretching in which uniaxial stretching is performed, or simultaneous biaxial stretching.
Moreover, in order to achieve the draw ratio of the said range, the extending | stretching of the vertical direction and a horizontal direction may each be performed by one-stage extending | stretching, and may be performed by extending | stretching two or more steps. For example, the stretching in the longitudinal direction is performed in two stages, and then the stretching in the transverse direction is performed in two stages.

The stretching is preferably performed at a temperature as high as possible below the melting point. Preferably it is room temperature (or 20 degreeC) -300 degreeC, More preferably, it is 250 degreeC -280 degreeC.
When stretching is performed at a low temperature, a porous film having a relatively large pore diameter and a high porosity is likely to be formed. When stretching is performed at a high temperature, a dense porous film having a small pore diameter is likely to be formed.
By combining these conditions, the pore diameter and porosity can be controlled. However, in the present invention, a relatively high stretching temperature is preferable in order to obtain a dense porous film having a small pore diameter.
Stretching may be performed in a first stage at a low temperature of 20 to 70 ° C., and then in a second stage under the above high temperature conditions.

Furthermore, it is preferable to perform heat setting to prevent shrinkage of the film after stretching.
In the present invention, the heat setting is important because the stretch ratio is particularly increased and the porous structure is not lost. It is preferably performed immediately after the stretching in the transverse direction, and when stretching in two or more stages is preferably performed after stretching in each stage.
The heat setting is usually carried out by holding the stretched film under tension, such as fixing both ends, and holding at an atmospheric temperature of 200 to 500 ° C. for 0.1 to 20 minutes.

Next, the stretched film is sintered. Sintering is carried out by heating at a sintering temperature of 327 ° C. or higher, which is the transition point of PTFE, and heating for several minutes to several tens of minutes, and in some cases, longer. Usually, it is appropriate to heat in a furnace maintained at 350 to 500 ° C.
By performing sintering, the tensile strength of the stretched film is rapidly increased, and it is possible to impart strength that can be filtered with a single membrane of the PTFE porous body. This is because the fibers of the stretched molded body that has been made into a fiber are melted together to increase the fiber diameter and make it uniform and increase the strength, while preventing thermal shrinkage and solvent shrinkage.

Filter of the present invention obtained in this way is as 20μm or less in thickness, preferably in the al is 15μm or less.
In the present invention, since the film is stretched at a high stretch ratio in the biaxial direction, a thin filter can be obtained.

As described above, the filter of the present invention has an average pore size of 0.01 to 0.20 μm. When the average pore diameter is within this range, high particle trapping properties can be secured.
In order to obtain higher particle trapping properties, the average pore diameter is preferably 0.01 to 0.05 μm, and most preferably 0.01 to 0.03 μm.
The average pore diameter is measured by a pore diameter distribution measuring device (a porous material automatic pore diameter distribution measuring system manufactured by Porus Materials, USA).

Furthermore, the value of (A) / (B) indicated by the measured values of the IPA flow rate (sec) and the IPA bubble point (kPa) (B) is set to 0.08 or less. More preferably, it is 0.06 or less.
The value of (A) / (B) can be used as an evaluation method for a filter having a small pore diameter and excellent permeability. In other words, the IPA bubble point increases as the pore size decreases, and the IPA flow rate decreases as the permeability increases. Therefore, it can be said that the smaller the value of (A) / (B), the better the filter.
Therefore, if the value of (A) / (B) is 0.08 or less, a filter having fine pores and excellent permeability can be obtained.

The IPA flow rate (sec) is preferably 10 or less. More preferably, it is 8 or less. An IPA flow rate exceeding 10 is not preferable because the pore size is large and the particle trapping property is deteriorated.
The IPA flow rate is the time required for 100 ml of isopropyl alcohol (IPA) to pass through 1 cm ² of the filter, and the differential pressure is 70 cmHg (0.0931 MPa).

  The IPA bubble point (kPa) is preferably 100 or more. More preferably, it is 120 or more. When the IPA bubble point is less than 100, the pore size is large, and the particle trapping property is deteriorated.

Furthermore, the maximum width of the skeleton surrounding the pores is preferably 2 μm or less. More preferably, it is 0.8 μm or less. This is because when the maximum width exceeds 2 μm, the surface area of the filter becomes small, so that sufficient permeability cannot be obtained.
The maximum width of the skeleton surrounding the pores is calculated by observing 3000 to 5000 times with a scanning electron micrograph and image processing software.

The porosity is preferably 80% or more and 95% or less. More preferably, it is 85% or more and 90% or less. This is because when the pore diameter is small as in the filter of the present invention, the flow rate tends to decrease when the porosity is less than 80%, and the strength may decrease when the porosity exceeds 95%.
The porosity is measured by the method described in ASTM-D-792. It shows that it is excellent in the permeability, so that this figure is high.

The air flow rate (galley second) is preferably 5 seconds or less. More preferably, it is 2 seconds or less. If the air flow rate exceeds 5 seconds, the filtration rate decreases, which is not preferable.
The air flow rate (galley second) is measured by the method described in ASTM-D-726, and the differential pressure is 13.16 mmH ₂ 0 (129 Pa), and 1 square inch (6.45 cm ² ) of sample is 100 ml of air. It is the time required to flow.

Furthermore, it is preferable that the particle capture rate of particles having a particle diameter of 0.05 μm is 90% or more. Further, it is preferably 95% or more, and most preferably 99% or more. This is because if the particle trapping rate is less than 90%, the filtration completeness is poor and the filter does not reach the object of the present invention.
The particle capture rate is measured by the following method.
The filter is punched into a circular shape with a diameter of 47 mm, set in a holder, and an aqueous solution containing 1.4 × 10 ¹⁰ particles / cm ² of polystyrene latex homogeneous particles (manufactured by Dow Chemical Co., Ltd.) having a particle diameter of 0.05 μm is prepared. Then, the film set with 32 cm ³ is filtered at a pressure of 41.2 kPa, the absorbance of the aqueous solution before filtration and the filtrate is measured, and the ratio is obtained. Absorbance was measured at a wavelength of 310 nm using a UV-visible spectrophotometer (Shimadzu UV-160) (measurement accuracy 1/100).

  Thus, since the filter of the present invention has a fine pore diameter, it has excellent permeability to liquids and gases despite having a high particle capture rate.

As described above, the filter of the present invention has a molded body obtained by paste extrusion of high molecular weight PTFE unsintered powder and liquid lubricant, 10 times to 40 times in the vertical direction and 20 times to 60 times in the horizontal direction. Since it is drawn at a high draw ratio, it can be a filter having a dense and thin fiber with substantially no knots as a skeleton. As a result, since a high surface area can be ensured, it is possible to manufacture a filter having a high porosity and flow rate despite having fine pores.

  Although the filter of the present invention has fine particle trapping properties due to its fine pores, it also has excellent permeability, so that it is particularly required for filtration completeness and processing speed in the semiconductor, liquid crystal field and food / medical field. It can be suitably used as a gas or liquid microfiltration filter used in the production process.

The manufacturing method of the filter of embodiment of this invention is explained in full detail.
First, as a first step, a liquid lubricant is blended at a ratio of 16 to 25 parts by mass with respect to 100 parts by mass of PTFE unsintered powder (fine polymer) and mixed.
As the PTFE unsintered powder, a high molecular weight one having a number average molecular weight of 15 million or more is used.
As the liquid lubricant, petroleum-based solvents such as solvent naphtha and white oil are used.

Subsequently, the obtained mixture is compression-molded by a compression molding machine to form a block-shaped molded body (preliminary molding), and the block-shaped molded body is sheet-shaped at a temperature of room temperature to 50 ° C. at a speed of 20 mm / min. Is extruded.
Furthermore, the obtained sheet-like molded object is rolled with a calendar roll etc., and it is set as the film-like molded object of thickness 300 micrometers.

  As a next step, in order to remove the liquid lubricant from the sheet-shaped molded product, the film-shaped molded product is dried by passing through a heating roll having a roll temperature of 130 to 220 ° C.

Next, the molded body obtained by the paste extrusion thus obtained is stretched in the longitudinal direction.
In the present embodiment, in the longitudinal stretching, the speed of the take-up roll is made larger than the speed of the feed roll and stretched due to the difference in peripheral speed. Longitudinal stretching is performed by two-stage stretching, with the first stage stretching ratio being 3 to 6 times, the second stage stretching ratio being 4 to 6 times, and stretching at a stretching ratio of 15 to 30 times in the entire longitudinal direction. doing. The roll temperature during longitudinal stretching is 250 to 280 ° C.

Next, it extends in the transverse direction. In the transverse stretching, two opposite sides of the longitudinally stretched film are grasped and stretched so as to widen the interval. The transverse stretching is also performed by two-stage stretching. The first-stage stretching ratio is 5 to 10 times, the second-stage stretching ratio is 6 to 8 times, and the entire transverse direction is stretched 30 to 60 times.
The transverse stretching is performed inside the furnace. The first stage is performed in a low temperature atmosphere of 50 ° C., and the second stage is performed in a high temperature atmosphere of 220 to 240 ° C. In order to prevent the film from shrinking after stretching at each stage, the film is heat-set by being held at 230 to 300 ° C. for 0.25 to 1 minute after stretching at each stage.

  Thus, the film-like molded product stretched biaxially in the longitudinal direction and the transverse direction is stretched by 300 times or more in terms of area ratio. The longitudinal / lateral stretch ratio is set to 1: 2 to 1: 2.2.

Next, the obtained stretched film is sintered. Sintering is performed by heating in a furnace kept at 350 to 370 ° C. for 15 to 25 minutes.
By performing the sintering, the tensile strength of the stretched molded body is rapidly increased, and the strength can be imparted to the single membrane of the PTFE filter.

The filter thus obtained has an average pore size of 0.01 to 0.03 μm, an IPA flow rate (sec) of 8 or less, an IPA bubble point (kPa) of 100 or more, and an IPA flow rate (sec) (A) of The value of (A) / (B) indicated by the measured value of IPA bubble point (kPa) (B) is 0.08 or less.
Thus, although it has a small pore size and a high particle trapping property, it is a filter with excellent permeability.

  Further, the filter is a particle of particles having a maximum width of a skeleton surrounding pores of 2 μm or less, a porosity of 80% to 95%, an air flow rate (galley second) of 2 seconds or less, and a particle size of 0.05 μm. The capture rate is 90% or more. Thus, there is substantially no nodule, the diameter of the fiber is thin and dense, and the porosity and the air flow rate are good and the permeability is high despite the high particle trapping rate.

  Hereinafter, although the Example and comparative example of the filter of this invention are described, the effect of this invention should not be limited and limited to an Example.

(Example)
Blended and mixed at a ratio of 18 parts by mass of liquid lubricant (Supersol FP-25, (component: naphtha)) of liquid lubricant (100 parts by mass of PTFE fine powder (PTFE 601A manufactured by DuPont). It was put and compression molded to obtain a block-shaped molded product.
Next, the block-shaped molded product is continuously extruded into a sheet shape, passed through a rolling roller, and further passed through a heating roll (130 to 220 ° C.) to remove the liquid lubricant, and wound on the roll. A sheet was obtained.
Next, the film was stretched 5 times in the machine direction (flow direction) at a roll temperature of 250 ° C. to 280 ° C., and further stretched 5 times under the same temperature conditions. That is, the longitudinal stretching was performed at a stretching ratio of 25 times in two stages.
Grasping both ends in the width direction of the film after longitudinal stretching with a chuck, stretching 5 times in a direction perpendicular to the flow direction in an atmosphere of 50 ° C., and holding it at 240 ° C. for 0.25 to 1 minute as it is Heat setting was performed. Subsequently, the film was stretched 7 times in an atmosphere at 150 ° C., and then heat-fixed by maintaining the temperature at 240 ° C. for 0.25 to 1 minute. That is, transverse stretching was performed at a stretching ratio of 35 times in two stages.
The sheet thus stretched was passed through a 360 ° C. heating furnace and sintered for 20 minutes to obtain a filter of the example.

(Comparative example)
Blended in a proportion of 18 parts by mass of liquid lubricant (Supersol FP-25, (component: naphtha) manufactured by Idemitsu Oil Co., Ltd.) to 100 parts by mass of PTFE fine powder (CD123 product number, molecular weight 12 million manufactured by Asahi Glass Co., Ltd.) Then, it put into the molding machine and compression-molded and obtained the block-shaped molding.
Next, this block-shaped molded product is continuously extruded into a sheet shape, passed through a rolling roller, and then wound on a roll through a heating roll (130 to 220 ° C.) to obtain a 300 μm sheet from which the liquid lubricant has been removed. It was.
Next, the film was stretched 6 times in the machine direction (flow direction) at a roll temperature of 250C to 280C.
Next, both ends in the width direction of the film were gripped with a chuck, and stretched 4 times in an atmosphere perpendicular to the flow direction at 150 ° C.
This sheet was passed through a heating furnace at 360 ° C. and sintered for 20 minutes to obtain a filter of a comparative example.

  Table 1 shows various characteristics of the obtained porous sheets of Examples and Comparative Examples.

The physical properties shown in Table 1 were measured by the same method as described above. That is,
(1) Average pore diameter (μm): Measured with a pore diameter distribution measuring device (a porous material automatic pore diameter distribution measuring system manufactured by Porus Materials, USA).
(2) IPA bubble point (kPa): Measured by the method described in ASTM-F-316 using isopropyl alcohol (IPA).
(3) IPA flow rate (sec): The time required for 100 ml of isopropyl alcohol (IPA) to pass through 1 cm ² of the filter was measured. The differential pressure was 70 cmHg.
(4) Maximum width of skeleton surrounding pores: calculated by observation with a scanning electron micrograph and image processing software.
(5) Porosity (%): Measured by the method described in ASTM-D-792.
(6) Air flow rate (galley second); measured by the method described in ASTM-D-726. With a differential pressure of 13.16 mmH ₂ 0 (129 Pa), 1 square inch (6.45 cm ² ) of the sample was taken as the time required for 100 ml of air to flow.
(7) Particle capture rate (%): The film of Example or Comparative Example was punched out into a circle having a diameter of 47 mm and set in a holder, and polystyrene latex homogeneous particles (Dow Chemical Co., Ltd.) having a particle diameter of 0.05 μm were obtained. An aqueous solution containing 1.4 × 10 ¹⁰ pieces / cm ² was prepared, and filtration was performed at a pressure of 41.2 kPa through a film in which 32 cm ³ was set.
The particle capture rate was determined by measuring the absorbance of the aqueous solution before filtration and the filtrate at a wavelength of 310 nm using an ultraviolet-visible spectrophotometer (UV-160, manufactured by Shimadzu Corporation). The measurement accuracy was 1/100.
(8) Film thickness (μm): The thickness of one film was measured using a dial gauge (anvil diameter φ10 mm).

  Furthermore, scanning electron micrographs of the filters of Examples and Comparative Examples were taken. A scanning electron micrograph (1000 times and 3000 times) of the filter of the example is shown in FIG. 1, and a scanning electron micrograph (3000 times) of the filter of the comparative example is shown in FIG.

The filter of the example (FIG. 1) does not have a lump portion (nodule) like the filter of the comparative example (FIG. 2), is formed of only thin fibers, has a small pore diameter, and variation in the pore diameter. Was also small. In addition, the ratio of the pores to the fiber portion was higher than that of the filter of the comparative example.
In addition, from the measurement results of each characteristic shown in Table 1, the filter of the example is substantially the same as the filter of the comparative example and the IPA bubble point, but the porosity is increased by 26%, and the IPA flow rate is 1/5. The air flow rate was about 1/10, and the permeability of gas and liquid was extremely excellent. That is, the filter of the present invention had excellent permeability despite having fine pores.

It is a scanning electron micrograph of the filter of the present invention obtained in the example ((A) is 1000 times, (B) is 3000 times). It is a scanning electron micrograph (3000 times) of the conventional filter obtained by the comparative example.

Claims (2)

Molecular weight 12 million or more high molecular weight PTFE (polytetrafluoroethylene) unsintered powder and obtained by paste extrusion of the liquid lubricant molded body, 10-fold to 40-fold in the longitudinal direction, the transverse direction 20 times to 60 times the It is a filter obtained by biaxial stretching at a stretch ratio and stretching after 300-fold or more area ratio to form a porous film and then sintering .
An average pore diameter of 0.01 to 0.20 μm, and
Filter over the value of the IPA flow rate (sec) (A) and IPA bubble point (kPa) represented by the measured value of (B) (A) / ( B) is characterized in that 0.08 or less. The maximum width of the skeleton surrounding the pores is 2 μm or less,
Porosity is 80% or more and 95% or less,
Air flow (galley second) is 5 seconds or less,
The particle capture rate of particles having a particle diameter of 0.05 μm is 90% or more,
Filter over of claim 1 is.