JP2016019971A - Porous film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous film having high air permeability and high adhesion strength.SOLUTION: A porous film has a first layer and a second layer. The first layer is made of a porous fluororesin. The second layer contains a first fiber and a second fiber. The first fiber of the second layer has an average fiber diameter of not less than 0.1 μm nor more than 15.0 μm. The second fiber of the second layer has an average fiber diameter of not less than 0.1 μm nor more than 15.0 μm. The first fiber and the second fiber satisfy at least one of conditions (1) and (2). A mass ratio of the first fiber and the second fiber in the second layer is 20:80 to 80:20.SELECTED DRAWING: None

Description

  The present invention relates to a porous membrane.

  As a film for filtering impurities such as dust in gas or liquid, a film (porous film) obtained by laminating a porous material having a high collection efficiency has been studied (Patent Document 1). Patent Document 1 describes a filter medium in which a blended nonwoven fabric is laminated on a porous fluororesin layer, and the blended nonwoven fabric includes a core-sheath fiber using polyester as a core and polyolefin as a sheath, a polyester fiber, and a core. Includes a core-sheath fiber using a polyester and a copolyester for the sheath.

JP 2013-173078 A

  According to the study by the present inventors, the porous film described in Patent Document 1 has low air permeability, and the laminated film sometimes peels off.

  Accordingly, an object of the present invention is to provide a porous membrane having high air permeability and high adhesion strength.

The above object is achieved by the present invention described below. That is, the porous film according to the first embodiment of the present invention has a first layer and a second layer, the first layer is formed of a porous fluororesin, and the second layer Contains the first fiber and the second fiber, the average fiber diameter of the first fiber diameter of the second layer is 0.1 μm or more and 15.0 μm or less, The average fiber diameter of the second fiber diameter is 0.1 μm or more and 15.0 μm or less, and the first fiber and the second fiber satisfy at least one of the following condition (1) and the following condition (2): And the mass ratio of said 1st fiber and said 2nd fiber in said 2nd layer is 20: 80-80: 20, It is characterized by the above-mentioned.
Condition (1): The average fiber diameter of the first fiber is larger than the average fiber diameter of the second fiber, and the average fiber diameter of the first fiber with respect to the average fiber diameter of the second fiber is 1. It is 2 times or more and 50.0 times or less.
Condition (2): The difference between the softening point of the first fiber and the softening point of the second fiber is 10 ° C. or more.
The porous membrane of the second embodiment according to the present invention has a first layer and a second layer, the first layer is formed of a porous fluororesin, and the second layer Contains fibers including the first material and the second material, the average fiber diameter of the fibers is 0.1 μm or more and 15.0 μm or less, the softening point of the first material, and the second The difference from the softening point of the material is 10 ° C. or more, and the mass ratio of the first material to the second material in the second layer is 20:80 to 80:20. And

  According to the present invention, a porous film having high air permeability and high adhesion strength can be provided.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments.

  When the present inventors examined the porous membrane of patent document 1, since the fiber diameter of the fiber used for the blended nonwoven fabric (2nd layer) is thick, a porous fluororesin layer (1st It was found that the air permeability was lowered due to the large adhesion area between the layer) and the second layer. Furthermore, the distance between the adhesion points is widened. As a result, the adhesion strength between the layers is low, and peeling occurs.

  Therefore, as a result of repeated studies on the average fiber diameter and softening point of the fibers used in the second layer laminated on the porous fluororesin layer (first layer), the present inventors satisfy the configuration of the present invention. Thus, it was found that both air permeability and interlayer adhesion strength can be achieved.

Specifically, in the first embodiment, the porous film has a first layer formed of a porous fluororesin and a second layer, and the second layer is the first layer. The first fiber diameter of the second layer is 0.1 μm or more and 15.0 μm or less, and the second fiber diameter of the second layer is the second fiber diameter of the second layer. The average fiber diameter is 0.1 μm or more and 15.0 μm or less, the first fiber and the second fiber satisfy at least one of the following condition (1) and the following condition (2), and in the second layer: It was found that the mass ratio of the first fiber to the second fiber needs to be 20:80 to 80:20.
Condition (1): The average fiber diameter of the first fiber is larger than the average fiber diameter of the second fiber, and the average fiber diameter of the first fiber with respect to the average fiber diameter of the second fiber is 1. It is 2 times or more and 50.0 times or less.
Condition (2): The difference between the softening point of the first fiber and the softening point of the second fiber is 10 ° C. or more [| (softening point of the first fiber) − (softening point of the second fiber)] | ≧ 10 ° C.].

  Moreover, as 2nd embodiment, it is set as the structure which has a 1st layer in which a porous film | membrane is formed with porous fluororesin, and a 2nd layer, and a 2nd layer is 1st material and The fiber containing the second material is contained, the average fiber diameter of the fiber is 0.1 μm or more and 15.0 μm or less, and the difference between the softening point of the first material and the softening point of the second material is 10 It was found that it is necessary to be 20:80 to 80:20 at a mass ratio of the first material and the second material in the second layer.

  In the present invention, the “softening point” means a melting point in the case of a fiber having a melting point, and a glass transition point in the case of a fiber having no glass melting point and having a glass transition point. Moreover, in the Example of this invention, the average fiber diameter of a fiber is obtained by observing the fiber surface with a scanning electron microscope, measuring the thickness of 10 or more arbitrary fibers, and calculating the average value. It was.

  Although the mechanism by which the effect can be obtained by such a configuration has not been clarified, the present inventors satisfy the above-mentioned conditions, thereby reducing the adhesion point between the first layer and the second layer, and the adhesion points to each other. It is considered that both the air permeability and the adhesion strength between layers can be improved.

[Porous membrane]
In the present invention, the porous membrane has a first layer and a second layer. Furthermore, it is preferable to have a third layer on the second layer, that is, to have a first layer, a second layer, and a third layer in this order. Another layer may be provided on the third layer. Moreover, if the effect of this invention is acquired, you may have another layer between each layer. In the present invention, the first layer and the second layer are preferably adjacent layers. In each layer, the pore diameter in the layer may be inclined in the depth direction.

  In the present invention, the plastic deformation start load per unit width in the tensile test specified by JIS L 1913: 2010 of the porous membrane is preferably 200 N / m or more, more preferably 300 N / m or more, It is preferably 4,000 N / m or less. In the examples of the present invention, the tensile test was measured with a tensile tester AKG-kNX (manufactured by Shimadzu Corporation). At that time, the size of the sample to be measured was 25 mm ± 0.5 mm × 150 mm, the grip interval was 50 mm ± 0.5 mm, and the tensile speed was 20 ± 0.02 mm / min. The value obtained by dividing the load at the start of plastic deformation by the specimen width is the plastic deformation start load per unit width.

  In the present invention, the air permeability of the porous membrane is such that the Gurley value measured by a Gurley tester specified in JIS P8117 is preferably 10 s or less, more preferably 7 s or less, and 3 s or less. Particularly preferred. A lower Gurley value means higher air permeability.

  Hereinafter, each layer constituting the porous membrane of the present invention will be described.

[First layer]
In the present invention, the first layer is a fluororesin. A fluororesin has low surface free energy and high cleaning properties. Specific examples of the fluororesin include polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), perfluoroalkoxy fluororesin (PFA), four Examples thereof include a fluorinated ethylene / hexafluoropropylene copolymer (FEP), an ethylene / tetrafluoroethylene copolymer (ETFE), and an ethylene / chlorotrifluoroethylene copolymer (ECTFE). These resins may be used singly or in combination of two or more as required, and may have a structure in which a plurality of films are laminated.

  In the present invention, the water pressure resistance defined by JIS L 1092 of the first layer is preferably 200 kPa or more, and more preferably 300 kPa or more.

  In the present invention, the thickness of the first layer is preferably 20 μm or less, more preferably 15 μm or less, and preferably 3 μm or more. In the examples of the present invention, the film thickness was obtained by measuring the film thickness at any 10 points with a straight-forward micrometer OMV_25 (manufactured by Mitutoyo) and calculating the average value.

  In the present invention, the arithmetic average roughness Ra defined by JIS B 0601: 2001 on the surface of the first layer is preferably 1.9 μm or less, more preferably 1.5 μm or less, and 1.0 μm. It is particularly preferable that the average particle size is 0.4 μm or less. Surface shape is measured using a laser microscope using a confocal optical system such as a pinhole (for example, a semiconductor laser having a wavelength of about 405 nm is used), and data obtained by scanning reflection in the observation measurement range in the Z-axis direction is synthesized. By doing so, the shape is obtained. In the embodiment of the present invention, the surface roughness was measured using the VK9710 laser microscope (manufactured by KEYENCE) with the objective lens 50 times (CF IC EPI PLAN Apo 50X made by Nikon) and data from the surface to a depth of 200 μm in the RPD mode. The obtained data was processed with a noise filter (median), the cut-off λc was 0.08 μm, and the surface roughness was calculated with a reference line length of 200 μm.

[Second layer]
In the present invention, the arithmetic average roughness Ra defined by JIS B 0601: 2001 on the surface of the second layer is preferably 10 μm or less, more preferably 6.0 μm or less, and 4.0 μm or less. It is particularly preferred.

  In the present invention, the average distance between local peaks defined by JIS B 0031 in the second layer is preferably 3 μm or more and 40 μm or less, and more preferably 3 μm or more and 15 μm or less. Surface shape is measured using a laser microscope using a confocal optical system such as a pinhole (for example, a semiconductor laser having a wavelength of about 405 nm is used), and data obtained by scanning reflection in the observation measurement range in the Z-axis direction is synthesized. By doing so, the shape is obtained. In the embodiment of the present invention, the average distance between the local peaks is obtained by using a laser microscope VK9710 manufactured by Keyence Co., Ltd., and using an objective lens 50 times (CF IC EPI PLAN Apo 50X made by Nikon) and data from the surface to a depth of 200 μm in the RPD mode. The obtained data was processed with a noise filter (median), the cut-off λc was 0.08 μm, and the average interval between the local peaks was calculated from the cross-sectional profile with a reference line length of 200 μm.

  In the present invention, the second layer is preferably a support layer having air permeability. Specific examples include materials that are more breathable than the first layer, such as nonwoven fabrics, woven fabrics, meshes (network nets), and other porous materials. Among these, a nonwoven fabric is preferable from the viewpoints of strength, flexibility, and workability.

  In the first embodiment of the present invention, the second layer contains two types of fibers. These two types of fibers may be mixed, or may form a core-sheath structure composed of a core structure and a sheath structure. The average fiber diameter of the second layer needs to be 0.1 μm or more and 15.0 μm or less. The average fiber diameter is preferably 0.1 μm or more and 10.0 μm or less, and more preferably 0.1 μm or more and 5.0 μm or less.

  The material of the second layer is not particularly limited, but polyolefin (polyethylene (PE), polypropylene (PP), etc.), polyurethane, nylon, polyamide, polyester (polyethylene terephthalate (PET), etc.), polysulfone (PSF) A single material such as a fluororesin or a composite material thereof is preferable.

[Third layer]
As described above, the porous membrane of the present invention may further have a third layer. As the material for the third layer, the same materials as those exemplified above as the material for the second layer can be used. Nonwoven fabric is preferred from the viewpoint of rigidity. The surface of the third layer is preferably smooth. The average pore size of the third layer is preferably larger than the average pore size of the second layer. In the present invention, the average pore diameter was measured with a palm porometer CFP-1200A (manufactured by PMI).

  In the present invention, the difference in softening point between the fiber having the lowest softening point in the fibers constituting the third layer and the fiber having the lowest softening point in the fibers constituting the second layer is 5 ° C. or more. It is preferable that In the present invention, a core-sheath structure may be used in which the softening point of the material outside the fiber core is low.

[Method for producing porous membrane]
In the present invention, the method for producing the porous membrane is not particularly limited, but a method having a step of producing the first layer, a step of producing the second layer, and a step of laminating each layer is preferable.

  A method for producing a porous film using PTFE as the first layer will be described below with an example.

  A lubricant is added to the PTFE fine powder and mixed uniformly. Examples of the PTFE fine powder include polyfluon F-104 (manufactured by Daikin Industries) and fullon CD-123 (manufactured by Asahi Glass). Examples of the lubricant include mineral spirits and naphtha.

  The lubricated PTFE fine powder is compressed in a cylinder to form pellets, extruded from a ram extruder in an unfired state and formed into a sheet, and an appropriate thickness, usually 0.05, by a pair of rolls Roll to ~ 0.7mm. The lubricant contained in the rolled sheet is removed by heating to obtain a PTFE sheet.

  Next, this PTFE sheet is stretched in the longitudinal direction (rolling direction) of the PTFE sheet while applying a temperature, and then stretched in the width direction of the PTFE sheet while applying a temperature. Porous bodies having various pore diameters, void ratios, and thicknesses can be formed by the method of heating and stretching the PTFE paste.

  When stretching, when stretched at a relatively high speed in the direction of one axis or more at a heating temperature lower than the softening point of PTFE, the porous PTFE body has large knots larger than 1 μm interconnected by extremely small fibers. It has a fiber structure including it, and its porosity is as high as 40 to 97%, which is extremely high strength.

  In addition, there are a method of stretching after the molded body is in a semi-fired state, a method of stretching after heating and firing to a temperature equal to or higher than the softening point (327 ° C.) of PTFE, or a method of stretching while heating and firing above the softening point.

  Moreover, you may use what formed into a film | membrane the fluororesin fiber obtained by the Electro Spinning (ES) method etc. with the hot pressure.

  When using a non-woven fabric as the second layer, the production method is as follows: a fleece is formed by a dry method, a wet method, a spunbond method, an ES method, etc., then a chemical bond method, a thermal bond method, a needle punch method, a water flow The method of joining between fibers by the confounding method etc. is mentioned.

  The method of laminating the first layer and the second layer to form the porous film is preferably thermal lamination. Although the method of applying heat is not particularly limited, lamination is performed between the rollers by appropriately adjusting the roller surface temperature, the passage time between the rollers, and the pressure between the rollers.

  When the third layer is further laminated, it may be laminated together with the first layer and the second layer, may be laminated sequentially, or the order of lamination may be appropriately selected.

  For example, in the method of laminating a porous film by thermal lamination, it is preferable to heat from the layer side having the lowest softening point among the fibers in the two layers contacting each other. By heating from the higher layer side, it is possible to heat only the vicinity of the surface of the lower layer that comes into contact with it, so that a reduction in air permeability can be suppressed.

  In the present invention, when laminating the third layer, since the first layer is made of a fluororesin, the lowest softening point of the fibers in the second layer and the third layer is A fiber having a softening point lower than that of the first layer may be selected. Therefore, when the lowest softening point in the fibers constituting the third layer is higher than the lowest softening point in the fibers constituting the second layer, the first layer side and the third layer By heating from both sides, three layers can be laminated at once. In addition, the three layers can be laminated by heating from the first layer side, and bonding the first layer and the second layer in advance and then heating from the third layer side. Further, the three layers can be laminated by heating from the third layer side, preliminarily bonding the second layer and the third layer, and then heating from the first layer side. On the other hand, when the lowest softening point in the fibers constituting the third layer is lower than the lowest softening point in the fibers constituting the second layer, heating from the first layer side Three layers can be stacked at a time. In addition, the three layers can be laminated by heating from the first layer side, heating the first layer side after previously bonding the first layer and the second layer. Further, the three layers can be laminated by heating from the second layer side, preliminarily bonding the second layer and the third layer, and then heating from the first layer side.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. The present invention is not limited in any way by the following examples as long as the gist thereof is not exceeded.

  As the first layer, a film thickness, an arithmetic average roughness Ra, and a PTFE film having a water pressure resistance described in Table 1 below were prepared.

  As the second layer, a film having the film thickness, the arithmetic average roughness Ra, and the average distance between the local peaks as shown in Tables 2 and 3 below were prepared. 2-a to 2-n are films containing a first fiber and a second fiber. Specifically, polyethylene and polypropylene fibers were used. 2-o is a film containing polyethylene (first fiber). 2-p, 2-q, 2-r is a membrane containing fibers including a first material (polyethylene) and a second material (polypropylene), and the first material is a “sheath structure”; The second material was a “core-sheath structure”, which is a “core structure”.

  As the third layer, a polyethylene film (3-a), a polyethylene terephthalate film (3-b), and a polypropylene (3-c) film as the film thickness and softening point described in Table 4 below were prepared.

  And with the combination of the following Table 5, the 1st layer, the 2nd layer, and the 3rd layer were laminated | stacked by the hot-pressure lamination, and the porous film was obtained. In Example 5, three layers were laminated by heating from both the first layer side and the third layer side. Furthermore, the plastic deformation start load and the Gurley value of the obtained porous film were measured by the above-described method. The results are shown in Table 5.

[Evaluation]
The porous film obtained above was evaluated by the following evaluation method. The evaluation results are shown in Table 6. In the present invention, AA to B of the evaluation criteria of the following evaluation items were set as preferable levels, and C was set as an unacceptable level.

<Breathability>
Based on the Gurley value measured above, air permeability was evaluated according to the following evaluation criteria.
A: Gurley value was 3 s or less A: Gurley value was greater than 3 s and 7 s or less B: Gurley value was greater than 7 s and 10 s or less C: Gurley value was greater than 10 s

<Adhesion strength>
When the porous film obtained above was used as a filter, the presence or absence of delamination between layers of the porous film was observed to evaluate the adhesion strength. The evaluation criteria are as follows.
B: Peeling between layers did not occur. C: Peeling occurred between layers.

<Local deformation suppression effect>
The deformation of the first layer was observed and evaluated when the porous membrane obtained above was used as a filter. The evaluation criteria are as follows.
B: Deformation was not seen. Or although a deformation | transformation was seen slightly, it was a level which was not worried C: A deformation | transformation was seen large.

<Filterability>
The porous membrane obtained above was set in a circular holder with an effective area of 100 cm ² and supplied with air containing dust (quartz dust so that particles with a particle diameter of 2 μm or less were 5 × 10 ⁵ particles / L ) At a transmission speed of 5.3 cm / second, and the upstream particle concentration (pieces / L) and the downstream particle concentration (pieces / L) were measured with a particle counter KC-18 (manufactured by Lion). And the collection efficiency was calculated | required using the following formula. Higher collection efficiency means higher filterability. The evaluation criteria are as follows.
Collection efficiency (%) = (1−downstream particle concentration / upstream particle concentration) × 100
A: The collection efficiency was 99% or more B: The collection efficiency was 98% or more and less than 99% C: The collection efficiency was less than 98%.

<Pressure distribution suppression effect>
In order to evaluate the suppression effect of pressure distribution, the porous film obtained above was used as a wiping member, and in maintenance of an ink jet printer, the porous film was used as a nozzle surface on which the nozzles of the head for discharging ink were formed. Ink droplets, dust, dust, paper powder, etc. adhering to the nozzle surface were wiped off by making the porous film and the head relatively move. The porous film was Roll to Roll and was transported by a take-up roller and used as a wiping member. The surface of the surface on which the nozzle was formed after wiping was observed with an optical microscope to evaluate the occurrence of wiping unevenness. It means that the suppression effect of pressure distribution is so high that the wiping nonuniformity is suppressed. The evaluation criteria are as follows.
A: No wiping unevenness was observed. B: Although slight wiping unevenness was observed, it was a level that was not noticeable. C: Wiping unevenness occurred.

<Transportability>
When the porous film obtained above was transported by Roll To Roll and used as a wiping member, the presence or absence of deformation due to the tension applied during transport was observed. The smaller the deformation, the higher the transportability. The evaluation criteria are as follows.
A: Plastic deformation was not observed, and tension was further applied. B: Plastic deformation was not observed. C: Plastic deformation was observed.

Claims (6)

A porous membrane having a first layer and a second layer,
The first layer is formed of a porous fluororesin;
The second layer contains a first fiber and a second fiber;
The average fiber diameter of the first fiber diameter of the second layer is 0.1 μm or more and 15.0 μm or less,
The average fiber diameter of the second fiber diameter of the second layer is 0.1 μm or more and 15.0 μm or less,
The first fiber and the second fiber satisfy at least one of the following condition (1) and the following condition (2);
The porous film characterized in that the mass ratio of the first fiber and the second fiber in the second layer is 20:80 to 80:20.
Condition (1): The average fiber diameter of the first fiber is larger than the average fiber diameter of the second fiber, and the average fiber diameter of the first fiber with respect to the average fiber diameter of the second fiber is 1. It is 2 times or more and 50.0 times or less.
Condition (2): The difference between the softening point of the first fiber and the softening point of the second fiber is 10 ° C. or more. A porous membrane having a first layer and a second layer,
The first layer is formed of a porous fluororesin;
The second layer contains fibers including a first material and a second material, and the average fiber diameter of the fibers is 0.1 μm or more and 15.0 μm or less,
The difference between the softening point of the first material and the softening point of the second material is 10 ° C. or more;
The porous film characterized in that the mass ratio of the first material and the second material in the second layer is 20:80 to 80:20. The porous membrane further has a third layer on the second layer,
The porous membrane according to claim 1 or 2, wherein the third layer has an average pore size larger than that of the second layer.   The difference in softening point between the fibers having the lowest softening point in the fibers constituting the third layer and the fibers having the lowest softening point in the fibers constituting the second layer is 5 ° C. or more. The porous membrane according to claim 3. The water pressure resistance defined by JIS L 1092 of the first layer is 200 kPa or more, and the film thickness is 20 μm or less,
The porous film according to any one of claims 1 to 4, wherein an average interval between local peaks defined by JIS B 0031 of the second layer is 3 µm or more and 40 µm or less. The arithmetic average roughness Ra defined by JIS B 0601: 2001 of the first layer is 1.9 μm or less,
The arithmetic average roughness Ra defined by JIS B 0601: 2001 of the second layer is 10 μm or less,
The porous membrane according to any one of claims 1 to 5, wherein a plastic deformation start load per unit width of the porous membrane is 200 N / m or more.