JP6478531B2 - Method for producing porous membrane - Google Patents

Description

  The present invention relates to a method for producing a porous membrane.

As a membrane for filtering solid matter such as dust contained in gas or liquid, a porous membrane in which a porous membrane having a high collection efficiency is laminated has been studied. Fluororesin porous membranes such as polytetrafluoroethylene (PTFE) porous membranes have excellent properties as filter media such as air permeability, water repellency, and fine particle collection properties, and in terms of strength, etc. Utilization as a laminated form is being studied.
In Patent Document 1, water is obtained by performing a smoothing process by heating and pressing at a temperature near the melting point of PTFE in a state in which a base fabric made of glass woven fabric or non-woven fabric and a web made of PTFE fiber are laminated. A method of manufacturing a filter element for processing is described. The purpose of the heating and pressurizing treatment for smoothing the surface of the web layer in this production method is to increase the fiber density, reduce the voids in the web layer, increase the water pressure resistance, and stabilize the shape.

JP 2002-204911 A

In order to make it possible to use the porous membrane as a highly accurate wiping member for liquids and solids adhering to the surface to be cleaned, in addition to the ability to collect deposits on the wiping surface of the porous membrane surface, Smoothness is important.
The smoothing of the surface of the PTFE web in Patent Document 1 is intended to increase the fiber density, reduce the voids in the web layer, increase the water pressure resistance and stabilize the shape, and wipe off when diverting to a wiping member The smoothness of the surface is not taken into consideration. Therefore, depending on the conditions of the heating and pressurizing process in the smoothing process of Patent Document 1, depending on the material of the pressure contact member for the heating and pressurizing process, the smoothness desired by the present invention is achieved. You may not get sex.
Therefore, an object of the present invention is to provide a method for producing a porous film that can impart smoothness that can be used as a wiping surface to the surface of a porous film containing a fluororesin with good controllability.

A method for producing a porous film according to the present invention is a method for producing a porous film having a first layer made of a porous film containing a fluororesin and a second layer made of a porous film,
Laminating the porous film for forming the first layer and the porous film for forming the second layer to form a laminate;
A step of pressing the pressing surface of the pressure contact member to the surface on the porous film side for forming the first layer of the laminated body under heating, and thermocompression bonding the laminated surface of each porous film of the laminated body;
Have
The first layer is a polytetrafluoroethylene (PTFE) stretched porous membrane;
The arithmetic average roughness (Ra) of the pressing surface of the pressing member is smaller than the arithmetic average roughness (Ra) of the surface of the porous film for forming the first layer to which the pressing surface is pressed, and
The compression elastic modulus of the pressure contact member is larger than the compression elastic modulus of the porous film for forming the first layer,
It is characterized by that.

  According to the present invention, by setting the physical properties of the pressure contact member used in the hot-pressure laminating process according to the constituent material of the porous film, the surface of the layer made of the porous film containing the fluororesin is controlled with good smoothness. The manufacturing method of the porous membrane which can be provided with sufficient property can be provided.

It is a figure for demonstrating operation | movement of the roller as a press-contact member in the manufacturing method for obtaining the porous film of 2 layer structure. It is a figure for demonstrating operation | movement of the roller as a press-contact member in the manufacturing method for obtaining the porous film of 3 layer structure. It is a figure for demonstrating operation | movement of the roller pair in the manufacturing method for obtaining the porous film of 2 layer structure using a pair of opposing roller. It is a schematic perspective view including the surface where the discharge port of the inkjet head used for evaluation as a wiping member of a porous membrane opens. It is a figure for demonstrating the evaluation method of a porous membrane.

The present inventors have examined requirements for making a porous film containing a fluororesin available as a wiping surface of a wiping member. Wiping liquids and solids from the surface to be cleaned with the porous membrane presses the surface of the porous membrane against the surface to be cleaned as a wiping surface, and moves the surface to be cleaned relative to the surface to be cleaned while bringing them into close contact with each other Is done by. At that time, if the smoothness of the surface of the porous film as the wiping surface is not sufficient, distribution occurs in the pressure when the wiping surface is pressed against the surface to be cleaned. If the pressure variation in the pressure distribution is large, it causes wiping unevenness. On the surface to be cleaned to which a liquid containing solid content (for example, pigment ink) adheres, there are various deposits such as a liquid containing solid content and a solid content separated from the liquid. In order to wipe off these deposits with higher accuracy, smoothness is required for the wiping surface that can maintain a uniform pressure from the wiping surface against the surface to be cleaned and allow them to adhere to each other. . Therefore, there is a need for a method that can efficiently impart the intended smoothness to the surface of the porous fluororesin membrane that becomes the wiping surface of the wiping member.
As a result of repeated studies on the smoothness and strength of the heat-welded member in the hot-pressure laminating process, the present inventors have satisfied the configuration of the present invention, thereby deteriorating the smoothness of the porous film that has undergone the hot-pressed laminating process. It was found that can be suppressed.

Hereinafter, the present invention will be described in detail with reference to preferred embodiments.
The method for producing a porous membrane of the present invention includes the following steps.
(1) A step of laminating a porous film for forming a first layer and a porous film for forming a second layer to form a laminate.
(2) The pressing surface of the pressure contact member is pressed against the surface of the laminate on the first membrane forming porous membrane side under heating, and the laminate surface of each porous membrane of the laminate is thermocompression bonded. Process.
In addition, a process (2) may be performed after a process (1), and a process (1) and a process (2) may be performed simultaneously.

The inventors have repeatedly studied the smoothness of the pressing surface of the first pressure contact member used in the hot-pressure laminating process as described above and the strength of the pressure contact member. As a result, it was found that deterioration of the smoothness of the surface of the porous film for forming the first layer can be suppressed by performing hot-press lamination under conditions satisfying the following expressions (1) and (2). . That is, in the present invention, a pressure contact member having a smoothness of the pressing surface higher than the surface (exposed surface) of the first porous membrane and a rigidity higher than that of the porous membrane for forming the first layer is used. Yes. As a result, the target smoothness can be imparted with good controllability to the surface (exposed surface) of the first layer of the porous film obtained through the hot-press laminating step.
Regarding formula (1), the difference between Ra _(RS1) and Ra _(PM1) is not particularly limited, but is preferably 0.1 μm or more. Regarding Formula (2), the difference between E _(RS1) and E _(PM1) is not particularly limited, but is preferably 100 MPa or more.
(I) Ra _(RS1) <Ra _(PM1) (Formula 1)
Ra _(RS1) : Arithmetic mean roughness of the pressing surface of the first pressure contact member Ra _(PM1) : Surface of the porous film for forming the first layer on which the pressing surface of the first pressure contact member is pressed (exposed surface) ) Arithmetic average roughness (ii) E _(RS1) > E _(PM1) (Formula 2)
E _(RS1) : Compression elastic modulus of the first pressure contact member E _(PM1) : Compression elastic modulus of the porous film for forming the first layer The surface smoothness is defined by JIS B 0601: 2011. The arithmetic average roughness Ra can be evaluated, and the smaller Ra is, the higher the smoothness is. The compression elastic modulus is a value specified by JIS K 7181: 2011.

  Regarding the mechanism by which the effect of the present invention can be obtained by such a configuration, the present inventors use a smooth and high-rigidity member for the pressure contact member, so that the surface of the porous film follows the pressure contact member. It is thought that deterioration of the smoothness of the film surface may be suppressed. On the other hand, although it is estimated that the pressing surface of the hot pressing member in Patent Document 1 is a smooth surface necessary for smoothing the surface of the web layer made of PTFE, the hardness is particularly referred to. It has not been. Therefore, in the smoothing process in Patent Document 1, it is considered that high smoothness cannot be obtained when the hot pressing member follows the porous film.

Hereinafter, the present invention will be described in more detail with reference to embodiments of the present invention.
[Laminated porous membrane]
The porous film produced in the present invention has a laminated structure including a first layer made of a porous film containing a fluororesin and a second layer made of a porous film, that is, a structure as a porous laminated body. . Each of the first layer and the second layer can be composed of a single layer or a plurality of layers. In addition, you may have another layer on the 2nd layer. Moreover, as long as the effect of this invention is acquired, you may have another layer between each layer, However, It is preferable that at least a 1st layer and a 2nd layer are adjacent layers.
The total number of layers constituting the laminated structure of the porous membrane is not particularly limited, but can be selected from a range of 2 to 5. Each layer constituting this laminated structure is bonded between the respective layers, and maintains the strength as a porous laminated body.

The porosity of the porous membrane can be evaluated by its air permeability. The air permeability can be defined by a Gurley value measured by a Gurley tester defined in JIS P8117. The Gurley value of the entire porous membrane obtained by the production method of the present invention is preferably 10 s or less. A lower Gurley value means higher air permeability. The lower limit of the Gurley value is not particularly limited, but can be set to about 0.3 s.
The porous film for forming the first layer has a porous structure made of a fluororesin, has a good ability to collect liquids and solids such as dust, and has an exposed surface (outer surface). Has smoothness. As a result, the exposed surface of the first layer constitutes a surface suitable for collecting deposits from the surface to be cleaned, particularly deposits made of a liquid in which solid content such as pigment ink is dispersed.

Hereinafter, each layer which comprises the porous film obtained by the manufacturing method of this invention is each demonstrated.
[First layer]
In the present invention, the first layer is made of a porous film containing a fluororesin. A fluororesin has low surface free energy and high cleaning properties. Moreover, when it uses as a wiping member, solid content cannot adhere easily. Specific examples of the fluoropolymer contained in the fluororesin include polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), and perfluoroalkoxy fluorine. Resin (PFA: perfluoroalkoxyalkane (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), ethylene / tetrafluoroethylene copolymer (ETFE) And ethylene / chlorotrifluoroethylene copolymer (ECTFE).
In the present invention, a polytetrafluoroethylene (PTFE) stretched porous membrane is used as the first layer.
In the present invention, the compressive elastic modulus of the porous film for forming the first layer is preferably 2 MPa or more. The upper limit value of the compression modulus is not particularly limited, but can be set to about 30 MPa.
The water pressure resistance defined by JIS L 1092 of the porous film for forming the first layer is preferably 200 kPa or more. The water pressure resistance is proportional to the pore size of the porous membrane, and a porous membrane with a large water pressure resistance is suitable because the pore size is small and high collection efficiency can be obtained. The upper limit value of the water pressure resistance is not particularly limited, but can be set to about 500 kPa.

The thickness of the first layer is preferably 100 μm or less. The thickness of the porous film can be obtained by measuring the layer thickness at any 10 points with a straight-forward micrometer OMV_25 (manufactured by Mitutoyo) and calculating the average value. Moreover, the lower limit of the thickness of the first layer is not particularly limited, and can be set according to the use of the porous membrane, and can be set to about 1 μm, for example.
The surface (exposed surface) of the first layer is formed as a smooth surface. When the porous film is used as a wiping member, the use of this smooth surface as the wiping surface suppresses the occurrence of pressure contact pressure distribution on the surface to be cleaned against the surface to be cleaned when pressed against the surface to be cleaned. As a result, it is possible to clean the surface to be cleaned without uneven wiping. The smoothness of the exposed surface of the first layer can be evaluated by arithmetic average roughness (Ra), and the arithmetic average roughness (Ra) is preferably 1.5 μm or less. In addition, the lower limit value of the arithmetic average roughness (Ra) is not particularly limited, but can be set to about 0.1 μm.

  Note that the measurement data of the surface shape when calculating the arithmetic average roughness (Ra) of the surface of the porous film is a laser microscope using a confocal optical system such as a pinhole (for example, a semiconductor laser having a wavelength of about 405 nm). ) Can be used. Surface shape measurement data can be obtained by combining data obtained by scanning reflection in the observation measurement range with a laser microscope in the Z-axis direction. Arithmetic mean roughness (Ra) can be calculated | required according to prescription | regulation of JISB0601: 2011 using the obtained surface shape data.

[Second layer]
The second layer of the porous membrane is a layer for obtaining a good collection force such as liquid and solid content and a sufficient collection capacity by constituting a laminated structure together with the first layer. Therefore, it is preferable that the second layer has a larger air permeability (average pore diameter) than the first layer, and the substance collected in the first layer is accommodated in the second layer, so that a higher collection capacity can be obtained. Can be provided.
The second layer is preferably a layer having air permeability and a function as a support for the porous membrane. The second layer preferably has higher air permeability than the first layer, that is, has a lower Gurley value than the first layer. Examples of the constituent material of the second layer include fibrous members such as nonwoven fabrics, woven fabrics, and meshes (network nets), and other various porous structures. Among these, from the viewpoints of strength, air permeability, flexibility, workability, and the like, a fibrous member is preferable, and a nonwoven fabric is more preferable. By using a porous film having a lower Gurley value than the first layer forming porous film for forming the second layer, a second layer having higher air permeability than the first layer can be obtained. .
The average pore diameter was measured by the bubble point method in accordance with JIS K3832. Palm porometer CFP-1200A (made by PMI) was used for the measuring apparatus.
The compressive elastic modulus of the porous film for forming the second layer is preferably 2 MPa or more. The upper limit value of the compression modulus is not particularly limited, but can be set to about 40 MPa. In addition, it is preferable to make 2nd compression elastic modulus larger than the compression elastic modulus of a 1st layer.

The arithmetic average roughness (Ra) of the surface (exposed surface) of the second layer is preferably 50 μm or less. The lower limit value of the arithmetic average roughness (Ra) of the exposed surface is not particularly limited, but can be set to about 0.5 μm.
The thickness of the second layer is preferably 300 μm or less. The lower limit of the thickness is not particularly limited, but can be set to about 10 μm. In addition, the thickness of the second layer is preferably larger than that of the first layer.
The average fiber diameter of the second layer is preferably 0.1 μm or more and 15.0 μm or less. The average fiber diameter is more preferably 0.1 μm or more and 10.0 μm or less. Further, the water pressure resistance of the second layer is preferably lower than that of the first layer.

  The material for forming the porous film as the second layer forming member is not particularly limited, but polyolefin (for example, polyethylene (PE), polypropylene (PP), etc.), polyurethane, nylon, polyamide, polyester (for example, polyethylene) And terephthalate (PET)), polysulfone (PSF), fluororesin, and the like. As the fluororesin, those mentioned above for forming the first layer can be used. One of these resins can be used alone or as a composite material in combination of two, for producing a porous film for forming the second layer. When using fibrous members, such as a nonwoven fabric, the fibrous member which consists of a fiber of a single material, and the fibrous member in which the fiber which consists of 2 or more types of different materials can be used are used.

[Multi-layer configuration of second layer]
The second layer of the porous membrane can be formed as a plurality of layers. When the second layer is formed of a plurality of layers, layers having different constituent materials and forms may be used in combination. As the constituent material of each layer when the second layer has a multi-layer structure, those exemplified above can be used. Even when the second layer has a multi-layer structure, it is preferable that the air permeability of the entire multi-layer structure is higher than that of the first layer as described above. Furthermore, the arithmetic surface roughness (Ra) of the surface (exposed surface) formed by the outermost layer in the multi-layer structure is also preferably set in the above range.
Further, when the second layer has a multi-layer structure, the air permeability is increased from the layer adjacent to the first layer to the outermost layer forming the exposed surface, that is, the average pore diameter is increased. These layers may be arranged in a layer. For example, when the second layer has a two-layer structure, it is preferable to set the average pore diameter of the outermost layer that forms the exposed surface larger than the layer adjacent to the first porous film. The average pore diameter of the porous membrane for forming each layer can be measured with a palm porometer CFP-1200A (manufactured by PMI).

[Method for producing porous membrane]
The porous film for forming the first layer may be any film as long as the desired first layer can be obtained in the porous film through the hot-pressure laminating process. Using a porous film forming method according to the type of fluororesin, a porous film having physical properties such as desired porosity, thickness, density, and surface smoothness is obtained, and the first layer forming It can be used as a member.
A method for producing a porous body made of PTFE that can be used as the porous film for forming 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.
A PTFE fine powder mixed with a lubricant is compressed in a cylinder to form pellets, extruded from a ram extruder in an unfired state, formed into a sheet, and further formed into an appropriate thickness by a pair of rollers, for example, Roll to a thickness selected from the range of 0.05 to 0.7 mm. 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. Stretched porous bodies (stretched porous membranes) having various pore diameters, void ratios, and thicknesses can be formed by changing the heating conditions and stretching treatment conditions (for example, the stretching ratio and stretching speed).
When stretching, when stretched at a relatively high speed in the direction of one axis or more at a heating temperature lower than the melting point of PTFE, the PTFE stretched porous body becomes a knot portion having a large dimension larger than 1 μm interconnected by extremely small fibers. Having a fiber structure. The porosity is as high as 40 to 97%, and the strength is extremely high.
In addition, there are a method of stretching the sheet-like molded body after making it into a semi-fired state, a method of stretching after heating and firing to a temperature higher than the melting point (327 ° C.) of PTFE, or a method of stretching while heating and firing to a temperature higher than the melting point.
Moreover, you may use as a porous film for 1st layer formation what formed into a porous film | membrane by making into a film | membrane the film | membrane by the hot pressure etc. the fluororesin fiber obtained by the Electro Spinning (ES) method.

In the present invention, a porous film for forming the first layer having a desired smoothness on its surface is used. In the present invention, the first layer of the porous film obtained after the hot-pressure laminating process can be subjected to the hot-pressure laminating process under the condition that the smoothness deterioration on the surface of the first layer forming porous film can be prevented. The target smoothness can be reliably obtained on the surface (exposed surface) with good controllability. That is, according to the present invention, the smoothness of the surface (exposed surface) of the first layer of the porous membrane can be easily controlled to obtain the desired smoothness.
The porous film for forming the second layer of the porous film may be any film as long as the desired second layer can be obtained in the porous film through the hot-pressure laminating step. In the case of using a nonwoven fabric as the porous film, the production method includes a dry method, a wet method, a spun bond method, an ES method, etc., and then a chemical bond method, a thermal bond method, a needle punch method, a water flow method. The method of joining between fibers by the confounding method etc. is mentioned. The nonwoven fabric produced by the needle punch method can prevent the deterioration of air permeability (low Gurley number) because the adhesion point between the porous films laminated in the hot-press laminate is reduced.

[Porous membrane lamination method]
The method for hot-pressure laminating a porous film in the present invention will be described.
The temperature applied during the hot-press lamination and the pressure applied by the pressure contact member are such that the thermocompression bonding between the porous membranes can achieve the desired pressure-bonding strength without damaging the physical properties and characteristics of each porous membrane. Selected. The temperature at the time of hot-press lamination is equal to or higher than the melting point of the resin material (at least one of a plurality of types of resin materials in the case of a plurality of types of resin materials) included in the porous film for forming the second layer. It is preferable. The temperature during the hot-press lamination is more preferably not higher than the melting point of the fluororesin contained in the first layer-forming porous membrane, and the melting point of the fluororesin contained in the first layer-forming porous membrane. More preferably, it is lower.
As the pressure contact member in the hot-pressure laminating step of the porous film, a material that satisfies the conditions of the above-described formulas (1) and (2) is used. The arithmetic average roughness (Ra) of the pressing surface of the first pressure contact member is preferably smaller than 1.5 μm.

In the present invention, it has a pressing surface having a smoothness higher than the surface of the porous film that becomes the surface of the first layer after hot-press lamination, has a smaller compression elastic modulus than this porous film, and is rigid. A high pressure contact member is used. As a result, it is possible to prevent a decrease in smoothness on the surface of the porous film during hot-press lamination, and it is possible to improve the smoothness in some cases. As a result, it is possible to eliminate unevenness in wiping off deposits from the surface to be cleaned when a porous film obtained by hot-press lamination is used as a wiping member.
Further, the second pressure contact member is disposed at a position facing the first pressure contact member, a nip portion is formed between these members, and the above-described thermocompression bonding process can be performed at the nip portion. The second pressure contact member is provided on the second layer-forming porous film side included in the laminate before the hot-pressure lamination, and the pressing surface thereof is the exposed surface of the second layer-forming porous film. Pressure contacted. The compression elastic modulus of the second pressure contact member and the arithmetic average roughness of the pressing surface have a relationship defined by the following equations (3) and (4) with respect to the porous film for forming the second layer. It is preferable to set so as to satisfy.
Regarding formula (3), the difference between Ra _(RS2) and Ra _(PM2) is not particularly limited, but is preferably 0.1 μm or more. Regarding formula (4), the difference between E _(RS2) and E _(PM2) is not particularly limited, but is preferably 100 MPa or more.
(I) Ra _(RS2) <Ra _(PM2) (Formula 3)
Ra _(RS2) : Arithmetic mean roughness of the pressing surface of the second pressure contact member Ra _(PM2) : Surface of the porous film for forming the second layer on which the pressing surface of the second pressure contact member is pressed (exposed surface) ) Arithmetic average roughness (ii) E _(RS2) > E _(PM2) (Formula 4)
E _(RS2) : Compression elastic modulus of the second pressure contact member E _(PM2) : Compression elastic modulus of the porous film for forming the second layer Note that the second pressure forming member of the second pressure contact member has The arithmetic average roughness (Ra) of the pressing surface to the porous membrane is preferably smaller than 1.5 μm.

The material for forming the pressure contact member is not particularly limited, and for example, metal, ceramic, resin, and the like are preferable. Among them, since it needs to be highly rigid, aluminum, iron, stainless steel, polyimide, PTFE, tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polyvinylidene fluoride (PVDF) , A material selected from tetrafluoroethylene / hexafluoropropylene copolymer (FEP), polyphenylene sulfide (PPS), polybutylene terephthalate (PBT) polyethylene, polyethylene terephthalate (PET), polyurethane, silica ceramics and alumina ceramics is used very suitably. It is done.
The shape of the pressure contact member is not particularly limited, but, for example, a roller-shaped pressure contact means can be suitably used in order to continuously perform the pressing operation.

Moreover, the heating at the time of hot-press lamination can be performed using a heating means, and the heating means may be provided on the pressure contact member or may be separately provided on the pressure contact member. When the heating means is provided in the pressure contact member, the heating means can be provided in at least the first pressure contact means, and further, the heating means can be provided in the second pressure contact means as necessary. A heating roller can be used as the pressure contact means having a function as a heating means. By using the heating roller, the heating and pressing work can be carried out continuously. The temperature of the heating roller is preferably 10 to 50 ° C. higher than the melting point of the material of the second layer and not more than the melting point of the material of the first layer. Preferably the pressure by the pressure is 0.2~10kg / cm ^2, more preferably 1-5 kg / cm ^2. Moreover, it is preferable that the adhesive force of each layer is 0.1-5N / 20mm in the method prescribed | regulated to the 90 degree peeling test method prescribed | regulated by JISZ0237.

An example of a hot-pressure laminating process when a pressure roller is used as the first pressure contact means will be described with reference to FIG.
First, the porous film 1 for forming the first layer and the porous film 2 for forming the second layer, both of which are formed in a long sheet shape, are conveyed from respective rollers (not shown) for storing them. The roller (not shown) is fed with tension. The delivered porous membrane 1 and the porous membrane 2 are superposed and laminated to form a laminate of porous membranes. Subsequently, the heating roller 3 is pressed against the laminated body from the exposed surface side of the porous film 1 for forming the first layer, and the entire laminated body is heated to a predetermined temperature while passing through the pressure contact portion by the heating roller 3. The porous film 1 for forming the first layer and the porous film 2 for forming the second layer are bonded together under pressure. The porous film thus obtained is wound and stored on a winding roller (not shown).
FIG. 2 shows an example in which the second layer has a two-layer structure. First, the first layer-forming porous membrane 1 and the second layer-forming porous membranes 2 and 4 that are both formed in a long sheet shape are each provided with rollers (not shown). ) From a feed roller (not shown) to feed and laminate to form a laminate. Subsequently, the heating roller 3 is pressed against the laminated body from the exposed surface side of the porous film 1 for forming the first layer, and the entire laminated body is heated to a predetermined temperature while passing through the pressure contact portion by the heating roller 3. The adjacent porous membranes are bonded together under pressure. In addition, formation of the laminated body by lamination | stacking of these porous films is performed by the method of laminating | stacking three porous membranes 1, 2, and 4 simultaneously, and the method of laminating | stacking these in order in this order or reverse order. The stacking order may be selected as appropriate.
In addition, when the strength and rigidity of the porous film for forming each layer are low, the porous film is transported to the stacking position with the support being supported by the support, and the porous film is peeled off from the support before stacking. You may make it use for lamination | stacking.

A pinch roller may be disposed at the heat pressure contact portion to the laminate as the second pressure contact member disposed opposite to the heating roller as the first pressure contact member. An example of a hot press laminating method in which a pinch roller is arranged at the hot press contact portion will be described using FIG. First, in the same manner as described with reference to FIG. 1, the first layer-forming porous film 1 and the second layer-forming porous film 2 are laminated to form a laminate. Subsequently, the laminated body is heated and pressed by the heating roller 3 and the pinch roller 5, and the entire laminated body is heated to a predetermined temperature while passing through the roller nip, and the porous film 1 for forming the first layer and the second layer are heated. The porous film 2 for layer formation is adhered.
In the example shown in FIGS. 1 to 3, the processing conditions are arbitrarily set such as changing the temperature of the heating roller 3, or changing the speed at which the laminate passes through the nip between the heating roller 3 and the pinch roller 5 in the example shown in FIG. 3. Can be controlled. Based on the heating temperature at the heating roller 3, the conveying speed of the laminate and the pressure applied to the laminate can be set so as to obtain adhesion on the intended laminate surface. Further, the pressure applied to the laminated body can be controlled by adjusting the position of the pinch roller 5.
As the material of the pinch roller 5, the same materials as those exemplified above as the material of the press contact member can be used. Although it does not specifically limit about the characteristic of a pinch roller, It is preferable that the requirements prescribed | regulated by Formula (3) and (4) mentioned above are satisfy | filled. If a pinch roller satisfying these conditions is used, a porous film having higher smoothness can be obtained.

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.
(Examples 1-8 and Comparative Examples 1-6)
As a material for forming the first and second layers of the porous membrane, a multi-layer membrane having the surface (porous PTFE exposed surface), compression elastic modulus, and film thickness of arithmetic average roughness Ra shown in Table 1 below Prepared.
The arithmetic average roughness (Ra) was determined by the following method.
Using a VK9710 laser microscope (manufactured by Keyence), data from the surface of the porous film to a depth of 200 μm was acquired in the RPD mode with an objective lens 50 times (CF IC EPI PLAN Apo 50X made by Nikon). The obtained data was processed with a noise filter (median), the cut-off λc was set to 0.08 μm, and the arithmetic average roughness (Ra) defined by JIS B 0601: 2001 was calculated with a reference line length of 200 μm.
The compression elastic modulus is calculated by acquiring stress-strain data up to 0.1 to 0.5 MPa with a measurement contact portion as a SUS cylinder having a diameter of 5 mm in accordance with JIS K 7181: 2011.
In Tables 1 and 2, the arithmetic average roughness and compression elastic modulus of the first layer and the second layer are values measured for the porous film as a material for forming these layers. For the roller, it is a value measured with respect to these pressing surfaces.
The thickness of the porous film of each layer of the porous film having a multi-layer structure is measured by measuring the layer thickness at any 10 points with a straight-forward micrometer OMV_25 (manufactured by Mitutoyo), and the average value is the thickness of the porous film. Calculated as

And using the heating roller and pinch roller of the following Table 2, the 1st layer and the 2nd layer were laminated | stacked with the hot-pressure laminating method shown in FIG. 3, and it was set as the porous film of 2 layer structure. The temperature of the heating roller was 180 ° C., and the nip pressure was 2 kg / cm ² .

[Evaluation]
The porous film obtained above was evaluated by the following evaluation method. The evaluation results are shown in Table 3. In the evaluation of repeated wiping properties, the evaluation criteria A to B in the following evaluation items were set to preferable levels, and C was set to an unacceptable level.
<Arithmetic mean roughness>
The arithmetic average roughness of the exposed surface of the first layer of the two-layer porous membrane obtained as described above was measured by the measurement method described above.
<Repeatable wiping>
In order to evaluate smoothness, the porous film obtained above was used as a wiping member, and a cleaning performance test in maintenance of an ink jet printer was performed. Specifically, as shown in FIGS. 4 and 5, the porous film 9 is brought into pressure contact with the nozzle surface 8 on which the nozzles 7 of the inkjet head 6 for discharging ink are formed by the pressing roller 10, and the porous film 9 and The inkjet head 6 was made relatively. By this operation, ink droplets, dust, dust, paper dust and the like attached to the nozzle surface 8 were wiped off. As a test apparatus, an apparatus of a system in which the porous film 9 is unwound from a roll and the porous film 9 is conveyed by winding on the conveyance winding roller 11 is used. In addition, BCI-320PGBK (made by Canon Inc.) black pigment ink was used for the ink for evaluation.
By observing the surface of the surface on which the nozzle was formed after wiping with an optical microscope, the presence or absence of wiping unevenness was evaluated. The smaller the wiping unevenness, the better. Further, the wiping unevenness is assumed to have a correlation with the smoothness of the porous film. The evaluation criteria are as follows.
A: No wiping unevenness was observed.
B: Slight wiping unevenness was observed, but at a level that was not a concern.
C: Wiping unevenness occurred.

DESCRIPTION OF SYMBOLS 1 Porous film | membrane 2 for 1st layer formation, 4 Porous film | membrane for 2nd layer formation 3 Heating roller 5 Pinch roller 6 Inkjet head 7 Nozzle 8 Nozzle surface 9 Porous film 10 Wiping member Pressing roller 11 Wiping member Conveyor take-up roller

Claims (8)

A method for producing a porous film having a first layer made of a porous film containing a fluororesin and a second layer made of a porous film,
Laminating the porous film for forming the first layer and the porous film for forming the second layer to form a laminate;
A step of pressing the pressing surface of the pressure contact member to the surface on the porous film side for forming the first layer of the laminated body under heating, and thermocompression bonding the laminated surface of each porous film of the laminated body;
Have
The first layer is a polytetrafluoroethylene (PTFE) stretched porous membrane;
The arithmetic average roughness (Ra) of the pressing surface of the pressing member is smaller than the arithmetic average roughness (Ra) of the surface of the porous film for forming the first layer to which the pressing surface is pressed, and
The compression elastic modulus of the pressure contact member is larger than the compression elastic modulus of the porous film for forming the first layer,
A method for producing a porous membrane. The pressure contact member arranged on the porous layer side for forming the first layer of the laminate is a first pressure contact member, facing the pressing surface of the first pressure contact member, and the second of the laminate The pressing surface of the second pressure contact member is disposed on the porous membrane side for layer formation, a nip portion is formed by these pressing surfaces, and the thermocompression bonding is performed at the nip portion,
The arithmetic surface roughness (Ra) of the pressing surface of the second press-contact member is the arithmetic average roughness of the surface of the porous film for forming the second layer with which the press surface of the second press-contact member is pressed ( Ra) and the compressive elastic modulus of the second pressure contact member is larger than the compressive elastic modulus of the porous film for forming the second layer,
The method for producing a porous membrane according to claim 1. The second layer serves as a support for the first layer, the manufacturing method of a porous membrane according to claim 1 or 2. The method for producing a porous membrane according to any one of claims 1 to 3 , wherein the porous membrane for forming the second layer is made of a nonwoven fabric. The method for producing a porous membrane according to claim 4 , wherein the nonwoven fabric is a nonwoven fabric in which fibers are joined by a needle punch method. The method for producing a porous film according to any one of claims 1 to 5 , wherein an arithmetic average roughness (Ra) of a surface of the porous film for forming the first layer is 1.5 µm or less. The method for producing a porous membrane according to any one of claims 1 to 6 , wherein a compression elastic modulus of the porous membrane for forming the first layer is 2 MPa or more. The method for producing a porous membrane according to any one of claims 2 to 7 , wherein the compression elastic modulus of the porous membrane for forming the second layer is 2 MPa or more.

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