JP6561380B2 - Laminate and method for producing laminate - Google Patents

Description

  The present invention relates to a laminate and a method for producing the laminate.

  In recent years, there has been a growing need for filters that can remove fine foreign matters and have a large processing flow rate, for example, in semiconductor cleaning applications. Since such a filter requires chemical resistance and heat resistance, a porous body using a fluororesin is preferably used as a separation membrane.

  The separation membrane of such a filter needs to have a small pore diameter and a thin film in order to improve the separation performance, but the mechanical strength is lowered accordingly. If the mechanical strength of the separation membrane is insufficient, the membrane may be damaged when modularized by pleat folding.

  Therefore, in order to increase the mechanical strength, for example, a porous composite (laminated body) in which a support layer and a reinforcing layer are laminated on a polytetrafluoroethylene porous membrane has been devised (see JP-A-2015-9219). In this porous laminate, a resin film is formed on a support layer, and these are stretched to form a porous separation membrane having a small pore diameter on the support layer, and a reinforcing layer is further laminated on the porous separation membrane. It is obtained by doing.

JP2015-9219

  In the porous laminate described above, as shown in FIG. 4, the reinforcing layer 101 and the porous film 102 are bonded via an adhesive (thermoplastic resin) 103. Therefore, there is a disadvantage that the pores of the porous film 102 are blocked by the adhesive 103 and the flow rate is reduced.

  The present invention has been made based on the above circumstances, and an object of the present invention is to provide a laminate having a relatively large permeation flow rate of a fluid such as a gas or a liquid and excellent in mechanical strength, and a method for producing the laminate. And

  The laminate according to one embodiment of the present invention includes a porous separation layer mainly composed of a fluororesin, a porous support layer mainly composed of a fluororesin and laminated on one surface of the separation layer, A porous protective layer comprising a fluororesin as a main component and laminated on the surface opposite to the support layer of the separation layer, the average flow pore size of the separation layer is smaller than the support layer and the protection layer, At least one of the separation layer and the protective layer has a fibrous portion at the interface between the separation layer and the protective layer, and the fibrous portion is joined by entering the void of the other layer.

  The method for producing a laminate according to one embodiment of the present invention includes a porous separation layer mainly composed of a fluororesin, and a porous layer mainly composed of a fluororesin and laminated on one surface of the separation layer. And a porous protective layer comprising a fluororesin as a main component and laminated on the surface of the separation layer opposite to the support layer, the average flow pore size of the separation layer being the support layer and the protection layer And a porous sheet forming step of forming a porous sheet comprising the separation layer and the support layer, and a surface of the porous sheet opposite to the support layer of the separation layer. A thermal laminating step of thermally laminating the protective layer at a temperature lower than the glass transition point when the melting point or melting point of the fluororesin as a main component of the separation layer and the protective layer does not exist.

  The laminate of the present invention has a relatively large fluid permeation flow rate and excellent mechanical strength. Moreover, according to the manufacturing method of the laminated body of this invention, such a laminated body can be manufactured easily and reliably.

FIG. 1 is a schematic cross-sectional view illustrating a stacked body according to one embodiment of the present invention. FIG. 2 is a cross-sectional photograph of a stacked body according to one embodiment of the present invention. FIG. 3A is a schematic cross-sectional view showing one step in a method for manufacturing a laminate according to one embodiment of the present invention. FIG. 3B is a schematic cross-sectional view showing one step in the method for manufacturing a laminate according to one embodiment of the present invention. FIG. 3C is a schematic cross-sectional view illustrating one step in the method for manufacturing a laminate according to one embodiment of the present invention. FIG. 4 is a cross-sectional photograph of a laminate in which a separation layer and a protective layer are joined by a conventional adhesive layer.

  A laminate according to an embodiment of the present invention includes a porous separation layer mainly composed of a fluororesin, a porous support layer mainly composed of a fluororesin and laminated on one surface of the separation layer, A porous protective layer comprising a fluororesin as a main component and laminated on the surface opposite to the support layer of the separation layer, the average flow pore size of the separation layer is smaller than the support layer and the protection layer, At least one of the separation layer and the protective layer has a fibrous portion at the interface between the separation layer and the protective layer, and the fibrous portion is joined by entering the void of the other layer.

  The laminate has a relatively high mechanical strength and a scratch resistance against pleat folding since the separation layer for separation is sandwiched between the support layer and the protective layer. Since these support layer and protective layer have a larger average flow pore size than the separation layer, they do not prevent the passage of fluids such as liquids and gases. In the laminate, since the separation layer and the protective layer are mechanically joined by the fibrous portion of one layer entering the void of the other layer without using an adhesive, by the melting of the fluororesin There is no blocking of holes or blocking of holes by adhesive. That is, according to the laminate, a filter having a relatively large fluid permeation flow rate and excellent mechanical strength can be obtained.

  The average flow pore size of the separation layer is preferably from 0.1 nm to 50 nm, and the average flow pore size of the support layer and the protective layer is preferably from 0.05 μm to 10 μm. By setting the average flow pore diameters of the separation layer, the support layer, and the protective layer within the above ranges, it is possible to obtain a separation ability and a fluid permeation flow rate suitable as a filter.

  The main component fluororesin of the separation layer, support layer or protective layer is preferably polytetrafluoroethylene. Thus, by using polytetrafluoroethylene as the main component of the separation layer and the like, the heat resistance, chemical resistance, and the like of the laminate can be improved.

  The glass transition point (hereinafter also referred to as “melting point or glass transition point T”) when the melting point or the melting point of the fluororesin as the main component of the separation layer and the protective layer does not exist is preferably 250 ° C. or more and 350 ° C. or less. By selecting a fluororesin having a melting point or glass transition point T in a specific range as described above, the separation layer and the protective layer can be easily and reliably joined only by pressure bonding, and as a result, the joint strength is increased. be able to.

  The peel strength of the protective layer is preferably 8 N / m or more. Thus, the mechanical strength of the said laminated body can further be improved by making peeling strength of a protective layer more than the said minimum.

  The manufacturing method of the laminated body which concerns on another embodiment of this invention is a porous separation layer which has a fluororesin as a main component, and the porous which has a fluororesin as a main component and is laminated | stacked on one side of the said separation layer And a porous protective layer comprising a fluororesin as a main component and laminated on the surface of the separation layer opposite to the support layer, the average flow pore size of the separation layer being the support layer and the protection layer And a porous sheet forming step of forming a porous sheet comprising the separation layer and the support layer, and a surface of the porous sheet opposite to the support layer of the separation layer. A thermal laminating step of thermally laminating the protective layer at a temperature lower than the glass transition point when the melting point or melting point of the fluororesin as a main component of the separation layer and the protective layer does not exist.

  In the manufacturing method of the laminate, the separation layer and the protection layer are directly bonded without using an adhesive by thermally laminating the protection layer on the separation layer laminated on one surface of the support layer. A laminate can be obtained. In this laminate, the separation layer for separation is sandwiched between the support layer and the protective layer, so that the mechanical strength is relatively high and scratch resistance against pleat folding is provided. Moreover, since these support layers and protective layers have a larger average flow pore size than the separation layer, they do not hinder the passage of fluid. That is, according to the laminate manufacturing method, a filter having a relatively large fluid permeation flow rate and excellent mechanical strength can be obtained.

  The temperature of the thermal laminate is preferably 10 ° C. or more lower than the glass transition point when the melting point or the melting point of the fluororesin as the main component of the separation layer and the protective layer does not exist. By performing thermal lamination at such a temperature, the separation layer and the protective layer can be joined while preventing the pore size of the separation layer from becoming coarse.

  The “main component” is a component having the highest content, for example, a component having a content of 50% by mass or more. The “average flow pore size” is an index corresponding to the average value of the pore size, and is obtained from the measurement result by the bubble point method (ASTM F316-86, JIS-K3832 (1990)) using a pore size distribution measuring device or the like. Specifically, the relationship between the differential pressure applied to the membrane and the air flow rate through the membrane is measured by the bubble point method when the membrane is dry and when the membrane is wet with liquid. The graphs obtained by this measurement are respectively a dry curve and a wet curve, and when the pressure difference at the intersection of the curve and the wet curve with the flow rate of the dry curve being ½ is P (Pa), the formula d = The value of d (μm) represented by cγ / P is “average flow pore size” (c is a constant 2860, and γ is the surface tension (dynes / cm) of the liquid). “Melting point” means a melting point peak measured by a differential scanning calorimeter (DSC) according to JIS-K-7121 (2012), and “glass transition point” means JIS-K-7121 ( 2012) means the midpoint glass transition temperature measured by a differential scanning calorimeter (DSC). “Peel strength” means a value measured according to JIS-K-6854-2 (1999).

[Details of the embodiment of the present invention]
Hereinafter, a laminate and a method for producing the laminate according to an embodiment of the present invention will be described in detail with reference to the drawings.

<Laminated body>
The laminate shown in FIG. 1 includes a porous separation layer 1 mainly composed of a fluororesin, a porous support layer 2 mainly composed of a fluororesin and laminated on one surface of the separation layer 1, It mainly includes a porous protective layer 3 that is mainly composed of a fluororesin and is laminated on the surface of the separation layer 1 opposite to the support layer 2. The average flow pore size of the separation layer 1 is smaller than that of the support layer 2 and the protective layer 3. Further, at least one of the separation layer 2 and the protective layer 3 has a fibrous part at the interface between them, and the fibrous part is joined by entering the void of the other layer.

  In the laminate, since the separation layer 1 for separation is sandwiched between the support layer 2 and the protective layer 3, the laminate has a relatively high mechanical strength and has scratch resistance against pleat folding. Since the support layer 2 and the protective layer 3 have an average flow pore size larger than that of the separation layer 1, they do not hinder the passage of fluid. In the laminate, since the separation layer 1 and the protective layer 3 are mechanically joined by the fibrous portion entering the gap of the other layer without using an adhesive, pores due to melting of the fluororesin No clogging or clogging of the hole by adhesive occurs. That is, according to the laminate, a filter having a relatively large fluid permeation flow rate and excellent mechanical strength can be obtained.

(Separation layer)
The separation layer 1 is a porous film containing a fluororesin as a main component, and has a function of separating fine foreign substances contained in a fluid such as gas.

  Examples of the main component fluororesin of the separation layer 1 include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), Examples thereof include ethylene-tetrafluoroethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), and tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether copolymer (EPA). Among these, PTFE excellent in heat resistance, chemical resistance and the like is preferable. These resins may be used alone or in combination of two or more.

  As a minimum of melting | fusing point or the glass transition point T of the said fluororesin, 250 degreeC is preferable and 280 degreeC is more preferable. On the other hand, the upper limit of the melting point or glass transition point T of the fluororesin is preferably 350 ° C., more preferably 330 ° C. When the melting point or glass transition point T of the fluororesin is less than the lower limit, the heat resistance of the laminate may be insufficient, or the separation layer 1 may be melted when bonded to the protective layer 3. On the other hand, when the melting point or glass transition point T of the fluororesin exceeds the upper limit, the heating temperature at the time of pressure bonding with the protective layer 3 is increased, and each layer may be thermally deteriorated or the manufacturing cost may be increased. .

  The separation layer 1 may contain other resins and additives other than the fluororesin as the main component. As a minimum of content of the fluororesin used as a main component, 80 mass% is preferable and 90 mass% is more preferable.

  The lower limit of the average flow pore size of the separation layer 1 is preferably 0.1 nm, more preferably 1 nm, and even more preferably 10 nm. On the other hand, the upper limit of the average flow pore size of the separation layer 1 is preferably 50 nm, and more preferably 35 nm. If the average flow pore size of the separation layer 1 is less than the lower limit, a fluid such as gas is difficult to permeate and the separation efficiency may be reduced. On the contrary, if the average flow pore diameter of the separation layer 1 exceeds the above upper limit, foreign substances are likely to permeate and the separation ability may be lowered, and the strength may be insufficient.

The lower limit of the IPA flow rate of the separation layer 1 is preferably 0.1 ml / min / cm ^{2 and} more preferably 0.5 ml / min / cm ² . On the other hand, the upper limit of the average flow pore size of the separation layer 1 is preferably 5 ml / min / cm ^{2 and} more preferably 3 ml / min / cm ² . If the IPA flow rate of the separation layer 1 is less than the above lower limit, it is difficult for fluid such as gas to permeate and the separation efficiency may be reduced. On the other hand, if the IPA flow rate of the separation layer 1 exceeds the above upper limit, foreign matter is likely to permeate and there is a risk that the separation performance will be reduced and the strength will be insufficient. The “IPA flow rate” means a flow rate measured by the method of ASTM-F-317 using isopropyl alcohol.

  The average thickness of the separation layer 1 is not particularly limited, but the lower limit of the average thickness of the separation layer 1 is preferably 0.5 μm and more preferably 1 μm. On the other hand, the upper limit of the average thickness of the separation layer 1 is preferably 10 μm and more preferably 5 μm. If the average thickness of the separation layer 1 is less than the above lower limit, foreign substances are likely to pass therethrough and the separation ability may be reduced, and the strength may be insufficient. On the other hand, when the average thickness of the separation layer 1 exceeds the upper limit, fluid such as gas is difficult to permeate and the separation efficiency may be reduced.

(Support layer)
The support layer 2 is a porous film containing a fluororesin as a main component and supports the separation layer 1. The support layer 2 has a relatively large pore diameter, and even if an adhesive is present between the support layer 2 and the separation layer 1, it is difficult to inhibit the passage of fluid. You may adhere | attach through the adhesive agent which has a plastic fluorine resin as a main component. Further, the support layer 2 may be directly bonded to the separation layer 1.

  As the main component fluororesin of the support layer 2, the same resin as the separation layer 1 can be used. The melting point or glass transition point T of this fluororesin is the same as that of the separation layer 1. In addition, it is preferable that the material of the separation layer 1 and the support layer 2 is the same from the viewpoint of connection strength.

  The average flow pore size of the support layer 2 is larger than the average flow pore size of the separation layer 1. The lower limit of the average flow pore size of the support layer 2 is preferably 0.05 μm, more preferably 0.1 μm, and even more preferably 0.3 μm. On the other hand, the upper limit of the average flow pore size of the support layer 2 is preferably 10 μm, more preferably 5 μm, and even more preferably 1 μm. There exists a possibility that the pressure loss of the said laminated body may become large that the average flow hole diameter of the support layer 2 is less than the said minimum. Conversely, if the average flow pore size of the support layer 2 exceeds the above upper limit, the strength of the support layer 2 may be insufficient.

The lower limit of the IPA flow rate of the support layer 2 is preferably 1 ml / min / cm ^{2 and} more preferably 10 ml / min / cm ² . On the other hand, the upper limit of the average flow pore size of the support layer 2 is preferably 100 ml / min / cm ^{2 and} more preferably 50 ml / min / cm ² . There exists a possibility that the pressure loss of the said laminated body may become it that the IPA flow rate of the support layer 2 is less than the said minimum. Conversely, if the IPA flow rate of the support layer 2 exceeds the above upper limit, the strength of the support layer 2 may be insufficient.

  The average thickness of the support layer 2 is not particularly limited, but the lower limit of the average thickness of the support layer 2 is preferably 5 μm and more preferably 10 μm. On the other hand, the upper limit of the average thickness of the support layer 2 is preferably 100 μm, and more preferably 50 μm. There exists a possibility that the intensity | strength of the support layer 2 may become inadequate that the average thickness of the support layer 2 is less than the said minimum. Conversely, if the average thickness of the support layer 2 exceeds the upper limit, the laminate may be unnecessarily thick.

(Protective layer)
The protective layer 3 is a porous film containing a fluororesin as a main component, and protects the surface of the separation layer 1 opposite to the support layer 2. Moreover, the protective layer 3 has one surface joined to the separation layer 1 by pressure bonding and is not fused. Specifically, as shown in the electron micrograph of FIG. 2, the fibrous portion that the protective layer 3 has on the surface on the separation layer 1 side enters the gap of the separation layer 1 and at the same time the protective layer 3 side of the separation layer 1. The fibrous portions on the surface of the protective layer 3 are mechanically joined by entering the voids of the protective layer 3. However, only the protective layer 3 may have a fibrous portion, and this fibrous portion may enter the gap of the separation layer 1, or conversely, only the separation layer 1 has a fibrous portion, and this fibrous portion is protected. It may enter the void of the layer 3. In addition, (a) of FIG. 2 is a 10,000 times microscope picture, (b) is a 30,000 times microscope picture of the same laminated body. These fibrous portions can be formed, for example, by thermal lamination at a temperature lower than the melting point or glass transition point T.

  As the main component fluororesin of the protective layer 3, the same one as that of the separation layer 1 can be used. The melting point or glass transition point T of this fluororesin is the same as that of the separation layer 1. From the viewpoint of connection strength, it is preferable to use the same material for the separation layer 1 and the protective layer 3.

  The average flow pore size of the protective layer 3 is larger than the average flow pore size of the separation layer 1. The lower limit of the average flow pore size of the protective layer 3 is preferably 0.05 μm, more preferably 0.1 μm, and still more preferably 0.2 μm. On the other hand, the upper limit of the average flow pore size of the protective layer 3 is preferably 10 μm, more preferably 5 μm, and even more preferably 1 μm. There exists a possibility that the pressure loss of the said laminated body may become large that the average flow hole diameter of the protective layer 3 is less than the said minimum. Conversely, if the average flow pore size of the protective layer 3 exceeds the upper limit, the strength of the protective layer 3 may be insufficient.

The lower limit of the IPA flow rate of the protective layer 3 is preferably 1 ml / min / cm ^{2 and} more preferably 10 ml / min / cm ² . On the other hand, the upper limit of the average flow pore size of the protective layer 3 is preferably 100 ml / min / cm ^{2 and} more preferably 50 ml / min / cm ² . There exists a possibility that the pressure loss of the said laminated body may become it that the IPA flow rate of the protective layer 3 is less than the said minimum. Conversely, if the IPA flow rate of the protective layer 3 exceeds the above upper limit, the strength of the protective layer 3 may be insufficient.

  The average thickness of the protective layer 3 is not particularly limited, but the lower limit of the average thickness of the protective layer 3 is preferably 5 μm and more preferably 10 μm. On the other hand, the upper limit of the average thickness of the protective layer 3 is preferably 100 μm, and more preferably 50 μm. There exists a possibility that the intensity | strength of the protective layer 3 may become inadequate that the average thickness of the protective layer 3 is less than the said minimum. Conversely, if the average thickness of the protective layer 3 exceeds the above upper limit, the laminate may be unnecessarily thick.

  The lower limit of the peel strength of the protective layer 3 with respect to the separation layer 1 is preferably 8 N / m, and more preferably 9 N / m. When the peel strength of the protective layer 3 is not less than the above lower limit, the mechanical strength of the laminate can be improved.

  The structure of the separation layer 1, the support layer 2, and the protective layer 3 is not particularly limited as long as it is a porous body, but is preferably a stretched film. That is, as the separation layer 1, the support layer 2, and the protective layer 3, a layer obtained by stretching a non-porous resin film formed by extrusion or casting is preferable. Examples of the stretched film include a multiaxially stretched film and a uniaxially stretched film. As described above, the stretched film is used for the separation layer 1, the support layer 2, and the protective layer 3, so that the separation layer 1, the support layer 2, and the protective layer mainly composed of a fluororesin and having an appropriate strength and an average flow pore size. 3 can be configured relatively easily.

  Moreover, the laminate may include a plurality of protective layers. That is, the laminated body may be a multilayer body in which the protective layer 3 laminated on the separation layer 1 is formed by pressure-bonding a plurality of protective layers.

  The lower limit of the average flow pore size of the laminate is preferably 0.1 nm, more preferably 1 nm, and even more preferably 10 nm. On the other hand, the upper limit of the average flow pore size of the laminate is preferably 50 nm, and more preferably 35 nm. If the average flow pore size of the laminate is less than the lower limit, fluid such as gas is difficult to permeate and the separation efficiency may be reduced. Conversely, if the average flow pore size of the laminate exceeds the above upper limit, foreign matter can easily pass through and the separation ability can be reduced, and the strength can be insufficient.

The lower limit of the IPA flow rate of the laminate is preferably 0.1 ml / min / cm ^{2 and} more preferably 0.5 ml / min / cm ² . On the other hand, the upper limit of the average flow pore size of the laminate is preferably 5 ml / min / cm ^{2 and} more preferably 3 ml / min / cm ² . If the IPA flow rate of the laminate is less than the lower limit, a fluid such as gas is difficult to permeate and the separation efficiency may be reduced. On the other hand, if the IPA flow rate of the laminate exceeds the above upper limit, foreign substances are likely to pass therethrough and the separability may be reduced, and the strength may be insufficient.

  The average thickness of the laminate is not particularly limited, but can be, for example, 15 μm or more and 500 μm or less.

<Application>
Since the laminate has a relatively high mechanical strength and has scratch resistance against pleat folding, it can be suitably used as a filter capable of removing fine foreign matters by disposing it in a casing after pleat folding. Further, since the average flow pore size of the separation layer is relatively small, the laminate can be used as a separation membrane such as a gas separation membrane or a reverse osmosis membrane (RO membrane). Moreover, you may use for uses other than isolation | separation.

<Method for producing laminate>
The method for producing the laminate includes a porous sheet forming step of forming a porous sheet comprising the separation layer and the support layer, and the protective layer on the surface of the porous sheet opposite to the support layer of the separation layer. A heat laminating step for heat laminating.

  In the manufacturing method of the laminate, the separation layer and the protection layer are directly bonded without using an adhesive by thermally laminating the protection layer on the separation layer laminated on one surface of the support layer. A laminate can be obtained. Therefore, according to the method for manufacturing the laminate, a filter having a relatively large fluid permeation flow rate and excellent mechanical strength can be obtained.

(Porous sheet forming process)
In this step, a porous sheet having a separation layer laminated on one surface of the support layer is formed. The method for forming the porous sheet is not particularly limited, and a method of laminating after separately forming the support layer and the separation layer may be used, but the following methods can be preferably used.

  First, as shown in FIG. 3A, a fluororesin-containing liquid in which a fluororesin powder that is a main component of the separation layer is mixed in a solvent is applied to the surface of a smooth support film A. For this coating, a coating machine such as a capillary system, a roll system, a die (lip) system, or a bar system can be used as a coating apparatus. Further, as the support film A, for example, an aluminum foil can be used.

  As the solvent, an aqueous medium such as water is usually used. The fluororesin powder is an aggregate of fine particles of fluororesin and can be obtained, for example, by emulsion polymerization. Moreover, as the said fluororesin containing liquid, what disperse | distributed the fluororesin powder which has PTFE as a main component in a dispersion medium is preferable. By using a fluororesin-containing liquid containing PTFE as a main component, a separation layer having excellent chemical resistance, heat resistance, and the like can be obtained. Furthermore, the fluororesin-containing liquid may contain a thermoplastic fluororesin powder in addition to the PTFE powder. Examples of this thermoplastic fluororesin include PFA, FEP, EPA, ETFE, etc. Among these, PFA is preferable. Since PFA tends to be less prone to thermal decomposition, defects generated in the separation layer can be reduced. These resins may be used alone or in combination of two or more.

  The upper limit of the blending amount of the thermoplastic fluororesin powder with respect to the total of the PTFE powder and the thermoplastic fluororesin powder is preferably 10% by volume, and more preferably 5% by volume. When the blending amount of the thermoplastic fluororesin powder is larger than the above upper limit, the thermoplastic fluororesin may aggregate on the skeleton of the porous film serving as the support layer due to the surface tension, and defects may easily occur.

  Moreover, the defect mentioned above can also be reduced by adding the water-soluble polymer which gelatinizes on high concentration conditions to a fluororesin containing liquid. The water-soluble polymer is preferably a nonionic polymer from the viewpoint of influence on the dispersibility of the fluororesin. Examples of such a water-soluble polymer include polyethylene oxide, polypropylene oxide, polyvinyl alcohol, starch, and agarose. Of these, polyethylene oxide is preferred. These water-soluble polymers may be used alone or in combination of two or more. Moreover, as a minimum of the weight average molecular weight of a nonionic water-soluble polymer, 100,000 is preferable and 1 million is more preferable. By setting the weight average molecular weight to the above lower limit or more, since the fluororesin-containing liquid gels and forms a film before the water is completely removed during drying, cracks caused by the surface tension of water Occurrence can be suppressed. Here, the “weight average molecular weight” means a weight average molecular weight obtained by standard polystyrene conversion value using gel permeation chromatography.

  As a minimum of water-soluble polymer content in a fluororesin content liquid, 0.5 mg / ml is preferred and 1.0 mg / ml is more preferred. On the other hand, the upper limit of the water-soluble polymer content is preferably 10 mg / ml, more preferably 5 mg / ml. When the content of the water-soluble polymer is smaller than the lower limit, the above-described action by the water-soluble polymer may not be sufficiently exhibited. On the other hand, when the content of the water-soluble polymer is larger than the above upper limit, the viscosity of the fluororesin-containing liquid becomes too high, and the handleability may be lowered.

  After apply | coating a fluororesin containing liquid to the smooth support film A, the dispersion medium contained in a fluororesin containing liquid is dried. Drying can be performed by heating to a temperature close to or higher than the boiling point of the dispersion medium. In this drying, it is preferable to perform heating in multiple stages while gradually raising the temperature. Specifically, for example, the first stage is 50 ° C. or more and 100 ° C. or less, the second stage is 200 ° C. or more and less than 300 ° C., the third stage is 300 ° C. or more and 400 ° C. or less, and the time of each stage is 0.5 hours or more. 2 hours or less. Thereby, the fluororesin film | membrane B which has a fluororesin as a main component is obtained.

  Next, a thermoplastic fluororesin having a melting point lower than the main components of the separation layer and the support layer (for example, PFA when PTFE is used for the separation layer and the support layer) is added to the surface of the obtained fluororesin coating B in a solvent. Apply the adhesive solution blended in The solvent of this adhesive liquid can be the same as that of the above-mentioned fluororesin-containing liquid. Further, the above water-soluble polymer may be added to the adhesive liquid.

  After application of the adhesive liquid, as shown in FIG. 3B, a porous film C mainly composed of a fluororesin serving as a support layer is superimposed on the surface of the fluororesin coating film B to which the adhesive liquid has been applied. This porous film C can be obtained, for example, by stretching a fluororesin film.

  After superposing the porous film C, the laminate is subjected to heat treatment. As a result, the solvent of the adhesive liquid is removed, and the porous film C and the fluororesin coating film B are bonded by the fluororesin contained in the adhesive liquid. Even in this heat treatment, heating in a plurality of stages may be performed while gradually raising the temperature. Specifically, for example, the first stage is 50 ° C. or more and 100 ° C. or less, the second stage is 200 ° C. or more and less than 300 ° C., the third stage is 300 ° C. or more and 400 ° C. or less, and the time of the first stage and the second stage is set. 0.5 hours or more and 2 hours or less, and the third stage time is 5 hours or more and 10 hours or less.

  Further, after the heat treatment, the support film A is removed. When this support film A is an aluminum foil, it can be removed by dissolution with an acid, for example.

  After the support film A is removed, as shown in FIG. 3C, the fluororesin coating film B is made porous by stretching the laminate, and the separation layer 1 is formed. As a result, a porous sheet 10 in which the separation layer 1 is laminated on one surface of the support layer 2 is obtained. As this stretching, biaxial stretching is preferable. For example, after stretching at a stretch rate of 100% or more and 300% or less in the width direction of the sheet, at a stretch rate of 30% or more and 100% or less in the longitudinal direction (the direction perpendicular to the width direction). It is good to stretch.

(Thermal lamination process)
In this step, the protective layer is thermally laminated on the surface of the porous sheet obtained in the porous sheet forming step on the side opposite to the support layer of the separation layer. Specifically, heat is applied to the surface of the separation layer of the porous sheet by directly superposing (without interposing another layer) a porous film mainly composed of a fluororesin serving as a protective layer, and applying pressure while heating. Laminate. This porous film can be obtained, for example, by stretching a fluororesin film. By such thermal lamination, the uneven structure resulting from the porosity of the surface of the separation layer and the protective layer grows into a fibrous shape without being fused, and mechanically engages, and the above-described fibrous portion is entangled. Since a structure is obtained, a laminate having high adhesive strength can be obtained.

  The heat laminating apparatus is not particularly limited, and for example, a press-type laminating apparatus can be used, but from the viewpoint of manufacturing efficiency, heat laminating with a pair of rolls is preferable. As this roll, what combined the metal roll (heating roll) and the rubber roll, for example can be used conveniently.

  The thermal lamination is performed at a temperature lower than the melting point or glass transition point T of the main component of the separation layer and the protective layer (porous film), and may be performed at a temperature lower than the melting point or glass transition point T by 10 ° C. or more. . Further, the upper limit of the temperature of the thermal laminate is preferably a temperature 30 ° C. lower than the melting point or glass transition point T, and more preferably a temperature lower by 60 ° C. On the other hand, the lower limit of the temperature of the thermal laminate is preferably a temperature 240 ° C. lower than the melting point or glass transition point T, and more preferably 150 ° C. lower. If the temperature of the thermal laminate exceeds the above upper limit, fusion may occur and the pore size of the separation layer may increase. Conversely, if the temperature of the thermal laminate is less than the lower limit, the bonding strength may be reduced. In addition, the temperature of the said thermal lamination means the temperature of a heating roll, when performing a thermal lamination using a roll.

  When PTFE is used as the main component fluororesin of the separation layer and the protective layer, the upper limit of the temperature of the thermal laminate is preferably 310 ° C, more preferably 290 ° C, and further preferably 260 ° C. On the other hand, the lower temperature limit of the thermal laminate is preferably 80 ° C, and more preferably 170 ° C.

  When using a roll, the lower limit of the nip pressure of the thermal laminate is preferably 0.10 kg / cm, and more preferably 0.25 kg / cm. On the other hand, the upper limit of the nip pressure is preferably 5.0 kg / cm, more preferably 2.5 kg / cm. If the nip pressure is less than the above lower limit, the bonding strength may be insufficient. Conversely, when the nip pressure exceeds the upper limit, each layer may be deformed. Moreover, when performing thermal lamination with a roll, as a feed rate, they are 1 m / min or more and 10 m / min, for example.

  When using a press, the lower limit of the press pressure of the thermal laminate is preferably 0.06 kPa, more preferably 0.12 kPa. On the other hand, the upper limit of the pressing pressure is preferably 10 kPa, and more preferably 5 kPa. If the pressing pressure is less than the above lower limit, the bonding strength may be insufficient. Conversely, if the pressing pressure exceeds the upper limit, each layer may be deformed. Moreover, when performing heat lamination by a press, as press time, it is 5 to 30 seconds, for example.

  In addition, when the said laminated body has a several protective layer, a laminated body provided with a multilayer protective layer can be obtained by carrying out the thermal lamination of the several porous film simultaneously.

[Other Embodiments]
The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is not limited to the configuration of the embodiment described above, but is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims. The

  The said laminated body may be provided with layers other than a support layer, a separation layer, and a protective layer in the range which does not inhibit the effect | action of this invention.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

<Example 1>
First, as a support layer and a protective layer, a stretched polytetrafluoroethylene (PTFE) film having an average flow pore size of 0.45 μm, an average thickness of 30 μm, and an IPA flow rate of 25.8 ml / min / cm ² (“PORFLON” manufactured by Sumitomo Electric Fine Polymer Co., Ltd.) (Registered trademark) HP-045-30 ").

  Next, PTFE dispersion (Asahi Glass "AD911"), perfluoromethyl vinyl ester copolymer (MFA) latex and PFA dispersion (DuPont "920HP") were mixed. The compounding ratio of these components was such that the volume ratio of the fluororesin solids represented by MFA / (PTFE + MFA + PFA) and FA / (PTFE + MFA + PFA) was 2%. To this mixed solution, polyethylene oxide (weight average molecular weight 2 million) was added so as to have a concentration of 3 mg / ml to prepare a fluororesin dispersion.

  Next, an aluminum foil having an average thickness of 50 μm was spread and fixed on the glass flat plate so as not to be wrinkled, and the fluororesin dispersion was dropped. Thereafter, the fluororesin dispersion was spread evenly on one surface of the aluminum foil by rolling a slide shaft (“Stainless Fine Shaft SNSF type” manufactured by Nippon Bearing Co., Ltd., outer diameter 20 mm, made of stainless steel).

  The above-mentioned fluororesin dispersion coated foil is dried at 80 ° C. for 1 hour, then heated at 250 ° C. for 1 hour, further heated at 340 ° C. for 1 hour, and then naturally cooled, so that one surface of the aluminum foil has an average thickness of 3 μm. The fluororesin film was formed.

  Next, the PFA copolymer dispersion was diluted to 4 times the volume with distilled water, and the polyethylene oxide was added to a concentration of 3 mg / ml to prepare a PFA diluted dispersion.

  Further, the laminate of the fluororesin coating and the aluminum foil is spread and fixed on the glass plate so that there is no wrinkle so that the fluororesin coating is on top, the PFA diluted dispersion is dropped, and the slide Using a shaft, it was spread uniformly on the fluororesin coating. Before the coating film was dried, the stretched PTFE film was overlaid. This aluminum foil, fluororesin coating and expanded PTFE film laminate was dried at 80 ° C. for 60 minutes, then heated at 250 ° C. for 1 hour, further heated at 320 ° C. for 1 hour, and finally at 317.5 ° C. for 8 hours. Heated for hours. After drying and heating, the aluminum foil was dissolved and removed with hydrochloric acid to obtain a laminate of the fluororesin coating and the stretched PTFE film.

The laminate of the fluororesin coating and the stretched PTFE film was stretched in the width direction using a tensile tester at a temperature of 15 ° C., a chuck interval of 55 mm, and a stroke of 165 mm (stretching rate of 200%). The porous sheet was stretched in a direction perpendicular to the width direction at a temperature of 60 ° C., a distance between chucks of 55 mm, and a stroke of 88 mm (stretching rate 60%) to obtain a porous sheet in which a support layer and a separation layer were laminated. The average flow pore size of this porous sheet was 33 nm, and it was shown that the fluororesin coating (separation layer) made porous by stretching has very fine continuous pores. The IPA flow rate of the porous sheet was 1.20 ml / min / cm ² .

  Next, another stretched PTFE film is thermally laminated at 220 ° C. with a roll at a feed rate of 3 m / min on the surface of the separation layer of the porous sheet, and the protective layer and the separation layer are mechanically joined to each other. 1 laminate was obtained.

<Example 2>
A porous sheet similar to that of Example 1 was prepared, and two kinds of stretched PTFE films ("Poreflon (registered trademark) HP-010-30" manufactured by Sumitomo Electric Fine Polymer Co., Ltd.) were used as protective layers on the surface of the separation layer of the porous sheet. ”, Average flow pore size 0.1 μm, average thickness 30 μm, IPA flow rate 5.4 ml / min / cm ² ,“ Poreflon (registered trademark) HP-020-30 ”from Sumitomo Electric Fine Polymer Co., Ltd., average flow pore size 0.2 μm , An average thickness of 30 μm, an IPA flow rate of 16.1 ml / min / cm ² , and “Poreflon (registered trademark) HP-045-30” manufactured by Sumitomo Electric Fine Polymer Co., Ltd.), HP-010-30, HP-020-30. And it laminated | stacked in order of HP-045-30, and it heat-laminates on the conditions similar to Example 1, and obtained the laminated body of Example 2 of 5 layers (a protective layer is 3 layers).

<Comparative Example 1>
A porous sheet similar to that of Example 1 was prepared, and a fluorine-based ion exchange resin dispersion (“AQUIIVION DISPERSION AC D83-24B” from Solvay Special Polymers Japan, solid content 24 was formed on the surface of the separation layer of the porous sheet. A solution obtained by diluting 20% by mass with a glass transition point of about 220 ° C. with water at a coating amount of 12 ml / m ² was applied uniformly with feathers. On this coating layer, a stretched PTFE film (HP-045-30) was superposed and heated and bonded at 220 ° C. for 120 minutes to obtain a laminate of Comparative Example 1.

<Comparative example 2>
A porous sheet similar to that of Example 1 was prepared, and a coating layer similar to that of Comparative Example 1 was formed on the surface of the separation layer of this porous sheet, and expanded PTFE similar to that of Comparative Example 1 was formed on this coating layer. While laminating the films, heat lamination was performed under the same conditions as in Example 1 to obtain a laminate of Comparative Example 2.

<Evaluation>
For the laminates of Examples 1 and 2 and Comparative Examples 1 and 2, the average flow pore size, the IPA flow rate, and the peel strength between the protective layer and the separation layer were measured. The results are shown in Table 1. The IPA flow ratio in the table is the protective layer (porous film) on the porous sheet with respect to the IPA flow rate (1.20 ml / min / cm ² ) of the porous sheet in which the support layer and the separation layer are laminated. The ratio of the IPA flow rate of the laminated body obtained by laminating is shown. The average flow pore size and IPA flow rate of the laminate can be regarded as the average flow pore size and IPA flow rate of the separation layer having the smallest value among the layers constituting the laminate.

As shown in Table 1, the laminate of Example 1 having a three-layer structure has an IPA flow rate of 1.0 ml / min / cm ² or more, excellent separation, and high peel strength. The laminate of Example 2 having a five-layer structure is also suitable for actual use because the IPA flow rate is 0.9 ml / min / cm ² or more. On the other hand, Comparative Example 1 and Comparative Example 2 are lower than Example 1 having a three-layer structure with the same IPA flow rate and peel strength. That is, it was shown that a laminate having a large fluid permeation flow rate and mechanical strength can be easily manufactured by mechanically joining the protective layer and the separation layer without fusing them.

  Since the laminated body has a relatively large fluid permeation flow rate and excellent mechanical strength, it can be suitably used as a filter for removing fine foreign matters. Moreover, according to the manufacturing method of the laminated body of this invention, such a laminated body can be manufactured easily and reliably.

DESCRIPTION OF SYMBOLS 1 Separation layer 2 Support layer 3 Protective layer 10 Porous sheet 101 Reinforcing layer 102 Porous membrane 103 Adhesive A Support film B Fluororesin film C Porous film

Claims (7)

A porous separation layer mainly composed of fluororesin;
A porous support layer mainly composed of a fluororesin and laminated on one surface of the separation layer;
A porous protective layer comprising a fluororesin as a main component and laminated on the surface opposite to the support layer of the separation layer,
The average flow pore size of the separation layer is smaller than the support layer and the protective layer,
A laminate in which at least one of the separation layer and the protective layer has a fibrous portion at the interface between the separation layer and the protective layer, and the fibrous portion is joined by entering a gap in the other layer.   The laminate according to claim 1, wherein the separation layer has an average flow pore size of 0.1 nm to 50 nm, and the support layer and the protective layer have an average flow pore size of 0.05 μm to 10 μm.   The laminate according to claim 1 or 2, wherein the fluororesin as a main component of the separation layer, the support layer or the protective layer is polytetrafluoroethylene.   4. The laminate according to claim 1, wherein the glass transition point is 250 ° C. or more and 350 ° C. or less when the melting point or melting point of the fluororesin as a main component of the separation layer and the protective layer is not present.   The laminate according to any one of claims 1 to 4, wherein the protective layer has a peel strength of 8 N / m or more. A porous separation layer mainly composed of fluororesin, a porous support layer composed mainly of fluororesin and laminated on one side of the separation layer, a fluororesin as a main component, A porous protective layer laminated on the surface opposite to the support layer, and a method for producing a laminate having an average flow pore size of the separation layer smaller than that of the support layer and the protective layer,
A porous sheet forming step of forming a porous sheet comprising the separation layer and the support layer;
Thermally laminating the protective layer on the surface of the porous sheet opposite to the support layer of the separation layer at a temperature lower than the glass transition point when the melting point or the melting point of the fluororesin as the main component of the separation layer and the protective layer is not present A laminate manufacturing method comprising: a heat laminating step.   The manufacturing method of the laminated body of Claim 6 whose temperature of the said thermal lamination is 10 degreeC or more lower than the glass transition point in case the melting | fusing point or melting | fusing point of the fluororesin of the main component of a separation layer and a protective layer does not exist.