JP2012144824A - Nonwoven fabric for reinforcing microporous film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reinforcing body that provides process stability during assembling and sufficient strength and chemical resistance as a product without impairing characteristics of a microporous film having a high porosity.SOLUTION: Provided is a nonwoven fabric for reinforcing a microporous film that contains a glass fiber having a fiber diameter of 3-12 μm and a polyolefinic fiber having a fiber diameter of 1 μm or more, and a thermal adhesion is formed by the polyolefinic fiber. The nonwoven fabric for reinforcing a microporous film has a porosity of 45% or more.

Description

  The present invention relates to a nonwoven fabric for reinforcing a microporous membrane having a high porosity. More specifically, the present invention relates to a reinforcing nonwoven fabric that imparts sufficient strength to a microporous membrane having a high porosity suitable for use as a filter or a separator and does not impair the properties of the microporous membrane.

  For filters such as air filters, bag filters and liquid filtration filters, and separators used in secondary batteries and capacitors, microporous membranes using polymer materials are widely used. In general, microporous membranes have higher strength than materials such as woven fabrics and nonwoven fabrics, and are excellent in denseness. Therefore, among the above-mentioned applications, in particular, microfiltration membranes and ultrafiltration membranes, and separators for lithium ion secondary batteries. As widely used as.

  In recent years, in order to further improve the filtration flow rate or the filtration life of the microporous membrane in the filter, and in the separator, the ion transfer speed between the electrodes is increased to obtain a secondary battery with high output and low battery resistance. Therefore, the porosity of the microporous film tends to be further increased. However, by increasing the porosity, the strength of the microporous film is reduced.

  Therefore, when a microporous membrane having a high porosity is used for a filter or a separator, measures such as increasing the thickness of the microporous membrane are taken in order to improve the strength of the microporous membrane. However, when the microporous membrane becomes thick, it leads to a decrease in flow rate or inhibition of ion movement, and it is difficult to cope with a required filtration rate or high output.

  As an attempt to improve the strength of the microporous membrane, for example, a glass fiber fabric having a thickness of 25 μm or less and produced by a method such as plain weave, twill weave and satin weave is impregnated with polyolefin to form a microporous membrane. A glass fiber fabric reinforced polyolefin microporous membrane having a porosity of 80% or less obtained is disclosed (for example, see Patent Document 1).

  In addition, for example, as a separator material or a support, there is a technique that uses a nonwoven fabric having a thickness of 30 μm or less that is chemically and / or thermally bonded, has a maximum tensile strength of 15 N / 5 cm, and a maximum tensile elongation of 35% at the maximum. It is disclosed (for example, see Patent Document 2). In this method, glass fiber is used as one of the fibers constituting the nonwoven fabric.

  Furthermore, a non-aqueous electrolyte battery separator that includes 20 to 80% by weight of inorganic fibers having an average fiber diameter of 3 μm or less, made of micro glass fibers, alumina fibers, alumina silica fibers, and the like has been proposed (for example, Patent Document 3). reference).

  In the method described in Patent Document 1, since a glass fiber fabric is used for the reinforcing body of the microporous membrane, the permeability and heat resistance are excellent, and the strength of the microporous membrane can be improved. On the other hand, the strength of the fabric varies depending on the density of the fibers to be woven (woven density: main / 25 mm), and the higher the fiber density, the higher the strength.

  For example, when a single yarn having a fiber diameter of 5 μm is produced by a plain weave having a weaving density of 56 yarns / 25 mm / 25 mm, the opening is about 440 μm in length and width. However, when the woven fabric is used as a reinforcing body, there are cases where obstacles such as penetration and breakage may occur when the wide opening is subjected to partial stress (such as piercing with filtered material).

  In particular, in the case of a woven fabric, since wide openings are distributed almost uniformly, there is a further concern about obstacles. Of course, the obstacle can be suppressed by further increasing the weave density. However, in this case, the cost required for production also increases, and when used as a material for a filter or separator, the cost increases significantly and is not practical.

Moreover, the specific gravity of the glass fiber described in Patent Document 2 is as high as 2.54 g / cm ³ , unlike the specific gravity of other polymer materials constituting the nonwoven fabric. Therefore, when a fiber made of a material having a low specific gravity, such as a polyolefin resin, and a glass fiber are mixed with the glass fiber, the technique disclosed in Patent Document 2 uniformly disperses at least two kinds of fibers. It is difficult to obtain a nonwoven fabric.

  Furthermore, since the nonwoven fabric obtained by the configuration of the method described in Patent Document 3 is very dense, when used as a reinforcing material for a microporous membrane having a high porosity, the pores of the nonwoven fabric are rate-limiting. For this reason, it becomes difficult to sufficiently develop the characteristics of the microporous membrane having a high porosity.

JP 2004-269579 A Japanese Patent Laid-Open No. 2005-054348 WO96 / 30954 pamphlet

  For these reasons, the object of the present invention is to provide reinforcement that provides process stability during production and sufficient strength and chemical resistance as a product without impairing the properties of the microporous membrane having a high porosity. To provide a body.

  The inventors of the present invention have made extensive studies in order to solve the above problems. As a result, the inventors have found that the above-mentioned problems can be solved by using a reinforcing nonwoven fabric having the following constitution as a reinforcing member for a microporous membrane, and have completed the present invention based on this finding.

The present invention has the following configuration.
[1] A nonwoven fabric for reinforcing a microporous membrane, comprising glass fibers having a fiber diameter of 3 to 12 μm and polyolefin fibers having a fiber diameter of 1 μm or more, and thermally bonded with the polyolefin fibers. A nonwoven fabric for reinforcing a microporous membrane having a porosity of 45% or more.
[2] The nonwoven fabric for reinforcing a microporous membrane according to [1], wherein the polyolefin fiber is at least one selected from the group consisting of fibril fibers and composite fibers.
[3] The nonwoven fabric for reinforcing a microporous membrane according to [1] or [2], wherein the nonwoven fabric for reinforcing a microporous membrane has a Young's modulus of 300 to 2500 MPa (MD).
[4] The nonwoven fabric for reinforcing microporous membrane according to any one of [1] to [3], wherein the glass fiber content is 10 to 80% by mass.
[5] The nonwoven fabric for reinforcing a microporous membrane according to any one of [1] to [4], wherein the microporous membrane has a porosity of 45% or more.

  The nonwoven fabric for reinforcing a microporous membrane of the present invention is excellent in chemical resistance by containing glass fibers having a fiber diameter of 3 to 12 μm and polyolefin fibers having a fiber diameter of 1 μm or more. In addition, the nonwoven fabric for reinforcing a microporous membrane of the present invention is thermally bonded with polyolefin fibers and has a porosity of 45% or more. Sufficient strength can be imparted without impairing the properties of the porous membrane.

  The present invention is a nonwoven fabric for reinforcing a microporous membrane comprising glass fibers having a fiber diameter of 3 to 12 μm and polyolefin fibers having a fiber diameter of 1 μm or more, and thermally bonded by the polyolefin fibers, The porosity of the nonwoven fabric is 45% or more.

I. Glass fiber Conventionally known glass fiber can be used as the glass fiber. Examples of the glass fiber composition include A glass, AR glass, E glass, ECR glass, and S glass, and it is particularly preferable to use a glass fiber having a general-purpose E glass composition.

  The fiber diameter of glass fiber is 3-12 micrometers, and it is preferable that it is 3-9 micrometers. If the fiber diameter of the glass fiber is less than 3 μm, the nonwoven fabric for reinforcing the microporous membrane becomes dense and affects the characteristics of the microporous membrane. Moreover, since it is necessary to reduce the thickness of the microporous membrane for the purpose of lowering the filtration rate of the filter and the resistance of the separator, the fiber diameter needs to be 12 μm or less.

  A commercially available glass fiber can be used. For example, “UPDE 1 / 8ZA505 (trade name)” manufactured by Unitika Ltd. can be used.

  The content of the glass fiber in the nonwoven fabric for reinforcing a microporous membrane is preferably 10 to 90% by mass, more preferably 10 to 80% by mass, and still more preferably 20 to 70% by mass, It is particularly preferably 30 to 60% by mass. By containing the glass fiber in the above range in the nonwoven fabric for reinforcing the microporous membrane, the strength of the microporous membrane having insufficient strength can be improved to a practical range.

  Although the fiber length of glass fiber is not specifically limited, It is preferable that it is 1-50 mm, It is more preferable that it is 2-25 mm, It is especially preferable that it is 2-10 mm. By setting the cut length of the glass fiber to 1 mm or more, sufficient bending elasticity can be obtained. Moreover, by setting it as 50 mm or less, it becomes easy to disperse | distribute glass fiber in water, and the uniform nonwoven fabric for microporous film reinforcement is obtained.

II. Polyolefin fibers Examples of the polyolefin fibers include fibril fibers, single fibers, and composite fibers, with fibril fibers and composite fibers being particularly preferable.

  The fiber diameter of the polyolefin fiber is 1 μm or more, preferably 1 μm to 50 μm, more preferably 1 to 30 μm, and particularly preferably 2 to 25 μm. By setting the fiber diameter of the polyolefin fiber to 1 μm or more, sufficient strength as a reinforcing nonwoven fabric can be obtained, and a reinforcing nonwoven fabric having a high porosity that does not hinder the pore characteristics of the microporous membrane can be produced.

  The fiber length of the polyolefin fiber is not particularly limited, but is preferably 1 to 50 mm, more preferably 2 to 25 mm, and particularly preferably 2 to 10 mm. By setting the fiber length of the polyolefin fiber within the above range, it becomes easy to obtain sufficient breaking strength by obtaining a plurality of fiber adhesion points, and the dispersibility in water is improved. can get.

  The content of the polyolefin fiber in the nonwoven fabric for reinforcing a microporous membrane is preferably 10 to 90% by mass, more preferably 20 to 90% by mass, and further preferably 30 to 80% by mass. 40 to 70% by mass is particularly preferable. By containing polyolefin fiber in the said range in the nonwoven fabric for microporous membrane reinforcement | strengthening, the intensity | strength of the microporous film | membrane in which intensity | strength is insufficient can be improved to a practical range.

  The glass fiber / polyolefin fiber (mass ratio) in the nonwoven fabric for reinforcing a microporous membrane is preferably 10/90 to 90/10, more preferably 20/80 to 80/20, and 30/70. It is especially preferable to set it to -70/30. By setting it as the said range, the nonwoven fabric for reinforcement in which the balance between the sufficient bending elasticity which glass fiber has, and the breaking strength obtained by heat bonding of polyolefin fiber can be taken can be obtained.

As a method for qualitatively and quantitatively confirming the fiber diameter or content of the glass fiber constituting the microporous membrane (hereinafter also referred to as a composite membrane) reinforced with the nonwoven fabric for reinforcing microporous membrane of the present invention, for example, The following methods (1) to (4) may be mentioned. Of course, it is not limited to these illustrated methods, and can be confirmed by other methods.
(1) The cross section of the composite film is directly observed with a scanning electron microscope (SEM).
(2) The composite film is baked in a high temperature atmosphere of 400 ° C. or higher where the fluoropolymer is thermally decomposed, and the mass is calculated from the remaining glass.
(3) When the raw material of the microporous membrane is particularly polyvinylidene fluoride, the polymer such as dimethylformamide and acetone is immersed in a solvent that can be dissolved, and the mass of the remaining nonwoven fabric for reinforcing the microporous membrane is measured. Then, similarly, it bakes in a 400 degreeC or more high temperature atmosphere, and mass is computed from the remaining glass part.
(4) The composite membrane is immersed in a chemical (for example, a fluorine-based chemical such as hydrofluoric acid), and the mass of the composite membrane after the glass fiber is decomposed and removed is subtracted.

II-1. Fibril fiber As the fibril fiber, a multi-branched synthetic fiber having a fibril shape made of polyolefin can be used. In particular, fine crimps possessed by fibril fibers are preferable because they can entangle glass fibers having a high specific gravity in water and contribute to the stable dispersion of glass fibers that are easy to settle and difficult to stably disperse. The entangled glass fiber can be linked to further improvement in strength by thermally bonding the fibril fiber in the heat treatment. Specifically, SWP EST-8 (trade name) manufactured by Mitsui Chemicals, Inc. can be used.

  Examples of the polyolefin resin used for the fibril fiber include high-density polyethylene, linear low-density polyethylene, low-density polyethylene, polypropylene (propylene homopolymer), ethylene-propylene copolymer mainly composed of propylene, and propylene. Ethylene-propylene-butene-1 copolymer as main component, polybutene-1, polyhexene-1, polyoctene-1, poly-4-methylpentene-1, polymethylpentene, 1,2-polybutadiene and 1,4-polybutadiene Etc.

  Further, in these homopolymers, a small amount of ethylene other than the monomer constituting the homopolymer or α-olefin such as butene-1, hexene-1, octene-1 and 4-methylpentene-1 is used as a copolymerization component. It may be contained. Further, other ethylenically unsaturated monomers such as butadiene, isoprene, 1,3-pentadiene, styrene and α-methylstyrene may be contained in a small amount as a copolymerization component. Two or more of the above polyolefin resins may be mixed and used. These are preferably not only polyolefin resins polymerized from ordinary Ziegler-Natta catalysts, but also polyolefin resins polymerized from metallocene catalysts, and copolymers thereof. The melt mass flow rate of the polyolefin resin that can be suitably used (hereinafter abbreviated as MFR) is not particularly limited as long as it can be spun, but is preferably 1 to 100 g / 10 minutes, more preferably, 5 to 70 g / 10 minutes.

  Physical properties of polyolefins other than the above MFR, such as physical properties such as Q value (weight average molecular weight / number average molecular weight), Rockwell hardness, number of branched methyl chains, etc., are not particularly limited as long as they satisfy the requirements of the present invention.

  In addition, by making the surface of the fibril fiber hydrophilic, papermaking properties can be improved and dispersibility in water can be improved.

  The content of fibril fibers in the microporous membrane reinforcing nonwoven is preferably 10 to 60% by mass, and more preferably 20 to 40% by mass. By containing the fibril fiber in the above range in the nonwoven fabric for reinforcing the microporous membrane, it is possible to contribute to improvement in breaking strength by thermal bonding and stable dispersibility in water.

  The fiber length of the fibril fiber is preferably 0.5 to 5 mm, and more preferably 0.5 to 3 mm. By setting the fiber length of the fibril fiber in the above range, the generation of lumps due to self-entanglement in water is small and good stable dispersibility can be obtained.

II-2. Single fiber As the single fiber, a fiber having a single cross-sectional structure made of a polyolefin resin can be used. Examples of the polyolefin resin used for the single fiber include the polyolefin resins listed in II-1.

  Moreover, by making the surface of a single fiber hydrophilic, papermaking properties can be improved and water dispersibility can be improved.

  The content of a single fiber in the nonwoven fabric for reinforcing a microporous membrane is preferably 10 to 80% by mass, and more preferably 20 to 50% by mass. By setting it within the range, sufficient breaking strength can be obtained by thermal bonding.

  The fiber diameter of the single fiber is 1 μm or more, preferably 1 to 50 μm, more preferably 1 to 30 μm, and particularly preferably 2 to 25 μm. By setting the fiber diameter of a single fiber within the range, sufficient strength as a reinforcing nonwoven fabric is obtained, and the nonwoven fabric for reinforcing a microporous membrane has a high porosity that does not impair the pore characteristics of the microporous membrane. Can be produced.

  Although the fiber length of a single fiber is not specifically limited, It is preferable that it is 1-50 mm, It is more preferable that it is 2-25 mm, It is especially preferable that it is 2-10 mm. By making the fiber length of a single fiber within this range, it becomes easy to obtain sufficient breaking strength by obtaining a plurality of fiber adhesion points, and dispersibility in water is improved, for uniform microporous membrane reinforcement A non-woven fabric is obtained.

II-3. Composite fiber As a composite fiber, a polyolefin resin is used as a first component, a thermoplastic resin having a melting point higher than that of the first component is used as a second component, and at least a part of the fiber surface continues in the length direction. A formed composite fiber having thermal adhesiveness can be used.

  As a specific form of the composite fiber, the first component is a sheath component, the second component is a core component, and the so-called eccentric sheath-core composite fiber in which the position in the cross section of the core component is eccentric, Also, a so-called parallel type composite fiber (side-by-side type composite fiber) that has a shape in which the first component and the second component are bonded together, and two or more first components and second components are alternately arranged and separated by physical stress. A split split type composite fiber to be split is preferably used.

  The ratio (composite ratio) of the first component and the second component in the cross-section of the parallel type composite fiber may be 1: 1, and one component occupies a larger cross-sectional area than the other component in the fiber cross-section. May be.

  In addition, by making the surface of the composite fiber hydrophilic, papermaking properties can be improved and water dispersibility can be improved.

  The volume ratio of the first component and the second component of the composite fiber (corresponding to the area ratio of the cross section when the fiber cross section is adopted = composite ratio) is usually 10 in the ratio of the first component to the second component. : 90 to 90:10 is preferable, and 30:70 to 70:30 is more preferable. It is preferable for the volume ratio of the first component and the second component to be in this range since the adhesiveness to the glass fiber becomes good.

  Examples of the polyolefin resin used for the first component include the polyolefin resins listed in II-1 and modified polyolefins using these as trunk polymers. The trunk polymer is preferably polyethylene in consideration of the melting point range and the ease of the graft reaction.

  The modified polyolefin can be produced by an ordinary method in which a modifier is graft-polymerized to a trunk polymer. The modifying agent used for the modified polyolefin is preferably a vinyl monomer containing at least one selected from unsaturated carboxylic acids and acid anhydrides thereof.

  Specific examples of the modified polyolefin include, for example, an unsaturated carboxylic acid selected from maleic anhydride, maleic acid, acrylic acid, methacrylic acid, and the like, or an anhydride thereof, and other vinyl monomers. be able to.

  As other vinyl monomers, general-purpose monomers having excellent radical polymerizability can be used. Examples of the vinyl monomer include styrenes such as styrene and α-methylstyrene, methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, 2-hydroxyethyl methacrylate and dimethylaminoethyl methacrylate, and similar acrylic monomers. An acid ester etc. can be mentioned.

  The concentration of the vinyl monomer in the modified polyolefin is preferably 0.05 to 2 mol / Kg. Among them, the total amount of unsaturated carboxylic acid or unsaturated carboxylic acid anhydride is preferably 0.03 to 2 mol / Kg.

  The carboxylic acid or unsaturated carboxylic anhydride in the modified polyolefin is a component that directly contributes to adhesion. In addition, the other vinyl monomer helps the adhesion from the side by helping the uniform dispersion of the acid in the polymer, imparts polarity to the polyolefin with poor polarity, improves the affinity with other materials, Contributes to improved uniform dispersion.

  The modified polyolefin may be used as a mixture of two or more kinds (a mixture of different polymers), or may be used as a mixture of the modified polyolefin and the backbone polymer. Even in the case of a mixture of different polymers, the content of the modifier in the polymer may be in the range of 0.05 to 2 mol / Kg.

  As the thermoplastic resin having a melting point higher than that of the first component used as the second component, the polyolefin resins listed in II-1 and crystalline polymers such as polyester and polyamide can be used. In the case of a polyolefin resin, the MFR (melt mass flow rate) is not particularly limited, and is not particularly limited as long as it can be spun, but is preferably 1 to 100 g / 10 minutes, more preferably, 5 to 70 g / 10 minutes. In the case of polyester, the IV (intrinsic viscosity) is preferably 0.49 to 1.0 dL / g.

  Among these polymers, from the viewpoint of chemical resistance and melting point, a propylene homopolymer, an ethylene-propylene copolymer containing propylene as a main component, or an ethylene-propylene-butene-1 copolymer containing propylene as a main component. Polymers are preferred.

  Further, when polyethylene terephthalate is used, a reinforcing nonwoven fabric excellent in elasticity can be obtained. That is, the second component can be selected for further added value and required performance.

  The content of the composite fiber in the nonwoven fabric for reinforcing a microporous membrane is preferably 10 to 80% by mass, and more preferably 20 to 50% by mass. By setting the content of the composite fiber of the nonwoven fabric for reinforcing a microporous membrane to 10% by mass or more, sufficient strength of the nonwoven fabric for reinforcing a microporous membrane can be obtained. Moreover, sufficient bending elasticity of the nonwoven fabric for microporous film reinforcement is acquired by setting it as 80 mass% or less.

  When the fibril fiber and the composite fiber are used in combination, the fibril fiber / composite fiber (mass ratio) is preferably 10/90 to 90/10, and more preferably 25/75 to 75/25. By setting it within this range, a uniform nonwoven fabric for reinforcing a microporous membrane can be obtained in which a balance between improvement in breaking strength by thermal bonding and stable dispersibility in water can be achieved.

  The fiber diameter of the composite fiber is 1 μm or more, preferably 1 to 50 μm, more preferably 1 to 30 μm, and particularly preferably 2 to 25 μm. By making the fiber diameter of the composite fiber within the range, sufficient strength as a nonwoven fabric for reinforcing the microporous membrane can be obtained, and the microporous membrane has a high porosity that does not hinder the pore characteristics of the microporous membrane. Nonwoven fabric can be produced.

  The fiber length of the composite fiber is not particularly limited, but is preferably 1 to 50 mm, more preferably 2 to 25 mm, and particularly preferably 2 to 10 mm. By making the fiber length of the composite fiber within this range, it becomes easy to obtain sufficient breaking strength by obtaining a plurality of fiber adhesion points, and the dispersibility in water is improved, and a uniform nonwoven fabric for reinforcing a microporous membrane is obtained. It is done.

III. Other Additives In the present invention, the polyolefin resin and the thermoplastic resin are antioxidants, light stabilizers, ultraviolet absorbers, neutralizers, nucleating agents, epoxy stabilizers, as long as the effects of the present invention are not hindered. Additives such as agents, lubricants, antibacterial agents, flame retardants, antistatic agents, pigments and plasticizers may be added as appropriate.

IV. Production Method The nonwoven fabric for reinforcing a microporous membrane of the present invention can be produced by methods such as a wet papermaking method, a dry papermaking method, and an airlaid method. Of these, glass fiber and polyolefin fibers can be uniformly mixed if manufactured by a wet papermaking method. Since water is used as a dispersing material when producing by a wet papermaking method, it is better that the surfaces of the glass fiber and the polyolefin fiber are subjected to hydrophilic treatment.

  As the hydrophilic treatment, a method of attaching a surfactant to the fiber surface can be used. As the surfactant, a commercially available hydrophilic oil agent is preferably used. For example, an alkyl phosphate K salt can be used.

  When producing the nonwoven fabric for reinforcing microporous membrane of the present invention by a wet papermaking method, glass fibers and polyolefin fibers are stirred in water in the presence of a dispersant, and uniformly using a device such as a beating machine. After mixing and dispersing to prepare a dispersion, the dispersion is dehydrated and mixed and dried to obtain a web.

  The paper machine used in the paper making process can be produced by arbitrarily using known equipment such as a normal round net, a long net, a short net and an inclined wire. In the drying step, the obtained web can be heated and dried using equipment such as a commonly used cylindrical dryer and Yankee dryer.

  Examples of the dispersant include polyvinyl alcohol, polyethylene oxide, carboxymethyl cellulose, amine-based surfactant, sulfosuccinic acid, and polyacrylamide. The content of the dispersant in the dispersion is preferably 0.1 to 5% by mass, and more preferably 0.1 to 3% by mass.

  The total content of the glass fiber and the polyolefin fiber in the dispersion is preferably 0.005 to 5% by mass, and more preferably 0.005 to 3% by mass.

  Furthermore, a thin nonwoven fabric with high strength can be produced by pressurizing and thermally bonding the web using facilities such as a flat roll such as a press and a Yankee dryer. A flat roll temperature of 100 to 160 ° C. can usually be selected depending on the polyolefin fiber used. The thermal bonding is a bonding by melting of polyolefin fibers in the web, that is, the web is thermally bonded without adding an adhesive, whereby a nonwoven fabric for reinforcing a microporous membrane is obtained.

V. Physical Properties of Microporous Membrane Reinforcing Nonwoven Fabric If the porosity of the microporous membrane reinforcing non-woven fabric of the present invention is 45% or more, the upper limit is not particularly limited, but is preferably 45 to 80%, preferably 50 to 50%. 75% is more preferable, and 50 to 70% is particularly preferable. If it is the said range, it will not impair the performance of the microporous membrane to reinforce, and can fully reinforce. The porosity of the nonwoven fabric for microporous membrane reinforcement is measured by the method described later in the examples.

The basis weight of the nonwoven fabric for reinforcing a microporous membrane of the present invention is not particularly limited, and may be a nonwoven fabric having a basis weight according to the type and application of the material resin to be used, and is preferably ² to 30 g / m 2. and more preferably 10 g / ^{m 2.}

  The Young's modulus of the nonwoven fabric for reinforcing a microporous membrane of the present invention is preferably 250 to 2500 MPa (MD), more preferably 300 to 2500 MPa (MD), and further preferably 500 to 2500 MPa (MD). It is preferably 800 to 2500 MPa (MD).

  By setting the Young's modulus to 300 MPa (MD) or more, process stability during production and sufficient strength as a product can be obtained. Moreover, by setting it as 2500 Mpa (MD) or less, the nonwoven fabric for reinforcement which does not have a cut defect and a moldability fall at the time of shaping | molding to a product can be obtained. The Young's modulus of the nonwoven fabric for reinforcing a microporous membrane is measured by the method described later in Examples.

  The thickness of the nonwoven fabric for reinforcing a microporous membrane of the present invention is not particularly limited, but is preferably 10 to 40 μm, and more preferably 15 to 30 μm. By setting the thickness to 10 μm or more, sufficient strength can be imparted to the microporous membrane. Moreover, by setting it as 40 micrometers or less, the fall of the filtration rate by the thickness increase and the increase in ion movement resistance can be suppressed to the minimum.

VI. Microporous membrane In the present invention, the term "microporous membrane" refers to a flat membrane-like molded body having symmetric or asymmetric communication holes with respect to the cross section in the thickness direction. In the present invention, the porosity of the microporous membrane to be reinforced is not particularly limited, but is preferably 45% or more, more preferably 50% or more, and particularly preferably 60% or more. . Note that the upper limit of the porosity is not particularly limited as long as the function of the microporous membrane is not impaired.

  Examples of the material for the microporous membrane include polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-ethylene copolymer, and polyvinylidene fluoride. Fluororesins such as polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate and polyethylene naphthalate, nylon-4, nylon-6, nylon-46, nylon-66, nylon-610, nylon-11 and nylon- Polyamide resin such as 12, polyolefin resin such as polyethylene, polypropylene, polymethylpentene and polybutadiene, polyvinyl chloride, polyvinylidene chloride Polyvinyl alcohol, ethylene - polyvinyl alcohol copolymer, may be mentioned polyacetal, polystyrene, cellulose, cellulose acetate, chitin, chitosan and polysulfone and the like. In particular, polyvinylidene fluoride, polyethylene, and cellulose, which can easily prepare a polymer solution, are preferable in terms of chemical resistance, open area ratio, and stability of pore size distribution.

  Examples of the method for reinforcing the microporous membrane with the nonwoven fabric for reinforcing microporous membrane of the present invention include the following methods (a) and (b).

(A) Method of laminating and integrating a microporous membrane reinforcing nonwoven fabric and a microporous membrane As a method of laminating and integrating a microporous membrane reinforcing nonwoven fabric and a microporous membrane into a composite membrane, for example, Examples include pasting and pressure bonding. The nonwoven fabric for reinforcing the microporous membrane may be laminated on one side of the microporous membrane or on both sides, the nonwoven fabric for reinforcing the microporous membrane is arranged in the middle layer, and the microporous membrane is arranged on both the upper and lower sides. May be.

(B) A method of solidifying a microporous membrane reinforcing nonwoven by impregnating, coating and drying a microporous membrane raw material. Specifically, for example, polyolefin, polyester, polyvinylidene fluoride, cellulose, etc. A polymer solution is prepared by dissolving in an organic or inorganic solvent and adding an appropriate amount of a solvent having low compatibility with the polymer as a porosifying agent. Thereafter, the reinforcing non-woven fabric is attached with a polymer solution by impregnation or coating. Thereafter, a composite membrane in which the nonwoven fabric for reinforcing the microporous membrane and the microporous membrane are integrated can be obtained by using a technique such as impregnation in a poor solvent such as water or alcohol or evaporation of the solvent by heat drying.

  A composite membrane reinforced by laminating the nonwoven fabric for reinforcing a microporous membrane of the present invention obtained by the above method, and a composite membrane obtained by impregnating a nonwoven fabric for reinforcing a microporous membrane into a solution of a microporous membrane raw material and solidifying it Can be used as filters and separators.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention in detail, this invention is not limited to these Examples. The terms and methods for measuring physical properties in Examples and Comparative Examples are as follows.

Young's modulus measurement method:
Using a Strograph R-3 (model, manufactured by Toyo Seiki Co., Ltd.) as a tensile tester, film load and elongation curve (stress-strain curve) based on a tensile test of a thin plastic sheet specified by ASTM D882 The Young's modulus was determined from the slope of the rise. For a reinforcing nonwoven fabric whose thickness was measured in advance, n = 5 test pieces of 120 mm × 10 mm were prepared, fixed at 50 mm between chucks, and then a stress-strain curve was created at a tensile speed of 5 mm / min. The weight at the time of 1% elongation is obtained from the rising gradient, and the value divided by the cross-sectional area is defined as the Young's modulus (unit: MPa). Young's modulus was measured at room temperature (23 ± 1 ° C.). For the cross-sectional area, an approximate value obtained by multiplying the average thickness of the sample by 10 mm which is the sample width was used.

Measuring method of breaking strength:
Using a Strograph R-3 (model, manufactured by Toyo Seiki Co., Ltd.) as a tensile tester, film load and elongation curve (stress-strain curve) based on a tensile test of a thin plastic sheet specified by ASTM D882 And the strength at break was determined. For a reinforcing nonwoven fabric whose thickness was measured in advance, n = 5 test pieces of 120 mm × 10 mm were prepared, fixed at 50 mm between chucks, and then a stress-strain curve was prepared at a tensile speed of 500 mm / min. The strength when the sample is broken is defined as the breaking strength (unit: MPa). The breaking strength was measured at room temperature (23 ± 1 ° C.). For the cross-sectional area, an approximate value obtained by multiplying the average thickness of the sample by 10 mm which is the sample width was used.

Method for measuring porosity:
The porosity is determined by measuring the area, average thickness, and dry mass of the non-woven fabric cut 15 cm long by 15 cm wide, and then infiltrating IPA (isopropyl alcohol). Was measured, the volume was determined based on the infiltrated IPA mass, and the porosity of the nonwoven fabric was calculated from the following formula (1).

Porosity (%) = Infiltrated IPA volume (cm ³ ) / theoretical volume of nonwoven fabric (cm ³ ) × 100 (1)
(The theoretical volume of the nonwoven fabric is calculated from the average thickness x area of the sample)

Moreover, the following fibers were used as glass fibers.
・ UPDE 1 / 8ZA505 (trade name): short glass fiber manufactured by Unitika Ltd. (fiber diameter 6 μm, cut length 3 mm)

The following fibers were used as polyolefin fibers.
SWP EST-8 (trade name): Synthetic pulp manufactured by Mitsui Chemicals Co., Ltd. ESC871 (trade name): PE / PP sheath-core composite fiber manufactured by Chisso Co., Ltd. [fiber diameter 15 μm (1.7 dtex), cut length 5 mm ]
ESC846 (trade name): PE / PP sheath-core composite fiber manufactured by Chisso Corporation (fiber diameter 12 μm (1.1 dtex), cut length 5 mm)
EDC810 (trade name): PE / PP composite split fiber manufactured by Chisso Corporation (fiber diameter 15 μm (1.7 dtex), cut length 5 mm)
EPC820 (trade name): PP / PP composite fiber manufactured by Chisso Corporation (fiber diameter 17.5 μm (2.2 dtex), cut length 5 mm)
INTACKS 810 (trade name): Modified PE / PP composite fiber manufactured by Chisso Corporation (fiber diameter 15 μm (1.7 dtex), cut length 5 mm)

[Examples 1 to 14]
Water in which a polyolefin fiber and glass fiber are added in a beaker at a ratio (mass ratio) shown in Table 1 so that the total mass of both becomes 1 g, and 0.5% by mass of polyethylene oxide is further dissolved. Was added and dispersed to prepare a sample. A total amount of this sample was used to make a paper using a TAPPI-compliant square paper machine to obtain a web.

  The obtained web was put on water-absorbing paper and dehydrated for 1 hour, and then further dewatered and consolidated using a calender roll. The obtained web was dried with a dryer at 60 ° C. for 3 hours and then heat-treated for 10 seconds with a Yankee dryer at 140 ° C. to produce the nonwoven fabric for reinforcing microporous membrane of the present invention. The porosity and Young's modulus of the obtained nonwoven fabric for reinforcing a microporous membrane were measured. The results are shown in Tables 1 and 2. The term “consolidation” as used herein refers to reducing the thickness of the web by applying a load to the web.

[Comparative Example 1]
Nittobo Co., Ltd. glass cloth WEA1027 (product symbol) was used as a reinforcing material as a glass woven fabric, and the porosity and Young's modulus were measured. The results are shown in Table 2.

  As shown in Table 1 and Table 2, the nonwoven fabrics of Examples 1 to 12, which are nonwoven fabrics for reinforcing a microporous membrane of the present invention, have a high porosity and a sufficient breaking strength, and are excellent. It was found to have a good performance. Moreover, by comparing Examples 1 to 10 and Examples 11 and 12, the content of glass fiber in the nonwoven fabric for reinforcing microporous membrane can be improved by 20 to 80% by mass. I understood.

  On the other hand, since the nonwoven fabric of Comparative Example 1 has a very high Young's modulus of about 3500 MPa and is rigid, when incorporated as a filter or separator, it was difficult to cut or mold.

[Example 15] (Reinforcement of microporous membrane by impregnation)
The solution, which is the raw material for the microporous membrane, was added by dissolving cellulose triacetate with an acetylation degree of 60.6% in dichloromethane so as to be 7% by mass, and then the same amount of n-octanol as cellulose triacetate was added. And prepared with sufficient agitation.

  The nonwoven fabric prepared in Example 8 was impregnated by passing it through a dip coater filled with the solution that was the raw material of the microporous membrane. After coating, the dichloromethane was evaporated by drying at 80 ° C. for 5 minutes, and then the remaining n-octanol was removed with methanol to obtain a composite film formed of cellulose triacetate. As a result of measuring the Young's modulus of the obtained composite film, it was 1400 MPa.

[Example 16] (Reinforcement of microporous membrane by impregnation)
After dissolving 6 g of polyvinylidene fluoride resin (Kynar 741 manufactured by Arkema) in 21 g of dimethylformamide and adding 3 g of polyethylene glycol (PEG 600 manufactured by Wako), the solution that is the raw material of the microporous membrane was sufficiently stirred. Prepared by degassing.

  The nonwoven fabric prepared in Example 1 was placed on a glass plate, and after adding 6 ml of the solution, which is a raw material for the microporous membrane, to the nonwoven fabric per 10 cm length × 10 cm width, the thickness was 250 μm using a commercially available applicator. It applied uniformly so that it might become.

  After the coating, it was immersed in a poor solvent for 10 minutes to precipitate a polyvinylidene fluoride resin, and after drying, a composite film formed of polyvinylidene fluoride was obtained. As a result of measuring the Young's modulus of the obtained composite film, it was 1400 MPa.

  From these results, it was found that the nonwoven fabric for reinforcing a microporous membrane of the present invention can impart sufficient breaking strength without hindering the characteristics of the microporous membrane having a high porosity.

  The nonwoven fabric for reinforcing a microporous membrane of the present invention can be used as a reinforcing material for filters and separators.

Claims (5)

  A non-woven fabric for reinforcing a microporous membrane, comprising glass fibers having a fiber diameter of 3 to 12 μm and polyolefin fibers having a fiber diameter of 1 μm or more, and thermally bonded by the polyolefin fibers. A nonwoven fabric for reinforcing a microporous membrane having a rate of 45% or more.   The microporous membrane reinforcing nonwoven fabric according to claim 1, wherein the polyolefin fiber is at least one selected from the group consisting of fibril fibers and composite fibers.   The nonwoven fabric for microporous membrane reinforcement according to claim 1 or 2, wherein the nonwoven fabric for microporous membrane reinforcement has a Young's modulus of 300 to 2500 MPa (MD).   Content of glass fiber is 10-80 mass%, The nonwoven fabric for microporous film reinforcement of any one of Claims 1-3.   The nonwoven fabric for microporous membrane reinforcement according to any one of claims 1 to 4, wherein the microporous membrane has a porosity of 45% or more.