JP2011187346A - Base material for lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a base material for lithium ion secondary battery with reduced variations in its surface when complexed, little desquamation of a complex compound, and less generation of a wrinkle. <P>SOLUTION: The base material for lithium ion secondary battery consists of a nonwoven fabric containing synthetic resin short fibers and fibrillated lyocell fibers as essential components, wherein a ratio (MDs/CDs) of a tensile strength in the flow direction (MDs) to a tensile strength in a width direction (CDs) is 3.0 or smaller. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a base material for a lithium ion secondary battery that can be suitably used for a lithium ion secondary battery such as a lithium ion secondary battery or a lithium ion polymer secondary battery.

  With the recent spread of portable electronic devices and higher performance, secondary batteries having high energy density are desired. As this type of battery, a lithium ion secondary battery using an organic electrolyte (non-aqueous electrolyte) has attracted attention. This lithium ion secondary battery has an energy density of about 3.7 V, which is about three times that of an alkaline secondary battery, which is a conventional secondary battery, and thus has a high energy density. Since a water-based electrolyte cannot be used, a non-aqueous electrolyte having sufficient oxidation-reduction resistance is used. Since non-aqueous electrolytes are flammable, there is a risk of ignition and the like, and careful attention is paid to safety in their use. There are several possible cases of exposure to fire and other hazards, but overcharging is particularly dangerous.

  In order to prevent overcharging, current non-aqueous secondary batteries are charged at a constant voltage and a constant current, and the battery is equipped with a precise IC (protection circuit). The cost required for this protection circuit is large, and it is a factor that increases the cost of non-aqueous secondary batteries.

  When overcharging is prevented by the protection circuit, it is naturally assumed that the protection circuit does not operate well, and it is difficult to say that it is intrinsically safe. The current non-aqueous secondary battery has a protective circuit that breaks when overcharged, and is equipped with a safety valve / PTC element and a device with a thermal fuse function in order to safely destroy the battery when overcharged. ing. However, even if equipped with the above-mentioned means, depending on the overcharge conditions, the safety during overcharge is not guaranteed, and in fact, non-aqueous secondary battery ignition accidents Is still happening.

  As the separator, a film-like porous film made of a polyolefin such as polyethylene is often used. When the temperature inside the battery reaches around 130 ° C., it melts and closes the micropores, thereby transferring lithium ions. Although there is a thermal fuse function (shutdown function) that cuts off the current and shuts off the current, it is suggested that if the temperature further increases due to some situation, the polyolefin itself melts and short-circuits, causing a thermal runaway. In view of this, a heat-resistant separator that does not melt and shrink even at temperatures close to 200 ° C. has been developed.

  As heat-resistant separators, there are non-woven fabrics composed of polyester fibers, and non-woven fabrics in which aramid fibers, which are heat-resistant fibers, are blended with polyester-based fibers. References 1-3). On the other hand, for example, by laminating a nonwoven fabric composed of polyester fibers on a film-like porous film made of polyolefin, and for compounding by inclusion of filler particles in a nonwoven fabric or woven fabric, or by resin surface coating Examples of imparting heat resistance have been reported (for example, see Patent Documents 4 to 6). However, the non-woven fabric used as the base material has large pores, so pinholes are generated when it is combined by surface coating such as filler particles or resin, and the surface smoothness is low. There have been quality problems such as a large variation in the surface when composited by construction, and the composites such as filler particles and resin are liable to fall off.

JP 2003-123728 A JP 2007-317675 A JP 2006-19191 A JP 2005-293891 A JP 2005-536857 A JP 2007-157723 A

  An object of the present invention is to provide a base material for a lithium ion secondary battery in which the variation in the surface when combined is small, the composite is not easily dropped, and the generation of wrinkles is small.

As a result of earnest research to solve the above problems, the present inventor,
(1) It consists of a nonwoven fabric containing synthetic resin short fibers and fibrillated lyocell fibers as essential components, and the ratio (MDs / CDs) of the tensile strength (MDs) in the flow direction to the tensile strength (CDs) in the width direction is 3. A base material for a lithium ion secondary battery that is 0.0 or less,
(2) The base material for a lithium ion secondary battery according to (1), wherein the content of fibrillated lyocell fiber is 10 to 80% by mass of the nonwoven fabric,
(3) The base material for a lithium ion secondary battery according to the above (1), wherein the resin constituting the synthetic resin short fiber is at least one selected from polyester resins, acrylic resins, and polyolefin resins,
I found.

  The base material (1) for a lithium ion secondary battery of the present invention comprises a nonwoven fabric containing, as essential components, synthetic resin short fibers and fibrillated lyocell fibers, and has a tensile strength (MDs) in the flow direction and a tensile strength in the width direction. The ratio of strength (CDs) (MDs / CDs) is 3.0 or less. The fibrillated lyocell fiber is entangled with the synthetic resin short fiber, so that the surface smoothness is high and the denseness is excellent. Less likely to occur. Moreover, the fibrillated lyocell fiber present on the surface of the base material is firmly bound to the composite, whereby the composite can be further prevented from falling off. Furthermore, by making the ratio (MDs / CDs) of tensile strength (MDs) in the flow direction and tensile strength (CDs) in the width direction to 3.0 or less, the composite was made by surface coating such as filler particles or resin. It is possible to suppress the occurrence of wrinkles on the occasion and the accompanying omission of composites.

  The base material (2) for a lithium ion secondary battery in which the fibrillated lyocell fiber content is 10 to 80% by mass of the nonwoven fabric is more excellent in the denseness and uniformity required as a base material.

  In the base material (3) for the lithium ion secondary battery in which the resin constituting the synthetic resin short fiber is at least one selected from a polyester resin, an acrylic resin, and a polyolefin resin, the damage to the base material is further suppressed and wrinkles are reduced. It is possible to obtain a lithium ion secondary battery base material having a high suppression effect and excellent density.

  Hereinafter, the lithium ion secondary battery substrate of the present invention will be described in detail.

  The base material for a lithium ion secondary battery of the present invention is composed of a nonwoven fabric containing synthetic resin short fibers and fibrillated lyocell fibers as essential components, and has a tensile strength (MDs) in the flow direction and a tensile strength (CDs) in the width direction. ) Ratio (MDs / CDs) is 3.0 or less. The value of (MDs / CDs) is preferably 2.5 or less, more preferably 2.0 or less, in terms of suppressing wrinkles that occur when the composite is formed by surface coating such as filler particles or resin. It is. More preferably, it is 1.5 or less.

  The tensile strength according to the present invention is measured based on the method defined in JIS P 8113, and the ratio (MDs / CDs) of the tensile strength (MDs) in the flow direction to the tensile strength (CDs) in the width direction is It is calculated from the measurement result.

  “Lyocell” of fibrillated lyocell fiber is a term defined in ISO standards and Japanese JIS standards, and refers to “cellulose fibers obtained by spinning directly in an organic solvent without spinning through cellulose derivatives”. is there.

  Lyocell fibers are beater and dispersion equipment such as beaters, PFI mills, single disc refiners (SDR), double disc refiners (DDR), ball mills and dyno mills used to disperse and pulverize pigments, etc. Can be fibrillated. It is desirable to use lyocell fibers that are optimally fibrillated using these dispersing facilities.

  In the base material for a lithium ion secondary battery of the present invention, the content mass ratio of the synthetic resin short fiber and the fibrillated lyocell fiber is preferably 90/10 to 20/80, more preferably 80/20 to 30/70. 70/30 to 40/60 is more preferable. When the content ratio of the fibrillated lyocell fiber is less than 10% by mass, the density and uniformity are not improved, and the value of (MDs / CDs) may not be achieved. Moreover, when the content ratio of the fibrillated lyocell fiber exceeds 80% by mass, the base material may be damaged during the formation of the composite.

  In the present invention, the resins constituting the synthetic resin short fibers include polyolefin resins, polyester resins, polyvinyl acetate resins, ethylene-vinyl acetate copolymer resins, polyamide resins, acrylic resins, and polyvinyl chloride resins. Resin, polyvinylidene chloride resin, polyvinyl ether resin, polyvinyl ketone resin, polyether resin, polyvinyl alcohol resin, diene resin, polyurethane resin, phenol resin, melamine resin, furan resin, urea resin Examples thereof include resins, aniline resins, unsaturated polyester resins, alkyd resins, fluorine resins, and silicone resins. Among these, when a polyester resin, an acrylic resin, or a polyolefin resin is used, a base material for a lithium ion secondary battery having a high base material damage suppressing effect and excellent in denseness can be obtained.

  Examples of the polyester resin include polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, and polyethylene isophthalate. Among these, when using for the base material for lithium ion secondary batteries, the polyethylene terephthalate type | system | group excellent in heat resistance is preferable.

  Acrylic resin is made of 100% acrylonitrile polymer, and acrylonitrile is copolymerized with (meth) acrylic acid derivatives such as acrylic acid, methacrylic acid, acrylic ester, methacrylic ester, vinyl acetate, etc. And the like.

  Examples of the polyolefin resin include polypropylene, polyethylene, polymethylpentene, ethylene-vinyl alcohol copolymer, olefin copolymer and the like. From the viewpoint of heat resistance, polypropylene, polymethylpentene, ethylene-vinyl alcohol copolymer, olefin copolymer and the like can be mentioned.

  The synthetic resin short fiber may be a fiber (single fiber) made of a single resin, or may be a fiber (composite fiber) made of two or more kinds of resins. Moreover, the synthetic resin short fiber contained in the base material for lithium ion secondary batteries of the present invention may be one kind or a combination of two or more kinds.

  In the base material for a lithium ion secondary battery of the present invention, a heat-fusible short fiber that functions as a binder can be used as at least one kind of synthetic resin short fiber. Examples of heat-fusible short fibers include core-sheath type, eccentric type, split type, side-by-side type, sea-island type, orange type, multiple bimetal type composite fibers, or single component fibers (single fibers). However, it is particularly preferable to contain unstretched polyester-based short fibers and core-sheath type heat-fusible short fibers in which a non-heat-bonding component is disposed in the core and a heat-bonding component is disposed in the sheath. Unstretched polyester short fibers are suitable in terms of improving uniformity, and the core-sheath type heat-fusible short fibers are softened, melted or melted by wet heat while maintaining the fiber shape of the core. Since the fibers are thermally bonded to each other, it is suitable for bonding the fibers without impairing the dense structure of the base material. High mechanical strength can be obtained by softening, melting or wet-heat-dissolving the heat-fusible short fibers by heating or wet heat heating, and heat-bonding the fibers to each other. Therefore, the value of (MDs / CDs) is 3 0.0 or less, and the generation of wrinkles when combined by surface coating can be reduced.

  In the base material for a lithium secondary battery according to the present invention, the content of the heat-fusible short fibers is preferably 5 to 40% by mass, more preferably 8 to 35% by mass with respect to the nonwoven fabric. More preferably, it is 10-30 mass%. If the content is less than 5% by mass, the mechanical strength of the substrate may be reduced, and if it exceeds 40% by mass, the thermal dimensional stability may be reduced.

  The fineness of the synthetic resin short fiber is preferably 0.007 to 1.3 dtex, more preferably 0.02 to 1.1 dtex, and further preferably 0.04 to 0.8 dtex. When the fineness of the synthetic resin short fibers exceeds 1.3 dtex, the number of fibers in the thickness direction decreases, and thus the required denseness may not be ensured. Moreover, the unevenness | corrugation may become large and the surface at the time of compound | complexing by surface coating may have a big variation. When the fineness of the synthetic resin short fiber is less than 0.007 dtex, stable production of the fiber becomes difficult.

  The fiber length of the synthetic resin short fiber is preferably 1 mm or more and 7 mm or less, more preferably 1 mm or more and 5 mm or less, and further preferably 1 mm or more and 3 mm or less. If the fiber length exceeds 7 mm, the formation may be poor or the value of (MDs / CDs) may be greater than 3.0. On the other hand, when the fiber length is less than 1 mm, the mechanical strength of the base material becomes low, and the base material may be damaged during the composite.

  In the present invention, a paper strength enhancer can be used as an additive. As the paper strength enhancer that can be used, one or more selected from synthetic polymers, semi-synthetic polymers, vegetable gums and starches can be used, and amphoteric or cationic polyacrylamide resins are preferred. In particular, in the amphoteric polyacrylamide resin having both anionic and cationic functional groups, the cation part is self-adsorbed with the lyocell fiber, and the anion part is bonded to each other with the polyacrylamide, thereby binding more firmly. Moreover, since it has both an anion part and a cation part, it is hard to receive the influence of the pH change in a system, and since the coupling | bonding between fibers can be reinforced stably, an amphoteric polyacrylamide resin is preferable. By using a paper strength enhancer, not only can the tensile strength in the flow direction be improved, but also the tensile strength in the width direction can be greatly improved, and the value of (MDs / CDs) should be 3.0 or less. Is possible.

  Examples of the method for adding the paper strength enhancer to the base material for a lithium ion secondary battery in the present invention include a method for internal addition at the time of making a nonwoven fabric, a method for impregnation or coating, and the like.

  In this invention, the addition amount of a paper strength enhancer is 0.01-20 mass% in conversion of solid content with respect to the fibrillated lyocell fiber, Preferably it is 0.1-10 mass%. If it is less than 0.01% by mass, the required strength may not be obtained, and if it is more than 20% by mass, the strength may decrease. In addition, in the case of internal addition at the time of nonwoven fabric papermaking, the viscosity increases, and the papermaking property may be impaired or the uniformity may be lost due to aggregation.

As for the basic weight of the base material for lithium ion secondary batteries of this invention, 3.0-30.0g / m < ² > is preferable, 6.0-20.0g / m < ² > is more preferable, 8.0-12.0g / M ² is more preferable. In order to achieve the value of (MDs / CDs), it is preferable for increasing the basis weight, but when the basis weight exceeds 30.0 g / m ² , the base material alone will occupy the majority of the separator. This makes it difficult to obtain the effect of the composite. If it is less than 3.0 g / m ² , it will be difficult to obtain uniformity, and a large variation may occur on the composite surface. In addition, basic weight means the basic weight based on the method prescribed | regulated to JISP8124 (paper and paperboard-basic weight measuring method).

  4-45 micrometers is preferable, as for the thickness of the base material for lithium ion secondary batteries of this invention, 6-40 micrometers is more preferable, and 8-30 micrometers is more preferable. If it exceeds 45 μm, the base material alone will occupy the majority of the separator, and it will be difficult to obtain the effect of the composite, and if it is less than 4 μm, the strength of the base will be too low and the base will be The material may be damaged. In addition, thickness means the value measured by the method prescribed | regulated to JISB7502, ie, the value measured with the outside micrometer at the time of 5N load.

  In the base material for a lithium ion secondary battery of the present invention, as a method for producing a nonwoven fabric, a method in which a fiber web is formed and the fibers in the fiber web are bonded, fused, and entangled can be used. The obtained nonwoven fabric may be used as it is or may be used as a laminate comprising a plurality of sheets. Examples of the method for producing the fiber web include a dry method such as a card method and an air array method, a wet method such as a papermaking method, a spunbond method, and a melt blow method. Among these, the web obtained by a wet method is uniform and dense, and can be suitably used as a base material for a lithium ion secondary battery. In the wet method, the main fiber and the binder fiber are first uniformly dispersed in water to form a uniform papermaking slurry, and then passed through processes such as screen (removal of foreign matters, lumps, etc.), and the final fiber concentration is 0.01-0. The paper is adjusted to a concentration of 50% by mass and made. In order to obtain a more uniform nonwoven fabric, chemicals such as a dispersion aid, an antifoaming agent, a hydrophilic agent, and an antistatic agent may be added during the process. In order to obtain a fiber web, a paper machine having at least one of a wire net such as a circular net, a long net, and an inclined type can be used for the paper making slurry. In this papermaking process, the value of (MDs / CDs) can be reduced to 3.0 or less by adjusting the papermaking slurry concentration, flow velocity, J / W ratio, inclination angle, draw and the like.

  As a method for producing a nonwoven fabric from a fibrous web, a hydroentanglement method, a needle punch method, a binder adhesion method, or the like can be used. In particular, when the wet method is used with emphasis on uniformity, it is preferable to include a heat-fusible short fiber and bond the heat-fusible short fiber by a binder bonding method. A uniform nonwoven fabric is formed from a uniform web by the binder bonding method. It is preferable to apply pressure to the wet nonwoven fabric produced in this way with a calender or the like to adjust and make the thickness uniform. Further, the ratio of tensile strength can be controlled by adjusting the tension of the calendar, and the value of (MDs / CDs) can be made 3.0 or less. However, it is preferable to apply pressure at a temperature at which the heat-fusible short fibers do not form a film (a temperature lower by 20 ° C. or more than the melting point of the heat-fusible short fibers).

  The composite of the base material for a lithium ion secondary battery of the present invention is not particularly limited, but is laminated with a porous film, impregnated or coated with filler particles, impregnated or coated with a polymer resin. Etc.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a present Example. In the examples, all parts and percentages are by mass unless otherwise specified.

Example 1
30 parts of oriented and crystallized polyethylene terephthalate (PET) fibers with a fineness of 0.1 dtex and fiber length of 3 mm, 20 parts of unstretched PET heat-fusible short fibers with a fineness of 0.2 dtex and fiber length of 3 mm, fibrillated 50 parts of fibrillated lyocell fiber (fiber diameter 15 μm, fiber length 4 mm, manufactured by Coatles Co., Ltd.) and 50 parts of fibrillated lyocell fiber obtained by repeated treatment using a double disc refiner were mixed together. And a uniform slurry for papermaking (1% concentration) was prepared under stirring by an agitator. This slurry for papermaking is made up by a wet method using a circular net paper machine, and unstretched PET heat-fusible short fibers are adhered by a cylinder dryer at 120 ° C. to develop a nonwoven fabric strength. A non-woven fabric having a width of 9 g / m ² and a width of 50 cm was produced. Next, a super calendar process was performed to produce a nonwoven fabric having a basis weight of 10.9 g / m ² and a thickness of 17 μm, which was used as a base material for a lithium ion secondary battery.

Example 2
10 parts of oriented and crystallized polyethylene terephthalate (PET) short fibers with a fineness of 0.1 dtex and fiber length of 3 mm, 10 parts of unstretched PET heat-fusible short fibers with a fineness of 0.2 dtex and fiber length of 3 mm, fibrillated 80 parts of fibrillated lyocell fiber (fiber diameter 15 μm, fiber length 4 mm, manufactured by Coatles Co., Ltd.) and 50 parts of fibrillated lyocell fiber obtained by repeated treatment using a double disc refiner were mixed together, And a uniform slurry for papermaking (1% concentration) was prepared under stirring by an agitator. This slurry for papermaking is made up by a wet method using a circular net paper machine, and unstretched PET-based heat-fusible short fibers are adhered by a cylinder dryer at 120 ° C. to develop a nonwoven fabric strength. A nonwoven fabric of 1 g / m ² and a width of 50 cm was produced. Next, a super calendar process was performed to produce a nonwoven fabric having a basis weight of 11.1 g / m ² and a thickness of 18 μm, which was used as a base material for a lithium ion secondary battery.

Example 3
72 parts of oriented and crystallized polyethylene terephthalate (PET) short fibers with a fineness of 0.1 dtex and fiber length of 3 mm, 20 parts of unstretched PET heat-fusible short fibers with a fineness of 0.2 dtex and fiber length of 3 mm, fibrillated 8 parts of fibrillated lyocell fiber (fiber diameter 15 μm, fiber length 4 mm, manufactured by Coatles Co., Ltd.) and 50 parts of fibrillated lyocell fiber obtained by repeated treatment using a double disc refiner were mixed together. And a uniform slurry for papermaking (1% concentration) was prepared under stirring by an agitator. This slurry for papermaking is made up by a wet method using a circular net paper machine, and unstretched PET heat-fusible short fibers are adhered by a cylinder dryer at 120 ° C. to develop a nonwoven fabric strength. A nonwoven fabric having a width of 6 g / m ² and a width of 50 cm was produced. Next, a super calendar process was performed to produce a nonwoven fabric having a basis weight of 10.8 g / m ² and a thickness of 17 μm, which was used as a base material for a lithium ion secondary battery.

Example 4
5 parts of oriented and crystallized polyethylene terephthalate (PET) short fibers with a fineness of 0.1 dtex and fiber length of 3 mm, 10 parts of unstretched PET heat-fusible short fibers with a fineness of 0.2 dtex and fiber length of 3 mm, fibrillated 85 parts of fibrillated lyocell fiber (fiber diameter 15 μm, fiber length 4 mm, manufactured by Coatles Co., Ltd.) and 50 parts of fibrillated lyocell fiber obtained by repeatedly using a double disc refiner were mixed together, And a uniform slurry for papermaking (1% concentration) was prepared under stirring by an agitator. This slurry for papermaking is made up by a wet method using a circular net paper machine, and unstretched PET heat-fusible short fibers are adhered by a cylinder dryer at 120 ° C. to develop a nonwoven fabric strength. A nonwoven fabric having a width of 8 g / m ² and a width of 50 cm was produced. Next, a super calendar process was performed to produce a nonwoven fabric having a basis weight of 10.8 g / m ² and a thickness of 18 μm, which was used as a base material for a lithium ion secondary battery.

Example 5
50 parts of oriented and crystallized polyethylene terephthalate (PET) short fibers with a fineness of 0.1 dtex and fiber length of 3 mm, 40 parts of unstretched PET heat-fusible short fibers with a fineness of 0.2 dtex and fiber length of 3 mm, fibrillated 10 parts of fibrillated lyocell fiber (fiber diameter 15 μm, fiber length 4 mm, manufactured by Coatles Co., Ltd.) and 50 parts of fibrillated lyocell fiber obtained by repeated treatment using a double disc refiner were mixed together, And a uniform slurry for papermaking (1% concentration) was prepared under stirring by an agitator. This slurry for papermaking is made up by a wet method using a circular net paper machine, and unstretched PET heat-fusible short fibers are adhered by a cylinder dryer at 120 ° C. to develop a nonwoven fabric strength. A non-woven fabric having a width of 9 g / m ² and a width of 50 cm was produced. Next, a super calendar process was performed to produce a nonwoven fabric having a basis weight of 10.9 g / m ² and a thickness of 17 μm, which was used as a base material for a lithium ion secondary battery.

Example 6
30 parts of oriented and crystallized polyethylene terephthalate (PET) fibers with a fineness of 0.06 dtex and a fiber length of 3 mm, a fineness of 1.1 dtex, a fiber length of 5 mm, a core part of polyethylene terephthalate (melting point 253 ° C.) and a sheath part of polyethylene terephthalate -Double a polyester core-sheath type heat-sealable short fiber of isophthalate copolymer (softening point 75 ° C.), unfibrillated lyocell monofilament (fiber diameter 15 μm, fiber length 4 mm, manufactured by Coatles) 50 parts of fibrillated lyocell fiber obtained by repeated processing 50 times using a disc refiner are mixed together, disaggregated in pulper water, and stirred uniformly with an agitator to make a uniform papermaking slurry (1% concentration) ) Was prepared. This papermaking slurry is made up by a wet method using a circular paper machine, and a polyester core-sheath type heat-fusible short fiber is adhered by a cylinder dryer at 120 ° C. to develop a nonwoven fabric strength. A non-woven fabric having a width of 0.0 g / m ² and a width of 50 cm was prepared, and then heat-treated by being brought into contact with a hot roll having a diameter of 1.2 m heated to 200 ° C. at a speed of 20 m / min. Further, a super calender treatment was performed to produce a nonwoven fabric having a basis weight of 11.0 g / m ² and a thickness of 18 μm, which was used as a base material for a lithium ion secondary battery.

Example 7
Addition of amphoteric polyacrylamide resin paper strength enhancer (made by Arakawa Chemical Industry Co., Ltd., trade name: Polystron 1250) to the pulverized lyocell fiber to 5% by mass in solid content. After stirring, 30 parts of a polyethylene terephthalate (PET) short fiber having a fineness of 0.06 dtex and a fiber length of 3 mm, an unstretched PET heat-fusible short fiber having a fineness of 0.2 dtex and a fiber length of 3 mm 20 parts of fibrillated lyocell fiber (fiber diameter 15 μm, fiber length 4 mm, manufactured by Coatles Co., Ltd.) 50 parts repeatedly using a double disc refiner Mix, disaggregate in pulper water, and prepare a uniform papermaking slurry (1% concentration) with stirring by an agitator. It was. This slurry for papermaking is made up by a wet method using a circular net paper machine, and unstretched PET heat-fusible short fibers are adhered by a cylinder dryer at 120 ° C. to develop a nonwoven fabric strength. A nonwoven fabric having a width of 7 g / m ² and a width of 50 cm was produced. Next, a super calendar process was performed to produce a nonwoven fabric having a basis weight of 10.7 g / m ² and a thickness of 17 μm, which was used as a base material for a lithium ion secondary battery.

Example 8
Addition of amphoteric polyacrylamide resin paper strength enhancer (made by Arakawa Chemical Industry Co., Ltd., trade name: Polystron 1250) to the pulverized lyocell fiber to 5% by mass in solid content. After stirring, 30 parts of polyethylene terephthalate (PET) short fibers having a fineness of 0.06 dtex and a fiber length of 3 mm, a fineness of 1.1 dtex, a fiber length of 5 mm, and a core part of polyethylene terephthalate (melting point 253 ° C.) / 20 parts of a polyester core-sheath type heat-fusible short fiber whose sheath is a polyethylene terephthalate-isophthalate copolymer (softening point 75 ° C.), fibrillar lyocell monofilament (fiber diameter 15 μm, fiber length 4 mm, Coatles Fibrillation obtained by repeated treatment 50 times using a double disc refiner Were mixed lyocell fibers 50 parts together, is macerated in water pulper under agitation by agitator, to prepare a uniform sheet-forming slurry (1% concentration). The papermaking slurry is made up by a wet method using a circular paper machine, and the polyester core-sheath-type heat-fusible short fibers are adhered by a cylinder dryer at 120 ° C. to develop a nonwoven fabric strength. A non-woven fabric having a width of 7 g / m ² and a width of 50 cm was produced. Next, a super calendar process was performed to produce a nonwoven fabric having a basis weight of 10.7 g / m ² and a thickness of 17 μm, which was used as a base material for a lithium ion secondary battery.

Example 9
30 parts of polypropylene short fibers having a fineness of 0.1 dtex and a fiber length of 3 mm, 20 parts of unstretched PET heat-fusible short fibers having a fineness of 0.2 dtex and a fiber length of 3 mm, fibrillated lyocell single fiber (fiber diameter 15 μm, Fiber length of 4 mm, manufactured by Coatles Co., Ltd.) was mixed 50 parts of fibrillated lyocell fiber obtained by repeated treatment 50 times using a double disc refiner, disaggregated in water of a pulper, and stirred with an agitator. A uniform papermaking slurry (1% concentration) was prepared. This slurry for papermaking is made up by a wet method using a circular net paper machine, and unstretched PET heat-fusible short fibers are adhered by a cylinder dryer at 120 ° C. to develop a nonwoven fabric strength. A nonwoven fabric having a width of 5 g / m ² and a width of 50 cm was produced. Next, a super calendar process was performed to produce a nonwoven fabric having a basis weight of 10.5 g / m ² and a thickness of 17 μm, which was used as a base material for a lithium ion secondary battery.

Example 10
30 parts of acrylic short fibers having a fineness of 0.1 dtex and a fiber length of 3 mm, 20 parts of unstretched PET-based heat-fusible short fibers having a fineness of 0.2 dtex and a fiber length of 3 mm, unfibrillated lyocell single fiber (fiber diameter 15 μm, Fiber length of 4 mm, manufactured by Coatles Co., Ltd.) was mixed 50 parts of fibrillated lyocell fiber obtained by repeated treatment 50 times using a double disc refiner, disaggregated in water of a pulper, and stirred with an agitator. A uniform papermaking slurry (1% concentration) was prepared. This slurry for papermaking is made up by a wet method using a circular net paper machine, and unstretched PET heat-fusible short fibers are adhered by a cylinder dryer at 120 ° C. to develop a nonwoven fabric strength. A nonwoven fabric having a width of 6 g / m ² and a width of 50 cm was produced. Next, a super calendar process was performed to produce a nonwoven fabric having a basis weight of 10.6 g / m ² and a thickness of 17 μm, which was used as a base material for a lithium ion secondary battery.

Example 11
30 parts of nylon 66 short fiber having a fineness of 0.1 dtex and a fiber length of 3 mm, 20 parts of unstretched PET-based heat-fusible short fiber having a fineness of 0.2 dtex and a fiber length of 3 mm, fibrillated lyocell single fiber (fiber diameter 15 μm, Fiber length of 4 mm, manufactured by Coatles Co., Ltd.) was mixed 50 parts of fibrillated lyocell fiber obtained by repeated treatment 50 times using a double disc refiner, disaggregated in water of a pulper, and stirred with an agitator. A uniform papermaking slurry (1% concentration) was prepared. This slurry for papermaking is made up by a wet method using a circular net paper machine, and unstretched PET heat-fusible short fibers are adhered by a cylinder dryer at 120 ° C. to develop a nonwoven fabric strength. A nonwoven fabric having a width of 8 g / m ² and a width of 50 cm was produced. Next, a super calendar process was performed to produce a nonwoven fabric having a basis weight of 10.8 g / m ² and a thickness of 17 μm, which was used as a base material for a lithium ion secondary battery.

(Comparative Example 1)
40 parts of PET short fibers oriented and crystallized with a fineness of 0.06 dtex and fiber length of 3 mm, 20 parts of PET short fibers oriented and crystallized with a fineness of 0.1 dtex and a fiber length of 3 mm, fineness of 0.2 dtex, fiber length 40 parts of 3 mm unstretched PET heat-fusible short fibers were mixed together, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This slurry for papermaking is made up by a wet method using a circular net paper machine, and unstretched PET heat-fusible short fibers are adhered by a cylinder dryer at 120 ° C. to develop a nonwoven fabric strength. A non-woven fabric having a width of 9 g / m ² and a width of 50 cm was produced. Next, a super calendar process was performed to produce a nonwoven fabric having a basis weight of 10.9 g / m ² and a thickness of 18 μm, which was used as a base material for a lithium ion secondary battery.

(Comparative Example 2)
20 parts of PET short fibers oriented and crystallized with a fineness of 0.06 dtex and fiber length of 3 mm, 36 parts of PET short fibers oriented and crystallized with a fineness of 0.1 dtex and a fiber length of 3 mm, fineness of 0.2 dtex, fiber length 40 parts of 3 mm unstretched PET-based heat-fusible short fibers and non-fibrillated lyocell single fibers (fiber diameter 15 μm, fiber length 4 mm, manufactured by Coatles Co., Ltd.) are repeatedly processed 50 times using a double disc refiner. 4 parts of the fibrillated lyocell fibers thus obtained were mixed together, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This slurry for papermaking is made up by a wet method using a circular net paper machine, and unstretched PET-based heat-fusible short fibers are adhered by a cylinder dryer at 120 ° C. to develop a nonwoven fabric strength. A nonwoven fabric of 1 g / m ² and a width of 50 cm was produced. Next, a super calendar process was performed to produce a nonwoven fabric having a basis weight of 11.1 g / m ² and a thickness of 18 μm, which was used as a base material for a lithium ion secondary battery.

(Comparative Example 3)
100 parts of fibrillated lyocell fibers obtained by repeatedly treating unfibrillated lyocell monofilament (fiber diameter 15 μm, fiber length 4 mm, manufactured by Coatles Co., Ltd.) 50 times using a double disc refiner, The pulper was disaggregated in water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This papermaking slurry is made up by a wet method using a circular paper machine, and then super calendered to produce a nonwoven fabric with a basis weight of 10.8 g / m ² and a thickness of 18 μm. A battery substrate was obtained.

(Comparative Example 4)
80 parts of polypropylene short fibers with a fineness of 0.1 dtex and fiber length of 3 mm and 20 parts of unstretched PET heat-fusible short fibers with a fineness of 0.2 dtex and fiber length of 3 mm are mixed together and disaggregated in the pulper water. A uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This slurry for papermaking is made up by a wet method using a circular net paper machine, and unstretched PET heat-fusible short fibers are adhered by a cylinder dryer at 120 ° C. to develop a nonwoven fabric strength. A non-woven fabric having a width of 9 g / m ² and a width of 50 cm was produced. Next, a super calendar process was performed to produce a nonwoven fabric having a basis weight of 10.9 g / m ² and a thickness of 17 μm, which was used as a base material for a lithium ion secondary battery.

(Comparative Example 5)
80 parts of acrylic short fibers with a fineness of 0.1 dtex and a fiber length of 3 mm, 20 parts of unstretched PET heat-fusible short fibers with a fineness of 0.2 dtex and a fiber length of 3 mm are mixed together and disaggregated in water of a pulper. A uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This slurry for papermaking is made up by a wet method using a circular net paper machine, and unstretched PET-based heat-fusible short fibers are adhered by a cylinder dryer at 120 ° C. to develop a nonwoven fabric strength. A nonwoven fabric of 1 g / m ² and a width of 50 cm was produced. Next, a super calendar process was performed to produce a nonwoven fabric having a basis weight of 11.1 g / m ² and a thickness of 18 μm, which was used as a base material for a lithium ion secondary battery.

(Comparative Example 6)
80 parts of nylon 66 short fibers with a fineness of 0.1 dtex and fiber length of 3 mm are mixed together and 20 parts of unstretched PET-based heat-fusible short fibers with a fineness of 0.2 dtex and fiber length of 3 mm are mixed together and disaggregated in pulper water. A uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This slurry for papermaking is made up by a wet method using a circular net paper machine, and unstretched PET heat-fusible short fibers are adhered by a cylinder dryer at 120 ° C. to develop a nonwoven fabric strength. A nonwoven fabric having a width of 6 g / m ² and a width of 50 cm was produced. Next, a super calendar process was performed to produce a nonwoven fabric having a basis weight of 10.6 g / m ² and a thickness of 17 μm, which was used as a base material for a lithium ion secondary battery.

(Comparative Example 7)
45 parts of PET short fibers oriented and crystallized with a fineness of 0.06 dtex and fiber length of 3 mm, 40 parts of PET short fibers oriented and crystallized with a fineness of 0.1 dtex and a fiber length of 3 mm, fineness of 0.2 dtex, fiber length 15 parts of 3 mm unstretched PET heat-fusible short fibers were mixed together, disaggregated in pulper water, and a uniform papermaking slurry (1% concentration) was prepared under stirring by an agitator. This slurry for papermaking is made up by a wet method using a circular net paper machine, and unstretched PET heat-fusible short fibers are adhered by a cylinder dryer at 120 ° C. to develop a nonwoven fabric strength. A non-woven fabric having a width of 9 g / m ² and a width of 50 cm was produced. Next, a super calendar process was performed to produce a nonwoven fabric having a basis weight of 10.9 g / m ² and a thickness of 18 μm, which was used as a base material for a lithium ion secondary battery.

<Substrate measurement>
About the base material for lithium ion secondary batteries obtained by the Example and the comparative example, ratio (MDs / CDs) of the tensile strength (MDs) of the flow direction and the tensile strength (CDs) of the width direction is the tensile strength. Table 1 shows the results of measurement and calculation based on the method defined in P8113.

<Evaluation>
The following evaluation was performed about the base material for lithium ion secondary batteries obtained by the Example and the comparative example, and the result was shown in Table 1.

[Preparation of separator]
Plate boehmite (average particle size: 1 μm, aspect ratio: 10), 1000 g of N-methylpyrrolidone, and 375 g of polyvinylidene fluoride are placed in a container and stirred with a stirrer (trade name: Three-One Motor, Shinto Kagaku Co., Ltd.). The mixture was stirred and dispersed for 1 hour to obtain a uniform slurry. Each of the nonwoven fabrics of Examples and Comparative Examples was passed through the slurry, and after applying the slurry by pulling up, it was passed through a gap having a predetermined interval and then dried to obtain a porous material having a thickness of 3 μm per side. A separator having a membrane was obtained.

[Evaluation of substrate coatability]
Measure the thickness of any 10 locations on the separator, and if the difference is 0.8 μm or less, ◎, if it exceeds 0.8 μm and 1 μm or less, ○ if it exceeds 1 μm and 2 μm or less. Δ, if it exceeds 2 μm, it is indicated by ×. In addition, thickness means the value measured by the method prescribed | regulated to JISB7502, ie, the value measured by the outside micrometer at the time of 5N load.

[Separator wrinkle evaluation]
About the produced separator, the state of the separator when the sheet | seat of 200 mm x 3 m was wound around the polytetrafluoroethylene rod of diameter 10mm was confirmed visually, and it evaluated by the following degree.
A: Wrinkle is not generated when winding.
○: Some wrinkles are observed when winding, but no creases occur.
(Triangle | delta): Although generation | occurrence | production of a wrinkle is seen and it bends when it winds, peeling does not arise in the surface porous film.
X: Wrinkles are observed when winding, creases are generated, and peeling is observed on the porous film on the surface.

[Strength of substrate]
The base material of an Example and a comparative example was cut and aligned in 50 mm width strip shape. The test piece was mounted on a 40 mmφ fixed frame installed on a tabletop material testing machine (trade name: STA-1150, manufactured by Orientec Co., Ltd.), and the tip was rounded (curvature: 1.6) with a diameter of 1.0 mm. The metal needle (manufactured by Orientec Co., Ltd.) was lowered at a constant speed of 50 mm / min. The maximum load (g) at this time was measured and used as the puncture strength. Measure the puncture strength at five or more locations for one sample, and the smallest puncture strength among all the measured values is ◎ if it is 50 g or more, ○ if it is 40 g or more and less than 50 g, Δ if it is 30 g or more and less than 40 g, 30 g If it was less than, it represented by x.

[Existence of dropout]
The produced separator was cut into a strip of 50 mm width × 300 mm, and the state of the porous membrane when it was wound around a polytetrafluoroethylene rod having a diameter of 10 mm was visually confirmed and evaluated according to the following degree.
A: There is no change in the state of the porous membrane.
○: Cracks occur on the surface portion of the porous film, but no peeling occurs.
(Triangle | delta): Although the crack has spread over the whole thickness of the porous film, peeling has not arisen.
X: Peeling has occurred.

  The base material for lithium ion secondary batteries obtained in the examples is composed of a nonwoven fabric containing short synthetic resin fibers and fibrillated lyocell fibers, and has a tensile strength (MDs) in the flow direction and a tensile strength (CDs) in the width direction. ) Ratio (MDs / CDs) of 3.0 or less, it has a dense structure, a small variation in the surface when composited by surface coating, and good results of less wrinkling are obtained. It was.

  From the comparison of Examples 1 to 4, when the content of the fibrillated lyocell fiber is 10 to 80% by mass, the surface variation when combined by surface coating is small, the strength is high, and the porous membrane No dropout was confirmed. In Example 3 in which the content of the fibrillated lyocell fiber was less than 10% by mass, the surface variation tended to increase. In Example 4 in which the content of the fibrillated lyocell fiber exceeded 80% by mass, the strength was slightly decreased.

  From the comparison of Examples 1 and 9 to 11, when the resin constituting the synthetic resin short fiber is a polyester resin, an acrylic resin or a polyolefin resin, the variation in the surface when combined by surface coating is small, The strength was high, and no loss of the porous membrane was confirmed.

  On the other hand, the base materials for lithium ion secondary batteries obtained in Comparative Examples 1 and 4 to 6 do not contain fibrillated lyocell fibers, and the tensile strength (MDs) in the flow direction and the tensile strength (CDs) in the width direction. Since the ratio (MDs / CDs) was greater than 3.0, the surface was uneven, the strength was low, and the generation of wrinkles and the loss of the porous film were larger than in the examples.

  Although the base material for lithium ion secondary batteries obtained in Comparative Example 2 contains synthetic resin short fibers and fibrillated lyocell fibers, the tensile strength in the flow direction (MDs) and the tensile strength in the width direction (CDs) ) Ratio (MDs / CDs) is larger than 3.0, so that the generation of wrinkles was larger than that of the example.

  Moreover, since the base material for lithium ion secondary batteries obtained in Comparative Example 3 did not contain synthetic resin short fibers, the strength was low, and the degree of dropout of the porous membrane was greater than that of the examples. .

  Furthermore, the base material for lithium ion secondary batteries obtained in Comparative Example 7 has a ratio (MDs / CDs) of tensile strength (MDs) in the flow direction to tensile strength (CDs) in the width direction of 3.0 or less. However, since it did not contain fibrillated lyocell fiber, the surface was uneven, the strength was low, and the generation of wrinkles and the loss of the porous membrane were larger than in the examples.

  The base material for lithium ion secondary batteries of this invention can be used conveniently for lithium ion secondary batteries, such as a lithium ion secondary battery and a lithium ion polymer secondary battery.

Claims (3)

  It consists of a nonwoven fabric containing synthetic resin short fibers and fibrillated lyocell fibers as essential components, and the ratio (MDs / CDs) of tensile strength (MDs) in the flow direction to tensile strength (CDs) in the width direction is 3.0 or less. The base material for lithium ion secondary batteries characterized by the above-mentioned.   The base material for a lithium ion secondary battery according to claim 1, wherein the content of the fibrillated lyocell fiber is 10 to 80% by mass of the nonwoven fabric.   The base material for a lithium ion secondary battery according to claim 1, wherein the synthetic resin constituting the synthetic resin short fiber is at least one selected from a polyester resin, an acrylic resin, and a polyolefin resin.