JP4705335B2 - Separator for electronic parts and method for manufacturing the same - Google Patents

Description

  The present invention relates to a separator used for an electronic component, particularly a lithium ion secondary battery or a polymer lithium secondary battery, and a method for producing the same.

International Publication No. WO01 / 67536 JP 2003-317802 A Japanese Patent No. 2992598 JP 2002-42867 A JP2003-317893A.

  In recent years, regardless of industrial equipment and consumer equipment, demand for electrical / electronic equipment and development of hybrid vehicles has greatly increased demand for lithium-ion secondary batteries and polymer lithium secondary batteries, which are electronic components. These electric / electronic devices are steadily becoming smaller and more functional. Lithium ion secondary batteries and polymer lithium secondary batteries are also required to be smaller and more functional.

  The lithium ion secondary battery and the polymer lithium secondary battery are a positive electrode in which an active material, a lithium-containing oxide, and a binder such as polyvinylidene fluoride are mixed with 1-methyl-2-pyrrolidone to form a sheet on an aluminum current collector. A negative electrode formed by mixing a carbonaceous material capable of inserting and extracting lithium ions and a binder such as polyvinylidene fluoride with 1-methyl-2-pyrrolidone into a sheet on a copper current collector, and a porous electrolyte membrane, An electrode body formed by winding or laminating a positive electrode, an electrolyte membrane, and a negative electrode in this order is impregnated with a driving electrolyte and sealed with an aluminum case. Conventionally, polyolefin-based porous membranes and nonwoven fabrics such as polyvinylidene fluoride and polyethylene have been used as separators for the lithium ion secondary battery and polymer lithium secondary battery.

  By the way, since the lithium ion secondary battery and the polymer lithium secondary battery are miniaturized as described above, the separator is also required to be thin. However, when a conventional separator is made thin, an internal short circuit occurs between the positive electrode and the negative electrode, a shutdown effect that contributes to the safety of the battery cannot be realized, or driving that is necessary for driving electronic components In addition to the problem that the electrolytic solution cannot be sufficiently retained, problems such as a decrease in mechanical strength and a decrease in product reliability due to loss of workability and productivity in the manufacturing process occur. The shutdown here is a phenomenon in which when the temperature in the battery rises due to some abnormality, the fine pores of the separator are closed at around 140 ° C. to 150 ° C. and the current flow is stopped.

  Various proposals have been made for the purpose of solving these problems. For example, in Patent Document 1, it is possible to use, as a separator, a microporous film (stretched film) produced by stretching a polyolefin and having through holes formed by a needle or a laser with a relatively high air permeability value. Proposed. However, in such a separator, for example, when a polymer porous layer that swells in an electrolytic solution is provided around the separator, the porous body constituting the polymer porous layer includes pores having a large diameter of several μm or more. If this is the case, there is a problem that a short-circuit occurs in a portion where the large-diameter hole of the through-hole and the polymer porous layer communicates in the vertical direction of the separator, and even if the microporous membrane itself has a shutdown function In the normal use environment at room temperature, there is a problem that the electrical insulation, which is the original function of the separator, is lowered.

  Patent Document 2 proposes a separator in which a nonwoven fabric made of polyethylene terephthalate having a relatively low value of air permeability is used as a base, and a composite material that swells in an electrolyte solution such as vinylidene fluoride resin on the nonwoven fabric. As specific manufacturing methods, a wet film forming method in which a nonwoven fabric and a resin are combined in a state containing an electrolytic solution and a dry film forming method in which the composite is formed in a state not including an electrolytic solution are described. However, the separator described in Patent Document 2 does not sufficiently exhibit the shutdown effect that contributes to the safety of the battery. In addition, in the wet film formation method, the electrolyte is already impregnated into the porous composite membrane before assembling the battery. Therefore, when handling the composite membrane, moisture in the atmosphere is absorbed and the battery performance is deteriorated. In addition, there is a possibility that the electrolytic solution may volatilize in the step of drying the organic solvent, and there is a problem that the amount of the electrolytic solution contained in the battery cannot be maintained at a constant amount.

  On the other hand, as a dry film forming method, a resin, an organic solvent, and a plasticizer are made into a paint, applied onto a nonwoven fabric, dried, and then the plasticizer is extracted with an organic solvent having an affinity for the plasticizer. And a dope obtained by applying a melt comprising a plasticizer on a nonwoven fabric, forming by cooling, and then forming a porous film by extracting the plasticizer with an organic solvent, and a resin dissolved in the organic solvent Is disclosed in which a nonwoven fabric is impregnated and brought into contact with another organic solvent that has an affinity for an organic solvent but does not dissolve a resin, and phase-separated to obtain a porous membrane. However, although these methods reduce the quantitativeness of the electrolytic solution and the risk of water being mixed into the electrolytic solution, the method includes extraction of a plasticizer with a solvent and contact with an organic solvent. There is a problem that manufacturing efficiency decreases due to an increase in the number of processes. That is, the method of extracting and removing the plasticizer with an organic solvent has a relatively good affinity between the plasticizer and the resin, so that the extraction takes time and the production efficiency is poor. Further, in the method of extracting the plasticizer, the pores of the formed porous film tend to have a relatively small pore diameter, so that the value of air permeability becomes high and does not contribute to the improvement of battery performance. In addition, the pore structure is likely to be specific in the method of phase separation by substitution with another organic solvent having affinity with the organic solvent. In other words, a skin layer is formed on the surface layer, the number of openings is reduced, and a large void is formed inside the film, which may cause a problem that the film strength is lowered and a short circuit is caused.

  Also, for example, in Patent Document 3, a separator is manufactured by a wet film forming method in which a nonwoven fabric is laminated or embedded in a state where a vinylidene fluoride resin dope is cast on a release material and solidified in a non-solvent. Is disclosed. However, the separator obtained by such a method improves the above-mentioned problems such as uniformity of film thickness, but the pore diameter tends to be asymmetric on the front and back of the separator, and the porous structure is uniform. The problem of conversion is not improved. Moreover, the shutdown effect cannot be fully exhibited.

  When lithium batteries are overcharged, dendrite is generated, but in the case of lithium batteries using a conventional stretched membrane as a separator, the dendrite generated by overcharging penetrates the separator all at once, so This causes a sudden short circuit, which increases the temperature inside the battery, which is dangerous and harms the battery performance. In order to solve this problem, for example, Patent Document 4 proposes to use a separator in which polyvinylidene fluoride is encapsulated in a nonwoven fabric. In this battery, vinylidene fluoride is swollen by the electrolyte, and further, since there are many voids derived from the nonwoven fabric, fine dendrite grows and short-circuits between both electrodes at the initial stage of overcharging ( Short circuit due to fine dendrite), thereby suppressing battery temperature rise. However, there is a problem that an internal short circuit is very likely to occur when the separator is made thin by increasing the volume of the electrode in response to the need for increasing energy capacity.

  Patent Document 5 discloses that a composite film is mixed with a filler such as polyethylene (PE) particles to provide a shutdown function for the purpose of ensuring safety in an environment where the battery is abnormally heated and overcharged. Has been proposed. And specifically, it is described that it is impregnated and coated with a vinylidene fluoride resin-containing coating liquid on a nonwoven fabric to which PE fine particles are adhered, and then immersed in a solvent aqueous solution to solidify and remove the solvent. . However, in Patent Document 5, no consideration is given to the pore diameter of the separator to be formed, the content of fine particles, the relationship between the fine particles and the pore size, and a sufficient shutdown effect cannot be expected. Furthermore, in the manufacturing method described in Patent Document 5, since filler particles are added, if the pore diameter of the porous structure is reduced, the probability that the communication holes are blocked increases, and therefore the air permeability value is reduced. There is a problem that the battery performance rises and hinders battery performance. Further, when the solvent is extracted, there are cases where defects such as wrinkles may occur, and the uniformity of the film thickness is hindered.

  In the case of adopting the above-described method of extracting and removing the plasticizer with an organic solvent in order to produce a separator made of a composite film containing filler particles, the pores of the formed porous structure have a small pore size. Therefore, there is a problem that the communication hole is blocked by the filler particles. Also, in the case of a method of replacing the organic solvent with another solvent without using a plasticizer, because the voids inside the composite are likely to be large, even if filler particles such as polyethylene melt in a certain temperature range, There is a problem that the gap cannot be filled evenly and the shutdown function is not sufficiently exhibited. Therefore, when filler particles are included, the filler particles do not block the communication holes of the composite at normal temperature, and when melted, it is necessary to quickly fill the holes, and control of the pore size of the porous structure is very important. It has become a challenge.

  The present invention has been proposed in view of the above circumstances, and the object thereof is a thin film and high ion conductivity, but does not cause a short circuit, and has excellent workability and productivity. Another object of the present invention is to provide a separator for electronic parts that has high mechanical strength and also has a shutdown effect, and a method for manufacturing the same.

The separator for electronic parts of the present invention is a separator for electronic parts for a lithium ion secondary battery or a polymer lithium secondary battery comprising a fibrous sheet base material and a porous structure containing thermoplastic resin fine particles that melt upon heating. The average pore size of the pores of the porous structure is 0.1 to 15 μm, the fine particles are contained in the separator in the range of 1 to 50 g / m ² , and the primary average particle size of the fine particles is wherein Ri 1% to 95% in the range near the pore diameter, the porous structure is made of polyvinylidene fluoride, it communicates with the other surface from one surface of the separator a number of pores connected, vertical separator surface There is no pinhole-shaped vertical through hole in the direction, and the diameter of each pore is smaller than the thickness of the separator .

  The manufacturing method of the separator for electronic components of this invention is for manufacturing said separator for electronic components, Comprising: The 1st aspect contains the thermoplastic resin microparticles | fine-particles fuse | melted by heating on a resin film. A step of placing a fibrous sheet substrate, a step of applying a coating solution containing a vinylidene fluoride resin and its good solvent and poor solvent on the fibrous sheet substrate, and a formed coating layer The process of forming a porous structure on the surface and / or inside of the fibrous sheet base by removing the solvent by drying, and then the thermoplastic melted by heating the fibrous sheet base by removing the resin film Including a step of obtaining a separator composed of a porous structure containing resin fine particles, wherein the amount of water contained in the coating solution is 0.7% by weight or less as measured by the Karl Fischer method And butterflies. The second aspect is a step of coating a resin film with a coating solution containing a vinylidene fluoride resin and its good and poor solvents to form a coating layer, and thermoplastic resin fine particles that are melted by heating. A step of superimposing a fibrous sheet base material containing the coating layer on the coating layer, and then forming a porous structure on the surface and / or inside of the fibrous sheet base material by drying to remove the solvent, then A step of obtaining a separator composed of a fibrous sheet base material and a porous structure containing thermoplastic resin fine particles that are melted by heating by removing the resin film, and the amount of water contained in the coating liquid is determined by a Karl Fischer method It is characterized by being 0.7% by weight or less.

  In the present invention, the fibrous sheet base material is preferably a woven fabric, a nonwoven fabric or a mesh (mesh), and the nonwoven fabric preferably contains at least 1% by weight of fibers having a fiber diameter of 0.15 denier or less.

  Moreover, it is preferable that the thermoplastic resin fine particles melted by heating are made of polyethylene and / or polypropylene.

Hereinafter, the present invention will be described in detail.
In the separator for electronic parts of the present invention, the porous structure has a large number of pores, and the average pore diameter of the pores by the bubble point method needs to be in the range of 0.1 to 15 μm. More preferably, it exists in the range of 0.5-5 micrometers. When the average pore size is less than 0.1 μm, ion conductivity may be inhibited, which is not preferable. In addition, the impregnation property of the electrolytic solution tends to decrease, and growth with the above-described minute dendrite is inhibited. On the other hand, if the thickness exceeds 15 μm, a problem such as a short circuit occurs particularly when the separator is thinned. The average pore size was measured by a bubble point method using a polymeter manufactured by Seika Sangyo Co., Ltd.

  The fibrous sheet base material, which is one of the constituent materials of the separator for electronic parts of the present invention, is made of paper made of cellulose pulp, bast fibers such as cotton, cannabis, jute, leaf vein fibers such as manila hemp, etc. Recycled fiber such as paper, regenerated cellulose fiber such as rayon and cupra and regenerated protein fiber, semi-synthetic fiber such as cellulose acetate fiber and promix, nylon aramid fiber, polyethylene terephthalate fiber, polyester fiber, acrylic fiber, polyethylene and polypropylene, etc. Polyolefin fiber, polyvinyl alcohol fiber, polyvinyl chloride fiber, polyvinylidene chloride fiber, vinyl chloride fiber, polyurethane fiber, polyoxymethylene fiber, polytetrafluoroethylene fiber, polyparaphenylene benzbisthiazole fiber, polyimide fiber, Amide fibers, glass fibers, ceramic fibers, non-woven fabric made of metal fiber or the like, can be mentioned woven and net product (mesh).

  A nonwoven fabric can be manufactured using a well-known technique. That is, it can be produced by a wet method, a dry method, a dry pulp method, a spun bond method, a melt blow method, a flash spinning method, a tow opening method, or the like. The opening of the nonwoven fabric is preferably as small as possible for the purpose of preventing a short circuit. For that purpose, the fiber diameter of the fibers used for the nonwoven fabric is desirably as thin as possible. That is, in the present invention, it is preferable to contain at least 1% by weight, more preferably 5% by weight or more of fibers having a denier of 0.15 or less. When the fiber having a denier of 0.15 or less is less than 1% by weight, the effect of reducing the opening is reduced, which is not preferable. However, even when the opening of the nonwoven fabric is relatively large, the porous structure described later is combined with the nonwoven fabric. When the pore diameter of the pores of the body is small, it is possible to suppress the occurrence of a short circuit even if the fiber does not necessarily contain 0.15 denier or less.

  The film thickness of the fibrous sheet base material is not particularly specified, but among electronic components, particularly when used for lithium ion secondary batteries and polymer lithium secondary batteries, etc., in order to enable miniaturization, It is preferable that the thickness of the separator is selected to be 50 μm or less, particularly 5 to 30 μm. However, even if the film thickness of the separator is 50 μm or more, the film thickness can be sufficiently reduced by performing the press treatment. On the other hand, some electronic components other than those described above do not necessarily need to be a thin film, and the thickness of the separator may be 50 μm or more. In the case of use as a thick film, two or more thin film separators of 50 μm or less can be used in an overlapping manner.

  In the separator for electronic parts of the present invention, it is preferred that the surface and / or the inside of the fibrous sheet base material containing one or more kinds of particles contains a porous structure of vinylidene fluoride resin. For example, when the fibrous sheet substrate is a nonwoven fabric or a woven fabric, the vinylidene fluoride resin is held between the fibers in the nonwoven fabric or the woven fabric, and the fibrous sheet substrate is a mesh (mesh). In this case, the vinylidene fluoride resin is held between the meshes. The net-like material (mesh) here includes a film having a large number of through holes in a direction perpendicular to the film surface.

  In this case, the polyvinylidene fluoride held between the fibers in the nonwoven fabric or the woven fabric, or the vinylidene fluoride resin held between the meshes is in the form of a porous structure. Necessary because of its excellent conductivity, but in order to prevent internal short circuit, the porous structure needs to be connected from one side of the separator to the other side by the connection of a large number of pores. It is necessary that the pore diameter is smaller than the thickness of the separator. And it is necessary not to have a pinhole-like through-hole in the direction substantially perpendicular to the separator surface. Here, the through-hole means a portion that can be seen through from one of the surfaces of the separator when the other surface is viewed substantially vertically without being covered by the member constituting the separator. . A separator having such a through-hole tends to cause a short circuit, and thus may significantly impede charge / discharge performance.

  In the present invention, examples of the vinylidene fluoride resin contained on the surface and / or inside of the fibrous sheet base material include a vinylidene fluoride homopolymer or a copolymer containing vinylidene fluoride. The vinylidene fluoride homopolymer is obtained by addition polymerization reaction of vinylidene fluoride monomer. The polymerization methods include radical polymerization, cationic polymerization, anionic polymerization, light / radiation polymerization, suspension polymerization, emulsion polymerization, solution polymerization, Examples thereof include bulk polymerization. The copolymer containing vinylidene fluoride is a resin obtained by copolymerizing vinylidene fluoride and other monomers. Examples of the other monomers include olefinic monomers such as ethylene and propylene, vinyl fluoride, and 3 fluorine. Fluorinated monomers such as ethylene fluoride, ethyl trifluoride, tetrafluoroethylene, hexafluoropropylene, fluoroalkyl vinyl ether, carboxyl group-containing monomers such as monomethyl maleate and monomethyl citraconic acid, and allyl glycidin Examples thereof include an epoxy group-containing vinyl monomer such as ether and glycidyl crotonic acid ester. Among these, a copolymer composed of vinylidene fluoride and any one or more of ethylene tetrafluoride or propylene hexafluoride is particularly preferable.

The thermoplastic resin particles to melt by heating to the holding surface and / or inside of the fiber sheet substrate, it is necessary to be contained in a range of ^{1g / m 2 ~50g / m 2} , preferably 3 g / m ² or more 30 g / ^{m 2} is contained in the following amounts. If the content is less than 1 g / m ² , the shutdown effect that contributes to the safety of the battery cannot be obtained, and if it is more than 50 g / m ² , the thickness of the separator becomes too thick, or by inhibiting ion migration, Impedance increases. Further, it is preferable to use two or more kinds of fine particles to be held having different softening points.

  The thermoplastic resin fine particles that melt by heating are preferably polyethylene particles and polypropylene particles. The thermoplastic resin preferably has a softening point in the range of 110 to 180 ° C. The primary average particle diameter of these fine particles needs to be in the range of 1 to 95% of the average pore diameter of the pores in the porous structure. When the primary average particle size of the fine particles is smaller than 1% of the average pore size of the fine pores, the temperature inside the battery rises above the normal use temperature range, and the fine particles are melted to derive from the porous structure and the nonwoven fabric. Since it becomes difficult to close the opening, a problem occurs in maintaining safety. On the other hand, when it is larger than 95%, the openings derived from the porous structure and the non-woven fabric are narrowed, which inhibits various properties that affect the battery performance such as ionic conductivity, and the fine dendrites described above are fine particles. The growth of the battery may be hindered, and the advantage over the anti-overcharge characteristic cannot be obtained. That is, in the present invention, according to the average pore diameter of the pores of the porous structure, the primary particle diameter of the fine particles is set in the above range so as to create an appropriate gap between the porous structure and the porous structure. By doing so, it is possible to obtain a separator that does not hinder the generation of minute dendrites that are effective in preventing overcharge and the minute short circuit between the electrodes. In the present invention, the primary average particle diameter of the particles is an average value of sampling particles number n = 100 in the SEM photograph, where the average value of the long and short diameters of the particles is the particle diameter.

As described above, in the present invention, the average primary particle diameter of the fine particles, by designing a small above ranges than the average pore diameter of the pores of the porous structure, the porous structure at a temperature of normal use In addition, since the openings of the nonwoven fabric are not completely filled, battery performance equivalent to or higher than that of a conventional separator can be imparted. In the present invention, since the density of the separator can be increased by the presence of fine particles, it is usually used as compared with the case of a composite membrane separator composed only of a nonwoven fabric and a porous structure without conventional fine particles. Short circuit in the temperature range can be prevented, and the battery yield can be significantly improved. For example, when a composite membrane separator composed only of a conventional nonwoven fabric and a porous structure is thinned to about 20 μm or less, short-circuiting frequently occurs, but short-circuiting does not occur in the separator of the present invention.

  Next, the manufacturing method of the separator for electronic components of this invention is described. In the present invention, the porous structure is formed only by the coating method, and in the step of removing the solvent contained in the coated surface after the coating, a method such as solvent substitution with another solvent or extraction is not used. Thus, the separator can be formed by only one pass of the drying process. In the present invention, as described later, the resin is added to the coating solution together with at least a solvent that does not substantially dissolve the resin (poor solvent) and a solvent that substantially dissolves the resin (good solvent). By controlling the process conditions, it is possible to efficiently form a porous structure. The good solvent and the poor solvent include various solvents as will be described later. However, the combination of azeotropic or a large difference in drying temperature and vapor pressure increases the frequency of occurrence of through holes typified by pinholes. In addition, it is not preferable in terms of production efficiency. The difference in boiling point between the good solvent and the poor solvent is preferably 50 ° C. or less, particularly 30 ° C. or less, in view of production efficiency. If the temperature exceeds 50 ° C., the production process speed cannot be increased, and the drying energy increases, which is not preferable. In addition, when it exceeds 50 ° C., when drying conditions are set stepwise, instantaneous condition switching in the process direction becomes practically impossible, which is not suitable for mass production. .

  In the present invention, when preparing a separator containing polyethylene particles as fine particles, it is preferable to treat the particles under a temperature condition where the particles do not melt. However, many solvents capable of dissolving the vinylidene fluoride resin have a high boiling point. In practice, a heating temperature of 70 to 180 ° C. is required. For this reason, it is only necessary to finish the drying in as short a time as possible by increasing the drying speed and further increasing the process speed while performing the drying at an early stage. When the heating temperature is lower than 70 ° C., the drying efficiency is poor and the production efficiency is not increased. On the other hand, when the temperature exceeds 180 ° C., most of the fine particles are melted, which adversely affects the provision of the shutdown function. In general, drying conditions are set in stages, and it is preferable to dry the poor solvent after drying the good solvent first, in order to form a porous structure. If not azeotroped, both solvents do not necessarily have to be separated and dried. The drying is desirably performed by determining the drying conditions while appropriately controlling the porosity and the pore diameter of the porous structure. In the present invention, the combination of the solvent formulation, the drying temperature, and the air flow rate are appropriately selected as described above, thereby realizing both the optimization of the separator shutdown function and other battery performance and the improvement of the production efficiency. be able to. Further, in the present invention, it is not necessary to provide a process for removing a poor solvent and a residual solvent using a solvent as in the above prior art, and a porous structure optimal as a separator can be obtained by passing a drying process once after coating. Can be easily produced. Therefore, since the production efficiency is very good, it is possible to provide a large amount of inexpensive and high-quality separators.

  In the present invention, the coating liquid for forming the porous structure may contain at least two good solvents that dissolve the resin and at least one poor solvent that does not dissolve the resin. . Since it is important to reduce the viscosity of the coating solution to some extent from the handling properties of the coating solution, an auxiliary good solvent having a relatively low viscosity is used in combination with a main good solvent different from this, and the coating solution viscosity It is desirable to reduce Such an auxiliary good solvent may be selected in consideration of the above solvent viscosity, the drying balance with the poor solvent, and the azeotropic property of the solvents. The auxiliary good solvent in the present invention is not limited to one type, and may be used in plural types, and any non-poor solvent that does not substantially dissolve the resin can be used, and may be appropriately selected according to the above selection guidelines. .

  In the present invention, in a coating solution in which a vinylidene fluoride resin, a poor solvent, and the like are dissolved, when a highly hygroscopic solvent is used as the solvent, it is necessary to prevent moisture from being mixed in as much as possible. In the present invention, the coating solution needs to have a water content of 0.7% by weight or less, preferably 0.5% by weight or less, as measured by the Karl Fischer method. If the water content exceeds 0.7% by weight, gelation progresses early and the storage period of the coating solution becomes extremely short, or the film thickness of the porous structure formed becomes extremely uneven. When the thickness is thick, the pore size becomes extremely small due to gelation of the coating liquid due to water mixing, and the proportion of pore sizes less than 0.1 μm increases. Further, since gelation shrinks when solidified by drying of the solvent, the portion having a thin film thickness (non-gel portion) is pulled, and the ratio of the pore diameter exceeding 15 μm increases. And since the gel is a partial occurrence, the porous structure as a whole has a large number of pores, and as a result, the average pore size by the bubble point method is larger than 15 μm, and the primary average of the filler particles The particle size is lower than 1% of the pore size. Further, in the solidified portion of the gel, ion migration is locally reduced, so that the battery performance is lowered and the cycle characteristics are also adversely affected.

  In the 1st aspect of the manufacturing method of this invention, the fibrous sheet base material containing microparticles | fine-particles is mounted on the resin film, and the coating liquid which contains a vinylidene fluoride resin, its good solvent, and a poor solvent on it , And the formed coating layer is dried to remove the solvent, thereby forming a porous structure on the surface and / or inside of the fibrous sheet base material and integrating them. Then, the separator which consists of a porous structure containing a fibrous sheet base material and microparticles | fine-particles can be obtained by removing a resin film. Further, in the second aspect, a fibrous sheet base material containing fine particles, wherein a coating layer is formed by coating a coating film containing a vinylidene fluoride resin and its good and poor solvents on a resin film. Is laminated on the coating layer (wet lamination), and then dried to remove the solvent, thereby forming a porous structure on the surface and / or inside of the fibrous sheet substrate. Thereafter, by removing the resin film, a separator composed of a fibrous sheet base material and a porous structure containing fine particles can be obtained.

  In the present invention, any of the above methods is preferably used. For example, when the nonwoven fabric has a large porosity, the latter method is preferable. That is, in the former case, since the coating liquid is coated on the nonwoven fabric on the resin film, air tends to remain in the gaps between the fibers constituting the nonwoven fabric, which may be a coating defect. It is. However, since the former method can previously wrap the non-woven fabric coaxially with the resin film, there is no need for an unwinding mechanism for unwinding the non-woven fabric as in the latter method. Good manufacturing is possible. Therefore, in the case of a nonwoven fabric having a relatively low porosity and no problem in film formability, the former method is suitable. The porosity of the non-woven fabric should be determined with priority given to battery design, and the composite method of non-woven fabric may be appropriately selected according to the design requirements. In the latter method, for example, it is possible to produce a homogeneous separator without coating defects regardless of the porosity of the nonwoven fabric. If a manufacturing method is selected in consideration of various physical properties of a representative nonwoven fabric, a homogeneous separator can be manufactured.

  In the present invention, it is very important to use the resin film in the method of combining with the nonwoven fabric. The selection of the resin film affects the properties of the separator formed in relation to the affinity with the coating liquid applied on the resin film and the releasability from the formed porous structure. In this invention, it is preferable to select the resin film whose peeling strength with respect to a porous structure is 0.1-75 g / 20mm, More preferably, it is 0.1-40 g / 20mm. That is, a tape-shaped test piece obtained by cutting out the porous structure formed on the resin film after coating and drying to a width of 20 mm was prepared, and a part of the porous structure at the end portion was prepared on the test piece. It is obtained when peeling and fixing the end of the porous structure at the end and the other non-peeled end to the upper and lower chucks of Tensilon and measuring the tension at a speed of 50 mm / sec. The tensile load for peeling is measured at five points, and the average value divided by the width of 20 mm, which is the cutout width, is taken as the evaluation value as the peeling strength.

  In the present invention, the peel strength defined above is preferably 0.1 to 75 g / 20 mm, and more preferably 0.1 to 40 g / 20 mm. That is, particularly in the case of the method using the wet lamination of the second aspect, the coating liquid is applied onto the resin film before the non-woven fabric is combined as described above, but the peel strength of the resin film is 0.1 g / 20 mm. In the case of a resin film with relatively good releasability, such as less than, when the coating solution viscosity is low, the coated surface in a wet state immediately after coating is not stable, and the coating amount per unit area of the coating solution is It fluctuates between immediately after coating and until wet lamination is performed, and the weight per unit area of the porous structure varies in the surface direction of the separator. This phenomenon is essentially derived from the surface tension of the resin film. Apart from this, when the peel strength of the resin film is less than 0.1 g / 20 mm, the separator may peel off from the resin film in the drying step, which is not preferable. On the other hand, in the film having high adhesiveness exceeding 75 g / 20 mm, the above-mentioned fluctuation is not observed, but it is not preferable because it is difficult to efficiently peel and remove the separator from the resin film. On the other hand, in the manufacturing method according to the first aspect of the present invention, after the nonwoven fabric is placed on the resin film and stacked, the coating liquid is applied directly onto the nonwoven fabric. Since the coating liquid is entangled with the nonwoven fabric after coating, it does not flow easily, and even when the peel strength of the resin film is less than 0.1 g / 20 mm, there is no variation in the coating amount as described above. The separator may peel off from the resin film, which is not preferable. On the other hand, in the manufacturing method of the first aspect, when a resin film having a peel strength exceeding 75 g / 20 mm is used, it is difficult to efficiently peel and remove the separator from the resin film.

  Further, as another advantage of using a resin film having a peel strength in the above range, the following contents are important in controlling the pore diameter of the porous structure. That is, although it is common to any of the above composite methods, when the peel strength is designed to be in a low range close to 0.1 g / 20 mm, the pore diameter of the pore on the separator surface in contact with the resin film is the separator corresponding to the coating surface layer. In contrast, when designed in a high range close to 75 g / 20 mm, the pore diameter of the separator surface in contact with the resin film is smaller than that of the separator surface corresponding to the coating surface layer. . In addition, if it is less than 0.1 g / 20 mm, the pores on the separator surface on the side in contact with the resin film may be blocked, and if it exceeds 75 g / 20 mm, the pores on the separator surface corresponding to the coating surface layer may be blocked. It becomes easy. Although the cause of these phenomena is not necessarily clear, even when materials having different surface tensions of the nonwoven fabric are used, the same front and back asymmetry of the pore diameter occurs, and it is considered that the phenomenon is caused by the strength of the surface tension. Therefore, in the present invention, even if the material of the nonwoven fabric is fixed due to the demand from the battery design, the symmetry of the pore diameter on both the front and back surfaces of the separator including the porous structure composited with the nonwoven fabric is the same as the surface property of the resin film. It becomes possible to control. In other words, in the present invention, the symmetry of the pore diameter can be controlled by setting the peel strength of the resin film as compared with the conventional case where the pore diameter symmetry of the pores on the front and back surfaces cannot always be controlled by the material of the nonwoven fabric. Control is possible.

  As described above, the separator for electronic parts of the present invention has a mechanical strength that does not impair workability and productivity even if it is a thin film and has high ion conductivity, and lithium ion using the separator. The secondary battery and the polymer lithium secondary battery do not cause an internal short circuit and have high safety against overcharge due to a shutdown effect.

  Hereinafter, the separator of the present invention will be described with an example of the production method thereof. However, the method of producing the separator of the present invention is not limited to this, and the separator of the present invention is produced by other production methods. It is possible.

  In the separator for electronic parts of the present invention, the vinylidene fluoride resin is contained inside the fibrous sheet base material, and in order to obtain such a separator for electronic parts, a thermoplastic that melts by heating. The resin fine particle is included in the fibrous sheet base material, and then applied to the fibrous sheet base material superposed on the resin film and then dried or coated with a solution containing a good solvent and a poor solvent of vinylidene fluoride resin. Apply a solution containing a good solvent and a poor solvent of vinylidene fluoride resin to the material and then dry, or impregnate a fibrous sheet base material with a solution containing the good solvent and the poor solvent of vinylidene fluoride resin and dry Can be obtained.

  The separator for electronic parts of the present invention includes a porous structure of vinylidene fluoride resin inside the fibrous sheet base material, and a vinylidene fluoride resin on one or both sides of the fibrous sheet base material. A film made of a porous structure may be formed.

  The separator is manufactured as follows. First, a vinylidene fluoride resin is added to a solvent. As the solvent, a solvent capable of dissolving the vinylidene fluoride resin (hereinafter referred to as “good solvent”) must be selected. Examples of the good solvent include N, N-dimethylacetamide, N, N-dimethylformamide, 1-methyl-2-pyrrolidone, N, N-dimethylsulfoxide and the like. The dispersion and dissolution of the vinylidene fluoride resin can be performed using a commercially available stirrer. Since the vinylidene fluoride resin is easily dissolved in the above-exemplified good solvent at room temperature, it is not particularly necessary to heat it for dissolution. Thereafter, a solvent in which the vinylidene fluoride resin does not dissolve (hereinafter referred to as “poor solvent”) is further added and mixed. As the poor solvent, a solvent having a boiling point higher than that of the good solvent is selected. Examples of the poor solvent include dibutyl phthalate, ethylene glycol, diethylene glycol, glycerin and the like. The concentration of the vinylidene fluoride resin in the coating solution can be appropriately set in consideration of the characteristics of the obtained separator.

  On the other hand, the fibrous sheet base material contains thermoplastic resin fine particles that melt by heating in advance by a method such as spraying. Next, the fibrous sheet base material is placed on and superposed on the resin film, and the obtained vinylidene fluoride resin-containing coating solution is applied onto the fibrous sheet base material. Examples of the resin film include resin films such as polypropylene and polyethylene terephthalate. The resin film may be subjected to a surface treatment such as a mold release treatment or an easy adhesion treatment. As a resin film, what has a softness | flexibility is preferable since it also has the function of the surface protective film of the separator for electronic components. In addition, when a resin film having flexibility is used, after the following drying process, it is possible to wind up and store and transport the laminate in a state where the separator for electronic parts is held on the resin film. Therefore, it is preferable.

  Examples of the method for applying the vinylidene fluoride resin on the fibrous sheet base material include application or casting by dip coating, spray coating, roll coating, doctor blade method, gravure coating, screen printing, etc. be able to. As a result, the vinylidene fluoride resin enters the inside of the fibrous sheet base material. Next, the solvent is evaporated by drying from the coated material containing the vinylidene fluoride resin on the coated fibrous sheet substrate to form a porous structure. The obtained separator can be peeled from the resin film to obtain the electronic component separator of the present invention.

  Although the Example of the separator for electronic components of this invention is described below, this invention is not limited to a following example. The average pore diameter was measured by the bubble point method on both the surface where the separator and the resin film were not in direct contact with each other and the surface where the separator was in contact. The pore size distribution in the thickness direction was observed with an electron microscope. In addition, the average pore diameter of the porous structure in the present invention was controlled by appropriately selecting the adjustment of the coating liquid, drying conditions, and pressing conditions.

A vinylidene fluoride homopolymer having a weight average molecular weight of 300,000 is dissolved in 1-methyl-2-pyrrolidone and dimethylacetamide (good solvent), dibutyl phthalate (poor solvent) is added, and the vinylidene fluoride homopolymer component is 10 weights The coating liquid adjusted so that it might become% was obtained. When the amount of water contained in this solution was measured by the Karl Fischer method, it was 0.6% by weight. Next, on the resin film surface made of polyethylene terephthalate, a 10 μm thick nonwoven fabric made of polyethylene terephthalate fiber was used to hold 1 g / m ² of polyethylene particles having a particle size of 5 μm and a softening point of 113 ° C. And the said coating liquid was apply | coated to the nonwoven fabric by the casting method. Next, the solvent in the coating solution contained in the nonwoven fabric is evaporated by heat, and the resin film is peeled off, whereby an electron having a thickness of 20 μm having a porous structure of vinylidene fluoride homopolymer between the nonwoven fabric fibers. A separator for parts was obtained. The peel strength of the resin film with respect to the porous structure was 15 g / 20 mm.

  When this electronic component separator was observed with an electron microscope, there were no through holes such as pinholes, and the porous structure was connected to one side of the separator from the other side by a large number of pores. The average pore diameter of each pore was smaller than the thickness of the separator. Moreover, the inclination of the pore diameter distribution was not recognized in the thickness direction of the separator, and it was confirmed that the porous structure was homogeneous in the thickness direction. The average pore size of the pores of the porous structure measured by the bubble point method was 6.0 μm, and it was confirmed that the primary average particle size of the polyethylene particles was 83.3% with respect to the pore size of the pores. did.

A vinylidene fluoride homopolymer having a weight average molecular weight of 300,000 is dissolved in 1-methyl-2-pyrrolidone and dimethylacetamide (good solvent), dibutyl phthalate (poor solvent) is added, and the vinylidene fluoride homopolymer component is 5 wt. The coating liquid adjusted so that it might become% was obtained. When the amount of water contained in this coating solution was measured by the Karl Fischer method, it was 0.65% by weight. Next, on a resin film surface made of polyethylene terephthalate, a polyethylene particle having a particle size of 1 μm and a softening point of 113 ° C. and a polyethylene particle having a particle size of 1 μm and a softening point of 132 ° C. on a 10 μm thick nonwoven fabric made of polyethylene terephthalate fiber in advance. Was kept at 15 g / m ² , and the coating solution was applied onto the nonwoven fabric by the casting method. Next, the solvent in the coating liquid contained inside the nonwoven fabric was evaporated by heat, and the resin film was peeled off to obtain a composite membrane having a porous structure of vinylidene fluoride homopolymer between the nonwoven fabric fibers. This was pressed to obtain a separator for electronic parts of the present invention having a thickness of 10 μm. The peel strength of the resin film with respect to the porous structure was 0.5 g / 20 mm.

  When this electronic component separator was observed with an electron microscope, there were no through holes such as pinholes, and the porous structure was connected to one side of the separator from the other side by a large number of pores. The pore diameter of each pore was smaller than the thickness of the separator. Further, almost no inclination of the pore size distribution was observed in the thickness direction of the separator. When the average pore diameter of the pores was measured by the bubble point method and found to be 2.1 μm, it was confirmed that the primary average particle diameter of the polyethylene particles was 47.6% with respect to the pore diameter of the pores.

A vinylidene fluoride homopolymer having a weight average molecular weight of 500,000 is dissolved in 1-methyl-2-pyrrolidone and dimethylacetamide (good solvent), dibutyl phthalate (poor solvent) is added, and the vinylidene fluoride homopolymer component is 5 weights The coating liquid adjusted so that it might become% was obtained. The amount of water contained in this coating solution was measured by the Karl Fischer method and found to be 0.5% by weight. Next, polyethylene particles having a particle size of 3 μm and a softening point of 113 ° C. and polypropylene particles having a particle size of 3 μm and a softening point of 148 ° C. on a 10 μm-thick non-woven fabric made of polyethylene terephthalate fiber in advance on the resin film surface made of polyethylene terephthalate. What was kept at 30 g / m ² was placed, and the coating solution was applied onto the nonwoven fabric by the casting method. Next, the solvent in the coating liquid contained inside the nonwoven fabric was evaporated by heat, and the resin film was peeled off to obtain a composite membrane having a porous structure of vinylidene fluoride homopolymer between the nonwoven fabric fibers. This was pressed to obtain a separator for electronic parts having a thickness of 25 μm. The peel strength of the resin film with respect to the porous structure was 65 g / 20 mm.

  When this electronic component separator was observed with an electron microscope, there were no through holes such as pinholes, and the porous structure was connected to one side of the separator from the other side by a large number of pores. The pore diameter of each pore was smaller than the thickness of the separator. No inclination of the pore size distribution was observed in the thickness direction of the separator, and it was confirmed that the porous structure was homogeneous in the thickness direction. When the average pore diameter of the pores was measured by the bubble point method and found to be 4.2 μm, it was confirmed that the primary average particle diameter of the polyethylene particles was 71.4% with respect to the pore diameter of the pores.

A vinylidene fluoride homopolymer having a weight average molecular weight of 200,000 is dissolved in 1-methyl-2-pyrrolidone and dimethylacetamide (good solvent), dibutyl phthalate (poor solvent) is added, and the vinylidene fluoride homopolymer component is 8 weights The coating liquid adjusted so that it might become% was obtained. The amount of water contained in this coating solution was measured by the Karl Fischer method and found to be 0.5% by weight. Next, a polyethylene film having a particle size of 3 μm and a softening point of 132 ° C. and a polypropylene particle having a particle size of 3 μm and a softening point of 148 ° C. on a 10 μm-thick non-woven fabric made of polyethylene terephthalate fiber are formed on the resin film surface made of polyethylene terephthalate. Of 5 g / m ² was placed, and the coating solution was applied onto the nonwoven fabric by the casting method. Next, the solvent in the coating liquid contained inside the nonwoven fabric was evaporated by heat, and the resin film was peeled off to obtain a composite membrane having a porous structure of vinylidene fluoride homopolymer between the nonwoven fabric fibers. This was pressed to obtain a separator for electronic parts having a thickness of 27 μm. The peel strength of the resin film with respect to the porous structure was 17 g / 20 mm.

  When this electronic component separator was observed with an electron microscope, there were no through holes such as pinholes, and the porous structure was connected to one side of the separator from the other side by a large number of pores. The pore diameter of each pore was smaller than the thickness of the separator. Moreover, the inclination of the pore diameter distribution was not recognized in the thickness direction of the separator, and it was confirmed that the porous structure was homogeneous in the thickness direction. When the average pore diameter of the pores was measured by the bubble point method and found to be 4.8 μm, it was confirmed that the primary average particle diameter of the polyethylene particles and the polypropylene particles was 62.5% with respect to the pore diameter of the pores. .

A vinylidene fluoride homopolymer having a weight average molecular weight of 300,000 is dissolved in 1-methyl-2-pyrrolidone and dimethylacetamide (good solvent), dibutyl phthalate (poor solvent) is added, and the vinylidene fluoride homopolymer component is 10 weights The coating liquid adjusted so that it might become% was obtained. The amount of water contained in this coating solution was measured by the Karl Fischer method and found to be 0.51% by weight. Next, on a resin film surface made of polyethylene terephthalate, polyethylene particles having a particle size of 0.5 μm and a softening point of 132 ° C. were held at 10 g / m ² in a 15 μm-thick nonwoven fabric made of polyethylene terephthalate fibers. The solution was placed on the nonwoven fabric by a casting method. Next, the solvent in the coating liquid contained inside the nonwoven fabric was evaporated by heat, and the resin film was peeled off to obtain a composite membrane having a porous structure of vinylidene fluoride homopolymer between the nonwoven fabric fibers. This was subjected to press treatment to obtain an electronic component separator having a thickness of 15 μm. The peel strength of the resin film with respect to the porous structure was 16 g / 20 mm.

  When this electronic component separator was observed with an electron microscope, there were no through holes such as pinholes, and the porous structure was connected to one side of the separator from the other side by a large number of pores. The pore diameter of each pore was smaller than the thickness of the separator. Moreover, the inclination of the pore diameter distribution was not recognized in the thickness direction of the separator, and it was confirmed that the porous structure was homogeneous in the thickness direction. When the average pore diameter of the pores was measured by the bubble point method and found to be 1.5 μm, it was confirmed that the primary average particle diameter of the polyethylene particles was 33.3% with respect to the pore diameter of the pores.

A vinylidene fluoride homopolymer having a weight average molecular weight of 500,000 is dissolved in 1-methyl-2-pyrrolidone and dimethylacetamide (good solvent), dibutyl phthalate (poor solvent) is added, and the vinylidene fluoride homopolymer component is 8 weights The coating liquid adjusted so that it might become% was obtained. When the amount of water contained in this coating solution was measured by the Karl Fischer method, it was 0.41% by weight. Next, a polyethylene film having a particle size of 5 μm and a softening point of 113 ° C. and a polypropylene particle having a particle size of 9 μm and a softening point of 148 ° C. on a non-woven fabric having a thickness of 15 μm previously made of polyethylene terephthalate fibers on the resin film surface made of polyethylene terephthalate Was kept at 8 g / m ² , and the coating solution was applied onto the nonwoven fabric by a casting method. Next, the solvent in the coating liquid contained inside the nonwoven fabric was evaporated by heat, and the resin film was peeled off to obtain a composite membrane having a porous structure of vinylidene fluoride homopolymer between the nonwoven fabric fibers. This was pressed to obtain a separator for electronic parts having a thickness of 20 μm. In addition, the peeling strength with respect to the porous structure of the resin film was 13 g / 20 mm.

  When this electronic component separator was observed with an electron microscope, there were no through holes such as pinholes, and the porous structure was connected to one side of the separator from the other side by a large number of pores. The pore diameter of each pore was smaller than the thickness of the separator. Moreover, the inclination of the pore diameter distribution was not recognized in the thickness direction of the separator, and it was confirmed that the porous structure was homogeneous in the thickness direction. The average pore diameter of the pores measured by the bubble point method was 10.5 μm, so the primary average particle diameters of the polyethylene particles and the polypropylene particles were 47.6% and 85.7% with respect to the pore diameters of the pores, respectively. It was confirmed that.

A vinylidene fluoride homopolymer having a weight average molecular weight of 200,000 is dissolved in 1-methyl-2-pyrrolidone and dimethylacetamide (good solvent), dibutyl phthalate (poor solvent) is added, and the vinylidene fluoride homopolymer component is 8 weights The coating liquid adjusted so that it might become% was obtained. The amount of water contained in this coating solution was measured by the Karl Fischer method and found to be 0.45% by weight. Next, on a resin film surface made of polyethylene terephthalate, polyethylene particles having a particle size of 12 μm and a softening point of 132 ° C. and polypropylene particles having a particle size of 1 μm and a softening point of 148 ° C. on a non-woven fabric having a thickness of 15 μm previously made of polyethylene terephthalate fibers Was kept at 3 g / m ² , and the solution was applied onto the nonwoven fabric by a casting method. Next, the solvent in the solution contained in the nonwoven fabric was evaporated by heat, and the resin film was peeled off to obtain a composite membrane having a porous structure of vinylidene fluoride homopolymer between the nonwoven fabric fibers. This was pressed to obtain a separator for electronic parts having a thickness of 18 μm. The peel strength of the resin film with respect to the porous structure was 18 g / 20 mm.

  When this electronic component separator was observed with an electron microscope, there were no through holes such as pinholes, and the porous structure was connected to one side of the separator from the other side by a large number of pores. The pore diameter of each pore was smaller than the thickness of the separator. Moreover, the inclination of the pore diameter distribution was not recognized in the thickness direction of the separator, and it was confirmed that the porous structure was homogeneous in the thickness direction. The average pore diameter of the separator measured by the bubble point method was 14.1 μm, so the primary average particle diameters of the polyethylene particles and the polypropylene particles were 85.1% and 7.1 respectively with respect to the pore diameter. %.

A vinylidene fluoride homopolymer having a weight average molecular weight of 500,000 is dissolved in 1-methyl-2-pyrrolidone and dimethylacetamide (good solvent), dibutyl phthalate (poor solvent) is added, and the vinylidene fluoride homopolymer component is 5 weights The coating liquid adjusted so that it might become% was obtained. When the amount of water contained in this coating solution was measured by the Karl Fischer method, it was 0.48% by weight. Next, a polyethylene film having a particle size of 0.5 μm and a softening point of 113 ° C. and a particle size of 5 μm and a softening point of 148 ° C. on a 20 μm-thick nonwoven fabric made of polyethylene terephthalate fiber in advance on the resin film surface made of polyethylene terephthalate The polypropylene particles held at 50 g / m ² were placed, and the coating solution was applied onto the nonwoven fabric by a casting method. Next, the solvent in the coating liquid contained inside the nonwoven fabric was evaporated by heat, and the resin film was peeled off to obtain a composite membrane having a porous structure of vinylidene fluoride homopolymer between the nonwoven fabric fibers. This was pressed to obtain a separator for electronic parts having a thickness of 25 μm. The peel strength of the resin film with respect to the porous structure was 21 g / 20 mm.

  When this electronic component separator was observed with an electron microscope, there were no through holes such as pinholes, and the porous structure was connected to one side of the separator from the other side by a large number of pores. The pore diameter of each pore was smaller than the thickness of the separator. Moreover, the inclination of the pore diameter distribution was not recognized in the thickness direction of the separator, and it was confirmed that the porous structure was homogeneous in the thickness direction. The average pore diameter of the pores measured by the bubble point method was 5.9 μm, so the primary average particle diameters of the polyethylene particles and the polypropylene particles were 8.5% and 84.7, respectively, with respect to the pore diameter of the pores. %.

A vinylidene fluoride homopolymer having a weight average molecular weight of 300,000 is dissolved in 1-methyl-2-pyrrolidone and dimethylacetamide (good solvent), dibutyl phthalate (poor solvent) is added, and the vinylidene fluoride homopolymer component is 5 wt. The coating liquid adjusted so that it might become% was obtained. The amount of water contained in this coating solution was measured by the Karl Fischer method and found to be 0.39% by weight. Next, a polyethylene film having a particle size of 3 μm and a softening point of 113 ° C. and a polypropylene particle having a particle size of 3 μm and a softening point of 148 ° C. on a 20 μm-thick non-woven fabric made of polyethylene terephthalate fiber in advance on the resin film surface made of polyethylene terephthalate Was held at 3 g / m ² , and the coating solution was applied onto the nonwoven fabric by the casting method. Next, the thickness of the composite film having a porous structure of vinylidene fluoride homopolymer between the nonwoven fabric fibers by evaporating the solvent in the coating solution contained in the nonwoven fabric by heat and peeling the resin film Obtained a separator for electronic parts having a thickness of 28 μm. The peel strength of the resin film with respect to the porous structure was 16 g / 20 mm.

  When this electronic component separator was observed with an electron microscope, there were no through holes such as pinholes, and the porous structure was connected to one side of the separator from the other side by a large number of pores. The pore diameter of each pore was smaller than the thickness of the separator. Moreover, the inclination of the pore diameter distribution was not recognized in the thickness direction of the separator, and it was confirmed that the porous structure was homogeneous in the thickness direction. The average pore diameter of the pores measured by the bubble point method was 4.6 μm, and it was confirmed that the primary average particle diameters of the polyethylene particles and the polypropylene particles were 65.2% of the pore diameters of the pores, respectively. did.

A vinylidene fluoride homopolymer having a weight average molecular weight of 200,000 is dissolved in 1-methyl-2-pyrrolidone and dimethylacetamide (good solvent), dibutyl phthalate (poor solvent) is added, and the vinylidene fluoride homopolymer component is 5 wt. The coating liquid adjusted so that it might become% was obtained. The amount of water contained in this coating solution was measured by the Karl Fischer method and found to be 0.54% by weight. Next, a polyethylene film having a particle size of 5 μm and a softening point of 113 ° C. and a polyethylene particle having a particle size of 5 μm and a softening point of 132 ° C. on a 20 μm-thick non-woven fabric made of polyethylene terephthalate fiber on the resin film surface made of polyethylene terephthalate. Of 10 g / m ² was placed, and the coating solution was applied onto the nonwoven fabric by the casting method. Next, the solvent in the coating liquid contained inside the nonwoven fabric was evaporated by heat, and the resin film was peeled off to obtain a composite membrane having a porous structure of vinylidene fluoride homopolymer between the nonwoven fabric fibers. This was pressed to obtain a separator for electronic parts having a thickness of 30 μm. The peel strength of the resin film with respect to the porous structure was 17 g / 20 mm.

  When this electronic component separator was observed with an electron microscope, there were no through holes such as pinholes, and the porous structure was connected to one side of the separator from the other side by a large number of pores. The pore diameter of each pore was smaller than the thickness of the separator. Moreover, the inclination of the pore diameter distribution was not recognized in the thickness direction of the separator, and it was confirmed that the porous structure was homogeneous in the thickness direction. When the average pore diameter of the pores was measured by the bubble point method, it was 6.3 μm. Therefore, it was confirmed that the primary average particle diameter of the polyethylene particles and the polypropylene particles was 79.4% with respect to the pore diameter of the pores.

  In Example 1, a separator for an electronic component was obtained in the same manner as in Example 1, except that a part of the fibers constituting the nonwoven fabric was replaced so that the fiber diameter was 0.1 denier so that the weight would be 10% by weight. It was. The thickness of the nonwoven fabric at this time was 9 μm. Moreover, the thickness of the obtained separator for electronic components was 18 μm. When this electronic component separator was observed with an electron microscope, there were no through holes such as pinholes, and the porous structure was connected to one side of the separator from the other side by a large number of pores. The pore diameter of each pore was smaller than the thickness of the separator. Moreover, the inclination of the pore diameter distribution was not recognized in the thickness direction of the separator, and it was confirmed that the porous structure was homogeneous in the thickness direction. When the average pore diameter of the pores was measured by the bubble point method and found to be 5.7 μm, it was confirmed that the primary average particle diameter of the polyethylene particles was 87.7% with respect to the pore diameter of the pores.

  In Example 1, a separator for an electronic component was obtained in the same manner as in Example 1 except that a part of the fibers constituting the nonwoven fabric was replaced so that the fiber diameter was 0.1 denier so that it was 50% by weight. . The thickness of the nonwoven fabric at this time was 8 μm. The thickness of the obtained separator for electronic parts was 16 μm. When this electronic component separator was observed with an electron microscope, there were no through holes such as pinholes, and the porous structure was connected to one side of the separator from the other side by a large number of pores. The pore diameter of each pore was smaller than the thickness of the separator. Moreover, the inclination of the pore diameter distribution was not recognized in the thickness direction of the separator, and it was confirmed that the porous structure was homogeneous in the thickness direction. When the average pore diameter of the pores was measured by the bubble point method and found to be 5.5 μm, it was confirmed that the primary average particle diameter of the polyethylene particles was 90.9% with respect to the pore diameter of the pores.

  In Example 1, the same coating solution as in Example 1 was applied to a resin film made of polyethylene terephthalate by direct casting, and the polyethylene particles of Example 1 were retained on the coated surface in a wet state immediately after application. The laminated nonwoven fabrics were stacked by wet lamination. Other than that was carried out similarly to Example 1, and obtained the separator for electronic components. The thickness of the obtained separator for electronic parts was 19 μm. When this electronic component separator was observed with an electron microscope, there were no through holes such as pinholes, and the porous structure was connected to one side of the separator from the other side by a large number of pores. The pore diameter of each pore was smaller than the thickness of the separator. Moreover, the inclination of the pore diameter distribution was not recognized in the thickness direction of the separator, and it was confirmed that the porous structure was homogeneous in the thickness direction. When the average pore diameter of the pores was measured by the bubble point method and found to be 5.9 μm, it was confirmed that the primary average particle diameter of the polyethylene particles was 84.7% with respect to the pore diameter of the pores.

  An electronic component separator was obtained in the same manner as in Example 13 except that the nonwoven fabric of Example 12 was used. The thickness of the obtained separator for electronic parts was 18 μm. When this electronic component separator was observed with an electron microscope, there were no through holes such as pinholes, and the porous structure was connected to one side of the separator from the other side by a large number of pores. The diameter of each pore was smaller than the thickness of the separator. Moreover, the inclination of the pore diameter distribution was not recognized in the thickness direction of the separator, and it was confirmed that the porous structure was homogeneous in the thickness direction. When the average pore diameter of the pores was measured by the bubble point method and found to be 5.7 μm, it was confirmed that the primary average particle diameter of the polyethylene particles was 87.7% with respect to the pore diameter of the pores.

[Comparative Example 1]
A nonwoven fabric made of polyethylene terephthalate fiber having a thickness of 20 μm was used as a separator for electronic parts for comparison.

[Comparative Example 2]
A vinylidene fluoride homopolymer having a weight average molecular weight of 300,000 is dissolved in 1-methyl-2-pyrrolidone and dimethylacetamide (good solvent), dibutyl phthalate (poor solvent) is added, and the vinylidene fluoride homopolymer component is 10 weights The coating liquid adjusted so that it might become% was obtained. The amount of water contained in this coating solution was measured by the Karl Fischer method and found to be 0.54% by weight. Next, a 15 μm-thick nonwoven fabric made of polyethylene terephthalate fibers was placed on the holding material surface made of polyethylene terephthalate, and the coating solution was applied onto the nonwoven fabric by a casting method. Next, the solvent in the coating liquid contained inside the nonwoven fabric was evaporated by heat to obtain a comparative separator having a thickness of 30 μm having a porous structure of vinylidene fluoride homopolymer between the nonwoven fabric fibers.

  When this electronic component separator was observed with an electron microscope, there were no through holes such as pinholes, and the porous structure was connected to one side of the separator from the other side by a large number of pores. The pore diameter of each pore was smaller than the thickness of the separator. Moreover, the inclination of the pore size distribution was not recognized in the thickness direction of the separator film, and it was confirmed that the porous structure was homogeneous in the thickness direction. When the average pore size of the pores was measured by the bubble point method, it was 3.7 μm.

[Comparative Example 3]
A vinylidene fluoride homopolymer having a weight average molecular weight of 500,000 is dissolved in 1-methyl-2-pyrrolidone and dimethylacetamide (good solvent), dibutyl phthalate (poor solvent) is added, and the vinylidene fluoride homopolymer component is 10 weights The coating liquid adjusted so that it might become% was obtained. When the amount of water contained in this coating solution was measured by the Karl Fischer method, it was 0.59% by weight. Next, on the resin film surface made of polyethylene terephthalate, polyethylene particles having a particle size of 3 μm and a softening point of 113 ° C. and polyethylene particles having a particle size of 1 μm and a softening point of 132 ° C. on a 10 μm thick nonwoven fabric made of polyethylene terephthalate fiber in advance. Was held at 0.5 g / m ² , and the coating solution was applied onto the nonwoven fabric by the casting method. Next, the solvent in the coating liquid contained inside the nonwoven fabric was evaporated by heat to obtain a comparative separator having a thickness of 15 μm having a porous structure of vinylidene fluoride homopolymer between the nonwoven fabric fibers.

  When this separator for comparison was observed with an electron microscope, there were no through holes such as pinholes, and the porous structure was connected by a large number of pores connected from one side of the separator to the other, The pore diameter of each pore was smaller than the thickness of the separator. Moreover, the inclination of the pore diameter distribution was not recognized in the thickness direction of the separator, and it was confirmed that the porous structure was homogeneous in the thickness direction. When the average pore diameter of the pores was measured by the bubble point method, it was 3.5 μm.

[Comparative Example 4]
A vinylidene fluoride homopolymer having a weight average molecular weight of 200,000 is dissolved in 1-methyl-2-pyrrolidone and dimethylacetamide (good solvent), dibutyl phthalate (poor solvent) is added, and the vinylidene fluoride homopolymer component is 8 weights The coating liquid adjusted so that it might become% was obtained. When the amount of water contained in this coating solution was measured by the Karl Fischer method, it was 0.50% by weight. Next, polyethylene particles having a particle size of 1 μm and a softening point of 113 ° C. and polypropylene particles having a particle size of 5 μm and a softening point of 148 ° C. on a 20 μm-thick non-woven fabric made of polyethylene terephthalate fibers in advance on the resin film surface made of polyethylene terephthalate. What was kept at 60 g / m ² was placed, and the coating solution was applied onto the nonwoven fabric by a casting method. Next, the solvent in the coating liquid contained inside the nonwoven fabric was evaporated by heat to obtain a composite film having a porous structure of vinylidene fluoride homopolymer between the nonwoven fabric fibers. This was pressed to obtain a comparative separator having a thickness of 40 μm.

  When this separator for comparison was observed with an electron microscope, there were no through holes such as pinholes, and the porous structure was connected by a large number of pores connected from one side of the separator to the other, The pore diameter of each pore was smaller than the thickness of the separator. Moreover, the inclination of the pore diameter distribution was not recognized in the thickness direction of the separator, and it was confirmed that the porous structure was homogeneous in the thickness direction. When an average pore diameter of the pores was measured by a bubble point method, it was 5.8 μm.

[Comparative Example 5]
A stretched polyethylene membrane having a thickness of 20 μm was used as a separator for electronic parts for comparison. [Comparative Example 6]
A polyethylene stretched porous membrane having a thickness of 10 μm was used as a separator for electronic parts for comparison.

[Comparative Example 7]
The coating material obtained by applying the coating solution by the casting method in the same manner as in Example 1 was immersed in water without being dried, replaced with a solvent, and then dried, and then the same as in Example 1. Thus, a separator for a comparative example was obtained. The thickness of this comparative separator was 24 μm.
When this comparative separator was observed with an electron microscope, it was found that there were no through holes such as pinholes, and that the porous structure communicated from one side of the separator to the other side by pores. However, it was confirmed that the pores in the separator were closed with a large number of polyethylene particles. Moreover, the hole diameter of each pore was smaller than the thickness of the separator. Further, it was confirmed that the separator surface on the contact surface side with the resin film had sparsely opened pores, and an extremely thin skin layer was formed. When the average pore size of the pores was measured by the bubble point method, it was found that the pore size was 3.2 μm, which was smaller than the particle size of the polyethylene particles.

[Comparative Example 8]
A coated material was obtained in the same manner as in Example 1 except that the poor solvent in Example 1 was changed to tripropylene glycol. The coated product was semi-dried until the poor solvent remained. Next, after the poor solvent remaining in the coated surface was extracted with alcohol, it was dried again to obtain a comparative separator. The film thickness of the obtained comparative separator was 25 μm.
When this separator for comparison was observed with an electron microscope, there were no through holes such as pinholes, and the porous structure was found to be connected to pores from one side of the separator to the other. The pore diameter was smaller than the thickness of the separator. However, when this separator was observed with an electron microscope, it was found that the pore diameter in the vicinity of the surface was very large although it was porous. Moreover, many states in which the pores were closed with polyethylene particles were observed inside the porous structure. When the average pore size of the pores was measured by the bubble point method, it was confirmed that the pore size was 3.4 μm, which was smaller than the particle size of the polyethylene particles.

[Comparative Example 9]
In Example 1, instead of polyethylene particles, calcium phosphate particles having an average particle diameter of 25 μ were mixed and dispersed in a coating solution by 10% by weight, and then treated in the same manner as in Example 1 to obtain a coated product. . After drying it, the calcium phosphate was further decomposed with dilute nitric acid, washed with water, and dried again to obtain a comparative separator. The film thickness of the obtained comparative separator was 28 μm.
When this comparative separator was observed with an electron microscope, through-holes such as pinholes were observed, and in the porous structure, connection of holes was recognized from one side of the separator to the other side. The diameter of each hole was almost the same as the thickness of the fibrous sheet substrate, and the average hole diameter measured by the bubble point method was 26 μm.

[Comparative Example 10]
A comparative separator having a film thickness of 22 μm was obtained in the same manner as in Example 1 except that no poor solvent was used in Example 1. When the obtained comparative separator was observed with an electron microscope, there were few communication holes in the film thickness direction, and a large number of blocked portions with polyethylene particles were confirmed. When an average pore diameter of the pores was measured by a bubble point method, it was 0.06 μm.

[Comparative Example 11]
In Example 1, a comparative separator having a specific film thickness of 21 μm was obtained in the same manner as in Example 1 except that dimethylacetamide was not used. In that case, about 1.5 times as much drying time as Example 1 was required.
When this separator for comparison was observed with an electron microscope, there were no through holes such as pinholes, and the porous structure was connected by a large number of pores connected from one side of the separator to the other, The pore diameter of each pore was smaller than the thickness of the separator. Moreover, the inclination of the pore size distribution was not recognized in the thickness direction of the separator, and it was confirmed that the porous structure was homogeneous in the thickness direction. However, the separator had a small pore diameter as a whole, and many places where the separator was clogged with polyethylene particles were observed. When the average pore diameter of the pores was measured by the bubble point method, the pore diameter was 0.05 μm, and it was found that the pore diameter was not more than the primary average particle diameter of the polyethylene particles.

[Comparative Example 12]
A comparative separator was produced in the same manner as in Example 1 except that the coating liquid produced in an open system was used in an atmosphere of 35 ° C. and 85% RH. The porous film of the obtained separator for comparison was a very non-uniform film in which the density of pore density can be clearly seen visually. The film thickness was about 24 μm. The water content of the coating solution used was 1.7% by weight as measured by the Karl Fischer method.

  The characteristics when the electronic component separators obtained in the above Examples and Comparative Examples were used in lithium ion secondary batteries were evaluated as follows.

[Ionic conductivity]
Ionic conductivity was evaluated for the 26 types of separators. For the measurement, a coin-type cell was prepared using the 26 kinds of separators. The results are shown in Table 1. The measurement environment and measurement apparatus are as follows.
Measurement environment: 20 ° C, 50% RH
Measuring device: Solartron's SI 1287 1255B

  As is clear from Table 1, it is clear that the separators of Examples 1 to 14 of the present invention are generally superior in ionic conductivity as compared with the comparative example. It is considered that this is because the low air permeability and the contact between the electrode and the separator with the resin layer on the separator surface without any gap are the factors that improve the ion conductivity. On the other hand, some of the comparative examples have good ionic conductivity, but good results were not always obtained in other characteristics described below.

[Tensile maximum point load]
As a measure of mechanical strength, the tensile strength was measured by the maximum tensile point load according to JIS K 7161 for 26 types of the above-mentioned Examples and Comparative Examples. The results are shown in Table 2. The measurement environment, measurement device, and measurement conditions are as follows.
Measurement environment: 25 ° C 65% RH
Measuring equipment: UCT-500 manufactured by ORIENTEC
Initial sample length: 10 mm
Tensile speed: 50 mm / min
Tensile direction: Longitudinal direction (MD)

  As is clear from Table 2, the separators of the examples have a strength equal to or greater than that of the comparative example in terms of the maximum point load per thickness. Therefore, it can be said that the separator does not impair workability and productivity during battery production. Although some of the comparative examples have high strength, there are those in which the pores of the porous structure are close to the closed state, and as described above, the ion conductivity is inferior, or the shutdown performance described later is achieved. It was inferior.

[Shutdown]
Shutdown performance was evaluated for the 26 types of separators. For the measurement, a coin-type cell was prepared using the 26 kinds of separators. The results are shown in Table 3. As a test method, the fully charged coin cell was further charged, the temperature change inside the battery at that time was measured, and the point at which the temperature began to fall was defined as the shutdown temperature.

  As can be seen from Table 3, the separator of the example is a separator having a shutdown property and contributes to the safety of the battery. Regarding Comparative Examples 7 to 12, since the polyethylene particles or the polypropylene particles block the pores of the porous structure, and the particles, the porous structure, and the fibers are in a close contact state, the softening of these particles Even if the temperature rises above the point and the shutdown function is manifested, the gap between the above particles and other materials is extremely small, so the growth of minute dendrites is suppressed and the battery reaction during overcharging cannot be suppressed. Inferred. On the other hand, since the separator of the example has a sufficient gap between the fine particles and other members, a minute dendrite grows through the gap and the runaway of the battery reaction due to overcharge is suppressed, and the shutdown is almost simultaneously performed. It is inferred that the function appeared and the double safety function worked.

Regarding Comparative Examples 4 and 5, although the runaway of the battery reaction was suppressed, it was inferior in ionic conductivity and could not be found in the Comparative Examples because it satisfied all the evaluation items of the present invention.

Claims (14)

A separator for electronic parts for a lithium ion secondary battery or a polymer lithium secondary battery comprising a fibrous sheet substrate and a porous structure containing thermoplastic resin fine particles that melt upon heating, wherein the porous structure The pores have an average pore size of 0.1 to 15 μm, the fine particles are contained in the separator in a range of 1 to 50 g / m ² , and the primary average particle size of the fine particles is 1% to 95% of the pore size. range near is, the porous structure is made of polyvinylidene fluoride, communicates with the other surface from one surface of the separator a number of pores connected, pinhole-shaped vertical penetration in the vertical direction of the separator surface The separator for electronic components characterized by not having a hole and having a pore diameter smaller than the thickness of the separator.   The separator for electronic parts according to claim 1, wherein the fibrous sheet base material is a woven fabric, a nonwoven fabric or a net-like material.   The separator for electronic parts according to claim 2, wherein the nonwoven fabric contains at least 1% by weight of fibers having a fiber diameter of 0.15 denier or less.   The separator for electronic parts according to claim 1, wherein the fine particles are made of polyethylene and / or polypropylene.   The separator for an electronic component according to claim 1, wherein the porous structure is formed on a surface and / or inside of a fibrous sheet base material. Electronic component separator according to any one of claims 1 to 5 the thickness of the separator is characterized in that it is a 5 to 30 [mu] m. It is a manufacturing method for obtaining the separator for electronic components of Claim 1, Comprising: The process of mounting the fibrous sheet base material containing the thermoplastic resin microparticles | fine-particles melted by heating on this resin film, This fibrous sheet A step of applying a coating solution containing a vinylidene fluoride resin and its good and poor solvents on the substrate, and drying the formed coating layer to remove the solvent, thereby removing the solvent from the fibrous sheet substrate. A step of forming a porous structure on the surface and / or inside, and then a step of obtaining a separator comprising a fibrous sheet base material and a porous structure containing thermoplastic resin fine particles that are melted by heating by removing the resin film. A method for producing a separator for electronic parts, characterized in that the amount of water contained in the coating liquid is 0.7% by weight or less as measured by the Karl Fischer method. It is a manufacturing method for obtaining the separator for electronic components of Claim 1, Comprising: On the resin film, the coating liquid containing a vinylidene fluoride resin, its good solvent, and a poor solvent is applied, and a coating layer is formed. A step of forming, a step of superimposing a fibrous sheet base material containing thermoplastic resin fine particles that melt upon heating on the coating layer, and then drying to remove the solvent and / or the surface of the fibrous sheet base material A step of forming a porous structure inside, and then a step of obtaining a separator composed of a fibrous sheet base material and a porous structure containing thermoplastic resin fine particles melted by heating by removing the resin film, A method for producing a separator for electronic parts, wherein the amount of water contained in the liquid is 0.7% by weight or less as measured by the Karl Fischer method. The method for producing a separator for electronic parts according to claim 7 or 8 , wherein the boiling point of the poor solvent in the coating solution is higher than the boiling point of the good solvent. The method for producing a separator for electronic parts according to claim 7 or 8 , wherein the fibrous sheet base material is a woven fabric, a nonwoven fabric or a net-like material. The method for producing an electronic component separator according to claim 10 , wherein the nonwoven fabric contains at least 1% by weight of fibers having a fiber diameter of 0.15 denier or less. The method for producing a separator for electronic parts according to claim 7 or 8 , wherein the fine particles are made of polyethylene and / or polypropylene. The method for producing a separator for electronic parts according to claim 7 or 8 , wherein the separator has a thickness of 5 to 30 µm. The method for producing a separator for electronic parts according to claim 7 or 8 , wherein the peel strength of the resin film with respect to the porous structure is 0.1 to 75 g / 20 mm.