JP6259501B2 - Three-layer laminated sheet for separator for power storage element - Google Patents

Description

  The present invention relates to a three-layer laminated sheet for a separator for a storage element.

  A separator for a storage element such as a battery, a capacitor, or a capacitor is required to have high performance from the viewpoints of safety, compactness, and long life.

  Especially for separators for lithium secondary batteries, with the spread of hybrid vehicles, electric vehicles, high-performance storage batteries, etc., the cell size has increased, the size of the battery has decreased significantly, the cost has been significantly reduced, Is urgently required to improve heat resistance and safety.

  The separator for the lithium secondary battery is required to have a basic function of holding the electrolyte uniformly and intimately insulating the electrodes by being in close contact with both the positive and negative electrodes. Other functions include a thin layer of 40 μm or less to increase the unit capacity of the battery, processability to withstand high-speed assembly, strength to withstand physical damage due to the generation of metal dendrites associated with multiple charge / discharge, Weather resistance and dimensional stability to withstand extremely low temperatures in polar regions and extremely high temperatures in tropical deserts are also required. In order to achieve such many functions, it is difficult to use a single-layer or single-layer structure, and a separator that is multilayered or combined with other types of functional materials is desirable.

  Conventionally, an olefin-based porous film represented by Hypore (trademark of Asahi Kasei Co., Ltd.) has been used as a separator for this lithium secondary battery. In recent years, because of the need for improvement in heat resistance, development research has been conducted in which a cellulose material having excellent heat resistance and electrochemical stability is used as a separator material. As such a cellulose material, nano serisch (Daicel), which has been further refined with a high-pressure homogenizer, especially microfibrillated cellulose (MFC) having an ultrafine diameter, biotechnology obtained by cultivation, separation, and purification of acetic acid bacteria Cellulose nanofibers such as cellulose are being developed.

In order to obtain a thinned separator from cellulose fibers having the above ultrafine diameter, the following two major problems are encountered.
(1) Cellulose fibers having a fine diameter have a huge hydration property and a strong hydrogen bonding property. Therefore, when a sheet is formed in its hydrated state, it becomes a so-called parched film sheet. As a result, the porous structure disappears and the ion permeability is almost lost.
(2) When a hydroxyl group of a cellulose molecule is substituted with a hydrophobic functional group or a hydrogen bond formation is blocked by alcohol substitution or the like to obtain a sheet that maintains a porous structure, It is lost and the required sheet strength cannot be maintained.

  As means for solving these problems, for example, as proposed in Patent Documents 1, 2, and 3, there is an attempt to chemically control the degree of hydrogen bonding. If an attempt is made to continuously produce a thinned sheet by such a method, it is difficult to set conditions and the process becomes complicated, which is extremely disadvantageous in commercial production.

As another means, as shown in Patent Documents 4, 5, 6 and 7 proposed by the present inventors, a nonwoven fabric is used as a strength support, and an ultrafine cellulose fiber layer having a porous structure and a nonwoven fabric are laminated. This is a method for obtaining a sheet. In Patent Document 4, a hydrophobic sheet such as a nonwoven fabric is used as a support for molding a fine cellulose layer, and after removing the solvent and drying in a laminated state, the support nonwoven fabric is peeled off to remove only the fine cellulose. Although a method for obtaining a thin layer made of a material is described (for example, Example 1), it seems more rational to appropriately select a support nonwoven fabric and use it in a state in which a fine cellulose fiber layer and a nonwoven fabric are laminated and integrated. It is. Patent Documents 5, 6 and 7 relate to a sheet obtained by laminating and integrating a fine cellulose fiber layer and a nonwoven fabric based on such a concept. This method is advantageous in that the conditions are easy to set and the process is relatively simple and easy to commercialize. On the other hand, the cellulose fiber layer and the nonwoven fabric need to have a certain thickness and basis weight, and it is difficult to make the layer thin or ultra thin. In particular, if the nonwoven fabric does not exceed at least 15 g / m ² , the cellulose fiber layer curls greatly due to drying shrinkage of the cellulose fiber layer. Since the cellulose fiber layer is also a single layer, it is difficult to prevent the generation of pinholes unless it is 10 g / m ² or more. Accordingly, the basis weight of the laminate is a thick sheet of 25 g / m ² or more, and the thickness is about 100 μm, which makes it difficult to use as a separator for a lithium secondary battery.

JP 2006-49797 A JP 2008-274461 A JP 2010-90486 A Japanese Patent Laid-Open No. 10-248872 JP 2007-230139 A JP 2010-240513 A International Publication No. 2010/044169 Pamphlet (WO2010 / 044169)

  As described above, conventional separators for storage elements, particularly separators for lithium secondary batteries have various problems, and improvements have been desired.

  A typical object of the present invention is to provide a three-layer laminate sheet excellent in sheet strength and productivity, a production method capable of being continuously produced commercially, and a storage element separator comprising the three-layer laminate sheet. There is.

  As a result of intensive studies to achieve the above object, the present inventor has completed a “new three-layer laminated sheet” having an extremely high function. Then, a “new three-layer laminated sheet” of 40 μm or less obtained by laminating and integrating a porous fiber layer on the upper layer and the lower layer with a non-woven fabric having many interfiber spaces as a core material is used for a lithium secondary battery. When used as a separator, the inventors have found that the necessary functions can be sufficiently exhibited, the heat resistance is improved, and further, a large compactness is achieved.

That is, the three-layer laminated sheet according to the present invention comprises a porous fiber layer mainly composed of a non-woven fabric mainly composed of thermoplastic fibers and having fine-diameter cellulose fibers as the upper layer and the lower layer. In the three-layer laminated sheet,
The air permeability of the three-layer laminated sheet measured by the Gurley method is 1000 sec / 100 ml or less,
The basis weight of the three-layer laminated sheet is in the range of ² g / m ^{2 to} 15 g / m ² ,
The three-layer laminated sheet has a thickness of 5 μm to 40 μm.

  The electrical storage element separator according to the present invention is an electrical storage element separator formed by the three-layer laminated sheet according to the present invention.

The production method according to the present invention is a method for producing a three-layer laminated sheet according to the present invention, wherein the upper porous fiber layer is the layer (P), the lower porous fiber layer is the layer (Q), When the non-woven fabric is a cloth (S), the layer (P) and the layer (Q) are stacked on both surfaces of the cloth (S) prepared in advance, and the three-layer stack is formed by pressure bonding in an overlapped state. It is a manufacturing method of a sheet.
The three-layer laminated sheet according to the present invention includes a first nonwoven fabric and a second nonwoven fabric mainly composed of a non-woven fabric mainly composed of thermoplastic fibers, and the upper layer and the lower layer mainly composed of fine-diameter cellulose fibers. In a three-layer laminated sheet provided with a porous fiber layer,
At least a portion extending from the interface between the nonwoven fabric and the first and second porous fiber layers in a region where the constituent fibers of the first and second porous fiber layers enter the inter-fiber gap of the nonwoven fabric. And in this region, the constituent fibers of the first and second porous fiber layers are joined to and integrated with the nonwoven fabric.

  According to the three-layer laminate sheet of the present invention, sheet strength and productivity can be improved. Moreover, according to the manufacturing method concerning this invention, the manufacturing method which can be produced commercially continuously can be provided.

It is a block diagram which shows the typical structure of the three-layer lamination sheet concerning this invention. It is a schematic diagram which shows one example of the two-layer lamination state shown as a comparative example. It is a schematic diagram which shows the structure of 3 layer lamination which shows the state which only laminated | stacked and joined. It is a schematic diagram which shows the structure of 3 layer lamination | stacking in which the upper and lower porous fiber layers were bitten in the nonwoven fabric layer. It is a schematic diagram which shows the structure of 3 layer lamination | stacking, when an upper and lower porous fiber layer adjoins mutually and thinning advances. It is a schematic diagram which shows the example of the 3 layer lamination sheet which selected and laminated | stacked and integrated 4 g / m < ² > and a material with a large opening as a nonwoven fabric. It is a SEM photograph which shows the state of the "interfiber opening" of the core nonwoven fabric used as an example. It is a figure which shows the flow of one Embodiment of the manufacturing method of the 3 layer lamination sheet concerning this invention. It is a figure which shows the flow of other embodiment of the manufacturing method of the three-layer lamination sheet concerning this invention. It is a figure which shows the flow of other embodiment of the manufacturing method of the three-layer lamination sheet concerning this invention. It is a figure which shows the flow of other embodiment of the manufacturing method of the three-layer lamination sheet concerning this invention. It is a figure which shows the flow of other embodiment of the manufacturing method of the three-layer lamination sheet concerning this invention. It is a figure which shows the flow of other embodiment of the manufacturing method of the three-layer lamination sheet concerning this invention. It is a characteristic view which shows the thermocompression bonding temperature and the change of thickness when a pressurization degree is made into 2 levels, 3MPa and 10MPa. It is a characteristic view which shows the change of thermocompression-bonding temperature and air permeability when a pressurization degree is made into 2 levels, 3MPa and 10MPa. It is a figure which shows concretely the manufacturing apparatus which implement | achieves the process laminated | stacked in the wet state shown in FIG. 5A. The figure which shows concretely the manufacturing apparatus which implement | achieves the process of laminating | stacking QR (or RP) supplied in the dry state prepared in advance with RP / S (or S / QR) obtained in the wet state shown in FIG. 5B. It is. It is a figure which shows an example of the cylindrical lithium secondary battery using the 3 layer lamination sheet concerning this invention.

  Hereinafter, typical embodiments according to the present invention will be described in detail with reference to the drawings.

1.3 Configuration of Laminate FIG. 1 is a diagram showing a typical structure of a three-layer laminate sheet according to an embodiment of the present invention. As shown in FIG. 1, an upper porous fiber layer (P) and a lower porous layer made of fine cellulose fibers (b) above and below a core non-woven fabric (S) made of thermoplastic fibers (a). The conductive fiber layer (Q) is disposed. Thus, the sheet | seat which laminated | stacked and integrated three layers is comprised. The upper and lower porous fiber layers (P), (Q) and the core non-woven fabric (S) are not simply stacked in three layers, but at least the porous fiber layers (P), (Q) It exists so that it may bite into a core nonwoven fabric (S), and this is an example of the meaning of lamination | stacking and integration. In this configuration, the region where the constituent fibers of the upper and lower porous fiber layers enter the inter-fiber gap of the core nonwoven fabric is partly extended from the interface with the upper and lower porous fiber layers of the core nonwoven fabric. In this region, the constituent fibers of the upper and lower porous fiber layers are joined and integrated with the core nonwoven fabric.

  Although the representative structure of the present embodiment has three layers as shown in FIG. 1, the constituent components are two components of a porous fiber layer and a nonwoven fabric. In the case of a two-component system, a two-layered structure can be considered first, but the reason why the two-layered structure causes a problem will be clarified.

  The laminated state of the three-layer laminated sheet of the present embodiment will be described in more detail using the schematic structures of FIGS.

FIG. 2A is a diagram showing an example of a two-layer laminated state shown as a comparative example. In the case of a two-layer laminated state, the following inconvenience occurs.
(1) The porous fiber layer is strongly hydrophilic, the nonwoven fabric composed of one thermoplastic fiber is hydrophobic, and the stretchability differs greatly depending on humidity and heating. It curls in the direction, and there are many wrinkles on the surface, and surface peeling tends to occur.
(2) Since the base nonwoven fabric needs to maintain strength as a support in the two-layer laminated state, the basis weight of the nonwoven fabric becomes relatively large, and usually around 20 g / m ² is required.
(3) In order to prevent the occurrence of pinholes due to the presence of only one porous fiber layer, the basis weight of the fiber layer needs to be relatively large, and air permeability resistance inevitably increases. Absent. Usually, about 10 g / m ² is required, and the air permeability exceeds 1000 sec / 100 ml.

FIG. 2B is a schematic diagram showing a state in which three layers are stacked, but simply stacked and bonded. Curling is eliminated and the porous fiber layer has a two-layer structure, so that the effect of preventing the occurrence of pinholes can be expected, but the following disadvantages occur.
(1) Delamination is likely to occur due to insufficient integration.
(2) Since the three-dimensional space of the nonwoven fabric layer remains as it is, the thickness increases.
(3) Arrangement of layers such as porous fiber layer / nonwoven fabric space layer / porous fiber layer occurs, and when used as a separator for a lithium secondary battery, it is easier to apply to a nonwoven fabric space layer into which an electrolyte solution easily penetrates, Ion migration becomes uneven and partial short-circuiting easily occurs. Therefore, it is desirable to minimize the presence of the nonwoven fabric space layer.

  The three-layer laminated sheet of FIG. 2C is substantially the same as the structure shown in FIG. 1, and the upper and lower porous fiber layers are bitten into the nonwoven fabric layer, and the nonwoven fabric space layer is greatly reduced.

  FIG. 2D is a result of thermocompression bonding with reference to the plasticizing temperature of the thermoplastic fiber constituting the nonwoven fabric layer of the three-layer laminated sheet of FIG. 2C, but the nonwoven fabric space layer almost disappears, and the upper and lower porous fiber layers are Thinning progresses greatly in close proximity to each other. As the thermoplastic fiber, for example, a fiber having a readily meltable resin component in the surface layer such as a PE / PET core-sheath composite fiber is employed. When such a fiber is used, when the thermocompression treatment is performed at a temperature higher than the melting temperature of the component, a so-called “welding phenomenon” occurs, and the thinning and strength reinforcement work more effectively, but on the other hand, the air permeability is hindered. In some cases, the selection of conditions is important. Regarding the “welding phenomenon”, refer to the patent documents proposed by the present inventors, Japanese Patent Laid-Open Nos. 8-216316 and 9-76388. Details of such a thermocompression bonding effect will be described later.

FIG. 3 shows an example of a three-layer laminated sheet obtained by laminating and integrating a nonwoven fabric with 4 g / m ² as a thin and flat space, that is, a material having a large opening. The upper porous fiber layer and the lower porous fiber layer penetrate each other through the inter-fiber gap of the nonwoven fabric at the contact surface with the nonwoven fabric, and the upper layer constituent fiber and the lower layer constituent fiber are mixed and joined to be integrated. Shows the state. In the structure of FIG. 3, the non-woven fabric space layer described with reference to FIGS. In some cases, the upper layer constituent fibers and the lower layer constituent fibers may all enter the nonwoven fabric. In this configuration, a region in which the constituent fibers of the upper layer and the lower layer porous fiber layer have entered the inter-fiber voids of the core nonwoven fabric has an entire region in the thickness direction of the core nonwoven fabric. The constituent fibers of the porous fiber layer are joined and integrated with the core nonwoven fabric.

The three-layer laminated sheet as described with reference to FIGS. 2D and 3 has an air permeability of 1000 sec / 100 ml or less measured by the Gurley method, and the basis weight of the three-layer laminated sheet is 2 g / m ² to It is important that the thickness is in the range of 15 g / m ² and the thickness of the three-layer laminated sheet is in the range of 5 μm to 40 μm. When the air permeability of the three-layer laminated sheet exceeds 1000 sec / 100 ml, the permeation of gas and ions is reduced and the use as a product is limited. Especially when it is used as a separator for a storage element, the ion per unit area is reduced. As the amount of permeation decreases, the efficiency of the battery decreases. When the basis weight of the three-layer laminated sheet is less than 2 g / m ^2, it becomes difficult to produce a uniform sheet, which is easily broken and difficult to handle. If the basis weight of the three-layer laminated sheet exceeds 15 g / m ² , it is difficult to make the air permeability 1000 sec / 100 ml or less, and it is difficult to make the thickness 40 μm or less. When the thickness of the three-layer laminated sheet is smaller than 5 μm, it is difficult to produce a uniform sheet, and it is easy to break and handling becomes difficult. When the thickness of the three-layer laminated sheet exceeds 40 μm, the volume of the product on which the sheet is mounted increases, and the productivity of the sheet deteriorates. In order to obtain a three-layer laminated sheet as described in FIGS. 2D and 3, it is important to form a desirable porous fiber layer, select a suitable nonwoven fabric, and devise a lamination method. Details will be described below.

2. Porous fiber layer constituting upper layer and lower layer (a) What is porous fiber layer? The porous fiber layer constituting the upper layer and lower layer is mainly composed of fine-sized cellulose fibers. The reason for using cellulose is as follows.
(1) Cellulose is a material that does not melt by heat and is stable even if it exceeds 300 ° C., and has high heat resistance and chemical stability.
(2) Cellulose is a highly pure material that is inexpensive and available in large quantities.

  The purpose of using the fine-diameter fibers is to increase the internal surface area of the fiber layer so as to generate and retain as many pores as possible. In that sense, the diameter of the constituent fiber should be as thin as possible. The fine-diameter cellulose fiber expressed in the present embodiment has a distribution within a certain range in the fiber diameter, and a fibrous fiber having an average fiber diameter (average fiber diameter) of 5 nm to 1 μm is preferably used.

  As raw materials for preparing fine-sized cellulose fibers, as long as they have the basic chemical structure of β-1,4-glucan structured polysaccharides, various types such as plant-derived, animal-derived, and chemically modified cellulose derivatives Are applicable. The fine-diameter cellulose fibers preferably used in this embodiment are a group called MFC (microfibrillated cellulose) obtained by mechanically crushing fibrous cellulose. This is made from cotton linter pulp, wood pulp, solvent-spun rayon (Lyocell) short fibers, etc., and further refined with a super grinder or high-pressure homogenizer after pretreatment with a beater, refiner, etc. A thing of 300 nm-1 micrometer level is expressed as MFC, it is easy to make comparatively easily, and cost is also comparatively cheap. This MFC is produced and prototyped in various places, but typical examples are “Serisch” (manufactured by Daicel Chemical Industries) and “S-MFC” (manufactured by Japan Absorbent Technology Laboratory). It is done. An ultrafine size MFC of 10 nm to 300 nm level is expressed as a cellulose nanofiber, and for example, “Nano Serisch” (manufactured by Daicel Chemical Industries) is known. The production of cellulose nanofibers requires higher energy and is relatively expensive. MFC and cellulose nanofibers have a large difference in fiber diameter as described above, but there is almost no difference in fiber length, and the average fiber length is in the range of about 0.05 mm to 1 mm.

  Another preferred example of cellulose nanofibers is a group called biocellulose (BC) that is cultured and harvested from microorganisms. A typical one is obtained by adding acetic acid bacteria (Acetobacter Xylinum, etc.) to a carbon source such as molasses, stirring and culturing to produce cellulose nanofibers outside the cells, separating and purifying. Prototypes are being produced in many companies and research facilities, but representatively, biocellulose produced by Ajinomoto Co. is well known. Although it is excellent in performance and suitable for the purpose of this embodiment, on the other hand, it easily perishes and is difficult to handle, and the refining cost is high, so that the cost is significantly increased as compared with MFC-based nanofibers. Therefore, in commercial use, a device that increases the amount of additives to reduce the amount used is required.

  What should be noted as the properties of biocellulose and MFC-based fine cellulose fibers used in the present embodiment is that it behaves as a hydrated gel in a water-containing medium, and its strength of hydration is a major feature. This “hydratability strength” is used for performance comparison in the specification of the present application, with the amount of hydration per gram of fiber as the “water retention amount”. Table 1 compares the characteristics of MFC and cellulose nanofiber.

  A clear difference in the table appears as a difference in "water content". This hydrated gel exhibits a strong non-Newtonian viscosity in aqueous media. For the definition of the “water content” and the viscosity characteristics of the MFC-based fine-diameter cellulose fibers, refer to the paper pamphlet of technical paper 53 (5), 637 (1999).

(A) Structure of porous fiber layer Important factors that determine the structure of the porous fiber layer are thickness and air permeability. The thickness of the layer is determined by the basis weight and density of the fiber layer. It is important to note that the porous fiber layer has a low density and slightly changes in thickness depending on the degree of pressure bonding. The three-layer laminated sheet of the present embodiment includes a thin layer composed of two upper and lower porous fiber layers. In order to form such a thin layer on the upper and lower sides of the nonwoven fabric, a precise molding method is adopted, and the following description will be made with an example employing a coating method. Here, the conditions required for the porous fiber layer of this embodiment are defined by the thickness and basis weight of each layer. ・ If the thickness is not at least 15 μm or less, it is difficult to secure the necessary thinness as a three-layer laminated sheet. It is preferably 8 μm to 2 μm. When it becomes thinner than 2 μm, it is difficult to form a homogeneous layer. Here, in this embodiment, since the porous fiber layer is bitten by the core nonwoven fabric, the thickness of the porous fiber layer is defined including the portion that has entered the core nonwoven fabric and the portion that has not penetrated.
・ If the basis weight is not at least 5 g / m ² , it is difficult to secure a thickness having a predetermined air permeability, and if it is less than 0.5 g / m ² , fading tends to occur during coating, and pinholes are generated. Risk increases. Preferably from ^{4g / m 2 ~1g / m 2} .

(C) Distribution of fine-diameter cellulose fibers in porous fiber layer In order to meet the above conditions, it is important to distribute fine-diameter cellulose fibers in accordance with the performance of the constituent components. In the present embodiment, MFC and cellulose nanofibers are the main components constituting the fine-diameter cellulose fiber. Although the fine-diameter cellulose fiber may be 100% MFC, in this case, since the fiber interval is relatively widened, the basis weight needs to be set higher in order to avoid the occurrence of pinholes. Therefore, it approaches the upper limit of the thickness and basis weight specified in (a).

  The fine cellulose fiber may be 100% cellulose nanofiber, but in this case, since the fiber interval is relatively narrow, the porous fiber layer becomes too dense and the airflow resistance increases. Therefore, in order to ensure a predetermined air permeability, it is necessary to set the basis weight low. As a result, it approaches the lower limit of the thickness and basis weight specified in (a).

Therefore, it is preferable to use a mixture of MFC and cellulose nanofiber.
-Blending amount of cellulose nanofiber in fine diameter cellulose fiber The blending amount of cellulose nanofiber is at least 20 wt% or more, preferably 30 wt% or more, more preferably 40 wt% to 70 wt%. If it is less than 20 wt%, it is difficult to obtain the effect of cellulose nanofibers. If it exceeds 70 wt%, the structure becomes too dense.
-Blending amount of MFC in fine-diameter cellulose fiber The blending amount of MFC is 30 wt% to 80 wt%, preferably 30 wt% to 60 wt%. If it is less than 30 wt%, it is difficult to produce the effect of MFC. If it exceeds 80 wt%, the structure becomes too rough.
-The total compounding quantity of the cellulose nanofiber and MFC in a porous fiber layer A cellulose nanofiber and MFC are the main components which comprise a porous fiber layer, and it is desirable to mix | blend at least 40 wt% or more in a total amount. More preferably, it is 50 wt% or more.

(D) Addition of other fiber components to the porous fiber layer Although the porous fiber layer is mainly composed of fine-sized cellulose fibers, the majority of the other components occupy the porosity promoting agent described in the next section. Addition. Although further limited in quantity, adding a fiber other than cellulose that is miscible with the fine cellulose fiber is one of the function improving means. These fiber types are inevitably thin and short because they are miscible, maintain porosity, and have little effect on thickness. A synthetic fiber with a fineness of 0.2d to 1.5d and a fiber length of about 1 mm to 6 mm. For example, PE, PP, PET and their composite fibers, PVA, EVA, etc. used for papermaking It is added and used for the purpose of reinforcing the strength of the porous fiber layer and adjusting the hydrogen bond strength. In selecting these fiber components, consideration must be given so as not to affect the heat resistance of the porous fiber layer, and the addition amount should preferably be 10 wt% or less.

(E) Control of self-adhesion based on hydrogen bonds and addition of a pore-forming accelerator The porous fiber layer composed of the above-mentioned fine-sized cellulose fibers having a large hydration function is composed of the proximity of fibers and hydrogen associated with dehydration and drying. While the formation of the bond shows strong self-adhesiveness, the entire surface becomes parchment, resulting in a cellophane-like film and loss of porosity. In order to prevent hydrogen bond formation by chemical principle, the following means can be considered.
A sheet is formed by using a slurry in which fine-diameter cellulose fibers are dispersed in an organic solvent-containing medium such as alcohol as a coating agent, and the formation of hydrogen bonds is prevented by removing the solvent and drying to form a porous fiber layer.
・ Disperse fine-sized cellulose fibers in an aqueous medium, form a sheet from the dispersion by a paper-like method, replace the organic solvent in the water-containing state, remove the solvent, and prevent hydrogen bond formation by drying. Form a layer.
・ Disperse in a water-based medium added with hydrophobic and oily substances that react and coordinate with the OH group of fine-sized cellulose fibers, and form a sheet from the dispersion by a method such as papermaking, and neutralize Drying prevents hydrogen bond formation and forms a porous fiber layer.

  Although these means are effective as a method for preventing hydrogen bond formation, they require the recovery of solvent, recovery of additives, waste water treatment, exhaust treatment, etc. Yes.

Another method is to provide a fine physical space between fine-sized cellulose fibers to prevent bonding between the fibers and the formation of hydrogen bonds, from maintaining and promoting porous performance by the spacer effect. The spacer material will be referred to as a “porosification accelerator”. Such “porosification promoter” is as follows.
・ Inorganic fine particles having electrical insulating properties such as silica, alumina, mica, talc and zeolite, preferably metal oxide fine particles such as silica and alumina, and at least an average particle size of 5 μm or less, preferably 2 μm or less These fine powders and fine particles are added in an amount of 10 wt% to 150 wt%, preferably 30 wt% to 100 wt%, with respect to the fine cellulose fibers. When the amount is less than 10 wt%, the effect is small, and when the amount exceeds 150 wt%, the formation of the porous fiber layer becomes heterogeneous. Fine powder and fine particles may be added in a dry state or in a suspended state.
Hydrophobic and electrically insulating organic fine particles such as polyethylene and polypropylene, which are fine powders and fine particles having an average diameter of 5 μm or less, preferably 2 μm or less. In contrast, 20 wt% to 100 wt% is added. If it is less than 20 wt%, the effect is small, and if it exceeds 100 wt%, the formation of the porous fiber layer becomes heterogeneous. When fine sheet cellulose fibers are dispersed in an aqueous medium or an organic solvent-containing medium to form a dispersion to form a sheet, fine powder and fine particles are added to the dispersion in the form of a suspension or emulsion.

When the porous fiber layer is formed by a hydrogen bond forming block, the porous size is relatively small because the structure becomes dense. Therefore, in order to keep the air permeability of 1,000 sec / 100 ml or less stable, the thickness of each fiber layer must be reduced to, for example, 10 μm or less, and the basis weight is 3 g / m ² or less, which may cause pinholes. Will also increase.

In a system in which a porosification agent is added to the porous fiber layer, the porous size becomes relatively large in the direction of sparse tissue. Therefore, the thickness of each fiber layer for maintaining air permeability of 1,000 sec / 100 ml or less can be increased to, for example, 10 μm to 15 μm and the basis weight can be increased to a maximum of 5 g / m ² . The risk of occurrence is also reduced.

  Further desirable conditions are a combination of both chemical means, hydrogen building blocks, and physical means, the addition of porosity promoters. By this combination effect, a fiber layer having a porous structure can be formed more easily. In the present embodiment, as described in Examples 2 and 3, for example, a high organic solvent-containing liquid is selected as a medium for dispersing fine-diameter cellulose fibers as a chemical means, and a porous accelerator is used as a physical means. Fine particles are added to exert the combination effect.

(F) Upper porous fiber layer and lower porous fiber layer The upper layer and the lower layer may have the same fiber configuration (material) and the same weight (weight). The upper layer and the lower layer have the same fiber configuration but may have different weights (weight per unit area). Furthermore, the upper layer and the lower layer may be different from each other in both fiber configuration and weight (weight per unit area).

3. Role of non-woven fabric as core material and required performance (a) Role of non-woven fabric as core material-The non-woven fabric is a core material existing near the center of the cross section of the three-layer laminated sheet, and the strength of the entire three-layer laminated sheet It works as a strength maintenance body that bears most of the body.
The non-woven fabric is in close contact with or bonded to almost the entire surface of the upper and lower porous fiber layers to form a support for the porous fiber layer.
-In order to more effectively demonstrate the role as a support, it is important that the upper and lower porous fiber layers and the nonwoven fabric layer have a stronger integrated relationship, and for that purpose, the nonwoven fabric layer is bonded by pressure bonding. It is more desirable that the fiber layer enters the fiber layer and that the non-woven fabric surface be easily melt-melted so that the non-woven fabric constituting fiber and the fine cellulose fibers constituting the fiber layer are fused and integrated.
When the porous fiber layer is formed by coating a dispersion slurry of fine cellulose fibers, the nonwoven fabric is used as a coating substrate, and the porous fiber layer is formed on the surface of the nonwoven fabric.

(I) Device for making the thickness of the nonwoven fabric as the core material as thin as possible In order to obtain an extremely thin three-layer laminated sheet as intended by the present invention, together with the porous fiber layer as the first component It is desired that the non-woven fabric as the second component be as thin as possible. The thickness of the nonwoven fabric is important when used as a raw material, but more importantly, it is integrated and thinned when three layers are laminated, and is further thinned by thermocompression bonding. Originally, since the nonwoven fabric has few constraints between fibers, it can be said that it is sufficiently thin even under 50 μm under no load, but it is at least 40 μm under load (20 g / cm ² ), preferably ² μm to 30 μm. When it becomes smaller than 2 μm, handling becomes difficult. That is, the thickness of the nonwoven fabric is at least 40 μm or less, preferably 2 μm to 30 μm as the raw material. However, the thickness of the nonwoven fabric component in the state that finally becomes a three-layer laminated sheet is integrated and thermocompression bonded. It is even thinner than that.
-Use of fibers having a fineness as the non-woven constituent fiber It is desirable that the denier of the fiber is as small as possible, but use a fiber of at least 2.0 denier, preferably 1.5 denier or less, more preferably 1.0 denier or less. It is desirable. In order to facilitate productivity and web formation, it is also recommended to use composite fibers or split fibers, or to adopt special molding methods such as melt blown, spray spinning, and electronic spin.
・ Make the basis weight as low as possible.
Basis weight of the nonwoven fabric is at least 10 g / ^{m 2} or less, preferably ^{8g / m 2 ~1g / m 2} , more preferably ^{6g / m 2 ~2g / m 2} . Even if a nonwoven fabric with a basis weight smaller than 1.0 g / m ² can be produced, it is difficult to handle.
-There is an opening or "opening between fibers" The core nonwoven fabric does not affect or impede the porosity of the porous fiber layer (of course, it does not affect the passage of ions) A) having a sufficiently large “opening between fibers”.
-Further effects and meaning of "opening between fibers" The "opening between fibers" of a nonwoven fabric is a structure having sufficient inter-fiber voids in another expression, and is an upper layer and a lower porous fiber layer. It is also necessary to have such a size that can be connected to each other through this “opening”. In addition, even a non-woven fabric composed of fibers having relatively large denier, for example, relatively thick fibers of about 1.5 denier, is subjected to opening processing, or has a net-like or mesh-like structure with “inter-fiber openings”. In this case, the basis weight can be lowered relatively, and this contributes to a stronger integrated relationship between the upper and lower porous fiber layers and the nonwoven fabric layer.
・ Method of expressing “aperture ratio between fibers” The nonwoven fabric used as the core also has a three-dimensional structure with a certain thickness, but it is very thin, and there is little overlap between the upper and lower fibers. The “interfiber opening ratio” was calculated from the surface photograph of a scanning electron microscope (SEM) by the following formula.

(Area of nonwoven fabric-Area occupied by fiber) / (Area of nonwoven fabric) x 100
= Interfiber opening rate (%)

FIG. 4 is a SEM photograph showing a state of “interfiber opening” of the core nonwoven fabric as an example.
-Interfiber opening ratio (%) required for the nonwoven fabric that is the core of this embodiment
It is at least 50% or more, preferably 60% or more, and more preferably 65% to 90%. When it becomes smaller than 50%, the eyes become too clogged as a non-woven fabric that becomes the core. If it exceeds 90%, the form is unstable and difficult to handle.

(C) Constituent fiber component of non-woven fabric serving as core material The constituent fiber component of the non-woven fabric is mainly composed of thermoplastic fibers. The meanings of the main components are those excluding additive components such as adhesives, lubricants and dispersants, and are used in the sense of components that occupy at least 50% or more, preferably 70% or more.
・ The nonwoven fabric used as the core material is required to have dimensional stability when wet, and the water resistance of the material is required, so use hydrophobic thermoplastic fibers such as various synthetic resin fibers. Is desirable.
・ Non-woven fabric used as the core material is required to be easily deformed and thinned by thermocompression bonding even if it is bulky and thick when used. For this purpose, it is required to use thermoplastic fibers. .
-Furthermore, imparting easy heat melting to a part of the fibers also contributes to promoting the integration of the laminated state. For that purpose, it is desirable to use a composite fiber or a split fiber in which an easily heat-meltable component coexists in addition to a thermoplastic component. In the case of a simple nonwoven fabric made of only an easily heat-meltable component, for example, PE or PP, the nonwoven fabric structure collapses and heat shrinks due to the heat melting treatment, and the entire skeleton disappears and dimensional stability cannot be maintained. However, for example, when a nonwoven fabric made of a composite fiber of PE / PET having a melting temperature difference of 140 ° C. between PE resin: 125 ° C. and PET resin: 265 ° C. is thermocompression bonded at around 130 ° C., which is the melting temperature of PE resin, PET fibers A tough, dimensional-stable sheet with the surface remaining as a film, leaving only the skeleton, and having a mesh opening, is obtained. Further, when the melting temperature of the PET resin is around 260 ° C., the whole becomes a transparent film and the openings disappear. Table 2 shows the results of tracing the surface change and thickness change of the nonwoven fabric composed of the composite fiber of PE / PET when the temperature was changed from room temperature to 280 ° C. under the condition of a pressurization degree of 3 MPa. .

  When a three-layer laminated sheet obtained by laminating a nonwoven fabric having such properties as the core and laminating with the upper and lower porous fiber layers at about 130 ° C., the upper and lower porous fiber layers are separated from the nonwoven fabric. The inter-fiber spaces of the nonwoven fabric are mutually penetrated at the contact surface of the non-woven fabric, so that the upper-layer constituent fibers and the lower-layer constituent fibers are mixed, fused, joined and integrated, so-called “welded” ultrathin A three-layer laminated sheet is obtained.

(D) Specific examples and specific examples of the non-woven fabric used as the core material include a single filament continuous filament made of EVA, PE, PP, PET resin, etc. Spunbond, meltblown, or spunbond composed of continuous filaments of composite fibers having a surface layer of an easily meltable resin component such as / PE, PE / PP, PP derivative / PP, PE / PET, and PET derivative / PET Collectively called so-called "spun melt nonwoven fabrics" such as SM (spunbond / meltblown), SMS (spunbond / meltblown / spunbond), SMMS (spunbond / meltblown / meltblown / spunbond), which are multilayers of meltblown A non-woven fabric group is a desirable example.
As another more specific example, EVA, PE, PP, PET in which the nonwoven fabric used as the core material has a fineness of 1.7 denier or less, a fiber length of 20 mm or less, preferably 1.0 denier or less, and a fiber length of 10 mm or less. The main component is a single fiber made of resin or the like, EVA / PE, PE / PP, PP derivative / PP, PE / PET, PET derivative / PET, etc. Another example is a so-called “wet nonwoven fabric” in which an aqueous dispersion is prepared and a sheet is formed by adding a binder or a viscosity modifier in some cases.

4). Steps for the formation of a porous fiber layer and the formation of a three-layer laminated structure In principle, if the porous fiber layer is laminated on and below the nonwoven fabric as the core and laminated in a sandwich shape, 3 of this embodiment A layered laminate sheet should be able to be formed.

  The core nonwoven fabric is a ready-made material. However, in the "porous fiber layer composed of fine cellulose fibers", the "porous fiber layer" itself is unstable, brittle and difficult to handle, so it does not exist as "off-the-shelf material" It is generated in the process of forming the structure and is directly incorporated into the three-layer laminated sheet as it is without being separated. Alternatively, when separated and used as a “porous fiber layer sheet”, it is one of the features of this embodiment that it is handled in a combined state in combination with a protective sheet. In addition, the “fine-sized cellulose fiber” used as a raw material is not present as each isolated fiber, but is obtained as an aggregate of water-containing and hydrated fibers. The aggregate is generally treated as a viscous dispersion obtained by diluting with water alone or a water-containing medium containing an organic solvent. Accordingly, “fine-sized cellulose fibers” are handled as fiber dispersions present in a water-containing medium at a concentration of 1 wt% or less as described below unless otherwise noted in the present embodiment.

(A) Specific step example of formation of “porous fiber layer composed of fine cellulose fibers” • For example, “MFC” (manufactured by Nippon Absorbent Technology Laboratory) is prepared as a fine cellulose fiber, and the concentration is set to 0. A 5 wt% ethanol / water (60/40) dispersion slurry is prepared.
When SMS (13 g / m ² ) is prepared as a base material and a protective sheet, the above dispersion is filled in an applicator, the opening clearance is set to 1.5 mm, and coating is performed on the SMS nonwoven fabric, the wet SMS / A coalescing sheet of fine cellulose fiber layers is obtained. This sheet was dried under tension to form a 3.5 g / m ² porous fiber layer with a protective sheet (referred to as R1 or R2). This is expressed as (R1P) because it is a combined body of the upper porous fiber layer (referred to as P) and the protective sheet (R1). Since this upper porous fiber layer has the same composition as the lower porous fiber layer (Q), it is a combination of the lower porous fiber layer (Q) and the protective sheet (R2). It can also be used as a porous fiber layer. Thus, the porous fiber layer united with the protective sheet is used as an element sheet for forming a three-layer laminated sheet in the form of either R1P or QR2.
-The protective sheets (R1, R2) also play an important role in the production of the three-layer laminated sheet. The non-woven fabric used as the protective sheet must be a non-woven fabric that is in close contact with the porous fiber layer but easily separated from the non-woven fabric, so that a smooth surface, hydrophobic, thin and sufficient liquid permeability is selected. The As a specific example, a so-called “spun melt non-woven fabric” such as a spunbond, a meltblown or a multi-layer of spunbond and meltblown composed of single filaments made of PP, PET resin or the like as a raw material is generically named. A group of nonwoven fabrics is a desirable example. Alternatively, a soft and fine nylon mesh or the like is another desirable example.

(A) Specific steps of forming a core non-woven fabric / porous fiber layer laminated sheet (P / S or S / Q) by coating on a non-woven fabric (S) serving as a core material The nonwoven fabric used as the material is a spunbonded nonwoven fabric ("Elves" manufactured by Unitika) composed of about 1.2 denier PE / PET composite fiber filaments, and has a thickness of 40 μm, a basis weight of 7 g / m ² , and 50 to 70 mesh. Has a net-like opening. The PE component constituting this fiber has a softening temperature of about 110 ° C., a heat melting temperature of 125 ° C., a PET component has a softening temperature of about 240 ° C., and a heat melting temperature of 265 ° C.
・ Prepare an MFC concentration 0.5 wt% ethanol / water (60/40) dispersion slurry, fill the dispersion into the applicator, set the opening clearance to 1.5 mm, and coat on the spunbonded nonwoven fabric To give a combined sheet of a spunbonded nonwoven fabric / fine-diameter cellulose fiber layer in a wet state. When this sheet was dried under tension, a 3.5 g / m ² porous fiber layer was formed which was bonded to the non-woven fabric to be the core material. This is a laminated sheet (P / S) or (S / Q) of a core nonwoven fabric / porous fiber layer. Such a laminated sheet of the core non-woven fabric / porous fiber layer is used as an element sheet for forming a three-layer laminated sheet in either P / S or S / Q form.

(C) Method of forming a three-layer laminated sheet characterized by laminating in a wet state As shown in FIG. 5A, the wet SMS / fine-diameter cellulose fiber layer (QR2) obtained in (a) above. (R1P / S) spunbond in which a protective sheet (SMS) is provided on the fiber layer surface and the wet spunbond nonwoven fabric / fine-diameter cellulose fiber layer combined sheet (P / S) obtained in (a) above The nonwoven fabric surface is overlaid (Steps S11 and S12), and is pressed and integrated in a wet state (Step S13). The solvent is removed under tension and dried (Step S14). Finally, protective sheets (SMS) provided on the upper and lower sides. By removing the, a very thin three-layer laminated sheet (P / S / Q) having a thickness of about 35 μm as expressed in FIG. 3 is obtained (step S15). In an actual manufacturing process, it is desirable to provide a protective sheet (SMS) up and down as shown by the flow sheet in FIG. 5A, but a protective sheet may be provided on one of the upper and lower sides.

(D) Method for forming a three-layer laminated sheet in which a porous fiber layer prepared in advance is laminated on a united sheet in a wet state As shown in FIG. 5B, a span in a wet state obtained in (a) above (R1P / S) provided with a protective sheet (SMS) on a bonded nonwoven fabric / fine-diameter cellulose fiber layer combined sheet (P / S) is prepared (step S11), and the wet state obtained in (a) above. SMS / fine diameter cellulose fiber layer (QR2) is prepared (step S12). The wet SMS / fine-diameter cellulose fiber layer (QR2) is desolvated and dried (step S16) to obtain a dried lower porous fiber layer (QR2) (step S17). Porous fiber of dry lower porous fiber layer (QR2) on spunbond nonwoven fabric surface of spunbond nonwoven fabric / fine-diameter cellulose fiber layer combined sheet (RP / S) provided with wet protective sheet (SMS) The layer surfaces are overlapped, pressure-bonded and integrated (step S13), desolvated and dried under tension (step S14), and finally the protective sheet (SMS) is removed to obtain a thickness as expressed in FIG. A very thin three-layer laminated sheet (P / S / Q) of about 35 μm is obtained (step S15). In the actual manufacturing process, as shown in the flow sheet of FIG. 5B, it is desirable to provide the protective sheet (SMS) vertically, but the protective sheet may be provided on one of the upper and lower sides.

  As shown in FIG. 5C, the SMS / fine-sized cellulose fiber layer (R1P) or (QR2) (step S12) in a wet state and a protective sheet (SMS) were provided on the dried S / Q and P / S. Combined with the laminated sheet (S / QR2) or (R1P / S) (steps S11, S18, S19) of the core non-woven fabric / porous fiber layer provided with the protective sheet, and bonded (step S13), The solvent is removed under tension and dried (step S14). Finally, the protective sheet (SMS) is removed to obtain a three-layer laminated sheet (P / S / Q) (step S15).

(E) Method of forming a three-layer laminated sheet characterized by integration by thermocompression bonding in a dry state As shown in FIG. 5D, a dry porous fiber layer (R1P), (QR2) combined with a protective sheet (Steps S12, S16, S17), and a laminated sheet (S / QR2), (R1P / S) of a core nonwoven fabric / porous fiber layer in a dry state combined with a protective sheet (Step S11, S18, S19) are combined, thermocompression bonded and integrated (step S13 ′), and finally the protective sheet (SMS) is removed to obtain a three-layer laminated sheet (P / S / Q) (step S15). .

(F) A method for forming a three-layer laminated sheet, wherein the core nonwoven fabric is integrated by sandwiching it at the end. In the method for forming a layer laminated sheet shown in FIGS. The laminated sheet (P / S) or (S / Q) is formed as one of the element sheets, but as shown in FIG. 6A and FIG. 6B, the core non-woven fabric (S ) Can be sandwiched between the porous fiber layers later. That is, (R1P) or (QR2) combined with the protective sheet is prepared (step S21), and the solvent is removed and dried (step S22). Thereafter, the dried (R1P) or (QR2) (step S23) and the wet SMS / fine diameter cellulose fiber layer (R1P) or (QR2) (step S12) or the dry SMS / fine diameter cellulose fiber When the layer (R1P) or (QR2) (step S17) is laminated and integrated, the core nonwoven fabric (S) is sandwiched between them.

  6A is a flow sheet in which one of (R1P) or (QR2) combined with a protective sheet is laminated in a dry state and the other in a wet state, and FIG. 6B is a flow sheet when both are laminated in a dry state. is there. 6A and 6B, the same steps as those in FIGS. 5A to 5D are denoted by the same reference numerals.

  Any one of (R1P) and (QR2) in the dry state shown in FIG. 5D, (S / QR2) and (R1P / S) in the dry state, or (R1P) and (QR2) in the dry state shown in FIG. 6B ) And any one of the core non-woven fabric (S) and the dried (QR2) and (R1P) are simply overlapped to form a three-layer laminated state with a protective sheet. In order to integrate them, thermocompression bonding using heat and pressure is required as shown in the flow sheet of step S13 'in FIGS. 5D and 6B. If this heat and pressure are not properly selected, the film will either lose its breathability or become too thick to be used. This thermocompression bonding process is necessary as a final finishing step regardless of which lamination method shown in FIGS. 5A to 5D is adopted, and will be described in more detail below.

(G) “Welding temperature” required for integration and pressure required for thinning In order to integrate, the upper and lower surfaces of the core nonwoven fabric, the upper layer and the lower porous fiber layer Must be joined. In this example, the PE component existing on the surface of the composite fiber constituting the nonwoven fabric serves as the binder. Therefore, the necessary temperature is a temperature around 130 ° C. at which this PE component is plasticized and further melted, and is expressed as “welding temperature”. The required pressure is the pressure that leads the three layers into close contact at this “welding temperature”.
-Relationship between temperature, pressure and thinning at the time of thermocompression Fig. 7 shows the change in thermocompression temperature and thickness when the degree of pressurization was set at two levels of 3MPa and 10MPa. Although the three-layer laminated sheet becomes thinner depending on the degree of pressurization, this is because the porous fiber layer is compressed. As will be described later, air permeability and pressurization are in a trade-off relationship. It is. The degree of pressurization is at least 30 MPa, preferably 20 MPa or less, more preferably 0.1 MPa to 10 MPa. When it is 30 MPa or more, it is impossible to maintain an appropriate air permeability level, and when it is 0.1 MPa or less, it is difficult to perform uniform pressing. Observing the change in thickness due to temperature, it can be seen that the thinning suddenly progresses from around 120 ° C., and the thinning further proceeds suddenly when it exceeds 260 ° C. This corresponds to the dissolution temperatures of PE and PET, which are nonwoven fabric components, respectively. Therefore, in order to effectively perform the welding process, it is desirable to set the pressurization degree to be low in the range of 120 to 130 ° C. However, if it is possible to increase the pressurization degree in consideration of the balance with the air permeability, it can be relatively easily set to 20 μm or less.

  When the degree of pressurization is increased above 260 ° C. above the melting temperature of PET, the appearance changes to a film shape, causing a rapid increase in air permeability.

As described above, Table 2 shows changes in the surface state and the thickness due to thermocompression bonding of the used core fabric woven fabric alone. It can be seen that the change in the thickness of the three-layer laminated sheet is also affected by the change due to the thermocompression bonding of the core cloth.
-Relationship between temperature, pressure and air permeability during thermocompression bonding FIG. 8 shows changes in thermocompression bonding temperature and air permeability when the pressurization degree is set at two levels of 3 MPa and 10 MPa. The air permeability of the three-layer laminated sheet increases according to the degree of pressurization, but this is because the porous fiber layer is compressed, so it is important to note that the air permeability and the degree of pressurization are in a trade-off relationship. It is. Observing the change in the air permeability according to the temperature, it can be seen that the air permeability rapidly increases from around 120 ° C., and when it exceeds 260 ° C., the air permeability increases further rapidly. This temperature corresponds to the melting temperature of PE and PET, which are nonwoven fabric components, respectively. Therefore, in order to effectively perform the welding process, when the easily meltable component is PE, it is desirable to set the pressurization degree at a low level within a range not exceeding 130 ° C. When it exceeds 130 ° C., it becomes difficult to maintain the air permeability level of 1000 sec / 100 ml or less, which is the target of the present invention. When thermocompression bonding is performed at a temperature corresponding to the melting temperature of PET exceeding about 260 ° C., it rapidly rises to 5000 sec / 100 ml or more, so that ion transmission stops. This principle can be applied as a so-called “shutdown effect” of ions to impart safety of the electricity storage device. In order to stably exhibit the “shutdown effect”, it is necessary to impart an air permeability of 10,000 sec / 100 ml or more.

  The core non-woven fabric composed of the composite fiber having the easily meltable component has been described. However, as PE / PP and PP derivative / PP, the softening between the easily meltable component and the core component and the melting temperature difference are reduced, and the preferred heating range Since it becomes narrow, care must be taken when setting the conditions. In particular, in the case of single component fibers, processing at the melting temperature increases the risk of filming too much or causing shrinkage, so the effect of thinning is reduced, but not at the melting temperature, but at the softening temperature. Determine the crimping temperature for the target. For example, in the case of PP single fiber, the range of 140 to 150 ° C is selected, and in the case of PET single fiber, the range of 240 to 250 ° C is selected.

5. Method for Producing Three-Layer Laminated Sheet A process for continuously producing an ultra-thin sheet of 40 μm or less and an air permeability of 1000 sec / 100 ml or less according to this embodiment will be described with reference to FIGS. 9 and 10. .
FIG. 9 is a view showing a manufacturing apparatus that executes the process of laminating in the wet state shown in FIG. 5A, and is configured to include the following unit steps.

  Reference numerals 101-1 and 101-2 are dispersion slurry supply devices in which the fine cellulose fibers are mixed and dispersed in a dispersion medium. For example, 0.5 wt% MFC is dispersed in an ethanol / water (60/40) medium. The finished slurry is supplied from this slurry supply device.

  An apparatus 102 unwinds the first protective sheet (R) and supplies the first protective sheet (R) to the first traveling net conveyor 100-1. As the protective sheet (R), for example, an PP nonwoven fabric made of PP resin is supplied.

  Reference numeral 103 denotes an apparatus for pre-coating the first protective sheet (R) with a pre-coat solvent on the traveling net conveyor 100-1, and as the pre-coat agent, for example, a mixed solvent of ethanol / water (40/60) is used.

  Reference numeral 104 denotes an apparatus for coating the first slurry on the first protective sheet (R) pre-coated on the traveling net conveyor 100-1 to a predetermined thickness. Here, a roll coater is illustrated as an example. An appropriate coating apparatus such as a coater or gravure coater may be employed.

  105-1 removes a predetermined amount of the dispersion medium from the fine cellulose fiber mat coated on the first protective sheet (R) on the traveling net conveyor 100-1, and the solvent-containing sheet (QR). Or it is an apparatus which shape | molds (RP). Here, a suction box using vacuum is installed under the net conveyor, and the dispersion medium is removed according to the degree of vacuum.

  106 is the unwinding of the nonwoven fabric (S) used as a core material, and the supply apparatus to the 2nd traveling net conveyor 100-2, 107 is a nonwoven fabric (S) on the traveling net conveyor 100-2, and applies a precoat solvent to the nonwoven fabric (S). It is an apparatus for pre-coating.

  108 is a device for coating the dispersed slurry to a predetermined thickness on the nonwoven fabric (S) pre-coated on the traveling net conveyor 100-2, and 105-2 is a nonwoven fabric (10) on the traveling net conveyor 100-2. S) An apparatus for removing a predetermined amount of a dispersion medium from a fine-diameter cellulose fiber mat coated thereon.

  No. 109 supplies the second protective sheet (R) from above to the fine-sized cellulose fiber mat, covers and integrates the surface of the fiber mat, and rolls and press-fits the sheet (RP / S) or (S / QR).

  110 is a solvent-containing sheet (QR) or (RP) on the first traveling net conveyor 100-1 and a solvent-containing sheet (RP / S) or (S / QR) on the second traveling net conveyor 100-2. ) And press roll pressure bonding to combine and join to form a sheet (RP / S / QR).

  111 is a device for drying and desolvation after the sheet (RP / S / QR) is integrated by pressure bonding, and 112 is a sheet (RP / S / QR) that removes the two protective sheets (R) and removes the sheet. This is a device for obtaining (P / S / Q).

  Sheets (P / S / Q) obtained in such a process are usually finished as separate lines, and are pressed at room temperature or under heating to finely adjust the thickness, surface finish, defect check, etc. To make the final product, but the detailed explanation is omitted.

  10 shows a sheet RP / S (or S / QR) obtained in the wet state shown in FIG. 5B (shown as R1P / S (or S / QR2) in FIG. 5B) and a dry state prepared in advance. There is a process flow sheet for laminating QR (or RP) supplied in (1). From the step of unwinding the protective sheet (R) by the apparatus 102 in FIG. 9 and supplying it to the first traveling net conveyor 100-1, the apparatus 105-1 forms the sheet (QR) or (RP) in a solvent-containing state. The process 114 is replaced with the device 114 for supplying the dry sheet QR (or RP) manufactured in advance, and the apparatus 113 is used to unwind the roll-shaped dry sheet (QR) or (RP) to obtain a solvent-containing sheet ( RP / S) or (S / QR) and press roll pressure bonding are combined and joined to form a solvent-containing sheet (RP / S / QR). Since the apparatus used in the process of FIG. 10 is the same except for the apparatuses 113 and 114, the same reference numerals are given and description thereof is omitted.

  The sheet (P / S / Q) obtained in the process described with reference to FIG. 10 is usually a finishing process provided as a separate line, and is pressed at room temperature or under heating to finely adjust the thickness and finish the surface. Then, defect check is performed to make the final product. 9 and FIG. 10, the two protective sheets are removed at the same time. 1) The two protective sheets are attached and wound up and subjected to finishing processing such as press processing and heat press processing as they are. Later, the protective sheet may be removed last. 2) Also, in the preliminary pressing step, one protective sheet is removed, and the protective sheet after the pressing process is performed with the protective sheet attached on one side (P / S / Q). A method of performing heat pressing is also performed.

  The process flow sheet for laminating the sheet QR (or RP) obtained in the wet state shown in FIG. 5C with the sheet RP / S (or S / QR) supplied in a dry state prepared in advance is the apparatus in FIG. Since the process using the apparatus 109 from 106 is replaced with a dry sheet RP / S (or S / QR) manufactured in advance, description of the manufacturing process is omitted, but FIG. 5B (FIG. 10), FIG. The processes shown in FIGS. 5C and 5D do not require two coating stations as in the process of FIG. 5A (FIG. 9), so there is an advantage that the capital investment cost can be significantly reduced.

  The present embodiment is an invention related to a three-layer structure product, but the protective sheet R is removed from the sheet RP / S (or S / QR) obtained in the intermediate process of manufacturing, and the sheet P / S (or S / Q). Similarly, the protective sheet R is removed from the sheet QR (or RP) obtained in the intermediate step of the production of the two-layer structure product, and a product composed of the single-layer sheet Q (or P) of the fine cellulose layer is also prepared. I also add what I can do.

6). Examples The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to these.

Each physical property evaluation in this example was measured by the following method.
・ Fiber diameter Fiber diameter is calculated by taking a scanning electron microscope (SEM) photograph of fine cellulose fibers, measuring 20 or more fiber diameters on the photograph, and converting the photographing magnification to calculate the average fiber diameter. did.
-Fiber length Fiber length was measured using a fiber length measuring machine ("FS-200" manufactured by Kayani). The measured fiber length is the mass weighted average fiber length.
-Sheet thickness Based on JIS L-1085, using a thickness measuring instrument ("FFA-12" manufactured by Ozaki Seisakusho Co., Ltd.), 10 arbitrary points on the sheet were measured, and the average value was obtained.
-Air permeability Based on JIS P-8117: 2009, the time for which 100 ml of air permeated was measured by the Gurley method. In the measurement using the Gurley method, a B-shaped Gurley tester was used. The ISO air permeability can be calculated by the following formula using data measured by the Gurley tester method.
P = (135.3) / t P: ISO air permeability [μm / (Pa · s)]
t: Average value of time for which 100 ml of air permeates (s)

Example 1
1. ) Preparation of raw material A) Preparation of fine-diameter cellulose fiber A water-containing MFC (manufactured by Nippon Absorbent Technology Laboratory) having the following performance and a solid content concentration of 7 wt% is prepared.

Average fiber diameter: 500 nm
Water holding amount: 38 ml / g
B) Preparation of core non-woven fabric A PE / PET composite fiber spunbonded non-woven fabric (manufactured by Unitika Ltd.) having the following properties formed from about 1.2 denier filament is prepared.

Weight per unit: 7 g / m ²
Thickness: 40 μm
Inter-fiber opening rate: 65%
Fiber component: sheath component PE Melting temperature 125 ° C
Core component PET Melting temperature 265 ° C
C) Preparation of Protective Sheet A PP non-woven fabric made of PP (Avgol) with a basis weight of 13 g / m ² is prepared.
2) Formation of porous fiber layer A three-layer laminated sheet is prepared by a procedure along the flow sheet of FIG. 5A.
A) Preparation of dispersion slurry of fine cellulose fiber ・ MFC is dispersed in a mixed solvent of ethanol / water (60/40) using a homomixer to prepare a dispersion slurry having a concentration of 0.5 wt%. The dispersed slurry is vacuum defoamed with an aspirator.
B) A silica gel coating applicator used for producing a thin layer chromatographic test plate is used as a coating / hand coater for the protective sheet of the dispersed slurry.
-A pre-coating solution of ethanol / water (60/40) is pre-coated on an SMS nonwoven fabric (R) made of PP, which is the protective sheet laid on a horizontal glass plate, using an applicator.
Subsequently, the opening clearance of the applicator is set to 1.5 mm, and a predetermined amount of coating is performed by filling the dispersion slurry of the 0.5 wt% concentration fine cellulose fibers.
-The protective sheet after coating is left as it is for a while to remove excess solvent to obtain wet (QR).
C) Coating of the dispersion slurry on the core non-woven fabric-In the same procedure as in the case of the protective sheet of B), the dispersion slurry of the fine cellulose fibers is placed on the PE / PET composite fiber spunbond nonwoven fabric (S) of the core nonwoven fabric. Apply a certain amount of coating and remove excess solvent to obtain wet (P / S).
D) The core nonwoven fabric coated with the fine cellulose fibers prepared in C) is superposed on the fine cellulose fiber layers on the protective sheet produced in the three-layer lamination and wet press B), and another one An SMS nonwoven fabric (R), which is a new protective sheet, is superposed on the sheet and the top layer to obtain a wet state (RP / S / QR).
· The superimposed double-sided laminated sheet sandwiched by acrylic plates, subjected to wet-pressed with a load of about 10 g / cm ^2.
E) In order to suppress excessive shrinkage in the process of desolvation, drying and drying, the laminated sheet is fixed to an acrylic plate with a clip and dried with hot air of 60 to 80 ° C.
F) Removal of protective sheet The protective sheets on both sides are removed from the dried and dried laminated sheet, and an integrated three-layer laminated sheet (P / S / Q) is taken out. The thickness of the obtained three-layer laminated sheet was 39 μm.
G) Hot press treatment ・ The obtained three-layer laminated sheet was sandwiched between stainless steel plates subjected to surface Teflon (registered trademark) processing and subjected to hot press at a setting condition of 130 ° C. × 3 MPa × 5 minutes, and a thickness of 28 μm. A separator for a storage element was obtained.
3) Properties of the obtained separator for a storage element The properties of the three-layer laminated sheet obtained in this example are shown in Table 3 (including the properties of the three-layer laminated sheet obtained in Examples 2 and 3).

4) Test results as a lithium secondary battery separator Table 4 shows the configuration of the lithium secondary battery when the three-layer laminated sheet obtained in the present invention was tested as a lithium secondary battery separator. The results are shown in Table 5.

  According to the evaluation by experts, this three-layer laminated sheet has a high AC impedance of 20,000 Hz, but other characteristics clear the reference value and function as a separator for a lithium secondary battery. It was evaluated that it was.

Example 2
1). Preparation of raw material A) Preparation of fine-diameter cellulose fiber The same MFC (manufactured by Nippon Absorbent Technology Laboratory) as prepared in Example 1, and water-containing biocellulose having a solid content concentration of 10 wt% having the following performance (Ajinomoto Co., Inc.) is prepared.

Average fiber diameter: 30 nm
Amount of water: 80 ml / g

B) Preparation of porosity promoter A water dispersion slurry (manufactured by Mizusawa Chemical Co., Ltd.) of wet process fine powder silica having an average particle size of 2 μm and a solid content concentration of 20 wt% is prepared as a porosity promoter.
C) Preparation of core nonwoven fabric A PET fiber wet nonwoven fabric (manufactured by Hirose Paper Co., Ltd.) having the following properties formed from a single fiber of PET resin having a fineness of 0.5 denier and a fiber length of 5 mm is prepared.

Weight per unit: 5 g / m ²
Thickness: 17 μm
Inter-fiber opening rate: 70%
Fiber component: PET Melting temperature 265 ° C
D) Preparation of protective sheet A non-woven fabric made of PP with a basis weight of 13 g / m ² (manufactured by Avgor) is prepared.
2) Formation of porous fiber layer Similarly to Example 1, a three-layer laminated sheet is produced by the procedure along the flow sheet of FIG. 5A.
A) Preparation of dispersion slurry of fine cellulose fibers ・ MFC, biocellulose and silica are mixed at 1: 1: 1 (the amount of silica added is 50 wt% with respect to fine cellulose fibers). Using a homomixer, disperse in a mixed solvent of ethanol / water (80/20) to prepare a dispersion slurry having a concentration of 0.45 wt%. Thereafter, this solution is vacuum defoamed with an aspirator to obtain a dispersion slurry for coating.
B) Coating of dispersion slurry on protective sheet-Precoat liquid of ethanol / water (80/20) is applied to the SMS non-woven fabric (R) made of PP, which is the protective sheet laid on a horizontal glass plate, using an applicator. .
Subsequently, the opening clearance of the applicator is set to 1.5 mm, and a predetermined amount of coating is performed by filling the dispersion slurry of 0.45 wt% fine cellulose fiber.
-The protective sheet after coating is left as it is for a while to remove excess solvent to obtain wet (QR).
C) Coating of the dispersion slurry on the core non-woven fabric-In the same procedure as in the case of the protective sheet of B), a predetermined amount of the fine-sized cellulose fiber dispersion slurry is coated on the PET nonwoven fabric (S) of the core nonwoven fabric. Excess solvent is removed to obtain wet (P / S).
D) The core nonwoven fabric coated with the fine cellulose fibers prepared in C) is superposed on the fine cellulose fiber layers on the protective sheet produced in the three-layer lamination and wet press B), and another one An SMS nonwoven fabric (R), which is a new protective sheet, is superposed on the sheet and the top layer to obtain a wet state (RP / S / QR).
· The superimposed double-sided laminated sheet sandwiched by acrylic plates, subjected to wet-pressed with a load of about 10 g / cm ^2.
E) In order to suppress excessive shrinkage in the process of desolvation, drying and drying, the laminated sheet is fixed to an acrylic plate with a clip and dried with hot air of 60 to 80 ° C.
F) Removal of protective sheet The protective sheets on both sides are removed from the dried and dried laminated sheet, and an integrated three-layer laminated sheet (P / S / Q) is taken out. As shown in Table 3, the obtained three-layer laminated sheet had a thickness of 22 μm and an air permeability of 65 sec / 100 ml.
G) Hot press treatment ・ The obtained three-layer laminated sheet is sandwiched between stainless steel plates subjected to surface Teflon (registered trademark) processing, and subjected to hot press under the setting conditions of 240 ° C. × 3 MPa × 5 minutes, thickness of 15 μm, A separator for a storage element having an air permeability of 115 sec / 100 ml was obtained.

Example 3
1) Preparation of material as raw material A) Preparation of fine-sized cellulose fiber The same water content biocellulose (manufactured by Ajinomoto Co., Inc.) having a solid content concentration of 10 wt% as prepared in Example 2 is prepared.
B) Preparation of porosity promoter A water dispersion slurry (manufactured by Mizusawa Chemical Co., Ltd.) of wet process fine powder silica having an average particle size of 2 μm and a solid content concentration of 20 wt% is prepared as a porosity promoter.
C) Preparation of core nonwoven fabric A PE / PP fiber wet nonwoven fabric (manufactured by Hirose Paper Co., Ltd.) having the following properties formed from a PE / PP composite fiber having a fineness of 0.5 denier and a fiber length of 5 mm is prepared.

Weight per unit: 3 g / m ²
Thickness: 13 μm
Inter-fiber opening rate: 83%
Fiber component: sheath component PE Melting temperature 125 ° C
Core component PP Melting temperature 165 ° C
D) Preparation of protective sheet A non-woven fabric made of PP with a basis weight of 13 g / m ² (manufactured by Avgor) is prepared.
2) Formation of porous fiber layer Similarly to Example 1, a three-layer laminated sheet is produced by the procedure along the flow sheet of FIG. 5A.
A) Preparation of a dispersion slurry of fine cellulose fibers ・ Using a homomixer, biocellulose and silica are mixed so that each solid content is 1: 1 (the amount of silica added to the fine cellulose fibers is 100 wt%). Disperse in a mixed solvent of isopropanol / water (75/25) to prepare a dispersion slurry having a concentration of 0.6 wt%. Thereafter, this solution is vacuum defoamed with an aspirator to obtain a dispersion slurry for coating.
B) Coating of dispersion slurry on protective sheet ・ Pre-coat liquid of isopropanol / water (75/25) is applied to the SMS SMS nonwoven fabric (R), which is the protective sheet laid on a horizontal glass plate, using an applicator. .
Subsequently, the opening clearance of the applicator is set to 1.2 mm, and a predetermined amount of coating is performed by filling the dispersion slurry of the 0.6 wt% concentration fine-diameter cellulose fibers.
-The protective sheet after coating is left as it is for a while to remove excess solvent to obtain wet (QR).
C) Coating of the dispersion slurry on the core non-woven fabric-In the same procedure as in the case of the protective sheet of B), a predetermined amount of the fine-sized cellulose fiber dispersion slurry is coated on the PET nonwoven fabric (S) of the core nonwoven fabric. Excess solvent is removed to obtain wet (P / S).
D) The core nonwoven fabric coated with the fine cellulose fibers prepared in C) is superposed on the fine cellulose fiber layers on the protective sheet produced in the three-layer lamination and wet press B), and another one An SMS nonwoven fabric (R), which is a new protective sheet, is superposed on the sheet and the top layer to obtain a wet state (RP / S / QR).
· The superimposed double-sided laminated sheet sandwiched by acrylic plates, subjected to wet-pressed with a load of about 10 g / cm ^2.
E) In order to suppress excessive shrinkage in the process of desolvation, drying and drying, the laminated sheet is fixed to an acrylic plate with a clip and dried with hot air of 60 to 80 ° C.
F) Removal of protective sheet The protective sheets on both sides are removed from the dried and dried laminated sheet, and an integrated three-layer laminated sheet (P / S / Q) is taken out. As shown in Table 3, the obtained three-layer laminated sheet had a thickness of 18 μm and an air permeability of 84 sec / 100 ml.
G) Hot press treatment ・ The obtained three-layer laminated sheet is sandwiched between stainless steel plates subjected to surface Teflon (registered trademark) processing and subjected to hot press under the setting conditions of 130 ° C. × 3 MPa × 5 minutes, thickness of 13 μm, A separator for an electricity storage element having an air permeability of 176 sec / 100 ml was obtained.
3) Properties of the obtained separator for electricity storage element Properties of the three-layer laminated sheet obtained in the present invention are shown in Table 3.
4) Test results as lithium secondary battery separator Table 4 shows the configuration of the lithium battery when the three-layer laminated sheet obtained in the present invention was tested as a lithium secondary battery separator. It is described in Table 5.

  This three-layer laminated sheet was evaluated as functioning as a separator for a lithium secondary battery, according to evaluation by experts.

  Hereinafter, the structural example of the lithium secondary battery as an electrical storage element using the three-layer lamination sheet concerning this invention as a separator is demonstrated.

  Examples of the lithium secondary battery having a separator include a cylindrical type, a square type, and a laminated type using a laminated film instead of a metal can. Various patent applications have been made for lithium secondary batteries, such as JP 2011-175810 A and JP 2011-129420 A.

  Hereinafter, a lithium secondary battery described in JP 2011-129420 A will be described as an example of a cylindrical lithium secondary battery with reference to FIG. 11. Here, the description will be made based on the contents described in FIG. 1 and paragraphs 0114-0117 of the publication.

  In the lithium secondary battery shown in FIG. 11, a wound electrode body 20 and a pair of insulating plates 12 and 13 are housed in a substantially hollow cylindrical battery can 11. The wound electrode body 20 is a wound laminated body in which a positive electrode 21 and a negative electrode 22 are laminated and wound via a separator 23.

  The battery can 11 has a hollow structure in which one end is closed and the other end is opened. The pair of insulating plates 12 and 13 are arranged so as to sandwich the wound electrode body 20 from above and below and to extend perpendicularly to the wound peripheral surface.

  A battery lid 14, a safety valve mechanism 15, and a heat sensitive resistor (PTC element) 16 are caulked through a gasket 17 at the open end of the battery can 11, and the battery can 11 is sealed. . The safety valve mechanism 15 and the thermal resistance element 16 are provided inside the battery lid 14, and the safety valve mechanism 15 is electrically connected to the battery lid 14 via the thermal resistance element 16. In the safety valve mechanism 15, when the internal pressure becomes a certain level or more due to an internal short circuit or external heating, the disk plate 15 </ b> A is reversed and the electric power between the battery lid 14 and the wound electrode body 20 is reversed. Connection is cut off. The heat sensitive resistance element 16 prevents abnormal heat generation due to a large current by increasing resistance in response to temperature rise. The gasket 17 is made of, for example, an insulating material.

  A center pin 24 may be inserted in the center of the wound electrode body 20. A positive electrode lead 25 formed of a conductive material such as aluminum is connected to the positive electrode 21, and a negative electrode lead 26 formed of a conductive material such as nickel is connected to the negative electrode 22. The positive electrode lead 25 is welded to the safety valve mechanism 15 and is electrically connected to the battery lid 14, and the negative electrode lead 26 is welded to the battery can 11 and electrically connected thereto.

  The separator 23 separates the positive electrode 21 and the negative electrode 22 and allows lithium ions to pass through while preventing a short circuit of current due to contact between the two electrodes. A sheet can be used.

  The lithium secondary battery can be suitably used for applications such as a power source for automobiles for hybrid vehicles, electric vehicles, etc., a power source for portable devices and electric tools, a power source for power storage, and the like. An example in which a lithium secondary battery is mounted as a power source for an automobile is described in, for example, Japanese Patent Application Laid-Open No. 2011-175749.

  While typical embodiments of the present invention have been described above, the present invention can be carried out in various other forms without departing from the spirit or main features defined by the claims of the present application. Can do. Therefore, each embodiment mentioned above is only an illustration, and should not be interpreted limitedly. The scope of the present invention is indicated by the scope of claims, and is not restricted by the description or the abstract. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention. In the claims, for ease of understanding, symbols such as R1, R2, S, P, and Q used in the embodiment are used. However, the scope of the present invention indicated in the claims is used in the embodiment. It is not particularly limited to the examples shown.

  This application claims the priority on the basis of Japanese Patent Application No. 2011-225871 for which it applied on October 13, 2011. As shown in FIG. And all the content disclosed by Japanese Patent Application No. 2011-225871 is contained in the content of this application.

P, Q porous fiber layer S

Claims (2)

The thermoplastic fibers and the central core material nonwoven whose main component, as the upper layer and the lower layer, the average fiber length 0.05mm~1mm der is, and an average fiber diameter of Ru der least 1μm below 5nm fine In a three-layer laminated sheet for a separator for an electricity storage device, comprising the first and second porous fiber layers mainly composed of a diameter cellulose fiber,
At least a portion extending from the interface between the nonwoven fabric and the first and second porous fiber layers in a region where the constituent fibers of the first and second porous fiber layers enter the inter-fiber gap of the nonwoven fabric. In the region, the constituent fibers of the first and second porous fiber layers are joined and integrated with the nonwoven fabric,
3 for a storage element separator, wherein the nonwoven fabric is composed of a continuous filament of any one of EVA, PE, PP, PET, EVA / PE, PE / PP, PP derivative / PP, PE / PET, and PET derivative / PET. Layer laminated sheet. The three-layer laminated sheet according to claim 1, wherein the region exists over the entire region in the thickness direction of the nonwoven fabric.