TWI601640B - Sealing film - Google Patents

Description

Sealing film

The present invention relates to a method for producing a sealing film for sealing an electrode of a power generating element such as a secondary battery or a capacitor housed in a bag body, and a sealing film.

The present application claims priority based on Japanese Patent Application No. 2010-252940, filed on Jan.

In recent years, the industry is gradually adopting, for example, a secondary battery or a capacitor housed in a bag containing a film as a power source for an electronic device such as a notebook computer or a mobile phone, or a battery for a hybrid car, a fuel cell car, or a battery car.

Conventionally, these secondary batteries or capacitors are formed by sealing a flat power generating element in a flat bag or a stretch-formed bag including a laminate film in which a sealing layer of polyolefin is laminated on a metal foil such as an aluminum foil. . On the film substrate of the bag body, one end of the electrode for charging and discharging is protruded to the outside and sealed. At the time of sealing, the strip-shaped electrode is sandwiched by the film substrate of the bag body and heat-sealed (electrode lead plate).

In such a secondary battery or the like (hereinafter, referred to as a "battery pack"), the electrode is thicker than the sealing layer of the bag body, so that it is difficult to rewind the resin around the thickness direction of the electrode without a gap during sealing. A gap is formed around the thickness direction of the electrode. When a gap is formed around the electrode, the sealing portion is deteriorated in a severe environment such as long-term use, high temperature, or high humidity, or the bonding strength between the bag body and the electrode of the sealing portion is lowered, and the electrolyte may leak from the sealing portion. Sex.

In response to such problems, in recent years, a method of sandwiching the front and back surfaces of an electrode with a sealing film and heat-sealing the film substrate of the bag body has been used. However, if the conditions of heating or pressurization at the time of sealing are strictly set in order to improve the adhesion between the bag and the electrode, the resin between the metal foil of the bag body and the electrode becomes thin, or the sealing film is deformed, causing The possibility of a short circuit.

Further, when the sealing film is sandwiched between the film substrate of the bag and the electrode and heat-sealed, for example, as disclosed in Patent Document 2, the sealing film is exposed to the opening end of the bag by several millimeters and heat-sealed. By exposing the sealing film in the above manner, it is possible to reliably prevent the short circuit. However, in the case of heat sealing, since the sealing rod contacts or approaches the exposed portion, there is a case where the sealing film is melted or deformed due to the contact of the sealing rod or the radiant heat at a high temperature. Thereby, the electrode becomes easy to come into contact with the metal foil of the film substrate of the bag body.

In order to solve such problems, for example, Patent Document 1 discloses a configuration in which a heat seal portion of a terminal material is covered with a covering material to prevent short-circuiting, and the covering material has a woven fabric, a non-woven fabric, or a super-adhesive film. A laminated structure made of a heat-resistant layer of high molecular weight polyethylene.

Further, Patent Document 2 discloses an adhesive film in which an electron beam crosslinked polyolefin layer and an acid-modified polyolefin are laminated.

[Previous Technical Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 62-61268

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2001-297748

Since the covering material disclosed in Patent Document 1 uses a woven fabric or a non-woven fabric to ensure heat resistance, it is necessary to select a woven fabric or a non-woven fabric to be difficult to melt. However, since the woven fabric or the non-woven fabric is not melted, it is difficult to laminate the thermal adhesive film with high adhesion. Therefore, there is a possibility that pinholes are easily formed and the sealing property is not improved. Sealing instead of falling Happening. Moreover, since ultrahigh molecular weight polyethylene is difficult to obtain, it is disadvantageous in terms of cost. Further, the ultrahigh molecular weight polyethylene cannot be laminated with a thermal adhesive film containing a polypropylene-based resin. Therefore, it is not possible to use a polypropylene-based resin in the sealing layer of the bag body, and it is difficult to improve the heat resistance of the bag body.

The adhesive film disclosed in Patent Document 2 is excellent in heat resistance. However, the film is produced by previously crosslinking the polyolefin film electron beam and extrusion laminating the acid-modified polyolefin layer, or by laminating the polyolefin layer and the acid-modified polyolefin layer by co-extrusion. Electron beam crosslinking. Therefore, the step of electron beam crosslinking is required by either method. Paragraph 0013 of Patent Document 2 discloses that since a usual polypropylene is decomposed by electron beam irradiation, it is necessary to use a specific resin. Further, when the polyolefin layer and the acid-modified polyolefin layer are laminated by co-extrusion and then subjected to electron beam crosslinking, the acid-modified polyolefin is also crosslinked to lower the flexibility, so that it becomes difficult to make The resin wraps around the thickness direction of the electrode without a gap.

The present invention has been made in view of the above background to provide a material which is easily obtained by rewinding the resin around the thickness direction of the electrode without a gap, and which can directly laminate the heat-resistant layer with a high bonding strength by a simple procedure. A method for producing a sealing film which is excellent in heat resistance and sealing property with an electrode adhesive layer, and a sealing film produced by the production method.

The inventors of the present invention have obtained the following knowledge in the study of a sealing film excellent in heat resistance and sealing property: the carboxyl group of the acid-modified polyolefin resin having a carboxylic acid grafting is easily bonded to a hydroxyl group, an amine group, an epoxy group, or the like. The reaction can be easily obtained by modification. The present invention has been completed based on this knowledge.

That is, according to the first aspect of the present invention, the following method for producing a sealing film can be provided.

(1) A method for producing a sealing film, which is a method for producing a sealing film which is sandwiched between an electrode of a power generating element housed in a bag body and an edge of a bag body, and has the following steps: a melt-kneading step of melt-kneading both the acid-modified polyolefin resin A graft-polymerized with a carboxylic acid and the resin B having a functional group reactive with the carboxyl group of the resin A to form a carboxyl group of the resin A The functional group of the resin B is chemically bonded to be modified into the resin C; the heat-resistant layer is formed by forming the resin C into a layer form to form a heat-resistant layer; and then a film forming step of the carboxylic acid-modified polyolefin The resin D is formed into a layer shape to form an electrode adhesion layer next to the electrode, and a lamination step is to directly laminate the heat-resistant layer and the electrode adhesion layer when either or both of the resin C and the resin D are in a molten state.

(2) The method for producing a sealing film according to (1), wherein the melt-kneading step is carried out in an extruder.

(3) The method for producing a sealing film according to (1) or (2), wherein the melt-kneading step and the heat-resistant layer forming step are continuously performed.

(4) The method for producing a sealing film according to any one of (1) to (3) wherein the laminating step is continuous with either or both of the heat-resistant layer forming step and the subsequent layer forming step get on.

(5) The method for producing a sealing film according to any one of (1) to (4) wherein the laminating step is carried out in a co-extrusion die.

(6) The method for producing a sealing film according to any one of (1) to (5), wherein the melt-kneading step is carried out by using a resin A of 99 to 90 and a resin B of 1 to 10 by weight. get on.

(7) A method for producing a sealing film according to any one of (1) to (6), wherein a resin having a melting point equal to or lower than a melting point of the resin A is used as the resin D.

Further, according to the second aspect of the present invention, the following sealing film can be provided.

(8) A sealing film which is sandwiched between the electrode of the power generating element housed in the bag body and the edge of the bag body, and has a heat-resistant layer containing the resin C directly laminated on the carboxylic acid-modified polyolefin resin D The electrode is formed on the layer by a layered structure, and the resin C is The acid-modified polyolefin resin A graft-polymerized with a carboxylic acid and the resin B having a functional group reactive with the carboxyl group of the resin A are melt-kneaded to chemically bond the carboxyl group of the resin A with the functional group of the resin B. Modified by the original.

(9) The sealing film of (8), wherein the resin B is one or more selected from the group consisting of a resin having a hydroxyl group, an amine group or an epoxy group.

(10) The sealing film according to (8) or (9), wherein the resin A is an acid-modified polyolefin resin obtained by graft-polymerizing maleic anhydride onto polypropylene.

(11) The sealing film according to any one of (8) to (10) wherein the laminated structure is formed by co-extrusion of the resin C and the resin D.

(12) The sealing film according to any one of (8) to (11), wherein the heat-resistant layer is laminated with a sealing layer thermally welded to the innermost layer of the bag body.

In the method for producing a sealing film of the present invention, the carboxyl group of the resin A is chemically bonded to the functional group of the resin B to be modified into the resin C. Therefore, a crosslinking step such as electron beam crosslinking is not required. Therefore, the heat resistance of the heat-resistant layer can be imparted by a simple procedure.

Since only the resin A and the resin B are melted and kneaded, they can be modified into the resin C in a usual extruder used in the film forming step.

In the present invention, when either or both of the resin C and the resin D are in a molten state, the heat-resistant layer and the electrode-attached layer are directly laminated. The lamination method combines an extruder with a film forming die to form a layer, and then extrusion laminates another layer. Another method of lamination is to coextrude the heat resistant layer with the electrode back layer. By these methods, in the present invention, the heat-resistant layer and the electrode-attached layer can be directly laminated with a high adhesion strength by a simple procedure. When the sealing film of these methods is heat-sealed, it is difficult to cause the sealing film to be melted or deformed due to the contact of the high-temperature sealing rod or the radiant heat. Thereby, it is difficult to cause a short circuit between the electrode and the metal foil of the bag body.

In particular, the co-extrusion of the heat-resistant layer and the electrode-attached layer can directly laminate the heat-resistant layer and the electrode-attached layer with a higher bonding strength by a simpler step.

The heat-resistant layer of the sealing film of the present invention has a resin C having a small melt flow property by chemically bonding a carboxyl group of the resin A to a functional group of the resin B. Thereby, the heat-resistant layer is hard to be thinned at the time of heat sealing, or the sealing film is hard to be thermally deformed. Therefore, it is difficult to cause a short circuit between the electrode and the metal foil of the bag body.

When the resin B is one or more selected from the group consisting of a hydroxyl group, an amine group, or an epoxy group, the carboxyl group of the resin A and the functional group of the resin B are easily chemically bonded, and are smoothly modified into the resin C. Since the resin A and the resin B are melt-kneaded to be modified into the resin C, the carboxyl group of the resin A and the functional group of the resin B are easily chemically bonded uniformly.

When the resin A is an acid-modified polyolefin resin obtained by graft-polymerizing maleic anhydride onto polypropylene, the carboxyl group of the resin A and the functional group of the resin B are easily chemically bonded, and are more smoothly modified into Resin C.

If the laminated structure of the sealing film is formed by co-extrusion of the resin C and the resin D, the bonding strength of the laminated structure is high, the sealing film is not thermally deformed during heat sealing, or the metal of the electrode and the bag body is hard to be caused. Short circuit of the foil.

When the sealing layer thermally fused to the innermost layer of the bag is laminated on the heat-resistant layer, the heat fusion strength between the innermost layer of the bag and the sealing film can be improved. Further, when the sealing layer is directly laminated on the heat-resistant layer, peeling of the interface due to the electrolytic solution can be prevented.

1‧‧‧ sealing film

2‧‧‧electrode layer

3‧‧‧Heat resistant layer

4‧‧‧ Sealing layer

10‧‧‧electrode with sealing film

11‧‧‧Electrode

20‧‧‧ laminated film of bag

21‧‧‧Metal foil for laminated film

22‧‧‧Layer film sealing layer

23‧‧‧ Film substrate of laminated film

Fig. 1 is a cross-sectional view showing an example of a sealing film of the present invention.

Fig. 2 is a cross-sectional view showing a state in which a laminate film and an electrode of a bag body are joined using the sealing film shown in Fig. 1.

Fig. 3A is a perspective view showing an electrode with a sealing film formed by attaching the sealing film shown in Fig. 1 to an electrode.

Fig. 3B is a cross-sectional view showing an electrode with a sealing film formed by attaching the sealing film shown in Fig. 1 to an electrode.

Hereinafter, the present invention will be described in detail based on the embodiments.

Fig. 1 is a cross-sectional view showing a schematic configuration of a sealing film 1 of the present invention.

Fig. 2 is a cross-sectional view showing the state in which the sealing film 1 shown in Fig. 1 is inserted between the laminate film 20 of the bag body and the electrode 11 and welded thereto, along the longitudinal direction of the electrode 11.

Fig. 3A is a perspective view showing the electrode 10 with the sealing film formed by attaching the sealing film 1 shown in Fig. 1 to the electrode 11. Fig. 3B is a cross-sectional view showing the electrode 10 with the same sealing film in a direction orthogonal to the longitudinal direction of the electrode 11.

The sealing film 1 of the present invention is sandwiched between the electrode of the power generating element housed in the bag body and the edge of the bag body. As shown in FIGS. 1 and 2, the basic layer structure of the film has a laminated structure including at least two layers formed by laminating the electrode underlayer 2 and the heat-resistant layer 3. The sealing film 1 of the present embodiment is a sealing layer 4 which is formed by laminating the heat-resistant layer 3 having a basic layer and directly laminating the sealing layer 22 of the innermost layer of the bag.

The thickness of the sealing film 1 of the present invention is preferably from 50 μm to 300 μm. If the thickness of the sealing film 1 is less than this range, the insulation property may fall. Furthermore, the thickness of the sealing film 1 may also be larger than this range. However, it is not expected to further improve the insulation property, and it becomes difficult to perform heat sealing.

The heat-resistant layer 3 contains a resin C which is melt-kneaded by both an acid-modified polyolefin resin A graft-polymerized with a carboxylic acid and a resin B having a functional group reactive with a carboxyl group of the resin A. The carboxyl group of the resin A is chemically bonded to the functional group of the resin B to be modified.

The blending ratio of the resin at this time is preferably from 99 to 90% by weight of the resin A, and the resin B is from 1 to 10% by weight. When the blending ratio of the resin B is less than the above range, the effect of modifying the resin C is small, and the heat resistance of the sealing film 1 is lacking. If the blending ratio of the resin B is higher than the range, the heat-resistant layer 3 is liable to become brittle. Therefore, when the battery pack is mounted, cracks may occur on the heat-resistant layer 3 due to the bending of the electrode 11.

The heat-resistant layer 3 ensures insulation between the metal foil 21 of the laminate film 20 of the bag body and the electrode 11. Resistant The heat layer 3 prevents thermal deformation of the sealing film 1 at the time of heat fusion, and is preferably thin as long as insulation can be ensured. The thickness of the heat-resistant layer 3 is preferably from 30 μm to 150 μm. When the thickness of the heat-resistant layer 3 is less than 50 μm, the sealing film 1 may be thermally deformed or thinned at the time of heat fusion, and may become insulative. Further, the thickness of the heat-resistant layer 3 may also exceed 150 μm. However, further improvement in insulation cannot be expected. The resin constituting the heat-resistant layer 3 is more polymerized than the resin A in the resin B than the resin A, and is relatively hard and has low melt fluidity. Therefore, when the heat-resistant layer 3 is thicker than necessary, when the electrode 11 is sandwiched between the two sealing films 1 and 1, the gap caused by the step of the thickness of the electrode 11 is hard to be filled at the time of heat fusion. Thereby, pinholes may be formed between the sealing films 1 and 1.

The acid-modified polyolefin resin A is a graft-polymerized unsaturated carboxylic acid or a derivative thereof by using a polyolefin obtained by polymerizing one or two or more kinds of alkylene monomers, for example, ethylene or propylene. Obtained by things.

As the polyolefin, for example, a homopolymer and a copolymer of polypropylene or polyethylene are used. As the copolymer, a random copolymer of propylene and 1 to 5% by weight of ethylene random copolymer (random PP) or block copolymer (block PP), ethylene and 1 to 10% by weight of propylene are used. A copolymer, a copolymer of propylene or ethylene and 1 to 10% by weight of an α-olefin having 4 or more carbon atoms, and a mixture thereof.

In order to use the sealing layer 22 of the laminated film 20 of the bag body as a polyethylene resin and the polyethylene resin as the base resin of the resin A in the heat-resistant layer 3 of the sealing film 1, it is preferred to use a melting point. It is a linear low-density polyethylene or high-density polyethylene of about 130 to 140 °C.

The base resin of the acid-modified polyolefin resin A is preferably a homopolypropylene and a propylene-ethylene random copolymer having a melt flow rate (MFR) of 0.5 to 30 g/10 min, particularly 5 to 15 g/10 min, or MFR Polyethylene and ethylene-α-olefin copolymers of 0.3 to 30 g/10 min.

The MFR of the resin C forming the heat-resistant layer 3 is preferably in the range of 0.5 g/10 min to 3 g/10 min. If the MFR is smaller than the range, it may be difficult to form. If the MFR is greater than the range, In the case of heat fusion, the heat-resistant layer 3 may be deformed or thinned, resulting in a decrease in insulation properties.

In the heat-resistant layer 3, it is difficult to melt or soften the sealing film 1 of the present invention when it is thermally welded to the electrode 11. Therefore, the higher the melting point of the resin C forming the better, the better. Specifically, in the case of a sealing film comprising a polypropylene resin, a resin having a melting point of 130 to 170 ° C as measured by a JIS K6921-2DSC method is preferred.

In order to obtain such a resin C, it is preferred to use an acid-modified polyolefin which is a homopolymer of polypropylene (PP), a random copolymer or block copolymer of ethylene and propylene or a polymer alloy of the above as a base resin. The resin was used as the resin A. PP-based resins are generally brittle in low temperature environments. Since the block copolymer of ethylene and propylene is excellent in flexibility even at a high melting point and is not brittle (cold resistance) in a low temperature environment, it is preferable.

Examples of the unsaturated carboxylic acid graft-polymerized on the base resin of the acid-modified polyolefin resin A include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, and citrine. An acid, such an acid anhydride, and derivatives of such esters, guanamines, quinones, metal salts, and the like. Among these unsaturated carboxylic acids, maleic acid is preferred, and maleic anhydride is most preferred. Further, in order to promote the reaction between the polyolefin and the unsaturated carboxylic acid, for example, an organic peroxide such as benzamidine peroxide or laurel, or a radical polymerization initiator such as azobisisobutyronitrile is preferably used. .

The amount of the unsaturated carboxylic acid to be graft-polymerized is usually 0.5 to 5% by weight based on the total weight of the monomers.

The method for graft-polymerizing an unsaturated carboxylic acid onto a polyolefin is, for example, a method of reacting a polyolefin with an unsaturated carboxylic acid in a molten state; and a method of reacting a polyolefin with an unsaturated carboxylic acid in a slurry state; A method of reacting a polyolefin with an unsaturated carboxylic acid in a gas phase state. Among these methods, the method of reacting in a molten state is preferred because of ease of handling. Specifically, a polymerization initiator such as a polyolefin, an unsaturated carboxylic acid or an organic peroxide as described above is sufficiently mixed by a roll, a Henschel mixer or the like. Thereafter, melt kneading The grafting reaction is carried out.

The method of melt kneading is not particularly limited, and for example, it can be carried out using a screw extruder, a Banbury mixer, a kneading roll or the like. Among these methods, the screw extruder can be preferably used because of its simple operation. The screw extruder can be a multi-axis spiral of uniaxial, biaxial, or more. The temperature of the melt kneading is preferably not less than the melting point of the polyolefin used and below the decomposition temperature of the organic peroxide used. The specific temperature and time are usually from 0.3 to 30 minutes at 160 to 280 ° C, preferably from 1 to 10 minutes at 170 to 250 ° C.

The resin C modified by melt-kneading the resin B in the acid-modified polyolefin resin A is formed into a layer shape to form a heat-resistant layer 3 which imparts heat resistance to the sealing film. The method of forming the heat-resistant layer 3 may be a calendering method in which the resin C is rolled between a plurality of rolls, and an extrusion method in which the molten resin C is extruded by a T-die or a ring mold. Among these methods, the extrusion method is preferred because the resin C which is melt-kneaded can be directly extruded by the extruder used in the modification step.

In the stage before the modification step of the resin C, it is preferred to add a step of modifying the polyolefin-modified polyolefin resin A by introducing the polyolefin and the unsaturated carboxylic acid into an extruder for melt-kneading. Thereafter, it is preferred to further introduce the resin B into the extruder to modify the resin A into the resin C.

Further, since an acid-modified polyolefin resin obtained by graft-polymerizing an unsaturated carboxylic acid is commercially available, a commercially available product can also be used.

The PP-based polymer obtained by graft-polymerizing an unsaturated carboxylic acid includes an ionic polymer obtained by neutralizing a carboxyl group with a metal hydroxide, an oxide, or a lower fatty acid salt.

Examples of the functional group which the resin B can react with the carboxyl group of the resin A include a hydroxyl group, an amine group, a carboxyl group, a methyl group, an epoxy group and the like. The resin B having such a functional group is not particularly limited, and is preferably a general-purpose resin which is easily available. Examples of such a general-purpose resin include polyethylene vinyl alcohol (EVOH), polyvinyl alcohol (PVA, polyvinyl alcohol), nylon 6 or nylon 66, and the like. Glycidyl methacrylate copolymer (E-GMA, ethylene- An epoxy group-containing resin such as glycidyl methacrylate). Therefore, as a preferable functional group which can react with the carboxyl group of the resin A, a hydroxyl group, an amine group, and an epoxy group are mentioned.

When EVOH is used as the resin B, the MFR is preferably from 1 to 30 g/10 min (230 ° C) from the viewpoint of compatibility with the resin A or workability. The MFR is preferably from 1 to 20 g/10 min, and more preferably from 3 to 16 g/10 min. As the ethylene content in the EVOH, ethylene is preferably from 20 to 60 mol%, more preferably from 25 to 50 mol%.

In the case where polyamine is used as the resin B, in order to stabilize the polyamine which blocks the terminal amine group and reduces the terminal amine group, it is preferred to use the same amount of the terminal amine group as the terminal carboxyl group. Polyammonium, or a polyamine having a molar ratio of terminal groups to terminal amino groups of 2 or more and terminal amino groups of 8.0 × 10 ^-5 mol/g or more. Such polyamine can increase the shear rate dependence of the melt viscosity of the resin C. The melting point of polyamine is relatively high in the general-purpose resin, and thus the resistance of the obtained resin C to thermal deformation is improved.

When an epoxy group-containing resin is used as the resin B, it is preferred to copolymerize the ethylene monomer from the viewpoint of compatibility with the resin B or workability. The carboxyl group of the resin A is ring-opened with an epoxy group containing an epoxy group, and the hydroxyl group formed by ring opening is esterified. This esterification is carried out in turn. As a result, the molecular structure of the resin C became a crosslinked structure, and the resistance against thermal deformation was improved.

The electrode adhesive layer 2 is a layer obtained by heat-pressing the sealing film 1 on the electrode 11 to be thermally welded. The electrode adhesive layer 2 contains a carboxylic acid-modified polyolefin resin D excellent in adhesion to a metal.

Resin D is a resin obtained by copolymerizing one or two or more kinds of an alkene monomer, for example, ethylene or propylene, with one or more of an unsaturated carboxylic acid or a derivative thereof. The copolymer may, for example, be a block copolymer, a graft copolymer or a random copolymer. In the case of using a graft copolymer, the same polyolefin as the resin A and the unsaturated carboxylic acid similar to the resin A may be graft-polymerized to form a carboxylic acid-modified polyolefin resin D.

The electrode underlayer 2 is preferably thin as long as it is thermally welded to the electrode 11. usually The thickness of the electrode underlayer 2 is 20 μm to 60 μm. If the thickness of the electrode underlayer 2 is smaller than the range, there is a case where the adhesion strength between the electrode underlayer 2 and the electrode 11 is lowered. If the thickness of the electrode underlayer 2 is larger than the range, the heat resistance of the sealing film 1 may become insufficient.

The melting point of the resin D forming the electrode subsequent layer 2 is preferably lower than the melting point of the resin C forming the heat-resistant layer 3. In the case of the sealing film 1 containing a polypropylene resin, the melting point of the resin D is preferably from 130 ° C to 150 ° C. If the melting point of the resin D is less than the above range, the heat resistance of the sealing film 1 may become insufficient. If the melting point of the resin D is higher than the range, it is difficult to increase the difference in melting point of the resin C which forms the heat-resistant layer 3. When the difference in melting point between the resin D and the resin C is 10 ° C or more, temperature management at the time of heat fusion is facilitated, which is preferable.

The melting point of the resin D is preferably equal to or lower than the melting point of the resin A. When the resin A is modified to the resin C, the molecules of the resin B are bonded to the molecules of the resin A, and the molecular weight of the resin C is increased, so that the melting point of the resin C becomes higher than that of the resin A. Thereby, the difference in melting point between the resin D and the resin C is easily made 10 ° C or more. When the same resin is used for the resin D and the resin A, the management of the resin becomes easy.

The method of forming the electrode subsequent layer 2 may be an extrusion method in which the molten resin D is extruded from a T die or a ring die using an extruder. When a graft copolymer is used as the resin D, when extruded by an extruder in the same manner as the resin A, a polyolefin and an unsaturated carboxylic acid can be graft-polymerized.

In order to form a sealing film comprising a polyethylene resin, in the case where an acid-modified polyethylene is used in the electrode adhesive layer 2, a maleic anhydride graft copolymerized polyethylene having a melting point of about 90 to 120 ° C is preferred. . The acid-modified polyethylene contains an ionic polymer obtained by neutralizing a carboxyl group.

The MFR of the acid-modified polyolefin resin D forming the electrode subsequent layer 2 is preferably in the range of 3 g/10 min to 30 g/10 min. The MFR is more preferably in the range of 5 g/10 min to 10 g/10 min. If the MFR is less than the above range, it is difficult for the acid-modified polyolefin to sufficiently rewind around the electrode 11 at the time of heat fusion. If the MFR is larger than the ranges, the electrode is subsequently thinned to the layer 2, so that the strength of the bonding is insufficient.

In the present invention, the MFR is measured at 230 ° C in the case of a polypropylene resin in accordance with JIS K7210, and is measured at 190 ° C in the case of a polyethylene resin.

Further, since a carboxylic acid-modified polyolefin resin is commercially available, a commercially available product can also be used.

The electrode underlayer 2 and the heat-resistant layer 3 are directly laminated, and are not laminated between the layers via the adhesive layer or the tackifier layer. Thereby, peeling by the penetration of the electrolytic solution to the laminated interface and deterioration of the flexibility of the sealing film 1 can be prevented. In the sealing film 1, not only the electrode is but also the layer 2, and the wrap around the electrode 11 of the heat-resistant layer 3 is also important. An adhesive can also be used for dry lamination as long as it does not affect softness or interaction with the electrolyte. Further, in the case of extrusion lamination, a tackifier may also be used.

As a method of directly laminating, a heat lamination is performed in which the formed electrode underlayer 2 and the heat-resistant layer 3 are superposed and heat-welded; and any one of the electrode subsequent layer 2 and the heat-resistant layer 3 is formed in advance, and one side is self-t The extrusion lamination method in which the other is extruded in a molten state while laminating, and when the electrode underlayer 2 and the heat-resistant layer 3 are in a molten state, they are laminated while being extruded from a co-extrusion die. Co-extrusion lamination. In these methods, the coextrusion lamination method is an extruder which extrudes the resin C while being melt-kneaded on one side, and is connected to the other extruder of the extruded resin D by coextrusion. The mold is placed on the mold and laminated directly in the co-extrusion mold. Thereby, the modification to the resin C, the formation of the heat-resistant layer 3, the formation of the electrode underlayer 2, and the lamination of the electrode underlayer 2 and the heat-resistant layer 3 can be carried out in one step, which is preferable.

In the present embodiment, the sealing layer 4 is laminated on the opposite surface of the heat-resistant layer 3 from the electrode subsequent layer 2. The sealing layer 4 is a layer which is heat-pressed and welded to the sealing layer 22 of the laminated film 20 of the bag body.

As the lamination method, the same method is employed for the same reason as the lamination of the electrode underlayer 2 and the heat-resistant layer 3. In these methods, the electrode adhesion layer 2 and the heat resistant layer 3 can be densely bonded. Since the sealing layer 4 is laminated at one time, it is preferable to laminate by a co-extrusion lamination method.

The sealing layer 4 is preferably thin as long as it is welded to the sealing layer 22 of the bag body. Usually, the thickness of the sealing layer 4 is 20 μm to 40 μm. If the thickness of the sealing layer 4 is less than the above range, the welding strength of the sealing layer 4 and the sealing layer 22 of the bag body is lowered. If the thickness of the sealing layer 4 is larger than the range, the heat resistance of the sealing film 1 becomes insufficient.

In the case where the sealing layer 22 of the laminated film 20 of the bag body is easily welded, the resin forming the sealing layer 4 (hereinafter referred to as the resin E) is preferably the same or the same resin as the resin constituting the sealing layer 22. In general, the sealing film 1 is composed of a PP resin in terms of excellent heat resistance.

In the case where the sealing film 1 is composed of a PP-based resin, the resin E may be a homopolymer of PP, a random copolymer or a block copolymer of ethylene and propylene or a mixture thereof, or a polymer thereof. Alloys, etc. Among these, a random copolymer of ethylene and propylene is preferred in terms of excellent flexibility.

In the case of a sealing film comprising a PP-based resin, the melting point of the resin E forming the sealing layer 4 is preferably from 130 ° C to 170 ° C. If the melting point of the resin E is less than the above range, the heat resistance of the sealing film 1 may become insufficient. When the melting point of the resin E forming the sealing layer 4 is higher than the range, it is difficult to increase the difference in melting point of the resin C which forms the heat-resistant layer 3. When the difference between the melting point of the resin E and the melting point of the resin C is 10° C. or more, temperature management when the laminated body 20 is welded to the bag body is facilitated, which is preferable.

When the sealing film 1 is made of a polyethylene resin and a polyethylene resin is used for the sealing layer 4, it is preferable to use a low density polyethylene or a linear low density polyethylene having a melting point of about 100 to 120 ° C. .

In the case of a sealing film containing a PP-based resin, the MFR of the resin E forming the sealing layer 4 is preferably in the range of 3 g/10 min to 30 g/10 min, more preferably in the range of 5 g/10 min to 10 g/10 min. If the MFR of the resin E is less than the above range, it is difficult to laminate by extrusion lamination or co-extrusion lamination. If the MFR of the resin E is larger than the above range, it is difficult to utilize the total The extrusion ring mold is formed.

Further, the sealing layer 4 is an arbitrary layer, and when the heat-resistant layer 3 is welded to the sealing layer 22 of the bag body, the sealing layer 4 may not be provided.

The sealing film 1 of the present invention is welded between the sealing layer 22 of the bag body and the electrode 11. When the sealing film 1 is welded, as shown in FIG. 2, the sealing film 1 of a specific width is exposed from the end of the laminated film 20 and welded. At this time, in order to facilitate the positioning of the sealing film 1, it is preferable to color at least one of the two sealing films 1 in advance. As the method of coloring, at least one layer of the layer constituting the sealing film 1 may be subjected to a method such as printing, dyeing, kneading of a coloring agent such as a dye or a pigment. Among these methods, the kneading of the coloring agent is simple, which is preferable. The colored layer can also be used to confirm whether the welding with the sealing layer 22 of the bag body is good. Therefore, the colored layer is preferably a heat-resistant layer 3 which is not deformed or melted at the time of welding.

In the sealing film of the present embodiment, in order to achieve the positioning of the sealing film 1 and to wrap the resin around the thickness direction of the electrode without a gap, as shown in FIG. 3A, it is preferable to use the electrode bonding layer of the sealing film 1 in advance. 2, the sealing film 1 of the present invention is thermally fused to at least one surface of the electrode 11, preferably on both sides. Thereby, the sealing layer 4 of the sealing film 1 or the heat-resistant layer 3 can be used, and the sealing layer 22 of the bag body can be easily and surely welded. At this time, when the sealing film 1 is colored, when the sealing film is thermally welded to the electrode lead plate which is welded to the innermost layer of the bag body, the photoreceptor can be used in the automated welding assembly line to laminate the electrode lead plate. Correct positioning with the sealing film 1.

In the heat fusion bonding of the sealing film 1 and the electrode 11, a heat sealing machine, an instant sealing machine, or the like can be used, and the sealing can be performed by heating with a sealing rod. Further, when the electrode 11 is directly heated by electromagnetic induction heating or electric heating during heating of the sealing film 1, the flow caused by the melting of the sealing layer 4 or the outer portion of the heat-resistant layer 3 is suppressed, and the heat-resistant layer 3 is promoted. The inner portion or the electrode is preferably softened or melted by the layer 2, so that it is preferred.

The shape of the electrode 11 can be exemplified by a belt shape or a round bar or the like. The size of the electrode 11 is not particularly limited. For example, if it is a strip shape, the thickness is 50 μm to 500 μm, and the width is 5 mm to 100. Mm, length is about 40mm~100mm. The strip-shaped electrode 11 can also round its ridge line (corner edge portion). Further, although the surface may be in the state of a processed surface which is subjected to calendering, it is preferably roughened by surface treatment such as sand blasting or etching. By roughening, the strength of the sealing film 1 is increased. Further, an underlayer process such as a chemical conversion process can also be performed.

As the material of the electrode 11, for example, a metal such as aluminum, copper, nickel, rhodium, gold, platinum or various alloys can be used. Among these, aluminum or copper is preferably used in terms of excellent electrical conductivity and advantageous in terms of cost. Among them, aluminum or copper has a case where the resistance to hydrogen fluoride (hydrofluoric acid) which is generated in the electrolytic solution is insufficient in the battery pack. Further, when the PP resin is in contact with copper, there is a possibility that the resin is deteriorated. Therefore, it is preferred to plate nickel having high conductivity and excellent resistance to hydrofluoric acid on the underlying metal of aluminum or copper.

For example, as shown in FIG. 2, the laminate film 20 to which the bag body of the sealing film 1 of the present invention is welded is formed by laminating a sealing layer 22 on one surface of the metal foil 21 and laminating the film substrate 23 on the other surface. Laminated film, etc. The laminate film 20 may also be laminated with other layers.

The laminated film 20 of the bag body is formed into a stretch-formed bag or a flat bag or the like. Examples of the metal foil 21 include an aluminum foil, a stainless steel foil, a copper foil, an iron foil, and the like. The metal foil 21 can also be subjected to an underlayer treatment such as a chemical conversion treatment.

The resin forming the sealing layer 22 of the laminate film 20 of the bag body is selected from a resin which can be welded to the sealing layer 4 of the sealing film 1. When the sealing layer 4 of the sealing film 1 is a PP-based resin, for example, a homopolymer of PP or a copolymer of PP and ethylene can be used. In the case of a polyethylene-based resin, low-density polyethylene or linear low-density polyethylene or the like can be used. The resin constituting the film substrate 23 is not particularly limited, and it is preferred to use polyamine, polyethylene terephthalate (PET), PP or the like having high strength. When the resin is stretched to form a film, a high physical strength can be obtained. The films may also be laminated in multiple layers.

The present invention has been described above based on preferred embodiments, but the present invention is not limited to the above embodiments, and various modifications can be made.

For example, the sealing film 1 is used to improve the adhesion, physical strength or insulation between the resin layers. Further, it may further contain other layers such as a resin layer. In this case, the other layer is preferably a layer which is difficult to melt and has high flexibility at the time of heat fusion. Moreover, the lamination strength between the layers can be controlled to an appropriate range, and the sealing film 1 can be provided with a function of a safety valve when the temperature or pressure in the bag abnormally rises.

[Examples]

Examples and comparative examples of the sealing film 1 shown in Table 1 were produced using the resins shown below.

Resin A: Maleic anhydride modified PP obtained by graft-polymerizing maleic anhydride onto a random PP (MFR 2.4 g/10 min (230 ° C), melting point 143 ° C)

Resin B

Resin B-1: EVOH having an ethylene ratio of 48 mol% (MFR 15 g/10 min (230 ° C), melting point 160 ° C)

Resin B-2: EVOH having an ethylene ratio of 32 mol% (MFR 3.6 g/10 min (230 ° C), melting point 183 ° C)

Resin B-3: Nylon 6 (relative viscosity 3.37, melting point 220 ° C)

Resin B-4: Nylon 6 (relative viscosity 4.08, melting point 220 ° C)

Resin B-5: E-GMA copolymer having a glycidyl methacrylate content of 6 wt% (MFR 3 g/10 min (190 ° C), melting point 105 ° C)

Resin D

Resin D-1: maleic anhydride modified PP obtained by graft-polymerizing maleic anhydride onto random PP (MFR 7.5 g/10 min (230 ° C), melting point 135 ° C)

Resin D-2: Maleic anhydride modified PP obtained by graft-polymerizing maleic anhydride onto random PP (MFR 7.0 g/10 min (230 ° C), melting point 140 ° C)

Resin E: block PP (MFR 2.3g (230 ° C) / 10 min, melting point 163 ° C)

<Examples 1 to 15>

Adding the resin A and the resin B to the hopper of the extruder in the mixing ratio shown in Table 1, The surface was modified to have a resin C extruded at the extrusion temperature shown in Table 1, and laminated in a co-extrusion T-die with a resin D extruded from another extruder, and the sealing film 1 was cast. Examples 1 to 15.

In the example in which the layer structure of Table 1 is three layers, in the co-extrusion casting molding, the resin E is further extruded from another extruder to perform co-extrusion lamination. Further, in the example in which the coloring agent in Table 1 is 3 parts, in the case of blending the resin A and the resin B, 3 parts by weight of a PP base pigment master batch is added.

The extrusion temperatures of Resin D and Resin E were both set to 240 °C.

In the above-described manner, a three-layer structure in which a laminated film of a two-layer structure including a heat-resistant layer 3 having a thickness of 40 μm and a heat-resistant layer 3 shown in the column of the heat-resistant layer of Table 1 and a sealing layer of 20 μm were laminated was formed. Laminated film. The laminated film was cut into a width of 25 mm to prepare Examples 1 to 15 of the sealing film 1.

<Comparative Example 1>

Resin D-1 and Resin E were respectively extruded at 240 ° C, and laminated in a co-extrusion T-die, and a laminated film of a two-layer structure including an electrode 2 of 20 μm and a sealing layer 4 of 80 μm was formed. The laminated film was cut into a width of 25 mm to prepare a sealing film 1 of Comparative Example 1.

In addition, the "parts" in Table 1 mean "parts by weight".

<Measurement of electrode strength>

As the electrode 11, a square aluminum foil having a thickness of 50 μm, a width of 50 mm, and a length of 50 mm was used. Each of Examples 1 to 15 and Comparative Example 1 of the sealing film 1 was cut into a length of 60 mm. The electrode subsequent layer 2 of the sealing film 1 is superposed on the electrode 11 as the inner side. The heat-sealing machine was used to heat the aluminum foil side at 200 ° C, 0.2 MPa, and 3 seconds, and the unwelded portion was left at one end, and the other end was thermally welded.

The peel strength of the electrode underlayer 2 and the electrode 11 of each sealing film 1 was measured using an Instron type tensile tester. In the measurement of the peeling strength, the end portion of the sealing film 1 not welded to the electrode 11 and the end portion of the electrode 11 were fixed to the two chucks of the tensile tester, and stretched at a speed of 300 mm/min. The 180 degree peel strength was measured. The electrode underlayer 2 of each sealing film 1 and the electrode 11 are heat-sealed at a sealing strength of 27.5 to 32.8 N/25 mm.

<Measurement of laminate film fusion strength>

A biaxially stretched PET film having a thickness of 12 μm as the film substrate 23, an aluminum foil having a thickness of 40 μm as the metal foil 21, and a random copolymer film of ethylene and propylene having a thickness of 40 μm as the sealing layer 22 were laminated by dry lamination. . The obtained laminated film was cut into a square having a side length of 100 mm to prepare a laminated film 20 of two bag bodies.

Examples 1 to 15 and Comparative Example 1 of the sealing film 1 were each cut into a length of 60 mm. Make The sealing layers 22 of the laminate film 20 of the two-piece bag body are opposed to each other with the sealing film 1 interposed therebetween. When the sealing film 1 was inserted, the sealing film 1 was exposed from the end of the laminated film 20 by 5 mm.

Heating was performed from both sides of the laminated film 20 of the two-piece bag body under the same conditions as the measurement of the adhesive strength of the electrode, and one end of the side on which the sealing film 1 was exposed was welded. The other end remains as an unwelded portion. When the sealing film 1 is welded, the root portion of the exposed portion of the sealing film 1 is brought into contact with the sealing rod by about 2 mm.

The end portion of the unwelded portion of the sealing film 1 and the end portion of the laminate film 20 are fixed to the two chucks of the tensile tester in the same manner as the measurement of the adhesive strength of the electrode, in the same manner as the measurement of the strength of the electrode. The heat seal strength of the sealing layer 4 or the heat-resistant layer 3 of each sealing film 1 and the laminate film 20 was measured under the conditions. Each of the sealing film 1 and the laminate film 20 is heat-sealed at a sealing strength of 124.2 to 143.3 N/25 mm.

Further, in the portion of the sealing film 1 in any of the embodiments from which the laminated film 20 is exposed, no evidence of thermal deformation or melting is observed. On the other hand, in the comparative example, the portion of the root portion exposed from the laminate film 20 was slightly reduced.

<MFR of mixed products>

A melt-kneaded product (resin C-) of 95 parts by weight of the resin A and 5 parts by weight of the melt-kneaded product of the resin B-1 (resin C-1), 95 parts by weight of the resin A and 5 parts by weight of the resin B-3 3) Extrusion separately, and measuring the MFR at 230 °C. The original resin A had an MFR of 2.4. The MFR of the resin C-1 was 1.9, and the MFR was lowered as compared with the resin A. Further, the MFR of the resin C-3 was 2.5, and the MFR was higher than that of the resin A. From this, it is presumed that the heat resistance of the sealing film 1 is improved in the present invention not only because the molecular weight of the carboxyl group of the resin A and the functional group of the resin B are increased, but also the molecular weight is increased, and partial crosslinking is also affected.

[Industrial availability]

The present invention can be widely applied to a method for producing a sealing film for an electrode of a power generating element such as a secondary battery or a capacitor housed in a sealed bag body, and a sealing film.

1‧‧‧ sealing film

2‧‧‧electrode layer

3‧‧‧Heat resistant layer

4‧‧‧ Sealing layer

10‧‧‧electrode with sealing film

11‧‧‧Electrode

20‧‧‧ laminated film of bag

21‧‧‧Metal foil for laminated film

22‧‧‧Layer film sealing layer

23‧‧‧ Film substrate of laminated film

Claims (4)

A sealing film having a heat-resistant layer containing a resin C directly laminated on the adhesive layer containing the carboxylic acid-modified polyolefin resin D when the resin C and the resin D are in a molten state In the laminated structure, the resin C is an acid-modified polypropylene resin A obtained by graft-polymerizing maleic anhydride onto polypropylene and a resin having a functional group reactive with the carboxyl group of the above resin A. B is melt-kneaded to modify the carboxyl group of the resin A and the functional group of the resin B to be chemically bonded, wherein the ratio of the resin A to the resin A is 99 to 90% by weight, and the ratio of the resin B is 1 to 10% by weight. The sealing film of claim 1, wherein the resin B is one or more selected from the group consisting of a resin having a hydroxyl group, an amine group or an epoxy group. The sealing film of claim 1 or 2, wherein the resin D is an acid-modified polypropylene resin obtained by graft-polymerizing maleic anhydride onto polypropylene. The sealing film of claim 1 or 2, wherein the laminated structure is formed by co-extrusion of a resin C and a resin D.