JPWO2012063764A1 - Manufacturing method of sealing film and sealing film - Google Patents

Abstract

The manufacturing method of the sealing film (1) sandwiched between the electrode (11) of the power generation element housed in the bag body (20) and the edge of the bag body (20) is an acid in which carboxylic acid is graft-polymerized. By melting and kneading both the modified polyolefin resin A and the resin B having a functional group capable of reacting with the carboxyl group of the resin A, the carboxyl group of the resin A and the functional group of the resin B are chemically bonded. A melt-kneading step for modifying to C, a heat-resistant layer forming step for forming the heat-resistant layer (3) by forming the resin C into a layer, and an electrode adhesion for forming the carboxylic acid-modified polyolefin resin D into a layer and adhering to the electrode Adhesive layer forming step for forming layer (2), and laminating step for directly laminating heat-resistant layer (3) and electrode adhesive layer (2) when either one or both of resin C and resin D are in a molten state And having.

Description

The present invention relates to a method for producing a sealing film for sealing an electrode of a power generation element such as a secondary battery or a capacitor housed in a bag, and a sealing film.
This application claims priority based on Japanese Patent Application No. 2010-252940 for which it applied to Japan on November 11, 2010, and uses the content here.

In recent years, for example, secondary batteries and capacitors housed in bags made of films have been adopted as power sources for electronic devices such as notebook computers and mobile phones, and hybrid vehicles, batteries for fuel cell vehicles, and battery vehicles. .
Conventionally, these secondary batteries and capacitors are configured by sealing a flat power generating element in a flat bag made of a laminate film in which a polyolefin sealant is laminated on a metal foil such as an aluminum foil, or a bag formed by drawing. On the film base material of the bag body, an electrode for charging and discharging is sealed with one end protruding outward. At the time of sealing, a tape-like electrode (electrode tab) is sandwiched between the film base materials of the bag body and heat sealed.

Since the electrodes of these secondary batteries and the like (hereinafter sometimes referred to as “pack batteries”) are thicker than the sealant of the bag body, the resin should wrap around the electrode in the thickness direction without sealing. Is difficult, and a gap may occur around the electrode in the thickness direction. If there is a gap around the electrode, the sealing part may deteriorate or the adhesive strength between the bag body and the electrode in the sealing part may deteriorate under long-term use, severe environments such as high temperature and high humidity, etc. Thus, there is a possibility that the electrolyte solution leaks from the sealing portion.
In recent years, for these problems, a method of heat-sealing with a film substrate of a bag body with a sealing film sandwiched between both front and back surfaces of an electrode has been used. However, in order to increase the adhesion between the bag body and the electrode, if the conditions of heating and pressurization at the time of sealing are strict, the resin between the metal foil of the bag body and the electrode becomes thin, or the sealing film There is a possibility that a short circuit occurs due to deformation.

  Further, when heat sealing with a sealing film sandwiched between the film base of the bag and the electrode, for example, as disclosed in Patent Document 2, several millimeters of the sealing film is exposed from the opening end of the bag. Heat seal. By exposing in this way, a short circuit can be reliably prevented. However, since the seal bar contacts or approaches the exposed portion during heat sealing, the sealing film may be melted or deformed by contact with the high temperature seal bar or radiant heat. By these, an electrode becomes easy to contact with the metal foil of the film base material of a bag.

In order to solve these problems, for example, Patent Document 1 discloses a laminated structure in which a heat seal portion of a terminal material is sandwiched between a heat-resistant film made of woven fabric, non-woven fabric, or ultrahigh molecular weight polyethylene with a heat-adhesive film. The structure which prevents a short circuit by coat | covering with the coating material which has is described.
Patent Document 2 describes an adhesive film in which an electron beam cross-linked polyolefin layer and an acid-modified polyolefin layer are laminated.

JP-A-62-61268 JP 2001-297748 A

  Since the coating material described in Patent Document 1 ensures heat resistance by a woven fabric or a nonwoven fabric, it is necessary to select a material that is difficult to melt as a woven fabric or a nonwoven fabric. However, since woven fabrics and nonwoven fabrics do not melt, it is difficult to laminate them with a heat-adhesive film with high adhesion. Therefore, pinholes are easily formed, and sealing performance may not be improved. In some cases, the sealability is rather reduced. Ultra high molecular weight polyethylene is difficult to obtain and is disadvantageous in terms of cost. Ultra high molecular weight polyethylene cannot be laminated with a heat-adhesive film made of a polypropylene resin. Therefore, polypropylene resin cannot be used for the sealant of the bag body, and it is difficult to increase the heat resistance of the bag body.

  The adhesive film described in Patent Document 2 is excellent in heat resistance. However, in this film production method, the polyolefin film is cross-linked by electron beam in advance and the acid-modified polyolefin layer is extrusion-laminated, or the polyolefin layer and the acid-modified polyolefin layer are laminated by coextrusion and then cross-linked by electron beam. Therefore, any method requires an electron beam crosslinking step. Paragraph 0013 of Patent Document 2 describes that a specific resin needs to be used because normal polypropylene is decomposed by electron beam irradiation. In addition, when electron beam crosslinking is performed after the polyolefin layer and the acid-modified polyolefin layer are laminated by coextrusion, the acid-modified polyolefin is also crosslinked to reduce flexibility. It becomes difficult.

  In the present invention made in view of the above background, the heat-resistant layer and the electrode adhesive layer can be easily wound around the electrode in the thickness direction by using a readily available material and in a simple process. Provided is a method for producing a sealing film that can be directly laminated with high adhesive strength and excellent in heat resistance and sealing properties, and a sealing film produced by this manufacturing method.

  The inventor of the present invention reacted with a hydroxyl group, an amino group, an epoxy group, or the like in a carboxyl group of an acid-modified polyolefin resin graft-polymerized with a carboxylic acid during research on a sealing film excellent in heat resistance and sealing properties. The knowledge that it was easy and could be modified | denatured easily was acquired. The present invention has been made based on this finding.

That is, according to the 1st aspect of this invention, the manufacturing method of the following sealing films is provided.
(1) A method for producing a sealing film sandwiched between an electrode of a power generation element housed in a bag body and an edge of the bag body, wherein the acid-modified polyolefin resin A and the resin A are graft-polymerized with carboxylic acid. Melting and kneading step in which both the carboxyl group of the resin A and the functional group of the resin B are chemically bonded to each other to melt and knead both the resin B having a functional group capable of reacting with the carboxyl group of the resin B, and kneading. And a heat-resistant layer film forming step for forming a heat-resistant layer by molding the resin C into a layer, and an adhesive layer film-forming step for forming an electrode adhesive layer for forming the carboxylic acid-modified polyolefin resin D into a layer and adhering to the electrode. And a lamination step of directly laminating the heat-resistant layer and the electrode adhesive layer when either one 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 performed 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 sealing film according to any one of (1) to (3), wherein the laminating step is performed continuously in either one or both of the heat-resistant layer forming step and the adhesive layer forming step. Manufacturing method.
(5) The method for producing a sealing film according to any one of (1) to (4), wherein the laminating step is performed in a coextrusion die.
(6) The melt-kneading step is performed by blending resin A in a weight percentage of 1 to 10 with respect to 99 to 90 for resin A (1) to (5). A method for producing a stop film.
(7) The 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 that of the resin A is used as the resin D.

Moreover, according to the 2nd aspect of this invention, the following sealing films are provided.
(8) A sealing film sandwiched between the electrode of the power generation element housed in the bag and the edge of the bag, and the carboxyl group of the resin A and the acid-modified polyolefin resin A grafted with carboxylic acid The resin B having a functional group capable of reacting with the resin B is melted and kneaded, whereby a heat-resistant layer made of the resin C modified by chemically bonding the carboxyl group of the resin A and the functional group of the resin B is A sealing film having a laminated structure directly laminated on an electrode adhesive layer made of acid-modified polyolefin resin D.
(9) The sealing film according to (8), wherein the resin B is one or more selected from resins having a hydroxyl group, an amino 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 to polypropylene.
(11) The sealing film according to any one of (8) to (10), wherein the laminated structure is formed by coextrusion of resin C and resin D.
(12) The sealing film according to any one of (8) to (11), wherein a sealant that is thermally welded to the innermost layer of the bag is laminated on the heat-resistant layer.

In the manufacturing method of the sealing film of the present invention, the carboxyl group of the resin A and the functional group of the resin B are chemically bonded to denature the resin C, so that a crosslinking step such as electron beam crosslinking is unnecessary. Therefore, heat resistance can be imparted to the heat-resistant layer by a simple process.
Since both resin A and resin B are only melted and kneaded, they can be modified to resin C in a normal extruder used in the film forming process.
In the present invention, the heat-resistant layer and the electrode adhesive layer are directly laminated when one or both of the resin C and the resin D are in a molten state. In the lamination method, one layer is formed by combining an extruder and a film forming die, and then the other layer is extrusion laminated. In another lamination method, the heat-resistant layer and the electrode adhesive layer are coextruded. By these methods, in the present invention, the heat-resistant layer and the electrode adhesive layer can be directly laminated with high adhesive strength by a simple process. Sealing films obtained by these methods are unlikely to melt or deform due to contact with a high-temperature seal bar or radiant heat during heat sealing. Thereby, a short circuit with an electrode and the metal foil of a bag body does not occur easily.
In particular, the co-extrusion of the heat-resistant layer and the electrode adhesive layer can be directly laminated with higher adhesive strength by a simpler process.

The sealing film of the present invention has a resin C having a low melt fluidity, in which the heat-resistant layer is modified by chemically bonding the carboxyl group of the resin A and the functional group of the resin B. Thereby, at the time of heat sealing, a heat-resistant layer becomes thin and a sealing film does not heat-deform easily. Therefore, a short circuit between the electrode and the metal foil of the bag body hardly occurs.
When the resin B is one or more selected from resins having a hydroxyl group, an amino 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 the modification to the resin C is smooth. It is. Since resin A and resin B are melted and kneaded to be modified into resin C, the carboxyl group of resin A and the functional group of resin B are likely to be chemically bonded uniformly.

When the resin A is an acid-modified polyolefin resin obtained by graft polymerization of maleic anhydride on polypropylene, the carboxyl group of the resin A and the functional group of the resin B are easily chemically bonded, and the modification to the resin C becomes smoother. .
When the laminated structure of the sealing film is formed by co-extrusion of the resin C and the resin D, the adhesive strength of the laminated structure is high, and the sealing film is not thermally deformed during heat sealing. Short circuit with metal foil hardly occurs.
When the sealant that is thermally welded to the innermost layer of the bag body is laminated on the heat resistant layer, the thermal welding strength of the innermost layer of the bag body and the sealing film can be increased. Further, when the sealant is directly laminated on the heat-resistant layer, it is possible to prevent the adhesion interface from being peeled off by the electrolytic solution.

It is sectional drawing which shows an example of the sealing film of this invention. It is sectional drawing which shows the state which joined the laminate film and electrode of the bag body using the sealing film shown in FIG. It is a perspective view which shows the electrode with the sealing film which adhere | attached the sealing film shown in FIG. 1 on the electrode. It is sectional drawing which shows the electrode with a sealing film which adhere | attached the sealing film shown in FIG. 1 on the electrode.

Hereinafter, the present invention will be described in detail based on 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 taken along the longitudinal direction of the electrode 11, showing a state in which the sealing film 1 shown in FIG. 1 is welded by being interposed between the laminate film 20 of the bag and the electrode 11.
FIG. 3A is a perspective view showing an electrode 10 with a sealing film in which the sealing film 1 shown in FIG. 1 is bonded to an electrode 11. FIG. 3B is a cross-sectional view in a direction orthogonal to the longitudinal direction of the electrode 11 showing the electrode with sealing film 10.

The sealing film 1 of this invention is inserted | pinched between the electrode of the electric power generation element accommodated in a bag body, and the edge of a bag body. As shown in FIGS. 1 and 2, the basic layer structure of this film has a laminated structure comprising at least two layers in which an electrode adhesive layer 2 and a heat-resistant layer 3 are laminated. In the sealing film 1 of this embodiment, a heat-resistant layer 3 having a basic layer structure is directly laminated with a sealant 4 that is thermally welded to the innermost sealant 22 of the bag body.
The thickness of the sealing film 1 of the present invention is preferably 50 μm to 300 μm. When the thickness of the sealing film 1 is smaller than this range, the insulating property may be lowered. In addition, the thickness of the sealing film 1 may be larger than this range. However, further improvement in insulation cannot be expected, and it becomes rather difficult to heat seal.

The heat-resistant layer 3 is obtained by melting and kneading both the acid-modified polyolefin resin A in which carboxylic acid is graft-polymerized and the resin B having a functional group capable of reacting with the carboxyl group of the resin A, so that the carboxyl group of the resin A It consists of a resin C modified by chemically bonding with a functional group of the resin B.
The blending ratio of the resin at this time is preferably 1 to 10% by weight of resin B with respect to 99 to 90% by weight of resin A. If the blending ratio of the resin B is lower than this range, the modification effect of the resin C is small, and the heat resistance of the sealing film 1 may be poor. If the blending ratio of the resin B is higher than this range, the heat resistant layer 3 tends to be brittle. For this reason, the heat-resistant layer 3 may be cracked by bending the electrode 11 when the battery pack is mounted.

  The heat-resistant layer 3 ensures the insulation between the metal foil 21 of the laminate film 20 of the bag body and the electrode 11. The heat-resistant layer 3 is preferably thin as long as it prevents thermal deformation of the sealing film 1 during heat welding and ensures insulation. The thickness of the heat resistant layer 3 is preferably 30 μm to 150 μm. If the thickness of the heat-resistant layer 3 is less than 50 μm, the sealing film 1 may be thermally deformed or thinned during heat welding, resulting in poor insulation. In addition, the thickness of the heat-resistant layer 3 may exceed 150 μm. However, further improvement in insulation cannot be expected. The resin constituting the heat-resistant layer 3 is polymerized more than the resin A because the resin B is chemically bonded to the resin A, and is relatively hard and has low melt fluidity. Therefore, when the heat-resistant layer 3 becomes thicker than necessary, when the electrode 11 is sandwiched between the two sealing films 1 and 1, the gap created by the step due to the thickness of the electrode 11 is difficult to fill at the time of heat welding. Thereby, a pinhole may generate | occur | produce between the sealing films 1 and 1.

The acid-modified polyolefin resin A is obtained by graft polymerization of an unsaturated carboxylic acid or a derivative thereof using, as a base resin, a polyolefin obtained by polymerizing one or more of alkylene monomers such as ethylene and propylene.
As the polyolefin, for example, homopolymers and copolymers of polypropylene and polyethylene are used. The copolymer includes a random copolymer (random PP) or a block copolymer (block PP) of propylene and 1 to 5% by weight of ethylene, and a random or block copolymer of ethylene and 1 to 10% by weight of propylene. A copolymer, a copolymer of propylene or ethylene and an α-olefin having 1 to 10% by weight of 4 or more carbon atoms, a mixture thereof, and the like are used.

When a polyethylene resin is used as the base resin of the resin A for the heat-resistant layer 3 of the sealing film 1 in order to make the sealant 22 of the laminate film 20 of the bag body a polyethylene resin, the melting point is about 130 to 140 ° C. It is preferable to use chain low density polyethylene or high density polyethylene.
The base resin of the acid-modified polyolefin resin A has a melt flow rate (MFR) of 0.5 to 30 g / 10 minutes, in particular, a homopolypropylene and propylene-ethylene random copolymer of 5 to 15 g / 10 minutes, or an MFR of 0. A polyethylene and ethylene-α olefin copolymer of 3 to 30 g / 10 min are preferably used.
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 this range, molding may be difficult. If the MFR is larger than this range, the heat resistance layer 3 may be deformed or thinned at the time of heat welding, and the insulation may be lowered.

The heat-resistant layer 3 is required to be hardly melted or softened when the sealing film 1 of the present invention is thermally welded to the electrode 11. Accordingly, the melting point of the resin C forming this is preferably as high as possible. Specifically, in the case of a sealing film made of a polypropylene resin, a resin having a melting point of 130 to 170 ° C. measured by JIS K6921-2 DSC method is preferable.
In order to obtain such a resin C, as the resin A, an acid-modified polyolefin resin using a polypropylene (PP) homopolymer, a random copolymer or block copolymer of ethylene and propylene, or a polymer alloy thereof as a base resin Is preferably used. In general, PP-based resins tend to be brittle under a low temperature environment. A block copolymer of ethylene and propylene is preferred because it has excellent flexibility even when the melting point is high and does not become brittle even in a low temperature environment (cold resistance).

Examples of the unsaturated carboxylic acid graft-polymerized to the base resin of the acid-modified polyolefin resin A include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, their acid anhydrides, and esters thereof. , Amides, imides, metal salts and other derivatives. Of these unsaturated carboxylic acids, maleic acid is preferred, and maleic anhydride is most preferred. In addition, in order to promote the reaction between the polyolefin and these unsaturated carboxylic acids, for example, an organic peroxide such as benzoyl peroxide or lauroyl peroxide, or a radical polymerization initiator such as azobisisobutyronitrile is used. Is preferred.
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 of graft polymerization of unsaturated carboxylic acid to polyolefin includes, for example, a method of reacting polyolefin and unsaturated carboxylic acid in a molten state, a method of reacting in a solution state, a method of reacting in a slurry state, and a reaction in a gas phase state. There is a method to make it. Among these methods, the method of reacting in a molten state is preferable because the operation is easy. Specifically, the polymerization initiators such as polyolefin, unsaturated carboxylic acid and organic peroxide shown above are sufficiently mixed with a tumbler, Henschel mixer or the like. Thereafter, it is melted and kneaded to carry out a grafting reaction.
The method for melt-kneading is not particularly limited, and can be performed using, for example, a screw extruder, a Banbury mixer, a mixing roll, or the like. Of these methods, a screw extruder is preferably used because of its simple operation. The screw extruder may be a single screw, twin screw or more multi-screw. The melt kneading temperature is preferably not lower than the melting point of the polyolefin used and not higher than the decomposition temperature of the organic peroxide used. The specific temperature and time are usually 160 to 280 ° C. for 0.3 to 30 minutes, preferably 170 to 250 ° C. for 1 to 10 minutes.

The heat-resistant layer 3 that gives heat resistance to the sealing film is formed by forming a resin C obtained by melting and kneading the resin B in the acid-modified polyolefin resin A into a layer. Examples of the method for forming the heat-resistant layer 3 include 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 with a T die or a ring die. Among these methods, the extrusion method is preferable because the melted and kneaded resin C can be extruded as it is with an extruder used in the modification step.
It is preferable to add a step in which the polyolefin and the unsaturated carboxylic acid are charged into an extruder and melt-kneaded to modify the acid-modified polyolefin resin A before the step of modifying the resin C. Thereafter, the resin B is preferably introduced into the extruder to denature the resin A to the resin C.
In addition, since the acid-modified polyolefin resin obtained by graft polymerization of unsaturated carboxylic acid is commercially available, a commercially available product can be used.
The PP polymer graft-polymerized with an unsaturated carboxylic acid contains an ionomer having a carboxyl group neutralized with a metal hydroxide, an alkoxide, a lower fatty acid salt or the like.

  Examples of the functional group that can react with the carboxyl group of the resin A included in the resin B include a hydroxyl group, an amino group, a carboxyl group, a formyl group, and an epoxy group. Although it does not restrict | limit especially as resin B which has these functional groups, The general purpose resin with easy acquisition is preferable. Such general-purpose resins include ethylene-vinyl alcohol copolymer (EVOH), polyvinyl alcohol (PVA), polyamide (PA) such as nylon 6 and nylon 6,6, and ethylene-glycidyl methacrylate copolymer (E-GMA). ) And the like. Accordingly, preferred functional groups capable of reacting with the carboxyl group of the resin A include a hydroxyl group, an amino group, and an epoxy group.

When EVOH is used as the resin B, one having an MFR of 1 to 30 g / 10 minutes (230 ° C.) is preferable from the viewpoint of compatibility with the resin A and workability. The MFR is more preferably 1 to 20 g / 10 min, and particularly preferably 3 to 16 g / 10 min. As ethylene content in EVOH, it is preferable that ethylene is 20-60 mol%, and it is more preferable that it is 25-50 mol%.
When a polyamide is used as the resin B, a polyamide having the same terminal amino group amount and terminal carboxyl group amount or a terminal amino group is used rather than a polyamide in which the terminal amino group amount is blocked to stabilize the terminal amino group. It is preferable to use a polyamide having a terminal carboxyl group molar ratio of 2 or more and a terminal amino group amount of 8.0 × 10 −5 mol / g or more. Such a polyamide can increase the shear rate dependence of the melt viscosity of the resin C. Since polyamide has a relatively high melting point among general-purpose resins, the resistance to thermal deformation of the obtained resin C is improved.
When an epoxy group-containing resin is used as the resin B, it is preferable that an ethylene monomer is copolymerized from the viewpoint of compatibility with the resin A and workability. The carboxyl group of the resin A opens the epoxy group of the epoxy group-containing resin, and esterifies the hydroxyl group generated by the ring opening. This esterification is repeated. As a result, the molecular structure of the resin C becomes a cross-linked structure, and resistance to thermal deformation is improved.

The electrode adhesive layer 2 is a layer in which the sealing film 1 is heat-pressed and heat-welded to the electrode 11. The electrode adhesive layer 2 is made of a carboxylic acid-modified polyolefin resin D that is excellent in adhesion to metal.
The resin D is a resin obtained by copolymerizing one or more alkylene monomers such as ethylene and propylene and one or more unsaturated carboxylic acids or derivatives thereof. Examples of the copolymer include a block copolymer, a graft copolymer, and a random copolymer. When the graft copolymer is used, a carboxylic acid-modified polyolefin resin D can be obtained by graft polymerization of a polyolefin similar to the resin A and an unsaturated carboxylic acid similar to the resin A.

The electrode adhesive layer 2 is preferably thin as long as thermal welding with the electrode 11 is ensured. Usually, the electrode adhesive layer 2 has a thickness of 20 μm to 60 μm. If the thickness of the electrode adhesive layer 2 is smaller than this range, the adhesive strength between the electrode adhesive layer 2 and the electrode 11 may be lowered. If the thickness of the electrode adhesive layer 2 is larger than this range, the heat resistance of the sealing film 1 may be poor.
The melting point of the resin D forming the electrode adhesive 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 made of a polypropylene resin, the melting point of the resin D is preferably 130 ° C to 150 ° C. If the melting point of the resin D is lower than this range, the heat resistance of the sealing film 1 may be poor. If the melting point of the resin D is higher than this range, it is difficult to increase the difference in melting point with the resin C forming the heat-resistant layer 3. It is preferable that the difference between the melting points of the resin D and the resin C is 10 ° C. or more because temperature management during heat welding is easy.
The melting point of the resin D is preferably the same as or lower than the melting point of the resin A. When the resin A is modified to the resin C, the molecule of the resin B is bonded to the molecule of the resin A, the molecular weight of the resin C is increased, and the melting point of the resin C is higher than that of the resin A. Thereby, it becomes easy to make the melting point difference between the resin D and the resin C 10 ° C. or more. When the resin D and the resin A are the same resin, the management of the resin becomes easy.

Examples of the method for forming the electrode adhesive layer 2 include 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, the polyolefin and the unsaturated carboxylic acid can be graft-polymerized when being extruded with an extruder as in the case of the resin A.
When acid-modified polyethylene is employed for the electrode adhesive layer 2 in order to obtain a sealing film made of a polyethylene resin, maleic anhydride graft copolymerized polyethylene having a melting point of about 90 to 120 ° C. is preferable. The acid-modified polyethylene contains an ionomer that has neutralized carboxyl groups.

The MFR of the acid-modified polyolefin resin D that forms the electrode adhesive 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 smaller than these ranges, the acid-modified polyolefin may not be sufficiently circulated around the electrode 11 during heat welding. If the MFR is larger than these ranges, the electrode adhesive layer 2 may become thin and the adhesive strength may be poor.
In the present invention, MFR is measured at 230 ° C. for all polypropylene resins and 190 ° C. for all polyethylene resins according to JIS K7210.
In addition, since carboxylic acid modified polyolefin resin is marketed, a commercial item can also be used.

The electrode adhesive layer 2 and the heat-resistant layer 3 are directly laminated without interposing an adhesive layer or an anchor agent layer. Thereby, peeling by the penetration | invasion to the lamination | stacking interface of electrolyte solution and the fall of the softness | flexibility of the sealing film 1 can be prevented. In the sealing film 1, not only the electrode adhesive layer 2 but also the wraparound of the heat-resistant layer 3 around the electrode 11 is important. If there is no influence of flexibility and interaction with the electrolyte, dry lamination may be performed using an adhesive. Moreover, you may use an anchor agent when carrying out extrusion lamination.
As a method of directly laminating, a heat laminate in which the molded electrode adhesive layer 2 and the heat-resistant layer 3 are stacked and heat-welded, or either one of the electrode adhesive layer 2 and the heat-resistant layer 3 is molded in advance and the other is in a molten state. Examples thereof include an extrusion laminating method of laminating while extruding from a T die, and a coextrusion laminating method of laminating while extruding from a coextrusion die when both the electrode adhesive layer 2 and the heat-resistant layer 3 are in a molten state. Among these methods, the co-extrusion laminating method is a method in which a co-extrusion die is connected to an extruder that extrudes resin C while being melt-kneaded and modified to resin C, and another extruder that extrudes resin D. Lamination can be done directly in the extrusion die. Thereby, modification to the resin C, formation of the heat-resistant layer 3, formation of the electrode adhesive layer 2, and lamination of the electrode adhesive layer 2 and the heat-resistant layer 3 can be performed in one step, which is preferable.

In this embodiment, the sealant 4 is laminated on the surface of the heat-resistant layer 3 opposite to the electrode adhesive layer 2. The sealant 4 is a layer that is heat-pressed and welded to the sealant 22 of the laminate film 20 of the bag.
As the lamination method, the same method is employed for the same reason as the lamination of the electrode adhesive layer 2 and the heat-resistant layer 3. Among these methods, since the electrode adhesive layer 2, the heat-resistant layer 3, and the sealant 4 can be laminated at a time, it is preferable to laminate them by a coextrusion laminating method.

The sealant 4 is preferably thin as long as welding with the sealant 22 of the bag is ensured. Usually, the thickness of the sealant 4 is 20 μm to 40 μm. If the thickness of the sealant 4 is smaller than these ranges, the welding strength between the sealant 4 and the sealant 22 of the bag body may be lowered. If the thickness of the sealant 4 is larger than these ranges, the heat resistance of the sealing film 1 may be poor.
The resin forming the sealant 4 (hereinafter referred to as “resin E”) is preferably the same or the same resin as the resin constituting the sealant 22 because it easily welds to the sealant 22 of the laminate film 20 of the bag. Usually, since the sealing film 1 is excellent in heat resistance, it is comprised with PP resin.
When the sealing film 1 is composed of a PP resin, the resin E may be a PP homopolymer, a random copolymer of ethylene and propylene, a block copolymer, or a mixture thereof, or a polymer alloy thereof. It is done. Among these, a random copolymer of ethylene and propylene is preferable because of excellent flexibility.

In the case of a sealing film made of PP resin, the melting point of the resin E forming the sealant 4 is preferably 130 ° C to 170 ° C. When the melting point of the resin E is lower than this range, the heat resistance of the sealing film 1 may be poor. If the melting point of the resin E forming the sealant 4 is higher than this range, it is difficult to increase the melting point difference from the resin C forming the heat-resistant layer 3. It is preferable that the difference between the melting point of the resin E and the melting point of the resin C is 10 ° C. or more because temperature management during welding of the bag body to the laminate film 20 is facilitated.
In order to use the sealing film 1 as a polyethylene resin, when a polyethylene resin is employed for the sealant 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 made of a PP resin, the MFR of the resin E forming the sealant 4 is preferably in the range of 3 g / 10 min to 30 g / 10 min, and in the range of 5 g / 10 min to 10 g / 10 min. Is more preferable. When the MFR of the resin E is smaller than these ranges, it may be difficult to laminate by extrusion lamination or coextrusion lamination. If the MFR of the resin E is larger than these ranges, it may be difficult to mold with a coextrusion ring die.
The sealant 4 is an arbitrary layer, and may not be provided when the heat-resistant layer 3 and the sealant 22 of the bag body are secured.

  The sealing film 1 of the present invention is welded between the sealant 22 of the bag body and the electrode 11. When the sealing film 1 is welded, as shown in FIG. 2, the predetermined width sealing film 1 is exposed from the end portion of the laminate film 20 and welded. At this time, in order to facilitate positioning of the sealing film 1, it is preferable to color at least one of the two sealing films 1. As the coloring method, a method such as printing, dyeing, or kneading a colorant such as a dye or a pigment can be used for at least one layer constituting the sealing film 1. Of these methods, the kneading of the colorant is simple and preferable. The layer to be colored can also be used for confirming whether or not the bag sealant 22 is welded. Accordingly, the heat resistant layer 3 that is not deformed or melted during welding is preferable as the coloring layer.

As shown in FIG. 3A, the sealing film 1 of the present embodiment has a sealing film 1 according to the present invention as shown in FIG. 1 is preferably heat-welded on at least one surface of the electrode 11, preferably on both surfaces, using the electrode adhesive layer 2 of the sealing film 1. Thereby, it can weld to the sealant 22 of a bag body easily and reliably using the sealant 4 and the heat-resistant layer 3 of the sealing film 1. At this time, when the sealing film 1 is colored, at the time of heat welding of the innermost layer of the bag and the electrode tab on which the sealing film is welded, the electrode tab can be The sealing film 1 can be positioned accurately.
For the thermal welding of the sealing film 1 and the electrode 11, heat sealing can be performed by using a heat sealer, an impulse sealer, or the like with a seal bar. Further, when the sealing film 1 is heated, if the electrode 11 is directly heated using electromagnetic induction heating or current heating, the flow due to melting of the outer part of the sealant 4 or the heat-resistant layer 3 is suppressed, and the inner part of the heat-resistant layer 3 is suppressed. And the electrode adhesive layer 2 is preferably softened and melted.

Examples of the shape of the electrode 11 include a tape and a round bar. Although the magnitude | size of the electrode 11 does not have a restriction | limiting in particular, For example, if it is a tape, thickness is 50 micrometers-500 micrometers, width 5 mm-100 mm, and length are about 40 mm-100 mm. As for the electrode 11 of a tape, the ridgeline (corner edge part) may be rounded. Further, the surface may be the processed surface as it is rolled, but is preferably roughened by a surface treatment such as sand blasting or etching. By roughening, the adhesive strength of the sealing film 1 is improved. In addition, base treatment such as chemical conversion treatment may be performed.
As a material of the electrode 11, for example, metals such as aluminum, copper, nickel, iron, gold, platinum, and various alloys can be used. Of these, aluminum and copper are preferably used because they are excellent in conductivity and advantageous in terms of cost. However, aluminum and copper may not have sufficient resistance to hydrogen fluoride (hydrofluoric acid), which is feared to be generated in the electrolyte solution in the battery pack. Moreover, when PP resin contacts copper, deterioration of resin may be accelerated | stimulated. Therefore, it is preferable to plate nickel, which is highly conductive and excellent in resistance to hydrofluoric acid, on an aluminum or copper base metal.

For example, as shown in FIG. 2, the laminate film 20 of the bag body to which the sealing film 1 of the present invention is welded is formed by laminating a sealant 22 on one surface of a metal foil 21 and a film base material 23 on the other surface. A laminated film etc. are mentioned. The laminate film 20 may be laminated with other layers.
The bag laminate film 20 is formed into a drawn bag, a flat bag, or the like. Examples of the metal foil 21 include aluminum foil, stainless steel foil, copper foil, and iron foil. The metal foil 21 may be subjected to a base treatment such as a chemical conversion treatment.

  As the resin that forms the sealant 22 of the laminate film 20 of the bag, a resin that can be welded to the sealant 4 of the sealing film 1 is selected. As such a resin, for example, when the sealant 4 of the sealing film 1 is a PP resin, a PP homopolymer or a copolymer of PP and ethylene can be used. In the case of a polyethylene resin, low density polyethylene, linear low density polyethylene, or the like can be used. The resin constituting the film base material 23 is not particularly limited, but high strength polyamide, polyethylene terephthalate (PET), PP, or the like is preferably used. When these resins are stretched films, high physical strength can be obtained. A plurality of these films may be laminated.

Although the present invention has been described based on the preferred embodiments, the present invention is not limited to the above-described embodiments, and various modifications can be made.
For example, the sealing film 1 may include other layers such as a further resin layer in order to improve adhesion between the resin layers, physical strength, insulation, and the like. In this case, the other layer is preferably a layer that is difficult to melt at the time of heat welding and has high flexibility. In addition, the function of a safety valve may be imparted to the sealing film 1 in case the temperature or pressure in the bag rises abnormally by controlling the laminate strength between the layers to an appropriate range.

The Example of the sealing film 1 shown in Table 1 and the comparative example were produced using resin shown below.
Resin A: Maleic anhydride-modified PP obtained by graft polymerization of maleic anhydride on 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 with 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 with 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 grafted with maleic anhydride on random PP (MFR 7.5 g / 10 min (230 ° C.), melting point 135 ° C.)
Resin D-2: Maleic anhydride-modified PP obtained by graft polymerization of maleic anhydride on random PP (MFR 7.0 g / 10 min (230 ° C.), melting point 140 ° C.)
Resin E: Block PP (MFR 2.3 g (230 ° C.) / 10 min, melting point 163 ° C.)

<Examples 1-15>
Resin A and resin B are put into the hopper of the extruder at the compounding ratio shown in Table 1, extruded while being modified to resin C at the extrusion temperature shown in Table 1, and extruded from another extruder and coextruded T-die Then, Examples 1 to 15 of the sealing film 1 were cast and laminated.
In an example in which the column of the layer structure in Table 1 is three layers, the resin E was extruded from another extruder and coextruded and laminated at the time of coextrusion cast molding. Further, in the example in which the column of the colorant in Table 1 is 3 parts, 3 parts by weight of a PP-based pigment master batch was added when the resin A and the resin B were blended.
The extrusion temperatures of Resin D and Resin E were both 240 ° C.

  In this way, a laminated film having a three-layer structure in which a laminated film having a two-layer structure composed of a 40 μm electrode adhesive layer 2 and a heat-resistant layer 3 having a thickness shown in the column of the heat-resistant layer in Table 1 and a 20 μm sealant 4 are laminated. Molded. The laminated film was slit to a width of 25 mm, and Examples 1 to 15 of the sealing film 1 were produced.

<Comparative Example 1>
Resin D-1 and Resin E were each extruded at 240 ° C. and laminated in a coextrusion T-die, and a two-layer laminated film composed of a 20 μm electrode adhesive layer 2 and an 80 μm sealant 4 was cast. This laminated film was slit to a width of 25 mm to produce a sealing film 1 of Comparative Example 1.

なお、表１における「部」は、全て「重量部」を意味する。

In Table 1, “parts” all mean “parts by weight”.

<Measurement of electrode adhesion 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. Examples 1 to 15 and Comparative Example 1 of the sealing film 1 were each cut to a length of 60 mm. The electrode 11 was placed on the electrode 11 with the electrode adhesive layer 2 of the sealing film 1 inside. Heating was performed from the aluminum foil side using a heat sealer at 200 ° C., 0.2 MPa for 3 seconds, and the other end was thermally welded, leaving an unwelded portion at one end.
The peel strength between the electrode adhesive layer 2 and the electrode 11 of each sealing film 1 was measured using an Instron type tensile tester. When measuring the peel strength, the end of the sealing film 1 and the end of the electrode 11 not welded to the electrode 11 are fixed to two chucks of a tensile tester, pulled at a speed of 300 mm / min, and peeled 180 degrees. The strength was measured. The electrode adhesive layer 2 and the electrode 11 of each sealing film 1 were heat-sealed with a sealing strength of 27.5 to 32.8 N / 25 mm.

<Measurement of laminate film welding 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 sealant 22 were laminated by dry lamination. The obtained laminated film was cut into a square having a side of 100 mm to produce a laminate film 20 of two bags.
Examples 1 to 15 and Comparative Example 1 of the sealing film 1 were each cut to a length of 60 mm. The sealant 22 of the laminate film 20 of two bags was faced each other, and the sealing film 1 was sandwiched therebetween. When sandwiching the sealing film 1, the sealing film 1 was exposed 5 mm from the end of the laminate film 20.
One end of the side where the sealing film 1 is exposed was welded by heating from both sides of the laminate film 20 of the two bags under the same conditions as the measurement of the electrode adhesive strength. The other end was left as an unwelded part. When the sealing film 1 was welded, the seal bar touched about 2 mm at the base of the exposed portion of the sealing film 1.

Similarly to the measurement of the electrode adhesive strength, the end of the non-welded portion of the sealing film 1 and the end of the laminate film 20 are fixed to the two chucks of the tensile tester, and under the same conditions as the measurement of the electrode adhesive strength, The heat seal strength of the sealant 4 or the heat-resistant layer 3 and the laminate film 20 of each sealing film 1 was measured. Each sealing film 1 and the laminate film 20 were heat-sealed with a sealing strength of 124.2 to 143.3 N / 25 mm.
Moreover, the heat-deformed or melted trace was not seen in the part exposed from the laminate film 20 of the sealing film 1 in any Example. On the other hand, in the comparative example, the root of the portion exposed from the laminate film 20 was slightly shrunk.

<MFR of kneaded product>
A melt-kneaded product (resin C-1) of 95 parts by weight of resin A and 5 parts by weight of resin B-1 and a melt-kneaded product of 95 parts by weight of resin A and 5 parts by weight of resin B-3 (resin C) -3) were extruded separately and MFR at 230 ° C. was measured. The MFR of the original resin A was 2.4. Resin C-1 had an MFR of 1.9, which was lower than that of Resin A. The MFR of Resin C-3 was 2.5, which was higher than that of Resin A. Thereby, the reason why the heat resistance of the sealing film 1 is improved in the present invention is not only because the molecular weight increases due to the chemical bond between the carboxyl group of the resin A and the functional group of the resin B, but also the partial crosslinking. Presumed to be affected.

  INDUSTRIAL APPLICABILITY The present invention can be widely applied to a manufacturing method of a sealing film and a sealing film for sealing an electrode of a power generation element such as a secondary battery or a capacitor housed in a bag.

DESCRIPTION OF SYMBOLS 1 ... Sealing film 2 ... Electrode adhesive layer 3 ... Heat-resistant layer 4 ... Sealant 10 ... Electrode 11 with sealing film ... Electrode 20 ... Laminate film 21 of a bag body ... Metal foil 22 of a laminate film ... Sealant 23 of a laminate film ... Lamination Film base film

Claims (12)

A method for producing a sealing film sandwiched between an electrode of a power generation element housed in a bag body and an edge of the bag body,
By melting and kneading both the acid-modified polyolefin resin A graft-polymerized with carboxylic acid and the resin B having a functional group capable of reacting with the carboxyl group of the resin A, the carboxyl group of the resin A and the function of the resin B A melt-kneading step in which a group is chemically bonded to modify the resin C;
Forming a heat-resistant layer by forming the resin C into layers,
An adhesive layer forming step for forming an electrode adhesive layer for forming a layer of the carboxylic acid-modified polyolefin resin D and adhering to the electrode;
A method for producing a sealing film comprising: a laminating step of directly laminating the heat-resistant layer and the electrode adhesive layer when either one or both of the resin C and the resin D are in a molten state.   The manufacturing method of the sealing film of Claim 1 with which the said melt-kneading process is performed within an extruder.   The manufacturing method of the sealing film of Claim 1 or 2 with which the said melt-kneading process and the said heat-resistant layer film forming process are performed continuously.   The manufacturing method of the sealing film as described in any one of Claim 1 to 3 by which the said lamination | stacking process is performed continuously in any one or both of the said heat-resistant layer film forming process and the said contact bonding layer film forming process.   The manufacturing method of the sealing film as described in any one of Claim 1 to 4 with which the said lamination process is performed within a coextrusion die.   The method for producing a sealing film according to any one of claims 1 to 5, wherein the melt-kneading step is performed by blending resin A in a weight percentage of 99 to 90 with respect to resin B being 1 to 10. .   The method for producing a sealing film according to any one of claims 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. A sealing film sandwiched between the electrode of the power generation element housed in the bag and the edge of the bag,
By melting and kneading both the acid-modified polyolefin resin A graft-polymerized with carboxylic acid and the resin B having a functional group capable of reacting with the carboxyl group of the resin A, the carboxyl group of the resin A and the functional group of the resin B A sealing film having a laminated structure in which a heat-resistant layer made of a resin C modified by chemical bonding is directly laminated on an electrode adhesive layer made of a carboxylic acid-modified polyolefin resin D.   The sealing film according to claim 8, wherein the resin B is one or more selected from resins having a hydroxyl group, an amino group, or an epoxy group.   The sealing film according to claim 8 or 9, wherein the resin A is an acid-modified polyolefin resin obtained by graft polymerization of maleic anhydride on polypropylene.   The sealing film according to claim 8, wherein the laminated structure is formed by coextrusion of a resin C and a resin D.   The sealing film according to any one of claims 8 to 11, wherein a sealant that is thermally welded to the innermost layer of the bag is laminated on the heat-resistant layer.

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