JP7040451B2 - "Protective film" - Google Patents

Description

The present invention relates to a protective film, a method for preventing the electrolytic solution from adhering to the periphery of the electrolytic solution injection port, and a method for manufacturing a battery.

In recent years, batteries such as lithium-ion batteries have been widely used in various applications such as electric vehicles, hybrid electric vehicles, personal computers, cameras, and mobile phones. When manufacturing such a battery, after the electrolytic solution is injected from the electrolytic solution injection port provided in the battery, the electrolytic solution injection port is sealed by the sealing member.

In the process of manufacturing such a battery, the electrolytic solution may adhere to the periphery of the electrolytic solution injection port before the electrolytic solution is injected from the electrolytic solution injection port. Further, in the process of manufacturing a battery, in general, after the electrolytic solution is injected into the inside of the battery, the battery may be subjected to aging in a high temperature environment before being sealed by the sealing member. During aging in this high temperature environment, the electrolytic solution inside the battery may bump and the electrolytic solution may adhere to the periphery of the electrolytic solution injection port. If the electrolytic solution adheres around the electrolytic solution injection port, various problems occur in the subsequent manufacturing process of the battery.

For example, when the electrolytic solution injection port and the sealing member are sealed by welding, it is known that welding defects occur in the portion to which the electrolytic solution adheres, and the sealing property of the battery may deteriorate. In order to solve such a problem, for example, in Patent Document 1 and Patent Document 2, the shape around the electrolytic solution injection port of the battery is devised to prevent the electrolytic solution from adhering to the welded portion. A method has been proposed.

Japanese Unexamined Patent Publication No. 2012-169254 Japanese Unexamined Patent Publication No. 2014-154482

As in Patent Document 1 and Patent Document 2, it is considered possible to suppress the adhesion of the electrolytic solution to the welded portion by devising the shape around the electrolytic solution inlet of the battery, but other than the welded portion. It was found that the electrolytic solution adhering to the portion of the above had a problem of corroding the periphery of the electrolytic solution injection port.

In order to solve such a problem, the present inventors attach an adhesive film having an adhesive layer such as acrylic resin or epoxy resin on the back surface of the film around the electrolytic solution injection port, and inject the electrolytic solution of the battery. It was examined to protect the periphery of the entrance with the adhesive film, inject the electrolytic solution, and then perform aging.

When such an adhesive film is used, it is required to have excellent electrolytic solution resistance when exposed to a high temperature environment after the electrolytic solution adheres, but acrylic resin, epoxy resin, etc. are used on the back surface of the film. When a protective film having an adhesive layer is used, the adhesive layer is invaded by the electrolytic solution and falls off in the battery manufacturing process, or the adhesive component elutes in the electrolytic solution and causes deterioration of battery performance. The electrolytic solution property was insufficient, and it was inappropriate as a protective film to be attached around the electrolytic solution injection port of the battery at the time of manufacturing the battery.

The present inventors have made diligent studies to solve the above problems. As a result, it is a protective film that is affixed around the electrolyte injection port of the battery at the time of manufacturing the battery and then peeled off, and is provided with a base material layer and an adhesive layer, and the base material layer is provided. The protective film contains a polyolefin resin and the adhesive layer contains a polyolefin resin, and the protective film has an adhesion strength after storage measured under the following conditions of 0.1 N / 15 mm or more and 13.0 N / 15 mm or less. A protective film has excellent electrolytic solution resistance when exposed to a high temperature environment after the electrolytic solution adheres, and the adhesive layer of the protective film is electrolyzed before the electrolytic solution is injected from the electrolytic solution injection port. It has been found that by sticking it around the liquid injection port, it is possible to suitably prevent the electrolytic solution from adhering to the periphery of the electrolytic solution injection port, and it is possible to peel it off after storage. The present invention has been completed by further studies based on these findings.

(Measurement of adhesion strength after storage)
The protective film is cut to prepare a strip-shaped test piece having a length of 120 mm and a width of 15 mm. Next, the adhesive layer of the test piece was adhered to an aluminum plate in an environment of 25 ° C., stored for 7 hours in an environment of 60 ° C., and the end not adhered to the test piece was subjected to a tensile tester at 50 mm / min. The adhesive strength between the test piece and the aluminum plate after storage is measured by pulling at the speed of.

That is, the present invention provides the inventions of the following aspects.
Item 1. A protective film that is affixed around the electrolyte inlet of a battery when the battery is manufactured and then peeled off.
The protective film includes a base material layer and an adhesive layer, and has an adhesive layer.
The base material layer contains a polyolefin resin and is
The adhesive layer contains a polyolefin resin and is
The protective film is a protective film having an adhesion strength of 0.1 N / 15 mm or more and 13.0 N / 15 mm or less after storage, which is measured under the following conditions.
(Measurement of adhesion strength after storage)
The protective film is cut to prepare a strip-shaped test piece having a length of 120 mm and a width of × 15 mm. Next, the adhesive layer of the test piece was adhered to an aluminum plate in an environment of 25 ° C., stored for 7 hours in an environment of 60 ° C., and the end portion not adhered to the test piece was subjected to a tensile tester. The test piece is pulled at a speed of 50 mm / min, and the adhesion strength between the test piece and the aluminum plate after storage is measured.
Item 2. Item 2. The protective film according to Item 1, wherein the protective film has an initial adhesion strength of 0.1 N / 15 mm or more measured under the following conditions.
The protective film is cut to prepare a strip-shaped test piece having a length of 120 mm and a width of 15 mm. Next, in an environment of 25 ° C., the adhesive layer of the test piece was adhered to an aluminum plate, and the end portion not adhered to the test piece was pulled by a tensile tester at a speed of 50 mm / min to obtain the test piece. And the initial adhesion strength between the aluminum plate and the aluminum plate are measured.
Item 3. Item 2. The protective film according to Item 1 or 2, wherein the adhesive layer contains an elastomer.
Item 4. Item 2. The protective film according to any one of Items 1 to 3, wherein the base material layer is made of polypropylene.
Item 5. Item 2. The protective film according to any one of Items 1 to 4, wherein the base material layer is composed of two or more layers.
Item 6. It is a method of preventing the electrolytic solution from adhering to the periphery of the electrolytic solution injection port when the electrolytic solution is injected from the electrolytic solution injection port of the battery at the time of manufacturing the battery.
A method for preventing electrolyte adhesion, comprising the following steps (A) and (B).
Step (A): A protective film having a base material layer containing a polyolefin resin and an adhesive layer containing an olefin resin is prepared.
Step (B): The adhesive layer of the protective film is attached around the electrolytic solution injection port of the battery before injecting the electrolytic solution.
Item 7. A method for manufacturing a battery, which comprises at least the following steps (A), (B), and (C) in this order.
Step (A): A protective film having a base material layer containing a polyolefin resin and an adhesive layer containing a polyolefin resin is prepared.
Step (B): The adhesive layer of the protective film is attached around the electrolytic solution injection port of the battery before injecting the electrolytic solution.
Step (C): The electrolytic solution is injected from the electrolytic solution injection port.

According to the present invention, it is a protective film that is attached around the electrolytic solution injection port of the battery at the time of manufacturing the battery and is used for the purpose of being peeled off thereafter, and is an electrolytic solution resistant liquid when exposed to a high temperature environment. It is possible to provide a protective film having excellent properties and which can be suitably peeled off after storage. By attaching the adhesive layer of the protective film of the present invention around the electrolytic solution injection port before injecting the electrolytic solution from the electrolytic solution injection port of the battery, the electrolytic solution adheres to the periphery of the electrolytic solution injection port. It can be suitably prevented.

Further, according to the present invention, there is provided a method of preventing the electrolytic solution from adhering to the periphery of the electrolytic solution injection port before injecting the electrolytic solution from the electrolytic solution injection port of the battery by using the protective film. can do. Further, according to the present invention, it is also possible to provide a method for manufacturing a battery using the protective film.

It is a figure which shows an example of the cross-sectional structure of the protective film of this invention. It is a figure which shows an example of the cross-sectional structure of the protective film of this invention. It is a figure which shows an example of the cross-sectional structure of the protective film of this invention. It is a schematic diagram for demonstrating the method of preventing the electrolytic solution from adhering around the electrolytic solution injection port of a battery using the protective film of this invention. It is a schematic cross-sectional view which shows the appearance that the protective film of this invention was attached around the electrolytic solution injection port of a battery (schematic sectional view near the electrolytic solution injection port of a battery). It is a schematic plan view of an example of the protective film of this invention.

The protective film of the present invention is a protective film that is attached around the electrolytic solution injection port of the battery at the time of manufacturing the battery and then peeled off. The protective film of the present invention includes a base material layer and an adhesive layer, the base material layer contains a polyolefin resin, and the adhesive layer contains a polyolefin resin, and the measurement is further carried out under the following conditions. The adhesion strength after storage is 0.1 N / 15 mm or more and 13.0 N / 15 mm or less. Hereinafter, the protective film of the present invention will be described in detail, a method for preventing the electrolytic solution from adhering to the periphery of the electrolytic solution injection port using the protective film, and a method for manufacturing a battery using the protective film will be described in detail. do.

(Measurement of adhesion strength after storage)
The protective film is cut to prepare a strip-shaped test piece having a length of 120 mm and a width of 15 mm. Next, the adhesive layer of the test piece was adhered to an aluminum plate in an environment of 25 ° C., stored for 7 hours in an environment of 60 ° C., and the end not adhered to the test piece was subjected to a tensile tester at 50 mm / min. The adhesive strength between the test piece and the aluminum plate after storage is measured by pulling at the speed of.

In the present specification, with respect to the numerical range, the numerical range indicated by "-" means "greater than or equal to" and "less than or equal to". For example, the notation of 2 to 15 mm means 2 mm or more and 15 mm or less.

1. 1. Protective film The protective film of the present invention is attached around the electrolytic solution inlet of the battery at the time of manufacturing the battery, so that the electrolytic solution is formed around the electrolytic solution injection port before (when) the electrolytic solution is injected into the battery. It is used to suppress adhesion and then peel off (after injection of the electrolytic solution).

The protective film of the present invention includes, for example, a base material layer 1 and an adhesive layer 2 as shown in FIGS. 1 to 3. The base material layer 1 may be either a single layer or a plurality of layers (two or more layers). For example, in FIG. 1, the base material layer 1 is composed of a single layer. Further, in FIG. 2, the base material layer 1 is composed of two layers, a first base material layer 11 and a second base material layer 12. Further, in FIG. 3, the base material layer 1 is composed of three layers of a first base material layer 11, a second base material layer 12, and a third base material layer 13. When the base material layer 1 is a plurality of layers, the number of layers thereof is not particularly limited, but preferably two or three layers. Further, the adhesive layer 2 may be either a single layer or a plurality of layers, but the adhesive layer 2 may usually be a single layer.

Further, the adhesive layer 2 may be provided on at least a part of the base material layer 1. For example, in the protective film 10 shown in FIG. 6, the adhesive layer 2 is provided only in the colored region 4.

The base material layer 1 is a layer that suppresses the adhesion of the electrolytic solution around the electrolytic solution injection port and further enhances the shape retention of the protective film. The base material layer 1 contains a polyolefin resin. One type of polyolefin resin may be used alone, or two or more types may be used in combination. The polyolefin resin has high electrolytic solution resistance, and the base material layer 1 is an electrolytic solution even in the electrolytic solution injection step after being attached around the electrolytic solution injection port of the battery at the time of manufacturing the battery and in the aging step in a high temperature environment. Can be prevented from being invaded by.

Specific examples of the polyolefin resin include polyethylene such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, and linear low-density polyethylene; homopolypropylene, a block copolymer of polypropylene (for example, a block copolymer of propylene and ethylene), and random polypropylene. Polypropylene such as copolymers (eg, random copolymers of propylene and ethylene); polyethylene-butene-propylene tarpolymers; and the like. Among these polyolefins, polyethylene and polypropylene are preferable, and polypropylene is more preferable. Further, as polypropylene, a random copolymer of polypropylene is preferable. The ratio of the propylene unit contained in polypropylene is usually 50% by mass or more.

Further, the polyolefin resin may be a cyclic polyolefin. The cyclic polyolefin is a copolymer of an olefin and a cyclic monomer, and examples of the olefin which is a constituent monomer of the cyclic polyolefin include ethylene, propylene, 4-methyl-1-pentene, butadiene, and isoprene. Examples of the cyclic monomer which is a constituent monomer of the cyclic polyolefin include cyclic alkenes such as norbornene; specifically, cyclic diene such as cyclopentadiene, dicyclopentadiene, cyclohexadiene, norbornadiene and the like. Among these polyolefins, cyclic alkene is preferable, and norbornene is more preferable. Moreover, styrene is also mentioned as a monomer.

The polyolefin resin may be an acid-modified polyolefin. The acid-modified polyolefin is a polymer modified by block-polymerizing or graft-polymerizing a polyolefin with a carboxylic acid or a carboxylic acid anhydride. Examples of the carboxylic acid or carboxylic acid anhydride used for modification include maleic acid, acrylic acid, itaconic acid, crotonic acid, maleic anhydride, and itaconic anhydride. Further, examples of the modified polyolefin include the above-mentioned polyolefin, and preferably polypropylene.

The polyolefin resin may be an acid-modified cyclic polyolefin. The acid-modified cyclic polyolefin means that a part of the monomer constituting the cyclic polyolefin is copolymerized in place of α, β-unsaturated carboxylic acid or its anhydride, or α, β-non-replaceable with respect to the cyclic polyolefin. It is a polymer obtained by block polymerization or graft polymerization of a saturated carboxylic acid or an anhydride thereof. The same applies to the modified cyclic polyolefin. Examples of the carboxylic acid or carboxylic acid anhydride used for modification include the same as those described above.

The proportion of the polyolefin resin contained in the base material layer 1 is not particularly limited, but is preferably 60% by mass or more, more preferably about 65 to 100% by mass, and further preferably about 70 to 100% by mass.

The base material layer 1 is preferably composed of only a polyolefin resin, more preferably only polyethylene or polypropylene, and further preferably only polypropylene.

The base material layer 1 may contain a resin other than the polyolefin resin, and examples of such a resin include polyester, polyamide, epoxy resin, acrylic resin, fluororesin, polyurethane, silicon resin, phenol resin, and polyether. Examples thereof include imide, polyimide, and mixtures and copolymers thereof.

When the base material layer 1 is composed of a plurality of layers, at least the layer located closest to the adhesive layer 2 may contain the polyolefin resin, and the other layers contain the polyolefin resin. You don't have to. When the other layer does not contain the polyolefin resin, the other layer can be made of, for example, a resin other than the above-mentioned polyolefin resin. When the base material layer 1 is composed of a plurality of layers, it is preferable that all the layers contain a polyolefin resin, and it is further preferable that all the layers are composed of a polyolefin resin.

The thickness of the base material layer 1 is not particularly limited, but from the viewpoint of effectively suppressing the adhesion of the electrolytic solution and enhancing the electrolytic solution resistance when exposed to a high temperature environment after the electrolytic solution is attached. , Preferably 27 μm or more. Further, in addition to the electrolytic solution resistance, the initial adhesion to the periphery of the electrolytic solution injection port, the followability to the shape around the electrolytic solution injection port, and the appropriate peeling after being subjected to aging in a high temperature environment. From the viewpoint of enhancing properties such as peelability, it is preferably about 25 to 80 μm, more preferably about 27 to 50 μm, and further preferably about 27 to 40 μm.

When the base material layer 1 is composed of a plurality of layers, the thickness of each layer is preferably about 7 to 35 μm, more preferably about 7 to 20 μm, still more preferably about 9 to 18 μm from the same viewpoint. Can be mentioned.

The adhesive layer 2 is provided on the base material layer 1, contains an adhesive component, and is a layer having adhesiveness. In the present invention, the adhesive layer 2 contains a polyolefin resin. In the protective film of the present invention, since both the base material layer 1 and the adhesive layer 2 contain the polyolefin resin, the adhesion between the two layers is excellent, and the protective film is exposed to a high temperature environment after the electrolytic solution adheres. It is possible to improve the electrolytic solution resistance in the case of

Examples of the polyolefin resin contained in the adhesive layer 2 include the same ones exemplified in the base material layer 1. Among the polyolefin resins, polyethylene and polypropylene are preferable, and polypropylene is more preferable. Further, as polypropylene, a random copolymer of polypropylene is preferable. The ratio of the propylene unit contained in polypropylene is usually 50% by mass or more. One type of polyolefin resin may be used alone, or two or more types may be used in combination.

The adhesive layer 2 may contain a resin other than the polyolefin resin, and examples of such a resin include polyester, polyamide, epoxy resin, acrylic resin, fluororesin, polyurethane, silicon resin, phenol resin, and polyetherimide. , Polyimide, and mixtures and copolymers thereof.

The proportion of the polyolefin resin contained in the adhesive layer 2 is not particularly limited, but is preferably 50% by mass or more, more preferably about 50 to 90% by mass, and further preferably about 60 to 90% by mass.

The adhesive layer 2 preferably has an appropriate initial adhesion to the periphery of the electrolytic solution injection port and an appropriate peelability that is appropriately peeled off after being subjected to aging in a high temperature environment. From this point of view, the adhesive layer 2 preferably contains an elastomer in addition to the polyolefin resin.

The elastomer is not particularly limited as long as it is blended with a polyolefin resin and exhibits adhesiveness, and for example, an elastomer composed of a thermoplastic resin (thermoplastic elastomer) is preferable.

Preferred examples of the elastomer include styrene-based elastomers, olefin-based elastomers, acrylic-based elastomers, silicone-based elastomers, urethane-based elastomers, polyester-based elastomers, polyamide-based elastomers, and rubber-based elastomers. One type of elastomer may be used alone, or two or more types may be used in combination.

The type of styrene-based elastomer is not particularly limited, and specific examples thereof include styrene-butadiene-styrene block copolymer, styrene-isoprene-styrene block copolymer, styrene-ethylene-butylene-styrene block copolymer, and styrene-ethylene-propylene. -Styrene block copolymer and the like.

Examples of the olefin-based elastomer include copolymers of α-olefins having 2 to 20 carbon atoms such as ethylene, propylene, 1-butene, 1-hexene and 4-methyl-pentene, and examples thereof include ethylene-propylene copolymers (EPRs). ), Ethylene-propylene-diene copolymer (EPDM) and the like are preferable. Further, examples thereof include a copolymer of α-olefin and a non-conjugated diene having 2 to 20 carbon atoms such as dicyclopentadiene, 1,4-hexadiene, cyclooctadiene, methylenenorbornene, ethylidenenorbornene, butadiene and isoprene. Further, carboxy-modified nitrile rubber obtained by copolymerizing methacrylic acid with a butadiene-acrylonitrile copolymer can be mentioned.

The acrylic elastomer contains an acrylic acid ester as a main component, and specifically, ethyl acrylate, butyl acrylate, methoxyethyl acrylate, ethoxyethyl acrylate and the like are preferably used. Further, as the cross-linking point monomer, glycidyl methacrylate, allyl glycidyl ether and the like are used. Furthermore, acrylonitrile and ethylene can be copolymerized. Specific examples thereof include an acrylonitrile-butyl acrylate copolymer, an acrylonitrile-butyl acrylate-ethyl acrylate copolymer, and an acrylonitrile-butyl acrylate-glycidyl methacrylate copolymer.

Examples of the silicone-based elastomer include organopolysiloxane as a main component, and examples thereof include polydimethylsiloxane-based, polymethylphenylsiloxane-based, and polydiphenylsiloxane-based elastomers.

The urethane elastomer consists of a structural unit consisting of a hard segment composed of low molecular weight ethylene glycol and diisocyanate and a soft segment composed of a polymer (long chain) diol and diisocyanate, and the polymer (long chain) diol is polypropylene glycol. Polytetramethylene oxide, poly (1,4-butylene adipate), poly (ethylene-1,4-butylene adipate), polycaprolactone, poly (1,6-hexylene carbonate), poly (1,6-hexylene adipate). Neopentylene glycol (adipate) and the like.

The polyester-based elastomer is obtained by polycondensing a dicarboxylic acid or a derivative thereof and a diol compound or a derivative thereof. Specific examples of the dicarboxylic acid include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, and naphthalenedicarboxylic acid, and aromatic dicarboxylic acids in which the hydrogen atom of these aromatic nuclei is substituted with a methyl group, an ethyl group, a phenyl group, or the like. Examples thereof include aliphatic dicarboxylic acids having 2 to 20 carbon atoms such as adipic acid, sebacic acid and dodecanedicarboxylic acid, and alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid. These compounds may be used alone or in admixture of two or more.

Specific examples of the diol compound include aliphatic diols such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,10-decanediol, and 1,4-cyclohexanediol. And alicyclic diols, and further include bisphenol A, bis- (4-hydroxyphenyl) -methane, bis- (4-hydroxy-3-methylphenyl) -propane, resorcin and the like. These compounds may be used alone or in admixture of two or more.

As the polyamide-based elastomer, polyamide is used as a hard segment component, polybutadiene, butadiene-acrylonitrile copolymer, styrene-butadiene copolymer, polyisoprene, ethylene-propylene copolymer, polyether, polyester, polybutadiene, polycarbonate, polyacrylate, etc. Examples thereof include block copolymers containing polymethacrylate, polyurethane, silicone rubber and the like as soft segment components.

Examples of the rubber-based elastomer include polyisobutylene and the like.

Effectively suppresses the adhesion of the electrolyte to the periphery of the electrolyte injection port, enhances the electrolyte resistance when exposed to a high temperature environment after the electrolyte adheres, and further to the periphery of the electrolyte injection port. Among elastomers, from the viewpoint of effectively enhancing properties such as initial adhesion, followability to the shape around the electrolyte injection port, and peelability that is appropriately peeled off after being subjected to aging in a high temperature environment. , Styrene-based elastomers and olefin-based elastomers are preferable, and styrene-based elastomers are particularly preferable.

The proportion of the elastomer contained in the adhesive layer 2 is not particularly limited, but is preferably about 50% by mass or less, more preferably about 10 to 50% by mass, still more preferably, from the viewpoint of effectively enhancing each of the above-mentioned characteristics. Is about 10 to 40% by mass.

The thickness of the adhesive layer 2 is not particularly limited, but from the viewpoint of effectively suppressing the adhesion of the electrolytic solution and enhancing the electrolytic solution resistance when exposed to a high temperature environment after the electrolytic solution is attached, the thickness is not particularly limited. It is preferably 3 μm or more. Further, in addition to the electrolytic solution resistance, the initial adhesion to the periphery of the electrolytic solution injection port, the followability to the shape around the electrolytic solution injection port, and the appropriate peeling after being subjected to aging in a high temperature environment. From the viewpoint of enhancing properties such as peelability, it is preferably about 3 to 55 μm, more preferably about 3 to 35 μm, and further preferably about 3 to 25 μm.

In the protective film of the present invention, a support may be laminated on the side of the base material layer 1 opposite to the adhesive layer 2. In the present invention, for example, a support that is peeled off from the base material layer 1 when the protective film of the present invention is attached around the electrolytic solution injection port can be used. Examples of the support include films, papers, non-woven fabrics and the like. The thickness of the support is not particularly limited, and is usually about 10 to 100 μm.

The thickness of the protective film of the present invention is not particularly limited, but from the viewpoint of effectively suppressing the adhesion of the electrolytic solution and enhancing the electrolytic solution resistance when exposed to a high temperature environment after the electrolytic solution is attached. Is preferably 30 μm or more. Further, in addition to the electrolytic solution resistance, the initial adhesion to the periphery of the electrolytic solution injection port, the followability to the shape around the electrolytic solution injection port, and the appropriate peeling after being subjected to aging in a high temperature environment. From the viewpoint of enhancing properties such as peelability, for example, it is about 25 to 120 μm, preferably about 30 to 120 μm, more preferably about 30 to 105 μm, and further preferably about 30 to 90 μm.

The area of the protective film of the present invention is not particularly limited and varies depending on the size of the battery, but is usually about 0.07 to 10 cm ² . Further, the protective film of the present invention preferably has an opening corresponding to the shape of the electrolytic solution injection port of the battery. 4 and 5 are schematic views showing how the protective film of the present invention having an opening corresponding to the shape of the electrolytic solution injection port of the battery is attached around the electrolytic solution injection port.

The diameter of the opening of the protective film of the present invention corresponds to the diameter Wa of the opening of the electrolytic solution injection port 21 of the battery 20 described later. The shape of the protective film of the present invention is not particularly limited, but is usually a substantially rectangular shape or a substantially circular shape when viewed in a plan view. Further, as shown in FIG. 6, the shape of the protective film may include a handle portion 6. Further, the protective film may have a handle of another member from the viewpoint of handling.

The protective film of the present invention preferably has an initial adhesion strength of 0.1 N / 15 mm or more, more preferably about 0.1 to 4.0 N / 15 mm, as measured under the following conditions.

<Measurement conditions for initial adhesion strength>
In the method for measuring the initial adhesion strength, first, the protective film is cut to prepare a strip-shaped test piece having a length of 120 mm and a width of 15 mm. Next, in an environment of 25 ° C., the adhesive layer of the test piece is adhered to the aluminum plate with a load of 2 kgf (the portion to be adhered to the aluminum plate is a portion having a length of 50 mm and a width of 15 mm of the test piece). The end part that is not adhered to is pulled with a tensile tester (manufactured by Shimadzu Corporation, AG-X Plus) at a speed of 50 mm / min and a pulling angle of 180 °, and the initial adhesion strength between the test piece and the aluminum plate is measured.

The protective film of the present invention is stored at 60 ° C. for 7 hours, and then the adhesion strength after high temperature storage measured under the following conditions is in the range of 0.1 to 13.0 N / 15 mm, preferably 0.1. ~ 12.2N / 15mm, 0.1 ~ 10.9N / 15mm, 0.2 ~ 13.0N / 15mm, 0.2 ~ 12.2N / 15mm, 0.2 ~ 10.9N / 15mm The degree is about 0.3 to 13.0 N / 15 mm, about 0.3 to 12.2 N / 15 mm, and about 0.3 to 10.9 N / 15 mm. Further, after storage at 120 ° C. for 8 hours, the adhesion strength after high temperature storage measured under the following conditions is preferably 0.3 N / 15 mm or more, about 0.3 to 7.3 N / 15 mm, 0. It is more preferably about 4.4 to 7.3 N / 15 mm. Further, after storage at 120 ° C. for 48 hours, the adhesion strength after high temperature storage measured under the following conditions is preferably 0.3 N / 15 mm or more, and is about 0.3 to 5.0 N / 15 mm, 1 More preferably, it is about 5.5 to 5.0 N / 15 mm.

<Measurement conditions for adhesion strength after high temperature storage>
In the method for measuring the adhesion strength after high temperature storage, first, the protective film is cut to prepare a strip-shaped test piece having a length of 120 mm and a width of 15 mm. Next, in an environment of 25 ° C., the adhesive layer of the test piece is adhered to the aluminum plate with a load of 2 kgf (the portion to be adhered to the aluminum plate is a portion having a length of 50 mm and a width of 15 mm of the test piece). Next, it is stored under the conditions of each temperature and application time (7 hours at 60 ° C, 8 hours at 120 ° C, or 48 hours at 120 ° C). Next, the end where the test piece and the aluminum plate are not adhered is pulled with a tensile tester (manufactured by Shimadzu Corporation, AG-X Plus) at a speed of 50 mm / min and a pulling angle of 180 °, and the test piece and the aluminum plate are separated. Measure the adhesion strength after high temperature storage.

The protective film of the present invention is a protective film that is attached around the electrolytic solution injection port of the battery and then peeled off (after the electrolytic solution is injected). For example, as shown in the schematic views A and B of FIG. 4, the protective film 10 of the present invention is attached to the periphery 22 of the electrolytic solution injection port 21 of the battery 20. Schematic cross-sectional views at this time are shown in FIGS. 5A and 5B.

As shown in FIG. 5A, the diameter Wa of the opening of the electrolytic solution injection port 21 of the battery 20 is not particularly limited and varies depending on the size of the battery, but is usually about 3 to 6 mm. Further, the distance Wb from the end of the opening to the peripheral end of the electrolytic solution injection port (the peripheral portion, at least to the end to which the protective film is attached) is not particularly limited. Although it depends on the size of the battery, it is usually about 0.5 to 50 mm. As shown in FIG. 5, the periphery of the electrolytic solution injection port may be lower than the outside thereof and may have a shape in which a step t is formed. The step t is not particularly limited and varies depending on the size of the battery, but is usually about 0.1 to 10 mm. In addition, there may be one or more steps in the portion to which the protective film of the present invention is attached.

The protective film 10 of the present invention may be preformed and have a shape corresponding to a step t around the electrolytic solution injection port. Further, as described above, even if the protective film 10 of the present invention is provided with an opening 3 corresponding to the opening of the electrolytic solution injection port 21, for example, as shown in B of FIG. 5 and the schematic diagram of FIG. good. Further, the protective film 10 of the present invention may be at least partially colored.

For example, FIG. 6 is a schematic plan view of an example of the protective film 10 of the present invention. In the protective film 10 shown in FIG. 6, in addition to the opening 3 corresponding to the opening of the electrolytic solution injection port 21, a colored region 4 is provided around the opening 3, and only the region 4 is provided. The adhesive layer 2 is provided. A transparent region 5 is provided around the region 4, which facilitates alignment when the protective film 10 is attached around the electrolytic solution injection port. For example, by making the colored region 4 and the transparent region 5 correspond to the shape of the step around the electrolytic solution injection port, the alignment when the protective film 10 is attached around the electrolytic solution injection port can be aligned. Especially easy. Further, in the protective film 10 shown in FIG. 6, a handle portion 6 is provided, which facilitates the work of attaching the protective film 10 to the periphery of the electrolytic solution injection port.

The material around the electrolytic solution injection port to which the protective film of the present invention is attached is not particularly limited, and examples thereof include metal and plastic. In particular, when the periphery of the electrolytic solution injection port is made of metal, the problem of corrosion due to the adhesion of the electrolytic solution is likely to occur, but by using the protective film of the present invention, such a problem is suitably solved. be able to. That is, the protective film of the present invention can be particularly preferably used for a battery using a metal case.

The metal constituting the periphery of the electrolytic solution injection port is not particularly limited, but examples thereof include aluminum alloy, copper, and stainless steel. Among these, aluminum alloy is preferable.

The surface roughness (Ra) around the electrolytic solution injection port (peripheral portion of the electrolytic solution injection port) is not particularly limited, but is preferably about 0.1 to 1.0 μm, more preferably 0.3 to 0. About 5 μm can be mentioned. The surface roughness (Ra) is a value measured by the method specified in JIS B 0601: 2013.

The battery to which the protective film of the present invention is applied is not particularly limited as long as it uses an electrolytic solution, and may be either a primary battery or a secondary battery. For example, the types of secondary batteries include lithium ion batteries, lead storage batteries, nickel / hydrogen storage batteries, nickel / cadmium storage batteries, nickel / iron storage batteries, nickel / zinc storage batteries, silver oxide / zinc storage batteries, polyvalent cation batteries, and condensers. Examples include capacitors. Among these batteries, a lithium ion battery can be mentioned as a suitable application target of the protective film of the present invention.

The protective film of the present invention is used, for example, as follows. That is, in the battery manufacturing process, the protective film of the present invention is attached so as to cover the periphery of the electrolytic solution injection port before injecting the electrolytic solution from the electrolytic solution injection port of the battery. In this state, the electrolytic solution is injected from the electrolytic solution injection port. Next, the electrolytic solution injection port is sealed with a separate member, and the battery is subjected to the aging step. The aging condition is 40 to 150 ° C. for about 1 to 72 hours. After the aging is completed, the protective film of the present invention is peeled off from the periphery of the electrolytic solution injection port, and the electrolytic solution injection port is sealed with a sealing member to manufacture a battery.

The method for producing the protective film of the present invention is not particularly limited, and a known method for producing a laminated film can be adopted. As a method for producing the protective film of the present invention, for example, a method for producing the protective film by co-extruding the resin composition constituting the base material layer 1 and the pressure-sensitive adhesive layer 2 to form a film, or a method for producing the base material layer 1 and the pressure-sensitive adhesive. Examples thereof include a method of laminating a resin film forming the other on a resin film forming one of the layers 2.

2. 2. A method for preventing the electrolytic solution from adhering to the periphery of the electrolytic solution injection port In the present invention, a method for preventing the electrolytic solution from adhering to the periphery of the electrolytic solution injection port during manufacturing of a battery (prevention of the electrolytic solution adhesion of the present invention). The method) is characterized in that the protective film of the present invention described in the above section "1. Protective film" is used before the electrolytic solution is injected from the electrolytic solution injection port of the battery.

Specifically, the method for preventing the adhesion of the electrolytic solution of the present invention is that the electrolytic solution adheres around the electrolytic solution injection port when the electrolytic solution is injected from the electrolytic solution injection port of the battery at the time of manufacturing the battery. It is a method for preventing the above, and is characterized by including the following steps (A) and (B).
Step (A): A protective film having a base material layer containing a polyolefin resin and an adhesive layer containing an olefin resin is prepared.
Step (B): The adhesive layer of the protective film is attached around the electrolytic solution injection port of the battery before injecting the electrolytic solution.

In the electrolytic solution adhesion prevention method of the present invention, first, the protective film of the present invention is prepared. Next, the step of sticking the adhesive layer 2 of the protective film around the electrolytic solution injection port of the battery is performed. By injecting the electrolytic solution from the electrolytic solution injection port with the protective film of the present invention attached around the electrolytic solution injection port of the battery, the electrolytic solution is prevented from adhering to the periphery of the electrolytic solution injection port. To.

Further, in the method for preventing the adhesion of the electrolytic solution of the present invention, as described above, the electrolytic solution injection port may be sealed and the battery may be subjected to the aging step. The aging conditions are as described above. By performing aging with the protective film of the present invention attached around the electrolytic solution injection port, even when the electrolytic solution suddenly boils during aging and the electrolytic solution is blown out from the electrolytic solution injection port, the electrolytic solution is also discharged. It prevents the electrolyte from adhering around the inlet.

Further, a battery is manufactured by peeling the protective film of the present invention from the periphery of the electrolytic solution injection port and sealing the electrolytic solution injection port with a sealing member.

3. 3. Battery Manufacturing Method The battery manufacturing method of the present invention is characterized in that the protective film of the present invention described in the above section "1. Protective film" is used before injecting the electrolytic solution from the electrolytic solution inlet of the battery. And.

Specifically, the method for manufacturing a battery of the present invention is characterized in that at least the following steps (A), (B), and (C) are provided in this order.
Step (A): A protective film having a base material layer containing a polyolefin resin and an adhesive layer containing a polyolefin resin is prepared.
Step (B): The adhesive layer of the protective film is attached around the electrolytic solution injection port of the battery before injecting the electrolytic solution.
Step (C): The electrolytic solution is injected from the electrolytic solution injection port.

In the method for manufacturing a battery of the present invention, first, the protective film of the present invention is prepared. Next, the step of sticking the adhesive layer 2 of the protective film around the electrolytic solution injection port of the battery is performed. Next, the battery is manufactured by performing a step of injecting the electrolytic solution from the electrolytic solution injection port with the protective film of the present invention attached around the electrolytic solution injection port of the battery. Similar to the above-described method for preventing the adhesion of the electrolytic solution of the present invention, the method for manufacturing the battery of the present invention also prevents the electrolytic solution from adhering to the periphery of the electrolytic solution injection port.

Further, in the method for producing electrolysis of the present invention, as described above, the electrolytic solution injection port may be sealed and the battery may be subjected to the aging step. The aging conditions are as described above. By performing aging with the protective film of the present invention attached around the electrolytic solution injection port, even when the electrolytic solution suddenly boiled during aging and blown out from the electrolytic solution injection port, the electrolytic solution injection port It prevents the electrolytic solution from adhering to the surroundings.

Further, a battery is manufactured by peeling the protective film of the present invention from the periphery of the electrolytic solution injection port and sealing the electrolytic solution injection port with a sealing member.

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. However, the present invention is not limited to the examples.

<Manufacturing of protective film>
Example 1
Each of the three types of polypropylene resin compositions was subjected to coextrusion molding to produce a protective film having a three-layer structure. The outermost layer on one side is a first base material layer, specifically made of polypropylene. Further, the intermediate layer is a second base material layer, and is specifically made of polypropylene. Further, the outermost layer on the other side is an adhesive layer, and specifically, is composed of a resin composition containing polypropylene and a styrene-based elastomer. The obtained three-layer protective film was biaxially stretched to obtain a biaxially stretched laminated film (protective film). In the obtained biaxially stretched laminated film, the thickness of the first base material layer was 9 μm, the thickness of the second base material layer was 18 μm, and the thickness of the adhesive layer was 3 μm (total thickness was 30 μm). The amount of the styrene-based elastomer added to the adhesive layer is 40% by mass.

Example 2
Each of the three types of polypropylene resin compositions was subjected to coextrusion molding to produce a protective film having a three-layer structure. The outermost layer on one side is a first base material layer, specifically made of polypropylene. Further, the intermediate layer is a second base material layer, and is specifically made of polypropylene. Further, the outermost layer on the other side is an adhesive layer, and specifically, is composed of a resin composition containing polypropylene and a styrene-based elastomer. The obtained three-layer protective film was biaxially stretched to obtain a biaxially stretched laminated film (protective film). In the obtained biaxially stretched laminated film, the thickness of the first base material layer was 9 μm, the thickness of the second base material layer was 18 μm, and the thickness of the adhesive layer was 3 μm (total thickness was 30 μm). The amount of the styrene-based elastomer added to the adhesive layer is 20% by mass.

Example 3
Each of the three types of polypropylene resin compositions was subjected to coextrusion molding to produce a protective film having a three-layer structure. The outermost layer on one side is a first base material layer, specifically made of polypropylene. Further, the intermediate layer is a second base material layer, and is specifically made of polypropylene. Further, the outermost layer on the other side is an adhesive layer, and specifically, is composed of a resin composition containing polypropylene and a styrene-based elastomer. The obtained three-layer protective film was biaxially stretched to obtain a biaxially stretched laminated film (protective film). In the obtained biaxially stretched laminated film, the thickness of the first base material layer was 9 μm, the thickness of the second base material layer was 18 μm, and the thickness of the adhesive layer was 3 μm (total thickness was 30 μm). The amount of the styrene-based elastomer added to the adhesive layer is 10% by mass.

Example 4
After melt-extruding the acid-modified polypropylene resin on one side of the polyethylene naphthalate film (PEN), the acid-modified polypropylene resin is melt-extruded on the other side of the polyethylene naphthalate film that has not been melt-extruded. An acid-modified polyethylene resin to which an olefin-based elastomer is added (addition amount: 20% by mass) is melt-extruded onto a surface obtained by melt-extruding an acid-modified polypropylene resin to form an acid-modified polypropylene resin layer (thickness 30 μm) / polyethylene naphthalate film. A protective film composed of (thickness 12 μm) / acid-modified polypropylene resin layer (thickness 30 μm) / acid-modified polyethylene resin layer (adhesive layer, thickness 33 m) to which an olefin-based elastomer was added was obtained.

Example 5
An acid-modified polyethylene resin having an olefin-based elastomer added (addition amount: 10% by mass) to one surface of biaxially stretched polypropylene (OPP) is melt-extruded to obtain biaxially stretched polypropylene (thickness 40 μm) / olefin-based elastomer. A protective film composed of the added acid-modified polyethylene resin layer (adhesive layer, thickness 50 μm) was obtained.

Example 6
An acid-modified polyethylene resin having an olefin-based elastomer added (addition amount: 20% by mass) to one surface of biaxially stretched polypropylene (OPP) is melt-extruded to obtain biaxially stretched polypropylene (thickness 30 μm) / olefin-based elastomer. A protective film composed of the added acid-modified polyethylene resin layer (adhesive layer, thickness 50 μm) was obtained.

Example 7
An acid-modified polyethylene resin having an olefin-based elastomer added (addition amount: 15% by mass) to one surface of biaxially stretched polypropylene (OPP) is melt-extruded to obtain biaxially stretched polypropylene (thickness 40 μm) / olefin-based elastomer. A protective film composed of the added acid-modified polyethylene resin layer (adhesive layer, thickness 35 μm) was obtained.

Example 8
An acid-modified polyethylene resin having an olefin-based elastomer added (addition amount: 15% by mass) to one surface of unstretched polypropylene (CPP) is melt-extruded, and unstretched polypropylene (thickness 40 μm) / olefin-based elastomer is added. A protective film (protective film) composed of an acid-modified polyethylene resin layer (adhesive layer, thickness 35 μm) was obtained.

Example 9
An acid-modified polypropylene resin is melt-extruded on one surface of a biaxially stretched polyethylene terephthalate (PET), and a resin composed of a resin composition containing polypropylene and a styrene-based elastomer is further melt-extruded onto the acid-modified polypropylene resin. , A protective film composed of biaxially stretched polyethylene terephthalate (thickness 24 μm) / acid-modified polypropylene resin layer (thickness 30 μm) / adhesive layer (thickness 26 μm) was obtained. The amount of the styrene-based elastomer added to the adhesive layer is 40% by mass.

Example 10
An acid-modified polypropylene resin is melt-extruded on one surface of biaxially stretched polyethylene naphthalate (PEN), and a resin composed of a resin composition further containing polypropylene and a styrene-based elastomer is melt-extruded onto the acid-modified polypropylene resin. A protective film composed of biaxially stretched polyethylene naphthalate (thickness 16 μm) / acid-modified polypropylene resin layer (thickness 30 μm) / adhesive layer (thickness 26 μm) was obtained. The amount of the styrene-based elastomer added to the adhesive layer is 40% by mass.

Comparative Example 1
As a protective film, a commercially available adhesive film (model number: 631S transparent manufacturer: Teraoka Seisakusho Co., Ltd.) was used. The structure of the protective film is as shown in Table 1.

Comparative Example 2
As a protective film, a commercially available adhesive film (model number: 631S black manufacturer: Teraoka Seisakusho Co., Ltd.) was used. The structure of the protective film is as shown in Table 1.

Comparative Example 3
A commercially available adhesive film (model number: 50600 green manufacturer: tesa SE) was used as the protective film. The structure of the protective film is as shown in Table 1.

Comparative Example 4
As a protective film, a commercially available adhesive film (model number: 642 blue, manufacturer: Teraoka Seisakusho Co., Ltd.) was used. The structure of the protective film is as shown in Table 1.

Comparative Example 5
As a protective film, a commercially available adhesive film (model number: ACH-6100, white, manufacturer: Chukoh Chemical Industries, Ltd.) was used. The structure of the protective film is as shown in Table 1.

Comparative Example 6
A commercially available adhesive film (model number: ACH-5001FR white, manufacturer: Chukoh Chemical Industries, Ltd.) was used as the protective film. The structure of the protective film is as shown in Table 1.

Comparative Example 7
A commercially available adhesive film (model number: 635F, manufacturer: Teraoka Seisakusho Co., Ltd.) was used as the protective film. The structure of the protective film is as shown in Table 1.

Comparative Example 8
A commercially available adhesive film (model number: 51108 manufacturer: tesa SE) was used as the protective film. The structure of the protective film is as shown in Table 1.

<Measurement of initial adhesion strength>
For each of the above protective films, the initial adhesion strength was measured under the following conditions. The measurement results are shown in Table 1. In the method for measuring the initial adhesion strength, first, each protective film was cut to prepare a strip-shaped test piece having a length of 120 mm and a width of 15 mm. Next, in an environment of 25 ° C., the adhesive layer of the test piece is loaded on an aluminum plate (1000 series (pure aluminum type), length 100 mm, width 25 mm, thickness 2 mm, surface roughness Ra 0.5 μm) with a load of 2 kgf. (The portion to be adhered to the aluminum plate is a portion having a length of 50 mm and a width of 15 mm of the test piece). Next, pull the end that is not adhered to the test piece with a tensile tester (manufactured by Shimadzu Corporation, AG-X).
The initial adhesion strength was measured by pulling at a speed of 50 mm / min and a pulling angle of 180 ° with Plus) and measuring the load at the time of peeling between the test piece and the aluminum plate.

<Measurement of adhesion strength after high temperature storage>
For each of the above protective films, the adhesion strength after high temperature storage was measured under the following conditions. The measurement results are shown in Table 1. In the method for measuring the adhesion strength after high temperature storage, first, each protective film was cut to prepare a strip-shaped test piece having a length of 120 mm and a width of 15 mm. Next, in an environment of 25 ° C., the adhesive layer of the test piece is loaded on an aluminum plate (1000 series (pure aluminum type), length 100 mm, width 25 mm, thickness 2 mm, surface roughness Ra 0.5 μm) with a load of 2 kgf. (The portion to be adhered to the aluminum plate is a portion having a length of 50 mm and a width of 15 mm of the test piece). Next, it was stored under the conditions of each temperature and application time shown in Table 1 (7 hours at 60 ° C, 8 hours at 120 ° C, or 48 hours at 120 ° C). Next, the end where the test piece and the aluminum plate are not adhered is pulled with a tensile tester (manufactured by Shimadzu Corporation, AG-X Plus) at a speed of 50 mm / min and a pulling angle of 180 °, and the test piece and the aluminum plate are separated. The adhesion strength after high temperature storage was measured by measuring the load at the time of peeling.

<Evaluation of peelability>
When the adhesion strength was measured after the high temperature storage, the peelability was evaluated from the following viewpoints as to whether the peeled adhesive layer remained on the aluminum plate. The results are shown in Table 1.
A: The adhesive layer does not remain on the aluminum plate and is excellent in peelability. B: The adhesive layer remains on the aluminum plate and is inferior in peelability.

<Evaluation of followability>
For each of the above protective films, the adhesive layer of the protective film was attached to an aluminum plate having a step t of 0.5 mm in an environment of 25 ° C. Next, this was stored at 120 ° C. for 48 hours, visually confirmed whether there was a problem in appearance such as peeling of the protective film at the stepped portion and wrinkles of the protective film, and evaluated according to the following criteria. The results are shown in Table 1.
A: The stepped portion is filled with the protective film and no wrinkles are formed. B: The protective film is peeled off at the stepped portion and the stepped portion is not filled, or wrinkles are generated on the protective film.

<Evaluation of electrolytic solution resistance>
Each of the above protective films was immersed in an electrolytic solution (a solution of 1M LiPF ₆ (ethylene carbonate: dimethyl carbonate: diethyl carbonate = 1: 1: 1, volume ratio), stored at 60 ° C. for 7 hours, and then taken out. The protective film was visually confirmed and evaluated according to the following criteria. The results are shown in Table 1.
A: The adhesive layer of the protective film is not melted and is not peeled off from the base material layer. C: The adhesive layer of the protective film is melted or peeled off from the base material layer.

The notations in Table 1 are as follows. PP indicates a polypropylene film. PPa represents a polypropylene film containing maleic anhydride-modified polypropylene. PEN indicates a polyethylene naphthalate film. CPP indicates an unstretched polypropylene film. Ny indicates a biaxially stretched nylon film. PET indicates a biaxially stretched polyethylene terephthalate film.

1 Base material layer 10 Protective film 11 First base material layer 12 Second base material layer 13 Third base material layer 2 Adhesive layer 20 Battery 21 Electrolyte solution injection port 22 Perimeter of electrolyte solution injection port 3 Opening 4 Coloring Area 5 Transparent area 6 Handle part t Step Wa Diameter of the opening of the electrolytic solution injection port Wb Distance from the end of the opening of the electrolytic solution injection port to the peripheral end of the electrolytic solution injection port

Claims (5)

A protective film that is affixed around the electrolytic solution injection port of a battery before the electrolytic solution is injected from the electrolytic solution injection port at the time of manufacturing the battery, and is used for peeling off after the electrolytic solution is injected .
The protective film includes a base material layer and an adhesive layer, and has an adhesive layer.
The base material layer contains a polyolefin resin and is
The adhesive layer contains a polyolefin resin and is
The protective film is a protective film having an adhesion strength of 0.1 N / 15 mm or more and 13.0 N / 15 mm or less after storage, which is measured under the following conditions.
(Measurement of adhesion strength after storage)
The protective film is cut to prepare a strip-shaped test piece having a length of 120 mm and a width of × 15 mm. Next, the adhesive layer of the test piece was adhered to an aluminum plate in an environment of 25 ° C., stored for 7 hours in an environment of 60 ° C., and the end portion not adhered to the test piece was subjected to a tensile tester. The test piece is pulled at a speed of 50 mm / min, and the adhesion strength between the test piece and the aluminum plate after storage is measured. The protective film according to claim 1, wherein the protective film has an initial adhesion strength of 0.1 N / 15 mm or more measured under the following conditions.
The protective film is cut to prepare a strip-shaped test piece having a length of 120 mm and a width of 15 mm. Next, in an environment of 25 ° C., the adhesive layer of the test piece was adhered to an aluminum plate, and the end portion not adhered to the test piece was pulled by a tensile tester at a speed of 50 mm / min to obtain the test piece. And the initial adhesion strength between the aluminum plate and the aluminum plate are measured. The protective film according to claim 1 or 2, wherein the adhesive layer contains an elastomer. The protective film according to any one of claims 1 to 3, wherein the base material layer is made of polypropylene. The protective film according to any one of claims 1 to 4, wherein the base material layer is composed of two or more layers.

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