WO2019193774A1 - Protective film, method for preventing liquid electrolyte from adhering to periphery of liquid-electrolyte injection opening, and method for manufacturing cell - Google Patents

Abstract

Provided is a protective film that is supplied for an application, in manufacturing of a cell, so as to be affixed to the periphery of a liquid-electrolyte injection opening of the cell before the liquid electrolyte is injected, the protective film then being peeled away, wherein the protective film has exceptional liquid-electrolyte resistance when exposed to a high-temperature environment. This protective film is supplied for an application, in manufacturing of a cell, so as to be affixed to the periphery of a liquid-electrolyte injection opening of the cell and then be peeled away, wherein the protective film is provided with a surface layer, and the surface layer includes a polyolefin.

Description

Protective film, method for preventing electrolyte from adhering around electrolyte inlet, and battery manufacturing method

The present invention relates to a protective film, a method for preventing the electrolytic solution from adhering around the electrolytic solution inlet, 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 electrolyte solution is inject | poured from the electrolyte solution injection port provided in the battery, electrolyte solution injection port is sealed with a sealing member.

In the manufacturing process of such a battery, when the electrolyte is injected from the electrolyte inlet, the electrolyte may adhere around the electrolyte inlet. In addition, in the battery manufacturing process, generally, after an electrolyte is injected into the battery, the battery may be subjected to aging in a high-temperature environment before the battery is sealed with a sealing member. In this aging under a high temperature environment, the electrolytic solution inside the battery may suddenly boil, and the electrolytic solution may adhere around the electrolytic solution inlet. If the electrolytic solution adheres around the electrolytic solution inlet, various problems occur in the subsequent battery manufacturing process.

For example, when the electrolytic solution inlet and the sealing member are sealed by welding, it is known that poor welding occurs in the portion where the electrolytic solution is adhered, and the sealing performance of the battery may be reduced. In order to solve such a problem, for example, in Patent Document 1 and Patent Document 2, it is possible to prevent the electrolyte from adhering to the welded portion by devising the shape around the electrolyte inlet of the battery. A method has been proposed.

JP 2012-169254 A JP 2014-154282 A

Although it is thought that it is possible to suppress that electrolyte solution adheres to a welding part by devising the shape around the electrolyte injection port of a battery like patent document 1 and patent document 2, except for a welding part It has been found that the electrolyte solution adhering to this part has a problem of corroding the periphery of the electrolyte injection port.

In order to solve such a problem, the present inventors attached an adhesive film having an adhesive layer such as an acrylic resin or an epoxy resin on the back surface of the film around the electrolyte inlet, and injected the electrolyte solution of the battery. We studied to protect the periphery of the entrance with the adhesive film and to inject the electrolyte and then perform aging.

When using such a pressure-sensitive adhesive film, it is required to have excellent resistance to electrolytic solution when exposed to a high temperature environment after the electrolytic solution adheres to it. When a protective film having an adhesive layer is used, the adhesive layer is eroded by the electrolytic solution and falls off in the battery manufacturing process, or the adhesive component is eluted in the electrolytic solution, leading to a decrease in battery performance. The electrolyte property was insufficient, and it was inappropriate as a protective film to be applied around the electrolyte injection port of the battery in the manufacture of the battery.

The present inventors have intensively studied to solve the above problems. As a result, in the manufacture of batteries, a protective film that is used for applications that are applied around the electrolyte inlet of the battery before being injected and then peeled off, the surface containing polyolefin In the production of a protective film having a layer, it is excellent in the resistance to electrolytic solution when exposed to a high temperature environment after the electrolytic solution is attached, and before injecting the electrolytic solution from the electrolytic solution inlet, It has been found that by sticking the surface layer around the electrolyte inlet, it is possible to suitably prevent the electrolyte from adhering around the electrolyte inlet, and to peel off after storage. The present invention has been completed by further studies based on these findings.

That is, this invention provides the invention of the aspect hung up below.
Item 1. In the production of the battery, before injecting the electrolyte, it is a protective film that is applied around the electrolyte injection port of the battery and then peeled off,
The protective film includes a surface layer,
The surface layer is a protective film containing polyolefin.
Item 2. Item 2. The protective film according to Item 1, wherein the resin constituting the surface layer has a polyolefin skeleton.
Item 3. Item 3. The protective film according to Item 1 or 2, wherein the polyolefin contains an acid-modified polyolefin.
Item 4. Item 4. The temporary sealing film according to any one of Items 1 to 3, wherein a peak derived from maleic anhydride is detected when the surface layer is analyzed by infrared spectroscopy.
Item 5. Item 5. The protective film according to any one of Items 1 to 4, wherein the protective film has an initial adhesion strength measured under the following conditions of 0.1 N / 15 mm or more.
In an environment of 25 ° C., the surface layer of the protective film is bonded to an aluminum plate, and the initial adhesion strength between the protective film and the aluminum plate is measured.
Item 6. Item 6. The protective film according to any one of Items 1 to 5, wherein the surface layer further contains an elastomer.
Item 7. Item 7. The protective film according to any one of Items 1 to 6, wherein the protective film further comprises a base material layer.
Item 8. Item 8. The protective film according to Item 7, wherein the base material layer contains polyolefin.
Item 9. Item 9. The protective film according to Item 7 or 8, wherein the base material layer is composed of two or more layers.
Item 10. Item 10. The protective film according to any one of Items 1 to 9, wherein the protective film further comprises an absorption layer.
Item 11. Item 11. The protective film according to Item 10, wherein the absorbent layer is a nonwoven fabric.
Item 12. Item 12. The protective film according to Item 11, wherein the basis weight of the nonwoven fabric is 20 g / m ² or more and 300 g / m ² or less.
Item 13. Item 13. The protective film according to Item 11 or 12, wherein the nonwoven fabric contains at least one of polyester and polyolefin.
Item 14. In manufacturing a battery, when injecting an electrolyte from the electrolyte inlet of the battery, a method for preventing the electrolyte from adhering around the electrolyte inlet,
An electrolytic solution adhesion preventing method comprising the following steps (A) and (B).
Step (A): A protective film having a surface layer containing polyolefin is prepared.
Step (B): The surface layer of the protective film is pasted around the electrolyte inlet of the battery before the electrolyte is injected.
Item 15. A method for manufacturing a battery, comprising at least the following steps (A), (B), and (C) in this order.
Step (A): A protective film having a surface layer containing polyolefin is prepared.
Step (B): The surface layer of the protective film is pasted around the electrolyte inlet of the battery before the electrolyte is injected.
Step (C): An electrolytic solution is injected from the electrolytic solution inlet.

According to the present invention, in the production of a battery, the protective film is provided for the purpose of being applied around the electrolyte inlet of the battery before being injected, and then being peeled off. It is possible to provide a protective film that has excellent electrolytic solution resistance when exposed to water and can be suitably peeled off after storage. Before injecting the electrolyte from the electrolyte inlet of the battery, the surface layer of the protective film of the present invention is pasted around the electrolyte inlet so that the electrolyte adheres around the electrolyte inlet. It can prevent suitably.

In addition, according to the present invention, by using the protective film, a method for preventing the electrolyte from adhering around the electrolyte inlet before the electrolyte is injected from the electrolyte inlet of the battery is provided. can do. Furthermore, according to this invention, the manufacturing method of the battery using the said protective film can also be provided.

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 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 that electrolyte solution adheres around the electrolyte solution injection port of a battery using the protective film of this invention. It is typical sectional drawing which shows a mode that the protective film of this invention was affixed around the electrolyte solution injection port of a battery (schematic cross-sectional view of the electrolyte solution injection port vicinity of a battery). It is a schematic plan view of an example of the protective film of the present invention. It is a schematic plan view of the example of the shape of the protective film of this invention.

The protective film of the present invention is a protective film provided for the purpose of being applied around the electrolyte inlet of the battery before injecting the electrolyte in the manufacture of the battery, and then being peeled off. The protective film of the present invention includes a surface layer, and the surface layer contains polyolefin. Hereinafter, regarding the protective film of the present invention, the method for preventing the electrolytic solution from adhering to the periphery of the electrolytic solution inlet using the protective film, and the method for producing the battery using the protective film will be described in detail. To do.

In this specification, the numerical range indicated by “to” means “above” or “below”. For example, the notation of 2 to 15 mm means 2 mm or more and 15 mm or less.

1. Protective film The protective film of the present invention is applied around the electrolyte inlet of the battery in the manufacture of the battery, so that the electrolyte is injected around the electrolyte inlet before (when) the electrolyte is injected into the battery. It is used to suppress adhesion and then peel off (after injection of the electrolyte).

The protective film of the present invention can be composed of a single layer or a plurality of layers, for example, as shown in FIGS. For example, in FIG. 1, the protective film is composed of a surface layer 2 (single layer), and the surface layer 2 contains polyolefin. The protective film shown in FIGS. 2 to 4 includes a base material layer 1 and a surface layer 2. The base material layer 1 may be either a single layer or multiple layers (two or more layers). For example, in FIG. 2, the base material layer 1 is composed of a single layer. In FIG. 3, the base material layer 1 is composed of two layers of a first base material layer 11 and a second base material layer 12. In FIG. 4, 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 multilayer, the number of layers is not particularly limited, but preferably about 2 or 3 layers. Further, the surface layer 2 may be either a single layer or a multilayer, but the surface layer 2 is usually a single layer.

As will be described later, in the protective film of the present invention, the base material layer 1 and the surface layer 2 may be made of the same resin. In this case, it is preferable that the base material layer 1 and the surface layer 2 of the protective film of the present invention both contain polyolefin.

Further, the surface 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. 7, the surface layer 2 can be provided only in the colored region 4.

The base material layer 1 is a layer provided as necessary in order to suppress the adhesion of the electrolytic solution around the electrolytic solution injection port and to exhibit the function of improving the shape retention of the protective film. When the protective film has the base material layer 1, the shape retention of the protective film is improved, and the handleability when the protective film is pasted and peeled around the electrolyte inlet can be improved.

The base material layer 1 is, for example, at least one of polyolefin, polyester, polyamide, epoxy resin, acrylic resin, fluororesin, polyurethane, silicon resin, phenol resin, polyetherimide, polyimide, and a mixture or copolymer thereof. It can be comprised with resin of this. Among these, it is preferable that the base material layer 1 contains polyolefin. Polyolefin may be used individually by 1 type and may be used in combination of 2 or more types. Polyolefin has a high resistance to electrolytic solution, and the base material layer 1 is made of an electrolytic solution even in an electrolytic solution injection step after being applied around the electrolytic solution injection port of the battery and an aging step in a high temperature environment in the manufacture of the battery. It can be prevented from being attacked.

The base material layer 1 can be formed of a resin film, or can be formed of paper or non-woven fabric like an absorption layer described later. The base material layer 1 can also constitute an absorption layer.

Specific examples of polyolefin include polyethylene such as low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, homopolypropylene, block copolymer of polypropylene (for example, block copolymer of propylene and ethylene), and random copolymer of polypropylene. Polypropylene (eg, a random copolymer of propylene and ethylene); ethylene-butene-propylene terpolymer, and the like. Among these polyolefins, polyethylene and polypropylene are preferable, and polypropylene is more preferable. As the polypropylene, a random copolymer of polypropylene is preferable. In addition, as a ratio of the propylene unit contained in polypropylene, 50 mass% or more is mentioned normally.

Further, the polyolefin may be a cyclic polyolefin. The cyclic polyolefin is a copolymer of an olefin and a cyclic monomer. Examples of the olefin that is a constituent monomer of the cyclic polyolefin include ethylene, propylene, 4-methyl-1-pentene, butadiene, and isoprene. In addition, examples of the cyclic monomer that is a constituent monomer of the cyclic polyolefin include cyclic alkenes such as norbornene; specifically, cyclic dienes 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 may be an acid-modified polyolefin. The acid-modified polyolefin is a polymer modified by block polymerization or graft polymerization of polyolefin with carboxylic acid or carboxylic anhydride. Examples of the carboxylic acid or carboxylic anhydride that modifies the polyolefin include maleic acid, acrylic acid, itaconic acid, crotonic acid, maleic anhydride, itaconic anhydride, and the like. Examples of the polyolefin to be modified include the above-mentioned polyolefins, and preferably polypropylene and polyethylene.

The polyolefin may be an acid-modified cyclic polyolefin. The acid-modified cyclic polyolefin is a copolymer obtained by copolymerizing a part of the monomer constituting the cyclic polyolefin in place of the α, β-unsaturated carboxylic acid or its anhydride, or α, β-unsaturated with respect to the cyclic polyolefin. It is a polymer obtained by block polymerization or graft polymerization of a saturated carboxylic acid or its anhydride. The cyclic polyolefin to be modified is the same as described above. Examples of the carboxylic acid or carboxylic acid anhydride that modifies the cyclic polyolefin include those described above.

The ratio of the polyolefin 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 only of polyolefin, more preferably composed only of polyethylene or polypropylene, and further preferably composed only of polypropylene.

The base material layer 1 may contain a resin other than polyolefin. Examples of such a resin include polyester, polyamide, epoxy resin, acrylic resin, fluororesin, polyurethane, silicon resin, phenol resin, and polyetherimide. , Polyimide, and a mixture or copolymer thereof.

In addition, when the base material layer 1 is comprised by the multilayer, it is preferable that the layer most located in the surface layer 2 side at least contains polyolefin, and another layer contains polyolefin. It does not have to be. When the said other layer does not contain polyolefin, another layer can be comprised with resin other than the above-mentioned polyolefin, for example. When the base material layer 1 is comprised by the multilayer, it is preferable that all the layers contain polyolefin, and it is still more preferable that all the layers are comprised by polyolefin.

Although the thickness of the base material layer 1 is not particularly limited, it is preferably 27 μm or more from the viewpoint of improving the handleability when the protective film is pasted and peeled around the electrolyte inlet. Furthermore, in addition to handling, it is suitable after being subjected to electrolyte resistance, initial adhesion to the periphery of the electrolyte inlet, followability to the shape of the electrolyte inlet, and aging in a high temperature environment From the viewpoint of improving properties such as peelability, it is preferably about 25 to 80 μm, more preferably about 27 to 50 μm, and still more preferably about 27 to 40 μm.

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

In the present invention, the surface layer 2 contains polyolefin. Furthermore, when both the base material layer 1 and the surface layer 2 of the protective film of the present invention contain polyolefin, the adhesiveness of both layers is excellent, and when the electrolytic solution is attached and exposed to a high temperature environment It is possible to particularly improve the resistance to electrolytes. In addition, as described above, the handleability is improved by having the base material layer 1.

In the protective film of the present invention, the base material layer 1 and the surface layer 2 may be made of the same resin. In this case, it is preferable that the base material layer 1 and the surface layer 2 of the protective film of the present invention both contain polyolefin. The base material layer 1 may contain an elastomer exemplified by the surface layer 2 described later.

The protective film of the present invention may be composed only of the surface layer 2. That is, when the protective film of the present invention is composed of a single layer, the layer exhibits a function as a surface layer.

In the protective film of the present invention, in the protective film of the present invention, the surface layer 2 is provided with appropriate initial adhesion to the periphery of the electrolyte injection port and appropriate releasability after being appropriately aged after being subjected to aging under a high temperature environment. It is preferable that polyolefin exists on the surface.

Examples of the polyolefin contained in the surface layer 2 include the same as those exemplified in the base material layer 1.

Among polyolefins, polyethylene, polypropylene, and acid-modified polyethylene are preferable. As the polypropylene, a random copolymer of polypropylene is preferable. In addition, as a ratio of the propylene unit contained in polypropylene, 50 mass% or more is mentioned normally. Polyolefin may be used individually by 1 type and may be used in combination of 2 or more types.

The surface layer 2 may contain a resin other than polyolefin. Examples of the resin other than polyolefin include polyester, polyamide, epoxy resin, acrylic resin, fluorine resin, polyurethane, silicon resin, phenol resin, polyetherimide, polyimide, and mixtures and copolymers thereof.

The ratio of the polyolefin contained in the surface 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.

It is preferable that the surface of the surface layer 2 has appropriate initial adhesion to the periphery of the electrolyte solution inlet and appropriate releasability to be appropriately peeled after being subjected to aging in a high temperature environment. From such a viewpoint, the surface layer 2 preferably contains an elastomer in addition to the polyolefin. In particular, it is preferable that the surface layer 2 has an elastomer in addition to the polyolefin. The acid-modified polyolefin is particularly preferably used together with an elastomer.

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

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

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

Examples of the olefin elastomer include copolymers of α-olefins having 2 to 20 carbon atoms such as ethylene, propylene, 1-butene, 1-hexene and 4-methyl-pentene. For example, ethylene-propylene copolymer (EPR) And ethylene-propylene-diene copolymer (EPDM). Further, there may be mentioned a copolymer of an α-olefin with a non-conjugated diene having 2 to 20 carbon atoms such as dicyclopentadiene, 1,4-hexadiene, cyclooctadiene, methylene norbornene, ethylidene norbornene, butadiene and isoprene. Furthermore, a carboxy-modified nitrile rubber obtained by copolymerizing methacrylic acid with a butadiene-acrylonitrile copolymer can be used.

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

The silicone elastomer is mainly composed of organopolysiloxane, and examples thereof include polydimethylsiloxane, polymethylphenylsiloxane, and polydiphenylsiloxane elastomers.

The urethane-based elastomer is composed of structural units 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. As the polymer (long chain) diol, 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 Neopentylene adipate) and the like.

The polyester elastomer is obtained by polycondensation of dicarboxylic acid or its derivative and diol compound or its derivative. 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 hydrogen atoms of these aromatic nuclei are substituted with methyl groups, ethyl groups, phenyl groups, and 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 can be used individually by 1 type or in mixture of 2 or more types.

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. Bisphenol A, bis- (4-hydroxyphenyl) -methane, bis- (4-hydroxy-3-methylphenyl) -propane, resorcin, and the like. These compounds can be used individually by 1 type or in mixture of 2 or more types.

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

Examples of rubber elastomers include polyisobutylene.

Effectively suppresses the electrolyte from adhering around the electrolyte inlet, improves the resistance to electrolyte when exposed to a high-temperature environment after the electrolyte has adhered, and further to the area around the electrolyte inlet From the viewpoint of effectively enhancing the properties such as initial adhesion, followability to the surrounding shape of the electrolyte inlet, and releasability that is appropriately peeled after being subjected to aging in a high temperature environment, among elastomers Styrenic elastomers and olefin elastomers are preferred, and styrene elastomers are particularly preferred.

The ratio of the elastomer contained in the surface layer 2 is not particularly limited, but is preferably about 50% by mass or less, more preferably about 10 to 50% by mass, and still more preferably from the viewpoint of effectively improving the above-described characteristics. Is about 10 to 40% by mass.

Although it does not restrict | limit especially as thickness of the surface layer 2, From a viewpoint of improving the electrolyte solution resistance at the time of being exposed to high temperature environment, after electrolyte solution adheres, suppressing the adhesion of electrolyte solution effectively, Preferably 3 micrometers or more are mentioned. Furthermore, in addition to the resistance to electrolytic solution, initial adhesion to the periphery of the electrolyte injection port, followability to the shape of the periphery of the electrolyte injection port, and appropriate peeling after being subjected to aging in a high temperature environment From the viewpoint of improving properties such as peelability, it is preferably about 3 to 55 μm, more preferably about 3 to 35 μm, and still more preferably about 3 to 25 μm.

The surface layer 2 preferably has adhesiveness (tackiness). When the surface layer 2 has adhesiveness, positioning of the protective film of the present invention is facilitated. Moreover, it is preferable that the surface layer 2 is a layer which contains the adhesion component and is equipped with adhesiveness. In the present invention, the term “adhesion” or “adhesiveness” means a property of joining a plurality of objects, is a concept included in a broad sense, and means a property of sticking (tackiness).

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 surface layer 2. In the present invention, as the support, for example, a support that can be peeled off from the protective film when the protective film of the present invention is applied around the electrolyte inlet can be used. Examples of the support include a film, paper, and non-woven fabric. The thickness of the support is not particularly limited, and can usually be about 10 to 100 μm. The surfaces on both sides of the support are preferably provided with releasability. Moreover, although it is not limited, when the protective film of this invention is a winding body, it is preferable to provide a support body.

In the protective film of the present invention, the side opposite to the side attached around the electrolyte inlet (if the protective film of the present invention has the base layer 1 and the surface layer 2, An absorption layer capable of absorbing the electrolytic solution may be laminated on the side opposite to the surface layer 2. As above-mentioned, the base material layer 1 may comprise the absorption layer. When the surface of the protective film (the side affixed around the electrolyte inlet) is provided with an absorption layer, the electrolyte drops from the electrolyte injection nozzle and adheres to the protective film. Moreover, it can suppress that electrolyte solution flows out to the periphery of a protective film, or scatters. For this reason, the manufacturing efficiency of a battery can be improved. Examples of the absorbing layer include paper and nonwoven fabric.

The material constituting the nonwoven fabric is not particularly limited, and preferably, the same resin as exemplified in the base material layer 1 is exemplified. The nonwoven fabric is preferably composed of at least one of polyester and polyolefin, and more preferably contains polyester because of excellent heat resistance. The polyester is preferably polyethylene terephthalate, and the polyolefin is preferably polypropylene.

As a basis weight of the nonwoven fabric, the lower limit is preferably about 20 g / m ² or more, more preferably about 30 g / m ² or more, and the upper limit is preferably about 300 g / m ² or less, more preferably about 200 g. / m ² or less. Examples of the preferred range, 20 ~ 300 g / m ² approximately, 20 ~ 200 g / m ² approximately, 30 ~ 300 g / m ² approximately, include about 30 ~ 200 g / m ^2.

As the fiber diameter of the fibers constituting the nonwoven fabric, the lower limit is preferably about 5 μm or more, more preferably about 15 μm or more, and the upper limit is preferably 60 μm or less, more preferably about 40 μm or less. Preferred ranges include about 5 to 60 μm, about 5 to 40 μm, about 15 to 60 μm, and about 15 to 40 μm.

In addition, when manufacturing the protective film of this invention, it is preferable to manufacture a nonwoven fabric and a surface layer by melt extrusion of resin which comprises a surface layer. From this viewpoint, it is preferable that the nonwoven fabric has heat resistance that retains at least a part of the structure of the nonwoven fabric (that is, a structure that absorbs the electrolytic solution) even by melt extrusion. Further, when the resin constituting the surface layer is melt-extruded into the nonwoven fabric, the voids of the nonwoven fabric may be impregnated with the resin. The impregnation ratio of the resin in the thickness direction of the nonwoven fabric is preferably less than 65%, more preferably 60% or less, and further preferably 50% or less. The lower limit of the impregnation ratio is, for example, 0%. When the impregnation ratio is 65% or more, voids in the nonwoven fabric are filled too much, and the absorbability of the electrolytic solution is likely to decrease. From the viewpoint of more effectively setting the impregnation ratio of the resin in the thickness direction of the nonwoven fabric to less than 65%, and more effectively suppressing the decrease in water absorption of the electrolyte accompanying the lamination of the nonwoven fabric and the surface layer, the resin constituting the nonwoven fabric The melting peak temperature is preferably 130 ° C. or higher for the lower limit, and preferably 300 ° C. or lower for the upper limit.

Moreover, in the protective film of this invention, the side affixed around the electrolyte inlet (if the protective film of this invention has the base material layer 1 and the surface layer 2, the base material layer 1 of the surface layer 2) A release film may be provided on the opposite side.

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

Further, the area of the protective film of the present invention is not particularly limited and is usually about 0.07 to 10 cm ² although it varies depending on the size of the battery. Furthermore, the protective film of the present invention preferably has an opening corresponding to the shape of the electrolyte inlet of the battery. 5 and 6 are schematic views showing a state in which the protective film of the present invention having an opening corresponding to the shape of the electrolyte inlet of the battery is attached around the electrolyte inlet.

The diameter of the opening of the protective film of the present invention corresponds to the diameter Wa of the opening of the electrolyte inlet 21 of the battery 20 described later. The shape of the protective film of the present invention is not particularly limited, but is usually approximately rectangular or approximately circular when viewed in plan. Further, as shown in FIG. 7, the shape of the protective film may include a handle portion 6. Moreover, 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 measured under the following conditions of 0.1 N / 15 mm or more, more preferably about 0.1 to 4.0 N / 15 mm.

<Measurement conditions for initial adhesion strength>
In the method for measuring the initial adhesion strength, first, the protective film is cut to produce 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 surface layer of the test piece was bonded to the aluminum plate with a load of 2 kgf (the part to be bonded to the aluminum plate is a part having a length of 50 mm and a width of 15 mm). The end of the aluminum plate not bonded to the aluminum plate and the aluminum plate were pulled at a speed of 50 mm / min with a tensile tester (manufactured by Shimadzu Corp., AG-X Plus) at a pulling angle of 180 °. Measure the initial adhesion strength. When the shape of the above test piece cannot be prepared due to circumstances such as a small sample, measurement is performed with a size that allows measurement, and the initial adhesion strength is calculated in terms of 15 mm width.

The adhesion strength of the protective film of the present invention after storage at 60 ° C. for 7 hours and after high-temperature storage measured under the following conditions is preferably about 0.1 to 13.0 N / 15 mm, 0.1 to About 12.2 N / 15 mm, about 0.1 to 10.9 N / 15 mm, about 0.2 to 13.0 N / 15 mm, about 0.2 to 12.2 N / 15 mm, about 0.2 to 10.9 N / 15 mm 0.3 to 13.0 N / 15 mm, 0.3 to 12.2 N / 15 mm, and 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 More preferably, it is about 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, about 0.3 to 5.0 N / 15 mm, More preferably, it is about 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 produce a strip-shaped test piece having a length of 120 mm and a width of 15 mm. Next, in a 25 ° C. environment, the surface layer of the test piece is bonded to the aluminum plate with a load of 2 kgf (the portion to be bonded to the aluminum plate is a portion having a length of 50 mm and a width of 15 mm). Next, it is stored under conditions of each temperature and sticking time (7 hours at 60 ° C., 8 hours at 120 ° C., or 48 hours at 120 ° C.). Next, the end of the test piece that was not bonded to the aluminum plate and the aluminum plate were 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 then tested. The adhesion strength between the piece and the aluminum plate after high-temperature storage is measured. In addition, when the shape of said test piece cannot be prepared due to circumstances such as a small sample, it is measured in a size that can be measured, and converted into a 15 mm width to calculate the adhesion strength.

The protective film of the present invention is a protective film that is affixed around the electrolyte inlet of the battery and then peeled off (after injection of the electrolyte). For example, as shown in the schematic diagrams A and B of FIG. 5, the protective film 10 of the present invention is attached to the periphery 22 of the electrolyte solution inlet 21 of the battery 20. 6A and 6B are schematic cross-sectional views at this time.

As shown in FIG. 6A, the diameter Wa of the electrolyte solution inlet 21 of the battery 20 is not particularly limited and is usually about 2 to 6 mm, although it varies depending on the size of the battery. Further, the distance Wb from the end of the opening to the end around the electrolyte injection port (periphery, at least up to the end is covered with a protective film) is not particularly limited, Although it varies depending on the size of the battery, it is usually about 0.5 to 50 mm. In addition, as FIG. 6 shows, the circumference | surroundings of electrolyte solution injection hole may be lower than the outer side, and may have the shape in which the level | step difference t was formed. The step t is not particularly limited and is usually about 0.1 to 10 mm, although it varies depending on the size of the battery. In addition, one or more steps may exist in the portion to which the protective film of the present invention is attached.

The protective film 10 of the present invention may be molded in advance and have a shape corresponding to the step t around the electrolyte inlet. Further, as described above, for example, as shown in the schematic diagram of FIG. 6B and FIG. 7, the protective film 10 of the present invention may be provided with the opening 3 corresponding to the opening of the electrolyte solution inlet 21. Good. Furthermore, at least a part of the protective film 10 of the present invention may be colored.

For example, FIG. 7 is a schematic plan view of an example of the protective film 10 of the present invention. The protective film 10 shown in FIG. 7 includes a colored region 4 around the opening 3 in addition to the opening 3 corresponding to the opening of the electrolyte inlet 21. The surface layer 2 may be provided only in the region 4. A transparent region 5 is provided around the region 4, and positioning when the protective film 10 is pasted around the electrolyte solution inlet is facilitated. For example, the colored region 4 and the transparent region 5 are made to correspond to the shape of the step around the electrolyte solution inlet, thereby aligning the protective film 10 around the electrolyte solution inlet. Especially easy. Furthermore, in the protective film 10 shown in FIG. 7, the handle part 6 is provided, and the affixing operation of the protective film 10 around the electrolyte solution inlet is facilitated.

The shape of the protective film of the present invention is not particularly limited as long as it is a shape that can be affixed around the electrolyte inlet, and can be various planar shapes as exemplified in FIG. The planar shape of the protective film of the present invention is preferably line symmetric. Moreover, the protective film of this invention may be provided with the area | region 4 and the transparent area | region 5 which were colored as mentioned above also in various shapes which are illustrated in FIG.

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

The metal constituting the periphery of the electrolyte injection port is not particularly limited, but preferably includes an aluminum alloy, copper, stainless steel, and the like. Among these, an aluminum alloy is preferable.

The surface roughness (Ra) around the electrolyte inlet (periphery of the electrolyte inlet) is not particularly limited, but is preferably about 0.1 to 1.0 μm, more preferably 0.3 to 0. For example, about 5 μm. The surface roughness (Ra) is a value measured by the method defined 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, capacitors, A capacitor etc. are mentioned. Among these batteries, a lithium ion battery is 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, before injecting the electrolyte from the electrolyte inlet of the battery, the protective film of the present invention is pasted so as to cover the periphery of the electrolyte inlet. In this state, the electrolytic solution is injected from the electrolytic solution inlet. Next, the electrolyte solution inlet is sealed with another member, and the battery is subjected to an aging process. Aging conditions include 40 to 150 ° C. and 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 production method of the protective film of the present invention is not particularly limited, and a known film production method can be employed. As a manufacturing method of the protective film of this invention, the method of manufacturing by extruding resin which comprises a protective film and shape | molding in a film form is mentioned, for example. In addition, if the protective film of the present invention has the base material layer 1 and the surface layer 2, a method for producing the film by coextruding the resin constituting the base material layer 1 and the surface layer 2 to form a film Alternatively, a method of laminating a resin film forming the other on the resin film forming one of the base material layer 1 and the surface layer 2 can be mentioned. Further, at least a part of the protective film 10 may be transparent. When the protective film 10 has a transparent portion, when the protective film 10 is attached to the electrolyte solution inlet, the alignment is easy, and the protective film 10 is easily protected.

2. Method for preventing electrolyte from adhering around electrolyte inlet In the present invention, a method for preventing electrolyte from adhering around electrolyte inlet in the production of a battery (electrolyte adhesion prevention according to the present invention) The method is characterized in that the protective film of the present invention described in the section “1. Protective film” is used before the electrolytic solution is injected from the electrolytic solution inlet of the battery.

Specifically, according to the method for preventing the electrolytic solution adhesion of the present invention, when the electrolytic solution is injected from the electrolytic solution injection port of the battery in the manufacture of the battery, the electrolytic solution adheres around the electrolytic solution injection port. The method includes the following steps (A) and (B).
Step (A): A protective film having a surface layer containing polyolefin is prepared.
Step (B): The surface layer of the protective film is pasted around the electrolyte inlet of the battery before the electrolyte is injected.

In the electrolytic solution adhesion preventing method of the present invention, first, the protective film of the present invention is prepared. Next, the process of sticking the surface layer 2 of the protective film around the electrolyte inlet of the battery is performed. By injecting the electrolyte from the electrolyte inlet while the protective film of the present invention is stuck around the electrolyte inlet of the battery, it is possible to prevent the electrolyte from adhering around the electrolyte inlet. The

Furthermore, in the electrolytic solution adhesion preventing method of the present invention, as described above, the electrolytic solution inlet may be sealed and the battery may be subjected to an aging process. The aging conditions are as described above. By performing aging in a state where the protective film of the present invention is stuck around the electrolyte injection port, even when the electrolyte solution bumps during aging and the electrolyte solution blows out from the electrolyte injection port, the electrolyte solution The electrolytic solution is prevented from adhering around the inlet.

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

3. Battery Manufacturing Method The battery manufacturing method of the present invention uses the protective film of the present invention described in the section “1. Protective film” before injecting the electrolytic solution from the electrolytic solution inlet of the battery. And

Specifically, the battery manufacturing method of the present invention includes at least the following steps (A), (B), and (C) in this order.
Step (A): A protective film having a surface layer containing polyolefin is prepared.
Step (B): The surface layer of the protective film is pasted around the electrolyte inlet of the battery before the electrolyte is injected.
Step (C): An electrolytic solution is injected from the electrolytic solution inlet.

In the battery manufacturing method of the present invention, first, the protective film of the present invention is prepared. Next, the process of sticking the surface layer 2 of the protective film around the electrolyte inlet 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 in a state where the protective film of the present invention is stuck around the electrolytic solution injection port of the battery. Similar to the electrolytic solution adhesion preventing method of the present invention described above, in the battery manufacturing method of the present invention, the electrolytic solution is prevented from adhering around the electrolytic solution inlet.

Furthermore, in the method for producing electrolysis of the present invention, as described above, the electrolyte solution inlet may be sealed and the battery may be subjected to an aging process. The aging conditions are as described above. By performing aging in a state where the protective film of the present invention is attached around the electrolyte injection port, even when the electrolyte solution bumps during aging and blows out from the electrolyte injection port, The electrolytic solution is prevented from adhering to the surroundings.

Furthermore, the battery is manufactured by peeling the protective film of the present invention from the periphery of the electrolyte injection port and sealing the electrolyte injection port with a sealing member. That is, the battery manufacturing method of the present invention may further include a step (D) of peeling the protective film after the step (C). Moreover, the process (E) which carries out the main sealing of the electrolyte solution injection port can be further provided after a process (D).

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.

<Manufacture of protective film>
Example 1
The acid-modified polyethylene resin to which the olefin elastomer (addition amount 10% by mass) was added was extruded into a film to obtain a protective film (thickness 40 μm).

Example 2
Each of the three types of polypropylene resin compositions was subjected to coextrusion molding to produce a three-layer protective film. The outermost layer on one side is a first base material layer, and is specifically made of polypropylene. The intermediate layer is a second base material layer, and is specifically made of polypropylene. Furthermore, the outermost layer on the other side is a surface layer, and is specifically 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 surface layer was 3 μm (total thickness was 30 μm). In addition, the addition amount of the styrene-type elastomer in a surface layer is 40 mass%.

Example 3
Each of the three types of polypropylene resin compositions was subjected to coextrusion molding to produce a three-layer protective film. The outermost layer on one side is a first base material layer, and is specifically made of polypropylene. The intermediate layer is a second base material layer, and is specifically made of polypropylene. Furthermore, the outermost layer on the other side is a surface layer, and is specifically 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 surface layer was 3 μm (total thickness was 30 μm). In addition, the addition amount of the styrene-type elastomer in a surface layer is 20 mass%.

Example 4
Each of the three types of polypropylene resin compositions was subjected to coextrusion molding to produce a three-layer protective film. The outermost layer on one side is a first base material layer, and is specifically made of polypropylene. The intermediate layer is a second base material layer, and is specifically made of polypropylene. Furthermore, the outermost layer on the other side is a surface layer, and is specifically 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 surface layer was 3 μm (total thickness was 30 μm). In addition, the addition amount of the styrene-type elastomer in a surface layer is 10 mass%.

Example 5
After melt-extrusion of 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 where the polyethylene naphthalate film is not melt-extruded. The acid-modified polypropylene resin layer (thickness 30 μm) / polyethylene naphthalate film is obtained by melt-extruding an acid-modified polyethylene resin to which an olefin elastomer has been added (addition amount 20% by mass) on the surface obtained by melt-extruding the acid-modified polypropylene resin. A protective film composed of (thickness 12 μm) / acid-modified polypropylene resin layer (thickness 30 μm) / acid-modified polyethylene resin layer (surface layer, thickness 33 μm) to which an olefin elastomer was added was obtained.

Example 6
On one surface of biaxially oriented polypropylene (OPP), an acid-modified polyethylene resin to which an olefinic elastomer is added (added amount of 10% by mass) is melt-extruded to obtain a biaxially oriented polypropylene (thickness of 40 μm) / olefinic elastomer. A protective film composed of the added acid-modified polyethylene resin layer (surface layer, thickness 50 μm) was obtained.

Example 7
On one surface of biaxially oriented polypropylene (OPP), an acid-modified polyethylene resin to which an olefinic elastomer is added (added amount 20% by mass) is melt-extruded to obtain a biaxially oriented polypropylene (thickness 30 μm) / olefinic elastomer. A protective film composed of the added acid-modified polyethylene resin layer (surface layer, thickness 50 μm) was obtained.

Example 8
On one surface of biaxially oriented polypropylene (OPP), an acid-modified polyethylene resin to which an olefinic elastomer is added (added amount of 15% by mass) is melt-extruded to obtain a biaxially oriented polypropylene (thickness of 40 μm) / olefinic elastomer. A protective film composed of the added acid-modified polyethylene resin layer (surface layer, thickness 35 μm) was obtained.

Example 9
On one surface of unstretched polypropylene (CPP), an acid-modified polyethylene resin to which an olefin elastomer has been added (addition amount 15% by mass) is melt-extruded to add unstretched polypropylene (thickness 40 μm) / olefin elastomer. A protective film composed of an acid-modified polyethylene resin layer (surface layer, thickness 35 μm) was obtained.

Example 10
On one surface of biaxially oriented polyethylene terephthalate (PET), an acid-modified polypropylene resin is melt-extruded, and a resin composed of a resin composition containing polypropylene and a styrene elastomer is further melt-extruded on 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) / surface layer (thickness 26 μm) was obtained. The addition amount of the styrene-based elastomer in the surface layer is 40% by mass.

Example 11
On one side of biaxially oriented polyethylene naphthalate (PEN), an acid-modified polypropylene resin is melt-extruded, and a resin composed of a resin composition containing polypropylene and a styrene elastomer is further melt-extruded on the acid-modified polypropylene resin. Thus, a protective film composed of biaxially stretched polyethylene naphthalate (thickness 16 μm) / acid-modified polypropylene resin layer (thickness 30 μm) / surface layer (thickness 26 μm) was obtained. The addition amount of the styrene-based elastomer in the surface layer is 40% by mass.

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

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

Comparative Example 3
As the protective film, a commercially available adhesive film (model number: 50600 green manufacturer: Tessa SE) was used. The structure of the protective film is as shown in Table 2.

Comparative Example 4
A commercially available adhesive film (model number: 642 blue, manufacturer: Teraoka Seisakusho Co., Ltd.) was used as the protective film. The structure of the protective film is as shown in Table 2.

Comparative Example 5
As the protective film, a commercially available adhesive film (model number: ACH-6100, white, manufacturer: Chuko Kasei Kogyo Co., Ltd.) was used. The structure of the protective film is as shown in Table 2.

Comparative Example 6
As the protective film, a commercially available adhesive film (model number: ACH-5001FR white, manufacturer: Chuko Kasei Kogyo Co., Ltd.) was used. The structure of the protective film is as shown in Table 2.

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 2.

Comparative Example 8
As the protective film, a commercially available adhesive film (model number: 51108, manufacturer: Tessa SE) was used. The structure of the protective film is as shown in Table 2.

Example 12
One side of a polyester-based nonwoven fabric (thickness 210 μm, fiber diameter about 20 μm, basis weight 30 g / m ² ) is melt-extruded with an acid-modified polyethylene resin to which an olefin-based elastomer is added (added amount 10% by mass), and the nonwoven fabric ( A protective film composed of an acid-modified polyethylene resin layer (surface layer, thickness 40 μm) to which an olefin-based elastomer was added was obtained.

<Measurement of initial adhesion strength>
About each said protective film, initial stage adhesive strength was measured on condition of the following. The measurement results are shown in Tables 1 and 2. In the method of measuring the initial adhesion strength, first, each protective film was cut to produce 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 surface layer of the test piece was applied to an aluminum plate (1000 series (pure aluminum series), length 100 mm, width 25 mm, thickness 2 mm, surface roughness Ra was 0.5 μm) with a load of 2 kgf. (The portion to be bonded to the aluminum plate is a portion having a test piece length of 50 mm and a width of 15 mm). Next, the end of the test piece that was not bonded to the aluminum plate and the aluminum plate were 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 then tested. The initial adhesion strength was measured by measuring the load at the time of peeling between the piece and the aluminum plate. The initial adhesion strength was an average value measured three times.

<Measurement of adhesion strength after high temperature storage>
About each said protective film, the adhesive strength after high temperature storage was measured on condition of the following. The measurement results are shown in Tables 1 and 2. In the method for measuring the adhesion strength after high-temperature storage, first, each protective film was cut to produce 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 surface layer of the test piece was applied to an aluminum plate (1000 series (pure aluminum series), length 100 mm, width 25 mm, thickness 2 mm, surface roughness Ra was 0.5 μm) with a load of 2 kgf. (The portion to be bonded to the aluminum plate is a portion having a test piece length of 50 mm and a width of 15 mm). Next, it was stored under the conditions of each temperature and sticking time shown in Tables 1 and 2 (60 ° C for 7 hours, 120 ° C for 8 hours, or 120 ° C for 48 hours). Next, the end of the test piece that was not bonded to the aluminum plate and the aluminum plate were 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 then tested. The adhesion strength after high-temperature storage was measured by measuring the load at the time of peeling between the piece and the aluminum plate. The adhesion strength was an average value measured three times.

<Evaluation of peelability>
When measuring the adhesion strength after high-temperature storage, whether or not the peeled surface layer remained on the surface of the aluminum plate was evaluated from the following viewpoints. The results are shown in Tables 1 and 2.
A: The surface layer does not remain on the aluminum plate and is excellent in peelability. B: The surface layer remains on the aluminum plate and is inferior in peelability.

<Evaluation of trackability>
About each said protective film, the surface layer of the protective film was affixed on the aluminum plate which has the level | step difference t of 0.5 mm in the environment of 25 degreeC, respectively. Next, this was stored at 120 ° C. for 48 hours, and it was visually confirmed whether there was any problem in appearance such as peeling of the protective film at the stepped portion or wrinkles of the protective film, and evaluated according to the following criteria. The results are shown in Tables 1 and 2.
A: The step portion is filled with the protective film, and no wrinkles are formed. B: The protective film is peeled off at the step portion, and the step portion is not filled, or wrinkles are generated in the protective film.

<Evaluation of electrolyte resistance>
Each of the protective films was immersed in an electrolytic solution (1M LiPF ₆ solution (ethylene carbonate: dimethyl carbonate: diethyl carbonate = 1: 1: 1, volume ratio) and stored at 60 ° C. for 7 hours. The protective film was visually confirmed and evaluated according to the following criteria, and the results are shown in Tables 1 and 2.
A: The surface layer of the protective film is not dissolved C: The surface layer of the protective film is dissolved or peeled off from the base material layer

The notations in Tables 1 and 2 are as follows. PP indicates a polypropylene film. PPa indicates 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.

From the results shown in Tables 1 and 2, the protective films of Examples 1 to 12 have appropriate initial adhesion strength and adhesion strength after high-temperature storage. It can be seen that it can be suitably applied and can be suitably peeled off after high temperature storage, and further has excellent resistance to electrolyte when exposed to a high temperature environment.

In addition, since the protective films of Examples 2 to 12 are provided with a base material layer, they have high shape retention, and particularly excellent handling properties when pasted around the electrolyte inlet and then peeled off. It was.

<Manufacture of protective film>
Example 13
A non-woven fabric obtained by laminating an acid-modified polyethylene resin to which a styrene-based elastomer is added (addition amount: 10% by mass) on one surface of a polyethylene terephthalate-based nonwoven fabric (weighing 30 g / m ² , fiber diameter of about 20 μm, thickness 210 μm) A protective film composed of (base material layer, thickness 210 μm) / acid-modified polyethylene resin layer (surface layer, thickness 40 μm) to which an olefin elastomer was added was obtained. In addition, three types of protective films were prepared by setting the temperature when the acid-modified polyethylene resin was laminated to the nonwoven fabric to 80 ° C., 120 ° C., and 150 ° C., respectively, and the electrolyte absorption characteristics described later were evaluated. . The same applies to Examples 14 to 20 below.

Example 14
A non-woven fabric is obtained by laminating an acid-modified polyethylene resin to which a styrene-based elastomer is added (added amount of 10% by mass) on one surface of a polyethylene terephthalate-based nonwoven fabric (weighing 260 g / m ² , fiber diameter of about 20 μm, thickness of 670 μm). A protective film composed of (base material layer, thickness 670 μm) / acid-modified polyethylene resin layer (surface layer, thickness 40 μm) to which an olefin elastomer was added was obtained.

Example 15
On one surface of a polyethylene terephthalate / polyethylene non-woven fabric (weighing 30 g / m ² , fiber diameter about 20 μm, thickness 230 μm), an acid-modified polyethylene resin to which a styrene elastomer is added (addition amount 10 mass%) is laminated. A protective film composed of a non-woven fabric (base layer, thickness 230 μm) / acid-modified polyethylene resin layer (surface layer, thickness 40 μm) to which an olefin elastomer was added was obtained.

Example 16
On one surface of a polyethylene terephthalate / polyethylene non-woven fabric (weighing 15 g / m ² , fiber diameter about 20 μm, thickness 100 μm), an acid-modified polyethylene resin to which a styrene-based elastomer is added (addition amount 10 mass%) is laminated. A protective film composed of a non-woven fabric (base material layer, thickness 100 μm) / acid-modified polyethylene resin layer (surface layer, thickness 40 μm) to which an olefin elastomer was added was obtained.

Example 17
On one surface of a polyethylene terephthalate / polyethylene non-woven fabric (weighing 20 g / m ² , fiber diameter about 20 μm, thickness 120 μm), an acid-modified polyethylene resin to which a styrene-based elastomer is added (addition amount 10 mass%) is laminated. A protective film composed of a nonwoven fabric (base material layer, thickness 120 μm) / acid-modified polyethylene resin layer (surface layer, thickness 40 μm) to which an olefin elastomer was added was obtained.

Example 18
On one surface of a polyethylene-based nonwoven fabric (weighing 30 g / m ² , fiber diameter of about 20 μm, thickness of 220 μm), an acid-modified polyethylene resin to which a styrene-based elastomer is added (added amount of 10% by mass) is laminated. A protective film composed of a base material layer (thickness 220 μm) / acid-modified polyethylene resin layer (surface layer, thickness 40 μm) to which an olefin elastomer was added was obtained.

Example 19
A non-woven fabric obtained by laminating an acid-modified polyethylene resin to which a styrene-based elastomer is added (addition amount: 10% by mass) on one surface of a polyethylene terephthalate-based non-woven fabric (weight per unit area: 70 g / m ² , fiber diameter: about 20 μm, thickness: 420 μm) A protective film composed of (base material layer, thickness 420 μm) / acid-modified polyethylene resin layer (surface layer, thickness 400 μm) to which a styrene elastomer was added was obtained.

Example 20
On one surface of a polyethylene terephthalate-based nonwoven fabric (weight is 90 g / m ² , fiber diameter is about 30 μm, thickness is 410 μm), an acid-modified polyethylene resin to which a styrene-based elastomer is added (added amount of 10% by mass) is laminated to form a nonwoven fabric. A protective film composed of (base material layer, thickness 410 μm) / acid-modified polyethylene resin layer (surface layer, thickness 40 μm) to which a styrene elastomer was added was obtained.

<Electrolytic solution absorption characteristics>
Each protective film obtained in Examples 13 to 20 (three types with different lamination temperatures of the base material layer and the surface layer, respectively) was dropped on the surface of the base material layer (nonwoven fabric) with 1 ml of an electrolyte solution with a dropper, It was visually confirmed whether or not the base material layer absorbed the electrolytic solution and droplets of the electrolytic solution were formed on the surface of the protective film. When droplets of electrolyte are formed on the surface of the protective film, it is necessary to wipe the droplets with a cloth when injecting the electrolyte into the battery. Went. The evaluation results are shown in Table 3.
A: Under the droplet, the droplet is absorbed on the surface of the protective film within 2 seconds. B: Under the droplet, the droplet is absorbed on the surface of the protective film within 5 seconds. C: The droplet is formed on the surface of the protective film. It is formed

<Resin impregnation ratio>
The protective film obtained in Example 19 was cut in the thickness direction using a trimming knife, and the cross section of the base material layer (nonwoven fabric) was observed with an optical microscope (Keyence VK9510). The ratio of the resin impregnated in the thickness direction in the nonwoven fabric was calculated from the thickness of the nonwoven fabric and the thickness impregnated with the resin, and was defined as the resin impregnation ratio of the nonwoven fabric. As a result, when the lamination temperature of the base material layer and the surface layer was 80 ° C., the impregnation ratio of the resin was 38%, when the lamination temperature was 120 ° C., 56%, and the lamination temperature was 150 ° C. If it was, it was 65%.

The notation in Table 3 is as follows. PE indicates polyethylene. PET indicates biaxially stretched polyethylene terephthalate.

As shown in Table 3, the protective films of Examples 13 to 20 function as an electrolyte absorption layer because the base material layer is composed of a nonwoven fabric, and the electrolyte was dropped onto the surface of the protective film. Even in this case, the electrolyte solution is absorbed by the non-woven fabric, and no droplets are formed on the surface, so that it is not necessary to wipe the droplets with a cloth when injecting the electrolyte solution into the battery, which can improve the work efficiency of battery manufacturing. I understand. Further, for example, in Examples 13 to 15, since the electrolyte solution absorption characteristics are excellent even when the temperature of the step of laminating the base material layer and the surface layer when producing the protective film is high, the base material layer and the surface layer There is an advantage that melt extrusion (a resin melted at a high temperature is laminated on a non-woven fabric) can be adopted for the lamination. Moreover, from the result of Example 19, in the protective film, by setting the impregnation rate of the resin of the nonwoven fabric to less than 65%, the electrolytic solution can be absorbed more quickly, and the reduction in work efficiency can be effectively suppressed. I understand.

DESCRIPTION OF SYMBOLS 1 Base material layer 10 Protective film 11 1st base material layer 12 2nd base material layer 13 3rd base material layer 2 Surface layer 20 Battery 21 Electrolyte injection port 22 Around electrolyte injection port 3 Opening part 4 Coloring Area 5 transparent area 6 handle part t step Wa diameter Wb of electrolyte inlet opening Wb distance from edge of electrolyte inlet opening to edge around electrolyte inlet

Claims (15)

1. In the production of the battery, before injecting the electrolyte, it is a protective film that is applied around the electrolyte injection port of the battery and then peeled off,
   The protective film includes a surface layer,
   The surface layer is a protective film containing polyolefin.
2. 2. The protective film according to claim 1, wherein the resin constituting the surface layer has a polyolefin skeleton.
3. The protective film according to claim 1 or 2, wherein the polyolefin contains an acid-modified polyolefin.
4. The temporary sealing film according to any one of claims 1 to 3, wherein when the surface layer is analyzed by infrared spectroscopy, a peak derived from maleic anhydride is detected.
5. The protective film according to any one of claims 1 to 4, wherein the protective film has an initial adhesion strength measured under the following conditions of 0.1 N / 15 mm or more.
   In an environment of 25 ° C., the surface layer of the protective film is bonded to an aluminum plate, and the initial adhesion strength between the protective film and the aluminum plate is measured.
6. The protective film according to any one of claims 1 to 5, wherein the surface layer further contains an elastomer.
7. The protective film according to any one of claims 1 to 6, wherein the protective film further comprises a base material layer.
8. The protective film according to claim 7, wherein the base material layer contains polyolefin.
9. The protective film according to claim 7 or 8, wherein the base material layer is composed of two or more layers.
10. The protective film according to any one of claims 1 to 9, wherein the protective film further comprises an absorption layer.
11. The protective film according to claim 10, wherein the absorption layer is a nonwoven fabric.
12. The basis weight of nonwoven fabric is 20 g / m ² or more 300 g / m ² or less, the protective film of claim 11.
13. The protective film according to claim 11 or 12, wherein the nonwoven fabric contains at least one of polyester and polyolefin.
14. In manufacturing a battery, when injecting an electrolyte from the electrolyte inlet of the battery, a method for preventing the electrolyte from adhering around the electrolyte inlet,
    An electrolytic solution adhesion preventing method comprising the following steps (A) and (B).
    Step (A): A protective film having a surface layer containing polyolefin is prepared.
    Step (B): The surface layer of the protective film is pasted around the electrolyte inlet of the battery before the electrolyte is injected.
15. A method for manufacturing a battery, comprising at least the following steps (A), (B), and (C) in this order.
    Step (A): A protective film having a surface layer containing polyolefin is prepared.
    Step (B): The surface layer of the protective film is pasted around the electrolyte inlet of the battery before the electrolyte is injected.
    Step (C): An electrolytic solution is injected from the electrolytic solution inlet.

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