JP3363382B2 - Conductive film for current collector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide such mechanical strength as no breakage or disconnection takes place at thermocompression bonding, by laminating a conductive resin layer on the side contacting an electrode, with a metal film as a base layer, comprising a hard coat layer of ultraviolet-setting type with specific thickness at an outer-most layer, with a specified specific resistance of the conductive resin layer. SOLUTION: Related to a current collector conductive film 6, a conductive resin layer of specific resistance 0.1 Ω.cm or less is laminated in the thickness of 1-10 μm on a metal film of 10-30 μm thickness on the side in contact at least with an electrode, with an ultraviolet-setting type hard coat layer provide on an outer-most layer. Related to a base resin of the conductive resin, a styrene-maleic acid copolymer is 5-30 pts.wt. by 100 pts.wt. of MMA(methylmeta acrylate)/BMA(butylmeta acrylate) copolymer while 10/1000 pts.wt. of thin oxide by a resin 100 pts.wt. is dispersed as conductive powder.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive film for a current collector for adhering a solid polarizable electrode used in an electric double layer capacitor using an aqueous electrolytic solution, and more particularly to a contact resistance for a polarizable electrode and an electrode plate. And a conductive film for a current collector for obtaining a stable contact state and conductivity.

[0002]

2. Description of the Related Art The basic structure of an electric double layer capacitor is as shown in FIG. 1, in which a pair of polarizable electrodes are embedded inside a sealing frame through a porous separator, and the polarizable electrodes are used as metal electrodes. It is formed by sealing with a plate. However, in this case, the polarizable electrode and the metal electrode plate are simply in contact with each other,
Poor contact may occur partially, leading to an increase in internal resistance. In order to solve this, as shown in FIG. 2, the polarizable electrode and the metal electrode plate are bonded with a conductive adhesive,
As shown in FIG. 3, it has been proposed to bond by thermocompression through a conductive thermoplastic film.

However, when the polarizable electrode and the metal electrode plate are bonded to each other with a conductive adhesive, non-uniform conductivity is often exhibited due to the effect of the cured state of the conductive adhesive and the residual solvent. There is a problem that the contact resistance is increased, the internal resistance is increased, and a large current cannot be taken out. When a conventional conductive thermoplastic film is used, a thermoplastic resin such as polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyurethane, polyamide, or polyimide is used for the resin constituting the film, and carbon black is used for this resin. Is dispersed into a film using a conventionally known molding method such as an extrusion method or a calendar rolling method, so that the moldability is remarkably poor when the content of the conductive agent is large, and the strength of the film itself is also very high. However, when the content of the conductive agent is reduced, the conductivity is remarkably lowered and the internal resistance is increased.

Therefore, in molding a conductive thermoplastic film, it is necessary to balance the conductivity and the film strength. When the conductive agent is acetylene black, it is necessary to add 60 to 100 parts by weight to 100 parts by weight of the resin in order to obtain good conductivity, but only 10 to 50 parts by weight in consideration of moldability. I couldn't add
The volume resistance value could not be lowered so much. Further, the thickness is preferably 20 μm or less in order to cover a high volume resistance value, but due to a molding problem, only a film having a thickness of about 30 to 100 μm can be obtained, and the current situation is that the conductivity is not increased to a desired level. Moreover, if a large amount of carbon black is filled in consideration of conductivity and the thickness is set to 20 μm level by coating, mechanical strength is insufficient, and breakage or breakage is likely to occur during thermocompression bonding. There was also a problem that the stay was significantly reduced.

[0005]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a conductive film for current collection in which a solid polarizable electrode used for an electric double layer capacitor is closely adhered. By carefully studying the manufacturing method,
An object of the present invention is to provide a conductive film for current collection, which has a low volume resistance value, has a mechanical strength that does not cause breakage or breakage during thermocompression bonding, has excellent adhesion to a polarizable electrode, and has low contact resistance.

[0006]

The present invention is a current collector film for an electric double layer capacitor using an aqueous electrolytic solution, which comprises a metal film as a base layer and a resin and a conductive agent at least on the side in contact with the electrode. A conductive resin layer is laminated, and an outermost layer has a UV-curable hard coat layer having a thickness of 0.1 to 1 μm, and the specific resistance of the conductive resin layer is 1
A conductive film for a current collector having an Ω · cm or less. Preferably, the resin of the conductive resin layer comprises 5 to 30 parts by weight of the styrene-maleic acid copolymer with respect to 100 parts by weight of the MMA (methyl methacrylate) / BMA (butyl methacrylate) copolymer resin, A conductive film for a current collector in which tin oxide as an agent is dispersed in an amount of 10 to 1000 parts by weight based on 100 parts by weight of the resin, and the thickness of the conductive resin layer is at least 1 to 10 μm on one side, The metal film in the film is either Al or Cu, the thickness is 10 to 30 μm, and the hard coat resin layer has a compounding ratio of epoxy acrylate and polyfunctional urethane acrylate of 30/70 to 70/30. It is a conductive film for electric bodies.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, a conductive resin layer having a sulfuric acid resistance and a specific resistance of 0.1 Ω · cm or less and having a resistance of 0.1 Ω · cm or less is provided on the conductive film for a current collector at least 1 to 10 μm.
In a system in which a UV curable hard coat layer is set as the outermost layer by laminating on a metal film having a thickness of 10 to 30 μm,
By carefully studying these material types, composition ratios, and manufacturing methods, the volume resistance value is lower than that of conventional conductive adhesives and conductive thermoplastic films, and even thin films with a thickness of 10 to 50 μm may be broken during thermocompression bonding. The present invention has been completed based on the finding that a conductive film for current collection having mechanical strength that does not cause breakage, excellent adhesion to a polarizable electrode, and low contact resistance can be obtained. Here, the reason why this structure was selected is that the metal foil is responsible for the conductivity in the thickness direction of the current collector and the water vapor barrier property of the system, and the conductive resin significantly reduces the contact resistance with the electrode. It acts as a binder when pinholes occur in the metal foil. In addition, the UV-curable resin in the outermost layer has resistance to sulfuric acid electrolyte and chemical resistance, and can be bonded to gaskets. Therefore, it has the same conductivity as metal and the chemical resistance and adhesion of resin. It is possible to be satisfied at the same time.

The conductive film used in the present invention is a system in which a conductive resin is laminated on a metal film. The conductive resin layer requires at least a single-sided layer on the electrode side. Preferably, both sides are laminated.

The base resin of the conductive resin is MMA / B
A blend of a copolymer of MA and a copolymer of styrene-maleic acid is used and is preferably crosslinked. However, a thermoplastic resin may be used as long as it has resistance to an aqueous sulfuric acid solution. The addition ratio of the above two resins is MMA / B
The styrene-maleic acid copolymer is 5 to 30 parts by weight, preferably 10 to 100 parts by weight of the MA copolymer.
20 parts by weight is good. The styrene-maleic acid copolymer plays the role of a softening agent that prevents the film cracking of the acrylic resin over time. If the amount of the styrene-maleic acid copolymer added exceeds 30 parts by weight, the compatibility between the two becomes extremely poor and it is difficult to form a coating material. Further, if the amount is less than 5 parts by weight, the effect of adding the styrene-maleic acid copolymer cannot be seen.

Tin oxide is dispersed as the conductive fine powder, and the amount of the conductive fine powder added is 10 to 1000 parts by weight, preferably 100 to 800 parts by weight, based on 100 parts by weight of the resin. If it is less than 10 parts by weight, sufficient conductivity cannot be obtained, and if it exceeds 1000 parts by weight, the dispersibility of tin oxide is significantly reduced and the viscosity of the paint is increased, resulting in poor practicality. Also,
The specific resistance of the conductive resin needs to be 1 Ω · cm or less, and if the specific resistance is exceeded, the contact resistance increases, and low resistance cannot be achieved. Furthermore, the thickness of the conductive resin layer is 1 to 10 μm for each layer.
Is suitable, and preferably 1 to 5 μm. If it is less than 1 μm, sufficient conductivity cannot be obtained, and if it exceeds 10 μm, the resin layer becomes brittle and cracks or peeling occurs during handling during the production process of the electric double layer capacitor.

The outermost hard coat layer has a thickness of 0.1.
A UV-curable acrylic resin of ˜1 μm is used. The resin is composed of epoxy acrylate and polyfunctional urethane acrylate, and the compounding ratio thereof is 30/70 to 70/30.
It is preferably 40/60 to 50/50. When the compounding ratio of the epoxy acrylate is less than 30, the flexibility becomes extremely poor. On the other hand, when it exceeds 70, the crosslinking is insufficient and the solvent resistance is deteriorated. Is not preferred because

As the metal film in the current collector, A
1 or Cu. Preferably, also in terms of cost, Al
Foil is good. The thickness of this metal film is 10 to 30 μm, preferably 10 to 20 μm. If the thickness is less than 10 μm, the metal film is too thin, and there is a risk that wrinkles or breakage may occur during assembly of the electric double layer capacitor. 30μ
If it exceeds m, the weight of the film will be heavy and the cost will increase.

[0013]

EXAMPLE An example of the present invention will be described below. However, the present invention is not limited to the following examples, and a conventionally known melt film-forming method is also possible. <Example 1> 100 weight of MMA / BMA copolymer resin having a molecular weight of 50,000 Parts and 10 parts by weight of styrene-maleic acid copolymer, 300 parts by weight of tin oxide, 5 parts by weight of isocyanate, and a mixed solvent of toluene / ethyl acetate (1/1) 60
0 parts by weight were dispersed and mixed in a ball mill for 24 hours to obtain a conductive paint. This conductive paint is roughened to a thickness of 2
Both sides were coated and dried on a 0 μm Al foil base material by a gravure coating method so that the film thickness after drying was 5 μm, and further epoxy acrylate / polyfunctional urethane acrylate was mixed at 40/60 on the surface, and an initiator, A solution made into a paint by adding a solvent was coated to a thickness of 0.2 μm by a kiss coating method, and cross-linked with ultraviolet rays of 70 mJ to form a film, thereby obtaining a 5-layer conductive film for a current collector. Volume resistance value of the obtained film,
Also, the average internal resistance value and the presence or absence of breakage or breakage during thermocompression bonding were evaluated when ten basic cells of the electric double layer capacitor shown in FIG. 3 were produced. The results are shown in Table 1.

<Examples 2 to 5> A 5-layer coating film was obtained in the same manner as in Example 1 according to the formulation shown in Table 1 to prepare a conductive film for a current collector. Table 1 shows the results of the same measurement as in Example 1 using the obtained film.
Shown in.

<Comparative Example 1> A masterbatch in which 100 parts by weight of polypropylene resin and 50 parts by weight of acetylene black are mixed and dispersed is melt-formed by an extrusion method to a thickness of 50 μm to obtain a conductive film of a comparative example. It was Table 2 shows the results obtained by performing the same measurement as in Example 1 using the obtained film.
Shown in. <Comparative Examples 2 to 4> Melt film-forming films were obtained in the same manner as in Comparative Example 1 according to the formulation shown in Table 2 to prepare conductive films for current collection. Table 2 shows the results of the same measurements as in Example 1 using the obtained film.

<Measurement Method> Regarding the gel fraction of the conductive resin, the residual weight of the electroconductive resin after immersion in xylene for 24 hours after crosslinking was measured. The specific resistance is 50m from the obtained conductive film
A m × 20 mm sample was cut out and measured using a four-point probe method (Loresta AP: manufactured by Mitsubishi Chemical Corporation). The average internal resistance was calculated by adding 1 kHz and 1 mA to the basic cell of the electric double layer capacitor shown in FIG. 3 and measuring the voltage at both ends, and those having an internal resistance of 1Ω or less were regarded as good products. The presence or absence of breakage was determined by observing the surface of 50 basic cells with an optical microscope. Regarding the resistance to the sulfuric acid-based electrolytic solution, a 50% strength sulfuric acid aqueous solution was dropped onto the film, and a change in appearance after 24 hours was observed.

[0017]

[Table 1]

[0018]

[Table 2]

[0019]

EFFECT OF THE INVENTION Since the conductive film for collecting electricity obtained in the present invention has a lower volume resistance value than the conventional conductive thermoplastic film, excellent conductivity can be obtained even with the same thickness. Further, since it has excellent mechanical strength, even if it is thinner than the conventional conductive thermoplastic film, it is possible to prevent breakage or breakage during thermocompression bonding. Further, it has excellent adhesion to a metal electrode plate or a polarizable electrode, can reduce contact resistance, and can reduce internal resistance and improve performance of an applied electric double layer capacitor.

[Brief description of drawings]

FIG. 1 is a sectional view showing a basic configuration of a conventional electric double layer capacitor.

FIG. 2 is a cross-sectional view showing the basic structure of an electric double layer capacitor in which a metal electrode plate and a polarizable electrode are bonded with a conductive adhesive.

FIG. 3 is a cross-sectional view showing a basic configuration of an electric double layer capacitor in which a metal electrode plate and a polarizable electrode are thermocompression bonded with a conductive film.

[Explanation of symbols]

1 ... Polarizable electrode 2 ... Porous separator 3 ... Sealing frame 4 ... Metal electrode plate 5: Conductive adhesive 6 ... Conductive film for current collection

Claims (5)

(57) [Claims] 1. A current collector film for an electric double layer capacitor using an aqueous electrolytic solution, comprising a metal film as a base layer and a conductive resin layer made of a resin and a conductive agent laminated on at least a side in contact with an electrode. In addition, the outermost layer has an ultraviolet curable hard coat layer having a thickness of 0.1 to 1 μm, and the specific resistance of the conductive resin layer is 1 Ω · cm or less. the film. 2. The resin of the conductive resin layer is MMA (methyl methacrylate) / BMA (butyl methacrylate).
5 to 30 parts by weight of a styrene-maleic acid copolymer based on 100 parts by weight of the copolymer resin, and the addition amount of tin oxide as a conductive agent is 10 to 100 parts by weight of the resin.
The conductive film for a current collector according to claim 1, wherein 0 part by weight is dispersed. 3. The thickness of the conductive resin layer is at least 1 on one side.
The conductive film for a current collector according to claim 1, which has a thickness of 10 μm. 4. The metal film in the conductive film is Al
The conductive film for a current collector according to claim 1, 2 or 3, which is either Cu or Cu and has a thickness of 10 to 30 µm. 5. The hard coat resin layer has a compounding ratio of epoxy acrylate and polyfunctional urethane acrylate of 30/7.
It is 0-70 / 30, The electrically conductive film for collectors of Claim 1, 2, 3 or 4.