JP5566214B2 - Stainless steel foil for power storage device container and method for producing the same - Google Patents

Description

  The present invention relates to a stainless steel foil for a power storage device container, a resin-coated stainless steel foil for a power storage device container, and a method for producing the same.

  Power storage devices such as secondary batteries and capacitors such as nickel-cadmium, nickel-hydrogen, and lithium-ion batteries for electronic devices and electronic parts, especially mobile phones, notebook computers, video cameras, satellites, electric / hybrid vehicles, etc. Is widely used. Conventionally, a secondary battery using a strong alkaline electrolyte such as nickel-cadmium, nickel-hydrogen, etc. has used a case made of a nickel-plated cold-rolled steel plate or a plastic case. Further, even in a battery using a non-aqueous electrolyte such as a lithium ion battery, an electrolyte incorporated in an aluminum pouch is wrapped in a plastic case, or a nickel-plated steel plate or a stainless steel plate case is used.

  In recent years, with the miniaturization of electronic and electrical components, there has been a demand for miniaturization and weight reduction of power storage devices such as secondary batteries and capacitors. Among these trends, the thinning of containers is attracting attention as a tool that can mount a large amount of electrolyte and ions in a limited volume and increase the electric capacity. However, if the strength of the container is reduced due to thinning, there is a risk that the content electrolyte solution may leak due to deformation or destruction when an external force or piercing is applied. There is a high possibility that the leakage of the electrolytic solution will cause a serious obstacle to the device in which the electricity storage device is built. Therefore, when the member of the container is plastic or aluminum, the strength is insufficient when the thickness is 200 μm or less, and a material with high strength is required for further thinning.

  Stainless steel foil is a material that satisfies these required characteristics. Stainless steel foil is a metal foil made by thinning stainless steel to a thickness of 200 μm or less, and the tensile strength and Vickers hardness of stainless steel are generally 2 to 10 times higher than that of plastic and aluminum. It is promising as a thin material for containers. It can be said that stainless steel foil is indispensable in the future development of electricity storage devices in order to achieve both a reduction in thickness for increasing the electric capacity and an improvement in strength for improving safety.

  A typical example of an electricity storage device that has been reduced in size and weight in the prior art is a lithium ion secondary battery, and metal foils for the container are disclosed in Patent Documents 1 to 5 and the like. As shown in these patent documents, a container of an electricity storage device using a metal foil is generally coated with a resin on one side or both sides of the metal foil. The main reason is to use a heat seal that is excellent for sealing small and light containers. Heat sealing heats and melts the resin to seal the container, so it can be easily implemented in a small, thin container, and is more economical than welding and winding. Yes. Generally, heat sealing used in a lithium ion secondary battery is made by fusing a polyolefin resin coated on the inner surface side of a container, and in recent years, polypropylene is often used. Using a polypropylene resin, the heat sealing is performed by heating to around 200 ° C. and instantly fusing. By this sealing (sealing), leakage of the electrolytic solution and entry of moisture from the outside can be prevented.

  Polyolefin resins having excellent chemical resistance and a relatively low moisture permeation amount among resin materials are suitably used in the above applications. Therefore, in order to use the metal foil for the electricity storage device container, it is necessary to satisfy the requirements that the metal foil can withstand the heat sealing temperature and can be coated with the polyolefin resin. In addition, when the resin is coated on both sides of the metal foil, one side of the metal foil on the outer surface side of the container is a polyester resin that can provide exterior protection such as insulation and corrosion resistance, designability as a label, workability, etc. In general, a polyamide resin, a polyolefin resin or the like is coated.

  In recent electronic products, particularly power storage devices using lithium ions, there have been many reports of fires, abnormal heat generation, and rupture accidents that are thought to be caused by some kind of product failure including contamination of dust and foreign substances. In addition to causing abnormalities in the contents and containers, it also causes a defective appearance of the product, so it is possible to achieve excellent cleanliness by eliminating dust and foreign substances, and eliminate defects in the adhesion between the resin and metal foil. It is important not to give out.

  Further, Patent Document 6 discloses a technique for obtaining a surface oxide film having excellent adhesion by heat-treating a stainless steel foil in a reducing atmosphere as a method for improving the adhesion with a resin without surface treatment. In addition to this, Patent Documents 7 to 9 disclose techniques for heat-treating stainless steel in a reducing atmosphere to refine the surface film and material structure.

Japanese Patent Laid-Open No. 10-208708 JP 2001-30407 A Japanese Patent Laid-Open No. 2001-266809 JP 2000-123800 A JP 2000-357494 A JP 2005-1245 A JP-A-8-92652 Japanese Patent Laid-Open No. 9-209033 JP-A-2005-213589

  However, when an electric storage device container is formed by coating a resin on both surfaces of a metal foil, as shown in Patent Documents 1 to 5, at least one surface of the metal foil, particularly the surface of the metal foil that is the inside of the container Has been subjected to a chromic conversion treatment such as chromate which can improve the adhesion so that the adhesion between the coating resin and the metal foil does not drop and the resin does not peel even when it comes into contact with the electrolyte. However, when the film obtained by the chromic conversion treatment is heated, the network structure of the hydrated chromium oxide is decomposed by the deoxygenation reaction, the molecular weight is lowered, the film defects increase, and the performance such as corrosion resistance deteriorates. Easy to do. Therefore, the electricity storage device container using the metal foil coated with resin is sealed by heat sealing, but the reduction of the molecular weight of the chromic conversion coating such as chromate proceeds at 200-300 ° C, so the film during heat sealing There is a problem that a defect enters and the adhesive force with the coating resin tends to be reduced.

  In addition, since the chromium conversion treatment method uses a chemical solution such as a chromic acid solution, it is difficult to say that it can sufficiently cope with environmental regulations that are more burdensome to environmental problems due to disposal of the chemical solution and become more severe in the future. .

  In addition, the method of chromic conversion treatment requires chemical solution coating, heat curing, solvent drying, curing, etc. on the metal foil as a base material, and therefore the number of processes is complicated, and the problem is that the economy is poor. There is. Further, in this method, dust and foreign matters are easily mixed, and if the wettability of the surface of the metal foil is insufficient, there is a strong concern that a coating failure portion such as coating failure will occur, leading to a product failure.

  Further, in the technique disclosed in Patent Document 6, the surface oxide film obtained by heat-treating the stainless steel foil in a reducing atmosphere has concentrated Si (an oxide film containing silicon oxide, or a silicate film and It contributes only to the adhesion of resin compositions such as epoxy and polyester. On the other hand, because the inside of the electricity storage device container is required to have an electrolyte solution resistance, it is coated with a polyolefin-based resin such as polyethylene or polypropylene with high chemical resistance, but these are low in polarity and difficult to adhere to a metal, This technique is not effective enough. In particular, in lithium ion secondary batteries, hydrogen fluoride is generated just by mixing a very small amount of water into the electrolyte, and hydrogen fluoride preferentially cleaves the bond between Si and oxygen (O) (SiO bond). Since the adhesive strength of the resin composition is reduced, it is not at all suitable for an electricity storage device container.

  In addition, the technique disclosed in Patent Document 7 requires rapid cooling after annealing, thereby avoiding the formation of Cr carbides and nitrides, so that Cr is hardly diffused into the oxide film. It has become. Such an oxide film cannot ensure adhesion with the polyolefin resin as described above. Therefore, these technologies cannot withstand the use in power storage device container applications.

  Further, in the techniques disclosed in Patent Documents 8 and 9, since the annealing temperature in a reducing atmosphere is carried out at a high temperature of 1000 ° C. or higher, the oxide film is reduced and removed, so that it can be used in power storage device container applications. An oxide film with a sufficient thickness cannot be obtained, and the coating resin is peeled off by contact with the electrolytic solution.

  Therefore, the present invention solves the above-mentioned problems, can ensure adhesion with a polyolefin-based resin without surface treatment such as chrome conversion treatment, and does not decrease adhesion even when contacted with an electrolytic solution. It is an object to provide a stainless steel foil and a method for producing the same. Furthermore, it aims at providing the resin-coated stainless steel foil for electrical storage device containers which is excellent in heat resistance, environmental impact reduction, and economical efficiency, and there are few product defects, and its manufacturing method.

  The present inventors applied various heat treatments to stainless steel foils having various surface roughnesses that have not been subjected to surface treatment such as chrome conversion treatment to coat a polyolefin resin, and after applying a high temperature corresponding to heat sealing, an electrolytic solution As a result of a detailed analysis of the resin composition exfoliation situation and the surface of the stainless steel foil, it was found that the polyolefin resin exfoliation situation differs depending on the oxide component and surface morphology of the stainless steel foil surface. . That is, an oxide film having a high Cr concentration diffused from the surface of the stainless steel foil can be obtained by heat-treating the stainless steel foil having a rough surface in a reducing atmosphere. It has been found that it has excellent adhesion to the composition and excellent heat resistance that can withstand high temperatures such as heat sealing, and has reached the present invention based on this finding. That is, the gist of the present invention is as follows.

  (1) A stainless steel foil having an oxide film containing 20 mol% or more and 60 mol% or less of oxygen and containing more Cr than Fe, the arithmetic average roughness Ral in the rolling direction on the surface of the oxide film, Or, the arithmetic average roughness Rac in the direction perpendicular to the rolling direction is 0.1 μm or more and less than the maximum depth Rt of the surface of the oxide film, and Rt is 0.8 μm or more and 50% of the thickness of the stainless steel foil. %, And the thickness of the oxide film is 6 nm or more and less than 150 nm.

  (2) A resin-coated stainless steel foil for an electricity storage device container, comprising a polyolefin resin laminated on both surfaces or one surface of the stainless steel foil for an electricity storage device container according to (1).

  (3) The arithmetic average roughness Rals of the surface in the rolling direction of the stainless steel foil, or the arithmetic average roughness Racs on the surface perpendicular to the rolling direction of the stainless steel foil is 0.1 μm or more and the maximum surface of the stainless steel foil A stainless steel foil having a depth of less than Rt and an Rts of 0.8 μm or more and 50% or less of the thickness of the stainless steel foil is annealed in a reducing atmosphere at a temperature of 600 ° C. or more and less than 800 ° C. The manufacturing method of the stainless steel foil for electrical storage device containers as described in (1).

  (4) The method for producing a stainless steel foil for an electricity storage device container according to (3), wherein the annealing is performed for 0.5 minutes or more and 3 minutes or less.

(5) The annealing is a heat treatment at a temperature of 600 to 800 ° C. in an atmosphere having a partial pressure ratio H ₂ / H ₂ O of hydrogen and water of 10 or more and a dew point of less than 40 ° C. (3) or (4) Manufacturing method of stainless steel foil for electricity storage device container.

  (3) A film of a polyolefin-based resin composition is laminated by thermocompression bonding on both surfaces or one surface of a stainless steel foil for an electricity storage device container obtained by the production method according to any one of (3) to (5). A method for producing a resin-coated stainless steel foil for a power storage device container.

  According to the present invention, an electricity storage device container capable of ensuring a strong adhesion that does not peel off the polyolefin-coated resin even when immersed in an electrolyte solution essential to the electricity storage device without performing a surface treatment using a chemical solution such as a chromic acid solution. Stainless steel foil can be provided. In addition, it is possible to provide a resin-coated stainless steel foil for power storage device containers that has excellent heat resistance, such as heat sealing, which does not deteriorate at all, and is excellent in reducing environmental impact and economy, and with few product defects. It contributes to development.

Cross-sectional structure of resin-coated stainless steel foil for power storage device containers

  Hereinafter, the present invention will be described in detail.

  FIG. 1 shows a typical cross-sectional structure diagram of a resin-coated stainless steel foil for a power storage device container according to the present invention. In FIG. 1, an oxide film 2 is formed on the surface of a stainless steel foil 1, and a polyolefin resin layer 3 such as polyethylene or polypropylene is further formed on the surface.

  In the stainless steel foil for an electricity storage device container of the present invention, in order to use it for an electricity storage device container, polyethylene or polypropylene-based polyolefin resin such as polypropylene is used on one side which is the inside of the container (FIG. 1), Even if it is not used for surface treatment with a chemical solution such as a chromic acid solution, it has excellent adhesion and heat resistance at the interface between the polyolefin resin and the stainless steel foil, and does not decompose or deteriorate at all at the heat seal temperature.

  On the other hand, as metal foils for power storage device containers coated with resin on at least one side, the metal foils described in Patent Documents 1 to 5 use a chromic acid solution to perform chromium conversion treatment such as chromate on the metal foil. The heat resistance is low and there is a risk of performance deterioration due to heat sealing, and the environmental load is also large. Furthermore, since the process becomes complicated, there is a risk of deterioration of economic efficiency and contamination of dust and foreign matters.

  In addition, the stainless steel plate described in Patent Document 6 has no effect on adhesion with polyethylene or polypropylene covering the inside of the electricity storage device container as described above. Moreover, in patent document 6, since Si will concentrate in an oxide film as an oxide, sufficient adhesiveness cannot be ensured, and as above-mentioned, it is not suitable for an electrical storage device container. In addition, the stainless steel sheets described in Patent Documents 7 to 9 have different components from the oxide film of the present invention, and as a result, sufficient adhesion cannot be ensured, and the effects of the present invention are not obtained at all.

  The stainless steel foil according to the present invention may be any one of austenite (SUS301, 304, 316, etc.), ferrite (SUS430, etc.), and martensite (SUS410, etc.), and is a foil having a thickness of 200 μm or less. From the viewpoint of processability and strength as an electricity storage device container, the thickness of the stainless steel foil is preferably 200 μm or less and 10 μm or more.

  An oxide film is present on the surface of the stainless steel foil according to the present invention. When the oxide film is as follows, the effects of the present invention as described above can be obtained.

  (I) The oxide film is an oxide containing 20 mol% or more and 60 mol% or less of oxygen O and containing Cr and Fe, and contains more Cr than Fe.

  (Ii) When the surface of the oxide film has an arithmetic average roughness Ral in the rolling direction or an arithmetic average roughness Rac in the direction perpendicular to the rolling direction of 0.1 μm or more, the maximum depth of the surface of the oxide film Is less than Rt.

  (Iii) The maximum depth Rt of the surface of the oxide film is 0.8 μm or more and 50% or less of the thickness of the stainless steel foil.

  (Iv) The oxide film has a thickness of 6 nm or more and less than 150 nm.

  Here, Ral and Rac are the arithmetic mean roughness of the surface of the oxide film on the surface of the stainless steel foil in the sheet passing direction of the stainless steel foil coil material and the vertical direction thereof, respectively. Rt is the maximum cross-sectional height of the roughness curve of the surface of the oxide film on the stainless steel foil surface. These roughnesses can be easily measured using a stylus type surface roughness measuring machine, a laser type surface roughness measuring machine, or the like. In the present invention, the effect of the present invention can be obtained if the value obtained by any one of the measuring machines is within the scope of the present invention.

  In addition, regarding the setting of the upper limits of Ral, Rac, and Rt in the above (ii) and (iii), Ral and Rac are not theoretically larger than Rt, and Rt was set to 50% or less of the thickness of the stainless steel foil. This is because if it exceeds 50% of the thickness of the stainless steel foil, the material strength and workability are adversely affected. As a specific example, when the surface of a stainless steel foil with a thickness of 100 μm becomes rough until Rt becomes larger than 50 μm, a part where the material thickness becomes 50 μm or less occurs, which is the starting point of strength reduction, fracture, and fracture As a result, the basic performance of the stainless steel foil is impaired. Therefore, when such a roughness is used, the adverse effect is very large.

  In addition, the mol% (atomic%) of Cr, Fe, and O atoms in the oxide film in (i) is X-ray photoelectron spectroscopy (commonly known as XPS, ESCA), Auger electron spectroscopy (commonly known as AES), high frequency It can be easily measured by general elemental analysis techniques such as glow discharge emission surface analysis (commonly known as GDS). In the present invention, the effect of the present invention can be obtained if the value obtained by any one of the analysis methods is within the scope of the present invention.

  Moreover, about the thickness of the oxide film in (iv), mol% (atomic%) of an oxygen atom (O atom) is measured, sputtering these elemental analysis by ion beams, such as argon, in the depth direction, In the differential profile of oxygen concentration, when there are half-values on both sides of the peak, the peak half-width, or when the surface side is higher than half-value and when only one of the peaks has half-value, the distance between the outermost surface and half-value, It was set as the thickness of the oxide film in the present invention.

  Regarding the structural requirements related to (i) above, the reason is that the oxide film containing a large amount of Cr atoms has a strong chemical interaction with the polyolefin resin and exhibits good adhesion to the polyolefin resin even in the electrolyte. Therefore, it is suitable for the electricity storage device container application. Therefore, on the contrary, an oxide film having few Cr atoms and many Fe atoms is not suitable for an electrical storage device container because it cannot exhibit good adhesion as an oxide film containing more Cr atoms than Fe atoms. Since Cr contained in the oxide film is indispensable to be trivalent due to the problem of reducing environmental burden, oxygen is 60 mol%, Cr atom is 40 mol%, and Fe atom is 0 mol%, considering adhesion. Ideally, however, oxygen is deficient due to lattice defects and Fe atoms are present, so oxygen is 20-60 mol%, Cr atoms are 10-60 mol%, Fe atoms are less than Cr atoms and 0 mol % Or more and less than 30 mol%. If the oxygen content is less than 20 mol%, oxygen deficiency due to lattice defects or the like is remarkable, and it is difficult to obtain performance such as improved adhesion as an oxide film. If there is more oxygen than 60 mol%, Cr may be hexavalent, which is not preferable. More preferably, oxygen is 30 to 60 mol%, Cr atoms are 15 to 40 mol%, Fe atoms are less than Cr atoms, and are present in the range of 0 to 20 mol%, and more preferably 0 to 10 mol%.

  Furthermore, since the surface of the oxide film is made to have a surface roughness as defined in the above (ii) and (iii), the polyolefin-based resin is coated so as to bite into the irregularities on the surface. The adhesion is promoted, and an excellent synergistic effect is brought about by the chemical interaction by the oxide film containing more Cr atoms than Fe atoms. Specifically, Ral or Rac needs to be 0.1 μm or more, and if both Ral and Rac are less than 0.1 μm, sufficient adhesion to a polyolefin resin cannot be obtained. In addition, the upper limit of Ral and Rac is theoretically (geometrically) not allowed to exceed the maximum depth Rt, and thus is set to be less than the maximum depth Rt. The Ral or Rac is preferably 0.4 to 2.0 μm.

  Further, the Rt needs to be 0.8 μm or more, and even when the Rt is less than 0.8 μm, sufficient adhesion with a polyolefin resin cannot be obtained. On the other hand, when Rt exceeds 50% of the thickness of the stainless steel foil, the stainless steel foil is deteriorated in strength and broken by press working, resulting in unsuitability for productivity.

  In addition, with respect to the constituent requirement according to (iv) above, the oxide film preferably has an appropriate thickness, and specifically, is 6 nm or more and less than 150 nm. If the thickness is less than 6 nm, it is not preferable because sufficient adhesion cannot be exhibited, and stable production cannot be achieved in actual use of the electricity storage device container. If it is 150 nm or more, the temper color peculiar to stainless steel is unstable, which adversely affects aesthetics and induces product defects. It is preferably 10 to 100 nm.

In addition, the stainless steel foil for the electricity storage device container of the present invention may be subjected to a base treatment. By performing the base treatment, the effects of the present invention can be more efficiently exhibited, and the chemical adhesion between the polyolefin resin and the resin composition coated on the outside of the container and the stainless steel foil can be increased. Specifically, a method of removing the oil and the scale on the surface of the stainless steel foil as necessary, or thereafter performing a non-chromate chemical conversion treatment without using Cr ⁺⁶ can be mentioned as the base treatment. Examples of scale removal treatment methods include pickling, sand blast treatment, grid blast treatment, and chemical conversion treatment methods. Non-chromate treatment without using Cr ⁺⁶ , strike plating treatment, epoxy primer treatment, silane coupling treatment, titanium cup, etc. A ring process etc. are mentioned.

  The stainless steel foil for an electricity storage device container of the present invention can be made into a resin-coated stainless steel foil for an electricity storage device container by laminating a polyolefin resin on both sides or one side.

  The polyolefin-based resin is a resin composition mainly composed of a resin having a repeating unit of the following (formula 1). Here, the main component is that the resin having the repeating unit of (Formula 1) constitutes 50% by mass or more.

-CR ¹ H-CR ² R ^3- (Formula 1)
(In the formula, R ¹ and R ² each independently represents an alkyl group having 1 to 12 carbon atoms or hydrogen, and R ³ represents an alkyl group having 1 to 12 carbon atoms, an aryl group or hydrogen.)
The polyolefin according to the present invention may be a homopolymer of these structural units or two or more kinds of copolymers. It is preferable that five or more repeating units are chemically bonded. If it is less than 5, the polymer effect is difficult to exert. Examples of repeating units include repeating units appearing when addition polymerization of terminal olefins such as propene, 1-butene, 1-pentene, 4-methyl-1pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, etc. In addition to aliphatic olefins such as repeating units when isobutene is added, and styrene monomer, o-methylstyrene, m-methylstyrene, p-methylstyrene, o-ethylstyrene, m-ethylstyrene, o-ethyl Aromatic olefins such as styrene monomer addition polymer units such as alkylated styrene such as styrene, ot-butylstyrene, m-t-butylstyrene, pt-butylstyrene, halogenated styrene such as monochlorostyrene, and terminal methylstyrene Is mentioned. For example, low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, cross-linked polyethylene, polypropylene, polybutene, polypentene, polyhexene, polyoctenylene, polyisoprene, polybutadiene, which are homopolymers of terminal olefins Etc. Examples of the copolymer of the above unit include ethylene-propylene copolymer, ethylene-butene copolymer, ethylene-propylene-hexadiene copolymer, ethylene-propylene-5-ethylidene-2-norbornene copolymer, etc. Aliphatic polyolefins, aromatic polyolefins such as styrene copolymers, and the like, but are not limited thereto, as long as the above repeating units are satisfied. Further, it may be a block copolymer or a random copolymer. These resins may be used alone or in combination of two or more.

  Most preferable from the viewpoints of handling properties and barrier properties of corrosion-causing substances are low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, cross-linked polyethylene, polypropylene or a mixture of two or more of these.

  In addition, the polyolefin according to the present invention only needs to have the olefin unit as a main component, and a vinyl monomer, a polar vinyl monomer, and a diene monomer, which are substitutes of the unit, are copolymerized in a monomer unit or a resin unit. Also good. The copolymer composition is 50% by mass or less, preferably 30% by mass or less, based on the above unit. If it exceeds 50% by mass, properties as an olefin resin such as a barrier property against a causative substance may be deteriorated. Examples of polar vinyl monomers include acrylic acid derivatives such as acrylic acid, methyl acrylate and ethyl acrylate, methacrylic acid derivatives such as methacrylic acid, methyl methacrylate and ethyl methacrylate, acrylonitrile, maleic anhydride and maleic anhydride. Examples thereof include imide derivatives and vinyl chloride.

  Further, the polyolefin resin used in the present invention includes an antioxidant, a heat stabilizer, a light stabilizer, a mold release agent, a lubricant, a pigment, a flame retardant, a plasticizer, an antistatic agent, an antibacterial agent, depending on the purpose. It is also possible to add an appropriate amount of a mold agent or the like.

  The polyolefin resin according to the present invention may be a single layer or a plurality of layers. A plurality of layers coated with different resins such as polyester, polyamide, and polyimide may be used.

  Whether the polyolefin resin is a single layer or a plurality of layers, the total thickness is preferably in the range of 5 to 200 μm, more preferably in the range of 10 to 150 μm. If it is less than 5 μm, functions such as processability, designability, and insulation may not be sufficiently imparted, and if it is thicker than 200 μm, the processability may be deteriorated. There is a fear and it is difficult to realize economic benefits. If the thickness is less than 5 μm, the strength of the seal portion when the container is molded by heat sealing is insufficient, and if it exceeds 200 μm, moisture permeation from the seal portion increases, which tends to adversely affect the electricity storage device. Moreover, you may coat | cover resin, such as polyolefin, polyester, polyamide, a polyimide, on the outermost surface of an electrical storage device container. In addition, an acrylic film or the like is laminated on the outermost coating resin to improve weather resistance, a hard coat film is laminated, or a hard coat agent is applied to improve surface hardness, or a printing layer is provided. Designability can be improved, corona treatment can be applied to improve printability, or a flame retardant, plastic, antistatic, antibacterial and antifungal layer can be laminated.

  The stainless steel foil for an electricity storage device container of the present invention is manufactured, for example, as follows. In particular, the oxide film of the stainless steel foil is formed, for example, as follows.

  The oxide film is formed using the following stainless steel foil.

  (I) The arithmetic average roughness Rals of the surface in the rolling direction of the stainless steel foil, or the arithmetic average roughness Racs on the surface perpendicular to the rolling direction of the stainless steel foil is 0.1 μm or more and the maximum surface of the stainless steel foil The depth is less than Rts. Here, when Rals and Racs are less than 0.1 μm, an oxide film containing more Cr than Fe according to the present invention cannot be obtained. Further, the upper limit of Rals and Racs cannot exceed the maximum depth Rts, and therefore is set to be less than the maximum depth Rts.

  (II) The maximum depth Rts of the surface of the stainless steel foil is 0.8 μm or more and 50% or less of the stainless steel foil thickness. Here, when Rts is less than 0.8 μm, an oxide film containing more Cr than Fe according to the present invention cannot be obtained. On the other hand, if Rts exceeds 50% of the thickness of the stainless steel foil, the stainless steel foil is deteriorated in strength and is broken by press working, so that the productivity becomes unsuitable.

  The stainless steel foil having the oxide film can be produced by annealing the stainless steel foil at a temperature of 600 ° C. or higher and lower than 800 ° C. in a reducing atmosphere.

  Since the main components of stainless steel are Fe and Cr, the oxide film on the surface of stainless steel tends to be an oxide containing a large amount of Fe atoms and Cr atoms. A film cannot be formed. By using a stainless steel foil processed to have a surface roughness as defined in (I) and (II) above, the surface of the stainless steel foil is work hardened and the diffusion coefficient of atoms changes, and in the heat treatment in a reducing atmosphere, Cr, which is more easily oxidized than Fe, becomes easier to diffuse on the surface of the stainless steel foil, and the oxide film according to the present invention can be formed. That is, in the roughness of the stainless steel foil, an oxide film containing more Cr than Fe is formed as compared with a stainless steel foil having a roughness less than that. Further, the roughness of the stainless steel foil as defined in the above (I) and (II) has a large surface area compared to the stainless steel foil having a roughness less than that, so that the amount of oxide on the surface increases and becomes stable. It is preferable because it becomes a thick film.

  In addition, since the oxide film according to the present invention is not a hydrated oxide such as chromate, the low molecular weight of the hydrated oxide due to the deoxygenation reaction at a heat sealing temperature and a temperature higher than 200 to 300 ° C. Does not happen.

  In addition, the method for roughening the surface of the stainless steel foil is not particularly limited, and examples thereof include using a known technique of hairline polishing, and using a rolling roll having a rough surface when stainless steel is rolled.

Further, the method for efficiently forming an oxide film having more Cr atoms than Fe atoms is not particularly limited, but it is preferable to perform heat treatment in a reducing atmosphere as described above. For example, the partial pressure ratio (molar ratio) of hydrogen to nitrogen is about 75:25, the partial pressure ratio H ₂ / H ₂ O of hydrogen to water is 10 or more, and the temperature is 600 to 800 ° C. in an atmosphere with a dew point of less than 40 ° C. ~ 3 minutes heat treatment. Under the above conditions, the heat treatment is preferably performed at 600 to 700 ° C. for 1 to 3 minutes. If the temperature is lower than this, or if the time is short, the reduction is insufficient and Cr atoms do not diffuse sufficiently to the surface, which may result in an oxide film with fewer Cr atoms than Fe atoms. There are cases where good adhesion of polyolefin resin cannot be expressed. If the temperature is too high, or if the time is too long, Cr atoms in the stainless steel will diffuse more than necessary on the surface, and Cr will be deficient in the base metal, and rust will easily occur. In some cases, the oxide film becomes too thick and the temper color specific to stainless steel is unstable, which adversely affects aesthetics and induces product defects. It is preferable to avoid excessive heat treatment exceeding the above temperature and time, but it is preferable to avoid excessive heat treatment so that the thickness of the oxide film to be formed is 150 nm or more There is also. That is, heat treatment is performed so that the thickness of the formed oxide film is less than 150 nm. In the heat treatment in which the thickness of the formed oxide film is 150 nm or more, Cr atoms diffuse to the surface more than necessary, and the base material becomes deficient in Cr, which may not be preferable. In addition, an extremely strong reducing atmosphere having a hydrogen / water partial pressure ratio H ₂ / H ₂ O of greater than 10 ⁶ may adversely affect the formation of an oxide film, which may be undesirable. The partial pressure ratio of hydrogen and nitrogen is not particularly limited as long as it is a reducing atmosphere, but is preferably in the range of 5:95 to 100: 0 from the viewpoint of production. The partial pressure ratio of hydrogen and nitrogen is more preferably in the range of 20:80 to 80:20. Partial pressure ratio H ₂ / H ₂ O of hydrogen and water from 50 to 10 ⁶ is more preferable. The dew point is more preferably 10 ° C or lower.

  The method for producing a resin-coated stainless steel foil for a power storage device container obtained by laminating a polyolefin-based resin on both sides or one side of the stainless steel foil for a power storage device container is not particularly limited. Covering both sides or one side by the following method can be mentioned. (1) A method in which a sheet or film obtained by extruding or molding a polyolefin resin in advance is thermocompression bonded to a stainless steel foil. (2) A method in which a sheet or film obtained by extruding or molding a polyolefin-based resin in advance is coated on a stainless steel foil with an adhesive such as dry lamination. In the case of (1) and (2), the polyolefin resin sheet or film may be stretched uniaxially or biaxially or may be laminated in a plurality of layers. (3) A method in which a polyolefin resin is melt-kneaded with an extruder equipped with a T-die to form a film, and is thermocompression bonded to the stainless steel foil immediately after extrusion. In this case, simultaneous extrusion of a plurality of layers may be performed. (4) A method in which a polyolefin resin is melted or dissolved in a solvent and coated on a stainless steel foil with a bar coater, roll coater, spin coater, spray or the like. (5) It can be coated by a method of immersing a stainless steel foil in a polyolefin resin melted or dissolved in a solvent. Among these, the methods (1), (2) and (3) are preferable from the viewpoint of work efficiency.

  Moreover, when the conditions of thermocompression bonding in the methods (1) and (3) are specifically exemplified, the polyolefin resin film has a thickness of 20 to 200 μm, and is 0.1 to 2.0 MPa in a temperature range of 100 to 200 ° C. And pressurizing and holding for 0.1 to 120 seconds. More preferably, the polyolefin resin film is pressurized to 0.5 to 1.5 MPa at a thickness of 30 to 100 μm and a temperature range of 150 to 180 ° C. and held for 0.2 to 60 seconds.

  In addition, the method for forming the polyolefin resin-coated stainless steel foil into a container shape is not particularly limited, and conventional methods such as pressing, ironing, and drawing can be used. The shape of the container is not particularly limited, such as a rectangular parallelepiped rectangular tube shape or a cylindrical shape. Further, in use as a container, it is preferable to seal the lid and the bottom together. At this time, stainless steel foils squeezed by pressing or the like may be bonded together, or only one of them may be squeezed. Further, as a method of sealing, a conventional bonding method can be used, and specifically, a method of bonding using an adhesive, a method of bonding by heat fusion by heat sealing, and the like are specifically limited. Although not intended, heat sealing is preferred in terms of manufacturability. In the case of heat sealing, it is preferable to match the surfaces on which the polyolefin resin is laminated.

  Next, the present invention will be described more specifically based on examples and comparative examples, but the present invention is not limited to the following examples.

  All the stainless steel foils used in the present examples and comparative examples were SUS304 having a thickness of 100 μm.

  The stainless steel foils of Examples 1 to 4, 7, 9 to 14 and Comparative Examples 1, 2, and 4 to 7 are based on JIS G 4305, and the surface is hairline polished using a polishing belt having an abrasive grain number of 180. did. The stainless steel foil of Example 5 was subjected to final finish rolling using a matte roll in accordance with JIS G 4305. The stainless steel foil of Example 6 was subjected to final finish rolling in the direction perpendicular to the rolling direction of the stainless steel foil of Example 5 using the same matte roll. The stainless steel foil of Example 8 was rubbed with the hairline-polished stainless steel foil 2000 times using a paper sand having a roughness of No. 100 to give a rough surface finish. The stainless steel foil of Comparative Example 3 was mirror-finished by No. 8 finish of JIS R 6001. The stainless steel foil of Comparative Example 8 was rubbed with the hairline-polished stainless steel foil 3,000 times using a paper sand having a roughness of 100 to give a rough surface finish.

  The arithmetic average roughness Rals, Racs, and the maximum roughness depth Rts of the stainless steel foil surface in the threading direction and the vertical direction of the stainless steel foil coil material are stylus type surface roughness measuring machines (manufactured by Tokyo Seimitsu Co., Ltd., Surfcom 575A-3D), using a standard pickup (stylus radius 5 μm), with a reference length of 0.25 mm, an evaluation length of 1.25 mm, and a moving speed of 0.06 mm / s. Further, the surface roughness of the oxide film was also measured by the same method.

  After carrying out the above-mentioned surface finish, the stainless steel foil was used in Examples 1 to 6, 8 to 14 and Comparative Examples 1 to 3 and 8, in an atmosphere of 75 vol% hydrogen, 25 vol% nitrogen, and dew point -65 ° C. 7. In Comparative Example 6, heat treatment was performed in an atmosphere of 47 vol% nitrogen, 50 vol% ammonia, and 3 vol% carbon dioxide under the conditions shown in Table 1 for temperature and time.

  In Comparative Examples 5 and 7, an aqueous solution containing chromium oxide and polyacrylic acid as the main components and a trivalent and hexavalent Cr content of 5 mg / ml was uniformly applied to the surface of the stainless steel foil, respectively, at 180 ° C. for 30 seconds. A dried stainless steel foil coated with coated chromate was obtained.

The thickness and composition of the oxide film on the surface of the stainless steel foil were measured using an Auger electron spectroscopy analyzer (PHI, FE type), electron beam 5 kV, 10 nA, beam size 0.05 μm, Ar ion beam 3 kV, sputtering rate about 10 nm. It was measured by / min (SiO ₂ conversion).

  After measuring the thickness and composition of the oxide film, Examples 1-8, 11-14, and Comparative Examples 1-8 were modified stainless steel foil with a 50 μm thick modified polypropylene film (manufactured by Tosero Co., Ltd., Admer QE060 # 50). A resin-coated stainless steel foil was obtained by thermocompression bonding to the stainless steel foil at a temperature of 175 ° C. and a pressure of 0.5 MPa. In Examples 9 and 10, a modified polypropylene (Mitsui Chemicals Co., Ltd., Admer QE060) and polyacetal (Nihon Polypenco Co., Ltd., POM-NC) were 50 and 60 wt% dry blended, respectively, and a film extrusion molding machine (Co., Ltd.) A 50 μm thick film prepared by kneading and extruding using 2D25F2) manufactured by Toyo Seiki Seisakusho was thermocompression bonded to the stainless steel foil at a temperature of 175 ° C. and a pressure of 0.5 MPa to obtain a resin-coated stainless steel foil.

  Visually confirm the appearance of the resin-coated stainless steel foil, ◯: no temper color, △: light yellow due to temper color, x: dark yellow to blue due to temper color, confirmed The aesthetics were evaluated based on Similarly, the presence or absence of rust was also visually confirmed, and rust prevention was evaluated based on the following criteria: ○: No rust, △: Rust with a diameter of 1 mm or less, ×: Rust with a diameter of 1 mm or more. .

  Furthermore, the above-mentioned resin-coated stainless steel foil was cut out to a size of 10 mm × 10 mm, immersed in an electrolytic solution (manufactured by Toyama Pharmaceutical Co., Ltd., 1MLiPF6 EC / DEC-1 / 1), kept at 80 ° C. for 1 week, and visually modified. The peeling condition of the polypropylene was confirmed, and the electrolytic solution resistance was evaluated on the basis of ○: no peeling, Δ: edge peeling, and x: whole surface peeling.

  Furthermore, environmentally hazardous substances were also evaluated according to the following criteria. ○: No environmentally hazardous substances used, ×: Environmentally causative substances (chromic acid etc.) used.

  Furthermore, manufacturability was also evaluated according to the following criteria. ○: Easily press working without strength reduction, breakage, etc., Δ: Not ruptured by pressing, but there is strength reduction, X: There is a portion broken by pressing. In addition, press work here was based on the following press-molded article manufacture.

  In all the above evaluations, one having at least one x was judged to be unsuitable as a stainless steel foil for an electricity storage device container.

  In addition, the resin-coated stainless steel foils of Examples 1 to 5 were subjected to drawing in a rectangular tube container shape often used as an electricity storage device container. The conditions are: Die 142 mm x 142 mm, corner R diameter 4 mm, punch 140 mm x 140 mm, corner R diameter 4 mm, wrinkle holding force 6 tons, lubricant mixed with Johnson WAX122 and machine oil 1: 1, press speed The blank size was 200 mm × 200 mm and the depth was 5 mm at 60 mm / min.

Also, two of these press-molded products were combined, and in that, electrolytic copper foil coated with graphite as a negative electrode material, separator, and aluminum foil coated with LiNiCo _0.15 Al _0.05 O ₂ as a positive electrode material were sequentially laminated, The electrolyte (1M LiPF ₆ EC / DEC-1 / 1 manufactured by Toyama Pharmaceutical Co., Ltd.) was injected into this, and the lithium ion secondary battery was sealed by vacuum sealing at 200 ° C, 0.4 MPa, and heat sealing conditions of 10 seconds. Produced. This battery was subjected to an initial charge / discharge characteristic evaluation test and a charge / discharge cycle characteristic evaluation test. In the initial charge / discharge characteristic evaluation test, the first charge was performed at 25 ° C., and the discharge was performed immediately after that to measure the ratio between the charge capacity and the discharge capacity. In the charge / discharge cycle characteristic evaluation test, the ratio between the discharge capacity and the initial discharge capacity after 300 charge / discharge cycles at 25 ° C. was measured, and 80% or more was determined to be acceptable.

  The results of the initial charge / discharge characteristic evaluation test and the charge / discharge cycle characteristic evaluation test of the batteries produced using Examples 1 to 14 were both 80% or more, and it was confirmed that the batteries were properly operated.

  In Example 1, all evaluation items were the best with ○. Example 2 is slightly inferior in electrolytic solution resistance because the reductive heat treatment time is slightly short and the oxide film is slightly thin.Example 3 is slightly inferior in aesthetics because reductive heat treatment is somewhat strong and temper color occurs. 14 is slightly stronger in reducing heat treatment, and the oxide film is slightly thicker and brittle, so it is slightly inferior in aesthetics and electrolyte resistance. In Examples 5 and 6, the surface roughness of the stainless steel foil is slightly less, so the oxide film is slightly thinner. In addition, since the roughness of the oxide film is slightly less, the electrolyte solution resistance is slightly inferior, and since Example 7 is a little inferior in electrolyte solution resistance because there is little oxygen in the oxide film and about 30 mol% of nitrogen is present, Example 8 is slightly inferior in manufacturability because the stainless steel foil has a slightly large surface roughness, and Example 9 is slightly inferior in electrolytic solution resistance because of a small proportion of polyolefin resin. 10 is the polyolefin resin The electrolyte solution resistance and rust resistance are slightly inferior because of the smaller amount, and Examples 11 and 13 are slightly inferior in electrolyte resistance and rust resistance because the ratio of Cr in the oxide film is small. The time of reductive heat treatment was slightly longer, and temper color was generated.

  On the other hand, Comparative Example 1 is not suitable for electrolytic solution resistance because the mol% of Cr and Fe in the oxide film is almost the same, and Comparative Example 2 is because the oxide film is too thick and brittle because the reduction heat treatment is too strong. Electrolytic solution resistance is unsuitable.Comparative Example 3 has an excessively thin oxide film because the surface roughness of the stainless steel foil is too small, and the anti-electrolyte solution is unsuitable because the oxide film is too coarse. In Comparative Example 4, since there is no reduction heat treatment, the amount of Cr in the surface oxide film is too small, and the oxide film is too thin, so that the electrolytic solution resistance is unsuitable. Comparative Examples 5 and 7 are trivalent and hexavalent. Since coated chromate is used, it is unsuitable from the viewpoint of an environmentally hazardous substance. In Comparative Example 6, the amount of oxygen in the oxide film is too small, and about 50 mol% of nitrogen is present, so the resistance to electrolyte solution is unsuitable. In Comparative Example 8, the surface roughness of the stainless steel foil is too large and the strength of the stainless steel foil is reduced. Fine stamping manufacturability and broken at the resulted unsuitable.

  From Examples 1 to 14 and Comparative Examples 1 to 8 above, the stainless steel foil of the present invention has a strong adhesive force that prevents the coating resin from being peeled even when immersed in an electrolyte solution essential for an electricity storage device, such as a chromic acid solution. Provided with resin-coated stainless steel foil for power storage device containers, which can be realized without surface treatment using chemicals, has heat resistance that does not deteriorate at all even at high temperatures such as heat sealing, is excellent in environmental impact and economy, and has few product defects It has been confirmed that it contributes to the future development of electricity storage devices.

Claims (4)

A stainless steel foil having an oxide film containing 20 mol% or more and 60 mol% or less of oxygen and containing more Cr than Fe, and on the surface of the oxide film , the arithmetic average roughness Ral in the rolling direction or the rolling direction The arithmetic average roughness Rac in the perpendicular direction is 0.1 μm or more and less than the maximum depth Rt of the surface of the oxide film, Rt is 0.8 μm or more and 50% or less of the stainless steel foil thickness, A stainless steel foil for an electricity storage device container, wherein a polyolefin resin is laminated on both sides or one side of the stainless steel foil having an oxide film thickness of 6 nm or more and less than 150 nm. The arithmetic average roughness Rals of the surface in the rolling direction of the stainless steel foil, or the arithmetic average roughness Racs on the surface perpendicular to the rolling direction of the stainless steel foil is 0.1 μm or more and the maximum depth Rts of the stainless steel foil surface. Annealing a stainless steel foil having a Rts of 0.8 μm or more and 50% or less of the thickness of the stainless steel foil in a reducing atmosphere at a temperature of 600 ° C. or more and less than 800 ° C. , both surfaces of the stainless steel foil 2. The method for producing a stainless steel foil for an electricity storage device container according to claim 1, wherein a resin composition film containing 50% by mass or more of a polyolefin resin is laminated on one surface by thermocompression bonding . The method for producing a stainless steel foil for a power storage device container according to claim 2 , wherein the annealing is performed for 0.5 minutes or more and 3 minutes or less. The electrical storage device container according to claim 2 or 3 , wherein the annealing is a heat treatment at a temperature of 600 to 800 ° C in an atmosphere having a hydrogen / water partial pressure ratio H ₂ / H ₂ O of 10 or more and a dew point of less than 40 ° C. Stainless steel foil manufacturing method.

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