Primer layer composition, secondary battery pouch film using same, and method for preparing same

Abstract

The invention discloses a preparation method of a secondary battery bag film, and the secondary battery bag film at least comprises an outer layer, a metal layer, a primer layer and a sealant layer or at least comprises the outer layer, the metal layer, the primer layer, a melt extrusion resin layer and the sealant layer according to a corresponding sequence. Comprising a drying step of applying a primer layer composition on a metal layer, heating the primer layer composition to dry the primer layer composition, and curing at least a portion of the primer layer composition, in which an organic solvent-based emulsion composition is used as the primer layer, the organic solvent-based emulsion composition comprising an acid-modified polypropylene and a curing agent, the curing initiation temperature is 150 DEG C or less, preferably 135 DEG C to 150 DEG C, and the drying step temperature is 150 DEG C or less, preferably 135 DEG C to 150 DEG C. In the method for producing the secondary battery pouch film, the thermal lamination step is not performed when the sealant layer is bonded.

Description

[0001] This application is a divisional application of a patent application with application date of November 5, 2020, application number 202011224201.1, and titled "Primer layer composition, secondary battery bag film using the composition, and preparation method thereof". Technical Field

[0002] The present invention relates to a primer layer composition, a secondary battery bag film using the same, and a method for preparing the same. Specifically, the present invention relates to a primer layer composition that improves initial peel strength, hydrofluoric acid resistance, electrolyte resistance, etc., and especially improves formability, a secondary battery bag film using the same, and a method for preparing the secondary battery bag film.

[0003] [Korean R&D project supporting this invention]

[0004] [Project number] 20007148

[0005] [Department name] Ministry of Trade, Industry and Energy

[0006] [Name of project management (specialized) organization] Korea Industrial Technology Evaluation and Management Institute

[0007] [Research Project Name] Material Component Technology Development - Material Component Packaging Type

[0008] [Research Topic Name] Performance evaluation of large and medium-sized secondary battery bags and empirical research on their application in demand enterprises

[0009] [Contribution rate] 1 / 1

[0010] [Project Execution Organization Name] Youl Chon ChemicAl Co., Ltd.

[0011] [Study period] September 1, 2019 to February 28, 2021 Background Art

[0012] Lithium secondary batteries (LiB) are suitable for many applications due to their various advantages such as high energy density and excellent output.

[0013] A secondary battery pouch is an outer material that covers the electrode group and electrolyte of such a secondary battery and needs to satisfy necessary properties such as adhesion between layers formed by metal film and polymer, thermal welding strength, electrolyte resistance, airtightness, moisture permeability, and formability.

[0014] Secondary battery bags are generally composed of an outer layer, a barrier layer, and an inner sealant layer. Usually, the outer layer or the outermost layer is composed of nylon or a mixture of nylon and polyethylene terephthalate (PET), oriented polypropylene (OPP), polyethylene, etc. This outer layer or the outermost layer is required to have properties such as heat resistance, pinhole resistance, chemical resistance, formability, and insulation.

[0015] The barrier layer is required to have barrier properties against water vapor or other gases and formability. In this regard, formable metals such as aluminum (Al), iron (Fe), copper (Cu), nickel (Ni), etc. are used in the barrier layer, and aluminum is currently the most commonly used.

[0016] The inner sealant layer is required to have thermal adhesiveness and moldability and to have electrolyte resistance and insulation resistance in view of being in contact with the electrolyte.

[0017] In particular, as the application fields of lithium-ion batteries expand from small fields to large and medium-sized fields such as automobiles, they are required to have characteristics suitable for large and medium-sized fields, such as hydrofluoric acid resistance, electrolyte resistance, and moldability. Summary of the invention

[0018] In an exemplary implementation of the present invention, on the one hand, there is provided a primer layer composition that improves initial peel strength, hydrofluoric acid resistance, electrolyte resistance, etc., while especially improving formability, a secondary battery bag film using the primer layer composition, and a method for preparing the above-mentioned secondary battery bag film.

[0019] In an exemplary implementation example of the present invention, a method for preparing a secondary battery bag film is provided, wherein the secondary battery bag film comprises at least an outer layer, a metal layer, a primer layer, and a sealant layer in corresponding order, or at least comprises an outer layer, a metal layer, a primer layer, a melt-extruded resin layer, and a sealant layer. The method for preparing the secondary battery bag film is characterized in that it comprises a drying process of applying a primer layer composition on the metal layer and heating to dry the primer layer composition and curing at least a portion of the primer layer composition, an organic solvent-based emulsion composition is used as the primer layer, the organic solvent-based emulsion composition comprises acid-modified polypropylene and a curing agent, the curing starting temperature is below 150°C, preferably 135°C to 150°C, the drying process temperature is below 150°C, preferably 135°C to 150°C, and in the method for preparing the secondary battery bag film, when the sealant layer is attached, a heat lamination process is not performed.

[0020] In an exemplary implementation example of the present invention, a method for improving the formability of a secondary battery bag film is provided, wherein the secondary battery bag film comprises at least an outer layer, a metal layer, a primer layer, and a sealant layer, or at least an outer layer, a metal layer, a primer layer, a melt-extruded resin layer, and a sealant layer in corresponding order, and the method for improving the formability of the secondary battery bag film is characterized in that it comprises a drying process of applying a primer layer composition on the metal layer and heating to dry the primer layer composition and curing at least a portion of the primer layer composition, an organic solvent-based emulsion composition is used as the primer layer, the organic solvent-based emulsion composition comprises an acid-modified polypropylene and a curing agent, the curing starting temperature is below 150°C, preferably 135°C to 150°C, the drying process temperature is below 150°C, preferably 135°C to 150°C, and in the preparation method, when the sealant layer is attached, a heat lamination process is not performed.

[0021] In an exemplary implementation example of the present invention, a primer layer composition for a secondary battery bag film is also provided, which is used in the preparation method of the above-mentioned secondary battery bag film and is sandwiched between the metal layer and the melt-extruded resin layer or the sealant layer of the secondary battery bag film, characterized in that the above-mentioned primer layer composition is formed by an organic solvent-type emulsion composition, and the above-mentioned organic solvent-type emulsion composition contains acid-modified polypropylene and a curing agent, the curing starting temperature is below 150°C, preferably 135°C to 150°C, and the drying process temperature is below 150°C, preferably dried at 135°C to 150°C.

[0022] In an exemplary implementation example of the present invention, a secondary battery bag film is also provided, as the above-mentioned secondary battery bag film includes a primer layer sandwiched between a metal layer and a melt-extruded resin layer or a sealant layer, characterized in that the above-mentioned primer layer is formed by an organic solvent-type emulsion composition, and the above-mentioned organic solvent-type emulsion composition contains acid-modified polypropylene and a curing agent, and the curing starting temperature is below 150°C, preferably 135°C to 150°C, and the drying process temperature is below 150°C, preferably 135°C to 150°C.

[0023] In addition, in an exemplary implementation example of the present invention, a secondary battery bag film is also provided, which includes a primer layer sandwiched between a metal layer and a melt-extruded resin layer or a sealant layer, and has a moldability of more than 6.5 mm, an initial peel strength of more than 14.0 N / 15 mm, a hydrofluoric acid resistance of more than 5.0 N / 15 mm, and an electrolyte resistance of more than 90% of the above-mentioned initial peel strength.

[0024] In an exemplary implementation of the present invention, when preparing a secondary battery bag film, a primer layer composition is sandwiched between a metal layer and a melt-extruded resin layer or a sealant layer, and a two-component curing composition-type organic solvent-type emulsion composition comprising an acid-modified polypropylene and a curing agent is used. The curing starting temperature and the drying process temperature are adjusted, and no heat lamination is performed, thereby achieving the effect of improving initial peel strength, hydrofluoric acid resistance, electrolyte resistance, etc. while achieving particularly excellent formability.

[0025] This application also involves the following technical solutions:

[0026] 1. A method for preparing a secondary battery bag film, wherein the secondary battery bag film comprises at least an outer layer, a metal layer, a primer layer, and a sealant layer in the corresponding order, or at least an outer layer, a metal layer, a primer layer, a melt-extruded resin layer, and a sealant layer, wherein the method for preparing the secondary battery bag film is characterized in that:

[0027] The method comprises a drying step of applying a primer layer composition on a metal layer and heating to dry the primer layer composition and curing at least a portion of the primer layer composition.

[0028] Using an organic solvent type emulsion composition as the above primer layer,

[0029] The organic solvent type emulsion composition comprises acid-modified polypropylene and a curing agent, wherein the curing starting temperature is below 150° C., the drying process temperature is below 150° C.,

[0030] In the method for producing the secondary battery pouch film, when the sealant layer is attached, a heat lamination process is not performed.

[0031] 2. The method for preparing a secondary battery pouch film according to item 1, characterized in that the curing starting temperature is 135°C to 150°C.

[0032] 3. The method for preparing a secondary battery pouch film according to item 2, characterized in that the drying process temperature is 135°C to 150°C.

[0033] 4. The method for preparing a secondary battery pouch film according to item 1, characterized in that the organic solvent-based emulsion composition is a two-component curable composition.

[0034] 5. The method for preparing a secondary battery pouch film according to item 4 is characterized in that the curing agent of the above-mentioned two-component curable composition-type organic solvent-type emulsion composition is an epoxy curing agent.

[0035] 6. The method for preparing a secondary battery bag film according to item 5 is characterized in that the above-mentioned two-component curable composition-type organic solvent-type emulsion composition contains acid-modified polypropylene as the main agent part, and contains epoxy curing agent and ether polymer as the curing agent part.

[0036] 7. The method for preparing a secondary battery pouch film according to item 1, characterized in that the organic solvent-based emulsion composition further comprises a catalyst for adjusting the curing starting temperature.

[0037] 8. The method for preparing a secondary battery pouch film according to item 1 is characterized in that, when the above-mentioned drying process is performed, the area of ​​the drying process is divided into multiple areas, and the set temperature of the non-end area between the first area and the last area is set to be higher than the set temperature of the first area and the set temperature of the last area.

[0038] 9. The method for preparing a secondary battery pouch film according to item 1, characterized in that, in the method for preparing a secondary battery pouch film, when the sealant layer is attached, an aging process is performed at room temperature.

[0039] 10. A method for improving the formability of a secondary battery bag film, the secondary battery bag film comprising at least an outer layer, a metal layer, a primer layer, and a sealant layer in the corresponding order, or at least an outer layer, a metal layer, a primer layer, a melt-extruded resin layer, and a sealant layer, the method for improving the formability of the secondary battery bag film being characterized in that:

[0040] The method comprises a drying step of applying a primer layer composition on a metal layer and heating to dry the primer layer composition and curing at least a portion of the primer layer composition.

[0041] Using a two-component curable composition type organic solvent type emulsion composition as the above-mentioned primer layer,

[0042] The organic solvent type emulsion composition comprises acid-modified polypropylene and a curing agent, wherein the curing starting temperature is 135° C. to 150° C., and the drying process temperature is 135° C. to 150° C.

[0043] In the method for preparing the secondary battery bag film, when the sealant layer is attached, no heat lamination step is performed.

[0044] In the method for preparing the secondary battery pouch film, when the sealant layer is attached, an aging process is performed at room temperature.

[0045] 11. A secondary battery pouch film prepared by the method for preparing a secondary battery pouch film according to item 1, comprising a primer layer sandwiched between a metal layer and a melt-extruded resin layer or a sealant layer, characterized in that:

[0046] Formability is 6.5mm or more,

[0047] The initial peel strength is above 14.0N / 15mm.

[0048] The hydrofluoric acid resistance is above 5.0N / 15mm.

[0049] The electrolyte resistance is more than 90% of the initial peel strength.

[0050] 12. The secondary battery pouch film according to item 11, characterized in that:

[0051] The initial peel strength of the secondary battery pouch film is 14.0N / 15mm or more.

[0052] The electrolyte resistance strength is 14.0N / 15mm or more.

[0053] The hydrofluoric acid resistance is above 5.0N / 15mm.

[0054] The puncture strength is 21.0N or more.

[0055] 13. The secondary battery pouch film according to item 12, characterized in that:

[0056] The moldability of the secondary battery bag film is 6.5 to 6.8 mm.

[0057] The initial peel strength is 14.0~15.0N / 15mm,

[0058] The electrolyte resistance strength is 14.0~14.5N / 15mm,

[0059] The hydrofluoric acid resistance is 6.0~6.4N / 15mm.

[0060] The puncture strength is 21.0~23.0N.

[0061] 14. The secondary battery pouch film according to item 11, characterized in that:

[0062] The secondary battery bag film is composed of a substrate layer, a metal layer, an anticorrosion layer formed on at least one side of the metal layer, a primer layer formed on the inner side of the metal layer, a polypropylene extrusion layer as a melt extruded resin layer, and an unstretched polypropylene (CPP) layer as a sealant layer.

[0063] The substrate layer is formed of one or more of a polyester film and a polyimide film.

[0064] The metal layer is formed of aluminum. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 FIG. 1 is a schematic diagram showing a secondary battery pouch film structure according to an exemplary implementation example of the present invention. DETAILED DESCRIPTION

[0066] Definition of terms

[0067] In this specification, when it is described that the layers of the secondary battery pouch film are sequentially included, this means that it is not necessarily constituted of only the corresponding layers but may include additional layers.

[0068] In this specification, when it is described as being formed “on the metal layer”, this includes not only the case where it is directly formed on the metal layer, but also the case where it is formed with another layer such as an anti-corrosion layer interposed therebetween.

[0069] In this specification, the curing initiation temperature refers to the temperature at which the curing reaction starts.

[0070] In this specification, the drying process refers to a process of evaporating the solvent of the emulsion composition used as the primer layer and promoting the curing reaction of the emulsion composition of the primer layer. Since this drying process is a process performed before laminating the sealant layer, it is distinguished from the heat lamination process.

[0071] In this specification, the drying process temperature refers to the temperature in the process of evaporating the solvent of the emulsion composition used as the primer layer and promoting the curing reaction of the emulsion composition of the primer layer, and is the maximum set temperature of such temperature.

[0072] In this specification, the heat lamination process refers to a process of laminating by heating in order to further promote the curing reaction of the emulsion composition of the primer layer when a primer layer is formed on a metal layer and then laminated with a sealant layer, or when a primer layer and a melt-extruded resin layer are formed on a metal layer and then laminated with a sealant layer.

[0073] In the present specification, when it is described that the sealant layer is attached (laminated) without performing a heat lamination process, this means that lamination is performed by applying only pressure without applying heat.

[0074] In this specification, moldability refers to a molding depth at which 10 or more test pieces are not broken when a test piece prepared from a secondary battery pouch film is molded using a mold. A moldability of 6.5 mm or more is considered to be excellent.

[0075] In this specification, the method for improving the formability of a secondary battery pouch film refers to a method for achieving properties such as initial peel strength, hydrofluoric acid resistance, and electrolyte resistance above the required level and improving the formability to 6.5 mm or more.

[0076] The appropriate electrolyte resistance strength needs to have a strength ratio of 90% or more relative to the initial peel strength, and the hydrofluoric acid resistance strength needs to be 5N / 15mm or more. Since the electrolyte resistance strength and hydrofluoric acid resistance strength are greatly affected by the initial peel strength, the appropriate initial peel strength should be 14N / 15mm or more.

[0077] Description of Exemplary Implementations

[0078] Hereinafter, exemplary implementation examples of the present invention are described in detail.

[0079] Figure 1 FIG. 1 is a schematic diagram showing a secondary battery pouch film structure according to an exemplary implementation example of the present invention.

[0080] like Figure 1 As shown, the secondary battery bag film of the exemplary implementation example of the present invention is a secondary battery bag film including at least an outer layer, a metal layer, a primer layer, and a sealant layer in corresponding order, or at least an outer layer, a metal layer, a primer layer, a melt-extruded resin layer, and a sealant layer.

[0081] The organic solvent emulsion used for the primer layer can be formed on the metal layer in a liquid state through a separate coating process. In this process, two process steps are generally performed to improve the adhesion and close contact between the metal layer and the sealant layer (or the melt-extruded resin layer and the sealant layer in the case where a melt-extruded resin layer is interposed).

[0082] First, in the first process step, the liquid agent used as the emulsion solvent is evaporated and a drying process is performed to promote the curing reaction. The second process step is divided into a heat lamination process in which lamination is performed by heating when the sealant layer is attached or when the sealant layer is attached after the melt-extruded resin layer is formed in order to once again promote the curing reaction of the primer layer composition.

[0083] Since the heat lamination process directly provides high temperature to the secondary battery bag, a large amount of heat can be transferred, and thus this process is very useful in promoting the curing reaction of the emulsion. However, the inventors have confirmed that in the heat lamination process, since the secondary battery bag is directly exposed to high temperature, the sliding property of the sealant layer is reduced, and thus the moldability may be reduced.

[0084] To this end, in an exemplary implementation of the present invention, a method for preparing a secondary battery bag film or a method for improving the formability of a secondary battery bag film is provided, wherein the secondary battery bag film includes at least an outer layer, a metal layer, a primer layer, a sealant layer or at least an outer layer, a metal layer, a primer layer, a melt-extruded resin layer, and a sealant layer in the corresponding order, and only a drying process is performed without the above-mentioned heat lamination process. In addition, a primer layer composition sandwiched between the metal layer and the melt-extruded resin layer or the metal layer and the sealant layer of the secondary battery bag film is formed by a two-component curing organic solvent-type emulsion composition, for example, containing acid-modified polypropylene and a curing agent. In addition, the curing start temperature and the drying process temperature are adjusted. As a result, it is possible to have excellent initial peel strength, hydrofluoric acid resistance, electrolyte resistance, etc., and at the same time have particularly excellent formability.

[0085] First, the organic solvent type emulsion composition is described. Emulsions can be roughly divided into water-based type and organic solvent type. For example, when water is used as a solvent for an emulsion containing acid-modified polypropylene and various polymers, it is called a water-based type, and when an organic solvent (cyclohexane (CH), ethyl acetate (EA), toluene (TOL), etc.) is used as an emulsion solvent, it is called an organic solvent type.

[0086] In an exemplary embodiment of the present invention, an organic solvent emulsion composition, preferably a two-component curing composition, is used as the primer layer. The two-component curing composition is composed of, for example, a first solution (main agent part) formed by dissolving acid-modified polypropylene in an organic solvent and a second solution (curing agent part) formed by dissolving a curing agent in an organic solvent.

[0087] By compounding the organic solvent emulsion composed of such a two-component curing type, the metal layer and the sealant layer are bonded, or preferably, the melt-extruded polypropylene layer and the metal layer are bonded.

[0088] If the above-mentioned organic solvent emulsion layer is formed between the metal layer and the sealant layer or preferably between the melt-extruded polypropylene layer and the metal layer, preferably a two-component curing organic solvent emulsion layer is formed and dried and adjusted to cure, then the inner sealant layer and the metal layer of the secondary battery bag film can be given adhesion, the hydrofluoric acid resistance and electrolyte resistance can be improved, and as mentioned above, the formability can also be improved.

[0089] For reference, when a water-based emulsion is used to form a primer layer, the process temperature can be set to a relatively low temperature (about 100°C), but there is a disadvantage of weak hydrofluoric acid resistance. On the contrary, when an organic solvent-based emulsion is used, hydrofluoric acid resistance is very excellent, but in order to promote the reaction in the emulsion, the process temperature needs to be set to a high temperature (above 150°C) or an additional hot lamination process is required. As the process temperature increases, the sliding properties of the sealant layer and the outer layer decrease, and thus there is a disadvantage of decreased moldability.

[0090] In an exemplary implementation, the two-component curing type can be classified according to the type of curing agent, and various types can be used, such as amines, anhydrides, polyamides, etc.

[0091] In an exemplary implementation example, the acid-modified polypropylene can be modified with various acid anhydrides such as acetic anhydride, glutaric anhydride, benzoic anhydride, phthalic anhydride and maleic anhydride.

[0092] In an exemplary implementation example, the above-mentioned curing agent can be an epoxy, acrolein (acrylic), or urethane (urethane) curing agent. Preferably, a two-component curing type using an epoxy curing agent can be used to improve electrolyte resistance and hydrofluoric acid resistance.

[0093] The epoxy two-component curing type can undergo a curing reaction with carboxylic acid and anhydride, and can achieve bonding between the metal layer and the sealant layer by undergoing a curing reaction. For reference, anhydride and epoxy curing agents can usually start a curing reaction at a high temperature above 200°C (i.e., the curing starting temperature is 200°C). Due to the high starting temperature, a catalyst is required to lower the starting temperature.

[0094] In an exemplary implementation example, for example, as a two-component curable organic solvent-based emulsion, a first solution (main agent part) and a second solution (curing agent part) can be used, the first solution is formed by dissolving a main agent substance containing additives in an organic solvent, the additives include acid-modified polypropylene, ammonium salt, 2,5-fulacone, etc., and the second solution is formed by dissolving a curing agent substance containing an epoxy curing agent, an ether polymer (which may also contain other additives) in an organic solvent, but is not limited to this.

[0095] For reference, in the above-mentioned first solution, the acid-modified polypropylene plays a role in improving the bonding strength between the polypropylene and the bonded sealant layer or the melt-extruded resin layer by adhering closely to the metal surface, and other additives can play a role in improving the chemical stability of the emulsion.

[0096] On the other hand, in the second solution, the ether polymerization agent can react with the emulsion close to the metal surface to form a chemical bond between the metal surface / emulsion / polypropylene layer (polypropylene layer of the sealant layer or the polypropylene layer of the melt-extruded resin layer), thereby achieving adhesion. In addition, it can improve the stability of the second solution and the high temperature stability and hydrofluoric acid resistance after the curing reaction. As the ether polymer, bisphenol A-bisphenol A diglycidyl ether polymer can be used, which can be used as a derivative that induces epoxy bonding.

[0097] On the other hand, in an exemplary implementation example, the curing start temperature is set to 150°C or lower, preferably 135-150°C.

[0098] Only when the curing initiation temperature is as described above, the drying process temperature can be finally lowered, and the properties such as hydrofluoric acid resistance, electrolyte resistance, and moldability can be improved.

[0099] That is, in order to bond the metal layer and the sealant layer, the curing reaction of the binder constituting the primer layer must be fully performed. In addition, since the primer layer plays a very important role in determining hydrofluoric acid resistance and electrolyte resistance, it must have excellent thermal properties and be chemically stable. Thermosetting resins are generally used because they meet these properties.

[0100] However, if the curing starting temperature at which the curing reaction can start is high and the curing reaction does not proceed sufficiently, the adhesiveness will decrease, and thus the hydrofluoric acid resistance and electrolyte resistance will also be affected. For this reason, when the above-mentioned high-temperature heat lamination process is performed, there is a fundamental disadvantage that the moldability of the secondary battery bag film decreases due to the high-temperature heat lamination process.

[0101] That is, during the high-temperature heat lamination process, the sliding properties of the outer layer and the sealant layer of the secondary battery pouch film decrease, which may lead to a decrease in formability. In addition, due to the high-temperature heat lamination process, the hardness of the adhesive layer and the primer layer present in the outer layer may increase, but as the hardness increases, the elasticity of the secondary battery pouch film decreases, which may lead to a decrease in formability.

[0102] Therefore, it is advantageous to lower the starting temperature to sufficiently carry out the curing reaction at a low process temperature, and in this regard, to make the curing starting temperature 150°C or less or 135 to 150°C.

[0103] Among them, the starting temperature can be adjusted by adding a catalyst, but it is difficult to reduce it significantly. The catalyst that reduces the activation energy to make the chemical reaction easier to occur is a substance that does not participate in the reaction. Even if the amount added increases, it is not proportional to the amount of activation energy reduction. In addition, since the catalyst does not participate in the reaction and it remains, using a large amount will have an adverse effect on the physical properties. Therefore, there is a limit to reducing the starting temperature. It is difficult to reduce the starting temperature to below 135°C.

[0104] In an exemplary implementation example, as a catalyst for lowering the starting temperature and promoting the curing reaction, tertiary amines (trimethylamine, triethylamine, N, N-dimethylpropylamine, etc.) or imidazoles can be used. In particular, tertiary amines play a role in promoting the reaction between anhydrides and epoxides for improving the adhesion to metals. Tertiary amines can be produced by reacting with secondary amines and epoxides, and the tertiary amines thus produced can act as catalysts.

[0105] On the other hand, the drying process temperature is set to 100° C. to 150° C., preferably 135° C. to 150° C. If the drying process temperature exceeds 150° C., the moldability is reduced as described in the experimental examples described later.

[0106] That is, when the drying process temperature is high, the bonding strength can be improved by promoting the curing reaction of the two-component curing type adhesive, but the sliding property of the outer layer and the sealant layer may be reduced, resulting in a decrease in formability. On the other hand, when the drying process temperature is low, the curing reaction of the two-component curing type adhesive may not be fully carried out. In order to solve this problem, as described above, if another high-temperature heat lamination process is further performed, the sliding property and formability may be reduced in this process.

[0107] In an exemplary implementation example, in the drying process of the emulsion, it is preferable to set the temperature so as to be gradually increased and decreased by dividing the drying process into zones in terms of moldability.

[0108] For example, in the above-mentioned drying process, in terms of formability, it is preferred to divide the drying process area into multiple areas, and set the set temperature of the non-end area between the first end area and the last end area to be higher than the set temperature of the first end area and the set temperature of the last end area.

[0109] In a non-limiting example, the drying process area can be divided into at least 3 areas and at most 15 areas, and the temperature of each area is set, and the temperature of the middle area is set to be the highest. The drying process temperature becomes the highest temperature among the set temperatures of each area.

[0110] In an exemplary implementation example, when considering initial peel strength, electrolyte resistance, hydrofluoric acid resistance, puncture strength and at the same time moldability, it is most preferred that the starting temperature of the above-mentioned curing reaction is 135-150°C and the drying process temperature is 135-150°C.

[0111] In an exemplary implementation, in the method for preparing the secondary battery pouch film, when the sealant layer is attached after the drying process, an aging process may be performed at room temperature to help complete the curing of the primer layer emulsion composition.

[0112] On the other hand, in an exemplary implementation example of the present invention, a primer layer composition for a secondary battery bag film is provided, characterized in that, as a primer layer composition used in the preparation method of the above-mentioned secondary battery bag film and sandwiched between the metal layer and the melt-extruded resin layer or the sealant layer of the secondary battery bag film, the above-mentioned primer layer composition is formed by an organic solvent-type emulsion composition, and the above-mentioned organic solvent-type emulsion composition is a two-component curing composition comprising acid-modified polypropylene and a curing agent, the curing starting temperature is below 150°C, and it is dried below 150°C.

[0113] In addition, in an exemplary implementation example of the present invention, a secondary battery pouch film is also provided, which is a secondary battery pouch film prepared by the above-mentioned secondary battery pouch film preparation method, including a primer layer sandwiched between a metal layer and a melt-extruded resin layer or a sealant layer, and has a formability of more than 6.5 mm, an initial peel strength of more than 14.0 N / 15 mm, a hydrofluoric acid resistance of more than 5.0 N / 15 mm, and an electrolyte resistance of more than 90% of the initial peel strength.

[0114] In an exemplary implementation example, the initial peel strength can be greater than 14.0N / 15mm, the electrolyte resistance can be greater than 14.0N / 15mm, the hydrofluoric acid resistance can be greater than 5.0N / 15mm, and the puncture strength can be greater than 21.0N.

[0115] In an exemplary implementation example, the formability can be 6.5-6.8 mm, the initial peel strength can be 14.0-15.0 N / 15 mm, the electrolyte resistance can be 14.0-14.5 N / 15 mm, the hydrofluoric acid resistance can be 6.0-6.4 N / 15 mm, and the puncture strength can be 21.0-23.0 N.

[0116] Refer again Figure 1 In an exemplary implementation example, the secondary battery bag film may be composed of a substrate layer, a metal layer, an anti-corrosion layer (acid-resistant coating layer) formed on at least one side of the metal layer, a primer layer formed on the inner side of the metal layer, a polypropylene extrusion layer as a melt-extruded resin layer, and an unstretched polypropylene (CPP) layer as a sealant layer.

[0117] The substrate layer may be formed of one or more of a polyester film and a polyimide film. For example, the outermost layer may be formed of a polyethylene terephthalate (PET) film, and the inner layer may be formed of a nylon film. The polyethylene terephthalate film and the nylon film may be bonded by a first bonding layer by solvent dry lamination (SDL). The nylon film and the metal layer may be bonded by a second bonding layer by solvent dry lamination (SDL).

[0118] The metal layer may be formed of aluminum which is typically used, thereby forming a chromate-based or non-chromate-based aluminum anticorrosion layer as the anticorrosion layer.

[0119] The unstretched polypropylene layer of the sealant layer may be formed into multiple layers, for example, three layers.

[0120] The exemplary implementation examples of the present invention will be described in more detail by the following examples. The embodiments disclosed in this specification are illustrated for illustrative purposes only, and the embodiments of the present invention can be implemented in various forms and should not be construed as being limited to the embodiments described in this specification.

[0121] Experiment 1: Comparative experiment based on the difference in curing reaction starting temperature and drying process temperature

[0122] like Figure 1As shown, when preparing a secondary battery bag, the base material layer (polyethylene terephthalate / nylon) and the Al metal layer formed with the Al anti-corrosion layer are first bonded, and then as the last step, the fabric bonded with the base material layer and the metal layer (Al metal layer formed with the Al anti-corrosion layer) and the sealant layer (CPP film) are bonded together. When bonding the sealant layer, in order to form a primer layer on the metal layer, the sealant layer is attached after the emulsion coating and drying process to prepare the secondary battery bag film. On the other hand, when attaching the sealant layer, a melt extrusion resin layer can also be further formed by extruding polypropylene.

[0123] As described above, in the emulsion drying process, the temperature is set to gradually increase and decrease by dividing the area, and the area can be divided into at least 3 areas and at most 15 areas and the temperature of each area can be set. In this experiment 1, the area is divided into 10 areas by way of example. The temperature of the middle area is set to the highest, and the process temperature represents the highest temperature among the set temperatures.

[0124] The two-component organic solvent emulsion for the primer layer of the secondary battery pouch film is made based on bisphenol A-type epoxy. The most representative characteristics of the epoxy type are excellent adhesion, chemical resistance, and high temperature characteristics.

[0125] The first solution (main agent part) prepared by dissolving a main agent substance containing acid-modified polypropylene in an organic solvent as described above and the second solution (curing agent part) prepared by dissolving a curing agent substance containing an epoxy curing agent or an ether polymer in an organic solvent can be used, but are not limited thereto.

[0126] As described above, as a catalyst for lowering the curing reaction starting temperature (hereinafter, starting temperature) and accelerating the curing reaction, a tertiary amine or imidazole can be generally used. In this Experiment 1, a tertiary amine was exemplarily used.

[0127] The comparative examples and embodiments are summarized below.

[0128] (Comparative Example 1) A secondary battery pouch film was prepared by setting the drying process temperature of a two-component solvent emulsion having a starting temperature of 175 to 190° C. to 100° C.

[0129] (Comparative Example 2) A secondary battery pouch film was prepared by setting the drying process temperature of a two-component solvent emulsion having a starting temperature of 175 to 190°C to 120°C.

[0130] (Comparative Example 3) A secondary battery pouch film was prepared by setting the drying process temperature of a two-component solvent emulsion having a starting temperature of 175 to 190°C to 135°C.

[0131] (Comparative Example 4) A secondary battery pouch film was prepared by setting the drying process temperature of a two-component solvent emulsion having a starting temperature of 175 to 190°C to 150°C.

[0132] (Comparative Example 5) A secondary battery pouch film was prepared by setting the drying process temperature of a two-component solvent emulsion having a starting temperature of 175 to 190°C to 165°C.

[0133] (Comparative Example 6) A secondary battery pouch film was prepared by setting the drying process temperature of a two-component solvent emulsion having a starting temperature of 175 to 190°C to 180°C.

[0134] (Comparative Example 7) A secondary battery pouch film was prepared by setting the drying process temperature of a two-component solvent emulsion having a starting temperature of 175 to 190° C. to 200° C.

[0135] (Example 1) A secondary battery pouch film was prepared by setting the process temperature of a two-component solvent emulsion whose starting temperature was lowered to 135 to 150°C to 100°C.

[0136] (Example 2) A secondary battery pouch film was prepared by setting the process temperature of a two-component solvent emulsion whose starting temperature was lowered to 135-150°C to 120°C.

[0137] (Example 3) A secondary battery pouch film was prepared by setting the process temperature of a two-component solvent emulsion whose starting temperature was lowered to 135-150°C to 135°C.

[0138] (Example 4) A secondary battery pouch film was prepared by setting the process temperature of a two-component solvent emulsion whose starting temperature was lowered to 135-150°C to 150°C.

[0139] (Comparative Example 8) A secondary battery pouch film was prepared by setting the process temperature of a two-component solvent emulsion whose starting temperature was lowered to 135 to 150°C to 165°C.

[0140] (Comparative Example 9) A secondary battery pouch film was prepared by setting the process temperature of a two-component solvent emulsion whose starting temperature was lowered to 135 to 150°C to 180°C.

[0141] (Comparative Example 10) A secondary battery pouch film was prepared by setting the process temperature of a two-component solvent emulsion whose starting temperature was lowered to 135 to 150°C to 200°C.

[0142] Table 1

[0143]

[0144] Characteristics evaluation

[0145] Initial peel strength evaluation

[0146] (1) A secondary battery pouch film was cut into pieces having a width of 1.5 cm and a length of 15 cm to prepare test pieces.

[0147] (2) The peel strength was measured by peeling the metal layer and the sealant layer.

[0148] Hydrofluoric acid resistance evaluation

[0149] (1) A secondary battery pouch film was cut into pieces with a width of 10 cm and a length of 20 cm and both sides were thermally bonded.

[0150] (2) A prepared solution (electrolyte solution + water (water concentration in the solution was 10000 ppm (about 1%))) was put into the secondary battery bag with both sides bonded, and thermal bonding was performed to prepare a package.

[0151] (3) Stored at high temperature (85°C) for 24 hours.

[0152] (4) The electrolyte in the package was discarded, and a test piece (1.5 cm in width and 15 cm in length) was prepared in the same manner as in the above-mentioned initial peel strength evaluation.

[0153] (5) The peel strength between the metal layer and the sealant layer was measured.

[0154] Evaluation of electrolyte resistance

[0155] (1) A secondary battery pouch film was cut into pieces having a width of 1.5 cm and a length of 15 cm to prepare test pieces.

[0156] (2) The prepared test piece was immersed in a standard electrolyte (1.0 M LiPF6 (EC / DEC / EMC: 1 / 1 / 1) and stored at high temperature (85°C) for 24 hours.

[0157] (3) After washing the electrolyte, the peel strength was measured by peeling the metal layer and the sealant layer.

[0158] Formability evaluation

[0159] (1) The prepared secondary battery pouch films were cut into a size of 15 cm×15 cm to prepare test pieces.

[0160] (2) Each sample was molded using a test mold (3 cm×4 cm in size) of Youl Chon Chemical Co., Ltd., Korea.

[0161] (3) Repeat the molding evaluation while changing the molding depth setting until at least 10 test pieces are free of damage.

[0162] (4) The depth of the molded parts without cracking more than 10 times was measured.

[0163] Puncture strength evaluation

[0164] (1) A test piece of a secondary battery pouch film having a width of 35 mm and a length of 600 mm was prepared.

[0165] (2) The puncture strength was measured at intervals of approximately 40 mm from the outer layer toward the inner layer.

[0166] (3) Measure the intensity 10 times and record the average value.

[0167] For reference, in the above case, the higher the moldability, the wider the molding process range can be when preparing the battery. Compared with the initial peel strength, the appropriate electrolyte resistance strength should have a strength of more than 90%, and the hydrofluoric acid resistance strength should be more than 5N / 15mm. Since the electrolyte resistance strength and hydrofluoric acid resistance strength are greatly affected by the initial peel strength, the appropriate initial peel strength should be more than 14N / 15mm.

[0168] Table 2 below shows the physical property evaluation according to the curing start temperature and the drying process temperature.

[0169] Table 2

[0170]

[0171]

[0172] As can be seen from the table above, when an emulsion with a starting temperature as high as 175-190°C (Comparative Examples 1, 2, 3, and 4) is used, the initial peel strength is very low, below 10 N, when the drying process temperature is below 150°C. Due to the low initial peel strength, when evaluating the electrolyte resistance and hydrofluoric acid resistance, the sealant layer and the metal layer were completely separated.

[0173] When the drying process temperature was 165-200°C (Comparative Examples 5, 6, and 7), the initial peel strength, electrolyte resistance strength, and hydrofluoric acid resistance strength were excellent, but the puncture strength increased to more than 24 N. Furthermore, the moldability did not reach 6.5 mm.

[0174] When an emulsion with a starting temperature lowered to 135-150°C was used, the initial peel strength was 10N / 15mm or less only when the drying process temperature was 100°C (Example 1), and the initial peel strength was 12N / 15mm or more under the drying process conditions of 120°C or more (Examples and Comparative Examples 8-10). It was confirmed that by lowering the starting temperature, the adhesion was improved even at a low drying process temperature.

[0175] However, under the condition of 120°C (Example 2), the hydrofluoric acid resistance did not reach 5N / 15mm. Under the condition of above 135°C (Examples 3 to 4, Comparative Examples 8 to 10), the initial peel strength, electrolyte resistance and hydrofluoric acid resistance were all excellent.

[0176] As in Comparative Examples 1 to 7, under the conditions of 165 to 200° C. (Comparative Examples 8 to 10), the puncture strength increased and the moldability did not reach 6.5 mm.

[0177] Under the condition of 135 to 150°C (Examples 3 and 4), although the puncture strength increased to 20N or more, the moldability was 6.5 mm or more, showing the best results.

[0178] Therefore, only under the drying process temperature condition corresponding to the starting temperature, all physical properties of initial peel strength, electrolyte resistance strength, and hydrofluoric acid resistance strength show appropriate physical properties. From the experimental examples, it can be seen that when the temperature exceeds 150°C, especially when the drying process temperature is above 165°C, the puncture strength of the secondary battery pouch film is greatly improved, which is accompanied by a decrease in formability.

[0179] Therefore, in order to ideally achieve all physical properties, it is preferred that the drying process temperature be lowered to 150° C. or lower. To this end, it is preferred that the starting temperature of the solvent-based emulsion be lowered to 150° C. or lower.

[0180] The above describes the non-limiting and exemplary embodiments of the present invention, but the technical concept of the present invention is not limited to the drawings or the above description. Various forms of deformation can be made without departing from the scope of the technical concept of the present invention, which is obvious to a person skilled in the art of the present invention, and such deformation belongs to the scope of the claims of the present invention.

Claims

1. Secondary battery bag film, including: A primer layer between the metal layer and the melt extruded resin layer or sealant layer, The secondary battery bag film has a moldability of 6.5 mm or more. The initial peel strength of the secondary battery pouch film is greater than 14.0 N / 15 mm.

2. The secondary battery pouch film according to claim 1, The hydrofluoric acid resistance of the secondary battery pouch film is 5.0 N / 15 mm or more, and The electrolyte resistance of the secondary battery pouch film is equal to or higher than 90% of the initial peel strength.

3. The secondary battery pouch film according to claim 2, The electrolyte resistance strength is 14.0 N / 15 mm or more.

4. The secondary battery pouch film according to claim 2, wherein the formability is 6.5 mm to 6.8 mm, The initial peel strength is 14.0 N / 15 mm to 15.0 N / 15 mm. The electrolyte resistance strength is 14.0N / 15mm to 14.5N / 15mm. The hydrofluoric acid resistance is 6.0 N / 15 mm to 6.4 N / 15 mm.

5. The secondary battery pouch film according to claim 2, The puncture strength of the secondary battery pouch film is 21.0N to 23.0N.

6. The secondary battery pouch film according to claim 1, The secondary battery pouch film includes a substrate layer, a metal layer, a primer layer, a sealant layer, or a melt-extruded resin layer and a sealant layer in corresponding order.

7. The secondary battery pouch film according to claim 6, in, The secondary battery pouch film is configured to include the base material layer, the metal layer, the anticorrosion layer formed on at least one side of the metal layer, the primer layer formed inside the metal layer, a polypropylene extrusion layer as the melt-extruded resin layer, and an unstretched polypropylene (CPP) layer as the sealant layer.

8. The secondary battery pouch film according to claim 7, in, The substrate layer is at least one of a polyester film and a polyimide film, and Wherein, the metal layer is made of aluminum.

9. The secondary battery pouch film according to claim 6, in, The secondary battery pouch film comprises, in order, the substrate layer, which includes a polyester film and a nylon film; an anticorrosion layer; the metal layer; an anticorrosion layer; the primer layer; the melt extrusion resin layer; and the sealant layer.

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