Adhesives, aluminum-plastic films and lithium batteries

Abstract

The present invention provides an adhesive, an aluminum-plastic film, and a lithium battery. The adhesive comprises an acid-modified ethylene-propylene copolymer resin and an acid-modified ethylene-octene copolymer resin, wherein the acid comprises at least one of a carboxylic acid and an acid anhydride. The adhesive not only has high bonding strength, good heat resistance, and strong resistance to electrolyte corrosion, but also does not produce viscosity increase or gelation during long-term storage, maintaining a good and long pot life. The aluminum-plastic film prepared using the adhesive has good heat sealing strength, high heat resistance, strong resistance to electrolyte corrosion, and high deep-draw performance.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium-ion battery soft packages, and particularly relates to an adhesive, an aluminum-plastic film and a lithium battery. Background Art

[0002] In recent years, with the development of new energy vehicles, 3C digital products, and microelectronics, the demand for lithium-ion batteries has continued to grow. Aluminum-plastic film, a crucial component of lithium-ion batteries, encapsulates the electrolyte and protects the battery. It primarily consists of a nylon layer, an outer adhesive layer, an aluminum foil layer, an inner adhesive layer, and a heat-seal layer. The inner adhesive layer must exhibit excellent bond strength, resistance to electrolyte corrosion, heat resistance, and good heat-seal strength. Currently, the inner adhesive layer of aluminum-plastic film cannot simultaneously meet all of these requirements. Therefore, the development of a new type of inner adhesive for aluminum-plastic film is an urgent task.

[0003] CN106459703.A discloses a polyolefin adhesive composition comprising an acid-modified chlorinated polyolefin, a glycidylamine epoxy resin, and a glycidyl ether epoxy resin, which is mixed with a curing agent and then applied. This adhesive does not increase viscosity or gel even after long-term storage, maintaining excellent pot life characteristics. Even when bonded and aged at low temperatures below 80°C, which have little effect on the thermal shrinkage of the polyolefin substrate, it simultaneously achieves good adhesion and chemical resistance between the polyolefin resin substrate and the metal substrate. However, this adhesive cannot meet application requirements such as electrolyte resistance at 85°C.

[0004] CN202010268184.5 reports a method for synthesizing an adhesive for aluminum-plastic film. The patent states that component A is first obtained by grafting bisphenol A-type epoxy resin E44 onto a maleic anhydride-modified polyolefin; component B is triglycidyl-p-aminophenol grafted onto a maleic anhydride-modified polyolefin; and product C is produced by copolymerizing hydroxy-terminated polybutadiene with hexamethylene diisocyanate. The three components are blended and mixed with a curing agent before the adhesive is applied. The patent discloses that the synthesized inner layer adhesive for aluminum-plastic film exhibits excellent electrolyte resistance, retaining over 70% of its initial peel strength after immersion in an 85°C electrolyte for 20 days. However, the adhesive's synthesis is complex, requiring a large amount of solvent, and only provides electrolyte resistance. Application properties such as ductility and stretchability fall short of the performance requirements for aluminum-plastic film in lithium batteries. Summary of the Invention

[0005] The present invention aims to solve, at least to a certain extent, one of the technical problems in the related art. To this end, one object of the present invention is to provide an adhesive, an aluminum-plastic film, and a lithium battery. The adhesive not only has high bonding strength, good heat resistance, and strong resistance to electrolyte corrosion, but also does not produce viscosity increase or gelation during long-term storage, maintaining a good, long pot life. The aluminum-plastic film prepared using the adhesive has good heat seal strength, high heat resistance, strong resistance to electrolyte corrosion, and high deep-draw performance.

[0006] In one aspect, the present invention provides an adhesive. According to an embodiment of the present invention, the adhesive comprises: an acid-modified ethylene-propylene copolymer resin and an acid-modified ethylene-octene copolymer resin, wherein the acid comprises at least one of a carboxylic acid and an acid anhydride.

[0007] The invention relates to a method for preparing an adhesive for aluminum-plastic film by mixing an acid-modified ethylene-propylene copolymer resin and an acid-modified ethylene-octene copolymer resin, wherein the acid comprises at least one of a carboxylic acid and an acid anhydride. Specifically, the acid-modified ethylene-propylene copolymer resin has shorter side chains, high crystallinity, regular structure and strong cohesion, thereby improving the bonding strength, heat sealing property and heat resistance of the adhesive; and the acid-modified ethylene-octene copolymer resin has longer side chains and high toughness, thereby improving the deep-drawing performance of the aluminum-plastic film. The two copolymer resins are mixed and cross-linked to form an interpenetrating network. Due to the entangled structure of the two copolymer resins, the advantages of the two copolymer resins are fully volatilized, thereby improving not only the bonding strength and heat resistance of the adhesive but also the density of the adhesive layer, thereby improving the electrolyte corrosion resistance of the aluminum-plastic film. Therefore, the adhesive not only has high bonding strength, good heat resistance, and strong resistance to electrolyte corrosion, but also will not produce viscosity increase or gelation under long-term storage, and can maintain a good and long application period. The aluminum-plastic film prepared with the adhesive has good heat sealing strength, high heat resistance, strong resistance to electrolyte corrosion and high deep drawing performance.

[0008] In addition, the adhesive according to the above embodiment of the present invention may also have the following technical features:

[0009] In some embodiments of the present invention, the Vicat softening point of the acid-modified ethylene-propylene copolymer resin and the acid-modified ethylene-octene copolymer resin after blending is 50-110° C. This can improve the bonding strength and pot life of the adhesive.

[0010] In some embodiments of the present invention, the grafting ratios of the acid-modified ethylene-propylene copolymer resin and the acid-modified ethylene-octene copolymer resin are independently 0.5-2%, thereby improving the bonding strength and electrolyte corrosion resistance of the adhesive.

[0011] In some embodiments of the present invention, the acid-modified ethylene-propylene copolymer resin contains 4-10% ethylene based on the total amount of the ethylene-propylene copolymer resin, thereby improving the adhesive bonding strength, heat sealing properties, and heat resistance.

[0012] In some embodiments of the present invention, the acid-modified ethylene-octene copolymer resin comprises 60-80% ethylene based on the total amount of the ethylene-octene copolymer resin, thereby improving the deep-drawing performance of the aluminum-plastic film.

[0013] In some embodiments of the present invention, the carboxylic acid includes an α,β-unsaturated carboxylic acid, and the acid anhydride includes an α,β-unsaturated carboxylic acid anhydride.

[0014] In some embodiments of the present invention, the α,β-unsaturated carboxylic acid includes at least one of maleic acid, itaconic acid, and citraconic acid.

[0015] In some embodiments of the present invention, the α,β-unsaturated carboxylic anhydride includes at least one of maleic anhydride, itaconic anhydride and citraconic anhydride, preferably maleic anhydride.

[0016] In some embodiments of the present invention, the mass ratio of the acid-modified ethylene-propylene copolymer resin to the acid-modified ethylene-octene copolymer resin is (2-5): 1. This can improve the heat resistance and heat seal strength of the adhesive.

[0017] In some embodiments of the present invention, the adhesive further includes a curing agent and a solvent.

[0018] In some embodiments of the present invention, the mass ratio of the total mass of the acid-modified ethylene-propylene copolymer resin and the acid-modified ethylene-octene copolymer resin to the curing agent is (12-14):1. This can improve the adhesive's bonding strength, electrolyte corrosion resistance, heat resistance, and heat seal strength.

[0019] In some embodiments of the present invention, the solid content of the adhesive is 14-16 wt %.

[0020] In another aspect, the present invention provides an aluminum-plastic film. According to an embodiment of the present invention, the aluminum-plastic film comprises a nylon layer, an outer adhesive layer, an aluminum foil layer, an inner adhesive layer, and a heat-seal layer, wherein the inner adhesive layer is the aforementioned adhesive. As a result, the aluminum-plastic film exhibits good heat-seal strength, high heat resistance, strong electrolyte corrosion resistance, and high deep-draw performance, thereby better protecting the battery.

[0021] In a third aspect, the present invention provides a lithium battery. According to an embodiment of the present invention, the battery cells of the lithium battery are assembled and sealed in the aforementioned aluminum-plastic film. As a result, the lithium battery has excellent safety performance and a long service life.

[0022] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. DETAILED DESCRIPTION

[0023] The embodiments of the present invention are described in detail below, which are intended to explain the present invention but are not to be construed as limiting the present invention.

[0024] In one aspect, the present invention provides an adhesive. According to an embodiment of the present invention, the adhesive comprises: an acid-modified ethylene-propylene copolymer resin and an acid-modified ethylene-octene copolymer resin, wherein the acid comprises at least one of a carboxylic acid and an acid anhydride.

[0025] The inventors have discovered that by mixing an acid-modified ethylene-propylene copolymer resin and an acid-modified ethylene-octene copolymer resin, wherein the acid comprises at least one of a carboxylic acid and an acid anhydride, the acid-modified ethylene-propylene copolymer resin has shorter side chains, high crystallinity, a regular structure, and strong cohesion, thereby improving the bonding strength, heat sealability, and heat resistance of the adhesive; the acid-modified ethylene-octene copolymer resin has longer side chains and high toughness, thereby improving the deep-draw performance of the aluminum-plastic film; and the two copolymer resins are mixed and cross-linked to form an interpenetrating network. Due to the entangled structure of the two copolymer resins, the advantages of the two copolymer resins are fully volatilized, thereby not only improving the bonding strength and heat resistance of the adhesive, but also improving the density of the adhesive layer, thereby improving the electrolyte corrosion resistance of the aluminum-plastic film. As a result, the adhesive not only exhibits high bonding strength, excellent heat resistance, and strong resistance to electrolyte corrosion, but also maintains a long shelf life without increasing viscosity or gelling even during long-term storage. The aluminum-plastic film prepared using the adhesive exhibits good heat-seal strength, high heat resistance, strong resistance to electrolyte corrosion, and high deep-draw performance. Furthermore, the carboxylic acid comprises an α,β-unsaturated carboxylic acid, and the acid anhydride comprises an α,β-unsaturated carboxylic anhydride. Specifically, the α,β-unsaturated carboxylic acid comprises at least one of maleic acid, itaconic acid, and citraconic acid; and the α,β-unsaturated carboxylic anhydride comprises at least one of maleic anhydride, itaconic anhydride, and citraconic anhydride, with maleic anhydride being preferred.

[0026] According to an embodiment of the present invention, the acid-modified ethylene-propylene copolymer resin comprises 4-10% of ethylene based on the total amount of the ethylene-propylene copolymer resin. The inventors have found that the proportion of ethylene cannot be too high, otherwise the rigidity and tensile strength of the copolymer resin will be reduced.

[0027] The heat resistance is reduced, which leads to a decrease in the bonding strength, heat sealing and heat resistance of the adhesive. Therefore, the present application adopts an ethylene-propylene copolymer resin with 4-10% ethylene to improve the bonding strength, heat sealing and heat resistance of the adhesive.

[0028] According to an embodiment of the present invention, the acid-modified ethylene-octene copolymer resin comprises 60-80% ethylene, based on the total amount of the ethylene-octene copolymer resin. The inventors have discovered that if the ethylene content is too low, the hard segments formed by the polyethylene crystals in the copolymer resin will be reduced, resulting in lower toughness and a decrease in the deep-draw performance of the adhesive. Therefore, the present application utilizes an ethylene-octene copolymer resin comprising 60-80% ethylene to improve the deep-draw performance of aluminum-plastic film.

[0029] According to an embodiment of the present invention, the Vicat softening point of the acid-modified ethylene-propylene copolymer resin and the acid-modified ethylene-octene copolymer resin after blending is 50-110°C. The inventors have discovered that if the Vicat softening point of the acid-modified ethylene-propylene copolymer resin and the acid-modified ethylene-octene copolymer resin after blending is too low, the bonding strength of the adhesive is weakened. If the Vicat softening point of the acid-modified ethylene-propylene copolymer resin and the acid-modified ethylene-octene copolymer resin after blending is too high, the stability and fluidity of the adhesive are reduced, making it difficult to operate during bonding. Therefore, the present application adopts a Vicat softening point of 50-110°C after blending the acid-modified ethylene-propylene copolymer resin and the acid-modified ethylene-octene copolymer resin, which can improve the bonding strength and pot life of the adhesive. It should be noted that no matter what the Vicat softening point of the acid-modified ethylene-propylene copolymer resin and the Vicat softening point of the acid-modified ethylene-octene copolymer resin are individually, as long as the Vicat softening point of the acid-modified ethylene-propylene copolymer resin and the acid-modified ethylene-octene copolymer resin after blending is 50-110°C, the effect of the present application can be achieved.

[0030] According to an embodiment of the present invention, the grafting ratio of the acid-modified ethylene-propylene copolymer resin and the acid-modified ethylene-octene copolymer resin is independently 0.5-2%. The inventors have discovered that if the grafting ratio of the acid-modified ethylene-propylene copolymer resin and the acid-modified ethylene-octene copolymer resin is too low, the crosslinking density of the adhesive is low, the bonding strength is reduced, and the electrolyte corrosion resistance is reduced; if the grafting ratio of the acid-modified ethylene-propylene copolymer resin and the acid-modified ethylene-octene copolymer resin is too high, the molecular weight of the copolymer resin is reduced, thereby weakening the cohesion of the copolymer resin and reducing the bonding strength. Therefore, using the acid-modified ethylene-propylene copolymer resin and the acid-modified ethylene-octene copolymer resin of the present application with an independent grafting ratio of 0.5-2% can improve the bonding strength and electrolyte corrosion resistance of the adhesive.

[0031] According to an embodiment of the present invention, the mass ratio of the acid-modified ethylene-propylene copolymer resin to the acid-modified ethylene-octene copolymer resin is (2-5):1. The inventors have found that if the mass ratio of the acid-modified ethylene-propylene copolymer resin to the acid-modified ethylene-octene copolymer resin is greater than 5, the resulting aluminum-plastic film has a decreased deep-drawing performance and a low yield rate; if the mass ratio of the acid-modified ethylene-propylene copolymer resin to the acid-modified ethylene-octene copolymer resin is less than 2, the heat-sealing strength of the adhesive decreases. Thus, the present application adopts a mass ratio of the acid-modified ethylene-propylene copolymer resin to the acid-modified ethylene-octene copolymer resin of (2-5):1, which can improve the heat resistance and heat-sealing strength of the adhesive and improve the deep-drawing performance of the aluminum-plastic film.

[0032] According to an embodiment of the present invention, the adhesive further comprises a curing agent and a solvent. It will be appreciated by those skilled in the art that curing agents and solvents are conventional preparations in the art, and those skilled in the art may select them according to actual conditions. For example, the curing agent comprises an epoxy resin having a functional group with a chelating effect in the molecule. In order to improve reactivity, adhesion, and heat resistance, it is preferred that one molecule of epoxy resin has two or more glycidyl groups and one or more epoxy resins having a functional group with a chelating effect. Specifically, the curing agent comprises at least one of a glycidyl ether epoxy resin, hexahydrophthalic acid glycidyl ester, dimer acid glycidyl ester, isocyanuric acid triglycidyl ester, 3,4-epoxycyclohexyl methyl carboxylate, epoxidized polybutadiene, epoxidized soybean oil, phenol novolac type epoxy resin, and cresol novolac type epoxy resin. The solvent includes an organic solvent that can dissolve the acid-modified copolymer resin and the curing agent. For example, the solvent includes at least one of benzene, toluene, xylene, hexane, heptane, octane, decane, cyclohexane, cyclohexene, methylcyclohexane, ethylcyclohexane, trichloroethylene, dichloroethylene, chlorobenzene, chloroform, methanol, ethanol, isopropyl alcohol, butanol, pentanol, hexanol, propylene glycol, phenol, acetone, methyl isobutyl ketone, methyl ethyl ketone, hexanone, cyclohexanone, isophorone, acetophenone, methyl cellosolve, ethyl cellosolve, methyl acetate, ethyl acetate, butyl acetate, methyl propionate, butyl formate, ethylene glycol mono-n-butyl ether, ethylene glycol mono-isobutyl ether, ethylene glycol mono-tert-butyl ether, diethylene glycol mono-n-butyl ether, diethylene glycol mono-isobutyl ether, triethylene glycol mono-n-butyl ether and tetraethylene glycol n-butyl ether.

[0033] According to an embodiment of the present invention, the total mass ratio of the acid-modified ethylene-propylene copolymer resin and the acid-modified ethylene-octene copolymer resin to the mass ratio of the curing agent is (12-14): 1. The inventors found that if the mass ratio of the curing agent is too large, the excess curing agent can self-crosslink, the brittleness of the formed adhesive layer is enhanced, and the flexibility is reduced, which is manifested as insufficient bonding strength of the adhesive, decreased electrolyte resistance and heat sealing performance, and precipitation phenomenon occurs in the adhesive system, and applicability is reduced; if the mass ratio of the curing agent is too small, it is easy to cause the cross-linking density of the adhesive layer to be low, thereby resulting in decreased bonding strength, electrolyte resistance and heat sealing performance. Therefore, the present application adopts the total mass ratio of the acid-modified ethylene-propylene copolymer resin and the acid-modified ethylene-octene copolymer resin to the mass ratio of the curing agent to be (12-14): 1, which can improve the bonding strength, electrolyte corrosion resistance, heat resistance and heat sealing strength of the adhesive. Furthermore, if the solid content of the adhesive is too low, the amount of solvent used is large, and a large amount of solvent evaporates during coating and drying, causing environmental pollution; if the solid content of the adhesive is too high, it is easy to cause the viscosity of the adhesive to be high, and it will become gel-like during storage and cannot be used. Therefore, in order to improve the shelf life of the adhesive and the operability of the coating, the solid content of the adhesive is 14-16wt%.

[0034] In another aspect, the present invention provides an aluminum-plastic film. According to an embodiment of the present invention, the aluminum-plastic film comprises a nylon layer, an outer adhesive layer, an aluminum foil layer, an inner adhesive layer, and a heat-seal layer, wherein the inner adhesive layer is the aforementioned adhesive. As a result, the aluminum-plastic film exhibits good heat-seal strength, high heat resistance, strong electrolyte corrosion resistance, and high deep-draw performance, thereby better protecting the battery. It should be noted that the features and advantages described above for the adhesive also apply to this aluminum-plastic film and will not be elaborated upon here.

[0035] In its third aspect, the present invention provides a lithium battery. According to an embodiment of the present invention, the cells of this lithium battery are assembled and sealed in the aforementioned aluminum-plastic film. As a result, this lithium battery has excellent safety performance and a long service life. It should be noted that the features and advantages described for the aforementioned aluminum-plastic film also apply to this lithium battery and will not be further elaborated here.

[0036] The present invention is described below with reference to specific examples. It should be noted that these examples are merely illustrative and do not limit the present invention in any way.

[0037] Example 1

[0038] The preparation method of adhesive and aluminum-plastic film is as follows:

[0039] (1) dissolving the acid-modified ethylene-propylene copolymer resin and the acid-modified ethylene-octene copolymer resin in an organic solvent at a dissolving temperature of 60-85°C, cooling to 22-25°C after complete dissolution, then slowly dripping the curing agent while stirring, stirring at high speed for 1 hour until uniform; standing for 2-10 minutes to deaerate, to obtain an inner layer adhesive;

[0040] (2) The inner layer adhesive is coated on the surface of the aluminum foil treated with a trivalent chromium agent, and the dry film thickness of the adhesive is controlled to be 2-4 μm. The aluminum foil coated with the adhesive layer is composited with the CPP film by hot pressing at a temperature of 90-110°C, and the composite is placed in an oven at 55-80°C for aging for 2-4 days to obtain an aluminum-plastic film semi-finished product.

[0041] Among them, 6 parts by weight of maleic anhydride modified ethylene propylene copolymer resin, based on the total amount of ethylene propylene copolymer resin, ethylene accounts for 5%, and its grafting rate is 1.2%;

[0042] 3 parts by weight of maleic anhydride-modified ethylene-octene copolymer resin, based on the total amount of the ethylene-octene copolymer resin, ethylene accounts for 60% and its grafting rate is 1.2%;

[0043] The Vicat softening point of the blended acid-modified ethylene-propylene copolymer resin and acid-modified ethylene-octene copolymer resin is 75°C;

[0044] 0.73 parts by weight of curing agent (glycidyl ether type epoxy resin);

[0045] Organic solvent: 40 parts by weight of cyclohexane, 15 parts by weight of butanone.

[0046] Example 2

[0047] The difference between Example 2 and Example 1 is:

[0048] Among them, 7 parts by weight of maleic anhydride modified ethylene propylene copolymer resin, based on the total amount of ethylene propylene copolymer resin, ethylene accounts for 7%, and its grafting rate is 1.2%;

[0049] 2 parts by weight of maleic anhydride modified ethylene octene copolymer resin, based on the total amount of the ethylene octene copolymer resin, ethylene accounts for 70% and the grafting rate is 1.2%.

[0050] Example 3

[0051] The difference between Example 3 and Example 1 is:

[0052] Wherein, 7.5 parts by weight of maleic anhydride modified ethylene propylene copolymer resin, based on the total amount of ethylene propylene copolymer resin, ethylene accounts for 8% and its grafting rate is 1.2%;

[0053] 1.5 parts by weight of maleic anhydride modified ethylene octene copolymer resin, based on the total amount of the ethylene octene copolymer resin, ethylene accounts for 80% and the grafting rate is 1.2%.

[0054] Example 4

[0055] The difference between Example 4 and Example 1 is:

[0056] Among them, 7 parts by weight of maleic anhydride modified ethylene propylene copolymer resin, based on the total amount of ethylene propylene copolymer resin, ethylene accounts for 7%, and its grafting rate is 1.2%;

[0057] 2 parts by weight of maleic anhydride-modified ethylene-octene copolymer resin, based on the total amount of the ethylene-octene copolymer resin, ethylene accounts for 70% and its grafting rate is 1.2%;

[0058] The Vicat softening point of the acid-modified ethylene-propylene copolymer resin and the acid-modified ethylene-octene copolymer resin after blending is 50°C.

[0059] Example 5

[0060] The difference between Example 5 and Example 1 is:

[0061] Among them, 7 parts by weight of maleic anhydride modified ethylene propylene copolymer resin, based on the total amount of ethylene propylene copolymer resin, ethylene accounts for 7%, and its grafting rate is 1.2%;

[0062] 2 parts by weight of maleic anhydride-modified ethylene-octene copolymer resin, based on the total amount of the ethylene-octene copolymer resin, ethylene accounts for 70% and its grafting rate is 1.2%;

[0063] The Vicat softening point of the acid-modified ethylene-propylene copolymer resin and the acid-modified ethylene-octene copolymer resin after blending is 60°C.

[0064] Example 6

[0065] The difference between Example 6 and Example 1 is:

[0066] Among them, 7 parts by weight of maleic anhydride modified ethylene propylene copolymer resin, based on the total amount of ethylene propylene copolymer resin, ethylene accounts for 7%, and its grafting rate is 1.2%;

[0067] 2 parts by weight of maleic anhydride-modified ethylene-octene copolymer resin, based on the total amount of the ethylene-octene copolymer resin, ethylene accounts for 70% and its grafting rate is 1.2%;

[0068] The Vicat softening point of the acid-modified ethylene-propylene copolymer resin and the acid-modified ethylene-octene copolymer resin after blending is 110°C.

[0069] Example 7

[0070] The difference between Example 7 and Example 1 is:

[0071] Among them, 7 parts by weight of maleic anhydride modified ethylene propylene copolymer resin, based on the total amount of ethylene propylene copolymer resin, ethylene accounts for 7%, and its grafting rate is 0.5%;

[0072] 2 parts by weight of maleic anhydride-modified ethylene-octene copolymer resin, based on the total amount of the ethylene-octene copolymer resin, ethylene accounts for 70% and its grafting rate is 0.5%;

[0073] The Vicat softening point of the acid-modified ethylene-propylene copolymer resin and the acid-modified ethylene-octene copolymer resin after blending is 75°C.

[0074] Example 8

[0075] The difference between Example 8 and Example 1 is:

[0076] Among them, 7 parts by weight of maleic anhydride modified ethylene propylene copolymer resin, based on the total amount of ethylene propylene copolymer resin, ethylene accounts for 7%, and its grafting rate is 2.0%;

[0077] 2 parts by weight of maleic anhydride-modified ethylene-octene copolymer resin, based on the total amount of the ethylene-octene copolymer resin, ethylene accounts for 70% and its grafting rate is 2.0%;

[0078] The Vicat softening point of the acid-modified ethylene-propylene copolymer resin and the acid-modified ethylene-octene copolymer resin after blending is 75°C.

[0079] Comparative Example 1

[0080] The difference between Comparative Example 1 and Example 1 is:

[0081] Among them, 8 parts by weight of maleic anhydride modified ethylene propylene copolymer resin, based on the total amount of ethylene propylene copolymer resin, ethylene accounts for 7%, and its grafting rate is 1.2%;

[0082] 1 part by weight of maleic anhydride-modified ethylene-octene copolymer resin, based on the total amount of the ethylene-octene copolymer resin, ethylene accounts for 70% and its grafting rate is 1.2%;

[0083] The Vicat softening point of the acid-modified ethylene-propylene copolymer resin and the acid-modified ethylene-octene copolymer resin after blending is 100°C.

[0084] Comparative Example 2

[0085] The difference between Comparative Example 2 and Example 1 is:

[0086] Among them, 7 parts by weight of maleic anhydride modified ethylene propylene copolymer resin, based on the total amount of ethylene propylene copolymer resin, ethylene accounts for 7%, and its grafting rate is 1.2%;

[0087] 2 parts by weight of maleic anhydride-modified ethylene-octene copolymer resin, based on the total amount of the ethylene-octene copolymer resin, ethylene accounts for 70% and its grafting rate is 1.2%;

[0088] The Vicat softening point of the acid-modified ethylene-propylene copolymer resin and the acid-modified ethylene-octene copolymer resin after blending is 40°C.

[0089] Comparative Example 3

[0090] The difference between Comparative Example 3 and Example 1 is:

[0091] Among them, 7 parts by weight of maleic anhydride modified ethylene propylene copolymer resin, based on the total amount of ethylene propylene copolymer resin, ethylene accounts for 7%, and its grafting rate is 1.2%;

[0092] 2 parts by weight of maleic anhydride-modified ethylene-octene copolymer resin, based on the total amount of the ethylene-octene copolymer resin, ethylene accounts for 70% and its grafting rate is 1.2%;

[0093] The Vicat softening point of the acid-modified ethylene-propylene copolymer resin and the acid-modified ethylene-octene copolymer resin after blending is 120°C.

[0094] Comparative Example 4

[0095] The difference between Comparative Example 4 and Example 1 is:

[0096] Among them, 7 parts by weight of maleic anhydride modified ethylene propylene copolymer resin, based on the total amount of ethylene propylene copolymer resin, ethylene accounts for 7%, and its grafting rate is 0.3%;

[0097] 2 parts by weight of maleic anhydride-modified ethylene-octene copolymer resin, based on the total amount of the ethylene-octene copolymer resin, ethylene accounts for 70% and its grafting rate is 0.3%;

[0098] The Vicat softening point of the acid-modified ethylene-propylene copolymer resin and the acid-modified ethylene-octene copolymer resin after blending is 75°C.

[0099] Comparative Example 5

[0100] The difference between Comparative Example 5 and Example 1 is:

[0101] Among them, 7 parts by weight of maleic anhydride modified ethylene propylene copolymer resin, based on the total amount of ethylene propylene copolymer resin, ethylene accounts for 7%, and its grafting rate is 2.5%;

[0102] 2 parts by weight of maleic anhydride-modified ethylene-octene copolymer resin, based on the total amount of the ethylene-octene copolymer resin, ethylene accounts for 70% and its grafting rate is 2.5%;

[0103] The Vicat softening point of the acid-modified ethylene-propylene copolymer resin and the acid-modified ethylene-octene copolymer resin after blending is 80°C.

[0104] Comparative Example 6

[0105] The difference between Comparative Example 6 and Example 1 is:

[0106] Among them, 7 parts by weight of maleic anhydride modified ethylene propylene copolymer resin, based on the total amount of ethylene propylene copolymer resin, ethylene accounts for 30%, and its grafting rate is 1.2%;

[0107] 2 parts by weight of maleic anhydride-modified ethylene-octene copolymer resin, based on the total amount of the ethylene-octene copolymer resin, ethylene accounts for 70% and its grafting rate is 1.2%;

[0108] The Vicat softening point of the acid-modified ethylene-propylene copolymer resin and the acid-modified ethylene-octene copolymer resin after blending is 75°C.

[0109] Comparative Example 7

[0110] The difference between Comparative Example 7 and Example 1 is:

[0111] Among them, 7 parts by weight of maleic anhydride modified ethylene propylene copolymer resin, based on the total amount of ethylene propylene copolymer resin, ethylene accounts for 7%, and its grafting rate is 1.2%;

[0112] 2 parts by weight of maleic anhydride-modified ethylene-octene copolymer resin, based on the total amount of the ethylene-octene copolymer resin, ethylene accounts for 30% and its grafting rate is 1.2%;

[0113] The Vicat softening point of the acid-modified ethylene-propylene copolymer resin and the acid-modified ethylene-octene copolymer resin after blending is 75°C.

[0114] Comparative Example 8

[0115] The difference between Comparative Example 8 and Example 1 is:

[0116] Among them, 7 parts by weight of maleic anhydride modified ethylene propylene copolymer resin, based on the total amount of ethylene propylene copolymer resin, ethylene accounts for 7%, and its grafting rate is 1.2%;

[0117] 2 parts by weight of maleic anhydride-modified ethylene-octene copolymer resin, based on the total amount of the ethylene-octene copolymer resin, ethylene accounts for 70% and its grafting rate is 1.2%;

[0118] The Vicat softening point of the blended acid-modified ethylene-propylene copolymer resin and acid-modified ethylene-octene copolymer resin is 75°C;

[0119] Curing agent (glycidyl ether type epoxy resin) 0.45 parts by weight.

[0120] The test method for the grafting rate of the acid-modified copolymer resin used in Examples 1-8 and Comparative Examples 1-8 is as follows:

[0121] (1) Grafting rate test method of anhydride modified copolymer resin:

[0122] 0.5 g of anhydride-modified copolymer resin was placed in a ground-mouth conical flask, and 60 mL of xylene, 50 μL of water, and 50 μL of pyridine were added. The mixture was heated to reflux for about 2 h. After the reflux was completed, the mixture was quickly titrated with a standardized KOH ethanol solution (with phenolphthalein as an indicator) while hot. No flocculent precipitate was produced during the titration process. At the same time, a blank experiment was performed under the same conditions to eliminate the influence of the external environment.

[0123] Grafting rate = m1×(V1-V0)×C / 2 / 1000 / m×100%

[0124] Where C is the concentration of the KOH-ethanol solution (mol / L), V0 is the converted volume of the KOH-ethanol solution required to titrate the blank sample (mL), V1 is the volume of the KOH-ethanol solution consumed to titrate the grafted sample (mL), m is the mass of the anhydride-modified polyolefin resin sample to be titrated (g), and m1 is the molecular weight of the grafted anhydride monomer.

[0125] (2) Grafting rate test method of carboxylic acid modified polyolefin resin:

[0126] 0.5 g of carboxylic acid-modified polyolefin resin was placed in a ground-mouth conical flask, 60 mL of xylene was added, and the mixture was heated to reflux for about 2 h. After the reflux was completed, the mixture was rapidly titrated with a standardized KOH ethanol solution (with phenolphthalein as an indicator) while hot. No flocculent precipitation was produced during the titration process. At the same time, in order to eliminate the influence of the external environment, a blank experiment was carried out under the same conditions.

[0127] Grafting rate = m1 × (V1-V0) × C / 1000 / m × 100%

[0128] Where C is the concentration of KOH-ethanol solution (mol / L), V0 is the converted volume of KOH-ethanol solution required for titration of the blank sample (mL), V1 is the volume of KOH-ethanol solution consumed for titration of the grafted sample (mL), m is the mass of the anhydride-modified polyolefin resin sample titrated (g), and m1 is the molecular weight of the grafted carboxylic acid monomer.

[0129] The test method for the Vicat softening point of the acid-modified copolymer resins in Examples 1-8 and Comparative Examples 1-8 is as follows:

[0130] The test is conducted in accordance with GB / T 1633, Determination of the Vicat softening temperature of thermoplastics. Samples of carboxylic acid or anhydride modified copolymer resins are made into square specimens with a thickness of 3-6.5 mm and a side length of 10 mm, or circular specimens with a diameter of 10 mm. The specimen surfaces should be parallel, flat and smooth, free of bubbles, sawtooth marks, dents, or side defects. The heating rate is 50±5℃ / h (5±0.5)℃ / 6min, and the total thrust applied to the specimen is 10N±0.2N. The Vicat softening point of the specimen is determined when the indenter penetrates the specimen to a depth of 1mm±0.01mm.

[0131] The performance of the aluminum-plastic films prepared in Examples 1-8 and Comparative Examples 1-8 was measured as follows:

[0132] (1) Bond strength test:

[0133] The ambient temperature was (23±2)°C and the relative humidity was (50±10)%. Long strip samples with a length greater than 150 mm and a width of (15±0.1) mm were cut and tested using a universal materials testing machine with a precision of 0.5. The initial distance between the clamps was (100±5) mm. The samples were peeled at a speed of (100±10) mm / min, and the average force was recorded.

[0134] (2) Heat sealing performance test

[0135] The aluminum-plastic film was cut to obtain two rectangular test pieces of 15 mm wide and 200 mm long. After overlapping the two test pieces with the heat seal layers in contact with each other, heat seal was performed using a heat sealer at a temperature of 190°C and a sealing pressure of 0.5 MPa. The end area of ​​the other side of the length direction of one of the two test pieces (the end that was not heat-sealed) was then clamped with the chuck of a tensile testing machine. The test piece was peeled off at 90 degrees with an initial chuck distance of 100 mm and a tensile speed of 100 mm / min. The heat seal strength of each 15 mm width was measured, and the whitening state of the peeled surface and the average force value were recorded.

[0136] (3) Test of electrolyte resistance

[0137] Preparation of electrolyte: Ethylene carbonate, diethyl carbonate, and dimethyl carbonate reagents are mixed in a ratio of 1:1:1, and lithium hexafluorophosphate is added to the mixture to prepare a solution with a lithium hexafluorophosphate content of 1.0 mol / L, which is the electrolyte. The free acid content of the electrolyte is not higher than 50 parts per million. The purity of the above reagents is analytical grade.

[0138] Cut the aluminum-plastic composite film into 15mm×100mm specimens and place the specimens in a container filled with electrolyte. The electrolyte must completely immerse the specimens. After sealing the container, place it in an (85±2)℃ oven and keep it in an (85±2)℃ environment for 45 days. Take it out and let it cool naturally to room temperature. Take out the specimens one by one, wipe them clean, and immediately check the appearance of the specimens and test the bonding strength. Record the average force value.

[0139] (4) Shell punching yield

[0140] The aluminum-plastic film was cut and prepared into a three-dimensional shape (50 mm in length × 60 mm in width × 6 mm in depth, with a flange) using a stamping die at an ambient temperature of (23±2)°C and a relative humidity of (50±10)%. The peripheral edges were heat-sealed together using a heat sealer at a temperature of 190°C and a sealing pressure of 0.5 MPa to form a battery case. The surface condition of the battery case was observed, and the yield rate was calculated.

[0141] (5) Evaluation of applicability

[0142] Pot life evaluation measures the stability of a solution obtained by mixing a curing agent with a carboxylic acid- or anhydride-modified copolymer resin, either immediately after mixing or after a period of time. Good pot life indicates minimal increase in solution viscosity, allowing for long-term storage. Poor pot life indicates increased viscosity, even gelling, making coating difficult and preventing long-term storage.

[0143] The performance test results of the aluminum-plastic films prepared in Examples 1-8 and Comparative Examples 1-8 are shown in Table 1.

[0144] Table 1

[0145]

[0146]

[0147] *Denotes gel-like state and cannot be tested.

[0148] As can be seen from Table 1, the inner layer adhesive for the aluminum-plastic film provided by the present invention can ensure that the aluminum-plastic film has excellent bonding strength, electrolyte corrosion resistance and heat sealing performance. The adhesive of the present invention can be used for bonding the aluminum foil layer and the heat sealing layer of the aluminum-plastic film.

[0149] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0150] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. An adhesive, characterized in that: include: Acid-modified ethylene-propylene copolymer resin and acid-modified ethylene-octene copolymer resin, wherein the acid comprises at least one of a carboxylic acid and an acid anhydride; The Vicat softening point of the acid-modified ethylene-propylene copolymer resin and the acid-modified ethylene-octene copolymer resin after blending is 50 to 110° C. The grafting rates of the acid-modified ethylene-propylene copolymer resin and the acid-modified ethylene-octene copolymer resin are independently 0.5-2%; In the acid-modified ethylene-propylene copolymer resin, ethylene accounts for 4-10% based on the total amount of the ethylene-propylene copolymer resin; In the acid-modified ethylene-octene copolymer resin, ethylene accounts for 60-80% based on the total amount of the ethylene-octene copolymer resin; The mass ratio of the acid-modified ethylene-propylene copolymer resin to the acid-modified ethylene-octene copolymer resin is (2-5):1; The adhesive further includes a curing agent and a solvent, and the mass ratio of the total mass of the acid-modified ethylene-propylene copolymer resin and the acid-modified ethylene-octene copolymer resin to the curing agent is (12-14):

1.

2. The adhesive according to claim 1, characterized in that: The carboxylic acid includes α,β-unsaturated carboxylic acid, and the acid anhydride includes α,β-unsaturated carboxylic acid anhydride.

3. The adhesive according to claim 2, characterized in that: The α,β-unsaturated carboxylic acid includes at least one of maleic acid, itaconic acid and citraconic acid; Optionally, the α,β-unsaturated carboxylic anhydride includes at least one of maleic anhydride, itaconic anhydride and citraconic anhydride.

4. The adhesive according to claim 3, characterized in that: The α,β-unsaturated carboxylic anhydride includes maleic anhydride.

5. The adhesive according to claim 1, characterized in that: The solid content of the adhesive is 14-16 wt %.

6. An aluminum-plastic film, characterized in that: The adhesive comprises a nylon layer, an outer adhesive layer, an aluminum foil layer, an inner adhesive layer and a heat-sealing layer, wherein the inner adhesive layer is the adhesive according to any one of claims 1 to 5.

7. A lithium battery, characterized in that: After the battery core is assembled, it is sealed in the aluminum-plastic film according to claim 6.

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