Pressure-sensitive adhesive composition, pressure-sensitive adhesive, preparation method of pressure-sensitive adhesive, adhesive tape and application

Abstract

The invention provides a pressure-sensitive adhesive composition, a pressure-sensitive adhesive, a preparation method of the pressure-sensitive adhesive, an adhesive tape and application. The pressure-sensitive adhesive composition comprises the following components in parts by weight: 20-99 parts of a modified polymer; 0-40 parts of a first polymer; 0 to 50 parts of tackifying resin; 0-50 parts of a plasticizer; 0.01 to 5 parts of an epoxy curing agent; the modified polymer comprises a polymer grafted and modified by carboxylic acid or anhydride, the storage modulus E'at 25 DEG C is 0.01-20 MPa, and the grafting rate is 0.1-10%. The pressure-sensitive adhesive and the adhesive tape have good initial adhesion, heat resistance (such as no adhesive overflow at high temperature) and electrolyte resistance at the same time, and can be used for protecting a lithium battery cell.

Description

Technical Field

[0001] This invention relates to a pressure-sensitive adhesive composition, a pressure-sensitive adhesive, a method for preparing the same, an adhesive tape, and its applications. Background Technology

[0002] Currently, lithium-ion batteries are widely used. These batteries require electrolytes, which can dissolve or swell most materials. Developing an electrolyte-resistant pressure-sensitive adhesive (PSA) can be applied to various processes within the battery, such as insulation protection, fixation, and marking. While existing non-reactive PSAs are widely used in battery cells, their electrolyte resistance is often not advantageous.

[0003] CN110234721B discloses an adhesive for lithium battery packaging, which is obtained by thermosetting anhydride-modified polyolefin with an isocyanate curing agent. However, this adhesive lacks pressure sensitivity and is unsuitable for use as a pressure-sensitive adhesive. CN109890926A discloses an adhesive for sealing electronic components, which is prepared by modifying polyolefin, multifunctional epoxy resin, curing accelerator, and silane coupling agent. The composition of this adhesive must contain a curing accelerator and a silane coupling agent, making the final adhesive lack pressure sensitivity and unsuitable for use as a pressure-sensitive adhesive.

[0004] Ordinary pressure-sensitive adhesives mainly consist of plasticizers, rubber, and tackifying resins, which are made compatible by heating or adding solvents. However, ordinary thermoplastic pressure-sensitive adhesives lack an internal cross-linking structure. Uncross-linked pressure-sensitive adhesives have poor heat resistance and are prone to overflow during high-temperature hot pressing. In addition, they are easily swollen or dissolved by electrolytes, leading to failure. Summary of the Invention

[0005] To overcome the shortcomings of existing adhesives, such as lack of pressure sensitivity, poor heat resistance, and poor electrolyte resistance, this invention provides a pressure-sensitive adhesive composition, a pressure-sensitive adhesive, its preparation method, an adhesive tape, and its applications. The pressure-sensitive adhesive and tape of this application simultaneously possess excellent initial tack, heat resistance (e.g., no adhesive overflow at high temperatures), and electrolyte resistance, making them suitable for protecting lithium battery cells.

[0006] The present invention achieves the above objectives through the following technical solutions:

[0007] This invention provides a pressure-sensitive adhesive composition, comprising, by weight: 20-99 parts of a modified polymer; 0-40 parts of a first polymer; 0-50 parts of a tackifying resin; 0-50 parts of a plasticizer; and 0.01-5 parts of an epoxy curing agent; wherein the modified polymer comprises a polymer grafted with carboxylic acid or anhydride, having a storage modulus E' of 0.01-20 MPa at 25°C and a grafting rate of 0.1%-10%.

[0008] It is understood that the storage modulus of the modified polymer in this invention is determined using a rheometer, specifically using a Discovery HR-1 rheometer from TA Instruments, at a frequency of 10 Hz, by cooling the modified polymer from 180°C at a rate of 3°C / min while testing.

[0009] It is understood that the grafting rate of the modified polymer in this invention is tested using a chemical titration method. Specifically, approximately 0.5g of the modified polymer is accurately weighed using a balance, placed in 200ml of xylene, refluxed at 140°C and stirred for 1 hour. After cooling to 50°C, 30ml of potassium hydroxide ethanol solution (concentration 0.05mol / L) is added, and the mixture is then refluxed for another 2 hours. Then, using phenolphthalein as an indicator, a 0.05mol / L solution of hydrogen chloride in isopropanol is used for back titration. The grafting rate is finally calculated using the following formula:

[0010]

[0011] V1 represents the volume of the potassium hydroxide solution, C1 represents the molar concentration of the potassium hydroxide solution, V2 represents the volume of the hydrogen chloride solution, C2 represents the molar concentration of the hydrogen chloride solution, m represents the mass of the modified polymer weighed, 98.06 is the molecular weight of maleic anhydride, and GD0 represents the grafting rate of the ungrafted sample measured by this method.

[0012] In this invention, the modified polymer has reactive groups that can react with epoxy groups in epoxy curing agents to construct a crosslinked system. Generally, a host resin with low cohesive strength has a low crosslinking density. Combining an appropriate amount of tackifying resin and a large amount of plasticizer can yield a pressure-sensitive adhesive with high initial tack and low heat resistance; conversely, it can yield a pressure-sensitive adhesive with high heat resistance and low initial tack. This application, by selecting modified polymers with specific performance parameters and combining them with epoxy curing agents and other components, obtains a pressure-sensitive adhesive composition that combines good initial tack, heat resistance, and electrolyte resistance.

[0013] In this invention, the modified polymer can be obtained by modifying a thermoplastic polymer.

[0014] In some embodiments, the modified polymer includes modified polyolefins and / or modified rubbers.

[0015] In a specific embodiment, the modified polyolefin is obtained by modifying a polyolefin, wherein the polyolefin includes self-polymers or copolymers of olefins, and the olefin is selected from at least one of ethylene, propylene, butene, hexene and octene.

[0016] In a specific embodiment, the modified rubber is obtained by modifying rubber, and the rubber is selected from at least one of styrene-butadiene-styrene block copolymer (SBS), styrene-ethylene-butadiene-styrene copolymer (SEBS), styrene-isoprene copolymer (SEP), styrene-ethylene / propylene-styrene block copolymer (SEPS), styrene-isoprene-styrene block copolymer (SIS), butyl rubber (IIR), polyisobutylene (PIB), nitrile rubber (NBR), isoprene rubber (IR), poly(butadiene-acrylonitrile) (PBAN), synthetic polyolefin rubber (SPR), poly(butadiene-styrene) (PBS), ethylene propylene diene monomer (EPDM), and thermoplastic polymers synthesized from butadiene and isoprene.

[0017] In some embodiments, the modified polymer contains a functional group selected from at least one of carboxyl, maleic anhydride, itaconic anhydride, and citraconic anhydride groups.

[0018] In some embodiments, the storage modulus E' of the modified polymer at 25°C is 0.01 to 5 MPa; when the storage modulus E' of the modified polymer is too high, it is difficult to prepare a pressure-sensitive adhesive with good initial tack.

[0019] In this invention, the grafting rate refers to the ratio of the mass of the grafted carboxylic acid or anhydride to the total mass of the modified polymer.

[0020] In some embodiments, the grafting rate of the modified polymer is 0.1% to 3%.

[0021] In this invention, preferably, the acid value of the modified polymer is 0.5 to 100 mg KOH / g; when the acid value of the modified polymer is too high, exceeding 100 mg KOH / g, it will affect the degree of reaction of the pressure-sensitive adhesive, thereby affecting the performance of the pressure-sensitive adhesive.

[0022] In this invention, preferably, the number-average molecular weight Mn of the modified polymer is 500 to 150,000.

[0023] In this invention, preferably, the melting point Tm of the modified polymer is below 120°C.

[0024] In this invention, the modified polymer is in a semi-crystalline or amorphous state; preferably, the modified polymer is liquid at room temperature and is a polymer with a melting point below room temperature.

[0025] In this invention, preferably, when the modified polymer is a solid, its melt index is greater than or equal to 1000 g / 10 min; while when the modified polymer is a liquid, it is not suitable for melt index testing.

[0026] In this invention, the melt index of the modified polymer is obtained under standard test conditions, specifically 190℃ / 2.16kg.

[0027] In a specific embodiment, the amount of the modified polymer used is 30-99 parts.

[0028] In a specific embodiment, when the modified polymer includes modified polyolefin and modified rubber, the mass ratio of the modified polyolefin to the modified rubber is 1:(0.1-8); preferably, the mass ratio of the modified polyolefin to the modified rubber is 1:(0.5-3).

[0029] In some embodiments, the first polymer comprises polyolefins and / or rubber.

[0030] The polyolefin may be the polyolefin of the modified polymer before its modification; preferably, the polyolefin includes self-polymers or copolymers of olefins, wherein the olefin is selected from at least one of ethylene, propylene, butene, hexene and octene.

[0031] The rubber may be the rubber of the modified polymer before its modification; preferably, the rubber is selected from at least one of styrene-butadiene-styrene block copolymer (SBS), styrene-ethylene-butadiene-styrene copolymer (SEBS), styrene-isoprene copolymer (SEP), styrene-ethylene / propylene-styrene block copolymer (SEPS), styrene-isoprene-styrene block copolymer (SIS), butyl rubber (IIR), polyisobutylene (PIB), nitrile rubber (NBR), isoprene rubber (IR), poly(butadiene-acrylonitrile) (PBAN), synthetic polyolefin rubber (SPR), poly(butadiene-styrene) (PBS), ethylene propylene diene monomer (EPDM), and thermoplastic polymers synthesized from butadiene and isoprene.

[0032] In some embodiments, the amount of the first polymer is 5-40 parts.

[0033] In some embodiments, the melt index of the first polymer is greater than or equal to 5 g / 10 min.

[0034] In this invention, the melt index of the first polymer is obtained under standard test conditions, specifically 190℃ / 2.16kg.

[0035] In some embodiments, the amount of the tackifying resin is 10-50 parts.

[0036] In some embodiments, the tackifying resin is selected from at least one of dicyclopentadiene resin (DCPD), coumarone-indene resin, styrene resin, terpene resin, C5 petroleum resin, C9 petroleum resin, C5-C9 copolymer resin, and their hydrogenated products.

[0037] In "C5 petroleum resin", "C9 petroleum resin", and "C5-C9 copolymer resin", the "C" refers to the number of carbon atoms.

[0038] Among them, "the products of hydrogenation" include the products of hydrogenation of dicyclopentadiene resin (DCPD), the products of hydrogenation of coumarone-indene resin, the products of hydrogenation of styrene resin, the products of hydrogenation of terpene resin, the products of hydrogenation of C5 petroleum resin, the products of hydrogenation of C9 petroleum resin, and the products of hydrogenation of C5-C9 copolymer resin.

[0039] In a specific embodiment, the tackifying resin includes C5 petroleum resin or C5-C9 copolymer resin, which can improve viscosity and has a higher glass transition temperature and lower melt viscosity.

[0040] In a preferred embodiment, the tackifying resin includes maleic anhydride-modified C5 petroleum resin or maleic anhydride-styrene copolymer, which are reactive tackifying resins to improve the electrolyte resistance of the pressure-sensitive adhesive.

[0041] In some embodiments, the amount of plasticizer used is 0.5-30 parts.

[0042] In some embodiments, the plasticizer is selected from liquid polyolefins that are flowable at room temperature; preferably, it is at least one of white oil, naphthenic oil, paraffin oil, low molecular weight polyolefins, and low molecular weight polyisobutylene.

[0043] In a preferred embodiment, the plasticizer is a low molecular weight polyisobutylene with a molecular weight of 1300-75000.

[0044] In some embodiments, the amount of the epoxy curing agent is 0.1-1 parts.

[0045] In some embodiments, the epoxy curing agent includes a liquid epoxy resin; wherein the epoxy groups can react with the modified polymer to form a cross-linked structure, significantly improving heat resistance.

[0046] In a specific embodiment, the epoxy curing agent is a hydrogenated epoxy resin with a functionality greater than 3, the molecular weight of the hydrogenated epoxy resin is less than 5000, and it is a liquid at room temperature.

[0047] In a preferred embodiment, the epoxy curing agent is a glycidylamine type epoxy resin or a glycidyl ether type epoxy resin.

[0048] In some embodiments, the pressure-sensitive adhesive composition further includes 0-20 parts of additives; the additives include organic solvents, inorganic fillers, wetting agents, tackifiers, antioxidants, UV stabilizers, or mildew inhibitors.

[0049] Preferably, the organic solvent includes toluene, xylene, or ethyl acetate; when the viscosity of the pressure-sensitive adhesive composition is high, the viscosity can be reduced by adding an organic solvent.

[0050] The present invention also provides a method for preparing pressure-sensitive adhesive, which uses the pressure-sensitive adhesive composition described above as a raw material and includes the following steps:

[0051] S1. The modified polymer, the first polymer, the tackifying resin and the plasticizer are heated and mixed to obtain a premix;

[0052] S2. Mix the cooled premix with the curing agent to obtain a pressure-sensitive adhesive.

[0053] In step S1 of the present invention, the heating and mixing are carried out in a preheated reaction device.

[0054] In some embodiments, in step S1, the temperature of the heating mixture is 80-150°C.

[0055] In some embodiments, in step S1, the viscosity of the premix is ​​controlled to be less than 10000 mPa·s at 25°C.

[0056] In some embodiments, in step S1, when the viscosity of the premix at 25°C is greater than or equal to 10000 mPa·s, an organic solvent is added to the premix.

[0057] In some embodiments, in step S1, the solid content of the premix is ​​10% to 20%.

[0058] In some embodiments, in step S2, the temperature of the premix before mixing with the curing agent is controlled to be below 35°C.

[0059] The present invention also provides a pressure-sensitive adhesive, which is prepared by the preparation method described above.

[0060] The present invention also provides an adhesive tape comprising a substrate and a pressure-sensitive adhesive coated on the substrate, the pressure-sensitive adhesive comprising the pressure-sensitive adhesive described above, and obtained after curing.

[0061] In this invention, the curing reaction conditions can be: curing temperature of 80-150℃ and curing time of 2-72h.

[0062] In this invention, the substrate includes polyethylene terephthalate (PET) or polyimide (PI).

[0063] In this invention, the tape is prepared by: applying the pressure-sensitive adhesive onto a substrate, curing it to form a pressure-sensitive adhesive, attaching a release film, and then rolling it up.

[0064] The present invention also provides the application of the pressure-sensitive adhesive or the tape described above in the bonding of battery cell components.

[0065] In this invention, the battery cell assembly is bonded by applying adhesive tape to the welding position of the electrode tabs, thereby effectively preventing weld slag from falling off and protecting the battery cell from short circuits. Simultaneously, there is almost no adhesive overflow during subsequent high-temperature and high-pressure battery cell processing steps; furthermore, because this pressure-sensitive adhesive has a cross-linking system, it will not be dissolved by the electrolyte and maintains high adhesion even when immersed in the electrolyte, far exceeding that of traditional thermoplastic rubber-type pressure-sensitive adhesives.

[0066] Compared with the prior art, the present invention has the following significant advantages:

[0067] This invention prepares a cross-linked pressure-sensitive adhesive by selecting specific modified polymers and suitable epoxy curing agents. Compared to traditional non-cross-linked pressure-sensitive adhesives, which are not resistant to electrolytes and suffer from the problem of difficulty in simultaneously achieving good initial tack and heat resistance, the pressure-sensitive adhesive of this application simultaneously possesses excellent initial tack, heat resistance, and electrolyte resistance; specifically, the initial tack is not less than 0.1 N / mm, the overflow width after hot pressing is less than 0.5 mm, and the adhesion retention rate after immersion in electrolyte is not less than 50%. The tape of this invention is highly suitable for the internal structure of lithium batteries. Detailed Implementation

[0068] The present invention will be further described in detail below through preferred embodiments, but the scope of protection of the present invention is not limited thereto.

[0069] Preliminary Examples 1-5

[0070] The preceding examples in this group correspond to five different modified polymers in the pressure-sensitive adhesive composition.

[0071] Modified polymer 1: self-made, the number average molecular weight Mn of the modified polymer is 2000, the acid value is 0.8mgKOH / g, the storage modulus at 25℃ is 0.8MPa, the melting point is -45℃, and the grafting rate is 1.5%.

[0072] The preparation method of this modified polymer includes the following steps:

[0073] S1. Weigh 100g of PPA330 (an amorphous propylene-ethylene copolymer, which is liquid at room temperature) from Clariant Ltd. and 500g of xylene into a four-necked flask and stir at 80°C to dissolve it.

[0074] S2. Add 10g of maleic anhydride and 2g of dicumyl peroxide (DCP), and stir at 90℃ for 6 hours. Cool to room temperature, wash with 500g of deionized water, and allow to stand. Take the clear supernatant, remove the solvent, and obtain the intermediate product, which is a maleic anhydride-grafted polyolefin. The grafting process is shown in Formula I:

[0075]

[0076] S3. Add 200g xylene and 50g methanol to the intermediate product, reflux and stir at 100℃ for 12h, wash with deionized water to remove solvent. Maleic anhydride grafted onto polyolefin reacts with methanol, undergoing ring-opening to convert maleic anhydride into carboxylic acid and methyl ester; the grafting process is shown in Formula II:

[0077]

[0078] The final product is a modified polyolefin with carboxyl groups in the side chain, which is a paste-like, flowable liquid at room temperature.

[0079] In formulas I and II, R represents a polymer chain segment.

[0080] Modified polymer 2: self-made, the number average molecular weight Mn of the modified polymer is 2300, the acid value is 0.6mgKOH / g, the storage modulus at 25℃ is 0.05MPa, the melting point is -55℃, and the grafting rate is 1.9%.

[0081] The preparation method of this modified polymer includes the following steps:

[0082] S1. Weigh 100g of Polyvest 110 (a liquid polybutadiene at room temperature) and 500g of xylene from Evonik and place them in a four-necked flask. Stir at 80°C to dissolve.

[0083] S2. Add 10g of maleic anhydride and 2g of dicumyl peroxide (DCP), and stir at 90℃ for 6 hours. Cool to room temperature, wash with 500g of deionized water, and let stand. Take the clear supernatant, remove the solvent, and obtain maleic anhydride-grafted liquid polybutadiene.

[0084] Modified polymer 3: Polyvest MA75 from Evonik (a polybutadiene with maleic anhydride side chains) was selected. It has a number-average molecular weight (Mn) of 3000, an acid value of 70-90 mg KOH / g, a storage modulus of 0.6 MPa at 25°C, a melting point of -25°C, and a grafting rate of 2%.

[0085] Modified polymer 4: Kraton FG1901 (a maleic anhydride-modified SEBS) was selected. The styrene content was 30%, the maleic anhydride grafting rate was 1.7%, the acid value was 70-90 mg KOH / g, the storage modulus E' at 25℃ was 35 MPa, and the melt index was 22 g / 10 min.

[0086] Modified polymer 5: Self-made. The modified polymer has a number-average molecular weight (Mn) of 2000, an acid value of 0.5 mg KOH / g, a storage modulus of 0.8 MPa at 25℃, a melting point of -45℃, and a grafting rate of 0.05%. The preparation method of this modified polymer includes the following steps:

[0087] S1. Weigh 100g of PPA330 (an amorphous propylene-ethylene copolymer, which is liquid at room temperature) from Clariant Ltd. and 500g of xylene into a four-necked flask and stir at 80°C to dissolve it.

[0088] S2. Add 1g of maleic anhydride and 0.2g of dicumyl peroxide (DCP), and stir at 90℃ for 1h. Cool to room temperature, wash with 500g of deionized water, and let stand. Take the clear supernatant, remove the solvent, and obtain maleic anhydride-grafted polyolefin.

[0089] Examples 1-6

[0090] This set of examples provides pressure-sensitive adhesive compositions, pressure-sensitive adhesives, and their preparation methods.

[0091] The pressure-sensitive adhesive composition of Example 1 consists of modified polymer 1 and epoxy curing agent 1.

[0092] The pressure-sensitive adhesive composition of Example 2 consists of modified polymer 2, first polymer, tackifying resin 1 and epoxy curing agent 1.

[0093] The pressure-sensitive adhesive composition of Example 3 consists of modified polymer 3 and epoxy curing agent 1.

[0094] The pressure-sensitive adhesive composition of Example 4 consists of modified polymer 1, modified polymer 3 and epoxy curing agent 1.

[0095] The pressure-sensitive adhesive composition of Example 5 consists of modified polymer 1, first polymer, tackifying resin 1, plasticizer and epoxy curing agent 1.

[0096] The pressure-sensitive adhesive composition of Example 6 consists of modified polymer 3, first polymer, tackifying resin 2, plasticizer and epoxy curing agent 1.

[0097] The preparation methods of the pressure-sensitive adhesives in Examples 1-6 include the following steps:

[0098] S1. Add the modified polymer, the first polymer, the tackifying resin, the plasticizer, and the additives to the preheated reaction equipment. Heat and stir thoroughly at 80-150°C to obtain a premix. If the viscosity of the premix exceeds 10000 mPa·s at 25°C, an organic solvent needs to be added to control the solid content between 10% and 20%.

[0099] S2. After cooling, control the system temperature below 35℃, add curing agent to the premix, and stir thoroughly to obtain cross-linked pressure-sensitive adhesive.

[0100] Comparative Examples 1-4

[0101] This comparative example provides pressure-sensitive adhesive compositions, pressure-sensitive adhesives, and their preparation methods.

[0102] The pressure-sensitive adhesive composition of Comparative Example 1 consists of modified polymer 2, modified polymer 4 and a first polymer.

[0103] The pressure-sensitive adhesive composition of Comparative Example 2 consists of a first polymer, tackifying resin 1, and a plasticizer.

[0104] The pressure-sensitive adhesive composition of Comparative Example 3 consists of modified polymer 4 and epoxy curing agent 2.

[0105] The pressure-sensitive adhesive composition of Comparative Example 4 consists of modified polymer 5 and epoxy curing agent 2.

[0106] The types and specific amounts of components in Examples 1-6 and Comparative Examples 1-4 are shown in Table 1. Table 1 shows the pressure-sensitive adhesive compositions of Examples 1-6 and Comparative Examples 1-4.

[0107] Table 1

[0108]

[0109] In the table above, modified polymers 1-5 are the modified polymers in the previous examples, and blank spaces indicate "content of 0".

[0110] Both SEBS rubber and APAO are first polymers (unmodified). The SEBS rubber used is Kraton G1726 from Kraton, with a styrene content of 30% and a melt index of 65. The APAO used is Vestoplast 751 from Evonik, with a ring and ball softening point of 99°C, a tensile strength of 1.5 MPa, and pressure sensitivity at room temperature.

[0111] The tackifying resin 1 is Kolon's SU 100, a modified DCPD resin with a ring and ball softening point of 100℃.

[0112] The tackifying resin 2 is Wingtack 95 from Creville, a C5 petroleum resin with a ring and ball softening point of 98°C.

[0113] The plasticizer currently used is PB 950 from Daelim Corporation of South Korea, which is polyisobutylene with a molecular weight of 950.

[0114] The epoxy curing agent 1 is trimethylolpropane triglycidyl ether, a trifunctional epoxy resin, CAS 30499-70-8.

[0115] Epoxy curing agent 2 is pentaerythritol tetraglycidyl ether, a tetrafunctional epoxy resin, CAS 3126-63-4.

[0116] Effect Example

[0117] This effective example tested the performance of the pressure-sensitive adhesives formed in Examples 1-6 and Comparative Examples 1-4.

[0118] The pressure-sensitive adhesives in Examples 1-6 were processed as follows: the pressure-sensitive adhesive composition was coated onto a PET or PI substrate at room temperature using a film scraper, and then baked at 80°C for 72 hours to obtain a pressure-sensitive adhesive film. The substrate thickness was 20 μm, and the adhesive layer thickness was 5 μm. The prepared pressure-sensitive adhesive film was used for subsequent testing.

[0119] The pressure-sensitive adhesive compositions of Comparative Examples 1-4 were directly mixed and coated onto PET or PI substrates to obtain adhesive films for subsequent testing.

[0120] The pressure-sensitive adhesive films formed in Examples 1-6 and Comparative Examples 1-4 were subjected to the following performance tests:

[0121] (1) Initial tack test

[0122] Test method: Cut the adhesive film into strips of 20mm × 100mm, attach them to a stainless steel plate, press them back and forth three times with a 2kg roller, and let them stand for 2 hours. Test the 180° peel force at 50mm / min, in N / mm.

[0123] (2) Glue overflow width test

[0124] Test method: A 20mm×100mm sample strip is attached to the surface of aluminum foil and rolled back and forth 3 times with a 2kg roller. It is then placed under a hot press and pressed for 1 hour at 85℃ and 1Mpa. The width of the adhesive overflow is measured in mm using a two-dimensional microscope.

[0125] (3) Electrolyte resistance test

[0126] Test method: A 20mm×100mm sample strip was attached to the surface of aluminum foil and rolled back and forth 3 times with a 2kg roller. After standing for 2 hours, it was immersed in an electrolyte (the electrolyte included ethylene carbonate, dimethyl carbonate, and lithium hexafluorophosphate, with the volume ratio of ethylene carbonate and dimethyl carbonate being 1:2 and lithium hexafluorophosphate accounting for 14% of the total mass). It was then placed in an 85℃ oven and removed after 4 hours. The surface electrolyte was wiped dry, and the adhesion of the adhesive film to the aluminum foil was tested after 30 minutes. The test method was the same as (1), and the 180° peel force was tested at a peel speed of 50mm / min, in N / mm. After the test, the interface damage mode was checked. AF refers to interface damage, with the adhesive remaining on the substrate; CF refers to adhesive cohesive damage, with adhesive on both the aluminum foil and the substrate.

[0127] Table 2 shows the performance data of the pressure-sensitive adhesives in Examples 1-6 and Comparative Examples 1-4.

[0128] Table 2

[0129]

[0130] As shown in Table 2, the pressure-sensitive adhesives of Examples 1-6 exhibited good initial tack, all exceeding 0.1 N / mm. Furthermore, the pressure-sensitive adhesives of Examples 1-6 demonstrated good heat resistance, with hot-press overflow widths all below 0.5 mm, significantly lower than those of Comparative Examples 1, 2, and 4. In addition, after immersion in the electrolyte, the adhesive strength of Comparative Examples 1, 2, and 4 decreased to 0.01 N / mm, and the failure mode was cohesive failure, with adhesive remaining on both the aluminum foil and the substrate. In contrast, the pressure-sensitive adhesives of Examples 1-6 showed better electrolyte resistance, retaining adhesive strength after immersion in the electrolyte, with an adhesion retention rate exceeding 50%, and the failure mode was interfacial failure, with the adhesive remaining on the substrate.

[0131] Comparative Example 3 used a modified rubber with ultra-high modulus (storage modulus E' of 35 MPa at 25°C), resulting in very low initial tack after the addition of the curing agent, almost no initial tack at room temperature, and no pressure sensitivity. Immersion in the electrolyte softened the polymer, and its adhesive strength increased somewhat. Comparative Example 4 used a modified polyolefin with a very low grafting rate, resulting in very high initial tack. However, due to the low grafting rate (0.05%), the crosslinking density with the curing agent was low, leading to a significant decrease in adhesive strength after immersion in the electrolyte and weak electrolyte resistance.

[0132] As can be seen, the pressure-sensitive adhesives in Examples 1-6 of this application contain modified polymers with reactive functional groups combined with epoxy curing agents to form a crosslinked pressure-sensitive adhesive with good heat resistance and low overflow width after hot pressing. In contrast, the non-crosslinked and weakly crosslinked thermoplastic formulations (Comparative Examples 1, 2, and 4) have higher overflow widths after hot pressing, making them unusable by customers. Furthermore, the crosslinked formulations, after being immersed in electrolyte, still possess good adhesion, and the failure mode is interfacial failure, with the adhesive itself not being dissolved by the electrolyte. In contrast, the non-crosslinked thermoplastic formulations, after being immersed in electrolyte, are severely swollen or dissolved, with significantly reduced cohesion, resulting in adhesive cohesive failure during peeling.

[0133] The pressure-sensitive adhesives of Examples 1-6 can be used to prepare tapes that can be used to protect the tabs on lithium battery cells.

Claims

1. A pressure-sensitive adhesive composition, characterized in that, By weight, it includes: 20-99 parts of modified polymer; First polymer: 0-40 parts; 0-50 parts of tackifying resin; Plasticizer 0-50 parts; 0.01-5 parts of epoxy curing agent; The modified polymer includes polymers grafted with carboxylic acids or anhydrides, with a storage modulus E' of 0.01 to 20 MPa at 25°C and a grafting rate of 0.1% to 10%.

2. The pressure-sensitive adhesive composition according to claim 1, characterized in that, The modified polymer satisfies at least one of the following conditions: i. The modified polymer includes modified polyolefins and / or modified rubber; ii. The modified polymer contains functional groups, which are selected from at least one of carboxyl groups, maleic anhydride groups, itaconic anhydride groups, and citraconic anhydride groups; iii. The storage modulus E' of the modified polymer at 25°C is 0.01–5 MPa; iv. The grafting rate of the modified polymer is 0.1% to 3%; v. The acid value of the modified polymer is 0.5–100 mg KOH / g; vi. The number-average molecular weight Mn of the modified polymer is 500 to 150,000; vii. The melting point Tm of the modified polymer is below 120°C; viii. When the modified polymer is a solid, its melt flow index is greater than or equal to 1000 g / 10 min.

3. The pressure-sensitive adhesive composition according to claim 2, characterized in that, The modified polymer satisfies at least one of the following conditions: i. The amount of the modified polymer used is 30-99 parts; ii. The modified polyolefin is obtained by modifying a polyolefin, wherein the polyolefin includes self-polymers or copolymers of olefins, and the olefin is selected from at least one of ethylene, propylene, butene, hexene and octene; iii. The modified rubber is obtained by modifying rubber, and the rubber is selected from at least one of SBS, SEBS, SEP, SEPS, SIS, IIR, PIB, NBR, IR, PBAN, SPR, PBS, EPDM, and thermoplastic polymers synthesized from butadiene and isoprene; iv. When the modified polymer comprises modified polyolefin and modified rubber, the mass ratio of the modified polyolefin to the modified rubber is 1:(0.5-3).

4. The pressure-sensitive adhesive composition according to claim 1, characterized in that, The first polymer satisfies at least one of the following conditions: i. The first polymer comprises a polyolefin and / or rubber; wherein the polyolefin comprises a self-polymer or copolymer of an olefin selected from at least one of ethylene, propylene, butene, hexene, and octene; and the rubber is selected from at least one of SBS, SEBS, SEP, SEPS, SIS, IIR, PIB, NBR, IR, PBAN, SPR, PBS, EPDM, and thermoplastic polymers synthesized from butadiene and isoprene. ii. The amount of the first polymer used is 5-40 parts; iii. The melt index of the first polymer is greater than or equal to 5 g / 10 min.

5. The pressure-sensitive adhesive composition according to claim 1, characterized in that, The pressure-sensitive adhesive composition satisfies at least one of the following conditions: i. The amount of the tackifying resin used is 10-50 parts; ii. The tackifying resin is selected from at least one of dicyclopentadiene resin, coumarone-indene resin, styrene resin, terpene resin, C5 petroleum resin, C9 petroleum resin, C5-C9 copolymer resin, and their hydrogenated products; iii. The amount of the plasticizer used is 0.5-30 parts; iv. The plasticizer is selected from liquid polyolefins that are free-flowing at room temperature; v. The amount of the epoxy curing agent used is 0.1-1 part; vi. The epoxy curing agent includes liquid epoxy resin; vii. The pressure-sensitive adhesive composition further includes: 0-20 parts of additives; the additives include organic solvents, inorganic fillers, wetting agents, adhesion promoters, antioxidants, UV-resistant additives, or mildew-resistant additives.

6. A method for preparing a pressure-sensitive adhesive, characterized in that, It uses the pressure-sensitive adhesive composition as described in any one of claims 1-5 as raw material, and includes the following steps: S1. The modified polymer, the first polymer, the tackifying resin and the plasticizer are heated and mixed to obtain a premix; S2. Mix the cooled premix with the curing agent to obtain a pressure-sensitive adhesive.

7. The preparation method according to claim 6, characterized in that, The preparation method satisfies at least one of the following conditions: i. In step S1, the temperature of the heating and mixing is 80-150℃; ii. In step S1, the viscosity of the premix at 25°C is controlled to be less than 10000 mPa·s; iii. In step S1, when the viscosity of the premix at 25°C is greater than or equal to 10000 mPa·s, an organic solvent is added to the premix. iv. In step S1, the solid content of the premix is ​​10% to 20%; v. In step S2, the temperature of the premix before mixing with the curing agent is controlled to be below 35°C.

8. A pressure-sensitive adhesive, characterized in that, It is prepared by the method described in claim 6 or 7.

9. A tape comprising a substrate and a pressure-sensitive adhesive coated on the substrate, characterized in that, The pressure-sensitive adhesive includes the pressure-sensitive adhesive as described in claim 8, and is obtained after curing.

10. The application of a pressure-sensitive adhesive as described in claim 8 or an adhesive tape as described in claim 9 in the bonding of battery cell assemblies.

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