An ultrathin termination adhesive tape, a preparation method and application thereof

Abstract

The application discloses an ultrathin termination adhesive tape and a preparation method and application thereof. The termination adhesive tape comprises a substrate layer and a dry adhesive layer coated on the surface of the substrate layer; the thickness of the dry adhesive layer is 2-3 microns, and the thickness of the substrate layer is 4-6 microns; the dry adhesive layer is obtained by drying pressure-sensitive adhesive; the pressure-sensitive adhesive comprises the following raw materials in parts by weight: ɑ-olefin copolymer 30-40 parts, hydrogenated styrene block copolymer 20-40 parts, rubber liquid 105-210 parts, tackifying resin 20-50 parts and composite antioxidant 2-12 parts. The application has the advantages of reducing the thickness of the adhesive tape and improving the peeling force, adhesion and electrolyte resistance of the adhesive tape.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, and in particular to an ultrathin terminating tape, its preparation method, and its application. Background Technology

[0002] With the development of new energy technologies, lithium-ion batteries are widely used in mobile phones, automobiles, laptops and other fields. Moreover, the requirements for lithium-ion batteries in various fields are getting higher and higher, and the research on high energy density and lightweight lithium-ion batteries has gradually become a research hotspot.

[0003] Reducing the thickness of the terminating tape can improve the energy density of lithium-ion batteries and achieve their lightweighting. However, the manufacturing technology of ultra-thin tapes is still immature. When the adhesive layer is ultra-thin, the final tape is difficult to meet the requirements for peel strength and initial tack. More seriously, during electrolyte resistance testing, the ultra-thin adhesive layer will peel off from the substrate surface and fail to meet the usage requirements. In addition, when the ultra-thin adhesive layer is coated on an ultra-thin substrate, uneven tension or high tension often results in the substrate being stretched and deformed or forming dead wrinkles.

[0004] In response to the increasing demand for thinner termination tapes in the lithium battery market, there is a need to provide an ultra-thin termination tape that can combine the electrochemical performance of lithium batteries with excellent peel strength, initial tack, and resistance to electrolyte aging. Summary of the Invention

[0005] To improve the peel strength, adhesion, and electrolyte resistance of ultrathin tapes, this application provides an ultrathin terminating tape, its preparation method, and its application.

[0006] In a first aspect, this application provides a termination tape, which adopts the following technical solution:

[0007] A terminating tape includes a substrate layer and a dry adhesive layer coated on the surface of the substrate layer; the thickness of the dry adhesive layer is 2-3 μm, and the thickness of the substrate layer is 4-6 μm;

[0008] The dry adhesive layer is obtained by drying the pressure-sensitive adhesive, which comprises the following raw materials in parts by weight: 30-40 parts of α-olefin copolymer, 20-40 parts of hydrogenated styrene block copolymer, 105-210 parts of rubber liquid, 20-50 parts of tackifying resin, and 2-12 parts of composite antioxidant.

[0009] The rubber liquid is obtained by mixing modified butyl rubber with an organic solvent, and the concentration of the rubber liquid is 2.5wt%-10wt%. The modified butyl rubber is prepared by a mixture of butyl rubber, maleic anhydride, and benzoyl peroxide through steps including mixing, stirring, heating, granulation, and drying.

[0010] The modified butyl rubber has an unsaturation degree of 2.5-3.5%, a weight-average molecular weight of 50,000-200,000, and a melt viscosity of 3,000-10,000 mPa·s at 180-200℃.

[0011] First, the introduction of modified butyl rubber improves its compatibility with other components. Furthermore, the modified butyl rubber can react with the hydroxyl groups in other components to form a cross-linked network structure, overcoming the poor self-adhesion and mutual adhesion of butyl rubber, thereby improving the adhesion performance of the dry adhesive layer. Second, by controlling the concentration of the rubber solution to 2.5wt%-10wt%, the viscosity of the rubber solution at this concentration can be controlled within an appropriate range, allowing other components in the pressure-sensitive adhesive to mix uniformly with the rubber solution. This results in a pressure-sensitive adhesive with excellent adhesion, peel resistance, and flame retardant properties, and ultimately... The prepared dry adhesive layer has high flexibility and is easy to bend, making it suitable for various application scenarios. Third, this invention introduces α-olefin copolymer, hydrogenated styrene block copolymer, and butyl rubber into the dry adhesive layer of the terminating tape. Butyl rubber has extremely low unsaturation, and its molecular chain is mostly composed of inert isobutylene segments, thus possessing excellent resistance to oxygen, chemical media, and heat aging. Combined with α-olefin copolymer and hydrogenated styrene block copolymer, the terminating tape exhibits excellent adhesion and chemical resistance, improving the stability between the battery electrode assembly and the outer packaging material, and enhancing the safety of the lithium battery. Fourth, because the total thickness of the terminating tape in this invention is reduced to below 10 μm, the energy density of the lithium battery can be significantly improved. By controlling the modified butyl rubber with the above-mentioned properties as a component of the pressure-sensitive adhesive in the rubber solution, the viscosity of the pressure-sensitive adhesive can be maintained within a certain range during the coating process, further improving the adhesion, flame retardancy, and electrolyte resistance of the dry adhesive layer formed by this pressure-sensitive adhesive.

[0012] The concentration of the rubber liquid refers to the mass percentage of modified butyl rubber in the rubber liquid.

[0013] Preferably, the organic solvent includes at least one of toluene and xylene.

[0014] Preferably, the modified butyl rubber is prepared by the following steps: butyl rubber is kneaded at 180-300 rpm for 25-35 minutes in an environment of 120-140℃, then mixed with maleic anhydride, heated to 145-155℃ and stirred for 50-70 minutes, benzoyl peroxide is added, and the temperature is further raised to 175-185℃ and stirred for 50-70 minutes, followed by granulation and drying.

[0015] Preferably, based on the modified butyl rubber, the modified butyl rubber comprises the following raw materials in parts by weight: 80-100 parts butyl rubber, 1-5 parts maleic anhydride, and 0.5-1 parts benzoyl peroxide.

[0016] By using the above preparation method, unsaturated double bonds and carboxyl groups are introduced into butyl rubber without changing the original molecular chain, which improves the reactivity of the modified butyl rubber liquid with each component and is beneficial to preparing a dry adhesive layer with excellent adhesion properties.

[0017] Preferably, the hydrogenated styrene block copolymer includes at least one of hydrogenated styrene thermoplastic elastomer SEBS and hydrogenated styrene thermoplastic elastomer SEPS, and the weight-average molecular weight of the hydrogenated styrene block copolymer is 20,000-50,000.

[0018] By adjusting the melt viscosity and weight-average molecular weight of the hydrogenated styrene block copolymer, it can be matched with the components in the pressure-sensitive adhesive, so that the molecular weight of the pressure-sensitive adhesive system is maintained within an appropriate range. This is beneficial to the dispersion of the adhesive system and the performance of each component, ultimately resulting in a pressure-sensitive adhesive with excellent electrolyte resistance and adhesion properties.

[0019] Preferably, the styrene content in the hydrogenated styrene block copolymer is 10wt-30wt%.

[0020] Preferably, based on the pressure-sensitive adhesive, the pressure-sensitive adhesive further includes 5-10 parts of flame retardant; the flame retardant includes at least one of decabromodiphenyl ether, octabromodiphenyl ether, and decabromodiphenyl ethane.

[0021] By selecting bromine-containing compounds as flame retardants, they can work together with butyl rubber in the rubber liquid to significantly improve the flame retardant and aging resistance of the pressure-sensitive adhesive.

[0022] Preferably, the α-olefin copolymer includes at least one of amorphous α-olefin copolymer and polyolefin elastomer POE; wherein the amorphous α-olefin copolymer has a melt viscosity of 3000-10000 mPa·s at 180-200℃ and a weight-average molecular weight Mw of 30000-80000, and the polyolefin elastomer POE has a melt index of 30-40 g / min at 180-200℃.

[0023] Preferably, the tackifying resin includes at least one of C5 petroleum resin, C5 hydrogenated petroleum resin, C9 hydrogenated petroleum resin, and terpene resin.

[0024] Preferably, the composite antioxidant includes a combination of at least one of antioxidant 1010, antioxidant 1076 or antioxidant 1726 and antioxidant 168.

[0025] Secondly, this application provides a method for preparing a termination tape, which adopts the following technical solution:

[0026] A method for preparing a terminating tape includes the following steps:

[0027] Step 1: Apply pressure-sensitive adhesive to the surface of the non-silicone release film in a heated environment using a micro-gravure coating method, and then dry it to form a dry adhesive layer on the surface of the non-silicone release film.

[0028] Step 2: The dry adhesive layer is bonded to the substrate layer to form a three-layer semi-finished product; the dry adhesive layer is then transferred onto the substrate layer to obtain an ultra-thin termination tape.

[0029] Preferably, the temperature during the drying process is 90-120℃.

[0030] Preferably, the drying process uses 6-8 drying ovens, and the length of each drying oven is 3-4m.

[0031] By employing microgravure coating, pressure-sensitive adhesive can be quantitatively coated onto the surface of the non-silicone release film to form a continuous, uniform, and evenly thick wet adhesive layer. After the wet adhesive layer is baked in an oven, it forms a dry adhesive layer, which is then bonded to the coated surface of the substrate layer. During post-processing, the non-silicone release film can be peeled off, and the dry adhesive layer can be 100% transferred to the substrate layer.

[0032] Preferably, in step one, the temperature of the pressure-sensitive adhesive is 60-85°C, and the ambient temperature when the pressure-sensitive adhesive is coated on the surface of the non-silicone release film is the same as the temperature of the pressure-sensitive adhesive.

[0033] At this temperature, the viscosity of the pressure-sensitive adhesive is 500-3000 cps. At this temperature, the pressure-sensitive adhesive has good flowability and can form a thin and uniform wet adhesive layer on the surface of the non-silicone release film.

[0034] Preferably, in step one, the thickness of the non-silicone release film is 12-25 μm, and the release force of the non-silicone release film is 100-300 g; in step one, the content of volatile organic compounds in the dry adhesive layer obtained after drying is ≤1 wt%.

[0035] By adjusting the release force of the non-silicone release film and the content of volatile organic compounds in the dry adhesive layer, the bonding performance between the pressure-sensitive adhesive and the non-silicone release film can be further improved, thereby enhancing the surface smoothness and thickness uniformity of the dry adhesive layer. At the same time, the dry adhesive layer exhibits excellent initial ball tack performance at room temperature, reducing the difficulty of bonding the dry adhesive layer to the substrate layer and facilitating the film-to-adhesive transfer operation in the post-processing stage, allowing the dry adhesive layer to be completely transferred to the surface of the substrate layer.

[0036] Preferably, in step two, the dyne value of the coating surface of the substrate layer is 42-52; during the coating process in step two, the bonding pressure between the dry adhesive layer and the substrate layer is 0.03-0.08 MPa.

[0037] This reduces the difficulty of bonding the dry adhesive layer to the substrate layer, allowing the dry adhesive layer to be completely transferred to the substrate layer. Furthermore, during the transfer of the dry adhesive layer, the deformation of the substrate layer is minimized to avoid the formation of dead wrinkles, thereby improving the safety performance of the termination tape.

[0038] Thirdly, this application provides a lithium battery, which adopts the following technical solution:

[0039] A lithium battery that uses the termination tape described above during its manufacturing process. Detailed Implementation

[0040] To better understand and implement this invention, the technical solution will be clearly and completely described below with reference to embodiments.

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0042] Unless otherwise stated, all numerical values ​​for the amounts of expressed components, reaction conditions, etc., used in the specification and claims are to be understood as being modified by the term "about". Therefore, unless otherwise indicated, the numerical parameters set forth herein are approximate values ​​that can be varied to obtain the desired performance.

[0043] The word “and / or” as used in this article refers to one or all of the elements mentioned.

[0044] The terms "include" and "contain" as used in this article cover both cases where only the mentioned elements exist and cases where other unmentioned elements exist in addition to the mentioned elements.

[0045] All percentages in this invention are weight percentages, unless otherwise stated.

[0046] Unless otherwise stated, the terms “a,” “an,” “an,” and “the” as used in this specification are intended to include “at least one” or “one or more.” For example, “a component” refers to one or more components, and therefore more than one component may be considered and may be employed or used in the implementation of the described embodiments.

[0047] Example

[0048] Example 1

[0049] 1. Preparation of ultra-thin termination tape

[0050] (1) Preparation of modified butyl rubber

[0051] 90g of butyl rubber was kneaded at 240rpm for 30min at 130℃ and then mixed with 3g of maleic anhydride. The mixture was heated to 150℃ and stirred for 60min. 1g of benzoyl peroxide was added, and the mixture was heated to 180℃ and stirred for 60min. Granulation was then carried out at 180℃. The granulated product was vacuum dried at 70℃ for 10h to obtain the modified butyl rubber.

[0052] (2) Preparation of pressure-sensitive adhesive

[0053] 35g polyolefin elastomer POE: The melt index of polyolefin elastomer POE at 180-200℃ is 30-35g / min; 30g hydrogenated styrene thermoplastic elastomer SEBS with a styrene content of 20wt% and a weight average molecular weight of 20000-50000; 35g C9 hydrogenated petroleum resin; 3g antioxidant 1010; 4g antioxidant 168; 105g of a 5wt% rubber liquid prepared from the above modified butyl rubber: wherein the degree of unsaturation of the modified butyl rubber in the rubber liquid is 2.5-3.5%, the weight average molecular weight is 50000-200000, and the melt viscosity of the modified butyl rubber at 180-200℃ is 3000-10000mPa.s; and toluene is selected as the solvent in the rubber liquid.

[0054] (3) Preparation of ultra-thin termination tape

[0055] Step 1: Apply pressure-sensitive adhesive at 70°C to the surface of a non-silicone release film with a thickness of 18μm and a release force of 200g using a microgravure coating method in an environment of 70°C. Dry the film in a 7-section oven to form a dry adhesive layer with a thickness of 3μm and a volatile organic compound content of 0.5wt% on the surface of the non-silicone release film.

[0056] Step 2: The dry adhesive layer is bonded to a substrate layer with a thickness of 5μm and a coating dyne value of 46 at 0.05MPa to form a three-layer semi-finished product. After the three-layer semi-finished product is automatically wound up, it is then rewound and the non-silicone release film is peeled off. The dry adhesive layer is transferred to the coating surface of the ultra-thin release film. After winding, slitting and other processes, the production is completed, and an ultra-thin termination tape with a total thickness of 8μm is obtained.

[0057] 2. Preparation of lithium batteries

[0058] The aforementioned ultra-thin termination tape is applied in the assembly of lithium batteries.

[0059] Example 2

[0060] 1. Preparation of ultra-thin termination tape

[0061] (1) Preparation of modified butyl rubber

[0062] 80g of butyl rubber was kneaded at 180rpm for 35min at 140℃ and then mixed with 1g of maleic anhydride. The mixture was heated to 145℃ and stirred for 70min. 0.8g of benzoyl peroxide was added, and the mixture was heated to 185℃ and stirred for 50min. Granulation was then carried out at 180℃. The granulated product was vacuum dried at 70℃ for 10h to obtain the modified butyl rubber.

[0063] (2) Preparation of pressure-sensitive adhesive

[0064] 30g of amorphous α-olefin copolymer: the amorphous α-olefin copolymer has a melt viscosity of 3000-10000 mPa·s at 180-200℃ and a weight-average molecular weight (Mw) of 30000-80000; 40g of hydrogenated styrene thermoplastic elastomer SEPS with a styrene content of 10wt% and a weight-average molecular weight of 20000-50000; 20g of C5 hydrogenated petroleum resin; 4g of antioxidant 1010; 8g of antioxidant 168; and 110g of a 10wt% rubber liquid prepared from the above modified butyl rubber: wherein the modified butyl rubber in the rubber liquid has an unsaturation degree of 2.5-3.5%, a weight-average molecular weight of 50000-200000, and a melt viscosity of 3000-10000 mPa·s at 180-200℃; and toluene is selected as the solvent in the rubber liquid.

[0065] (3) Preparation of ultra-thin termination tape

[0066] Step 1: Apply pressure-sensitive adhesive at 60°C to the surface of a non-silicone release film with a thickness of 12μm and a release force of 300g using a microgravure coating method in an environment of 60°C. Dry the film in an 8-section oven to form a dry adhesive layer with a thickness of 2μm and a volatile organic compound content of 0.2wt% on the surface of the non-silicone release film.

[0067] Step 2: The dry adhesive layer is bonded to a substrate layer with a thickness of 6μm and a coating dyne value of 42 at 0.08MPa to form a three-layer semi-finished product. After the three-layer semi-finished product is automatically wound up, it is then rewound and the non-silicone release film is peeled off. The dry adhesive layer is transferred to the coating surface of the ultra-thin release film. After winding, slitting and other processes, the production is completed, and an ultra-thin termination tape with a total thickness of 8μm is obtained.

[0068] 2. Preparation of lithium batteries

[0069] The aforementioned ultra-thin termination tape is applied in the assembly of lithium batteries.

[0070] Example 3

[0071] 1. Preparation of ultra-thin termination tape

[0072] (1) Preparation of modified butyl rubber

[0073] 100g of butyl rubber was kneaded at 300rpm for 25min at 120℃ and then mixed with 5g of maleic anhydride. The mixture was heated to 155℃ and stirred for 50min. 0.5g of benzoyl peroxide was added, and the mixture was heated to 175℃ and stirred for 70min. Granulation was then carried out at 180℃. The granulated product was vacuum dried at 70℃ for 10h to obtain the modified butyl rubber.

[0074] (2) Preparation of pressure-sensitive adhesive

[0075] 40g of amorphous α-olefin copolymer: the amorphous α-olefin copolymer has a melt viscosity of 3000-10000 mPa·s at 180-200℃ and a weight-average molecular weight (Mw) of 30000-80000; 20g of hydrogenated styrene thermoplastic elastomer SEBS with a styrene content of 30wt% and a weight-average molecular weight of 20000-50000; 50g of C9 hydrogenated petroleum resin; 1g of antioxidant 1726; 1g of antioxidant 168; and 205g of a 2.5wt% rubber liquid prepared from the above modified butyl rubber: wherein the modified butyl rubber in the rubber liquid has an unsaturation degree of 2.5-3.5%, a weight-average molecular weight of 50000-200000, and a melt viscosity of 3000-10000 mPa·s at 180-200℃; and xylene is selected as the solvent in the rubber liquid.

[0076] (3) Preparation of ultra-thin termination tape

[0077] Step 1: Apply pressure-sensitive adhesive at 85°C to the surface of a non-silicone release film with a thickness of 25μm and a release force of 100g using a microgravure coating method in an environment of 85°C. Dry the film in a 6-section oven to form a dry adhesive layer with a thickness of 3μm and a volatile organic compound content of ≤1wt% on the surface of the non-silicone release film.

[0078] Step 2: The dry adhesive layer is bonded to a substrate layer with a thickness of 4μm and a coating dyne value of 50 at 0.03MPa to form a three-layer semi-finished product. After the three-layer semi-finished product is automatically wound up, it is then rewound and the non-silicone release film is peeled off. The dry adhesive layer is transferred to the coating surface of the ultra-thin release film. After winding, slitting and other processes, the production is completed, and an ultra-thin termination tape with a total thickness of 7μm is obtained.

[0079] 2. Preparation of lithium batteries

[0080] The aforementioned ultra-thin termination tape is applied in the assembly of lithium batteries.

[0081] Example 4

[0082] The difference between this embodiment and Example 1 is that the weight-average molecular weight of the hydrogenated styrene block copolymer is 5000-10000; all other aspects are consistent with Example 1.

[0083] Example 5

[0084] The difference between this embodiment and Example 1 is that the weight-average molecular weight of the hydrogenated styrene block copolymer is 60,000-70,000; all other aspects are consistent with Example 1.

[0085] Example 6

[0086] The difference between this embodiment and Embodiment 1 is that the pressure-sensitive adhesive also includes 8g of flame retardant; otherwise, it is consistent with Embodiment 1.

[0087] Example 7

[0088] The difference between this embodiment and Embodiment 1 is that the pressure-sensitive adhesive also includes 5g of flame retardant; otherwise, it is consistent with Embodiment 1.

[0089] Example 8

[0090] The difference between this embodiment and Embodiment 1 is that the pressure-sensitive adhesive also includes 10g of flame retardant; otherwise, it remains the same as Embodiment 1.

[0091] Example 9

[0092] The difference between this embodiment and Embodiment 1 is that the release force of the non-silicone release film in step one is 50g; all other aspects are consistent with Embodiment 1.

[0093] Example 10

[0094] The difference between this embodiment and Embodiment 1 is that the release force of the non-silicone release film in step one is 350g; all other aspects are consistent with Embodiment 1.

[0095] Example 11

[0096] The difference between this embodiment and Embodiment 1 is that the content of volatile organic compounds in the dried adhesive layer obtained after drying is 1.5%; all other aspects are consistent with Embodiment 1.

[0097] Example 12

[0098] The difference between this embodiment and Embodiment 1 is that the dyne value of the substrate layer in step two is 40; all other aspects are consistent with Embodiment 1.

[0099] Example 13

[0100] The difference between this embodiment and Embodiment 1 is that the dyne value of the substrate layer in step two is 55; all other aspects are consistent with Embodiment 1.

[0101] Example 14

[0102] The difference between this embodiment and Embodiment 1 is that the bonding pressure between the dry adhesive layer and the substrate layer in step two is 0.01 MPa; all other aspects are consistent with Embodiment 1.

[0103] Example 15

[0104] The difference between this embodiment and Embodiment 1 is that the bonding pressure between the dry adhesive layer and the substrate layer in step two is 0.1 MPa; all other aspects are consistent with Embodiment 1.

[0105] Comparative Example

[0106] Comparative Example 1

[0107] The difference between this comparative example and Example 1 is that an equal weight of toluene is used instead of the rubber solution in this application; all other aspects are consistent with Example 1.

[0108] Comparative Example 2

[0109] The difference between this comparative example and Example 1 is that the temperature during the stirring and kneading of the butyl rubber in the preparation of the modified butyl rubber is 115°C; the degree of unsaturation of the final modified butyl rubber is 1.6-2.0%, and the weight-average molecular weight is 20,000-40,000; all other aspects are consistent with Example 1.

[0110] Comparative Example 3

[0111] The difference between this comparative example and Example 1 is that, in the process of preparing the modified butyl rubber, the stirring time after the butyl rubber is kneaded and mixed with maleic anhydride is 40 min, the temperature is 140℃, and the temperature during the final kneading is 115℃; the final modified butyl rubber has a melt viscosity of 1000-2000 mPa·s at 180-200℃; all other aspects are consistent with Example 1.

[0112] Comparative Example 4

[0113] The difference between this comparative example and Example 1 is that the concentration of the rubber liquid is 1 wt%; all other aspects are the same as in Example 1.

[0114] Comparative Example 5

[0115] The difference between this comparative example and Example 1 is that the thickness of the dry adhesive layer in the ultra-thin termination tape is 1 μm, and the thickness of the substrate layer is 3 μm; all other aspects are the same as in Example 1.

[0116] Comparative Example 6

[0117] The difference between this comparative example and Example 1 is that the thickness of the dry adhesive layer in the ultra-thin termination tape is 4 μm, and the thickness of the substrate layer is 8 μm; the rest are the same as those in Example 1.

[0118] Testing method

[0119] I. Peel strength test

[0120] 1. Peel strength PS0 test of the initial state of the ultra-thin termination tape

[0121] The ultra-thin termination tapes prepared in Examples 1-15 and Comparative Examples 1-6 were subjected to peel strength tests according to the method described in the national standard GB / T 2792-2014; the specific test method is as follows: The ultra-thin termination tape was cut into a tape sample with a width of 25 mm, the tape sample was pasted on a clean stainless steel plate, and a 2 kg rubber roller was used to roll back and forth 3 times at a speed of 10 mm / s. After standing for 20 min under the conditions of 23±1℃ and 55±5%, a universal tensile testing machine was used to pull it at an angle of 180 degrees and a speed of 300 mm / min. The average peel strength between 20-80 mm displacement was measured and recorded in Table 1.

[0122] 2. Peel strength PS1 test of the ultra-thin termination tape after hot pressing and soaking in electrolyte

[0123] The ultra-thin termination tapes obtained in Examples 1-15 and Comparative Examples 1-6 were subjected to peel strength tests after hot pressing; the specific test method is as follows: The ultra-thin termination tape was cut into a tape sample with a width of 25 mm, the tape sample was pasted on a 12 μm aluminum foil, and a 2 KG roller was used to roll back and forth 3 times. The bonded tape sample was allowed to stand for 20 min to obtain a test sample. The test sample was folded in half and placed in a bottle, and electrolyte was poured in. The test sample needed to be completely immersed in the electrolyte. Among them, the mass ratio of the electrolyte was as follows: EC / PC / DEC / EP = 30 / 10 / 30 / 30, and the mass ratio of 1M LiPF6 lithium salt was calculated at 12.5%. After covering the bottle cap and sealing, it was placed in an 85℃ oven and baked for 24H. After baking for 24H, the sample was taken out and placed in a fume hood to stand and wipe the electrolyte. The tape was tightly bonded to the substrate without displacement or shedding, the electrolyte did not change color or fade, the tape did not show electrolyte erosion or degumming, and no wrinkles appeared, which was considered qualified; after cooling to room temperature, the peel strength test was carried out according to the method described in the national standard GB / T 2792-2014. The test data was recorded in Table 1.

[0124] II. Initial adhesion performance test

[0125] The initial tack performance of the ultra-thin termination tapes of Examples 1-15 and Comparative Examples 1-6 was tested according to the inclined plane rolling ball method in the national standard GB / T 4582-2002. The median of the steel ball number (ball number) of the rolling ball test results of the three samples during the formal test is shown in Table 1.

[0126] III. Flame retardant properties

[0127] Flame retardancy tests were conducted on the ultra-thin termination tapes of Examples 1-15 and Comparative Examples 1-6. The flame retardancy of the samples was determined according to the method in GB / T2408-2008 standard, and the test results are recorded in Table 1.

[0128] Table 1

[0129]

[0130]

[0131] Combining Examples 1-3, Comparative Examples 1-4, and Table 1, by adding modified butyl rubber and controlling the unsaturation degree of the modified butyl rubber to be 2.5-3.5%, the weight-average molecular weight to be 50,000-200,000, and the melt viscosity at 180-200°C to be 3,000-10,000 mPa·s, and controlling the concentration ratio of modified butyl rubber in the rubber solution, the modified butyl rubber can be made compatible with α-olefin copolymers and hydrogenated benzene without changing the initial molecular chain structure of the butyl rubber. The synergistic effect of ethylene block copolymers is maximized, which is conducive to the formation of a three-dimensional network molecular structure in the reaction system, overcoming the defect of poor mutual adhesion of butyl rubber, and improving the oxidation resistance, heat resistance and electrolyte resistance of pressure-sensitive adhesive. Furthermore, by introducing polar groups into butyl rubber, it is beneficial for the modified butyl rubber and the components in the pressure-sensitive adhesive to cooperate with each other to form a pressure-sensitive adhesive with uniform composition and stable performance. This results in a soft adhesive layer with excellent adhesion and electrolyte resistance in the final ultra-thin termination tape.

[0132] Based on Example 1, Comparative Examples 5-6, and Table 1, when the dry adhesive layer and substrate layer in the ultra-thin termination tape are too thin, the peel strength and initial tack of the tape will decrease significantly, the flame retardant properties will decrease, and the coating uniformity and appearance flatness of the tape will be negatively affected. On the other hand, when the dry adhesive layer and substrate layer in the ultra-thin termination tape are too thick, although the initial tack and peel strength of the tape are improved, the tape thickness is too large. When applied to lithium batteries, this will negatively affect the energy density of the lithium batteries and affect the application of pressure-sensitive adhesives in lithium batteries.

[0133] Based on Examples 1, 4-5, and Table 1, when the weight-average molecular weight of the hydrogenated styrene block copolymer used in the pressure-sensitive adhesive layer of Examples 4-5 increases, it is detrimental to the wetting and dispersion of the pressure-sensitive adhesive system, and it is not conducive to obtaining a pressure-sensitive adhesive with excellent adhesion and peel strength. Conversely, when the weight-average molecular weight of the hydrogenated styrene block copolymer decreases, the cohesion of the pressure-sensitive adhesive system decreases, and cohesive failure is more likely to occur during peeling. Therefore, when the weight-average molecular weight of the hydrogenated styrene block copolymer is between 20,000 and 50,000, the peel strength, adhesion, and electrolyte resistance of the terminating tape are optimal.

[0134] In conjunction with Examples 1, 7-8 and Table 1, the combined action of modified butyl rubber and bromine-containing compounds can significantly improve the flame retardant properties of the tape without affecting its peel strength and initial tack.

[0135] In conjunction with Examples 1, 9-11 and Table 1, adjusting the release force of the non-silicone release film and the content of volatile substances in the dry adhesive layer can ensure good adhesion between the dry adhesive layer and the non-silicone release film. This allows the dry adhesive layer to achieve excellent initial tack performance while ensuring 100% transfer to the substrate layer during the subsequent film-to-adhesive transfer process, achieving complete adhesion to the substrate layer and avoiding wrinkles during the transfer process. Therefore, the peel strength and initial tack performance of the tape in Examples 9-11 are slightly lower than those in Example 1.

[0136] In conjunction with Examples 1, 12-15 and Table 1, by adjusting the dyne value of the substrate layer and the adhesion force between the dry adhesive layer and the substrate layer, the surface of the substrate layer and the dry adhesive layer are better bonded, improving the surface smoothness and thickness uniformity of the adhesive layer, reducing the tensile deformation of the substrate layer, and improving the peel strength and adhesion of the tape.

[0137] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A termination tape, characterized in that: It includes a substrate layer and a dry adhesive layer coated on the surface of the substrate layer; the thickness of the dry adhesive layer is 2-3 μm, and the thickness of the substrate layer is 4-6 μm; The dry adhesive layer is obtained by drying the pressure-sensitive adhesive, which comprises the following raw materials in parts by weight: 30-40 parts of α-olefin copolymer, 20-40 parts of hydrogenated styrene block copolymer, 105-210 parts of rubber liquid, 20-50 parts of tackifying resin, and 2-12 parts of composite antioxidant. The hydrogenated styrene block copolymer includes at least one of hydrogenated styrene thermoplastic elastomer SEBS and hydrogenated styrene thermoplastic elastomer SEPS, and the weight-average molecular weight of the hydrogenated styrene block copolymer is 20,000-50,000. The rubber liquid is obtained by mixing modified butyl rubber with an organic solvent, and the concentration of the rubber liquid is 2.5wt%-10wt%. The modified butyl rubber is prepared from raw materials including butyl rubber, maleic anhydride, and benzoyl peroxide through steps including mixing, stirring, heating, granulation, and drying. The modified butyl rubber has an unsaturation degree of 2.5-3.5%, a weight-average molecular weight of 50,000-200,000, and a melt viscosity of 3,000-10,000 mPa·s at 180-200℃.

2. The termination tape according to claim 1, characterized in that: The modified butyl rubber is prepared by the following steps: butyl rubber is kneaded at 180-300 rpm for 25-35 minutes in an environment of 120-140℃, then mixed with maleic anhydride, heated to 145-155℃ and stirred for 50-70 minutes, benzoyl peroxide is added, and the temperature is further raised to 175-185℃ and stirred for 50-70 minutes before granulation and drying.

3. The termination tape according to claim 1, characterized in that: Based on the modified butyl rubber, the modified butyl rubber comprises the following raw materials in parts by weight: 80-100 parts butyl rubber, 1-5 parts maleic anhydride, and 0.5-1 parts benzoyl peroxide.

4. The termination tape according to claim 1, characterized in that: Based on the pressure-sensitive adhesive, the pressure-sensitive adhesive further includes 5-10 parts of flame retardant; the flame retardant includes at least one of decabromodiphenyl ether, octabromodiphenyl ether, and decabromodiphenyl ethane.

5. The method for preparing the terminating tape according to any one of claims 1-4, characterized in that: Includes the following steps: Step 1: Apply pressure-sensitive adhesive to the surface of the non-silicone release film in a heated environment using a micro-gravure coating method, and then dry it to form a dry adhesive layer on the surface of the non-silicone release film. Step 2: The dry adhesive layer is bonded to the substrate layer to form a three-layer semi-finished product; the dry adhesive layer is then transferred onto the substrate layer to obtain an ultra-thin termination tape.

6. The method for preparing a terminating tape according to claim 5, characterized in that: In step one, the temperature of the pressure-sensitive adhesive is 60-85℃, and the ambient temperature when the pressure-sensitive adhesive is coated on the surface of the non-silicone release film is the same as the temperature of the pressure-sensitive adhesive.

7. The method for preparing a terminating tape according to claim 5, characterized in that: In step one, the thickness of the non-silicone release film is 12-25 μm, and the release force of the non-silicone release film is 100-300 g; in step one, the content of volatile organic compounds in the dry adhesive layer obtained after drying is ≤1 wt%.

8. The method for preparing a terminating tape according to claim 5, characterized in that: In step two, the dyne value of the coating surface of the substrate layer is 42-52; during the coating process in step two, the bonding pressure between the dry adhesive layer and the substrate layer is 0.03-0.08 MPa.

9. A lithium-ion battery, characterized in that: The termination tape as described in any one of claims 1-4 is used in the preparation process.

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