Ultra-thin double-sided adhesive tape and preparation method therefor

Abstract

The present invention relates to the field of adhesives, and particularly to an ultra-thin double-sided adhesive tape and a preparation method therefor. The ultra-thin double-sided adhesive tape has a structure comprising, from top to bottom, an adhesive layer, a substrate layer, and a release film; wherein the raw materials for preparing the adhesive layer comprise, in parts by mass: 10-60 parts of a binder, 0.05-0.3 parts of a curing agent, and 60-90 parts of an adhesive layer solvent; and the raw materials for preparing the substrate layer comprise, in parts by mass: 10-30 parts of a hard monomer, 20-40 parts of a soft monomer, 10-30 parts of a chain extender, 1-3 parts of a catalyst, 2-5 parts of an end-capping agent, 20-50 parts of a substrate layer solvent, and 3-5 parts of a crosslinking agent. The ultra-thin double-sided adhesive tape provided by the present invention has a thickness of less than 0.01 mm, exhibits excellent bonding performance and high mechanical properties, and is particularly suitable for use in bonding precision electronic products.

Description

An ultra-thin double-sided adhesive tape and its preparation method Technical Field

[0001] This invention relates to the field of adhesives, and in particular to an ultrathin double-sided adhesive and its preparation method. Background Technology

[0002] As electronic devices evolve towards thinner, lighter, and higher-performance designs, higher demands are placed on the integration and assembly precision of internal components. Traditional double-sided tapes, primarily using polyethylene terephthalate (PET) film, non-woven fabric, or polyurethane (PU) as substrates, combined with acrylic pressure-sensitive adhesive layers, offer certain bonding strength and versatility, but suffer from limitations in ultra-thinness, elastic recovery, thermal conductivity, and process compatibility. For instance, Chinese patent application CN105295761A discloses an ultra-thin double-sided tape, mainly composed of a release film, an adhesive layer, a PET film layer, and a lower release film layer. However, the PET substrate is prone to brittleness during ultra-thinning, and the non-woven fabric substrate exhibits poor thickness uniformity and struggles to balance support and elasticity. Existing tapes often employ a single substrate structure, making further compression of the overall thickness difficult and resulting in insufficient elastic modulus.

[0003] Currently, the thickness of double-sided adhesive substrates is generally above 0.01mm, which is insufficient to meet the ultra-thin requirements of less than 0.005mm. Furthermore, it suffers from insufficient elasticity and resilience, low elastic modulus of the substrate, poor adaptability to dynamic stress, and a tendency to lead to adhesive failure. Thermal conductivity is also limited due to the large thickness and high thermal resistance of the substrate, affecting heat dissipation efficiency. Additionally, it exhibits poor process compatibility, with complex manufacturing processes, high costs, and low yields for ultra-thin tapes. To address these technical issues, adhesive R&D companies have functionally modified the raw materials of double-sided adhesives, such as using highly elastic polymers like thermoplastic polyurethane (TPU) to replace traditional substrates and developing "integrated" designs. However, existing improvement solutions still have limitations, such as the difficulty in achieving both elasticity and thickness in TPU substrates and insufficient interfacial compatibility between the adhesive layer and the substrate.

[0004] In view of the shortcomings of existing technologies, this invention proposes a novel ultra-thin double-sided adhesive tape, which aims to meet the technical requirements of the electronics industry for ultra-thin, highly elastic tapes. Summary of the Invention

[0005] To address the aforementioned technical problems, the first aspect of this invention provides an ultra-thin double-sided adhesive tape. The structure of the ultra-thin double-sided adhesive tape, from top to bottom, comprises: a release film, an adhesive layer, a substrate layer, and another release film; wherein the thickness of the adhesive layer is 1-3 μm, and the thickness of the substrate layer is 1-2 μm; wherein the raw materials for preparing the adhesive layer include an adhesive, a curing agent, and an adhesive layer solvent; and the raw materials for preparing the substrate layer include: a soft monomer, a hard monomer, a chain extender, a catalyst, a crosslinking agent, a capping agent, and a substrate layer solvent.

[0006] Adhesive layer

[0007] As an feasible example, the raw materials for preparing the adhesive layer, by weight, include: 10-60 parts of adhesive, 0.05-0.3 parts of curing agent, and 60-90 parts of adhesive layer solvent.

[0008] As an implementable example, the adhesive includes at least one of the following: isooctyl acrylate, butyl acrylate, cellulose acetate, acrylic acid, methyl methacrylate, ethyl methacrylate, ethylene ethyl acrylate, 2-hydroxy acrylate, 2-hydroxyethyl methacrylate, and acrylic pressure-sensitive adhesive.

[0009] Furthermore, the adhesive is an acrylic pressure-sensitive adhesive, model number: SW-3101, purchased from Hubei Shunwei Adhesive Co., Ltd.

[0010] As an implementable example, the curing agent includes one of toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), and hydrogenated diphenylmethane diisocyanate (HMDI).

[0011] As an implementable example, the solvent for the adhesive layer includes one or more of the following: methyl ethyl ketone, acetone, butanone, cyclohexanone, ethyl acetate, tetrahydrofuran, methanol, ethanol, n-propanol, isopropanol, dioctanoic acid, n-hexane, toluene, and xylene.

[0012] Substrate layer

[0013] As an feasible example, the raw materials for preparing the substrate layer include, by mass parts: 10-30 parts hard monomer, 20-40 parts soft monomer, 10-30 parts chain extender, 1-3 parts catalyst, 2-5 parts end-capping agent, 20-50 parts substrate layer solvent and 3-5 parts crosslinking agent.

[0014] As an implementable example, the hard monomer comprises a polyisocyanate having a functionality of not less than 2.

[0015] Furthermore, the hard monomer includes one of TDI, MDI, HDI, and IPDI.

[0016] As an implementable example, the soft monomer includes one of the following: polyether polyol, polyester polyol, and polycarbonate polyol.

[0017] Furthermore, the soft monomer includes polyether polyols.

[0018] Furthermore, the polyether polyols include polyether diols.

[0019] Furthermore, the polyether diol is graded N210 (1000D) and was purchased from Jiangsu Haian Petrochemical Co., Ltd.

[0020] As an example of implementation, the chain extender includes at least one of amine chain extenders and alcohol chain extenders.

[0021] Furthermore, the alcohol chain extender includes one of the following: ethylene glycol, 1,2-propanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, 1,4-cyclohexanediol, dimethylolpropionic acid, 1,5-pentanediol, glycerol, diethylene glycol, and ethylene glycol.

[0022] Furthermore, the amine chain extender includes one of MOCA (3,3'-dichloro-4,4'-diaminodiphenylmethane), benzidine, ethylenediamine, and 1,6-hexanediamine.

[0023] As an example of an implementable approach, the catalysts include: organic amine catalysts, organophosphorus catalysts, and organometallic catalysts.

[0024] Furthermore, the catalyst is an organometallic catalyst, which includes one of stannous octoate, dibutyltin dilaurate, and dimethyltin diolate.

[0025] As an feasible example, the terminator includes one of the following: amine terminator, alcohol terminator, phenol terminator, and ketoxime terminator.

[0026] Furthermore, the end-capping agent is an alcohol-based end-capping agent, which includes poly(1,4-butanediol glutarate) terminal hydroxyl groups, CAS number 52256-54-9.

[0027] The terminal hydroxyl groups of poly(1,4-butanediol glutarate) can chemically react with the active groups on the surface of the adherends to form covalent bonds or hydrogen bonds, thereby enhancing the bonding strength. The terminal hydroxyl groups of poly(1,4-butanediol glutarate) molecules have flexible chain segments that can interact with the adhesive layer through van der Waals forces, hydrogen bonds, etc., increasing intermolecular bonding forces and making the bonding interface more stable. It can also regulate the molecular structure and properties of the substrate layer, making the double-sided adhesive more flexible after curing, reducing brittleness, and better adapting to the deformation of the adherends under external forces, avoiding problems such as cracking and detachment at the bonding interface. Furthermore, the terminal hydroxyl groups of poly(1,4-butanediol glutarate) can be uniformly dispersed in the substrate layer system, cooperating with other components, and can better penetrate into the microstructure of the adherend surface, increasing the contact area and interaction with the adherends, thereby improving the bonding performance.

[0028] As an implementable example, the solvent for the substrate layer includes one or more of the following: methyl ethyl ketone, acetone, butanone, cyclohexanone, ethyl acetate, tetrahydrofuran, methanol, ethanol, n-propanol, isopropanol, dioctanoic acid, n-hexane, toluene, and xylene.

[0029] As an implementable example, the crosslinking agent includes one of TDI, MDI, HDI, IPDI, tetramethylene diisocyanate, naphthalene diisocyanate, and tetramethylxylene diisocyanate (TMXDI).

[0030] Furthermore, the crosslinking agent is tetramethylxylene diisocyanate.

[0031] The presence of benzene rings in TMXDI molecules gives the substrate layer a certain degree of rigidity and strength. At the same time, the methyl groups on the molecule increase steric hindrance and reduce the reactivity of isocyanates, making the reaction process easier to control. This results in a more uniform and regular polymer network structure, reducing defects and weak points, thereby improving mechanical properties. TMXDI also imparts higher adhesion to the substrate layer, forming a stronger bond between it and the layers to be bonded, improving the interfacial bonding strength. Under stress, it can more effectively transfer stress, avoiding the decline in mechanical properties caused by interfacial debonding, and thus improving the overall mechanical properties of the double-sided adhesive.

[0032] Release film

[0033] This invention does not further limit the type of release film; any component that can isolate and protect the adhesive layer and the substrate layer, making the double-sided adhesive easier to process and use, is acceptable.

[0034] A second aspect of the present invention provides a method for preparing ultrathin double-sided adhesive tape, comprising:

[0035] S1. Add the soft monomer, hard monomer, crosslinking agent and catalyst into the reactor, heat to 70-80℃, then add and stir at 100-150 rpm for 25-35 min. Then add half of the total amount of solvent in the substrate layer and stir for 15-30 min to obtain the prepolymer.

[0036] Add the remaining substrate layer solvent and chain extender to the prepolymer, react for 100-150 minutes, then add the end-capping agent, stir evenly, discharge the material, coat and cure to obtain the substrate layer.

[0037] S2. Add the adhesive to the reactor, then add the glue layer solvent, stir at 30-40℃ and 200-500rpm for 15-30min, then add the curing agent, stir at 40-50℃ and 100-200rpm for 10-20min, then discharge the material, coat and cure to obtain the glue layer.

[0038] S3. From top to bottom, hot-press the release film, adhesive layer, substrate layer, adhesive layer and release film to obtain the final product. Beneficial effects

[0039] (i) By adopting a high-elasticity TPU substrate layer design, the thickness of the double-sided adhesive can be controlled to below 0.005mm, which significantly reduces the volume occupied between electronic device layers, and realizes product lightweighting and thinning. It is especially suitable for bonding precision components such as graphite sheets and nanocrystalline heat sinks.

[0040] (ii) Based on the special formula of high elastic TPU substrate, the elastic modulus of the ultra-thin double-sided adhesive product provided by the present invention can reach 600-700MPa, and the elastic recovery rate is as high as 80%-90%. It can still quickly recover its original shape after repeated stretching or compression, thus improving the reliability of long-term use.

[0041] (iii) The adhesive layer prepared by combining acrylic pressure-sensitive adhesive and isocyanate curing agent in this invention enables the shear adhesion of ultra-thin double-sided adhesive to reach 265-280N, the tack to be ≥500g, and the holding force to be 0.1-0.2mm. It can also maintain stable adhesion under high and low temperature environments, avoiding problems of peeling or displacement.

[0042] (iv) Due to the ultra-thin structure of double-sided adhesive, it can reduce interlayer thermal resistance, maximize heat conduction efficiency, and adhere tightly to the surface of heat dissipation components, significantly improving the heat dissipation performance of electronic devices. It is suitable for bonding high-power chips.

[0043] (v) In the preparation process of the substrate layer, the present invention makes the molecular weight distribution in the substrate layer more uniform by synthesizing prepolymer and adding crosslinking agent, reduces oligomer residue, and improves the yield. At the same time, the use of conventional solvents can effectively reduce production costs, and the ultra-thin double-sided tape is suitable for large-scale production. Detailed Implementation Example 1

[0044] The first aspect of this example provides an ultra-thin double-sided adhesive tape. The structure of the ultra-thin double-sided adhesive tape from top to bottom consists of: a release film, an adhesive layer, a substrate layer, and another release film; wherein the thickness of the adhesive layer is 1.5 μm and the thickness of the substrate layer is 1 μm.

[0045] The raw materials for preparing the adhesive layer, by weight, are: 50 parts adhesive, 0.1 parts curing agent and 70 parts adhesive layer solvent.

[0046] The adhesive is an acrylic pressure-sensitive adhesive, model number: SW-3101, purchased from Hubei Shunwei Adhesive Co., Ltd.

[0047] The curing agent is hydrogenated diphenylmethane diisocyanate.

[0048] The solvent for the adhesive layer is ethyl acetate.

[0049] The raw materials for preparing the substrate layer, by mass parts, are: 15 parts hard monomer, 35 parts soft monomer, 10 parts chain extender, 2 parts catalyst, 2 parts end capping agent, 26 parts substrate layer solvent and 3 parts crosslinking agent.

[0050] The hard monomer mentioned is HDI.

[0051] The soft monomer is a polyether diol, the grade of which is N210 (1000D), purchased from Jiangsu Haian Petrochemical Co., Ltd.

[0052] The chain extender is 1,4-butanediol.

[0053] The catalyst is stannous octoate.

[0054] The capping agent is poly(1,4-butanediol glutarate) with hydroxyl-terminated hydroxyl groups, CAS number 52256-54-9.

[0055] The solvent for the substrate layer is acetone.

[0056] The crosslinking agent is tetramethylxylene diisocyanate.

[0057] The second aspect of this example provides a method for preparing ultrathin double-sided tape, specifically as follows:

[0058] S1. Add the soft monomer, hard monomer, crosslinking agent and catalyst into the reactor, heat to 75°C, then add stirring at 100 rpm for 30 min, then add half of the total amount of solvent in the substrate layer, stir for 30 min, and obtain the prepolymer.

[0059] Add the remaining substrate layer solvent and chain extender to the prepolymer, react for 120 minutes, then add the end-capping agent, stir evenly, discharge the material, coat and cure to obtain the substrate layer.

[0060] S2. Add the adhesive to the reactor, then add the glue layer solvent, stir at 35°C and 400 rpm for 30 min, then add the curing agent, stir at 50°C and 200 rpm for 20 min, then discharge the material, coat and cure to obtain the glue layer.

[0061] S3. From top to bottom, hot-press the release film, adhesive layer, substrate layer, adhesive layer and release film to obtain the final product. Example 2 The first aspect of this example provides an ultra-thin double-sided adhesive tape. The structure of the ultra-thin double-sided adhesive tape from top to bottom consists of: a release film, an adhesive layer, a substrate layer, and another release film; wherein the thickness of the adhesive layer is 1.5 μm and the thickness of the substrate layer is 1 μm.

[0062] The raw materials for preparing the adhesive layer, by weight, are: 55 parts adhesive, 0.1 parts curing agent, and 75 parts adhesive layer solvent.

[0063] The adhesive is an acrylic pressure-sensitive adhesive, model number: SW-3101, purchased from Hubei Shunwei Adhesive Co., Ltd.

[0064] The curing agent is hydrogenated diphenylmethane diisocyanate.

[0065] The solvent for the adhesive layer is ethyl acetate.

[0066] The raw materials for preparing the substrate layer, by mass parts, are: 25 parts hard monomer, 25 parts soft monomer, 15 parts chain extender, 2 parts catalyst, 2 parts end capping agent, 23 parts substrate layer solvent and 4 parts crosslinking agent.

[0067] The hard monomer mentioned is HDI.

[0068] The soft monomer is a polyether diol, the grade of which is N210 (1000D), purchased from Jiangsu Haian Petrochemical Co., Ltd.

[0069] The chain extender is 1,4-butanediol.

[0070] The catalyst is stannous octoate.

[0071] The capping agent is poly(1,4-butanediol glutarate) with hydroxyl-terminated hydroxyl groups, CAS number 52256-54-9.

[0072] The solvent for the substrate layer is acetone.

[0073] The crosslinking agent is tetramethylxylene diisocyanate.

[0074] The second aspect of this example provides a method for preparing ultrathin double-sided tape, specifically as follows:

[0075] S1. Add the soft monomer, hard monomer, crosslinking agent and catalyst into the reactor, heat to 75°C, then add stirring at 100 rpm for 30 min, then add half of the total amount of solvent in the substrate layer, stir for 30 min, and obtain the prepolymer.

[0076] Add the remaining substrate layer solvent and chain extender to the prepolymer, react for 120 minutes, then add the end-capping agent, stir evenly, discharge the material, coat and cure to obtain the substrate layer.

[0077] S2. Add the adhesive to the reactor, then add the glue layer solvent, stir at 35°C and 400 rpm for 30 min, then add the curing agent, stir at 50°C and 200 rpm for 20 min, then discharge the material, coat and cure to obtain the glue layer.

[0078] S3. From top to bottom, hot-press the release film, adhesive layer, substrate layer, adhesive layer and release film to obtain the final product.

[0079] Comparative Example 1

[0080] The first aspect of this example provides an ultra-thin double-sided adhesive tape. The structure of the ultra-thin double-sided adhesive tape from top to bottom consists of: a release film, an adhesive layer, a substrate layer, and another release film; wherein the thickness of the adhesive layer is 1.5 μm and the thickness of the substrate layer is 1 μm.

[0081] The raw materials for preparing the adhesive layer, by weight, are: 55 parts adhesive, 0.1 parts curing agent, and 75 parts adhesive layer solvent.

[0082] The adhesive is an acrylic pressure-sensitive adhesive, model number: SW-3101, purchased from Hubei Shunwei Adhesive Co., Ltd.

[0083] The curing agent is hydrogenated diphenylmethane diisocyanate.

[0084] The solvent for the adhesive layer is ethyl acetate.

[0085] The raw materials for preparing the substrate layer, by mass parts, are: 25 parts hard monomer, 25 parts soft monomer, 40 parts chain extender, 2 parts catalyst, 3 parts end capping agent, 25 parts substrate layer solvent, and 4 parts crosslinking agent.

[0086] The hard monomer mentioned is HDI.

[0087] The soft monomer is a polyether diol, the grade of which is N210 (1000D), purchased from Jiangsu Haian Petrochemical Co., Ltd.

[0088] The chain extender is 1,4-butanediol.

[0089] The catalyst is stannous octoate.

[0090] The capping agent is poly(1,4-butanediol glutarate) with hydroxyl-terminated hydroxyl groups, CAS number 52256-54-9.

[0091] The solvent for the substrate layer is acetone.

[0092] The crosslinking agent is tetramethylxylene diisocyanate.

[0093] The second aspect of this example provides a method for preparing ultrathin double-sided tape, specifically as follows:

[0094] S1. Add the soft monomer, hard monomer, crosslinking agent and catalyst into the reactor, heat to 75°C, then add stirring at 100 rpm for 30 min, then add half of the total amount of solvent in the substrate layer, stir for 30 min, and obtain the prepolymer.

[0095] Add the remaining substrate layer solvent and chain extender to the prepolymer, react for 120 minutes, then add the end-capping agent, stir evenly, discharge the material, coat and cure to obtain the substrate layer.

[0096] S2. Add the adhesive to the reactor, then add the glue layer solvent, stir at 35°C and 400 rpm for 30 min, then add the curing agent, stir at 50°C and 200 rpm for 20 min, then discharge the material, coat and cure to obtain the glue layer.

[0097] S3. From top to bottom, hot-press the release film, adhesive layer, substrate layer, adhesive layer and release film to obtain the final product.

[0098] Comparative Example 2

[0099] The first aspect of this example provides an ultra-thin double-sided adhesive tape. The structure of the ultra-thin double-sided adhesive tape from top to bottom consists of: a release film, an adhesive layer, a substrate layer, and another release film; wherein the thickness of the adhesive layer is 1.5 μm and the thickness of the substrate layer is 1 μm.

[0100] The raw materials for preparing the adhesive layer, by weight, are: 50 parts adhesive, 0.1 parts curing agent and 70 parts adhesive layer solvent.

[0101] The adhesive is an acrylic pressure-sensitive adhesive, model number: SW-3101, purchased from Hubei Shunwei Adhesive Co., Ltd.

[0102] The curing agent is hydrogenated diphenylmethane diisocyanate.

[0103] The solvent for the adhesive layer is ethyl acetate.

[0104] The substrate layer is a PET film.

[0105] The second aspect of this example provides a method for preparing ultrathin double-sided tape, specifically as follows:

[0106] S1. Add the adhesive to the reactor, then add the glue layer solvent, stir at 35°C and 400 rpm for 30 min, then add the curing agent, stir at 50°C and 200 rpm for 20 min, then discharge the material, coat and cure to obtain the glue layer.

[0107] S2. From top to bottom, hot-press the release film, adhesive layer, substrate layer, adhesive layer and release film to obtain the final product.

[0108] Comparative Example 3

[0109] The first aspect of this example provides an ultra-thin double-sided adhesive tape, the structure of which from top to bottom consists of: a release film, an adhesive layer, and another release film; wherein the thickness of the adhesive layer is 1.5 μm.

[0110] The raw materials for preparing the adhesive layer, by weight, are: 50 parts adhesive, 0.1 parts curing agent and 70 parts adhesive layer solvent.

[0111] The adhesive is an acrylic pressure-sensitive adhesive, model number: SW-3101, purchased from Hubei Shunwei Adhesive Co., Ltd.

[0112] The curing agent is hydrogenated diphenylmethane diisocyanate.

[0113] The solvent for the adhesive layer is ethyl acetate.

[0114] The second aspect of this example provides a method for preparing ultrathin double-sided tape, specifically as follows:

[0115] S1. Add the adhesive to the reactor, then add the glue layer solvent, stir at 35°C and 400 rpm for 30 min, then add the curing agent, stir at 50°C and 200 rpm for 20 min, then discharge the material, coat and cure to obtain the glue layer.

[0116] S3. From top to bottom, heat press the release film, adhesive layer and release film together to obtain the final product. Performance Evaluation

[0117] Test subjects: Ultra-thin double-sided tapes prepared in Examples 1-2 and Comparative Examples 1-3.

[0118] The test methods and test results are detailed in Table 1.

[0119] Table 1

[0120]

[0121] As can be seen from the comparison of Examples 1-2, the ultra-thin double-sided adhesive provided by Examples 1-2 of the present invention has a large shear bonding force and a moderate elastic modulus, and both have good prospects for practical application. The elastic recovery rate of Example 1 is greater and the holding force is only 0.1mm, which is the optimal implementation scheme.

[0122] Comparing Examples 1-2 and Comparative Example 1, it can be seen that the excessive use of chain extender will significantly increase the molecular weight of the product and accelerate the polymerization rate. However, the faster polymerization reaction will result in a wider molecular weight distribution and the product will contain a large amount of low molecular weight oligomers, which will affect the elastic modulus and elastic recovery rate of the product.

[0123] Comparing Examples 1-2 and Comparative Example 2, it can be seen that although using PET film as the substrate layer increases the elastic modulus of the ultra-thin double-sided adhesive, the shear adhesion and elastic recovery rate are relatively low.

[0124] Comparing Examples 1-2 and Comparative Example 3, it can be seen that: due to the lack of a substrate layer, the ultra-thin double-sided adhesive has no elasticity at all, resulting in direct breakage and making the product difficult to use normally.

Claims

1. An ultra-thin double-sided adhesive, characterized in that, The structure of the ultra-thin double-sided tape, from top to bottom, consists of: release film, adhesive layer, substrate layer, adhesive layer, and release film; the thickness of the adhesive layer is 1-3μm, and the thickness of the substrate layer is 1-2μm. The raw materials for preparing the adhesive layer include adhesive, curing agent and adhesive layer solvent; The raw materials for preparing the substrate layer include soft monomers, hard monomers, chain extenders, catalysts, crosslinking agents, end-capping agents, and substrate layer solvents.

2. The ultra-thin double-sided adhesive according to claim 1, characterized in that, The raw materials for preparing the adhesive layer, by weight, include 10-60 parts of adhesive, 0.05-0.3 parts of curing agent, and 60-90 parts of adhesive layer solvent.

3. The ultra-thin double-sided adhesive according to claim 2, characterized in that, The adhesive includes at least one of isooctyl acrylate, butyl acrylate, cellulose acetate, acrylic acid, methyl methacrylate, ethyl methacrylate, ethylene ethyl acrylate, 2-hydroxy acrylate, 2-hydroxyethyl methacrylate, or acrylic pressure-sensitive adhesive.

4. The ultra-thin double-sided adhesive according to claim 2, characterized in that, The curing agent includes one of toluene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, or hydrogenated diphenylmethane diisocyanate.

5. The ultra-thin double-sided adhesive according to any one of claims 1-4, characterized in that, The raw materials for preparing the substrate layer, by mass parts, include 10-30 parts hard monomer, 20-40 parts soft monomer, 10-30 parts chain extender, 1-3 parts catalyst, 2-5 parts end-capping agent, 20-50 parts substrate layer solvent and 3-5 parts crosslinking agent.

6. The ultra-thin double-sided adhesive according to claim 5, characterized in that, The hard monomers include polyisocyanates, and the functionality of the polyisocyanates is not less than 2.

7. The ultra-thin double-sided adhesive according to claim 5, characterized in that, The soft monomers include one of polyether polyols, polyester polyols, or polycarbonate polyols.

8. The ultra-thin double-sided adhesive according to claim 5, characterized in that, The chain extender includes at least one of amine chain extenders and alcohol chain extenders.

9. The method for preparing ultrathin double-sided adhesive according to claim 5, characterized in that, The terminator includes one of amine terminators, alcohol terminators, phenol terminators, or ketoxime terminators.

10. A method for preparing ultrathin double-sided adhesive according to any one of claims 1-9, characterized in that, include: S1. Add the soft monomer, hard monomer, crosslinking agent and catalyst into the reactor, heat to 70-80℃, stir at 100-150rpm for 25-35min, then add half of the total amount of solvent in the substrate layer, stir for 15-30min to obtain the prepolymer. Add the remaining substrate layer solvent and chain extender to the prepolymer, react for 100-150 minutes, then add the end-capping agent, stir evenly, discharge the material, coat and cure to obtain the substrate layer. S2. Add the adhesive to the reactor, then add the glue layer solvent, stir at 30-40℃ and 200-500rpm for 15-30min, then add the curing agent, stir at 40-50℃ and 100-200rpm for 10-20min, then discharge the material, coat and cure to obtain the glue layer. S3. From top to bottom, hot-press the release film, adhesive layer, substrate layer, adhesive layer and release film to obtain the final product.

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