Substrate-centered thermally expanding microsphere foamed creep-resistant double-sided adhesive tape and its preparation method

Abstract

This invention proposes a centrally located, thermally expandable microsphere-foamed, creep-resistant double-sided adhesive tape and its preparation method. The preparation method includes PET substrate surface pretreatment, initial adhesive coating on the first side of the substrate followed by release film separation and winding, secondary adhesive coating on the second side of the substrate followed by release film separation and winding, and overall heating and foaming of the preform tape. This results in a centrally located, thermally expandable microsphere-foamed, creep-resistant double-sided adhesive tape. The double-sided adhesive tape of this invention utilizes the PET substrate to provide core support against high-temperature plastic deformation, inhibiting Z-axis creep of the adhesive layer. The symmetrical foamed adhesive layers on both sides ensure completely uniform heating and stress distribution, eliminating stress imbalance and preventing tape warping, thus achieving creep resistance performance from the structural root. It achieves synergistic performance targets for creep resistance, high activation, and impact resistance, adapting to the complex operating environments of high-end electronic devices.

Description

Technical Field

[0001] This invention relates to the field of thermally expandable microsphere foamed double-sided adhesive tape, specifically to thermally expandable microsphere foamed creep-resistant double-sided adhesive tape with a centrally located substrate and its preparation method. Background Technology

[0002] Foamed double-sided adhesive tape is a core material for structural bonding and component fixing in high-end electronic devices such as smartphones, tablets, and wearable devices. The high-end electronics industry demands stringent creep resistance requirements, including a Z-axis creep gap of ≤0.12mm after 72 hours of loading a 1kg weight at 70℃. Simultaneously, it must meet comprehensive performance indicators such as a thickness tolerance of ±0.03mm, a retention rate of ≥70% under high temperature and humidity conditions at 65℃ and 95%RH, an activation rate of ≥75%, and impact resistance of ≥30 cycles. Thermally expanded microsphere foamed adhesive layers have become the mainstream adhesive layer forming method for high-end foamed tapes due to their excellent elasticity, cushioning, and adhesion. However, current thermally expanded microsphere foamed adhesive layers have not yet solved the industry pain points of easy deformation and substandard creep resistance under continuous high-temperature loads.

[0003] Existing thermally expandable microsphere foamed double-sided adhesives mainly fall into two categories in terms of core technology solutions: substrate-free pure thermally expandable microsphere foamed adhesive layer structure and single-layer PET substrate single-sided thermally expandable microsphere foamed structure. The supporting processes are all conventional coating and foaming, without any special structural and process design for creep resistance. The current application of PET substrate in tapes is mostly to enhance the tensile strength and tear resistance of the tape, and it has not been used to solve the Z-axis creep resistance problem of the foamed adhesive layer.

[0004] 1. Substrate-free pure thermal expansion microsphere foam adhesive layer structure: It is composed of only two layers of thermal expansion microsphere foam adhesive layer without rigid substrate support. The adhesive layer is a pure elastomer structure, which is prone to plastic deformation under continuous high temperature load. The Z-axis creep gap is far beyond 0.12mm, and the creep resistance performance is completely substandard. In addition, the lack of restraint during the foaming process makes it easy for the adhesive layer to bulge and overflow, and the thickness control accuracy is low.

[0005] 2. Single-layer PET substrate with single-sided thermal expansion microsphere foaming structure: The thermal expansion microsphere foaming adhesive layer is coated only on one side of the PET substrate, while the other side is a regular pressure-sensitive adhesive layer. The asymmetrical structure leads to uneven heating and stress during foaming and use, resulting in stress bias. This not only causes excessive Z-axis creep gap, but also easily leads to problems such as tape warping and adhesive layer delamination, resulting in poor environmental stability.

[0006] In addition, the existing preparation process of thermal expansion microsphere foam adhesive layer is a one-time coating process, and the foaming is carried out directly without a film or adhesive layer isolation and protection measures. After coating, it is easy to stick and contaminate. During the foaming process, hot air directly impacts the adhesive layer, resulting in asynchronous foaming of the two-sided adhesive layer and loose closed-cell structure. This further aggravates the fluctuation of properties such as creep resistance and activation, and cannot meet the mass production requirements of high-end electronics.

[0007] In summary, existing technologies have not formed a complete technical solution for the creep resistance requirements of high-end electronics. The industry urgently needs a thermal expansion microsphere foamed double-sided adhesive tape that can achieve creep resistance performance and excellent overall performance. Summary of the Invention

[0008] This invention addresses the performance defects of thermally expandable microsphere foam adhesive layers and the creep resistance requirements of high-end electronics. It employs a centrally located, double-sided symmetrical sandwich structure design with a single-layer PET substrate, organically combining the rigid deformation resistance of the PET substrate with the elastic buffering properties of the thermally expandable microsphere foam adhesive layer. This structurally solves the problem of insufficient creep resistance. Simultaneously, a proprietary process is designed, including step-by-step adhesive application, release film isolation and winding, sandwich structure foaming with film, and single-variable control of foaming time. This ensures symmetrical and uniform foaming of the double-sided adhesive layer, precise control of thickness and foaming ratio, and ultimately produces a thermally expandable microsphere foam double-sided adhesive tape with satisfactory creep resistance, excellent overall performance, and high mass production consistency, filling a gap in existing technology in the high-end electronics field. To achieve the above objectives, this invention proposes the following solutions.

[0009] This invention proposes a method for preparing a creep-resistant double-sided adhesive tape with centrally located thermally expanding microspheres, comprising the following steps: Step 1: Substrate pretreatment; PET substrate is selected, and the surface of the substrate is first treated with a corona discharge device to make the surface energy of the PET substrate ≥50dyn / cm; Step 2: First application of adhesive and separation from release film and winding; one side of the pretreated PET substrate is coated with acrylic thermal expansion microsphere foam adhesive, and the release film is immediately attached after the adhesive is applied and the substrate is wound up to form a semi-finished product consisting of "lower release film - PET substrate - first foaming layer"; Step 3: Secondary adhesive coating and release film separation and winding; Apply acrylic thermal expansion microsphere foaming adhesive with the same formula and wet thickness as the first coating to the uncoated side of the semi-finished PET substrate, using the same process parameters as the first coating, to ensure that the thickness deviation of the foaming adhesive layer on both sides is ≤0.005mm; Immediately after coating, attach the release film and wind up to form a blank with a sandwich structure of "upper release film - first foaming adhesive layer - PET substrate - second foaming adhesive layer - lower release film"; Step 4: Overall foaming of the blank with film; The blank is sent into a continuous hot air foaming oven, and the temperature of each temperature zone in the oven is kept constant at 150~160℃. After the first and second layers of adhesive to be foamed are heated and foamed, an acrylic thermal expansion microsphere foaming layer is formed; By adjusting the residence time of the blank in the oven, i.e. the foaming time, the foaming ratio and the final thickness of the double-sided tape are controlled.

[0010] The double-sided tape of this invention adopts a double-sided symmetrical thermally expanding microsphere foam sandwich structure with a single-layer PET substrate in the center. The PET substrate is clearly defined as a rigid anti-Z-axis creep support layer, and the double-sided acrylic thermally expanding microsphere foam adhesive layer is an elastic bonding buffer layer. The two work together: the PET substrate provides the core support force to resist high-temperature plastic deformation and inhibits Z-axis creep of the adhesive layer; the double-sided symmetrical foam adhesive layer ensures that the heat and stress are completely uniform, eliminates stress bias, and avoids tape warping, thus achieving the required creep resistance performance from the structural source.

[0011] The double-sided adhesive tape of this invention features the following technological advancements: 1. Step-by-step adhesive application and release film separation during winding ensure consistent double-sided adhesive layer thickness (deviation ≤ 0.005 mm), preventing adhesive layer adhesion and contamination before foaming; 2. Overall foaming of the tape with release film provides physical constraint and uniform heat conduction for the double-sided adhesive layer, ensuring synchronous and uniform expansion of the microspheres and preventing bulging and adhesive overflow; 3. Single-variable control of foaming time at a constant temperature, adjusting the foaming ratio and thickness solely by adjusting the foaming time eliminates interference from multiple variables and achieves precise control. This process system is fundamentally different from existing thermal expansion microsphere foaming processes.

[0012] This invention achieves synergistic performance of creep resistance, high activation, and impact resistance in thermally expanded microsphere foamed adhesive layers through the synergy of structure and process. It solves the technical contradiction in the prior art that "increased creep resistance leads to decreased activation, and increased buffering leads to decreased deformation resistance." The Z-axis creep gap is ≤0.12mm at 70℃ for 1kg over 72 hours, and the retention rate is ≥70% at 65℃ and 95%RH under high temperature and high humidity, with activation ≥75% and impact resistance ≥30 times. This comprehensive performance effect is an unexpected effect that cannot be achieved by the prior art.

[0013] Furthermore, the PET substrate is selected from high-rigidity PET films with a thickness of 0.05~0.055mm.

[0014] The single-layer PET rigid support substrate used in this invention has a thickness of 0.05~0.055mm. It is a high-rigidity PET film pretreated by plasma, which serves as the core anti-Z-axis creep support layer to suppress the plastic deformation of the adhesive layer under continuous high temperature load. The substrate thickness is the optimal value after experimental verification. If it is too thick, the tape will become too hard and its activation will decrease. If it is too thin, it will not be able to provide sufficient anti-creep support force.

[0015] In steps 2 and 3, the wet thickness of the adhesive coating is 0.216~0.22mm, and the thickness before the solvent dries and foams is 0.108~0.11mm.

[0016] The acrylic thermally expandable microsphere foaming layer of the present invention is a symmetrically distributed homogeneous and uniformly thick foaming layer, with a dry thickness of 0.125~0.15mm after foaming.

[0017] Furthermore, in step 1, the corona treatment equipment has a processing power of 1.0-1.2KW and a processing time of 3-5s; in steps 2 and 3, the adhesive is applied by an adhesive applicator using a direct blade coating process at a speed of 8-10m / min; in steps 2 and 3, the release film bonding pressure is 0.2MPa; in step 2, the winding tension is controlled at 5-6N; in step 3, the winding tension is controlled at 6-8N; in step 4, the hot air velocity in the oven is 2-3m / s; the release film is a 0.05mm thick PET release film.

[0018] Furthermore, the acrylic thermally expandable microsphere foam adhesive, by weight, comprises the following components: 100 parts of acrylate copolymer; 5-8 parts of core-shell thermally expandable microspheres; 5-8 parts of tackifying resin; 0.5-1 part of crosslinking agent; 0.2-0.5 parts of defoamer; and 30 parts of solvent; the acrylate copolymer has a solid content of 50% and a glass transition temperature of -20 to -15°C; the core-shell thermally expandable microspheres have a foaming temperature of 150-160°C.

[0019] The acrylate copolymer of this invention serves as the adhesive layer base material, ensuring the adhesion and elasticity of the adhesive layer; core-shell thermally expandable microspheres are the sole foaming agent, forming a closed-cell structure through high-temperature expansion; tackifying resin enhances the initial tack and activation of the adhesive layer, ensuring peel force under low-pressure activation of 0.2 MPa; crosslinking agent enhances the cohesive strength and high-temperature resistance of the adhesive layer, preventing cohesive damage of the adhesive layer at high temperatures; defoamer eliminates bubbles generated during the coating process, ensuring the uniformity of the adhesive layer.

[0020] The acrylic thermally expandable microsphere foamed adhesive layer of the present invention is a symmetrically distributed homogeneous adhesive layer of uniform thickness, with a dry thickness of 0.125~0.15mm after foaming. The foaming ratio is precisely controlled between 1.15 and 1.25. The adhesive layer has a uniform and dense closed-cell foam structure. It is formed by adding 5~8 parts by weight of core-shell thermally expandable microspheres to the acrylic copolymer as the base material and foaming at high temperature. The closed-cell structure ensures the elasticity, cushioning and adhesion of the adhesive layer. The foaming ratio is the optimal range after experimental verification. If it is too low, the adhesive layer will have insufficient cushioning and reduced activation. If it is too high, the adhesive layer will have insufficient rigidity and reduced creep resistance.

[0021] Furthermore, the core-shell type thermally expandable microspheres include a core and a shell.

[0022] The outer shell comprises at least one of polyacrylonitrile copolymer, polymethacrylate copolymer, and polyacrylonitrile-methacrylate modified copolymer; its function is to provide microsphere structural strength and thermal responsiveness, soften at high temperatures and allow the core to expand, form a stable closed-cell skeleton after foaming, and ensure the elasticity and resilience of the adhesive layer.

[0023] The core comprises a mixture of low-boiling-point hydrocarbons; the low-boiling-point hydrocarbon mixture includes at least two of isobutane, n-butane, isopentane, and n-pentane; its function is to generate expansion pressure upon heating and vaporization, which drives the outer shell to expand and form a closed-cell structure, giving the adhesive layer buffering properties, lightweight, and controllable thickness.

[0024] Furthermore, in step 4, the matching relationship between the double-sided tape and the foaming time is as follows: ① When the thickness of the target double-sided tape is 0.3±0.03mm, the foaming time is 3~6min, and the foaming ratio of the thermal expansion microspheres is 1.15~1.18; ② When the thickness of the target double-sided tape is 0.35±0.03mm, the foaming time is 6~9min, and the foaming ratio of the thermal expansion microspheres is 1.18~1.25.

[0025] During the foaming process, the double-sided foamed adhesive layers expand synchronously and uniformly under the constraint of the release film and the effect of uniform temperature, forming a dense closed-cell foam structure, which is integrally molded with the PET substrate without delamination or gaps.

[0026] The overall thickness of the double-sided tape of the present invention is 0.3±0.03mm or 0.35±0.03mm, and the thickness deviation of the double-sided foamed adhesive layer is ≤0.005mm, which ensures the symmetry of the structure and the uniformity of the stress, and avoids stress bias from the perspective of structural parameters.

[0027] Furthermore, the acrylate copolymer is copolymerized from acrylate monomers through a polymerization reaction; the acrylate monomers include soft monomers, hard monomers, and functional monomers; In the acrylate monomers, the mass ratio of soft monomers, hard monomers and functional monomers is (55-65):(25-35):(5-15).

[0028] Specifically, the soft monomer includes at least one of butyl acrylate, isooctyl acrylate, lauryl acrylate, and isodecanyl acrylate; its main function is to provide the adhesive layer with flexibility, initial tack and low-temperature flexibility, reduce the glass transition temperature of the copolymer, and improve the wettability and adhesion of the adhesive layer to the substrate.

[0029] The hard monomer includes at least one of methyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, and isobornyl methacrylate; its main function is to improve the cohesive strength, heat resistance, and creep resistance of the adhesive layer, and enhance its high-temperature holding power and dimensional stability.

[0030] The functional monomers include at least one of acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxypropyl acrylate, glycidyl methacrylate, and acrylamide; their main function is to introduce polar groups, improve the adhesion of the adhesive layer to different substrates, provide cross-linking reaction active sites, and improve the water resistance, aging resistance, and cohesive strength of the adhesive layer.

[0031] Furthermore, the tackifying resin is at least one of rosin resin and terpene phenolic resin; the softening point of the tackifying resin is 100~110℃.

[0032] Furthermore, the crosslinking agent is an isocyanate crosslinking agent, and the solid content of the crosslinking agent is 50%.

[0033] Furthermore, the defoamer is a polyether-modified silicone defoamer.

[0034] Furthermore, the solvent is ethyl acetate or toluene, used to adjust the viscosity of the adhesive to a suitable viscosity for coating.

[0035] The present invention also proposes a double-sided adhesive tape with a centrally located substrate, which is made by the above-mentioned method for preparing a double-sided adhesive tape with a centrally located substrate, comprising, from the inside out, a first acrylic thermally expanding microsphere foam layer, a PET substrate, and a second acrylic thermally expanding microsphere foam layer.

[0036] The core principle of this invention is: 1. Creep Resistance Principle of PET Central Rigid Support: A single-layer PET substrate acts as a rigid anti-deformation layer in the center. Its elastic modulus is much higher than that of the thermal expansion microsphere foam layer. Under continuous high temperature load of 70℃, the PET substrate can effectively counteract the plastic deformation tendency of the adhesive layer and limit the Z-direction displacement of the adhesive layer, thus inhibiting creep deformation structurally. At the same time, the double-sided symmetrical foam layer completely cancels out the forces on both sides of the PET substrate, without stress concentration or bias, avoiding bending deformation of the substrate due to unilateral force, and further ensuring creep resistance.

[0037] 2. The principle of uniform temperature and force in double-sided symmetrical foaming: The double-sided foaming adhesive layer is a symmetrical structure of the same material and thickness. During the application, foaming and actual use, the thermal expansion coefficient and stress state of the two sides of the adhesive layer are completely consistent. When heated, they expand synchronously and when loaded, they bear pressure synchronously. There is no warping or local deformation of the tape caused by stress bias, which ensures the full adhesion between the adhesive layer and the bonding surface, and at the same time improves the environmental stability of the tape.

[0038] 3. Adhesive layer protection principle of step-by-step coating + release film isolation: The adhesive is applied to both sides of the PET substrate in two steps. After each coating step, it is immediately bonded to the PET release film at the tail end of the machine and rolled up, achieving immediate isolation and protection of the adhesive layer. This prevents the adhesive layer from being contaminated by dust, scratched, damaged, or stuck during transportation and secondary coating, ensuring the initial thickness consistency of the double-sided adhesive layer. At the same time, the isolation effect of the release film keeps the adhesive layer surface stable, improves the intermolecular bonding force between the adhesive layer and the PET substrate, and prevents the adhesive layer from delaminating after foaming.

[0039] 4. The principle of constrained temperature uniformity in sandwich structure foaming with film: After the second coating, a sandwich structure is formed consisting of "upper release film - first foaming adhesive layer - PET substrate - second foaming adhesive layer - lower release film". The entire film is placed into the oven for foaming. The release film physically constrains the double-sided adhesive layers, limiting the irregular free expansion of thermally expanding microspheres, avoiding bulging and edge overflow of the adhesive layer, and ensuring the flatness of the adhesive layer and the density of the closed-cell structure. At the same time, the PET release film has good thermal conductivity, allowing the hot air in the oven to be evenly conducted to the adhesive layer through the release film. This avoids the rapid surface curing and internal solvent evaporation caused by the direct impact of hot air on the adhesive layer, ensuring synchronous and uniform foaming of the double-sided adhesive layers and eliminating performance fluctuations caused by uneven foaming.

[0040] 5. Precise control principle of foaming time as a single variable: The expansion degree of core-shell thermal expansion microspheres is linearly positively correlated with heating time at a constant temperature. This invention fixes the foaming oven temperature at 150~160℃ (matching the foaming start temperature of the thermal expansion microspheres), and controls the final expansion degree of the microspheres by adjusting the foaming time alone. This eliminates the mutual interference of multiple variables such as adhesive amount and temperature fluctuation, and achieves precise control of foaming ratio of 1.15~1.25 (fluctuation ±0.02) and tape thickness of ±0.03mm. Moreover, this control method has been verified by a large number of experiments and has excellent repeatability and mass production performance.

[0041] The technical solution of this invention achieves technical effects that are impossible to achieve with existing technologies through structural collaborative innovation and process-specific innovation, while also taking into account production costs and mass production feasibility. The specific advantages and effects are as follows: 1. Creep resistance meets standards from the source, and core indicators meet the requirements of high-end electronics: Through the synergistic structural design of central rigid support of the substrate and symmetrical foaming of double-sided adhesive layers, the Z-axis creep gap is ≤0.12mm after 72 hours of hanging a 1kg weight in a 70℃ environment. This completely solves the industry pain point of the existing thermal expansion microsphere foam adhesive layer failing to meet creep resistance standards. Moreover, the tape does not show significant decay in creep resistance after temperature shock of -40~70℃ and high temperature and humidity of 65℃ / 95%RH, and has excellent environmental stability.

[0042] 2. Precise control of thickness and foaming ratio, ensuring high consistency in mass production: Through a process system that ensures consistent initial thickness by applying adhesive in stages, uniform foaming by film-coated foaming, and single-variable control of foaming time, the foaming ratio is stable at 1.15~1.25 with a fluctuation of only ±0.02. The overall thickness tolerance of the tape is precisely controlled within ±0.03mm, and the thickness deviation of the double-sided adhesive layer is ≤0.005mm. No manual screening is required, meeting the mass production consistency requirements of high-end electronics.

[0043] 3. Achieving synergistic performance standards in creep resistance, high activation, and impact resistance: The tape of this invention not only meets the creep resistance standard, but also takes into account the elastic buffering characteristics of the thermal expansion microsphere foam adhesive layer. The activation (0.2MPa / 20s activation peel force ÷ 0.5MPa / 20s activation peel force) is ≥75%, meeting the requirements of rapid low-pressure bonding processes in high-end electronics; the impact resistance is ≥30 times, which can withstand the impact load during equipment assembly and use. It solves the technical problem of contradictory performance in the prior art, and its comprehensive performance far exceeds that of existing thermal expansion microsphere foam double-sided tapes.

[0044] 4. Strong adhesion between the adhesive layer and the substrate, no foaming defects, and excellent environmental stability: The surface energy of the PET substrate is increased after corona pretreatment, and the intermolecular bonding force between the substrate and the adhesive layer is increased by more than 40%; the isolation and protection of step-by-step coating and the temperature uniformity of film foaming avoid defects such as bubbles, pinholes, bulges, and glue overflow in the adhesive layer, and the adhesive layer has a dense closed-cell structure; after being placed in a high temperature and high humidity environment of 65℃ / 95%RH for 120 hours and subjected to 24 cycles of temperature shock from -40 to 70℃, the tape has no appearance defects such as delamination, wrinkles, or bubbles, and the peel strength retention rate is ≥70%, which can adapt to the complex operating environment of high-end electronic equipment.

[0045] 5. Low production cost, strong process adaptability, and easy industrial mass production: The entire process uses a single-layer PET substrate, which reduces substrate consumption by more than 50% compared to the double-layer substrate process; the PET release film used for separation has no adhesive residue and can be recycled and reused after cleaning, reducing auxiliary material costs by 20%; the preparation process uses conventional coating machines, ovens and other equipment, requiring only the addition of a release film unwinding device, without the need for large-scale modification of existing equipment, and each step is a continuous production, with seamless connection between coating, winding and foaming, and a production efficiency of ≥10m / min, suitable for large-scale industrial mass production. 6. Strong structural and process versatility and good scalability: The structural design and supporting process system of "centered PET substrate + symmetrical foaming of double-sided adhesive layer" of the present invention can adjust the thickness of PET substrate, foaming ratio and overall thickness of tape according to different application scenarios, adapting to the bonding requirements of different high-end electronic products such as smartphones, tablets, wearable devices, and smart homes, with excellent versatility and scalability. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the structure of the double-sided adhesive tape prepared in Examples 1-3 of the present invention.

[0047] Figure 2 This is a schematic diagram of the structure of the double-sided adhesive tape prepared in Comparative Example 1 of the present invention.

[0048] Figure 3 This is a schematic diagram of the structure of the double-sided adhesive tape prepared in Comparative Example 2 of the present invention.

[0049] Figure 4 This is a schematic diagram of the structure of the double-sided adhesive tape prepared in Comparative Example 3 of the present invention.

[0050] Figure 5 This is a linear relationship graph showing the foaming time and foaming ratio of the acrylic thermal expansion microsphere foam adhesive of the present invention.

[0051] Figure 6 This is a schematic diagram of the appearance of the acrylic thermal expansion microsphere foam layer of the double-sided tape prepared in Example 2 of the present invention.

[0052] Figure 7 This is a schematic diagram of the appearance of the acrylic thermal expansion microsphere foam layer of the double-sided tape prepared in Comparative Example 3 of the present invention.

[0053] Figure 8 This is a schematic diagram illustrating the operation of the Z-axis creep resistance test according to the present invention.

[0054] Figure 9 This is a side view of the impact resistance test sample of the present invention.

[0055] Figure 10 This is a top view of the impact resistance test sample of the present invention.

[0056] Figure 11 This is a schematic diagram of the instrument for testing the impact resistance of the present invention.

[0057] Figure 12 This is a schematic diagram of the groove in the fixture for testing the impact resistance of the present invention.

[0058] Figure 13 and Figure 14 This is a schematic diagram of the adhesive removal operation at different angles during the adhesive removal performance test of the present invention.

[0059] Explanation of reference numerals in the attached drawings: 1. PET substrate; 2. Acrylic thermal expansion microsphere foam layer; 3. Release film; 4. Acrylic adhesive layer. Detailed Implementation

[0060] A method for preparing a creep-resistant double-sided adhesive tape with a centrally located thermally expandable microsphere foam includes the following steps: Step 1: Pretreatment of PET substrate; Select a high-rigidity PET film with a thickness of 0.05~0.055mm as the substrate, and treat it with a corona treatment device with a treatment power of 1.0-1.2KW and a treatment time of 3~5s to make the surface energy of the substrate reach ≥50dyn / cm, enhance the intermolecular bonding force between the substrate and the adhesive layer, and prevent the adhesive layer from delaminating after foaming.

[0061] Step 2: Initial adhesive application and release film separation and winding; Place the pretreated PET substrate on the head of the adhesive coating machine, and apply acrylic thermal expansion microsphere foam adhesive to one side of the substrate using a doctor blade direct coating process. The doctor blade gap is adjusted according to the target wet coating thickness, which is 0.216~0.22mm. The thickness before foaming after solvent drying is 0.108~0.11mm. The coating speed is 8~10m / min to ensure that the coating layer is uniform, without pinholes or scratches. Immediately after the adhesive is applied, it is bonded to the 0.05mm thick PET release film at the tail of the machine with a bonding pressure of 0.2MPa. The film is then wound up to form a semi-finished product consisting of "lower release film - PET substrate - first foaming adhesive layer". The winding tension is controlled at 5~6N to avoid over-tight winding that could cause the adhesive layer to be squeezed or over-loose winding that could cause the release film to fall off.

[0062] The acrylic thermally expandable microsphere foam adhesive comprises, by weight, the following components: 100 parts acrylate copolymer; 5-8 parts core-shell thermally expandable microspheres; 5-8 parts tackifying resin; 0.5-1 part crosslinking agent; 0.2-0.5 parts defoamer; and 30 parts solvent.

[0063] The acrylate copolymer is copolymerized from acrylate monomers through a polymerization reaction; the acrylate monomers include soft monomers, hard monomers and functional monomers; in the acrylate monomers, the mass ratio of the soft monomers, hard monomers and functional monomers is 60:30:10.

[0064] In each embodiment, the soft monomer is isooctyl acrylate, the hard monomer is isobornyl methacrylate, and the functional monomer is acrylic acid.

[0065] The preparation method of acrylate copolymer is as follows: 60 parts of soft monomer, 30 parts of hard monomer, and 10 parts of functional monomer are added to a reaction vessel, along with 30 parts of solvent (ethyl acetate or toluene) and initiator (AIBN, the amount of which is 0.3~0.5% of the total mass of acrylate monomer); nitrogen gas is purged, the temperature is raised to 75~80℃, and the reaction is maintained for 6~8 hours to obtain an acrylate copolymer solution with a solid content of 48~52%, which is then cooled to room temperature for later use.

[0066] The preparation method of acrylic foam adhesive is as follows: Measure the acrylate copolymer according to the above ratio, add the core-shell thermally expandable microspheres, tackifying resin, crosslinking agent and defoamer in sequence, and stir evenly; then add solvent to adjust the viscosity, and stir until the system is homogeneous to obtain the acrylic thermally expandable microsphere foam adhesive.

[0067] Step 3, Secondary Glue Coating and Release Film Separation and Rewinding: With the uncoated side of the semi-finished PET substrate facing the glue coating machine head, apply acrylic thermal expansion microsphere foaming adhesive with the same formula and wet thickness as the first coating using the same process parameters. The wet coating thickness is 0.216~0.22mm, and the thickness before foaming after drying the solvent is 0.108~0.11mm, ensuring that the thickness deviation of the foaming adhesive layer on both sides is ≤0.005mm. Immediately after coating, it is bonded to another roll of 0.05mm PET release film at the tail end of the machine with a bonding pressure of 0.2MPa. Rewind to form a blank with a sandwich structure of "upper release film - first foaming adhesive layer - PET substrate - second foaming adhesive layer - lower release film". The winding tension is controlled at 6~8N, ensuring that the adhesive layers do not contact, stick, or shift throughout the process.

[0068] Step 4: Overall foaming of the preform with film: The preform is directly fed into a continuous hot air foaming oven. The temperature in each zone of the oven is kept constant at 150~160℃, and the hot air velocity is 2~3m / s to ensure uniform temperature without dead zones. After the first and second layers of adhesive to be foamed are heated and foamed, an acrylic thermal expansion microsphere foam layer is formed. By adjusting the residence time of the preform in the oven, i.e., the foaming time, the foaming ratio and the final thickness of the tape are controlled. No other process parameters are adjusted. The specific matching relationship is as follows: ①Target tape thickness 0.3±0.03mm: foaming time 3~6min, thermal expansion microsphere foaming ratio 1.15~1.18; ②Target tape thickness 0.35±0.03mm: foaming time 6~9min, thermal expansion microsphere foaming ratio 1.18~1.25.

[0069] like Figure 5 As shown, the linear relationship between foaming time and foaming ratio of adhesive layer at a constant temperature of 150~160℃ is presented. The curve is stable and without fluctuation, which intuitively verifies the accuracy and effectiveness of the "single variable control of foaming time" of the present invention.

[0070] The following embodiments, prepared according to the above method, use foaming ratios of 1.15, 1.18, and 1.25, corresponding to double-sided tape thicknesses of 0.3±0.03mm, 0.3±0.03mm, and 0.35±0.03mm, to further describe the scheme of this application: Example 1 A method for preparing a creep-resistant double-sided adhesive tape with a centrally located thermally expandable microsphere foam includes the following steps: Step 1: Select a high-rigidity PET film with a thickness of 0.05mm as the substrate, and treat it with a corona treatment device with a power of 1.0KW and a treatment time of 3s.

[0071] Step 2: Place the pretreated PET substrate on the head of the coating machine. Apply acrylic thermal expansion microsphere foam adhesive to one side of the substrate using a doctor blade direct coating process. Adjust the doctor blade gap according to the target wet coating thickness. The wet coating thickness is 0.22mm, and the thickness before foaming is 0.11mm. The coating speed is 8~10m / min. Immediately after coating, bond it to the 0.05mm thick PET release film at the tail of the machine. The bonding pressure is 0.2MPa. The film is then wound up to form a semi-finished product consisting of "lower release film - PET substrate - first foaming layer". The winding tension is controlled at 5N.

[0072] The acrylic thermally expandable microsphere foam adhesive comprises, by weight, the following components: 100 parts acrylate copolymer, 5 parts core-shell thermally expandable microspheres, 2.5 parts rosin resin, 2.5 parts terpene phenolic resin, 0.5 parts isocyanate crosslinking agent, 0.2 parts polyether modified silicone defoamer, and 30 parts ethyl acetate.

[0073] Step 3, Secondary Glue Coating and Release Film Separation and Rewinding: With the uncoated side of the semi-finished PET substrate facing the glue coating machine head, apply acrylic thermal expansion microsphere foaming adhesive of the same formula and wet thickness to this side using the same process parameters as the first coating. The wet thickness of the adhesive is 0.22mm, and the thickness before foaming is 0.11mm after the solvent dries, ensuring that the thickness deviation of the foaming adhesive layer on both sides is ≤0.005mm. Immediately after coating, it is bonded to another roll of 0.05mm PET release film at the tail end of the machine with a bonding pressure of 0.2MPa. Rewind to form a sandwich structure blank of "upper release film - first foaming adhesive layer - PET substrate - second foaming adhesive layer - lower release film". The winding tension is controlled at 6N.

[0074] Step 4: Overall foaming of the preform with film: The preform is directly fed into a continuous hot air foaming oven. The temperature in each zone of the oven is kept constant at 160℃, the hot air velocity is 2~3m / s, the foaming time is 3min, and the foaming ratio is 1.15; a double-sided tape with the structure of "release film 3-acrylic thermal expansion microsphere foam layer 2-PET substrate 1-acrylic thermal expansion microsphere foam layer 2-release film 3" is obtained, as shown below. Figure 1 As shown.

[0075] The finished parameters of the double-sided tape are: overall thickness 0.29~0.3mm, and dry thickness of each double-sided foam adhesive layer 0.126mm.

[0076] Example 2 A method for preparing a creep-resistant double-sided adhesive tape with a centrally located thermally expandable microsphere foam includes the following steps: Step 1: Select a high-rigidity PET film with a thickness of 0.05mm as the substrate, and treat it with a corona discharge device with a processing power of 1.1KW and a processing time of 4s.

[0077] Step 2: Place the pretreated PET substrate on the head of the coating machine. Apply acrylic thermal expansion microsphere foam adhesive to one side of the substrate using a doctor blade direct coating process. Adjust the doctor blade gap according to the target wet coating thickness. The wet coating thickness is 0.22mm, and the thickness before foaming is 0.11mm. The coating speed is 8~10m / min. Immediately after coating, bond it to the 0.05mm thick PET release film at the tail of the machine. The bonding pressure is 0.2MPa. The film is then wound up to form a semi-finished product consisting of "lower release film - PET substrate - first foaming layer". The winding tension is controlled at 5.5N.

[0078] The acrylic thermally expandable microsphere foam adhesive comprises, by weight, the following components: 100 parts acrylate copolymer, 7 parts core-shell thermally expandable microspheres, 2.5 parts rosin resin, 2.5 parts terpene phenolic resin, 0.8 parts isocyanate crosslinking agent, 0.2 parts polyether modified silicone defoamer, and 30 parts ethyl acetate.

[0079] Step 3, Secondary Glue Coating and Release Film Separation and Rewinding: With the uncoated side of the semi-finished PET substrate facing the glue coating machine head, apply acrylic thermal expansion microsphere foaming adhesive of the same formula and wet thickness to this side using the same process parameters as the first coating. The wet thickness of the adhesive is 0.22mm, and the thickness before foaming is 0.11mm after the solvent dries, ensuring that the thickness deviation of the foaming adhesive layer on both sides is ≤0.005mm. Immediately after coating, it is bonded to another roll of 0.05mm PET release film at the tail end of the machine with a bonding pressure of 0.2MPa. Rewind to form a sandwich structure blank of "upper release film - first foaming adhesive layer - PET substrate - second foaming adhesive layer - lower release film". The winding tension is controlled at 7N.

[0080] Step 4: Integral foaming of the blank with film: The blank is directly fed into a continuous hot air foaming oven. The temperature of each temperature zone in the oven is kept constant at 160℃, the hot air velocity is 2~3m / s, the foaming time is 6min, and the foaming ratio is 1.18; a double-sided tape with the structure of "release film 3-acrylic thermal expansion microsphere foam layer 2-PET substrate 1-acrylic thermal expansion microsphere foam layer 2-release film 3" is obtained.

[0081] The finished parameters of the double-sided tape are: overall thickness 0.30~0.31mm, and dry thickness of each double-sided foam adhesive layer 0.13mm.

[0082] During the foaming process, the two-sided foamed adhesive layers expand synchronously and uniformly under the constraint of the release film and the effect of uniform temperature, forming a dense closed-cell foam structure. The acrylic thermal expansion microsphere foamed adhesive layer is smooth and free of bulges, as shown in the image. Figure 6 As shown, it is integrally molded with the PET substrate, without delamination or gaps.

[0083] Example 3 A method for preparing a creep-resistant double-sided adhesive tape with a centrally located thermally expandable microsphere foam includes the following steps: Step 1: Select a high-rigidity PET film with a thickness of 0.05mm as the substrate, and treat it with a corona discharge device with a power of 1.2KW and a processing time of 5s.

[0084] Step 2: Place the pretreated PET substrate on the head of the coating machine. Apply acrylic thermal expansion microsphere foam adhesive to one side of the substrate using a doctor blade direct coating process. Adjust the doctor blade gap according to the target wet coating thickness. The wet coating thickness is 0.26mm, and the thickness before foaming after drying the solvent is 0.13mm. The coating speed is 8~10m / min. Immediately after coating, bond it to the 0.05mm thick PET release film at the tail of the machine. The bonding pressure is 0.2MPa. The film is then wound up to form a semi-finished product consisting of "lower release film - PET substrate - first foaming layer". The winding tension is controlled at 6N.

[0085] The acrylic thermally expandable microsphere foaming adhesive comprises, by weight, the following components: 100 parts acrylate copolymer, 8 parts core-shell thermally expandable microspheres, 2.5 parts rosin resin, 2.5 parts terpene phenolic resin, 1 part isocyanate crosslinking agent, 0.2 parts polyether modified silicone defoamer, and 30 parts ethyl acetate.

[0086] Step 3, Secondary Glue Coating and Release Film Separation and Rewinding: With the uncoated side of the semi-finished PET substrate facing the glue coating machine head, apply acrylic thermal expansion microsphere foaming adhesive of the same formula and wet thickness to this side using the same process parameters as the first coating. The wet thickness of the adhesive is 0.26mm, and the thickness before foaming is 0.13mm after the solvent dries, ensuring that the thickness deviation of the foaming adhesive layer on both sides is ≤0.005mm. Immediately after coating, it is bonded to another roll of 0.05mm PET release film at the tail end of the machine with a bonding pressure of 0.2MPa. Rewind to form a sandwich structure blank of "upper release film - first foaming adhesive layer - PET substrate - second foaming adhesive layer - lower release film". The winding tension is controlled at 8N.

[0087] Step 4: Integral foaming of the blank with film: The blank is directly fed into a continuous hot air foaming oven. The temperature of each temperature zone in the oven is kept constant at 160℃, the hot air velocity is 2~3m / s, the foaming time is 9min, and the foaming ratio is 1.25. A double-sided tape with the structure of "release film 3-acrylic thermal expansion microsphere foam layer 2-PET substrate 1-acrylic thermal expansion microsphere foam layer 2-release film 3" is obtained.

[0088] The finished parameters of the double-sided tape are: overall thickness 0.33~0.37mm, and dry thickness of each double-sided foam adhesive layer 0.16mm.

[0089] Comparative Example 1 A double-sided adhesive tape, without a PET substrate, consisting only of a pure thermally expanded microsphere foam adhesive layer structure; its preparation method differs from that of Example 2 above in that: The PET substrate is eliminated during preparation; adhesive (acrylic thermal expansion microsphere foaming adhesive) is directly applied to the release film. This involves sandwiching the two layers of release film together for heating and foaming. The resulting double-sided tape has the following structure: Figure 2 As shown.

[0090] The formulation, adhesive layer thickness, coating, winding, and foaming process parameters of the acrylic thermally expandable microsphere foam adhesive are the same as those in Example 2.

[0091] Comparative Example 2 A double-sided adhesive tape is a single-layer PET substrate with a single-sided thermally expanding microsphere foam structure. Its preparation method differs from Example 2 above in that the acrylic thermally expanding microsphere foam adhesive used in step 3 is replaced with an acrylic adhesive of the same formulation system without added core-shell thermally expanding microspheres. The resulting double-sided adhesive tape structure is: "Release film 3 - Acrylic adhesive layer 4 - PET substrate 1 - Acrylic thermally expanding microsphere foam adhesive layer 2 - Release film 3", as shown below. Figure 3 As shown.

[0092] Comparative Example 3 A double-sided adhesive tape, the preparation method of which differs from that of Example 2 above, is as follows: step 3 omits the release film lamination operation, i.e., after the PET is coated with adhesive a second time, it is directly rolled up without the film; and before step 4, the release film of the first adhesive coating is peeled off; i.e., both sides are placed in the oven for foaming without the film. Figure 4 As shown, the structure of the prepared double-sided tape is: "Acrylic thermally expandable microsphere foam layer 2 - PET substrate 1 - Acrylic thermally expandable microsphere foam layer 2". The appearance of the acrylic thermally expandable microsphere foam layer is as follows. Figure 7 As shown, without the constraint of the release film, the acrylic thermal expansion microsphere foam layer bulges and foams unevenly.

[0093] The double-sided adhesives prepared in the above embodiments and comparative examples were used as samples for performance testing: Test items and test methods Z-axis creep resistance test: Referring to GB / T4851-2014 Test Method for Adhesive Tape Holding Power, the test is adjusted to load weights in the Z-axis of the sample. The Z-axis in this scheme refers to the direction perpendicular to the length of the double-sided tape, i.e., the thickness direction. The specific test method is as follows: ①, such as Figure 8 As shown, two T-shaped sample blocks are arranged in a cross shape facing each other. The sample (with adhesive backing) is cut into a ring with an outer diameter of 25mm and an inner diameter of 18mm, i.e., a width of 3.5mm, and pasted between the two T-shaped sample blocks.

[0094] ② Pressurize with 200N for 30 seconds, then let stand at room temperature for 24 hours.

[0095] ③ Hang a 1kg weight on the vertical end of the T-shaped sample block below, i.e., the Z-axis weight of the sample (adhesive backing). Maintain the temperature at 70℃ for 72 hours and observe whether the T-shaped sample block detaches. If detachment occurs, record the test conditions (time) for this sample (adhesive backing). If the sample (adhesive backing) does not detach, remove it after 72 hours and let it stand for 30 minutes. Use a thickness gauge to measure the thickness corresponding to the four corners of the T-shaped sample block, take the average value, and record it. Subtract the sample thickness to obtain the creep clearance value.

[0096] 2. Activation test: Refer to GB / T2792-2014 Test method for peel strength of adhesive tape, test the ratio of 180° peel force of the sample activated at 0.2MPa / 20s and 0.5MPa / 20s.

[0097] 3. Impact resistance test: ① Cut the tape sample into a ring with an outer diameter of 25mm, an inner diameter of 21mm, and a width of 2mm; remove the release film from one end of the ring sample and attach it to the center area of ​​the cleaned aluminum alloy ejector sample, ensuring there are no air bubbles or wrinkles; remove the release film from the other side and cover the double-sided tape with the ink glass, ensuring that the center positions of the ink glass, the aluminum alloy ejector sample, and the double-sided tape are basically consistent. Figure 9 and Figure 10 As shown in the figure, the "adhesive backing" refers to the circular adhesive tape sample.

[0098] ② Pressurize with 200N for 30 seconds, then let stand at room temperature for 24 hours.

[0099] ③ Place the prepared sample flat in the groove of the fixture, with the round hole facing upwards, as shown. Figure 12 As shown, a 200g weight was manually picked up and dropped from a height of 80mm with an impact interval of 2s. The number of times the weight broke was recorded.

[0100] 4. Dynamic shear force test: Refer to GB / T33332-2016 Test method for dynamic shear strength of adhesive tape.

[0101] 5. High temperature and high humidity performance test: According to the test method of GB / T2792-2014 for peel strength of adhesive tape, the sample was placed in a high temperature and high humidity environment of 65℃ and 95%RH for 120h, and then placed at room temperature for 2h. The peel strength retention rate and appearance were then tested. Peel strength retention rate = peel strength after high temperature and high humidity treatment / initial peel strength × 100%.

[0102] 6. Temperature shock performance test: According to the test method of GB / T2792-2014 for peel strength of adhesive tape, the sample was subjected to 24 cycles of temperature shock at -40~70℃. After being placed at room temperature for 2 hours, the peel force retention rate and appearance were tested; peel force retention rate = peel force after shock treatment / initial peel force × 100%.

[0103] 7. Flatness (warping) test: Referring to the measurement principle of GB / T 20920-2007, an electronic level was used to test the warpage of the tape sample. The specific steps are as follows: ① Cut the prepared double-sided tape into 100mm×100mm samples, remove the release film, and paste it flat onto the surface of a standard float glass substrate, ensuring that there are no bubbles or wrinkles during the bonding process; ② Place the sample in a standard environment with a temperature of 23℃±2℃ and a relative humidity of 50%±5% for 24 hours to allow the stress to be fully released; ③ Using an electronic level, measure the horizontal height difference at multiple points along the length and width of the sample, and calculate the maximum height difference between the edge and center of the sample. This is used to characterize the warpage of the tape. The smaller the height difference, the better the flatness.

[0104] 8. Adhesive Removal Performance Test: Visual inspection method. Apply 10mm*40mm double-sided tape to the aluminum alloy interface (6013 AnAl) used in the standard peel force test. Roll back and forth three times with 50N. Place the sample in an 85℃ / 85%RH environment for 120 hours, then remove it and allow it to stand at room temperature for at least 12 hours. Manually peel the sample to begin the test and observe the residual adhesive. The tearing direction includes... Figure 13 and Figure 14 The two directions are shown in the diagram.

[0105] Test data

[0106] Test Results Explanation 1. All embodiments of the present invention meet the performance standards and have the best overall performance: The Z-axis creep gap of embodiments 1 to 3 is ≤0.12mm, the activation rate is ≥75%, the number of impacts is ≥30, there is no appearance defect after high temperature and high humidity / temperature impact, the peel force retention rate is ≥70%, and the flatness is excellent. All indicators meet the stringent requirements of high-end electronic devices, and the performance indicators meet the standards in a coordinated manner, which verifies the effectiveness of the structural and process co-design of the present invention.

[0107] 2. Comparative Example 1 (without PET) suffered severe high-temperature plastic deformation of the adhesive layer due to the lack of rigid support, and the creep gap far exceeded the standard. Comparative Example 2 (PET single-sided foaming) suffered excessive creep and warping due to stress bias in the asymmetrical structure. Only the PET centered and double-sided symmetrical foaming structure of this invention can suppress creep deformation from the source and ensure that the core creep resistance index meets the standard.

[0108] 3. Comparative Example 3 has the same structure as the present invention, but due to the use of conventional non-film winding and non-film foaming processes, the adhesive layer sticks, foaming is uneven, creep gap exceeds the standard, and the adhesive removal and environmental performance are reduced. This shows that the step-by-step adhesive coating, release film isolation and film foaming process of the present invention are necessary conditions for realizing the structural performance value.

[0109] This invention achieves synergistic effects between structure and process. It is not simply a structural innovation, but rather a solution that matches structural design with a dedicated process, thus solving the problem of "performance failing to meet standards due to superior structure but mismatched process," and forming a complete technical solution. Compared with the structural defects and conventional processes of existing technologies, the dual innovation of structure and process in this invention achieves a qualitative improvement in performance, and all trial production data can corroborate this, demonstrating its strong practicality.

[0110] The above preferred embodiments should be regarded as illustrative examples of the embodiments of the present application. Any technical deductions, substitutions, improvements, etc. that are similar to or based on the present application should be considered within the scope of protection of this patent.

Claims

1. A method for preparing a creep-resistant double-sided adhesive tape with centrally located thermally expanding microspheres foamed in the substrate, characterized in that, Includes the following steps: Step 1: Substrate pretreatment; PET substrate is selected, and the surface of the substrate is first treated with a corona discharge device to make the surface energy of the PET substrate reach ≥50dyn / cm; Step 2: First application of adhesive and separation from release film and winding; one side of the pretreated PET substrate is coated with acrylic thermal expansion microsphere foam adhesive, and the release film is immediately attached after the adhesive is applied and the substrate is wound up to form a semi-finished product consisting of "lower release film - PET substrate - first foaming layer"; Step 3: Secondary adhesive coating and release film separation and winding; Apply acrylic thermal expansion microsphere foaming adhesive with the same formula and wet thickness as the first coating to the uncoated side of the semi-finished PET substrate, using the same process parameters as the first coating, to ensure that the thickness deviation of the foaming adhesive layer on both sides is ≤0.005mm; Immediately after coating, attach the release film and wind up to form a blank with a sandwich structure of "upper release film - first foaming adhesive layer - PET substrate - second foaming adhesive layer - lower release film"; Step 4: Overall foaming of the blank with film; The blank is sent into a continuous hot air foaming oven, and the temperature of each temperature zone in the oven is kept constant at 150~160℃. After the first and second layers of adhesive to be foamed are heated and foamed, an acrylic thermal expansion microsphere foaming layer is formed; By adjusting the residence time of the blank in the oven, i.e. the foaming time, the foaming ratio and the final thickness of the double-sided tape are controlled.

2. The method for preparing the substrate-centered thermally expanding microsphere foamed creep-resistant double-sided adhesive tape according to claim 1, characterized in that: The PET substrate is a high-rigidity PET film with a thickness of 0.05~0.055mm; In steps 2 and 3, the wet thickness of the adhesive coating is 0.216~0.22mm, and the thickness before the solvent dries and foams is 0.108~0.11mm.

3. The method for preparing the substrate-centered thermally expanding microsphere foamed creep-resistant double-sided adhesive tape according to claim 1, characterized in that: In step 1, the corona treatment device has a processing power of 1.0-1.2KW and a processing time of 3-5s; In steps 2 and 3, the adhesive is applied using an adhesive applicator with a direct blade coating process at a speed of 8-10 m / min. In steps 2 and 3, the bonding pressure of the release film is 0.2 MPa; In step 2, the winding tension is controlled at 5~6N; in step 3, the winding tension is controlled at 6~8N. In step 4, the air velocity of the hot air inside the oven is 2~3 m / s; The release film is a 0.05mm thick PET release film.

4. The method for preparing the substrate-centered thermally expanding microsphere foamed creep-resistant double-sided adhesive tape according to any one of claims 1-3, characterized in that: The acrylic thermally expandable microsphere foam adhesive comprises, by weight, the following components: 100 parts acrylate copolymer; 5-8 parts core-shell thermally expandable microspheres; 5-8 parts tackifying resin; 0.5-1 part crosslinking agent; 0.2-0.5 parts defoamer; and 30 parts solvent. The acrylate copolymer has a solid content of 50% and a glass transition temperature of -20 ~ -15℃. The foaming temperature of the core-shell thermal expansion microspheres is 150~160℃.

5. The method for preparing the substrate-centered thermally expanding microsphere foamed creep-resistant double-sided adhesive tape according to claim 4, characterized in that: The core-shell thermal expansion microspheres include a core and a shell; The outer shell comprises at least one of polyacrylonitrile copolymer, polymethacrylate copolymer, and polyacrylonitrile-methacrylate modified copolymer; The core comprises a mixture of low-boiling-point hydrocarbons; the mixture of low-boiling-point hydrocarbons comprises at least two of isobutane, n-butane, isopentane, and n-pentane.

6. The method for preparing the substrate-centered thermally expanding microsphere foamed creep-resistant double-sided adhesive tape according to claim 5, characterized in that: In step 4, the matching relationship between the double-sided tape and the foaming time is as follows: ① When the thickness of the target double-sided tape is 0.3±0.03mm, the foaming time is 3~6min, and the foaming ratio of the thermal expansion microspheres is 1.15~1.18; ② When the thickness of the target double-sided tape is 0.35±0.03mm, the foaming time is 6~9min, and the foaming ratio of the thermal expansion microspheres is 1.18~1.

25.

7. The method for preparing the substrate-centered thermally expanding microsphere foamed creep-resistant double-sided adhesive tape according to claim 5, characterized in that: The acrylate copolymer is copolymerized from acrylate monomers through a polymerization reaction; the acrylate monomers include soft monomers, hard monomers, and functional monomers. In the acrylate monomers, the mass ratio of soft monomers, hard monomers and functional monomers is (55-65):(25-35):(5-15).

8. The method for preparing the substrate-centered thermally expanding microsphere foamed creep-resistant double-sided adhesive tape according to claim 5, characterized in that: The soft monomer includes at least one of butyl acrylate, isooctyl acrylate, lauryl acrylate, and isodecanyl acrylate; The hard monomer includes at least one of methyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, and isobornyl methacrylate; The functional monomers include at least one of acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxypropyl acrylate, glycidyl methacrylate, and acrylamide.

9. The method for preparing the substrate-centered thermally expanding microsphere foamed creep-resistant double-sided adhesive tape according to claim 5, characterized in that: The tackifying resin is at least one of rosin resin and terpene phenolic resin; the softening point of the tackifying resin is 100~110℃. The crosslinking agent is an isocyanate-based crosslinking agent, and the solid content of the crosslinking agent is 50%. The defoamer is a polyether-modified silicone defoamer; The solvent is ethyl acetate or toluene.

10. A type of thermally expandable microsphere foamed creep-resistant double-sided adhesive tape with a centrally located substrate, characterized in that: The substrate-centered thermally expandable microsphere foamed creep-resistant double-sided adhesive tape is prepared by any one of the above-described 1-9 methods; the substrate-centered thermally expandable microsphere foamed creep-resistant double-sided adhesive tape comprises, from the inside out, a first acrylic thermally expandable microsphere foamed adhesive layer, a PET substrate, and a second acrylic thermally expandable microsphere foamed adhesive layer.

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