Waterproof buffer hot melt type foam adhesive for display screen pasting and production process

Abstract

The application discloses a waterproof buffer hot-melt type foam adhesive for display screen sticking and a production process, relates to the technical field of display device manufacturing, and comprises the following process steps: providing a hot-melt adhesive base body, wherein the components of the hot-melt adhesive base body comprise a thermoplastic elastomer, a tackifying resin and a solvent; dispersing unfoamed material in the hot-melt adhesive base body, wherein the foaming temperature of the unfoamed material is not lower than the boiling point of the solvent, and a mixed adhesive liquid is formed; coating the mixed adhesive liquid on a release substrate, and forming an unfoamed adhesive film layer after drying; in a display screen sticking process, the release substrate is torn off, and the adhesive film layer after sticking is heated and pressurized, the adhesive film layer is synchronously triggered to activate adhesion, and the unfoamed material is synchronously triggered to foam and expand, so that a foam adhesive layer with a closed pore structure is formed. The application has the characteristics of high adhesion reliability, dynamic buffer adaptability and easy rework.

Description

Technical Field

[0001] This invention relates to the field of display device manufacturing technology, and in particular to a waterproof, cushioning, hot-melt foam adhesive for bonding display screens and its manufacturing process. Background Technology

[0002] With the rapid development of display technology, the performance requirements for precision bonding materials in display modules are becoming increasingly stringent, especially in consumer electronics such as smartphones and tablets. Foam tape, which combines high-strength adhesion, shock absorption, waterproof sealing, and easy rework, has become a key material. Traditional technologies commonly use polyethylene (PE) based foam tape or acrylic foam tape (VHB) as the bonding medium for displays, but both have significant limitations in structural design and material performance.

[0003] Taking PE-based foam tape as an example, its porous structure, formed through physical foaming, provides some cushioning performance. However, due to the low polarity of polyethylene itself, the interfacial bonding strength is insufficient (typically ≤12N / in). More importantly, PE foam has low cohesive strength, making it prone to interlayer delamination under long-term stress or temperature variations, severely impacting sealing reliability. On the other hand, VHB tape employs a three-layer composite structure (acrylic foam layer / double-sided adhesive layer / release film). While its acrylic polymer provides high initial tack, the excessively high crosslinking density limits the material's tensile strength (approximately 1MPa), resulting in an elongation at break of only 400%. This characteristic makes complete tape removal difficult during screen rework, and residual adhesive is hard to clean. Furthermore, the complex three-layer structure requires multiple processes (typically ≥3) including coating, lamination, and curing, leading to high production costs and contradicting green manufacturing trends.

[0004] Furthermore, existing technologies attempt to resolve the conflict between cushioning and adhesive strength by incorporating foamed microspheres (such as unfoamed microspheres or AC foaming agents) into the adhesive layer, as exemplified by the cushioning and waterproof acrylic foam functional tape structure disclosed in Chinese Patent CN117363256 A. However, the foaming process is typically completed during the tape production stage. While this pre-foaming process can create a cellular structure, it causes the material to lose its cushioning effectiveness due to cellular collapse during subsequent screen bonding. Moreover, the increased roughness of the adhesive surface after foaming weakens the interfacial bonding strength. More importantly, traditional processes often rely on solvent-based adhesive systems to adjust rheological properties, and their volatile organic compound (VOC) emissions pose a challenge to the production environment and the environmental friendliness of the products.

[0005] In summary, existing foam tapes for display screen bonding face multiple technical bottlenecks in terms of bonding strength, mechanical property balance, process efficiency, and environmental friendliness. Summary of the Invention

[0006] One of the objectives of this invention is to provide a production process for a waterproof, cushioning, hot-melt foam adhesive for display screen bonding, in order to solve the problems mentioned in the background art and provide an integrated solution that combines high bonding reliability, dynamic cushioning adaptability, and easy rework characteristics.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a production process for a waterproof and cushioning hot-melt foam adhesive for display screen bonding, comprising the following steps:

[0008] (1) A hot melt adhesive matrix is ​​provided, wherein the hot melt adhesive matrix comprises a thermoplastic elastomer, a tackifying resin and a solvent, wherein the thermoplastic elastomer is at least one of SIS and SBS, the tackifying resin is at least one of petroleum resin and rosin resin, and the solvent is at least one of ethyl acetate, acetone or toluene;

[0009] (2) Disperse the unfoamed material in the hot melt adhesive matrix to form a mixed adhesive solution, wherein the foaming temperature of the unfoamed material is not lower than the boiling point of the solvent, and the unfoamed material is at least one of thermal expansion microspheres or AC foaming agent;

[0010] (3) The mixed adhesive solution is applied to the release substrate and dried to form an unfoamed adhesive film layer;

[0011] (4) In the display screen bonding process, the adhesive film layer after the release substrate is removed and bonding is completed is heated and pressurized, which simultaneously triggers the bonding activation of the adhesive film layer and the foaming expansion of the unfoamed material to form a foam adhesive layer with a closed-cell structure.

[0012] Preferably, the hot melt adhesive matrix further includes a softener and an anti-aging agent, wherein the softener is naphthenic oil or paraffin.

[0013] More preferably, the particle size of the unfoamed material is 5-50 μm; the amount of the unfoamed material added is 0.5-10 wt% of the total mass of the hot melt adhesive matrix. A black material for light blocking is also added to the hot melt adhesive matrix.

[0014] More preferably, in step (4), the heating temperature is 90-120°C and the pressurization pressure is 0.4-0.8 MPa.

[0015] More preferably, the coating thickness of the adhesive film layer is 0.1-0.5 mm.

[0016] In addition, the present invention also provides a waterproof and cushioning hot-melt foam adhesive for display screens, which is prepared by the above-mentioned production process and includes a hot-melt adhesive layer. The hot-melt adhesive layer contains unfoamed material, which is microspheres or foaming agent particles in the unfoamed state. The unfoamed material expands under hot-pressing conditions to form a closed-cell structure.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] 1. By simultaneously triggering adhesive activation and foaming expansion, the molten thermoplastic elastomer and the display substrate form an adhesive during the hot pressing process. This can eliminate the interface micropore defects caused by pre-foaming of traditional foam adhesives, significantly improving peel strength and long-term aging resistance. The dense closed-cell network formed by foaming expansion can block the water vapor diffusion path, prevent water molecules from eroding the adhesive interface, and achieve waterproof sealing.

[0019] 2. Delayed foaming of unfoamed materials ensures more uniform cell size. The closed-cell structure absorbs energy through elastic deformation under dynamic impact, while the thermoplastic elastomer skeleton provides rebound support, which is suitable for the multi-directional stress buffering needs of display components in scenarios such as vibration and drop.

[0020] 3. Thermoplastic elastomers soften reversibly during secondary heating, allowing the foam adhesive layer to be completely peeled off from the display substrate without any residue, thus making rework easier and overcoming the disassembly damage problem caused by the irreversible cross-linking of traditional thermosetting adhesives. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the overall structure of the foam adhesive when the release liner has not been removed in the embodiment.

[0022] In the picture:

[0023] a. Hot melt adhesive matrix; b. Release substrate; c. Unfoamed material. Detailed Implementation

[0024] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments and accompanying drawings. The content mentioned in the embodiments is not intended to limit the present invention.

[0025] Example 1

[0026] The manufacturing process of waterproof cushioning hot-melt foam adhesive for bonding flexible OLED displays includes the following steps:

[0027] (1) Preparation of hot melt adhesive matrix.

[0028] Formulation composition (based on the total mass of the hot melt adhesive matrix):

[0029] Thermoplastic elastomer: 40wt% SIS (styrene-isoprene-styrene block copolymer);

[0030] Tackifying resin: 30wt% petroleum resin;

[0031] Solvent: 25wt% ethyl acetate (boiling point 77℃);

[0032] Softener: 3wt% paraffin;

[0033] Anti-aging agent: 2wt% benzotriazole UV absorber.

[0034] SIS, petroleum resin, paraffin, and benzotriazole UV absorbers were added to a double planetary mixer and heated to 120°C to melt and mix for 1 hour. After cooling to 60°C, ethyl acetate was added and stirred at 800 rpm for 30 minutes to form a homogeneous colloid.

[0035] (2) Dispersion of unfoamed materials.

[0036] Add 3wt% thermally expanded microspheres (foaming temperature 95-125℃) to the adhesive solution in step (1), and stir at a low speed of 200rpm for 15 minutes to avoid microsphere breakage, forming a mixed adhesive solution containing uniformly dispersed unfoamed material.

[0037] (3) Coating and drying to form a film.

[0038] The mixed adhesive solution was applied to the surface of a PET release film (50 μm thick), resulting in a wet film thickness of 1.2 mm. It was then dried in an 80°C hot air circulating oven for 10 minutes, with a solvent residue rate of <0.5%, forming an unfoamed adhesive film layer (dry film thickness of 0.5 mm).

[0039] (4) Adhesion and synchronous foaming.

[0040] Remove the PET release film, attach the adhesive film layer to the back panel of the flexible OLED screen, apply 0.5 MPa pressure and heat to 110°C for 20 seconds, causing the thermally expanded microspheres to foam and form a closed-cell structure. At this point, the SIS melts and flows, forming a molecular-level bond with the substrate.

[0041] (5) Rework test.

[0042] The bonded screen is heated to 100°C and pressure of 0.3 MPa is applied. The adhesive layer is completely peeled off within 5 minutes, leaving no adhesive residue or damage to the substrate.

[0043] Furthermore, the foam adhesive prepared in this embodiment has a density of 0.1 g / cm3-0.8 g / cm3 and a 25% CFD of 80 kPa-800 kPa.

[0044] Example 2

[0045] The manufacturing process for waterproof, cushioning, hot-melt foam adhesive used for bonding automotive displays includes the following steps:

[0046] (1) Preparation of hot melt adhesive matrix.

[0047] Formulation composition (based on the total mass of the hot melt adhesive matrix):

[0048] Thermoplastic elastomer: 30wt% SBS (styrene-isoprene-styrene block copolymer);

[0049] Tackifying resin: 25wt% rosin resin;

[0050] Solvent: 40wt% isopropanol (boiling point 82℃);

[0051] Softener: 2wt% naphthenic oil;

[0052] Anti-aging agent: 2wt% benzotriazole UV absorber;

[0053] Filler: 1 wt% carbon black.

[0054] SBS, rosin resin, naphthenic oil, benzotriazole UV absorber and carbon black were added to a double planetary mixer and heated to 120°C to melt and mix for 1 hour. After cooling to 60°C, ethyl acetate was added and stirred at 800 rpm for 30 minutes to form a homogeneous colloid.

[0055] (2) Dispersion of unfoamed materials.

[0056] Add 5wt% AC foaming agent to the adhesive solution in step (1) and stir at a low speed of 200 rpm for 15 minutes to avoid microsphere breakage, forming a mixed adhesive solution containing uniformly dispersed unfoamed material.

[0057] (3) Coating and drying to form a film.

[0058] Same as Example 1.

[0059] (4) Adhesion and synchronous foaming.

[0060] Remove the PET release film, attach the adhesive film layer to the back panel of the flexible OLED screen, apply 0.5 MPa pressure and heat to 110°C for 20 seconds to allow the AC foaming agent to foam and form a closed-cell structure. At this time, the SBS melts and flows, forming a molecular-level bond with the substrate.

[0061] (5) Rework test.

[0062] The bonded screen is heated to 100°C and pressure of 0.3 MPa is applied. The adhesive layer is completely peeled off within 4 minutes, leaving no adhesive residue or damage to the substrate.

[0063] Comparative Example 1

[0064] The traditional PE foam adhesive manufacturing process for bonding flexible OLED displays includes the following steps:

[0065] (1) Provide PE substrate: Mix polyethylene resin (density 0.92g / cm³) with foaming agent (azodicarbonamide, foaming temperature 160-180℃) and melt blend in a twin-screw extruder at 180℃.

[0066] (2) Foaming molding: The molten mixture is extruded into a film and foamed at a high temperature (180°C) to form a porous foam layer.

[0067] (3) Coating and laminating: Apply acrylic adhesive (40% solid content) to both sides of the foamed PE foam layer and laminate it with release film to form a three-layer structure (foam layer / adhesive layer / release film).

[0068] (4) Bonding process: Remove the release film, attach the tape to the back of the flexible OLED screen, and apply pressure of 0.5MPa for 30 seconds at room temperature.

[0069] In the above steps, the PE foam layer thickness is 0.5 mm (after foaming). Adhesive components include acrylic polymer, tackifying resin (rosin resin), and solvent (ethyl acetate), with no delayed foaming mechanism for unfoamed materials. Bonding conditions are room temperature pressure application, without heating steps.

[0070] (5) Rework test: The screen after bonding is heated to 100°C and pressure of 0.3MPa is applied. It takes 10 minutes to completely peel off the adhesive layer. The peeling process is difficult and the cleaning of residual adhesive is time-consuming.

[0071] Comparative Example 2

[0072] This comparative example also prepared a waterproof, cushioning, hot-melt foam adhesive for bonding flexible OLED displays, but the only difference from Example 1 was in steps (2) and (4). Specifically:

[0073] Add 0.1 wt% thermally expanded microspheres in step (2).

[0074] In step (4), the PET release film is removed, the adhesive film layer is attached to the back of the flexible OLED screen, and a pressure of 0.5 MPa is applied, but the heating temperature is reduced to 70°C and held for 20 seconds.

[0075] Rework test results: After the screen was heated to 100°C and pressure of 0.3MPa was applied, more than 8 layers of adhesive peeled off, and some residual adhesive remained. The peeling was incomplete because the adhesive was not fully activated.

[0076] The performance of the foam adhesives prepared in Examples 1-2 and Comparative Examples 1-2 was tested, and the data are shown in the table below.

[0077] Table 1. Performance test results of foam adhesive

[0078]

[0079] This invention is based on the design logic of "unfoamed adhesive film layer + synchronous triggering of bonding". It constructs an adhesive skeleton by using thermoplastic elastomer and tackifying resin in the formulation, and introduces low boiling point solvent to adjust the coating performance of the adhesive, so that the unfoamed material (such as thermally expandable microspheres) is stably dispersed in the dried adhesive film. In the final bonding stage, the bonding fluidity of thermoplastic elastomer and the foaming behavior of unfoamed material are activated simultaneously by heating and pressurizing. By utilizing the synergistic effect of solvent evaporation and foaming agent expansion, the in-situ integrated molding of the bonding interface and closed-cell foam structure is achieved.

[0080] Furthermore, compared to traditional PE foam adhesives, this invention significantly improves the bonding strength of foam. Specifically, the delamination force of the foam adhesive prepared in Example 1 is ≥30 N / in, while that of PE foam is only ≥12 N / in; the peel force of the foam adhesive prepared in Example 1 is ≥40 N / in, while that of PE foam is ≥10 N / in.

[0081] Compared to traditional VHB foam, the present invention significantly improves the tensile strength of foam. Specifically, the foam adhesive prepared in Example 1 has a tensile strength ≥3MPa and an elongation of 500%, while the VHB foam has a tensile strength of 1MPa and an elongation of 400%.

[0082] This solution overcomes the limitations of traditional step-by-step foam bonding and foaming processes, endowing the adhesive layer with high bonding strength, cushioning, and waterproof sealing effects. Simultaneously, it leverages the reversible properties of thermoplastic materials to achieve rapid, non-destructive rework. The process utilizes a simultaneous "coating-storage-lamination and foaming" workflow, improving production efficiency. Compared to traditional multi-layered PE and VHB foams, the process is more streamlined, offering superior efficiency, cost, and performance. This provides a new, high-performance, and low-cost solution for the bonding and protection of precision electronic components.

[0083] To facilitate understanding by those skilled in the art of the improvements of this invention over the prior art, some of the accompanying drawings and descriptions have been simplified. The above embodiments are preferred implementations of this invention. In addition, this invention can be implemented in other ways. Any obvious substitutions without departing from the concept of this technical solution are within the protection scope of this invention.

Claims

1. A manufacturing process for a waterproof, cushioning, hot-melt foam adhesive for bonding displays, characterized in that, Includes the following steps: (1) A hot melt adhesive matrix is ​​provided, wherein the hot melt adhesive matrix comprises a thermoplastic elastomer, a tackifying resin and a solvent, wherein the thermoplastic elastomer is at least one of SIS and SBS, the tackifying resin is at least one of petroleum resin and rosin resin, and the solvent is at least one of ethyl acetate, acetone or toluene; (2) Disperse the unfoamed material in the hot melt adhesive matrix to form a mixed adhesive solution, wherein the foaming temperature of the unfoamed material is not lower than the boiling point of the solvent, and the unfoamed material is at least one of thermal expansion microspheres or AC foaming agent; (3) The mixed adhesive solution is applied to the release substrate and dried to form an unfoamed adhesive film layer; (4) In the display screen bonding process, the adhesive film layer after the release substrate is removed and bonding is completed is heated and pressurized, and the bonding activation of the adhesive film layer and the foaming expansion of the unfoamed material are triggered simultaneously to form a foam adhesive layer with a closed-cell structure; the heating temperature is 90-120℃ and the pressurization pressure is 0.4-0.8MPa; The hot melt adhesive matrix also includes a softener and an anti-aging agent, wherein the softener is naphthenic oil or paraffin. The particle size of the unfoamed material is 5-50 μm; the amount of the unfoamed material added is 0.5-10 wt% of the total mass of the hot melt adhesive matrix. The hot melt adhesive matrix also contains a black material for light blocking.

2. The production process of the waterproof cushioning hot-melt foam adhesive for display screen bonding according to claim 1, characterized in that: The coating thickness of the adhesive film layer is 0.1-0.5 mm.

3. A waterproof, cushioning, hot-melt foam adhesive for bonding displays, characterized in that, Prepared by the production process described in claim 1, the product includes a hot melt adhesive layer, wherein unfoamed material is dispersed in the hot melt adhesive layer, wherein the unfoamed material is microspheres or foaming agent particles in the unfoamed state, and wherein the unfoamed material expands under hot and pressure conditions to form a closed-cell structure.

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