Acrylate pressure-sensitive adhesive, support film adhesive tape, preparation method and application

Abstract

The invention belongs to the technical field of supporting films, and particularly relates to an acrylate pressure-sensitive adhesive, a supporting film adhesive tape, a preparation method and application. The acrylate pressure-sensitive adhesive is prepared from the following raw materials in parts by weight: 60 to 90 parts of acrylate soft monomer, 5 to 20 parts of polar functional monomer, 5 to 20 parts of high-Tg hard monomer, 0.1 to 0.5 part of initiator, 0.5 to 3 parts of polyfunctional thermocuring cross-linking agent and a proper amount of solvent. According to the acrylate pressure-sensitive adhesive disclosed by the invention, the acrylate pressure-sensitive adhesive which has the characteristics of low modulus and high cohesion microcosmically is prepared under a solution polymerization and thermocuring process through a specific'soft monomer-hard monomer-crosslinking agent 'formula system design. The pressure-sensitive adhesive macroscopically realizes the performance balance, which is difficult to realize at the same time, among adhesion, buffering and impact resistance.

Description

Technical Field

[0001] This invention belongs to the field of support film technology, specifically relating to an acrylic pressure-sensitive adhesive, a support film tape, its preparation method, and its application. Background Technology

[0002] OLED displays, with their advantages of flexibility, ultra-thinness, and wide color gamut, are widely used in smartphones, wearable devices, and flexible display terminals. Flexible OLED screens use PI (polyimide) as a substrate, replacing the glass substrate in rigid OLEDs. Compared to glass OLED displays, they are thinner and lighter, offering greater durability that is not easily broken and can be bent.

[0003] During the production, transportation, and assembly of OLED modules, the screen is extremely susceptible to external impacts, scratches, and bending stress, which can damage the delicate light-emitting layer and electrode circuits inside the device, resulting in bright spots, dark spots, or even complete failure.

[0004] The support film (also known as the protective film or buffer film) is a key material attached to the back of an OLED screen, providing protection and support. Its core functional layer is pressure-sensitive adhesive (PSA). While commonly used acrylic pressure-sensitive adhesives have advantages such as good initial tack and excellent weather resistance, they still have the following shortcomings when applied to OLED screens: Insufficient cushioning performance: Conventional adhesives for support films generally reduce their fluidity and minimize air bubbles during the high-temperature bonding process by increasing the high-temperature modulus of the adhesive. However, increasing the modulus leads to a harder adhesive, resulting in poorer filling of step differences. This is especially problematic when the display is pressed or subjected to significant impacts, easily causing noticeable back pressure indentations and affecting the screen's visual performance. Specifically: Traditional pressure-sensitive adhesives use single soft monomers or highly cross-linked formulations, resulting in low energy absorption efficiency from falling ball impacts. After an impact, interface debonding or cohesive tearing easily occurs, failing to effectively protect the screen. Excessively high modulus at 25°C (>300kPa) reduces cushioning performance; reducing the modulus to achieve cushioning results in insufficient adhesion (<5N / 25mm) or poor creep resistance.

[0005] Balancing adhesion and cohesion is challenging: To ensure no adhesive residue after processing, the support film needs to possess moderate adhesion. However, reducing adhesion often leads to a decrease in cohesion, making it easier to produce adhesive residue or damage to the adhesive layer during peeling. How to impart excellent impact resistance and cushioning properties to the adhesive layer while ensuring easy peeling is a key technical challenge.

[0006] Poor overall performance: Existing pressure-sensitive adhesives are unable to simultaneously achieve excellent adhesion, high cushioning performance, and high impact resistance.

[0007] Therefore, developing a novel acrylic pressure-sensitive adhesive that combines moderate adhesion, extremely high drop ball impact performance, and low modulus is of great significance for improving the yield and reliability of OLED displays. Summary of the Invention

[0008] The purpose of this invention is to provide an acrylic pressure-sensitive adhesive, a support film tape, its preparation method, and its application.

[0009] The first aspect of this application provides an acrylic pressure-sensitive adhesive, comprising the following raw materials by weight: 60-90 parts of acrylate soft monomer 5-20 parts of polar functional monomers 5-20 parts of high Tg hard monomer Initiator 0.1-0.5 parts 0.5-3 parts of multifunctional thermosetting crosslinking agent 5-20 parts of tackifying resin Use an appropriate amount of solvent.

[0010] In one embodiment of this application, the acrylate soft monomer includes one or more of butyl acrylate (BA), 2-ethylhexyl acrylate (2-EHA), and isooctyl acrylate (IOA). This component can provide the adhesive segments of the pressure-sensitive adhesive and a lower glass transition temperature (Tg).

[0011] In one embodiment of this application, the polar functional monomer includes one or more of acrylic acid (AA), methacrylic acid (MAA), hydroxyethyl acrylate (HEA), and hydroxypropyl acrylate (HPA). This component can provide cohesive forces and crosslinking reaction sites.

[0012] The high Tg hard monomer includes one or more of methyl methacrylate (MMA), styrene (St), acrylonitrile (AN), and vinyl acetate (VAc). This component can be used to adjust the modulus and cohesive strength of the pressure-sensitive adhesive.

[0013] In one embodiment of this application, the initiator is a thermally decomposable initiator. Preferably, the initiator can be azobisisobutyronitrile (AIBN).

[0014] In one embodiment of this application, the multifunctional thermosetting crosslinking agent includes isocyanate crosslinking agents (such as Desmodur L75) and epoxy crosslinking agents. The crosslinking agent can react with the functional groups of the functional monomers during the thermosetting stage to form a three-dimensional network structure.

[0015] In one embodiment of this application, the tackifying resin includes one or more of the following: terpene phenol resin, terpene resin, α-pinene-phenolic resin, terpene diene-phenolic resin, C5 or C9 petroleum resin, hydrogenated rosin ester, and polymerized rosin ester. Preferably, it can be a terpene phenol resin.

[0016] In one embodiment of this application, the solvent includes one or more of ethyl acetate, toluene, and acetone. The solvent weight fraction can be 1-2 times the total weight of the monomers.

[0017] A second aspect of this application provides a method for preparing the acrylic pressure-sensitive adhesive as described above, comprising: Under nitrogen protection, a portion of the solvent, all the acrylate soft monomers, all the polar functional monomers, a portion of the high Tg hard monomers and a portion of the initiator are added to the reactor, and the temperature is raised to 75-85℃ for prepolymerization. Subsequently, the remaining monomer, initiator and solvent mixture is slowly added dropwise over 2-4 hours, and the reaction is kept at the temperature for 4-6 hours to obtain an acrylate polymer solution with a solid content of 30%-50%. To the acrylate polymer obtained above, a tackifying resin and a multifunctional thermosetting crosslinking agent are added to prepare an acrylate pressure-sensitive adhesive.

[0018] A third aspect of this application provides a method for preparing a support film tape, comprising: The acrylic pressure-sensitive adhesive described above is uniformly coated onto a PET substrate that has undergone antistatic coating treatment using a coating machine. The solvent is removed by thoroughly drying in a heated oven. Then, a double-sided antistatic coated silicone release film is laminated to obtain a semi-finished tape. The finished support film tape is obtained after curing.

[0019] In some embodiments, the thickness of the PET substrate can be 75 μm; the thickness of the adhesive layer after being thoroughly dried in a heated oven to remove solvent can be 13 μm; and the thickness of the double-sided antistatic coated silicone release film can be 50 μm.

[0020] In some embodiments, the curing temperature may be 40°C and the curing time may be three days.

[0021] The fourth aspect of this application is a support film tape prepared using the preparation method described above.

[0022] The fifth aspect of this application is the application of the support film tape described above on an OLED screen.

[0023] The beneficial effects of this invention are: Unlike existing technologies, the acrylate pressure-sensitive adhesive of this application comprises the following raw materials by weight: 60-90 parts of acrylate soft monomer, 5-20 parts of polar functional monomer, 5-20 parts of high Tg hard monomer, 0.1-0.5 parts of initiator, 0.5-3 parts of multifunctional thermosetting crosslinking agent, and an appropriate amount of solvent. The acrylate pressure-sensitive adhesive of this invention, through a specific "soft monomer-hard monomer-crosslinking agent" formulation system design, prepares an acrylate pressure-sensitive adhesive with "low modulus and high cohesion" characteristics at the microscopic level under solution polymerization and thermosetting processes. This pressure-sensitive adhesive achieves a macroscopic balance between the difficult-to-achieve properties of "adhesion, cushioning, and impact resistance."

[0024] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention are realized and obtained through the structures particularly pointed out in the description. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1 Preparation of pressure-sensitive adhesive: In a four-necked flask equipped with a stirrer, condenser, thermometer, and nitrogen inlet tube, add 100 parts ethyl acetate, 50 parts butyl acrylate (BA), 10 parts isooctyl acrylate (2-EHA), 5 parts acrylic acid (AA), 10 parts methyl methacrylate (MMA), and 0.1 parts AIBN. Purge with nitrogen gas and heat to 80°C for 1 hour; A mixture consisting of 20 parts ethyl acetate, 0.2 parts AIBN, and 5 parts MMA was slowly added dropwise over 2 hours. After the addition was complete, the reaction was continued at 80°C for 4 hours to obtain a pale yellow viscous polymer solution. Cool to room temperature, add 8 parts of terpene phenol resin and 1.5 parts of isocyanate crosslinking agent (Desmodur L75), and stir at low speed for 30 minutes.

[0027] The obtained adhesive is evenly coated on a 75μm antistatic coated PET substrate using a coating machine. After being thoroughly dried in a heated oven to remove the solvent, the adhesive layer thickness is 13μm. Then, a 50μm double-sided antistatic coated silicone release film is laminated to obtain a semi-finished tape. After curing at 40℃ for three days, the support film tape product is obtained.

[0028] Example 2 Adjust the monomer ratio: BA 40 parts, 2-EHA 30 parts, AA 8 parts, MMA 12 parts, styrene 5 parts. The amount of crosslinking agent is 2.0 parts. The rest is the same as in Example 1.

[0029] Comparative Example 1 (High Modulus Comparison) The following high proportion of hard monomers were used: BA 30 parts, 2-EHA 20 parts, AA 5 parts, MMA 30 parts, and styrene 15 parts. The amount of crosslinking agent was 2.5 parts. The rest was the same as in Example 1.

[0030] Comparative Example 2 (without hard monomers) No hard monomers used: BA 50 parts, 2-EHA 40 parts, AA 10 parts. Crosslinking agent dosage is 1.0 part. The rest is the same as in Example 1.

[0031] The support film and the adhesive film of the same thickness prepared from the pressure-sensitive adhesive were subjected to the following tests: Adhesion (180° Peel Strength): According to ASTM D3330, the adhesion to stainless steel sheet is tested at a rate of 300 mm / min.

[0032] Holding Power: 1kg weight, used to test the adhesion time to a stainless steel plate.

[0033] Impact resistance (buffering performance) evaluation: using a falling ball impact tester.

[0034] The prepared support film was attached to a standard OLED analog glass substrate (size: 50mm × 50mm × 0.7mm).

[0035] The substrate with the support film is rigidly fixed, ensuring that the area below the impact point is suspended in the air. Using a steel ball with a mass of 32.0 g ± 0.1 g, the steel ball is dropped freely from the initial height to impact the center point of the substrate.

[0036] After each impact, the presence of visible microcracks in the substrate is determined by monitoring with an acoustic emission sensor and / or examination with an optical microscope. The drop height H is gradually increased in increments (e.g., 5 cm) until the substrate fails (microcracks appear). The critical drop height H that causes substrate failure is recorded, and the critical impact energy E that causes substrate failure is calculated. This energy is absorbed by the support film-adhesive layer system.

[0037] Storage modulus (G'): Tested using dynamic mechanical analysis (DMA) at 25°C to 200°C and 1Hz frequency.

[0038] The test results are shown in the table below: Example 1 exhibited the highest E_critical value (203.8 mJ), significantly higher than Comparative Example 1 (78.4 mJ) and Comparative Example 2 (141.1 mJ). This directly demonstrates from an energy absorption perspective that the pressure-sensitive adhesive formulation of this invention can withstand and dissipate greater impact energy, providing superior protection for OLED screens.

[0039] Comparative Example 1 suffered damage to the substrate under very low impact energy (78.4 mJ) due to excessively high modulus, overly hard adhesive layer, and poor buffering capacity.

[0040] Although Comparative Example 2 has a low modulus, it lacks physical crosslinking points and cohesive forces provided by hard monomers, resulting in insufficient cohesive strength. The adhesive layer is easily "broken down" during ball impact, and its holding power is very poor. When subjected to high-energy impact (141.1 mJ), the adhesive layer undergoes cohesive failure, and its protective function is compromised. The buffering effect is still not as good as that of the present invention.

[0041] Compared to Comparative Example 1, the embodiments of the present invention significantly reduce the modulus of the pressure-sensitive adhesive by reducing the content of hard monomers, making it softer and thus greatly improving its resistance to falling ball impact. At the same time, the adhesion and holding power are relatively balanced.

[0042] Compared with Comparative Example 2, the present invention achieves a balance between cushioning and durability by introducing an appropriate amount of hard monomers, while maintaining a low modulus and ensuring sufficient cohesion.

[0043] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. An acrylic pressure-sensitive adhesive, characterized in that, The following ingredients are included by weight: 60-90 parts of acrylate soft monomer 5-20 parts of polar functional monomers 5-20 parts of high Tg hard monomer Initiator 0.1-0.5 parts 0.5-3 parts of multifunctional thermosetting crosslinking agent 5-20 parts of tackifying resin Use an appropriate amount of solvent.

2. The acrylic pressure-sensitive adhesive according to claim 1, characterized in that, The acrylate soft monomers include one or more of butyl acrylate, 2-ethylhexyl acrylate, and isooctyl acrylate; The polar functional monomers include one or more of acrylic acid, methacrylic acid, hydroxyethyl acrylate, and hydroxypropyl acrylate; The high Tg hard monomer includes one or more of methyl methacrylate, styrene, acrylonitrile, and vinyl acetate.

3. The acrylic pressure-sensitive adhesive according to claim 1, characterized in that, The initiator is a thermally decomposable initiator; The multifunctional thermosetting crosslinking agents include isocyanate crosslinking agents and epoxy crosslinking agents.

4. The acrylic pressure-sensitive adhesive according to claim 1, characterized in that, The tackifying resin includes one or more of the following: terpene resin, terpene phenol resin, C5 or C9 petroleum resin, hydrogenated rosin ester, and polymerized rosin ester.

5. The acrylic pressure-sensitive adhesive according to claim 1, characterized in that, The solvent includes one or more of ethyl acetate, toluene, and acetone.

6. The acrylic pressure-sensitive adhesive according to claim 1, characterized in that, The solvent is in parts by weight 1-2 times the total weight of the monomers.

7. A method for preparing an acrylic pressure-sensitive adhesive as described in any one of claims 1-6, characterized in that, include: Under nitrogen protection, a portion of the solvent, all the acrylate soft monomers, all the polar functional monomers, a portion of the high Tg hard monomers and a portion of the initiator are added to the reactor, and the temperature is raised to 75-85℃ for prepolymerization. Subsequently, the remaining monomer, initiator and solvent mixture is slowly added dropwise over 2-4 hours, and the reaction is kept at the temperature for 4-6 hours to obtain an acrylate polymer solution with a solid content of 30%-50%. To the acrylate polymer obtained above, a tackifying resin and a multifunctional thermosetting crosslinking agent are added to prepare an acrylate pressure-sensitive adhesive.

8. A method for preparing a support film adhesive tape, characterized in that, include: The acrylic pressure-sensitive adhesive as described in any one of claims 1-6 is uniformly coated onto a PET substrate that has undergone antistatic coating treatment using a coating machine. The solvent is removed by thoroughly drying in a heated oven. Then, a double-sided antistatic coated silicone release film is laminated to obtain a semi-finished tape. The finished support film tape is obtained after curing.

9. A support film tape prepared by the preparation method described in claim 8.

10. An application of the support film tape as described in claim 9 on an OLED screen.

Images