Yellowing-resistant OCA adhesive film preparation process, adhesive film and screen

Abstract

The invention relates to the field of preparation methods of adhesives, and particularly discloses a preparation process of an anti-yellowing OCA adhesive film, the adhesive film and a screen. The process comprises the following steps: S1, uniformly mixing the main body and the tackifier, and dehydrating and degassing to obtain a first mixture; s2, under a protective atmosphere, adding a light stabilizer and an antioxidant, uniformly mixing to obtain a second mixture, and dividing the second mixture into two parts; s3, sequentially adding a catalyst and a photoinitiator into one part of the second mixture to obtain a third mixture; sequentially adding a catalyst and a multifunctional master batch into the other part of the second mixture to obtain a fourth mixture; s4, extruding the third mixture from a middle channel of a co-extrusion die head, and synchronously extruding the fourth mixture from a top channel and a bottom channel of the co-extrusion die head to obtain a primary sheet; and S5, carrying out light curing on the primary sheet, and then cooling and rolling to obtain the adhesive film. According to the invention, the performance of the raw materials is fully utilized, so that the performance of the adhesive film is integrally improved.

Description

Technical Field

[0001] This invention relates to the field of adhesive preparation methods, and more specifically to a method for preparing a screen adhesive film and the adhesive film thereof, and a screen using the adhesive film. Background Technology

[0002] With the development and use of various electronic products, the display screen, as the core window for human-computer interaction, has also been continuously evolving. In conventional screens, a complex module is typically constructed by precisely stacking multiple layers of optical components, including a cover glass, polarizer, touch sensor, and display panel. Optically transparent adhesives play an indispensable role in bonding these layers together.

[0003] OCA adhesive is a common bonding agent used to bond various functional layers within a screen. It not only provides durable adhesive strength to withstand the mechanical and environmental stresses generated during long-term screen use, but also possesses the optical properties required by the screen, such as high light transmittance and low haze. However, current conventional OCA adhesives still have many drawbacks, such as yellowing and aging of the OCA adhesive layer after long-term use.

[0004] In existing technologies, improvements typically focus on modifying the composition of OCA adhesive to better suit screen bonding. For example, patent application CN114806418B discloses a composition for an OCA optical adhesive. This composition results in OCA adhesive with fast curing speed, energy efficiency, and low pollution. Furthermore, this OCA adhesive possesses advantages such as high and stable film peel strength, high light transmittance, low haze, refractive index close to glass, no corrosion to touchscreens, no residue under constant temperature and humidity, no overflow, and excellent resistance to yellowing. Therefore, it is well-suited for the needs of touchscreen bonding processes.

[0005] However, in actual production scenarios, for some manufacturers who have been engaged in the production of OCA adhesive for a long time, their production lines and processes are relatively fixed. Directly improving and adjusting the original components of OCA adhesive can easily lead to large-scale adjustments to the entire production line and process, resulting in a significant increase in improvement costs. Therefore, there is an urgent need for an improvement method that can improve the performance of OCA adhesive at a relatively lower modification cost, making it more suitable for use in the electronic screen field. Summary of the Invention

[0006] One of the objectives of this invention is to provide a yellowing-resistant OCA film preparation process based on improved processing procedures, which can improve the performance of OCA film by adjusting processing steps, etc.

[0007] The second objective of this invention is to provide an OCA film with good resistance to yellowing, obtained by the above-mentioned OCA film preparation process.

[0008] The third objective of this invention is to provide a screen with better resistance to yellowing obtained by processing with the above-mentioned OCA film.

[0009] This invention is achieved through the following technical solution:

[0010] In a first aspect, the present invention provides a process for preparing a yellowing-resistant OCA film, comprising the following steps: S1. Mixing and stirring a polyurethane elastomer and a tackifier uniformly under vacuum and then dehydrating and degassing; S2. Adding a light stabilizer and an antioxidant to the dehydrated first mixture under a protective atmosphere and stirring and mixing uniformly to obtain a second mixture, and then dividing the second mixture into two portions. For example, the protective atmosphere can be a nitrogen atmosphere, an inert gas atmosphere, etc.; S3. Placing one portion of the second mixture into the first mixing section of a screw extruder, and during screw stirring, sequentially adding a catalyst and a photoinitiator to the second mixture. A third mixture is obtained; another portion of the second mixture is placed in the second mixing section of the screw extruder, and during the screw stirring process, a catalyst and a multifunctional masterbatch are added to the second mixture in sequence to obtain a fourth mixture; S4. The third mixture and the fourth mixture are combined and output through the same co-extrusion die. The third mixture is extruded through the middle channel, and the fourth mixture is extruded simultaneously through the top channel and the bottom channel to obtain a primary sheet; S5. The primary sheet is photocured, then cooled and wound to obtain a yellowing-resistant OCA film; wherein, the multifunctional masterbatch contains at least a carrier resin, an ultraviolet absorber, a light stabilizer, and a photoinitiator.

[0011] In this invention, the main purpose of improving the OCA optical adhesive is to enhance its resistance to yellowing. The improvement is mainly based on the improvement of the processing flow, rather than the change of the OCA adhesive composition.

[0012] The main improvement of this invention is that after the second mixture is prepared, it is divided into two parts and then fed into different screw extruders for processing. During the process, different additives are added to process the second mixture into a fourth mixture rich in protective components and a third mixture with a relatively low content of protective components. Finally, during the extrusion, a co-extrusion die is used to process the OCA film with a three-layer structure.

[0013] The OCA film prepared using the above approach forms a non-uniform protective material distribution structure, allowing each layer of the OCA film to perform different functions. Specifically, when the film is used in a screen, its top and bottom layers are usually more exposed to ultraviolet light. However, in this invention, the top and bottom structures of the OCA film use a fourth mixture rich in anti-UV components, which allows for the formation of a relatively dense and complete protective and reactive layer. This more effectively eliminates the impact of UV exposure on the overall adhesive layer, resulting in better UV resistance and improved overall yellowing resistance of the OCA film. Conversely, the middle structure of the film is mainly composed of a third mixture, which contains few protective components but maintains good adhesive properties, ensuring that the OCA film still possesses the basic adhesive capabilities required for its overall performance. Overall, this invention, through adjustments and improvements to the preparation process, achieves a non-uniform distribution of limited raw materials. This allows materials with different functions to accumulate in different locations within the film, fully utilizing their respective roles and avoiding waste of some material properties. This improves the overall performance of the OCA film without large-scale adjustments to the raw materials. Furthermore, under this improved method, the differences in the properties of the raw materials used in each layer are not too significant, thus preventing delamination of the OCA film and ensuring that the improved OCA film retains its basic OCA film properties.

[0014] As a further improvement of the present invention, in S1, dehydration and degassing are continuously carried out at 110~120℃ and 30~50rpm for 2~3h.

[0015] As a further improvement of the present invention, in S1, the dehydrated mixture is cooled to 65~75°C. Under these processing conditions, the mixing process can be ensured smoothly, and the reaction and denaturation of raw materials such as polyurethane elastomers during stirring can be limited.

[0016] As a further improvement of the present invention, in S2, the mixture is stirred at 60-80 rpm for 60-100 min.

[0017] As a further improvement of the present invention, in S3, the screw stirring duration in the first mixing section and the second mixing section is 1 to 3 minutes.

[0018] As a further improvement of the present invention, in S4, the extrusion temperature of the co-extrusion die is 80~110°C.

[0019] As a further improvement of the present invention, in S5, during the photocuring step, the UV wavelength is either 365nm or 385nm; the energy density is 150~400mJ / cm². 2Under these processing conditions, the trace amounts of photoinitiator enriched on the surface are activated by the use of mild UV radiation, initiating slight cross-linking in the top and bottom structures of the film. This ensures that the UV-resistant components are effectively "anchored" in the corresponding areas, thereby further fixing and strengthening the uneven distribution structure of protective substances and other components in the OCA film. At the same time, it ensures that the middle structure does not cure due to insufficient light and low photoinitiator concentration, thus maintaining excellent initial tack and adhesion.

[0020] As a further improvement of the present invention, step S5 also includes the following step: after cooling, curing at 25~30°C for 36~72 hours before winding. In the present invention, the curing of the film is completed under relatively mild conditions, which ensures that the adhesive strength, cohesive strength and modulus of the film reach a state of balance for use, and also avoids adverse effects such as delamination of the OCA film caused by aggressive curing conditions.

[0021] Secondly, the present invention provides a yellowing-resistant OCA film, which is prepared by any of the above-mentioned yellowing-resistant OCA film preparation processes.

[0022] Thirdly, the present invention provides a screen in which any of the above-mentioned yellowing-resistant OCA adhesive films is used for bonding between components.

[0023] The beneficial effects of this invention include:

[0024] (1) In this invention, the improved OCA film preparation process enables the UV-resistant components in the film to be mainly distributed on the surface of the film, thereby achieving enrichment of the components on the surface structure of the film without changing the total amount of raw materials; at the same time, the middle part of the film still retains the basic film components and a small amount of UV-resistant components and other protective components, thus ensuring that the middle structure retains basic protective performance and adhesion to the surface structure; overall, the film has basic adhesion and does not delamination, while optimizing the distribution of different functional components in the film, so that different functional components can fully play their role, thereby achieving full utilization of the raw material performance without changing the total amount of raw materials, and thus improving the overall performance of the OCA film.

[0025] (2) In the overall preparation process, the improvement of equipment mainly relies on multi-layer co-extrusion equipment, while the use of raw materials is only adjusted in terms of the timing of material addition without adjusting its composition. Therefore, when the preparation process in this invention is actually put into use in the factory, there is no need to make large-scale changes to the overall OCA production line, which greatly reduces the cost of production improvement and is conducive to the promotion and use of this method.

[0026] (3) In the improved idea of ​​the present invention, advanced OCA film preparation processes such as masterbatch technology are fully utilized, which avoids the risks brought about by solvents in some traditional OCA glue preparation processes. Moreover, the improved process can directly produce OCA films that are easier to store, transport and use, making the preparation process more in line with novel preparation processes and more advanced. Detailed Implementation

[0027] The invention will now be described in further detail with reference to specific implementation examples.

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail with reference to the embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0029] Example 1:

[0030] This embodiment provides an OCA adhesive, which is prepared using the following process:

[0031] S1. The polyurethane elastomer and the tackifier are stirred at a low temperature of 45 rpm for 3 hours under conditions of -0.095 MPa and 115°C to achieve mixing between materials and dehydration and degassing to obtain a first mixture. The first mixture is then cooled to 70°C before being put into subsequent processing. For example, the tackifier used in this embodiment is hydrogenated petroleum resin.

[0032] S2. Under a nitrogen atmosphere, maintain 70°C, and add a light stabilizer and an antioxidant to the first dehydrated mixture. Mix the mixture at 75 rpm for 30 minutes to obtain a second mixture, and then divide the second mixture into two portions. For example, in this embodiment, the light stabilizer used is Tinuvin 770, and the antioxidant is Irganox 1010.

[0033] S3. Exemplarily, the screw extruder in this embodiment is a conventional commercially available co-extrusion kit, which includes two mixing sections. Both the first and second mixing sections contain twin screws rotating in the same direction. The two mixing sections can respectively perform the mixing processing of the two types of mixtures. Then, the two materials are combined through guide channels in the screw extruder and finally output through the same co-extrusion die. In this embodiment, a portion of the second mixture is placed in the first mixing section, and during screw stirring, a catalyst and a photoinitiator are added sequentially to the second mixture to obtain a third mixture. Exemplarily, the catalyst is Momentive T-12, and the photoinitiator is Irgacure 819. Simultaneously, another portion of the second mixture is placed in the second mixing section, and during screw stirring, a catalyst and a multifunctional masterbatch are added sequentially to the second mixture to obtain a fourth mixture. Exemplarily, the catalyst used in the second mixture is still Momentive T-12. T-12, the multifunctional masterbatch, is composed of a carrier resin carrying an ultraviolet absorber, a light stabilizer, and a photoinitiator. The carrier resin used can be any resin that is compatible with polyurethane elastomer. For example, in this embodiment, it is a polyurethane elastomer. In addition, the ultraviolet absorber is Tinuvin 329, the light stabilizer is still Tinuvin 770, and the photoinitiator is still Irgacure 819.

[0034] During this period, the duration of screw stirring of the mixture in the first and second mixing sections is controlled to be around 2 minutes, so as to avoid the viscosity of the third and fourth mixtures being too high or too low, which would be not conducive to extrusion or make it difficult to meet the requirements for the use of OCA adhesive.

[0035] S4. The third mixture and the fourth mixture are gathered into the same co-extrusion die through the guide channel in the screw extruder and extruded at 100°C. The die mainly includes three extrusion channels stacked vertically. The middle channel is connected to the first mixing section, so the third mixture is extruded through the middle channel. The top channel and the bottom channel are connected to the second mixing section, so the fourth mixture can be extruded simultaneously through the top channel and the bottom channel. This results in the extrusion of a primary sheet with a three-layer structure, with the top and bottom layers composed of the fourth mixture and the middle layer composed of the third mixture.

[0036] S5. Select UV light with a wavelength of 365nm and control the energy density to 200mJ / cm². 2 The primary sheet is photocured, and then cooled and transferred to a curing processing area. In this area, the sheet is cured at 28°C for 48 hours, and finally wound up to obtain a yellowing-resistant OCA film.

[0037] Example 2:

[0038] This embodiment provides an OCA adhesive film, which differs from the one in Example 1 in that, in the film preparation process, during the photocuring step S5, the UV wavelength is 385nm and the energy density is 370mJ / cm². 2 .

[0039] Example 3:

[0040] This embodiment provides an OCA adhesive film, which differs from the one in Embodiment 1 in that, in the preparation process of the adhesive film, in S5, no curing process is carried out, and the film is directly collected after cooling.

[0041] Comparative Example 1:

[0042] This comparative example provides an OCA film, which differs from the film in Example 1 in that, under the premise of using the same raw materials, it is prepared using a traditional OCA film preparation process, which ensures that all components are mixed evenly in the OCA film.

[0043] Performance testing:

[0044] In this embodiment, the refractive index, yellowing resistance, transmittance, haze, peel strength, and adhesion under constant temperature and humidity of the adhesive films in Examples 1-3 and Comparative Example 1 were tested. The refractive index was tested according to the method in GB / T40293-2021; the yellowing resistance test was conducted according to the method in ASTM D2244, requiring the testing of two sets of yellowing values ​​before and after aging of the adhesive layer. During this aging process, the samples were placed in a BGD 856 standard fluorescent ultraviolet aging chamber (refer to GB / T 14522-2008) for 600 hours before performance testing; transmittance and haze were directly measured using appropriate measuring instruments; the peel strength test mainly involved 180° peel strength testing, and in this embodiment, the peel speed was 30 mm / min; the adhesion under constant temperature and humidity was tested according to the method in GB / T 10586-2025, with a testing duration of 3 days. For experimental methods that do not specify conditions, the determination is usually carried out according to national standards. If there is no corresponding national standard, then the generally accepted international standards, standard conditions, or conditions recommended by the manufacturer shall be followed.

[0045] The test results for each performance aspect are shown in Table 1.

[0046] Table 1 Summary of OCA film performance test results project Refractive index (R) Light transmittance (%) Haze (%) 180° peel strength (N / 25mm) Constant temperature and humidity 60℃ / 90%RH Yellowing value (initial stage) Yellowing value (after aging) Example 1 1.477 94.0 0.24 30.6 No glue overflow, no bubbling 0.51 0.68 Example 2 1.482 94.2 0.25 29.4 No glue overflow, no bubbling 0.52 0.72 Example 3 1.488 93.8 0.25 31.1 No glue overflow, no bubbling 0.49 0.71 Comparative Example 1 1.465 95.5 0.19 30.5 No glue overflow, no bubbling 0.69 0.78 .

[0047] The test results above show that, after improving the preparation process, the OCA film in the examples still retains similar adhesion and adhesion retention capabilities to the film in Comparative Example 1. Furthermore, as an optical adhesive for screens, the refractive index, transmittance, and haze of the film in the examples all meet the corresponding usage requirements and are similar in performance to the film in the comparative example. Moreover, the initial yellowing values ​​of the OCA films in the examples are relatively lower than those in the comparative example, and even after aging treatment, the change in yellowing values ​​is still relatively small, indicating that they still possess good yellowing resistance even after prolonged use. Therefore, the preparation process in this example can produce OCA films for screens that meet basic screen adhesion requirements while also exhibiting improved yellowing resistance.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A process for preparing a yellowing-resistant OCA adhesive film, characterized in that, It includes the following steps: S1. Mix the polyurethane elastomer and tackifier evenly under vacuum and then dehydrate and degas them; S2. Under a protective atmosphere, add light stabilizer and antioxidant to the dehydrated first mixture and stir to mix evenly to obtain a second mixture, and then divide the second mixture into two portions; S3. Place one portion of the second mixture into the first mixing section of the screw extruder, and during the screw stirring process, add a catalyst and a photoinitiator to the second mixture in sequence to obtain a third mixture; place another portion of the second mixture into the second mixing section of the screw extruder, and during the screw stirring process, add a catalyst and a multifunctional masterbatch to the second mixture in sequence to obtain a fourth mixture; S4. The third mixture and the fourth mixture are combined and output through the same co-extrusion die. The third mixture is extruded through the middle channel, and the fourth mixture is extruded simultaneously through the top channel and the bottom channel to obtain a primary sheet. S5. The primary sheet is photocured, then cooled and wound up to obtain a yellowing-resistant OCA film; The multifunctional masterbatch contains at least a carrier resin, an ultraviolet absorber, a light stabilizer, and a photoinitiator.

2. The process for preparing a yellowing-resistant OCA film according to claim 1, characterized in that, In S1, dehydration and degassing are carried out continuously at 110~120℃ and 30~50rpm for 2~3h.

3. The process for preparing a yellowing-resistant OCA film according to claim 1, characterized in that, In S1, the dehydrated mixture is cooled to 65~75℃.

4. The process for preparing a yellowing-resistant OCA film according to claim 1, characterized in that, In S2, stir and mix at 60-80 rpm for 60-100 min.

5. The process for preparing a yellowing-resistant OCA film according to claim 1, characterized in that, In S3, the screw stirring duration in the first mixing section and the second mixing section is 1 to 3 minutes.

6. The process for preparing a yellowing-resistant OCA film according to claim 1, characterized in that, In S4, the extrusion temperature of the co-extrusion die is 80~110℃.

7. The preparation process of a yellowing-resistant OCA film according to claim 1, characterized in that, In S5, during the photocuring step, the UV wavelength is either 365nm or 385nm; the energy density is 150~400mJ / cm². 2 .

8. The process for preparing a yellowing-resistant OCA film according to claim 1, characterized in that, S5 also includes the following steps: After cooling, cure at 25~30℃ for 36~72 hours before winding.

9. A yellowing-resistant OCA adhesive film, characterized in that, It is prepared using the yellowing-resistant OCA film preparation process described in any one of claims 1 to 8.

10. A screen, characterized in that, The yellowing-resistant OCA adhesive film described in claim 9 is used for bonding between components.