Yellowing-resistant release film and preparation method thereof

Abstract

The invention belongs to the technical field of release film production and processing, and particularly discloses an anti-yellowing release film and a preparation method thereof, and the preparation method comprises the following steps: (1) coating a buffer layer on a base film to form a film A; and (2) coating the film A with silicon resin to form the yellowing-resistant release film. Wherein the silicon resin has a methyl structure, the silicon resin with the methyl structure has a release effect, and the silicon resin coating with a certain thickness has relatively high strength, so that small molecules or impurities in an epoxy resin mixture can be effectively prevented from entering and adhering to the silicon resin coating; the tough buffer coating acts as a buffer layer to prevent the silicon coating from cracking as the time of use extends. The anti-yellowing release film obtained by the method can effectively improve the yellowing phenomenon of a film coating after thermal injection molding or hot pressing on the premise of not changing the performance of the film coating, so that the requirement of a client for repeated use is met.

Description

Technical Field

[0001] The invention belongs to the technical field of release film production and processing, and in particular is a yellowing-resistant release film and a preparation method thereof. Background Art

[0002] In the electronics industry, epoxy resin is used as a binder for the core material of PCB / FPC, the plastic encapsulation material and epoxy film in the semiconductor industry. Epoxy resin has good temperature resistance and weather resistance, and is then cured by hot injection molding or hot pressing. In the process of hot injection molding or hot pressing of epoxy resin to form a film, a release film is required to play an isolation role to prevent it from adhering to the metal surface of the equipment and achieve the purpose of continuous production. However, after the epoxy resin is hot-injected or hot-pressed and cured, the release film will have a serious yellowing problem and cause contamination of the metal surface of the equipment. The metal contact surface needs to be cleaned regularly, and the film cannot be reused.

[0003] Usually under heating conditions, the main reason for the yellowing of release films is that the film coating itself turns yellow or ages due to the increase in temperature. In this case, antioxidants and other additives can be added to the coating to slow down the occurrence of yellowing. However, when the main reason is that small molecules or impurities in the epoxy resin and other substances overflow to the surface of the film coating under pressure during hot injection molding or hot pressing curing, causing yellowing, adding antioxidants cannot inhibit the yellowing.

[0004] For example, the technical achievement of Zhejiang Kaiyang New Materials Co., Ltd., "Anti-ultraviolet TPU film, Cheng Lei, Li Feng, Chen Minghui, Zhao Haibin, Shao Wei, CNKI Scientific and Technological Achievement Database, 2019", introduces a self-made TPU film product that inhibits yellowing through three methods, namely: (1) anti-ultraviolet and yellowing formula design; (2) selecting composite antioxidants, ultraviolet absorbers, and high molecular weight light stabilizers to form a ternary system to give full play to the synergistic effect between the stabilizers; (3) using optimized special equipment to prepare yellowing-resistant TPU film. It can be seen that the method mainly involves adding various additives, including anti-ultraviolet agents, antioxidants, etc. The film prepared by this method can prevent most of the yellowing phenomena that occur during transportation, storage and use. However, in some usage scenarios, the yellowing of the film cannot be solved when it is caused by a mixture of external factors and the film's own factors. Taking silicone release film as an example, during the hot injection molding or hot pressing process of epoxy resin mixture, silicone release film plays the role of isolating and protecting the mold. However, due to the different types of epoxy resin mixtures, a comparison before and after injection molding found that the release film had yellowing after injection molding. Adding antioxidants, anti-yellowing agents and anti-ultraviolet agents to the release film could not improve the yellowing phenomenon of the release film. This is because under high temperature and high pressure, during the hot injection molding / hot pressing process, small molecules or impurities in the epoxy resin mixture precipitate due to pressure, adhere to the surface of the release film, or even enter the surface layer of the release film, and then yellowing occurs at high temperature, affecting the appearance and failing to meet the client's needs for repeated use (such as Figure 1 as shown).

[0005] Therefore, it is necessary to develop a yellowing-resistant release film that can effectively improve the yellowing phenomenon of the film coating after hot injection molding or hot pressing without changing the performance of the film coating to meet the needs of clients for repeated use. Summary of the invention

[0006] In order to solve the problems raised in the above background technology, the present invention provides a yellowing-resistant release film and a preparation method thereof.

[0007] To achieve the above object, the present invention provides the following technical solution, a method for preparing a yellowing-resistant release film, comprising the following steps: (1) Coating a buffer layer on the base film to form a thin film A; (2) coating silicone resin on film A to form a yellowing-resistant release film; The silicone resin has a methyl structure.

[0008] Furthermore, the buffer layer material is silicone rubber, acrylic resin or silicone pressure-sensitive adhesive.

[0009] Furthermore, the base film is PET, PEN or PI.

[0010] Furthermore, the silicone resin is methyl or dimethyl silicone resin. In order to obtain a dense and pure silicone coating, the silicone resin is preferably Dow Corning 805 silicone resin.

[0011] Furthermore, in step (1), after the buffer layer is coated, the film is dried in a drying oven at 50-150° C. for 1-30 min, and then activated at 40-150° C. for 4-48 h to obtain the A film.

[0012] Furthermore, in step (2), after coating with silicone resin, the film is dried in a drying oven at 50-150° C. for 1-30 min, and then activated at 40-150° C. for 4-48 h to obtain a yellowing-resistant release film.

[0013] Furthermore, the yellowing detection method of the yellowing-resistant release film is to cut the film into 5×5 cm pieces, put it into a mold, add epoxy resin mixture particles, and observe whether the surface of the film turns yellow after hot pressing.

[0014] The present invention also claims to protect a yellowing-resistant release film, which is prepared by the above-mentioned preparation method.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The silicone resin in the present invention has a methyl structure, and the silicone resin with a methyl structure has a release effect. The silicone resin coating with a certain thickness has a high strength and can effectively prevent small molecules or impurities in the epoxy resin mixture from entering and adhering to the silicone resin coating. The tough silicone resin buffer coating acts as a buffer layer to prevent the silicone coating from cracking as the use time increases.

[0016] If the silicone coating is directly applied on the base film, as time goes by and the temperature changes, the silicone coating will become brittle and crack, thus separating from the base film, causing the film to lose its original function. However, by adding a soft buffer coating on the base film, the Si-OH functional groups in the silicone coating and the -OH functional groups on the buffer layer form chemical bonds through shrinkage, making the silicone coating and the buffer layer fit more closely. In addition, due to the presence of the soft buffer layer, the silicone coating is not easy to crack and can remain intact, allowing the film to maintain its original performance for a long time.

[0017] The yellowing-resistant release film obtained by the method of the present invention can effectively improve the yellowing phenomenon of the film coating after hot injection molding or hot pressing without changing the performance of the film coating, thereby meeting the needs of clients for repeated use. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of small molecules attached to and embedded in a conventional release film after heat pressing.

[0019] Figure 2It is a schematic diagram showing that it is difficult for small molecules to adhere to the release film of the present invention after hot pressing.

[0020] Figure 3 The invention discloses a preparation process of the yellowing-resistant release film.

[0021] Among them, 1. base film; 2. ordinary silicone release agent coating; 3. epoxy resin mixture adhesive; 4. small molecules or impurities; 5. silicone resin coating; 6. buffer coating. DETAILED DESCRIPTION

[0022] like Figure 1 As shown, the conventional release film structure includes a base film 1 and a common silicone release agent coating 2 attached to the base film 1. When the epoxy resin mixture 3 is hot-injected or hot-pressed onto the surface of the release film, small molecules or impurities 4 in the epoxy resin mixture 3 are easily attached to and embedded in the common silicone release agent coating 2, causing the release film to turn yellow.

[0023] like Figure 2 and 3 As shown, the yellowing-resistant release film of the present invention is improved by coating a tough coating as a buffer coating 6 on a PET (or PEN, PI) base film 1, and then coating a silicone resin coating 5 with a moderate thickness and a methyl structure.

[0024] Among them, the silicone resin with a methyl structure has a release effect, and the silicone resin coating 5 with a certain thickness has a high strength, which can effectively prevent small molecules or impurities 4 in the epoxy resin mixture 3 from entering and adhering to the silicone resin coating 5. The tough silicone resin as a buffer coating 6 acts as a buffer layer to prevent the silicone coating from cracking as the use time increases. The yellowing-resistant release film obtained by this method can effectively improve the yellowing phenomenon of the film coating after hot injection molding or hot pressing without changing the performance of the film coating, thereby meeting the customer's needs for repeated use.

[0025] The method for preparing the yellowing-resistant release film of the present invention comprises the following specific steps: (1) coating a buffer layer on the base film, drying it in a 50-150°C oven for 1-30 minutes; then aging it at a temperature of 40-150°C for 4-48 hours to obtain a film A; Among them, the base film is PET, PEN or PI film, and the buffer layer is silicone rubber, acrylic resin or silicone pressure-sensitive adhesive.

[0026] (2) Coating the silicone resin on the surface of film A, drying it in a drying oven at 50-150°C for 1-30 minutes; then aging it at a temperature of 40-150°C for 4-48 hours to obtain a composite film.

[0027] Film yellowing detection method: Cut the film into 5×5cm, put it into the mold of a vertical injection molding machine, add epoxy resin mixture particles, and after hot pressing, observe whether the film surface turns yellow.

[0028] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] Among the following raw materials, silicone resin is selected from Dow Corning 805 series silicone resin; acrylic resin and curing agent used as buffer layer are self-made acrylic resin AB glue (prepared with reference to the preparation method of Kraft AB glue); organic silicone pressure-sensitive adhesive is selected from Dow Corning SJ series. Equipment: Ohaus electronic balance CP214, KEWLAB MSH-R-03 magnetic stirrer, Taifu Machinery vertical injection molding machine.

[0030] Example 1 Raw materials: 5 parts of acrylic resin AB glue, 0.5 parts of silicone resin.

[0031] Film preparation process: (1) Adding acrylic resin AB glue into a disperser according to the corresponding component ratio, stirring at a speed of 800-1500 rpm for 15 minutes, and then coating it on a PET base film, drying it in a drying oven at 90°C for 2 minutes, and then aging it at 60°C for 24 hours to obtain A film; (2) Silicone resin was coated on the surface of film A, and then dried in a 90°C oven for 2 min, and then aged at 60°C for 12 h to obtain a final film with a film thickness of 25 µm.

[0032] Example 2 Raw materials: 5 parts of acrylic resin AB glue and 3 parts of silicone resin.

[0033] Film preparation process: (1) Adding acrylic resin AB glue into a disperser according to the corresponding component ratio, stirring at a speed of 800-1500 rpm for 15 minutes, and then coating it on a PET base film, drying it in a drying oven at 90°C for 2 minutes, and then aging it at 60°C for 24 hours to obtain A film; (2) Silicone resin was coated on the surface of film A, and then dried in a 90°C oven for 2 min, and then aged at 60°C for 12 h to obtain a final film with a film thickness of 25 µm.

[0034] Example 3 Raw materials: 5 parts of acrylic resin AB glue and 6 parts of silicone resin.

[0035] Film preparation process: (1) Adding acrylic resin AB glue into a disperser according to the corresponding component ratio, stirring at a speed of 800-1500 rpm for 15 minutes, and then coating it on a PET base film, drying it in a drying oven at 90°C for 2 minutes, and then aging it at 60°C for 24 hours to obtain A film; (2) Silicone resin was coated on the surface of film A, and then dried in a 90°C oven for 2 min, and then aged at 60°C for 12 h to obtain a final film with a film thickness of 25 µm.

[0036] Example 4 Raw materials: 5 parts of silicone resin.

[0037] Film preparation process: The silicone resin was coated on the surface of the PET film, and then dried in a 90°C oven for 2 minutes, and then aged at 60°C for 12 hours to obtain a final film with a film thickness of 10µm.

[0038] Example 5 Raw materials: 5 parts of silicone resin.

[0039] Film preparation process: The silicone resin was coated on the surface of the PET film, and then dried in a 90°C oven for 2 minutes, and then aged at 60°C for 12 hours to obtain a final film with a film thickness of 20µm.

[0040] Example 6 Raw materials: 6 parts of silicone pressure-sensitive adhesive and 6 parts of silicone resin.

[0041] Film preparation process: (1) Add the silicone pressure-sensitive adhesive into a disperser, stir at a speed of 800-1500 rpm for 15 min, then coat it on a PET base film, dry it in a drying oven at 90° C. for 2 min, and then age it at 60° C. for 24 h to obtain a film A; (2) Silicone resin was coated on the surface of film A, and then dried in a 90°C oven for 2 min, and then aged at 60°C for 12 h to obtain a final film with a film thickness of 25 µm.

[0042] Comparative Example 1 Common commercially available silicone release film.

[0043] Film yellowing detection method: Cut the above film into 5×5 cm, put it into a mold, add epoxy resin mixture particles, and after hot pressing, observe whether the film surface turns yellow.

[0044] The yellowing results of the films obtained in Examples 1-6 and Comparative Example 1 are shown in Table 1.

[0045] Table 1 Yellowing results of films As shown in Table 1 above, a tough coating is applied on the base film as a buffer layer, and then a moderately thick silicone resin coating with a methyl structure and a release effect is applied thereon to improve the yellowing phenomenon of the coating. This is because a silicone resin coating with a certain thickness has a strong structural strength, which can effectively prevent small molecules or impurities in the epoxy resin mixture from entering or adhering to the coating. The tough coating as a buffer layer can prevent the silicone coating from cracking over time. This method can effectively improve the yellowing phenomenon of the film coating after hot injection molding / pressing without changing the performance of the film coating, thereby meeting the client's needs for repeated use.

[0046] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a yellowing-resistant release film, characterized in that: The steps include: (1) Coating a buffer layer on the base film to form a thin film A; (2) coating silicone resin on film A to form a yellowing-resistant release film; The silicone resin has a methyl structure.

2. The method for preparing the yellowing-resistant release film according to claim 1, wherein: The buffer layer material is silicone rubber, acrylic resin or organic silicone pressure-sensitive adhesive.

3. The method for preparing the yellowing-resistant release film according to claim 1, characterized in that: The base film is PET, PEN or PI.

4. The method for preparing the yellowing-resistant release film according to claim 1, characterized in that: The silicone resin is methyl or dimethyl silicone resin. Preferably, the silicone resin is Dow Corning 805 silicone resin.

5. The method for preparing the yellowing-resistant release film according to claim 1, characterized in that: In step (1), after the buffer layer is coated, the film is dried in a drying oven at 50-150° C. for 1-30 min, and then activated at 40-150° C. for 4-48 h to obtain the A film.

6. The method for preparing the yellowing-resistant release film according to claim 1, characterized in that: In step (2), after coating with silicone resin, the film is dried in a drying oven at 50-150° C. for 1-30 min, and then activated at 40-150° C. for 4-48 h to obtain a yellowing-resistant release film.

7. The method for preparing the yellowing-resistant release film according to claim 1, characterized in that: The yellowing detection method of the yellowing-resistant release film is to cut the film into pieces of 5×5 cm, put it into a mold, add epoxy resin mixture particles, and observe whether the surface of the film turns yellow after hot pressing.

8. A yellowing-resistant release film, characterized in that: The method is prepared according to any one of claims 1 to 7.

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