Composite release film, method of making and use thereof

Abstract

The application provides a composite release film, a preparation method and application thereof. The composite release film comprises a release layer, an adhesive layer and a substrate layer which are sequentially stacked, wherein the release layer is a PVDF layer, the adhesive layer is an epoxy acrylate layer, and the substrate layer is a PET layer. The release layer and the substrate layer in the composite release film can be well bonded due to the presence of the adhesive layer, the tensile strength of the obtained composite release film is 130-135 MPa, the elongation at break is 75-87%, the heat shrinkage at 160 DEG C is less than 1%, the thickness of the release layer is 1-4 mu m, the water contact angle is 76-79 DEG, and the peeling force between the release layer and the proton exchange membrane is 9-13 gf. After being applied to the proton exchange membrane casting coating process, the perfluorosulfonic acid resin solution on the composite release film can be well coated, can be easily peeled off, and the release agent transfer does not occur.

Description

Technical Field

[0001] This invention relates to the field of fuel cells, and more specifically, to a composite release membrane, its preparation method, and its application. Background Technology

[0002] Release film, also known as release film, peel film, or separation film, is a common type of plastic film. Common release film products are made by coating the surface of PET, PI, PP, and other plastic films with silicone oil, fluorine, or non-silicone release agents, giving them extremely light and stable release force. Due to its advantages such as non-stickiness, isolation, and protection, release film is now widely used in packaging, printing, screen printing, electronics, and other industries.

[0003] As a core component of proton exchange membrane fuel cells (PEMFCs), the proton exchange membrane (PEM) plays a crucial role in conducting protons, serving as an electrode reaction medium and catalyst support, and isolating cathode and anode reactants. Its fabrication process is currently a hot research topic in the industry. PEM fabrication processes are divided into casting coating and melt extrusion, with casting coating being the more commonly chosen process due to its lower equipment requirements. In the casting coating process, key parameters such as the contact angle between the release membrane and the perfluorosulfonic acid resin solution, the temperature resistance of the release membrane, its peel strength, and the amount of release agent transferred significantly affect the performance of the resulting PEM. However, commonly available silicone oil-based or fluorine-based release membranes can prevent perfluorosulfonic acid resin solution from forming a film or causing silicon transfer, while the non-silicone release membranes commonly used in China have higher peel strength.

[0004] In this context, polyvinylidene fluoride (PVDF) serves as a good release agent material, possessing advantages such as temperature resistance, self-lubrication, and chemical stability. It can be used as a release coating on high-temperature resistant PET films to reduce their peel strength. However, both PVDF and PET have low surface energies. When PVDF is used as a coating, its adhesion to PET films is weak, making it impossible to form a consistent and stable composite film.

[0005] CN114292554A (Shanghai Water Cube New Materials Co., Ltd.) discloses a modified nano-silica-reinforced waterborne PVDF coating and its preparation method. The method involves reacting a waterborne PVDF / fluorinated acrylic composite emulsion with a fluorinated polysiloxane component, and adding surface-modified nano-silica to increase the compatibility between the components. While ensuring film formation, it also increases the adhesion between the coating and the metal, exhibiting excellent resistance to damp heat. The coating also possesses excellent hydrophobic properties, as well as superior resistance to hydrolysis and acids / alkalis. It can effectively adhere to various metal substrates, forming a stable film and demonstrating excellent practicality. However, this invention patent introduces an epoxy acrylic component, which cannot provide good peel strength. Furthermore, the siloxane and silica components can lead to silicon transfer.

[0006] Therefore, there is an urgent need in the field to provide a novel release membrane for proton exchange membranes to solve the problems of poor temperature resistance, high peeling force, and release agent transfer in existing release membranes for proton exchange membranes. Summary of the Invention

[0007] The main objective of this invention is to provide a composite release membrane, its preparation method, and its application, in order to solve the problems of poor temperature resistance, high peeling force, and release agent transfer in existing release membranes for proton exchange membranes.

[0008] To achieve the above objectives, the present invention provides a composite release film comprising a release layer, an adhesive layer, and a substrate layer stacked sequentially, wherein the release layer is a PVDF layer, the adhesive layer is an epoxy acrylate layer, and the substrate layer is a PET layer.

[0009] Furthermore, the thickness of the release layer is 1–4 μm, the thickness of the adhesive layer is 1–5 μm, and the thickness of the substrate layer is 75–175 μm.

[0010] Another aspect of the present invention provides a method for preparing the above-mentioned composite release film, the method comprising:

[0011] Step S1: Provide a substrate layer having opposing first and second surfaces;

[0012] Step S2: Provide an epoxy acrylate coating as an adhesive slurry, and formulate PVDF resin into a release slurry;

[0013] Step S3: Apply adhesive slurry to the first surface of the substrate layer, and after drying, form an adhesive layer on the first surface;

[0014] Step S4: The release slurry is applied to the surface of the adhesive layer away from the substrate layer, and then dried to form a release layer, thereby obtaining a composite release film.

[0015] Furthermore, in step S2, the epoxy acrylate coating agent is selected from one or more of polyurethane-modified epoxy acrylate, bisphenol A epoxy acrylate, and anhydride-modified epoxy acrylate.

[0016] Furthermore, in step S3, the wet film thickness of the adhesive slurry coating is 10–50 μm.

[0017] Furthermore, during the drying process of forming the adhesive layer in step S3, the temperature is 80–150°C and the time is 1–3 min.

[0018] Furthermore, the preparation method of the release slurry in step S2 includes:

[0019] Step S2-1: Disperse PVDF resin in a solvent to obtain a mixture;

[0020] Step S2-2: Heat the mixture to 40-80℃ and stir for 1-4 hours to obtain release slurry;

[0021] Preferably, the solvent is a mixture of N,N-dimethylformamide and ethyl acetate, with a mass ratio of N,N-dimethylformamide to ethyl acetate of (1-4):1; preferably, the solid content of PVDF resin in the mixture is 4-10%.

[0022] Furthermore, in step S4, the wet film thickness of the release slurry coating is 30–100 μm, and the drying temperature is 120–160 °C for 3–5 min.

[0023] Furthermore, before applying the adhesive slurry, the first surface of the substrate layer is subjected to corona treatment.

[0024] Another aspect of the present invention provides an application of the above-described composite release membrane in a proton exchange membrane casting coating process.

[0025] The composite release membrane prepared by this invention exhibits excellent adhesion between the release layer and the substrate layer due to the presence of the adhesive layer. The resulting composite release membrane has a tensile strength of 130–135 MPa, an elongation at break of 75–87%, a thermal shrinkage of less than 1% at 160°C, a release layer thickness of 1–4 μm, a water contact angle of 76–79°, and a peel force with the proton exchange membrane of 9–13 gf, while preventing release layer transfer. When applied to the proton exchange membrane casting process, the perfluorosulfonic acid resin solution on it forms a good film that can be easily peeled off without release agent transfer. Attached Figure Description

[0026] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0027] Figure 1 This is a schematic diagram of the composite release film in this application;

[0028] The labels represent the following:

[0029] 10. Release layer; 20. Adhesive layer; 30. Substrate layer. Detailed Implementation

[0030] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0031] As described in the background section, existing release membranes for proton exchange membranes suffer from poor temperature resistance, high high-temperature peeling force, and release agent transfer. To address these technical problems, this application provides a composite release membrane, such as... Figure 1 As shown, it includes a release layer 10, an adhesive layer 20 and a substrate layer 30 stacked in sequence, wherein the release layer 10 is a PVDF layer, the adhesive layer 20 is an epoxy acrylate layer and the substrate layer 30 is a PET layer.

[0032] This invention utilizes a PVDF layer to achieve excellent release properties, uses high-temperature resistant PET as the base layer to give the release film good temperature resistance and tensile strength, and uses an epoxy acrylate layer as the adhesive layer to enhance the adhesion between the PET base layer and the release layer. The adhesive layer is an epoxy acrylate layer, which, compared to other adhesives, exhibits better bonding performance, especially for hydrophobic materials like PVDF, demonstrating excellent adhesion. It also possesses high weather resistance, water resistance, and chemical resistance, thus maintaining the overall stability of the composite release film during application. Through extensive and repeated experiments, the inventors discovered that compared to other adhesives such as silicone, polyurethane, acrylic, and polyacrylic acid primers (obtained by dissolving resin particles), silicone primers cannot bond the PVDF layer, and polyurethane, acrylic, and polyacrylic acid all swell due to the solvent in PVDF. The epoxy acrylate layer disclosed in this invention, however, exhibits superior bonding performance. Furthermore, the composite release film with an epoxy acrylate layer as the adhesive layer obtained in this invention demonstrates better structural stability during proton exchange membrane preparation. The resulting composite release film has good mechanical strength, temperature resistance and excellent release effect, and the release layer does not transfer.

[0033] To ensure good release properties on the surface of the composite release membrane in contact with the proton exchange membrane, and to improve the compatibility of the release layer 10 with other components in the composite release membrane, the thickness of this layer is controlled to be 1–4 μm. The thickness of the adhesive layer 20 is controlled to be 1–5 μm to achieve better adhesion and improve the structural continuity of the resulting composite membrane. To enable the substrate layer to better support the composite release membrane and provide better physical and mechanical properties, thereby resulting in better mechanical properties and temperature resistance of the final composite release membrane, the thickness of the substrate layer 30 is limited to 75–175 μm.

[0034] Another aspect of the present invention provides a method for preparing the above-mentioned composite release film, the method comprising:

[0035] Step S1, providing a substrate layer 30 having opposing first and second surfaces;

[0036] Step S2: Provide an epoxy acrylate coating as an adhesive slurry, and formulate PVDF resin into a release slurry;

[0037] Step S3: Apply adhesive slurry to the first surface of substrate layer 30, and after drying, form adhesive layer 20 on the first surface;

[0038] Step S4: The release slurry is applied to the surface of the adhesive layer 20 away from the substrate layer 30, and dried to form the release layer 10, thereby obtaining the composite release film.

[0039] The method for preparing the composite release film provided by this invention can easily obtain a composite release film that is easy to peel, has good temperature resistance and mechanical properties, and does not experience release agent transfer using conventional equipment. Specifically, in step S1, a high-temperature resistant PET film is used as the substrate to give the resulting composite release film good temperature resistance and tensile strength; in step S2, an epoxy acrylate coating is used as the adhesive slurry so that it forms an adhesive layer with good adhesion, compatibility, and weather resistance after drying; PVDF resin is used as the coating slurry for the release layer to obtain excellent release effect; in the preparation process provided in this application, the two are first prepared into a slurry and then coated and dried sequentially. Compared with processes such as co-extrusion, this method can effectively improve the compatibility between the components of each layer, without damaging the heat resistance of the material, and can achieve a multilayer structure with special functions under conditions of simple operation and simple equipment; and after obtaining the above-mentioned composite release film, the roughness of the release film is tested by a white light interferometer to ensure its flatness.

[0040] To improve the adhesion between the substrate layer 30 and the release layer 10, and to achieve a more stable composite release film with superior performance, the epoxy acrylate coating used in this invention is selected from one or more of polyurethane-modified epoxy acrylate, bisphenol A epoxy acrylate, and anhydride-modified epoxy acrylate. Compared with other bonding materials such as silicone elastomers and styrene-butadiene-styrene copolymers, the epoxy acrylate coating used in this invention is usually a low-viscosity liquid, which is more convenient to use in experiments, reduces the difficulty of the process, and can also achieve rapid drying at lower temperatures without the need for pressurization. At the same time, it has strong resistance to media, chemicals, and atmospheric aging, and more importantly, it has good adhesion, exhibiting superior bonding strength to polymer films. Furthermore, after modification with epoxy resin, the adhesion, water resistance, and flexibility of the acrylic adhesive are further improved due to the advantages of strong adhesion, good stability, and strong chemical corrosion resistance of epoxy resin itself. At the same time, the disadvantages of it becoming brittle at low temperatures and sticky at high temperatures are improved, ultimately enhancing the mechanical properties and weather resistance of the resulting composite release film, making it applicable to various experimental environments.

[0041] Based on the above, the wet film thickness of the adhesive slurry is controlled to be 10–50 μm so that it can better exert its bonding effect and at the same time maintain the integrity and consistency of the resulting composite film structure to a greater extent.

[0042] In a preferred embodiment, the drying process of the adhesive layer 20 is carried out at a temperature of 80-150°C for 1-3 minutes. The drying temperature and time are controlled within this range to control the evaporation rate of the solvent, thereby reducing adhesive loss or embrittlement and effectively shortening the production cycle.

[0043] The preparation of the release slurry involves first dispersing PVDF resin in a solvent to obtain a mixture, then heating the mixture to 40–80°C and stirring for 1–4 hours to obtain a uniform release slurry. In a typical embodiment, the solvent used for dispersion is a mixture of N,N-dimethylformamide (DMF) and ethyl acetate (EA), with a mass ratio of (1–4):1. Selecting these two solvents and controlling their mass ratio within the range of (1–4):1 yields a solvent with a polarity closer to that of the PVDF resin, which helps to achieve better dissolution, resulting in a uniformly composed wet film after coating and complete evaporation during drying. Preferably, the solid content of the PVDF resin in the mixture is 4–10%. Controlling the solid content of the PVDF resin within this range not only allows it to better exhibit release properties but also helps to improve its leveling properties during coating, thereby improving its appearance properties.

[0044] During the coating process of the release slurry, the thickness of the wet film is controlled at 30-100 μm to obtain a release layer with better release performance and comprehensive mechanical properties; the drying temperature and time are controlled at 120-160℃ and 3-5 min respectively to improve the appearance quality of the composite release film and effectively shorten the production cycle.

[0045] In a typical embodiment, prior to applying the adhesive slurry, the first surface of the substrate layer 30 is subjected to corona treatment to increase the surface roughness of the PET film, thereby enhancing its composite effect with the adhesive layer 20 and enabling the components of each layer to bond better.

[0046] Another aspect of the present invention provides an application of the above-described composite release membrane in a proton exchange membrane casting coating process. In the casting coating process based on the above-described composite release membrane, the perfluorosulfonic acid resin solution can form a film well and can be easily peeled off without release agent transfer, thereby enabling large-scale mass production while ensuring the performance of the proton exchange membrane itself.

[0047] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0048] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0049] Example 1

[0050] Preparation of a composite release film:

[0051] Step S1. Single-sided corona treatment of PET film: 100μm thick high-temperature resistant PET film, single-sided corona treatment.

[0052] Step S2. Preparation of release agent: Prepare a mixed solvent by mixing DMF and EA in a ratio of 2.33:1. Add PVDF with a solid content of 10% to the mixed solvent of DMF and EA. Heat the mixture in an oil bath to 60°C and stir for 2 hours.

[0053] Step S3. Preparation of adhesive layer: Polyurethane modified epoxy acrylate adhesive is coated on the corona-treated surface of PET film with a wet film thickness of 30 μm. The film is heated at 100℃ for 1-2 min to prepare the adhesive layer. The adhesive layer thickness after drying is 2 μm.

[0054] Step S4. Preparation of the release layer: A PVDF solution with a solid content of 10% is coated onto the substrate of the PET film, with a wet film thickness of 40 μm. The film is then heated at 150℃ for 3-5 minutes to prepare the PVDF release film layer. A schematic diagram of its structure is shown below. Figure 1 .

[0055] Example 2

[0056] Preparation of a composite release film:

[0057] Step S1. Single-sided corona treatment of PET film: 100μm thick high-temperature resistant PET film, single-sided corona treatment.

[0058] Step S2. Preparation of release agent: Prepare a mixed solvent by mixing DMF and EA in a ratio of 2.33:1. Add PVDF with a solid content of 6% to the mixed solvent of DMF and EA. Heat the mixture in an oil bath to 60°C and stir for 2 hours.

[0059] Step S3. Preparation of adhesive layer: Polyurethane modified epoxy acrylate adhesive is coated on the corona-treated surface of PET film with a wet film thickness of 10 μm. The film is heated at 100℃ for 1-2 min to prepare the adhesive layer. The adhesive layer thickness after drying is 1 μm.

[0060] Step S4. Preparation of release layer: A PVDF solution with a solid content of 6% is coated on the base coat of a PET film, with a wet film thickness of 30μm. The film is heated at 150℃ for 3-5 minutes to prepare a PVDF release film layer.

[0061] Example 3

[0062] Preparation of a composite release film:

[0063] Step S1. Single-sided corona treatment of PET film: 100μm thick high-temperature resistant PET film, single-sided corona treatment.

[0064] Step S2. Preparation of release agent: Prepare a mixed solvent by mixing DMF and EA in a ratio of 2.33:1. Add PVDF with a solid content of 4% to the mixed solvent of DMF and EA. Heat the mixture in an oil bath to 60°C and stir for 2 hours.

[0065] Step S3. Preparation of adhesive layer: Polyurethane modified epoxy acrylate adhesive is coated on the corona-treated surface of PET film with a wet film thickness of 10 μm. The film is heated at 100℃ for 1-2 min to prepare the adhesive layer. The adhesive layer thickness after drying is 1 μm.

[0066] Step S4. Preparation of release layer: A PVDF solution with a solid content of 4% is coated on the base coat of a PET film, with a wet film thickness of 40μm. The film is heated at 150℃ for 3-5 minutes to prepare a PVDF release film layer.

[0067] Example 4

[0068] Preparation of a composite release film:

[0069] Step S1. Single-sided corona treatment of PET film: 100μm thick high-temperature resistant PET film, single-sided corona treatment.

[0070] Step S2. Preparation of release agent: Prepare a mixed solvent by mixing DMF and EA in a ratio of 2.33:1. Add PVDF with a solid content of 10% to the mixed solvent of DMF and EA. Heat the mixture in an oil bath to 60°C and stir for 2 hours.

[0071] Step S3. Preparation of adhesive layer: Polyurethane modified epoxy acrylate adhesive is coated on the corona-treated surface of PET film with a wet film thickness of 60 μm. The film is heated at 100℃ for 1-2 min to prepare the adhesive layer. The adhesive layer thickness after drying is 6 μm.

[0072] Step S4. Preparation of release layer: A PVDF solution with a solid content of 10% is coated on the base coat of a PET film, with a wet film thickness of 40 μm. The film is heated at 150℃ for 3-5 min to prepare a PVDF release film layer.

[0073] The difference from Example 1 is that the adhesive layer thickness is 6 μm.

[0074] Example 5

[0075] Preparation of a composite release film:

[0076] Step S1. Single-sided corona treatment of PET film: 100μm thick high-temperature resistant PET film, single-sided corona treatment.

[0077] Step S2. Preparation of release agent: Prepare a mixed solvent by mixing DMF and EA in a ratio of 2.33:1. Add PVDF with a solid content of 10% to the mixed solvent of DMF and EA. Heat the mixture in an oil bath to 60°C and stir for 2 hours.

[0078] Step S3. Preparation of adhesive layer: Polyurethane modified epoxy acrylate adhesive is coated on the corona-treated surface of PET film with a wet film thickness of 5 μm. The film is heated at 100℃ for 1-2 min to prepare the adhesive layer. The adhesive layer thickness after drying is 0.5 μm.

[0079] Step S4. Preparation of release layer: A PVDF solution with a solid content of 10% is coated on the base coat of a PET film, with a wet film thickness of 40 μm. The film is heated at 150℃ for 3-5 min to prepare a PVDF release film layer.

[0080] The difference from Example 1 is that the adhesive layer thickness is 0.5 μm.

[0081] Example 6

[0082] Preparation of a composite release film:

[0083] Step S1. Single-sided corona treatment of PET film: 100μm thick high-temperature resistant PET film, single-sided corona treatment.

[0084] Step S2. Preparation of release agent: Prepare a mixed solvent by mixing DMF and EA in a ratio of 2.33:1. Add PVDF with a solid content of 10% to the mixed solvent of DMF and EA. Heat the mixture in an oil bath to 60°C and stir for 2 hours.

[0085] Step S3. Preparation of adhesive layer: Polyurethane modified epoxy acrylate adhesive is coated on the corona-treated surface of PET film with a wet film thickness of 30 μm. The film is heated at 170℃ for 1-2 min to prepare the adhesive layer. The adhesive layer thickness after drying is 2 μm.

[0086] Step S4. Preparation of release layer: A PVDF solution with a solid content of 10% is coated on the base coat of a PET film, with a wet film thickness of 40 μm. The film is heated at 150℃ for 3-5 min to prepare a PVDF release film layer.

[0087] The difference from Example 1 is that the drying temperature of the adhesive is 170°C.

[0088] Example 7

[0089] Preparation of a composite release film:

[0090] Step S1. Single-sided corona treatment of PET film: 100μm thick high-temperature resistant PET film, single-sided corona treatment.

[0091] Step S2. Preparation of release agent: Prepare a mixed solvent by mixing DMF and EA in a ratio of 2.33:1. Add PVDF with a solid content of 10% to the mixed solvent of DMF and EA. Heat the mixture in an oil bath to 60°C and stir for 2 hours.

[0092] Step S3. Preparation of adhesive layer: Polyurethane modified epoxy acrylate adhesive is coated on the corona-treated surface of PET film with a wet film thickness of 30 μm. The film is heated at 60℃ for 1-2 min to prepare the adhesive layer. The thickness of the adhesive layer after drying is 2 μm.

[0093] Step S4. Preparation of release layer: A PVDF solution with a solid content of 10% is coated on the base coat of a PET film, with a wet film thickness of 40 μm. The film is heated at 150℃ for 3-5 min to prepare a PVDF release film layer.

[0094] The difference from Example 1 is that the drying temperature of the adhesive is 60°C.

[0095] Example 8

[0096] Preparation of a composite release film:

[0097] The difference from Example 1 is that the solid content of PVDF resin in the mixture is 2%.

[0098] Example 9

[0099] Preparation of a composite release film:

[0100] The difference from Example 1 is that the solid content of PVDF resin in the mixture is 12%.

[0101] Example 10

[0102] Preparation of a composite release film:

[0103] The difference from Example 1 is that the adhesive used is bisphenol A epoxy acrylate.

[0104] Example 11

[0105] Preparation of a composite release film:

[0106] The difference from Example 1 is that the adhesive used is an anhydride-modified epoxy acrylate.

[0107] Comparative Example 1

[0108] Preparation of a composite release film:

[0109] The difference from Example 1 is that no adhesive layer is provided.

[0110] Comparative Example 2

[0111] Preparation of a composite release film:

[0112] The difference from Example 1 is that the adhesive used is polydimethylsiloxane, an organosilicon elastomer.

[0113] Comparative Example 3

[0114] Preparation of a composite release film:

[0115] The difference from Example 1 is that the adhesive used is a styrene-butadiene-styrene olefin copolymer.

[0116] Comparative Example 4

[0117] Preparation of a composite release film:

[0118] The difference from Example 1 is that the adhesive used is ethylene-vinyl acetate (EVA) hot melt adhesive.

[0119] Comparative Example 5

[0120] Preparation of a composite release film:

[0121] The difference from Example 1 is that the adhesive slurry and release agent slurry are mixed and then applied to the substrate layer.

[0122] The test methods for various performance parameters of the above embodiments and comparative examples in this invention are as follows, wherein:

[0123] Mechanical properties: Dumbbell-shaped test strips conforming to the thin film tensile test standard are prepared using a punching machine. The thickness of each sample is measured using a thickness gauge. The sample is placed in the two clamps of the testing machine. The tensile speed of the universal tensile testing machine is set (50 mm / min). The testing machine is started for testing. After the sample breaks, the relevant performance parameters are read.

[0124] Release layer adhesion: Refer to GB / T 33049—2016 "Determination of Adhesion of Optical Thin Film Coating for Polarizing Films", specifically: Cut a 150mm×100mm sample, use a cross-cutting tool to cut the sample surface vertically with uniform pressure, rotate the test sample 90°, and cut the sample surface again to form a grid pattern. Apply test tape parallel to a set of cutting lines onto the grid. Within 5 minutes of applying the tape, tear it off and observe with a magnifying glass whether the coating surface has peeled off at the cut edges or intersections of the cuts, and calculate the proportion of the peeled area.

[0125] Temperature resistance: Take a 100mm × 100mm release film sample and test its longitudinal (MD) and transverse (TD) dimensions before heating. Then, place it in a 160℃ oven for 15 minutes, remove it, cool it, and test its dimensions after heating. MD heat shrinkage rate = (MD dimension before heating - MD dimension after heating) × 100% / MD dimension before heating; TD heat shrinkage rate = (TD dimension before heating - MD dimension after heating) × 100% / TD dimension before heating. Perform three tests and take the average value.

[0126] Room temperature peel strength: Apply double-sided adhesive tape parallel to the long side of the stainless steel plate, and adhere the release film side of the sample strip to it. Roll the strip back and forth twice with a pressure roller at a speed of approximately 10 mm / s. Peel off approximately 2 cm of the proton exchange membrane from one end of the sample strip. Then, place the stainless steel plate and the peeled proton exchange membrane into the lower and upper clamps of the tensile testing machine, respectively, ensuring that the steel plate and the sample strip are vertically upward. Perform the peel test at a speed of 300 mm / min ± 10 mm / min, stopping when the peel reaches the upper end of the steel plate. Record the peel strength F1 of the measured sample strip in gf. Measure the peel strength of all samples sequentially, and the average value is the 180° peel strength of the release film.

[0127] Contact angle: Lay the sample flat on a glass slide with the release surface facing up. Add a small amount of pure water to the contact angle measuring instrument and, following the instrument's operating procedures, drop 3-5 μL of pure water onto the release film surface. Record the contact angles of the sample at 5s, 10s, and 15s. Repeat this process three times and record the contact angles.

[0128] Release agent transfer: The test sample and reference sample are placed in a SEM gold sputtering instrument for chromium (or platinum) sputtering treatment. The treated samples are then subjected to SEM+EDS testing for elemental identification and content analysis. Test voltage: 15KV, current: 0.06mA. The elemental types (C, O, F, S) of the test sample and reference sample are identified respectively, and the contents of the corresponding elements are compared to see if they are close or consistent.

[0129] The performance parameter test results of the above embodiments and comparative examples are shown in Table 1 and Table 2, respectively.

[0130] Table 1. Physical and mechanical properties of release films obtained in each embodiment and comparative example.

[0131]

[0132]

[0133] Table 2 Performance parameters of release films obtained from each embodiment and comparative example.

[0134]

[0135]

[0136] As can be seen from the above description, the embodiments of the present invention use high-temperature resistant PET film as the substrate, giving the release film good temperature resistance and tensile strength. Epoxy acrylate is used as the adhesive, and PVDF is used as the release agent. By determining the appropriate solid content, coating wet thickness, and drying temperature, the PVDF layer and PET layer achieve good adhesion, and the release layer produces a good release effect. The prepared high-temperature resistant release film has a tensile strength of 130–135 MPa, an elongation at break of 75–87%, a heat shrinkage of less than 1% at 160°C, a release layer thickness of 1–4 μm, a water contact angle of 76°–79°, a peel force with the proton exchange membrane of 9 gf–13 gf, and no release layer transfer.

[0137] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented, for example, in a sequence other than those described herein.

[0138] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A composite release film, characterized in that, The composite release film comprises a release layer (10), an adhesive layer (20), and a substrate layer (30) stacked sequentially, wherein: The release layer (10) is a PVDF layer, the adhesive layer (20) is an epoxy acrylate layer, and the substrate layer (30) is a PET layer; the epoxy acrylate layer is a polyurethane modified epoxy acrylate layer, a bisphenol A epoxy acrylate layer, or an anhydride modified epoxy acrylate layer. The thickness of the release layer (10) is 1~4μm, the thickness of the adhesive layer (20) is 1~5μm, and the thickness of the substrate layer (30) is 75~175μm.

2. A method for preparing the composite release film according to claim 1, characterized in that, The preparation method includes: Step S1, providing a substrate layer (30) having opposing first and second surfaces; Step S2: Provide epoxy acrylate as an adhesive slurry and formulate PVDF resin into a release slurry; Step S3: The adhesive slurry is applied to the first surface of the substrate layer (30), and after drying, the adhesive layer (20) is formed on the first surface. Step S4: The release slurry is applied to the surface of the adhesive layer (20) away from the substrate layer (30), and dried to form the release layer (10), thereby obtaining the composite release film.

3. The preparation method according to claim 2, characterized in that, The wet film thickness of the adhesive slurry coating in step S3 is 10~50μm.

4. The preparation method according to claim 2 or 3, characterized in that, In the drying process of forming the adhesive layer (20) in step S3, the temperature is 80~150℃ and the time is 1~3min.

5. The preparation method according to claim 2, characterized in that, The method for preparing the release slurry in step S2 includes: Step S2-1: Disperse the PVDF resin in a solvent to obtain a mixture; Step S2-2: Heat the mixture to 40~80℃ and stir for 1~4 hours to obtain the release slurry; The solvent is a mixture of N,N-dimethylformamide and ethyl acetate, wherein the mass ratio of N,N-dimethylformamide to ethyl acetate is (1~4):1; The solid content of the PVDF resin in the mixture is 4-10%.

6. The preparation method according to claim 2 or 5, characterized in that, The wet film thickness of the release slurry in step S4 is 30~100μm, and the temperature in the drying process is 120~160℃, and the time is 3~5min.

7. The preparation method according to claim 2 or 3, characterized in that, Before applying the adhesive slurry, the preparation method further includes a step of corona treatment on the first surface of the substrate layer (30).

8. The application of the composite release membrane according to claim 1 in the proton exchange membrane casting coating process.

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