Single-sided adhesive-coated PI (Polyimide) film for heating film and preparation method of PI film

Abstract

The invention discloses a single-sided adhesive-coated PI film for a heating film and a preparation method thereof.The PI film comprises a release layer, a rubber modified epoxy adhesive layer and a PI film layer which are sequentially arranged in a stacked mode. Ethylene glycol of micromolecular dihydric alcohol is adopted as an initial raw material to prepare polyurethane modified epoxy resin which serves as a main material of the adhesive layer; adding a rubber toughening agent to prepare a heating film; through the toughening effect of the rubber, the flexibility, the bonding strength and the soldering resistance stability of the epoxy resin can be remarkably improved; the rubber has a high wetting and bonding effect on various metal substrates and is relatively good in cohesion, so that the bonding effect of the rubber layer on the metal heating wire and the PI film can be greatly improved, and the protection effect is enhanced; meanwhile, as the selected dihydric alcohol is ethylene glycol, carbamate bonds contained in the prepared polyurethane modified epoxy resin are small in spacing and can be adhered to the surfaces of filler particles at the same time, the compatibility of the filler and the resin is obviously improved, and the aging resistance of the material is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of heating film materials, and in particular to a single-sided adhesive-coated PI film for heating films and its preparation method. Background Technology

[0002] Heating films are functional materials widely used in various fields, primarily for providing a stable heat source. They play a crucial role in electronics, automobiles, aerospace, medical equipment, and home heating. A typical heating film consists of a heating element, a polyimide (PI) film, and an intermediate adhesive layer. The performance of the adhesive layer has a critical impact on the overall performance of the heating film. Traditional heating films use silicone (CN119603805A), thermoplastic polyurethane, phenoxy resin (CN119256059A), and polyolefin resins. However, since metal wire connections often require soldering, high demands are placed on the PI adhesive layer's solder resistance, thermal stability, and high-temperature adhesion. Furthermore, most liquid flame retardants are phosphate esters, which have poor aging resistance. While DOPO and cyclophosphonitrile flame retardants offer relatively better aging resistance, they possess abundant rigid cyclic structures and generally have poor compatibility with epoxy resins, especially in flexible films and during aging, leading to significant performance degradation.

[0003] In general, existing heating films have the following shortcomings: 1. Currently, mainstream thermoplastic hot melt adhesives, such as polyurethane and phenoxy resin adhesives, generally have poor resistance to humid heat aging.

[0004] 2. There are also different types of polyolefin adhesives on the market. They have relatively good resistance to damp heat, but they have more easily decomposed branches, and their solderability is generally poor. After soldering, the peel strength decreases or even decomposes and produces bubbles.

[0005] 3. In order to meet the requirements of flame retardant performance, existing heating films have added flame retardants, which has a serious negative impact on the aging resistance of the heating film. Therefore, it is necessary to improve existing technologies to provide more reliable solutions. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a single-sided coated PI film for heating film and its preparation method, in order to address the shortcomings of the prior art.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a single-sided coated PI film for heating films, comprising a release layer, a rubber-modified epoxy adhesive layer, and a PI film layer stacked sequentially, wherein the rubber-modified epoxy adhesive layer is obtained by coating with rubber-modified epoxy adhesive and then curing it, and the raw materials of the rubber-modified epoxy adhesive include, by weight: 30-50 parts of polyurethane-modified epoxy resin; 20-35 parts of nitrile rubber; 3-8 parts of amine curing agent; Curing accelerator 0.01-0.03 parts; 10-20 parts flame retardant; Antioxidant 0.05-0.5 parts; Solvent 70-150 parts.

[0008] Preferably, the polyurethane-modified epoxy resin is obtained by reacting polyurethane with epoxy resin E-20.

[0009] Preferably, the polyurethane-modified epoxy resin is prepared by the following method: Ethylene glycol and hexamethylene diisocyanate were added to a reactor at a molar ratio of 2:3 and reacted at 80°C for 2 hours to polymerize isocyanate-terminated polyurethane. While keeping the temperature constant, epoxy resin E-20 with a mass of 20 times that of the product was added to the product, and the reaction was continued for 2 hours to obtain polyurethane-modified epoxy resin.

[0010] Preferably, the nitrile rubber is one or a combination of several of the following: carboxyl-terminated nitrile rubber, amino-terminated nitrile rubber, secondary amino-terminated nitrile rubber, and epoxy-terminated nitrile rubber.

[0011] Preferably, the amine curing agent is one or a combination of several of diaminodiphenyl sulfone (DDS), dicyandiamide (DICY), diaminodiphenylmethane (DDM), m-phenylenediamine (MPDA), and isophorone diamine (IPDA).

[0012] Preferably, the curing accelerator is an imidazole accelerator: 2-ethyl-4-methylimidazolium (EMI); tertiary amine accelerators 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30) and benzyl dimethylamine (BDMA); or a combination of one or more of the substituted urea accelerators N-(2-hydroxyphenyl)-N',N'-dimethylurea.

[0013] Preferably, the flame retardant is one or a combination of several of the following: aluminum diethylphosphite (OP935), magnesium hydroxide (Mg(OH)2), expanded graphite, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), and melamine cyanurate.

[0014] Preferably, the antioxidant is one or a combination of several of the following: tetrakis(2,4-di-tert-butylphenyl-4,4'-biphenyl)bisphosphonite, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], bis(3,5-di-tert-butyl-4-hydroxyphenylpropionyl)hydrazine, 4,4'-bis(phenylisopropyl)diphenylamine, and tris(2,4-di-tert-butylphenyl) phosphite.

[0015] Preferably, the thickness of the release layer, the rubber-modified epoxy adhesive layer, and the PI film layer are all 10μm-100μm.

[0016] The present invention also provides a method for preparing a single-sided coated PI film for heating films as described above, comprising the following steps: Polyurethane modified epoxy resin, nitrile rubber, amine curing agent, curing accelerator, flame retardant, and antioxidant are added to a solvent and mixed evenly to obtain rubber modified epoxy adhesive. Rubber-modified epoxy adhesive is coated onto the PI film layer and baked at 140-180℃ for 2-10 minutes to form a rubber-modified epoxy adhesive layer. Then, a release layer is laminated onto the adhesive surface to obtain the single-sided coated PI film for heating film.

[0017] The beneficial effects of this invention are: 1) This invention proposes an innovative and improved single-sided adhesive PI film for heating films. It uses ethylene glycol, a small-molecule diol, as the starting material to prepare a polyurethane-modified epoxy resin as the main adhesive layer material, and adds a rubber toughening agent to prepare the heating film. Through the toughening effect of rubber, the flexibility, bonding strength, and solderability of the epoxy resin can be significantly improved. Furthermore, because rubber has high wetting and adhesion properties to various metal substrates and good cohesion, it can greatly improve the adhesion of the adhesive layer to the metal heating wire and the PI film, enhancing its protective effect. Simultaneously, since the selected diol is ethylene glycol, the polyurethane-modified epoxy resin contains small-spaced urethane bonds, which can simultaneously adhere to the surface of filler particles, significantly improving the compatibility between the filler and the resin, and greatly improving the material's aging resistance. In summary, the single-sided adhesive PI film for heating films provided by this invention has excellent performance and can meet various requirements for high-performance heating films.

[0018] 2) Traditional heating films use materials such as silicone, thermoplastic polyurethane, phenoxy resin, and polyolefin resin as the adhesive layer, which have the disadvantage of being susceptible to soldering defects. This invention uses rubber-modified epoxy resin, thus avoiding the disadvantage of being susceptible to soldering defects.

[0019] 3) The nitrile rubber selected in this invention has a large number of cyano groups, which improves the adhesion and wetting effect on various substrates and has a good adhesion effect on PI film and metal heating wires such as aluminum-magnesium alloy, which can play a good protective role. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to embodiments, so that those skilled in the art can implement it based on the description.

[0021] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0022] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials and reagents used in the following examples are commercially available. For examples where specific conditions are not specified, conventional conditions or conditions recommended by the manufacturer are followed. For reagents or instruments whose manufacturers are not specified, they are all commercially available products.

[0023] This invention provides a single-sided coated PI film for heating films, comprising a release layer, a rubber-modified epoxy layer, and a PI film layer stacked sequentially. The rubber-modified epoxy layer is obtained by coating with rubber-modified epoxy and then curing it. The raw materials of the rubber-modified epoxy include, by weight, the following: 30-50 parts of polyurethane-modified epoxy resin; 20-35 parts of nitrile rubber; 3-8 parts of amine curing agent; Curing accelerator 0.01-0.03 parts; 10-20 parts flame retardant; Antioxidant 0.05-0.5 parts; Solvent 70-150 parts.

[0024] In a preferred embodiment, the polyurethane-modified epoxy resin is obtained by reacting polyurethane with epoxy resin, and the epoxy resin is selected from at least one of bisphenol A type epoxy resins E-20, E-15, and E-35.

[0025] In a preferred embodiment, the polyurethane-modified epoxy resin is prepared by the following method: Ethylene glycol and hexamethylene diisocyanate were added to a reactor at a molar ratio of 2:3 and reacted at 80°C for 2 hours to polymerize isocyanate-terminated polyurethane. While keeping the temperature constant, epoxy resin E-20 with a mass of 20 times that of the product was added to the product, and the reaction was continued for 2 hours to obtain polyurethane-modified epoxy resin.

[0026] In a preferred embodiment, the nitrile rubber is one or a combination of several of the following: carboxyl-terminated nitrile rubber, amino-terminated nitrile rubber, secondary amino-terminated nitrile rubber, and epoxy-terminated nitrile rubber.

[0027] In a preferred embodiment, the amine curing agent is one or a combination of several of diaminodiphenyl sulfone (DDS), dicyandiamide (DICY), diaminodiphenylmethane (DDM), m-phenylenediamine (MPDA), and isophorone diamine (IPDA).

[0028] In a preferred embodiment, the curing accelerator is one or a combination of several of the following: imidazole accelerators: 2-ethyl-4-methylimidazolium (EMI); tertiary amine accelerators: 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30), benzyl dimethylamine (BDMA); and substituted urea accelerators: N-(2-hydroxyphenyl)-N',N'-dimethylurea.

[0029] In a preferred embodiment, the flame retardant is one or a combination of several of the following: aluminum diethylphosphite (OP935), magnesium hydroxide (Mg(OH)2), expanded graphite, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), and melamine cyanurate.

[0030] In a preferred embodiment, the antioxidant is one or a combination of several of the following: tetrakis(2,4-di-tert-butylphenyl-4,4'-biphenyl)bisphosphonates, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], bis(3,5-di-tert-butyl-4-hydroxyphenylpropionyl)hydrazine, 4,4'-bis(phenylisopropyl)diphenylamine, and tris(2,4-di-tert-butylphenyl) phosphite.

[0031] In a preferred embodiment, the thickness of the release layer, the rubber-modified epoxy adhesive layer, and the PI film layer are all 10μm-100μm.

[0032] The present invention also provides a method for preparing a single-sided coated PI film for heating films as described above, comprising the following steps: Polyurethane modified epoxy resin, nitrile rubber, amine curing agent, curing accelerator, flame retardant, and antioxidant are added to a solvent and mixed evenly to obtain rubber modified epoxy adhesive. Rubber-modified epoxy adhesive is coated onto the PI film layer and baked at 140-180℃ for 2-10 minutes to form a rubber-modified epoxy adhesive layer. Then, a release layer is laminated onto the adhesive surface to obtain a single-sided coated PI film for heating film.

[0033] In the rubber-modified epoxy adhesive layer of the present invention, the rubber-modified epoxy resin has excellent heat resistance and excellent performance after soldering.

[0034] Traditional heating films use large-molecule thermoplastic materials in their adhesive layers, which have poor wetting and bonding effects on the substrate. This invention uses thermosetting materials such as nitrile rubber and epoxy resin, which have small molecular weights, good wetting effects, strong bonding effects on various substrates, and good protection for the heating film.

[0035] To address the issue of decreased aging resistance of existing heating films due to flame retardants, this invention uses ethylene glycol, a small-molecule diol, as a starting material to prepare polyurethane-modified epoxy resin. This significantly improves the compatibility between the resin and the flame-retardant filler, resulting in a marked improvement in the aging resistance of the heating film.

[0036] The above is the general concept of the present invention. Based on this, detailed embodiments and comparative examples are provided below to further illustrate the present invention.

[0037] The polyurethane-modified epoxy resins used in the following examples and comparative examples were prepared by the following methods: Ethylene glycol and hexamethylene diisocyanate were added to a reactor at a molar ratio of 2:3 and reacted at 80°C for 2 hours to polymerize isocyanate-terminated polyurethane. While keeping the temperature constant, epoxy resin E-20 with a mass of 20 times that of the product was added to the product, and the reaction was continued for 2 hours to obtain polyurethane-modified epoxy resin.

[0038] Example 1 A single-sided adhesive PI film for heating film includes a release layer, a rubber-modified epoxy layer and a PI film layer stacked sequentially, wherein the thicknesses of the release layer, the rubber-modified epoxy layer and the PI film layer are 25μm, 35μm and 50μm respectively. The preparation method of this PI film is as follows: By weight, 30 parts of polyurethane modified epoxy resin, 20 parts of carboxyl-terminated nitrile butadiene rubber NANCAR 1072 (Taiwan Nan-Di), 3 parts of DDS (Shenzhen Huiya), 0.01 parts of DMP-30, 10 parts of OP935 (Switzerland Clariant), and 0.05 parts of tetrakis(2,4-di-tert-butylphenyl-4,4'-biphenyl) bisphosphonates (Tianjin Lianlong) were dissolved in 100 parts of DMF to prepare a rubber-modified epoxy adhesive. The rubber-modified epoxy adhesive was then coated onto a PI film, and after baking at 160°C for 5 minutes, a release film was applied to the surface to obtain a single-sided coated PI film for heating.

[0039] Example 2 A single-sided adhesive PI film for heating film includes a release layer, a rubber-modified epoxy layer and a PI film layer stacked sequentially, wherein the thicknesses of the release layer, the rubber-modified epoxy layer and the PI film layer are 25μm, 35μm and 50μm respectively. The preparation method of this PI film is as follows: By weight, 50 parts of polyurethane modified epoxy resin, 35 parts of carboxyl-terminated nitrile butadiene rubber NANCAR 1072 (Taiwan Nan-Di), 8 parts of DDS (Shenzhen Huiya), 0.03 parts of EMI, 20 parts of DOPO (Dongguan Xingyuan Chemical), and 0.5 parts of tetrakis(2,4-di-tert-butylphenyl-4,4'-biphenyl) bisphosphonates (Tianjin Lianlong) were dissolved in 150 parts of butanone to prepare rubber-modified epoxy adhesive. The rubber-modified epoxy adhesive was applied to a PI film, and after baking at 160°C for 5 minutes, a release film was applied to the surface to obtain a single-sided coated PI film for heating.

[0040] Example 3 A single-sided adhesive PI film for heating film includes a release layer, a rubber-modified epoxy layer and a PI film layer stacked sequentially, wherein the thicknesses of the release layer, the rubber-modified epoxy layer and the PI film layer are 25μm, 35μm and 50μm respectively. The preparation method of this PI film is as follows: By weight, 30 parts of polyurethane modified epoxy resin, 20 parts of carboxyl-terminated butadiene-acrylonitrile rubber NANCAR 1072 (Taiwan Nan-Ti), 3 parts of DICY (Peng-Cai Chemical), 0.01 parts of DMP-30, 20 parts of OP935 (Clariant, Switzerland), and 0.5 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (Tianjin Lialong) were dissolved in 150 parts of butanone to prepare rubber-modified epoxy adhesive; the rubber-modified epoxy adhesive was coated onto a PI film, and after baking at 160°C for 5 minutes, a release film was covered on the surface to obtain a single-sided coated PI film for heating film.

[0041] Comparative Example 1 A single-sided adhesive PI film for heating film includes a release layer, a rubber-modified epoxy layer and a PI film layer stacked sequentially, wherein the thicknesses of the release layer, the rubber-modified epoxy layer and the PI film layer are 25μm, 35μm and 50μm respectively. The preparation method of this PI film is as follows: By weight, 60 parts of polyurethane modified epoxy resin, 20 parts of carboxyl-terminated nitrile butadiene rubber NANCAR 1072 (Taiwan Nan-Ti), 3 parts of DDS (Shenzhen Huiya), 0.01 parts of DMP-30, 10 parts of OP935 (Switzerland Clariant), and 0.05 parts of tetrakis(2,4-di-tert-butylphenyl-4,4'-biphenyl) bisphosphonate (Tianjin Lianlong) were dissolved in 100 parts of DMF to prepare a rubber-modified epoxy adhesive. The rubber-modified epoxy adhesive was then coated onto a PI film. After baking at 160°C for 5 minutes, a release film was applied to the surface to obtain a single-sided coated PI film for heating applications.

[0042] Comparative Example 2 A single-sided adhesive PI film for heating film includes a release layer, a rubber-modified epoxy layer and a PI film layer stacked sequentially, wherein the thicknesses of the release layer, the rubber-modified epoxy layer and the PI film layer are 25μm, 35μm and 50μm respectively. The preparation method of this PI film is as follows: By weight, 50 parts of polyurethane modified epoxy resin, 35 parts of carboxyl-terminated nitrile butadiene rubber NANCAR 1072 (Taiwan Nan-Ti), 8 parts of DDS (Shenzhen Huiya), 0.03 parts of EMI, 5 parts of DOPO (Dongguan Xingyuan Chemical), and 0.5 parts of tetrakis(2,4-di-tert-butylphenyl-4,4'-biphenyl) bisphosphonate (Tianjin Lianlong) were dissolved in 150 parts of methyl ethyl ketone to prepare a rubber-modified epoxy adhesive. The rubber-modified epoxy adhesive was then coated onto a PI film. After baking at 160°C for 5 minutes, a release film was applied to the surface to obtain a single-sided coated PI film for heating applications.

[0043] Comparative Example 3 A single-sided adhesive PI film for heating film includes a release layer, a rubber-modified epoxy layer and a PI film layer stacked sequentially, wherein the thicknesses of the release layer, the rubber-modified epoxy layer and the PI film layer are 25μm, 35μm and 50μm respectively. The preparation method of this PI film is as follows: By weight, 30 parts of polyurethane modified epoxy resin, 20 parts of carboxyl-terminated butadiene-acrylonitrile rubber NANCAR 1072 (Taiwan Nan-Ti), 15 parts of DICY (Peng-Cai Chemical), 0.01 parts of DMP-30, 20 parts of OP935 (Clariant, Switzerland), and 0.5 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (Tianjin Lialong) were dissolved in 150 parts of butanone to prepare rubber-modified epoxy adhesive; the rubber-modified epoxy adhesive was coated onto a PI film, and after baking at 160°C for 5 minutes, a release film was covered on the surface to obtain a single-sided coated PI film for heating film.

[0044] Comparative Example 4 A single-sided adhesive PI film for heating film includes a release layer, a rubber-modified epoxy layer and a PI film layer stacked sequentially, wherein the thicknesses of the release layer, the rubber-modified epoxy layer and the PI film layer are 25μm, 35μm and 50μm respectively. The preparation method of this PI film is as follows: By weight, 30 parts of polyurethane modified epoxy resin, 20 parts of carboxyl-terminated nitrile butadiene rubber NANCAR 1072 (Taiwan Nan-Di), 3 parts of DDS (Shenzhen Huiya), 0.005 parts of DMP-30, 10 parts of OP935 (Switzerland Clariant), and 0.05 parts of tetrakis(2,4-di-tert-butylphenyl-4,4'-biphenyl) bisphosphonate (Tianjin Lianlong) were dissolved in 100 parts of DMF to prepare rubber-modified epoxy adhesive. The rubber-modified epoxy adhesive was coated onto a PI film, and after baking at 160°C for 5 minutes, a release film was covered on the surface to obtain a single-sided coated PI film for heating film.

[0045] Comparative Example 5 A single-sided adhesive PI film for heating film includes a release layer, a rubber-modified epoxy layer and a PI film layer stacked sequentially, wherein the thicknesses of the release layer, the rubber-modified epoxy layer and the PI film layer are 25μm, 35μm and 50μm respectively. The preparation method of this PI film is as follows: By weight, 50 parts of polyurethane modified epoxy resin, 35 parts of carboxyl-terminated nitrile butadiene rubber NANCAR 1072 (Taiwan Nan-Ti), 8 parts of DDS (Shenzhen Huiya), 0.03 parts of EMI, and 20 parts of DOPO (Dongguan Xingyuan Chemical) were dissolved in 150 parts of methyl ethyl ketone to prepare rubber-modified epoxy adhesive. The rubber-modified epoxy adhesive was then coated onto a PI film, and after baking at 160°C for 5 minutes, a release film was applied to the surface to obtain a single-sided coated PI film for heating.

[0046] Comparative Example 6 A single-sided adhesive PI film for heating film includes a release layer, a rubber-modified epoxy layer and a PI film layer stacked sequentially, wherein the thicknesses of the release layer, the rubber-modified epoxy layer and the PI film layer are 25μm, 35μm and 50μm respectively. The preparation method of this PI film is as follows: By weight, 30 parts of polyurethane modified epoxy resin, 20 parts of carboxyl-terminated butadiene-acrylonitrile rubber NANCAR 1072 (Taiwan Nan-Ti), 3 parts of DICY (Peng-Cai Chemical), 0.01 parts of DMP-30, 20 parts of OP935 (Clariant, Switzerland), and 0.5 parts of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (Tianjin Lialong) were dissolved in 50 parts of butanone to prepare rubber-modified epoxy adhesive. The rubber-modified epoxy adhesive was applied to a PI film, and after baking at 160°C for 5 minutes, a release film was applied to the surface to obtain a single-sided coated PI film for heating film.

[0047] Comparative Example 7 A single-sided adhesive PI film for heating film includes a release layer, a rubber-modified epoxy layer and a PI film layer stacked sequentially, wherein the thicknesses of the release layer, the rubber-modified epoxy layer and the PI film layer are 25μm, 35μm and 50μm respectively. The preparation method of this PI film is as follows: By weight, 30 parts of polyurethane modified epoxy resin (with dodecyl glycol replacing ethylene glycol), 20 parts of carboxyl-terminated butadiene nitrile rubber NANCAR 1072 (Taiwan Nan-Di), 3 parts of DDS (Shenzhen Huiya), 0.01 parts of DMP-30, 10 parts of OP935 (Switzerland Clariant), and 0.05 parts of tetrakis(2,4-di-tert-butylphenyl-4,4'-biphenyl) bisphosphonates (Tianjin Lianlong) were dissolved in 100 parts of DMF to prepare a rubber-modified epoxy adhesive. The rubber-modified epoxy adhesive was then applied to a PI film, and after baking at 160°C for 5 minutes, a release film was applied to the surface to obtain a single-sided coated PI film for heating.

[0048] The specific preparation method of the polyurethane-modified epoxy resin in this example is as follows: Dodecyl glycol and hexamethylene diisocyanate were added to a reactor at a molar ratio of 2:3 and reacted at 80°C for 2 hours to polymerize isocyanate-terminated polyurethane. While keeping the temperature constant, epoxy resin E-20 with a mass of 20 times that of the product was added to the product, and the reaction was continued for 2 hours to obtain polyurethane-modified epoxy resin.

[0049] The following performance tests were conducted on the single-sided adhesive PI films used for heating films prepared in Examples 1-3 and Comparative Examples 1-7.

[0050] 1. T-Peeling Force Test (1) After taking samples from different locations on the tape, let them stand for 24 hours under standard conditions; (2) Cut the tape into 5 pieces, each 25.4mm*300mm in size; (3) Remove the release layer of the tape, and at 60°C, use a rubber roller to stick the two adhesive surfaces together or stick them onto an aluminum-magnesium alloy foil. After hot pressing at 120-180°C for 20-60 seconds, a heating film is obtained.

[0051] (4) Place it at 160-180℃ and cure for about 2 hours.

[0052] (5) After curing, the test shall be carried out in accordance with GB / T 2792-2014 standard, and the requirement is: >2500gf / inch; 2. 300℃ soldering test (1) Prepare the heating film according to the test item described in 1. (2) The heating film with single-sided adhesive PI film was tested according to IPC-TM-650 2.4.13, and the test conditions were 300℃×10s; (3) The appearance has no obvious changes and there are no phenomena such as layering or bubbles; 3. Thermal aging test (1) Prepare bonding samples of aluminum-magnesium alloy metal foil according to the test procedure of test item 1; (2) Place the mating and mating aluminum-magnesium alloy foil samples in an oven at 130℃ and bake for about 500 hours. Remove them and test them according to GB / T2792-2014 standard. The requirement is: >2000gf / inch 4. Vertical burning tests of UL 94 VTM-0, VTM-1, and VTM-2 Test method: Flame retardancy test of uncured PI tape was conducted according to UL-94 test standard. The required flame retardancy rating is VTM-0.

[0053] The test results are shown in Table 1 below: Table 1 Compared to Example 1, Comparative Example 1 used too much polyurethane modified epoxy resin, resulting in a higher proportion of rigid structures in the adhesive. This significantly reduced the peel strength to the aluminum-magnesium alloy foil, failing to meet the performance requirement of 2500 gf / inch.

[0054] Compared to Example 2, Comparative Example 2 used too little flame retardant, resulting in a significant decrease in flame retardant performance, which failed to meet the performance requirements of UL-94 test VTM-0.

[0055] Compared to Example 3, Comparative Example 3 used too much amine curing agent, and the epoxy was insufficient to react with the excess curing agent. A certain amount of small molecule amine curing agent remained in the system. During the soldering test, these small molecule amine curing agents sublimated or decomposed and vaporized, forming various small bubbles between the adhesive and the P film, resulting in a no-response test.

[0056] Compared to Example 1, Comparative Example 4 used too little curing accelerator, resulting in insufficient catalytic effect on epoxy curing. Under curing conditions of 160℃×1h, the curing reaction could not proceed completely, leaving some residual small molecule amine curing agent. In the soldering test, a bubble phenomenon similar to that of Comparative Example 3 was generated.

[0057] Compared to Example 2, Comparative Example 5, without the addition of antioxidants, showed that the double bonds of the nitrile rubber aged rapidly at 130°C, resulting in a significant decrease in the toughness of the adhesive layer and a rapid reduction in peel strength, leading to a failed test.

[0058] Compared to Example 3, Comparative Example 6 used too little solvent, resulting in excessively high viscosity of the rubber-modified epoxy adhesive and insufficient leveling properties. During baking, the solvent evaporated, and the rubber-modified epoxy adhesive failed to level, leading to a large number of bubbles on the adhesive surface.

[0059] Comparative Example 7, compared to Example 1, used dodecyl glycol instead of ethylene glycol to prepare a polyurethane-modified epoxy resin. Due to the increased molecular weight of the diol and the increased spacing of the terminal hydroxyl groups, the urethane bonds in the synthesized polyurethane had larger spacing, preventing the formation of multiple hydrogen bond sites with the same filler particles. This resulted in limited improvement in the compatibility between the filler and the resin, and a significant decrease in peel strength after aging.

[0060] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details.

Claims

1. A single-sided coated PI film for heating films, characterized in that, It includes a release layer, a rubber-modified epoxy layer, and a PI film layer stacked sequentially. The rubber-modified epoxy layer is obtained by coating with rubber-modified epoxy and then curing it. The raw materials of the rubber-modified epoxy include, by weight, the following: 30-50 parts of polyurethane-modified epoxy resin; 20-35 parts of nitrile rubber; 3-8 parts of amine curing agent; Curing accelerator 0.01-0.03 parts; 10-20 parts flame retardant; Antioxidant 0.05-0.5 parts; Solvent 70-150 parts.

2. The single-sided adhesive-coated PI film for heating film according to claim 1, characterized in that, in, The polyurethane-modified epoxy resin is obtained by reacting polyurethane with epoxy resin, and the epoxy resin is bisphenol A type epoxy resin E-20.

3. The single-sided adhesive-coated PI film for heating film according to claim 2, characterized in that, The polyurethane-modified epoxy resin is prepared by the following method: Ethylene glycol and hexamethylene diisocyanate were added to a reactor at a molar ratio of 2:3 and reacted at 80°C for 2 hours to polymerize isocyanate-terminated polyurethane. While keeping the temperature constant, epoxy resin E-20 with a mass of 20 times that of the product was added to the product, and the reaction was continued for 2 hours to obtain polyurethane-modified epoxy resin.

4. The single-sided adhesive-coated PI film for heating film according to claim 1, characterized in that, The nitrile rubber is one or a combination of several of the following: carboxyl-terminated nitrile rubber, amino-terminated nitrile rubber, secondary amino-terminated nitrile rubber, and epoxy-terminated nitrile rubber.

5. The single-sided adhesive-coated PI film for heating film according to claim 1, characterized in that, The amine curing agent is one or a combination of several of the following: diaminodiphenyl sulfone, dicyandiamide, diaminodiphenylmethane, m-phenylenediamine, and isophorone diamine.

6. The single-sided adhesive-coated PI film for heating film according to claim 1, characterized in that, The curing accelerator is one or a combination of several of the following: imidazole accelerators: 2-ethyl-4-methylimidazolium; tertiary amine accelerators: 2,4,6-tris(dimethylaminomethyl)phenol, benzyldimethylamine; and substituted urea accelerators: N-(2-hydroxyphenyl)-N',N'-dimethylurea.

7. The single-sided adhesive-coated PI film for heating film according to claim 1, characterized in that, The flame retardant is one or a combination of several of the following: aluminum diethylphosphite, magnesium hydroxide, expanded graphite, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and melamine cyanurate.

8. The single-sided coated PI film for heating film according to claim 1, characterized in that, The antioxidant is one or a combination of several of the following: tetrakis(2,4-di-tert-butylphenyl-4,4'-biphenyl)bisphosphonite, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], bis(3,5-di-tert-butyl-4-hydroxyphenylpropionyl)hydrazine, 4,4'-bis(phenylisopropyl)diphenylamine, and tris(2,4-di-tert-butylphenyl) phosphite.

9. The single-sided adhesive-coated PI film for heating film according to claim 1, characterized in that, The thickness of the release layer, the rubber-modified epoxy adhesive layer, and the PI film layer are all 10μm-100μm.

10. A method for preparing a single-sided adhesive-coated PI film for heating films as described in any one of claims 1-9, characterized in that, Includes the following steps: Polyurethane modified epoxy resin, nitrile rubber, amine curing agent, curing accelerator, flame retardant, and antioxidant are added to a solvent and mixed evenly to obtain rubber modified epoxy adhesive. Rubber-modified epoxy adhesive is coated onto the PI film layer and baked at 140-180℃ for 2-10 minutes to form a rubber-modified epoxy adhesive layer. Then, a release layer is laminated onto the adhesive surface to obtain the single-sided coated PI film for heating film.

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