Hot melt adhesive film with high metallic viscosity and high hydrolysis resistance as well as preparation method and application of hot melt adhesive film

Abstract

The invention discloses a hot melt adhesive film with high viscosity metallicity and high hydrolysis resistance, which is characterized in that the hot melt adhesive film comprises a base material and a hot melt adhesive layer which are sequentially connected from bottom to top, and the hot melt adhesive layer is obtained by drying and UV curing of UV hot melt adhesive coated on the base material; the UV hot melt adhesive comprises the following components in parts by mass: 20-50 parts of maleic anhydride modified polyolefin resin, 1-10 parts of maleic anhydride modified rubber resin, 1-3 parts of a photoinitiator and 30-60 parts of a flame retardant, the softening point of the maleic anhydride modified polyolefin resin is 140 to 160 DEG C, and the softening point of the maleic anhydride modified rubber resin is 150 to 160 DEG C. The hot melt adhesive film with high metal viscosity and high hydrolysis resistance provided by the invention has excellent metal viscosity and hydrolysis resistance on the premise of accelerating the hot pressing speed, so that on one hand, the hot melt adhesive film can be applied to a high-temperature and high-humidity environment, and on the other hand, the production efficiency of an FFC (Flexible Flat Cable) wire rod is ensured, and the defects in the prior art are overcome.

Description

Technical Field

[0001] This invention relates to the field of hot melt adhesive film technology, and more particularly to hot melt adhesive films with high metal adhesion and high hydrolysis resistance, as well as their preparation methods and applications. Background Technology

[0002] FFC (Flexible Flat Cable) is a product made by hot-melt adhesive film and extremely thin metal conductors through automatic roll forming lamination machine. It has the advantages of being flexible, easy to bend and fold, thin, small in size and easy to solve electromagnetic shielding, and is widely used in signal transmission of various consumer products such as printers, plotters and copiers.

[0003] Common hot melt adhesive films typically consist of a substrate and a hot melt adhesive layer applied to the substrate. Currently, the main resins used in hot melt adhesives fall into two categories:

[0004] (1) Polyester resin, although it is widely used, the ester group of polyester resin is easily hydrolyzed under high temperature and high humidity conditions. On the one hand, it affects the hydrolysis resistance of the hot melt adhesive layer, making the hydrolysis resistance of the hot melt adhesive film worse. On the other hand, polyester resin is easily affected by environmental moisture and swells, which makes the adhesion between the substrate and the hot melt adhesive layer worse, and the metal adhesion of the hot melt adhesive film also decreases. The above factors make it impossible for the hot melt adhesive film obtained by using polyester resin to meet the use requirements under high temperature and high humidity conditions.

[0005] (2) Polyolefin resin, as a non-polar resin, has weak metal adhesion, which makes it difficult to effectively wrap the metal conductor when used in high temperature and high humidity environments. This can easily cause the metal conductor to fall off and be exposed to air for oxidation, resulting in the failure of FFC wire. The above factors also make it impossible to meet the usage requirements of hot melt adhesive film obtained by using polyolefin resin in high temperature and high humidity environments.

[0006] Furthermore, due to their inherent properties, polyolefin resins typically have a high softening point, resulting in hot melt adhesive layers prepared from them often having a softening point in the range of 170–200°C. In the fabrication of FFC wires, controlling the hot-pressing temperature is crucial. If the hot-pressing temperature is too low, the hot melt adhesive layer cannot soften sufficiently, resulting in insufficient fluidity and difficulty in adequately wetting and tightly wrapping the metal conductor surface. If the hot-pressing temperature is too high, it may cause deformation of the substrate, and the high fluidity of the hot melt adhesive layer reduces metal adhesion, preventing the hot melt adhesive film from effectively wrapping the metal conductor. Therefore, to ensure that the hot melt adhesive film can effectively wrap the metal conductor without deformation, the hot-pressing temperature is usually strictly controlled below 210°C, and the softening process of the hot melt adhesive film cannot be accelerated by excessively increasing the hot-pressing temperature. Because the softening point of the polyolefin resin-based hot melt adhesive layer is high, when the hot-pressing speed is too fast, the hot melt adhesive layer cannot soften sufficiently in a short time, thus affecting its wetting and wrapping effect on the metal conductor surface. Therefore, in order to ensure that the hot melt adhesive film softens sufficiently and tightly wraps the metal conductor without deformation, the production process of FFC wires requires low-speed hot pressing, resulting in low production efficiency.

[0007] In summary, the hot melt adhesive film produced by existing technology not only fails to simultaneously possess both metal adhesion and hydrolysis resistance to meet the requirements of high temperature and high humidity environments, but also has a low hot pressing speed, resulting in low production efficiency of FFC wires. Summary of the Invention

[0008] The primary objective of this invention is to propose a hot melt adhesive film with high metal adhesion and high hydrolysis resistance, ensuring that it possesses excellent metal adhesion and hydrolysis resistance while accelerating the hot pressing speed. This ensures its applicability in high-temperature and high-humidity environments and also helps ensure the production efficiency of FFC wires, thus overcoming the shortcomings of existing technologies.

[0009] The second objective of this invention is to provide a method for preparing a hot melt adhesive film with high metal adhesion and high hydrolysis resistance. The preparation method is simple and easy to operate, ensuring that the obtained hot melt adhesive film has excellent metal adhesion and hydrolysis resistance while accelerating the hot pressing speed, thus meeting the requirements of actual use.

[0010] The third objective of this invention is to provide an application of a hot melt adhesive film with high metal adhesion and high hydrolysis resistance, which is used to prepare flexible flat cables, ensuring that the hot melt adhesive film can effectively bond metal conductors and produce flexible flat cables while accelerating the hot pressing speed.

[0011] To achieve this objective, the present invention adopts the following technical solution:

[0012] A hot melt adhesive film with high metal adhesion and high hydrolysis resistance includes a substrate and a hot melt adhesive layer connected sequentially from bottom to top. The hot melt adhesive layer is obtained by drying and UV curing a UV hot melt adhesive coated on the substrate.

[0013] The UV hot melt adhesive comprises, by weight, 20-50 parts of maleic anhydride modified polyolefin resin, 1-10 parts of maleic anhydride modified rubber resin, 1-3 parts of photoinitiator and 30-60 parts of flame retardant.

[0014] The softening point of the maleic anhydride-modified polyolefin resin is 140–160°C, and the softening point of the maleic anhydride-modified rubber resin is 150–160°C.

[0015] Furthermore, the mixing ratio of the maleic anhydride modified rubber resin and the maleic anhydride modified polyolefin resin is 1:(5-20) based on the mass ratio.

[0016] Furthermore, the maleic anhydride-modified polyolefin resin includes maleic anhydride-modified polyethylene resin and maleic anhydride-modified homopolymer polypropylene resin.

[0017] The softening point of the maleic anhydride-modified polyethylene resin is 105–135°C, and the softening point of the maleic anhydride-modified homopolymer polypropylene resin is 160–170°C.

[0018] Furthermore, the maleic anhydride modified rubber resin includes any one or more combinations of maleic anhydride modified styrene-butadiene rubber, maleic anhydride modified hydrogenated styrene-butadiene rubber, maleic anhydride modified SBS rubber, maleic anhydride modified SEBS rubber, maleic anhydride modified SIS rubber, and maleic anhydride modified SEPS rubber.

[0019] Furthermore, the flame retardant comprises decabromodiphenyl ethane and antimony trioxide;

[0020] The mixing ratio of the decabromodiphenyl ethane and the antimony trioxide, calculated by mass ratio, is (5-9):(1-5).

[0021] Furthermore, the UV hot melt adhesive also includes a light stabilizer, titanium dioxide, and a solvent;

[0022] According to the mass fractions, the UV hot melt adhesive comprises 20-50 parts of maleic anhydride modified polyolefin resin, 1-10 parts of maleic anhydride modified rubber resin, 0.1-2 parts of light stabilizer, 1-3 parts of photoinitiator, 30-60 parts of flame retardant, 5-15 parts of titanium dioxide, and 57.1-140 parts of solvent.

[0023] The sum of the mass fractions of the maleic anhydride-modified polyolefin resin, the maleic anhydride-modified rubber resin, the light stabilizer, the photoinitiator, the flame retardant, and the titanium dioxide is the same as the mass fraction of the solvent.

[0024] A method for preparing a hot melt adhesive film with high metal adhesion and high hydrolysis resistance, comprising the following steps:

[0025] A. After mixing the maleic anhydride-modified polyolefin resin, maleic anhydride-modified rubber resin and solvent in the specified amounts, a mixture is obtained;

[0026] B. Add the flame retardant, titanium dioxide, light stabilizer and photoinitiator in the specified amounts to the mixture in sequence. After stirring, grinding and filtering, UV hot melt adhesive is obtained.

[0027] C. Apply UV hot melt adhesive to the surface of the substrate, and after drying and UV curing, a hot melt adhesive layer is formed, resulting in a hot melt adhesive film with high metal adhesion and high hydrolysis resistance.

[0028] Furthermore, in step C, the specific method for the drying step is as follows:

[0029] The UV hot melt adhesive coated on the surface is dried multiple times;

[0030] The drying temperature for the first drying is 70-80℃, and the drying temperature for the last drying is 170-180℃. The drying temperature between the first drying and the last drying increases sequentially by 10-20℃ from the drying temperature of the first drying to the drying temperature of the last drying.

[0031] Further, step C specifically involves: performing corona treatment on the surface of the substrate, coating the corona-treated substrate surface with UV hot melt adhesive, and forming a hot melt adhesive layer after drying and UV curing to obtain a hot melt adhesive film with high metal adhesion and high hydrolysis resistance.

[0032] The application of hot melt adhesive films with high metal adhesion and high hydrolysis resistance in the preparation of flexible flat cables involves the following steps: Take two uncured hot melt adhesive films and place their hot melt adhesive layers opposite each other; place a metal conductor between the hot melt adhesive layers of the two uncured hot melt adhesive films; dry the conductor first, then perform hot pressing, cooling, and UV curing in sequence; and finally cut the conductor to obtain a flexible flat cable.

[0033] The technical solution provided by this invention may include the following beneficial effects:

[0034] 1. Maleic anhydride, introduced into maleic anhydride-modified polyolefin resin, possesses high polarity, allowing it to form chemical bonds or undergo physical adsorption with metal conductors, thereby enhancing the metal adhesion of the hot melt adhesive film. Simultaneously, the high flexibility of the maleic anhydride-modified polyolefin molecular chains facilitates better spreading and penetration onto the metal conductor surface, creating more adhesion points between the metal conductor and the maleic anhydride-modified polyolefin, thus improving the metal adhesion of the hot melt adhesive film. Furthermore, the excellent hydrolysis resistance of the maleic anhydride-modified polyolefin resin prevents swelling of the hot melt adhesive layer due to moisture in the external environment, ensuring adhesion between the substrate and the hot melt adhesive layer, thereby maintaining the metal adhesion of the hot melt adhesive film. These combined characteristics result in a hot melt adhesive film with high metal adhesion.

[0035] 2. In maleic anhydride-modified rubber resin, not only can strong covalent bonds be formed between maleic anhydride and polyolefin resin molecular chains, enhancing the chemical stability of the maleic anhydride-modified rubber resin, but the introduction of maleic anhydride also constructs a hydrolysis barrier, effectively slowing down the erosion rate of water molecules on the modified rubber resin. These two aspects together enhance the hydrolysis resistance of the hot melt adhesive film. Furthermore, maleic anhydride-modified rubber resin can fully utilize the high polarity of maleic anhydride to enhance the adhesion between the hot melt adhesive film and the metal conductor, thereby improving the metal adhesion of the hot melt adhesive film.

[0036] 3. This technical solution involves UV curing of the UV hot melt adhesive. Under the action of a photoinitiator, the unsaturated double bonds in the maleic anhydride-modified polyolefin resin and maleic anhydride-modified rubber resin in the UV hot melt adhesive are cured by UV to form a cross-linked network structure. This cross-linked network structure not only forms a protective barrier, effectively slowing down the erosion rate of water molecules on the hot melt adhesive film, but also contributes to higher chemical stability of the hot melt adhesive layer, resisting the effects of hydrolysis, thereby improving the hydrolysis resistance of the hot melt adhesive film. Furthermore, the cross-linked network structure greatly increases the encapsulation of functional groups, limiting the hydrolysis of easily hydrolyzed groups even if the hot melt adhesive film contains such groups, thus improving the hydrolysis resistance of the hot melt adhesive film. These multiple effects result in the hot melt adhesive film exhibiting extremely high hydrolysis resistance.

[0037] 4. The cross-linked network structure formed by unsaturated double bonds during the curing process increases the cohesive energy of the hot melt adhesive layer, allowing the hot melt adhesive film to adhere more firmly to the metal surface and further enhancing its metal adhesion. Additionally, the excellent hydrolysis resistance of the hot melt adhesive layer prevents swelling caused by moisture in the external environment, thus also contributing to ensuring its metal adhesion. Detailed Implementation

[0038] This technical solution provides a hot melt adhesive film with high metal adhesion and high hydrolysis resistance, comprising a substrate and a hot melt adhesive layer connected sequentially from bottom to top. The hot melt adhesive layer is obtained by drying and UV curing a UV hot melt adhesive coated on the substrate.

[0039] The UV hot melt adhesive comprises, by weight, 20-50 parts of maleic anhydride modified polyolefin resin, 1-10 parts of maleic anhydride modified rubber resin, 1-3 parts of photoinitiator and 30-60 parts of flame retardant.

[0040] The softening point of the maleic anhydride-modified polyolefin resin is 140–160°C, and the softening point of the maleic anhydride-modified rubber resin is 150–160°C.

[0041] To address the shortcomings of existing hot melt adhesive films in meeting practical application requirements, this technical solution proposes a hot melt adhesive film with high metal adhesion and high hydrolysis resistance. This film comprises a substrate and a hot melt adhesive layer connected sequentially from bottom to top. By optimizing the formulation and curing process of the UV hot melt adhesive, it achieves excellent metal adhesion and hydrolysis resistance while accelerating the hot pressing speed. This ensures its applicability in high-temperature and high-humidity environments and also helps maintain the production efficiency of FFC wires, meeting practical application needs.

[0042] Specifically, the raw materials for UV hot melt adhesive are maleic anhydride-modified polyolefin resin, maleic anhydride-modified rubber resin, photoinitiator, and flame retardant. The maleic anhydride-modified polyolefin resin is formed by free radical polymerization of maleic anhydride and polyolefin resin, thus possessing the inherent properties of polyolefin resin. The presence of covalent bonds in the polyolefin resin molecular chain, which are not easily disrupted by water molecules, gives it good hydrolysis resistance. Simultaneously, the non-polar nature of polyolefin resin and the relatively weak intermolecular forces make it difficult for water molecules to penetrate into its molecular chain, further reducing the likelihood of hydrolysis. Furthermore, the flexibility of the polyolefin resin molecular chain also helps reduce intermolecular forces, lowering the possibility of attack by water molecules, thereby enhancing its hydrolysis resistance.

[0043] Furthermore, the introduction of maleic anhydride not only enhances the intermolecular interactions of the maleic anhydride-modified polyolefin resin but also improves its chemical stability, thereby enhancing the hydrolysis resistance of the hot melt adhesive film. Simultaneously, the maleic anhydride group exhibits higher hydrolysis resistance compared to ester groups, forming a hydrolysis barrier to a certain extent, effectively slowing down the rate of water erosion of the resin and further enhancing the hydrolysis resistance of the hot melt adhesive film.

[0044] In summary, maleic anhydride-modified polyolefin resin, formed by free radical polymerization of maleic anhydride and polyolefin resin, exhibits excellent hydrolysis resistance due to its multiple advantages.

[0045] Furthermore, the maleic anhydride introduced into the maleic anhydride-modified polyolefin resin has high polarity, which allows it to form chemical bonds or physical adsorption with metal conductors, thereby enhancing the metal adhesion of the hot melt adhesive film. Simultaneously, the high flexibility of the maleic anhydride-modified polyolefin molecular chains facilitates better spreading and penetration onto the metal conductor surface, creating more adhesion points between the metal conductor and the maleic anhydride-modified polyolefin, thus improving the metal adhesion of the hot melt adhesive film. In addition, the excellent hydrolysis resistance of the maleic anhydride-modified polyolefin resin prevents swelling of the hot melt adhesive layer due to moisture in the external environment, ensuring adhesion between the substrate and the hot melt adhesive layer, thereby maintaining the metal adhesion of the hot melt adhesive film. These multiple characteristics contribute to the high metal adhesion of the hot melt adhesive film.

[0046] Secondly, although introducing maleic anhydride-modified polyolefin resin into UV hot melt adhesives can effectively improve the metal adhesion and hydrolysis resistance of the hot melt adhesive film, thereby improving its adaptability in high-temperature and high-humidity environments, the above improvements are still insufficient to fully meet the high-performance requirements of hot melt adhesive films under certain extreme high-temperature and high-humidity environments. Therefore, this technical solution adds maleic anhydride-modified rubber resin to UV hot melt adhesives. In maleic anhydride-modified rubber resin, not only can strong covalent bonds be formed between maleic anhydride and polyolefin resin molecular chains, improving the chemical stability of the maleic anhydride-modified rubber resin, but the introduction of maleic anhydride also constructs a hydrolysis barrier, effectively slowing down the erosion rate of water molecules on the modified rubber resin. These two aspects together enhance the hydrolysis resistance of the hot melt adhesive film. Furthermore, the maleic anhydride-modified rubber resin can also fully utilize the high polarity of maleic anhydride to enhance the adhesion between the hot melt adhesive film and the metal conductor, thereby improving the metal adhesion of the hot melt adhesive film.

[0047] Furthermore, although introducing maleic anhydride-modified polyolefin resin and maleic anhydride-modified rubber resin into UV hot melt adhesives can effectively improve the metal adhesion and hydrolysis resistance of hot melt adhesive films, thereby improving their adaptability in high-temperature and high-humidity environments, the above improvements are still insufficient to fully meet the high-performance requirements of hot melt adhesive films under high-temperature and high-humidity environments. Therefore, this technical solution involves UV curing of the hot melt adhesive, causing the unsaturated double bonds in the maleic anhydride-modified polyolefin resin and maleic anhydride-modified rubber resin to form a cross-linked network structure under the action of a photoinitiator. This cross-linked network structure not only forms a protective barrier, effectively slowing down the erosion rate of water molecules on the hot melt adhesive film, but also contributes to higher chemical stability of the hot melt adhesive layer, enabling it to resist the effects of hydrolysis, thereby improving the hydrolysis resistance of the hot melt adhesive film. In addition, the cross-linked network structure greatly increases the encapsulation of functional groups, so that even if the hot melt adhesive film contains easily hydrolyzed groups, it can limit the hydrolysis of these groups, thereby improving the hydrolysis resistance of the hot melt adhesive film. The aforementioned factors contribute to the extremely high hydrolysis resistance of the hot melt adhesive film.

[0048] Furthermore, the cross-linked network structure formed by unsaturated double bonds during the curing process increases the cohesive energy of the hot melt adhesive layer, allowing the hot melt adhesive film to adhere more firmly to the metal surface, further enhancing its metal adhesion. Additionally, the excellent hydrolysis resistance of the hot melt adhesive layer prevents swelling caused by moisture in the external environment, thus also contributing to ensuring its metal adhesion.

[0049] Furthermore, since the unsaturated double bonds in maleic anhydride-modified polyolefin resin and maleic anhydride-modified rubber resin require high temperatures for thermal curing, these high temperatures can easily deform the substrate, leading to deformation of the resulting hot melt adhesive film and a decrease in its metal adhesion properties. Therefore, this technical solution employs UV curing to cure the maleic anhydride-modified polyolefin resin and maleic anhydride-modified rubber resin, thereby helping to ensure the metal adhesion properties of the hot melt adhesive film.

[0050] Finally, in this technical solution, the softening point of the maleic anhydride-modified polyolefin resin is 150-160℃, the softening point of the maleic anhydride-modified rubber resin is 150-160℃, and the addition amount of maleic anhydride-modified polyolefin resin is limited to 20-50 parts and the addition amount of maleic anhydride-modified rubber resin is limited to 1-10 parts, so that the softening point of the hot melt adhesive layer is reduced to below 160℃. Compared with the existing hot melt adhesive layer with a softening point of 170-200℃, its softening point is reduced, thereby allowing the hot melt adhesive film to effectively wrap the metal conductor while accelerating the hot pressing speed, ensuring the production efficiency of FFC wire.

[0051] It should be noted that the molecular chains constituting rubber are typically composed of thousands of carbon-carbon bonds. These chain segments can undergo internal rotation, giving maleic anhydride-modified rubber resin high flexibility, which is beneficial for ensuring the flexibility of the hot melt adhesive film. However, if the amount of maleic anhydride-modified rubber resin added exceeds 10 parts, although the flexibility of the hot melt adhesive film will be further improved, excessive maleic anhydride-modified rubber resin will disrupt the continuity of the maleic anhydride-modified polyolefin resin matrix, resulting in a decrease in the overall mechanical properties of the hot melt adhesive film, especially a significant decrease in tensile strength. If the amount of maleic anhydride-modified rubber resin added is less than 1 part, the maleic anhydride-modified rubber resin is insufficient to form an effective flexible network in the maleic anhydride-modified polyolefin resin matrix, resulting in poor flexibility of the hot melt adhesive film. Therefore, this technical solution limits the addition amount of maleic anhydride modified rubber resin to 1 to 10 parts, so that the maleic anhydride modified rubber resin can be effectively dispersed in the maleic anhydride modified polyolefin resin matrix to form a flexible network structure, while maintaining the continuity of the polymaleic anhydride modified polyolefin resin, thereby ensuring the flexibility of the hot melt adhesive film and giving the hot melt adhesive film high tensile strength.

[0052] In addition, adding 30-60 parts of flame retardant allows the hot melt adhesive layer to achieve a UL94VTM-0 flame retardant rating. Adding 1-3 parts of photoinitiator helps to fully cure the unsaturated double bonds in the maleic anhydride-modified polyolefin resin and maleic anhydride-modified rubber resin to form a cross-linked network structure, ensuring product performance.

[0053] Preferably, the substrate is a PET film;

[0054] The thickness of the PET film is 25–75 μm; the thickness of the hot melt adhesive layer is 18–50 μm.

[0055] In a preferred embodiment of this technical solution, the substrate is a PET film (polyethylene terephthalate film). The PET film has high strength, low heat shrinkage, high temperature resistance and high stability. Hot melt adhesive is coated on it, so that the resulting hot melt adhesive film not only has the excellent hydrolysis resistance and metal adhesion of the hot melt adhesive film itself, but also has the high strength, low heat shrinkage, high temperature resistance and high stability of the PET film itself, making it more suitable for use in high temperature and high humidity environments.

[0056] In another preferred embodiment of this technical solution, the PET film has a thickness of 25–75 μm, providing a certain supporting function to ensure the strength and hardness of the hot melt adhesive film; the hot melt adhesive layer has a thickness of 18–50 μm, allowing it to encapsulate the metal conductor and prevent it from being exposed to air, thus affecting the performance of the FFC wire. Furthermore, limiting the thickness of the PET film and the hot melt adhesive layer ensures that the FFC wire is relatively thin, avoiding excessive thickness that would increase production and transportation costs.

[0057] Preferably, the photoinitiator comprises any one of 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2-isopropylthioxanthone, 1-hydroxycyclohexylphenyl ketone, benzoyl dimethyl ether, 2-methyl-2-(4-morpholino)-1-[4-(methylthio)phenyl]-1-propanone, and 2-phenylbenzyl-2-dimethylamine-1-(4-morpholinobenzylphenyl)butanone.

[0058] 2-Hydroxy-2-methyl-1-phenyl-1-propanone (1173), 2-isopropylthioxanthone (ITX), 1-hydroxycyclohexylphenyl ketone (1104), benzoyl dimethyl ether (651), 2-methyl-2-(4-morpholino)-1-[4-(methylthio)phenyl]-1-propanone (907), and 2-phenylbenzyl-2-dimethylamine-1-(4-morpholinobenzylphenyl)butanone (369) are photoinitiators that react quickly and have fewer side reactions in commonly used ultraviolet wavelengths. Therefore, this technical solution preferably uses the above-mentioned types of photoinitiators to ensure product performance.

[0059] To further explain, the mixing ratio of the maleic anhydride modified rubber resin and the maleic anhydride modified polyolefin resin, calculated by mass ratio, is 1:(5-20).

[0060] By limiting the mixing ratio of maleic anhydride modified rubber resin and maleic anhydride modified polyolefin resin, it is not only beneficial to improve the metal adhesion and hydrolysis resistance of the hot melt adhesive film, but also to further ensure the flexibility of the hot melt adhesive film while giving it high tensile strength.

[0061] To further explain, the maleic anhydride-modified polyolefin resin includes maleic anhydride-modified polyethylene resin and maleic anhydride-modified homopolymer polypropylene resin.

[0062] The softening point of the maleic anhydride-modified polyethylene resin is 105–135°C, and the softening point of the maleic anhydride-modified homopolymer polypropylene resin is 160–170°C.

[0063] By preferably using maleic anhydride-modified polyolefin resin and maleic anhydride-modified polyethylene resin and maleic anhydride-modified homopolymer polypropylene resin, and by limiting the softening point of maleic anhydride-modified polyethylene resin and maleic anhydride-modified homopolymer polypropylene resin, the softening point of the maleic anhydride-modified polyolefin resin obtained by mixing maleic anhydride-modified polyethylene resin and maleic anhydride-modified homopolymer polypropylene resin is 140-160℃, which is beneficial to further ensure the performance of the hot melt adhesive film.

[0064] To further clarify, the maleic anhydride modified rubber resin includes any one or more combinations of maleic anhydride modified styrene-butadiene rubber, maleic anhydride modified hydrogenated styrene-butadiene rubber, maleic anhydride modified SBS rubber, maleic anhydride modified SEBS rubber, maleic anhydride modified SIS rubber, and maleic anhydride modified SEPS rubber.

[0065] By optimizing the types of maleic anhydride-modified rubber resins, and by selecting the maleic anhydride-modified rubber resins with high cost performance, it is not only beneficial to select appropriate raw materials according to actual needs and improve the flexibility of the formulation, but also beneficial to save production costs while ensuring the performance of hot melt adhesive films.

[0066] To further explain, the flame retardant includes decabromodiphenyl ethane and antimony trioxide;

[0067] The mixing ratio of the decabromodiphenyl ethane and the antimony trioxide, calculated by mass ratio, is (5-9):(1-5).

[0068] Decabromodiphenyl ethane releases bromine free radicals during combustion. These free radicals can effectively capture and interrupt free radicals in the combustion chain reaction, thereby inhibiting the combustion process. Antimony trioxide, as a synergistic flame retardant, reacts with decabromodiphenyl ethane to form antimony bromide. Under high-temperature conditions, antimony bromide decomposes into a gaseous substance. This gaseous substance not only dilutes the combustible gas but also carries away a large amount of heat, further slowing down the combustion rate. Therefore, this technical solution combines decabromodiphenyl ethane with antimony trioxide, strictly limiting their mixing ratio to ensure optimal flame retardant effect.

[0069] Furthermore, the limitation on the mixing ratio in this technical solution is based on the following considerations: when the proportion of decabromodiphenyl ethane is too high, it may interfere with the chemical bonding and physical interactions in the hot melt adhesive layer, leading to a decrease in the metal adhesion performance of the hot melt adhesive film. Therefore, by reasonably setting the mixing ratio of the two, both flame retardant performance and metal adhesion performance of the hot melt adhesive film can be guaranteed.

[0070] To further explain, the UV hot melt adhesive also includes a light stabilizer, titanium dioxide, and a solvent;

[0071] According to the mass fractions, the UV hot melt adhesive comprises 20-50 parts of maleic anhydride modified polyolefin resin, 1-10 parts of maleic anhydride modified rubber resin, 0.1-2 parts of light stabilizer, 1-3 parts of photoinitiator, 30-60 parts of flame retardant, 5-15 parts of titanium dioxide, and 57.1-140 parts of solvent.

[0072] The sum of the mass fractions of the maleic anhydride-modified polyolefin resin, the maleic anhydride-modified rubber resin, the light stabilizer, the photoinitiator, the flame retardant, and the titanium dioxide is the same as the mass fraction of the solvent.

[0073] Light stabilizers absorb, reflect, or scatter ultraviolet (UV) light, preventing UV rays from directly affecting the surface of the hot melt adhesive film, thereby inhibiting photoaging and extending the film's lifespan. Additionally, titanium dioxide can mask metal conductors, ensuring the aesthetic appeal of the hot melt adhesive film. Solvents provide the UV hot melt adhesive with suitable viscosity, improving its stability and leveling properties, thus ensuring the adhesion to metals and hydrolysis resistance of the resulting hot melt adhesive layer after coating and UV curing. Therefore, this technical solution, by adding light stabilizers, titanium dioxide, and solvents to the UV hot melt adhesive, helps ensure product performance.

[0074] Furthermore, this solution optimizes the proportions of each raw material in the UV hot melt adhesive, which helps to control the viscosity of the UV hot melt adhesive within the range of 6000 to 10000 mPa·s, thus further ensuring its performance after coating and UV curing.

[0075] Preferably, the solvent includes toluene and ethyl acetate, and the mixing ratio of toluene and ethyl acetate is (2-2.2):1 by mass.

[0076] Compared to other solvents, toluene and ethyl acetate exhibit better solubility for maleic anhydride-modified polyolefin resins. Therefore, this technical solution uses toluene and ethyl acetate as solvents, and limits their mixing ratio to ensure that the maleic anhydride-modified polyolefin resin is fully dissolved, thereby ensuring the performance of the hot melt adhesive film.

[0077] It should be noted that the light stabilizer can be 2-(2'-hydroxy-5'-methylphenyl)benzotriazole (UV-P), 2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole (UV-326), 2-(2'-hydroxy-3',5'-di-tert-butylphenyl)-5-chlorobenzotriazole (UV-327), etc., and the specific type is not limited here.

[0078] A method for preparing a hot melt adhesive film with high metal adhesion and high hydrolysis resistance, comprising the following steps:

[0079] A. After mixing the maleic anhydride-modified polyolefin resin, maleic anhydride-modified rubber resin and solvent in the specified amounts, a mixture is obtained;

[0080] B. Add the flame retardant, titanium dioxide, light stabilizer and photoinitiator in the specified amounts to the mixture in sequence. After stirring, grinding and filtering, UV hot melt adhesive is obtained.

[0081] C. Apply UV hot melt adhesive to the surface of the substrate, and after drying and UV curing, a hot melt adhesive layer is formed, resulting in a hot melt adhesive film with high metal adhesion and high hydrolysis resistance.

[0082] This technical solution also proposes a method for preparing a hot melt adhesive film with high metal adhesion and high hydrolysis resistance. The preparation method is simple and easy to operate, ensuring that the obtained hot melt adhesive film has excellent metal adhesion and hydrolysis resistance while accelerating the hot pressing speed, thus meeting the actual application requirements.

[0083] Specifically, in step A, maleic anhydride-modified polyolefin resin, maleic anhydride-modified rubber resin, and solvent are first mixed. This not only helps to accelerate the dissolution rate of maleic anhydride-modified polyolefin resin and maleic anhydride-modified rubber resin, thereby shortening the production time of UV hot melt adhesive and improving production efficiency, but also helps to promote the uniform mixing of subsequent raw materials such as flame retardants, titanium dioxide, light stabilizers, and photoinitiators in the system, thereby ensuring the performance of the product.

[0084] Preferably, in step A, the stirring speed is 500-1000 r / min and the stirring time is 5-10 min;

[0085] In step B, the stirring speed is 800-1200 r / min and the stirring time is 5-10 min; the grinding time is 30-50 min; and the filter mesh size is 150-200 mesh.

[0086] Limiting the stirring speed and time in steps A and B promotes uniform mixing of raw materials, ensuring the performance of the UV hot melt adhesive. Furthermore, grinding further refines the particles, improving the fineness and uniformity of the raw materials, thereby enhancing the appearance and performance of the final product. Limiting the grinding time to 30–50 minutes ensures that over-grinding does not damage or deteriorate the material. Additionally, filtration using a 150–200 mesh screen removes large impurities from the UV hot melt adhesive, ensuring its purity and uniformity.

[0087] To further explain, the specific method for the drying step in step C is as follows:

[0088] The UV hot melt adhesive coated on the surface is dried multiple times;

[0089] The drying temperature for the first drying is 70-80℃, and the drying temperature for the last drying is 170-180℃. The drying temperature between the first drying and the last drying increases sequentially by 10-20℃ from the drying temperature of the first drying to the drying temperature of the last drying.

[0090] By subjecting the surface-coated UV hot melt adhesive to multiple drying cycles and limiting the initial drying temperature, final drying temperature, and temperature increment of each cycle, it is beneficial to ensure that the UV hot melt adhesive is completely dry before UV curing, which promotes complete curing of the UV hot melt adhesive and thus ensures the performance of the hot melt adhesive film.

[0091] It should be noted that the drying temperature from the first drying to the last drying in increments of 10-20℃ means that if the number of drying cycles is six, then the drying temperature for the first drying is 70℃, the drying temperature for the second drying is 90℃, the drying temperature for the third drying is 110℃, and so on.

[0092] To further explain, step C specifically involves: performing corona treatment on the surface of the substrate, coating the corona-treated substrate surface with UV hot melt adhesive, and then drying and UV curing to form a hot melt adhesive layer, thereby obtaining a hot melt adhesive film with high metal adhesion and high hydrolysis resistance.

[0093] This technical solution improves the adhesion of the hot melt adhesive layer to the substrate surface by performing corona treatment, thereby enhancing the adhesion of metals.

[0094] The application of hot melt adhesive films with high metal adhesion and high hydrolysis resistance in the preparation of flexible flat cables involves the following steps: Take two uncured hot melt adhesive films and place their hot melt adhesive layers opposite each other; place a metal conductor between the hot melt adhesive layers of the two uncured hot melt adhesive films; dry the conductor first, then perform hot pressing, cooling, and UV curing in sequence; and finally cut the conductor to obtain a flexible flat cable.

[0095] This technical solution also proposes the application of hot melt adhesive films with high metal adhesion and high hydrolysis resistance in the preparation of flexible flat cables. The specific application method is as follows: take two uncured hot melt adhesive films and place the hot melt adhesive layers of the two uncured hot melt adhesive films opposite each other; place a metal conductor between the hot melt adhesive layers of the two uncured hot melt adhesive films, dry them first, and then perform hot pressing, cooling and UV curing in sequence. After cutting, a flexible flat cable is obtained.

[0096] It should be noted that if the hot melt adhesive film is first UV cured and then wrapped around the metal conductor, it is not easy to achieve the purpose of efficient bonding of the metal conductor. Therefore, in this technical solution, the flexible flat cable is prepared by first wrapping the metal conductor and then UV curing.

[0097] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0098] Performance testing:

[0099] (1) Hot pressing speed: Take two uncured hot melt adhesive films and place the hot melt adhesive layers of the two uncured hot melt adhesive films opposite each other; place a tin-plated flat copper wire with a thickness of 0.035 mm and a width of 0.3 mm between the hot melt adhesive layers of the two uncured hot melt adhesive films, dry it and place it in a flat press machine, and perform hot pressing at a hot pressing temperature of 195℃ and a hot pressing pressure of 0.5 MPa. Record the hot pressing speed when the pre-pressed hot melt adhesive film completely presses the tin-plated flat copper wire.

[0100] (2) Hydrolysis resistance: Take two uncured hot melt adhesive films and place the hot melt adhesive layers of the two uncured hot melt adhesive films opposite each other; place a tin-plated flat copper wire with a thickness of 0.035 mm and a width of 0.3 mm between the hot melt adhesive layers of the two uncured hot melt adhesive films, dry it, and place it in a flatbed press. Hot press it at a temperature of 195℃ and a pressure of 0.5 MPa. After cooling to room temperature, UV cure it. Finally, cut it into flexible flat cables with a length of 200 mm and a width of 25 mm; test the peel strength of the flexible flat cable by placing it in a high-temperature cooking pot at 121℃ for 72 hours using a tensile testing machine with a peel speed of 50 mm / min. If the peel value is greater than 13 N / mm, it is qualified.

[0101] (3) Metal Adhesion: Take two uncured hot melt adhesive films and place their hot melt adhesive layers opposite each other. Place a 0.035mm thick and 0.3mm wide tin-plated flat copper wire between the two uncured hot melt adhesive layers. After drying, place the wire in a flatbed press and hot-press it at a temperature of 195℃ and a pressure of 0.5MPa. After cooling to room temperature, perform UV curing. Finally, cut the wire into a flexible flat cable with a length of 200mm and a width of 25mm. After placing the flexible flat cable at a temperature of 85℃ and a relative humidity of 85% for 1000 hours, test its peel strength using a tensile testing machine with a peel speed of 50mm / min. If the peel value is greater than 10N / 15mm, it is considered qualified.

[0102] Example 1

[0103] A. 50 parts of maleic anhydride-modified polyolefin resin with a softening point of 160℃, 10 parts of maleic anhydride-modified styrene-butadiene rubber with a softening point of 160℃, and 137.5 parts of solvent are stirred at 800 r / min for 8 min to obtain a mixture; wherein, the maleic anhydride-modified polyolefin resin includes maleic anhydride-modified polyethylene resin with a softening point of 135℃ and maleic anhydride-modified homopolymer polypropylene resin with a softening point of 170℃.

[0104] B. Add 60 parts of flame retardant, 15 parts of titanium dioxide, 0.5 parts of 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, and 2 parts of 2-hydroxy-2-methyl-1-phenyl-1-propanone sequentially to the mixture. After stirring, grinding, and filtering, a UV hot melt adhesive is obtained. The stirring speed is 800 r / min, and the stirring time is 10 min. The grinding time is 50 min. The filter mesh size is 200 mesh. The mass ratio of decabromodiphenyl ethane to antimony trioxide in the flame retardant is 9:1. The mass ratio of toluene to ethyl acetate in the solvent is 2:1.

[0105] C. The surface of a 50μm thick PET film is subjected to corona treatment. UV hot melt adhesive is then coated onto the corona-treated PET film surface. After drying and UV curing, a 25μm thick hot melt adhesive layer is formed, resulting in a hot melt adhesive film with high metal adhesion and high hydrolysis resistance. The specific method for the drying step is as follows: the UV hot melt adhesive coated on the surface is dried six times. The drying temperature for the first drying is 70℃, and the drying temperature for the last drying is 170℃. The drying temperature between the first and last drying cycles increases by 20℃ from the first drying temperature to the last drying temperature.

[0106] Example 2

[0107] A. 30 parts of maleic anhydride-modified polyolefin resin with a softening point of 150℃, 2 parts of maleic anhydride-modified hydrogenated styrene-butadiene rubber with a softening point of 150℃, and 85 parts of solvent are stirred at 1000 r / min for 5 min to obtain a mixture; wherein, the maleic anhydride-modified polyolefin resin includes maleic anhydride-modified polyethylene resin with a softening point of 120℃ and maleic anhydride-modified homopolymer polypropylene resin with a softening point of 160℃.

[0108] B. Add 40 parts of flame retardant, 10 parts of titanium dioxide, 1 part of 2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole, and 2 parts of 1-hydroxycyclohexylphenyl ketone sequentially to the mixture. After stirring, grinding, and filtering, a UV hot melt adhesive is obtained. The stirring speed is 1000 r / min, and the stirring time is 8 min. The grinding time is 40 min. The filter screen mesh is 150 mesh. The mass ratio of decabromodiphenyl ethane and antimony trioxide in the flame retardant is 1:1. The mass ratio of toluene and ethyl acetate in the solvent is 2.1:1.

[0109] C. The surface of a 75μm thick PET film is subjected to corona treatment. UV hot melt adhesive is then coated onto the corona-treated PET film surface. After drying and UV curing, a 30μm thick hot melt adhesive layer is formed, resulting in a hot melt adhesive film with high metal adhesion and high hydrolysis resistance. The specific method for the drying step is as follows: the UV hot melt adhesive coated on the surface is dried seven times. The drying temperature for the first drying is 80℃, and the drying temperature for the last drying is 170-180℃. The drying temperature between the first and last drying cycles increases by 15℃ from the first drying temperature to the last drying temperature.

[0110] Example 3

[0111] A. 20 parts of maleic anhydride-modified polyolefin resin with a softening point of 155℃, 1 part of maleic anhydride-modified SBS rubber with a softening point of 155℃, and 74.3 parts of solvent are stirred at 1000 r / min for 5 min to obtain a mixture; wherein, the maleic anhydride-modified polyolefin resin includes maleic anhydride-modified polyethylene resin with a softening point of 120℃ and maleic anhydride-modified homopolymer polypropylene resin with a softening point of 160℃.

[0112] B. 40 parts of flame retardant, 10 parts of titanium dioxide, 0.3 parts of 2-(2'-hydroxy-3',5'-di-tert-butylphenyl)-5-chlorobenzotriazole, and 3 parts of 2-methyl-2-(4-morpholino)-1-[4-(methylthio)phenyl]-1-propanone were sequentially added to a mixture. After stirring, grinding, and filtering, a UV hot melt adhesive was obtained. The stirring speed was 800 r / min, and the stirring time was 8 min. The grinding time was 30 minutes. The filter screen mesh size was 200 mesh. The mass ratio of decabromodiphenyl ethane to antimony trioxide in the flame retardant was 4:1. The mass ratio of toluene to ethyl acetate in the solvent was 2:1.

[0113] C. The surface of a 30μm thick PET film is subjected to corona treatment. UV hot melt adhesive is then coated onto the corona-treated PET film surface. After drying and UV curing, a hot melt adhesive layer with a thickness of 18μm is formed, resulting in a hot melt adhesive film with high metal adhesion and high hydrolysis resistance. The specific method of the drying step is as follows: the UV hot melt adhesive coated on the surface is dried six times. The drying temperature of the first drying is 70℃, and the drying temperature of the last drying is 170℃. The drying temperature between the first and last drying cycles increases by 20℃ from the first drying temperature to the last drying temperature.

[0114] Comparative Example 1

[0115] The preparation methods and raw materials of Comparative Example 1 and Example 2 are the same, except that the resin in the UV hot melt adhesive formulation of Comparative Example 1 is a polyolefin resin with a softening point of 180°C.

[0116] Comparative Example 2

[0117] The preparation methods and raw materials of Comparative Example 2 and Example 2 are the same, except that maleic anhydride modified polyolefin resin was not added to the UV hot melt adhesive formulation of Comparative Example 2.

[0118] Comparative Example 3

[0119] The preparation method and raw materials of Comparative Example 3 are the same as those of Example 2. The difference is that maleic anhydride modified styrene-butadiene rubber was not added to the UV hot melt adhesive formulation of Comparative Example 3.

[0120] Hot melt adhesive films were prepared using the preparation methods described in the above embodiments and comparative examples, and the performance of the hot melt adhesive films was tested. The results are shown in Table 1 below.

[0121] Table 1. Test results of relevant performance of hot melt adhesive film

[0122] Performance testing items Hot pressing speed (m / min) Hydrolysis resistance Adhesive metal properties Example 1 1.3 qualified qualified Example 2 1.2 qualified qualified Example 3 1.4 qualified qualified Comparative Example 1 0.65 qualified Unqualified Comparative Example 2 1.2 Unqualified Unqualified Comparative Example 3 1.2 Unqualified Unqualified

[0123] As can be seen from the test results in Table 1, compared with the hot melt adhesive in the prior art of Comparative Example 1, the hot melt adhesive film prepared by this technical solution has better hot pressing speed, hydrolysis resistance and metal adhesion than Comparative Example 1. The hot melt adhesive film obtained by this technical solution can ensure that it has excellent metal adhesion and hydrolysis resistance while accelerating the hot pressing speed. On the one hand, it can be applied to high temperature and high humidity environments, and on the other hand, it is conducive to ensuring the production efficiency of FFC wire.

[0124] In Comparative Example 2, the lack of maleic anhydride-modified polyolefin resin in the UV hot melt adhesive formulation resulted in the inability to utilize the hydrolysis resistance and metal adhesion properties of the maleic anhydride-modified polyolefin resin. Consequently, the hydrolysis resistance and metal adhesion properties of the hot melt adhesive film in Comparative Example 2 decreased, failing to meet the requirements for use in high temperature and high humidity environments.

[0125] In Comparative Example 3, the lack of maleic anhydride-modified styrene-butadiene rubber in the UV hot melt adhesive formulation resulted in a decrease in the hydrolysis resistance and metal adhesion of the maleic anhydride-modified styrene-butadiene rubber, thus failing to meet the requirements for use in high temperature and high humidity environments.

[0126] It should be noted that the hot melt adhesive film obtained by this technical solution needs to be UV cured. The UV curing step is simply placed in the application process, and the UV curing conditions for preparing flexible flat cables in each embodiment and each comparative example correspond to the UV curing conditions for preparing hot melt adhesive films in each embodiment and each comparative example.

[0127] The technical principles of the present invention have been described above with reference to specific embodiments. These descriptions are merely for explaining the principles of the invention and should not be construed as limiting the scope of protection of the invention in any way. Based on this explanation, those skilled in the art can readily conceive of other specific embodiments of the invention without inventive effort, and these embodiments will all fall within the scope of protection of the present invention.

Claims

1. A hot melt adhesive film with high metal adhesion and high hydrolysis resistance, characterized in that, It includes a substrate and a hot melt adhesive layer connected sequentially from bottom to top, wherein the hot melt adhesive layer is obtained by drying and UV curing a UV hot melt adhesive applied to the substrate; The UV hot melt adhesive comprises, by weight, 20-50 parts of maleic anhydride modified polyolefin resin, 1-10 parts of maleic anhydride modified rubber resin, 1-3 parts of photoinitiator and 30-60 parts of flame retardant. The softening point of the maleic anhydride-modified polyolefin resin is 140–160°C, and the softening point of the maleic anhydride-modified rubber resin is 150–160°C.

2. The hot melt adhesive film with high metal adhesion and high hydrolysis resistance according to claim 1, characterized in that, The mixing ratio of the maleic anhydride modified rubber resin and the maleic anhydride modified polyolefin resin, calculated by mass ratio, is 1:(5-20).

3. The hot melt adhesive film with high metal adhesion and high hydrolysis resistance according to claim 1, characterized in that, The maleic anhydride-modified polyolefin resin includes maleic anhydride-modified polyethylene resin and maleic anhydride-modified homopolymer polypropylene resin. The softening point of the maleic anhydride-modified polyethylene resin is 105–135°C, and the softening point of the maleic anhydride-modified homopolymer polypropylene resin is 160–170°C.

4. The hot melt adhesive film with high metal adhesion and high hydrolysis resistance according to claim 1, characterized in that, The maleic anhydride modified rubber resin includes any one or more combinations of maleic anhydride modified styrene-butadiene rubber, maleic anhydride modified hydrogenated styrene-butadiene rubber, maleic anhydride modified SBS rubber, maleic anhydride modified SEBS rubber, maleic anhydride modified SIS rubber, and maleic anhydride modified SEPS rubber.

5. The hot melt adhesive film with high metal adhesion and high hydrolysis resistance according to claim 1, characterized in that, The flame retardant includes decabromodiphenyl ethane and antimony trioxide; The mixing ratio of the decabromodiphenyl ethane and the antimony trioxide, calculated by mass ratio, is (5-9):(1-5).

6. The hot melt adhesive film with high metal adhesion and high hydrolysis resistance according to claim 1, characterized in that, The UV hot melt adhesive also includes a light stabilizer, titanium dioxide, and a solvent; According to the mass fractions, the UV hot melt adhesive comprises 20-50 parts of maleic anhydride modified polyolefin resin, 1-10 parts of maleic anhydride modified rubber resin, 0.1-2 parts of light stabilizer, 1-3 parts of photoinitiator, 30-60 parts of flame retardant, 5-15 parts of titanium dioxide, and 57.1-140 parts of solvent. The sum of the mass fractions of the maleic anhydride-modified polyolefin resin, the maleic anhydride-modified rubber resin, the light stabilizer, the photoinitiator, the flame retardant, and the titanium dioxide is the same as the mass fraction of the solvent.

7. A method for preparing a hot melt adhesive film with high metal adhesion and high hydrolysis resistance, characterized in that, The method for preparing the hot melt adhesive film with high metal adhesion and high hydrolysis resistance as described in claim 6 includes the following steps: A. After mixing the maleic anhydride-modified polyolefin resin, maleic anhydride-modified rubber resin and solvent in the specified amounts, a mixture is obtained; B. Add the flame retardant, titanium dioxide, light stabilizer and photoinitiator in the specified amounts to the mixture in sequence. After stirring, grinding and filtering, UV hot melt adhesive is obtained. C. Apply UV hot melt adhesive to the surface of the substrate, and after drying and UV curing, a hot melt adhesive layer is formed, resulting in a hot melt adhesive film with high metal adhesion and high hydrolysis resistance.

8. The method for preparing a hot melt adhesive film with high metal adhesion and high hydrolysis resistance according to claim 7, characterized in that, In step C, the specific method for the drying step is as follows: The UV hot melt adhesive coated on the surface is dried multiple times; The drying temperature for the first drying is 70-80℃, and the drying temperature for the last drying is 170-180℃. The drying temperature between the first drying and the last drying increases sequentially by 10-20℃ from the drying temperature of the first drying to the drying temperature of the last drying.

9. The method for preparing a hot melt adhesive film with high metal adhesion and high hydrolysis resistance according to claim 7, characterized in that, Step C specifically involves: performing corona treatment on the surface of the substrate, coating the corona-treated substrate surface with UV hot melt adhesive, and then drying and UV curing to form a hot melt adhesive layer, thereby obtaining a hot melt adhesive film with high metal adhesion and high hydrolysis resistance.

10. The application of hot melt adhesive films with high metal adhesion and high hydrolysis resistance in the preparation of flexible flat cables, characterized in that... The application method of using the hot melt adhesive film with high metal adhesion and high hydrolysis resistance as described in any one of claims 1 to 6 is as follows: take two uncured hot melt adhesive films and place the hot melt adhesive layers of the two uncured hot melt adhesive films opposite each other. A metal conductor is placed between two hot melt adhesive layers of uncured hot melt adhesive films. The conductor is first dried, then hot-pressed, cooled, and UV-cured in sequence. After cutting, a flexible flat cable is obtained.