Migration-resistant film hot-melt adhesive and method for preparing the same

Abstract

This invention belongs to the field of adhesive materials technology, specifically relating to an anti-migration film-type hot melt adhesive and its preparation method. Addressing the current problem that improving anti-migration properties requires increasing crosslinking or hardness, which leads to brittle films and easy cracking at low temperatures, this invention uses a styrene-isoprene-styrene block copolymer as a base material, containing high aspect ratio synthetic mica filler modified with a long-chain alkylsilane coupling agent. Functional masterbatch is prepared through a special process, and during melt extrusion casting, the mica sheets are horizontally oriented and distributed within the film. Subsequently, the surface of the initially formed film is subjected to a gradient penetration coating treatment with photoinitiators, enriching different wavelengths of photoinitiators in the surface and deep layers of the film respectively. The film is then cured stepwise under partitioned UV light in a low-oxygen environment, forming a gradient distribution. Finally, the film is reheated and stress-relieved using a warm water roller and then wound up to obtain the finished product.

Description

Technical Field

[0001] This invention belongs to the field of adhesive materials technology, specifically relating to an anti-migration film-type hot melt adhesive and its preparation method. Background Technology

[0002] Hot melt adhesives for films are widely used in electronic component bonding, optical film lamination, and packaging sealing due to their ease of use and excellent bonding performance (CN121375170A). However, in some applications, adhesive components may migrate or ooze out, leading to interface contamination, performance degradation, and severely affecting product stability. To improve the anti-migration properties of adhesive products, common technical measures include increasing the cross-linking density within the adhesive or increasing the hardness of the adhesive layer, thereby limiting the flow and outward migration of low-molecular-weight components. However, these measures introduce new problems: excessively high cross-linking or overly hard adhesive layers can reduce the flexibility of the adhesive film, resulting in increased brittleness, which is particularly noticeable at low temperatures.

[0003] Other improvements exist in existing technologies, such as adding inorganic fillers to adhesives to hinder component migration, or using a multilayer structure to add a barrier layer on the surface to reduce the exudation of low-molecular-weight substances. However, conventional inorganic fillers often lead to a decline in film performance due to poor compatibility with the organic matrix and uneven dispersion; at the same time, simply adding a barrier layer without effective bonding may cause delamination or peeling problems. Additionally, there is UV-cured hot melt adhesive technology, which improves heat resistance and adhesion by adding photosensitive prepolymers or photoinitiators to the hot melt adhesive formulation and using ultraviolet light to perform overall cross-linking and curing of the adhesive layer. However, traditional UV curing often involves simultaneous irradiation of the entire adhesive layer, which causes high cross-linking throughout the entire adhesive layer, making the film hard and brittle. Furthermore, UV curing requires avoiding oxygen interference and is usually carried out in a nitrogen environment, which increases the complexity of the process.

[0004] In summary, there is an urgent need for a new material formulation and process that can controllably fix or block the low molecular weight components inside the film, while the film as a whole still maintains the necessary flexibility and low temperature resistance. Summary of the Invention

[0005] This invention provides an anti-migration film-type hot melt adhesive and its preparation method. It aims to achieve effective locking and blocking of easily migratable components in the adhesive film through specific formulation design and segmented curing process, thereby solving the problem that traditional methods rely on increasing the overall crosslinking degree, which leads to increased film brittleness and easy cracking in low-temperature environments.

[0006] The specific technical solution is as follows:

[0007] An anti-migration film-type hot melt adhesive and its preparation method are as follows: S1: Preparation of anti-migration functional masterbatch.

[0008] S11: Add dodecyltriethoxysilane to anhydrous ethanol, adjust the pH to 4-5, stir, and obtain a coupling agent hydrolysate; add the coupling agent hydrolysate to dry synthetic mica powder, heat and stir, cool to room temperature, and obtain surface-modified synthetic mica; S12: The surface-modified synthetic mica prepared in S11 is mixed with styrene-isoprene-styrene substrate, melt-extruded, cooled to room temperature, pelletized, and dried to obtain anti-migration functional masterbatch.

[0009] S2: High-shear casting film formation, which involves mixing styrene-isoprene-styrene substrate, C9 petroleum resin, anti-migration functional masterbatch prepared by S12, and antioxidant 1010, melting and extruding, and then cooling and shaping through casting cooling rollers to obtain the initial film.

[0010] S3: Surface gradient penetration.

[0011] S31: Add photoinitiator TPO, photoinitiator 1173, and reactive diluent 1,6-hexanediol diacrylate to a mixed solution of isopropanol and n-hexane in a volume ratio of 9:1, and stir to obtain an initiator solution.

[0012] S32: The initiator solution prepared in S31 is coated onto the primary film prepared in S2 by non-contact ultrasonic spraying, and then dried to obtain a gradient-permeable film.

[0013] S4: UV partition curing and post-treatment. The gradient-penetrating adhesive film prepared in S32 is UV partition cured, cooled to 35°C, warmed by a water roller, cooled to room temperature, and then wound up to obtain a hot melt adhesive film.

[0014] Furthermore, the dodecyltriethoxysilane described in S11 has a mass of 1% to 3% of the mass of the synthesized mica powder.

[0015] The heating and stirring described in S11 has the following parameters: temperature 100-110℃, rotation speed 500-1500rpm, and duration 30-60min.

[0016] The surface-modified synthetic mica described in S12 has a mass ratio of 1:4 to a styrene-isoprene-styrene substrate.

[0017] The melt extrusion described in S12 has the following parameter settings: Zone 1 temperature 155~165℃, Zone 2 temperature 165~175℃, Zone 3 temperature 170~180℃, Die head temperature 175~185℃, and Screw speed 200~400rpm.

[0018] The drying process described in S12 has the following parameters: temperature 50-60℃, duration 2-4h.

[0019] Furthermore, the melt extrusion described in S2 has the following parameter settings: Zone 1 temperature 135-145℃, Zone 2 temperature 150-160℃, Zone 3 temperature 160-170℃, and die head temperature 165-175℃.

[0020] The casting cooling roller described in S2 has constant temperature circulating cooling water inside, and the roller surface temperature is 30°C.

[0021] The stretching ratio of the traction roller linear velocity to the melt flow velocity at the die lip, as described in S2, is 4 to 6.

[0022] The initial film described in S2 has the following composition of raw materials: based on 100 parts of styrene-isoprene-styrene substrate, 60-120 parts of C9 petroleum resin, 10-40 parts of anti-migration functional masterbatch, and 0.5-2 parts of antioxidant 1010.

[0023] Furthermore, the photoinitiator TPO described in S31 has a mass ratio of 1:1 to 3:1 with the photoinitiator 1173.

[0024] The reactive diluent 1,6-hexanediol diacrylate described in S31 accounts for 30% to 70% of the total mass of the solute.

[0025] The initiator solution described in S31, wherein the total mass percentage of photoinitiator TPO, photoinitiator 1173, and reactive diluent 1,6-hexanediol diacrylate is 1%.

[0026] The non-contact ultrasonic spray described in S32 has the following parameter settings: atomization frequency 100-200kHz, solution flow rate 0.5-2mL / min, spray height 5-15cm, and film travel speed 5-15m / min.

[0027] The drying process described in S32 has the following parameters: temperature 40℃, duration 20s.

[0028] Furthermore, the UV zone curing described in S4 uses LED lamps with an oxygen concentration of <200ppm. It first enters the first zone, then the second zone. The parameter settings are as follows: first zone wavelength 395nm, energy density 50–200mJ / cm³. 2 Peak irradiance 100–300 mW / cm 2 Duration 0.5–2 s; second region wavelength 365 nm, energy density 500–1500 mJ / cm² 2 Peak irradiance 1000–2000 mW / cm 2 Duration: 0.5–1 second.

[0029] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention constructs a multi-layered and highly efficient anti-migration barrier by combining the physical barrier of mica with UV-induced gradient chemical cross-linking, thereby inhibiting the migration of small molecules.

[0030] 2. This invention induces mica orientation through high-ratio stretching, achieves micron-level gradient penetration of initiators through ultrasonic spraying, and precisely controls the crosslinking density distribution through zoned UV curing. Attached Figure Description

[0031] Figure 1 This is a process flow diagram for the preparation of an anti-migration film-type hot melt adhesive.

[0032] Figure 2 This is a microscopic morphology diagram of the hot melt adhesive film finally prepared in Example 1.

[0033] Figure 3 This is the Raman spectrum of the hot melt adhesive film finally prepared in Example 1.

[0034] Figure 4 This is the normalized Raman spectrum curve of the hot melt adhesive film finally prepared in Example 1. Detailed Implementation

[0035] The following embodiments further explain and illustrate the technical solutions of the present invention. It should be specifically noted that each specific embodiment is a concretization and explanation of the technical solution and should not be considered as a limitation on the scope of protection of the present invention. Those skilled in the art still have the right to modify the technical solutions of these embodiments and make equivalent substitutions for some or all of the technical features, and these modifications or substitutions do not change the essence of the corresponding technical solutions, nor do they cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions described in the present invention.

[0036] This invention proposes an anti-migration film-type hot melt adhesive and its preparation method, solving the problem that increasing the degree of crosslinking or hardness can lead to brittle adhesive films that are prone to cracking at low temperatures. (See attached diagram) Figure 1 The image shows a method for preparing an anti-migration film-type hot melt adhesive, the detailed technical solution of which is as follows: 1. Preparation of anti-migration functional masterbatch Dodecyltriethoxysilane was added to anhydrous ethanol, the pH was adjusted, and the mixture was stirred to obtain a coupling agent hydrolysate. The coupling agent hydrolysate was added to dry synthetic mica powder, heated and stirred, and then cooled to room temperature to obtain surface-modified synthetic mica. The surface-modified synthetic mica was mixed with styrene-isoprene-styrene (SIS) substrate, melt-extruded, cooled to room temperature, granulated, and dried to obtain anti-migration functional masterbatch.

[0037] High aspect ratio synthetic mica is used as the core filler. Its lamellar structure is designed to oriented through shear force during film casting, forming a "maze effect" within the film to extend the diffusion path of small molecule migrants, thereby improving anti-migration properties. Long-chain alkylsilane coupling agents are used to surface-treat the mica. After hydrolysis, the alkoxy groups form covalent bonds with the hydroxyl groups on the mica surface, while the dodecyl chains at the other end physically entangle and bind with the SIS matrix during melt processing. This improves the interfacial compatibility between inorganic mica and organic resin, prevents mica agglomeration, and ensures its nanoscale dispersion in the matrix. Instead of directly adding the entire amount of mica to the final formulation, a concentrated masterbatch is first prepared with a portion of the SIS. This ensures that the mica is fully dispersed under the high shear of a twin-screw extruder. Furthermore, only the masterbatch needs to be simply mixed in during final film formation, simplifying the process and ensuring the stability of the mica dispersion quality.

[0038] 2. High-shear casting film formation Styrene-isoprene-styrene substrate, C9 petroleum resin, anti-migration functional masterbatch, and antioxidant 1010 are mixed, melt-extruded, and then cooled and shaped by casting and cooling rollers to obtain a primary film.

[0039] When the functional masterbatch melt containing high aspect ratio mica flakes flows through a slit die and is subsequently stretched by a high-speed traction roller, the melt is subjected to enormous shear stress and tensile stress. Under this stress field, its planar orientation is highly ordered along the melt flow direction and the film planar direction. This horizontal orientation structure forms a layered physical barrier layer inside the film, extending the diffusion path of small molecule migrants. After leaving the die, the melt is rapidly adhered to a low-temperature cooling roller, and its heat is quickly carried away, causing the SIS to rapidly cool from the molten state to below the glass transition temperature. This process instantly freezes the orientation structure of the mica and the molecular chain conformation of the polymer, preventing a decrease in orientation due to relaxation. By precisely controlling the stretching ratio, the orientation degree of the polymer molecular chains and mica flake layers is regulated. Appropriate orientation can establish an effective barrier network while avoiding excessive stretching that would cause the molecular chains to be excessively straightened and internal stress to be too high, thus preserving the necessary toughness and elasticity of the film.

[0040] 3. Surface gradient penetration Photoinitiator TPO, photoinitiator 1173, and reactive diluent 1,6-hexanediol diacrylate (HDDA) were added to a mixed solution of isopropanol and n-hexane in a volume ratio of 9:1 and stirred to obtain an initiator solution. The initiator solution was then coated onto the primary film using non-contact ultrasonic spraying and dried at 40°C to obtain a gradient-penetrated adhesive.

[0041] The photoinitiator TPO has a large molecular weight and strong lipid solubility, exhibiting excellent compatibility with SIS / tackifying resin systems. Upon heating, it continuously diffuses deep into the film. The photoinitiator 1173 has a smaller molecular weight and some hydrophilicity, resulting in relatively greater diffusion resistance in non-polar film systems, making it more likely to remain near the surface. The reactive diluent 1,6-hexanediol diacrylate, as a small-molecule acrylate, is both a good solvent for the initiator and can participate in subsequent UV curing reactions, carrying initiator molecules along with the diffusion and adjusting the viscosity of the mixture. Isopropanol has good solubility for both initiators and can slightly swell the film surface, opening channels for initiator penetration. Hexane is highly compatible with the film matrix, has a lower boiling point, and preferentially evaporates. The combination of these two initiators ensures uniform coating while, due to differences in evaporation rate and interaction forces with the film, inducing non-uniform diffusion of the initiator upon heating. Ultrasonic spraying is used to generate micron-sized droplets to achieve an ultra-thin and uniform coating. During drying, if the temperature is too high, the initiator and solvent will penetrate too quickly and too deeply, and the gradient will be smoothed out. If the temperature is too low, the penetration will be insufficient, resulting in a gradient distribution with enrichment of photoinitiator 1173 on the surface, mixing of photoinitiator TPO and photoinitiator 1173 in the subsurface layer, and photoinitiator TPO as the main component in the deep layer.

[0042] 4. UV zone curing and post-treatment The gradient-penetrated adhesive film is UV-cured in sections, cooled to 35°C, warmed by a water roller, cooled to room temperature, and then wound up to obtain a hot melt adhesive film.

[0043] Oxygen in the air is a highly efficient inhibitor of free radical polymerization, consuming surface free radicals and leading to incomplete curing, sticky surfaces, and a non-dense protective shell. Reducing the oxygen concentration in the curing environment to below 200 ppm can greatly eliminate the oxygen inhibition effect, ensuring the rapid formation of a dense layer with high cross-linking density during high-energy curing of the surface layer. The photoinitiator TPO has strong absorption at long wavelengths, while photoinitiator 1173 has weak absorption in this region. Using a low-energy 395nm light source can gently and selectively activate TPO molecules that have penetrated deeper into the film, initiating deep and internal polymerization and cross-linking. Low energy avoids excessive reaction and heat accumulation of the surface photoinitiator 1173, ensuring the formation of a moderate and uniform cross-linking network internally, enhancing cohesion without causing embrittlement; photoinitiator 1173 has strong absorption in the 330–365nm range. Using a high-energy 365nm light source can quickly and thoroughly activate the 1173 molecules enriched on the surface of the film. At high energy density, the surface active diluent HDDA and the polymer unsaturated bonds undergo rapid free radical polymerization, forming a highly dense cross-linked network in a short time, constituting a hard "anti-migration protective shell".

[0044] Table 1 Main Raw Materials

[0045] Example 1 A method for preparing an anti-migration film-type hot melt adhesive is as follows: S1: Preparation of anti-migration functional masterbatch.

[0046] S11: Add dodecyltriethoxysilane to anhydrous ethanol, adjust the pH to 4.5, stir, and obtain a coupling agent hydrolysate; add the coupling agent hydrolysate to dry synthetic mica powder, heat and stir, cool to room temperature, and obtain surface-modified synthetic mica; wherein, the mass of dodecyltriethoxysilane is 2% of the mass of synthetic mica powder; the heating and stirring parameters are set as follows: temperature 105℃, speed 1000rpm, duration 45min.

[0047] S12: The surface-modified synthetic mica prepared in S11 was mixed with a styrene-isoprene-styrene substrate, melt-extruded, cooled to room temperature, pelletized, and dried to obtain an anti-migration functional masterbatch. The mass ratio of the surface-modified synthetic mica to the styrene-isoprene-styrene substrate was 1:4. The melt extrusion parameters were: zone 1 temperature 160℃, zone 2 temperature 170℃, zone 3 temperature 175℃, die head temperature 180℃, and screw speed 300 rpm. The drying parameters were: temperature 55℃, drying time 3 hours.

[0048] S2: High-shear casting film formation involves mixing styrene-isoprene-styrene substrate, C9 petroleum resin, anti-migration functional masterbatch prepared by S12, and antioxidant 1010, followed by melt extrusion and cooling and shaping through a casting cooling roller (roller surface temperature 30℃) while being stretched and shaped to obtain a preliminary film. The melt extrusion parameters are set as follows: zone 1 temperature 140℃, zone 2 temperature 155℃, zone 3 temperature 165℃, and die head temperature 170℃. The stretching ratio between the traction roller linear speed and the melt flow rate at the die lip is 5. The composition of the raw materials for the preliminary film is as follows: based on 100g of styrene-isoprene-styrene substrate, 90g of C9 petroleum resin, 25g of anti-migration functional masterbatch, and 1.3g of antioxidant 1010.

[0049] S3: Surface gradient penetration.

[0050] S31: Photoinitiator TPO, photoinitiator 1173, and reactive diluent 1,6-hexanediol diacrylate are added to a mixed solution of isopropanol and n-hexane in a volume ratio of 9:1, and stirred to obtain an initiator solution. The mass ratio of photoinitiator TPO to photoinitiator 1173 is 2:1; the reactive diluent 1,6-hexanediol diacrylate accounts for 50% of the total solute mass; and the total mass percentage of photoinitiator TPO, photoinitiator 1173, and reactive diluent 1,6-hexanediol diacrylate is 1%.

[0051] S32: The initiator solution prepared in S31 is coated onto the primary membrane prepared in S2 using non-contact ultrasonic spraying, and then dried at 40℃ for 20s to obtain a gradient-permeable membrane. The non-contact ultrasonic spraying parameters are set as follows: atomization frequency 150kHz, solution flow rate 1.2mL / min, spray height 10cm, and membrane travel speed 10m / min.

[0052] S4: UV zone curing and post-treatment. The gradient-penetrating adhesive film prepared in S32 is subjected to UV zone curing, cooled to 35℃, warmed by a water roller, cooled to room temperature, and then wound up to obtain a hot melt adhesive film. For the UV zone curing, LED lamps are used, with an oxygen concentration of <200ppm. The curing proceeds first to the first zone, then to the second zone. The parameters are set as follows: first zone wavelength 395nm, energy density 125mJ / cm². 2 Peak irradiance 200mW / cm 2 Duration 1.3s; second region wavelength 365nm, energy density 1000mJ / cm² 2 Peak irradiance 1500 mW / cm 2 Duration: 0.7s.

[0053] Example 2 The composition and preparation process are the same as in Example 1, except that: In the preparation process, S11 has a pH of 4, the mass of dodecyltriethoxysilane is 1% of the mass of the synthesized mica powder, and the other components are the same.

[0054] The heating and stirring parameters in step S11 of the preparation process are set as follows: temperature 100℃, rotation speed 500rpm, duration 30min, and other steps are the same.

[0055] The melt extrusion parameters for the S12 preparation process are set as follows: Zone 1 temperature 155℃, Zone 2 temperature 165℃, Zone 3 temperature 170℃, die head temperature 175℃, screw speed 200rpm. The drying parameters are set as follows: temperature 50℃, duration 2h, and other components are the same.

[0056] The melt extrusion parameters in S2 of the preparation process are set as follows: Zone 1 temperature 135℃, Zone 2 temperature 150℃, Zone 3 temperature 160℃, die head temperature 165℃, and the stretching ratio of the traction stretching is 4. Other steps are the same.

[0057] The initial membrane of S2 prepared by the process has the following composition of raw materials: based on 100g of styrene-isoprene-styrene substrate, 60g of C9 petroleum resin, 10g of anti-migration functional masterbatch, and 0.5g of antioxidant 1010, with other components being the same.

[0058] In the preparation process S31, the mass ratio of photoinitiator TPO to photoinitiator 1173 is 1:1, and the reactive diluent 1,6-hexanediol diacrylate accounts for 30% of the total mass of the solute. The other components are the same.

[0059] The non-contact ultrasonic spray parameters in step S32 of the preparation process are set as follows: atomization frequency 100kHz, solution flow rate 0.5mL / min, spray height 5cm, film flow rate 5m / min, and other steps are the same.

[0060] UV zone curing parameters in S4 of the preparation process are set as follows: first zone wavelength 395nm, energy density 50mJ / cm². 2 Peak irradiance 100mW / cm 2 Duration: 0.5s; Second region wavelength: 365nm; Energy density: 500mJ / cm³ 2 Peak irradiance 1000mW / cm 2 The duration is 0.5 seconds, and the other steps are the same.

[0061] Example 3 The composition and preparation process are the same as in Example 1, except that: In the preparation process, S11 has a pH value of 5, the mass of dodecyltriethoxysilane is 3% of the mass of the synthesized mica powder, and the other components are the same.

[0062] The temperature and stirring parameters in step S11 of the preparation process are set as follows: temperature 110℃, rotation speed 1500rpm, duration 60min, and other steps are the same.

[0063] The melt extrusion parameters for the S12 preparation process are set as follows: Zone 1 temperature 165℃, Zone 2 temperature 175℃, Zone 3 temperature 180℃, die head temperature 185℃, screw speed 400rpm. The drying parameters are set as follows: temperature 60℃, duration 4h, and other components are the same.

[0064] The melt extrusion parameters in S2 of the preparation process are set as follows: Zone 1 temperature 145℃, Zone 2 temperature 160℃, Zone 3 temperature 170℃, die head temperature 175℃, and the stretching ratio of the traction stretching is 6. Other steps are the same.

[0065] The initial membrane of S2 prepared by the process has the following composition of raw materials: based on 100g of styrene-isoprene-styrene substrate, 120g of C9 petroleum resin, 40g of anti-migration functional masterbatch, and 2g of antioxidant 1010, with other components being the same.

[0066] In the preparation process S31, the mass ratio of photoinitiator TPO to photoinitiator 1173 is 3:1, and the reactive diluent 1,6-hexanediol diacrylate accounts for 70% of the total mass of the solute. The other components are the same.

[0067] The non-contact ultrasonic spray parameters in step S32 of the preparation process are set as follows: atomization frequency 200kHz, solution flow rate 2mL / min, spray height 15cm, film flow rate 15m / min, and other steps are the same.

[0068] UV zone curing parameters in S4 of the preparation process are set as follows: first zone wavelength 395nm, energy density 200mJ / cm². 2 Peak irradiance 300mW / cm 2 Duration: 2 seconds; Second region wavelength: 365 nm; Energy density: 1500 mJ / cm³ 2 Peak irradiance 2000mW / cm 2 The duration is 1 second, and the other steps are the same.

[0069] Example 4 The composition and preparation process are the same as in Example 1, except that: In the preparation process S11, the pH value was 4.3, the mass of dodecyltriethoxysilane was 2.5% of the mass of the synthesized mica powder, and the other components were the same.

[0070] The heating and stirring parameters in step S11 of the preparation process are set as follows: temperature 108℃, rotation speed 1200rpm, duration 35min, and other steps are the same.

[0071] The melt extrusion parameters for the S12 preparation process are set as follows: Zone 1 temperature 163℃, Zone 2 temperature 167℃, Zone 3 temperature 172℃, die head temperature 181℃, screw speed 350rpm. The drying parameters are set as follows: temperature 52℃, duration 3.5h. Other components are the same.

[0072] The melt extrusion parameters in S2 of the preparation process are set as follows: Zone 1 temperature 141℃, Zone 2 temperature 152℃, Zone 3 temperature 167℃, die head temperature 172℃, and the stretching ratio of the traction stretching is 4.5. Other steps are the same.

[0073] The initial membrane of S2 prepared by the process has the following composition of raw materials: based on 100g of styrene-isoprene-styrene substrate, 100g of C9 petroleum resin, 35g of anti-migration functional masterbatch, and 1.8g of antioxidant 1010, with other components being the same.

[0074] In the preparation process S31, the mass ratio of photoinitiator TPO to photoinitiator 1173 is 2.5:1, and the reactive diluent 1,6-hexanediol diacrylate accounts for 55% of the total mass of the solute. The other components are the same.

[0075] In the preparation process S32, the non-contact ultrasonic spray parameters are set as follows: atomization frequency 100-200kHz, solution flow rate 1.6mL / min, spray height 8cm, film flow rate 12m / min, and other steps are the same.

[0076] UV zone curing parameters in S4 of the preparation process are set as follows: first zone wavelength 395nm, energy density 150mJ / cm². 2 Peak irradiance 250mW / cm 2 Duration: 0.6s; Second region wavelength: 365nm; Energy density: 1200mJ / cm³ 2 Peak irradiance 1200mW / cm 2 The duration is 0.9 seconds, and the other steps are the same.

[0077] Comparative Example 1 The composition and preparation process are the same as in Example 1, except that: In step S2 of the preparation process, the anti-migration functional masterbatch is removed and replaced with ordinary unmodified mica (aspect ratio 50), while the other steps remain the same.

[0078] Comparative Example 2 The composition and preparation process are the same as in Example 1, except that: In step S3 of the preparation process, UV partitioning curing is removed, and a single high-energy UV zone (1000 mJ / cm²) is used instead. 2 The curing process is performed in one step, and the other steps are the same.

[0079] Samples of the hot melt adhesive film prepared in Example 1 were taken and cut along the mechanical direction (5mm × 5mm). The samples were fixed on the sample stage and cooled with liquid nitrogen throughout. The cross-section of the samples was polished using an argon ion beam, followed by gold sputtering. Observation was performed using a field emission scanning electron microscope (equipped with a backscattered electron detector) (accelerating voltage 8kV, working distance 8mm). Figure 2As shown, the mica sheets exhibit a highly ordered parallel arrangement within the SIS matrix, with the long axis of the sheets parallel to the film surface. This demonstrates the "maze effect" created by high-shear casting. The mica sheets show good individual dispersion with no obvious agglomerates. Furthermore, the bond between the mica and the SIS matrix is ​​tight, with no obvious voids or gaps. This indicates that the long-chain alkylsilane coupling agent improves the compatibility between the mica and the SIS resin, prevents agglomeration, and enhances interfacial bonding. Moreover, the mica sheets maintain a high aspect ratio without severe breakage, indicating that shear orientation was achieved during twin-screw extrusion and casting while avoiding excessive shearing that could lead to sheet breakage. The top layer of the film is an extremely thin and continuous dense layer, which is due to the photoinitiator 1173 and the reactive diluent HDDA enriched on the surface. Under 365nm high-energy UV light irradiation, these substances rapidly undergo free radical polymerization, forming a highly cross-linked, migration-resistant protective shell.

[0080] Samples of the hot melt adhesive film prepared in Example 1 were taken and tested using a laser confocal Raman microscope (wavelength 785 nm, confocal pinhole 50 μm, scanning step size 1 μm, scanning range 0–80 μm). Figure 3 and Figure 4 As shown, in Figure 3 In the image, the characteristic peak of photoinitiator 1173 is due to the carbonyl C=O vibration. This characteristic peak gradually disappears with increasing depth. Meanwhile, in... Figure 4 In the middle, the normalized signal of photoinitiator 1173 reaches its maximum value at the surface, then drops sharply in the 0-10 μm range, and decays to almost zero after a depth of 20 μm, indicating that photoinitiator 1173 is mainly enriched on the surface; in Figure 3 In the image, the characteristic peak of the photoinitiator TPO is the P=O double bond stretching vibration peak, and its characteristic peak gradually appears with increasing depth. Figure 4 In the middle layer, the signal intensity of photoinitiator TPO is low on the surface. As the depth increases, the signal shows a gradual or even slightly increasing trend, and maintains a stable high concentration distribution in the deep layer, indicating that photoinitiator TPO penetrates into the deep layer.

[0081] Based on Examples 1-4 and Comparative Examples 1-2, samples of the final prepared hot melt adhesive film were taken for mass loss rate testing: a sample of hot melt adhesive film (50mm×50mm) was cut and weighed, and the weight of aluminum foil (60mm×60mm) was recorded as m. The hot melt adhesive film was tightly adhered to the aluminum foil, and the sample mass was obtained by subtracting the aluminum foil mass from the original mass, which was recorded as M1. The sample was then aged at 70℃ for 7 days. After being removed and cooled to room temperature, the adhesive film and aluminum foil were separated, and the mass of the cooled adhesive film was recorded as M2. The results were calculated, and 5 groups of tests were conducted, and the average value was taken.

[0082] Based on Examples 1-4 and Comparative Examples 1-2, samples of the final prepared hot melt adhesive film were taken for bending crack rate testing: samples (100mm×25mm) were cut along the mechanical direction and longitudinal direction, and then placed in a constant temperature environment of -25℃ for 2h. The samples were taken out and placed with the test side facing outward (i.e. the side in contact with the outside world). The samples were quickly placed on the bending fixture, and the center line of the sample was aligned with the metal cylindrical shaft (diameter 6mm) of the fixture. The samples were quickly folded 180° to align the two ends. A constant pressure (500g weight, duration 3s) was applied to the crease through the pressure head. The samples were unfolded to restore the flat state and observed for cracking. 100 sets of tests were conducted (50 samples each in the mechanical direction and longitudinal direction). Cracking criteria: (1) Fine cracks with a length of less than 1mm are visible under a 10x magnifying glass, (2) Cracks with a length of ≥1mm are visible to the naked eye, or breakage occurs.

[0083] The specific test results are shown in Table 2. Figure 2 , Figure 3 , Figure 4 As shown: Table 2 Comparison of core performance of Examples 1-4 and Comparative Examples 1-2

[0084] The comparison results above show that Example 1 exhibits the best anti-migration properties. The mica modification forms a robust interface, and no cracks were observed during bending at -25°C, thanks to the UV gradient curing process. This indicates that Example 1 successfully resolved the contradiction between anti-migration properties and low-temperature toughness. Examples 2 to 4 show slightly lower anti-migration and bending cracking performance compared to Example 1, but still maintain a high level. This demonstrates that excellent performance balance was achieved even with a wide range of parameter variations. Comparative Example 1 did not use anti-migration masterbatch, thus failing to form an effective barrier. Small molecules easily migrated out, resulting in complete failure of anti-migration properties. Although the cracking rate was extremely low due to the lack of reinforcement and toughening, the overall performance balance failed. Comparative Example 2 used a single high-energy curing method, leading to excessive and uneven cross-linking, extreme embrittlement of the film, and fully highlighting the low-temperature cracking problem. However, due to the use of the anti-migration masterbatch from Example 1, its anti-migration performance was relatively good.

[0085] In summary, it can be clearly seen from the above embodiments and comparative examples that the anti-migration film-type hot melt adhesive provided by the present invention has achieved good results in terms of anti-migration performance and low-temperature toughness. This is attributed to the surface modification of mica barrier and UV gradient curing, thereby solving the performance balance problem of film-type hot melt adhesives.

Claims

1. An anti-migration film-type hot melt adhesive, comprising a substrate and additives, characterized in that: The anti-migration film-type hot melt adhesive has a multi-layer cross-linked structure, consisting of a primary film made of styrene-isoprene-styrene substrate, C9 petroleum resin, anti-migration functional masterbatch, and antioxidant 1010, and a cured shell layer formed on the surface of the primary film; the cured shell layer is formed by photo-induced cross-linking, and the cross-linking density is gradient-distributed from high to low in the direction from the cured shell layer to the interior of the primary film.

2. The anti-migration film-type hot melt adhesive according to claim 1, characterized in that: The initial film has the following raw material ratios: based on 100 parts of styrene-isoprene-styrene substrate, 60-120 parts of C9 petroleum resin, 10-40 parts of anti-migration functional masterbatch, and 0.5-2 parts of antioxidant 1010.

3. The anti-migration film-type hot melt adhesive according to claim 1, characterized in that: The anti-migration functional masterbatch is composed of surface-modified synthetic mica and styrene-isoprene-styrene substrate; the mass ratio of the surface-modified synthetic mica to the styrene-isoprene-styrene substrate is 1:

4.

4. The anti-migration film-type hot melt adhesive according to claim 1, characterized in that: The photo-induced crosslinking is triggered by a composite photoinitiator, which consists of photoinitiator TPO, photoinitiator 1173, and reactive diluent 1,6-hexanediol diacrylate. The mass ratio of photoinitiator TPO to photoinitiator 1173 is 1:1 to 3:1, and the reactive diluent 1,6-hexanediol diacrylate accounts for 30% to 70% of the total mass of the solute. The gradient distribution is caused by the difference in the distribution of the composite photoinitiator. Specifically, the cured shell layer is crosslinked by photoinitiator 1173, the interior of the primary film is crosslinked by photoinitiator TPO, and the crosslinking between the cured shell layer and the interior of the primary film is initiated by a mixture of photoinitiator 1173 and photoinitiator TPO.

5. The anti-migration film-type hot melt adhesive according to claim 1, characterized in that... The mass loss rate of the film-type hot melt adhesive after aging at 70°C for 168 hours is ≤2%.

6. A method for preparing the anti-migration film-type hot melt adhesive according to any one of claims 1-5, characterized in that, Includes the following steps: S1: Preparation of anti-migration functional masterbatch; S11: Add dodecyltriethoxysilane to anhydrous ethanol, adjust the pH to 4-5, stir, and obtain a coupling agent hydrolysate; add the coupling agent hydrolysate to dry synthetic mica powder, heat and stir, cool to room temperature, and obtain surface-modified synthetic mica; S12: The surface-modified synthetic mica prepared in S11 is mixed with styrene-isoprene-styrene substrate, melt-extruded, cooled to room temperature, pelletized, and dried to obtain anti-migration functional masterbatch; S2: High shear casting film formation, styrene-isoprene-styrene substrate, C9 petroleum resin, anti-migration functional masterbatch prepared by S12, antioxidant 1010 are mixed, melt extruded, and then cooled and shaped by casting cooling rollers to obtain the initial film. S3: Surface gradient penetration; S31: Add photoinitiator TPO, photoinitiator 1173, and reactive diluent 1,6-hexanediol diacrylate to a mixed solution of isopropanol and n-hexane in a volume ratio of 9:1, stir, and obtain an initiator solution; S32: The initiator solution prepared in S31 is coated onto the primary film prepared in S2 by non-contact ultrasonic spraying, and then dried to obtain a gradient-permeable film. S4: UV partition curing and post-treatment. The gradient-penetrating adhesive film prepared in S32 is UV partition cured, cooled to 35°C, warmed by a water roller, cooled to room temperature, and then wound up to obtain a hot melt adhesive film.

7. The method for preparing an anti-migration film-type hot melt adhesive according to claim 6, characterized in that: The dodecyltriethoxysilane described in S11 has a mass of 1% to 3% of the mass of the synthesized mica powder; The heating and stirring described in S11 has the following parameters: temperature 100-110℃, rotation speed 500-1500rpm, and duration 30-60min. The melt extrusion described in S12 has the following parameter settings: Zone 1 temperature 155~165℃, Zone 2 temperature 165~175℃, Zone 3 temperature 170~180℃, Die head temperature 175~185℃, and Screw speed 200~400rpm. The drying process described in S12 has the following parameters: temperature 50-60℃, duration 2-4h.

8. The method for preparing an anti-migration film-type hot melt adhesive according to claim 6, characterized in that: The melt extrusion described in S2 has the following parameter settings: Zone 1 temperature 135-145℃, Zone 2 temperature 150-160℃, Zone 3 temperature 160-170℃, and die head temperature 165-175℃. The casting cooling roller described in S2 has constant temperature circulating cooling water inside, and the roller surface temperature is 30°C. The stretching ratio of the traction roller linear velocity to the melt flow velocity at the die lip, as described in S2, is 4 to 6.

9. A method for preparing an anti-migration film-type hot melt adhesive according to claim 6, characterized in that: The initiator solution described in S31, wherein the total mass percentage of photoinitiator TPO, photoinitiator 1173, and reactive diluent 1,6-hexanediol diacrylate is 1%; The non-contact ultrasonic spray described in S32 has the following parameter settings: atomization frequency 100-200kHz, solution flow rate 0.5-2mL / min, spray height 5-15cm, and film travel speed 5-15m / min. The drying process described in S32 has the following parameters: temperature 40℃, duration 20s.

10. A method for preparing an anti-migration film-type hot melt adhesive according to claim 6, characterized in that: The UV zone curing described in S4 uses LED lamps with an oxygen concentration of <200ppm. It first enters the first zone, then the second zone. The parameter settings are: first zone wavelength 395nm, energy density 50–200mJ / cm³. 2 Peak irradiance 100–300 mW / cm 2 Duration 0.5–2 s; second region wavelength 365 nm, energy density 500–1500 mJ / cm² 2 Peak irradiance 1000–2000 mW / cm 2 Duration: 0.5–1 second.

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