Electrically detachable acrylate modified polyurethane hot melt adhesive, preparation method and application thereof

Abstract

The application belongs to the field of adhesives, and relates to a kind of electrically detachable acrylate modified polyurethane hot melt adhesive as well as a preparation method and application thereof.The electrically detachable acrylate modified polyurethane hot melt adhesive contains polyurethane prepolymer mixture, ionic liquid, acrylate compound and photoinitiator.The two ends of the prepolymer contained in the polyurethane prepolymer mixture are capped with isocyanate.The isocyanate structural units contained in the polyurethane prepolymer mixture are derived from low-viscosity low-free polyurethane prepolymer, and the polyol structural units are derived from low-viscosity polyol compound with a glass transition temperature below 0 DEG C and a melting point below 40 DEG C.The polyurethane hot melt adhesive provided by the application has low free isocyanate content, low melt viscosity, can be dispensed at room temperature, has high initial bonding strength and final bonding strength, fast curing speed and electrically detachable performance, and has wide practical application prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of adhesives, and particularly relates to a kind of electrically detachable acrylate modified polyurethane hot melt adhesive and its preparation method and application. BACKGROUND

[0002] In the electronic products such as smart phones, tablet computers, smart watches and TWS earphones, reactive polyurethane hot melt adhesives are often used to bond and fix the parts of electronic products. The parts of electronic products bonded by reactive polyurethane hot melt adhesives often have high value. When there are problems such as poor assembly, product after-sales repair and recycling of valuable electronic product parts, the bonded parts often need to be disassembled. Therefore, the adhesive is usually required to have excellent bonding reliability and easy disassembly function under certain conditions.

[0003] Reactive polyurethane hot melt adhesives mainly use isocyanate-terminated oligomers as the main body. The isocyanate groups in the isocyanate-terminated oligomers can react with moisture in the air. After complete curing, a cross-linked chemical structure can be formed, thereby achieving high bonding strength. However, the covalent bond obtained by the reaction of isocyanate groups with moisture is irreversible, and the cross-linked structure is difficult to be destroyed. After complete curing, it is usually difficult to disassemble the adhesive. If the bonded materials need to be separated, it is often necessary to use large external force, high temperature, chemical reagents and other conditions. In the process of disassembling the adhesive, the bonded materials may be damaged, causing great economic loss.

[0004] In recent years, some technologies have added ionic liquids or alkali metal salts and solventized matrices to polyurethane hot melt adhesives to give polyurethane hot melt adhesives that can be disassembled under the condition of electricity. However, the existing electrically disassemblable polyurethane hot melt adhesives have the function of being disassembled under the condition of electricity. However, due to the high melt viscosity of such polyurethane hot melt adhesives, they are solid substances at room temperature, which are difficult to apply at room temperature. Generally, they need to be heated to a melt temperature (usually 90℃-160℃) or higher to be extruded and applied. At this time, it is usually necessary to use professional heating and application equipment. However, this not only increases the cost of using the adhesive, but also greatly limits the application scenarios of such polyurethane hot melt adhesives. For example, such polyurethane hot melt adhesives cannot be used in places where it is inconvenient to provide heating equipment, such as homes and repair markets, thereby greatly limiting the widespread application of such one-component polyurethane hot melt adhesives.

[0005] The low-viscosity polyurethane hot melt adhesive that can be applied at room temperature in the prior art usually needs to add a large excess of isocyanate monomer to reduce the viscosity. Although adding a large amount of isocyanate monomer can reduce the viscosity to a lower level, the large amount of residual free isocyanate monomer in the adhesive system is harmful to human health, not only stimulates the respiratory tract, but also has the risk of causing cancer, which is not conducive to human health. At the same time, the low-viscosity polyurethane hot melt adhesive that can be applied at room temperature has a slow curing speed and a low initial bonding strength, and has a large performance gap in curing speed and bonding strength compared with traditional PUR hot melt adhesive, which is difficult to meet the performance requirements of actual application scenarios. In addition, the existing acrylate-modified polyurethane hot melt adhesive is a UV and moisture dual-curable polyurethane hot melt adhesive prepared by modifying the polyurethane hot melt adhesive through physical blending or chemical modification of acrylate compounds. The acrylate-modified polyurethane hot melt adhesive has a fast UV curing speed. After UV irradiation, the acrylate component in the acrylate-modified polyurethane hot melt adhesive can be quickly cured by light, thereby effectively improving the slow defect of the polyurethane hot melt adhesive relying on moisture curing. However, the existing acrylate-modified polyurethane hot melt adhesive still has many problems such as difficulty in disassembly after curing, difficulty in applying glue at room temperature, and difficulty in effectively bonding non-light-transmitting substrates.

[0006] In summary, there is an urgent need to develop a low-free-isocyanate-content, low-melt-viscosity, room-temperature-applicable, high-initial-bonding-strength, high-bonding-strength, fast-curing, and electrically disassemblable adhesive to meet the application requirements of the market. SUMMARY

[0007] The first object of the present application is to provide an acrylate-modified polyurethane hot melt adhesive with low free isocyanate content, low melt viscosity, room-temperature-applicability, high initial bonding strength and final bonding strength, fast curing speed, and electrical disassembly.

[0008] The second object of the present application is to provide a preparation method of the acrylate-modified polyurethane hot melt adhesive.

[0009] The third object of the present application is to provide an application of the acrylate-modified polyurethane hot melt adhesive in electronic product bonding.

[0010] Specifically, the application provides an electrically detachable acrylate modified polyurethane hot melt adhesive containing a polyurethane prepolymer mixture, an ionic liquid, an acrylate compound and a photoinitiator, both ends of the prepolymer in the polyurethane prepolymer mixture are capped with isocyanate, the isocyanate structural unit in the polyurethane prepolymer mixture is derived from a low-viscosity low-free polyurethane prepolymer and the polyol structural unit is derived from a low-viscosity polyol compound with a glass transition temperature below 0°C and a melting point below 40°C, the mass ratio of the polyurethane prepolymer mixture to the acrylate compound is 1:(0.06-0.9), the total content of isocyanate groups in the electrically detachable acrylate modified polyurethane hot melt adhesive is 2-8% and the free isocyanate monomer content is below 0.1%, the viscosity of the electrically detachable acrylate modified polyurethane hot melt adhesive at 25°C is in the range of 1000-150000 cps and the adhesion strength attenuation rate after power supply at a voltage of 1-100 V is above 80%.

[0011] The application provides a preparation method of the electrically detachable acrylate modified polyurethane hot melt adhesive.

[0012] S1, dehydrating a low-viscosity polyol compound, an ionic liquid and optional rheological modifier, silane coupling agent and water absorbent to obtain a pretreated product;

[0013] S2, stirring and reacting the pretreated product, a low-viscosity low-free polyurethane prepolymer and optional catalyst at 70-90°C for 1-5 h to obtain a prepolymer containing a polyurethane prepolymer mixture;

[0014] S3, uniformly mixing the prepolymer, an acrylate compound and a photoinitiator to obtain the electrically detachable acrylate modified polyurethane hot melt adhesive.

[0015] The inventors of the present application have found, after in-depth and extensive research, that the polyurethane prepolymer mixture with isocyanate functional groups selected by the existing electrically disassemblable polyurethane hot melt adhesive is a product obtained by reacting polyol compounds with excess polyisocyanate compounds. The molar equivalent ratio of isocyanate groups in such polyisocyanate compounds to hydroxyl groups in polyol compounds is usually set at (1.5-2.5):1 (i.e. the molar ratio of NCO / OH is (1.5-2.5):1). According to this stoichiometric relationship, the isocyanate content of the polyurethane prepared is low, the molecular weight of the polyurethane is large, and the interaction force between the molecular chains is large, thereby resulting in a high melt viscosity of the final polyurethane prepolymer mixture, which is not conducive to gluing at room temperature. In addition, part of the polyol compounds used in such polyurethane prepolymer mixtures with isocyanate functional groups have strong crystallinity or high glass transition temperature (Tg) at room temperature. The polyurethane prepolymer mixture prepared by reacting room temperature crystalline polyols or high Tg polyols with isocyanate compounds is usually a solid substance at room temperature. Therefore, the currently prepared electrically disassemblable polyurethane hot melt adhesive according to the traditional method is usually a solid substance at room temperature, and needs to be heated above the melting point (90-160°C) to melt and glue. Therefore, the currently used electrically disassemblable polyurethane hot melt adhesive which needs to be heated for use greatly increases the threshold for using such polyurethane hot melt adhesive, increases the cost of equipment for using the adhesive, and also increases the risk of burns to the operator during the use of the adhesive.

[0016] The existing electrically disassemblable polyurethane hot melt adhesive is prepared by adding ionic liquids or alkali metal salts and solventized matrices to the polyurethane hot melt adhesive, and using the Faraday reaction of the anions and cations in the ionic liquids or alkali metal salts under the condition of electricity to give the polyurethane hot melt adhesive the function of being disassemblable under the condition of electricity. The liquid substances such as ionic liquids and solventized matrices introduced into the polyurethane hot melt adhesive are beneficial to the realization of the electric disassembly function, but such liquid substances cannot participate in the curing of the polyurethane hot melt adhesive, and still exist in the initial low viscosity state after the curing of the polyurethane hot melt adhesive, thus having a certain negative effect on the final adhesive strength of the adhesive. In addition, since the equivalent ratio of isocyanate to hydroxyl group in the isocyanate-terminated polyurethane is low (the equivalent ratio of NCO / OH is between 1.5 and 2.5), the isocyanate content of the finally prepared polyurethane is low, and thus the crosslinking density of the polyurethane after the final wet curing is low, resulting in a low adhesive strength of the adhesive after curing. After the negative influence of the liquid components such as ionic liquids and solventized matrices, the adhesive strength will be further reduced. Therefore, although the use of ionic liquids or alkali metal salts in combination with solventized matrices added to the polyurethane hot melt adhesive can prepare electrically disassemblable polyurethane hot melt adhesive, the final adhesive strength is still greatly insufficient, which is not conducive to the application and promotion of such products.

[0017] The existing acrylate modified polyurethane hot melt adhesive is a UV wet dual-curable polyurethane hot melt adhesive prepared by modifying the polyurethane hot melt adhesive by physical blending or chemical modification of acrylate compounds. The UV curing speed is fast. After UV irradiation, the acrylate component in the acrylate modified polyurethane hot melt adhesive can be quickly photocured, effectively improving the slow curing speed of the polyurethane hot melt adhesive relying on moisture. However, the adhesive strength of the acrylate modified polyurethane hot melt adhesive after curing is relatively strong, and it is also difficult to achieve easy disassembly. In addition, the adhesives that can achieve electrical disassembly generally require the bonded substrate to be conductive. Typically, such conductive substrates are opaque substrates such as stainless steel, aluminum, copper and other metals. For opaque substrates, it is difficult to use UV light-cured adhesives and UV moisture-cured adhesives that generally use acrylate compounds as the main UV light-cured component. This is because the adhesive composition with a light-cured component as the main component will instantly cure after UV irradiation, and the re-adhesion is quickly lost after UV irradiation. Therefore, most UV light-cured adhesives or UV moisture-cured adhesives can only be used for bonding at least one light-transmitting substrate. Therefore, even if the known electrical disassembly composition that can provide electrical disassembly function is directly added to the existing UV acrylate adhesive or UV moisture-cured adhesive with UV acrylate compounds as the main component, it is also difficult to be directly applied to the bonding of opaque metal substrates. In addition, some existing acrylate modified polyurethane hot melt adhesives that can be used for bonding opaque substrates mainly use polyurethane prepolymers as the main component, and a small amount of acrylate compounds for modification. Although this type of acrylate modified polyurethane hot melt adhesive can be used for bonding opaque substrates, the melt viscosity of this type of acrylate modified polyurethane hot melt adhesive is relatively high, and a heating device is usually required for dispensing. The reason why this type of acrylate modified polyurethane hot melt adhesive is difficult to apply at room temperature is mainly that the proportion of low-viscosity acrylate compounds is small, which weakens the dilution capacity of the polyurethane main body, and on the other hand, the polyurethane itself still uses some polyols with high glass transition temperature and / or strong crystallinity at room temperature during preparation. The melt viscosity of such polyurethane main body itself is relatively high. Therefore, the final acrylate modified polyurethane hot melt adhesive is difficult to melt and dispense at room temperature, and a heating device is required for dispensing.

[0018] The key of the present application is to break the design limitation of setting the equivalent ratio of isocyanate group and hydroxyl group between (1.5-2.5):1 and selecting high Tg and / or high melting point polyol compound in the preparation process of traditional electrically disassemblable polyurethane hot melt adhesive, and innovatively react the polyol compound with low crystallinity and low glass transition temperature at room temperature with the low viscosity polyurethane prepolymer with excessive free isocyanate content, and simultaneously introduce low viscosity acrylate compound and ionic liquid, so that the final obtained electrically disassemblable acrylate modified polyurethane hot melt adhesive has the advantages of low free isocyanate content, low melt viscosity, dispensing at room temperature, high initial bonding strength and final bonding strength, fast curing speed and electrically disassemblable performance. The reason is probably that: the acrylate compound and the ionic liquid have good flowability at room temperature, both have low viscosity, the simultaneous introduction of the acrylate compound and the ionic liquid into the polyurethane hot melt adhesive can realize the "first" reduction of the system viscosity, improve the flowability of the adhesive at room temperature, and the selection of the low viscosity polyol compound with a glass transition temperature below 0 DEG C and a melting point below 40 DEG C can reduce the melt viscosity of the polyurethane hot melt adhesive at room temperature from the root, realize the "second" reduction of the system viscosity, that is, the present application reduces the viscosity of the system from two dimensions of the synergistic external viscosity reduction of the acrylate compound and the ionic liquid and the internal viscosity reduction of the low viscosity polyol compound, which is beneficial to the direct application of the polyurethane hot melt adhesive at room temperature, greatly reduces the application threshold of the polyurethane hot melt adhesive, reduces the equipment cost required for the application of the polyurethane hot melt adhesive, and effectively avoids the risk of the operator being scalded during the use of the adhesive. In addition, the acrylate compound can rapidly undergo free radical polymerization reaction after UV irradiation, quickly establish a high initial bonding strength, control the amount of low viscosity low free polyurethane prepolymer in a large excess, so that the content of isocyanate group in the system is increased, thereby increasing the crosslinking density, and the initial curing is provided by the acrylate compound in the system, the significantly excessive isocyanate group provides the post-curing through the moisture curing, and after complete curing, a polyurethane-polyacrylate interpenetrating network structure can be formed, thereby giving the polyurethane hot melt adhesive a high final bonding strength. In addition, the ionic liquid can undergo Faraday reaction after being electrified, and the introduction of the ionic liquid into the polyurethane hot melt adhesive can give it the electrically disassemblable performance. Furthermore, the present application uses the polyurethane prepolymer with low free isocyanate content instead of the isocyanate monomer used in the traditional way, which can significantly reduce the residual free isocyanate monomer in the adhesive system. As described above, the polyurethane hot melt adhesive provided by the present application relies on the acrylate compound to improve the initial bonding strength in the early stage, and relies on the polyurethane-polyacrylate interpenetrating network structure to improve the final bonding strength in the later stage, so that even if the ionic liquid is not cured, the initial bonding strength and the final bonding strength can still be relatively high.In conclusion, the electrically detachable acrylate modified polyurethane hot melt adhesive provided by the present application has low free isocyanate content, low melt viscosity, high initial and final bonding strength, fast curing speed, and electrically detachable performance, and has wide practical application prospects. DETAILED DESCRIPTION

[0019] The acrylate modified polyurethane hot melt adhesive provided by the present application has a viscosity of 1000-150000 cps at 25 DEG C, and specifically can be 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 30000, 50000, 70000, 90000, 110000, 130000, 150000 cps or any value therebetween.

[0020] The acrylate modified polyurethane hot melt adhesive provided by the present application has a bonding strength decay rate of more than 80% after being powered at a voltage of 1-100 V, and specifically can be 80%, 82%, 85%, 88%, 90%, 92%, 95%, 98%, 99%, 100% or any value therebetween. The voltage required for the electrically detachable acrylate modified polyurethane hot melt adhesive is preferably 1-100 V, and specifically can be 1 V, 3 V, 5 V, 8 V, 10 V, 20 V, 30 V, 40 V, 50 V, 60 V, 70 V, 80 V, 90 V, 100 V or any value therebetween; the time required for power supply is preferably 1 s-60 min, such as 1 s, 5 s, 10 s, 30 s, 1 min, 5 min, 10 min, 15 min, 20 min, 30 min, 40 min, 50 min, 60 min or any value therebetween.

[0021] In the present application, the total content of isocyanate groups in the electrically detachable one-component reactive polyurethane hot melt adhesive is 2-8%, such as 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8% or any value therebetween. The content of free isocyanate monomers in the electrically detachable one-component reactive polyurethane hot melt adhesive is 0.1% or less, such as 0.1%, 0.08%, 0.05%, 0.03%, 0.02%, 0.01% or any value therebetween. In the present application, the total content of isocyanate groups refers to the ratio of the total weight of all unreacted isocyanate functional groups (including both the isocyanate functional groups on the end groups of the prepolymer and the isocyanate functional groups in the free isocyanate monomers) to the total weight of the polyurethane hot melt adhesive.

[0022] In the present application, the electrically detachable acrylate modified polyurethane hot melt adhesive contains a polyurethane prepolymer mixture, an ionic liquid, an acrylate compound and a photoinitiator. The introduction of polyol structural units with weak crystallinity or low glass transition temperature in the polyurethane prepolymer mixture and the addition of the acrylate compound and the ionic liquid together reduce the viscosity of the system, impart the performance of direct gluing at room temperature, and further, the introduction of the acrylate compound improves the initial bonding strength and curing speed of the polyurethane hot melt adhesive, the control of the mass ratio of the polyurethane prepolymer mixture to the acrylate compound improves the final bonding strength, and the introduction of the ionic liquid imparts the electrically detachable performance of the polyurethane hot melt adhesive. The polyol structural units contained in the polyurethane prepolymer mixture are derived from low-viscosity polyol compounds. The glass transition temperature (Tg) of the low-viscosity polyol compound is 0°C or lower, and can be 0°C, -2°C, -4°C, -6°C, -8°C, -10°C, -12°C, -14°C, -16°C, -18°C, -20°C, -22°C, -24°C, -26°C, -28°C, -30°C, -32°C, -34°C, -36°C, -38°C, -40°C, etc. The melting point of the low-viscosity polyol compound is 40°C or lower, and can be 40°C, 38°C, 36°C, 34°C, 32°C, 30°C, 28°C, 26°C, 24°C, 22°C, 20°C, 18°C, 16°C, 14°C, 12°C, 10°C, 8°C, 6°C, 4°C, 2°C, 0°C, -5°C, -10°C, -15°C, -20°C, -30°C, etc. In the present application, the term "polyurethane prepolymer mixture" refers to the product obtained by the addition reaction of low-viscosity low-free polyurethane prepolymer and low-viscosity polyol compounds. Since the product contains polymers of different molecular weights and possibly unreacted monomers, it is a mixture of multiple substances, and is therefore referred to as "polyurethane prepolymer mixture".

[0023] The electrically detachable acrylate modified polyurethane hot melt adhesive provided by the present application is a liquid or paste at room temperature, has low melt viscosity, can be point-glued at room temperature, has high initial bonding strength and final bonding strength, fast curing speed and electrically detachable performance.

[0024] In a preferred embodiment, the electrically detachable acrylate modified polyurethane hot melt adhesive contains low-viscosity low-free polyurethane prepolymer, low-viscosity polyol compound, ionic liquid, acrylate compound and photoinitiator, and optionally rheological modifier, silane coupling agent, water absorbent and catalyst. The molar equivalent ratio of isocyanate groups in the low-viscosity low-free polyurethane prepolymer to hydroxyl groups in the low-viscosity polyol compound is preferably (8-13):1, such as 8:1, 9:1, 10:1, 11:1, 12:1, 13:1 or any value therebetween.

[0025] In the present application, the mass ratio of the total content of the low viscosity low free polyurethane prepolymer and the low viscosity polyol compound to the content of the ionic liquid is preferably (2.5-40): 1, and specifically can be 2.5: 1, 3.5: 1, 5: 1, 7: 1, 9: 1, 11: 1, 13: 1, 15: 1, 17: 1, 21: 1, 23: 1, 25: 1, 27: 1, 30: 1, 32: 1, 34: 1, 36: 1, 38: 1, 40: 1, or any value therebetween. The mass ratio of the acrylate compound to the ionic liquid is preferably (0.3-18): 1, and specifically can be 0.3: 1, 0.5: 1, 1: 1, 2: 1, 5: 1, 8: 1, 10: 1, 12: 1, 15: 1, 18: 1, or any value therebetween. The mass ratio of the photoinitiator to the ionic liquid is preferably (0.005-2.5): 1, and specifically can be 0.005: 1, 0.01: 1, 0.05: 1, 0.1: 1, 0.5: 1, 0.8: 1, 1: 1, 1.5: 1, 2: 1, 2.5: 1, or any value therebetween. The mass ratio of the rheology modifier to the ionic liquid is preferably (0-5): 1, and specifically can be 0, 0.1: 1, 0.5: 1, 1: 1, 1.5: 1, 2: 1, 2.5: 1, 3: 1, 3.5: 1, 4: 1, 4.5: 1, 5: 1, or any value therebetween. The mass ratio of the silane coupling agent to the ionic liquid is preferably (0-1.5): 1, and specifically can be 0, 0.005: 1, 0.01: 1, 0.05: 1, 0.1: 1, 0.3: 1, 0.5: 1, 0.8: 1, 1: 1, 1.2: 1, 1.5: 1, or any value therebetween. The mass ratio of the water absorbing agent to the ionic liquid is preferably (0-1): 1, and specifically can be 0, 0.005: 1, 0.01: 1, 0.05: 1, 0.1: 1, 0.3: 1, 0.5: 1, 0.8: 1, 1: 1, or any value therebetween. The mass ratio of the catalyst to the content of the ionic liquid is preferably (0.005-1): 1, and specifically can be 0.005: 1, 0.01: 1, 0.05: 1, 0.1: 1, 0.3: 1, 0.5: 1, 0.8: 1, 1: 1, or any value therebetween.

[0026] In a preferred embodiment, the total content of the low viscosity low free polyurethane prepolymer and the low viscosity polyol compound is 40-80%, such as 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or any value therebetween, based on the total weight of the raw materials for preparing the electrically detachable acrylate modified polyurethane hot melt adhesive; the content of the ionic liquid is 2-15%, such as 2%, 5%, 8%, 10%, 12%, 15%, or any value therebetween; the content of the acrylate compound is 5-35%, such as 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, or any value therebetween; the content of the photoinitiator is 0.1-5%, such as 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or any value therebetween; the content of the rheology modifier is 2-10%, such as 2%, 5%, 8%, 10%, or any value therebetween; the content of the silane coupling agent is 0.1-3%, such as 0.1%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, or any value therebetween; the content of the water absorbent is 0.1-2%, such as 0.1%, 0.5%, 0.8%, 1%, 1.5%, 2%, or any value therebetween; and the content of the catalyst is 0.1-2%, such as 0.1%, 0.5%, 0.8%, 1%, 1.5%, 2%, or any value therebetween.

[0027] In the present application, the low viscosity low free isocyanate monomer content of the low viscosity low free polyurethane prepolymer is preferably 0.1% or less, and can be specifically 0.1%, 0.08%, 0.05%, 0.03%, 0.02%, 0.01%, or any value therebetween. The low viscosity low free polyurethane prepolymer is liquid at 50°C or less. The viscosity of the low viscosity low free polyurethane prepolymer at 50°C is preferably 100,000 cps or less, and can be specifically 100,000 cps, 90,000 cps, 80,000 cps, 70,000 cps, 60,000 cps, 50,000 cps, 40,000 cps, 30,000 cps, 20,000 cps, 10,000 cps, 5,000 cps, 3,000 cps, 2,000 cps, 1,000 cps, or any value therebetween. The low viscosity low free polyurethane prepolymer can be obtained by reacting a polyether polyol with a polyisocyanate monomer. The polyether polyol can be at least one of, for example, an open-chain polymer of ethylene glycol, propylene glycol, tetrahydrofuran, 3-methyltetrahydrofuran, or a random copolymer or block copolymer of ethylene glycol, propylene glycol, tetrahydrofuran, 3-methyltetrahydrofuran, or a derivative thereof. The polyisocyanate monomer can be at least one of, for example, isophorone diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, hexamethylene diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenylmethane-2,4'-diisocyanate, hydrogenated MDI, polymeric MDI, 1,5-naphthalene diisocyanate, 1,4-phenylene diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate, norbornane diisocyanate. Commercially available low free polyether polyol-based polyurethane prepolymer can be, for example, Adiprene LF TE 915, Adiprene LF TE 1050, Adiprene LF TE 980, Adiprene LF TE 330, Adiprene LF TE 365, Adiprene LF TE 440, Adiprene LFM G730, Adiprene LFM G750, Adiprene LFM G600, Adiprene LFMI G600, etc. of Rhone-Poulenc.

[0028] In the present application, the number average molecular weight of the low viscosity polyol compound is preferably 400 to 6000 g / mol, such as 400, 500, 800, 1000, 1200, 1500, 1800, 2000, 2500, 3000, 3500, 4000, 4500, 5000, 5500, 6000 g / mol, or any value therebetween. The low viscosity polyol compound can be any of the various polyol compounds having a glass transition temperature of 0°C or less and a melting point of 40°C or less, specific examples of which include, but are not limited to, at least one of a liquid polyester polyol, a liquid polyether polyol, a liquid polycarbonate polyol, a liquid polycaprolactone polyol, a fatty acid dimer diol, a castor oil derivative polyol, and a hydroxyl-terminated polybutadiene polyol.

[0029] In the present application, the melting point of the ionic liquid is preferably 25°C or less, such as 25°C, 23°C, 20°C, 18°C, 15°C, 13°C, 10°C, 8°C, 5°C, 2°C, 0°C, -5°C, -10°C, -15°C, -20°C, -30°C, -40°C, etc. The ionic liquid is composed of a cation and an anion. The cation is preferably selected from at least one of imidazole-based cations, pyrrole-based cations, quaternary ammonium salt-based cations, quaternary phosphonium salt-based cations, pyrrolidine-based cations, and piperidine-based cations. The anion is preferably selected from at least one of triflate anions, tetrafluoroborate anions, hexafluorophosphate anions, bisfluorosulfonimide anions, hydrogen sulfate anions, ethyl sulfate-based anions, and p-toluenesulfonate anions. Specific examples of the above ionic liquid can include, but are not limited to, at least one of 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-ethyl-3-methylimidazolium triflate, 1-ethyl-2,3-dimethylimidazolium triflate, 1-octyl-3-methylimidazolium triflate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-propyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-2,3-dimethylimidazolium tetrafluoroborate, 1-propyl-2,3-dimethylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium ethyl sulfate, 1-ethyl-2,3-dimethylimidazolium ethyl sulfate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1,3-diethylimidazolium bis(trifluoromethanesulfonyl)imide, 1-propyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1,2-dimethyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide, 1-ethyl-2,3-dimethylimidazolium bisfluorosulfonimide, N-butylpyridinium tetrafluoroborate, hexyltriethylammonium bis(trifluoromethanesulfonyl)imide, methyltrioctylphosphonium bis(trifluoromethanesulfonyl)imide, N-butyl-N-methylpyrrolidinium bisfluorosulfonimide, N-butyl-N-methylpyrrolidinium triflate, and N-propyl-N-methylpiperidinium bis(trifluoromethanesulfonyl)imide.

[0030] In the present application, the acrylate compound can be at least one of various acrylate monomers that can be photocured, such as octadecyl acrylate, tetrahydrofurfuryl acrylate, dodecyl acrylate, 2-phenoxyethyl acrylate, isodecyl acrylate, isooctyl acrylate, tridecyl acrylate, trimethylolpropane formal acrylate, monoacrylate of methoxypolyethylene glycol, alkoxylated tetrahydrofurfuryl acrylate, 1,3-butanediol diacrylate, 1,4-butanediol diacrylate, diethylene glycol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, tetraethylene glycol diacrylate, triethylene glycol diacrylate, tripropylene glycol diacrylate, dipropylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, and 1,3-butanediol dimethacrylate.

[0031] In the present application, the photoinitiator can be at least one of various compounds that absorb energy in the ultraviolet region or the visible region to generate radicals to initiate polymerization of the acryl functional group, such as benzophenone-based compounds, acetophenone-based compounds, acylphosphine oxide-based compounds, titanocene-based compounds, oxime ester-based compounds, benzoin ether-based compounds, and thioxanthone.

[0032] In the present application, the rheology modifier is preferably fumed silica, and specific examples thereof include, but are not limited to, at least one of AEROSIL A150, AEROSIL A200, AEROSIL A300, AEROSIL A380, AEROSIL R972, AEROSIL R974, AEROSIL R202, AEROSIL R812, HDK V15, HDK N20, HDK T30, HDK T40, HDK H13L, HDK H15, HDK H15L, HDK H16, HDK H17, HDK H18, HDK H2000, HDK H20, HDK H21, HDK H30, HDK H30RM, LM-150, M-5, E-5, EH-5, TS610, TS620, TS622, TS720, TS530, and TSUBOND. The specific surface area of the fumed silica is preferably 90 to 380 m 2 / g, and can be specifically 90, 100, 120, 150, 180, 200, 220, 240, 260, 280, 300, 320, 340, 360, 380 m 2 / g or any value therebetween.

[0033] In the present application, specific examples of the silane coupling agent include, but are not limited to, at least one of 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropylmethyldiethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-(2-aminoethyl)aminopropyltrimethoxysilane, 3-(2-aminoethyl)aminopropyltriethoxysilane, 3-(2-aminoethyl)aminopropylmethyldimethoxysilane, 3-acryloyloxypropyltrimethoxysilane, 3-(meth)acryloyloxypropyltrimethoxysilane, 3-(meth)acryloyloxypropyltriethoxysilane, 3-(meth)acryloyloxypropylmethyldimethoxysilane, 3-(meth)acryloyloxypropylmethyldiethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, and 3-isocyanatepropyltrimethoxysilane.

[0034] In the present application, the water absorbing agent can be selected from at least one of a molecular sieve desiccant, an oxazolidine water removing agent, p-toluenesulfonylisocyanate, and triethyl orthoformate.

[0035] In the present application, the catalyst can be selected from at least one of dibutyltin dilaurate, stannous octoate, zinc isooctoate, bismuth isooctoate, triethylamine, diethylenetriamine, triethylenediamine, N-ethylmorpholine, and 2,2-dimorpholinodiethyl ether.

[0036] The present application provides a preparation method of the electrically detachable acrylate modified polyurethane hot melt adhesive, which comprises the following steps:

[0037] S1, dehydrating a low-viscosity polyol compound, an ionic liquid, and optionally a rheological modifier, a silane coupling agent, and a water absorbing agent to obtain a pretreated product;

[0038] S2, stirring and reacting the pretreated product and a low-viscosity low-free polyurethane prepolymer, and optionally a catalyst, at 70-90°C for 1-5h to obtain a prepolymer containing a polyurethane prepolymer mixture;

[0039] S3, uniformly mixing the prepolymer, an acrylate compound, and a photoinitiator to obtain the electrically detachable acrylate modified polyurethane hot melt adhesive.

[0040] In the present application, in step S1, the conditions of the dehydration treatment preferably include a temperature of 100-120℃, such as 100℃, 102℃, 104℃, 106℃, 108℃, 110℃, 112℃, 114℃, 116℃, 118℃, 120℃, or any value therebetween; a rotation speed of 100-200r / min, such as 100r / min, 110r / min, 120r / min, 130r / min, 140r / min, 150r / min, 160r / min, 170r / min, 180r / min, 190r / min, 200r / min, or any value therebetween; and a time of 1-5h, such as 1h, 2h, 3h, 4h, 5h, or any value therebetween.

[0041] In the present application, in step S2, the temperature of the stirring reaction is preferably 70-90℃, and can be specifically 70℃, 72℃, 74℃, 76℃, 78℃, 80℃, 82℃, 84℃, 86℃, 88℃, 90℃, or any value therebetween; the rotation speed of the stirring reaction is preferably 100-200r / min, and can be specifically 100r / min, 110r / min, 120r / min, 130r / min, 140r / min, 150r / min, 160r / min, 170r / min, 180r / min, 190r / min, 200r / min, or any value therebetween; and the time of the stirring reaction is preferably 1-5h, and can be specifically 1h, 2h, 3h, 4h, 5h, or any value therebetween.

[0042] In the present application, in step S3, the conditions of the mixing preferably include a temperature of 70-90℃, and can be specifically 70℃, 72℃, 74℃, 76℃, 78℃, 80℃, 82℃, 84℃, 86℃, 88℃, 90℃, or any value therebetween; a stirring rotation speed of 100-200r / min, and can be specifically 100r / min, 110r / min, 120r / min, 130r / min, 140r / min, 150r / min, 160r / min, 170r / min, 180r / min, 190r / min, 200r / min, or any value therebetween; and a time of 30min-2h, and can be specifically 30min, 40min, 50min, 60min, 80min, 100min, 120min, or any value therebetween.

[0043] The present application also provides the use of the electrically detachable acrylate modified polyurethane hot melt adhesive in electronic product bonding.

[0044] The electrically detachable acrylate-modified polyurethane hot melt adhesive provided by the present application is used for a substrate with electrical conductivity.

[0045] The present application will be described in detail below by way of examples. The examples are intended to explain the present application and should not be construed as limiting the present application. If a specific technique or condition is not mentioned in the examples, the technique or condition described in the literature in the art or according to the product manual is used. If the manufacturer of a reagent or instrument is not mentioned, it is a conventional product that can be commercially available.

[0046] Example 1

[0047] 5.49 g (2.746 mmol) of liquid polycaprolactone diol (PLACCEL L220AL; Tg < 0℃; melting point = 0-5℃) with a number average molecular weight of 2000, 5.49 g (2.746 mmol) of polytetramethylene ether glycol (PTMEG-2000; Tg = -76℃; melting point = 24℃) with a number average molecular weight of 2000, 7.00 g of 1-butyl-3-methylimidazolium tetrafluoroborate, 5.0 g of fumed silica HDK H20, 1.5 g of 3-mercaptopropyltrimethoxysilane, 1.1 g of water absorption additive Additive OF were heated to 110℃, vacuum dehydrated for 2 h under stirring at 150 r / min, cooled to 80℃, and then 50.42 g (54.919 mmol) of a low free polyurethane prepolymer (Adiprene LF TE 915; viscosity at 50℃ of 2000-4000 cps; free isocyanate monomer content of 0.1% or less), 0.5 g of dibutyltin dilaurate were added, and reacted for 2 h under stirring at 150 r / min, and then 1.5 g of a photoinitiator ITX, 12.0 g of tetrahydrofurfuryl acrylate, and 10.0 g of triethylene glycol diacrylate were added, mixed for 1 h under stirring at 150 r / min, and then discharged to obtain an electrically detachable acrylate-modified polyurethane hot melt adhesive, which was stored in a vacuum-sealed container in the dark.

[0048] Example 2

[0049] By weight, 5.38 g (5.376 mmol) of polycaprolactone diol (PLACCEL 210N; Tg = -17°C; melting point = 32-37°C) with a number average molecular weight of 1000, 5.38 g (1.792 mmol) of liquid polycarbonate diol (Kuraray polyol C3090; Tg = -42°C; melting point < 25°C) with a number average molecular weight of 3000, 3.00 g of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, 2.0 g of fumed silica AEROSIL R202, 0.3 g of 3- aminopropyltriethoxysilane, 0.7 g of water absorption agent Additive OF were heated to 110°C, vacuum dehydration was carried out at 150 r / min for 2 h, then the temperature was lowered to 80°C, 67.65 g (78.844 mmol) of low free polyurethane prepolymer (Adiprene LF TE 980; viscosity at 50°C of 8000-16400 cps; free isocyanate monomer content of 0.1% or less), 0.1 g of stannous octoate were added, and reaction was carried out at 150 r / min for 2 h, then 0.5 g of photoinitiator TPO, 10.0 g of 1,6-hexanediol diacrylate, 5.0 g of trimethylolpropane formaldehyde acrylate were added, and after mixing at 150 r / min for 1 h, the product was discharged to obtain an electrically detachable acrylate-modified polyurethane hot melt adhesive, which was stored in a vacuum-sealed lightproof container.

[0050] Example 3

[0051] By weight, 7.62 g (1.386 mmol) of liquid polyester diol (Wingzone 7250; Tg = -50°C; melting point < 25°C) with a number average molecular weight of 5500, 5.54 g (2.772 mmol) of polyether diol (voranol 2120; Tg < 0°C; melting point < 25°C) with a number average molecular weight of 2000, 8.00 g of N-butylpyridinium tetrafluoroborate, 4.0 g of fumed silica AEROSIL R972, 2.0 g of vinyltrimethoxysilane, 1.5 g of water absorption agent Additive TI were heated to 110°C, vacuum dehydration was carried out at 150 r / min for 2 h, then the temperature was lowered to 80°C, 43.03 g (37.42 mmol) of low free polyurethane prepolymer (Adiprene LF G730; viscosity at 50°C of 22750 cps; free isocyanate monomer content of 0.1% or less), 1.1 g of 2,2-dimorpholinodiethyl ether were added, and reaction was carried out at 150 r / min for 2 h, then 2.2 g of photoinitiator 184, 10.0 g of neopentyl glycol diacrylate, 15.0 g of isooctyl acrylate were added, and after mixing at 150 r / min for 1 h, the product was discharged to obtain an electrically detachable acrylate-modified polyurethane hot melt adhesive, which was stored in a vacuum-sealed lightproof container.

[0052] Example 4

[0053] Example 4 2.31 g (1.155 mmol) of liquid polycarbonate diol (DURANOL T5652; Tg <0°C; melting point <-5°C) with a number average molecular weight of 2000, 4.62 g (2.31 mmol) of liquid polyester diol (stepanpol PH-56; Tg = -15°C; melting point <25°C) with a number average molecular weight of 2000, 10.00 g of 1-octyl-3-methylimidazolium trifluoromethanesulfonate, 3.0 g of fumed silica HDK H18, 0.5 g of 3-glycidoxypropyltriethoxysilane, 1.2 g of water absorption agent Additive OF were heated to 110°C, vacuum dewatered for 2 h under stirring at 150 r / min, then cooled to 80°C, 46.57 g (41.58 mmol) of low free polyurethane prepolymer (Adiprene LF G750; viscosity at 50°C of 32000 cps; free isocyanate monomer content of 0.1% or less), 0.8 g of zinc isooctoate were added, and reacted for 2 h under stirring at 150 r / min, then 3.0 g of photoinitiator 819, 14.0 g of diethylene glycol diacrylate, 14.0 g of tridecyl acrylate were added, mixed for 1 h under stirring at 150 r / min, and then discharged to obtain an electrically disassemblable acrylate-modified polyurethane hot melt adhesive, which was stored in a vacuum-sealed container in the dark.

[0054] Example 5

[0055] By weight, 2.28 g (2.276 mmol) of polyether diol with number average molecular weight of 2000 (voranol 220-110; Tg <0 ℃; melting point <25 ℃), 3.98 g (1.138 mmol) of liquid polyester diol with number average molecular weight of 3500 (Dynacoll 7230; Tg =-30 ℃; melting point <25 ℃), 12.00 g of N-propyl-N-methylpiperidine bis(trifluoromethanesulfonyl)imide salt, 3.0 g of fumed silica TS620, 0.5 g of 3-aminopropyltrimethoxysilane, 1.5 g of water absorption agent Additive TI were heated to 110 ℃, vacuum dehydration was carried out for 2 h under the condition of stirring at 150 r / min, then cooled to 80 ℃, 38.24 g (27.315 mmol) of low free polyurethane prepolymer (Adiprene LF G600; viscosity at 50 ℃ is 3975 cps; free isocyanate monomer content is 0.1% or less), 1.2 g of bismuth iso-octoate were added, and reaction was carried out for 2 h under the condition of stirring at 150 r / min, then 4.0 g of photoinitiator 369, 20.0 g of triethylene glycol diacrylate, 12.0 g of dodecyl acrylate were added, and after mixing for 1 h under the condition of stirring at 150 r / min, the product was discharged to obtain an electrically disassemblable acrylate modified polyurethane hot melt adhesive, which was stored in vacuum and in the dark.

[0056] Comparative Example 1

[0057] By weight, 39.42 g (11.262 mmol) of polyester diol with number average molecular weight of 3500 (Evonik Dynacoll 7360; Tg =-60 ℃; melting point = 55 ℃), 22.52 g (11.262 mmol) of polytetramethylene ether glycol with number average molecular weight of 2000 (PTMG 2000; Tg =-76 ℃; melting point = 28 ℃), 15.0 g of thermoplastic acrylic resin BM751 (Tg = 49 ℃), 5.0 g of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate, 5.0 g of propylene carbonate, 1.0 g of 3-mercaptopropyltrimethoxysilane, 0.5 g of water absorption agent Additive OF were heated to 110 ℃, vacuum dehydration was carried out for 2 h under the condition of stirring at 150 r / min, then cooled to 80 ℃, 12.03 g (48.123 mmol) of 4,4'-diphenylmethane diisocyanate (MDI), 0.3 g of stannous octoate were added, and after reaction for 2 h under the condition of stirring at 150 r / min, the product was discharged to obtain a reference electrically disassemblable acrylate modified polyurethane hot melt adhesive, which was stored in vacuum and in the dark.

[0058] Comparative Example 2

[0059] The reference electrically dismountable acrylate-modified polyurethane hot melt adhesive was prepared according to the method of Example 1, except that the low free polyurethane prepolymer Adiprene LF TE 915 was replaced by the same molar amount of low free polyurethane prepolymer Adiprene LF S300 which was solid at 50°C, and the other conditions were the same as those in Example 1, to obtain the reference electrically dismountable acrylate-modified polyurethane hot melt adhesive which was stored in vacuum and in the dark.

[0060] Comparative Example 3

[0061] The reference electrically dismountable acrylate-modified polyurethane hot melt adhesive was prepared according to the method of Example 1, except that the molar equivalent ratio of isocyanate groups in the low viscosity low free polyurethane prepolymer to hydroxyl groups in the low viscosity polyol compound was adjusted from 10:1 to 2:1, as follows:

[0062] The reference electrically dismountable acrylate-modified polyurethane hot melt adhesive was prepared according to the method of Example 1, except that the molar equivalent ratio of isocyanate groups in the low viscosity low free polyurethane prepolymer to hydroxyl groups in the low viscosity polyol compound was adjusted from 10:1 to 2:1, as follows:

[0063] Comparative Example 4

[0064] The reference electrically dismountable acrylate-modified polyurethane hot melt adhesive was prepared according to the method of Example 1, except that the low free polyurethane prepolymer Adiprene LF TE 915 was replaced by the same weight amount of 4,4'-diphenylmethane diisocyanate (MDI) monomer, and the other conditions were the same as those in Example 1, to obtain the reference electrically dismountable acrylate-modified polyurethane hot melt adhesive which was stored in vacuum and in the dark.

[0065] Comparative Example 5

[0066] The reference electrically dismountable acrylate modified polyurethane hot melt adhesive was prepared according to the method of Example 1, except that 1-butyl-3-methylimidazolium tetrafluoroborate was not added, and the rest was the same as Example 1, to obtain the reference electrically dismountable acrylate modified polyurethane hot melt adhesive, which was stored in a vacuum sealed and light-proof manner.

[0067] Comparative Example 6

[0068] The reference electrically dismountable acrylate modified polyurethane hot melt adhesive was prepared according to the method of Example 1, except that tetrahydrofurfuryl acrylate and triethylene glycol diacrylate were not added, and the rest was the same as Example 1, to obtain the reference electrically dismountable acrylate modified polyurethane hot melt adhesive, which was stored in a vacuum sealed and light-proof manner.

[0069] Comparative Example 7

[0070] The reference electrically dismountable acrylate modified polyurethane hot melt adhesive was prepared according to the method of Example 1, except that the addition amount of tetrahydrofurfuryl acrylate and triethylene glycol diacrylate was increased to 50 g each, and the rest was the same as Example 1, to obtain the reference electrically dismountable acrylate modified polyurethane hot melt adhesive, which was stored in a vacuum sealed and light-proof manner.

[0071] Comparative Example 8

[0072] The reactive polyurethane hot melt adhesive was prepared in the manner of Example 1, except that the low-viscosity polyol compound used in Example 1 was replaced with a high-melting-point or high-Tg polyol, as follows:

[0073] By weight, 5.49 g (2.746 mmol) of crystalline polyester diol with a number average molecular weight of 2000 (Hoopol F-900; melting point = 53℃), 5.49 g (2.746 mmol) of polycarbonate diol with a number average molecular weight of 2000 (UH-CARB200; melting point = 50℃), 7.00 g of 1-butyl-3-methylimidazolium tetrafluoroborate, 5.0 g of fumed silica HDK H2O, 1.5 g of 3-mercaptopropyltrimethoxysilane, and 1.1 g of water-absorbing agent Additive OF were heated to 110℃ and vacuum dehydrated for 2 h under stirring at 150 r / min. The mixture was then cooled to 80℃, and 50.42 g (54.919 mmol) of low-free polyurethane prepolymer (Adiprene LF) was added. TE915 (viscosity at 50℃: 2000-4000 cps; free isocyanate monomer content: less than 0.1%), 0.5 g dibutyltin dilaurate, reacted under stirring at 150 r / min for 2 h, then 1.5 g photoinitiator ITX, 12.0 g tetrahydrofuran acrylate, and 10.0 g triethylene glycol diacrylate were added, mixed under stirring at 150 r / min for 1 h, and then discharged to obtain a reference electrically removable acrylate-modified polyurethane hot melt adhesive, which was vacuum-sealed and protected from light.

[0074] Test case

[0075] The samples from the examples and comparative examples were compared and tested using the following method:

[0076] (1) Viscosity at 25℃: Samples of polyurethane hot melt adhesives obtained from the above examples and comparative examples were taken into a cone-plate viscometer and the viscosity of the adhesives at 25℃ and 1 rpm was tested using the cone-plate viscometer. The results are shown in Table 1.

[0077] (2) Bond strength at different curing times: The polyurethane hot melt adhesives obtained in the above embodiments and comparative examples were applied at room temperature using a dispensing machine (if solid at room temperature, the dispensing temperature was set to 110℃). A rectangular adhesive line of 25mm × 4mm was applied to a stainless steel substrate, and then the adhesive was irradiated with a 365nm UV-LED light source at 2000mJ / cm². 2 After irradiation with the required energy, another stainless steel substrate was bonded to the original stainless steel substrate. Following bonding, the sample was cured at 25°C and 50% RH for 5 min, 30 min, and 48 h. Then, a universal testing machine was used to run the bonded sample along the shear direction at a speed of 10 mm / min until the bond failed. The maximum force value displayed by the instrument was recorded, and the shear bond strength of the polyurethane hot melt adhesive to the stainless steel substrate before energization was calculated based on the bond area. The results are shown in Table 1.

[0078] (3) Adhesion strength after power on: The polyurethane hot melt adhesive obtained in each of the above examples and comparative examples was dispensed at room temperature using a dispenser (if it was solid at room temperature, the dispensing temperature was set at 110°C), a 25 mm x 4 mm rectangular glue line was coated on a stainless steel substrate, then a 365 nm UV-LED light source was used to irradiate the glue with an energy of 2000 mJ / cm 2 After the irradiation, another stainless steel substrate was attached to the stainless steel substrate, and after the attachment was completed, the sample was cured in an environment of 25°C and 50% RH for 48 h. Then, the positive and negative leads of a direct current power source were clamped at both ends of the sheared sample, and a certain voltage was applied for a certain time. After the power on, the sheared sample was removed, and the adhesive sample was run at a speed of 10 mm / min along the shearing direction until the adhesive sample failed, and the maximum force value displayed by the instrument was recorded. The shearing adhesion strength of the polyurethane hot melt adhesive to the stainless steel substrate after power on was calculated based on the adhesion area. The results are shown in Table 1.

[0079] (4) Isocyanate group content: The isocyanate group content of the polyurethane hot melt adhesive obtained in each of the above examples and comparative examples was determined according to standard HG / T2409-92. (2±0.2) g of the polyurethane hot melt adhesive was accurately weighed (to 0.001 g) and placed in a conical flask. 10 mL of di-n-butylamine-toluene solution was accurately transferred into the conical flask using a pipette, then 20 mL of toluene was added and shaken gently to dissolve, and finally 80 mL of anhydrous isopropyl alcohol was added. After standing for 15 min, the solution was titrated with 0.5 mol / L hydrochloric acid standard solution using bromocresol green as an indicator. When the solution changed from blue to yellow and did not change color for 30 s, the titration end point was reached (the blank test was performed in the same way). The isocyanate group content of the polyurethane hot melt adhesive sample was calculated based on the difference in the amount of hydrochloric acid consumed in the blank test and the polyurethane hot melt adhesive sample. The results are shown in Table 1.

[0080] (5) Free isocyanate monomer content: A high performance liquid chromatograph (HPLC) was used, liquid was used as the mobile phase, and a high pressure infusion system was used to pump the mobile phase into a chromatographic column containing a stationary phase. After the components were separated in the column, they were detected by a detector to obtain a chromatogram of the detected substances. The external standard method was used to quantitatively calculate the content of free isocyanate monomers in the polyurethane hot melt adhesive. The chromatograms of the sample to be tested and the standard were recorded, and the content of free isocyanate in the sample to be tested was calculated based on the integral area of the specific peak on the chromatogram. The results are shown in Table 1.

[0081] Table 1

[0082]

[0083] As can be seen from the results of Table 1, the electrically detachable acrylate modified polyurethane hot melt adhesive provided by the present application has a lower viscosity at room temperature, can be directly dispensed at room temperature, significantly improves the defect that the reactive polyurethane hot melt adhesive needs to be applied with heating, increases the convenience of use of the adhesive, and reduces the risk of scalding of the operator in the process of using the heating equipment. According to practical experience, the bonding strength at room temperature below 2.0 MPa indicates that the polyurethane hot melt adhesive has electrically detachable property, otherwise it does not have electrically detachable property. As can be seen from the results of Table 1, the acrylate modified polyurethane hot melt adhesive provided by the present application can quickly establish a high initial bonding strength after UV irradiation, has the function of realizing preliminary positioning in a short time, has excellent final bonding strength after complete curing, and the bonding strength of the adhesive can obviously decay after power-on, and even can directly fall off, has excellent power-on detachable performance. In summary, the electrically detachable acrylate modified polyurethane hot melt adhesive provided by the present application also has extremely low free isocyanate monomer residue, can significantly reduce the risk of harm to human health in the process of using the hot melt adhesive. In summary, the acrylate modified polyurethane hot melt adhesive provided by the present application has low free isocyanate content, can be dispensed at room temperature, has high initial bonding strength and final bonding strength, has fast curing speed, and at the same time has detachable function under power-on condition, has broad practical application prospect.

[0084] Although the embodiments of the present application have been shown and described above, it should be understood that the above-mentioned embodiments are exemplary and should not be construed as limiting the present application, and those of ordinary skill in the art can make changes, modifications, replacements and variations to the above-mentioned embodiments without departing from the principles and purposes of the present application within the scope of the present application.

Claims

1. An electrically detachable acrylate-modified polyurethane hot melt adhesive, characterized by, The electrically detachable acrylate-modified polyurethane hot melt adhesive contains a polyurethane prepolymer mixture, an ionic liquid, an acrylate compound, and a photoinitiator, the prepolymer contained in the polyurethane prepolymer mixture has isocyanate end-capping at both ends, the isocyanate structural unit contained in the polyurethane prepolymer mixture is derived from a low-viscosity low-free polyurethane prepolymer, and the polyol structural unit is derived from a low-viscosity polyol compound having a glass transition temperature of 0°C or lower and a melting point of 40°C or lower, the mass ratio of the polyurethane prepolymer mixture to the acrylate compound is 1:(0.06-0.9), the total content of isocyanate groups in the electrically detachable acrylate-modified polyurethane hot melt adhesive is 2-8%, and the free isocyanate monomer content is 0.1% or less; the viscosity of the electrically detachable acrylate-modified polyurethane hot melt adhesive at 25°C is in the range of 1000-150000 cps, and the adhesion strength attenuation rate after power supply at a voltage of 1-100 V is 80% or more; and the raw materials for preparing the electrically detachable acrylate-modified polyurethane hot melt adhesive contain a low-viscosity low-free polyurethane prepolymer, a low-viscosity polyol compound, an ionic liquid, an acrylate compound, and a photoinitiator, as well as optionally a rheological modifier, a silane coupling agent, a water absorbent, and a catalyst, and the molar equivalent ratio of isocyanate groups in the low-viscosity low-free polyurethane prepolymer to hydroxyl groups in the low-viscosity polyol compound is (8-13):

1.

2. The electrically detachable acrylate-modified polyurethane hot melt adhesive according to claim 1, characterized in that, Based on the total weight of the raw materials for preparing the electrically detachable acrylate-modified polyurethane hot melt adhesive, the total content of the low-viscosity low-free polyurethane prepolymer and the low-viscosity polyol compound is 40-80%, the content of the ionic liquid is 2-15%, the content of the acrylate compound is 5-35%, the content of the photoinitiator is 0.1-5%, the content of the rheological modifier is 2-10%, the content of the silane coupling agent is 0.1-3%, the content of the water absorbent is 0.1-2%, and the content of the catalyst is 0.1-2%.

3. The electrically detachable acrylate-modified polyurethane hot melt adhesive according to claim 1, characterized in that, The free isocyanate monomer content in the low-viscosity low-free polyurethane prepolymer is 0.1% or less, and the low-viscosity low-free polyurethane prepolymer is liquid at 50°C and has a viscosity of 100000 cps or less at 50°C.

4. The electrically detachable acrylate-modified polyurethane hot melt adhesive according to claim 1, characterized in that, The number average molecular weight of the low-viscosity polyol compound is 400-6000 g / mol, and the low-viscosity polyol compound is selected from at least one of liquid polyester polyols, liquid polyether polyols, liquid polycarbonate polyols, liquid polycaprolactone polyols, fatty acid dimer diols, castor oil derivative polyols, and hydroxyl-terminated polybutadiene polyols.

5. The electrically detachable acrylate-modified polyurethane hot melt adhesive according to claim 1, characterized in that, The ionic liquid has a melting point of 25°C or lower.

6. The electrically detachable acrylate-modified polyurethane hot melt adhesive according to claim 1, characterized in that, The ionic liquid is composed of a cation selected from at least one of imidazole cation, pyrrole cation, quaternary ammonium salt cation, quaternary phosphonium salt cation, pyrrolidine cation, and piperidine cation, and anion selected from at least one of triflate anion, tetrafluoroborate anion, hexafluorophosphate anion, bisfluoromethanesulfonylimide anion, hydrogen sulfate anion, ethyl sulfate anion, and p-toluene sulfonate anion.

7. The electrically detachable acrylate-modified polyurethane hot melt adhesive according to claim 1, characterized in that, The ionic liquid is at least one of 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-ethyl-3-methylimidazolium triflate, 1-ethyl-2,3-dimethylimidazolium triflate, 1-octyl-3-methylimidazolium triflate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-propyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-2,3-dimethylimidazolium tetrafluoroborate, 1-propyl-2,3-dimethylimidazolium tetrafluoroborate, 1-butyl-2,3-dimethylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium ethyl sulfate, 1-ethyl-2,3-dimethylimidazolium ethyl sulfate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1,3-diethylimidazolium bis(trifluoromethanesulfonyl)imide, 1-propyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1,2-dimethyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide, 1-ethyl-2,3-dimethylimidazolium bisfluorosulfonylimide, N-butylpyridinium tetrafluoroborate, hexyltriethylammonium bis(trifluoromethanesulfonyl)imide, methyltrioctylphosphonium bis(trifluoromethanesulfonyl)imide, N-butyl-N-methylpyrrolidinium bisfluorosulfonylimide, N-butyl-N-methylpyrrolidinium triflate, and N-propyl-N-methylpiperidinium bis(trifluoromethanesulfonyl)imide.

8. The electrically detachable acrylate-modified polyurethane hot melt adhesive according to claim 1, characterized in that, The acrylate compound is at least one of stearyl acrylate, tetrahydrofurfuryl acrylate, dodecyl acrylate, 2-phenoxyethyl acrylate, isodecyl acrylate, isooctyl acrylate, tridecyl acrylate, trimethylolpropane formal acrylate, methoxypolyethylene glycol monoacrylate, alkoxylated tetrahydrofurfuryl acrylate, 1,3-butanediol diacrylate, 1,4-butanediol diacrylate, diethylene glycol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, tetraethylene glycol diacrylate, triethylene glycol diacrylate, tripropylene glycol diacrylate, dipropylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, and 1,3-butanediol dimethacrylate.

9. The electrically detachable acrylate-modified polyurethane hot melt adhesive according to any one of claims 1 to 8, characterized in that The photoinitiator is at least one of benzophenone-based compounds, acetophenone-based compounds, acylphosphine oxide-based compounds, titanocene-based compounds, oxime ester-based compounds, benzoin ether-based compounds, and thioxanthone.

10. The electrically detachable acrylate-modified polyurethane hot melt adhesive according to any one of claims 1 to 8, characterized in that, The rheology modifier is fumed silica.

11. The electrically detachable acrylate-modified polyurethane hot melt adhesive according to any one of claims 1 to 8, characterized in that The silane coupling agent is at least one of 3-mercaptopropyl trimethoxysilane, 3-mercaptopropyl triethoxysilane, 3-mercaptopropyl methyldimethoxysilane, 3-mercaptopropyl methyldiethoxysilane, 3-glycidoxypropyl trimethoxysilane, 3-glycidoxypropyl triethoxysilane, 3-glycidoxypropyl methyldimethoxysilane, 3-glycidoxypropyl methyldiethoxysilane, 2-(3,4-epoxycyclohexyl)ethyl trimethoxysilane, 3-glycidoxypropyl methyldiethoxysilane, 3-aminopropyl trimethoxysilane, 3-aminopropyl triethoxysilane, 3-(2-aminoethyl)aminopropyl trimethoxysilane, 3-(2-aminoethyl)aminopropyl triethoxysilane, 3-(2-aminoethyl)aminopropyl methyldimethoxysilane, 3-acryloyloxypropyl trimethoxysilane, 3-(meth)acryloyloxypropyl trimethoxysilane, 3-(meth)acryloyloxypropyl triethoxysilane, 3-(meth)acryloyloxypropyl methyldimethoxysilane, 3-(meth)acryloyloxypropyl methyldiethoxysilane, vinyl trimethoxysilane, vinyl triethoxysilane, and 3-isocyanate propyl trimethoxysilane.

12. The electrically detachable acrylate-modified polyurethane hot melt adhesive according to any one of claims 1 to 8, characterized in that The water absorbing agent is at least one of molecular sieve desiccant, oxazolidine water removing agent, p-toluenesulfonyl isocyanate, and triethyl orthoformate.

13. The electrically detachable acrylate-modified polyurethane hot melt adhesive according to any one of claims 1 to 8, characterized in that The catalyst is at least one of dibutyl tin dilaurate, stannous octoate, zinc isooctoate, bismuth isooctoate, triethylamine, diethylenetriamine, triethylenediamine, N-ethylmorpholine, and 2,2-dimorpholinodiethylether.

14. Process for the preparation of the electrically detachable acrylate-modified polyurethane hot-melt adhesive according to any one of claims 1 to 13, characterized in that, The method comprises the following steps: S1, dehydrating the low-viscosity polyol compound, the ionic liquid, and optionally the rheology modifier, the silane coupling agent, and the water absorbing agent to obtain a pretreated product; S2, stirring and reacting the pretreated product, the low-viscosity low-free polyurethane prepolymer, and optionally the catalyst at 70-90°C for 1-5h to obtain a prepolymer containing a polyurethane prepolymer mixture; S3, uniformly mixing the prepolymer, the acrylate compound, and the photoinitiator to obtain the electrically detachable acrylate-modified polyurethane hot melt adhesive.

15. Use of the electrically detachable acrylate-modified polyurethane hot melt adhesive according to any one of claims 1-13 in bonding electronic products.

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