Electrically-detachable acrylate-modified polyurethane hot-melt adhesive, and preparation method therefor and use thereof

Abstract

The present invention belongs to the field of adhesives, and relates to an electrically-detachable acrylate-modified polyurethane hot-melt adhesive, and a preparation method therefor and the use thereof. The electrically-detachable acrylate-modified polyurethane hot-melt adhesive comprises a polyurethane prepolymer mixture, an ionic liquid, an acrylate compound and a photoinitiator, wherein two ends of a prepolymer contained in the polyurethane prepolymer mixture are terminated with isocyanate groups; and an isocyanate structural unit contained in the polyurethane prepolymer mixture is derived from a low-viscosity low-free-polyurethane prepolymer, and a polyol structural unit contained therein 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 polyurethane hot-melt adhesive provided by the present invention has the properties of a low content of free isocyanates, low melt viscosity, dispensability at room temperature, high initial tack and final bond strength, a fast curing speed and electrically-induced detachability; and has wide practical application prospects.

Description

An electrically detachable acrylate-modified polyurethane hot melt adhesive, its preparation method and application

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese Patent Application No. 2024114606203, filed on October 18, 2024, entitled "An electrically detachable acrylate-modified polyurethane hot melt adhesive and its preparation method and application", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention belongs to the field of adhesives, specifically relating to an electrically detachable acrylate-modified polyurethane hot melt adhesive, its preparation method, and its application. Background Technology

[0004] Reactive polyurethane hot melt adhesives are often used to bond and fix electronic components in electronic products such as smartphones, tablets, smartwatches, and TWS earphones. The electronic components bonded by reactive polyurethane hot melt adhesives are often of high value. When there are situations such as poor assembly, product after-sales repair, or recycling of valuable electronic components, it is usually necessary to disassemble the bonded parts. Therefore, the adhesive usually needs to have excellent bonding reliability while also being easy to disassemble under certain conditions.

[0005] Reactive polyurethane hot melt adhesives are mainly composed of isocyanate-terminated oligomers. The isocyanate groups in the isocyanate-terminated oligomers can react with moisture in the air. After complete curing, they can form a cross-linked chemical structure, thereby achieving high bonding strength. However, the covalent bonds formed by the reaction of isocyanate groups with moisture are irreversible, and the cross-linked structure is difficult to destroy. After complete curing, it is usually difficult to disassemble the adhesive. If it is necessary to separate the bonded materials, it is often necessary to use large external forces, high temperatures, chemical reagents, etc., and the disassembly of the adhesive may cause damage to the bonded materials, resulting in significant economic losses.

[0006] In recent years, some technologies have also been developed to add ionic liquids or alkali metal salts and solvation matrices to polyurethane hot melt adhesives, thereby giving them the ability to be disassembled under electrical conditions. However, while existing electrically disassembleable polyurethane hot melt adhesives possess this disassembly capability, their high melt viscosity and solid state at room temperature make them difficult to apply. They typically require heating to a melting temperature (usually 90℃~160℃) or higher before extrusion. This usually necessitates the use of specialized heating and application equipment, which increases costs and significantly limits the application scenarios of these polyurethane hot melt adhesives. For example, they are unsuitable for use in homes, repair shops, or other locations where heating equipment is inconvenient, thus greatly restricting the widespread adoption of these single-component polyurethane hot melt adhesives.

[0007] Existing low-viscosity polyurethane hot melt adhesives suitable for room temperature application typically require the addition of excessive amounts of isocyanate monomers to reduce viscosity. While adding large amounts of isocyanate monomers can lower the viscosity to a very low level, the large amount of free isocyanate monomers remaining in the adhesive system poses significant health risks, including respiratory irritation and carcinogenicity. Furthermore, low-viscosity polyurethane hot melt adhesives suitable for room temperature application have slow curing speeds and low initial bond strengths. Their performance in terms of curing speed and bond strength is significantly inferior to traditional PUR hot melt adhesives, making it difficult to meet the performance requirements of practical applications. Furthermore, existing acrylate-modified polyurethane hot melt adhesives are polyurethane hot melt adhesives that can be cured by both UV and moisture by modifying polyurethane hot melt adhesives with acrylate compounds through physical blending or chemical modification. The UV curing speed is fast, and the acrylate components in the acrylate-modified polyurethane hot melt adhesive can be quickly cured after UV irradiation, thus effectively improving the defect of slow curing speed of polyurethane hot melt adhesives that rely on moisture. However, existing acrylate-modified polyurethane hot melt adhesives still have many problems such as difficulty in disassembling after curing, difficulty in applying adhesive at room temperature, and difficulty in effectively bonding to opaque substrates.

[0008] In summary, there is an urgent need to develop an adhesive with low free isocyanate content, low melt viscosity, room temperature dispensing capability, high initial and final bond strength, fast curing speed, and electrical disassembly capability to meet market application demands. Summary of the Invention

[0009] The primary objective of this invention is to provide an acrylate-modified polyurethane hot melt adhesive with low free isocyanate content, low melt viscosity, can be dispensed at room temperature, high initial and final bond strength, fast curing speed, and is electrically removable.

[0010] A second objective of this invention is to provide a method for preparing the above-mentioned acrylate-modified polyurethane hot melt adhesive.

[0011] A third objective of this invention is to provide the application of the above-mentioned acrylate-modified polyurethane hot melt adhesive in the bonding of electronic products.

[0012] Specifically, the electrically removable acrylate-modified polyurethane hot melt adhesive provided by the present invention contains a polyurethane prepolymer mixture, an ionic liquid, an acrylate compound, and a photoinitiator. The prepolymer in the polyurethane prepolymer mixture has isocyanate end caps at both ends. The isocyanate structural units in the polyurethane prepolymer mixture are derived from low-viscosity, low-free polyurethane prepolymers, and the polyol structural units are derived from low-viscosity polyol compounds 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 isocyanate group content in the electrically removable acrylate-modified polyurethane hot melt adhesive is 2–8%, and the free isocyanate monomer content is less than 0.1%. The viscosity range of the electrically removable acrylate-modified polyurethane hot melt adhesive at 25°C is 1000–150000 cps, and the attenuation rate of the adhesive strength after applying a voltage of 1–100V is greater than 80%.

[0013] The method for preparing the electrically detachable acrylate-modified polyurethane hot melt adhesive provided by this invention includes:

[0014] S1. The low-viscosity polyol compound and ionic liquid, along with optional rheology modifiers, silane coupling agents and dehydrating agents, are dehydrated to obtain a pretreated product.

[0015] S2. The pretreated product, low-viscosity, low-free polyurethane prepolymer, and optional catalyst are stirred and reacted at 70-90°C for 1-5 hours to obtain a prepolymer containing a mixture of polyurethane prepolymers.

[0016] S3. Mix the prepolymer, acrylate compound and photoinitiator evenly to obtain the electrically detachable acrylate-modified polyurethane hot melt adhesive.

[0017] After in-depth and extensive research, the inventors of this invention discovered that the polyurethane prepolymer mixtures with isocyanate functional groups used in existing electrically disintegratable polyurethane hot melt adhesives are products obtained by reacting polyol compounds with an excess of polyisocyanate compounds. In these polyisocyanate compounds, the molar equivalent ratio of isocyanate groups to hydroxyl groups in the polyol compound is typically set at (1.5–2.5):1 (i.e., the molar ratio of NCO / OH is (1.5–2.5):1). Polyurethane prepared according to this stoichiometric relationship has a low isocyanate content, a large molecular weight, and strong intermolecular forces, resulting in a high melt viscosity in the final polyurethane prepolymer mixture, which is unfavorable for application at room temperature. Furthermore, some of the polyol compounds used in these isocyanate functional group polyurethane prepolymer mixtures have strong crystallinity or a high glass transition temperature (Tg) at room temperature. Polyurethane prepolymer mixtures prepared by reacting room-temperature crystalline polyols or high-Tg polyols with isocyanate compounds are typically solid substances at room temperature. Therefore, electrically disintegratable polyurethane hot melt adhesives prepared using traditional methods are typically solid at room temperature and require heating to above their melting point (90℃~160℃) before they can be melted and applied. As a result, these electrically disintegratable polyurethane hot melt adhesives that require heating to be used significantly raise the barrier to entry for using such adhesives, increase the cost of adhesive application equipment, and also increase the risk of burns to operators during the application process.

[0018] Existing electrically degradable polyurethane hot melt adhesives achieve this by adding ionic liquids or alkali metal salts and a solvating matrix. The Faraday reaction between the anions and cations in the ionic liquids or alkali metal salts under energized conditions imparts the degradability to the polyurethane hot melt adhesive. While the ionic liquids and solvating matrices introduced into the polyurethane hot melt adhesive facilitate this electrical degradability, these liquids do not participate in the curing process. After curing, the adhesive remains in its initial low-viscosity state, negatively impacting the final bond strength. Furthermore, the isocyanate-terminated polyurethanes currently have a low isocyanate-to-hydroxyl equivalence (NCO / OH equivalence ratio between 1.5 and 2.5), resulting in a low isocyanate content. Consequently, these polyurethanes exhibit low crosslinking density after final wet curing, leading to inherently low bond strength. The negative effects of the ionic liquids and solvating matrices further reduce this bond strength. Therefore, although it is possible to prepare electrically disintegratable polyurethane hot melt adhesives by adding ionic liquids or alkali metal salts in combination with solvation matrices to polyurethane hot melt adhesives, their final adhesion is still significantly lacking, which is not conducive to the application and promotion of such products.

[0019] Existing acrylate-modified polyurethane hot melt adhesives are UV-curable (UV-curable and moisture-curable) polyurethane hot melt adhesives prepared by modifying polyurethane hot melt adhesives with acrylate compounds through physical blending or chemical modification. They offer fast UV curing; after UV irradiation, the acrylate components in acrylate-modified polyurethane hot melt adhesives can quickly achieve photocuring, effectively overcoming the slow curing speed of polyurethane hot melt adhesives that rely on moisture. However, the adhesive strength formed after curing of current acrylate-modified polyurethane hot melt adhesives is relatively strong, making it difficult to achieve easily removable properties. Furthermore, currently available adhesives capable of electrical disassembly generally require conductive substrates to be bonded. These conductive substrates are typically opaque, such as stainless steel, aluminum, and copper. Bonding opaque substrates is difficult using conventional UV-curing adhesives and UV moisture-curing adhesives primarily composed of acrylate compounds and other UV-curing components. This is because, after UV irradiation, adhesive compositions primarily composed of photocuring components cure instantly and quickly lose their re-adhesion. Therefore, most UV-curing adhesives or UV moisture-curing adhesives can only be used for bonding substrates that are transparent on at least one side. Thus, even if known electrical disassembly compositions are directly added to existing UV acrylate adhesives or UV moisture-curing adhesives primarily composed of UV acrylate compounds, they are difficult to directly apply to bonding opaque metal substrates. Furthermore, some existing acrylate-modified polyurethane hot melt adhesives suitable for bonding opaque substrates primarily consist of polyurethane prepolymers modified with a small amount of acrylate compounds. While these adhesives can be used for bonding opaque substrates, their high melt viscosity typically necessitates heating equipment for dispensing. The difficulty in applying these adhesives at room temperature stems primarily from two factors: firstly, the low proportion of low-viscosity acrylate compounds results in limited dilution of the polyurethane matrix; secondly, the polyurethane itself incorporates polyols with high glass transition temperatures and / or strong crystallinity at room temperature, leading to inherently high melt viscosity. Therefore, the final acrylate-modified polyurethane hot melt adhesive is difficult to dispense at room temperature and requires heating equipment for application.

[0020] The key to this invention lies in breaking away from the design limitations of traditional electrically disassembled polyurethane hot melt adhesive preparation processes, which require setting the equivalence ratio of isocyanate groups to hydroxyl groups between (1.5 and 2.5):1 and simultaneously selecting polyol compounds with high Tg and / or high melting points. The invention innovatively reacts polyol compounds with low crystallinity and low glass transition temperature at room temperature with an excess of low-viscosity polyurethane prepolymer with low free isocyanate content. Simultaneously, low-viscosity acrylate compounds and ionic liquids are introduced. This results in an electrically disassembled acrylate-modified polyurethane hot melt adhesive with advantages such as low free isocyanate content, low melt viscosity, room-temperature dispensing capability, high initial and final bond strength, fast curing speed, and electrical disassembly. The reason for this is speculated to be that: acrylate compounds and ionic liquids have good fluidity at room temperature and both have low viscosity. Introducing acrylate compounds and ionic liquids into polyurethane hot melt adhesives simultaneously can achieve an "initial" reduction in system viscosity, improving the fluidity of the adhesive at room temperature. Selecting low-viscosity polyol compounds with a glass transition temperature below 0°C and a melting point below 40°C can fundamentally reduce the melt viscosity of polyurethane hot melt adhesives at room temperature, achieving a "second" reduction in system viscosity. In other words, this invention reduces the viscosity of the system through the combined effects of external viscosity reduction by acrylate compounds and ionic liquids, and internal viscosity reduction by low-viscosity polyol compounds. This facilitates the direct application of polyurethane hot melt adhesives at room temperature, greatly lowering the application threshold of polyurethane hot melt adhesives, reducing the equipment costs required for their application, and effectively avoiding the risk of burns to operators during the adhesive application process. Furthermore, acrylate compounds can rapidly undergo free radical polymerization after UV irradiation, quickly establishing high initial bond strength. By controlling the amount of low-viscosity, low-free-isocyanate polyurethane prepolymer in a significant excess, the isocyanate group content in the system can be increased, thereby improving the crosslinking density. The acrylate compounds provide initial curing, while the significantly excess isocyanate groups provide post-curing through moisture curing. After complete curing, a polyurethane-polyacrylate interpenetrating network structure can be formed, giving the polyurethane hot melt adhesive high final bond strength. Moreover, ionic liquids can undergo Faraday reactions upon electrolysis; introducing ionic liquids into polyurethane hot melt adhesives can impart electrolytic disintegration properties. In addition, this invention uses a polyurethane prepolymer with low free isocyanate content instead of the traditionally used isocyanate monomer, 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 invention relies on acrylate compounds to improve the initial bonding strength in the early stage and on the polyurethane-polyacrylate interpenetrating network structure to improve the final bonding strength in the later stage. Even if affected by the uncured ionic liquid, it can still maintain a relatively high initial bonding strength and final bonding strength.In summary, the electrically detachable acrylate-modified polyurethane hot melt adhesive provided by this invention has the advantages of low free isocyanate content, low melt viscosity, room temperature dispensing capability, high initial and final bond strength, fast curing speed, and electrical detachability, and has broad prospects for practical application. Detailed Implementation

[0021] The electrically detachable acrylate-modified polyurethane hot melt adhesive provided by this invention has a viscosity range of 1000 to 150000 cps at 25°C, specifically 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 30000, 50000, 70000, 90000, 110000, 130000, 150000 cps or any value between them.

[0022] The acrylate-modified polyurethane hot melt adhesive provided by this invention exhibits a bond strength attenuation rate of over 80% after being energized with a voltage ranging from 1 to 100V. Specifically, this attenuation rate can be 80%, 82%, 85%, 88%, 90%, 92%, 95%, 98%, 99%, 100%, or any value between these values. The voltage required for disassembling the acrylate-modified polyurethane hot melt adhesive is preferably 1 to 100V, specifically 1V, 3V, 5V, 8V, 10V, 20V, 30V, 40V, 50V, 60V, 70V, 80V, 90V, 100V, or any value between these values. The energizing time is preferably 1s to 60min, such as 1s, 5s, 10s, 30s, 1min, 5min, 10min, 15min, 20min, 30min, 40min, 50min, 60min, or any value between these values.

[0023] In this invention, 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 between them. The content of free isocyanate monomers in the electrically detachable one-component reactive polyurethane hot melt adhesive is less than 0.1%, such as 0.1%, 0.08%, 0.05%, 0.03%, 0.02%, 0.01%, or any value between them. In this invention, the total content of isocyanate groups refers to the ratio of the total weight of all unreacted isocyanate functional groups in the system (including isocyanate functional groups on the prepolymer end groups and isocyanate functional groups in the free isocyanate monomers) to the total weight of the polyurethane hot melt adhesive.

[0024] In this invention, the electrically removable acrylate-modified polyurethane hot melt adhesive contains a polyurethane prepolymer mixture, an ionic liquid, acrylate compounds, and a photoinitiator. The viscosity of the system is reduced by introducing polyol structural units with weak crystallinity or low glass transition temperatures from the polyurethane prepolymer mixture, along with the addition of acrylate compounds and ionic liquids, thus giving it the ability to be applied directly at room temperature. Furthermore, the introduction of acrylate compounds improves the initial bond strength and curing speed of the polyurethane hot melt adhesive, and the final bond strength is improved by controlling the mass ratio of the polyurethane prepolymer mixture to the acrylate compounds. The introduction of the ionic liquid imparts electrically removable properties to 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 below 0℃, specifically 0℃, -2℃, -4℃, -6℃, -8℃, -10℃, -12℃, -14℃, -16℃, -18℃, -20℃, -22℃, -24℃, -26℃, -28℃, -30℃, -32℃, -34℃, -36℃, -38℃, -40℃, etc. The melting point of the low-viscosity polyol compound is below 40°C, specifically 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 this invention, the term "polyurethane prepolymer mixture" refers to the product obtained by an addition reaction of a low-viscosity, low-free polyurethane prepolymer and a low-viscosity polyol compound. Because this product contains polymers of different molecular weights and potentially unreacted monomers, it is a mixture of multiple substances, hence the name "polyurethane prepolymer mixture."

[0025] The electrically detachable acrylate-modified polyurethane hot melt adhesive provided by this invention is a liquid or paste at room temperature. It has the characteristics of low melt viscosity, room temperature dispensing capability, high initial and final bond strength, fast curing speed, and electrical detachability.

[0026] In a preferred embodiment, the raw materials for preparing the electrically detachable acrylate-modified polyurethane hot melt adhesive contain a low-viscosity, low-free-polymer polyurethane prepolymer, a low-viscosity polyol compound, an ionic liquid, an acrylate compound, a photoinitiator, and optionally a rheology modifier, a silane coupling agent, a water-absorbing agent, and a catalyst. The preferred molar ratio of isocyanate groups in the low-viscosity, low-free-polymer polyurethane prepolymer to hydroxyl groups in the low-viscosity polyol compound is (8–13):1, such as 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, or any value between them.

[0027] In this invention, the preferred 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 (2.5–40):1, specifically 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 between them. The preferred mass ratio of the acrylate compound to the ionic liquid is (0.3–18):1, specifically 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 between them. The preferred mass ratio of the photoinitiator to the ionic liquid is (0.005–2.5):1, specifically 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 between them. The preferred mass ratio of the rheology modifier to the ionic liquid is (0–5):1, specifically 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 between them. The preferred mass ratio of the silane coupling agent to the ionic liquid is (0–1.5):1, specifically 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 between them. The preferred mass ratio of the water-absorbing agent to the ionic liquid is (0–1):1, specifically 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 between them. The mass ratio of the catalyst to the ionic liquid is preferably (0.005 to 1):1, and can specifically 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 between them.

[0028] In a preferred embodiment, 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%, such as 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or 80%; the content of the ionic liquid is 2-15%, such as 2%, 5%, 8%, 10%, 12%, or 15%, or any value between them; the content of the acrylate compound is 5-35%, such as 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, or 35%, or any value between them; the photoinitiator... The content of the rheology modifier is 0.1-5%, such as 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or any value between them; the content of the rheology modifier is 2-10%, such as 2%, 5%, 8%, 10%, or any value between them; 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 between them; the content of the desiccant is 0.1-2%, such as 0.1%, 0.5%, 0.8%, 1%, 1.5%, 2%, or any value between them; the content of the catalyst is 0.1-2%, such as 0.1%, 0.5%, 0.8%, 1%, 1.5%, 2%, or any value between them.

[0029] In this invention, the free isocyanate monomer content in the low-viscosity, low-free polyurethane prepolymer is preferably below 0.1%, specifically 0.1%, 0.08%, 0.05%, 0.03%, 0.02%, 0.01%, or any value between them. The low-viscosity, low-free polyurethane prepolymer is liquid at temperatures below 50°C. The viscosity of the low-viscosity, low-free polyurethane prepolymer at 50°C is preferably below 100,000 cps, 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 between them. The low-viscosity, low-free-polymer polyurethane prepolymer can be obtained by reacting a polyether polyol with a polyisocyanate monomer. The polyether polyol may include at least one ring-opening polymer of ethylene glycol, propylene glycol, tetrahydrofuran, or 3-methyltetrahydrofuran, or a random copolymer or block copolymer of ethylene glycol, propylene glycol, tetrahydrofuran, 3-methyltetrahydrofuran, or their derivatives. The polyisocyanate monomer may include at least one of 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, phenylenediamine diisocyanate, tetramethylxylene diisocyanate, and norbornene diisocyanate. Commercial raw materials for low-free polyether polyol-based polyurethane prepolymers include Lanxess's 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, and Adiprene LFMI G600.

[0030] In this invention, the number-average molecular weight of the low-viscosity polyol compound is preferably 400–6000 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 between them. The low-viscosity polyol compound can be any existing polyol compound with a glass transition temperature below 0°C and a melting point below 40°C, specific examples including but not limited to: liquid polyester polyol, liquid polyether polyol, liquid polycarbonate polyol, liquid polycaprolactone polyol, fatty acid dimer diol, castor oil derivative polyol, and at least one of hydroxyl-terminated polybutadiene polyol.

[0031] In this invention, the melting point of the ionic liquid is preferably below 25°C, 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 cations and anions. The cations are preferably selected from at least one of imidazole cations, pyrrole cations, quaternary ammonium salt cations, quaternary phosphate salt cations, pyrrolidine cations, and piperidine cations. The anions are preferably selected from at least one of trifluoromethanesulfonate anion, tetrafluoroborate anion, hexafluorophosphate anion, difluoromethanesulfonylimide anion, hydrogen sulfate anion, ethyl sulfate anion, and p-toluenesulfonate anion. Specific examples of the aforementioned ionic liquids may include, but are not limited to: 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate, 1-ethyl-2,3-dimethylimidazolium trifluoromethanesulfonate, 1-octyl-3-methylimidazolium trifluoromethanesulfonate, 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-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium ethyl sulfate, 1-ethyl-2,3-dimethylimidazolium ethyl sulfate, and 1-butyl-3-methylimidazolium bis(trifluoromethane) At least one of the following: sulfonyl bis(trifluoromethanesulfonyl)imide salt, 1,3-diethylimidazolium bis(trifluoromethanesulfonyl)imide salt, 1-propyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, 1,2-dimethyl-3-propylimidazolium bis(trifluoromethanesulfonyl)imide, 1-ethyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide salt, N-butylpyridine tetrafluoroborate, hexyltriethylammonium bis(trifluoromethanesulfonyl)imide salt, methyltrioctylphosphonium bis(trifluoromethanesulfonyl)imide salt, N-butyl-N-methylpyrrolidine bis(trifluoromethanesulfonyl)imide salt, N-butyl-N-methylpyrrolidine trifluoromethanesulfonate, and N-propyl-N-methylpiperidine bis(trifluoromethanesulfonyl)imide salt.

[0032] In this invention, the acrylate compound can be any of the existing photocurable acrylate monomers, such as at least one of octadecyl acrylate, tetrahydrofuran acrylate, dodecyl acrylate, 2-phenoxyethyl acrylate, isodecanyl acrylate, isooctyl acrylate, tridecyl acrylate, trimethylolpropane formaldehyde acrylate, methoxy polyethylene glycol monoacrylate, alkyl tetrahydrofuran 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.

[0033] In this invention, the photoinitiator can be any existing compound that absorbs energy in the ultraviolet or visible light region to generate free radicals to initiate the polymerization reaction of acrylic functional groups, such as at least one of benzophenone compounds, acetophenone compounds, phosphine oxide compounds, dicocene compounds, oxime ester compounds, benzoin ether compounds, and thioxanone.

[0034] In this invention, the rheology modifier is preferably fumed silica, and specific examples 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 90–380 m². 2 / g, specifically 90, 100, 120, 150, 180, 200, 220, 240, 260, 280, 300, 320, 340, 360, 380m 2 / g or any value in between.

[0035] In this invention, specific examples of the silane coupling agent include, but are not limited to: 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropylmethyldiethoxysilane, 3-epoxypropoxypropyltrimethoxysilane, 3-epoxypropoxypropyltriethoxysilane, 3-epoxypropoxypropylmethyldimethoxysilane, 3-epoxypropoxypropylmethyldiethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-epoxypropoxypropylmethyldiethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane. The first of the following: methyl silane, 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-isocyanate propyltrimethoxysilane.

[0036] In this invention, the desiccant may be selected from at least one of molecular sieve desiccant, oxazolidine desiccant, p-toluenesulfonyl isocyanate, and triethyl orthoformate.

[0037] In this invention, the catalyst may be selected from at least one of dibutyltin dilaurate, stannous octoate, zinc isooctanoate, bismuth isooctanoate, triethylamine, diethylenetriamine, triethylenediamine, N-ethylmorpholine, and 2,2-dimorpholinodiethyl ether.

[0038] The method for preparing the electrically detachable acrylate-modified polyurethane hot melt adhesive provided by this invention includes:

[0039] S1. The low-viscosity polyol compound and ionic liquid, along with optional rheology modifiers, silane coupling agents and dehydrating agents, are dehydrated to obtain a pretreated product.

[0040] S2. The pretreated product, low-viscosity, low-free polyurethane prepolymer, and optional catalyst are stirred and reacted at 70-90°C for 1-5 hours to obtain a prepolymer containing a mixture of polyurethane prepolymers.

[0041] S3. Mix the prepolymer, acrylate compound and photoinitiator evenly to obtain the electrically detachable acrylate-modified polyurethane hot melt adhesive.

[0042] In this invention, in step S1, the dehydration treatment conditions preferably include a temperature of 100–120°C, such as 100°C, 102°C, 104°C, 106°C, 108°C, 110°C, 112°C, 114°C, 116°C, 118°C, 120°C, or any value between them; a rotation speed of 100–200 r / min, such as 100 r / min, 110 r / min, 120 r / min, 130 r / min, 140 r / min, 150 r / min, 160 r / min, 170 r / min, 180 r / min, 190 r / min, 200 r / min, or any value between them; and a time of 1–5 h, such as 1 h, 2 h, 3 h, 4 h, 5 h, or any value between them.

[0043] In this invention, in step S2, the temperature of the stirring reaction is preferably 70-90°C, specifically 70°C, 72°C, 74°C, 76°C, 78°C, 80°C, 82°C, 84°C, 86°C, 88°C, 90°C, or any value between them; the stirring speed is preferably 100-200 r / min, specifically 100 r / min, 110 r / min, 120 r / min, 130 r / min, 140 r / min, 150 r / min, 160 r / min, 170 r / min, 180 r / min, 190 r / min, 200 r / min, or any value between them; the stirring time is preferably 1-5 h, specifically 1 h, 2 h, 3 h, 4 h, 5 h, or any value between them.

[0044] In this invention, in step S3, the mixing conditions preferably include a temperature of 70–90°C, specifically 70°C, 72°C, 74°C, 76°C, 78°C, 80°C, 82°C, 84°C, 86°C, 88°C, 90°C, or any value between them; a stirring speed of 100–200 r / min, specifically 100 r / min, 110 r / min, 120 r / min, 130 r / min, 140 r / min, 150 r / min, 160 r / min, 170 r / min, 180 r / min, 190 r / min, 200 r / min, or any value between them; and a time of 30 min–2 h, specifically 30 min, 40 min, 50 min, 60 min, 80 min, 100 min, 120 min, or any value between them.

[0045] The present invention also provides the application of the electrically detachable acrylate-modified polyurethane hot melt adhesive in the bonding of electronic products.

[0046] The adhesive substrate used in the electrically detachable acrylate-modified polyurethane hot melt adhesive provided by this invention is a conductive substrate.

[0047] The present invention will be described in detail below through embodiments. These embodiments are intended to explain the invention and should not be construed as limiting it. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0048] Example 1

[0049] By weight, 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 polytetrahydrofuran ether diol (PTMEG-2000, purchased from PTG Corporation, Korea; Tg = -76℃; melting point = 24℃), 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 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) was added. LF TE 915 (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 electrically detachable acrylate-modified polyurethane hot melt adhesive, which was vacuum-sealed and stored away from light.

[0050] Example 2

[0051] By weight, the following components were added: 5.38 g (5.376 mmol) of polycaprolactone diol (PLACCEL 210N; Tg = -17℃; melting point = 32~37℃) with a number average molecular weight of 1000, 5.38 g (1.792 mmol) of liquid polycarbonate diol (Kuraray polyol C3090; Tg = -42℃; melting point <25℃) 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, and 0.7 g of water-absorbing agent Additive. The 0°C was heated to 110°C and vacuum dehydrated for 2 hours under stirring at 150 rpm. The mixture was then cooled to 80°C, and 67.65 g (78.844 mmol) of low-free polyurethane prepolymer (Adiprene LF TE 980; viscosity at 50°C: 8000–16400 cps; free isocyanate monomer content: less than 0.1%) and 0.1 g of stannous octoate were added. The mixture was reacted for 2 hours under stirring at 150 rpm. Then, 0.5 g of photoinitiator TPO, 10.0 g of 1,6-hexanediol diacrylate, and 5.0 g of trimethylolpropane formal acrylate were added. The mixture was stirred at 150 rpm for 1 hour and then discharged to obtain an electrically detachable acrylate-modified polyurethane hot melt adhesive. The adhesive was then vacuum-sealed and stored away from light.

[0052] Example 3

[0053] By weight, 7.62 g (1.386 mmol) of liquid polyester diol with a number-average molecular weight of 5500 (Evonik 7250; Tg = -50℃; melting point <25℃), 5.54 g (2.772 mmol) of polyether diol with a number-average molecular weight of 2000 (Voranol 2120; Tg <0℃; melting point <25℃), 8.00 g of N-butylpyridine tetrafluoroborate, 4.0 g of fumed silica AEROSIL R972, 2.0 g of vinyltrimethoxysilane, and 1.5 g of water-absorbing agent Additive TI were heated to 110℃ and vacuum dehydrated for 2 h under stirring at 150 r / min. The mixture was then cooled to 80℃, and 43.03 g (37.42 mmol) of low-free polyurethane prepolymer (Adiprene LF) was added. G730 (viscosity at 50℃: 22750cps; free isocyanate monomer content: less than 0.1%), 1.1g of 2,2-dimorpholinodiethyl ether, reacted under stirring at 150r / min for 2h, then 2.2g of photoinitiator 184, 10.0g of neopentyl glycol diacrylate, and 15.0g of isooctyl acrylate were added, mixed under stirring at 150r / min for 1h, and then discharged to obtain electrically detachable acrylate-modified polyurethane hot melt adhesive, which was vacuum-sealed and stored away from light.

[0054] Example 4

[0055] By weight, 2.31 g (1.155 mmol) of liquid polycarbonate diol with a number average molecular weight of 2000 (DURANOL T5652; Tg < 0℃; melting point < -5℃), 4.62 g (2.31 mmol) of liquid polyester diol with a number average molecular weight of 2000 (Stepanpol PH-56; Tg = -15℃; melting point < 25℃), 10.00 g of 1-octyl-3-methylimidazolium trifluoromethane sulfonate, 3.0 g of fumed silica HDK H18, 0.5 g of 3-epoxypropoxypropyltriethoxysilane, and 1.2 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 46.57 g (41.58 mmol) of low-free polyurethane prepolymer (Adiprene LF) was added. G750 (viscosity at 50℃: 32000cps; free isocyanate monomer content: less than 0.1%), 0.8g zinc isooctanoate, reacted at 150r / min for 2h, then 3.0g photoinitiator 819, 14.0g diethylene glycol diacrylate, and 14.0g tridecyl acrylate were added, mixed at 150r / min for 1h, and then discharged to obtain electrically disintegratable acrylate-modified polyurethane hot melt adhesive, which was vacuum-sealed and protected from light.

[0056] Example 5

[0057] By weight, 2.28 g (2.276 mmol) of polyether glycol (voranol 220-110; Tg < 0℃; melting point < 25℃) with a number-average molecular weight of 2000, 3.98 g (1.138 mmol) of liquid polyester glycol (Dynacoll 7230; Tg = -30℃; melting point < 25℃) with a number-average molecular weight of 3500, 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, and 1.5 g of water-absorbing agent Additive TI were heated to 110℃ and vacuum dehydrated for 2 h under stirring at 150 r / min. The mixture was then cooled to 80℃, and 38.24 g (27.315 mmol) of low-free polyurethane prepolymer (Adiprene LF) was added. G600 (viscosity at 50℃: 3975cps; free isocyanate monomer content: less than 0.1%), 1.2g bismuth isooctanoate, reacted at 150r / min for 2h, then 4.0g photoinitiator 369, 20.0g triethylene glycol diacrylate, and 12.0g dodecyl acrylate were added, mixed at 150r / min for 1h, and then discharged to obtain an electrically decomposable acrylate-modified polyurethane hot melt adhesive, which was vacuum-sealed and protected from light.

[0058] Comparative Example 1

[0059] By weight, the following components were used: 39.42 g (11.262 mmol) of polyester diol with a number-average molecular weight of 3500 (Evonik Dynacoll 7360; Tg = -60℃; melting point = 55℃), 22.52 g (11.262 mmol) of polytetrahydrofuran ether diol with a number-average molecular weight of 2000 (PTMG2000; 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, and 0.5 g of water-absorbing agent Additive. The 4,4'-diphenylmethane diisocyanate (MDI) was heated to 110°C and vacuum dehydrated for 2 hours under stirring at 150 rpm. The mixture was then cooled to 80°C, and 12.03 g (48.123 mmol) of MDI and 0.3 g of stannous octoate were added. The mixture was reacted for 2 hours under stirring at 150 rpm and then discharged to obtain a reference electrically removable acrylate-modified polyurethane hot melt adhesive. The adhesive was then vacuum-sealed and stored away from light.

[0060] Comparative Example 2

[0061] A reference electrically removable 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 with the same molar amount of low-free polyurethane prepolymer Adiprene LF S300, which is solid at 50°C. The other conditions were the same as in Example 1. The reference electrically removable acrylate-modified polyurethane hot melt adhesive was obtained and stored in a vacuum-sealed, light-protected container.

[0062] Comparative Example 3

[0063] A reference electrically detachable 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 reduced from 10:1 to 2:1, as detailed below:

[0064] By weight, 16.01 g (8.003 mmol) of liquid polycaprolactone diol (PLACCEL L220AL; Tg = <0℃; melting point = 0-5℃) with a number-average molecular weight of 2000, 16.01 g (8.003 mmol) of polytetrahydrofuran ether diol (PTG Corporation, Korea, brand name PTMEG-2000; Tg = -76℃; melting point = 24℃), 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 were added. The solution was heated to 110°C and vacuum dehydrated for 2 hours under stirring at 150 rpm. Then, it was cooled to 80°C, and 29.39 g (32.013 mmol) of low-free polyurethane prepolymer (Adiprene LF TE 915; viscosity at 50°C 2000–4000 cps; free isocyanate monomer content less than 0.1%) and 0.5 g of dibutyltin dilaurate were added. The mixture was reacted for 2 hours under stirring at 150 rpm. Then, 1.5 g of photoinitiator ITX, 12.0 g of tetrahydrofuran acrylate, and 10.0 g of triethylene glycol diacrylate were added. The mixture was stirred at 150 rpm for 1 hour and then discharged to obtain a reference electrically removable acrylate-modified polyurethane hot melt adhesive, which was then vacuum-sealed and stored away from light.

[0065] Comparative Example 4

[0066] A reference electrically removable 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 with the same amount of 4,4'-diphenylmethane diisocyanate (MDI) monomer. The other conditions were the same as in Example 1. The reference electrically removable acrylate-modified polyurethane hot melt adhesive was obtained and stored in a vacuum-sealed, light-protected container.

[0067] Comparative Example 5

[0068] A reference electrically removable 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. The rest was the same as in Example 1. The reference electrically removable acrylate-modified polyurethane hot melt adhesive was obtained and stored in a vacuum-sealed, light-protected container.

[0069] Comparative Example 6

[0070] A reference electrically removable acrylate-modified polyurethane hot melt adhesive was prepared according to the method of Example 1, except that tetrahydrofuran acrylate and triethylene glycol diacrylate were not added. The rest was the same as in Example 1. The reference electrically removable acrylate-modified polyurethane hot melt adhesive was obtained and stored in a vacuum-sealed, light-protected container.

[0071] Comparative Example 7

[0072] A reference electrically removable acrylate-modified polyurethane hot melt adhesive was prepared according to the method of Example 1, except that the amount of tetrahydrofuran acrylate and triethylene glycol diacrylate added was increased to 50g, while the rest was the same as in Example 1. The reference electrically removable acrylate-modified polyurethane hot melt adhesive was obtained and stored in a vacuum-sealed, light-protected container.

[0073] Comparative Example 8

[0074] The reactive polyurethane hot melt adhesive was prepared according to the method described in 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 detailed below:

[0075] 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 TE) was added. 915; viscosity at 50℃ is 2000~4000cps; free isocyanate monomer content is less than 0.1%), 0.5g dibutyltin dilaurate, reacted under stirring at 150r / min for 2h, then 1.5g photoinitiator ITX, 12.0g tetrahydrofuran acrylate, 10.0g triethylene glycol diacrylate were added, mixed under stirring at 150r / min for 1h and then discharged to obtain a reference electrically removable acrylate modified polyurethane hot melt adhesive, which was vacuum sealed and stored away from light.

[0076] Test case

[0077] The samples from the examples and comparative examples were compared and tested using the following method:

[0078] (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.

[0079] (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.

[0080] (3) Bonding strength after energization: Using a dispensing machine, the polyurethane hot melt adhesive obtained in the above embodiments and comparative examples was dispensed at room temperature (if it is solid at room temperature, the dispensing temperature was set to 110℃). A rectangular adhesive line of 25mm×4mm was applied to the 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 48 hours. Then, the positive and negative terminals of a DC power supply were clamped to both ends of the sheared sample. A specific voltage was applied for a certain time. After energizing, the sample was removed, and 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 displayed by the instrument was recorded, and the shear bond strength of the polyurethane hot melt adhesive to the stainless steel substrate was calculated based on the bond area. The results are shown in Table 1.

[0081] (4) Isocyanate group content: Determined according to standard HG / T2409-92. Take (2±0.2)g or more of the polyurethane hot melt adhesive sample obtained from the comparative example and the embodiment (accurate to 0.001g) and place it in an Erlenmeyer flask. Accurately transfer 10mL of di-n-butylamine-toluene solution into the Erlenmeyer flask with a pipette, then add 20mL of toluene and gently shake to dissolve. Finally, add 80mL of anhydrous isopropanol, let stand for 15min, and titrate with 0.5mol / L hydrochloric acid standard solution using bromocresol green as an indicator. The titration endpoint is when the solution changes from blue to yellow and does not change color for 30s (perform a blank test in the same way). Calculate the isocyanate group content in the polyurethane hot melt adhesive sample based on the difference between the amount of hydrochloric acid consumed in the blank titration and the amount consumed in the polyurethane hot melt adhesive sample. The results are shown in Table 1.

[0082] (5) Free isocyanate monomer content: High-performance liquid chromatography (HPLC) was used with liquid as the mobile phase. A high-pressure delivery system was employed to pump the mobile phase into a chromatographic column packed with the stationary phase. After separation within the column, the components were detected by a detector to obtain the chromatogram of the target substance. The content of free isocyanate monomer in the polyurethane hot melt adhesive was quantitatively calculated using the external standard method. The chromatograms of the test sample and the standard were recorded separately. Based on the integrated area of ​​a specific peak on the chromatogram, the content of free isocyanate in the test sample was calculated. The results are shown in Table 1.

[0083] Table 1

[0084] As shown in Table 1, the electrically removable acrylate-modified polyurethane hot melt adhesive provided by this invention has a low viscosity at room temperature, allowing for direct application at room temperature. This significantly improves upon the drawback of reactive polyurethane hot melt adhesives requiring heating for application, increasing the convenience of adhesive use and reducing the risk of burns to operators using heating equipment. Based on practical experience, a bond strength below 2.0 MPa at room temperature indicates that the polyurethane hot melt adhesive is electrically removable; otherwise, it is not. Table 1 also shows that the acrylate-modified polyurethane hot melt adhesive provided by this invention, which can be applied at room temperature, can quickly establish a high initial bond strength after UV irradiation, enabling preliminary positioning in a short time. After complete curing, it exhibits excellent final bond strength, and the adhesive strength significantly decreases after energization, even leading to direct detachment, demonstrating excellent energized removability. In summary, the electrically removable acrylate-modified polyurethane hot melt adhesive provided by this invention also has extremely low free isocyanate monomer residue, significantly reducing the risk of health hazards during hot melt adhesive use. In summary, the acrylate-modified polyurethane hot melt adhesive provided by this invention has a low free isocyanate content, can be dispensed at room temperature, has high initial and final bond strength, and a fast curing speed. It also has the function of being disassembled under power conditions, and has broad prospects for practical applications.

[0085] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. An electrically detachable acrylate-modified polyurethane hot melt adhesive, characterized in that, The electrically removable acrylate-modified polyurethane hot melt adhesive contains a polyurethane prepolymer mixture, an ionic liquid, acrylate compounds, and a photoinitiator. The prepolymer in the polyurethane prepolymer mixture has isocyanate end caps at both ends. The isocyanate structural units in the polyurethane prepolymer mixture are derived from low-viscosity, low-free polyurethane prepolymers, and the polyol structural units are derived from low-viscosity polyol compounds 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 compounds is 1:(0.06–0.9). The total isocyanate group content in the electrically removable acrylate-modified polyurethane hot melt adhesive is 2–8%, and the free isocyanate monomer content is less than 0.1%. The viscosity range of the electrically removable acrylate-modified polyurethane hot melt adhesive at 25°C is 1000–150000 cps, and the bond strength attenuation rate after applying a voltage of 1–100V is greater than 80%.

2. The electrically detachable acrylate-modified polyurethane hot melt adhesive according to claim 1, characterized in that, 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, a photoinitiator, and optional rheology modifiers, silane coupling agents, water-absorbing agents, and catalysts. 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.

3. The electrically detachable acrylate-modified polyurethane hot melt adhesive according to claim 2, 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 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 rheology 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%.

4. The electrically detachable acrylate-modified polyurethane hot melt adhesive according to claim 2, characterized in that, The free isocyanate monomer content in the low viscosity, low free polyurethane prepolymer is less than 0.1%; the low viscosity, low free polyurethane prepolymer is liquid at 50°C and has a viscosity of less than 100,000 cps at 50°C.

5. The electrically detachable acrylate-modified polyurethane hot melt adhesive according to claim 2, characterized in that, The number average molecular weight of the low-viscosity polyol compound is 400-6000 g / mol; the low-viscosity polyol compound is selected from at least one of liquid polyester polyol, liquid polyether polyol, liquid polycarbonate polyol, liquid polycaprolactone polyol, fatty acid dimer diol, castor oil derivative polyol and hydroxyl-terminated polybutadiene polyol.

6. The electrically detachable acrylate-modified polyurethane hot melt adhesive according to claim 2, characterized in that, The melting point of the ionic liquid is below 25°C.

7. The electrically detachable acrylate-modified polyurethane hot melt adhesive according to claim 2, characterized in that, The ionic liquid is composed of cations and anions. The cations are selected from at least one of imidazole cations, pyrrole cations, quaternary ammonium salt cations, quaternary phosphate salt cations, pyrrolidine cations, and piperidine cations. The anions are selected from at least one of trifluoromethanesulfonate anion, tetrafluoroborate anion, hexafluorophosphate anion, difluoromethanesulfonylimide anion, hydrogen sulfate anion, ethyl sulfate anion, and p-toluenesulfonate anion.

8. The electrically detachable acrylate-modified polyurethane hot melt adhesive according to claim 2, characterized in that, The ionic liquid is selected from 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate, 1-ethyl-2,3-dimethylimidazolium trifluoromethanesulfonate, 1-octyl-3-methylimidazolium trifluoromethanesulfonate, 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-methylimidazolium 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(tri) At least one of the following: fluoromethanesulfonyl imide salt, 1,3-diethylimidazolium bis(trifluoromethanesulfonyl) imide salt, 1-propyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide salt, 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide salt, 1,2-dimethyl-3-propylimidazolium bis(trifluoromethanesulfonyl) imide, 1-ethyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl) imide salt, N-butylpyridine tetrafluoroborate, hexyltriethylammonium bis(trifluoromethanesulfonyl) imide salt, methyltrioctylphosphonium bis(trifluoromethanesulfonyl) imide salt, N-butyl-N-methylpyrrolidine bis(trifluoromethanesulfonyl) imide salt, N-butyl-N-methylpyrrolidine trifluoromethanesulfonate, and N-propyl-N-methylpiperidine bis(trifluoromethanesulfonyl) imide salt.

9. The electrically detachable acrylate-modified polyurethane hot melt adhesive according to claim 2, characterized in that, The acrylate compounds are selected from at least one of octadecyl acrylate, tetrahydrofuran acrylate, dodecyl acrylate, 2-phenoxyethyl acrylate, isodecanyl acrylate, isooctyl acrylate, tridecyl acrylate, trimethylolpropane formaldehyde acrylate, methoxy polyethylene glycol monoacrylate, alkyloxytetrahydrofuran 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.

10. The electrically detachable acrylate-modified polyurethane hot melt adhesive according to claim 1, characterized in that, The photoinitiator is selected from at least one of benzophenone compounds, acetophenone compounds, acylphosphine oxide compounds, dicocene compounds, oxime ester compounds, benzoin ether compounds, and thioxanone.

11. The electrically detachable acrylate-modified polyurethane hot melt adhesive according to claim 2, characterized in that, The rheology modifier is fumed silica.

12. The electrically detachable acrylate-modified polyurethane hot melt adhesive according to claim 2, characterized in that, The silane coupling agent is selected from 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropylmethyldiethoxysilane, 3-epoxypropoxypropyltrimethoxysilane, 3-epoxypropoxypropyltriethoxysilane, 3-epoxypropoxypropylmethyldimethoxysilane, 3-epoxypropoxypropylmethyldiethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-epoxypropoxypropylmethyldiethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-(2 At least one of the following: (-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-isocyanate propyltrimethoxysilane.

13. The electrically detachable acrylate-modified polyurethane hot melt adhesive according to claim 2, characterized in that, The desiccant is selected from at least one of molecular sieve desiccant, oxazolidine desiccant, p-methylbenzenesulfonyl isocyanate, and triethyl orthoformate.

14. The electrically detachable acrylate-modified polyurethane hot melt adhesive according to claim 2, characterized in that, The catalyst is selected from at least one of dibutyltin dilaurate, stannous octoate, zinc isooctanoate, bismuth isooctanoate, triethylamine, diethylenetriamine, triethylenediamine, N-ethylmorpholine, and 2,2-dimorpholinodiethyl ether.

15. The method for preparing the electrically detachable acrylate-modified polyurethane hot melt adhesive according to claim 1, characterized in that, The method includes the following steps: S1. The low-viscosity polyol compound and ionic liquid, along with optional rheology modifiers, silane coupling agents and dehydrating agents, are dehydrated to obtain a pretreated product. S2. The pretreated product, low-viscosity, low-free polyurethane prepolymer, and optional catalyst are stirred and reacted at 70-90°C for 1-5 hours to obtain a prepolymer containing a mixture of polyurethane prepolymers. S3. Mix the prepolymer, acrylate compound and photoinitiator evenly to obtain the electrically detachable acrylate-modified polyurethane hot melt adhesive.

16. The application of the electrically detachable acrylate-modified polyurethane hot melt adhesive of claim 1 in the bonding of electronic products.

Images