Acrylate-modified polyurethane hot-melt adhesive, preparation method therefor, and use thereof

Abstract

The present invention belongs to the field of adhesives, and relates to an acrylate-modified polyurethane hot-melt adhesive, a preparation method therefor, and a use thereof. The acrylate-modified polyurethane hot-melt adhesive has a viscosity at 25°C in the range of 1,000cps to 150,000cps, and exhibits a bonding strength decay rate of over 80% after being energized at a voltage of 1V to 100 V. The acrylate-modified polyurethane hot-melt adhesive contains a polyurethane prepolymer mixture, an acrylate compound, an ionic liquid, and a photoinitiator. The polyol structural units in the polyurethane prepolymer mixture 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 (1.5-9):1. The polyurethane hot-melt adhesive provided by the present invention has low melt viscosity, can be dispensed at room temperature, has high initial and final bonding strength, cures rapidly, and also possesses a detachable function under energized conditions.

Description

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

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese Patent Application No. 2024114606218, filed on October 18, 2024, entitled "An Acrylic Ester 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 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, 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 mean they typically require heating to above their melting temperature (usually 90℃~160℃) before extrusion. This generally necessitates the use of specialized heating and application equipment, which increases costs and significantly limits their application scenarios. For example, they are unsuitable for use in homes or repair shops where heating equipment is inconvenient, thus severely restricting their widespread adoption. Furthermore, while existing electrically disassembleable polyurethane hot melt adhesives offer some degree of disassembly, they suffer from low final bond strength, poor reliability, and slow curing speed, exhibiting a significant performance gap compared to traditional reactive polyurethane hot melt adhesives, making it difficult to meet the performance requirements of practical applications.

[0007] Existing acrylate-modified polyurethane hot melt adhesives are prepared by modifying polyurethane hot melt adhesives with acrylate compounds through physical blending or chemical modification. These adhesives are capable of both UV and moisture curing, offering rapid UV curing. After UV irradiation, the acrylate components in the acrylate-modified polyurethane hot melt adhesive can quickly achieve photocuring, effectively overcoming the slow curing speed of polyurethane hot melt adhesives that rely on moisture. However, current acrylate-modified polyurethane hot melt adhesives still suffer from several problems, such as difficulty in disassembling after curing and difficulty in applying at room temperature.

[0008] In summary, there is an urgent need to develop an adhesive with low melt viscosity, capable of being dispensed at room temperature, 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 electrically detachable acrylate-modified polyurethane hot melt adhesive that has low melt viscosity, can be dispensed at room temperature, has high initial and final bond strength, and cures quickly.

[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 acrylate-modified polyurethane hot melt adhesive provided by this invention has a viscosity range of 1000-150000 cps at 25°C and a bond strength attenuation rate of over 80% after being energized with a voltage of 1-100V. The acrylate-modified polyurethane hot melt adhesive contains a polyurethane prepolymer mixture, acrylate compounds, ionic liquids, and photoinitiators. Both ends of the prepolymer contained in the polyurethane prepolymer mixture are isocyanate-terminated. The polyol structural units contained in the polyurethane prepolymer mixture 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 (1.5-9):1.

[0013] The method for preparing 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, polyisocyanate compound and optional catalyst are stirred and reacted at 70-90°C for 1-5 hours to obtain a prepolymer containing a polyurethane prepolymer mixture.

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

[0017] After in-depth and extensive research, the inventors of this invention discovered that the polyurethane polymers with isocyanate functional groups used in existing electrically disintegratable polyurethane hot melt adhesives are polyurethane prepolymers 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 prepolymers prepared according to this stoichiometric relationship have low isocyanate content, large molecular weight, and strong intermolecular forces, resulting in a high melt viscosity and making them difficult to dispense at room temperature. Furthermore, some of the polyol compounds used in these isocyanate functional group polyurethane prepolymers have strong crystallinity or high glass transition temperature (Tg) at room temperature. Polyurethane prepolymers prepared by reacting room-temperature crystalline polyols or high-Tg polyols with isocyanate compounds are typically solid substances at room temperature. Therefore, the electrically disintegratable polyurethane hot melt adhesives prepared by traditional methods are usually solid at room temperature and need to be heated to above the melting point (90℃~160℃) to melt and apply. This greatly raises the barrier to entry for using such polyurethane hot melt adhesives, increases the cost of adhesive application equipment, and also increases 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 of the polyurethane hot melt adhesive. While the introduction of ionic liquids and solvating matrices facilitates electrical degradation, these liquids do not participate in the curing process. After curing, they remain in their initial low-viscosity state, negatively impacting the final adhesive strength. Furthermore, the isocyanate-terminated polyurethane prepolymers 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 prepolymers exhibit low crosslinking density after wet curing, leading to inherently low adhesive strength. The negative effects of ionic liquids and solvating matrices further reduce this adhesive 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] While existing acrylate-modified polyurethane hot melt adhesives can improve curing speed and effectively overcome the slow curing speed of polyurethane hot melt adhesives reliant on moisture, the resulting adhesion is relatively strong, making it difficult to achieve easy disassembly. Furthermore, current adhesives capable of electrical disassembly generally require conductive substrates, typically opaque materials such as stainless steel, aluminum, and copper. For opaque substrates, it is difficult to use conventional UV-curing adhesives and UV moisture-curing adhesives primarily composed of acrylate compounds. This is because, after UV irradiation, the adhesive composition based on photocurable components cures instantly and quickly loses its re-adhesion. Therefore, most UV-curing or UV moisture-curing adhesives can only be used for bonding substrates that are transparent on at least one side. Thus, even if known electrically disassembly compositions are directly added to existing UV acrylate adhesives or UV moisture-curing adhesives based on 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 with a small amount of acrylate compounds for modification. While these adhesives can be used for bonding opaque substrates, their high melt viscosity typically necessitates the use of 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 prepolymer; secondly, the polyurethane prepolymer itself incorporates polyol compounds with high glass transition temperatures and / or strong crystallinity at room temperature, leading to its 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 using polyol compounds with low glass transition temperatures and low crystallinity at room temperature to react with an excess of isocyanate compounds to prepare a polyurethane prepolymer mixture with isocyanate double end capping. At the same time, it innovatively introduces acrylate compounds and ionic liquids into this polyurethane prepolymer mixture and strictly controls the ratio between the polyurethane prepolymer mixture and the acrylate compounds. This gives the final acrylate-modified polyurethane hot melt adhesive advantages such as low melt viscosity, room temperature dispensing capability, high initial and final bond strength, fast curing speed, and electrical disassembly capability. The reason for this is speculated to be that both acrylate compounds and ionic liquids have good fluidity at room temperature and 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. Using 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 the polyurethane prepolymer 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 / ionic liquids and internal viscosity reduction by the polyurethane prepolymer. 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. Subsequently, the polyurethane prepolymer further enhances the system's bond strength through a moisture-curing reaction. After curing, a polyurethane-polyacrylate interpenetrating network structure is formed, imparting high final bond strength to the polyurethane hot melt adhesive. In addition, the Faraday reaction that occurs when ionic liquids are energized allows for the introduction of ionic liquids into acrylate-modified polyurethane hot melt adhesives, giving them electrolytic disintegration properties. Moreover, as described above, the polyurethane hot melt adhesive provided by this invention relies on acrylate compounds to enhance initial bond strength in the early stages and on the polyurethane-polyacrylate interpenetrating network structure to enhance final bond strength in the later stages. Even when affected by the uncured ionic liquid, it can still maintain relatively high initial and final bond strength. Detailed Implementation

[0021] The 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 bonding strength attenuation rate of over 80% after being energized with a voltage of 1 to 100V. Specifically, it can be 80%, 82%, 85%, 88%, 90%, 92%, 95%, 98%, 99%, 100%, or any value between them. The voltage required for disassembling the acrylate-modified polyurethane hot melt adhesive is preferably 1 to 100V, specifically 1V, 3V, 5V, 7V, 9V, 10V, 20V, 30V, 40V, 50V, 60V, 70V, 80V, 90V, 100V or any value between them; the required energizing time is preferably 1s to 60min, such as 1s, 2s, 5s, 15s, 30s, 40s, 50s, 1min, 5min, 10min, 15min, 20min, 30min, 40min, 50min, 60min or any value between them.

[0023] In this invention, the acrylate-modified polyurethane hot melt adhesive contains a polyurethane prepolymer mixture, acrylate compounds, an ionic liquid, and a photoinitiator. The viscosity of the system is reduced by introducing polyol structural units with weak crystallinity or low glass transition temperatures into 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 controlling the mass ratio of the polyurethane prepolymer mixture to the acrylate compounds improves the final bond strength. The introduction of the ionic liquid imparts electrolytic disintegration 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 low-viscosity polyol compound has a melting point 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. The mass ratio of the polyurethane prepolymer mixture to the acrylate compound is (1.5~9.0):1, specifically 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1, or any value between them. In this invention, the term "polyurethane prepolymer mixture" refers to a prepolymer obtained by addition reaction of polyisocyanate compounds and low-viscosity polyol compounds. Since the prepolymer contains polymers of different molecular weights and possibly unreacted monomers, it is a mixture of multiple substances and is therefore called "polyurethane prepolymer mixture".

[0024] The acrylate-modified polyurethane hot melt adhesive provided by this invention is a liquid or paste at room temperature, and has the characteristics of low melt viscosity, room temperature dispensing capability, high initial and final bond strength, fast curing speed, and electrical disassembly capability.

[0025] In a preferred embodiment, the raw materials for preparing the acrylate-modified polyurethane hot melt adhesive contain a polyisocyanate compound, a low-viscosity polyol compound, an acrylate compound, an ionic liquid, a photoinitiator, and optionally a rheology modifier, a silane coupling agent, a water-absorbing agent, and a catalyst. The molar equivalent ratio of isocyanate groups in the polyisocyanate compound to hydroxyl groups in the low-viscosity polyol compound is (2.5–5):1. Specifically, the molar equivalent ratio of isocyanate groups in the polyisocyanate compound to hydroxyl groups in the low-viscosity polyol compound can be 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, or any value between them.

[0026] In this invention, the preferred mass ratio of the total content of the polyisocyanate compound and the low-viscosity polyol compound to the content of the ionic liquid is (3-40):1, specifically 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 7:1, 9:1, 11:1, 13:1, 15:1, 17:1, 19:1, 20:1, 22:1, 25:1, 28:1, 30:1, 32:1, 35:1, 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 catalyst to the ionic liquid is (0.005–1):1, specifically 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 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 absorbent 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.

[0027] In a preferred embodiment, based on the total weight of the raw materials for preparing the acrylate-modified polyurethane hot melt adhesive, the total content of the polyisocyanate compounds and low-viscosity polyol compounds is 45-80%, such as 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or any value between them; the content of the acrylate compounds is 5-35%, such as 3%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, or any value between them; the content of the ionic liquid is 2-15%, such as 2%, 5%, 8%, 10%, 12%, 15%, or any value between them; the content of the photoinitiator is... The amount 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 water absorbent 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.

[0028] In this invention, the polyisocyanate compound is a compound with two or more isocyanate groups at the molecular chain terminal, specifically an aromatic isocyanate and / or an aliphatic isocyanate, including but not limited to: at least one of isophorone diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenylmethane-2,4'-diisocyanate, hydrogenated phenyldimethyl diisocyanate, 1,5-naphthalene diisocyanate, 1,5-pentane diisocyanate, 1,4-phenyl diisocyanate, phenyldimethyl diisocyanate, tetramethylxylene diisocyanate, norbornene dimethyl isocyanate, lysine diisocyanate, triphenylmethane triisocyanate, triphenyl thiophosphate triphenyl isocyanate, and 1,6,11-undecane triisocyanate.

[0029] 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.

[0030] 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.

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

[0033] 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.

[0034] 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.

[0035] In this invention, the desiccant may be selected from at least one of molecular sieve desiccant, oxazolidine desiccant, p-toluenesulfonyl isocyanate, and triethyl orthoformate.

[0036] 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.

[0037] The method for preparing acrylate-modified polyurethane hot melt adhesive provided by the present invention includes the following steps: S1, dehydrating a low-viscosity polyol compound and an ionic liquid, as well as an optional rheology modifier, a silane coupling agent and a water absorbent, to obtain a pretreated product; S2, stirring the pretreated product, a polyisocyanate compound and an optional catalyst at 70-90°C for 1-5 hours to obtain a prepolymer containing a polyurethane prepolymer mixture; S3, mixing the prepolymer with an acrylate compound and a photoinitiator uniformly to obtain the acrylate-modified polyurethane hot melt adhesive.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] The present invention also provides the application of the acrylate-modified polyurethane hot melt adhesive in the bonding of electronic products.

[0042] The adhesive substrate used in the acrylate-modified polyurethane hot melt adhesive provided by this invention is a conductive substrate.

[0043] 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.

[0044] Example 1

[0045] By weight, 15.96 g (5.320 mmol) of liquid polyether glycol (Dow Voranol WD2130; Tg < 0℃; melting point < 25℃) with a number-average molecular weight of 3000, 31.92 g (15.960 mmol) of liquid polyester diol (Stepanpol PH-56; Tg = -15℃; melting point < 25℃) with a number-average molecular weight of 2000, 6.00 g of 1-ethyl-3-methylimidazolium tetrafluoroborate (melting point = 15℃), 4.5 g of fumed silica HDK H18, 0.3 g of 3-aminopropyltrimethoxysilane, and 0.4 g of water-absorbing agent Additive were added. OF, heated to 110℃, vacuum dehydrated for 2 hours under stirring at 150 r / min, then cooled to 80℃, added 18.62 g (74.48 mmol) of diphenylmethane-4,4'-diisocyanate (MDI) and 0.3 g of dibutyltin dilaurate, reacted for 2 hours under stirring at 150 r / min, then added 2.0 g of photoinitiator ITX, 10.0 g of 1,6-hexanediol diacrylate and 10.0 g of trimethylolpropane formal acrylate, mixed for 1 hour under stirring at 150 r / min, and discharged to obtain acrylate-modified polyurethane hot melt adhesive, which was vacuum sealed and stored away from light.

[0046] Example 2

[0047] By weight, 24.89 g (7.111 mmol) of liquid polyester diol with a number-average molecular weight of 3500 (Dynacoll 7230; Tg = -30℃; melting point <25℃), 14.22 g (7.111 mmol) of liquid polyether diol with a number-average molecular weight of 2000 (Dow Voranol 2120; Tg <0℃; melting point <25℃), 10.00 g of 1-butyl-3-methylimidazolium tetrafluoroborate (melting point = -71℃), 6.5 g of fumed silica TS-610, 0.7 g of 3-mercaptopropyltrimethoxysilane, and 1.2 g of water-absorbing agent Additive were added. TI was heated to 110℃ and vacuum dehydrated for 2 hours under stirring at 150 rpm. Then, it was cooled to 80℃, and 8.89 g (35.56 mmol) of diphenylmethane-4,4'-diisocyanate (MDI) and 0.6 g of stannous octoate were added. The mixture was stirred at 150 rpm for 2 hours. Then, 3.0 g of photoinitiator 369, 15.0 g of triethylene glycol diacrylate and 15.0 g of tetrahydrofuran acrylate were added. The mixture was stirred at 150 rpm for 1 hour and then discharged to obtain acrylate-modified polyurethane hot melt adhesive, which was then vacuum-sealed and stored away from light.

[0048] Example 3

[0049] By weight, 42.10 g (14.032 mmol) of liquid polycarbonate diol with a number-average molecular weight of 3000 (Kuraray polyol C3090; Tg = -42℃; melting point <25℃), 14.03 g (14.032 mmol) of liquid polyether diol with a number-average molecular weight of 1000 (Dow Voranol 220-110; Tg <0℃; melting point <25℃), 4.00 g of hexyltriethylammonium bis(trifluoromethanesulfonyl)imide salt (melting point = 20℃), 2.5 g of fumed silica AEROSIL R202, 0.5 g of 3-epoxypropoxypropyltrimethoxysilane, and 1.0 g of water-absorbing agent Additive were added. TI was heated to 110℃ and vacuum dehydrated for 2 hours under stirring at 150 rpm. Then, it was cooled to 80℃, and 23.57 g (140.317 mmol) of hexamethylene diisocyanate (HDI) and 1.2 g of zinc isooctanoate were added. The mixture was stirred at 150 rpm for 2 hours. Then, 1.1 g of photoinitiator 819, 5.0 g of triethylene glycol diacrylate, and 5.0 g of dodecyl acrylate were added. The mixture was stirred at 150 rpm for 1 hour and then discharged to obtain acrylate-modified polyurethane hot melt adhesive. The adhesive was then vacuum-sealed and stored away from light.

[0050] Example 4

[0051] By weight, 29.82 g (14.908 mmol) of liquid polyester diol with a number-average molecular weight of 2000 (Stepanpol PH-56; Tg = -15℃; melting point <25℃), 14.91 g (14.908 mmol) of liquid polycarbonate diol with a number-average molecular weight of 1000 (Kuraray polyol C1050; Tg <0℃; melting point <25℃), 13.00 g of N-butyl-N-methylpyrrolidine difluorosulfonylimide salt (melting point = -15℃), 3.5 g of fumed silica AEROSIL R972, 1.5 g of 3-isocyanate propyltrimethoxysilane, and 0.8 g of water-absorbing agent Additive were added. TI was heated to 110℃ and vacuum dehydrated for 2 hours under stirring at 150 rpm. Then, it was cooled to 80℃, and 26.48 g (119.263 mmol) of isophorone diisocyanate (IPDI) and 1.5 g of bismuth isooctanoate were added. The mixture was stirred at 150 rpm for 2 hours. Then, 0.5 g of photoinitiator TPO, 4.0 g of neopentyl glycol diacrylate and 4.0 g of isooctyl acrylate were added. The mixture was stirred at 150 rpm for 1 hour and then discharged to obtain acrylate-modified polyurethane hot melt adhesive, which was then vacuum-sealed and stored away from light.

[0052] Example 5

[0053] By weight, 28.95 g (8.272 mmol) of liquid polyester diol with a number-average molecular weight of 3500 (Dynacoll 7210; Tg = -15℃; melting point <25℃), 16.54 g (16.544 mmol) of liquid polycarbonate diol with a number-average molecular weight of 1000 (PLACCEL 210N; Tg = -17℃; melting point = 32~37℃), 8.00 g of 1,3-diethylimidazolium bis(trifluoromethanesulfonyl)imide salt (melting point = 12.4℃), 4.0 g of fumed silica HDK H2O, 1.7 g of 3-acryloyloxypropyltrimethoxysilane, and 0.5 g of water-absorbing agent Additive were added. TI was heated to 110℃ and vacuum dehydrated for 2 hours under stirring at 150 rpm. Then, it was cooled to 80℃, and 19.50 g (74.446 mmol) of dicyclohexylmethane-4,4'-diisocyanate (HMDI) and 1.3 g of stannous octoate were added. The mixture was stirred at 150 rpm for 2 hours. Then, 1.5 g of photoinitiator 184, 10.0 g of diethylene glycol diacrylate and 8.0 g of tridecyl acrylate were added. The mixture was stirred at 150 rpm for 1 hour and then discharged to obtain acrylate-modified polyurethane hot melt adhesive, which was then vacuum-sealed and stored away from light.

[0054] Comparative Example 1

[0055] By weight, 39.41 g (13.137 mmol) of liquid polycarbonate diol with a number average molecular weight of 3000 (Kuraray polyol C3090; Tg = -42℃; melting point <25℃), 8.76 g (4.379 mmol) of liquid polyether diol with a number average molecular weight of 2000 (Dow Voranol 2120; Tg <0℃; melting point <25℃), 4.38 g (4.379 mmol) of liquid polyether diol with a number average molecular weight of 1000 (Dow Voranol 220-110; Tg <0℃; melting point <25℃), 5.5 g of fumed silica HDK H17, 0.3 g of 3-aminopropyltrimethoxysilane, and 0.5 g of water-absorbing agent Additive were added. OF, heated to 110℃, vacuum dehydrated for 2h under stirring at 150r / min, then cooled to 80℃, added 41.05g (164.211mmol) diphenylmethane-4,4'-diisocyanate (MDI) and 0.1g dibutyltin dilaurate, reacted for 2h under stirring at 150r / min, and then discharged to obtain reference polyurethane hot melt adhesive, which was vacuum sealed and stored.

[0056] Comparative Example 2

[0057] By weight, 42.11 g (12.031 mmol) of polyester diol with a number-average molecular weight of 3500 (Evonik Dynacoll 7380; melting point = 70℃), 24.06 g (12.031 mmol) of liquid polyether diol with a number-average molecular weight of 2000 (Dow Voranol 2120; Tg < 0℃; melting point < 25℃), 10.0 g of thermoplastic acrylic resin BM751 (Tg = 49℃), 5.0 g of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (melting point = -12℃), 5.0 g of propylene carbonate, 1.0 g of 3-mercaptopropyltrimethoxysilane, and 0.5 g of water-absorbing agent Additive were added. OF, heated to 110℃, vacuum dehydrated for 2h under stirring at 150r / min, then cooled to 80℃, added 12.03g (48.123mmol) diphenylmethane-4,4'-diisocyanate (MDI) and 0.3g stannous octoate, reacted for 2h under stirring at 150r / min, and then discharged to obtain reference polyurethane hot melt adhesive, which was vacuum sealed and stored.

[0058] Comparative Example 3

[0059] The polyurethane hot melt adhesive was prepared according to the method of Example 1, except that the liquid polyether diol and liquid polyester diol were replaced with the same molar amounts of solid polyester diol and solid polycarbonate diol with melting points higher than 40°C, respectively. The other conditions were the same as in Example 1, as follows:

[0060] By weight, 15.96 g (5.320 mmol) of solid polyester diol with a number-average molecular weight of 3000 (Hoopol F-580; melting point = 50℃), 31.92 g (15.960 mmol) of solid polycarbonate diol with a number-average molecular weight of 2000 (UH-CARB200; melting point = 50℃), 6.00 g of 1-ethyl-3-methylimidazolium tetrafluoroborate (melting point = 15℃), 4.5 g of fumed silica HDK H18, 0.3 g of 3-aminopropyltrimethoxysilane, and 0.4 g of water-absorbing agent Additive were added. OF, heated to 110℃, vacuum dehydrated for 2 hours under stirring at 150 r / min, then cooled to 80℃, added 18.62 g (74.48 mmol) of diphenylmethane-4,4'-diisocyanate (MDI) and 0.3 g of dibutyltin dilaurate, reacted for 2 hours under stirring at 150 r / min, then added 2.0 g of photoinitiator ITX, 10.0 g of 1,6-hexanediol diacrylate and 10.0 g of trimethylolpropane formal acrylate, mixed for 1 hour under stirring at 150 r / min, and discharged to obtain the reference polyurethane hot melt adhesive, which was vacuum sealed and stored away from light.

[0061] Comparative Example 4

[0062] The polyurethane hot melt adhesive was prepared according to the method of Example 1, except that the molar equivalent ratio of the isocyanate group in the polyisocyanate compound of Example 1 to the hydroxyl group in the low viscosity polyol compound was adjusted from 3.5:1 to 1.8:1. In this case, the polyurethane prepolymer could not achieve isocyanate double end-capping, as detailed below:

[0063] By weight, 18.47 g (6.157 mmol) of liquid polyether glycol (Dow Voranol WD2130; Tg < 0 °C; melting point < 25 °C) with a number-average molecular weight of 3000, 36.94 g (18.472 mmol) of liquid polyester diol (Stepanpol PH-56; Tg = -15 °C; melting point < 25 °C) with a number-average molecular weight of 2000, 6.00 g of 1-ethyl-3-methylimidazolium tetrafluoroborate (melting point = 15 °C), 4.5 g of fumed silica HDK H18, 0.3 g of 3-aminopropyltrimethoxysilane, and 0.4 g of water-absorbing agent Additive were added. OF, heated to 110℃, vacuum dehydrated for 2 hours under stirring at 150 r / min, then cooled to 80℃, and 11.08 g (44.333 mmol) of diphenylmethane-4,4'-diisocyanate (MDI) and 0.3 g of dibutyltin dilaurate were added. The mixture was stirred at 150 r / min for 2 hours, then 2.0 g of photoinitiator ITX, 10.0 g of 1,6-hexanediol diacrylate and 10.0 g of trimethylolpropane formal acrylate were added. The mixture was stirred at 150 r / min for 1 hour and then discharged to obtain the reference polyurethane hot melt adhesive, which was vacuum sealed and stored away from light.

[0064] Comparative Example 5

[0065] The polyurethane hot melt adhesive was prepared according to the method of Example 1, except that no ionic liquid was added. The other conditions were the same as in Example 1, as follows:

[0066] By weight, 15.96 g (5.320 mmol) of liquid polyether glycol (Dow Voranol WD2130; Tg < 0℃; melting point < 25℃) with a number-average molecular weight of 3000, 31.92 g (15.960 mmol) of liquid polyester diol (Stepanpol PH-56; Tg = -15℃; melting point < 25℃) with a number-average molecular weight of 2000, 4.5 g of fumed silica HDK H18, 0.3 g of 3-aminopropyltrimethoxysilane, and 0.4 g of water-absorbing agent Additive were added. OF, heated to 110℃, vacuum dehydrated for 2 hours under stirring at 150 r / min, then cooled to 80℃, added 18.62 g (74.48 mmol) of diphenylmethane-4,4'-diisocyanate (MDI) and 0.3 g of dibutyltin dilaurate, reacted for 2 hours under stirring at 150 r / min, then added 2.0 g of photoinitiator ITX, 10.0 g of 1,6-hexanediol diacrylate and 10.0 g of trimethylolpropane formal acrylate, mixed for 1 hour under stirring at 150 r / min, and discharged to obtain the reference polyurethane hot melt adhesive, which was vacuum sealed and stored away from light.

[0067] Comparative Example 6

[0068] The polyurethane hot melt adhesive was prepared according to the method of Example 1, except that 1,6-hexanediol diacrylate and trimethylolpropane formal acrylate were not added. All other conditions were the same as in Example 1, as detailed below:

[0069] By weight, 15.96 g (5.320 mmol) of liquid polyether glycol (Dow Voranol WD2130; Tg < 0℃; melting point < 25℃) with a number-average molecular weight of 3000, 31.92 g (15.960 mmol) of liquid polyester diol (Stepanpol PH-56; Tg = -15℃; melting point < 25℃) with a number-average molecular weight of 2000, 6.00 g of 1-ethyl-3-methylimidazolium tetrafluoroborate (melting point = 15℃), 4.5 g of fumed silica HDK H18, 0.3 g of 3-aminopropyltrimethoxysilane, and 0.4 g of water-absorbing agent Additive were added. OF was heated to 110℃ and vacuum dehydrated for 2 hours under stirring at 150 r / min. Then, it was cooled to 80℃, and 18.62 g (74.48 mmol) of diphenylmethane-4,4'-diisocyanate (MDI) and 0.3 g of dibutyltin dilaurate were added. The mixture was stirred at 150 r / min for 2 hours. Then, 2.0 g of photoinitiator ITX was added, and the mixture was stirred at 150 r / min for 1 hour before being discharged to obtain the reference polyurethane hot melt adhesive. The adhesive was then vacuum sealed and stored away from light.

[0070] Comparative Example 7

[0071] The polyurethane hot melt adhesive was prepared according to the method of Example 1, except that the amount of 1,6-hexanediol diacrylate and trimethylolpropane formal acrylate added was increased to 40.0 g, while the rest was the same as in Example 1, as follows:

[0072] By weight, 15.96 g (5.320 mmol) of liquid polyether glycol (Dow Voranol WD2130; Tg < 0℃; melting point < 25℃) with a number-average molecular weight of 3000, 31.92 g (15.960 mmol) of liquid polyester diol (Stepanpol PH-56; Tg = -15℃; melting point < 25℃) with a number-average molecular weight of 2000, 6.00 g of 1-ethyl-3-methylimidazolium tetrafluoroborate (melting point = 15℃), 4.5 g of fumed silica HDK H18, 0.3 g of 3-aminopropyltrimethoxysilane, and 0.4 g of water-absorbing agent Additive were added. OF, heated to 110℃, vacuum dehydrated for 2 hours under stirring at 150 r / min, then cooled to 80℃, added 18.62 g (74.48 mmol) of diphenylmethane-4,4'-diisocyanate (MDI) and 0.3 g of dibutyltin dilaurate, reacted for 2 hours under stirring at 150 r / min, then added 2.0 g of photoinitiator ITX, 40.0 g of 1,6-hexanediol diacrylate and 40.0 g of trimethylolpropane formal acrylate, mixed for 1 hour under stirring at 150 r / min, and discharged to obtain the reference polyurethane hot melt adhesive, which was vacuum sealed and stored away from light.

[0073] Test case

[0074] The samples from the examples and comparative examples were compared and tested using the following method:

[0075] (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.

[0076] (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. 2After 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 on the instrument was recorded. 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.

[0077] (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 sheared 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 value displayed on the instrument was recorded. The shear bond strength of the polyurethane hot melt adhesive to the stainless steel substrate after energizing was calculated based on the bond area. The results are shown in Table 1.

[0078] Table 1

[0079] As shown in Table 1, the acrylate-modified polyurethane hot melt adhesive provided by this invention has a low viscosity at room temperature, allowing for direct dispensing 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 adhesive is 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 initial positioning within a short time. After complete curing, it exhibits excellent final bond strength, and the bond strength significantly decreases after energization, even leading to direct detachment, demonstrating excellent energized disassembly performance. In summary, the acrylate-modified polyurethane hot melt adhesive provided by this invention has low melt viscosity, can be dispensed at room temperature, exhibits high initial and final bond strengths, and cures quickly. Furthermore, it possesses energized disassembly capability, making it a promising candidate for practical applications.

[0080] 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 acrylate-modified polyurethane hot melt adhesive, characterized in that, The acrylate-modified polyurethane hot melt adhesive has a viscosity range of 1000–150000 cps at 25°C and a bond strength attenuation rate of over 80% after being energized with a voltage of 1–100V. The acrylate-modified polyurethane hot melt adhesive contains a polyurethane prepolymer mixture, acrylate compounds, ionic liquids, and photoinitiators. Both ends of the prepolymer contained in the polyurethane prepolymer mixture are isocyanate-terminated. The polyol structural units contained in the polyurethane prepolymer mixture 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 (1.5–9):

1.

2. The acrylate-modified polyurethane hot melt adhesive of claim 1, wherein, The raw materials for preparing the acrylate-modified polyurethane hot melt adhesive contain polyisocyanate compounds, low-viscosity polyol compounds, acrylate compounds, ionic liquids, photoinitiators, and optional rheology modifiers, silane coupling agents, water absorbents, and catalysts. The molar equivalent ratio of isocyanate groups in the polyisocyanate compounds to hydroxyl groups in the low-viscosity polyol compounds is (2.5–5):

1.

3. The acrylate-modified polyurethane hot melt adhesive of claim 2, wherein, Based on the total weight of the raw materials for preparing the acrylate-modified polyurethane hot melt adhesive, the total content of the polyisocyanate compounds and low-viscosity polyol compounds is 45-80%, the content of the acrylate compounds is 5-35%, the content of the ionic liquid is 2-15%, 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 acrylate-modified polyurethane hot melt adhesive of claim 2, wherein, The polyisocyanate compound is selected from at least one of isophorone diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenylmethane-2,4'-diisocyanate, hydrogenated phenyldiisocyanate, 1,5-naphthalene diisocyanate, 1,5-pentane diisocyanate, 1,4-phenyl diisocyanate, phenyldiisocyanate, tetramethylxylene diisocyanate, norbornene diisocyanate, lysine diisocyanate, triphenylmethane triisocyanate, triphenyl thiophosphate, and 1,6,11-undecane triisocyanate.

5. The acrylate-modified polyurethane hot melt adhesive of claim 2, wherein, 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 acrylate-modified polyurethane hot melt adhesive of claim 2, wherein, 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.

7. The acrylate-modified polyurethane hot melt adhesive of claim 2, wherein, The melting point of the ionic liquid is below 25°C.

8. The acrylate-modified polyurethane hot melt adhesive of claim 2, wherein, The ionic liquid is composed of organic cations and anions. The organic 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.

9. The acrylate-modified polyurethane hot melt adhesive of claim 2, wherein, 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-ethyl-3-methylimidazolium ethyl sulfate, 1-ethyl-2,3-dimethylimidazolium ethyl sulfate, and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide. At least one of the following: 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(fluoromethanesulfonyl)imide salt, N-butylpyridine tetrafluoroborate, hexyltriethylammonium bis(trifluoromethanesulfonyl)imide salt, methyltrioctylphosphonium bis(trifluoromethanesulfonyl)imide salt, N-butyl-N-methylpyrrolidine bis(fluoromethanesulfonyl)imide salt, N-butyl-N-methylpyrrolidine trifluoromethanesulfonate, and N-propyl-N-methylpiperidine bis(trifluoromethanesulfonyl)imide salt.

10. The acrylate-modified polyurethane hot melt adhesive of claim 2, wherein, The photoinitiator is selected from at least one of benzophenone compounds, acetophenone compounds, acylphosphine oxide compounds, diacetic acid compounds, oxime ester compounds, benzoin ether compounds, and thioxanone. 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; The rheology modifier is fumed silica.

11. The acrylate-modified polyurethane hot melt adhesive of claim 2, wherein, 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.

12. The acrylate-modified polyurethane hot melt adhesive of claim 2, wherein, The desiccant is selected from at least one of molecular sieve desiccant, oxazolidine desiccant, p-toluenesulfonyl isocyanate, and triethyl orthoformate.

13. The method for preparing the 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, polyisocyanate compound and optional catalyst are stirred and reacted at 70-90°C for 1-5 hours to obtain a prepolymer containing a polyurethane prepolymer mixture. S3. Mix the prepolymer with the acrylate compound and the photoinitiator evenly to obtain the acrylate-modified polyurethane hot melt adhesive.

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

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