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

Abstract

The invention belongs to the field of adhesives, and relates to an electrically detachable acrylate modified polyurethane hot melt adhesive as well as a preparation method and application thereof. The electrically detachable acrylate modified polyurethane hot melt adhesive contains a polyurethane prepolymer mixture, an ionic liquid, an acrylate compound and a photoinitiator, and the two ends of a prepolymer contained in the polyurethane prepolymer mixture are provided with isocyanate end caps. An isocyanate structural unit contained in the polyurethane prepolymer mixture is derived from a low-viscosity low-free polyurethane prepolymer, and a polyhydric alcohol structural unit contained in the polyurethane prepolymer mixture is derived from a low-viscosity polyhydric alcohol compound with the glass transition temperature being 0 DEG C or below and the melting point being 40 DEG C or below. The polyurethane hot melt adhesive provided by the invention has the properties of low content of free isocyanate, low melt viscosity, capability of dispensing at room temperature, high initial bonding strength and final bonding strength, high curing speed and electrical detachability, and has a wide practical application prospect.

Description

Technical Field

[0001] The invention belongs to the field of adhesives, and in particular relates to an electrically detachable acrylate-modified polyurethane hot-melt adhesive and a preparation method and application thereof. Background Art

[0002] Reactive polyurethane hot melt adhesive is often used to bond and fix electronic product components in electronic products such as smartphones, tablets, smart watches, and TWS headsets. Electronic product components bonded with reactive polyurethane hot melt adhesives are often of high value. When poor assembly, after-sales product repairs, or recycling of valuable electronic product components occur, it is usually necessary to disassemble some of the bonded components. Therefore, the adhesive is usually required to have excellent bonding reliability while being easy to disassemble under certain conditions.

[0003] Reactive polyurethane hot melt adhesive is mainly composed of isocyanate-terminated oligomers. The isocyanate groups in the isocyanate-terminated oligomers can react with moisture in the air and form a cross-linked chemical structure after complete curing, thereby achieving high bonding strength. However, the covalent bonds obtained by the reaction of isocyanate groups with moisture are irreversible, and the cross-linked structure is difficult to destroy. It is usually difficult to disassemble the adhesive after complete curing. If the bonded materials need to be separated, it is often necessary to use large external forces, high temperatures, chemical reagents and other conditions, and the bonded materials may be damaged during the disassembly of the adhesive, resulting in large economic losses.

[0004] In recent years, there are also technologies that add ionic liquids or alkali metal salts and solvated matrices to polyurethane hot melt adhesives to give polyurethane hot melt adhesives the function of being disassembled under power-on conditions. However, although the existing electrically disassembled polyurethane hot melt adhesives have the function of being disassembled under power-on conditions, due to the high melt viscosity of such polyurethane hot melt adhesives, they are a solid substance at room temperature and are difficult to apply glue at room temperature. They usually need to be heated to a melting temperature (usually 90°C to 160°C) or above before they can be extruded and applied. At this time, professional heating and gluing equipment is generally required. However, this will greatly limit the application scenarios of such polyurethane hot melt adhesives while increasing the cost of glue. For example, it is inconvenient to use such polyurethane hot melt adhesives in places such as homes and repair markets where it is inconvenient to equip heating equipment, thereby greatly limiting the widespread application and promotion of such single-component polyurethane hot melt adhesives.

[0005] Existing low-viscosity polyurethane hot melt adhesives that can be used at room temperature usually require the addition of a large amount of isocyanate monomers to reduce the viscosity. Although adding a large amount of isocyanate monomers can reduce the viscosity to a lower level, the large amount of free isocyanate monomers remaining in the adhesive system is very harmful to human health. It not only irritates the human respiratory tract, but also has a carcinogenic risk, which is not good for human health. At the same time, low-viscosity polyurethane hot melt adhesives that can be used at room temperature have a slow curing speed and low initial bonding strength. There is a large performance gap between the curing speed and bonding strength and traditional PUR hot melt adhesives, and it is difficult to meet the performance requirements of actual application scenarios. Furthermore, the existing acrylate-modified polyurethane hot melt adhesive is a polyurethane hot melt adhesive that can be UV-moisture dual-cured and prepared by modifying the polyurethane hot melt adhesive through physical blending or chemical modification of acrylate compounds. The UV curing speed is fast. After UV light exposure, the acrylate components in the acrylate-modified polyurethane hot melt adhesive can be quickly photocured, thereby effectively improving the defect of the polyurethane hot melt adhesive that relies on slow moisture curing speed. However, the existing acrylate-modified polyurethane hot melt adhesive still has many problems such as being difficult to disassemble after curing, difficult to apply glue at room temperature, and difficult to effectively bond to opaque substrates.

[0006] In summary, there is an urgent need to develop an adhesive with low free isocyanate content, low melt viscosity, dispensing ability at room temperature, high initial bonding strength and bonding strength, fast curing speed and electrical disassembly function to meet the application needs of the market. Summary of the invention

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

[0008] The second object of the present invention is to provide a method for preparing the above-mentioned acrylate-modified polyurethane hot melt adhesive.

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

[0010] Specifically, the electrically detachable 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, wherein both ends of the prepolymer contained in the polyurethane prepolymer mixture are capped with isocyanate, the isocyanate structural unit contained in the polyurethane prepolymer mixture is derived from a low-viscosity and low-free polyurethane prepolymer, and the polyol structural unit contained in the polyurethane prepolymer mixture is derived from a low-viscosity polyol compound having a glass transition temperature of less than 0°C and a melting point of less than 40°C, the mass ratio of the polyurethane prepolymer mixture to the acrylate compound is 1:(0.06-0.9), the total content of isocyanate groups in the electrically detachable acrylate-modified polyurethane hot melt adhesive is 2-8%, and the content of free isocyanate monomers is less than 0.1%; the viscosity range of the electrically detachable acrylate-modified polyurethane hot melt adhesive at 25°C is 1000-150000cps, and the attenuation rate of the bonding strength after powering on at a voltage of 1-100V is more than 80%.

[0011] The preparation method of the electrically detachable acrylate-modified polyurethane hot melt adhesive provided by the present invention comprises:

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

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

[0014] S3. Evenly mix the prepolymer, the acrylate compound and the photoinitiator to obtain the electrically removable acrylate-modified polyurethane hot melt adhesive.

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

[0016] The existing electrically disassembled polyurethane hot melt adhesive is to add ionic liquid or alkali metal salt and solvated matrix to the polyurethane hot melt adhesive, and utilize the Faraday reaction of anions and cations in ionic liquid or alkali metal salt under the condition of power on, so as to give the polyurethane hot melt adhesive the function of disassembly under the condition of power on. Among them, although the liquid substances such as ionic liquid and solvated matrix introduced into the polyurethane hot melt adhesive are conducive to realizing the function of electrical disassembly, such liquid substances cannot participate in the curing of the polyurethane hot melt adhesive, and still exist in the state of initial low viscosity after the polyurethane hot melt adhesive is cured, so it has a certain negative effect on the final bonding strength of the adhesive. In addition, since the equivalent ratio of isocyanate to hydroxyl in the current isocyanate-terminated polyurethane is relatively low (the equivalent ratio of NCO / OH is between 1.5 and 2.5), the isocyanate content of the polyurethane finally obtained is low, so the crosslinking density of such polyurethane after the final wet curing is low, so that the adhesive itself has a low bonding strength after curing, and the bonding strength will be further reduced after being negatively affected by the liquid components such as ionic liquid and solvated matrix. Therefore, although the electrically disassembled polyurethane hot melt adhesive can be prepared by adding ionic liquid or alkali metal salt in combination with a solvating matrix to the polyurethane hot melt adhesive, its final adhesion still has great deficiencies, which is not conducive to the application and promotion of such products.

[0017] The existing acrylate-modified polyurethane hot melt adhesive is a kind of polyurethane hot melt adhesive that can be UV-wet dual-cured and prepared by modifying polyurethane hot melt adhesive by physical blending or chemical modification of acrylate compounds. It has a fast UV curing speed. After UV light exposure, the acrylate components in the acrylate-modified polyurethane hot melt adhesive can be quickly photocured, effectively improving the defect of the polyurethane hot melt adhesive that relies on moisture for slow curing speed. However, the adhesive force formed by the acrylate-modified polyurethane hot melt adhesive after curing is relatively strong, and it is also difficult to achieve the function of easy disassembly. In addition, currently, adhesives that can achieve electrical disassembly generally require that the substrate to be bonded needs to be conductive. Usually, such conductive substrates are all opaque substrates such as stainless steel, aluminum, copper and other metals. It is difficult to use UV light-curing glue and UV moisture-curing adhesives with UV light-curing components such as acrylate compounds as the main body for bonding opaque substrates. This is because after UV light exposure, the adhesive composition with light-curing components as the main body will instantly cure after UV light exposure, and quickly lose re-adhesion after UV light exposure. Therefore, most UV light-curing glue or UV moisture-curing adhesive can only be used for bonding substrates with at least one side transparent. Therefore, even if the electrical disassembly composition known to provide electrical disassembly function is directly added to the existing UV acrylate glue or UV moisture-curing adhesive with UV acrylate compounds as the main body, it is difficult to directly apply it to the bonding of opaque metal substrates. In addition, some existing acrylate-modified polyurethane hot melt adhesives that can be used for bonding opaque substrates are mainly composed of polyurethane prepolymers as the main component, with a small amount of acrylate compounds for modification. Although such acrylate-modified polyurethane hot melt adhesives can be used for bonding opaque substrates, the melt viscosity of such acrylate-modified polyurethane hot melt adhesives is relatively high, and usually heating equipment is still required for dispensing. The reason why such acrylate-modified polyurethane hot melt adhesives are difficult to apply at room temperature is mainly that on the one hand, the proportion of low-viscosity acrylate compounds is small, and the dilution ability of the polyurethane body is weak. On the other hand, the preparation process of the polyurethane itself still uses some polyol compounds with relatively high glass transition temperatures and / or relatively strong crystallinity at room temperature, and the melt viscosity of such polyurethane body itself is relatively high. Therefore, the acrylate-modified polyurethane hot melt adhesive finally prepared is difficult to melt and dispense at room temperature, and heating equipment is required for dispensing.

[0018] The key to the present invention is to break the design limitation of setting the equivalent ratio of isocyanate group to hydroxyl group between (1.5 and 2.5):1 and selecting high Tg and / or high melting point polyol compounds in the traditional preparation process of electrically disassembled polyurethane hot melt adhesive, and innovatively reacting polyol compounds with low crystallinity and low glass transition temperature at room temperature with a large excess of low-viscosity polyurethane prepolymers with low free isocyanate content, and introducing low-viscosity acrylate compounds and ionic liquids at the same time, thereby giving the final electrically disassembled acrylate-modified polyurethane hot melt adhesive the advantages of low free isocyanate content, low melt viscosity, dispensing at room temperature, high initial bonding strength and final bonding strength, fast curing speed and electrical disassembly. It is speculated that the reason may be that: acrylate compounds and ionic liquids have good fluidity at room temperature and both have low viscosity. The simultaneous introduction of acrylate compounds and ionic liquids into the polyurethane hot melt adhesive can achieve the "initial" reduction in the viscosity of the system and improve the fluidity of the adhesive at room temperature. The selection of 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 hot melt adhesive at room temperature and achieve a "secondary" reduction in the viscosity of the system. That is, the present invention reduces the viscosity of the system from two dimensions: the synergistic external viscosity reduction of acrylate compounds and ionic liquids and the internal viscosity reduction of low-viscosity polyol compounds. This is conducive to the direct application of polyurethane hot melt adhesive at room temperature, greatly lowers the application threshold of polyurethane hot melt adhesive, reduces the equipment cost required for the application of polyurethane hot melt adhesive, and effectively avoids the risk of operators being scalded during the glue application process. Furthermore, the acrylate compound can rapidly undergo free radical polymerization after UV irradiation, quickly establish a high initial bonding strength, and control the amount of low-viscosity, low-free polyurethane prepolymer to be greatly excessive, so that the content of isocyanate groups in the system can be increased, thereby increasing the crosslinking density, and the system is provided with initial curing by the acrylate compound, and the significantly excessive isocyanate groups provide post-curing via moisture curing, and after being fully cured, a polyurethane-polyacrylate interpenetrating network structure can be formed, giving the polyurethane hot melt adhesive a higher final bonding strength. Furthermore, the Faraday reaction that can occur in ionic liquids after power is applied can give the polyurethane hot melt adhesive an electrically disassembled property by introducing ionic liquids. In addition, the present invention selects polyurethane prepolymers with low free isocyanate content to replace the traditionally used isocyanate monomers, which can significantly reduce the residual free isocyanate monomers in the adhesive system. As described above, the polyurethane hot melt adhesive provided by the present invention relies on acrylic compounds to improve the initial bonding strength in the early stage, and relies on the polyurethane-polyacrylate interpenetrating network structure to improve the final bonding strength in the later stage. Even if it is affected by the uncured ionic liquid, it can still maintain relatively high initial bonding strength and final bonding strength.In summary, the electrically detachable acrylate-modified polyurethane hot-melt adhesive provided by the present invention has the properties of low free isocyanate content, low melt viscosity, dispensing at room temperature, high initial bonding strength and final bonding strength, fast curing speed and electrically detachable, and has broad practical application prospects. DETAILED DESCRIPTION

[0019] The electrically detachable acrylate modified polyurethane hot melt adhesive provided by the present 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 therebetween.

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

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

[0022] In the present invention, the electrically detachable acrylate-modified polyurethane hot melt adhesive contains a polyurethane prepolymer mixture, an ionic liquid, an acrylate compound and a photoinitiator. The viscosity of the system is reduced by introducing a polyol structural unit with weaker crystallinity or lower glass transition temperature in the polyurethane prepolymer mixture and adding an acrylate compound and an ionic liquid, thereby giving it the performance of direct gluing at room temperature. Furthermore, the initial bonding strength and curing speed of the polyurethane hot melt adhesive are improved by introducing an acrylate compound, the final bonding strength is improved by controlling the mass ratio of the polyurethane prepolymer mixture to the acrylate compound, and the polyurethane hot melt adhesive is given the performance of electrically disassembling by introducing an ionic liquid. The polyol structural unit contained in the polyurethane prepolymer mixture is derived from a low-viscosity polyol compound. Among them, the glass transition temperature (Tg) of the low-viscosity polyol compound is below 0°C, specifically 0°C, -2°C, -4°C, -6°C, -8°C, -10°C, -12°C, -14°C, -16°C, -18°C, -20°C, -22°C, -24°C, -26°C, -28°C, -30°C, -32°C, -34°C, -36°C, -38°C, -40°C, etc. The melting point of the low-viscosity polyol compound is 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 the present invention, the term "polyurethane prepolymer mixture" refers to a product obtained by addition reaction of a low-viscosity, low-free polyurethane prepolymer and a low-viscosity polyol compound. Since the product contains polymers of different molecular weights and possible unreacted monomers, it is a mixed state of multiple substances, so it is called a "polyurethane prepolymer mixture".

[0023] The electrically detachable acrylate modified polyurethane hot melt adhesive provided by the present invention is a liquid or paste at room temperature, and has the characteristics of low melt viscosity, room temperature dispensing, high initial bonding strength and final bonding strength, fast curing speed and electrical disassembly.

[0024] In a preferred embodiment, the raw materials for preparing the electrically removable acrylate-modified polyurethane hot melt adhesive contain low-viscosity and low-free polyurethane prepolymer, low-viscosity polyol compounds, ionic liquids, acrylate compounds and photoinitiators, as well as optional rheology modifiers, silane coupling agents, water absorbents and catalysts. The molar equivalent ratio of isocyanate groups in the low-viscosity and low-free polyurethane prepolymer to hydroxyl groups in the low-viscosity polyol compounds is preferably (8 to 13):1, such as 8:1, 9:1, 10:1, 11:1, 12:1, 13:1 or any value therebetween.

[0025] In the present invention, the mass ratio of the total content of the low-viscosity low-free polyurethane prepolymer and the low-viscosity polyol compound to the content of the ionic liquid is preferably (2.5-40):1, 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 therebetween. The mass ratio of the acrylate compound to the ionic liquid is preferably (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 therebetween. The mass ratio of the photoinitiator to the ionic liquid is preferably (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 therebetween. The mass ratio of the rheology modifier to the ionic liquid is preferably (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 therebetween. The mass ratio of the silane coupling agent to the ionic liquid is preferably (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 therebetween. The mass ratio of the water absorbent to the ionic liquid is preferably (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 therebetween. The mass ratio of the catalyst to the ionic liquid is preferably (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 therebetween.

[0026] In a preferred embodiment, based on the total weight of the raw materials for preparing the electrically removable 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%, 80%; the content of the ionic liquid is 2-15%, such as 2%, 5%, 8%, 10%, 12%, 15% or any value therebetween; the content of the acrylate compound is 5-35%, such as 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35% or any value therebetween; the content of the photoinitiator is 10%. The content is 0.1-5%, such as 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5% or any value therebetween; the content of the rheology modifier is 2-10%, such as 2%, 5%, 8%, 10% or any value therebetween; the content of the silane coupling agent is 0.1-3%, such as 0.1%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3% or any value therebetween; the content of the water absorbent is 0.1-2%, such as 0.1%, 0.5%, 0.8%, 1%, 1.5%, 2% or any value therebetween; the content of the catalyst is 0.1-2%, such as 0.1%, 0.5%, 0.8%, 1%, 1.5%, 2% or any value therebetween.

[0027] In the present invention, the free isocyanate monomer content in the low-viscosity and low-free polyurethane prepolymer is preferably 0.1% or less, specifically 0.1%, 0.08%, 0.05%, 0.03%, 0.02%, 0.01% or any value therebetween. The low-viscosity and low-free polyurethane prepolymer is in liquid form below 50° C. The viscosity of the low-viscosity and low-free polyurethane prepolymer at 50° C. is preferably 100,000 cps or less, specifically 100,000 cps, 90,000 cps, 80,000 cps, 70,000 cps, 60,000 cps, 50,000 cps, 40,000 cps, 30,000 cps, 20,000 cps, 10,000 cps, 5,000 cps, 3,000 cps, 2,000 cps, 1,000 cps or any value therebetween. The low-viscosity, low-free polyurethane prepolymer can be obtained by reacting a polyether polyol with a polyisocyanate monomer. The polyether polyol may be a ring-opening polymer of ethylene glycol, propylene glycol, tetrahydrofuran, 3-methyltetrahydrofuran, or a random copolymer or block copolymer of ethylene glycol, propylene glycol, tetrahydrofuran, 3-methyltetrahydrofuran or a derivative thereof. The polyisocyanate monomer may be a isophorone diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, hexamethylene diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenylmethane-2,4'-diisocyanate, hydrogenated MDI, polymerized MDI, 1,5-naphthalene diisocyanate, 1,4-phenylene diisocyanate, xylene diisocyanate, tetramethylxylene diisocyanate, and norbornane diisocyanate. Examples of commercially available low-free polyether polyol-based polyurethane prepolymers include Adiprene LF TE 915, Adiprene LF TE 1050, Adiprene LF TE 980, Adiprene LF TE330, Adiprene LF TE 365, Adiprene LF TE 440, Adiprene LFM G730, Adiprene LFMG750, Adiprene LFM G600, and Adiprene LFMI G600 from LANXESS.

[0028] In the present 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 therebetween. The low viscosity polyol compound can be any existing polyol compound having a glass transition temperature of 0°C or less and a melting point of 40°C or less, and specific examples thereof include but are not limited to 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 hydroxy-terminated polybutadiene polyol.

[0029] In the present 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 phosphonium salt cations, pyrrolidine cations and piperidine cations. The anions are preferably selected from at least one of trifluoromethanesulfonate anions, tetrafluoroborate anions, hexafluorophosphate anions, bisfluoromethanesulfonyl imide anions, hydrogen sulfate anions, ethyl sulfate anions and p-toluenesulfonate anions. Specific examples of the above-mentioned ionic liquids 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, 1-butyl-3-methylimidazolium bis(trifluoromethane) at least one of bis(trifluoromethanesulfonyl)imide salts, 1,3-diethylimidazolium bis(trifluoromethanesulfonyl)imide salts, 1-propyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salts, 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salts, 1,2-dimethyl-3-propylimidazolium bis(trifluoromethanesulfonyl)imide salts, 1-ethyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide salts, N-butylpyridinium tetrafluoroborate, hexyltriethylammonium bis(trifluoromethanesulfonyl)imide salts, methyltrioctylphosphonium bis(trifluoromethanesulfonyl)imide salts, N-butyl-N-methylpyrrolidine bis(trifluoromethanesulfonyl)imide salts, N-butyl-N-methylpyrrolidine trifluoromethanesulfonate salts and N-propyl-N-methylpiperidinium bis(trifluoromethanesulfonyl)imide salts.

[0030] In the present invention, the acrylate compound can be various existing photocurable acrylate monomers, such as octadecyl acrylate, tetramethylene glycol acrylate, dodecyl acrylate, 2-phenoxyethyl acrylate, isodecyl acrylate, isooctyl acrylate, tridecyl acrylate, trimethylolpropane formal acrylate, methoxy polyethylene glycol monoacrylate, alkoxylated tetramethylene glycol acrylate, 1,3-butanediol diacrylate, 1,4-butanediol diacrylate, diethylene glycol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, tetraethylene glycol diacrylate, triethylene glycol diacrylate, tripropylene glycol diacrylate, dipropylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate and 1,3-butanediol dimethacrylate.

[0031] In the present invention, the photoinitiator can be any of the existing various compounds that absorb energy in the ultraviolet light region or the 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, acylphosphine oxide compounds, titanocene compounds, oxime ester compounds, benzoin ether compounds and thioxanthone.

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

[0033] In the present invention, specific examples of the silane coupling agent include, but are not limited to: 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropylmethyldiethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, At least one of 3-(2-aminoethyl)aminopropyltrimethoxysilane, 3-(2-aminoethyl)aminopropyltriethoxysilane, 3-(2-aminoethyl)aminopropylmethyldimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, 3-(meth)acryloxypropylmethyldiethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane and 3-isocyanatepropyltrimethoxysilane.

[0034] In the present invention, the water absorbent may be selected from at least one of a molecular sieve desiccant, an oxazolidine dehydrating agent, p-toluenesulfonyl isocyanate and triethyl orthoformate.

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

[0036] The preparation method of the electrically detachable acrylate-modified polyurethane hot melt adhesive provided by the present invention comprises:

[0037] S1, dehydrating the low-viscosity polyol compound and the ionic liquid and the optional rheology modifier, silane coupling agent and water absorbent to obtain a pretreated product;

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

[0039] S3. Evenly mix the prepolymer, the acrylate compound and the photoinitiator to obtain the electrically removable acrylate-modified polyurethane hot melt adhesive.

[0040] In the present invention, in step S1, the conditions for the dehydration treatment 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 therebetween; a rotation speed of 100-200r / min, such as 100r / min, 110r / min, 120r / min, 130r / min, 140r / min, 150r / min, 160r / min, 170r / min, 180r / min, 190r / min, 200r / min or any value therebetween; and a time of 1-5h, such as 1h, 2h, 3h, 4h, 5h or any value therebetween.

[0041] In the present 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 therebetween; the speed of the stirring reaction is preferably 100-200r / min, specifically 100r / min, 110r / min, 120r / min, 130r / min, 140r / min, 150r / min, 160r / min, 170r / min, 180r / min, 190r / min, 200r / min or any value therebetween; the time of the stirring reaction is preferably 1-5h, specifically 1h, 2h, 3h, 4h, 5h or any value therebetween.

[0042] In the present invention, in step S3, the mixing conditions preferably include a temperature of 70 to 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 therebetween; a stirring speed of 100 to 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 therebetween; and a time of 30 min to 2 h, specifically 30 min, 40 min, 50 min, 60 min, 80 min, 100 min, 120 min or any value therebetween.

[0043] The invention also provides application of the electrically detachable acrylate-modified polyurethane hot-melt adhesive in bonding electronic products.

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

[0045] The present invention will be described in detail below by way of examples. The examples of the embodiments are intended to explain the present invention and should not be construed as limiting the present invention. If no specific techniques or conditions are specified in the embodiments, the techniques or conditions described in the literature in this area or the product instructions are used. If no manufacturer is specified for the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0046] Example 1

[0047] By weight, 5.49 g (2.746 mmol) of liquid polycaprolactone diol with a number average molecular weight of 2000 (Daicel PLACCEL L220AL; Tg<0°C; melting point = 0-5°C), 5.49 g (2.746 mmol) of polytetrahydrofuran ether diol with a number average molecular weight of 2000 (purchased from PTG Company of South Korea, brand name PTMEG-2000; Tg = -76°C; melting point = 24°C), 7.00 g of 1-butyl-3-methylimidazole tetrafluoroborate, 5.0 g of fumed silica HDK H20, 1.5 g of 3-mercaptopropyltrimethoxysilane, and 1.1 g of water absorbent Additive OF were heated to 110°C, vacuum dehydrated for 2 h under stirring conditions of 150 r / min, and then cooled to 80°C, and 50.42 g (54.919 mmol) of low free polyurethane prepolymer (Adiprene LF TE 915; viscosity at 50°C is 2000-4000cps; free isocyanate monomer content is less than 0.1%), 0.5g dibutyltin dilaurate, react for 2h under stirring conditions at 150r / min, then add 1.5g photoinitiator ITX, 12.0g tetrahydrofuran acrylate, 10.0g triethylene glycol diacrylate, mix for 1h under stirring conditions at 150r / min, and then discharge to obtain an electrically detachable acrylate-modified polyurethane hot melt adhesive, which is vacuum sealed and stored away from light.

[0048] Example 2

[0049] By weight, 5.38 g (5.376 mmol) of polycaprolactone diol (PLACCEL210N; Tg = -17 ° C; melting point = 32-37 ° C) with a number average molecular weight of 1000, 5.38 g (1.792 mmol) of liquid polycarbonate diol (Kuraray polyol C3090; Tg = -42 ° C; melting point <25 ° C) with a number average molecular weight of 3000, 3.00 g of 1-butyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt, 2.0 g of fumed silica AEROSIL R202, 0.3 g of 3-aminopropyl triethoxysilane, and 0.7 g of water absorbent Additive OF were heated to 110 ° C, vacuum dehydrated for 2 h under stirring conditions of 150 r / min, and 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 is 8000-16400cps; free isocyanate monomer content is less than 0.1%), 0.1g stannous octoate, react for 2h under stirring conditions at 150r / min, then add 0.5g photoinitiator TPO, 10.0g 1,6-hexanediol diacrylate, and 5.0g trimethylolpropane formal acrylate, mix for 1h under stirring conditions at 150r / min, and then discharge the material to obtain an electrically detachable acrylate-modified polyurethane hot melt adhesive, which is vacuum-sealed and stored away from light.

[0050] Example 3

[0051] By weight, 7.62 g (1.386 mmol) of a liquid polyester diol with a number average molecular weight of 5500 (Evonik 7250; Tg = -50 ° C; melting point <25 ° C), 5.54 g (2.772 mmol) of a polyether diol with a number average molecular weight of 2000 (voranol 2120; Tg <0 ° C; melting point <25 ° C), 8.00 g of N-butylpyridinium tetrafluoroborate, 4.0 g of fumed silica AEROSIL R972, 2.0 g of vinyl trimethoxysilane, and 1.5 g of water absorbent Additive TI were heated to 110 ° C, vacuum dehydrated for 2 h under stirring conditions of 150 r / min, and then cooled to 80 ° C, and 43.03 g (37.42 mmol) of a low-free polyurethane prepolymer (Adiprene LF G730; viscosity at 50°C is 22750cps; free isocyanate monomer content is less than 0.1%), 1.1g 2,2-dimorpholinyl diethyl ether, react for 2h under stirring at 150r / min, then add 2.2g photoinitiator 184, 10.0g neopentyl glycol diacrylate, 15.0g isooctyl acrylate, mix for 1h under stirring at 150r / min, and then discharge to obtain an electrically removable acrylate modified polyurethane hot melt adhesive, which is vacuum sealed and stored away from light.

[0052] Example 4

[0053] By weight, 2.31 g (1.155 mmol) of a liquid polycarbonate diol with a number average molecular weight of 2000 (DURANOL T5652; Tg <0°C; melting point <-5°C), 4.62 g (2.31 mmol) of a liquid polyester diol with a number average molecular weight of 2000 (stepanpol PH-56; Tg = -15°C; melting point <25°C), 10.00 g of 1-octyl-3-methylimidazole trifluoromethanesulfonate, 3.0 g of fumed silica HDK H18, 0.5 g of 3-glycidoxypropyltriethoxysilane, and 1.2 g of a water absorbent Additive OF were heated to 110°C, vacuum dehydrated for 2 h under stirring at 150 r / min, and then cooled to 80°C, and 46.57 g (41.58 mmol) of a low-free polyurethane prepolymer (Adiprene LF G750; viscosity at 50°C is 32000cps; free isocyanate monomer content is less than 0.1%), 0.8g zinc isooctanoate, react for 2h under stirring condition of 150r / min, then add 3.0g photoinitiator 819, 14.0g diethylene glycol diacrylate, 14.0g tridecyl acrylate, mix for 1h under stirring condition of 150r / min, and then discharge to obtain electrically decomposable acrylate modified polyurethane hot melt adhesive, which is vacuum sealed and stored away from light.

[0054] Example 5

[0055] By weight, 2.28 g (2.276 mmol) of polyether diol with a number average molecular weight of 2000 (voranol220-110; Tg <0°C; melting point <25°C), 3.98 g (1.138 mmol) of liquid polyester diol with a number average molecular weight of 3500 (Dynacoll 7230; Tg = -30°C; melting point <25°C), 12.00 g of N-propyl-N-methylpiperidinium bis(trifluoromethanesulfonyl)imide salt, 3.0 g of fumed silica TS620, 0.5 g of 3-aminopropyltrimethoxysilane, and 1.5 g of water absorbent Additive TI were heated to 110°C, vacuum dehydrated for 2 h under stirring conditions of 150 r / min, and then cooled to 80°C, and 38.24 g (27.315 mmol) of low free polyurethane prepolymer (Adiprene LF G600; viscosity at 50°C is 3975cps; free isocyanate monomer content is less than 0.1%), 1.2g bismuth isooctanoate, react for 2h under stirring conditions at 150r / min, then add 4.0g photoinitiator 369, 20.0g triethylene glycol diacrylate, 12.0g dodecyl acrylate, mix for 1h under stirring conditions at 150r / min, and then discharge the material to obtain an electrically decomposable acrylate-modified polyurethane hot melt adhesive, which is vacuum sealed and stored away from light.

[0056] Comparative Example 1

[0057] By weight, 39.42 g (11.262 mmol) of polyester diol with a number average molecular weight of 3500 (Evonik Dynacoll7360; Tg = -60 ° C; melting point = 55 ° C), 22.52 g (11.262 mmol) of polytetramethylene glycol with a number average molecular weight of 2000 (PTMG2000; Tg = -76 ° C; melting point = 28 ° C), 15.0 g of thermoplastic acrylic resin BM751 (Tg = 49 ° C), 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 absorbent Additive OF was heated to 110°C, vacuum dehydrated for 2 h at 150 r / min, then cooled to 80°C, 12.03 g (48.123 mmol) of 4,4'-diphenylmethane diisocyanate (MDI) and 0.3 g of stannous octoate were added, and the mixture was reacted for 2 h at 150 r / min to obtain a reference electrically removable acrylate-modified polyurethane hot melt adhesive, which was then vacuum sealed and stored away from light.

[0058] Comparative Example 2

[0059] 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 by the same molar amount of low free polyurethane prepolymer Adiprene LF S300 which was solid at 50°C, and the other conditions were the same as those in Example 1 to obtain a reference electrically removable acrylate modified polyurethane hot melt adhesive, which was vacuum sealed and stored away from light.

[0060] Comparative Example 3

[0061] A reference electrically removable acrylate-modified 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 low-viscosity and low-free polyurethane prepolymer to the hydroxyl group in the low-viscosity polyol compound was adjusted from 10:1 to 2:1, as follows:

[0062] By weight, 16.01 g (8.003 mmol) of liquid polycaprolactone diol with a number average molecular weight of 2000 (Daicel PLACCEL L220AL; Tg = <0°C; melting point = 0-5°C), 16.01 g (8.003 mmol) of polytetrahydrofuran ether diol with a number average molecular weight of 2000 (purchased from PTG, South Korea, brand name PTMEG-2000; Tg = -76°C; melting point = 24°C), 7.00 g of 1-butyl-3-methylimidazole tetrafluoroborate, 5.0 g of fumed silica HDK H20, 1.5 g of 3-mercaptopropyltrimethoxysilane, and 1.1 g of water absorbent Additive OF was heated to 110°C, vacuum dehydrated for 2 hours under stirring conditions of 150 r / min, then cooled to 80°C, 29.39 g (32.013 mmol) of low-free polyurethane prepolymer (Adiprene LF TE 915; viscosity at 50°C is 2000-4000 cps; free isocyanate monomer content is less than 0.1%) and 0.5 g of dibutyltin dilaurate were added, and the mixture was reacted for 2 hours under stirring conditions of 150 r / min. Then, 1.5 g of photoinitiator ITX, 12.0 g of tetrahydrofuran acrylate, and 10.0 g of triethylene glycol diacrylate were added, and the mixture was mixed for 1 hour under stirring conditions of 150 r / min, and then the material was discharged to obtain a reference electrically removable acrylate-modified polyurethane hot melt adhesive, which was vacuum sealed and stored away from light.

[0063] Comparative Example 4

[0064] 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 by the same weight portion of 4,4'-diphenylmethane diisocyanate (MDI) monomer, and the other conditions were the same as in Example 1 to obtain a reference electrically removable acrylate-modified polyurethane hot melt adhesive, which was vacuum sealed and stored away from light.

[0065] Comparative Example 5

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

[0067] Comparative Example 6

[0068] A reference electrically-detachable 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 Example 1 to obtain a reference electrically-detachable acrylate-modified polyurethane hot melt adhesive, which was vacuum-sealed and stored away from light.

[0069] Comparative Example 7

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

[0071] Comparative Example 8

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

[0073] By weight, 5.49 g (2.746 mmol) of crystalline polyester diol with a number average molecular weight of 2000 (Hoopol F-900; melting point = 53° C.), 5.49 g (2.746 mmol) of polycarbonate diol with a number average molecular weight of 2000 (UH-CARB200; melting point = 50° C.), 7.00 g of 1-butyl-3-methylimidazole tetrafluoroborate, 5.0 g of fumed silica HDK H20, 1.5 g of 3-mercaptopropyltrimethoxysilane, and 1.1 g of water absorbent Additive OF were heated to 110° C., vacuum dehydrated for 2 h under stirring at 150 r / min, and then cooled to 80° C., and 50.42 g (54.919 mmol) of low free polyurethane prepolymer (Adiprene LF TE915; viscosity at 50°C is 2000-4000cps; free isocyanate monomer content is less than 0.1%), 0.5g dibutyltin dilaurate, react for 2h under stirring conditions at 150r / min, then add 1.5g photoinitiator ITX, 12.0g tetrahydrofuran acrylate, 10.0g triethylene glycol diacrylate, mix for 1h under stirring conditions at 150r / min, and then discharge the material to obtain a reference electrically removable acrylate modified polyurethane hot melt adhesive, which is vacuum sealed and stored away from light.

[0074] Test Case

[0075] The samples of the embodiment and the comparative example were subjected to comparative tests in the following manner:

[0076] (1) Viscosity at 25°C: The polyurethane hot melt adhesive samples obtained in the above embodiments and comparative examples were respectively sampled into a cone-plate viscometer, and the viscosity of the adhesive was tested at 25°C and 1 rpm using the cone-plate viscometer. The results are shown in Table 1.

[0077] (2) Bonding strength at different curing times: The polyurethane hot melt adhesive obtained in the above embodiments and comparative examples was dispensed at room temperature using a dispensing machine (if it was solid at room temperature, the dispensing temperature was set at 110°C), a rectangular adhesive line of 25 mm × 4 mm was applied on a stainless steel substrate, and then a 365 nm UV-LED light source was used to irradiate the adhesive at 2000 mJ / cm 2 After the irradiation, another stainless steel substrate was bonded to the stainless steel substrate. After bonding, the sample was cured in an environment of 25°C and 50% RH for 5 minutes, 30 minutes and 48 hours. Then, a universal material testing machine was used to run the prepared bonding sample along the shear direction at a speed of 10 mm / min until the bonding of the sample failed. The maximum force value displayed by the instrument was recorded, and the shear bonding strength of the polyurethane hot melt adhesive to the stainless steel substrate before power was applied was calculated in combination with the bonding area. The results are shown in Table 1.

[0078] (3) Adhesion strength after power on: The polyurethane hot melt adhesive obtained in the above embodiments and comparative examples was dispensed at room temperature using a dispensing machine (if it is solid at room temperature, the dispensing temperature was set at 110°C), and a rectangular adhesive line of 25 mm × 4 mm was applied on a stainless steel substrate. Then, a 365 nm UV-LED light source was used to irradiate the adhesive at 2000 mJ / cm 2 After the irradiation, another stainless steel substrate is bonded to the stainless steel substrate. After the bonding is completed, the sample is cured in an environment of 25°C and 50% RH for 48 hours. Then, the positive and negative wires of the DC power supply are clamped at both ends of the shear sample, and the power is turned on for a certain period of time at a certain voltage. After the power is turned on, the shear sample is removed, and the universal material testing machine is used to run the prepared bonding sample along the shear direction at a speed of 10mm / min until the sample fails to bond. The maximum force value displayed by the instrument is recorded, and the shear bonding strength of the polyurethane hot melt adhesive to the stainless steel substrate after power is turned on is calculated in combination with the bonding area. The results are shown in Table 1.

[0079] (4) Isocyanate group content: According to standard HG / T2409-92, (2±0.2) g of the polyurethane hot melt adhesive sample obtained in the above comparative example and example (accurate to 0.001 g) was taken and placed in a conical flask, 10 mL of di-n-butylamine-toluene solution was accurately pipetted into the conical flask, and then 20 mL of toluene was added and gently shaken to dissolve it, and finally 80 mL of anhydrous isopropanol was added, and the mixture was allowed to stand for 15 min. Bromocresol green was used as an indicator and titrated with 0.5 mol / L hydrochloric acid standard solution. When the solution changed from blue to yellow and did not change color for 30 s, the titration endpoint was reached (a blank test was performed in the same manner), and the isocyanate group content in the polyurethane hot melt adhesive sample was calculated based on the difference between the amount of hydrochloric acid consumed by the blank titration test and the polyurethane hot melt adhesive sample. The results are shown in Table 1.

[0080] (5) Free isocyanate monomer content: Use a high performance liquid chromatograph (HPLC) with liquid as the mobile phase and a high pressure infusion system to pump the mobile phase into a chromatographic column containing a stationary phase. After the components are separated in the column, they enter the detector for detection to obtain a chromatogram of the test substance. Use the external standard method to quantitatively calculate the content of free isocyanate monomer in the polyurethane hot melt adhesive. Record the chromatograms of the sample to be tested and the standard respectively. Calculate the content of free isocyanate in the sample to be tested based on the integrated area of ​​the specific peak on the chromatogram. The results are shown in Table 1.

[0081] Table 1

[0082]

[0083] As can be seen from the results of Table 1, the electrically detachable acrylate-modified polyurethane hot melt adhesive provided by the present invention has a lower viscosity at room temperature, and can be directly dispensed at room temperature, which significantly improves the defect that the reactive polyurethane hot melt adhesive needs to be heated for gluing, increases the convenience of using the adhesive, and reduces the risk of being scalded by the operator during the use of the heating equipment. According to practical experience, if the bonding strength at room temperature is less than 2.0MPa, it means that the polyurethane hot melt adhesive has electrical detachability, otherwise it does not have electrical detachability. As can be seen from the results of Table 1, the acrylate-modified polyurethane hot melt adhesive provided by the present invention, which can be glued at room temperature, can quickly establish a higher initial bonding strength after UV light, has the function of realizing preliminary positioning in a short time, has excellent final bonding strength after being fully cured, and the bonding strength of the adhesive can be significantly attenuated after power-on, and can even fall off directly, with excellent power-on disassembly performance. In summary, the electrically detachable acrylate-modified polyurethane hot melt adhesive provided by the present invention also has extremely low free isocyanate monomer residues, which can significantly reduce the risk of harm to human health during the use of hot melt adhesives. In summary, the acrylate modified polyurethane hot melt adhesive provided by the present invention has a low free isocyanate content, can be dispensed at room temperature, has high initial bonding strength and final bonding strength, has a fast curing speed, and can be disassembled under power-on conditions, and has broad practical application prospects.

[0084] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. An electrically detachable acrylate-modified polyurethane hot melt adhesive, characterized in that: The electrically detachable acrylate-modified polyurethane hot melt adhesive contains a polyurethane prepolymer mixture, an ionic liquid, an acrylate compound and a photoinitiator. Both ends of the prepolymer contained in the polyurethane prepolymer mixture are capped with isocyanate. The isocyanate structural unit contained in the polyurethane prepolymer mixture is derived from a low-viscosity and low-free polyurethane prepolymer, and the polyol structural unit contained in the polyurethane prepolymer mixture is derived from a low-viscosity polyol compound with a glass transition temperature of less than 0°C and a melting point of less than 40°C. The mass ratio of the polyurethane prepolymer mixture to the acrylate compound is 1:(0.06-0.9). The total content of isocyanate groups in the electrically detachable acrylate-modified polyurethane hot melt adhesive is 2-8%, and the content of free isocyanate monomers is less than 0.1%. The viscosity of the electrically detachable acrylate-modified polyurethane hot melt adhesive at 25°C ranges from 1000 to 150000 cps, and the attenuation rate of the bonding strength is more than 80% after power is applied at a voltage of 1-100V.

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 low-viscosity and low-free polyurethane prepolymer, low-viscosity polyol compound, ionic liquid, acrylate compound and photoinitiator, as well as optional rheology modifier, silane coupling agent, water absorbent and catalyst. The molar equivalent ratio of isocyanate group in the low-viscosity and low-free polyurethane prepolymer to hydroxyl group 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 and low-free polyurethane prepolymer and the low-viscosity polyol compound is 40-80%, the content of the ionic liquid is 2-15%, the content of the acrylate compound is 5-35%, the content of the photoinitiator is 0.1-5%, the content of the 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 and low-free polyurethane prepolymer is less than 0.1%; the low-viscosity and low-free polyurethane prepolymer is liquid below 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 terminal hydroxyl 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; Preferably, 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 phosphonium salt cations, pyrrolidine cations and piperidine cations, and the anions are selected from at least one of trifluoromethanesulfonate anions, tetrafluoroborate anions, hexafluorophosphate anions, bisfluoromethanesulfonyl imide anions, hydrogen sulfate anions, ethyl sulfate anions and p-toluenesulfonate anions; Preferably, 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 disulfide at least one of (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-butylpyridinium 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-methylpiperidinium bis(trifluoromethanesulfonyl)imide salt.

7. The electrically detachable acrylate-modified polyurethane hot melt adhesive according to claim 2, characterized in that: The acrylate compound is selected from at least one of octadecyl acrylate, tetramethylene glycol acrylate, dodecyl acrylate, 2-phenoxyethyl acrylate, isodecyl acrylate, isooctyl acrylate, tridecyl acrylate, trimethylolpropane formal acrylate, monoacrylate of methoxy polyethylene glycol, alkoxylated tetramethylene glycol 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.

8. The electrically detachable acrylate-modified polyurethane hot melt adhesive according to any one of claims 1 to 7, characterized in that: The photoinitiator is selected from at least one of benzophenone compounds, acetophenone compounds, acylphosphine oxide compounds, titanocene compounds, oxime ester compounds, benzoin ether compounds and thioxanthone; Preferably, the rheology modifier is fumed silica; Preferably, the silane coupling agent is selected from 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropylmethyldiethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3- at least one of (2-aminoethyl)aminopropyltrimethoxysilane, 3-(2-aminoethyl)aminopropyltriethoxysilane, 3-(2-aminoethyl)aminopropylmethyldimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, 3-(meth)acryloxypropylmethyldiethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane and 3-isocyanatepropyltrimethoxysilane; Preferably, the water absorbent is selected from at least one of a molecular sieve desiccant, an oxazolidine dehydrating agent, p-toluenesulfonyl isocyanate and triethyl orthoformate; Preferably, 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-dimorpholinyl diethyl ether.

9. The method for preparing the electrically detachable acrylate-modified polyurethane hot melt adhesive according to any one of claims 1 to 8, characterized in that: The method comprises the following steps: S1, dehydrating the low-viscosity polyol compound and the ionic liquid and the optional rheology modifier, silane coupling agent and water absorbent to obtain a pretreated product; S2, stirring the pretreated product, the low-viscosity, low-free polyurethane prepolymer and an optional catalyst at 70 to 90° C. for 1 to 5 hours to obtain a prepolymer containing a polyurethane prepolymer mixture; S3. Evenly mix the prepolymer, the acrylate compound and the photoinitiator to obtain the electrically removable acrylate-modified polyurethane hot melt adhesive.

10. Use of the electrically detachable acrylate-modified polyurethane hot melt adhesive according to any one of claims 1 to 8 in bonding electronic products.

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