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

Abstract

The present invention belongs to the technical field of polyurethane hot-melt adhesives, and particularly relates to an electrically-detachable acrylate-modified polyurethane hot-melt adhesive having good adhesive performance, and a preparation method therefor and the use thereof. The raw materials for preparing the acrylate-modified polyurethane hot-melt adhesive comprise an acrylate monomer, an alkali metal salt, a polyol compound, a polyisocyanate compound, a photoinitiator, an optional silane coupling agent, an optional catalyst and an optional water absorbent, wherein the mass ratio of the acrylate monomer to the alkali metal salt is (1-10):1; and the mass ratio of the acrylate monomer to the polyol compound to the polyisocyanate compound is 1:(1.3-6.4):(0.15-2.3). In the present invention, by introducing a UV-curable acrylate monomer and alkali metal salt at a specific ratio and by adjusting and controlling the ratio of the acrylate monomer to the polyol compound and the polyisocyanate compound, the electrically-detachable acrylate-modified polyurethane hot-melt adhesive having good adhesive performance is obtained.

Description

An acrylic-modified polyurethane hot melt adhesive with excellent bonding properties and electrical disintegration, its preparation method and application.

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese Patent Application No. 202411459624X, filed on October 18, 2024, entitled "An Acrylic-Modified Polyurethane Hot Melt Adhesive with Excellent Adhesive Performance and Electrically Disassembled, 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 polyurethane hot melt adhesive technology, specifically relating to an acrylate-modified polyurethane hot melt adhesive with excellent bonding performance and electrical disassembly, as well as its preparation method and application. Background Technology

[0004] The curing principle of reactive polyurethane hot melt adhesives mainly involves the reaction of isocyanate with moisture in the air to form a chemical cross-linked structure, thereby achieving high bonding strength. They are widely used in electronic products such as smartphones, tablets, smartwatches, and TWS earphones. Because electronic product components often have high value, situations such as assembly defects, product repairs, and the recycling of valuable electronic components usually require the disassembly of the bonded parts. Therefore, adhesives typically need to possess excellent bonding reliability while also being easily removable under certain conditions.

[0005] However, fully cured polyurethane hot melt adhesives are typically difficult to disassemble because the covalent bonds formed by the reaction of isocyanate with moisture are irreversible, making the cross-linked structure difficult to break. Currently, common disassembly methods typically rely on high temperatures, chemical reagents, or external force, which can easily cause significant damage to the bonded substrate. In recent years, research has shown that electrical disassembly is a gentler method, primarily achieved by adding alkali metal salts and solvating matrices to the polyurethane hot melt adhesive, giving it the ability to be disassembled under electrical conditions. However, while existing electrically disassembleable polyurethane hot melt adhesives possess this disassembly capability, they still lag significantly behind traditionally widely used polyurethane hot melt adhesives in terms of bond strength, curing speed, and heat resistance. Current technologies for electrically disassembled polyurethane hot melt adhesives are still insufficient to meet the performance requirements of practical applications.

[0006] Therefore, there is an urgent need to develop an adhesive that is detachable under power conditions while also having excellent bonding performance to meet the market demand for high-performance detachable adhesives. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing polyurethane hot melt adhesives, which are difficult to combine electrical disassembly and excellent adhesive properties, by providing an acrylate-modified polyurethane hot melt adhesive with excellent adhesive properties and electrical disassembly, as well as its preparation method and application.

[0008] In a first aspect, the present invention provides an acrylate-modified polyurethane hot melt adhesive, wherein the raw materials for preparing the acrylate-modified polyurethane hot melt adhesive contain acrylate monomers, alkali metal salts, polyol compounds, polyisocyanate compounds, photoinitiators, and optionally silane coupling agents, catalysts, and water-absorbing agents; the mass ratio of the acrylate monomers to the alkali metal salts is (1-10):1; and the mass ratio of the acrylate monomers, polyol compounds, and polyisocyanate compounds is 1:(1.3-6.4):(0.15-2.3).

[0009] In some specific embodiments, the content of the acrylate monomer is 10-30 parts by weight, the content of the alkali metal salt is 3-15 parts by weight, the content of the polyol compound is 35-66 parts by weight, the content of the polyisocyanate compound is 5-25 parts by weight, the content of the photoinitiator is 0.5-5 parts by weight, the content of the silane coupling agent is 0-3 parts by weight, the content of the catalyst is 0-2 parts by weight, and the content of the water absorbent is 0-2 parts by weight.

[0010] In some specific embodiments, the viscosity of the acrylate monomer at 25°C is 0.1–30 mPa·s.

[0011] In some specific embodiments, the acrylate monomer is selected from at least one of octadecyl acrylate, tetrahydrofuran acrylate, dodecyl acrylate, 2-phenoxyethyl acrylate, isodecanyl acrylate, isooctyl acrylate, tridecyl acrylate, trimethylolpropane formal 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, and dipropylene glycol diacrylate.

[0012] In some specific embodiments, the alkali metal salt is a compound composed of an alkali metal cation and at least one anion selected from organic acid anion, inorganic acid anion, and organic sulfonamide anion.

[0013] In some specific embodiments, the alkali metal salt is selected from at least one of lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide, lithium chloride, lithium sulfate, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium hexafluoroantimonate, lithium nitrate, sodium trifluoromethanesulfonate, sodium bis(trifluoromethanesulfonyl)imide, sodium chloride, sodium sulfate, sodium tetrafluoroborate, sodium hexafluorophosphate, sodium hexafluoroantimonate, sodium nitrate, potassium trifluoromethanesulfonate, potassium bis(trifluoromethanesulfonyl)imide, potassium chloride, potassium sulfate, potassium nitrate, potassium tetrafluoroborate, potassium hexafluorophosphate, and potassium hexafluoroantimonate.

[0014] In some specific embodiments, the polyol compound is selected from at least one of polyester polyols, polyether polyols, polycarbonate polyols, and polyalkylene polyols.

[0015] In some specific embodiments, the number-average molecular weight of the polyol compound is 1000–4000 g / mol.

[0016] In some specific embodiments, 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 phenylenedimethylene diisocyanate, 1,5-naphthalene diisocyanate, 1,5-pentane diisocyanate, 1,4-phenylenedimethylene diisocyanate, m-phenylenedimethyl isocyanate, tetramethylphenylenedimethylene diisocyanate, norbornene diisocyanate, lysine diisocyanate, triphenylmethane triisocyanate, triphenyl thiophosphate triphenyl isocyanate, and 1,6,11-undecane triisocyanate.

[0017] In some specific embodiments, the photoinitiator is selected from at least one of benzophenone compounds, acetophenone compounds, acylphosphine oxide compounds, dicocene compounds, oxime ester compounds, benzoin ether compounds, and thioxanone.

[0018] In some specific embodiments, the silane coupling agent is selected from at least one of mercaptosilane, epoxysilane, aminosilane, alkenylsilane, and isocyanate-based silane.

[0019] In some specific embodiments, the catalyst is selected from at least one of dibutyltin dilaurate, stannous octoate, triethylamine, diethylenetriamine, triethylenediamine, N-ethylmorpholine, and 2,2-dimorpholinodiethyl ether.

[0020] In some specific embodiments, the desiccant is selected from at least one of molecular sieve desiccant, oxazolidine desiccant, p-toluenesulfonyl isocyanate, and triethyl orthoformate.

[0021] Secondly, the present invention provides a method for preparing the above-mentioned acrylate-modified polyurethane hot melt adhesive, the method comprising mixing acrylate monomers, alkali metal salts, polyol compounds, polyisocyanate compounds, photoinitiators, and optionally silane coupling agents, catalysts, and water-absorbing agents uniformly to obtain acrylate-modified polyurethane hot melt adhesive.

[0022] Thirdly, the present invention also provides the application of the above-mentioned acrylate-modified polyurethane hot melt adhesive in the bonding of electronic products.

[0023] Existing electrically degradable polyurethane hot melt adhesives typically employ the introduction of alkali metal salts and a solvated matrix to form a liquid electrolyte, thereby imparting their electrical degradability. However, because the liquid electrolyte cannot undergo a curing reaction during the adhesive curing process, it remains in the adhesive system as a "plasticizer" after curing. This "plasticizer" affects the internal structure of the cured adhesive, negatively impacting the bond strength and causing a significant decrease in adhesive strength. Therefore, addressing the issue of "plasticizers" in the cured adhesive is crucial for improving the bonding performance of electrically degradable polyurethane hot melt adhesives.

[0024] The key to this invention lies in introducing a specific ratio of UV-curable acrylate monomers and alkali metal salts. On one hand, the introduced acrylate monomers ensure the uniform dissolution and dispersion of the alkali metal salts within the polyurethane hot melt adhesive, imparting electrolytic disintegration under energized conditions. On the other hand, under the action of a photoinitiator, the acrylate monomers undergo a curing reaction. Compared to the commonly used, difficult-to-cure solvated matrices in existing technologies, this solves the negative impact of the "plasticizer" formed by uncured solvated matrices on the adhesive properties of polyurethane hot melt adhesives. Furthermore, the decrease in ionic conductivity after curing is relatively small compared to the uncured state, having minimal impact on the ion migration ability of the cured system. This is presumably because ion migration is influenced not only by the solvated matrix but also by the dissociated ions and polymers. The interaction between polymer chain segments is related to the dipole interaction, and the movement of polymer chain segments can help ion migration. Therefore, the acrylate monomer can still maintain good electrical disassembly performance after curing. At the same time, the ratio of acrylate monomer to polyol compound and polyisocyanate compound was also controlled, so that the acrylate modified polyurethane hot melt adhesive can quickly establish initial bond strength after UV curing, while maintaining a certain open time. The UV curing and moisture curing reaction processes in the system can play a good synergistic role, which not only helps to improve the initial bond strength, but also makes it possible to apply the UV and moisture dual-curing acrylate modified polyurethane hot melt adhesive to the bonding of opaque conductive metal substrates, which significantly improves the poor bonding performance of existing electrically disassembly adhesives.

[0025] In summary, this invention introduces a specific ratio of acrylate monomers and alkali metal salts, and further adjusts the ratio of acrylate monomers to polyol compounds and polyisocyanate compounds. The resulting acrylate-modified polyurethane hot melt adhesive exhibits both excellent adhesive properties and electrical disassembly capabilities, and has broad prospects for practical applications. Detailed Implementation

[0026] The raw materials for preparing the acrylate-modified polyurethane hot melt adhesive provided by this invention contain acrylate monomers, alkali metal salts, polyol compounds, polyisocyanate compounds, photoinitiators, and optionally silane coupling agents, catalysts, and water-absorbing agents. The mass ratio of the acrylate monomer to the alkali metal salt is (1–10):1, such as 1:1, 2:1, 5:1, 8:1, 10:1, or any value between them. The mass ratio of the acrylate monomer to the polyol compound is 1:(1.3–6.4), such as 1:1.3, 1:1.5, 1:1.8, 1:2, 1:3, 1:4, 1:5, 1:6, 1:6.4, or any value between them. The mass ratio of the acrylate monomer to the polyisocyanate compound is 1:(0.15~2.3), such as 1:0.15, 1:0.18, 1:0.2, 1:0.5, 1:1, 1:1.5, 1:2, 1:2.3, or any value between them. When the content of the acrylate monomer is too high, the acrylate curing reaction is faster and the degree of curing is higher after UV irradiation, resulting in a significant decrease in the adhesion of the adhesive surface. This reduces the adhesion between the acrylate-modified polyurethane hot melt adhesive and the bonded substrate, and consequently, the final bond strength after curing is also significantly reduced. Therefore, in addition to controlling the mass ratio of the acrylate monomer to the alkali metal salt to ensure good electrical conductivity of the acrylate-modified polyurethane hot melt adhesive, it is also necessary to adjust the mass ratio of the acrylate monomer to the polyol compound and the polyisocyanate compound, ensuring the components work together to simultaneously improve the curing speed and bond strength of the acrylate-modified polyurethane hot melt adhesive.

[0027] In this invention, the content of the acrylate monomer is preferably 10-30 parts by weight, such as 10, 12, 15, 18, 20, 22, 25, 28, 30 parts by weight or any value between them; the content of the alkali metal salt is preferably 3-15 parts by weight, such as 3, 5, 7, 10, 12, 15 parts by weight or any value between them; the content of the polyol compound is preferably 35-66 parts by weight, such as 35, 38, 40, 42, 45, 48, 50, 52, 55, 58, 60, 62, 66 parts by weight or any value between them; the content of the polyisocyanate compound is preferably 5-25 parts by weight, such as 5, 8, 10, 12, 15, 18, 20, 22, 25 parts by weight or any value between them. The photoinitiator content is preferably 0.5 to 5 parts by weight, such as 0.5, 1, 2, 3, 4, 5 parts by weight or any value between them; the silane coupling agent content is preferably 0 to 3 parts by weight, such as 0, 0.1, 0.2, 0.5, 0.8, 1, 1.5, 2, 2.5, 3 parts by weight or any value between them; the catalyst content is preferably 0 to 2 parts by weight, such as 0, 0.1, 0.2, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2 parts by weight or any value between them; the water absorbent content is preferably 0 to 2 parts by weight, such as 0, 0.1, 0.2, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2 parts by weight or any value between them.

[0028] In this invention, the type of acrylate is not specifically limited, as long as it is a compound containing at least one photocurable acrylate group. Specific examples include, but are not limited to, at least one of the following: octadecyl acrylate, tetrahydrofuran acrylate, dodecyl acrylate, 2-phenoxyethyl acrylate, isodecanyl acrylate, isooctyl acrylate, tridecyl acrylate, trimethylolpropane formal 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, and dipropylene glycol diacrylate. The viscosity of the acrylate monomer at 25°C is preferably 0.1–30 mPa·s, such as 0.1 mPa·s, 0.5 mPa·s, 1 mPa·s, 5 mPa·s, 10 mPa·s, 15 mPa·s, 20 mPa·s, 25 mPa·s, 30 mPa·s, or any value between them. When the viscosity of the acrylate monomer is within the above-mentioned preferred range, it is more conducive to the uniform dispersion of the alkali metal salt within the polyurethane hot melt adhesive system, thereby imparting good electrolytic disintegration properties to the system.

[0029] In this invention, the alkali metal salt can be a compound composed of an alkali metal cation and at least one anion selected from organic acid anions, inorganic acid anions, and organic sulfonamide anions, preferably a fluorine-containing alkali metal lithium salt. The inventors of this invention have discovered that when the alkali metal salt is preferably a fluorine-containing alkali metal lithium salt, it can impart better electrical disassembly performance to the polyurethane hot melt adhesive. Specifically, the alkali metal cation of the alkali metal salt can be at least one selected from lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs), preferably at least one selected from lithium (Li), sodium (Na), and potassium (K). The anion of the alkali metal salt can be at least one of trifluoromethanesulfonate ion, carboxylate ion, sulfinate ion, chloride ion, sulfate ion, sulfite ion, tetrafluoroborate ion, hexafluorophosphate ion, hexafluoroantimonate ion, nitrate ion, and bis(trifluoromethanesulfonyl)imide ion, preferably trifluoromethanesulfonate ion, tetrafluoroborate ion, hexafluorophosphate ion, hexafluoroantimonate ion, or bis(trifluoromethanesulfonyl)imide ion. Specific examples of the alkali metal salt include, but are not limited to, at least one of lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide, lithium chloride, lithium sulfate, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium hexafluoroantimonyate, lithium nitrate, sodium trifluoromethanesulfonate, sodium bis(trifluoromethanesulfonyl)imide, sodium chloride, sodium sulfate, sodium tetrafluoroborate, sodium hexafluorophosphate, sodium hexafluoroantimonyate, sodium nitrate, potassium trifluoromethanesulfonate, potassium bis(trifluoromethanesulfonyl)imide, potassium chloride, potassium sulfate, potassium nitrate, potassium tetrafluoroborate, potassium hexafluorophosphate, and potassium hexafluoroantimonyate. More preferably, the alkali metal salt is at least one of lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium hexafluorophosphate, and lithium hexafluoroantimonyate.

[0030] In this invention, the polyol compound is preferably selected from at least one of polyester polyols, polyether polyols, polycarbonate polyols, and polyalkylene polyols. The number-average molecular weight (Mn) of the polyol compound is preferably 1000–4000 g / mol, such as 1000 g / mol, 1500 g / mol, 2000 g / mol, 2500 g / mol, 3000 g / mol, 3500 g / mol, 4000 g / mol, or any value between these values. Specifically, the type and source of the polyester polyol are not particularly limited; it can be any commercially available polyester polyol, or a polyester polyol obtained through the reaction of a polycarboxylic acid with a polyol, or a poly-ε-caprolactone polyol obtained by ring-opening polymerization of ε-caprolactone. The polycarboxylic acid is preferably at least one selected from terephthalic acid, isophthalic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, decamethyldicarboxylic acid, and dodecamethyldicarboxylic acid. The polyol is preferably at least one selected from ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, and cyclohexanediol. The type and source of the polyether polyol are not particularly limited; it can be any commercially available polyether polyol, or a modified polyoxyethylene polymer, random copolymer, block copolymer, or bisphenol-type polyoxyethylene polymer derived from ethylene glycol, propylene glycol, tetrahydrofuran, 3-methyltetrahydrofuran, or bisphenol-type polyoxyethylene. The bisphenol-type polyoxyethylene modifier is a polyether polyol obtained by adding an epoxide to the active hydrogen portion of the bisphenol-type molecular backbone. It can be a random copolymer or a block copolymer. The epoxide can be at least one of ethylene oxide, propylene oxide, butane oxide, and isobutane oxide. There are no particular restrictions on the type and source of the polycarbonate polyol, but specific examples include, but are not limited to, at least one of: 1,6-hexanediol polycarbonate, 1,4-butanediol-1,6-hexanediol polycarbonate, 1,5-pentanediol-1,6-hexanediol polycarbonate, caprolactone hexylene diol, 1,4-cyclohexanediol-1,6-hexanediol polycarbonate, ethylene carbonate diol, propylene carbonate diol, butylene carbonate diol, and hexylene carbonate diol. There are no special restrictions on the type and source of the polyalkylene polyols, and specific examples include, but are not limited to, at least one of polybutadiene polyols, hydrogenated polybutadiene polyols, and hydrogenated polyisoprene polyols.

[0031] In this invention, there are no special restrictions on the type and source of the polyisocyanate compound. It can be any compound containing two or more isocyanate groups. Specific examples include, but are not limited to, at least one of the following: 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, m-phenylenedimethyl isocyanate, tetramethylphenyldimethyl diisocyanate, norbornene dimethyl isocyanate, lysine diisocyanate, triphenylmethane triisocyanate, triphenyl thiophosphate, and 1,6,11-undecane triisocyanate.

[0032] In this invention, there are no special restrictions on the type and source of the photoinitiator. It can be any compound that can initiate the curing reaction of acrylate monomers under UV light. It can be a conventional choice in the art, preferably 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 type and source of the silane coupling agent are not particularly limited, but are preferably selected from at least one of mercaptosilanes, epoxysilanes, aminosilanes, alkenylsilanes, and isocyanate-based silanes. Specific examples 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-epoxypropoxypropyltrimethoxysilane, etc. At least one of propylmethyldiethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-(2-aminoethyl)aminopropyltrimethoxysilane, 3-(2-aminoethyl)aminopropyltriethoxysilane, 3-(2-aminoethyl)aminopropylmethyldiethoxysilane, 3-(meth)acryloyloxypropyltrimethoxysilane, 3-(meth)acryloyloxypropyltriethoxysilane, 3-(meth)acryloyloxypropylmethyldiethoxysilane, 3-(meth)acryloyloxypropylmethyldiethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, and 3-isocyanate propyltrimethoxysilane.

[0034] In this invention, there are no special restrictions on the type and source of the catalyst, which can be conventional choices in the field. Specific examples include, but are not limited to, at least one of: dibutyltin dilaurate, stannous octoate, triethylamine, diethylenetriamine, triethylenediamine, N-ethylmorpholine, and 2,2-dimorpholinodiethyl ether.

[0035] In this invention, there are no special restrictions on the type and source of the desiccant, and it can be a conventional choice in the art. Specific examples include, but are not limited to, at least one of molecular sieve desiccant, oxazolidine desiccant, p-toluenesulfonyl isocyanate and triethyl orthoformate.

[0036] The method for preparing acrylate-modified polyurethane hot melt adhesive provided by the present invention includes uniformly mixing acrylate monomers, alkali metal salts, polyol compounds, polyisocyanate compounds, photoinitiators, and optionally silane coupling agents, catalysts, and water-absorbing agents to obtain acrylate-modified polyurethane hot melt adhesive. The present invention does not particularly limit the mixing method. In a preferred embodiment, the above mixing method specifically includes the following steps: S1. Performing a first mixing treatment on acrylate monomers, alkali metal salts, polyol compounds, polyisocyanate compounds, and optionally catalysts and water-absorbing agents to obtain an acrylate-modified polyurethane prepolymer mixture; S2. Performing a second mixing treatment on the acrylate-modified polyurethane prepolymer with a photoinitiator and optionally a silane coupling agent to obtain the acrylate-modified polyurethane hot melt adhesive.

[0037] In the above-mentioned method for preparing acrylate-modified polyurethane hot melt adhesive, step S1 can specifically be as follows: first, the acrylate monomer, alkali metal salt, polyol compound, and water-absorbing agent are mixed and then vacuum dehydrated to obtain a pretreated product; then, the pretreated product is mixed with a polyisocyanate compound and a catalyst for a first mixing treatment to obtain an acrylate-modified polyurethane prepolymer mixture. The vacuum dehydration conditions include: a temperature preferably of 100–120°C, such as 100°C, 105°C, 110°C, 115°C, 120°C, or any value between them; a time preferably of 1–5 h, such as 1 h, 2 h, 3 h, 4 h, 5 h, or any value between them; a stirring speed preferably of 100–200 r / min, such as 100 r / min, 120 r / min, 150 r / min, 180 r / min, 200 r / min, or any value between them; and a vacuum degree that can be a conventional choice in the art. The conditions for the first mixing treatment include: a temperature preferably of 70–90°C, such as 70°C, 75°C, 80°C, 85°C, 90°C, or any value between them; a time preferably of 1–5 h, such as 1 h, 2 h, 3 h, 4 h, 5 h, or any value between them; a stirring speed preferably of 100–200 r / min, such as 100 r / min, 120 r / min, 150 r / min, 180 r / min, 200 r / min, or any value between them; and preferably, the treatment is carried out under vacuum conditions, and the vacuum level can be a conventional choice in the art.

[0038] In the above-mentioned method for preparing acrylate-modified polyurethane hot melt adhesive, in step S2, the conditions for the second mixing treatment include: the temperature is preferably 70-90℃, such as 70℃, 75℃, 80℃, 85℃, 90℃ or any value between them; the time is preferably 0.5-2h, such as 0.5h, 0.75h, 1h, 1.5h, 2h or any value between them; the stirring speed is preferably 100-200r / min, such as 100r / min, 120r / min, 150r / min, 180r / min, 200r / min or any value between them; preferably, the treatment is carried out under vacuum conditions, and the vacuum degree can be a conventional choice in the art.

[0039] The acrylate-modified polyurethane hot melt adhesive provided by this invention can be applied to products requiring debonding and where the adhesive substrate is electrically conductive. Specifically, the debonding conditions include: the voltage for debonding can be 1–100V, such as 1V, 3V, 5V, 7V, 9V, 10V, 20V, 50V, 60V, 80V, 100V, or any value between them; the debonding time can be 1s–60min, such as 1s, 2s, 5s, 10s, 20s, 30s, 50s, 1min, 2min, 5min, 10min, 20min, 30min, 40min, 50min, 60min, or any value between them. Furthermore, the adhesive substrate used with the acrylate-modified polyurethane hot melt adhesive is a conductive substrate.

[0040] The present invention will be described in detail below through specific embodiments.

[0041] All parts mentioned in the following examples and comparative examples refer to parts by weight.

[0042] The raw materials and their sources in the following examples and comparative examples are as follows:

[0043] Polyhexyl adipate diol, purchased from Qingdao Xinyutian Chemical Co., Ltd., brand name POL-538, Mn = 3000 g / mol; polypropylene oxide ether diol, purchased from Dow Chemical Company, brand name Voranol-2120, Mn = 2000 g / mol; polytetrahydrofuran ether diol, purchased from BASF, brand name PolyTHF 1000, Mn = 1000 g / mol; polypentyl adipate diol, purchased from Qingdao Xinyutian Chemical Co., Ltd., brand name POL-756, Mn = 2000 g / mol; polyester polyol, purchased from Evonik Specialty Chemicals, brand name DYNACOLL. 7360, Mn = 3500 g / mol; polyoxypropylene ether diol, purchased from Dow Chemical Company, brand name Voranol-220-110, Mn = 1000 g / mol; polycaprolactone diol, purchased from Daicel, brand name PLACEL 240, Mn = 4000 g / mol; poly(ethylene phthalate) diol, purchased from Stepan Chemical Company, brand name PS-70L, Mn = 1600 g / mol; poly(1,5-pentanediol-1,6-hexanediol) diol, purchased from Asahi Kasei Chemicals Co., Ltd., brand name Duranol T5652, Mn = 2000 g / mol.

[0044] p-Toluenesulfonyl isocyanate desiccant was purchased from Borchers GmbH, Germany, brand name Additive TI; triethyl orthoformate desiccant was purchased from Borchers GmbH, Germany, brand name Additive OF; molecular sieve desiccant was purchased from Arkema GmbH, brand name Siliporite SA1702.

[0045] Example 1

[0046] The following ingredients were added: 32.65 parts polyhexanediol adipate diol POL-538, 21.77 parts polyoxypropylene ether diol Voranol-2120, 12.00 parts 2-phenoxyethyl acrylate (viscosity 7-12 mPa·s at 25°C), 13.00 parts 1,6-hexanediol diacrylate (viscosity 5-8 mPa·s at 25°C), 7.00 parts lithium trifluoromethanesulfonate, and 0.50 parts water-absorbing agent Additive. TI was added to a reaction flask and heated to 110°C. The mixture was then vacuum dehydrated for 2 hours with stirring at 150 rpm. The temperature was then lowered to 80°C, and 10.88 parts of 4,4'-diphenylmethane diisocyanate (MDI) and 0.20 parts of stannous octoate were added. The mixture was stirred at 150 rpm for 2 hours to obtain an acrylate-modified polyurethane prepolymer mixture. Then, 1.00 parts of photoinitiator 184 and 1.00 parts of 3-mercaptopropyltrimethoxysilane were added. The mixture was stirred at 150 rpm for 1 hour and then discharged to obtain an acrylate-modified polyurethane hot melt adhesive, which was then vacuum-sealed and stored away from light.

[0047] Example 2

[0048] The following ingredients were added: 37.81 parts polytetrahydrofuran ether diol (PolyTHF 1000), 25.21 parts polypentyl adipate diol (POL-756), 5.00 parts 1,4-butanediol diacrylate (viscosity 2-10 mPa·s at 25°C), 5.00 parts tetrahydrofuran acrylate (viscosity 2-5 mPa·s at 25°C), 3.00 parts lithium bis(trifluoromethanesulfonyl)imide, and 0.10 parts water-absorbing agent (Additive). OF was added to the reaction flask and heated to 110°C. The mixture was then vacuum dehydrated for 2 hours under stirring at 150 rpm. The temperature was then lowered to 80°C, and 22.69 parts of 4,4'-diphenylmethane diisocyanate (MDI) and 0.50 parts of dibutyltin dilaurate were added. The mixture was stirred at 150 rpm for 2 hours to obtain an acrylate-modified polyurethane prepolymer mixture. Then, 0.50 parts of photoinitiator 819 and 0.20 parts of 3-epoxypropoxypropyltrimethoxysilane were added. The mixture was stirred at 150 rpm for 1 hour and then discharged to obtain an acrylate-modified polyurethane hot melt adhesive, which was then vacuum-sealed and stored away from light.

[0049] Example 3

[0050] The following ingredients were added: 30.45 parts of polyester polyol DYNACOLL 7360, 8.70 parts of polyoxypropylene ether diol Voranol-220-110, 15.00 parts of tripropylene glycol diacrylate (viscosity 10-15 mPa.s at 25℃), 15.00 parts of tridecyl acrylate (viscosity 3-11 mPa.s at 25℃), 15.00 parts of lithium tetrafluoroborate, and 1.00 part of water-absorbing agent Siliporite. SA1702 was added to a reaction flask and heated to 110°C. The mixture was then vacuum-dehydrated for 2 hours with stirring at 150 rpm. The temperature was then lowered to 80°C, and 5.85 parts of hexamethylene diisocyanate (HDI) and 0.20 parts of 2,2-dimorpholinodiethyl ether were added. The mixture was stirred at 150 rpm for 2 hours to obtain an acrylate-modified polyurethane prepolymer mixture. Then, 3.00 parts of photoinitiator TPO and 2.00 parts of 3-isocyanate propyltrimethoxysilane were added. The mixture was stirred at 150 rpm for 1 hour and then discharged to obtain an acrylate-modified polyurethane hot melt adhesive, which was then vacuum-sealed and stored away from light.

[0051] Example 4

[0052] The following ingredients were added: 43.65 parts polycaprolactone diol PLACEL 240, 10.91 parts polyoxypropylene ether diol Voranol-220-110, 10.00 parts tripropylene glycol diacrylate (viscosity 10-15 mPa.s at 25℃), 10.00 parts trimethylolpropane formal acrylate (viscosity 12-18 mPa.s at 25℃), 9.00 parts lithium hexafluorophosphate, and 1.00 part water-absorbing agent Additive. TI was added to a reaction flask and heated to 110°C. The mixture was then vacuum dehydrated for 2 hours with stirring at 150 rpm. The temperature was then lowered to 80°C, and 11.44 parts of 4,4-diisocyanate dicyclohexylmethane (HMDI) and 1.00 parts of dibutyltin dilaurate were added. The mixture was stirred at 150 rpm for 2 hours to obtain an acrylate-modified polyurethane prepolymer mixture. Then, 4.00 parts of photoinitiator ITX and 0.50 parts of 3-epoxypropoxypropyltrimethoxysilane were added. The mixture was stirred at 150 rpm for 1 hour and then discharged to obtain an acrylate-modified polyurethane hot melt adhesive, which was then vacuum-sealed and stored away from light.

[0053] Example 5

[0054] The following ingredients were added: 36.84 parts of poly(ethylene phthalate) diol PS-70L, 23.03 parts of polycarbonate-1,5-pentanediol-1,6-hexanediol diol Duranol T5652, 10.00 parts of neopentyl glycol diacrylate (viscosity 10 mPa·s at 25°C), 5.00 parts of isodecanyl acrylate (viscosity 2-8 mPa·s at 25°C), 4.00 parts of potassium trifluoromethanesulfonate, and 1.50 parts of water-absorbing agent Additive. OF was added to the reaction flask, heated to 110°C, and vacuum dehydrated for 2 hours under stirring at 150 r / min. Then, the temperature was lowered to 80°C, and 15.33 parts of isophorone diisocyanate (IPDI) and 0.50 parts of stannous octoate were added. The mixture was stirred at 150 r / min for 2 hours to obtain an acrylate-modified polyurethane prepolymer mixture. Then, 2.00 parts of photoinitiator 369 and 1.50 parts of 3-mercaptopropyltrimethoxysilane were added, and the mixture was stirred at 150 r / min for 1 hour before being discharged to obtain an acrylate-modified polyurethane hot melt adhesive, which was then vacuum-sealed and stored away from light.

[0055] Example 6

[0056] Acrylic-modified polyurethane hot melt adhesive was prepared according to the method of Example 1, except that the same amount of ethoxylated nonylphenol acrylate with a viscosity of 100-160 mPa·s at 25°C was used instead of 2-phenoxyethyl acrylate (viscosity of 7-12 mPa·s at 25°C) and 1,6-hexanediol diacrylate (viscosity of 5-8 mPa·s at 25°C). All other conditions were the same as in Example 1. Acrylic-modified polyurethane hot melt adhesive was thus obtained and stored in a vacuum-sealed, light-protected container.

[0057] Example 7

[0058] Acrylic-modified polyurethane hot melt adhesive was prepared according to the method of Example 1, except that the same amount of lithium nitrate was used instead of lithium trifluoromethanesulfonate, and all other conditions were the same as in Example 1. The resulting acrylic-modified polyurethane hot melt adhesive was then vacuum-sealed and stored away from light.

[0059] Comparative Example 1

[0060] A reference polyurethane hot melt adhesive was prepared according to the method of Example 1, except that the same amount of propylene carbonate was used instead of 2-phenoxyethyl acrylate and 1,6-hexanediol diacrylate, and all other conditions were the same as in Example 1, thereby obtaining the reference polyurethane hot melt adhesive.

[0061] Comparative Example 2

[0062] A reference polyurethane hot melt adhesive was prepared according to the method of Example 1, except that 2-phenoxyethyl acrylate and 1,6-hexanediol diacrylate were not added, and all other conditions were the same as in Example 1, thereby obtaining the reference polyurethane hot melt adhesive.

[0063] Comparative Example 3

[0064] A reference polyurethane hot melt adhesive was prepared according to the method of Example 1, except that lithium trifluoromethanesulfonate was not added, while all other conditions were the same as in Example 1, thereby obtaining the reference polyurethane hot melt adhesive.

[0065] Comparative Example 4

[0066] The reference polyurethane hot melt adhesive was prepared according to the method of Example 1, except that the amount of 2-phenoxyethyl acrylate and 1,6-hexanediol diacrylate added was increased to 30.00 parts each, and the other conditions were the same as in Example 1, thereby obtaining the reference polyurethane hot melt adhesive.

[0067] Test case

[0068] The polyurethane hot melt adhesives prepared in the above examples and comparative examples were tested for adhesion performance, heat resistance performance, and high temperature and humidity resistance performance before and after energization using the following methods. The results are shown in Table 1.

[0069] (1) Bond strength test at different curing times before power-on: The hot melt adhesive obtained in the examples and comparative examples was dispensed at 110°C using a dispensing machine to coat a rectangular adhesive line of 25mm*4mm on a stainless steel substrate; 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 stainless steel substrate. After bonding, the sample was cured in an environment of 25℃ and 50%RH for 1 min, 15 min, and 1 day, respectively. Then, the bonded sample was run along the shear direction at a speed of 10 mm / min using a universal testing machine until the bond failed. The maximum force value displayed by the instrument was recorded, and the shear bond strength of the adhesive to the stainless steel substrate after curing for 1 min, 15 min, and 1 day was calculated based on the bonded area.

[0070] (2) Bonding strength after energization: After curing the adhesive for 1 day according to the method in (1), the sample to be tested is obtained. The positive and negative wires of the DC power supply are clamped at both ends of the sample. The sample is energized for 30 minutes or 20 minutes at 48V or 60V. After the energization is completed, the sample is removed. The bonded sample is run along the shear direction at a speed of 10mm / min using a universal testing machine until the sample fails to bond. The maximum force value displayed by the instrument is recorded. The shear bonding strength of the adhesive to the stainless steel substrate after energization is calculated in combination with the bonding area (when the bonding strength is below 2MPa, it is removable).

[0071] (3) Heat resistance (80℃): After curing the adhesive for 1 day according to the method in (1), the sample to be tested was obtained. The bonded sample was placed in an oven at 80℃ for 20 minutes. The bonded sample was then placed in an environment at 80℃ and run along the shear direction at a speed of 10 mm / min until the bond failed. The maximum force value displayed by the instrument was recorded. The shear bond strength of the adhesive to the stainless steel substrate under the high temperature environment of 80℃ was calculated in combination with the bonding area.

[0072] (4) High temperature and high humidity resistance (85℃, 85%RH): After curing the adhesive for 1 day according to the method in (1), the sample to be tested was obtained. After placing the bonded sample in a high temperature and high humidity oven at 85℃ and 85%RH for 7 days, the bonded sample was run along the shear direction at a speed of 10mm / min until the bond of the sample failed. The maximum force value displayed by the instrument was recorded. The shear bond strength of the adhesive to the stainless steel substrate after high temperature and high humidity aging was calculated in combination with the bonding area.

[0073] Table 1

[0074] The results of Examples 1-7 show that the acrylate-modified polyurethane hot melt adhesive provided by the present invention exhibits a significant decrease in bond strength after energization, dropping below 2 MPa, while maintaining removability. Simultaneously, it possesses excellent adhesive properties before energization, exhibiting high bond strength and good heat resistance and high-temperature and high-humidity resistance. The results of Example 1 and Comparative Example 1 indicate that, compared to traditional polyurethane hot melt adhesives containing alkali metal salts and a solvating matrix (propylene carbonate), the acrylate-modified polyurethane hot melt adhesive provided in Example 1 not only has a reduced bond strength below 2 MPa after energization and maintains removability, but also possesses superior adhesive properties (high bond strength and good heat resistance and high-temperature and high-humidity resistance). The results of Example 1, Comparative Examples 2 and 3 show that, lacking either the acrylate monomer or the alkali metal salt, not only does the bond strength after energization not decrease significantly, but it remains above 2 MPa, lacks removability, and the bond strength, heat resistance, and high-temperature and high-humidity resistance of the polyurethane hot melt adhesive before energization are all inferior to those of Example 1. The results of Example 1 and Comparative Example 4 show that when the amount of acrylate added is too large, it will lead to a significant decrease in adhesive properties (adhesive strength before energization, heat resistance, and resistance to high temperature and humidity).

[0075] In summary, the acrylate-modified polyurethane hot melt adhesive provided by this invention has both excellent bonding properties (high bonding strength, good heat resistance and high temperature resistance) and electrical disassembly properties, and has broad prospects for practical applications.

[0076] 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 raw materials for preparing the acrylate-modified polyurethane hot melt adhesive contain acrylate monomers, alkali metal salts, polyol compounds, polyisocyanate compounds, photoinitiators, and optional silane coupling agents, catalysts, and water-absorbing agents; the mass ratio of the acrylate monomers to the alkali metal salts is (1-10):1; the mass ratio of the acrylate monomers, polyol compounds, and polyisocyanate compounds is 1:(1.3-6.4):(0.15-2.3).

2. The acrylate-modified polyurethane hot melt adhesive of claim 1, wherein, The acrylate monomer content is 10-30 parts by weight, the alkali metal salt content is 3-15 parts by weight, the polyol compound content is 35-66 parts by weight, the polyisocyanate compound content is 5-25 parts by weight, the photoinitiator content is 0.5-5 parts by weight, the silane coupling agent content is 0-3 parts by weight, the catalyst content is 0-2 parts by weight, and the water absorbent content is 0-2 parts by weight.

3. The acrylate-modified polyurethane hot melt adhesive of claim 1, wherein, The viscosity of the acrylate monomer at 25°C is 0.1–30 mPa·s; The acrylate monomer is selected from at least one of octadecyl acrylate, tetrahydrofuran acrylate, dodecyl acrylate, 2-phenoxyethyl acrylate, isodecanyl acrylate, isooctyl acrylate, tridecyl acrylate, trimethylolpropane formal 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, and dipropylene glycol diacrylate.

4. The acrylate-modified polyurethane hot melt adhesive of claim 1, wherein, The alkali metal salt is a compound composed of an alkali metal cation and at least one anion selected from organic acid anions, inorganic acid anions, and organic sulfonamide anions.

5. The acrylate-modified polyurethane hot melt adhesive of claim 4, wherein, The alkali metal salt is selected from at least one of lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide, lithium chloride, lithium sulfate, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium hexafluoroantimonate, lithium nitrate, sodium trifluoromethanesulfonate, sodium bis(trifluoromethanesulfonyl)imide, sodium chloride, sodium sulfate, sodium tetrafluoroborate, sodium hexafluorophosphate, sodium hexafluoroantimonate, sodium nitrate, potassium trifluoromethanesulfonate, potassium bis(trifluoromethanesulfonyl)imide, potassium chloride, potassium sulfate, potassium nitrate, potassium tetrafluoroborate, potassium hexafluorophosphate, and potassium hexafluoroantimonate.

6. The acrylate-modified polyurethane hot melt adhesive of claim 1, wherein, The polyol compound is selected from at least one of polyester polyols, polyether polyols, polycarbonate polyols, and polyalkylene polyols.

7. The acrylate-modified polyurethane hot melt adhesive of claim 1, 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 phenylenedimethylene diisocyanate, 1,5-naphthalene diisocyanate, 1,5-pentane diisocyanate, 1,4-phenylenedimethylene diisocyanate, m-phenylenedimethyl isocyanate, tetramethylphenylenedimethylene diisocyanate, norbornene diisocyanate, lysine diisocyanate, triphenylmethane triisocyanate, triphenyl thiophosphate triphenyl isocyanate, and 1,6,11-undecane triisocyanate.

8. The acrylate-modified polyurethane hot melt adhesive of claim 1, 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 silane coupling agent is selected from at least one of mercaptosilane, epoxysilane, aminosilane, alkenylsilane, and isocyanate-based silane; The catalyst is selected from at least one of dibutyltin dilaurate, stannous octoate, triethylamine, diethylenetriamine, triethylenediamine, N-ethylmorpholine, and 2,2-dimorpholinodiethyl ether; The desiccant is selected from at least one of molecular sieve desiccant, oxazolidine desiccant, p-toluenesulfonyl isocyanate and triethyl orthoformate.

9. The method of preparing the acrylate-modified polyurethane hot melt adhesive of claim 1, characterized by, The method involves uniformly mixing acrylate monomers, alkali metal salts, polyol compounds, polyisocyanate compounds, photoinitiators, and optionally silane coupling agents, catalysts, and water-absorbing agents to obtain acrylate-modified polyurethane hot melt adhesives.

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

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