Uv light-cured masking glue, preparation method and application thereof

Abstract

This invention discloses a UV-curable masking adhesive, its preparation method, and its application, belonging to the field of masking adhesive technology. The UV-curable masking adhesive includes a polyurethane resin, which is obtained by reacting a polyol with an isocyanate monomer. The polyol includes polyether polyol and polyester polyol, with the polyether polyol having a hydroxyl value of 25-40 mgKOH / g and the polyester polyol having a hydroxyl value of 45-65 mgKOH / g. The masking adhesive has an elongation at break of 200-400% and a peel strength of 1-5 N / cm. The masking adhesive of this invention possesses high elongation at break and appropriate adhesion, effectively meeting the needs of masking adhesives in specific scenarios. The high elongation at break allows the masking adhesive to tightly adhere to narrow gaps and curved structures, making it suitable for complex substrates such as precision electronic components and irregularly shaped automotive parts. The moderate peel strength ensures that the masking layer does not detach during vapor deposition and can be peeled off without residue, significantly improving the yield of vapor deposition products.

Description

Technical Field

[0001] This invention belongs to the field of masking adhesive technology, specifically relating to a UV-cured masking adhesive, its preparation method, and its application. Background Technology

[0002] Masking adhesives, as critical protective materials, are widely used in automotive painting, circuit board protection, machinery coating, and substrate surface masking in vapor deposition processes. When applied in vapor deposition, masking adhesives typically cover the non-deposition areas of the substrate, then cure with heat or UV to form a stable protective layer, which is peeled off after deposition is complete. However, existing masking adhesives have significant drawbacks: 1. Insufficient elongation at break, resulting in insufficient flexibility and inability to adapt to deformation requirements, making it difficult to adequately cover narrow or micro-structured substrates (such as gaps in precision electronic components), leading to incomplete masking; 2. Uneven adhesion, with excessively strong adhesion causing peeling difficulties, resulting in residue or incomplete peeling after curing, while insufficient adhesion causes the masking adhesive to detach during processing.

[0003] Therefore, there is an urgent need to develop a UV-curable masking adhesive that combines high elongation at break with appropriate adhesion to meet the stringent requirements of the precision manufacturing industry.

[0004] It should be noted that this part of the present invention only provides background technology related to the present invention, and does not necessarily constitute prior art or known technology. Summary of the Invention

[0005] This invention provides a UV-curable masking adhesive, its preparation method, and its application, which at least solves the problem that existing masking adhesives are difficult to fully cover narrow or microstructures and are difficult to peel off or remove residues after the vapor deposition process.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a UV-curing masking adhesive, comprising a polyurethane resin obtained by reacting a polyol with an isocyanate monomer; the polyol comprising a polyether polyol and a polyester polyol, wherein the hydroxyl value of the polyether polyol is 25-40 mgKOH / g and the hydroxyl value of the polyester polyol is 45-65 mgKOH / g; the elongation at break of the masking adhesive is 200-400%, and the peel strength of the masking adhesive is 1-5 N / cm.

[0007] Preferably, the mass ratio of polyether polyol to polyester polyol is (0.6~1.5):1.

[0008] Preferably, the functionality of the polyether polyol is 2 to 2.5, and the functionality of the polyester polyol is 2 to 2.5.

[0009] Preferably, the isocyanate monomer includes at least one of diphenylmethane diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate.

[0010] Preferably, the molar ratio of the -NCO group of the isocyanate monomer to the -OH group of the polyol is (1.2~2):1.

[0011] Preferably, the polyurethane resin comprises the following raw material components by weight: 10-20 parts isocyanate monomer, 40-60 parts polyether polyol, 40-60 parts polyester polyol, 2-12 parts end-capping agent, 0.01-0.05 parts catalyst, and 0.05-0.09 parts polymerization inhibitor.

[0012] Preferably, the capping agent includes at least one of 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate.

[0013] Preferably, the catalyst comprises dibutyltin dilaurate.

[0014] Preferably, the polymerization inhibitor includes 2,6-di-tert-butyl-p-cresol.

[0015] Preferably, the method for preparing polyurethane resin includes the following steps:

[0016] S102. Add the catalyst, polyether polyol, and polyester polyol into the reaction vessel;

[0017] S104. Stir the reaction vessel at a speed of 200~300 rpm, heat the reaction vessel at an oil bath temperature of 75~80℃, and maintain the vacuum degree in the reaction vessel between -0.08~-0.1Mpa for vacuum dehydration for 2~3 hours.

[0018] S106. Convert the reaction vessel to a dry air atmosphere, adjust the oil bath temperature to 70~75℃, add isocyanate monomer to the reaction vessel, adjust the rotation speed to 50~100rpm, and continue the reaction for 2~3h.

[0019] S108. Add end-capping agent and polymerization inhibitor to the reaction vessel, and continue the reaction for 2-3 hours to obtain polyurethane resin.

[0020] Preferably, the masking adhesive comprises the following raw material components by weight: 80-95 parts of polyurethane resin, 5-10 parts of active monomer, 3-6 parts of photoinitiator, and 0.1-0.2 parts of pigment.

[0021] Preferably, the active monomer includes isoborneol acrylate.

[0022] Preferably, the photoinitiator includes at least one of photoinitiator 184 and photoinitiator 819.

[0023] Preferably, the pigment includes at least one of ultramarine, cobalt blue, and pigment blue 27.

[0024] Secondly, the present invention provides a method for preparing the above-mentioned UV-curing masking adhesive, comprising the following steps:

[0025] S202. Add polyurethane resin, reactive monomer, and photoinitiator to a mixing container and mix at 1500-2500 rpm for 100-150 seconds, repeating 2-3 times.

[0026] S204, then add pigment, mix at 1500~2500rpm for 100~150s, repeat 2~3 times to obtain UV curing masking adhesive.

[0027] Thirdly, the present invention provides an application of a UV-curing masking adhesive prepared according to the above-described UV-curing masking adhesive or preparation method in covering non-deposition areas of a substrate during a vapor deposition process.

[0028] The beneficial effects of this invention are as follows:

[0029] 1. This invention, by synergistically controlling the ratio and hydroxyl value range of polyether polyol and polyester polyol, forms a microphase separation structure in polyurethane resin, giving the masking adhesive high elongation at break and appropriate adhesion, effectively meeting the needs of masking adhesives in specific scenarios. The flexible polyether segments provide high elastic deformation capability, significantly improving the elongation at break of the masking adhesive. This high elongation at break allows the masking adhesive to closely adhere to narrow gaps and curved surfaces, making it suitable for complex substrates such as precision electronic components and irregularly shaped automotive parts. The rigid polyester segments form an intermolecular hydrogen bond network through strongly polar ester groups, giving the material moderate peel strength, ensuring that the masking layer does not detach during vapor deposition and can be peeled off without residue, significantly improving the yield of vapor deposition products.

[0030] 2. This invention optimizes the isocyanate end-capping process and controls the -NCO / -OH molar ratio to achieve precise regulation of crosslinking density. Excess isocyanate reacts completely with the end-capping agent, avoiding embrittlement caused by side reactions initiated by unreacted -NCO groups; simultaneously, it combines with low-functionality polyols to form a uniform crosslinking network, maintaining an appropriate crosslinking density and avoiding excessively high hardness of the masking adhesive due to over-crosslinking or excessively low crosslinking density affecting the elongation at break.

[0031] 3. The active monomers of this invention synergistically improve UV curing efficiency and application compatibility with the polyurethane resin system. Polyurethane resins typically have high viscosity, which is not conducive to coating or dispensing operations. IBOA, as a low-viscosity monomer, can effectively reduce the viscosity of the system and improve the workability of the masking adhesive. The isoborneol group of IBOA has a large rigid structure. Its introduction increases the molecular chain spacing, reduces interchain forces, and enhances the chain segment slippage ability, making the material more flexible and thus improving the elongation at break. IBOA molecules contain acrylate groups (C=C double bonds), which can participate in free radical polymerization reactions with the acrylate end groups in polyurethane resin under UV irradiation to form a moderately cross-linked network, ensuring both adhesive strength (no delamination during processing) and avoiding excessive cross-linking (no residue upon peeling). The high reactivity of IBOA allows the masking adhesive to quickly complete UV curing and form a dense protective layer. Detailed Implementation

[0032] In this invention,

[0033] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0034] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0035] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. The terms "optional" and "discretionary" mean that they may or may not be included (or may or may not be present).

[0036] This invention provides a UV-curable masking adhesive, comprising a polyurethane resin obtained by reacting a polyol with an isocyanate monomer; the polyol includes polyether polyol and polyester polyol, wherein the hydroxyl value of the polyether polyol is 25-40 mgKOH / g, and the hydroxyl value of the polyester polyol is 45-65 mgKOH / g; the elongation at break of the masking adhesive is 200-400%, and can be 200%, 220%, 240%, 260%, 280%, 300%, 320%, 340%, 360%, 380%, 400%, and any value between them. The peel strength of the masking adhesive is 1-5 N / cm, and can be 1 N / cm, 1.5 N / cm, 2 N / cm, 2.5 N / cm, 3 N / cm, 3.5 N / cm, 4 N / cm, 4.5 N / cm, 5 N / cm, and any value between them.

[0037] This invention defines the elongation at break (the maximum percentage of deformation a material can withstand before tensile fracture) and peel strength (the force required to separate the adhesive interface per unit width) of the masking adhesive, which are directly related to its masking effect on precision substrates and subsequent peeling performance in vapor deposition processes. High elongation at break means that the material has excellent ductility and flexibility, enabling it to tightly adhere to and completely cover substrates with narrow gaps, deep holes, or complex curved surfaces (such as precision electronic components) through large deformation, thereby solving the problem of incomplete masking in existing products; while moderate peel strength ensures that the masking adhesive can withstand process stresses (such as thermal cycling and vacuum environments) during vapor deposition without falling off, and can be completely peeled off after the process without damaging the substrate or leaving any adhesive residue, thus solving the problem of adhesive imbalance, i.e., residual adhesive due to excessive adhesive force or premature detachment due to insufficient adhesive force. This performance balance is achieved through molecular design. Specifically, the flexible segments of the polyether polyol provide the molecular basis for high elongation, allowing the molecular chains to slide and extend under external forces; the rigid segments of the polyester polyol, through the formation of intermolecular forces and physical cross-linking points by strong polar ester groups, contribute cohesive strength and controllable adhesion. The synergistic effect of these two components through the microphase separation structure enables the material to simultaneously achieve high elasticity and moderate adhesion on a macroscopic scale, ultimately meeting the full-process requirements of vapor deposition for tight coverage, firm adhesion, and clean peeling of the masking material.

[0038] Preferably, the hydroxyl value of the polyether polyol is 25~40 mgKOH / g, which can be 25 mgKOH / g, 28 mgKOH / g, 30 mgKOH / g, 32 mgKOH / g, 35 mgKOH / g, 38 mgKOH / g, 40 mgKOH / g, and any value between them.

[0039] Preferably, the hydroxyl value of the polyester polyol is 45~65 mgKOH / g, and can be 45 mgKOH / g, 48 mgKOH / g, 50 mgKOH / g, 52 mgKOH / g, 55 mgKOH / g, 58 mgKOH / g, 60 mgKOH / g, 62 mgKOH / g, 65 mgKOH / g, and any value between them.

[0040] This invention achieves synergistic optimization of the elongation at break and peel strength of the masking adhesive by controlling the hydroxyl value range of polyether polyols and polyester polyols. The hydroxyl value of the polyether polyol is controlled within the range of 25-40 mgKOH / g. A lower hydroxyl value corresponds to a higher molecular weight and fewer terminal hydroxyl groups, resulting in longer flexible segments and significantly improving the material's ductility and elongation at break. The polyester polyol has a hydroxyl value of 45-65 mgKOH / g. A lower hydroxyl value ensures a higher molecular weight and a greater number of polar ester groups. These ester groups can form strong intermolecular hydrogen bonds, enhancing cohesion and interfacial adhesion, thus contributing moderate peel strength. The rigid structure and polarity of the polyester segments provide the necessary adhesive force while avoiding embrittlement caused by excessive crosslinking, while the polyether segments ensure high elongation through their flexibility. The two complement each other through a microphase separation structure, achieving a balance between flexible and rigid segments at the molecular level, meeting the comprehensive requirements of vapor deposition processes for masking materials.

[0041] Furthermore, the hydroxyl value, as an important indicator of the hydroxyl content in the polyol molecular chain, directly determines its chain extension ability and the final polymer molecular conformation in the polyurethane synthesis reaction. For polyether polyols, when the hydroxyl value is in the lower range of 25~40 mgKOH / g, it means that the number of hydroxyl groups per molecule is relatively small, and the corresponding number-average molecular weight is usually high. These high molecular weight polyether segments mainly constitute flexible soft segments in the polyurethane network. The internal rotation barrier of a large number of ether bonds (-O-) in their molecular backbone is extremely low, giving the segments excellent flexibility and mobility. Under external force, these long and flexible polyether chains can effectively disperse stress and absorb deformation energy through chain extension, slippage, and reorientation, thus exhibiting extremely high elongation at break on a macroscopic scale. If the hydroxyl value of the polyether polyol is too high, the molecular weight will be low and the chain segments will be short. The flexibility and slip space of the molecular chain will be limited, resulting in the material becoming brittle and the elongation at break will decrease significantly. Conversely, if the hydroxyl value is too low, although the chain segments will be longer and the flexibility will be better, it may lead to insufficient functionality of the system, making it difficult to form an effective network structure and reducing the cohesive strength. At the same time, the excessively long chain segments may also increase chain entanglement, which may restrict the movement of chain segments under certain conditions.

[0042] For polyester polyols, limiting their hydroxyl values ​​to the range of 45-65 mgKOH / g is based on their functional role as rigid hard segments in polyurethane systems. Polyester polyols within this hydroxyl value range have suitable molecular weights, ensuring both sufficient chain length for constructing continuous hard-phase microdomains and a adequate number of polar ester groups (-COO-). These ester groups possess strong polarity and the ability to form intermolecular hydrogen bonds, enabling the construction of a dense physical crosslinking network in the polyurethane system. Specifically, the carbonyl oxygen atom in the ester group acts as a hydrogen bond acceptor, forming strong hydrogen bonds with the NH groups of the urethane bonds in adjacent segments. These hydrogen bonds, as reversible physical crosslinking points, can dissociate and recombine under stress, effectively dissipating energy and significantly enhancing the cohesive strength and modulus of the material, thus providing the necessary peel strength for the masking adhesive. Simultaneously, the inherent rigidity of the polyester segments (derived from the planar rigidity of the ester groups) causes them to tend to aggregate in polyurethane to form hard-segment microdomains. These microdomains, acting as physical crosslinking points, are dispersed in the continuous soft phase (polyether phase), constituting a typical microphase separation structure. This structure is key to the material's simultaneous high elasticity and high strength. If the hydroxyl value of the polyester polyol is too high, the molecular weight will be too small, the hard segment length will be insufficient, making it difficult to form stable and complete hard segment microregions. The density and strength of physical crosslinking points will be insufficient, resulting in insufficient peel strength. Furthermore, the presence of too many short-chain hard segments may disrupt microphase separation and impair elasticity. If the hydroxyl value is too low, although the molecular chain will be longer and the size of the hard segment microregions may increase, the excessively long hard segments may cause the microregions to be too rigid and brittle, easily becoming stress concentration points under stress and causing early failure. At the same time, an excessively low hydroxyl value may also lead to a mismatch in reactivity with isocyanates, affecting the control of the polymerization process.

[0043] The synergistic design of the hydroxyl values ​​of polyether polyols and polyester polyols further optimizes the degree and morphology of microphase separation by controlling the molecular weight of the soft and hard segments and their volume fraction in the final polymer. An ideal microphase separation structure requires appropriate incompatibility between the soft and hard segments to allow them to aggregate and form nanoscale phase regions. The hydroxyl value range selected in this invention ensures that the polyether soft segments have sufficiently long chain lengths and excellent flexibility to form a continuous phase responsible for the material's large deformation capacity; while the polyester hard segments have appropriate chain lengths and extremely strong polarity, enabling them to form dispersed hard segment microregions that serve as physical crosslinking points, providing strength and adhesion. The two are connected by chemical bonds (urethane bonds), achieving effective stress transfer between the soft and hard phases. When masking adhesives are applied to complex substrates, their high elongation at break allows the material to deform significantly to fit narrow gaps or curved surfaces, while moderate peel strength ensures that the masking layer adheres firmly to the substrate without displacement or detachment under harsh conditions such as vacuum and thermal cycling in vapor deposition processes. At the same time, after the process is completed, it can be completely and cleanly peeled off by overcoming the forces mainly of physical hydrogen bonds, avoiding the problem of residual adhesive caused by excessive chemical cross-linking.

[0044] Furthermore, the choice of hydroxyl value is closely related to the synthesis process of polyurethane prepolymers and their subsequent UV curing behavior. A suitable hydroxyl value ensures that the reaction between the polyol and isocyanate monomers produces a prepolymer with a narrow molecular weight distribution and well-defined end-group structures. This is crucial for the subsequent quantitative end-capping of excess -NCO groups using end-capping agents. The completeness of the end-capping reaction directly affects the resin's storage stability and UV curing activity. If the hydroxyl value of the polyol deviates from the specified range, it may lead to an excessively wide molecular weight distribution or significant differences in end-group reactivity in the prepolymer, thus affecting the end-capping efficiency. Residual -NCO groups may react with moisture in the environment to form urea bonds, introducing unnecessary rigid structures, causing material embrittlement, and potentially leading to uneven curing. During the UV curing stage, the acrylate groups introduced by the end-capping agent copolymerize with the active monomers under the action of a photoinitiator, forming the final crosslinked network. The hydroxyl value of the polyol indirectly regulates the crosslinking density and chain segment mobility of the UV-cured network by affecting the chain length and structure of the prepolymer, thus jointly determining the final mechanical property balance of the masking adhesive.

[0045] In summary, this invention optimizes the length, polarity, hydrogen bond density, and microphase separation structure of polyurethane resin at the molecular level by precisely defining and synergistically controlling the hydroxyl values ​​of polyether polyol and polyester polyol. This endows the UV-curing masking adhesive with unique comprehensive properties that combine high elongation at break and moderate peel strength, enabling it to meet the stringent requirements of masking material adhesion, adhesion firmness, and peelability in vapor deposition processes.

[0046] As the polyester polyol, any suitable polyester polyol may be used without impairing the effects of the present invention. Examples of such polyester polyols include those obtained by reacting an acid component with a diol component. Examples of acid components include terephthalic acid, adipic acid, azelaic acid, sebacic acid, phthalic anhydride, isophthalic acid, and trimellitic acid. Examples of diol components include ethylene glycol, propylene glycol, diethylene glycol, butanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 3,3'-dimethylolheptane, polyoxyethylene glycol, polyoxypropylene glycol, 1,4-butanediol, neopentanediol, and butylethylpentanediol. Examples of polyol components include glycerol, trimethylolpropane, and pentaerythritol. In addition, examples of polyester polyols obtained by ring-opening polymerization of lactones such as polycaprolactone, poly(β-methyl-γ-valerol), and polyvalerol may also be included.

[0047] As the polyether polyol, any suitable polyether polyol can be used without impairing the effects of the present invention. Examples of such polyether polyols include those obtained by polymerizing ethylene oxide compounds such as ethylene oxide, propylene oxide, ethylene oxide, and tetrahydrofuran using low molecular weight polyols such as water, propylene glycol, ethylene glycol, glycerol, and trimethylolpropane as initiators. Examples of such polyether polyols include polyether polyols with two or more functional groups, such as polypropylene glycol, polyethylene glycol, and polybutanediol.

[0048] Polyether polyols can be partially replaced with glycols such as ethylene glycol, 1,4-butanediol, neopentyl glycol, butylethylpentanediol, glycerol, trimethylolpropane, and pentaerythritol, or polyamines such as ethylenediamine, N-aminoethylethanolamine, isophorone diamine, and xylene diamine, as needed, and then used in combination. As polyether polyols, only difunctional polyether polyols can be used, or polyether polyols with at least three or more hydroxyl groups in one molecule can be used in combination.

[0049] Preferably, the mass ratio of polyether polyol to polyester polyol is (0.6~1.5):1, which can be (0.6:1), (0.7:1), (0.8:1), (0.9:1), (1:1), (1.1:1), (1.2:1), (1.3:1), (1.4:1), (1.5:1) and any value between them.

[0050] This invention achieves a balance between the elongation at break and peel strength of the masking adhesive by controlling the mass ratio of polyether polyol to polyester polyol within the range of (0.6~1.5):1. When the proportion of polyether polyol is relatively high, its compliant ether bonds dominate the material structure, and the molecular chains are easy to slide and extend, giving the masking adhesive extremely high elongation at break, enabling it to fully adapt to complex deformations. However, excessive polyether polyol will weaken the cohesive strength and rigidity of the material, resulting in insufficient peel strength, and the masking layer is prone to accidental detachment during processing. Conversely, when the proportion of polyester polyol increases, its highly polar ester groups form a dense network of intermolecular hydrogen bonds, significantly enhancing the rigidity, cohesive force, and adhesion to the substrate of the material, thereby providing higher peel strength. However, excessive polyester polyol will make the material too rigid and hinder chain segment movement, resulting in a decrease in elongation at break, making the masking adhesive brittle, and difficult to peel completely from gaps or curved surfaces without leaving residue. Therefore, controlling the mass ratio within this specific range essentially regulates the microscopic phase separation structure of the flexible soft segments and rigid hard segments in the polyurethane resin. This allows the flexible polyether segments to absorb energy and generate deformation, while the rigid polyester segments act as physical crosslinking points to provide strength and adhesion. The synergistic effect of the two ultimately enables the masking adhesive to possess both the excellent adhesion brought by high elongation and the processing stability and peelability ensured by moderate peel strength.

[0051] Preferably, the functionality of the polyether polyol is 2 to 2.5, and can be 2, 2.1, 2.2, 2.3, 2.4, 2.5 and any value between them; the functionality of the polyester polyol is 2 to 2.5, and can be 2, 2.1, 2.2, 2.3, 2.4, 2.5 and any value between them.

[0052] This invention ensures that the masking adhesive achieves both high elongation at break and moderate peel strength by controlling the functionality of both polyether polyols and polyester polyols to a low range, starting from the molecular structure design stage. Lower functionality means fewer active hydroxyl groups per polyol molecule, which directly determines the appropriate polyurethane polymer chain length and crosslinking network density. The long-chain structure provides ample space for the free rotation and slippage of molecular chain segments, which is key to the material exhibiting high elongation at break, allowing it to undergo significant deformation without breaking. Regarding peel strength, while lower functionality limits the number of chemical crosslinking points, peel strength also relies on physical forces. Specifically, the highly polar ester groups (-COO-) on the polyester polyol chains can form strong intermolecular hydrogen bonds. These hydrogen bond networks, acting as reversible physical crosslinking points, provide sufficient cohesive force and adhesion to the substrate during processing, ensuring a firm and non-detaching masking layer. During peeling, these forces can be gradually overcome, achieving clean peeling. Therefore, the core principle of selecting low-functionality polyols is to avoid forming a brittle and hard structure due to high cross-linking density, while utilizing the flexibility imparted by long linear molecular chains to achieve high elongation at break, and relying on the inherent strong polar physical bonds of rigid chain segments to provide controllable and moderate peel strength.

[0053] As the isocyanate monomer, any suitable isocyanate monomer may be used without impairing the effects of the present invention. Examples of such isocyanate monomers include aromatic polyisocyanates, aliphatic polyisocyanates, aromatic aliphatic polyisocyanates, and alicyclic polyisocyanates.

[0054] Examples of aromatic polyisocyanates include: 1,3-phenyl diisocyanate, 4,4'-diphenyl diisocyanate, 1,4-phenyl diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-toluidine diisocyanate, 2,4,6-toluene triisocyanate, 1,3,5-phenyl triisocyanate, bianisidine diisocyanate, 4,4'-diphenyl ether diisocyanate, and 4,4',4”-triphenylmethane triisocyanate.

[0055] Examples of aliphatic polyisocyanates include: trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, heptamethylene diisocyanate, 1,2-propylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, dodecamethyl diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate.

[0056] Examples of aromatic aliphatic polyisocyanates include: ω,ω'-diisocyanate-1,3-dimethylbenzene, ω,ω'-diisocyanate-1,4-dimethylbenzene, ω,ω'-diisocyanate-1,4-diethylbenzene, 1,4-tetramethylbenzene dimethyl diisocyanate, and 1,3-tetramethylbenzene dimethyl diisocyanate.

[0057] Examples of alicyclic polyisocyanates include: 3-isocyanate methyl-3,5,5-trimethylcyclohexyl isocyanate, 1,3-cyclopentane diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 4,4'-methylene bis(cyclohexyl isocyanate), 1,4-bis(isocyanate methyl)cyclohexane, and 1,4-bis(isocyanate methyl)cyclohexane.

[0058] As an isocyanate monomer, it can be used in combination with trimethylolpropane adduct, biuret after reaction with water, and trimer with isocyanurate ring.

[0059] Preferably, the isocyanate monomer includes at least one of diphenylmethane diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate. By selecting at least one of diphenylmethane diisocyanate (MDI), isophorone diisocyanate (IPDI), and hexamethylene diisocyanate (HDI) as the isocyanate monomer, the present invention regulates the rigidity, regularity, and reactivity of the polyurethane network at the molecular structure level, providing support for achieving a balance between high elongation at break and moderate peel strength in the masking adhesive. MDI, as an aromatic isocyanate, has a rigid benzene ring structure that effectively enhances the cohesive strength and intermolecular forces of the hard segments of polyurethane, providing significant rigidity and high peel strength to the material. IPDI, an alicyclic isocyanate, has a cyclohexane structure that provides good rigidity and thermal stability, while its asymmetric structure helps to suppress excessive crystallization and maintain a certain chain segment mobility, thus contributing strength while avoiding excessive embrittlement of the material. HDI, as a linear alicyclic isocyanate, has a flexible methylene long chain that gives the soft segments higher flexibility and chain segment mobility, resulting in extremely high elongation at break. The rational selection of isocyanate monomers enables the final polyurethane resin to construct a network with an ideal microphase separation structure. The hard segments composed of isocyanate act as physical crosslinking points, providing the necessary cohesive force and peel strength to ensure that the masking adhesive remains firmly attached during processing. The synergistic effect between the masking adhesive and the flexible soft segments (polyether polyols) ensures that the material can undergo significant deformation under external force through the slippage and extension of molecular chains, thus possessing both excellent elasticity and controllable adhesion properties, meeting the requirements of vapor deposition processes for masking materials.

[0060] Preferably, the molar ratio of the -NCO group of the isocyanate monomer to the -OH group of the polyol is (1.2~2):1, which can be (1.2:1), (1.3:1), (1.4:1), (1.5:1), (1.6:1), (1.7:1), (1.8:1), (1.9:1), (2.0:1) and any value between them.

[0061] This invention achieves dual regulation of the molecular structure and final crosslinking network of polyurethane prepolymers by controlling the molar ratio of -NCO groups in isocyanate monomers to -OH groups in polyols at (1.5~2):1. The excess -NCO groups primarily ensure that all -OH groups at the polyol chain ends participate in the reaction, thereby forming a long linear prepolymer chain with a complete structure and high molecular weight. This provides the molecular basis for the material's high elastic deformation and segment slip, directly contributing to extremely high elongation at break. Secondly, the excess -NCO groups can be converted into stable, UV-exciteable acrylate end groups through a subsequent quantitative reaction with end-capping agents (such as HEA / HBA). This conversion process not only avoids the risk of material embrittlement caused by the reaction of unreacted -NCO with moisture in the air, but more importantly, these introduced acrylate groups can become additional active crosslinking points during the UV curing stage. Under the action of photoinitiators, these components, together with reactive monomers (such as IBOA), participate in free radical polymerization to form a three-dimensional network that incorporates both the original microphase separation structure of the polyurethane soft and hard segments and introduces appropriate chemical crosslinking. The crosslinking density of this network is precisely determined by the molar ratio. Specifically, too low a crosslinking density will lead to insufficient cohesive strength and adhesion (insufficient peel strength), while too high a density will restrict chain segment movement and make the material brittle (decreased elongation at break). An appropriate molar ratio ensures that a sufficiently dense crosslinking network is formed after UV curing to provide excellent cohesive strength and adhesion, while avoiding over-crosslinking. This maximizes the preservation of the inherent flexibility and chain segment mobility of the polyurethane soft segments, ultimately enabling the material to achieve both high macroscopic elongation at break and controllable peel strength.

[0062] Preferably, the polyurethane resin comprises the following raw material components by weight: 10-20 parts isocyanate monomer, 40-60 parts polyether polyol, 40-60 parts polyester polyol, 2-12 parts end-capping agent, 0.01-0.05 parts catalyst, and 0.05-0.09 parts polymerization inhibitor.

[0063] This invention constructs a polyurethane resin system with long-chain flexibility, moderate crosslinking density, and UV-curable end groups through the synergistic effect of its components. The formulation ensures a suitable mass ratio of polyether to polyester polyol, facilitating the formation of an ideal microphase separation structure. This allows the flexible soft segments and rigid hard segments to aggregate sufficiently, respectively responsible for high elongation and intrinsic strength. The amount of isocyanate monomer is calculated based on the molar ratio of its -NCO groups to the total -OH groups of the two polyols. This ratio ensures a relative excess of -NCO, guaranteeing effective chain extension of all polyol chains to form sufficiently long prepolymer molecular chains, a prerequisite for achieving high elongation at break. Simultaneously, the excess -NCO groups provide reaction sites for subsequent end-capping reactions. The amount of end-capping agent is stoichiometrically designed to react completely with all excess -NCO groups, converting them into acrylate end-capping groups. This avoids the material instability and embrittlement risks associated with residual -NCO groups, and introduces necessary and controllable active crosslinking sites for the final UV curing process. These crosslinking sites copolymerize with the active monomers under UV irradiation, forming a three-dimensional network that provides sufficient cohesion (ensuring peel strength) without excessive crosslinking (maintaining high elongation). Trace amounts of catalyst and polymerization inhibitor precisely control the reaction kinetics, ensuring efficient and controllable synthesis while avoiding side reactions and gelation.

[0064] Preferably, the end-capping agent includes at least one of 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate. This type of end-capping agent has a bifunctional structure, with one end being a primary hydroxyl group (-OH) that reacts rapidly with isocyanate (-NCO), and the other end being an acrylate double bond (C=C) that can be cured by ultraviolet (UV) light. During the synthesis stage, its primary hydroxyl group reacts quantitatively with excess -NCO groups in the prepolymer to form stable urethane bonds, thereby achieving precise end-capping of the polymer chain. This process first completely eliminates residual -NCO groups, preventing them from reacting with moisture in the air during storage or use to form brittle urea bonds, which would lead to material performance degradation and ensure the storage stability and uniformity of the final mechanical properties of the resin. More importantly, the end-capping reaction successfully introduces UV-curable acrylate groups into the end of each polyurethane prepolymer molecular chain via covalent bonds, transforming these prepolymer molecules into photoreactive monomers. In the final application stage, these introduced acrylate groups, under UV light and photoinitiator action, can copolymerize with active monomers (such as IBOA) in the formulation, rapidly constructing a moderately cross-linked three-dimensional network structure. This newly formed network works synergistically with the inherent microphase separation structure of polyurethane. Its cross-linking density and strength are precisely controlled by the number of introduced acrylate groups. It provides sufficient cohesive and adhesive strength to ensure that the shielding layer remains firmly in place in the harsh environment of vapor deposition. Furthermore, because the cross-linking points mainly originate from the chain ends and the density is controllable, it minimizes the restriction on the mobility of polyurethane soft segment molecular chains, thereby preserving the material's high elongation at break.

[0065] Preferably, the catalyst comprises dibutyltin dilaurate (DBTDL); the polymerization inhibitor comprises 2,6-di-tert-butyl-p-cresol (BHT). The purpose of the catalyst and polymerization inhibitor is to control the kinetics of the polyurethane synthesis reaction, thereby ensuring the acquisition of a prepolymer with regular molecular structure, stable performance, and intact end groups. DBTDL, as a highly efficient and selective organotin catalyst, can significantly reduce the activation energy of the reaction between isocyanate (-NCO) and alcohol hydroxyl group (-OH). Under relatively mild temperature conditions, it greatly promotes the rate and conversion of chain extension reaction and subsequent end-capping reaction, ensuring that the -NCO group can react rapidly and quantitatively with the -OH of the polyol and the -OH of the end-capping agent. This not only improves production efficiency but also ensures that all polymer chains achieve the expected molecular weight and consistent chain end structure, guaranteeing the uniformity and reproducibility of the final material properties. As a highly efficient free radical scavenger (polymerization inhibitor), BHT can promptly quench any free radicals that may be accidentally generated in the system, effectively inhibiting any premature homopolymerization or crosslinking tendency of acrylate double bonds during the synthesis stage. This ensures that all UV-curable acrylate end groups are intact and are only activated to participate in curing and crosslinking under the preset UV light conditions during final application. This is crucial for preventing prepolymer gelation, maintaining its storage stability, and ensuring the controllability and completeness of the final UV curing reaction.

[0066] Preferably, the method for preparing polyurethane resin includes the following steps:

[0067] S102. Add the catalyst, polyether polyol, and polyester polyol into the reaction vessel;

[0068] S104. Stir the reaction vessel at a speed of 200~300 rpm, heat the reaction vessel at an oil bath temperature of 75~80℃, and maintain the vacuum degree in the reaction vessel between -0.08~-0.1Mpa for vacuum dehydration for 2~3 hours.

[0069] S106. Convert the reaction vessel to a dry air atmosphere, adjust the oil bath temperature to 70~75℃, add isocyanate monomer to the reaction vessel, adjust the rotation speed to 50~100rpm, and continue the reaction for 2~3h.

[0070] S108. Add end-capping agent and polymerization inhibitor to the reaction vessel, and continue the reaction for 2-3 hours to obtain polyurethane resin.

[0071] The core of the UV-curing masking adhesive described in this invention lies in its specific polyurethane resin structure. This resin is formed by the reaction of polyether polyol, polyester polyol, and excess diisocyanate monomer. The reaction is mainly a chain extension reaction, and its general molecular chain structure and reaction mechanism are shown below:

[0072] The general formula for the synthesis reaction of polyurethane resins is:

[0073] OCN-R-NCO+HO~~A~~OH+HO~~B~~OH→OCN-(-R-NH-C(O)-O~~A~~OC(O)-NH-R-)-NH-C(O)-O~~B~~OC(O)-NH-(-R-NCO) k

[0074] OCN-R-NCO represents a diisocyanate monomer, where R represents its skeletal structure, such as diphenylmethane (MDI), isophorone (IPDI), or hexamethylene (HDI).

[0075] HO~~A~~OH represents polyether polyol, where ~~A~~ represents its flexible polyether segment (such as polyoxypropylene segment), and the ether bond (-O-) in the segment gives the molecular chain high flexibility.

[0076] HO~~B~~OH represents polyester polyol, where ~~B~~ represents its rigid polyester segment. The polar ester group (-C(O)O-) in the segment can form strong intermolecular hydrogen bonds and provide rigidity.

[0077] k represents the excess -NCO terminal base.

[0078] Preferably, the masking adhesive comprises the following raw material components by weight: 80-95 parts of polyurethane resin, 5-10 parts of active monomer, 3-6 parts of photoinitiator, and 0.1-0.2 parts of pigment.

[0079] This invention achieves multi-objective optimization of workability, curing rate, mechanical properties, and masking effect through the specific functions and synergistic effects of each component in the system. The high proportion of polyurethane resin serves as the framework and performance foundation of the entire system. Its internal structure, through a polyether / polyester microphase separation and acrylate-terminated groups, exhibits intrinsically high elongation and cohesive strength, laying the foundation for the masking adhesive's high elongation at break and moderate adhesion. The addition of reactive monomers in appropriate proportions serves several purposes: First, it effectively reduces the overall viscosity of high-content resin systems, significantly improving the rheological properties of the masking adhesive, making it easier to apply or coat, and smoothly filling tiny gaps. Second, the groups insert into the polyurethane molecular chains, acting as spacers, increasing interchain spacing, reducing interchain entanglement and forces, thereby further promoting chain slip and contributing positively to improving the final elongation at break. Third, during UV curing, it participates in the free radical copolymerization reaction with the acrylate end groups of the polyurethane resin itself, jointly forming the final cross-linked network. Insufficient reactive monomers may lead to insufficient cross-linking and poor cohesive strength (weak peel strength), while excessive amounts may lead to over-cross-linking and network brittleness (decreased elongation). An appropriate concentration of photoinitiator ensures the generation of sufficient free radicals to rapidly initiate and complete the entire curing process, allowing both the material surface and interior to thoroughly cure and form a dense protective layer, avoiding stickiness or performance degradation caused by incomplete curing.

[0080] Preferably, the active monomer includes isobornyl acrylate. This invention, by selecting isobornyl acrylate (IBOA) as the active monomer, utilizes its molecular structure to achieve a multi-faceted synergistic improvement in the masking adhesive's performance, from application properties to final mechanical properties. Firstly, the large isobornyl group in the IBOA molecule is a rigid hydrophobic structure. Its significant steric hindrance effect physically acts as a spacer between molecular chains, effectively increasing the distance between polyurethane molecular chains, weakening van der Waals forces and entanglement, thereby significantly reducing the viscosity of the entire resin system and greatly improving the rheological properties of the masking adhesive. This makes it easy to dispense and apply, allowing it to smoothly flow into and completely fill the narrow gaps and complex contours of precision substrates. More importantly, this increase in interchain spacing is retained after curing, creating greater space for the free rotation and slippage of polymer chain segments under external forces. Meanwhile, the acrylate groups (C=C double bonds) at the ends of IBOA molecules make them highly reactive crosslinking points. Under UV light, they can undergo rapid free radical copolymerization reactions with the acrylate end groups of the polyurethane resin itself and other IBOA molecules to jointly construct a uniform and moderate three-dimensional crosslinking network. This newly formed network provides cohesive strength and adhesion, ensuring the firmness of the shielding layer during processing. Its moderateness stems from the restriction of the crosslinking point mobility by the rigid groups of IBOA and its own low functionality (monofunctional group), avoiding material embrittlement caused by excessive crosslinking density. Thus, while giving the material the necessary peel strength, it maximizes its ductility.

[0081] Preferably, the photoinitiator includes at least one of photoinitiator 184 and photoinitiator 819. The photoinitiator absorbs light energy under ultraviolet (UV) irradiation, generating active free radicals that initiate free radical polymerization of the acrylate-terminated groups and active monomers (such as IBOA) in the polyurethane resin, forming a cross-linked network structure, thereby achieving rapid curing of the masking adhesive.

[0082] Preferably, the pigment includes at least one of ultramarine, cobalt blue, and pigment blue 27. The pigment is mainly used for visual identification and confirmation of the masking effect. Its color facilitates observation during application to ensure that the coating is even and completely covers non-deposited areas, and helps determine whether there are any residues during subsequent peeling.

[0083] The present invention also provides a method for preparing the above-mentioned UV-curing masking adhesive, comprising the following steps:

[0084] S202. Add polyurethane resin, reactive monomer, and photoinitiator to a mixing container and mix at 1500-2500 rpm for 100-150 seconds, repeating 2-3 times.

[0085] S204, then add pigment, mix at 1500~2500rpm for 100~150s, repeat 2~3 times to obtain UV curing masking adhesive.

[0086] The present invention also provides an application of a UV-curing masking adhesive prepared according to the above-described UV-curing masking adhesive or preparation method in covering non-deposition areas of a substrate during a vapor deposition process.

[0087] The UV-curable masking adhesive of this invention exhibits superior application advantages in vapor deposition processes due to its unique combination of properties. Vapor deposition processes, such as physical vapor deposition (PVD) or chemical vapor deposition (CVD), are key technologies in modern precision manufacturing for depositing functional thin films on substrate surfaces. These processes are typically carried out in harsh environments, often under vacuum or specific atmospheres, and may involve high temperatures or plasma activation. Effective and reliable masking of non-deposition areas of the substrate is crucial during this process. Traditional masking materials often struggle to simultaneously meet the following requirements: adaptability to increasingly complex substrate geometries (including narrow gaps, deep holes, and curved surfaces) such as precision electronic components and irregularly shaped automotive parts; ability to withstand process stresses (such as thermal cycling, particle bombardment, and vacuum pressure) during deposition while maintaining firm adhesion, without displacement or lifting; and complete and clean peeling after the process, leaving no residue or damaging the substrate surface. The UV-curable masking adhesive provided by this invention is designed to address these issues, achieving a balance between high elongation at break and moderate peel strength, making it an ideal masking material for vapor deposition processes.

[0088] Specifically, the high elongation at break (200%–400%) of the masking adhesive endows it with exceptional flexibility and deformation capabilities. When applied to the substrate surface via dispensing or coating, even in narrow gaps at the micron or submicron level, complex three-dimensional curved surfaces, or stepped structures, the masking adhesive can undergo significant deformation under external force or its own rheological properties, tightly filling and adhering to every contour detail of the substrate to form a continuous, gapless masking layer. This excellent adhesion ensures that deposited materials cannot penetrate into the masked area during vapor deposition, thus achieving precise and complete protection of non-deposition areas and effectively avoiding deposition contamination, short circuits, or functional failures caused by insufficient masking. In contrast, masking materials with lower elongation at break are prone to problems such as poor adhesion or incomplete coverage when encountering complex morphologies, forming masking blind spots and leading to deposition process failure.

[0089] Meanwhile, the moderate peel strength of 1~5 N / cm possessed by the masking adhesive of this invention is another key characteristic enabling its successful application in vapor deposition processes. During deposition, the substrate and masking layer need to undergo potential thermal expansion and contraction, degassing stress in a vacuum environment, and impact from deposited particle streams. Moderate peel strength ensures sufficient adhesion and cohesion between the masking adhesive and the substrate interface, resisting these process stresses and preventing localized peeling, edge lifting, or complete detachment of the masking layer during processing. This ensures the continuous stability of the masking effect and significantly improves the yield of vapor deposition. More importantly, this peel strength is controllable. It mainly stems from physical forces such as the intermolecular hydrogen bond network formed by the polar ester groups of the polyester hard segments in the polyurethane system, rather than irreversible, excessive chemical crosslinking. Therefore, when the deposition process is complete and the masking layer needs to be removed, appropriate mechanical peeling (e.g., combined with laser cutting pretreatment) can effectively overcome these physical bonds, achieving complete peeling of the masking adhesive. Because it avoids the restriction of chain segment movement and increased brittleness caused by excessive cross-linking, the peeling process usually does not produce residual adhesive or damage the delicate substrate surface, thus meeting the cleanliness and integrity requirements of high-end manufacturing.

[0090] Furthermore, the UV curing properties of the masking adhesive of this invention further enhance its process adaptability and efficiency in vapor deposition applications. Upon irradiation with ultraviolet light, the masking adhesive can rapidly cure within seconds to tens of seconds, forming a stable protective layer. This rapid curing characteristic helps to increase production cycle time, and the curing process is typically at room temperature or low temperature, avoiding potential damage to heat-sensitive substrates.

[0091] The present invention will now be specifically described by way of examples and comparative examples, but by way of example, the present invention is not limited to these examples.

[0092] In the examples and comparative examples, the preparation method of the polyurethane resin includes the following steps:

[0093] S102. Add the catalyst, polyether polyol, and polyester polyol to a dry three-necked flask.

[0094] S104. Place the three-necked flask in an oil bath, load a top stirrer at 250 rpm, and connect it to a double-row pipe to stir the inside of the three-necked flask. Heat the three-necked flask at an oil bath temperature of 80℃ to maintain the vacuum degree inside the three-necked flask between -0.08 and -0.1 MPa for vacuum dehydration for 2 hours.

[0095] S106. Turn on the air compressor, adjust the double-row pipe to make the three-necked flask a dry air atmosphere, adjust the oil bath temperature to 70°C, inject isocyanate monomer into the three-necked flask, adjust the rotation speed to 80 rpm, and continue the reaction for 2 hours.

[0096] S108. Add end-capping agent and polymerization inhibitor to the reaction vessel, and continue the reaction at 70°C for 2 hours in a dry air atmosphere to obtain polyurethane resin.

[0097] The raw materials of the polyurethane resin in the examples and comparative examples are specifically as follows, according to the composition and content listed in Table 1.

[0098] Table 1

[0099]

[0100] Among them, polyether polyol A is selected from WANOL® C2040D of Wanhua Chemical, with a hydroxyl value of 28 mg KOH / g and a functionality of 2; polyether polyol B is selected from WANOL® C2030 of Wanhua Chemical, with a hydroxyl value of 37 mg KOH / g and a functionality of 2; polyether polyol C is selected from WANOL® 2020 of Wanhua Chemical, with a hydroxyl value of 56 mg KOH / g and a functionality of 2; and polyether polyol D is selected from INOVOL® C280 of Wanhua Chemical, with a hydroxyl value of 14 mg KOH / g and a functionality of 2.

[0101] Polyester polyol E was selected from Zhejiang Huafeng's JF-PE-3556, with a hydroxyl value of 56 mg KOH / g and a functionality of 2; polyester polyol F was selected from Zhejiang Huafeng's JF-PE-7762, with a hydroxyl value of 62 mg KOH / g and a functionality of 2; polyester polyol G was selected from Zhejiang Huafeng's JF-PE-1415, with a hydroxyl value of 75 mg KOH / g and a functionality of 2; polyester polyol H was selected from Asahi Kasei Chemical's XCP-3000PM, with a hydroxyl value of 37.4 mg KOH / g and a functionality of 2.

[0102] In the examples and comparative examples, the polyurethane resin prepared according to Table 1 was used to make a masking adhesive, and the preparation method included the following steps:

[0103] S202. Add polyurethane resin, reactive monomer, and photoinitiator to a mixing tank and mix at 2000 rpm for 120 seconds, repeating 3 times.

[0104] S204. Add pigment and mix at 2000 rpm for 120 seconds, repeating 3 times to obtain masking adhesive.

[0105] In addition to Examples 7 and 8, the polyurethane resin in the other examples and comparative examples had a mass fraction of 90, the active monomer was selected from IBOA with a mass fraction of 10, the photoinitiator was selected from photoinitiator 184 with a mass fraction of 6, and the pigment was selected from ultramarine with a mass fraction of 0.2.

[0106] In Example 7, the polyurethane resin had a mass fraction of 90, the active monomer was selected from IBOA with a mass fraction of 7, the photoinitiator was selected from photoinitiator 184 with a mass fraction of 6, and the pigment was selected from ultramarine with a mass fraction of 0.2.

[0107] In Example 8, the polyurethane resin had a mass fraction of 90, the active monomer was selected from IBOA with a mass fraction of 5, the photoinitiator was selected from photoinitiator 184 with a mass fraction of 6, and the pigment was selected from ultramarine with a mass fraction of 0.2.

[0108] Test case

[0109] To verify the performance of the product of this invention, relevant performance tests were conducted on the masking adhesives prepared in the examples and comparative examples. The specific methods are as follows, and the specific test results are shown in Table 2:

[0110] For specific testing methods of elongation at break, please refer to GB / T 30776-2014;

[0111] For specific testing methods of peel strength, please refer to GB / T 2792-2014;

[0112] The masking adhesive was applied to the non-deposition areas of the substrate using a dispensing method, and then fully cured using ultraviolet (UV) light (energy: 500~1000 mJ / cm²). 2 The substrate undergoes a vapor deposition process. After the vapor deposition process, the substrate is removed, and the masking adhesive is observed to ensure it has not peeled off. The standard is that, after removal and throughout the entire subsequent process, the masking adhesive coating should show no signs of lifting, curling, separation from the substrate, or overall displacement, whether observed with the naked eye or using a 10x magnifying glass. The masking adhesive is then removed using laser cutting. After the masking adhesive is peeled off, any residue is observed. The standard is that the substrate surface should be clean, with no visible black carbonized residue, charring marks, or adhesive residue, whether observed with the naked eye or using a 10x magnifying glass.

[0113] Table 2

[0114]

[0115] Analysis of the performance data from Examples 1 to 8 shows that when the mass ratio of polyether polyol (hydroxyl value 25-40 mg KOH / g) to polyester polyol (hydroxyl value 45-65 mg KOH / g) is maintained within the range of 0.6:1 to 1.5:1, the prepared UV-curable masking adhesive achieves a balance between high elongation at break and moderate peel strength. This invention, by optimizing the type of polyol and controlling its ratio, successfully forms an effective microphase separation structure in polyurethane resin. The flexible segments (polyether) ensure excellent ductility and deformation capability, allowing the masking adhesive to adhere tightly to complex substrates; the rigid segments (polyester) provide the necessary cohesive strength and adhesion to the substrate through intermolecular forces formed by polar ester groups, ultimately ensuring that the masking adhesive remains firmly attached during vapor deposition and can be peeled off without residue after the process.

[0116] By comparing the examples with the comparative examples, it can be seen that Comparative Examples 1, 3, and 5, due to the use of high-hydroxyl-value polyols or excessively high polyester ratios, resulted in excessively high crosslinking density or excessive rigidity, causing the materials to become brittle, with a sharp decrease in elongation at break, and residual adhesive after peeling. Comparative Examples 2, 4, and 6, due to the use of low-hydroxyl-value polyols or excessively high polyether ratios, resulted in insufficient intermolecular forces and cohesive strength, leading to excessively low peel strength, inability to maintain adhesion during processing, and premature detachment.

[0117] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A UV-curable masking adhesive, characterized in that, The masking adhesive includes a polyurethane resin, which is obtained by reacting a polyol and an isocyanate monomer. The polyols include polyether polyols and polyester polyols, wherein the hydroxyl value of the polyether polyols is 25~40 mgKOH / g, and the hydroxyl value of the polyester polyols is 45~65 mgKOH / g; The mass ratio of the polyether polyol to the polyester polyol is (0.6~1.5):1; By weight, the masking adhesive comprises the following raw material components: 80-95 parts polyurethane resin, 5-10 parts active monomer, 3-6 parts photoinitiator, and 0.1-0.2 parts pigment; The active monomer includes isoborneol acrylate; The elongation at break of the masking adhesive is 200-400%, and the peel strength of the masking adhesive is 1-5 N / cm. The masking adhesive is used to cover non-deposition areas of the substrate during the vapor deposition process.

2. The UV-curing masking adhesive according to claim 1, characterized in that, The functionality of the polyether polyol is 2 to 2.5, and the functionality of the polyester polyol is 2 to 2.

5.

3. The UV-curing masking adhesive according to claim 1, characterized in that, The isocyanate monomer includes at least one of diphenylmethane diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate.

4. The UV-curing masking adhesive according to claim 1, characterized in that, The molar ratio of the -NCO group of the isocyanate monomer to the -OH group of the polyol is (1.2~2):

1.

5. The UV-curing masking adhesive according to claim 1, characterized in that, The polyurethane resin comprises the following raw material components by weight: 10-20 parts isocyanate monomer, 40-60 parts polyether polyol, 40-60 parts polyester polyol, 2-12 parts end-capping agent, 0.01-0.05 parts catalyst, and 0.05-0.09 parts polymerization inhibitor.

6. The UV-curing masking adhesive according to claim 5, characterized in that, The capping agent includes at least one of 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate; And / or, the catalyst comprises dibutyltin dilaurate; And / or, the polymerization inhibitor includes 2,6-di-tert-butyl-p-cresol.

7. The UV-curing masking adhesive according to claim 5, characterized in that, The method for preparing the polyurethane resin includes the following steps: S102. Add the catalyst, polyether polyol, and polyester polyol into the reaction vessel; S104. Stir the reaction vessel at a speed of 200~300 rpm, heat the reaction vessel at an oil bath temperature of 75~80℃, and maintain the vacuum degree in the reaction vessel between -0.08~-0.1Mpa for vacuum dehydration for 2~3 hours. S106. Convert the reaction vessel to a dry air atmosphere, adjust the oil bath temperature to 70~75℃, add isocyanate monomer to the reaction vessel, adjust the rotation speed to 50~100rpm, and continue the reaction for 2~3h. S108. Add end-capping agent and polymerization inhibitor to the reaction vessel, and continue the reaction for 2-3 hours to obtain polyurethane resin.

8. The UV-curing masking adhesive according to claim 1, characterized in that, The photoinitiator includes at least one of photoinitiator 184 and photoinitiator 819; And / or, the pigment includes at least one of ultramarine, cobalt blue, and pigment blue 27.

9. A method for preparing a UV-curing masking adhesive as described in any one of claims 1 to 8, characterized in that, Includes the following steps: S202. Add polyurethane resin, reactive monomer, and photoinitiator to a mixing container and mix at 1500-2500 rpm for 100-150 seconds, repeating 2-3 times. S204, then add pigment, mix at 1500~2500rpm for 100~150s, repeat 2~3 times to obtain UV curing masking adhesive.

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