A UV hot melt acrylic pressure-sensitive adhesive and its preparation method

Abstract

This invention discloses a UV hot-melt acrylate pressure-sensitive adhesive and its preparation method, belonging to the field of polymer materials and adhesives technology. The invention first employs the Fenton reaction under mild conditions for controlled free radical polymerization to prepare a hydroxyl-terminated, narrowly distributed acrylate polymer. Then, this hydroxyl-terminated polymer undergoes a chain extension reaction with diisocyanate and diol to obtain a polyurethane acrylate copolymer resin. Finally, a tackifying resin, antioxidant, and photocrosslinking agent are added in the molten state and blended to obtain a hot-melt coating and UV crosslinking pressure-sensitive adhesive composition. This invention is the first to use the Fenton reaction for controlled polymerization of acrylates. The process is green, solvent-free, and leaves no toxic catalyst residues. The resulting product has a narrow molecular weight distribution, high cohesive strength, and excellent heat resistance, with a holding time of more than 10 hours at 85°C. It is suitable for high-end applications such as electronic die-cutting, medical patches, high-end labels, and flexible packaging.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials and adhesives technology, specifically relating to a UV hot melt acrylic pressure-sensitive adhesive and its preparation method, and more particularly to a solvent-free, UV crosslinkable hot melt pressure-sensitive adhesive prepared based on the Fenton reaction with hydroxyl-terminated polyacrylate and chain extended by polyurethane. Background Technology

[0002] Pressure-sensitive adhesives are functional materials that can bond under slight pressure and are widely used in packaging, electronics, medical, automotive and other industries. Traditional solvent-based and emulsion-based acrylic pressure-sensitive adhesives have problems such as VOC emissions, high energy consumption and long drying time, and have been gradually replaced by solvent-free UV-cured pressure-sensitive adhesives.

[0003] Existing UV-curable acrylic pressure-sensitive adhesives mostly employ free radical photopolymerization, mixing low molecular weight prepolymers with reactive diluent monomers, and crosslinking them into a network structure under the action of photoinitiators. However, such systems generally have the following problems: (1) the prepolymer has a wide molecular weight distribution, resulting in uneven cohesion; (2) the crosslinking density is difficult to control, and brittleness or creep is likely to occur; (3) it is difficult to balance initial tack and holding power; (4) toxic catalysts (such as organotin) are used in the synthesis process, posing a risk of residue.

[0004] To address these issues, existing technologies such as atom transfer radical polymerization (ATRP) require precious metal catalysts, which are costly and difficult to remove; reversible addition-fragmentation chain transfer (RAFT) polymerization is complex and difficult to industrialize. (Fenton reaction) It is a classic advanced oxidation technology, widely used for the degradation of organic pollutants, but there are currently no reports on its use for the controlled polymerization of acrylates to prepare pressure-sensitive adhesives. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to overcome the shortcomings of existing technologies and provide a green, environmentally friendly, structurally controllable, and high-performance UV hot-melt acrylate pressure-sensitive adhesive and its preparation method.

[0006] Technical solution A method for preparing a UV hot melt acrylate pressure-sensitive adhesive includes the following steps: (1) under the catalysis of Fenton reagent, acrylate monomers are solution polymerized to obtain a hydroxyl-terminated polyacrylate prepolymer; (2) the prepolymer is reacted with diisocyanate to generate a polyurethane prepolymer, and then a diol is added to carry out a chain extension reaction to obtain a polyurethane acrylate resin; (3) the resin is blended with tackifying resin, antioxidant and photocrosslinking agent in a molten state, cooled and packaged to obtain a UV hot melt acrylate pressure-sensitive adhesive.

[0007] Beneficial effects (1) The Fenton reaction was used for the first time for controlled polymerization of acrylates. The reaction conditions were mild and there were no toxic catalyst residues. (2) A prepolymer of polyacrylate with double-terminated hydroxyl groups and narrow distribution was prepared. The PDI was <1.5 and the structure was controllable. (3) The main chain was constructed by polyurethane chain extension, which significantly improved the cohesive strength and thermal stability. (4) Solvent-free hot melt coating + UV crosslinking is a highly efficient and environmentally friendly process that is suitable for continuous production. (5) The product has an initial tack of 10# steel ball, a peel strength of 7.8 N / cm, and a holding time of >10 h at 85℃, which meets the needs of high-end applications. Attached Figure Description

[0008] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0009] Figure 1 This is the equation for the synthesis of dihydroxyl-terminated polyacrylate and the chain extension reaction of polyurethane in this invention; Figure 2 Infrared spectrum of hydroxyl-terminated polyacrylate prepolymer; Figure 3 This is a molecular weight distribution diagram of GPC, a prepolymer with hydroxyl-terminated polyacrylate. Detailed Implementation

[0010] Example 1: (1) Synthesis of hydroxyl-terminated polyacrylate prepolymer: 8 g of butyl acrylate and 2 g of isooctyl acrylate were dissolved in 50 g of ethyl acetate. 0.05 g (50 ppm) of ferrous sulfate was added, and 30% butyl acrylate was added dropwise at 50°C. 0.12 g was reacted for 6 hours. The solvent and unreacted monomers were removed by vacuum distillation to obtain a hydroxyl-terminated polyacrylate prepolymer (Mn=2100, PDI=1.1).

[0011] (2) Chain extension reaction to prepare polyurethane acrylate resin: Take 100 g of the above prepolymer, add 12.5 g of MDI (NCO / OH=1.1:1), and react at 70℃ for 2 hours to form polyurethane prepolymer. Then add 6.8 g of 1,4-butanediol and continue to react for 3 hours to obtain polyurethane acrylate resin.

[0012] (3) Preparation of pressure-sensitive adhesive by melt blending: Heat 100 g of the above resin to 90°C, add 20 g of terpene resin, 0.5 g of antioxidant BHT and 0.1 g of photocrosslinking agent, melt blend for 20 minutes, degas under vacuum, cool to 55°C and then package.

[0013] Example 2: (1) Synthesis of prepolymer: 7 g butyl acrylate, 3 g isooctyl acrylate, 50 g ethyl acetate, 60 ppm, 1.2% was added, and the mixture was reacted at 55°C for 5 hours to obtain a terminal hydroxyl prepolymer with Mn=12000.

[0014] (2) Chain extension reaction: 100 g of prepolymer, 13.0 g of IPDI, react at 75°C for 2 hours; 7.2 g of 1,6-hexanediol, continue to react for 3 hours.

[0015] (3) Melt blending: Add 25 g of rosin resin, 0.8 g of antioxidant TPP and 0.2 g of photocrosslinking agent to 100 g of resin, blend at 100℃ for 15 minutes, degas under vacuum, cool and package.

[0016] Example 3: (1) Synthesis of prepolymer: 6 g butyl acrylate, 4 g isooctyl acrylate, 50 g ethyl acetate, 70 ppm, 1.5% was added and reacted at 60℃ for 4 hours to obtain a prepolymer with Mn=15000.

[0017] (2) Chain extension reaction: 100 g of prepolymer, add 14.0 g of HDI, react at 80°C for 2 hours; add 10.5 g of polytetrahydrofuran ether diol, and continue the reaction for 3 hours.

[0018] (3) Melt blending: Add 30 g of phenolic resin, 1.0 g of BHT and 0.2 g of photocrosslinking agent to 100 g of resin, blend at 110℃ for 10 minutes, cool and package.

[0019] Example 4: (1) Synthesis of prepolymer: 9 g butyl acrylate, 1 g isooctyl acrylate, 50 g ethyl acetate, 40 ppm, 0.8% was added, and the reaction was carried out at 45°C for 7 hours to obtain a prepolymer with Mn=8000.

[0020] (2) Chain extension reaction: 100 g of prepolymer, 11.8 g of TDI, react at 65°C for 3 hours; 6.2 g of ethylene glycol, continue reaction for 2 hours.

[0021] (3) Melt blending: Add 15 g of terpene resin, 0.3 g of BHT and 0.1 g of photocrosslinking agent to 100 g of resin, blend at 85°C for 25 minutes, cool and package.

[0022] Example 5: (1) Synthesis of prepolymer: 8 g butyl acrylate, 2 g isooctyl acrylate, 50 g ethyl acetate, 55 ppm, 1.1% was reacted at 52℃ for 5.5 hours to obtain a prepolymer with Mn=11000.

[0023] (2) Chain extension reaction: 100 g of prepolymer, add 12.8 g of MDI, react at 72℃ for 2.2 hours; add 7.0 g of 1,4-butanediol, and continue the reaction for 2.5 hours.

[0024] (3) Melt blending: Add 22 g of rosin resin, 0.6 g of TPP and 0.18 g of photocrosslinking agent to 100 g of resin, blend at 95°C for 18 minutes, degas under vacuum, cool and package.

Claims

1. A method for preparing a UV hot-melt acrylic pressure-sensitive adhesive, characterized in that, Includes the following steps: (1) A hydroxyl-terminated acrylate polymer was prepared by Fenton reaction; (2) The hydroxyl-terminated acrylate polymer was reacted with diisocyanate and diol to obtain a polyurethane acrylate copolymer UV hot melt acrylate resin; (3) Tackifying resin, antioxidant and photocrosslinking agent were added to the polyurethane acrylate copolymer resin and stirred evenly to obtain a UV hot melt acrylate pressure-sensitive adhesive.

2. The preparation method according to claim 1, characterized in that, Step (1) specifically involves: under nitrogen protection, dissolving the acrylate monomer in an inert solvent, and adding... Salt, add drop by drop The reaction was carried out at 2560℃ for 48 hours, and the solvent and unreacted monomers were removed by vacuum distillation to obtain a hydroxyl-terminated polyacrylate prepolymer with a number average molecular weight of 1000-20000 and a PDI of <1.

5.

3. The preparation method according to claim 2, characterized in that: The The salt is ferrous sulfate, with a concentration of 10,100 ppm; The mass concentration is 30%, and the dosage is 0.52% of the number of moles of the monomer.

4. The preparation method according to claim 2, characterized in that: The acrylate monomer is selected from one or more of butyl acrylate, isooctyl acrylate, methyl acrylate, ethyl acrylate, methyl methacrylate, butyl methacrylate, and isobornyl methacrylate.

5. The preparation method according to claim 2, characterized in that: The inert solvent is selected from one or more of ethyl acetate, isooctyl acetate, dimethyl carbonate, toluene, cyclohexane, and tetrahydrofuran.

6. The preparation method according to claim 1, characterized in that, Step (2) specifically involves mixing the hydroxyl-terminated acrylate polymer with diisocyanate at an NCO / OH molar ratio of 1.0 to 1.2:1, reacting at 60-80°C for 13 hours, and then adding diol to continue the reaction for 24 hours to obtain the chain-extended polyurethane acrylate copolymer.

7. The preparation method according to claim 6, characterized in that: The diisocyanate is selected from one or more of MDI, TDI, IPDI, and HDI; the diol is selected from one or more of 1,4-butanediol, ethylene glycol, hexanediol, polybutylene adipate, polypropylene glycol, polyethylene glycol, polytetrahydrofuran ether, and polycaprolactone.

8. The preparation method according to claim 1, characterized in that, Step (3) specifically involves melting the polyurethane acrylate copolymer at 130-160℃, adding tackifying resin, antioxidant, and photocrosslinking agent, and stirring until uniform to obtain a pressure-sensitive adhesive that can be hot-melt coated and UV crosslinked.

9. The preparation method according to claim 8, characterized in that: The tackifying resin is selected from one or more of hydrogenated petroleum resin, hydrogenated rosin glycerol ester, solid acrylic resin, and terpene phenolic resin; the antioxidant is selected from one or more of antioxidant 1010, antioxidant 1076, BHT, antioxidant 168, and dilauryl thiodipropionate; the photocrosslinking agent is selected from one or more of hydroxyethoxybenzophenone, 4-hydroxybenzophenone, 1-hydroxycyclohexylphenyl ketone, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, and 2-methyl-1-(4-methylthiophenyl)-2-morpholino-1-acetone.

10. A UV hot melt acrylic pressure-sensitive adhesive, characterized in that, Prepared by the preparation method according to any one of claims 19.

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