Transparent pressure-sensitive adhesive based on cationic photocuring and preparation method thereof

Abstract

The invention relates to the technical field of pressure-sensitive adhesives, in particular to a vinyl ether functionalized optical transparent pressure-sensitive adhesive based on cationic photocuring and a preparation method of the vinyl ether functionalized optical transparent pressure-sensitive adhesive. The transparent pressure-sensitive adhesive is prepared from the following raw materials in parts by mass: 5 to 7 parts of vinyl ether functionalized prepolymer, 2 to 4 parts of vinyl ether bifunctional monomer, 1 to 3 parts of reactive diluent and 0.1 to 0.3 part of cationic photoinitiator. Wherein the vinyl ether functionalized prepolymer is prepared from the following raw materials: polytetrahydrofuran glycol, isophorone diisocyanate, a catalyst, a chain extender and a first end-capping reagent; the vinyl ether bifunctional monomer is prepared from the following raw materials: isophorone diisocyanate, a catalyst and a second end-capping reagent. The transparent pressure-sensitive adhesive prepared by the invention is high in light transmittance and excellent in adhesive property, and is especially suitable for adhesion of display devices.

Description

Technical Field

[0001] This invention relates to the field of pressure-sensitive adhesive technology, specifically to a vinyl ether functionalized optically transparent pressure-sensitive adhesive based on cationic photocuring and its preparation method. Background Technology

[0002] Pressure-sensitive adhesives (PSAs), as an important type of bonding material, are widely used in many fields such as electronic devices and displays. Their adhesive performance directly affects the assembly quality and stability of related products. However, traditional photocurable acrylic PSAs face a key technical bottleneck in practical applications: oxygen suppression during the curing process. Oxygen molecules readily react with free radicals in the polymerization reaction to generate highly stable peroxide free radicals, causing premature termination of the polymerization reaction. This not only reduces the curing efficiency and degree of curing of the PSA but also negatively impacts the material's core properties such as optical transparency and adhesion strength, limiting its application in high-end display and other fields.

[0003] To address the technical challenge of oxygen inhibition, existing technologies primarily employ nitrogen protection or the addition of photosensitizers. However, nitrogen protection requires additional sealed reaction equipment and a nitrogen supply system, increasing the complexity of the production process and equipment costs. While adding photosensitizers can alleviate oxygen inhibition to some extent, the introduction of photosensitizers may alter the chemical composition of the pressure-sensitive adhesive, adversely affecting the material's optical purity and weather resistance, making it difficult to simultaneously meet the dual requirements of process simplification and performance stability. Against this backdrop, cationic photocurable systems have emerged as an ideal alternative. Their cationic active species are less likely to react with oxygen during polymerization, naturally possessing antioxidant and polymerization-inhibiting properties, fundamentally avoiding the series of problems caused by oxygen inhibition, and providing a new direction for the upgrading of pressure-sensitive adhesive technology.

[0004] Chinese invention patent CN119193063B discloses a technical solution that utilizes the synergistic effect of organosilicon-modified alicyclic epoxy resin and rosin ester diol to prepare a cationic photocurable pressure-sensitive adhesive with high adhesion and antioxidant polymerization inhibition characteristics, verifying the application potential of this system. However, such photocurable pressure-sensitive adhesives based on cationic epoxy resins still have significant defects. Their molecular structure results in high material hardness, insufficient flexibility, and poor dynamic recovery performance, which cannot meet the high requirements of emerging fields such as flexible electronics for adhesive materials to quickly recover their original shape after repeated bending and deformation. This seriously limits the promotion and application of cationic photocurable pressure-sensitive adhesives in cutting-edge fields such as flexible displays and wearable devices. Therefore, it is urgent to develop a new type of pressure-sensitive adhesive material that combines antioxidant polymerization inhibition, high optical performance, excellent flexibility, and dynamic recovery. Summary of the Invention

[0005] To address the aforementioned technical problems, the first aspect of this invention provides a transparent pressure-sensitive adhesive based on cationic photocuring. The raw materials for preparation, by weight, include 5-7 parts of vinyl ether functionalized prepolymer, 2-4 parts of vinyl ether bifunctional monomer, 1-3 parts of reactive diluent, and 0.1-0.3 parts of cationic photoinitiator. The raw materials for preparing the vinyl ether functionalized prepolymer include polytetrahydrofuran glycol, isophorone diisocyanate, a catalyst, a chain extender, and a first capping agent. The raw materials for preparing the vinyl ether bifunctional monomer include isophorone diisocyanate, a catalyst, and a second capping agent.

[0006] This invention utilizes a cationic photocuring system, with vinyl ether functionalized prepolymers and vinyl ether bifunctional monomers as core reactive components, combined with a specific cationic photoinitiator. The active species in the cationic photocuring system are not easily reactive with oxygen, naturally possessing antioxidant polymerization-inhibiting properties. This fundamentally avoids the problem of polymerization termination caused by the reaction of oxygen with free radicals in traditional photocurable acrylic pressure-sensitive adhesives. It eliminates the need for complex oxygen-barrier measures such as nitrogen protection or the addition of photosensitizers, simplifying the production process and avoiding the increased costs and risks of optical performance damage associated with such additional measures.

[0007] Through the precise selection and formulation design of the aforementioned raw materials, the defects of traditional cationic photocurable pressure-sensitive adhesives, such as poor flexibility and insufficient dynamic recovery, are effectively overcome, while the optical transparency and uniformity of the pressure-sensitive adhesive are optimized. The raw materials for synthesizing the vinyl ether functionalized prepolymer are limited to polytetrahydrofuran diol, isophorone diisocyanate, and a chain extender. Polytetrahydrofuran diol possesses a flexible molecular chain structure, while isophorone diisocyanate provides rigid support while also exhibiting a certain degree of steric hindrance. Combined with the chain extender, the molecular chain length and crosslinking density of the prepolymer can be flexibly controlled, fundamentally avoiding the problems of high hardness and poor flexibility caused by the excessive rigidity of the molecular structure in traditional epoxy resin-based cationic pressure-sensitive adhesives. Furthermore, the synergistic ratio of 5-7 parts prepolymer to 2-4 parts vinyl ether bifunctional monomers constructs a controllable crosslinking structure. The network structure ensures the structural stability of the pressure-sensitive adhesive (PSA) and enhances its deformation capability through the rational distribution of flexible segments. Combined with the plasticizing and cross-linking regulation effects of the reactive diluent, the PSA exhibits excellent dynamic recovery performance, meeting the requirements of flexible display devices for rapid recovery after repeated bending. This overcomes the limitation of existing cationic photocurable PSA that cannot be adapted to flexible electronic products. At the same time, it ensures the formation of a uniform polymer network structure after curing, reducing light scattering and thus improving the transmittance and reducing haze of the PSA, meeting the application requirements of optically transparent PSA in display devices.

[0008] As an implementable example, the chain extender includes one of ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, 1,4-cyclohexanediol, polyethylene glycol, or 2-methyl-1,3-propanediol; preferably 1,4-butanediol.

[0009] As an example of implementation, the catalyst is a tin-based catalyst.

[0010] Furthermore, the tin-based catalyst includes one of dibutyltin dilaurate, dibutyltin diacetate, or stannous octoate.

[0011] As an implementable example, both the first and second capping agents comprise at least one of 2-hydroxyethyl vinyl ether, 3-hydroxypropyl vinyl ether, 4-hydroxybutyl vinyl ether, or cyclohexylmethyl vinyl ether.

[0012] As an feasible example, the preparation method of the vinyl ether functionalized prepolymer includes: mixing isophorone diisocyanate and a catalyst, adding it dropwise into polytetrahydrofuran diol, reacting for 1-3 hours, then adding a chain extender, continuing the reaction for 1-3 hours, then adding a first end-capping agent, and reacting for 1-2 hours to obtain the vinyl ether functionalized prepolymer.

[0013] The structural formula of the vinyl ether functionalized prepolymer in this invention is: .

[0014] As an feasible example, the method for preparing the vinyl ether bifunctional monomer includes: adding a catalyst and a second capping agent to isophorone diisocyanate and reacting for 1-3 hours to obtain the vinyl ether bifunctional monomer.

[0015] The structural formula of the vinyl ether bifunctional monomer in this invention is as follows: .

[0016] As an implementable example, the active diluent includes one of triethylene glycol divinyl ether, diethylene glycol divinyl ether, butanediol divinyl ether, or N-vinylcaprolactam, preferably triethylene glycol divinyl ether.

[0017] As an implementable example, the cationic photoinitiator comprises one of 4-isobutylphenyl-4'-methylphenyliodothionium hexafluorophosphate, 4-(phenylthio)phenyldiphenylthionium hexafluorophosphate, 4-(phenylthio)phenyldiphenylthionium hexafluoroantimonate, or bis(4-tert-butylphenyl)iodothionium hexafluorophosphate, preferably 4-(phenylthio)phenyldiphenylthionium hexafluoroantimonate.

[0018] A second aspect of this invention provides a method for preparing a transparent pressure-sensitive adhesive based on cationic photocuring, comprising the following steps: The vinyl ether functionalized prepolymer, vinyl ether bifunctional monomer, reactive diluent and cationic photoinitiator are mixed evenly, degassed under vacuum, coated on a release film, and photocured to obtain a transparent pressure-sensitive adhesive.

[0019] As an feasible example, the intensity of the photocuring is 170-180 mw / cm². 2 The curing time is 1-3 minutes.

[0020] Beneficial effects (i) The present invention adopts a vinyl ether-based cationic photocuring system. The cationic active species are not easily reacted with oxygen and naturally have antioxidant polymerization inhibition properties. There is no need to use additional nitrogen protection, vacuuming and other complex oxygen isolation measures, which greatly simplifies the production process, reduces equipment and energy consumption costs, and is more conducive to large-scale mass production.

[0021] (ii) Through molecular structure design, such as the construction of a controllable cross-linking network by vinyl ether functionalized prepolymer and bifunctional monomer, the defects of high hardness and poor flexibility of traditional epoxy resin-based cationic photocurable pressure-sensitive adhesive are completely improved. After 100 cycles of stretching at 20% strain, the recovery time is <7 seconds, which can fully meet the repeated bending requirements of display devices.

[0022] (iii) The transparent pressure-sensitive adhesive prepared by the present invention has a visible light transmittance of over 99% and a haze value of <1%, with extremely high optical transparency, which fully meets the stringent requirements of high-end display devices for image clarity and light transmittance.

[0023] (iv) The transparent pressure-sensitive adhesive has high adhesion strength. The 180° peel strength on the steel plate can reach more than 18 N / 25mm, and the ring initial tack can reach more than 17 N / 25mm. Furthermore, the adhesion performance can be controlled by adjusting the ratio of prepolymer and bifunctional monomer, and it can stably bond different functional layers such as cover window, touch sensor and light-emitting layer in display devices.

[0024] (v) It combines multiple advantages such as anti-oxidation and polymerization inhibition, high light transmittance, high flexibility, fast recovery and strong adhesion. The various performance indicators are matched in a coordinated manner, which solves the single shortcoming problem of traditional pressure-sensitive adhesives in optics, mechanics and adhesion, and provides a high-performance integrated bonding solution for display devices. Attached Figure Description

[0025] Figure 1 The diagram shows the light transmittance and haze values ​​of the transparent pressure-sensitive adhesives in Examples 1-3, where (a) is a light transmittance diagram and (b) is a haze value diagram.

[0026] Figure 2The diagrams show the 180° peel strength and annular initial tack of the transparent pressure-sensitive adhesives in Examples 1-3, where (a) is a diagram of the 180° peel strength and (b) is a diagram of the annular initial tack.

[0027] Figure 3 The stress-strain diagrams are for the transparent pressure-sensitive adhesives in Examples 1-3.

[0028] Figure 4 Figure 1 shows the strain test curves and recovery time diagrams after strain stretching cycles of the transparent pressure-sensitive adhesives in Examples 1-3. Figure 1(ac) shows the strain test curve after 100 cycles of stretching with a 20% strain, and Figure 2(df) shows the recovery time diagram after the 100th 20% strain stretching cycle. Detailed Implementation

[0029] Example 1 The first aspect of this example provides a transparent pressure-sensitive adhesive based on cationic photocuring, the raw materials for which, by weight, include 7g of vinyl ether functionalized prepolymer, 2g of vinyl ether bifunctional monomer, 1g of reactive diluent triethylene glycol divinyl ether, and 0.3g of cationic photoinitiator 4-(phenylthio)phenyl diphenylthionium hexafluoroantimonate.

[0030] The preparation method of the vinyl ether functionalized prepolymer is as follows: 100 g of polytetrahydrofuran diol is weighed into a 500 mL three-necked round-bottom flask and placed in a vacuum drying oven at 110 °C for 3 hours to remove moisture. Then, 44.46 g of isophorone diisocyanate is weighed into a constant-pressure dropping funnel, and 0.05 g of dibutyltin dilaurate catalyst is added to the constant-pressure dropping funnel. The three-necked round-bottom flask is placed in an oil bath at 50 °C, and under argon protection, the mixture is continuously stirred while isophorone diisocyanate is added dropwise. After the isophorone diisocyanate is completely added, the reaction temperature is raised to 70 °C and the reaction continues for 2 hours. Next, 1g of chain extender 1,4-butanediol was added, and the reaction was continued for 2 hours. Then, the reaction temperature was lowered to 50°C, and 23.81g of the first end-capping agent 4-hydroxybutyl vinyl ether was added. After the reaction was continued for 1 hour, vinyl ether functionalized polyurethane prepolymer was obtained.

[0031] The method for preparing the vinyl ether bifunctional monomer is as follows: 44.46 g of isophorone diisocyanate is weighed into a 500 mL three-necked flask, 46.46 g of 4-hydroxybutylvinyl ether is weighed into a constant-pressure dropping funnel, and then 0.05 g of dibutyltin laurate catalyst is added. Then, under argon protection and at 50°C, the mixture is continuously stirred and 4-hydroxybutylvinyl ether is added dropwise. After the addition of 4-hydroxybutylvinyl ether is complete, the reaction continues for 2 hours to obtain the vinyl ether bifunctional monomer.

[0032] The second aspect of this example provides a method for preparing a transparent pressure-sensitive adhesive based on cationic photocuring, including the following steps: Vinyl ether functionalized prepolymer, vinyl ether bifunctional monomer, and reactive diluent triethylene glycol divinyl ether were mixed evenly. Then, the cationic photoinitiator 4-(phenylthio)phenyldiphenylthionium hexafluoroantimonate was added and stirred until completely dissolved. The mixture was then subjected to vacuum degassing in a homogenizer at 2000 rpm for 5 minutes to obtain a resin mixture. The homogenized resin mixture was poured onto a PET release film, and a 100 µm thickness coater was used to coat the resin. The film was then placed in a UV curing oven for 2 minutes at a UV intensity of 175 mw / cm². 2 A transparent pressure-sensitive adhesive with a thickness of 100~120µm was obtained.

[0033] The transparent pressure-sensitive adhesive obtained in this example is designated as PSA-1.

[0034] Example 2 The specific implementation method of this example is the same as that of Example 1, except that: the raw materials for preparing the transparent pressure-sensitive adhesive, by weight, include 6g of vinyl ether functionalized prepolymer, 3g of vinyl ether bifunctional monomer, 1g of reactive diluent triethylene glycol divinyl ether, and 0.3g of cationic photoinitiator 4-(phenylthio)phenyl diphenylthionium hexafluoroantimonate.

[0035] The transparent pressure-sensitive adhesive obtained in this example is designated as PSA-2.

[0036] Example 3 The specific implementation method of this example is the same as that of Example 1, except that: the raw materials for preparing the transparent pressure-sensitive adhesive, by weight, include 5g of vinyl ether functionalized prepolymer, 4g of vinyl ether bifunctional monomer, 1g of reactive diluent triethylene glycol divinyl ether, and 0.3g of cationic photoinitiator 4-(phenylthio)phenyl diphenylthionium hexafluoroantimonate.

[0037] The transparent pressure-sensitive adhesive obtained in this example is designated as PSA-3.

[0038] Schematic diagrams of the light transmittance and haze values ​​of transparent pressure-sensitive adhesives in Examples 1-3 are shown below. Figure 1 As shown, (a) is a schematic diagram of light transmittance, and (b) is a schematic diagram of haze value.

[0039] Schematic diagrams of the 180° peel strength and initial ring tack of the transparent pressure-sensitive adhesives in Examples 1-3 are shown below. Figure 2 As shown, (a) is a schematic diagram of 180° peel strength, and (b) is a schematic diagram of annular initial adhesion.

[0040] The stress-strain diagrams of the transparent pressure-sensitive adhesives in Examples 1-3 are shown below. Figure 3 As shown.

[0041] The strain test curves and recovery time diagrams after strain-tensile cycles of the transparent pressure-sensitive adhesives in Examples 1-3 are shown below. Figure 4 As shown, Figure (ac) is the test curve of 100 cycles of tensile strain at 20% strain, and Figure (df) is a schematic diagram of the recovery time after the 100th cycle of tensile strain at 20% strain.

[0042] 1. Optical performance testing The transmittance of the transparent pressure-sensitive adhesives in Examples 1-3 was tested using a UV spectrophotometer (UV-8000), and the haze was tested using a haze meter (YK-SGW810).

[0043] 2. Mechanical property testing According to ASTM D882 standard, the dimensions of 25×150mm were tested on a universal testing machine (SHIMADZU AG-X plus). 2 The tensile strength and elongation at break of the pressure-sensitive adhesive were tested at 300 mm / min. A 15×50 mm size was used. 2 The transparent pressure-sensitive adhesive was subjected to 100 repeated cycles at 20% strain using a speed of 300 mm / min.

[0044] 3. Adhesion performance test The 180° peel test of the pressure-sensitive adhesive was performed using an electronic tensile testing machine (XLW(EC)-A) according to ASTM D3300 standard. A 100 μm thick transparent pressure-sensitive adhesive to be tested was attached to SUS and pressed four times with a 2 kg rubber-coated roller. After standing for 20 min, it was peeled at a peel angle of 180°, and the average peel force was recorded in N / 25 mm. The ring initial tack of the pressure-sensitive adhesive was tested using a ring initial tack tester (KJ-6031) according to PSTC-16 standard, in N / 25 mm.

[0045] The test results for the above tests are detailed in Table 1.

[0046] Table 1

[0047] The cationic photocurable vinyl ether functionalized polyurethane optically transparent pressure-sensitive adhesive provided by this invention has multiple advantages: First, it exhibits natural antioxidant and polymerization-inhibiting properties during the curing process, eliminating the need for complex oxygen-barrier protection measures such as nitrogen purging or vacuuming, thus simplifying the production process; second, compared with traditional epoxy resin-based cationic photocurable systems, this pressure-sensitive adhesive effectively overcomes the problems of high hardness and poor flexibility, significantly improving flexibility through molecular structure design, specifically manifested in increased elongation at break; the resulting pressure-sensitive adhesive exhibits excellent overall performance, including high light transmittance (approximately 99%), low haze (less than 1%), and excellent adhesion properties, with a 180° peel strength on steel plates reaching 18.2 N / 25 mm.

Claims

1. A transparent pressure-sensitive adhesive based on cationic photocuring, characterized in that, The raw materials for preparation include, by mass, 5-7 parts of vinyl ether functionalized prepolymer, 2-4 parts of vinyl ether bifunctional monomer, 1-3 parts of reactive diluent, and 0.1-0.3 parts of cationic photoinitiator; The raw materials for preparing the vinyl ether functionalized prepolymer include polytetrahydrofuran diol, isophorone diisocyanate, catalyst, chain extender and first capping agent; The raw materials for preparing the vinyl ether bifunctional monomer include isophorone diisocyanate, a catalyst, and a second capping agent.

2. The transparent pressure-sensitive adhesive according to claim 1, characterized in that, The chain extender includes one of ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, polyethylene glycol, or 2-methyl-1,3-propanediol.

3. The transparent pressure-sensitive adhesive according to claim 1, characterized in that, The catalyst is a tin-based catalyst.

4. The transparent pressure-sensitive adhesive according to claim 3, characterized in that, The tin-based catalysts include one of dibutyltin dilaurate, dibutyltin diacetate, or stannous octoate.

5. The transparent pressure-sensitive adhesive according to claim 1, characterized in that, Both the first and second capping agents comprise at least one of 2-hydroxyethyl vinyl ether, 3-hydroxypropyl vinyl ether, 4-hydroxybutyl vinyl ether, or cyclohexylmethyl vinyl ether.

6. The transparent pressure-sensitive adhesive according to claim 1, characterized in that, The method for preparing the vinyl ether functionalized prepolymer includes: Isophorone diisocyanate and catalyst are mixed and added dropwise into polytetrahydrofuran diol. The reaction is carried out for 1-3 hours. Then, a chain extender is added and the reaction is continued for 1-3 hours. Finally, the first end-capping agent is added and the reaction is carried out for 1-2 hours to obtain the vinyl ether functionalized prepolymer.

7. The transparent pressure-sensitive adhesive according to claim 1, characterized in that, The method for preparing the aforementioned vinyl ether bifunctional monomer includes: Add a catalyst and a second capping agent to isophorone diisocyanate and react for 1-3 hours to obtain a vinyl ether bifunctional monomer.

8. The transparent pressure-sensitive adhesive according to claim 1, characterized in that, The active diluent includes one of triethylene glycol divinyl ether, diethylene glycol divinyl ether, butanediol divinyl ether, or N-vinylcaprolactam.

9. The transparent pressure-sensitive adhesive according to claim 1, characterized in that, The cationic photoinitiator includes one of 4-isobutylphenyl-4'-methylphenyliodohexafluorophosphate, 4-(phenylthio)phenyldiphenylthiodohexafluorophosphate, 4-(phenylthio)phenyldiphenylthiodohexafluoroantimonate, or bis(4-tert-butylphenyl)iodohexafluorophosphate.

10. A method for preparing a transparent pressure-sensitive adhesive based on cationic photocuring according to any one of claims 1-9, characterized in that, Includes the following steps: The vinyl ether functionalized prepolymer, vinyl ether bifunctional monomer, reactive diluent and cationic photoinitiator are mixed evenly, degassed under vacuum, coated on a release film, and photocured to obtain a transparent pressure-sensitive adhesive.

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