OCA optical pressure-sensitive adhesive with high elongation at break and preparation method thereof

Abstract

The invention relates to the technical field of adhesives, and discloses an OCA optical pressure-sensitive adhesive with high elongation at break and a preparation method thereof.The pressure-sensitive adhesive is prepared from, by mass, 50-95 parts of prepolymer, 0.01-10 parts of reactive diluent, 0.01-5 parts of photoinitiator, 0-10 parts of antioxidant and 0-30 parts of tackifying resin, all the substances are mixed and then subjected to photocuring to prepare the pressure-sensitive adhesive; the prepolymer is prepared by adopting reversible addition fragmentation chain transfer solution polymerization, the structure of the prepolymer is (M1-ran-M3)-b-M1-b-(M1-ran-M3) or (M1-ran-M3)-b-(M1-ran-M2)-b-(M1-ran-M3), the content of a soft monomer is 40 to 99.99 percent, the content of a functional monomer is 0 to 40 percent, and the content of a multi-double bond monomer is 0.01 to 5 percent; by adopting a method of combining solution polymerization and UV curing, the elasticity of the pressure-sensitive adhesive is greatly improved, and the product has excellent flexibility, excellent peel strength, high elongation at break, high rebound resilience, high light transmittance and the like even under the condition of no tackifying resin.

Description

Technical Field

[0001] The present invention relates to the technical field of adhesives, and particularly relates to an OCA optical pressure-sensitive adhesive with a high elongation at break and a preparation method thereof. Background Art

[0002] In the current field of optical device manufacturing, high-quality OCA optical pressure-sensitive adhesives play an indispensable role. The manufacturing process of optical devices requires high-quality OCA optical pressure-sensitive adhesives to meet the applications of OCA optical adhesives in various functional scenarios, such as being bendable, rollable, and so on. The preparation formula of acrylate pressure-sensitive adhesives usually consists of acrylate oligomers, copolymers containing functional monomers, polymerizable monomers, photoinitiators, tackifying resins, and other additives. Acrylate oligomers usually have an uncontrollable structure, and their control over molecular weight and molecular weight distribution is relatively poor. Although the optical adhesives prepared by traditional methods can meet basic requirements, there are still some challenges in precisely controlling the structure of prepolymers and product quality control.

[0003] In traditional emulsion polymerization technology, due to its inherent dispersibility and stability, it is often used for the polymerization of hydrophobic or low-hydrophilic monomers. However, when it comes to polymerizing a large amount of hydrophilic monomers, traditional emulsion polymerization methods face a series of challenges. These hydrophilic monomers tend to aggregate in the aqueous phase, making it difficult for the reaction to proceed uniformly, thus affecting the efficiency of the polymerization reaction and the quality of the product. In addition, traditional emulsion polymerization often requires the introduction of a large amount of surfactants or stabilizers to maintain the stability of the emulsion when dealing with hydrophilic monomers, but this may have an adverse impact on the performance and application of the product. Therefore, in order to achieve the effective polymerization of a large amount of hydrophilic monomers, a more innovative and efficient method is needed to overcome the limitations of traditional emulsion polymerization.

[0004] However, in the prior art, the mechanical strength of OCA optical pressure-sensitive adhesives is not high, and there are problems such as poor elasticity or low peel strength. It is often necessary to add additives such as tackifying resins to improve the peel strength.

[0005] As disclosed in CN114507502 A, an OCA optical transparent adhesive and its preparation method are provided. The OCA optical transparent adhesive is obtained by mixing graphene oxide, prepolymer, tackifying resin, photoinitiator, and reactive diluent. The prepolymer includes one or more of polyurethane acrylate, polyester acrylate, and polyether acrylate. The OCA optical transparent adhesive is fully adhered to the touch screen, and then a release film is attached to one side of the OCA optical transparent adhesive layer to obtain a fully adhered OCA touch screen. Due to the addition of an appropriate amount of graphene oxide, it not only has excellent adhesion performance, chemical resistance, and high light transmittance, but also can effectively reduce the blue light transmittance of the display screen. The provided fully adhered OCA touch screen also avoids the problem of uneven stress on the upper and lower surfaces of the polarizer in the prior art due to the large difference in the thickness of the PSA adhesive and the OCA adhesive layer on the upper and lower surfaces of the polarizer, but it does not give the mechanical properties of the product.

[0006] CN111154430 A discloses an ultraviolet curable OCA pressure-sensitive adhesive film, which includes a film layer and an OCA pressure-sensitive adhesive layer provided on the film layer. The OCA pressure-sensitive adhesive layer includes the following raw materials by mass percentage: 7-11% of tackifying resin; 3-7% of photoinitiator; 3-4.5% of first reactive diluent; 3-4.5% of second reactive diluent; the balance is polyurethane acrylate prepolymer. The product has advantages such as good adhesion, long holding power, high light transmittance, and good heat resistance, but it also does not report the mechanical properties of the colloid. In the prior art, the ultraviolet curing technology is widely used, and the structure and synthesis method of the prepolymer have an important impact on the performance of the final optical adhesive product, but it is often difficult to control the crosslinking sites in the prior art, and the product performance is also difficult to control. Summary of the Invention

[0007] Aiming at the problems of insufficient mechanical strength and poor elasticity of OCA pressure-sensitive adhesives in the prior art, the present invention provides an OCA optical pressure-sensitive adhesive with high elongation at break, high peel strength, and low modulus. By combining solution polymerization and UV curing methods, the elasticity of the pressure-sensitive adhesive is greatly improved, and the product has excellent flexibility, excellent peel strength, high elongation at break, high resilience, high light transmittance, etc. even in the absence of tackifying resin.

[0008] To achieve the above object, the technical solution adopted by the present invention is:

[0009] An OCA optical pressure-sensitive adhesive with high elongation at break, characterized in that, by mass parts, it includes the following raw material components: 50-95 mass parts of prepolymer, 0.01-10 mass parts of reactive diluent, 0.01-5 mass parts of photoinitiator, 0-10 mass parts of antioxidant, and 0-30 mass parts of tackifying resin;

[0010] The prepolymer is prepared by reversible addition-fragmentation chain transfer solution polymerization, and its structure is (M1-ran-M3)-b-M1-b-(M1-ran-M3), or (M1-ran-M3)-b-(M1-ran-M2)-b-(M1-ran-M3), where M1, M2, and M3 are copolymer monomers; M1 is composed of soft monomers; M2 is composed of functional monomers; M3 is composed of multi-double bond monomers; the content of soft monomers is 40-99.99%, the content of functional monomers is 0-40%, and the content of multi-double bond monomers is 0.01-5%;

[0011] The preparation method of the OCA optical pressure-sensitive adhesive includes the steps of dissolving the prepolymer in an inactive diluent, adding a photoinitiator, an active diluent, an antioxidant, and a tackifying resin, mixing them and then coating, and curing with ultraviolet light to obtain the OCA optical pressure-sensitive adhesive.

[0012] In the present invention, a prepolymer with a multi-double bond monomer structure is obtained by solution polymerization, and by means of reversible addition-fragmentation chain transfer solution polymerization, its sites can be controlled at the head and tail ends. It is dissolved in an inactive diluent together with an active diluent, a photoinitiator, an antioxidant, and a tackifying resin containing active groups, and then combined with the UV curing method to prepare a pressure-sensitive adhesive with high elongation at break, high peel strength, low modulus, and high resilience. In the prior art, the ultraviolet light curing technology is widely used, and the structure and synthesis method of the prepolymer have an important impact on the performance of the final optical adhesive product. The prepolymer prepared by reversible addition-fragmentation chain transfer solution polymerization can effectively control the crosslinking sites, such as controlling the crosslinking sites on both sides, thereby improving the performance of the optical adhesive. The selection of monomers and the synergistic effect of reversible addition-fragmentation chain transfer solution polymerization and the optical adhesive enhance the overall performance of the optical adhesive. Among them, the multi-double bond monomers play a role in crosslinking. The additional double bonds can crosslink with the double bonds on other molecular chains through the active diluent as a medium under the action of the initiator, making the overall optical adhesive have a crosslinked network structure and thus have elasticity.

[0013] The soft monomers include one or more of ethyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, isooctyl acrylate, octyl acrylate, 2-propylheptyl acrylate, isononyl acrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, isooctyl methacrylate, butadiene, isoprene, ethylene-butene, and methacrylic acid, and the formed block glass transition temperature range is -90 to -30 °C;

[0014] The functional monomers include one or more of methacrylic acid, acrylic acid, itaconic acid, β-acryloyloxypropionic acid, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, ethyl dimethylamine methacrylate, methacrylamide, N-hydroxymethylacrylamide, glycidyl methacrylate, and maleic anhydride.

[0015] In the structure of the prepolymer, both ends contain multi-double bond monomers, and the multi-double bond monomers play a cross-linking role. Among them, the additional double bonds can cross-link with the double bonds on other molecular chains through the active diluent under the action of the initiator. In addition, by designing the multi-double bond monomers at both ends of the prepolymer molecular chain and combining the characteristics of the controllable molecular chain structure of reversible addition-fragmentation chain transfer solution polymerization, the cross-linked points of the optical adhesive after photocuring have a longer molecular weight, so that the optical adhesive has properties such as high elongation at break, high peel strength, low modulus, and high resilience.

[0016] The multi-double bond monomers include but are not limited to one or more of 3-cyclohexene-1-methylene acrylate and vinyl acrylic acid; among them, containing multiple double bonds, under the action of a photoinitiator, it can initiate polymerization, so that the prepolymers cross-link.

[0017] Preferably, the molecular weight of the prepolymer is 0.1-100,000 g / mol; the soft segment is the main unit in the prepolymer, and the prepolymer has a low modulus and good elasticity.

[0018] Preferably, when the content of the functional monomer in the prepolymer is below 20%, the dosage of the tackifying resin is not zero. The functional monomer mainly provides peel strength. When the content of the functional monomer is low, it is necessary to increase the tackifying resin to improve the peel strength to ensure the comprehensive performance of the pressure-sensitive adhesive.

[0019] Preferably, when the content of the functional monomer in the prepolymer is below 20%, the tackifying resin is 10-30 parts.

[0020] The active diluent contains one or more hydroxyl, carboxyl, ether bond, aldehyde or carbonyl active groups; the main function of the active diluent is to connect two molecular chains containing multi-double bond monomers. Under the catalysis of the photoinitiator, the double bond can react with the active diluent to form a chemical bond and thus connect.

[0021] Preferably, the active diluent includes but is not limited to one or more of 1,3-propanedithiol, β-hydroxyethyl methacrylate, 1,6-hexanediol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, and isobornyl acrylate. Preferably 1,3-propanedithiol, β-hydroxyethyl methacrylate, 1,6-hexanediol diacrylate, and its effect is to cross-link two prepolymer molecular chains containing multi-double bond monomers.

[0022] The photoinitiator includes, but is not limited to, one or more of 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone, α-hydroxyacetophenone, and dialkoxyacetophenone;

[0023] The antioxidant includes one or more of dialkyl phosphite, triisooctyl phosphite, thiophosphoryl disulfide, antioxidant 1010, or antioxidant 168.

[0024] The tackifying resin includes one or more of T-801, T-801L, 900L, 901L, and 803L;

[0025] The non-reactive diluent includes one or more of acetone, toluene, ethyl acetate, ethyl acetate, xylene, ethyl pyruvate, or n-butanol.

[0026] The present invention combines reversible addition-fragmentation chain transfer solution polymerization and UV photocuring technologies to achieve the preparation process of high-performance OCA adhesive. First, through reversible addition-fragmentation chain transfer solution polymerization, hydrophilic monomers can be uniformly dispersed in a solvent, and a high degree of polymerization of the monomers can be achieved, thus avoiding the problems arising from traditional emulsion polymerization. This method is not only applicable to the polymerization of hydrophilic monomers but also enables precise control of the structure of the prepolymer. By controlling the types and amounts of monomers, a customized structure of the prepolymer can be obtained. Subsequently, the prepolymer is dissolved in a non-reactive diluent to ensure uniform dispersion of the prepolymer. Subsequently, additives such as photoinitiators, reactive diluents, tackifying resins, and antioxidants are introduced. Through precise formulation, the properties of the material are further adjusted. Finally, through UV photocuring, an optical pressure-sensitive adhesive with high elongation at break, high peel strength, low modulus, and high resilience is prepared.

[0027] The present invention also provides a method for preparing the OCA optical pressure-sensitive adhesive with high elongation at break. For the structure (M1-ran-M3)-b-M1-b-(M1-ran-M3), its preparation includes the steps:

[0028] Step 1: Mix 1 / 30 - 1 / 5 of the soft monomer, 1 / 5 - 4 / 5 of the multi-double bond monomer, an initiator, and a small molecule reversible addition-fragmentation chain transfer reagent in a reaction solvent, heat to 50 - 80 °C, and react for 2 - 10 h in an oxygen-free environment; then add 4 / 5 - 14 / 15 of the soft monomer to the reaction system, react for 2 - 10 h in an oxygen-free environment, and finally add the remaining soft monomer and multi-double bond monomer, and continue to react for 2 - 10 h;

[0029] Step 2: Naturally cool the system to room temperature, slowly pour the solution into a precipitating agent to precipitate, and obtain the prepolymer through washing, drying, and drying;

[0030] Step 3: Dissolve the prepolymer in an inert diluent, add a photoinitiator, an active diluent, an antioxidant, and a tackifying resin, mix them, coat the film, and cure it by ultraviolet light to obtain the OCA optical pressure-sensitive adhesive.

[0031] For the structure (M1-ran-M3)-b-(M1-ran-M2)-b-(M1-ran-M3), the preparation steps are as follows:

[0032] Step 1: Mix 1 / 30 - 1 / 5 of the soft monomer, 1 / 5 - 4 / 5 of the multi-double bond monomer, an initiator, and a small molecule reversible addition-fragmentation chain transfer agent in a reaction solvent, heat it to 50 - 80 °C, and react for 2 - 10 h in an anaerobic environment; then add all the functional monomers and 4 / 5 - 14 / 15 of the soft monomer to the reaction system, react for 2 - 10 h in an anaerobic environment, and finally add the remaining soft monomer and multi-double bond monomer, and continue to react for 2 - 10 h.

[0033] Step 2: Naturally cool the system to about room temperature, slowly pour the solution into a precipitating agent to precipitate, wash, dry in the air, and dry to obtain the prepolymer;

[0034] Step 3: Dissolve the prepolymer in an inert diluent, add a photoinitiator, an active diluent, an antioxidant, and a tackifying resin, mix them, coat the film, and cure it by ultraviolet light to obtain the OCA optical pressure-sensitive adhesive.

[0035] The chemical structural formula of the small molecule reversible addition-fragmentation chain transfer agent is: R-X; where R is isopropyl acid group, acetic acid group, 2-cyanoacetic acid group, or 2-aminoacetic acid group; the X group is an alkyl dithiocarbonate group or an alkyl trithiocarbonate group; the mass of the small molecule reversible addition-fragmentation chain transfer agent is 1 / 100 - 1 / 10 of the total mass of the copolymerizable monomers.

[0036] The initiator includes any one of 2,2'-azobis(2-methylpropionamidine) dihydrochloride, 2,2'-azobis(2-methylpropionitrile) hydrochloride, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, sodium persulfate / potassium persulfate redox initiator, and sodium persulfate / ammonium persulfate redox initiator. The molar amount of the initiator is 1 / 50 - 1 of the molar amount of the small molecule reversible addition-fragmentation chain transfer agent.

[0037] The precipitating agent includes methanol, ethanol, acetone, methyl ethyl ketone, nitromethane, methyl phthalate, hexane, chlorohexane, ether, aliphatic hydrocarbon, aromatic hydrocarbon, ethyl acetate, dioxane, cyclohexanol, aliphatic alcohol, petroleum ether, cyclohexane, tetrahydrofuran, and water, etc. The reaction solvent is dioxane, and the dosage should be controlled so that the overall solid content is 10 - 70%.

[0038] The wavelength of the ultraviolet curing is 300 - 400 nm, and the energy is 1600 - 3000 mJ / cm 2, with a time of 30 - 120 min;

[0039] The present invention organically combines solution polymerization and UV curing to give full play to their respective advantages. Reversible addition-fragmentation chain transfer solution polymerization ensures precise control of the structure of the prepolymer, while UV photocuring ensures the stability of the curing process and the optical properties of the final product. The preparation method proposed by the present invention brings a new prospect for the manufacture of optical devices. This OCA optical pressure-sensitive adhesive not only has excellent performance in terms of optical properties, but also solves the problems that may exist in traditional methods during the preparation process. The customized structure of the prepolymer and the control of the curing process provide a new solution for the manufacture of high-performance optical devices and are expected to be widely used in the fields of optical display and the like.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] (1) In the present invention, a soft monomer is used as the main monomer, and multi-double bond monomers are designed at both ends of the prepolymer. The prepolymer prepared by reversible addition-fragmentation chain transfer solution polymerization can effectively control the positions of the multi-double bond monomers, thereby controlling the crosslinking sites. For example, controlling the crosslinking sites on both sides can improve the performance of the optical adhesive.

[0042] (2) Reversible addition-fragmentation chain transfer solution polymerization can polymerize functional monomers that emulsion polymerization cannot, such as acrylic acid, which can effectively improve the peel strength of the optical adhesive. Photocuring can form crosslinks of molecular chains to improve the elasticity of the optical adhesive. The selection of monomers and the synergistic effect of reversible addition-fragmentation chain transfer solution polymerization and photocuring enhance the overall performance of the optical adhesive.

[0043] (3) Through the form of UV photocuring, the present invention successfully increases the crosslinking degree between polymer chains, enhances the mechanical strength and stability of the optical pressure-sensitive adhesive, and also improves its heat resistance and chemical resistance, enabling the optical pressure-sensitive adhesive to still have excellent peel strength while maintaining excellent mechanical properties. And the prepared optical pressure-sensitive adhesive still has high peel strength without adding tackifying resin. Description of the Drawings

[0044] Figure 1 It is the GPC curve graph of the prepolymer prepared in Example 1.

[0045] Figure 2 It is the mechanical tensile curve graph of the OCA optical pressure-sensitive adhesive prepared in Example 1.

[0046] Figure 3 It is the DMA dynamic mechanical property graph of the OCA optical adhesive prepared in Example 1.

[0047] Figure 4The graph of the peel strength results of the OCA optical adhesive prepared in Examples 1-4.

[0048] Figure 5 The graph of the optical transmittance results of the OCA optical adhesive prepared in Example 1. Detailed implementation manners

[0049] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Those skilled in the art who make modifications or equivalent replacements based on the understanding of the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention shall all be covered by the protection scope of the present invention.

[0050] The raw materials used in the following detailed implementation manners are all purchased from the market. The reactive diluent uses 1,3-propanedithiol, the photoinitiator uses 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, the multi-double bond monomer uses 3-cyclohexene-1-ylmethyl acrylate, the antioxidant uses antioxidant 168, and the tackifying resin uses T-801.

[0051] Example 1

[0052] An OCA optical pressure-sensitive adhesive and its preparation method, the formula is: 50 parts by mass of prepolymer, 0.01 part by mass of 1,3-propanedithiol and 0.01 part by mass of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone.

[0053] In this example, the prepolymer is prepared by the RAFT reversible addition-fragmentation chain transfer solution polymerization method. The specific synthesis steps of the OCA optical pressure-sensitive adhesive are as follows:

[0054] Step 1, mix 2 parts by mass of isooctyl acrylate, 2 parts by mass of n-butyl acrylate, 0.25 part by mass of 3-cyclohexene-1-ylmethyl acrylate, 0.06 part by mass of 2,2'-azobis(2-methylpropionamidine) dihydrochloride, and a small molecule reversible addition-fragmentation chain transfer reagent in a reaction solvent, heat up to 60 °C, and react for 3 h in an anaerobic environment;

[0055] Then add 26 parts by mass of isooctyl acrylate, 15 parts by mass of acrylic acid and 6 parts by mass of n-butyl acrylate to the reaction system, react for 5 h in an anaerobic environment, and finally add 2 parts by mass of isooctyl acrylate, 2 parts by mass of n-butyl acrylate, 0.25 part by mass of 3-cyclohexene-1-ylmethyl acrylate, and continue to react for 5 h.

[0056] The chemical structural formula of the small molecule reversible addition-fragmentation chain transfer reagent is:

[0057]

[0058] Step 2: After the reaction is completed, naturally cool the system to around room temperature, slowly pour the solution into cyclohexane for precipitation, wash, stir, and roll it repeatedly until it becomes fine sand-like, then put it into a mortar and dry it in a fume hood, and finally vacuum dry it at 35 °C to obtain the prepolymer.

[0059] Step 3: Dissolve 50 parts by mass of the prepolymer, 0.01 part by mass of 1,3-propanedithiol, and 0.01 part by mass of 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone in 100 parts by mass of ethyl acetate, coat it into a film in an argon atmosphere, the wavelength of photocuring is 300 nm, the energy is 3000 mJ / cm 2 , the time is 30 min, dry it, and finally obtain the OCA optical adhesive.

[0060] The molecular weight characterization of the polymer is carried out on a gel permeation chromatography Waters 1525-2414-717 GPC instrument, the eluent is tetrahydrofuran, and it is calibrated with a narrow distribution polystyrene standard sample.

[0061] The mechanical properties of the polymer are tested by a universal material testing machine (Zwick / Roll Z020). Cut the polymer film in the above fourth step into dumbbell-shaped specimens with a standard cutting knife for standby. The testing method adopts GB 16421-1996, the tensile rate is 30 mm / min, and the test of each sample is repeated at least three times.

[0062] The stress relaxation and recovery performance of the polymer is tested by DMA (TAQ800). Cut the OCA optical pressure-sensitive adhesive film in the above fifth step into specimens with a width of 5 mm and a length of 25 mm, apply a constant stress of 30 kPa and hold it for 6 s, and record the recovery curve after removing the stress and recovering for 60 s.

[0063] The dynamic mechanical properties of the polymer are characterized by a rotational rheometer (HAAKE MARS 60). Cut the polymer film into circular specimens with a diameter of 2 cm, the test frequency is 0.01 Hz - 1 Hz, and the test temperature is 25 °C. Record the loss factor tanδ of the material during the measurement process.

[0064] The peel strength of the polymer is tested by an adhesive shear strength testing machine (KJ-1066A). Cut the OCA optical pressure-sensitive adhesive film in the above fifth step into specimens with a width of 25 mm and a length of about 300 mm. The testing method adopts GB / T 2792-2014, and the test of each sample is repeated at least three times.

[0065] The optical transmittance of the OCA optical pressure-sensitive adhesive was measured by a UV spectrophotometer (Cary 5000, Agilent, USA). The samples were cut into circles with a diameter of 2 mm. The adhesive film and the glass sheet were used as the test sample and the reference sample respectively. The wavelength scanning range was 300 - 800 nm. Before the test, the transmittance had to be scanned with the glass sheet as the background. Subsequently, the prepared adhesive film was peeled off the upper release protective film and adhered to the glass sheet, and then the lower release protective film was peeled off, and the transmittance was scanned again.

[0066] Figure 1 The GPC curve of the prepolymer, with molecular weights of 50,000 respectively and a molecular weight distribution of 4.1. Table 1 and Figure 2 The mechanical property curve of the OCA optical adhesive. This polymer has a low modulus of 120.3 KPa, a low stress of 0.35 MPa, and a high elongation at break of 1100%. The elongation at break of commercial products is usually about 600%. It has excellent tensile toughness and tensile strength, and its values far exceed those of commercial products.

[0067] Figure 3 The modulus and loss factor data of the OCA optical pressure-sensitive adhesive. At 1 Hz, its shear storage modulus is only 24.2 kPa, and the loss factor is only 0.21. It shows that this method can effectively reduce the modulus below 30 kPa, which is lower than that of the photosensitive adhesives in the prior art and has a higher elongation at break.

[0068] Figure 4 The peel strength data of the OCA optical pressure-sensitive adhesive. When the thickness of the adhesive film is 25 μm, the peel strength of this OCA optical pressure-sensitive adhesive film is 15.40 N / 25 mm. Figure 5 The optical transmittance data of the OCA optical pressure-sensitive adhesive, with its transmittance exceeding 99%.

[0069] Comparative Example 1

[0070] Comparative Example 1 is roughly the same as Example 1 in the preparation method. The difference is that the formulation does not contain an active diluent. Its formulation is: 50 parts by mass of prepolymer, 0.01 part by mass of 2,2'-azobis(2-methylpropionamidine) dihydrochloride, and no active diluent is added in the third step, and the other steps are the same.

[0071] Comparative Example 2

[0072] Comparative Example 2 is roughly the same as Example 1 in the preparation method. The difference is that there is no photo-curing step in the third step. After the prepolymer is prepared, it is directly dissolved in tetrahydrofuran for film formation.

[0073] The mechanical properties of the pressure-sensitive adhesives in Example 1 and Comparative Examples 1-2 are shown in Table 1. It can be seen that without an active diluent or photocuring, simple blending is difficult to improve the modulus and elasticity of the material, and its peel strength is also relatively low. After the cross-linking reaction, the pressure-sensitive adhesive has both high mechanical strength, tensile toughness, and resilience.

[0074] Table 1 Mechanical properties of Example 1 and Comparative Examples 1-2

[0075]

[0076] Example 2

[0077] An OCA optical pressure-sensitive adhesive and its preparation method, with the formula: 90 parts by mass of prepolymer, 10 parts by mass of 1,3-propanedithiol, 5 parts by mass of 2,2'-azobis(2-methylpropionamidine) dihydrochloride, 10 parts by mass of antioxidant 168, and 30 parts by mass of tackifying resin T-801.

[0078] In this example, the prepolymer is prepared by the RAFT (reversible addition-fragmentation chain transfer) solution polymerization method. The specific synthesis steps of the OCA optical pressure-sensitive adhesive are as follows:

[0079] Step 1: Mix 5 parts by mass of isooctyl acrylate, 2 parts by mass of n-butyl acrylate, 1 / 2 of 3-cyclohexene-1-ylmethyl acrylate, 0.06 parts by mass of 2,2'-azobis(2-methylpropionamidine) dihydrochloride, and a small molecule reversible addition-fragmentation chain transfer reagent in a reaction solvent, heat to 65 °C, and react for 3 h in an oxygen-free environment;

[0080] Then add 26 parts by mass of isooctyl acrylate and 14 parts by mass of n-butyl acrylate to the reaction system, react for 5 h in an oxygen-free environment, and finally add 5 parts by mass of isooctyl acrylate, 2 parts by mass of n-butyl acrylate, and 1 / 2 of 3-cyclohexene-1-ylmethyl acrylate, and continue to react for 5 h. The chemical structural formula of the small molecule reversible addition-fragmentation chain transfer reagent is:

[0081]

[0082] Step 2: After the reaction is completed, naturally cool the system to room temperature, slowly pour the solution into cyclohexane for precipitation, wash, stir, and roll it repeatedly until it becomes fine sand-like, then put it into a mortar and dry it in a fume hood, and finally vacuum dry it at 25 °C to obtain the prepolymer.

[0083] Step 3: 90 parts by mass of prepolymer, 10 parts by mass of 1,3-propanedithiol, 5 parts by mass of 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone, 10 parts by mass of antioxidant 168, and 30 parts by mass of tackifying resin T-801 are dissolved in 400 parts by mass of ethyl acetate, coated into a film in an argon environment, and the wavelength of photocuring is 300 nm, with an energy of 3000 mJ / cm 2 , and the time is 30 min. After drying, an OCA optical adhesive is finally obtained.

[0084] Among them, the dosages of the poly-double bond monomers are 0 parts (Comparative Example 3), 0.2 parts, 0.5 parts, 1 part, 1.5 parts, and 2 parts respectively to prepare different pressure-sensitive adhesives, and their properties are tested. The mechanical property test of the polymer is similar to that in Example 1. Figure 4 The data of the peel strength with 1 part by mass of 3-cyclohexene-1-ylmethyl acrylate added in this example are shown. When the thickness of the adhesive film is 25 μm, the peel strength of this example is 17.4 N / 25 mm. The properties of the pressure-sensitive adhesives with different poly-double bond monomers are shown in Table 2. It can be seen that when reaching a certain amount, as the poly-double bond monomer increases, the crosslinking degree of the polymer becomes higher, which will lead to a decrease in its elongation at break, an increase in modulus, and a deterioration of the peel strength. However, the poly-double bond monomer cannot be absent, otherwise the polymer will not crosslink, resulting in no resilience of the polymer and poor various properties.

[0085] Table 2 Properties of Pressure-Sensitive Adhesives Prepared with Different Poly-Double Bond Monomers

[0086]

[0087] Example 3

[0088] An OCA optical pressure-sensitive adhesive and its preparation method, with the formula: 95 parts by mass of prepolymer, 5 parts by mass of 1,3-propanedithiol, 5 parts by mass of 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone, 5 parts by mass of antioxidant 168, and 5 parts by mass of tackifying resin T-801.

[0089] In this example, the prepolymer is prepared by the RAFT reversible addition-fragmentation chain transfer solution polymerization method.

[0090] The specific synthesis steps of the OCA optical pressure-sensitive adhesive are as follows:

[0091] Step 1, mix 1 / 15 of isooctyl acrylate, 2 parts by mass of n-butyl acrylate, 0.25 parts by mass of 3-cyclohexene-1-ylmethyl acrylate, 0.06 parts by mass of 2,2′-azobis(2-methylpropionamidine) dihydrochloride, and a small molecule reversible addition-fragmentation chain transfer reagent in a reaction solvent, heat to 60 °C, and react for 3 h in an oxygen-free environment;

[0092] Then, 13 / 15 of isooctyl acrylate and 6 parts by mass of n-butyl acrylate were added to the reaction system, and the reaction was carried out for 5 h in an anaerobic environment. Finally, 1 / 15 of isooctyl acrylate, 2 parts by mass of n-butyl acrylate, and 0.25 part by mass of 3-cyclohexene-1-ylmethylene acrylate were added, and the reaction was continued for 5 h. The chemical structural formula of the small molecule reversible addition-fragmentation chain transfer reagent is:

[0093]

[0094] Step 2: After the reaction was completed, the system was naturally cooled to about room temperature, and the solution was slowly poured into cyclohexane for precipitation. It was repeatedly washed, stirred, and rolled into a fine sand-like shape, and then placed in a mortar and dried in a fume hood, and then vacuum dried at 45 °C to obtain a prepolymer.

[0095] Step 3: 95 parts by mass of the prepolymer, 5 parts by mass of 1,3-propanedithiol, 5 parts by mass of 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone, 5 parts by mass of antioxidant 168, and 5 parts by mass of tackifying resin T-801 were dissolved in 300 parts by mass of ethyl acetate, coated into a film in an argon environment, and the wavelength of photocuring was 300 nm, the energy was 3000 mJ / cm 2 , and the time was 30 min. After drying, the OCA optical adhesive was finally obtained.

[0096] In this example, the total amounts of isooctyl acrylate were 20 parts, 50 parts, and 70 parts respectively. The pressure-sensitive adhesives prepared were tested, and the mechanical properties of the polymers were similar to those in Example 1. The results are shown in 3 and Figure 4 shown. Figure 4 Among them are the peel strength data of this example with 50 parts by mass of isooctyl acrylate. When the thickness of the adhesive film is 25 μm, the peel strength of this example is 14.6 N / 25 mm.

[0097] Table 3 Properties of Optical Pressure-Sensitive Adhesives with Different Amounts of Isooctyl Acrylate

[0098]

[0099] Example 4

[0100] An OCA optical pressure-sensitive adhesive and its preparation method, the formula is: 90 parts by mass of prepolymer, 2 parts by mass of 1,3-propanedithiol, 2 parts by mass of 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone, 2 parts by mass of antioxidant 168, and 10 parts by mass of tackifying resin T-801.

[0101] The specific synthesis steps of the OCA optical pressure-sensitive adhesive are as follows:

[0102] Step 1: Mix 2 parts by mass of isooctyl acrylate, 2 parts by mass of n-butyl acrylate, 0.15 parts by mass of 3-cyclohexene-1-ylmethylene acrylate, 0.05 parts by mass of 2,2'-azobis(2-methylpropionamidine) dihydrochloride, and a small molecule reversible addition-fragmentation chain transfer agent in a reaction solvent, heat up to 70 °C, and react for 3 h in an anaerobic environment;

[0103] Then add 32 parts by mass of isooctyl acrylate, 14 parts by mass of n-butyl acrylate, 9 parts by mass of 2-propylheptyl acrylate, and 9 parts by mass of acrylic acid to the reaction system, react for 5 h in an anaerobic environment, and finally add 2 parts by mass of isooctyl acrylate, 2 parts by mass of n-butyl acrylate, and 0.15 parts by mass of 3-cyclohexene-1-ylmethylene acrylate, and continue to react for 5 h. The chemical structural formula of the small molecule reversible addition-fragmentation chain transfer agent is:

[0104]

[0105] Step 2: After the reaction is completed, naturally cool the system to about room temperature, slowly pour the solution into cyclohexane for precipitation, repeatedly wash, stir, and roll it into a fine sand shape, then put it into a mortar and dry it in a fume hood, and finally vacuum dry it at 35 °C to obtain a prepolymer.

[0106] Step 3: Dissolve 90 parts by mass of the prepolymer, 2 parts by mass of 1,3-propanedithiol, 2 parts by mass of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, 2 parts by mass of antioxidant 168, and 10 parts by mass of tackifying resin T-801 in 300 parts by mass of ethyl acetate, coat and form a film in an argon environment, the wavelength of photocuring is 300 nm, the energy is 3000 mJ / cm 2 , the time is 30 min, dry it, and finally obtain the OCA optical adhesive.

[0107] The molecular weight characterization of the polymer in this example and the mechanical property test of the polymer are similar to those in Example 1. Figure 4 The data of the peel strength in this example are shown in the table. When the thickness of the adhesive film is 25 μm, the peel strength of this example is 14.0 N / 25 mm.

[0108] Comparative Example 4

[0109] Comparative Example 4 is different from Example 4 in the synthesis step of the first step. Specifically:

[0110] Step 1: Dissolve 36 parts by mass of isooctyl acrylate, 18 parts by mass of octyl acrylate, 9 parts by mass of 2-propylheptyl acrylate, 9 parts by mass of acrylic acid, 0.05 parts by mass of 2,2'-azobis(2-methylpropionamidine) dihydrochloride, 0.002 parts by mass of a small molecule reversible addition-fragmentation chain transfer agent, and 0.3 parts by mass of 3-cyclohexene-1-ylmethyl acrylate in 500 parts by mass of dioxane, stir until evenly mixed, heat up to 80 °C, and react for 12 h in an anaerobic environment; the chemical structural formula of the small molecule reversible addition-fragmentation chain transfer agent is:

[0111]

[0112] Step 2: After the reaction is completed, naturally cool the system to about room temperature, slowly pour the solution into cyclohexane for precipitation, wash, stir, and roll it repeatedly until it becomes fine sand-like, then put it into a mortar and dry it in a fume hood, and then vacuum dry it at 35 °C to obtain a prepolymer.

[0113] Step 3: Dissolve 90 parts by mass of the prepolymer, 2 parts by mass of 1,3-propanedithiol, 2 parts by mass of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, 2 parts by mass of antioxidant 168, and 10 parts by mass of tackifying resin T-801 in 300 parts by mass of ethyl acetate, coat a film in an argon environment, the wavelength of photocuring is 300 nm, the energy is 3000 mJ / cm 2 , the time is 30 min, dry it, and finally obtain an OCA optical adhesive.

[0114] In Comparative Example 4, it is a random copolymerization. Compared with Comparative Example 4, the overall performance of Example 4 is better, especially in terms of elongation at break. The mechanical properties of the two are shown in Table 4. It can be seen that by controlling the position of the multi-double bond monomers, the elongation at break of the polymer can be improved, and the modulus of the polymer can be reduced, so that the peel strength can be more effectively improved.

[0115] Table 4 Performance of the pressure-sensitive adhesives of Example 4 and Comparative Example

[0116]

[0117] The above embodiments are used to explain the present invention, rather than limit the present invention. Any modifications and changes made within the spirit and scope of the protection of the present invention fall within the protection scope of the present invention.

Claims

1. An OCA optical pressure-sensitive adhesive with a high elongation at break, characterized in that, By mass parts, it includes the following raw material components: 50 - 95 mass parts of prepolymer, 0.01 - 10 mass parts of reactive diluent, 0.01 - 5 mass parts of photoinitiator, 0 - 10 mass parts of antioxidant, and 0 - 30 mass parts of tackifying resin; The prepolymer is prepared by reversible addition-fragmentation chain transfer solution polymerization, and its structure is (M1-ran-M3)-b-M1-b-(M1-ran-M3), or (M1-ran-M3)-b-(M1-ran-M2)-b-(M1-ran-M3), where M1, M2, and M3 are copolymer monomers; M1 is composed of soft monomers; M2 is composed of functional monomers; M3 is composed of multi-double bond monomers; among them, the content of soft monomers is 40 - 99.99%, the content of functional monomers is 0 - 40%, and the content of multi-double bond monomers is 0.01 - 5%; The preparation method of the OCA optical pressure-sensitive adhesive includes the steps of dissolving the prepolymer in an inert diluent, adding a photoinitiator, a reactive diluent, an antioxidant, and a tackifying resin, mixing them and then coating, and curing with ultraviolet light to obtain the OCA optical pressure-sensitive adhesive.

2. The OCA optical pressure-sensitive adhesive with high elongation at break according to claim 1, wherein The soft monomers include one or more of ethyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, isooctyl acrylate, octyl acrylate, 2-propylheptyl acrylate, isononyl acrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, isooctyl methacrylate, butadiene, isoprene, ethylene-butene, and methacrylic acid, and the formed block glass transition temperature range is -90 to -30 °C; The functional monomers include one or more of methacrylic acid, acrylic acid, itaconic acid, β-acryloyloxypropionic acid, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, N,N-dimethylaminoethyl methacrylate, methacrylamide, N-hydroxymethylacrylamide, glycidyl methacrylate, and maleic anhydride.

3. The OCA optical pressure-sensitive adhesive with high elongation at break according to claim 1, characterized in that, The multi-double bond monomers include one or more of 3-cyclohexene-1-ylmethyl acrylate and vinyl acrylate.

4. The OCA optical pressure-sensitive adhesive with high elongation at break according to claim 1, characterized in that, When the content of the functional monomer in the prepolymer is less than 20%, the dosage of the tackifying resin is not 0.

5. The OCA optical pressure-sensitive adhesive with high elongation at break according to claim 1, characterized in that, The reactive diluent includes one or more of 1,3-propanedithiol, 2-hydroxyethyl methacrylate, 1,6-hexanediol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, and isobornyl acrylate; The photoinitiator includes one or more of 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone, α-hydroxyacetophenone, and dialkoxyacetophenone; The antioxidant includes one or more of dialkyl phosphite, tris(2-ethylhexyl) phosphite, phosphorothioyl disulfide, antioxidant 1010, or antioxidant 168; The tackifying resin includes one or more of T-801, T-801L, 900L, 901L, and 803L; The inert diluent includes one or more of acetone, toluene, ethyl acetate, ethyl acetate, xylene, ethyl pyruvate, or n-butanol.

6. The preparation method of the OCA optical pressure-sensitive adhesive with high elongation at break according to any one of claims 1-5, characterized in that, For the structure (M1-ran-M3)-b-M1-b-(M1-ran-M3), its preparation includes the steps: Step 1: Mix 1 / 30 - 1 / 5 of the soft monomer, 1 / 5 - 4 / 5 of the multi-double bond monomer, an initiator, and a small molecule reversible addition-fragmentation chain transfer agent in a reaction solvent, heat to 50 - 80 °C, and react for 2 - 10 h in an anaerobic environment; then add 4 / 5 - 14 / 15 of the soft monomer to the reaction system, react for 2 - 10 h in an anaerobic environment, and finally add the remaining soft monomer and multi-double bond monomer, and continue to react for 2 - 10 h; Step 2: Naturally cool the system to about room temperature, slowly pour the solution into a precipitating agent to precipitate, wash, dry in air, and dry to obtain the prepolymer; Step 3: Dissolve the prepolymer in an inactive diluent, add a photoinitiator, an active diluent, an antioxidant, and a tackifying resin, mix and coat the film, and cure with ultraviolet light to obtain the OCA optical pressure-sensitive adhesive.

7. The preparation method of the OCA optical pressure-sensitive adhesive with high elongation at break according to any one of claims 1-5, characterized in that, For the structure (M1-ran-M3)-b-(M1-ran-M2)-b-(M1-ran-M3), its preparation includes the steps: Step 1: Mix 1 / 30 - 1 / 5 of the soft monomer, 1 / 5 - 4 / 5 of the multi-double bond monomer, an initiator, and a small molecule reversible addition-fragmentation chain transfer agent in a reaction solvent, heat to 50 - 80 °C, and react for 2 - 10 h in an anaerobic environment; then add all the functional monomers and 4 / 5 - 14 / 15 of the soft monomer to the reaction system, react for 2 - 10 h in an anaerobic environment, and finally add the remaining soft monomer and multi-double bond monomer, and continue to react for 2 - 10 h; Step 2: Naturally cool the system to about room temperature, slowly pour the solution into a precipitating agent to precipitate, wash, dry in air, and dry to obtain the prepolymer; Step 3: Dissolve the prepolymer in an inactive diluent, add a photoinitiator, an active diluent, an antioxidant, and a tackifying resin, mix and coat the film, and cure with ultraviolet light to obtain the OCA optical pressure-sensitive adhesive.

8. The preparation method of the OCA optical pressure-sensitive adhesive with high elongation at break according to claim 6 or 7, characterized in that, The chemical structural formula of the small molecule reversible addition-fragmentation chain transfer agent is: R-X; where R is isopropyl acid group, acetic acid group, 2-cyanoacetic acid group or 2-aminoacetic acid group; the X group is an alkyl dithiocarbonate group or an alkyl trithiocarbonate group; the mass of the small molecule reversible addition-fragmentation chain transfer agent is 1 / 100 - 1 / 10 of the total mass of the copolymerizable monomers.

9. The preparation method of the OCA optical pressure-sensitive adhesive with high elongation at break according to claim 6 or 7, characterized in that, The initiator includes any one of azodiisobimidazoline hydrochloride, azodiisobutyramidine hydrochloride, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, sodium persulfate / potassium persulfate redox initiator, and sodium persulfate / ammonium persulfate redox initiator, and the molar amount of the initiator is 1 / 50 - 1 of the molar amount of the small molecule reversible addition-fragmentation chain transfer agent; The precipitating agent includes any one or more of methanol, ethanol, acetone, butanone, nitromethane, methyl phthalate, hexane, chlorohexane, ether, aliphatic hydrocarbon, aromatic hydrocarbon, ethyl acetate, dioxane, cyclohexanol, aliphatic alcohol, petroleum ether, cyclohexane, tetrahydrofuran, and water.

10. The preparation method of the OCA optical pressure-sensitive adhesive with high elongation at break according to claim 6 or 7, characterized in that, The wavelength of the photocuring is 300 - 400 nm, the energy is 1600 - 3000 mJ / cm 2 , and the time is 30 - 120 min.

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