High-temperature-resistant and high-humidity-resistant OCA optical pressure-sensitive adhesive and preparation method thereof

Abstract

The invention discloses a high-temperature-resistant and high-humidity-resistant OCA optical pressure-sensitive adhesive and a preparation method thereof. The OCA optical pressure-sensitive adhesive is prepared from 100 parts by mass of copolymer and 2-5 parts by mass of tackifying resin, the structural general formula of the copolymer is M1-b-(M2-ran-M3-ran-M4)-b-M1, the number-average molecular weight is 80000-30000 g / mol, M1 is a hard monomer, M2 is an alkyl acrylate soft monomer, M3 is a nitrogen-containing polar monomer, and M4 is a carboxyl or hydroxyl-containing functional monomer. The OCA optical pressure-sensitive adhesive prepared by adjusting the proportion of the monomers and the tackifying resin can keep good adhesive force in a high-temperature and high-humidity environment, the conditions of whitening and degumming of the optical adhesive are avoided, the refractive index and the glass strength are increased, and the service life of the optical pressure-sensitive adhesive is prolonged. Therefore, the optical cement can ensure good light transmittance in various environments such as high temperature, high humidity, low temperature and low humidity, and has strong folding resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of adhesives, and in particular to an OCA optical pressure-sensitive adhesive resistant to high temperature and high humidity and a preparation method thereof. Background Art

[0002] OCA optical pressure-sensitive adhesives are often used in various optical devices, but they may face challenges and problems in high temperature and high humidity environments. Some of the main problems include: (1) High temperature and high humidity environments may cause the adhesion of OCA adhesives to decrease. This may affect its adhesion between optical components and surfaces, thereby reducing the stability and reliability of the assembly. For example, during the use of some folding screen mobile phones, when encountering high temperature and high humidity environments, debonding and whitening may occur, resulting in the phone being returned for repair; (2) Under high temperature and high humidity conditions, OCA optical adhesives will undergo yellowing, resulting in a decrease in their transparency. (3) The mechanical properties of OCA optical adhesives, such as folding resistance, may be affected under high temperature and high humidity conditions.

[0003] Solving these problems is also a significant challenge. For example, increasing peel strength often leads to increased modulus, which in turn weakens the folding resistance of the optical adhesive. Alternatively, improving the yellowing resistance of the optical adhesive can weaken the peel strength. The coordination of these properties requires a well-balanced ratio of different monomers.

[0004] CN111607341A discloses a high-performance optical adhesive, its preparation method, and its application. It is prepared by chemically reacting a composition comprising an acrylic polymer monomer, a multifunctional monomer, a polar group-containing monomer, a silane coupling agent, a crosslinking agent, a chain transfer agent, an initiator, and a solvent. While the adhesive exhibits moderate peel strength, it is susceptible to delamination in high-temperature and high-humidity environments, resulting in whitening.

[0005] CN116333653A discloses an OCA optical adhesive for bonding vehicle-mounted display screens and its preparation method. The raw materials for preparing the optical adhesive include, by weight: 15 to 25 parts of a hydroxyl-containing acrylic functional monomer, 0.5 to 2 parts of a methyl- and nitrogen-containing acrylic functional monomer, 10 to 30 parts of an acrylic hard monomer with a glass transition temperature higher than 130°C, 45 to 75 parts of an acrylic soft monomer with a glass transition temperature lower than -30°C, 0.02 to 0.2 parts of a photoinitiator, 0.1 to 0.5 parts of a multifunctional comonomer, 0.1 to 0.5 parts of a silane coupling agent, and 0.1 to 0.5 parts of a light stabilizer. The present invention provides an OCA optical adhesive having excellent optical properties, heat resistance, high temperature and high humidity resistance, UV resistance, and bonding properties. It can ensure perfect bonding with special materials of vehicle-mounted display screens and can maintain excellent performance in very harsh high temperature and high humidity environments. However, its high modulus makes it difficult to apply in the field of folding-resistant optical adhesives.

[0006] The difficulty in balancing flexibility and resilience, as well as the need to balance high-temperature, high-humidity, and yellowing resistance, in optical adhesives necessitates further research into optical adhesives with superior performance. This will have broad implications for expanding the application of optical adhesives in harsh environments like deserts and oceans, where high temperatures and high humidity are common, and for adapting them to a wider range of applications. Summary of the Invention

[0007] The present invention addresses the problem of optical adhesive failure in high-temperature and high-humidity environments and provides an OCA optical pressure-sensitive adhesive that is resistant to high temperature and high humidity. By selecting and blending monomers, the refractive index and peel strength of the optical adhesive are enhanced, so that the optical pressure-sensitive adhesive still has good adhesion in high-temperature and high-humidity scenarios.

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

[0009] A high temperature and high humidity resistant OCA optical pressure-sensitive adhesive, the OCA optical pressure-sensitive adhesive comprising 100 parts by mass of a copolymer and 2-5 parts by mass of a tackifying resin;

[0010] The general structural formula of the copolymer is M1-b-(M2-ran-M3-ran-M4)-b-M1, and the number average molecular weight is 80,000 to 300,000 g / mol, wherein M1 is a hard monomer, M2 is a soft monomer of alkyl acrylate, M3 is a nitrogen-containing polar monomer, and M4 is a functional monomer containing a carboxyl group or a hydroxyl group.

[0011] The present invention uses alkyl acrylate soft monomers as the main component, and adds nitrogen-containing polar monomers and functional monomers containing hydroxyl or carboxyl groups. Due to their strong polarity, they cause uneven electron distribution within the molecule, thereby affecting its refractive index. The selected monomers have a higher refractive index than alkyl acrylates. In addition, the optical adhesive containing polar monomers has stronger adhesion to the adherend. This is because polar molecules have strong intermolecular interactions and generally have higher surface energy, which has a better wetting effect on the adherend, thereby enhancing its peel strength. In addition, polar molecules will attract each other and agglomerate to form a more ordered structure, thereby enhancing its heat resistance. The amount of tackifying resin used is reduced, and the prepared OCA optical pressure-sensitive adhesive can maintain good adhesion in high temperature and high humidity environments. The optical adhesive will not whiten or debond, also because the monomers in the copolymer are not easily oxidized and degraded. In addition, the amount of tackifying resin added is significantly reduced, which reduces decomposition and discoloration during use and increases the possibility of yellowing of the colloid, making it more suitable for use in high temperature and high humidity environments.

[0012] The copolymer is prepared from the following raw materials in parts by mass through reversible addition-fragmentation chain transfer emulsion polymerization: 60-90 parts of alkyl acrylate soft monomer, 5-20 parts of hard monomer, 5-20 parts of nitrogen-containing polar monomer, and 0.5-5 parts of functional monomer containing carboxyl or hydroxyl groups.

[0013] The hard monomer includes one or more of styrene, methyl acrylate, isobornyl acrylate, cyclohexyl acrylate, methyl methacrylate, acrylamide, acrylonitrile and vinyl acetate, and its glass transition temperature ranges from 60 to 150° C.;

[0014] The alkyl acrylate soft monomer includes 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, and isooctyl methacrylate, and its glass transition temperature ranges from -90 to -30°C.

[0015] Preferably, the alkyl acrylate soft monomer is isooctyl acrylate or octyl acrylate, which has a low polymer modulus and a low glass transition temperature. The prepared optical adhesive is soft and more suitable for foldable screens.

[0016] The nitrogen-containing polar monomer includes one or more of ethylenedimethylamine methacrylate, methacrylic acid amine, N-hydroxymethyl acrylamide, N-methylpyrrolidone, N,N-dimethylacrylamide, 2-nitrohexyl cyclopentane, 3-dimethylamino acrolein, N-methyl-2-pyrrolidone, 1-formylpyrrolidine, and N-ethylacrylamide; the monomer contains a nitrogen-containing polar monomer, and the prepared optical adhesive has higher peeling strength and can be tightly bonded to the adherend.

[0017] Preferably, the nitrogen-containing polar monomer is methacrylic acid amine, N-hydroxymethyl acrylamide, or N,N-dimethyl acrylamide, which are cheaper and easier to obtain.

[0018] The functional monomer containing carboxyl or hydroxyl groups includes one or more of methacrylic acid, acrylic acid, itaconic acid, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, and hydroxypropyl methacrylate. These monomers contain carboxyl or hydroxyl groups, which can effectively improve the peel strength of the optical adhesive.

[0019] Preferably, the functional monomer containing carboxyl or hydroxyl groups is methacrylic acid or acrylic acid, which has strong polarity, low raw material cost and is easily available.

[0020] The tackifying resin includes one or more of DMER-95, GA-90, GA-100, GB-120, TP2019, T801, and T801 / L.

[0021] Preferably, the copolymer preparation comprises the steps of:

[0022] Step 1: dissolving an amphiphilic macromolecular reversible addition-fragmentation chain transfer agent in water and adding a hard monomer to mix; adding a first initiator and reacting at 70-90° C. for 1-3 hours to obtain a homopolymer emulsion;

[0023] Step 2: Add an inorganic base to the emulsion of step 1 to adjust the pH to alkaline, then add an alkyl acrylate soft monomer, a nitrogen-containing polar monomer and water, mix, add a second initiator at 40-60° C., and react in an oxygen-free environment for 20-60 minutes; then dropwise add a carboxyl or hydroxyl functional monomer to the solution, and continue the reaction for 3-7 hours; then add a hard monomer and continue the reaction for 5-10 hours to obtain a copolymer emulsion;

[0024] Step 3: adding hydrogen peroxide and hydrochloric acid to the copolymer emulsion, reacting at 40-60° C. for 1.5-3 hours, and washing and drying the precipitated product to obtain the copolymer.

[0025] The reversible addition-fragmentation chain transfer emulsion polymerization technology is used to synthesize copolymers, which can accurately regulate the structure of the copolymer and the content of each segment, and can precisely control the molecular weight of the polymer and its distribution is narrow and controllable. In addition, this method is applicable to a wide range of monomers, suitable for designing polymers with complex structures, and has a high conversion rate. This method can ensure a high conversion rate of monomers and can achieve stable quality of the synthesized polymers.

[0026] The chemical structural formula of the amphiphilic macromolecular reversible addition-fragmentation chain transfer agent is: R-(Mn1-b-Nn2)-X; wherein R is an isopropyl group, an acetic acid group, a 2-cyanoacetic acid group or a 2-aminoacetic acid group; in Mn1, M is a methacrylic acid monomer or an acrylic acid monomer unit, n1 is the average polymerization degree of M, and n1 ranges from 10 to 30; in Nn2, N is a styrene monomer, a n-butyl acrylate monomer, a methyl acrylate, an isooctyl acrylate or a methyl methacrylate monomer unit, n2 is the average polymerization degree of N, and n2 ranges from 1 to 8; and the X group is an alkyl dithioester group or an alkyl trithioester group.

[0027] The added mass of the amphiphilic macromolecular reversible addition-fragmentation chain transfer agent is 1 / 200-1 / 50 of the mass of all comonomers.

[0028] The first initiator includes any one of ammonium persulfate, potassium persulfate, hydrogen peroxide and a hydrogen peroxide derivative, and the mass of the first initiator is 1 / 200-1 / 50 of the mass of all comonomers;

[0029] The second initiator includes any one of azobisisobutylimidazoline hydrochloride, azobisisobutylamidine hydrochloride, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, sodium persulfate / potassium persulfate redox initiator and sodium persulfate / ammonium persulfate redox initiator, and the mass of the second initiator is 1 / 200-1 / 50 of the mass of all comonomers.

[0030] The present invention also provides a method for preparing the high-temperature and high-humidity resistant OCA optical pressure-sensitive adhesive, comprising the steps of dissolving a copolymer and a tackifying resin in a dispersion medium, forming a film under an inert gas environment, and drying to obtain the OCA optical pressure-sensitive adhesive.

[0031] The dispersion medium includes one or more of 2-butanone, acetone, and tetrahydrofuran.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The patent prepares the OCA optical pressure-sensitive adhesive by adjusting the ratio of monomers and tackifying resins, which can maintain good adhesion in high temperature and high humidity environments. The optical adhesive will not turn white or debond. The increase in the refractive index and glass strength enables the optical adhesive to maintain good light transmittance in various environments such as high temperature and high humidity, low temperature and low humidity, and has strong folding resistance.

[0034] (2) The monomers added to the optical adhesive prepared by this patent will not be oxidized or degraded when used for a long time in a high temperature environment. Also, because the amount of tackifying resin used is significantly reduced, no obvious yellowing phenomenon will occur under high temperature and high humidity conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Graphs of the OCA optical pressure-sensitive adhesives obtained in Example 1 and Comparative Example 1 after undergoing folding resistance in a high-temperature environment.

[0036] Figure 2 Graphs of the OCA optical pressure-sensitive adhesives obtained in Example 1 and Comparative Example 1 after being placed in a high-humidity environment for 24 hours.

[0037] Figure 3 The peel strength of the OCA optical pressure-sensitive adhesive obtained in Example 2 and Comparative Example 2 increases with the monomer content.

[0038] Figure 4 This is a comparison chart of the OCA optical adhesive prepared before and after adding the tackifying resin obtained in Example 3. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with embodiment. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Those skilled in the art will make modifications or equivalent substitutions based on understanding the technical solution of the present invention, without departing from the spirit and scope of the technical solution of the present invention, and all should be encompassed within the protection scope of the present invention.

[0040] The raw materials used in the following specific embodiments are all purchased from the market.

[0041] Example 1

[0042] Poly(styrene-b-(isooctyl acrylate-ran-N-methylpyrrolidone-ran-hydroxyethyl acrylate)-b-styrene), wherein the nitrogen-containing polar monomer (N-methylpyrrolidone) has different mass fractions

[0043] This example uses RAFT reversible addition fragmentation chain transfer emulsion polymerization to prepare the material, and the specific steps are as follows:

[0044] Step 1: 1 part by mass of an amphiphilic macromolecular RAFT agent (amphiphilic macromolecular reversible addition fragmentation chain transfer agent) and 13 parts by mass of water are stirred until completely dissolved, and then 5 parts by mass of styrene are added and stirred and mixed. The chemical structure of the amphiphilic macromolecular RAFT agent is:

[0045]

[0046] Step 2: Add the above raw materials to a four-necked flask, deoxygenate with nitrogen at room temperature for 0.5h, heat the water bath to 70°C, add an initiator potassium persulfate aqueous solution (0.02 parts by mass of potassium persulfate dissolved in 12 parts by mass of water), and react for 1h. Then slowly add sodium hydroxide aqueous solution (1 part by mass of sodium hydroxide dissolved in 10 parts by mass of water), then add 90 parts by mass of isooctyl acrylate, different parts by mass of N-methylpyrrolidone and 50 parts by mass of water, and then add 0.02 parts by mass of azobisisobutylimidazoline hydrochloride. After reacting for 30min, add 2 parts by mass of hydroxyethyl acrylate by dropwise addition, and control the time to be 10min. After the dropwise addition is completed, react for another 4h. Finally, add 5 parts by mass of styrene and react for 1.5h to obtain a copolymer latex;

[0047] Step 3: Place polymer latex, 30 wt% hydrogen peroxide, and 7.5 wt% hydrochloric acid in a beaker at a volume ratio of 2:1:2, stir for 15 minutes until uniform, heat to 50°C, and react in an air environment for 1.5 hours.

[0048] Step 4: After the reaction is completed, the precipitated product is washed with distilled water several times until neutral, dried in a vacuum oven at 120°C for 12 hours, and finally white copolymer particles are obtained;

[0049] Step 5: 90 parts of the copolymer and 10 parts of T801L tackifying resin were dissolved in butanone, and an OCA optical pressure-sensitive adhesive film with a thickness of about 25 μm was prepared using a wire rod coater for peel strength testing.

[0050] The mechanical properties of the prepared optical adhesive were tested using a universal material testing machine (Zwick / Roll Z020). The prepared optical adhesive was cut into dumbbell-shaped specimens using a standard cutting knife. The test method adopted GB 16421-1996, the tensile rate was 30 mm / min, and the test of each sample was repeated at least three times.

[0051] The dynamic mechanical properties of the optical adhesive were characterized using a rotational rheometer (HAAKE MARS 60). The polymer film was cut into circular strips with a diameter of 2 cm. The test frequency was 0.01 Hz to 1 Hz and the test temperature was 25°C. The loss factor (tan) of the material was recorded during the measurement.

[0052] like Figure 1 As shown, (a) is the state of an optical adhesive containing 10 parts by mass of a nitrogen-containing polar monomer placed in a high humidity environment (70RH%) for 24 hours, without whitening; (b) is comparative example 1, an optical adhesive without a nitrogen-containing polar monomer, which whitens after being placed in a high humidity environment for 24 hours.

[0053] Table 1 shows the mechanical properties, resilience, and peel strength of optical adhesives prepared with varying amounts of nitrogen-containing polar monomers. The peel strength of the optical adhesive increases with increasing amounts of nitrogen-containing polar monomers. Notably, the decrease in peel strength at high humidity (70% RH) is significantly less than that at 50% RH. Furthermore, as the amount of nitrogen-containing polar monomer increases, the decrease in strain recovery at 80°C decreases significantly, while the rebound rate significantly increases, compared to normal temperature.

[0054] Table 1 Properties of optical adhesives prepared with different nitrogen-containing polar monomers

[0055]

[0056] Example 2

[0057] Poly(styrene-b-(isooctyl acrylate-ran-N-hydroxymethyl acrylamide-ran-acrylic acid)-b-styrene), wherein the carboxyl-containing acrylic acid has different mass fractions. This embodiment uses RAFT reversible addition fragmentation chain transfer emulsion polymerization to prepare the material, and the specific steps are as follows:

[0058] Step 1: 1 part by mass of an amphiphilic macromolecular RAFT agent (amphiphilic macromolecular reversible addition fragmentation chain transfer agent) and 13 parts by mass of water are stirred until completely dissolved, and then 5 parts by mass of styrene are added and stirred and mixed. The chemical structure of the amphiphilic macromolecular RAFT agent is:

[0059]

[0060] Step 2: Add the above raw materials to a four-necked flask, deoxygenate with nitrogen at room temperature for 0.5h, heat the water bath to 70°C, add an initiator potassium persulfate aqueous solution (0.02 parts by mass of potassium persulfate dissolved in 12 parts by mass of water), and react for 1h. Then slowly add sodium hydroxide aqueous solution (1 part by mass of sodium hydroxide dissolved in 10 parts by mass of water), then add 90 parts by mass of isooctyl acrylate, 5 parts by mass of N-hydroxymethyl acrylamide and 50 parts by mass of water, and then add 0.02 parts by mass of azobisisobutylimidazoline hydrochloride. After reacting for 30hmin, different parts by mass of acrylic acid are added dropwise, and the time is controlled within 10min. After the addition is completed, react for another 4h. Finally, add 5 parts by mass of styrene and react for 1.5h to obtain a copolymer latex;

[0061] Step 3: Place polymer latex, 30 wt% hydrogen peroxide, and 7.5 wt% hydrochloric acid in a beaker at a volume ratio of 2:1:2, stir for 15 minutes until uniform, heat to 50°C, and react in an air environment for 1.5 hours.

[0062] Step 4: After the reaction is completed, the precipitated product is washed with distilled water several times until neutral, dried in a vacuum oven at 120°C for 12 hours, and finally white copolymer particles are obtained;

[0063] Step 5: 100 parts of the copolymer and 2 parts of T801L tackifying resin were dissolved in butanone, and an OCA optical pressure-sensitive adhesive film with a thickness of about 25 μm was prepared using a wire rod coater for peel strength testing.

[0064] like Figure 2 As shown, (a) is the state of the optical adhesive with an acrylic acid addition amount of 2 parts by mass after 10w times of folding in a high humidity environment (70RH%), and there is no debonding. (b) is the state of comparative example 2 after 10w times of folding in a high humidity environment (70RH%), and there is debonding.

[0065] Figure 3 This graph shows the peel strength trend of OCA optical pressure-sensitive adhesives as the acrylic acid content increases. As the mass percentage of alkyl acrylates containing carboxyl or hydroxyl groups increases, the peel strength of the optical adhesive also increases. Optical adhesives without acrylic acid are more susceptible to debonding at high humidity and are less resistant to high temperature and humidity environments. At 50% relative humidity, which is considered normal, increasing humidity without acrylic acid causes a rapid drop in peel strength. The addition of acrylic acid can mitigate this rapid drop in peel strength caused by humidity.

[0066] Table 2 shows the mechanical properties, resilience, and peel strength of optical adhesives prepared with different carboxyl- or hydroxyl-containing functional monomers. It can be seen that as the weight percentage of carboxyl- or hydroxyl-containing functional monomers increases, the peel strength of the optical adhesive also increases. Although increasing the weight percentage of carboxyl- or hydroxyl-containing functional monomers has a clear benefit in improving peel strength, the polymerization efficiency will be affected by the limitations of reversible addition-fragmentation chain transfer emulsion polymerization on the polymerization of hydrophilic monomers.

[0067] In addition, as the mass fraction of functional monomers containing carboxyl or hydroxyl groups increases, the modulus of the optical adhesive will not increase significantly, and its flexibility characteristics can be guaranteed. As the mass fraction of functional monomers containing carboxyl or hydroxyl groups increases, the strain recovery rate of the optical adhesive will decrease. This is because the hydrogen bonds formed between functional monomers containing carboxyl or hydroxyl groups will cause the rebound rate of the optical adhesive to decrease, and its folding resistance performance has little effect.

[0068] Table 2 Optical adhesive properties of different functional monomers containing carboxyl or hydroxyl groups

[0069]

[0070] Example 3

[0071] Poly(styrene-b-(isooctyl acrylate-ran-N-hydroxymethyl acrylamide-ran-acrylic acid)-b-styrene), wherein the tackifying resin has different weight parts, is prepared by RAFT reversible addition fragmentation chain transfer emulsion polymerization in this embodiment, and the specific steps are as follows:

[0072] Step 1: 1 part by mass of an amphiphilic macromolecular RAFT agent (amphiphilic macromolecular reversible addition fragmentation chain transfer agent) and 13 parts by mass of water are stirred until completely dissolved, and then 5 parts by mass of styrene are added and stirred and mixed. The chemical structure of the amphiphilic macromolecular RAFT agent is:

[0073]

[0074] Step 2: Add the above raw materials to a four-necked flask, deoxygenate with nitrogen at room temperature for 0.5h, heat the water bath to 70°C, add an initiator potassium persulfate aqueous solution (0.02 parts by mass of potassium persulfate dissolved in 12 parts by mass of water), and react for 1h. Then slowly add sodium hydroxide aqueous solution (1 part by mass of sodium hydroxide dissolved in 10 parts by mass of water), then add 90 parts by mass of isooctyl acrylate, 5 parts by mass of N-hydroxymethyl acrylamide and 50 parts by mass of water, and then add 0.02 parts by mass of azobisisobutylimidazoline hydrochloride. After reacting for 30hmin, add 1 part by mass of acrylic acid by dropwise addition, and the time is controlled within 10min. After the dropwise addition is completed, react for another 4h. Finally, add 5 parts by mass of styrene and react for 1.5h to obtain a copolymer latex;

[0075] Step 3: Place polymer latex, 30 wt% hydrogen peroxide, and 7.5 wt% hydrochloric acid in a beaker at a volume ratio of 2:1:2, stir for 15 minutes until uniform, heat to 50°C, and react in an air environment for 1.5 hours.

[0076] Step 4: After the reaction is completed, the precipitated product is washed with distilled water several times until neutral, dried in a vacuum oven at 120°C for 12 hours, and finally white copolymer particles are obtained;

[0077] Step 5: 100 parts of the copolymer and different parts by weight of T801L tackifying resin were dissolved in butanone, and an OCA optical pressure-sensitive adhesive film with a thickness of about 25 μm was prepared using a wire rod coater for peel strength testing.

[0078] Table 3 shows the mechanical properties, resilience, peel strength and other data of optical adhesive. Figure 3 、 Figure 4 As shown in Table 1, with the increase of tackifying resin, the peel strength of the optical adhesive is also increased, but its color will obviously turn yellow ( Figure 4 (a is Comparative Example 3, b is Comparative Example 4); this is because the chemical bonds in the tackifying resin break upon heating, causing the color change. Therefore, when formulating an actual optical adhesive, the tackifying resin content is reduced, and a portion of alkyl acrylate containing carboxyl or hydroxyl groups is added to comprehensively adjust the peel strength of the optical adhesive, thereby achieving a balance between various properties.

[0079] Table 3 Mechanical properties, resilience, peel strength and other data of optical adhesive

[0080]

[0081]

[0082] Comparative Example 1: In Comparative Example 1, no nitrogen-containing polar monomer was added and the weight fractions were different. The remaining preparation steps were the same as those in Example 1.

[0083] Comparative Example 2: In Comparative Example 2, no alkyl acrylate containing carboxyl or hydroxyl groups was added, and other preparation steps were the same as those in Example 2.

[0084] Comparative Example 3: No tackifying resin was added to Comparative Example 2, and the other preparation steps were the same as those in Example 3.

[0085] Comparative Example 4: In Comparative Example 4, the amount of tackifying resin added was 10 parts by mass, and the other preparation steps were the same as in Example 3.

Claims

1. A high temperature and high humidity resistant OCA optical pressure-sensitive adhesive, characterized in that: The OCA optical pressure-sensitive adhesive is composed of 100 parts by mass of a copolymer and 2-5 parts by mass of a tackifying resin; The general structural formula of the copolymer is M1-b-(M2-ran-M3-ran-M4)-b-M1, and the number average molecular weight is 80,000 to 300,000 g / mol, wherein M1 is a hard monomer, M2 is a soft monomer of alkyl acrylate, M3 is a nitrogen-containing polar monomer, and M4 is a functional monomer containing a carboxyl group or a hydroxyl group.

2. The high temperature and high humidity resistant OCA optical pressure sensitive adhesive according to claim 1, characterized in that: The copolymer is prepared from the following raw materials in parts by mass through reversible addition-fragmentation chain transfer emulsion polymerization: 60-90 parts of alkyl acrylate soft monomer, 5-20 parts of hard monomer, 5-20 parts of nitrogen-containing polar monomer, and 0.5-5 parts of functional monomer containing carboxyl or hydroxyl groups.

3. The high temperature and high humidity resistant OCA optical pressure sensitive adhesive according to claim 1, characterized in that: The hard monomer includes one or more of styrene, methyl acrylate, isobornyl acrylate, cyclohexyl acrylate, methyl methacrylate, acrylamide, acrylonitrile and vinyl acetate, and its glass transition temperature ranges from 60 to 150° C.; The alkyl acrylate soft monomer includes 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, and isooctyl methacrylate, and its glass transition temperature ranges from -90 to -30°C.

4. The high temperature and high humidity resistant OCA optical pressure sensitive adhesive according to claim 1, characterized in that: The nitrogen-containing polar monomer includes one or more of ethylenedimethylamine methacrylate, methacrylic acid amine, N-hydroxymethyl acrylamide, N-methylpyrrolidone, N,N-dimethylacrylamide, 2-nitrohexyl cyclopentane, 3-dimethylamino acrolein, N-methyl-2-pyrrolidone, 1-formylpyrrolidine, and N-ethylacrylamide; The functional monomer containing carboxyl or hydroxyl groups includes one or more of methacrylic acid, acrylic acid, itaconic acid, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, and hydroxypropyl methacrylate.

5. The high temperature and high humidity resistant OCA optical pressure sensitive adhesive according to claim 1, characterized in that: The tackifying resin includes one or more of DMER-95, GA-90, GA-100, GB-120, TP2019, T801, and T801 / L.

6. The high temperature and high humidity resistant OCA optical pressure sensitive adhesive according to claim 1, characterized in that: The copolymer preparation comprises the steps of: Step 1: dissolving an amphiphilic macromolecular reversible addition-fragmentation chain transfer agent in water and adding a hard monomer to mix; adding a first initiator and reacting at 70-90° C. for 1-3 hours to obtain a homopolymer emulsion; Step 2: Add an inorganic base to the emulsion of step 1 to adjust the pH to alkaline, then add an alkyl acrylate soft monomer, a nitrogen-containing polar monomer and water, mix, add a second initiator at 40-60° C., and react in an oxygen-free environment for 20-60 minutes; then dropwise add a carboxyl or hydroxyl functional monomer to the solution, and continue the reaction for 3-7 hours; then add a hard monomer and continue the reaction for 5-10 hours to obtain a copolymer emulsion; Step 3: adding hydrogen peroxide and hydrochloric acid to the copolymer emulsion, reacting at 40-60° C. for 1.5-3 hours, and washing and drying the precipitated product to obtain the copolymer.

7. The high temperature and high humidity resistant OCA optical pressure sensitive adhesive according to claim 6, characterized in that: The chemical structural formula of the amphiphilic macromolecular reversible addition-fragmentation chain transfer agent is: R-(Mn1-b-Nn2)-X; wherein R is an isopropyl group, an acetic acid group, a 2-cyanoacetic acid group or a 2-aminoacetic acid group; in Mn1, M is a methacrylic acid monomer or an acrylic acid monomer unit, n1 is the average polymerization degree of M, and n1 ranges from 10 to 30; in Nn2, N is a styrene monomer, a n-butyl acrylate monomer, a methyl acrylate, an isooctyl acrylate or a methyl methacrylate monomer unit, n2 is the average polymerization degree of N, and n2 ranges from 1 to 8; and the X group is an alkyl dithioester group or an alkyl trithioester group. The added mass of the amphiphilic macromolecular reversible addition-fragmentation chain transfer agent is 1 / 200-1 / 50 of the mass of all comonomers.

8. The high temperature and high humidity resistant OCA optical pressure sensitive adhesive according to claim 6, characterized in that: The first initiator includes any one of ammonium persulfate, potassium persulfate, hydrogen peroxide and a hydrogen peroxide derivative, and the mass of the first initiator is 1 / 200-1 / 50 of the mass of all comonomers; The second initiator includes any one of azobisisobutylimidazoline hydrochloride, azobisisobutylamidine hydrochloride, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, sodium persulfate / potassium persulfate redox initiator and sodium persulfate / ammonium persulfate redox initiator, and the mass of the second initiator is 1 / 200-1 / 50 of the mass of all comonomers.

9. The method for preparing the high temperature and high humidity resistant OCA optical pressure sensitive adhesive according to any one of claims 1 to 8, characterized in that: The method comprises the following steps: dissolving a copolymer and a tackifying resin in a dispersion medium, forming a film under an inert gas environment, and drying the film to obtain the OCA optical pressure-sensitive adhesive.

10. The method for preparing the high temperature and high humidity resistant OCA optical pressure sensitive adhesive according to claim 9, characterized in that: The dispersion medium includes one or more of 2-butanone, acetone, and tetrahydrofuran.

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