OCA optical pressure-sensitive adhesive capable of enhancing dynamic mechanical properties and preparation method of OCA optical pressure-sensitive adhesive

Abstract

The invention relates to the technical field of adhesives, and discloses an OCA optical pressure-sensitive adhesive with enhanced dynamic mechanical properties and a preparation method thereof, the optical pressure-sensitive adhesive comprises 100 parts by mass of a block copolymer, 2-20 parts by mass of a silica graft modified polymer and 2-30 parts by mass of tackifying resin; the silicon dioxide graft modified polymer is polystyrene which is connected with silicon dioxide through a silane coupling agent containing double bonds. The silicon dioxide is grafted with the hard monomer, so that the silicon dioxide is effectively combined on the styrene site, and the free movement and agglomeration phenomena of the silicon dioxide in the polymer are avoided. Meanwhile, styrene cut off from silicon dioxide is combined with a hard monomer in the block copolymer to form a local enhanced area, so that the overall strength and toughness of the optical adhesive, particularly the dynamic mechanical property, are effectively improved, and relatively high transparency is kept.

Description

Technical Field

[0001] The present invention relates to the technical field of adhesives, and in particular to an OCA optical pressure-sensitive adhesive with enhanced dynamic mechanical properties and a preparation method thereof. Background Art

[0002] Amid the rapid development of electronic terminal products, optically clear adhesive (OCA), a key material, is widely used in liquid crystal displays, touch screens, display panels, and other fields. With its excellent transparency, adhesion, and mechanical properties, OCA is a key factor in ensuring the high-quality performance of display devices.

[0003] However, OCA optical adhesives face challenges in their application, such as improving dynamic mechanical properties, increasing die-cutting yield, and enhancing heat resistance. Traditional methods improve the performance of OCA optical adhesives by blending SiO2 with copolymer solutions, but random mixing of SiO2 can affect the material's performance, resulting in reduced transparency.

[0004] Compared to patent CN111607342A, the OCA optical pressure-sensitive adhesive is made of the following components by weight: 10-20 parts methyl acrylate; 20-40 parts butyl acrylate; 20-40 parts methyl methacrylate; 5-15 parts ethylene glycol dimethacrylate; 5-10 parts diaminoethyl methacrylate; 5-10 parts isooctyl acrylate; 20-40 parts ethyl methacrylate; 5-10 parts emulsifier; 0.1-0.2 parts initiator; 30-40 parts deionized water; and 5-15 parts nano-silica. Directly adding nano-silica to the optical adhesive system can easily lead to poor dispersion, reduced transparency, and increased modulus.

[0005] CN115895523 A discloses an OCA optical adhesive for folding screens, its preparation method, and application. The adhesive comprises a modified allyl polyether derivative with alkenyl groups at both ends and a Congo red structure in the middle, which is then cross-linked and polymerized with isobutyl acrylate, butyl methacrylate, hydroxyethyl acrylate, and glycidyl acrylate under the initiation of benzoyl peroxide. Antioxidant-modified nanosilica is used as an inorganic filler to prepare the OCA optical adhesive. The OCA optical adhesive, under the action of the modified allyl polyether derivative and modified silica, exhibits excellent heat stability, aging resistance, and blue light protection, facilitating its application in folding screens for electronic devices such as mobile phones and tablets. In this solution, silica easily agglomerates, significantly reducing the transparency of the optical adhesive and diminishing the display quality of electronic products.

[0006] Therefore, silica-modified optical adhesive is used to further achieve improvements in microphase separation structure, maintain transparency, and enhance performance, making OCA optical adhesive have a broader application prospect in the fields of electronic products and optical devices. Summary of the Invention

[0007] The present invention addresses the problems of poor effect and decreased transparency in improving the dynamic mechanical properties of OCA optical adhesives using silica. A method for preparing an OCA optical pressure-sensitive adhesive with enhanced dynamic mechanical properties is provided. A hard monomer is polymerized on the surface of silica and then blended with a block copolymer to prepare the optical pressure-sensitive adhesive. The colloid has excellent dynamic mechanical properties.

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

[0009] An OCA optical pressure-sensitive adhesive with enhanced dynamic mechanical properties, characterized by comprising 100 parts by mass of a block copolymer, 2-20 parts by mass of a silica graft-modified polymer, and 2-30 parts by mass of a tackifying resin;

[0010] The silicon dioxide grafted modified polymer is polystyrene connected to silicon dioxide via a silane coupling agent containing double bonds.

[0011] In this invention, silica is grafted onto hard monomers, effectively binding them to styrene sites, preventing silica from freely moving and agglomerating within the polymer. Furthermore, the styrene-terminated silica binds to the hard monomers in the block copolymer to form localized reinforcement regions, effectively improving the overall strength and toughness of the optical adhesive, particularly its dynamic mechanical properties. Furthermore, while silica agglomeration in traditional methods can reduce transparency, the present invention reduces agglomeration by controlling the microphase separation structure, maintaining the high transparency of the optical adhesive.

[0012] The modulus of low modulus cross-linked polymer elastomers is not only proportional to the cross-link density, but also affected by the chain entanglement density, which can be described by the following formula:

[0013]

[0014] Where E is the elastic modulus, G is the shear modulus, ρ is the polymer density, R is the ideal gas constant, T is the temperature, and M c is the average molecular weight between cross-linking points, M eIt is the molecular weight of polymer chain entanglement. The higher the cross-linking density, the more complete the cross-linking network structure. Silica combined with styrene sites can improve the integrity of the cross-linking network structure, affecting various parameters of the polymer and being significantly affected. When the polymer is stretched, the styrene chain is not easily broken. However, simply adding silica will lead to the ineffective effect of silica. It only acts as a composite reinforcement mechanism to increase the mechanical properties of the polymer, but it cannot play a role in the cross-linking network of the polymer. In addition, it will also lead to M e , which further leads to an increase in the polymer modulus, but the network structure is not enhanced at all.

[0015] The preparation of the silica graft modified polymer includes the following steps: stirring nano silica particles in a silane coupling agent solution to react to obtain silica modified by the silane coupling agent; and initiating polymerization of the silica modified by the silane coupling agent and styrene under the action of an initiator to obtain the silica graft modified polymer.

[0016] Grafting silica and styrene with a silane coupling agent containing double bonds enhances the bonding between the two, helping to form a stable microphase separation structure. This is more conducive to improving the mechanical properties of the material when subsequently mixed with block copolymers.

[0017] Preferably, the mass ratio of the silica, silane coupling agent and hard monomer is 1:3-10:5-30;

[0018] Preferably, the stirring reaction is carried out at room temperature for 10-36 hours; and the initiation polymerization is carried out at 45-70° C. for 4-15 hours.

[0019] Further preferably, the preparation of the silica grafted modified polymer specifically comprises the steps of:

[0020] Step 1, placing the nano-silica particles in a solvent for ultrasonic cleaning and drying;

[0021] Step 2, placing the cleaned nano-silica in a solution of a silane coupling agent, stirring and grafting at room temperature, centrifuging, washing, and drying to obtain silane coupling agent-modified silica;

[0022] Step 3: Initiate polymerization of silica modified with a silane coupling agent, styrene and an initiator in an organic solvent, and wash and dry the product to obtain the silica graft-modified polymer.

[0023] The organic solvent includes one or more of toluene, ethyl acetate, n-hexane, and dioxane;

[0024] The solvents in step 1 or 2 are all conventional solvents, such as one or more of water, ethanol, acetone, etc.

[0025] The silane coupling agent includes one or more of methacrylic silane, vinyl silane, acrylate silane, and acryltrimethoxysilane. These silane coupling agents all contain double bonds that polymerize with styrene, and also contain silyl methoxy groups that chemically condense with hydroxyl groups (Si-OH) on the surface of silica to form silicon-oxygen-silicon bonds (Si-O-Si).

[0026] The particle size of the silicon dioxide is 5-25 nm. Nano-silicon dioxide can more effectively enhance the mechanical strength without causing poor compatibility between inorganic and organic substances due to its large size.

[0027] The initiator includes one or more of ammonium persulfate, potassium persulfate, hydrogen peroxide and hydrogen peroxide derivatives.

[0028] The block copolymer has a general structural formula of M1-b-M2...-bM j , where j ranges from 3 to 11; where M1, M2...M j It is a comonomer in the block copolymer, and the number average molecular weight of the block copolymer is 80,000 to 800,000 g / mol; M1, M2...M j They are selected from soft monomers, hard monomers or functional monomers respectively; and the mass contents of the soft monomers, hard monomers and functional monomers in the block copolymer are 70-98%, 2-30% and 0-5% respectively.

[0029] The hard monomer includes one or more of styrene, methyl acrylate, isobornyl acrylate, cyclohexyl acrylate, methyl methacrylate, acrylamide, acrylonitrile and vinyl acetate, and the glass transition temperature range of the hard monomer is 60-150°C.

[0030] The 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, isooctyl methacrylate, butadiene, isoprene, ethylene-butene and methacrylic acid, and the glass transition temperature ranges from -90 to -30°C.

[0031] The functional monomers include one or more of methacrylic acid, acrylic acid, itaconic acid, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, ethylenedimethylamine methacrylate, methacrylic acid amine, N-hydroxymethyl acrylamide, glycidyl methacrylate and maleic anhydride.

[0032] The tackifying resin includes one or more of DMER-95, GA-90, GA-100, GB-120, TP2019, T801, and T801 / L.

[0033] The present invention also provides a method for preparing the OCA optical pressure-sensitive adhesive with enhanced dynamic mechanical properties, comprising the steps of: mixing a silica grafted modified polymer, a block copolymer and a tackifying resin in a solvent, and curing and drying the mixture to obtain the OCA optical pressure-sensitive adhesive.

[0034] Preferably, one or more means such as stirring, ultrasound, heat treatment, etc. are used to uniformly disperse the silica grafted modified polymer, the block polymer, and the tackifying resin.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) The present invention provides a unique method for grafting a hard monomer onto the surface of SiO2, enabling it to polymerize with the hard segment in the copolymer to form a microphase separation structure. Compared with the direct blending method, SiO2 is not randomly dispersed in the copolymer, but is fixed in the hard segment, thereby improving the compatibility and stability of the material and maintaining the transparency of the OCA optical adhesive. In particular, the dynamic mechanical properties of the OCA optical adhesive are significantly improved, making it more stable and reliable during use. In addition, this method enhances the entanglement between the hard segment molecular chains, making the material exhibit better toughness.

[0037] (2) The preparation method of the OCA optical pressure-sensitive adhesive in the present invention is simple, and the transparency of the OCA optical adhesive will not be reduced due to the random blending of SiO2; and the final blend has significant advantages in performance, and the dynamic mechanical properties of the OCA optical adhesive are greatly improved.

[0038] (3) Due to the introduction of silica grafted modified polymer, the shear storage modulus of the OCA optical pressure-sensitive adhesive of the present invention is effectively increased and improved, which can greatly improve the yield of die-cutting processing and reduce the burrs generated during the die-cutting process. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 The mechanical curves of the OCA optical pressure-sensitive adhesives obtained in Example 1 and Comparative Example 1 are shown.

[0040] Figure 2 It is a comparison diagram of the principle diagrams of Example 2 and Comparative Example 2.

[0041] Figure 3 The figure shows the dynamic mechanical properties of the OCA optical pressure-sensitive adhesive obtained in Example 2 and Comparative Example 2.

[0042] Figure 4 This is the optical transmittance diagram of the OCA optical adhesive obtained in Example 3. DETAILED DESCRIPTION

[0043] 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.

[0044] The raw materials used in the following embodiments were purchased from the market, and the block copolymer was prepared according to the method of Example 1 of CN115260921A. Nano-silica model UG-SP15F was obtained from Suzhou Youzi Nanomaterial Co., Ltd., with a particle size of 10-20 nm.

[0045] Example 1

[0046] Preparation of silica grafted modified polymers:

[0047] Step 1: Place 1 part by mass of nano-SiO2 particles in ethanol and ultrasonically clean them for 30 minutes, then dry them to remove surface impurities and adsorbents.

[0048] Step 2: Add 5 parts by mass of vinylsilane solution to the cleaned nano-SiO2 particles, then add 40 parts by mass of ethanol, stir the reaction at room temperature for 24 hours, centrifuge and disperse, rinse the lower layer product with ethanol three times, and dry it at 80°C to obtain vinylsilane-modified silica.

[0049] Step 3: Add vinylsilane-modified silica, different parts by mass (5, 15, and 30, respectively) of styrene monomer, and 0.3 parts by mass of potassium persulfate to 30 parts by mass of toluene, and carry out polymerization reaction at 45° C. for 8 hours; remove the residual solvent in a vacuum or by drying by washing and drying to obtain a silica-grafted modified polymer.

[0050] Optical adhesive preparation:

[0051] Step 1: 8 parts by mass of a silica-grafted modified polymer, 90 parts by mass of a block copolymer (prepared according to Example 1 of CN115260921A) and 2 parts by mass of TP2019 tackifying resin were mixed and dissolved in a tetrahydrofuran solution;

[0052] Step 2: stirring until the mixture is uniformly mixed so that the silica nanoparticles are uniformly dispersed in the copolymer; curing and drying the treated mixture to prepare an OCA optical adhesive with excellent performance;

[0053] The mechanical properties of OCA optical adhesive were tested using a universal materials testing machine (Zwick / Roll Z020). The optical adhesive prepared above 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.

[0054] The dynamic mechanical properties of OCA optical adhesive were characterized by a rotational rheometer (HAAKE MARS 60). The polymer film was cut into circular specimens with a diameter of 2 cm. The test frequency was 0.01 Hz-1 Hz and the test temperature was 25°C.

[0055] The number average molecular weight (M n ), weight average molecular weight (M w ) and molecular weight distribution (PDI) were characterized using a gel chromatography permeameter (GPC, Water 1525 / 2414, Waters, USA). The sample was prepared as a 3 mg / mL tetrahydrofuran solution before testing and filtered using a 0.45 μm GHP filter to prevent large impurities from clogging the chromatographic column. Tetrahydrofuran (THF) was used as the mobile phase, polystyrene (PS) was used as the standard, and the test temperature was 30°C.

[0056] Table 1 shows the mechanical properties, dynamic mechanical properties, bonding strength and other data of the OCA optical adhesive finally prepared by grafting silica with styrene segments of different lengths, with Example 1 of CN115260921A as comparative example 1. Since the addition ratio is fixed, the polymers of SiO2 with different molecular weights grafted onto the surface of polystyrene essentially affect the addition ratio of SiO2. The smaller the mass fraction of polystyrene, the higher the proportion of SiO2 added. The modulus of SiO2 itself is higher than that of styrene. Therefore, as the proportion of SiO2 increases, the modulus of the optical adhesive is improved, and its dynamic mechanical properties are also enhanced. At the same time, other properties, such as elongation at break, strain recovery rate, and peel strength do not change significantly. The larger the mass fraction of polystyrene, the lower the proportion of SiO2 added. Mechanical properties such as Figure 1 shown.

[0057] Table 1 Properties of optical adhesives prepared with different contents of silica in Example 1

[0058]

[0059] Example 2

[0060] An optical adhesive was prepared using the silica-modified polymer prepared from 15 parts by mass of styrene in Example 1 as a raw material. 10-30 parts by mass of the silica-modified polymer and 70-90 parts by mass of the copolymer were mixed and dissolved in acetone according to a mass ratio. The mixture was stirred at room temperature for 2 hours and ultrasonicated for 30 minutes. If any undissolved polymer remained, the temperature was raised to 40° C. and stirring was continued until the polymer was completely dissolved, thereby uniformly dispersing the silica nanoparticles in the copolymer. The treated mixture was cured at room temperature for 2 days and then dried in a 120° C. oven to prepare an OCA optical adhesive with excellent performance.

[0061] Table 2 shows the mechanical properties, dynamic mechanical properties, bonding strength and other data of OCA optical adhesives prepared with different mass fractions of silica-modified polymers. As the mass fraction of silica-modified polymers increases, the shear storage modulus of the optical adhesive also increases, and the dynamic mechanical properties are optimized. The modulus data are as follows: Figure 3 However, at the same time, the peel strength of the optical adhesive is reduced due to the increase of the silica-modified polymer with poor bonding strength, and the elongation at break is also reduced.

[0062] The internal principle comparison diagram of the optical adhesive (a) in Example 2 and the optical adhesive (b) in Comparative Example 2 is as follows: Figure 2 Compared with the unmodified ordinary nano-silica in Comparative Example 2, the silica can aggregate into the styrene microphase instead of agglomerating in the poly(2-ethylhexyl acrylate), and its light transmittance is significantly improved.

[0063] Table 2 Properties of optical adhesives prepared with different silica-modified polymers

[0064]

[0065]

[0066] Comparative Example 2

[0067] The difference from Example 2 is that in the preparation of the optical adhesive, 8 parts by mass of the silica grafted modified polymer are replaced with ordinary nano-silica particles, which are ultrasonically cleaned for 30 minutes and then dried to remove surface impurities and adsorbents, and then directly blended with the block copolymer and the tackifying resin. The subsequent steps are the same.

[0068] Example 3

[0069] Preparation of silica grafted modified polymers:

[0070] Step 1: Place 1 part by mass of nano-SiO2 particles in ethanol and ultrasonically clean them for 30 minutes, then dry them to remove surface impurities and adsorbents.

[0071] Step 2: Add 5 parts by mass of vinylsilane solution to the cleaned nano-SiO2 particles, then add 40 parts by mass of ethanol, stir the reaction at room temperature for 24 hours, centrifuge and disperse, rinse the lower layer product with ethanol three times, and dry it at 80°C to obtain vinylsilane-modified silica.

[0072] Step 3: Add vinylsilane-modified silica, 15 parts by mass of methyl methacrylate or acrylonitrile monomer, and 0.3 parts by mass of potassium persulfate to 30 parts by mass of toluene, and carry out polymerization reaction at 45°C for 8 hours; remove the residual solvent by washing and drying in a vacuum or by drying to obtain silica-grafted polymethyl methacrylate SiO2-PMMA and silica-grafted polyacrylonitrile SiO2-PAN, which are compared with the silica-grafted polystyrene SiO2-PSt prepared in equal parts in Example 1.

[0073] Optical adhesive preparation:

[0074] Step 1: 8 parts by mass of silica-grafted modified polymers (SiO2-PMMA and SiO2-PAN), 88 parts by mass of block copolymer and 4 parts by mass of TP2019 tackifying resin were mixed and dissolved in tetrahydrofuran solvent;

[0075] Step 2: stirring until the mixture is uniformly mixed so that the silica nanoparticles are uniformly dispersed in the copolymer; curing and drying the treated mixture to prepare an OCA optical adhesive with excellent performance;

[0076] Table 3 shows the mechanical properties, dynamic mechanical properties, bonding strength and other data of the above two optical adhesives and the optical adhesive prepared from 15 parts of styrene in Example 1. The glass transition temperature of polymethyl methacrylate (PMMA) is higher than that of polystyrene (PSt) and polyacrylonitrile (PAN), so the better the effect of enhancing the mechanical properties, the glass transition temperature of polystyrene and polyacrylonitrile are similar, so SiO2-PMMA and SiO2-PAN have similar effects on enhancing the mechanical properties. Due to the better compatibility between polystyrene and the better compatibility between SiO2-PSt and the copolymer, the higher the transmittance, the better the transmittance data. Figure 4 shown.

[0077] Table 3 Properties of optical adhesives prepared by different silica-modified polymers

[0078]

Claims

1. An OCA optical pressure-sensitive adhesive with enhanced dynamic mechanical properties, characterized in that: The invention comprises 100 parts by mass of a block copolymer, 2-20 parts by mass of a silica grafted modified polymer and 2-30 parts by mass of a tackifying resin; The silicon dioxide grafted modified polymer is polystyrene connected to silicon dioxide via a silane coupling agent containing double bonds.

2. The OCA optical pressure-sensitive adhesive with enhanced dynamic mechanical properties according to claim 1, characterized in that: The preparation of the silicon dioxide grafted modified polymer comprises the steps of: The nano-silica particles are stirred and reacted in a silane coupling agent solution to obtain silane coupling agent-modified silica; the silane coupling agent-modified silica and styrene are polymerized under the action of an initiator to obtain the silica graft-modified polymer.

3. The OCA optical pressure-sensitive adhesive with enhanced dynamic mechanical properties according to claim 2, characterized in that: The mass ratio of the silicon dioxide, the silane coupling agent and the hard monomer is 1:3-10:5-30.

4. The OCA optical pressure-sensitive adhesive with enhanced dynamic mechanical properties according to claim 2, characterized in that: The stirring reaction is carried out at room temperature for 10-36 hours; the polymerization is initiated at 45-70°C for 4-15 hours.

5. The OCA optical pressure-sensitive adhesive with enhanced dynamic mechanical properties according to claim 2, characterized in that: The silane coupling agent includes one or more of methyl acryloyl silane, vinyl silane, acrylate silane, and acryltrimethoxy silane.

6. The OCA optical pressure-sensitive adhesive with enhanced dynamic mechanical properties according to claim 2, characterized in that: The particle size of the silicon dioxide is 5-25 nm; And / or, the initiator includes one or more of ammonium persulfate, potassium persulfate, hydrogen peroxide and hydrogen peroxide derivatives.

7. The OCA optical pressure-sensitive adhesive with enhanced dynamic mechanical properties according to claim 1, characterized in that: The block copolymer has a general structural formula of M1-b-M2...-bM j , where j ranges from 3 to 11; where M1, M2...M j It is a comonomer in the block copolymer, and the number average molecular weight of the block copolymer is 80,000 to 800,000 g / mol; M1, M2...M j They are selected from soft monomers, hard monomers or functional monomers respectively; and the mass contents of the soft monomers, hard monomers and functional monomers in the block copolymer are 70-98%, 2-30% and 0-5% respectively.

8. The OCA optical pressure-sensitive adhesive with enhanced dynamic mechanical properties according to claim 7, 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 soft monomer comprises 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 glass transition temperature range is -90 to -30°C; The functional monomers include one or more of methacrylic acid, acrylic acid, itaconic acid, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, ethylenedimethylamine methacrylate, methacrylic acid amine, N-hydroxymethyl acrylamide, glycidyl methacrylate and maleic anhydride.

9. The OCA optical pressure-sensitive adhesive with enhanced dynamic mechanical properties 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.

10. The method for preparing an OCA optical pressure-sensitive adhesive with enhanced dynamic mechanical properties according to any one of claims 1 to 9, characterized in that: The method comprises the following steps: mixing a silicon dioxide graft modified polymer, a block copolymer and a tackifying resin in a solvent, and curing and drying the mixture to obtain the OCA optical pressure-sensitive adhesive.

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