Optical adhesive for curved surface and preparation method thereof

Abstract

The present invention discloses an optical adhesive for curved surfaces. The raw materials for preparing the optical adhesive include an acrylic resin, a thermal initiator, an acrylic monomer, and a solvent. The acrylic resin comprises, by mass, 85-95 parts of a soft monomer, such as butyl acrylate and / or isooctyl acrylate; 5-15 parts of a functional monomer, such as acrylic acid and / or hydroxyethyl acrylate; 0.5-1 part of a photoinitiator; a polyurethane macromolecular modified azo initiator, or an isocyanate-terminated initiator; and the acrylic monomers include one or more of butyl acrylate, isooctyl acrylate, methyl methacrylate, isooctyl methacrylate, acryloylmorpholine, and N-vinyl pyrrolidone. The optical adhesive for curved surfaces exhibits excellent elongation, flexibility, and elastic deformation.

Description

Technical Field

[0001] The present invention relates to the technical field of optical adhesives, and in particular to an optical adhesive for curved surfaces and a preparation method thereof. Background Art

[0002] 3D curved glass screens offer advantages such as lightness, transparency, cleanliness, anti-glare, strength, scratch resistance, weather resistance, and excellent plasticity. 3D curved glass screen phones are a major trend in the current mobile phone industry. A commonly used protective film for curved phone screens is a TPU-based explosion-proof film, which is then fixed to the 3D curved glass screen via optical adhesive, providing comprehensive protection for the phone screen. Therefore, optical adhesive not only meets the requirements of conventional bonding and brightness enhancement, but also requires bendability, high temperature resistance, and stability. Existing protective films formed from optical adhesives and substrates are prone to wrinkling, warping, and bubbles at the bent edges, and the optical adhesive also suffers from poor adhesion.

[0003] Therefore, it is necessary to improve the optical adhesive for curved surfaces in the prior art. Summary of the Invention

[0004] One of the purposes of the present invention is to overcome the defects in the prior art and provide an optical adhesive for curved surfaces, which has good elongation, softness and elastic deformation.

[0005] In order to achieve the above-mentioned process effect, the technical solution of the present invention is: an optical adhesive for curved surfaces, wherein the raw materials for preparing the optical adhesive include acrylic resin, a thermal initiator, an acrylic monomer and a solvent; in parts by mass, the raw materials for preparing the acrylic resin include:

[0006] 85-95 parts of soft monomer, which is butyl acrylate and / or isooctyl acrylate;

[0007] 5 to 15 parts of functional monomer, which is acrylic acid and / or hydroxyethyl acrylate;

[0008] 0.5-1 part of photoinitiator;

[0009] The thermal initiator is a polyurethane macromolecular modified azo initiator, and the thermal initiator is an isocyanate-terminated initiator;

[0010] The acrylic monomer includes one or more of butyl acrylate, isooctyl acrylate, methyl methacrylate, isooctyl methacrylate, acryloylmorpholine and N-vinyl pyrrolidone.

[0011] The preferred technical solution is that, by weight, the raw materials for preparing the optical adhesive include 100 parts of acrylic resin, 0.2 to 1 part of thermal initiator, 85 to 95 parts of acrylic monomer and 200 to 320 parts of solvent.

[0012] The preferred technical solution is that the thermal initiator is a polyurethane molecule-modified azo initiator; the polyurethane molecule-modified azo initiator is prepared by reacting with 4,4'-azobis(4-cyanopentanol) under the action of a polyurethane prepolymer catalyst; the polyurethane prepolymer is prepared by polymerization of polyol and polyisocyanate; the molar ratio of the polyol to the polyisocyanate to 4,4'-azobis(4-cyanopentanol) is 1:(2-2.25):(0.5-0.7).

[0013] A preferred technical solution is that, by weight, the acrylic monomer includes 90-95 parts of butyl acrylate, 3-5 parts of methyl methacrylate and 3-5 parts of N-vinyl pyrrolidone.

[0014] The preferred technical solution is that the solvent is ethyl acetate.

[0015] A preferred technical solution is that the polyol is a polyether diol.

[0016] A preferred technical solution is that the polyisocyanate is an aliphatic diisocyanate.

[0017] A preferred technical solution is that the photoinitiator is one or more of 2-hydroxy-2-methyl-1-phenyl-1-propanone, (2,4,6-trimethylbenzoyl)diphenylphosphine oxide and 1-hydroxycyclohexylphenyl ketone.

[0018] A second object of the present invention is to overcome the defects in the prior art and provide a method for preparing an optical adhesive for curved surfaces, comprising the following steps:

[0019] S1: Preparation of acrylic resin;

[0020] S2: The thermal initiator is dissolved in a solvent, the temperature is increased, and acrylic acid monomer is added to cause a polymerization reaction;

[0021] S3: Cooling the mixed copolymer obtained in S2 under stirring, and adding the acrylic resin to obtain an optical adhesive.

[0022] The preferred technical solution is that the temperature of the S2 heating is 80-85°C.

[0023] The advantages and beneficial effects of the present invention are:

[0024] The optical adhesive for curved surfaces can control the molecular weight of acrylic resin through a photoinitiator, so that the resulting acrylic resin has fewer side chains and moves more flexibly, thereby improving the softness of the colloid. The hydroxyl and / or carboxyl groups in the acrylic resin react with the isocyanate-terminated initiator to cross-link, thereby increasing the compatibility between the polyacrylic resin and the polyurethane macromolecules and improving the aging resistance of the colloid. The introduction of polyurethane molecules into the colloid also increases the extensibility of the colloid, so that the colloid will not warp or bubble at the edge curvature when used on curved glass. The cross-linking density is also controlled by modifying the polyurethane macromolecule with an azo initiator to improve the elastic deformation ability of the colloid. DETAILED DESCRIPTION

[0025] The following examples are only used to illustrate the technical solution of the present invention more clearly, and are not intended to limit the scope of protection of the present invention.

[0026] raw material

[0027] Isooctyl acrylate was produced by Shanghai Huayi Company;

[0028] Butyl acrylate was purchased from Shanghai Huayi Company;

[0029] Methyl methacrylate was purchased from Formosa Plastics Group in Taiwan, China;

[0030] Acrylic acid was purchased from Formosa Plastics Group in Taiwan, China;

[0031] Hydroxyethyl acrylate was purchased from LG Group in South Korea;

[0032] Azobisisobutyronitrile was purchased from Jiangsu Quanwei Chemical Co., Ltd.;

[0033] 4,4'-Azobis-4-cyanopentanol was purchased from Wuhan Profu Biotechnology Co., Ltd.

[0034] acrylic resin

[0035] Soft monomers and functional monomers mainly provide flexible molecular chains, giving the colloid good bonding properties.

[0036] The soft monomer is butyl acrylate and / or isooctyl acrylate. Furthermore, the soft monomer is butyl acrylate. Polybutyl acrylate has good flexibility and strong chain segment mobility, which can provide a larger free volume for the polymer, not only providing viscosity to the colloid, but also improving the colloid's extensibility.

[0037] The functional monomers are acrylic acid and / or hydroxyethyl acrylate. During photoinitiated polymerization, the hydroxyl-containing acrylic monomers polymerize to improve the thermal stability of the colloid; the carboxyl-containing acrylic monomers improve the dispersibility of the polymer and the stability of the colloid. Furthermore, the functional monomers are acrylic acid and hydroxyethyl acrylate, and the mass ratio of acrylic acid to hydroxyethyl acrylate is 1:(1-2).

[0038] Photoinitiator

[0039] The photoinitiator is one or more of 2-hydroxy-2-methyl-1-phenyl-1-propanone (1173), (2,4,6-trimethylbenzoyl)diphenylphosphine oxide (TPO), and 1-hydroxycyclohexylphenyl ketone (184). Furthermore, the photoinitiator is 184, which has no α-H group ortho to the benzoyl group in its molecular structure and has good thermal stability, thereby controlling the molecular weight and chain length of the acrylic resin.

[0040] solvent

[0041] Ethyl acetate has good solubility, low boiling point and low toxicity. It is not only environmentally friendly, but also improves the solubility of polyurethane macromolecular modified azo initiators and is compatible with the initiation temperature of polyurethane macromolecular modified azo initiators.

[0042] Acrylic monomer

[0043] Methyl methacrylate and isooctyl methacrylate are hard monomers, and the cohesion and flexibility of the polymer can be adjusted by adjusting the addition amount of the hard monomers. Further, the acrylic monomer includes methyl methacrylate.

[0044] Acryloylmorpholine and N-vinylpyrrolidone are modified monomers that enhance the toughness of the colloid, imparting excellent warpage resistance. Even under high temperature and humidity conditions (85°C, 85%) for 72 hours, the colloid exhibits excellent warpage resistance, preventing warping or blistering at the edges of curved glass. Furthermore, the acrylic monomer includes N-vinylpyrrolidone.

[0045] polyols

[0046] The polyether diol has good low-temperature flexibility, aging resistance, good hydrolysis resistance, and low cost. Commonly used polyether diols are polyoxypropylene glycol (PPG) and polytetramethylene glycol (PTMEG). Furthermore, the polyether diol is polytetramethylene glycol, which can improve the cohesive properties, low-temperature flexibility, low-temperature resistance, and hydrolysis resistance of the colloid.

[0047] polyisocyanates

[0048] Including but not limited to one or more of aliphatic isocyanates and aromatic isocyanates. Furthermore, the polyisocyanate is an aliphatic diisocyanate. The aliphatic isocyanate is one or more of hexamethylene-1,6-diisocyanate (HDI) and isophorone diisocyanate (IPDI). Furthermore, the aliphatic isocyanate is isophorone diisocyanate (IPDI). IPDI has two different types of -NCO groups, and the group activities are different. The reaction conditions can be controlled, and the polyether polyol selectively reacts with the -NCO on the aliphatic primary position to form an -NCO-terminated polyurethane prepolymer.

[0049] Preparation of acrylic resin

[0050] In the presence of a photoinitiator, butyl acrylate, acrylic acid, and hydroxyethyl acrylate undergo free radical polymerization. Polymerization is initiated by irradiation with a mixed UV lamp at a wavelength of 365 nm and a low-pressure mercury lamp at a wavelength of 300 nm. The reaction is terminated when the viscosity of the reaction system reaches a viscosity of 1000 to 5000 mPa·s. Furthermore, the viscosity of the reaction system reaches a viscosity of 2500 to 4000 mPa·s. Excessively high viscosity results in a high crosslink density in the resulting acrylic resin, and hydroxyl and / or carboxyl groups are encapsulated within the polymer, hindering crosslinking with -NCO groups during thermal reactions. This negatively impacts the elongation and elastic deformation capacity of the colloid.

[0051] Preparation of Polyurethane Macromolecule Modified Azo Initiator

[0052] S11: Place polytetrahydrofuran diol (PTMEG) in a reactor protected by N2, heat to 110°C, reduce pressure and distill for dehydration for 2.5 to 3.5 hours, cool and set aside. Take the molar ratio of PTMEG to isophorone diisocyanate (IPDI) as 1: (2 to 2.2), first dissolve PTMEG in dimethylformamide (DMF) solvent, and heat to 60 to 65°C to fully dissolve; in another reaction vessel protected by N2, heat IPDI to 60 to 65°C, then add PTMEG dissolved in DMF solvent at a rate of 1 to 2 drops / 1s to react with IPDI, and after the addition is completed, stir the reaction thoroughly for 1.5 to 2 hours until the remaining -NCO content in the solution is less than 0.5wt%, to obtain a polyurethane prepolymer;

[0053] S12: Take the molar ratio of PTMEG and 4,4'-azobis-4-cyanopentanol (ACPA) to be 1:(0.5-0.6); cool the polyurethane prepolymer to room temperature, add 0.3%-0.4% of dibutyltin dilaurate (DBTDL) based on the total mass of the polyurethane prepolymer dropwise, and add ACPA dissolved in DMF solvent to the polyurethane prepolymer reactor. Fully react for 2-3 days, filter the product, place it in a vacuum oven and dry it at room temperature for later use.

[0054] Preparation method of optical adhesive for curved surface

[0055] S1: preparing acrylic resin by the above method;

[0056] S2: dissolving the thermal initiator prepared above in ethyl acetate solvent, heating to 80-85°C, and simultaneously adding acrylic acid monomer to initiate polymerization reaction;

[0057] S3: Cool the mixed copolymer obtained in S2 while stirring, and add acrylic resin to obtain optical adhesive.

[0058] Among them, acrylic resin sample 1: 91 parts of butyl acrylate, 3 parts of acrylic acid, and 6 parts of hydroxyethyl acrylate are taken by mass, and a mixture of ultraviolet lamp with a wavelength of 365nm and low-pressure mercury lamp with a wavelength of 300nm is irradiated to initiate polymerization. The reaction is stopped when the viscosity of the reaction system reaches a viscosity of 3500mPa.s.

[0059] Acrylic resin sample 2: Take 91 parts of isooctyl acrylate, 3 parts of acrylic acid, and 6 parts of hydroxyethyl acrylate, calculated by mass, and irradiate them with a mixture of a UV lamp with a wavelength of 365nm and a low-pressure mercury lamp with a wavelength of 300nm to initiate polymerization. Stop the reaction when the viscosity of the reaction system reaches 3500mPa.s.

[0060] Preparation method of thermal initiator sample 11: S11: Place polytetrahydrofuran diol (PTMEG) in a reactor protected by N2, heat to 110°C, reduce pressure and distill for dehydration for 2.5 to 3.5 hours, cool and set aside. Take the molar ratio of PTMEG to isophorone diisocyanate (IPDI) as 1:2.1, first dissolve PTMEG in dimethylformamide (DMF) solvent and heat to 60°C to fully dissolve; in another reaction vessel protected by N2, heat IPDI to 60°C, then add PTMEG dissolved in DMF solvent at a rate of 1.5 drops / 1s to react with IPDI, and after the addition is completed, stir and react for 1.5 hours to obtain a polyurethane prepolymer;

[0061] S12: Take the molar ratio of PTMEG and 4,4'-azobis-4-cyanopentanol (ACPA) to be 1:0.55; cool the polyurethane prepolymer to room temperature, add 0.3% of dibutyltin dilaurate (DBTDL) based on the total mass of the polyurethane prepolymer dropwise, and add ACPA dissolved in DMF solvent to the polyurethane prepolymer reactor. Fully react for 36 hours, filter the product, place it in a vacuum oven and dry it at room temperature for later use.

[0062] Preparation method of thermal initiator sample 12: Compared with thermal initiator sample 11, 1,4-butanediol is used instead of polytetrahydrofuran diol, and the other ingredients remain unchanged.

[0063] Combination 1 of acrylic monomers is 92 parts of butyl acrylate, 4 parts of methyl methacrylate and 5 parts of N-vinyl pyrrolidone.

[0064] Combination 2 of acrylic monomers was 92 parts of butyl acrylate and 4 parts of methyl methacrylate, and did not include N-vinyl pyrrolidone.

[0065] The raw materials for preparing optical adhesive are shown in Table 1:

[0066]

[0067] Example 6

[0068] The method for preparing optical adhesive for curved surfaces comprises the following steps:

[0069] S1: Preparation of thermal initiator sample 11;

[0070] S2: Thermal initiator sample 11 was dissolved in ethyl acetate solvent and heated to 82°C. The copolymer mixture was prepared by weight as follows: 91 parts of butyl acrylate, 4 parts of methyl methacrylate, 3 parts of acrylic acid, 6 parts of hydroxyethyl acrylate, and 5 parts of N-vinyl pyrrolidone. The amount of thermal initiator sample 11 added was 0.21% of the total mass of the copolymer mixture.

[0071] Preparation of protective film:

[0072] S111: preparing a TPU substrate;

[0073] S112: adding 0.1% of dibutyltin dilaurate by weight to the optical adhesive prepared above, and then coating the resultant on the surface of the TPU substrate;

[0074] S113: drying and curing to obtain an optical adhesive layer;

[0075] S114: Covering the surface of the optical adhesive layer facing away from the TPU substrate with a PET release film to prepare a protective film.

[0076] The optical adhesives of the embodiment and comparative example were coated on the surface of the TPU substrate and dried and cured to obtain an optical adhesive layer, wherein the thickness of the TPU substrate layer was 50 μm, the thickness of the optical adhesive layer was 20 μm, and the thickness of the PET release film was 50 μm.

[0077] Performance tests of protective film samples prepared in the examples and comparative examples:

[0078] (1) Peel strength: According to the standard GB / T2792-2014, the optical adhesive was made into a standard tape (25 mm * 200 mm), attached to a stainless steel plate wiped clean with alcohol, and pressed back and forth with a 2 kg roller. After being left at room temperature for a period of time, it was tested using a peel strength tester. The measurements were taken more than three times and the average value was calculated.

[0079] (2) Bending resistance: The inner bending radius (R) of the protective film sample is 1.5mm, and the protective film sample is folded in half along the center line. A dynamic bending test of 180° is performed 100,000 to 200,000 times to check whether there are cracks or ruptures in the bent part. The outer bending radius (R) of the protective film sample is 2mm, and the protective film sample is folded in half along the center line. A dynamic bending test of 180° is performed 100,000 to 200,000 times to check whether there are scratches in the bent part and whether there is peeling between layers.

[0080] (3) Light transmittance: WGT-S light transmittance tester.

[0081] (4) Aging resistance: The tape made of optical adhesive was placed in a constant temperature and humidity aging box at 70°C and 95% humidity for 72 hours, and then the peel strength was measured.

[0082] (5) Appearance: Observe the protective film for white spots and bubbles, and for warping after one week. Place the protective film in a constant temperature and humidity aging box at 85°C and 90% humidity, and observe after aging for 72 hours.

[0083] The performance test results of the embodiments and comparative examples are as follows:

[0084]

[0085] Compared with Example 1, in Example 2, polyether diol is not used in the polyurethane prepolymer in the preparation of the thermal initiator, and the bending resistance of the protective film is reduced.

[0086] In Example 3, compared with Example 1, the acrylic monomer does not include N-vinyl pyrrolidone. After the obtained colloid is aged at high temperature and high humidity (85° C.*90%)*72 hours, the protective film shows a warping phenomenon.

[0087] In Example 4, compared with Example 1, under the same conditions of the addition amount of reactants, the addition amount of thermal initiator is increased, the reaction crosslinking density is increased, the texture of the obtained colloid becomes harder, the protective film has slight warping, and the bending resistance is poor.

[0088] The performance of the colloids in Example 5 is similar to that in Example 1, and the texture of the protective film in Example 1 is softer.

[0089] In Example 6, premature curing occurred during the preparation of the optical adhesive, and the cross-linking density was too high, resulting in a decrease in bonding strength. Bubbles and white spots appeared on the resulting protective film, and the texture of the colloid became hard, with obvious warping.

[0090] Compared with Example 1, the thermal initiator in Comparative Example 1 and Comparative Example 2 was not modified, and the resulting colloid had poor bending resistance.

[0091] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. An optical adhesive for curved surfaces, characterized in that: The raw materials for preparing the optical adhesive include acrylic resin, thermal initiator, acrylic monomer and solvent; in parts by mass, the raw materials for preparing the acrylic resin include: 85-95 parts of soft monomer, which is butyl acrylate and / or isooctyl acrylate; 5-15 parts of functional monomer, which is acrylic acid and / or hydroxyethyl acrylate; 0.5~1 part of photoinitiator; The thermal initiator is a polyurethane macromolecular modified azo initiator, and the thermal initiator is an isocyanate-terminated initiator; The acrylic monomer includes one or more of butyl acrylate, isooctyl acrylate, methyl methacrylate, isooctyl methacrylate, acryloylmorpholine and N-vinyl pyrrolidone.

2. The optical adhesive for curved surfaces according to claim 1, wherein: The raw materials for preparing the optical adhesive include, by mass, 100 parts of acrylic resin, 0.2-1 parts of thermal initiator, 85-95 parts of acrylic monomer and 200-320 parts of solvent.

3. The optical adhesive for curved surfaces according to claim 1 or 2, wherein: The thermal initiator is a polyurethane molecule-modified azo initiator; the polyurethane molecule-modified azo initiator is prepared by reacting with 4,4'-azobis(4-cyanopentanol) under the action of a polyurethane prepolymer catalyst; the polyurethane prepolymer is prepared by polymerizing a polyol and a polyisocyanate; the molar ratio of the polyol to the polyisocyanate to the 4,4'-azobis(4-cyanopentanol) is 1:(2-2.25):(0.5-0.7).

4. The optical adhesive for curved surfaces according to claim 1 or 2, wherein: Calculated by weight, the acrylic monomer includes 90-95 parts of butyl acrylate, 3-5 parts of methyl methacrylate and 3-5 parts of N-vinyl pyrrolidone.

5. The optical adhesive for curved surfaces according to claim 1 or 2, characterized in that: The solvent is ethyl acetate.

6. The optical adhesive for curved surfaces according to claim 3, wherein: The polyol is a polyether diol.

7. The optical adhesive for curved surfaces according to claim 3, wherein: The polyisocyanate is an aliphatic diisocyanate.

8. The optical adhesive for curved surfaces according to claim 1 or 2, characterized in that: The photoinitiator is one or more of 2-hydroxy-2-methyl-1-phenyl-1-propanone, (2,4,6-trimethylbenzoyl)diphenylphosphine oxide and 1-hydroxycyclohexylphenyl ketone.

9. A method for preparing an optical adhesive for curved surfaces, characterized in that: The optical adhesive for curved surfaces according to any one of claims 1 to 8 comprises the following steps: S1: Preparation of acrylic resin; S2: The thermal initiator is dissolved in a solvent, the temperature is increased, and acrylic acid monomer is added to cause a polymerization reaction; S3: Cooling the mixed copolymer obtained in S2 under stirring, and adding the acrylic resin to obtain an optical adhesive.

10. The method for preparing an optical adhesive for curved surfaces according to claim 9, wherein: The temperature of the S2 is raised to 80-85°C.

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