Preparation method of flexible, strong waterproof and high temperature resistant OCA optical adhesive and OCA optical adhesive film

Abstract

The application provides a preparation method of flexible, strong waterproof and high-temperature-resistant OCA optical adhesive and an OCA optical adhesive film, and relates to the technical field of adhesives.The polyurethane acrylate prepolymer and the double bond-terminated polydimethylsiloxane prepolymer are first synthesized, and then the two are blended with a heat-resistant functional acrylate monomer mixture to obtain the OCA optical adhesive.The preparation method is simple and easy to control, and the situation that the reaction activity is too high to cause easy gelation during the reaction of the binary amine chain extender does not occur, and the OCA optical adhesive can be cured at medium temperature.The OCA optical adhesive prepared by the application has high waterproofness and stability at high temperature, and has high transmittance, good flexibility and mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, specifically to a method for preparing a flexible, highly waterproof, and high-temperature resistant OCA optical adhesive and an OCA optical adhesive film. Background Technology

[0002] With the development of smartphones, touchscreens, as an input device, have enormous potential for growth. A typical touchscreen display mainly consists of a protective screen (glass / plastic), a touchscreen (glass / plastic with an indium tin oxide (ITO) semiconductor transparent conductive film pattern), and a display screen (liquid crystal display / active-matrix organic light-emitting diode display (LCD / AM-OLED)). To improve the optical effect, touch sensitivity, and mechanical reliability of the display, these three parts need to be filled and bonded (commonly known as lamination). Lamination between screens can be divided into frame lamination and full lamination. Frame lamination suffers from poor performance due to air gaps between the screens, causing light refraction and affecting the user's viewing experience. Full lamination uses OCA or liquid optical adhesive to seamlessly bond the screens together, significantly improving the visual effect.

[0003] OCA optical adhesives typically require high light transmittance, a curing refractive index similar to the screen, low modulus, low shrinkage, easily obtainable curing process conditions, and high reliability in harsh environments. UV curing requires external ultraviolet light irradiation for curing. However, since touch panels or other devices have opaque edges, ultraviolet light cannot penetrate for curing, thus affecting product performance. Thermal curing, on the other hand, is not subject to this limitation; it can be cured simply by heating, and the temperature does not need to be too high.

[0004] Chinese patent CN201110211090.5 discloses a liquid optically transparent adhesive composition and its use. After curing, the liquid optically transparent adhesive has sufficient softness to reduce the stress introduced between the adhesive and the bonded substrate, thereby maintaining a good and stable bond between the substrates. The cured adhesive composition has good optical transparency and can be used to bond various substrates. However, this patent does not have the high temperature resistance and water resistance of optically transparent adhesives.

[0005] Chinese patent CN202110357881.2 discloses an OCA adhesive with high light transmittance, low storage modulus, and self-healing function, and its preparation method. This OCA optical adhesive contains dynamically cross-linkable disulfide bonds and polymer segments with low storage modulus. It uses a polyether diol with poor crystallinity and a benzene ring-free diisocyanate to synthesize polyurethane acrylate, thereby giving the prepared OCA optical adhesive high transmittance and low storage modulus, thus improving its bending resistance. The introduction of dynamic disulfide bonds into the polyurethane acrylate molecular chain endows the OCA optical adhesive with self-healing function under certain conditions, improving its bending resistance. However, this patent does not mention the stability and water resistance of the OCA optical adhesive under high-temperature conditions. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a flexible, highly waterproof, and high-temperature resistant OCA optical adhesive and an OCA optical adhesive film. The OCA optical adhesive prepared by this invention has high waterproofness and high-temperature stability, as well as high transmittance, good flexibility, and mechanical properties.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] This invention provides a method for preparing a flexible, highly waterproof, and high-temperature resistant OCA optical adhesive, comprising the following steps:

[0009] Under a protective atmosphere, polyester polyol, diisocyanate and a first catalyst are mixed and subjected to a first polyaddition reaction to obtain a prepolymer; the prepolymer is then mixed with hydroxyl acrylate and subjected to a second polyaddition reaction to obtain a polyurethane acrylate prepolymer.

[0010] Under a protective atmosphere, hydroxyl polydimethylsiloxane, modified isocyanate, and a second catalyst are mixed and subjected to a third polyaddition reaction to obtain a double-bond-terminated polydimethylsiloxane prepolymer.

[0011] The polyurethane acrylate prepolymer, the double-bond-terminated polydimethylsiloxane prepolymer, a mixture of heat-resistant functional acrylate monomers, and a first solvent are mixed to obtain a mixture; the heat-resistant functional acrylate monomer mixture includes (meth)acrylate alkyl esters, (meth)acrylate hydroxyalkyl esters, and heat-resistant monomers.

[0012] The mixture is combined with the remaining heat-resistant functional acrylate monomer mixture, thermal initiator and second solvent, and then subjected to polymerization to obtain OCA optical adhesive.

[0013] Preferably, the polyester polyol includes one or more of polyester diol, polycaprolactone diol, and polycarbonate diol;

[0014] The diisocyanate includes one or more of toluene diisocyanate, diphenylmethane diisocyanate, 1,6-hexanediisocyanate and isophorone diisocyanate;

[0015] The hydroxy acrylate includes one of hydroxyethyl methacrylate, hydroxypropyl acrylate, and 2-hydroxyethyl acrylate.

[0016] Preferably, the temperature of the first polyaddition reaction is 80–90°C; and the time of the first polyaddition reaction is 2–6 hours.

[0017] Preferably, the temperature of the second polymerization reaction is 50–60°C; and the time of the second polymerization reaction is 1–3 hours.

[0018] Preferably, the molecular weight of the hydroxyl polydimethylsiloxane is 750-950;

[0019] The modified isocyanate includes one of vinyl isocyanate, ethyl isocyanate methacrylate, and ethyl isocyanate acrylate.

[0020] Preferably, the third polymerization reaction is carried out at room temperature; the time of the third polymerization reaction is 2 to 6 hours.

[0021] Preferably, the mass ratio of (meth)acrylate alkyl ester, (meth)acrylate hydroxyalkyl ester and heat-resistant monomer in the heat-resistant functional acrylate monomer mixture is 2-8:2-8:11.

[0022] Preferably, the alkyl methacrylate includes one or more of methyl methacrylate, acrylate, ethyl acrylate, butyl acrylate, isoamyl acrylate, tert-butyl acrylate, and isooctyl acrylate;

[0023] The (meth)acrylate hydroxyalkyl ester includes one or two of hydroxypropyl acrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, and hydroxypropyl methacrylate;

[0024] The heat-resistant monomers include one or more of maleimide, N-vinylpyrrolidone, and N-vinylcarbazole.

[0025] Preferably, the polymerization reaction temperature is 45–80°C; the polymerization reaction time is 2–6 hours.

[0026] This invention provides an OCA optical adhesive film, which is formed by thermally curing the OCA optical adhesive prepared by the preparation method described above.

[0027] This invention provides a method for preparing a flexible, highly waterproof, and high-temperature resistant OCA optical adhesive. In this invention, the polyurethane acrylate prepolymer has low crystallinity, which can improve the flexibility of the adhesive film; the double-bond-terminated polydimethylsiloxane prepolymer contains hydrophobic flexible segments, which can greatly improve the waterproofness of the OCA optical adhesive. This invention first synthesizes the polyurethane acrylate prepolymer and the double-bond-terminated polydimethylsiloxane prepolymer, and then blends the two with a mixture of heat-resistant functional acrylate monomers to obtain the OCA optical adhesive. The preparation method of this invention is simple, easy to control, and avoids the situation of excessively high reactivity leading to easy gelation, such as in the reaction of diamine chain extenders. It can be cured at a medium temperature (temperature range of 60-80℃).

[0028] The OCA optical adhesive prepared by this invention combines the characteristics of polyurethane, acrylate, and polydimethylsiloxane in terms of molecular structure and properties, such as good flexibility and excellent adhesion. The introduction of heat-resistant monomers enhances the heat resistance of the OCA optical adhesive, leaving no residue at high temperatures and exhibiting good stability at high temperatures, making it suitable for extreme hot environments. Polyester polyol and polydimethylsiloxane, as soft segments, enhance the flexibility of the OCA optical adhesive. The complete reaction of NCO groups in the system, along with the introduction of polydimethylsiloxane, reduces sensitivity to moisture in the air.

[0029] The OCA optical adhesive obtained by this invention exhibits good flexural strength, strong water resistance, long holding time at high temperatures, and leaves no residue even at high temperatures, thus extending the service life of the OCA optical adhesive. The results of the examples show that the OCA optical adhesive prepared by this invention has high transmittance, good flexibility, high water resistance, and high-temperature stability. It has low initial tack (only for a #2 ball), holding power exceeding 240 hours, and high 180° peel strength. Detailed Implementation

[0030] This invention provides a method for preparing a flexible, highly waterproof, and high-temperature resistant OCA optical adhesive, comprising the following steps:

[0031] Under a protective atmosphere, polyester polyol, diisocyanate and a first catalyst are mixed and subjected to a first polyaddition reaction to obtain a prepolymer; the prepolymer is then mixed with hydroxyl acrylate and subjected to a second polyaddition reaction to obtain a polyurethane acrylate prepolymer.

[0032] Under a protective atmosphere, hydroxyl polydimethylsiloxane, modified isocyanate, and a second catalyst are mixed and subjected to a third polyaddition reaction to obtain a double-bond-terminated polydimethylsiloxane prepolymer.

[0033] The polyurethane acrylate prepolymer, the double-bond-terminated polydimethylsiloxane prepolymer, a mixture of heat-resistant functional acrylate monomers, and a solvent are mixed to obtain a mixture; the heat-resistant functional acrylate monomer mixture includes (meth)acrylate alkyl esters, (meth)acrylate hydroxyalkyl esters, and heat-resistant monomers.

[0034] The mixture is combined with the remaining heat-resistant functional acrylate monomer mixture and subjected to a polymerization reaction to obtain OCA optical adhesive.

[0035] This invention involves mixing a polyester polyol, a diisocyanate, and a first catalyst under a protective atmosphere to undergo a first polyaddition reaction, yielding a prepolymer. In this invention, the polyester polyol preferably comprises one or more of polyester diol, polycaprolactone diol, and polycarbonate diol; the average molecular weight of the polyester polyol is preferably 1000–4000. In this invention, the diisocyanate preferably comprises one or more of toluene diisocyanate, diphenylmethane diisocyanate, 1,6-hexamethylene diisocyanate, and isophorone diisocyanate. In this invention, the first catalyst preferably comprises one or more of stannous octoate, dimethyltin dilaurate, dibutyltin dilaurate, and ethylenediamine. In this invention, the molar ratio of the hydroxyl groups of the polyester polyol to the NCO groups of the diisocyanate is preferably 1.5:1. In this invention, the amount of the first catalyst is preferably 0.01–0.05 wt% of the polyester polyol.

[0036] In this invention, the protective atmosphere is preferably a nitrogen atmosphere, and the present invention uses a protective atmosphere to isolate air.

[0037] In this invention, the preferred temperature for the first polyaddition reaction is 80–90°C; the preferred time for the first polyaddition reaction is 2–6 hours. Preferably, during the first polyaddition reaction, the content of NCO groups in the reaction system is determined by titration every 30 minutes. When the content of NCO groups in the reaction reaches the theoretical design value, the resulting system is cooled to 50–60°C to obtain the prepolymer.

[0038] After obtaining the prepolymer, the present invention mixes the prepolymer with a hydroxyl acrylate and performs a second polyaddition reaction to obtain a polyurethane acrylate prepolymer. In the present invention, the hydroxyl acrylate preferably includes one of hydroxyethyl methacrylate, hydroxypropyl acrylate, and 2-hydroxyethyl acrylate. In the present invention, the molar ratio of the hydroxyl groups of the hydroxyl acrylate to the NCO groups of the diisocyanate is preferably 1:1. In the present invention, the hydroxyl acrylate is used as a capping agent.

[0039] In this invention, the temperature of the second polyaddition reaction is preferably 50–60°C; the time of the second polyaddition reaction is preferably 1–3 hours, more preferably 2 hours. In a specific embodiment of this invention, the reaction is preferably terminated when the NCO groups have completely reacted. Preferably, during the second polyaddition reaction, the content of NCO groups in the reaction system is determined by titration every 30 minutes.

[0040] In this invention, after the second polyaddition reaction, the resulting product is cooled to room temperature to obtain a polyurethane acrylate prepolymer.

[0041] This invention involves mixing hydroxyl polydimethylsiloxane, modified isocyanate, and a second catalyst under a protective atmosphere to undergo a third polyaddition reaction, yielding a double-bond-terminated polydimethylsiloxane prepolymer. In this invention, the molecular weight of the hydroxyl polydimethylsiloxane is preferably 750-950, specifically preferably one or two of 750, 850, and 950. In this invention, the hydroxyl polydimethylsiloxane is preferably dehydrated before mixing. In this invention, the dehydration treatment preferably includes sequential vacuum dehydration and molecular sieve dehydration; the vacuum dehydration is preferably carried out in an oil bath; the temperature of the vacuum dehydration is preferably 10°C higher than the boiling point of the hydroxyl polydimethylsiloxane; the vacuum dehydration time is preferably 70 min; the molecular sieve dehydration temperature is preferably room temperature; and the molecular sieve dehydration time is preferably 12 h.

[0042] In this invention, the modified isocyanate preferably comprises one of vinyl isocyanate, vinyl isocyanate, ethyl isocyanate methacrylate, and ethyl isocyanate acrylate. In this invention, the second catalyst preferably comprises one or more of stannous octoate, dimethyltin dilaurate, dibutyltin dilaurate, and ethylenediamine. In this invention, the molar ratio of the hydroxyl groups of the hydroxyl polydimethylsiloxane to the NCO groups of the modified isocyanate is preferably 1:1. In this invention, the amount of the second catalyst is preferably 0.01–0.05 wt% of the hydroxyl polydimethylsiloxane.

[0043] In this invention, the protective atmosphere is preferably a nitrogen atmosphere.

[0044] In this invention, the third polyaddition reaction is preferably carried out at room temperature; the duration of the third polyaddition reaction is preferably 2–6 hours, more preferably 3–4 hours. Preferably, during the third polyaddition reaction, the content of NCO groups in the reaction system is determined by titration every 30 minutes.

[0045] After obtaining the polyurethane acrylate prepolymer and the double-bond-terminated polydimethylsiloxane prepolymer, the present invention mixes the polyurethane acrylate prepolymer, the double-bond-terminated polydimethylsiloxane prepolymer, a portion of the heat-resistant functional acrylate monomer mixture, and a first solvent to obtain a mixture. In the present invention, the heat-resistant functional acrylate monomer mixture includes (meth)acrylate alkyl esters, (meth)acrylate hydroxyalkyl esters, and heat-resistant monomers. In the present invention, the preferred mass ratio of (meth)acrylate alkyl esters, (meth)acrylate hydroxyalkyl esters, and heat-resistant monomers in the heat-resistant functional acrylate monomer mixture is 2–8:2–8:11, more preferably 6:6:1. In this invention, the alkyl (meth)acrylate preferably includes one or more of methyl methacrylate, acrylate, ethyl acrylate, butyl acrylate, isoamyl acrylate, tert-butyl acrylate, and isooctyl acrylate; the hydroxyalkyl (meth)acrylate preferably includes one or two of hydroxypropyl acrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, and hydroxypropyl methacrylate; and the heat-resistant monomer preferably includes one or more of maleimide, N-vinylpyrrolidone, and N-vinylcarbazole.

[0046] In this invention, the mass ratio of the polyurethane acrylate prepolymer, the double-bond-terminated polydimethylsiloxane prepolymer, and the mixture of some heat-resistant functional acrylate monomers is preferably 12:8:1 to 3, and more preferably 12:8:2.

[0047] In this invention, the first solvent is preferably ethyl acetate, chloroform, toluene, isobutanol, or acetone. In this invention, the mass of the first solvent is preferably 10-30% of the total mass of the polyurethane acrylate prepolymer, the double-bond-terminated polydimethylsiloxane prepolymer, and a portion of the heat-resistant functional acrylate monomer mixture, more preferably 18%.

[0048] After obtaining the mixture, the present invention mixes the mixture with the remaining heat-resistant functional acrylate monomer mixture, a thermal initiator, and a second solvent, and carries out a polymerization reaction to obtain OCA optical adhesive. In the present invention, the mass ratio of the partial heat-resistant functional acrylate monomer mixture to the remaining heat-resistant functional acrylate monomer mixture is preferably 1:2 to 7, more preferably 1:4. The stepwise addition of the heat-resistant functional acrylate monomer mixture in the present invention can further improve the heat resistance of the OCA film.

[0049] In this invention, the thermal initiator is preferably one of azobisisobutyronitrile, azobisisoheptanenitrile, ammonium persulfate, di-tert-butyl peroxide, and benzoyl peroxide. In this invention, the mass of the thermal initiator is preferably 0.2-2% of the mass of the heat-resistant functional acrylate monomer mixture, more preferably 0.26-1%.

[0050] In this invention, the second solvent is preferably ethyl acetate, chloroform, toluene, isobutanol, or acetone. In this invention, the mass of the second solvent is preferably 5000-8000% of the mass of the thermal initiator, more preferably 7500%.

[0051] In this invention, the mixing of the mixture, the remaining heat-resistant functional acrylate monomer mixture, the thermal initiator, and the second solvent preferably comprises: dissolving the remaining heat-resistant functional acrylate monomer mixture and the thermal initiator in the second solvent to obtain a mixed solution; and adding the mixed solution dropwise to the mixture. In this invention, the dropping rate is preferably 1 drop / 2 s. Preferably, the mixture is heated to the polymerization reaction temperature before the mixed solution is added dropwise.

[0052] In this invention, the polymerization reaction temperature is preferably 45–80°C, more preferably 60–70°C; the polymerization reaction time is preferably 2–6 hours, more preferably 3–4 hours. In this invention, the polymerization reaction time is started from the point when all materials have been added.

[0053] Preferably, after the polymerization reaction, the resulting system is cooled to room temperature to obtain OCA optical adhesive.

[0054] The OCA optical adhesive prepared by this invention has the characteristics of low initial tack, high holding power, anti-aging properties, and high transparency. The OCA optical adhesive prepared by this invention has a transmittance greater than 94%, a contact angle greater than 100°, excellent thermal stability (no residue appears even at 50°C), an initial tack of only 2# ball, a holding power greater than 240h, a 180° peel strength greater than 12N / 25mm, and a yellowing index between 5.5 and 7.

[0055] This invention also provides an OCA optical adhesive film, which is formed by thermal curing of the OCA optical adhesive prepared by the preparation method described above. In this invention, the thickness of the OCA optical adhesive film is preferably 200 μm. In this invention, the thermal curing is preferably carried out in a vacuum drying oven; the thermal curing temperature is preferably 60–80°C, more preferably 60°C; and the thermal curing time is preferably 10–30 min, more preferably 15 min.

[0056] In a specific embodiment of the present invention, the preparation method of the OCA optical adhesive film includes: coating the OCA optical adhesive onto a release film, then covering it with another release film to form a BAB-type adhesive film, wherein B refers to the release film and A refers to the OCA optical adhesive; then performing heat curing; and finally removing the release film to obtain the OCA optical adhesive film. Preferably, the present invention uses an applicator to coat the OCA optical adhesive onto the release film.

[0057] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0058] In the examples, PCDL is polycarbonate diol, PCDL1000 refers to PCDL with a molecular weight of 1000, PCDL2000 refers to PCDL with a molecular weight of 2000, IPDI is isophorone diisocyanate, DBTL is dibutyltin dilaurate, HEMA is hydroxyethyl methacrylate, HO-PDMS-OH is hydroxyl polydimethylsiloxane, HO-PDMS-OH750 refers to hydroxyl polydimethylsiloxane with a molecular weight of 750, HO-PDMS-OH850 refers to hydroxyl polydimethylsiloxane with a molecular weight of 850, MOI is isocyanate methacrylate, BA is butyl acrylate, 2-HEA is hydroxyethyl acrylate, MMA is methyl methacrylate, AA is acrylate, MAL is maleimide, NVP is N-vinylpyrrolidone, NVA is N-vinylcarbazole, EA is ethyl acetate, AIBN is azobisisobutyronitrile, and PPG is polypropylene glycol.

[0059] Example 1

[0060] 1) Preparation of polyurethane acrylate prepolymer

[0061] According to the proportions in Table 1, 100g of PCDL1000 was added to a four-necked flask equipped with a stirrer. The mixture was heated to 120°C in an oil bath and dehydrated under vacuum for 2 hours until no more bubbles were generated. The temperature was then lowered to 80°C, and 33.34g of IPDI and 0.1g of catalyst DBTL were added. Nitrogen gas was introduced into the flask to isolate it from air, and the reaction was allowed to proceed for 4 hours. During this period, samples were taken every 30 minutes to measure the NCO content in the reaction system until the NCO content reached the theoretical value. The temperature was then lowered to 60°C, and 13.01g of end-capping agent HEMA was added to the flask. The reaction was continued for 1 hour, with samples taken every 30 minutes to measure the NCO content in the reaction system until the NCO content was completely reduced. The reaction was then stopped, and the mixture was cooled to obtain polyurethane acrylate prepolymer (PUA), which was then sealed and stored.

[0062] 2) Preparation of double-bond-terminated polydimethylsiloxane prepolymers

[0063] According to the proportions in Table 1, 75g of HO-PDMS-OH dehydrated with molecular sieve was added to a four-necked flask, and then MOI dehydrated with molecular sieve was added dropwise to the flask. After stirring for 10 minutes to mix the two evenly, one drop of catalyst DBTL was added to the flask and the reaction was carried out for 4 hours. During this period, the NCO content in the reaction system was measured every 30 minutes until the NCO content in the system was completely reacted, and double bond-terminated polydimethylsiloxane prepolymer (V-PDMS) was obtained.

[0064] 3) Preparation of flexible, highly waterproof and high-temperature resistant OCA optical adhesive

[0065] According to the proportions in Table 1, before the reaction, BA, 2-HEA, MMA, AA, and MAL were vacuum dehydrated for 70 min at a temperature 10°C higher than their respective boiling points, and then dehydrated by molecular sieve adsorption for 12 h. The molecular sieve was then removed and set aside. 60 g of PUA prepared in step 1) was poured into a four-necked flask, and 40 g of V-PDMS prepared in step 2) was added to the four-necked flask. The mixture was stirred for 10 min to ensure homogeneity. 15 g of BA, 15 g of 2-HEA, 15 g of MMA, 2.5 g of AA, and 2.5 g of MAL were weighed and mixed thoroughly to obtain a heat-resistant functional acrylate monomer mixture. 1 / 5 of the heat-resistant functional acrylate monomer mixture was dissolved in 20 g of EA and added to the four-necked flask. The four-necked flask was then placed in an oil bath and heated. During the heating process, 0.4 g of AIBN was weighed and dissolved in 30 g of EA. The remaining heat-resistant functional acrylate monomer mixture was then added and mixed thoroughly. The resulting solution was transferred to a dropping funnel. Once the oil bath temperature reached 70°C, the dropping rate was adjusted to 1 drop / 2 s, and the solution was added dropwise to the four-necked flask. After the addition of the solution was complete, the reaction continued for 4 hours, followed by cooling to room temperature to obtain OCA optical adhesive.

[0066] Table 1 Raw material formula for Example 1

[0067]

[0068] Example 2

[0069] 1) Preparation of polyurethane acrylate prepolymer

[0070] According to the proportions in Table 2, 100g of PCDL was added to a four-necked flask equipped with a stirrer. The mixture was heated to 120°C in an oil bath and dehydrated under vacuum for 2 hours until no more bubbles were generated. The temperature was then lowered to 80°C, and 22.29g of IPDI and 0.1g of catalyst DBTL were added. Nitrogen gas was introduced into the flask to isolate it from air, and the reaction was allowed to proceed for 4 hours. During this period, samples were taken every 30 minutes to measure the NCO content in the reaction system until the NCO content reached the theoretical value. The temperature was then lowered to 60°C, and 13.01g of end-capping agent HEMA was added to the flask. The reaction was continued for 1 hour, and samples were taken every 30 minutes to measure the NCO content in the reaction system until the NCO content was completely reduced. The reaction was then stopped, and the mixture was cooled to obtain polyurethane acrylate prepolymer (PUA), which was then sealed and stored.

[0071] 2) Preparation of double-bond-terminated polydimethylsiloxane prepolymers

[0072] According to the proportions in Table 2, 75g of HO-PDMS-OH dehydrated with molecular sieve was added to a four-necked flask, and then MOI dehydrated with molecular sieve was added dropwise to the flask. After stirring for 10 minutes to mix the two evenly, one drop of catalyst DBTL was added to the flask and the reaction was carried out for 4 hours. During this period, the NCO content in the reaction system was measured every 30 minutes until the NCO content in the system was completely reacted, and double-bond-terminated polydimethylsiloxane prepolymer (V-PDMS) was obtained.

[0073] 3) Preparation of flexible, highly waterproof and high-temperature resistant OCA optical adhesive

[0074] According to the proportions in Table 2, before the reaction, BA, 2-HEA, MMA, AA, and MAL were vacuum dehydrated for 70 min at a temperature 10°C higher than their respective boiling points, and then dehydrated by molecular sieve adsorption for 12 h. The molecular sieve was then removed and set aside. 60 g of PUA prepared in step 1) was poured into a four-necked flask, and 40 g of V-PDMS prepared in step 2) was added to the four-necked flask. The mixture was stirred for 10 min to ensure homogeneity. 15 g of BA, 15 g of 2-HEA, 15 g of MMA, 2.5 g of AA, and 5 g of MAL were weighed and mixed thoroughly to obtain a heat-resistant functional acrylate monomer mixture. 1 / 5 of the heat-resistant functional acrylate monomer mixture was dissolved in 20 g of EA and added to the four-necked flask. The four-necked flask was then placed in an oil bath and heated. During the heating process, 0.4 g of AIBN was weighed and dissolved in 30 g of EA. The remaining heat-resistant functional acrylate monomer mixture was then added and mixed thoroughly. The resulting solution was transferred to a dropping funnel. Once the oil bath temperature reached 70°C, the dropping rate was adjusted to 1 drop / 2 s, and the solution was added dropwise to the four-necked flask. After the addition of the solution was complete, the reaction continued for 4 hours, followed by cooling to room temperature to obtain OCA optical adhesive.

[0075] Table 2 Raw material formula for Example 2

[0076]

[0077] Example 3

[0078] 1) Preparation of polyurethane acrylate prepolymer

[0079] According to the proportions in Table 3, 75g of PCDL1000 and 50g of PCDL2000 were mixed evenly and added to a four-necked flask equipped with a stirrer. The mixture was heated to 120°C in an oil bath and dehydrated under vacuum for 2 hours until no more bubbles were generated in the flask. The temperature was then lowered to 80°C, and 33.34g of IPDI and 0.125g of catalyst DBTL were added to the flask. Nitrogen gas was introduced into the flask to isolate it from air, and the reaction was allowed to proceed for 4 hours. During this period, samples were taken every 30 minutes to measure the NCO content in the reaction system until the NCO content reached the theoretical value. The temperature was then lowered to 60°C, and 13.01g of end-capping agent HEMA was added to the flask. The reaction was continued for 1 hour, and samples were taken every 30 minutes to measure the NCO content in the reaction system until the NCO content was completely reduced. The reaction was then stopped, and the mixture was cooled to obtain polyurethane acrylate prepolymer (PUA), which was then sealed and stored.

[0080] 2) Preparation of double-bond-terminated polydimethylsiloxane prepolymers

[0081] According to the proportions in Table 3, 85g of HO-PDMS-OH dehydrated with molecular sieve was added to a four-necked flask, and then MOI dehydrated with molecular sieve was added dropwise to the flask. After stirring for 10 minutes to mix the two evenly, one drop of catalyst DBTL was added to the flask and the reaction was carried out for 4 hours. During this period, the NCO content in the reaction system was measured every 30 minutes until the NCO content in the system was completely reacted, and double-bond-terminated polydimethylsiloxane prepolymer (V-PDMS) was obtained.

[0082] 3) Preparation of flexible, highly waterproof and high-temperature resistant OCA optical adhesive

[0083] According to the proportions in Table 3, before the reaction, BA, 2-HEA, MMA, AA, and NVP were vacuum dehydrated for 70 min at a temperature 10°C higher than their respective boiling points, and then dehydrated by molecular sieve adsorption for 12 h. The molecular sieve was then removed and set aside. 60 g of PUA prepared in step 1) was poured into a four-necked flask, and 40 g of V-PDMS prepared in step 2) was added to the four-necked flask. The mixture was stirred for 10 min to ensure homogeneity. 15 g of BA, 15 g of 2-HEA, 15 g of MMA, 2.5 g of AA, and 2.5 g of NVP were weighed and mixed thoroughly to obtain a heat-resistant functional acrylate monomer mixture. 1 / 5 of the heat-resistant functional acrylate monomer mixture was dissolved in 20 g of EA and added to the four-necked flask. The four-necked flask was then placed in an oil bath and heated. During the heating process, 0.4 g of AIBN was weighed and dissolved in 30 g of EA. The remaining heat-resistant functional acrylate monomer mixture was then added and mixed thoroughly. The resulting solution was transferred to a dropping funnel. Once the oil bath temperature reached 70°C, the dropping rate was adjusted to 1 drop / 2 s, and the solution was added dropwise to the four-necked flask. After the addition of the solution was complete, the reaction continued for 4 hours, followed by cooling to room temperature to obtain OCA optical adhesive.

[0084] Table 3 Raw material formula for Example 3

[0085]

[0086] Example 4

[0087] 1) Preparation of polyurethane acrylate prepolymer

[0088] According to the proportions in Table 4, 50g of PCDL1000 and 100g of PCDL2000 were mixed evenly and added to a four-necked flask equipped with a stirrer. The mixture was heated to 120°C in an oil bath and dehydrated under vacuum for 2 hours until no more bubbles were generated in the flask. The temperature was then lowered to 80°C, and 33.34g of IPDI and 0.15g of catalyst DBTL were added to the flask. Nitrogen gas was introduced into the flask to isolate it from air, and the reaction was allowed to proceed for 4 hours. During this period, samples were taken every 30 minutes to measure the NCO content in the reaction system until the NCO content reached the theoretical value. The temperature was then lowered to 60°C, and 13.01g of end-capping agent HEMA was added to the flask. The reaction was continued for 1 hour, and samples were taken every 30 minutes to measure the NCO content in the reaction system until the NCO content was completely reduced. The reaction was then stopped, and the mixture was cooled to obtain polyurethane acrylate prepolymer (PUA), which was then sealed and stored.

[0089] 2) Preparation of double-bond-terminated polydimethylsiloxane prepolymers

[0090] According to the proportions in Table 4, 75g of HO-PDMS-OH dehydrated with molecular sieve was added to a four-necked flask, and then MOI dehydrated with molecular sieve was added dropwise to the flask. After stirring for 10 minutes to mix the two evenly, one drop of catalyst DBTL was added to the flask and the reaction was carried out for 4 hours. During this period, the NCO content in the reaction system was measured every 30 minutes until the NCO content in the system was completely reacted, and double bond-terminated polydimethylsiloxane prepolymer (V-PDMS) was obtained.

[0091] 3) Preparation of flexible, highly waterproof and high-temperature resistant OCA optical adhesive

[0092] According to the proportions in Table 4, before the reaction, BA, 2-HEA, MMA, AA, and NVA were vacuum dehydrated for 70 minutes at a temperature 10°C higher than their respective boiling points, and then dehydrated by molecular sieve adsorption for 12 hours. The molecular sieve was then removed and set aside. 60g of PUA prepared in step 1) was poured into a four-necked flask, and 40g of V-PDMS prepared in step 2) was added to the four-necked flask. The mixture was stirred for 10 minutes to ensure homogeneity. 15g of BA, 15g of 2-HEA, 15g of MMA, 2.5g of AA, and 2.5g of NVA were weighed and mixed thoroughly to obtain a heat-resistant functional acrylate monomer mixture. 1 / 5 of the heat-resistant functional acrylate monomer mixture was dissolved in 20g of EA and added to the four-necked flask. The four-necked flask was then placed in an oil bath and heated. During the heating process, 0.4 g of AIBN was weighed and dissolved in 30 g of EA. The remaining heat-resistant functional acrylate monomer mixture was then added and mixed thoroughly. The resulting solution was transferred to a dropping funnel. Once the oil bath temperature reached 70°C, the dropping rate was adjusted to 1 drop / 2 s, and the solution was added dropwise to the four-necked flask. After the addition of the solution was complete, the reaction continued for 4 hours, followed by cooling to room temperature to obtain OCA optical adhesive.

[0093] Table 4 Raw material formula for Example 4

[0094]

[0095] Comparative Example

[0096] 1) Preparation of polyurethane acrylate prepolymer

[0097] According to the proportions in Table 5, 50g of PCDL1000 and 100g of PCDL2000 were mixed evenly and added to a four-necked flask equipped with a stirrer. The mixture was heated to 120°C in an oil bath and dehydrated under vacuum for 2 hours until no more bubbles were generated in the flask. The temperature was then lowered to 80°C, and 33.34g of IPDI and 0.15g of catalyst DBTL were added to the flask. Nitrogen gas was introduced into the flask to isolate it from air, and the reaction was allowed to proceed for 4 hours. During this period, samples were taken every 30 minutes to measure the NCO content in the reaction system until the NCO content reached the theoretical value. The temperature was then lowered to 60°C, and 13.01g of end-capping agent HEMA was added to the flask. The reaction was continued for 1 hour, and samples were taken every 30 minutes to measure the NCO content in the reaction system until the NCO content was completely reduced. The reaction was then stopped, and the mixture was cooled to obtain polyurethane acrylate prepolymer (PUA), which was then sealed and stored.

[0098] 2) Preparation of OCA optical adhesive

[0099] According to the proportions in Table 5, before the reaction, BA, 2-HEA, MMA, AA, and NVA were vacuum dehydrated for 70 min at a temperature 10°C higher than their respective boiling points, and then dehydrated by molecular sieve adsorption for 12 h. The molecular sieve was then removed and set aside. 60 g of PUA prepared in step 1) was poured into a four-necked flask and stirred for 10 min. 15 g of BA, 15 g of 2-HEA, 15 g of MMA, 2.5 g of AA, and 2.5 g of NVA were weighed and mixed thoroughly to obtain a heat-resistant functional acrylate monomer mixture. 1 / 5 of the heat-resistant functional acrylate monomer mixture was dissolved in 20 g of EA and added to the four-necked flask. The four-necked flask was placed in an oil bath and heated. During the heating process, 0.4 g of AIBN was weighed and dissolved in 30 g of EA, and the remaining heat-resistant functional acrylate monomer mixture was added. The mixture was mixed thoroughly, and the resulting solution was transferred to a dropping funnel. After the oil bath temperature reaches 70℃, adjust the dropping rate to a suitable rate (1 drop / 2 s) and begin adding the mixed solution to the four-necked flask. After the mixed solution has been added, continue the reaction for 5 hours, then cool to room temperature to obtain OCA optical adhesive.

[0100] Table 5 Comparative Example Raw Material Formulation

[0101]

[0102] Test case

[0103] The OCA optical adhesive prepared in Examples 1-4 and the comparative example were evenly applied onto the release film using an applicator, and then another release film was placed on top to form a BAB-type adhesive film, where B refers to the release film and A refers to the OCA optical adhesive. The film was then heat-cured in a vacuum drying oven. After removing the release film, the OCA optical adhesive film was obtained. The heat curing temperature was 60°C, and the time was 15 minutes.

[0104] The OCA optical films prepared in Examples 1-4 and the comparative examples were subjected to performance tests, and the test results are shown in Table 6.

[0105] When testing optical properties, transmittance was tested according to GB / T2410-2008 standard, and yellowing index according to GB / T2409-1980 standard. When testing mechanical properties, initial tack was tested according to GB / T4852-2002 standard, holding tack according to GB / T4851-2014 standard, and 180° peel force according to GB / T2790-1995 standard. Contact angle was tested according to standard.

[0106] Table 6 Performance test results of Examples 1-4 and comparative examples.

[0107]

[0108] As can be seen from the test results in Table 6, the transmittance of the OCA optical adhesives prepared in the examples is all above 94%. Therefore, the optical properties of the optical adhesive film prepared by this invention meet the requirements of any current industry. This is mainly due to the selection of polycarbonate diol in the raw materials, which has low crystallinity and reacts with isocyanate to form a transparent viscoelastic, thus improving the transmittance of the optical adhesive to a certain extent.

[0109] The initial tack of the OCA optical adhesives prepared in the examples was not high, and the values ​​were moderate, meeting industry requirements. This is mainly because the ratio of soft to hard monomers in the formulation was moderate, resulting in a moderate degree of polymer crosslinking. At the same time, the OCA optical adhesives prepared in the examples had high holding power, all greater than 240h, meeting industry requirements. According to GB / 2792-2014 standard, the 180° peel force of the adhesive film was measured at 70°C. The peel strength of the samples in the examples was moderate, and there was no residue. Because the adhesive film was sufficiently wetted with the substrate, peeling required greater energy dissipation, ensuring the normal use of the samples at high temperatures.

[0110] The water contact angles of the OCA optical adhesives prepared in the examples are all greater than 100°, which is a significant improvement compared to the comparative examples. This is mainly due to the introduction of polydimethylsiloxane into the OCA optical adhesive, which endows the OCA optical adhesive with a certain degree of water resistance, thus improving upon previous methods.

[0111] The OCA optical adhesives prepared in the examples have very low yellowing indices, all not exceeding 7, and their yellowing resistance is significantly improved compared to the comparative examples.

[0112] After conducting flexibility tests on the OCA optical films prepared in Examples 1-4 and the comparative examples, it was observed that after 100,000 folds, the films did not show any creases or peel off, demonstrating the good flexibility of the films.

[0113] In summary, this invention utilizes low-crystallinity, yellowing-resistant polycarbonate diol isocyanate for reaction, followed by grafting with acrylate to synthesize a polyurethane acrylate prepolymer. Simultaneously, flexible and hydrophobic polydimethylsiloxane and heat-resistant acrylate functional monomers are introduced into the reaction system. The resulting OCA optical adhesive possesses advantages such as high transmittance, good water resistance, stable adhesion at high temperatures, and high resistance to yellowing.

[0114] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a flexible, highly waterproof, and high-temperature resistant OCA optical adhesive, comprising the following steps: Under a protective atmosphere, polyester polyol, diisocyanate and a first catalyst are mixed and subjected to a first polyaddition reaction to obtain a prepolymer; the prepolymer is then mixed with hydroxyl acrylate and subjected to a second polyaddition reaction to obtain a polyurethane acrylate prepolymer. Under a protective atmosphere, hydroxyl polydimethylsiloxane, modified isocyanate, and a second catalyst are mixed and subjected to a third polyaddition reaction to obtain a double-bond-terminated polydimethylsiloxane prepolymer. The polyurethane acrylate prepolymer, the double-bond-terminated polydimethylsiloxane prepolymer, a mixture of heat-resistant functional acrylate monomers, and a first solvent are mixed to obtain a mixture; the heat-resistant functional acrylate monomer mixture includes (meth)acrylate alkyl esters, (meth)acrylate hydroxyalkyl esters, and heat-resistant monomers. The mixture is mixed with the remaining heat-resistant functional acrylate monomer mixture, thermal initiator and second solvent, and a polymerization reaction is carried out to obtain OCA optical adhesive; The modified isocyanate includes one of vinyl isocyanate, ethyl isocyanate methacrylate, and ethyl isocyanate acrylate; The heat-resistant monomers include one or more of maleimide, N-vinylpyrrolidone, and N-vinylcarbazole.

2. The production method according to claim 1, characterized by, The polyester polyol includes one or more of polyester diol, polycaprolactone diol, and polycarbonate diol; The diisocyanate includes one or more of toluene diisocyanate, diphenylmethane diisocyanate, 1,6-hexanediisocyanate and isophorone diisocyanate; The hydroxy acrylate includes one of hydroxyethyl methacrylate, hydroxypropyl acrylate, and 2-hydroxyethyl acrylate.

3. The preparation method according to claim 1 or 2, characterized in that, The temperature of the first polymerization reaction is 80–90°C; the time of the first polymerization reaction is 2–6 h.

4. The preparation method according to claim 1 or 2, characterized in that, The temperature of the second polymerization reaction is 50–60°C; the time of the second polymerization reaction is 1–3 hours.

5. The preparation method according to claim 1, characterized in that, The molecular weight of the hydroxyl polydimethylsiloxane is 750 to 950.

6. The preparation method according to claim 1 or 5, characterized in that, The third polymerization reaction is carried out at room temperature; the reaction time is 2 to 6 hours.

7. The preparation method according to claim 1, characterized in that, The mass ratio of (meth)acrylate alkyl ester, (meth)acrylate hydroxyalkyl ester and heat-resistant monomer in the heat-resistant functional acrylate monomer mixture is 2-8:2-8:

11.

8. The preparation method according to claim 1 or 7, characterized in that, The alkyl methacrylates include one or more of methyl methacrylate, acrylate, ethyl acrylate, butyl acrylate, isoamyl acrylate, tert-butyl acrylate, and isooctyl acrylate; The (meth)acrylate hydroxyalkyl ester includes one or two of hydroxypropyl acrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, and hydroxypropyl methacrylate.

9. The preparation method according to claim 1, characterized in that, The polymerization reaction is carried out at a temperature of 45–80°C and for a duration of 2–6 hours.

10. An OCA optical adhesive film, formed by thermosetting the OCA optical adhesive prepared by any one of claims 1 to 9.

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