A low-refractive-index adhesive containing hollow silica and its preparation method

Abstract

This invention discloses a low-refractive-index adhesive containing hollow silica and its preparation method. The adhesive comprises a hollow silica dispersion, 3,3,5-trimethylcyclohexanol acrylate, propoxylated neopentyl glycol diacrylate, propoxylated trimethylolpropane triacrylate, BYK-UV 3530, TOP-L, and 184 initiator. The preparation method involves taking an appropriate amount of hollow silica dispersion, adding 3,3,5-trimethylcyclohexanol acrylate, propoxylated neopentyl glycol diacrylate, and propoxylated trimethylolpropane triacrylate respectively, and mechanically stirring for several minutes under a nitrogen atmosphere. Then, BYK-UV 3530, TOP-L, and 184 initiator are added respectively, and stirring is continued for several minutes under a nitrogen atmosphere. Finally, the mixture is filtered and purified to obtain the final product. The film cured by spin coating of this invention exhibits good leveling properties and excellent adhesion to optical glass substrates.

Description

Technical Field

[0001] This invention relates to the field of low-refractive-index adhesives, specifically to a low-refractive-index adhesive containing hollow silica and its preparation method. Background Technology

[0002] The optical technology of AR glasses is at a point of rapid iteration. From a product form perspective, surface relief grating (SRG) waveguides have become the mainstream technology for consumer-grade AR glasses. From an underlying principle perspective, the precise combination of high and low refractive index materials is the cornerstone of achieving excellent optical performance. The core lies in designing the optical path through micro-nano structures, rather than relying on the semi-transparent mirrors of traditional geometric optics. Regardless of the technology approach, the core of its optical design depends on the precise control of the refractive index.

[0003] Refractive index matching is the cornerstone of optical path construction. In diffractive waveguides, the coupling of light rays depends on the grating structure. The efficiency of the grating is directly related to the difference (Δn) in refractive index between the grating material and the surrounding medium. A larger Δn means a stronger diffraction effect and higher optical efficiency. A typical waveguide structure includes: a high-refractive-index waveguide layer for conducting light; and a low-refractive-index cladding layer to ensure total internal reflection of light within the waveguide layer.

[0004] In the field of optical waveguides, low-refractive-index materials are key to achieving efficient optical coupling and imaging. Currently, the mainstream low-refractive-index UV resin technology is fluorinated acrylate. However, fluorinated resins are a double-edged sword; while providing excellent optical and surface properties, they also bring many challenges.

[0005] Adhesion challenges: Low surface energy is a double-edged sword. While providing excellent hydrophobicity, it can also lead to poor adhesion of fluorinated resins to many substrates. This is one of the most common challenges in applications, usually requiring substrate pretreatment or the addition of adhesion promoters (such as silane coupling agents or phosphate esters) to resolve. Compatibility issues: The significant structural differences between fluorinated segments and non-fluorinated materials can lead to poor compatibility with other resins, monomers, or additives in the formulation, thus affecting the transparency and performance of the coating. Therefore, careful evaluation of the overall system compatibility is necessary during material selection, greatly increasing the difficulty of subsequent formulation optimization. Higher cost: The high cost of fluorinated monomers and synthesis processes results in fluorinated modified resins being significantly more expensive than ordinary acrylic resins.

[0006] Compared to fluorinated resins, the core advantage of hollow silica particles lies in their hollow interior. By precisely controlling the porosity, their effective refractive index can be designed within an extremely wide range of 1.10 to 1.45, and even as low as 1.07–1.35. This is difficult for fluorinated resins to achieve, as the refractive index of organic materials is rarely below 1.35. This ultra-low refractive index makes them ideal for use as single-layer or multi-layer antireflective coatings. For example, studies have used hollow silica coatings to reduce the reflectivity of polymethyl methacrylate (PMMA) substrates from 7% to 0.5% and increase the transmittance from 92% to 98%. Due to its moderate surface energy, the surface of hollow silica is easily chemically modified, and hollow silica coatings exhibit good adhesion to various substrates such as glass, metal, and plastics. This greatly facilitates the construction of multifunctional coatings. Therefore, hollow silica particles have significant advantages in achieving ultra-low refractive indices, improving mechanical properties, and constructing functional optical surfaces in the preparation of low-refractive-index materials, and are particularly suitable for applications with high overall performance requirements. Summary of the Invention

[0007] The purpose of this invention is to provide a low-refractive-index adhesive containing hollow silica and its preparation method, so as to replace the current mainstream low-refractive-index adhesives related to fluorine-modified resins in the field of optical waveguides.

[0008] The technical solution of the present invention is as follows: A low-refractive-index adhesive containing hollow silica, comprising a hollow silica dispersion, 3,3,5-trimethylcyclohexanol acrylate, propoxylated neopentyl glycol diacrylate, propoxylated trimethylolpropane triacrylate, BYK-UV3530, TOP-L, and 184 initiator.

[0009] The hollow silica dispersion contains 90% of the following components: 3,3,5-trimethylcyclohexanol acrylate, 7.22% of the following components: propionyl oxyneopentyl glycol diacrylate, 0.91% of the following components: propionyl oxytrimethylolpropane triacrylate, 0.24% of the following components: BYK-UV 3530, 0.18% of the following components: TOP-L, and 0.09% of the following components: 184 initiator.

[0010] The preparation method of the above-mentioned low-refractive-index adhesive containing hollow silica includes the following steps: S1. Preparation of hollow silica; S2. Preparation of hollow silica dispersion; S3. Prepare low-refractive-index adhesive; Take an appropriate amount of hollow silica dispersion and add 3,3,5-trimethylcyclohexanol acrylate, propoxylated neopentyl glycol diacrylate, and propoxylated trimethylolpropane triacrylate, respectively. Under a nitrogen atmosphere, mechanically stir for several minutes. Then, add BYK-UV 3530, TPO-L, and 184 initiators, respectively. Continue stirring for several minutes under a nitrogen atmosphere. Finally, filter and purify to obtain the final product.

[0011] Step S1 includes: S11. In a clean 500ml beaker, add 180ml deionized water, 0.24g acryloyloxyethyltrimethylammonium chloride, 1.2ml methacrylic acid, and 10ml styrene. Stir mechanically for 60min to ensure thorough mixing with the water. Then, purge with nitrogen and stir mechanically for 30min to remove air. Maintain the stirring speed at 250rpm under a nitrogen atmosphere and raise the system temperature to 90°C, holding at that temperature for 45min. Add 10ml of a pre-prepared aqueous solution containing 0.08g AIBA as an initiator to the reaction system. After 1 hour of polymerization, add 0.3ml of EGDMA as a crosslinking agent. Finally, polymerize at 90°C for 24 hours to obtain crosslinked polystyrene microspheres. S12. In a clean 500ml beaker, add 200ml of anhydrous ethanol and 0.5g of CTAB, and mix thoroughly. Then, adjust the pH of the mixture to 11 with an appropriate amount of ammonia water (28wt%), and mechanically stir for 45min to ensure the solution is homogeneous. Next, under stirring conditions, add a mixture of polystyrene microspheres and ethanol (5g polystyrene microspheres + 100ml ethanol) dropwise to the above mixture, and then ultrasonically disperse for 30min. After ultrasonic dispersion, transfer to a 500ml three-necked flask. Heat to 60 degrees Celsius, rotate at 180 rpm, and reflux. Add TEOS ethanol dilution (5 ml + 50 ml ethanol) dropwise, and continue aging for 120 min after the addition is complete. Centrifuge and wash, then wash with ethanol after centrifugation, repeat 6 times, and dry under vacuum at low temperature. Calcination: transfer the washed particles to a muffle furnace for programmed temperature calcination, from room temperature to 120 degrees Celsius (5 degrees Celsius / min), hold at 120 degrees Celsius for 45 min, then from 120 degrees Celsius to 550 degrees Celsius (1 degree Celsius / min), hold at 550 degrees Celsius for 4 h, and allow to cool naturally.

[0012] In step S2, 5g of the prepared powder is weighed and added to isopropanol, along with 10wt% (relative to the powder) MMA. Under a nitrogen atmosphere, the mixture is heated to 80℃, rotated at 180r / min, and then refluxed for 4 hours for acidification. After acidification, the powder is centrifuged, washed and centrifuged multiple times with ethyl acetate. The acidified powder is then transferred to an appropriate amount of PGMEA for the first modification. An appropriate amount of 3-methacryloyloxypropyltrimethoxysilane (10wt% of the powder) is weighed and refluxed at 100℃ under a nitrogen atmosphere for 2 hours at 180r / min. After modification, the powder is purified by centrifugation followed by further purification using a two-component ether. The powder is dissolved and dispersed in chloromethane, then precipitated with n-heptane and centrifuged to obtain a wet powder. For the second modification, the wet powder is added to an appropriate amount of PGMEA, and 10 wt% (relative to the powder) (methoxytriethylene glycol ether propyl)trimethoxysilane is added for a second surface modification. The modification is carried out at 100°C under a nitrogen atmosphere, at 180 r / min, and refluxed for 2 h. After modification, purification is performed, first by centrifugation, then by dissolving and dispersing in dichloromethane, followed by precipitating with n-heptane and centrifugation to obtain the final surface-modified wet powder. Finally, the wet powder is added to PGMEA to prepare a 5%-15% concentration dispersion as needed.

[0013] In step S3, 100g of a suitable amount of 10% hollow silica dispersion was taken, and 8g of 3,3,5-trimethylcyclohexanol acrylate, 1g of propionyl oxyneopentyl glycol diacrylate, and 1.5g of propionyl oxytrimethylolpropane triacrylate were added respectively. The mixture was mechanically stirred for 45min under a nitrogen atmosphere. Then, 0.27g of BYK-UV 3530, 0.2g of TPO-L, and 0.1g of 184 initiator were added respectively. The mixture was stirred for another 120min under a nitrogen atmosphere. Finally, the mixture was filtered and purified using a 0.1µm organic filter membrane to obtain the final product.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The film surface of the hollow silica-containing low-refractive-index adhesive prepared by the present invention has good leveling properties after spin coating and curing, while existing products, with the same spin coating process, have a surface full of pits after curing. 2. The hollow silica-containing low-refractive-index adhesive prepared by this invention has better adhesion to optical glass substrates, compared to the poor adhesion of existing products to glass substrates (OB test). Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 Surface phenomena diagram of existing products; Figure 2 A surface phenomenon diagram of a low-refractive-index adhesive containing hollow silica provided by the present invention; Figure 3 For existing products, use a 100-grid test pattern; Figure 4 This invention provides a cross-cut adhesion test pattern for a low-refractive-index adhesive containing hollow silica. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0018] To illustrate the technical solution described in this invention, specific embodiments are described below.

[0019] Example This embodiment provides a low-refractive-index adhesive containing hollow silica, the components of which include hollow silica dispersion, 3,3,5-trimethylcyclohexanol acrylate, propoxylated neopentyl glycol diacrylate, propoxylated trimethylolpropane triacrylate, BYK-UV 3530, TOP-L and 184 initiator.

[0020] The hollow silica dispersion contains 90% of the following components: 3,3,5-trimethylcyclohexanol acrylate, 7.22% of the following components: propionyl oxyneopentyl glycol diacrylate, 0.91% of the following components: propionyl oxytrimethylolpropane triacrylate, 0.24% of the following components: BYK-UV 3530, 0.18% of the following components: TOP-L, and 0.09% of the following components: 184 initiator.

[0021] The preparation method of the above-mentioned low-refractive-index adhesive containing hollow silica includes the following steps: S1. Preparation of hollow silica; Step S1 includes: S11. In a clean 500ml beaker, add 180ml deionized water, 0.24g acryloyloxyethyltrimethylammonium chloride, 1.2ml methacrylic acid, and 10ml styrene. Stir mechanically for 60min to ensure thorough mixing with the water. Then, purge with nitrogen and stir mechanically for 30min to remove air. Maintain the stirring speed at 250rpm under a nitrogen atmosphere and raise the system temperature to 90°C, holding at that temperature for 45min. Add 10ml of a pre-prepared aqueous solution containing 0.08g AIBA as an initiator to the reaction system. After 1 hour of polymerization, add 0.3ml of EGDMA as a crosslinking agent. Finally, polymerize at 90°C for 24 hours to obtain crosslinked polystyrene microspheres. S12. In a clean 500ml beaker, add 200ml of anhydrous ethanol and 0.5g of CTAB, and mix thoroughly. Then, adjust the pH of the mixture to 11 with an appropriate amount of ammonia water (28wt%), and mechanically stir for 45min to ensure the solution is homogeneous. Next, under stirring conditions, add a mixture of polystyrene microspheres and ethanol (5g polystyrene microspheres + 100ml ethanol) dropwise to the above mixture, and then ultrasonically disperse for 30min. After ultrasonic dispersion, transfer to a 500ml three-necked flask. Heat to 60 degrees Celsius, rotate at 180 rpm, and reflux. Add TEOS ethanol dilution (5 ml + 50 ml ethanol) dropwise, and continue aging for 120 min after the addition is complete. Centrifuge and wash, then wash with ethanol after centrifugation, repeat 6 times, and dry under vacuum at low temperature. Calcinate, transfer the washed particles to a muffle furnace for programmed temperature calcination, from room temperature to 120 degrees Celsius (5 degrees Celsius / min), hold at 120 degrees Celsius for 45 min, then from 120 degrees Celsius to 550 degrees Celsius (1 degree Celsius / min), hold at 550 degrees Celsius for 4 h, and allow to cool naturally. S2. Preparation of hollow silica dispersion; Weigh 5g of the prepared powder and add it to isopropanol. Add 10wt% (relative to the powder) of MMA. Under a nitrogen atmosphere, heat to 80℃, rotate at 180r / min, and cool and reflux for 4h. After acidification, centrifuge, wash and centrifuge repeatedly with ethyl acetate, and then transfer the acidified powder to an appropriate amount of PGMEA for the first modification. Weigh an appropriate amount of 3-methacryloyloxypropyltrimethoxysilane and 10WT% of the powder. Modify at 100℃, under a nitrogen atmosphere, by cooling and reflux at 180r / min for 2h. After modification, purify by centrifugation and then by dissolving in dichloromethane. After dedispersing, the powder precipitated by n-heptane was centrifuged to obtain a wet powder. For the second modification, the wet powder was added to an appropriate amount of PGMEA, and 10 wt% (relative to the powder) (methoxytriethylene glycol ether propyl)trimethoxysilane was added for a second surface modification. The modification was carried out at 100°C under a nitrogen atmosphere, at 180 r / min, and refluxed for 2 h. After modification, purification was performed, first by centrifugation, then by dissolving and dispersing in dichloromethane, followed by precipitation of the powder by n-heptane and centrifugation to obtain the final surface-modified wet powder. Finally, the wet powder was added to PGMEA to prepare a 5%-15% concentration dispersion as needed. S3. Prepare low-refractive-index adhesive; Take 100g of a suitable amount of 10% hollow silica dispersion, add 8g of 3,3,5-trimethylcyclohexanol acrylate, 1g of propoxylated neopentyl glycol diacrylate, and 1.5g of propoxylated trimethylolpropane triacrylate, and stir mechanically for 45min under a nitrogen atmosphere. Then, add 0.27g of BYK-UV 3530, 0.2g of TPO-L, and 0.1g of 184 initiator, and continue stirring for 120min under a nitrogen atmosphere. Finally, filter and purify the product using a 0.1µm organic filter membrane to obtain the final product.

[0022] The performance comparison between the hollow silica-containing low-refractive-index adhesive prepared in this embodiment and existing products is shown in the following table:

[0023] The hollow silica-containing low-refractive-index adhesive prepared in this embodiment has the following advantages over existing products in terms of glass substrate performance: Figure 1-4 As shown: 1. The film surface after spin coating and curing has good leveling properties. Existing products with the same spin coating process have a surface full of pits after curing. 2. It must have good adhesion to optical glass substrates. Existing products have very poor adhesion to glass substrates, as shown in the cross-cut adhesion test (OB).

[0024] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-refractive-index adhesive containing hollow silica, characterized in that, The components of this hollow silica low-refractive-index adhesive include hollow silica dispersion, 3,3,5-trimethylcyclohexanol acrylate, propoxylated neopentyl glycol diacrylate, propoxylated trimethylolpropane triacrylate, BYK-UV 3530, TOP-L, and 184 initiator.

2. The low-refractive-index adhesive containing hollow silica according to claim 2, characterized in that, The hollow silica dispersion contains 90% silica, 7.22% 3,3,5-trimethylcyclohexanol acrylate, 0.91% propionyl oxyneopentyl glycol diacrylate, 1.36% propionyl oxytrimethylolpropane triacrylate, 0.24% BYK-UV 3530, 0.18% TOP-L, and 0.09% 184 initiator.

3. A method for preparing a low-refractive-index adhesive containing hollow silica, characterized in that, Includes the following steps: S1. Preparation of hollow silica; S2. Preparation of hollow silica dispersion; S3. Prepare low-refractive-index adhesive; Take an appropriate amount of hollow silica dispersion and add 3,3,5-trimethylcyclohexanol acrylate, propoxylated neopentyl glycol diacrylate, and propoxylated trimethylolpropane triacrylate, respectively. Under a nitrogen atmosphere, mechanically stir for several minutes. Then, add BYK-UV 3530, TPO-L, and 184 initiators, respectively. Continue stirring for several minutes under a nitrogen atmosphere. Finally, filter and purify to obtain the final product.

4. The method for preparing a low-refractive-index adhesive containing hollow silica according to claim 3, characterized in that, Step S1 includes: S11. In a clean 500ml beaker, add 180ml deionized water, 0.24g acryloyloxyethyltrimethylammonium chloride, 1.2ml methacrylic acid, and 10ml styrene. Stir mechanically for 60min to ensure thorough mixing with the water. Then, purge with nitrogen and stir mechanically for 30min to remove air. Maintain the stirring speed at 250rpm under a nitrogen atmosphere and raise the system temperature to 90°C, holding at that temperature for 45min. Add 10ml of a pre-prepared aqueous solution containing 0.08g AIBA as an initiator to the reaction system. After 1 hour of polymerization, add 0.3ml of EGDMA as a crosslinking agent. Finally, polymerize at 90°C for 24 hours to obtain crosslinked polystyrene microspheres. S12. In a clean 500ml beaker, add 200ml of anhydrous ethanol and 0.5g of CTAB, and mix thoroughly. Then, adjust the pH of the mixture to 11 with an appropriate amount of ammonia water (28wt%), and mechanically stir for 45min to ensure the solution is homogeneous. Next, under stirring conditions, add a mixture of polystyrene microspheres and ethanol (5g polystyrene microspheres + 100ml ethanol) dropwise to the above mixture, and then ultrasonically disperse for 30min. After ultrasonic dispersion, transfer to a 500ml three-necked flask. Heat to 60 degrees Celsius, rotate at 180 rpm, and reflux. Add TEOS ethanol dilution (5 ml + 50 ml ethanol) dropwise, and continue aging for 120 min after the addition is complete. Centrifuge and wash, then wash with ethanol after centrifugation, repeat 6 times, and dry under vacuum at low temperature. Calcination: transfer the washed particles to a muffle furnace for programmed temperature calcination, from room temperature to 120 degrees Celsius (5 degrees Celsius / min), hold at 120 degrees Celsius for 45 min, then from 120 degrees Celsius to 550 degrees Celsius (1 degree Celsius / min), hold at 550 degrees Celsius for 4 h, and allow to cool naturally.

5. The method for preparing a low-refractive-index adhesive containing hollow silica according to claim 3, characterized in that, In step S2, 5g of the prepared powder was weighed and added to isopropanol, along with 10wt% (relative to the powder) of MMA. Under a nitrogen atmosphere, the mixture was heated to 80℃, rotated at 180r / min, and then cooled and refluxed for acidification for 4h. After acidification, the mixture was centrifuged, washed and centrifuged multiple times with ethyl acetate, and then the acidified powder was transferred to an appropriate amount of PGMEA for the first modification. An appropriate amount of 3-methacryloyloxypropyltrimethoxysilane and 10WT% of the powder were weighed and modified under a nitrogen atmosphere at 100℃ and 180r / min for 2h by cooling and reflux. After modification, the powder is purified by centrifugation, followed by dissolution and dispersion with dichloromethane, then precipitation of powder with n-heptane and centrifugation to obtain wet powder. For the second modification, wet powder was added to an appropriate amount of PGMEA, and 10wt% (relative to the powder) (methoxytriethylene glycol ether propyl)trimethoxysilane was added for the second surface modification. The modification was carried out at 100℃ in a nitrogen atmosphere, at 180r / min, and cooled and refluxed for 2h. After modification, the powder is purified by centrifugation, followed by dissolution and dispersion with dichloromethane, then precipitation of powder with n-heptane and centrifugation to obtain the final surface-modified wet powder. Finally, the wet powder is added to PGMEA to prepare a dispersion with a concentration of 5%-15% as required.

6. The method for preparing a low-refractive-index adhesive containing hollow silica according to claim 3, characterized in that, In step S3, take 100g of a suitable amount of 10% hollow silica dispersion, add 8g of 3,3,5-trimethylcyclohexanol acrylate, 1g of propoxylated neopentyl glycol diacrylate, and 1.5g of propoxylated trimethylolpropane triacrylate, and stir mechanically for 45min under a nitrogen atmosphere; then, add 0.27g of BYK-UV 3530, 0.2g of TPO-L, and 0.1g of 184 initiator, and continue stirring for 120min under a nitrogen atmosphere; finally, filter and purify using a 0.1µm organic filter membrane to obtain the final product.

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