High refractive index hot melt optical adhesive film and preparation method thereof

Abstract

This invention specifically relates to a high-refractive-index hot-melt optical adhesive film and its preparation method, belonging to the field of optical adhesive technology. The hot-melt optical adhesive film is prepared from the following components by weight: 40-85 parts of a high-refractive-index monomer composite, 10-20 parts of a styrene-butadiene copolymer, 10-50 parts of a flexible diluent monomer, 0.5-5 parts of a thermal initiator, 1-15 parts of a tackifying resin, 5-20 parts of nano-inorganic filler, and 0.1-1 parts of an antioxidant. The hot-melt optical adhesive film provided by this invention is solid at room temperature, exhibits excellent storage stability, and can be thermally crosslinked and cured at 100-120℃, providing a wide operating window. After curing, the film has a refractive index of 1.6-1.65 and a light transmittance of 88-98%, possessing both high hardness and high adhesion performance. It can effectively bond various substrates such as optical glass and optical PC sheets, exhibits excellent aging resistance, and is particularly suitable for optical bonding and encapsulation of VR / AR optical waveguide components.

Description

Technical Field

[0001] This invention relates to the field of optical adhesives, specifically to a high refractive index hot melt optical adhesive film and its preparation method. Background Technology

[0002] With the rapid development of virtual reality (VR) and augmented reality (AR) technologies, optical waveguide components, as core optical elements, have placed stringent demands on the thinness, high brightness, and imaging quality of optical systems. Optical waveguide technology relies on the principle of total internal reflection to transmit light; therefore, adhesives used to bond optical waveguide lenses to other optical components (such as optical glass and PC films) must have extremely high refractive indices (typically >1.6) to reduce light loss at the interface and improve light extraction efficiency.

[0003] Currently, the mainstream optical adhesives mainly include optically transparent adhesives (OCA) and thermosetting epoxy adhesives. Although OCA adhesives have good light transmittance, their refractive index is generally low (about 1.4-1.5), making it difficult to meet the requirements for high refractive index. Although traditional thermosetting epoxy adhesives can increase the refractive index through doping, they have problems such as high viscosity, short operating window, and easy generation of bubbles during high-temperature curing. After curing, the light transmittance is usually less than 85%, which is difficult to meet the requirements of high-definition displays. Summary of the Invention

[0004] The purpose of this invention is to provide a high refractive index hot melt optical adhesive film and its preparation method, thereby solving the above-mentioned problems.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a high refractive index hot-melt optical adhesive film, wherein the hot-melt optical adhesive film is prepared from the following components in parts by weight:

[0006] The composition comprises 40-85 parts of a high refractive index monomer composite, 10-20 parts of a styrene-butadiene copolymer, 10-50 parts of a flexible diluent monomer, 0.5-5 parts of a thermal initiator, 1-15 parts of a tackifying resin, 5-20 parts of a nano-inorganic filler, and 0.1-1 parts of an antioxidant; wherein the hot melt optical adhesive film is solid at room temperature and is thermally crosslinked and cured at 100-120℃, and the refractive index after curing is 1.6-1.65;

[0007] The high refractive index monomer complex is selected from at least one of phenoxyethyl acrylate, benzyl methacrylate, 2-phenoxyethyl acrylate, and methyl thiomethacrylate;

[0008] The nano-inorganic filler is a high-refractive-index metal oxide, and it has been modified with a surface silane coupling agent.

[0009] Furthermore, the flexible diluent monomer includes at least one of isobornyl acrylate, isobornyl methacrylate, lauryl acrylate, and dodecyl methacrylate, and the glass transition temperature of the flexible diluent monomer is below 50°C.

[0010] Furthermore, the thermal initiator includes at least one of benzoyl peroxide, azobisisobutyronitrile, and dicumyl peroxide.

[0011] Furthermore, the nano-inorganic filler includes at least one of titanium dioxide, zirconium oxide, and zinc sulfide.

[0012] Furthermore, the tackifying resin includes at least one of hydrogenated rosin resin, terpene phenolic resin, and polyurethane acrylate oligomer, with a softening point of 60-100°C.

[0013] Furthermore, the antioxidant is a hindered phenolic antioxidant or a phosphite antioxidant.

[0014] The present invention also provides a method for preparing the hot melt optical adhesive film, comprising the following steps:

[0015] Step A: After freezing the tackifying resin, antioxidant, styrene-butadiene copolymer, and thermal initiator, pulverize and sieve them into powders smaller than 10 micrometers. Add the tackifying resin powder, styrene-butadiene copolymer powder, thermal initiator powder, and nano-inorganic filler to a planetary mixer that can be vacuumed and jacketed for temperature control. Vacuum the mixer to remove the air trapped in the powder.

[0016] Step B: Under vacuum conditions, the high refractive index monomer complex and the flexible dilution monomer are pumped into the vacuum chamber of the planetary mixer by vacuum suction or gear pump, maintaining the vacuum and temperature below 20°C, and the materials are mixed evenly.

[0017] Step C: Under vacuum conditions, the above-mixed materials are pumped out by a temperature-controlled gear pump and evenly coated onto a peelable substrate to form an adhesive film. The adhesive film is pressed by a 50°C pressure roller for 10 seconds and then quickly cooled by a 5-15°C cooling roller to obtain a thermally crosslinkable hot melt adhesive film.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] This invention utilizes a synergistic blend of high-refractive-index monomers containing sulfur or aromatic rings with high-refractive-index nano-inorganic fillers to achieve a stable refractive index of 1.6-1.65 after curing, while maintaining high light transmittance, thus meeting the high refractive index requirements of optical waveguide components for optical adhesives.

[0020] This invention employs a hot-melt adhesive film design, which is solid at room temperature, exhibits excellent storage stability, and facilitates die-cutting and bonding; it cures rapidly at low and medium temperatures of 100-120℃, providing a wide process window and avoiding thermal damage to precision optical components caused by high temperatures.

[0021] This invention effectively inhibits the premature decomposition of thermal initiators through a staged temperature-controlled preparation process, ensuring the consistency of the film's performance during storage and application.

[0022] The adhesive film of this invention, after curing, possesses high bonding strength, high light transmittance, and excellent aging resistance, making it particularly suitable for precision bonding and encapsulation of VR / AR optical waveguide components. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1:

[0025] This embodiment provides a high refractive index hot melt optical adhesive film, the composition of which is as follows by weight:

[0026] High refractive index monomer complex: 50 parts of phenoxyethyl acrylate;

[0027] Styrene-butadiene copolymer: 20 parts;

[0028] Flexible dilution monomer: 25 parts of isobornyl methacrylate;

[0029] Tackifying resin: 8 parts of hydrogenated rosin resin (softening point 85℃);

[0030] Nano-inorganic filler: 12 parts of nano-TiO2 (modified with KH-570 silane coupling agent);

[0031] Thermal initiator: 2 parts benzoyl peroxide;

[0032] Antioxidant: 0.5 parts of hindered phenolic antioxidant 1010;

[0033] The preparation method is as follows:

[0034] Step A: After freezing the tackifying resin, antioxidant, styrene-butadiene copolymer, and thermal initiator with liquid nitrogen, pulverize and sieve them into powders smaller than 10 micrometers. Add the tackifying resin powder, styrene-butadiene copolymer powder, thermal initiator powder, and nano-inorganic filler to a planetary mixer that can be vacuumed and jacketed for temperature control. Vacuum the mixture to remove the air trapped in the powder.

[0035] Step B: Under vacuum conditions, the high refractive index monomer complex and the flexible dilution monomer are pumped into the vacuum chamber of the planetary mixer by vacuum suction or gear pump, maintaining the vacuum and temperature below 20°C, and the materials are mixed evenly.

[0036] Step C: Under vacuum conditions, the above-mixed materials are pumped out by a temperature-controlled gear pump and evenly coated onto a peelable substrate to form an adhesive film. The adhesive film is pressed by a 50°C pressure roller for 10 seconds and then quickly cooled by a 5-15°C cooling roller to obtain a thermally crosslinkable hot melt adhesive film with a thickness of 50-500μm.

[0037] The performance of the obtained adhesive film was tested, and the results are as follows:

[0038] Refractive index: 1.62 (Abbe refractometer, 25°C)

[0039] Transmittance (550nm): 95% (UV-Vis spectrophotometer)

[0040] Curing conditions: Hot pressing at 110℃ for 15 minutes

[0041] Peel strength (for optical glass): 48 N / 25 mm (universal tensile testing machine, 180° peel).

[0042] Example 2:

[0043] This embodiment provides a high refractive index hot melt optical adhesive film, the composition of which is as follows by weight:

[0044] High refractive index monomer complex: 60 parts of methyl thiomethacrylate;

[0045] Styrene-butadiene copolymer: 10 parts;

[0046] Flexible dilution monomer: 20 parts lauryl acrylate;

[0047] Tackifying resin: 10 parts of polyurethane acrylate oligomer (softening point 75℃);

[0048] Nano-inorganic filler: 15 parts of nano-ZrO2 (modified with KH-570 silane coupling agent);

[0049] Thermal initiator: 3 parts azobisisobutyronitrile;

[0050] Antioxidant: Phosphite antioxidant 168 0.8 parts;

[0051] The preparation method is the same as in Example 1.

[0052] Performance test results:

[0053] Refractive index: 1.65;

[0054] Transmittance (550nm): 93%;

[0055] Curing conditions: Hot pressing at 105℃ for 20 minutes;

[0056] Peel strength (for optical PC sheets): 42 N / 25 mm;

[0057] Example 3:

[0058] This embodiment provides a high refractive index hot melt optical adhesive film, the composition of which is as follows by weight:

[0059] High refractive index monomer complex: 42 parts of benzyl methacrylate;

[0060] Styrene-butadiene copolymer: 15 parts;

[0061] Flexible dilution monomer: 35 parts of dodecyl methacrylate;

[0062] Tackifying resin: 12 parts of terpene phenolic resin (softening point 95℃);

[0063] Nano-inorganic filler: 8 parts of nano-ZnS (modified with KH-570 silane coupling agent);

[0064] Thermal initiator: 1.5 parts dicumyl peroxide;

[0065] Antioxidant: Hindered phenolic antioxidant 1076 0.3 parts;

[0066] The preparation method is the same as in Example 1.

[0067] Performance test results:

[0068] Refractive index: 1.62;

[0069] Transmittance (550nm): 97%;

[0070] Curing conditions: Hot pressing at 115℃ for 12 minutes;

[0071] Peel strength (for optical glass): 44 N / 25 mm;

[0072] Example 4:

[0073] This embodiment provides a high refractive index hot melt optical adhesive film, the composition of which is as follows by weight:

[0074] High refractive index monomer complex: 82 parts of 2-phenoxyethyl acrylate;

[0075] Styrene-butadiene copolymer: 20 parts;

[0076] Flexible dilution monomer: 12 parts of isobornyl acrylate;

[0077] Tackifying resin: 5 parts of hydrogenated rosin resin (softening point 80℃);

[0078] Nano-inorganic filler: 18 parts of nano-TiO2 (modified with KH-570 silane coupling agent);

[0079] Thermal initiator: 4 parts azobisisobutyronitrile;

[0080] Antioxidant: Phosphite antioxidant 626 0.6 parts;

[0081] The preparation method is the same as in Example 1.

[0082] Performance test results:

[0083] Refractive index: 1.65;

[0084] Transmittance (550nm): 91%;

[0085] Curing conditions: Hot pressing at 100℃ for 25 minutes;

[0086] Peel strength (for optical glass): 40 N / 25 mm;

[0087] Comparative Example 1:

[0088] This comparative example uses commercially available ordinary OCA optical adhesive (refractive index 1.48) as a reference.

[0089] Performance test results:

[0090] Refractive index: 1.48;

[0091] Transmittance (550nm): 92%;

[0092] Curing conditions: Cannot be fully cured below 120℃;

[0093] Peel strength: 35 N / 25 mm;

[0094] Comparative Example 2:

[0095] The difference between this comparative example and Example 1 is that no nano-inorganic filler is added, while the remaining components and preparation methods are the same as in Example 1.

[0096] Performance test results:

[0097] Refractive index: 1.52;

[0098] Light transmittance (550nm): 98%;

[0099] Curing conditions: 110℃ / 15min;

[0100] Peel strength: 32 N / 25 mm;

[0101] Comparative Example 3:

[0102] The difference between this comparative example and Example 1 is that the high refractive index monomer complex is replaced with an equal amount of methyl acrylate (ordinary acrylate), while the remaining components and preparation methods are the same as in Example 1.

[0103] Performance test results:

[0104] Refractive index: 1.49;

[0105] Transmittance (550nm): 96%;

[0106] Curing conditions: 110℃ / 15min;

[0107] Peel strength: 30 N / 25 mm.

[0108] First, the refractive index of the cured products in Examples 1-4 all reached above 1.60, which is significantly higher than that in Comparative Examples 1-3 (1.48-1.52). This indicates that the present invention effectively improves the refractive index of the film by synergistically combining high refractive index monomers containing aromatic rings or sulfur atoms with high refractive index nano-inorganic fillers.

[0109] Secondly, Examples 1-4 can complete thermal cross-linking and curing at 100-120℃, while Comparative Example 1 cannot be completely cured below 120℃, indicating that the adhesive film of the present invention has better low-temperature curing performance and avoids thermal damage to precision optical components caused by high temperature.

[0110] Third, the refractive indices of Comparative Example 2 (without nano-inorganic filler) and Comparative Example 3 (without high refractive index monomer) are both below 1.6, and the peel strength is significantly reduced, proving that the high refractive index monomer and nano-inorganic filler have a synergistic effect in this application, and neither can be dispensed with.

[0111] Fourth, the light transmittance of Examples 1-4 is all above 91%, with the highest reaching 97%, and the peel strength reaches 40-48 N / 25mm. They have excellent comprehensive performance and can meet the comprehensive requirements of VR / AR optical waveguide components for high refractive index, high light transmittance, high bonding strength and low temperature curing of optical films.

[0112] In this invention, unless otherwise explicitly specified and limited, the terms "connected," "linked," "fixed," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0113] The above embodiments are used to further illustrate the present invention, but do not limit the present invention to these specific embodiments. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be understood as falling within the protection scope of the present invention.

Claims

1. A high refractive index hot melt optical adhesive film, characterized in that: The hot-melt optical adhesive film is prepared from the following components in parts by weight: 40-85 parts of high refractive index monomer complex, 10-20 parts of styrene-butadiene copolymer, 10-50 parts of flexible dilution monomer, 0.5-5 parts of thermal initiator, 1-15 parts of tackifying resin, 5-20 parts of nano-inorganic filler, and 0.1-1 parts of antioxidant; The styrene-butadiene copolymer has a softening point of 100-110℃, and the hot melt optical adhesive film is solid at room temperature and is thermally crosslinked and cured at 100-120℃, with a refractive index of 1.6-1.65 after curing. The high refractive index monomer complex is selected from at least one of phenoxyethyl acrylate, benzyl methacrylate, 2-phenoxyethyl acrylate, and methyl thiomethacrylate. The nano-inorganic filler is a high-refractive-index metal oxide, and it has been modified with a surface silane coupling agent.

2. The high refractive index hot melt optical adhesive film according to claim 1, characterized in that: The flexible diluting monomer includes at least one of isoborneol acrylate, isoborneol methacrylate, lauryl acrylate, and dodecyl methacrylate.

3. The high refractive index hot melt optical adhesive film according to claim 1, characterized in that: The thermal initiator includes at least one of benzoyl peroxide, azobisisobutyronitrile, and dicumyl peroxide.

4. The high refractive index hot melt optical adhesive film according to claim 1, characterized in that: The nano-inorganic filler includes at least one of titanium dioxide, zirconium oxide, and zinc sulfide.

5. The high refractive index hot melt optical adhesive film according to claim 1, characterized in that: The styrene-butadiene copolymer is specifically a styrene-butadiene copolymer with a styrene content of 33-38%.

6. The high refractive index hot melt optical adhesive film according to claim 1, characterized in that: The tackifying resin includes at least one of hydrogenated rosin resin, terpene phenolic resin, and polyurethane acrylate oligomer, with a softening point of 60-100℃.

7. The high refractive index hot-melt optical adhesive film according to claim 1, characterized in that, The antioxidant is a hindered phenolic antioxidant or a phosphite antioxidant.

8. A method for preparing a high refractive index hot-melt optical adhesive film as described in any one of claims 1-6, characterized in that: Includes the following steps: Step A: After freezing the tackifying resin, antioxidant, styrene-butadiene copolymer, and thermal initiator, pulverize and sieve them into powders smaller than 10 micrometers. Add the tackifying resin powder, styrene-butadiene copolymer powder, thermal initiator powder, and nano-inorganic filler to a planetary mixer that can be vacuumed and jacketed for temperature control. Vacuum the mixer to remove the air trapped in the powder. Step B: Under vacuum conditions, the high refractive index monomer complex and the flexible dilution monomer are pumped into the vacuum chamber of the planetary mixer by vacuum suction or gear pump, maintaining the vacuum and temperature below 20°C, and the materials are mixed evenly. Step C: Under vacuum conditions, the above-mixed materials are pumped out by a temperature-controlled gear pump and evenly coated onto a peelable substrate to form an adhesive film. The adhesive film is pressed by a 50°C pressure roller for 10 seconds and then quickly cooled by a 5-15°C cooling roller to obtain a thermally crosslinkable hot melt adhesive film.

9. The preparation method according to claim 8, characterized in that: The freezing method described in step A is specifically liquid nitrogen freezing.

10. The preparation method according to claim 8, characterized in that: The thickness of the hot melt adhesive film mentioned in step C is 50-500 μm.