Highly transparent room temperature moisture-cured phenyl silicone hot melt adhesive and method of making same

Abstract

The present application relates to hot melt adhesive technical field, specifically to a kind of high transparent room temperature moisture curing phenyl silicone resin hot melt adhesive and its preparation method, with hexamethyldisiloxane as end-capping agent, phenyl trimethoxysilane, vinyl trimethoxysilane and other monomers are co-hydrolyzed and condensed under acidic condition, and phenyl silicone resin intermediate is obtained;Again with trimethoxysilane as grafting agent, introduce alkoxy functional group by hydrosilylation, compound moisture curing catalyst, stabilizer and crosslinking agent, and single-component hot melt adhesive is prepared.The phenyl content of the product in silicone resin is 20.8%~38.8%, it is solid and has hot melt property at 25 DEG C.The light transmittance of product reaches 80.3%~90.6%, tensile shear strength reaches 2.5~3.3MPa after 7 days moisture curing, with high transparency, strong adhesion, excellent weather resistance characteristics, suitable for optical devices, electronic appliances and medical devices bonding and sealing.

Description

Technical Field

[0001] This invention relates to the field of hot melt adhesive technology, specifically to a highly transparent room temperature moisture-curing phenyl silicone resin hot melt adhesive and its preparation method. Background Technology

[0002] Hot melt adhesives are solvent-free, malleable polymers that are solid at room temperature but melt into a flowable, viscous liquid when heated to a certain temperature. Existing hot melt adhesive systems include ethylene-vinyl acetate copolymer (EVA), polyester (PES), polyamide (PA), polyolefin (PO), silicone, and block copolymers. Among these, silicone hot melt adhesives combine the rapid positioning capabilities of hot melt adhesives with the temperature resistance, weather resistance, and electrical insulation properties of silicone materials, making them promising for applications in electronics, automotive, and medical fields.

[0003] Organosilicon hot melt adhesives are mainly divided into two categories: one is the blend-modified type, which uses thermoplastic organosilicon copolymers (such as polysiloxane-polyester, polysiloxane-polyamide) as the matrix. For example, the invention patent of Hohai University, publication number CN103320077B, proposes a high-strength polyester hot melt adhesive, the core of which is the interpenetrating network (IPN) structure formed by linear polyester and methylphenyl silicone resin. In use, it is applied after heating and melting, and after cooling, it solidifies through physical changes and generates adhesive strength, which can reach 10MPa. However, due to the lack of chemical crosslinking, its solvent resistance is generally poor, it is prone to swelling after long-term immersion, and its upper temperature resistance limit is its melting temperature. A similar technology is the invention patent of Dow Chemical Company, publication number CN111868196B, which is a polyorganosiloxane hot melt adhesive composition using polyolefin and polydiorganosiloxane copolymer. Patent CN119119951B discloses a copolyamide hot melt adhesive and its preparation method, which combines hot melt polyamide with a product side-linked with hydrogen-containing silicone oil to obtain a blended modified hot melt adhesive. Another type is the pure organosilicon type, which typically involves mixing solid silicone resin and liquid silicone oil in a certain proportion and then end-capping to obtain a reactive organosilicon hot melt adhesive. For example, US patent US5473026A discloses a moisture-curing hot melt organosilicon pressure-sensitive adhesive composition, which introduces alkoxy groups by reacting hydroxyl-functionalized MQ resin with an alkoxy-containing compound; however, the lack of reactivity between the resin and the polymer results in insufficient creep resistance and solvent extraction resistance. Building upon this, Dow Corning's invention patents, CN105008432B and US10370572B2, proposed an improved solution: The composition comprises a reactive resin (A), a reactive polymer (B), a moisture-curing catalyst (C), and a crosslinking agent (D). The reactive resin (A) introduces alkoxy groups through a hydrosilylation reaction between an alkenyl-functionalized MQ resin and a hydrogen-containing alkoxysilane, and the reactive polymer (B) similarly introduces alkoxy groups through hydrosilylation. Because both resin (A) and polymer (B) are reactive and can crosslink with each other, this composition shows significant improvements in creep resistance and solvent extraction resistance compared to US5473026A. However, systems based on MQ resin have inherent limitations: the MQ resin's excessive structural rigidity and limited compatibility with silicone polymers result in insufficient transparency of the cured adhesive layer, making it difficult to meet the high-transparency bonding requirements of fields such as optical devices and precision electronics.

[0004] Dow Toray Industries, Inc.'s invention patent, publication number CN106459419B, further discloses a hot-melt silicone and a curable hot-melt composition. This patent involves a hydrogen-containing polysiloxane containing alkenyl groups (at least 10 mol% of which are phenyl groups bonded to silicon atoms) undergoing a hydrosilylation reaction with a hydrogen-containing polysiloxane in the presence of a catalyst. Partial crosslinking results in a product that is non-flowable at 25°C and has a low melt viscosity at 100°C, while retaining alkenyl groups for subsequent curing. The patent also discloses a curable hot-melt composition formed by compounding the hot-melt silicone with additional high-hydrogen-content polysiloxanes and a catalyst. The curing mechanism involves a hydrosilylation reaction between the alkenyl group and SiH, which requires heating and is therefore unsuitable for bonding heat-sensitive substrates. Furthermore, the final curing depends on the addition of a high-hydrogen-content crosslinking agent, making it a two-component or precisely proportioned system, limiting its usability.

[0005] In summary, existing one-component moisture-curing silicone hot melt adhesive systems generally suffer from insufficient transparency, unclear control over the relationship between phenyl content and softening point / hardness, and poor long-term weather resistance. Therefore, there is an urgent need in this field for a one-component room-temperature moisture-curing phenyl silicone resin hot melt adhesive product that combines high transparency, excellent weather resistance, and good adhesion. Summary of the Invention

[0006] To overcome the aforementioned technical problems, this invention provides a method for preparing a highly transparent phenyl silicone resin hot melt adhesive. The method involves a co-hydrolysis and condensation reaction of phenyltrimethoxysilane, vinyltrimethoxysilane, methyltrimethoxysilane, and dimethyldimethoxysilane under specific conditions to first generate a vinyl-containing phenyl silicone resin intermediate. Then, through a hydrosilylation reaction between trimethoxysilane and vinyl groups, alkoxy functional groups are introduced into the resin molecular structure, combining the phenyl silicone resin backbone with alkoxy moisture-curing properties, ultimately yielding an alkoxy silicone resin that exhibits both hot melt and moisture-curing reactivity. This resin, combined with a moisture-curing catalyst, stabilizer, and crosslinking agent, forms a one-component room-temperature vulcanizing organosilicon hot melt adhesive.

[0007] The technical solutions to the above technical problems are as follows: A method for preparing a highly transparent phenyl silicone resin hot melt adhesive includes the following steps: S1: Place 10-20 parts hexamethyldisiloxane, 120-300 parts water, 200-400 parts solvent A, 80-150 parts solvent B, and 30-80 parts hydrochloric acid in a reactor, heat to 40°C, and stir until homogeneous; wherein solvent A is one or more of toluene, xylene, methylcyclohexane, ethylcyclohexane, straight-chain alkanes, or branched-chain alkanes; solvent B is one of methanol, ethanol, isopropanol, or n-butanol. S2: 200-600 parts of phenyltrimethoxysilane, 30-150 parts of vinyltrimethoxysilane, 50-100 parts of methyltrimethoxysilane and 12-20 parts of dimethyldimethoxysilane are premixed and added dropwise to the reactor. The dropping time is controlled at 1-1.5 h, the reaction temperature is controlled at <50℃, and after the dropping is completed, the reaction is kept at 40℃ for 1 h. S3: Heat the reaction system to 72°C, keep it under reflux for 5 hours, let it stand to separate into layers, and take the lower organic phase. S4: The organic phase is washed with water until neutral, dried with anhydrous magnesium sulfate, filtered and then dried to obtain phenyl silicone resin intermediate powder; S5: Add 100 parts of the phenyl silicone resin intermediate powder, 5.35-21.4 parts of trimethoxysilane and 3-10 ppm of platinum catalyst to a reactor, heat to 80-100°C and react for 3 hours to obtain alkoxysilane resin; the preferred reaction temperature is 100°C; the platinum catalyst is one of Karstedt type platinum catalyst or Speier type platinum catalyst; S6: Take 100 parts of the alkoxysilicone resin, add 0.1 to 2 parts of moisture curing catalyst, 0.1 to 1 part of stabilizer and 2 to 4 parts of crosslinking agent, mix evenly, discharge the material, and seal it in an aluminum tube for storage; The moisture-curing catalyst is one or more of dibutyltin dilaurate, dibutyltin diacetate, chelated tin, n-butyl titanate, or isopropyl titanate; the stabilizer is antioxidant 1010 or antioxidant 168; and the crosslinking agent is one or more of methyltrimethoxysilane, vinyltrimethoxysilane, or isobutyltrimethoxysilane.

[0008] Another object of the present invention is to provide a highly transparent phenyl silicone resin hot melt adhesive prepared by the above method, wherein the silicone resin molecule contains alkoxy moisture-curing reactive functional groups and the phenyl content in the molecule is 20.8% to 38.8%, and the silicone resin is solid at 25°C and has hot melt properties.

[0009] Furthermore, the light transmittance of this hot melt adhesive is 80.3%–90.6%. After curing in moisture for 7 days, its hardness is 40–70, and its softening point is 68–99℃.

[0010] Furthermore, the phenyl content is a key parameter determining the overall performance of phenyl silicone resin hot melt adhesives, and it exists within a critical range. When the phenyl content is below 20.8%, although the product can still achieve high light transmittance, the insufficient rigid phenyl units in the resin skeleton lead to a significant decrease in the softening point, failing to meet the requirements of electronic and electrical components used in high-temperature environments, while also significantly deteriorating weather resistance. When the phenyl content is above 38.8%, due to the excessively high condensation reactivity of phenyltrimethoxysilane, a large number of highly cross-linked gel particles are generated during the co-hydrolysis condensation process, making it impossible to obtain a soluble and fusible phenyl silicone resin intermediate. Subsequent hydrosilylation reactions cannot proceed, and hot melt adhesive products cannot be prepared. Therefore, the phenyl content of 20.8%–38.8% is not a simple parameter optimization, but rather a critical range obtained through extensive experimental exploration between "preparability" and "optimal performance."

[0011] Furthermore, after 7 days of hot melt curing and moisture curing, the hot melt adhesive underwent a weather resistance test according to GB / T 3511-2018, and its appearance remained unchanged.

[0012] Furthermore, the hot melt adhesive was tested for tensile shear strength according to GB / T 7124-2008. The initial strength after 15 minutes of hot melt curing was 1.3-1.7 MPa, the strength after 60 minutes of moisture curing was 2.0-2.6 MPa, and the strength after 7 days of moisture curing was 2.5-3.3 MPa.

[0013] Another object of the present invention is to provide the application of the highly transparent phenyl silicone resin hot melt adhesive in the bonding of optical devices, the fixation of electronic and electrical components, or the sealing of medical devices.

[0014] The highly transparent phenyl silicone resin hot melt adhesive prepared by this invention has the following beneficial effects: (1) This invention is a single-component product, which is convenient to use and does not require precise proportioning of two components, thus reducing equipment costs and the threshold for use; (2) The product adopts a dual curing mechanism of "hot melt positioning - moisture curing". After hot melt curing, it provides initial bonding strength, and then secondary moisture crosslinking curing is carried out through the alkoxy groups on the silicone resin to form a three-dimensional network structure. The tensile shear strength reaches 1.3-1.7 MPa after 15 min of hot melt curing, increases to 2.0-2.6 MPa after 60 min of moisture curing, and further increases to 2.5-3.3 MPa after 7 days of moisture curing, which reflects the continuously enhanced bonding performance brought about by the dual curing mechanism; (3) By adjusting the phenyl content in the molecular structure, the softening point and hardness of the product can be flexibly adjusted to meet the differentiated requirements of different application scenarios for the softening point and hardness of hot melt adhesives. The higher the phenyl content, the higher the softening point, but the hardness and light transmittance will decrease accordingly.

[0015] (4) After the product is cured by hot melt curing and moisture curing, it is tested for weather resistance in accordance with GB / T 3511-2018. There is no change in appearance, no cracking or whitening, and it shows excellent weather resistance. (5) The product has good transparency and good adhesion to a variety of substrates. It is suitable for fields with high requirements for transparency and reliability, such as bonding of optical devices, fixing of electronic and electrical components and sealing of medical devices. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0017] Unless otherwise specified, all reagents and raw materials used in the following examples were commercially available, and their specific sources are not detailed here. In the following examples, unless otherwise specified, "parts" refers to parts by weight. Example 1:

[0018] S1: Place 20 parts hexamethyldisiloxane, 200 parts water, 300 parts toluene, 100 parts ethanol and 30 parts hydrochloric acid in a reactor, heat to 40°C and stir until homogeneous; S2: Premix 200 parts of phenyltrimethoxysilane, 150 parts of vinyltrimethoxysilane, 61 parts of methyltrimethoxysilane and 12 parts of dimethyldimethoxysilane, and add them dropwise to the reactor over a period of 1 to 1.5 hours, while controlling the temperature to <50°C; after the addition is complete, keep the reactor at 40°C for 1 hour. S3: Heat the reaction system to 72°C, keep it under reflux for 5 hours, let it stand to separate into layers, and take the lower organic phase. S4: The organic phase is washed with water until neutral, dried with anhydrous magnesium sulfate, filtered and then dried to obtain phenyl silicone resin intermediate powder; S5: 100 parts of phenyl silicone resin intermediate powder, 21.4 parts of trimethoxysilane and 3 ppm of Karstedt type platinum catalyst were added to the reactor and heated to 100℃ for 3 h to obtain alkoxy silicone resin. S6: Take 100 parts of alkoxy silicone resin, add 0.1 parts of dibutyltin dilaurate, 0.1 parts of antioxidant 1010 and 4 parts of methyltrimethoxysilane, mix evenly to obtain a high-transparency phenyl silicone resin hot melt adhesive; discharge the material and seal it in an aluminum tube for storage. Example 2:

[0019] S1: Place 10 parts hexamethyldisiloxane, 160 parts water, 250 parts xylene, 90 parts methanol and 40 parts hydrochloric acid in a reactor, heat to 40°C and stir until homogeneous; S2: Premix 235 parts of phenyltrimethoxysilane, 100 parts of vinyltrimethoxysilane, 50 parts of methyltrimethoxysilane and 20 parts of dimethyldimethoxysilane, and add them dropwise to the reactor over a period of 1 to 1.5 hours, while controlling the temperature to <50°C; after the addition is complete, keep the mixture at 40°C for 1 hour. S3: Heat the reaction system to 72°C, keep it under reflux for 5 hours, let it stand to separate into layers, and take the lower organic phase. S4: The organic phase is washed with water until neutral, dried with anhydrous magnesium sulfate, filtered and then dried to obtain phenyl silicone resin intermediate powder; S5: 100 parts of phenyl silicone resin intermediate powder, 12.77 parts of trimethoxysilane and 4 ppm of Speier type platinum catalyst were added to the reactor and heated to 90℃ for 3 h to obtain alkoxy silicone resin. S6: Take 100 parts of alkoxy silicone resin, add 0.5 parts of dibutyltin diacetate, 0.5 parts of antioxidant 1010, 0.5 parts of antioxidant 168 and 3 parts of vinyltrimethoxysilane, mix evenly to obtain a high-transparency phenyl silicone resin hot melt adhesive; discharge the material and seal it in an aluminum tube for storage. Example 3:

[0020] S1: Place 16 parts hexamethyldisiloxane, 120 parts water, 100 parts methylcyclohexane, 100 parts ethylcyclohexane, 80 parts isopropanol and 30 parts hydrochloric acid in a reactor, heat to 40°C and stir until homogeneous. S2: Premix 200 parts of phenyltrimethoxysilane, 60 parts of vinyltrimethoxysilane, 80 parts of methyltrimethoxysilane and 16 parts of dimethyldimethoxysilane, and add them dropwise to the reactor over a period of 1 to 1.5 hours, while controlling the temperature to <50°C; after the addition is complete, keep the mixture at 40°C for 1 hour. S3: Heat the reaction system to 72°C, keep it under reflux for 5 hours, let it stand to separate into layers, and take the lower organic phase. S4: The organic phase is washed with water until neutral, dried with anhydrous magnesium sulfate, filtered and then dried to obtain phenyl silicone resin intermediate powder; S5: 100 parts of phenyl silicone resin intermediate powder, 9.8 parts of trimethoxysilane and 5 ppm of Speier type platinum catalyst were added to the reactor and the temperature was raised to 80℃ and reacted for 3 hours to obtain alkoxy silicone resin. S6: Take 100 parts of alkoxy silicone resin, add 1.0 part of dibutyltin diacetate, 0.8 parts of antioxidant 168 and 2 parts of isobutyltrimethoxysilane, mix evenly to obtain a high-transparency phenyl silicone resin hot melt adhesive; discharge the material and seal it in an aluminum tube for storage. Example 4:

[0021] S1: Place 16 parts hexamethyldisiloxane, 180 parts water, 280 parts isooctane, 100 parts ethanol and 50 parts hydrochloric acid in a reactor, heat to 40°C and stir until homogeneous; S2: Premix 235 parts of phenyltrimethoxysilane, 30 parts of vinyltrimethoxysilane, 50 parts of methyltrimethoxysilane and 12 parts of dimethyldimethoxysilane, and add them dropwise to the reactor over a period of 1 to 1.5 hours, while controlling the temperature to <50°C; after the addition is complete, keep the mixture at 40°C for 1 hour. S3: Heat the reaction system to 72°C, keep it under reflux for 5 hours, let it stand to separate into layers, and take the lower organic phase. S4: The organic phase is washed with water until neutral, dried with anhydrous magnesium sulfate, filtered and then dried to obtain phenyl silicone resin intermediate powder; S5: 100 parts of phenyl silicone resin intermediate powder, 5.35 parts of trimethoxysilane and 8 ppm of Karstedt type platinum catalyst were added to the reactor and the temperature was raised to 85℃ and reacted for 3 hours to obtain alkoxy silicone resin. S6: Take 100 parts of alkoxy silicone resin, add 2.0 parts of tetrabutyl titanate, 1 part of antioxidant 1010 and 2 parts of methyltrimethoxysilane, mix evenly to obtain a high-transparency phenyl silicone resin hot melt adhesive; discharge the material and seal it in an aluminum tube for storage. Example 5:

[0022] S1: Place 10 parts hexamethyldisiloxane, 200 parts water, 300 parts ethylcyclohexane, 100 parts n-butanol and 50 parts hydrochloric acid in a reactor, heat to 40°C and stir until homogeneous; S2: Premix 300 parts of phenyltrimethoxysilane, 60 parts of vinyltrimethoxysilane, 100 parts of methyltrimethoxysilane and 16 parts of dimethyldimethoxysilane, and add them dropwise to the reactor over a period of 1 to 1.5 hours, controlling the temperature to <50°C; after the addition is complete, keep the reactor at 40°C for 1 hour. S3: Heat the reaction system to 72°C, keep it under reflux for 5 hours, let it stand to separate into layers, and take the lower organic phase. S4: The organic phase is washed with water until neutral, dried with anhydrous magnesium sulfate, filtered and then dried to obtain phenyl silicone resin intermediate powder; S5: 100 parts of phenyl silicone resin intermediate powder, 7.72 parts of trimethoxysilane and 10 ppm of Speier type platinum catalyst were added to the reactor and the temperature was raised to 95℃ and reacted for 3 hours to obtain alkoxy silicone resin. S6: Take 100 parts of alkoxy silicone resin, add 1.0 part of isopropyl titanate, 0.3 parts of antioxidant 1010 and 0.7 parts of antioxidant 168, mix evenly to obtain a high-transparency phenyl silicone resin hot melt adhesive; discharge the material and seal it in an aluminum tube for storage. Example 6:

[0023] S1: Place 10 parts hexamethyldisiloxane, 250 parts water, 400 parts n-octane, 120 parts ethanol and 60 parts hydrochloric acid in a reactor, heat to 40°C and stir until homogeneous; S2: Premix 400 parts of phenyltrimethoxysilane, 30 parts of vinyltrimethoxysilane, 50 parts of methyltrimethoxysilane and 12 parts of dimethyldimethoxysilane, and add them dropwise to the reactor over a period of 1 to 1.5 hours, while controlling the temperature to <50°C; after the addition is complete, keep the mixture at 40°C for 1 hour. S3: Heat the reaction system to 72°C, keep it under reflux for 5 hours, let it stand to separate into layers, and take the lower organic phase. S4: The organic phase is washed with water until neutral, dried with anhydrous magnesium sulfate, filtered and then dried to obtain phenyl silicone resin intermediate powder; S5: 100 parts of phenyl silicone resin intermediate powder, 5.35 parts of trimethoxysilane and 8 ppm of Karstedt type platinum catalyst were added to the reactor and heated to 100℃ for 3 h to obtain alkoxy silicone resin. S6: Take 100 parts of alkoxy silicone resin, add 2.0 parts of tetrabutyl titanate, 1 part of antioxidant 1010 and 2 parts of methyltrimethoxysilane, mix evenly to obtain a high-transparency phenyl silicone resin hot melt adhesive; discharge the material and seal it in an aluminum tube for storage. Example 7:

[0024] S1: Place 10 parts hexamethyldisiloxane, 300 parts water, 400 parts n-heptane, 150 parts ethanol and 80 parts hydrochloric acid in a reactor, heat to 40°C and stir until homogeneous; S2: Premix 600 parts of phenyltrimethoxysilane, 30 parts of vinyltrimethoxysilane, 50 parts of methyltrimethoxysilane and 12 parts of dimethyldimethoxysilane, and add them dropwise to the reactor over a period of 1 to 1.5 hours, while controlling the temperature to <50°C; after the addition is complete, keep the mixture at 40°C for 1 hour. S3: Heat the reaction system to 72°C, keep it under reflux for 5 hours, let it stand to separate into layers, and take the lower organic phase. S4: The organic phase is washed with water until neutral, dried with anhydrous magnesium sulfate, filtered and then dried to obtain phenyl silicone resin intermediate powder; S5: 100 parts of phenyl silicone resin intermediate powder, 5.35 parts of trimethoxysilane and 8 ppm of Karstedt type platinum catalyst were added to the reactor and heated to 100℃ for 3 h to obtain alkoxy silicone resin. S6: Take 100 parts of alkoxy silicone resin, add 2.0 parts of tetrabutyl titanate, 1 part of antioxidant 1010 and 2 parts of isobutyltrimethoxysilane, mix evenly to obtain a high-transparency phenyl silicone resin hot melt adhesive; discharge the material and seal it in an aluminum tube for storage. Example 1: (Phenyl content too low)

[0025] Alkoxysilicone resin was prepared using the same method as in Example 1, except that the amount of phenyltrimethoxysilane in S2 was adjusted to 150 parts, while all other conditions remained unchanged. The resulting silicone resin had a phenyl content of 15.2%, a softening point of 52°C, a hardness of 75, and a light transmittance of 92.5%. After 7 days of moisture curing, a weather resistance test was conducted, and a slight whitening appeared on the surface.

[0026] The hot melt adhesive was prepared according to step S6 of Example 1, and its performance was tested. The results showed that the softening point of this sample was only 52℃, far lower than 68℃ in Example 1. Significant softening and deformation occurred above 65℃, which could not meet the requirements for use of electronic and electrical components in high-temperature environments (≥80℃). At the same time, due to the low phenyl content, the crosslinking density was insufficient. After 7 days of moisture curing, the adhesive layer had high hardness and increased brittleness. In the UVA-340 accelerated weathering test, the adhesive layer showed slight whitening, and its weather resistance was significantly worse than that of Examples 1-7. Its tensile shear strength was only 1.1 MPa after 15 min of hot melt curing, 1.5 MPa after 60 min of moisture curing, and 1.8 MPa after 7 days of moisture curing, all of which were significantly lower than the corresponding values ​​of each example. Example 2: (Phenyl content is too high, exceeding 38.8%)

[0027] Alkoxysilicone resin was prepared using the same method as in Example 7, except that the amount of phenyltrimethoxysilane in S2 was adjusted to 700 parts, while all other conditions remained unchanged. The results showed that severe gelation occurred in the reaction system during the hydrolysis-condensation reaction, making it impossible to obtain phenylsilicone resin intermediate powder. Consequently, the hydrosilylation reaction in step S5 could not proceed, and hot melt adhesive products could not be prepared. The high-transparency phenyl silicone resin hot melt adhesives obtained in Examples 1-7 were subjected to weather resistance tests according to GB / T 3511-2018. Test method: UVA-340 lamp was used to accelerate weather aging, and the products were subjected to ultraviolet irradiation under a blackboard at 50°C through a dry-condensation-spray wet-dry cycle. Data were collected by observing the appearance of the film. The adhesive strength of the product is tested according to the GB / T 7124-2008 method.

[0028] The test results are shown in Table 1 below: Table 1 Performance test data of Examples 1-7

[0029] [1] The test samples were tested after being cured in moisture for 7 days. [2] The adhesive strength of the test sample is the tensile shear strength, and the adhesive substrate is iron-iron. As shown in Table 1, the phenyl content of the high-transparency phenyl silicone resin hot melt adhesives prepared in Examples 1-7 ranged from 20.8% to 38.8%. With increasing phenyl content, the transmittance and hardness decreased significantly. The decrease in transmittance is related to the phenyl conjugated system; phenyl absorption at longer wavelengths exhibits absorption tailing, resulting in a decrease in transmittance between 400 and 450 nm. Furthermore, at high phenyl content, the refractive indices of the groups (phenyl region n≈1.5, methyl region n≈1.41) differ significantly, further exacerbating the dispersion effect and increasing the transmittance differences across wavelengths. In the condensation system, the steric hindrance effect resulting from the increased phenyl content dominates, hindering the approach of active groups at the silicon end groups and significantly reducing the crosslinking efficiency and density. Although phenyl itself has high rigidity, the loose crosslinking network cannot support chain segment movement at high temperatures, ultimately leading to a decrease in resin hardness.

[0030] As the phenyl content increases, the softening point continuously rises. This is because the rigid structure of phenyl means that the higher the content, the greater the proportion of hard segments in the overall system, and the more significant the increase in softening point.

[0031] The high-transparency phenyl silicone resin hot melt adhesive prepared by this invention has a dual curing mechanism. After the product is hot melt cured, it undergoes secondary moisture curing through the alkoxy groups on the silicone resin. After weather resistance testing, there is no obvious change in appearance, and there is no cracking or whitening.

[0032] Meanwhile, the room temperature vulcanizing silicone hot melt adhesive features a dual curing mechanism, providing not only excellent weather resistance but also stronger adhesion than before. In the initial stage of hot melt curing, the tensile shear strength of the product is between 1.3 and 1.7 MPa. After 1 hour of moisture curing, the tensile shear strength increases to 2.0–2.6 MPa; after 7 days of moisture curing, the value is in the range of 2.5–3.3 MPa. The improvement effect is positively correlated with the methoxyl content of the product; the higher the methoxyl content, the faster the increase in tensile shear strength and the stronger the adhesion.

[0033] As shown in Table 1, Comparative Example 1, with a phenyl content of 15.2%, achieved higher light transmittance than the other examples, but this came at the cost of reduced softening point, hardness, and weather resistance. Its softening point was only 52°C, far lower than the 68°C of Example 1. Slight whitening was observed in the weather resistance test, while no change was observed in the other examples. The tensile shear strength at each stage was significantly lower than that of the other examples. This indicates that simply increasing light transmittance is not the goal of this invention; rather, it aims to achieve high transparency while ensuring excellent overall performance.

[0034] As shown in Comparative Example 1, when the phenyl content is less than 20.8%, although solid silicone resin can still be obtained, its softening point is significantly reduced, which leads to a sharp decrease in the bonding strength of the hot melt adhesive when used in high-temperature environments. At the same time, insufficient crosslinking density results in poor solvent resistance, which cannot meet the reliability requirements of heat resistance and solvent resistance in the fields of electronics and electrical appliances.

[0035] As can be seen from Comparative Example 2, when the phenyl content is too high, the condensation reaction activity of phenyltrimethoxysilane in the system is too high, resulting in the generation of a large number of highly cross-linked gel particles during the hydrolysis condensation process. It is impossible to obtain a soluble and fusible silicone resin intermediate, so that the subsequent hydrosilylation reaction to introduce alkoxy groups cannot proceed, and the hot melt adhesive product required by this invention cannot be prepared.

[0036] In summary, the phenyl content of 20.8%–38.8% is not a simple parameter selection, but a critical range obtained through extensive experimentation between "preparability" and "optimal performance." Below the lower limit of this range, the heat resistance and solvent resistance of the product deteriorate significantly; above the upper limit, the reaction system gels, and the product cannot be prepared.

[0037] The high-transparency phenyl silicone resin hot melt adhesive of the present invention can be used in the fields of optical device bonding, electronic and electrical component fixing and medical device sealing, and has significant industrial practical value.

[0038] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for preparing a highly transparent room-temperature moisture-curing phenyl silicone resin hot melt adhesive, characterized in that, Includes the following steps: S1: Place 10-20 parts hexamethyldisiloxane, 120-300 parts water, 200-400 parts solvent A, 80-150 parts solvent B and 30-80 parts hydrochloric acid in a reactor, heat to 40°C and stir until homogeneous; S2: 200-600 parts of phenyltrimethoxysilane, 30-150 parts of vinyltrimethoxysilane, 50-100 parts of methyltrimethoxysilane and 12-20 parts of dimethyldimethoxysilane are premixed and added dropwise to the reactor. The dropping time is controlled at 1-1.5 h, the reaction temperature is controlled at <50℃, and after the dropping is completed, the reaction is kept at 40℃ for 1 h. S3: Heat the reaction system to 72°C, keep it under reflux for 5 hours, let it stand to separate into layers, and take the lower organic phase. S4: The organic phase is washed with water until neutral, dried with anhydrous magnesium sulfate, filtered and then dried to obtain phenyl silicone resin intermediate powder; S5: Add 100 parts of the phenyl silicone resin intermediate powder, 5.35-21.4 parts of trimethoxysilane and 3-10 ppm of platinum catalyst to a reactor, heat to 80-100℃ and react for 3 hours to obtain alkoxy silicone resin. S6: Take 100 parts of the alkoxysilane resin, add 0.1 to 2 parts of moisture curing catalyst and 0.1 to 1 part of stabilizer, mix evenly, discharge and seal for storage.

2. The preparation method according to claim 1, characterized in that, In step S1, solvent A is one or more of toluene, xylene, methylcyclohexane, ethylcyclohexane, straight-chain alkanes, or branched-chain alkanes; solvent B is one of methanol, ethanol, isopropanol, or n-butanol.

3. The preparation method according to claim 1, characterized in that, The platinum catalyst mentioned in step S5 is either a Karstedt-type platinum catalyst or a Speier-type platinum catalyst.

4. The preparation method according to claim 1, characterized in that, In step S6, 2 to 4 parts of a crosslinking agent are added, wherein the crosslinking agent is one or more of methyltrimethoxysilane, vinyltrimethoxysilane, or isobutyltrimethoxysilane.

5. The preparation method according to claim 1, characterized in that, The moisture curing catalyst mentioned in step S6 is one or more of dibutyltin dilaurate, dibutyltin diacetate, chelated tin, n-butyl titanate, or isopropyl titanate; the stabilizer is antioxidant 1010 or antioxidant 168.

6. A high-transparency room-temperature moisture-curing phenyl silicone resin hot melt adhesive, characterized in that, The hot melt adhesive is prepared by the preparation method according to any one of claims 1-5, wherein the silicone resin molecule contains alkoxy moisture-curing reactive functional groups and the phenyl content in the molecule is 20.8% to 38.8%, and the silicone resin is solid at 25°C and has hot melt properties.

7. The high-transparency room-temperature moisture-curing phenyl silicone resin hot melt adhesive according to claim 6, characterized in that, The light transmittance of the hot melt adhesive is 80.3% to 90.6%.

8. The application of the high-transparency room temperature moisture-curing phenyl silicone resin hot melt adhesive according to claim 7 in the bonding of optical devices, fixing of electronic and electrical components, or sealing of medical devices.

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