Solventless silicone pressure sensitive adhesive

Abstract

This invention relates to the field of organosilicon, specifically to a solvent-free organosilicon pressure-sensitive adhesive, comprising 2-40 parts of vinyl-terminated hyperbranched polyalkoxysilane, 100 parts of hydrogen-containing silicone oil, 40-80 parts of MQ silicone resin, 3-8 parts of catalyst, and 0.05-1 parts of inhibitor. This solvent-free organosilicon pressure-sensitive adhesive introduces hyperbranched polyalkoxysilane as a key component, completely breaking the "molecular weight-viscosity" positive correlation limitation from the molecular structure source, while overcoming the dual defects of "high-temperature harsh process" and "compromise on inferior performance." It constructs a highly chemically cross-linked network, achieving a significant leap in cohesive strength and peel strength, fundamentally eliminating the problem of silicone oil residue.

Description

Technical Field

[0001] This invention relates to the field of organosilicon, and more specifically to a solvent-free organosilicon pressure-sensitive adhesive. Background Technology

[0002] Silicone pressure-sensitive adhesives are pressure-sensitive adhesives with a polysiloxane main chain structure, typically composed of silicone rubber, MQ silicone resin, and crosslinking agents. Their core characteristics lie in combining many excellent properties of silicone materials: long-term stable operation within an extreme temperature range of -75℃ to 300℃; excellent chemical resistance, weather resistance, and electrical insulation properties; and, importantly, the ability to bond low surface energy materials that ordinary adhesives cannot adhere to, such as untreated polyolefins, fluoroplastics, and polyimides.

[0003] Traditional silicone pressure-sensitive adhesives typically require the addition of over 50% organic solvents (such as ethyl acetate, benzene, toluene, etc.) to reduce system viscosity and facilitate coating application. These solvents volatilize during the baking and curing process, causing energy consumption and environmental pollution, a long-standing technical challenge in the industry. Therefore, developing solvent-free or high-solids-content silicone pressure-sensitive adhesives has become a cutting-edge research topic in the industry.

[0004] The patent application filed by Zhejiang Xin'an Chemical Group Co., Ltd., entitled "A Solvent-Free Organosilicon Pressure-Sensitive Adhesive and its Preparation Method" (Publication No. CN119979112A), uses linear polysiloxane and branched polysiloxane as the main resins, methyl MQ silicone resin as the tackifying resin, and linear methyl hydrosiloxane as the crosslinking agent. It is prepared by "heating to 90℃~180℃ and removing low-molecular-weight substances under a reduced pressure of 0.09~0.1MPa for 1h~5h". However, this technical solution still has the following technical defects: Although branched polysiloxane is introduced, its main component is still linear polysiloxane. Due to the entanglement between the linear polymer molecular chains, the intrinsic viscosity of the system is high. Therefore, harsh process conditions such as high temperature and high vacuum must be used to reduce the viscosity of the system to achieve mixing and coating. This not only increases equipment requirements and energy consumption but also restricts production efficiency and cost control.

[0005] The paper "Solvent-Free Organosilicon Pressure-Sensitive Adhesive Prepared from Vi-MQ Silicone Resin and Its Properties" published in *Guangzhou Chemistry* reports a method for preparing a solvent-free organosilicon pressure-sensitive adhesive. This method uses vinyl-terminated MQ silicone resin as the tackifying resin and low-molecular-weight silicone oil as the main component to achieve solvent-free properties. However, this technical solution has the following inherent drawbacks: Because low-molecular-weight silicone oil is difficult to form effective molecular chain entanglement or cross-linking networks, the cohesive force of the pressure-sensitive adhesive system is severely insufficient, with a maximum peel strength of only 20 g / 25 mm, far below the basic requirements for industrial applications. Simultaneously, unreacted or free low-molecular-weight silicone oil in the system is prone to migration and precipitation during long-term use, causing surface contamination of the adhered objects and degradation of adhesive performance, severely limiting its practical application value. Summary of the Invention

[0006] To overcome the aforementioned technical problems, this invention provides a solvent-free silicone pressure-sensitive adhesive using hyperbranched polyalkoxysilane as a key component. Unlike linear polymers, hyperbranched polymers, due to their unique dendritic three-dimensional structure and the absence of molecular chain entanglement, exhibit an inverse correlation of "high molecular weight, low viscosity," remaining liquid and exhibiting good flowability at room temperature. Therefore, this invention allows for uniform mixing of all components under normal temperature and pressure conditions using a conventional reactor, completely eliminating the dependence on harsh process conditions such as high temperature and high vacuum. It achieves low-viscosity coating while maintaining high molecular weight, demonstrating significant technological advancements and industrial cost advantages.

[0007] The technical solutions to the above technical problems are as follows: A solvent-free silicone pressure-sensitive adhesive, comprising, by weight: Vinyl-terminated hyperbranched polyalkoxysilane 2-40 parts, hydrogen-containing silicone oil 100 parts, MQ silicone resin 40-80 parts, catalyst 3-8 parts, inhibitor 0.05-1 parts; The terminal vinyl hyperbranched polyalkoxysilane has the following structure: ; Furthermore, the aforementioned vinyl-terminated hyperbranched polyalkoxysilane is prepared by a hydrosilylation reaction of AB2-type monomers formed by the nucleophilic substitution reaction of methyldichlorosilane and 2-hydroxypropyl acrylate under the catalysis of an amine catalyst. The specific preparation method is as follows: Step 1): Synthesis of AB2 type monomers In a reaction vessel equipped with an ice-water bath, 2-hydroxypropyl acrylate, pyridine, and tetrahydrofuran were added in a molar ratio of 1:1:3-5. Then, 0.05% (by molar weight) of dimethylaminopyridine was added. Stirring was started, and after homogeneous mixing, a pre-prepared 50% (w / w) tetrahydrofuran solution of methyldichlorosilane was added dropwise to the reaction system. The molar ratio of methyldichlorosilane to 2-hydroxypropyl acrylate was 1:2. After the addition was complete, the reaction was continued to be stirred at room temperature for at least 3 hours. The mixture was then filtered, washed with water, dried, and distilled under reduced pressure to obtain the AB2 type monomer. The reaction is as follows: ; Step 2) Preparation of vinyl-terminated hyperbranched polyalkoxysilanes by hydrosilylation reaction of AB2 type monomers In a constant-temperature oil bath reaction vessel at 70–90°C, xylene was added as the reaction solvent. Under magnetic stirring, the AB2-type monomer and chloroplatinic acid catalyst prepared in step 1) were added, with the catalyst added at 1–2% of the mass of the AB2-type monomer. During the reaction, the progress was monitored by FT-IR. The reaction was terminated when no characteristic absorption peak of silane-hydrogen bonds was observed in the reaction system. The characteristic absorption peak of silane-hydrogen bonds is IR: 2160 cm⁻¹. -1 Then, xylene is removed by vacuum distillation to obtain vinyl-terminated hyperbranched polyalkoxysilane. Its reaction is as follows:

[0008] The weight-average molecular weight (Mw) of the terminal vinyl hyperbranched polyalkoxysilane is 1,000 to 30,000, preferably 5,000 to 20,000, and more preferably 8,000 to 15,000.

[0009] Furthermore, the hydrogen-containing silicone oil is an end-hydrogen-containing silicone oil or a side-hydrogen-containing silicone oil, preferably an end-hydrogen-containing silicone oil, wherein the hydrogen content of the hydrogen-containing silicone oil is 0.1% to 1.0%, preferably 0.1% to 0.3%, and the viscosity is <2000 mPa·s.

[0010] Furthermore, the MQ silicone resin is any one or a mixture of several of methyl MQ silicone resin, methyl phenyl MQ silicone resin, and methyl hydrogen-containing MQ silicone resin.

[0011] Furthermore, the catalyst is a Karstedt-type platinum catalyst or a Speier-type platinum catalyst.

[0012] Furthermore, the inhibitor is any one or a mixture of several of methylbutynol, ethynylcyclohexanol, and diethyl maleate.

[0013] The preparation method of this pressure-sensitive adhesive is as follows: According to the above formula, vinyl-terminated hyperbranched polyalkoxysilane and MQ silicone resin were added to a reaction vessel, stirred, and heated to 90℃~110℃. Dehydration was carried out under reduced pressure until the moisture content of the system dropped below 300ppm. Then, it was cooled to room temperature, and inhibitors, hydrogen-containing silicone oil, and platinum catalyst were added in sequence. The mixture was stirred and mixed evenly to obtain solvent-free silicone pressure-sensitive adhesive.

[0014] The method for preparing silicone pressure-sensitive tape using this pressure-sensitive adhesive is as follows: The solvent-free silicone pressure-sensitive adhesive prepared above is uniformly coated on the surface of the substrate, and the coating thickness is controlled to form the required adhesive layer. The substrate is selected from PET film, PI film, crepe paper or fiberglass cloth. Then the coated substrate is placed in an oven at 120°C and baked for 2 minutes to cure the pressure-sensitive adhesive layer, thus obtaining the silicone pressure-sensitive tape product. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the crosslinked network structure of the pressure-sensitive adhesive prepared in Example 1 of the present invention.

[0016] The solvent-free silicone pressure-sensitive adhesive prepared by this invention breaks away from the traditional design thinking of linear polymers and introduces hyperbranched polyalkoxysilanes as key components. It completely breaks the "molecular weight-viscosity" positive correlation limitation from the molecular structure source, achieving the following technological breakthroughs: 1. It overcomes the dual defects of "high-temperature harsh process" and "compromise on inferior performance".

[0017] The hyperbranched polyalkoxysilane used in this invention exhibits a unique dendritic three-dimensional structure with no entanglement between molecular chains, resulting in a reverse correlation between "high molecular weight and low viscosity." On one hand, it is a highly fluid liquid at room temperature, allowing for uniform mixing of the components at room temperature and pressure without the need for harsh conditions such as high temperature or high vacuum during mixing. Dehydration is a pretreatment step for the raw materials and does not affect the operability at room temperature and pressure during coating application. On the other hand, its high molecular weight ensures the integrity of the crosslinked network skeleton after curing.

[0018] 2. A highly chemically cross-linked network was constructed, achieving a significant leap in cohesive force and peel strength.

[0019] This invention uses vinyl-terminated hyperbranched polyalkoxysilane as the main component, utilizing its densely packed active end groups on the molecular periphery to undergo a full hydrosilylation reaction with hydrogen-containing silicone oil under the action of a platinum catalyst. This forms a highly chemically cross-linked network with hyperbranched molecules as rigid nodes and hydrogen-containing silicone oil as flexible chain segments. This structure results in extremely strong cohesion in the pressure-sensitive adhesive, achieving an order-of-magnitude leap in peel strength, truly meeting industrial application standards.

[0020] 3. It fundamentally eliminates the problem of silicone oil residue.

[0021] Thanks to the numerous active reaction sites on the periphery of hyperbranched molecules, hydrogen-containing silicone oils can be completely fixed in the cross-linked network through chemical bonds, rather than being physically blended or existing in a free state. This completely solves the problem of free silicone oil migration and precipitation that is common in conventional solvent-free systems, ensuring the performance stability and cleanliness of the product during long-term use.

[0022] In summary, by introducing a hyperbranched structure, this invention simultaneously achieves the unity of "mild process at room temperature and pressure", "excellent performance of high peel strength and high cohesion" and "high purity" in the same technical solution, thus solving a long-standing technical problem recognized by the industry. Detailed Implementation

[0023] 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.

[0024] Unless otherwise specified, all reagents and raw materials used in the following examples are commercially available, and their specific sources are not detailed here.

[0025] ① Synthesis of AB2 type monomers In a reaction vessel equipped with an ice-water bath, 2-hydroxypropyl acrylate, pyridine, and tetrahydrofuran were added in a molar ratio of 1:1:3-5. Then, dimethylaminopyridine was added at 0.05% of the total molar amount of the reaction system. Stirring was started, and after the mixture was stirred evenly, a pre-prepared tetrahydrofuran solution with a mass concentration of 50% methyldichlorosilane was added dropwise to the reaction system. The molar ratio of methyldichlorosilane to 2-hydroxypropyl acrylate was 1:2. After the addition was complete, the reaction was stirred at room temperature for at least 3 hours. After filtration, the product was washed with water, dried, and distilled under reduced pressure to obtain the AB2 type monomer. ② Preparation of vinyl-terminated hyperbranched polyalkoxysilanes In a constant-temperature oil bath reaction vessel at 70–90°C, xylene was added as the reaction solvent. Under magnetic stirring, the aforementioned AB2-type monomer and chloroplatinic acid catalyst were added, with the catalyst added at 1–2% of the mass of the AB2-type monomer. During the reaction, the progress was monitored by FT-IR. The reaction was terminated when no characteristic absorption peak of silane-hydrogen bonds was observed in the reaction system. The characteristic absorption peak of silane-hydrogen bonds is IR: 2160 cm⁻¹. -1 Then, xylene was removed by vacuum distillation to obtain end-vinyl hyperbranched polyalkoxysilane, and the weight-average molecular weight (Mw) was determined to be 12,000–15,000 by laser light scattering.

[0026] The molecular weight of vinyl-terminated hyperbranched polyalkoxysilanes affects their ability to build crosslinked networks in pressure-sensitive adhesives. When the molecular weight is too low (<1000), it is difficult to form an effective crosslinked backbone, resulting in insufficient cohesion; when the molecular weight is too high (>30000), the system viscosity is too high, affecting coating uniformity, and excessive crosslinking may lead to a decrease in the flexibility of the adhesive layer. This invention achieves synergistic optimization of low-viscosity coating and high crosslinking density by controlling the molecular weight within the range of 1000–30000.

[0027] Examples 1 through 6 all used the same batch of terminal vinyl hyperbranched polyalkoxysilane synthesized. Example 1:

[0028] Two parts of vinyl-terminated hyperbranched polyalkoxysilane and 40 parts of MQ silicone resin were added to a reactor, stirred, and heated to 90℃~110℃. The mixture was then dehydrated under reduced pressure until the moisture content dropped below 300ppm. After cooling to room temperature, 0.05 parts of inhibitor, 100 parts of hydrogen-containing silicone oil, and 3.5 parts of catalyst were added sequentially, and the mixture was stirred and mixed thoroughly. A schematic diagram of the crosslinked network structure of the pressure-sensitive adhesive is attached. Figure 1 As shown. Example 2:

[0029] Ten parts of vinyl-terminated hyperbranched polyalkoxysilane and 60 parts of MQ silicone resin were added to a reactor, stirred, and heated to 90℃~110℃. The mixture was then dehydrated under reduced pressure until the moisture content of the system dropped below 300ppm. After cooling to room temperature, 0.1 parts of inhibitor, 100 parts of hydrogen-containing silicone oil, and 4 parts of catalyst were added sequentially, and the mixture was stirred and mixed thoroughly. Example 3:

[0030] Add 15 parts of vinyl-terminated hyperbranched polyalkoxysilane and 60 parts of MQ silicone resin to a reactor, start stirring, and heat to 90℃~110℃. Dehydrate under reduced pressure until the moisture content of the system drops below 300ppm. Then cool to room temperature, add 0.2 parts of inhibitor, 100 parts of hydrogen-containing silicone oil and 5 parts of catalyst in sequence, and continue stirring to mix evenly. Example 4:

[0031] 20 parts of vinyl-terminated hyperbranched polyalkoxysilane and 60 parts of MQ silicone resin were added to a reactor, stirred, and heated to 90℃~110℃. The mixture was then dehydrated under reduced pressure until the moisture content of the system dropped below 300ppm. After cooling to room temperature, 0.3 parts of inhibitor, 100 parts of hydrogen-containing silicone oil, and 6 parts of catalyst were added sequentially, and the mixture was stirred and mixed thoroughly. Example 5:

[0032] Add 30 parts of vinyl-terminated hyperbranched polyalkoxysilane and 60 parts of MQ silicone resin to a reactor, start stirring, and heat to 90℃~110℃. Dehydrate under reduced pressure until the moisture content of the system drops below 300ppm. Then cool to room temperature, add 0.5 parts of inhibitor, 100 parts of hydrogen-containing silicone oil and 7 parts of catalyst in sequence, and continue stirring to mix evenly. Example 6:

[0033] 40 parts of vinyl-terminated hyperbranched polyalkoxysilane and 80 parts of MQ silicone resin were added to a reactor, stirred, and heated to 90℃~110℃. The mixture was then dehydrated under reduced pressure until the moisture content of the system dropped below 300ppm. After cooling to room temperature, 1 part of inhibitor, 100 parts of hydrogen-containing silicone oil, and 8 parts of catalyst were added sequentially, and the mixture was stirred and mixed thoroughly. Example 7:

[0034] Five parts of vinyl-terminated hyperbranched polyalkoxysilane and 50 parts of methylphenyl MQ silicone resin were added to a reactor, stirred, and heated to 95°C. The mixture was then dehydrated under reduced pressure until the moisture content of the system dropped below 300 ppm. After cooling to room temperature, 0.08 parts of methylbutyninol, 100 parts of side-containing hydrogen silicone oil, and 7.5 parts of Karstedt-type catalyst were added sequentially, and the mixture was stirred and mixed thoroughly to obtain a solvent-free silicone pressure-sensitive adhesive. The hydrogen content of the hydrogen silicone oil was 1%, and its viscosity was 1980 mPa·s. Example 8:

[0035] 30 parts of vinyl-terminated hyperbranched polyalkoxysilane, 40 parts of methylphenyl MQ silicone resin, and 40 parts of methyl hydrogen-containing MQ silicone resin were added to a reactor. Stirring was started, and the temperature was raised to 100°C. Dehydration was carried out under reduced pressure until the moisture content of the system dropped below 300 ppm. The mixture was then cooled to room temperature, and 0.75 parts of methylbutyninol, 0.1 parts of diethyl maleate, 0.1 parts of etynylcyclohexanol, 100 parts of hydrogen-containing silicone oil, and 7.5 parts of Karstedt-type catalyst were added sequentially. The mixture was stirred and mixed thoroughly to obtain a solvent-free silicone pressure-sensitive adhesive. The hydrogen content of the hydrogen-containing silicone oil was 0.5%, and its viscosity was 600 mPa·s. Example 9:

[0036] 25 parts of vinyl-terminated hyperbranched polyalkoxysilane, 15 parts of methyl MQ silicone resin, 15 parts of methyl phenyl MQ silicone resin, and 30 parts of methyl hydrogen-containing MQ silicone resin were added to a reactor. Stirring was started, and the temperature was raised to 110°C. Dehydration was carried out under reduced pressure until the moisture content of the system dropped below 300 ppm. The mixture was then cooled to room temperature, and 0.2 parts of diethyl maleate, 0.15 parts of ethynylcyclohexanol, 100 parts of hydrogen-containing silicone oil, and 5.5 parts of Karstedt-type catalyst were added sequentially. The mixture was stirred and mixed thoroughly to obtain a solvent-free silicone pressure-sensitive adhesive. The hydrogen content of the hydrogen-containing silicone oil was 0.2%, and its viscosity was 1600 mPa·s. Comparative Example 1:

[0037] Add 30 parts of vinyl-terminated polysiloxane and 40 parts of MQ silicone resin to a reactor, start stirring, and heat to 90℃~110℃. Dehydrate under reduced pressure until the moisture content of the system drops below 300ppm. Then cool to room temperature, and add 0.1 parts of inhibitor, 100 parts of hydrogen-containing silicone oil and 3.5 parts of catalyst in sequence, and continue stirring to mix evenly. Comparative Example 2:

[0038] Referring to the invention patent technology of "A solvent-free organosilicon pressure-sensitive adhesive and its preparation method" (publication number CN119979112A) applied for by Zhejiang Xin'an Chemical Group Co., Ltd., the solvent-free organosilicon pressure-sensitive adhesive was prepared according to the formulation and process of Example 1 in its specification. Comparative Example 3:

[0039] Referring to the method reported in the paper "Solvent-free organosilicon pressure-sensitive adhesive prepared by Vi-MQ silicone resin and its properties" published by Qiao Jinfei et al. in Guangzhou Chemistry, a solvent-free organosilicon pressure-sensitive adhesive was prepared using low molecular weight silicone oil as the main component and vinyl-terminated MQ silicone resin as the tackifying resin. For ease of performance comparison, Examples 1-6 and Comparative Example 1 all used hydrogen-terminated silicone oil with a viscosity of 800-1500 mPa•s, a molecular weight (Mn) of 15000-25000, and a hydrogen content of 0.1-0.3%, model XHG-202H-6005; MQ silicone resin was methyl MQ silicone resin with a molecular weight (Mw) of 4000-6000, model Silmer Q30; the catalyst was a Speier type platinum catalyst with a Pt content of 3000 ppm, model CAT-SPL-030; and the inhibitor was ethynylcyclohexanol. The specific formulations of Examples 1-6 and Comparative Example 1 are shown in Table 1 below:

[0040] Table 1. Composition and components of Examples 1-6 and Comparative Example 1 Performance testing methods

[0041] Viscosity of pressure-sensitive adhesive: The silicone pressure-sensitive adhesives prepared in Examples 1 to 6 and Comparative Example 1 were measured using a rotational viscometer in accordance with GB / T 2794-2022 "Determination of viscosity of adhesives".

[0042] The solvent-free silicone pressure-sensitive adhesives prepared in Examples 1-6 and Comparative Examples 1-3 were uniformly coated onto the surface of a PET film substrate with a thickness of 35 μm. The coating thickness was controlled to ensure that the cured adhesive layer reached the target thickness. The coated PET film was then placed in an oven at 120°C for 2 minutes to fully cure the pressure-sensitive adhesive layer, resulting in silicone pressure-sensitive adhesive tape samples with a dry adhesive thickness of 20 μm. The performance of each sample was then characterized according to the following test methods.

[0043] Adhesive layer thickness: determined in accordance with GB / T 7125-2014 "Test method for thickness of adhesive tape".

[0044] Peel strength: The test was conducted in accordance with GB / T 2792-2014 "Test Method for Peel Strength of Adhesive Tapes".

[0045] Cohesion: Characterized by static holding power at high temperature, and tested according to GB / T 4851-2014 "Test method for holding power of adhesive tapes" at a test temperature of 70℃.

[0046] The test results are shown in Table 2 below: Table 2 Performance test data of Examples 1-6 and Comparative Example 1

[0047] As shown in Table 2, the viscosity of the silicone pressure-sensitive adhesives prepared in Examples 1-6 and Comparative Examples 1-3 is not high. Examples 1-6 all incorporated terminal vinyl hyperbranched polyalkoxysilane, which effectively improved the peel strength of the pressure-sensitive adhesive. The peel strength was highest at 20 parts of terminal vinyl hyperbranched polyalkoxysilane, reaching 18.1 N / 25 mm. Compared to Comparative Example 3, the peel strength jumped from the order of 0.196 N / 25 mm to 18.1 N / 25 mm, achieving a nearly 100-fold performance improvement; compared to Comparative Example 1, the peel strength also increased by approximately 36 times, representing a significant leap. Simultaneously, the cohesive force of the silicone pressure-sensitive tape also increased with the increase in the amount of terminal vinyl hyperbranched polyalkoxysilane. Therefore, the addition of terminal vinyl hyperbranched polyalkoxysilane plays a decisive role in product performance. Comparing Examples 1-6 with Comparative Examples 1-3, it can be seen that the peel strength of polyalkoxysilanes without end-vinyl hyperbranched polyalkoxysilanes is <1N / 25mm and the cohesive force is only 2.5 hours at most, which confirms that end-vinyl hyperbranched polyalkoxysilanes are the core for building cross-linked networks and ensuring performance.

[0048] The solvent-free silicone pressure-sensitive adhesive prepared by this invention breaks away from the traditional design thinking of linear polymers and introduces hyperbranched polyalkoxysilanes as key components. It completely breaks the "molecular weight-viscosity" positive correlation limitation from the molecular structure source, achieving the following technological breakthroughs: 1. It overcomes the dual defects of "high-temperature harsh process" and "compromise on inferior performance".

[0049] The hyperbranched polyalkoxysilane used in this invention exhibits a unique dendritic three-dimensional structure with no entanglement between molecular chains, resulting in a reverse correlation between "high molecular weight and low viscosity." On one hand, it is a highly fluid liquid at room temperature, allowing for uniform mixing of the components at room temperature and pressure without the need for harsh conditions such as high temperature or high vacuum during mixing. Dehydration is a pretreatment step for the raw materials and does not affect the operability at room temperature and pressure during coating application. On the other hand, its high molecular weight ensures the integrity of the crosslinked network skeleton after curing.

[0050] 2. A highly chemically cross-linked network was constructed, achieving a significant leap in cohesive force and peel strength.

[0051] This invention uses vinyl-terminated hyperbranched polyalkoxysilane as the main component, utilizing its densely packed active end groups on the molecular periphery to undergo a full hydrosilylation reaction with hydrogen-containing silicone oil under the action of a platinum catalyst. This forms a highly chemically cross-linked network with hyperbranched molecules as rigid nodes and hydrogen-containing silicone oil as flexible segments.

[0052] 3. It fundamentally eliminates the problem of silicone oil residue.

[0053] Thanks to the numerous active reaction sites on the periphery of hyperbranched molecules, hydrogen-containing silicone oils can be completely fixed in the cross-linked network through chemical bonds, rather than being physically blended or existing in a free state. This completely solves the problem of free silicone oil migration and precipitation that is common in conventional solvent-free systems, ensuring the performance stability and cleanliness of the product during long-term use.

[0054] In summary, by introducing a hyperbranched structure, this invention simultaneously achieves the unity of "mild process at room temperature and pressure", "excellent performance of high peel strength and high cohesion" and "high purity" in the same technical solution, thus solving a long-standing technical problem recognized by the industry.

[0055] 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 solvent-free silicone pressure-sensitive adhesive, characterized in that, By weight, it includes: Vinyl-terminated hyperbranched polyalkoxysilane 2-40 parts, hydrogen-containing silicone oil 100 parts, MQ silicone resin 40-80 parts, catalyst 3-8 parts, inhibitor 0.05-1 parts; The terminal vinyl hyperbranched polyalkoxysilane has the following structure: 。 2. The solvent-free silicone pressure-sensitive adhesive according to claim 1, characterized in that: The terminal vinyl hyperbranched polyalkoxysilane is prepared by a nucleophilic substitution reaction between methyldichlorosilane and 2-hydroxypropyl acrylate under the catalysis of an amine catalyst to form an AB2 type monomer, which is then subjected to a hydrosilylation reaction.

3. The solvent-free silicone pressure-sensitive adhesive according to claim 1, characterized in that: The hydrogen-containing silicone oil is an end-hydrogen-containing silicone oil or a side-hydrogen-containing silicone oil, wherein the hydrogen content of the hydrogen-containing silicone oil is 0.1% to 1.0% and the viscosity is < 2000 mPa·s.

4. The solvent-free silicone pressure-sensitive adhesive according to claim 3, characterized in that: The hydrogen-containing silicone oil is an end-hydrogen-containing silicone oil, and the hydrogen content of the hydrogen-containing silicone oil is 0.1% to 0.3%.

5. The solvent-free silicone pressure-sensitive adhesive according to claim 1, characterized in that: The MQ silicone resin is any one or a mixture of several of methyl MQ silicone resin, methyl phenyl MQ silicone resin, and methyl hydrogen-containing MQ silicone resin.

6. The solvent-free silicone pressure-sensitive adhesive according to claim 1, characterized in that: The catalyst is either a Karstedt-type platinum catalyst or a Speier-type platinum catalyst.

7. The solvent-free silicone pressure-sensitive adhesive according to claim 1, characterized in that: The inhibitor is any one or a mixture of several of methylbutynol, ethynylcyclohexanol, and diethyl maleate.

8. The solvent-free silicone pressure-sensitive adhesive according to claim 2, characterized in that: The terminal vinyl hyperbranched polyalkoxysilane is synthesized according to the following steps: Step 1): Synthesis of AB2 type monomers In a reaction vessel equipped with an ice-water bath, 2-hydroxypropyl acrylate, pyridine, and tetrahydrofuran were added in a molar ratio of 1:1:3-5. Then, 0.05% (by molar weight) of dimethylaminopyridine was added. Stirring was started, and after homogeneous mixing, a pre-prepared 50% (w / w) tetrahydrofuran solution of methyldichlorosilane was added dropwise to the reaction system. The molar ratio of methyldichlorosilane to 2-hydroxypropyl acrylate was 1:

2. After the addition was complete, the reaction was continued to be stirred at room temperature for at least 3 hours. The mixture was then filtered, washed with water, dried, and distilled under reduced pressure to obtain the AB2 type monomer. The reaction is as follows: ； Step 2) Preparation of vinyl-terminated hyperbranched polyalkoxysilanes by hydrosilylation reaction of AB2 type monomers In a constant-temperature oil bath reaction vessel at 70–90°C, xylene was added as the reaction solvent. Under magnetic stirring, the AB2 type monomer and catalyst prepared in step 1) were added. During the reaction, the progress was monitored by FT-IR. The reaction was terminated when no characteristic absorption peak of silane-hydrogen bonds was observed in the reaction system. The characteristic absorption peak of silane-hydrogen bonds is IR: 2160 cm⁻¹. -1 Then, xylene is removed by vacuum distillation to obtain vinyl-terminated hyperbranched polyalkoxysilane; the reaction is as follows: 。 9. The solvent-free silicone pressure-sensitive adhesive according to claim 8, characterized in that: The catalyst mentioned in step 2) is a chloroplatinic acid catalyst, and the amount added is 1 to 2% of the mass of the AB2 type monomer.

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