Tackifiers for one-component addition-type thermosetting liquid silicone rubber, their preparation methods, and applications

Abstract

The present application relates to the technical field of liquid silicone rubber, and particularly discloses a tackifier for single-component addition type heat-curable liquid silicone rubber, a preparation method and application thereof. The tackifier is synthesized by heating and reacting a compound with epoxy, a benzene ring and a vinyl group and hydrogen-containing siloxane under the action of a platinum gold catalyst. The tackifier is good in compatibility with silicone rubber, simple to make and convenient to use. When added to single-component addition type liquid organic silicone rubber, the silicone rubber can react with a polar substrate surface active group to form a firm bonding effect when heated at high temperature, and no oil seepage and adhesion occurs after compression sealing at high temperature, so that lossless disassembly and repair can be realized.

Description

Technical Field

[0001] This invention belongs to the field of liquid silicone rubber, specifically relating to a tackifier for a one-component addition-type thermosetting liquid silicone rubber, its preparation method, and its application. Background Technology

[0002] With the rapid development of my country's industry, emerging technologies in various sectors such as new energy vehicles, 5G communications, electronics, photovoltaics, and energy storage are flourishing. In industrial production, assembly processes such as shell sealing, flange sealing, and flat and curved surface sealing are crucial components, making workpiece sealing extremely important. Single-component addition-curing silicone rubber, due to its unique cross-linking and curing mechanism, features rapid heating and curing, good compression resilience, no low-molecular-weight release, and environmental friendliness, making it highly suitable for CIPG sealing technology (Cured-In-Place Gasket, a curing-type in-line molding sealing ring process, which involves first applying a liquid sealant to a flange or other sealing surface, rapidly curing it, and then assembling it to achieve single-sided bonding and double-sided compression sealing).

[0003] Currently, single-component addition-curing silicone rubber suffers from poor adhesion to metal substrates, leading to misalignment or even detachment of the sealing strip during transportation. The simplest and most effective solution is to add a silane coupling agent to the system. However, conventional silane coupling agents are problematic. Amino-based coupling agents cause platinum catalysts to degrade, rendering them unusable; epoxy-based coupling agents cannot participate in the crosslinking reaction, and after prolonged compression following sealant curing, they are prone to precipitation, which is detrimental to the long-term, safe, and stable operation of internal components; while acryloyloxy-based coupling agents can participate in the crosslinking reaction, they affect the curing speed and mechanical properties; and highly reactive methoxy or ethoxy groups in silane coupling agents cause the cured strip to continue reacting with the substrate surface after prolonged compression, resulting in adhesion and hindering non-destructive disassembly and repair. Therefore, it is essential to develop a tackifier for single-component addition-curing thermosetting silicone rubber that not only exhibits excellent adhesion to the substrate during high-temperature curing but also allows for non-destructive disassembly and repair after prolonged environmental aging.

[0004] Chinese patent CN105131291A discloses a tackifier for addition-cure liquid silicone rubber and its preparation method, as well as an adhesive addition-cure liquid silicone rubber containing the tackifier and its preparation method. The method involves hydrolyzing and condensing methyldimethoxysilane and dimethyldimethoxysilane under the catalysis of hydrochloric acid solution to obtain terminal hydroxymethylhydrosilane. Then, the terminal hydroxymethylhydrosilane is reacted with γ-(2,3-epoxypropoxy)propyltrimethoxysilane and γ-(methacryloyloxy)propyltrimethoxysilane under the catalysis of titanate ester to obtain the tackifier. When used in addition-cure liquid silicone rubber, this tackifier achieves 100% cohesive failure on aluminum, glass, and stainless steel, with a maximum shear strength of 2.0 MPa. However, the addition-cure liquid silicone rubber in this invention contains alkoxy groups. After the liquid silicone rubber cures, unreacted alkoxy groups in the tackifier hydrolyze after prolonged aging to form silanol groups, which are prone to reacting with the contact surface, thus posing a serious risk of adhesion.

[0005] Chinese patent CN113801626A discloses a method for preparing a one-component addition-type adhesive by adding a titanate coupling agent and a portion of an alkoxy tackifier to a base adhesive in stages, obtaining a prepolymer, and then adding the alkoxy tackifier again. This adhesive is then combined with hydrogen-containing polysiloxane and a weakly acidic pH adjuster, among other additives. This tackifier requires two different types to be used in combination, a staged addition process, and pH adjustment; otherwise, the bond strength will significantly decrease. The adhesive preparation process is complex and not conducive to industrial production.

[0006] Chinese patent CN104892942A discloses a method for preparing an addition-type silicone rubber tackifier using an acidic cationic resin as a catalyst via hydrolysis-condensation. The method involves using three or more alkoxysilanes with different functionalities as raw materials, methanol or ethanol as solvent to control the degree of condensation, and using the acidic cationic resin as a catalyst. Partial co-hydrolysis-condensation is performed at 40–80°C. After filtering to remove the cationic resin and removing the solvent and low-volatile components under reduced pressure, a colorless, transparent siloxane oligomer tackifier with a degree of polymerization of 3–6 is obtained. While the addition-type silicone rubber prepared by this tackifier exhibits good adhesion to various substrates, it requires heat pretreatment followed by prolonged high-temperature curing, resulting in poor efficiency and high energy consumption, causing significant inconvenience in practical applications.

[0007] Currently, there are many domestic inventions of tackifiers for addition-cured silicone rubber applications. However, much research focuses on the adhesion between silicone rubber and the substrate, neglecting the problem of silicone rubber sticking to the top cover after long-term use, making disassembly and repair impossible, as well as the complexity of manufacturing and application processes. Therefore, inventing a tackifier that helps silicone rubber achieve excellent adhesion to the substrate after curing, and allows for non-destructive disassembly and repair even after long-term environmental aging, with a simple process, can greatly increase the value of silicone rubber in industrial applications. Summary of the Invention

[0008] In order to overcome the shortcomings and disadvantages of the existing technology, the primary objective of this invention is to provide a method for preparing a tackifier for a one-component addition-type thermosetting liquid silicone rubber.

[0009] The second objective of this invention is to provide a tackifier for a one-component addition-type thermosetting liquid silicone rubber prepared by the above preparation method.

[0010] A third objective of this invention is to provide the application of the above-mentioned tackifier for single-component addition-curing thermosetting liquid silicone rubber in liquid silicone rubber.

[0011] The primary objective of this invention is achieved through the following technical solution:

[0012] A method for preparing a tackifier for a one-component addition-type thermosetting liquid silicone rubber includes the following steps:

[0013] (1) Stir hydrogen-containing polydimethylsiloxane, catalyst and auxiliary agent A evenly, heat to react, remove impurities under vacuum, filter, and obtain liquid B;

[0014] (2) After liquid B cools to room temperature, add activated carbon, stir to adsorb, and then filter to obtain thickener.

[0015] Preferably, the hydrogen-containing polydimethylsiloxane in step (1) is end-side hydrogen-containing polydimethylsiloxane (abbreviated as: end-side hydrogen-containing silicone oil), and the hydrogen content of the hydrogen-containing polydimethylsiloxane is 0.36% to 0.75%.

[0016] Preferably, the catalyst in step (1) is at least one of platinum-1,3-divinyltetramethyldisiloxane complex, bis(1,3-divinyl-1,1,3,3-tetramethyldisiloxane)platinum, platinum-1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane complex, vinyl chloroplatinate complex, and methyl phthalate solution, with a platinum content of 1000–5000 ppm. The catalyst can catalyze the reaction of hydrogen-containing polydimethylsiloxane and auxiliary agent A, causing auxiliary agent A to react with the Si-H groups of the hydrogen-containing polydimethylsiloxane, thereby attaching auxiliary agent A to the hydrogen-containing polydimethylsiloxane. In this invention, the platinum content of the catalyst in step (1) can be selected from the range of 1000 to 5000 ppm, such as 1000 ppm, 1500 ppm, 2000 ppm, 2500 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm, 5000 ppm, etc., but is not limited to these listed platinum contents.

[0017] Preferably, the additive A in step (1) is at least one of 4-(epoxyethyl)styrene, bisphenol A dielyl ether, methyl 4-vinylbenzoate, and (4-vinylphenyl)trimethoxysilane. The molecular structure of additive A contains vinyl groups, epoxy groups, and benzene ring groups. The vinyl groups in the molecular structure of additive A connect additive A to a hydrogen-containing polydimethylsiloxane, thereby giving the tackifier epoxy groups and benzene ring groups. If the tackifier also retains vinyl groups, these vinyl groups will affect the vulcanization rate of the silicone rubber when the tackifier is used in a one-component addition-curing thermosetting liquid silicone rubber. For example, when additive A is bisphenol A dielyl ether, it will cause the vinyl groups to remain on the tackifier.

[0018] Preferably, the molar ratio of hydrogen-containing polydimethylsiloxane to additive A in step (1) is 1:1 to 3. By controlling the molar ratio of hydrogen-containing polydimethylsiloxane to additive A, it is ensured that additive A is attached to the terminal hydrogen of the hydrogen-containing polydimethylsiloxane, and the side hydrogen of the hydrogen-containing polydimethylsiloxane is retained, so that the final tackifier retains the side chain Si-H. In this invention, the molar ratio of hydrogen-containing polydimethylsiloxane to additive A in step (1) can be selected from the range of 1:1 to 3, for example, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, etc., but is not limited to these listed molar ratios. Preferably, the molar ratio of hydrogen-containing polydimethylsiloxane to additive A is 1:1 to 2.5. If the amount of additive A is too low, there will be too little additive A linked to hydrogen-containing polydimethylsiloxane; if the amount of additive A is too high, there will be a large amount of Si-H side chains of hydrogen-containing polydimethylsiloxane linked to additive A. This invention retains the side Si-H of hydrogen-containing polydimethylsiloxane in the tackifier. The Si-H of the tackifier can undergo a crosslinking reaction with the base polymer in the one-component addition-type thermosetting liquid silicone rubber, thus preventing oil seepage during long-term compression.

[0019] Preferably, the heating reaction temperature in step (1) is 60–100°C, and the reaction time is 2–4 h. In this invention, the reaction temperature of step (1) can be selected from the range of 60–100°C, for example, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, etc., but is not limited to these listed temperature values. The preferred reaction temperature is 60–70°C, which ensures that the additive A is attached to the terminal hydrogen of the hydrogen-containing polydimethylsiloxane and that the side hydrogen of the hydrogen-containing polydimethylsiloxane is retained, so that the final tackifier retains the side chain Si-H. When the temperature is further increased, the local reaction temperature may be higher, which may increase the hydrogen activity of the side chain of the hydrogen-containing polydimethylsiloxane. The reaction between the vinyl group and the hydrogen of the side chain causes the group of the additive A to be attached to the side chain of the hydrogen-containing polydimethylsiloxane, which ultimately affects the viscosity stability of the one-component addition-cured silicone rubber, thereby affecting the storage stability of the one-component addition-cured silicone rubber.

[0020] Preferably, the reaction time for adding activated carbon and stirring in step (2) is 8–24 hours. The function of activated carbon is to adsorb and remove the platinum catalyst in liquid B, thereby removing impurities.

[0021] The term "impurity removal" refers to the removal of small molecule impurities from the reaction products. These small molecule impurities include components such as low-cyclic vinyl silicone oils (D3-D10). Impurity removal methods can include vacuum removal, activated carbon removal, or other conventional methods.

[0022] The above-mentioned method for preparing the tackifier uses simple steps and easily achievable process conditions (heating, stirring, vacuum) to efficiently (with short reaction time) synthesize a hydrogen-containing siloxane tackifier with epoxy and benzene ring groups.

[0023] The second objective of this invention is achieved through the following technical solution:

[0024] A one-component addition-type thermosetting liquid silicone rubber tackifier prepared by the above method has the following structural formula:

[0025]

[0026] Where m = 1 to 8, n = 8 to 30 are natural numbers, and R1 is any one of the following groups:

[0027]

[0028] In some embodiments of the present invention, the above-mentioned thickeners with m = 4 to 5 and n = 10 to 23 natural numbers can be used.

[0029] In some embodiments of the present invention, the main component of the tackifier is any one of the following:

[0030]

[0031]

[0032] The structural characteristics and working principle of the thickener prepared by this invention are as follows:

[0033] In CIPG compression sealing applications, the sealing material not only needs to firmly adhere to the sealing surface on one side to prevent displacement or even detachment, but also needs to be easily disassembled and non-adhesive after environmental aging. This is an application contradiction that conventional one-component addition-curing thermosetting liquid silicone rubber cannot solve. The tackifier for one-component addition-curing thermosetting liquid silicone rubber described in this invention is a hydrogen-containing siloxane tackifier designed and synthesized with epoxy and benzene ring groups. When the one-component addition-curing silicone rubber prepared with this tackifier is cured at high temperature, the epoxy groups can react with the active groups on the substrate surface to form a strong adhesive effect. After curing, due to the helical coiling of the molecular chain segments, the non-polar benzene ring macromolecules, and the side groups that can shield the polarity of the epoxy groups and silicon-oxygen bonds, the colloidal interface exhibits a low surface energy, resulting in weak molecular forces between the colloid and the substrate, thus avoiding adhesion during long-term compression. The Si-H in the tackifier can undergo a cross-linking reaction with the base polymer, preventing oil seepage during long-term compression. Using this tackifier solves the problems of poor adhesion to the substrate, re-adhesion, and oil seepage associated with traditional one-component addition-curing thermosetting liquid silicone rubber.

[0034] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0035] The single-component addition-type thermosetting liquid silicone rubber tackifier prepared by this invention contains active groups that are not easily hydrolyzed, has low requirements for storage environment, and only requires mixing of base rubber, tackifier, crosslinking agent and catalyst when preparing rubber compound. It is simple to operate, has high production efficiency, and is suitable for industrial production.

[0036] The AL-AL shear strength measured by applying adhesive to the aluminum alloy shell (AL) is ≥3 MPa, and it can be disassembled after heat aging. The anti-adhesion grade reaches MB:B-0 or above (GB / T 23982-2009). It can be seen that the silicone rubber of the present invention can achieve non-destructive disassembly and repair after long-term environmental aging.

[0037] The single-component addition-type thermosetting liquid silicone rubber tackifier prepared by this invention has good compatibility with the organosilicon matrix (i.e., the base rubber). The prepared rubber compound does not show delamination or oil seepage after being stored at room temperature (25-30℃) for 6 months, and the viscosity change rate is <20%. Moreover, it can achieve rapid curing at 150℃ in only 10 minutes.

[0038] The third objective of this invention is achieved through the following technical solution:

[0039] The above-mentioned tackifier is used as a tackifier in the preparation of liquid silicone rubber, especially in one-component addition-type thermosetting liquid silicone rubber.

[0040] The Si-H in the tackifier can undergo a cross-linking reaction with the base polymer (mainly polymerized from vinyl silicone oil) in the one-component addition-curing thermosetting liquid silicone rubber, preventing oil seepage during long-term compression. Using this tackifier solves the problems of poor adhesion to substrates, re-adhesion, and oil seepage associated with traditional one-component addition-curing thermosetting liquid silicone rubber. The one-component addition-curing liquid silicone rubber achieves a shear strength of 2.4 MPa to 4.1 MPa on aluminum alloy substrates, with an anti-adhesion rating of A0 to B2, and the adhesive strip does not detach or seep oil. Detailed Implementation

[0041] The present invention will be specifically described below through embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments based on the content of the present invention.

[0042] Tackifier Example 1:

[0043] (1) In a three-necked flask equipped with a thermometer, condenser, and mechanical stirrer, 83g of end-side hydrogen-containing silicone oil with a hydrogen content of 0.6% (m=5, n=11) and 0.1g of platinum-1,3-divinyltetramethyldisiloxane complex (3000ppm) were added. After stirring for 15min, 20.5g of auxiliary agent A1 (4-(epoxyethyl)styrene) (the molar ratio of hydrogen-containing silicone oil to auxiliary agent A1 was 1:2) were added. The temperature was raised to 65℃ and the reaction was maintained for 2h. Then, the temperature was raised to 160℃ and vacuum was applied for 3h to remove unreacted small molecules, yielding liquid B. The reaction equation is shown below:

[0044]

[0045] Note: The following reaction mechanism is the same as that of C1.

[0046] (2) After liquid B is cooled to room temperature, 5g of porous activated carbon is added, the mixture is stirred and reacted for 24h, and then filtered 3 times to obtain liquid thickener C1.

[0047] Tackifier Example 2:

[0048] The difference between the preparation process and Implementation Case 1 is that the molar ratio of hydrogen-containing silicone oil to additive A1 in step (1) is replaced with 1:1 to obtain liquid thickener C2.

[0049] Tackifier Example 3:

[0050] The difference between the preparation process and Implementation Case 1 is that the molar ratio of hydrogen-containing silicone oil to additive A1 in step (1) is replaced with 1:3 to obtain liquid thickener C3.

[0051] Tackifier Example 4:

[0052] The difference between the preparation process and Implementation Case 1 is that the equimolar amount of auxiliary agent A1 (4-(epoxyethyl)styrene) in step (1) is replaced with auxiliary agent A2 (bisphenol A dielyl ether) to obtain liquid thickener C4.

[0053] Tackifier Example 5:

[0054] The difference between the preparation process and Implementation Case 1 is that the equimolar amount of auxiliary agent A1 (4-(epoxyethyl)styrene) in step (1) is replaced with auxiliary agent A3 (4-vinyl-benzoate methyl ester) to obtain liquid thickener C5.

[0055] Tackifier Example 6:

[0056] The preparation process is similar to that of Implementation Case 1, except that the equimolar amount of auxiliary agent A1 (4-(epoxyethyl)styrene) in step (1) is replaced with auxiliary agent A4 ((4-vinylphenyl)trimethoxysilane) to obtain liquid thickener C6.

[0057] Tackifier Example 7:

[0058] The preparation process is similar to that of Example 1, except that the end-side hydrogen-containing silicone oil in step (1) is replaced with end-side hydrogen-containing silicone oil with a hydrogen content of 0.36% (m=5, n=23) (the replacement amount is calculated according to the same hydrogen content as the hydrogen-containing silicone oil in Example 1), to obtain liquid thickener C7.

[0059] Tackifier Example 8:

[0060] The preparation process is similar to that of Example 1, except that the end-side hydrogen-containing silicone oil in step (1) is replaced with end-side hydrogen-containing silicone oil with a hydrogen content of 0.75% (m=6, n=10) (the replacement amount is calculated according to the same hydrogen content as the hydrogen-containing silicone oil in Example 1), to obtain liquid thickener C8.

[0061] Tackifier Example 9:

[0062] (1) In a three-necked flask equipped with a thermometer, a condenser, and a mechanical stirrer, add 83g of end-side hydrogen-containing silicone oil with a hydrogen content of 0.6% (m=5, n=11) and 0.1g of platinum-1,3-divinyltetramethyldisiloxane complex (3000ppm). After stirring for 15min, add 20.5g of auxiliary agent A1 (4-(epoxyethyl)styrene) (the molar ratio of hydrogen-containing silicone oil to auxiliary agent A1 is 1:2). Heat to 90℃ and keep the reaction at this temperature for 2h. Then heat to 160℃ and vacuum for 3h to remove unreacted small molecules to obtain liquid B.

[0063] (2) After liquid B is cooled to room temperature, add 5g of porous activated carbon, stir and react for 24h, and filter 3 times to obtain liquid thickener C9.

[0064] To better illustrate the present invention, the present invention uses additive A1 and the tackifiers obtained in Examples 1 to 9 to prepare a one-component addition-type liquid silicone rubber, and then uses the one-component addition-type liquid silicone rubber to bond an aluminum alloy shell, and tests the aging anti-adhesion.

[0065] The preparation method of one-component addition-type liquid silicone rubber is as follows:

[0066] 40 parts of high-viscosity vinyl silicone oil with a viscosity of 120000 mPa·s, 60 parts of low-viscosity vinyl silicone oil with a viscosity of 5000 mPa·s, and 35 parts of [unclear text - possibly a specific surface area] with a specific surface area of ​​300 m² / s were mixed. 2 / g of fumed silica, 6 parts of hexamethyldisiloxane, and 2 parts of deionized water were mixed uniformly under vacuum in a kneader, heated to 130°C and stirred for 2 hours, then heated to 180°C and stirred under vacuum for 2 hours. After cooling and grinding, the mixture was formulated into a base material.

[0067] Take 70 parts of base material, 30 parts of 1000 mPa·s vinyl silicone oil, 1 part of 1.0% hydrogen-containing silicone oil, 0.1 parts of 1-methyl-1-butyninol, and 0.2 parts of bis(3-phenyl-1-butyn-3-ol)-cyclooctyl-1,5-diene platinum complex (3000 ppm). Mix tackifiers C1 to C9 separately until homogeneous to prepare one-component addition-type liquid silicone rubbers as shown in Table 1 (Examples 1-9). Simultaneously, establish Comparative Examples 1-3 as shown in Table 1 (without tackifiers, with commercially available tackifiers and additive A1). The schemes are as follows:

[0068] Table 1. Preparation of one-component addition-cure liquid silicone rubber

[0069]

[0070] The tackifiers prepared in Examples 1-9 and the silicone rubbers prepared therefrom in Examples 1-9, as well as the silicone rubbers in Comparative Examples 1-3, were subjected to relevant tests:

[0071] 1. Compatibility test:

[0072] Poor compatibility between additives or tackifiers and the base polymer can lead to oil seepage in silicone rubber during storage, and prolonged compression after curing may also cause oil seepage. Conversely, good compatibility between additives or tackifiers and the base polymer can prevent oil seepage during storage, but if they haven't participated in the crosslinking reaction, prolonged compression after curing may still result in oil seepage. Conversely, good compatibility between additives or tackifiers and the base polymer, coupled with participation in the crosslinking reaction, makes silicone rubber less prone to oil seepage during storage and prolonged compression. Therefore, compatibility testing is used to evaluate the likelihood of oil seepage in silicone rubber during storage.

[0073] To demonstrate the effectiveness of the reaction between 4-(epoxyethyl)styrene and end-hydrogen-containing silicone oil, this project mixed vinyl silicone oil with additives A1 (4-(epoxyethyl)styrene), A2 (bisphenol A dielyl ether), A3 (methyl 4-vinylbenzoate), A4 ((4-vinylphenyl)trimethoxysilane), and synthetic tackifiers C1-C9 at a mass ratio of 1:1. After uniform mixing and standing for 24 hours, compatibility tests were conducted, and the results are shown in Table 2.

[0074] Table 2 Compatibility Test

[0075]

[0076]

[0077] When two substances are mixed, the greater the difference in structural polarity, the worse the compatibility. As can be seen from Table 2, vinyl silicone oil does not show stratification after being mixed evenly with (4-vinylphenyl)trimethoxysilane, but stratification occurs after being mixed with 4-(epoxyethyl)styrene, bisphenol A dielyl ether, and methyl 4-vinylbenzoate. After grafting reaction with end-hydrogen-containing silicone oil, no stratification occurs. This indicates that the introduction of the siloxane structure increases the compatibility between the additive and the silicone oil base polymer, allowing the tackifier to be evenly dispersed in the system. However, the excessive introduction of 4-(epoxyethyl)styrene by the C3 additive still results in stratification after mixing with vinyl silicone oil.

[0078] 2. Curing performance comparison test:

[0079] Take 4g of the above-mentioned single-component addition-cure silicone rubber and place it in a rotorless vulcanizing apparatus. Set the mold temperature to 150℃ and the curing time to 10min. Test its curing speed at high temperature. The test results are shown in Table 3 below:

[0080] Table 3 Curing Test (Unit: seconds)

[0081] plan TC 10 TC 50 TC 90 plan TC 10 TC 50 TC 90 Example 1 14 23 80 Example 7 16 26 89 Example 2 10 16 56 Example 8 15 25 86 Example 3 17 25 90 Example 9 14 23 87 Example 4 23 37 117 Comparative Example 1 17 26 90 Example 5 16 23 83 Comparative Example 2 16 27 91 Example 6 17 25 89 Comparative Example 3 19 36 115

[0082] The comparative analysis in Table 3 shows that Comparative Example 1, without the addition of a tackifier, has a better curing effect, while Comparative Example 2, with the addition of a commercially available tackifier, has a better curing effect. In Comparative Example 3, the addition of additive A1 (4-(epoxyethyl)styrene) to the one-component addition-type liquid silicone rubber slows down the curing speed. Example 1, however, has a faster curing speed than Comparative Example 1. This indicates that adding additive A slows down the curing speed of the one-component addition-type liquid silicone rubber. Adding a self-made tackifier, obtained by grafting additive A1 (4-(epoxyethyl)styrene) with hydrogen-containing silicone oil, to the one-component addition-type liquid silicone rubber is more conducive to curing, and the curing speed is even better than using a commercially available tackifier or not using a tackifier at all.

[0083] Because Example 4 uses tackifier C4 obtained by grafting hydrogen-containing silicone oil with additive A2 instead of A1, tackifier C4 has two vinyl groups, which leads to a slower curing speed.

[0084] 3. Viscosity change aging test:

[0085] The viscosity of the one-component addition-type silicone rubbers of Comparative Examples 1-3 and Examples 1-9, without the addition of catalysts and inhibitors, was tested. The viscosity after being stored at room temperature (25℃-30℃) for 6 months was also tested. The test results are shown in Table 4 below:

[0086] Table 4 Viscosity Test

[0087]

[0088]

[0089] As can be seen from Table 4, the viscosity of the one-component addition-cure silicone rubbers in the various examples and comparative examples changed little after being stored at room temperature for 6 months, indicating that the one-component addition-cure silicone rubbers in the examples and comparative examples have good storage stability. Therefore, the tackifier prepared by the present invention has no negative impact on the viscosity of the one-component addition-cure silicone rubber and can maintain the good storage stability of the silicone rubber.

[0090] 4. Adhesion test and anti-adhesion test:

[0091] The shear strength of the one-component addition-type liquid silicone rubbers prepared by the adhesives of Comparative Examples 1-3 and Examples 1-9 of this invention was tested. Adhesive strips with a width of 3±0.2 mm and a height of 1.9±0.2 mm were applied to an aluminum alloy shell. The rubber was cured at 150°C for 30 min, allowed to cool to room temperature for 24 h, and then the top cover was tightened. The adhesion and anti-adhesion properties were tested after aging at 125°C for 300 h. The test results are shown in Table 5.

[0092] Table 5 Performance Test Results

[0093]

[0094] As can be seen from Table 5 above, among the examples grafted with hydrogen-containing silicone oil, Example 1 exhibits the best shear strength and an anti-adhesion grade of A0. The tackifier C1 in Example 1 has a longer molecular chain than 4-(epoxyethyl)styrene. After being added to the one-component addition-cured liquid silicone rubber, the epoxy groups are activated by high temperature, reacting with the active groups on the substrate surface to form an adhesive. After high-temperature aging, due to the helical coiling of the molecular chain segments and the non-polar benzene ring macromolecules and side groups that can shield the polarity of the epoxy groups and silicon-oxygen bonds, the entire molecule is in a highly saturated state, exhibiting low surface energy and weak molecular forces with the substrate, thus avoiding oil seepage and adhesion phenomena during long-term compression.

[0095] As shown in Table 2-5, 4-(epoxyethyl)styrene exhibits better compatibility with silicone oil after being grafted with hydrogen-containing silicone oil. When added to a one-component addition-type liquid silicone rubber, it can be rapidly cured at a high temperature of 150°C and has good storage stability at room temperature. After high-temperature aging compression test, its anti-blocking grade reaches A0.

[0096] In Examples 2 and 3, A1 was also used to prepare the tackifier, and everything else was the same as in Example 1. However, the anti-blocking grade could not reach A0 because the molar ratio of hydrogen-containing silicone oil and additive A1 was different. The optimal molar ratio of hydrogen-containing silicone oil and additive A1 is 1:2. In Example 3, the amount of A1 was too high (the molar ratio of hydrogen-containing silicone oil and additive A1 was 1:3), which caused the silicone rubber to eventually exhibit oil seepage.

[0097] Examples 1, 4, and 9 all achieved an anti-adhesion grade of A0. However, the shear strength of Example 4 was slightly lower, while the shear strength of Examples 1 and 9 was higher. This is because Examples 1 and 9 used A1, while Example 4 used A2, indicating that the two additives have different performance characteristics.

[0098] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A tackifier for one-component addition-cure liquid silicone rubber, characterized by comprising, The structure of the tackifier is as follows: wherein m = 1-8, n = 8-30 natural numbers, R1 is any one of the following groups:

2. Process for the preparation of adhesion promoters for one-component addition-cure liquid silicone rubbers, characterized in that The method comprises the following steps: (1) uniformly stirring hydrogen-containing polydimethylsiloxane, a catalyst, and an auxiliary A, heating and reacting, then removing impurities in vacuum, filtering, and obtaining liquid B; the hydrogen-containing polydimethylsiloxane is end-side hydrogen-containing polydimethylsiloxane with a hydrogen content of 0.36%-0.75%; the auxiliary A is at least one of 4-(epoxyethyl)styrene, bisphenol A diallyl ether, 4-vinyl-benzoic acid methyl ester, and (4-vinylphenyl)trimethoxysilane, and the molar ratio of the hydrogen-containing polydimethylsiloxane to the auxiliary A is 1:1-2; (2) after liquid B is cooled to room temperature, adding activated carbon, stirring and adsorbing, and then filtering to obtain the tackifier.

3. The preparation method of the tackifier for one-component addition type heat-curable liquid silicone rubber according to claim 2, characterized in that, the catalyst is at least one of platinum-1,3-divinyltetramethyldisiloxane complex, bis(1,3-divinyl-1,1,3,3-tetramethyldisiloxane)platinum, platinum-1,3,5,7-tetra-vinyl-1,3,5,7-tetramethylcyclotetrasiloxane complex, and vinyl platinum chloride phthalate solution, and the platinum content is 1000-5000 ppm.

4. The method for preparing an adhesion promoter for one-component addition-cure liquid silicone rubber according to claim 3, characterized by, The temperature of the heating reaction in step (1) is 60-100°C, and the reaction time is 2-4 h.

5. The method for preparing an adhesion promoter for one-component addition-cure liquid silicone rubber according to claim 3, characterized by, The temperature of the heating reaction in step (1) is 60-70°C, and the reaction time is 2-4 h.

6. The tackifier for one-component addition type heat-curable liquid silicone rubber prepared by the preparation method of any one of claims 2-5.

7. Use of the tackifier according to claim 6, characterized in that It is applied as a tackifier in one-component addition type heat-curable liquid silicone rubber.

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