Sealing glue for heating tube and preparation process of sealing glue

Abstract

The invention belongs to the technical field of adhesives, and particularly relates to sealing glue for a heating tube and a preparation process of the sealing glue. The sealing glue for the heating tube is prepared from the following raw materials in parts by mass: 90 to 130 parts of alkoxy-terminated alpha, omega-dihydroxy polydimethylsiloxane, 10 to 20 parts of cerium chloride doped phenolic modified silicone oil, 5 to 15 parts of carbon hydroxyl-terminated polydimethylsiloxane, 80 to 120 parts of filler, 3 to 8 parts of cross-linking agent, 1 to 5 parts of catalyst and 1 to 3 parts of coupling agent. The filler comprises spherical silicon resin and modified montmorillonite; the mass ratio of the spherical silicon resin to the modified montmorillonite is 1: (1-3). The sealing glue for the multiple heating pipes has good high-temperature resistance, high-temperature edible oil resistance, cold and hot cycle resistance and heat and humidity resistance, and can meet the requirements of the sealing glue for the heating pipes of various electric appliances.

Description

Technical Field

[0001] The invention belongs to the technical field of adhesives, and in particular relates to sealing glue for a heating tube and a preparation process thereof. Background Art

[0002] The heating tube (electric heating tube) is made of a metal tube as the outer shell, with a high-resistance electric heating alloy wire as the heating material inside, and high-purity magnesium oxide powder with a high thermal conductivity is filled around the heating wire as an insulating filler. As an important heating element, the heating tube is widely used in electrical appliances (coffee machines, water dispensers, sandwich machines, kettles, bread machines, rice cookers, microwave ovens, deep fryers, washing machines). Since magnesium oxide powder has a strong moisture absorption, it will cause the insulation resistance to drop quickly, resulting in short circuits or electric shocks, which is unsafe when used. Therefore, the ends of the electric heating elements should be sealed with sealing glue to prevent the entry of humid air and dust.

[0003] In the prior art, a Chinese patent with the authorization publication number CN105255447B discloses a sealing material for electric heating pipes and electric heating pipes, wherein the sealing material for electric heating pipes is prepared from the following components in weight proportion: 50-200 parts of zirconium silicate powder; 0.2-0.5 parts of methyl high hydrogen silicone oil; 1-20 parts of activated alumina powder; 5-15 parts of epoxy resin; 5-15 parts of fumed silica. The preparation method of the sealing material for electric heating pipes comprises the following steps: 1. Mixing zirconium silicate powder with methyl high hydrogen silicone oil; 2. Drying the mixed powder; 3. Mixing the dried powder with activated alumina powder; 4. Mixing epoxy resin with fumed silica; 5. Mixing the materials in step 3 and 4 and drying them; 6. Grinding to obtain the sealing material for electric heating pipes. The sealing material for electric heating pipes of the technical solution can effectively prevent moisture invasion as a seal for electric heating pipes, greatly extending the service life of the electric heating pipes. However, the heating tube will generate high temperature during operation, which requires the sealing material used to have ideal high temperature resistance. Although the zirconium silicate powder and activated alumina powder in the above technical solution can improve the temperature resistance of the sealing material to a certain extent, epoxy resin, as one of the main adhesives, usually has an upper temperature resistance limit of no more than 200°C, which may not meet the requirements of long-term use.

[0004] The Chinese patent with publication number CN113956835A discloses a silicone sealant for U-shaped heating tubes, which includes the following components by mass ratio: 100-150 parts of α,ω-dihydroxy polysiloxane, 10-20 parts of ketoxime crosslinking agent, 0-100 parts of filler, 1-5 parts of organic titanium catalyst, 1-3 parts of aminosilane coupling agent, 50-150 parts of vinyl silicone oil, and 0.1-0.5 parts of peroxide. This technical solution uses vinyl silicone oil and peroxide to retain the original heat resistance and high temperature to enable the silicone sealant to be deeply cured, while the mechanical properties are greatly improved. The silicone sealant prepared by this technical solution has the advantages of single component, high temperature resistance, low cost, and is suitable for U-shaped heating tubes and other parts with high requirements for deep curing and temperature resistance, and can be widely used. However, this technical solution uses a relatively large amount of ketoxime crosslinking agent, which releases ketone byproducts (such as methyl ethyl ketone) during the curing process. These byproducts may have an impact on the environment and human health, so this technical solution is not environmentally friendly. Summary of the invention

[0005] In view of the above problems, the present invention provides a sealing glue for heating tubes and a preparation process thereof. The sealing glue for heating tubes of the present invention has good high temperature resistance, high temperature edible oil resistance, resistance to cold and hot cycles and resistance to moisture and heat, and can meet the requirements of sealing glue for heating tubes of various electrical appliances.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] The first aspect of the present invention provides a sealing glue for a heating pipe, wherein the raw materials include, by weight: 90-130 parts of alkoxy-terminated α,ω-dihydroxy polydimethylsiloxane, 10-20 parts of cerium chloride-doped terminal phenol-modified silicone oil, 5-15 parts of carbon hydroxyl-terminated polydimethylsiloxane, 80-120 parts of filler, 3-8 parts of cross-linking agent, 1-5 parts of catalyst, and 1-3 parts of coupling agent;

[0008] The filler comprises spherical silicone resin and modified montmorillonite; the mass ratio of the spherical silicone resin to the modified montmorillonite is 1:(1-3);

[0009] The preparation method of the modified montmorillonite comprises the following steps:

[0010] (1) 2-Hydroxyethyl disulfide reacts with isocyanate methyltrimethoxysilane to obtain a siloxane compound containing a disulfide bond;

[0011] (2) a siloxane compound containing a disulfide bond, a silica dispersion and a KH550 hydrolyzate are reacted to obtain modified silica;

[0012] (3) Dispersing montmorillonite in deionized water, adding modified silica, and cooling to room temperature after the reflux reaction is completed, washing, and drying to obtain modified montmorillonite.

[0013] In some preferred embodiments, the method for preparing the alkoxy-terminated α,ω-dihydroxy polydimethylsiloxane comprises the following steps:

[0014] Under nitrogen protection, α,ω-dihydroxypolydimethylsiloxane is heated to 70-80°C, vinyltrimethoxysilane is added and stirred evenly, potassium hydroxide is added, and the reaction is kept warm for 60-80 minutes; the temperature is raised to 100-110°C, and the volatile matter is removed to obtain the product.

[0015] In some preferred embodiments, the mass ratio of the α,ω-dihydroxypolydimethylsiloxane, vinyltrimethoxysilane and potassium hydroxide is (90-100): (0.9-1): (0.009-0.01).

[0016] In some preferred embodiments, the α,ω-dihydroxy polydimethylsiloxane has a viscosity of 5000-10000 mm at 25°C. 2 / s.

[0017] The inventors have found that the use of alkoxy-terminated α,ω-dihydroxypolydimethylsiloxane can improve the high temperature resistance of the sealing glue for heating tubes compared to α,ω-dihydroxypolydimethylsiloxane. The alkoxy-terminated polydimethylsiloxane can form a more complex three-dimensional network structure through the condensation reaction between the alkoxy groups during the curing process, thereby increasing the cross-linking density of the sealing glue for heating tubes and further improving its high temperature resistance. However, the inventors have found that the obtained sealing glue for heating tubes has poor resistance to high temperature edible oils. When used to seal the heating tube of a deep fryer, the performance decreases.

[0018] In some preferred embodiments, the method for preparing the cerium chloride-doped phenol-terminated modified silicone oil comprises the following steps: reacting phenol-terminated polydimethylsiloxane and cerium chloride at a pH of 6.5-7 for 2-3 hours to obtain the obtained product.

[0019] Preferably, the mass ratio of the phenol-terminated polydimethylsiloxane to cerium chloride is 1:(3-6).

[0020] Preferably, the phenol-terminated polydimethylsiloxane has a viscosity of 60-160 mm at 25°C. 2 / s, preferably 70-130mm 2 / s.

[0021] In order to solve the problem of poor high-temperature edible oil resistance of the sealing glue for heating tubes, the present invention creatively adds cerium chloride-doped terminal phenol-modified silicone oil, which not only improves the high-temperature edible oil resistance of the sealing glue for heating tubes, but also further improves its high-temperature resistance. The inventors speculate that this is because the presence of the terminal phenol group can increase the polarity of the surface of the sealing glue for heating tubes, improve the ability to repel grease, and reduce the penetration of oil molecules into the interior of the sealing glue for heating tubes; at the same time, the cerium chloride doping and terminal phenol group modification work together to improve the cross-linking density, and the formed network structure is more compact, thereby reducing the penetration of grease and improving high-temperature resistance.

[0022] In some preferred embodiments, the carbon hydroxyl-terminated polydimethylsiloxane has a hydroxyl value of 1.6-2 mmol / g and a viscosity of 30-50 mm at 25°C. 2 / s.

[0023] During the frying process, the temperature in the fryer will experience frequent high and low temperature changes. When cold food is put into hot oil, the oil temperature will temporarily drop; and the heating system will quickly restore the oil temperature to the set working temperature. This rapid temperature change requires the sealing glue for the heating tube to be able to withstand repeated high and low temperature cycle shocks. However, when alkoxy-terminated α, ω-dihydroxy polydimethylsiloxane and cerium chloride-doped end-phenol modified silicone oil are used, the high and low temperature cycle resistance of the sealing glue for the heating tube is poor. The inventors unexpectedly found that when carbon hydroxyl-terminated polydimethylsiloxane is added, the obtained sealing glue for the heating tube is not The invention not only has good high and low temperature cycle resistance, but also further improves its high temperature edible oil resistance. The inventors speculate that this is because the carbon hydroxyl-terminated polydimethylsiloxane can form a more uniform and dense cross-linked network through the combination with alkoxy-terminated α, ω-dihydroxy polydimethylsiloxane and cerium chloride-doped terminal phenol-modified silicone oil. This network, combined with the antioxidant effect of cerium chloride, can further improve the stability of the sealing glue for heating tubes under high temperature edible oil; at the same time, the cured sealing glue for heating tubes has better flexibility and elasticity, so that the sealing glue for heating tubes is not easy to become brittle after high and low temperature cycles.

[0024] In some preferred embodiments, the average particle size of the spherical silicone resin is 1-2 μm, preferably 1-1.4 μm.

[0025] In some preferred embodiments, the mass ratio of the 2-hydroxyethyl disulfide to isocyanate methyltrimethoxysilane is 1:(2-4).

[0026] In some preferred embodiments, the reaction temperature in step (1) is 70-90° C. and the reaction time is 1-3 h.

[0027] In some preferred embodiments, the mass ratio of the disulfide bond-containing siloxane compound, the silicon dioxide dispersion and the KH550 hydrolyzate is (0.1-0.3):(100-120):(2-4).

[0028] In some preferred embodiments, the silicon dioxide dispersion is silicon dioxide dispersed in an ethanol aqueous solution.

[0029] Preferably, the concentration of the silicon dioxide dispersion is 2-3 wt %.

[0030] Preferably, the mass ratio of ethanol to water is (70-90):(10-30).

[0031] Preferably, the KH550 hydrolyzate is obtained by hydrolyzing KH550 in water.

[0032] Preferably, the mass ratio of KH550 to water is 1:(20-30).

[0033] In some preferred embodiments, the reaction temperature in step (2) is 70-90° C. and the reaction time is 5-7 h.

[0034] In some preferred embodiments, the mass ratio of the montmorillonite, deionized water and modified silica is (3-5):100:(0.3-0.5).

[0035] In some preferred embodiments, the reflux reaction temperature in step (3) is 100-120° C. and the reaction time is 8-12 h.

[0036] The inventors have found that when the filler in the present invention includes spherical silicone resin and silica intercalated montmorillonite modified by a siloxane compound containing a disulfide bond, not only the high temperature edible oil resistance of the sealing glue for the heating tube is improved, but also the moisture and heat resistance of the sealing glue for the heating tube is improved, thereby meeting the requirements of the sealing glue for heating tubes such as coffee machines, water dispensers, kettles, rice cookers, washing machines, etc. It is speculated that this is because the lamellar structure of the spherical silicone resin and the silica intercalated montmorillonite is interspersed in the cross-linked structure formed by the alkoxy-terminated α, ω-dihydroxy polydimethylsiloxane, the cerium chloride-doped terminal phenol-modified silicone oil and the carbon hydroxyl-terminated polydimethylsiloxane, thereby improving the physical barrier effect of the heating tube sealing glue, which helps prevent edible oil and moisture in a hot and humid environment from entering the interior of the material; at the same time, the siloxane compound containing a disulfide bond can provide additional chemical cross-linking points, increase the interaction force between the molecules of the heating tube sealing glue, and thus improve its resistance to edible oil and moisture.

[0037] In some preferred embodiments, the crosslinking agent includes at least one of methyltrimethoxysilane, ethyltrimethoxysilane, dimethyldimethoxysilane, methyltriethoxysilane, and propyltrimethoxysilane.

[0038] In some preferred embodiments, the catalyst is an organotin catalyst; the organotin catalyst includes at least one of dibutyltin dilaurate and stannous octoate.

[0039] In some preferred embodiments, the coupling agent is selected from at least one of γ-aminopropyltrimethoxysilane and γ-aminopropyltriethoxysilane.

[0040] The second aspect of the present invention provides a preparation process of the above-mentioned sealing glue for the heating tube, comprising the following steps:

[0041] The alkoxy-terminated α,ω-dihydroxy polydimethylsiloxane, cerium chloride-doped terminal phenol-modified silicone oil, carbon hydroxyl-terminated polydimethylsiloxane, filler, crosslinking agent, coupling agent and catalyst are stirred and mixed uniformly to obtain the product.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] 1. The alkoxy-terminated α,ω-dihydroxy polydimethylsiloxane used in the present invention can improve the high temperature resistance of the sealing glue for the heating tube compared to α,ω-dihydroxy polydimethylsiloxane. The alkoxy-terminated polydimethylsiloxane can form a more complex three-dimensional network structure through the condensation reaction between the alkoxy groups during the curing process, thereby increasing the crosslinking density of the sealing glue for the heating tube, thereby improving its high temperature resistance.

[0044] 2. The present invention creatively adds cerium chloride-doped terminal phenol-modified silicone oil, which not only improves the high-temperature edible oil resistance of the sealing glue for the heating tube, but also further improves its high-temperature resistance.

[0045] 3. When carbonyl-terminated polydimethylsiloxane is added to the present invention, the obtained sealing glue for the heating tube not only has good high and low temperature cycle resistance, but also further improves its high temperature edible oil resistance.

[0046] 4. When the filler in the present invention includes spherical silicone resin and silica intercalated montmorillonite modified by a siloxane compound containing a disulfide bond, it not only improves the high temperature edible oil resistance of the sealing glue for the heating tube, but also improves the moisture and heat resistance of the sealing glue for the heating tube, thereby meeting the requirements of the sealing glue for heating tubes of coffee machines, water dispensers, kettles, rice cookers, washing machines, etc. DETAILED DESCRIPTION

[0047] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, a specific implementation scheme is now described in detail.

[0048] The present invention is further described below in conjunction with the embodiments, but the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to the different requirements of specific use, and the implementation conditions not indicated are conventional conditions in the industry. The technical features involved in each embodiment of the present invention can be combined with each other as long as they do not conflict with each other.

[0049] In the following examples and comparative examples, unless otherwise specified, all raw materials used were commercially available or prepared by conventional methods in the art.

[0050] Example 1

[0051] A sealing glue for a heating pipe, wherein the raw materials include, by weight: 90 parts of alkoxy-terminated α,ω-dihydroxy polydimethylsiloxane, 10 parts of cerium chloride-doped terminal phenol-modified silicone oil, 5 parts of carbon hydroxyl-terminated polydimethylsiloxane, 80 parts of filler, 3 parts of cross-linking agent, 1 part of catalyst, and 1 part of coupling agent; the filler includes spherical silicone resin and modified montmorillonite; the mass ratio of the spherical silicone resin to the modified montmorillonite is 1:2.

[0052] The preparation method of the alkoxy-terminated α,ω-dihydroxy polydimethylsiloxane comprises the following steps: under nitrogen protection, heating the α,ω-dihydroxy polydimethylsiloxane to 75°C, adding vinyl trimethoxysilane and stirring evenly, then adding potassium hydroxide and keeping the temperature for reaction for 70 minutes; heating the temperature to 110°C and removing volatiles to obtain the alkoxy-terminated α,ω-dihydroxy polydimethylsiloxane.

[0053] The mass ratio of the α,ω-dihydroxypolydimethylsiloxane, vinyltrimethoxysilane (CAS: 2768-02-7) and potassium hydroxide is 100:1:0.01.

[0054] The viscosity of the α,ω-dihydroxy polydimethylsiloxane at 25° C. is 8000 mm 2 / s, purchased from Anhui Mingyi Silicon Industry Co., Ltd., model: V8000.

[0055] The preparation method of the cerium chloride doped terminal phenol-modified silicone oil comprises the following steps: phenol-terminated polydimethylsiloxane and cerium chloride are reacted at a pH of 6.8 for 2.5 hours to obtain the obtained silicone oil.

[0056] The mass ratio of the phenol-terminated polydimethylsiloxane to cerium chloride (CAS: 7790-86-5) is 1:5.

[0057] The viscosity of the phenol-terminated polydimethylsiloxane at 25° C. is 100±30 mm 2 / s, purchased from Suzhou Qitian New Materials Co., Ltd., product code: Cheersil 8724.

[0058] The carbon hydroxyl-terminated polydimethylsiloxane has a hydroxyl value of 1.8±0.2 mmol / g and a viscosity of 40±10 mm at 25°C. 2 / s, purchased from Suzhou Qitian New Materials Co., Ltd., product code: Cheersil8300.

[0059] The spherical silicone resin has an average particle size of 1.2±0.2 μm and is purchased from Suzhou Qitian New Materials Co., Ltd., product code: Cheerspearl 7100.

[0060] The preparation method of the modified montmorillonite comprises the following steps:

[0061] (1) 2-Hydroxyethyl disulfide (CAS: 1892-29-1) reacts with isocyanate methyltrimethoxysilane (CAS: 78450-75-6) to obtain a siloxane compound containing a disulfide bond;

[0062] (2) a siloxane compound containing a disulfide bond, a silica dispersion and a KH550 hydrolyzate are reacted to obtain modified silica;

[0063] (3) Dispersing montmorillonite in deionized water, adding modified silica, and cooling to room temperature after the reflux reaction is completed, washing, and drying to obtain modified montmorillonite.

[0064] Montmorillonite was purchased from Hebei Mojin Biotechnology Co., Ltd.

[0065] The mass ratio of the 2-hydroxyethyl disulfide to the isocyanate methyltrimethoxysilane is 1:3.

[0066] The reaction temperature in step (1) is 80° C. and the reaction time is 2 h.

[0067] The mass ratio of the disulfide bond-containing siloxane compound, the silicon dioxide dispersion and the KH550 hydrolyzate is 0.2:110:3.

[0068] The silicon dioxide dispersion is prepared by dispersing silicon dioxide in an ethanol aqueous solution.

[0069] The concentration of the silicon dioxide dispersion is 3 wt %.

[0070] The mass ratio of ethanol to water is 80:20.

[0071] The KH550 hydrolyzate is obtained by hydrolyzing KH550 in water.

[0072] The mass ratio of KH550 to water is 1:25.

[0073] The reaction temperature in step (2) is 80° C. and the reaction time is 6 h.

[0074] The mass ratio of the montmorillonite, deionized water and modified silicon dioxide is 4:100:0.4.

[0075] The temperature of the reflux reaction in step (3) is 110° C. and the time is 10 h.

[0076] The crosslinking agent is methyltrimethoxysilane (CAS: 1185-55-3).

[0077] The catalyst is an organic tin catalyst; the organic tin catalyst is stannous octoate (CAS: 301-10-0).

[0078] The coupling agent is γ-aminopropyltrimethoxysilane (CAS: 13822-56-5).

[0079] The preparation process of the sealing glue for the heating tube comprises the following steps:

[0080] The alkoxy-terminated α,ω-dihydroxy polydimethylsiloxane, cerium chloride-doped terminal phenol-modified silicone oil, carbon hydroxyl-terminated polydimethylsiloxane, filler, crosslinking agent, coupling agent and catalyst are stirred and mixed uniformly to obtain the product.

[0081] Example 2

[0082] The difference from Example 1 is that the sealing glue for the heating tube includes, by mass, 130 parts of alkoxy-terminated α, ω-dihydroxy polydimethylsiloxane, 20 parts of cerium chloride-doped phenol-modified silicone oil, 15 parts of carbon hydroxyl-terminated polydimethylsiloxane, 120 parts of filler, 8 parts of cross-linking agent, 5 parts of catalyst, and 3 parts of coupling agent, and the rest are the same.

[0083] Example 3

[0084] The difference from Example 1 is that the sealing glue for the heating tube includes, by mass, 110 parts of alkoxy-terminated α, ω-dihydroxy polydimethylsiloxane, 15 parts of cerium chloride-doped terminal phenol-modified silicone oil, 10 parts of carbon hydroxyl-terminated polydimethylsiloxane, 100 parts of filler, 5 parts of cross-linking agent, 3 parts of catalyst, and 2 parts of coupling agent, and the rest are the same.

[0085] Comparative Example 1

[0086] The difference from Example 3 is that the alkoxy-terminated α,ω-dihydroxypolydimethylsiloxane is replaced with α,ω-dihydroxypolydimethylsiloxane of the same mass, and the rest is the same.

[0087] Comparative Example 2

[0088] The difference from Example 3 is that the cerium chloride-doped terminal phenol-modified silicone oil is replaced with terminal phenol-modified silicone oil of equal mass, and the rest is the same.

[0089] Comparative Example 3

[0090] The difference from Example 3 is that the cerium chloride-doped terminal phenol-modified silicone oil is replaced with carbon hydroxyl-terminated polydimethylsiloxane of equal mass, and the rest is the same.

[0091] Comparative Example 4

[0092] The difference from Example 3 is that the carbon hydroxyl-terminated polydimethylsiloxane is replaced by an equal mass of cerium chloride-doped phenol-terminated modified silicone oil, and the rest is the same.

[0093] Comparative Example 5

[0094] The difference from Example 3 is that the spherical silicone resin is replaced by modified montmorillonite of the same mass, and the rest is the same.

[0095] Comparative Example 6

[0096] The difference from Example 3 is that the modified montmorillonite is replaced by spherical silicone resin of the same mass, and the rest are the same.

[0097] Comparative Example 7

[0098] The difference from Example 3 is that the preparation method of the modified montmorillonite comprises the following steps: dispersing montmorillonite in deionized water, adding silicon dioxide, cooling to room temperature after the reflux reaction is completed, washing and drying to obtain modified montmorillonite; the rest are the same.

[0099] Performance Test:

[0100] The sealing glue of the heating tubes of Examples 1-3 and Comparative Examples 1-7 was used to seal the tube openings of the electric heating tubes. The electric heating tubes all had a tube diameter of 10.9 mm and the same preparation process. The following experiments were performed:

[0101] 1. High temperature resistance: Place the electric heating tube at 200℃ for 200h, take out the sample after the test, observe whether the sealing part of the tube mouth softens, flows, becomes brittle, or decomposes, and test the insulation performance;

[0102] 2. High temperature edible oil resistance: Soak the electric heating tube and the sample in edible oil (soybean oil) at 200℃ for 200 hours. Take out the sample after the soaking, and observe whether the sealing part of the tube mouth softens, flows, becomes brittle, or decomposes after the electric heating tube is completely dried, and test the insulation performance;

[0103] 3. High and low temperature cycle resistance: Place the electric heating tube and the sample in the high and low temperature test box respectively, and complete 30 cycles between 100℃±2℃ and 200℃±2℃. The relative humidity should be maintained within the set value of 85%RH±5%RH. In one cycle, keep stable for 8h at the highest temperature and keep stable for 0.5h at the lowest temperature. After the end, take out the sample and observe whether the seal of the tube mouth softens, flows, becomes brittle, or decomposes after the electric heating tube is completely dried, and test the insulation performance;

[0104] 4. Resistance to humidity and heat: Place the electric heating tubes in a humidity and heat aging box for 1500 hours at a constant humidity and heat test box at 85℃±2℃ and a relative humidity of 85%RH±5%RH. After the test, take out the samples and test the insulation performance after the electric heating tubes are completely dry.

[0105] The judgment principle of the above experiment is: if the sealing performance of the sealing glue used for the heating tube is damaged, the external moisture or cooking oil will penetrate the sealing glue and enter the interior of the heating tube, reducing its insulation ability and causing the insulation resistance value to drop significantly. The results are shown in Table 1:

[0106] Table 1 Performance test results of sealing glue for heating tubes of Examples 1-3 and Comparative Examples 1-7

[0107]

[0108] It can be seen from Table 1 that the sealing glue for the heating tube using Examples 1-3 has good high temperature resistance, high temperature edible oil resistance, high and low temperature cycle resistance and moisture and heat resistance;

[0109] In Comparative Example 1, since the alkoxy-terminated α,ω-dihydroxy polydimethylsiloxane is replaced with α,ω-dihydroxy polydimethylsiloxane of equal mass, the high temperature resistance and high temperature edible oil resistance of the obtained sealing glue for the heating tube are reduced;

[0110] In Comparative Example 2, since the cerium chloride-doped terminal phenol-modified silicone oil was replaced with terminal phenol-modified silicone oil of equal quality, the high temperature resistance and high temperature edible oil resistance of the obtained sealing glue for the heating tube decreased;

[0111] In Comparative Example 3, since the cerium chloride-doped terminal phenol-modified silicone oil was replaced with carbon hydroxyl-terminated polydimethylsiloxane of equal mass, the high temperature resistance and high temperature edible oil resistance of the obtained sealing glue for the heating tube decreased;

[0112] In Comparative Example 4, since the carbon hydroxyl-terminated polydimethylsiloxane was replaced with an equal mass of cerium chloride-doped terminal phenol-modified silicone oil, the high-temperature edible oil resistance and high-low temperature cycle resistance of the obtained sealing glue for the heating tube decreased;

[0113] In Comparative Example 5, since the spherical silicone resin is replaced with modified montmorillonite of equal mass, in Comparative Example 6, since the modified montmorillonite is replaced with spherical silicone resin of equal mass, and in Comparative Example 7, since silicon dioxide is directly intercalated into montmorillonite, the high temperature edible oil resistance and moisture and heat resistance of the obtained sealing glue for the heating tube are both reduced; and Comparative Examples 5 and 6 show that the spherical silicone resin and modified montmorillonite have a synergistic effect.

[0114] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A sealing glue for a heating tube, characterized in that: The raw materials include, by mass: 90-130 parts of alkoxy-terminated α,ω-dihydroxy polydimethylsiloxane, 10-20 parts of cerium chloride-doped terminal phenol-modified silicone oil, 5-15 parts of carbon hydroxyl-terminated polydimethylsiloxane, 80-120 parts of filler, 3-8 parts of crosslinking agent, 1-5 parts of catalyst, and 1-3 parts of coupling agent; The filler comprises spherical silicone resin and modified montmorillonite; the mass ratio of the spherical silicone resin to the modified montmorillonite is 1:(1-3); The preparation method of the modified montmorillonite comprises the following steps: (1) 2-Hydroxyethyl disulfide reacts with isocyanate methyltrimethoxysilane to obtain a siloxane compound containing a disulfide bond; (2) a siloxane compound containing a disulfide bond, a silica dispersion and a KH550 hydrolyzate are reacted to obtain modified silica; (3) Dispersing montmorillonite in deionized water, adding modified silica, and cooling to room temperature after the reflux reaction is completed, washing, and drying to obtain modified montmorillonite.

2. The sealing glue for the heating tube according to claim 1, characterized in that: The preparation method of the alkoxy-terminated α,ω-dihydroxy polydimethylsiloxane comprises the following steps: Under nitrogen protection, α,ω-dihydroxypolydimethylsiloxane is heated to 70-80°C, vinyltrimethoxysilane is added and stirred evenly, potassium hydroxide is added, and the reaction is kept warm for 60-80 minutes; the temperature is raised to 100-110°C, and the volatile matter is removed to obtain the product.

3. The sealing glue for the heating tube according to claim 2, characterized in that: The α,ω-dihydroxy polydimethylsiloxane has a viscosity of 5000-10000 mm at 25°C. 2 / s.

4. The sealing glue for the heating tube according to claim 3, characterized in that: The preparation method of the cerium chloride doped terminal phenol-modified silicone oil comprises the following steps: phenol-terminated polydimethylsiloxane and cerium chloride are reacted at a pH of 6.5-7 for 2-3 hours to obtain the obtained silicone oil.

5. The sealing glue for the heating tube according to claim 4, characterized in that: The carbon hydroxyl-terminated polydimethylsiloxane has a hydroxyl value of 1.6-2 mmol / g and a viscosity of 30-50 mm at 25°C. 2 / s.

6. The sealing glue for the heating tube according to claim 5, characterized in that: The mass ratio of the disulfide bond-containing siloxane compound, the silicon dioxide dispersion and the KH550 hydrolyzate is (0.1-0.3):(100-120):(2-4).

7. The sealing glue for the heating tube according to claim 6, characterized in that: The mass ratio of the montmorillonite, deionized water and modified silicon dioxide is (3-5):100:(0.3-0.5).

8. The sealing glue for the heating tube according to claim 7, characterized in that: The crosslinking agent includes at least one of methyltrimethoxysilane, ethyltrimethoxysilane, dimethyldimethoxysilane, methyltriethoxysilane and propyltrimethoxysilane.

9. The sealing glue for the heating tube according to claim 8, characterized in that: The catalyst is an organic tin catalyst; the organic tin catalyst includes at least one of dibutyltin dilaurate and stannous octoate.

10. The preparation process of the sealing glue for the heating tube according to any one of claims 1 to 9, characterized in that: The following steps are involved: The alkoxy-terminated α,ω-dihydroxy polydimethylsiloxane, cerium chloride-doped terminal phenol-modified silicone oil, carbon hydroxyl-terminated polydimethylsiloxane, filler, crosslinking agent, coupling agent and catalyst are stirred and mixed uniformly to obtain the product.

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