A sealing glue for heating tubes and its preparation process

Abstract

The present invention belongs to the technical field of adhesives, and particularly relates to a sealing glue for heating tubes and a preparation process thereof. The sealing glue for heating tubes, by mass, comprises: 90-130 parts of alkoxy-terminated α,ω-dihydroxypolydimethylsiloxane, 10-20 parts of cerium chloride-doped terminal phenol group 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 sealing glue for multiple heating tubes of the present invention has good high temperature resistance, high temperature edible oil resistance, thermal cycle resistance, and damp heat resistance, and can meet the requirements of sealing glue for heating tubes of various electrical appliances.

Description

Technical Field

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

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

[0003] The Chinese patent with the authorized publication number of CN105255447B in the prior art discloses a sealing material for electric heating tubes and an electric heating tube. The sealing material for the electric heating tube is prepared from the following components in parts by weight: 50 - 200 parts of zirconium silicate powder; 0.2 - 0.5 parts of methylhydrogen polysiloxane; 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 the electric heating tube includes the following steps: 1. Mix the zirconium silicate powder and methylhydrogen polysiloxane; 2. Dry the mixed powder; 3. Mix the dried powder with the activated alumina powder; 4. Mix the epoxy resin and fumed silica; 5. Dry the materials obtained in steps 3 and 4 after mixing; 6. Grind to obtain the sealing material for the electric heating tube. The sealing material for the electric heating tube in this technical solution can effectively prevent moisture intrusion when used as a seal for the electric heating tube, greatly extending the service life of the electric heating tube. However, the heating tube generates high temperatures during operation, which requires the sealing material used to have ideal high-temperature resistance. Although components such as 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, as one of the main adhesives, the upper temperature limit of epoxy resin usually does not exceed 200°C, which may not meet the requirements for long-term use.

[0004] A Chinese patent with the publication number CN113956835A discloses an organosilicon sealant for U-shaped heating tubes. By mass ratio, it includes the following components: 100 - 150 parts of α,ω-dihydroxypolysiloxane, 10 - 20 parts of ketoxime crosslinking agent, 0 - 100 parts of filler, 1 - 5 parts of organotitanium catalyst, 1 - 3 parts of aminosilane coupling agent, 50 - 150 parts of vinyl silicone oil, and 0.1 - 0.5 parts of peroxide. Based on the original heat resistance performance, through high temperature, this technical solution enables the organosilicon sealant to be deeply cured by the vinyl silicone oil and peroxide, while significantly improving the mechanical properties. The organosilicon sealant prepared by this technical solution has the characteristics of single-component, high temperature resistance, low manufacturing cost, and is suitable for U-shaped heating tubes and other components with high requirements for deep curing and temperature resistance, and can be widely used. However, a relatively large amount of ketoxime crosslinking agent is used in this technical solution. During the curing process, the ketoxime crosslinking agent will release ketone by-products (such as methyl ethyl ketone). These by-products may have an impact on the environment and human health, so the environmental protection performance of this technical solution is poor. Summary of the Invention

[0005] In view of the above problems, the present invention provides a sealing glue for heating tubes and its preparation process. The sealing glue for multiple heating tubes of the present invention has good high temperature resistance, high temperature edible oil resistance, thermal cycling resistance, and damp heat resistance, and can meet the requirements of sealing glue for heating tubes of various electrical appliances.

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

[0007] In the first aspect of the present invention, a sealing glue for heating tubes is provided. By mass parts, the raw materials include: 90 - 130 parts of alkoxy-terminated α,ω-dihydroxypolydimethylsiloxane, 10 - 20 parts of cerium chloride-doped terminal phenol-based 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;

[0008] The filler includes 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 includes the following steps:

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

[0011] (2) The silicon-oxygen compound containing a disulfide bond, silicon dioxide dispersion liquid, and KH550 hydrolysis liquid react to obtain modified silicon dioxide;

[0012] (3) Disperse montmorillonite in deionized water, add modified silica, after the reflux reaction is completed, cool to room temperature, wash and dry to obtain modified montmorillonite.

[0013] In some preferred embodiments, the preparation method of the alkoxy-terminated α,ω-dihydroxypolydimethylsiloxane comprises the following steps:

[0014] Under nitrogen protection, heat α,ω-dihydroxypolydimethylsiloxane to 70 - 80 °C, add vinyltrimethoxysilane and stir evenly, then add potassium hydroxide, keep the temperature for reaction for 60 - 80 min; heat to 100 - 110 °C to remove volatile components, thus obtaining.

[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 viscosity of the α,ω-dihydroxypolydimethylsiloxane at 25 °C is 5000 - 10000 mm 2 / s.

[0017] The present inventors found that, compared with α,ω-dihydroxypolydimethylsiloxane, using alkoxy-terminated α,ω-dihydroxypolydimethylsiloxane can improve the high-temperature resistance of the sealing glue for heating tubes. The alkoxy-terminated polydimethylsiloxane can form a more complex three-dimensional network structure through the condensation reaction between alkoxy groups during the curing process, thereby increasing the crosslinking density of the sealing glue for heating tubes and further improving its high-temperature resistance. However, the present inventors found that the high-temperature edible oil performance of the obtained sealing glue for heating tubes is poor, and the performance deteriorates when applied to seal the heating tube of a deep fryer.

[0018] In some preferred embodiments, the preparation method of the cerium chloride-doped terminal phenol-modified silicone oil comprises the following steps: React phenol-terminated polydimethylsiloxane and cerium chloride under the condition of pH 6.5 - 7 for 2 - 3 h to obtain.

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

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

[0021] In order to solve the problem of poor high-temperature cooking oil resistance of the sealing glue for heating tubes, the present invention creatively adds cerium chloride-doped terminal phenol group modified silicone oil, which not only improves the high-temperature cooking oil resistance of the sealing glue for heating tubes, but also further improves its high-temperature resistance. The inventor guesses that the presence of the terminal phenol group can increase the polarity of the surface of the sealing glue for heating tubes, improve the repulsion ability to oils and fats, and reduce the penetration of oil molecules into the interior of the sealing glue for heating tubes; at the same time, the combined action of cerium chloride doping and terminal phenol group modification improves the crosslinking density, and the formed network structure is more compact, thereby reducing the penetration of oils and fats and improving the high-temperature resistance.

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

[0023] During the frying process of a frying pan, the temperature inside the frying pan will experience frequent high and low temperature changes. When cold food is put into hot oil, the oil temperature will drop temporarily; and the heating system will quickly restore the oil temperature to the set working temperature. This rapid temperature change requires that the sealing glue for heating tubes can also withstand repeated high and low temperature cycle impacts. When alkoxy-terminated α,ω-dihydroxypolydimethylsiloxane and cerium chloride-doped terminal phenol group modified silicone oil are used, the high and low temperature cycle resistance of the sealing glue for heating tubes is poor. The inventor unexpectedly found that when carbon hydroxyl-terminated polydimethylsiloxane is added, the obtained sealing glue for heating tubes not only has good high and low temperature cycle resistance, but also further improves its high-temperature cooking oil resistance. The inventor guesses that by combining with alkoxy-terminated α,ω-dihydroxypolydimethylsiloxane and cerium chloride-doped terminal phenol group modified silicone oil, carbon hydroxyl-terminated polydimethylsiloxane can form a more uniform and dense crosslinked network. 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 cooking oil; at the same time, the cured sealing glue for heating tubes has better flexibility and elasticity, making the sealing glue for heating tubes not easy to become brittle after high and low temperature cycling.

[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 2-hydroxyethyl disulfide to isocyanatomethyltrimethoxysilane is 1:(2 - 4).

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

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

[0028] In some preferred embodiments, the silica dispersion is formed by dispersing silica in an ethanol aqueous solution.

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

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

[0031] Preferably, the KH550 hydrolysis solution 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 temperature of the reaction in step (2) is 70 - 90 °C, and the 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 temperature of the reflux reaction in step (3) is 100 - 120 °C, and the time is 8 - 12 h.

[0036] The inventors of the present invention have found that when the filler in the present invention includes spherical silicone resin and silica intercalated montmorillonite modified with a disulfide bond-containing siloxane compound, not only the high-temperature cooking oil resistance of the sealing glue for heating tubes is improved, but also the moisture and heat resistance of the sealing glue for heating tubes is improved. Furthermore, it can meet the requirements of the sealing glue for heating tubes in coffee machines, water dispensers, kettles, rice cookers, washing machines, etc. It is speculated that because the spherical silicone resin and the lamellar structure of the silica intercalated montmorillonite are interspersed in the cross-linked structure formed by alkoxy-terminated α,ω-dihydroxypolydimethylsiloxane, cerium chloride-doped terminal phenolic modified silicone oil, and carbon hydroxyl-terminated polydimethylsiloxane, the physical barrier effect of the sealing glue for heating tubes is improved. This physical barrier effect helps prevent cooking oil and moisture in the moist and hot environment from entering the material interior; at the same time, the disulfide bond-containing siloxane compound can provide additional chemical cross-linking points, increasing the intermolecular interaction force of the sealing glue for heating tubes, thereby improving its resistance to cooking 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 for the sealing glue of the above-mentioned heating tube, including the following steps:

[0041] Mix alkoxy-terminated α,ω-dihydroxypolydimethylsiloxane, cerium chloride-doped terminal phenol group-modified silicone oil, carbon hydroxyl-terminated polydimethylsiloxane, filler, crosslinking agent, coupling agent, and catalyst evenly by stirring to obtain the product.

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

[0043] 1. By using alkoxy-terminated α,ω-dihydroxypolydimethylsiloxane in the present invention instead of α,ω-dihydroxypolydimethylsiloxane, the high-temperature resistance of the sealing glue for the heating tube can be improved. The alkoxy-terminated polydimethylsiloxane can form a more complex three-dimensional network structure through the condensation reaction between alkoxy groups during the curing process, thereby increasing the crosslinking density of the sealing glue for the heating tube and further improving its high-temperature resistance.

[0044] 2. The present invention creatively adds cerium chloride-doped terminal phenol group-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 carbon hydroxyl-terminated polydimethylsiloxane is added in 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 with a disulfide bond-containing siloxane compound, 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, and can thus meet the requirements of the sealing glue for heating tubes in coffee machines, water dispensers, kettles, rice cookers, washing machines, etc. Specific Embodiments

[0047] In order to have a clearer understanding of the technical features, objectives, and effects of the present invention, specific implementation examples are described in detail below.

[0048] The present invention will be further described below in conjunction with embodiments, but the present invention is not limited to the following embodiments. The implementation conditions adopted in the embodiments can be further adjusted according to different requirements of specific uses. The implementation conditions not specified are conventional conditions in the industry. The technical features involved in each implementation manner 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, the raw materials used are all commercially available or prepared by conventional methods in the art.

[0050] Example 1

[0051] A sealing glue for heating tubes, by mass, the raw materials include: 90 parts of alkoxy-terminated α,ω-dihydroxypolydimethylsiloxane, 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 crosslinking agent, 1 part of catalyst, 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-dihydroxypolydimethylsiloxane includes the following steps: Under nitrogen protection, α,ω-dihydroxypolydimethylsiloxane is heated to 75 °C, vinyltrimethoxysilane is added and stirred evenly, and then potassium hydroxide is added, and the reaction is carried out at a constant temperature for 70 min; the temperature is raised to 110 °C to remove volatile components, and then obtained.

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

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

[0055] The preparation method of the cerium chloride-doped terminal phenol-modified silicone oil includes the following steps: The reaction is carried out for 2.5 h under the condition that the pH of the phenol-terminated polydimethylsiloxane and cerium chloride is 6.8 to obtain.

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

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

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

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

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

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

[0062] (2) The disulfide bond-containing siloxane compound, silica dispersion, and KH550 hydrolysis solution react to obtain modified silica;

[0063] (3) Montmorillonite is dispersed in deionized water, modified silica is added, after the reflux reaction is completed, it is cooled to room temperature, washed, and dried to obtain modified montmorillonite.

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

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

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

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

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

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

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

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

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

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

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

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

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

[0077] The catalyst is an organotin catalyst; the organotin catalyst is stannous octanoate (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 described above includes the following steps:

[0080] Mix alkoxy-terminated α,ω-dihydroxypolydimethylsiloxane, cerium chloride-doped terminal phenol-based modified silicone oil, carbon hydroxyl-terminated polydimethylsiloxane, filler, crosslinking agent, coupling agent, and catalyst evenly to obtain.

[0081] Example 2

[0082] The difference from Example 1 is that for the sealing glue of the heating tube, by mass, the raw materials include: 130 parts of alkoxy-terminated α,ω-dihydroxypolydimethylsiloxane, 20 parts of cerium chloride-doped terminal phenol-based modified silicone oil, 15 parts of carbon hydroxyl-terminated polydimethylsiloxane, 120 parts of filler, 8 parts of crosslinking 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 for the sealing glue of the heating tube, by mass, the raw materials include: 110 parts of alkoxy-terminated α,ω-dihydroxypolydimethylsiloxane, 15 parts of cerium chloride-doped terminal phenol-based modified silicone oil, 10 parts of carbon hydroxyl-terminated polydimethylsiloxane, 100 parts of filler, 5 parts of crosslinking 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 alkoxy-terminated α,ω-dihydroxypolydimethylsiloxane is replaced with α,ω-dihydroxypolydimethylsiloxane of the same mass, and the rest are the same.

[0087] Comparative Example 2

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

[0089] Comparative Example 3

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

[0091] Comparative Example 4

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

[0093] Comparative Example 5

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

[0095] Comparative Example 6

[0096] The difference from Example 3 is that the modified montmorillonite is replaced with the same mass of spherical silicone resin, 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 includes the following steps: dispersing montmorillonite in deionized water, adding silica, after the reflux reaction is completed, cooling to room temperature, washing and drying to obtain the modified montmorillonite; the rest are the same.

[0099] Performance test:

[0100] Use the sealing adhesives of the heating tubes of Examples 1-3 and Comparative Examples 1-7 to dot-seal the orifices of the electric heating tubes respectively. The electric heating tubes all have a diameter of 10.9 mm, and the preparation processes are the same, and the following experiments are carried out:

[0101] 1. High temperature resistance: Place the electric heating tubes at 200 °C for 200 h respectively. After the end, take out the samples and observe whether there are phenomena such as softening, flowing, embrittlement, or decomposition at the sealed orifice of the tube and test the insulation performance;

[0102] 2. High temperature edible oil resistance: Immerse the samples of the electric heating tubes in edible oil (soybean oil) at 200 °C for 200 h respectively. After the end, take out the samples. After the electric heating tubes are completely dried, observe whether there are phenomena such as softening, flowing, embrittlement, or decomposition at the sealed orifice of the tube and test the insulation performance;

[0103] 3. High and low temperature cycling resistance: Place the specimens into a high and low temperature test chamber using an electric heating tube, and complete 30 cycles between 100°C ± 2°C and 200°C ± 2°C. The relative humidity should be maintained within the set value of 85% RH ± 5% RH. Within one cycle, maintain stability for 8 hours at the highest temperature and 0.5 hours at the lowest temperature. After completion, take out the samples. After the electric heating tube is completely dried, observe whether there is softening, flowing, embrittlement, or decomposition at the sealed part of the tube mouth and test the insulation performance;

[0104] 4. Damp heat resistance: Place the electric heating tubes into a damp heat aging chamber and conduct a 1500-hour constant damp heat test in a chamber at 85°C ± 2°C and relative humidity of 85% RH ± 5% RH. After completion, take out the samples. After the electric heating tube is completely dried, test the insulation performance;

[0105] Judgment principle of the above experiments: If the seal of the heating tube with the sealing glue is damaged, moisture or cooking oil from the outside will penetrate through the sealing glue and enter the interior of the heating tube, reducing its insulation ability and causing a significant drop in the insulation resistance value. The results are shown in Table 1:

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

[0107]

[0108] It can be seen from Table 1 that the sealing glue for the heating tubes using Examples 1-3 has good high temperature resistance, high temperature cooking oil resistance, high and low temperature cycling resistance, and damp heat resistance;

[0109] In Comparative Example 1, since the alkoxy-terminated α,ω-dihydroxypolydimethylsiloxane was replaced with the same mass of α,ω-dihydroxypolydimethylsiloxane, the high temperature resistance and high temperature cooking oil resistance of the sealing glue for the heating tube obtained decreased;

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

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

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

[0113] In Comparative Example 5, since the spherical silicone resin was replaced with the same mass of modified montmorillonite, in Comparative Example 6, since the modified montmorillonite was replaced with the same mass of spherical silicone resin, and in Comparative Example 7, since silica was directly intercalated in montmorillonite, the high-temperature resistance to edible oil and the resistance to damp heat of the sealing glue for the heating tube obtained both decreased; and Comparative Examples 5 and 6 indicate that the spherical silicone resin and the 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 protection scope of the present invention. Any simple modification or equivalent replacement made by those of ordinary skill in the art to the technical solution of the present invention shall not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A sealing glue for a heating pipe, 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 alkoxy-terminated α,ω dihydroxy polydimethylsiloxane is vinyl trimethoxysilane-terminated α,ω dihydroxy polydimethylsiloxane; 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 dihydroxy polydimethylsiloxane is heated to 70-80°C, vinyl trimethoxysilane 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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