Adhesion promoter for silicone rubber protective coating and preparation and use method thereof

Abstract

The present invention discloses an adhesion promoter for silicone rubber surfaces, comprising a silane coupling agent, water, a diol, an elastic isocyanate prepolymer, a wetting aid, a catalyst, and a mixed solvent. Because the adhesion promoter has a hydrolysis-polycondensation reaction with a silane coupling agent that is similar in molecular structure to silicone rubber, and the synthesized hydrocarbon functional groups of the adhesion promoter form hydrogen bonds with the silicone rubber substrate, the adhesion promoter exhibits excellent adhesion to the silicone rubber. Furthermore, the polar groups on the adhesion promoter surface form chemical bonds and hydrogen bonds with the polar groups of the silicone rubber protective coating, allowing the adhesion promoter to form an organic bond between the silicone rubber and the protective coating, thereby improving the adhesion of the silicone rubber protective coating to the silicone rubber. This adhesion promoter can improve the bonding performance between silicone rubber and the protective coating, particularly ensuring that the protective coating can protect the silicone rubber and meet usage requirements in long-term oil and solvent environments.

Description

Technical Field

[0001] The present invention relates to the field of protective coatings, in particular to an adhesion promoter for silicone rubber protective coatings and a preparation and use method thereof. Background Art

[0002] With the development of my country's rubber industry and the continuous improvement of scientific and technological levels, silicone rubber is widely used in the aerospace, electronics, computer, automotive, and medical industries due to its excellent electrical insulation, high and low temperature resistance, ozone and corrosion resistance, low reactivity, low flammability, non-toxicity, good air permeability, physiological inertness, and high safety. However, silicone rubber has poor resistance to oil, solvents, acids, and alkalis. When used as a sealant and shock absorber in the aerospace and automotive fields, it comes into contact with oils and solvents. Long-term immersion in oils or solvents can cause silicone rubber to deform and expand in volume, significantly reducing its mechanical properties. This can lead to a loss of the sealing effect of silicone rubber seals and the damping performance of shock absorbers.

[0003] To address the oil and solvent resistance of silicone rubber, a common approach is to apply a protective coating to the surface of the silicone rubber substrate to address some of the shortcomings or problems of silicone rubber and expand its scope of use. However, as a typical non-polar material, it has disadvantages such as low surface energy, a weak boundary surface layer, poor adsorption, and difficulty in wetting. As a result, the protective coating has difficulty in wetting the surface of the silicone rubber substrate, a problem that limits its widespread application in industry. Therefore, in order to ensure that the protective coating has excellent adhesion and wettability on silicone rubber, it is necessary to develop an adhesion promoter with excellent adhesion to silicone rubber, thereby improving the adhesion and other oil and solvent resistance of the protective coating to the silicone rubber substrate in the aerospace or automotive fields. At the same time, this method has low processing costs, simple operation, obvious modification effects, and is also applicable to the surfaces of silicone rubber products with complex shapes, making it more suitable for large-scale industrial applications. Summary of the Invention

[0004] The present invention primarily addresses the problems of silicone rubber's poor oil and solvent resistance, requiring a protective coating, low surface energy, and difficulty wetting, as well as the difficulty of the protective coating adhering to the surface of the silicone rubber substrate. The present invention involves specialized bulk modification (although bulk modification can improve the adhesion between silicone rubber and other materials to a certain extent, it can affect the physical and chemical properties of the silicone rubber itself (mechanical properties, corrosion resistance, etc.)), surface modification (surface treatment methods are used to modify the silicone rubber substrate to ensure the silicone rubber's bulk structure while achieving good interfacial adhesion. While surface treatment methods such as low-temperature plasma and ultraviolet ozone can effectively improve the adhesion of silicone rubber surfaces to a certain extent, these methods are expensive and difficult to treat substrates with complex surface shapes, hindering their widespread industrial use), and technical research on surface coating adhesion promoters. Ultimately, an adhesion promoter was selected that not only exhibits excellent adhesion to silicone rubber but also introduces polar groups and reactive functional groups, resulting in excellent interlayer adhesion with the protective coating. The adhesion promoter can improve the bonding performance between silicone rubber and protective coating, especially to ensure that the protective coating can protect silicone rubber and meet the use requirements in a long-term oil and solvent environment.

[0005] The invention provides an adhesion promoter for silicone rubber surface. The adhesion promoter consists of a silane coupling agent, water, diols, elastic isocyanate prepolymer, a wetting aid, a catalyst and a mixed solvent.

[0006] Furthermore, the adhesion promoter is composed of the following components by mass percentage:

[0007] Silane coupling agent 10%~16%

[0008] Water 2.5%~4%

[0009] Diols 2.5%~4.5%

[0010] Elastic isocyanate resin 63%~75%

[0011] Wetting additive 0.2%~0.3%

[0012] Catalyst 0.4%~0.5%

[0013] Mixed solvent A 9%~13%

[0014] The silane coupling agent is a silane coupling agent containing an isocyanate group; the silane coupling agent containing an isocyanate group is one or a mixture of two of 3-isocyanatepropyltrimethoxysilane, 3-isocyanatepropyltriethoxysilane, and 1,3,5-tris(trimethoxysilylpropyl)isocyanate;

[0015] The water is distilled water or tap water;

[0016] The diols are one or a mixture of two of ethylene glycol, propylene glycol, 1,4-butanediol, and hexanediol;

[0017] The elastic isocyanate resin is prepared by addition polymerization of one or more polyol resins selected from polyether polyol, polycarbonate polyol, polyester polyol, and butanediol resin, trimethylolpropane, and one or more diisocyanates selected from IPDI, MDI, and HDI, and a solvent, and has an NCO percentage of 3% to 5%;

[0018] The wetting agent is at least one of BYK-358N, BYK-320, BYK-323, and BYK-306;

[0019] The catalyst is at least one of dibutyltin dilaurate, stannous octoate, and dibutyltin diacetate;

[0020] The mixed solvent is one or more of cyclohexanone, ethyl acetate, xylene and butyl acetate.

[0021] The present invention provides a method for preparing an adhesion promoter. The materials are prepared according to the above-mentioned formula, and the preparation process is as follows:

[0022] (1) Preparation method of elastic isocyanate resin: polyol resin, trimethylolpropane and solvent are heated and refluxed for dehydration, and then diisocyanate is added and kept at 70℃ for 1 hour, and kept at 90℃ for 5~6 hours. The NCO percentage is 3%~5%, and the material is filtered out to obtain elastic isocyanate resin.

[0023] (2) Synthesis of silane coupling agent containing hydroxyl group: first put the silane coupling agent containing isocyanate group, 25~36% catalyst and diol into the reactor, keep it at 70℃ for 1h, keep it at 90℃ for 3~4h, test the actual hydroxyl value to reach the theoretical hydroxyl value, cool it down and discharge the material. The theoretical hydroxyl value of different monomers is different, ranging from 130mgKOH / g to 220mgKOH / g.

[0024] (3) Preparation method of adhesion promoter: put the hydroxyl-containing silane coupling agent, elastic isocyanate resin and the remaining catalyst into the reactor for polycondensation reaction, keep it at 90℃ for 8~9h, and when the NCO percentage is 0, add the wetting agent and mixed solvent A under stirring, cool and discharge the material to obtain the adhesion promoter.

[0025] (4) The adhesion promoter is reacted with water to form a film to form an adhesion promoter for the silicone rubber surface.

[0026] The present invention provides a method for using an adhesion promoter: wipe the silicone rubber substrate clean with a solvent or lightly sandpaper it before wiping with the solvent. After the surface of the substrate is cleaned of oil stains, the silicone rubber adhesion promoter is sprayed or brushed on, with the dry film thickness controlled to 5 to 10 microns. After drying at room temperature for 24 hours or baking at 80°C for 1 hour, a protective coating for the silicone rubber is sprayed on to provide oil and solvent resistance.

[0027] The beneficial effects of the present invention are:

[0028] Since the adhesion promoter has a hydrolysis and condensation reaction of a silane coupling agent with a similar molecular structure to that of silicone rubber, and the synthesized carbon-hydrogen functional groups of the adhesion promoter form hydrogen bonds with the silicone rubber substrate, the adhesion promoter has excellent adhesion to silicone rubber, with the cross-hatch adhesion test being level 0. At the same time, the polar groups on the surface of the adhesion promoter form chemical bonds and hydrogen bonds with the polar groups of the silicone rubber protective coating, so that the adhesion promoter forms an organic combination between the silicone rubber and the protective coating, thereby improving the adhesion of the silicone rubber protective coating to the silicone rubber.

[0029] Since silicone rubber is an elastic material, general adhesion promoters will crack and fall off in large pieces during the deformation of the silicone rubber after being coated on the silicone rubber to form a film, thereby losing the effect of improving adhesion. The present invention modifies the adhesion promoter by elastic isocyanate resin, which significantly improves the elastic matching performance between the adhesion promoter and silicone rubber, thereby providing a permanent adhesion promotion guarantee effect.

[0030] Due to the low surface tension of the silicone rubber substrate, the presence of a weak boundary layer and poor interfacial wettability, most adhesion promoters have difficulty in wetting the silicone rubber well. The present invention reduces the surface tension of the adhesion promoter by adding a suitable silicone wetting agent, thereby improving the wetting performance of the adhesion promoter on the silicone rubber substrate and further enhancing the wet adhesion. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Provides a schematic diagram of adhesion for the adhesion promoter of the present invention DETAILED DESCRIPTION

[0032] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention. Example

[0033] Elastic isocyanate resin TNH-1: Add 32kg of polyester resin, 5kg of polycaprolactone resin, 2.5kg of trimethylolpropane, and 40kg of xylene to a reactor. Raise the temperature to reflux, dehydrate for 1 hour, then cool to 50°C, add 38kg of IPDI, and heat and maintain the reaction for 4 hours. When the NCO content is measured to be between 2.5% and 3.5%, elastic isocyanate resin TNH-1 is obtained.

[0034] Synthesis of hydroxyl-containing silane coupling agent SiOH-1: First, 38.76 kg of 3-isocyanatepropyltrimethoxysilane, 0.57 kg of dibutyltin dilaurate and 11.72 kg of ethylene glycol were put into a reactor, kept at 70 ° C for 1 hour, and kept at 90 ° C for 3 to 4 hours. When the actual hydroxyl value reached the theoretical hydroxyl value of 210.21 mgKOH / g, the temperature was lowered and the material was discharged to obtain the hydroxyl-containing silane coupling agent SiOH-1.

[0035] Adhesion promoter FZL-1: 51.05 kg of hydroxyl-containing silane coupling agent SiOH-1, 264 kg of elastic isocyanate resin TNH-1 and 1 kg of dibutyltin dilaurate are added to a reactor for condensation reaction. The reaction is kept at 90°C for 8 to 9 hours. When the NCO percentage is measured to be 0, 0.94 kg of wetting agent BYK-306, 20 kg of xylene and 13.65 kg of butyl acetate are added under stirring. The temperature is lowered and the material is discharged to obtain adhesion promoter FZL-1.

[0036] 350.64 kg of adhesion promoter FZL-1 and 10.2 kg of water were reacted to form a film to obtain an adhesion promoter for silicone rubber surface. Example

[0037] (1) Elastic isocyanate resin TNH-1: Add 32 kg polyester resin, 5 kg polycaprolactone resin, 2.5 kg trimethylolpropane, and 40 kg xylene into a reactor, heat to reflux, dehydrate for 1 hour, cool to 50 °C, add 38 kg IPDI, heat and keep the reaction for 4 hours. When the NCO percentage is measured to be between 2.5% and 3.5%, elastic isocyanate resin TNH-1 is obtained.

[0038] (2) Synthesis of hydroxyl-containing silane coupling agent SiOH-2: First, 38.76 kg of 3-isocyanatepropyltriethoxysilane, 0.34 kg of stannous octoate and 14.10 kg of 1,4-butanediol were added to the reactor, kept at 70 ° C for 1 hour, and kept at 90 ° C for 3 to 4 hours. When the actual hydroxyl value reached the theoretical hydroxyl value of 166.68 mgKOH / g, the temperature was lowered and the material was discharged to obtain the hydroxyl-containing silane coupling agent SiOH-2.

[0039] (3) Adhesion promoter FZL-2: 52.86 kg of hydroxyl-containing silane coupling agent SiOH-2, 219.69 kg of elastic isocyanate resin TNH-1 and 1 kg of stannous octoate were added to a reactor for polycondensation reaction. The mixture was kept at 90 °C for 8 to 9 hours. When the NCO percentage was measured to be 0, 0.80 kg of wetting agent BYK-320 and 32.32 kg of xylene were added under stirring. The mixture was cooled and discharged to obtain adhesion promoter FZL-2.

[0040] (4) 307.01 kg of adhesion promoter FZL-2 and 8.47 kg of water were reacted to form a film to form an adhesion promoter for the silicone rubber surface. Example

[0041] (1) Elastic isocyanate resin TNH-2: Add 32kg polyester resin, 4kg polycarbonate resin, 2.5kg trimethylolpropane, and 40kg xylene into a reactor, heat to reflux, dehydrate for 1 hour, then cool to 50°C and add 46kg IPDI. Heat and keep the reaction for 4 hours. When the NCO percentage is measured to be between 2.5% and 3.5%, elastic isocyanate resin TNH-2 is obtained.

[0042] (2) Synthesis of hydroxyl-containing silane coupling agent SiOH-3: First, 25.19 kg of 3-isocyanatepropyltrimethoxysilane, 13.57 kg of 1,3,5-tris(trimethoxysilylpropyl)isocyanate, 0.29 kg of dibutyltin dilaurate and 6.77 kg of ethylene glycol were added to the reactor, and kept at 70 ° C for 1 hour and at 90 ° C for 3 to 4 hours. When the actual hydroxyl value reached the theoretical hydroxyl value of 139.52 mgKOH / g, the temperature was lowered and the material was discharged to obtain the hydroxyl-containing silane coupling agent SiOH-3.

[0043] (3) Adhesion promoter FZL-3: 44.53 kg of hydroxyl-containing silane coupling agent SiOH-3, 152.86 kg of elastic isocyanate resin TNH-2 and 0.7 kg of dibutyltin dilaurate were added to a reactor for polycondensation reaction. The mixture was kept at 90 °C for 8 to 9 hours. When the NCO percentage was measured to be 0, 0.59 kg of wetting agent BYK-320, 20.35 kg of xylene and 10 kg of cyclohexanone were added under stirring. The mixture was cooled and discharged to obtain adhesion promoter FZL-3.

[0044] (4) 229.32 kg of adhesion promoter FZL-3 and 8.84 kg of water were reacted to form a film to form an adhesion promoter for the silicone rubber surface.

[0045] The silicone rubber substrate was first lightly polished with sandpaper and then wiped clean with a solvent. After the oil on the substrate surface was cleaned, the products of Examples 1-3 were sprayed on the silicone rubber substrate. The dry film thickness of the adhesion promoter was 5μm~10μm. The solid content, drying performance, pot life and cross-hatch adhesion of the adhesion promoter for the silicone rubber surface were tested. At the same time, the elastic properties of the adhesion promoter were tested when the film thickness was 1mm. See Table 1

[0046] Table 1 Performance test table

[0047] Test items standard Example 1 Example 2 Example 3 Solid content GB / T 1725 60.13% 59.98% 63.80% Touch dry, room temperature GB / T 1728 1h 1h 1h Hard dry, room temperature GB / T 1728 10h 8h 9h 7d room temperature curing performance GB / T 1728 Cured Cured Cured Applicable period Place it in a covered container and measure its viscosity. If the change does not exceed 20%, it is qualified. 1h 1h 1h Cross-cut adhesion GB / T 9286 Level 0 Level 0 Level 0 Elongation at break GB / T 528 172.02% 159.39% 166.80% tensile strength GB / T 528 12.12MPa 12.60Mpa 13.27Mpa

[0048] After drying at room temperature for 24 hours or baking at 80℃ for 1 hour, the silicone rubber protective coating produced by our company was sprayed on the adhesion promoter. The dry film thickness was 25μm~35μm. After drying for 7 days, the adhesion, peel strength and media resistance performance tests were carried out. The test results are shown in Table 2:

[0049] Table 2 Performance test after spraying silicone rubber protective coating

[0050] Test items standard Example 1 Example 2 Example 3 Adhesion GB / T 9286 Level 0 Level 0 Level 0 Peel strength GB / T 14905 2.12KN / m 2.35KN / m 2.07KN / m Oil resistance, room temperature, 21 days GB / T 9274 No blistering, no wrinkling, no discoloration No blistering, no wrinkling, no discoloration No blistering, no wrinkling, no discoloration Xylene resistance, room temperature, 24h GB / T 9274 No blistering, no wrinkling, no discoloration No blistering, no wrinkling, no discoloration No blistering, no wrinkling, no discoloration

[0051] The present disclosure has been described using the aforementioned embodiments. However, the aforementioned embodiments are merely exemplary embodiments of the present disclosure. It should be noted that the disclosed embodiments do not limit the scope of the present disclosure. On the contrary, modifications and alterations made without departing from the spirit and scope of the present disclosure are within the scope of patent protection of the present disclosure.

Claims

1. An adhesion promoter for silicone rubber protective coating, characterized by: Calculated by mass percentage, it is composed of the following components: Silane coupling agent 10%~16% Water 2.5%~4% Diols 2.5%~4.5% Elastic isocyanate resin 63%~75% Wetting additive 0.2%~0.3% Catalyst 0.4%~0.5% Mixed solvent A 9%~13%; The elastic isocyanate resin is prepared by addition polymerization of one or more polyol resins selected from polyether polyol, polycarbonate polyol, polyester polyol, and butanediol resin, trimethylolpropane, one or more diisocyanates selected from IPDI, MDI, and HDI, and a solvent, and has an NCO content of 3% to 5%. The silane coupling agent is a silane coupling agent containing an isocyanate group; the silane coupling agent containing an isocyanate group is one or a mixture of 3-isocyanatepropyltrimethoxysilane, 3-isocyanatepropyltriethoxysilane, and 1,3,5-tris(trimethoxysilylpropyl)isocyanate; and the mixed solvent A is one or more selected from cyclohexanone, ethyl acetate, xylene, and butyl acetate. The method comprises the following steps: firstly, placing an isocyanate group-containing silane coupling agent, 25-36% of a catalyst, and a diol into a reactor, and keeping the temperature at 70°C for 1 hour, and then keeping the temperature at 90°C for 3-4 hours. When the actual hydroxyl value reaches the theoretical hydroxyl value, the reaction mixture is cooled and discharged to obtain a hydroxyl-containing silane coupling agent; then, placing the prepared hydroxyl-containing silane coupling agent, an elastic isocyanate resin, and the remaining catalyst into a reactor for a condensation reaction, and keeping the temperature at 90°C for 8-9 hours. When the NCO percentage is measured to be 0, a wetting agent and a mixed solvent A are added under stirring, and the reaction mixture is cooled and discharged to obtain an adhesion promoter.

2. The adhesion promoter for silicone rubber protective coating according to claim 1, characterized in that: The diols are one or a mixture of ethylene glycol, propylene glycol, 1,4-butanediol and hexanediol.

3. The adhesion promoter for silicone rubber protective coating according to claim 1, characterized in that: The water is distilled water or tap water.

4. The adhesion promoter for silicone rubber protective coating according to claim 1, characterized in that: The wetting aid is at least one of BYK-358N, BYK-320, BYK-323, and BYK-306; and the catalyst is at least one of dibutyltin dilaurate, stannous octoate, and dibutyltin diacetate.

5. The method for preparing the adhesion promoter for silicone rubber protective coating according to any one of claims 1 to 4, characterized in that: The steps include: (1) Preparation method of elastic isocyanate resin: polyol resin, trimethylolpropane and solvent are heated and refluxed for dehydration, and then diisocyanate is added and kept at 70℃ for 1 hour, and kept at 90℃ for 5-6 hours, and the NCO percentage is 3%-5%. The material is filtered and discharged to obtain elastic isocyanate resin; (2) Synthesis of silane coupling agent containing hydroxyl group: first put the silane coupling agent containing isocyanate group, 25~36% of catalyst and diol into the reactor, keep it at 70℃ for 1h, keep it at 90℃ for 3~4h, test the actual hydroxyl value to reach the theoretical hydroxyl value, cool it down and discharge the material; (3) Preparation method of adhesion promoter: put the hydroxyl-containing silane coupling agent, elastic isocyanate resin and the remaining catalyst into a reactor for polycondensation reaction, keep the temperature at 90°C for 8-9 hours, and when the NCO percentage is 0, add the wetting agent and mixed solvent A under stirring, cool and discharge the material to obtain the adhesion promoter; (4) The adhesion promoter is reacted with water to form a film to form an adhesion promoter for the silicone rubber protective coating.

6. A method for using the adhesion promoter for silicone rubber protective coating according to any one of claims 1 to 4, characterized in that: The method comprises the following steps: lightly polishing the silicone rubber substrate with sandpaper, then wiping it clean with a solvent, and after the oil stains on the surface of the substrate are cleaned, spraying or brushing a silicone rubber adhesion promoter, with the dry film thickness controlled at 5 microns to 10 microns; drying at room temperature for 24 hours or baking at 80°C for 1 hour, and then spraying a silicone rubber protective coating to provide oil and solvent resistance.

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