Surface coating agent for sealing gasket of automobile exhaust pipe and preparation method of surface coating agent

Abstract

The invention relates to the technical field of automobile exhaust pipe coating preparation, and particularly discloses a surface coating agent for an automobile exhaust pipe sealing gasket and a preparation method thereof.The preparation method comprises the steps that acetone, polyvinyl alcohol and benzophenone tetracarboxylic dianhydride are taken and added into a reaction kettle in proportion to be subjected to an esterification reaction, and an ester solution is obtained; alkali liquor and epoxy resin are added into the ester solution to react for 2-4 h, a waterborne epoxy emulsifier is obtained, and waterborne epoxy resin emulsion is prepared from the waterborne epoxy emulsifier and epoxy resin under preset conditions; and adding the water-borne epoxy resin emulsion, the filler, the dispersing agent and the thickening agent into the reaction kettle, uniformly mixing, adding the stabilizer and the defoaming agent, and uniformly mixing again to obtain the surface coating agent for the automobile exhaust pipe sealing gasket. Compared with the prior art, the obtained surface coating agent and a curing agent work together to improve the adhesive force of a coating, meanwhile, formation of pores and pinholes of an obtained coating structure is avoided, the corrosion resistance and compactness of the coating are improved, and then the acid resistance and water resistance of the sealing gasket are improved.

Description

Technical Field

[0001] The invention relates to the technical field of automobile exhaust pipe coating preparation, in particular to a surface coating agent for automobile exhaust pipe sealing gaskets and a preparation method thereof. Background Art

[0002] Automobile exhaust pipes are generally connected by multiple components such as exhaust manifolds, front exhaust pipes, center exhaust pipes, catalytic converters, rear exhaust pipes, mufflers and tail pipes. In order to prevent exhaust gas from leaking or overflowing from the joints, a gasket is required at the joints between the two components. Currently, most gaskets are non-metallic rubber composite gaskets, rubber-metal composite gaskets and metal gaskets. However, there are a large number of pores on the surface and inside of non-metallic rubber composite gaskets and rubber-metal composite gaskets, and the surface of metal gaskets is rough, resulting in poor sealing effect. To solve this technical problem, the traditional method is to apply a layer of silicone resin anti-stick coating that acts as a micro-seal on the surface of the gasket, and then apply a layer of silicone rubber coating. This method requires the application of two different layers of coating, and the steps are relatively cumbersome. Therefore, on this basis, a surface coating agent that only needs to be applied in one or once is prepared. The existing technologies for surface coating gaskets are:

[0003] CN202111477641.2 discloses a metal gasket surface treatment agent with good sealing performance, specifically disclosing a molybdenum disulfide anti-friction coating as a single-component coating. The components and weight parts of the coating are as follows: 60% wear-resistant agent, 10% binder, 10% A additive, 10% corrosion-resistant agent, and 10% B additive. The metal gasket is coated with the surface treatment agent on one side or both sides to achieve long-term use at a temperature of -20-500°C, but the main component of the surface treatment agent is molybdenum disulfide, the coating density is poor, and the use of highly chlorinated polyethylene as a corrosion-resistant agent causes high VOC emissions. The main components of automobile exhaust are sulfur dioxide (SO2), nitrogen oxides (NO x ), carbon monoxide, water vapor and other gases, as well as incompletely burned organic acids, require the coating to have good resistance to chemical corrosion.

[0004] CN202111407273.4 discloses a metal gasket surface treatment agent for preventing adhesion, specifically disclosing that 30-35 parts by weight of anhydrous ethanol are added to 100 parts by weight of the surface treatment agent, and the surface treatment agent is a colorless milky white liquid. The surface treatment agent is divided into the following categories according to weight percentage: 5-80% hydroxy silicone oil, 10-40% polyamide wax, and 5-10% polyethylene wax or liquid paraffin. It solves the problem that the metal fluororubber gasket of the engine cylinder head is prone to adhesion to the flange under the action of temperature and pressure, affecting the sealing performance. However, the main components are hydroxy silicone oil and polyamide wax, which are easily hydrolyzed under the action of oxidizing media, and the main components of automobile exhaust are sulfur dioxide (SO2), nitrogen oxides (NOx ), gases such as carbon monoxide, water vapor, and incompletely burned organic acids cause the coating formed by the surface treatment agent to deteriorate, which in turn causes the gasket to deteriorate.

[0005] To solve the above problems, it is necessary to prepare a surface coating agent for automobile exhaust pipe gaskets to form a coating with good chemical corrosion resistance and good density on the surface of the exhaust pipe gaskets to prevent the coating from deteriorating and falling off, thereby extending the service life of the exhaust pipe gaskets while preventing exhaust gas leakage from the gaskets. Summary of the Invention

[0006] The purpose of the present invention is to provide a surface coating agent for automobile exhaust pipe gaskets, aiming to solve the problems of low coating density and poor chemical corrosion resistance after application of existing gasket surface coating agents. After application on automobile exhaust pipe gaskets, the coating is prone to deterioration, which reduces the service life of the gaskets and makes exhaust gas easily leak from the gaskets.

[0007] The present invention also aims to provide a method for preparing a surface coating agent for automobile exhaust pipe sealing gaskets, aiming to solve the problem that the existing water-based epoxy emulsifier has a poor emulsification effect.

[0008] To achieve the above object, the present invention provides a method for preparing a surface coating agent for an automobile exhaust pipe sealing gasket, the method comprising:

[0009] S1, preparing a water-based epoxy resin emulsion: adding acetone, polyvinyl alcohol, and benzophenone tetracarboxylic dianhydride in a certain proportion to a reactor for esterification to obtain an ester solution, adding alkaline solution and epoxy resin to the ester solution and reacting for 2-4 hours to obtain a water-based epoxy emulsifier, mixing the water-based epoxy emulsifier and epoxy resin, and adding deionized water dropwise at a rotation speed of 700-900 rpm to obtain a water-based epoxy resin emulsion;

[0010] S2, preparing a surface coating agent: adding a water-based epoxy resin emulsion, a filler, a dispersant, and a thickener to a reactor, stirring at a speed of 1000-1200 rpm for 30-50 minutes, adding a stabilizer and a defoaming agent, and stirring at a speed of 600-800 rpm for 30-50 minutes to obtain a surface coating agent for automobile exhaust pipe sealing gaskets.

[0011] Preferably, in the above technical solution, the filler is one or both of modified silica and colloidal graphite, and the alkali solution is one of sodium hydroxide and sodium bicarbonate.

[0012] According to the above technical solution, the present invention prepares a water-based epoxy emulsifier with an amphiphilic structure. The hydrophilic group reduces the epoxy resin-water interfacial tension, and the hydrophobic segment anchors the epoxy resin particles to maintain the epoxy resin in stable suspension, promoting uniform coating spreading. During application, the emulsifier, epoxy resin, and curing agent form an interpenetrating polymer network (IPN). The use of modified silica enhances the interfacial bonding between the filler, epoxy resin, and gasket, improving the coating's adhesion, corrosion resistance, and gasket sealing performance. It also reduces pores and pinholes in the coating structure, improving the coating's density and chemical corrosion resistance.

[0013] Preferably, in the above technical solution, the modified silica preparation steps are as follows:

[0014] Calcinate silica, cool, mix and grind the baked silica with ethanol, and dry at 50-60°C. Stir the phosphoric acid solution and the ground silica at a speed of 800-1200 rpm for 2-4 hours, heat to 50-60°C, and stir at a constant temperature of 500-600 rpm for 12-16 hours. Use a PTFE microporous membrane to filter the modified silica under reduced pressure, wash with deionized water, and dry in a vacuum oven at 50-60°C to obtain modified silica.

[0015] According to the above technical solution, the present invention increases the surface area ratio and surface activity of silica by high-temperature calcination of silica and combines it with ethanol grinding, thereby facilitating the introduction of more phosphate groups on the silica surface; utilizes a PTFE microporous membrane to perform reduced-pressure filtration on the modified silica to obtain modified silica with a small particle size, thereby ensuring that the formed coating is smooth and reducing the components in the exhaust gas from being trapped on the surface of the coating-coated sealing gasket for a long time.

[0016] Preferably, in the above technical solution, in the step of adding acetone, polyvinyl alcohol and benzophenone tetracarboxylic dianhydride in proportion to the reaction kettle for esterification reaction, the ratio of acetone, polyvinyl alcohol and benzophenone tetracarboxylic dianhydride is 15-18:6-7:1-1.5 by mass.

[0017] Preferably, in the above technical solution, in the step of adding acetone, polyvinyl alcohol, and benzophenone tetracarboxylic dianhydride in proportion to a reactor for esterification reaction, the reaction conditions of the esterification reaction include: reaction temperature of 80-90°C, rotation speed of 200-300 rpm, and reaction time of 4-5h.

[0018] Preferably, in the above technical solution, the reaction conditions of the saponification reaction include: reaction temperature of 100-110° C., rotation speed of 100-150 rpm, and reaction time of 1-3 h.

[0019] Preferably, in the above technical solution, in step S2, the components of the surface coating agent are 70-110g of water-based epoxy resin emulsion, 33-65g of filler, 4-8g of dispersant, 8-14g of thickener, 21-35g of stabilizer, and 15-23g of defoaming agent.

[0020] Preferably, in the above technical solution, the step of adding alkali solution and epoxy resin to the ester solution and reacting for 2-4 hours to obtain a water-based epoxy emulsifier refers to adding sodium hydroxide and epoxy resin to the ester solution at a reaction temperature of 100-110°C and a rotation speed of 300-400 rpm for 3-5 hours to obtain a water-based epoxy emulsifier.

[0021] A surface coating agent prepared by the preparation method as described above comprises 70-110 g of waterborne epoxy resin emulsion, 33-65 g of filler, 4-8 g of dispersant, 8-14 g of thickener, 21-35 g of stabilizer and 15-23 g of defoamer.

[0022] An application of the surface coating agent as described above comprises mixing 35-40 parts of the surface coating agent with 40-45 parts of water and 10-15 parts of a curing agent, and applying one or more protective layers to the surface of an automobile exhaust pipe gasket by spraying and / or dipping. The types of automobile exhaust pipe gaskets include non-metallic rubber composite gaskets, rubber-metal composite gaskets, and metal gaskets.

[0023] Compared with the prior art, the beneficial technical effects of this application are:

[0024] (1) The water-based epoxy emulsifier forms a stably dispersed water-based epoxy resin emulsion with the epoxy resin. When the coating is cured, the emulsifier, epoxy resin and curing agent form an interpenetrating polymer network, which improves the interfacial bonding between the sealing gasket and the coating, enhances the density of the coating, reduces the formation of structural pores in the coating, and improves the corrosion resistance of the coating; and the modified silica has a small particle size and contains phosphate groups, which cooperates with the colloidal graphite to promote the formation of a uniformly spread and well-adhesive coating, avoids the formation of pinholes in the coating, and jointly improves the corrosion resistance of the coating;

[0025] (2) The fillers are modified silica and colloidal graphite. Under the lubricating effect of colloidal graphite, the dispersing effect of dispersant and the effect of thickener, the phosphate groups on the modified silica form a sealing gasket substrate-Si-P-epoxy resin structure with the epoxy resin during coating, thereby improving the adhesion of the coating. At the same time, the modified silica has the characteristics of neutralizing acidic or alkaline media, thereby improving corrosion resistance. The addition of colloidal graphite to the filler promotes the uniform dispersion of the modified silica, while improving the flexibility and wear resistance of the coating interface, thereby increasing the service life of the automobile exhaust pipe gasket. Colloidal graphite can also improve the high temperature resistance of the coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a product diagram of a water-based epoxy resin emulsion prepared in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort shall fall within the scope of protection of the present invention.

[0028] Example 1

[0029] A method for preparing a surface coating agent for an automobile exhaust pipe sealing gasket, the method comprising:

[0030] S1, preparing a water-based epoxy resin emulsion: dissolving 120 g of polyvinyl alcohol and 20 g of benzophenone tetracarboxylic dianhydride in 300 mL of acetone in a proportionate manner into a reactor, and conducting an esterification reaction at a reaction temperature of 90° C. and a rotation speed of 200 rpm for 4 hours to obtain an ester solution. Sodium hydroxide and an epoxy resin are added to the ester solution and reacted at a reaction temperature of 110° C. and a rotation speed of 300 rpm for 4 hours to obtain a water-based epoxy emulsifier. The water-based epoxy emulsifier and the epoxy resin are mixed, and deionized water is added dropwise at a rotation speed of 900 rpm to obtain a water-based epoxy resin emulsion;

[0031] S2, preparing a surface coating agent: adding 93 g of waterborne epoxy resin emulsion, 55 g of filler, 8 g of dispersant, and 14 g of thickener to a reactor, stirring at 1000 rpm for 30 min, adding 26 g of stabilizer and 19 g of defoamer, and stirring at 800 rpm for 30 min to obtain a surface coating agent for automobile exhaust pipe sealing gaskets, wherein the filler is modified silica and colloidal graphite, and the modified silica is prepared as follows:

[0032] The silica was calcined at 900°C in a muffle furnace and cooled. The calcined silica was mixed with ethanol and ground, dried at 60°C, and the mixture was stirred with a phosphoric acid solution and the ground silica at a speed of 1000 rpm for 4 hours. The mixture was heated to 60°C and stirred at a constant temperature of 500 rpm for 15 hours. The modified silica was filtered under reduced pressure using a PTFE microporous membrane, washed with deionized water, and dried in a vacuum oven at 60°C to obtain modified silica.

[0033] Example 2

[0034] A method for preparing a surface coating agent for an automobile exhaust pipe sealing gasket, the method comprising:

[0035] S1, preparing a water-based epoxy resin emulsion: dissolving 200 g of polyvinyl alcohol and 30 g of benzophenone tetracarboxylic dianhydride in 350 mL of acetone solution and adding the mixture in proportion to each other into a reactor, conducting an esterification reaction at a reaction temperature of 80° C. and a rotation speed of 200 rpm for 5 hours to obtain an ester solution, adding sodium hydroxide and an epoxy resin to the ester solution, reacting at a reaction temperature of 110° C. and a rotation speed of 300 rpm for 4 hours to obtain a water-based epoxy emulsifier, mixing the water-based epoxy emulsifier and the epoxy resin, and adding deionized water dropwise at a rotation speed of 800 rpm to obtain a water-based epoxy resin emulsion;

[0036] S2, preparing a surface coating agent: adding 85 g of waterborne epoxy resin emulsion, 47 g of filler, 6 g of dispersant, and 10 g of thickener to a reactor, stirring at 1200 rpm for 50 min, adding 30 g of stabilizer and 22 g of defoamer, and stirring at 600 rpm for 50 min to obtain a surface coating agent for automobile exhaust pipe sealing gaskets, wherein the filler is modified silica and colloidal graphite, and the modified silica is prepared as follows:

[0037] The silica was calcined at 900°C in a muffle furnace and cooled. The calcined silica was mixed with ethanol and ground, dried at 55°C, and the mixture was stirred with a phosphoric acid solution and the ground silica at a speed of 1200 rpm for 4 hours. The mixture was heated to 50°C and stirred at a constant temperature of 600 rpm for 16 hours. The modified silica was filtered under reduced pressure using a PTFE microporous membrane, washed with deionized water, and dried in a vacuum oven at 55°C to obtain modified silica.

[0038] Example 3

[0039] A method for preparing a surface coating agent for an automobile exhaust pipe sealing gasket, the method comprising:

[0040] S1, preparing a water-based epoxy resin emulsion: dissolving 120 g of polyvinyl alcohol and 20 g of benzophenone tetracarboxylic dianhydride in 200 mL of acetone in a proportionate manner into a reactor, and conducting an esterification reaction at a reaction temperature of 80° C. and a rotation speed of 250 rpm for 5 hours to obtain an ester solution. Sodium hydroxide and an epoxy resin are added to the ester solution and reacted at a reaction temperature of 100° C. and a rotation speed of 400 rpm for 4 hours to obtain a water-based epoxy emulsifier. The water-based epoxy emulsifier and the epoxy resin are mixed, and deionized water is added dropwise at a rotation speed of 700 rpm to obtain a water-based epoxy resin emulsion;

[0041] S2, preparing a surface coating agent: adding 93 g of waterborne epoxy resin emulsion, 55 g of filler, 8 g of dispersant, and 14 g of thickener to a reactor, stirring at 1200 rpm for 50 min, adding 30 g of stabilizer and 23 g of defoamer, and stirring at 800 rpm for 30 min to obtain a surface coating agent for automobile exhaust pipe sealing gaskets, wherein the filler is modified silica and colloidal graphite, and the modified silica is prepared as follows:

[0042] The silica was calcined at 900°C in a muffle furnace and cooled. The calcined silica was mixed with ethanol and ground, dried at 60°C, and the phosphoric acid solution and the ground silica were stirred at a speed of 1200 rpm for 4 hours. The temperature was raised to 60°C, and stirred at a constant temperature of 500 rpm for 16 hours. The modified silica was filtered under reduced pressure using a PTFE microporous membrane, washed with deionized water, and dried in a vacuum oven at 60°C to obtain modified silica.

[0043] Comparative Example 1

[0044] Step S2 is the same as in Example 1, except that:

[0045] S1, preparing a water-based epoxy resin emulsion: taking 60g of polyethylene glycol and 120g of phthalic anhydride, dissolving them in 300mL of acetone and adding them to a reactor in proportion, carrying out an esterification reaction at a reaction temperature of 90°C and a rotation speed of 200rpm for 4h to obtain an ester solution, adding sodium hydroxide to the ester solution and reacting at a reaction temperature of 110°C and a rotation speed of 300rpm for 4h to obtain a water-based epoxy emulsifier, mixing the water-based epoxy emulsifier with the epoxy resin, and adding deionized water dropwise at a rotation speed of 900rpm to obtain a water-based epoxy resin emulsion.

[0046] Comparative Example 2

[0047] Step S2 is the same as in Example 1, except that:

[0048] S1, preparing a water-based epoxy resin emulsion: taking 120g of polyvinyl alcohol and 20g of phthalic anhydride, dissolving them in 300mL of acetone and adding them to a reactor in proportion, carrying out an esterification reaction at a reaction temperature of 90°C and a rotation speed of 200rpm for 4h to obtain an ester solution, adding sodium hydroxide to the ester solution, and reacting at a reaction temperature of 110°C and a rotation speed of 100rpm to obtain a water-based epoxy emulsifier, mixing the water-based epoxy emulsifier with the epoxy resin, and adding deionized water dropwise at a rotation speed of 900rpm to obtain a water-based epoxy resin emulsion.

[0049] Comparative Example 3

[0050] Step S1 is the same as in Example 1, except that:

[0051] S2, preparing a surface coating agent: adding 93 g of water-based epoxy resin emulsion, 55 g of filler, 8 g of dispersant, and 14 g of thickener to a reactor, stirring at 1000 rpm for 30 min, adding 26 g of stabilizer and 19 g of defoamer, stirring at 800 rpm for 30 min, to obtain a surface coating agent for automobile exhaust pipe sealing gaskets, wherein the filler is zinc powder.

[0052] Comparative Example 4

[0053] Step S1 is the same as in Example 1, except that:

[0054] S2, preparing a surface coating agent: adding 93 g of aqueous epoxy resin emulsion, 55 g of filler, 8 g of dispersant, and 14 g of thickener to a reactor, stirring at 1000 rpm for 30 min, adding 26 g of stabilizer and 19 g of defoamer, and stirring at 800 rpm for 30 min to obtain a surface coating agent for automobile exhaust pipe sealing gaskets, wherein the fillers are nanosilica and colloidal graphite.

[0055] Comparative Example 5

[0056] Step S1 is the same as in Example 1, except that:

[0057] S2, preparing a surface coating agent: adding 93g of water-based epoxy resin emulsion, 55g of filler, 8g of dispersant, 14g of thickener, 26g of stabilizer, and 19g of defoamer to a reactor, stirring at 1000rpm for 30min to obtain a surface coating agent for automobile exhaust pipe sealing gaskets, wherein the filler is silica, which is placed in a muffle furnace and calcined at 900°C, cooled, and ground into powdered calcined nano-silica.

[0058] Preparation of gasket surface coating:

[0059] Take 80g of the surface coating agent prepared in Example 1 and mix it with 80g of water and 30g of curing agent (benzophenone tetracarboxylic dianhydride) to form a coating liquid 1. The non-metallic rubber composite sealing gasket is immersed in the coating liquid 1 for 20 minutes, taken out and allowed to stand vertically until the coating is dry and solidified, and then immersed in the coating liquid 1 for 1-3 minutes, taken out and allowed to stand vertically until the coating is dry and solidified, sealing gasket 1.

[0060] Take 80g of the surface coating agent prepared in Example 2 and mix it with 80g of water and 30g of curing agent (benzophenone tetracarboxylic dianhydride) to form coating liquid 2. The non-metallic rubber composite sealing gasket is immersed in coating liquid 2 for 20 minutes, taken out and allowed to stand vertically until the coating is dry and solidified, and then immersed in coating liquid 2 for 1-3 minutes, taken out and allowed to stand vertically until the coating is dry and solidified. Sealing gasket 2.

[0061] 80 g of the surface coating agent prepared in Example 3 was mixed with 80 g of water and 30 g of a curing agent (benzophenone tetracarboxylic dianhydride) to form a coating liquid 3. The non-metallic rubber composite sealing gasket was immersed in the coating liquid 3 for 20 minutes, taken out and allowed to stand vertically until the coating dried and solidified, and then immersed in the coating liquid 3 for 1-3 minutes, taken out and allowed to stand vertically until the coating dried and solidified to prepare a sealing gasket 3.

[0062] Take 80g of the surface coating agent prepared in Comparative Example 1 and mix it with 80g of water and 30g of curing agent (benzophenone tetracarboxylic dianhydride) to form a coating liquid 4. The non-metallic rubber composite sealing gasket is immersed in the coating liquid 4 for 20 minutes, taken out and allowed to stand vertically until the coating is dry and solidified, and then immersed in the coating liquid 4 for 1-3 minutes, taken out and allowed to stand vertically until the coating is dry and solidified to prepare a sealing gasket 4.

[0063] Take 80g of the surface coating agent prepared in Comparative Example 2, mix it with 80g of water and 30g of curing agent (benzophenone tetracarboxylic dianhydride) to form a coating liquid 5, immerse the non-metallic rubber composite sealing gasket in the coating liquid 5 for 20 minutes, take it out and let it stand vertically until the coating is dry and solidified, then immerse it in the coating liquid 5 for 1-3 minutes, take it out and let it stand vertically until the coating is dry and solidified, to prepare a sealing gasket 5.

[0064] Take 80g of the surface coating agent prepared in Comparative Example 3 and mix it with 80g of water and 30g of curing agent (benzophenone tetracarboxylic dianhydride) to form a coating liquid 6. The non-metallic rubber composite sealing gasket is immersed in the coating liquid 6 for 20 minutes, taken out and allowed to stand vertically until the coating is dry and solidified, and then immersed in the coating liquid 6 for 1-3 minutes, taken out and allowed to stand vertically until the coating is dry and solidified to prepare a sealing gasket 6.

[0065] Take 80g of the surface coating agent prepared in Comparative Example 4, mix it with 80g of water and 30g of curing agent (benzophenone tetracarboxylic dianhydride) to form a coating liquid 7, immerse the non-metallic rubber composite sealing gasket in the coating liquid 7 for 20 minutes, take it out and let it stand vertically until the coating is dry and solidified, then immerse it in the coating liquid 7 for 1-3 minutes, take it out and let it stand vertically until the coating is dry and solidified, to prepare a sealing gasket 7.

[0066] Take 80g of the surface coating agent prepared in Comparative Example 5 and mix it with 80g of water and 30g of curing agent (benzophenone tetracarboxylic dianhydride) to form a coating liquid 8. The non-metallic rubber composite sealing gasket is immersed in the coating liquid 8 for 20 minutes, taken out and allowed to stand vertically until the coating is dry and solidified, and then immersed in the coating liquid 8 for 1-3 minutes, taken out and allowed to stand vertically until the coating is dry and solidified to prepare a sealing gasket 8.

[0067] After applying a layer of anti-sticking liquid on the glass and drying it, apply the above dispersants 1-8 respectively. After waiting for them to dry and solidify, peel them off and immerse them in 5% sulfuric acid solution for 24h, 48h, 72h, and 96h respectively. Dry and weigh them before and after the test to calculate their loss rate in the acidic solution.

[0068] Table 1 Loss of coatings in acidic solution

[0069]

[0070] The components of the aqueous epoxy emulsion prepared by the present invention have an important influence on the acid corrosion resistance of the surface coating agent. From the above data, it can be concluded that the aqueous epoxy emulsifier prepared using polyvinyl alcohol, benzophenone tetracarboxylic dianhydride, and epoxy resin is used to prepare the surface coating agent. When applied, the surface coating agent promotes the formation of an interpenetrating polymer network structure among the molecules, and synergistically promotes the formation of a uniformly spread and well-adhesive coating with modified silica and colloidal graphite, thereby enhancing the density of the coating, avoiding the formation of structural pores and pinholes in the coating, and improving the corrosion resistance of the coating.

[0071] The sealing gaskets 1-8 were placed in a 5% sulfuric acid solution for 7 days, washed with clean water, and the surface moisture was wiped dry. The gaskets were placed in a cool place to dry naturally for 3-4 days, and the appearance of the gaskets was observed.

[0072] Table 2

[0073]

[0074]

[0075] The surface coating agent of each example was subjected to performance testing. The hardness test was carried out according to GB / T 6739-1996 "Determination of Hardness of Coating Films by Pencil Method", the adhesion test was carried out according to GB / T 5210-2006 "Paints and Varnishes - Adhesion Test by Pull-Off Method", the flexibility test was carried out according to the bending test, the viscosity of the emulsion was tested at room temperature using a viscometer, and the water resistance test was carried out according to GB / T 1733-1993 "Determination of Water Resistance of Paint Films".

[0076] Table 3 Performance test results of surface coating agents

[0077]

[0078] The present invention can be implemented in various ways and is not limited to the embodiments described above. A person skilled in the art will appreciate that the present invention can be implemented in other specific ways without changing the technical concept or essential features of the present invention. Therefore, it should be understood that the embodiments described above are illustrative and not intended to limit the present invention.

Claims

1. A method for preparing a surface coating agent for automobile exhaust pipe sealing gasket, characterized in that: include: S1, preparing a water-based epoxy resin emulsion: adding acetone, polyvinyl alcohol, and benzophenone tetracarboxylic dianhydride in a certain proportion to a reactor for esterification to obtain an ester solution, adding alkaline solution and epoxy resin to the ester solution and reacting for 2-4 hours to obtain a water-based epoxy emulsifier, mixing the water-based epoxy emulsifier and epoxy resin, and adding deionized water dropwise at a rotation speed of 700-900 rpm to obtain a water-based epoxy resin emulsion; S2, preparing a surface coating agent: adding a water-based epoxy resin emulsion, a filler, a dispersant, and a thickener to a reactor, stirring at a speed of 1000-1200 rpm for 30-50 minutes, adding a stabilizer and a defoaming agent, and stirring at a speed of 600-800 rpm for 30-50 minutes to obtain a surface coating agent for automobile exhaust pipe sealing gaskets.

2. The method for preparing a surface coating agent for automobile exhaust pipe gasket according to claim 1, characterized in that: The filler is one or both of modified silicon dioxide and colloidal graphite, and the alkali solution is one of sodium hydroxide and sodium bicarbonate.

3. The method for preparing a surface coating agent for automobile exhaust pipe gasket according to claim 2, characterized in that: The modified silicon dioxide preparation steps are as follows: Calcinate silica, cool it, mix the baked silica with ethanol, grind it, and dry it at 50-60°C. Stir the phosphoric acid solution and the ground silica at a speed of 800-1200 rpm for 2-4 hours, heat it to 50-60°C, and stir it at a constant temperature of 500-600 rpm for 12-16 hours. Use a PTFE microporous membrane to filter the modified silica under reduced pressure, wash it with deionized water, and dry it in a vacuum oven at 50-60°C to obtain modified silica.

4. The method for preparing a surface coating agent for automobile exhaust pipe gasket according to claim 1, wherein: In the step of adding acetone, polyvinyl alcohol and benzophenone tetracarboxylic dianhydride into a reaction kettle in proportion to carry out esterification reaction, the ratio of acetone, polyvinyl alcohol and benzophenone tetracarboxylic dianhydride is 15-18:6-7:1-1.5 by mass.

5. The method for preparing a surface coating agent for automobile exhaust pipe gasket according to claim 4, characterized in that: In the step of adding acetone, polyvinyl alcohol, and benzophenone tetracarboxylic dianhydride in proportion to a reaction kettle for esterification reaction, the reaction conditions of the esterification reaction include: reaction temperature of 80-90° C., rotation speed of 200-300 rpm, and reaction time of 3.5-5 h.

6. The method for preparing a surface coating agent for automobile exhaust pipe gasket according to claim 1, characterized in that: In step S2, the surface coating agent comprises 70-110 g of waterborne epoxy resin emulsion, 33-65 g of filler, 4-8 g of dispersant, 8-14 g of thickener, 21-35 g of stabilizer, and 15-23 g of defoamer.

7. The method for preparing a surface coating agent for automobile exhaust pipe gasket according to claim 1, characterized in that: The step of adding alkali solution and epoxy resin to the ester solution and reacting for 2-4 hours to obtain a water-based epoxy emulsifier refers to adding sodium hydroxide and epoxy resin to the ester solution at a reaction temperature of 100-110° C. and a rotation speed of 300-400 rpm and reacting for 3-5 hours to obtain a water-based epoxy emulsifier.

8. A surface coating agent prepared by the preparation method according to claims 1 to 7, characterized in that: The surface coating agent comprises 70-110 g of waterborne epoxy resin emulsion, 33-65 g of filler, 4-8 g of dispersant, 8-14 g of thickener, 21-35 g of stabilizer and 15-23 g of defoamer.

9. Use of the surface coating agent according to claim 8, characterized in that: 35-40 parts of a surface coating agent are mixed with 40-45 parts of water and 10-15 parts of a curing agent, and one or more protective layers are applied to the surface of an automobile exhaust pipe gasket by spraying or / and dipping. The types of automobile exhaust pipe gaskets include non-metallic rubber composite gaskets, rubber-metal composite gaskets and metal gaskets.

10. Use of the surface coating agent according to claim 9, characterized in that: The curing agent is benzophenone tetracarboxylic dianhydride.

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