Polytetrafluoroethylene emulsion copolymer, polytetrafluoroethylene glass fiber cloth and preparation method and application of polytetrafluoroethylene emulsion copolymer and polytetrafluoroethylene glass fiber cloth

Abstract

The invention belongs to the field of high polymer materials, and relates to a polytetrafluoroethylene emulsion copolymer, polytetrafluoroethylene glass fiber cloth, and preparation methods and applications of the polytetrafluoroethylene emulsion copolymer and the polytetrafluoroethylene glass fiber cloth. The polytetrafluoroethylene glass fiber cloth is obtained by performing single dip-coating and high-temperature forming on a polytetrafluoroethylene emulsion copolymer prepared by specific synthesis and glass fiber cloth subjected to thorough dewaxing treatment. The invention relates to a polytetrafluoroethylene emulsion copolymer, which is prepared by taking a tetrafluoroethylene monomer, vinyltrimethoxysilane, tridecafluorooctyltrimethoxysilane, 2, 3, 5, 6-tetrafluoro-p-xylylenediamine and 2-vinyl hexafluoroisopropanol as main raw materials through polymerization. The polytetrafluoroethylene glass fiber cloth has the advantages of being high in solid content, low in viscosity, small in surfactant dosage, good in binding force with specially-treated glass fiber cloth and the like, the feeding amount of 2-3 times of dip-coating of a conventional common polytetrafluoroethylene emulsion can be achieved through single-time coating, and the polytetrafluoroethylene glass fiber cloth which is high in coating compactness and can be used as a gas stove pad is obtained through high-temperature sintering forming.

Description

Technical Field

[0001] The invention belongs to the field of polymer materials, and specifically relates to a polytetrafluoroethylene emulsion copolymer and a preparation method thereof, as well as a polytetrafluoroethylene glass fiber cloth prepared from the polytetrafluoroethylene emulsion copolymer, and a preparation method and application thereof. Background Art

[0002] At present, polytetrafluoroethylene glass fiber cloth (also called Teflon glass fiber cloth) is a product obtained by dipping and molding glass fiber cloth with commercially available ordinary specifications of polytetrafluoroethylene emulsion for multiple times. This product has good corrosion resistance and is widely used in high temperature resistant and oil-repellent fields such as conveyor belts, high temperature resistant test paper raw materials, and demoulding cloth, such as CN201610634357.4, CN201610981818.5, etc. In the ordinary civilian field, polytetrafluoroethylene glass fiber cloth has excellent oil-repellent performance and can be used as a composite material for kitchen gas stove pads, which has the effects of anti-oil, waterproof and easy to clean.

[0003] However, the current use of polytetrafluoroethylene glass fiber cloth as a gas stove pad also has the following shortcomings in the production and application process: (1) At present, the glass fiber cloth is mainly dipped in ordinary polytetrafluoroethylene emulsion available on the market. Due to the high viscosity of ordinary polytetrafluoroethylene emulsion products available on the market, it is often necessary to dilute it to a solid content of 20-45% for dip coating during use, resulting in the production process generally requiring 3 or more dip coating, sintering and other processes to achieve the required film thickness, a long process flow and low production efficiency. In addition, in order to ensure the stability of the emulsion, the amount of surfactant used in ordinary commercial polytetrafluoroethylene emulsion is relatively large, basically more than 6%. Since surfactants are small molecular compounds, these surfactants will escape from the polytetrafluoroethylene emulsion coating when the polytetrafluoroethylene glass fiber cloth is sintered at high temperature. If the amount is too large, it will cause excessive escape during high-temperature sintering, affecting the density of the coating and the adhesion between the coating and the glass fiber cloth. (2) In the production process, in order to increase the adhesion between polytetrafluoroethylene emulsion and glass fiber cloth, the industry basically adopts a high-temperature dewaxing process (280-320℃). The problem is that due to the low dewaxing temperature, the dewaxing is not thorough. The basic wax content after dewaxing is about 1%, which seriously affects the adhesion between the polytetrafluoroethylene coating and the glass fiber cloth, and also affects the color difference of the final product. If you want to completely achieve high-temperature dewaxing, it often requires a high temperature of 420-450℃ and a high-temperature dewaxing time of more than 20 minutes. This not only leads to high energy consumption, but also the excessively high temperature and excessively long dewaxing time cause the mechanical strength of the glass fiber cloth to decrease significantly, and the tensile strength decreases by more than 30%, making it difficult to meet the mechanical performance application requirements of the product. (3) In order to improve the adhesion between polytetrafluoroethylene emulsion and glass fiber cloth, the industry often adopts the method of adding silane coupling agent to polytetrafluoroethylene emulsion. However, since silane coupling agent itself is a small molecule compound, its boiling point is generally lower than 300℃, while the final sintering molding temperature of polytetrafluoroethylene glass fiber cloth is basically above 360℃, the added silane coupling agent evaporates from the coating during the sintering process, which not only fails to enhance the adhesion, but also brings defects such as pinholes caused by gas escape to the coating. This also leads to the need for repeated dipping of polytetrafluoroethylene emulsion on the glass fiber cloth to eliminate coating defects.

[0004] These problems affect the adhesion between the polytetrafluoroethylene coating and the glass fiber cloth, as well as the high temperature resistance and high temperature solvent resistance. In addition, the multiple dipping and sintering processes result in long processes and high energy consumption, which is not only environmentally friendly, but also causes the prepared products to be exposed to high temperature, high oil pollution and other environments for a long time when used in gas stove pads, making it easy for the polytetrafluoroethylene coating to bubble, deform, or even fall off, seriously affecting the long-term application of the product in the field of gas stove pads. Summary of the invention

[0005] In view of the above-mentioned problems, the purpose of the present invention is to provide a polytetrafluoroethylene emulsion copolymer, a high-adhesion polytetrafluoroethylene glass fiber cloth prepared therefrom, and their preparation methods and applications. The polytetrafluoroethylene emulsion copolymer of the present invention is obtained by polymerization of tetrafluoroethylene monomer, vinyl trimethoxysilane, tridecafluorooctyl trimethoxysilane, 2,3,5,6-tetrafluoro-p-phenylenediamine, and 2-vinyl hexafluoroisopropanol as main raw materials. The polytetrafluoroethylene glass fiber cloth is obtained by single dipping and high-temperature molding of the polytetrafluoroethylene emulsion copolymer prepared by the specific synthesis and the glass fiber cloth treated thoroughly by dewaxing.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a polytetrafluoroethylene emulsion copolymer, which is prepared from the following raw materials in molar parts: Tetrafluoroethylene 100-108 parts Deionized water 1450-1680 parts Vinyltrimethoxysilane 0.8-1.1 parts Tridecafluorooctyltrimethoxysilane 0.6-0.9 parts 2,3,5,6-tetrafluoro-p-phenylenediamine 0.8-1 part 2-vinyl hexafluoroisopropanol 2-2.5 parts 6-8 parts of organic solvent As well as catalysts, dispersants, initiators, stabilizing agents and surfactants.

[0007] In some embodiments, the organic solvent is acetonitrile, methyl ethyl ketone or a combination of the two, preferably acetonitrile.

[0008] The invention uses vinyl trimethoxysilane and tridecafluorooctyl trimethoxysilane to carry out grafting reaction on 2,3,5,6-tetrafluoro-p-phenylenediamine to obtain a macromolecular fluorine-containing silane coupling agent intermediate having alkenyl, amino and multiple methoxy groups.

[0009] In the present invention, the catalyst is used to catalyze the grafting reaction of 2,3,5,6-tetrafluoro-p-phenylenediamine with vinyltrimethoxysilane and tridecafluorooctyltrimethoxysilane to achieve chain extension of the coupling agent and introduce functional groups such as alkenyl and amino groups.

[0010] In some embodiments, the catalyst is selected from tetramethylammonium hydroxide, potassium hydroxide, or a combination of the two, preferably tetramethylammonium hydroxide.

[0011] The amount of the catalyst used is 0.03-0.05% of the mass of 2,3,5,6-tetrafluoro-p-phenylenediamine.

[0012] In some embodiments, the dispersant is selected from one of ammonium perfluorooctanoate and perfluorodimethylammonium dioxanonanoate or a combination of the two, preferably a composite of ammonium perfluorooctanoate and perfluorodimethylammonium dioxanonanoate, with a mass ratio of 1:1.5-2.

[0013] The amount of the dispersant used is 0.05-0.08% of the mass of deionized water.

[0014] In some embodiments, the dispersant is dissolved in 25-30° C. deionized water to form a 7-8 wt % aqueous solution before use, and then slowly added to the reaction system in the form of an aqueous solution.

[0015] In some embodiments, the initiator is selected from one or a combination of two or more of persulfate (such as ammonium persulfate, potassium persulfate, etc.), organic peroxide, persulfate-ferrous ion, organic peroxide-ferrous ion, wherein the organic peroxide includes benzoyl peroxide, peroxysuccinic acid, etc. The initiator is preferably ammonium persulfate.

[0016] The dosage of the initiator is 2-4 ppm based on the mass of deionized water.

[0017] In some embodiments, the initiator is dissolved in 25-30° C. deionized water to form a 4 wt % aqueous solution before use, and then added to the reaction system in the form of an aqueous solution.

[0018] In some embodiments, the stabilizing aid is liquid paraffin.

[0019] The amount of the stabilizing agent used is 0.5-0.8% of the mass of deionized water.

[0020] In some embodiments, the surfactant is a complex of sodium salt of dioctyl sulfonated succinate and isomeric tridecanol polyoxyethylene ether, and the mass ratio of the two is 0.5:1-1.3. The present invention adopts a composite surfactant, which has high efficiency in stabilizing the emulsion of the present invention, has the characteristics of small dosage and good emulsion stabilization effect.

[0021] The dosage of the surfactant is 0.6-1.0% of the mass of deionized water.

[0022] In a second aspect, the present invention provides a method for preparing the polytetrafluoroethylene emulsion copolymer described in the first aspect, comprising the following steps: S1: In an organic solvent, 2,3,5,6-tetrafluoro-p-phenylenediamine, tridecafluorooctyltrimethoxysilane and vinyltrimethoxysilane are sequentially grafted at 75-78° C. under the catalysis of a catalyst, and the solvent is removed after the reaction to obtain a macromolecular fluorinated silane coupling agent intermediate; S2: In a reaction kettle with an oxygen content not exceeding 40 ppm, tetrafluoroethylene monomer is introduced into water containing 2-vinyl hexafluoroisopropanol and a stabilizing agent, and an initiator and a dispersant are added to carry out a polymerization reaction at 80-85°C, and the reaction pressure is maintained at 2.0-2.3 MPa; S3: When the amount of tetrafluoroethylene monomer introduced reaches one-half to two-thirds of the formula amount, add the macromolecular fluorine-containing silane coupling agent intermediate obtained in step S1, and heat to 88-92° C. for copolymerization reaction. After the introduction of the formula amount of tetrafluoroethylene is completed, continue to keep the temperature for reaction; S4: When the particle size distribution D50 of the copolymer in the kettle is 0.29-0.35 μm, the polymerization reaction is stopped, and the formulated amount of surfactant is added, mixed evenly, and then concentrated under reduced pressure to obtain a polytetrafluoroethylene emulsion copolymer with a solid content of 67-71%.

[0023] In some embodiments, step S1 comprises the following steps: S1-1: dissolving a formulated amount of 2,3,5,6-tetrafluoro-p-phenylenediamine in an organic solvent, adding a catalyst, adding a formulated amount of tridecafluorooctyltrimethoxysilane, and performing a grafting reaction at 75-78° C., while removing methanol as a byproduct of the reaction; S1-2: When the content of free 2,3,5,6-tetrafluoro-p-phenylenediamine in the reaction system is less than 5% of the original amount added, a formulated amount of vinyltrimethoxysilane is added and the temperature is kept high to carry out a secondary grafting reaction; S1-3: When the content of free vinyltrimethoxysilane in the reaction system is less than 2% of the original added amount, the organic solvent is removed under reduced pressure to obtain a macromolecular fluorinated silane coupling agent intermediate.

[0024] In some embodiments, in step S2, the dispersant needs to be slowly added to the reaction system, and the time is controlled within 1.5-2 hours to promote the uniformity of the emulsion particle size.

[0025] In some embodiments, in step S4, the vacuum degree of the reduced pressure concentration is controlled between -0.097 MPa and -0.099 MPa.

[0026] The polytetrafluoroethylene emulsion copolymer prepared by the invention has a solid content of 67-71%, a surfactant content volatile at 380°C / 30min of 1.5-2.5wt%, and a viscosity (25°C) of 11-17mPa·s.

[0027] In a third aspect, the present invention provides a method for preparing a polytetrafluoroethylene glass fiber cloth, comprising the following steps: S5: soaking the alkali-free glass fiber cloth in a dewaxing solvent for chemical immersion dewaxing treatment, and then performing a high-temperature dewaxing treatment at 350-360°C; S6: The alkali-free glass fiber cloth dewaxed in step S5 is immersed in the polytetrafluoroethylene emulsion copolymer described in the first aspect or the polytetrafluoroethylene emulsion copolymer prepared by the preparation method described in the second aspect. After a single immersion, the polytetrafluoroethylene glass fiber cloth is dried, formed, and sintered to obtain the polytetrafluoroethylene glass fiber cloth.

[0028] In some embodiments, in step S5, the dewaxing solvent is selected from one of ethylene glycol monobutyl ether and dimethylformamide (DMF) or a combination of the two, preferably a mixture of ethylene glycol monobutyl ether and DMF, and the mass ratio of the two is 2.5-3:1.

[0029] In some embodiments, in step S5, the temperature of soaking the alkali-free glass fiber cloth in the dewaxing solvent is 130-135° C., and the soaking time is 1-1.5 min.

[0030] In some embodiments, in step S5, the high temperature dewaxing treatment lasts for 2-3 minutes.

[0031] After the dewaxing treatment in step S5, the wax content of the alkali-free glass fiber cloth is less than 0.1 wt %.

[0032] In some embodiments, in step S6, the immersion time is 1-1.5 min.

[0033] In some embodiments, in step S6, the drying temperature is 125-130° C., and the drying time is 10-15 min.

[0034] In some embodiments, in step S6, the molding temperature is 265-270° C., and the molding time is 8-10 min.

[0035] In some embodiments, in step S6, the sintering temperature is 370-375° C., and the sintering time is 4-6 min.

[0036] In a fourth aspect, the present invention provides polytetrafluoroethylene glass fiber cloth prepared by the preparation method described in the third aspect.

[0037] In a fifth aspect, the present invention provides the use of the polytetrafluoroethylene glass fiber cloth described in the fourth aspect in the preparation of gas stove pads and kitchen stove oil and fireproof pads.

[0038] Beneficial effects achieved by the technical solution of the present invention: (1) The polytetrafluoroethylene emulsion copolymer of the present invention introduces special silane coupling agent groups containing amino, vinyl, fluorine and multiple methoxy groups, and 2-vinylhexafluoroisopropanol into the polytetrafluoroethylene copolymer molecular chain through polymerization reaction, and forms a branched structure with polytetrafluoroethylene. Compared with ordinary commercially available polytetrafluoroethylene emulsions, the polytetrafluoroethylene emulsion copolymer product of the present invention has the advantages of high solid content, low viscosity, small amount of surfactant used, and good bonding strength with specially treated glass fiber cloth. A single coating can achieve the same amount of material as 2-3 times of dipping of conventional ordinary polytetrafluoroethylene emulsion, and then high-temperature sintering molding is performed to obtain a coating with high density, which can be used as polytetrafluoroethylene glass fiber cloth for gas stove pads.

[0039] (2) The polytetrafluoroethylene coating on the surface of the polytetrafluoroethylene glass fiber cloth of the present invention has excellent adhesion. When used for gas stove pads or kitchen high temperature resistant oil-proof pads, it will not cause bubbling, deformation, discoloration, etc. when used in high temperature and high oil pollution environment for a long time, and the prepared product has almost no obvious color difference. 2 After the alkali-free glass fiber cloth is specially dewaxed, the performance of the glass fiber cloth obtained by single coating molding using the polytetrafluoroethylene emulsion copolymer product of the present invention can reach the performance of ordinary polytetrafluoroethylene emulsion after three coating molding, and has the characteristics of simple molding process, short process, low cost and better comprehensive performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a transmission electron microscopy image of the polytetrafluoroethylene emulsion copolymer prepared in Example 1.

[0041] Figure 2 This is a test chart of the particle size D50 of the polytetrafluoroethylene emulsion copolymer prepared in Example 1. DETAILED DESCRIPTION

[0042] In order to better understand the technical solution provided by the present invention, the present invention is described in detail below through specific implementation methods, but the claims of the present invention are not limited to these embodiments, and the embodiments only provide some experimental conditions for achieving the purpose of the present technical invention.

[0043] Unless otherwise specified, the raw materials, reagents, methods, etc. used in the examples are conventional commercially available raw materials, reagents, and methods in the art.

[0044] Reagents and sources: Silane coupling agent vinyl trimethoxy silane was purchased from Jiangxi Chenguang New Materials Co., Ltd., model: CG-171.

[0045] The silane coupling agent tridecafluorooctyltrimethoxysilane was purchased from Hangzhou Jessica Chemical Co., Ltd., model: KH-1331.

[0046] 2-Vinylhexafluoroisopropanol was purchased from TCI (Shanghai) Chemical Trading Co., Ltd.

[0047] The stabilizing agent liquid paraffin was purchased from Nanjing Tianshi New Material Technology Co., Ltd., model: TP-33.

[0048] The surfactant dioctyl sulfonated succinate sodium salt was purchased from Hai'an Petrochemical Plant, Jiangsu Province.

[0049] The surfactant isomeric tridecanol polyoxyethylene ether was purchased from Hai'an Petrochemical Plant in Jiangsu Province, model: E-1308.

[0050] Alkali-free glass fiber cloth, purchased from Jiangsu Changhai Composite Materials Co., Ltd., product model EWR300, weight 300g / m 2 .

[0051] The present invention will be further described below in conjunction with embodiments, but the present invention is not limited thereto.

[0052] Example 1 This embodiment provides a high-adhesion polytetrafluoroethylene glass fiber cloth, which is prepared by the following steps: (1) Preparation of polytetrafluoroethylene emulsion copolymer The raw materials of the polytetrafluoroethylene emulsion copolymer are calculated by molar parts as follows: 100 parts of tetrafluoroethylene, 1480 parts of deionized water, 0.8 parts of vinyltrimethoxysilane, 0.6 parts of tridecafluorooctyltrimethoxysilane, 0.8 parts of 2,3,5,6-tetrafluoro-p-phenylenediamine, 2.1 parts of 2-vinylhexafluoroisopropanol, and 6 parts of acetonitrile; and the catalyst is tetramethylammonium hydroxide, and the amount used is 0.04% of the mass of 2,3,5,6-tetrafluoro-p-phenylenediamine; the dispersant is The complex of ammonium perfluorooctanoate and perfluorodimethylammonium dioxanonanoate, the mass ratio of the two is 1:1.7, and the dosage is 0.05% of the mass of deionized water; the initiator is ammonium persulfate, the dosage is 2.5ppm of the mass of deionized water; the stabilizing agent is liquid paraffin, the dosage is 0.55% of the mass of deionized water; the surfactant is a complex of sodium salt of dioctyl sulfonate succinate and isomeric tridecyl alcohol polyoxyethylene ether, the mass ratio of the two is 0.5:1.1, and the dosage is 0.7% of the mass of deionized water.

[0053] The preparation steps are as follows (1-1) to (1-4): (1-1) Preparation of graft-modified olefin-containing coupling agent products (i) adding a formulated amount of an organic solvent and 2,3,5,6-tetrafluoro-p-phenylenediamine into a 500 mL reactor, starting stirring, heating to 77° C. to fully dissolve the mixture, and maintaining the temperature, adding a formulated amount of a catalyst, mixing the mixture evenly, and then adding a formulated amount of tridecafluorooctyltrimethoxysilane to carry out a reaction at the same temperature, while removing methanol, a byproduct of the reaction; (ii) taking a sample and testing it by high performance liquid chromatography. When the content of free 2,3,5,6-tetrafluoro-p-phenylenediamine in the reaction system is less than 5% of the original amount added, it indicates that the grafting reaction is basically completed. At this time, vinyl trimethoxysilane is added in a formulated amount and the temperature is kept constant to carry out a secondary grafting reaction; (iii) taking a sample and testing it by gas chromatography. When the content of free vinyltrimethoxysilane is less than 2% of the original amount added, it indicates that the secondary grafting reaction has been completed. The organic solvent is removed under reduced pressure to obtain a macromolecular fluorine-containing silane coupling agent intermediate for standby use. (1-2) Add the formulated amount of deionized water, stabilizing agent and 2-vinylhexafluoroisopropanol to a 20L autoclave, seal the autoclave, start stirring, evacuate, and replace the oxygen in the autoclave with high-purity nitrogen. When the oxygen content is lower than 35ppm, raise the temperature to 83°C, continue to introduce tetrafluoroethylene monomer, maintain the pressure in the autoclave at 2.2Mpa, then use feeding pump 1 to add the formulated amount of initiator at one time (before use, the initiator is dissolved in 26°C deionized water to form a 4wt% aqueous solution, and then added to the reaction system in the form of an aqueous solution) and then keep the temperature for reaction; at the same time, continue to slowly add the dispersant solution (before use, the dispersant is dissolved in 26°C deionized water to form a 7.5wt% aqueous solution) using feeding pump 2, and control the feeding time to 1.8h; (1-3) When the amount of tetrafluoroethylene monomer introduced reaches three-fifths of the formula amount, the graft-modified olefin-containing coupling agent product obtained in step 1-1 is added, and the temperature is raised to 90° C. for copolymerization reaction; after the introduction of the formula amount of tetrafluoroethylene is completed, the reaction is continued at the temperature; (1-4) Sampling and testing. When the particle size distribution D50 of the copolymer in the kettle is 0.29-0.35 μm, stop the reaction, slowly release the pressure to normal pressure, then add the surfactant in the formula, stir evenly and start vacuum to reduce pressure and concentrate (the vacuum degree is controlled at -0.098 MPa). When the solid content reaches 67-71%, cool to room temperature and discharge the material to obtain a polytetrafluoroethylene emulsion copolymer product. The transmission electron microscopy image and particle size D of the polytetrafluoroethylene emulsion copolymer are as follows: 50 The test pictures are shown in Figure 1 and Figure 2 .

[0054] The solid content of the polytetrafluoroethylene emulsion copolymer product is 70.4%; the content of surfactant that can volatilize at 380°C / 30min is 1.7%; and the viscosity (25°C) is 16mPa·s.

[0055] (2) Dewaxing treatment of alkali-free glass fiber cloth The alkali-free glass fiber cloth is vertically hung on the conveying rod and conveyed to the first temperature zone (maintaining the temperature at 137°C), the base cloth is heated to 133°C, and then conveyed through a dewaxing tank containing a dewaxing solvent for chemical immersion dewaxing treatment (the dewaxing solvent is a mixture of ethylene glycol monobutyl ether and DMF, and the mass ratio of the two is 2.8:1), the immersion time is 58s, and then conveyed into a high-temperature drying tunnel at 353°C / 2.5min for another thorough high-temperature dewaxing treatment. The wax content of the glass fiber cloth base cloth after final treatment is 0.08%.

[0056] (3) Preparation of polytetrafluoroethylene glass fiber cloth The polytetrafluoroethylene emulsion copolymer prepared in step (1) is placed in an emulsion tank, and the alkali-free glass fiber cloth subjected to dewaxing treatment in step (2) is subjected to a single immersion treatment in the emulsion tank for 1.4 minutes, and then subjected to low-temperature drying (128°C / 13 minutes), medium-temperature molding (266°C / 9 minutes), and high-temperature sintering (374°C / 5 minutes) in sequence to obtain a high-adhesion polytetrafluoroethylene glass fiber cloth, which can be used as a composite material for a gas stove pad.

[0057] Example 2 The present embodiment provides a high-adhesion polytetrafluoroethylene glass fiber cloth, which is prepared according to the method of embodiment 1, wherein the raw materials of the polytetrafluoroethylene emulsion copolymer are calculated by molar parts as follows: 107 parts of tetrafluoroethylene, 1668 parts of deionized water, 1.1 parts of vinyltrimethoxysilane, 0.9 parts of tridecafluorooctyltrimethoxysilane, 1 part of 2,3,5,6-tetrafluoro-p-phenylenediamine, 2.5 parts of 2-vinylhexafluoroisopropanol, and 8 parts of methyl ethyl ketone; and the catalyst is tetramethylammonium hydroxide, the amount of which is 2,3,5,6-tetrafluoro-p-phenylenediamine, 2.5 parts of 2-vinylhexafluoroisopropanol, and 8 parts of methyl ethyl ketone. The mass ratio of the dispersant is 1:1.9, and the dosage is 0.07% of the mass of deionized water. The initiator is ammonium persulfate, and the dosage is 4ppm of the mass of deionized water. The stabilizing agent is liquid paraffin, and the dosage is 0.75% of the mass of deionized water. The surfactant is a complex of sodium salt of dioctyl sulfonate succinate and isomeric tridecyl alcohol polyoxyethylene ether, and the mass ratio of the two is 0.5:1.3, and the dosage is 1% of the mass of deionized water.

[0058] The obtained polytetrafluoroethylene emulsion copolymer product has a solid content of 68.8%; a surfactant content volatile at 380°C / 30min: 1.9%; and a viscosity (25°C): 14 mPa·s.

[0059] Example 3 The present embodiment provides a high-adhesion polytetrafluoroethylene glass fiber cloth, which is prepared according to the method of Example 1, wherein the raw materials of the polytetrafluoroethylene emulsion copolymer are calculated by molar parts as follows: 105 parts of tetrafluoroethylene, 1610 parts of deionized water, 1 part of vinyl trimethoxy silane, 0.8 parts of tridecafluorooctyl trimethoxy silane, 0.9 parts of 2,3,5,6-tetrafluoro-p-phenylenediamine, 2.3 parts of 2-vinyl hexafluoroisopropanol, and 7 parts of acetonitrile; and the catalyst is potassium hydroxide, and the amount of 2,3,5,6-tetrafluoro-p-phenylenediamine is 0.9 parts of 2,3,5,6-tetrafluoro-p-phenylenediamine. The dosage is 0.03% of the mass of fluoroparaphenylenediamine; the dispersant is a complex of ammonium perfluorooctanoate and ammonium perfluorodimethyldioxanonanoate, the mass ratio of the two is 1:1.6, and the dosage is 0.06% of the mass of deionized water; the initiator is ammonium persulfate, the dosage is 3ppm of the mass of deionized water; the stabilizing agent is liquid paraffin, the dosage is 0.6% of the mass of deionized water; the surfactant is a complex of sodium salt of dioctyl sulfonate succinate and isomeric tridecyl alcohol polyoxyethylene ether, the mass ratio of the two is 0.5:1.2, and the dosage is 0.9% of the mass of deionized water.

[0060] The obtained polytetrafluoroethylene emulsion copolymer product has a solid content of 67.3%; a surfactant content volatile at 380°C / 30min: 2.0%; and a viscosity (25°C): 13 mPa·s.

[0061] Example 4 The present embodiment provides a high-adhesion polytetrafluoroethylene glass fiber cloth, which is prepared according to the method of embodiment 1, wherein the raw materials of the polytetrafluoroethylene emulsion copolymer are calculated by molar parts as follows: 102 parts of tetrafluoroethylene, 1565 parts of deionized water, 0.9 parts of vinyltrimethoxysilane, 0.7 parts of tridecafluorooctyltrimethoxysilane, 0.85 parts of 2,3,5,6-tetrafluoro-p-phenylenediamine, 2.2 parts of 2-vinylhexafluoroisopropanol, and 6.5 parts of acetonitrile; and the catalyst is tetramethylammonium hydroxide, the amount of which is 2,3,5,6-tetrafluoro-p-phenylenediamine, 2.2 parts of 2-vinylhexafluoroisopropanol, and 6.5 parts of acetonitrile; The amount of the dispersant is 0.07% of the mass of deionized water; the initiator is ammonium persulfate, and the amount is 3ppm of the mass of deionized water; the stabilizing agent is liquid paraffin, and the amount is 0.7% of the mass of deionized water; the surfactant is a complex of sodium salt of dioctyl sulfonate succinate and isomeric tridecyl alcohol polyoxyethylene ether, and the mass ratio of the two is 0.5:1, and the amount is 0.8% of the mass of deionized water.

[0062] The obtained polytetrafluoroethylene emulsion copolymer product has a solid content of 69.2%; a surfactant content volatile at 380°C / 30min: 2.3%; and a viscosity (25°C): 15 mPa·s.

[0063] Comparative Example 1 This comparative example provides a polytetrafluoroethylene glass fiber cloth, which is prepared according to the method of Example 1, except that in step (2): the alkali-free glass fiber cloth is vertically suspended on a conveying rod and conveyed into a high-temperature drying tunnel for high-temperature dewaxing treatment at 355°C / 3min, and the wax content of the glass fiber cloth base cloth after the treatment is 1.1%.

[0064] Comparative Example 2 This comparative example provides a polytetrafluoroethylene glass fiber cloth, which is prepared according to the method of Example 1, except that in step (2): the alkali-free glass fiber cloth is vertically suspended on a conveying rod and conveyed into a high-temperature drying tunnel at 425°C / 10min for high-temperature dewaxing treatment, and the wax content of the glass fiber cloth base cloth after the treatment is 0.63%.

[0065] Comparative Example 3 This comparative example provides a polytetrafluoroethylene glass fiber cloth, in which the polytetrafluoroethylene emulsion copolymer prepared in step (1) is replaced with a common commercially available polytetrafluoroethylene emulsion product, and the alkali-free glass fiber cloth dewaxed in step (2) is treated in the manner of step (3).

[0066] Among them, the commercially available polytetrafluoroethylene emulsion product was purchased from Jinhua Yonghe Fluorine Chemical Co., Ltd., model: R-200, and its parameters are as follows: solid content: 59.4%; 380°C / 30min volatile surfactant content: 6.7%; viscosity (25°C): 37mPa·s.

[0067] Comparative Example 4 This comparative example provides a polytetrafluoroethylene glass fiber cloth, which is prepared according to the method of comparative example 3, except that 1% of the mass of the polytetrafluoroethylene emulsion of the silane coupling agent tridecafluorooctyltrimethoxysilane and 1% of vinyltrimethoxysilane are added to the common commercially available polytetrafluoroethylene emulsion in comparative example 3 and stirred evenly.

[0068] Comparative Example 5 The present comparative example provides a polytetrafluoroethylene glass fiber cloth, which is prepared according to the method of comparative example 3, except that deionized water is added to the common commercially available polytetrafluoroethylene emulsion in comparative example 3 to dilute it to a solid content of 25%, and 0.5% of tridecafluorooctyltrimethoxysilane and 0.5% of vinyltrimethoxysilane are added respectively, stirred evenly, and then three dipping steps of "dipping-low temperature drying-medium temperature molding-high temperature sintering" are carried out respectively three times to complete the coating film preparation, and the process parameters of each step are the same as those in Example 1.

[0069] Comparative Example 6 This comparative example provides a polytetrafluoroethylene glass fiber cloth, which adopts the current mainstream polytetrafluoroethylene composite material preparation process in the market. The process parameters are basically the same as those in comparative example 5, except that the dewaxing process of comparative example 5 is changed to 330°C / 15min. After dewaxing treatment, the wax content of the glass fiber cloth is 0.89%.

[0070] Test method: The solid content and volatile surfactant content of polytetrafluoroethylene emulsion are tested according to the thermal gravimetric determination method in section 5.2.2 and the surfactant content method in section 5.3 of T / FSI067-2021 "Polytetrafluoroethylene concentrate for repeated dipping and sintering".

[0071] The viscosity (25° C.) was measured using a rotational viscometer.

[0072] The tensile breaking strength and adhesion strength are tested according to JC / T 171.2-2019 "Coated Glass Fiber Cloth Part 2: Polytetrafluoroethylene Emulsion Coated Glass Fiber Cloth". The adhesion of the coating is determined by the adhesion strength. The greater the adhesion strength, the stronger the adhesion of the coating.

[0073] The high temperature resistance is tested in a forced air oven at 260°C for 48h.

[0074] High temperature solvent resistance: 350SN base oil was heated to 230℃ and the sample was cut into The square specifications were put into 230℃ base oil and soaked at high temperature for 24 hours. After being taken out, the base oil was washed off with anhydrous ethanol, and the sample was dried and the surface condition of the sample was observed.

[0075] High temperature resistance and high temperature solvent resistance can not only judge the quality of the sample's high temperature resistance and solvent resistance, but also indirectly judge the adhesion from the bubbling and shedding of the coating.

[0076] The flame retardant properties are tested according to the vertical burning test method in GB / T 2408-2021 "Horizontal and vertical methods for determination of combustion performance of plastics".

[0077] The performance test results of the polytetrafluoroethylene glass fiber cloth prepared in Examples 1-4 and Comparative Examples 1-6 are shown in Table 1.

[0078] Table 1. Performance test results of polytetrafluoroethylene glass fiber cloth

[0079] As can be seen from Table 1, the present invention uses a polytetrafluoroethylene emulsion copolymer product prepared by a specific copolymer formula and process, and a single dip coating on a glass fiber cloth treated by a thorough dewaxing process, followed by drying, molding, and sintering to obtain a high-performance, high-adhesion polytetrafluoroethylene glass fiber cloth composite material product. Moreover, the product has a smooth appearance, excellent mechanical properties and flame retardant properties, and a flame retardant grade of V-0. It has good high temperature resistance. After continuous high temperature blasting at 260℃ / 48h, its surface still has no color change and no bubbling phenomenon; the adhesion strength is basically above 1130N / m, and the high temperature solvent resistance is excellent. In 230℃ 350SN base oil for 24h, the surface has no color change, no swelling, no bubbling, and excellent oil resistance. It can be used as a composite material for gas stove pads or kitchen stove cleaning pads, and has excellent oil resistance, high temperature resistance, and high adhesion.

[0080] Comparative Example 1 only uses short-time high-temperature dewaxing (355°C / 3min) without using a chemical dewaxing step, so the dewaxing is not thorough and the wax content is still high. Although the polytetrafluoroethylene emulsion uses the high-adhesion polytetrafluoroethylene emulsion copolymer specially prepared by the present invention, it still affects its adhesion to the glass fiber cloth, resulting in the final prepared polytetrafluoroethylene glass fiber cloth composite material having very slight bubbling under continuous high-temperature blowing (250°C / 48h), and the adhesion strength is also reduced to 952N / m. Slight bubbling also occurs under long-term high-temperature resistant solvent.

[0081] Compared with Comparative Example 1, Comparative Example 2 increases the temperature and time of high-temperature dewaxing, and the dewaxing effect is improved, but it has an adverse effect on the mechanical properties of the glass fiber cloth. After being dip-coated with the polytetrafluoroethylene emulsion copolymer prepared by the present invention, the tensile breaking strength in the warp and weft directions is significantly reduced.

[0082] In Comparative Example 3, on the basis of thorough dewaxing of the glass fiber cloth, ordinary commercially available polytetrafluoroethylene emulsion is used, which has a high solid content and a large viscosity, does not contain a silane coupling agent structure in the molecular chain segment, and has poor adhesion to the glass fiber cloth. As a result, the polytetrafluoroethylene glass fiber cloth composite material after a single dip coating has relatively poor adhesion strength and a relatively poor surface performance under continuous high-temperature blowing (250°C / 48h) and high-temperature solvent immersion (230°C / 24h), and has obvious deficiencies in adhesion.

[0083] Compared with Comparative Example 3, Comparative Example 4 additionally added 1% of silane coupling agent tridecafluorooctyltrimethoxysilane and 1% of vinyltrimethoxysilane. Although it is beneficial to more uniform dip coating in the early stage, these small molecule coupling agents will quickly escape during the high-temperature sintering (375°C / 5min) process, resulting in slightly worse appearance than the products of Examples 1-4 and Comparative Example 3. The final adhesion strength, high temperature resistance and high temperature solvent resistance are not significantly improved compared with Comparative Example 3, and are far lower than the products of Examples 1-4 of the present invention.

[0084] Comparative Example 5 uses the method of diluting the commercially available ordinary emulsion product of Comparative Example 3 with deionized water, adding a coupling agent, and then respectively adopting three dip coating and high temperature molding processes to complete it. Although the number of steps is increased and the process cost is increased, since less coupling agent is volatilized each time at high temperature sintering, the appearance and adhesion are improved compared with Comparative Example 3. However, its adhesion strength, high temperature resistance and high temperature solvent resistance are still significantly lower than the product of the present invention.

[0085] Comparative Example 6 adopts the current mainstream polytetrafluoroethylene glass fiber cloth preparation process in the market. Compared with Comparative Example 5, it adopts a dewaxing process (330°C / 15min), with a relatively low temperature, but a slightly longer time, and the dewaxing is still not thorough. Finally, the performance of the polytetrafluoroethylene glass fiber cloth composite material after three dip-coating and sintering is lower than that of Comparative Example 5, and is significantly lower than the product of the present invention.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A polytetrafluoroethylene emulsion copolymer, characterized in that: The polytetrafluoroethylene emulsion copolymer is prepared from the following raw materials in molar parts: Tetrafluoroethylene 100-108 parts Deionized water 1450-1680 parts Vinyltrimethoxysilane 0.8-1.1 parts Tridecafluorooctyltrimethoxysilane 0.6-0.9 parts 2,3,5,6-tetrafluoro-p-phenylenediamine 0.8-1 part 2-vinyl hexafluoroisopropanol 2-2.5 parts 6-8 parts of organic solvent As well as catalysts, dispersants, initiators, stabilizing agents and surfactants.

2. The polytetrafluoroethylene emulsion copolymer according to claim 1, characterized in that: The organic solvent is acetonitrile, methyl ethyl ketone or a combination of the two; and / or The catalyst is selected from tetramethylammonium hydroxide, potassium hydroxide or a combination thereof; the amount of the catalyst is 0.03-0.05% of the mass of 2,3,5,6-tetrafluoro-p-phenylenediamine; and / or The dispersant is selected from one of ammonium perfluorooctanoate and ammonium perfluorodimethyldioxanonanoate or a combination of the two; the amount of the dispersant is 0.05-0.08% of the mass of deionized water; and / or The initiator is selected from one or a combination of two or more of persulfate, organic peroxide, persulfate-ferrous ion, organic peroxide-ferrous ion; the amount of the initiator is 2-4ppm of the mass of deionized water; and / or The stabilizing agent is liquid paraffin; the amount of the stabilizing agent is 0.5-0.8% of the mass of deionized water; and / or The surfactant is a complex of sodium salt of dioctyl sulfonate succinate and isomeric tridecanol polyoxyethylene ether, and the mass ratio of the two is 0.5:1-1.3; the dosage of the surfactant is 0.6-1.0% of the mass of deionized water.

3. The method for preparing the polytetrafluoroethylene emulsion copolymer according to claim 1 or 2, characterized in that: The preparation method comprises the following steps: S1: In an organic solvent, 2,3,5,6-tetrafluoro-p-phenylenediamine, tridecafluorooctyltrimethoxysilane and vinyltrimethoxysilane are sequentially grafted at 75-78° C. under the catalysis of a catalyst, and the solvent is removed after the reaction to obtain a macromolecular fluorinated silane coupling agent intermediate; S2: In a reaction kettle with an oxygen content not exceeding 40 ppm, tetrafluoroethylene monomer is introduced into water containing 2-vinyl hexafluoroisopropanol and a stabilizing agent, and an initiator and a dispersant are added to carry out a polymerization reaction at 80-85°C, and the reaction pressure is maintained at 2.0-2.3 MPa; S3: When the amount of tetrafluoroethylene monomer introduced reaches one-half to two-thirds of the formula amount, add the macromolecular fluorine-containing silane coupling agent intermediate obtained in step S1, and heat to 88-92° C. for copolymerization reaction. After the introduction of the formula amount of tetrafluoroethylene is completed, continue to keep the temperature for reaction; S4: When the particle size distribution D50 of the copolymer in the kettle is 0.29-0.35 μm, the polymerization reaction is stopped, and the formulated amount of surfactant is added, mixed evenly, and then concentrated under reduced pressure to obtain a polytetrafluoroethylene emulsion copolymer with a solid content of 67-71%.

4. The preparation method according to claim 3, characterized in that: Step S1 includes the following steps: S1-1: dissolving a formulated amount of 2,3,5,6-tetrafluoro-p-phenylenediamine in an organic solvent, adding a catalyst, adding a formulated amount of tridecafluorooctyltrimethoxysilane, and performing a grafting reaction at 75-78° C., while removing methanol as a byproduct of the reaction; S1-2: When the content of free 2,3,5,6-tetrafluoro-p-phenylenediamine in the reaction system is less than 5% of the original amount added, a formulated amount of vinyltrimethoxysilane is added and the temperature is kept high to carry out a secondary grafting reaction; S1-3: When the content of free vinyltrimethoxysilane in the reaction system is less than 2% of the original added amount, the organic solvent is removed under reduced pressure to obtain a macromolecular fluorinated silane coupling agent intermediate.

5. The preparation method according to claim 3, characterized in that: In step S2, the dispersant is added for a time period of 1.5-2 hours; and / or In step S4, the vacuum degree of the reduced pressure concentration is controlled between -0.097 MPa and -0.099 MPa.

6. A method for preparing polytetrafluoroethylene glass fiber cloth, characterized in that: The preparation method comprises the following steps: S5: soaking the alkali-free glass fiber cloth in a dewaxing solvent for chemical immersion dewaxing treatment, and then performing a high-temperature dewaxing treatment at 350-360°C; S6: impregnating the alkali-free glass fiber cloth dewaxed in step S5 into the polytetrafluoroethylene emulsion copolymer according to claim 1 or 2 or the polytetrafluoroethylene emulsion copolymer prepared by the preparation method according to any one of claims 3 to 5, and drying, molding and sintering after a single impregnation to obtain the polytetrafluoroethylene glass fiber cloth.

7. The preparation method according to claim 6, characterized in that: In step S5: The dewaxing solvent is selected from ethylene glycol monobutyl ether, dimethylformamide or a combination of the two; and / or The alkali-free glass fiber cloth is immersed in the dewaxing solvent at a temperature of 130-135° C. for 1-1.5 min; and / or The high temperature dewaxing treatment time is 2-3min; and / or After the dewaxing treatment in step S5, the wax content of the alkali-free glass fiber cloth is less than 0.1 wt %.

8. The preparation method according to claim 6, characterized in that: In step S6: The immersion time is 1-1.5 min; and / or The drying temperature is 125-130°C and the drying time is 10-15min; and / or The molding temperature is 265-270°C and the molding time is 8-10 minutes; and / or The sintering temperature is 370-375° C., and the sintering time is 4-6 minutes.

9. The polytetrafluoroethylene glass fiber cloth prepared by the preparation method according to any one of claims 6 to 8.

10. Use of the polytetrafluoroethylene glass fiber cloth according to claim 9 in preparing gas stove pads, kitchen stove oil and fireproof pads.

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