Polytetrafluoroethylene emulsion copolymer, polytetrafluoroethylene glass fiber cloth, and their preparation methods and applications

Abstract

The present invention belongs to the field of polymer materials and relates to a polytetrafluoroethylene emulsion copolymer, a polytetrafluoroethylene glass fiber cloth, and their preparation methods and applications. The polytetrafluoroethylene glass fiber cloth of the present invention is obtained by single dipping and high-temperature molding of a polytetrafluoroethylene emulsion copolymer prepared by a specific synthesis and a thoroughly dewaxed glass fiber cloth. The polytetrafluoroethylene emulsion copolymer is obtained by polymerization of tetrafluoroethylene monomer, vinyltrimethoxysilane, tridecafluorooctyltrimethoxysilane, 2,3,5,6-tetrafluoro-p-phenylenediamine, and 2-vinylhexafluoroisopropanol as main raw materials. It has the advantages of high solid content, low viscosity, low amount of surfactant used, and good bonding with specially treated glass fiber cloth. It can achieve the same loading amount of conventional ordinary polytetrafluoroethylene emulsion 2-3 times of dipping in a single coating, and then obtain a high-density coating film through high-temperature sintering molding, which can be used as a polytetrafluoroethylene glass fiber cloth for gas stove pads.

Description

Technical Field

[0001] The present invention belongs to the field of polymer materials, and in particular 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] Currently, polytetrafluoroethylene fiberglass cloth (also known as Teflon fiberglass cloth) is made by repeatedly dipping and molding glass fiber cloth with commercially available polytetrafluoroethylene emulsion. This product offers excellent corrosion resistance and is widely used in high-temperature, oil-repellent applications such as conveyor belts, high-temperature test paper raw materials, and release fabrics, as shown in CN201610634357.4 and CN201610981818.5. In civilian applications, polytetrafluoroethylene fiberglass cloth exhibits excellent oleophobic properties and is used as a composite material for kitchen gas stove mats, offering oil- and water-repellent properties and easy cleaning.

[0003] However, the current use of polytetrafluoroethylene glass fiber cloth as a gas stove pad also has the following deficiencies in production and application: (1) Currently, 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. As a result, the production process generally requires three or more dip coating, sintering and other processes to achieve the required film thickness, which is 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) During the production process, in order to increase the adhesion between the polytetrafluoroethylene emulsion and the glass fiber cloth, the industry generally adopts a high-temperature dewaxing process (280-320℃). The problem is that the dewaxing temperature is too low, resulting in incomplete dewaxing. 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, with the tensile strength decreasing 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 to the coating caused by gas escape. 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 its 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. In addition, the prepared products are 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] To address the above-mentioned problems, the present invention provides a polytetrafluoroethylene emulsion copolymer, a high-adhesion polytetrafluoroethylene glass fiber cloth prepared therefrom, and methods for their preparation and use. The polytetrafluoroethylene emulsion copolymer of the present invention is obtained by polymerizing tetrafluoroethylene monomer, vinyltrimethoxysilane, tridecafluorooctyltrimethoxysilane, 2,3,5,6-tetrafluoro-p-phenylenediamine, and 2-vinylhexafluoroisopropanol as primary raw materials. The polytetrafluoroethylene glass fiber cloth is obtained by combining this specifically synthesized polytetrafluoroethylene emulsion copolymer with thoroughly dewaxed glass fiber cloth through a single dip coating and high-temperature molding process.

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

[0007] In a first aspect, the present invention provides a polytetrafluoroethylene emulsion copolymer, which is prepared from the following raw materials in molar parts:

[0008] 100-108 parts of tetrafluoroethylene

[0009] 1450-1680 parts of deionized water

[0010] 0.8-1.1 parts vinyltrimethoxysilane

[0011] 0.6-0.9 parts of tridecafluorooctyltrimethoxysilane

[0012] 0.8-1 part of 2,3,5,6-tetrafluoro-p-phenylenediamine

[0013] 2-2.5 parts of 2-vinyl hexafluoroisopropanol

[0014] 6-8 parts organic solvent

[0015] As well as, catalysts, dispersants, initiators, stabilizing agents and surfactants.

[0016] In some embodiments, the organic solvent is acetonitrile, methyl ethyl ketone, or a combination of the two, preferably acetonitrile.

[0017] The invention uses vinyltrimethoxysilane and tridecafluorooctyltrimethoxysilane to carry out grafting reaction on 2,3,5,6-tetrafluoro-p-phenylenediamine to obtain a macromolecular fluorine-containing silane coupling agent intermediate with alkenyl, amino and multiple methoxy groups.

[0018] 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.

[0019] In some embodiments, the catalyst is selected from tetramethylammonium hydroxide, potassium hydroxide, or a combination thereof, preferably tetramethylammonium hydroxide.

[0020] The amount of the catalyst used is 0.03-0.05% of the mass of 2,3,5,6-tetrafluoro-p-phenylenediamine.

[0021] In some embodiments, the dispersant is selected from one of perfluorooctanoic acid ammonium, perfluorodimethyldioxanonanoic acid ammonium, or a combination of the two, preferably a composite of perfluorooctanoic acid ammonium and perfluorodimethyldioxanonanoic acid ammonium, with a mass ratio of 1:1.5-2.

[0022] The amount of the dispersant used is 0.05-0.08% of the mass of deionized water.

[0023] 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.

[0024] In some embodiments, the initiator is selected from one or a combination of two or more of persulfates (e.g., ammonium persulfate, potassium persulfate, etc.), organic peroxides, persulfate-ferrous ions, and organic peroxide-ferrous ions, wherein the organic peroxides include benzoyl peroxide, succinic acid peroxide, etc. The initiator is preferably ammonium persulfate.

[0025] The amount of the initiator used is 2-4 ppm based on the mass of deionized water.

[0026] 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.

[0027] In some embodiments, the stabilizing aid is liquid paraffin.

[0028] The amount of the stabilizing agent used is 0.5-0.8% of the mass of deionized water.

[0029] In some embodiments, the surfactant is a complex of sodium dioctyl sulfosuccinate and isomeric tridecanol polyoxyethylene ether, with a mass ratio of 0.5:1-1.3. The present invention uses a composite surfactant, which is highly efficient in stabilizing the emulsion of the present invention, has the characteristics of low dosage and good emulsion stabilization effect.

[0030] The amount of the surfactant used is 0.6-1.0% of the mass of deionized water.

[0031] 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:

[0032] S1: In an organic solvent, under the catalysis of a catalyst, 2,3,5,6-tetrafluoro-p-phenylenediamine is grafted with tridecafluorooctyltrimethoxysilane and vinyltrimethoxysilane in sequence at 75-78°C. After the reaction, the solvent is removed to obtain a macromolecular fluorinated silane coupling agent intermediate;

[0033] S2: In a reactor with an oxygen content not exceeding 40 ppm, tetrafluoroethylene monomer is introduced into water containing 2-vinylhexafluoroisopropanol and a stabilizing agent, and an initiator and a dispersant are added. The polymerization reaction is carried out at 80-85°C and the reaction pressure is maintained at 2.0-2.3 MPa;

[0034] S3: When the amount of tetrafluoroethylene monomer introduced reaches one-half to two-thirds of the formula amount, the macromolecular fluorinated silane coupling agent intermediate obtained in step S1 is added, and the temperature is raised to 88-92°C for copolymerization reaction. After the introduction of the formula amount of tetrafluoroethylene is completed, the reaction is continued at this temperature;

[0035] 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 a 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%.

[0036] In some embodiments, step S1 includes the following steps:

[0037] S1-1: Dissolve the formulated amount of 2,3,5,6-tetrafluoro-p-phenylenediamine in an organic solvent, add a catalyst, add the formulated amount of tridecafluorooctyltrimethoxysilane, and carry out a grafting reaction at 75-78°C while removing the byproduct methanol;

[0038] S1-2: When the free 2,3,5,6-tetrafluoro-p-phenylenediamine content in the reaction system is less than 5% of the original amount added, vinyltrimethoxysilane is added in the formula amount and the temperature is maintained to perform a secondary grafting reaction;

[0039] 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 fluorine-containing silane coupling agent intermediate.

[0040] 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.

[0041] In some embodiments, in step S4, the vacuum degree of the reduced pressure concentration is controlled between -0.097 MPa and -0.099 MPa.

[0042] 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.

[0043] In a third aspect, the present invention provides a method for preparing polytetrafluoroethylene glass fiber cloth, comprising the following steps:

[0044] 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;

[0045] S6: Immerse the alkali-free glass fiber cloth dewaxed in the first aspect or the polytetrafluoroethylene emulsion copolymer prepared by the preparation method of the second aspect. After a single immersion, dry, shape, and sinter to obtain the polytetrafluoroethylene glass fiber cloth.

[0046] In some embodiments, in step S5, the dewaxing solvent is selected from one of ethylene glycol monobutyl ether, dimethylformamide (DMF), or a combination of the two, preferably a mixture of ethylene glycol monobutyl ether and DMF, with a mass ratio of the two being 2.5-3:1.

[0047] In some embodiments, in step S5, the alkali-free glass fiber cloth is immersed in the dewaxing solvent at a temperature of 130-135° C. for 1-1.5 minutes.

[0048] In some embodiments, in step S5, the high-temperature dewaxing treatment lasts for 2-3 minutes.

[0049] After the dewaxing treatment in step S5, the wax content of the alkali-free glass fiber cloth is less than 0.1 wt %.

[0050] In some embodiments, in step S6, the immersion time is 1-1.5 minutes.

[0051] In some embodiments, in step S6, the drying temperature is 125-130° C., and the drying time is 10-15 minutes.

[0052] In some embodiments, in step S6, the molding temperature is 265-270° C., and the molding time is 8-10 minutes.

[0053] In some embodiments, in step S6, the sintering temperature is 370-375° C., and the sintering time is 4-6 minutes.

[0054] In a fourth aspect, the present invention provides polytetrafluoroethylene glass fiber cloth prepared by the preparation method described in the third aspect.

[0055] 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-proof and fire-proof pads.

[0056] The beneficial effects achieved by the technical solution of the present invention are:

[0057] (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 commercial polytetrafluoroethylene emulsions, the polytetrafluoroethylene emulsion copolymer product of the present invention has the advantages of high solid content, low viscosity, low 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 after high-temperature sintering and molding, a coating with high density is obtained, which can be used as polytetrafluoroethylene glass fiber cloth for gas stove pads.

[0058] (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 environments for a long time, and the prepared product has almost no obvious color difference. The present invention uses a 300g / m 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 molded by three coatings, and has the characteristics of simple molding process, short process, low cost and better comprehensive performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 This is a transmission electron microscope image of the polytetrafluoroethylene emulsion copolymer prepared in Example 1.

[0060] Figure 2 This is a test chart of the particle size D50 of the polytetrafluoroethylene emulsion copolymer prepared in Example 1. DETAILED DESCRIPTION

[0061] 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. The embodiments only provide some experimental conditions for achieving the purpose of this technical invention.

[0062] 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.

[0063] Reagents and sources:

[0064] Silane coupling agent vinyltrimethoxysilane was purchased from Jiangxi Chenguang New Materials Co., Ltd., model: CG-171.

[0065] Silane coupling agent tridecafluorooctyltrimethoxysilane was purchased from Hangzhou Jessica Chemical Co., Ltd., model: KH-1331.

[0066] 2-Vinylhexafluoroisopropanol was purchased from Tokyo Chemical Industry (Shanghai) Co., Ltd.

[0067] The stabilizing agent liquid paraffin was purchased from Nanjing Tianshi New Material Technology Co., Ltd., model: TP-33.

[0068] The surfactant dioctyl sulfosuccinate sodium salt was purchased from Hai'an Petrochemical Plant in Jiangsu Province.

[0069] The surfactant isomeric tridecanol polyoxyethylene ether was purchased from Hai'an Petrochemical Plant in Jiangsu Province, model: E-1308.

[0070] Alkali-free glass fiber cloth, purchased from Jiangsu Changhai Composite Materials Co., Ltd., product model EWR300, weight 300g / m 2 .

[0071] The present invention will be further described below with reference to the embodiments, but the present invention is not limited thereto.

[0072] Example 1

[0073] This embodiment provides a high-adhesion polytetrafluoroethylene glass fiber cloth, which is prepared by the following steps:

[0074] (1) Preparation of polytetrafluoroethylene emulsion copolymer

[0075] 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, the amount of which is 0.04% of the mass of 2,3,5,6-tetrafluoro-p-phenylenediamine; the dispersant is The complex of ammonium perfluorooctanoate and ammonium perfluorodimethyldioxanonanoate, 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 sulfosuccinate 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.

[0076] Preparation steps are as follows (1-1) to (1-4):

[0077] (1-1) Preparation of graft-modified olefin-containing coupling agent products

[0078] (i) adding a formulated amount of an organic solvent and 2,3,5,6-tetrafluoro-p-phenylenediamine to a 500 mL reactor, starting stirring, heating to 77° C. to allow for full dissolution, and maintaining the temperature; adding a formulated amount of a catalyst, mixing uniformly, and then adding a formulated amount of tridecafluorooctyltrimethoxysilane to carry out a reaction at this temperature, while simultaneously removing methanol, a byproduct of the reaction;

[0079] (ii) sampling and testing 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, the grafting reaction is basically completed. At this time, the formulated amount of vinyltrimethoxysilane is added and the temperature is maintained to continue the secondary grafting reaction;

[0080] (iii) sampling and testing by gas chromatography. When the free vinyltrimethoxysilane content is less than 2% of the original amount added, indicating 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 future use;

[0081] (1-2) Add the formulated amount of deionized water, stabilizing agent, and 2-vinylhexafluoroisopropanol to a 20 L autoclave. After sealing the autoclave, start stirring, evacuate, and replace the oxygen in the autoclave with high-purity nitrogen. When the oxygen content is lower than 35 ppm, raise the temperature to 83°C, continuously introduce tetrafluoroethylene monomer, maintain the pressure in the autoclave at 2.2 MPa, and then use feeding pump 1 to add the formulated amount of initiator at once (before use, the initiator is dissolved in 26°C deionized water to form a 4 wt% 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 dispersant solution (before use, the dispersant is dissolved in 26°C deionized water to form a 7.5 wt% aqueous solution) using feeding pump 2, and control the feeding time to 1.8 h;

[0082] (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. to carry out a copolymerization reaction; after the introduction of the formula amount of tetrafluoroethylene is completed, the reaction is continued at the same temperature;

[0083] (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, start vacuum and concentrate (vacuum degree controlled at -0.098 MPa), when the solid content reaches 67-71%, cool to room temperature, discharge, and obtain the polytetrafluoroethylene emulsion copolymer product. The transmission electron microscope image and particle size D of the polytetrafluoroethylene emulsion copolymer are shown in FIG. 50 The test images are shown in Figure 1 and Figure 2 .

[0084] The polytetrafluoroethylene emulsion copolymer product has a solid content of 70.4%, a surfactant content that can volatilize at 380°C / 30 min of 1.7%, and a viscosity (25°C) of 16 mPa·s.

[0085] (2) Dewaxing treatment of alkali-free glass fiber cloth

[0086] The alkali-free glass fiber cloth is vertically hung on the conveying rod and conveyed to the first temperature zone (maintained 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, with a mass ratio of 2.8:1). The immersion time is 58 seconds. The cloth is then conveyed into a high-temperature drying tunnel at 353°C / 2.5 minutes for another thorough high-temperature dewaxing treatment. The wax content of the glass fiber cloth after final treatment is 0.08%.

[0087] (3) Preparation of polytetrafluoroethylene glass fiber cloth

[0088] 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 then immersed in the emulsion tank once for 1.4 minutes. The cloth is 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 gas stove pads.

[0089] Example 2

[0090] This 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 mole 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, used in amounts of 2,3,5,6-tetrafluoro-p-phenylenediamine, 2.5 parts of 2-vinylhexafluoroisopropanol, and 8 parts of methyl ethyl ketone. The dosage of the dispersant 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 sulfosuccinate 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.

[0091] The obtained polytetrafluoroethylene emulsion copolymer product had a solid content of 68.8%, a surfactant content volatile at 380°C / 30 min of 1.9%, and a viscosity (25°C) of 14 mPa·s.

[0092] Example 3

[0093] This 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 mole as follows: 105 parts of tetrafluoroethylene, 1610 parts of deionized water, 1 part of vinyltrimethoxysilane, 0.8 parts of tridecafluorooctyltrimethoxysilane, 0.9 parts of 2,3,5,6-tetrafluoro-p-phenylenediamine, 2.3 parts of 2-vinylhexafluoroisopropanol, 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 fluoro-p-phenylenediamine; 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 sulfosuccinate 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.

[0094] The obtained polytetrafluoroethylene emulsion copolymer product had a solid content of 67.3%, a surfactant content volatile at 380°C / 30 min of 2.0%, and a viscosity (25°C) of 13 mPa·s.

[0095] Example 4

[0096] This 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 mole 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, used in an amount of 2,3,5,6-tetrafluoro-p-phenylenediamine. The dosage of the dispersant is 0.07% of the mass of deionized water; the initiator is ammonium persulfate, and the dosage is 3ppm of the mass of deionized water; the stabilizing agent is liquid paraffin, and the dosage is 0.7% of the mass of deionized water; the surfactant is a complex of sodium salt of dioctyl sulfosuccinate and isomeric tridecyl alcohol polyoxyethylene ether, and the mass ratio of the two is 0.5:1, and the dosage is 0.8% of the mass of deionized water.

[0097] The obtained polytetrafluoroethylene emulsion copolymer product had a solid content of 69.2%, a surfactant content volatile at 380°C / 30 min of 2.3%, and a viscosity (25°C) of 15 mPa·s.

[0098] Comparative Example 1

[0099] 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 hung on a conveying rod and conveyed into a high-temperature drying tunnel for high-temperature dewaxing treatment at 355°C / 3min. After the treatment, the wax content of the glass fiber cloth base cloth is 1.1%.

[0100] Comparative Example 2

[0101] 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 hung on a conveying rod and conveyed into a high-temperature drying tunnel for high-temperature dewaxing treatment at 425°C / 10min. After the treatment, the wax content of the glass fiber cloth base cloth is 0.63%.

[0102] Comparative Example 3

[0103] This comparative example provides a polytetrafluoroethylene glass fiber cloth, which replaces the polytetrafluoroethylene emulsion copolymer prepared in step (1) with a common commercially available polytetrafluoroethylene emulsion product, and treats the alkali-free glass fiber cloth dewaxed in step (2) in the manner of step (3).

[0104] 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%; surfactant content volatile at 380°C / 30 min: 6.7%; viscosity (25°C): 37 mPa·s.

[0105] Comparative Example 4

[0106] 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 by weight of a silane coupling agent tridecafluorooctyltrimethoxysilane and 1% of vinyltrimethoxysilane are added to the ordinary commercially available polytetrafluoroethylene emulsion in comparative example 3 and stirred evenly.

[0107] Comparative Example 5

[0108] This 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 ordinary 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 performed respectively to complete the coating film preparation. The process parameters of each step are the same as those in Example 1.

[0109] Comparative Example 6

[0110] 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 in comparative example 5 is changed to 330°C / 15min. After dewaxing treatment, the wax content of the glass fiber cloth is 0.89%.

[0111] Test method:

[0112] 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".

[0113] The viscosity (25° C.) was measured using a rotational viscometer.

[0114] The tensile breaking strength and adhesion strength are respectively carried out 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.

[0115] The high temperature resistance was tested in a forced air oven at 260°C for 48h.

[0116] High temperature solvent resistance: 350SN base oil is heated to 230℃, and the sample is cut into The square specifications were placed in 230℃ base oil and soaked at high temperature for 24 hours. After taking out, the base oil was washed off with anhydrous ethanol, and the sample was dried and the surface condition of the sample was observed.

[0117] High temperature resistance and high temperature solvent resistance can not only determine the quality of the sample's high temperature resistance and solvent resistance, but also indirectly determine the adhesion strength from the bubbling and shedding of the coating.

[0118] The flame retardant properties are tested according to the vertical burning test method in GB / T 2408-2021 "Plastics - Determination of combustion performance - Horizontal and vertical methods".

[0119] 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.

[0120] Table 1. Performance test results of PTFE glass fiber cloth

[0121]

[0122] As shown in Table 1, the present invention utilizes a polytetrafluoroethylene emulsion copolymer product prepared using a specific copolymer formulation and process, which is then dip-coated onto thoroughly dewaxed glass fiber cloth, followed by drying, molding, and sintering to produce a high-performance, high-adhesion polytetrafluoroethylene glass fiber cloth composite material. This product exhibits a smooth appearance, excellent mechanical and flame retardancy, both achieving a V-0 flame retardancy rating, and excellent high-temperature resistance: even after 260°C / 48 hours of continuous high-temperature air blast, the surface exhibits no discoloration or blistering. Its adhesion strength is generally above 1130 N / m, and its resistance to high-temperature solvents is excellent: after 24 hours in 350SN base oil at 230°C, the surface exhibits no discoloration, swelling, or blistering. Its excellent oil resistance makes it suitable for use as a composite material for gas stove mats or kitchen stove cleaning mats, demonstrating excellent oil resistance, high-temperature resistance, and high adhesion.

[0123] Comparative Example 1 only uses a short-term high-temperature dewaxing process (355°C / 3 min) without using a chemical dewaxing step. As a result, 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, its adhesion to the glass fiber cloth is still affected. As a result, the finally prepared polytetrafluoroethylene glass fiber cloth composite material exhibits very slight bubbling under continuous high-temperature blowing conditions (250°C / 48h), and the adhesion strength is also reduced to 952 N / m. Slight bubbling also occurs under long-term high-temperature solvent conditions.

[0124] 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 dipping with the polytetrafluoroethylene emulsion copolymer prepared by the present invention, the tensile breaking strength in the warp and weft directions is significantly reduced.

[0125] In Comparative Example 3, based on the thorough dewaxing of the glass fiber cloth, a commercially available ordinary polytetrafluoroethylene emulsion was used. This emulsion has a high solid content and a large viscosity, and does not contain a silane coupling agent structure in the molecular chain segment, resulting in 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, continuous high-temperature air blowing (250°C / 48h) and high-temperature solvent immersion (230°C / 24h), and has obvious deficiencies in adhesion.

[0126] Compared with Comparative Example 3, Comparative Example 4 additionally added 1% of the silane coupling agent tridecafluorooctyltrimethoxysilane and 1% of vinyltrimethoxysilane. Although this was beneficial for more uniform dip coating in the early stage, these small molecule coupling agents quickly escaped during the high-temperature sintering process (375°C / 5 min), resulting in an appearance slightly worse than that of the products in Examples 1-4 and Comparative Example 3. The final adhesion strength, high-temperature resistance, and high-temperature solvent resistance were not significantly improved compared to Comparative Example 3, and were far lower than those of the products in Examples 1-4 of the present invention.

[0127] Comparative Example 5 uses the commercially available ordinary emulsion product of Comparative Example 3 to be diluted with deionized water, and a coupling agent is added, and then three dip coating and high-temperature molding processes are respectively used to complete the process. Although the number of steps is increased and the process cost is increased, the appearance and adhesion are improved compared with Comparative Example 3 because less coupling agent is volatilized during each high-temperature sintering. However, its adhesion strength, high-temperature resistance and high-temperature solvent resistance are still significantly lower than the product of the present invention.

[0128] 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). The temperature is relatively low, but the time is slightly longer, 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 that of the product of the present invention.

[0129] 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 above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some or all of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to 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: 100-108 parts of tetrafluoroethylene 1450-1680 parts of deionized water 0.8-1.1 parts vinyltrimethoxysilane 0.6-0.9 parts of tridecafluorooctyltrimethoxysilane 0.8-1 part of 2,3,5,6-tetrafluoro-p-phenylenediamine 2-2.5 parts of 2-vinyl hexafluoroisopropanol 6-8 parts organic solvent and, catalysts, dispersants, initiators, stabilizing aids, and surfactants; The preparation method of the polytetrafluoroethylene emulsion copolymer comprises the following steps: S1: In an organic solvent, under the catalysis of a catalyst, 2,3,5,6-tetrafluoro-p-phenylenediamine is grafted with tridecafluorooctyltrimethoxysilane and vinyltrimethoxysilane in sequence at 75-78°C. After the reaction, the solvent is removed to obtain a macromolecular fluorinated silane coupling agent intermediate; S2: In a reactor with an oxygen content not exceeding 40 ppm, tetrafluoroethylene monomer is introduced into water containing 2-vinylhexafluoroisopropanol and a stabilizing agent, and an initiator and a dispersant are added. The polymerization reaction is carried out 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, the macromolecular fluorinated silane coupling agent intermediate obtained in step S1 is added, and the temperature is raised to 88-92°C for copolymerization reaction. After the introduction of the formula amount of tetrafluoroethylene is completed, the reaction is continued at this temperature; 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 a 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%.

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 one of tetramethylammonium hydroxide and 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 perfluorooctanoic acid ammonium and perfluorodimethyldioxanonanoic acid ammonium or a combination thereof; 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 2-4 ppm based on 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 sulfosuccinate and isomeric tridecanol polyoxyethylene ether, with a mass ratio of 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, under the catalysis of a catalyst, 2,3,5,6-tetrafluoro-p-phenylenediamine is grafted with tridecafluorooctyltrimethoxysilane and vinyltrimethoxysilane in sequence at 75-78°C. After the reaction, the solvent is removed to obtain a macromolecular fluorinated silane coupling agent intermediate; S2: In a reactor with an oxygen content not exceeding 40 ppm, tetrafluoroethylene monomer is introduced into water containing 2-vinylhexafluoroisopropanol and a stabilizing agent, and an initiator and a dispersant are added. The polymerization reaction is carried out 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, the macromolecular fluorinated silane coupling agent intermediate obtained in step S1 is added, and the temperature is raised to 88-92°C for copolymerization reaction. After the introduction of the formula amount of tetrafluoroethylene is completed, the reaction is continued at this temperature; 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 a 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: Dissolve the formulated amount of 2,3,5,6-tetrafluoro-p-phenylenediamine in an organic solvent, add a catalyst, add the formulated amount of tridecafluorooctyltrimethoxysilane, and carry out a grafting reaction at 75-78°C while removing the byproduct methanol; S1-2: When the free 2,3,5,6-tetrafluoro-p-phenylenediamine content in the reaction system is less than 5% of the original amount added, vinyltrimethoxysilane is added in the formula amount and the temperature is maintained to perform 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 fluorine-containing silane coupling agent intermediate.

5. The preparation method according to claim 3, characterized in that In step S2, the dispersant is added for 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, drying, forming, 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 one of ethylene glycol monobutyl ether and dimethylformamide or a combination of the two; and / or Soak the alkali-free glass fiber cloth in a dewaxing solvent at a temperature of 130-135° C. for 1-1.5 minutes; and / or The high temperature dewaxing treatment time is 2-3 minutes; 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 dipping time is 1-1.5 min; and / or The drying temperature is 125-130° C. and the drying time is 10-15 minutes; and / or The molding temperature is 265-270° C. and the molding time is 8-10 min; and / or The sintering temperature is 370-375° C., and the sintering time is 4-6 minutes.

9. 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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