CN111004462B - PTFE composite belt for aerospace cable and preparation method thereof - Google Patents

PTFE composite belt for aerospace cable and preparation method thereof Download PDF

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CN111004462B
CN111004462B CN201911328756.8A CN201911328756A CN111004462B CN 111004462 B CN111004462 B CN 111004462B CN 201911328756 A CN201911328756 A CN 201911328756A CN 111004462 B CN111004462 B CN 111004462B
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ptfe
titanium dioxide
mass
coupling agent
dispersion liquid
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CN111004462A (en
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李秋影
刘鹏英
蔡春华
车延超
陈辉
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Jiangsu Tongguang Electronic Wire & Cable Corp ltd
Shanxi Funuoou New Material Technology Co ltd
East China University of Science and Technology
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Jiangsu Tongguang Electronic Wire & Cable Corp ltd
Shanxi Funuoou New Material Technology Co ltd
East China University of Science and Technology
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K9/00—Use of pretreated ingredients
    • C08K9/04—Ingredients treated with organic substances
    • C08K9/06—Ingredients treated with organic substances with silicon-containing compounds
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
    • C08K3/20—Oxides; Hydroxides
    • C08K3/22—Oxides; Hydroxides of metals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
    • H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
    • H01B3/30—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes
    • H01B3/44—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins
    • H01B3/443—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes vinyl resins; acrylic resins from vinylhalogenides or other halogenoethylenic compounds
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
    • C08K3/20—Oxides; Hydroxides
    • C08K3/22—Oxides; Hydroxides of metals
    • C08K2003/2237—Oxides; Hydroxides of metals of titanium
    • C08K2003/2241—Titanium dioxide
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K2201/00—Specific properties of additives
    • C08K2201/002—Physical properties
    • C08K2201/003—Additives being defined by their diameter
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L2203/00—Applications
    • C08L2203/20—Applications use in electrical or conductive gadgets
    • C08L2203/202—Applications use in electrical or conductive gadgets use in electrical wires or wirecoating

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  • Health & Medical Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Medicinal Chemistry (AREA)
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  • Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
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Abstract

The invention provides a PTFE composite tape for aerospace cables and a preparation method thereof. In the PTFE composite belt, the mass of PTFE accounts for 97-99% of the total mass of the PTFE composite belt, the mass of titanium dioxide accounts for 1-3% of the mass of PTFE, and the mass of a coupling agent accounts for 0.5-2.5% of the mass of titanium dioxide. The method for preparing the PTFE composite belt comprises the steps of surface modification of titanium dioxide, preparation of PTFE powder and preparation of the PTFE composite belt. The PTFE composite tape has uniform thickness and higher ultraviolet absorptivity, has excellent thermal stability 2 before 500 ℃, has the tensile strength of 12.17MPa, the elongation of 122 percent and the insulating dielectric strength of more than 95kV/mm, and meets the performance requirement of SAE AS22795 of the American military standard on the high-temperature resistant PTFE composite tape for aerospace.

Description

PTFE composite belt for aerospace cable and preparation method thereof
Technical Field
The invention belongs to the field of cable materials, and particularly relates to a PTFE composite tape for aerospace cables and a preparation method thereof.
Background
Polytetrafluoroethylene (PTFE) composite tape is one of key materials of insulating layers and sheathing materials in aerospace high-temperature-resistant wires and cables, is a material with high technological content and high added value, and the core technology for manufacturing the product is still mastered by DuPont company in the United states until now. Therefore, the PTFE composite belt used in the high-end high-temperature-resistant cable is developed, the monopoly position of foreign companies in the material field is broken, the blank of localization of key materials in the high-end high-temperature-resistant cable field is filled, the situation of long-term dependence on import is changed, and the localization of the high-end high-temperature-resistant cable has very important strategic significance and economic benefit.
Titanium dioxide is required to be added into the PTFE composite belt, and the aim is to color and play a role in resisting ultraviolet aging. In addition, the PTFE composite belt has extremely high requirements on thickness uniformity, thermal stability, mechanical property and dielectric property, and the tensile strength is more than or equal to 10.34MPa, the elongation at break is more than or equal to 70 percent, the insulating dielectric strength is more than or equal to 27.56kV/mm, and the initial thermal decomposition temperature is more than or equal to 500 ℃.
However, because of high technical threshold and great research and development difficulty, the invention patent of the composite belt is not available in China. In connection with the above, patent CN201611141368.5 "a special wire and cable for aerospace and preparation method thereof" directly uses PTFE, ETFE and additives to prepare the insulating layer of the cable by a push extrusion method, and patent CN201710141681.7 "polytetrafluoroethylene/polyimide composite insulating smooth wire and cable and preparation method" and patent CN201520191847.2 "polytetrafluoroethylene film and polytetrafluoroethylene emulsion coating seamless lapped wire for aerospace" also use the PTFE composite tape as the insulating layer material of the cable for aerospace, but the patent does not relate to the preparation method of the composite tape, and does not describe the source of the tape.
At present, the PTFE composite tape for aerospace cables cannot be produced at home, and the PTFE tape mentioned in the existing research method cannot meet the special requirements of aerospace environment. For example, a PTFE film for a cable (Zhoujianggang. processing and application of Polytetrafluoroethylene (PTFE) diaphragm sheet [ J ] plastic development, 1993.) reported by Zhoujianggang plastics research institute Zhongjia in 1992 has a thickness of 35 + -3 μm, a tensile strength of 29.42MPa or more, an elongation at break of 30% or more, an insulating dielectric strength of 70kV/mm or more, a thickness and an elongation at break both of which do not meet the requirements, and ultraviolet oxidation resistance research has not been carried out. For another example, 2016 reports a "colored semi-oriented polytetrafluoroethylene film" (Junqiu, Zhoufei, Humei, et al, research on colored semi-oriented polytetrafluoroethylene film [ J ]. proceedings of Wuhan ship occupational technology academy 2016 (4)), which has satisfactory tensile strength, elongation at break, and dielectric strength, but has poor thermal stability, an initial thermal decomposition temperature of 386 ℃, and no mention of its uvioresistant properties.
The PTFE composite tape has a plurality of key factors influencing whether the PTFE composite tape can meet the use requirement of aviation cables, and mainly relates to the molecular weight of PTFE raw materials, the modification of titanium dioxide, the blending uniformity of the PTFE raw materials and the titanium dioxide, and the processing technology and the processing conditions of the composite tape. These critical PTFE composite tape fabrication techniques remain to be solved.
The PTFE composite tape for the wire and the cable for aerospace is required to have excellent performances in the aspects of electrical, mechanical, physical, chemical corrosion resistance, solvent resistance and the like, but the existing PTFE composite tape for the wire and the cable made in China is not manufactured independently, the used material is seriously dependent on import, and only the American DuPont exclusive company is sold as a commodity. Therefore, breaking the foreign technical blockade, the development of the insulating material with the proprietary intellectual property rights is of great importance.
Disclosure of Invention
In order to solve the problems, the invention provides a PTFE composite tape for an electric wire and a cable for aerospace and a preparation method thereof. The performance of the high-temperature resistant PTFE composite belt for the aerial antenna can meet the performance requirement of the high-temperature resistant PTFE composite belt for the aerospace required by the US military standard SAE AS 22795.
Specifically, the invention provides a PTFE composite belt or PTFE powder, which comprises PTFE, titanium dioxide and a coupling agent, wherein the mass of the PTFE accounts for 97-99% of the total mass of the PTFE composite belt or the PTFE powder, the mass of the titanium dioxide accounts for 1-3% of the mass of the PTFE, and the mass of the coupling agent accounts for 0.5-2.5% of the mass of the titanium dioxide.
In one or more embodiments, the PTFE composite tape or PTFE powder does not include a surfactant.
In one or more embodiments, the PTFE has a number average molecular weight of 423 ten thousand to 702 ten thousand.
In one or more embodiments, the titanium dioxide has a particle size of 50nm to 300 nm.
In one or more embodiments, the coupling agent is one or more of phenyltrimethoxysilane, gamma-aminopropyltriethoxysilane, and gamma-propyltrimethoxysilane.
In one or more embodiments, the PTFE composite tape or PTFE powder is prepared using a PTFE emulsion having one or more of the following characteristics:
(1) in the PTFE emulsion, the average grain diameter of PTFE is 0.2-0.3 μm;
(2) the solid content of the PTFE emulsion is 20-30%;
(3) in the PTFE emulsion, the number average molecular weight of PTFE is 423-702 ten thousand;
(4) the PTFE emulsion is prepared by adopting a dispersing free radical polymerization method; and
(5) the PTFE emulsion does not contain a surfactant.
The invention provides a method for preparing PTFE powder, which comprises the following steps:
(1) surface modification of titanium dioxide
Adjusting the pH value of a mixture of water and ethanol with the mass ratio of 1:7-1:9 to 9-12 by using alkali, adding a coupling agent with the mass of 80-120% of the mass of water, and uniformly mixing to obtain a coupling agent dispersion liquid; mixing titanium dioxide and ethanol according to the mass ratio of 1:5-1:6, and uniformly dispersing to obtain titanium dioxide dispersion liquid; adding the coupling agent dispersion liquid into the titanium dioxide dispersion liquid, wherein the mass of the coupling agent in the added coupling agent dispersion liquid is 0.5-2.5% of the mass of the titanium dioxide in the titanium dioxide dispersion liquid, and uniformly dispersing to obtain a modified titanium dioxide dispersion liquid; and
(2) preparation of PTFE powder
Diluting the PTFE emulsion with water to a density of 1.0-1.2g/cm3Adjusting the pH value of the diluted PTFE emulsion to 9-11 by using alkali to obtain PTFE diluent; mixing the modified titanium dioxide dispersion liquid prepared in the step (1) with the PTFE diluent according to the mass ratio of 1:400-3:400, so that the titanium dioxide and the PTFE emulsion are subjected to co-coagulation to form PTFE/titanium dioxide composite particles, taking out the PTFE/titanium dioxide composite particles, washing and drying to obtain PTFE powder.
In one or more embodiments, the PTFE emulsion has a number average molecular weight of 423 ten thousand to 702 ten thousand PTFE.
In one or more embodiments, the PTFE emulsion has an average particle size of PTFE ranging from 0.2 μm to 0.3. mu.m.
In one or more embodiments, the PTFE emulsion is prepared using a dispersion free radical polymerization process.
In one or more embodiments, the PTFE emulsion has a solids content of 20% to 30%.
In one or more embodiments, the PTFE emulsion does not include a surfactant.
In one or more embodiments, the titanium dioxide has a particle size of 50nm to 300 nm.
In one or more embodiments, the coupling agent is one or more of phenyltrimethoxysilane, gamma-aminopropyltriethoxysilane, and gamma-propyltrimethoxysilane.
In one or more embodiments, in step (1), aqueous ammonia is added to the mixture of water and ethanol at 40 ℃ to 60 ℃ to adjust the pH.
In one or more embodiments, in step (1), the titanium dioxide is dispersed into ethanol using a high speed disperser at 1000rpm to 2500 rpm.
In one or more embodiments, in step (2), the mixture of the PTFE emulsion and the modified titanium dioxide dispersion from step (1) is stirred in a propeller, paddle, or turbine mixer to co-agglomerate the titanium dioxide and PTFE emulsions.
In one or more embodiments, in step (2), the mixture of the PTFE emulsion and the modified titanium dioxide dispersion prepared in step (1) is stirred at 400rpm to 600rpm, so that the titanium dioxide and the PTFE emulsion are co-coagulated.
The invention also provides PTFE powder prepared by the method for preparing PTFE powder in any embodiment of the invention; preferably, the PTFE powder is the PTFE powder of any of the embodiments herein.
The present invention also provides a method of making a PTFE composite tape, comprising the steps of:
(a) sieving and mixing: sieving the PTFE powder by using a screen with the aperture of 1-3mm, adding an extrusion aid with the volume of 15-25% of the volume of the PTFE powder into the sieved PTFE powder, and uniformly mixing to obtain a mixed material;
(b) pushing: extruding the mixed material obtained in the step (a) into strips by using a pushing machine at the temperature of 50-150 ℃ to obtain a columnar prefabricated product;
(c) and (3) calendering and forming: calendering the columnar preform obtained in the step (b) into a sheet by using a double-roll calender at the temperature of 90-100 ℃, and then calendering the sheet by using the double-roll calender at room temperature to obtain a PTFE composite belt semi-finished product; and
(d) semi-sizing: heating the PTFE composite tape semi-finished product obtained in the step (c) for 12-20s at 320-330 ℃ to obtain the PTFE composite tape.
In one or more embodiments, in step (a), the PTFE powder is the PTFE powder of any of the embodiments herein.
In one or more embodiments, in step (a), the PTFE powder and extrusion aid are mixed at a temperature of less than 20 ℃.
In one or more embodiments, in step (b), the pressing speed is 10 to 20 cm/min.
In one or more embodiments, in step (c), the sheet has a thickness of 0.066 to 0.070mm, and the PTFE composite tape intermediate product has a thickness of 0.058 to 0.066 mm.
The present invention also provides a PTFE composite tape made using the method of making a PTFE composite tape according to any of the embodiments herein; preferably, the PTFE composite tape is the PTFE composite tape of any embodiment herein.
The invention also provides a wire or cable having an insulation or jacket prepared from the PTFE composite tape of any embodiment herein.
Drawings
Fig. 1 is a schematic view of a calendering process in the PTFE composite tape manufacturing method of the present invention.
FIG. 2 is a graph of the UV absorption curves of the inlet composite tape and the PTFE composite tapes of examples 1-3.
FIG. 3 is a graph of the thermal weight loss of the inlet composite tape and the PTFE composite tapes of examples 1-3.
Detailed Description
To make the features and effects of the present invention comprehensible to those skilled in the art, general description and definitions are made below with reference to terms and expressions mentioned in the specification and claims. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
The theory or mechanism described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, i.e., the present disclosure may be practiced without limitation to any particular theory or mechanism.
The numerical ranges described herein should be considered to have covered and specifically disclosed all possible subranges and any individual numerical value within the range.
Herein, when embodiments or examples are described, it is to be understood that they are not intended to limit the invention to these embodiments or examples. On the contrary, all alternatives, modifications, and equivalents of the methods and materials described herein are intended to be included within the scope of the invention as defined by the appended claims.
In this context, for the sake of brevity, not all possible combinations of features in the various embodiments or examples are described. Therefore, the respective features in the respective embodiments or examples may be arbitrarily combined as long as there is no contradiction between the combinations of the features, and all the possible combinations should be considered as the scope of the present specification.
In the present invention, a Polytetrafluoroethylene (PTFE) composite tape has a meaning well known in the art and generally refers to a polymer composite film having PTFE as a main polymer component.
The PTFE composite belt or the PTFE powder comprises PTFE, titanium dioxide (titanium dioxide powder) and a coupling agent, wherein the mass of the PTFE accounts for 97-99% of the total mass of the PTFE composite belt or the PTFE powder, the mass of the titanium dioxide accounts for 1-3% of the mass of the PTFE, and the mass of the coupling agent accounts for 0.5-2.5% of the mass of the titanium dioxide. The PTFE composite tape or PTFE powder of the present invention preferably does not contain a surfactant. In some embodiments, the PTFE composite tape or PTFE powder of the present invention comprises PTFE, titanium dioxide, and a coupling agent in the above-described proportions. The PTFE powder can be used for preparing PTFE composite belts.
Preferably, in the PTFE composite tape or PTFE powder of the present invention, the number average molecular weight of PTFE is 423 ten thousand to 702 ten thousand.
Preferably, in the PTFE composite belt or the PTFE powder, the particle size of the titanium dioxide is 50nm-300 nm.
Coupling agents suitable for use in the present invention are preferably one or more of phenyltrimethoxysilane, gamma-aminopropyltriethoxysilane and gamma-propyltrimethoxysilane.
The performance of the PTFE composite tape can meet the requirements of SAE AS22795 standard of America and army, namely, in certain embodiments, the thickness of the PTFE composite tape is 0.0635 +/-0.006 mm, the tensile strength is more than or equal to 8.96MPa, the longitudinal elongation is more than or equal to 70%, the insulating dielectric strength is more than or equal to 27.56kV/mm, and the PTFE composite tape meets the ROHS standard.
Preferably, the PTFE composite tape of the present invention has a thickness in the range of 0.058mm to 0.066 mm.
Preferably, the tensile strength of the PTFE composite tape of the present invention is 10.34MPa or more, more preferably 11.34MPa or more.
Preferably, the PTFE composite tape of the present invention has a longitudinal elongation of 75% or more, more preferably 80% or more.
Preferably, the insulating dielectric strength of the PTFE composite tape is more than or equal to 28kV/mm, and more preferably more than or equal to 28.4 kV/mm.
In certain embodiments, the PTFE composite tape of the present invention has an initial thermal decomposition temperature of 500 deg.C or greater.
The method for preparing PTFE powder comprises the following steps: (1) surface modification of titanium dioxide and (2) preparation of PTFE powder.
In the step (1), the surface modification of the titanium dioxide is carried out by using a coupling agent. Generally, the coupling agent and the titanium dioxide are respectively dispersed in a proper solvent to obtain a coupling agent dispersion liquid and a titanium dioxide dispersion liquid, and then the coupling agent dispersion liquid and the titanium dioxide dispersion liquid are mixed to realize the surface modification of the titanium dioxide by the coupling agent to obtain a modified titanium dioxide dispersion liquid.
In certain embodiments, the present invention disperses a coupling agent in a mixture of water and ethanol to provide a coupling agent dispersion; the mass ratio of water to ethanol in the mixed solvent is preferably 1:7 to 1: 9; preferably, the pH value of the mixture of water and ethanol is adjusted to 9-12 by using alkali (such as ammonia water), and then a coupling agent is added; preferably, the pH is adjusted at 40-60 deg.C, preferably while stirring, preferably by slowly adding the base while stirring; preferably, the addition amount of the coupling agent is 80-120% of the mass of water in the mixture of water and ethanol; the coupling agent is preferably one or more of Phenyltrimethoxysilane (PTMS), gamma-aminopropyltriethoxysilane (KH 550) and gamma-propyltrimethoxysilane. In the present invention, the concentration of the aqueous ammonia may be conventional, and is usually 20% to 30% by weight. In the present invention, the water is preferably deionized water.
In some embodiments, the titanium dioxide is dispersed in ethanol to obtain a titanium dioxide dispersion; preferably, the mass ratio of the titanium dioxide to the ethanol is 1:5 to 1: 6; preferably, a high-speed dispersion machine is used for dispersing the mixture of titanium dioxide and ethanol at the speed of 1000-2500 rpm; the dispersion time is generally 15-60 min; generally dispersed at room temperature; the particle size of the titanium dioxide is preferably 50nm-300 nm. In the present invention, ethanol is preferably anhydrous ethanol.
And adding the coupling agent dispersion liquid into the titanium dioxide dispersion liquid, and uniformly dispersing to obtain the modified titanium dioxide dispersion liquid. Preferably, the mass of the coupling agent in the added coupling agent dispersion liquid is 0.5-2.5% of the mass of the titanium dioxide in the titanium dioxide dispersion liquid. Preferably, a high-speed dispersion machine is used for dispersing the mixture of the coupling agent dispersion liquid and the titanium dioxide dispersion liquid at the speed of 1000-; the dispersion time is generally 15-60 min; usually dispersed at room temperature. The invention improves the dispersion of titanium dioxide in PTFE and the bonding strength between titanium dioxide and PTFE by adding the coupling agent.
In the step (2) of preparing the PTFE powder, the titanium dioxide and the PTFE emulsion are subjected to co-coagulation to form PTFE/titanium dioxide composite particles. Typically, step (2) comprises: and stirring the mixture of the PTFE emulsion and the modified titanium dioxide dispersion liquid to ensure that the titanium dioxide and the PTFE emulsion are subjected to co-coagulation to form PTFE/titanium dioxide composite particles, taking out the PTFE/titanium dioxide composite particles, washing and drying to obtain PTFE powder.
PTFE emulsions are used herein in the art to mean aqueous dispersions of PTFE. The PTFE emulsion suitable for use in the present invention is preferably a PTFE emulsion prepared by a dispersion radical polymerization method. In the invention, the solid content of the PTFE emulsion is preferably 20-30%; the PTFE emulsion preferably does not contain a surfactant; in the PTFE emulsion, the number average molecular weight of PTFE is preferably 423 ten thousand to 702 ten thousand, and the average particle diameter is preferably 0.2 μm to 0.3. mu.m. In certain embodiments, the present invention uses a PTFE emulsion prepared using a dispersion free radical polymerization process, and which contains no surfactant, has a solid content of 20% to 30%, contains PTFE having a number average molecular weight of 423 ten thousand to 702 ten thousand, and has an average particle size of 0.2 μm to 0.3 μm; the PTFE emulsion is different from the PTFE emulsion which is sold in the market and contains 50-60% of solid content and a surfactant, and can be co-coagulated with titanium dioxide more easily by adopting mechanical equipment; the PTFE emulsion is commercially available, and for example, PTFE emulsion (22 wt% in terms of solid content, 423 ten thousand in terms of the number average molecular weight of PTFE, and 0.3 μm in average particle size) produced by Zhejiang Kyowa Kagaku Co., Ltd, PTFE emulsion (30% in terms of solid content, 702 ten thousand in terms of the number average molecular weight of PTFE, and 0.29 μm in average particle size) produced by Shanghai Hanjiang Utsu Dynasty.
In the present invention, the term "co-aggregation" has a meaning known in the art, and generally refers to an operation or a phenomenon in which polymer emulsion particles and inorganic particles are aggregated at the same time to form polymer composite particles (co-aggregated particles) in the presence of an appropriate electrolyte as a coagulant or in the absence of a coagulant. The co-coagulation can be achieved by mixing and stirring the polymer emulsion and the inorganic particles or their dispersion with a mechanical device. The mechanical equipment used in the co-coagulation is also referred to as coagulation equipment.
In some embodiments, the PTFE emulsion is diluted with water to obtain a PTFE diluent, and the PTFE diluent and the modified titanium dioxide dispersion are mixed. Preferably, the PTFE emulsion is diluted with water to a density of 1.0 to 1.2g/cm3. In some embodiments, the PTFE emulsion is diluted with water, the pH of the PTFE emulsion is adjusted to 9-11 with a base (e.g., aqueous ammonia) to provide a PTFE diluent, and the PTFE diluent and the modified titanium dioxide dispersion are mixed.
When the PTFE emulsion (PTFE diluent in some embodiments) and the modified titanium dioxide dispersion are mixed, the mass ratio of the modified titanium dioxide dispersion to the PTFE emulsion (or PTFE diluent) is preferably 1:400-3: 400; preferably, the mixing is carried out at a stirring speed of 400-600 r/min; the stirring time is preferably 15min-50 min; mixing the modified titanium dioxide dispersion with the PTFE emulsion (or PTFE diluent) is typically carried out at room temperature.
The stirring form of the coagulation equipment influences indexes such as the particle size and the particle size distribution, the apparent density, the specific surface area of particles and the particle form of the co-coagulated composite particles, and the indexes influence the post-processing of the PTFE composite tape and finally influence the performance of the PTFE composite tape. The stirring mode of the agglomerating device used in the present invention is preferably a push type stirring mode in which the middle part of the material is pushed downwards and the peripheral part of the material is overturned upwards. Propulsive agitation, in which the material is propelled down in the middle and tumbled up in the periphery, can be accomplished using agitators known in the art, including, but not limited to, propeller, paddle, and turbine agitators, for example. Herein, propeller, paddle, and turbine mixers have meanings well known in the art. In certain embodiments, the present invention utilizes a propeller, paddle, or turbine agitator as the agglomerating device to mix the modified titanium dioxide dispersion with the PTFE emulsion (or PTFE diluent) to co-agglomerate the two. The blades of the coagulation apparatus used in the present invention may be in the form of three-or four-bladed pitched paddles or turbine blades. In certain embodiments, the present invention uses a propeller stirrer, a three-or four-bladed pitched blade (also called a flap) paddle stirrer, or a pitched blade (also called a flap) turbine stirrer as the agglomerating device.
It will be appreciated by those skilled in the art that the PTFE/titanium dioxide composite particles are removed from the dispersion system by avoiding shearing (e.g., kneading, pinching) to avoid shear deformation or fibrillation of the PTFE. Herein, shearing action has the meaning well known in the art. The washing is usually water washing, and may be carried out once or more (e.g., 1 to 3 times). The temperature for drying the PTFE/titanium dioxide composite particles can be conventional drying temperature, such as 100-170 ℃; the drying time can be determined routinely.
The PTFE powder prepared by the method for preparing PTFE powder can be used for preparing a PTFE composite belt, and the PTFE composite belt prepared from the PTFE powder can have the characteristics of the PTFE composite belt. The invention therefore also includes the PTFE powder obtained by the process for the preparation of PTFE powder according to any of the embodiments of the invention. The PTFE powder can be prepared by the method for preparing the PTFE powder.
The method for preparing the PTFE composite belt comprises the following steps: (a) sieving and mixing, (b) pressing, (c) calendaring and (d) semi-shaping.
In the sieving and mixing step (a), the PTFE powder is sieved by using a screen mesh, and then the extrusion aid is added into the sieved PTFE powder and uniformly mixed to obtain a mixed material. Preferably, the PTFE powder is sieved using a sieve having a pore size of 1 to 3 mm. It will be appreciated by those skilled in the art that the sieving may be performed one or more times, for example, agglomerated particles that did not pass through the sieve during the first sieving may be left for a period of time, dispersed by colliding with the walls of the container, and sieved again. It will be appreciated by those skilled in the art that the sieving is performed to prevent shear deformation or fibrillation of the PTFE. The extrusion aid may be an extrusion aid conventional in the art, such as paraffin oil. The volume of the extrusion aid added is preferably 15-25% of the volume of the PTFE powder. In certain embodiments, the present invention utilizes a three-dimensional blender to mix the screened PTFE powder and extrusion aid. The mixing of the PTFE powder and the extrusion aid is preferably carried out at a temperature below 20 ℃ at which the PTFE is not easily fiberized. It will be appreciated by those skilled in the art that after the PTFE powder and extrusion aid are mixed, they may be left for a period of time to cure sufficiently to ensure that each PTFE particle is coated with the extrusion aid before further processing.
The PTFE powder suitable for use in the method of making a PTFE composite tape of the present invention may be a PTFE powder known in the art, preferably a PTFE powder of the present invention.
In the pushing of step (b), the mixed material obtained in step (a) is pushed into a rod shape using a pushing machine to obtain a columnar preform. The pusher may be a pusher commonly used in the art. The pressing is preferably carried out at from 50 ℃ to 150 ℃. The pressing speed is preferably 10 to 20 cm/min. The pressing is preferably performed at a constant speed.
In the calendering of step (c), as shown in fig. 1, the cylindrical preform obtained in step (b) is first calendered into a sheet (preferably having a thickness of 0.066mm to 0.070mm, for example, about 0.068 mm) by means of a two-roll calender at a relatively high temperature (for example, 90 to 100 ℃), and then is calendered into a PTFE composite tape semi-finished product (preferably having a thickness of 0.058mm to 0.066mm, for example, about 0.0635 mm) by means of a two-roll calender at a relatively low temperature (for example, room temperature). As will be appreciated by those skilled in the art, calendering orients the PTFE molecular chains in the machine direction and adds some cross-linking.
In the step (d), in the semi-shaping, the PTFE composite belt semi-finished product obtained in the step (c) is heated for 12 to 20 seconds at the temperature of 320 to 330 ℃ to obtain the PTFE composite belt. Heating may be performed in an oven. In continuous production, the PTFE composite tape semi-finished product may be passed through an oven of a certain size at a certain rate to complete heating, as long as the heating time of the PTFE composite tape semi-finished product is within the range of 12-20s, for example, the PTFE composite tape semi-finished product may be passed through an oven having a length of 2m at a rate of 6-10 m/min. The invention carries out semi-shaping treatment on the PTFE composite belt, and obviously improves the mechanical property of the PTFE composite belt.
Another method of making a PTFE composite tape of the present invention comprises the steps of: (1) the surface modification of titanium dioxide, the preparation of PTFE powder and the preparation of PTFE composite belt, wherein the step (3) comprises the following steps: (a) sieving and mixing, (b) pushing, (c) calendaring and forming and (d) semi-shaping; wherein, the steps (1), (2) and (3) (including the step (a), (b), (c) and (d) in the step (3)) are as described in any embodiment of the present invention, and the PTFE powder used in the step (a) is the PTFE powder prepared in the step (2).
In certain embodiments, the method of making a PTFE composite tape of the present invention comprises:
(1) surface modification of titanium dioxide
Slowly adding alkali (such as ammonia water with the concentration of 20-30 wt%) into a mixture of water and ethanol with the mass ratio of 1:7 to 1:9 at the temperature of 40-60 ℃ under stirring, testing the pH value of the solution, stopping adding the alkali when the pH value reaches 9-12, adding a coupling agent (such as phenyltrimethoxysilane, gamma-aminopropyltriethoxysilane and/or gamma-propyltrimethoxysilane) with the mass of 80-120% of the mass of water, and uniformly mixing to obtain a coupling agent dispersion liquid; mixing titanium dioxide (the particle size is preferably 50-300 nm) and ethanol according to the mass ratio of 1:5 to 1:6, and uniformly dispersing (preferably dispersing for 5-60min at the speed of 1000-; adding the coupling agent dispersion liquid into the titanium dioxide dispersion liquid, wherein the mass of the coupling agent in the added coupling agent dispersion liquid is 0.5-2.5wt% of the mass of the titanium dioxide in the titanium dioxide dispersion liquid, and uniformly dispersing (preferably dispersing for 5-60min at the speed of 1000-2500rpm by using a high-speed dispersion machine) to obtain the modified titanium dioxide dispersion liquid;
(2) preparation of PTFE powder
Diluting a PTFE emulsion (preferably a PTFE emulsion prepared by a dispersion radical polymerization method, preferably containing no surfactant, and having a solid content of preferably 20-30%, a PTFE content of preferably 423-702 ten thousand and an average particle diameter of preferably 0.2-0.3 μm) with water to a density of 1.0-1.2g/cm3Then, adjusting the pH value of the PTFE emulsion to 9-11 by adopting alkali (such as ammonia water with the concentration of 20wt% -30 wt%) to obtain PTFE diluent; mixing the modified titanium dioxide dispersion liquid prepared in the step (1) with PTFE diluent according to the mass ratio of 1:400-3:400, and pouring the mixture into a condenserIn the polymerization kettle, preferably stirring for 15-50min at the stirring speed of 400-600r/min, so that the titanium dioxide and the PTFE emulsion are subjected to co-coagulation to form PTFE/titanium dioxide composite particles; taking out the PTFE/titanium dioxide composite particles carefully to avoid shearing action, and washing and drying (for example, drying at 100 ℃ and 170 ℃ for 24 hours) to obtain PTFE powder;
(3) preparation of PTFE composite tape
Sieving and mixing: sieving the PTFE powder obtained in the step (2) by using a sieve with the aperture of about 1-3 mm; the particles can be sieved for multiple times, the agglomerated particles which do not pass through the screen for the first time can be placed for a period of time, collide with the wall of the container to be dispersed, and are sieved again; sieving is careful to prevent shearing; adding an extrusion aid (such as paraffin oil) with the volume of about 15-25% of the volume of the PTFE powder into the sieved PTFE powder, then uniformly mixing (such as fully mixing in a three-dimensional mixer), and preferably standing for a period of time for fully curing to ensure that each PTFE particle is wrapped by the extrusion aid to obtain a mixed material; preferably, the PTFE powder and the extrusion aid are mixed at the temperature of below 20 ℃;
pushing: putting the mixed material into a die cavity of a pushing machine, and pushing the mixed material into strips at the temperature of 50-150 ℃ (constant-speed pushing is preferred, and the pushing speed is 10-20 cm/min) to obtain a columnar prefabricated product;
and (3) calendering and forming: calendering the cylindrical preform into a sheet (preferably 0.066-0.070mm thick, for example around 0.068 mm) using a two-roll calender at 90-100 ℃, and then calendering the sheet using a two-roll calender at room temperature to obtain a PTFE composite tape semi-finished product (preferably 0.058-0.066mm thick, for example around 0.0635mm thick);
semi-sizing: heating the PTFE composite tape semi-finished product for 12-20s at 320-330 ℃ to obtain the PTFE composite tape.
High performance PTFE composite tapes, such as the PTFE composite tapes of the present invention, can be made using the methods of the present invention for making PTFE composite tapes. Accordingly, the present invention also includes a PTFE composite tape made by the method of making a PTFE composite tape according to any of the embodiments of the present invention.
The PTFE composite tape of the present invention can be produced by the method for producing a PTFE composite tape of the present invention, that is, the PTFE composite tape produced by the method for producing a PTFE composite tape of the present invention can have the characteristics of the PTFE composite tape of the present invention.
The invention solves the key technology for manufacturing the PTFE composite belt for the aerospace cable, provides the PTFE composite belt for the aerospace cable insulating layer and the preparation method thereof, fills the blank of the domestic technology in the aspect, and meets the performance requirement of the high-temperature resistant PTFE composite belt for the aerospace required by the American military standard SAE AS 22795. The composite tape has uniform thickness, higher ultraviolet absorptivity, excellent thermal stability at 500 ℃, tensile strength of 12.17MPa, elongation of 122 percent, insulating dielectric strength of more than 95kV/mm and performance far higher than the performance requirements of foreign similar products.
The invention is described below by way of specific examples, which are intended to better understand the content of the invention. It is to be understood that these examples are illustrative only and not limiting. The reagents used in the examples are, unless otherwise indicated, commercially available. The methods used in the examples are conventional methods unless otherwise specified.
In the following examples, the imported PTFE tape was a PTFE tape produced by du pont china group ltd, titanium dioxide was titanium dioxide R104 (particle size: about 220 nm) produced by du pont china group ltd, the PTFE emulsions used in examples 1, 2 and 1 were PTFE emulsions (solid content: 22wt%, PTFE number average molecular weight: 423 ten thousand, average particle size: 0.3 μm) produced by zhejiang university ltd, and the PTFE emulsion used in example 3 was a PTFE emulsion produced by shanghai han dynasty new material science and technology ltd (solid content: 30%, PTFE number average molecular weight: 702, average particle size: 0.29 μm).
Example 1
A PTFE composite tape was prepared by the following steps:
(1) surface modification of titanium dioxide
According to deionized water: coupling agent Phenyltrimethoxysilane (PTMS): weighing deionized water, a coupling agent PTMS and absolute ethyl alcohol according to the mass ratio of absolute ethyl alcohol =1:1:8, dripping the deionized water and the absolute ethyl alcohol into a beaker, continuously stirring at the constant temperature of 50 ℃, meanwhile slowly dripping 25wt% of ammonia water under stirring, testing the pH value of the solution, stopping dripping the ammonia water when the pH value reaches 11, and finally adding the coupling agent PTMS and continuously stirring to obtain a coupling agent dispersion liquid. Adding titanium dioxide (the particle size is about 220 nm) into absolute ethyl alcohol, wherein the mass ratio of the titanium dioxide to the absolute ethyl alcohol is 1:5, then dispersing for 30min at the room temperature under the condition of 2000rpm by using a high-speed dispersion machine, adding the coupling agent dispersion liquid, wherein the mass of the coupling agent in the added coupling agent dispersion liquid is 1.5wt% of the mass of the titanium dioxide, and continuously dispersing for 30min at the room temperature under the condition of 2000rpm to obtain the modified titanium dioxide dispersion liquid.
(2) Preparation of PTFE powder
Adopting deionized water to dilute PTFE emulsion (the solid content of the PTFE emulsion is 22 percent, the number average molecular weight of the PTFE is 423 ten thousand, and the average particle size is 0.3 mu m) to the density of 1.06g/cm3Then, the pH value of the diluted PTFE emulsion is adjusted to 10 by using ammonia water with the concentration of 25wt% to obtain PTFE diluent. Mixing the modified titanium dioxide dispersion liquid prepared in the step (1) with PTFE diluent according to the mass ratio of 1:200, pouring the mixture into a three-blade inclined-blade paddle stirrer, and stirring the mixture for 40min at the stirring speed of 550rpm to ensure that the titanium dioxide and the PTFE emulsion are co-coagulated to form PTFE/titanium dioxide composite particles.
And carefully taking out the PTFE/titanium dioxide composite particles to avoid shearing action, adding enough deionized water to wash for 1-3 times, and drying at 140 ℃ for 24 hours to obtain PTFE powder.
(3) Preparation of PTFE composite tape
Sieving and mixing: and (3) selecting a screen with the aperture of about 2mm, and sieving the PTFE powder. The agglomerated particles that do not pass through the screen for the first time may be left for a period of time, hit the walls of the container to be dispersed, and screened again. Sieving is careful to prevent shearing. Adding paraffin oil with the volume of about 20% of that of the PTFE powder into the sieved PTFE powder, then fully mixing in a three-dimensional mixer, standing for a period of time, fully curing, and ensuring that each PTFE particle is wrapped by the paraffin oil to obtain a mixed material; the mixing process is carried out below 19 c, at which temperature PTFE is not prone to fibrillation.
Pushing: the mixture was placed in a clean mold cavity and extruded into a rod form at a rate of 15cm/min in a extruder at 100 ℃ to give a cylindrical preform.
And (3) calendering and forming: the cylindrical preform was calendered at 100 c using a two-roll calender to a sheet thickness of about 0.068mm and then calendered at room temperature using a two-roll calender to produce a PTFE composite tape half-product having a thickness of about 0.0635 mm. The calendering process orients the PTFE molecular chains in the machine direction and adds some cross-linking.
Semi-sizing: and heating the PTFE composite belt semi-finished product in an oven for 12s at the temperature of 330 ℃ to obtain a PTFE composite belt finished product.
Example 2
A PTFE composite tape was prepared by the following steps:
(1) surface modification of titanium dioxide
According to deionized water: compounding a coupling agent: weighing deionized water, a compound coupling agent and absolute ethanol according to the mass ratio of absolute ethanol =1:1:8, wherein the compound coupling agent is prepared by mixing PTMS and gamma-aminopropyltriethoxysilane (KH 550) according to the ratio of 4: 1, dripping deionized water and absolute ethyl alcohol into a beaker, continuously stirring at the constant temperature of 50 ℃, slowly dripping 25wt% of ammonia water while stirring, testing the pH value of the solution, stopping dripping the ammonia water when the pH value reaches 11, and finally adding the compound coupling agent and continuously stirring to obtain the coupling agent dispersion liquid. Adding titanium dioxide (the particle size is about 220 nm) into absolute ethyl alcohol, wherein the mass ratio of the titanium dioxide to the absolute ethyl alcohol is 1:5, then dispersing for 30min at the room temperature under the condition of 2000rpm by using a high-speed dispersion machine, adding the coupling agent dispersion liquid, wherein the mass of the coupling agent in the added coupling agent dispersion liquid is 1.5wt% of the mass of the titanium dioxide, and continuously dispersing for 30min at the room temperature under the condition of 2000rpm to obtain the modified titanium dioxide dispersion liquid.
(2) Preparation of PTFE powder
The procedure was followed in step (2) of example 1.
(3) Preparation of PTFE composite tape
The procedure was followed in step (3) of example 1.
Example 3
A PTFE composite tape was prepared by the following steps:
(1) surface modification of titanium dioxide
The procedure was followed in step (1) of example 2.
(2) Preparation of PTFE powder
Adopting deionized water to dilute PTFE emulsion (the solid content of the PTFE emulsion is 30 percent, the number average molecular weight of the PTFE is 702 ten thousand, and the average particle size is 0.29 mu m) to the density of 1.06g/cm3Then, the pH value of the diluted PTFE emulsion is adjusted to 10 by using ammonia water with the concentration of 25wt% to obtain PTFE diluent. Mixing the modified titanium dioxide dispersion liquid prepared in the step (1) with PTFE diluent according to the mass ratio of 1:200, pouring the mixture into a three-blade inclined-blade paddle stirrer, and stirring the mixture for 40min at the stirring speed of 550rpm to ensure that the titanium dioxide and the PTFE emulsion are co-coagulated to form PTFE/titanium dioxide composite particles.
And carefully taking out the PTFE/titanium dioxide composite particles to avoid shearing action, adding enough deionized water to wash for 1-3 times, and drying at 140 ℃ for 24 hours to obtain PTFE powder.
(3) Preparation of PTFE composite tape
The procedure of (3) in example 2 was followed.
The PTFE composite tapes obtained in examples 1 to 3 were tested for their properties, and the results are shown in Table 1. In Table 1, the tensile strength was measured in accordance with GB/T 1040.3-2006 standard, the longitudinal elongation was measured in accordance with GB/T 1040.3-2006 standard, the dielectric strength was measured in accordance with GB/T1408 standard, and the ROHS was measured in accordance with IEC62321 standard.
Table 1: results of measuring the properties of the PTFE composite tapes of examples 1 to 3
Figure 233342DEST_PATH_IMAGE001
The test results show that the PTFE composite tapes obtained in the examples 1 to 3 have the thickness, dielectric property, tensile strength, longitudinal elongation and ROHS indexes meeting the requirements of SAE AS 22759. Rohs (restriction of Hazardous substations) is a mandatory standard set by the european union legislation, which is collectively called "directive on limiting the use of certain Hazardous components in electrical and electronic equipment", and defines the upper limit solubility of lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls, and polybrominated diphenyl ethers in electrical and electronic products, wherein the upper limit concentration of cadmium is 100ppm, and the upper limit concentration of the remaining five Hazardous components is 1000 ppm.
The ultraviolet absorptivity of the PTFE composite tape prepared by the method of the present invention is compared with that of an imported PTFE composite tape (DuPont China group Co., Ltd.) as shown in FIG. 2. As can be seen from fig. 2, the PTFE composite tapes of examples 1-3 have uv absorbencies as high as the imported PTFE composite tapes.
The thermal stability of the PTFE composite tape produced by the method of the present invention versus imported PTFE composite tape is shown in fig. 3. As can be seen in fig. 3, the PTFE composite tapes of examples 1-3 had excellent thermal stability up to 500 ℃, with the thermal weight loss curve substantially coinciding with that of the imported composite tape. As can be seen from fig. 3, after the PTFE composite tapes of example 1, example 2, and example 3 are heated, the final remaining mass percentages are 2.5%, 1.5%, and 1.5%, respectively, which are the titanium dioxide content of the PTFE composite tapes.
Comparative example 1
A PTFE composite tape was prepared by the following steps:
(1) surface modification of titanium dioxide
The procedure was followed in step (1) of example 1.
(2) Preparation of PTFE powder
The procedure was followed in step (2) of example 1.
(3) Preparation of PTFE composite tape
The procedure of example 1 was followed in step (3), except that the semisetting treatment was omitted.
The performance of the PTFE composite tape obtained in comparative example 1 was measured, and the results are shown in table 2. In Table 2, the tensile strength was measured in accordance with GB/T 1040.3-2006 standard, the longitudinal elongation was measured in accordance with GB/T 1040.3-2006 standard, the dielectric strength was measured in accordance with GB/T1408 standard, and the ROHS was measured in accordance with IEC62321 standard.
Table 2: comparative example 1 PTFE composite tape Performance test results
Figure 628552DEST_PATH_IMAGE002
The results in table 2 show that the PTFE composite tape obtained in comparative example 1 has a tensile strength far below the performance index requirements, except for individual product thicknesses that do not meet the requirements.
Comparative example 2
A PTFE composite tape was prepared by the following steps:
(1) surface modification of titanium dioxide
The procedure was followed in step (1) of example 1.
(2) Preparation of PTFE powder
Diluting a conventional PTFE emulsion (the solid content of the PTFE emulsion is about 60 percent and contains a surfactant) to a density of 1.06g/cm by adopting deionized water3Then, the pH value of the diluted PTFE emulsion is adjusted to 10 by using ammonia water with the concentration of 25wt% to obtain PTFE diluent. And (2) mixing the modified titanium dioxide dispersion liquid prepared in the step (1) with PTFE diluent according to the mass ratio of 1:200, pouring the mixture into a three-blade inclined-blade paddle stirrer, and stirring for 40min at the stirring speed of 550 rpm. The result shows that the conventional PTFE emulsion cannot generate the co-coagulation reaction with the titanium dioxide.

Claims (9)

1. A process for preparing PTFE powder, comprising the steps of:
(1) surface modification of titanium dioxide
Adjusting the pH value of a mixture of water and ethanol with the mass ratio of 1:7-1:9 to 9-12 by using alkali, adding a coupling agent with the mass of 80-120% of the mass of water, and uniformly mixing to obtain a coupling agent dispersion liquid; mixing titanium dioxide and ethanol according to the mass ratio of 1:5-1:6, and uniformly dispersing to obtain titanium dioxide dispersion liquid; adding the coupling agent dispersion liquid into the titanium dioxide dispersion liquid, wherein the mass of the coupling agent in the added coupling agent dispersion liquid is 0.5-2.5% of the mass of the titanium dioxide in the titanium dioxide dispersion liquid, and uniformly dispersing to obtain a modified titanium dioxide dispersion liquid; and
(2) preparation of PTFE powder
Diluting the PTFE emulsion with solid content of 20-30% and no surfactant with water to density of 1.0-1.2g/cm3Adjusting the pH value of the diluted PTFE emulsion to 9-11 by using alkali to obtain PTFE diluent; mixing the modified titanium dioxide dispersion liquid prepared in the step (1) with the PTFE diluent according to the mass ratio of 1:400-3:400, so that the titanium dioxide and the PTFE emulsion are subjected to co-coagulation to form PTFE/titanium dioxide composite particles, taking out the PTFE/titanium dioxide composite particles, washing and drying to obtain PTFE powder.
2. The method of claim 1, wherein the method has one or more of the following features:
(1) in the PTFE emulsion, the number average molecular weight of PTFE is 423 ten thousand to 702 ten thousand, and the average grain diameter is 0.2 mu m to 0.3 mu m;
(2) the PTFE emulsion is prepared by adopting a dispersing free radical polymerization method;
(3) the particle size of the titanium dioxide is 50nm-300 nm;
(4) the coupling agent is one or more of phenyl trimethoxy silane, gamma-aminopropyl triethoxy silane and gamma-propyl trimethoxy silane;
(5) in the step (1), adding ammonia water to a mixture of water and ethanol at 40-60 ℃ to adjust the pH;
(6) in the step (1), dispersing titanium dioxide into ethanol by using a high-speed dispersion machine at 1000-2500 rpm;
(7) in the step (2), stirring the mixture of the PTFE emulsion and the modified titanium dioxide dispersion liquid prepared in the step (1) in a propelling type stirrer, a paddle type stirrer or a turbine type stirrer to ensure that the titanium dioxide and the PTFE emulsion are subjected to co-coagulation; and
(8) in the step (2), the mixture of the PTFE emulsion and the modified titanium dioxide dispersion liquid prepared in the step (1) is stirred at 400-600 rpm, so that the titanium dioxide and the PTFE emulsion are subjected to co-coagulation.
3. PTFE powder obtained by the process according to claim 1 or 2.
4. The PTFE powder of claim 3, wherein the PTFE powder comprises PTFE, titanium dioxide and a coupling agent, wherein the mass of the PTFE accounts for 97-99% of the total mass of the PTFE powder, the mass of the titanium dioxide accounts for 1-3% of the mass of the PTFE, and the mass of the coupling agent accounts for 0.5-2.5% of the mass of the titanium dioxide.
5. A PTFE composite tape produced by using the PTFE powder of claim 3 or 4.
6. A method of making a PTFE composite tape, comprising the steps of:
(a) sieving and mixing: sieving the PTFE powder of claim 3 or 4 by using a screen with the aperture of 1-3mm, adding an extrusion aid with the volume of 15-25% of the volume of the PTFE powder into the sieved PTFE powder, and uniformly mixing to obtain a mixed material;
(b) pushing: extruding the mixed material obtained in the step (a) into strips by using a pushing machine at the temperature of 50-150 ℃ to obtain a columnar prefabricated product;
(c) and (3) calendering and forming: calendering the columnar preform obtained in the step (b) into a sheet by using a double-roll calender at the temperature of 90-100 ℃, and then calendering the sheet by using the double-roll calender at room temperature to obtain a PTFE composite belt semi-finished product; and
(d) semi-sizing: heating the PTFE composite tape semi-finished product obtained in the step (c) for 12-20s at 320-330 ℃ to obtain the PTFE composite tape.
7. The method of claim 6, wherein the method has one or more of the following features:
(1) in the step (a), PTFE powder and extrusion aid are mixed at the temperature of below 20 ℃;
(2) in the step (b), the pushing speed is 10-20 cm/min; and
(3) in the step (c), the thickness of the sheet is 0.066-0.070mm, and the thickness of the PTFE composite belt semi-finished product is 0.058-0.066 mm.
8. A PTFE composite tape produced by the method of claim 6 or claim 7.
9. A wire or cable wherein the insulation or sheath of the wire or cable is prepared from the PTFE composite tape of claim 5 or 8.
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