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The preparation and properties of high-performance PTFE coated membrane filter

Currently,the handling of flue gas, dust mainly adopts bag dust removal, bag filter bag filter material mainly selects the aramid amine fiber, and d, PPS fiber, poly (aromatic phthalein imide fiber, etc. Although these have different optimal glass fiber bag filter, with different properties of flue gas, dust, there are also different, such as aromatic poly phthalein amine fiber with moisture and chemical composition point temperature will reduce operation, especially in the SOX exist, with moisture, will be corrosion, strength retention; PPS fiber is sensitive to oxidant; Poly (aromatic phthalein imide fiber resist to hydrolysis, and high prices; The glass fiber of hydrofluoric acid, strong alkali corrosion resistance is poor. These problems will be in practice to reduce the service life of the bag, and make the bag filter machine for the inefficiency of flue gas, dust processing, at the same time, the effect filter continuous normal work of the machine. Therefore, the project, on the basis of traditional bag filter with filter material, combine the company of PTFE membrane and to develop a high performance fiber production process of pure PTFE (PTFE) coated filter material manufacturing process, namely, the company produced PTFE film materials, process such as fiber, woven, composite filter material. Production of pure PTFE filter material, this method possesses short process flow, simple operation, low cost, easy to mass production, etc.

Experimental section
Materials and equipment
PTFE microporous membrane, PTFE fiber and PTFE needled felt all made for this project; Hydrogen peroxide, concentrated ammonia are analytically pure; Distilled water is homemade. Tectorial membrane unit is homemade.
Production process of PTFE coated filter material
PTFE staple fiber→PTFE fiber mesh(PTFE high strength and low stretch base fabric carding and laying)→High density acupuncture→High temperature heat setting→PTFE needle felt→PTFE film polymerize→PTFE acupuncture felt film filter material

Base fabric as skeleton of needled felt filter material,  has an effect on enhancement ;In the process of needle, first will be through a certain process of PTFE with short fibers compressed into netting, then press base fabric in the middle with two fiber webs (upper 、 lower has a web respectively), and then through the two processes and the main acupuncture needle, after a certain thermal setting process, finally get needled felt; tectorial membrane divided into resin coated and hot laminating, its purpose is to combined with PTFE membrane on the surface of needled felt, to further improve the physical and chemical performance of needled felt, make its surface level off smooth, not easy to be blocked by dust, high chemical stability, with resistance to high temperature, high humidity, corrosion resistance, wear resistance, high filtration precision, easy to, etc.

The results and analysis
Component analysis of pure PTFE coated filter material
Figure 2 is the infrared spectra of pure PTFE coated filter material, figure 3, 4 respectively the base cloth of the filter material and the surface of the DSC analysis.
Figure 2
Figure 2 Infrared spectrum of pure PTFE coated filter material

Figure 3
Figure 3 DSC analysis of pure PTFE coated filter material base fabric

Figure 4
Figure 4 DSC analysis of pure PTFE coated filter material layer

Figure 2 shows that in 150 cm – 1 and 1200 cm – 1 has two strong bands, near for PTFE characteristic absorption peak, this is – CF2 stretching vibration peak; In the range of 500 ~ 850 cm – 1 a series of bands come from vibration peak PTFE amorphous area. After PTFE resin and fiber, and then with the base fabric needle punched felt, after laminating into filter material processing, the band was not found. Figure 3 and figure 4, with ir spectrum and DSC analysis, can know PTFE coated filter material is made of pure PTFE.

Electron microscopy of pure PTFE coated filter material

Figure 5 is pure PTFE coated filter material longitudinal section electron microscopic photograph.
Figure 5
Figure 5 100% PTFE coated filter material longitudinal section electron micrograph

Pure PTFE coated filter material is based on PTFE fabric as substrate (FIG. 5 longitudinal section electron micrograph middle coarser fiber is the Teflon long fiber), through the acupuncture of different fineness of PTFE staple fiber, and at the completion of needle-punched process on one side of the filter material, a layer of PTFE membranes made of compound. PTFE fiber and PTFE microporous membrane layer have good bonding properties, which in the mechanical properties of pure PTFE coated filter material can be well reflected. Figure 2 ~ 4 did not show a new absorption peak, it shows that it does not form new chemical bonds between PTFE microporous membrane and PTFE base fabric, just rely on the role of high temperature melt to produce high temperature thermal bonding effect.

Figure 6 is pure PTFE coated fiber filter material surface electron microscopic photograph.
Figure 6
Figure 6 pure PTFE coated fiber filter material surface electron microscopic photograph

Figure 6 shows that, due to the special structure of PTFE microporous membrane, made of pure PTFE coated filter material surface without the straight hole, the dust can’t through the membrane surface to the interior of the membrane or base material, the only through the dust and gas or withholding material on the surface of the membrane surface filtering approach is called filtering. In addition, the low surface tension of PTFE membrane which has the good non-stick performance for powder. Trapped and dust or material not like traditional filtering method in the filter material surface form thicker filter cake, don’t blow will not be able to continue to work, instead reaching a certain thickness fall off automatically from the surface of the filter material. So using PTFE coated filter material filter bag won’t cause the system pressure to rise continuously, instead the basic stable state of stress.

Performance metrics of pure PTFE coated filter material
Pure PTFE coated filter material performance is: the surface density is about 850 g/m2, thickness is about 1. 5 mm, 127 Pa pressure ventilation quantity is 25 ~ 40 L/m2 s., continuous working temperature 260 ℃, instantaneous temperature 280 ℃, and the breaking strength is 800 N / 5 cm or more, heat shrinkage rate < 1%, the shortest service life of four years or more, resistance to pH range of 0 ~ 14, no oxidation, no hydrolysis. Ultrafine PTFE fiber layer surface level off, the PTFE film plays a supporting role, make it not easy to damage, and can have quite good protection effect. PTFE crude fiber layer contained in crude fiber make the pore enlargement, increased ventilation volume, greatly reduce the filtering resistance PTFE base cloth for the skeleton, keep high strength making warp/weft to fiber, and guarantee the stability of the size of the filter material, to strengthen the role of filter material. High and low temperature resistance of pure PTFE gradient effect of filtering material, acid and alkali resistance, especially the resistance to high sulfur, high humidity, excellent chemical stability, and filtering channel to gradually form a gradient from small to large, therefore, in process of filtering and ash removal, gas flow rate of filter material increased significantly, the filtering efficiency, filtering speed, high dust removal ability, little resistance during operation, soot cleaning frequency is low, service life is long, not only make the energy consumption dropped substantially, also reduces the maintenance workload and the costs of spare parts and other investments. Pure PTFE coated filter material performance comparison with ordinary filter material Pure PTFE coated filter material compared with the performance of several kinds of filter material shows in table 1. Table 1 pure PTFE coated filter material compared with the performance of several kinds of filter material Table 1
Table 1 shows that only the glass fiber and pure PTFE coated filter material of continuous operating temperature can reach 260 ℃, the instantaneous temperature reached 280 ℃.Due to the temperature tolerance is one of the important indicators; bag filter is expected to run as a result, the pure PTFE and glass fiber has more advantages. But because of work in the bag filter process, the need to repeatedly to injection of filter bag, stripping absorption in thin film on the surface of the particles, filter bag need wear and fold reciprocating back and forth, and glass fiber wear-resisting performance is poor, therefore, compared with the traditional effect of filter material, pure PTFE coated fabric more can satisfy the requirement of high temperature, high humidity and high corrosive flue gas dust removal.

The application prospect of pure PTFE coated filter material
Pure PTFE coated filter material because of its high temperature resistance, corrosion resistance and high filtration efficiency, excellent performance, fully competent control of PM2. 5 particulate matter .Compared with PTFE microporous membrane filter material, PTFE coated filter material can make the dust filter from conventional deep filter into a surface, thus to improve filtration efficiency by an order of magnitude, filtration efficiency of PM10 lab reaches 99. 999%, filtration efficiency of PM2.5 reaches 99. 95%, almost zero emissions, its service life can reach more than 10 years, has the high cost performance.

If you need more information about our products, please contact us: system@corefrp.com ,our engineers will answer you and provide free samples.

pdfThe preparation and properties of high-performance PTFE coated membrane filter.pdf

Manufacturing, application and development of PTFE/Teflon coated fiber glass fabric

PTFE/Teflon coated fiber glass fabric is made of glass fiber cloth as the substrate, impregnated with PTFE dispersion. Impregnated fiberglass cloth surface, coated with a thin layer of fluororesin small particles, and then through the drying, baking, sintering and other processes, the dispersion of volatile and leaving F4 tiny particles, tightly attached to the surface and pores of the fiber glass cloth, intensive continuous as a whole, to achieve the purpose of fiberglass cloth and F4 firm bonding, it become a new material which not only has the characteristics of fiber glass, but also has many excellent properties of fluorine plastic. According to different needs, in the dispersion can also be added inorganic or organic filler, to further improve its electrical properties, anti-aging properties and wear resistance, add a different pigment and then increase its excellent decorative performance.

Process Research
Raw material
A. PTFE commonly known as “plastic king”, it is one of the best performance varieties of plastic. It has excellent temperature resistance and corrosion resistance, excellent insulation properties, non-stick, non-toxic and odorless, harmless to the human body.
B. Fiberglass fabric
The substrate of the coated materials should have high temperature resistance and good tensile strength, glass fiber compared with natural fibers and chemical fiber, it has high strength, elongation is small, good chemical stability, etc., and it can make up for the lack of F4, to maintain the size of the stability.

Production process and key technology
A. Production process
Treated fiberglass fabric and F4 dispersion liquid→Impregnation→Drying→Take-up→Sintering→Take-up→Checking→Finished product pakcaging→ Storage
B. The main key technology of the processes of fiberglass impregnated with F4 dispersion are the following three aspects.
a. F4 dispersion concentration, impregnation temperature and velocity
The concentration of F4 dispersion directly affects the surface finish, flatness, thickness and resin content of the product. High concentration, the thickness is large after each impregnation, the number of times to complete the dipping can be reduced accordingly; But if the impregnated F4 is too thick, it is easy to produce products surface cracking after drying. In order to ensure product quality, should use low concentration of dispersion, after several times impregnation is better.

The temperature distribution of the impregnation furnace is divided into three zones according to the elevation. Respectively, to complete the impregnation, drying and baking three processes.

Low temperature zone: The temperature of the first section of the lower part of the impregnation unit, it is affect the surface temperature of the dipping tank directly, and related to the liquid surface bubble burst rate and and flow marks and other defects. The temperature of the area is too high, will make the glass cloth dispersion too fast drying, thus producing bubble and flow marks. At the same time, the higher temperature of the area to radiate the bottom, so that F4 liquid surface crust, the impregnated fiberglass cloth will remain on the surface of the F4 pimple, serious damage to the fabric quality.

Medium temperature zone: When the impregnated cloth enters the second section of the middle part of the unit, it is needs to gradually complete the evaporation of water, the temperature is too low will make water evaporation is not complete, impact the effect of the next process of impregnation; Excessive temperature is not conducive to the uniform escape of water, also hindered the next section of the temperature control.

High temperature zone: When entering the upper third section, the residual moisture, the surfactant and the low molecular weight in the resin should be completely volatilized to facilitate the effect of the next impregnation process. If the temperature of this area is too high, will cause local F4 sintering, impact the effect of the next process of impregnation; If the temperature is too low, it will make the fabric sticky, the cloth will be stick together when coiling.

Although the impregnation unit is divided to three temperature zones from the bottom to the top, but they are not completely separated, but continuous gradient, there is no significant deviation between the sections. According to the test results, the temperature distribution of the longitudinal section of the impregnation unit is shown in Fig.2.
Fig.2
Fig.2 Temperature distribution diagram

The transmission speed of glass fiber cloth is one of the key factors affecting production efficiency and product quality. If the speed is slow, disperse evenly through the fabric, to avoid the flow marks, reduce product defects, to get good quality cloth. But if the speed is too slow will reduce production efficiency and cost will be increased. If the speed is too fast, easy to produce bubbles, flow marks and other defects, and cause dry time is not enough, dry through, causing the fabric sticky.

b. Sintering temperature and velocity
F4 resin is different from thermosetting resin, it does not have “curing” stage, but must be sintered at high temperatures. Sintering furnace is divided into two layers, The lower layer further removes the low molecular weight of the surfactant and F4 resin, and the upper layer completes the “plasticization” process of the F4 resin, which is characterized by the cloth immediately discolor, white products from pure white to soil white, black products from grey-blue into pitch-black. The upper temperature is too high or too long time in the plasticization temperature, will make the fabric brittle and performance reduction.

The choice of sintering speed must meet the temperature requirements, sintering speed and temperature are two closely related factors, must meet the temperature requirements of the premise to choose the appropriate speed, If not reached the temperature required for plasticization, speed is slow and even pause is not possible to complete the sintering, and once the plasticizing temperature is reached, the sintering is completed in just a few seconds. So the transmission speed does not affect the plasticization. At the same time, impregnated F4 glass cloth thickness uniform, and relatively thin, so heat quickly, it is easy to sintering.

c. The quality requirements of glass fiber base fabric
The requirement of PTFE products on the quality of the base fabric is extremely high, the main factors affecting the quality of the product are the glass mattress material and the technical maturity of the impregnation process. The base fabric can not exist cloth wrinkles, yarn joints, broken yarn, oil and other serious defects, the fabric flatness, density and other quality requirements are higher than the general fabric.

Application research
Glass fiber coated with PTFE products with its excellent performance widely used in aviation, electronics, textiles, food, building materials, medicine, clothing and other fields.

Architectural membrane material
This is the most promising area of PTFE/Teflon coated fiber glass products. Since the glass fiber “silver top” come out in 1975, buildings with various woven fabrics for roofs are emerging in the United States and Western Europe. “Light roof” has become a new type of soft shell structure, the coating has become a new type of roofing materials. This new building with its simple design, easy installation, huge size, shape color changeable to get much attention. It has been widely used in large span buildings since 1980s, such as pontoon roof, inflatable dome, suspension structure hall, sports venues, amusement parks, exhibition centers, music halls and warehouses and other soft shell structure. The most widely used in this type of architectural membrane is PTFE/Teflon coated fiber glass fabric.

This kind of glass fiber is made of B grade superfine glass fiber yarn, its tensile strength is higher than steel, and has a high tear strength and elastic modulus, good dimensional stability, no combustion, and PTFE coating has long-term weather resistance, no adhesion, can be automatically cleaned. The hardness of such materials is about 10 times that of organic polymer textile fibers. The use of this new building film construction of the building has the following advantages:
A. The weight of the roof is very light
B. Good aging resistance
C. Translucent and high energy efficiency
D Safety.

Insulation Materials
The volume of glass fiber is higher than the resistance, it can be used for aviation, electrical and electronic industry in the high-frequency high-temperature conveyor belt; Because of its good air tightness, bursting high strength, can be used as a solenoid valve diaphragm to prevent the leakage of dielectric materials; Tetrafluoroethylene casing can be used as wire and cable; thin cloth can be used for printed circuit boards.

Microwave drying conveyor belt
Because it does not absorb microwave, non-stick, high temperature, good insulation properties, is the ideal material for microwave conveyor belt. The previous food machinery conveyor belt is made of canvas, but the canvas is not high temperature, not easy to clean; and than be changed into chemical fiber, but it is easy to deformation. Using PTFE/Teflon coated fiber glass anti-stick belt instead of canvas and chemical fiber, completely overcome the above disadvantages. PTFE/Teflon coated fiber glass belt is high temperature, no deformation, inert, non-toxic side effects, no-clean, can also be used as the microwave transport belt in medical machinery.

Clothing fusing machine conveyor belt
Previously, people used horse hair cloth and ironing to produce shirts and suits, but temperature uniformity is poor, not high temperature and easy to stick. Now, with the use of anti-adhesive belt, the horse hair cloth has been gradually replaced by resin lining.

Flexible compensator
Flexible compensator is a new species of compensator for the gas transport and other areas, also known as non-metallic compensator, expansion joints, bellows, etc., the market share is expanding. As the PTFE/Teflon coated glass fabric with corrosion resistance, high temperature and high pressure, it can be used as pipeline lining of compensator.

Friction material
PTFE wear, the friction coefficient is small, it can be used for oil-free lubrication.in high temperature environment.

If you need more information about our products, please contact us: system@corefrp.com ,our engineers will answer you and provide free samples.

pdfManufacturing, application and development of PTFE Teflon coated fiber glass fabric.pdf

Preparation technology of PTFE fiber

Carrier spinning method
Wet spinning
Wet spinning of PTFE usually in viscose or polyvinyl alcohol (PVA) as the carrier, mix with PTFE powder or emulsion dispersion, and add a small amount of boric acid, make spinning solution , perform wet spinning, spinning head placed in sodium sulfate and ammonium sulfate coagulation bath, dope from the nozzle in the coagulation bath solidified into fiber, fiber after leaching roller soft water leaching, again after oil roller and drying roller respectively, in 380 ~ 400 ℃ high temperature sintering, remove PVA carrier carbide, stretch to make PTFE fiber under 350 ℃. This method of spinning spend process cumbersome, high processing cost and energy consumption and time-consuming. Guo Yu-hai and others invented a highly efficient rapid method of preparation of PTFE fiber. This method will first evenly mix low relative molecular mass of volatile organic solvent with water, in under the condition of stir with PVA, continue to stir until completely dissolved, mixture of PVA water solution. Then the PVA water solution and persulfate, PTFE dispersion mixing uniformity, dope. Then borate or boric acid dissolved in water, with alkaline pH adjustment as alkaline, mixture coagulation bath. Finally adopt the wet spinning equipment of conventional , the spinning fluid conveying to the nozzle, through metering pump metering, direct spinning in the coagulation bath, then drying, sintering and stretch, the PTFE fiber is made.

Dry spinning

This method is PTFE gel realized by dry spinning. PTFE is first concentrated dispersion and PVA blended, add gel regulator boric acid or Borate salts and alkalis adjust the pH to alkaline, whisking to a sudden increase in the viscosity and gel formation, are spinning solution. And then dry them using conventional spinning equipment, gas pressure or screw spinning liquid to the spinning head, measured in metering pumps, dry spinning, and then dried, prepared mixture of PTFE and PVA fiber. Finally using conventional sintering and stretching equipment, will be mixed sintering to remove PVA fiber, finally after stretching process stretching, PTFE fiber preparation.

Carrier spinning method is the most mature method of preparing PTFE fiber, and has been one of the few companies to realize industrialization. Among them, Japan toray company USES mass fraction 60%, the average particle size was 0. 3 microns of PTFE, and the mass fraction of 2% sodium alginic acid aqueous solution of the emulsoid mixed spinning, the fiber by coagulation, bath again after washing, drying, and under 380 ℃ hot stretching, removal of alginic acid sodium, gain PTFE fiber, its monofilament linear density of 0. 67 dtex and fracture strength of l. 25 cN/dtex, elongation at break of up to 59%, the method of spinning dope spinnability better than with viscose as carrier of PTFE dope spinnability. Showa industries, the use of the 114 mass fraction of 60% PT – 100 FE dispersed emulsion and cellulose of mass fraction of 8.9% viscose spinning solution spinning, after solidification of the nascent fibers by water, squeeze liquid, with 0. 05 mol/L Na0H processing, and the fiber heat treatment under 280 ℃ and hot stretching under 320 ℃, the final heat treatment 72 h under 320 ℃, the fiber’s breaking strength for 1. 16 cN/dtex elongation at break was 16.1%. In addition, Beijing demonstration plant will be 60% mass fraction of PTFE emulsion and 10% mass fraction of PVA solution in proportion of 1:1.5 the spinning solution spinning, after solidification of the fiber by acetal, washing, drying, sintering and stretch to PTFE fiber system.

Cutting film splitting method
Cutting film crack method in the early 1970 s by the Austrian Lenzing company development and industrialization, in the preparation of PTFE fiber, need to make PTFE powder sinter cylindrical PTFE parison, cutting it up with a certain thickness of the film, and then by serrated tool divided into silk, above the melting point (327 ℃) sintering, then through stretching and end up with PTFE fiber heat treatment. This method can get the fiber with microporous structure, and high strength. Multifilament can be used as the sealing filler material, short fibers, can be used in the needle felt.

In addition, the PTFE film or sheet can also be cut into tiny width, and then direct tensile narrow fabric made of high strength PTFE fibers. But it is difficult to maintain uniform obtained by cutting along the longitudinal direction through the narrow width of the fabric, and narrow fabric tends to end part of fibril, so much stretch in narrow fabric PTFE fibers easily broken or through partial cutting in the longitudinal direction of the film are filament PTFE membrane orientation. Along the membranes of the longitudinal direction and in the transverse direction of the film with a z shape or linear-convex shape embossed and cut, the resulting filament including individual fibrils partially broken rule the network structure. PTFE fibers produced this way the individual fibrils with small average size and uniform size.

Japan Asahi of into Corporation through cutting film crack legal into has high stretch strength, and resistance chemical performance excellent of PTFE yarn. will containing hole rate 48% of PTFE film tear into 222 dtex of fiber, again on its added twist to 750 twist/m, in 440 ℃ and 1 000 m/min Xia stretch, get of fiber line density for 55 dtex, and containing hole rate 1%, modulus up to 294 cN/dtex.

Paste extrusion spinning method
Paste extrusion spinning usually PTFE powder 16% ~ 25% with mass fraction of volatile lubricants mixes, tune into a paste, made of shaped prefabricated embryos, and under certain pressure through a spinneret with a strip of die extrusion spinning, and then by drying, sintering, high stretch under high temperature, non-uniform white yarn. In addition, can also squeeze film extrusion equipment or thin strips, then by a rolling process to remove additives, and longitudinal cutting, drawing and fluffy after processing, are PTFE fibers were made by paste extrusion of thin wall, small diameter and permeability of PTFE hollow fiber. PTFE powder in conditions below its melting point made of PTFE hollow fiber, and then fired 10 min at 350 ℃, 250 ℃ under 400%, was 0.76 mm inner diameter and wall thickness of 0.10 mm, diameter of less than 0.15 mm hollow fibers.

In 1997, M. Shimizu proposes a method for preparing high strength and PTFE fibers by paste extrusion. Added to the PTFE powder mass fraction 20% of lubricants, embryo, extrusion, gained single wire, heated treatment and then 350 ℃ 1.5h, and 387 ℃ to 50 mm/min of speed stretching 10 times, received strength as much as 1.56 ~ 2.82 GPa PTFE fibers.

The PTFE powder was mixed with a lubricant (isoparaffin oil Isopar-E) to form a paste, standing at 0 ℃ 180 h at 40 ℃ cure 30 h, make the mix full wetting and swelling, then press embryo and extrusion , handle 2 h under 340 ℃, and then to 0. 5 c/min speed down to room temperature, finally stretching to get in a 370 c PTFE fiber, 3.5 ~ 4.0 cN/dtex the fracture strength, elongation at break is 22%.

Melt spinning method

Melt spinning is PTFE content to 4% ~5% of perfluorinated ethylene copolymer of perfluoro-n-propyl ether mixed spinning melt, after spinning by screw extrusion machines pump quantitative pressure injection hole, making it into a fine stream into the air, and cooling in the spinning channel into the wire. PTFE fibers high strength of this method, but PTFE supermolecular structure changes after melting, leading to its ductility disappeared and molecular chain orientation stretch is blocked, together with PTFE high viscosity and apparent flexibility, PTFE melt fiber prepared by screw extruder for direct comparison difficult, difficult to achieve industrialization. Plunger extrusion method can overcome this difficulty. The plunger in the extrusion process, due to extremely low surface energy of PTFE and wall-slip phenomenon, reduce unnecessary shear in the flow process, so they can be on PTFE melt spinning. Li Min and other person in Donghua university, are prepared by the PTFE fibre with high molecular weight. Tervoort by high relative molecular mass such as PTFE and PTFE mixed with low relative molecular mass, melt processing, preparing PTFE filament. Properties of PTFE fibers produced this way worse than that of pure PTFE fiber with high molecular weight.

Comparison of advantages and disadvantages of these different spinning methods are shown in table 1.
Table 1 Advantages and disadvantages of PTFE spinning method
Table 1

pdfThe research progress of PTFE fiber preparation technology.pdf