Properties of ptfe film and its composite fabric process

Ptfe films are prepared by biaxial tensile method. Scanning electron microscope can observe that the films are made of crisscrossing fiber filaments connected with each other, and the gaps between fiber filaments form microholes in the films.

 

There are many micropores on the surface of the film, about 9 billion micropores per square inch, and the micropores are mainly distributed in the diameter of 0.8~1 micron. The minimum pore diameter of thin film micropores is only about 0.6 micron, while the maximum pore diameter is about 1.6 micron, and the diameter of water vapor is 0.0004 micron. Thus, water vapor molecules can easily penetrate the pores, allowing the membrane to function as a moisture permeator. The smallest liquid you can get your hands on is light fog, with droplets 20 microns in diameter. Therefore, the membrane also has the function of waterproof. The moisture permeability of ptfe film is 8450g/m2·24h, which is much higher than that of 3000g/m2·24h when human body feels comfortable. At the same time, the ptfe film also has good wind resistance. When the wind pressure rises to the equivalent of wind pressure of level 10, the permeability of the film is 28.85mm/s, while when the permeability exceeds 30mm /s, the film loses its wind resistance.

 

Polyamide (COPA) hot melt adhesive as the adhesive, the use of flat vulcanizing machine will be fabric, hot melt adhesive, ptfe film, hot melt adhesive, lining five layers by hot pressing made of waterproof and permeable laminated fabric. Orthogonal tests of nine laminating processes with four factors and three levels were carried out. Under the condition of nine kinds of technology of laminated fabric including moisture permeability, peel strength, high hydrostatic pressure and permeability test, finally USES the grey nearly optimal theory to deal with data process 2 for the optimal process, namely between the fabric and ptfe film gluing quantity to 12 g/m2, the material between the membrane and the amount of glue is 24 g/m2, laminating temperature is 140 ℃, laminated time of 10 s, to achieve the optimal performance of the laminated fabric.

 

The properties of laminated fabrics made of four kinds of different fabrics are compared. It is found that the three most important properties of the composite fabrics, namely moisture permeability, heat preservation and peeling strength, are superior. Therefore, it is more ideal to choose brocade and cotton interweave as the layer of waterproof and moisture permeable laminated fabric. In the use of water-soluble adhesive, the surface of the material wetting, and other substances between the bond strength.

 

In order to further improve the peeling strength of laminated fabric, ptfe film was treated with hydrophilic modification. In the process of modification, 1ml Fe Cl3 solution was used to prepare Fe(OH)3 colloid, which had the best treatment effect on the film. The optimal solution for the  ptfe film repolymerization of hydrophilic monomer acrylic acid adsorbed with Fe(OH)3 colloid is A3B2C1D2, that is, the polymerization temperature is 70℃, the acrylic monomer concentration is 20%, the polymerization time is 20min, and the initiator dosage is 1%.In addition to a slight decrease in moisture permeability, hydrostatic pressure resistance and permeability rate, the peel strength value of the laminated fabric after modification was greatly improved and reached the enterprise standard of 5N/2.5cm.

 

Effect of PTFE on Properties of PE-UHMW

 

In order to obtain ultra high molecular weight polyethylene (PE-UHMW) matrix composites which get high wearresistance and high heat resistance , and the poly tetrafluorethylene (PTFE) was modifed to improve the wear resistance and heatresistance of PE-UHMW. The test results show that the Shore hardness of the composite reach the highest that is 67.08, and thewear resistance is the best when the mass fraction of PTFE is 5%, the friction coeficient to 15CrMoV steel is 0.235 and the wearrate is 0.081 4%, and the thermal deformation temperature of the composite is increased by 21% when the load is 10.0 N and thedeformation amount is 0.06 mm. Under the action of KH-~550 coupling agent, the PTFE can achieves a uniform distribution in the PE-UHMW matrix, and the formation of dense binding. With the increase of PTFE content, the creep of the composites is graduallyincreased.

 

Since its inception, ultra-high molecular weight polyethylene (PE-UHMW) has been widely used in mechanical textile, medicine and other fields with its excellent physical and mechanical properties, becoming an engineering plastic that can replace metal materials. PE-UHMW has good impact resistance, wear resistance, chemical corrosion resistance, self-lubrication and other properties. However, PE-UHMW's low hardness and thermal deformation temperature defects cannot meet some high requirements of field applications. At present, modification methods of PE-UHMW mainly focus on chemical modification and physical modification. People often add organic and inorganic particles or fibers to PE-UHMW to improve its performance. By contrast, organic modifiers are easier to form firm bonds with PE-UHMW molecular chains.

 

Polytetrafluoroethylene (PTFE) holds the title of "the king of plastic, PTFE, with its excellent corrosion resistance, wear resistance, low friction coefficient, is only 1/5 of the polyethylene, between 0.01 ~ 0.10, as additives to improve the PE-UHMW abrasion resistance and heat resistance. It has obvious effect, Fang Zheng equality of polyoxymethylene, polyamide, PTFE linear low density polyethylene (PE-LLD) such as blending modification, the results found that Adding appropriate amount of modified PTFE can significantly improve the compatibility between PTFE and polymer. When PE-LLD is modified with PTFE, the mechanical properties, processing properties and stability of composites are greatly improved, and the friction coefficient is significantly reduced. PTFE was selected to blend and modify PE-UHMW in order to prepare composites with excellent wear resistance and heat resistance, reduce the friction coefficient of PE-UHMW and expand its application field.

 

Study on Sintering of Ptfe

 

From the perspective of the three factors that determine the properties of PTFE products -- molecular weight, crystallinity and voidage, the voidage is mainly affected by the preforming pressure, and the molecular weight and crystallinity all change with the different sintering conditions. Therefore, sintering process conditions play a decisive role in the final properties of products such as density, hardness, permeability and mechanical properties.

 

Wang ping found that the sintering process of PTFE was affected by the rising and falling speed, sintering temperature and sintering time. The larger the product, the slower the speed of rising and cooling, the longer the sintering time. The sintering temperature of suspension resin is higher than that of dispersion resin. The sintering temperature of pure material products is higher than that of filled products. In general, the rate of warming is faster than the rate of cooling. In the same sintering furnace, pure material and filling products cannot be mixed; Products with different sintering conditions cannot be mixed. Products of different raw materials cannot be mixed. Taking the production of 3-layer molded circular plate with diameter of 1 m, thickness of 20 mm, double layer as pure ptfe and middle layer as filled ptfe as an example, the compression strength, bending strength, hardness and other mechanical properties of the circular laminated plate produced by this technology have been greatly improved.

 

Liu xianlan studied the forming process characteristics, forming method and mold design characteristics of PTFE, analyzed the defects and causes of PTFE products produced by cold pressing and sintering, and put forward the treatment methods. PTFE can be molded by a variety of preforming processes, such as molding, extrusion, hydraulic molding, push molding and secondary processing, and then sintered to the final product.PTFE molding is mostly made of suspended resin. When the thickness of sheet is less than 1.5mm, disperse resin is used. Its technological process: resin - sieve (suspension resin after pounding, loose, and the 20 mesh mesh sieve) - press (PTFE powder loading the mould under pressure from 20 to 35 MPa, after press compaction forming) - sintering (in 370 ~ 380 "C temperature sintering in sintering furnace) - moulded products (under free state within the mold or after cooling to finalize the design as required by the board, rods, tubes, gaskets and packing products, etc.).Hydraulic method is also called the equilibrium method or rubber molding in its operating process is: put rubber bag in die - connected to the water pump, filling the water swell the rubber bag into a cylindrical - resin evenly join between bag and external mold mold closing - continue to gradually increase the water pressure, water filling up to 12 ~ 13 mpa pressure maintaining 30 min: after water - decompression, ripping, sintering, cooling is the use of bright and clean appearance. Push is also called the paste extrusion molding, 20 ~ 30 mesh sieve dispersion resin and organic liquid (such as toluene, petroleum ether, the solvent oil) mixture 1:5 paste mixture, preloading into thick wall cylinder billet, push into the compressor cylinder, heating, with a plunger push molding, after drying in the 360 ~ 380 ° C temperature sintering, after cooling products have strong push tube, rod, etc.Extrusion molding can be divided into two types: screw extrusion and plunger extrusion. The pre-sintered resin after crushing and sifted is added to the material cylinder. Through screw rotation or reciprocating push of plunger, the raw material is transported to the extruder at the same time of compaction.

 

Wang ping studied the forming process of PTFE foam material. Suspended polytetrafluoroethylene is used as raw material, and condensed cyclic aromatic hydrocarbons are selected as pore-forming agent. After mixing, preforming products are preformed and sintered. At the initial stage of sintering, drying process is adopted to make pore-forming agent escape, and then resintering stage is entered. Foam materials with different dielectric constants can be prepared in different proportions to meet various requirements.

 

Chen xu et al. conducted compression test and sintering test on PTFE, discussed the relationship between density, compression strength and compression modulus, and analyzed the compression strength of specimens under different sintering processes, and obtained more appropriate molding pressure and sintering process. The results showed that the compression strength of PTFE decreased with the increase of pressing pressure, and the compression modulus increased with the increase of pressing pressure. The molding pressure was 27.5mpa, sintering temperature was 380 C, and the insulation time was 4h.

 

In order to overcome the disadvantages of pure ptfe, such as poor abrasion resistance and large thermal expansion coefficient, Raytheon studied the bronze-filled particles in ptfe, and expanded the application scope of ptfe. The conventional warm pressing molding of ptfe is characterized by long cycle, poor performance, low dimensional accuracy and smoothness, while the warm pressing molding in this study has fewer working procedures, short cycle and significantly improved mechanical properties.

 

Properties of molded products

Molded products have excellent electrical properties (especially anti-leakage properties), mechanical properties, heat resistance, fire resistance, chemical corrosion resistance and dimensional stability, and can be adjusted according to the needs of each component type and dosage to obtain products with special performance requirements. The main performance is as follows：

1.Electrical property

Molded plastics are widely used in high voltage electrical applications due to their arc resistance, acer performance, flame resistance, dimensional stability, moulding and low cost. The ability of arc suppression is mainly due to the presence of inert inorganic fillers such as hydrated alumina, silica and ceramic. Add a small amount of polyethylene powder (5% by weight) and use nylon fiber to improve arc resistance. In order to obtain better arc resistance, the resin and glass fiber content should be reduced to the minimum, however, such results reduce the mechanical properties.

2. Mechanical property

The mechanical properties of molding materials vary with the types and proportions of reinforced fibers and resin substrates used. In DMC, when the fiber length exceeds 6.35mm, the modification of product properties is very small.

Most SMC products are made from short-cut felt, and there is no published data on the effect of fiber length changes. Although the length of the general fiber is 50mm, this length is not necessarily suitable for all applications.

Increasing the content of reinforcing materials can improve the mechanical properties, but too much fiber content will bring inconvenience to molding. For example, when the fiber content in DMC exceeds 20%, it has little influence on its mechanical properties.

3. Heat resistance or fire resistance

Heat resistance refers to the ability of products to withstand thermal decomposition for long periods of time below the flammable temperature. "Short-term thermal strength" or "thermal strength" is related to the thermal deformation temperature of the resin. Although some fillers can improve the heat resistance of products, the heat resistance and thermal strength mainly depend on the properties of the resin. Flammability is a measure of apparent combustion, divided into "non-ignition", "self-extinguishing" and "flame-retardant" according to the ability and speed with which a material is able to extinguish easily or when the ignition source is removed. Polyester resins achieve flame resistance by adding halogen and phosphorous compounds and by using alumina hydrate as the main filler in the components.

Phenolic resins are inherently fire-resistant. Halogen compounds and phosphorous compounds, as well as HET anhydride used as hardener, can make epoxy resins flame resistant.

4.Dimensional stability

General molding materials have good dimensional stability, water absorption rate: small, thermal expansion coefficient and aluminum is very similar, when continuous exposure to high temperature, size is almost no change.

5. Corrosion resistance

The chemical resistance or corrosion resistance of molding material mainly depends on the selected resin matrix. The suitable resin and filler can be used to prepare the moulded material which can meet the requirement of resisting special bristle dew

DMC can be made of acid-resistant and alkali-resistant ligulates and acid-resistant epoxy resins. The choice of a resin for SMC is currently limited because the resin must also have a chemical structure that thickens easily. In common fillers, clay and silica have better corrosion resistance and other properties.

6.Contractility

 The shrinkage of moulded material is very low after release, the typical maximum shrinkage rate is 0.004, and the shrinkage rate of many moulded materials is close to 0.001, which is mainly due to the small thermal shrinkage of glass fiber and inorganic filler. However, the combination of low-shrinkage, high-strength fibers with the resin systems commonly used for rapid curing and high thermal shrinkage results in greater stress on the resin matrix between the fibers. The collateral effects of this stress cause surface ripples, cracks, warping, and internal voids. These defects can be reduced by the use of organic fiber reinforced materials compatible with resin shrinkage or by the use of short or filamentous glass fibers.

 

 

 

 

 

An sintering oven used for producing ptfe

A used in the production of teflon sintering oven, drying oven, including housing, the top surface of box body is set with solar tank and vent, solar-thermal box right side set solar monitoring device, before the end of box set oven door, the right side of box body is provided with electric control cabinet, electric control cabinet set a timing device, temperature control device, inlet valve, exhaust valve and switch button, box body including shell and inner cavity, and setting of between shell and inner cavity has a heat preservation cotton, inner chamber set on two cooling board, two fans and purification device, casing set inside the rack and put tray, put aside content disc set for both have cooling hole, The bottom center of the shelf plate is provided with a connecting disk. The utility model has a simple structure and strong practicability. 

Through the combined heating method of solar energy and electric energy, not only the styling effect is improved, but also the service life is extended, the yield rate is increased, the energy consumption is reduced, the cost is saved, and the comprehensive utilization efficiency is improved.

Sintering oven used in the production of ptfe, whose character is: the Sintering oven including enclosure, as described in the top surface of box body is set with solar tank and vent, solar-thermal box right side set solar monitoring device, in the right side of the hole is located in the solar energy collection hot box, the box body front end face of the oven door, oven door includes the first oven door and the oven door and the oven door and described the oven door all set door the mouth and observation, the right side of box body is provided with electric control cabinet, electric control cabinet set timing device, temperature control device, Air intake valve and exhaust valve and switch button, temperature control device is set on the first heating button and the second heating button, switch the power button, button, and explosion-proof fan button button, box includes shell and inner cavity, with mentioned lumen between shell and a heat preservation cotton, inner chamber set on two cooling board, two fans and purification device, both on the heating panel Settings have mica heat sink, purification plant is located in between two mentioned fan, box set inside the rack and put tray, the bottom of the rack set wheels, put aside content disc set for both have cooling hole, Plate center set up at the bottom of the shelf are connecting disk, disk and a partition at connections, on the other side of the baffle plate and described shelf plate connected, put aside material plate is divided into four equal, connecting the center of the disk set has a hole, the bottom of the box body set with wheel groove HeJinKong, wheel to match the wheel groove and the stated, air inlet connected with the outside world.