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FEP (Fluorinated ethylene propylene), also known as polytetrafluoroethylene propylene, is the abbreviation of tetrafluoroethylene and hexafluoropropylene polymer resin. This material has a glossy surface, and its transparency varies with thickness: it is transparent when thin and becomes translucent when thickened. FEP is a thermoplastic resin manufactured using common processing techniques such as melt extrusion and forming.
In appearance and feel, FEP is similar to polyethylene, but its specific gravity is more than double that of polyethylene. In terms of performance and application, FEP is similar to polytetrafluoroethylene, but its operating temperature is about 50¡ãC lower. At the same time, FEP has higher hardness and strength than polytetrafluoroethylene. It is a standard thermoplastic.
The physical density of FEP is in the range of 2.14~2.17, and its crystallinity varies with the heat treatment temperature: the crystallinity of the quenched material is 40~50%, and after 16 hours of treatment at 246 degrees Celsius, the crystallinity will increase to 50~57%. In addition, the water absorption of FEP is less than 0.01%, and the film with a thickness of less than 0.25 mm has excellent transparency. Its refractive index is 1.338.
The material does not ignite and can prevent the spread of flames. It has excellent wear resistance and a low coefficient of friction, and can be used from low temperature to 392F. The material can be made into granular products for extrusion and molding, used as powder for fluidized bed and electrostatic coating, and can also be made into aqueous dispersions. Semi-finished products include films, plates, rods and single fibers. The FEP sold in the US market include Teflon brand of DUIPont, Neoflo brand of Daikin, and IHoustaflow brand of Hoechst Celanese. Its main uses are to make the inner lining of pipes and chemical equipment, the surface layer of rollers, and various wires and cables, such as aircraft hook lines, booster cables, alarm cables, flat cables, and oil well logging cables. FEP film has been used as a thin coating for solar collectors.
Fluorinated ethylene propylene FEP or F46 is a copolymer of tetrafluoroethylene and hexafluoropropylene, with a hexafluoropropylene content of about 15%. It is a modified material of polytetrafluoroethylene.
F-46 resin has both similar properties to polytetrafluoroethylene and good processing properties of thermoplastics. Therefore, it makes up for the difficulty of processing polytetrafluoroethylene, making it a material that replaces polytetrafluoroethylene. In the production of wires and cables, it is widely used in the insulation layer of electronic equipment transmission wires used at high temperature and high frequency, the connecting wires inside electronic computers, aerospace wires and special-purpose installation wires, oil pump cables and submersible motor winding wires.
According to processing needs, F-46 can be divided into three types: pellets, dispersions and paints. Among them, pellets can be used for molding, extrusion and injection molding according to their different melt indexes; dispersions are used for impregnation and sintering; paints are used for spraying, etc.
F-46 resin is also a fully fluorinated structure like polytetrafluoroethylene propylene. The difference is that some fluorine atoms in the main chain of polytetrafluoroethylene are replaced by trifluoromethyl (-CF3). The structural formula is as follows:
It can be seen that although F-46 resin and polytetrafluoroethylene are both composed of carbon-fluorine elements, and the carbon chain is completely surrounded by fluorine atoms, F-46 has branches and side chains on its main chain of macromolecules. This structural difference has no great influence on the upper limit of the temperature range of the material under long-term stress. The upper limit temperature of F-46 is 200¡æ, while the highest use temperature of polytetrafluoroethylene is 260¡æ. However, this structural difference makes F-46 resin have a fairly certain melting point, and it can be molded and processed by general thermoplastic processing methods, which greatly simplifies the processing technology. This is not available for polytetrafluoroethylene. This is the main purpose of modifying polytetrafluoroethylene with hexafluoropropylene.
The content of hexafluoropropylene in F-46 has a certain influence on the performance of the copolymer. The content of hexafluoropropylene in the currently produced F-46 resin is usually around 14%-25% (mass fraction).
There is currently no feasible method for determining the molecular weight of F-46 resin. However, its melt viscosity at 380¡æ is lower than that of polytetrafluoroethylene, which is 103-104Pa.s. It can be seen that the molecular weight of F-46 is much lower than that of polytetrafluoroethylene.
The melting point of F-46 varies with the composition of the copolymer. When the content of hexafluoropropylene in the copolymer increases, the melting point becomes lower. According to the results measured by differential thermal analysis, the melting point of domestic F-46 resin is mostly between 250-270¡æ, which is lower than that of polytetrafluoroethylene.
F-46 resin is a crystalline polymer with a lower crystallinity than polytetrafluoroethylene. When the F-46 melt is slowly cooled to a temperature below the crystal melting point, the macromolecules recrystallize and the crystallinity is between 50% and 60%; when the melt is rapidly cooled by quenching, the crystallinity is smaller, between 40% and 50%. The crystal structure of F-46 is a spherulite structure, and it varies with the resin, processing temperature and heat treatment method.
The electrical insulation properties of F-46 are very similar to those of polytetrafluoroethylene. Its dielectric constant is almost unchanged from deep cold to the highest operating temperature, and in a wide range from 50Hz to 1010Hz ultra-high frequency, and is very low, only about 2.1. The dielectric loss tangent changes somewhat with frequency, but not much with temperature.
The volume resistivity of F-46 resin is very high, generally greater than 1015¦¸¡¤m, and changes very little with temperature, and is not affected by water and moisture. The arc resistance is greater than 165s.
The breakdown field of F-46 increases with the reduction of thickness. When the thickness is greater than 1mm, the breakdown field strength is above 30kV/mm, but does not change with temperature.
The heat resistance of F-46 resin is second only to polytetrafluoroethylene, and can be used continuously in the temperature range of -85-+200¡æ. Even in the extreme cases of -200¡æ and +260¡æ, its performance does not deteriorate and can be used for a short time.
The thermal decomposition temperature of F-46 resin is higher than the melting point temperature. It will not decompose significantly until it is above 400¡æ. The decomposition products are mainly tetrafluoroethylene and hexafluoropropylene. Since the terminal groups usually carried by F-46 macromolecules will also decompose at temperatures above the melting point, proper ventilation must be taken into account when processing at temperatures above 300¡æ. F-46 is quite stable below the melting point temperature, but the mechanical strength loss is large at a high temperature of 200¡æ. Figure 2 shows the instantaneous change of the melt index of F-46 resin at constant temperature. The melt index indicates the number of grams of F-46 flowing through a specified aperture within 10 minutes at 372¡æ and 5000g gravity. Therefore, the increase in the melt index can be used to analyze the decrease in melt viscosity and the thermal decomposition of the copolymer. Figure 3 shows the life curve of F-46 and F-4 insulated wires compared.
F-46 is still not completely hard and brittle at -250¡æ, and still maintains a small elongation and a certain degree of flexibility, which is even better than polytetrafluoroethylene and is unmatched by all other types of plastics.
F-46 has excellent chemical stability similar to that of polytetrafluoroethylene. Except for reactions with fluorine elements, molten alkali metals and chlorine trifluoride at high temperatures, it is not corroded when in contact with other chemicals.
Compared with polytetrafluoroethylene, F-46 has slightly higher hardness and tensile strength, and a slightly larger friction coefficient than polytetrafluoroethylene. At room temperature, F-46 has good creep resistance; but when the temperature is higher than 100¡æ, the creep resistance is not as good as that of polytetrafluoroethylene.
F-46 resin has very good oxidation resistance in the atmosphere and high atmospheric stability. The radiation resistance of F-46 is better than that of polytetrafluoroethylene, but slightly inferior to that of polyethylene. In air and at room temperature, the minimum absorbed dose for F-46 to begin to change its performance is 105-106 rad?, i.e. 103-104 Gy, so it can be used as a radiation-resistant material.
F-46 has good processing performance. It can be used to coat the insulation layer of wires and cables by the usual extrusion method. In order to correctly design the extruder and mold, control and master the processing conditions of F-46 resin, the rheological properties of F-46 should be understood first. The relationship between shear stress and shear rate of F-46 at 390¡æ. Its viscosity ¦ÌA decreases with increasing shear rate. The critical shear rate of F-46, if the shear rate exceeds this value, will cause the plastic to flow unevenly, resulting in a rough, dull and layered surface of the product. The critical shear rate value of F-46 is very different from that of polyethylene and nylon, so the problem of melt fracture is particularly serious.
F-46 resin has two characteristics in processing, namely, it has a tendency to melt fracture and has a very high stretchability in the molten state. In order to eliminate or improve melt fracture and improve productivity in the production of wires and cables, the following measures are usually taken: First, use an extrusion tube die and expand the opening of the die to slow down the flow rate of the polymer at the die mouth, so that the resin can be extruded at a moderate extrusion speed below the critical shear rate and improve productivity; second, without causing the resin to decompose, the temperature of the molten resin is increased as much as possible to reduce the viscosity of the resin, thereby increasing its critical shear rate.
F-46 extruders generally use single-head full-thread, equidistant, sudden compression screws. In order to ensure the full plasticization of F-46 resin, the length of the homogenization zone of the screw usually accounts for about 25% of the total length of the screw; the top of the screw is conical to prevent stagnation and decomposition of the resin.
The main technical parameters of the screw are as follows:
L/D ratio 20 Pitch 1D
Feeding zone length 15.5D Compression zone length 0.5D
Homogenizing zone length 4D Thread width 0.1D
Feeding zone thread groove depth?h1 1/6D
Homogenizing zone thread groove depth?h2 1/18D
Compression ratio?h1/h2 3
1) Feeding: Before extruding F-46, it is advisable to pre-bake it at 120¡æ for about 3h.
2) Preheating of conductive wire core: In order to ensure the uniform temperature of the inner and outer layers of the extruded F-46 insulation layer, the conductive wire core should be preheated to 300-350¡æ.
3) Temperature distribution of extruder: Generally, the temperature distribution of extruder is better to rise linearly from 280¡æ (feed port) to 380¡æ (die head); the temperature fluctuation range of die head is not more than ¡À5¡æ, and the temperature of die head should be increased as much as possible without causing resin decomposition to reduce the melt viscosity of resin. The reference temperature of extruder body (from feed port to die head), die head and die sleeve is as follows:
The first section of the body is 280-310¡æ, the second section is 315-330¡æ
The third section is 340-360¡æ, the fourth section is 360-380¡æ
The die head is 380¡æ, and the die sleeve is 380-410¡æ
4) Stretch ratio of die sleeve: It is better to choose within the range of 50-200.
5) Screw speed: After adjusting the screw speed with the coordinated temperature, do not change it frequently during the extrusion process of F-46 resin. If necessary, it can be slightly adjusted. The screw speed should vary with the size of the conductive wire core cross section, generally 5-15r/min.
6) Mold die insulation: The insulation area should cover the entire stretching area, and the insulation temperature should be 350-380¡æ to avoid the formation of stress due to sudden cooling of the surface of the F-46 cone before molding, which will cause insulation cracking.
7) Cooling of insulated wires: The wires extruded from the extruder are water-cooled. The distance between the die and the water tank should be close, and it is recommended not to exceed 20cm.
8) Set up a filter. In order to improve the plasticization and mixing quality of F-46 resin and increase the back pressure, 2-3 layers of filter screens should be added to the end of the extruder screw.
9) Each batch of F-46 materials should strive to extrude in the best condition to ensure good plasticization, transparent cone, no bubbles, smooth surface, and no "eye mucus" between the cone and the die sleeve. Each batch of materials should be well recorded in the process to accumulate information and process data, which is conducive to quality analysis.
When the resin quality of F-46 insulated wire is poor and the extrusion process is improper, the insulation layer will crack. The main reasons are:
(a) The insulation layer has internal stress. There are many reasons for the production of internal stress, such as poor plasticization caused by uneven resin composition during processing and improper processing technology.
(b) There are few molecular chains connecting the interface between large spherulites and lamellar crystals in the insulation, or the spherulites are too large and fragile
(c) Chain breaking of macromolecules produced by unstable groups
(d) The molecular weight of the resin is too small or the distribution is too wide, which reduces the strength of the material.
(e) The content of hexafluoropropylene is too low and the composition distribution is uneven.
FEP resin has similar properties to polytetrafluoroethylene and has the good processing technology of thermoplastics, making it an important material to replace polytetrafluoroethylene. F-46 is widely used in the production of wires and cables for electronic equipment transmission lines used at high temperatures and high frequencies, connecting lines inside electronic computers, aerospace wires, and other special-purpose installation lines, oil and mine logging cables, submersible motor winding wires, micromotor lead wires, etc.
FEP: (front-end-processor) front-end processor. It is set between the central computer and the communication line and is responsible for communication control.
From the computer, FEP receives data in packets. The header part of the packet is not generated for encryption/decryption. The front-end processing transmits the encrypted information to the network layer, or receives information from the network layer. Forefront Endpoint Protection (FEP)
The predecessor of FEP 2010 is Forefront Client Security, which is a paid product, but Microsoft has provided a free trial version. FEP 2010 can simplify and improve endpoint protection while significantly reducing infrastructure costs. It is based on System Center Configuration Manager 2007 R2 and R3, allowing customers to use their existing client management infrastructure to deploy and manage endpoint protection. This shared infrastructure reduces the cost of ownership while providing greater visibility and control over endpoint management and security.
FEP 2010 is suitable for all types of businesses, from small businesses to large enterprises.
Microsoft Forefront Endpoint Protection
An enterprise-class antivirus software from Microsoft. Forefront Endpoint Protection 2010 (FEP) is the next generation version of Forefront Client Security, which simplifies and improves the protection capabilities of enterprise endpoints (clients and servers) while greatly reducing the cost of basic deployment and implementation. It must be deployed on System Center Configuration Manager 2007 R2, allowing administrators to use existing client management infrastructure to deploy and manage FEP. This common shared infrastructure reduces the cost of ownership while providing a more comprehensive management mechanism for endpoint security.
Free erythrocyte protoporphyrin (FEP)
During the synthesis of hemoglobin, protoporphyrin and iron form heme under the action of iron complexing enzyme. When iron is deficient, protoporphyrin and iron cannot combine to form heme, resulting in an increase in free protoporphyrin (FEP) in red blood cells, or the formation of zinc protoporphyrin (zonic protoporphyrin) under the action of complexing enzyme
¢ÙMale: 0.56¡«1.00¦Ìmol/L. ¢ÚFemale: 0.68¡«1.32¦Ìmol/L.
1. Increased FEP Increased FEP is common in iron deficiency anemia, sideroblastic anemia, paroxysmal nocturnal hemoglobinuria (PNH) and lead poisoning. For the diagnosis of iron deficiency, the FEP/Hb ratio is more sensitive.
2. Decreased FEP is common in megaloblastic anemia, pernicious anemia and hemoglobinopathy.
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