Unsintered Tape

Major applications of unsintered polytetrafluoroethylene are as tape in thread sealing and wrapping electrical cables, and as rod and tape in packings. Important properties of PTFE like chemical resistance, broad service temperature, low friction, flexibility, high machine direction strength, and deformability in the cross direction make unsintered fine powder PTFE ideal for these applications. 

Thread sealant tape is used in pipes and fittings in a variety of industries including water pipe, chemical, pharmaceutical, semiconductor manufacturing, food processing, and others. 

Electrical grade tape is wrapped around the cable or wire, and then the constmction is sintered to obtain good insulation and electrical properties. The same concept is applied to produce pipe liners, by tape wrapping a cylindrical mandrel. After sintering, the mandrel is removed and the liner is fitted into metal pipe casing. 

Some tape is sintered, treated to impart adherability, and then coated with pressure-sensitive adhesive for wrapping objects to reduce friction or provide quick-release properties. 

Another important area is oriented tapes and webs which are used in the fabrication of porous fiber, fabric, tube, and sheet. These porous articles find applications for protective clothing, waterproof and weatherproof fabrics, gaskets, filter bags, and many other items. 

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To produce unsintered tape by paste extmsion, the fine powder is lubricated and preformed according to the procedure described above. The preform is extmded in the form of rods, which are calendered on hot roUs to the desired width and thickness (109,110). 

Tape may be made by a similar process. In this case the lubricant selected is a non-volatile oil. The preform is placed in the extruder and a rod extruded. The rod is then passed between a pair of calender rolls at about 60-80°C. The unsintered tape is often used for lapping wire and for making lapped tube. Sintering is carried out after fabrication. The current most important application of unsintered tape is in pipe-thread sealing. 

The production of unsintered tape from extruded rod normally consists of the following sequence of operations ... 

Unsintered tape is used for sealing threads of pipes for water and other liquids. Pressure-sensitive tapes with silicone or acrylic adhesives are made from skived or cast PTFE films. 

This section discusses the fabrication of PTFE, known asfine powder or coagulated dispersion powder, into shapes and articles. The most common fabricated commercial forms include rods, tapes, wire insulation, tubing, sheeting, and other profiles. Tube diameters range from a fraction of a millimeter to almost a meter with wall thicknesses of 100 pm to a few millimeters. Rods up to 5 cm diameter can be produced and calendared, prior to sintering, to produce tapes. Unsintered tapes are broadly applied as... 

The amount of lubricant in the compound depends on the type of product, equipment design, and the desired extrusion pressure. Its content should be as low as possible but not so low that the extrusion pressure would be excessively high. A less volatile extrusion aid is often recommended for the manufacture of an unsintered tape. The range of lubricant content is 15%-25% of the total weight of the compound. 

The unsintered tape is not directly produced in the final thickness and width. Rather, it is made by the extrusion of either a round or rectangular bead (thick ribbon) followed by calendaring which converts it to a thin tape. Calendaring is necessary to obtain tapes that are thin enough to be conformable to the pipe threads. Normally, the lower limit of thickness is 50-75 pm, but 25 pm thick tape can be made by calendaring. The important properties of electri-... 

PTFE-filled unsintered tapes, which are made from a uniform dispersion of non-thermally cycled EPS milled to an average particle size of about 1 to about 20 /rm provide a good degree of flexibility and durability, when sintered. The properties are significantly better than PTFE alone, or PTFE compositions containing milled PPS, which is heat-treated prior to milling. A significant improvement in durability and insulation properties is further observed by the addition of 1 to 3% of poly(p-oxybenzoate) to the PTFE/PPS composition. " ... 

Fine Powder Resins. Fine powder PTFE resins are extremely sensitive to shear. They must be handled gendy to avoid shear, which prevents processing. However, fine powder is suitable for the manufacture of tubing and wire insulation for which compression molding is not suitable. A paste-extmsion process may be appHed to the fabrication of tubes with diameters from fractions of a millimeter to about a meter, walls from thicknesses of 100—400 )J.m, thin rods with up to 50-mm diameters, and cable sheathing. Calendering unsintered extmded soHd rods produces thread-sealant tape and gaskets. 

ASTM D6040-01 Standard Guide to Standard Test Methods for Unsintered Polytetrafluoroethylene (PTFE) Extruded Film or Tape... 

MPa. The foamed PTFE had a void content of 40%. In another experiment, an unsintered cylindrical shape (billet) of PTFE was foamed by the supercritical carbon monoxide at 325°C at a final pressure of 29 MPa. The billet was cooled to 250°C over 25 minutes before venting the CO2. Skived tape from the billet had a void content of 33%. 

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