This versatile material is used in many ways in heatsealing set-ups. It is sometimes used beneath the heatseal band on the heatseal jaw face. When 3 mil Cover Strip (See Anti-Stick Provisionsis) is used, it has the advantage of providing marginally adequate electrical insulation and little thermal insulation.
This is good when rapid cooling is needed as in high speed automatic machines. It must, however, be replaced frequently to assure that it is not worn through so as to allow the heatseal band to become grounded to the jaw. Other materials are safer and more durable for this application.
Anti-Stick Provisions - Keep the hot plastic from sticking.
When making heat seals on plastic materials the softened plastic will tend to adhere to the heated seal bar or platen. This can damage the seal, foul the seal bar, and prevent the material from moving freely through the machine. It is therefore necessary to provide a means of assuring the release of the material from the heatseal jaw bar after sealing.
There are various means of achieving a satisfactory release of the plastic material after sealing; PTFE- tape to cover the heatseal band, a PTFE- coating on the band itself, or other proprietary coatings, together with precise time and temperature control.
PTFE- Impregnated Fiberglass Tape
Commonly called "PTFE-Tape" is primarily used as a covering over heatseal bands to prevent the hot plastic material from sticking to the band as well as over the silicone elastomers on the opposite jaw. It is also occasionally used as an electrical insulator between the heatseal band and the jaw when a minimum thermal insulation is desired. The proper selection of thickness and style is imperative if good consistent seals are to be obtained.
After quality, thickness is the most important consideration in selecting a "PTFE-Tape" for heatsealing applications. Although the tapes are available in thicknesses of 3 to 10 mil (.003" to .010") the most popular thicknesses for heatseal applications are 3, 5 and 6 mil. Thin material, 3 mil, has the advantage of permitting the heat to flow faster from the heatseal band through the tape and into the plastic material to be sealed; thus reducing sealing time and permitting higher production rates. The use of thick tapes to cover the heatseal band is undesirable because heatseal band temperatures must be increased by as much as 50°C to compensate for the insulating affect of the tape. A 5 mil, self adhesive tape is appropriate for covering the silicone elastomer that is mounted on the jaw face opposite the heatseal band. It is true that thin tapes must be replaced more frequently, but when thick tapes are used, the heatseal bands must be replaced more frequently because it must be operated at elevated temperatures for a prolonged heating cycle to allow for the slower heat flow through the tape in both heating and cooling.
PTFE- tapes can be supplied in virtually any width, but standard sizes are more readily available. When determining width it is important to allow an adequate width of tape that is not adhesive coated in the zone that comes in contact with the heatseal band. Adhesive in contact with the heatseal band impedes free movement, as the band expands and contracts with temperature change. This can cause the heatseal band to buckle or distort or cause the tape to wrinkle. Either way, the quality of the heatseal is adversely affected. For these reasons, PTFE- tapes are offered in several styles.
For heat sealing applications, standard grade is commonly used; however, Premium grade is available in most configurations. Premium grade (Grade A) is made with a heavier coating of PTFE- which produces a smoother surface and better release characteristics at the expense of slightly slower heat transfer. A 5 mil, premium grade, self-adhesive PTFE- tape is a good selection for covering the elastomers on a heat seal jaw. Premium grade 3 mil, cover strip, is the best selection for covering heatseal bands.
PTFE- Cloth ( non-adhesive)
This material is most commonly used to cover special profile bands and platens or irregular shapes where a self adhesive (pressure sensitive) tape cannot be used because of adhesive contact with the heatseal band or other adhesive free surface.
S/A Tape( self-adhesive)
Provided with about 1.5 mils of silicone adhesive on the back, these tapes are used for covering the opposing, unheated, jaw and for various general purposes such as covering machine surfaces, for example; formers, to reduce friction or silicone elastomers for anti-stick purposes. 3 to 6 mil tapes of premium grade are usually best in these applications.
This is a composite tape made up of cloth tape to which a paper or glass filament adhesive strips have been adhered along the edges. The adhesive strips are covered with a peel-able backing strip. Supplied routinely in premium grade of 3 and 5 mil, with adhesive strips extending 12 mm beyond the edges of the PTFE- cloth. This KB tape can be supplied slit to the customer specifications. The effective width of KB tape is the distance between the inside edges of the adhesive strips, and must be specified when ordering.
Available in premium grade of any width greater than 40 mm, and any thickness, this tape is PTFE- cloth strip to which a 12 mm wide strip of double back adhesive has been adhered along each edge. Excellent for demanding applications where additional holding power is needed or for uneven surfaces where the thicker adhesive layer can conform to the surface. The effective width is always 24 mm less than the full width of the PTFE- cloth strip.
This most popular tape has an adhesive free strip down the center. It is excellent in the 3 mil thickness as an anti-stick cover for heatseal bands because it allows free movement of the band while it is expanding and contracting. It is also valuable on long jaws as a means of holding the heatseal band in position without the contamination of the adhesive in contact with the band. Cover strip is premium grade plain PTFE- cloth tape to which a specific width of silicone adhesive has been applied along the edges. The uncoated zone, effective width, can be as narrow as 10 mm and the adhesive width can be as wide or as narrow as needed. The adhesive has adequate adherence and strips away clean when removed for replacement. This style has found numerous applications where configurations or space limitations demand a tape that is specially designed to fit. The most common size is 3 mil, 35 mm wide with 12mm adhesive free in the center.
PTFE- and other Coating
Surface coatings can be applied directly to the heatseal bands as a means of producing an anti-stick surface. PTFE- coatings come in a variety of compositions, some with fillers such as Silverstone. Direct coating of heatseal bands produces a very effective band with minimal heat loss through the coating, however, the coatings are not hard and the anti-stick quality of the coating may not last too long. Care must be exercised to assure that the band temperature does not exceed the limits of the coating. The upper temperature limit for safe operation with PTFE- coatings is 250°C, as with all PTFE- products.
Release Agent Anti stick spray
RH-200 - Is a sliding agent especially produced for PVC foil, and Silicone profiles, etc.- Food safe lubricant, does run, effective up to +200°C