How to convert Tyvek
3. How to convert Tyvek®
Tyvekwill stretch up to 30% before breaking. To minimize distortion or neck down during roll fed converting, keep tension less than 1.4N/cm (0.75 pounds/inch). This is especially important when die cutting Tyvekbusiness forms with rotary punched sprocket holes. Tyvekcan be converted in much the same way as paper or plastic films and using the same equipment.
3.2 Slitting, sheeting, cutting
Because Tyvekfibres are very strong, each must be completely severed; hangers will not break off. Knives, dies and punches must be set to close tolerances. A sharp, slightly rounded edge gives longer service than a pointed edge for crush cutting, but a sharp edge is preferred for other slitting methods.
3.3 Rotary die punching
Because soft steel male/female rotary dies dull quickly when set to the close tolerances required to punch Tyvekcleanly, the use of rotary dies made of hardened tool steel or tungsten carbide is recommended.
3.4 Die cutting
Tyvekcan be die-cut using either steel rule, male/female or closed dies. Tyvekfibres must be completely cut and dies must be in good condition with sharp, nick-free edges. Dull dies cause edges to curl. When using closed dies, the use of a side cutter with internal relief is recommended. De-aerate and keep lift height below 7.2cm (3 inches) when die cutting to avoid oversizing top blanks.
Tyvekcan be punched on tag, letterpress and rotary line-hole equipment. Best results are obtained from sharp, well registered and close fitting punches. Punches may be either smooth or serrated and cut best if ground concave on the ends. A soft self-honing male punch in a hardened female die is recommended.
Tyvekwill take a dead fold and can be folded on conventional bindery folders. An increase in roller and spring tension will produce sharper creases. Due to the inherent slippery surface of Tyvek, soft, rubber-covered rollers will aid feeding.
To make clean tearing perforations a 10:1 cut to reserve ratio is recommended, e.g. 8.0 mm cut: 0.8 mm reserve (5/16 in.: 1/32 in.). Tear initiation can be assured by positioning a cut at the edge of the sheet.
Tyvekcan be embossed with either high or low pressure equipment. Cold embossing does not significantly reduce the strength of Tyvek. It does, however, reduce opacity. Embossing cylinders used for Tyvekusually are very shallow, having a depth of only 0.13-0.65 mm (5-25
mils). A shore “D” hardness of 70-80 for the rubber backup cylinder is preferred.
3.9 Hot Foil Stamping
This is readily accomplished on Tyvekdue to its thermoplastic nature. A variety of foils is available from suppliers for label and book cover applications. A foil that will transfer cleanly to Tyvekbetween 135 -160°C should be chosen. Large, solid foil-stamped areas tend to pucker and distort Tyvekand should be avoided. To avoid pucker and distortion, Tyvek105g/m2 or selfadhesive coated Tyvekis recommended.
Conventional textile dyeing processes do not impart permanent colour to Tyvek. However, Tyvekcan be printed on by flexographic or gravure processes.
Tyvekcan be extrusion-, adhesive-, flame-, ultrasonic-, thermal- and calender laminated. Extruded low density polyethylene (LDPE) is an excellent adhesive for laminating foil and film to Tyvek. Polyurethane adhesives can be used to adhere a variety of films and fabrics to Tyvek. When laminating Tyvek to paper or board, it is important to completely cover Tyvekwith adhesive to prevent bubble formation. Polyurethane adhesives or Hotmelt (Euromelt 772 from Henkel or Lunamelt KC2010 from H.B.Fuller) are recommended. Recycled board is not recommended, since the board can contain remaining solvents or binders, which can cause bubble formation.
Coatings are used to colour, improve print fidelity, add gloss or mask the fibre pattern in Tyvek. Air-knife coating is preferred for aqueous coating because it applies a uniform thickness. Usually an increase in binder content is needed to achieve acceptable coating adhesion to Tyvek. The air knife also produces a very smooth surface which is ideal for printing. Gravure coating is preferred for solvent-based systems, particularly where deep coloration is required. Tyvekcan be extrusion coated using special polymers. When coating or laminating Tyvek, the web temperature should not exceed 80°C.
3.13 Heat Sealing, Dielectric Sealing, Ultrasonic Sealing
High seal strength can be achieved using hot-bar or impulse techniques sealing directly on Tyvek.Heat sealing Tyvekto itself or other films is usually accomplished by applying a heat seal coating such as branched (low density) polyethylene (LDPE) to one of the materials. Tyvekcannot be dielectrically sealed under ordinary conditions because it is non-polar. Ultrasonic sealing can be used to create fiber tearing seals with most of Tyvekstyles and without the puckering that is often associated with heat seals.
Natural product adhesives based on dextrin, casein or animal by-products can be used to adhere Tyvek®to itself and a variety of paper materials. Water based synthetic lattices such as the ethylene/vinyl acetate adhesives form fibre tearing bonds with Tyvek. Hot melt polyamide adhesives are available which form good bonds to Tyvekwith a variety of materials. Acrylic pressure sensitive adhesives are commonly used with a release liner. Please refer to the solvents list on table 3 before using your adhesive. Some of the components may interact with Tyvek.
Tyvekcan be sewn on conventional sewing machines. Best results are obtained with machines equipped with puller or drop-feed. Smooth, rubber covered rolls should be used rather than knurled metal rolls, which tend to leave impressions on Tyvek. When stitching Tyvek, lowest possible stitch frequency (2-3 stitches/cm with low tension) and the smallest needle practical should be used. The needle should have a flat point to produce perforating slits. It can be recommended to use chain and aligned stitches, especially 2,5 cm chain stitch.
3.16 Converting tips for continuous business forms
Tyvekis more elastic than paper and tends to stretch under tension but recovers after perforating punching. Tension has to be controlled so that perforation is according to DIN 6771. The following qualities are recommended for business forms: 1057D (55 g/m2) 1073D (75 g/m2) 1082D (105 g/m2)
As the machine speed increases, the tension adjustment decreases. If the hole distance is short, at a particular tension (i.d. at 100 m/mn), it will be shorter at 300 m/mn.
Best results are obtained with sharp, well registered and closely fit punches.
Rotary sprocket punching
Rotary sprocket punching of Tyvekshould be done with male-female dies made from hardened tool steel or tungsten carbide.
To make clean tearing perforation, use the maximum practical number of cuts with the smallest land between them and a 10 to 1 ratio. Tear initiation can be assured by positioning a cut across the edge of the sheet.
Please refer to printing sections in this brochure. DuPont is committed to the efficient and safe handling of plastics waste and advocates a resource optimisation and waste management system with the following priorities:
1. Resource minimisation
3. Recover energy
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