Your applications have never been in better shape.
DuPontTM Tyvek® can easily be used in place of other materials for converting. Whether you produce tags and labels, or maps and banners, or documents and envelopes, Tyvek® adds strength, durability and long life to virtually every application.
And while Tyvek® is processed in much the same way as paper or plastic films and on the same equipment, it does require different handling techniques for optimum results. For this reason, we strongly recommend that those who have never worked with Tyvek® conduct a pilot run to fully test each conversion operation before beginning full-scale production. Here are a few tips to keep in mind:
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- Tyvek® cannot be crush-cut as easily as paper. Its filaments are very strong and each must be completely severed; “hangers” will not break off.
- Tyvek® elongates more than paper and will stretch up to 15% to 25% before breaking.
To minimize distortion or neck-down, keep web tension as low as practical—0.75 lb/lineal in (1.4 N/cm)—during processing.
- Tyvek® is a thermoplastic material and it melts sharply at 275°F (135°C).
- When coating or laminating Tyvek®, the web temperature in the oven should not exceed 175°F (79°C).
- Because of its inherent “memory,” Tyvek® may occasionally curl when sheeted. Conventional decurler (breaker bar) equipment can be used at minimum tension.
- Before binding Tyvek® with printed paper, check compatibility because it may buckle or distort. Many publications contain residual solvents that can also cause distortion. When bound along the spine, paper will respond to changes in humidity. Tyvek® won’t. This usually produces a buckled appearance along the spine of the publication.
- Type 10 styles with a “D” suffix (e.g., 1073D) and Tyvek® 1079 are treated with an antistatic agent to reduce static during sheet handling operations. Antistatic agents function best at a relative humidity of 50% or more. Below 20% relative humidity, antistatic agents lose their effectiveness and sheet feeding will become noticeably difficult. These styles have also been treated by corona discharge to improve adhesion of inks, coatings and adhesives. Type 14 styles with an “R” suffix (e.g., 1443R) are treated in a like manner. Tyvek® styles with a “B” suffix (1059B) do not contain an antistatic agent. These styles can build a static charge and should not be handled in areas where the potential for explosive vapor/air mixtures exists.
- Die-cutting lubricants should be avoided because some contain low molecular weight hydrocarbons that can cause swelling and distortion.
SLITTING, SHEETING AND CUTTING
Tyvek® hard structure (Type 10) styles can be slit and cut into sheets on most commercial equipment using conventional paper-cutting techniques. However, the inherent strength of the material requires that all cutting parts be kept clean and sharp, with true, well-supported, nickfree edges. 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.
Multiple roll sheeting (four to six rolls) works well and is preferred for the lightweight styles (less than 2.2 oz/yd2 [76.3 g/m2]).
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| The microfiber technology of DuPont™ Tyvek® used for graphics applications offers high-strength, durability and opacity resulting in the best characteristics of paper, film and fabric in one substrate. (Shown 200 times.) |
In sheeting operations, best results are obtained by using styles with a “D" suffix. These are treated with an antistatic agent to reduce static during sheeting. When it is necessary to sheet non-antistatic styles, the use of conductive “tinsel” or ionized air produced by an electrostatic generator or a radiation bar, will usually reduce the build up of static. Antistatic agents or aerosol sprays should not be used on Tyvek® 1059B that will then be used for packaging sterile medical products and direct food label applications.
Type 14 soft structure styles can be cut much like fabric with conventional straight-knife machines. However, if the knife blade gets too hot, these soft structure materials can melt and edge-fuse. To minimize cutting problems:
- Replace straight-edged blades with blades that have a wavy or serrated edge.
- Use blades coated with Teflon® TFE fluorocarbon or lubricated with a non-staining silicone spray.
- Reduce the cutting stroke from 1.5 in (3.8 cm) down to 1 in (2.5 cm).
- Operate at 1,800 rpm instead of 3,600 rpm.
DIE-CUTTING
Sheets of Tyvek® can be die-cut using either steel rule (sharp edge) or male/female dies. Because of the inherent toughness of the material, male/female dies should be manufactured to close tolerances; steel rule dies are preferred. Tyvek® fibers must be completely cut which requires dies to be kept in good condition, with sharp, true, nick-free, well-supported edges. Dull dies cause cut edges to curl. On steel rule or high dies, slight internal relief helps reduce heat buildup. When working with closed dies, the strength of Tyvek® might require the use of a side cutter or chisel edge to speed up release and prevent die and product damage. Dies should be hardened to Rockwell C 50 to 60 to extend their life.
When die-cutting Tyvek® materials, keep the lift heights below 3 in. (7.6 cm). This avoids over sizing the top blanks resulting from edge compression as the die is lowered. Use of a center-die pressure cylinder can help de-aerate and compact the lift, as well as minimize slippage.
CONVERTING DUPONT™ TYVEK® FOR CONTINUOUS APPLICATIONS
Tyvek® is often used in continuous printing when the application requires strength and durability. But, because of its toughness, Tyvek® is more difficult to perforate and punch than paper. It can be successfully punched on tag, letterpress and rotary line-hole equipment. The higher tensile strength styles (i.e., 1085D, 1073D and 1079) are recommended for tags and labels. Tyvek® is more elastic than paper and tends to stretch under tension, but recovers after perforating/ punching. This creates the effect of shrinkage in the final printed form. It is necessary to convert at low tension and to hold the distance between sprocket holes within ±0.02 in. (0.5 mm) in a 100-in. (2.5-m) length sheet.
Unlike paper, as the machine speed increases, the tension adjustment decreases. If the hole distance is short at a particular tension at 330 ft/min (100 m/min), it will be less short at 1,150 ft/min (350 m/min). Rotary sprocket punching should be done with male/female dies made from hardened tool steel or tungsten carbide. Because of the close tolerances required to punch Tyvek®, soft steel dies dull quickly and increase downtime. Most manufacturers can provide the correct rotary dies for use with Tyvek®.
PUNCHING
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| Punched and spiral bound, the pages of this fishing guide are water-, tear-, puncture- and rip-resistant because they’re DuPont™ Tyvek®. |
Tyvek® can be punched on tag, letterpress and rotary line-hole equipment. Best results are obtained from sharp, well-registered and closely fit punches. Punches may be either smooth or serrated, and will cut best if ground concave on the ends. Most manufacturers of punching equipment suggest use of longer punches or deeper punch penetration, or both, to ensure a cleaner hole. A soft, self-honing male punch in a hardened female die is recommended. Gear backlash should be kept to an absolute minimum. The lowest practical tension should be used to avoid stretch and misregistration in web operations. If drilling, avoid excessive clamp pressure that can leave an impression on the sheet.
PERFORATING
To make clean-tearing perforations, use the maximum practical number of cuts with the smallest land (reserve) between them. An 8:1 ratio (1/4-in. [6.4-mm] cut with 1/32-in [0.8-mm] reserve) is suggested. To ensure tear initiation, position a cut at the edge of the sheet.
LAMINATING/COATING
Tyvek® can be extrusion-, adhesive-, flame-, ultrasonic- and thermal-laminated. Laminates are used for protective covers, automotive parts protection, medical packaging and worker protection garments. Tyvek® can be air-knife or gravure-coated with heat-seal coatings for medical packaging applications.
When there is a need to improve the fidelity of printing and/or to eliminate the appearance of fiber swirl, the best approach is to apply a coating. Tyvek® is routinely coated with a wide range of solvent and water-based materials applied with conventional equipment. Air-knife coating is preferred for aqueous coating systems because it deposits a uniform thickness of coating. It also produces a very smooth surface that is ideal for offset lithographic printing. Gravure coating has been used successfully for solvent-based coating systems, particularly where deep coloration is required. Pyroxylin coating formulations containing a high concentration of isopropyl alcohol (25%) are preferred for obtaining deep coloration.
DYEING
Conventional textile dyeing processes do not impart permanent color to Tyvek®. For this reason, Type 14 soft structure styles are usually printed using the flexographic or gravure process combined with either solvent or water-based inks. Dye sublimation printing is not recommended because of the high temperatures used.
HEAT-SEALING / DIELECTRIC SEALING / ULTRASONIC SEALING
Although it is possible to fuse Tyvek® to itself using only heat, it is difficult to obtain strong seals. Melting the material destroys its fiber structure, thus reducing both flexibility and tear strength in the seal area. If, however, it is required, non-corona-treated and non-antistat styles are preferred for heat-sealing Tyvek® to itself.
The preferred method for heat sealing is to apply a coating to Tyvek® with a melting point below that of Tyvek®, such as branched polyethylene. With such a coating, high seal strengths can be achieved using hot-bar or impulse techniques. Alternatively, trim seal dies designed with a springloaded restraining plate have been used successfully for heat sealing.
Tyvek®, like polyethylene film, cannot be dielectrically sealed by conventional methods. However, commercial proprietary processes have been developed that allow it to be dielectrically sealed using conventional radio-frequency equipment.
Ultrasonic sealing can be used to create fiber tearing seals with most styles without the puckering that is often associated with heat seals. This process also forms strong seals to a variety of plastic films and nonwovens.
GLUING
A number of adhesives can be used to glue Tyvek®, either to itself or to other substrates. In general, water-based adhesives that provide quick tack and fast drying are preferred. The first step in choosing an adhesive is to determine how it will react with Tyvek®. Laboratory testing is the best way to make this determination. Table V on page 34 contains a list of solvents that are preferred in adhesives.
Natural-product adhesives based on starch, dextrin, casein or animal by-products are preferred to synthetic-based adhesives. Hot animal glue is an excellent adhesive for adhering Tyvek® to paperboard.
Water-based synthetic adhesives bond Tyvek® to itself and to a variety of substrates. Ethylene/ vinyl acetate adhesives and the acrylic pressure-sensitive adhesives work well with Tyvek®. The synthetic adhesives that contain low-molecular weight materials can act as solvents at elevated temperatures, causing swelling and wrinkling. Polyurethane adhesives provide optimum adhesion (lap and shear), flexibility and water resistance for adhering Tyvek® to itself and to a variety of substrates.
Hot-melt adhesive technology has been demonstrated in a number of applications using Tyvek®, including the construction of envelopes, tags and medical packaging. Care must be exercised in adhesive selection and consultation with the adhesive manufacturer is recommended.
EMBOSSING AND FOIL STAMPING
Tyvek® can be embossed with either high-or low-pressure equipment. Done properly, cold embossing does not significantly reduce the strength; however, it does reduce opacity in the embossed area. Embossing cylinders used with Tyvek® usually are very shallow, having a depth of only 5 to 25 mil (0.13 to 0.65 mm). A Shore “D” hardness of 70 to 80 for the rubber backup cylinder is preferred. Material that is going to be printed should never be deeply embossed because it is difficult to fill this deep embossing pattern with ink. Foil stamping of Tyvek® is recommended when it is used with type or small designs, such as corporate logos. Solid areas greater than 2 sq. in. will bubble and distort in the stamped area.
Embossing is not recommended if it is to be followed by film lamination. The depth of embossing should be adjusted so that there is only a 2 to 3 point loss in opacity. Embossing roll temperatures should not exceed 175°F (79°C) and roll tension should be kept below 0.75 lb/lineal in (1.4 N/cm). Due to the thermoplastic/elastic nature of Tyvek® when exposed to heat and tension, super calendering is not recommended.
Foil stamping is easily accomplished on Tyvek® due to its thermoplastic nature. A variety of foils are available from suppliers for label and book cover applications. A foil should be chosen that transfers cleanly and adheres with a temperature/dwell time that is compatible with the melting point of 275°F (135°C).
SEWING
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| DuPont™ Tyvek® Soft Structure doesn’t just feel like fabric, it can be printed on then sewn into many items typically made from fabric. Plus it has the durability and resistance to liquids that fabrics typically don’t. |
Uncoated or non-laminated Tyvek® can be sewn satisfactorily on any conventional sewing machine. Best results are obtained from machines equipped with puller- or drop-feeds. Smooth, rubber-covered rolls should be used rather than knurled metal rolls, which tend to leave impressions on the material.
When stitching DuPont™ Tyvek®, use 5 or less stitches per inch and the smallest needle practical for maximum resistance to tearing. Both lock stitches and chain stitches work well, especially a 1-in. (2.5-cm) chain stitch, which can prevent raveling.
SEWING HARD STRUCTURE STYLES, TYPE 10
- Use 3 to 5 stitches/in (1.2 to 2 stitches/cm) at low tension to eliminate skipping.
- Use #036 (Union Special) or #14 (Singer) needle, or equivalent.
- Use a flat-tipped needle that cuts slit-like perforations. “Rock Point” (Union Special) or “Narrow Wedge” (Singer) will permit top-speed operation with the same thread used for round-point needles.
- The informal industry standard of 25/4 tex (24/4 cc) glacé thread of short staple cotton in #14 and #036 needles has given satisfactory performance in outdoor banners when coupled with 16.5/3 tex (36/6 cc) soft looper thread. If smaller diameter thread is required, 14.5/4 tex (40/4 cc) glacé thread of “Sak” quality should provide satisfactory results.
- When sewing banners, avoid stitches at or near the edge to reduce the chance for edge-tear. Pressure-sensitive adhesive tabs of DuPont™ Tyvek® spunbonded olefin or DuPont™ Mylar® polyester film wrapped around a sewn seam at each edge will further reduce the possibility of edge tear.
SEWING SOFT STRUCTURE STYLES, TYPE 14
- Use up to 12 stitches/in (4.7 stitches/cm); however, 6 to 8 stitches/in (2.4 to 3.1 stitches/cm) provides the highest seam strength (greatest resistance to postage stamp tear).
- Use a fine-tooth feed dog; 12 to 21 teeth/in (4.7 to 8.3 teeth/cm).
- Decrease presser-foot tension until the sheet just feeds through the machine without slipping. Approximately 10-lb (4.5-kg) force should be sufficient.
- Decrease bobbin tension until the bobbin just slips down the thread: 3 oz (85 g).
- Wind bobbin with thread tension set so that thread just slips through the disc: 2 oz (57g).
- After setting bobbin tension, adjust needle tension to produce a balanced stitch.
- Conventional threads of cotton/synthetic or 100% synthetic threads of nylon or polyester can be used.
- Spun-filament polyester is stronger than cotton thread and is preferred for flame-resistant considerations.
IDENTIFICATION OF CORONA TREATMENT AND ANTISTATIC TREATMENT
All styles of Tyvek® with a “D” or “R” suffix and 1079 are corona treated and anti-stat treated on both sides (e.g., Styles 1073D and 1443R).
The critical surface tension of Tyvek® (high density polyethylene) is 30 dynes/cm2. Corona treatment increases the surface tension to 40 to 42 dynes/cm2. As a comparison, distilled water is 73 dynes/cm2.
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