Topics

1. Flexographic Printing
2. Lithographic Printing
3. Screen Printing
4. Gravure Printing
5. Letterpress Printing
6. Ink Jet Printing
7. Laser (Electrostatic) Printing

1. Slitting, Sheeting, and Cutting
2. Die Cutting

1. Heat Sealing
2. Dielectric Sealing
3. Ultrasonic Sealing
4. Glueing

1. Laminating
2. Coating

1. Mechanical Recycling
2. Chemical Feedstock Recycling

• 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 20-30% before breaking. To minimize distortion or neck-down, keep web tension as low as practical -- 0.75 lb/in. (1.3 N/cm) -- during processing.
• Tyvek^® may occasionally curl when sheeted because of its inherent "memory." Conventional decurler (breaker bar) equipment can be used at minimum tension."
• Tyvek^® has its own natural lubricity and does not contain abrasive fillers or binders. It therefore requires no additional lubricants for processing. In fact, lubricants should be avoided since some contain low-molecular-weight hydrocarbons which can cause swelling and distortion.
• Flying splices can be made with all styles of Tyvek^®. A pressure-sensitive tape is recommended for butt splices.
• 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).

Please contact us for the names of lithographic and/or flexographic printers that have experience with Tyvek^®. Undoubtedly, there are other printers who are capable of producing satisfactory results when printing on Tyvek^®. This list is intended only as a guide and is not a recommendation of any specific company.

Flexographic Printing

Flexography is the recommended technique for printing on "type 10" styles of Tyvek^®. For best results, use the smooth side of the sheet. The difference between the rough ("wire") side and the smooth side is minor, but can usually be felt. Rolls supplied directly from DuPont are wound smooth side out. Rolls supplied from a converter may be wound differently. Be sure to check with your converter or supplier to determine how your rolls are wound. Other important recommendations are listed here.

Press Conditions

Ensuring optimum press conditions will help prevent sheet distortion, registration problems in multi-color work, softening of adhesives and ink pick-off.

• Tensions -- Keep tensions below 0.75 lb/lineal in. (1.3 N/cm) of width.
• Temperatures -- Maintain web temperatures below 175°F (79°C).
• Chilled Rolls -- Use chilled rolls before windup.

Printing Plates

Selecting the appropriate type of printing plate to use will depend on the nature of the job.

• For Overall Print Uniformity (even with type as small as 4 points) -- Use DuPont Cyrel^® photopolymer plates with a 50 Durometer hardness (Shore A), mounted with 15 mil to 20 mil (0.38 mm to 0.51 mm) of sticky-back, closed-cell foam.
• For Fine-Line Reverses Greater than 13 Mil (0.33 mm) -- Use soft natural rubber plates with a 30 Durometer hardness (Shore A), backed up with 15 mil to 20 mil (0.38 mm to 0.51 mm) of sticky-back, closed-cell foam.

Using the proper ink is important for achieving high-quality results.

• Alcohol-Based Polyamide Inks -- These solvent-based inks typically provide the best adhesion and rub resistance. Adding microcrystalline wax will reduce offsetting.
• Water-Based Inks -- These inks help users remain in compliance with state environmental regulations while achieving high-quality results.

Please contact us for the names of some of the companies that supply inks which can be used with Tyvek^® in both the lithographic and flexographic processes. Undoubtedly, there are other suppliers who are capable of producing satisfactory inks for use with Tyvek^®. This list is intended only as a guide and is not a recommendation of any specific company.

Lithographic Printing

Although flexography is the recommended method for printing on "type 10" styles of Tyvek^®, offset lithography can produce acceptable print quality. For best results, use the smooth side of the sheet. Although either side prints well, the smooth side, with a slight downward curl at the edges, is preferred because it makes sheet feeding slightly easier. The difference between the rough ("wire") side and the smooth side is minor, but can usually be felt. Rolls supplied directly from DuPont are wound smooth side out. Rolls supplied from a converter/distributor may be wound differently. Be sure to check with your supplier to determine how your rolls are wound. Other important recommendations are listed here.

Offset Blankets

Selecting the appropriate type of blanket to use will depend on whether or not the Tyvek^® is coated.

• For Adhesive-Coated Tyvek^® -- Use conventional offset blankets of medium hardness.
• For Uncoated Tyvek^® -- Use compressible offset blankets.

Squeeze

Applying an additional 3 mil to 4 mil (0.08 mm to 0.10 mm) of squeeze between the blanket and back cylinder is required compared to that used for paper of equivalent average thickness. This additional impression, coupled with the compressibility of Tyvek^®, compensates for the thickness variation of Tyvek^®.

Inks

Using the proper ink and following these specific recommendations are important for achieving high-quality results.

• Low-Solvent-Content Inks -- Use inks with <3% volatile solvent because hydrocarbon solvents found in many litho inks tend to swell and distort Tyvek^®. Using low-solvent-content inks also benefits the environment because these materials release fewer volatile organic compounds (VOCs) than traditional offset inks.
• Extra Strong Colors -- Use extra strong colors to keep ink film thickness to a minimum (<0.3 mil [<0.008 mm]). This will help minimize sheet distortion and dot gain.
• Tint Creation -- Use opaque white rather than an extender when creating tints to minimize the appearance of fiber swirl.
• Fountain Solution -- Maintain fountain solution at a minimum level. Either conventional water or alcohol/water dampening systems can be used. Alcohol substitutes also work well. If your images appear dull or washed out, reduce the amount of dampening solution in the fountain; do not increase the ink volume.
• Drying -- Because litho inks dry more slowly on Tyvek^® than they do on paper, be sure that pile height does not exceed 20 in. (0.5 m). Winding the sheets and maintaining the fountain solution at a pH between 4 and 5 will also accelerate drying.

Special Notes for Adhesive-Coated Tyvek^®

When selecting offset inks, it is important to advise the ink supplier if the Tyvek^® has an adhesive coating because special ink formulations may be required to prevent ink set-off to the coated surface. In some cases, printing is done on the adhesive side. This also should be discussed with the ink supplier to ensure optimum compatibility between the ink and the coating.

Other Printing Methods

Although the overwhelming majority of converters of Tyvek^® use flexography and lithography for printing, some prefer to use other methods for certain low-volume and specialty applications.

Screen process printing has been used successfully to print on Tyvek^® for specific applications, especially short press runs of jobs using large type and simple graphics. Because of the high potential for static and/or ink pick-off, the use of paper slip sheets is sometimes required.

The inks used must be specially formulated for the lower surface tension encountered when printing on untreated styles of Tyvek^®. Lacquer-type inks are preferred because they produce a minimum amount of distortion. Water-based inks work well because they minimize distortion -- even with heavy ink-film thicknesses. Ultraviolet-cured screen inks also have been used successfully. Screen "poster inks" and enamels, which both contain a high percentage of mineral spirits, should be avoided.

Tyvek^® is high-density polyethylene (HDPE), with a melting point of 275°F (135°C). When using conveyor ovens instead of room-temperature drying, the sheet temperature should be kept below 175°F (79°C). When using UV-cured screen inks, cooling is required to prevent sheet distortion or shrinkage.

Gravure is a high-quality printing technique that uses costly engraved metal cylinders to print extremely long runs of multiple-color jobs. Since gravure printing uses basically the same ink formulations that are used in flexography, no problems are anticipated; however, we advise careful testing before using this technique on Tyvek^®.

Letterpress is a technique used for short press runs involving a single color, relatively small sheet sizes and simple graphics and line art. Due to the tendency of untreated styles of Tyvek^® to generate static electricity, multiple press passes should be avoided (e.g., a one-color press should not be used for multiple-color printing). As in screen printing, paper slip sheets are sometimes required, particularly when printing on Tyvek^® with an adhesive coating.

To minimize the tendency of Tyvek^® to curl or pucker, the least possible ink film thickness should be applied, with a goal of 0.3 mil (0.0076 mm). Because of the high compressibility of Tyvek^®, more plate packing is required than for an equivalent thickness of paper. To obtain proper ink fill, deep and sharp embossing patterns should be avoided.

Inks for use in letterpress printing on Tyvek^® are similar to offset/litho inks, and are typically formulated from rosin esters and long oil alkyds. These inks can be diluted with drying oils, such as tung (chinawood oil) or linseed oil. High-boiling, "quick-dry" petroleum solvents and aliphatic hydrocarbon resins, which can cause distortion and sheet swelling, should not be used. "Dry pigment grinds" should be used to avoid the residual solvent found in pigments made from flushes.

Ink jet printing is used primarily for lot and batch marking in automatic form-fill-seal processes in the sterile packaging industry. Tests conducted by DuPont have shown that solvent-based ink systems (ketone/ alcohol) work well with Tyvek^® in the ink jet process. On the other hand, most of the water-based inks that we tested would feather and blur to some extent. In addition, they are slower to dry.