A Guide to Printing on Tyvek® for Medical Packaging Applications
Printing on Tyvek® medical and pharmaceutical packaging styles can be done using standard commercial printing equipment and suitable inks. It is important to note that because of the unique requirements for pharmaceutical and medical packaging, these styles of Tyvek® have no antistatic coating or corona treatment. Therefore, special steps must be taken to obtain optimum printing results. When printing on Tyvek® medical and pharmaceutical packaging styles, we recommend testing before proceeding with production operations.
Flexographic Printing Guidelines
The recommended technique for printing on Tyvek® medical and pharmaceutical packaging styles is flexography. 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 by a sterile packaging manufacturer (SPM) may be wound differently. Check with your SPM or supplier to be sure. Because it is more difficult to tell the difference between the two sides on Tyvek® 2FS™, a simple procedure has been developed to help you more easily distinguish the smooth side from the rough side.
Please refer to the media gallery “Determining Rough vs. Smooth Side” on the Lidstock for Thermoformed Trays page. This illustrates a simple process to help you to determine the smooth side of Tyvek®.
Press Conditions for Flexography
Optimizing press conditions will help prevent sheet distortion, registration problems in multi-color work, softening of adhesives and ink pick-off. Keep tensions below 0.75 lb/in. (1.3 N/cm) of width; maintain web temperatures below 175°F (79°C); and use chilled rolls before windup.
Printing Plates for Flexography
Selecting the appropriate type of printing plate is dependent upon the nature of the printing job. General printing best practices should be followed to optimize the conditions of the pressroom for ultimate performance. Printing variables include the plate, cushion, ink and anilox. As always, it is best to clean the printing plate with 100% alcohol prior to inking to enhance ink transfer.
For printing solids, type and other fine detail-oriented images, it is best to use a medium durometer plate. This should be complemented with a medium or firm density cushion. Anilox selection should be based on a line screen and volume that does not over-ink the plate. Please seek ink manufacturer’s guidelines for viscosity, pH and other transfer properties that are dependent on your ink application and resistance properties.
Digital Solvent—use DuPont™ Cyrel® DSP or Cyrel® DPL
Digital FAST—use Cyrel® DFP or Cyrel® DFM
Analog—use Cyrel® NOWS or Cyrel® EXL
For images that include fine line screens with dots, it is best to use a harder durometer plate. This should be complemented with a soft or medium density cushion. Anilox selection should be based on a line screen volume that does not over-ink the plate. Please seek manufacturer’s guidelines for viscosity, pH and other transfer properties that are dependent on your ink application and resistance properties.
Digital Solvent—use Cyrel® DSP or Cyrel® DPR
Digital FAST—use Cyrel® DFP or Cyrel® DFR
Analog—use Cyrel® NOWS or Cyrel® EXL
Inks for Flexography
It is important to not only choose the proper ink for the process, but to verify the suitability of the ink in applications where direct contact with the medical device is likely. Alcohol-based polyamide inks typically provide the best adhesion and rub resistance. Adding microcrystalline wax to alcohol-based polyamide inks will reduce the offsetting. On the other hand, water-based inks make it possible to achieve high-quality results while complying with environmental regulations.
Lithographic Printing Guidelines
Although flexography is the recommended method for printing on Tyvek® medical and pharmaceutical packaging styles, offset lithography can produce acceptable print quality. For best results, use the smooth side of the sheet, as it makes sheet feeding slightly easier. The difference between the rough (“wire”) and smooth side is minor, but can usually be felt. Rolls supplied directly from DuPont are wound smooth side out. Rolls supplied from a sterile packaging manufacturer (SPM) may be wound differently. Be sure to check with your SPM or supplier to determine how your rolls are wound. Because it is more difficult to tell the difference between the two sides on Tyvek® 2FS™, a simple procedure (see above) has been developed to help you more easily distinguish the smooth side from the rough side.
Offset Blankets for Lithography
The appropriate choice of blanket to use will depend on whether the Tyvek® is coated. For adhesive-coated Tyvek®, use conventional offset blankets of medium hardness. For uncoated Tyvek®, use compressible offset blankets.
Squeeze Recommendations for Lithography
Applying an additional 3 mil to 4 mil (0.08 mm to 0.10 mm) of squeeze between the blanket and the back cylinder is required compared to that used for paper of equivalent average thickness. This additional amount of squeeze, coupled with the compressibility of Tyvek®, compensates for possible thickness variations of Tyvek®.
Inks for Lithography
It is important to not only choose the proper ink for the process, but to verify the suitability of the ink in applications where direct contact with the medical device is likely. In addition, follow these specific recommendations for printing on Tyvek® medical and pharmaceutical packaging styles.
Use inks with <3% volatile solvent because hydrocarbon solvents used in many litho inks tend to swell and distort Tyvek®. These inks also release fewer volatile organic compounds (VOCs) compared to traditional offset inks, reducing the environmental impact.
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.
Use opaque white instead of an extender when creating tints to minimize the appearance of fiber swirl.
Maintain fountain solution at a minimum level. Either conventional water or alcohol/water dampening systems can be used. Alcohol substitutes also work well. Do not increase the ink volume if your images appear dull or washed out. Instead, cut down on the amount of dampening solution in the fountain.
Litho inks dry more slowly on Tyvek® than on paper, so be sure pile height does not exceed 20 in. (0.5 m). You can accelerate drying by winding the sheets and maintaining the fountain solution at a pH between 4 and 5.
A list of ink manufacturers familiar with the unique requirements of printing on Tyvek® medical and pharmaceutical packaging styles can be obtained by contacting your regional DuPont representative.
Special Notes for Adhesive-Coated Tyvek®
It is important to tell your offset 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. Also let your ink supplier know if printing is to be done on the adhesive side so optimum compatibility between the ink and the coating can be ensured.
Variable Information Printing
Electronically controlled printing devices can output variable information such as lot, production date, sequential numbering, product codes and bar codes. Tyvek® medical and pharmaceutical packaging styles are compatible with some of these processes.
Thermal Transfer Printing
The most common process for printing variable information uses heated pins to activate a pigmented wax, resin or wax/resin blend carried on a ribbon. The image is created when the molten ink transfers to the substrate. For best results on Tyvek® medical and pharmaceutical packaging styles (which are not corona treated), use wax ribbons. If more image durability is required, use a 90/10 wax/resin blend ribbon. This blend ribbon may need to be custom manufactured because many ribbon manufacturers only stock 50/50 blend ribbons.
Excellent results in printing alpha-numeric information have been achieved using 300- to 600-dpi printers. Because of the inherent thickness variability of Tyvek®, thermal transfer printing on Tyvek® tends to produce D-C ANSI bar code quality. If a high-density bar code is needed or a higher-quality bar-code rating is specified, a label should be used.
Tyvek® medical and pharmaceutical packaging styles have been printed successfully using continuous and drop-on-demand ink jet printers. However, solvent-based inks must be used because Tyvek® is made of high-density polyethylene (HDPE) and does not absorb moisture. Most water-based inks are slower drying and tend to feather on Tyvek®, resulting in a blurry image. Ultraviolet (UV) and change-of-phase inks have also been used successfully because they cure almost instantly. Typically, 200- to 300-dpi print heads are used.
Laser (Electrostatic) Printing
Conventional laser printing is not recommended for Tyvek®. The high temperatures used to set the toner can distort the Tyvek® and even melt it if a jam occurs. Cool-process (flash-fusion) laser printers are compatible with Tyvek®; however, the printed image is not as sharp as it is with thermal transfer or ink jet printers.