While it is possible to fuse Tyvek® to itself using only heat, strong seals are difficult to obtain. This is due to the fact that melting Tyvek® destroys the fiber structure, reducing both flexibility and tear strength in the seal area. However, if Tyvek® is heat-sealed to itself, those styles with no antistat coating and no corona treatment (such as styles 1059B and 1073B) should be used. This is because the molecular film of oxide and antistat on the surface of corona-treated/antistated styles causes Tyvek® to melt unevenly, which reduces seal strength.
Trim seal dies, designed with a spring-loaded restraining plate, have been used successfully for heat sealing. However, the preferred method is to apply a coating such as branched polyethylene, which has a lower melting point than Tyvek®. With such a coating, high seal strengths can be achieved using hot-bar or impulse techniques
Tyvek®, like polyethylene film, cannot be dielectrically sealed by conventional methods. However, commercial proprietary processes have been developed that allow Tyvek® to be dielectrically sealed using conventional radio-frequency equipment.
Recent developments in ultrasonic sealing have also demonstrated fiber tearing seals with most styles of Tyvek®, without the puckering that is often associated with heat seals of Tyvek®. This process also forms strong seals to a variety of plastic films and nonwovens. For more information on sealing, please contact us.
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. However, 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.
Natural-product adhesives based on starch, dextrin, casein or animal by-products are preferred to synthetic-based adhesives. Synthetic adhesives often contain low-molecular-weight materials that can act as solvents at elevated temperatures and cause swelling and wrinkling. Hot animal glue is an excellent adhesive for adhering Tyvek® to paperboard. Water-based synthetic lattices also bond Tyvek® to itself and a variety of substrates. Ethylene/vinyl acetate adhesives are especially useful, as are the acrylic pressure-sensitive adhesives. Solvent-based single-component polyurethane adhesives provide optimum adhesion (lap and shear), flexibility and water-resistance for adhering Tyvek® to itself and a variety of substrates.
Hot-melt adhesive technology has been amply demonstrated in a number of applications involving Tyvek®, including the construction of desiccants, envelopes, and medical packaging. Care must be exercised in adhesive selection and consultation with the adhesive manufacturer is recommended.