Decisions you make during the screenmaking stage can have a major impact on the success of the printing process. Learn about the choices you face in frame selection and in securing your mesh to the frame.
By Eric Klein
With recent changes, urethane and epoxy adhesive systems have gained popularity. Newer laws and regulations have made these adhesives a lot milder than they were a few years ago. With these changes, the products are easier to work with both in application and removal. Unfortunately, the solvents used in most of these systems are very similar to the solvents used to remove ink from screens, so care is needed when choosing screen washes. It is highly recommended to test the adhesive with the solvents in your shop to determine whether they are compatible. Typically, you will find urethanes to have better solvent resistance and more flexibility than epoxy-type adhesive.
A variety of catalyzed adhesives are available, including formulations for just about any application, mesh count, frame type, and environment. Most manufacturers have multiple viscosities from which you can choose to accommodate coarse mesh (24-196 threads/in.) or fine mesh (230-460 threads/in.). The viscosity is important because it influences how well the adhesive penetrates the fabric to reach the frame. The viscosity also relates to the solids content of the adhesive, which determines how well the adhesive bridges the gaps between the fabric and the frame. If you use a thin viscosity adhesive on a coarse mesh, as the solvent evaporates and the adhesive shrinks it could leave air pockets between the mesh and the frame, which can cause bonding problems. Most catalyzed adhesives are not surface sensitive and are approved for use on wood and metal frames alike.
When mixing catalyzed systems, most users fall into the catalyst trap. Mixing the product properly is key. The old adage, “if a little is good, a lot is better” does not apply when adding catalyst. In most cases, adding more catalyst will help with the chemical resistance but it will slow down the reaction time of the adhesive. Normally the two-part epoxy systems are tack dry in 5-20 min but are not fully cured for 24 hr.
Did you enjoy this article? Click here to subscribe to the magazine.