by Chris A. Paschke, CPF GCF
The LA Framer – GLAC Newsletter January 2012
"Pressure Sensitive Adhesives"
As the perfect follow-up to bone burnishers is a little more info on pressure-sensitive adhesives. Pressure-sensitive adhesives are thermoplastics, which require no moisture or heat for application. PSA is a permanently tacky substance that bonds to a poster, photo, or digital image at room temperature, with only the application of pressure. They are meant to always retain their tack and this in turn is why they have lesser permanent bond than heat-set adhesives. They are dry, synthetic adhesives that are clean, easy to use, odorless and use no solvents.
The following information was compiled from a mounting comparison test completed by me in 2006. For additional comparisons and test results see the PDF chart available at http://www.DesignsInkArt.com/library.htm under Articles by Subject, Charts, Pressure Sensitive Comparisons, June 2006.
Assorted P-S adhesive boards included
Bainbridge, Crescent, Elmer's, Drytac,
Hartman, Gilman, and Savage
Low, Medium and High Tack
There are three levels of tack available with pressure-sensitive adhesives as low, medium and high tack. Low tack is not suitable for the longevity of framing demands, and is least likely to be found on boards. It is most often found as a temporary positioning tack used in preparation for other bonding, as with HA adhesives such as laminates with liners such as PrintGuard or Hot Press Heat-seal Film.
Medium tack is used most in picture framing is found in repositionable brands including Crescent PerfectMount, Bainbridge SA Foam, and Elmer's Quick Stick LT. Other nonrepositionable medium tack boards include Alcan Fome-Cor LT and Harman HarTac. These adhesives work best when mounting porous papers, but even repositionable p-s boards will grab aggressively when being bonded to a smooth or coated material like a clay coated foam center board.
High tack adhesive is immediately aggressive and most difficult to hand apply since it has no repositioning potential. They create a rather permanent bond between two smooth surfaces like a photo and clay coat foam with no forgiveness. Boards in this category include Elmer's Quick Stick HT Self Adhesive, Alcan Fome-Cor HT, Drytac P-S Boards, Gilman High Tack Foam, Savage NuCor and Prestax.
P-S films are yet another category. 3M PMA is pure film adhesive while Crescent PerfectMount film has a carrier, and both are considered medium tack, though running them through a roller machine or placing in a vacuum press helps the bond longevity. Neschen Gudy 870 and 831 are both high tack films that are best applied with a roller machine to help align and prevent trapped air. The beauty of P-S films is the flexibility to mount to your substrate of choice, which really allows for added design and framing capabilities.
PSAs may be either permanent or removable. In this case, permanent means impossible to remove without destruction of the substrate or mounting, such as a mailing label or poster mounting. Historically, coated papers are the most difficult to adhere (RC photographs) because of their lack of absorption and require softer more aggressive pressure-sensitive adhesive to bond well, making high tack the best choice.
Application vs. use temperature will effect bond permanence. A permanent high tack pressure-sensitive applied at room temperature may fail at freezing temperatures if placed outside, or in an excessively humid bathroom. High moisture content also makes pressure-sensitive adhesion difficult. Moisture is a physical barrier to adhesion and long term bonding. Coldness to the touch is often an indicator of moisture content in boards, so really learn to feel what you are touching when selecting boards. If you only have cold mounting facilities it is nearly impossible to dry out moist materials prior to mounting for a truly permanent bond, making them prone to bond failure. Dry storage is imperative.
Just as removable pressure-sensitives may not always remove, permanent pressure-sensitives may not always be permanent. Never select a pressure-sensitive product without knowing the exhibition conditions as where and how the end product is to be displayed.
Copyright © Chris A Paschke, 2011
For more articles on mounting basics look under the mounting section in Articles by Subject.
Additional information on all types of mounting and creative applications in:
The Mounting and Laminating Handbook, Second Edition, 2002,
The Mounting And Laminating Handbook, Third Edition, 2008,
Creative Mounting, Wrapping and Laminating, 1999.
Chris Paschke, CPF GCF
Tehachapi, CA 93561