Mounting Matters
by Chris A. Paschke, CPF GCF
visit http://www.DesignsInkArt.com/library.htm
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.
photo 1
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.
P-S
Permanence
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.
END
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
Designs Ink
Tehachapi, CA 93561
P 661-821-2188
chris@designsinkart.com
http://www.designsinkart.com/library.htm