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Articles by Chris A. Paschke, CPF GCF CMG

"Pressure-Sensitive and Heat Activated Adhesive Boards"

May 2002

While looking back through past articles I noticed I had not yet given time to the topic of preadhesived boards. These are mounting boards that have already had adhesive applied to them during production and are ready for mounting when arriving from the manufacturer. They may be designed for either cold or hot mounting applications; with or without liners; may be tacky to the touch or smooth and dry. They have numerous benefits including being a time saver for high production shops; overall ease of use; being health safe; and are an economical approach to mounting.

PREADHESIVED MATERIALS

Cold pressure-sensitive adhesives are also known as P-S and PSA. Thermal activated adhesives are also known as HA or heat activated dry mount adhesives. There is a significant difference between ready to mount products and the more time intensive preparation of sizing tissues, films and boards prior to bonding.

Pressure-sensitive adhesives are thermoplastics, which require no moisture or heat for application. Although there are p-s products that are available as films with single and double release liners it is the p-s boards I am concerned with. 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.

HIGH, MEDIUM AND LOW TACK PRESSURE-SENSITIVES

There are three levels of tack available with pressure-sensitive adhesive: high, medium and low tack. High tack is aggressive and most difficult to hand apply since it has no repositioning potential. They will immediately grab to a smooth nonporous or coated stock (photo) with no forgiveness. Medium tack is the one most frequently used in picture framing. It may be somewhat repositionable during mounting with porous papers, but even repositionable p-s boards will grab more aggressively to a smooth or coated material.

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 (PrintGuard or Hot Press Heat-seal Film).

PRESSURE-SENSITIVE 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 (where the project is to be used).

SUPPORTING DOCUMENTS AND INFORMATION

Technology and adhesives evolve and have changed over the years. As stated in "The Permanence and Care of Color Photographs" by Henry Wilhelm, 1993, 3M Company stated the following for their tapes and adhesives in relation to longevity and archival applications: "3M tapes and adhesives form a physical bond to surfaces that are not soluble in water. They can be loosened with solvents or reversed with heat but...are not without risk of damage to the artwork...we know most of our adhesive products have an indefinite age...we do not have a test that will predict how a product will hold up after 50 or 100 years...these products are designed for general purpose use in bonding on items of limited value...". A more current report from 2001, ISO 18902:2001, International Standards Organization (section 4.5 Adhesives) states: "pressure-sensitive adhesives have poor stability characteristics and should be avoided".

Even when the elements of proper mounting (time, temperature, pressure, moisture) are attended to, and when all preadhesived boards are mounted to manufacturer's specifications there are still limitations. With cold mounting PSAs, we may never know for sure how long they will hold, there are too many variables.

Decorative art is not in need of archival applications and it is likely under normal conditions that P-S boards will hold adequately for most framing applications. When an image is applied by hand to a P-S board it may only activate 20-25% of the adhesive capability. In order for the adhesive to have a higher percentage of activation it needs to be run through high pressure rollers or burnished down after application, though it is difficult to hand burnish through a board. The higher the adhesive tack and the more aggressive the pressure during the initial bond, the better the longevity of any P-S adhesive board.

PRESSURE-SENSISITVE BOARDS

Pressure-sensitive boards have their basic p-s adhesive film already applied to a mount board or foam board with a protective release paper liner that is removed before mounting. Although some are considered acid free, always remember that permanently attaching anything to a backing board is NEVER archival. It is not that an adhesive will damage artwork but rather the fact adhesive soaks into the art, that makes it non-conservation. Check specifications for p-s board products in the framing industry from manufacturers including: Crescent Perfect Mount Boards, Hartman Hartac Boards, Savage Nucor, Hunt/Bienfang P-S Boards, and International Paper Self-Adhesive Fome-Cor and Gator boards. Also check the low, medium and high tack factor. Know what you are using.

Having just returned from the PPFA Conference in Orlando, Florida, under the presentation of PMA (Photo Marketing Association), I have located many new potential products for framers. Though still untested by me for this industry, there are additional manufacturers and distributors of pressure-sensitive boards available through the digital and photo companies not mentioned here.

HEAT ACTIVED ADHESIVES

Now, let's examine preadhesived boards requiring heat. Dry mounting adhesives are easiest to understand when examined by their four basic characteristics. Once the type of bond (permanent or removable); physical composition (tissue-core or film); porosity (breathable or nonbreathable); and acidity level (tissue pH) have been identified, then all adhesives may be compared and matched up.

The difference with preadhesived heat activated boards is not the type of adhesive as much as it is the impact of the elements instead. HA boards appear to be more like the adhesives from the side of a tissue-core adhesive that has been applied to a board instead of a carrier. So rather than a roll of tissue with adhesive on either side of it, the HA board is a thin layer of adhesive applied to a 4-ply, 8-ply, 1/8" or 3/16" board instead.

BASIC BOARDS IN FRAMING

There have been a series of HA boards in the framing market for at least the past ten years, most of them having somewhat the same basic nature. They have heat activated adhesive applied to an existing substrate that will mount in any heat system at an average mounting temperature of 185°F in 2-4 minutes. Adhesives vary in their smoothness of adhesive application which in turn impacts the results.

Some boards have thicker adhesive applied allowing them to be used with fabrics while others are better geared to porous papers. I have seen preadhesived HA boards that have such highly textured (not smooth) adhesive applied to the board it encourages orange peel even under thin paper prints much like can occur with an RC photo.

NOT JUST ANOTHER PRETTY HA BOARD

There is one HA board that stands alone in its category and deserves a round of applause, SpeedMount by Bainbridge. It begins as just another HA board but its adhesive application is so even and smoothly applied it feels like a sheet of tissue-core dry mount adhesive cut from a roll. Unlike other HA boards on the market it activates in a mechanical press at 150°F in 15 seconds for mounting photos and porous paper.

Though some thicknesses of paper and nonporous media may require an increase in temperature to 170°F or additional time in the press of 30 seconds, to date, it stands alone in the framing industry with no actual competition. It is also totally dry to the touch when removed from the case, making it free from the need for interleaving sheets to protect the adhesive layers during storage. What appears as a thinner application of adhesive to the board surface makes it less desirable for the mounting of fabrics.

SHOPPING BY PRICE

Originally, HA preadhesived boards were designed to equal the base price of a sheet of mounting board and a piece of tissue adhesive. It wasn't a higher priced product, but rather an alternative to traditional dry mounting materials. It targeted the production framer and the custom framer who competes by quick turn around frame times.

Purchasing a preadhesived HA board strictly by price is not the best idea. One must consider the physical characteristics of the board. Examine the product for cleanliness making certain it appears free from dirt and alien particles. We have enough trouble keeping mountings clean with mat cutter paper dust and wood chips flying around our shops. Also check for the actual adhesive application, is it smoothly applied and does it appear even across the surface?

Consider the time and temperature aspects of the boards when shopping too. It might be in your best interest, with the likeliness of digitals and photos becoming the norm, to notice that digitals frequently tolerate 150°F but not necessarily 170°F, and most often not 185°F at all. SpeedMount may run 10-15% higher to purchase than the other HA boards, but the low temperature makes it very appealing. Regardless of the product, if any product is selected for a special or specific mounting situation (photos or digitals) then that added cost should be passed onto the retail price of that project.

COMMON NAMES AND FACES

Preadhesived boards are available in the framing market from all the usual suspects. The makers of sticky tapes, adhesive films, and board products as mentioned earlier in this article are your sources for p-s boards. Heat activated preadhesived boards come from the familiar board manufacturers and dry mounting companies including Single Step from Hunt Bienfang, HartMount, MHA from Drytac, ThermoMount, Nucor Heat Activated from Savage, Heat Activated FomeCor, and SpeedMount from Bainbridge to name a few. There are also assorted private label brands but be certain to check for the adhesive coating, mounting temperature and basic tackiness of the board during storage. Also check porosity for use with photos.

FINAL MOUNTING

Preadhesived boards may not be for everyone, in fact they really don't fit a fine art preservation custom framing repertoire, but they are an innovative approach as an alternative form of adhesive application when mounting paper and photos. If production mounting is an element in your market then preadhesive boards might be the answer, particularly HA boards. Whether cold or hot, there is a product for the speed conscious.

END

For more articles on this topic search under Articles by Subject.

Additional information on mounting basics is found in The Mounting and Laminating Handbook, Second Edition, 2002, and The Mounting And Laminating Handbook, Third Edition, 2008. Creative Mounting, Wrapping, And Laminating, 2000 will teach you everything you need to know about getting the most from your dry mount equipment and materials as an innovative frame designer. All books are available from Designs Ink Publishing through this website.

For live consultations with Chris Paschke, CPF GCF call Designs Ink, 661.821.2188. A flat fee of $25 will be charged for each new technical problem. Unlimited calls or emails are allowed for each established mounting problem.

Chris A Paschke, CPF GCF

Designs Ink

Designs Ink Publishing

785 Tucker Road, Suite G-183

Tehachapi, CA 93561

661.821.2188