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Articles by Chris A. Paschke, CPF GCF

"Adhesive Trends: Part 1"

January 1992

So what's "new" in adhesives for '92? It may not be what's new as much as what's environmentally improved or healthier to use that is creating the "trend" for the new year. Industry experts have pointed out the trends include a movement toward environmentally safe products such as spray adhesives and boards produced without the use of fluorocarbons; pressure sensitive mounting is leaning more toward the one-step peel and stick foam and mounting boards; and the continuing concern of dry mounting at low temperatures remains strong. For a number of years now there has been increased concern by manufacturers about lowering the mounting temperatures of dry mount tissues and films. Their successful results have shown us a lowered average recommended temperature ranging 165ºF-185ºF from what used to be 200ºF-225ºF.

Thus the new trends are pretty general in scope but may best be understood by becoming more knowledgeable with the basics of mounting adhesives some of their similarities, and perhaps differences. Adhesives are broken into four major groups: wet, spray, pressure-sensitive and dry mount. Let's cover the bases by covering the basics!

Wet Adhesives

"Wet mounting" means using a wet glue, paste or adhesive to adhere the project to the substrate. The wet mounting process is extremely economical though more time consuming that some of the other options, and although many manufacturers claim them to be permanent in bonding ability, permanence may vary with individual mounting skill and many do have a tendency to release over time. Just as there are pros and cons to any situation, such is also the case with adhesives. Wet glues are a great "back-up" process for over-sized projects, but can be messy and a little tricky to get a balanced even coat on the mounting project.

Often wet glues are applied with brushes or brayers by first placing a small glob of paste onto a palette of glass or plastic and then rolling the brayer through it to thin and evenly distribute it for application. This method is a great alternative to mounting large or oversized prints which may not fit into your vacuum mounting press. Although a vacuum press is not a requirement for mounting with wet glues using one in combination with the "wet" process will definitely create a much better bond. In either event it is necessary to apply weight to the mounted artwork while it dries. Wet glues are generally water soluble as well as non-staining meaning they are removable, however this does not make them reversible. I will be addressing this "removable" issue later in this article.

Spray Adhesives

One of the major issues concerning spray adhesives has been raised by OSHA recently in relation to employee and user health safety regulations. When using spray adhesives (or any spray for that matter), stricter ventilation requirements to avoid potential health hazards will continue to be stressed. Though this may not qualify as a "new trend in '92" it is of utmost importance within the industry and should not be taken lightly. It is also an area of concern when weighing the pros and cons of individual mounting methods for your store.

There are a number of aerosol spray adhesives on the market by a number of different manufacturers. These glues are fast, simple and are also considered permanent in many cases, and need only to have even pressure applied to the mounted article to ensure a good bond. As mentioned with wet glues, sprays are messy, require good ventilation and are successful based on an even, adequate, and uniform application.

Apply a spray adhesive in what is called an "x" pattern, or spraying the glue in a slightly overlapping pattern first horizontally across the substrate then vertically. This will ensure adequate coverage and good adhesion, though be certain to follow all instructions noted by each individual manufacturer on their own can "tack" time and procedure vary.

Pressure Sensitive Adhesives

Pressure sensitive adhesives come precoated onto mounting boards with a "tacky" bonding glue and removable protective release paper backing. They were designed for quick, easy mounting of prints and photographs by simply applying pressure by hand or brayer to set. The recent development of improved pressure-sensitive acid-free boards has also increased their use when mounting needlework as an alternative method to conventional stretched mountings.

PMA or "positional mounting adhesive" is a similar form of pressure sensitive adhesive though the process used to mount it is often called "cold mounting". The roll of adhesive which unlike other pressure sensitives is not premounted to a mounting board or substrate, is like two sided tape with removable release paper on either side and was designed to be used on relatively small projects (not larger than 16x20) then burnished down with a brayer or squeegee upon completing placement.

PMA is considered a "two-step" pressure sensitive adhesive since it needs to be first cut and applied to the substrate (step 1) then the exposed release paper is removed and the art or photo is positioned (step 2). The clean print or photo would then be covered with release paper and brayered into permanent position. PMA has taken a bit of a back seat with the increase of new "one-step" pressure sensitive boards in the 90s, yet the self trimming methods as explained here remain exclusive to this product in the world of pressure sensitives.

Remove release paper from PMA, press the print onto the adhesive which in turn transfers the adhesive (when print is lifted) to the back of that print for immediate application to the desired substrate. This method is somewhat self trimming and ideal for use in montage projects or multiple photographic mountings where adhesive needs to be isolated into select areas.

Dry Mounting Adhesives

Recent trends in dry mount tissues include the attempt to "whiten" the tissue core for greater opacity when desired, a general striving for a more balanced adhesive/core neutral pH level as well as low mounting temperatures.

Dry mounting adhesives come in both rolls and precut sheets, and are produced by a number of manufacturers. They are not tacky to the touch and are fused by a process of applying the proper ratio and control of TIME, TEMPERATURE, PRESSURE and HUMIDITY, in mechanical or hot/cold vacuum presses.

Dry mounting is fast, dependable, predictable, and quite cost effective as a result of the increased speed of mounting. Yes, the initial investment of a mechanical or hot vacuum press needs to be taken into account, but the additional creativity and laminating possibilities will maximize quick equipment payoff and return (refer to numerous mounting/laminating/mat design articles PFM February '91, June '91, August '91).

There are many different dry mounting adhesives on the market which fall into permanent, removable, tissue-core and non-core categories. The first category or, "tissue core" sheet adhesives, are constructed from a tissue center or base sandwiched between two layers of thin heat activated adhesive. Although many tissues will suitably work with many of the same materials, be certain the tissue is compatible with the material being mounted in terms of breathability. Of the tissue core adhesives there are both porous (breathable paper based) and non-porous (non-breathable glassine based) tissues. Simply keep in mind the layers of materials being mounted and make certain the trapped air has an escape. If a non-porous glassine based tissue is used to mount a non-porous material, say a photograph, the result could be air trapped between the two elements.

Tissues are generally white and somewhat opaque in nature even the non-porous glassine tissue core designed specifically for porous paper mounting. Porous or breathable tissue core adhesives (the bulk of what is produced) may be used to bond either porous paper and fabric or non-porous photographs, thus it is one of the easiest to use and therefore generally the best seller.

Thought and care should be taken when selecting the proper tissue to use, for they are each designed for specific needs. Any time you integrate a white tissue core adhesive behind any mounted surface you run the risk of introducing that opaque white color once again. In select cases it would be most desirable to have a colorless adhesive to mount the project. A spray or wet glue fits that description, but if a dry mount mechanical or heat vacuum press is to be used, a sheet of pure non-tissue core adhesive would be recommended.

Colorless "pure adhesive" film has no tissue core and is also available in both precut sheets and rolls just as the above tissue core adhesives. Unlike other tissues, pure adhesive film may be pieced together since it totally melts during the heat bonding process and ridges cannot be formed by any core tissue. Be careful not to pile too many layers together when you are mounting a thinner paper or fabric for it may bleed through.

The overall bondability is excellent since pure adhesive thoroughly melts in the press and is exceptional for fusing very porous materials such as fine art papers ("Tiered Matting", PFM February `91), heavy fabrics ("Shadow Boxes", PFM November '91), or multiple uneven layers involving non-porous laminating films ("Leather-look", PFM June '91), and it is perfect for mounting newspaper with black type onto a black substrate thus preventing "ghosting" from the back.

Permanent and Removable

Permanent adhesives are quite simply those that have been designed to be permanently set once heat has been applied. The bond is created under pressure and heat while in the press. They are considered permanent because they are not easily removed and therefore the process of removing them is rather involved and time consuming. It is however notable that even "permanent" adhesives under the proper conditions can, at times, be removed without damage. Liquid solvents are necessary to release their bond from the substrate through soaking or applying said solvents with an eye dropper. Common solvents include UnSeal, Bestine thinner, mineral spirits, acetone and toluene. One need also consider once again that "time is money", and it may very well be faster and less costly to replace the problem mount rather than to try to remove it once a permanent tissue has been used.

Removable adhesives liquefy in the heated press yet the formal bonding process occurs outside of the press under a cooling weight. Thus the very nature of the removable tissue or film is for the flexibility of optional removal. Turn the press temperature up to approximately 200ºF, reposition the project to be released in the press and depending on the size and density of the project leave it in the heat for a few minutes. Since the adhesive reliquefies under heat the artwork should be easily lifted or peeled from the substrate/adhesive when removed from the press.

Take care to separate the art from the actual adhesive immediately, for as soon as the papers begin to cool the adhesive will reset. Also the art needs to be separated from the adhesive in preparation for potential remounting. Separation of reheated removable adhesives is very easy and feels like removing the release sheet from the back of laminating film. If there is a resistance or the paper ply splits or appears to be separating, the piece was not heated warm or long enough.

It is extremely important to remember that removable does not mean reversible. For even though there are "archival" mounting tissues being marketed, once artwork has been heat mounted there will always be adhesive residue remaining in the paper if removed. In fact there is enough residue from a separated print remaining on the back to actually remount it to a new substrate without a sheet of mounting tissue needed at all. "Reversible" generally means remaining able to always take the artwork back to its original unmounted state or never altering it in any way. Thus adhesives may be removable, most definitely, but you will have always altered their original state somewhat.

Manufacturers readily supply end users with all the information required to make quality decisions concerning appropriate equipment selection, mounting techniques and step-by-step procedures. Quite often technical bulletins or information sheets are packed with adhesives concerning permanency, pH, temperatures and dwell times. These should be read, saved, and referred to as needed. Suggested mounting methods and recommended materials best suited to individual adhesives are also supplied, and should be respected for best results.

Adhesives should never be feared...merely respected. Never surge ahead on any artwork without proper knowledge or training, but don’t ever be afraid to test, push and play with scraps and disposables. Thus the trends for 1992 seem to be branching out and discovering what's already out there that might make your mounting more cost and time effective.

Copyright © 1992 Chris A Paschke

For more articles on mounting basics look under the mounting section in Articles by Subject.
Additional information on all types of mounting is found in:
The Mounting and Laminating Handbook, Second Edition, 2002,
The Mounting And Laminating Handbook, Third Edition, 2008 and
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.

Chris A Paschke, CPF GCF
Designs Ink
Designs Ink Publishing
785 Tucker Road, Suite G-183
Tehachapi, CA 93561
P 661-821-2188