Adhesives for Use Inside Exhibit Cases
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Adhesives used to secure case liners, graphics and other elements to the case interior must meet conservation standards for low outgassing and stability, and must continue to function well over time.
Which adhesives should I avoid using inside a case?[edit | edit source]
Most adhesives emit large quantities of solvents and un-reacted monomer volatile substances during their drying or setting phase. Even after this initial period, lower levels of outgassing can continue indefinitely. In the past, a wide variety of glues and adhesive systems were used indiscriminately in exhibit assembly. Today a myriad of new and complex formulations are available on the adhesives market making the selection of a conservation-appropriate adhesive a difficult process.
Research has shown that some of the most damaging adhesives fall into the categories of "contact" and "pressure sensitive" adhesives. Rubber-based adhesives, either vulcanized or synthetic, age badly due to sulfur and chloride content. Traditional hide glues can be problematic due to their sulfur content. Two-part adhesive systems, such as epoxy and polyester types, also have a poor track record for stability.
Adhesive types to avoid within close proximity to exhibit objects[edit | edit source]
- Rubber-based: Avoid any adhesive that is based on or contains natural or synthetic rubber because of its poor aging characteristics.
- Animal glues: This adhesive type contains residual sulfur and is therefore not a good choice for use in enclosed spaces.
- Vinyl emulsions: Emulsion-type adhesives in which a resin is dispersed in water, include polyvinyl acetate emulsions. These "white glues" do outgas, especially once the shelf life has expired.
Adhesives types considered acceptable[edit | edit source]
- Acrylics: Acrylic adhesives are a stable class of adhesives that can be chosen for most museum applications. Acrylics are used in many types of solvent adhesives, adhesive tapes, hot-melt adhesives, and stick formulations.
- Hot melt: Acrylic hot-melt adhesive sticks used in heat guns are approved for exhibit use; these are usually clear sticks. Opaque sticks with a yellow cast often contain waxes and other additives that make them a less desirable choice.
How can adhesives be used safely within the case?[edit | edit source]
Careful design of exhibits can actually lessen the need to use adhesives. Exhibit cases can be designed so that adhesives do not interface with the display chamber. When adhesives must be used inside the display chamber, joints should be sealed with a conservation-appropriate caulk. Alternatively, a laminate can be applied over seams. Unfamiliar adhesives systems require investigation and careful scrutiny; the key guidelines for selection are:
- Use mechanical fastening techniques. Whenever feasible, use a mechanical attachment method, such as staples, pins or construction overlap. In particular, attaching fabric case liners mechanically greatly reduces the amount of adhesive exposure within a case.
- Exclude adhesives from the case interior. Design the exhibit case and use construction techniques to limit the use of adhesives inside the case itself. Use conservation acceptable laminates and caulks to create effective barriers at joints to prevent infiltration of volatile adhesive components.
- Use conservation-quality adhesive. Use adhesive systems which have a track record and include acceptable chemical components, such as acrylic resins and high-temperature, hot-melt adhesives.
- Aerate the adhesive. Allow sufficient time for the curing and setting of adhesives before objects are enclosed in the exhibit case. A minimum period of three weeks is recommended during which time the case doors should be open and bonnets left off.
Are adhesive tapes all right to use inside an exhibit case?[edit | edit source]
There are two types of tapes that have applications in case construction: adhesive transfer and double-sided. Adhesive transfer systems use paper backings to support the deposition of a layer of adhesive onto a surface. Double-sided film tapes have two surfaces of adhesive with a plastic carrier sandwiched between. The adhesive systems are usually based on rubber or acrylic adhesives. An acrylic adhesive should be chosen. The carrier films of pressure sensitive tapes are generally stable enough to use within a museum setting. An acrylic carrier is preferable to polyurethane.
If sufficient surface area is covered, such tapes can be used in a variety of case applications including adhering wood veneer and fabrics and boards. Some tapes are actually manufactured as replacements for mechanical fasteners.
Mention of a product, manufacturer, or supplier by name in this publication is for information only and does not constitute an endorsement of that product or supplier by the National Park Service. Listed materials have been used successfully in past applications. It is suggested that readers also seek alternate product and vendor information to assess the full range of available supplies and equipment.
General Adhesive Sources
- Conservator's Emporium
- Scotch VHB (Very High Bond) Foam Tape 4910, and VHB Adhesive Transfer tape F9460PC (VHB) (Double coated and adhesive transfer tapes with acrylic adhesive;
- 3M Tapes 8671, 8672, 8681, 8663 (Scotch Polyurethane Protective Outdoor Grade; polyurethane with pressure-sensitive acrylic adhesive.)
- Scotch VHB (Very High Bond) Foam Tape
- Archival Filmoplast and 3M #415 Tapes (A range of archival quality pressure sensi tive tapes; some double-sided; range of carriers and adhesives)