Using High Pressure Laminates in Exhibit Case Construction
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During the past two decades decorative laminates have had considerable use within cases. The major melamine resin brands of high pressure laminates, if carefully used, can be employed safely in museum exhibits.
What is a high pressure laminate?
High pressure laminates are rigid sheets made of a paper composite. A decorative top sheet is impregnated with melamine resin (an amino resin made from formaldehyde and melamine) and then laminated under high pressure to multiple sheets of Kraft paper embedded with phenol formaldehyde resin (Formica uses a water-based rather than a solvent-based phenolic resin). The surface texture or effects are made by impression with a textured paper or a metal sheet.
Do the laminates outgas harmful chemicals?
The high pressures and heat used during manufacturing eliminate much of the solvent from the adhesive systems. There appears to be no significant outgassing of formaldehyde from the resins. When newly manufactured laminate sheets are cut, heated, or worked in some manner, some release has been recorded. One manufacturer recommends letting a laminate set from six months up to a year to dissipate any potential formaldehyde emission.
Wilson Art and Formica Corporation have tested their products with the Formaldehyde Test Method-2 1985 (also referred to as the large chamber test) and found emissions of between 0.01 and 0.04 ppm. These levels fall far below (up to 75 times) the maximum level for safety in the work place (current OSHA Standard is 0.75 ppm in 8 hours) and below the threshold for object damage.
Certain laminates include a fire retardant additive, for example, aluminum tri-hydrate(ATH). In general they are to be avoided in exhibit case construction because of possible salt formation and outgassing problems. In some instances salt crystals have formed on the back side of fire retardant laminates.
How are laminates used in exhibit construction?
High pressure laminates are used in museum cases as a decorative and/or protective layer over a substrate such as a wood product. Exhibit designers and fabricators use laminates for aesthetic reasons. If applied correctly, laminates can also provide the following conservation benefits:
- Act as an effective barrier against the outgassing from wood and wood products: The EPA considers these products to be encasing materials, indicating that they will function as a vapor barrier against volatile emissions from particleboard and other substrates.
- Assist in stabilizing a microclimate in sealed exhibit cases: Because the melamine layer is impermeable to water vapor, the laminate can reduce moisture interference from wood and wood products used to construct the case. The phenolic resins, however, swell with water; this can cause a laminate in a case maintained at a high relative humidity to warp.
There are a number of precautions to follow when using a laminate inside an exhibit case.
- Avoid the re-moldable laminates: Because they are under-cured compared to the general purpose laminate grade, these products can be heated and shaped. It is likely that re-molded laminates are less moisture resistant and more likely to outgas formaldehyde then the general purpose grades.
- Use adhesives carefully: The adhesives used to glue the laminates onto a substrate such as particleboard are a major potential source of volatile contaminates. These contact cements should be used outside of the exhibit area where adequate ventilation exists; use no more than the amount recommended by the manufacturer. Remove all adhesive residue from the laminate surface and allow at least three weeks curing time before objects are located inside the case.
- Make sure that there are no raw edges of a laminate exposed inside an exhibit case; all edges must be tightly fitted and gaps along seams filled with appropriate caulk sealant to prevent emissions.
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.
High Pressure Laminates
- Formica Laminate, Formica Corporation
- Wilson Art Laminate, Wilson Art
- Nevamar and Micarta Pionite, International Paper
- Decorative Laminate, Pioneer Industries