Developing a Bond Between Adhesives and Overlays
Proper surface preparation and adhesive use will prevent delamination.
By Larry Sloan and George Carter
The laminating industry encompasses a broad range of products, which include furniture, cabinets and floor coverings. Adhesives, naturally, play an important role in both structural integrity and aesthetics. Proper surface preparation and selection of the right adhesive will help ensure a long-lasting bond and prevent delamination from occurring.
The Adhesive and Sealant Council estimates the total U.S. market size in 2002 for lamination adhesives used for decorative overlays (excluding saturated papers and edgebanding) at 54 million dry pounds. This figure is predicted to grow 2.5 percent annually over the next five years.
The array of adhesive types is shown in the following table. These figures exclude wood veneer and assembly adhesives, as well as all packaging film-to-film adhesives and similar type adhesives.
Overlay Shipment Figures
Excluded from the data table are saturated papers that are used for thermofused melamine panels. These overlays do not require an adhesive since the resin compound saturated into the paper acts as the bonding agent by cross-linking with the wood fibers on the surface of the substrate.
Many Factors Determine Adhesive Choice
Price is also a consideration. The end-user may need to figure in the price of storage and application equipment to come up with the total cost of using a particular adhesive. Don’t forget to include labor and utilities as well. A typical PURHM (polyurethane hotmelt) adhesive can be seven times more expensive per pound than a PVA (polyvinyl acetate), but may save time and money in the long run.
The Lamination Process
Regulations limiting the use of products containing potentially hazardous VOCs may necessitate the use of other products that may seem less ideal. As an example, solvent-based contact cements have been under attack for many years. Fortunately, however, many alternative adhesive formulations have been developed which oftentimes perform better than the incumbents. The adhesive industry is constantly researching ways to “build a better product” that will stay ahead of the environmental curve without compromising performance.
Wide temperature swings inside a production plant should also be considered. For example, typical PVA glues will have a minimum use temperature. If ambient temperatures fall below this point, the adhesive may not perform as well and result in a weaker bond joint. Another example is PURHM formulations. Initial green strength and total process time can be affected if temperatures in the plant fluctuate too much.
Of course, storage and feed equipment must be operated according to manufacturers’ guidelines. Tank/tote storage conditions, pumping rates and pressures and application monitoring all need to be considered.
New Adhesive Trends Benefit Laminating
In addition, there is a new class of hot press PVA adhesives that permits bonds to be formed, even if the glue is dry before the high pressure laminate is laid up. According to Franklin International, this helps compensate for line stoppages without wasted material. It also permits companies to continue to glue up panels even if the hot press is a bottleneck.
Reactive hotmelt and polyurethane technologies also speed up processing, and are appropriate when gluing difficult or non-porous substrates. Other technologies already on the market include: high solids, web coat, pre-applied and heat- and pressure-activated products.
Larry Sloan is the director of marketing and member services for The Adhesive and Sealant Council. For information, contact the ASC at (301) 986-9700 or visit www.ascouncil.org.
George Carter is the executive director of the Laminating Materials Assn. Contact the LMA at (201) 664-2700.
Have something to say? Share your thoughts with us in the comments below.