MATERIAL INNOVATIONS |
CONTINUING EDUCATION SERIES:
The Evolution of the Wood Panel

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In the beginning there was wood, and wood was the word—the last word, that is, in construction materials for furniture and interiors, and the primary resource for mankind’s first built environments.

For millennia, solid wood has been used for floors, walls, ceilings, and everything in between, including cabinetry, tables, seating, and worktops. It was abundant, easy to harvest and work with, durable, and beautiful; it was nature’s perfect building block.

Working with solid wood created a significant amount of waste, or offal, however, which either became fuel for the hearth or was hauled off as garbage.

As man’s demands for ever-more elaborate structural designs evolved, solid wood began to reach its engineering limits. Variances in its consistency and its inherent susceptibility to changes in temperature and humidity (leading to warping and splitting) created a demand for something more uniformly stable, and something that is available in large sizes and volumes.

Enter plywood. Plywood is created by harvesting whole trees and peeling the lumber into veneer, which is sliced into sheets, laid up and glued at 90-degree angles to create a panel. This cross-grain construction method counterbalances wood’s natural tendencies to expand in the direction of the grain, so plywood panels are far more dimensionally stable than even edge-glued solid lumber.

While plywood makes far more efficient use of wood fiber than working with solid lumber, there is still a lot of waste involved in its manufacture; waste that (still) must be landfilled or burned … or preferably, used to create the next generation of wood-based panels.

MODERN ENGINEERED PANELS
Particleboard and MDF represent the highest level of evolution in maximizing the use of wood fiber left behind by other manufacturing processes from lumber mills, plywood plants and furniture fabrication. Particleboard, as the name implies, is made up of small wood particles or chips bound together by any of several different resin systems under heat and pressure. In MDF (medium-density fiberboard) the wood chips are further refined down to cellulosic fibers, producing a panel with a smoother surface and a more homogenous core than particleboard. By volume, these panels consist of mostly reclaimed wood fiber (more than 90 percent by volume).

Both are well suited for specific interior and furniture applications: particleboard, for applications that require a stable, economical substrate that will be surfaced with a decorative overlay (a veneer or laminate); and MDF, for components that will be finished with paint, lacquer or thinner decorative overlays that might “telegraph” the less-homogenous texture of a particleboard surface.

MDF is also the material to choose for designs that call for machining details into the core of the panel: e.g., radiused edges and rounded corners; channels or recesses in the interior of the panel for integrated door and drawer pulls; and, designs that mimic raised-panel and other door designs.

Special grades of particleboard and MDF are available for specific applications, including enhanced moisture and fire resistance, increased dimensional stability in extreme conditions, higher density, greater screw-holding properties, and lighter weight. The resin systems can also be engineered to meet and exceed indoor air quality regulations and consumer demand.

ADDING THE DECORATIVE SURFACE
Although some designs call for finishing raw particleboard and MDF with lacquers or a powder coat, the overwhelming majority of these substrates receive a decorative overlay or laminate.

The standard bearer in laminates is, of course, HPL (high-pressure laminate)—that wondrous jet-age material made famous by Formica and Wilsonart. Like engineered wood panels, HPL is mostly wood fiber—several layers of core, or “kraft” paper (similar to that used for brown paper bags), topped with a solid color or printed decorative layer and a protective wear layer. The lower-cost phenolic resins are dark in color, which accounts for that brown line you see at the edges of a sheet of HPL. Costlier melamine resins are clear and don’t interfere with the aesthetic integrity of the décor layer.

When you laminate a substrate with HPL, you are basically joining two products that are manufactured, shipped, sold and stored separately in what amounts to a third process: gluing them together. The advantage to this is, it’s convenient for small fabrication shops to use, and can even be done right on the job site. The disadvantage is, it’s expensive in terms of materials costs and labor, and involves a larger number of processing and manufacturing steps than is necessary to satisfy the demands of many end-use applications. But, we’re getting ahead of ourselves.

THE BIRTH OF TFM
More than a quarter century ago, European panel manufacturers began bonding the decorative paper layer directly to the panel faces, producing a laminated panel with fewer manufacturing steps. Under heat and pressure the resins in the decorative layer actually crosslink to those in the board, creating a homogenous decorative panel, without need for an adhesive.

Known as thermally fused melamine (TFM) panels or direct-pressure laminate, these products quickly proved themselves durable enough for vertical and many horizontal applications, even comparing favorably to HPL in wear resistance (impact resistance too, with a high-density substrate), thereby offering a lower-cost and truly “value-engineered” option. TFM’s edges are finished with the same materials you’d use on an HPL panel.

Its limited initial color offering, however—white, almond or gray—relegated TFM largely to cabinet interiors and other pedestrian applications. A small range of colors, woodgrains and abstract patterns found their way onto TFM, but manufacturers remained focused on large-volume single-color runs to maximize efficiency. Switching décor papers too often “wasted” valuable press time.

Then, Pergo happened.

Pergo, of course, is laminate flooring, which nearly everyone knows by now. What few people realize though is that Pergo is TFM. The shear volumes involved in producing flooring for consumers pushed the TFM industry into overdrive, creating higher density MDF cores, more wear-resistant melamine overlays to protect the decorative layer, and high-precision fabrication technology.

This rush to floor the world also required TFM to finally embrace a wider variety of design. Striving for ever-greater realism, producers pioneered advanced technologies like sophisticated surface finishes and in-register embossing, with which the woodgrain surface texture aligns perfectly with the “ticking” printed on the décor paper. Extremely stable and thin grades of MDF were engineered to resist impact, less-than-perfect installation techniques and even the levels of direct moisture encountered in bathrooms.

These important innovations reinvigorated TFM suppliers’ vision of what the material could bring to a wider range of furniture and interior applications. And with a design range as far-reaching as HPL, TFM is now increasingly specified for casework, worktops and even wall paneling in hospitality—a perfect value-engineered alternative for veneers, metals, and other materials in health care, retail, food service, corporate, and other applications.

In addition to TFM’s value as a durable, cost-effective material choice, specifiers are also drawn to the material’s inherent environmental benefits:

• It consists of wood fiber wasted by other processes that would otherwise be landfilled or burned
• It’s manufactured in efficient, state-of-the-art plants located throughout North America
• Water-based inks are used in printing the decorative layers
• Specifying a cherry, walnut, zebrano or wenge surface has zero impact on those, or any other, precious wood species
• Because of its durability, its useful life is years longer than a veneered or solid wood component

FORMALDEHYDE, MELAMINE AND THE TRUTH ABOUT IAQ
Both formaldehyde and melamine are used in the production of TFM, and both have been featured in health-related news stories lately, so it’s important to know the facts.

Almost every living organism emits formaldehyde, including human beings. It occurs naturally in the air we breathe, the foods we eat, and the wood used in furniture and panels. In very high concentrations it can cause irritation of the eyes, nose and throat. It has been indicated in some reports to be a “known human carcinogen,” although other scientific data refutes this.

What is known is, at typical day-to-day levels of exposure, the risk of related cancer is essentially non-existent. This exposure includes formaldehyde’s use in pill coatings, cosmetics, vaccines, wall coverings, shampoo, cleansers, disinfectants, and wrinkle-free clothing products, to name just a few. We also know that it does not accumulate in our bodies, and is broken down when exposed to sunlight.

Urea-formaldehyde is the basic building block for adhesives, like those used to bind the elements of particleboard and MDF. Different adhesive formulations carry different levels of formaldehyde, and manufacturers are switching to “no-added formaldehyde” adhesive systems that satisfy new indoor air quality limits like CARB ATCM (California Air Resources Board Air Toxic Control Measure).

While the CARB standard applies to raw panels, it’s important to note that when a panel is laminated it is essentially sealed, reducing even these safe emission levels by up to 98 percent.

Melamine formaldehyde resin is impregnated into the decorative paper and wear overlays as a bonding agent. This resin system is what bonds the surface to the panel in the TFM press—no additional adhesives are used. The production of melamine crosslinks the formaldehyde component more completely than in urea-formaldehyde, minimizing the potential for emission.

You might be familiar with melamine resin products from your grade school days; e.g., the indestructible plastic plates and cafeteria trays you still find there are made of melamine.

3-D LAMINATES AND MATCHING SURFACES
In recent years, TFM has been increasingly mated with 3-D laminates (3DLs) in unique and functional component designs. 3DLs are thin, formable overlays created from PVC or polyethylene polymers in solid colors, metallic and printed designs (also known as rigid thermofoils [RTF] or vinyl films). They can be specified in a variety of surface textures, including realistic woodgrain ticking and high-gloss, as well as with enhanced chemical resistant properties. Many 3DL products offer wear resistance comparable to that of HPL.

3DL is unique in that it can be pressed onto a panel, usually MDF, with 3-D details machined into its edges or face, as well as onto unconventionally shaped panels and panel edges. A heated pneumatic membrane literally squeezes and stretches the 3DL into and over the recessed and edge details of the panel. The material’s ability to “self edge”—wrap seamlessly around the edges and interior cut-outs of a panel—reduces processing steps and helps seal the panel core from moisture and bacteria. This ability also helps create “soft” edges that mimic shaped solid wood or stone.

Typically, a 3DL component will have a melamine decorative surface on one side, and 3DL on the other five. Many TFM and 3DL suppliers share design data for perfect matches on such panels, so when you open that woodgrain cabinet door, for instance, you’re not shocked by a solid white back.

3DL components have gained popularity as the office furniture industry has embraced nonstandard shapes and soft edges for worktops, and are increasingly being specified for unique store fixtures and displays. They are also commonly found on cabinet doors and drawer fronts, and are making their mark in health care applications because of their seamless construction and ease of cleaning.

In many ways, TFM and 3DL are a perfect design match, but there are still more matching material options—in HPL for the highest wear surfaces in a project, and in decorative paper overlays for light-duty vertical and interior casework surfaces, and, of course, edge treatments. If veneers are part of your project, they can be finished to match the TFM/3DL if necessary.

With so many surface options and application-specific mechanical properties, the TFM/3DL combination is poised to be a benchmark building block for modern interiors and furniture. Factor in its frugal use of raw materials and environmental friendliness, and it quickly rises to the top of responsible material choices.

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Freelance journalist and photographer Kenn Busch has been covering the furniture industry since 1990, and publishes www.materialintelligence.com.