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Membrane technology presses forward.

Even though membrane presses can amaze woodworkers with their ability to overlay complex 3-D shapes, their price tag continues to hinder sales.

Up to now, membrane presses have been a tough sell. Most of the equipment suppliers interviewed for this article estimated that only 20 to 40 membrane presses are currently being used in North America.

If membrane presses were less expensive and easier to operate, they would probably enjoy widespread use. Anyone who has seen a membrane press thermofuse a veneer or vinyl face perfectly snug to every edge, corner, recess and flat surface of a platen full of raised panels can appreciate the benefits and design possibilities this impressive technology brings to the woodworking industry.

If lumber prices continue to soar and finishing regulations become more stringent, suppliers say price will become even less of an object because the versatility of membrane presses will help justify costs. Not only can membrane presses be used to apply veneer to flat or 3-D MDF or other core materials that are less costly and require fewer machining steps than solid wood, they can also apply vinyl overlays to achieve a painted look in one step and with no finishing emission problems.

"The U.S. is just getting out of the starting gate," said Henry Van Brussel, president of Veneer Systems, North Bay, Ontario. "There could easily be ten times more membrane presses in operation by the end of this decade."

On a mission

Most membrane press suppliers said they have spent more time educating customers than selling to them.

"Sometimes," said Michael Ermel, Friz product manager for Holzma-U.S., Gastonia, N.C., "I feel like a missionary in 19th century Africa trying to convince the natives to wear sandals. They ask me, |Why should I wear sandals? My father did not wear sandals. My grandfather did not wear case of high gloss, it seems like you paint and sand forever. With a membrane press, you get the same look in one press and with no finishing emissions."

A long learning curve

A second factor that has hampered membrane press sales is the relatively lengthy learning curve that can run six months or more for operators to feel comfortable with the technology. Operators should expect to endure a lot of trial and error to find the right combination of heat, pressure, glue and cycle time that will successfully thermofuse a given overlay to a substrate.

"I tell my customers that when you buy a membrane press, you don't buy a machine, you buy a technology," said Ermel. "Running the press is not that hard. The real difficulty is in the setup because there are so many variables that come into play .... Pressing veneers is no piece of cake, but they pose fewer problems than vinyls. Sometimes 15 seconds of cycle time or a couple degrees of temperature can make the difference between a beautiful product and a reject."

To lessen the challenge of "finding a good harmony" between all of the variables involved in the pressing process, Van Brussel said, "I advise my customers to buy a complete membrane press package, including glues and materials that we have had experience working with successfully. The initial cost might be greater but it can substantially reduce the learning curve."

Frank Bean, sales manager of Sorbilite, said his company operates a training facility at its headquarters in Virginia Beach, Va. "Our goal is to shorten the learning curve by making sure that our customers understand that there are differences between adhesives or that overlaying a 40-mil vinyl creates a whole different set of operating parameters than working with a 7-mil material."

Bean added, "Believe it or not, one of the most critical steps occurs before you put the workpiece in the press. If you don't apply the adhesive evenly, you're opening yourself up to delamination problems."

"It might take six months or longer to learn," said Willy Volk, president of European Woodworking Machinery Co., Franklinton, N.C., "but once you get good at it, you have a tremendous advantage over your competition because you can make great looking cabinet doors, desktops, toilet seats, end panels and other products without using valuable solid lumber. This technology can help us stretch our timber resources."

Pressing veneers

Membrane presses can thermofuse veneers to flat panels or to shaped panels. One of the most common applications is substituting solid wood with MDF or particleboard to make raised panel cabinet doors and passage doors.

Typically, a substrate that has been shaped on a CNC router becomes the core of a sandwich covered top and bottom with veneer sheets, to which PVA or urea resin glue has been applied. The workpiece is loaded onto the membrane press platen either manually or automatically.

When the platen comes down, the membrane and the veneer conforms to the shape of the workpiece. With the chamber frame forming a tight seal, about 100 psi of pressure and 75C to 80C of heat is applied for up to four minutes to cure the glue and thermofuse the veneer to the substrate.

"One advantage veneered MDF panels made with a membrane press have over glued-up solid wood panels is that they are less likely to warp or crack," Ermel said. "Another advantage is that the face is more uniform because you can match grains by laying up the veneer anyway you want."

Pressing vinyls

Melamine-backed MDF is the substrate of choice for most companies that thermofuse vinyls on their membrane presses to emulate the white painted look. MDF is preferred over particleboard because it is less likely to telegraph substrate flaws through the vinyl.

Up to three coats of PVA or urea resin adhesive can be sprayed onto the MDF panels immediately after they have been shaped on a CNC router. Once the glue has dried, the panel can be fed into the membrane press face up. A vinyl sheet is unrolled from a spool and made to come into loose contact with the substrate. The vinyl is preheated so that it softens just enough to conform to the workpiece's shape. To eliminate bubbling, a vacuum evacuates any air that would otherwise be trapped between the substrate and the vinyl. The glue is reactivated by heat and combined with pressure, the vinyl is fused to the substrate.

Van Brussel noted that because of their elasticity, vinyls can better negotiate complex curves and sharp angles than veneers can. "You can stretch vinyl but you can't stretch veneer," he said.

Some of the presses on the market do not require a membrane to thermofuse vinyls. Volk said that in the case of the Buerkle multiform press his company offers, the foil acts as the membrane. "The membrane has its place but it slows down press time and increases energy consumption because heat has to travel through the membrane to get to the vinyl," Volk said.

Harodt said silicon membranes, though more expensive than rubber membranes, last longer because they are more durable and because small tears can be repaired using liquid silicon. He added that silicon membranes can operate at higher temperatures and will not yellow vinyls like rubber membranes can.

Van Brussel said replacing a membrane can cost $1,000 to $3,000. Its life expectancy is about 3,000 to 4,000 press cycles for veneers and about 1,000 to 1,500 cycles for vinyls, he added.

New material choices

The potential growth of membrane press use has not gone unnoticed by manufacturers of decorative overlays. Several companies are developing products specifically engineered for membrane pressing.

One of them is Riken, a Japanese manufacturer of decorative vinyl overlays. Peter Zimmerman, Riken's North American sales consultant, Westport, Conn., said one of the company's newest developments is a smooth vinyl that makes it less difficult to achieve a high-gloss look.

"Up to now most of the vinyls that have been used in membrane pressing have been textured vinyls because smooth vinyls are more prone to telegraphing problems." To illustrate his point, Zimmerman said, "Because the machined groove of an MDF raised panel is less smooth than the flat surface, when glue is applied, the grain can raise and the groove can show through the vinyl." He added that the "pebble-grained" pattern of a 6- to 9-mil textured vinyl can hide some flaws that a smooth vinyl cannot.

To combat telegraphing problems, Zimmerman said Riken has developed a smooth vinyl up to 40 mils thick. "Because of its thickness it hides machining flaws well," Zimmerman said, "but it is also a more difficult material to work with because more pressure and heat is required for the thicker vinyl to conform well to the substrate. Also, applying too much heat for too long can deform the vinyl. It takes a lot of technique but there are companies, particularly in Germany and Italy, that have been very successful with it."

Another company that is beefing up its line of decorative overlays for membrane pressing is American Mirrex Corp. of Delaware City, Del. The company recently introduced a 16-mil rigid vinyl with a matte embossed finish.

"This is the heaviest gauge vinyl that we offer for furniture and cabinet applications," said Diana Roman, marketing manager of American Mirrex. "Our customers like it because it looks like a painted surface and is thick enough to hide telegraphing problems. Consumers like it because vinyls are stain- and scratch-resistant and are easy to clean."

Precoated adhesive vinyls represent another recent overlay development, Harodt said. "Using a vinyl precoated with adhesive eliminates the problem of uneven glue spraying and eliminates another environmental hazard," he said.

Van Brussel said he is aware of companies that use two-layered vinyls. "The topcoat might be white and the bottom coat might be silver gray," he said. "After the vinyl is pressed onto the panel, the manufacturer can carefully rout out the top layer to achieve the look of a color inlay."

The advent of new decorative overlay options will help make membrane pressing look even more attractive to potential customers, Bean said. "Membrane pressing already allows tremendous design possibilities. Creativity is mainly limited to the materials available, but that is changing rapidly. As material suppliers develop new products, the market for membrane presses will expand."
COPYRIGHT 1992 Vance Publishing Corp.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1992, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

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Title Annotation:new vinyl overlaying process on flat and 3-D wood panels promises to solve volatile organic compound emission problems
Author:Christianson, Rich
Publication:Wood & Wood Products
Date:May 1, 1992
Words:1705
Previous Article:Economic impact of VOC reductions.
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