Several weeks ago I addressed the problems that can occur when equipment is purchased without understanding the limitations associated with a particular technology. I briefly discussed vacuum formers but didn’t spend a lot of time on other press technologies. Whether you are looking to buy a press or just need to qualify a potential vendor, no decisions should be made until you understand the distinctions.
Though some mistakenly refer to them all as “membrane presses,” there are four basic types of 3D Laminating systems:
* bladder (liquid filled) presses,
* membrane presses,
* membrane-less presses, and
* vacuum formers.
(For a definition of these and other related terms, please see my 3D Laminating Glossary.)
Each technology has its place, but not all do every job equally as well. We’ll discuss each one over the next few weeks starting with the most unknown of the four.
Bladder presses are the oldest of the 3D Laminating technologies, having been developed in the 1960s. Since 3D Laminate (RTF, thermofoil) wasn’t developed until the ‘80s, bladder presses were originally used for veneered raised panels. A bladder press does incorporate a membrane, but the chamber behind the membrane is filled with thermal oil. Since liquid pressure is safer than air pressure (think of how an air balloon pops vs. how a water balloon bursts), bladder presses are characterized by much higher pressure capacities.This extra pressure is helpful when producing veneered raised panels,especially when pressing more difficult species. (See video below as Dave Ortmayer of Italpresse USA demonstrates in detail how a liquid-filled press applies veneer onto raised panels.)
Bladder presses aren’t only used for wood veneer. Though they are not ideal for 3D Laminate (3DL), some companies have successfully taken advantage of the extra pressure capacity to press highly detailed profiles. In addition, since high gloss 3DLs are very sensitive to heat, the ability to hold the thermal oil at a constant temperature even when pressurized can be a tremendous advantage when trying to get a true mirror finish.
There are several reasons behind why bladder presses haven’t been widely accepted for pressing 3DL. Most liquid filled presses have been built without vacuum systems to eliminate air between the 3DL and the platen, requiring the material to be cut to size for each individual part rather than simply pulling a full sheet over the entire bed. Since there is no way to inject air in between the membrane and the 3DL, there is no means of cooling the laminate and adhesive under pressure. Without this ability, 3DLs that are less rigid can tend to pull out of the profiles and lose the high definition created by the extra pressure capacity. Finally, tearing of the membrane can result in an oily mess inside the press. Though this concern is real, the problem is often overstated by competitors as many operators avoid this concern all together by putting membrane replacement on a maintenance schedule.