Last week I started a brief series highlighting the distinctions between the four main 3D laminating press technologies, and briefly looked at bladder presses In order to allow for more detail on each, I’ve decided to cover membrane-less presses today and membrane presses next week. (See: 3D Laminating Glossary)
As I mentioned last week, all four of the technologies are often mistakenly referred to as membrane presses. In my early days in 3D laminating it seemed odd that a press without a membrane could be referred to as a membrane press. Recently I’ve noticed an increase in the number of people who err in calling 3D laminate (3DL) a membrane. I’m wondering if membrane-less “membrane presses” are the source of this confusion. You’ll see what I mean in a minute.
A membrane is a highly flexible and durable sheet of natural rubber or silicone that is mounted inside a 3D laminating press. It is not a laminate, but a replacement part on the press. Pressure that is built up behind the membrane forces 3DL that has been softened by heat into the detail of a 3-dimensionally shaped part.
click image to zoomThe diagram above shows the typical membrane-less pressing chamber. Closing the press creates sealed chambers above and below the 3D laminate. Vacuum is pulled below the 3D laminate and air pressure is applied from above. Membrane-less Presses
Membrane-less presses use positive air pressure but do not use a membrane. In a membrane-less press the 3D laminate must act as both the laminate and the membrane. A full sheet of 3DL must be used to completely cover the press tray and seal along all edges as the press is closed. This creates separate enclosed chambers above and below the 3DL.
The cycle starts by either using air pressure below the 3DL or vacuum above to bring the material in contact with the upper platen for pre-heating. After the 3DL is sufficiently heated, it is typically drawn down around the parts with vacuum. Air pressure is then injected from above for added profile definition and bond strength.
Membrane-less presses were highly problematic when first introduced. Adhesives used for this process required activation temperatures of 160F to 175F, which proved to be very difficult for membrane-less systems. Without a membrane to act as a heating blanket, the3DL had to hold enough heat when pulled away from the platen to activate the adhesive when it came in contact with the board. The balancing act of activating the adhesive but not overheating the 3DL was quite challenging, often resulting in very high scrap rates.