Overview

Winding webs in vacuum is different from winding webs at atmospheric pressure for the obvious reason that in vacuum there is, in effect, no air. The effect of this is that there is no boundary layer of air to be dragged along by the web to act as a lubricant when the web travels over rolls. There is also no air to become entrained as the web is rewound into a roll. Without this air layer, the rewound roll will always be harder wound in comparison to air wound webs. This is true even with only a small amount of tension used on the web during rewinding. Also without this air, acting as a lubricant, there is the opportunity for micro-scratches to be put into the web or coating as the web travels over rolls in hard surface-to-surface contact. The lack of air and hard roll will mean that, once rewound in vacuum, any web profile problems will become clearly apparent.

It has often been said that a good winding system can help minimize the problems caused by poor quality film whereas a poor winding system is likely to add additional winding problems.

23.1 System Design

In general, the manufacturer building the vacuum system will design the winding system. The vacuum system will often be separated into two separate zones, the winding zone and the deposition zone. One aim tends to be to minimize the chamber volume and so the winding system will be made as compact as possible.