Vacuum Web Coating

Another question

The question was.

During our normal maintenance of our vacuum chamber, we recently open two of the diffusion pumps, the maintenance people notice a heavy critallized deposit at the top part of both pump. It's something we never had observed in the past. The cristallized deposit is white and oily. If you applied heat to it, it liquify.

Have you ever heard of something similar ? If yes, what can cause it ?

My answer.

When you say a white deposit was crystallized but also say it is white & oily I am assuming that you mean condensed rather than crystallized. Crystallized would, to me, suggest that the deposit has a hard and crystalline nature.

If the deposit is white & oily it would suggest a soft condensed material. Typically this can be as a result of the likes of moisture up-take.  Have a look at the oil in the backing pumps. Are they a transparent brown colour or is it a white more opaque emulsion? If it is the latter it would suggest that you are pumping a large amount of water through the system & some of the water is being taken up by the oil & forming an emulsion.

If this is the case simply gas ballasting the backing pump so that it runs hotter & evaporates more of the water through the pump will help & the colour should revert to being transparent brown & lose the whiter & more opaque look.

The question then to ask is where is all the water coming from?

Have you changed substrates?

Have you noticed a slower pump-down time recently & possibly getting worse?

If the pump-down is getting progressively worse you may have a water leak on the system.

I hope this helps. If anyone else has suggestions comments feel free to add your comments.

Help required - new question

We currently extrusion laminate PET to SBS rollstock. I'd like to reduce the amount (~20#/ream) of PET resin by switching to a film (48 ga.)lamination. This is a new process for us. The application is for a microwavable frozen food tray. We do not have a coater or priming station, so can you suggest a pre-treated PET film and compatable extrudable resin that will work and still achieve good adhesion. LDPE is an affordable choice, but has a low melt point in the microwave.
Any input would be greatly appriciated.

I am not the right expert to suggest the best film & can only suggest asking the film suppliers for their recommendations.

However I am sure there will be readers of this blog that might be able to suggest something.  So can anyone out there help & suggest a suitable film?

Thanks.

Helium Leak sets

I've had two recent incidents highlighting the usefulness of a Helium leak detector.  Both cases were on production metallizers that have run for years with no major leaks.  Then suddenly we had leaks big enough  to stop production,  resulting in major panics, customers hassling, people yelling  and lots of stress all round.

Of course neither site had a Helium leak detector (hadn't needed one in years), but suddenly we needed one urgently and didn't know where to get one from in a hurry.  In each case we tracked one down for hire and had it delivered (so a couple of days delay). Once we had the leak set then each problem only took a couple of hours to find and solve (we also found several other small leaks that had been slowing down the process for years, but hadn't been a big enough issue to worry about).

So the moral of the tale is :- If you don't have a Helium leak detector, then either get one or  find out now 2 or 3 places where you can rent or borrow one from.   It'll be much better making a plan now, than trying to sort it out when you actually need the leak detector (I've got the gray hairs to prove it).

                      Rick Spencer