Thanks a lot Alan (& Graham[seems busy = I pop it on Net for him])
paul

PS May I just add I've had good experience with multicore's Spot on .
     Some of the fab applied temp's (blue) I've had to just about chissel
off .

-----Original Message-----
From: Alan Brewin [mailto:[log in to unmask]]
Sent: Thursday, 14 October 1999 0:36
To: [log in to unmask]
Cc: Graham Naisbitt
Subject: Latex Mask


Dear Sir,

Graham Naisbitt has asked me to forward some comments to you regarding latex
masks.

There are two main types. Natural and Synthetic.

Natural Latex gives a really good self bond strength and elasticity which I
have yet to see matched in any synthetic formulation. This is why it is more
popular, it 'feels' better, and de-masks easier when cured. Pre-vulcanised
natural ammonia needs an alkaline pH to stabilise it in water, otherwise it
will drop out. In our attempts to reduce ammonia this is the most obvious
side effect. The material will separate.

You can make an ammonia free natural latex solution but by using KOH or
other alkaline additives which puts you back in the same position. Ammonia
works best at the low levels. Bottom line is, I do not know of a way to make
a completely NEUTRAL pH natural liquid latex.

Synthetic latexes are man made polymeric solutions, e.g. acrylics with
hydrophilic groups. In order to get properties approaching that of natural
latex additives for flexibility and waxes for easy de-masking must be added.
Synthetic latex solutions can be neutral, ammonia is not needed to stabilise
them. They are not as easy to use in production, however, they break more
easily if stuck around components etc.

I hope this helps, Graham maybe you would take what you wish from my reply
and post it on the TechNet?

Best Regards,

Alan Brewin - Chief Chemist
Concoat Ltd.
Albany Park, Frimley Road,
Camberley. Surrey. GU15 2PL.
+44 (0)1276 691100
+44 (0)1276 691227

##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
the body:
To subscribe:   SUBSCRIBE TECHNET <your full name>
To unsubscribe:   SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or
847-509-9700 ext.5365
##############################################################