Denis

Sounds like you have a real problem, or rather five of them. My only
suggestions are:
a) have a certified explosion-proof zone for all these operations
b) impose the use of suitable activated carbon gas masks or breathing
apparatus for the workers
c) impose the use of suitable protective clothing, including gloves
against cutaneous absorption
d) clean all portable parts in an ad hoc cleaning machine which is
emission-free
e) ignore all VOC regulations that Canada has or proposes to have and
pay the fines imposed.

Other than this, I suggest you change the mask supplier to one that does
not require such procedures.

As for diglycol ethers or similar, the first thing to establish is
whether they, or blends thereof, can do the work. If so, their
combustibility (as opposed to flammability) should not present a
problem. Their lower vapour pressure at room temperature and lower odour
may be acceptable as is for occasional exposure. Gloves will still be
required for hand wiping. As you say, their low vapour pressure will
produce extremely slow drying but this can be easily overcome by a water
rinse. Water will dry off at least 10 times faster. As water rinsing
will dilute the residues, it is possible that, if it is insufficient, a
very thin film of solvent may remain on the parts. Check with the mask
maker whether this will cause any problems.

Brian

Denis Bégin wrote:
>
> The workers at a printed wiring board manufacturer use a mixture of
> volatile solvents (e.g. MEK, toluene) to clean liquid photoimageable solder
> masks (LPISM) inside the machines (Ichinose SMT-200 from Toshin Kogyo Co.,
> and DP-2000 from Circuit Automation inc.)  used to apply the masks on the
> boards and to clean off the masks on the screens and other instruments when
> they must change the mask.  The masks are not cured when this task is
> performed.  Workers perform this task manually using solvent soaked rags.
> The workers' breathing air concentration of MEK and toluene is very high
> while doing this task.  I was wondering if any of you know of a safer
> solvent that I might recommend to this company.  Alternatively, is there
> another way of applying the masks that would eliminate the use of cleaning
> solvents?  To date, I have had suggestions from two LPISM manufacturers.
> One of the suggested solvent mixture is even more toxic than the one
> presently used!  The other suggestion I got is a safer solvent but from the
> nature of the solvents (dibasic esters and glycol ethers) I suspect that it
> will not evaporate fast enough...
>
> Denis Begin, M.Sc.
> Research Assistant
> University of Montreal
> Faculty of Medicine
> Department of Occupational and Environmental Health
> PO Box 6128, Main Station
> Montreal (Quebec) H3C 3J7
> Canada
> Tel: 514-343-2170
> Fax: 514-343-2200
> [log in to unmask]
>
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