Printech Archive, September, 1999: Re: Automatic Blanket Wash, low VOC

Re: Automatic Blanket Wash, low VOC
Wed, 22 Sep 1999 09:39:23 EDT

Date: Wed, 22 Sep 1999 09:39:23 EDT
Subject: Re: Automatic Blanket Wash, low VOC


The immediate answer your question about the existence of any formal studies
on cleaning solutions for automatic blanket wash systems is no. I am not
aware of any studies on the subject and would be very interested in seeing
the results of the study you mentioned that has been done in Europe. The lack
of studies can be attributed to several factors.

Probably the most important factor influencing the lack of studies is that
the choice of an automatic blanket wash solution is in part dependent upon
the type of system being used on the press. The systems currently available
use several different approaches to accomplish the same goal and include
spray, brush, cloth/bladder, and the new impregnated cloth type. The spray,
brush, and cloth/bladder systems all use liquid cleaning solutions and can be
mixed with water prior the actual cleaning cycle. The spray and brush washers
can also be equipped with a solvent collection and recovery system, although
this is not common. The bladder/cloth approach, as the name implies,
utilizes a cloth that is on a roll. During the cleaning cycle, the cloth is
flooded with a small amount of cleaning solution while the bladder inflates
with air and presses against the rotating blanket cylinder. There is no
liquid to collect and recover.

Since these three automatic blanket wash systems use reservoirs, pumps,
lines, seals, etc., the cleaning solution must be compatible with all of the
rubber and other critical components. As the different manufacturers do not
use the same materials, it is difficult to recommend a specific cleaning
solution. Generally, the vendors of the equipment will specify the cleaning
solutions that have been tested and approved for their system. At best, you
could only specify the physical characteristics of the cleaning solution
desired and see if one is available or if the solvent supplier can formulate
one that meets these properties as well as be compatible with the specific
blanket wash system being used on the press.

Two of the critical physical characteristics are flashpoint and VOC content.
If the printer is mixing the cleaning solution with water at the point of
application, then the flashpoint will be reduced. Technically the VOC content
will not be reduced as water cannot be used to lower the VOC content. Based
on my experience, the use of terpene and vegetable oil or vegetable oil
derived cleaning solutions has not met with a tremendous amount of success, I
would tend to avoid them. Some of the problems reported with these washes is
the reduced drying time, lack of solvency, deposition of a film on the
blanket, spontaneous combustion, and high costs. It would be better to focus
on cleaning solutions with low composite VOC vapor pressures. According to
EPA's ACT for Offset Lithography, a cleaning solution with a composite VOC
vapor pressure of 10 mm Hg at 68oF is equivalent to a wash containing 30% by
weight VOC. There are some newer washes that have vapor pressures less than
10 that can be explored for use.

While the use of vegetable oil or vegetable oil derived washes in liquid form
have not met with success in the above automatic blanket wash systems, there
has been some success with the use of these types of solutions when
impregnated into a cloth type system. The cloth is fed from a roll and during
the cleaning cycle, presses against the rotating blanket. This system is the
newest one on the market and has met with general success. Although, some
problems with it have been reported.

>From your description, it is not apparent what type of system is being used
on the press in question. I hope this answer provides some insight and
direction. I would be very interested in receiving any information you may
uncover in your quest for data.

Gary Jones
Graphic Arts Technical Foundation



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