Page 249 - Handbook of Adhesives and Sealants

218 Chapter Six

vents for cleaning substrates prior to bonding. They will not attack
steel, copper, zinc, or other metals, and they are economical. They have
many of the same advantages as trichloroethane without the problem
of ozone depletion.
The solvent industry has also made significant strides in developing
newer grades and blends of solvents for a variety of applications that
are either biodegradable and/or EPA compatible. New low volatile sol-
vents are taking the place of the older, less environmentally safe sol-
vents in the adhesive and sealant industries. Substitute solvents for
methyl ethyl ketone; 1,1,1-trichloroethane, and freon 113, have been
found acceptable for surface cleaning in many industrial applica-
tions. 19
Since the surface cleanliness is difficult to measure, special precau-
tions are necessary to prevent the solvent from becoming contami-
nated. For example, the wiping cloth should never touch the solvent
container, and new wiping cloths must be used often. A clean cloth
should be saturated with the solvent and wiped across the area to be
bonded until no signs of residue are evident on the cloth or substrate.
With solvent wiping, the cleanliness of the surfaces tends to be de-
pendent on the training and attention given by the operator. Auto-
mated spray or immersion processes are less dependent on the oper-
ator’s skill. After cleaning, the parts should be air-dried in a clean,
dry environment before being bonded. Usually they are placed in a
drying oven with circulating warm air.
The solvent immersion method is more suited for production vol-
umes, and it is often sufficient to remove light contamination and soil.
In this method, the part is immersed in a container of solvent and
mildly agitated by tumbling, solvent mixing, brushing, or wiping. Af-
ter being soaked and scrubbed, the parts must be rinsed by a clean
flowing liquid or spray. A number of different solvents may be used in
this process. It is important to note that the parts will be no cleaner
than the final rinse solvent.
The multiple bath method of solvent immersion, Fig. 6.6, is the most
common immersion method. The first tank is the wash tank in which
scrubbing may be performed. The second and third tanks are rinse
tanks. With this method, one must prevent contamination of the
cleaner solvents by continually changing the scrub and rinse solvents.
The spray method of solvent cleaning is very efficient due to the
scrubbing effect produced by the impingement of high speed particles
on the surfaces being cleaned. The spray causes flow and drainage on
the surface of the substrate which washes away loosened soil. Tri-
chloroethylene and perchloroethylene are generally used for spraying.
Vapor degreasing is a form of solvent cleaning that is attractive
when many parts must be prepared. This method is also more repro-