Note: Descriptions are shown in the official language in which they were submitted.
2 1 ~
[W71atfollows below ~fter this bracketed note, exceptfor the edge line nul7lbers ~Id
bottom page nl~mbers, is a trarlslation into English of the German langunge original
specificationforPCTApplication No. PCT/EP92/02686fïled on November 21, 1992.
This translation should be used as the equivalent of the original specification for the
National Stage of tllis PCT applicatiorl.]
METHOD OF REMOVING PAINT
This invention relates to a process using a hot lacquer remover for cleaning objects
soiled with fresh paint and/or lacquer residues.
In addition to acidic and neutral lacquer removers, highly aL~caline hot lacquer re~
movers are used for removing lacquer from objects. They may be applied by spraying or
5 dipping. To compensate for the consumption of active substance, the lacquer remover is
normally continuously replenished. If dry lacquer is removed from the objects, a sludge
is formed during lacquer removal, generally sinking to the bottom where it can be re~
moved under suction via a sloping surface.
In the removal of fresh paint or lacquer residues, for example in the cleaning of
10 used cans for paints and lacquers containing still liquid and partly dried residues, the lac-
quer removal bath contains a suspension of very fine suspended particles andlor a solution
of the paints or lacquers. If the lacquer remover is applicd by spraying, it can only be re-
: ::
. :- `: .. . .
` 212~4
plenished until the viscosity becomes ~oo high for the pressure pump or until the spray
nozzles become blocked with bath soil. Hitherto, the entire lacquer removal bath was then
discarded. The disadvantage of this lies on the one hand in the cost of disposal and on
the other hand in the loss of the still relatively high proportion of bot lacquer remover
s present in the spent lacquer removal bath. Accordingly, econornic regeneration of the lac-
quer removal bath would be desirable. Unfortunately, no such process is known.
By contrast, a regeneration by filtration- is known for the lacquer removal bath, if
old paint and lacquer residues were separated during chemical lacquer removal, so that the
residues sink to the bottom of the bath as sludge. However, in tne removal of fresh paint
10 and lacquer residues, the filters become blocked.
The use of a plate-type phase separator, vhich successfully regenerates lacquer re-
moval baths for old lacquer, also does not produce the required result here. ;~
Regeneration ought in principle to be possible by tne use of an ultracentrifuge.However, the use of an ultracentrifuge for this purpose is not economical.
The addition of coagulants to flocculate the impurities only has tbe desired effect
if the lacquer removal bath is cooled and diluted with water beforehand. This in turn
means more wastewater to be disposed of.
Accordingly, the problem addressed by the present invention was to provide a lac-
quer removal process, of the type mentioned at the beginning, in which the lacquer remov-
20 al bath would be economically regenerated without any significant reduction in its activesubstance content.
According to the invention, the solution to this problem is characterized in that the
water-containing lacquer removal bath is regenerated by microfiltration. To this end, the
bath liquid is passed in crossflow through a ceramic membrane without significant cool-
25 ing, at a minimum flow rate and with a minimum transmembranal pressure difference.The retentate is discharged.
Surprisingly, in the process according to the invention, hardly any active substance,
i.e. hot lacquer remover, is discharged with the solid, instead it remains in the pe~llneate.
Accordingly, it does not have to be replenished. A reduction in temperature before re-
30 generation is also unneccssary. Since regeneration takes place at the elevated temperature,it may be carried out at relatively long time intervals because, despite the resulting higher
degree of soiling, the viscosity of the bath remains low enough.
Basically, the membrane filtration process may be cariied out with a relatively low
2~2'~3~
,
- transmembranal pressure difference and at a correspondingly low flow rale so that the
coating which forrns on the surface of the membrane additionally functions as a filter
medium. However, the process according to the invention is carried out at a relatively
high flow rate and with a high transmembranal pressure difference. Accordingly, a mini-
5 mum flow rate and a minimum pressure difference are observed. The problem of mem-
brane blockage does not arise, despite the relatively high temperature of around 90 to 95 :
C and the relatively high pH value of around 14 typical of hot lacquer removers. The
useful life of the microfihration module is also sufficient for practical purposes despite
these conditions. :;
Chemical lacquer removal may be carried out by dipping or spraying. The inven-
tion is particularly advantageous in the second of these two variants because the problem
of nozzle blockage no longer arises. -- -~
The invention affords further particular advantages in the removal of residues from ~ ~
used containers for printing inks. In this case, the bath liguid is particularly difficult to ~ .
15 regenerate without the use of the process according to the invention, insofar as printing ` ;
inks often contain oil and carbon black particles. Despite the carbon black particles, mi-
crofiltration can be used as tests have shown.
Further advantages are obtained if the articles are cleaned with an alkaline hot lac-
quer remover at temperatures of around 90 C and higher. These conditions, the high al-
20 kalinity and the relatively high temperatures, lead to serious problems in other regenera-
tion processes. :Particularly long useful lives without blockage of the membrane are achieved ifthe bath liquid is allowed to flow through the membrane surface at a rate of at least 2 m/s
and more particularly 4 m/s and at a transmernbranal pressure difference of at least 3 bar.
25 The ratio of permeate to concentrate is then at least 2:1.
The invention may be carried out in single-stage or multistage lacquer removal in-
stallations. If the articles are cleaned in several successive stages each with its own lac-
quer removal bath, it is of advantage to regenerate the bath of the first stage continuously
or discontinuously by microfiltration, to add its permeate to the bath of the last stage and
~o to make up the bath losses by the bath liquid of the following stage (cascade arrange-
ment). In this wayr the bath liquid is utilized particularly economically.
According to the invention, only the concentrate, i.e. a considerably smaller
amount of waste, has to be disposed of. There is no need for additional chemicals, such
- - as flocculants for example. In other words, the waste is not additionally polluted. The
energy costs involved in ~he removal of soil from the bath are minimal because the pro-
cess according to the invention does not entail any reducflion in temperature or reheating.
In addilion, the process is simple and can be universally applied. Around 99 %
s of the soiling impurities are rernoved by microfiltration, so that cleaning can be safely
completed.
Two embodiments of the invention are described by way of example in the follow-
ing with reference to the accompanying drawings, wherein:
Figure I is a schematic llow chart of a lacquer removal process. .
Figure 2 is a schemalic flow chart of another, particularly advantageous lacquerremoval process.
In both embodiments, ~he articles from which lacquer is to be removed, for exarn-
ple soiled containers I for printing inks, are subjected firsl to preliminary cleaning 2 and
then to final cleaning 3. A sidestream from the prelirninary cleaning bath is processed in
15 a microfiltration module 4. The permeate S is returned. The retentate 6 and hence 99 %
of the impurities are disposed of.
In the variant shown in Fig. 1, the impurities are only removed in the preliminary
cleaning stage 2. Since 9S % of the impurities collect in the first stage, most of ~he total
ink residue is thus removed. In this case, the permeate 5 is directly returned to the pre-
20 liminary cleaning stage 2. The losses arising from removal of the concen~rate ~retentate)6 and from evaporation are made up by fresh water 7. Fina11y, the arrow 8 denotes the
cleaned container.
In Fig. 2, the same rererence numerals as in Fig. I denote the sarne parts. In con-
trast to the process illustrated in Fig. 1, the permeate is delivered to the final cleaning
25 stage 3. The preliminary and final cleaning stages 2 and 3 are lirlked to one another in
a cascade arrangement so that the final cleaning stage 3 is always supplied with a clean
lacquer removal bath. Bath losscs are made up by the introduction of fresh water 7 into
thc final cleaning stage 3.
Tcsts have shown that thc aLcalinity of the lacquer removal bath is not reduced by
30 thc process according to the invention. The active-substance componcnts of the hot lac-
quer remover are also not retained by the microfiltration membrane. There is no need for
replcnishmeIlt as a result of regeneration.
~ ` ~` ~?
212~4
List of Reference Numerals
Soiled container
2 Preliminary cleaning
3 Final cleaning
4 Microfiltration module
5 Permeate
6 Retentate, concentrate
7 Fresh water ~ - -
8 Arrow
"'; ~
