Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
` 3 2~79~3
Herber~s Gesallschaft mit beschrankter Kaftung
A ~t~od o~ rec~v~ri~ the ovQrspr~y rom aqueous coati~
~e3~ u~ed_in s~ray booth~
The invention relates to a method of xecovering the
overspray ~rom aqueous coating agents used in s~ra~ booths,
the o~erspray being recycle~ in the coating agent used in
the s~ray booth.
It is ~ecoming increa~ingly important, or known
environmental reasons, to use water~dilUtable systems in
place ~f lac~uers diluted with organic solvents. When
~ater-dilutable sys~ems are used, the aiX is less
contaminated, if at all, by emission o~ sol-~ents. One
general weakness, howe~er, as ~egaxds processing of coating
agents such ~s water-dilu~able lacquers by spraying, is that
there are pro~lems in disposing of the overspray (the
lac~uer mist). These problems occUr pa~ticularly in large-
scale seri~s lacquering operations, as in the car industry.
It is known to purify the exhaust air ~rom spray c~bins by
washing wi~h water in order ~o dispose of the overspra~.
For example, DE-A~-29 45 523 desc~ibes a process in which
~he o~exsp~ay fxom conventional solvent-dilutable lacquers
is washe~ with water, and the ~ater is subjected to
ultrafiltration.
~E-A1-32 27 227 describes a similar system for disposing of
the ove~spray occurring when using wa~er lacquers. The
ove~sp~ay is absorbed on ~he walls o~ t~e spray booth, which
are sprin~led with water, and the sp~inkling water is
conveyed in a circuit and processed in an ultra~ilter. It
has been shown, ho~e~er, that t~e ove~pray collected in ~he
sprinkling water cannot be re-used in co~ing agents and
therefore has to be dumped. ~dmittedly, ultrafi}~ratio~ is
2~79693
applied to waste-water puriCication and particularly to the
removal of ~ndesired lo~-molecular substances during
elec~rodeposi~ion coating, thus improving the e~icienc~ by
recycling (D~-C2-21 58 668, D~-~2- ~2 2~ 6?7, EP-Al-o 127
685, EP-Al-0 137 877, US-A-3 663 405 and US-A-3 663 405),
but problems occur when usi~g ultra~iltration for recycling
o overspray. Ultra~iltratlon of electro~eposition coa~ing
lacquers is a me~hod of recycling the pe~meate and the
retentate to the bath material, whereas when overspra~ from
water l~cquers is re~ycled, the di~er~nt form o~
~ppli~ation ~spraying instead o~ electrodeposition) and the
re~ulting greater differQnces in ~iscosity lead ~o stability
pro~lems, such as the risX of coagulation, sedimentation,
phase separation ox formation of deposits. In 3E-Al-34 28
300, to a~oid the stability proble~s resulting from the
method accordin5 to DE~ 32 27 227, it is reco~mended to
use demineralised water for sprinXling the spra~ booth, I~
has been shown, however, that even the use o~ demineralised
water as a sprin~ g li~uid is not su~ficient to improve
the stability o~ the absorbed overspray until it is suitable
for re-use in the lacquer material. In W0 91/09666 an
efort is made to solve the stability pro~lems in the methcd
in DE-Al-32 27 2Z7 by sprinkling ~he spray booth with ~a~er
mixed with an anti-coalescence agent, i.e. amin~s. Thi5
involves addition of environmentally polluting substances
and also the composition o the lac~uer is altered by t~e
a~ded c~emicals.
In addi~ion, when vverspray absorbed in ~ater is
concentrate~ by ultra~ ration, there are considerable
~hanges in the aqueous coating agent, because
ult~afiltration pre~erentially results in withdraWal o
wa er-soluble and low-molecular constituen~s such as
solvents or neutralising agents, which are impo~tant in
s~abilising the a~ueous lao~uer dis~ersions and their
properties as lacquers.
$ ~ ~
~irk Saarbach and Georg Schlumpf, in Ober~lache + JO~ 19gl,
Part 3, pages 18 ~o 20, "~ie NasslackierUng ohne ~missiQnen
oder Sondermull" ~ Wet lacquering without emission or
special ~e~use"] describe lac~uering of office ~urni~ure and
recycling the water lacquer. A continuous circui~ is ~lso
described. It is mentioned that the compo~ents of the
sy~tem, i.e~ "wa~er-dilutable stoving lacquer",
~'ultra~iltration techni~ue" and "spra~ s~stem", ha~e to be
adapted to one another. The addition o~ substances to the
recycling process is also de~cribed. However, therP i~ no
suggestion as to how the process ca~ be free from stabillty
problems, and also the composition of ~he original lacquer
is altered by the addi~i~es.
This process is suitable onl~ ~o~ lacquers which do not
coagulate or become unstable in other ~ays which a fe~t
theix properties as lac~uer, when concentrated by
ultrafiltratio~.
The aim of ~he invention there~o~e is to provide a method o~
recovexing the overspray ~rom aqueous coating agents so as
to ena~le the oversp~a~ to be re-used in the aqueous coating
agent and so as to avoid problems of stability and e~able
high-qualit~ coa~ing age~t~ (w~ are usua~ly sensitive),
such as a~ueou~ ca~ lac~uers, to be used on an industrial
scale.
It has bee~ ound that this problem can be solved by ~
method of recovering the overspray ~rom aqueous coa~ing
agents applied in sp~ay booths, the overspray being
collected in an ~queous washing liquid which is continuously
supplied to the spray booth in a circuit A, a part of the
w~shing liquid containing the overspray being supplied fro~
the ci~uit A to an ultra~iltration cixcuit B, and permeate
being withdrawn from the ult~afiltxation circuit ~ and
returned ~o the cirouit A to make up the washing liquid,
2~7~93
characterised in that the washing liquid is the aqueous
coatin~ agent used or spraying in the booth, after dilution
with water, the li~uid in the ultra~iltration circuit B is
the aqueous coating agent used for spraying in the booth,
optionally diluted with water, and the process is performed
conti~uously, the washing liquid in circ~it A having an
approximately constant co~ten~ o~ solids i~ the range f~om
4 - 20 Wt.~, and the liquid in ~he ultrafiltration circuit B
being kept by withdxawal of pe~meate a~ an approximately
constant content o~ solids in the range ~rom 15 wt.~ to ~he
contént of ~olids oc~urring at the spray viscosit~ of the
aqueous coating agent and higher than the content of solids
in circuit A, and a pa~t of the li~uid in the ultra-
filtration circuit B is used as the aqueous coating agent
for 5praying in the boo~h, or for preparation thereof~
The li~uid i~ the ul~rafiltration circuit B is the a~ueous
coating agent used or spraying, either in t~e state ready
for spraying or in a form diluted wi~h water~ ~he liquid in
~he ultra~iltration circuit B, therefore, can be su~plied to
the spray units in the booth either directly or after
processing. For the purpose of processing, in a preferred
embodiment, a ~a~ o~ ~he liquid in the ultraCiltration
circuit B can be mixed with fresh topping-Up
~oncentrate fro~ the aqueous coating agent and optionall~
with w~ter and/ar cptionally other coating agen~
constituen~s. A separate mixer can optionally ~e used for
mixing. In another preferred embodiment, the topping-up
concen~rate, optionally ~ith wa~er and/o~ o~her coating-
agent constituents, can be added in metered manner,
optionally via a mixer, ~o the liquid in the ultrafiltration
circui~ B, s~ that the spray units can be directly supplied
with t~e liquid in the ultrafiltration circuit B.
In the method according to the invention, in cont~aS~ to the
prior art, the washing liquid in circuit A is not water,
~7~93
which in the prior art must either be completely
demineralised or contain chemical additives. According to
the inve~ior~ e ci~cUi~ .~ is sta~ted and continued with
the aqueous coatins agent used for spraying, aftex dilution
with water.
In the method according to the in~ention, contin~ous
recycling occurs in a number o~ ci~cuits. In ~i~cuit A,
which constitutes the booth circulatin~ sy~tem, the process
i~ startéd b~ using a washing li~uid in t~e form o~ the
aqueous ~oating agent diluted with water. The coatin~ a~ent
ab~or~s overspra~ and is con~inuously supplied to circuit B,
an ultraf1ltration circuit~ ~t the same time, circuit A
continuo~sly a~sor~s aqueous permeate from circuit B. B~
varyin~ the pxopor~ion of overspxa~ a~so~ed to the
propo~tion delivered to circuit 3, thç content of ~olid~ in
circult A can be ~ept approximately co~tant at a value of
at least 4 wt.%, pxeferably at least 7 wt.% and up to
20 wt.~.
The ~ltraf iltration circuit B, in which the aqueous coating
agent is dilu~ed o~ circulated at the spxay consistency, is
used for an ultrafiltration process in which a~ueaus
perm~ate is ~upplied to circuit A~ and the ovexsp~ay
concentrated in the ul~rafiltration ~ixcuit B is discha~ged
for mixing with a topping-up concentra~e for the a~ueous
coatin~ agent. In circuit ~, the co~tent o~ solid in ~he
circulated dilute aqueous coating ayent is kept at a
constant value between lS wt. % and the content o~ solids at
the spray viscosity, the concentration in circuit B bein~
always higher ~han in circuit A. In the method according to
the invention, circuits ~ an~ ~ are adapted to on another,
by means of the amount of washing fluid withdrawn from A and
the amount of retenta~e and per~eate taken ~om CirC'lit B,
so as to o~tain the pre~iously~explained approximate
constant content of solids in the two circui's.
8 2~7~93
The ~ercen~a~es b~ weight given hereinbefore for circuit A
and circuik ~ relate in each case to the ~otal weight of the
a~ueous circulated s~stem.
The topping-up concentrate ~or ~he aqueous coatins age~ is
mixed with the circuit liquid B until it has the viscosity
~or spraying, and is supplie~ for spra~ving.
The method according to the invention, the matching of
circuit A and 3 and the use o~ dilu~e aqueous coating agent
as ~he sp~inkling li~id in the spray booth eliminates the
stability problems arising in the prior art. The methad
according to the invention, ~herefore, ena~les direct re-use
to be made of the overspra~ ~rom a~ueous coating agents even
when they tend to become unstable or to lose ~heir .
pro~ertie~ as lac~uex (e.g. a chan~e in viscosity) when
concentrated by ultra~iltration, as is o~se~ved particularly
in the case of high-~uality lac~uexs for series lac~uering
of cars.
The method ac~ordin~ to the invention a~oids use of an
additional quantity of tap water or completel~ demineralised
water for s~rin~ling ~e sp~ay-booth walls, as was necessar~
i~ the p~ior art and adversely a~fected the stability of the
overspray when collected. ~o~ optimum absorption of the
oversp~ay, the booth walls are sprinkled wi~h dilu~e aqueous
coating agent. Demineralised wa~er is used only as a
replacement for ~ater wi~hdrawn in the proc~ss, e.g. by
eva~ora~ion.
The ~d~antage o~ the me~ho~ accordin~ to the invention is
that the composition and the equilibrium in the cixcuits are
retained, ~hus avoiding m~jor cha~es in the composition o~
the ~ueous coating agent~ Thi~ prevent5 interfering
~actors leading to instability, and practi~ally 100~ o~ the
overspray can be ~ecycled withouk expensive adj ustments and
2~7~693
wi~h inexpensive analysis.
I~ contrast to the known methods, ~e recycling circuits can
be operated practically without additives. This ensures
that no subsequently-introduced additives change and
possi~l~ impair the prope~ies of the a~ueous coating
agents. All necessary additives, e.g. anti-foaming agents,
additi~e~ ~or a~oiding sur~ace disturbances, o~ levelling
addi~ives can be incorporated e.g. in the topping-up lacquer
concentrate.
The e~uilibriu~ can be adjus~ed in simple manner with
conventional apparatus. It can be controlled e.g. via the
ratio of the amount discharged to the amoun~ collected in
the respective circuits, the area and capacity of the
ultraf~ltration membranes, t~e concentration o the ~opping-
up concentrate ~or aqueous coating agent, and the throughput
of the aqueous coating a~ent in the spray boot.h. These
parameters can easil~ be determlned by the skilled man, by
txial and calculation.
The method accoxdin~ to the invention can be carried out on
normal apparatus, and ther~or~ does not need any specia~
adaptation o~ existin~ eguipment.
The spray boo~h~ use~ acco~ding to the i~ention are
conventional spray booths. They can oper~te with ~
conventio~al air-supply and exhaus~-air circuit. The spray
booths can e.g. be e~uipped with at least one wet sprinkling
wall or with a ~entu~i washing system, a5 is usual
particularly in the motor-vehicle lacquering lndustry. In
the case of wet sprin~ling walls, all the walls can be used
~or wet sp~inkling. If wet sprin~ling walls are present,
thè washing liquid ser~es as a sprin~ling liquid. The
was~ing liquid ca~ e~g~ ~e c~llected at ~he bottom o~ the
spra~ booth and ~eturned to the circuit fox repeated
207~3
sprinkling of the walls or for repeated Venturi ~ashing.
spray booths of this ~ind are well-~noWn to the skilled man.
They are used fox the booth circuit, circuit ~.
A conventional ultrafiltration u~it is used in ci~cuit B.
The aqueous coating agent in circuit B is circulated by the
ultrafiltration unit, e.~. via a heatable ox coolable
container ~ox t~e ultxafiltration xetentate (also called
concentrate in this s~eci~ication)~ ~he ultrafiltration
retentate is ~eturned from the container to the
~ltra~iltr~tion unit. ~ pre-filter for removlng coaxse
impuxi~ies can be connected upstream of the ultrafiltration
unit. Aque~us coatins agent enriched wi~h o~erspray and
diverted from the circuit A i5 supplied to the cixcuit ~,
e.g. to the container for ultrafiltration concentrate. The
a~ueous pexmeate can be returned fro~ the filtration unit
directly to circuit ~, e.g. to ~he ~ottom o~ the spray
booth, which can be trough-shaped. optionally all or part
~ he aqueous perme~te can be con~eyed ~-hrough a
hypex~iltxation unit, whexe reverse osmosis occurs, a~ a
result of which low-molecular constituents are withdrawn
from the aqueous permeate, and can be returned to circuit B,
e.~. to the container for the ultra~iltration concent~ate.
The water coming out o~ the hyperfil~ration unit is xeturned
to cixcuit ~, e.g. to the base of t~e spra~ booth.
Ultrafiltration, xevexse osmosis a~d hyperfiltration are
known to the s~illed man. They can be carried out in
conventional units. These filter processes are descxibed in
the opening parts of the a~orementioned pat~nt applications
and paten~ s~e~ifications and also e.~. by ~ilhelm R. A.
Auck and ~errmann A. M~ller in "Grundoperationen chemischer
Verfahre~stechnik" ~= "Basic operations in chemical
processing t2chnology"J, Verlag Chemie, 1982, pages 153 -
155, or by Robext Rau~enbach and Rainer Albrecht in
"Grundlagen de~ chemischen Technik, ~embrantrennverfahren,
2~79693
11
Ul~rafiltra~ion und U~kehrosmose" [= "Principles o~ chemicai
engineering, membrane separatio~ processes, ultraflltration
and re~erse osmo~is"~, Otto Salle Verlag and Verlag
S~uerl~nder, t 981, and by Thomas D. ~xock in ~'Membrane
~iltration", Springer Verlag, lg~3.
No high pressures axe ~e~uired for ultra~iltration in the
method according to the invention. The pressure must be a~
le~st suf~i~ien~ ~o drive the water and low-molecular
substance at a measurable speed through the membrane. These
pressures are e.g. of th~ orde~ of 0.7 to 11 bar, prefexably
about 5 bar.
The pressure for xevexse osmosis is, by defini~ion, greater
than the osmotic pressure. There ls no sharp boundaxy
~etween ultra~iltration and reverse osmosis or
hyper~iltration. Irl the me~od a~coxdin~ to the invention,
"revexse osmosisl' or "hyper~iltration" means e.g. filtration
at which low-molecular components of the permeate are
~ubstantially completely separated ~rom wa~e~.
Since hyperfiltration units can be used in the method
acc~rding to the in~ention, there is the additional
advantage o~ being a~le to rec~cle water-soluble components
which partly or completely enter the p~rmeate during
ul~afiltration, e.g. water-soluble synthetic resins ~uc~ as
polyvin~l alcohol, special water-soluble melamine xesins,
e.g~ Cymel 327, ~r the water-soluble component o~ org~ni~
solvents or low-molecular compounds as de~c~ibed e.g. in the
report by Die~rich Saa~weber in "Untersuchungen zum Einfl~ss
der Ultrailtration auf die ~igenscha~ten von
~lektrotauchlac~en" ~= "The e~ect of ultrafiltration on ~he
pro~erties of elect~odeposi~ion coatinq lacquers"~ VII
FATIP~C KONGR~SS, Kongress-3uch pages 467 - 474. ~ny
changes in the proportions by weigh~ of co~ponents which do
not enter the permeate and components which enter the
~7~3
permeate, e.g. resulting from accidental loss of
ultrafiltrate, can optionally be made up by suitably
formulating the topping-up concentrate for the aqueous coating
agents. Alternatively, as previously described, the
components can be withdrawn from the permeate by reverse
osmosis or hype~filtration and can flow directly back into
circuit B. If desired, electrolytes, which may have been
brought in during the process, can be removed from the
permeate with ion exchangers by usual methods.
The accompanying drawing is a flow chart illustrating the
process according to the invention, or the device used
according to the invention in the case of an example, the
example constituting a preferred embodiment of the method
according to the invention.
The drawing shows a conventional spray booth 1 supplied from
above, through a duct 2 with air which can be introduced into
an exhaust air duct 5 with baffles 4 at the bottom 3 of the
spray cabin.
The overspray 7 (spray mist) formed during spraying with the
spray unit 6 is collected on a wet sprinkling wall 8. The
sprinkling liquid flowing down the wall 8 is collected in the
trough-like bottom 3 of the spray booth and returned thence
through a line 9, a pump 10 and an overflow 11 to the top end
of the wet sprinkling wall 8.
The booth circuit, circuit A, is thus formed by the wet
sprinkling wall 8, the bottom 3 of the spray booth, th~ line 9
and pump 10, and the overflow 11. The sprinkling liquid is
the aqueous coating agent used in the spray unit 6 in the
booth and diluted with water and kept at a solids content
having an approximately constant value in the range from 4 to
20 wt.%.
A line 12 branches off the line 9 shown in the drawing and
leads via a control evice 13 to a container 14 for
recei~ing the u7tra~iltration reten~ate. The container '4
c~n have cooling devices 15 and heating devices 16 for
adjusting the desired operating temperatures. The
sprinkli~g liquid ~rom line 12, enriched with overspray, is
mixed with the cixculating liquid i~ container 14.
The ul~xafiltration retentate f~om container 1~, together
~ith the liquid introduced from circuit A, is conveyed
through line 17, a pump 18 and an optionally connected ~re-
filtex 19 to an ultra~iltration unit 20, ~rom which permeate
is ~ontinuously withdrawn. The rete~tate is returned
t~rough line 21 to the container 14.
Usually the outpu~ of permeate during ult~afiltration is
e.g. below 1~ of the volume flowing ~hrough the filter, so
that the ~etentate has practicall~ ~he same composition as
the circulating li~uid flowing into the system, pa~ticularly
when the volume of the containex 14 is very lar~e compared
with the volu~e flowing thxough the ultrafiltration uni~.
By means ~f this ee~l the overspray from circuit A can be
concentrated b~ t~e method according ~o the invention
without substantially altering the composition and the
content of solids in circui~ 3.
Ac~ording to the invention, an ultra~iltration circuit,
circuit B, is made up o~ the container 14, the line ~7 ~ith
the pump 18 and the optionally connected pre-filter 19, the
ultrafiltration unit 20 and the line 21. In the method
acco~din~ to the in~ention, ~he ~ircuit ~ in combina~ion
with the control system 13, which xegulates the suppl~ of
oYerspxa~-en~iched sprinkling li~uid from circuit A, is
adjusted ~o that the li~uid in circuit B is kept at a solids
content a~ an approxi~ately cons~ant ~alue in ~he range
between lS wt.~ and th~ cont~nt a~ which t~e coating agent
has the viscosity for spraying.
2~7~3
14
Permeate obtained fxom the ultra il~ration unit 20 is
withdrawn through line 2~ and returned to the circui~ A via
the base 3 of the spray booth 1.
line 23 can be connected to and bxan~ of~ from the line
22 and leads ~o a hyperfiltration unit 24, in which
di~solved or lo~r-molecular components are separated by
xeverse osmosis ~rom the aqueous permeate and returned
through a line 25 to container 14. After ~eing separated
from dissolved or low-molecula~ consti~uents, the pexmeate
~rom the hyper-~iltration unit 24 can be returned through
lin~ 26 to the base 3 of the spray booth 1 and thence ~o ~e
c~rcuit ~.
line 27 branches ~rom and can be connected to t~e line 21,
which returns ultra~iltration retent2te ~rom the ult~a-
iltration unit 20 to the container 14. Line 2/ conveys a
part of the concentrate ~rom the ultrafiltration unit to a
topping-up de~ice 28. Device 28 is supplied through a line
29 with topping up con~2~t~ate which is diluted by mixin~
wi~h the ultrafilt~a~ion retentate to obtain the a~ueous
coa~in~ agent, which can be used ~or spra~ing in the spray
unit 6 i~ ~ooth 1. The topping-up device 2~ can thus be
connected to the spray unit 6 via a line 30, optio~ally via
a st~rage ~ontai~er 31, Other constituents can be added ~o
the mixtu~e in the topping-up device 2~, e.g. water or
volatile constituen.s which were withdrawn from circuit ~ or
B during ~he process.
The method acco~ing to the invention can be worked ~ith
water-dilutable coating agents which are comme~cially
available and ~amiliar to the skilled man, e.g. wa~er-
diluta~le lac~uers as used for series lacquering o~ cars or
motor vehicles. The method can also be applied to w~ter-
dilutable coating agent~ having a high conten~ of solids,
e.g~ water-dilutable ~illers, likewise used in series
~07~9~
lacquering of cars.
The method according to the invention is preferably applied to
aqueous coating agents having a solids content of 15 to 80
wt.%, preferably equal or greater to the solids content of the
liquid in the ultrafiltration circuit B.
The solids content of the aqueous coating agent can be
determined in the individual circuits, e.g. to DIN 53216.
Preferably, a weighed portion of the sample to be determined
is placed on a flat-bottomed metal dish and first heated to
about 95C for half an hour. This evaporates part of the
water, so that the results cannot be distorted by spraying.
The water-dilutable coating agents, e.g. water-dilutable
lacquers and fillers, can optionally contain pigments and/or
extender pigments, or can be formulated as clear lacquers.
They can contain organic solvents or be free from organic
solvents.
As mentioned, the water-dilutabl2 coating agents used in the
method according to the invention can be transparent or
pigmented. They can optionally contain extender pigments,
additives, coalescence agents, volatile organic liquids or
other conventional raw materials for lacquers. They can dry
by physical or chemical means. The systems can be self-cross-
linking or they can contain external crosslinking agents, e.g.
for stoving lacquers.
The water-dilutable lacquers suitable for the method according
to the invention are e.g. aqueous dispersions, e.g. systems
comprising finely divided polymers or synthetic resins in
~ater and based on homopolymers or copolymers of styrene,
vinyl chloride, vinyl acetate, maleic anhydride, maleic acid
ester, maleic acid semi-ester, vinyl propionate, (meth)acrylic
acid and esters thereof, amid~s and nitriles. Examples of
these coating agents can be found in the Lehrbuch der Lacke
und Beschichtungen [= Manual of
' ' ' . ~ ' ' . ~ ' '
~9~
lac~uers and coatings], ~ublished by Dr. Hans ~itte~, Volume
1, Part 3, Ve~lag W. A. Colomb in der ~. Heenemann Gmb~,
1974, pages ~20 to 1001 and in Lackkunstharze ~= Synthetic
lacquer re~ins~ by Hans Wagner and Hans Friedrich Sarx, Carl
H~nser Vex~ag, ~unich, 1971, pages 207 to 242, and in A
Manual o~ ~esins ~or Surface Coatings, SIT~ ~echnology,
London, 1987, Volume II, ~ages 24g to 29~. .
Water-dilutable lacquers consti~uting emulsions of polymers
o~ plastics are other e~amples. The~ can e.g. contain
bi~ders, ~issolved in sol~ent or solven~ ee, optionally
wlth cross linki~q agents and emulsified in watex.
~mulsions with particularly finely dis~ributed binder
droplets are ealled micro-emulsions. The large grou~ of
water-dllutable lacquers produced Cro~ "water-soluble"
pol~me~s o~ synthetic resins, which are further examples o~
the method according to the invention, contain binders which
bear acid or basic groups, e.g. car~oxyli~ acid groups,
carboxylic anhydride groups, sulphonic aci~ ~roups,
primary, secondary or ~er~iary amino groups, sulphonium
groups or phosphonium groups. The polymers or synt~etic
resins are con~erted in~o a water-diluta~le form by
neutralis~tion or partial neutralisation o the groups with
basic compounds, e.g. wi~h amine, alk~nolamine, ammonia,
sodium hydroxide or potassium hydroxide, or with acid
compou~ds, e.g. formic acid, acetic acid, lactic acid, al~l
phosphoric actd or carbon dioxide. The binder basis
consists e.g. o one or more binders in the group consisting
of polyurethane resins, polyes~er resins, poly(me~h~acr~late
~esins, epoxy Xesins, epo~y ~esin esters, fatty oils (e.g.
li~seed oil) and synthetic oils (e.g. polybutadiene oil).
~amples ~f "wa~er-soluble~ lacquers are given in ~eh~buch
der Lac~e und Beschicht~ngen, published by Dr. Hans Xittel,
Volume I, Pax~ 3, Verlag W~ ~. Colomb in de~ ~. Heenemann
Gmb~, 1974, pages ~7~ - 919 and A Man~al of Resins or
9 ~
17
Surface Coating5, SIT~ Technology London, 1987, Volume III,
pages 169 - 280 and in ~P-A-0 032 S54, EP-A-0 270 7g5 and
~P-~-0 3~g ~01.
~ixtures o~ aqueous dispersions with "wate~-soluble"
S polymers or s~nthetic ~esins, known as hyb~id systems, are
also suitable ~o~ the method according to ~he invention.
~he cross~lin~ing ag~nts ~or the aqueous coating agents can
e.g. be urea resins, triazine ~esins (such as mela~ine resin
or benzoguanamine resins~, phenolic resins, bloc~ed
polyisocyanates (such as blocked diisocyanates,
triisocyanates, isocyanurates, diurets or prepolymers of
isocyanates) and mix~ures of va~ious cross~ king age~ts.
The method according to the inve~tion is particularly
~u~table fo~ wate~-dilutable lacquers described e.g. in
DE-A-36 2~ 124, PE-A-36 28 125, DE~A-37 39 332,
D~ 38 05 629, DE-A-3% 38 179, EP-A-0 038 1~7,
~P-~-0 089 497, E~-A-0 123 939, EP-~-0 15~3 Q99,
EP-~-0 ~6 171, EP-A-0 238 037, EP-A-0 23~ 361.
EP-A 0 298 148, EP-A` 0 287 1~4, :EP~-0 300 612,
~P-~-0 315 7Q2, EP-A-0 346 886, EP-A-~ 39g 4~7,
US~ 22 685, US-A-4 794 147 and W0 87/05305, and used in
the form o~ sp~ays ~manual, aU~OmatiC o~ electrostatic~ for
series l~c~uering of cars, and thQ method is par~iculaxl~
prefe~ed ~o~ wate~-dilutable fillers (hydxofille~s)
describ~d in e.g~ E~-A-0 015 035, ~P-~-0 269 32Z,
~P-~-0 272 524 or W0 89/103~7 and water-clear lac~uers for
series lacquering of cars, described e.g. ~E-A-0 266 15~
The method accordi~g ~o the in~ention can also be preferably
applied to water-dilutable anti-gravel lacquers, a~
described e.g. in DE-A-38 05 629. These anti-gravel
lac~uers can be applied di~ec~ly to metal substrates t or to
metal substrates initially primed with usual primer
~7g~3
18
media, e.g. electrodeposition coating lac~uer, op~ionally
covered with ~ filier. They impro~e the gravel resis~ance
of multi-layer lac~uers.
The inve~tion provides a method of substantially ~omplete
re-use, without di~ficulty, of o~exspray prod~ced during
spraying of aqueous coa~ing agents. The method according to
the invention is pa~ticularly suitable in connection with
manual, automatic or electrostatic spraying, as car~ied out
particularl~ in series lacqueri~g o~ cars. It can the~efore
be applied e.g. L~o wa~er-dilutable lacquers for se~ies
lacquering OL cars, e~g. pigment-containing single-colou~
lacquexs o~ lacquer~ containing deoo~ative pigments, ~.g.
metallic lacquers, and is p~eferably applied to water-
dilutable ~illers (h~drofille~s) and to water-dilutable
clear lacquers for series lacquering of cars. I~ e~ables
practicall~ 100~ of the o~erspray to be re-u~ed, thus
protecting ~he environment. It is surprising that stable
re-usable lacquer ma~e~ials are o~tained without the need
f or subsequent additives.
The ~ollowing example illustrates the invention.
~xample
A h~d~o~illex (aqueous ~iller) with a solids conten~ of
50 wt.96 was used for spraying in a booth 1 in a device as
de~cribed in the pre~erred embodimen~ in the accomp~nying
dxawing. The same hydro~iller w~s used for wet sprinkling
of the booth, i.e. in the booth cir~uit A, and was dilu~ed
with demineralised water to a sol~ds co~tent of lo w..~.
~ux~ng each working day, the booth circuit absorbed about 1%
o its volume of overspray of the sprayed hydro~iller, i.e.
about ~0~ of ~he volume of sprayed hydrofiller.
The ult~afiltration circui~ 3 was fllled with 40 wt~% dilute
. 2~ 93
19
hydrofille~. Its Yolume was about 25% of the volume of
~ircuit A.
During each wo~king day, abou~ 6.5% o~ the ~olume of circuit
~ was continuo~sly trans~erred to ci~cuit B. The liquid
from ci~cuit B was continuo~sl~ conveyed through an
ul~rafiltration plant 20 suitable fo~ the lacquered
material. During each working day, a~out 20% o~ the volume
of ult~a~iltrate was wi~hdrawn f~om circuit B a~d supplied
to ci~cuit ~ through line ~2.
In the tvpping-u~ device 28, three par~s o~ an approximately
53~ hydrofiller topping-up concentrate were con~inuousl~
mixed with 1 paxt of the material from circuit ~ and
supplied thro~h a ~ilter to the spray unit 6 in booth 1,
ei~her directly or via a storage container 3~.
The hydrofiller topping-up co~centrate was adjus'ed so th~t
when mixed with the material from circuit B, the h~dro~iller
was ready for spraying. To this end, t~e topping-up
concentrate also contained the volatile organic constituents
which had been lost in circuit A during t~e separation of
20 booth air and cixculatin~ liquid. The amounts to be added
we~e calculated b~ analysis o~ the retentate obtained in
circuit B.
Water loss~s resulting e.g. from e~aporation can be
compensated by direct addition OL demi~exal~sed water to
circuit A~
In the pre~eding example, the solids content was determined
to DIN 53216. Time/tempe~a~ure combination: half an hour at
95C plus 1 hour at 125C.
