Note: Descriptions are shown in the official language in which they were submitted.
-CA 02314450 2000-07-21
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Use of powder coatings and powder coating waste materials in aaodically
depositable electrodeposition lacquers
The invention provides the use of powder coatings and/or powder coating waste
materials as additives inn anodically dcpositable electrodeposition lacquers,
as well as
the electrodeposition lacquers provided in this way, a process for pxeparing
them and
a process for anodic deposition lacquering which pxoduce improved throwing
power,
Coating with powder coatings is one of the particularly environmentally
friendly
methods of coating. Organic solvents can be largely dispensed with during the
preparation and processing of powder coatings and also only small losses occur
during their application.
lx~ general, powder coatings are prepared by mixing the individual
constituents such
as, for example, resin, hardener, additives and optionally pigments, and
homogenising these in a melt process. The resultixig melt is cooled and
crushed to a
size suitable for a subsequent milling process. The product is then milled to
the
desired particle size in suitable milling equipment.
The finest particles arc removed from the range of particle sizes produced in
so-
called air separators, this being required for certain applications and also
from the
health and safety at work aspect (see H. Kittel, Lehrbuch tier Lacke and
Beschichtungen, vol. VIII, part 2, appendix pages 13 to 24). In the first
instance, the
finest particles are a waste product.
When coating with powder coatings, it is inevitable that some of the coating
powder
does not reach the substrate or falls away from the substrate. In general,
this powder
coating overspray cannot be directly recycled to the coating process because
the
CA 02314450 2000-07-21
_Z_
original particle size distribution has been shi8ed and in the fast instance
is also a
waste product.
For economic and ecological reasons, it is desirable to take the waste
products being
produced through a procedure which makes them reuseable. A number of processes
has been suggested for doing this and they all include a relatively costly
working up
procedure using remelting and milling.
The principle of elxtrodeposition lacquering is familiar to a person skilled
in the art
and is described extensively in the literature (for example in
Metalloberflache 31
(1977) 10, pages 455 - 459), Electrodeposition lacquering is a fully
automated,
environmentally friendly and economic method of application and is us~1 in
practice
in the mass-production lacquering of electrically conductive surfaces, in
particular of
metal surfaces. It is then a fully automated method of application with a high
degree
of deposition, The process preferably takes place in sealed circuits and
enables the
recovery of excess lacquer material and of the auxiliary substances and
operating
matcnials used.
In the case of anodic electrodeposition lacquering (ADL), a workpiece with an
electrically conductive surface consisting of metal or consisting of
electrically
conductive plastic material or consisting of a substrate provided with an
electrically
conducrive coating is placed in an aqueous ADL bath and connected to a source
of
direct current as the anode. On applying a direct electric current, the
polymer
particles which have been made water-soluble or water-dispersible by at least
partial
salt formation migrate from the aqueous dispersion in the ADL bath to the
anode and
there react with the ions being produced by simultaneous electrolysis of the
water to
again produce water-insoluble polymers which coagulate out of the aqueous
phase
and, with the additives dispersed therein, are deposited on the anode as a
lacquer
film.
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DE-A-23 64 642 describes the preparation of thick, film-like coatings by means
of
anodic electmdeposition lacquering. In order to achieve a thick layer, water-
insoluble resin powders with particle sizes of 10 to 100 p,m are added to the
coating
agents, wherein the most frequently occurring particle sixes are in the range
25 to 50
pm. The proportion of water-soluble resin in the coating agent is limited, It
has been
shown that coatings obtained with these coating agents have only a wary low
throwing power and are not suitable for coating workpieces with
multidimensional
geometry or with cavities.
DE-A-33 66 973 describes the electrolytic deposition of powdered polymers on
an
anode. For this purpose, the polymer particles are coated with as amphoteric
metal
oxide or hydroxide in order to enable them to migrate to the anode under the
effect
of the charge. The fired-on film is slightly porous and has a reduced throwing
power,
DE-A-21 64 844 describes the electrophoretic deposition of powdered high
molecular weight compounds at the anode. For this purpose, the powder
particles are
moistened with an organic solvent which is not miscible with water and are
suspended in water which contains a surface-active compound. A resin support
component is not used.
The object of the present invention is to provide a method for re-using powder
coatings, for example non-recyclable powder coatings from overproduction and
powder coating waste materials which are produced durix<g the pr~cparation
and/or
processing of powder coatings, in an economically viable and environmentally
friendly manner without a costly conditioning step.
It has been shown that this object can be achieved by a use, forming one
object of
the in~cntion, of pawder coatings and/or powder coating waste materials as
additives
in anodically depositable electrodeposition lacquers.
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Surprisingly, this is possible without impairing, rather in fact improving,
the
throwing power of an electrodeposiHon lacquer coating obtained from an
eleEtrodeposition lacquer prepared via this use.
Powder coatings, powder coating waste materials or mixtures thereof which can
be
used according to the invention have a particle size distribution of 0,5 to
100 p,m,
wherein preferably 40 to 60 wt.% of the powder coating and/or powder coating
waste material has a particle size of less than 10 ~m and up to 20 wt.% has a
particle
size of less titan 5 p,m. The most frequently occurring sizes are particularly
preferably in the xange 0.5 to 10 pro at the largest. It has been shown that
the use of
this type of fine powder in anodically depositable electzodeposition lacquers
especially beneficially improves the throwing power of the anodieally
deposited
layers produced therefrom. For example, pigments and/or fillers and/or binders
can
also be at least partly replaced by this type of fine powder when formulating
1 S anodically depositable electrodeposition lacquers.
Accordingly, the present invention also provides anodicaUy depositable dip
lacquers
which contain one or more binders, water and optionally one or more cross-
linlting
agents, pigments, fillers andlor conventional additives and are characterised
in that
they contain one or. more powder coatings and/or one or more powder coating
waste
materials with a particle size distribution of 0.5 to 100 ~,m, wherein 40 to
60 wt.% of
the powder coatings and/or powder coating waste materials has a particle size
of less
than 10 Nxn and up to 20 wt.% has a particle size of less than 5 pro.
The powder coatings and/or powder coating waste materials are preferably used,
according to the invention, in such a way that the anodically depositable
electrodeposition lacquer obtained contains 50 to less than 200 parts by
weight of
powder coating and/or powder coating waste material with respect to 100 parts
by
weight of binder plus optionally present cross-Linking agent.
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According to a preferred crnbodiment, the invention provides an anodically
depositable electrodeposition lacquer containing
A) 67 to 33 wt.% of a water-dilutable component consisting of one or more
binders and optionally one or more cross-linking agents and optionally one
or more pigments and/or fillers,
B) 33 to 67 wt.% of one or more powder coatings and/or powder coating waste
materials with a particle size distribution of 0.5 to 100 pcn, wherein 40 to
60
wt.% has a particle size of less than 10 prn and up to 20 wt.% has a particle
size of less than 5 ~.nn,
as well as water and optionally one ox more conventional additives, wherein
the ratio
by weight of binder to cross-linking agent in component A) is 100 : 0 to 65 :
35 and
the ratio by weight of pigment to binder in component A) is 0.1 : 1 to 1.5 :
1.
The anodically depositable electrodeposition lacquer is prepared by mixing one
or
mote suitable binder dispersions) with optionally one or more cross-linking
agents)
and optionally conventional additives, lacquer additives such as, fox example,
catalysts, Light stabilisers, optical brighteners, biocidc components, neutral
resins,
layer-producers, emulsifiers and optionally pigments and/or fillers. The
powder
coating and/or powder coating waste material fraction can be admixed at any
time.
Suitable binders far the aqueous binder dispersions in the anodically
depositable
electrodeposition lacquers provided in accordance with the invention are any
conventional bindex systems for anodically depositable electrodeposition
lacquers
(ADLs). They contain anionic groups or acidic groups which can be converted
into
anionic groups by neutralisation. Acidic groups may be, for example, carboxyl
groups, sulfonic acid groups, phosphoric acid groups, preferably carboxyl
groups.
The acid value of the binder is preferably 20 to 150, particularly preferably
20
to 120.
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Binder systems which contain further functional groups, in particular hydroxyl
groups, arc particularly preferably used. The hydroxyl value is preferably 20
to 150,
particularly preferably 20 to 120.
Examples of binder systems acre those which are generally well-known for
aqueous
binder systems, in particular for anodic dectrodeposition lacquer coatings.
These
include, for example, polyester, polyacrylate and polyurethane resins such as,
for
example, alkyd resins, uxethanised polyester resins or acrylated polyester or
polyurethane resins, maleated oils, epoxyesters, maleated polybutadiene oils
and
mixtures of these resins. Polyester resins are preferred.
Suitable polyester resins are, for example, carboxyl group and hydroxyl group-
containing polyesters with an acid value of 20 to 150 and a hydroxyl value of
20 to
150. They may be prepared, for example, by processes known to a person skilled
in
the art, by the reaction of polyhydric alcohols and polybasie carboxylic acids
or
carboxylic anhydrides, and optionally aliphatic and/or aromatic monocarboxylic
acids. The hydroxyl group content is adjusted in a manner known per se by
appropriate choice of the type and ratios by weight of the starting
components. The
carboxyl groups may be introduced, for example, by semi-ester formation from a
previously prepared hydroxyl group-containing polyester resin, using acid
anhydrides, The incorporation of carboxyl groups may also take place, for
example,
by the joint use of hydroxycarboxylic acids during the polycondensation
reaction.
The polycarboxylic acids, for example dicarboxylic acids, and polyols may be
aliphatic, cycloaliphatic or aromatic.
The polyols used to prepare the polyesters are, for example, diols such as
alkylene
glycols such as, for example, ethylene glycol, butylene glycol, hexanediot,
hydrogenated bisphenol A, 2, 2-butyl-ethyl-propanediol, neopentyl glycol
and/or
other glycols such as, for example, dimethylolcyclohexaae. Higher functional
or
mixtures of higher and monofunctional OH components such as, for example,
CA 02314450 2000-07-21
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trimethylolpropane, pentaerythritol, glycerol, hexanetriol; polyethers which
are
condcnsates of glycols with alkylene oxides; monoethers of such glycols such
as
diethylene glycol monoethyl ether, tripropylene glycol monomethyl ether, mar
also
be used.
The acid component of the polyester preferably consists of low molecular
weight
dicarboxylic acids ar their anhydrides with 2 tol8 carbon atoms.
Suitable acids are, for example, phthalic acid, isophthalic acid, terephthalic
acid,
hexahydrophthalic acid, adipic acid, azelaic acid, sebacic acid, fumaric acid,
malefic
acid, glutaric acid, succinic acid, itaconic acid and/or 1,4-
cyclohexanedicarboxylic
acid. The methyl esters or anhydrides of these acids, if they exist, may also
be used
instead of the acids. It is also possible, in order to obtain branched
polyesters, to add
a proportion ofhigher functional carboxylic acids such as, for example,
trifunctional
carboxylic acids, trimellitic acid, malic acid, aconitic acid,
bishydmxyethyltaurine
and dimethylolpropionic acid, dimethylolbutyric acid or bisanhydrides.
Polycarboxylic acids which do not form cyclic anhydrides are preferred.
The polyester resins may also be modified, for example, by incorporating
unsaturated compounds, isocyanate group-containing compounds or by fixation or
graft polymerisation with cthylenically unsaturated compounds. Preferred
polyesters
are, for example, carboxyl group-containing polyesters with an said value of
20 to
120 and a hydroxyl value of 20 to 150, preferably 60 to 120. They are, for
example,
reaction products of di- and/or polyhydric aliphatic or cyeloaliphatic
saturated
alcohols, aliphatic, cycloaliphatic and/or monocyclic aromatic di- or
polybasic
polycarboxylic acids and optionally linear or branched, saturated or
unsaturated
aliphatic and/or cycloaliphatic C3 to C20 monoalcohols or monocarbvxylic
acids.
The ratios by weight of stattit~g components are calculated from the molar
ratios
which lead to the desired acid values and hydroxyl values of the resin. The
choice of
individual starting components is known to a person skilled in the art, taking
into
consideration the objectives.
CA 02314450 2000-07-21
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The number average molecular weight Mn of suitable polyesters, measured
against
polystyrene as a calibration substance, is, for example, 1000 to 6000,
preferably
2000 to 4000.
Carboxyl group-containing oil-free polyesters such as are described e,g. in
D>r-A-32
47 756 are particularly preferred. These polyesters preferably contain 0.3 to
3.0,
particularly preferably 0.5 to 2.5 milliequivalents of cocondensed aliphatic,
cycloaliphatic and/or aromatic dicarboxylic acids per gram of resin. 0.8 to
2.0,
preferably 0.9 to 1.8, particularly preferably 1,1 to I .5 millimoles of
tribasic or
polybasic cyclic carboxylic acids per gram of resin are expediently bonded via
only
one carboxyl group to the polyester. Tribasic and/or polybasic polycarboxylic
acids,
preferably tribasic and/or tetrabasic acids, are used as polycarboxylic acids.
The
preparation of these polyesters may take place by polycondensation of the
stating
materials in a manner known per se, wherein the process is preferably
performed
stepwise in order to avoid turbidity and gel formation.
The esterification of preferably aromatic and cycloaliphatic diearboxyIic
acids which
cannot form an iuntramolecular anhydride, preferably takes place with
dialcohoIs
which contain either secondary OH groups or else primary OH groups which are
sterically hindered by substituents, wherein an OH group-containing polyester
is
produced by using an excess of alcohol, The alcohols preferably contain 2 to
21,
particularly preferably 4 to 18, carbon atoms. The dicarboxylic acids
preferably
contain 5 to 10 carbon atoms, particularly preferably 6 carbon atoms.
Bxamples of these are isophthalic acid, terephthalic acid, 1,3- and 1,4-
cyclohexanedicarboxylic acid or alkyl-substituted dicarboxylic acids such as
butylisophthalic acid. Isophthalic acid is particularly preferred.
On the other hand, dimethyl esters such as dimethyl tcrephthalate or dimethyl
1,4-
cyclohexanedicarboxylatc may also be introduced into the polyester by
transesterification, optionally in the presence of transesterification
catalysts.
CA 02314450 2000-07-21
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A corresponding amount of tricarboxylic acids such as trimellitic anhydride
may be
cocondensed into the resin molecule instead of some of the dicatboxylic acid
in
order to produce a branched structure.
Neopentyl glycol, neopentyl glycol hydroxypivalate, hexane-2,5-diol, 1,4-
bis(hydroxymethyI)cyclohexane,1,1-isvpyrilidine-bis-(p-phenoxy)-2-propanol,
2,2,4-trimethylolpentane-1,3-diol, and mixtures thereof are preferably used as
dialcohols.
The glycidyl esters of branched fatty acids, such as versatic acid, may also
be used
for example as dialcohols because the fatty acid is incorporated into the
molecular
structwe in a hydrolysis-stable form. rn special cases, the use of epoxide
resins in
which the epoxy groups have been reacted with monoalcohols is also possible.
A proportion of polyols with more than two OH groups, such as
tnimethylolpropane
or pentaerythritol, may also be used in order to adjust to suitable hydroxyl
values
and viscosities. This also applies to elastification due to a very small
degree of
modification with long-chain dialcohols such as hexatle-1,6-diol, or aliphatic
dicarboxylic acids such as adipic acid.
fisterification (first stage) is performed azeotropically or in the melt at
elevated
temperature (above 190°C) in a known way cad provides a clear product
with an
acid value of 0 to 50, preferably 5 to 25 and a viscosity of 200 to 3000 mPas,
measured at 25°C in a 75 % strength butyl glycol solution.
Additional carboxyl groups have to be introduced into the OH group-containing
polyester in order to facilitate solubility in the aqueous alkaline medium.
Reaction at
temperatures below 190°C (second stage) with an aromatic or
cycloaliphatic
dicarboxylic acid which has preferably boon produced from a polycarboxylic
acid
with three or four carboxyl groups such as, for example, trimesie acid,
hemimellitic
acid, prehnitic acid and mellophanic acid by dcfunctionalisation with a long-
chain,
CA 02314450 2000-07-21
10-
aliphatic hydrophobic monoalcohol is performed for this purpose. A process
which
makes use of anhydride-containing compounds such as trimellitic anhydride,
pyromellitic anhydride or corresponding hydrogenated ring systems, as well as
cyclopentanetctracarboxylic anhydride or pyrazinetetracarboxylic anhydride is
particularly simple.
Mo~noalcohols which may be used are, for example, straight-chain and/or
branched
saturated and/or unsaturated primary, secondary and/or tertiary, preferably
primary
and/or secondary, alcohols. Mixtures may also be used, in particular isomeric
mixtures of these alcohols. Aliphatic C6 to C18 monoaleohols and benzyl
alcohol
and its alkyl-substitution products arc preferred. Hranched C8 to C13 iso-
monoalcohols are particularly preferred. Particularly hydrolysis resistant
semi-esters
are obtained by the use of branched monoalcolnols or secondary monoalcohols
such
as cyclohexanol or secondary methyloctyl alcohol. The structure of the resin
ensures
that optional breakdown products (monoalcohols and monoesters of trimellitic
acid)
which may be produced by hydrolysis are electrophoretically deposited with the
film
without causing problems.
The polycarboxylic acids may be stoichiometrically reacted, for example in a
two-
pot process, with enough monoalcohol to make sure that a dicarboxylic acid is
still
present and this is subsequently added to the OH group-containing polyester at
temperatures of about 150 to 190°C.
In practice, it has been shown that preparation of the carboxyl group-
containing
polyester in a one-pot process can be achieved by adding approximately
stoichiometric amaunts of monoalcohol and trimellitic anhydride to tho OI-T
group-
containing polyester ran the given sequence.
The incorporation of carboxyl groups may also be performed, for example, by
the
use of hydroxyearboxylic acids, such as e.g. diznethylolpropionic acid, during
the
polycondensation reaction, the free carboxyl groups in these generally not
CA 02314450 2000-07-21
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participating in the polycondensation reaction due to steric hindrance so that
the
incorporation of these acids takes place exclusively via the hydroxyl groups.
The molar ratios in the overall formulation for preparing the polyester sure
chosen so
that a viscosity which is appropriate for the particular ultimate purpose is
achieved.
This is, for example, about 200 to 3000, preferably 250 to 2000 and in
particular 300
to 1500 mPas, measured at 50 % strength in butyl glycol at 25°C. It can
also be
adjusted, as can the molecular weight, by mixing in resins with lower and
higher
viscosities or lower and high molecular weights respectively. The upper limit
for the
acid value is preferably less than 100, particularly preferably less than 60;
the lower
limit for the acid value is preferably greater than 35, particularly
preferably greater
than 40. The carboxyl group-containing polyester contains at Feast one,
preferably at
least two, carboxyl groups per molecule in order to produce water dilutability
due to
salt formation with a low molecular weight base. If the acid value is too low,
then
the solubility is inadequate; if it is too high, then the high degree of
neutralisation
can cause increased electrolysis in the ADL bath, which can lead to surface
defects.
The excess of alcohol chosen produces a hydroxyl value, in the final resin, of
about
to 150, preferably 60 to 120. Preferred resins have a relatively high hydroxyl
value and a low acid value.
Polycondensation is performed, for example, azeotropically or in the melt, for
example at reaction temperatures between 160 and 240°C, preferably
between 160
and 2I0°C. After reaching the desired final value with respect to
viscosity and acid
value, the mixture is cooled to a temperature at which the product has a
viscosity
which enables the incorporation of water. In practice, that means that the
melt
viscosity should not be greater than 40 000 mPa.s. If not working under
pressure, the
temperatures arc up to about 100°C. At least some of the carboxyl
groups in the
polycondensation product are neutralised by the addition of a neutralising
agent, in
order to convent to an aqueous solution or dispersion. The neutralising agent
may be
added before or during the addition of water, but it may also be initially
introduced
in the water in which the polycondensation product is dispersed. High-speed
disc
CA 02314450 2000-07-21
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agitators, rotor/stator mixers or high pressure homogenisers, foi example, are
used
for this. Organic solvents rnay optionally be removed by distillation during
or after
conversion into the aqueous solution or dispersion.
Suitable neutralising agents arc conventional bases such as, for example,
arnmonia,
NaOH, KOH, LiOH, primary, secondary and tertiary amines such as diethylamine,
triethylamine, rnorpholine; alkanolamincs such as diisopropanolaminc,
dimethylaminoethanol, triisopropanolamine, dimethylamino-2-methylpropanol;
quaternary ammonium hydroxides or optionally also sraall amounts of alkylene
polyarrrines such as ethylene diamine. Mixtures of these types of neutralising
agents
may also be used.
The amount of neutralising agent is chosen so that a MEQ value of 15 to 90,
preferably 20 to 60, is achieved.
Suitable polyacrylate resins are, for example, carboxyl group-containing
and/or
sulfone group-containing copolymers which may also contain hydroxyl groups
with
an acid value of 20 to 150 and a number average molecular weight Mn of 1000 to
10 000 and, if hydroxyl groups are present, with a hydroxyl value of 20 to
200.
They are prepared by conventional processes, by copolymerisation of
olefinically
unsaturated monomers, wherein monomers containing acid groups are
copolymerised with other monomers. The use of acid group-containing monomers
has the objective of incorporating carboxyl and/or sulfonic acid groups in the
copolymers in order to ensure the water solubility or water dispersibility of
the
copolymers by at least partial neutralisation of these groups.
Suitable monomers which contain acids groups are in principle any oleftnieally
unsaturated polymerisable compounds which contain at least one carboxyl and/or
sulfonic acid group such as, for example, olefinically unsaturated
monocarboxylic or
dicarboxylic acids such as (meth)acrylic acid, crotonic acid, fumaric acid,
malefic
CA 02314450 2000-07-21
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acid, itaconic acid or the semi-esters of fumaric acid, malefic acid and
itaconic acid or
sulfonic acid group-containing olefinically unsatwated compounds such as, for
example, 2-acrylamido-2-methylpropanesulfo~nic acid or any mixture of these
types
of olefinically unsaturated acids. Acrylic acid and methacrylic acid are
particularly
preferred.
In order to produce desired application oriented properties in the final
lacquer, the
copolymers may contain other monomers which contain functional groups with
which, for example, cross-linking reactions may be performed, in addition to
the
acid groups. Thus, both self cross-linking of the copolymer and also external
cross-
linking with other components which have also been introduced into the lacquer
can
take place. Furthermore, in principle, any non-functional olefinically
unsaturated
monomers may also be used when preparing the copolymers.
Examples of these types of functional groups aro hydroxyl, amino, amido, keto,
aldehyde, lactam, 'lactone, isocyanate, epoxy and silane groups. Olehnically
unsaturated monomers which contain these types of functional groups are known.
Hydroxyl and epoxy groups are preferred.
Suitable noon-functional monomers are, for example, esters of acrylic and
methacrylic acids in which the alcohol component contains 1 to 18 carbon
atoms,
vinylaromatic compounds, vinyl esters of aliphatic monocarboxylic acids,
acrylonitrile and methacrylonitrile.
The copolymers may be prepared by polymerisation using conventional processes.
The copolymers are preferably prepared in organic solvents. Continuous or
batchwise polymerisa'on processes may be used.
Suitable solvents are aromatic compounds, esters, ethers and ketones. Glycol
ethers
are preferably used.
CA 02314450 2000-07-21
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Copolymerisation is preferably performed at temperatures between 80 and
180°C
using conventiou~al initiators such as, for example, aliphatic azo compounds
or
peroxides. In order to regulate the molecular weight of the copolymers,
conventional
regulators may be used. After completion of polymerisation, the copolymers, as
described for polycondensation resins, are neutralised and converted into an
aqueous
solution or dispersion, wherein the organic solvent may optionally be
distilled off,
Examples of basic neutralising agents are those described above for
neutralising
polyester resins.
Suitable polyurethane resins are, for example, anionic polyurethane resins
which
contain carboxyl, sulfonic acid and/or phosphoric acid groups present in the
salt
form. They arc prepared in a manner known per se from polyols, polyisocyaaates
and optionally chain-lengthening agents.
The polyurethane resins may be prepared either in bulk or also in organic
solvents
which do not react with isocyanates, They are, as described for the
polycondensation
resins, converted into the aqueous phase after neutralisation of the acid
groups. In
many cases it is expedient to prepare polyurethane resins in a stepwise
manner.
Thus, for example, it is possible to first prepare a prepolymer with acid
groups and
terminal isocyanate groups in organic solvents and then, after neutralisation
of the
acid groups with tertiary amines, to chain-Icngthe~n this prcpolymer and
convert it
into the aqueous phase, wherein the organic solvents may be removed by
distillation.
The polyols used to prepare tln~e prepolymers may be of low or high molecular
weight and may also contain anionic groups.
Low molecular weight polyols preferably have a number average molecular weight
Mn of 60 to 400 and may contain aliphatic, alicyclic or aromatic groups. They
may
be used as up to 30 wt.% of the total polyol constituents.
CA 02314450 2000-07-21
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Suitable low molecular weight polyols are, for example, diols, triols and
polyols
such as ethylene glycol, diethylene glycol, triethylene glycol, 1,2-
propanediol,1,3-
propanediol, 1,4-butanediol, 1,2-butylene glycol, 1,6-hexanediol,
trimethylolpropane, castor oil or hydrogenated castor oil, pentaerythritol,
1,2-
cyclohexanediol, 1,4-cyclohexane-dimethanol, bisphenol A, bisphcnol F,
hydrogenated bispheaol A and mixtures of these polyols.
High molecular weight polyols consist of linear or branched polyols with an OH
value of 30 to 150. They are preferably saturated or unsaturated
polyesterdiols
and/or polyetherdiols and/or polycarbonatediols with a molecular weight Mn of
400
to 5000 or mixtures of these.
Suitable linear or branched polyetherdiols are, for example,
poly(oxyethylcne)glycols, poly(oxypropylene)glycols and/or
poly(oxybutylene)glyeols.
Polycsterdiols are preferred and arc prepared in a known manner by
esterification of
dicarboxylic acids or their anhydrides with diols. In order to produce
branched
polyesters, small amounts of polyols or polycarbvxylic acids with a higher
functionality may be used.
The groups capable of forming anions may arise from the polyester or they are
incorporated into the prepolymers by using compounds which have two H-active
groups which can react with isocyanates and at least one group capable of
forming
an anion. Suitable groups which can react with isocyanates are in particular
hydroxyl
groups and also priimary and/or secondary amine groups. Groups which are
capable
of forming anions are, for example, carboxyl, sulfonic acid and/or phosphoric
acid
groups. Examples of such compounds are dihydroxycarboxylic acids such as
dihydroxypmpionic acid, dihydroxybutyric acid, dihydroxysuccinic acid,
diaminosuccinic acid and, preferably, oe,a-dimethylolalkanoic acids such as
e.g,
dimcthylolpropionic acid.
CA 02314450 2000-07-21
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Suitable polyisocyanates are aliphatic, cycloaliphatic and/or aromatic
polyisocyanates with at least two isocyanate groups per molxule and the
derivatives
of these diisocyanates knowm per se containing biurct, allophanate, urethane
and/or
isocyanurate groups and also mixtures of these polyisocyanates. Ysomers or
isomeric
mixtures of organic diisocyanates are preferably used,
The polyisocyanate component used to prepare the prepolymer may also contain
small proportions of higher functional polyisocyanates.
The prepolymer is expediently prepared in the presence of catalysts such as
e.g.
organotin compounds or tertiary amines.
Conversion of the polyurethane resin into the aqueous phase is performed, as
described in the case of polyester resins, by neutralisation of the acid
groups in the
polyurethane resin with a basic neutralising agent, optionally with removal of
organic solvents by distillation.
Examples of basic neutralising agents are those described above for
neutralising
polyester resins.
The binder dispcrsion(s) according to the invention are cross-linked,
preferably
during stoving, by reaction with a cross-linking component, Cross-linking
components are familiar to a person skillod in the art. Examples are amino
resins, in
particular melamine/fotmaldehyde resins; phenol resins; blocked
polyisocyanates or
transesterification cross-linking agents such as polyesters or polyurethane
esters with
hydroxyalkyl ester groups, alkyl ester derivatives of acetoacetic acid or
malonie
acid, tris(alkoxyearbonylamino)triazine derivatives and mixtures of these
components which can produce highly cross-linked coatings with or without the
use
of catalysts. Blocked polyisocyanates are preferred.
CA 02314450 2000-07-21
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The blocked polyisoeyanates contain on average more than one isocyanate group,
preferably ax least two isocyanate groups, per molecule. They should be
storage
stable in the aqueous phase at an approximately neutral to weakly basic pH,
decompose under the effect of heat at about 100 to 200°C and cross-link
with the
reactive hydroxyl andlor carboxyl groups present in the rosin structure.
Blocked polyisocyanates are obtained by reacting polyisocyanates with
monofunctional compounds with active hydrogen atoms,
Polyisocyanates which are suitable for use individually or as a mixture in the
blocked form as cross-linking agents are any organic diisocyanates and/or
polyisocyanates with aliphatically, cycloaliphatically and/or aromatically
bonded,
free isocyanate groups.
Polyisocyanates which contain about 3 to 36, preferably 8 to 15, carbon atoms
are
preferred. Examples of suitable diisocyanates are toluylene diisocyanate,
diphenylmethane diisocyanate and in particular hexamethylene diisocyanate,
tetramethylxylylene diisocyanate, isophorone diisocyanate, dicylohexylmethane
diisocyanate and cyclohexanc diisocyanate.
Extremely suitable polylsocyanates are, for example, "lacquer polyisocyanates"
based on hexamethylene diisoeyanate, isophorone diisocyanate and/or
dicyclohexylmethane diisocyanate, wherein the polyisocyanates are derivatives
of
these diisocyanates known per se which contain biuret, urethane, uretdione
and/or
isocyanurate groups.
Monofunctional compounds with active hydrogen atoms which can be used to block
the polyisocyanates are known to a person skilled in the art. The following
are
examples of compounds which may be used: CH-acid compounds such as
acetylacetone; CH-acid esters such as alkyl acetoacetates, dialkyl rnalonaxes;
(cyclo)aliphatie alcohols such as n-butanol, 2-ethylhexanol, cyclohexanol;
glycol
CA 02314450 2000-07-21 --
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ethers such as butyl glycol, butyl diglycol; phenols such as cresol, tert.-
butylphenol;
diaminoalcohols such as dimethylaminoethanol; oximes such as butanone oxime,
acetone oxime cyclohexanone oxime; lactams such as ~-caprolactam or
pyrrolidone-
2; imides; hydroxyalkyl esters; hydroxamic acids and their esters; pyrazoles.
The polyisocyanates may be blocked with identical or different blocking agents
within one molecule. Mixtures of identically or differently blocked
polyisocyanates
may also be used,
Melamine/formaldehyde resins cross-link with the hydroxyl groups in the
polyester
resin to form ether groups, ~'hese cross-linking agents are, for example,
triazines
such as melamine or benzoguanamine condensed with aldehydes, in particular
formaldehyde, in the presence of alcohols such as methanol, ethanol, propanol,
butanol or hexanol, using known industrial methods. They are preferably
methanol-
I S etherified znelamin.e resins such as e.g. Cymel 325m, Cymel 32'7, Cymel
350,
Cymel 370~, Maprenal MF 92'1; butanol or isobutanol ethcrified melamine resins
such as e.g. Setamin US 138m or Maprenal MF 610; mixed etherified melamine
resins and in particular hexamethylolmelamine resins such as e.g. Cymel 301e
or
Cymel 303m.
Conventional pigments, fillers, corrosion inhibitors and lacquer auxiliary
substances
may be used to pigment the anodic elxtmdeposition lacquer, as long as they do
not
enter into any disruptive reaction with water in the weakly basic to neutral
pH range
and do not introduce any water-soluble foreign ions which could cause
problems.
The pigments and fillers are fillers which are conventionally used in the
lacquer
industry and inorganic or organic colour and/or effect-providing pigments and
anti-
corrosive pigments. Examples of inorganic colour-providing pigments are
titanium
dioxide, micronised titanium dioxide, zinc sulfide, lithopone, lead carbonate,
lead
sulfate, tin oxide, antimony oxide, iron oxides, chrome yellow, nickel
titanium
yellow, chrome orange, molybdenum red, mineral violet, ultramarine violet,
CA 02314450 2000-07-21
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ultramarine blue, cobalt blur, chro~anium oxide green and carbon black,
Examples of
colour-providing organic pigments are those from the group of azo,
phthalocyanine,
quinacridone, perylene, perinone, anthraquinone,. thioindigo and
diketopyrrolvpyrrole pigments. Examples of effect-providing pigments are metal
pigments, for example of aluminium, copper or other metals; interference
pigments
such as for example, metal oxide coated metal pigments or metal oxide coated
mica;
pearl gloss pigrnemts and optically variable pigments (OVPs).
Examples of anti-corrosive pigments are zinc chromate, strontium chromate,
zinc
phosphate, lead silicochromate, barium metaborate arid zinc berate.
Examples of fillers are calcium carbonate, barium sulfate, talcum, silicon
oxide,
aluminium silicates, magnesium silicates, mica, aluminium hydroxide and
silicas.
The fillers may also be modif ed (coated) with organic compounds, wherein the
organic compounds may also contain W-curable groups. Examples of fillers
modified in this way are coated microniscd aluminium oxide or coated
micronised
silicon dioxide.
The pigments may be dispersed in conventional ways, known to a person skilled
in
the art, in some of the binder dispersion or in a special paste resin. The
composition
of the constituents for optimum dispersion is determined separately for each
dispersing unit. Suitable dispersing units are, for example, disc agitators,
throe-roll
mills, ball mills or preferably sand or pearl mills, During the dispersion
procedure,
conventional auxiliary substances such as, for example, antifoam agents,
dispersion
aids and agents for controlling the Theology may also be added.
The anodically depositable aqueous elcctrodeposition lacquers according to the
invention may also contain conventional lacquer auxiliary substances and
additives
such as biocides, light stabilisers, flow control agents, Further hydrophilic
and/or
hydrophobic polymers with or without reactive ~roups or mixtures of these
polymers
may also be used,
CA 02314450 2000-07-21
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Examples of such polymers are saturated or unsaturated acrylate, polyurethane
or
polyester resins, acrylic-modified acrylate, polyurethane or polyester resins,
epoxide
resins, amino resins, phenol resins, hydrocarbon resins, silicone-modified
acrylatc,
polyurethane or polyester resins, copolymers of butadiene and acrylonitrile,
styrene/aJ.lyl aleohal copolymers.
A,ny known powder coatings may be used in the process according to the
invention,
wherein they preferably do not contain any low molecular weight acidic water-
soluble constituents.
Examples of powder coating compositions are described in Kittel "Lehrbuch der
Lacke and Beschichtungen", vol. VIII, part 2, in the appendix, page 11 et seq.
Powder coatings which can be used according to the invention contain a binder
component consisting of a film-forming resin component and a hardener
component,
wherein the resin component generally makes up at least 50 wt.% of the basic
resinlhardener mixture, while the hardener component amounts to at most 50
wt.%
of this combination,
Suitable resin components arc, for example, plastics resins which are
conventionally
used in the preparation of powder coatings such as polyester resins, epoxide
resins,
poly(meth)acrylate resins, phenol resins, polyurethane resins and siloxane
resins
with a number average molecular weight Mn of S00 to 20 000, preferably 500 to
10 000 and a glass transition temperature between +20°C and
+100°C, preferably
between +40°C and +'70°C.
The hardener components have, for example, number average molecular weights Mn
of 84 to 3 000, preferably 84 to 200.
The resin and hardener components contain functional groups which are
complementary one to the other and react with each other under the stowing
CA 02314450 2000-07-21
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conditions for powder coating and thus lead to cross-linking of the powder
coating.
Examples of such functional groups are epoxide groups, hydroxyl groups,
carboxyl
groups, anhydride groups, isocyanate groups, blocked isocyanate groups,
primary or
secondary amine groups, blockod amine groups, N-heterocyclic groups capable of
ring-opening addition such as, for example, oxazoline groups, (meth)aeryloyl
groups, CH-acid groups such as, for example, acctoacetate groups, aminoether
groups.
The choice of functional groups which react with each other is familiar to a
person
skilled in the art (see also H. I~ittel, Lehrbuch der r,acke and
Beschichtungen, vol.
VIII, part 2, page 12).
Clptionally, several different functional groups may also be combined with
each
other, provided these do not react with each other under the conditions of
preparation of powder coatings. This situation may occur, for example when the
resin component contains different functional groups or when mixtures of
dit~erent
resin and/or hardener components are used.
The resin and hardener components contain on average at least two functional
groups per molecule. In general, the ratio of resin to hardener component is
98 : 2, to
50 : 50; it is preferably between 95 : 5 and 70 : 30,
The binder component should be present in a brittle and muillable condition at
room
temperature. A sharp drop in melt viscosity should take place in the
temperature
range from +100°C; to +160°C in order to favour wetting of the
substrate, flow of the
coating and Frlm formation.
The process is particularly suitable for using or re-using powder coatings
based on
epoxy-functional, hydroxy-functional and carboxy-functional binder components
or
mixtures thereof.
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Suitable epoxy-functional binder components are, for example, epoxide group-
containing polyacrylate resins, epoxide group-containing condensation resins
or
oligomeric polyepoxides with, for example, polycarboxylic acids,
polycarboxylic
anhydrides, acid polyesters, acid acrylate resins, dieyanodiamide and its
derivatives,
amino and/or amide group-containing compounds, blocked polyisocyanates,
phenolic compounds or mixtures thereof as the hardener component,
Epoxide group-containing polyacrylate resins can be prepared by generally
known
methods by rauiical polymerisation o;f at least one ethylenically unsaturated
monomer
with at least one cpoxide group in the molecule and at least one other
ethylenically
unsaturated monomer without epoxide groups in the molecule.
Glycidyl acrylate, glycidyl rnethacrylate and/or allyl glycidyl ether or
mixtures of
these monomers, for example, may be used as ethylcnically unsaturated monomers
with at least one epoxide group.
Examples of ethylenically unsaturated monomers which do not contain an epoxide
group are alkyl esters of acrylic and methacrylic acid with 1 to 20 carbon
atoms in
the alkyl group, vinylaromatic compounds, nitrites, vinyl halides or
vinylidene
halides. Small amounts of compounds with more than one ethylenically
unsaturated
centre xnay also be used. The ethylenically unsaturated monomers which do not
contain an epoxide group are preferably used as a mixture. Epoxide group-
containing condensation resins may be prepared, for example, by etherification
of
polyhydric phenols or polyhydric aliphatic or cycloaliphatic alcohols with
epichlorhydrin in the presence of an alkali.
Suitable hydroxyl-functional binder components may be, for example, polyester,
polyether, polyurethane and/or polyacrylate resins with, for example,
carboxylic
anhydrides, acid polyester resins, acid acrylate resins, blocked
polyisocyanates,
~i-hydroxyalkylamides, substituted glycolurils or mixtures thereof as hardener
components.
CA 02314450 2000-07-21
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Suitable hydroxyl-functional polyesters have, for example, an OH value of 10
to
200 mg KOH/ g of resin and an acid value of less than 5 mg KOH/g of resin.
They
are prepared by methods known to a person skilled in the art, by
esterification of
organic dicarboxylic acids and/or their anhydrides with organic dialcohols
and/or
polyalcohols.
Suitable hydroxyl-functional polyethers are, fox example, polyalkylene ethers
with 2
to 100 alkylene units per polymer molecule and at least one free OH group per
alkylene unit, Suitable hydroxyl-functional polyurethanes are obtained by
reacting
aliphatic and/or cycloaliphatic and/or aromatic diisocyanates with aliphatic
and/or
cycloaliphatic and/or araliphatic aleohols with 2 to 6 OH groups and/or with
the
previously mentioned hydroxyl-functional polyesters and/or polyethers.
Hydroxyl-functional polyacrylate resins may be prepared by generally known
methods by radical polymerisation of at least one ethylenically unsaturated
monomer
with at least one hydroxyl group in the molecule and at least one other
ethylenically
unsaturated monomer without hydroxyl groups in the molecule.
Ethylenically unsaturated monomers with at least one hydroxyl group which may
be
used are, for example, hydroxyalkyl esters of (meth)acrylic acid such as e.g.
hydroxyethyl (meth)acrylate and/or hydroxypropyl (meth)acrylate and/or
hydroxybutyl (meth)acrylatc or mixtures thereof.
Examples of ethylenically unsaturated monomers which do not contain hydroxyl
groups are alkyl esters of acrylic and methacrylic acid with 1 to 20 carbon
atoms in
the alkyl group, vinylaromatic compounds, nitrites, vinyl halides or
vinylidene
halides_ Small amounts of compounds with more than one ethylenically
unsaturated
centre may also be used. The ethylenically unsaturated monomers which do not
contain hydroxyl groups are preferably used as a mixture,
CA 02314450 2000-07-21
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Suitable carboxyl-functional binder components are, for example, acid
polyester or
acid acrylate resins with epoxide resins, epoxyacrylate resins, hydroxyl group-
containing polyester or polyacrylate resins, oxazolines, triglycidyl
isocyanurate, (3-
hydroxy-alkylamides, substituted glycolurils ox mixtures thereof as hardener
components.
Suitable carboxyl-functional polyesters have, for example, an acid value of 20
to
I 00 mg KOH/g of resin and an OH value of less than 10 mg KOH/g of resin. They
are prepared by methods known to a person skilled in the art by esterification
of
organic dicarboxylic acids and/or their anhydrides with organic dialcohols
andlor
polyalcohols,
Carboxyl-functional polyacrylate resins may be prepared by generally known
methods by radical polymerisation of at least one ethylenicalIy unsaturated
monomer
with at least one carboxyl group in the molecule and at least one other
ethylenically
unsaturated monomer without carboxyl groups in the molecule,
Ethylenically unsaturated monomers with at least one carboxyl group which may
be
used are, for example, olefinically unsaturated mono or dicarboxylic acids
such as
e.g, acrylic acid, methacrylic acid, malefic acid, itaconic acid or mixtures
thereof.
Examples of ethylenically unsaturated monomers which do not contain hydroxyl
groups are alkyl esters of acrylic and methacrylic acid with 1 to 20 carbon
atoms in
the alkyl group, vinylaromatic compounds, nitrites, vinyl halides or
vinylidene
halides. Small amounts of compounds with more than one ethylenically
unsaturated
centre may also be used. 'The ethylenically unsaturated monomers which do not
contain hydroxyl groups are preferably used as a mixture.
However, self cross-linking powder coatings may also be used in the process
according to the invention, these containing, for example, polymers with
olefinically
unsaturated groups as binder components. Suitable polymers are, for example,
CA 02314450 2000-07-21
- 25 -
unsaturated polyester resins, unsaturated acrylate resins, polyurethane resins
with
(meth)acryloyl groups or mixtures of these resins which cure at the stowing
temperature far anodic deposition lacquers or under additional energy-rich
iwadiation.
The powder coatings may also contain pigments such as, for example, those
which
are specified for anodic electrodeposition lacquers.
Furthermore, conventional additives for powder coatings may be contained in
the
powder coatings, such as, for example, flow control agents, catalysts, waxes,
degassing agents, antioxidants, light stabilisers, adhesion promoters and
agents to
control the melt rheology.
The powder coatings are prepared by methods lmown to a person skilled in the
art
1 S such as are descr;bed, for example, in "Lehrbuch der Lacke and
Beschichtungen",
Dr. Hens Kittel, vol. V~Z, part 2, pages 1 to 25.
For use according to the invention, the particle sizes in the powder coating
may be 1
to 100 ~Cm.
These are preferably powder coating residues or powder coating waste materials
in
which ai least 40 to 60 % has a particle size of less than 10 pm and up to 20
% has a
particle size of less than 5 lun.
Examples:
1. Preparation of an aqueous binder dispersion for anodic electrodeposition
lacquering
A mixture of 1.80 parts by weight of diethanolamine and 3 parts by weight of
fully deionised water are added to 57.00 parts by weight of a polyester resin
CA 02314450 2000-07-21
-26-
with an acid value of 49 and a hydroxyl value of 60 (prepared from 26.17
parts by weight of neopentyl glycol, 5.43 parts by weight of
trimethylolpropane, 10.83 parts by weight of isophthalic acid, 21.45 parts by
weight of isodecanol and 36.12 parts by weight of trimcllitic anhydride) at
100°C in a reaction vessel provided with stirrer, thermometer and
reflux
condenser and stirred homogeneously for 10 minutes, then 0.15 parts by
weight of a commercial biocide are added and the mixture is again stirred
homogeneously for 10 minutes. 38.05 parts by weight of fully deionised
water are added, with stirring. The mixture is stirred for 90 minutes at
80°C
and then rapidly cooled to 25°C,
Characteristics:
Solids: 53.5
(30 minutes 180°C')
MBQ value; 27.1 nailliequivalents of a~anine per 100 g of solid resin
Solvent content: < 0.1
2. Particle size distribution of the powder coating fines fraction
The paxticle size distribution of a powder coating fines fraction from a white
powder coating (prepared from 910 parts by weight of Crylcoat 801 (UCB
Co.), 90 parts by weight of Araldite PT 910 (CIBA Co.), 540 pacts by weight
of titanium dioxide 2160 (Kronos Co.) and 3 parts by weight of benxoin) was
determined using a Master Sizer X from the Malvern Co.
60 % of all the particles had a particle size of less than 10 Nxrt, 20 % of
all the
particles had a particle size of less than 5 pm.
3. Preparing a powder coating-containing electrodeposition lacquer bath
150.0 parts by weight of the powder coating fines fraction from example 2
were added slowly, with stirring, to 280.0 parts by weight of the binder
CA 02314450 2000-07-21
-27-
dispersion from example 1. Then, with further stirring, the batch was dilutod
with a mixture of 1554.9 parts by weight of fully deionised water and 15.1
parts by weight of dimethylethanolamine.
Characteristics:
Solids: 15
MEQ value: 70 milliequivalents of amine per 100 g of solid resin
Powder : binder 1 : 1
Pigment : binder 0.2 : 1
4. Comparison trial
50.0 parts by weight of titanium dioxide 2160 (Kronos Co.) were worked
into 467.3 parts by weight of binder dispersion from example 1 in as agitator.
Then, with further slow stirring, the batch was diluted with a mixture of
1470.1 paxts by weight of fully deionised water and 12.6 parts by weight of
dimethylethanolarnine.
Characteristics:
Solids: 15
MEQ value: 70 milliequivalents of amine pcr 100 g of solid resin
Pigment : binder 0.2 : 1
5. Testing the throwing power
Throwing power determinations were performed in accordance with "Ford
Laboratory Test Method B 1 120-02" at a total immersion depth of 24 cm, in
electmdepasition lacquer baths according to examples 3 and 4.
CA 02314450 2000-07-21
. 28 _
Example 3 Example 4 (comparison)
Bath temperature 30C 30C
Coating voltage 250 Volts 250 Volts
Coating time 2 minutes 2 minutes
Thickness of layer, 18 ~m 21 ~m
outside
Thickness of layer, 20 1 N,m 23 1 ~m
inside
7 ~.m lirnit 15 cm 11 cm
1 ~m limit I S cm 13 cm
Range, inside, total85.7 % 59
