U.S. patent application number 10/901023 was filed with the patent office on 2005-01-06 for pseudoplastic powder lacquer slurry free of organic solvents, method for production and the use thereof.
Invention is credited to Berg, Jan, Jung, Werner-Alfons, Ott, Gunther, Rockrath, Ulrike, Woltering, Joachim.
Application Number | 20050004301 10/901023 |
Document ID | / |
Family ID | 7627582 |
Filed Date | 2005-01-06 |
United States Patent
Application |
20050004301 |
Kind Code |
A1 |
Rockrath, Ulrike ; et
al. |
January 6, 2005 |
Pseudoplastic powder lacquer slurry free of organic solvents,
method for production and the use thereof
Abstract
A pseudoplastic powder clearcoat slurry which is free from
organic solvents and comprises solid and/or highly viscous,
particles which are dimensionally stable under storage and
application conditions and have an average size of from 0.8 to 20
.mu.m, at least 99% of the particles having a size .ltoreq.30
.mu.m, which is preparable by 1) emulsifying an organic solution
comprising binder and crosslinking agent to give an emulsion of the
oil-in-water type, 2) removing the organic solvent or solvents, and
3) wet grinding the resulting slurry; and also the use of the
powder clearcoat slurry to produce clearcoats for automotive OEM
finishing and automotive refinish, for furniture coating and for
industrial coating, including coil coating, container coating and
the coating of electrical components.
Inventors: |
Rockrath, Ulrike; (Senden,
DE) ; Ott, Gunther; (Munster, DE) ; Berg,
Jan; (Munster, DE) ; Jung, Werner-Alfons;
(Ascheberg, DE) ; Woltering, Joachim; (Munster,
DE) |
Correspondence
Address: |
BASF CORPORATION
ANNE GERRY SABOURIN
26701 TELEGRAPH ROAD
SOUTHFIELD
MI
48034-2442
US
|
Family ID: |
7627582 |
Appl. No.: |
10/901023 |
Filed: |
July 29, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10901023 |
Jul 29, 2004 |
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10169699 |
Jun 20, 2002 |
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10169699 |
Jun 20, 2002 |
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PCT/EP01/00260 |
Jan 11, 2001 |
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Current U.S.
Class: |
524/507 |
Current CPC
Class: |
C08J 3/07 20130101; C08L
75/04 20130101; C08G 18/8025 20130101; C08G 2150/20 20130101; C09D
133/066 20130101; C09D 5/02 20130101; C08G 18/807 20130101; C08G
18/0866 20130101; C09D 175/04 20130101; C08G 18/6254 20130101; C09D
133/066 20130101; C08L 2666/14 20130101 |
Class at
Publication: |
524/507 |
International
Class: |
C08L 075/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 15, 2000 |
DE |
100 01 442.9 |
Claims
What is claimed is:
1. A method comprising 1) emulsifying an organic solution
comprising at least one binder, at least one crosslinking agent,
and at least one organic solvent to give an emulsion, 2) removing
the at least one organic solvent to provide a slurry, and 3) wet
grinding the slurry to form a pseudoplastic powder clearcoat slurry
that is free from organic solvents and comprises solid and/or
highly viscous particles that are dimensionally stable under
storage and application conditions and have an average size of from
0.8 to 20 .mu.m, at least 99% of the particles having a
size.ltoreq.30.mu.m.
2. The method of claim 1 further comprising filtering the
wet-ground slurry.
3. The method of claim 1 further comprising replacing the removed
solvent at least partially with water.
4. The method of claim 1, wherein the pseudoplastic powder
clearcoat slurry has an ion-forming group content of from 0.05 to 1
meq/g and a neutralizing agent content of from 0.05 to 1 meq/g.
5. The method of claim 1, wherein the pseudoplastic powder
clearcoat slurry has a viscosity of (i) from 50 to 1,000 mPas at a
shear rate of 1,000 s.sup.-1 and (ii) from 150 to 8000 mPas at a
shear rate of 100 s.sup.-1.
6. The method of claim 1, wherein the pseudoplastic powder
clearcoat slurry has a solids content of from 10 to 60% by
weight.
7. The method of claim 1, wherein the average size of the particles
is from 2 to 6 .mu.m.
8. The method of claim 1, wherein the pseudoplastic powder
clearcoat slurry further comprises ionic thickeners and nonionic
associative thickeners.
9. The method of claim 1, wherein the binder comprises a polyol and
the crosslinking agent comprises a blocked polyisocyanate and/or a
tris(alkoxycarbonylamino)triazine.
10. The method of claim 1, wherein the binder comprises a
polyacrylate and the crosslinking agent comprises a blocked
polyisocyanate.
11. The method of claim 1, wherein the particles have a minimum
film-forming temperature of at least 0.degree. C.
12. The slurry of claim 1, wherein the particles have a minimum
film-forming temperature of at least 10.degree. C.
13. The method of claim 1, wherein the removing of the organic
solvents is conducted at a temperature below the minimum
film-forming temperature of the particles.
14. The method of claim 1, wherein the pseudoplastic powder
clearcoat slurry is free from external emulsifiers.
15. The method of claim 1, wherein the wet grinding is conducted at
a temperature above the minimum film-forming temperature of the
particles.
16. The method of claim 2, wherein the method consists of the
emulsifying, the removing, the wet grinding, the filtering, and,
optionally, replacing the removed solvent at least partially with
water.
17. The method of claim 1 further comprising applying the
pseudoplastic powder clearcoat slurry to at least one surface of an
article.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. Ser. No.
10/169,699, filed on Jun. 20, 2002, which is a 371 of
PCT/EP01/00260, filed Jan. 11, 2001, which claims priority to
DE10041442.9, filed Jan. 15, 2000, all of which are incorporated
herein by reference.
BACKGROUND
[0002] The present invention relates to a novel powder clearcoat
slurry, free from organic solvents, which possesses
pseudoplasticity. The present invention also relates to a novel
process for preparing this powder clearcoat slurry. The invention
relates not least to the use of the novel powder clearcoat slurry
for producing clearcoats for the automotive sector and for the
industrial sector.
[0003] For the coating of automobile bodies, preference is given
today to the use of liquid coating materials, i.e., spray paints.
These give rise to numerous environmental problems owing to their
solvent content. The same applies to cases where waterborne
clearcoat materials are used, since they still always contain
certain amounts of organic solvents.
[0004] Waterborne clearcoat materials of this kind are known from
the German patent DE 196 23 371 A1. Directly after application, the
conventional waterborne clearcoat materials do not dry to a powder
but instead flow out to form a continuous film. They comprise
aqueous secondary dispersions and are used in the automotive sector
for aqueous multicoat systems or aqueous one-component or
two-component clearcoats. The aim here is for sedimentation-stable
dispersions having an average particle size of from about 10 to
about 200 nm. The reason for this is the experience, familiar to
the skilled worker, whereby, the better the stabilization and the
smaller the size of dispersion particles, the less their tendency
to settle. For reliable application characteristics and in order to
reduce the popping tendency, however, it is necessary to use up to
20% by weight of solvents as well.
[0005] For this reason, increased efforts have been made in recent
years to use powder coating materials for the coating. The results
to date, however, have not been satisfactory; in particular, powder
clearcoat materials still show weaknesses with regard to chemical
resistance and yellowing.
[0006] In the meantime, many developments have aimed to provide
powder clearcoat materials in the form of aqueous dispersions that
can be processed using liquid coating technologies. These
dispersions are also referred to as powder clearcoat slurries.
These customary and known powder clearcoat slurries, in
contradistinction to the powder clearcoat materials, may be
processed in conventional wet coating plants and may be applied at
substantially lower coat thicknesses of about 40 .mu.m, relative to
about 80 .mu.m in the case of powder coating materials, with good
leveling and with a chemical resistance which is comparable with
that of the powder coating materials.
[0007] For instance, the European patent EP 0 652 264 A1 or the
German patent application DE 196 18 657 A1 discloses a powder
clearcoat slurry in which the solid binder and crosslinker
components and, if desired, additives are, as is usual for the
production of powder coating materials, first of all coextruded and
then subjected to dry grinding, after which, in a further step of
wet grinding, they are converted into a powder clearcoat slurry
with the aid of emulsifiers and wetting agents.
[0008] In order that in the course of wet grinding there is no
clogging of the grinding equipment--the stirred ball mills, for
example--the powder clearcoat slurries or the particles present
therein are required in accordance with the aforementioned German
patent application to have a glass transition temperature of from
20 to 90.degree. C., preferably from 40 to 70.degree. C. This
boundary condition considerably restricts the scope for variation
of the material composition of the known powder clearcoat slurries.
And yet it is not possible to do without wet grinding, since
otherwise the coarse particle fraction of the powder clearcoat
slurry is not reduced in size.
[0009] The known clearcoat powder slurry must on the one hand, on
performance grounds, contain comparatively coarse particles with an
average size of from 2 to 6 .mu.m. On the other hand, it has to be
filtered prior to application. In the course of this filtering
operation, even very small coarse particle fractions (particle
size>10 .mu.m) result in clogging of the filters, so that the
production process has to be stopped--a disadvantage both
technically and economically.
[0010] The German patent DE 196 17 086 A1 discloses a powder
clearcoat slurry in which the average size of the solid particles
is from 0.1 to 10 .mu.m. It is preferred in this case to employ
average particle sizes of from 0.23 to 0.43 .mu.m. For
stabilization, it is necessary, in addition to the ionic
stabilization, to employ external emulsifiers as well--generally
polyethylene oxide adducts, which decrease the resistance of the
coating to water and moisture. Moreover, these known powder
clearcoat slurries still always include certain amounts of organic
cosolvents or leveling agents, which cannot be removed since they
are essential to the leveling properties of the partly dried film.
Moreover, special equipment such as pressure release homogenizing
nozzles are necessary for their preparation. Prior to their
application, they are adjusted to the application viscosity using
thickeners. A complex viscosity behavior is not described.
Furthermore, the patent does not give any teaching as to how the
problem of filterability in connection with powder clearcoat
slurries might be solved.
[0011] The German patent application DE 198 41 842.6, unpublished
at the priority date of the present specification, describes a
powder clearcoat slurry which is free from organic solvents and
external emulsifiers and comprises solid spherical particles with
an average size of from 0.8 to 20 .mu.m and a maximum size of 30
.mu.m, the powder clearcoat slurry having an ion-forming group
content of from 0.05 to 1 meq/g, a neutralizing agent content of
from 0.05 to 1 meq/g, and a viscosity of (i) from 50 to 1 000 mPas
at a shear rate of 1 000 s.sup.-1, (ii) from 150 to 8 000 mPas at a
shear rate of 10 s.sup.-1, and (iii) from 180 to 12 000 mPas at a
shear rate of 1 s.sup.-1.
[0012] This powder clearcoat slurry can be prepared with a smaller
number of processing steps than the known powder clearcoat
slurries; owing to its typical powder slurry properties, however,
with residual solvent contents of <1%, and its comparable
particle sizes, it has application characteristics similarly
advantageous to the known slurries. In contrast to the known
waterborne clearcoat materials, it has reliable application
characteristics in terms of popping marks at the required film
thicknesses of about 40-50 .mu.m even without the aid of organic
solvents. Moreover, it and the process for its preparation continue
to exhibit the main advantage of the mixing of components in
solution, namely the very good homogeneity of the resulting
particles. It has been found that even this powder clearcoat slurry
must be filtered prior to its application and in the course of such
filtration gives rise to problems similar to those encountered with
the known powder clearcoat slurries. Whether and, if so, under what
boundary conditions the powder clearcoat slurry described in
DE-A-198 41 842.6 can be subjected to wet grinding is not stated
therein.
SUMMARY OF THE INVENTION
[0013] It is an object of the present invention to provide a novel
powder clearcoat slurry which no longer has the disadvantages of
the prior art. In particular, the novel powder clearcoat slurry
should be preparable with a smaller number of processing steps than
the conventional powder clearcoat slurries. However, on the basis
of its typical powder slurry properties, with residual solvent
contents of <1%, and its comparable particle sizes, it should
have similarly advantageous application characteristics to said
conventional powder clearcoat slurries. In contrast to the known
waterborne clearcoat materials, the novel powder clearcoat slurries
should ensure reliable application characteristics with regard to
popping marks at the required film thicknesses of approximately
40-50 .mu.m, even without the assistance of organic solvents.
Moreover, they should be able to be subjected to wet grinding
without any problems. In this context their material composition
ought to be able to be varied with considerably greater width than
that of the known powder clearcoat slurries, without any problems
occurring during wet grinding. In other words, the novel powder
clearcoat slurry ought to have a considerably wider processing
window in terms of wet grinding than the known slurries. After wet
grinding, the novel powder clearcoat slurry should be filterable
without problems.
[0014] A further object of the present invention was to find a
novel process for preparing powder clearcoat slurries which
continues to ensure the essential advantage of the mixing of the
components in solution: the very good homogeneity of the resulting
particles.
[0015] The invention accordingly provides the novel, pseudoplastic
powder clearcoat slurry which is free from organic solvents and
comprises solid and/or highly viscous, particles which are
dimensionally stable under storage and application conditions and
have an average size of from 0.8 to 20 .mu.m, at least 99% of the
particles having a size<30 .mu.m, which is preparable by
[0016] 1) emulsifying an organic solution comprising binder and
crosslinking agent to give an emulsion of the oil-in-water
type,
[0017] 2) removing the organic solvent or solvents, and
[0018] 3) wet grinding the resulting slurry.
DETAILED DESCRIPTION
[0019] In the text below, the novel, pseudoplastic powder clearcoat
slurry free from organic solvents is referred to for short as the
"slurry of the invention".
[0020] Further subject matter of the invention will emerge from the
description.
[0021] In the light of the prior art it was surprising and
unforeseeable for the skilled worker that the object on which the
present invention is based could be achieved by means of the slurry
of the invention. A particular surprise was that the slurry of the
invention could be wet-ground at temperatures which lay above the
minimum film-forming temperature (MFFT) of its particles without
any problems occurring. A further surprise was that the slurry of
the invention was stable even without external emulsifiers.
[0022] For the slurry of the invention it is essential for the
average size of the solid particles to be from 0.8 to 20 .mu.m, and
particularly preferably from 2 to 6 .mu.m. The average particle
size is understood as meaning the 50% median determined according
to the laser diffraction method, i.e., 50% of the particles have a
diameter.ltoreq.the median and 50% of the particles have a
diameter.gtoreq.the median.
[0023] Slurries having average particle sizes of this kind and a
solvent content of <1% exhibit better application
characteristics and, at the applied film thicknesses of >30
.mu.m as presently practiced in the automotive industry for the
finishing of automobiles, exhibit much less of a tendency toward
popping and "mudcracking" than conventional powder clearcoat
slurries.
[0024] The upper limit of particle size is reached when the size of
the particles means that they are no longer able to flow out fully
on baking, and thus the film leveling is adversely affected. In
cases where requirements regarding the appearance are not very
stringent, however, the limit may also be higher. 30 .mu.m is
considered a sensible upper limit, since above this particle size
the rinse ducts of the highly sensitive application apparatus are
likely to become blocked.
[0025] The particles in the slurry of the invention are solid
and/or highly viscous. In the context of the present invention,
"highly viscous" means that the particles behave essentially like
solid particles under the customary and known conditions of the
storage and application of powder clearcoat slurries.
[0026] The particles in the slurry of the invention are also
dimensionally stable. In the context of the present invention,
"dimensionally stable" means that the particles, under the
customary and known conditions of the storage and application of
powder clearcoat slurries, neither agglomerate nor breakdown into
smaller particles but instead essentially retain their original
form even under the influence of shear forces.
[0027] The slurry of the invention is free from organic solvents.
In the context of the present invention this means that it has a
residual volatile solvent content of <1% by weight, preferably
<0.5% by weight, and with particular preference <0.2% by
weight. In accordance with the invention it is of very particular
advantage if the residual content is below the gas-chromatographic
detection limit.
[0028] The above-described particle sizes for use in accordance
with the invention are obtained even without the aid of additional
external emulsifiers if the binder has an ion-forming group content
corresponding to an average acid number or amine number of from 3
to 56 g KOH/g solids (MEQ acid or MEQ amine of from 0.05 to 1.0
meq/g solids), preferably up to 28 (MEQ acid or MEQ amine: up to
0.5 meq/g solids), and in particular up to 17 (MEQ acid or MEQ
amine: up to 0.3 meq/g solids).
[0029] In accordance with the invention, the general aim is for a
low amount of such groups, since, when the customary crosslinking
agents are used, such as blocked polyisocyanates, for example, free
groups of this kind may remain in the film and may reduce the
strength with regard to environmental substances and chemicals. On
the other hand, the acid group content must still be sufficiently
high to ensure the desired stabilization.
[0030] The ion-forming groups are neutralized 100%, or else only
partially neutralized to <100%, with the aid of neutralizing
agents. The amount of neutralizing agent is chosen such that the
MEQ value of the slurry of the invention is below 1, preferably
below 0.5, and in particular below 0.3 meq/g solids. In accordance
with the invention it is of advantage if the amount of neutralizing
agent corresponds at least to an MEQ value of 0.05 meq/g
solids.
[0031] In general, therefore, the chemical nature of the binder is
not restrictive provided it comprises ion-forming groups which are
convertible by neutralization into salt groups and so are able to
take on the function of ionically stabilizing the particles in
water.
[0032] Suitable anion-forming groups are preferably acid groups
such as carboxylic, sulfonic or phosphonic acid groups.
Accordingly, the neutralizing agents used are bases, such as alkali
metal hydroxides, ammonia, or amines. Alkali metal hydroxides are
suitable for use only to a limited extent, since the alkali metal
ions are nonvolatile on baking and, owing to their incompatibility
with organic substances, may cloud the film and lead to instances
of loss of gloss. Consequently, ammonia or amines are preferred. In
the case of amines, preference is given to water-soluble tertiary
amines. By way of example, mention may be made of
N,N-dimethylethanolamine or aminomethylpropanolamine (AMP).
[0033] Suitable cation-forming groups are preferably primary,
secondary or tertiary amines. Accordingly, neutralizing agents used
are, in particular, low molecular mass organic acids such as formic
acid, acetic acid or lactic acid.
[0034] Binders which contain cation-forming groups are known from
the field of electrodeposition coating materials. By way of
example, reference may be made to the patents EP-A-0 012 463,
EP-A-0 612 818 or U.S. Pat. No. 4,071,428.
[0035] For the preferred use of the slurry of the invention as
unpigmented clearcoat materials in automotive finishing, preference
is given to polymers or oligomers containing acid groups as
ion-forming groups, since these so-called anionic binders are
generally more resistant to yellowing than the class of the
cationic binders.
[0036] Nevertheless, cationic binders with groups convertible into
cations, such as amino groups, are likewise suitable for use in
principle provided the field of use is tolerant of their typical
secondary properties, such as their tendency toward yellowing.
[0037] As binders which contain anion-forming groups, it is
possible to use any desired resins containing the abovementioned
acid groups. However, it is important that they also carry further
groups which ensure crosslinkability. In accordance with the
invention, hydroxyl groups are preferred.
[0038] Suitable oligomers and polymers of this kind for use in
accordance with the invention include hydroxyl-containing,
preferably linear and/or branched and/or block, comb and/or random
poly(meth)acrylates, polyesters, alkyds, polyurethanes, acrylated
polyurethanes, acrylated polyesters, polylactones, polycarbonates,
polyethers, (meth)acrylatediols or polyureas.
[0039] Besides the hydroxyl groups, the oligomers and polymers may
also include other functional groups such as acryloyl, ether,
amide, imide, urethane, urea, thio, carbonate or epoxide groups,
provided these do not disrupt the crosslinking reactions.
[0040] These oligomers and polymers are known to the skilled
worker, and many suitable products are available on the market.
[0041] In accordance with the invention, the polyacrylates, the
polyesters, the alkyd resins, the polyurethanes and/or the
acrylated polyurethanes are of advantage and are therefore used
with preference.
[0042] Examples of suitable polyacrylates are described in the
European patent application EP-A-0 767 185 and the American patents
U.S. Pat. Nos. 5,480,493, 5,475,073 or 5,534,598. Further examples
of particularly preferred polyacrylates are sold under the brand
name Joncryl.sup.R, such as Joncryl.sup.R SCX 912 and 922.5, for
instance. The preparation of these polyacrylates is widely known
and is described, for example, in the standard work Houben-Weyl,
Methoden der organischen Chemie, 4.sup.th edition, volume 14/1,
pages 24 to 255, 1961.
[0043] The preparation of the polyesters and alkyd resins which are
used with preference in accordance with the invention is widely
known and is described, for example, in the standard work Ullmanns
Encyklopdie der technischen Chemie, 3.sup.rd edition, volume 14,
Urban & Schwarzenberg, Munich, Berlin, 1963, pages 80 to 89 and
pages 99 to 105, and also in the following books: "Rsines
Alkydes-Polyesters" by J. Bourry, Paris, Dunod, 1952, "Alkyd
Resins" by C. R. Martens, Reinhold Publishing Corporation, New
York, 1961, and "Alkyd Resin Technology" by T. C. Patton,
Interscience Publishers, 1962.
[0044] The polyurethanes and/or acrylated polyurethanes whose use
is particularly preferred in accordance with the invention are
described, for example, in the patents EP-A-0 708 788, DE-A-44 01
544 or DE-A-195 34 361.
[0045] Suitable crosslinkers include all crosslinking agents which
are customary in the field of light-stable clearcoat materials.
Examples thereof are etherified melamine-formaldehyde resins,
benzoguanamine resins, resins or compounds containing siloxane
groups, resins or compounds containing anhydride groups, resins or
compounds containing epoxide groups, blocked and/or unblocked
polyisocyanates, and/or tris(alkoxycarbonylamino)triazines, as
described in the patents U.S. Pat. No. 4,939,213, U.S. Pat. No.
5,084,541, U.S. Pat. No. 5,288,865. or EP-A-0 604 922. In
accordance with the invention, the blocked polyisocyanates are of
advantage and are therefore used with particular preference.
Examples of suitable blocked polyisocyanates are described in the
German patents DE-A-196 17 086 and 196 31 269 and also in the
European patents EP-A-0 004 571 and 0 582 051.
[0046] The slurry of the invention comprises preferably nonionic
and ionic thickeners. This effectively counters the tendency of the
comparatively large solid particles toward sedimentation, and at
the same time pseudoplasticity is brought about.
[0047] Examples of nonionic thickeners are hydroxyethylcellulose
and polyvinyl alcohols. Nonionic associative thickeners are
likewise available on the market in diverse selection. They consist
for example of water-dilutable polyurethanes, which are the
reaction products of water-soluble polyetherdiols, aliphatic
diisocyanates and monofunctional hydroxy compounds containing an
organophilic radical.
[0048] Likewise commercially available are ionic thickeners. These
usually contain anionic groups and are based for example on special
polyacrylate resins containing acid groups, some or all of which
may have been neutralized.
[0049] Examples of suitable thickeners for use in accordance with
the invention are known from the textbook "Lackadditive" [Additives
for coatings] by Johan Bieleman, Wiley-VCH, Weinheim, N.Y., 1998,
pages 31 to 65.
[0050] For the slurry of the invention it is especially
advantageous if both of the above-described types of thickener are
present therein. The amount of thickeners to be added and the ratio
of ionic to nonionic thickener is guided by the desired viscosity
of the slurry of the invention, which in turn is determined by the
required sedimentation stability and by the special requirements of
spray application. The skilled worker will therefore be able to
determine the amount of the thickeners and the ratio of the
thickener types to one another on the basis of simple
considerations, possibly with the aid of preliminary tests.
[0051] Preferably, a viscosity range of from 50 to 1 500 mPas at a
shear rate of 1 000 s.sup.-1 and from 150 to 8 000 mPas at a shear
rate of 10 s.sup.-1 is set.
[0052] This viscosity behavior, known as "pseudoplasticity",
describes a state which does justice both to the requirements of
spray application, on the one hand, and to the requirements in
terms of storage and sedimentation stability, on the other: in the
state of motion, such as when pumping the slurry of the invention
in circulation in the ring circuit of the coating installation and
when spraying, for example, the slurry of the invention adopts a
state of low viscosity which ensures easy processability. Without
shear stress, on the other hand, the viscosity rises and thus
ensures that the coating material already present on the substrate
to be coated has a reduced tendency to form runs on vertical
surfaces. In the same way, a result of the higher viscosity in the
stationary state, such as during storage, for instance, is that
sedimentation of the solid particles is largely prevented or that
any slight degree of settling of the powder slurry of the invention
during the storage period can be removed again by agitation.
[0053] In addition to the essential constituents described above,
the solid particles of the slurry of the invention may comprise
additives such as are commonly used in clearcoat materials. In this
context it is essential that these additives do not substantially
lower the minimum film-forming temperature (MFFT) or the glass
transition temperature Tg of the binders.
[0054] Examples of suitable additives are polymers, crosslinking
catalysts, defoamers, adhesion promoters, additives for improving
substrate wetting, additives for improving surface smoothness,
flatting agents, light stabilizers, corrosion inhibitors, biocides,
flame retardants, and polymerization inhibitors, especially
photoinhibitors, as described in the book "Lackadditive" by Johan
Bielemann, Wiley-VCH, Weinheim, N.Y., 1998.
[0055] Crosslinking components of polyol type, reactive diluents or
leveling assistants which may be incorporated by crosslinking in
the film may be added to the slurry of the invention. It is
important, however, that these components are located preferably in
the external, aqueous phase of the slurry of the invention and not
in the disperse organic phase, where they would bring about a
lowering of the MFFT of the particles contained herein and thus
coalescence or coagulation of any sedimented particles.
[0056] Examples of suitable compounds of this kind are oligomeric
polyols, which are obtainable by hydroformylation and subsequent
hydrogenation from oligomeric intermediates themselves obtained by
metathesis reactions of acyclic monoolefins and cyclic monoolefins;
examples of suitable cyclic monoolefins are cyclobutene,
cyclopentene, cyclohexene, cyclooctene, cycloheptene, norbornene or
7-oxanorbornene; examples of suitable acyclic monoolefins are
present in hydrocarbon mixtures which are obtained in petroleum
processing by cracking (C.sub.5 cut); examples of suitable
oligomeric polyols for use in accordance with the invention have a
hydroxyl number (OHN) of from 200 to 450, a number-average
molecular weight Mn of from 400 to 1 000, and a mass-average
molecular weight M.sub.w of from 600 to 1 100; further examples of
suitable compounds of this kind are branched, cyclic and/or acyclic
C.sub.9-C.sub.16 alkanes functionalized with at least two hydroxyl
groups, especially positionally isomeric diethyloctanediols, and
also cyclohexanedimethanol, neopentyl glycol hydroxypivalate,
neopentyl glycol, trimethylolpropane or pentaerythritol.
[0057] It is of advantage in accordance with the invention to
prepare the slurry of the invention by means of the process of the
invention.
[0058] In the process of the invention, the ionically stabilizable
binders and the crosslinking agents and also, if appropriate, the
additives are mixed in organic solution and dispersed together in
water with the aid of neutralizing agents by the secondary
dispersion process. The system is then diluted with water, while
stirring. A water-in-oil emulsion is formed first of all, which on
further dilution changes to become an oil-in-water emulsion. This
point is generally reached at solids contents of <50% by weight,
based on the emulsion, and is evident externally from a relatively
sharp drop in viscosity in the course of dilution.
[0059] The emulsion thus obtained, which still contains solvent, is
subsequently freed from solvents (stripping) by means of azeotropic
distillation.
[0060] In accordance with the invention it is of advantage if the
minimum film-forming temperature of the binders is at least
0.degree. C., preferably at least 10.degree. C., with particular
preference at least 15.degree. C., with very particular preference
at least 20.degree. C., and in particular at least 25.degree. C.
The minimum film-forming temperature may be determined by drawing
down the dispersion onto a glass plate using a bar coater and
heating it in a gradient oven. The temperature at which the
pulverulent layer films is designated the minimum film-forming
temperature. For further details, refer to Rompp Lexikon Lacke und
Druckfarben, Georg Theime Verlag, Stuttgart, N.Y., 1998 "minimum
film-forming temperature", page 391.
[0061] It is of advantage in accordance with the invention if the
solvents to be removed are distilled off at a distillation
temperature below 70.degree. C., preferably below 50.degree. C. and
in particular below 40.degree. C. If appropriate, the distillation
pressure is chosen so that in the case of higher-boiling solvents
this temperature range is still maintained.
[0062] At its simplest, the azeotropic distillation may be realized
by stirring the emulsion at room temperature in an open vessel for
several days. In the preferred case, the solvent-containing
emulsion is freed from the solvents by a vacuum distillation.
[0063] In order to avoid high viscosities, the amount of water and
solvents removed by distillation or evaporation is preferably
replaced by water. The water may be added before, during and/or
after, preferably before, the evaporation or distillation, in
portions.
[0064] After the solvents have been lost, the MFFT of the dispersed
particles rises, and instead of the previous solvent-containing
emulsion (liquid-in-liquid dispersion) a solid-in-liquid dispersion
is formed. In the context of the present invention, the concept of
a solid-in-liquid dispersion also embraces a dispersion of highly
viscous particles in water.
[0065] In accordance with the invention, the particles of the
resulting slurry are mechanically comminuted in the wet state, this
being referred to in the context of the present invention as wet
grinding of the slurry. In this grinding process, conditions are
employed such that the temperature of the ground material does not
exceed 70.degree. C., preferably 60.degree. C., and in particular
50.degree. C. The specific energy input during the grinding process
is preferably 10 to 1 000, more preferably from 15 to 750, and in
particular from 20 to 500 Wh/g.
[0066] Wet grinding can be carried out using any of a wide variety
of apparatus which produces high or low shear fields.
[0067] Examples of suitable apparatus which produces low shear
fields includes customary and known stirred tanks, slot
homogenizers, microfluidizers or dissolvers.
[0068] Examples of suitable apparatus which produces high shear
fields include customary and known stirred mills or inline
dissolvers.
[0069] In accordance with the invention it is particularly
preferred to employ the apparatus which produces high shear fields.
Among such apparatus, the stirred mills are particularly
advantageous in accordance with the invention and are therefore
used with very particular preference.
[0070] In general, in the course of wet grinding, the slurry is
supplied to the apparatus described above by means of suitable
equipment such as pumps, and is circulated through said apparatus
until the desired particle size has been reached and the slurry of
the invention is obtained.
[0071] In accordance with the invention it is of advantage in
particular for energy reasons if the slurry to be ground contains
only some--preferably from 5 to 90% by weight, more preferably from
10 to 80% by weight, and in particular from 20 to 70% by weight--of
the above-described thickeners present in the slurry of the
invention. Where this variant of the process of the invention is
employed, the remaining amount of thickener is to be added after
wet grinding, so giving the slurry of the invention.
[0072] The slurry of the invention advantageously has a solids
content of from 10 to 60% by weight, in particular from 20 to 50%
by weight.
[0073] Preferably, the slurry of the invention is filtered before
being used. For this purpose use is made of the customary and known
filtration apparatus and filters, such as are also suitable for the
filtration of the known powder clearcoat slurries. The mesh size of
the filters may vary widely and is guided primarily by the particle
size and size distribution of the particles of the slurry of the
invention. The skilled worker is therefore able to determine the
appropriate filters with ease on the basis of this physical
parameter. Examples of suitable filters include bag filters. These
bag filters are available in the market under the brand name
Pong.RTM. or Cuno.RTM.. It is preferred to use bag filters having
mesh sizes of from 10 to 50 .mu.m, examples being Pong.RTM. 10 to
Pong.RTM. 50.
[0074] In the course of filtration the further particular advantage
of the slurry of the invention becomes evident, namely that it can
be filtered without problems even when in the course of wet
grinding the minimum film-forming temperature of the particles
present therein was exceeded.
[0075] To produce the clearcoats of the invention, the slurry of
the invention is applied to the substrate that is to be coated. No
special measures need be taken here; instead, the application may
take place in accordance with the customary and known techniques,
which is another particular advantage of the slurry of the
invention.
[0076] Following its application, the slurry of the invention dries
without problems and does not film at the processing temperature,
generally at room temperature. In other words, the slurry of the
invention applied as a wet film loses water when flashed off at
room temperature or slightly elevated temperatures, without the
particles present therein altering their original solid form. The
solid film in powder form loses the residual water by evaporation
more easily than a flowing wet film. As a result, the risk of
bubbles of evaporated water enclosed in the cured film (popping) is
reduced. Moreover, the tendency toward mudcracking is extremely
low.
[0077] In the subsequent baking step, the now substantially
water-free powder layer is melted and caused to crosslink. In some
cases, it may be of advantage to carry out the leveling process and
the crosslinking reaction with a chronological offset, by operating
in accordance with a staged heating program or a so-called heating
ramp. The appropriate crosslinking temperature for the present
examples is between 120 and 160.degree. C. The corresponding baking
time is between 20 and 60 minutes.
[0078] The clearcoat which results in this case has outstanding
performance properties. For instance, it adheres firmly to all
customary and known basecoats or to substrates such as metal,
glass, wood or plastic. It is of high gloss, smooth,
scratch-resistant, stable to weathering and free from defects. On
the basis of its advantageous profile of properties, moreover, the
slurry of the invention is also suitable for applications other
than automotive finishing, especially for the coating of furniture
and for industrial coating, including coil coating and container
coating, and the coating of electrical components.
EXAMPLES
Preparation Example 1
[0079] The Preparation of a Solution Polyacrylate Resin
[0080] 445.3 parts by weight of methyl ethyl ketone (MEK) were
introduced into a reaction vessel and heated to 80.degree. C. The
initiator solution, consisting of 47.6 parts by weight of TBPEH
(tert-butyl perethylhexanoate) and 31.1 parts by weight of MEK, and
the monomer mixture, consisting of 183.3 parts by weight of
tert-butyl acrylate, 71.4 parts by weight of n-butyl methacrylate,
95.2 parts by weight of cyclohexyl methacrylate, 121.4 parts by
weight of hydroxyethyl methacrylate and 4.76 parts by weight of
acrylic acid, were metered into this initial charge at 80.degree.
C. with stirring over the course of 5 h from two separate feed
vessels. The reaction mixture was then heated to 80.degree. C. for
two hours, and a fraction of the volatile components of the
reaction mixture was stripped off under reduced pressure at 500
mbar for 5 h. The resin solution was then cooled to 50.degree. C.
and discharged.
[0081] The resin solution had the following characteristics:
1 Solids: 71.4% by weight (1 h at 130.degree. C.) Viscosity: 8.0
dPas (cone and plate viscometer at 23.degree. C.; 55% strength
solution) Acid number: 10.1 mg KOH/g resin solids.
Preparation Example 2
[0082] The Preparation of a Blocked Polyisocyanate Crosslinker
[0083] 837 parts of isophorone diisocyanate were introduced into an
appropriate reaction vessel, and 0.1 part of dibutyltin dilaurate
was added. A solution of 168 parts of trimethylolpropane and 431
parts of methyl ethyl ketone was then run in slowly. As a result of
the exothermic reaction, the temperature rose. After it had reached
80.degree. C., the temperature was kept constant by external
cooling and the rate of addition of the feed stream was reduced
slightly if necessary. After the end of the feed stream, the
mixture was held at this temperature for about 1 hour until the
isocyanate content of the solids had reached 15.7% by weight based
on the solids. The reaction mixture was subsequently cooled to
40.degree. C. and a solution of 362 parts of 3,5-dimethylpyrazole
in 155 parts of methyl ethyl ketone was added over the course of 30
minutes. After the reaction mixture had heated up to 80.degree. C.,
owing to the exothermic reaction, the temperature was kept constant
for 30 minutes until the NCO content had dropped to less than 0.1%
by weight. Then 47 parts of n-butanol were added to the reaction
mixture, which was held at 80.degree. C. for a further 30 minutes
and then, after brief cooling, was discharged.
[0084] The reaction product had a solids content of 70% by weight
(1 h at 130.degree. C.).
Example 1
[0085] The Preparation of an Inventive Powder Clearcoat Slurry
[0086] 975.1 parts by weight of the acrylate resin solution from
preparation example 1 and 567.7 parts by weight of the crosslinker
solution from preparation example 2 were mixed at room temperature
in an open vessel for 15 minutes with stirring. Then 10.9 parts by
weight of Cyagard.RTM. 1164 L (UV absorber from Cytec), 10.9 parts
by weight of Tinuvin.RTM. liquid 123 (sterically hindered amine
"HALS" from Ciba Geigy) and 9.5 parts by weight of
N,N-dimethylethanolamine were added and the resulting mixture was
stirred at room temperature for a further two hours. The mixture
was then diluted with 645.9 parts by weight of deionized water in
small portions. After an interval of 15 minutes, a further 780.0
parts by weight of water were added. This gave an aqueous emulsion
of low viscosity with a theoretical solids content of 37% by
weight, which was stirred at room temperature for a further 48
hours. The amount of liquid evaporated off was supplemented by
adding deionized water until the original level was regained. This
gave a powder clearcoat slurry having the following
characteristics:
2 Solids (2 h, 80.degree. C.): 36.7% by weight Solvent content:
<0.05% (by gas chromatography).
[0087] In order to produce the desired pseudoplasticity, 22.6 parts
by weight of Acrysol.RTM. RM 8 (nonionic associative thickener from
Rohm & Haas) and 6.0 parts of Viskalex.RTM. HV 30 (anionic
thickener based on polyacrylate resin, from Allied Colloids) were
incorporated by stirring into 1 000 parts by weight of this powder
clearcoat slurry. The viscosity profile of the resultant inventive
powder clearcoat slurry 1 was as follows:
[0088] 820 mPas at a shear rate of 100 s.sup.-1
[0089] 210 mPas at a shear rate of 1 000 s.sup.-1.
[0090] The resultant powder clearcoat slurry had a minimum
film-forming temperature of 45.degree. C. It was ground by means of
a stirred ball mill. For this purpose the powder clearcoat slurry,
using a pump, was supplied to the mill and circulated through the
mill until the desired quality [particle sizes: x.sub.50 2.5 .mu.m;
x.sub.max<10 .mu.m (oversize: laser diffraction measuring
instrument from Malvern)] had been reached.
[0091] The wet-ground powder clearcoat slurry, i.e., the slurry of
the invention, was filtered without problems using bag filters
(Pong.RTM. 50) without any clogging of the filters.
[0092] After storage at room temperature for 4 weeks, there was a
very slight sediment, which had only settled loosely, and which
could be reagitated again to homogeneity within 5 minutes using a
simple laboratory stirrer.
Example 2
[0093] The Use of the Inventive Powder Clearcoat Slurry as Part of
a Multicoat Color or Effect Paint System to Produce a Clearcoat
[0094] The inventive powder clearcoat slurry of example 1 was
applied with preparation of a so-called integrated system, which is
descibed below for a gray metallic shade.
[0095] Using a gravity feed gun, a functional coat (Ecoprime.RTM.
from BASF Coatings AG) was applied to steel panels coated
cathodically with a commercial electrocoat material. After flashing
off at room temperature for 5 minutes, a gray aqueous metallic
basecoat (Ecostar.RTM. from BASF Coatings AG) was applied in the
same way to this coat and was subsequently predried at 80.degree.
C. for 5 minutes.
[0096] After the panels had been cooled, the inventive powder
clearcoat slurry was applied in the same way. Thereafter, the
panels were first flashed off for 5 minutes and then predried at
40.degree. C. for 15 minutes. They were subsequently baked at
145.degree. C. for 30 minutes.
[0097] This gave an aqueous metallic overall paint system in a gray
shade. The applied wet films had been chosen so that, after baking,
the dry film thicknesses for the functional coat and for the
aqueous metallic basecoat were each 15 .mu.m. The inventive
clearcoat had a film thickness of from 40 to 45 .mu.m. The
inventive multicoat paint system had an outstanding overall
appearance. At the applied clearcoat thickness, no defects in the
form of popping marks and mudcracking are evident in the
clearcoat.
[0098] The table below gives an overview of the tests conducted and
the results obtained in them.
3TABLE The performance properties of the inventive clearcoat
Properties Example 2 Clearcoat thickness 40-45 .mu.m Gloss at
20.degree.*.sup.) 77 Haze*.sup.) 80 Appearance bright Leveling very
good Popping marks none Mudcracking none
* * * * *