WO 95/29961 PCT/EP95/01568
2189236
Coating- eomy~osition whose ",rerceived color dey~ends on
the viewingr_ ancle, and use thereof in basecoats for
multi-coat paint systems
The invention relates to coating compositions
which are suitable for producing coatings having a
perceived color which is particularly bright and
depends on the viewing angle. These coating
compositions are, in particular, basecoats.
Coating compositions which permit the
production of coatings whose perceived color is
dependent on the angle of :incident light and/or on the
viewing angle are known, in particular, as effect
basecoats. In the context of effect basecoats, there is
the requirement for a continually increasing number of
effect colors. The effect basecoats comprise
plateletlike special-effect pigments which bring about
a so-called brightness flop and/or color flop. On the
basis of pure metal flake pigments for producing a
brightness flop, for example those of aluminum, a large
number of further plateietlike special-effect pigments
have been developed which are suitable for use in
effect basecoats. Examples of further plateletlike
special-effect pigments are interference pigments, for
example metal pigments coated with metal oxide, an
example being aluminum coated with titanium d.i oxide or
with mixed oxide, and coated micas, for instance micas
coated with titanium dio~:ide, and graphite special-
effect pigments. It is also common to combine such
special-effect pigments with one another; for example,
aluminum Bake pigments are combined with mica-based
interference pigments in effect basecoats .or vehic~e
finishing. Lsing the known interference pigments, cnly
a relat~.vely weak color flc>p can be dbtained.
German Patent App:Lication P 42 40 743.5
published June 9, 1994 describes pigments whose
,.
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color depends on the viewing angle, which consist of
oriented, three-dimensionally crosslinked substances
having a liquid-crystalline structure with a chiral
phase.
EP-A-0 357 844 describes water-dilutable
coating compositions which comprise a combination of
flop effect pigments and encapsulated, thermochromic,
liquid-crystal pigments. Coat:_ngs produced therewith
change their perceived color z-eversibly in dependence
on the temperature.
The object of the invention is to provide
coating compositions, especial:Ly basecoats, and which
permit the production of coatings with novel color
effects, in which context their perceived color is to
be independent of the temperature.
It has been found that this object can be
achieved by a coating composition which is suitable as
a basecoat for multicoat paint systems and comprises:
- one or more customary paint. binders,
- one or more plateletlike: pigments whose color
depends on the viewing angle, which consist of
oriented, three-dimen:~ionally crosslinked
substances of liquid-crystalline structure with a
chiral phase,
- one or more customary special-effect pigments
which differ therefrom,
- if desired, one or more crosslinking agents,
- if desired, one or more colored absorption
pigments and/or fillers, and
- if desired, customary paint additives.
The pigments whose color depends on the viewing
angle, which consist of oriented, three-dimensionally
crosslinked substances of liquid-crystalline structure
with a chiral phase, are referred to below as LCP
pigments LCP - liquid crystal polymeri. The LCP
pigments can be obtained by subjecting one or more
three-dimensionally crosslinkable liquid-crystalline
substances with a chiral phase to orientation, then to
three-dimensional crosslinking and subsequently to
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comminution to the desired particle size. This can be
carried out, for example, by first applying the three-
dimensionally crosslinkable liquid-crystalline sub-
stances with a chiral phase to a substrate in a thin
layer, for example by knife coating, crosslinking the
layer on this substrate, then detaching it from the
substrate and comminuting i.t to the desired particle
fineness. This produces plateletlike pigments which are
transparent and colorless per se. By means of
appropriate chemical stru<aure-forming measures in
relation to the molecular structure, LCP pigments
having different effective interference colors can be
produced. The plateletlike LCP pigments preferably have
a diameter of from 1 to 100 Vim, particularly preferably
from 10 to 60 Vim, and a thi~~kness of preferably from 3
to 15 Vim, particularly preferably from 5 to 10 Vim.
In accordance with the invention it is
possible, for example, to use those LCP pigments as
described in the German Patent
Application P 42 40 743.5, to which reference is hereby
made. Reference is also made here to the starting
substances for the preparation of the LCP pigments, and
details on the preparation techniques, which are
described therein.
In accordance with German Patent Application
P 42 40 743.5, liquid-crystalline substances which are
suitable as starting substances for the preparation of
the LCP pigments have a twi;ated structure with a pitch
which corresponds to a wavelength of light in the range
from W to IR. This structure is found, for example, in
cholesteric liquid crystals. Cholesteric liquid
crystals, or, in general, liquid-crystalline substances
with a chiral phase, which ;possess a twisted structure
with a desired pitch, can be obtained from nematic,
smectic or ciscctic struorures by adding to them a
chiral substance. '.'he nature and proportion of the
chiral substance determine the pitch of the twisted
structure and therefore the wavelength of the reflected
light. The twisting of the structure may be either
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left-handed or right-handed. The starting substances
must additionally comprise groups which can be
polymerized by addition polymerization, condensation
polymerization or polyaddition and of which at least
some are in the form of difunctional, trifunctional or
more highly functional units. Examples of such groups
are methacryloxy and acryloxy groups.
Examples of suitable materials and their
preparation are described, for example, in DE-C2
3 604 757, in EP-A2-358 208, i.n EP-A-0 066 137 (corres
ponds to US 4 388 453) or in the literature cited in
D. J. Broer et al . in 14th Int . Liquid Conf . , Abstracts
II, 921 (1992).
Three-dimensionally crosslinkable polyorgano
siloxanes which are preferably suitable are those
according to EP-A-0 358 208.
As starting materials for the preparation of
the LCP pigments, however, it is possible in principle
to use all cholesteric liquid crystals. It is possible
to employ one type of cholesteric liquid crystal, or
else a mixture of at least two of these liquid
crystals. In addition to these liquid crystals, other
dyes and/or pigments can be used as further components
in the preparation of the LCP pigments. It is possible
to employ one colorant or else mixtures of at least two
colorants.
In a preferred embodiment, the colorant to be
employed is a pigment, for example gas black. The
colorant to be employed is, in a further preferred
embodiment, soluble in the :Liquid crystal (mixture)
employed. Preference is given to the employment not of
a mixture of two or more cholesteric liquid-crystalline
substances but of a single, pure, cholesteric liquid-
crystalline substance.
The admixing of the pigments and/o.w dyes to the
other starting substances is carried out in a customary
manner, for example by incorporation with stirring. The
admixing of the dyes and/or pigments brings about,
within the LCP pigment, a combination of the angle-
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dependent color effects of the liquid-crystalline
substances with the known color effects) of the
respective substances admixed. The admixing of these
substances does not, however, alter the subsequent
process steps for the preparation of the LCP pigments.
A particularly desired LCP pigment color can
also be obtained by mixing defined liquid-crystal base
mixtures in appropriate proportions. In this case too,
there is no change in the subsequent process steps for
the preparation of the LCP pigments. The subsequent
description of the preparation process, therefore,
applies to all variants of the ~~CP pigments.
Liquid crystals with twisted phases C~PVP1 fl Y1
t.'~eir optical properties only when the individual
molecules are arranged in layers and are ordered
uniformly within a layer. In this context, the
molecules change their preferential direction from
layer to layer, producing helical structures as a
result. In order to achieve this, the molecules are
aligned (oriented) by means of known methods, for
example by alignment layers or electrical or magnetic
fields. Such methods are known, for example, from the
following references: CA113 (22), 201523y: CA113 (14),
124523u; CA112 (18), 169216s; CA112 (16), 149138q;
CA112 (4), 21552c; CAlll (16), 144258y; CAll1 (4),
24780r.
In the course of the preparation of the LCP
pigments, the starting substances cited as examples are
oriented in a known manner. This can be accomplished,
for example, by knife coating onto a metal, plastics or
glass substrate. The knife coating of liquid-
crystalline,polyorganosiloxanes onto a film is known,
for example, from ~P-A-0 358 20E3.
The oriented liquid-cr~~stalline substances are
crosslinked as is known from the prior art for the
respective material. For example, liquid-crystalline
polyorganosiloxanes can be crosslinked thermally by the
method described in EP-A-0 066 137. The liquid
crystalline polyorganosiloxanes described in EP-A
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0 358 208 can be three-dimensionally crosslinked
photochemically, for example by irradiation with W
light. An overview of methods for the photochemical
crosslinking of oriented starting materials can be
found in C.G. Roffey, Photopolymerization of Surface
Coatings (1982), John Wiley b: Sons, Chichester, pp.
137-208.
Examples of special-ef:Eect pigments which can
be used in addition to the LCP pigments in the novel
coating composition, generall~r plateletlike special-
effect pigments, are the customary pigments used, for
example, in effect coating materials, such as metal
pigments, for example of titanium, aluminum or copper,
interference pigments, such as metal oxide-coated metal
pigments, for example titanium dioxide-coated or mixed-
oxide-coated aluminum, coated mica, for example
titanium dioxide-coated or mixed-oxide-coated mica,
microtitanium dioxide and graphite special-effect
pigments, plateletlike iron oxide (micaceous iron
oxide), molybdenum disulfide pigments, plateletlike
copper phthalocyanine pigments and bismuth oxychloride
flakes, and coated glass flakes. It is possible for the
mixed-oxide-coated aluminum pigments and mica pigments
to have a covering of organic p_Lgments.
The particular perceived color or color effect
of the coatings produced from ~~he coating compositions
according to the invention i:~ a result of parallel
alignment of the plateletlike :GCP pigments and of the
further special-effect piginent;s in the coating fi lm.
The regular structure of the LCP pigments and the
uniform molecular arrangement within these liquid-
crystalline units gives rise to considerable
interference phenomena with t:he incident light. As
these phenomena are overlayed with the customary color
properties of the further effE~ct-imparting component,
the perceived color changes not only depending on the
incident angle of the light but also, in addition, on
the viewing angle. When viewing a three-dimensional
article with such a coating, for example, this results
2189236
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in a perceived color which varies over the entire
article.
The coating composit~.on according to the
invention may be physicall~~ drying or may be
crosslinkable with the formation of covalent bonds. The
coating compositions which crosslink with the formation
of covalent bonds may be autocrosslinking or externally
crosslinking systems. The systE~ms may comprise one or
two components. They may be aqueous or solvent-based
coating compositions.
The aqueous coating compositions according to
the invention comprise water-dilutable binders. To
assure their dilutability in water, these binders
comprise nonionic and/or ionic groups which impart
hydrophilicity.
Examples of suitable nonionically stabilized
binders are those binders whose dilutability in water
is achieved by the incorporation of polyether segments
into the resin molecule. Examples of polyurethane
resins or polyurethane acrylat:e resins stabilized in
this way are described in EP-A-0 354 261, EP-A-
0 422 357 and EP-A-424 705.
The water-dilutable binders which carry ionic
groups may be binders carrying cationic or anionic
groups.
Examples of appropriate cationically stabilized
binders are described in DE--A-40 11 633. These are
completely or partially neutralized, cationic,
(meth)acrylic copolymer resins, polyester resins,
polyurethane resins and/or polyurethaneurea resins,
especially those having a number-average molar mass
(Mn) of from 500 to 500, 000, an OH number of from 0 to
450, an amine number of from 20 to 200 and a glass
transition temperature of from -50 to +150°C.
Pz::ferred binders arE~ those stabilized by
anionic groups. They comprise one or more film-forming
resins as are customary in aqueous coating
compositions, especially in aqueous basecoats. The
film-forming resins can, for e~;ample, have a polyester,
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(meth)acrylic copolymer or, preferably, a polyurethane
basis. They may be autocrosslinking, externally
crosslinking or physically drying. Examples of
appropriate water-dilutable (meth)acrylic copolymers
are described in EP-A-0 399 427 and EP-A-0 287 144.
Examples of appropriate water-dilutable
polyester resins are described :in DE-A-29 26 854, DE-A-
38 32 142 and EP-A-0 301 300.
It is also possible to employ mixtures of
binders. Particularly suitable binders are those in
which (meth)acrylic copolymer and polycondensation
resin are present bonded covale:ntly or in the form of
interpenetrating resin molecules. Examples of such a
combination of (meth)acrylic copolymer and polyester
resin which can be used are described in EP-A-
0 226 171.
Examples of the anionically stabilized
polyurethane resins which are particularly preferred
are described in great diversity in the literature.
These are aqueous polyurethane dispersions or
polyurethane solutions, or binders in which
(meth)acrylic copolymer and ~~olyurethane resin are
present bonded covalently ~~r in the form of
interpenetrating resin molecules. Suitable polyurethane
dispersions are stable, aqueous dispersions with a
solids content of from 20 to 50o by weight. The weight-
average molar mass (Mw) of the resins can vary within
wide limits, for example from 1000 to 500,000.
Further examples of Polyurethane dispersions
which can be used are those which can be prepared by
the chain extension of isocyanate-functional
prepolymers with polyamine and/or polyol. They are
described, for example, in EP-A-0 089 497, EP-A
0 228 003, DE-A-36 28 124 and El?-A-0 512 524.
Further examples are polyurethane dispersions
which can be prepared by the chain extension of
isocyanate-functional prepolymers with water, as set
out, for example, in DE-A-39 15 459 and DE-A-42 24 617.
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It is also possible to use polyurethane
dispersions which are prepared by the chain extension
of polyisocyanate-reactive polyurethane prepolymers
which contain active hydrogen with polyisocyanates, as
described, for example, in DE;-A-39 03 804 and DE-A-
40 O1 841. -
Further examples of anionically stabilized
polyurethane (PU) dispersions which can be used are
described in DE-A-42 28 510. These are aqueous
polyurethane dispersions which are obtainable by the
chain extension of
one or more polyurethane resins comprising at
least one CH-acidic group in the molecule, by
reaction in aqueous or nonaqueous medium with
- at least one compound which is able to react with
at least two CH-acidic groups, and
- if desired, transfer of a reaction product
obtained in a nonaqueous medium to the aqueous
phase.
Examples of anionically stabilized,
polyurethane-based binders in which (meth)acrylic
copolymer and polyurethane resin are present bonded
covalently or in the form of interpenetrating resin
molecules are described, for example, in EP-A-
0 353 797, EP-A-0 297 576, DE--A-41 22 265 and DE-A
41 22 266. These are polymer hybrids prepared by
emulsion polymerization of free-radically polymerizable
monomers in the presence of anionically stabilized
polyurethanes, which may also be functionalized with
unsaturated functions.
The coating compositions according to the
invention can comprise an aqueous binder, or else two
or more aqueous binders can be present in combination.
Preferably, the aaueous coating compositions according
to the invention comprise aqueous binc:~=rs based on
anionically stabilized polyurethanes. It may be
expedient for some, for example up to 50% by weight, of
the polyurethane binders to be replaced by resins based
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on a combination of (meth)acrylic copolymer and
polyester resin.
It is also possible for water-dilutable binders
based on cellulose to be present.
The novel solvent-based coating compositions
comprise binders which are dispersed or dissolved in
organic solvents. As film-forming binders it is
possible, for example, for polyester resin, alkyd
resin, polyurethane resins, poly(meth)acrylate resins
and/or resins based on cellulose esters, for example
cellulose acetobutyrate, to be present. Examples of
such binder systems which can be employed in the novel
coating composition are described in EP-A-0 289 997,
WO-,0.100 895, DE-A-37 15 254, DE-A-39 13 001, DE-A-41
15 948 and DE-A-42 18 106.
To prepare the coating compositions according
to the invention it is possible to use various
crosslinking agents, such as, f:or example, formaldehyde
condensation resins, such as phenol-formaldehyde
condensation resins and amine-formaldehyde condensation
resins, and also free or bloc'.ted polyisocyanates. The
crosslinking agents can be employed individually and as
a mixture. The mixing ratio of crosslinking agent to
binder resin is preferably from 10:90 to 40:60,
particularly preferably from 20:80 to 30:70, based in
each case on the weight of solids.
Amine resins which are suitable crosslinking
agents include, for example, alkylated condensation
products prepared by react:.ng aminotriazines and
amidotriazines with aldehydes. In accordance with known
technical processes, amines or compounds carrying amino
groups, such as melamine, gu~anamine, acetoguanamine,
benzoguanamine, dicyandiamide or urea, are subjected to
condensation in the presence of alcohols, such as
methanol, ethanol, propanol, butanol or hexanol, with
aldehydes, especially formaldehyde. Examples of such
resins and their preparation are described in Houben-
Weyl, Methoden der organischen Chemie, 1963, page 357.
These products are available commercially.
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It is possible to employ free or blocked
polyisocyanates as crosslinking agents. The
polyisocyanates are any desired organic diisocyanates
and/or polyisocyanates having free isocyanate groups
which are attached to aliphatic, cycloaliphatic,
araliphatic and/or, less preferably, to aromatic
structures and which are liquid at room temperature or
are liquefied by adding organic solvents or which, in
dissolved form at 23°C, general:Ly have a viscosity of
from 0.5 to 2000 mPas, preferably of more than 1 and
below 1000 mPas, particularly preferably below
200 mPas. Preferred diisocyanates are those containing
from about 3 to about 36 carbon atoms, in particular
from about 8 to 15 carbon atomso. Examples of suitable
diisocyanates are hexametlzylene diisocyanate,
tetramethylxylylene diisoc~~anate, isophorone
diisocyanate and dicyclohexylmethane diisocyanate.
Preference is given t:o the use of poly
isocyanates of relatively high isocyanate func
tionality, for example polyisocyanates prepared by di
and/or trimerization of the abovementioned diiso-
cyanates. Further examples are polyisocyanates which
contain biuret groups and are prepared by reacting the
abovementioned diisocyanates with water, or
polyisocyanates which contain urethane groups and are
prepared by reaction with polyols.
In the case of the blocked polyisocyanates, it
is possible to use any desired organic polyisocyanates
which are suitable for crosslin:king, for example those
mentioned above, in which the isocyanate groups have
been reacted with a compound such that the blocked
polyisocyanate formed is resistant to hydroxyl groups
and water at room temperature but reacts at elevated
temperatures, in general in the range from about 90 to
about 250°C.
The blocked polyisocyanates which can be
employed as crosslinking agents can be blocked with
customary, volatile, monovalent blocking agents as are
employed, for example, in paint chemistry. Examples
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thereof are various alcohols, oximes, phenols, amines,
beta-keto compounds, phthalimide, etc. Within a
molecule, the polyisocyanates can be blocked with
identical or different blocking agents. As crosslinking
agents it is also possible to use mixtures of
differently blocked polyisocyanates, and also
polyisocyanates which are blocked differently within
the molecule.
The coating compositions according to the
invention can additionally comprise polymer micro
particles which are known to the person skilled in the
art and are customary in the paints sector. Crosslinked
or noncrosslinked micropartic:Les can be employed.
Examples of such polymer microparticles are described
in EP-A-0 038 127 and EP-A-0 234 362.
The coating compositions can additionally
comprise technical paint additives, for example agents
which influence the rheology, such as highly disperse
silicic acid, inorganic phyllosilicates or polymeric
urea compounds. Examples of other effective thickeners
in the aqueous coating compositions according to the
invention are water-soluble ce::lulose ethers, such as
hydroxyethylcellulose, methylcellulose or
carboxymethylcellulose, and synthetic polymers having
ionic groups and/or groups with an associated action,
such as polyvinyl alcohol, poly(meth)acrylamide,
poly(meth)acrylic acid, polyvinylpyrrolidone, styrene-
maleic anhydride or ethylene- malefic anhydride
copolymers and their derivatives, or else
hydrophobically modified, ethoxylated polyurethanes or
polyacrylates. It is also possible to employ
antisettling agents, leveling agents, light stabilizers
(for example of the HALS type', of the benzotriazole
type, micro-titanium dioxide), antifoams, for example
silicone-:~ntaining compounds, wetting agents, and
adhesion-promoting substances. In order to accelerate
curing, it is possible if desired to employ catalysts.
Small amounts of solvents, for example
customary technical paint. solvents, may also be present
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in the aqueous coating compositions according to the
invention. These solvents can come from the preparation
of the binders or are added separately. Examples of
such solvents are mono- or polyhydric alcohols, for
example propanol, butanol and hexanol~ glycol ethers or
glycol esters, for example diethylene glycol dialkyl
ethers, dipropylene glycol dia7.ky1 ethers, each with
C1-C6-alkyl, ethoxypropanol and butylglycol; glycols,
for example ethylene glycol, propylene glycol and
oligomers thereof, N-methylpyrrolidone, and ketones
such as methyl ethyl ketone, acetone and cyclohexanone;
aromatic or aliphatic hydrocarbons, for example toluene
and xylene, or linear or branched, aliphatic, C6-C12
hydrocarbons.
The nonaqueous coating compositions according
to the invention contain customary organic paint
solvents, for example aromatic compounds, such as
toluene, xylenes, ethylbenzene, Solvesso 100~ (mixture
of aromatic hydrocarbons having ;3 boiling range of from
153 to 180°C); esters, for examp.Le ethyl acetate, butyl
acetate, amyl acetate; glycol ether esters, for example
ethoxypropyl acetate, ethyl glycol acetate,
methoxypropyl acetate; glycol ethers, for example
ethylene glycol dimethyl ether; ketones, for example
methyl ethyl ketone, diisobutyl ketone, cyclohexanone,
isophorone; and alcohols, for example propanol,
hexanol, isobutanol.
By way of the choice of :solvents it is possible
to influence the flow and viscosity of the coating
composition. By way of the boiling point of the solvent
mixture employed, it is possible to influence the
evaporation properties.
The coating composition according to the
invention comprises at least one LCP pigment, at least
one further plateletlike special--effect pigment and, if
desired, one or more inorganic and/or organic color-
imparting absorption pigments, if desired one or more
fillers, and also, if desired, one or more soluble
organic dyes. The absorption pigments and dyes are
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preferably dark in nature, since then the special color
effect aimed at in accordance with the invention is
reinforced to a particular degree. The absorption
pigments and dyes can, with regard to their color, be
adapted to the effective interference color of the LCP
pigment or can differ from it. l?referably, the coating
composition according to the invention comprises only
one LCP pigment and only one: further plateletlike
special-effect pigment. However, it is also possible to
employ mixtures of LCP pigments of different effective
interference colors and mixtures of further special-
effect pigments. Preferably, no additional dyes or
absorption pigments are present. By way of the mixing
of a plurality of LCP pigments with different effective
interference colors, there are no limits on the
establishment of all conceivable shades of color.
Examples of color-imparting absorption pigments
and/or fillers, which may be organic or inorganic in
nature, are titanium dioxide, iron oxide pigments,
carbon black, silicon dioxide, barium sulfate, talc,
azo pigments, phthalocyanine pigments, quinacridone
pigments or pyrrolopyrrole pigments.
In the case of nonaqueous coating compositions
according to the invention, the LCP pigments are
incorporated directly by stirring into the binder
present in organic phase. The further special-effect
pigments are incorporated into t:he coating composition,
for example, as follows: interference pigments are
incorporated similarly to the LCP pigments, whereas
metal flake pigments in the f~~rm, for example, of a
customary commercial paste are first of all suspended
in an appropriate solvent, for example in one of the
abovementioned solvents, before being added to the
binder present in organic phase.
The color-imparting ab~.orption p.4gments and/or
fillers are generally dispersed in a portion of the
binders, or dispersion can be carried out in a specific
paste resin. Dispersion takes place in customary
equipment which is known to the person skilled in the
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art. Subsequently, the finished color pigment
dispersion is made up with the :remainder of the binder
or of the paste resin.
In the case of aqueous coating compositions,
the pulverulent LCP pigments are first of all processed
with preferably water-dilutable organic solvents and
additives to form a paste. In preparing the paste, it
may be expedient to add the above-described water
dilutable binders and/or a paste resin. The further
special-effect pigments are introduced first of all, in
the form for example of a customary commercial paste,
water-dilutable organic solvent and additives are added
to them, and then this composition is mixed with the
aqueous resin solution, with shearing. Pulverulent
special-effect pigments are first of all processed with
solvent and additives to form a paste.
The color-imparting absorption pigments and/or
fillers are generally dispersed in a portion of the
water-dilutable binders. Dispersion can also,
preferably, take place in a specific water-dilutable
paste resin. One example of a paste resin which is
based on an anionically stabilized polyurethane resin
and which can be employed with preference in the
aqueous basecoat according to the invention can be
found in DE-A-40 00 889. Dispersion takes place in
customary equipment which is known to the person
skilled in the art. Subsequently, the finished color-
pigment dispersion is made up with the remainder of the
aqueous binder or of the aqueou:~ paste resin.
when processing the plateletlike LCP pigments
and the further special-effect pigments, care should be
taken that these pigments are not damaged mechanically
during the mixing operation.
If paste resins are present in the coating
composition, they add to binder plus any crosslinking
agent present.
Where the basecoats according to the invention
are aqueous basecoats formulated on the basis of
cationically stabilized binders, they contain acids as
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neutralizing agents. Examples are formic acid, acetic
acid and lactic acid.
Where the basecoats according to the invention
are aqueous basecoats formulated on the basis of
anionically stabilized binders, they contain bases as
neutralizing agents. Examples are ammonia or organic
amines, such as triethylam:W e, N-methylmorpholine, or
amino alcohois such as dimethylisopropanolamine,
dimethylethanolamine and 2-amino-2-methyl-1-propanol.
The coating compositions according to the
invention can be provided, :Eor example, in the form of
a mixer system consisting of mix coating materials.
The basecoats according to the invention can
also be prepared in the form of so-called modules, from
which the basecoats are ultimately prepared by mixing
directly before use. For example, the LCP pigments and
the further special-effect pigments can be part of an
effect module. In addition, for example, the binders
can be part of a binder module and, if desired, of a
color module and/or effect module prepared separately
therefrom. The crosslinking agents, for example, can be
part of a crosslinking module. Other constituents can
be present in the form of further separate modules. An
example of an aqueous modular system of this kind is
described in German Patent Application P 43 O1 991 from
the same applicant published July 28, 1994.
The coating composition according to the
invention, for example a basecoat according to the
invention, has a solids content which is, for example,
from 10 to 50% by weight, ~~referably from 15 to 30% by
weight. The ratio of pigment to binder in the coating
composition according to t:he invention is preferably
prom 0.03:1 to 1:1, particularly preferably from 0.06:1
to 0.5:1, based in each case on the weight of solids.
The ratio of LCP pigment plus further special-effect
pigment to binder in the coating composition according
to the invention is preferably from 0.03:1 to 0.5:1,
particularly preferably from 0.06:1 to 0.25:1. The
volume ratio of LCP pigment to further special-effect
A:
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pigment is preferably from 1:10 and 10:1. In the
abovementioned data relating to the weight ratios, the
term "binder" comprises the b:~nder as such plus any
crosslinking agent present plus any paste resin
present.
The coating compositions according to the
invention can be applied by cuss=omary methods. They are
preferably applied by spraying in a dry-film thickness
of, for example, from 15 to 40 ~.m. When used as
basecoats for the production of multicoat paint
systems, they are preferably applied by the wet-on-wet
technique; in other words, after a flash-off phase, for
example at from 20 to 80°C, th~~ basecoat films can be
overcoated with a customary clearcoat in a dry-film
thickness of preferably from 30 to 80 ~.m and the two
coats can be dried together or crosslinked at
temperatures of, for example, from 20 to 140°C. The
drying conditions of the topcoat layer (basecoat and
clearcoat) depend on the clearcoat system used. They
may, for example, be from 20 to 150°C. For refinish
purposes, temperatures of from a0 to 80°C, for example,
are preferred. For production-line finishing, preferred
temperatures are generally above 80°C, for example
above 100°C. Suitable clearcoats are, in principle, all
known clearcoats or coating compositions pigmented with
transparent pigments. In this case it is possible to
employ either solvent-containin~3 one-component or two-
component coating materials, wat=er-dilutable clearcoats
or powder clearcoats. It may be. expedient to choose a
clearcoat thickness which is in the region above 50 Vim,
for example by applying two cle:arcoat films comprising
identical or different liquid clearcoats, or a
corresponding powder clearcoat film. These multicoat
paint systems can be applied to various kinds of
substrate. The substrates are generally metallic or
plastics substrates, and are frequently precoated; that
is to say that plastics substrates, for example, can be
provided with a polymer primer, metallic substrates
genera-lly possess an electrophoretically applied primer
_. 2189236
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and, if desired, one or more f~.zrther coats in addition,
for example a filler coat. In general, these coats are
cured.
The substrates to be coated with the coating
composition according to the invention are preferably
dark substrates. The term substrate in this context is
to be understood not only as a substrate which is
provided on its surface with a dark coat of paint but
also a substrate, for example a plastics substrate,
with inherently dark pigmentation. Examples of dark
coats of paint are primers, for example primers applied
electrophoretically or by spray painting, polymer
primers, filler coats or anti-stonechip coats, or else
solid-color basecoats or topcoats. The dark substrates
or dark coats of paint are pigmented with dark
absorption pigments, special-effect pigments being
expressly excluded. Examples of dark substrates are
those which are dark blue, dark red, dark green or,
preferably, dark gray, with black being particularly
preferred. In such cases, the effect aimed at with the
coating composition according to the invention stands
out with particular distinction. The coating compo-
sitions according to the invention can, of course, also
be applied to substrates with a relatively light color,
but then the special color effect aimed at in
accordance with the invention is effective only to a
lesser extent.
The coating composition according to the
invention permits the production of bright-colored
multicoat paint systems with a surprisingly strongly
pronounced color flop, which is overlaid by the
customary color properties of the further effect-
imparting components which are present in the coating
composition in addition to the LCP pigments. The
perceived color of the 'rinished substrates changes in
dependence on the incident angle of the light and, in
addition, on the viewing angle, but is independent of
external temperature effects.
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The multicoat paint sysr_ems obtained using the
coating compositions according to the invention meet
the requirements which are nowadays customary in the
finishing of automobiles. The: coating compositions
according to the invention are therefore suitable for
the OEM finishing and refinishing of vehicles,
especially as a basecoat, but c:an also be employed in
other sectors, for example in the painting of plastics,
especially the painting of automotive components.
Example l,i
Polyiaanos~~oYanes with metha ~rloxl-functional side
chains
A solution of 233 g of 4-(prop-2-en-1-oxy)ben
zoic acid cholesterol ester (obtainable in accordance
with DE-A-3 110 048), 178 g of 4-trimethylsiloxyphenyl
4-(prop-2-en-1-oxy)benzoate (obtainable in accordance
with EP-A-0 358 208, page 9, Section C) and 56.9 g of
tetramethylcyclotetrasiloxane in 400 ml of toluene was
boiled under reflux in the presence of 24 mg of
dicyclopentadiene platinum dichloride for 1 hour and,
following the addition of a solution of 1.2 g of NaOH
in 50 ml of ethanol, for a further 7 hours, in order to
cleave the silyl ether. The reaction mixture was
concentrated to 1/3 of its volume in a rotary
evaporator, 7.5 g of p-toluenesulfonic acid and 154 g
of methacrylic anhydride were added, and the mixture
was heated at 100°C for 1 hour. After removal of the
volatile constituents by distillation, the residue was
reprecipitated twice from methy7.ene chloride/ethanol.
The product had the following physical and
thermodynamic data:
Glass transition point: 14°C, cJ_earing point: 141°C.
Examrle 2:
pre~arat~on of a solymerizable monomer
4-ethylphenyl methacryloxybenzoate
A solution of 16.9 g of 4-ethylphenyl 4-tri-
methylsilyloxybenzoate (prepared according to the
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instructions in EP-A-0 358 208, page 9, section C) in
15 ml of toluene and 10 ml of ethanol was boiled under
reflux for one hour and then freed from volatile
constituents by heating at 100°C for 60 minutes. The
13.3 g of 4-ethylphenyl 4-hydroxybenzoate which
remained were dissolved, together with 30 g of
methacrylic anhydride and 1.2 g of toluenesulfonic
acid, in 15 ml of toluene and the solution was heated
at 100°C for 1 hour. After c~~oling, the product was
precipitated with hexane and recrystallized from
ethanol.
Exaa~gle 3:
prA~arat-; r,~ of a red liquid-crystal mixture
6 g of the polyorgano:~iloxane prepared as in
Example 1 were dissolved in 50 ml of toluene . 1 . 5 g of
4-ethylphenyl methacryloxyben2;oate (prepared as in
Example 2) and 7.5 mg of aluminum cupferron (obtainable
under the name Q 1301 from Wako Chemicals GmbH, Neuss)
were added to this solution. The toluene was then
removed at 70°C under vacuum in a rotary evaporator.
A viscous LC mass is formed which has the
following physical and thermodynamic data:
Glass transition point: -2°C, clearing point: 124°C.
E~sle 4:
prps,arat-~ ~n of a blue licruid-cr5rstal mixture
6 g of the polyorganosiloxane were prepared as
described in Example 1. This was dissolved in 50 ml of
toluene. 2.6 g of methacrylic acid cholesterol ester
(prepared as in De Visser et al., J. Polym. Sci., A
1(9), 1893 (1971)) and 9 mg of aluminum cupferron
(obtainable under the name Q 1301 from Wako Chemicals
GmbH, Neuss) were added to this solution. The toluene
was then removed at 70°C under vacuum in the rotary
evaporator.
A viscous LC mass was formed which has the
following physical and thermod~rnamic data:
Glass transition point: 4°C, clearing point: 132°C.
y:~. ~ 2189236
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le 5:
~) Preparation of a green licruid-crvatal mixture
2.8 g of the red color mixture (prepared as
described in Example 3), 1.2 g of the blue color
mixture (prepared as described in Example 4) and 0.11 g
of 2-methyl-1-[4-(methylt.hio)phenyl]-2-morpholino-1
propanone (obtainable under the name Irgacure 907 from
Ciba Marienberg GmbH, Bensheim) were homogeneously
mixed with stirring.
A viscous LC mass with a greenish gleam is
obtained which has the following thermodynamic data:
Glass transition point: 2°C, clearing point: 128°C.
4 g of the LC mass prepared as described above
under A) were heated to 70"C and mixed homogeneously,
with stirring, with 0.11 g~ of 2-methyl-1-[4-(methyl-
thio)phenyl]-2-morpholino-1-propanone (obtainable under
the name Irgacure'1'"' 907 from Ciba Marienberg GmbH,
Bensheim). The liquid-cryst~~lline material was applied
at 80°C using a doctor blade to a polyethylene
terephthalate film (Hoechst AG, Films Division,
Wiesbaden) in coat thicknesses of 7 micrometers, the
film being advanced under the fixed blade at a rate of
about 2 meters per minute. The liquid-crystalline
molecules are simultaneously oriented owing to the
shear gradient between blade and film. This coat was
subsequently irradiated for 5 seconds with a mercury
discharge lamp (80 watts,/cm) and thus was three-
dimensionally crosslinked. 'the coating film produced on
the PET film was tack-free and brittle in the hot and
the cold state. T_t had a reflection wavelength of 530
nanometers (angle of incidence and viewing angle 45°).
The mechanical separation of the liquid-crystalline
material obtained in this way from the substrate was
achieved by guiding the film over a deflection roller
with a diameter of 10 cm and, in this way, peeling the
crosslinked material from the substrate. The grinding
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of the crosslinked, substrate-free material was carried
out in a universal mill. Grinding of the crosslinked
polyorganosiloxanes, which werE~ obtained predominantly
in the form of leaflets (size: a few millimeters to
centimeters), for five minutes gave a pulverulent
fraction. The ground material 'was then subjected to a
sieving process in order to narrow the particle-size
distribution.
E~~le 6: ,
Preparation of a binder module
The following constituents are mixed together
thoroughly with stirring:
26.2 parts of a PU dispersion according to DE-A-
4 224 617, Preparation Example 3,
8.8 parts of hexamethoxymei~hylmelamine,
5 parts parts of n-butanol,
3.5 parts of a commercial i~hickener based on poly
acrylic acid,
0.25 part of N,N-dimethylethanolamine, and
56.25 part of deionized water.
Ex~sle 7:
Preparation of an effect module
The following constitue=nts are present in the
effect module:
parts parts of the PU dispersion from Example
6,
9 parts of the LCP pigme:at according to Example
30 5 B (particle-size fraction: 1-100 ~tm) ,
5 parts of a commercially available aluminum
paste which contains 60% of aluminum and
is suitable for an aqueous basecoat,
25 parts of butylglycol,
35 1.8 par:.s of the thickener from Example 6, and
0.2 part of N,N-dimethylethanolamine.
The LCP pigments and the aluminum paste are
each pasted up with solvents and additives . The binder
is then
added
to the
mixture
of the
two
pastes
and
the
~1892~~
- 23 -
whole is mixed thoroughly. This mixture is then diluted
with 22 parts of deionized water.
E~nn 1 a 8
P~enaration of an aaueous effect basecoat
80 parts of the binder module from Example 6
and 20 parts of the effect module from Example 7 were
mixed uniformly in order to formulate storage-stable
aqueous effect basecoats.
Example 9:
Preparation of a multicoat paint system
The aqueous effect basecoat from Example 8 is
applied by spraying, in a dry-film thickness of 20
micrometers, to customary, phosphatized metal bodywork
panels which have been precoate:d by cathodic deposition
and with a black filler. Following the application, the
coating is flashed off at room temperature for 10
minutes and then predried at 80°C for 10 minutes. A
commercial two-component polyurethane clearcoat based
on acrylate resin is then applied in a dry-film
thickness of 50 micrometers, and the resulting paint
system is dried at 100°C (panel temperature) for 30
minutes.
A multicoat paint system is obtained which has
a bright/dark flop and a strongly pronounced color flop
whose color changes from green to blue.
