Note: Descriptions are shown in the official language in which they were submitted.
213 l~i8r~
HOECHST AKTIENGESELLS~HAFT HO~ 89/F 174 Dr. ZR/sch
Description
Coating material, process for the preparation of coatings
and 8ubstrate8 coated therewit]h
The importance of metallic paints in the automobile
industry has increased greatly in xecent years. Whereas
earlier a large fraction of coachworks was treated with
one-layer metallic paints, nowadays automobile6 are
painted virtually exclusivPly by the multi(2)-layer
metallic process, the so-called "wet-on-wet process". In
this process a base paint which dries essentially by
physical means and which is pigmented with aluminium, to
which other coloring pigments may first be added, and
then, after brief exposure to air, a clear lacquer is
applied as a finish. Thiæ base paint consists mainly of
organic solvent, a binder which dries by physical means,
such as a cellulose ester, in particular cellulose
acetobutyrate ~CAB), a film-forming resin, such as an
oil-free polyester, a crosslinking agent, ~uch as a
melamine resin, and pigments (cf., inter alia, German
Offenlegungsschrift 1,949,372). A well as a more rapid
physical drying of the paint film, the cellulose esterl
inter alia, also produces an improvement in the metallic
effect. Considerable amoun~s of the cellulose e~ter,
which is soluble in base paint solvents, are, howe~ver,
required for this purpose.
Apart from aluminum and Iriodin, the pi~ments used are
both inorganic pigments, such as titanium dioxide and
iron oxides, and organic pigments, such as phthalocyan-
ines, quinacridones and/or halogenated thioindigo pig-
ments. The solids content of the base paints, which is in
most cases around 15 %, is fairly low. The remainder is
volatile ~olvent, composed for the most part of esters,
such as ethylene glycol monoethyl ether acetate, butyl
acetate and ethyl acetate, and aromatic compounds, such
as toluene or xylene.
2 (3 ~ 7
- 2 -
The second layer, applied after a time of exposure of air
of only a few minutes, is a clear lacquer which can be an
air-drying or artifically dried lacquer, such as r for
instance, in the case of coachwork repair, or a baking
lacquer, such as is used in conveyor belt automotive
painting. In the latter case both coat~ of paint are
cured together under the customary baking conditions (10
to 30 minutes at 120 to 150C). The hi~h content of
solvent in the base paint con6titutes considerable
pollution for the environment and, in addition, also
results in corresponding expense, i.e. the additional
charge caused by the use of solvents and their removal
80 as to protect the en~ironment.
There has, therefore, been no lack of attempts to in-
crease ths solids content or to reduce the proportion of
volatile solvents. In the course of this it has been
found that paints having a solids content increased in
the customary manner have too high a vi6cosity, ~an only
be applied with difficulty and result in paint layers
having unsatisfactory technical properties in use. ~his
route to the preparation o~ paints, in particular base
paints, which are le~s harmful to the environment and, as
a result of the higher solids content, are more product-
ive and hence economical, cannot therefore be taken.
The invention therefore relates to a coating material for
the preparation of coatings, in particular ~ulti-layer
paint coatings composed of at least one ba~e layer and,
if appropriate, at least one transparent top coat, the
coating material containing film-forming resin~ (A),
cellulose esters ~B), solvellts (C), preferably metallic
pi~ments (D~ and, if appropriate, crosslinking sgent~ (E)
and also, if appropriate, further paint addi~ives (F),
wherein the cellulose ester (B) has an acetyl content of
2.0 to 30 ~ by weight, a butyryl content of 17 to 53 ~ by
weight and an average molecular weight k~ of at least
25,000, this cellulose ester (B) having been introduced
into the coating material in the form of a pasty,
8 ~ ~ 7
-- 3 --
thixotropic premix.
The invention also relates ~o a process for the prepar-
ation of a multi-layer coa~inS~ using this coating mater-
ial and to the substrates thus l~oated.
It was surprising and not to be foreseen that, in the
coating material according to the invention, the amount
of cellulose ester can be reduced from the approx 40 ~
hitherto customary to about one half. This makes p~ssible
an increase in the ~olids content from approx. 15 % to
approx. 30 %, preferably 26 ~, and hence a considerable
saving of solvent. It was al~o surprising that a paint of
such a composition has a low viscosity, in spite of its
high solids content; it can therefore be applied without
difficulties and, in ~he case of a metallic paint,
produces a fault~free metal effect. As a result of the
special rheological behavior and the rapid drying, there
is also no sagging on vertical suraces and no blushing~
In the case of a mul~i~layer paint coat it is also
possible to overpaint without difficulties even after a
few minutes dryins~ at room temperature, i.e. no in~ipient
dissolution of the incipiently dried base paint takes
place as a result of the finish applied later. In gener-
al, ~he tLme of exposure to air after which the layer of
base paint can be o~erpainted is 2 to 10 minutes, prefer-
ably 3 to 6 minutes, at 15 to 30DC, preferably 20 to
25C.
The cellulose ester (B) is preferably cellulose aceto-
butyrate; in addition cellulose propionate, cellulo~e
butyrate and cellulose acetopropionate and al~o mixtures
of the various cellulose esters are also 6uitable. The
cellulose acetobutyrate which is preferably employed has
an acetyl content of 2 to 5 % by weight, particularly 3
to 5 % by weis~ht, and a butyryl content of, preferably,
47 to 53 ~ by weight, especially 50 to 52 ~ by weight.
The hydroxyl c:ontent is usually 0 5 ~o 1.8 ~ by weight,
preferably 0.6 to 1.0 ~ by weight. The average molecular
weight Mn preferably has values between 30,000 and 60,000,
especially between 54,000 and 60,000.
The amount of cellulose ester (B) in the coatin~ material
is generally 0.5 to 6, pxaferably 1 to 3, % by weight,
relative to the sum of (A) and (B) and also, if appropri-
ate, (~) (solids content). ~rhe cellulose e~ter (B)
according to the invention can also, if appropriate, be
employed as a mixture with conventional cellulose e~ter~,
for example those described in German Offenlegungs6chrift
1,949,372 which was mentioned initially.
In accordance with the invention the cellulose ester (B)
is added to the coating material in the form of a pasty
(viscous), thixotropic premix (master bakch) which
preferably has a gelatinous consistency. In addition to
the cellulose ester, this premix contains a diluen which
essentially swells the cellulose ester only incipiently.
The boiling point (under normal pressure) of this diluent
is generally at least 70~C, preferably between 70 and
250C. Examples of these diluents are aromatic or ali-
phatic hydrocarbons, such as ben2ene, toluene, thevarious xylenes, higher-boiling mineral oil fractions,
such as ~)Solvesso, higher alcohols having at least
4 carbon atoms, preferably 4 to 10 carbon atoms, such as
n-butanol, isobutanol, pentanols, hexanols etc. or
corresponding mixtures. ~he amount of cellulose ster (B)
in this premix i8 usually l to 10 % by weight, preferably
2 to 6 % by weight, relative to this premix.
In a further embodiment this premix also contains, în
addition, polymers or prepol~mers, especially tho~e which
are in any case used in the coating material according tD
the invention. These polymers/prepolymers can be at least
partly soluble in the diluent used for the premi~.
E~amples of pol~mers/prepolymers of this type are, intex
alia, customary ~mino resins, such as polycondensates
formed from melamine, benzoguanamine and/or ur~a with
formaldehyde which are etherified, for example with
monoalcohols, e~amples of suitable monoalcohols being
(3 ~ ~ 7
-- 5 --
methanol, ethanol, propanol or butanol. Methylated,
propylated or butylated methylolmelamine may be men~ioned
here. Further examples are polyester resins, preferably
free from oil, and acrylate re~ins.
This premix is prepared by combining the cellulose
ester (B) with the other constituent(s) of the mixture
for 30 to 180 minutes, preferably 100 to 140 minllte~, at
an elevated temperature, the :Level of the temperature
under normal conditions being at least 70C, preferably
between 70 and 250C.
Suitable film-foxmin~ resins (A), the average molecular
weights M~ ~determined by gel permeation chromatography
aga.inst a polystyrene standard) of which are usually
within the range from about 500 to 50,000, preferably
about 1,000 to 20,000, are the pol~mers known for this
purpose which contain active groups for crosslinking,
above all hydroxyl and/or amino groups. Ex2mples of these
are synthetic resins (polyols) containing OH groups, such
as polyether-polyols, polyacetal-polyols, polyester-amide
polyols, epoxy resin polyols or reaction products thereof
with CO2, phenolic resin polyols, polyurea-polyols,
polyurethane-polyGls, partly saponified homopolymers and
copolymers of vinyl esters, partly acetalized polyvinyl
alcohols, polyester-polyols or acrylate resin polyols.
Phenolic, urea or melamine resins containing OH are also
suitable in this respect. Polyols of this type, which can
also be employed as a mixture, are described, for
example, in German Offenlegungsschriften 2,314,513 and
3,124,784 and in European Published Applications 123,880
and 189,728. Other resins (A~ for the base paint which
are suitable according to the invention are also dis-
closed, for example~ in German Offenlegun~sschriften
1,949,372, ~,818,093, 2,818,100 and 3,720,984 and
European Published Applications 5,428 and 80,340.
Epoxy resin polyols, polyester-polyols, polyuxethane-
polyols, polyether-polyols and acrylate resin polyols are
preferred.
-- 6 --
In one embodiment of the invention these film-forming
resins can be self-curing because, for example, some of
the hydroxyl groups have been reacted w:ith partly masked
isocyanates.
The amount of component (A) in the coating material
according to the invention is generally between
and 90 % by weight, preferably betwsen 5 and 30 % by
weight, relative to the coating material.
Sui.table solvents (C) are, above all, (cyclo)aliphatic
and/or aromatic hydrocarbons, ~uch as hexane~ heptane,
cyclohexane, benzene, toluene, the various xylenes and
aromatic solvents within a boiling range of approx. 150
to 180C (higher-boiling mineral oil fraction~, such as
~R~Solvesso); also halogenated hydrocarbons, ethers and
glycol ethers, such as diethyl ether, 1,2-dLmetho~y-
ethane, ethylene glycol dibutyl e~her, tetrahydrofuran or
dioxane; ketones, such as, for example, acetone, methyl
ethyl ketone, methyl isobutyl ketone, cyclohexanone and
the like; esters, such as ethyl acetate, butyl acetate/
ethylene glycol monoethyl ether acetate and methoxypropyl
acetate; N-methylpyrrolidone; monohydric or polyhydric
alcohols, such as butanol, ethylene glycol monoethyl-
(butyl~ ether etc~ The amount of this solvent should be
such that the coating material can be handled in an
optimum manner depending on the method of application
chosen and that the paint films applied level out to an
adequate extent. In general, amounts of 70 to 85, prefer-
ably 70 to 80, % by weight, relative to the coating
material, are sufficient for this.
The coating materials according to the invention contain
- if appropr:iate as well as customary non-metallic
(colored) pigments (in this regard see under (F) below) -
metallic pi~ments (D), preferably in powder form, on
their own or as a mi~ture, such as aluminum bronzes or
copper bron~es, preferably aluminum powder. The amount
thereof is generally 0.5 to 60, preferably 0.5 to 40, ~
:
2 ~
-- 7 --
by weight, relative to (A).
These metallic pigments are advantageously incorporated
into the coating material in the form of pigment pastes.
In addition to the metallic pigment and sol~ent, this
pigment paste contains a so-c:alled grinding resin or
paste resin, such as polyesters or acrylic resin~.
The grinding resin can often be equivalent to the
film-forming resin (A).
Suitable crosslinking agents (E) - in the event that (A)
is not self-curing - are the curing agents customary for
extraneously crosslinking two-component lac~uers, for
example amino resins, such as melamine/formaldehyde,
benzoguanamine/formaldehyde~ ureatformaldehyde or thio-
urea/formaldehyde condensates, in particular melamine/
formaldehyde condensates which have been etherified with
alkanols; also phenolic resins, (masked) polyisocyanates,
~-hydroxyesters of polycarboxylic acids, poly~ hydroxy-
urethanes), polyepoxide compounds, reaction products of
dialkylmalona~es with aldehydes and ketones which react
with the elimination of water to give unsaturated dicar-
boxylic acid esters (Knoevenagel æynthesis), transesteri-
fication or transamidation curing agents and also Michael
addition products, for example those described in German
Offenlegungsschriften 3,315,469, 3,417,441 and 3,436,345.
The crosslinking agents (E) are usually employed in
amounts of 5 to 90 ~ by weight, preferably 10 to 70 % by
weight, relative to the film-forming resin (~.
Exampl~s of customary paint additives (F) which can, if
appropriate, be present in the coating material according
to the invention are (colored) pigments and fillers and
also paint auxiliaries, for example anti-settling agents,
foaming agents and/or wetting agents, levelling agents,
reactive thin:ners, plasticiæers, stabilizers, catalysts,
rheology auxiliaries ~such as microgels or polyurea
derivatives) and the like. At least some of these
20~53~87
-- 8
additives can be added to the coating material aæ late as
immediately before processing.
Addition to the individual components or to the whole
mixture is also possible. The selection and the
S proportionation of these substcmces are known to ~hose
skilled in the art.
Iron oxides (iron red or iron black), lead vxides, lead
silicates, titanium dioxide, z.inc oxide, ~inc sul~ide,
chrome-titanium yellow, ultramarine blue, carbon black,
phthalocyanine complexes, quinacridone~, halogenated
thioindigo pigments, ~lavanthrone yellow, indanthrone
blue, perylene red etc. and also effect pigments, such as
Iriodin, should be mentioned as examples of (colored)
pigments, which can have an inorganic or organic nature.
These pigments are usually employed in amounts of 0.1
to 20, preferably 0.5 to 5, % by weight, relative to
component (A).
The total solids content (including the metallic pig-
ments (D) and the paint additives (F)~ in the coating
materials according to the invention i8 generally 10 to
30 % by weight, preferably 15 to 30 % by weight and
particularly 20 to 30 ~ by weight (120C/1 hour). The
solids content varies with the application and in the
case of metallic paints ( content of component (D~)
is, as a rule, somewhat lower than in the case of so-
called self-colored paints (which do not contain (D)).
The coating materials according to tha invention are
prepared by the usual methods of paint formulation.
The application of the coating materials according to the
invention for the preparation of the base layer is
effected in a known mannex, preferably by spraying using
the compressed air process or by means of airless or
electrostatic spraying processes; examples of othex
suitable processes are knife coating, dipping and
rolling. Iron and steel are the preferred substrates in
2 ~ 7
_ 9 _
this case, but other metals, for e~xample aluminum,
copper, magnesium or alloys, are al~o suitable. Fur~her-
more, it is also possible in principle to u~e nonmetallic
substrates, such as ceramic materials, plastics and the
like, provided that they withstand the curing tempera-
tures.
~emperature~ from eo to 180C, preferably 120 to 150C,
are generally used for curing the applied coat~ of paint,
in the case of l-K system~. The curing ~ime i8 u~ually 10
to 40 minutes, preferably 15 to 30 minutes. In the case
of 2-K systems the temperature~i are, as a rule, between
20 and 180C, preferably 20 and 80C, and the curing
times are usually between 30 minutPs and 24 hour~.
Curing is preferably effected only after coating with the
finish, it being possible to employ predrying or, pre~er-
ably, the wet-on-wet proces 8 .
The layer thicknesses of the dried films are pre~erably
4 to 80, preferably lO to 40, ~m for the coatings ob-
tained from the coating materials according to the
invention; if a finish i~ employed, the layer thicknesses
of the dried film are in this case generally lO to 100,
preferably 20 to 60, ~m.
The composition of the clear finish i8 not critical, on
the contrary all known non-pigmented or only transparent-
ly pigmented coating agents are in principle, suitablefor this purpose. These can be conventional solvent-con-
taining clear lacquers, water-dilutable clear lacquers or
powder lacquers. It is preferable to use "high-solids" as
clear finishes. In this connection reference ~hould be
made, for example, to German Offer,legungsschriften
1,949,372 and 2,818,100 and to ~uropean Published
Application 38,127 ~nd US Patent 4,5~1,533.
The examples which follow illustrate ~he invention.
lo p~ js3 3~ ~
,
~ompari~on E~ample 1
1 a~ Preparation of a commercially available metallic
base paint corresponding to ~he s~ate o~ the art
60 parts of a 70 % strength solution in ~Solvesso 100 of
a commercially available oil-free polye~ter resin (acid
number: 10, dynamic viscoæity (source material) 5,500-
7,000 mPas/20C, commexcial product: (R)Alftalat ~N 9S1~,
1 part of highly disperse silica, 222.2 parts of an 18 %
strength solution of cellulose acetc)butyrate in butyl
acetate having an acetyl content of 13 %, a butyryl
content of 37 % and an average molecular weight of 20,000
(commercial product CAB 381-0.1), 32.7 parts of melamine
resin partially etherified with isobutanol (approx. 55 %
strength in 44:1 isobutanol/xylene, melamine:~ormaldehyde
molar ratio 1:4, etherified with 3 mol of isobutanol,
dyn~mic viscosity 500 mPas/20C, commercial product
(~)Maprenal MF 590), 14 paxts of aluminum paste (metal
content 65 %, solvent: white spirit or solvent naphtha),
6 parts of Solvesso 150, 5 parts of methoxypropyl
acetate, 33 parts of a 5 ~ strength dispersion of a
comme.rcially available wax (HO~CHST WACHS 371 FP~ in
30 parts of xylene and 64 parts of butyl acetate,
10.5 parts of xylene and 10.5 parts of butyl acetate were
processed to give a paint. By adding ~ylene and butyl
acetate mixed in a 1:1 ratio the base paint was diluted
to a spraying consistency (DIN cup with 4 mm orifice as
specified i~ DIN 53,211, 23C) of 15 ~econds. This
resulted in a solids content of 18 % (2 g, 1 hol~x,
120C). ~he base paint was sprayed onto a commercially
available automobile filler (subetrate: steel sheet) to
a dry film thickness of 18 ~m. After exposure to air for
5 minutes the following clear lacquer was sprayed on.
1 b) Clear lac:quer for a two-coat metallic paint coating
28.33 parts of co~mercially available, extraneously
crosslinking acrylic resin (65 % strength ~olution in 3~1
xylene/butanol, ~ynamic viscosity ~50 % strength in
;,
.
. ' , .
xylene) 1140 mPas/20C, acid number 13, relative to solid
resin, commercial product: ~R)Synthacryl SC 303), 24.54
parts of commercially available, ex~raneously crosslink-
ing acrylic resin (75 ~ strength ~olution in
Solvesso 100, dynamic viscosity 2g5 mPas/20C, acid
number: lO, relative to solid resin, commercial product:
Synthacryl SC 370), 28.7 parts of mel~mine re~in
partially etherified with isobutanol (approx. 55 ~
strength in 44:1 isobutanol/xylene, melami.ne:formald2hyde
molar ratio 1:4, etherified with 3 mol of i~obutanol,
dynamic viscosity 500 mPas/20"C, commercial product:
Maprenal NF 650), O.5 part of commercially available W
absorber ~R~Tinuvin 292 as curing component, 0.5 part of
commercially available HAL stabilizer ~R~Tinuvin 900,
5.12 parts of i60butanol, 3.12 parts of an aromatic
hydrocarbon mixture of boiling range 180-200DC, and
9.19 parts of an aliphatic hydrocarbon mixture of boiling
range 145-200C wexe mixed. The spraying viscosity (DIN
cup with 4 mm orifice as specified in DIN 53,211, 23C)
of this clear lacquer was then adjusted to 26 seconds by
means o~ a hydrocarbon mixture of boiling range 150-
180C, and the lacquer was applied in a dry film thick-
ness of 40 ~m. Both layers were baked in one operation in
25 minutes at 140C.
Comp~ri~on Esample 2
Comparison Example la) was repeated, with the differ~nce
that only 111.1 parts of an 18 % strength solution of
cellulose acetobutyrate in butyl acetate were employed
instead of 222.2 parts of the same cellulo~e acetobuty-
rate solution. This gave a solid~ content of 27 % (2 g,
1 hour, 120C). Further processing was carried out aR in
Comparison Example la), a clear 1 cquer of the ~ame
composition ~s in Comparison Example lb) being spr~yed on
an~ both layers being baked in an operation la~ting
25 minutes at 140C.
- 12 -
Example 3
Comparison Example 2 was repeated with the differences
that 80 parts of the commercially available, oil-free
polyester Alftalat ~N 951 in ';olvesso 100 were employed
instead of 60 parts of the 70 ~ strength solution of the
same resin, and that 46 parts of a thixotropic premix
were employed instead of 32 . 7 parts of the 55 % strength
commercially a~ailable butylated melamine resin
Maprenal MF 590. This premix was prepared by introducing
a cellulose acetobutyrate having a 4 % acetyl content, a
51 % butyryl content/ a hydro~yl content of 0.8 and an
average molecular weight of 57,000 (commercial product
CAB 500-5) in solid form into the abovementioned melamine
resin solution (Maprenal MF 590) at a temperature of 80-
100C and maintaining this temperature level for approx.120 minutes. A solids content of 26 % (2 g, 1 hour,
120C) was obtained. Further processing was carried out
as in Comparison Example 2.
Example ~
Comparison Example 2 was repeated with the differences
that only 54.6 parts of the commercially available, oil-
free polyester Alftalat AN 951 were employed instead of
60 parts of the 70 ~ strength solution of the same resin
in Sol~esso 100 and that 27 parts of a thixotropic premix
were additionally employed. This premix was prepared by
introducing the cellulose acetobutyrate according to
Example 3 in solid form into the oil-f~ee polyester resin
Alftalat AN 951 at a temperature of 120C and maintaining
this temperature level for approx. 120 minutes. A8 a
further difference from Comparison Example 2, 45 parts of
a 55 ~ strength commercially available butylated melamine
resin (commercial product: Maprenal MF 590) were now
employed instea~ of 32.7 parts of this resin. This
resulted in a solids content of 26 % (2 g, 1 hour,
120C). Further processing was carried out as in
Comparison Example 2.
2 0 1 ~ :rj
- 13 -
~xample 5
Comparison Example 2 was repeated with the diffQrences
that 51 parts of a 65 % strength solution in 3:1 xylene/
butanol of the commercially available t extraneously
crosslinking acrylic resin ~dynamic viscosity (50 %
strength solution in xylene) 1140 mPas/20C, acid
number 13, relative to solid resin, trade name:
Synthacryl SC 303) were employed inst~ad of 60 parts of
the 70 % solution in Sol~esso 100 of the commercially
available, oil-free polyester resin Alftalat ~N 951, and
that 36.6 parts of a thixotropic pxemix wera additionally
employed. This premix was prepared by introdu~ing the
cellulose acetobutyrate according to Example 3 into the
abovPmentioned acrylic resin at a temperature of 120C.
As a further difference from Comparison Example 2,
45 parts of the 55 % strength butylated melamine resin
Maprenal MF 590 were employed instead of 3~.7 parts of
the same resin. A solids content of 23 % (2 g, 2 hours,
120C) was obtained. Further processing was carried out
as in Comparison Example 2.
~ample 6
Example 3 was repeated with the differences that 45 paxts
of the butylated melamine resin Maprenal MF 590 and
26 parts of a premix made by introducing the cellulose
acetobutyrate according to Example 3 into boiling toluene
in the course of approx. 120 minutes, were employed
instead of 46 parts of the premix described in Example 3.
A solids content of ~6 % (2 g, 1 hour, 120C~ was
obtained. Further processing was carried out as in
Comparison Example 2.
The properties and the behavior of the paints and paint
coats obtained in Comparison Example 1 and 2 and in
Examples 3 to 6 (invention~ are shown in the table below.
Assessment of the baked paint coatings was carried out
visually.
5 ~ 7
-- 14 --
~n
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a PC
~D I O
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I '1 1
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o o ~ o ~ ~ ~ ~ ~ ~
O ~ ~~ o u a~ ~ ~ O
e ~ w ~
IJ w ~ rl h h ~ .-1
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O ~C I 1` IIJ U ~ O ~ 1 0--I o o ~ ~C
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