Note: Descriptions are shown in the official language in which they were submitted.
~ 1329303
27293-45
sAsF Lacke + Farben AG
Process for the production of a~ multi-layered coatinq
S aqueou coating compositions water dilutable polyacry-
late resins and proces~ for the preparation of water-
dilutable polyacrylate resins
The invention relates to a process for the
production of a multi-layered protective and/or decora-
tive coating on a substrate qurface, in which
(1) a suLtable pigmented ba~e coating composition iq
applied to the ~ubstrate surface,
(2) a polymer film is formed from the oompo~ition
applied in ~tage (1),
(3) a transparent aqueous top coating composition
containing a water-dilutable polyacrylate re~in as
the binder and an aminopla~t re~in as the crosslink-
ing agent is applisd to the base layer thus
obtained, and
(4) the base layer is then stoved together with the top
layer.
The invention also relates to aqueous coating
composition~, water-dilutable polyacrylate resins and a
process for the preparation of water-dilutable polyacry-
late resins.
~x~esses for productlon of a multi-layered protective and/or
decorative o~ting on a substrate surface are hx~n. They are u ~ in y~-
ticular for the preparation of automobile metallic effect
lacquerings ~compare, for example, US-A-3,639,147, DE-A-
33 33 072 and EP-A-38,127).
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` 1329303
- 2 -
For economic and ecological reason~, it is
desirable to employ aqueous top coating compositions in
stage t3) of the ~o-called ~base coat clear coat" process
described above.
It must be possible to apply the top coating
compositions by spraying with the aid of automatic
lacgueriny lineY. For this, they must have such a high
solids content at the spraying viscosity that lacquer
films of adequate layer thickne~s are obtained with one
to two spray passes (cros3 passes), and they must produce
~toved lacquer films which exhibit a good appearance
~good flow, high glo~s, good top lacquer status...).
The aqueous top coating composition disclosed in
Example 2 of EP-A-38,127 doe~ not meet all the abovemen-
tioned requirements.
The ob~ect on which the present invention is
based consists of provlding aqueous top coating compo~i-
tions which meet the abovementioned requirements.
Surprisinqly, this ob~ect is achieved by top
coating compositions which contain, as the binder, a
water-dilutable polyacrylate resin which is obtainable by
(I) adding a mixture of
; (al) a ~meth)acrylic acid ester which is copoly
merizable with ~a2), ~a3)~ ~blj and ~b2) and is
essentially free from carboxyl groups, or a
mixture of such ~meth)acrylic acid esters and
~a2) an ethylenically unsaturated monomer which is
copolymerizable with ~al), ~a3), ~bl) and ~b2),
carrles at least onQ hydroxyl group per mole-
,
` 1~29303
- 3 -
cule and is essentially free from carboxyl
group~, or a mixture of such monomers, and if
appropriate
(a3) an ethylenically unsaturated monomer which is
S copolymeri~able with (al), (a2), (bl) and (b2)
and is essentially frae from carboxyl groups,
or a mixture of such monomers,
to an organic solvent or solvent mixture and poly-
merizing the mixture in the pre~ence of at least one
polymerization initiator, and
(II) when at least 80% by weight of the mixture con~i~t-
ing of (al), (a2) and if appropriate (a3) haQ been
added, addinq
(bl) 60 - 100% by weight of an ethylenically un-
saturated monomer which carries at least one
carboxyl group per molecule and i8 copolymeriz-
able with (al), (a2) and (a3), or of a mixture
of such monomer~, together with
7 (b2) 0 to 40% by weight of an ethylenically un-
saturated monomer which i~ free from carboxyl
group~ and is copolymerizable with (al), (a2),
(a3) and (bl), or of a mixture of such mono-
. mers,
': ~ and further polymerizing the mixture, and
(III)when the polymerization has ended, at least partly
l neutralizing the resulting polyacrylate resin and
i dispersing it in water, the sum of the amount3 by
weight of (bl) and (b2) alway~ giving 100% by weight
~ and tho nature and ~mount of (al), (a2), (a3), (bl)
gl
s,
:
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,,
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` ` _ 4 _ 1329303
and (b2) being chosen ~o that the polyacrylate resin
has a hydroxyl number of 40 to 200, preferably 60 to
140, an acid number of 20 to 100, preferably 25 to
50, and a glass transition temperature (TG),of -40C
to +60C, preferably -20-C ~o +40-C.
The piqmented base coating composition~ to be
applied in stage (1) of the process according to the
invention are well-known tcompare, for example, US-A-
3,639,147, EP-A-38,127, DE-A-33 33 072 and EP-~-279,813).
~ase coating compositions preferably containing metal
pigments, in particular aluminum pigments, are employed
in stage (1). Metallic effect lacquerings are in this way
obtained.
Before the preparation of the polyacrylate resins
to be employed according to the invention is described in
more detail, two explanations of terms will first be
givens
1.) (Meth)acrylic acid is occadionally used as an
abbreviation for "methacrylic acid or acrylic acid~'.
2.) The formulation ~essentially free from carboxyl
groups~ is intended to mean that the components
(al), ~a2) and (a3) can have a low content of
., .
carboxyl qroups (but at most enough for a polyacry-
~; late resin prepared from components (al), (a2) and
(a3) to have an acid number of at most 10). However,
it i8 preferable to keep the content of carboxyl
1 groups in component~ (al), (a2) and (a3) as low as
;, possible. (al), (a2) and (a3) components which are
~ fre- from carboxyl groups are particularly
. , ,~ .
s- 13~3~3
preferably employed.
To prepare the polyacrylate resinito be employed
according to the invention, any-ester of (meth)acrylic
acid which is copolymerizable with (a2), (a3), (bl) and
(b2) and i8 essentially free from carboxyl group~i, or a
mixture of such (meth)acrylic acid ester~, can be
employed as component ~al). Examples which are mentioned
are alkyl acrylates and alkyl me~hacrylates having up to
20 carbon atoms in the alkyl radical, such a~, for
example, methyl, ethyl, propyl, butyl, hexyl, ethylhexyl,
stearyl and lauryl acrylate and methacrylate, and cyclo-
aliphatic (meth)acrylic acid esters, such as, for ex-
ample, cyclohexyl (methjacrylate. Mixtures of alkyl
acrylates and/or alkyl methacrylates which consist to the
extent of at least 25% by weight of n-butyl and/or t-
, butyl acrylate andJor n-butyl and/or t-butyl methacrylate
are preferably employed as the (al) component.
All ethylenically unsaturated monomers which are
copolymerizable with (al), (a3), (bl) and (b2), carry at
lea~t one hydroxyl group per molecule and ara essentially
free from carboxyl groups, or a mixture of 3uch monomer~,
can be employed as component ~a2). Hydroxyalkyl e~ters of
acrylic acid, methacrylic acid or another ~,~-ethylenic-
ally unsaturated carboxylic acid are mentioned as ex-
ample~. These esters can be derived from an alkyleneglycol, which is esterifLed with the acid, or they can be
obtained by react~on of the acid wi~h an alkylene oxide.
Hydroxyalkyl e~ter~ of acrylic acid and methacrylic acid
ln which the hydroxyalkyl group contains up to 4 carbon
tj
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c,
,'
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~329303
-- 6 -
atoms, reaction products of cyclic esters, such as, for
example, ~-caprolactone and these hydroxyalkyl e~ters, or
mixtures of these hydroxyalkyl esters or 6-caprolactone-
modified hydroxyalkyl esters are preferably employed a8
component (a2). Examples which may be mentioned of such
hydroxyalkyl esters are 2-hydroxyethyl acrylate, 2-
hydroxypropyl acrylate, 3-hydroxypropyl acrylate, 2-
hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate,
2-hydroxyethyl methacrylate, 4-hydroxybutyl acrylate and
4-hydroxybutyl methacrylate. Corresponding esters of
other unsaturated acids, such as, for example, ethacryl~c
acid, crotonlc acid and similar acids having up to about
6 carbon atoms per molecule, can also be employed.
All ethylenically unsaturated monomers which are
lS copolymerizable with (al), ~a2), (bl) and (b2) and are
essentially free from carboxyl groups, or mixtures of
such monomers, can be employed as somponent (a3). Vinyl-
aromatic hydrocarbons, such as styrene, ~-alkylstyrene
and vinyltoluene, are preferably employed a~ component
(a3).
If appropriate, components (al), (a2) and if
appropr$ate (a3) are mixed in a suitable organic solvent
and added to an organic solvent or solvent mixture and
are polymerizad there in the presence of at least one
2S polymerization initiator. The solvents and polymerization
initiators which are customary for the preparation of
polyacrylate resins and suitable for the preparation of
aqueous dispersions are employed as organic solvents and
polymerizatLon initiators. Examples which may be men-
13293~3
- 7 -
tioned of solvents which can be used are butylglycol, 2-
methoxypropanol, n-butanol, methoxybutanol, n-propanol,
ethylene glycol monomethyl ether, ethylene glycol mono-
ethyl ether, ethylene glycol monobutyl ether, diethylene
glycol monomethyl ether, diethylene glycol monoethyl
ether, diethylene glycol disthyl ether, diethylene glycol
monobutyl ether and 3-methyl-3-methoxybutanol. Examples
which may be mentioned of polymerization initiator~ which
can be used are initiator~ which form free radicals, such
as, for example, benzoyl peroxide, azobisisobutyronitrile
and t-butyl perbenzoate. The polymerization is carried
out at a temperature of 80 to 160~C, preferably 120 to
160-C. The mixture of ~al), (a2) and if appropriate (a3)
i~ added to the organic solvent or solvent mixture in the
cour~e of 2 to 8 hour~, preferably in the cour~e of 3 to
6 hours, and is polymerized there in the presence of at
least one initiator which forms free radicals.
When at least 80% by weight, preferably 100% by
weight, of the mixture consisting of (al), (a2) and if
appropriate (a3) has been added,
(bl) 60 - 100% by weight of an ethylenically unsaturated
monomer which carries at least one carboxyl group
per molecule and is copolymerizable with (al), (a2)
and ~a3), or a mixture of ~uch monomers, together
with
~b2) 0 - 40% by weight of an ethylenically unsaturated
monomer which is free from carboxyl groups and is
copolymerizable w1th (al), (a2), ~a3) and (bl), or
a mlxture of ~uch monomer~,
. ^
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13293~3
- 8 -
are added to ~tage (II) and the mixture ~8 polymerized
further until the monomers added in stage ~I) and (II)
have been essentially reacted completely.
It is preferable to add 100% by weight of com-
ponent (bl) in stage (II). In other words: it is prefer-
able to employ component (bl) in sta~e (II) without
admixing component (b2).
Any ethylenically unsaturated monomer which
carries at lea~t one carboxyl group per molecule and is
copolymerizable with (al), ~a2) and (a3), or a mixture of
~uch monomers, can be employed as component (bl). Acrylic
acid and/or methacrylic acid are preferably employed as
components (bl). However, it is also possible to employ
other ethylenically unsaturated acid~ having up to 6
lS carbon atoms in the molecule. Examples of ~uch acids
which may be mentioned are ethacrylic acid, crotonic
acid, maleic acid, fumaric acid and itaconic acid.
Mono(meth)acryloyloxyethyl maleate, mono(meth)acryloyl-
oxyethyl succinate and mono(meth)acryloyloxyethyl phthal-
ate can also be employed a8 component (bl).
Any ethylenically unsaturated monomer whlch i~copolymerizable with (al), (a2), (a3) and (bl), or a
mixturo of ~uch monomers, can be employed a~ component
(b2). All the monomers listed in the description of
components ~al), (a2) and (a3) can be employed a~ com-
ponent (b2).
Components (bl) and if appropriate (b2) are
preferably added in the course of 10 to 60 minutes,
particularly preferably ln the cour~e of lS to 45
- 9 - 1 3293 ~3
minute~.
When the addition of the monomers (bl) and if
appropriate (b2) has ended, the mixture i~ further
polymerized until all the monomers employed have been
essentially reactad completely.
The nature and amount of components (al), (a2),
(a3)~ (bl) and ~b2) are chosen so that the reaction
product has a hydroxyl numbor of 40 to 200, preferably 60
to 140, an acid numbar of 20 to 100, preferably 25 to 50,
and a glass transition temperature (TG) of -40C to +60C,
preferably -20-C to +40C.
The gla~s transition temperature~ of polyacrylate
resins can be calculated from the following formula:
n=x W
1 =~ n
TG ~ TGn
n.l
lS Ta - gla~s transition temperature of the
polyacrylate re~in
x - number of various monomer~ copolymerized
in the polyacrylate resin
Wn ~ weight content of the nth monomer
T~ - glass transition temperature of the
homopolymer from the nth monomer
The amount and rate of addition of the initiator
are preferably chosen 80 that a polyacrylate rasin having
a number-average molecular woight of 2,500 to 20,000 is
:
.~ ,
lO- 1329303
obtained. It is preferable to ~tart the addition of the
initiator at the same time as the addition of the mixture
of components ~al), (a2) and if appropriate (a3), and to
end the addition about half an hour after the addition of
component (bl) and if appropriate (b2) has ended. The
initiator is preferably added in a constant amount per
unit time. When the addition of initiator has ended, the
reaction mixture is kept at the polymerization tempera-
ture until (as a rule about 1 1/2 hours) all the monomers
employed have been essentially reactad completely.
~E~3entially reacted completely" is intended to mean that
preferably 100% by weight of the monomer~ employed have
béen reacted, but that it i8 also po~ible for a small
re~idual monomer content of not more than up to about
0.5% by weight, based on the weight of the reaction
mixture, to remain unreacted.
The polyacrylate resins according to the inven-
tion are prepared by employing 40 to 87.5% by weight,
preferably 55 to 80% by weight, of component ~al), 10 to
45% by weight, preferably 12 to 35% by weight, of com-
ponent (a2), 0 to 25% by weight, preferably 8 to l8% by
weight, of component (a3), 2.5 to 15% by weight, prefer-
ably 3 to 7% by weiqht, of component (bl) and 0 to 6% by
weight of component (b2), the sum of the amount~ by
welght of ~al), (a2), (a3), (bl) and (b2) alway~ giving
100% by waight.
When the polymerization ha~ ended, the re~ulting
polyacrylate resin 18 at least partly neutralized and
dlspersed in water.
'.~ ,
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3293Q3
~ oth organic bases and inorganic bases, such as
ammonia and hydrazine, can be used for the neutraliza-
tion~ Primary, secondary and tertiary amines, such a~,
for ex~mple, ethylamine, propylamine, dimethylsmine,
dibutylamine, cyclohexylamine, benzyla~ine, morpholine,
piperidine and triethanolsmine, are preferably used.
Tertiary amines, in particular dimethylethanolamine,
triethylamine, tripropylamine and tributylamine, are
particularly preferably employed as neutralizing agents.
The neutralization reaction i~ in general carried
out by mixing the neutralizing base with the polyacrylate
resin. The base is preferably added here in an amount
such that the top coating composition has a pH of 7-8.5,
preferably 7.2 to 7.8.
The partly or completely neutralized polyacrylate
resin is then dispersed by addition of water. An aqueou~
poly~crylate re~in dlspersion i8 formed here. If
appropriate, ~ome or all the organic ~olvent csn be
distilled off. The polyacrylate resin dispersions accord-
ing to the invention cont~in polyacrylate re~in particles
of average particle size of preferably between 60 and
250 nm (mea~urement method~ la~er light separation (sic),
measuring lnstrument2 Malvern Autosizer 2C).
Top coating compositions according to the inven-
tion are obtained from the resulting aqueous polyacrylate
re~ln disper~ions by generally ~nown methods by admixing
an aminoplast resin and if approprlate other additives,
such a~, for example, flow control auxiliarie8, W
stabilizers, tr~n-par-nt pigment- and the like.
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- 12 _ 13293~3
The top coating compo~itions according to the
invention preferably contain aminoplast resin in an
amount such that the weight ratio between the poly-
acrylate re3in solid and aminoplast resin solid i~
S 60 : 40 to 90 : 10, particularly preferably 70 : 30
to 85 : lS.
In principle, all aminopla~t resins which can be
processed with the polyacrylate resin according to the
invention to give a stable top coating composition can be
employed a~ cros~linking agents. Melamine-formaldehyde
re~Lns which are partly or completely etherified with
aliphatic alcohols which preferably contain 1 to 4 carbon
atom~ per molecule are preferably employed a~ the cross-
linking agents.
lS Before application, the top coating compositions
according to the invention are ad~u~ted to the spraying
viscosity (in general 20 to 40 seconds flow time from DIN
cup 4 ~DIN 53 211 (1974)) and a pN of 7.0 to 8.5, prefer-
ahly 7.2 to 7.8.
The top coating compo~it~ons according to the
invention
- have at the peak ~sic) viscosity such a high ~olid~
content (20 to 45% by weight, preferably 32 to 40%
by weight) that lacquer films of ~ufficient layer
thickness (the thickness of the stoved lacquer film
should preferably be between 25 and 45 ~m) are
obtained with ono to two spray passes (cross passes)
.~ ~
- give stoved lacquer films with a very good appear-
` ~ .
,, ~
:,
.:;
- 13 - 1329303
ance ~good flow, high gloss, good top lacquer
status...) and good mechanical-technological proper-
ties and
- have a relatively low content of organic cosolvents
(les~ than 35% by weight, based on the total solids
content of binders and crosslinking agents).
If the top coating compositions according to the
invention are u3ed for the production of metallic effect
lacquerings together with water-dilutable base coating
compositions, metallic effect lacquerings in which the
trsnsparent top layer adheres particularly well to the
base layer are obtained.
In addition to the polyacrylate resin employed
according to the invention, the top coating compositions
according to the invention can also additionally contain
cro~slinked polymer microparticles, such as are des-
cribed, for example, in EP-A-38,127, and/or other com-
: patible re~ins, such as, for example, water-dilutable or
- water-soluble polyacrylate resins, polye~ter resins,
~ 20 alkyd resin~ or epoxy resin esters, and they can also be
pigmented.
The invention is explained in more detail.in the
foll~wing examples~
A. Prepsration o water-dilutable polYacrylate resin~
2S accordlna to the invention
:~ 20 p~rt~ by weight of butylglycol are initially
introduced into a 4 1 steel kettle eauipped with two
monomer feeds, an initiator feed, stirrer, thermometer,
oil heating and reflux condenser and are heated up to
;s
. .
:, .
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` 14 1329303
140-C. A solution of 4.5 parts by weight of butyl per-
benzoate in 5 parts by weight of butylglycol is then
added at a rate such,that the addition has ended after 4
hours 30 minutes. With the ~tart of the addition of the
S butyl perbenzoate solution, the addition of the mixture
of (al)~ ta2) and (a3) is also started (compare Table 1).
The mixture of (al), (a2) and (a3) i~ added at a rate
such that the addition has ended after 3 hours S0 min-
utes. When all the mixture consisting of (al), (a2) and
(a3) ha~ been added, component (bl) (compare Table 1) i~
added in the course of 20 minutes.
- 15- 13293~3
oc~o. o. o.
.~ o o ~ ~ ~ l U~
~D ~ ~ ~
P~ .
o o o U~ o U~ o
o Ul ~I~ ~ t~
~; N ~ _I N
P~ .___.
~p, 0 00 O .0 O
_
_~ O O O O
Il~ I` ~ ~ I I ~ ~1 Itl
~ ~ _i ~ _~
D- ~
O O O O O O
.j ~ ~'I O U~ I I 1~ It~ 11-
, ~ y _~ N _I _ ~
'. ~ OOO O O O
P. ~ ~ In I I ~ 1~
~,
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S,~: :
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- 16 - 1329303
The resin solution thus obta$ned ~ neutralized
with dimethylethanolamine at about 95C up to a degree
of neutralization of 80%. Water is then added in an
amount such that the solids content of the dispersion i~
S about 60% by weight. The re~ulting disper~ions have the
following parameters.
Table 2
Pl P2 P3 P4 P5 P6
Solid~
(in % by weight;
1 hour, 130'C) 59.4 59.4 59.0 59.6 59.0 59.5
Acid number
theoretical 23.3 38.9 38.9 38.9 38.9 38.9
measured 27.0 38.4 36.4 37.7 39.0 38.0
Degree of
neutralization
~) 80 80 80 80 80 80
OH number 100 100 60 100 100 100
Partlcle size
~nm)l 114 143 186 106 119 120
The particle size wa~ determined by laser light
scattering. Instrument: Malvern Autosizer 2 C.
B. Preparation of tran~parent aqueou~ top coating
compositions accordinq to the invention
Transparent top coating compositions are prepared
from 60.00~ by weight of a polyacrylate dispersion
prepared accord~nq to point A, 10.00~ by weight of a 90~
strength solution of a commercially available water-
;
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- 17 - 13293~3
dilutable melamine-formaldehyde resin in isobutanol
(Cymel~ 327), 0.05~ by weight of a commercially available
flow control agent (Fluorad~ PC 430) and 29.95% by weight
of distilled water and are ad~usted with a 10% strength
aqueou~ dimethylethanolamine solution and distilled water
to the spraying viscosity (24 ~econds flow time from DIN
cup 4 (DIN S3 211 (1974)) and a pH of 7.4 to 7.5. The top
coating compositions contain 20% by weight of cosolvent,
based on the total solids content of polyacrylate resin
and melamine-formaldehyde resin.
C. ApplLcation of the transparent top coating composi-
tions according to the inve~tion and testing of the
stoved lacquer films
A water-dilutable base coating composition,
pigmented with aluminum platelets, according to EP-A-
279,813 i~ applied to a phosphated steel sheet coated
with a commercially available electro-dip coat lacquering
and a commercially available filler to give a dry film
thickness of 12 - lS ~m. The base coating composition
applied is dried at room temperature for 10 minute~ and
at ~O-C for 10 minutes. A top coating composition
obtained according to point B is then sprayed onto the
base layer in two cro3~ passes with an intermediate air
exposure time of one minuts. Finally, the ~heet is dried
at room temperature for 20 minutes and stoved in a
circulating air oven at 130-C for 30 minutes. The multi-
layered coating~ thus obtained were sub~ected to several
te~ts. The test results are summarized in the following
tablet
- 18 - 1~29303
Table 3
P1 P2 P3 P4 PS P6
Application
solid~ content
tl hour, 130C,
in % by weight) 42.0 37.2 39.1 36.8 36.0 36.5
Thickne3s of the
tran~parent top
. 10 layer (in ~m) 41 39 43 33 35 32
Cross-hatch~ 0 0 0 0 0 0
Gloss~2~ 90 92 89 90 90 90
DOI 86.5 84.3 86.7 81.2 83.7 83.0
Degree of
. 15 bubbling~3~ after
exposure~) MOGO MOGO MOGO MOGO MOGO MOGO
Gloss~2~ after
expo~ure~" 85 85 84 82 82 82
DOI after
exposure~ 73.4 80.6 76.7 78.4 78.5 78.2
(1) Testing in accordance with DIN 53 151, including
Tesa peel test
j (2) Degree of gloss Ln accordance with DIN 67 530,
.; angle 20-
. 25 ~3) In accordance with DIN 53 209
~; ~4) 240 hour~ at 40-C RK (in ~ccord~nce with DIN 50 017)
D. Compari~on Example
The monomers (al), (a2), ~a3) and ~bl) employed
for the prep~r~tion of the polyacrylate resin P2 accord-
~ '
! ~ r
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19 13293~3
ing to the invention are mixed and polymerized. The
polymerization conditions are the same a~ for the pre-
paration of the polyacrylate resin P2 according to the
invention. The only difference from the preparation of
the polyacrylate resin according to the invention is that
component (bl) is added not after addition of the mixture
of ~al)t (a2) and (a3) but together with (al), (a2) and
(a3). An aqueous top coating composition prepared in
accordance with B from the polyacrylate resin V thus
prepared has a solids content of only 24.1S by weight at
a viscosity of 24 DIN seconds (flow time from DIN cup 4
(DIN 53 211 (1974)) and a pH of 7.4 to 7.5.
The following diagra~ shows the viscosity of the
polyacrylate dispersion P2, prepared according to A and
diluted with water, as a function of the solids content
of the dispersion in comparison with an analogous disper-
sion of polyacrylate resin V (pH of the two dispersions:
7.8). It i3 clear that the vi~cosity of polyacrylate
resin disper~ion P2 according to the invention at solids
contents of 25 to about 53% by weight is lower than the
vi8c08ity of the comparable dispersion of polyacrylate
resln V.
` " ' ' . ;
132g303 ,
-- 20 --
¦ vi~c08ity (log m Pa 8)
S ~ P 2
-- v
~,5
SC - ~olids content
, ' . ` . !
" :` ~
