Note: Descriptions are shown in the official language in which they were submitted.
~ 27293-32
1329291
The invention relates to a process for the prepara-
tion of aqueous dispersions that contain modified epoxide-amine
adducts as binders and polyisocyanates blocked by amino groups as
crosslinking agents. The aqueous dispersions can be further
processed to electro-coating paints with baking temperatures
below 160C and baking times not greater than 30 minutes.
Cathodic electro-coating is a painting process fre-
quently used particularly for priming, in which water-thinnable
synthetic resins carrying cationic groups are deposited on electri-
i, 10 cally conducting objects with the aid of direct current. Binders
which are suitable for the cathodic deposition contain predomin-
antly amino groups which are neutralized with acids in order to
render the binders soluble in water.
A particularly preferred group of binders is repre-
sented by the group of binders which are based on modified epoxy
resins. Binders of this type are disclosed, for example, in
the following patent documents: US-PS 4,031,050, US-PS
3,799,854, US-PS 3,984,299, US-PS 4,252,703, US-PS 4,332,711 and
DE-PS 3,108,073.
,
;
,-'' ' ' " ' ' - ~
~" - 2 - 1329291
They are crossLinkable by virtue of admixed poly-
isocyanates blocked by amino groups. These crosslinking
agents thus contain at room temperature urea groups (=
blocked isocyanate groups). The blocking components are
then split off at elevated temperatures and the isocyanate
groups are regenerated. Subsequently, these isocyanate
groups may effect the crosslinking of the binders via the
hydroxyl groups and/or the primary and/or secondary amino
groups contained therein. Such non-selfcrosslinking binder
systems represent the present state of the art. Their
structure and preparation are described, for example, in
DE-PS 3,108,073, particularly in Examples 1 to S, or in EP
; 74,634 A2, Example A.
The crosslinking agents used therein react, because
of the structure of their blocking components, only at tem-
- peratures above 160C. The method described in the examples
can therefore be followed without any difficulties.
However, in recent years the demand has steadily
- grown for crosslinking agents which become active at con-
siderably lower baking temperatures. This is due in the
automotive industry, for example, to the joint use of
,~
- plastic components in the construction of automobile
~ :,
bodies.
Attempts have therefore been made to prepare suit-
able blocked polyisocyanates as crosslinking agents for re-
duced baking temperatures. A blocking component particularly
suitable for this purpose is the secondary amino group.
Such crosslinking agents based on aliphatic and aromatic
polyisocyanates having secondary dialkylamines as blocking
3 1329291
components are described, for example, in DE-OS
3,311,516. However, if these crosslinking agents are
used instead of the crosslinking agents described above,
the resultant paint surface lacks reproducible properties
and exhibits breakdown phenomena and poor flow-out.
It is thus the object of the invention to make
available a process which would make it possible, even
when using crosslinking agents with low baking temper-
atures and modified epoxide-amine adducts as binders, to
obtain aqueous dispersions which give rise, after being
further processed to electrocoating paints, to reproduc-
ible surfaces formed by cathodic electrocoating with very
~: good mechanical properties.
This object is achieved according to the inven-
. 15 tion by a process for the preparation of aqueous binder/
crosslinking agent dispersions, wherein
t1) (A) polyepoxides and
(B) compounds which contain one or more, preferably
. 2, hydroxyl groups attached to aromatic and/
or (cyclo)aliphatic molecular fragments per
molecule,
are reacted in the presence of catalysts at elevated
temperatures, preferably at from 100 to 180C, to
furnish
Z5 (C) epoxide-containing intermediates;
(2) (D) a solvent or a mixture of solvents is added
with cooling by a secondary circuit (for ex-
ample cooling via cooling coils filled with
heat transfer oil or water) and the resultant
.
~ 4 ~ I3 29 29 ~
resin solution is caused to boil under reflux, if
necessary by application of a vacuum, until the
temperature of the solution drops to 95C to 20C;
(3) (E) amines are added onto the epoxide groups which
are still present in a free state in the epoxide
resin and either
(4a) these reaction products are dispersed in a water-
acid mixture and the crosslinking agent (F) is ad-
mixed, or
(4b) the crosslinking agent (F) is mixed with these pro-
ducts and this mixture is dispersed in a water-acid
mixture.
In the first stage of the process according to
the invention epoxide-containing intermediates are first
prepared from the components (A) and (8) in the presence
of catalysts.
Any compound whose molecule contains on average
more than 1 epoxide group, may be used as the component
(A). Preferred compounds are those which contain 2
epoxlde groups in the molecule and have a relatively low
molecular weight of not more than 750, preferably 350 to
5ûO.
Particularly preferred epoxide compounds are poly-
glycidyl ethers of polyphenols prepared from polyphenols
and epihalohydrins. 8isphenol A may preferably be used
as the polyphenol.
Polyglycidyl esters of polycarboxylic acids may
also be used. Glycidyl adipate and glycidyl phthalate
are typical examples.
- s 1329291
Hydantoin epoxides, epoxidized polybutadiene and
polyepoxicle compounds which are obtained by epoxidation
of an olefinically unsaturated alicyclic compound, are
furthermore suitable.
; 5 Compounds which contain one or more, preferably
2, hydroxyl groups attached to aromatic and/or (cycLo)-
aliphatic molecular fragments per molecule, are used as
the component (8).
Compounds which are suitable as the component (~),
include both low-molecular and high-molecular compounds.
Suitable low-molecular components (a) are phen-
olic, aliphatic and/or polyfunctional alcohols of a
molecular weight below 350.
Examples of these are:
diols, such as ethylene glycol, dipropylene glycol,
triglycol, 1,2-propanediol, 1,3-propanediol, 2,2-dimethyl-
1,3-propanediol, 2-methyl-2-propyl-1,3-propaned;ol, 1,2-
butanediol, 1,4-butanediol, 2-ethyl-1,4-butanediol, 2-
.~ ~
butene-1,4-diol, 1,2-pentanediol, 1,5-pentanediol, 3-
methyl-1,5-pentanediol, 1,6-hexanediol, 2-hydroxyethyl
hydroxyacetate, 2,2-dimethyl-3-hydroxypropyl 2,2-dimethyl-
hydroxypropionate, 4,4'-methylenebiscyclohexanol and
4,4'-isopropylidenebiscyclohexanol. 2,2-Dimethyl-1,3-
propanediol and 3-methyl-1,5-pentanediol are some of the
preferred diols.
Examples of higher molecular components (~) are
polyester polyols, polyether polyols or polycaprolac-
tone polyols of various functionality and molecular
weight.
- 6 _ 1329291
Polyalkylene ether polyols suitable as the com-
ponent (B) correspond to the general formula:
r
H ~ o -(CHR)n ¦ OH
in which R = hydrogen or a lower alkyl radical which may
carry various substituents, n = 2 to 6 and m = 3 to 50
or even higher. Examples are poly(oxytetramethylene)
glycols and poly(oxyethylene) glycols.
The preferred polyalkylene ether polyols are
poly(oxytetramethylene) glycols of a molecular weight in
the range from 350 to 1,000.
Polyester polyols may also be used as the com-
ponent (8). The polyester polyols may be prepared by
polyesterification of organic polycarboxylic acids or
their anhydrides with organic polyols containing primary
hydroxyl groups. The polycarboxylic acids and the poly-
ols are usually aliphatic or aromatic dicarboxylic acids
and diols.
The diols used for the preparation of the poly-
esters include alkylene glycols such as ethylene glycol,
butylene glycol, neopentyl glycol or other glycols such
as cyclohexanedimethanol.
The acid component of the polyester consists pri-
marily of low-molecular carboxylic acids or their anhyd-
rides of 2 to 18 carbon atoms in the molecule. Suitable
~ _ 7 _ 1329291
acids are, for example, phthalic acid, isophthalic acid,
terephthalic acid, tetrahydrophthalic acid, hexahydro-
phthalic acid, adipic acid, azelaic acid, sebacic acid
and glutaric acid. The anhydrides of these acids may also
S be used, insofar that they exist.
Furthermore, it is also possible to employ poly-
ester polyols derived from lactones, as the component (a)~
These products are obtained by the reaction of an e-capro-
lactone with a polyol. Such products are described in
US-PS 3,169,945.
The polylactone polyols obtained by the react;on,
are distinguished by the presence of a terminal hydroxyl
group and recurring polyester moieties, derived from the
lactone. These recurring molecular moieties may corres-
pond to the formula
- C )n CH2
. .
in which n is at least 4, preferably 4 to 6, and the sub-
stituent is hydrogen, an alkyl radical, a cycloalkyl
; radical or an alkoxy radical.
Compounds containing, for example, one or more
basic nitrogen atoms may be employed as the catalyst.
Tertiary amines, such as, for example, N,N-di-
methylbenzylamine, tributylamine, dimethylcyclohexylamineand dimethyl-C12/C14-amine (C12/C14 represents an aliphatic
chain containing 12 to 14 carbon atoms) are preferably used.
The catalyst is usually used in an amount from 0.1
to 2% by weight, based on the intermediate produced from
,,, ~
- 1329291
- 8 - 27293-32
the components (A) and (B).
The reaction between the components (A) and (B) is car-
ried out at temperatures between 100 and 190C, preferably between
100 and 180C.
In the second stage of the process according to the
invention a solvent or a mixture of solvents is added to the resin
solution with cooling by a secondary circuit (for example cooling
via cooling coils filled with heat transfer oil or water). Sol-
vents preferably to be added are those which cannot react with the
epoxide groups still present and/or which can in any case be later
added as solvents to the electrocoating paint. Particularly
preferred solvents are ketones such as, for example, acetone,
methyl ethyl ketone, methyl isobutyl ketone, mesityl oxide; acet-
,i ates such as, for example, propyl acetate, butyl acetate; ethers
such as, for example, dioxane, dibutyl ether; aromatic compounds
such as, for example, toluene, xylene, ethylbenzene or mixtures
of the solvents. The resin solution is caused to boil by careful
application of a vacuum. Any foaming is brought under control by
an appropriate lowering of the vacuum. As the temperature decreases,
~ 20 the pressure is gradually lowered further to achieve uniform boil-
- ing. If desired, further solvent may be added while the mixture
cools, either continuously or in portions. The cooling is to
reduce the temperature of the resin solution to a value in the
range 95C`to 20C, preferably not less than 50C.
In stage (3), primary and/or secondary amines may be
employed as the component (E), the secondary amines being parti-
cularly preferred components (E).
The amine should preferably be a water-soluble
~ 9 - 1329291
compound. Examples of such amines are monoalkylamines
and dialkylamines such as methylamine, ethylamine, pro-
pylamine, butylamine, dimethylamine, diethyLamine, dipro-
pylamine, methylbutylamine and the like. AlkanoLamines,
such as, for example, methylethanolamine, diethanolamine
and the like, are also suitable. Dialkylaminoalkylamines
such as, for example, dimethylaminoethylamine, diethyl-
aminopropylamine, dimethylaminopropylamine and the like,
are likewise suitable. Low-molecular amines are used in
the majority of cases, but it is also possible to employ
higher-molecular monoamines.
Polyamines with primary and secondary amino groups
may react with the epoxide groups in the form of their
ketimines. The ketimines are prepared from the poly-
amines in a known manner.
The amines may also contain other groups, but
these must not interfere with the reaction of the amine
with the epoxide group nor must they induce gelling of
the reaction mixture.
The reaction between the amines and the compounds
containing epoxide groups often commences just by mix;ng
the coreactants. Depending on the desired course of the
reaction - particularly to ensure that the reaction runs
to completion - it is recommended to raise the reaction
: 25 temperature to 50 to 150C in the course of the reaction.
The crosslinking agent tF) for reduced baking
temperatures added to the last stage of the process ac-
cording to the invention is a polyisocyanate blocked with
amino groups. These crosslinking agents are prepared by
~"
"
- 10 - 132929~
reacting a polyisocyanate with the corresponding secon-
dary amine. The isocyanates may be aliphatic or aromatic,
aromatic isocyanates being preferred for crosslinking
agents for reduced baking temperatures.
S Alkylene isocyanates such as, for example, tri-
methylene diisocyanate, tetramethylene diisocyanate,
pentamethylene diisocyanate, hexamethylene diisocyanate,
1,2-propylene diisocyanate, 1,2-butylene diisocyanate,
2,3-butylene diisocyanate, 1,3-butylene diisocyanate,
ethylidene diisocyanate and butylidene diisocyanate as
~ well as cycloalkylene isocyanates such as, for example,
- 1,3-cyclopentane diisocyanate, 1,4-cyclohexane d;iso-
i.l
cyanate, 1,2-cyclohexane diisocyanate and isophorone di-
isocyanate are typical examples of aliphatic polyiso-
cyanates.
Arylene isocyanates such as, for example,
m-phenylene diisocyanate, p-phenylene diisocyanate,
4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate
and 1,4-naphthalene diisocyanate as well as alkarylene
isocyanates such as, for example, 4,4'-diphenylmethane
diisocyanate, 2,4-toluylene diisocyanate or 2,6-toluylene
diisocyanate or a mixture of 2,4- and 2,6-toluylene di-
isocyanates, 4,4'-toluidine diisocyanate and 1,4-xylylene
- diisocyanate as well as substituted aromatic systems such
as, for example, dianisidine diisocyanate, 4,4'-diphenyl
ether diisocyanate or chlorodiphenylene diisocyanate,
1,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene
and 4,4'-diphenyldimethylmethane 2,2',5,5'-tetraisocyanate
as well as polymerized isocyanates are typical examples
'` ''
:' . '~ .
.
11 - 13292~1
of aromatic polyisocyanates.
For crosslinking agents for reduced baking tem-
peratures, secondary amines are preferably used for block-
ing the isocyanate group.
Examples of suitable monoam;nes are particularly
secondary aliphatic, cycloaliphatic or araliphatic amines
with a boiling point below 200C, those with a boiling
point between 100 and 200C being preferred. Examples of
suitable secondary aliphatic amines are dimethylamine,
diethylamine, dipropylamine, dibutylamine, dipentylamine,
dihexylamine and isomers thereof, such as, for example,
diisopropylamine, as well as asymmetrical compounds, such
as N-ethyl-1-propanamine. Examples of suitable cyclo-
aliphatic and araliphatic amines are dicyclohexylamine
and N-methylaniline.
The reaction is carried out under conditions custo-
mary for isocyanate reactions; the reaction temperature may
be from room temperature to about 150C. If the starting
materials and the reaction product are liquids at reaction
temperature, it is possible to carry out the reaction with-
out solvent; however, the reaction is generally carried
?~ out in an inert solvent such as ether, ester, ketone or
hydrocarbon.
The crosslinking agent described above may be added
directly at the end of stage (3) of the process according
to the invention and the resultant mixture then dispersed
in a water/acid mixture; however, first dispersing the
reaction products from stage (3) in a water/acid mixture
and only then adding the crosslinking agent is preferred.
.,
,
:, ,
~ ' ~, ' .
1329291
- 12 - 27293-32
Organic acids, such as, ~or example, formic acid,
acetic acid or lactic acid, are employed for the preparation of
the water/acid mixtures.
After preparation of the aqueous dispersion the sol-
vent is preferably removed in vacuo at a temperature below 65C.
The procedure of the process according to the invention
for the preparation of aqueous dispersions to be further processed
to electro-coating paints with low baking temperatures is elucidat-
ed in greater detail by the examples below. The percentages given
are percentages by weight, unless indicated otherwise.
Example 1
The example below describes the synthesis of an
epoxide-amine resin modified with a monophenol compound, the addi-
tion of a crosslinking agent and the preparation of an aqueous
dispersion of this mixture.
The crosslinking agent (I) is first prepared as
follows: 2440 g of triisocyanurated hexamethylene diisocyanate
are placed in a suitable reaction vessel in an atmosphere of nitro-
gen. 850 g of methyl isobutyl ketone (MIBK) are added and the
mixture is heated to 50C. 1560 g of di-n-butylamine are then
added. The rate of the addition is controlled in such a manner
that the temperature is kept to 60-70C. At the end of the addi-
tion the temperature is raised to 75C, and maintained at this
level for one hour; 150 g of n-butanol are then added. The product
has a solids content of 80% (130C, 1 h). Both the NCO-and the
amine equivalent are above 20,000.
' '
1329291
- 12a - 27293-32
To synthesize the epoxy resin, 1884 g of an epoxy
resin based on bisphenol A with an epoxide equivalent weight
(EEW) of 188, 286 g of bisphenol A, 623 g of dodecylphenol
. .
, .:
~ . ,
"., . . ~ ~ .
1329291
- 13 -
and 147 9 of xyLene are placed in a double-walled reaction
vessel which can be heated by means of heat transfer oil and
is provided with a stirrer, a reflux condenser, a water sep-
arator, an inlet tube for inert gas and a vacuum connection,
S and the mixture is heated to 110C. Traces of water are
removed by distillation via a water separator in a continu-
ous cycle by application of a slight vacuum. The reaction
mixture is then heated to 130C and 11 9 of N,N-dimethyl-
benzylamine are added, when the temperature briefly rises
1û to 150C. The mixture is then cooled to 130C and this
temperature is maintained until an EEW of 1240 is reached
(about S hours). To terminate the reaction, the reaction
mixture is cooled via a secondary circuit and 225 9 of
xylene and 52 9 of butylglycol are added in rapid succes-
sion. The solution of the resin is caused to boil underreflux by careful application of a vacuum; any foaming is
brought under control by an appropriate lowering of the
vacuum. When a little later 95C is reached, the vacuum
is released and 783 9 of a 70% solution of a reaction
product obtained from 1 mole of diethylenetriamine and 2
mole of methyl isobutyl ketone (MIBK) in MIBK are added.
After the exothermic reaction has subsided, the reaction
mixture is heated to 120C in the course of 30 minutes and
; this temperature is maintained for a further 2 hours. A
sample of the resin has the following characteristics:
Solids content (30 min, 180C): 80%
Base content: 1.47 meq/g of resin solids
910 9 of this resin solution are mixed with 390 9
of the crosslinking agent (I) and 19 9 of glacial acetic
acid are added. 850 9 of water are then added in portions
,
. , . :, :
`
!'
with stirring. The mixture is homogenized for a brief
; period and diluted with 960 9 of water added in small
~ portions to the final solids content.
; The dispersion is freed by subsequent vacuum dis-
S tillation from volatile solvents, the solvent removed by
distillation being replaced by equal amounts of water.
The dispersion is then filtered tsolids content 33.2%
(1 h, 130C)).
Example 2
The example below describes the synthesis of an
epoxide-amine resin modified with a monophenol compound,
the addition of a crosslinking agent and the preparation
of an aqueous dispersion of this mixture.
The crosslinking agent (II) is first prepared as
follows: 2088 9 of toluylene diisocyanate and 1746 9 of
MIBK are placed in a reaction vessel in an atmosphere of
- nitrogen and heated to 50C. 536 9 of trimethylolpropane
are then added in portions. The temperature is maintained
at SS-60C. At the end of the addition the reaction mix-
ture is maintained at this temperature for 1 hour, is then
cooled to 60C and 1450 9 of di-n-butylamine are added
at such a rate that the temperature is maintained at 70-
75C. The reaction is allowed to proceed for a further
1 hour after the end of the addition. The product has
a solids content of 70%. The amine equivalent and the
isocyanate equivalent are both above 20,000.
To synthesize the epoxy resin, the procedure of
Example 1 is followed.
910 9 of the resin solution and 390 9 of the
.
~''' ' ~. -
'. ` ,
. ~
- 15 _ I 3 2 92 9I
cross-linking agent (II) are mixed and Z1 9 of glacial
acetic ac;d are added. 850 9 of water are then added in
portions with stirring. The reaction mixture is homogenized
for a brief period and then diluted with 960 9 of water
added in small portions to the final solids content.
The dispersions are freed by subsequent vacuum dis-
tillation from volatile solvents, the solvent removed by
distillation being replaced by equal amounts of water.
The dispersion is then filtered (solids content 33.4%
(1 h, 130C)).
Comparison example
The procedure of Example 1 is followed until the
- EE~ of 1240 is reached. 1785 9 of the crosslinking agent
(I) and 783 9 of a 70% solution of a reaction product
obtained from diethylenetriamine and methyl isobutyl ketone
in methyl isobutyl ketone are added. The reaction mixture
is adjusted to a temperature of 112C and this temperature
is maintained for 1 hour.
19 9 of glacial acetic acid are added to 1200 9 of
this resin solution and 850 9 of water are added in por-
tions with stirring. The mixture is homogenized for a
brief period and diluted with 960 9 of water added in small
portions to the final solids content.
The dispersion is freed in subsequent vacuum dis-
tillation from volatile solvents, the solvent removed bydistillation being replaced by equal amounts of water.
The dispersion is then filtered (solids content 35.1% (1 h,
130C)).
Electrocoating baths are prepared from the binder
, :
:
. ~ .
~ - 16 - 1329291
dispersions described in Examples 1 and 2 and in the com-
parison example with a gray pigment paste.
To prepare a gray pigment paste, 800 parts of butyl-
glycol are added to 953 parts of a commercially available
S epoxy resin based on bisphenol A (epoxide equivalent weight
of 890) and the mixture is heated to 80C. 221 parts of a
reaction product obtained from 101 parts of diethanolamine
and 120 parts of 80% aqueous lactic acid are then added to
the resin solution. The reaction is carried out at 80C
until the acid value has dropped below 1.
1800 parts of this product are mixed with 2447
parts of deionized water and this mixture is treated with
2460 parts of TiO2, 590 parts of an extender based on alu-
minum silicate, 135 parts of lead silicate and 37 parts of
carbon black. This mixture is ground in a millbase to a
Hegman fineness of 5 to 7. 1255 parts of deionized water
are then added in order to reach the desired paste con-
sistency.
The electrocoating baths are obtained by mixing:
2280 parts of deionized water
25 parts of 10% acetic acid
1920 parts of aqueous crosslinking agent/epoxide-amine
adduct dispersion
775 parts of pigment paste.
The deposition of the paint films is carried out at a
bath temperature of 26C for 120 seconds. Zinc phosphated
panels are connected as cathode for this purpose and coated.
The curing of the deposited films is carried out for 20 minutes
in a circulating air oven at temperatures indicated in the
~ - 17 - 1 3 2 9 2 9 1
table together with deposition data.
The deposition results are summarized in the tables
below:
Deposition data:
Deposition data Example 1 Example 2 Comparison
example
-
Deposit;on voltage (V) 300 320 330
Film thickness t~m) 23 21 19
Baking temperature (C) 145 130 145
FORD throwing
power (cm) 20.5 22 20
Mechanical properties:
Test method Example 1 Example 2 Comparison
example
. 15 Erichsen indentation
(mm) 8 4 6
. Crosshatch O 0
(O best, 5 worst)
-, Bending test pass pass pass
. 20 Impact test
: (m kg) 0.920.69 0.69
Flow-out 0.5 1.5 4.5
(O best, 5 worst)
,, - , . . .
