Note: Descriptions are shown in the official language in which they were submitted.
2151/US-3140
131216~ .
F I E LD OF I NVE NT I ON
This invention relates to a process for catalyzing
the crosslinking of cathodically depositable paint binders
based on binder resins containing ethylenic double bonds.
More particularly, the invention relates to cathodically
depositable paint binders containing resins having ethylenic
double bonds catalyzed with iron-acetylacetonate.
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BACKGROUND OF INVENTION
It is known that the crosslinking reaction of ca-
thodically depositable paint binders which are crosslinked
by transurethanization can be catalyzed by the use of metal
compounds, thereby reducing the hardening temperature re-
quired or shortening the stoving time. Thus, according to
DE-OS 25 41 234, the acetates, naphthenates, oleates, chro-
mates, phosphates, and the like of bismuth, lead, tin, iron,
cobalt, nickel, aluminium, zinc, manganese, copper, zircon-
ium, and the like are used for this purpose. Further, the
addition of water-soluble metal salts to improve corrosion
resistance is also known, According to DE-OS 24 57 437,
water-soluble salts of cobalt, nickell cadmium, tin, antimony,
zinc, or copper are used for this purpose. DE-OS 28 14 439
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discloses water-soluble lead compounds, particularly lead
acetate and lead lactate, added to an electrodeposition
bath.
According to EP-A-12 463, the catalysts used for
transesterification reactions are metal salts or metal com-
plexes which are soluble in liquid hydrocarbons, such as the
octoates or naphthenates of lead, zinc, calcium, barium,
iron, and a large number of other metals. EP-A-82 214 dis-
closes that octoates, naphthenates, borates or acetylaceton-
ates o cobalt r copper, lead, nickel, and manganese when
used as catalysts can be reàcted with the paint binder in
order to prevent separation during ultra~iltration. Accord-
ing to the prior art, paints based on these binders ars for-
mulated with a certain amount of lead ions which are intro-
duced either by using partially acid-soluble lead pigments
or by adding soluble lead salts.
In practice, iron compounds are not added as cata-
lysts in cathodically depositable paints since experience
has shown that if any iron ions are accidentally ~ormed in
the deposition system by the use o~ non-stainless steel
parts (so-called instaIlation corrosion), they will cause
the precipitated and stoved paint films to become extremely
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brittle. Surprisingly, it has now been found that iron-
acetylacetonate exhibits a specific catalytic effect in the
~` crosslinking of cationic paint binders which contain poly-
merizable ethylenic double bonds in the end or terminal
position.
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SUMMARY OF INVENT ION
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The present invention, therefore, is directed to
a process for catalyzing the crosslinking of cathodically
depositable paint binders which contain polymerizable ethy-
lenic double bonds in the end or terminal position, charac-
terized in that before water is added to the binder, 0.01
to 2.0% by weight, based on the non-volatile binder content,
preerably 0.1 to 2.0~ by weight of iron-acetylacetonate,
calculated as the metal, is added to the resin binder and
i5 homogeneously mixed therein.
The invention further relates to the cathodically
depositable electrodeposition paint catalyzed with the iron-
acetylacetonate.
.
-~ The process of the present invention makes it
possible to retain the good qualities of the paint films,
particularly from the standpoint of rapid curing time and
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2151/US-3140 ~ 3 1 2 1 ~ ~
corrosion resistance, while avoiding the environmentally
undesirable lead content of binders and without the aid of
anti-corrosion pigments. The corrosion tests on degreased
steel panels are substantially improved in many cases by
using the catalyst according to the present invention.
GENERAL DESCRIPTION OF INVENTION
The binder resins which are particularly suitable
for catalyzing according to the present invention are de-
scribed, for example, in U.S. Patent Nos. 4,238,594;
4,320,220; 4,147,676, and 4,174,332; and in EP-A-30 692.
Paint binders based on polycondensation or polyaddition
polymerization, more particularly binders based on modified
epoxy resins which have double bonds present in an end or
terminal position, such as binders where double bonds have
been introduced by reacting resins which carry OH-groups
with unsaturated monoisocyanates, e.g., reaction products of
equimolar quantities of a diisocyanate and a hydroxyalkyl-
(meth)acrylate, are particularly useful. The products har-
den essentially by thermal polymerization.
The iron-acetylacetonate can be added to the binder
as a 10 to 15~ solution in acetone. Preferably, the iron-
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2151/US-3140
acetylacetonate is added to the binder as a powder together
with the pigments and/or extenders, e.g., carbon black, alu-
minium silicate and titanium dioxide, dispersed therein and
the mixture ground. If desired, the catalyst can be added
to a resinous mixing component or to a pigment paste con-
taining a resinous dispersion medium before the resin com-
ponent or binder (system) is diluted with water. The iron-
acetylacetonate is added in a quantity, calculated as metal,
of from 0.01 to 2~0% by weight, based on the non-volatile
binder content. Preferably, the iron content is at least
0.1% by weight of metal, based on 100% resin solids.
The ormulation of cathodically depositable paints,
the processing thereof, particularly by the electrodeposi-
tion method, and the testing of the paint films are known to
those skilled in the art.
PRESENTLY PREFERRED EMBODIMENTS
The examples which follow illustrate the invention
without restricting its scope. All the quantities given in
parts or percentages refer to units by weight, unless other-
wise stated.
The resin binders used in the examples are binders
as disclosed in AT-PS 353,369, corresponding to U.S. Patent
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2151/US-3140 ~ 3 ~ 2 1 ~ ~
No. 4,174,332 issued November 13, 1979. These binders are
cathodically depositable resin combinations having a double
bond number of at least 0.8. The double bond number (DBn)
is defined as the number of double bonds in the end and side
positions for every 1000 molecular weight units. The number
of basic groups per thousand molecular weight units is given
by the BNz.
Binder Component (A)
(Al) In a reaction vessel equipped with stirrer, ther-
mometer, dropping funnel and reflux condenser, 1000 g of an
epoxy resin based on bisphenol-A and epichlorohydrin, having
an epoxy equivalent of about 500, are dissolved in 492 g of
ethylglycol acetate at 60 to 70C. 0~2 9 hydroquinone and
144 g of acrylic acid are added, and the temperature is
increased to 100 to 110C. The reaction is carried out at
this temperature until an acid number of less than 5 mg
KOH/g is obtained to provide a DBn value of 1.75. The reac-
tion product is then mixed at 60 to 70C with 652 g of a 70%
solution in ethylglycol acetate of a basic monoisocyanate
prepared from equimolar quantities of toluylene diisocyanate
and dimethylethanolamine and reacted until an NCO-value of
virtually zero is obtained. The binder has a DBn of 1.25
and a BNz of 1.1.
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2151/US-3140 ~ 31~
(A2) 520 g of an epoxy resin based on bisphenol-A and
epichlorohydrin, having an epoxy equivalent of about 260,
are dissolved in 465 9 ethylglycol acetate and reacted as
in (Al) with 564 g of a semiester of tetrahydrophthalic acid
anhydride and hydroxyethyl methacrylate to provide a DBn of
1.85. The reaction product was further reacted with 750 g
of the solution of a basic monoisocyanate as used in (Al) to
provide a D~n of 1.24 and a BNz of 1.24.
Binder ComPonent (B)
(Bl) In a reaction vessel fitted with stirrer, ther-
mometer, dropping funnel and reflux condenser, 400 9 of an
epoxy resin based on bisphenol-A and epichlorohydrin, having
an epoxy equivalent o about 200, are dissolved in 172 g of
ethylglycol acetate at 60 to 70C. Over a period of one
hour 210 9 of diethanolàmine are added dropwise at 90 to
120C. The mixture is then heated to 150C and reacted for
another hour. After this, the reaction product is reacted
at 60 to 70C with 830 g of a 70~ solution in ethylglycol
acetate of an unsaturated monoisocyanate prepared from
equimolar quantities of toluylene diisocyanate and hydroxy-
ethyl acrylate until an NCO-value of virtually zero is
obtained. The binder has a DBn of 1.68 and a BNz of 1.68.
(B2) 500 g of an epoxy resin based on bisphenol-A and
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epichlorohydrin, having an epoxy equivalent of about 250,
dissolved in 215 g of ethylglycol acetate, are reacted ac-
cording to the procedure of (Bl) with 210 g of diethanola-
mine and then reacted with 995 g of the monoisocyanate
solution which is used in (Bl). The binder has a DBn of
1.71 and a BNz of 1.42.
Binder Combinations
Binder combinations are prepared from components
and proportions based on 100% resin solids by mixing binders
at a temperature of not more than 70C as follows:
BM I : 100 parts (Al) + 33 parts (B2)
BM II : 100 parts ~A2) + 30 parts (Bl)
An iron-acetylacetonate catalyst is added to the
resin and mixed thoroughly therein. Thereafter, the binder
combinations are mixed with 40 millimole of acetic acid per
100 g o solid resin and diluted with water to give a solids
content o~ 12~ by weight. The clear varnish is deposited
onto phosphatized steel panels connected as the cathode of
an electrodeposition system. A film is deposited having a
dry film thickness of 20 to 22 microns.
The degree of crosslinking was tested after 24
hours' storage of the coated panels at ambient temperature
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131216~
using the so-called acetone test. The time shown is the
maximum duration after which the paint film affected by a
drop of acetone can still not be damaged using the finger-
nail.
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The salt spray test was carried out in accordancewith ASTM B 117-64 on degreased steel panels which had not
been pre-treated. After the time specified, there is corro-
sive damage up to a width of about 2 mm, measured from the
cross-shaped cut.
~ The stone-chipping resistance is tested by blasting
;~ sharp-edged steel shot (0.5 kg, 3 bar of compressed air)
against the paint surface twice, and then applying and re-
moving self-adhesive film. The remaining paint film adher-
ing is given as a percentage of the total surface area.
The results of the tests are shown in the table
which follows. Irrespective of the way in which the cata-
lyst is added, i.e., either as a solution or as a solid
substance with the pigment, virtually identical test results
are obtained.
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Binder/StovingAcetone Test ( Clear Varnish ) Seconds
Conditions% Iron as Iron-Acetylacetonate
(Min/C) 0 0.2 0.5 1.0 2.0
about about over over
BM I lS/160C 5 60 120 120 120
about over over over
BM I 15/180C 5 90 120 120 120
____________________________________________________________
about about over
BM II 15/160C5 10 30 75 120
about about over
BM II 15/180C5 20 45 120 120
Salt Spray Test (Clear Varnish) Hours
over
BM I 15/160C96 240 288 360 360
over over
BM I 15/180C168 240 360 360 360
_____ _________ ____________________________________________
BIM II 15/160C48 96 120 216 312
over
BM II 15~180C96 120 168 336 360
Stone-Chieping Resistance (Clear Varnish) %
BM I 15/180C60 ` 80 90 95 95
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BM II 15/180C 40 70 80 95 90
As will be apparent to one skilled in the art,
various modif ications can be made within the scope of the
aforesaid description . Such modif ications being within the
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i31216~
ability of one skilled in the art form a part of the present
: invention and are embraced by the appended claims.
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