U.S. patent application number 09/363652 was filed with the patent office on 2002-01-10 for propylene ureas and process for their preparation..
Invention is credited to GAUDL, KAI-UWE, GRAHE, GERWALD, LACHOWICZ, ARTUR.
Application Number | 20020004599 09/363652 |
Document ID | / |
Family ID | 7876069 |
Filed Date | 2002-01-10 |
United States Patent
Application |
20020004599 |
Kind Code |
A1 |
GAUDL, KAI-UWE ; et
al. |
January 10, 2002 |
PROPYLENE UREAS AND PROCESS FOR THEIR PREPARATION.
Abstract
Urea derivatives of formula 1 for the hardening of hydroxyl
group-containing polymers. 1 wherein each of R.sup.1-R.sup.7 is a
hydrogen atom or a linear or branched C.sub.1-C.sub.4-alkyl group,
preferably methyl, ethyl, n-propyl, isopropyl, n-butyl or isobutyl,
R.sup.1-R.sup.7 being identical or different, and R.sup.8 is a
linear or branched C.sub.1-C.sub.6-alkyl group, preferably methyl,
ethyl, n-propyl, isopropyl, n-butyl or isobutyl. The compounds 1
are prepared by reacting a compound 2 2 wherein R.sup.9 is a member
selected from the group consisting of --CHO, --CH(OH) --OR.sup.8
and --CH(OH).sub.2 with a urea derivative 3 3 optionally followed
by etherification of the reaction product with an alcohol X--OH,
wherein X is a linear or branched C.sub.1-C.sub.4-alkyl group.
Inventors: |
GAUDL, KAI-UWE; (BERLIN,
DE) ; LACHOWICZ, ARTUR; (BERLIN, DE) ; GRAHE,
GERWALD; (BERLIN, DE) |
Correspondence
Address: |
ARMSTRONG,WESTERMAN, HATTORI,
MCLELAND & NAUGHTON, LLP
1725 K STREET, NW, SUITE 1000
WASHINGTON
DC
20006
US
|
Family ID: |
7876069 |
Appl. No.: |
09/363652 |
Filed: |
July 30, 1999 |
Current U.S.
Class: |
544/318 |
Current CPC
Class: |
D06M 15/423 20130101;
C07D 239/10 20130101 |
Class at
Publication: |
544/318 |
International
Class: |
C07D 239/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 31, 1998 |
DE |
198 34 684.0 |
Claims
1. Compounds of the formula 1 21in which each of R.sup.1-R.sup.7
represents a hydrogen atom or a linear or branched
C.sub.1-C.sub.4-alkyl group, wherein R.sup.1-R.sup.7 may be
identical or different, and R.sup.8 represents a linear or branched
C.sub.1-C.sub.6-alkyl group.
2. Compounds according to claim 1, wherein the linear or branched
C.sub.1-C.sub.4-alkyl group is a methyl, ethyl, n-propyl,
isopropyl, n-butyl or isobutyl group.
3. A process for preparing compounds of the formula 1 22in which
each of R.sup.1-R.sup.7 represents a hydrogen atom or a linear or a
branched C.sub.1-C.sub.4-alkyl group, wherein R.sup.1-R.sup.7 may
be identical or different, and R.sup.8 represents a linear or
branched C.sub.1-C.sub.6-alkyl group, comprising reacting a
compound of the formula 2 23in which R.sup.9 is selected from the
group consisting of --CHO, --CH(OH) --OR.sup.8, and --CH(OH).sub.2
and R.sup.8 is defined as above, with a urea derivative of the
formula 3 24in which R.sup.1-R.sup.6 are defined as above, and the
reaction product obtained is optionally reacted with an alcohol of
the general formula X--OH, in which X represents a linear or
branched C.sub.1-C.sub.4-alkyl group.
4. A process according to claim 3, wherein the linear or branched
C.sub.1-C.sub.4-alkyl group is a methyl, ethyl, n-propyl,
isopropyl, n-butyl or isobutyl group.
5. A process according to claim 3, wherein the compound of the
formula 2 is reacted with the urea derivative of the formula 3 at a
temperature of 25-100.degree. C.
6. A process according to claim 4 wherein the compound of the
formula 2 is reacted with the urea derivative of the formula 3 at a
temperature of 25-100.degree. C.
7. A process according to claim 5, wherein the reaction is
performed at a temperature in the range of 25-70.degree. C.
8. A method according to claim 6, wherein the reaction is performed
at a temperature in the range of 25-70.degree. C.
9. A method of hardening a hydroxyl group-containing polymer, said
method comprising reacting said hydroxyl-group containing polymer
with a compound of the formula 1 25in which each of R.sup.1
-R.sup.7 represents a hydrogen atom or a linear or branched
C.sub.1-C.sub.4-alkyl group, preferably methyl, ethyl, n-propyl,
isopropyl, n-butyl or isobutyl, wherein R.sup.1-R.sup.7 may be
identical or different, and R.sup.8 represents a linear or branched
C.sub.1-C.sub.6-alkyl group.
10. A cross-linking agent for hardening hydroxyl group-containing
polymers, comprising at least one propylene urea of the formula 1
26in which each of R.sup.1-R.sup.7 represents a hydrogen atom or a
linear or branched C.sub.1-C.sub.4-alkyl group, wherein
R.sup.1-R.sup.7 may be identical or different, and R.sup.8
represents a linear or branched C.sub.1-C.sub.6-alkyl group.
Description
[0001] The invention relates to new urea derivatives of the formula
1, 4
[0002] in which each of R.sup.1-R.sup.7 represents a hydrogen atom
or a linear or branched C.sub.1-C.sub.4-alkyl group, in particular
methyl, ethyl, n-propyl, isopropyl, n-butyl or isobutyl, wherein
R.sup.1-R.sup.7 may be identical or different, and R.sup.8
represents a linear or branched C.sub.1-C.sub.6-alkyl group, in
particular methyl, ethyl, n-propyl, isopropyl, n-butyl or isobutyl.
The invention also relates to a process for preparing compounds of
the general formula 1. In addition, the invention relates to the
use of compounds of the formula 1 for hardening hydroxyl
group-containing polymers.
[0003] Reaction products of ethylene ureas and glyoxylic acid
derivatives are known from U.S. Pat. No. 4,770,668. They are used
to cross-link hydroxyl group-containing polymers, in particular for
cross-linking hydroxyl groups within cellulose fibers. These
cross-linking agents are prepared at temperatures of
100-140.degree. C. In this temperature range oligomerization of
these reactive cross-linking agents already takes place because
they can also react with themselves, such as is the case, e.g., for
urea/formaldehyde amino resins (R. Wegler in Houben-Weyl "Methoden
der organischen Chemie", Volume 14/2 (1963), pages 320-328).
Oligomerization causes a reduction in effectiveness as
cross-linking agents, particularly when cross-linking cellulose
fibers, since the oligomerized cross-linking agent can no longer
penetrate sufficiently far into the cellulose fiber due to its
increased weight and size.
[0004] Furthermore, the high temperatures of preparation also lead
to some discoloration of the products (see Examples 4.2, 4.4 and
4.5 in U.S. Pat. No. 4,770,668), which is a disadvantage when they
are used to coat or impregnate colorless materials.
[0005] The object of the invention is therefore to overcome the
defects in the prior art mentioned above, in particular the
production of oligomeric fractions and discoloration, and to
provide improved cross-linking agents based on urea which are free
of the disadvantages mentioned above.
[0006] This object is achieved by the invention. The invention
provides compounds of the formula 1, 5
[0007] in which each of R.sup.1-R.sup.7 represents a hydrogen atom
or a linear or branched C.sub.1-C.sub.4-alkyl group, in particular
methyl, ethyl, n-propyl, isopropyl, n-butyl or isobutyl, wherein
R.sup.1-R.sup.7 may be identical or different, and R.sup.8
represents a linear or branched C.sub.1-C.sub.6-alkyl group, in
particular methyl, ethyl, n-propyl, isopropyl, n-butyl or
isobutyl.
[0008] The invention also provides a process for preparing
compounds of the formula 1 6
[0009] in which each of R.sup.1-R.sup.7 represents a hydrogen atom
or a linear or branched C.sub.1-C.sub.4-alkyl group, in particular
methyl, ethyl, n-propyl, isopropyl, n-butyl or isobutyl, wherein
R.sup.1-R.sup.7 may be identical or different, and R.sup.8
represents a linear or branched C.sub.1-C.sub.6-alkyl group, in
particular methyl, ethyl, n-propyl, isopropyl, n-butyl or isobutyl,
which is characterized in that a compound of the formula 2 7
[0010] in which R.sup.9 represents a member selected from the group
comprising --CHO, --CH(OH) --OR.sup.8 and --CH(OH).sub.2 and
R.sup.8 is defined as above, is reacted with a urea derivative of
the formula 3, 8
[0011] in which R.sup.1-R.sup.6 are defined as above, and the
reaction product obtained is optionally reacted with an alcohol of
the formula X--OH, in which X represents a linear or branched
C.sub.1-C.sub.4-alkyl group.
[0012] The invention also provides the use of compounds of the
formula 1, 9
[0013] in which each of R.sup.1-R.sup.7 represent a hydrogen atom
or a linear or branched C.sub.1-C.sub.4-alkyl group, preferably
methyl, ethyl, n-propyl, isopropyl, n-butyl or isobutyl, wherein
R.sup.1-R.sup.7 may be identical or different, and R.sup.8
represents a linear or branched C.sub.1-C.sub.6-alkyl group,
preferably methyl, ethyl, n-propyl, isopropyl, n-butyl or isobutyl,
for hardening hydroxyl group-containing polymers.
[0014] As specified above, new compounds of the formula 1 according
to the invention, 10
[0015] in which the substituents R.sup.1-R.sup.7 and R.sup.8 are
defined as above are provided. Examples of compounds in accordance
with the present invention which are defined by the formula 1 given
above, are as follows:
[0016] methyl
hydroxy-[3-(hydroxy-methoxycarbonyl-methyl)-2-oxo-tetrahydro-
-pyrimidin-1-yl] acetate,
[0017] methyl
hydroxy-[3-(hydroxy-ethoxycarbonyl-methyl)-2-oxo-tetrahydro--
pyrimidin-1-yl] acetate,
[0018] butyl
hydroxy-[3-(hydroxy-butoxycarbonyl-methyl)-2-oxo-tetrahydro-p-
yrimidin-1-yl] acetate,
[0019] methyl
methoxy-[3-(methoxy-methoxycarbonyl-methyl)-2-oxo-tetrahydro-
-pyrimidin-1-yl] acetate,
[0020] ethyl
ethoxy-[3-(ethoxy-ethoxycarbonyl-methyl)-2-oxo-tetrahydro-pyr-
imidin-1-yl] acetate,
[0021] butyl
butoxy-[3-(butoxy-butoxycarbonyl-methyl)-2-oxo-tetrahydro-pyr-
imidin-1-yl] acetate,
[0022] methyl
hydroxy-[3-(hydroxy-methoxycarbonyl-methyl)-5,5-dimethyl-2-o-
xo-tetrahydro-pyrimidin-1-yl] acetate and,
[0023] methyl
hydroxy-[3-(hydroxy-methoxycarbonyl-methyl)-5,5-dimethyl4iso-
propyl-2-oxo-tetrahydro-pyrimidin-1-yl] acetate.
[0024] Preferred examples of compounds according to the invention
having the formula 1 mentioned above are methyl
hydroxy-[3-(hydroxy-methoxycarbo-
nyl-methyl)-2-oxo-tetrahydro-pyrimidin-1-yl] acetate, ethyl
hydroxy-[3-(hydroxy-ethyloxycarbonyl-methyl)-2-oxo-tetrahydro-pyrimidin-1-
-yl] acetate and butyl
hydroxy-[3-(hydroxy-butoxycarbonyl-methyl)-2-oxo-te-
trahydro-pyrimidin-1-yl] acetate.
[0025] The compounds according to the invention are prepared by
first reacting a compound of the formula 2 11
[0026] in which R.sup.9 and R.sup.8 are defined as above, with a
urea derivative of the formula 3 12
[0027] in which R.sup.1-R.sup.6 are defined as above.
[0028] Preferred examples of starting compounds of the formula 2
are:
[0029] methyl glyoxylate,
[0030] methyl glyoxylate hydrate,
[0031] ethyl glyoxylate,
[0032] propyl glyoxylate,
[0033] butyl glyoxylate,
[0034] methyl glyoxylate methyl-hemiacetal,
[0035] ethyl glyoxylate ethyl-hemiacetal,
[0036] propyl glyoxylate propyl-hemiacetal,
[0037] butyl glyoxylate butyl-hemiacetal.
[0038] Some of the glyoxylates and glyoxylate alkyl-hemiacetals can
be obtained commercially or they may be prepared using known
methods in organic chemistry such as, e.g., by esterification of
glyoxylic acid with alcohols or by ozonolysis of dialkyl maleates.
Hydrates such as, e.g., methyl glyoxylate hydrate and butyl
glyoxylate hydrate may be prepared from methyl or butyl tartrate by
oxidative C--C cleavage using periodic acid (L. D. M. Lolkema et
al., Tetrahedron 50 (24) (1994) 7115-7128).
[0039] Compounds of the formula 3 are obtainable commercially such
as, e.g., propylene urea. Otherwise they may be prepared using
known methods in organic chemistry such as, e.g., by reacting
amines with carbon dioxide or phosgene (C. Ferri, "Reaktionen der
Organischen Chemie", Georg Thieme Verlag Stuttgart, 1978, page
657). Examples of these types of substituted propylene ureas
are:
[0040] 5-methyl-2-oxo-tetrahydro-pyrimidine,
[0041] 5,5-dimethyl-2-oxo-tetrahydro-pyrimidine and
[0042] 5,5-dimethyl-4-isopropyl-2-oxo-tetrahydro-pyrimidine
[0043] (see GB patent 1 173 432).
[0044] The reaction of propylene ureas of the formula 3 with
derivatives of the formula 2 can be performed in the temperature
range from room temperature to elevated temperatures. In general a
temperature range of 25-100.degree. C. is expedient. Reaction
temperatures in the range of 25-70.degree. C. are preferred, in
particular 50-70.degree. C. In the temperature range of
70-100.degree. C. no noticeable production of secondary products is
observed. Reaction above 70.degree. C., however, provides no
further advantages with respect to yield or purity of the
compounds.
[0045] Catalysts which are used according to the prior art for
catalyzing reactions between ureas and carbonyl compounds, such as,
e.g., inorganic bases such as sodium carbonate or sodium hydroxide
are not required. The reaction may generally be performed without a
solvent since compounds of the formula 2 are liquid. If a solvent
is used, then any organic solvent which is inert towards aldehydes
and ureas under the reaction conditions mentioned above are
suitable; ethyl acetate or methylethyl ketone or toluene are
preferred. The reaction is performed stoichiometrically, or
preferably with a small excess of the more easily separated
component. A molar ratio of 2.01-2.40 to 1, with respect to the
component of the formula 2 to the component of the formula 3, is
particularly advantageous. Reaction times are generally 1 to 5
hours.
[0046] In the following, the different reactions leading to
compounds according to the invention, depending on the starting
compound of the formula 2 which is used, are described in more
detail.
[0047] 1. When reacting a free aldehyde of the formula 2
(R.sup.9=--CHO) with a urea derivative of the formula 3 no cleavage
products are formed. 13
[0048] 2. When reacting a glyoxylate alkyl-hemiacetal of the
formula 2 (R.sup.9=--CH(OH) --OR.sup.8) with a urea derivative of
the formula 3, cleavage products, such as, e.g., alcohols, are
produced which can be removed under reduced pressure. 14
[0049] 3. When reacting a stable hydrate of a glyoxylic acid
derivative of the formula 2 (R.sup.9=--CH(OH).sub.2) with a urea
derivative of the formula 3, water is produced as a cleavage
product which may be removed under reduced pressure. 15
[0050] The reaction products obtained are usually isolated by
precipitating in a solvent. Solvents for this purpose which readily
dissolve compounds of the formula 2 are used in order to separate
the excess of glyoxylic acid derivative.
[0051] Suitable solvents are, e.g., ketones, esters, aromatic
hydrocarbons, preferably acetone, ethyl acetate or toluene. The
products obtained are colorless and generally crystalline, water
soluble and monomeric. The purity is more than 90%, often more than
95%. Products with longer alkyl chains are produced as pale oils
and are only slightly water-soluble. The product may be purified by
removing excess reactants by distillation under reduced
pressure.
[0052] If the compounds according to the invention for use in
mixtures are intended to be soluble in non-polar organic solvents,
the reaction products obtained in the first stage may be etherified
with an alcohol (X--OH, wherein X represents a linear or branched
C.sub.1-C.sub.4-alkyl group, in particular methyl, ethyl, n-propyl,
isopropyl, n-butyl or isobutyl). This leads to products of the
formula 1 in which R.sup.7 represents a linear or branched
C.sub.1-C.sub.4-alkyl group, in particular methyl, ethyl, n-propyl,
isopropyl, n-butyl or isobutyl and R.sup.1-R.sup.6 and R.sup.8 are
defined as above. 16
[0053] For etherification, the reaction products obtained which
contain free hydroxyl groups are reacted with a 2 to 10-fold excess
of alcohol, preferably 2 to 5-fold, in the presence of an acid
catalyst. Methanol, ethanol, propanol, isopropanol, n-butanol and
isobutanol are preferably used as alcohols. Medium to strong acids
may be used as catalysts, preferably sulfuric acid, phosphoric
acid, methane-sulfonic acid, chlorosulfonic acid, benzenesulfonic
acid, p-toluenesulfonic acid, naphtholsulfonic acid, chloroacetic
acid or oxalic acid. The water produced during reaction is
distilled off together with excess alcohol. If the alcohol used is
not miscible with water, such as, e.g., n-butanol, it is distilled
off azeotropically.
[0054] The compounds of the formula 1 according to the invention
produce d from propylene ureas and glyoxylate derivatives are
colorless and thus advantageously differ from some of the reaction
products described in U.S. Pat. No. 4,770,668 produced from
ethylene ureas and glyoxylate derivatives, which are often dark
colored. Analytical methods such as, e.g., gel permeation
chromatography show that the compounds according to the invention
contain no oligomeric fractions and are thus highly suitable for
hardening polymers which contain hydroxyl groups.
[0055] Examples of hydroxyl group-containing polymers are hydroxyl
group-containing polyacrylates and polyester polyols. The
preparation of these types of polymers is known and is part of the
general prior art. The polymers may be present as emulsions,
dispersions, as solutions in water or organic solvents or as
solids. Hardening the polymers with the compounds according to the
invention of the formula 1 may be performed by reacting the
compounds according to the invention with the polymers in any of
the forms mentioned above, in the temperature range of
25-180.degree. C., preferably 100-150.degree. C. This cross-linking
reaction may also be performed in the presence of an acid catalyst
which accelerates the reaction. Organic acids or Lewis acids such
as benzenesulfonic acid, p-toluenesulfonic acid,
naphthalenesulfonic acid, oxalic acid, chloroacetic acid,
methanesulfonic acid, citric acid, magnesium chloride, ammonium
tetrafluoroborate and 2-hydroxyethylamino hydrochloride are
suitable for this purpose.
[0056] The invention is explained by the following examples to
which the invention is not limited.
EXAMPLE 1
Preparation of methyl
hydroxy-[3-(hydroxy-methoxycarbonyl-methyl)-2-oxo-te-
trahydro-pyrimidin-1-yl] acetate.
[0057] 17
[0058] 100.0 g (1.0 mol) of propylene urea were mixed with 245.0 g
(2.04 mol) of methyl glyoxylate methyl-hemiacetal (manufacturer DSM
Chemie Linz). The mixture was then stirred for 4 hours at
60.degree. C. 500 ml of acetone were then added to the mixture, it
was stirred and the precipitate was filtered off and dried.
[0059] Yield: 193.3 g
[0060] Melting point: 129.degree. C.
[0061] .sup.1H-NMR (300 MHz, D.sub.2O): .delta.=5.61 (s, 2H), 4.65
(s, 6H), 3.65 (s, 6H), 3.40 (m, 2H), 3.25 (m, 2H), 1.95 (m,
2H).
[0062] .sup.13C-NMR (300 MHz, D.sub.2O): .delta.=172.3 (C.dbd.O),
157.5 (C.dbd.O), 79.2 (C--H), 54.4 (O--CH.sub.3), 42.2, 20.5.
EXAMPLE 2
Preparation of ethyl
hydroxy-[3-(hydroxy-ethoxycarbonyl-methyl)-2-oxo-tetr-
ahydro-pyrimidin-1-yl] acetate
[0063] 18
[0064] 100.0 g (1.0 mol) of propylene urea were mixed with 408.0 g
(2.00 mol) of ethyl glyoxylate (50% solution in toluene,
manufacturer Fluka). This was stirred for 4 hours at 65.degree. C.
The solvent toluene was then removed under reduced pressure. The
product was then obtained as a colorless residue.
[0065] Yield: 501 g
[0066] .sup.1H-NMR (300 MHz, d.sup.6-acetone): .delta.=5.54 (d,
2H), 4.23 (m, 4H), 3.45 (m, 2H), 3.30 (q, 4H), 1.05 (t, 6H).
[0067] .sup.13C-NMR (300 MHz, d.sup.6-acetone): .delta.=171.5
(C.dbd.O), 156.1 (C.dbd.O), 79.8 (C--H), 66.4 (O--CH.sub.2) , 42.4,
20.6, 15.8 (CH.sub.3).
EXAMPLE 3
Preparation of butyl
[3-(hydroxy-butoxycarbonyl-methyl)-2-oxo-tetrahydro-p-
yrimidin-1-yl] acetate
[0068] 19
[0069] 16.0 g (0.16 mol) of propylene urea were mixed with 49.4 g
(0.38 mol) of butyl glyoxylate (manufacturer: Hoechst France) .
This mixture was stirred for 3 hours at 60.degree. C., wherein the
urea went into solution. A pale colored oil was produced. Then the
excess of butyl glyoxylate was removed under vacuum (p=0.1 mbar) at
50.degree. C.
[0070] Yield: 58.3 g
[0071] .sup.1H-NMR (300 MHz, d.sup.6-acetone): .delta.=551 (d, 2H)
, 4.20 (m, 4H) , 3.45 (m, 2H), 3.30 (m, 2H), 1.97 (m, 2H), 1.65 (m,
4H), 1.45 (m, 4H), 0.95 (t, 6H)
[0072] .sup.13C-NMR (300 MHz, d.sup.6-acetone): .delta.=171.3
(C.dbd.O) , 156.2 (C.dbd.O), 719.5 (C--H), 66.0 (O--CH.sub.2) ,
42.4, 31.0, 23.5, 19.9, 13. (CH.sub.3)
EXAMPLE 4
Etherification of the Hydroxyl Groups in the Products Obtained in
Example 1 with n-butanol
[0073] 82.5 g (0.29 mol) of the product from Example 1 were mixed
with 214.6 g (2.40 mol) of n-butanol and then 1.0 g of
p-toluenesulfonic acid was added. Water which was produced during
reaction was removed by azeotropic distillation. After removal of
the water had terminated, the mixture was neutralized with caustic
soda solution and the excess n-butanol removed by distillation. The
product was obtained as a colorless, viscous residue which was
readily soluble in cyclohexane. Gas chromatographic analysis showed
complete etherification of the hydroxyl groups.
[0074] Yield: 114 g
EXAMPLE 5
Preparation of methyl
hydroxy-[3-(hydroxy-methoxycarbonyl-methyl)-5,5-dime-
thyl-2-oxo-tetrahydro-pyrimidin-1-yl] acetate
[0075] 20
[0076] 128.0 g (1.0 mol) of
5,5-dimethyl-2-oxo-tetrahydro-pyrimidine (prepared from
1,3-diamino-2,2-dimethyl-propane and urea) were mixed with 245.0 g
(2.04 mol) of methyl glyoxylate methyl-hemiacetal (manufacturer DSM
Chemie Linz). This was stirred for 4 hours at 70.degree. C. 500 ml
of acetone were added, the mixture was stirred and the precipitate
filtered and dried.
[0077] Yield: 206 g
[0078] Melting point: 110-114.degree. C.
[0079] .sup.13C-NMR (300 MHz, d.sup.6-DMSO): .delta.=173.3
(C.dbd.O), 155.5 (C.dbd.O), 79.2 (C--H), 55.5 (O--CH.sub.3), 41.2,
31.5, 26.8.
EXAMPLE 6
Cross-linking with Hydroxyl Group-containing Polymers
[0080] 13.0 g of the product from Example 4 and 0.7 g of
p-toluenesulfonic acid were added to 100 g of a 60 % resin solution
consisting of a hydroxyl group-containing polyacrylate (having the
composition: methyl methacrylate/ethylhexyl acrylate/hydroxyethyl
acrylate =50/25/25) and methylethyl ketone as solvent. A 50 .mu.m
thick layer of cross-linking mixture was applied to a steel sheet
and cured for 20 minutes at a temperature of 140.degree. C. The
hardened film had a gel fraction of 96% and a very good solvent
resistance towards methylethyl ketone and xylene.
[0081] Other embodiments of the present invention will be apparent
to those skilled in the art from consideration of the specification
and practice of the invention disclosed herein. It is intended that
the specification and examples be considered as exemplary only,
with a true scope and spirit of the invention being indicated by
the following claims.
* * * * *