Note: Descriptions are shown in the official language in which they were submitted.
Mo3554
- LeA 27,591
AQUEOUS, CLEAR, COATING COMPOSITION
CONTAINING EMULSION COPOLYMERS AND
COATED SUBSTRATES PREPARED THEREFROM
BACKGROUND OF THE INVENTION
S Field of the Invention
This invention relates to aqueous, clear, coating
compositions containing mixtures of certain emulsion copolymers
and melamine resins as the binder and their use for preparing
coated substrates, particularly the uppermost top coat for
motor vehicle bodies.
Description of the Invention
The preparation of coatings for motor vehicles may be
carried out by any of various processes conventionally used
industrially. Although the primer is generally applied in the
aqueous phase by electro dip priming, both water dilutable and
organically dissolved systems may be used as fillers and base
coat;ngs (base coa~). Water dilutable coating systems are
preferred for reasons of safety in work and environmental
protection as well as for saving raw materials, but at present
there are various technical problems in achieving a build up of
motor vehicle coatings from the aqueous phase. In particular,
there is no technically useful solut;on to the problem of
applying the aqueous clear coating (clear coat) as the fourth
layer over base coats (metallic or pigmented) so that a
complete build up of coatings from the aqueous phase has not
previously been achieved.
Although numerous publications deal with the
preparation of aqueous binders based on copolymers of
olefinically unsaturated compounds, the present invention for
the first time provides an aqueous clear coating which
satisfies all of the requirements of an aqueous clear coat for
coating motor vehicles in serîes.
US-PS 3,611,827 (Ashland Oil) relates to a process
for the preparation of a water dispersible acrylic coating
35376TWR201~
compound which is not an emulsion polymer. In the opinion of
the authors of DE-OS 2,357,152, th;s product does not satisfy
the requirements of manufacturers of passenger cars and trucks
for a first class aqueous coating.
DE-OS 2,357,152 (US-PS 4,164,488) describes ~queous,
heat hardening acrylic coating compositions which are
said to be the first aqueous systems to provide suitable
coatings for motor vehicles. The special suitability of this
product is said to be particularly apparent when it is used as
a pigmented coating binder but the specification does not
describe the particular use or suitability of this product as a
clear coating. It is evident from the description that the
products prepared according to DE-OS 2,357,152 are solution
polymers.
A partial solubility of the completed polymer in watPr is
achieved by special measures in providing the composition. It
is stated that due to a COOH:OH group ratio of from 1:0.2 to
1:1.8, about 30 to 50% by weight of the polymer is in a
dispersed form while the remaining 50 to 70% are soluble and
present in a dissolved form in the aqueous medium.
US-PS 3,862,071 describes similar systems of
partially soluble, partially dispersed polymers containing at
least 0.25% by weight of a dispersed aluminum bronze. This
application also shows that thermosetting motor vehicle
coatings based on acrylic resins cross-linked with amino resins
provide particularly useful results if partially water-soluble
polymers are used.
This principle is applied in DE-PS 2,918,067 to a
combination of special emulsion polymers. These aqueous
coating systems are also cross-linked with amino resins but the
products are unsatisfactory in various respects, e.g., the
hardness of the films in sp;te of the high stoving temperature,
the resistance to solvents or the adherence to the underlying
surface. It is clear from the description that the polymer
amino resin mixtures according to the invention are to be used
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in particular for the preparation of pigmented coatings and
there is no indication that the mixtures are particularly
suitable for clear coats, let alone clear coats for motor
vehicles.
Aqueous coating systems based on acrylate emulsion
polymers and melamine resins are described in DE-OS 2,531,802.
These products are said to be superior, for example, to the
products of US-PS 3,862,071 (see above~. The acrylic polymers
of DE-OS 2,531,802, however, only differ from those of US-PS
3,862,071 in that the dispersed component is prepared by the
emulsion polymerization technique and the binder mixture
contains a lower percentage of water-soluble acrylic
copolymers; the product according to DE-OS 2,531,802 does not
dispense with such a soluble component.
i~ European Patent Application EP-A-0,253,251 mentions
clear coatings based on acrylic resins with aminoplasts as
second component. In the presence of solubili~ing or
dispersing carboxylate groups, these coatings may be applied as
aqueous systems. Since these products must be capable of
developing deep drawable coatings if applied from tins, no
functional groups such as hydroxyl groups are used in the
acrylic polymers, i.e., the copolymers contain no hydroxyalkyl
acrylates or methacrylates as monomer units.
In EP-A-0,029,597, the teaching oF DE-O~ ~,357,152 by
the same applicant is varied. While otherwise similar polymers
are used, UV stabilizers are used in add;tion for the purpose
of improving the resistance to weathering, e.g., in clear
coatings. In addition, the patent application also states that
for obtaining good coating properties the products are required
to contain considerable proportions of acrylic polymers
dissolved in water in addition to 50% of d;spersed components.
The Applicant also emphasizes that the product must not contain
external emulsifiers.
Numerous technical instructions for the preparation
of optimum aqueous acrylic coating compositions, all pointing
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in the same direction, may be found in the article by
Y.Nakayama, T.Watanabe and I.Toyomoto (Kansai Paint) "High
Performance Coatings from Blends of Emulsions and Water-Soluble
Resins" in the Journal of Coatings Technology, V01.569 No.716,
September 1984, page 73 et seq. The article emphasizes the
necessity of mixing aqueous, dispersible acrylic polymers with
water-soluble acrylic polymers and points out the harmfulness
of surface-active additives such as emulsifiers (surfactants)
for the water resistance and adherence to the underlying
surface in the presence of high moisture contents. So-called
soap-free acrylic emulsions are therefore recommended and
produced.
The disadvantage of aqueous emulsion polymers
prepared with low molecular weight emulsifiers is also
particularly mentioned in EP-A-0,001,489. The presence of the
emulsifiers required for stabilizing the polymer dispersion
considerably reduces, for example, the resistance of the
coating films to the influences of moisture and weather. For
overcoming these technical disadvantages, the preparation of
so-called "sterically stabilized" dispersion polymers is
described in EP-A-0,001,489. In the application the polymers
are not prepared in an aqueous phase or aqueous emulsion, but
rather are converted into an aqueous dispersion only after
completion of the various steps of polymerizatibn which are to
be carried out in non-aqueous solvents.
This idea is also present in EP-B-0,038,127.
Pseudoplastic or thixotropic microgel emulsions based on
acrylate copolymers cross-linked with amino resins are
described for the aqueous metallic base coat in EP-B-0,038,127.
Various possibilities are described in EP-B-0,038,127
for the acrylate binders for the clear coats applied over the
metallic coating:
1) Solution polymers in non-aqueous solvents (Examples 1, 2,
4, 5)
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2) Solution polymers prepared in non-aqueous, water miscible
solvents such as isopropanol and subsequently converted
into an aqueous solution (Example 3)
3) Aqueous dispersion polymers (no Example, column 14, lines
22-29).
The use of an acrylic polymer prepared by the
emulsion polymerization technique is also suggested as a
possib;lity for the clear coat if it is to be applied from the
aqueous phase (column 14, lines 30-32, no Example). No details
are gi~en as to the technical procedures which would be
necessary for preparing a workable clear coating (additives,
cross-linking agents and auxiliary agents used). Further, the
examples of practical applica~ion give no indication that
aqueous emulsion polymers, which are not in the form of
1, microgels, are particularly useful.
The acrylate solution described in EP-B-0,038,127 is
prepared by a two-stage and therefore complicated manufacturing
process and is not an emulsion polymer. In view of the
numerous doubts raised inter alia in EP-A-0,001,489 by the same
applicant against the use of emulsifiers in emulsion polymers
and against systems which are dispersed in water alone, without
the presence of substantial quant;ties of dissolved polymers,
it may be inferred from EP-B-0,038,127 in conjunction with the
remainder of the art that no technically useful aqueous clear
coat for motor vehicles comparable to the clear coatings
according to the invention may be obtained.
It is known from DE-OS 3,803,522 that water
dispersible acrylic polymers used in combination with special
hydrophobic melamine resins having molecular weights of at
least 500 as cross-linking agents can be worked up to produce
pigmented coating systems, in particular systems containing
metallic pigments. According to the teachings of ~E-OS
3,802,522, these systems are particularly suitable for use as
the lower layer of two coats to be applied wet-on-wet. There is
no indication as to the suitability of the coating systems for
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clPar coats. Instead, the pigment is specif;cally claimed as
integral component of the coating composition. The only clear
coats mentioned ;n DE-OS 3,803,522 are products d;ssolved in
organic solvents.
The binder systems of DE-OS 3,803,522 (acryl;c
copolymer + hydrophobic, h;gh molecular weight melamine resin)
g;ve poor gloss values in clear coat;ngs when the pigment ;s
omitted and do not satisfy practical processing requ;rements
due to the technical complication of incorporating the
hydrophob;c melam;ne resin into the aqueous system. Thus,
there is no indication that a useful clear coat system could be
obtained according to DE-OS 3,803,522.
EP-A-0,287,144 describes acrylic polymers prepared by
at least two stages of emuls;on polymerization and having a
special composition adapted exclusively to their use as
metallic base coats. Apart from the complicated method of
preparation, the specification contains no indication of the
use of the products as clear coats.
DE-OS 3,734,755 descr;bes polyacrylate emulsions and
dispersions as temporary surface protection with a reduced
tendency to corrode. No teaching ~or the preparation of
aqueous clear coats can be derived from these non-crosslinked
coatings which are readily removed again from the substrate.
Water-soluble acrylic stoving coatings are described
in DE-OS 2,840,574. These products are solution polymers for
metal effect coatings but due to the insufficient metallic
effect and the complicated method of preparation, they have not
become established industrially. These products are unsuitable
for use as aqueous clear coats due to the unfavorable
rheological properties of the aqueous solutions, which must be
compensated for by the addition of considerable quantities of
organic auxiliary solvents, which is undesirable from an
environmental point of view. These products are also
unsuitable due to the hydrophilic character of the binder
system, which is a disadvantage, for example for wet-on-wet
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application on an aqueous base coat7 because of ~he faults
produced in the film and the li~itation of the products to
special~ selected cross-linker resins.
Summarizing, it is found that technically useful
aqueous clear coatings for motor vehicles have not prevlously
been described. Accordingly, it is an object of the present
invent;on to provide aqueous clear coating compositions which
overcome the deficiencies of the prior art.
This object may be achieved in accordance with the
present invention as described hereinafter.
SUMMARY OF THE INVENTION
The present ;nvention relates to aqueous, clear,
coating compositions containing
A) 60 to 90% by weight, based on the total weight of
components A) and B), of an emulsion copolymer which is
the reaction product of
a) O to 50% by weight of styrene, ~-methyl-styrene or a
mixture of these monomers,
b) O to 50% by weight of methyl methacrylate7
c) 10 to 45% by weight of at least one alkyl acrylate
having 1 to 8 carbon atoms in the alkyl group,
d) 5 to 30% by weight of hydroxyethyl-, 2- or
3-hydroxypropyl- or 2-, 3- or 4-hydroxybutyl-
(meth)acrylate or any mixture of these monomers,
e) 1 to 15% by weight of acrylic acid, methacrylic acid
or any mixture of these acids and
f~ O to 15% by weight of other comonomers,
wherein
i ) O to 100, preferably 0 to 80 and most preferably 0 to 50% of ~e carboxyl
3Q groups are neutralized with an aliphatic amine or with ammon~
ii) the percentages a) - f) adding up to 100, based on
the total weight of a) - f) and
iii) the combined weight of monomers a) and b) being
10 - 70% by we;ght, based on the total weight of
monomers a) - f),
Mo3554
B3 10 to 40% by weight, basPd on the total weight of
components A) and B), of a melamine resin and
C) water.
The present invention also relates to coated
substrates, particularly coated motor vehicle substrates,
prepared from these aqueous, clear, coating compositions.
DETAILED DESCRIPTION OF THE INYENTION
Based on the weight of components A) and B), the
aqueous, clear, coating compositions according to the invention
contain 60 to 90% by weight, preferably 65 to 85% by weight of
component A) and 10 to 40% by weight, preferably 15 to 35% by
weight of component B).
The mixture of components A) and B) ;s the primary
binder component according to the present inven~ion. Component
C) may include, in addition to water, known auxil;ary agents
and additives such as additional cross-linking agents,
auxiliary rheological agents, wetting agents, catalysts,
organic solvents and light protect;ve agents.
Component A), which is essential for the invention,
is based on an emuls;on copolymer of the above-mentioned
monomers a) to f). Monomer c) includes methyl acrylate, ethyl
acrylate, n-butyl acrylate, n-hexyl acrylate and n-octyl
acrylate. Optional monomer f) includes vinyl toluene; alkyl
methacrylates having from 2 to 18 carbon atoms in the alkyl
group; alkyl acrylates having 9 to 18 carbon atoms in the alkyl
group; N-vinylpyrrolidone; vinyl-alkyl-ketones having 1 to 4
carbon atoms; vinyl-alkyl-carboxylates having 1 to 18 carbon
atoms in the alkyl group; alkyl esters of maleic, fumaric or
itaconic acid in each case having 1 to 4 carbon atoms in the
alkyl group; vinyl sulphonic acid salts and mixtures thereof.
Particularly preferred emulsion copolymers A) are
based on the reaction product of
a) 0 to 40, most preferably 20 to 40% by weight of s~yrene
b) 5 to S0, most preferably 5 to 20% by weight of me~yl methaclylate,
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c) 25 to 40% by weight of at least one alkyl acrylate having
4 to 8 carbon atoms in the alkyl group,
d) 12 to 20% by weight of hydroxyethyl-, 2- or
3-hydroxypropyl-methacrylate or mixtures of these
monomers,
e~ 2 to 10% by weight of methacrylio acid and
f) O to 15% by weight of other comonomers
wherein the combined weight of monomers a) and b) being 35 -
50, pre~erably 35 - 45% by weight, based on the total weight of monomers a) - f).
Preferably, monomers d) and e~ are used in an amount
which corresponds to an equivalent ratio of carboxyl groups to
hydroxyl groups of 1:1.5 to 1:4.5, more preferably 1:1.9 to
1:4.5.
The preparation of emulsion polymer A) may be carried
out by the conventional emulsion polymerization process as
described e.g. in Houben-Weyl, Methoden der Organischen Chemie,
Supplements to the 4th Edition, Volume E 20/Part 1, pages
218-313. The known polymerization auxiliaries are used when
the emulsion polymers are prepared in an aqueous medium.
20 . The quantity of water is generally calculated to
result in aqueous polymer emulsion having solids contents of 20
to 60% by weight, preferably 35 to 50% by weight.
The emulsion polymers thus prepared and present as
aqueous emulsions are combined with the other components to
produce the clear coating compositions of the present
invent;on.
The cross linking agents B) are melamine resins which
may be unetherified or partially or completely etherified with
saturated alcohols containing 1 to 4 carbon atoms. Preferred
melamine resins are fully methyl etherified melamine resins as
described, for example, in FR-PS 943,411 sr in 7he Chemistry of
Organic Filmformers by D.H.Solomon, John Wiley & Sons, Inc.,
New York, 1967, pages 235r240.
It is in many cases advisable to use acid catalysts
to ensure adequate cross-linking of the cvating films. The
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nature and concentration of these catalysts will depend on the
stoving conditions and the nature of the melamine resins.
Suitable acid catalysts include alkyl benzene sulphonic acids
such as toluene sulphonic ac;ds and dialkylnaphthalene mono-
and disulphonic ac;ds which may be free or blocked w;th amines.
Commercially available thickeners such as those based
on polyacrylates or polyurethanes are frequently used to
;mprove the rheological properties. These properties may in
addition be influenced by varying the pH either by the nature
and concentration of the neutralization amines added or by the
addition of auxiliary solvents.
Although the emulsion polymers are stable in storage
due to the presence of the external emulsifiers generally used
duling emulsion polymerization, up to 100, preferably up to 80% and most preferably
up to 50% of the carboxyl ,groups in the copolymers may b~ n~u~cralized using ammonia
aliphatic amines as neutralizing agents. Examples of aliphatic
amines include triethylamine, ethanolamine,
dimethylethanolamine and triethanolamine.
Examples of suitable auxiliary solvents, which may
optionally be used in quantities of up to 10% by weight, based
on the total quantity of coating composition, include
monohydric and polyhydric alcohols, hydrocarbons, ethers,
esters and ketones, e.g., ethyl or butyl glycol and their
acetates, ethyl and butyl diglycol, ethylene glycol
~5 dimethylether and methoxy propanol.
The other auxiliary agents and additives pre~iously
ment;oned may also be used in the preparation of the clear,
ready-for-use coating compositions. The clear coating
compositions have a solids content of 25 to 50% by weight,
preferably 30 to 45% by weight, and a viscosity of 15 to 60
sec, preferably 18 to 40 sec (DIN 4 cup/25~C).
The coating may be applied by known methods employed
in coating technology, preferably by spraying wlth a flow cup
gun. The coatin~ may be applied wet^on-wet (after brief pauses
for ventilation) or on pre-dried base coating containing
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solvent. It is particularly environmentally desirable for the
entire coatings bu;ld-up to apply the clear coat;ng composition
according to the invention to a layer of an aqueous base coat.
This application may be carried out either wet-on-wet (after
brief intervals for ventilation) or on a pre-dried aqueous base
coat.
The substrates coated with the clear coating
composition are generally ventilated at a temperature of 10 to
50~C, preferably 25 to 40C, for a short ~ime after application
and then stoved at about 100 to 160C, preferably 120 to 140C,
for a period of about 10 to 60, preferably 20 to 30 minutes.
For relatively thick coatings, it is in many cases advisable
also to carry out an intermediate drying at 8QC to reduce
blistering. The stoved coatings thus obtained are
distinguished by excellent optical and mechanical properties
comb;ned with good solvent resistance.
In the examples which follow, all the parts and
percentages are by weight unless otherwise specified.
ExamPles of preparation of aaueous emulsion polvmers to be used
accordinq to the invention
AcrYlate dispersion 1
The following components were reacted by the known
emulsion polymerization at 800 in a glass reactor with
stirrer:
613.50 parts of deionized water,
3.90 parts of polyethoxylated 3-benzyl-4-hydroxy-
biphenyl (about 10 moles of ethylene oxide
per mole of hydroxy compound)
(Emulsifier 1)
0.75 parts of sodium-di-sec.-butyl-naphthalene
sulphonate (Emulsifier 2),
1.25 parts of ammon~um peroxydisulphate,
117.00 parts of styrene,
53.00 parts of methyl methacrylate,
35- 141.00 parts of butyl acrylate,
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72.00 parts of hydroxyethylmethacryla~,
25.00 parts of methacryl;c acid and
7.40 parts of dodecylmercaptan.
When polymerization had been terminated, a post-
polymerization was carried out at 80C by the addition of 0.25
parts of ammonium peroxydisulphate~ and the product was then
partially neutralized with 3.26 parts of dimethylethanolamine.
The emulsion was still perfect and free from ground
settlement after ~ year's storage at 23C.
AcrYlate disDersion 2
Sam2 as acrylate d;spersion 1 but neutralized with
1.63 parts of dimethylethanolamine.
Acrylate dispersion 3
Same as acrylate dispsrs;on 1 but neutral;zed with
1~ 6.52 parts of dimethylethanolamine.
Acrylate disDersion_4
Same as acrylate dispersion 1 but neutralized with
5.47 parts of triethanolamine.
AcrYlate dispers;on 5
Same as acrylate dispersion 1 but neutralized with
3.67 parts of triethylamine.
Acrvlate disDersion 6
Same as acrylate dispersion 1 but neutralized w;th
1.75 parts of 33% aqueous ammonia.
AcrYlate disDersion 7
The following components were reacted using the
method set forth for acrylate dispers;on 1:
613.80 parts of deionized water,
3.90 parts of Emulsifier 1,
0.75 parts of Emulsifier 2,
1.25 parts of ammonium peroxydisulphate,
117.00 parts of styrene,
63.00 parts of methyl methacrylate,
141.00 parts of butyl acrylate,
72.00 parts of hydroxyethylmethacryla~,
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11.10 parts of methacrylic acid and
7.40 parts of dodecylmercaptan.
When polymerizat;on had been term;nated, a post-
polymerization was carried out at 800 by the addition of 0.25
5parts of ammonium peroxydisulphate and the product was then
partially neutrali7ed with 3.26 parts of dimethylethanolamine.
Acrylate dis~ersion 8
The following components were reacted using the
method set forth for acrylate dispersion 1:
~614.50 parts of deionised water
3.90parts of Emulsifier 1,
0.75 parts of Emulsifier 2,
1.63 parts of ammonium peroxydisulphate,
117.00 parts of styrene,
1553.00 parts of methyl methacrylate,
141.00 parts of butyl acrylate,
72.00 parts of hydroxyethyl methacrylate,
21.00 parts of methacrylic acid and
9.62 parts of dodecylmercaptan.
20When polymerization had been terminated, a post-
polymerization was carried out by the addition of 0.325 parts
of ammonium peroxydisulp~ate at 80C and the product was then
partially neutralized with 3.26 parts of dimethylethanolamine.
Acrylate dispers;on 9
25The following components were reacted us;ng the
method set forth for acrylate dispersion 1:
613.00 parts of deionized water,
3.90 parts of Emulsifier 1,
0.75 parts of Emulsifier 2,
300.63 parts of ammon~um peroxydisulphate,
117.00 parts of styrene,
53.00 parts of methyl methacrylate,
141.00 parts of butyl acrylate,
72.00 parts of hydkoxyethylmethacrylate,
3521.00 parts of methacrylic acid and
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3.70 parts of dodecylmercaptan.
When polymer kation had been terminated, a post-
polymerization was carried out by the addition of 0.125 parts
of ammonium peroxydisulphate at 80C and the product was then
partially neutralized with 3.26 parts of dimethylethanolam;ne.
AcrYlate dispersions 10-14
The components summarized in Table 1 below were
reacted using the method set forth for acrylate dispersion l;
the number in Table 1 represent parts.
Table 1
11 12 13 14 Acrylate
dispersions
1247.01251.01246.0 1251.0 1250.0 de;onized water
7.8 7.8 7.8 7.8 7.8 Emulsifier 1
1.5 1.5 1.5 1.5 1.5 Emulsifier 2
2.5 2.5 ~.5 2.5 2.5 ammonium peroxy-
disulphate
105.0105.0 105.0 339.0 105.0 styrene
234.0281.0 247.0 - 247.0 methyl
methacrylate
283.0283.0 272.0 283.0 72.0 butyl acrylate
144.0 97.0 141.0 144.0 - hydroxyethyl
methacrylate
- - - -141.0 hydroxypropyl
methacrylate
47.0 43.0 47.0 43.0 43.0 methacrylic
acid
14.8 14.8 14.~ 14.8 14.8 dodecylmercaptan
_
Commercial mixture of 2- and 3-hydroxypropyl-
methacrylate
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Post-polymerization was carried out in all cases by
the addition of 0.5 parts of ammonium peroxydisulphate at 80C
after termination of the polymerization and the product was
then partially neutralized with 6.5 parts of
~imethylethanolam;ne.
PreDaration of an aqueous clear coatinq
The formulations used to prepare aqueous clear coat;ng
compositions are set forth in Table 2.
Table 2 Formulations of the clear coating compositions
Formulation No. 1 2 3 4 5 6 7
Melamine resin 1* 11.0 11.0
Melamine resin 2* 10.2 10.2 10.2 10.2 10.5
Levelling agent 1* 1.2 1.2 1.2 1.2 1.2 1.2 1.2
Levelling agent 2* 0.6 0.6 0.6 0.6 0.6 0.6 0.6
Butyl glycol 3.9 4.0 4.1 4.1 4.1
1, Ethyl diglycol/
butyl diglycol 3.2 3.3
Acid catalyst 1* 0.3
Acid catalyst 2* 0.8 0.8 0.8 0.8
Light protective
agent 1* 1.8 1.8 1.8 1.8 1.7 1.7 1.8
Light protective
agent 2* 1.8 1.8
Light protective
agent 3* 1.& 1.8 1.7 1.7 1.8
Dimethylethanolamine,
10% in water 6.1 6.0 5.g 5.~ 5.8 5.8 6.0
Wetting auxiliary* 1.2 1.2 1.2 1.2 1.2 1.2 1.2
deionized water 6.8 8.1 8.1 9.2 9.9 9.5 7.8
Acrylate dispersion 1 60.6 60.2
Acrylate dispersion 6 - 59.5 59.1
Acrylate dispersion 8 57.8
Acrylate dispersion 9 58.3 59.7
Th;ckener* 5.0 4.9 4.9 4.9 5.0 4.9 5.0
Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0
========================================================= ===========
Outflow v;s~os;ty 2~ 20 1~ 17 19 26 26
in sec
(DIN 4 cup, 25C~
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Melamine resin 1: Cymel 327 (Cyanamid Int., Wayne,
N.J. 90% solids content in
i-propanol
Melamine resin 2: Cymel 303 (Cyanamid Int., Wayne,
N.J.)
98% solids content in water
Levelling agent 1: Additol XW 395 (Hoechst AG,
Frankfurt/M, BRD) 50% in butyl
~lycol
Levelling agent 2: Resiflow W 50 (Worlee-Chem;e GmbH,
Hamburg, BRD) 50% in butyl
glycol/isopropanol 4:1
Wetting auxiliary: Fluorotensid FT 929 (Bayer AG,
Leverkusen,
BRD~ 10% in water/ethanol 8:1
Acid catalyst 1: Nacure 2501 (King Industries Inc.,
Norwalk CT) 25% in isopropanol
Acid catalyst 2: Nacure 1051 (King Industries Inc.,
Norwalk CT) 50% ;n butyl glycol
Light protective agent 1: Tinuvin 1130 (Ciba-Geigy Marienberg
6mbH, Lautertal, BRD~ 20% ;n ethyl
diglycol/butyl diglycol 1:1
Light protective agent 2: Tinuvin 292 (Ciba-Geigy Marienberg
GmbH, Lautertal, BRD) 20% in ethyl
diglycol/butyl diglycol 1:1
0 Light protective agent 3: Tinuvin 440 (Ciba-Geigy Marienberg
GmbH, Lautertal, BRD) 20% in butyl
glycol
Thickener: Viscalex HV 30 (Allied Colloids
GmbH,
Hamburg, BRD) 5% in water
25 The indiv;dual components were successively stirred in at a
uniform rate and homogenized with a dissolver.
Application of the aqueous clear coatinq
A steel sheet which had been prepared with an electro
dip primer (KTL), filler and base coat (aqueous or containing
solvent) was coated with the clear coating.
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A temperature of 20-25C and relativQ humid;ty of 40 to 70% was
maintained during the application of this coating. The outflow
rate from the flow cup gun was 300-~00 ml/min, depending upon
the viscosity of the formulation. The spray gun was fitted
with a 1.2 mm no~zle and operated at a pressure of 3.5-5.0 bar.
The coating was applied in three stages with a brief
interruption for ventilation after the first spraying stage.
DrYing of the clear coatings
The coated steel sheets were ventilated at 40C for 1
to 5 minutes, pre-dried at 80C and stoved at 140C for 20
minutes. Increasing the duration of the ventilating phases
provided a marked reduction in the formation of blisters. The
clear coating film obtained had a layer thickness of 35-60 ~m.
Testinq of the clear coatinq films
The lacquered substrates were first assessed
optically after the stoving process. The Erichsen cupping (DIN
IS0 1520) was then determined as a measure of the elasticity,
the pendulum hardness (DIN 53157) was determined as a measure
oF the hardness of the film and the degree of gloss was
determined (at an angle of 20 and at 60). The ease with
which the films were attacked by the solvent action of toluene,
butyl acetate, methoxypropyl acetate and acetone was then
tested by placing a wad of cotton wool impregnated with solvent
for 1 minute directly on the coating surface and the results
were assessed optically and mechanically. The best result was
denoted by 0 (unchanged surface) and the worst by 5 (coating
film became detached). The res;stance of the films to solvents
and water was then tested by exposing the films to the action
of the solvents (ethanol, xylene/10 minutes) and water (for 24
h) and then assessing the result as described above for the
test for solvent action.
The detailed test results for the clear coating
formulations according to the invention are summarized in Table
3.
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Table 3: Test results nf clear coating formulations
Formulation No. 1 2 3 4 5 6 7
Layer thickness
(~m) 50 40 45 50 40 50 45
Formation of film 0 0 0 0 1 0
Gloss according
to Lange 20~ 88 89 ~7 94 95 96 96
Erichsen cupping
(DIN IS0 1520)
(mm) 7.0 5-5 5.0 5.5 7.0 6.0 7.0
Pendulum hardness
according to Konig
(DIN 53157) (s)180 169 187 184 171 171 185
Action of sol-
vent (1 min)
(Tol/BuAc/
MPA/Ac) 0000 0000 0000 0000 0000 0000 0000
Resistance to
xylene
(10 min) 0 0 0
Resistance to
ethanol
(10 min) 0 0 0 0 1 0
Resistance to
water (24 h) 0 0 0 0 0 0 0
Practical tests carried out on clear coating fiims
showed no differences when applied to base coats containing
solvent and aqueous base coats. The adh~rence of the clear
coating film was good on both substrates.
Although the invention has been described in detail
in the foregoing for the purpose of illustration9 it is to be
understood that such detail is solely for that purpose and that
variations can be made therein by those skilled in the art
without departing from the spirit and scope of the invention
except as it may be limited by the claims.
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