U.S. patent application number 09/878552 was filed with the patent office on 2001-10-11 for aqueous binder solutions and dispersions.
Invention is credited to Gross, Lutz-Werner, Poth, Ulrich.
Application Number | 20010029280 09/878552 |
Document ID | / |
Family ID | 7783603 |
Filed Date | 2001-10-11 |
United States Patent
Application |
20010029280 |
Kind Code |
A1 |
Poth, Ulrich ; et
al. |
October 11, 2001 |
Aqueous binder solutions and dispersions
Abstract
Aqueous solutions or dispersions of binders for preparing
aqueous coating materials are produced, including as an aqueous
component water of reaction which is obtained during the
condensation of alcohols with carboxylic acids.
Inventors: |
Poth, Ulrich; (Munster,
DE) ; Gross, Lutz-Werner; (Haltern, DE) |
Correspondence
Address: |
BASF CORPORATION
ANNE GERRY SABOURIN
26701 TELEGRAPH ROAD
SOUTHFIELD
MI
48034-2442
US
|
Family ID: |
7783603 |
Appl. No.: |
09/878552 |
Filed: |
June 11, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09878552 |
Jun 11, 2001 |
|
|
|
08784936 |
Jan 15, 1997 |
|
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Current U.S.
Class: |
524/845 |
Current CPC
Class: |
C09D 167/00 20130101;
C08L 2666/54 20130101; C09D 5/02 20130101; C09D 167/00
20130101 |
Class at
Publication: |
524/845 |
International
Class: |
C08L 067/00; C08K
003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 25, 1996 |
DE |
196 02 555.9 |
Claims
What is claimed is:
1. A method of preparing a solution or dispersion of an aqueous
coating composition comprising dissolving or dispersing at least
one binder in an aqueous component, wherein the aqueous component
comprises a water of reaction, wherein the water of reaction (i) is
produced by a condensation reaction of at least one alcohol with at
least one carboxylic acid and (ii) has been separated from the
condensation reaction.
2. The method of claim 1, wherein at least some of the binder is
prepared by the condensation reaction.
3. The method of claim 1 further comprising adding deionized or
distilled water to the binder.
4. The method of claim 1 further comprising mixing the water of
reaction with deionized or distilled water prior to dissolving or
dispersing the binder.
5. The method of claim 1, wherein the water of reaction comprises
water and contaminants consisting of those selected from the group
consisting of polyols, monoalcohols, partial aldehydes of polyols,
acetals, cyclic oxygen-containing compounds, unreacted reactants,
water-soluble degradation products, and mixtures thereof.
6. The method of claim 1, wherein the carboxylic acids are selected
from the group consisting of trimellitic acids, trimesic acids
(1,3,5-benzenetricarboxylic acid), pyromellitic acids, trimeric
fatty acids, dimethylolpropionic acid, phthalic acids, isophthalic
acids, terephthalic acids, fumaric acids, maleic acids, and
mixtures thereof.
7. The method of claim 1, wherein alcohols are polyalcohols
selected from the group consisting of ethylene glycol,
propanediols, butanediols, pentanediols, hexanediols, diethylene
glycol, glycerol, trimethylolethane, trimethylolpropane,
pentaerythritol, dispentaerythritol,
2-methyl-2-propyl-1,3-propanediol, 2,2,4-trimethyl-1,3-pentanediol,
neopentylglycol hydroxypivalate, and mixtures thereof.
8. The method of claim 1, wherein the aqueous component comprises
from 0.1 to 80% by weight of water of reaction, based on the total
weight of the aqueous component.
9. The method of claim 1, wherein the at least one binder is
selected from the group consisting of polyester, alkyd, acrylate,
epoxy, polyurethane, amino, epoxide modified polyester resins, and
mixtures thereof.
10. A method of preparing a solution or dispersion of an aqueous
coating composition comprising preparing a binder by a condensation
reaction of alcohols and carboxylic acids, wherein water from the
reaction remains in the aqueous coating composition.
11. The method of claim 10, wherein the alcohols are polyols and
the carboxylic acids are polycarboxylic acids.
12. The method of claim 10 further comprising adding deionized or
distilled water to the aqueous coating composition.
13. The method of claim 10 further comprising adding additional
binders.
14. The method of claim 13, wherein the binders are selected from
the group consisting of polyester, alkyd, acrylate, epoxy,
polyurethane, amino, epoxide modified polyester resins, and
mixtures thereof.
15. The method of claim 10, wherein the water from the reaction
comprises water and contaminants consisting of those selected from
the group consisting of polyols, monoalcohols, partial aldehydes of
polyols, acetals, cyclic oxygen-containing compounds, unreacted
reactants, water-soluble degradation products, and mixtures
thereof.
16. The method of claim 10, wherein the carboxylic acids are
selected from the group consisting of trimellitic acids, trimesic
acids (1,3,5-benzenetricarboxylic acid), pyromellitic acids,
trimeric fatty acids, dimethylolpropionic acid, phthalic acids,
isophthalic acids, terephthalic acids, fumaric acids, maleic acids,
and mixtures thereof.
17. The method of claim 10, wherein alcohols are polyalcohols
selected from the group consisting of ethylene glycol,
propanediols, butanediols, pentanediols, hexanediols, diethylene
glycol, glycerol, trimethylolethane, trimethylolpropane,
pentaerythritol, dispentaerythritol,
2-methyl-2-propyl-1,3-propanediol, 2,2,4-trimethyl-1,3-pentanediol,
neopentylglycol hydroxypivalate, and mixtures thereof.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a divisional application of U.S.
Ser. No. 08/784,936, filed on Jan. 15, 1997, which claims priority
from DE 196 02 555.9, filed on Jan. 25, 1996, both of which are
incorporated herein by reference.
[0002] The present invention relates to aqueous solutions and
dispersions of binders for preparing aqueous coating materials, and
to processes for their preparation.
[0003] The condensation of alcohols with carboxylic acids produces
per crosslinked hydroxyl or carbonyl-group one molecule of water,
H20:
R.sub.1--OH+HOOC--R.sub.2.fwdarw.R.sub.1--O--CO--R.sub.2+H.sub.2O
alcohol+carboxylic acid.fwdarw.ester+water
[0004] Since the ester is the reaction product which is of
interest, in the prior-art preparation processes the water produced
is removed from the reaction mixture as so-called "water of
reaction". This water of reaction is generally contaminated with
other components of the reaction and must therefore be disposed of.
A procedure of this kind is necessary, for example, in the coatings
industry in connection with the preparation of coating binders.
[0005] In the coatings industry, the preparation of polyesters and
alkyd resins from polycarboxylic acids and/or polycarboxylic
anhydrides and polyalcohols and, if desired, monocarboxylic acids
by condensation reactions gives rise to a quantity of about 5 to
11%, based on the polymer produced, of water of reaction. The water
of reaction is normally removed effectively from the reaction
mixture with the assistance of entrainers (for example xylene).
[0006] The vapor mixture comprising water of reaction and entrainer
is--especially where saturated polyesters are being
prepared--passed through a column whose function is to separate
volatile polymer building blocks (especially lower polyalcohols)
from the vapor mixture by liquid/vapor exchange and thereby to
avoid losses of these building blocks from the reaction mixture.
For polyesters and alkyd resins, which contain no constituents
which are volatile--under the reaction conditions in the reactor or
with steam--an overflow pipe is employed.
[0007] In each case, however, the vapor mixture is subsequently
liquefied in a condenser and is collected in a separation receiver.
In the separation receiver, an aqueous phase of relatively high
specific gravity separates from the organic phase of lower specific
gravity. The organic phase consists almost entirely of the
entrainer employed; it is separated from the aqueous phase by means
of an overflow and is passed into the reactor at the head of the
column (circulation technique) possibly under control and by means
of the use of a pump (possibly a metering pump).
[0008] Another possibility is to operate without entrainer. In this
case there is no need for a separation receiver but only for a
single receiver into which aqueous phase is collected.
[0009] Although the aqueous phase contains high proportions of
water, it is always contaminated with relatively small amounts of
volatile or steam-volatile building blocks (mostly lower polyols)
and/or with water-soluble degradation products from the building
blocks of the polyester as well. Degradation products which may be
produced and may be present in the aqueous phase of the water of
reaction are monoalcohols, partial aldehydes of polyols, acetals,
and in special cases cyclic, oxygen-containing compounds as
well.
[0010] Separation of the secondary constituents from the aqueous
phase during the preparation of polyesters and alkyd resins, by
distillation or extraction, is complex and does not lead to
reusable materials. Simple disposal of the distillate, for example
by way of settling basins, is a risk. Usually, therefore, despite
its small content of organic constituents the water of reaction is
incinerated, usually together with other residues which are richer
in organic substances. This requires separation and storage of the
waters of reaction and special control as they are fed to the
incinerator.
[0011] Because of their ecological advantages, water-dilutable
coating materials have increasingly been used in the coatings
industry in recent years. With these coating materials it is
possible largely or completely to dispense with organic solvents
whose evaporation as the coating material dries leads to emissions
and to the known, associated environmental problems. In the course
of preparing such aqueous coating systems, the binders of the
coating material must be brought into the form of an aqueous
solution or dispersion. Dispersions of this kind are highly
unstable. Even small quantities of impurities may destroy or
severely hinder the dispersibility of the binders. For example, a
solution of this kind cannot be prepared using tap water (drinking
water, mains water), which contains inorganic constituents. It is
therefore necessary to employ deionized or distilled water. This
implies more complex preparation and therefore increased
preparation costs as well.
[0012] The object which the present invention has set itself is to
avoid the disadvantages of the prior art, described above, which
occur in particular during the disposal of water of reaction and
during the preparation of binder dispersions.
[0013] This object is achieved in accordance with the invention by
an aqueous solution or dispersion of a binder for preparing aqueous
coating materials, which solution or dispersion includes as at
least one aqueous component the water which can be prepared by
condensation of alcohols with carboxylic acids and can be separated
off from the condensation mixture.
[0014] It has surprisingly been found that during the preparation
of polyesters or alkyd resins (which are then preferably employed
for water-dilutable coating systems, the water of reaction is able
to replace a portion of the distilled or deionized water which is
otherwise used to prepare the aqueous colloidal solution or
dispersion of the polyester or alkyd resin. Unlike tap water
(drinking water, mains water), which contains certain proportions
of inorganic constituents which impair the usefulness for preparing
aqueous colloidal solutions or dispersions of coating binders, it
is possible with fractions of the waters of reaction to prepare
stable aqueous colloidal solutions. The use of these aqueous
polyester-resin or alkyd-resin solutions or dispersions in aqueous
coating systems has only an insignificant influence on their
properties. This effect was completely surprising in view of the
sensitivity of the binder dispersions to impurities. On the basis
of conventional experience, the opposite was to be expected.
However, it is found that in most cases the secondary constituents
act as cosolvents. If aqueous coating systems are employed on
application lines with stoving furnaces--which is generally the
case with the industrial use of aqueous coating systems--the
abovementioned substances accompanying the water of reaction do not
become volatile until they are in the stoving furnace, although
some of them also participate in film forming (for example reaction
with amine resins). Environmental pollution as a result of the
constituents, therefore, is largely ruled out, and in any case the
waste air from staving furnaces includes organic cleavage products
and is therefore cleaned by means of catalytically processes or
filters.
[0015] In the text below, the term water of reaction is intended
always to denote the water which is eliminated during the
condensation of alcohols with carboxylic acids and which is or can
be separated off from the condensation mixture.
[0016] In accordance with the invention, the water of reaction is
preferably taken from reactions in which the alcohols are present
as polyalcohols, the term polyol referring to an organic compound
which bears at least 2 hydroxyl groups. Examples of suitable
polyols are ethylene glycol, propanediols, butanediols,
pentanediols, neopentylglycol, hexanediols, diethylene glycol,
glycerol, trimethylolethane, trimethylol- propane, pentaerythritol,
dipentaerythritol, neopentylglycol hydroxypivalate,
2-methyl-2-propyl-1,3-propanediol,2,2,4-trimethyl-1,3-pentanediol
and 2,2,5-trimethyl-1,6-hexanediol It is preferred to employ
neopentylglycol, 1,6-hexanediol and neopentylglycol
hydroxypivalate. The polyols can of course be employed in pure form
or as mixtures.
[0017] In the case of the novel preparation of the water of
reaction, polycarboxylic acids are preferably employed. These may
comprise a polycarboxylic acid containing at least three carboxyl
groups, or derivatives of such an acid (e.g. anhydride, ester or
halide). It is likewise possible to employ a mixture of such acids
and/or acid derivatives. As examples there are, trimellitic acid,
trimesic acid (1,3,5-benzenetricarboxylic acid), pyromellitic acid
and trimeric fatty acids. Trimellitic acid is preferably
employed.
[0018] As carboxylic acid' it is also possible to employ a polyol
which has at least one carboxyl group. Dimethylolproponic acid is
preferably employed. It is likewise possible to employ any
polycarboxylic acid which contains two carboxyl groups and is
suitable for preparing polyesters, or to employ a reactive
derivative (e.g. anhydride, ester or halide) or a mixture of such
acids and/or acid derivatives. Examples of suitable acids which may
be mentioned are: phthalic acid, isophthalic acid, terephthalic
acid, fumaric acid, maleic acid, endomethylenetetrahydrophthalic
acid, succinic acid, adipic acid, suberic acid, acelaic acid,
sebacic acid and dimeric fatty acids. It is preferred to employ
phthalic acid, isophthalic acid, adipic acid and dimeric fatty
acids.
[0019] As its aqueous component the novel aqueous solution or
dispersion of a binder may include a mixture of the water of
reaction according to the invention and deionized water. This is
sensible, for example, if owing to the production process there is
not sufficient water of reaction available to prepare the desired
quantity of dispersion. The aqueous component preferably includes
from 0.1 to 80% by weight, and with very particular preference from
1 to 20 by weight, of the water of reaction in the sense of the
invention.
[0020] Suitable binders from which it is intended to prepare an
aqueous solution or dispersion are in principle all binders known
for this purpose. Particularly suitable binders are: polyester,
alkyd, acrylate, epoxy, polyurethane and/or epoxide-modified
polyester resins, and also modifications of these binders. The
preparation of epoxide-modified polyester resins, for example,
takes place in accordance with techniques which are known per
se.
[0021] The novel water-dilutable coating compositions may in
principle contain all binders suitable for water-dilutable coating
compositions.
[0022] Binders which can be used are, accordingly, both refined
natural products, for example from rosins or oils or cellulose
nitrates, and resins built up entirely by synthetic means. The
latter include phenolic resins, amine resins (e.g. urea resins,
melamine resins), alkyd resins, polyvinyl acetates, epoxy resins,
polyurethane resins, polyester resins, rosin-modified phenolic
resins, chlorinated rubbers, chlorinated polypropylene, cyclized
rubbers, ketone resins and acrylate resins.
[0023] Amino resins, polyester resins, polyacrylate resins and
polyurethane resins which can be prepared in organic solution and
which are water-dispersible or water-dilutable, and mixtures
thereof, are employed in particular as binders.
[0024] The polyurethane resins employed as binders are known in
principle. Examples of suitable polyurethane resins are those
described in the literature for use in waterborne coating
materials, provided these polyurethane resins--in a modification of
the preparation described in the respective literature--can be
prepared in the form of organic solutions.
[0025] Examples of suitable polyurethane resins are the resins
described in the following documents:
[0026] EP-A-355433, DE-A 3545618, DE-A 3813866 and the as yet
unpublished German Patent Application DE 4005961.8. For further
details of the preparation of the polyurethane resins and examples
of suitable compounds, therefore, reference may be made to these
documents.
[0027] The polyacrylate resins employed as binders are likewise
known and are described, for example, in DE-A 3832826. Suitable
polyacrylate resins are General water-dilutable and/or
water-dispersible polyacrylate resins which can be prepared in the
form of organic solutions.
[0028] Also suitable as binders are polyester resins which are
water-dilutable or water-dispersible and can be prepared in the
form of organic solutions. Use is made, for example, of
corresponding commercially available water-dilutable or
water-dispersible polyester resins, and of the polyester resins
which are customarily employed in waterborne coating materials.
[0029] Water-dilutable and water-dispersible amino resins are also
suitable as binders. It is preferred to employ water-dilutable
melamine resins. Generally, these are etherified
melamine-formaldehyde condensation products.
[0030] The water-solubility of the amino resins depends apart--from
the degree of condensation, which should be as low as possible--on
the etherification component, with only the lowest members of the
alcohol or ethylene glycol monoether series giving rise to
water-soluble condensation products. The methanol-etherified
melamine resins are of greatest importance. If solubilizers are
used, butanol-etherified melamine resins can also be dispersed in
aqueous phase. Another possibility is to incorporate carboxyl
groups into the condensation product. Transetherification products
of highly etherified formaldehyde condensation products with
hydroxycarboxylic acids are water-soluble via their carboxyl
groups, after neutralization, and may be present in the base
paints.
[0031] As binders it is of course also possible to employ mixtures
of the binders mentioned and, in addition or alone, other
water-dilutable or water-dispersible binders.
[0032] The novel coating compositions may include customary
additions, such as solvents, fillers, plasticizers, stabilizers,
wetting agents, dispersion auxiliaries, leveling agents, antifoams
and catalysts, and also additives, individually or in a mixture in
the customary quantities. These substances may be added to the
individual components and/or to the overall mixture.
[0033] Examples of suitable fillers are talc, mica, kaolin, chalk,
quartz flour, absestos flour, slate flour, barium sulfate, various
silicic acids, silicates, glass fibers, organic fibers or the
like.
[0034] In addition to water, the novel coating compositions may
include the customary solvents, for example aliphatic or aromatic
hydrocarbons, mono- or polyhydric alcohols, ethers, esters, glycol
ethers and their esters, ketones, such as, for example, toluene,
xylene, butanol, ethyl- or butylglycol (=ethylene glycol monoethyl
or -butyl ether) and their acetates, butyl diglycol (ethylene
glycol dibutyl ether), ethylene glycol dimethyl ether, diethylene
glycol dimethyl ether, cyclohexanone, methyl ethyl ketone, acetone,
isophorone or mixtures thereof.
[0035] It is additionally possible to add crosslinked polymeric
microparticles, as are disclosed, for example, in EP-A-38 127,
and/or customary inorganic or organic additives to the novel
basecoats. Thus examples of effective thickeners are water-soluble
cellulose ethers, such as hydroxyethyl cellulose, methylcellulose
or carboxymethylcellulose, and also synthetic polymers having ionic
and/or associative groups, such as polyvinyl alcohol,
poly(meth)acrylic acid, polyvinylpyrrolidone, styrene-maleic
anhydride or ethylene-maleic anhydride copolymers and their
derivatives, or else hydrophobically modified ethoxylated
piperidine and triethanolamine used [sic]. With particular
preference, tertiary amines are employed as neutralizing agents,
especially dimethylethanolamine, triethylamine, tripropylamine and
tributylamine.
[0036] The novel basecoat compositions may include all dyes or
pigmets which are known and are customary in the coatings
industry.
[0037] Examples of dyes and pigments, which may be inorganic or
organic in nature, are titanium dioxide, graphite, carbon black,
zinc chromate, strontium chromate, barium chromate, lead chromate,
lead cyanamide, lead silicochromate, zinc oxide, cadmium sulfide,
chromium oxide, zinc sulfide, nickel-titanium yellow,
chromium-titanium yellow, iron oxide red, iron oxide black,
ultramarine blue, phthalocyanine complexes, naphthol red,
quinacridones, halogenated thioindigo pigments or the like.
[0038] As particularly preferred pigments use is made of metal
powders, individually or in a mixture, such as copper, copper
alloys, aluminium and steel, preferably aluminium powders, in at
least the predominant proportion, namely in a quantity of from 0.5
to 25% by weight based on the overall binder solids content of the
coating compositions. Preferred metallic pigments are those
commercially available metal powders which have been specially
pretreated for aqueous systems. The metal powders may also be
employed together with one or more of the abovementioned
nonmetallic pigments and/or dyes. In this case their proportion is
chosen such that the desired metallic effect is not suppressed.
[0039] The novel binder solution or binder dispersion is preferably
used for producing aqueous coating materials. For this purpose it
is processed further, together with crosslinkers (e.g. amino
resins, especially those of the type hexamethoxymethylmelamine,
urea resin, water-dilutable epoxy resin and the like) optionally
further binders, pigments, fillers and other customary additives,
to form an aqueous coating material. In addition to water, the
latter may also, to a minor extent, comprise organic solvents as
diluents.
[0040] The scope of the present invention also includes the aqueous
coating material obtained by using the described binder solution or
binder dispersion. The present invention started out, inter alia,
from the object of avoiding the problems associated with the water
of reaction which occurs in the case of condensation reactions. In
the prior art, this water of reaction is separated off from the
reaction mixture and then disposed of expensively. The invention,
by contrast, proposes employing the water of reaction as an aqueous
component in the preparation of aqueous dispersions or solutions of
organic substances. Examples of such substances and/or of such a
use is the above-described preparation of aqueous binder
dispersions and binder solutions. However, it is obvious that the
use of the water of reaction is not restricted to these specific
groups of substances. Rather, the water of reaction can be employed
as solvent whenever the contaminants which it may still contain are
harmless for the dispersion or solution to be prepared. The
advantage of such a water of reaction is that its composition and
the possible accompanying substances which are present in it are
known with great precision, provided one knows the precursors of
the underlying condensation reaction. In particular, the water of
reaction has none of the inorganic impurities of customary tap
water.
[0041] The invention also relates to a process for preparing binder
solutions or binder dispersions for aqueous coating materials,
which is characterized by the following steps:
[0042] a) water of reaction eliminated during the condensation of
alcohols and carboxylic acids is separated off from the
condensation mixture,
[0043] b) if desired, the water of reaction separated off is mixed
with deionized water, and
[0044] c) the binder is dissolved or dispersed in the aqueous
component obtained in accordance with a) and b).
[0045] The water of reaction in process step a) may in principle
come from a condensation reaction which has nothing to do with the
binder concerned. Preferably, however, at least part of the binder
is prepared by the condensation reaction of step a). This is
because a particularly rational process is one in which the water
of reaction of a polyester or alkyd resin which is employed in
aqueous coating systems is employed directly by decantation from
the separating receiver in the course of preparing the aqueous
colloidal solution of the polyester concerned in a dilution vessel
which in most cases is connected to the reactor.
[0046] In a further, independent process for preparing binder
solutions or binder dispersions for aqueous coating materials, the
following steps are carried out:
[0047] a) binder is prepared by condensation of polyol and poly- or
monocarboxylic acids, with the water of reaction eliminated during
the condensation remaining in the condensation mixture,
[0048] b) if desired, deionized water is added, and
[0049] c) if desired, further binders are added.
[0050] This process can be employed whenever at least some of the
binder is prepared in a condensation reaction of polyols and
carboxylic acids and when the water of reaction which occurs in
this condensation reaction, including the impurities which may
still be present, does not impair the dispersion which is to be
prepared. In this case the process described is particularly
advantageous, since it avoids the step of separating off the water
of reaction from the condensation mixture. Since the water of
reaction in some cases is not present in sufficient quantities for
the dispersion to be prepared, it is possible if required to add
further deionized water.
[0051] The invention is explained below with reference to a working
example.
[0052] 1. Conventional preparation of a polyester (cf. EP 0 269
828
[0053] 442.4 g of 1,6-hexanediol and 166.6 g of a technical-grade
polymeric fatty acid (dimer content at least 80% by weight, trimer
content not more than 20% by weight, monomer content not more than
1% by weight) are weighed into a stainless steel reaction vessel
which can be heated by means of heat transfer oil and is provided
with an anchor stirrer, a packed column, a vapor condenser with
receiver, an inert-gas supply line (N.sub.2) and temperature
sensors for the temperature of the reaction material and the vapor
temperature at the column head, and are heated to 130.degree. C.
Then 184.3 g of isophthatic [sic] acid are added, and heating is
continued. As soon as water of condensation is formed (from about
160.degree. C.), the temperature of the reaction material is raised
to not more than 220.degree. C., while distilling off the water of
condensation, at such a slow rate that the vapor temperature at the
column head does not exceed 103.degree. C. Condensation is
continued at 220.degree. C. until the reaction material has reached
an acid number of 10.5. After cooling to 140.degree. C., 266.7 g of
trimellitic anhydride are introduced with stirring and in portions
into the reaction material. Subsequently, the mixture is heated to
150.degree. C. and esterification is carried out until the reaction
material has reached an acid number of 67.7. It is then cooled to
120.degree. C. and diluted with ethylene glycol monobutyl ether to
give a solution having a solids content of 85% by weight
(determined after drying at 130.degree. C. for 60 minutes in a
convection oven). A sample diluted with ethylene glycol monobutyl
ether to 50% by weight exhibits a solution viscosity of 420 mPas
(23.degree. C. ICI plate-cone viscometer). The 85% strength
polyester solution is heated to 140.degree. C., and 209.8 g of an
epoxy resin of bisphenol A and epichlorohydrin, of an epoxide
equivalent weight of 490, are added in portions and with stirring.
The mixture is then reacted at 140.degree. C. until an epoxide
equivalent weight of more than 50,000 and an acid number of 42.1
(based on solids) have been reached. The mixture is then cooled to
100.degree. C. and is neutralized with 64.6 g of
N,N-dimethylethanotamine [sic]. The reaction material is then
discharged with stirring into 2000 g of deionized water which has
been heated to 60.degree. C., and by intensive stirring a stable
binder dispersion is produced which is adjusted with 180 g of
deionized water and N,N-dimethylothanolamine [sic] to a solids
content of 35% by weight (determined after drying at 130.degree. C.
for 60 minutes in a convection oven) and to a pH at 23.degree. C.
of 6.67.
[0054] 2. Modification of the polyester preparation, in accordance
with the invention
[0055] The procedure set out under 1. is repeated. In the first two
reaction steps, 79.04 g of water of reaction are obtained. In
contrast to the method mentioned, the described addition of 180 g
of water is reduced by this quantity, and the water of reaction
mentioned is separated from the organic phase in a decanter and
then added, following the first addition of water, to the colloidal
aqueous polyester solution, followed by 100.96 g of deionized water
as a make-up quantity.
[0056] The polyester solution prepared in this way was tested in
comparison with the polyester solution prepared by the customary
process. Both solutions are weakly opaque and stable, and after
aging at 40.degree. C. for 5 days exhibit a sufficient comparable
stability (acid number, pH, viscosity). Both polyesters were used
as described in EP 0 269 828 to formulate and apply water-based
primer-surfacers and a comparison was carried out. There are no
significant differences in application characteristics (leveling,
gloss, topcoat holdout) or in the technical properties of the
water-based primer-surfacers (hardness, elasticity and stone-chip
resistance).
* * * * *