This invention relates to waterborne thixotropic resin
systems, a process for their production, and a method of use thereof.
Waterborne thixotropic alkyd resins systems have been described,
i. a. in
EP 1 264 861 A2
. These comprise a thixotropy agent which is made by reacting a polyfunctional
aliphatic isocyanate and an olefinically unsaturated aliphatic hydroxy compound
to form an olefinically unsaturated monoisocyanate which in turn is reacted with
ammonia or an amine having at least one primary amino group.
In the experiments underlying the present invention, it
has been found that the amount of such thixotropy agent introduced into a waterborne
alkyd resin system is limited by the storage stability of such modified resins,
crystallisation occurring when the mass fraction of thixotropy agent with regard
to the total mass of solids in the said system exceeds about 3 %. On the other hand,
this limitation in storage stability did not allow to increase the level of thixotropy
to the extent desired. This limitation in storage stability is particularly relevant
for the application in alkyd resins.
The problem to be solved was therefore to improve the storage
stability and thereby increase the tolerance of the resin system towards a higher
level of thixotropy modification.
This object is achieved by providing a novel thixotropy
agent B which is an olefinically unsaturated hydrophilic urethane modified urea
comprising moieties derived from
- olefinically unsaturated monohydroxy compounds,
- polyfunctional isocyanates,
- aliphatic polyether polyols,
- aliphatic polyamines, and optionally,
- saturated aliphatic monohydroxy compounds.
In these thixotropy agents, the components B2 and
B3 are preferably reacted in a way that at least two of the hydroxy groups
of B3 are consumed by addition to an isocyanate group of B2 to form
The thixotropy agents B may be obtained by reaction
of component B1 or of a mixture of the components B1 and
B5 with a stoichiometric excess of the isocyanate component B2, whereupon
component B3 is added to the reaction mixture, or by first reacting
B3 and B2, and thereafter adding B1, optionally in mixture
with B5, or by charging B2, and adding, in sequence, or in mixture,
components B1, B3, and B5.
This reaction mixture produced in either way is then added
to the amine component, B4, which is either charged as a solution in a solvent
which is inert towards isocyanate groups, or preferably charged in the form of an
admixture of B4 to a resin A emulsified in water. Due to the higher affinity
of isocyanate groups towards amine groups than to water or hydroxyl groups in the
resin A, formation of a urea compound is the predominant reaction in this
Particularly good results have been obtained by using the
compounds B1 to B5 in the following quantities:
- the ratio of the amount of substance of amino groups in B4 to the amount
of substance of isocyanate groups in B2 is from 0.3 mol/mol to 0.7 mol/mol,
preferably from 0.35 mol/mol to 0.65 mol/mol, and particularlypreferred from 0.4
mol/mol to 0.6 mol/mol,
- the ratio of the amount of substance of hydroxyl groups in B3 to the
amount of substance of isocyanate groups in B2 is from 0.2 mol/mol to 0.4
mol/mol, preferably from 0.22 mol/mol to 0.38 mol/mol,
- the ratio of the amount of substance of hydroxyl groups in B1 to the
amount of substance of isocyanate groups in B2 is from 0.05 mol/mol to 0.30
mol/mol, preferably from 0.1 mol/mol to 0.25 mol/mol,
- the amount of substance of isocyanate groups in B2 is from 0.5 to 5 times
that of the amount of substance of hydroxyl groups in B3, preferably this
ratio is from 0.7 to 4.5, and especially preferred, from 0.9 to 4.
A further object of this invention is a method of use of
such thixotropy agents B in aqueous compositions comprising resins A, especially
those that comprise alkyd resins A1, which method comprises the steps of
- preparation of an isocyanate functional intermediate by reacting hydroxy functional
components B1, B3, and optionally, B5, with a stoichiometric excess
of a polyfunctional isocyanate, B2,
- adding this isocyanate functional intermediate to a mixture comprising a polyamine,
B4, and an aqueous dispersion of a resin A which preferably has olefinically
Such resins A are preferably selected from the group consisting
of alkyd resins A1, acrylic resins A2, polyester resins
A3, polyurethane resins A4, aminoplast resins A5, silicone
resins A6, and epoxy resins A7. They can be made by reaction of oligomeric
base resins with reactive olefinically unsaturated compounds that provide the reaction
products with groups that take part in a radiation induced polymerisation reaction.
Acrylic compounds such as acrylic acid itself, and derivatives thereof such as acrylamide,
hydroxyethyl acrylate, and glycidyl acrylate are especially suitable for providing
the said base resins with the property of being radiation curable.
Resins comprising olefinically unsaturated groups can also
conventionally be air-drying, in particular air-drying alkyd resins A1 which
do not need the additional modification to impart olefinic unsaturation. The curing
reaction of these can be accelerated in a known manner by adding siccatives, which
are preferably organic salts of transition metals such as cobalt or manganese octoate.
Particularly preferred alkyd resins are those alkyd resins based at least partly
on fatty acids grafted with olefinically unsaturated acids such as acrylic or methacrylic
acids which upon at least partial neutralisation with ammonia or an amine, render
the alkyd resins water-dilutable without the need of adding external emulsifiers.
Preferred alkyd resins of this type have a Staudinger-Index
g of from 6 cm3/g to 16 cm3/g, preferably of from
8 cm3/g to 14 cm3/g. Their acid value is preferably between
20 mg/g and 80 mg/g, particularly preferably between 30 mg/g and 60 mg/g.
The quantity formerly often referred to as "intrinsic viscosity",
named "Staudinger-Index" J
g in accordance with DIN 1342, Part 2.4, is the limiting value of the
v with decreasing concentration and shear rate, wherein J
v stands for the relative change in viscosity divided by the mass concentration
&bgr;B = m B / V of the solute B (having a
B in the volume V of the solution), according to the formula
Jv = (&eegr;
r -1) /&bgr;B . &eegr;
r -1 is the relative change in viscosity, according to &eegr;
- 1 = (&eegr; - &eegr;
s) / &eegr;
s. The relative viscosity &eegr; ris the ratio of
the viscosity &eegr; of the solution under consideration, and the viscosity
&eegr; s of the pure solvent. The unit conventionally used for
J is "cm3/g"; formerly often also "dl/g".
The acid value or acid number is defined, according to
DIN EN ISO 2114 (formerly DIN 53 402), as the ratio of that mass
KOH of potassium hydroxide which is needed to neutralise the sample under
examination, and the mass
B of this sample, or the mass of the solids in the sample in the case
of a solution or dispersion; its customary unit is "mg/g".
The alkyd resins A1 which are preferentially used
in the context of this invention are made by a fusion process, where a conventional
alkyd resin is reacted with grafted fatty acids at temperatures of from 160 °C
to 230 °C.
The polycarboxylic acids A11 or anhydrides thereof
used in the synthesis of the preferred alkyd resins are selected from the group
consisting of phthalic acid, phthalic anhydride, tetrahydrophthalic acid, trimellithic
anhydride, pyromellithic anhydride, maleic anhydride, adipic acid, succinic acid,
and among the olefinically unsaturated fatty acids A12 and derivatives thereof,
mention shall be made of linseed oil fatty acid, soybean oil fatty acid, sunflower
oil fatty acid, safflower oil fatty acid, dehydrated castor oil oil fatty acid,
cotton seed oil fatty acid, groundnut oil fatty acid, tung oil fatty acid, tall
oil fatty acid, synthetic olefinically unsaturated C12- to C22-fatty
acids and derivatives thereof made by conjugation, isomerisation or dimerisation
of the said unsaturated fatty acids, and also aromatic or saturated aliphatic monocarboxylic
acids such as benzoic acid, hydroxybenzoic acid, tert.-butyl benzoic acid, coconut
oil fatty acid, and 2-ethyl hexanoic acid.
Suitable polyhydric alcohols A13 used in the synthesis
of the alkyd resins A1 include those having from 1 to 6, and preferably from
2 to 4, hydroxyl groups per molecule, such as ethylene glycol, 1,2- and 1,3-propylene
glycol, 1,2- and 1,4-butane diol, neopentyl glycol, 2-methyl-1,3-propane diol, cyclohexane
dimethanol, 2-ethyl- 1,3-propane diol, 1,6-hexane diol, ether alcohols such as diethylene
glycol and triethylene glycol, trimethylol ethane, trimethylol propane, glycerol,
pentaerythritol, dipentaerythritol, mannitol and sorbitol.
The compounds B1 to B5 used in the synthesis
of the thixotropy agent B are described hereinbelow.
The olefinically unsaturated monohydroxy compounds
B1 are aliphatic linear, or branched compounds having at least one olefinic
unsaturation, and one hydroxy group. Preferably, the olefinically unsaturated group
is easily accessible, which is the case with terminal or chain-pendant olefinically
unsaturated groups. Suitable compounds are monoesters of olefinically unsaturated
carboxylic acids, such as acrylic, methacrylic, crotonic, isocrotonic or vinyl acetic
acids, with dihydroxy compounds such as ethylene and propylene glycol, 1,2- and
1,4-butylene glycol, or hexane 1,6-diol. Particularly preferred are hydroxyethyl
and hydroxy propylacrylate. Also suited are unsaturated diesters of trihydroxy compounds,
such as glycerol diacrylate, and trimethylol propane diacrylate, and esters of other
polyvalent alcohols with olefinically unsaturated acids where one hydroxyl group
remains unesterified. Other suitable compounds are ethers of olefinically unsaturated
alcohols such as allyl or methallyl alcohol with polyethylene or polypropylene glycols,
or of trimethylol propane.
The polyfunctional isocyanates B2 are compounds
having two or more isocyanate groups per molecule. Preferred are linear, branched
or cyclic aliphatic isocyanates, particularly diisocyanates; mixtures of isocyanates
(mono-, di-, tri- and higher functional isocyanates) can also be used, with the
proviso that the average isocyanate functionality (the average number of isocyanate
groups per molecule) shall be at least 1.8, and preferably at least 2.0. Examples
for suitable linear polyfunctional isocyanates are 1,2-diisocyanato ethane, 1,3-diisocyanato
propane, 1,4-diisocyanato butane, hexamethylene diisocyanate, 1,8-diisocyanato octane
and 1,12-diisocyanato dodecane, as well as the dimeric and trimeric polyisocyanates
(uretdiones and biurets) and allophanates and reaction products of polyfunctional
linear isocyanates with diols; compounds having two isocyanate groups being preferred.
It is also possible, but less preferred, to use short chain branched aliphatic alpha,omega-diisocyanates
such as those substituted with one or more methyl groups, 1,5-diisocyanato-2-methyl
pentane, and 2,2,4- or 2,4,4-trimethyl diisocyanato hexane being mentioned. Among
the cycloaliphatic isocyanates, especially isophorone diisocyanate is mentioned.
The aliphatic polyether polyols B3 can be diethylene
glycol, triethylene glycol, and the higher oligomers, preferably up to a degree
n of polymerisation of 100. It is also possible to use mixed polyether alcohols
based on ethylene and propylene glycols, which may be random or block copolymers,
likewise preferably with a degree n of polymerisation of up to 100.
The aliphatic polyamines B4 are preferably diprimary
aliphatic linear, branched or cyclic amines having from 2 to 40 carbon atoms, preferably
from 4 to 12 carbon atoms, such as ethylene diamine, 1,3-diaminopropane, 1,4-diaminobutane,
Among the saturated aliphatic monohydroxy compounds
B5, which preferably have from 6 to 20 carbon atoms, mention shall be made
of hexanol-1, 2-ethylhexanol-1, n-octanol, n-decanol, 2-decanol, 4-decanol, 1-dodecanol,
1-tetradecanol, 1-hexadecanol, 1-octadecanol, and iso-tridecanol. It is also possible
to use the mixtures of aliphatic monohydroxy compounds made by reduction of mixtures
of fatty acids, especially those made by reduction of mixtures of naturally occurring
The thixotropy agents of the present invention are preferably
made in accordance with the following procedure:
- in the first step, a mixture of B1, and B3, and optionally,
B5, is prepared, wherein the composition of the mixture is such that in the
sum of the amounts of substance of hydroxyl groups in B1, B3, and
B5, the amount-of-substance fraction of hydroxyl groups of B1 is from
0.25 mol/mol to 0.7 mol/mol, the amount-of-substance fraction of hydroxyl groups
of B3 is from 0.30 mol/mol to 0.75 mol/mol, and the amount-of-substance fraction
of hydroxyl groups of B5 is from 0 mol/mol to 0.3 mol/mol,
- in the second step, this mixture is added to component B2, to form an
isocyanate functional intermediate,
- and in the third step, the aliphatic polyamines B4 are reacted with this
In an alternative procedure,
- in the first step, component B1, and optionally, component
B5, to component B2, are reacted to form an addition product containing
- to which, in the second step, component B3 is added, under formation
of an addition product containing urethane groups, wherein the amounts of
B1, B3, and B5 are chosen in a way that in the sum of the amounts
of substance of hydroxyl groups in B1, B3, and B5, the amount-of-substance
fraction of hydroxyl groups of B1 is from 0.25 mol/mol to 0.7 mol/mol, the
amount-of-substance fraction of hydroxyl groups of B3 is from 0.30 mol/mol
to 0.75 mol/mol, and the amount-of-substance fraction of hydroxyl groups of
B5 is from 0 mol/mol to 0.3 mol/mol, and,
- in the third step, the aliphatic polyamines B4 are reacted with the mixture
of those reaction products formed in the second step.
In either of these procedures, the last step can preferably
be conducted in the presence of an aqueous dispersion of a water-reducible resin
selected from the group consisting of alkyd resins, acrylic resins, polyester resins,
polyurethane resins, and epoxy resins.
In this preferred procedure, a mass fraction of between
50 % and 100 % of the resin to be modified, preferably in the form of an aqueous
dispersion, is already present in the reaction of the polyamines B4 with
the isocyanate functional reaction products of the second step, the remainder of
the resin being added to the mixture in the course of the reaction or thereafter.
In the reaction of the third step between the polyamines
B4 and the isocyanate functional intermediate formed in the first and second
steps, the ratio of the amount of substance of amino groups to the amount of substance
of isocyanate groups is preferably from about 0.7:1 to about 1.3:1, particularly
preferred from about 0.9:1 to 1.1:1. Especially preferred are ranges exactly corresponding
to these limits mentioned supra.
It has been found that addition of salts of metals such
as tin, titanium, and zirconium significantly accelerate the formation of the thixotropy
agents described herein.
The mass fraction of thixotropy agent comprised in the
resin thus modified is preferably from 0.5 % to 25 %, particularly preferred from
1 % to 15 %. As usual, a mass fraction W
B denotes the ratio of the mass m
B of a component B to the sum
of masses of all components (solvents or dispersing agents such as water being
excluded here) present in the mixture considered.
Particularly good results have been obtained if the content
of unsaturated groups in the thixotropy agents, expressed as the ratio of the amount
of substance of unsaturated groups in the said thixotropy agent to the mass of the
said thixotropy agent, is from 0.2 mol/kg to 2 mol/kg, preferably from 0.4 mol/kg
to 1.8 mol/kg, and particularly preferred, from 0.5 mol/kg to 1.7 mol/kg.
Furthermore, particularly good results have been obtained
if the content of urethane type nitrogen atoms in the thixotropy agents, expressed
as the ratio of the amount of substance of urethane type nitrogen atoms in the said
thixotropy agent to the mass of the said thixotropy agent, is from 1.5 mol/kg to
5 mol/kg, preferably from 2 mol/kg to 4 mol/kg, and particularly preferred, from
2.5 mol/kg to 3.5 mol/kg.
Furthermore, particularly good results havebeen obtained
if the content of urea type nitrogen atoms in the thixotropy agents, expressed as
the ratio of the amount of substance of urea type nitrogen atoms in the said thixotropy
agent to the mass of the said thixotropy agent, is from 1.5 mol/kg to 5 mol/kg,
preferably from 2 mol/kg to 4 mol/kg, and particularly preferred, from 2.5 mol/kg
to 3.5 mol/kg.
The compositions prepared in accordance with the present
invention for use as coating compositions may also comprise at least one each of
pigments, extenders, colourants, and additives selected from the group consisting
of levelling agents, flow modifiers, antifoaming agents, wetting agents, antisettling
agents, dispersing agents, antiskinning agents, siccatives, thickeners, catalysts,
coalescing agents, adjuvants for film formation, and antifouling agents.
It is especially preferred to use the thixotropy agent
in combination with alkyd resins.
Further customary additives, viz., antiskinning agents
(methyl ethyl ketoxime and cyclohexanone oxime being mentioned as preferrred), especially
in the case of alkyd resins, siccatives such as cobalt or manganese carboxylates,
and biocides such as methyl isothiaolinone and derivatives thereof may also be used.
The invention is further illustrated by the following examples.
Example 1 Isocyanate Functional Intermediates
As stated in table 1, the said educts or starting materials,
viz., diisocyanates, 2-hydroxyethyl methacrylate, and the other hydroxy functional
compounds were mixed using the mentioned amounts of substance:
Table 1 Educts for the Isocyanate functional Intermediates 1a through 1e
Component (Amount of Substance in mol)
Hexamethylene Diisocyanate Dimer (Uretdione)
Polyethylene Glycol 600 *
Polypropylene Glycol 1000 *
Mass Fraction of Isocyanate Groups in %+
*number average molar mass of
600 g/mol, or 1000 g/mol
+ determined according to DIN 53185
The diisocyanates were charged to the reaction vessel;
at a temperature of 30 °C, the other constituents were slowly added. Due to
the exothermic reaction, the temperature rose to about 40 °C which temperature
was kept constant until the hydroxyl groups were completely consumed.
2262 g of an aqueous dispersion of a waterborne acrylic
modified alkyd resin having an oil length of 58 % and a mass fraction of solids
of 42 %, an acid value of 45 mg/g and a viscosity at room temperature of 1200 mPa.s
were blended with a diamine according to the ratios given in table 2. The dispersion
was then stirred at 100 min-1 for thirty minutes at 30 °C. Isocyanate
functional precursors as detailed in table 1 were then added, and the reaction mixture
was (300 min-1) stirred at 30 °C for another hour. By addition of
water, the mass fraction of solids was again adjusted to 42 %. Thixotropic dispersions
of waterborne alkyd resins were obtained.
Table 2 Thixotropic Alkyd Resin Dispersions
Hexamethylene Diamine (mass in g)
m-Xylylene Diamine (mass in g)
Isocyanate Functional Intermediate of Table 1
mass in g
mass of thixotropy agent in g
Viscosity* at 1s-1
Viscosity* at 10 s-1
Viscosity* at 100 s-1
* dynamical viscosity in mPa·s
measured in each case at 23 °C on an aqueous dispersion at the shear gradient
The advantage of this thixotropy agent in comparison of
those of the state of the art (cf.
EP 1 264 861
DE 101 27 287
) is that much higher amounts of thixotropy agent can be used without the
risk of crystallisation of these modifiers. Moreover, while compositions of the
prior art proved to be unstable under strong shear, especially during pumping, it
has been found, surprisingly, that the thixotropic compositions according to this
invention show unimpaired recovery of their thixotropic properties after strong