Dispersants for preparing aqueous pigment pastes

Details Dispersants for preparing aqueous pigment pastes Dispersants for preparing aqueous pigment pastes

1999-08-09

2001-05-22

Cain, Edward J. (Department: 1714)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

C528S393000

Reexamination Certificate

active

06235813

ABSTRACT:

RELATED APPLICATIONS
This application claims priority to German application no. 198 36 253.6, filed Aug. 11, 1998, herein incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to polymethacrylates which are transesterified with polyetherdiols or amidated with polyetherdiamines and are subsequently functionalized at the ends, and to their use as dispersants for preparing aqueous pigment preparations.
2. Background of the Invention
In order to facilitate and to improve the dispersion of solids in liquid media it is common to employ dispersants, which at the same time are also intended to have a stabilizing effect on the resultant dispersions and to prevent reagglomeration or flocculation of the particulate solids. As surfactants, the dispersants promote wetting of the particulate solids to be dispersed, and aid in the disruption of agglomerates.
They are particularly important, for example, for the dispersion of pigments in the preparation of printing inks, paints and other coated materials and in the pigmentation of polymer compounds.
In addition, specific dispersants may act as compatibilizers to increase the compatibility between chemically different polymer types. This is of particular importance, for example, for the preparation of sheet molding compounds (SMC) and bulk molding compounds (BMC).
In the production of paints and other coating materials, wetting agents and dispersants facilitate the incorporation of pigments and fillers, which are important formulation constituents that significantly determine the visual appearance and the physicochemical properties of coatings. Optimum use requires firstly that these solids are distributed uniformly in paints and inks and secondly that the state of distribution, once attained, is stabilized. However, numerous problems may occur during the preparation and processing of aqueous pigment pastes:
difficulties in incorporating the pigments, poor wetting
high viscosities of color pastes, paints and other coating materials
sedimentation
vertical separation of pigments (flooding)
horizontal separation of pigments (floating)
low degree of gloss
low hiding power
inadequate color strength
poor shade reproducibility, shade shift
excessive tendency of coating materials to run
There has therefore been no lack of attempts to provide effective dispersing additives for solids, especially pigments. For example, water-soluble polyisocyanate adducts containing hydrophilic polyether chains (EP-A-0 731 148), acidic poly(meth)acrylates (U.S. Pat. No. 3,980,602, WO-A-94/21701), phosphate esters of polyalkylene oxide block polyesters (WO-A-97/19948) or alternating copolymers of vinyl monomers and dicarboxylic diesters (WO-A-96/14347, EP-A-0 791 024), especially copolymers based on maleic acid derivatives and vinyl monomers, are described for this purpose.
However, the use of such products is also associated with a multiplicity of disadvantages. Frequently, for instance, high levels of dispersing additives are required, the levels of paste pigmentation that can be achieved are unsatisfactorily low, the stability of the pastes and thus of their viscosity is inadequate, and flocculation and aggregation cannot always be avoided; in many cases, there is also a lack of consistency of shade following storage of the pastes and a lack of compatibility with various binders. In many cases the use of known dispersing additives also has an adverse effect on the water resistance or light stability of coatings and, moreover, provides additional stabilization of the unwanted foam which is formed in the course of the preparation in processing. Furthermore, owing to deficiencies in the compatibility of the dispersing resins in numerous vehicles, there is often an undesirable impairment of the gloss.
The phosphoric esters of amphiphilic block copolymers, in particular, are characterized by poor stability of the phosphoric ester group to hydrolysis. The water resistance of coatings prepared with these esters is also adversely affected. Furthermore, these acidic phosphoric esters generally require an addition of amine base—undesirable in the amount required—in order, for example, to establish the optimized pH of a coating system.
OBJECT OF THE INVENTION
It is therefore an object of the present invention to overcome a multiplicity of the above disadvantages, the aim being to exert a positive influence on the important processing parameters of stability of paste viscosity, substantial avoidance of flocculation and aggregation, consistency of shade after paste storage, and resistance to water of coatings produced from the pastes.
A further aim of using these products is to improve the compatibility of chemically incompatible substances.
SUMMARY OF THE INVENTION
Surprisingly, it was discovered that these and other objects could be achieved, with the inventive dispersants, based on block-polymethacrylate-block-polyalkylene oxide copolymers with terminal carboxylic acid, of the general formula I
where
R
1
is the radical of a conventional chain regulator or initiator which is free from active hydrogen atoms,
R
2
are identical or different alkyl radicals or alternatively, optionally, are substituted aryl radicals, perfluoroalkyl radicals or dialkylamino radicals,
R
3
are identical or different alkyl radicals or azyl radicals,
R
4
is an organic radical having at least one carboxylic acid or carboxylate function,
X is oxygen or NH,
a is from 4 to 20,
b is from 20 to 100, and
c is from 0 to 20, the ratio b/c being ≧ about 4.
DESCRIPTION OF PREFERRED EMBODIMENTS
The radical R
1
is a conventional chain regulator or initiator. In accordance with the prior art, mention may be made of azo compounds or peroxides, by way of example. Examples of chain regulators are mercaptans, chloroform, isopropylbenzene and isopropanol. R
1
is preferably an aliphaticthio, more preferably an alkylthio of 1 to 22 carbon atoms, with the radical —S—C
12
H
25
especially preferred. Further examples of radicals originating from the chain regulator, which are especially preferred, are the radicals derived from tert-dodecyl mercaptan, octadecyl and tetradecyl mercaptan.
R
2
is preferably an alkyl radical of 1 to 22 carbon atoms, more preferably 1 to 4 carbon atoms, with a methyl or butyl radical especially preferred. Preferred perfluoroalkyl radicals are those having 1 to 22 carbon atoms. Examples of especially preferred perfluoroalkyl radicals are the trifluoroethyl, pentafluoropropyl, nonafluorohexyl and tridecafluorooctyl radicals.
X is an oxygen atom if &agr;,&ohgr;-polyalkoxyetherdiols are used and an NH group if &agr;,&ohgr;-polyetherdiamines are used.
R
3
is an alkyl or aryl group. Preferably R is an alkyl group of 1 to 4 carbon atoms. Most preferably, R
3
is a methyl or phenyl group.
The indices b and c can be identical or different and are usually within the range from 20 to 100 for b and in the range from 0 to 20 for c. The ratio b:c here is preferably ≧ about 4. The different alkoxy units can be incorporated in blocks or else at random in the polyalkoxy chain. Examples of suitable alkoxylating agents are ethylene carbonate, propylene carbonate, styrene oxide, butylene oxide, especially propylene oxide and, in particular, ethylene oxide, and also mixtures thereof.
The radical R
4
contains at least one carboxylic acid unit or at least one carboxylate unit. Preferred radicals are aliphatic radicals having at least one carboxylic acid unit or at least one carboxylate unit. Examples of R
4
are all products resulting from the reaction of an alcohol with anhydrides. Preferred anhydrides are succinic anhydride, maleic anhydride, phthalic anhydride and trimellitic anhydride. Similarly, where X=NH the analogous monoamide compounds are formed.
Examples of R
4
:
Z is a cation. Preferably, Z is an alkali metal or ammonium radical which may optionally be alkyl-bstituted. Examples of such substituted ammonium radicals are the radicals —NH(CH
3
)
3
, —NH(C
2
H
5
)
3
and —NH(CH
2
—C
6
H
5
)(CH
3
)
2
. It is also possible to select the cations k

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