Organic compounds -- part of the class 532-570 series – Organic compounds – Four or more ring nitrogens in the bicyclo ring system
Reexamination Certificate
1999-08-09
2003-01-14
Sergent, Rabon (Department: 1711)
Organic compounds -- part of the class 532-570 series
Organic compounds
Four or more ring nitrogens in the bicyclo ring system
C516S203000, C528S049000, C528S053000, C560S025000, C560S026000, C560S115000, C560S158000, C564S038000
Reexamination Certificate
active
06506899
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to polymeric pigment dispersants prepared by reacting an isocyanate with a hydrophilic poly(ethylene glycol)alkyl ether, a hydrophobic polyester or polyacrylate, and a diamine.
The materials described in this application are cationic dispersants. The cationic substitution allows their use with anionic pigments, particularly carbon black and surface treated organic pigments. In addition, the use of mixed arms provides broader solubility characteristics and utility with a wider range of coatings vehicles. These materials can therefore be considered “universal dispersants”.
There are currently several trends in the coatings industry which dictate the need to use cationic dispersants, and are therefore relevant to this invention. First, the use of isocyanate crosslinked coatings is becoming more important because, in part, they generally do not have a cure inhibition problem with cationic dispersants. Also, partially condensed melamine resins show increasing importance as used in coatings, because they are generally not so strongly inhibited by cationic dispersants. Yet another trend is that pigment suppliers are providing more pigments, particularly phthalocyanines, which have anionic surface treatments (i.e.; the pigment is acidic) which made cationic dispersants the ideal choice to achieve strong pigment-to-dispersant interaction.
The lack of emphasis in prior work on cationic functional dispersants, particularly those comprising tertiary amines, was at least partly caused by the use of dispersants in industrial and automotive coatings, which were formulated to depend on acid catalysis of melamine resins for crosslinking. Amine functional dispersants usually cause some cure inhibition in such coatings. The urea functionality incorporated using ammonia was sufficiently adsorbed on many pigments and did not interfere with the cure mechanism.
The present invention differs from prior art dispersants in that it encompasses a unique combination of hydrophobic arm(s), hydrophilic arm(s) and amine arm(s) functionality on an urethane backbone.
SUMMARY OF THE INVENTION
The present invention provides a pigment dispersant comprising a urethane polymer having at least three urethane groups, wherein
(a) a hydrophilic poly(ethylene glycol)alkyl ether;
(b) a hydrophobic polymer selected from the group consisting of polyesters and polyacrylates; and
(c) a diamine comprising a primary amine group and a tertiary amine group.
The isocyanate oligomer may be chosen from isocyanurates or biurets of toluene diisocyanate(“TDI”), hexamethylene diisocyanate (“HDI”), and mixtures thereof.
DETAILED DESCRIPTION OF THE INVENTION
The dispersants described herein are the reaction product of a multifunctional isocyanate with a polyester or polyacrylate, a polyethylene ether and a diamine. The polyester or polyacrylate and polyethylene ether “arms” have widely different solubility profiles and provide entropic stabilization for the dispersant in a wide range of solvent systems. The amine “arm” provides a functional group that can strongly interact with an acidic pigment for dispersion stability. Most preferably, the dispersants of this invention comprise the reaction product described above wherein 10 to 50 mole % of the isocyanate groups on the oligomer are reacted with a polyester or polyacrylate, 3 to 30 mole % are reacted with the poly(ethylene glycol) methyl ether and 30 to 65 mole % of the isocyanate groups are reacted with the diamine, with the proviso that 100% of the isocyanate groups are reacted.
Isocyanurates that may be used in this invention to provide the isocyanate oligomer are obtained from toluene diisocyanate (“TDI”; Desmodur IL), hexamethylene diisocyanate (“HDI”; Desmodur 3300); mixtures of TDI and HDI (Desmodur HL). A biuret that may be used is that obtained from hexamethylene diisocyanate (Desmodur N). These may be obtained from sources indicated in the Examples.
The isocyanate oligomers must have an average functionality of three or more, meaning that a molecule of the isocyanate contains, on statistical average, at least three free isocyanate groups. The average functionality, as opposed to the absolute number of isocyanate groups, is used because the isocyanates are obtained as isomeric mixtures of isocyanates having 3, 4, 5 or more functional groups. The average functionality can be determined experimentally by titrating to determine the weight % of isocyanate, determining the number average molecular weight (“Mn”) of the oligomer (such as by Gel Permeation Chromatography “GPC”), and then calculating the average number of isocyanate groups.
The dispersants of this invention are prepared by sequentially reacting the polyester or polyacrylate, the poly(ethylene glycol), and the diamine with the selected isocyanate oligomer. At the conclusion of the synthesis, all of the isocyanate groups have been reacted.
The polyesters suitable for use in the invention have the general formula:
HO(C
5
H
10
—CO
2
)
n
R
where R is an alkyl of 1 to 12 carbons and n is an integer of 6 to 10. These polyesters are conveniently prepared by reacting caprolactone with an alcohol. The length of the polyester arm for any particular dispersion is determined by a balance between its being long enough to give good pigment dispersion and yet not so long that it crystallizes too readily to produce a unstable solution. A typical synthesis of the polyester arm using n-decanol and caprolactone, is shown in the following figure:
The length of the arm containing six repeat units (i.e., n=6) is calculated at 6.63 nm and the length of the arm containing nine repeat units (n=9) is 9.25 nm.
Polyacrylates useful in the present invention are hydroxy-terminated (meth)acrylic polymers. Such polymers are prepared by reacting (meth)acrylic monomers with 2-mercaptoethanol in the presence of a free radical initiator. Azo initiators such as azobisisobutyronirile (VAZO® 64, E. I du Pont de Nemours & Co., Wilmington, Del.) are particularly useful. Other useful monomer compositions and initiating conditions are described in U.S. Pat. No. 4,032,698, the disclosure of which incorporated herein in its entirety. The preparation of the polyacrylate arm is illustrated schematically by the following equations:
Poly(ethylene glycol)alkyl ether polymers useful in this invention are those having the general formula
H(O—CH
2
—CH
2
)
n
—OR
where n is an integer of 15 to 67 and R is an alkyl of 1 to 4 carbons, preferably methyl. The poly(ethylene glycol)alkyl ethers have a number average molecular weight (“Mn”) between 750 and 3000, preferably between 900 and 2500, and all ranges encompassed therein. The poly(ethylene glycol)alkyl ethers have a single hydroxyl functional group. Such polymers are commercially available from Aldrich Chemical and other sources. Alternatively, poly(ethylene glycol)alkyl ether polymers can easily be prepared using conventional techniques well known to those skilled in the art.
Suitable diamines useful in the invention are those having a primary amine and a tertiary amine. Such diamines have the general formula:
where n is an integer of 2 to 5, preferably 3, R
1
and R
2
are each independently an alkyl of 1 to 4 carbons or together form a saturated or unsaturated 5 to 8 member ring optionally containing N or O. Three diamines which are preferred are:
1-(3-aminopropyl)imidazole is the most preferred. It has the complexing activity of pyridine, but is more basic. It has a relatively low equivalent weight, and is commercially available. In the experimental results reported herein, it was necessary to use a 10 to 15% calculated excess of isocyanate to ensure complete consumption of all of the diamine used in the last step of the synthesis.
The dispersants of this invention can thus be schematically illustrated by the figure below, in which a tri-functional isocyanate has been reacted with a diamine, a polyester and a poly(ethylene glycol)methyl ether. It should be recognized that, in accordance with the invention, the polyester could be substituted with a pol
Benjamin Steven C.
E. I. du Pont de Nemours and Company
Sergent Rabon
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