Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-07-16
2001-06-19
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S600000, C524S832000, C526S318200, C526S318300, C526S318400, C526S318440
Reexamination Certificate
active
06248826
ABSTRACT:
This invention is concerned with polymer dispersions. More particularly, the present invention concerns polymer dispersions which are capable of demonstrating low viscosities over a broad pH range.
Aqueous dispersions of carboxylic acid containing polymers are known to have many applications, including use as binders in coating compositions. Typically, these polymer dispersions are formed from the emulsion polymerization of a mixture of ethylenically unsaturated monomers comprising up to 20% by weight of a carboxylic acid containing monomer, such as acrylic acid (AA) or methacrylic acid (MAA). Such polymer dispersions demonstrate relatively low viscosities at low pH levels, e.g. pH 3-5, but tend to demonstrate significantly higher viscosity's at higher pH levels, e.g. pH 8 to 10. Polymer dispersions with low viscosities can be formulated to comprise higher polymer solids, e.g. 50% by weight polymer solids, whereas in comparison dispersions with high viscosity's can only be formulated to comprise lower polymer solids, e.g. 40% by weight polymer solids. Accordingly, to minimize transport costs, the polymer manufacturer would prefer to supply customers with low pH, high polymer solids dispersions.
Since coating compositions, such as paints, are usually formulated at a pH in the range 8 to 10, and since the polymer manufacturer likes to supply the coatings manufacturer with a ready-to-use dispersion, the polymer dispersion is preferably supplied at an appropriately high pH. However, formulating high solids polymer dispersions into paints at high pH can result in coagulation or gellation of the formulation. Consequently, the carboxylic acid containing polymer dispersions which are traditionally supplied at the high pH either have a relatively lower solids content and/or comprise a significant quantity of anionic surfactant. This means that not only are the polymer manufacturer's transport costs higher, as he has to transport relatively more water in the dispersion, but also the coating compositions have to contain relatively higher quantities of water and/or surfactant.
These problems are particularly acute where it is desired to manufacture high solids polymer dispersions where the particle size of the polymer is required to be very small, e.g. 100 nm or less. These dispersions tend to be highly viscous at high pHs, and consequently require very high levels of anionic surfactants to enable their manufacture even at relatively low polymer solids.
A process for the preparation of finely particulate plastics dispersions from a monomer mixture comprising various ethylenically unsaturated monomers, including 0.1 to 5% by weight of an &agr;,&bgr;-unsaturated monocarboxylic acid is disclosed in U.S. Pat. No. 4,193,902. The process involves metering the monomer mix simultaneously with an initiator into an aqueous liquor containing from 0.5 to 10% by weight of an anionic emulsifier, polymerizing the monomers to form the dispersion, and adjusting the dispersion to a pH of 7 to 10. The quantitative ratio of monomers to water is chosen in such a manner that the resulting dispersion contains from 20 to only 45% of solids.
Dispersions of polymers formed from a monomer mix comprising 8 to 20% by weight of an olefinically unsaturated C
3
-C
5
mono- or C
4
-C
8
-dicarboxylic acid or anhydride are disclosed in U.S. Pat. No. 5,356,968. The dispersions, which may comprise 10 to 60% by weight solids, are obtained by emulsion polymerization of the monomers in the presence of an emulsifier mixture comprising at least two anionic emulsifiers and optionally one or more nonionic emulsifiers. The mixture is present in an amount of from 0.5 to 7% by weight based on the weight of monomers. The average particle size of the polymer in the dispersion is from 60 to 100 nm. Though it is disclosed that to produce only a small increase in viscosity at about pH 7-10, relatively large amounts of free radical initiator are required, the increase in viscosity as pH increases to 7-10 is still quite significant.
U.S. Pat. No. 5,141,814 discloses non-ionically stabilized core-sheath addition polymer particles of 100 nm maximum average diameter, the core comprising addition polymer and being water insoluble and the sheath comprising polyoxyalkylene chains of average chain length of from 6 to 25 oxyalkylene units per chain. At least 20 percent of the chains are covalently bonded to the core and there being present on the core sufficient chains such that the mass ratio of core to sheath is from 98:2 to 60:40. Though these sterically stabilized dispersions are described to be relatively insensitive to pH changes and the dispersions are exemplified to have high solids content, only small proportions, e.g. up to 5% by weight of the core polymer, of ionic monomers such as acrylic acid and methacrylic acid can be tolerated. Further, environmental pressures are being placed on manufacturers to reduce or eliminate the use of polyoxyalkylenes.
In DE-A-4026640, it is disclosed that oligomeric carboxylic acids can be used as stabilizers for the emulsion polymerization of olefinically unsaturated monomers and that this leads to fine particulate polymer dispersions that are coagulate-free and extremely shear stable. The dispersions may contain 20 to 65% by weight dispersed polymer with a mean particle diameter of less than 100 nm. In the worked examples, the stabilizer is present in an amount of from 16-46% by weight of polymer. There is no disclosure or suggestion that the oligomeric carboxylic acids would be useful for stabilizing carboxylic-containing polymer dispersions.
Aqueous coating and lacquer compositions comprising a graft copolymer having carboxylic-acid functional macromonomers attached at a terminal end thereof to a polymeric backbone are described in WO-A-9532228 and WO-A-95322255, respectively. Though the references generally refer to the macromonomer being polymerized from carboxylic functional monomers, such as acrylic acid, methacrylic acid, maleic acid, itaconic acid and their anhydrides, methacrylic acid based macromonomers are clearly preferred and only these methacrylic acid based macromonomers are exemplified. High solids dispersions of copolymers formed from methacrylic acid based macromonomers can be prepared with small particle sizes. However, the worked examples (see, for example, worked Example 8), indicate that copolymers formed from methacrylic acid based macromonomers are not capable of demonstrating low viscosities at high pH, such as at pH 9.
It is an object of the present invention to provide a dispersion of carboxylic-acid containing polymer which is capable of demonstrating low viscosities over a broad pH range. It is a further object of this invention that the dispersion can be manufactured by conventional emulsion polymerization techniques and does not essentially require the use of significant quantities of anionic surfactant.
In accordance with the present invention, there is provided an aqueous dispersion of a copolymer formed by the emulsion polymerization of a monomer mixture comprising:
a) from 0.1 to 20% by weight of one or more terminally unsaturated oligomers of the formula:
wherein N is a residue of the formula:
wherein M is the residue of an ethylenically unsaturated monomer;
wherein said N and M residues are randomly arranged in said oligomer;
wherein m is the total number of M residues in said oligomer and is in the range 0 to 47;
wherein n is the total number of N residues in said oligomer and is in the range 2 to 140; and
wherein the sum of n and m is in the range from 3 to 150; and
b) from 80 to 99.9% by weight of at least two monomers selected from the group consisting of esters of acrylic and methacrylic acid with alcohol containing from 1 to 24 carbons, amides of acrylic and methacrylic acid, vinyl esters of carboxylic acids containing from 1 to 20 carbons, vinyl-aromatic compounds containing compounds containing up to 20 carbons, ethylenically unsaturated nitrites containing from 3 to 6 carbons, vinyl halides, and non-aromatic hydrocarbons containing from 2 to
Greenblatt Gary David
Solomon Robert David
Egwim Kelechi C.
Rohm and Haas Company
Wu David W.
LandOfFree
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