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
2001-09-13
2004-10-26
Cheung, William K. (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...
C524S458000, C524S601000
Reexamination Certificate
active
06809141
ABSTRACT:
The present invention relates to an aqueous dispersion of a segmental copolymer, wherein films formed from the aqueous dispersion display an improved balance of properties related to hardness and softness, and to the segmental copolymer of which the aqueous dispersion is comprised.
Polymeric films are typically formed by deposition of a solution or dispersion of a polymer in a solvent or dispersing medium, respectively. Evaporation of the layer thus formed will result in a continuous film for some polymer compositions, but not for others. For example, a dispersion including polymeric particles, the polymeric chains of which have a glass transition temperature in the range of −40° C. to 70° C., may form a continuous film, with the likelihood of such formation increasing for polymers having Tg values near, or below, the temperature at which film formation is attempted, often room temperature. Unfortunately, films that are easily formed often exhibit poor hardness related properties. They tend to be “soft” and tacky. This tackiness translates into a tendency for the surface of the film to retain dirt particles that contact it. Tackiness also translates into “block”, the tendency for two films to stick to one another, or for a single film to stick to itself. The softness further translates into unrecoverable deformation, called “print”. “Print” is observed when an object is placed upon a film and, upon removal, the imprint of the object does not go away.
It is, therefore, highly desirable to form films that have a “hardness” component. This hardness translates into films having surfaces that resist scratching, dirt pick-up, and block. Truly “hard” films are difficult to achieve because the relatively high glass transition temperature, “Tg”, required to produce such films renders the actual formation of films difficult or impossible. When these “hard” films are achieved, for example, by adding high levels of a coalescent to an aqueous dispersion of a hard polymer, these films often are so dominated by the hardness characteristic that they fail to exhibit softness characteristics that can contribute to overall performance of the film. Hard films are often brittle films lacking the flexibility to elongate and bend, especially at low temperature (i.e., below 20° C.), a common requirement during use.
The invention of U.S. Pat. No. 6,060,532 sought, for example, to provide coatings having a good balance of low temperature flexibility, tensile strength, and dirt pick up resistance. Low temperature flexibility is a “softness” characteristic, while tensile strength and dirt pick up resistance are characteristic of “hardness”. Coatings were formed from a binder polymer which was an elastomeric multi-stage emulsion polymer obtained by sequentially polymerizing, under emulsion polymerization conditions, a first monomer system free from polyethylenically unsaturated monomers, and which yields a first-stage polymer having a glass transition temperature from about −30° C. to about −60° C., and a second monomer system, likewise free from polyethylenically unsaturated monomers, and which yields a second-stage polymer, incompatible with the first-stage polymer, and having a glass transition temperature from 0° C. to 60° C. Used herein, these two-stage polymers are referred to a “soft/hard elastomers”, or “SHE” polymers. While the SHE polymers of U.S. Pat. No. 6,060,532 did improve the balance of hard and soft properties over that of single stage polymers having similar overall compositions, there remained a need for yet further improvement in the hard/soft balance. It was further desired to achieve that improvement while maintaining excellent film formation behavior for aqueous binder systems completely free of coalescing agents, or containing only low levels of them.
We have, surprisingly, found that aqueous dispersions of segmental copolymers can be formed into films having an outstanding balance of properties related to hardness and softness. In particular, we have been able to produce comb copolymers and aqueous dispersions of comb copolymers by a commercially viable method and form them into films having an outstanding balance of properties related to hardness and softness. The polymers can, for example, be utilized in films cast onto substrate surfaces and in free standing films.
A first aspect of the present invention relates to an aqueous dispersion, comprising at least one segmental copolymer, wherein said aqueous dispersion has a Hard/Soft Balance Advantage value of at least 25%.
A second aspect of the present invention relates to a method of forming a film comprising the steps of:
(a) forming an aqueous dispersion of a segmental polymer;
(b) applying said aqueous dispersion to a substrate; and
(c) drying, or allowing to dry, said applied aqueous dispersion;
wherein said aqueous dispersion has a Hard/Soft Balance Advantage value of at least 25%.
A third aspect of the present invention relates to a method of forming a film comprising the steps of:
(a) forming an aqueous dispersion comprising a plurality of comb copolymer particles:
wherein said comb copolymer particles comprise a comb copolymer; and
wherein said comb copolymer comprises a backbone and at least one graft segment attached thereto;
(b) applying said aqueous dispersion to a substrate; and
(c) drying, or allowing to dry, said applied aqueous dispersion;
wherein said aqueous dispersion has a Hard/Soft Balance Advantage value of at least 25%.
A fourth aspect of the present invention relates to a film produced by the method of either the second aspect or the third aspect.
A further aspect relates to an aqueous dispersion wherein the comb copolymer is produced by a polymerization method comprising the steps of:
(a) forming a macromonomer aqueous emulsion comprising a plurality of water-insoluble particles of macromonomer, wherein said macromonomer comprises polymerized units of at least one first ethylenically unsaturated monomer, said macromonomer further having:
(i) a degree of polymerization of from 10 to 1000;
(ii) at least one terminal ethylenically unsaturated group;
(iii) less than 5 weight percent polymerized acid-containing monomer, based on the weight of said macromonomer; and
(iv) less than one mole percent of polymerized mercaptan-olefin compounds;
(b) forming a monomer composition comprising at least one second ethylenically unsaturated monomer; and
(c) combining at least a portion of said macromonomer aqueous emulsion and at least a portion of said monomer composition to form a polymerization reaction mixture; and
(d) polymerizing said macromonomer with said second ethylenically unsaturated monomer in the presence of an initiator to produce said plurality of comb copolymer particles.
In a still further aspect, the comb copolymer has a weight average molecular weight of 50,000 to 2,000,000.
In yet another aspect, the graft segment of the comb copolymer is derived, as a polymerized unit, from a macromonomer; wherein the graft segment comprises, as polymerized units, from 5 weight percent to 50 weight percent of a non-methacrylate monomer, based on the weight of the macromonomer.
In another aspect, the graft segment of the comb copolymer is derived, as a polymerized unit, from a macromonomer; wherein the graft segment comprises, as polymerized units, less than 5 weight percent acid containing monomer, based on the total weight of said macromonomer.
In another aspect, the graft segment of the comb copolymer is derived, as a polymerized unit, from a macromonomer, wherein said graft segment has a degree of polymerization of from 10 to 1,000, where the degree of polymerization of said graft segment is expressed as the degree of polymerization of said macromonomer.
In another aspect, the graft segment of the comb copolymer has a glass transition temperature of 30° C. to 130° C.
In another aspect, the backbone of the comb copolymer has a glass transition temperature of −90° C. to 50° C.
Used herein, the following terms have these definitions:
The “backbone” of a polymer chain is a collection of polymer
Bromm Karl A.
Fasano David M.
Larson David A.
Lau Willie
Thibeault Jack C.
Cheung William K.
Clikeman Richard R.
Rohm and Haas Company
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