Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-01-21
2001-12-11
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C525S311000
Reexamination Certificate
active
06329447
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to alkene latex copolymer compositions and processes for producing the copolymer compositions whereby enhanced incorporation of the alkene, e.g., ethylene, can be achieved at low reaction pressures, e.g., 4 million pascals (“MPa”).
BACKGROUND OF THE INVENTION
Latex paint coatings are typically applied to substrates and dried to form continuous films for decorative purposes as well as to protect the substrate. Such paint coatings are often applied to architectural interior or exterior surfaces, where the coatings are sufficiently fluid to flow out, form a continuous paint film, and dry at ambient temperatures.
A latex paint ordinarily comprises an organic polymeric binder, i.e., latex, pigments, and various paint additives. In dried paint films, the polymeric binder functions as a binder for the pigments and provides adhesion of the dried paint film to the substrate. The pigments may be organic or inorganic and functionally contribute to opacity and color in addition to durability and hardness, although some paints contain little or no opacifying pigments and are described as clear coatings. The manufacture of paints involves the preparation of a polymeric binder, mixing of component materials, grinding of pigments in a dispersant medium, and thinning to commercial standards.
Two types of copolymers commonly used in formulating latex paints include: (i) an all acrylic system, e.g., copolymers of methyl methacrylate, butyl acrylate or 2-ethylhexyl acrylate with small amounts of functional monomers, such as, carboxylic acids; and (ii) vinyl acetate-based copolymers usually in combination with a small proportion of the above-mentioned lower alkyl acrylates, such as, for example, butyl acrylates. Because of its low cost, vinyl acetate is an attractive alternative to certain acrylate monomers, e.g., methyl methacrylate, for use in architectural coating latexes. Unfortunately, vinyl acetate suffers from poor hydrolytic stability especially under alkaline conditions and accordingly, finds only limited application in exterior coatings. Alkali resistance is extremely important, for example, when paints are applied over an alkaline construction material, such as, for example, cement.
Ethylene is a desirable comonomer for polymerization with vinyl acetate to form latexes because ethylene has properties which can compensate for the shortcomings of vinyl acetate. More specifically, because of ethylene's low molecular weight, it permits a high level of introduction of non-hydrolyzable segments on a per weight basis which can improve the hydrolytic stability properties of the vinyl acetate copolymer. Stated another way, the hydrocarbon segments provided by the ethylene tend to reduce water solubility, thus imparting greater hydrolytic stability. Moreover, ethylene has a low glass transition temperature which can provide enhanced copolymer hydrophobicity and enhanced water and alkali resistance.
However, ethylene is a gas at normal temperatures and pressures and does not readily react with vinyl acetate unless at elevated pressures. The reaction normally requires special reactors with suitable wall thicknesses, pressure resistant seals and valves and other apparatus which are not necessary in conventional emulsion polymerization. Therefore, plant costs are often significantly higher for polymerizations involving ethylene than for conventional latex polymerization processes. As a result, the benefits expected from the use of ethylene can be offset or nullified by the high costs associated with using ethylene.
Accordingly, new latex copolymer compositions based on the use of alkenes, e.g., ethylene, as comonomers are desired which do not require high pressure apparatus commonly associated with the polymerization of alkene copolymers. Desirably, such compositions would have utility in a variety of applications, particularly for use as latex paints. Also, efficient processes for the production of such latex copolymers are desired which can provide enhanced levels of alkene incorporation at a given reaction pressure.
SUMMARY OF THE INVENTION
By the present invention, alkene latex copolymers are provided which are suitable for use as latex paints as well as in other applications where latex copolymers may be used.
The alkene latex copolymer compositions comprise an inner particulate material and an outer copolymer copolymerized from the alkene and other monomer(s). Lower vinyl esters, e.g., vinyl acetate, are used as comonomers with the alkenes in order to provide the latex copolymer composition with desirable properties.
Quite surprisingly in accordance with the present invention, it has been found that the presence of the inner particulate material can enhance the incorporation of the alkene into the latex copolymer. As a result, it is now possible to prepare alkene latex copolymer compositions at significantly lower pressures than previously efficiently possible, e.g., typically about 4 MPa and often to as low as about 0.2 MPa.
In addition, the present invention provides improved processes for the production of the alkene latex copolymers. In one aspect of the invention, the process comprises introducing the inner particulate material to a reaction zone either prior to or during the introduction of an alkene monomer, e.g., ethylene, and a lower vinyl ester monomer, e.g., vinyl acetate, and optionally other monomers, e.g., higher vinyl esters, such as, for example, vinyl neodecanoate. In another aspect of the invention, the process involves a polymerization of at least one vapor monomer, e.g., ethylene, and at least two liquid monomers, e.g., vinyl acetate and vinyl neodecanoate, wherein the two liquid monomers are introduced to the reaction zone at feed rates which are varied in a manner effective to enhance the incorporation of the vapor monomer into the latex copolymer.
DETAILED DESCRIPTION OF INVENTION
The alkene monomers suitable use in accordance with the present invention comprise unsaturated hydrocarbons, e.g., olefins, typically having from 2 to about 12, preferably 2 to about 8 and more preferably from 2 to about 6 carbon atoms per molecule. The alkenes may have a straight chain structure, branched chain structure or a cyclic structure and may, or may not, by hetereogeneous, e.g., contain oxygen, nitrogen or sulfur. Often, the alkene monomers are vapor monomers. The vapor monomers suitable for use in accordance with the present invention include all monomers which exist in a vapor state at standard temperature and pressure, e.g., 0.1 MPa at 25° C. Preferred vapor monomers include lower alkene monomers, e.g., ethylene, propylene and butylene. Other suitable vapor monomers include vinyl halides, e.g., vinyl chloride, vinyl bromide and vinyl fluoride and suitable aliphatic conjugated dienes, such as 1,3 butadiene and butadiene monomers, such as methyl-2-butadiene, 2,3-dimethyl butadiene, blends of the diene monomers and the like. In one aspect of the invention, an ethylene-propylene monomer mixture is used but different vapor monomer combinations can be used as desired in order to achieve desired copolymer properties, such as Tg, for example. The amount of the alkene monomers used in the latex copolymer compositions of the present invention is from about 0.5 to 95 wt. %, preferably from about 0.5 to 60 wt. % and more preferably from about 2 to 40 wt.%, based upon the total weight of the outer copolymer; that is, the total weight of monomers used to make the outer copolymer, exclusive of the inner particulate material when used. For instance, if the inner particulate material is a vinyl acetate copolymer having a total weight of 5 grams, the outer copolymer contains 20 grams of vinyl acetate, and the total weight of the monomers used to make the outer copolymer is 100 grams, then the concentration of vinyl acetate is 20 weight percent. Suitable alkene monomers for use in accordance with the present invention are commercially available.
The lower vinyl esters suitable for use in accordance with the present invention include all lower
Avramidis Kostas S
Bassett David R
Jenkins Richard D.
Tan Chee B
Black Edward W.
Michl Paul R.
Union Carbide Chemicals & Plastics Technology Corporation
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