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
1997-02-13
2003-07-08
Reddick, Judy M. (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...
C522S071000, C522S083000, C522S084000, C522S085000, C522S086000, C523S402000, C523S409000, C523S410000, C523S411000, C523S412000, C523S415000, C524S556000, C524S558000, C524S591000, C524S612000, C524S560000, C524S549000
Reexamination Certificate
active
06590025
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to latex compositions, particularly one-pack storage-stable latex compositions. The present invention is especially useful for latex compositions which are capable of undergoing radiation-curing. Such latex compositions are useful in coatings (especially on wood and wood products, metal, plastic, and leather), adhesives, inks, and caulks. Such compositions exhibit improved dry speed.
Dry speed is an important property in many applications. In the early stages of drying, waterborne latex formulations are soft and tacky, and can therefore be easily damaged. (The faster the dry speed, the faster the hardness develops in the coating, ink, caulk, etc.) Rapid dry speed is particularly important in production lines where faster line speeds lead to higher rates of production. For example, in the printing industry, the dry speed of the ink is critical in maintaining the fastest possible press speeds. Another area where dry speed in critical is waterborne ultraviolet (UV) curable compositions. If the coated composition has not dried sufficiently prior to cure, the application of UV radiation will permanently entrap any water or other solvent still remaining in the film. As many waterborne compositions are milky in the wet state, this permanent entrapment of water can cause the resultant films to appear milky or streaked.
EP 313 179 A2 (Bogdany) discloses a modified latex composition having improved adhesion and drying rates. The modification is the addition of an aromatic or alkyl substituted aromatic polyisocyanate to the latex shortly before application of the composition to the substrate. Such composition is useful for forming a coating on a primary carpet substrate, or for other adhesive applications.
A significant drawback to Bogdany is the short pot life of the modified latex composition. Bogdany teaches that the polyisocyanate should be added just before application of the composition to an appropriate substrate in order to control the increase in viscosity of the resulting composition. This is due primarily to the well-known propensity of isocyanates to react prematurely with the latex, and to “gel out” while still in the container.
What is desired, then, is an one-pack, storage-stable latex composition having improved drying speed.
STATEMENT OF THE INVENTION
One aspect of the present invention is directed to a modified latex having improved drying speed, comprising a polymer having one or more pendant side chains, such side chain comprising the product of the reaction between a mono- or poly-functional group capable of reacting with an acid or hydroxyl unit, and such units present on the precursor polymer.
Another aspect of the present invention is directed to a method for providing a crosslinked protective coating on a substrate, comprising the steps of: applying a coating of the composition of the present invention to the substrate; and allowing the composition to cure at ambient temperature or greater, or applying radiation to the composition to effect curing.
DETAILED DESCRIPTION OF THE INVENTION
As used in this specification, the following terms have the following definitions, unless the context clearly indicates otherwise. “Latex” or “latex composition” refers to a dispersion of a water-insoluble polymer which may be prepared by conventional polymerization techniques such as, for example, by emulsion polymerization. “Precursor latex” or “precursor latex composition” refers to the latex of the present invention prior to addition of the pendant side chains. “Crosslinkable” and “crosslinking” refer to the formation of new chemical bonds between existing polymer chains, and “curing” refers to the crosslinking polymers after application to the substrate. “Storage-stable” refers to a composition wherein the reactive components do not substantially crosslink within the storage container itself, even after prolonged storage. “Pot life” or “shelf life” refers to the period of time a composition is storage-stable. “Two-pack” or “two-component” refers to coating compositions (or systems) wherein the components are stored separately, then are mixed together just before use; on the other hand, “one-pack” or “one-component” refers to coating compositions wherein the components are stored in one container. Ranges specified are to be read as inclusive, unless specifically identified otherwise.
In the present invention, the precursor latex compositions of the present invention include but are not limited to: acrylic emulsions, vinyl addition emulsions, polyurethane emulsions, styrene butadiene emulsions, alkyd emulsions, epoxy emulsions, polyether emulsions, polyester emulsions, polyurea emulsions, and combinations thereof (e.g. acrylic/polyurethane hybrid emulsion or blend). These polymers may be single or multi-staged latex particles. Multi-staged latex particles will comprise at least two mutually incompatible copolymers having any of a number of morphological configurations, for example: core/shell; core/shell particles with shell stages incompletely encapsulating the core; core/shell particles with a multiplicity of cores, interpenetrating network particles; and the like, where the greater portion of the surface area of the particles will be occupied by at least one outer stage, and the interior of the particle will be occupied by at least one inner stage.
The present invention is particularly applicable to radiation-curable polymers. Examples of anionically stabilized, radiation-curable polymers useful in the present invention include but are not limited to those disclosed and described in: U.S. Pat. No. 4,287,039 (Buethe, et al.), DE 4,011,353 and DE 4,011,349 (Kressdorf et al.), DE 4,031,732 and DE 4,203,546 (Beck et al.), EP 399,160 (Flakus, W.), EP 392,552 (Haberle et al.), EP 518,020 (Flakus), CA 2,07,097 (Mexiner, et al.), U.S. Pat. No. 5,306,744 (Wolfersberger et al.), U.S. Pat. No. 4,730,021 (Zom et al.), U.S. Pat. No. 4,107,013 (McGinniss et al.), and EP 442,653 (Pears, et al.). The contents of these patents are hereby incorporated by reference herein.
Depending on the particular use, the precursor latex compositions of the present invention will generally contain between 10 wt % and 70 wt % of polymer solids. For coating applications, it is preferred to use between 20 wt % and 50 wt % of polymer solids, most preferably between 25 wt % and 50 wt %.
The side chains of the modified latex of the present invention comprise any mono- or poly-functional group capable of reacting with an acid or hydroxyl unit. Such side chains are attached to the precursor polymer by reaction of the mono- or poly-functional group with acid or hydroxyl units present on the precursor polymer. Such groups include but are not limited to mono- or poly-functional: aziridines, carbodiimides, isocyanates, epoxies, epoxysilanes, aminoplasts, and oxazoline. Such compounds include but are not limited to: 1-aziridinepropanoic acid, 2-methyl, 2-ethyl-2-[3-(2-methyl-1-aziridinyl)-1-oxopropoxylmethyl]-1,3propanediylester octyl isocyanate, and glycidoxypropyl(trimethoxysilane). It is preferred to use materials that are easily incorporated into the emulsion such as epoxysilanes, carbodiimides and aziridines.
The side chains are added to the precursor latex using methods known to those skilled in the art. The simplest method is to blend an appropriate amount of the side chain functionality with the appropriate amount of precursor latex with stirring, and then allow the mixture to react for a period of time, typically 24-48 hours. Depending on the type of side chain functionality being attached, and the particular use for the resultant latex, the side chain functional group will be added to the precursor latex in an amount between 1 and 20 wt %, based on the total weight of the polymer, preferably between 2.5 and 10%.
Surfactants are commonly used in emulsion or dispersion polymerization to provide stability, as well as to control particle size. Conventional surfactants include anionic or nonionic emulsifiers or their combination. Typical
Beckley Ronald Scott
Carlson Virginia Ann
Reddick Judy M.
Rohm and Haas Company
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