Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-12-05
2003-02-25
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S406000, C523S408000, C523S409000, C523S412000, C523S459000, C525S329700, C525S385000
Reexamination Certificate
active
06525115
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of making an aqueous dispersion of particles comprising epoxy-functional and acid-functional materials. Coating compositions made from such a dispersion can be used to protect various substrates.
BACKGROUND OF THE INVENTION
Aqueous dispersions of epoxy-containing particles have been prepared by various methods known in the art. One such method of preparing an aqueous dispersions is the so-called “inverse emulsification” technique such as disclosed in U.S. Pat. No. 5,741,835 to Stark. The process typically involves melting an epoxy compound and a surfactant together. Optionally a base is added to the melt. Hot water is then slowly added to the epoxy melt at vigorous agitation until inversion takes place, from a water in oil to an oil in water mixture, after which additional water can be added. Stark states that the invention provides a stable good aqueous dispersion having an average particle size of preferably less than about 2 &mgr;m, more preferably less than about 1 &mgr;m.
U.S. Pat. No. 4,446,258 to Chu et al. discloses dispersing the reaction product of an epoxy resin and an acid polymer. Preferably, the ionic epoxy-resin-acid polymer product is dispersed in water with an ammonia or an amine, to neutralize the polymer product, in the presence of a polymeric surfactant.
Such water-borne products of carboxy-functional polymers and epoxy-functional polymers have been widely used in coatings for decorative and/or protective purposes, for example, in the fields of architectural, automotive, and industrial coatings. Such coatings have general utility for coating metallic and various other substrates and articles, including, for example, metallic cans. As mentioned in U.S. Pat. No. 4,247,439 to Matthews et al. such coatings can provide, for example, corrosion resistance, gloss, hydrolytic stability, non-adulterating of foods and beverages in contact therewith.
Particle dispersions of photographically useful compounds have been prepared using an evaporated solvent technique. For example, U.S. Pat. No. 2,801,171; U.S. Pat. No. 2,835,579; and U.S. Pat. No. 2,949,360 disclose a suspension technique that involves dissolving a particle material in a water immiscible solvent, dispersing the solution as fine liquid droplets in an aqueous solution, and removing the solvent by evaporation or other suitable means.
In the field of imaging, there have been attempts over the years to provide a protective coating for gelatin based photographic products that will protect the images from damage by water or aqueous solutions. A number of patents describe methods of solvent coating a protective layer on the image after photographic processing is completed, for example, U.S. Pat. Nos. 2,259,009, 2,331,746, 2,798,004, 3,113,867, 3,190,197, 3,415,670 and 3,733,293. A drawback for a solvent coating method is the health and environmental concern of those chemicals to the coating operator.
A number of patents have been directed to water-resistant protective coatings that can be applied to a photographic element prior to development. U.S. Pat. No. 5,853,926 to Bohan et al. discloses a protective coating for a photographic element, involving the application of an aqueous coating comprising polymer particles and a soft polymer latex binder. This coating allows for appropriate diffusion of photographic processing solutions, and does not require a coating operation after exposure and processing. The hydrophobic polymer particles must be fused to form a protective coating that is continuous and water-impermeable. U.S. Pat. No. 5,856,051 describes the use of hydrophobic particles with gelatin as the binder in an overcoat formulation. This invention demonstrated an aqueous coatable, water-resistant protective overcoat that can be incorporated into the photographic product, and allows for appropriate diffusion of photographic processing solutions. The hydrophobic polymers exemplified in U.S. Pat. No. 5,856,051 include polyethylene having a melting temperature (Tm) of 55 to 200° C. A layer comprised of such polymers is capable of becoming water-resistant by fusing the layer at a temperature higher than the Tm of the polymer, after the sample has been processed to generate the image.
An objective of the present invention is to provide an improved method of making an aqueous dispersion involving epoxy-containing particles for use in a coating composition that can be used to cover and protect various substrates. It is desirable that one such use be to protect imaged elements such as photographic or other prints, so that the coated product resists fingerprints, common stains, and spills.
SUMMARY OF THE INVENTION
The present invention relates to a method of making an aqueous dispersion of particles comprising epoxy-functional and acid-functional materials for use in coating compositions. Such coatings can be used to protect various substrates including photographic prints.
The method of making an aqueous dispersion of epoxy-functional particles comprises (a) dissolving into a volatile solvent mixture an oil-soluble epoxy-functional resin and a polymer having acid groups, preferably characterized by an acid number between 30 and 200, wherein the volatile solvent mixture comprises a water-immiscible organic solvent as the major component and a water-miscible organic solvent as a minor component; (b) adding to the organic solvent medium a base to neutralize the acid groups to a degree of neutralization less than 95%; (c) dispersing the resulting organic phase into an aqueous medium; and (d) removing the volatile solvent mixture. In one embodiment, the thus produced epoxy-containing particles comprise (1) at least 50%, by dry weight of the particle, of a solid epoxy resin, which particles having a glass transition temperature of greater than 20° C. and a mean particle size of not more than 500 nm, and (2) a polymer having acid groups. Optionally, further components such as binders, surfactants, lubricants, thickeners, or other additives may also be present in the dispersion or coating made therefrom.
Another aspect of the invention provides a method of forming a coating by applying a coating composition according to the present invention to a substrate and drying the composition to produce a clear or colored coating that protects the substrate from environmental damage.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention provides a simple and inexpensive way to make an aqueous dispersion of epoxy-containing particles. In accordance with the invention, a coating composition comprising such particles can be applied over a substrate. For example, an overcoat formulation according to the present invention can be applied to the emulsion side of photographic products, particularly photographic prints that may encounter frequent handling and abuse by end users.
In one embodiment, a preferred method of making epoxy-containing particles for use in a coating composition according to the present invention comprises (1) dissolving into a volatile solvent mixture an oil-soluble epoxy-functional compound and a polymer having an acid number greater than 30 and less than 250, preferably greater than 60 and less than 150, and optionally a surfactant, (2) adding to the organic solvent mixture a base to neutralize the acid groups to a degree of neutralization less than 95%, preferably less than 90%, (3) dispersing the resulting organic phase into an aqueous medium optionally containing a surfactant, and (4) removing the volatile solvent mixture. Preferably, the volatile solvent mixture comprises a water immiscible organic solvent as the major component and a water miscible organic solvent as a minor component. Such a process advantageously provides very fine submicron particles having a narrow particle size distribution. The average particle size is less than 500 nm. This contributes to improved coating properties. The dispersions also have excellent stability during storage.
Suitably, in steps (1), (2) and (3), the temperature is essentially maintained at a temper
Bello James L.
O'Connor Kevin M.
Schroeder Kurt M.
Wang Yongcai
Aylward D.
Dawson Robert
Eastman Kodak Company
Konkol Chris P.
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