Package making – Methods – With contents treating
Reexamination Certificate
2000-03-20
2002-03-12
Gerrity, Stephen F. (Department: 3721)
Package making
Methods
With contents treating
C053S467000, C053S474000, C053S1110RC
Reexamination Certificate
active
06354063
ABSTRACT:
This invention pertains to latex air dry paints and more specifically to a method of inhibiting non-water-dispersible paint skin formation on the interior lids of containers for latex paints.
BACKGROUND OF THE INVENTION
Paint coatings are surface coatings applied to substrates and dried to form continuous films for decorative purposes as well as to protect the substrate. Most consumer paint coatings are air-drying aqueous coatings applied primarily 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 to protect the substrate surface. A paint coating ordinarily comprises an organic polymeric binder, 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. Some paint coatings contain little or no opacifying pigments and are described as clear coatings. The manufacture of paint coatings involves the preparation of a polymeric binder, mixing of component materials, grinding of pigments in a dispersant medium, and thinning to commercial standards.
Latex paints for the consumer market ordinarily are based on polymeric binders prepared by emulsion polymerization of ethylenic monomers. A typical consumer latex paint binder may contain a vinyl acetate copolymer consisting of polymerized vinyl acetate (80%) and butyl acrylate (20%). The hardness of the latex polymer must be balanced to permit air drying and film formation at ambient temperatures, which requires soft polymer units. At the same time the polymer must be hard enough in the final dry film to provide resistance properties, which requires hard polymer units. Coalescing solvents function to externally and temporarily plasticize the latex polymer for time sufficient to develop film formation, but then diffuse out of the coalesced film after film after film formation, which permits film formation and subsequent development of the desired film hardness by the volatilization of the coalescent. Such latex paints are prone to develop water insoluble films, commonly known as “skins”, on the non-submerged interior surfaces of plastic or metal containers used for shipping paint products. Skinning on container lids is a particularly troublesome problem. A paint skin formed in the absence of an inhibitor will not uniformly re-disperse into the bulk paint during shaker mixing that is normally carried out prior to application of the paint product. Unattractive defects in the dried paint film will result from including pieces of the skin due to their irregular shape and size. Paint skin fragments also can lead to troublesome clogging of spray guns that are often used for application of the paints.
Skinning of latex-based paint products in closed containers has been a puzzling phenomenon known in the paint industry for many years. Prevalent thinking suggests that latex paint skinning is a drying process that requires moisture to escape from the closed container by permeating through the container walls and/or by escaping from leaks caused by insufficient sealing of the lid to the container body. The use of inhibiting mixtures of water and relatively volatile glycols, particularly ethylene glycol, to inhibit skinning in latex paint cans is disclosed in U.S. Pat. No. 4,228,893, which teaches that inhibiting aqueous glycol mixtures having a volatility greater than the volatile portion of the paint composition can be placed on the surface of the liquid paint, ordinarily one to three inches thick layer, and should be more viscous than the paint composition in the can. In practice however, it was found that such relatively high viscosity skin inhibiting mixtures mixed extensively into the bulk of the paint during handling and shipping, and, consequently became sufficiently diluted and ineffective skin inhibitors.
A method and composition now have been found to inhibit waterborne paint products from developing water insoluble films, commonly known as skins, on the non-submerged interior surfaces of the plastic or metal containers. The inhibiting composition relies on the use of a relatively small amount of a mixture consisting primarily of low volatility diethylene glycol added to the container after the paint product itself has been added. The low volatility glycol and water mixtures of the present invention resist evaporation to the point where even though most or all of the water has evaporated from the paint/inhibitor mixture, sufficient low volatility glycol remains to enable the resultant pasty mixture to be re-dispersed into the bulk paint during normal pre-use mixing with a paint shaker. The low volatility diethylene glycol mixture is purposefully not mixed into the paint but rather is allowed to float on the surface of the previously added latex paint. In accordance with this invention, diethylene glycol having relatively low volatility is used as the major or only component of the skin inhibiting mixture formulated to have relatively low viscosity and used in relatively small amounts. It has been found that useful skin inhibiting aqueous glycol mixtures containing diethylene glycol which is less volatile than the major volatile portion of the latex paint and provides excellent skin inhibiting properties to the latex paint in a container. It has been found that aqueous glycol mixtures which are less viscous than the bulk paint remain on the top of the paint bulk surface during handling and shipping of the filled containers. The layer of inhibiting aqueous glycol can be well below one inch and as low as {fraction (1/16)} of an inch thickness. These and other advantages of this invention will become more apparent by referring to the detailed description and illustrative examples.
SUMMARY OF THE INVENTION
Briefly, the invention pertains to a composition and method of inhibiting a waterborne latex paint from forming insoluble films, commonly known as skinning, on the interior surfaces of the lid and exposed wall surfaces of containers filled with latex paint. The inhibiting composition consists of non-viscous, low volatility diethylene glycol having a volatility considerably less than the volatility of the volatile portion (water+organic solvent) of the paint. The diethylene glycol preferably is dispersed in water. The inhibiting diethylene glycol is inserted into the paint container and onto the paint surface after the container is filled with paint prior to shipping. The inhibiting diethylene glycol is maintained as a distinct layer on top of the paint and intentionally is not mixed with the paint.
DETAILED DESCRIPTION OF THE INVENTION
The invention is based on low volatility, non-viscous, inhibiting diethylene glycol or diethylene glycol mixtures containing small amounts of water mixed with diethylene glycol. The inhibiting diethylene glycol exhibits low volatility and low viscosity to provide a small but distinct barrier layer of inhibiting composition on the latex paint surface in a container. These useful inhibiting glycol mixtures are substantially less volatile than the volatile portion (water+organic solvent) of the latex paint being protected. Mixtures useful for inhibiting skin formation comprise diethylene glycol alone or a mixture of glycols containing by weight between about 95% and 100% diethylene glycol. The inhibiting glycol mixtures can contain between 5% and 80% water based on the total weight of glycol and water mixture.
Low viscous diethylene glycol+water mixtures being less viscous than the paint in accordance with this invention effectively inhibits the latex paint from skinning in the container since the low viscous glycol+water mixture remains on top of the paint surfaces during handling and shipping of the paint filled containers. In contrast, high viscosity glycol+water mixtures undesirably become diluted within the paint during
Gerrity Stephen F.
Schmitz Thomas M.
The Glidden Company
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