Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Including application of internal fluid pressure to hollow...
Reexamination Certificate
2000-04-07
2003-11-18
McDowell, Suzanne E. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Including application of internal fluid pressure to hollow...
C264S165000, C264S310000, C264S319000, C264S328800
Reexamination Certificate
active
06649122
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns an aqueous colorant. More particularly, the invention concerns an aqueous colorant for incorporation into plastics and a method for use of such an aqueous colorant.
BACKGROUND OF THE INVENTION
Traditionally, color has been incorporated into plastic materials by a variety of different methods. These methods include (i) pre-colored plastics which mix pigments and/or dyes with a polymer melt in a compounding process (ii) pellet concentrate where a dry color containing pellet is mixed with an uncolored virgin resin at the process equipment (iii) dry color concentrates which can be added to process equipment while making the finished parts, and (iv) liquid color concentrates where pigments are mixed with an organic liquid carrier.
When developing a product to color thermoplastic resins, the skilled artisan will consider the handling, storage, incorporation and dispersion characteristics of a delivery system. Each of the above described colorant systems provide advantageous characteristics. However, each colorant system also demonstrates drawbacks.
With respect to solid systems, handling, precision and cleanliness of the work environment are concerns. For example, the effect of the carrier resin on the characteristics of the colored thermoplastic resin can be a concern in pellet based systems. Similarly, solid colorants often do not uniformly mix with the plastic, do not disperse uniformly during molding, and can segregate from the plastic during pre-molded handling.
To address some of these concerns, some artisans use colorant dispersion phase transfer pigments from an aqueous to a non-aqueous phase, in discrete form, while still in an unconcentrated slurry through preferential wetting by surface contact between the pigment and a hydrophobic polymer solution emulsified in water. This material can then be concentrated in a plate and frame press or by flocculation, flotation or settling. After filtration, the resultant material (“a phase-transferred presscake”) somewhat resembles conventional presscake, but contains an organic phase as well as only 10 to 45 percent water, whereas conventional presscake contains 55 to 90 percent water. This type of pigment-hydrophobic organic vehicle product is disclosed in U.S. Pat. No. 4,634,471. Importantly, the emulsion and the pigment slurry mixture is forced through a concentration zone and flushed with a hydrophilic organic vehicle. Accordingly, introduction of the colorant to the plastic material is via a liquid organic medium.
Liquid color concentrates have also become increasingly attractive to overcome the drawbacks of traditional solid colorants. For example, in U.S. Pat. No. 3,956,008, a liquid colorant dispersion for plastics is disclosed which is comprised of 5-70 weight percent colorant and 95-30 weight percent vehicle. The vehicle is stated to be comprised of two major components, 1) from 5-25 weight percent of a physically-active, chemically-inert solid in the form of fine particles, and 2) from 95-75% of a surfactant system. The preferred surfactant system is stated to be a sorbitan ester surfactant, such as sorbitan trioleate. The applicability of this system, however, has been substantially limited because the carrier may experience pigment settling, incompatibility with the host polymeric material, insufficient heat stability causing processing problems, interference with the mechanical and physical properties of the end-product, or any combination of these undesirable factors.
Several techniques have also been developed in order to better achieve uniform dispersion and storage stable liquid colorant concentrates. For example, U.S. Pat. Nos. 3,956,008 and 4,167,503 disclose colorants having surfactant based vehicles that improve pigment dispersion and allow relatively high pigment loadings at viscosities suitable for use in standard in-line metering equipment. In the '503 patent, a liquid carrier system for dispersing into polymeric compositions is disclosed as comprised of an alkylated phenoxy poly(ethyleneoxy) ethanol carrier wherein the alkyl moiety of the ethoxylated phenol is selected from the group consisting of phenols and substituted phenols and a colorant in an amount from 0. 1% to 80% based on the weight of the carrier.
U.S. Pat. No. 4,341,565 discloses a liquid gel colorant that comprises a suspension of organic pigments in a liquid vehicle that is a plasticizer and which is gelled by an organophilic, expanding lattice clay that is ion exchanged with alkyl ammonium ions. The gel is modified by the addition of certain hydroxyalkyl fatty amines or fatty imidazolinium quaternaries, while the plasticizer is stated to be, for example, esters of saturated mono- or di-basic alcohols or tri-basic, saturated aliphatic or aromatic acids, or phosphoric acids.
In U.S. Pat. No. 4,571,416, a polyolefin compatible liquid colorant concentrate is disclosed that is a dispersion of a colorant and/or other additive in a non-surfactant based vehicle. The vehicle includes a low molecular weight addition polymer and an essentially non-volatile solvent for the low molecular weight addition polymer. The vehicle may also contain a dispersion aid, such as oleic acid, especially when the colorant is an inorganic pigment. The concentrate is stated to be comprised of a vehicle containing a low molecular weight addition polymer, such as polybutylene, polystyrene, polyalpha-methyl styrene/vinyl toluene copolymer or an acrylic copolymer and an essentially non-volatile solvent for the low molecular weight polymer which has a boiling point of at least about 450° F.
Turning next to U.S. Pat. No. 5,308,395, a liquid concentrate for incorporation into polymeric resins is disclosed as comprised of a vehicle of at least one organic rosin material, at least one surfactant, and at least one colorant or additive.
U.S. Pat. No. 5,759,472, provides a rare disclosure of a liquid color system including even a minor amount of water. More particularly, the liquid color system includes from about 10% to about 75% by weight carrier, from about 0% to about 15% by weight water, from about 0.01% to about 10% by weight dispersant, and from about 10% to about 80% by weight colorant. The carrier is stated to be a material selected from the group consisting of propylene glycol, ethylene glycol, diethylene glycol, tri(ethylene glycol), glycerine, and mixtures of such materials.
Accordingly, liquid colorant systems have relied on an organic vehicle. Thus, there has previously been no disclosure of an aqueous based system for use as a color concentrate for the coloration of plastic material. This focus on organic vehicles in the art may arise because in injection molding, for example, a common surface defect in molded parts is “splay,” which is the result of moisture in the resin. Splay is eliminated by drying the resin in an oven or hopper dryer prior to use. Similarly, steam generated from moisture can cause foaming in parts that reduces strength. Accordingly, there is no motivation in the art, and in fact, a recognized reason to avoid use of any material in treating plastics which contains significant quantities of water.
Of course, this perception has been carried forward to liquid colorant systems, which as shown above, rely on organic vehicles. Notwithstanding this prior reluctance to utilize water in liquid colorant systems, the present invention is directed to an aqueous based liquid colorant system demonstrating an excellent ability to color various thermoplastic materials in many commonly used molding or extrusion operations.
SUMMARY OF THE INVENTION
The present invention provides a new and improved liquid colorant system that is designed for the coloring of plastics. The invention more particularly relates to a liquid colorant system comprised of a colorant, a dispersant and at least 25% water. The colorant system is particularly suited to use in injection molding, extrusion, blow molding and rotational molding of plastic materials.
It is an advantage of the present invention to achieve a higher pigment loadi
Jacobs Michael A.
Lough Larry L.
Standish John V.
Fay Sharpe Fagan Minnich & McKee LLP
McDowell Suzanne E.
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