Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1998-04-20
2001-01-23
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S171000, C524S440000, C524S441000
Reexamination Certificate
active
06177486
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to dispersions of lamellar pigment particles that are useful in forming coating compositions, i.e. metal pigment-containing paints, mica-containing paints and others. Such paints are used, for example, for coatings in the automotive, plastics, can coatings, and coil coatings industries, and for forming metallic coatings for roofs and other similar structural surfaces. The particles generally are used in a flake like form.
Typically, in order to avoid stability problems and decrease shipping costs, the lamellar pigment particles for use in such coating compositions have been provided to the customer (i.e. a paint manufacturer or ultimate end user) in the form of a highly concentrated paste. The paste is then mixed with a suitable vehicle for forming the final coating composition.
However, in practice it has been difficult for the paint manufacturer or end user to form a paint with the pigment paste, especially with the finer grade pigment pastes. It has been time-consuming and relatively labor intensive to ensure that the paste is completely mixed with the paint vehicle. In addition, the difficulty in mixing the paste with the vehicle has resulted in the use of relatively severe mixing techniques that can damage the metal flakes, e.g. by bending, curling or tearing. Generally, the paste will be added to a tank containing the paint vehicle or some component thereof. As the paste is added, the mixture is stirred with a propeller or Cowles blade or the like. Such procedures are not effective in separating the particles in the paste and can result in the damage to the particles discussed above, and also requires additional processing such as filtration to remove undispersed particles. This causes problems such as batch-to-batch inconsistency and less desirable aesthetic properties. It also has been found that the paste can be difficult to remove from bulk containers such as drums.
SUMMARY OF THE INVENTION
The present invention seeks to overcome the disadvantages associated with the use of lamellar pigment pastes for forming coating compositions. In accordance with the present invention, the lamellar pigment particles are provided in the form of a dispersion containing 20-55% by weight of lamellar pigment particles. The dispersion also includes a carrier that is liquid at room temperature and is compatible with a vehicle for forming a coating composition. The lamellar pigment particles are dispersed in the carrier and preferably are capable of remaining in a dispersed state in the dispersion without separation indefinitely when stored at ambient temperatures, although in some cases a soft settling of the particles after two weeks or so may occur, which is acceptable.
The dispersion of the present invention is easily mixed with a vehicle for a coating composition, thereby reducing the time and labor needed to formulate the coating composition. In addition, since less severe mixing techniques can be used, the damage to the pigment particles can be reduced, thereby improving consistency and aesthetic properties. The demands on equipment will be lessened, and less equipment time will be needed to make batch adjustments. The dispersion can be readily removed from bulk containers such as drums. In addition, the dispersion of the present invention can improve shelf stability as opposed to a paste form, especially for non-leafing grades that are coated with unsaturated fatty acids. Shelf stability is largely dependent on the exposure of the pigment particles to air. This exposure will cause solvent evaporation and oxidation of the lubricant, resulting in flake agglomeration. Dispersions will further help to exclude air, thus maintaining the integrity of the pigment.
DETAILED DESCRIPTION
The present invention provides a lamellar pigment particle dispersion useful for forming coating compositions when mixed with a suitable vehicle. The preferred lamellar pigment is aluminum, although other lamellar pigments such as zinc, bronze, iron, pearlescent and graphite flakes can be used if desired. The present invention is particularly useful for relatively fine flakes, especially of aluminum, e.g. those having a median particle size of about 100 microns or less, especially 10 microns or less, since such particles have a relatively high surface area and can be difficult to mix with a paint vehicle in the paste form.
The pigment particles can be in the form of leafing grades or non-leafing grades, although the present invention may be particularly advantageous with the non-leafing grades, whose fatty acid coatings tend to render such particles more susceptible to oxidation and agglomeration in the form of “cold welding” to form undesirable seeds. When the pigment particles are in the dispersion of the present invention, the particles are further separated and are protected to some extent by the presence of the dispersion carrier.
The amount of lamellar pigment solids in the dispersion is 20-55% by weight, preferably 40-50%. Lower amounts may be difficult to hold in suspension, while higher amounts may tend to form a composition that is too paste-like.
The dispersion also includes a dispersion carrier. The dispersion carrier should be compatible with the lamellar pigment particles. It also should be compatible with the vehicle of the coating composition with which it will be used. Thus, some dispersion carriers will be selected for use with aqueous coating composition vehicles, while others can be used for organic solvent coating composition vehicles.
In general, the dispersion carrier can be selected from plasticizers, solvents, resins and oils. Specific examples of the resins include thermosetting acrylic resins, thermoplastic acrylic resins, alkyd resins, epoxy resins, polyester resins, hydrocarbon resins, melamine resins, phenolic resins, polyamide resins, silicone resins, styrene resins, urea resins, urethane resins, and vinyl resins. Specific examples of the plasticizers include phthalates such as dioctyl phthalate, diisodecylphthalate and butyl benzyl phthalate, adipates such as diisobutyl adipate and diisodecyl adipate, phosphates such as tricresyl phosphate and trioctyl phosphate, polymeric plasticizers such as polyester and polyester adipate plasticizers, epoxy plasticizers such as epoxidized soy bean oil and epoxidized octyl oleate, citrates such as triethyl citrate, glycols such as butyl phthalyl butyl glycolate, and sebacates such as disebacate. Specific examples of the solvents include, substituted and unsubstituted aliphatic and aromatic hydrocarbons, for example having up to twenty carbon atoms, and oxygen-containing solvents such as ketones, alcohols, glycol ethers, esters and nitroparaffins, for example containing up to twenty carbon atoms. Specific examples of the oils include animal, vegetable and synthetic oils such as linseed oil, tung oil, castor oil, fish oil, rapeseed oil, oticica oil and soya bean oil, fatty acids and others.
The carrier also can be provided with rheology agents. Examples include montmorillonites, attapulgites, pyrogenic silicas, hydrogenated castor oils, high molecular weight polyolefins, calcium sulfonates and polyamides.
The viscosity of the dispersion is generally in the range of about 4,000-200,000 centipoise, preferably 10,000-90,000 centipoise, as measured on a Brookfield RVT viscometer using a number
7
spindle at 5 rpm.
The dispersion of the present invention shows stability. That is, the lamellar pigment particles will remain dispersed and not separate upon standing. For the purposes of the present invention, it is considered that the dispersion shows sufficient stability if it does not separate to form a compacted layer of lamellar pigment particles on the bottom and a clear (i.e. free from lamellar pigment particles) layer of carrier at the top, upon standing for about one year at ambient temperature.
The lamellar pigment particles should be completely separated with the liquid dispersion carrier in the dispersion. Therefore, it is preferred to form the dispersion using mixing equipment
Cain Edward J.
Merchant & Gould P.C.
Silberline Manufacturing Co., Inc.
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