Drug – bio-affecting and body treating compositions – Preparations characterized by special physical form – Particulate form
Reexamination Certificate
1999-02-23
2002-10-15
Page, Thurman K. (Department: 1615)
Drug, bio-affecting and body treating compositions
Preparations characterized by special physical form
Particulate form
C424S070100, C424S070400, C424S490000, C424S491000, C252S363500
Reexamination Certificate
active
06465015
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to sonic (e.g., ultrasound) methods of making suspensions of uniform, non-agglomerated particles, and more particularly to methods for making a chemical reaction product that is a suspension, dispersion or emulsion of non-agglomerated, uniformly shaped particles at high production rates of up to 100 gallons per minute or higher. When the chemical reaction is effected in the presence of sonic energy, in close proximity to the point of contact of the reactants in the reactor, intimate mixing of the reactants is achieved to facilitate a more complete, uniform reaction than is achieved using conventional bladed-mixer systems.
2. Description of the Prior Art
Suspensions of very small, solid or liquid particles are useful in many applications, including personal care products (e.g., shampoos, soaps, etc.), cleaning products, paints, coatings, foodstuffs, fertilizers, pool chemicals, and the like. Generally, a well-dispersed suspension or emulsion of uniformly sized, non-agglomerated particles is desired because such suspensions provide a large and uniform surface area which results in improved performance of these products. Accordingly, much effort has been expended to develop methods to prepare well-dispersed suspensions of uniformly sized, non-agglomerated small particles, particularly such particles in the range of from submicron size to a few microns in size. One method involves using chemistry to control the particles size and/or shape during their formation in the chemical reaction employed to produce the particles. Another method uses physical mixing of the particles, during or after their production in a liquid suspension or emulsion, or grinding of the particles that are formed, to provide a desired size or shape. As another alternative, a combination of these methods has been investigated heretofore.
Chemical methods for control of particle size and/or shape generally focus upon manipulating the parameters of the precipitation reaction under which the particles are formed. For example, the use of additives, such as surfactants, to the particle-forming precipitation reaction mixture is suitably utilized to provide a suspension of specific shaped particles having a particle size distribution within the range of from about 0.5 to 30 microns (micrometers or “&mgr;m”) in size. However, it is difficult to achieve suspensions of small solid or liquid particles having an “essentially uniform size and shape” using surfactant additives alone. The term “essentially uniform size” as used herein, is intended to designate that the particles referred to have dimensions that do not vary by more than twenty percent, preferably not more that ten percent, between individual particles in the particulate product. The term “essentially uniform shape”, as used herein, is intended to designate that the particles referred to have essentially identical shapes, i.e., that the shapes of the particles within a given particle distribution are essentially identical. More specifically, if the particles in a distribution referred to as “essentially uniform in shape” are largely hexagonal in shape, then at least 80%, preferably at least 90%, of the particles in this distribution would be hexagonal in shape.
By changing other reaction parameters, such as by decreasing the temperature of the precipitation reaction, in combination with the use of a surfactant additive, it is possible to produce suspensions of solid particles having dimensions in a particle size range of from 0.5 to 5 &mgr;m. However, this range of size distribution is still greater than might otherwise be desired. Accordingly, there is a continuing need in the dispersions, suspensions and emulsions manufacturing community for particulate products having a particle distribution that is essentially uniform in size and shape. The present invention provides one answer to that need.
Heretofore, various mixing and/or grinding techniques have been employed in an effort to further reduce particle size without impairing the configuration or shape of the particle. Generally, conventional mixing procedures utilize a blade-type mixing apparatus such as a blender. The blade portion of the apparatus rotates at a specified rate to generate shear forces that physically reduce the sizes of the particles. Unfortunately, however, these bladed mixers pose a number of problems in the manufacture of suspensions of small particles, such as biocides. For example, bladed mixers tend to pull air into the reaction medium, and the entering air can cause unwanted foaming or thickening of the suspension. Blade-type mixers also have the undesirable effect of providing non-uniform mixing at various points within the reaction chamber. This result is believed to be attributable to the fact that the amount of shear force generated at the edge of the blade is greater than elsewhere in the reaction vessel, such as the surface, bottom or sides of the reactor vessel. Needless to say, differing applied shear forces at different points within the reactor vessel can adversely influence the chemistry of particle formation.
In view of these problems and disadvantages, it is difficult to prepare a well-dispersed suspension of uniformly sized and shaped, non-agglomerated particles using a bladed mixing approach. Nonetheless, in the production of solid biocides, bladed mixing, grinding, and centrifugation have found widespread use. For example, the biocides iodopropargylbuylcarbamate (so-called “IPBC”) and pyrithione are typically produced using bladed mixing or centrifugation, and the resulting product is generally size- and shape-determined by virtue of the reactants and reaction parameters that are employed. In the past, biocide manufacturers have used grinding to further reduce the size, or alter the shape, vis-à-vis the size and shape of the particles that result from the reaction itself. Unfortunately, however, grinding tends to have an adverse effect on the desired uniformity of shape of the biocide particles, as discussed in more detail hereinbelow.
Specific examples of useful pyrithione biocides include polyvalent metal salts of pyrithione (also known as 1-hydroxy-2-pyridinethione; 2-pyridinethiol-1-oxide; 2-pyridinethione; 2-mercaptopyridine-N-oxide; pyridinethione; and pyridinethione-N-oxide). These pyrithiones have enjoyed widespread application as fungicides and bactericides in paints and personal care products such as anti-dandruff shampoos. The polyvalent metal salts of pyrithione are solids that are only sparingly soluble in water and include magnesium pyrithione, barium pyrithione, bismuth pyrithione, strontium pyrithione, copper pyrithione, zinc pyrithione, cadmium pyrithione, and zirconium pyrithione. The most widely used divalent pyrithione salts are zinc pyrithione and copper pyrithione. Both zinc and copper pyrithione are useful as antimicrobial agents active against gram-positive and negative bacteria, fungi, and yeasts. Zinc pyrithione is used as an antidandruff component in shampoos, while technical suspensions of zinc pyrithione and/or copper pyrithione are used as preservatives in paints and polymers. Synthesis of polyvalent pyrithione salts are described in U.S. Pat. No. 2,809,971 to Berstein et al. Other patents disclosing similar compounds and processes for making them include U.S. Pat. Nos. 2,786,847; 3,589,999; 3,590,035; and 3,773,770.
The size limitations on pyrithione salt particle production made by conventional bladed mixing methodology demonstrate the drawbacks of using such processing. Illustratively, known methods for producing insoluble polyvalent salts of pyrithione typically result in solid particles having an average size greater than one micrometer (&mgr;m). However, as discussed above, smaller particles of pyrithione salts (i.e., less than one micron in size) are often desired because they more easily form suspensions and provide a larger surface area for enhanced biocidal activity. In addition, smaller particles, particularly in the low submicron range (e.g
Jardas John J.
Mohseni Saeed H.
Arch Chemicals Inc.
Carlson Dale Lynn
Garabedian Todd
Tran S.
Wiggin & Dana LLP
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