Method and apparatus for producing uniform small portions of fine powders and articles thereof

Abstract

Uniform portions of fine powders are deposited on a substrate by electrostatic attraction in which the charge of the electric field and polarity of the charged particles are varied repeatedly to form a buildup of powder on the carrier surface.

Description

BACKGROUND OF THE INVENTION [0001] This invention is directed towards the deposition of small (usually fractional gram) masses on a generally electrically non-conductive substrate. One of the most common methods for accomplishing the goal is practiced by manufacturers of photocopiers and electrophotographic electronic printers. This involves causing charged toner particles to migrate with an electric field to a charged area on a photoreceptor, so-called electrostatic deposition. While electrostatic deposition has been proposed for packaging powdered drugs (see U.S. Pat. Nos. 5,669,973 and 5,714,007 to Pletcher), electrostatic deposition is limited by the amount of mass that can be deposited in a given area. [0002] This limitation is intrinsic to electrostatic deposition technology and is determined by the combination of the amount of charge that can be placed on the photoreceptor and the charge to mass ratio of the toner particles. The mass that can be deposited in an area of a subs...

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Benefits of technology

[0005] The above disadvantages are overcome in the present invention by providing an alternating electric field for depositing particles onto a dielectric substrate. More particularly, the present invention comprises a method and apparatus for depositing particles from an aerosol onto a dielectric substrate wherein the method comprises and the apparatus embodies the following steps: charging the aerosol particles, positioning them in a deposition zone proximate to the dielectric, and applying an alternating field to the deposition zone by which the aerosol particles are removed from the aerosol and deposited on the dielectric substrate thus forming a deposit. The alternating field provides the means to deposit charged particles and / or ions such that the accumulation of charge on the dielectric substrate does not prevent further deposition of particles thus enabling electrostatic deposition of a deposit with relatively high mass.

[0006] In one embodiment of the invention, the particles are alternately charged in opposite polarities and deposited on the substrate with the alternating electric field, thus preventing charge accumulation on the dielectric substrate.

Problems solved by technology

While electrostatic deposition has been proposed for packaging powdered drugs (see U.S. Pat. Nos. 5,669,973 and 5,714,007 to Pletcher), electrostatic deposition is limited by the amount of mass that can be deposited in a given area.

This limitation is intrinsic to electrostatic deposition technology and is determined by the combination of the amount of charge that can be placed on the photoreceptor and the charge to mass ratio of the toner particles.

This variation prevents the reliable deposition of a controlled mass on the substrate.

Furthermore, low charge to mass ratio particles limit the overall speed of deposition because the force of a particle, which sets the particle velocity, from an electrostatic field is proportional to the charge carried by the particle.

This approach is subject to limitations in mixing uniformity and the aspiration of extraneous matter.

However, from this discussion it is apparent, aside from the disadvantages, that dry powder particles may also be used.

However, an apparatus for depositing powder on a dielectric (i.e. a powder carrying package) using the Pressman approach also suffers from the above described maximum amount of powder that can be deposited on the dielectric.

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