Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Process of making developer composition
Reexamination Certificate
2002-04-12
2004-07-20
Goodrow, John L (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Process of making developer composition
C523S300000
Reexamination Certificate
active
06764801
ABSTRACT:
This invention is generally directed to a method and apparatus for dispersal of aggregates in a fluid medium. The present invention employs a sonic or ultrasonic device to efficiently breakup particle agglomerates by driving the ultrasonic signal over a small range of frequencies around the acoustic slow wave frequency of the saturated agglomerate. At this frequency, the fluid vibrates out of phase with the solid and is forced out through the pore structure in the agglomerate, exerting stresses on the aggregate frame which cause breakup.
BACKGROUND OF THE INVENTION
Cross reference is made to the following applications filed on Oct. 30, 2000: U.S. Ser. No. 09/699,703 entitled “Process And Apparatus For Obtaining Ink Dispersing By Subjecting The Liquid Inks To An Ultrasonic Or Sonic Signal”, U.S. Ser. No. 09/699,862 entitled “Method For Improving Oil Recovery Using An Ultrasound Technique”, U.S. Ser. No. 09/699,871 entitled “A Method For Removing Trapped Impurity Aggregates From A Filter”, U.S. Ser. No. 09/699,882 entitled “Ultrasonic Cleaner And Toner Agglomerate Disperser For Liquid Ink Development (LID) Systems Using Second Sound”, U.S. Ser. No. 09/699,804 entitled “Method For Dispersing Red And White Blood Cells”, and U.S. Ser. No. 09/699,876 entitled “Ultrasonic Drying of Saturated Porous Solids Via Second Sound”.
Liquid electrostatic developers having chargeable toner particles dispersed in an insulating nonpolar liquid are well known in the art and are used to develop latent electrostatic images. Ideally, such liquid developers should be replenishable in the particular equipment in which they are used. In general, high solids concentration toners are used for replenishment because relatively low concentrations (e.g., in the range of 10 to 15% by weight solids) result in greater liquid build-up in the equipment, which then must be removed and disposed of as hazardous waste. Thus, it is desirable to initially use a toner containing less liquid, and to maintain the working source located within the equipment, thereby minimizing the undesirable accumulation of carrier liquid in the equipment. When toners are present in the liquid developer in more concentrated form, however, they become difficult to redisperse in the carrier. For example, aggregates may be formed. This can cause serious problems in the replenishment of the liquid developer in the equipment being use. It has been known to use high shear forces between two closely spaced cylindrical surfaces to dissociate liquid toner particles as disclosed in U.S. Pat. Nos. 5,004,165, 5,048,762, 5,078,504, and 5,492,788.
In printing applications these aggregation effects result in grainy images, poor coating uniformity, and poor image to image uniformity and image quality. Breaking up aggregates will result in better image quality. Dispersed particles in inks are subject to many effects that lead to coagulation, limiting shelf life. The liquid-based inks (LID, CEP, and any liquid-based dispersion of small particles) tend to coagulate if left on the shelf for long periods before use. Particles tend to settle under the influence of gravity, producing a sludge layer at the bottom of the container. Brownian motion of the particles due to thermal effects tends to bring particles into contact with one another, leading to coagulation and settling. Charge variations, especially in systems having both sign particles, leads to settling of ink particles. Therefore, it is desirable to have a method and apparatus to readily disperse the particles.
It is desirable to have a method and apparatus to obtain good color saturation. It is known that the color saturation, or chroma level, that can be achieved by color toners consisting of color pigments dispersed in a transparent binder is influenced to a large degree by the completeness of the dispersion of the pigments. Aggregated pigments tend to produce toners with washed-out or less bright colors than those achieved with well-dispersed pigments. On the other hand, it is difficult to achieve good dispersion with color pigments. This is due to the strong van der Waals forces that exist between these pigments, leading to strong, hard to disperse, aggregates.
The number of color pigments that can be used in the manufacture of EA toner is severely limited. In many cases one is forced to use pigments that have unwanted optical absorptions (i.e., absorb light at frequencies we don't want), giving colors that aren't exactly what we want, because we can disperse these pigments with the techniques at hand (e.g., sonicators, microfluidizers, Brinkman Polytrons are cited for example in U.S. Pat. No. 5,482,812 to Hopper et al. patent). There are many other pigments we would like to use, either for general application because their absorption spectrum is more in line with the color we want, or for custom purposes (e.g., to match the specific colors desired for a specific account: Kodak orange, John Deere green, etc.). Indeed, the color gamut of our copiers and printers is limited, not by the optical properties of the pigments available, but by the available pigments we can disperse. For example, there are 13 commonly available blue pigments, of which we typically use 1; there are 30 commonly available yellow pigments, of which we typically use 4; and there are 62 commonly available red pigments, or which we typically use 2. The other pigments are not used for several reasons. There may be health problems associated with their use; there may be problems associated with their effects on toner charging or tribo. However, these are not the primary characteristic that limits pigment use. Pigments are primarily rejected because their high adhesion characteristics make them too hard to disperse.
As noted above, pigment particles are found to be especially hard to disperse due to strong adhesion forces between the particles. This turns out to be a fundamental result of their bright color. The vivid color is a result of strong light absorption over a frequency band, i.e., a high imaginary part of the dielectric constant over a range of frequencies. The Lifshitz theory of van der Waals forces (discussed in Abrikosov, Gorkov, and Dzaloshinski, Methods of Quantum Field Theory in Statistical Physics) shows that the strength of the force between two bodies 1 and 2 is proportional to:
F
vdW
∝∫d&ohgr;
1
∫d&ohgr;
2
[Im
(∈(&ohgr;
1
))
Im
(∈(&ohgr;
2
))/(&ohgr;
1
+&ohgr;
2
)]
d&ohgr;
1
d&ohgr;
2
. (1)
where Im(∈(&ohgr;
1
)) is the imaginary part of the frequency-dependant dielectric constant of pigment particle i, and &ohgr;=2&pgr;f, and f is the frequency of light. The term Im(∈(&ohgr;
1
)) is the term that gives absorption of light at certain frequencies, resulting in color. Thus, colorful materials which have high Im(∈(&ohgr;
1
)), such as pigments, also tend to be sticky materials because of their high van der Waals forces, as indicated via Eq. (1). As a result, all color pigments tend to be especially difficult to disperse by their very nature.
A somewhat older model of van der Waals forces is due to London (1930). While this model is not as accurate as the Lifshitz (1955) model (mentioned above), it can readily be used to predict pigment-pigment cohesion, and it's predictions are generally in agreement with experimental trends. In this model the van der Waals force between two bodies is proportional to the atomic polarizability per unit volume of each of the constituent elements. Polarizability per unit volume is a dimensionless number, independent of the unit system utilized. A simple model that accounts for many of the van der Waals adhesion properties of pigments is obtained by assigning a unique atomic polarizability to each element, regardless of the type of its molecular bonding in a compound. These polarizabilities can be obtained from published tables, or via simple least squares fitting procedures using published tables of molecular polarizabilities (CRC Handbook of Chemistry and Physics, 80th Edition). Similarly, elemental
Bean II Lloyd F.
Goodrow John L
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