US3377286A

US3377286A - Developer powder containing black magnetic iron oxide

Info

Publication number: US3377286A
Application number: US426678A
Authority: US
Inventors: Stricklin Buck
Original assignee: Minnesota Mining and Manufacturing Co
Current assignee: 3M Co
Priority date: 1965-01-19
Filing date: 1965-01-19
Publication date: 1968-04-09
Anticipated expiration: 1985-04-09

Description

United States Patent No Drawing. Filed Jan. 19, 1965, Ser. No. 426,678 3 Claims. (Cl. 25262.ll)

This invention relates to the copying art, a d i ticular to the preparation of visible copies of printed or other PhlC intelligence by procedures involving the powder development of metastable liquid latent images of such intelligence. In one aspect the invention relates to specific developer powder materials.

In my copending application, Ser. No. 189,029, I have described a copying process involving the formation of a fluid metastable liquid condensate latent image and the subsequent development of the latent image to a visible image or reproduction of a graphic original. As an example, an intermediate or transfer sheet lightly coated on one surface with benzil or equivalent transfer mate rial is heated at image areas while in face-to-face contact with a paper receptor or copy sheet. The heat causes the benzil to transfer to the copy-sheet where it condenses as a metastable liquid. The sheet is then treated with a mass of colored powder, which powder is retained by the liquid condensate at the image areas but is easily dislodged from the adjoining background areas. Carbon black and various powdered pigmented thermoplastic resins and polymers are mentioned as useful image developer powders.

Copending application Ser. No. 406,417 describes an apparatus in which the developing process is most suitably performed. The sheet carrying the latent image is caused to pass through a mass of the powder, some of which is adherently captured at the image areas and is later fused in place. The remaining loose powder is removed by gentle vibration.

The present invention provides novel image developer or image toner powders which are peculiarly adapted for use in developing metastable liquid latent images containing benzil or equivalent transfer material. The powder is firmly retained by the liquid but is easily and completely removed from the uncoated paper of the QPY' sheet when the sheet is subjected to gentle vibration. The annoying dustiness accompanying the use of carbon black, organic dyes, and many resinous powders as image development powders is largely eliminated. Smooth uniform images of good density and sharp outline are easily attained.

These and other advantages are realized by employing as the developer powder a mass of colored particles coming within controlled limits of particle size and density and containing coloring agents, densifying agents, and thermoplastic binder.

The particles are most easily and economically produced by mixing the remaining components homogeneously into the molten binder, crushing the cooled and solidified mixture, and recovering the desired fraction by air classification. Particles of irregular blocky or chunky shapes are obtained. Alternatively, the molten mixture may be directly converted to spheroidal particles by spray-chilling; or the coloring and densifying materials may be mixed with a solution or dispersion of the binder in a volatile liquid vehicle and the mixture then subjected to spray drying and air classification.

Suitable binders include thermoplastic resins and polymers such as arylsulfonamide-formaldehyde resins, polystyrene, poly-alphamethylstyrene, polyethylene, phenol- "ice formaldehyde resins, polyamide resins, epoxy resins. Organic and inorganic pigments, dyes and other coloring agents, e.g., carbon black, Prussian blue, iron oxide, phthalocyanine dyes and many others are all useful. In some instances the coloring agent may additionally serve the function of a densifying agent; for example, iron oxide and lead oxide are dense pigments which with proper amounts of thermoplastic binder form particles of appropriate size, weight and color density without further additions. Other densifying agents include the various metals such as iron, copper or lead, metal oxides and sulfides such as copper oxide, molybdenum sulfide, and other high density materials, e.g., barium ferrite, pyrolusite, zinc blende, barytes.

The ability of the thermoplastic binder to soften and flow at elevated temperatures within the range of about -150 C. makes possible the fixing or permanentizing of the powder image by heating to an appropriate temperature. For this purpose the proportionate amount of the binder should be at least about one-third the total Weight of the particle, and may be as high as about twothirds, depending on the densities of the several components and on the hiding power and effectiveness of distribution of the coloring agents. Where image fixing is to be accomplished by infrared heating as in the apparatus hereinbefore referred to, the particles are required to be absorptive of infrared radiation.

Significantly, the particle size as well as the particle density must fall within rather narrow limits if effective development of thelatent image is to be achieved. More particularly, the particle size should be between 10 and 40 microns, with essentially the entire bulk of the developer powder coming within the preferred particle size range of 20 to 35 microns; and the specific gravity must be within the range of 1.5 to 2.3. It is additionally necessary that the particles be capable of being wetted and adherently retained by the liquid material of the latent image. a 0

Particle size may best be determined by micromerograph analysis. Separation by air classification 1s a preferred method, the Sharples K-8 centrifugal air classifier having been found useful for this purpose. Specific gravity of the mass of particles is best determined on a r Beckman Model 930 air comparison pycnometer. Benzil being a pure organic compound serves as a useful test material for determining adherency. A suitable test involves simply rubbing a piece of the compound across a sheet of writing paper, or alternatively applying a very small amount of the compound in powder form with a brush; briefly heating the sheet to C.; with the sheet at room temperature, permitting a small portion of the developer powder to slide across the treated surface; and observing whether or not the powder is retained at the areas treated.

Powders prepared as hereinbefore described and having the indicated specific gravity, particle size and other characteristics are found to produce permanent well-formed dense uniform images without any significant backgrounding when employed in the process and apparatus previously noted. On the contrary, toner powders as conventionally used in the developing of electrostatic latent images are either completely incapable of use, or introduce such severe problems, particularly as to darkening of background areas and evolution of dust, as to make the process completely unacceptable in any commercial applications in the apparatus described.

The following specific examples, in which all proportions are in parts by weight, will serve further to illustrate but not to limit the invention.

Example 1 Parts Epoxy resin, M.P. 75-85 C. (Epon 1002 resin)--- 50 Black magnetic iron oxide powder 50 The powder is mixed into the heated liquefied resin. The mass is cooled and solidified, and is ground to a fine powder. The powder is passed through a centrifugal air classifier and the portion having a particle size of 20-35 microns is retained; the remainder may be reprocessed.

In analternative procedure which is better suited to commercial production, the hot plastic mass is first extruded and cooled in thin sheets which are pulverized and the powder then classified as before. The product has a specific gravity of 1.89 as determined on the air comparison pycnometer.

A developer apparatus as described in patent application Ser. No. 406,417 is loaded with an appropriate quantity of the powder. A paper copy-sheet carrying a metastable liquid latent image is passed through the powder mass, suspended in vertical position and subjected to gentle vibration to remove loose powder, and then briefly exposed to intense infra-red radiation. The latent image areas retain a portion of the powder which fuses and forms clearly defined smooth uniform dark image areas. The background areas remain essentially free of the powder.

Example 2 A mixture of:

Parts Barium ferrite powder, specific gravity 5.28, 325- mesh and finer 100 Epoxy resin Epon 1004 (M.P. 85-9?) 77 Uhlich black pigment #2039L-.. 7 Carbon black 4 chloroform -1 412 is blended by stirring or ball milling and then spray dried in a laboratory spray dryer. Air classification of the spheroidal particles in a microparticle classifier isolates a fraction with a particle size of 10-40 microns, mostly in the -35 micron range, and a density of 1.6 and which produces excellent copies when employed in the apparatus previously referred to.

What is claimed is as follows:

1. A developer powder adapted for developing a permanent visible image on a paper copy-sheet having a fluid metastable liquid latent image, comprising a mass of colored particles of a mixture of components consisting essentially of a thermoplastic binder and a black magnetic iron oxide powder, said particles having a particle size within the range of 10-40 microns and mostly within the range of about 20-35 microns, a specific gravity within the range of 1.892.3, and being adherently retained when placed momentarily in contact with cooled liquefied benzil.

2. A developer powder adapted for developing a permanent visible image on a paper copy-sheet having a fluid metastable liquid latent image, comprising a mass of infra-red-absorptive colored particles of a mixture of components consisting essentially of a thermoplastic resinous binder and a black magnetic iron oxide powder, the amount of said binder being at least about one-third by weight of the mass, the particles having a particle size within the range of about 10-40 microns and mostly within the range of about 20-35 microns, a specific gravity within the range of 1.89-2.3, and said particles being adherently retained when placed momentarily in contact with cooled liquefied benzil.

3. A developer powder adapted for developing a permanent visible image on a paper copy-sheet having a fluid metastable liquid latent image while being easily and completely removed from the non-image areas of the copy sheet by gentle vibration and without any substantial dustiness, said powder consisting of particles of a solidified uniform fused mass of approximately equal parts by weight of epoxy resin melting at -85 C. and of black magnetic iron oxide powder, having a specific gravity of at least about 1.89 and with essentially the entire bulk of the powder coming within the particle size range of 20 to 35 microns.

References Cited UNITED STATES PATENTS 2,857,290 10/1958 Bolton 252-62.l 3,244,633 3/1966 Yel'lin et al. 252-62.1 2,936,287 5/ 1960 Kazenas 252-625 LEON D. ROSDOL, Primary Examiner.

I. D. WELSH, Assistant Examiner.

Claims

1. A DEVELOPER POWDER ADAPTED FOR DEVELOPING A PERMANENT VISIBLE IMAGE ON A PAPER COPY-SHEET HAVIG A FLUID METASTABLE LIQUID LATENT IMAE, COMPRISING A MASS OF COLORED PARTICLES OF A MIXTURE OF COMPONENTS CONSISTING ESSENTIALLY OF A THERMOPLASTIC BINDER AND A BLACK MAGNETIC IRON OXIDE POWDER, SAID PARTICLES HAVING A PARTICLE SIZE WITHIN THE RANGE OF 10-40 MICRONS AND MOSTLY WITHIN THE RANGE OF ABOUT 20-35 MICRONS, A SPECIFIC GRAVITY WITHIN THE RANGE OF 1.89-2.3, AND BEING ADHERENTLY RETAINED WHEN PLACED MOMENTARILY IN CONTACT WITH COOLED LIQUIFIED BENZILE.