US3080251A - Method of xerographic development - Google Patents

Description

March 5, 1963 c. J. CLAUS 3,080,251

METHOD OF XEROGRAPHIC DEVELOPMENT Filed. March 13, 1958' YDROPHILIC COLLOID YDROPHOBIC RESIN ATTORNEY been limited to heat OI-SOIVCI1 vapor, although-other methods such as United Se ates "3,080,251 -METI-ID' OF XEROGRAPHIC DEVELOPMENT -"CarlJ.- Claus, Rochester,fN.Y., assignor toXerox 1 Corporation, ar-corporationzof New.Y.ork :.1Filed Mar; .13, .1958, :Ser; No. 721,201

.This; invention. relates. in gener.a1 to. electrostatic. vrecording and r in: particular to. materials and methods for :Inthe art ofxerography, itis usual to forman. elec- Ltrostaticimage on a suitable .insulating orphotoconduc- =.tive insulating surface and to develop this image, or in .other words'make it visible, by presenting to thesurface ran electroscopic marking material. In the. usual embodiv.ments .of xerographyzthe electrostatic image is formed on a photoconductive insulating surface by charging the surface and exposing it to an image of light and shadow .to is dissipated bearing surface with such as, forexample, Because of requirements xerographic develop- In these permanently other surfaceas shall be desired for a final image supportqmember. Existing fixing operations have generally fusing the. image material by means of lacquer spraying, overlaying and the like have occasionally been employed.

An. object of the. present invention is to provide new imagematerials and methods for electrostatic recording wherein an. electrostatic image may be developed and Another object of the invention is to provide a new electroscopic image developing material for-xerographic recording which .image material is capable of being deposited in response to an. electrostatic charge. pattern and subsequently madevisible .on'the image support surface bymeans ofpressure.

Anadditional-object of .the invention is to provide anew xerographic developing material comprisingancn- .capsulatedmarking material includinga liquid .dropletof a color .forming composition within ashell having. surface .triboelectric. properties. suitable for electrostatic. deposi- .tion.

A' further. object is to provide new. materials ..and

..methodsfor xerographywherein an encapsulateddevelop- ..ing materialiscombined with an active photoconductor .to produce a permanent, visible image.

.Additional. objects .of the..invention will in part .be obvious. and willin -part become apparent from-the following specification and drawing in which:

..The FIGUREisa diagrammatic viewof a developer powder particle-according to one form ofthe. invention. 1 l Ithas. recently... been found thatsuitable liquid, ma- =.Yl'.6l2l3.lS-. can..bel formed. into ..an extremely finelydivided 'dry composition by separate encapsulation of appropriate ..liquid droplets within red a hydrophilic shell. "For example,

.I in U.S.' Patent 2,800,458, there is disclosed a manufacchemical or physical reagent.

tured' preparation. of oil-containing capsulesbf hardened gelatin. Such compositions have numerous usesin pres- .sure recording arts. .Unfortunately, it has been found Ithat "these compositions are essentially unsatisfactory for electrostatic recording because of'their extreme variability in triboelectric properties depending on humidity in the atmosphere. It has nowbeen found that image forming powders of proper triboelectric properties can'be pro- .duced by encapsulating a liquid droplet ,of a suitable color forming material within a hydrophilic coating such ..as gelatinv or the like, and in turn encapsulating the hydrophilic material within a tough hydrophobic resin coating. In particular, outer coatings of the polystyrene familyincluding polymerized styrene, polystyrene homologues and mixtures and copolymers'thereof, and resins of the acrylic esters acrylic amide and methacrylic esters and amides and mixtures of copolymers thereof, as well as mixtures of styrene and acrylic resins may be produced on hydrophilic capsules by immersion in polymer solutions followed by drying 0r evaporation of the solvent to produce developer materials for Xerography.

The new developer powder composition includes essentially three separate phases or components, such as, for example a liquid droplet 10 encased in a hydrophilic coating 11, in turn within a hydrophobic resin coating 12. Theliquid composition comprises essentially an oil base dye intermediate capable of forming, by chemical or physical reactions, a highly colored material, or other composition in liquid form capable of reacting to produce a permanent color visible on a support sheet such as, for example, a sheet of paper or the like having a photoconductive coating thereon. Suitable oil bases include oils and other ,non-polarfluids generally not miscible with water but such as for example waxes, mineral oils, animal oils and the like, aswell as vegetable oils such as olive oil, castor oil, and the like. Desirably, an oil composition may include asolution of a resin material in a suitable solvent such as for example a hydrocarbon solvent together with the col-or forming material.

An essential active agent included in the liquid droplet within the encapsulated particle is the color forming compound, optionally in itself substantially colorless, capable of producing a highly colored material upon release by pressure rupture of the capsule in contact with a suitable According to a presently preferred embodiment of the invention the reagent for reaction with such colorless color forming compound. is an acidic adsorbent photoconductive material capable of inclusion in an insulating resin binder to produce a photoconductive insulating layer. Thus, for example, photoconductive, insulators such as zinc oxide, mercuric iodide,

Zinc sulfide, cadmium sulfide, cadmium dioxide, and the like, may be included in insulating resinbinders such as siliconeresins, acrylicresins, polystyrene and the like, as

. is known in the art, to produce image forming xerographic layers. Such layers generally act as acidic type adsorb- ..entsandaccordingly are reactive with manycolor form- 'color .forming compounds may be included in the encapsulated liquid droplet: Crystal violet lactone (3,3-bis- ('4- dimethylaminophenyl) 6-dimethylamino-phthalide), malachite green lactone (3,3 bis (4 dimethylaminophenyl)-phthalide), dimethyl malachite green lactone (3, 3 his (4 -dimethylamino-3-methylphenyl)-phthalide), Michiers hydrol (bis-(4-dimethylaminophenyl)-c-arbinol), Michlers hydrol methyl ether (bis-(4-dimethylarninophenyl)-methyl methyl ether), diethyl crystal violet lactone (3,3 bis-(4-dimethylamino-3-ethylphenyl)-6-dimethylamino-phthalide), and mono-methylamino crystal violet lactone (3 ,3-bis l-methylaminophenyl) -6-methylamino-phthalide) The oil composition is contained within a hydrophilic colloid material such as, for example, gelatin casing or the like and may be formed into an encapsulated powder with materials and methods disclosed in Green et al. U.S. Patent 2,800,457. Suitable encapsulating material includes gelatin, hydrophilic cellulose materials such as hydrophilic cellulose esters and ethers, gums and the like.

Suitable capsules such as, for example, capsules as disclosed in the Green et al. patent may be coated with a resin to form a xerographic developer composition. As a preferred procedure, the gelatin capsule material is dipped or immersed into a solution of a mixture of polystyrene and polystyrene homologues dissolved in toluene, xylene, or a similar non-aqueous organic solvent. The mixture is suitably agitated and dried by spray drying or the like to produce capsules substantially uniformly coated with the polystyrene type resin. According to a presently preferred procedure a polystyrene type material believed to consist of a polymerized mixture of styrene and styrene homologues and available under the name Piccolastic Dl is employed. This resin is dissolved in xylene, and the capsules are immersed in the solution. Excess liquid is filtered off and the coated capsules air dried with occasional mixing. Alternatively the capsules may be dried according to conventional spray drying procedures.

In one procedure for producing a xerographic developer the polystyrene coated capsule powder is mixed with a granular bead-like carrier material such as disclosed in Walkup Patent U.S. 2,816,551, generally in the amount of 1% of the powder composition and 99% of the carrier composition. The mixed developer material is useful in xerographic image development as, for example, by cascading the mixture across the surface of the electrostatic image bearing xerographic plate or across the surface of an electrostatic image bearing insulating surface.

Alternatively, the powder material may be employed for image development by blowing it into an air cloud and directing the air cloud to the image surface, by mixing the powder material with a ferromagnetic material and magnetically conveying the mixture into brushing contact with the image surface, or by dusting the powder material into a brush such as, for example, a fur brush and brushing the image surface. Other image development methods may include dispersing the powder in an inert liquid and applying a liquid suspension by dipping or immersing or by pouring the liquid suspension across the image surface or the like.

Upon image development in any of these methods it has been found that a powder image is formed on the image bearing surface. The image may be made permanently visible and afiixed to the original image surface by means of pressure rollers or the like, or may be transferred to an adjacent surface and subsequently afiixed to such an adjacent surface. Thus, for example, a xerographic image may be formed on a selenium coated metal plate or drum by applying an electrostatic charge to the selenium surface. The image may be developed by the methods of the invention and transferred to a piece of coated paper placed in contact with the image bearing selenium plate or drum by means of corona discharge or the like and the image permanently affixed to the paper by means of pressure rollers. According to a presently preferred embodiment of the invention the electric image is directly formed on a paper backed photoconductor such Al as zinc oxide in an insulating silicone, polystyrene, acrylic resin or the like and is developed and fixed in situ.

As an illustrative example of the present invention an encapsulated material may be prepared of one of the color formers, such as crystal violet lactone. This color former is encased in a hardened gelatin encapsulating wall coated with a polystyrene layer as described hereinbefore. In a preferred embodiment of the invention the toner composition produced by the methods described is mixed with iron filings in a ratio of about 20 parts iron filings to 1 part toner by weight and the mixture employed as a developer according to the method of Young U.S. 2,786,- 441. A suitable zinc oxide containing xerographic paper compatible with the toner composition is available under the name LectroX Paper, from the Haloid Company, Rochester, New York, and includes a photoconductive layer having as an active agent zinc oxide capable of imparting photoconductivity to the layer and capable of re acting with the active agent Within the encapsulated droplet. An electrostatic image is formed on the coated paper by electrically charging the paper and exposing the charged paper to an image of light and shadow to be recorded. The mixture of iron filings and toner material is then brushed across the surface of the xerographic paper hearing an electrostatic image, and the toner deposits in image configuration. The resulting powder deposit can be made highly colored and permanently visible on the zinc oxide layer by rupturing the encapsulating walls, for example, bynpassing the image bearing paper through hard pressure ro ers.

The present invention permits the use for xerography of a wide variety of color forming materials without regard to the triboelectric properties of such color formers. There may be employed, moreover, carbon black and other carbonaceous materials and other color intensifying materials in the liquid droplet or in the particle shell itself in additou to the color formers dispersed or dissolved in oil base. The xerographic developer compositions prepared with such marking materials are independent of the triboelectric characteristics of the composition of the droplet itself or of the encapsulating materials in which the color forming materials are mutually encased. It has been found that desired triboelectricity and humidity resistance can be imparted to the composition by polymerized styrene and polymerized acrylic resins and that such resins may be employed without regard to the nature of the color former or the oil base.

What is claimed is:

1. The method of xerography comprising forming an electrostatic image comprising information to be recorded on a composite photoconductive layer wherein zinc oxide is the photoconductive constitutent by the combined action of light and electric field acting on said layer, developing the image bearing layer by electrostatically depositing thereon a xerographic toner composition consisting of particles triboelectrically adapted independently of ambient humidity and in a size range for use in conjunction With a xerographic carrier to form a toner carrier system for developing xerographic images, said particles consisting of an inner core of a substantially colorless color forming liquid capable of reacting with an acidic adsorbent to form a highly colored material and encapsulated in a rupturable hardened hydrophilic colloid shell, and an outer rupturable shell of hydrophobic resin coated on said colloid shell, said hydrophobic resin being triboelectrically adapted for use with a xerographic carrier and selected from the group consisting of polystyrene resins and polyacrylic resins, and rupturing said particles on the photoconductor layer to cause a color forming reaction between the liquid in said particles and the zinc oxide photoconductor.

2. The method of claim 1 in which said color forming liquid includes as an active ingredient thereof a material selected from the group consisting of crystal violet lactone (3,3 bis-(4-dimethyl-aminophenyl)-6-dimethyl- References Cited in the file of this patent UNITED STATES PATENTS 2,512,192 Yen et al. June 20, 1950 2,712,507 Green July 5, 1955 2,730,456 Green et a1. Jan. 10, 1956 2,735,784 Greig et a1 Feb. 21, 1956 6 Greig Feb. 21, 1956 Walkup Mar. 5, 1957 Rheinfrank et a1. Apr. 9, 1957 Green July 23, 1957 Mayer Mar. 10, 1959 Green et a1 Sept. 20, 1960 FOREIGN PATENTS Great Britain of 1910 Great Britain Aug. 10, 1955 France Nov. 9, 1955 Great Britain Oct. 31, 1956 OTHER REFERENCES Young st 211.: Electrofax, R.C.A. Review, December 1954, pp. 469 to 484, vol. XV, No.4.

Claims (1)

1. THE METHOD OF XEROGRAPHY COMPRISING FORMING AN ELECTROSTATIC IMAGE COMPRISING INFORMATION TO BE RECORDED ON A COMPOSITE PHOTOCONDUCTIVE LAYER WHEREIN ZINC OXIDE IS THE PHOTOCONDUCTIVE CONSTITUTENT BY THE COMBINED ACTION OF LIGHT AND ELECTRIC FIELD ACTING ON SAID LAYER, DEVELOPING THE IMAGE BEARING LAYER BY ELECTROSTATICALLY DEPOSITING THEREON A XEROGRAPHIC TONER COMPOSITION CONSISTING OF PARTICLES TRIBOELECTRICALLY ADAPTED INDEPENDENTLY OF AMBIENT HUMIDITY AND IN A SIZE RANGE FOR USE IN CONJUNCTION WITH A XEROGRAPHIC CARRIER TO FORM A TONER CARRIER SYSTEM FOR DEVELOPING XEROGRAPHIC IMAGES, SAID PARTICLES CONSISTING OF AN INNER CORE FO A SUBSTANTIALLY COLORLESS COLOR FORMING LIQUID CAPABLE OF REACTING WITH AN ACIDIC ADSORBENT TO FORM A HIGHLY COLORED MATERIAL AND ENCAPSULATED IN A RUPTURABLE HARDENED HYDROPHILIC COLLOID SHELL, AND AN OUTER RUPTURABLE SHELL OF HYDROPHOBIC RESIN COATED ON SAID COLLOID SHELL, SAID HYDROPHOBIC RESIN BEING TRIBOELECTRICALLY ADAPTED FOR USE WITH A XEROGRAPHIC CARRIER AND SELECTED FROM THE GROUP CONSISTING OF POLYSTYRENE RESINS AND POLYACRYLIC RESINS, AND RUPTURING SAID PARTICLES ON THE PHOTOCONDUCTOR LAYER TO CAUSE A COLOR FORMING REACTION BETWEEN THE LIQUID IN SAID PARTICLES AND THE ZINC OXIDE PHOTOCONDUCTOR.

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