CA1122460A - Electrographic developer comprising a free-flowing non-aqueous liquid-containing powder composition - Google Patents

Abstract

COMPOSITION AND PROCESS
FOR FORMING VISUAL IMAGES

Abstract of the Disclosure A composition and process for forming visual images are described. The composition comprises droplets containing a colorant and a liquid surrounded by dry, discrete particles. The surface energy of the dry, discrete particles is less than the interfacial tension between the particles and the droplets of liquid and colorant, i.e., the droplets do not wet the particles. The composition is a free-flowing, dry-appearing powder and contains more than about 60 percent by weight of colorant-containing droplets. The process comprises forming an electrostatic latent image on a surface and developing this latent image by contacting it with the composition described above.

Description

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BACKGRO~ND OF THE INVENTION
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Field of the Invention The present invention relates to a composition, and a process for using said composition to form ~isual images, which employs a free-flowing dry-appearing powder containing a large amount of a colorant-containing liquid.
The invention is especially useful ~or the development o~
electrostatic latent images, i.e., electrostatic charge patterns.
Description of the Related Art In the past, development of electrostatic charge patterns formed by various electrographic techniques has been carried on chiefly by means of dry, electrographic toner powder-containing developers or liquid electroaraphic developers composed of charge-bearing toner particles dispersed in electrically insulating hydrocarbon liquid media. Many modifications and improvements have been made in the formulations of dry toner-containing developer compositions. One example is the use of two-component dry developer compositions containing a triboelectric mixture of carrier particles and toner powder, such as in various "cascade" developer compositions. Another example is the use of magnetically attractable particulate materials as the carrier particles in various "magnetic brush"
developer compositions. Similarly, many improvements and modifications have been made in the formulation of liquid developers, e.g., improved pig~ents, binders, stabilizing addi.tives, and the like.

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Nevertheless, significant disadvantages are present in conventional dry and liquid developer compositions, and there has been a considerable on-going effort to provide simpler, less expensive electrographic developex composi~ions ~or example, a well known problem associated with most dry toner powder-containing developers is the considerable amount of heat energy required to fuse and thereby fix the dry toner ~powder image to a suitable receiver sheet. ~lthough such energy requirements may not be as great a problem with respect to conventional liquid electrographic developers, these developers have generally been avoided for use in conventional high-speed, large-volume electrographic copying devices because of the difficulties associated with the large amounts of'highly volatile hydrocarbon liquids employed in such liquid developers.
One modification that has been'suggested for both liquid and dry developer compositions i5 to incorporate silica (silicon dioxide) or modified silica as an addenda in conventional dry toner powder-containing developers and liquid developer cornpositions. 'For example, U.S. Patent 2,986,521; U.S. 3,041,169, U.S. 3,392,139; and U,S. 3,720,617 each describe the use of various forms of silicon dioxide as a coating material for a toner powder composition ~r as a separate third component in a dry toner powder-col-taini.ng composition composed of toner powder and carrier particles. Such use oE silicon dioxide as set forth in the aforementioned patents allegedly provides various improvements such as improvements in dry toner powder flowability properties, improvements in the shape of the dry -- 3 -- .

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toner partic~es, enhanced triboelcctric properties of thc dry toner powder-containing developers, improved image densities upon development ~y such dry toner powders, and the like.
In addition, in U.S. Patcnt 3~236,77G and U.S. 3,188,225 various silicon dioxide and silicate-containing materials are proposed for use as componcnts to be blended into a dry toner powder composition.
Similarly, various high~surface-area, finely divided particulate materials such as silica have been proposed for incorporation into conventional liquid developer compositions, for example, to control viscosity or to minimize settling of the toner particles contained in such liquid developers.
For example, see U.S. Patent 2,g90,174 issued June 9, 1959.
Still other patent publications have described the use of various high surface area particulate materials such as silica as dry conductive printing ink powders for developing electrostatic charge patterns. In this regard, U.S. 3,280,036 issued October 18, 1966 describes the use of porous, non-vitreous ceramic materials such as finely divided alumina-silica gel particles in preparing a conductive electrographicprinting ink. In such compositions, the porous, non-vitreous ceramic particulate material appears to be used as an absorbing medium ~or an el~ctrically conductive, li~uid-dye mixture.
In addition, the use of materials such as modified pyrogenic silica to encapsulate, without ~bsorbing, large amounts of water or aqueous liquids has ~een described in _ ~ _ i3L;~2g~0 U.S. Patent 3,393,155, where it is suggested that such compositions may be useful as fire extinguishing agents or as additives for various paper and textile coating formulations. Such water-containing powders have also been described and suggested for use in plant germination and growth media, where they can provide a means for controlling moisture release to root systems.
A description of this use can be found in a brochure on Tullano 500 from Tulco, Inc., p. 12, 1429/572/5M. This brochure also suggests using a modified silica as an agent to main~ain viscosity in liquid lithographic inks. However, it has not previously been known that a finely-divided, low-surface-energy material such as a modified silica might be useful for surrounding liquid droplets other than water or a~ueous liquids, or that it might be possible to so surround liquid droplets containing a colorant component to obtain a composition that would be useful as a developer of latent images. ~or has it been known that if colorant-containing liquid droplet could be so surrounded, the resultant dry-appearing powder would genexate a triboelectric relationship between the dry, discrete particles and the droplets o colorant-containing liquid and would be especiall~ usefu:L for the development of electrostatic charye patterns.
As is apparent from the aforementioned patents and other publications, conventional electrographic dry toner powders, including conductive printing ink powders, and conventlonal liquid developer compoitions ha~e used various types of finely divided particulate ~z~

materials such as silicon dioxide to modify certain properties of these developer compositions. However, it does not appear that any of these patent publications have used finely divided, low-surface-energy particulate ~aterials to alter the fundamental physical state of the developer composition in which it is incorporated (for example, to make a liquid developer appear to behave as though it were a dry toner powder or to modify a dry toner powder so that it is capable of containing ~arge amounts of a liquid composition ~uch as a liquid printing ink without losing the physical appearance or handling properties of a powder). Although such fundamental changes in conventional dry toner powder-containing developers and conventional liquid developer compositions are not disclosed in the aforementioned publications, significant advantages could be realized if such modifications could be achieved.
For example, if a developer composition could be devised which had the appearance and the characteristics of a free-flowing, dry toner powder, yet contained large amounts of a liquid, one could in effect produce a developer composition for developing electrostatic c~arge patterns which possesses the ease of handling common to dry ~ree-flowing toner co,mpositions, but at the same time possesses the ease of fixi.ng exhibited by various conventional liquid developers. More~over, if such a composition were developed which contained liquid and colorant materials therein, one could avoid many of the problems associated with conventional liquid electrographic developer compositions which contain large amounts of organic liquids, ..~

e.g., the problem of disposing of hydrocarbon liquids without the objectionable ~dors and environmental hazards that commonly arise in dealing with organic solvents.

S~MMARY OF THE INVENTION
In accordance with ~he present invention there is provided a composition and a process for producing visual images. The composition is a dry-appearing, free-flowing, powder-like material that contains at least about 6~ percent and no more than about 98 percent by weight of droplets comprising a colorant-containing li~uid. The droplets are completely surrounded by dry, discrete partic~es that constitute at least about 2 percent and no more than about 40 percent by weight of the total composition. The surface energy of the dry, discrete particles is less than the interfacial tension between the dry, discrete particles and the droplets they surround, i.e., the droplets do not wet the dry, discrete particles. The composition is particularly useful in the process of the present invention for forming visual images which comprises forming an electrostatic charge pattern on a ~urace and contactiny that charge pattern with the composition described above~
It has been found, quite unexpectedly, that the composition of the present invention forms a seemingly dry powder-The composition possesses the free-flowing characteristics and ease of handllng o~ a dry electrographic toner powder, yet exhibits ~1~24~i~

the advantages of a liquid electrographic printing ink, namely ease of fixing without the high energy normally required to fuse and fix conventional dry electrographic toner powders.

D ESC R I PT I ON OF THE PREFERRED EMBOD II~ENTS
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Although the precise mechanism by which the developer compositions of the present invention provide development of an electrostatic charge pattern is not, at present, fully under-stood, the following theory is presented by way of partial explanation of the mechanism which is believed to be functioning in the developer composition of the present invention. Stated briefly, it is believed that the colorant-containing droplets, which are present in the dry-appearing powder composition, tend to acquire an electrostatic char~e having either a positive or negative polarity with respect to the dry discrete par-ticles used to surround and prevent coalescence of the droplets.
Whether these droplets tend to acquire either a positive or negative polarity with resp~ct to the dry, discrete particles is believed to depend upon the particular composition used to for~ the droplets. That is, it is,believed i~
that by incorporation of appropriate colorant materials, pQlymeric binders, dispersing aids and other materials in the drople-ts as described in greater detail hereinafter, it i5 possible to prepare a dry-appearing, liquid~containing developer composition in accordance with the present invention, wherein the coLoran=-contatning ropl ts present ln t e composition tend to Z4~

exhibit either a positive or negative polarity dependin~ upon the particular composition of the droplets. Similarly, it is believed that the polarity of the droplets contained in tl-e given developer composition of the invention can be changed by varying the material used to prepare the dry, dis-crete particles which surround and prevent coalescence of the droplets within the developer composition.
As will be appreciated from the foregoing description of the mechanism by which the compositions of the present invention are believed to function, the electrical properties of the developer of the present invention are somewhat similar to conventional two-component dry developers composed of a triboelectric mixture of dry toner particles and dry carrier particles. However, this analogy between the developers of the present invention and conventional two-component dry developer mixes is not a perfect one and cannot be carried too far.
For example, as is well known~ there is a finite depletion rate associated with convention~l two-ccmponent dry electrographic developer compositions containing a triboelectric mixture of carrier particles and electrostatically attractable toner particles, which governs the rate at which toner particles are depleted ~rom the composition during the development o~
electrostatic charge patterns. Accordingly, when such two component developers are used to develop a series of electro-static charge patterns, one must provide some means by which .. _ ........................... ... .

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to replenish the composition, i.e., to add additional toner particles to the composition to make up for the depletion of toner particles used in the development process. ~his replenishment process itself is a problem associated with conventional two-component developers, in that it is of~en quite difficult to add additional toner particles to an existing developer composition without destroying the stabllity e~-isting between the carrier particles and toner particles already present in the developer system.
In contrast, although not fully understood, it has been found that with the dry-appearing, liquid-containing developer compositions of the present invention one does not encounter a depletion or replenishment problem of the type associated with conventional two-component dry developer compositions. Rather, it has been found that, although the developers of the present invention appear to act, electrically or triboelectrically, in a manner analogous to known tw~component dry developer compositions ~as described above), there i~ ~o uneven depletion of the colorant-containing d~oplet~ and the dry, discrete particles from the composition. In other words, in relation to depletion, the deve:lopers o~ the present inv~ntion appear to act like a single component devcloper.
One is not faced with the problem of attempting to replenish a composition from which the various components are beiny depleted at different rates. Accordingly, it is believed that the dry-appearing, liquid-containing develope~ compositions of the present invention do not require concentration monitoring ~uring usage as is ordinarily the case wil:h ~onvention~l two component dry developer compositions.
When a developer compositio~ of the present invention is used in a process to develop electrostatic charge patterns, one can make up ~or the amount of developer ma~erial which i.s used up in the process simply by adding additional bulk quantities of the composition without having to provide separate mechanisms for monitoring toner particle concentration and for adding toner particles to the developer. In this respect, the composition of the present invention acts much like a conventional liquid ink material which is simply used up in the process of making ink images and can be "replenished" simply by feeding additional liquid ink into the imaging process.
The replenishment problem associated with conventional two-component dry developer compositions as described above is also encountered in many conventional liquid electrographic developer compositions containing electrostatically attractable toner particles. In addition, one also encounters an additional sort of replenishment problem when dealing with such liquid developer compositions. That is~ the electrostatic charge images which are developed by such liquid developer compositions tend to draw ouk a certain amount of this liquid hydrocarbon ma~erial (often the amount is quite large). Thus, when the image is dried, one is faced with the problem of venting or removing the liquid hydrocarbon vayor which is formed as a li~uid-developed irnagc is dried. In many conven~ional liquid dcvclopcr systems, the hydrocarbon vapor is simply vented into the air as the image is dried and fixed and accordingly presents environmental and possibly contamination,problems, unless the process is run at a rate slow enough so Lhat the amount o~
hydrocarbon vapor vented into the air is kept within an Z~

acceptable limit. For this reason, many conventional liquid developer compositions are commercially unacceptable in high speed copy 5y5 tems where one is faced with the problem Df venting or removing large amounts of hydrocarbon vapor because of the high rate of ~mage development which would be ~ccurring.
In contrast, the compositions of the present invention do not contain such carrier-vehicle liquids, and thus avoid the problem of the evaporation of such liquids during the development process.
In order for a developer composition to function in accordance withthe present invention the droplets of liquid and colorant and the dry, discrete particles must have a certain relationship to each other~ based on their surface energies. In order for any given combination of droplets a~d dry, discrete particles to be satisfactory for the practice of the present invention, the surface energy of the dry, discrete particles must be less than the interfacial tension !
between the dry, discrete particles and the liquid droplets.
Thi5 iq another way of saying that in working combinations of droplets and dry, discrete particles, the droplets d~ not "wet" khe dry, discrete particles.
Those conversant in the field of surface chemistry refer to contact angles when trying to determine if a given liquid will "wet" a given solid. The contact agle is a measurement of the internal angle formed be~2en the surface of a droplet of the liquid in question and a surface of the solid in question at th~ point where the ~urface of the liquid , first comes into contact with a surface of ~he solid. The measurement can be made by placing a droplet of the liquid in question onto a flat surface consisting of the solid in question and visually measuring the angle ormed at the point of contact by using a microscope with a protractor ~uperimposed over the eyepiece. The angle measured in this way is sometimes referred to as the "advancing angle", because it is the equilibrium angle formed when liquid is added to the ~urface of the solid. Similarly, one can measure the "receding angle", the equilibrium angle formed when some of the liquid is removed from the solid, for example, by inclining the flat, solid surface to allow some of the liquid to roll off the solid and then measuring the angle formed between the solid and any liquid still remaining on the surface of tha t solid .
Surface chemists express the relationship between the contact angle and the surface energetics of the system in question as follows:
I Cos A = ~S - TSL
EL

wherein A is the contact angle, Es is the surface energy of the solid, EL ls the surface energy of the liquid, and TSL

is the interfacial tension between the solid and the liquid when in contact with each other. A liquid is said not to "wet" a solid, and thus provide a liquid-solid combination useful in the present invention, whenever the advancing contact angle is greater than 90 degrees or the receding contact angle i6 greater than ~ degrees. By substituting these ~alues into equation I, above, one o~tains the foll~wing 4~;~

descriptions of solid-liquid combinations useful in the present invention: when the receding angle is measured, II ES ~ TSL c 1.0 .
EL

or III ~ ~ ES ~ TSL

and when the advancing angle is measured, IV ES TSL c O
EL

or ES ~ TSL

Because ES, EL, and Ts~ are always positive numbers, both equations III and V, which respectively describe the relationships that hold when receding angles and advancing angles are measured for solid-liquid c~mbinations useful in the present invention, are satisfied whenever the surface energy of the dry, discrete particles ~Es) is less than the interfacial tension between the dry, discrete particles and the droplets (TSL)~ It is recognized th~t at the present -time the~e sur~ace energy relationships are not directly measurable by any readily con~enient means; however these relationships can be determined indirectly by simple procedures ~uch as the two methods described below.
In one method that will suffice for choosing combinativns of droplets and dry, discrete particles havin~ surface-ener~y relationships useful in the present invention, one need only measure either the receding or the advancing co~tact angle of the system as described previously. The dry,`discrete particles can be f~rmed into a ~lid ~urface for this measurement - -. 14 4~;~

by depositing the particles onto a glass slide ~at has just been coated with a layer of acrylic adhesive that has not yet dried. Care must be taken to cover the adhesive layer with sufficient quantities of dry, discrete particles so that the resulting surface of the slide will consist totally of the particles themselves; otherwise the adhesive will interfere with the liquid-solid sur~ace energetics and result in incorrect angle measurements. If the measured advancing angle is greater than 90 degrees, or if the measured receding angle is greater than 0 degrees9 the dry, discrete particles can be used to surround the droplets of colorant-containing liquid without being wet by the droplets and thus form a composition in accordance with the present invention. Further information about contact angles and their measurement can be found in, Adamson, A. W., Physical Chemistrv of Surfaces, 2d ed., N.Y., Wiley & Sons, 1967.
An alternative and perhaps simpler method of deciding ~hether a liquid-solid combination has surface-energy relationships in accordance with the present invention, i.e., the droplets do not wet the dry, discrete particles, is first to form a surface of the dry, discrete particles on the glass slide as described above. The slide is then dipped into a solution or dispersion of the liquid and colorant in question. When the slide is withdrawn from the solution or dispersion, it is visually observed to determine if a continuous film of the solution or dispersion still remains on the solid surface. If it does not, then the liquid does not wet the solid and the combination has Z4~;/CI

sur~ace-energy relationships sufficient for the practice of the present invention. Further description of this method is provided in the Examples.
Although any of the eombinatlons of droplets and dry, discrete particles chosen according to the criteria described above can be useful in compositions ~r forming visual images, certain components will be more useful for particular applications.
For example, if the comp~sition is~to be used to form visual images from electrostatic charge patterns, the liquid component of the droplets comprises a liquid such as water, various polyols, certain amides, and the like.
Typical of useful polyols are the lower alkyl polyols containing two or more hydroxy groups and from one to about seven carbon atoms in the alkyl group. A partial listing representative of such polyols includes glycerol (sometimes referred to as glycerin), ethylene glycol, propylene glycol, mixtures of the foregoing materials and other similar highly polar glycols, i.e., diols, triols and mixtures thereof.
An especially preferred class o~ liquids which have 20 been found us~ul in the present invention, because of the ;
extremely high surface energy exhibited by the liquids, are such liquids as water, glycerol, ethylene glycol, formamide, mixtures of the foregoing materials with each other and mixtures of the foregoing materials with other liquids, for example various other lower alkyl polyols such as those lis ted above.

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As noted above, the amount of colorant-containing droplets employed in the developer composition of the present invention is less than about 98 percent and greater than about 60 percent by weight and, preferably, is greater than about 90 percent by weight, based on the total weight o~ the developer composition. The amount o~ liquid component present in the droplet phase of the developer compositions of the invention often represents more than about 40 weight percent of the total weight of the developer composition (which is equivalent to more than about 67 weight percent of the total weight of the droplet phase of the compositions). However, it has been found that useful results can be attained wherein the liquid component of the drople~ phase represents no more than about 5 percent by weight of the total weight of the developer composition (which is equivalent to about 8 percent by weight of the droplet phase), the remaining portion of the droplet phase con~aining other necessary or desirable addenda as set out hereinafter such as colorants, dispersing aids, binders, magnetic materials, etc.
An essential feature of the droplets contained in the developer compositions of the invention is the colorant component.
A wide variety of suitable materials useful as colorants may be employed in the droplets of the present invention. The colorant material may be dissolved in the liquid (for example, a water soluble dye in the case where the droplet contains an aqueous liquid base), or lt may be dispersed in the liquid in the form of a pigment material. For example, finely-divided carbon black materials have been found to provide especially useful colorants for the developer compositions of the present invention. Of course, as will be appreciated, a large number of suitable dyes and pigments have been effectively employed in various printing ink and electrographic liquid developer compositions and therefore would be available for use in the present invention depending upon ~Z4~0 the particular color which is desired, and the particular physical, chemical and electrical properties which one may wish to impart to the liquid droplets. It may be noted, as suggested hereinabove and dernonstrated in the examples below, that the choice of a particular colorant material can have an effect on the electrical properties of the droplets contained in the developer composition of the present invention. That is, it has been found that by varying the particular colorant material used in a given composltion, one can apparently modify the electrical properties associated with the composition such that the composition preferentially tends to develop either negative charge patterns or positive charge patterns.
The particular amount of colorant which is employed in the composition of the present invention may vary depending upon the desired image density, the compatability of a given colorant with the liquid media of the developer composition and the associated dry, discrete particles, the covering power of the colorant material and the like.

Typically, the amount of colorant present represents an amount within the range of from about 0.5 to about 50 weight percent based on the total weight o~ the developer composition.
In addition to a colorant material, the liquid droplets used in the present invention may ~lso contain, if desired, various dispersing agents which are typically employed in the pr~nting ink and electrographic liquid developer lndustry to facilitate the incorporation of various colorant materials into the liquid droplets and to prevent settling out of the colorant material from the liquid droplets. Various such materials are known in the art for this purpose and are commercially available as common surfactants or as dispersing aids for ink compositions.

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In addition to a dispersing aid, the liquid droplets employed in the compositions of the present invention may also contain any of various polymeric binders dispersed, suspended, or dissolved in the liquid media to serve as useful fixing agent to adhere the resultant colorant image to a desired receiving sheet. A variety of such polymeric materials, typically referred to as polymeric binders, are available and well known in the printing ink and electrographic liquid developer industry including such materials as: gums such as gum arabic and xanthan gum, waxes, starch, cellulose derivatives such as methyl cellulose, carboxy methyl cellulose, ethyl hydroxyethyl cellulose, poly(vinyl acetate), poly(vinyl alcohol), polytvinyl butyral), poly~vinyl fonmal~ J
poly(vinyl chloride), polyolefins, acrylic resins, polytalkyl vinyl ethers), poly(methyl vinyl ether-co-maleic anhydride), shellac, rosin and rosin derivatives, asphalts, phenolic resins, :~
alkyd resins, coumarone/indene resins, urea-formaldehyde resins, polyamide resins, rubbers, and epoxy xesins.
When dispersing aids and polymeric binder materials such as those noted hereinabove are employed in the colorant-containing droplets employed in the compositions o~ invention, it is generally desirable to use such materials in amounts ranging :~rom about 0.5 to about 50 weight percent based on the total welght of the developer compos:Ltlon, including both the droplets o:r the compositlon and the dry, discrete particles.
In addltion, i:r it is desired to apply the composition of the present invention to a sur~ace bearing an electrostatic latent image by use o~ a magnetic applicator system, the liquid-containing droplets may also contain an amount of magnetically attractable par-ticles, such as iron, nickel3 cobalt, magnetics, ferrites, and the like, e~ective to render the 4~
resultant composition magnetically attractable to known magnetic applicators, such as magnetic brush applicators used in conventional electrographic magnetic brush development systems.
A further essential c~mponent of the dry-appearing, li~uid~containing developer composition of the present invention is the finely divided particulate material that forms a network of dry, discrete particles surrounding and preventing coalescence of the colorant-containing droplets contained in the composi-tion of the invention. These modi~ied silicon dioxide powders which have been found use~ul are finely-divided silicon dioxide powders having a surface area in excess of 50 m2/g of powder, typica~ly in excess of about 150 m2/g, and which have been treated such that the exposed surface of an individual silicon dioxide particle, rather than being comprised of hydroxy groups which normally populate the surface of silicon dioxide powders, is modified, at least in part, by organo-silicon groups such as trimethylsiloxyl groups, by chemically bonding the silicon atoms of the desired organo-silicon groups to oxygen atoms at the surface of the typical silicon dioxide particle. By replaciny a number of the hydroxyl groups which normally populate the surfaces of a typical silicon dioxide powder, with the above-described organo-silicon groups, one creates surfaces on the resultant powder that have a low surface energy relative to certain liquids. Such surface-modified silicon dioxide materials can be obtained by contacting ~n ordinary pyrogenic s.ilicon dioxide powder with a compound containing hydrocarbon groups, for example, alkyl, aryl, alkaryl or aralkyl groups under conditions which ~ause a ~hemical reaction to occur with a ~ubstantial portion of the hydroxyl groups typically prexent on a ~urfac~ of p~rogenic .

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silicon dioxide particles, whereby new ~urface structures largely composed of such hydrocarbon groupings are created on the outer exposed portions of the silicon dioxide particles.
The preparation of such low-surface-energy silicon dioxlde powders is descri~ed, for example, in U.S. Patent 3,393,155, as is the use of these powders to surround large amounts of aqueous liquids. Such modified silicon dioxicle pow~ers are available commercially from Degussa, Inc. under the trademark Aerosil R 972 and also from the Tulco Corporation under the trademark Tullanox 500. Technical literature concerning Aerosil R 972 and Tullanox 500 can be obtained from both Degussa, Inc. and the Tulco Corporation describing further properties of such modified silicon dioxide powders.
Although the above-described ~odified silicon dioxide powder has been found to provide an especially preferred em~odi-ment of the present invention, other finely-divided particulate materials have been found to be useful in the practice of the invention. Any of such dry, discrete particles that have a surface energy less than the interfa~ial tension between these particles and the llquid-containing droplets o:~ cholce, as deter-mlned by the contact-angle measurement~ or wettability dip tes-t described above will be useful in the practice of this invention.
For ex~mple, finely-divided, particulate materials such as polyolefin wax particles, polytetrafluoroethylene particles, and the like also provide useful powders for the compositions of the present invention providing that the surface energy of these particles has the ~ppropriate ~elationship to the liquid ~roplets as described above, so that the particles ~an ~urround ~2~

and prevent coalescence of the colorant-contain~ng droplets without absorbing them.

Othcr useful dry, discrcte particles may bc those formed as part of an autophobic system. Autophobic systems are those in which adsorption of a layer of molecules from the liquid of choice onto the dry, discrete particles results in a new "solid" surface on these particles having an energy so low that the liquid no longer wets the surface. Fatty acids, for example, can be deposited on a solid surface by a retraction method from a solution or melt of the fatty acids to give a new surface which comes out "dry" as the sclid is removed from the liquid solution or melt. Such systems are described in Adamson, A. W., Physical Chemistry of Surfaces, 2d ed., N.Y., Wiley & Sons, 1967, p. 197.
The amount of dry, discrete particles which is present in the dry-appearing, liquid-containing compositions of the invention is typically relatively small in comparison to the rather large amount o~ colorant-contai~ing droplets contained in the resultant developer~ In general, composltions containing no more than about 40 percent by weight and typically less than about 10 percent by weight of the dry, discrete particles provide satisfactory results in accord with the invention.
Generally, it is found that at least about 2 percent and preferably from 5 to about 20 percent by weight based on the total weight o the resultant developer composition is composed of the above-noted dry, discrete particles.
The dry, free-flowing, liquid-containing powder compositions of the present invention may be prepared by several of various techniques. For example, useful developer .

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compositions of the invent~ on have been prepared simply bymixing small amounts of approximately 10 percent by weight of the above-described surface-modified silicon dioxide particles into a blender containing approximately 90 percent by weight of the above-described colorant- and liquid-contalning composition. The blender is turned on for less than a minute. As a consequence, one obtains the desired dry-appearing, finely-divided, liquid-containing powder material of the invention. Such a mixture has the appearance of a powder and when the resultant mixture is contacted with a charge pattern produced by any of the well known electrophotographic or electrographic techniques on a suitable support, one finds that the charge pattern is developed into a visible image corresponding to the original charge pattern.
Such relatively simple blending and milling techniques as admixing the dry, discrete particles with the colorant- and liquid-containing composition to form the desired developer composition of the invention, comprising colorant-containing droplets surrounded by dry, discrete particles, are especially e~fective with low ~iscosity liquid mediums comprising, liquids such as water, glycerol, ethylene glycol, ~ormamide and mixtures thereof, and low-surface-energy particles .such as the above-described modi~ied silicon dioxide particles. In other cases wherein the liquid medium of the composition is composed o~ a liqui.d which has a sur~ace energy not quite as high as water, glycerol, ethylene glycol, or foL~amide or in situations where the dry, discrete particles do not possess a surface energy quite so low as the above-described modified silicon dioxide particles, lt has been Z2~i0 found useful to first prepare the colorant- and liquid-containing composition into finely-divided droplets such as by atomizing the liquid to ~orm a fine mist of colorant-containing droplets and then propelling such a mist into a second mist composed solely of the dry, discrete particles. Alternatively, one can co-atomize the colorant- and liquid-containing composition together with a suitable amount of appropriate dry, discrete particles to form the resultant developer composition of the present invention. Further details concerning such mixing techniques are presented hereinafter LO in the Examples (Note: in some of the Examples Silano ~ 101, formerly availa~le rom Cabot Corporation, is used. This materi21 is no longer available, but Tullano ~ 500 from Tulco Corporation is identical in performance to Silano ~ 101.) Example 1 Table I below lists contact angle measurements of various liquids in combination with Silano ~ 101 (a modified silicon dioxide powder from the Cabot Corporation). The results indicate that contact angle measurements are predictive of utility in the practice of the present invention. Useful 'O compositions exhibited advancing angles greater than 90 degrees and receding angles greater than O degrees.

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Example 2 - Wettability Tes t A glass microscope slide was sprayed with a clear acrylic lacquer ~Krylo ~ ~o. 1301 from Borden, Inc.). Before the lacquer dried, the slide was repeatedly pressed into the powder to be ~ested. The object was to obtain a continuous coating of embedded particles. The lacquer was then allowed to dry. The slide was then dipped into the liquid in question ~or five seconds. If, upon removal of the slide, a continuous film of liquid coated the embedded particles, the liquid was said to wet the particles. If a continuous film was not formed, the liquid was said~not to wet the particles. Useful liquids for the present invention are ~hose which do not we~ the particles.
Several liquids were subjected to the wettability test to determine whether they would wet Silano ~ 101 (Cabo~ Corp.) particles. The liquids were then tested for usefulness in the present invention by placing in a Micro-Mill 10 grams liquid and 4.3 grams Silano ~ 101. The Micro-Mill was turned on for 5 seconds and the result examined. The liquid was deemed useful with Si.lano ~ 101 if the product was a dry-appearing powder.
The liquid was not useful if the product was a paste or liquid.

The wettability test was a good predictox in determi.ning whether a combination of liquid and particle was useful in the present invention (Table II).

- ~6 -- , 24~i~

TABLE II

Wettability Tests Of Various kiquids In Combination Wi~h Silano*~ 101 Liquid - Silanox~ 101 Does Liq~id Wet Combination Useful in Lic~uldSilano ~ 101? Present Invention? __ water no yes ethanol/water (20/80) no yes ethanol/water (30/70) no yes 10 ethanol/water ~35/65) yes no ethanol/water (40/60) yes no ethanol yes no glycerol no yes formamide no yes ethylene glycol no yes methanol yes no acetone yes no triethylene glycol no yes butyl lactate yes no ethyl lactate yes no diethylene glycol no yes Example 3 The following were added to a Micro-Mill (Chemical Rubber Company):

10 grams -- Carter's Black Stamp Pad Ink 0.5 gram -- CM ~ Cellulose Gum, Type 7-MP
lHercules Powder Company]
The mill was operated for 20 seconds resulting in a black paste.
To the mill was then added 1.0 gram of Silano ~ 101 (Cabot Corp~),

3 coated fumed silica, and the mill operated for ano~her 20 seconds.
The result was a black fluffy powder.
A photoconductor element was charged to -1000 volts, `; exposed 4.5 seconds to an image cc~prising both line copy and solid areas. Weyerhauser E28AK dielectric coatecl paper was placed on the photoconductor, hand rubbed on the photoconductor, :
.

~Z2~i0 and then removed from the photoconductor. 'rhe transferred charge pattern on the paper was then developed by cascade methods using the above-descri~ed powder. Fringe development resulted and image quality was good with low background.
The experiment was repeated except that the photo-conductor layer was charged to ~1000 volts. Image quality was poor with little development in the image areas indicating that the developer is charged positively.

Example 4 A photoconductor element was charged to -100 volts, exposed and developed as described in Example 3. The developed image was then transferred and fixed by placing a sheet of International~ Xerographic white paper (Substance 20) on the photoconductor layer, passing a rubber roll over the sandwich, and removing the paper.

Example 5 An ink was prepared by dissolving 3 grams of Methylene Blue in 100 grams of distilled water. To a CRC
Micro-mill was added 20 grams of this ink and 2 grams of Silano ~ 101. The Inill was operated for 20 ~econds and the result was a blue powder.
The photoconductor element was charged to ~1000 volts and exposed to an image for 4.5 seconds. 'rhe latent electrostatic image was charge ~ransferred to Weyerhauser E28AK paper and developed by the technique described in ~xample 2. Fringe development resulted and image quality was good with low background.

~he experLment was repeated except the ph~toconductor 8 ~

was charged t~ -1000 volts. Image quality was poor wit~ little development in khe image areas indica~ing ~hat this develvper is charged negatively.

~xample 6 An ink was prepared by dissolving 2 grams of ~ethylene Blue ln 100 grams of distilled water. Ten grams of ~his ink was frozen and placed in a cooled ~icro-Mill ~Chemical Rubber Co.). Three gr~ms of Nopcowa~ 22-DS powder ~a synthetic, 1QW-molecular-weight polyolefin wax from N~pco Chemical Division 1~ of Diamond Sham,rock Chemical . ) was cooled and al~ placed in the Micro-Mill.
The Micro-Mill was turned on in short burst~ vf 5 seconds followed by longer coDling periods in dry ice. The resulting blue developer was then allowed to warm ~o room temperature.
This developer was found to have a positive ~harge.
A visible image was produced by cascading the powdered developer over a dielectric surface containing a negative latent electro-static image. This image wa~ ~ressure transferred ~o paper at room temperature with two steel rolls.

Exam~le 7 Example 6 was repeated except that Whitco~ S TFE
powder (a polytetrafluoroethylene powder from WhitfordChemical Corp.) was used in place vf Nopcowax 22-DS.

~ - 29 -.

4~0 This developer was found to have a negative charge.
A visible image was produced by cascading the powdered ~eveloper over a dielectric ~urface concaining a positive latent electr~-static image. This image was pressure transferred to paper at room temperature with two steel rDlls.

Example 8 An ink was prepared by blending together on a ball mil~ for 6.5 days:

83.9 grams glyce~ine 1~ 1.1 grams Tamol SN ~Rohm and ~aas - sodium ~alt of a condensed aryl sulfonic acid) grams Rega~30~ carbon black (Cabot ~orp.) Fif~een grams of this ink was placed in a Micr~-~ill wlth ).5 grams of Silano~101 (Cabot Corp.). The mill was run for 15 seconds resulting in a ~lack powdered developer which was then passed through a 325 mesh screen to remove any large drople t5 .
The developer was found to have a positive charge.
A visible image was produced by cascading the powdered developer over 8 dielectric ~urface containing a negative }atent electro-~tatic image. This image was pressure transferred to paper ac room temperature wit~ two ~teel roll5 .

Example 9 An ink was prepared by blending together in a Waring 91ender the following:

100 gr~ms ethylene glycol 2 grams Tamo~ SN
10 grams Regal~300R Carbon Black - 30 ~-4~i~

Final dispersing was achieved ultrasonically.
Two grams of Silanox 101 was placed in a p~lyethylene beaker and fluidized using a magnetic stirrer. Twenty grams of -the ink was sprayed into the fluidized Silanox 101 thereby producing a black ~owdered developer. The clevelnper was sieved through a 325 mesh screen to remove any large droplets This developer was found to have a posi~ive charge.
A visible image was produced by cascading the powdered developer over a dielectric surface containing a negative latent electro-static image. This image was pressure transferred to paper atroom temperature with two steel rolls.

Example 10 , An ink was prepared by blending together in a Waring Blender the following:

200 grams formamide 1 gram Tamol SN
~0 grams Regal 300R Carbon Black Final di5persing was achieved ultrasonically.
Ten grams of this ink was fxozen and placed in a cooled Micro-Mill. One gram of cooled Silanox 101 was also placed in the Micro-Mill. The Micro-Mill was turned on in short bursts of 5 seconds followed by longer cooling periods in dry ice. The resulting powdered developer was then allowed to warm to room temperature.

. . . - . . ~ ~ . .

Z~

This developer was ~ound to have a positive charge.
A visi~le image was produced by cascading the p~wdered developer ~ver a dielectric surface containing a negative latent electro-static Image. This Lmage was pressure transferred ko paper at room temperature with two steel rolls.

Example 11 -- PolYmer Binder Dissolved in Liquid ~n ink was prepar~d by blending together:

10.~ grams -- Gantre~ AN-139 [poly(methyl vinyl ether-co-maleic anhydride~ from GAF].
0.6 grams -- CMC Cellulose Gum (Hercules P~wder Co.).

O.S grams -- Tamo~ SN ~a sodium salt of a condensed aryl sulfonic acid ~ram ~ohm and ~aas).
8.5 grams -- Rega~ 300R carbon ~lack (Cabot Corp.).
47.1 grams ;- water 33.3 grams -- glycerol ~ wenty grams of this ink was placed in a Micro-Mill with 2 grams of Silano ~ 101. The mill was run for 5 ~econds resulting in a black powdered developer.
The developer was cascaded over a latent electrostatic 20 image on a dielectric ~urface. The resulting Lmage was pressure transferred to paper at room temperature with two 8 teel rolls.

Example 12 -- Polvmer Binder Dispersed in Liquid An ink was prepared by dispersing together:

25 grams -- J-Pry~ P-20~ (carboxylated ~tyrene latex fxom lonac Corp.).
39.4 grams -- glycerol O.8 grams -- water 9 5 grams -- Rega~ 300R carbon b~ac~ (Cabot Corp.).
0. rams -- ~amo~ 5~ ~R~hm and ~aas3.

3~ f~.fiO

Fif teen grams of this ink was placed in a ~icro-Mill with 1~5 grams of Silano ~ 101 tCabot Corp.). The mill was run for 5 seconds resulting in a black powdered developer.
Ihe developer was cascaded over an electrostatic image on a dielectric surface. The resulting image was pressure transferred to paper at room temperature with two steel rolls.

Example 13 -- Maqnetic Component in DeveloPer An ink was prepared by blending together:
53.5 grams -- glycerol 26.7 grams -- ethylene glycol 16.0 grams -- Mapic ~ 81ack (an iron oxide from Columhian Carbon Co.).
2.7 grams -- Regal 300R carbon black (Cabot Corp.).
1.1 grams -- Tamol SN (Rohm and Haas).
Fifteen grams of this ink were placed in a Micro-Mill with 1.5 grams of Silano ~ 101. The mill was run for 7 seconds resulting in a black powdered developer.
A latent electrostatic image on a dielectric surface was developed using magnets to transport the black powder. The resulting image was pressure transferred to paper at room temperature with two steel xolls.
The invention has been described in detail with ; particular reference to certain preferred embodiments thereof but it will be unders~-ood that variations and modifications can be effected within the spirit and scope of the invention.

Claims (30)

WHAT IS CLAIMED IS:

1. An electrographic developer for producing visual images from electrostatic latent images, said developer being essentially non-aqueous and comprising a free-flowing, liquid-containing powder composition consisting essentially of:
a) at least about 60 percent and no more than about 98 percent by weight of droplets comprising a non-aqueous liquid and a colorant useful in electrographic developers, and b) at least about 2 percent and no more than about 40 percent by weight of dry, discrete particles surrounding said droplets;
wherein the surface energy of said dry, discrete particles is less than the interfacial tension between said dry, discrete particles and said droplets.

2. A free-flowing, liquid-containing powder composition as defined in Claim 1, wherein said droplets further comprise a polymeric binder dispersed or dissolved in said liquid.

3. A free-flowing, liquid-containing powder composition as defined in Claim 1, wherein said droplets further comprise a dispersing aid to facilitate the incorpo-ration of said colorant in said droplets.

4. A free-flowing, liquid-containing powder composition as defined in Claim 1, wherein said liquid is selected from the group consisting of glycerol, formamide, ethylene glycol, and mixtures thereof.

5. A free-flowing, liquid-containing powder composition as defined in Claim 1, wherein said dry, discrete particles are selected from the group consisting of poly-olefin wax particles, polytetrafluoroethylene particles, and modified pyrogenic silicon dioxide particles, said modified pyrogenic silicon dioxide particles having hydrophobic hydro-carbon groups distributed over the surface thereof.

6. A free-flowing, liquid-containing powder composition as defined in Claim 1, wherein said droplets further comprise magnetically attractable particles.

7. An electrographic developer for producing visual images from electrostatic latent images, said developer being essentially non-aqueous and comprising a free-flowing, liquid-containing powder composition consisting essentially of:
a) at least about 60 percent and no more than about 98 percent by weight of droplets comprising a non-aqueous liquid and a colorant useful in electrographic developers, and b) at least about 2 percent and no more than about 40 percent by weight of dry, discrete particles surrounding said droplets;

wherein said droplets do not wet a surface comprising said dry, discrete particles when said surface is dipped into and then removed from a solution or dispersion comprising said droplets.

8. A free-flowing, liquid-containing powder composition as defined in Claim 7, wherein said droplets further comprise a polymeric binder dispersed or dissolved in said liquid.

9. A free-flowing, liquid-containing powder composition as defined in Claim 7, wherein said droplets further comprise a dispersing aid to facilitate the incorpo-ration of said colorant in said droplets.

10. A free-flowing, liquid-containing powder composition as defined in Claim 7, wherein said droplets further comprise magnetically attractable particles.

11. An electrographic developer for producing visual images from electrostatic latent images, said developer being essentially non-aqueous and comprising a free-flowing, liquid-containing powder composition consisting essentially of:
a) at least about 60 percent and no more than about 98 percent by weight of droplets comprising a non-aqueous liquid and a colorant useful in electrographic developers, and b) at least about 2 percent and no more than about 40 percent by weight of dry, discrete particles surrounding said droplets;
wherein the advancing angle formed between a surface of one of said droplets and a surface comprising said dry, discrete particles is greater than 90 degrees, and the receding angle formed between a surface of one of said droplets and a surface comprising said dry, discrete particles is greater than 0 degrees.

12. A free-flowing, liquid-containing powder composition as defined in Claim 11, wherein said droplets further comprise a polymeric binder dispersed or dissolved in said liquid.

13. A free-flowing, liquid-containing powder composition as defined in Claim 11, wherein said droplets further comprise a dispersing aid to facilitate the incorpo-ration of said colorant in said droplets.

14. A free-flowing, liquid-containing powder composition as defined in Claim 11, wherein said droplets further comprise magnetically attractable particles.

15, A process for forming a visual image comprising the steps of:
1) forming an electrostatic latent image on a surface; and 2) contacting said electrostatic latent image with a developer bearing an electrostatic charge opposite in polarity to said electrostatic latent image and compris-ing a free-flowing, liquid-containing powder composition consisting essentially of:
a) at least about 60 percent and no more than about 98 percent by weight of droplets comprising a liquid and a colorant useful in electrographic developers, and b) at least about 2 percent and no more than about 40 percent by weight of dry, discrete particles surrounding said droplets, wherein the suirface energy of said dry, discrete particles is less than the interfacial tension between said dry, discrete particles and said droplets, and said electrostatic charge consists of essentially of charge generated by interaction of the components of said composition with each other.

16. A process for forming a visual image as described in Claim 15, wherein said droplets further comprise a polymeric binder dispersed or dissolved in said liquid.

17. A process for forming a visual image as described in Claim 15, wherein said droplets further comprise a dispersing aid to faciliate the incorporation of said colorant in said droplets.

18. A process for forming a visual image as described in Claim 15, wherein said droplets further comprise magnetically attractable particles.

19. A process for forming a visual image as described in Claim 15, wherein said liquid is selected from the group consisting of water, glycerol, formamide, ethylene glycol, and mixtures thereof.

20. A process for forming a visual image as described in Claim 15 wherein said dry, discrete particles are selected from the group consisting of polyolefin wax particles, polytetrafluoroethylene particles, and modified pyrogenic silicon dioxide particles having hydrophobic hydro-carbon groups distributed over the surface thereof.

21. A process for forming a visual image comprising the steps of:
1) forming an electrostatic latent image on a surface; and 2) contacting said electrostatic latent image with a developer bearing an electrostatic charge opposite in polarity to said electrostatic latent image and compris-ing a free-flowing, liquid-containing powder composition consisting essentially of:
a) at least about 60 percent and no more than about 98 percent by weight of droplets comprising a liquid, a colorant, a polymeric binder dispersed or dissolved in said liquid, and a dispersing aid to facilitate the incorporation of said colorant in said droplets, and b) at least about 2 percent and no more than about 40 percent by weight of dry, discrete particles surrounding said droplets, wherein the surface energy of said dry, discrete particles is less than the interfacial tension between said dry, discrete particles and said droplets, and said electrostatic charge consists essentially of charge generated by interaction of the components of said composition with each other.

22. A process for forming a visual image as described in Claim 21, wherein said droplets further comprise magnetically attractable particles.

23. A process for forming a visual image comprising the steps of:
1) forming an electrostatic latent image on a surface; and 2) contacting said electrostatic latent image with an essentially non-aqueous developer comprising a free-flowing, liquid-containing powder composition consisting essentially of:
a) at least about 60 percent and no more than about 98 percent by weight of droplets comprising a non-aqueous liquid and a colorant; and b) at least about 2 percent and no more than about 40 percent by weight of dry, discrete particles surrounding said droplets, wherein the surface energy of said dry, discrete particles is less than the interfacial tension between said dry, discrete particles and said droplets.

24. A process for forming a visual image as described in Claim 23, wherein said droplets further comprise a polymeric binder dispersed or dissolved in said liquid.

25. A process for forming a visual image as described in Claim 23, wherein said droplets further comprise a dispersing aid to facilitate the incorporation of said colorant in said droplets.

26. A process for forming a visual image as described in Claim 23, wherein said droplets further comprise magnetically attractable particles.

27. A process for forming a visual image as described in Claim 23, wherein said non-aqueous liquid is selected from the group consisting of glycerol, formamide, ethylene glycol, and mixtures thereof.

28. A process for forming a visual image as described in Claim 23, wherein said dry, discrete particles are selected from the group consisting of polyolefin wax particles, polytetrafluoroethylene particles, and modified pyrogenic silicon dioxide particles having hydrophobic hydro-carbon groups distributed over the surface thereof.

29. A process for forming a visual image comprising the steps of:
1) forming an electrostatic latent image on a surface; and 2) contacting said electrostatic latent image with an essentially non-aqueous developer comprising a free-flowing, liquid-containing powder composition consisting essentially of:

a) at least about 60 percent and no more than about 98 percent by weight of droplets comprising a non-aqueous liquid, a colorant, a polymeric binder dispersed or dissolved in said non-aqueous liquid, and a dispersing aid to facilitate the incorporation of said colorant in said droplets and b) at least about 2 percent and no more than about 40 percent by weight of dry, discrete particles surrounding said droplets, wherein the surface energy of said dry, discrete particles is less than the interfacial tension between said dry, discrete particles and said droplets.

30. A process for forming a visual image as described in Claim 29, wherein said droplets further comprise magnetically attractable particles.