GB2176904A - Preparing toner particles for liquid developer compositions - Google Patents

Abstract

Toner particles having a plurality of fibers or tendrils are formed by plasticizing a thermoplastic polymer in a non polar liquid at elevated temperature adding a pigment and then diluting the plasticized polymer-pigment with further non polar liquid while cooling and constantly stirring to prevent the forming of a sponge. When cool, the diluted composition will have a concentration of toner particles formed with a plurality of fibers. The toner particles are used in liquid developer compositions for electrostatic images.

Description

1 # 10 GB 2 176 904 A 1

SPECIFICATION

Improved toner for use in compositions for developing latent electrostatic images, method of making the same, and liquid composition using the improved toner In the prior art, a latent electrostatic i mage is developed by dry toner particles or by toner particles dispersed in an insulating nonpolar liquid. The dry toner particles cannot be too fine, since they will become airborne and be disadvantageous to health shou I d they escape i nto the circurnam bient atmosphere. Furthermore, the dry toner particles must be fixed by fusing at elevated temperatures, which requires a source of energy. The developing of latent electrostatic images by d ry toners results in i mages which do not have the deg ree of resol ution wh ich is desirabl e. Liq uid-ca rried toners, however, may be as fine as one can ma ke them, since there is no danger of their becoming air-borne. Accordingly, they may be employed to produce copy of increased resolution.

An electrostatic image may be produced by providing a photoconductive layerwith a uniform electrostatic charge and thereafter discharging the electrostatic charge by exposing itto a modulated beam of radiant energy. It wi I I be understood that other methods maybe employed to form an electrostatic image, such, for example, as providing a carrier with a dielectric surface and transferring a preformed electrostatic charge to the surface. The charge maybe formed from an array of styluses.

This invention will be described in respect of office copiers, though it is to be understood that it is applicable to other uses involving electrophotography.

In an office copier, after the latent electrostatic image has been formed, usually by projecting the desired information upon a charged photoconductor in the dark, the image is developed by a liquid comprising pigmented toner particles dispersed in a nonpolar, nontoxic liquid having a high-volume resistivity in excess of 109 ohm centimeters, a low dielectric constant below 3.0, and a high vapour pressure. Suitable liquids, acting as dispersants, are the aliphatic isomerized hydrocarbons prepared by the Exxon Corporation and sold 25 under such trademarks as ISOPAR-G, ISOPAR-H, ISOPAR-L and ISOPAR-M, each having different end points and vapor pressures.

Afterthe image has been developed, it istransferred to a carrier sheet. During transfer,there occurs a degree of smudging, smearing, or squashing of the image. This reducesthe resolution. Furthermore,the entire image does not transfer from the photoconductor to the carrier sheet. This leaves a residue of toner on the photoconductor which formed the image just transferred. The squash effect maybe avoided by providing a gap between the developed image on the photoconductor and the carrier sheet to which the image is to be transferred. The density of the image and the resolution of the gap- transfer method are good, but are improved by the present invention.

Our invention relates to improved toner particles adapted to develop latent electrostatic images with 35 increased density and high resolution when dispersed in a nonpolar liquid carrier, a method of making said particles, and a liquid composition for dispersing the toner particles. Our invention relates to a toner particle, preferably pigmented, which is formed with fibers, tendrils, tentacles, threadlets, fibrils, ligaments, hairs, extensions, elongations, bristles, peaks, orthe like (hereinafter referred to as "fibers").

Blanchette eta/3,278,439 shows a dry developer mix in which irregularly shaped carrier particles, formed of 40 ferromagnetic material, are adapted to interlock, intertwine, or linkto forma brush-like structure adapted to carry electroscopic thermoplastic powder. This patent does not teach our invention.

Wright3,419,41 1 seeks to provide a developing liquid having a pigment and a "lattice-forming material" (Column 2,line 12 etseq). The patentee describes his "lattice-forming substance" as "polymeric materials presenting a branched as distinguished from either a linear or closed chain molecule... whichwhenin apparentsolution in a liquid has a molecular structure in which one dimension is at least one order greater than its dimensions in two other dimensions at right angles to each other (Column 2, line 31 etseq; emphasises ours). Wright hypothecates that molecules, linear in one direction only, are not capable of for ming a lacy fiber (Column 2, line 48 etseq). It is believed thatthe theory setforth is irrelevant. The molecular dimensions deal in orders of magnitude of 10 A. This conrasts with toner particles where the orders of magni- 50 tude dealt with are thousands of A. In Example 1, Wright disperses a pigment in rubber modified polystyrene.

It is understood that Solvesso 100 has a Kauri-butanol value of 93. It will dissolvethe rubber compound. The solution is more like a coating than a "lattice". The image will be supported bythe rubber coating. In Example 2, a varnish of polymerized linseed oil does the holding. Paraffin wax merely carries the pigment. The pat entee designates the varnish as a "grinding aid". Similarly, in Example 3, a varnish, comprising hydrogena55 ted rosin and polymerized linseed oil, are used. Again, the varnish is designated as a "grinding aid". In Example 4, paraffin wax and varnish are used in each of the fourtoners and again are designated as a 11 grinding aid". It is signifi-to note that, when paraffin wax is used, the high KB value of Solvesso is such that it will dissolve the paraffin wax. Accordingly, in connection with Example 4, the KB value of Solvesso has to be decreased by diluting it with Shellsol T, which has a KB value of only 26. It is pointed outthat, when a low KB 60 value is used, good resolution is not possible without a halftone screen (Column 6, line 1 etseq). Example 5 is the same as Example 4, exceptthatthe varnish eliminates the hydrogenated rosin and substitutes calcium resinate. In Example 6, the toners shown use Lucite in toluol and ethyl cellulose in Solvesso. Toluol has a KB value of over 100. Judging from the specification, it would appearthatthe pigment develops the image and a coating of varnish, wax, ethyl cellulose, rubber modified polystyrene, or Lucite isformed overthe deposited 65 2 GB 2 176 904 A 2 pigment. This coating is formed as the resin or wax is deposited as the solvent evaporates. It is the coating deposited overthe pigment which prevents the spreading of the pigment particles. The toner particles thems elves do not have any fibers as contemplated in the instant invention.

Machida eta/3,668,127 discloses a toner particle having a first resinous coating for a pigment. This coating is insoluble in the dispersing agent. The particle, however, is coated with a second resinous coating which is 5 swellable --that is, solvatable --in the dispersant. In the instant invention, the resin must be insoluble at ambienttemperatures and solvatable only at elevated temperatures. The swellability of the resin indicates that solvation has occurred. In Machida, there is no disclosure of fibers extending from the toner particle, which fibers are adapted to intertwine, interdigitate, or mat so as to accomplish the objects of the instant invention.

Gifflams eta/3,909,433 relates to a toner particle formed by coating a pigment with a resin derived from rosin. The coated particle is then ground to a fine powder. This powder is then suspended in a nonpolar carrier liquid togetherwith an alkyl ated polymer of a heterocyclic N-vi nyl monomer to impart positive polarityto the resin-coated toner particle. There is no teaching of fibers.

Lawson eta/3,949,116 seeks to avoid wetting the photoconductor bearing the latent electrostatic image, or 15 the carrier sheet to which the developed image is to be transferred, with an excess of liquid. The patentees do this by forming a gel of a pigmented resin and a dispersant liquid, which gel has thixotropic properties. When it is desired to develop a latent image, the gel is fed under a roller, or the like, to convert the developer from a gelatinous state to a liquid state in the vicinity of the roller. Only the area under shear stress is converted into a liquid state. When the shear stress is dissipated, the developer reverts to the gelatinous state. No toner having 20 fibers istaught.

Tsuneda 3,998,746 relatesto a toner comprising colored particlescoated with a rubber.The rubbercoating is appliedfrom a solution ofthe rubberwhich has been subjectedto an elevated temperature in excess of 150'C.While no disclosure of atoner particle having fibers appears, itwill be clear that any fibers, which are the salientfeature of the instant invention, will becoated overwith the rubberandthus defeatthe objects of 25 this invention.

Brechfin eta/4,157,974 is an improvement of Smith etal Patent 3,939,085, which discloses a liquid dev eloper organosol for developing a latent electrostatic image to provide a tacky developed image. This image may be transferred to a carrier sheet merely bythetackiness of the image and without the use of an electrical field. The difficulty of this type of developer is that it agglomerates when not in use. Brechlin eta/seekto provide protective colloids to prevent agglomeration of the pigmented polymer in the dispersing liquid. The patentees form pigmented polymers which are tacky. The images developed with these toners can be trans ferred by simple contact (Column 10, line 57 etseq). The tackiness can be increased by adding an aromatic hydrocarbon solvent, such as Solvesso 100 (Column 10, line 62 etseq). Furthermore, the toner particles are spherical in form (Column 7, line 18 etseq). There is no disclosure of a toner formed with fibers.

Landa eta/4,411,976 discloses a toning composition designed for use in developing a latent electrostatic image across a gap between the carrier sheet and the developed image. It is true thatthe composition can be used for developing an image by contacttransfer of the developing liquid with the latent electrostatic image to be developed. However, squash -- which is the salient object of this invention to eliminate -- would occur.

No toner particles having the essential fibers are taught bythis reference. With contact development, instead 40 of gap development, the developed image, when transferred to a paper carrier sheet, will exhibit bleed through in many instances.

The Japanese patent publication of Application No. Sho 56/1981-93330, filed June 16,1981, which was laid open on December 18,1982 as Laid Open Patent Publication No Sho 57/1982- 207259, discloses the formation of small projections on the surface of a spherical toner particle. These projections are formed of a resin incorporating an insoluble powder. The purpose of the projections is to enable the ready removal of a dev eloped image from the surface on which itwas developed, so thatthe blade which cleans the surface will have a longer life. The preferred material is a thermosetting resin. There is no disclosure whatever of anyformation of f i bers.

Japanese Patent Application 58-2851, published January 8,1983, in which Obata is the inventor, discloses 50 the manufacture of a wettonerfor making printing plates. In Obata, a partially saponified ethylene-vinyl acetate copolymer and carbon black are mixed with toluene and the polymer is dissolved by heating to 80'C.

The heated solution is then cooled while stirring in n-hexane. Particles are formed which are precipitated to the bottom of the container. A latent electrostatic image was developed from the toner as described. One example given is ethylene-vinyl acetate polymer dipped in liquid nitrogen and then pulverized with a hammer. Powderthus obtained was dispersed in Isopar H. There is no disclosure of plasticizing the polymer and then eitherforming a sponge or preventing the formation of the sponge in order to produce f i bers. No disclosure appears of forming fibers anywhere in the disclosure. Indeed, the formation of a powder with a hammer negates the presence of any particle having fibers.

In general, our invention contemplates the production of a toner particle possessing a morphology of a 60 plurality of fibers as the term is defined above. These fibers are formed from a thermoplastic polymer and are such thatthey may interdigitate, intertwine, or interlink physically in an image developed with a developing liquid through which has been dispersed the toner particles of the instant invention. The result is an image having superior sharpness, line acuity --that is, edge acuity --and a high degree of resolution. The salient feature of the developed image is that it has good compressive strength, so that it maybe transferred from the 65 1# c 11 It 3 GB 2 176 904 A 3 11 10 surface on which it is developed to a carrier sheet without squash. Because of the intertwining of thetoner particles,we may build athicker image and still obtain sharpness. Thethicknesscan be controlled byvarying the charge potential on the photoconductor, byvarying the development time, byvarying thetoner-particle concentration, by varying the conductivity of the toner particles, by varying the charge characteristics of the toner particles, by varying the particle size, or by varying the surface chemistry of the particles. Any or a combination of these methods may be used.

In addition to being thermoplastic and being able to form fibers as above defined, the polymer must have the following characteristics:

1. It must be ableto disperse a pigment (if a pigmentis desired).

2. It must be insoluble in the dispersant liquid attemperatures below 40'C, so that itwill notdissolve or 10 solvate in storage.

3. It must be ableto solvate attemperatures above 50'C.

4. It must be ableto be ground to form particles between 0.1 micron and 5 microns in diameter.

5. It must be able to form a particle of lessthan 10 microns.

6. It must be ableto fuse attemperatures in excess of 700C.

7. For photocopy applications a spongeformed from it (as hereinafter described) must have a hardness, as measured by a Precision Universal Penetrometer, greaterthan 120,though in many instances a polymer of this hardness would betoo soft.

Bysolvation,the polymers forming the toner particles will become swollen or gelatinous. This indicates the formation of complexes bythe combination of the molecules of the polymerwith the molecules of the dis persant liquid.

We havefound three methods of forming toner particles having the desired fibrous morphology. In es sence, we disperse or dissolve a pigment in a plasticized polymer attemperatures between 65'C and 1 OO'C.

The plasticized material when cooled hastheform of a sponge. The sponge isthen broken into smaller pieces and ground. This method will be described more fully hereinafter.

Another method of forming ourtoner particles is to dissolve one or more polymers in a nonpolar dis persant, together with particles of a pigment such as carbon black orthe like. The solution is allowed to cool slowly while stirring, which is an essential step in this method of forming ourfiber-bearing toner particles. As the solution cools, precipitation occurs, and the precipitated particles will befound to havefibers extending therefrom.

Athird method isto heat a polymer above its melting point and disperse a pigmentthrough it. In this method,fibers areformed by pulling the pigmented thermoplastic polymer apart without first forming a sponge.

Thefibroustoner particles, formed by any of the foregoing methods, are dispersed in a nonpolar carrier liquid, together with a charge director known to the art,to form a developing composition.

One object of our invention isto provide a densercleveloped electrostatic imagethan the prior art has been able to achieve.

Another object of our invention isto provide a developing composition, including a toner, which will enable substantially complete transfer of the developed electrostatic image.

Still another object of our invention isto enable thetransfer of a developed electrostatic image to a carrier 40 sheet with no squash.

Afurther object of our invention is to provide a developed electrostatic image capable of being transferred with high resolution.

Astill further object of our invention is to provide a developed electrostatic image capable of being transfer red with exceptional contrast.

An additional object of our invention is to provide a developed electrostatic image which maybe transfer red to a carrier sheet with no bleed-through.

Still another object of our invention is to provide developed electrostatic images which maybe transferred to carrier media of various materials having various degrees of surface roughness.

Afurther object of our invention isto provide a novel method of making an improved toner particle. 50 Astill further object of our invention is to provide a liquid composition, using our improved toner particles, for developing liquid electrostatic images. Other and further objects of our invention will appearfrom thefollowing description. Figure 1 is a photomicrograph taken with a transmission electron beam microscope at a magnification of 55 13,000 times, showing a dispersion containing the toner particles of our invention. Figure 2 is a photom icrog raph taken with a transmission electron beam microscope of a toner particle shown in Figure 1, at a magnification of 45,000 times. Figure 3 is a photomicrogra ph taken with a transmission electron beam microscope of another toner particle of our invention shown in Figure 1, at a magnification of 45,000 times. 60 Figure 4 is a photomicrograph taken with a scanning electron beam microscope at a magnification of 1,000 60 times, showing a sponge achieved during an intermediate step of one method of manufacturing our improved toner particle. Figure 5 is a photomicrograph taken with a scanning electron beam microscope at a magnification of 23,800 times, showing a plurality of toner particles of our invention.

Figure 6 is a photomicrograph taken with a scanning electron beam microscope at a magnification of 65 4 GB 2 176 904 A 4 38,400 times, showing a plurality of toner particles of ourinvention.

Figure 7isa photomicrograph taken with a scanning electron beam microscopeata magnification of 20,000 times, showing a plurality of toner particlesof ourinvention made byanothermethod of manufacturing the toner particles of ourinvention.

6 The salient feature of ourinvention is a toner particle formed with a plurality of fibers --thatisto say,one with such morphology.The novel toner particle enables ustoform a developing composition for developing latent electrostatic images by dispersing the toner particles in small amounts in a nonpolar liquid such asan ISOPAR. The weight of the toner particle may be as lowasO.2 percent by weight of the weight of thedispersant liquid. The toner particle is pigmented andformed of a polymeric resin. A charge director is addedto thecomposition insmall amounts,which maybeas lowasone-tenth percent by weight of theweightofthe toner particles in the developing composition. The charge director maybe selected to imparteithera positive ora negative charge to the toner particles, depending onthecharge ofthe latent image. Those intheartwill understand that the charge on the toner particles is generally opposite in polarity to that carried bythelatent electrostatic image.

The nonpolar dispersant liquids are, preferably, branched-chain sliphatic hydrocarbons -- more particularly, ISOPAR-G, ISOPAR-H, ISOPAR-K, ISOPAR-L, and ISOPAR-M. These ISOPARS are narrow cuts of isoparaffinic hydrocarbon fractions with extremely high levels of purity. For example, the boiling range of ISOPAR-G is between 156'C and 176'C. ISOPAR-L has a mid-boiling point of approximately 1940C. ISOPAR-M has a flash point of 770C and an auto-ignition temperature of 3380C. Stringent manufacturing specifications, such as sulphur, acids, carboxyl, and chloride are limited to a few parts per million. They are substantially odorless, possessing only a very mild paraffinic odor. They have excellent odor stability and are all manu factured bythe Exxon Corporation. Light mineral oils, such as MARCOL 52 or MARCOL 62, manufactured by the Humble Oil and Refining Company, may be used. These are higher boiling aliphatic hydrocarbon liquids.

All of the dispersant liquids have an electrical volume resistivity in excess of 10' ohm centimeters and a dielectric constant below 3.0 The vapor pressures at 25'C are less than 10 Torr. A desirable ISOPAR is ISOPAR- 25 G, which has a flash point, determined by the tag closed cup method, of 40'C. ISOPAR-L has a flash point of 61'C, determined by the same method, while ISOPAR-M has a flash point, determined by the Pensky-Martens method, of 77'C. While we have described the preferred dispersants, the essential characteristics are the volume resistivity and the dielectric constant. In addition, a feature of the dispersants is a low Kauri-butanol value, in the vicinity of 27 or 28, determined byASTM D 1133.

The polymers used must be thermoplastic, and the preferred polymers are known as ELVAX 11 (trademark), manufactured by E. 1. DuPont de Nemours &Company. The original ELVAX resins (EVA) were the ethyl vinyl acetate copolymers. The new family of ELVAX resins, designated ELVAX [[,are ethylene copolymers combining carboxylic acid functionality, high molecular weight, and thermal stability. The acid numbers range as follows:

Resin is Acid MeltIndex Number at 1900C 5550 54 10 40 5610 60 500 5640 60 35 5650T 60 11 5720 66 100 5950 90 25 45 "T" denotes Terpolymer The greaterthermal stability and higherstrength properties of ELVAX 11 resins are dueto two factors. First, the presence of an alkyl group on the same carbon atom on the polymerchain to which is attached a car boxylic acid group increasesthe chain stiff ness and the energy required for rotation of the polymerchain. 50 Second, hydrogen bonding, brought about by intermolecular and intramolecular dimerization, establishes a resonance stabilized configuration.

The preferred ethylene copolymer resins arethe ELVAX 115720 and 5610. Other polymerswhich we have tested are isotactic polypropylene (crystalline). Other polymers which are usable arethe original ELVAX copolymers and polybutyl terethalate. Other polymerstested arethe ethylene ethyl acrylate series made by 55 Union Carbide and sold under the trademark BAKELITE. They arethe DPD 6169, DPDA 6182 Natural, and DTDA9169 Natural. Still other useful polymers made by Union Carbide arethe DQDA 6479 Natural 7 and DQDA6832 Natural 7. These are ethylenevinyl acetate resins.

Anotherclass of polymers useful in practicing our invention arethose manufactured by E. 1. du Pont de Nemours & Company and sold under the trademark ELVACITE. These are methacrylate resins, such as poly- 60 butyl methacrylate (Grade 2044), polyethyl methacrylate (Grade 2028), and polymethyl methacrylate (Grade 2041). If desired, a minoramount of carnauba wax may be added tothe composition. However, this tends to produce bleed-through and an oil fringe on the copy and is not preferred. Furthermore, if a hard polymersuch as 5650Tis used, a minoramountof hydroxy-ethyl cellulose may be added. This is not preferred.

The polymers are normally pigmented so asto renderthe latent image visible, though this need not be i 11 GB 2 176 904 A 5 done in some applications. The pigment may be present in the amount of 10 percentto 35 percent byweight in respectof theweight of the polymer, if the pigmentbe Cabot Mogul L(black pigment). If the pigment is a dye, it may be presentin an amount of between 3 percent and 25 percent byweightin respectof theweightof the polymer. If no dye is used -- as,forexample, in making a toner for developing a latent imagefor a printing plate --an amount of silica such as Cabosil maybe added to make the grinding easier. Examples of pigments are Monastral Blue G (C.I. Pigment Blue 15 C.I. No. 74160).Toluidine Red Y (C.I. Pigment Red 3), Quindo Magenta (Pigment Red 122), Indo Brilliant ScarletToner (Pigment Red 123, C.I. No. 71145),Toluidine Red B (C.I. Pigment Red 3), Watchung Red B (C.I. Pigment Red 48), Permanent Rubine F61313-1731 (Pigment Red 184), Hansa Yellow (Pigment Yellow 98), Dalamar Yellow (Pigment Yellow 74, C.I. No. 11741), Toluidine Yellow G (C.I. Pigment Yellow 1), Monastral Blue B (C.I. Pigment Blue 15), Monastral Green B (C.I. Pigment 10 Green 7), Pigment Scarlet (C.I. Pigment Red 60), Auric Brown (C.I. Pigment Brown 6), Monastral Green G (Pigment Green 7), Carbon Black, and Stirling NS N 774 (Pigment Black 7, C.I. No. 77266).

If desired, a finely ground ferromagnetic material maybe used as a pigment. While about40 percentto about 80 percent by weight of Mapico Black is preferred, with about 65 percent Mapico Black being optimum, other suitable materials such as metals including iron, cobalt, nickel, various magnetic oxides including 15 Fe203, Fe304, and other magnetic oxides; certain ferrites such as zinc, cadmium, barium, manganese; chromium dioxide; various of the perm-alloys and other alloys such as cobalt-phosphorus, cobalt-nickel, and the like; or mixtures of any of these may be used.

A preferable first step, in the method of making our newtoner particle, includes the forming of a gel or an open-cell sponge having a hardness of at least 120 as measured by a Precision Universal Penetrometer (with 20 timer) No. 73515, manufactured by GCA Precision Scientific, of Chicago, Illinios, and used according to ASTM D5-83 procedure. A 1.02 mm diameter weighted needle (total weight 50 grams) penetratesthe samplesfor 5 seconds.

In our method,the plasticizer may bethe same asthe carrier liquid or a heavier liquid such as ISOPAR-M, or mineral oil USP (viscosity 36 centistokes). This is preferred forthe ELVAX 11 resins. With polyvinyl chloride as 25 the polymer, dioctyl phthalate is the plasticizer of choice. With Nylon (polyamide), benzyl alcohol may be used as the plasticizer. The useful range of plasticization ratios ranges from 1: 1 to 1:5 by weight.

The addition of waxy substances such as carnauba wax reduces the grinding time. In addition to carnauba wax, otherwaxy substances such as cocoa butter, Japan wax, beeswax, microcrystalline wax, and low molec ularweight polyolefins such as polyethylene and ethylenevinyl acetate copolymer may be added. Care 30 should be taken notto employ waxes which may act as charge directors.

In its simplest aspect, our method begins, as pointed out above, by plasticizing a quantity of a desired polymerwith a pigment, together with a plasticizer, and mixing until homogeneity is achieved. After thorough mixing, the material is removed f rom the mill and allowed to cool. It will have the form of a sponge.

As pointed out above, the sponge should have a hardness of at least 120. A hardness of between 25 and 45 is 35 preferable. The temperature for mixing may range f rom between 650 and 1 OOOC -- preferably 900C. Mixing times may range between 10 minutes and 3 hours. A preferable time is about 90 minutes. Any suitable mixing or blending device may be employed -- as, for example, the Ross double planetary mixer (manufactured by Charles Ross and Son, of Hauppauge, New York).

Afterthe mixture has been cooled, it is sliced into strips and ground in a General Slicing meat grinder 40 (manufactured by General Slicing/Red Goat Dispensers, of Murfreesboro, Tennessee). The ground material is then charged to an attritor, disk mill, sand mill, impeller attrition mill, vibro-energy mill, orthe like. The object of the grinding is to pull the larger particles apart and, in so doing, to form fibers on.the toner particles. This is in contradistinction to the toners of the prior art, in which the purpose of grinding is merelyto reduce the particle size.

An importantfeature of this method is to wet-grind the composition. The liquid used during the grinding operation may be ISOPAR-H, which is present in the amount of 70 percent to 90 percent by weight in respect of the polymer. During the grinding, the particle size is determined by centrifugal analysis, using a Horiba Centrifugal Particle Size Analyzer, Model CAPA 500, manufactured by Horiba Instruments, Inc., of Irvine,California. Thermal transitions are measured, using a Du Pont 1090 Thermal Analyzer System with dual cell, 50 DSC 0912, using non-hermetic pans, a scan rate of 20'C/min, a temperature range of -40'C-200'C and mult iple scans.

Toner-performance evaluation is conducted as follows: A 5-percent solution of basic barium petronate (Witco Chemical, Sonneborne Division, New York, New York) in ISOPAR-H is prepared. Toner concentrate is diluted to 1.5 percent solids with ISOPAR-H, and 2 Kg of this dispersion are placed in the development tank of 55 a Savin 870 office copier (Savin Corporation, Stamford, Connecticut). The basic barium petronate, which functions as a charge-directing agent, is added in increments, allowing 24 hours for equilibration after each addition. At each equilibrated level of charge director, the conductivity of the dispersion is measured (using a device constructed by Savin Corporation, Johnson City, New York) and toner performance is evaluated. Solid area density, the inf luence of fusion on density, line resolution, and eff iciency of image transferfrom photoconductorto substrate, and general image quality are evaulated on several substrates: Plainwell offset en amel, Savin 2200 and 2100 and Gilbert Bond (50-percent rag) papers, and Savin transparency material (smooth and matte).

After grinding has been completed,the composition may befiltered or centrifuged. Thefiltrate isthen dispersed in ISOPAR-H and mixed with a charge director to forma concentrate. This concentrate has a solids 65 6 GB 2 176 904 A contentof 10 percentto30 percent by weight. The amountof charge director is dependent on itscharacteristics and the requirements of the use of which the toner is to be put.

In one process in which the original polymer has not been plasticized, it is not desirable to use a polymer which has a melting point in excess of 160'C. The mixing step and the wet-grinding step take much longer with an unplasticized polymer. We have found that it is advantageous to add a plasticizer, in the first step, in the ratio of in the order of three parts of plasticizer by weightto one part of resin by weight.

Examples of the method bywhich we obtain toner particles formed with fibers are given byway of illustration, and not byway of limitation.

6 Example 1

In a Ross planetary mixer, we combined 50Ogramsof ELVAXII polymer5720and 50Ogramsof ISOPAR-Lat 78'C. After mixing for thirty minutes, 125grams of carbon black(Mogul L)wereadded,and mixingwas continuedforan hour at 82'C. At this time, the adidtion of 100Ogramsof ISOPAR-L was started andcontinued forone hour.The material was discharged atgO'Cthrough a 0.5 mm orifice into icewater,This material had the form of a sponge. The sponge was passed through a meat grinder, which shredded the sponge into pieces 15 of a size adapted to pass through a 50 mesh screen. The pieces were then passed to the wet-grinding step. We ground 28.8 grams of the sponge pieces with 171.2 grams of ISOPAR-H fora period of 75.5 hours in a Type 0-1 attritor (Union Process Company) equipped with tap-water cooling and 3116- inch steel bails. The grinding pulled the elastomeric polymer particles apart, forming fibers present in concentration. We diluted the con centrate to 2 percent solids and added a charge director to form a developing liquid. The charge director was 20 added to a number of samples in amounts varying from 1 to 100 milligrams per gram of toner solids. A developing liquid was then diluted with ISOPAR-G, so thatthe toner particles were present in the amount of 0.2 percent by weight in respect of the dispersant ISOPAR, and copies were made on a Savin 870 copier. After transfer of the developed electrostatic image to a carrier sheet, the copier was stopped and strips of adhesive tape were placed on the photoconductor to remove the residue of the toned image from the photoconductor. 25 We found that the transfer was over 90 percent.

Example2

In a Ross planetary mixer were combined 750 grams of ELVAX 115610 and 353 grams of ISOPAR-G at 85'C.

After mixing forthirty minutes, aground mixture of 132 grams of Monastral BT-383-D blue pigment and 397 30 grams of ISOPAR-H were added and mixed for an hour. Atthis time, 2250 grams of ISOPAR-G were added over one hour, and then the mixture was stirred forthirty minutes. A sponge thus formed was then cooled to 80'C and discharged with a pump into al u minu m pans. After the sponge was cooled, it was abraded to small particle size as in Example 1. A Model S-0 attritor, equipped with tap- water cooling and 3/16-inch steel balls, was charged with 1101 grams of the sponge particles and 899 grams of ISOPAR-H. The mixture was ground 35 for 65 hours. The ground material was then employed as in Example 1, to form a development liquid, and poortransferwas noted.

Example 3

The procedure of Example 1 was followed with a blend of 25 parts by weight of ELVAX 11 5650T resin, 50 40 parts by weig ht of UN I REZ (a U nion Camp polyamide resin), and 25 parts by weight of carbon black i n respect of the solids content of the mixture. During the grinding step, it was found that no suitable fibers were formed.

This formulation is not preferred, since many fibers are fractured owing to their brittleness.

Example4

When the procedure of Example 1 was followed, using poly (4-methyl pentene), itwas found that the polymerwould not easily disperse carbon black.

v Example 5

We mixed 500 grams of Union Carbide's BAKELITE DPD 6169 with 500 grams of ISOPAR-L in a Ross plane- 50 tary mixer at 1 OOOC for an hour. We then added 166.6 grams of carbon black (Mogul L) to the mixture and mixed it for another hour, at which time it was a homogeneous mixture. This was then discharged into cake pans and allowed to cool. The procedure of Example 1 was followed and excellent results were obtained.

Substantially complete transfer was made to a carrier sheet comprised of clay-coated paper stock (printer's stock). This has a smooth, non-absorbent surface. No squash or smudging was observed, and there was remarkably exceptional edge definition and acuity. This test has proven to be particularly difficult with liquid carried toners of the prior art.

Example 6

We charged 37-1/2 parts byweight of carnauba wax, 37-1/2 parts by weight of polypropylene, and 25 parts 60 byweight of carbon black into a Ross planetary mixer and blended the mixture until itwas homogeneous. The mixturewasthen removed, allowed to cool, and treated as in Example 1. It remained in the attritorfor36 hours and wasthen tested. Itwas found thatthe transfer of the developed image, instead of being 90 percent or more, was only in thevicinity of 60 percent. However, a satisfactory image was achieved.

k 7 GB 2 176 904 A 11 10 1 1 1 Example 7

In a Ross planetary mixerwere combined one kilogram of ELVAX 115720 and one kilogram of ISOPAR-L at 85C and mixed forthirty minutes. Atthis time, 176 grams of Cabosil (silica) were added and the material was mixed for one hour. The material was then discharged into aluminum pans and cooled to room temperature. After being abraded into particles, as in Example l,the spongewas subjected to grinding in an attritorfor 25 hours. The presence of silica makesthe grinding easlier. No black or colored pigmentwas present in the toner. Thistoner may be employed as an etch-resistfor making printed circuit boards orfor making printing plates and the like.

Example8

In a Ross planetary jacketed mixer, we blended 500 grams of 5720 ELVAX 11 polymerwith 250 grams of ISOPAR-L at a temperature of 90'C to plasticize the polymer. We then added 166.6 grams of carbon black (Mogul Q and mixed the mixture until the pigment was dispersed. This occurred in about one hour, when it was a viscous mass. We continued stirring while adding 1750 additional grams of ISOPAR-L over a period of two hours. When the material is homogeneous we cease heating and continue stirring. The mixture wil I have 15 reached ambient temperature of about 25.060C. It is a critical feature of this method of forming toner particles having a plurality of fibers to continue stirring while cooling the mixture. This prevents the formation of a sponge and permits the precipitation of pigmented toner particles out of the dispersion formed by the addi tion of the added ISOPAR-L and encapsulates or otherwise associates the pigment with the polymer. The mixing elements of the mixer are operated to revolve at about 20 revolutinos per minute. When the newly 20 formed pigmented toner particles have been thus made, they wil I be present in about 30 percent by weight with respect to the weight of the I iquid. It is to be understood that other non polar liquids having elevated vapor pressures, such as other ISOPARs or light hydrocarbon oils, maybe used as I iquids. The developing liquid with a high concentration of toner particles may be packaged and diluted in a copy machine, as is known to the art. If desired, the mixing vessel may be water-cooled with tap water and the formation of the fiber-bearing toner particles accelerated. We may employ a mixture of a number of different polymers simu ltaneously. A suitable charge director may be added during the stirring period or at any convenienttime. The liquid developer composition is then drawn from the vessel. The concentration of the toner particles was reduced to 2 percent by weightwith ISOPAR and a tonerthus made employed to develop a latent electrostatic image in a Savin office copier. the developed image was transferred to a carrier sheet and was found to have 30 the improved characteristics of high density and superior resolution. Furthermore, there was excellenttrans ferfrom the surface of the photoconductorto a carrier sheetwith reduced residue on the photoconductor surface.

Example9

Into a Ross planetary mixer we deposited 166 grams of Mogul, 500 grams of ELVAX 11 Grade 5720 and 500 grams of ISOPAR-L, the mixture being heated to a temperature of 90'C. The mixture was vigorously stirred and the temperature was maintained at 90'C 1 O'C until the pigment was thoroughly dispersed. 1500 grams of ISOPAR-L were then slowly added. The homogeneous mixture was then discharged to a shallow metal pan and cooled to room temperature to give a gelatinous material having a pentrometer reading of 35 0.5. This 40 sponge-like material was then sliced into small strips and ground up, using a General Slicing meat grinder (manufactured by General Slicing/Red Goat Dispensers, Murfreesboro, Tennessee). ISOPAR-H and 665 grams of the ground sponge-like material were charged to a Type 1 -S Attritor storred ball mill (Union Process Company, Akron, Ohio) containing 3/16-inch stainless steel balls forthe final particle size reduction. The mill was run at slow speed during charging. After completion of the addition, the milling speed was increased and 45 milling was continued for about 30 hours to give a particle size distribution that showed that less than 10 percent of the particles were greaterthan 3 microns (by area) and average particle size (by area) was 1.0 _L 0.5 Rm. The mill was discharged and the dispersion was diluted with an additional amount of ISOPAR-H to give a 2 percent solids liquid electrographic developing composition.

Performance was evaluated at two levels of charge director -- 37 mg/g toner solids and 47 mg/g toner solids 50 -- using the procedure described earlier. The 47 mg/g level is close to optimum for image quality. Overall image quality is good, with little squashing and good edge acuity, relative to images obtained with commer cial Savin 870 toner. The efficiency of image transfer is also improved relative to that observed with the commercial toner. Solid density and line resolution are also improved.

On Plainwell offset enamel paper, the improved developing liquid made with toner particles of the instant 55 invention showed a remarkably high desnity of 3.0 with a resolution of 9 line pairs/mm. On Savin 2100 paper, the resolution remained at9, butthe density as measured by a Macbeth reflectance densitometer dropped to 1.6. On transparent matte material,the resolution dropped to 8 and the density dropped to 1.6. On transparent smooth material, the density increased to 1.9 and the resolution was 9. On Gilbert bond, the density dropped to land the resolution was 6.3. This compares with the Savin prior- arttoner, in which the density was 1.6 for 60 the Plainwell offset enamel paper, with a resolution of 8; a density of 1. 4forthe 2100 paper, with a resolution of 8; with a transparent smooth material, a density of 1.2, with a resolution of 5; with a transparent matte material, a density of 1.2, with a resolution of 5. The transfer efficiency of an image developed with our new toner is about 80% as compared with 60% forthe prior art.

8 GB 2 176 904 A 8 Example 10

Into a Ross double planetary mixerwe charged 500 grams of ISOPAR-L, heatedto a temperature of 1 10'C, togetherwith 214.2 grams of Mogul 1 and 500 grams of ELVAX 11 resin, Grade 5720. The mixture was thoroughlystirred until the pigmentwas dispersed. 2000 grams of ISO PAR-L were then slowly added until the mixture became homogeneous. Itwasthen discharged, cooled, sliced, and ground as in Example 9. The sponge thus formed had a penetrometer reading of 35.0 -t 0.5. Toner quality was determined bythe procedure described in Example 9.Thefinal particle size reduction was achieved as in Example9. Excellent resolution, transfer and optical densitywere achieved.

Example 11

Example9was repeated (500 grams ElvaxO Q, exceptthat88.2 grams of Mogul Lwere used.The mixture wasstirred at70'C and this temperature was maintained until the pigmentwas thoroughly dispersed. No additional plasticizerwas added. 330 grams of ground sponge material and 1800 grams of IsoparO H were used forthe grinding step. The pigmented resin spongewasfound to have penetrometer reading of 1.0:t 0.5.

Toner performance was equal to Example 1.

Example 12

We prepared a magnetic-electrostatic toner composition using Day Ferrix 8600 (Fe304,0.2 microns) as pigment. Elvax 11 resin 5720 (25 grams) and Isopar15 L (125 grams), Day Ferrox (25 grams) were charged in an 01 air attritor at 90'C until a homogeneous mixture was obtained. The attritorwas cooled to room temperature with continuous milling, and IsoparO H (150 grams) was added. Milling was continued at room temperature until a particle size in the vicinity of 2 microns was achieved. The dispersion was then diluted with IsoparO Hand charge-directed. This toner was used in the following manner.

A magnetic printing plate was made byflash imaging a magnetically structured Cr02 coated film (aluminized 4 mil MylarO base coated with 200 micro-inch layer of Cr02. The Cr02 was magnetically structured 25 with 1000 1 ines/inch. Flash imaging was done using a Cirtrak imager operating at an energy setting of 87. The magnetic printing plate was then mounted on the print drum of a Savin 770 copier in place of the selenium layer normally used. The machine was charged with the magnetic- electrostatic toner described above.

Images were obtained on paper by running the machine in the usual fashion exceptthe charging electrode wasturnecloff and the development electrode and the Cr02fiIrn were grounded.

Metal surfaceswill also be imaged bythis method.

Example 13

Wefollowed the same procedure as in Example 9, using 450 grams of ELVAX 115720 resin in a Baker-Perkins mixer in which the jacket temperature was raised to 125'Cwith steam, and mixing was started and continued 35 atthis temperature until the resin was melted. Thistook place at 1030C. Mixing was continued while 125.5 grams of Quindo Magenta and 23.9 grams of Indo Brilliant Scarlet toner were added. The melt dispersion was continued for23 hours; then 450 grams of ISOPAR-Lwere added and blending was continued until a homogeneous mixturewas obtained. This mixturewasthen discharged into a pan and cooled to give 856.1 grams of afirst pigmented polymersponge. This sponge was cryogenically cooled with liquid nitrogen and 40 then broken up with a hammer. The lumps thusformed were placed in a vacuum oven at 50'Cto remove waterwhich had condensed on the chilled fragments.

Another pigmented gel was prepared bythis procedure with ELVAX 115610, except thatthe temperature cluringthe preparation of the resin meltwas maintained at 1220C and the melt dispersion was continued for 19 hours, afterwhich the temperature of thejacketwas lowered to 1 OOOC priorto the addition of ISOPAR-L.

Stirring was continued for2 hours thereafterto give 934.3 grams of a second pigmented polymer sponge.

A mixture of 71 grams of thefirst pigmented polymersponge and 29 grams of the second pigmented polymer sponge, together with 129 grams of ISOPAR-L,were placed in a plastic beaker equipped with a Jiffy mixerand a high torque stirrer. The beakerwas placed in a 90OCwater bath and stirred for 2 hours. The hot mixturewasthen poured into a jarto give 197.5 grams of a magenta polymersponge having a penetrometer 50 reading of 34. This spongewasthen pulverized. 120 grams of ISOPAR-H were placed in a Type 01 attritor (Union Process Company) equipped with 3/16-inch stainless steel balls. The air motorwas started at a slow speed while 128 grams of the pulverized magenta polymersponge were added. Afterthe addition of the pulverized sponge,the air supplyto the motorwas increased 40 pounds persquare inch and thejacket of the attritorwas cooled with cold tap water. The attritorwas run for 29-1/2 hours to form a tonerslurry. Thiswas 55 run through a coarse paintfilter, using an additional amountof ISOPAR-H to give a 2 percentsolids magenta content in the toner. A particle size analysis shows the average particle size (by area) to be 1.21 microns. The resulting toner produced unsatisfactory images.

Example 14

We heated75grams of ELVAX 115610 resinto 100OCand melted itontothe rollersof a rubbermill.We added 15gramsof mineral oil (MARCOL52) and blended in 15grams of carbon black. The mixturebecame homogeneous in aboutan hourandthe meltwasthen removedfromthe rollers. This mixture was cooled by liquid nitrogen and transferred to a Brinkman ZM1 centrifugal grinding mill.Wethen placed 29.2grams ofthe ground material with 160 grams of ISOPAR-H in a research attritor (Union Process Company Model 01) 65 9 W 10 GB 2 176 904 A 9 equipped with tap water cooling and 1/4-inch steel balls. The mixture was ground for 24hours and was found to have the morphology of our invention --namely, a plurality of fibers. It should be noted that, where a dry powder is formed from the grinding, we routinely pass the ground material through a 140 mesh screen. After grinding, we di I uted the dry powder, to forma liquid composition, and added a charge director. We made a plura I ity of samples with various amounts of charge director between land 100millig rams per gram of toner 5 solids. If sufficient platicizer is added to the polymer in the first step to forma sponge, it is sufficiently soft so that it need not be cryogenically ground.

It isto be understood thatwe may mix a number of polymers with the ethylene vinyl acetate copolymers, such as polypropylene, polyamides, and the like. We have noted thatthe use of additives, such as polyethylene, carnauba wax, orthe like, reduces the grinding time and that it also reduces the number of fibers attached to the polymer nuclei. We have made a large number of toner particles having fibers f rorn various thermoplastic resins. Liquid toner compositions having our improved toner particles dispersed therethrough show various degrees of improvement in respect of increased density and increased resolution. These liquid compositions have the abilityto develop electrostatic images, and the developed images have an increased ability to transferfrorn the photoconductor or dielectric surface to a carrier sheet. 15 The improved results are also exhibited on carrier sheets having surfaces of various degrees of roughness.

Example 15

Following the procedure of Example 1, we used 37.5 percent byweight of ELVAX 11 Grade 5610 resin, 37.5 percent by weight of ELVAX 11 Grade 5640 resin, and 25 percent by weight of carbon black (Mogul L). A developing liquid having a 2 percent solids content of the concentrate thus formed, when used to develop latent electrostatic images, produced dense images and excellent line resolution. Furthermore, there was excellent efficiency of the image-tra nsfer from the photoconductor to the carrier sheet when used in a Savin 870 copying machine.

so Example 16

This example is similarto Example 15, exceptthat37.5 percent byweight of ELVAX 11 Grade 5720 resin was employed instead of ELVAX 11 Grade 5640 resin. The images and transfer efficiency were similar or superior to Example 15.

Example 17

The procedure of Example 1 was followed, using 97 percent byweightof ELVAX 11 Grade 5720 polymer and 3 percentof Monastral Blue G pigment (manufactured by E. I Du Pont De Nemours & Company). Unsatisfactory images were produced.

Example 18

Example 23 belowwas repeated using 2.7 grams of BT-383D CPC blue pigment and 8.0 gramsfumed silica (Cab-O-Sil EH-5) in place of Mogul L (carbon black). Resolution was 9, Transfer Efficiencywas 75% and Densitywas2A Example 19

Example 23 belowwas repeated using 0.6 gram RV6300,11 grams RV6803 (both magenta pigments) and 4.8grams Cab-O-Sil EH-5 in place of Mogul L (Carbon black). Resolution was 6.3, Transfer Efficiencywas 84% and Density was 1. 7.

Example20

Example8was repeated using 35 grams of YT-858D Dalamar yellow and 95 grams Cab-O-Sil EH-5 in place of Mogul L(carbon black). Resolution was 4. 5, Transfer Efficiency was 40% and Densitywas.9. Poor image quality resultedfrom excessive, highly tentacular and excessive adhesive.

Example2l

Atonerimage on a conducting substratewas prepared. Thiscould be done, for example, using tonerfrorn Example 1 in Savin 870 copierwith aluminized MylarO asthe substrate or bytransferring atonerimagefrom an intermediateto a copperboard. The exposed metal was etched using an acid etching solution (161 grams cupricchloricle clihydrate, 568 ml-concentrated hydrochloric acid and 350 mLwater). The tonerwas then 55 dissolved (hot 1:1 toluene: n-butanol) to give a conductive pattern of the same image qualityasthe original toned image.

Example22

The Ross mixerwas chargedwith 500 g of IsoparO Land 500 g of Elvax 11 grade 5720.The mixturewas stirred 60 and heated at85-900 until the resinwas melted. Then 66.7 g of Dalamar Yellow YT-858D and 100 g of Cab-o-Sil M-5were added. Mixing was continued atthe sametemperature until the pigmentswere dispersed. Then 1500 g of additional Isopar') Lwas added atsuch a rate asto maintain the temperature at85-900C. When all of the IsoparOwas added,the liquid gel was poured outinto cake pans and allowedto cool to room temperature.

A portion of this gel was ground in aWaring Blender. 100 g ofthe ground gel and 100 g of IsoparO H were 65 GB 2 176 904 A placed in a ceramic mill jarcontaining 750 g of 112" by 1/2" Burundum cylinders. The mill jarwas placed on a 250 rpm rollerand was rolledfor 186 h. The resulting concentratewas removed fromthe mill jarandwas diluted withfurther IsoparsH and charge directoras in Example 1 to give a yellowtoner. Resolution was 6.3. Transfer Efficiency was 63% and Densitywas 1.4-1.5.

Example23

This procedure allowsforthe preparation of liquid tonerin a single piece of equipmentand without handlingthe material between steps. 25 g Elvax 11 resin 5720 and 125 g IsoparO Lare heatedto 900C in an 01 air attritorand milled 3/16 inch stainless steel balls; whenthe resin and solvent mixture is homogeneous 8.0 g carbon black (Mogul Q is added and milled until dispersed. Alternately, the pigment maybe added simultaneously with the resin and Isopar'5L and milled at 900C until the pigment is dispersed. The attritor is cooled to room temperature while milling is continued and then 130 g IsoparsH is added. Milling is continued at room temperature until the desired particle size is achieved (1 -2 microns). The dispersion is then diluted with IsoparsH and charge-directed. Toner prepared by this procedure is equivalentto that of Example 9.

Using this procedure, 200 grams of Elvax 11 resin 5720,67 grams Mogul L, 1000 grams IsoparO L, and 700 grams IsoparO Hare milled in a 1 -S attritor to produce toner which also is equivalent to that of Example 9.

Referring nowto the drawings, the toner particles shown in Figures 1, 2, and 3 and the sponge shown in Figure 4 are all formed with Elvax 11 grade 5720 resin. These photornicrographs were taken by the transmission method. In it, a copper grid was coated with a layer of collodion which had been evaporated at room temperature. A drop of developing liquid, diluted with 3 percent toner solids, was placed on the 20 thus-prepared grid and allowed to evaporate. The specimen was then placed directly in the cavity of the electron beam microscope and examined In Figure 1, thetoner particle 2 shows tendrils orfibers 4,5, and 6. Thetendrils 7 and 8 have become associated with a clump of toner particles. Toner particle 10,which happens to be detached, isformed with fibers 12 and 14. The magnification was 13,000 times.

F1gure2 is a photomicrograph of toner particle 2 of Figure 1, magnified 45,000 times. It will bee seen that fiber 8 is attached to the clump of toner particles 2, while fiber 7 extends from an adjacent toner particle.

Figure 3 is a photomicrograph of toner particle 10, shown in Figure 1, magnified 45,000 times. Itwill be seen that fibrils extend from toner particle 10 to an adjacent clump of toner particles.

It should be noted that it is difficu It to obtain good pictures of the toner morphology. since the electron beam tends to melt the fibers and disguise their morphology to some extent.

Figure 4 shows a sponge which, as has been described, is formed from a plasticized polymer. The magnification in this photomicrograph is 1,000 diameters, and the eleven dots shown at the bottom of the photomicrograph extend through 30 microns.

Figures 5,6, and 7are photornicrographs taken with the scanning method. In carrying outthis method, a 35 drop of developing liquid having a toner content of 2 percent is allowed to evaporate on a glass slide. After the carrier liquid has evaporated at room temperaturer the slide is fractured and apiece or pieces are mounted with a conductive adhesive on an aluminum stub or stubs. The stubs are then coated with a layer of gold, 100 Ain thickness, by vacuum deposition, and the specimen is then placed in the cavity of the electron beam microscope.

The specimen shown in Figure 5 is one taken with the developing liquid shown in Example 15. The magnification was 23,800 diameters. Several levels of toner particles are clearlyvisible in this photomicrograph. The toner particle 30 has fibrils 32,34, and 36 extending therefrom. Toner particle 29 has a fibril 18 extending therefrom. Fibers 24 and 26 extend from a toner particle which appears at a lower level.

Toner particle 19 has fibrils 16 and 22 extending therefrom. Toner particle 23 has a fibril extending therefrom. 45 It will be appreciated that, in taking the photomicrograph, many of the fibers, vestiges of which appear, have been melted by the electron beam.

Figure 6 is another photomicrograph taken with the scanning method and having the formulation of Example 15. The magnification was 38,400 diameters. The alternate black and white lines atthe right-hand side of the drawing indicate one micron. The fibers at various levels are clearly shown in this drawing. From 50 toner particle 60, fibers 62,64, and 66 are shown. Fiber 68 is also shown, extending from an unidentified toner particle. Otherfibers are shown at lower levels.

Figure7 shows a pluralityof toner particles made in accordancewith the method of Example 8,which is the preferred method. The resin was ELVAX 11 Grade 5720,the preferred polymer. The magnification was 20,000 diameters. Thetoner particles having a plurality of fibers, many interdigitated, are clearly shown in thisview. 55 Whilewe are not bound bytheories, itwould appearthat, in dispersion, all of thetoner particles havethe same polarityof charge. When the particles approach each other,they are repelled, owing to thefactthat each possesses a charge of the same polarity. When the latent electrostatic image is developed, the toner particles are impelledto go to the latent electrostatic image,which has a higher potential and a charge of opposite polarity. Thisforces thetoner particlesto associatewith each other and to mat or interdigitate. The strength of 60 the image is such that, if the paper has a rough surface,the imagewill bridge the hollowsWhen the image is transferred to a carriersheet, since thetransferring charge is also greaterthan the charge of the developed image. The fact thatth e toner particles in the developed image are matted enables a more complete transfer from the photoconductorto be madeto the carriersheet. The matting also prevents spreading of the edges of the image and thus preserves its acuity. The small diameter of the toner particles ensures good resolution, -w c 11 GB 2 176 904 A 11 1 along with the other results outlined above.

ftwill be seen thatwe have accomplished the objects of our invention. We have provided a toner particle adapted to form a denser electrostatic image than has been achieved bythe prior art. The toner particles of our invention are adapted to form a mat, in developing a latent electrostatic image, and thus enable complete transfer of the developed image to a carrier sheet by contact transfer. An imageformed with a liquid developing composition employing a dispersion of ourtoner particles may betransferred to a carrier sheet without any squash. Images developed with the toner particles of our invention exhibit no bleed-through. Our toner particles may be used to form a concentrate, which concentrate may be diluted to a liquid composition having a tonersolids content of as little as 0.2 percent. We have disclosed several novel methods of producing toner particles having fibers extending therefrom. Some includethe step of plasticizing a polymer. In one method,the plasticized polymer is allowedtoform sponge. In another method, a dispersantis continuously added and stirred so that no sponge is permitted to form.

It will be observed that it is a necessary feature of our invention thatthe toner particles be charged, and we have pointed outthe addition of a charge director. Since these charge directors are known to the art, we have not particularly setthern forth in this specification. It is known that, in orderto impart a negative charge to the particles, such charge directors as magnesium petronate, magnesium sulfonate, calcium petronate, calcium sulfonate, barium petronate, barium sulfonate, orthe like, may be used. The negatively charged particles are used to develop images carrying a positive charge, as is the casewith a selenium-based photoconductor.

With a cadmium-based photoconductor, the latent image carries a negative charge and thetoner particles must therefore be positively charged. We may impart a positive charge to the toner particles with a charge 20 director such as aluminium stearate. The amount of charge director added depends on the composition used and can be determined empirically by adding various amountsto samples of the developing liquid, aswe have pointed out in Example 1.

[twill be understood that certain features and subcombinations are of utility and maybe employed without reference to other features and su bcombi nations. This is contemplated by and is within the scope of our 25 claims. It is further obvious that various changes maybe made in details within the scope of our claims without departing from the spirit of our invention. It is, therefore, to be understood that our invention is notto be limited to the specific details shown and described.

Claims (11)

1. A method of producing toner particles adapted for electrophoretic movement through a nonpolar liquid comprising the steps of plastizicing a thermoplastic polymer at an elevated temperature with a nonpolar liquid, stirring a pigment into the plasticized polymerto disperse the pigment, continuing the stirring step to prevent the formation of a sponge while reducing the viscosity of the mixture by adding additional nonpolar liquid to the mixture to forma dispersion, cooling the dispersion while continuing the stirring to permitthe precipitation of the pigmented polymer out of the dispersion to form pigmented toner particles having a plurality of fibers, and withdrawing the dispersion having a concentration of toner particles from the mixing step.

2. A method as in claim 1 in which the thermoplastic polymer comprises an ethylene copolymer resin. 40

3. A method as in claim 1 in which the pigment comprises a finely divided ferromagnetic material.

4. A method as in claim 1 in which the pigment comprises silica.

5. A method as in claim 1 in which the pigment comprises carbon black.

6. A method as in claim 1 in which the pigment comprises a colored material.

7. A method as in claim 1 in which a charge director is added to the dispersion to impart an electrostatic 45 charge of predetermined polarity to the toner particles.

8. A method as in claim 1 in which the cooling step is accelerated.

9, A method as in claim 1, in which a plurality of thermoplastic polymers are employed in the plasticizing step.

10. A method as in claim 1 including the additional step of diluting the dispersion with more nonpolar 50 liquid.

11. A method as in claim 10 in which the diluting step is conducted to reduce the concentration of toner particles to between 3 percent by weight and 0.2 percent by weight in respect of the nonpolar liquid.

Printed in the UK for HMSO, D8818935, 11186, 7102. Published by The Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.