US3925219A - Pressure-fixable developing powder containing a thermoplastic resin and wax - Google Patents

Abstract

A pressure-fixable developing powder comprising a wax component and a thermoplastic resin, the powder having defined physical characteristics.

Description

O United States Patent 1 u 11 Strong Dec. 9, 1975 PRESSURE-FIXABLE DEVELOPING [56] References Cited POWDER CONTAINING A UNITED STATES PATENTS THERMOPLASTIC RESIN AND WAX 3,236,776 2/l966 Kunitzer 252/621 P Inventor: L. Su-ong we t mke| d 3,639,245 NCISOI'I 4 l l v g T w 3,7l5,2l9 2/[973 Kurz et al ashmgton Count)" 3,775,326 ll/l973 Westdalc l v 252/621 3,829,3l4 8/1974 Shelfi'o 252/62.l [73] Assignee: Minnesota Mining and Manufacturing Company, St. Paul, m y in samue e nbe g Minn. Assistant Examiner-P. A. Nelson Attorney, Agent, or Firm-Alexander, Sell, Steldt & [22] Filed. June 29, 1973 DeLaHum [21] Appl. No.: 375,169

[ ABSTRACT [52] US. Ci. 252l62.l P A pressure-Emma developing powder comprising a [51] Int. Cl. G03G 9/00 wax Component and a thermoplastic resin the powder 58 Field of Search 252/621 P having defined Physical characterisfl 9 Claims, 2 Drawing Figures U.S. Patent Dec. 9, 1975 3,925,219

PRESSURE-FIXABLE DEVELOPING POWDER CONTAINING A THERMOPLASTIC RESIN AND WAX This invention relates to a dry ink powder suitable for use in electrographic recording. More particularly, the invention relates to a developing powder which is pressure responsive so that it can be fixed as an imaging material to an image-bearing surface by the application of pressure.

Known developing powder (i.e., toner) formulations used in electrographic recording processes are generally permanently affixed to the substrate by heat. See, e.g., the developing powder described in Nelson, U.S. Pat. No. 3,639,245 wherein the powder is described as being thermoplastic and heat-fusible in the range of 80 to 115C. Such heat-fusible powders are fixed after image formation by raising the temperature of the powder to its melting or softening point, causing the particles to coalesce, flow together, and adhere permanently to the substrate.

Although such heat-fusing developing powders have been widely used and have met with commercial success, there are certain disadvantages which are inherent in the use of such powders. Such disadvantages relate to the speed and efficiency of the fixing process.

For example, the speed of the fixing process, and hence the speed of the copying or recording process, is limited by the time required to effect fusion of the developer powder. Although the use of more heat to fuse the powder may shorten the fixing time required, this approach is limited by the flammability of the substrate on which the image is fixed. Since paper is widely used as the image-bearing support, care must be taken to avoid charring of the paper during the fixing process. Although the speed of the fixing process may also be increased by using lower melting point thermoplastic resins, the resulting image may be smeary and may exhibit poor character definition.

Another disadvantage associated with the use of heat-fusible powders is the significant power consumption of the equipment used for fixing. A further disadvantage is the significant loss of heat energy to the environment.

Yet another disadvantage associated with the use of heat-fusible powders is that the fixing rolls or other equipment used for fixing must first be heated to the requisite temperature before the copying or recording process can begin.

These disadvantages are overcome with the use of the developing powder of this invention.

SUMMARY OF THE INVENTION In accordance with the invention there is provided a flowable, pressure-fixable, dry powder comprising thermo-plastic, essentially spherical particles, the binder material of which has a conductivity of at most mho/cm and which comprises (a) about 50 to 100 parts by weight of a wax component having a melting point between about 45 C. and 150 C., and (b) about 2 to 50 parts by weight of thermoplastic resin having a softening point above about 60 C.; wherein electrically conductive particles are firmly anchored in said binder material, said electrically conductive particles having a conductivity of at least 10 mho/cm and an average diameter below about 100 millimicrons forming a radially disposed zone; and wherein said essentially spherical particles exhibit:

a. an electronic conductivity ranging monatonically without decreasing from between about 10 and 10 mho/cm in a [00 v./cm. DC electrical field to between about 10 and i0 mho/cm in a 10,000 v./cm. DC electrical field,

b. a number average particle diameter below about 20 microns, and c. a volume ratio of said electrically conductive parti cles to said total particle volume of between 0.011100 and 4/100; wherein the dry powder exhibits a transfer density of less than about 0.15 and a "paper abrasion density" of less than about 0.15, as hereinafter defined.

The developing powder of this invention exhibits the very desirable electrical properties exhibited by the powder described in U.S. Pat. No. 3,639,245 and is pressure-fixable. Consequently, the disadvantages associated with the use of heat-fusible developing powders are avoided. Furthermore, because of the significant power consumption reduction in processes using these powders, recording and copying processes become more versatile and economical.

Another advantage derived from the use of such powders is that there is no wait for the machine to warm up to operating temperature. Also, the equipment necessary for fixing the powders of this invention is less expensive and less complicated than conventional heat-fusing equipment. Consequently, the fixing equipmentis more reliable and more easily serviced than conventional heat fusing equipment.

The developing powders of this invention can be fixed directly to a photoconductive surface, in an imagewise fashion, or they can be transferred to a receiving sheet (e.g., untreated bond paper) to which pressure is subsequently applied (e.g., with a steel roll) to fix the image. The powders are useful with known photoconductive materials, e.g., amorphous or vitreous selenium, selenium alloys with tellurium and arsenic, cadmium sulfide, zinc oxide in a resin binder, and organic photoconductive materials.

Although pressure-fixable developing powders have been suggested generally in British Patent No. 1,210,665, the developing powder of the present invention represents an improvement thereover. This British patent generally suggests that an aliphatic wax can be used, either by itself or in admixture with a thermoplastic resin, as the developing powder. However, it has been found that all waxes and many blends of wax and resin produce developing powders which, although easily pressurefixable, are commercially unacceptable due to their case of smearing and carbon paper" transfer. The developing powders of the present invention alleviate these disadvantages.

The developing powders of this invention also differ from those described in British Patent 1,210,665 in another material respect, viz., in terms of electrical prop erties. The novel developing powders exhibit the highly desirable electrical properties described in U.S. Patent No. 3,639,245, whereas the developing powders described in the aforementioned British patent are not electrically conductive. Consequently, the developing powders described in the British patent are useful only in conventional electrostatic copying srocesses wherein electroscopic toner powders are use DETAILED DESCRIPTION OF THE INVENTIQN FIG. I shows apparatus for determining the tranSfI density" value for a particular developing powder.

FIG. 2 shows apparatus for measuring the paper abrasion density for a particular developer powder.

The developer powders of this invention have the electrical conductivity properties of the heat-fusible powders described in Nelson, US. Pat. No. 3,639,245, incorporated herein by reference. The novel powders have a number average diameter below about 20 microns, and preferably in the range of about 10-15 microns. Preferably, the average particle size range is such that at least about 95 number percent of the particles have a diameter greater than about microns, while no more than about 5 number percent have a diameter greater than about 25 microns.

The developing powders are pressure fixable in the sense that the application of pressure thereto causes them to flow and coalesce and also to adhere to the desired support surface (i.e., the image-bearing surface). The binder material in which the electrically conductive particles are anchored comprises a blend of a wax component and a thermoplastic resin, wherein the weight ratio of thermoplastic resin to wax component is about 0.02/1 to ill (preferably about 0.1/1 to 0.5/1 The binder material has a conductivity of at most mho/cm.

The wax component has a melting or softening point in the range of about 45 C. to about 150 C. (preferably between about 65 C. and 125 C.) and is normally selected from the group consisting of aliphatic compounds such as waxes (natural or synthetic), fatty acids, metal salts of fatty acids, hydroxylated fatty acids or amides, ethylene homopolym'ers, or a mixture of two or more of these materials. Aromatic or polymeric waxlike materials can also be used, e.g., dicyclohexylphthalate and diphenylphthalate. All of these materials are well known in the art.

Representative useful aliphatic waxes include paraffin wax, microcrystalline wax, carnauba wax, montan wax, ouricury wax, ceresin wax, candellila wax, and sugar cane wax.

Representative useful fatty acids include stearic acid, palmitic acid, and behenic acid. Representative useful metal salts of fatty acids include aluminum stearate, lead stearate, barium stearate, magnesium stearate, zinc stearate, lithium stearate, and zinc palmitate. Representative amide hydroxy waxes include N(betahydroxyethyl)ricinoleamide (commercially available under the trade name Flexricin 1 l5"), N,N'-ethylenebis-ricinoleamide (commercially available under the trade name Flexricin 185"), N(2-hydroxyethyl)-l2- hydroxystearamide (commercially available under the trade name Paracin 220"), and N,N'-ethylene-bisl2- hydroxystearamide (commercially available under the trade name Paracin 285").

Representative fatty acid derivatives include castor was (glyceryl tris-l2-hydroxy stearate), methyl hydroxy stearate (commercially available under the trade name Paracin l"), ethylene glycol monohydroxy stearate (commercially available under the trade name Paracin l5") and hydroxy stearic acid.

The thermoplastic resin has a ring and ball softening point above about 60 C. (and preferably between 120 C. and 200 C.) and is normally selected from the group consisting of polyamides (e.g., Versamid 950"), commercially available from General Mills); polystyrenes (e.g., 2000 mol. wt); bisphenol A epoxy resins (e.g., Epon 1004", commercially available from Shell Chemical Corp); acrylic resins (e.g., Elvacite 2044, an N-butyl methacrylate commercially available from DuPont); vinyl resins such as polyvinyl butyral (e.g., Butvar B72-A," commercially available from Monsanto Company), polyvinyl acetate (e.g., Gelva V-100", commercially available from Monsanto Company); vinyl copolymers such as vinyl chloride/vinyl acetate (e.g., VYHH", commercially available from Union Carbide Corp.), ethylene/vinyl acetate copolymers; cellulose esters such as cellulose acetate butyrate (e.g., EAB-l7 [-25, commercially available from Eastman Chemical Products, Inc.), cellulose acetate propionate (e.g., CAPPLFS commercially available from celanese Corp.), and cellulose ethers. The ring and ball softening point is measured according to ASTMzE28.

Various other materials may be usefully incorporated in or on the developer particles on this invention, e.g., plasticizers, dyestuffs, pigments, magnetically permeable particles, etc. Magnetically permeable particles having an average major dimension of 1 micron or less are particularly preferred, including magnetite, barium ferrite, nickel zinc ferrite, chromium oxide, nickel ox ide, etc. A magnetically permeable core may also be used. Powdered flow agents may also be added to the dry particles to improve their flow characteristics.

The developing powder is prepared by first obtaining a blend of appropriate composition by any of several conventional techniques. For example, the wax component and thermoplastic resin may be heated to obtain a melt to which solid filler (e.g., magnetite) may be added and dispersed. The melt may then be atomized so as to obtain particles which, upon solidifying, are ready for further processing. Alternatively, the melt may be allowed to cool and solidify in mass after which it is ground into particles and classified according to the appropriate number average particle size range of about 5 to 20 microns.

The solid particles obtained in accordance with either of the foregoing procedures is then "spheroidized by the following method. The powder is aspirated into a moving gas stream, preferably air, to create an aerosol. This aerosol is directed perpendicular to and through a stream of hot air, which has been heated to about 9001,l00 F., in a cooling chamber where the powder is then allowed to settle by gravity while it cools. The resulting powder now comprises substantially spherical particles. It is then dry blended with conductive powder (e.g., conductive carbon black) and the mixture is directed perpendicular and through a stream of gas, preferably air, heated to a temperature (e.g., 700-800 F.) which can at least soften and desirably melt the thermoplastic binder in the particles and maintain that softened or melted condition for a period of time sufficient to permit the conductive powder to become firmly anchored to the surface of the particle. The particles are then collected, such as by cyclone separation, and are preferably blended with a flow agent (e.g., CAB-O-SIL", finely divided silica, commercially available from the Cabot Corporation) to insure that it will be free flowing.

In order to be commercially acceptable, the resulting developing powder must exhibit a transfer density" of less than about 0.15 and a paper abrasion density" of less than about 0.15. The transfer density" value for a particular developing powder is determined by first using the apparatus depicted in FIG. 1. Referring to the drawing, there is shown apparatus 10 comprising base 12 on which there is fastened an imaged copy sheet 14 (wherein the image comprises a solid black line or stripe about 1 inch wide) covered by an unimaged copy sheet 16. The image on sheet 14 has been made using the pressure-fixable developing powder to be tested, and sheet 16 is laid over and in direct contact with the image. Tape strips 18 and clip 20 hold sheets 14 and 16 in position.

Sheets 14 and 16 are Type 350" copy paper commercially available from 3M Company, and comprise 45 pound Weyerhauser GRS" paper coated on one side with zinc oxide in a binder. The binder comprises a blend of acrylic resin and alkyd resin, and the ratio of zinc oxide to total binder is 6:1. The weight of dried coating on the paper is 2.2-2.4 grams per square foot.

Twelve conventional medium point ball-point pen cartridges 22 are positioned (in free moving vertical position) within holding device 24. Four of the cartridges 22 are each vertically loaded with a weight 26 of 4.25 ounces (121 grams); four of the cartridges are loaded with a weight 28 of 8.8 ounces (250 grams); and 4 of the cartridges are loaded with a weight 30 of 17.3 ounces (492 grams), as shown in FIG. 1. These particular weight loadings encompass the range of writing pressures normally encountered.

Holding device 24 is then rolled across the unimaged copy sheet so that each of the cartidges 22 makes an inked line on sheet 16. The holding device 24 is then indexed 1/64 inch (0.397 millimeters) laterally via indexing device 32 and threaded shaft 34 before the holding device 24 is again passed over sheet 16. This procedure is repeated until about 20-25 passes have been made over sheet 16 with the loaded cartridges 22. The number of passes should be sufficient to obtain an area large enough to permit measuring of the diffuse reflection optical density of the developing powder transferred from the solid image area of sheet 14 to the back side of sheet 16. The optical density are proportional to the amount of image material transferred, and the optical density reading (e.g., 0.1) is taken as the transfer density" value for the particular powder being tested. Conventional diffuse reflection densitometers (e.g,, MacBeth Quanta-Log Diffuse Reflection Densitometer, Model RD-lOO) can be used to measure the optical density. For the purposes of this invention useful developing powders exhibit a transfer density" of less than about 0.15 when testing image samples in the foregoing test using a pen cartridge loading of 17.3

ounces.

The paper abrasion density" is measured by first using the apparatus of FIG. 2 wherein there is depicted a base 40 having mounted thereon arm 42. Rod 44 is 7% inch (12.7 millimeters) in diameter and 6% inches (16.5 centimeters) long. Rod 44 is loaded with 8 pounds of force pushing it against base 40 via spring 46. Pad 48, firmly attached to the bottom of rod 44, is formed of a silicone elastomer (hardness of 35 Shore A).

A copy sheet 50 bearing a solid image stripe 52 formed by pressure fixing the developing powder to be tested is positioned on base 40, with image side up, and 4 inches centimeters) into the throat of the apparatus. Sheet 54 is then placed over and in direct contact with image 52 on sheet 50 after which rod 44 (loaded with 8 pounds force) is placed in contact with sheet 54. Then, while holding sheet 54 in its stationary position, sheet 52 is pulled in the direction of the arrow at the rate of about 2-10 inches per second for a distance of 4 inches (10 centimeters). The diffuse reflection optical density of the material transferred to the back side of sheet 54 is then measured using a conventional diffuse reflection densitometer (e.g., MacBeth Quanta- Log Diffuse Reflection Densitometer. Model RD The optical density reading is taken as the paper abrasion density" value for the particular powder being tested.

Copy sheet 50 is Type 350" copy paper commercially available from 3M Company. Sheet 54 is a conventional 20 pound mimeo paper (Nekoosa Ardor" Mimeo, Sub-20) which is placed with the wire side against the image stripe in the paper abrasion density test.

The invention is illustrated by means of the following examples wherein the term parts" refers to parts by weight unless otherwise indicated.

EXAMPLE 1 A developing powder is prepared using the following ingredients in the amounts shown:

Parts Paraffin wax ("Shellwax 300", melting point 71 C., commercially available from Shell Chemical Company) Ethylene/vinyl acetate copolymer ("Elvair 250", commercially available from DuPont), ball and ring softening 8 point of 138 C. Magnetite The wax is first heated to melting after which the ethylene/vinyl acetate copolymer is added with stirring and continued heating until a hot melt solution or dispersion is obtained. The magnetite (0.2-0.4 micron particles) is then added with continued stirring and heating until a homogeneous dispersion is obtained, after which the dispersion is spread in a thin layer on polyester film to cool and solidify.

The solidified composition is then broken into flakes, chilled with dry ice, and reduced to fine powder particles using a hammer mill (e.g., a Mikro-Pulverizer", commercially available from MikroPul). A fraction having a diameter less than 45 microns is then collected and blended with 0.1% by weight of a flow agent (e.g., Aerosil"; an amorphous colloidal silica commercially available from Degussa, Inc.).

The resulting dry developing powder is then used in a copying process wherein an image is formed electrographically on zinc oxide coated paper and developed using a magnetic roller of the type disclosed in US. Pat. No. 3,455,276 (Anderson). The developed image on the zinc oxide coated paper is then pressure fixed, for example by passing the imaged and developed paper between two smooth, polished steel rolls (approximately 2 inches in diameter) at a pressure of 200 pounds per lineal inch.

The resulting finished copy has sharp black image areas of high quality with no backgrounding. The transfer density of the finished copy is measured and found to be 0.031 at a pen cartridge loading of 17.3 ounces (492 grams). The paper abrasion density of the finished copy is measured and found to be 0.04.

EXAMPLE 2 A pressure-fixable developing powder is prepared using the following ingredients in the amounts stated:

The resulting dry developing powder is used to make Parts finished copies as described in Example 1. The transfer Ethylene glycol monmhydwxy same density of such coples is measured and found to be 0403 ("Paracin l5". melting point 66 cs 5 at a pen cartridge loading of 173 ounces (492 grams). commercially available from Baker Cask" oflcompany) 34 The paper abrasion density IS measured and found to Cellulose ether ("Ethocel N-200. be

commercially available from Hercules, lne, ball and ring softening point EXAMPLE 5 of r93 C.) 6 Magnetite 60 A dry pressure-fixable developing powder is prelo pared with the following ingredients using the procedures of Example 1: A hot melt dispersion is prepared with the stated in gredients using the procedure of Example I. The dis- Pam persion is then solidified and reduced to a powder. after which a small amount of conventional flow agent is 5 ;.."E P

t melting point) 32 added- Ethylene/vinyl acetate copolyrner (Elvax The resulting dry developing powder is then used in a 3". f m y available g Pg 8 copying process wherein an image is formed electrog a"; mung o 60 graphically on zinc oxide coated paper and developed using a magnetic roller of the type disclosed in US. Pat. 2 (Andersolll devcloped 8 The resulting dry developing powder is used to make the Zmc oxlde coined pal?er Pressure fixedfor finished copies as described in Example 1. The transfer example by passmg the 'maged and da'velop6d Paper density of such copies is measured and found to be 0.07 between f 9 Steel rolls at a Pmssure of 200 at a pen cartridge loading of 17.3 ounces (492 grams). Pounds per llneal The paper abrasion density is measured and found to The resulting finished copy has sharp black image be areas of high quality with no backgrounding. The transfer density of the finished copy is measured and found EXAMPLE 6 2 1 g El-2 9 A dry pressure-fixable developing powder is preg epaper a raslon enslty o t e flushed pared with the following ingredients using the procecopy is measured and found to be 0.075. dures of Example EXAMPLE 3 A dry, pressure-fixable developing powder is pre- Pam pared with the following ingredients using the procey y slearic acid 3 me ting point) dures of Example Cellulose ether (Ethocel n-zoo",

commercially available from Hercules, lnc., ball and ring softening point of l9 3C.) a Castor wax (melting point 87 C, 40 Magnum 60 commercially available from Baker Castor Oil Company) 35 Cellulose ether ("Ethocel N-200",

commercially available from Hercules, The resulting dry developing powder 15 used to make s gi fl wflemng s finished copies as described in Example 1. The transfer Magnet: 60 density of such copies is measured and found to be 0.09 at a pen cartridge loading of I73 ounces (492 grams). The paper abrasion density is measured and found to The resultin dr develo in owder is used to make be 0.07).

. g y P S P finished copies as described in Example 1. The transfer EXAMPLE 7 density of such copies is measured and found to be 0.09 at a pen cartridge loading of l7.3 ounces (492 grams). A dry pressure-fixable developing powder is pre- The paper abrasion density is measured and found to pared with the following ingredients using the procebe 0.075. dures of Example 1:

EXAMPLE 4 I I Parts A dry pressure-fixable developing powder lS pre- C 87 C 32 pared with the following ingredients using the procexxx; f 'mfg f fi ga ring dures of Example 1: softening point of l8BC. "Butvar B72-A". commercially available from Monsanto) 8 Parts Magnetite 60 IZ-hydroxy stcaric acid (75 C. melting oipl, tommelgilall availab)le from 32 a er astor l ompany Emma/vinyl ewe copoymer (Emx The result ng dry developing powder is used to make 250", commercially available from finished copies as described 111 Example I. The transfer 3 522-6?" 8 density of such copies is measured and found to be 0 l 0 Magnetite (,0 at a pen cartridge loading of 17.3 ounces (492 grams) The paper abrasion density is measured and found to be 0.09,

EXAMPLE 8 A dry pressure-fixable developing powder is prepared with the following ingredients using the procedures of Example 1:

Parts Ethylene glycol mono-hydroxy stearate ("Paracin 15", melting point 66C., commercially available from Baker Castor Oil Co.)

N-butyl methacrylate (ball and ring softening point of 132 C., Elvacite 2044", commercially available from DuPont) 8 Magnetite EXAMPLE 9 A dry pressure-fixable developing powder is prepared with the following ingredients using the procedures of Example 1:

Parts N( 2-hydroxyethyl)- l 2-hydro1ty stearamide (melting point 104 C., "Paracin 220", commercially available from Baker Castor Oil Co.)

Polyvinyl butyral (ball and ring softening point of 188 C., "Butvar B72-A, commercially available from Monsanto) Magnetite The resulting dry developing powder is used to make finished copies as described in Example 1. The transfer density of such copies is measured and found to be 0.10 at a pen cartridge loading of 17.3 ounces (492 grams). The paper abrasion density is measured and found to be 0.09.

What is claimed is:

l. A flowable, pressure-fixable, dry powder comprising thermoplastic, essentially spherical particles, the binder material of which has a conductivity of at most 10'" mho/cm and which comprises (a) about 50 to 100 parts by weight of a wax component having a melting point between about 45 C. and 150 C., and (b) about 2 to 50 parts by weight of thermo-plastic resin having a softening point above about 60 C.; wherein electrically conductive particles are firmly anchored in said binder material, said electrically conductive particles having a conductivity of at least l0- mho/cm and an average diameter below about 100 millimicrons forming a radially disposed zone; and wherein said essentially spherical particles exhibit:

a. an electronic conductivity ranging monatonically without decreasing from between about 10'" and 10 mho/cm in a 100 v./cm. DC electrical field to between about 10 and 10 mho/cm in a 10,000 v./cm. DC electrical field,

b. a number average particle diameter below about 20 microns, and

c. a volume ratio of said electrically conductive particles to said total particle volume of between 0.01/100 and 4/100;

wherein the dry powder exhibits a transfer density of less than about 0.15 and a paper abrasion density of less than about 0.15.

2. A flowable, pressure-fixable, dry powder in accordance with claim 1 wherein said wax component is selected from the group consisting of polyethylene, aliphatic waxes, and hydroxylated fatty acids.

3. A flowable, pressure-fixable, dry powder in accordance with claim 1 wherein said thermoplastic resin is selected from the group consisting of cellulose esters, vinyl resins, vinyl copolymers, polyamides and polystyrene.

4. A fiowable, pressure-fixable, dry powder in accordance withclaim 1 wherein said wax component comprises about parts by weight of polyethylene and said thermoplastic resin comprises about 20 parts by weight of ethylene/vinyl acetate copolymer.

5. The dry powder of claim 1 in which said electrically conductive particles are particles of highly conductive carbon having a conductivity of at least 10 rnho/cm.

6. The dry powder of claim I in which the particle size range of said spherical particles is such that at least about number percent of the particles have a diameter greater than about 5 microns and no more than 5 number percent have a diameter greater than 25 microns.

7. The dry powder of claim 1 in which said spherical particles have an electronic conductivity ranging monatonically without decreasing from between 10" and 10" mho/cm in a v./cm. DC electrical field to between 10" and 10" mho/cm in a 10,000 v./cm. DC electrical field.

8. The dry powder of claim 1 in which said essentially spherical particles contain therein magnetizable particles.

9. The dry powder of claim 8 wherein said magnetizable particles comprise magnetite.

l I k l

Claims (9)

1. A FLOWABLE PRESSURE-FIXABLE, DRY POWDER COMPRISING THERMOPLASTIC, ESSENTIALLY SPHERICAL PARTICLES, THE BINDER MATERIAL OF WHICH HAS A CONDUCTIVITY OF AT MOST 10-12MHO/CM AND WHICH COMPRISES (A) ABOUT 50 TO 100 PARTS BY WEIGHT OF A WAX COMPONENT HVING A MELTING POINT BETWEEN ABOUT 45*C. AND 150*C. AND (B) ABOUT 2 TO 50 PARTS BY WEIGHT OF THERMO-PLASTIC RESIN HAVING A SOFTENING POINT ABOVE ABOUT 60*C.; WHEREIN ELECTRICALLY CONDUCTIVE PARTICLES ARE FIRMLY ANCHORED IN SAID BINDER METERIAL, SAID ELECTRICALLY CONDUCTIVE PARTICLES HAVING A CONDUCTIVELY OF AT LEAST 10-2NHO CM AND AN AVERAGE DIAMETER BELOW ABOUT 100 MILLIMCRONS FORMING A RADICALLY DISPOSED ZONE; AND THEREIN SAID ESSENTIALLY SPHERICAL PARTICLES EXHIBIT: A. AN ELECTRONIC CONDUCTIVITY RANGING MONATONICALLY WITHOUT DECREASING FROM BETWEEN ABOUT 10-11 AND 10-4NHO/CM IN A 100C. CM. DC ELECTRICAL FIELD TO BETWEEN ABOUT 10-8 AND 10-3 NHO CM, IN A 10,000 V. CM, DC ELECTRICAL FIELD,

2. A flowable, pressure-fixable, dry powder in accordance with claim 1 wherein said wax component is selected from the group consisting of polyethylene, aliphatic waxes, and hydroxylated fatty acids.

3. A flowable, pressure-fixable, dry powder in accordance with claim 1 wherein said thermoplastic resin is selected from the group consisting of cellulose esters, vinyl resins, vinyl copolymers, polyamides and polystyrene.

4. A flowable, pressure-fixable, dry powder in accordance with claim 1 wherein said wax component comprises about 80 parts by weight of polyethylene and said thermoplastic resin comprises about 20 parts by weight of ethylene/vinyl acetate copolymer.

5. The dry powder of claim 1 in which said electrically conductive particles are particles of highly conductive carbon having a conductivity of at least 10 2 mho/cm.

6. The dry powder of claim 1 in which the particle size range of said spherical particles is such that at least about 95 number percent of the particles have a diameter greater than about 5 microns and no more than 5 number percent have a diameter greater than 25 microns.

7. The dry powder of claim 1 in which said spherical particles have an electronic conductivity ranging monatonically without decreasing from between 10 9 and 10 5 mho/cm in a 100 v./cm. DC electrical field to between 10 7 and 10 4 mho/cm in a 10,000 v./cm. DC electrical field.

8. The dry powder of claim 1 in which said essentially spherical particles contain therein magnetizable particles.

9. The dry powder of claim 8 wherein said magnetizable particles comprise magnetite.

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