DE2306004A1 - METHOD OF MANUFACTURING CARRIER MATERIALS FOR USE IN ELECTROPHOTOGRAPHIC PROCESSES - Google Patents

Description

Process for the production of support materials for use in electrophotographic processes

The use of carrier particles in two-component developer mixes in electrophotographic processes is known. The carrier particles form the second required component for a triboelectric charge on the toner particles for use in developing the electrostatic latent images which supported on a photoconductive layer in an electrophotographic process.

A more complete discussion of the use of carrier particles in such a developer mixture can be found in German patent applications P 22 03.622.1, P 22 OJ 718.9 and P 22 26 478.4, as well as the patent application by the same applicant on the same day entitled "Enveloped carrier particles for use in an improved electrophotographic process " and the internal registration number Docket LE 972 002.

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Some requirements for these carrier beads to use in such a copying process were determined. Some of these requirements are that the carrier beads have a "generally have uniform coating and the coating as a whole must be of high quality, although they are relatively thin must be kept. Additional factors relating to the coatings on these carrier beads include that which are used Materials have certain relatively predetermined and determinable triboelectric properties. Lots of materials that Having desirable triboelectric properties are extremely difficult to apply to small nuclei to form more uniform ones thinner coatings higher. To apply quality. Furthermore, as a result of the various speeds and Types of developer equipment of various core materials found to be satisfactory in various development environments, Each development environment has its own requirements regarding particle shapes, densities, particle sizes, dynamic Has properties and magnetic sensitivity.

The previous working methods for the formation of carrier materials are generally procedures that can be referred to as agitation and agitation techniques, in which the core material is placed in a container and the coating material is then mixed in until a uniform mixture is obtained. During this mixing process, the coating material is deposited as a resin or polymer on the core materials and is dried or otherwise adhered to the core materials. This technique has proven to be acceptable to many triboelectrically proven advantageous coatings. However, the mixing method is not particularly satisfactory if Materials in the form of a latex, an emulsion or a dispersion are intended to be used for coating. The mixed media is particularly advantageous or particularly acceptable if that is to be layered triboelectric material is in the form of a solution. Other problems arise with mixing technology,

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when substrates of extremely fine particle size or extremely high densities can be used. The extremely small particle size and extremely high densities favor agglomeration, due to the uniform coating thickness and high quality as well as thin coating thicknesses not in the entire batch can be achieved.

Pluidate beds have so far been used to coat materials used »Gaseous fluidized beds were used to coat bodies with a relatively low or extreme density fine particles of materials with higher densities are used. In general, coatings have been applied to these materials, To achieve a preservation of the surface treatment or in the case of medicines and pills, to give them a better taste for the consumer.

It is an object of the present invention to provide carrier beads improved quality «,

Another object of the invention is to provide carrier core materials to successfully coat the have not yet been successfully applied by means other than a layer "

A further object of the invention is to improve the properties of the coatings applied by the coating process steer"

Still another object of the invention is to control hardening the properties of the coating on a carrier

Forner is an object of the invention to provide coating to improve.

CohlJesr;] I is another goal of the invention, maximum flexj-

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2308004

flexibility with regard to the choice of a wide variety of triboelectric To enable materials on a wide variety of cores for coating *

According to the present invention, a carrier core material is selected in terms of its physical properties in consideration of the developing apparatus in which it is used. Once the core material has been selected, it is placed in an upwardly directed gas flow and the flow is adjusted so that the core particles are suspended in the flow. The gas flow can be heated depending on the relative volatility of the solvent or suspending medium then injected or sprayed into the gaseous air stream in which the cores are suspended in a volatile carrier liquid. _B

Small droplets of the coating mixture hit the floating cores due to the effect of the pluid flow and coat them the same »The volatile fluid carrier medium is then driven off by the heated or unheated gas stream, wherein on the surface of the core materials there is a thin, substantially uniform coating of the previously selected one triboelectrically effective material remains * after thorough The carrier beads are then dried if necessary hardened by additional heating. This is a modification of the physical and / or chemical properties the outer coating by any of several processes such as polymerization / sintering, coalescing (Growing together) or melting.

The invention thus relates to a process for the preparation of carrier beads of high quality for use in a developer mixture in an electrophotographic process _o. Carrier core materials are suspended or fluidized in an upwardly directed gas stream, and the triboelectric coating

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** 5

processing material is introduced into the gas stream, in which the carrier cores are in suspension. The residue of the coating composition accumulates on the core material, and there are so nuclei that are substantially uniform and are completely coated on their outer surface, »The outer coating is then dried and heated hardened.

The method described above gives great flexibility with regard to the processing of a wide variety of carrier beads with the widest choice of core materials with very different physical, electrical and chemical properties and also enables a very wide selection of coating materials that are applied as a coating from solutions, latices, emulsions or dispersions can.,

The invention is described below with reference to the drawing are explained in more detail, which is a schematic view of a gas fluidate bed or fluidized bed coating device used according to the invention shows.

The Kernrnaterialien that can be used in this method for the preparation of carrier beads for eiektrophotographische developer mixtures can be any of any particulate material that has the desired physical parameters such as density, shape _J size, weight, dynamic / properties and the like.. Some of the known core material ions are sand, glass spheres, steel _{grit, ferromagnetic particles 3} such as worked steel grit, iron filings, nickel grit and other electrically conductive particles such as aluminum or copper particles or grit. This list is not exhaustive and any material which is in particulate form and which has the desired physical and / or electrical properties can be used as the core material. Of the . The densities of the core materials can range from about 2.0 to

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be about 12.0 with the preferred range about 2.3 'for sand is up to about 8 for steel.

A carrier bead can generally be composed of a small particulate Core material ranging in size from about 50 microns to 1,000 microns in diameter and generally in a range of 100 to βΟΟ microns in diameter in order to turboelectrically charge and / or increase the toner To achieve carrier life, the core material is coated with a coating material, usually a polymer or a Resin, coated "that has a desired triboelectric relationship with the toner with which it is used. Such triboelectric relationships are known and have been published as triboelectric series »In general, the coating should be thin and uniform on the beads and additionally have a high degree of integrity, i.e., the coating is said to be continuous and generally not to suffer deterioration from abrasion, peeling, crumbling or tearing.

The coating materials that have been found to be very useful because of their physical properties or their triboelectric properties or because of both properties are generally not uniformly soluble in common solvents. These materials come in a wide variety of forms and are generally only made of a liquid medium as a layer applicable. Some can form solutions, such as polyvinylbenzene methylammonium chloride (trade name Dow ECR-J ² I-, available from Dow Chemical Company) "This material is soluble in water and can be applied from an aqueous solution. An example of another form in which a material can be coated onto the cores is a material known as Elvax D-I249 which is carboxylated polyethylene ionomer (commercially available from E. I. Dupont de Nemours and Company). This carboxylated "" polyethylene ionomer is an aqueous dispersion, namely a latex. ·

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Another example of a form in which a material is coated may be present is a solid substance such as an ethyl cellulose (N-type), together with an Orasol Red "B" dye (commercially available from Ciba Chemical and Dye Company) dissolved in an organic solvent such as Methyl ethyl ketone (MEK).

Another example of a latex obtained according to the invention Method that can be applied as a layer is polytetrafluoroethylene (Trade name Teflon 852-201 available from E.I. Dupont de Nemours and Company). More examples of materials and modes of operation are discussed in more detail below. Curing of a carrier grain coating can be accomplished by heating of the entire bead can be made after the coating has dried. Examples of different types of hardening are the Polymerization of materials that have been applied to the spheres as a layer, the sintering of material particles that have been deposited on the Cores have been applied, the melting of a material that has been applied to the cores, or the chemical alteration of the Coating material by heating to obtain aeren triboelectric properties either in terms of the triboelectric charge size or the triboelectric polarity.

Reference is now made to the drawing. The device for the fluidized bed gas flow coating has an air supply 10, through the air by a fan 12 or other high speed air supply device and is supplied in large quantities. The air flow can at this point by any means, for example a flow control 14, a fan with adjustable speed or a blind arrangement controlling the flow of air coming out of the fan, or any other Airflow control device. The air is forced through a temperature control zone 16 in which heating elements 18 with the air flow come into contact and thus bring its temperature to the desired value. The temperature of the air in the coating zone

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20 is at this point due to heat transfer from the heating elements 18 controlled on the air, creating a precisely adjusted Temperature in the coating zone 20 is obtained.

After the air has emerged from the temperature control zone 16, it flows through the rest of the air supply line 22 up to a point just before the fluidization zone 20 Droplets can be introduced. The nozzle is selected taking into account the material to be applied as a layer, and the nozzle openings are designed in such a way that a fine mist of the coating mixture can be sprayed into the air stream. It has been found that a double nozzle is very effective / in which air exiting an outer ring * sprays the coating material which exits from an inner opening * The coating material can be precisely metered by a controllable metering pump 28 or by another device . The coating mixture is fed to a nozzle 24 from a feed container or tank 26 by a pump 28 and a slide valve j30. There is therefore always a positive pressure for injecting the desired amount of coating material in the air stream. When the gas enters the fluidization zone 20, it flows through an air distribution plate 21 and a support grid 23 for the bed. The air distribution plate 21 distributes the air flow across the cross section of the fluidized bed. Usually, a scheme of varying air velocities is preferably used. This leads to a uniform rotation of the carrier cores and thus promotes good uniformity of the coating. The bed support grid 23 prevents support cores from falling back into the air supply duct 22.

After the G & sstronis has emerged from the fluidization zone 20, ■ the speed from »thereby increasing the ability of the air flow to move in Airborne materials- "wearing" diminishes what allows the airflow and the volatile part of the loading

layering fluid upwards with a noticeable swoop ^ - but at a sufficiently slow rate not to avoid any core materials being coated should take with you. After the air flow has passed through the upper wider chamber 32 to accommodate and slow the gas flow is, the air flow is discharged through an exhaust system 3 ^ and either vented to the atmosphere or to remove any undesirable materials present in the air stream be carried along, cleaned before the air flow to the Atmosphere is vented. The carrier cores are continuously kept in circulation in the plumbing zone 20 until the desired Coating amount applied 1st.

It should be noted that if it is appropriate to coat materials in a particular environment, for example beads to coat in an environment of an inert gas, the exhaust gas * manifold 3 ^ · can be connected to the inlet section 10, and instead of using air as the gas stream, the inert gas can be introduced into the system at the desired rate The degree of purity can be brought under inert conditions prior to the operation

The temperature control zone 16, in which the gas stream is brought to a higher temperature, is the main variable control factor for adjusting the evaporation rate of the volatile liquids during the coating process and also for adjusting the temperature of the core material and then the coated cores. The pluidate bed or gas flow device described above can be made of high temperature resistant materials to permit the application of temperatures in the range of 370 to 485 ^° C (700 to 900 ^° F) in the gas flow and thus curing and sintering or heat treatment of the coated cores after the coating has been applied by spraying the coating material into the air stream.

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Alternatively, the core materials can be obtained from the fluidized bed coater removed and, if desired, heat treated in a separate heat treatment furnace, hardened or be sintered. The following specific examples serve to further illustrate the invention, in particular regarding the operation of the fluidized bed coating apparatus and the coating conditions for application of e.g. selected materials on cores for use as electrophotographic carrier beads,

Example 1

6.35 kg (14 pounds) of machined steel shot having an average particle size of about 270 microns was placed in a fluidized bed coater. An aqueous dispersion of carboxylated polyethylene ionomer (trade name Elvax D-1249, available from E. Dupont) was diluted with 2 parts of water per 1 part of Elvax D-1249 dispersion such that the percentage of solids was about 14 to 16 $ and 580 ml of the diluted dispersion was obtained. Then, air was pressed under pressure into the fluidized bed coating apparatus at 76-88 ⁰ C (170 to 190 ⁰ F), and the resulting dispersion was pumped through a spray nozzle 24 at a rate such that a uniform coating was carried out and the rate low enough was to allow the steel shot to be coated in small amounts and partially dried before the steel shot was held in the fluidized bed for a second coating. This repetitive coating of the shot was continued until all of the shot in the feed was coated to the desired thickness, which was about 3 to 3 1/2 microns, the approximate rate at which the diluted dispersion was sprayed and introduced into the air stream was was 10 ml / min _e the total volume of the coating material after dilution was about 58o ml for a loading of 6.35 kg (14 pounds) machined Stahlschrö'tmit an average particle size of about 270 microns * after completion of the loading

.- 11 -

Layering, the steel shot coated with Elvax D-1249 was then circulated in a heated stream of air for about 50 minutes at an introduction ^{temperature of about 82 to 94 °} C (180 to 200 ^° F). "This drying step removed most of the remaining water, hardening the coating and left a load of coated steel shot carrier that was essentially dry and unagglomerated.

The hardening described above in addition to peeling off the Remaining solvent or the carrier liquid helps to achieve the best possible bond between the coating material and the steel core. Because the temperature to which it is heated during the curing time is above the glass transition temperature of the Coating, any surface irregularities, Roughness or particles of carboxylated polyethylene ionomer, which have not previously been thoroughly melted and / or softened to give a uniform smooth coating, then heated to a temperature that allows the coating to have a uniform thickness with a smooth exterior Shift takes,

Example 2

A coating composition was prepared by dissolving conductive resin (Dow ECR-34) in aqueous solution in an amount of about 2 volumes to one volume with water with stirring at room temperature. This coating composition was applied to Ottawa sand having a density of about 2.3 and an average diameter of about 650 microns in the above-described fluidized bed coating apparatus at a temperature of about 95 ° C (200 ⁰ F) at a rate of about 20 sprayed on ml / min. About 50 ml was used per 0.45 kg of sand. The coating was then dried for about 20 minutes in the tower at about 93 ° C (200 ^e F). A second coating was then applied. The second coating was a composition containing about 1 ton weight percent Exon 497 resin (commercially available from

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from Firestone Plastics Company) and about 1% by weight of Orasolred "B" dye (commercially available from Ciba Chemical and Dye Company) dissolved in methyl ethyl ketone by stirring at room temperature. This' composition was sprayed onto the sand in the fluidized bed apparatus at a temperature of about 38 ⁰ C (10O ⁰ F) at a rate of about 20 ml / min, to about 50 ml per 0.45 kg of sand were applied. The coating was then ^{dried at about 58 °} C (100 ^° F) for about 20 minutes. The resulting coating was uniform, smooth and relatively free of agglomerates. It can then be hardened at a suitable temperature in an oven or in the fluidized bed tower. This example shows the possibility of applying a two-component coating system, one coating being carried out from an aqueous medium and the other from an organic solvent.

Example 3 .

A coating composition comprising a fluoropolymer and a modified resin (commercially available from Dupont as 954-101 light green Teflon-S) was reduced to J volumes to 1 volume with methyl ethyl ketone by stirring at room temperature diluted and sprayed onto steel balls an average diameter of about 450 microns. The fluoropolymer is a copolymer of tetrafluoroethylene and hexafluoropropylene, which has thermal properties close to the 1: 1 Has copolymers. The modifying resin is an epoxy resin,

The coating composition of 954-101 light green Teflon-S is a solution that contains solvents and a pigment in addition to the fluoropolymer and the "modifying resin. The modifying resin is essentially in the solvents dissolved, which is a mixture of methyl isobutyl ketone and xylenes in Contain weight ratios of 2 s 3 ,, The pigment * das is a chromium oxide, and the fluoropolymers are together in the

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Solution of the solvents and the modifying resin suspended. The fluoropolymer makes up about J56 wt .- ^ of the total solution, the modifying resin comprises about 18.5 wt, ~ $ of the total solution, the solvent is about 41.5 percent, - $ of the total solution and the pigment is about 4 wt -.% Of the total solution ,

About 50 ml of the diluted material per 0.45 kg steel beads were applied "The material was sprayed onto the beads in a fluidized bed tower at a Beschiohtungstemperatur of about 38 ⁰ C (100 ⁰ F). The microscopic examination of the coating after this stage showed that the coating was relatively uniform and relatively free of scars, discontinuities and scales »

The coated cores were then placed in an oven and the temperature of the beads was brought to about 302 ^° C (575 ^° F). The beads were left at 302 ^° C (575 ^° F) for about 15 minutes and then removed from the oven. The beads were cooled to room temperature by cooling with ambient air. The coated particles were then _{sieved through a U 8} S. standard JO mesh sieve to remove agglomerates.

Example 4

A steel primer coating composition (850-201 Teflon Primer, available from Dupont) was diluted in a ratio of about 2 volumes to 1 volume with distilled water with stirring at room temperature and applied to steel beads an average diameter of about 300 microns and one sprayed for adhesion cleaned surface. The steel primer coating composition (850-201 Teflon) is a solution containing about -35% by weight polytetrafluoroethylene, about 12% by weight chromic and phosphoric acid, and about 55% by weight water. The material was applied to the beads in a fluidized bed apparatus at a temperature of about 77 ⁰ C (170 ⁰ F). Approximately 35 ml of the diluted material were added to each 0.45 kg of beads

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I 1)

-U-

turns. The primer coated beads were ^: then removed from the device and placed in an oven, and the temperature of the beads was brought to about 550 ^{° F (277 °} C) and held there for about 11 minutes. The beads were then removed from the oven, cooled to room temperature by cooling with ambient air, and then reintroduced into the fluidized bed tower: λ ■

A coating composition of clear Teflon enamel (852-201 Clear Teflon Enamel, Dupont), diluted in a ratio of about 2 volumes to 1 volume with water by stirring at room temperature, was now applied to the beads in the fluidized bed tower sprayed on at a coating temperature of about 77 ° C (170 ⁰ F). The coating composition of 852-201 Teflon Clear Enamel contains about 48 wt -.% Of polytetrafluoroethylene, about 3 wt - $ surfactant (Triton, Alkylarylpolyätheralkohol- mixture of organic sulfonate) and about 49 wt .- ^ water and toluene in a ratio of 95! 5 »Approximately 45 ml of the diluted material was slowly applied per 0.45 kg of beads. '- "■ -"'

The beads were then introduced from the tower removed and placed in an oven and the temperature of the beads was brought to about 416 ° C (78o F ⁰⁾ and held about 11 minutes at this value. The material was then cooled to room temperature by cooling with ambient air and then sieved through a US standard sieve with 35 mesh to remove agglomerates · After testing, the carrier had relatively smooth, uniform surfaces that were relatively free from defects »

Example 5

A coating composition having a content of about 0.6 wt -.% Dye Orasolred "B" (available from Ciba Chemical and Dye Company, Fairlawn, New Jersey), and about 4.4

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Wt -.% Ethyl cellulose (N-type) (available from Hercules, Inc., Wilmington, Delaware), dissolved in methyl ethyl ketone by stirring at room temperature, was sprayed on steel beads having an average diameter of about 450 microns and a form suitable for adhesion surface .

Approximately 100 ml of the solution per 0.45 kg steel beads were used, the hatten.- a density of about 8 The material was applied to the beads in a fluidized bed coater at a coating temperature of about 27 ⁰ C (-80 ⁰ F) in the Applied in the manner described in Example 1 "Microscopic examination of the carrier coating after this stage showed that the coating had excellent uniformity and was essentially free of scars and scales."

The coated cores were then placed in an oven and the temperature of the beads was (F 19O ⁰⁾ brought to about 88 ⁰ C and held for about 24 hours at this value * At this time, the temperature to about 132 ⁰ C (was 270 ⁰ F) brought for another hour. The hardened beads were now removed from the oven, cooled to room temperature by ambient air cooling, and passed through a U, S, standard mesh screen to remove agglomerates.

Examples 1 through 5 demonstrate the utility of a gas fluidized bed coating tower for coating various substrates including sand, S-70 steel shot, S-110 steel shot, and 270 micron machined steel shot. Other substrates such as Glass and other metallic materials can also be coated. Besides the five coating compositions, which were used for coating in Examples 1 to 5 and solutions and dispersions of aqueous or organic media, belong to other coating compositions that can be used for coating, Polyethylene, 958 TFE-S series (Dupont), 955 single-layer Teflon series (Dupont), 959 single-coat Teflon series (Du-

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pont) \ ond chlorinated polyisoprene,

Classes of materials that have been coated and found to be useful include halogenated Vinyl resins, vinylidene resins, chlorinated polyisoprene, polyofefins and halogenated polyolefins, phenoxy resins, epoxy resins, acrylic polymers and acrylate copolymers, polycarbonate, styrene copolymers and terpolymers, cellulose-based products, polyamides and polyesters »

Special materials within the above classes that -as Layer applied to particulate substrates for use as carrier beads in an electrophotographic process are given in Table I below ..

Table I.

Carrier coating materials Polymer Trade name / Manufacturer number 1 · Carboxylated poly- »:
vinyl chloride Geon 130X17 BP Goodrich
Chemical Co,
(Division) 2 «polyvinyl dichloride
acrylonitrile Saran PJOO The Dow Chemical Co j5, polytetrafluoroethylene Teflon 852
201 EGG. DuPont de
Nemours & Co, 4, chlorinated polyvinyl "
chloride Geon 602X580 B _e P, Goodrioh
Chemical Co. 5, acrylonitrile vinyl «
chloride copolymer Dynel Union Carbide Corp, € · .Vinyl Chloride-Vinyl
acetate copolymer Exon 497 Firestone Plastics
Co ₉ (division) 7 * carboxylated poly »
ethylene ionomer Slvax Dt249 B ₈ I, DuPont de
Nemours & Qo * 8 · polyvinyl butyral. Butvar B «74 Monsanto Co ₀ 109834/1037

9 # chlorinated polyisoprene

10 · chlorinated polypropylene

11, polyvinyl dichloride acrylate

12, phenoxy resin

13. Polyvinyl difluoride

14. Styrene-butadiene copolymers

15 · styrene-acrylate copolymer

16, polycarbonate

17 · Cellulose acetate butyrate

18, acrylonitrile butadiene « Copolymer

19, polyethylene

20, acrylonitrile-butadiene-styrene copolymer

21 · polyvinylbenzene methylammonium chloride

22, methyl methacrylate-n-butyl methacrylate copolymer

23 "polyvinyl carbazole

24, polysulfone

25, polyethylene acetate

26, ethyl cellulose 27 _β polyvinyl formal

28 · Hexafluoropropylene-Traf1uorethylene Copolymer + epoxy resin + pigment (Teflon-S)

29. Acrylhydrosol

Parlon S-10 Parlon P-20 Diofan I90D

Bakelite PKHH Kynar 202

Pliolite S-5A .Pliolite AC

Lexan film EAB-272-3

EAF 400-81N polyem-40

TyIac ™ 3868B

Dow ECR-34

Hercules Inc.

Hercules Ine ,, BASF Corp.

Union Carbide Corp.

Pennsalt Chemical Corp,

The Goodyear Tire & Rubber Co.

.The Goodyear Tire & Rubber Co,

General Electric Co,

Eastman Chemical Products * Inc. (Subsidiary)

General Aniline & Film Corp,

Cosden Oil & Chemical Co.

Tylac Chemicals (Division)

The Dow Chemical Co.

Acryloid B-66 'Rohm & Haas Co.

- BASF Corp, Sulfone 47 Union Carbide Corp. Slvace EP
1965 ■ EI, DuPont de
Nemours & Co, N type Hercules Inc. Formvar 7 / 95E Monsanto Co. Teflon-S
954-101 EI DuPont de
Nemours & Co. PB-9012 EI, DuPont de
Nemours & Co.

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30, vinyl alcohol Bakelite Union Carbide Corp. Vinyl acetate "BA-28-18

Copolymer

31, polyamide Milvex 4000 General Mills

32, epoxy resin Epirez 2287 Celanese 'Resins

(Division)

33 · Polyvinyl alcohol Elvanol 72-60 E.I, DuPont de

Nemours & Co,

34. Hexafluoropropylene-PEP 856-200 E, I, DuPont de Tetrafluoroethylene- Nemours & Co,

Gopolymeres.

Each of the above materials in the table and the other mentioned in the text. Materials has favorable properties as triboelectric carrier coating for carrier beads shown. Some of these materials are best for cascade developers and some are best for magnetic brush developers.

The. The above examples show the extraordinarily wide range of materials which can be used successfully by the process according to the invention can be applied as a layer »

The above examples and the cited materials referring to relatively small core materials, but high density materials, for the formation of electrophotographic carrier beads show the flexibility of the fluidate bed coating process to achieve a high quality triboelectric coating on particulate! material of sufficient size and density and sufficient dynamic properties, to serve as a carrier material for use as one of the components in a developer mix »

In all of the above examples and for the coating of any of the materials listed above, the process can generally be described as a process in which a high volume of a relatively rapid air flow in aie

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Receiving manifold or the receiving line 22 of a fluidized bed coating device is introduced and this air flow is passed through a temperature control zone 16 in which the air can be heated to a set temperature. The air-

stream is then passed into the fluidization zone 20, which is also called Coating zone is used. The air flow is then out of the fluidizing zone 20 in an enlarged zone J2, in which the air speed drops considerably and so the air flow loses its ability to remove the core or carrier parts carried along in the To keep the vortex state. This reduced speed air stream is then removed from the coating device.

The coating material is introduced into the air stream through a nozzle 24 introduced for the finest crushing under such a pressure, that the fluid is finely atomized and sprayed into the flowing air. This sprayed coating material hits then on the core materials that are in the coating zone 20 are suspended immediately above and adjacent to this location, causing small amounts of the coating material on the Outer of the cores are deposited. By varying the speed of the air flow in the coating zone 20 the particles have a tendency to rise and fall in the coating zone 20, causing a cyclical movement of the particles after is obtained above, below and all around in the coating zone 20. When the particles reach the bottom of the coating zone 20 approach, the finely crushed jet of coating material settles more strongly on the particles, and when the current carries the particles upwards, 'there is a depletion of the available standing coating material, and the already applied coating has a tendency to dry out or to peel off to deposit the volatile carrier liquid. After applying the desired amount of coating material to the airborne Core materials is applied, the feed system

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for the coating material are switched off, whereby the coating part of the operation is terminated. At this point, the air flow can continue to flow through the fluidized bed device to thoroughly dry all particles Core materials deposited material is hardened. When the entire core coating apparatus consists of temperature-resistant materials, temperatures in which the particulate material is held by the · air flow in the suspension are generated (70 to 900 ° P) in the coating zone 20, in the order of magnitude from 21 to 485 ⁰ C, and hardening can thus be carried out at a high temperature.

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Claims (1)

- 21 claims sassss; as ss ss SS si as sa. SS as sas SS ^ HmJSS j; as as A method of making triboelectric carrier beads for use in an electrophotographic reproduction machine, characterized in that a particulate core material having the desired physical properties is selected a coating material with the desired physical, mechanical and triboelectric properties is selected is, the core material is suspended in a gas stream generally flowing upwards at a set temperature the coating material and a volatile carrier medium is introduced into the gas stream at a rate such that that the material moves at a desired rate and thickness for maximum coating integrity separates that the suspension of the core material is maintained in the stream until essentially all of the volatile Carrier medium has volatilized, and. the carrier beads are heated to a temperature and for a period of time to the desired to give physical and / or triboelectric properties to the coating. 2 »The method according to claim 1, characterized in that it is heated to a temperature and for a period of time which are sufficient to coalesce particles that make up the coating, 3. The method according to claim 1, characterized in that Cores with an average diameter of 50 to 1000 Microns and a density of 2.0 to 12 are used, 4. The method according to claim J5, characterized in that as Coating material a latex is used. 309834/1037 5 «Method according to claim J>, characterized in that an emulsion is used as the coating material. 6 «The method according to claim 3, characterized in that as Coating material a solution is used * 7. The method according to claim 3, characterized in that
the heating stage is carried out in the gas stream. 8 * The method according to claim 3> characterized in that the heating step after removing the beads from the gas stream
is made. 9. The method according to claim 3 »characterized in that the coating comprises a triboelectrically negative resin. 10.- Method according to claim 3. » characterized in that the Coating comprises a triboelectrically positive resin, 11. The method according to claim 3 * characterized in that a Coating material which is substantially insoluble in common solvents is used. 12 * The method according to claim '11, characterized in that as Coating material a fluorocarbon from the group of polytetr'afluoroethylene and fluorinated ethylene-propylene copolymer is used. 13, the method according to claim 12, characterized in that on a temperature and heated for a period of time sufficient to to sinter the fluorocarbon materials into a substantially continuous uniform coating. 309834/1037