DE2007003A1 - Process for the production of magnetically responsive carrier particles - Google Patents

Description

Eastman Kodak Company, 343 State Street, Rochester, New York State, United States of America

Process for the production of magnetically responsive carrier particles

The invention relates to a method for producing magnetically responsive carrier particles for applying electroscopic toner material for electrostatic charge images.

Electrophotographic imaging processes are from numerous patent specifications and from other literature sources, z. B. from U.S. Patents 2,221,776, 2,277,013,

2 297 691, 2 357 809, 2 551 582, 2 825 814, 2 833 648,

3,220,324, 3,220,831 and 3,220,833 are known. It is common to all of these processes in general that a normally insulating, photoconductive recording material is used which, when exposed imagewise, responds to electromagnetic radiation, producing a latent electrostatic charge image. This electrostatic charge image is then made visible by attaching the photoconductive surface to the charged surface

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Brings recording material with a suitable developer mixture in contact.

One method of applying the developer mixture is the well-known magnetic brush method. In this process can an apparatus such as that described in U.S. Patent 3 003 46 2, which often a non-magnetic, rotatably attached Z / linder with a magnetic device attached to the inside. The cylinder is attached in such a way that that it can rotate so that part of its surface is immersed in a reservoir with the developer mixture or otherwise comes into contact with it. The granular mass constituting the developer mixture is of the Surface of the cylinder is magnetically attracted. If the developer mix is within the sphere of influence of the Magnetic device arrives within the cylinder generated magnetic field, the particles are directed Developer mix borite-shaped, creating the image a brush. The bristle-shaped alignment of the developer mix is along the lines of magnetic flux and near the poles they stand upright, while practically lying flat when the mix is moving outside the vicinity of the magnetic poles. The continuously rotating cylinder increases with one revolution developer mixture from the storage container and leads this then partially or completely back to the storage container. This way of working ensures that there is always freshness on the surface of the photoconductive recording material at the point of contact with the brush Developer mix is present. In a typical rotation cycle, the roller picks up developer mix, then a brush forms, the brush comes with the photo-

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conductive recording material in contact, collapses again and finally the developer mix is again returned to the storage container.

In magnetic brush development of electrostatic images, a triboelectric mixture is usually used as the developer Fine toner powder used, made from a colored or

thermo-.
pigmented / plastic resin with coarser carrier particles made of a soft magnetic material, e.g. B. "ground chemical iron ¹¹ (iron filings), reduced iron oxide particles or the like. Due to the electrical conductivity of the ferromagnetic carrier particles, which m form the" bristles "of a magnetic brush, the effect of a developer electrode occurs with a very small distance to the surface of the With the help of this developer electrode it is possible to a certain extent to develop some of the color tones in pictures and black paper as well as line copies. This possibility of achieving a solid surface development by magnetic brush development is sometimes advantageous if other copies are to be produced as a simple line copies. An occurring in this counter electrode development difficulty is that the achievable exposure latitude is limited. as a result, it is desirable for certain uses, the Gegenelektro- Λ deneffekt to suppress to achieve a wider exposure width. One method of suppressing the counter electrode effect is to use a substrate with a high electrical resistance.

The iron powders currently available on the market, however, by no means have a uniform electrical conductivity and a uniform specific resistance. The currently

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available materials generally have too high a specific resistance so that they do not allow solid surface development and they have too high an electrical conductivity to completely suppress the counter-electrode effect. One reason for the lack of uniformity in electrical properties is that the particles dirt on the surface, e.g. B. grease, oil and other impurities.

US Pat. No. 2,874,063 has already indicated that typical iron carrier particles can be used to remove, for example, the fat and oil with methanol, isopropanol and other alcohols can be treated. The iron so treated is called "alcohol treated iron".

However, it has not yet been recognized that the surface of the known iron powder is heterogeneous in nature and that as a result difficulties arise in the development of magnetic brushes resulting from the use of this known material. However, the dirt on the outer surface of the previously known iron particles is only part of the problem. In addition to the dirt, the iron particles always contain unevenly distributed iron oxide and often also pyrite, e.g. B. iron sulfide, as well as other iron compounds. When such materials are used in conventional magnetic brush processes, are located the iron girders are in constant motion and due to the constant friction of the particles against each other and against the different ones mechanical parts, parts of this uneven surface material are gradually removed. This abrasion to the Iron particles naturally vary from point to point, depending on the nature of the deposit, depending on thickness, brittleness, adhesion strength on the underlying structure and the like.

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With the previously known carrier materials, for example, the character of the iron surface changes constantly during use. The nature of the added toner material also changes accordingly, since it changes with that of the surface of the carrier material detached fine particles is contaminated.

There has therefore long been a need for iron girders » which have a more homogeneous surface and, with continued use, uniform triboelectric and other properties own. In addition, efforts were made to produce iron support particles which would increase the counter-electrode effect and thereby with the help of the magnetic brush development process improve achievable solid surface development, or to produce such iron carrier particles which can suppress the counter electrode effect, so that color fringes develop is induced, in which the exposure width is improved at the same time.

The object of the invention was therefore to provide a simple, economical Specify a process for the production of magnetically influenceable carrier particles, the surface of which is that described above Does not have disadvantages »but which have a homogeneous surface with the desired properties.

The invention now relates to a process for producing magnetically responsive carrier particles for applying electroscopic toner material to electrostatic charge images, which is characterized in that one

a) iron powder dispersed by stirring in a dilute aqueous acid bath,

b) the powder removed from the acid bath,

c) Remove the powder by washing with water

Acid residues freed,

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d) the powder forming a uniform,, thin iron oxide layer on the surface of the individual iron particles dries and

e) optionally the particles of the iron powder with at least one uniformly thin one Cover made of an iron-free material.

Examples of carrier materials! which according to the procedure of Invention can be treated are ferromagnetic carrier materials, e.g. B. iron powder, in the most varied To shape. The term "iron powder" as used herein includes a wide variety of particulate, magnetically responsive Materials the surface of which can be easily oxidized, e.g. B. iron-containing materials, in the form of e.g. reduced iron oxide particles, particles produced by spraying molten metal and subsequent cooling of the droplets by grinding, grinding, filing or turning produced particles as well as particles of iron alloys with oxidizable iron in the surface, z. B. stainless steel and iron alloys containing nickel and / or cobalt.

The ferromagnetic carrier particles used can vary in size and shape, with average particle sizes from about 1200 to about 40 microns good results are obtained. Particularly good results are achieved with average particle sizes of around 600 to about 60 microns. The size of the carrier particles used will of course depend on various factors, e.g. B. the The type of fully developed final images and the desired thickness of the subsequently applied layers.

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The commercially available iron powder is first treated with an acid according to the method of the invention. This acid treatment can be carried out using a dilute acid aqueous solution. A wide variety of acids, in particular sulfuric acid, hydrochloric acid, nitric acid and other mineral acids, can be used for this purpose. Sulfuric acid is particularly preferred because it is cheap, readily available, and not very volatile. In addition, certain organic acids, e.g. B. acetic acids, especially trichloroacetic acid, can be used. The acid concentrations that can be used can generally be varied between about 1n and ettfa 3n. For certain amounts of iron to be treated, certain average particle sizes, or other such variables, it can sometimes be advantageous to use higher or lower acid concentrations. The treatment of the iron particles with acid according to the method of the invention can be carried out by any method for applying the acid. The acid treatment can be carried out, for example, by spraying on, by sprinkling and / or by any other suitable method. A very convenient method is to form a slurry of the iron powder in dilute acid for a while, the period of time can be varied depending on the type and concentration of the A acid used, depending on the stirring used, the required chemical attack of the acid, the particle size of the Iron powder and the property and thickness of the surface material to be removed. When using technical iron powder with an average particle size of about 100 to about 400 microns, it is generally sufficient ^{to stir the iron powder in a 5 * strength aqueous solution of, for example, sulfuric acid at about 25 °} C. for about 1 minute.

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If the action of the acid on the carrier powder is to be stopped, an alkaline solution can be added to the acid suspension can be added. The action can also be stopped by diluting with cold water. However, it is generally easier and more efficient to start with an acid concentration such that the rate of reaction at the end of the treatment time is sufficiently low to allow the iron powder to settle out and to remove the excess To facilitate fluid. As indicated above, the required acid concentration can vary at different Iron powders depending on the amount used and the average size of the particles and depending on the nature of the surface of the Starting material vary.

Despite the adverse effects of the on the technical iron powders various surface contaminants present, these contaminants represent only a small fraction of the total Weight of the powder. In most cases this is due to the removal of undesired surface impurities and partial dissolution of elemental iron in the treatment of technical iron powders by the process of Invention achieved weight reduction on the order of about 1 to about 2 weight percent or less. The acid treatment should not be extended beyond what is necessary to remove the heterogeneous surface contaminants. If the acid treatment is continued until the loss of metallic iron is about 2% by weight, neither will another Reduction in surface contamination still improves surface uniformity · The through Dissolution-induced loss of metallic iron should therefore preferably be less than about 1 tonne by weight of the iron powder be. Excessively long treatment not only leads to unnecessary acid consumption and dissolution of iron, but has in some cases also been detrimental

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Effects by exposing trapped particles of acid-insoluble material to the action of acid.

After treating the iron powder in the aqueous acid solution the acid is removed and the iron is washed by sprinkling or some other method to remove any To remove acid residues. Much of the material removed from the surface of the powder is often insoluble and a preferred method of removing both residual acid and suspended reaction products insists on reducing the iron particles by decanting. A simple decantation process can be carried out by slurrying the iron in clean, cold water, then the iron particles with a suitable particle size settle on the bottom of the liquid. To upon settling, the above liquid is quickly decanted, so that the undesirable impurities with the Liquid can be washed away. This washing process can be repeated until the washing water is clear or until a certain degree of cloudiness is reached.

The method of the invention can be used to produce iron particles can be used with a very high surface conductivity. The one after the. Process of the invention producible Particles with high electrical conductivity have surface resistances that are below normal when measuring Magnetic brush test conditions several orders of magnitude lower are considered to be the best technical iron powders available on the market. For comparison samples, the resistance of the carrier particles was measured according to a customary resistance test. This The test was carried out each time with an amount of 15 g of carrier material. A magnet with a cylindrical shape with a circular forehead curse of about 6.25 cm was added

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used to attract the carrier particles and turn them into a Hold brush. After the brush was formed, it became the bar magnet with the end carrying the brush at a distance of about 0.5 cm, almost parallel to a polished copper plate appropriate. Then the resistance of the particles in the magnetic brush between the magnet and the copper plate was measured. It was found that the uncoated, electrically conductive particles produced by the process of the invention generally have a resistance of less than about 50 ohms, with particles having a resistance of less than around 20 OhA are particularly preferred.

Metallic iron is a very good electrical conductor and the clean surface of elemental iron of the carrier iron produced by the process of the invention resulted, as already indicated above, in an iron powder with a high electrical conductivity. However, iron is also a very reactive metal and oxidizes easily in air. It is therefore extremely important in the production of carrier materials with high electrical conductivity according to the method of the invention to suppress the oxidation during the washing and drying stages as well as during the subsequent storage. The oxidation suppression can take place in the most varied of ways. A practicable way to suppress the oxidation consists in adding an antioxidant or a reducing agent to the wash water and in particular to the last wash water. A wide variety of known antioxidants or reducing agents can be used to prevent oxidation in the subsequent drying stage. In general, it is completely sufficient for this purpose to add, for example, 0.5 l of hydrazine sulfate or sodium nitrite. Oxidation can also be kept to a minimum by treating the carrier particles once or several times with a water-miscible organic solvent, e.g. B. acetone or

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a short chain alcohol such as methanol, ethanol and isopropanol washes. When using these solvents, the remaining water is removed from the iron and the subsequent drying is accelerated. In addition, the temperature and relative humidity of the drying air must be carefully controlled. One reason for the necessary careful control is that when the iron powder is heated, oxidation is favored, while conversely if the iron cools down too quickly so that the temperature falls below the dew point, water condenses on the iron, which also promotes surface oxidation . In the preparation of _Λ electrically conductive carrier particles, it is therefore necessary that the drying% under such temperature and relative humidity conditions is carried out, that the formation is prevented of Oberflächenoxyden.

In general, the iron powder with high electrical conductivity treated by the process of the invention can be dried by constantly stirring it in a stream of warm air. The temperature of the air Homes is generally within a range of about 15 to about 40, preferably between about 20 and about 3O ⁰ C. In addition, the drying temperature should be maintained above the dew point of the surrounding atmosphere in order to avoid an unnecessary condensation. J In addition, the relative humidity of the air used for drying should be kept low. In general, relative humidity values less than about 30, and preferably less than about 201, can provide good results. Under these temperature and humidity conditions, the powder obtained has a very high surface conductivity. However, if even higher surface conductivity values are required, the iron can be stored in an inert, practically oxygen-free atmosphere, for example hydrogen or

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Nitrogen, to be dried. After drying, the iron must be protected from oxidation until it is used. this can easily be done by keeping it in a sealed container in an inert atmosphere. When using the carrier particles are mixed with a toner material with suitable triboelectric properties, wherein the toner forms a physical coating which reduces any further oxidation of the carrier particles during use. This makes it possible to use the improved surface conductivity that can be produced by the method of the invention Carrier particles for long periods of use in magnetic brush devices to maintain away.

It is of course also possible to do so by the method of the invention improved surface conductivity of the carrier particles through an additional surface treatment of the carrier particles to stabilize. A particularly suitable surface treatment is to apply the carrier particles individually with a thin, uniform layer of an electrically conductive non-ferrous metal, which is more resistant to air oxidation than iron, to cover. Examples of materials suitable for coating or plating the electrically conductive bearing particles are especially non-ferrous metals, which are much more resistant to surface oxidation than iron and iron alloys. Suitable coating materials that have a greater resistance to air oxidation than iron are, for. B. the Metals in Groups VIa, VIII, Ib and Hb of the Periodic Table of the Elements, as described in Coton and Wilkinson, "Advanced Inorganic Chemistry ", 1962, page 30. Particularly suitable metals are, for example, cadmium, chromium, copper, gold, Nickel, silver, zinc and platinum group elements e.g. B. ruthenium, rhodium, palladium, osmium, iridium and platinum, as well as mixtures or alloys of these elements. Most of these metals are more electronegative than the iron parent

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material, which is an advantage for certain coating processes is. In other coating processes it may be useful to use more electropositive metals than iron, e.g. B. Chromium, Zinc and cadmium, to use.

The useful electrically conductive metals all have a greater resistance to corrosion or air oxidation than iron. The terms "corrosion resistance" or "resistance to atmospheric oxidation" as used herein are understood to mean the ability of a metal to be resistant to oxidative corrosion, which impairs electrical conductivity. The type of corrosion that is to be prevented, % is generally the progressive air oxidation or the rapid air oxidation, which considerably reduce the electrical conductivity of a metal. B. Air / air, carbon dioxide, water and ozone caused corrosion and not to the chemical attack of solutions of strong acids or bases. Coatings of this type are described in the patent application filed by the same applicant on the same day under internal file number Reg. No. 122,214.

The 'coated with metal by the method of the invention' Carrier particles generally have a resistance of less than 10, preferably less than 1 ohm. These electrically conductive carrier particles are ideal for use in developing magnetic brushes which it is desirable to have a devel ek trotdeneffekt aim ex, causing the solid surface development. However, if a solid surface development fails

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is desired, this developing electrode effect must be suppressed will. The simplest way is to use highly insulating carrier particles. When insulating Carrier particles are used, the developer electrode effect is suppressed and there is a color fringing.

According to the process of the invention, iron carrier particles with a high resistance can be obtained by washing them with acid as indicated above and rinsing them and then treating them to form a uniform iron oxide surface with a high specific resistance adhering to the individual particles. In this embodiment of the invention, however, the washing to remove the acid residues and waste products is carried out without the addition of an antioxidant. After washing with water, the iron is dehydrated to remove excess moisture and then dried without subsequent solvent treatment. The drying takes place at elevated temperatures in order to initiate the formation of surface oxides. Good results are obtained with drying temperature doors receive from about 40 to about 80 ^0C. During the drying process, the wet powder is slowly mixed in order to keep the temperature and the water content the same throughout the powder mass. As the iron dries, its color gradually turns from gray to brown. After drying, the treated powder had a very high surface resistivity. The optimum drying conditions required to produce the desired thin, uniform oxide coatings, ie temperature, humidity and stirring conditions, depend on the iron powder used as the starting material in each case. Simple manual tests can easily determine which conditions are optimal for the powder selected in each case. Generally, air drying at temperatures within the range of about

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40 to about 80 C, preferably from about 45 to about 60 C _{1 have given} good results. The relative humidity of the air used for drying can be varied widely, but good results are obtained at values of 40% relative humidity and above. The air used for drying preferably has a relative humidity of 60% and above. The oxide-coated particles produced in this way had an electrical ΐ
can be.

ο electrical resistance up to more than about 10 ohms

When the high resistance carrier particles of the type specified above are mixed with a suitable toner material will reduce the resulting developer composition very strong the development electrode effect Magnetic brush. In addition, such a developer composition the color fringing is initiated, with the exposure width being increased at the same time. The iron oxide coating This carrier particle can also be used to further increase the resistance of the carrier material with a thin Plastic film are coated, whereby the color fringing is improved. In particular, the carrier particles covered with continuous, uniform layers of a film-forming, electrically insulating resin material will. For coating the carrier particles that can be produced according to the invention A wide variety of polymers or resins are suitable. The appropriate resins must be able to form a film and they must generally be electrically insulating so that when they are applied in the desired amounts, the carrier particles give the desired electrical resistance. Suitable resins are, for example, those that are crosslinked, hardened or otherwise made insoluble, so

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that when a resin layer is subsequently applied, it practically does not penetrate into an adjacent layer. Thermosetting resins are also suitable when using Heat cure, as well as photosensitive resins that cure when exposed to actinic light. Combinations of Resins having various solubility properties can also be used. The various suitable Types of resins can be used either alone or in various combinations.

Examples of suitable photosensitive or photo-curable resins are polymeric derivatives of cinnamic acid, e.g. B, Polyvinyl cinnamate, cinnamylated polystyrene, ethylene-vinyl cinnamate copolymers, cellulose cinnamate, N- (cinnamylphenyl) methane derivatives of hydroxylated polymers, e.g. B. partially hydrolyzed polyvinyl acetate, cellulose acetate, and epoxy resins esterified with cinnamyl chloride. Polyvinyl cinnamate succinate and polyvinyl cinnamate phthalate are particularly suitable, since they are applied from an aqueous solution can. In addition, photo-crosslinkable compositions containing an insensitive resin and a photosensitive crosslinking agent are suitable. See compositions may contain an alcohol-soluble nylon-type polyamide with, for example, benzophenone as a catalyst.

A wide variety of substances can be used as the thermosetting or thermosetting resins, the formaldehyde condensation products being particularly easily accessible. Particularly those with urea, melamine or various phenols, e.g. B. xylenol, cresol, trimethylphenol, phenol or Soligenin, formed formaldehyde condensation products are used. However, other resins can also be used, e.g. thermosetting epoxy resins and polyester styrene resins.

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Examples of other suitable resins are cellulose resins, e.g. 3. Cellulose nitrate, cellulose acetate butyrate, and polymers of short-chain alkyl methacrylate with 1 to 4 carbon atoms in the alkyl group. In general, film-forming polyesters, polyolefins, polyamides and polycarbonates can also be used, provided that they are applied in a suitable carrier liquid which does not soften the previously applied layer. A method for applying multiple layers of these resins are described in by the same applicant on the same date under the internal file reference Reg no. 122,214 filed Patentanmel- A dung. Of course, individual layers of suitable polymers can also be used. The resin particles coated in this way generally have an electrical

1 2

electrical resistance greater than approximately 10 ohms.

From the magnetically responsive carrier particles obtainable by the method of the invention, electroscopic developer compositions can be prepared by about 90 to about 99 wt .-% of the acid-washed, magnetically responsive carrier particles with about 10 to about 1 wt .-% of a suitable electroscopic toner material mixed. As a toner a variety of materials, together with the inventively prepared carrier particles comparable% will apply which give the developed image the desired physical properties? have the correct triboelectric ratio so that they mate with the carrier particles used. In general, any known toner powders can flägerpartikeln with the invention obtainable according to the "are mixed to form a Entwicklerzusanunensetzung. If the selected toner powder is used with ferromagnetic carrier particles in a magnetic brush developing device, the toner due to _e IIAF Lot

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triboelectric attraction on the carrier particles. The carrier particles are all charged with the same polarity and the toner particles are charged with the opposite Polarity charged. If now the carrier is mixed with a resin toner, the one in the triboelectric series above stands, the toner is normally positively charged and the carrier is negatively charged.

Suitable toner powders usable in the present invention are preferred prepared by finely grinding a resin material and treating it with a coloring material, e.g. B. a pigment or a dye. Then the mixture is ground in the ball mill for a few hours and heated until the Resin becomes liquid and envelops the dye. The mass is cooled down into small lumps and finely ground again. According to this process, the toner powder particles are generally about 0.5 to about 25 microns in size with an average Size from about 2 to about 15 microns.

The most varied of substances can be used as resins for the production of the toner, for example natural resins, modified natural resins and synthetic resins. Examples of suitable natural resins are balsam resins, rosin and shellac. Examples Suitable modified natural resins are phenolic resins modified with rosin and others of those listed below Resins with a large amount of rosin. Suitable synthetic resins are all synthetic resins known as Toners can be used, for example polymers, e.g. vinyl polymers, in particular polyvinyl chloride, polyvinylidene chloride, Polyvinyl acetate, polyvinyl acetate, polyvinyl ether and polyacrylic acid and polymethacrylic acid esters; Polystyrene and substituted polystyrene or polycondensates, e.g. polyester, in particular phthalate / xrz, terephthalic acid and

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Isqphthalic acid polyester, maleic resin and with rosin mixed esters of higher alcohols; Phenol-formaldehyde resins, in particular phenol-formaldehyde condensates modified with rosin, Aldehyde resins, ketone resins, polyamides and polyadducts, e.g. B. Polyurethanes. In addition, polyolefins, z. B. Various polyethylenes * polypropylenes, polyisobutylenes and chlorinated rubber are suitable. More suitable Toner materials are disclosed in U.S. Patents 2,917,460, 2,788,288, 2,638,416, 2,618,551, 2,659,670 and known from USA Reissue Patent 25,136.

Color additives suitable for toners are preferably dyes and colored pigments. These substances have the task of coloring the toner and making it more visible. Besides. they sometimes influence the polarity of the toner in a known way. In principle, all in the Color Index, Volume I and II, 2nd edition, 1956, specified compounds can be used as dyes. Examples of this large number Suitable dyes are such substances as soluble alcohol nigrosine (CI. 50415), Hansa-Gelb G (CI. 11680}., Chromogenic black ETOO (CI. 14645), Rhodamine B (CI. 45170), Solvent Black 3 (CI. 26150), Fuchsin N (CI. 42510) and C.I. Basic Blue 9 (CI. 52015).

The following examples are intended to explain the invention in more detail. example 1

2500 g of a technical iron powder (Glüden Iron 388, Glidden-Durkee Div. SCM Corp.) were poured into 1500 ml of a 2N sulfuric acid solution over a period of 10 seconds. The iron powder used had such a particle size

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that it passed through a 0.104 mm (140 mesh) mesh screen and was retained in a 0.088 mm (170 mesh) mesh screen. The resistance of the iron support, which was determined as indicated above according to a customary resistance test, was 2400 ohms. After the iron had been added to the sulfuric acid, the mixture was stirred for a further 60 seconds, after which the reaction mixture was diluted to 4000 ml with cold tap water. The mixture was allowed to settle for 10 seconds and then the brown liquid above was decanted off along with a substantial amount of black, greasy foam on the surface. The washing by decanting was repeated an additional 8 rcal with 2000 ml of water. After each addition of wash water, the slurry was stirred so as to briefly suspend all of the iron powder. After suspension, the powder was allowed to settle and the above liquid was again decanted off along with suspended dirt and other undesirable materials. After the last wash with Kasser, the iron was dehydrated and washed 4 times with 600 ml of anhydrous methanol, carefully stirring after each addition and decanting after a settling period of 10 seconds. After the final washing with alcohol, the dehydrated iron was sucked off in a Buchner funnel and the moist powder obtained was dried in a thin layer (0.16 cm or less) on a glass plate. The powder was continuously mixed while drying under the action of heat from two 250 watt infrared lamps placed about 45 cm from the powder. The two infrared lamps provided enough heat to prevent the powder from cooling down too much due to the evaporation of the remaining methanol. The ambient air had a temperature of about 21 ⁰ C and a relative humidity of less than 40 tons. After drying, the resistance of the powder was measured according to the general test method outlined above

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it was 16 ohms. The dry powder weighed 2468 g, so the total loss of dirt, surface oxide, Pyrite and very finely divided iron powder decanted off during washing, approx. 1.3%. One in which from the starting product Removed impurities attracted only a small amount of material, which implies that only very little of the decanted material was iron. .

Two magnetic brush developer compositions were then prepared, one made from with. Acid washed iron and another ir.it an equal amount of untreated starting material J, sYou two supports were each coated with 3 GeV / -% of a 'scnwarzen Styrolmischpolymerisattoners with a particle size of 1 to 5 microns mixed. The toner material charged positively on the carrier particles. The two developer mixtures were tested in a magnetic brush developer device. The device used for the test contained a cylindrical aluminum tube which was arranged so that it could rotate axially in a horizontal position about a fixed permanent magnet. The poles of the permanent magnet were oriented such that a magnetic brush was formed in the presence of magnetic particles on the top of the cylinder. In carrying out the test, this device was operated so that the magnetic brush was 15 minutes with a elektrophotograpliischen M recording material in contact, consisting of an electrically conductive layer support and a photoconductive layer of an organic photoconductor in a resin binder. The developer made using the untreated carrier particles had a strong tendency to leave a foam or deposit on the photoconductor with repeated use, while the developer containing the acid-treated carrier particles had very little tendency to foam. When the two carrier particles are in the same device ο use

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A toner tested was produced during the test in use the acid-treated carrier particles no visible deposits, while when using the untreated carrier particles a black layer was deposited which had a density of about 0.8. The two developer mixes an electrophotographic recording material was then used for this purpose, as described above, on the photoconductive layer develop an existing electrostatic latent image. The one containing the acid treated carrier particles Developer provided better image quality with more solid surface development and was less sensitive versus the changes in the electrical voltage applied to the magnetic brush.

Example 2

454 g of a high density electrolytic pilaster powder (Glidden 475, Glidden-Durkee Div. SCM Corp.) were quick with stirring in 250 ml of a 5% hydrochloric acid solution in one Cast 11 cups. The iron powder had such a particle size that it passed through a sieve with a clear mesh size of 0.25 mm (60 mesh) and from a sieve nit a clear 120 mesh was retained. Of the The resistance of this iron powder measured according to the above-described conventional resistance test was 640,000 ohms. The slurry of iron powder and hydrochloric acid Mixed continuously for 2 minutes, after which the reaction of the acid with the iron powder stopped. The acid treated iron was then four times by decanting with 70 ml of a 0.5ligen Washed solution of sodium nitrate in distilled water. After the final wash with Aassar, the iron was drained and washed twice with anhydrous ethanol. Then the

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Remove excess alcohol by filtering for 10 minutes using a Buchner light. The moist powder was dried quickly by repeatedly allowing it to trickle through a stream of dry air at a temperature of about 30 ^° C. and a relative humidity of less than 30%. The powder was completely dry in about 4 minutes. The yield was 450 g. After drying, the resistance of the acid-treated powder was measured, which was 0.2 ohms,

Thereafter, the acid-treated carrier particles were placed in the mechanical magnetic brush device described in Example 1. The device was operated for 15 minutes using the treated carrier particles. Thereafter, no visible foam was deposited on the electrophotographic recording material used. When an equivalent amount of untreated carrier material (comparison material) was used in the same test device, a deposit formed on the photoconductive layer of the electrophotographic recording material after 15 minutes, which had a density of 0.25, which was determined using a conventional densitometer. Thereafter, the acid-treated support and the comparative carrier xvurden each mixed with 5% servings of a blue toner powder, and again the conventional foaming d test subject * The developer prepared using the acid washed carrier particles showed only a small amount of foam, which barely visible whereas the comparative developer provided a large amount of easily visible foam. In addition, a large amount of toner was lost when the comparative developer was used, while considerably less toner was lost when the developer prepared according to the invention was used. The two developer compositions were then used to develop the electrostatic latent image on an electrophotographic recording material. The one containing the acid washed carrier

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- 24 -

Developer provided good image quality with excellent solid surface development both with and without bias on the magnetic brush. The comparative developer did produce a certain amount of image development, but the solid surface was developed very unevenly. The hue of the two developed images indicated that the image made with the comparative developer was less saturated than the image made with the developer containing the acid washed vehicle. Of the acid-treated carrier containing developer was then placed in an open 1 1 beaker and (about 2O ⁰ C and 45% RH) maintained under ordinary room conditions for 3 weeks. Thereafter, the resistance of the developer was measured. It was found that it had practically not changed from the resistance value determined at the beginning of the test. When this developer was re-examined when developing an image, the results obtained were essentially the same as when a freshly prepared developer described above was used.

Example 3

5 kg of spherical iron particles with a size such that they passed a sieve with a clear mesh size of 0.104 mm (150 mesh) and were retained by a sieve with a clear mesh size of 0.074 mm (200 mesh) were in 3: 1 ratio of 1:15 diluted, concentrated nitric acid of 20 ⁰ C poured. The mixture was slurried for 2 minutes and then diluted to 10 1 ^{with tap water from about 5 ° C.} The diluted mixture was allowed to settle for about 10 seconds and the above liquid and suspended impurities were decanted off. That

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originally black iron powder was nasli this acid treatment silver gray. The acid-treated iron was then washed 5 times with tap water at 2O ⁰ C and decanted, then the excess water was removed by aspiration in a Buchner funnel from the iron powder. The wet iron powder was spread into a plastic dish to a layer approximately 2.54 cm thick and allowed to dry. Four 250 watt infrared lamps were used to heat the powder while it was drying. During the drying process, the iron was constantly mixed, always maintaining an average depth of about 2.5 cm for the layer. As the powder dried, its color gradually changed to brown. The weight of the dry powder was 4986 g. After drying, the resistance of the powder was

9 6

measure and it was 2 10 ohms compared to 2.8 χ 10 ohms for the source material. Then became a hand-held one Bar magnet used to attract the treated substrate. The amount of des Determined carrier material, the magnet was cleaned and this process was repeated using the untreated Iron particles. It was found that the bar magnet was 5% by weight more treated carrier material than untreated Carrier material tightened. '

Thereafter, using the treated carrier and the untreated carrier (comparative carrier) developer compositions manufactured. Each developer contained 4% by weight of one black toner powder with an average particle size of 2 microns containing a nigrosine dye in a styrene polymer binder contained. Then the two developer compositions were in the mechanical method described in Example 1 Brush developing device used. The one with Developers containing acid treated carriers provided quality

009834/1714 _B ad original

Relatively good pictures, with excellent color fringing was achieved. In addition, when the developer containing the acid-treated carrier was used, a large one became Exposure width achieved. The comparative developer gave only a very limited exposure width and only a weak one Color fringing development.

Example 4

200 g iron powder in the form of flat iron platelets with a particle size such that they can clear a sieve with a Mesh size of 0.25 mm (60 mesh) passed and of one Sieve with a mesh size of 0.17 mm (80 mesh) were retained on the bottom of a glass tube with brought an inner diameter of about 3 cm and a length of about 60 cm. It became 1 l of a 1 oily trichloroacetic acid solution pumped up through the iron in the pipe. The solution was repeated four times over the course of 5 1/2 minutes Iron powder led. Before returning the solution, the suspended dirt and other impurities were in retained by a wool felt filter. Then the acid was replaced with cold tap water, which was then replaced by the Iron powder bed was passed through at such a rate that the undesirable small particles of contaminants were removed were removed without taking with them noticeable amounts of the screened carrier material. The flow rate of the Water was about 11 per 100 seconds. After 15 minutes of washing, the wet material was used to remove the excess Moisture transferred to a suction funnel. The upper end of the funnel was fitted with a plastic cap, to exclude air and nitrogen was introduced into this cap at such a rate that this cap was prevented from collapsing. After 30 minutes, the almost dry powder was taken out and

009834/1714

dried quickly over, by causing it to repeatedly trickle through a dry air stream of about 2O ⁰ C and a relative humidity of about 40%. The resistance of the end product, determined according to a customary test as described above, was 37 ohms compared to 1200 ohms for the starting material.

For the preparation of Entwicklerzusämmensetzungen, each "3 ^wt? Ö containing the black toner described in Example 1, equal amounts of the untreated and acid-treated carrier material used. In their ^ use in the development of electrostatic latent images * supplied both developer in A conventional magnetic brush developer developed solid surface development, but the developer with the acid-treated carrier with high electrical conductivity gave significantly better surface properties and was less sensitive to changes in the electrical bias of the magnetic brush than the control developer.

Example 5

1600 g of technical iron powder in the form of flat granules (Glidden Iron 412, Glidden-Durkee BiV. SCM Corp.) was obtained from fol- A

gender with. Was the iron powder starting material had a particle size such that it has a sieve with a mesh size of 0.25 mm (60 mesh) occurred and a sieve having a mesh aperture of O _1, 124 mm (120 mesh) retained: acid treated . However, the powder had an extremely large proportion (about 15%) of much more finely divided material. The starting material was placed on a plastic sieve with a mesh size of 0.124 mm (120 mesh) and ^{sprayed with an acid solution containing 200 ml of concentrated sulfuric acid and 3 liters of tap water at about 15 °} C. The iron was uniformly over an area of about 700 em distributed and at a rate of about 25 ml

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sprayed evenly with the acid through a plastic nozzle under a pressure of about 4.54 kg per second. The power of the spray nozzle helped separate the small contaminants and swim them through the plastic screen. The powder was then washed with a 0.2% hydrazine sulfate solution. After about 10 1 of washing solution had been sprayed over the iron, the material was dehydrated by spraying with 2 1 of isopropanol, anhydrous and dried in a dry air stream with a temperature of ettia 32 ⁰ C and a relative humidity of about $ 35. The speed of the air flow was adjusted so that it was sufficient to produce constant movement of the powder during drying. In addition, the iron was moved while it was drying by brushing it with a small brush. After the iron was completely dry, the air was deflated and hand brushing continued for 3 minutes to help screen out particles below 0.124 mm in size. Then the resistance of the treated material was measured. It was 7 ohms compared to 900 ohms for the starting material.

The carrier material was then mixed with 3% by weight of a yellow styrene-based toner which was negatively charged with respect to the iron carrier particles. The developing composition thus obtained was used to develop positively charged electrostatic latent images on an electrophotographic recording material. Excellent solid surface release was obtained, and the image obtained was of good quality with a bright yellow tint. A prepared using the same yellow toner and the iron carrier starting material compared developer of the fine particles had been sieved to reduce the number, provided images of high quality with essential Ichlechter

009834/1714

lent less brightening and considerably worse Saturation of the color shade * This loss of color gloss was on loose dirt and oxide on the surface of the control substrate attributed ^ to the toner mixed and transferred to the electrostatic image became. The comparative developer was also bad in that when he was much more sensitive to changes in the bias on the magnetic brush.

Example 6 *

'■■■ - ■' ■ ■ ■■ - ■ "'' ■■ i

2 kg of treated as in Example 1 were Bisen "coated t; .- '' by 30-minute electroless plating at about 95 ⁰ C in a bath of the following composition with a thin continuous Nickels.chieh .."

'-Nickel (containing> chloride NiCl ₂ .6H ₂ O 67.5 g

Sodium _{citrate Na 3} C ₆ H ₅ O ₇ · 2Η ₂ Ο 123.0 g

• ammonium chloride NH ^ Cl 75.0 g

2S ammonia solution 150.0 ml

Sodium hypophosphite NaH ₂ PO ₂ ⁸ H ₂ P 16.5 g

'' Water ad 1500 ml

The nickel placed powder was removed from the bath and ™ washed six times with cold water and three times with ethanol, suctioned off and dried at room temperature. The resistance of the dry powder, as determined by conventional resistance testing, was less than 0.5 ohms. The one coated with nickel Carrier was then used as in Example 1 to prepare a developer composition. Electrostatic latent images developed by the developer exhibited excellent solid surface whiteness.

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Example 7

700 g of a stainless steel iron powder having a particle size such that it passed through a sieve with a mesh size of 0.074 mm (200 mesh) and was retained by a sieve with a mesh size of 0.0044 mm (325 mesh) was as in Example 1 treated with acid using 500 ml of an aqueous sulfuric acid solution diluted in the ratio of 1s19, then ^{washed 12 times with 1500 ml of water of 38 0} G and decanted. After the final water wash, the remaining water was removed by placing the iron in a suspended cotton sack for 15 minutes. The iron was then transferred to a flat glass dish and dried with a stream of air at room temperature, keeping the thickness of the iron layer at about 1.25 cm and stirring the iron by hand with a spatula every 2 to 3 minutes. The iron turned gray as it dried. The resistance determined by conventional resistance measurement was 10 megohms compared to 22,000 ohms for the starting material.

The carrier obtained was used as in Example 1 for production a developer composition and used to develop an electrostatic latent image. Using this developer achieved good color fringing. A corresponding developer composition made using the untreated comparative carrier and the in Example 1 indicated toner produced neither good solid surface development nor good color fringing development.

009834/1714

2007Q03

- 31 -

Example 8

1 kg of iron powder, which was produced as in Example 3, was mixed with 300 ml of a 7% solution of photosensitive polyvinyl cinnamate resin in methyl cellosolve acetate. That Powder was spread on a glass plate and kept at room temperature dried. Then the dried powder was irradiated for 10 minutes with an arc lamp of 35 A, whereby during this time liurde constantly stirred in order to achieve an even To achieve exposure. This procedure was repeated four times, leaving four different 'resin coatings on each particle were achieved. Then by usual resistance measurement

1 the wid

fraud.

g 15 measured the resistance of the particles, which was greater than about 10 ohms

Using this carrier, as in Example 1, a developer composition was made and this was used to develop an electrostatic latent image. There were Excellent fringing developed over a wide exposure range Get pictures ,,

00983 U 1714

Claims (1)

Claims Process for the production of magnetically responsive carrier particles, for applying electroscopic clay on electrostatic charge patterns, characterized in that one a) iron powder dispersed by stirring in a dilute aqueous acid bath, b) the powder is removed from the acid bath again, c) by washing with water the powder from the acid residues freed, d) the powder forming an even, thin layer of iron oxide on the surface of each ''. Iron particle dries and e) if necessary, the particles of the iron powder with min- - * des least an even, thin coating of one iron-free material. 2. The method according to claim 1, characterized in that, Iron powder is used, the particles of which range from 60 to 600 microns in diameter. S. Process according to claims 1 and 2, characterized in that an aqueous © for the preparation of the acid bath Mineral acid solution used. 0098 34/1714 4. Process according to claims 1 to 3, characterized in that
contains. net that the IVasser used in stage c) is an antioxidant 5. The method according to claims 1 to 4, characterized in that the iron powder after washing with water with ^ a water-miscible organic solvent for
Removal, the remaining water is washed. 6. The method according to claims 1 to S, characterized in that · net that the iron powder is dried at a temperature above the .M dew point of the surrounding atmosphere. 7. The method according to claim 6, characterized in that the
Iron powder in air at a temperature of about 45 to
about 7O ⁰ C is dried. 8. The method according to claims 1 to 6, characterized in that that the iron powder in a practically oxygen-free Atmosphere is dried. . 9. The method according to claims T to 8, characterized in that the iron particles are optionally coated w.erden with at least% of a uniform thin shoulder of an electrically conductive, iron-free metal., 10. The method according to claims 1 to 8, characterized in that the iron particles optionally with at least
an even thin layer of an electrically ...
insulating polymer film are coated. 009834/1714