Developer composition and process for using same

© Start of patent term: May 15, 1974 Longest possible duration:

© Issued on: March 10, 1975 © inventor:

© dependence:

© Pamphlets considered to delineate the prior art:

US-PS 3 650 797 - 2 -

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The invention relates to imaging systems, in particular to improved electrostatographic developer materials, their preparation and use.

The formation and development of images on the surface of photoconductive materials by electrostatic means is known. The basic electrophotographic process is from CF Carlson in U.S. Pat. No. 2,297,691; it consists of applying a uniform electrostatic charge to a photoconductive insulating layer, exposing the layer to a light and shadow image so that the charge is selectively distributed on the exposed areas of the layer, and developing the resulting electrostatic latent image by: a finely divided electroscopic material is deposited on the image, which is commonly referred to as toner. The toner is normally drawn onto those parts of the layer which contain a charge to form a toner image corresponding to the latent electroscopic image. This toner image can then be transferred to a support surface, such as paper, where it is now permanently fixed by heat. Instead of forming the latent image by uniformly treating the photoconductive layer and then exposing this layer to a light and shadow image, the latent image can also be created by loading the layer directly into the configuration of the image. The powder image can be fixed on the photoconductive layer, if you do not want to transfer the powder image. Instead of the heat-fixing step, other suitable fixatives such as a solvent or coating treatment may be used.

There are many methods for applying the electroscopic toner particles to the latent electrostatic image to be developed. One development method is the "Cascade" development described by EN Wise in US Pat. No. 2,618,552. Hiebei the developer material, which consists of relatively large carrier particles, on the surface electrostatically adhere finely-dispersed toner particles, applied to the latent electrostatic image bearing surface or rolled over in cascades. The composition of the carrier particles is chosen such that the toner particles are triboelectrically charged to the desired polarity. As the mixture rolls in cascades across the image-bearing surface, in the positive development process, the toner particles are electrostatically deposited on the loaded portions of the latent image and held there while not being held captive by the unloaded or background portions of the image. The "cascade" development process has the distinct advantage that most of the toner particles randomly deposited on the background portion are removed by the rolling support. This is probably due to the relatively greater electrostatic attraction between the toner and the carrier as compared to the attraction between the toner and the unloaded background. The carrier particles and the unused toner particles are then reused in the cycle. The cascade development process is especially useful for the development of bar-type copies.

Another method of developing electrostatic latent images is the magnetic brushing method described, for example, in U.S. Pat. No. 2,874,063. Herein, a developer material containing toner and magnetically attractable carrier particles is carried by a magnet. The magnetic field of this magnet causes alignment of the magnetic carrier in a brush-like configuration. This magnetic brush is brought into contact with an electrostatic image-bearing surface, with the toner particles being drawn from the brush onto the latent image by electrostatic attraction.

Another method of developing electrostatic latent images is the "powder cloud" method described, for example, by CF Carlson in U.S. Pat. No. 2,221,776. Herein, a developer material containing electrically charged toner particles in a gas stream is passed along a surface carrying the latent electrostatic image. The toner particles are drawn from the gas onto the latent image by electrostatic attraction. This method is particularly suitable for continuous toner development.

Another development method is RW Gundlach's "Touchdown" method according to US Pat. No. 3,166,432. In this case, loaded powder is removed from the evenly dusted surface of a preferably transparent conductive material by means of an electrostatic field over a loaded and exposed selenium plate to form a slide.

The commercial electrostatographic development systems generally use automatic machines. Since automatic electrostatographic imaging devices are designed to operate with a minimum of maintenance costs, the developer used in these machines must be able to be recycled many thousands of times. Automatic xerographic devices typically use an electrophotographic plate which is loaded, exposed and then developed by contact with a developer mixture. In some automatic machines, the toner image formed on the electrophotographic plate is transferred to a receiver surface and the electrophotographic plate is then cleaned prior to reuse. The transfer is effected by a corona generating device which generates an electrostatic charge by which the powder is drawn from the electrophotographic plate to the receiver surface.

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The polarity of the charge required for image transfer depends on the visual form of the original copy relative to the reproduction, and also on the electroscopic properties of the developer material used for development. For example, if one wants to make a positive reproduction of a positive original, one usually uses a corona discharge of positive polarity to effect the transfer of a negatively charged toner image to the support surface. On the other hand, if one wishes to produce a positive reproduction from a negative original, one usually uses a positively charged developer material which is repelled from the loaded areas of the plate to the unloaded portions to form a positive image resulting from a corona discharge of negative polarity can be transferred. In any case, usually a residual powder image remains on the image after transfer. Since the disk is to be reused for the following cycle, it is required that the residual image be removed to prevent the formation of ghost images on the subsequent copies as well as the formation of a toner film on the photoreceptor surface. In a positive-positive reproduction, as described above, the residual powder is firmly retained on the plate surface by a phenomenon which is not fully understood; hiebei the complete transfer of the powder is prevented on the support surface, in particular in the imaging areas. The incomplete transfer of toner particles is undesirable because the image density of the final copy is reduced and because strong rubbing cleaning procedures are needed to remove the residual toner from the photoreceptor surface. This imaging process is usually repeated on each copy which is reproduced by the machine during the life of the developer and the electrophotographic plate surface.

Various cleaning devices for electrostatographic plates are known, such as the brush "and" tissue "cleaning apparatus. A typical brush cleaning apparatus has been described by LE Walkup et al. In U.S. Pat. No. 2,832,977. The brush cleaning device generally consists of one or more rotating brushes, which remove the remaining powder from the plate and deliver it into an air stream which is blown off by a filter system. A typical tissue cleaning device is described by WE Graff Jr. et al. in U.S. Pat. No. 3,186,838. Hiebei the remaining powder is removed from the plate by passing a fabric of fiber materials over the plate surface. Another system for removing residual toner particles consists of a flexible cleaning blade which wipes the remaining toner from the photoreceptor surface. Scratches when moving the surface along the blade.

Unfortunately, the above cleaning systems are not quite sufficient to remove all types of toner particles from all types of reusable photoreceptors. This is not a fault of the cleaning system, but a defect of the special toner used with special photoreceptors. If special toners did not tend to adhere as a residual film to a particular photoreceptor, the described cleaning systems would be sufficient to remove all residual toner. However, many commercial toners inherently tend to form residual films on reusable photoreceptors. The formation of such films is undesirable because it affects the quality of the undeveloped and developed image. The problem of filming these particular toners is particularly acute in high-speed copying and duplicating machines, where developer-to-image surface contact is much more frequent and much faster than conventional electrostatographic systems. Finally, so much toner is built up that copying or duplication is compromised. As a result, more effective measures, such as solvent treatment, are needed to remove this film. Frequent shutdown of the apparatus for cleaning the photoreceptor surface is, of course, undesirable as the machine is taken out of service and repeated actions of this nature wear the photoreceptor surface.

There is therefore a constant need for a method by which the build-up of toner films on the surface of a photoreceptor is prevented. Electrostatographic systems, and in particular the imaging, development and purification of these systems would be significantly improved if the above problems could be effectively solved.

The invention relates to a developer composition in which the formation of toner films is avoided, thereby obtaining an improved print density of the solid districts and a reduced background density of the copies. The inventive processing composition has improved and stabilized triboelectric properties; it allows for long-term prevention of toner films on reusable photoreceptors. The new developer mass has a longer life, which means more prints per unit weight of developer. The processing composition of the present invention provides copies of relatively high optical density.

With these developer materials, the cleaning of reusable electrostatographic imaging surfaces is enhanced; these developer mixtures are readily transferable from an electrostatographic surface to a transfer surface. With the new developer masses one obtains pictures and copies without dissolution loss; Also, there is no reduction in meltability and less tendency for toner blocking. The developer compositions according to the invention increase the lifetime of the imaging surface cleaning devices.

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The electrostatographic developer material according to the invention is characterized in that it consists of the following particles: 1. a finely divided electroscopic toner material; Second a small amount (based on the weight of the toner) of a finely divided solid friction-reducing material whose hardness is lower than that of the toner material and whose friction-reducing properties are greater than that of the toner material, wherein the friction-reducing material has a greater tendency to form a thin adhesive film has a surface as the toner material when exposing a mixture of these materials to shearing force; and 3. a small amount (based on the weight of the toner material) of a finely divided, non-lubricating, abrasive material whose hardness is greater than that of the friction-reducing and toner materials, and optionally, a support material.

The developer composition according to the invention thus consists of at least three components, namely a toner material and two additives, u.zw. a friction reducing material and a finely divided abrasive material.

A preferred cyclic imaging and development process using the processing composition of the present invention is to form a latent electrostatic image on an image surface and develop that image by contacting the image surface with the inventive electrostatographic developer mixture followed by at least a portion the remaining developed image is removed from the image surface by a force which causes that the developer mixture wipes over at least a portion of the image surface; after which this procedure is repeated at least once.

Within the scope of the invention, the toner material used may be any electroscopic toner which is preferably pigmented or dyed. Typical toner materials are polystyrene resin, acrylic resin, polyethylene resin, polyvinyl chloride resin, polyacrylamide resin, methacrylate resin, polyethylene terephthalate resin, polyamide resin and copolymers, and mixtures thereof. Vinyl resins having a melting point or melting range beginning at at least about 43 ° C are particularly useful for use as the toner of the present invention. These vinyl resins may also be homopolymers or copolymers of 2 or more vinyl monomers. Typical monomeric units that can be used to form vinyl polymers include styrene, vinylnaphthalene, mono-olefins such as ethylene, propylene, butylene, isobutylene, etc., vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate, etc., esters of α Methylene-aliphatic monocarboxylic acids such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, dodecyl acrylate, N-octyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, etc .; Vinyl ethers such as vinyl methyl ether, vinyl isobutyl ether, vinyl ethyl ether, etc .; Vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, methyl isopropenyl ketone, etc .; and mixtures thereof. Suitable materials for toners usually have an average molecular weight of about 3,000 to 500,000.

Suitable pigments or dyes may be used to color the toner particles. Such toner dyes are known, for example, carbon black, nigrosine dye, aniline blue, calco oil blue, chrome yellow, ultramarine blue, du Pont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green oxalate, lamp black , Rose Bengal and mixtures thereof. The pigments or dyes should be present in the toner in a sufficient amount so that it is highly colored and forms a clearly visible image on the receiving device. For example, if one wishes to prepare conventional xerographic copies of typed documents, the toner may contain a black pigment, such as carbon black or a black dye, eg, Amaplast Black Dye (National Aniline Products, Inc.). It is preferable to use the dye in an amount of about 1 to 30% by weight based on the total weight of the colored toner. If a dye is used to dye the toner, substantially smaller quantities are sufficient.

For the use of the toner material of the present invention in the above development processes, the toner should have an average particle size of less than 30 μ.

The solid friction lubricating additive used in the present invention is a material which can form a thin adhesive film on the image surface of a reusable photoreceptor during repetitive cycles of an electrostatographic system. This material does not need to form a completely continuous film on the image surface; however, many of these materials form a continuous film. Other friction reducing materials tend to fill the valleys of the surface, while small hills are coated with only a monolayer of the friction reducing material. This material must have such properties that it is deposited on an image surface more easily than the toner material used. The hardness of the friction reducing material undoubtedly depends on its ability to form a deposit or film on the image surface. The friction-reducing material must therefore be softer than the toner material. All conventional standard hardness tests can be used to determine if a selected friction reducing material is softer than the toner material of interest. If you use eg the Shore durometer Α, B, C or D hardness scales according to the method ASTMD-1706, one can use any material which has a lower hardness than the selected toner, provided that it also has the other properties recorded below , The melting point of the friction reducing additive is essentially limited by the temperature of the environment when copying; it should be at least slightly higher than this temperature.

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The friction-reducing material must also have greater friction-reducing properties than the selected toner material. Any dynamic method can be used to determine the relative friction reducing properties of the selected friction reducing material as compared to the toner materials. In general, the test is only a comparison of the friction reduction caused by the friction reducing material as compared to the toner material, by bringing both materials into relative motion between two contacting surfaces. The. Materials of contacting surfaces should be quite flat; each of these materials should also have a kinetic coefficient of friction greater than that of the friction-reducing material and the toner material.

A useful procedure is as follows: A blade of rubbery material is passed over image bearing surfaces which have been treated with the materials to be tested, whereupon the relative coefficients of friction of the applied materials are determined.

A blade holder and a carriage mechanism are used together with a support for the image surface. The blade is a strip of commercially available rubbery polyurethane (3.8 cm long, 0.16 cm thick and 1.27 cm wide). The strip end which is to come into contact with the image surface is trimmed or beveled at an angle of 60 ° to the horizontal. The blade is held so that the chamfered side is turned away from the transverse direction of the blade. It is held in a wiping (not chiseling) position at an angle of 22 ° to the image surface. The image surfaces are selenium coated aluminum plates (about 30 X 35 cm). The coefficient of friction is determined using an Instron ™ type of instron (Instron Coporation, Canton, Massachusetts), which is connected to the blade holder carriage. The force required to pull the carriage alone is determined and then subtracted from the force needed to pull the carriage and move the blade across the image surface. This provides the kinetic frictional force needed to pull the blade alone. The normal force for moving the blade across the image surface is determined with a force meter. The kinetic force divided by this value gives the kinetic friction coefficient.

It determines the coefficient of friction for as many selenium plates as materials are to be investigated. Any plate with a value that deviates from the mean of more than 10% is discarded. For each material to be examined, another plate and blade are used, each plate being treated in the same way with the material to be examined. The same amount by weight of the material is used when applied to the plates.

In this way, one skilled in the art can determine the friction-reducing properties of selected materials as compared to toner materials. Specific examples of the materials tested are given below.

The friction-reducing materials must also have a sufficiently high resistance so that they do not disturb the latent image on the image surface.

Typical friction reducing materials having the above properties are, for example: saturated or unsaturated, substituted or unsubstituted fatty acids, preferably having from 8 to 35 carbon atoms, or metal salts of such fatty acids; Fatty alcohols corresponding to these acids; monohydric and polyhydric alcohol esters of these acids and corresponding amides; Polyethylene glycols and methoxy-polyethylene glycols; Terephthalic acid, isophthalic acid, 2,5-dimethyl terephthalic acid; 2,5-dichloroterephthalic acid; p-phenylenediacrylic acid; Anisic acid, terephthalaldehyde, metal terephthalates, eg, sodium terephthalate; Cholesterol; Dechloran, ie perchloropentacyclodecane, polycaprolactone with one mole. less than about 4000, and low molecular weight fluorocarbon compounds, eg, the waxy, short chain telomeres of tetrafluoroethylene, low molecular weight, lubricious polytetrafluoroethylene powders, etc. The metal salts of the abovementioned fatty acids are, for example, the salts of lithium, sodium, potassium, copper, rubidium, silver, magnesium, calcium, zinc, strontium, cadmium, barium, mercury, aluminum, chromium, tin, titanium, zirconium, lead, manganese , Iron, cobalt and nickel and mixtures of these salts. Ammonium and substituted ammonium salts of the fatty acids are also useful. Specific fatty acids include, for example, caprylic, pelargonic, capric, undecane, lauric, tridecane, myristic, pentadecane, palmitic, margarine, stearic, arachidic, beehive, lignocerin, cerotic acid and Mixtures thereof. Also, the corresponding solid fatty alcohols, esters, amides, derivatives thereof and mixtures are useful.

Special mono- and polyhydric alcohol esters of fatty acids are derived from Cj to C₂ o-alcohols, which form esters with fatty acids, which are solid under the intended conditions of use. Mention may be made, by way of example, of methanol, ethanol, propanol, etc. Alcohols or alkylenediols and triols having 2 to 10 carbon atoms which are at least partially Ce to C;_3SFatty acids are esterified. Specific examples are methyl stearate, ethylene glycol monostearate, glycerol tri (12-hydroxy stearate), 1,2,4-butanetriol tristearate, etc.

The polyethyleneglycols and methoxy-polyethyleneglycols are condensation products commercially available under the name Carbowaxe; they are solid, wax-like materials with one

Mol Wt. up to about 6000.

If one uses a development machine containing a friction reducing material for general

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Copying purposes, it will be noted that this additive is excessively built up on the image surface in approximately the same manner as is otherwise the case with the toner without additive. This construction takes place particularly in high-speed copying and duplicating machines, where the contact between the developer and the image surface is much more frequent and faster than with conventional electrostatographic systems. It has been found that excellent performance is achieved with the use of a relatively hard, finely divided, non-lubricious abrasive together with the friction reducing material.

It is believed that a friction reducing material of the above type, when used as the sole developer additive, forms a lubricating film on the image surface very easily, virtually eliminating a toner film. This lubricating film not only allows effective removal of the residual toner material, but also increases the life and effectiveness of the cleaning device used to remove residual developer. However, with the use of the friction reducing material, it builds up to an extent that the quality of the copies is gradually reduced. By adding a small amount of finely divided, non-lubricious, mild abrasive to the developer composition, a control of the build up of the friction reducing material due to the abrasive action of that material is obtained when a cleaning device removes the residual developer from the image surface with a force which causes the developer mixture to wipe over at least causes a part of the image surface. This combination of additives results in the friction reducing material exerting its function while the abrasive prevents the build up of an excessive interfering layer of the lubricant. In addition, the proper triboelectric difference between charge agents, eg, carrier particles, and the toner material is at least stabilized as the abrasive material prevents this disappearance of toner from depositing on the charge agents.

Suitable abrasives are, for example, colloidal silica, surface-modified organophilic silica, aluminum silicate, surface-treated aluminum silicate, titanium dioxide, aluminum oxide, calcium carbonate, antimony trioxide, barium titanate, calcium titanate or strontium titanate, CaSiC> 3, MgO, ZnO, ZrO₂ etc. and mixtures thereof.

Particularly preferred materials are those whose surface is modified to have hydrophobic properties. For example, hydrophobic silicas are obtained by treating freshly prepared colloidal silica with at least one organic silicon compound bearing hydrocarbon groups and hydrolyzable groups on the silicon atom. In such a process, the reactants and steam are added pneumatically in parallel stream to a fluidized bed reactor heated to about 400 ° C. The organic silicon compounds react with silanol groups on the surface of the SiO₂Particles, and there is a chemical link between the silicon atom of the organic silicon compound and the silicon atom of the SiO₂ via an oxygen atom. Any suitable hydrocarbon or substituted hydrocarbon may be used to prepare modified silicas wherein the organic group is directly linked to a silicon atom of the organic silicon compound. Preferably, such organic groups are used which impart hydrophobic properties to the abrasive material to improve the stability of the developer material under varying humidity conditions. The organic groups may be saturated or unsaturated hydrocarbon radicals or derivatives thereof. Saturated organic groups are methyl, ethyl, propyl, butyl, chloropropyl and chloromethyl. Examples of typical organic silicon compounds are dimethyldichlorosilane, trimethylchlorosilane, methyltrichlorosilane, vinyltriethoxysilane. The nature of the organic groups can influence the triboelectric properties of the developer. For example, silica treated with aminopropylsilane can be used to make inversion type developers.

The particle size of the abrasive additives is less than 1 μ and is about 1 to 500, preferably 10 to 100 mju.

As for the relative hardness of the abrasive, the material must be harder than the toner material and the friction reducing material. Most of the materials mentioned can be described as very hard materials in the sense of the Mohs hardness scale. However, it is also possible to use material of lower hardness than talc according to the Mohs hardness scale, as long as it is harder than the toner material and the friction-reducing material. Materials softer than talc are commonly classified by the Shore Durometer Penetration technique and classified into the A, B, C, and D scales of this method.

The chemical composition of the abrasive additive is not critical so long as it does not introduce harmful contaminants or adversely affect the imaging and developmental aspects of an electrostatographic system. Also, the shape of each abrasive particle is not particularly critical since both circular and irregular shaped additives are effective. Preferred materials are Aerosil R 972, a hydrophobic silica from DeGussa Incorporated, New York, and Kaophil-2, a hydrophobic aluminosilicate from Georgie Kaolin Company, Elizabeth, New Jersey.

The composition according to the invention is found in all known electrostatographic

Development systems use, eg in systems with a carrier material, such as the magnetic

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Brush development and cascade development, as well as in systems that do not necessarily require a substrate, such as powder cloud development, fiber brush development, and touchdown development.

Suitable coated and uncoated carrier materials for cascade development are known. The support sections are made of any suitable solid material, provided that the support particles have a charge of opposite polarity to the toner particles when brought into contact with the toner particles so that the toner particles adhere to and encase the carrier particles. If a positive reproduction of the electrostatic image is desired, the carrier particles are selected such that the toner particles have a charge of opposite polarity to the electrostatic image. If one wants a reverse reproduction of the electrostatic image, one selects the support so that the toner particles have a charge of the same polarity as the electrostatic image. The materials of the carrier particles are therefore selected according to their triboelectric properties in comparison to the electroscopic toner; when mixed or contacted, one component of the developer positively charges when the other component in the triboelectric series is below the first component, but charges negatively when the other component in the triboelectric series is above the first one Component stands. By suitable selection of the materials according to their triboelectric properties, such polarities of their charge are achieved during mixing that the electroscopic toner particles adhere to and coat the surface of the carrier particles; The toner particles also adhere to the part of the electrostatic image-bearing surface which has a greater attraction for the toner than for the carrier particles. Typical supports include steel, flint shot, aluminum potassium chloride, Rochelle salt, nickel, potassium chlorate, granulated zircon, granular silica, methyl methacrylate, glass, etc. The supports may be used with or without coating. Many of the foregoing and other typical supports are described in U.S. Pat. No. 2,618,552. Preference is given to finished coated particles having a diameter of about 50 to 2000 μ, because the carrier particles then have a sufficient density and inertia, so that adherence to the electrostatic images during the cascade development is avoided. Adhesion of carrier beads to electrostatic drums is undesirable because of the formation of deep scratches on the surface during image transfer and drum cleaning. Also, it causes damage to the print when large carrier beads adhere to the xerographic imaging surfaces. For magnetic brush development, carrier particles having an average particle size of less than about 800 μ are sufficient. In general, satisfactory results are obtained when about 1 part of toner with about 10 to 1000 parts by weight of carrier is used in cascade and magnetic brush development.

Regarding the broad relative Megen ratios of the toner material compared to the additional materials, the following should be said: The friction-reducing material should be present at least in such an amount that during the cyclic use of the image surface at least 20% of the same are provided with a uniformly distributed adhesive layer of the material , Preferably, about 100% of the image area is coated with the friction reducing material. It has been found that about 0.01 to 10% by weight of the friction reducing material (based on the weight of the toner material) is sufficient to achieve such coverage. A particularly preferred proportion is about 0.1 to 2% by weight of the friction reducing material (based on the weight of the toner).

The abrasive material must be present in a relative amount such that the thickness of the friction-reducing film remains below 1 μ (ie, less than 10,000 Å), so that a spurious film is avoided. However, the amount should not be so large that the friction-reducing film is removed or its formation is prevented. If the amount is so large that no film is formed, the mild abrasive will act directly on the photoreceptor, and in prolonged use, this will shorten the life of the photoreceptors and the detergents used in this system. As long as there are about 5 Å of the friction-reducing material as the lower limit on the image surface, the advantageous effects of the invention occur. The person skilled in the art can easily determine the optimum proportions of the two additives by observing the thickness of the remaining friction-reducing film. The use of radioactive tags in the pitch reducing material is an effective means of optimizing the proportions. Long-lasting comparative experiments are also instructive. In general, from about 0.01 to 10% by weight of the abrasive material (based on the weight of the toner material) gives the desired results; particularly preferred are about 0.1 to 2 wt .-%.

The toner compositions of this invention can be used to develop electrostatic images on any suitable electrostatic latent image bearing surface, eg, in conventional photoconductive surfaces. Known photoconductive materials are glassy selenium, organic or inorganic photoconductors embedded in a non-photoconductive matrix, organic or inorganic photoconductors embedded in a photoconductive matrix, etc. Such photoconductive materials are described, for example, in the following patents: U.S. Pat. Nos. 2,803,542 (Ullrich), No. 2,970,906 (Biby), No. 3,121,006 (Middleton), No. 3,121,007 (Middleton), and No. 3,151,092 (Corrsin).

U.S. Patent No. 2,986,521 (Wielicki) discloses a reversal type electrostatic printing developer; it consists of electroscopic material, ie a toner, with

-8No.321106 a finely divided colloidal silica is coated. The toner material must 1. have a positive triboelectric ratio to the silica and 2. the silica-coated toner must be repelled by the negatively charged particles of the image surface. The only effective stated

The purpose of the silica is to reduce the stickiness and to improve the free-flowing properties of the developer powder.

It is stated in British Patent No. 1,172,839 that by adding a small amount of a hydrophobic metal salt of a fatty acid to an electrostatic developer, certain problems associated with the use of known toner and support materials are overcome. Among these problems is the tendency of the toner to form undesirable deposits which affect the quality of the copies and the storage time friction effects of the carriers and some toners. The metal salts of fatty acids can overcome these problems; however, it has been observed that excessive deposition of the metal salts also results in reduction of copy quality.

U.S. Patent No. 3,552,850 (Stephen F. Royka et al.) Teaches that a dry lubricant can be used when using a blade cleaner in an electrostatographic imaging system. However, this patent does not specify how to control the harmful deposit of the dry lubricant.

The following examples describe the preparation of the developer systems according to the invention and their use in development and purification processes. Unless otherwise indicated, parts and percentages are by weight. The examples show various preferred embodiments of the invention, examples 1 and 2 being comparative examples.

Example 1: The glass selenium drum of an automatic copying machine is positively charged to about 800 V using a corona generator, then exposed to a light and shade image to form a latent electrostatic image. The selenium drum is rotated by a magnetic brush development station.

A control developer consists of two parts of toner containing a polystyrene resin and about 100 parts of steel carrier beads. The toner particles have an average particle size of about 12 μ, the carrier beads of about 125 μ. After the latent electrostatic image has been developed in the developer station, the resulting toner image in the transfer station is transferred to a paper sheet. The remaining toner particles left on the drum after passing through the transfer station are removed by three different methods. In any case (also in the following examples) a clean selenium drum is used.

The first method uses a cylindrical polypropylene (15 denier) brush with a diameter of about 10 cm, with a pile height of about 6.45 cm and a fiber density of about 54000 fibers / 2.5 cm², The brush is located on the drum so that the fiber interference is about 0.25 cm, and is rotated at about 175 rpm. The quality of the copies is first excellent; however, after 25000 copies, the background density is very high, the resolution is considerably reduced, the image fill as a whole and the line copy as well as the corner sharpness are poor. Visiting the drum you will see slight signs of wear and a considerable build-up of toner on the surface.

The second method uses a cleaning fabric according to U.S. Pat. No. 3,186,838 (WP Graff, Jr. et al). Hiebei use a nonwoven fabric of rayon fabric, which under a pressure of about 1.26 kg / cm² in contact with the cable drum; the relative speed between tissue and photoreceptor is about 3.8 cm / sec, the distance from the tissue contact to the arch is about 0.32 cm. Repeating the copying process 5000 times, the copies show a good line contrast and little background precipitation. However, large, solid areas have a washed-out appearance. A micrographic examination of the drum surface shows that a considerable toner film has built up.

The third method uses a squeegee to remove residual toner. A rectangular 0.16 cm thick strip of rubbery polyurethane material, one end of which is chamfered so that the cleaning end forms an angle of about 60 °, is mounted parallel to the drum axis. The beveled end of the blade is held in chisel attitude (not wiping) with respect to the moving drum. The resulting vertical force needed to press the entire blade against the drum surface is about 1.4 kg (read on a spring balance). The first copies initially show good qualities in every respect; after about 2000 copies, however, the image quality is significantly worse, it shows a high background density, low image filling and a reduced resolution. Examination of the drum reveals a considerable buildup of toner on the image surface.

In the foregoing, the problem is exhibited that occurs with the use of a typical toner material, which by its nature tends to crack open on the photoreceptor. The increasing structure is undoubtedly the main cause for the reduction of the copy quality.

Example 2: The development process according to Example 1 is repeated, but the developer is modified in the following manner: About 0.1 part of zinc stearate with a particle size of approximately 0.75 to 40 μ becomes

-9No.321106 mixed gently with a part of toner. The resulting mixture is thoroughly milled for about 10 minutes in a Szegvari® processor. After transferring the developed image as in Example 1, the doctor blade and the method are used as in Example 1, but the blade force is 0.09 kg. After about 2000 cycles, the copies have high density and high background precipitation. The surface of the selector drum shows a thick film. The deposited film consists of either zinc stearate or a combination thereof with toner.

By increasing the blade force applied to the photoreceptor drum to about 1.4 kg, the copy quality remains good over 2000 cycles.

This example shows that by using a friction reducing material, namely zinc stearate, in the processing composition, along with cleaning devices that provide adequate cleaning power, the build-up of harmful films can be effectively controlled.

In the following examples, it is shown that using a mild abrasive together with the film-forming lubricant gives copies of exceptionally high quality, whereby the structure of the film can be more effectively controlled.

Example 3: The development process according to Example 1 is repeated, but the developer is modified in the following way: The toner according to Example 1 is mixed with 0.25% zinc stearate and ground for 10 minutes in a Szegvari-Verreiber. Subsequently, 1.0 wt .-% of a pretreated silica whose particle size is less than 1 μ, and mill for a further 10 min. The pretreated silica particles are obtained by decomposition of pure silicon tetrachloride by flame hydrolysis in the gas phase, u.zw. in an oxygen-hydrogen flame of about 1100 ° C, and subsequent reaction with dimethyldichlorosilane in a heated fluidized bed reactor. About 75% of the silanol groups present on the surface of the freshly prepared silica particles react with the silane in the fluidized bed reactor. The silica particles have about 3 silanol groups per 100 Ų their surface before the reaction with the silane. The analysis of the final product gives 99.8% SiO₂, the remainder consists of carbon, chlorine, heavy metals, Fe₂O₃, Al₂O₃, TiO₂ and Na₂O₃, The particle size is between about 10 to 30 mp, the surface is about 90 to 150 m²/G.

The relative coefficient of friction of the various materials is determined by the methods described above and has the following values: selenium 5.23, toner 3.92, zinc stearate 0.67. The toner has a Shore durometer hardness of more than 100 (on the A and B scale), zinc stearate 66 (on the A scale), and 52 (on the B scale). The pretreated silica has a hardness of about 5 on the Moh's scale. After transfer of the developed image as in Example 1, the cleaning method with the doctor blade according to Example 1 is used, using a blade force of about 1.4 kg. After 2000 cycles, the copies are characterized by the same exceptionally high image quality as the original copies. Examination of the selenium drum shows that the deposited film is less than 300 Å thick.

Example 4: The procedure according to Example 3 is repeated except that a two-component additive consisting of 0.25% of a cadmium stearate (particle size 10 to 20 μ) and 1.0% of kaophile 2 (a commercially available hydrophobic aluminum silicate, particle size 200 m / Z) is used. The coefficient of friction of cadmium stearate is 0.25, the Shore Durometer hardness is 78 (on the A scale) and 66 (on the B scale). After 2000 cycles, this developer provides copies that are of exceptional quality in every respect. The deposited on the photoreceptor film is at most 500 Å thick.

Example 5: The procedure according to Example 3 is repeated, but the two-component additive consists of 0.25% glycerol monostearate (particle size 2 to 14μ) and 1.0% of the pretreated silicon dioxide according to Example 3. The coefficient of friction of the glycerol monostearate is 1.57, the Shore durometer hardness on the A scale 67, on the B scale 31. After 2000 cycles, this developer provides copies that are of outstanding quality in every respect. The deposited on the photoreceptor film is at most 300 Å thick.

Example 6: The procedure of Example 3 is repeated, except that the two-component additive is 4.0% Carbowax 4000, (a commercial polyethylene glycol having an average molecular weight of about 4000 and a particle size of 2 to 14 μ) and 6.0 % Aerosil R 972 (a commercial material which is virtually identical to the pretreated silica of Example 3). The friction coefficient of the Carbowax 4000 is 1.63, the Shore Durometer hardness on the A-scale 95. The remainder of the developer remaining on the selector drum after passing through the transfer station is removed by a rotating cylinder brush and a vacuum system. After 2000 cycles, this developer provides copies of excellent quality. The deposited on the photoreceptor film is at most 700 Å thick.

Example 7: The procedure of Example 3 is repeated except that the two-component additive consists of 0.25% cholesterol and 1.0% Aerosil R 972. The cholesterol has a particle size of 5 to 140 μ, a coefficient of friction of 2.1, and a Shore Durometer hardness on the B-scale of 72. After 2000 cycles, copies of excellent quality are obtained. The deposited on the photoreceptor film is 300 Å thick.

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Example 8: The procedure of Example 3 is repeated except that the two-component additive consists of 0.25% PCL-150 (a commercial polycaprolactone of molecular weight about 4000) and 1.0% Aerosil R 972. The PCL-150 has a particle size of 2 to 140 μ, a coefficient of friction of 2.0 and a Shore Durometer hardness on the A-scale of 95. After 2000 cycles, this developer provides copies that are of outstanding quality in every respect , The film deposited on the photoconductor is at most 300 Å thick.

Example 9: The procedure of Example 3 is repeated except that the bicomponent additive consists of 0.25% Vydax (a low molecular weight, waxy, lubricious telomer of tetrafluoroethylene, EI DuPont, Wilmington, Delaware) and 1.0% Aerosil R 972. Vydax has a particle size of 2 to 100 μ, a coefficient of friction lower than that of the toner material, a Shore Durometer hardness of 72 on the B scale, and a Fp of 300 ° C. After 2000 cycles, this developer gives copies comparable in quality to those obtained in Examples 3 to 8. The rest of the film is at most 300 Å thick.

Example 10: The procedure of Example 3 is repeated except that the two-component additive consists of 0.25% terephthalic acid and 1.0% Aerosil R 972. The terephthalic acid has a coefficient of friction of 0.40 and a Shore Durometer hardness of 96 on the B scale. This developer gives copies after 2,000 cycles, the quality of which is similar to that of the copies in Examples 3 to 8. The rest of the film is at most 400 Å thick.

Example 11: The procedure of Example 3 is repeated except that the two-component additive consists of 0.25% perchloropentacyclodecane and 1.0% titanium dioxide. The perchloropentacyclodecane has a coefficient of friction of 1.0 and a Shore durometer hardness of 87 on the B scale. The titanium dioxide has an average particle size of about 30 πιμ. This developer gives copies after 2,000 cycles, the quality of which is similar to that of the copies in Examples 3 to 8. The rest of the film is at most 300 Å thick.

Example 12: The procedure of Example 3 is repeated except that the two-component additive consists of 0.25% stearyl alcohol and 1.0% antimony trioxide. The stearyl alcohol has a coefficient of friction which is lower than that of the toner; the Shore Durometer hardness is lower than that of the toner. The Antimontrioxydpulver has an average particle size of 100 ιημ. This developer gives copies after 2,000 cycles, the quality of which is similar to that of the copies in Examples 3 to 8. The rest of the film is at most 400 Å thick.

Example 13: The procedure of Example 3 is repeated except that the two-component additive consists of 0.25% zinc stearate and 1.0% untreated submicron silica having a particle size below 1μ. The silica is the same as in Example 3, but has not been pretreated to make it organophilic. The process is carried out at a relative humidity of about 80% and at an average temperature of about 24 ° C. The background density, resolution, image filling in line copies and the corner sharpness are good in the original copies. However, after about 900 copies, the background density has more than doubled, the resolution is reduced, the image filling in line copies and the corner sharpness are weak. The photoreceptor shows a dull, wet, clay-like film that can not be removed by conventional cleaning methods.

Performing the same procedure at a relative humidity of 30% and about 24 ° C yields excellent copies after about 2000 cycles, and no clay-like film is observed on the photoreceptor surface.

If the pretreated silicon dioxide according to Example 3 is used in the developer composition at a relatively high atmospheric humidity of approximately 80% and 24 ° C., the image quality remains excellent and no deposition of colloidal silicon dioxide is observed on the photoreceptor.

It is believed that the bulky untreated silica with its high surface area acts as a desiccant, with the water taken up by the additive being detrimental to the development and purification stages of the process in all respects. In a relatively dry atmosphere this is not observed.

Example 14: The procedure according to example 2 is repeated, but a development with reversal is used. Approximately 100 parts of 250μ diameter steel spheres coated with a blend of a copolymer of polyvinyl chloride and polyvinyl acetate with Luxol Fast Blue (a commercial dye) are mixed with a portion of a toner consisting of 65% polystyrene, 35 % Poly-n-butyl methacrylate and 10% carbon black. This reversal developer also contains (in addition to the zinc stearate of Example 2, 1.0% by weight of AljO₃ (based on the weight of the toner). The Αΐ₂Ο₃ has a mean particle size of 30 ιημ. An efficient development is achieved in the discharged parts of the image surface. After 1000 cycles, the copies are excellent in every respect. The remaining developer on the image surface is at most 3000 Å thick.

Example 15: The development process of Example 3 is repeated, but using

Place of zinc stearate 0.25% copper stearate. The friction coefficient of the copper stearate is lower than that of the

Toners, the Shore Durometer hardness is also lower than that of the toner. After 2000 cycles this delivers

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Developers Copies that are of good quality in every way. The film on the photoreceptor is not thicker than 300 Å.

Although specific materials and reaction conditions are shown in the above examples, these are only to illustrate the invention. Also, various other toner components, additives, dyes, carriers and development methods of the kind specified can be used to obtain the same results as in the examples described above. It is also possible to add further materials to the toner or carrier to sensitize, synergistically influence or otherwise improve the image properties or other desired properties of the system.