US3518969A - Development apparatus - Google Patents

Description

July 7, 1970 c. SNELLl-NG DEVELOPMENT APPARATUS Filed Feb. 23, 1968 INVENTOR. CHRISTOPHER SNEL ING BY MC 4117.

ES 6 ATTORNEYS United States Patent 3,518,969 DEVELOPMENT APPARATUS Christopher Snelling, Penfield, N.Y., assignor to Xerox Corporation, Rochester, N.Y., a corporation of New York Filed Feb. 23, 1968, Ser. No. 707,573 Int. Cl. B05b 5/00 U.S. Cl. 118637 4 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This invention relates to an imaging system and, more specifically, to an improved development system.

In electrostatic recording, as typified by the process of xerography, it is usual to form an electrostatic latent image on an insulating or photoconductive insulating surface generally conforming to the information to be reproduced. The resulting electrostatic latent image may then be developed or made visible by the application of elec trostatic marking particles which are deposited in conformity with the latent image to produce a visible record. In the usual embodiments of xerographic development, it is conventional to employ finely divided insulating materials, generally powders, which are presented to the image bearing surface in a particular manner. Thus, the electrostatic latent image is generally developed by cascading across the image surface a mixture of carrier head or granules and finely divided pigmented insulating electroscopic marking particles. Similarly, developer particles may be presented to the image bearing surface by means of a brush or brush-like fiber such as a fur brush or a simulated brush as in magnetic brush development in which instance a magnetic carrier material is used in conjunction with the developer particles. Insulating or conductive dust or liquid ink have also been presented to the latent image in an air suspension development process. Additional development techniques have been utilized such as the deposition of a powder by electrophoresis from dispersion in a liquid with a high electrical resistivity.

Although the above techniques have been found to be useful in the development of images depending upon the variations in electric field attraction there are several inherent disadvantages in their use. Generally, under normal operating conditions, the entire image bearing surface is contacted with the particular developer material. Such surface contact leads to a degradation of the image support member, as well as increasing tendencies to produce low density images having poor resolution characteristics, and, in addition, the surface must be cleaned of residual developer following each exposure step. Furthermore, it is generally necessary that the developer composition be continuously replenished so as to maintain a certain consistency in the density of the image reproductions.

SUMMARY OF THE INVENTION Therefore, it is an object of this invention to provide an imaging system which will overcome the above noted disadvantages.

It is a further object of this invention to provide a "ice novel imaging apparatus capable of producing high contrast, low background images.

Another object of this invention is to provide a novel development system capable of producing unlimited broad area coverage.

It is still a further object of this invention to provide a novel development system of high speed capabilities adaptable to both dry and wet development systems.

Yet, still a further object of this invention is to provide a novel development apparatus which is new and simplified when compared with previously known developing systems.

The foregoing objects and others are accomplished in accordance with the present invention, generally speaking, by providing a developer chamber having a first orifice located in the outer surface of its enclosure for introducing air in conjunction with a developer composition. Located within the inner cavity of the specific structure is a screen, the central axis of which coincides with the axis of the chamber enclosure and which is capable of rotating within the cavity. At a second location in the periphery of the chamber wall there is a hiatus to allow for the passage of developer material out of the chamber and onto the surface of an image support member which is passed in a manner so as to be tangent with the periphery of the developer chamber at the location of the discharge opening for the developer. Located within the inner area of the rotatable screen at a position opposite the opening for discharge of the developer material is at least one coronode unit which, in conjunction with the rotating screen, functions in the manner of a scoro tron. Developer material is introduced into the developing apparatus through the first orifice by way of an air blast and, as a result of the electric field established between the image support member and the rotating screen, the developer particles, which derive their charge from the coronode, will be directed to either the surface of the image support member or to the screen. The developer particles deposited on the screen will be subsequently reintroduced into the chamber by the air jet at the first; orifice and thus returned to the corona discharge environment. The developer particles introduced into the system may be in the form of resinous toner particles or in the form of a liquid whereby a mist would be generated at the orifice of the air knife.

The development system of the present invention, it has been determined, may be used in conjunction with various imaging modes depending upon the magnitudes and polarities of the screen, coronode and image support member potentials. Thus, the development apparatus of the present invention may be utilized in developing either the image or background areas of a xeroprint master or in conjunction with direct or reversal development of an imaged photoconductive plate. In addition, the apparatus herein described may be used as a means of depositing developer material on a particular substrate which may be utilized as a donor dispenser in subsequent development processes such as are described in U.S. Pat. 3,166,432. In addition, the development apparatus of the present invention provides a system of obtaining unlimited broad area coverage and may be utilized in conjunction with either liquid or powder developers.

DETAILED DESCRIPTION The invention is illustrated in the accompanying drawing which shows a diagrammatic View of the development apparatus of the present invention. Referring now to the illustration, there is seen a development apparatus generally designated 1 comprising a shield of cylindrical Walled chamber 2, rotatable screen 3 and coronode 4. Located in the surface of the shield 2 is an orifice 5 U which allows for the introduction of air and developer material into the inner-chamber. This orifice opening is herein designated as an air knife. At a second position in the outer surface of the cylinder 2 is found a second opening 6 through which the developer particles are subsequently discharged onto the surface of the particular image support member herein generally designated 10 and represented as a xeroprint master. Developer material in the form of powdered toner particles or atomized liquid is introduced by way of the air knife 5 into the inner chamber of cylinder 2. The resulting smoke-like disper sion in the case of the toner particles or mist in the case of the liquid developer passes into close proximity to the coronode 4 to which is applied a voltage in the range of from about 5 to about 10 kv. As a result of the field established between the screen 3 connected to voltage source 8 and the image support member 10, the developer particles, as a result of their imputed charge, will either be attracted to the screen surface or will pass through the interstices of the screen to the particlar image support member or master which is passed or rotated in close proximity to the discharge opening 6 in the periphery of the cylinder 2. Those particles which pass through the opening 6 will deposit and develop the image support member depending upon the respective magnitude and polarities of the several components within the system while those particles attracted to the screen will be re turned as the screen continues to rotate to the air knife 5 where the air jet will release the toner or resinous pigmented particles from the screen and introduce them back into the system. Thus, the unused developer particles are refluxed into the system.

The image support member used in conjunction with the present invention may take one of several forms. In one instance, as is represented in the instant illustration, the image support member 110 may comprise a substrate made up of conductive or substantially conductive material 11 supporting on its surfac in an imagewise configuration a dielectric or insulating material 12, the resulting configuration generally being referred to as a xeroprint master. When used in this capacity, any suitable substantially conductive material may be utilized as the support substrate. Typical materials include brass, aluminum, copper, conductive glass such as glass coated with conductive materials such as tin oxide, copper, copper iodide or similar materials, and metallized transparent films such as cellulose acetate, polyester materials such as Mylar, a polyethylene terephthalate commercially available from E. I. du Pont de Nemours Co., Inc. and

polycarbonates such as Plestar commercially available from General Aniline and Film. The particular dielectric material is such that it need only satisfy one requirement, that is, that its resistivity be substantially greater than that of its underlying conductive substrate. Thus, materials having resistivity at least about 10 ohms-cm. are

generally utilized. Typical dielectric materials are polyethylene, polyurethane, polyethylene terephthalate, and various ester materials such as a product known as KPR, a cinnamate ester commercially available from the Eastman Kodak Co.

The xeroprint master 10 will be precharged by any suitable technique such as the application of a corona charge by a corona discharge unit to the image support member such that a latent image 13 herein represented as a positive charge is formed on the insulating areas 12 of the image support member. The base substrate 11 is connected to ground as represented. With the charge 13 applied to the dielectric image 12 having a greater poten tial than that ap lied to the screen 3 by voltage source 8 the fields of force existing between the screen and the dielectric will be greater in the direction of the screen. Thus, the developer particles charged electrostatically by coronode 4 will be directed towards the screen when the charged dielectric image passes beneath the opening 6 and will be directed towards the background areas of the image support member or the support 11 when the latter is beneath the opening 6 to develop image 14 on the surface of the image support member. If the dielectric areas 12 are precharged to a negative polarity and the conductive support biased to a positive polarity then the dielectric image areas will be developed.

When the image support member is represented as a photoreceptor, any suitable photoconductive material may be utilized such as disclosed in U.S. Pat. Nos. 3,121,006 and 3,121,007. Typical photoconductor materials include doped polyvinyl carbazole, doped polycarbonates, selenium selenium-tellurium alloys, seleniumarsenic alloys, cadmium sulfoselenides, phthalocyanine compositions, and mixtures thereof. The doping agents utilized when necessary include 2,4,7-dicyano-trinitrofluorene and 2,4,7-trinitrofluorenone as well as other typical materials. When the photoreceptor member is used in conjunction with the present invention, the electrostatic latent image is formed by the conventional xerographic process as is disclosed in U.S. Pat. No. 2,297,691. Either the latent image or background areas are developed in a manner similar to that discussed above for the xeroprint master.

In addition to utilizing the apparatus of the present invention as a means of developing images, it may also be used to distribute developer particles on a dispensing member which itself is used in various sundry image development systems. Thus, in addition to the loading techniques disclosed in U.S. Pat. 3,166,432 such as powder cloud loading, cascade and liquid loading, the present apparatus may be utilized in a more controlled and discriminating process for preparing a donor dispenser which may be used in conjunction with a number of image development system such as are disclosed in the above cited patent.

The developer material utilized in conjunction with the present invention may comprise either finely divided pigmented resinous particles or atomized liquid developers. The resinous material of the present invention comprises finely divided pigmented particles having a particle size generally less than about 20 microns and preferably between about 5 to 15 microns in average particle size in order to obtain optimum results. The pigment is generally present in sufficient quantity so as to satisfy the development characteristics of the present invention. Typical pigments are: titanium dioxide, carbon black, for example, lamp black, channel black and furnace black, white lead, zinc oxide, calcium carbonate and various mixtures thereof. Desirably, the pigment is employed in an amount of least about 5 percent based on total weight of the resinous toner and generally between about 5 to about 10 percent to obtain optimum results. The particular pigment ingredient is used in conjunction with any suitable electroscopic toner or resinous powder. Typical toner materials are styrene polymers and copolymers including substituted styrene such as the Piccolastic resins commercially available from the Pennsylvania Industrial Chemical Corporation, phenol formaldehyde resins, acrylonitrile resins, polytetrafluoroethylene, as well as other similar type resins such as those disclosed in U.S. Pat. 2,788,288; 3,079,- 342; and Reissue 25,136.

When a liquid developer system is utilized, any of the conventional high resistance, low dielectric constant materials comprising a liquid carrier in combination with various dyes and pigments may be used. A liquid developer comprises a suspension of finely divided particles in a dielectric liquid. Any suitable organic liquid having a high volume resistivity, preferably at least about 10 ohms-cm. or greater and a low dielectric constant preferabl less than about 3.4 may be used. Typical liquids include aromatic hydrocarbons such as benzene, toluene and xylene; aliphatic hydrocarbons such as hexane, cyclohexane and heptane; halogenated hydrocarbons such as trichloroethylene or carbon tetrachloride, silicone oils and mixtures thereof. Other suitable saturated hydrocarbons include decane, dodecane, N-tetradecane, molten paraffin, molten beeswax and other molten thermoplastic materials, Sohio Odorless Solvent, a kerosene fraction commercially available from Standard Oil of Ohio, Isopar G, a long chain saturated aliphatic hydrocarbon commercially available from the Humble Oil Co. of New Jersey, and mixtures thereof. Typical opaque pigment particles which are utilized in conjunction with the above carriers include talcum powder, charcoal, aluminum, bronze, sulfur, pulverized resins of all varieties such as ordinary rosin, sealing wax, coumarone indene resin, treated pine resins sold under the trade name Vinsol resin and various other synthetic and natural resins.

When the liquid developer is used, it is presented in the form of a liquid mist or spray into the inner cavity of the chamber containing the rotatable screen. The liquid developer is introduced into the inner chamber at the air knife thereby atomizing the developer and producing a mist which drifts downward into the vicinity of the coronode in the form of minute droplets to be charged according to the potential and polarity applied to the coronode. In a similar manner the resinous developer particles discussed above are charged and utilized in the present system.

As stated above, various modes of operation are possible according to the magnitudes and polarities of the screen, coronode, background area and image area potentials. The outer chamber wall or shield 2 generally is biased with respect to the screen to prevent deposition on its inner wall and therefore limit deposition to the opening area 6. The screen is biased relative to the master to enhance deposition in image areas and inhibit deposition in background areas by virtue of the direction of electric field between the screen and the master surface. Thus, when desirable, a potential of from about 100 to about 1,000 volts may be applied to the surface of the shield with preferred operational voltages being in the range of from about 200 to 600 volts. The rotatable screen within the chamber will generally rotate at a surface speed of about 2 to about i.p.s. with maximum developer efiiciency being obtained in a range of from about 4 to about 6 i.p.s.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention is further illustrated in the following examples which are meant to represent and not limit the subject matter of the present invention. Parts and percentages are by weight unless otherwise stated.

EXAMPLE I An apparatus similar to the structure of the illustration with a stainless steel outer chamber wall and a brass screen rotata-bly mounted in the inner cavity of the chamber is utilized. A Corotron wire is longitudinally connected in a position about 2 cm. from the central axis of the configuration opposite the opening in the outer wall of the stainless steel shield through which'the developer material used in the system will subsequently pass. With the screen biased at a potential of about 700 volts toner particles comprising polystyrene are introduced by an air jet through the air knife orifice discussed above. A voltage of about +8 kv. is applied to the Corotron wire. As the particles descend by gravitational force to the vicinity of the Corotron wire, the toner particles take on a positive charge and are directed by the focusing effect of the resulting corona current towards the interstices of the screen which is rotating at a surface speed of about 6- i.p.s. In close proximity to the developer opening is passed a Xeroprint master comprising an aluminum substrate with a KPR image formed on the surface. A corona charge of about +200 volts is applied to the surface of the xeroprint master prior to its positioning beneath the developer discharge opening of the development apparatus. As the insulating areas of the image support member pass the respective opening the developer particles are repelled to the screen and held thereto to be returned to the air knife opening and be reintroduced into the inner cavity of the apparatus. When the background or conductive areas of the image support member are positioned beneath the developer opening the toner particles are attracted to the respective conductive surface and adhere thereto to produce the desired image. After development of the conductive areas of the xeroprint master, the latter is removed and contected with a paper transfer sheet with a corona charge of about 600 volts applied to the back side of the transfer sheet opposite in polarity to the charge on the toner particles. Thus, the developed image is transferred to the surface of a transfer copy sheet. The resulting image is then fixed in a conventional manner to the transfer sheet by the application of heat.

EXAMPLE II A process utilizing the apparatus of the present invention of Example I is repeated with the exception that the polarity of the charge on the imaging member is reversed. As a result of this change, the dielectric areas of the image support member are developed in a manner similar to that described in Example I. Thus, there is demonstrated the capability of reversal development.

EXAMPLE III Example I is repeated with the exception that a zinc oxide photoreceptor paper is utilized in place of the xeroprint master with a negative electrostatic latent image formed on the imaging surface thereof. Everything else being the same, the latent image of the photoreceptor is developed.

EXAMPLE IV The procedure of Example I is repeated with the exception that the image support member is replaced with a brass conductive substrate Which is to be subsequently used as a donor dispenser to develop an image at some remote location. In this instance, the conductive substrate is uniformly developed with the developer particles by means of the rotating screen ion stream development apparatus while the conductive brass substrate is connected to ground. The resulting donor dispenser produced is then contacter with a Mylar substrate which has a negative electrostatic latent image formed on its surface by corona charging through an image stencil. The Mylar substrate is superimpose on a conductive brass surface. With both the brass substrate of the donor dispenser and the brass substrate supporting the Mylar sheet being connected to ground, the toner particles are transferred from the donor dispenser to the Mylar substrate in an imagewise pattern conforming to the electrostatic latent image. This example demonstrates the use of a development apparatus of the present invention in a preparation of a donor dispenser which may subsequently be used in an imaging process at a remote location.

Although the present examples were specific in terms of conditions and materials used, any of the above listed typical materials may be substituted when suitable in the above examples with similar results. In addition to the steps used in the application and use of the development apparatus of the present invention, other modifications may be used, if desirable. For example, several coronode units may be installed within the inner chamber of the specific apparatus, if desirable. In addition, other materials may be incorporated in the shield or screen material, the developer materials, and other variations may be made in the apparatus which will enhance, synergize, or otherwise desirably affect the function of the apparatus of the present invention. For example, additional air jets may be introduced into the system to assist in the maintenance of the necessary dispersion of the particulate developer particles utilized in the system. In addition, it is to be noted that although the apparatus illustrated is in the form of a cylinder, it may take any suitable shape which will satisfy the requirements of the present invention. Thus, for example, the apparatus may take the form of an endless belt configuration.

Anyone skilled in the art will have other modifications occur to him based on the teachings of the present invention. These modifications are intended to be encompassed within the scope of this invention.

What is claimed:

1. A development apparatus comprising in combination: an enclosed chamber, means for introducing a developer into said chamber, means for imparting a charge to said developer, a rotatably mounted biased screen positioned within said chamber and means to discharge said developer from said chamber.

2. An image development apparatus comprising in combination an enclosed chamber having at least one opening in its outer wall for introducing air in conjunction with a developer, a rotatably mounted screen within the inner cavity of said chamber, the central axis of said screen coinciding with that of said chamber, a second opening in the surface of said chamber wall said opening providing a means for the discharge of said developer material, means for applying potential to said screen, and means for applying a potential to said developer material.

3. The apparatus as disclosed in claim 2 wherein said source of potential to said developer is located in a position opposite said developer discharge opening and lies in a plane which passes through the axis of said chamber and which is perpendicular to a plane tangent to the outer wall of said chamber at the location of said discharge opening.

4. The apparatus as disclosed in claim 2 wherein said source of potential to said developer is generated by a corotron wire.

References Cited UNITED STATES PATENTS 2,832,511 4/1958 Stockdale et a1. 1l717.5 XR 2,843,295 7/1958 Ricker 117-175 XR 3,263,649 8/1966 Heyl et al ll8637 3,357,403 12/1967 Donalies 118-637 PETER FELDMAN, Primary Examiner US. Cl. X.R. l1717.5

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