US3556050A

US3556050A - Liquid development apparatus

Info

Publication number: US3556050A
Application number: US739326A
Authority: US
Inventors: William Trachtenberg; Gene H Robinson; Orville C Rodenberg
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1968-06-24
Filing date: 1968-06-24
Publication date: 1971-01-19
Anticipated expiration: 1988-01-19
Also published as: GB1271750A; FR2011582A1; BE734994A; CH492241A; DE1931601A1

Abstract

A liquid developer is contained in a receptacle and a carrier having a latent electrostatic image thereon is guided through the liquid developer together with a development electrode for a distance sufficient to give a developed image of optimum density. In the several embodiments of the invention disclosed and described, the carrier is maintained in spaced relation to the development electrode and both are moved substantially in synchronism so that the developer therebetween is moved therewith at substantially the same linear speed as the carrier. By this arrangement with which the liquid developer is moved, a high degree of density uniformity and solid area coverage is obtained to provide an image of optimum density.

Description

United States Patent [72] Inventors William Trachtenberg;

Gene H. Robinson; Orville C. Rodenberg,

Rochester, N.Y. [21] Appl. No. 739,326 [22] Filed June 24, 1968 [45] Patented Jan. 19, 1971 [73] Assignee Eastman Kodak Company Rochester, N.Y. a corporation of New Jersey [54] LIQUID DEVELOPMENT APPARATUS Primary Examiner-Morris Kaplan Attorneys-William H. J. Kline, Robert F. Crocker and Lloyd F. Seebach ABSTRACT: A liquid developer is contained in a receptacle and a carrier having a latent electrostatic image thereon is guided through the liquid developer together with a development electrode for a distance sufficient to give a developed image of optimum density. [n the several embodiments of the invention disclosed and described, the carrier is maintained in spaced relation to the development electrode and both are moved substantially in synchronism so that the developer therebetween is moved therewith at substantially the same linear speed as the carrier. By this arrangement with which the liquid developer is moved, a high degree of density uniformity and solid area coverage is obtained to provide an image of optimum density.

PATENTED mu 9 I9?! SHEET 2 BF 2 DEVELOPER 1 REPLEN/SHER WILL/AM TRACHTENBE/il GENE H. ROB/NSOA ORV/LLE C. RODENBERC INVENTORS %4 fiz w 1 LIQUID DEVELOPMENT APPARATUS FIELD OF THE INVENTION DESCRIPTION OF THE PRIOR ART It is well known in the prior art to apply a liquid composition to the surface of a movable web of material by means of a saturated pad that is held in contact with the material, or by means of a cylindrical surface which carries a liquid composition from a reservoir to the surface of the material on which the liquid composition is to be applied. In each of such applicator arrangements, a pressure roll is usually necessary for maintaining the web of material in contact with the pad or cylindrical surface. It is also known in the field of xerography to move a web or carrier having latent electrostatic images thereon over an applicator, the liquid developer being applied under pressure against the surface of the carrier bearing the images. with any one of the aforementioned arrangements the liquid composition is often applied nonuniformly and/or with streaks which can vary in thickness.

In the field of xerography, the development of a latent electrostatic image on the surface of a photoconductive material can be accomplished by a process referred to as liquid development. This process uses a developer comprising an insulating liquid carrier in which charged toner particles are dispersed uniformly. In order to provide an optimum image, it is necessary that the toner particles be deposited uniformly throughout the image areas, thereby providing a legible image of uniform density. Such results have been attempted by the prior art through the use of a toner roller in a liquid developer followed by a set of squeegee rollers, a magnetic brush submerged in a liquid developer for achievingsolid uniform area development, application of a liquid developer to a continuous web of film, as well as plate applicators of the type mentioned above.

In all of the aforementioned devices for developing an electrostatic image by means of a liquid developer, the amount of toner in the developer can decrease to the point where the carrier has very few, if any, toner particles left for transfer to the material before being separated therefrom. As the rate of the development increases, that is the rate of movement of the xerographic material increases, the development efficiency falls off considerably rather than increasing. Since the spacing between the developer head and the image-bearing surface is very small, the developer liquid therebetween is easily and very quickly depleted of its toner particles. Another disadvantage of the developing devices mentioned above is the production of flow streaks in the finished print due to the depletion of the toner particles or their being collected at some downstream site. It is therefore desirable to provide a liquid developer device which will provide a developed image of maximum uniform density with no background deposits or flow streaks and which will give such results with a relatively high rate of movement of the carrier through the liquid developer.

.SUMMARY OF THE INVENTION are usually prevalent when a carrieris drawn over an applicator or through a liquid developer.

Still another object of the invention is to provide a device for the liquid development of latent electrostatic images on a carrier in which a development electrode is movable with the carrier andmaintained in a fixed spaced relationship thereto and is also movable in synchronism with the carrier through the developer'at a relatively high linear speed.

And yet another object of the invention is to provide a device for the liquid development of latent electrostatic images on a carrier which is at least partially immersed in the liquid developer and by which the liquid developer between the carrier and a movable development electrode in the developer is moved at substantially the same linear speed as the carrier.

A Other objects and advantages of the invention will be apparent to those skilled in the art' when the more detailed description thereof is read in conjunction with the accompanying drawings. I

The above objects of the invention are attained by a device comprising means for moving a carrier through a liquid developer in spaced relation to a developer electrode. The liquid developer is contained in a receptacle and the carrier is guided through the liquid developer together with a development electrode for a distance sufficient to give a developed image of optimum density. In the several embodiments of the invention disclosed and described hereinafter. the carrier is maintained in spaced relation to the development electrode and both are moved substantially in synchronism so that the developer therebetween is moved therewith at substantially the same linear speed as the carrier. By this arrangement with which the liquid developer is moved, a high degree of density uniformity and solid area coverage is obtained to provide an optimum density image. Further, since the liquid developer is moved with the carrier, the resulting developed image is free of any development or flow streaks.

DESCRIPTION OF THE DRAWINGS Reference is now made to the accompanying drawings wherein like reference numerals designate like parts and wherein:

FIG. 1 is a vertical sectional view through one embodiment of a liquid developer apparatus in accordance with the invention;

FIG. 2 is a vertical sectional view taken along line 2-2 of FIG. 1 and showing the structure of the drum for supporting the carrier and the development electrode;

FIG. 3 is a vertical sectional view through another embodiment of a liquid developer apparatus in accordance with the invention in which the length of the development path has been increased; and

FIG. 4 is a vertical sectional view through still another embodiment of the invention in which the length of the development path is determined by the spacing of several separate sets of drums and which discloses a system for drying the carrier after development of the image.

DESCRIPTIONOF THE EMBODIMENTS OF THE INVENTION With reference to FIGS. 1 and 2, a web or carrier 10 comprises a length of xerographic material having a photoconductive layer which hasbeen exposed and bears a latent electrostatic image. Such image is on the surface 11 of the carrier 10. A liquid developer 12 is contained in a receptacle 13 in which a drum 14 is rotatably mounted. Drum 14 comprises a core 15 and can be provided withflangcs 16 secured to said core as shown in FIG. 2. Core 15 is rotatably supported on a shaft 17 that is journaled in an extension 18 fixed to each of sidewalls 19 of receptacle 13. By means of a nut 20 and packing material 21, core 15 is scaled so that developer 12 cannot leak past shaft 17. Core 15 can be a conductive material, such as stainless steel, a plastic material, or a plastic material with its peripheral surface 22 covered with a metallic sleeve 23, as shown in FIG. 2. Flanges 16 can be of a metallic or a plastic material and provided with a shoulder 24 for supporting carrior 10. It may be necessary to electrically insulate core from flanges 16 if both are made of an electrically conductive material. As shown in FIG. 2, the width of the core 15 and the distance between the flanges 16 can be varied to accommodate any width of carrier 10. Also, the diameters of core 15 and shoulders 24 can be of a size as determined by the length of path and electrode spacing necessary to obtain proper development of the images. Carrier 10 is guided by an electrically grounded roll 25 for entry into liquid developer 12 and engagement with shoulders 24 of flanges 16. On leaving liquid developer 12 in receptacle l3, carrier 10 moves over an electrically grounded drive roll 26 which is driven by means of a motor 27 and a suitable coupling arrangement designated by the numeral 28. As drive roll 26 is rotated, carrier 10 causes drum 14 to rotate due to tension exerted thereon and the friction between the carrier and flanges 16. Both grounded rolls act to make electrical contact with the conducting layer of the web. At this point, it should be noted that the image bearing surface 11 of carrier 10 faces core 15 or sleeve 23 which serves as a development electrode. Drum 14 is substantially immersed in the liquid developer. Since the drum 14 and the carrier 10 are moved in synchronism, the liquid developer between the sleeve 23 and the surface 11 of the carrier is moved with the carrier and drum at substantially the same linear speed. The sleeve 23, or core 15 if it is made conductive, can be connected to a DC power supply 30 or grounded to provide solid area development. If the core 15 is of an insulating material and power supply 30 is disconnected, then fringe development of the images will result. The liquid developer 12 can be replenished from a reservoir 31 which can be manually operated or automatically operated in response to developer concentration and/or level. The distance between the peripheral surface of sleeve 23 or the core 15 and the surface 11 of the carrier 10 can be between 0.0050.l50 inch, a distance of 0.020'O.1OO inch providing an optimum spacing.

A strip of mm-wide xerographic material that was charged and contact exposed to a negative master was developed by the apparatus shown in FIG. 1. After development, the images were dried and fixed. Using the developing apparatus just described, images resulted which were free of streaking and trailing effects. Uniformity of development was very good and the maximum achievable density was about 2.00. The resolution capability of the developing unit was above 350 lines per millimeter and the spacing between the image surface and the electrode was about 0.080 inch.

With respect to FIG. 3 is a plurality of

drums

40, 41 and 42 are arranged substantially as shown in a receptacle 43 filled with a liquid developer 44. The drums 42 are substantially the same in structure as the one disclosed and described with respect to FIGS. 1 and 2. However, in place of a sleeve, an endless belt 45 is used as the development electrode and engages the peripheral surface of the core of each drum. Carrier having electrostatic images on the surface 51 thereof is threaded over the electrically grounded guide roll 52 and held thereby in contact with the drum 40, around the drums 41 and 42, again into contact with drum 40 with which it is held in contact on the opposite side by the position of electrically grounded drive roll 53. The drive roll 53 is driven by a motor 54 which can also be connected through a suitable coupling 55 to one of the drums 4042. A DC supply 56 is connected to one of the drums 4042 or to the belt 45. Also, a developer replenisher 57 can be provided for use as described above with respect to FIG. 1.

In the arrangement disclosed in FIG. 3, a longer development path is obtained with a constant size gap being maintained between the belt 45 and the carrier 50. The effective path length can be varied by changing the relationship of the drums 4042, or by changing the level of the liquid developer. Also, the gap between the photoconductor and the electrode can be changed by using flanges having a shoulder of the requisite diameter. By charging and exposing and then developing a strip of photoconductive material by the a paratus disclosed in FIG. 3, it was found that a maximum density of 1.3 resulted and characteristics of uniformity of development and freedom from streaking and trailing were as evident as in the embodiment disclosed in FIG. 1.

Another embodiment of the invention is disclosed in FIG. 4. in which a set of

rolls

70 and 71 guide and move a carrier 72 through a liquid developer 73 in a receptacle 74. In this embodiment, the carrier 72 is arranged with its surface 75, which bears the images, facing outwardly and toward a development electrode 76. A second set of rolls 77-78 is arranged in receptacle 74 and completely immersed in the liquid developer 73. The development electrode 76 comprises a flexible stainless steel belt which encompasses the

rolls

77 and 78. In this arrangement, the

rolls

77 and 78 are conductive and connected to a DC supply 79. On the other hand, rolls 70-71 are held at ground potential at all times. A motor 80 is connected through a suitable coupling 81 to one of the

rolls

70 or 71 and 77 or 78 to provide means for moving the carrier 72 and the belt 76 in synchronism. Since the rolls 7071 are also at least partially immersed in the liquid developer 73, the liquid developer between the surface 75 and the electrode 76 is moved at substantially the same rate of speed as these elements. A developer replenisher 82 is provided as in the previously-described embodiments. The length of the development path can be varied by making one of the

rolls

70, 71 adjustable relative to the other in the direction of the path length, preferably, the roll that is not driven as roll 70 in FIG. 4. By spacing the

rolls

77, 78 at a maximum distance relative to the length of the receptacle, the roll 70 can be adjusted to provide quite a range in path length.

The embodiments of the invention described hereinabove can be operated with carrier movement of 20 feet to 150 feet per minute. This range of speed of carrier movement for development of the image thereon is considerably greater than that attainable by any of the prior art devices. Also, by making drums 14 and 4042 of insulating materials and making

belts

45 and 76 of insulating materials, the images can be fringe developed. In any case, the developed images are free from streaking and trailing due to the movement of the carrier through the liquid developer.

As shown in FIG. 4, the carrier 72 can be dried at a high rate of speed when subjected to a vacuum knife 83, an air knife 84 and a heated drum 85 or a heat gun 86, such elements being arranged beyond the receptacle 74 in the direction of carrier movement and constitute means for removing liquid developer from the carrier and drying the same. For greatest efficiency, the vacuum knife 83 is oriented generally perpendicular to the plane of the carrier 72 and as close to the receptacle 74 as possible. On the other hand, the air knife 84 is tilted at an angle of 3045 with respect to the plane of the carrier 72 and has its discharge opening about only an inch away from the vacuum knife 83. It has been found that the vacuum knife 83 will remove about 50-6O percent of excess liquid as the carrier passes beneath it. Air knife 84 then effectively pushes back most of the liquid that has escaped vacuum knife 83. The carrier is about 95 percent dried when it passes the air knife 84. The remaining moisture is completely removed by means of a continuous blast of heat from the gun 86, or by means of the heated drum 85.

One of the important advantages of the development techniques described above with respect to the several embodiments of the invention is that the final tonal sense of duplicates can be chosen independently of the tonal sense of the original images. The reason for this is that the design comprises an electrode that can be grounded or biased. Since the volume of liquid developer carried between the carrier and electrode surfaces is moved at about the same speed as the carrier, so that little or no differential velocity exists between the carrier and the developer, streaking and trailing of the images is eliminated. The embodiments described represent an improvement over the units where the carrier is pulled through a stationary liquid. In such apparatus the toner particles can be easily removed or displaced from their original sites due to the friction between the toner particles and the liquid developer. In the present invention there is no relative motion between the carrier and the developer, so that any external forces that could effect the position of the toner particles is eliminated.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

We claim:

1. Apparatus for developing a latent electrostatic image on one surface of a carrier, comprising:

a receptacle containing a liquid developer;

at least one drum having a peripheral electroconductive surface and a pair of spaced, dielectric flanges for supporting said carrier for movement with said one surface in spaced relation to at least the portion of said peripheral surface that is immersed in said liquid developer;

a source of electrical potential connected to said electroconductive surface; and

means for moving said carrier and said drum in synchronism, whereby the liquid developer between said one surface and said peripheral surface is moved with and at substantially the same linear speed as said carrier.

2. Apparatus for developing a latent electrostatic image on one surface of a carrier, comprising:

a receptacle containing a liquid developer;

a plurality of drums interconnected by an endless, electroconductive belt for establishing a path of movement for said carrier;

said carrier being maintained by said drums with said one surface in spaced relation to at least the portion of said belt immersed in said liquid developer;

each of said drums comprising a central hub for engaging said belt and a pair of spaced, dielectric flanges for supporting said carrier in spaced relation to said belt;

the hub of at least one of said drums being electrically conductive;

a source of electrical potential connected to said belt; and

means for moving said carrier and belt substantially in synchronism, whereby the liquid developer between said one surface and said portion of said belt is moved with and at substantially the same linear speed as said carrier.

Claims

2. Apparatus for developing a latent electrostatic image on one surface of a carrier, comprising: a receptacle containing a liquid developer; a plurality of drums interconnected by an endless, electroconductive belt for establishing a path of movement for said carrier; said carrier being maintained by said drums with said one surface in spaced relation to at least the portion of said belt immersed in said liquid developer; each of said drums comprising a central hub for engaging said belt and a pair of spaced, dielectric flanges for supporting said carrier in spaced relation to said belt; the hub of at least one of said drums being electrically conductive; a source of electrical potential connected to said belt; and means for moving said carrier and belt substantially in synchronism, whereby the liquid developer between said one surface and said portion of said belt is moved with and at substantially the same linear speed as said carrier.