US3431890A - Apparatus for replenishing developer in an electrophotographic system - Google Patents

Description

March 11, 1969 R. R. ULARY APPARATUS FOR REPLENISHING DEVELOPER IN AN ELEGTROPHOTOGRAPHIC SYSTEM Filed Sept. 28, 1967 R mY Hum A v Arm n! United States Patent US. Cl. 118-637 15 Claims Int. Cl. G03g 15/10; Bb 5/02; 1305c 11/10 ABSTRACT OF THE DISCLOSURE Apparatus for replenishing principal developer, originally present in an electrophotographic system in the form of a solid meltable body, comprises a container for holding solid melta-ble replenisher developer. Heating means within the container are energized periodically to melt small portions of the replenisher developer as the principal developer is consumed. The container is formed with a lower opening and disposed so that the small portions of molten replenisher developer can fall through the lower opening onto the principal developer to replenish the latter periodically.

Background of invention This invention relates generally to apparatus for replenishing developer material in an electrophotographic system. More particularly the invention relates to improved apparatus for periodically replenishing principal developer, originally present as a solid meltable body, in an electrophotographic system. The improved apparatus is particularly applicable to electrophotographic systems employing solid (hot-melt) developers of the electroscopic type described in US. Patent No. 3,079,272, issued to H. G. Greig, on Feb. 26, 1963, for Method of Developing an Electrostatic Image.

By the term hot-melt developer, as use-d herein, is meant a developer that is solid at normal room temperature and that comprises finely-divided electroscopic toner particles dispersed in an electrically-insulating thermoplastic carrier material having a melting point substantially Within a range of, e.g., from 50 C. to 200 C.

In electrophotographic systems wherein hot-melt developer is used in a molten state to develop a charge pattern on an insulating surface, it has been found desirable to replenish the developer periodically as it is consumed in the developing process. For the optimum and reproducible development of charge patterns, it has been found desirable to maintain the hot-melt developer at a substantially constant quantity or level. Unless the quantity of hot-melt developer, however, is continuously monitored and corrected in such electrophotographic systems, the quantity of developer material can vary from excessive to exhausted, thereby affecting the quality of development and the optimum operation of the apparatus involved.

Summary of the invention Briefly stated, the improved replenishing apparatus comprises means for adding replenisher hot-melt developer to principal hot-melt developer originally provided as a solid body in apparatus for developing an electrostatic image on an insulating surface. The improved replenishing apparatus comprises a container for solid replenisher hot-melt developer. Heating means Within the container are energized periodically to melt portions of the replenisher hot-melt developer as the principal hotmelt developer is consumed during the developing process.

3,431,890 Patented Mar. 11, 1969 The container is disposed so that an opening therein permits quantities. of molten replenisher hot-melt developer to be added automatically and periodically to the principal hot-melt developer.

In a preferred embodiment of the improved replenishing apparatus, the heating means are energized at least once during the formation of each image on the insulating surface so that a small quantity of replenisher hotmelt developer can be added to the principal hot-melt developer to compensate the latter for the quantity of hotmelt developer consumed in the development of the image.

Brief description of the drawing FIG. 1 is a schematic drawing of automatic apparatus for developing an electrostatic image on an insulating surface, utilizing the improve-d replenishing apparatus for adding replenisher hot-melt developer periodically to principal hot-melt developer;

FIG. 2 is an enlarged, fragmentary, perspective view of a portion of the apparatus shown in FIG. 1, illustrating details of the replenisher hot-melt developer means and the principal hot-melt developer means;

FIG. 3 is a cross-section of the container of FIG. 2 for replenisher hot-melt developer, taken along a vertical plane parallel to, and adjacent, a side of the container, and viewed in the direction indicated by the arrows 3 in FIG. 2, the hot-melt developer being shown in phantom, and

FIG. 4 is a cross-sectional view of the container for the replenisher hot-melt developer, taken along the line 44 in FIG. 3, the replenisher hot-melt developer being shown in phantom.

Description of a preferred embodiment Referring, now, particularly to FIG. 1 of the drawing, there is shown apparatus 10 for developing electrostatic latent images (or charge patterns) on a photoconductive insulating surface 11 of an electrophotographic recording medium 12 by (principal) hot-melt developer 14. The recording medium .12 comprises a web of relatively electrically conductive backing paper 13, 'having thereon the insulating surface 11 of a photoconductive material, such as zinc oxide.

The recording medium 12 is pulled from a supply roll 16 by an idler roller 17 and a driven roller 18, driven by a motor 19 coupled to the roller 18 by any suitable means. The recording medium 12 is thus pulled past a charging station 22, an exposure station 24, and a developing station 26 of the apparatus 10, in the direction of the arrow 28. With the exception of the use of the hotmelt developer 14, the method of developing electrostatic images by the apparatus 10 is described in an article, Electrofax, Direct Electrophotographic Printing on Paper, by C. J. Young and H. G. Greig, RCA Review, De-, cember 1954, vol. XV, No. 4.

The recording medium 12 is charge-d at the charging station 22 with a suitable electrostatic charge from a suitable unidirectional power supply 30 The power supply 30 is capable of providing about :6000 volts with respect to a reference potential, such as ground. The photoconductive insulating surface 11, if zinc oxide, is usually charged uniformly negatively, as from a corona discharge device 32, and the paper backing is charged uniformly positively, as from a corona discharge device 34. The electrostatic charging operation is performed in the absence of light.

The uniformly-charged photoconductive insulating surface 11 of the recording medium 12 is exposed with a light image, as from a projection of light through a photographic slide in a photographic enlarger 36, to discharge the uniform negative electrostatic charge selectively, in accordance with the amplitude of light from the projected image. Thus, there is formed a latent electrostatic image on the photoconductive insulating surface 11.

At the developing station 26, the latent electrostatic image is developed by the principal hot-melt developer 14, in a manner to be described hereinafter in detail. The electrostatic image developed by the hot-melt developer 14 is substantially self-fixing so that no additional fixing or glossing operations are necessary. The developed image on the recording medium 12 now moves in the direction of the arrow 38 and may be cut from the web by any suitable means, as desired.

The projector 36 is energized from a source of suitable electrical energy connected to a pair of terminals 42 and 40. The terminal 40 is connected to the projector 36 through a normally open switch 46. The switch 46 is actuated at an appropriate time, and for a suitable duration, by a control circuit 48, in a manner well known in the art of automatic electrophotographic systems of which the apparatus is one. A pair of terminals YY is connected to the terminals 42 and 44, respectively, through the switch 46 for the purpose hereinafter appearing.

The motor 19 is energized, through a switch 50, from a source of suitable electrical energy applied to a pair of terminals 52 and 54. The switch 50 is also actuated by the control circuit 48 to control the movement of the recording medium 12 as desired in the apparatus 10. A winding 56 around a field pole piece 58 of the motor 19 has a pair of terminals XX for the purpose hereinafter appearing.

The hot-melt developer 14 is a solid at room temperature. When heated to melting and applied in the molten form to a (latent) electrostatic image on the recording medium 12, the developer 14 functions substantially as a liquid developer and the electrostatic image is developed to a visible image and substantially fixed. The hot-melt developer 14 comprises a mixture of (1) a low melting carrier material which upon heating becomes quite fluid and which is electrically-insulating in character, and (2) a dispersed phase in the carrier material of finely-divided toner particles. The hot-melt developer 14 has a melting point preferably between 50 C. and 200 C. and a viscosity not in excess of about 500 centipoises at a temperature within that range. The toner particles may comprise liquid droplets or solids, but they should be substantially insoluble in the carrier material, and, when dispersed therein, should have an electrical characteristic such that it takes on an electrical charge. A number of examples of suitable hot-melt developers are described in detail in the aforementioned US. Patent 3,079,272.

A typical hot-melt developer, for example comprises paraffin wax (melting point 55 C. to 79 C.) and carbon black. Finely-divided carbon black is dispersed in the melt of the wax in proportions of up to 5 parts by Weight of carbon black and 95 parts by weight of wax. The mixture is continuously stirred until a uniform dispersion is obtained. The mixture is then allowed to cool to form a solid block or cake developer. Such a developer, when remelted and applied to a surface bearing an electrostatic image, will develop that image as a result of the electrophoretic deposition of carbon black particles in the charged areas of the image. This hot-melt developer will, during development, provide a smooth glossy finish on the photoconductive insulating surface 11.

Referring, now, paticularly to FIG. 2, the principal hot-melt developer 14 is shown in a container or trough 60. A hollow idler roller 62 is disposed to rotate about its axis so that its peripheral surface 63 extends into the trough 60. A stationary electrical heating element 64 is disposed within the hollow roller 62 and is connected to a pair of electrical terminals 66 and 68 for energization from a suitable source of electrical energy to a temperature above that at which the principal hot-melt developer 14 melts. The peripheral surface 63 of roller 62 4 is in frictional contact with the peripheral surface 65 of the roller 17.

The roller 17 is also hollow and has a stationary electrical heating element 70 disposed therein. The heating element 70 is energized from a suitable source of electrical energy connected to a pair of terminals 72 and 74. Energizing the heating elements 64 and 70 causes at least a portion of the principal hot-melt developer 14 to melt in the trough 60 and to wet the surface 63 of the roller 62. The molten hot-melt developer 14, which also wets the surface 65 of the roller 17 by contact with the roller 62, is maintained in a liquid state on the heated rollers 62 and 17 as the rollers are rotated by the driven roller 18. The liquified hot-melt developer 14 is applied to the photoconductive insulating surface 11 of the recording medium 12, at the developing station 26, to develop the latent electrostatic image as the recording medium 12 is moved in the direction of the arrows 28 and 38.

During the developing operation for each latent electrostatic image, a small portion of the principal hot-melt developer 14 is consumed and the quantity, as well as the level, of the hot-melt developer 14 in the trough 60 consequently tends to decrease. The improved apparatus 10 comprises means to maintain the quantity, and the level, of hot-melt developer 14 in the trough 60 substantially constant. T 0 this end, there is provided a container 80, preferably of heat resistant, electrically insulating, plastic material, for holding a block or cake 82 of replenisher hot-melt developer. The composition of the replenisher hot-melt developer 82 is substantially similar to that of the principal hot-melt developer 14.

In the embodiment shown in FIGS. 2, 3, and 4, the container is substantially wedge-shaped for receiving therein a complementary wedge-shaped portion 84 of the block 82 of replenisher hot-melt developer. The container 80 has a pair of opposite, parallel sides 86 and 88, and a pair of opposite, downwardly and inwardly sloping sides 90 and 92, as shown in FIG. 3.

A heating element 94, such as a strip of Nichrome wire, is disposed within the container 80 along the inner surfaces of the sides 90 and 92. One end of the heating element 94 is fastened to the inner surface of the side 90 by a rivet or screw 96, and the other end of the heating element 94 is fastened to the inner surface of the side 92 by a rivet or screw 98. The rivets or screws 96 and 98 provide electrical contact means for electrical connectors 100 and 102, respectively, as shown in FIG. 3, for energizing the heating element 94 periodically in a manner hereinafter to be described.

The container 80 is formed with a relatively small lower opening 104 between the lower edges of the sides 90 and 92. A bight portion 106 of the heating element 94, intermediate the ends thereof, preferably extends through the lower opening 104 of the container 80 to provide an intense concentration of heat for melting relatively small portions of the cake of replenisher hot-melt developer 82 and for directing the molten small portions to a desired target, the trough 60.

The conductors 100 and 102 may be connected to either the terminal XX, respectively, of the winding 56 or to the terminals YY, respectively, in parallel with connections to the projector 36, to energize the heating element 94 periodically. A variable resistor 108 (FIG. 1) may be inserted in series between the conductor 102 and either one of the terminals X or Y, if needed, for controlling the current through the heating element 94, thereby regulating its temperature to a desired value.

The container 80 is disposed above the trough 60 by any suitable means, as by a bracket 109 (FIG. 3) fixed to the side 90 and to a suitable part (not shown) of the apparatus 10, so that replenisher hot-melt developer 82, when molten, can flow through the lower opening 104 and fall into the trough 60 to replenish the principal hotmelt developer 14 as the latter is consumed.

In operation, the block or cake 82 of replenisher hot melt developer 82 is inserted through a large upper opening 110 of the wedge-shaped container 80 with the Wedge-shaped portion 84 of the cake in a complementary in turn melts a small portion of the replenisher hot-melt developer 82 adjacent to the heating element 94. Because of the sloping, wedge-shaped contours of the sides 90 and 92 of the container 80, the molten small portion of the replenisher hot-melt developer 92 falls through the lower opening 104 onto the principal hot-melt developer 14 in the trough 60. Also, as the block or cake of solid replenisher hot-melt developer 82 is consumed, it is advanced automatically, by gravity, into the container 80 so that a portion of it is always adjacent the heating element 94.

Since the photoconductive insulating surface 11 of the recording medium 12 is exposed each time it is desired to copy an image with the apparatus 10, the heating element 94 is energized each time the projector 36 is energized, thereby melting a small portion of the replenisher hot-melt developer 82 each time the recording element 12 is exposed with a light image. The portion 106 of the heating element 94 that protrudes through the opening 104 provides an intense concentration of heat and also directs the molten replenisher hot-melt developer 84 to the trough 60. By controlling the current to the heating element 94 to a desired value, as by adjusting the variable resistor 108, it is possible to add a small quantity of replenisher hot-melt developer 82 to the principal hotmelt developer 14 that is substantially the quantity of principal hot-melt developer 14 consumed by the development of a typical electrostatic latent image at the developing station 26 during the development process. In this manner, it is possible to maintain the quantity, and thus the level, of the principal hot-melt developer 14 in the trough 60 substantially constant during operation of the apparatus for the development of a plurality of electrostatic images.

Instead of being connected to the terminals YY, the conductors 100 and 102 can be connected to the terminals XX, respectively, of the coil 56. The variable resistor 108 is also connected in series with the conductor 102 for adjusting the current through the heating element 94. When energized from the coil 56, the heating element 94 is heated every time the motor 19 is energized, that is, every time it is necessary to move the recording element 12 in the process of making a visible copy of an image projected from the projector 36. Regardless of whether the heating element 94 is energized from the terminals XX or YY, however, it is apparent that the heating element 94 is energized periodically, that is, every time an image is produced on the recording medium 12.

Thus, there has ben shown and described an improved apparatus for replenishing principal hot-melt developer with replenisher hot-melt developer in an automatic electrophotographic system as the principal hot-melt developer is consumed. While the replenisher hot-melt developer has been shown and described as a block or cake, it can also be in other solid forms, such as solid granules, for example. Also, the heating element within the container for the replenisher hot-melt developer may be energized intermittently or continuously from other components in the electrophot-ographic system than from those described.

What is claimed is:

1. In apparatus for developing an electrostatic image on an insulating surface, wherein principal developer is a solid body comprising finely-divided electroscopic toner particles dispersed in an electrically-insulating thermoplastic carrier material having a melting point substantially within a range from 50 C. to 200 C., wherein said solid body is heated to melt at least a portion thereof, and wherein said molten portion is applied to said insulating surface to produce thereon a visible image with said toner particles, the improvement comprising:

a container for a quantity of melta-ble solid replenisher developer, said container having an upper opening, for receiving said replenisher developer, and a lower opening,

heating means cooperatively associated with said container for heating said container,

means connected to said heating means to energize said heating means and to melt at least a small portion of said replenisher developer, and means to dispose said container above said principal developer, whereby said molten portion of replenisher developer may emerge through said lower opening for addition to said principal developer.

2. In apparatus for developing an electrostatic image as defined in claim 1, said apparatus comprises:

a plurality of components adapted to be energized selectively from a source of electrical energy, and

said means connected to said heating means comprises means connected in circuit to at least one of said components to be energized simultaneously therewith.

3. In apparatus for developing an electrostatic image as defined in claim 2, said one component is an electric motor.

4. In apparatus for developing an electrostatic image as defined in claim 2, said one component is a light-image projector.

5. In apparatus for developing an electrostatic image as defined in claim 1, at least a lower portion of the interior of said container is wedge-shaped, and said replenisher developer comprises at least a lower portion that is wedge-shaped and adapted to conform to said interior of said wedge-shaped container, whereby said replenisher developer may be advanced by gravity into said container as portions of said replenisher developer are melted.

6. In apparatus for developing an electrostatic image as defined in claim 1, said heating means comprises a heating element, and a portion of said heating element extends through said lower opening of said container, whereby to direct said replenisher developer, when molten, in a desired direction.

7. In apparatus for developing an electrostatic image as defined in claim 1, said apparatus is substantially automatic and comprises a trough for said principal developer, and heatable roller means disposed partially within said trough to melt said principal developer and to apply said principal developer, when molten, to said insulating surface to develop said electrostatic image.

8. In apparatus for developing an electrostatic image on an insulating surface of a recording medium, wherein said apparatus comprises a trough for principal hot-melt developer, a roller disposed within said trough, means to heat said principal hot-melt developer to melt it, and means to apply said molten principal hot-melt developer to said electrostatic image to develop it, the improvement comprislng:

replenishing means for replenishing said principal hotmelt developer as it is consumed, said replenishing means comprismg a container for replenisher hot-melt developer,

means to melt at least a portion of said replenisher hot-melt developer in said container, and

means to add said melted portion to said principal hotmelt developer, whereby to replenish said principal hot-melt developer.

9. In apparatus for developing an electrostatic image as defined in claim 8,

said apparatus is substantially automatic and comprises a plurality of components adapted to be energized from a source of electrical energy, and

said means to melt a portion of said replenisher hotmelt developer comprises a heating element disposed within said container and connected in circuit with at least one of said components for simultaneous energization therewith.

10. In apparatus for developing an electrostatic image as defined in claim 8,

said means to heat said principal hot-melt developer comprises a heating element disposed within said roller,

said means to apply said molten principal hot-melt developer to said electrostatic image comprise a second roller, in rolling contact with said first-mentioned roller, and means including a third roller disposed to move said recording medium between it and said second roller, and

said container comprises a lower opening therein,

whereby molten replenisher hot-melt developer may emerge therethrough for addition to said principal hot-melt developer.

11. In apparatus for developing an electrostatic image as defined in claim 8,

said container is wedge-shaped, having a relatively large upper opening for receiving solid replenisher hot-melt developer, and a relatively smaller lower opening through which molten replenisher hot-melt developer may emerge for addition to said principal hot-melt developer.

12. In apparatus for developing an electrostatic image as defined in claim 11, said solid replenisher hot-melt developer comprises at least a portion that is wedgeshaped and substantially conforms to the contour of the interior of said container, whereby said replenisher hot-melt developer is advanced by gravity into said container as it is melted.

13. In apparatus for developing an electrostatic image as defined in claim 8,

said container has a lower opening therein,

said means to melt at least a portion of said replenisher hot-melt developer comprises a heating element disposed within said container, and

said means to add said portion to said principal hotmelt developer comprises means to dispose said container above said trough so that said portion of replenisher hot-melt developer, when molten, may fall through said lower opening for addition to said principal hot-melt developer.

14. In apparatus for developing an electrostatic image as defined in claim 13,

said heating element in said container has a portion 10 which protrudes through said lower opening of said container, whereby to direct said molten portion of replenisher hot-melt developer to said trough.

15. Apparatus for feeding a hot-melt developer to a recording medium, in an electrostatic printing process,

said apparatus comprising:

(a) a first container from which hot-melt developer is applied to said recording medium,

(b) first heating means for melting developer material disposed in said first container,

(c) a second container disposed above said first container and including an opening at the bottom thereof through which developer material in said second container may be discharged into said first container to replenish the developer in said first container consumed by application to said recording medium, and

(d) second heating means for melting developer material disposed in said second container.

References Cited UNITED STATES PATENTS PETER FELDMAN, Primary Examiner.

US. Cl. X.R.

Images