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US3666518A - Development means and methods for developing electrostatic images - Google Patents

Development means and methods for developing electrostatic images Download PDF

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Publication number
US3666518A
US3666518A US24265A US3666518DA US3666518A US 3666518 A US3666518 A US 3666518A US 24265 A US24265 A US 24265A US 3666518D A US3666518D A US 3666518DA US 3666518 A US3666518 A US 3666518A
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US
United States
Prior art keywords
development
zone
developer material
toner
finishing
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US24265A
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English (en)
Inventor
Erwin W Luttman
Harold C Medley
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
International Business Machines Corp
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International Business Machines Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by International Business Machines Corp filed Critical International Business Machines Corp
Application granted granted Critical
Publication of US3666518A publication Critical patent/US3666518A/en
Anticipated expiration legal-status Critical
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Classifications

    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G15/00—Apparatus for electrographic processes using a charge pattern
    • G03G15/06—Apparatus for electrographic processes using a charge pattern for developing
    • G03G15/08—Apparatus for electrographic processes using a charge pattern for developing using a solid developer, e.g. powder developer
    • G03G15/0801—Apparatus for electrographic processes using a charge pattern for developing using a solid developer, e.g. powder developer for cascading

Definitions

  • the present invention relates to electrostatography and, more particularly, relates to novel development means and methods for developing electrostatic images.
  • an electrostatic latent image is formed on a photoconductive insulating member and is developed or made visible by the attraction thereto of finely divided pigmented material, commonly known as toner.
  • One prior art development method for rendering the electrostatic image visible is known as parallel flow cascade development in which a developer material is poured or cascaded over the surface of the photoconductive insulating member, while it is moving in a parallel direction with the developer material, as shown in the figure marked prior art.
  • This developer material contains a mixture of particles known in the art as carrier and much smaller pigmented powder particles or toner which are charged by and electrostatically adhere to the carrier particles.
  • the toner patricles are attracted to the electrostatic image from the carrier particle's and deposited on the photoconductive insulating member to render the electrostatic latent image visible.
  • the velocity of the cascading development material must exceed the velocity of the moving photoconductive member for high quality image development.
  • the velocity of the photoconductive member is only four inches per second, the velocity of the developer material can easily exceed the velocity of the moving photoconductive member by merely dropping or flowing the developer material onto the member, as shown in the prior art figure. In this situation, an individual electrostatic charge on the member will be contacted by a number of carrier particles full of toner powder for transfer thereto.
  • the photoconductive member is in the form of a drum or cylinder, as shown in the prior art figure, and the diameter of the drum is decreased, the above effects show up at lower velocities because the electrostatic image is in contact with the developer material for a shorter period of time.
  • the developer material can exceed the velocity of the photoconductive memebr because, in the known parallel flow development method, the development of the electrostatic image begins at the point of entry of the developer material onto the photoconductive member and completed at a point distant from the entry of the development material.
  • the carrier particles are in a toner depleted state as they leave the developed image, and it their velocity is sufiiciently high, they will scrub oil or remove portions of the developed image, thereby degrading the image quality.
  • an object of the present invention is to provide novel development means and methods which are capable of high speed development of electrostatic images, such as as great as and even greater than 32 inches per second, and which produce high quality toner images.
  • Another object of the present invention is to provide novel development means and methods which are capable of such high speed development without degradation of the finished toner image.
  • a further object of the present invention is to provide novel development means and methods in which the background ot the finished toner image is cleaned as the finished toner image goes out of contact with the developer material.
  • Another object of the present invention is to provide development means and methods which are capable of high speed development, but in which the development material initially contacts the insulating member carrying the electrostatic image at a low velocity, relative to parallel flow development, so as to minimize damage to the insulating member during initial contact therewith.
  • Another object of the present invention is to provide high speed development means and methods in which the surface of the insulating member is subjected to a polishing action during the development of the electrostatic image, thereby minimizing toner filming of the insulating member.
  • Another object of the present invention is to provide development means and methods which permits the design of an electrostatographic machine configuration with simplified and convenient paper handling.
  • the foregoing objects are achieved by a development method in which the flow of developer material moves downward and in a direction opposite to the direction of the insulating surface carrying the electrostatic image and which can be termed counterflow cascade development.
  • the flow of developer material is directed onto the insulating surface such that a finishing development zone is formed at the point of entry of the developer material to a point upward therefrom whereby the development of the electrostatic image is completed in the finishing development zone, but begun at a point a distance from and downward from the point of entry of the developer mate rial.
  • Another aspect of the present invention for achieving the foregoing objects is the provision of means in the flow of development material onto the insulating surface for either deflecting upwardly or restricting downwardly the developer material to cause the formation of the finishing development Zone.
  • FIG. 1 is a schematic cross-sectional view of one embodiment of the development means of the present inventron.
  • FIG. 2 is a cross-sectional schematic view of another embodiment of the development means of the present invention.
  • FIG. 3 is a cross-sectional schematic view of the development means with electrical means to show one embodiment of another aspect of the present invention.
  • FIG. 4 is a cross-sectional schematic view of the development means with magnetic means to show another embodiment of the other. aspect of the present invention.
  • a moving member 11 having an insulating surface 12 carrying an electrostatic charge pattern and moving around a roller 13 in the direction of the arrow 14.
  • the member 11 comprises a photoconductive layer and the electrostatic charge pattern is formed by uniformly electrostatically charging the surface 12 by conventional corona discharge charging means (not shown) and exposing the photoconductive layer to a light image from a light source (not shown), either indirectly as reflected from a document or directly from a cathode ray tube.
  • a photoconductive layer is not required and the electrostatic charge pattern can be selectively deposited by charging means, such as a pin tube, known in the art.
  • a development station 15 For developing the electrostatic charge pattern carried on the member 11, a development station 15 is provided and employs the novel development means and methods of the present invention.
  • the station 15 comprises a reservoir 16 of developer material 17 which is a mixture of carrier particles and toner powder which electrostatically adheres to the carrier particles.
  • the developer material 17 is carried upwardly from the reservoir 16 to a receptacle 18 via known means such as a feed screw or conveyer buckets, shown schematically by the endless dash lines.
  • a toner dispenser (not shown), which is well known in the art, is included in the development station to continually add new toner to the developer material in the reservoir.
  • the development station 15 must include means for creating a finishing development zone from the point of entry of the developer material onto the member 11 to a point upward therefrom whereby development of the electrostatic image is finished or completed in said zone.
  • the creation and maintenance of the finishing development zone are accomplished in the following way.
  • the receptacle 18 is formed with two rigid walls 19, 20 and a laterally sliding wall 21, which, when moved, changes the width of the throat 22 of the receptacle.
  • deflector means 23 adjacent the receptacle 18 and in the path of the developer fiow onto the member 11 is deflector means 23 for imparting an upward movement to the developer material 17.
  • the undeveloped electrostatic charge pattern on the insulating surface 12 of the member 11 first sees the developer material 17 as it enters the development station 15.
  • the developer material 17 which first comes into contact with the electrostatic image is partially depleted of toner inasmuch as some of the toner was given out to previous electrostatic images.
  • the electrostatic image continues in the upward direction, further development of the image occurs, but not complete development until it passes through the finishing development zone 24.
  • the carrier particles in the lower and middle portions are heavily laden with toner and complete the development of the partially toned electrostatic image.
  • the carrier particles in the uppermost position are substantially depleted of toner and, because of this condition, scavage loose toner lying in the background areas of the image.
  • the path of these substantially toner depleted carrier particles is in a counterclockwise direction back into the path of the incoming developer material where they pick off toner from the incoming toner laden carrier particles and either go back into the zone 24- or are carried downward along the surface 12 into the reservoir 16.
  • the electrostatic image is partially developed prior to reaching the finishing development zone where during the initial stages it is completely developed and in the latter stages, the background areas are cleaned of loose toner.
  • FIG. 2 Another embodiment of the present invention is shown in FIG. 2 in which the moving member 11 having an insulating surface 12 takes the form of a drum so that the developing surface is curved rather than planar.
  • the development station 15 of FIG. 2 includes a reservoir 16 for providing a supply of developer material 17 to the receptacle 18 via carrying means schematically shown by the endless dash lines.
  • the deflector means 23 of FIG. 1 is not included, but instead the finishing development zone is, at least, partially controlled by means for changing the angle of the chute, herein receptacle wall 19.
  • the receptacle 18 is rotatably mounted on a pivot 27 which is slidable in a slotted member 28.
  • the pivot 27 can be moved out of the uppermost slot in the slotted member 28 downward to one of the three other slots. As this is done, the receptacle 18 is rotated upwardly and the wall 19 is moved from its present position to three other positions, each of which places the wall 19 of the reservoir 18 more towards a horizontal attitude. It should be apparent that, as the reservoir wall 19 is moved into a more horizontal attitude, there will be an increase in the size of the finishing development zone. (lonversely, returning the pivot 27 back up to the uppermost slot of the slotted member 28 will cause the receptacle 18 to rotate downwardly and move the receptacle wall 19 back into a lesser horizontal latitude. This will cause a decrease in the size of the finishing development zone 24. While the chute has been shown as the receptacle wall 19 in FIG. 2, it should be understood that the deflector 23 of FIG. 1 can also be similarly mounted so as to change the angle of the deflector 23.
  • V average velocity over the length of the developer zone.
  • V velocity of photoconductor surface.
  • d average diameter of carrier particles.
  • the velocity of the development material in the finishing development zone is low relative to the velocity of the developer material being introduced onto the insulating surface and gives the visual appearance of being essentially stationary. Accordingly, developer material at the point of entry and in the finishing development zone is being replenished at a rapid rate and consequently a large supply of toner is available for transfer to the electrostatic image on the insulating surface. However, the rate of replenishment of development material is lower in the finishing development zone farthest removed from the point of entry. This serves to enhance the image quality because developer material in this area becomes slightly depleted of toner and picks up loose background toner from the insulating surface.
  • the finishing development zone would be in the range of about one-half inch to about two inches. It has been found that, under these conditions, a finishing development zone of less than about a half an inch does not develop the electrostatic image to optimum density and the background of the developed image will contain some loose toner due to the absence of denuded carrier particles in the upper portion of the zone and their background cleaning action. Moreover, under these conditions, if the finishing development zone exceeds about two inches, the developer material in the uppermost portion of the finishing development zone is sufiiciently depleted of toner that it tends to not only clean up the loose toner from the background, but also partially erase the developed image.
  • the size of the finishing development zone can be varied by changing the flow rate of the developer material, both out of the receptacle 18 and down the insulating surface 12 of the member 11. That is, the throat 22 of the receptatcle 18 can be increased in size to increase the flow rate and thereby increase in size the finishing development zone. Conversely, the throat 22 can be reduced in size to decrease the fiow rate and thereby reduce in size the finishing development zone. Moreover, the end 26 of the receptacle wall 19 in FIG.
  • an additional parameter which can be varied in order to change the size of the development zone is the angle of the member 11. As shown in FIG. 1, the angle of the member 11 is about 45. If the angle is increased greater than 45, the gravity force on the developer material will be increased, this will reduce the size of the finishing zone, whereas an angle less than 45 will increase the size of the finishing zone because the gravity force on the material will be decreased. Preferably, for web and belt configuration, the angle should be about 45 As pointed out previously, the carrier particles as they reach the uppermost part of the finishing development zone are partially depleted of toner and, because of this, pick up loose undesirable background toner on the image. The degree of the toner depletion on the carrier particles is also dependent upon the size of the finishing development zone.
  • FIG. 3 is an embodiment of this aspect of the present invention and shows a voltage source applied to an insulated mounted chute in the form of a deflector 23.
  • the potential applied to the chute brings about a change in the net charge of carrier particles when they become denuded or depleted of toner such that they do not stick to the surface of the member 11 which, for illustration purposes, has been shown as a solid curved line in the form of a drum and a straight dashed line in the form of a web or endless belt.
  • the electrical potential applied to this chute must be kept at a polarity opposite to the triboelectric charge on the carrier particles and at a voltage level sufficient to prevent the toner depleted carrier particles from being carried upwardly and out of the finishing development zone.
  • the core of the carrier particles may be either insulating, such as glass or sand, or conductive, such as iron.
  • FIG. 4 Another embodiment for regulating the toner depleted carrier in the uppermost portion of the finishing development zone is shown in FIG. 4.
  • a non-magnetic cylinder 29 rotates about a stationary magnetic hub 30 having one or more axially aligned strip magnets 31 adjacent the inside of the rotating cylinder.
  • the cylinder 29 is rotated in a direction opposite to the movement of the member 11 and in the direction of the arrow 32.
  • Magnetic fields originating from the strip magnets 31 of the hub extend through the nonmagnetic cylinder and attract the toner depleted carrier particles having magnetically attractable cores, such as iron.
  • the rotational direction of the cylinder 29 carries the carrier particles back into the developer flow from the reservoir 18 and out of the magnetic fields whereby the toner depleted carrier particles are released into the flow and become retoned from the toner laden carrier particles fresh from the reservoir. Accordingly, not only does the rotating cylinder through the magnetic fields carry denuded or toner depleted car rier particles back into the developer flow, but it also can be used to control the number of toner depleted carrier particles in the upper portion of the finishing development zone. That is, by increasing the rotational speed of the cylinder, the number of such carrier particles will be decreased in the zone due to the increased number of them being carried out of the zone and back into the flow of developer material. It should be apparent that further control over the size of the zone can be accomplished through the field strength of the magnetic field.
  • the cylinder 29 is metallic, a potential can be applied to it from a voltage source 33 and perform a further function as a development electrode for improving solid area development of the electrostatic image.
  • the potential applied to the cylinder must be slightly greater than the background voltage level and substantially less than the voltage level of the image or pattern.
  • negative electrostatic charge pattern normally has a surface potential of --700 volts in the pattern areas and a potential of -l volts in the background areas.
  • the voltage applied to the cylinder 29 should be about l50.
  • the insulating member carrying the electrostatic image is moving in a direction opposite to the direction of the developer flow, the initial velocity of the developer material can be very low relative to parallel flow development and the initial contact of the developer material with the surface of the insulating member is more of sliding action and, therefore, non-destructive to the surface.
  • the insulating member receives a polishing action during the development method of the present invention, which is believed to be due to the sliding action of the developer material against the insulating surface.
  • the developed electrostatic image leaves the upper end of the developer station, it developed image next proceeds to a transfer station in which the image is transferred to a substrate such as paper, the transfer station will be located at the top of the electrostatographic machine. Because of this, the design of the paper handling is simplified due to the short path length for incoming plain paper to the outgoing copy paper carrying the develoed image. Moreover, it is on a convenient level for the operator of the machine.
  • controlling force 18 an electric field opposite in polarity to the triboelectric charge on the toner depleted carrier particles so as to change their net charge and thereby prevent them from electrostatically sticking to the insulating surface and being carried upwardly and out of said zone.
  • said controlling force is a magnetic field and said carrier particles comprise a magnetically attractable material whereby, through magnetic attraction of the toner depleted carrier particles to a rotating member, the particles are carried back into said flow of developer material.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Dry Development In Electrophotography (AREA)
US24265A 1970-03-31 1970-03-31 Development means and methods for developing electrostatic images Expired - Lifetime US3666518A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US2426570A 1970-03-31 1970-03-31

Publications (1)

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US3666518A true US3666518A (en) 1972-05-30

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US24265A Expired - Lifetime US3666518A (en) 1970-03-31 1970-03-31 Development means and methods for developing electrostatic images

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US (1) US3666518A (de)
JP (1) JPS5019934B1 (de)
AT (1) AT315643B (de)
BE (1) BE764337A (de)
CA (1) CA934232A (de)
CH (1) CH521613A (de)
DE (1) DE2113446C3 (de)
ES (1) ES389598A1 (de)
FR (1) FR2083977A5 (de)
GB (1) GB1320487A (de)
NL (1) NL7103024A (de)
SE (1) SE361751B (de)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3989007A (en) * 1973-12-07 1976-11-02 U.S. Philips Corporation Developing chamber for electrostatic latent images
US4081571A (en) * 1974-08-01 1978-03-28 Mita Industrial Co. Ltd. Method for developing electrostatic latent images
US4126100A (en) * 1974-08-01 1978-11-21 Mita Industrial Company Ltd. Apparatus for causing a developer powder to make an irregular motion in a developing zone

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS52106580A (en) * 1976-03-03 1977-09-07 Nippon Steel Corp Low noise convey roll
JPS53136786U (de) * 1977-03-31 1978-10-28
JPS5445090A (en) * 1977-09-13 1979-04-10 Ichikawa Woolen Textile Silent roll for conveyance

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3989007A (en) * 1973-12-07 1976-11-02 U.S. Philips Corporation Developing chamber for electrostatic latent images
US4081571A (en) * 1974-08-01 1978-03-28 Mita Industrial Co. Ltd. Method for developing electrostatic latent images
US4126100A (en) * 1974-08-01 1978-11-21 Mita Industrial Company Ltd. Apparatus for causing a developer powder to make an irregular motion in a developing zone

Also Published As

Publication number Publication date
BE764337A (fr) 1971-08-16
NL7103024A (de) 1971-10-04
CH521613A (de) 1972-04-15
DE2113446C3 (de) 1978-12-07
FR2083977A5 (de) 1971-12-17
JPS5019934B1 (de) 1975-07-10
DE2113446B2 (de) 1978-04-20
DE2113446A1 (de) 1971-10-14
GB1320487A (en) 1973-06-13
AT315643B (de) 1974-06-10
CA934232A (en) 1973-09-25
ES389598A1 (es) 1974-03-01
SE361751B (de) 1973-11-12

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