US3508824A - Means for handling electrophotographic transfer sheets - Google Patents

Description

April 28, 1970 L |NBA ET AL 3,508,824

MEANS FOR HANDLING ELECTROPHOTOGRAPHIC TRANSFER SHEETS Filed March 8, 1967 RlCHARD K. LEINBACH THADDEUS SWANKE INVENTORS fMu/M ATTORNEYS BY MM 372%)- United States Patent 1 3,508,824 MEANS FOR HANDLING ELECTROPHOTO- GRAPHIC TRANSFER SHEETS Richard K. Leinbach and Thaddeus Swanke, Rochester,

N.Y., assignors to Eastman Kodak Company, Rochester, N .Y., a corporation of New Jersey Filed Mar. 8, 1967, Ser. No. 621,565 Int. Cl. G03g 15/00 US. Cl. 355-3 9 Claims ABSTRACT OF THE DISCLOSURE An electrophotographic reproducing apparatus, with an electrically conductive guide plate for conveying a transfer sheet from a photoconductive member to a fixing station without disturbing a loose powder image on the transfer sheet. The transfer sheet is stripped from the photoconductive member by advancing the photoconductive member through a bend near the guide plate to cause the leading edge of the transfer sheet to be separated from the photoconductive member by the resistance of the transfer sheet to bending. The guide plate is electrostatically attractive to the transfer sheet. The guide plate is positioned to contact the non-image side of the separated leading portion of the transfer sheet.

' The leading portion of the transfer sheet is guided to This invention relates to means for handling an electrophotographic transfer sheet having a loose powder image on one surface thereof. More specifically, this invention relates to means for stripping a transfer sheet from a moving photoconductive member and for guiding the transfer sheet to a fusing station without disturbing the loose powder image.

In transfer electrophotography, typically, an electrostatic image is formed on a photoconductive surface and that image is developed by application of charged toner powder. The powder image thus formed is transferred to a transfer sheet placed in face contact with the powder image. This transfer can be accomplished by electrostatically charging the non-image side of the transfer sheet so as to attract the toner particles from the photoconductive surface to the sheet. The transfer sheet bearing the loose powder image is then removed from the photoconductive surface and conveyed to a fixing station where the powder image is fixed to the sheet, for example by heat or vapor fusion.

The means for stripping the transfer sheet from the photoconductive surface after the transfer step and for conveying that transfer sheet to the fusing station are critical, because the powder image should not be contacted or disturbed. Prior to the fusing step, the powder image loosely adheres to the transfer sheet by electrostatic attraction, and any physical contacting of the image may displace the powder and smear the image.

The stripping of the transfer sheet. has been accomplished several ways in the prior art, such as by stripper blades or synchronized blasts from air jets. Some of these prior art means are complicated by the requirement of synchronization or movement, and others contact the image side of the transfer sheet.

3,508,824 Patented Apr. 28, 1970 The prior art has also employed a variety of mechanical means for conveying the transfer sheet, such as belt conveyors or chain conveyors carrying mechanical sheet grippers. Drive rollers, of course, are usually not practical because they contact the transfer sheet on both sides and smear the image. The belt conveyors do not provide positive sheet attachment, and are limited as to location in the copier since they rely on gravity. The chain conveyors require tripping mechanisms or synchronization of the sheet grippers. Moreover, these devices all require their own driving means.

It is an object of this invention to provide means for stripping a transfer sheet in electrophotographic reproducing apparatus from a moving flexible photoconductive member and for conveying the transfer sheet to a sheet receiving means without disturbing a powder image carried by the transfer sheet and without the use of additional drive means or moving parts, other than the moving photoconductive member.

It is another object of this invention to provide means for guiding the leading portion of a transfer sheet by electrostatic force from a photoconductive member to a fusing station in electrophotographic reproducing apparatus as the trailing portion of the transfer sheet is advanced by the photoconductive member.

These and other objects are attained by a sheet handling means comprising two cooperating components; namely, stripping means and guide means. The stripping means separates the transfer sheet from the flexible photoconductive member by moving the photoconductive member through a bend which is sufliciently sharp to cause a leading portion of the transfer sheet to separate from the photoconductive member due to the resistance of the transfer sheet to bending. The stripping of the transfer sheet may be assisted by attraction of the sheet to the guide means, which is located near the bend and is electrostatically attractive to the transfer sheet. The guide means comprises a conductive plate that is permanently positioned to contact the non-image side of the separated leading portion of the transfer sheet and to guide that leading portion by electrical attraction to a sheet receiving means, usually the fixing station, as the sheet is moved forward through decreasing contact with the moving photoconductive member. The guide plate may be made electrically attractive to the transfer sheet in any desired manner, but when the transfer sheet carries an electrostatic charge, it is preferable that the guide plate be grounded to provide electrostatic bias with respect to the sheet. This invention also comprehends the above guide means in combination with any other means for stripping the leading portion of the transfer sheet from the photoconductive member.

In the accompanying drawings:

FIG. 1A is a diagrammatical side view of the one embodiment of the invention.

FIG. 1B is a perspective view of the embodiment shown in FIG. 1A.

FIG. 2 is a diagrammatical side view of another embodiment of the invention.

According to. one embodiment of this invention, as illustrated in FIGS. 1A and 1B, a flexible photoconductive member 1, comprising a photoconductive insulating layer 2 and a conductive layer 3, advances in the direction indicated by the arrow through a plurality of process stations (not all shown) in an electrophotographic reproducing apparatus.

In a typical electrophotographic reproducing apparatus, the several processing stations in the path of movement of the photoconductive member, which are not shown and do not form part of the invention, may be functionally described as follows:

A charging station, at which an electrostatic charge is deposited on the photoconductive member;

An exposure station, at which a light image to be reproduced is projected onto the photoconductive member to dissipate the charge in the exposed areas of the photoconductive member and thereby form a latent electrostatic image; and

A developing station, at which a toner powder having an electrostatic charge opposite to that of the latent image is brushed or cascaded over the surface of the photoconductive member, whereby the toner particles adhere to the electrostatic latent image to from a powder image.

The three processing stations described above are only one example of several known electrophotographic reproducing processes, in which a loose powder image is formed on a photoconductive member. In such processing apparatus, the loose powder image on the photoconductive member is transferred to a transfer sheet, which is then stripped from the photoconductive member and conveyed to a fixing station where the loose powder image is fixed onto the transfer sheet.

In FIGS. 1A and 1B the photoconductive member 1 carries on one surface a loose powder image 5, which has been formed by any of the known electrophotographic methods. A transfer sheet 6 is fed by rollers 7 onto the powder image 5. The photoconductive member I carrying the powder image and the transfer sheet 6 advances under a corona charger 8, which places an electrostatic charge opposite to that of the toner powder on the surface of the transfer sheet opposite the powder image. The powder image 5 is thereby caused to electrostatically adhere to the transfer sheet 6. Following this powder image transfer, the flexible photoconductive member 1 is caused to go around a bend at the desired stripping point. This bend is defined by the location of a roller 4, around which the flexible photoconductive member 1 travels. When the photoconductive member 1, carrying the sheet 6 with the powder image 5, starts into the bend at roller 4, the stiffness of the transfer sheet 6 causes it to resist bending. The bend is made sufficiently sharp, as determined by the diameter of roller 4, that the stiffness of the transfer sheet 6 overcomes the electrostatic attraction between the transfer sheet 6 and the photoconductive member 1, and separation of a leading portion of the transfer sheet is initiated. There is a tendency for retacking of the transfer sheet 6 to occur when the separated portion becomes long enough to overcome the stiffness of the sheet 6. To prevent this retacking, a conductive plate 9 is positioned with one end 10 adjacent to the stripping point. Since the conductive plate 9 is connected to ground at 11, the highly charged sheet material 6 is electrostatically attracted to the grounded plate. This electrostatic attraction assists the stripping of the transfer sheet 6 from the photoconductive member and draws the separated portion of the transfer sheet into contact with conductive plate 9. The separated leading portion of the transfer sheet 6 is thereby caused to electrostatically adhere to the conductive plate 9, while the trailing portion of the transfer sheet is still in electrostatic contact with the photoconductive member 1 which continues to move and advance the transfer sheet 6 along the surface 12 of the conductive plate 9. Since the transfer sheet 6 is at least partially insulating, its high charge does not drain olf rapidly to the conductive plate. Therefore, the bias between the sheet and the plate is maintained for a sufficient period of time to permit the leading portion of the transfer sheet 6 to be guided to a. sheet receiving means 13, usually the fusing station, adjacent to the end 14 of plate 9. The plate may be curved to guide the sheet in any desired direction, so that flexibility in locating the fuser is provided.

Any fusing means may be used in the practice of this invention, but the powder image should not be disturbed prior to fusing. An example of a fuser which would work satisfactorily with this guide plate is described in US. Patent 2,701,765. It will be seen that the powder image 5 is never contacted or disturbed in any way by the subject stripping and conveying means.

The present invention can be used in combination with rigid photoconductive members or plates as well as with flexible photoconductors. As seen in FIG. 2, the photoconductor 1 is supported on a rigid drum support 15. The sheet feed and transfer steps of the process are identical to those described for FIG. 1. After the transfer stage, the leading portion of the transfer sheet 6 is stripped from the photoconductor 1 by any desired means, such as, for example, a pick-01f blade 16. When the leading portion of transfer sheet 6 is stripped from the rigid photoconductor 1, it is attracted to the conductive guide plate 9 in the same manner, as in the FIG. 1 embodiment, by the electrostatic bias between the grounded conductive plate 9 and the charged transfer sheet. The plate 9 then functions as a curved guide and as an electrostatic support for the transfer sheet 2, as it is advanced by the moving photoconductor 1.

In either of the embodiment described in FIGS. 1 and 2, it is preferable that the end-portion 10 of the plate 9 adjacent the stripping point be somewhat curved, so that good contact is established with the separated leading portion of the transfer sheet 6 after stripping, regardless of the angle at which the sheet approaches the plate.

In both embodiments, described in the drawings and above, the guide plate 9 is grounded and the transfer sheet is electrostatically charged. This method of providing a bias is entirely satisfactory regardless of whether the charge on the sheet material 6 is positive or negative. It is also immaterial in the practice of this invention whether the guide plate 9 is grounded or connected to an electric potential, so long as there is an electric attraction between the guide plate 9 and the transfer sheet. The use of an electric potential for providing bias is necessary if the transfer sheet does not carry an electrostatic charge. However, grounding is preferable because of simplicity, when the transfer sheet carries an electrostatic charge deposited by the transfer electrode.

It should be evident that any method of stripping the leading edge of the transfer copy sheet 6 may be used in the practice of this invention, but the stripping means should not disturb or contact the powder image 5. If the photoconductive member is not continuous, the transfer copy sheet could be superimposed on it with the leading edge of the sheet overhanging the leading edge of the photoconductive member, so that the free leading edge of the sheet is available to contact the guide means. If the photoconductor is continuous or if it is not desirable or practical to provide an overhang of the transfer sheet, many other mechanical separators are suitable. Suction rollers, air jet strippers or mechanical blade strippers are some examples of known means for initiating the stripping of the leading edge of the transfer sheet 6. However, when mechanical strippers are used, the guide plate 9 should be positioned to electrically attract the transfer sheet 6 away from the stripping initiator 16, before the image area of the transfer sheet is contacted. Of course, when a flexible photoconductive member is used, stripping of the transfer sheet is preferably accomplished automatically by providing the relatively sharp bend in the flexible member, described in FIGS. 1A and 1B as a feature of the invention.

Although the invention has been described in considerable detail with reference to certain preferred embodiments thereof, it will be understood that variations and modifications can be effected without departing from the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. In electrophotographic and similar reproducing apparatus having a movable flexible photoconductive member, means to form an electrostatic latent image on the photoconductive member, means to develop the electrostatic latent image with toner powder, means to superimpose a transfer sheet on the developed powder image, means to transfer the powder image to a surface of the superimposed transfer sheet creating an electrostatic charge on said transfer sheet, and means to fix the transferred powder image onto the transfer sheet, the improvement comprising:

means for advancing the flexible photoconductive member in a path having a bend of sufficient curvature to cause a leading portion of a transfer sheet to which an unfixed powder image has been transferred, to be separated from the movable flexible photoconductive member, and

electrically conductive, grounded means positioned to contact the leading portion of a transfer sheet so separated, on the surface opposite to the image-bearing surface for electrically attracting and guiding the separated leading portion toward said fixing means while the transfer sheet is advanced by the movable photoconductive member.

2. In electrophotographic and similar reproducing apparatus of the type having a movable flexible photoconductive member, means for forming an electrostatic latent image on the photoconductive member, means for developing the electrostatic latent image with toner powder, means for superimposinga transfer sheet on the developed powder image, means for transferring the powder image to a surface of the transfer sheet, and means for fixing the transferred powder image onto the transfer sheet, the improvement comprising:

means for advancing said flexible photoconductive member in a path having a bend of sufficient curvature to cause a leading portion of a transfer sheet to which an unfixed powder image has been transferred to be separated from the movable flexible photoconductive member, and

grounded conductive guide means positioned to contact the leading portion of the transfer sheet so separated, on the surface opposite tot he image carrying surface for electrostatically supporting and guiding said transfer sheet toward said fixing means.

3. In electrophotographic and similar reproducing apparatus of the type having a movable photoconductive member, means for moving said photoconductive member along an operative path, means for forming an electrostatic latent image on the photoconductive member, means for developing the electrostatic latent image with toner powder, means for superimposing a transfer sheeton the developed powder image, means for imparting an electrostatic charge to the transfer sheet to effect transfer of the powder image to the contingent surface of the transfer sheet, and means for fixing the transferred powder image to the transfer sheet, the improvement comprising:

means for causing separation of a leading portion of the transfer sheet from the movable photoconductive member after transfer of a powder image to the sheet, and

grounded, electrically conductive guide means, positioned to contact the leading portion of the transfer sheet so separated on the surface opposite to the image carrying surface, for electrostatically supporting and guiding the separated transfer sheet during movement toward said fixing means.

4. In electrophotographic and similar reproducing apparatus having a movable flexible photoconductive member, means for forming an electrostatic latent image on the photoconductive member, means for developing the electrostatic latent image with toner powder, means for superimposing-a transfer sheet on the developed powder image, means for imparting an electrostatic charge to the superimposed transfer sheet to effect the transfer of the powder image to the contingent surface of the transfer sheet, and means for fixing the transferred powder image onto the transfer sheet, an improved device for separating an image-bearing transfer sheet from said photoconductive member and for guiding the separated transfer sheet toward said fixing means with minimal disturbance of the powder image, "said device comprising:

a grounded electrically conductive guide member located between said powder image transferring means and'said fixing means, and

means for advancing said photoconductive member in a path having a bend located sufficiently close to said guide member and with sufiicient curvature to cause a leading portion of the transfer sheet to be separated from the portion of the photoconductor moving around said bend, whereby the leading portion of the transfer sheet is supported and guided by said guide member for movement towards said fixing station.

5. A device 'for handling a transfer sheet in electrophotographic %and similar apparatus, said transfer sheet being electrostatically charged and carrying on one surface thereof an unfixed powder image, said device comprising:

receiving means;

a flexible photoconductive surface for supporting said transfer sheet;

means for ad vancng said photoconductive surface along a path having a bend of sufficient curvature to cause a leading portion of the image carrying transfer sheet supported thereon to be separated from said photocon'diictive surface; and

grounded conductive guide means, positioned to contact said separated leading portion of said transfer sheet on the surface opposite said image carrying surface, for electrostatically supporting and guiding said leading portion of said transfer sheet towards said receiving means.

6. Means for handling an electrostatically charged transfer sheet in electrophotographic and similar apparatus, the transfer sheet carrying on one surface thereof an unfixed powder image, said handling means comprising:

receiving means;

a movable surface for supporting and driving said transfer sheet;

means for separating a leading portion of said transfer sheet from the movable surface; and

electrically grounded guide means positioned to contact said separated leading portion of the transfer sheet on the surface opposite to said image carrying surface for electrostatically supporting and guiding said leading portion of the transfer sheet towards the sheet receiving means while the transfer sheet is driven by the movable surface.

7. A device for use in electrophotographic apparatus to effect separation of a transfer sheet having a powder image electrostatically carried thereon from a moving photoconductive web which supports the transfer sheet, said powder image having been transferred to the transfer sheet from said web, said device comprising:

(a) means for moving said web along a path having a bend of suflicient curvature to cause the leading end of the transfer sheet supported thereon to separate from the web; and

(b) electrically grounded means located with respect to said web moving means at a position such that the electrostatic charge on the separated leading end of a transfer sheet will cause the side of the leading end of the sheet opposite the powder image to move into contact with said electrically grounded means.

8. The invention defined in claim 7 wherein said electrically grounded means comprises a guide surface for 7 trically grounded means comprises a guide surface fro directing a separated transfer sheet which is attracted thereto toward subsequent treating stations of the electrophotographic apparatus.

9. The invention defined in claim 7 wherein said moving means moves said web and supported sheet along a flat path upstream from said bend.

References Cited UNITED STATES PATENTS 3,351,340 11/1967 Levine 226-94 XR 3,139,013 6/1964 Graves 3553 NORTON ANSHER, Primary Examiner L. H. MCCORMICK, 111., Assistant Examiner U.S. Cl. X.R. 27118

Images