US3461843A

US3461843A - Toner application apparatus

Info

Publication number: US3461843A
Application number: US684704A
Authority: US
Inventors: Alonzo W Noon
Original assignee: Stanford Research Institute
Current assignee: SRI International Inc
Priority date: 1967-11-21
Filing date: 1967-11-21
Publication date: 1969-08-19
Anticipated expiration: 1986-08-19

Description

Aug. 19, 1969 A. w. NOON 3,461,843

TONER APPLICATION APPARATUS Filed Nov. 21, 1967 2 Sheets-Sheet 1 1 y IMAGIE IMAGE ELEcmosn-Anc- FIXING: v D E \fEL.OPlNC-| Lylggg STATION STATION TRANSDUCER 'ro currea l FROM supmv ROLL TO VAC UU M Hz. o/vzo ml. Moo/q INVENTOR.

QT Q JE vs United States Patent O 3,461,843 TONER APPLICATION APPARATUS Alonzo W. Noon, Los Altos, Califi, assignor to Stanford Research Institute, Menlo Park, Califl, a corporation of California Filed Nov. 21, I967, Ser. No. 684,704 lint. Cl. 1805c /02; G03g 13/10 U.S. 'Cl. 11d637 13 Claims ABSTRACT OF THE DISCLOSURE Apparatus useful in electrostatic printing systems to apply liquid toner to a paper for developing an image, comprising an applicator chamber having a slot extending across the Width of the paper and a divider plate within the chamber directing the flow of liquid toner past the slot. The apparatus also includes a flat air bearing on the side of the paper opposite the chamber slot to push the paper against the slot, and a vacuum cleaning system for removing excess toner positioned near the point of contact of a capstan.

BACKGROUND OF THE INVENTION This invention relates to an electrostatic image developing system and more particularly to improvements therein.

An electrostatic printing system usually comprises a transducer which can deposit a latent charge image on a suitable web such as zinc oxide-coated paper. Where developers of the type utilizing a liquid vehicle with particles in suspension are employed, the web is passed between applicator rollers or a pet fountain to apply the developer thereto, and is then passed by a blade or roller squeegee for removing the excess developer. It has generally been found difiicult to remove and recover the excess developer sufficiently well to permit rapid drying of the remainder without smearing. Furthermore, the large physical size of the apparatus resulted in long lengths of web extending between the station where charges were deposited and the station where the web emerged and could be viewed, thus delaying the viewing of the copy and requiring long blank leaders between copies. Some improved developing systems have been employed, such as one wherein the developer, or liquid toner, is passed through a tube extending across the width of the web, and having a slot through which toner is applied to the web. However, it has been found that in such systems the liquid toner becomes depleted of toner particles as it moves down the tube, and developing is not uniform throughout the width of the Web. Furthermore, excess toner is still deposited on the web, particularly in high speed operation, and this results in smeared copies.

Accordingly, an important object of the invention is to provide an electrostatic image developing apparatus which provides uniform developing even during high speed operation.

Another object of the invention is to provide an electrostatic image developing apparatus of small physical size to enable immediate viewing of the copy and eliminate long blank leaders between copies.

A further object is to provide an apparatus to enable use in mobile applications, and which creates a minimum of excess evaporation to reduce noxious fumes.

SUMMARY OF THE INVENTION The present invention provides an image developing apparatus for applying liquid toner to a web, which may be a strip of paper, comprising a container with a nar- 3,461,843 Patented Aug. 19, 1969 row slot extending across the width of the web. The container includes a divider plate dividing the inside thereof into an inlet chamber for receiving liquid toner and an outlet chamber through which liquid toner not deposited on the web is removed. The only direct connection between the two chambers is around an edge of the divider plate located adjacent to the slot in the container. A circulating pump continuously draws liquid toner out of the outlet chamber so that a high speed flow of toner occurs around the edge of the divider plate, and therefore past the slot in the chamber, to assure sufficient fresh toner for development of the electrostatic image even at high web speeds. The inlet and outlet chambers also assure that the flow of toner around the edge of the divider plate is relatively uniform throughout the length of the slot, so that the web is uniformly developed along its width. The suction applied to the outlet chamber helps to assure that a vacuum is maintained at the slot, to help draw the web against the slot.

In addition to the container which applies liquid toner to the web, the apparatus includes a flat air bearing disposed against the web on aside thereof opposite the slot in the container. The bearing continuously ejects air which pushes the web against the slot in the container with uniform pressure along the entire width of the web. The web is moved by a capstan and pinch roller combination. To remove excess toner, a vacuum cleaner is positioned adjacent to the nip of the capstan (the area where the capstan contacts the web), inasmuch as it has been found that excess toner accumulates at the nip.

A more complete understanding of the invention may be had by considering the following specification and claims taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a simplified schematic diagram of an electrostatic printing system;

FIGURE 2 is a perspective view of an image developing station constructed in accordance with the invention;

FIGURE 3 is a side sectional view of an applicator of the apparatus of FIGURE 2;

FIGURE 4 is an enlarged, partial view of the applicator of FIGURE 3, showing the portion adjacent to the web;

FIGURE 5 is a perspective view of the air bearing of the apparatus of FIGURE 2;

FIGURE 6 is a side elevation view of the vacuum cleaner portion of the apparatus of FIGURE 2; and

FIGURE 7 is a perspective view of a vacuum cleaner system constructed in accordance with another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGURE 1 is a schematic diagram of an electrostatic printing system which utilizes a toner applicator apparatus of the present invention. A moving web 10, which may be paper, is passed through an electrostatic image transducer 12. Thereafter, the web 10 is passed through an image developing station 14 and an image fixing station 16, and subsequently through cutting apparatus or to a take-up roll.

The electrostatic image transducer 12 can be any of several which have been developed, such as the one shown in Patent No. 3,060,423 or Patent No. 2,955,894. Alternatively, the electrostatic image transducer may be a selenium drum on which a latent charge image has been deposited which transfers this latent charge image to the Web. The image developing station 14 represents apparatus which applies the toner to the latent image for developing it, and which may include apparatus for removing excess toner. The image fixing station 16 represents apparatus for fixing the toner to the web by a drying process.

FIGURE 2 illustrates an image developing arrangement in accordance with the invention. The apparatus comprises a reservoir 18 that contains the liquid toner or developer which may include a liquid carrier containing fine particles that form the printing on the web, in applicator 20 for applying the liquid toner to the web 22, an air bearing 24- for facilitating contact of the web with the applicator, a capstan 26 and pinch roller 28 for driving the web, and a vacuum cleaner 30 for removing excess toner from the web. The reservoir 18 is connected through an inlet tube 32 to one side of the applicator 20 to carry liquid toner thereto. The applicator 20 is connected back to the reservoir 18 through an outlet tube 34, to enable constant circulation of liquid toner between the reservoir and applicator. A circulating pump 36 draws liquid toner from the applicator 20 and pumps it to the reservoir 18 to maintain a constant circulation of liquid toner through the applicator. The applicator has a lower end 38 which is located adjacent to the web 22 for applying liquid toner thereto. The air bearing 24 has a narrow slot 78 facing the web 22 for supplying pressured air, received through an inlet 40, to form a thin cushion of air pushing the web 22 against the lower end 38 of the applicator.

After the web 22 has passed between the applicator 20 and air bearing 24, it passes between the capstan 26 and pinch roller 28. The capstan and pinch roller serve to drive the web 22, and additionally squeeze the toner on the web.

It has been found that liquid with toner suspended in it accumulates on the side of the capstan 26 opposite the applicator 20, this area often being referred to as the nip. The vacuum cleaner 30 gathers the excess toner which accumulates at the nip, to provide a clean web.

FIGURE 3 is a more detailed view of the applicator 20' and air bearing 24. The applicator comprises a troughshaped container having

side walls

42 and 46 and a cover 48. A divider plate 50 has an upper end 52 attached to the cover 48 by blocks 54. The area between the divider plate 50 and side wall 46 forms an inlet chamber 62 for receiving liquid toner, and the area between the divider plate 50' and side wall 42 forms an outlet chamber 64, from which liquid toner is removed. The

side walls

42 and 46 are positioned to form a trough or V-shape with the tip of the converging walls, or lower portions 56 forming a slot 58. The lower edge 60 of the divider plate 50 extends to an area close to the slot 58, so that the only direct connection between the inlet chamber 62 and outlet chamber 64 is around the lower edge 60. The area below the level of the edge 60 of the divider plate may be considered as a transition means interposed between the inlet and outlet chambers having a slot for applying, or directing a portion at the fluid received from the inlet chamber to the web and for passing the rest of the fluid to the outlet chamber.

Developing liquid, generally in the form of a liquid toner comprising particles suspended in a carrier liquid, enters the applicator 20 through an inlet 66, and fills the inlet chamber 62. The liquid toner 68 then flows down to the lower portion 56 of the applicator and to the slot 58. Most of the liquid passes around the lower edge 60 of the divider plate and into the outlet chamber, and from thence flows out of the applicator through an outlet 70. The circulating pump connected to the outlet 70 supplies a suction or partial pressure, which draws the liquid toner out of the outlet chamber 64, thereby drawing toner from the inlet chamber 62 around the lower edge of the divider plate. Some of the liquid toner flows out of the slot 58 onto the web 22, to develop the electrostatic image thereon.

The web 22 is held adjacent to the slot 58 partially by reason of the suction applied at the outlet 70 of the applicator. Holding the web 22 against the slot 58 is necessary to prevent the flow of excessive toner therefrom onto the web. Further aid in maintaining the web 22 adjacent to the slot 58 is provided by the air bearing 24. The air bearing 24, which is located on a side of the web 22 opposite the applicator, includes an inlet nozzle 72 through which air is pumped into an air chamber 74. A top plate 76 has a narrow air slot 78 formed therein through which compressed air emerges. The air flowing through the slot 78 forms a thin cushion of air between the top plate 76 and the lower surface of the Web 22 to minimize friction between them and to assure that a uniform pressure is applied to the web across its entire width. The air bearing is supported on springs 80 which rest on a base 82. The springs are compressed so that the top plate 76, in conjunction with the air cushion, acts to push the web 22 upwardly against the applicator slot 58. Rods 84 attached to the air bearing help to align the springs.

FIGURE 5 is a perspective View of the air bearing 24, showing the extension of the slot 78 across the width of the web. The slot 78 has a width slightly smaller than that of the web 22 to reduce air leakage out of the sides of the web.

FIGURE 4 is an enlarged view of the area of the applicator adjacent to the web 22. The application of toner 68 to the web occurs by reason of the passage of the toner around the lower edge 60 of the divider plate from the inlet chamber 62 to the outlet chamber 64. Some of the toner flows onto the web 22 to develop the image thereon. The passage of liquid toner 68 around the lower edge of the divider plate entails flow at high speeds and with sharp changes in direction of flow. This results in the bringing of large quantities of the liquid toner adjacent to the web 22, so that the liquid in contact with the web has a high concentration of toner particles suspended in the carrier liquid, and even if considerable quantities of the particles are attracted to the electrostatically charged web 22 out of the carrier liquid, the supply is constantly replenished. The rapid change in direction of the liquid toner 68 between passage downwardly in the inlet chamber 62 and passage upwardly into the outlet chamber 64 results in the creation of centrifugal forces. These forces tend to throw the particles suspended in the carrier liquid down against the web 22 to further assure that large quantities of toner particles will be applied thereto. The replenishment of particles and the centrifugal forces pushing particles against the web helps to assure full developing even if the web 22 moves past the slot 58 at high speeds.

The shape of the lower edges of the

side walls

46 and 42 are of importance in assuring good toner flow onto the web 22, while preventing excessive flow.

Inserts

86 and 88 attached to the lower portions of the

side walls

42 and 46, respectively, have accurately shaped edges for this purpose. A space exists between the tips of the walls forming the toner slot 58 and the web 22, and a meniscus 90 of liquid toner occupies the space by reason of capillary action. The surface tension forming the meniscus helps to maintain a seal which prevents uncontrolled flow of liquid toner 68 onto the web 22. The integrity of the meniscus 90 is aided by providing a curvature on the downstream edge 92 (downstream with respect to web motion) of the toner slot walls. The shape of the upstream edge 94 of the slot walls can be similarly shaped, or can be provided with a simple bevelled edge whose extreme tip is flattened.

The proper spacing of the lower edge 60 of the divider plate from the edges of the toner slot 58 these being the upstream and

downstream edges

94 and 92, is important in assuring good flow. If the distance D is very small, insuflicient fluid will pass around the divider plate and into the outlet chamber 64; as a result, either excessive fluid will flow onto the web 22 or the toner particles will be rapidly depleted from the liquid, and in any case it is diflicult to control the amount of fluid flowing onto the Web 22. Even if the distance D is somewhat small, adequate flow of liquid toner around the divider plate requires high suction at the outlet chamber 64, and the divider plate 50 has a tendency to bend toward the outlet chamber 64 under the excessive differential pressures. A

separation D of the lower edge of the divider plate 50 from the extreme outer edge of the toner slot walls approximately equal to the width of the toner slot 58 has been found to provide well controlled and adequate liquid toner flow.

In the operation of the applicator 20, the two

chambers

62 and 64 are generally completely filled with liquid toner. The outlet chamber 64 is at relatively low pressure, while the inlet chamber 62 is at a higher pressure, which, how: ever, is lower than atmospheric pressure. Although the vacuum and liquid toner supplies are connected only at the relatively small outlet 70 and inlet 66, the chambers assure equalization of pressures throughout the entire length of the trough-shaped applicator, to assure uniform application of liquid toner to the web 22 across its entire width.

When the web 22 leaves the applicator 20*, it passes between a capstan 26 and pinch roller 28, shown more clearly in FIGURE 6. The capstan and pinch roller move the web 22 along its length. It has been found that in high speed operation an excess of carrier liquid and toner particles therein may be carried along on the web. When this condition occures, the toner particles tend to float on the surface of the liquid and are not attracted to the charged areas on the web. When the web passes between the capstan and

pinch rollers

26 and 28, most of the excess liquid and toner particles are removed therefrom, and retained in the nip 96. The nip 96 is herein referred to as the area adjacent to the roller which contacts the imaged side of the web, and which is located on the downstream side of that roller or, in other words, the side wherein the web is passing away from the rollers.

In FIGURE 6, the capstan 26 is in contact with the imaged side 23 of the web. As the web 22 passes through this nip, the image areas are brought into contact with many toner particles which gather there at high speed operation and the image areas are thereby further developed. However, excessive accumulation of toner in the nip must be prevented to insure uniform operation. In accordance with the present invention, a vacuum cleaner 30 is provided to gather up excess liquid toner at the nip. The vacuum cleaner comprises a tube 98 attached to a cleaner head 100, the head having a slot opening which is directed at, or located adjacent to, the nip 96, along the entire width of the web 22. The vacuum cleaner allows small amounts of the liquid toner to remain in the nip, while drawing off excessive amounts that would otherwise blot the web.

Toner applicator apparatus has been constructed in accordance with the foregoing, for developing electrostatic images at various speeds of the web, including relatively high speeds. Applicators of the type shown in detail in FIGURES 3 and 4 have been constructed in various configurations. An applicator with toner slot 58 of 0.050 inch width has been constructed, and the divider plate 50 has been located with its lower edge 60 at various distances D from the tip of the toner slot walls. With a divider edge spacing D of 0.015 inch, good liquid toner flow has been achieved, but difiiculty has been experienced in keeping the divider 50 straight, inasmuch as large pressure differentials were required to move sufficient quantities of liquid toner. A lower edge spacing D of 0.050 inch has been found to provide good liquid toner application, as occurred for the 0.015 inch spacing, throughout the length of the slot, yet without giving rise to substantial difficulties in maintaining the position of the divider plate 50 against bending forces. Various configurations of the downstream edge 92 of the toner slot opening have been tested. Reasonably gOOd results have been achieved with a plain bevelled edge, ending in an approximately 100 inch wide flat end. However, with the convexly curved end shown in FIGURE 4, controlled toner application at higher speeds was obtained than with the straight bevelled edge. The air bearing 24 was found to function well with a slot 78 of six-thousands inch width.

Image developing apparatus constructed in accordance with the above has been operated utilizing a suction pressure at the outlet 70 of the applicator 20 of approximately 10 inches water pressure (and a reservoir 18 at atmospheric pressure), providing a flow rate of approximately 1680 millilitres per minute, for a web of 2% inches width. The air bearing 24 was supplied with air pressures of between 2 and 4 pounds per square inch. It was found that good toner application was achieved for web speeds in excess of 30 inches per second. This may be compared with prior art systems which have been tested under similar conditions and wherein excessive toner flowed out at web speeds greater than approximately 10 inches per second. Even at speeds less than 10 inches per second in prior sys terns tested, developing was not uniform throughout the width of the web.

The vacuum cleaner head shown in FIGURE 6 provides suction along the entire width of the web 22, but is difficult to position close to the nip and complicates threading of the web in the machinery. Another cleaner head shown in FIGURE 7 utilizes two

tubes

102 and 104 disposed on either side of the capstan and

pinch rollers

106 and 108 and facing the nip formed between them. The

tubes

102 and 104, which are connected to a vacuum source, draw off excessive toner without interferring with the web 110 and are eflicient, especially in the case of webs which are not excessively wide. The ends of the tubes should be placed very close to the ends of the rollers to maximize their efliciency.

I claim:

1. Apparatus for applying liquid toner to an electrostatically charged web comprising:

a container having converging walls forming a converging portion;

divider plate means disposed in said container for dividing said converging portion into a converging inlet and converging outlet; and

walls defining an elongated slot in said container at the tip of said converging portion;

said divider plate means extending to an area spaced from said tip in a direction away from said web a distance no more than several times the width of said slot.

2. Apparatus as defined in claim 1 wherein:

said spacing of said end of said divider plate means from said tip is approximately equal to the width of said slot.

3. Apparatus as defined in claim 1 including:

means for moving a web past said slot; and wherein the external surface of one wall of said tip of said container disposed downstream from the other tip with respect to movement of said web, is convexly curved for encouraging the maintenance of a meniscus fluid area between it and said web.

4. Apparatus as defined in claim 1 wherein:

said slot is approximately 0.050 inch wide along a majority of its length and the spacing between the end of said divider plate means and said tip is approximately 0.050 inch.

5. Apparatus as defined in claim 1 including:

an air bearing means disposed opposite said slot and having an air slot extending substantially parallel to said slot in said container and substantially aligned therewith, for blowing air to push a web against said slot in said container.

6. Apparatus as defined in claim 5 including:

spring means disposed against said air bearing means for biasing said air bearing means toward said container.

7. Apparatus for applying a liquid toner to an electrostatically charged web comprising:

a trough-shaped container having a lower portion of substantially V-shaped cross-section, disposed with its bottom adjacent to said web;

a divider plate within said container dividing the inside of said container into an inlet chamber and an outlet chamber, both having a lower portion of V-shaped cross-section;

an inlet connected to said inlet chamber for receiving said liquid toner; and

an outlet connected to said outlet chamber for discharging said liquid toner;

said bottom of said container defining an elongated slot extending across said web;

said divider plate extending to an area close to said slot but spaced further from said web than the walls of said slot for confining flow of liquid toner between said inlet chamber and outlet chamber to an area passing across said slot.

8. Apparatus as defined in claim 7 including:

a pump connected to said outlet for drawing fluid therefrom, to provide a partial pressure less than atmospheric pressure in said outlet chamber.

9. Apparatus as defined in claim 7 wherein:

the spacing of the edge of said divider plate at said area close to said slot, from said slot opening is of substantially the same magnitude as the width of said slot.

10. Apparatus as defined in claim 7 wherein:

the outer portion of at least one wall of said slot has a convex curvature to encourage the maintenance of a liquid seal between said wall and said web.

11. Applicator apparatus for applying a fluid to a web moving relative thereto comprising:

walls forming a chamber, said walls having an inlet opening for permitting fluid to enter said chamber and an outlet opening for permitting the discharge of said fiuid, said chamber having a substantially V- shane with the tip of the V adjacent to said web;

said chamber having a slot opening at said tip with the wall ends at said slot opening substantially in the plane of the web, and having wall means spaced from said slot to enable at least a portion of said fluid to move between said inlet and outlet openings without intermediate deposition on said web. 12. The applicator apparatus described in claim 11 wherein:

the tip portion of said V-shaped chamber defines an acute angle. 13. The applicator apparatus described in claim 11 including:

means disposed opposite said slot opening for pressing said Web toward said slot.

References Cited UNITED STATES PATENTS 3,392,707 7/1968 Marx 118--637 2,234,153 3/1941 Herbert 15306 XR 3,027,821 4/ 1962 Wright 89 3,038,442 6/1962 Jones et al 118-309 XR 3,081,687 3/1963 Takats 95--89 3,133,484 5/1964 Wright 95l.7 3,141,793 7/1964 Oliphant 117-37 XR 3,363,530 l/l968 Rice 11850 XR 3,371,651 3/1968 Johnson et al 118-637 FOREIGN PATENTS 1,048,829 11/ 1966 Great Britain.

PETER FELDMAN, Primary Examiner US. Cl. X.R.

l5302; 9589; l17-37, 120; 1184l0