US3392708A - Liquid developing system - Google Patents

Description

y 1968 F. HUNSTIGER 3,392,708

LIQUID DEVELOPING SYSTEM Filed Sept. 1, 1966 TONER CCNCENTRATE THINNER SUPPLY 30 FIG -2 INVENTOR FRANCIS HUNSTIGER ATTORNEYS United States Patent Ofiiice 3,392,708 Patented July 16, 1968 3,392,708 LIQUID DEVELOPING SYSTEM Francis Hunstiger, Parma Heights, Ohio, assignor to Harris-Intertype Corporation, Cleveland, Ohio, a corporation of Delaware Filed Sept. 1, 1966, Ser. No. 576,592 4 Claims. (Cl. 118-637) ABSTRACT OF THE DISCLOSURE A roll-type electrostatic liquid developer with an impeller shaft mounted transversely of the output side of the tank, impellers on the shaft for circulating the developer liquid peripherally of the tank, and a supply of thinner and a separate supply of toner for admittance into a mixing zone including the impeller for peripheral circulation to the inlet side of the developer.

The invention relates to improvements in systems for developing electrostatic and electrophotographic images, and more particularly to a developer tank and developer mixing and circulating structure for such systems.

In liquid developing systems of the type indicated, a web bearing a latent electrophotographi-c image is brought into contact with a developer liquid, and a visible image is formed thereon by the deposition of toner particles from the developer liquid onto a surface of the sheet material. A system of this general type is shown and described in the copending application of Hunstiger et al., Ser. No. 372,503 filed June 4, 1964, now Patent No. 3,307,458, and assigned to the same assignee as this invention. In such systems, it is desired to maintain a relatively constant level of developer within the tank. However, it is necessary constantly to replenish the developer in the tank as the various sheets or lengths of material pass through the developer tank or as a continuous web of such material passes through, whichever may be the case.

The developer liquid may be as described in the copending applications of Fauser et al., Ser. No. 762,756, filed Sept. 23, 1958, now Patent No. 3,311,490, and Ser. No. 420,449, filed Dec. 22, 1964, now abandoned, all assigned to the same assignee as this invention. Such developers include particles of toner which are in suspension in an insulating thinner. Toner particles may be formed of controlled agglomerations of pigments and resins, known as association complexes, and may be made up of a pigment and one or more bonding resins, held in suspension in a suitable hydrocarbon thinner liquid, as described in application Ser. No. 420,449.

Not only is it desirable to maintain a constant level of developer in the developer tank, but it is also highly desirable to maintain a constant concentration of the toner complexes with respect to the thinner. However, the toner and thinner are each being depleted somewhat independently of each other during the operation of the system. It is therefore desirable to add toner from a supply of toner concentrate to the tank independently of the supply of thinner, and each according to demand, in order to maintain desired concentration of toner-to-thinner in the developer liquid, to maintain constant quality of reproduction of the latent images. It is also desirable to maintain such concentration uniformly across the width of the incoming sheet material to avoid streaking and thinly developed areas on the material.

The developer, as described above, is susceptible to degradation due to excessive mechanical shear or agitation. This is believed due to the fact that the complexes of resin and toner are broken, wherein charge is lost, by excessive mechanical working or friction, reducing the total effectiveness of the developer liquid. It is accordingly important to avoid such shear and stresses which would result in degradation of the developer.

These desired objects are met by the apparatus of this invention which provides for the addition of thinner from a thinner supply and independently the addition of toner from a supply of toner concentrate. These separate parts are supplied in accordance with demand and are directed to a mixing zone in the apparatus which is remote from the inlet side of the developer tank into which the sheet material is being fed.

The system also includes apparatus for effecting a circular or peripheral flow of developer liquid through the mixing zone at a rate which is sufficient to mix the toner concentrate and thinner but which does not cause degradation of the toner. This mixing apparatus preferably forms a peripheral circulation around the tank which constantly supplies developer liquid at a desired and uniform concentration to the region of the tank at which the sheet material enters.

Preferably, the sheet material is guided and supported for movement through the tank on a drum roll. Due to friction between the sheet material and the liquid developer, the movement of the sheet material with the rolls acts as a pump and causes circulation of developer from the inlet to an outlet side of the tank. The tank construction of this invention provides for a secondary circulation of the developer in a peripheral manner around the tank by flow in spaces between the ends of the ends of the developer roll. Preferably, this circulation is sulficient to maintain makeup developer at the inlet side, and therefore exceeds the rate of liquid developer withdrawn due to the pumping action by reason of the sheet material moving through the tank.

It is accordingly a primary object of this invention to provide a liquid developer system, as outlined above, in which a liquid developer tank is provided with a mixing zone remote from the inlet side of the tank, together with apparatus for adding toner concentrate and thinner substantially at said mixing zone.

A further object of this invention is the provision of developing apparatus, as outlined above, in which a toner concentrate and a thinner are each added through independently controlled supply conduits to a developer tank.

A further object of this invention is the provision of a developing system, as outlined above, in which mechanical mixers and pumping elements are provided in a mixing zone to provide a peripheral or a secondary circulation of developer fluid for mixing a toner concentrate with a thinner and for maintaining a uniform concentration of developer at the inlet side of the tank.

These and other objects and advantages of the present invention will be apparent from the following description, the accompanying drawing and the appended claims.

In the drawing.

FIG. 1 is a perspective and somewhat diagrammatic view of a developer system constructed according to this invention; and

FIG. 2 is a perspective view of one of the impellers used with this invention.

Referring to the drawing, which illustrates a preferred embodiment of the invention, an open-top liquid developer tank is shown at 10 in FIG. 1 as including a partially semi-circular bottom 11 enclosed with opposite end walls 12 and 13.

The open top of the tank 10 receives a drum roll 15 therein so that the surface of the drum roll forms a relatively close running fit with the semi-circular bottom 11. The drum roll 15 has a diameter which is greater than the depth of the tank 10, so that an upper portion of the drum roll extends above the open side of the tank 10,

3 and has a length less than the width of the tank to define spaces 16 and 17 at each end thereof with the respective end walls 12 and 13.

The drum roll provides the means for supporting movement of sheet material 18 through the developer tank 10 from an inlet side 19 of the tank generally to an outlet side 20 in a direction of movement indicated by the arrows 21. The sheet material 18 may consist either of individual sheets or a continuous web of indeterminate length, upon which an electrophotographic image is formed.

As shown in FIG. 1, the inside surface of the sheet material 18 engages the drum roll 15 in intimate contact therewith prior to entering the tank 10, so that the inside surface of the sheet material 18 is in contact with the outside surface of the drum roll 15 at all times which is submerged within the tank and accordingly remains dry, while the outside surface becomes fully immersed within the liquid developer within the tank. The latent image on the outside surface of the sheet material 18 is developed as it passes through the developer 25 in the manner described in the above-identified applications.

As the material 18 leaves the tank 10 at the outlet side 20, it is subjected to the developer removing action of a nip formed between a squeegee roll 26 and the drum 15. The squeegee roll 26 may be partially submerged within the liquid developer 25, or may be positioned above the level of the developer, as shown in FIG. 1, and removes the excess developer fluid from the image side of the sheet material 18 as it leaves the tank.

Since the outer surface of the sheet material 18 is wetted by the developer, at certain amount of the thinner is removed from the developer 25. This is constantly made up to maintain a liquid level in the tank from a thinner supply 30-by a pump 31 connected to a float chamber 32 mounted on the end wall 12. The chamber 32 opens into the tank 10 and contains a float and needle valve assembly 33 which is responsive to the level of the liquid 25 and maintains this level constant by admitting thinner from the thinner supply 30 into the adjacent end space 16 formed between the end of the drum 15 and the adjacent wall 12.

Toner is removed from the developer 25 by deposition onto the sheet material in accordance with the density of the image. Means for separately adding toner includes a supply 40 of toner connected by a tube 41 to an electrically solenoid-operated valve 42 which is controlled by a solenoid 43. The valve 42 is positioned to discharge toner concentrate into one end of a mixing zone 45 formed on the tank adjacent the tank outlet side 20 and remote from the inlet side 19. For this purpose, the tank 10 is formed with a forwardly extending bottom portion 48 formed as a continuation of the bottom 11 but having a depth which is substantially less than the overall depth of the tank at the roll 15. The bottom portion 48 is terminated with an upwardly formed front wall 49 and forms with the previously described end walls 12 and 13 a tank extension positioned forwardly and adjacent to the outlet side 20 and in generally underlying relation to the squeegee roll 26, defining the zone 45.

The mixing zone 45 is accordingly in communication with the liquid 25 within the tank and may be considered as being formed as an integral extension of the tank, and extends the full width of the tank, to receive liquid therein from the peripheral end spaces 16 and 17 as well as from the circulation due to the movement of the material 18 from the inlet side 19 to the outlet side 20. The toner concentrate from the tank 40 is admitted substantially at one end of the mixing zone 45, preferably at the same side of the tank 10 at which the thinner is added by the float chamber 32.

The mixing zone 45 includes mixing and impeller means for mixing the toner concentrate and thinner with the liquid 25 and for forming a peripheral or circular endwise circulation of the liquid, designated by the arrows 1 4 v 50. This impeller means includes a plurality of disk-like impellers 52 (FIG. 2) mounted on a common shaft 53 extending for rotation through the zone 45 between the end walls 12 and 13. The shaft 53 is positioned such that all of the impellers 52 are submerged beneath the level of the liquid 25.

A relatively slow-tuming drive motor 55 is connected to rotate the shaft 53 at a rate which is suflicient to cause the impellers 52 to mix the incoming thinner and toner concentrate and to direct the same in the general direction of the arrows 50 peripherally by flow through the end spaces 16 and 17 formed at the opposite ends of the drum, and across the inlet side 19 of the tank 10. The rate of circulation is not critical, but preferably exceeds that caused by the pumping action of the roll 15 and material 18, as indicated by the broken arrows 58, so that a fresh supply of developer is at all times supplied across the width of the web 18 in the inlet side 19.

As shown in FIG. 2, the impeller 52 may include a hub on which a slotted disk 63 of sheet material is formed with partially radially extending slots 65 defining four vanes 68. The vanes 68 are suitably angulated to form an impeller of high lift pitch. Good results have been obtained with impellers of approximately 1% inches in diameter at 5-6 inch spacing along the shaft 53, operating at 300 r.p.m., but these sizes, spacing and speed are not considered critical as lOng as the volumetric displacement of the combined impellers is sufiicient to provide the peripheral circulation in excess of the requirements at the inlet side 19 of the tank, with sufficient motion to mix the added toner concentrate with the added insulating thinner and liquid 25 without degradation of the toner agglomerations.

The supply of toner is controlled by the periodic operation of the solenoid 43. This may be controlled, in turn, in accordance with a timed cycle, but is preferably controlled in accordance with the amount of printing on the material 18 moving through the system. For this purpose, the drum roll 15, or a proceeding roll in the system, may be supplied with a suitable timing cam which operates a timer whose setting is adjusted proportional to the printed area which operates solenoid 43 intermittently. In this manner, the amount of toner is added as a function of the printed area on the sheet material 18.

It will therefore be seen that this invention provides a developer system in which the insulating thinner and the toner concentrate are separately added and are mixed in a zone remote from the inlet side of the tank and in which a secondary or peripheral circulation is maintained to supply a recharged developer mixture at the input or inlet side of the drum, providing uniform developing across the width of the drum and a uniform quality of the developer liquid.

While the form of apparatus herein described constitutes a preferred embodiment of the invention, it is to be understood that the invention is not limited to this precise form of apparatus, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

1. In an electrostatic liquid developing system, the improvement in developer construction comprising a liquid developer tank, means for guiding sheet material having an electrostatic image thereon into an inlet side of said tank and out of an outlet side thereof causing the development of said electrostatic image by deposition of toner material from the developer liquid in said tank and causing a first circulation of developer fluid in said tank generally from said inlet to said outlet sides by reason of the movement of said sheet material therethrough, means for adding developer thinner to said tank maintaining a predetermined level of developer thereon, means in said tank defining a developer mixing zone remote from said inlet side, means for adding toner concentrate into said tank substantially at said mixing zone, and impeller means in said zone for combining said thinner and said toner concentrate and effecting a secondary circulation of said liquid peripherally about said sheet guiding means for supplying make up developer at said inlet side maintaining a balanced concentration of said developer, said impeller means being eflective to cause said secondary circulation at a rate which exceeds that of said first circulation.

2. The developer system of claim 1 in which said sheet material guiding means comprises a drum partially submerged in said tank for guiding said sheet material from said inlet side to said outlet side, a squeegee roll positioned to apply pressure against said drum positioned generally above said outlet side for removing excess developer from said sheet material, means in said tank at the opposite ends of said drum defining open spaces providing for said peripheral circulation of said developer fluid past the ends of said drum.

3. The system of claim 2 in which said mixing zone is positioned adjacent said outlet side in said tank, and extending transversely substantially the width of said drum, said impeller means comprising a plurality of impellers positioned in said mixing zone for effecting said peripheral circulation, and motor driven means connected to rotate said impellers at a rate suflicient to supply makeup developer liquid through said peri heral circulation to the said inlet side of said tank while preventing excessive shear and agitation which would cause degradation of said developer.

4. In an electrostatic liquid developing system, the improvement in developer construction comprising a liquid developer tank having end walls and a semi-circular bottom, 9. roll partially received in said tank for guiding sheet material having an electrostatic image thereon into an inlet side of said tank and out of an outlet side thereof causing the development of said electrostatic image by deposition of toner material from the developer liquid in said tank and effecting a circulation of developer fluid in said tank generally from said inlet to said outlet sides by reason of the movement of said sheet material therethrough, means between said tank end walls and the ends of said roll defining passageways for the flow of developer liquid therethrough, means in said tank defining a developer mixing zone adjacent the said outlet side of said tank opening into each of said passageways, float means for adding developer thinner to said tank for mixing in said zone, means for adding toner concentrate into said tank for mixing at said mixing zone, and impeller means in said zone for combining said thinner and said toner concentrate and effecting a secondary circulation of said liquid through said passageways for supplying make up developer at said inlet side maintain a balanced concentration of said developer.

References Cited UNITED STATES PATENTS 3,227,549 1/1966 Ullrich et al 96-1 3,242,902 3/1966 Ulary 118-637 3,284,224 11/1966 Lehmann 117-17.5 3,299,787 1/1967 Kolb et al. 118637 XR FOREIGN PATENTS 938,349 10/1963 Great Britain.

CHARLES A. WILLMUTH, Primary Examiner. PETER FELDMAN, Assistant Examiner.

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