US3532071A - Development apparatus - Google Patents

Description

United States Patent inventor Alan F. McCarroll Rochester, New York Appl. No. 669,839 Filed Sept. 22, 1967 Patented Oct. 6, 1970 Assignee Xerox Corporation, Rochester, N.Y.,

a corporation of New York DEVELOPMENT APPARATUS 6 Claims, 2 Drawing Figs.

U.S. Cl 118/637, 222/406 Int. Cl B05b 5/00 Field ofSearch 118/637,

308-312: lI7/l7.5, (lnquired); 222/406; 95/109; 346/(ES) References Cited UNITED STATES PATENTS 10/1936 Wallach et al. l l8/(Anti-ol'fset1UX 9/1959 Greaves 1 18/637 10/1964 Schaffert r. 118/637 2/1967 Rarey et al.. 1l7/l7.5UX 5/1967 l-lojo et al... 118/637 12/1967 Bhagat l 18/637 l/l968 Olden ll7/l7.5UX 9/1968 Gawron 118/637 Primary Examiner-Morris Kaplan Atmrneys- Stanley Z. Cole and Norman E. Schrader ABSTRACT: An applicator-brush-roll in an electrostatic developing apparatus is charged with toner particles by employing an apertured donor member which rotates in mesh with the development brush causing a portion of the fibers on the development brush to physically penetrate the donor member and pick up toner particles.

Patented Oct. 6, 1970 INVENTOR. ALAN F. MC CARROLL BY I v ATTORNEYS 1 DEVELOPMENT APPARATUS BACKGROUND OF THE INVENTION This invention relates in general to xerography and in particular to an improved apparatus for developing electrostatic latent images on a xerographic plate.

In many copying techniques, such as Xerography, a latent image is first formed on the recording surface and then developed with a marking material. In the case of xerography the marking material normally used is a finely divided colored material called toner. To develop the latent image with toner one technique is to pass a brush loaded with charged toner particles across the surface bearing the latent image. As the fibers on the brush interfere with the surface holding the electrostatic charge pattern, the toner particles are attracted and adhere to the surface in imagewise configuration.

One type of brush commonly used in this apparatus is a brush having pile-like fibers which protrude from a backing material. These brushes can be made of either a natural material such as rabbit fur or a synthetic material such as velvet. In any event, the material is characterized by short, soft and dense pile-like fibers which carry toner particles. Although the pile-like development brush generally-yields excellent images, this type of brush has some practical problems in use.

One problem is loading the fibers with toner particles. When a pile-like material such as natural rabbit fur is employed in the development brush, best development occurs when the toner particles are evenly dispersed through the individual fibers on the brush. Merely allowing the'fur brush to pass through a reservoir of toner particles to accomplish loading is undesirable because the reservoir soon becomes packed due to the contact and vibrations of the brush therebymaking loading very inefficient. This packed condition is somewhat averted by placing augers in the reservoir to keep the toner particles in aloose consistency, but some degree of packing will still occur.

Another problem in loading a fibrous brush is that the individual fibers become matted, or entwined and tangled, as the brush comes into contact with the surface'bearing the latent electrostatic charge pattern and/or the reservoir of toner particles. A matted brush cannot be loaded with as many toner particles as a brush with fibers that are combed, or in an untangled condition, and, further, cannot deposit as many toner particles on the surface bearing the latent image.

A third problem in loading a pile-like brush with toner particles results from the inability of a brush to retain a uniform charge on the toner particles. The latent electrostatic charge pattern is developed by depositing finely divided charged toner particles on it. The toner particles are held in image configuration by electrostatic attraction between them and the image charge pattern. Where the charge is greatest on the surface, the greatest amount of toner is deposited; and where the charge is least on the surface, little or no toner is deposited. Once the toner particles assume image configuration, they must remain in place until the image is made permanent. Therefore, a uniform charge of sufficient potential must be placed on the toner particles before the image is developed.

Accordingly it is an object of this invention to improve the apparatus for loading pile-like development brushes with charged toner particles.

It is a further object to improve the apparatus for loading a pile-like development brush by preventing matting of the individual fibers on the brush.

A still further object is to improve the apparatus for charging toner particles uniformly as they are loaded onto apilelike development brush.

A still further object is to improve the apparatus for controlling the amount of toner powder cloud generated while developing with a pile-like development brush.

SUMMARY The means for loading a development brush with charged toner particles in this invention includes a rotatable donor member having toner particles therein which is placed in mesh with the fibers on a pile-like development brush. The donor member is made of an apertured material having an electrostatic property different from the electrostatic property of the toner particles and fibers. The apertures in the donormember are large enough to allow toner particles and fibers to pass through it, and when the peripheral speed of the donor member approximates the peripheral speed of the fibers on the development brush, the individual fibers, as they are brought adjacent to the donor member, mesh with the donor member and protrude into the supply of toner particles held within the donor member. The donor member and development brush continue to rotate and the fibers that entered the donor member are withdrawn carrying toner particles from the donor member. As the toner particles pass through the donor member they rub against the donor member material and are charged triboelectrically.

DESCRIPTION OF THE DRAWINGS For a better understanding of the invention as well as other objects and further features thereof, reference is had'to the following detailed description of the invention to be used in conjunction with the accompanying drawings:

FIG. 1 is a schematic illustration showing a typical Xerographic device in which the present method of development can be used, and

FIG. 2 is a schematic illustration showing the relative positions of the surface being developed, donor member and development brush.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings, FIG. 1 shows a typical xerographic machine in which the present mode of development can be used. The principal element of the machine is photosensitive member 11. This member consists of drum 12 which is driven about shaft 16 by a motor (not shown). The drum is covered with layer 13 of electrically conductive .material which, in turn, is covered on its outer surface with layer 14 of photoconductive insulating material such as vitreous selenium. As electrostatic latent image is formed on member 11 by passing it under sensitizing station 24 and exposing station 17. The sensitizing station consists of any suitable means for placing a uniform charge on layer 14 such as corotron 26; that is, a corona charging device. The exposing station has light source 23 and lens 18, and transparency l9 feedably disposed between the light source and lens. The transparency is fed from reel 21 through the beam of light generated bysource 23 and then rewound on reel 22 after being exposed. The light, transparency and lens, working in combination, project on the photosensitive member an optical image whose movement is synchronized with that of the drum. The projected optical image causes selective charge dissipation in illuminated areas of layer 14, thus forming an electrostatic image. Other means of forming electrostatic latent images including means for forming images on ordinary insulating surfaces are known in the art and may be used instead of the one shown. I

After the sensitizing and exposing steps are completed, the photosensitive member passes by development station 27 which will be described more fully in conjunction with FIG. 2-. Following image development, the image is transferred from photosensitive member 11 to a web of paper or the like 37 between guide rolls 38 and 39, which act to position web 37 against photosensitive member 11, by a second corona device 41. Web 37 is fed from reel 34 before transfer and is rewound on reel 36 after transfer and fusing. Fusing element 42 is positioned to heat the transferred image and thus fix and per-.

up of rotary cylindrical brush 44 which contacts the photosensitive member subsequent to image transfer and removes any residual image material from layer 14 thereby readying it for reuse. The above described process and apparatus are conventional in the art as is evidenced in U.Sv Pat. No. 3,117,891. Any of the many known equivalents of process or apparatus elements may be employed in connection with the present invention.

Now referring to FIG. 2, the photosensitive surface of drum 46 has a latent electrostatic charge pattern existent on its outer periphery which is developed with charged toner particles administered to the drum by development brush 47. Brush 47 and donor member 52 are the primary elements of the development system. Donor member 52 is shaped in the form of a hollow cylinder and can be made of any suitable nonconductive material, or in the alternative, any suitable material having an electrostatic property different than the electrostatic properties of the toner particles and fibers on brush 47. The significance of using a material of a different electrostatic property than the fibers or toner particles will be discussed in detail hereafter.

The latter alternative in the construction of donor member 52 is shown in FIG. 2. The donor member is constructed in two layers; inside layer 53 and outer layer 54. Inside layer 53 is made ofa rigid material such as brass which forms the general shape of the member. This layer is grounded so that it does not affect electrically any charged toner particle as it passes through the donor member. Outer layer 54 is made of any suitable material which occupies a position in the triboelectric series which is different from the position occupied by the toner particles so that as toner particles are withdrawn from the donor member they will be charged triboelectrically. One example of a suitable material that can be used in layer 54 is silk. Both inner layer 53 and outer layer 54 should have apertures which are large enough to allow the free passage offibers on brush 47 and toner particles.

Development brush 47 comprises core 48 having rigidly fastened thereto a fur pad. The core can be either nonconductive and grounded, or biased in the polarity opposite the polarity existent on the toner particles before they are withdrawn from the donor member or placed on the toner particles triboelectrically as they pass through the donor member. The fur pad is composed of two distinct, but unified components; a backing material 49 corresponding to the hide of the animal from which the fur pad is made and bristles or fibers 51 which protrude outwardly from the backing material and which carry the toner particles to the surface being developed, The development brush can be made of any suitable material which has the ability to carry toner particles to the surface bearing the latent image; for instance, natural fur, cloth such as velvet having a fibrous surface or other similar material bearing a multiplicity of the elongated carrier members on the surface. The brush shown in FIG. 2 is rabbit fur since it has been found that this type of fur yields excellent development quality.

As indicated by the arrow on drum 46, it is rotated in the clockwise direction (drive means not shown). Development brush 47 can be rotated in either direction, but it has been found that it is preferable to rotate it in the counterclockwise direction, when the drum rotates in the clockwise direction, at approximately the same peripheral speed as the peripheral speed of the drum to assure efficient development. According to the present invention, when the development brush rotates in the counterclockwise direction, the donor member should rotate (means not shown) in the clockwise direction to assure that the fibers on the development brush properly mesh with the donor member, as indicated by the arrow on the donor member. Housing 45 encircles both the development brush and donor member keeping all toner particles within its boundaries. Member 52 and brush 47 mesh with one another as they rotate due to the fact that the fibers on the brush interfere with the donor member.

The toner particles held within the donor member represent the supply of toner with which the brush is loaded and can be in either a charged or an uncharged condition before being removed by the fibers. Assuming that the toner particles are in an uncharged condition while within the donor member, the charge necessary for development is placed on the toner particles triboelectrically as they are withdrawn from the donor member. The fibers protrude into the quantity of toner particles held within the donor member and pick up individual toner particles to be withdrawn. The particles are held by the fibers due to an electrostatic charge placed on the fibers as they pass through the donor member on their way in. In the alternative, the fur brush could be biased in order to assure that the toner particles were attracted to the fibers. As the tonerladen fibers are withdrawn from the member, the individual toner particles rub against the silk layer of the member and an electrostatic charge is placed on the particles triboelectrically. If, on the other hand, the toner particles were charged prior to being placed in the donor member, the silk layer would not be necessary on the donor member. Instead of charging device. the donor member would serve merely as a loading device. However, it is more advantageous to keep the silk layer in the donor member even though the toner particles are charged before being loaded on the development brush to assure that the toner particles all bear a uniform and sufficient charge when being deposited on the drum.

Another measure that can be taken to assure that the toner particles have a sufficient charge during development is the placement of mixing vanes 55 in the donor member. These rigid vanes, spaced around the inside surface of the member, are covered with any suitable material having an electrostatic property different from that of the toner particles so that as the toner particles rub against the vanes they acquire a charge triboelectrically. In addition to being charged, the quantity toner particles in the donor member will be kept in a loose consistency by the vanes thereby facilitating the loading of fibers on the development brush.

Charged toner particles can also be held in the donor member in the form of a developer mixture. Such developer is a mixture of charged toner particles and oppositely charged carrier beads. The carrier beads which function to carry the toner particles and to generate triboelectric charges on the toner particles, normally comprise a core, base or interior composed of any selected material which may be of high specific gravity such as glass or steel beads, covered with and encased in a suitable covering which imparts the necessary triboelectric properties to the granular carrier material.

Similar to the relationship between the toner particles and layer 54 and the toner particles and vanes 55, the triboelectric relationship between the toner powders and granular carrier depends on their relative positions in the triboelectric series. In triboelectrification theory materials are arranged in a column in such a way that each material is charged with positive electricity when contacted with any material below it in the series and with negative electricity when contacted with any material above it in the series. It is desirable to select the toner particles and granular carrier materials so that their mutual electrification is considerable. The degree of such electrification is governed in most cases by the distance between the positions in the triboelectric series; that is, the greater distance they are removed from one another, the greater the mutual electrification and the closer they are together in the series the less the mutual electrification. For a better description of how the triboelectric charge is generated on the toner particles, reference is had to U.S. Pat. No. 2,618,551.

When such a developer mixture is used, the donor member should have apertures large enough to allow the toner particles and fibers to pass through it, yet small enough to retain the carrier beads within the donor member at all times. In this way the carrier beads will always be retained in the donor member and only the toner will have to be replenished. As the donor member revolves, the carrier beads and toner particles are constantly being mixed within the donor member thereby causing the two to continuously rub against each other and to fully develop the triboelectriccharge on the toner particles. This constant mixing and impact also separates some of the charged toner particles from their respective carrier beads allowing them to be picked up by the fibers which protrude through the donor member.

As the donor member and development brush mesh, the individual fibers on the development brush protrude through the member and immerse themselves in the loose bed of toner particles held within the donor member. Then, as the donor member and development brush continue to rotate the fibers will eventually be withdrawn from the donor member carrying with them particles of toner.

In addition to charging the individual toner particles with the requisite charge for development as described above, the meshing action of the fibers with the donor member as the fibers are being withdrawn creates a small powder cloud in the area between the development brush, donor member and drum. This powder cloud is a result of the inherent flicking action the individual fibers experience as they are removed from the donor member. It has been found that the fibers, just as they complete withdrawal from the donor member, are deflected from their natural stance and are actually set in a pendulum-like motion. This action flicks some of the toner particles held by the fiber towards the latent image on the drum. The generation of such a powder cloud of toner is advantageous especially in solid area development. It is for this reason that housing 47 is so designed as to leave a small area for the powder cloud to form and contact the drum. In addition to the toner particles being picked up by the fibers protruding through the donor member, some quantity of toner particles pass through the donor member at points other than where the fibers mesh. For this reason, housing 45 surrounds the development brush and donor member almost completely,

to contain all loose toner particles which have escaped from within the donor member or the brush. Such loose toner particles are brought around to the normal loading point (where meshing occurs) for the brush fibers by the continuous rotation of the brush and donor member, and eventually are loaded on the fibers of the brush.

In addition to the apparatus outlined above many other modifications and/or additions to this invention will be readily apparent to those skilled in the art upon reading this disclosure, and these are intended to be encompassed with the scope of the invention.

Iclaim:

1. In an apparatus for developing latent electrostatic images wherein a development brush having toner-laden, pile-like fibers is rotated in interference with a latent image-bearing surface to selectively deposit toner particles in accordance with the electrostatic charge pattern thereon, the improved apparatus for loading the development brush comprising:

a. a cylindrical, hollow, apertured donor member adjacent to and in mesh with the fibers of the development brush, said donor member containing toner particles therein; and

b. means to rotate the peripheral surface of the donor member approximately the same speed as the speed of the fibers on the development brush whereby a portion of the fibers adjacent the donor member penetrate the member and contact the toner particles held within the member.

2. In an apparatus for developing latent electrostatic images wherein a development brush having toner-laden, pile-like fibers is rotated in interference with the latent image-bearing surface to selectively deposit charged toner particles in accordance with the electrostatic charge pattern, the improved apparatus for placing an electrostatic charge on the toner particles comprising: I

a. a hollow, apertured donor member adjacent to and in mesh with the fibers of the development brush, said donor member being made of a material having an electrostatic property and containing a quantity of toner particles having an electrostatic property dr ferent than the donor member; and

b. means to rotate the peripheral surface of the donor member approximately the same speed as the speed of the fibers on the development brush whereby the toner particles are charged triboelectrically as they are withdrawn from the donor member by the fibers.

3. The apparatus in claim 2 in which the development brush comprises rabbit fur.

4. The apparatus in claim 2 further including mixing vanes rigidly attached to the inner surface of the donor member, said mixing vanes having an electrostatic property different from that of the toner particles whereby as the donor member rotates, the mixing vanes maintain the toner particles in a loose consistency and place an electrostatic charge on the toner particles triboelectrically.

5. The apparatus according to claim 2 in which the donor member comprises silk.

6. The apparatus of claim 2 in which the donor member contains developer consisting of a mixture of charged toner particles and oppositely charged carrier beads.

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