Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Process of making radiation-sensitive product
Reexamination Certificate
1999-11-24
2001-04-10
Chapman, Mark (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Process of making radiation-sensitive product
C430S132000, C430S134000, C118S621000, C118S624000, C264S452000, C425S174600, C427S457000, C427S470000
Reexamination Certificate
active
06214513
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention generally relates to a process for applying a coating material to a surface of a substrate. More particularly, this invention relates to a process for applying a charge generating material to a photoreceptor substrate, and to photoreceptors made by such a process.
2. Description of Related Art
Among the many conventional methods of coating a substrate with a coating material is the use of an extrusion or slot die from which the coating material is extruded onto the substrate. Using such slot coating of thin layers, the window of operating parameters is extremely small and is affected by factors such as the coating thickness, the speed of the substrate, the theological properties of the coating liquids, the vacuum pressure, the relative speed of the extruded coating material, the amount of pressure applied to the coating material as it progresses through the extrusion slot, etc.
Extrusion coating methods for forming thin layers are described in U.S. Pat. Nos. 4,521,457 and 5,614,260, the entire disclosures of which are totally incorporated herein by reference.
Such extrusion coating methods have conventionally been used to manufacture Xerographic photoreceptors. Xerographic photoreceptors are typically prepared using either a single layer configuration or a multilayer configuration. The multilayer arrangement is more common. In the multilayer configuration, the active layers are the charge generation layer (CGL) and the charge transport layer (CTL). Charge generation layers are usually prepared as dispersions of pigment particles in a polymer host. Most charge generation layers conventionally range from between 0.1 and 5 microns in dry thickness. In contrast, transport layers conventionally range from about 20 to 29 microns thick. In the multilayer configurement, additional layers, such as blocking, adhesion, overcoat and undercoard layers may optionally be included as desired.
Generally, each of the charge generation and charge transport layers is applied separately onto a substrate. The charge generation layer is typically coated onto a blocking layer, under which there can be an undercoat layer for providing adhesion and optionally a blocking function over the substrate. Then, the charge transport layer is typically coated over the charge generation layer.
The use of conventional extrusion slot die methods of forming thin coatings of dispersions of photoconductive particles can produce defects resembling brush marks along each edge of the deposited coating. These brush marks can remain as defects in the dried coating and can ultimately print out as undesirable artifacts in the final electrophotographic copy.
The coating materials for charge generation layers of photoreceptors can be Newtonian but are often made of Non-Newtonian dispersions, which show shear thinning, thixotropic and yield stress behaviors. The dispersion shows little or no deformation up to the yield stress, which can lead to flocculation of dispersion particles in the coated film.
U.S. Pat. No. 5,531,872 to Forgit et al., the entire disclosure of which is incorporated herein by reference, discloses a static process for fabricating a photoconductive member including depositing a photoconductive material, such as a charge generating material, and a charge transport material on a substrate, sequentially in any order, or simultaneously. The photoconductive material, the charge transport material, or both, are electrophoretically deposited onto the substrate from a liquid composition using a voltage of from 8 to 60 volts to create an electric field. The electrophoretic deposition is accomplished by maintaining the electric field for up to five minutes.
SUMMARY OF THE INVENTION
It is difficult to slot coat a high quality single layer coating of a charge generation layer onto a substrate because of generally low liquid viscosity, shear thinning and yielding stress due to the nature of the dispersion and the typically extremely thin layer requirements. For example, the benzimidazole perylene (BzPe) and Hydroxygallium phthalocyanine (HOGaPc) binder system solutions that are commonly used to produce photoreceptors have very narrow coating windows. The resulting coating yields can be lower than desired. Thus, a need exists for improved coating methods that provide higher yield and higher quality of coated substrates.
This invention provides systems and methods for coating a moving substrate using a slot die with an applied electric field.
In various exemplary embodiments of the systems and methods of this invention, a charge generator layer dispersion is fed from a coating die containing a single slot onto a moving substrate. An electrical field is imposed between the coating die and the moving substrate. The dispersion particles that form the charge generation layer have charges. Thus, under the electrical field, these particles deposit on the substrate while still in the coating gap region.
A charge generating layer can be “developed” out using the single slot die to provide a CGL or both a CGL and a CTL simultaneously with the single slot. Thus, a two layer coating can be produced using only a single slot die and a single coating solution. This eliminates one entire coating step while improving both productivity and yield. Alternatively, a simultaneous two slot coating can be used with the CGL and CTL being initially separated and deposited from the separate slots.
This invention can be used to produce electrostatographic charge generating material with an increased yield, better layer properties, thinner layers and increased throughput.
These and other features and advantages of this invention are described in or are apparent from the following detailed description of the preferred embodiments.
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Cai Jian
Dunham Robert F.
Morrison Ian D.
Scharfe Merle Emil
Chapman Mark
Oliff & Berridg,e PLC
Xerox Corporation
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