Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
2000-03-16
2002-01-22
Dote, Janis L. (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C430S056000, C430S058600, C430S079000, C399S162000, C548S440000, C548S444000
Reexamination Certificate
active
06340548
ABSTRACT:
BACKGROUND
This invention relates to organic photoreceptors suitable for use in electrophotography.
In electrophotography, a photoreceptor in the form of a plate, belt, or drum having an electrically insulating photoconductive element on an electrically conductive substrate is imaged by first uniformly electrostatically charging the surface of the photoconductive layer, and then exposing the charged surface to a pattern of light. The light exposure selectively dissipates the charge in the illuminated areas, thereby forming a pattern of charged and discharged areas. A liquid or solid toner is then deposited in either the charged or discharged areas to create a toned image on the surface of the photoconductive layer. The resulting visible toner image can be transferred to a suitable receiving surface such as paper. The imaging process can be repeated many times.
Both single layer and multilayer photoconductive elements have been used. In the single layer embodiment, a charge transport material and a charge generating material are combined with a polymeric binder and then deposited on the electrically conductive substrate. In the multilayer embodiment, the charge transport material and charge generating material are in the form of separate layers, each of which can optionally be combined with a polymeric binder, deposited on the electrically conductive substrate. Two arrangements are possible. In one arrangement (the “dual layer” arrangement), the charge generating layer is deposited on the electrically conductive substrate and the charge transport layer is deposited on top of the charge generating layer. In an alternate arrangement (the “inverted dual layer” arrangement), the order of the charge transport layer and charge generating layer is reversed.
In both the single and multilayer photoconductive elements, the purpose of the charge generating material is to generate charge carriers (i.e., holes and electrons) upon exposure to light. The purpose of the charge transport material is to accept these charge carriers and transport them through the charge transport layer in order to discharge a surface charge on the photoconductive element.
To produce high quality images, particularly after multiple cycles, it is desirable for the charge transport material to form a homogeneous solution with the polymeric binder and remain in solution. In addition, it is desirable to maximize the amount of charge which the charge transport material can accept (indicated by a parameter known as the acceptance voltage or “V
acc
”), and to minimize retention of that charge upon discharge (indicated by a parameter known as the residual voltage or “V
res
”).
Liquid toners generally produce superior images compared to dry toners. However, liquid toners also can facilitate stress crazing in the photoconductive element. Stress crazing, in turn, leads to printing defects such as increased background. It also degrades the photoreceptor, thereby shortening its useful lifetime. The problem is particularly acute when the photoreceptor is in the form of a flexible belt included in a compact imaging machine that employs small diameter support rollers (e.g., having diameters no greater than about 40 mm) confined within a small space. Such an arrangement places significant mechanical stress on the photoreceptor, and can lead to degradation and low quality images.
SUMMARY
In a first aspect, the invention features an organic photoreceptor that includes:
(a) a change transport compound having the formula
where R
1
and R
2
, independently, are hydrogen, an alkyl group (e.g., a C
1
-C
6
alkyl group), or an aryl group (e.g., a phenyl or naphthyl group);
R
3
is hydrogen or a hydrazone group having the formula
R
4
and R
5
, independently, are hydrogen, an alkyl group (e.g., a C
1
-C
6
alkyl group), or an aryl group (e.g., a phenyl or naphthyl group);
R
6
is an aryl group (e.g., a phenyl or naphthyl group); straight or branched alkyl group having at least 7 carbon atoms; a group having the formula —(CH
2
)
n
—Ar where n is at least 3, Ar represents an aryl group (e.g., a phenyl or naphthyl group), and one or more methylene groups is optionally substituted with a hetero atom; or a carbazole group having the formula
where R
7
, R
8
, R
9
, and R
10
, independently, are hydrogen, an alkyl group (e.g., a C
1
-C
6
alkyl group), or an aryl group (e.g., a phenyl or naphthyl group); n is at least 3; and one or more methylene groups is optionally substituted with a heteroatom;
(b) a charge generating compound; and
(c) an electroconductive substrate.
The organic photoreceptor may be provided in the form of a flexible belt. In one embodiment, the organic photoreceptor includes: (a) a charge transport layer comprising at least one of the charge transport compounds and a polymeric binder; (b) a charge generating layer comprising the charge generating compound and a polymeric binder; and (c) the electroconductive substrate. The charge transport layer preferably has a glass transition temperature of at least about 80° C. In one embodiment, the charge transport layer includes two of the charge transport compounds in a ratio with one another of about 9:1 to about 1:1. The charge transport layer may be intermediate the charge generating layer and the electroconductive substrate. Alternatively, the charge generating layer may be intermediate the charge transport layer and the electroconductive substrate.
In one preferred embodiment, a charge transport compound is selected in which R
3
is a hydrazone group, R
4
is a methyl group, and R
5
is a phenyl group. Specific examples of suitable charge transport compounds have the following formulae:
The charge transport compounds may be used alone or in combination with each other. The invention also features the charge transport compounds themselves.
In a second aspect, the invention features an electrophotographic imaging apparatus that includes (a) a plurality of support rollers and (b) the above-described organic photoreceptor in the form of a flexible belt supported by the support rollers. Preferably, at least one of the support rollers has a diameter no greater than about 40 mm. The apparatus preferably further includes a liquid toner dispenser.
In a third aspect, the invention features an electrophotographic imaging process that includes (a) applying an electrical charge to a surface of the above-described organic photoreceptor; (b) imagewise exposing the surface of the organic photoreceptor to radiation to dissipate charge in selected areas and thereby form a pattern of charged and discharged areas on the surface; (c) contacting the surface with a liquid toner that includes a dispersion of colorant particles in an organic liquid to create a toned image; and (d) transferring the toned image to a substrate.
In a preferred embodiment, the organic photoreceptor is in the form of a flexible belt, e.g., a flexible belt supported by a plurality of support rollers, at least one of which has a diameter no greater than about 40 mm.
The invention provides organic photoreceptors featuring a combination of good mechanical properties and electrostatic properties. These photoreceptors can be used successfully with liquid toners to produce high quality images even when subjected to significant mechanical stresses encountered when the photoreceptor is in the form of a flexible belt supported by a plurality of small diameter rollers. The high quality of the images is maintained after repeated cycling.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof and from the claims.
DETAILED DESCRIPTION
The invention features organic photoreceptors that include charge transport compounds having the formulae set forth in the Summary of the Invention, above. The charge transport compounds are aryl hydrazone-functional carbazoles. They are preferably prepared via N-alkylation of a carbazole, followed by a Vielsmayer reaction to form an aldehyde group on the carbazole molecule, and then reaction of the aldehyde with a hydrazin
Jubran Nusrallah
Smith Terrance P.
Tokarski Zbigniew
Buharin Amelia A.
Dote Janis L.
Imation Corp.
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