Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
1999-12-21
2001-04-10
Martin, Roland (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C430S058600, C430S058650, C430S083000, C399S159000
Reexamination Certificate
active
06214503
ABSTRACT:
BACKGROUND OF THE INVENTION
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 OF THE INVENTION
In a first aspect, the invention features an organic photoreceptor that may be provided, e.g., in the form of a drum or flexible belt. The photoreceptor includes:
(a) a first charge transport compound having the formula:
where X is an N-alkyl-substituted carbazole (e.g., where the alkyl group is a C
1
-C
6
alkyl group), an N-aryl-substituted carbazole (e.g., where the aryl group is a phenyl or naphthyl group), or a p-(N,N-disubstituted)arylamine (e.g., a dialkyl-substituted phenyl or naphthyl amine); Ar is a group having the formula:
R
1
is a hydrogen, halogen, or alkyl group (e.g., a C
1
-C
6
alkyl group);
R is a hydrogen, halogen, OH, CN, OR
2
, or OCOR
3
group;
R
2
is an alkyl (e.g., a C
1
-C
6
alkyl), aryl (e.g., phenyl or naphthyl), or alkaryl (e.g., tolyl) group;
R
3
is a hydrogen, alkyl (e.g., a C
1
-C
6
alkyl), aryl (e.g., phenyl or naphthyl), or haloalkyl (e.g., chlorophenyl or chloronaphthyl) group; n is 0 or 1;
A is a group having the formula:
Z is O or S;
Q is O, S, or CH
2
; and
m is 0 or 1;
(b) a charge generating compound; and
(c) an electroconductive substrate.
The charge transport compound may or may not be symmetrical. Thus, for example, groups X, Ar, and R for one “arm” of the compound may be the same or different from the X Ar, and R groups in the other “arm” of the compound.
The charge transport compound can function as both a charge transport compound and a binder, thereby facilitating the preparation of layered structures. For example, in one embodiment, the organic photoreceptor includes a layer deposited on the electroconductive substrate, in which the layer includes the charge transport compound and the charge generating compound.
In a second embodiment, the organic photoreceptor includes (a) a charge transport layer that includes the charge transport compound (and, optionally, a second charge transport compound having a different structure); (b) a charge generating layer that includes the charge generating compound (and, optionally, the charge transport compound); and (c) the electroconductive substrate. In one arrangement, the charge transport layer is intermediate the charge generating layer and the electroconductive substrate, while in another arrangement the charge generating layer is intermediate the charge transport layer and the electroconductive substrate. The charge transport layer, the charge generating layer, or both, may further include a separate polymeric binder such a polyvinyl butyral or polycarbonate.
Specific examples of suitable materials for the first charge transport compound include compounds having the following formulae:
The invention also features the charge transport compounds themselves, as well as charge transport compounds, and organic photoreceptors based upon such charge transport compounds, that are the reaction product of a multi-functional isocyanate (i.e., an isocyanate reactant having two or more isocyanate groups available for reaction) and the above-described compounds in which R is a hydroxyl group. The isocyanate groups react with the hydroxy groups to form charge transport compounds having urethane linkages.
In a second aspect, the invention features an electrophotographic imaging apparatus that includes (a) a plurality of support rollers, at least one of which has a diameter no greater than about 40 mm; and (b) the above-described organic photoreceptor supported by these rollers. The apparatus preferably includes a liquid toner dispenser as well.
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 comprising 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 o
Gaidelis Valentas
Gavutiene Janina
Getautis Vytautas
Grazulevicius Juozas Vidas
Jankauskas Vygintas
Buharin Amelia A.
Imation Corp.
Martin Roland
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