U.S. patent application number 12/640255 was filed with the patent office on 2011-06-23 for undercoat layer and imaging members comprising same.
This patent application is currently assigned to XEROX CORPORATION. Invention is credited to Robert P. Altavela, Nancy L. Belknap, Helen R. Cherniack, Kent J. Evans, Edward F. Grabowski, Adilson P. Ramos, Yuhua Tong, Jin Wu.
Application Number | 20110151363 12/640255 |
Document ID | / |
Family ID | 44151587 |
Filed Date | 2011-06-23 |
United States Patent
Application |
20110151363 |
Kind Code |
A1 |
Tong; Yuhua ; et
al. |
June 23, 2011 |
UNDERCOAT LAYER AND IMAGING MEMBERS COMPRISING SAME
Abstract
Disclosed are undercoat layers comprising a metal oxide, a
polymer, and a citrate of Formula (I): ##STR00001## wherein R.sub.1
is H, alkyl, or COR'; wherein R' is alkyl; and wherein R.sub.2,
R.sub.3, and R.sub.4 are independently alkyl. The undercoat layers
are useful in imaging members because they are easily separated
from the substrate. This reduces the number of steps necessary to
reclaim the substrate.
Inventors: |
Tong; Yuhua; (Webster,
NY) ; Wu; Jin; (Pittsford, NY) ; Altavela;
Robert P.; (Webster, NY) ; Grabowski; Edward F.;
(Webster, NY) ; Evans; Kent J.; (Lima, NY)
; Ramos; Adilson P.; (Bahia, BR) ; Belknap; Nancy
L.; (Rochester, NY) ; Cherniack; Helen R.;
(Rochester, NY) |
Assignee: |
XEROX CORPORATION
Norwalk
CT
|
Family ID: |
44151587 |
Appl. No.: |
12/640255 |
Filed: |
December 17, 2009 |
Current U.S.
Class: |
430/56 ; 430/97;
524/283 |
Current CPC
Class: |
B09B 5/00 20130101; C11D
7/5004 20130101; G03G 5/144 20130101; G03G 5/102 20130101; G03G
5/142 20130101 |
Class at
Publication: |
430/56 ; 430/97;
524/283 |
International
Class: |
G03G 15/00 20060101
G03G015/00; G03G 13/06 20060101 G03G013/06 |
Claims
1. An imaging member comprising an undercoat layer, the undercoat
layer comprising: a metal oxide; a polymer; and a citrate of
Formula (I): ##STR00011## wherein R.sub.1 is H, alkyl, or COR';
wherein R' is alkyl; and wherein R.sub.2, R.sub.3, and R.sub.4 are
independently alkyl.
2. The imaging member of claim 1, wherein the metal oxide is a
titanium oxide.
3. The imaging member of claim 1, wherein the metal oxide is
titanium dioxide or zinc oxide.
4. The imaging member of claim 1, wherein the citrate is acetyl
tributyl citrate represented by Formula (II): ##STR00012##
5. The imaging member of claim 1, wherein the citrate is tri
(n-butyl)citrate represented by Formula (III): ##STR00013##
6. The imaging member of claim 1, wherein the polymer is selected
from the group consisting of a phenolic resin, a melamine resin, an
epoxy resin, a polyamide resin, a polyvinyl butyral resin, a
polyurethane resin, a poly(vinyl carbazole), an organosilane,
nylon, polyesters, polyvinylidene chloride resin, silicone resins,
fluorocarbon resins, polycarbonates, polyacrylates and
methacrylates, copolymers of vinyl chloride and vinyl acetate,
phenoxy resins, poly(vinyl alcohol), polyacrylonitrile,
polystyrene, poly(vinylbenzyl alcohol), poly(2-hydroxyethyl
methacrylate), poly(2-hydroxyethyl acrylate), poly(3-hydroxypropyl
methacrylate), and mixtures thereof.
7. The imaging member of claim 1, wherein the polymer is a phenolic
resin.
8. The imaging member of claim 1, wherein the metal oxide is
titanium dioxide, the polymer is a phenolic resin, and the citrate
is acetyl tributyl citrate represented by Formula (II):
##STR00014##
9. The imaging member of claim 1, wherein the metal oxide is
titanium dioxide, the polymer is a phenolic resin, and the citrate
is tri(n-butyl)citrate represented by Formula (III):
##STR00015##
10. An imaging member comprising, in sequence: a substrate; an
undercoat layer; and a photosensitive layer; wherein the undercoat
layer is formed from a dispersion comprising a metal oxide, a
polymer, and a citrate of Formula (I): ##STR00016## wherein R.sub.1
is H, alkyl, or COR'; wherein R' is alkyl; and wherein R.sub.2,
R.sub.3, and R.sub.4 are independently alkyl.
11. The imaging member of claim 10, wherein the metal oxide is
titanium dioxide.
12. The imaging member of claim 10, wherein the polymer is selected
from the group consisting of a phenolic resin, a melamine resin, an
epoxy resin, a polyamide resin, a polyvinyl butyral resin, a
polyurethane resin, a poly(vinyl carbazole), an organosilane,
nylon, polyesters, polyvinylidene chloride resin, silicone resins,
fluorocarbon resins, polycarbonates, polyacrylates and
methacrylates, copolymers of vinyl chloride and vinyl acetate,
phenoxy resins, poly(vinyl alcohol), polyacrylonitrile,
polystyrene, poly(vinylbenzyl alcohol), poly(2-hydroxyethyl
methacrylate), poly(2-hydroxyethyl acrylate), poly(3-hydroxypropyl
methacrylate), and mixtures thereof.
13. The imaging member of claim 10, wherein the polymer is a
phenolic resin.
14. The imaging member of claim 10, wherein the citrate comprises
from about 0.1 to about 30 weight percent of the undercoat
layer.
15. The imaging member of claim 10, wherein the metal oxide is
titanium dioxide, the polymer is a phenolic resin, and the citrate
is acetyl tributyl citrate represented by Formula (II):
##STR00017##
16. The imaging member of claim 10, wherein the metal oxide is
titanium dioxide, the polymer is a phenolic resin, and the citrate
is tri(n-butyl)citrate represented by Formula (III):
##STR00018##
17. A method for reclaiming a substrate from an imaging member,
comprising: providing an imaging member comprising a substrate and
an undercoat layer, the undercoat layer comprising a metal oxide, a
polymer, and a citrate of Formula (I): ##STR00019## wherein R.sub.1
is H, alkyl, or COR'; wherein R' is alkyl; and wherein R.sub.2,
R.sub.3, and R.sub.4 are independently alkyl; and immersing the
imaging member in a stripping solution to separate the undercoat
layer from the substrate.
18. The method of claim 17, wherein the stripping solution
comprises a solvent selected from the group consisting of
N-methylpyrrolidone, ethanol, dimethylsulfoxide,
N,N'-dimethylformamide, N,N'-dimethylacetamide, and mixtures
thereof.
19. The method of claim 17, wherein the stripping solution
comprises an acid selected from the group consisting of citric
acid, acetic acid, nitric acid, oxalic acid, phosphoric acid,
hydrochloric acid, sulfuric acid, and mixtures thereof.
20. The method of claim 17, wherein the imaging member further
comprises a charge generating layer and a charge transport layer.
Description
BACKGROUND
[0001] Disclosed herein, in various embodiments, are undercoat
layers useful in various imaging members and the imaging members
themselves. Among other things, the undercoat layers can be readily
removed, allowing the substrate to be more easily recycled.
[0002] Electrophotographic imaging members, i.e. photoreceptors,
typically include a photoconductive layer formed on an electrically
conductive substrate. The photoconductive layer is an insulator in
the dark so that electric charges can be retained on its surface.
Upon exposure to light, the charge is dissipated.
[0003] An electrostatic latent image is formed on the photoreceptor
by first uniformly depositing an electric charge over the surface
of the photoconductive layer by one of the many known means in the
art. The photoconductive layer functions as a charge storage
capacitor with charge on its free surface and an equal charge of
opposite polarity on the conductive substrate. A light image is
then projected onto the photoconductive layer. The portions of the
layer that are not exposed to light retain their surface charge.
After development of the latent image with toner particles to form
a toner image, the toner image is usually transferred to a
receiving substrate, such as paper.
[0004] A photoconductive imaging member may comprise a supporting
substrate, an optional electrically conductive layer, an optional
adhesive layer, a charge generating layer, a charge transport
layer, and an optional protective or overcoat layer. One or more of
these layers may also be combined or added to other layers to form
the imaging member.
[0005] Conventional electrophotographic imaging members may also
comprise an undercoat layer located between the substrate and
charge generating layer. Some examples of conventional undercoat
layers can be seen in U.S. Pat. Nos. 4,265,990, 4,921,769,
5,958,638, 6,132,912, 6,287,737, and 6,444,386, the disclosures of
which are incorporated herein by reference in their entireties. In
particular, such undercoat layers may be applied directly on the
substrate.
[0006] Undercoat layers are desirable because they extend the
functional lifetime for photoreceptors and enable the use of less
expensive substrates. They may also assist in the adhesion of the
photosensitive layers to the substrate. Undercoat layers also
prevent foreign materials such as carbon fiber penetration into
photoreceptors thus preventing "color spots."
[0007] It may be desirable to recycle the substrate at the end of
an imaging member's service life. However, the various layers
deposited on the substrate of the imaging member must be removed
before the substrate can be reused or sold. The process for
removing these layers, known as substrate reclamation, is an
expensive and somewhat time-consuming process. An example of a
substrate reclamation process which includes lathing and cleaning
photoreceptor substrates is disclosed in U.S. Pat. No.
5,346,556.
[0008] It would be desirable to develop an undercoat layer that
allows for easy removal of the coating layers on the substrate
without sacrificing performance of the electrophotographic imaging
member.
BRIEF DESCRIPTION
[0009] The present application discloses, in various embodiments,
undercoat layers comprising a metal oxide, a polymer, and a
citrate. Imaging members, particularly photoconductors or
photoconductive imaging members, which comprise the undercoat
layers are also disclosed. These undercoat layers simplify the
process of substrate reclamation without affecting the electrical
properties of the imaging member.
[0010] In embodiments, an imaging member is disclosed which
comprises an undercoat layer. The undercoat layer comprises a metal
oxide; a polymer; and a citrate of Formula (I):
##STR00002##
wherein R.sub.1 is H, alkyl, or COR'; wherein R' is alkyl; and
wherein R.sub.2, R.sub.3, and R.sub.4 are independently alkyl.
[0011] The metal oxide may be a titanium oxide, particularly
titanium dioxide or zinc oxide.
[0012] The citrate may be acetyl tributyl citrate represented by
Formula (II):
##STR00003##
[0013] Alternatively, the citrate may be tri(n-butyl)citrate
represented by Formula (III):
##STR00004##
[0014] The polymer may be selected from the group consisting of a
phenolic resin, a melamine resin, an epoxy resin, a polyamide
resin, a polyvinyl butyral resin, a polyurethane resin, a
poly(vinyl carbazole), an organosilane, nylon, polyesters,
polyvinylidene chloride resin, silicone resins, fluorocarbon
resins, polycarbonates, polyacrylates and methacrylates, copolymers
of vinyl chloride and vinyl acetate, phenoxy resins, poly(vinyl
alcohol), polyacrylonitrile, polystyrene, poly(vinylbenzyl
alcohol), poly(2-hydroxyethyl methacrylate), poly(2-hydroxyethyl
acrylate), poly(3-hydroxypropyl methacrylate), and mixtures
thereof. In specific embodiments, the polymer is a phenolic
resin.
[0015] In some specific embodiments, the metal oxide is titanium
dioxide, the polymer is a phenolic resin, and the citrate is acetyl
tributyl citrate represented by Formula (II):
##STR00005##
[0016] In other specific embodiments, the metal oxide is titanium
dioxide, the polymer is a phenolic resin, and the citrate is
tri(n-butyl)citrate represented by Formula (III):
##STR00006##
[0017] In still other embodiments is disclosed an imaging member
comprising, in sequentially formed layers: a substrate; an
undercoat layer; and a photosensitive layer. The photosensitive
layer may include a charge generating layer and a charge transport
layer. The undercoat layer is formed from a dispersion comprising a
metal oxide, a polymer, and a citrate of Formula (I):
##STR00007##
wherein R.sub.1 is H, alkyl, or COR'; wherein R' is alkyl; and
wherein R.sub.2, R.sub.3, and R.sub.4 are independently alkyl.
[0018] The citrate may comprise from about 2 to about 10 weight
percent of the undercoat layer.
[0019] Also disclosed in embodiments are methods for reclaiming a
substrate from an imaging member. An imaging member is provided
which comprises a substrate and an undercoat layer, the undercoat
layer comprising a metal oxide, a polymer, and a citrate of Formula
(I):
##STR00008##
wherein R.sub.1 is H, alkyl, or COR'; wherein R' is alkyl; and
wherein R.sub.2, R.sub.3, and R.sub.4 are independently alkyl. The
imaging member is immersed in a stripping solution to separate the
undercoat layer from the substrate.
[0020] The stripping solution may comprise a solvent selected from
the group consisting of N-methylpyrrolidone, ethanol,
dimethylsulfoxide, N,N'-dimethylformamide, N,N'-dimethylacetamide,
and the like and mixtures thereof.
[0021] The stripping solution may also comprise an acid selected
from the group consisting of citric acid, acetic acid, nitric acid,
oxalic acid, phosphoric acid, hydrochloric acid, sulfuric acid, and
the like and mixtures thereof.
[0022] These and other non-limiting characteristics of the
disclosure are more particularly disclosed below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The following is a brief description of the drawings, which
are presented for the purposes of illustrating the exemplary
embodiments disclosed herein and not for the purposes of limiting
the same.
[0024] FIG. 1 illustrates an exemplary embodiment of an imaging
member fabricated according to the present disclosure.
DETAILED DESCRIPTION
[0025] A more complete understanding of the components, processes,
and apparatuses disclosed herein can be obtained by reference to
the accompanying drawings. These figures are merely schematic
representations based on convenience and the ease of demonstrating
the present disclosure, and are, therefore, not intended to
indicate relative size and dimensions of the devices or components
thereof and/or to define or limit the scope of the exemplary
embodiments.
[0026] Although specific terms are used in the following
description for the sake of clarity, these terms are intended to
refer only to the particular structure of the embodiments selected
for illustration in the drawings, and are not intended to define or
limit the scope of the disclosure. In the drawings and the
following description below, it is to be understood that like
numeric designations refer to components of like function.
[0027] The modifier "about" used in connection with a quantity is
inclusive of the stated value and has the meaning dictated by the
context (for example, it includes at least the degree of error
associated with the measurement of the particular quantity). When
used in the context of a range, the modifier "about" should also be
considered as disclosing the range defined by the absolute values
of the two endpoints. For example, the range of "from about 2 to
about 10" also discloses the range "from 2 to 10."
[0028] The present disclosure relates to undercoat layers that are
useful in making coatings easier and cheaper to remove during
substrate reclamation. The undercoat layers comprise a metal oxide,
a polymer, and a citrate. The metal oxide and the citrate may be
dissolved or dispersed in the polymer.
[0029] In FIG. 1, an imaging member is shown that has an undercoat
layer 20, a charge generating layer 30, and a charge transport
layer 40 disposed on an electrically conductive substrate 10. One
of ordinary skill understands that there may be additional layers
in the imaging member. An optional adhesive layer may be applied
between the undercoat layer and the charge generating layer. An
optional ground strip layer may operatively connect the charge
generating layer and the charge transport layer to the substrate.
An opposite anti-curl back layer may be applied to the side of the
substrate opposite from the electrically active layers. An optional
overcoat layer may be placed upon the charge transport layer. In
particular embodiments, the undercoat layer directly contacts the
substrate. The undercoat layer 20 comprises a metal oxide, a
polymer, and a citrate.
[0030] The metal oxide may generally be any conductive metal which
can be oxidized. In particular embodiments, the metal may be
titanium (Ti), tin (Sn), zinc (Zn), indium (In), silicon (Si),
aluminum (Al), zirconium (Zr), or molybdenum (Mb). In specific
embodiments, the metal oxide is titanium dioxide (TiO.sub.2) or
zinc oxide (ZnO).
[0031] In embodiments, the metal oxide (like TiO.sub.2) used in the
undercoat layer can be either surface treated or untreated. Surface
treatments include, but are not limited to, mixing the metal oxide
with aluminum laurate, alumina, zirconia, silica, silane,
methicone, dimethicone, sodium metaphosphate, and the like, and
mixtures thereof. Commercially available examples of TiO.sub.2
include MT-150W.TM. (surface treatment with sodium metaphosphate,
available from Tayca Corporation), STR-60N.TM. (no surface
treatment, available from Sakai Chemical Industry Co., Ltd.),
FTL-100.TM. (no surface treatment, available from Ishihara Sangyo
Laisha, Ltd.), STR-60.TM. (surface treatment with Al.sub.2O.sub.3,
available from Sakai Chemical Industry Co., Ltd.), TTO-55N.TM. (no
surface treatment, available from Ishihara Sangyo Laisha, Ltd.),
TTO-55A.TM. (surface treatment with Al.sub.2O.sub.3, available from
Ishihara Sangyo Laisha, Ltd.), MT-150AWT.TM. (no surface treatment,
available from Tayca Corporation), MT-150A.TM. (no surface
treatment, available from Tayca Corporation), MT-100S.TM. (surface
treatment with aluminum laurate and alumina, available from Tayca
Corporation), MT-100HD.TM. (surface treatment with zirconia and
alumina, available from Tayca Corporation), MT-100SA.TM. (surface
treatment with silica and alumina, available from Tayca
Corporation), and the like.
[0032] The metal oxide may be present in suitable amounts, such as
for example, from about 5 to about 80 weight percent, and more
specifically, from about 30 to about 70 weight percent, of the
undercoat layer. In embodiments, the metal oxide has a diameter of
from about 5 to about 300 nanometers. More specifically, the metal
oxide may possess a primary particle size diameter of from about 10
to about 25 nanometers, and yet more specifically, about 15
nanometers with an aspect ratio (i.e. ratio of longest axis to
shortest axis) of from about 4 to about 5. The metal oxide may
optionally be surface treated with a component containing from
about 1 to about 3 percent by weight of alkali metal, such as a
sodium metaphosphate.
[0033] The polymer may be a binder resin such as a thermosetting or
thermoplastic resin. The polymer is, in embodiments, a phenolic
resin, a melamine resin, an epoxy resin, a polyamide resin, a
polyvinyl butyral resin, a polyurethane resin, a poly(vinyl
carbazole), an organosilane, nylon, polyesters, polyvinylidene
chloride resin, silicone resins, fluorocarbon resins,
polycarbonates, polyacrylates and methacrylates, copolymers of
vinyl chloride and vinyl acetate, phenoxy resins, poly(vinyl
alcohol), polyacrylonitrile, polystyrene, poly(vinylbenzyl
alcohol), poly(2-hydroxyethyl methacrylate), poly(2-hydroxyethyl
acrylate), poly(3-hydroxypropyl methacrylate), or mixtures thereof.
In specific embodiments, the polymer is a phenolic resin. The
polymer may comprise from about 20 to about 95 weight percent of
the undercoat layer, including from about 30 to about 70 weight
percent.
[0034] A phenolic resin is generally formed as the condensation
product of an aldehyde with a phenol source in the presence of an
acidic or basic catalyst.
[0035] The phenol source can be, for example, phenol;
alkyl-substituted phenols such as cresols and xylenols;
halogen-substituted phenols such as chlorophenol; polyhydric
phenols such as resorcinol or pyrocatechol; polycyclic phenols such
as naphthol and bisphenol A; aryl-substituted phenols,
cyclo-alkyl-substituted phenols, aryloxy-substituted phenols, and
combinations thereof. Exemplary phenol sources include 2,6-xylenol,
o-cresol, p-cresol, 3,5-xylenol, 3,4-xylenol, 2,3,4-trimethyl
phenol, 3-ethyl phenol, 3,5-diethyl phenol, p-butyl phenol,
3,5-dibutyl phenol, p-amyl phenol, p-cyclohexyl phenol, p-octyl
phenol, 3,5-dicyclohexyl phenol, p-phenyl phenol, p-crotyl phenol,
3,5-dimethoxy phenol, 3,4,5-trimethoxy phenol, p-ethoxy phenol,
p-butoxy phenol, 3-methyl-4-methoxy phenol, p-phenoxy phenol,
multiple ring phenols, such as bisphenol A, and combinations
thereof.
[0036] The aldehyde used to make the phenolic resin can be, for
example, formaldehyde, paraformaldehyde, acetaldehyde,
butyraldehyde, paraldehyde, glyoxal, furfuraldehyde,
propinonaldehyde, benzaldehyde, and combinations thereof. In
various embodiments, the aldehyde can be formaldehyde.
[0037] Phenolic resins include dicyclopentadiene type phenolic
resins, phenol novolak resins, cresol novolak resins, phenol
aralkyl resins, and combinations thereof. Exemplary phenolic resins
include formaldehyde polymers with phenol, p-tert-butylphenol, and
cresol, such as VARCUM.TM. 29159 and 29101 (OxyChem. Co.) and
DURITE.TM. 97 (Borden Chemical); formaldehyde polymers with
ammonia, cresol, and phenol, such as VARCUM.TM. 29112 (OxyChem.
Co.); formaldehyde polymers with 4,4'-(1-methylethylidene)
bisphenol such as VARCUM.TM.29108 and 29116 (OxyChem. Co.);
formaldehyde polymers with cresol and phenol such as VARCUM.TM.
29457 (OxyChem. Co.), DURITE.TM. SD-423A, SD-422A (Borden
Chemical); or formaldehyde polymers with phenol and
p-tert-butylphenol such as DURITE.TM. ESD 556C (Border
Chemical).
[0038] In embodiments, the phenolic resins are base-catalyzed
phenol formaldehyde resins that are generated with a
formaldehyde/phenol mole ratio of equal to or greater than one, for
example, from about 1 to about 2; or from about 1.2 to about 1.8;
or about 1.5. The base catalyst, such as an amine, is generally
miscible with the phenol resin.
[0039] The citrate is a citrate of Formula (I):
##STR00009##
wherein R.sub.1 is H, alkyl, or COR', wherein R' is alkyl; and
R.sub.2, R.sub.3, and R.sub.4 are independently alkyl. The term
"alkyl" refers to a radical composed entirely of carbon atoms and
hydrogen atoms which is fully saturated and of the formula
--C.sub.nH.sub.2n+1. The term "alkyl" should be considered to
include both linear and branched chains. Generally, the alkyl
chains of the citrate may have from 1 to about 20 carbon atoms. In
some embodiments, R.sub.2, R.sub.3, and R.sub.4 are independently
C.sub.1-C.sub.6 alkyl. In specific embodiments, R.sub.2, R.sub.3,
and R.sub.4 are the same. In further specific embodiments, R.sub.2,
R.sub.3, and R.sub.4 are n-butyl. In other embodiments, R.sub.1 is
acetyl (--CO--CH.sub.3).
[0040] In specific embodiments, the citrate may be selected from
the group consisting of acetyl tributyl citrate shown in Formula
(II) and tri(n-butyl)citrate shown in Formula (III):
##STR00010##
[0041] Other exemplary citrates that may be included in the
undercoat layer are triethyl citrate, triethyl acetylcitrate,
tri-2-ethylhexyl acetylcitrate, n-octyldecyl acetylcitrate, and the
like and mixtures thereof.
[0042] In particular embodiments, the citrate comprises from about
0.1 to about 30 weight percent of the undercoat layer. In more
specific embodiments, the citrate comprises from about 1 to about
20 weight percent or from about 2 to about 10 percent by weight of
the undercoat layer.
[0043] The undercoat layer thickness can be of any suitable value,
such as for example, from about 0.1 to about 30 microns, from about
1 to about 20 microns, or from about 3 to about 15 microns.
[0044] The undercoat layer may be applied by any suitable
conventional technique such as spraying, dip coating, draw bar
coating, gravure coating, silk screening, air knife coating,
reverse roll coating, vacuum deposition, chemical treatment and the
like. For convenience in obtaining thin layers, the undercoat layer
is preferably applied in the form of a dilute solution, with the
solvent being removed after deposition of the coating by
conventional techniques such as by vacuum, heating and the like.
The undercoat layer may be dried at a temperature of from about 40
to about 200.degree. C. for a suitable period of time, such as from
about 1 minute to about 10 hours, under stationary conditions or in
an air flow.
[0045] Generally, citrates are soluble in solvents such as xylene,
1-butanol, methyl ethyl ketone, tetrahydrofuran,
1-methoxy-2-propanol, and the like and mixtures thereof. For
example, they are soluble in a solvent mixture of 50% xylene and
50% 1-butanol. Appropriate solvent mixtures can be used to form a
dispersion of the metal oxide, phenolic resin, and citrate. The
order in which these three ingredients is added to the dispersion
is not important. The dispersion is then applied and the solvent
evaporated to form the undercoat layer. The undercoat layer may be
useful, for example, as a charge blocking layer.
[0046] It has been found that the incorporation of a citrate into
the undercoat layer enhances removal of coating layers from a
substrate. In particular, because the undercoat layer directly
contacts the substrate or the conductive layer on top of the
substrate, simply removing the undercoat layer removes the other
layers of the imaging member from the substrate as well. Thus, the
layers can be removed with a mild solution stripping process
without the need for a pre-lathing step to remove the layers on top
of the undercoat layer. Photo-induced discharge, cyclic stability,
background, ghosting, and adhesion properties are either comparable
or better in imaging members manufactured in accordance with the
present disclosure.
[0047] Methods for removing layers of an imaging member from a
substrate are contemplated. In particular, substrate reclamation is
easier for an imaging member comprising a substrate and an
undercoat layer that comprises a metal oxide, a polymer, and a
citrate. The methods comprise immersing the imaging member in a
stripping solution. The stripping solution comprises a solvent, an
acid, and water. The immersion separates the undercoat layer, and
the other layers on top of the undercoat layer, from the substrate.
In some embodiments, the imaging member needs to be immersed for as
little as 5 minutes or even 3 minutes to remove all residue from
the substrate.
[0048] The solvent used in the stripping solution may comprise
N-methylpyrrolidone, ethanol, dimethylsulfoxide,
N,N'-dimethylformamide, N,N'-dimethylacetamide, similar solvents,
and mixtures thereof. The stripping solution may comprise an acid
selected from the group consisting of citric acid, acetic acid,
nitric acid, oxalic acid, phosphoric acid, hydrochloric acid,
sulfuric acid, similar acids, and mixtures thereof. In some
embodiments, the acid is citric acid. In a specific embodiment, the
solution comprises 80 wt % N-methylpyrrolidone, 8 wt % citric acid,
and 12 wt % water.
[0049] In particular embodiments, the undercoat layer is free of
zirconium-containing compounds.
[0050] Without being limited by theory, it appears that the citrate
is physically dispersed in the undercoat layer and does not
interact chemically with the polymer or the metal oxide. As a
result, the undercoat layer swells, allowing the undercoat layer to
be removed more easily. The adhesion between the undercoat layer
and the substrate is a little weakened to an extent that it
facilitates layer removal by the solution stripping process but is
still satisfactory for imaging member performance. The citrate will
not form a chelate with the metal oxide.
[0051] U.S. Patent Publication No. 2009/0197191 describes an
undercoat layer containing dialkylcitrate-chelated zirconate.
There, the dialkylcitrate-chelated zirconate can chemically
interact (i.e. crosslink) with a functional group such as a
hydroxyl group or carboxyl group included in the binder resin and
metal oxide particles, and thus prevents agglomeration or gelation
of the metal oxide particles. In other words, the
dialkylcitrate-chelated zirconate acts as a dispersant. In
addition, the crosslinking can strengthen the adhesion between the
undercoat layer and the substrate. However, the
dialkylcitrate-chelated zirconate does not allow the undercoat
layer to be more easily removed from the substrate.
[0052] The charge transport layer 40 of FIG. 1 comprises charge
transport materials which are capable of supporting the injection
of photogenerated holes or electrons from the charge generating
layer 30 and allowing their transport through the charge transport
layer to selectively discharge the surface charge on the imaging
member surface. The charge transport layer, in conjunction with the
charge generating layer, should also be an insulator to the extent
that an electrostatic charge placed on the charge transport layer
is not conducted in the absence of illumination. It should also
exhibit negligible, if any, discharge when exposed to a wavelength
of light useful in xerography, e.g., about 4000 Angstroms to about
9000 Angstroms. This ensures that when the imaging member is
exposed, most of the incident radiation is used in the charge
generating layer beneath it to efficiently produce photogenerated
charges.
[0053] The charge transport materials may include triarylamines
such as TPD, tri-p-tolylamine,
1,1-bis(4-di-p-tolylaminophenyl)cyclohexane, and other similar
triarylamines. The additional charge transport molecules may, e.g.,
help minimize background voltage.
[0054] The charge transport layer also comprises a polymer binder
resin in which the charge transport molecule(s) or component(s) is
dispersed. The resin should be substantially soluble in a number of
solvents, like methylene chloride or other solvent so that the
charge transport layer can be coated onto the imaging member.
Typical binder resins soluble in methylene chloride include
polycarbonate resin, polyvinylcarbazole, polyester, polyarylate,
polyacrylate, polyether, polysulfone, polystyrene, polyamide, and
the like. Molecular weights of the binder resin can vary from, for
example, about 20,000 to about 300,000, including about
150,000.
[0055] The charge transport layer of the present disclosure in
embodiments comprises from about 25 weight percent to about 60
weight percent of the charge transport molecule(s) and from about
40 weight percent to about 75 weight percent by weight of the
polymer binder resin, both by total weight of the charge transport
layer. In specific embodiments, the charge transport layer
comprises from about 40 weight percent to about 50 weight percent
of the charge transport molecule(s) and from about 50 weight
percent to about 60 weight percent of the polymer binder resin.
[0056] Generally, the thickness of the charge transport layer is
from about 10 to about 100 micrometers, including from about 20
micrometers to about 60 micrometers, but thicknesses outside these
ranges can also be used. In general, the ratio of the thickness of
the charge transport layer to the charge generating layer is in
embodiments from about 2:1 to 200:1 and in some instances from
about 2:1 to about 400:1. In specific embodiments, the charge
transport layer is from about 10 micrometers to about 40
micrometers thick.
[0057] The substrate provides support for all layers of the imaging
member. Its thickness depends on numerous factors, including
mechanical strength, flexibility, and economical considerations;
the substrate for a flexible belt may, for example, be from about
50 micrometers to about 150 micrometers thick, provided there are
no adverse effects on the final electrophotographic imaging device.
The substrate support is not soluble in any of the solvents used in
each coating layer solution, is optically transparent, and is
thermally stable up to a high temperature of about 150.degree. C. A
typical substrate support is a biaxially oriented polyethylene
terephthalate. Another suitable substrate material is a biaxially
oriented polyethylene naphthalate, having a thermal contraction
coefficient ranging from about 1.times.10.sup.-5/.degree. C. to
about 3.times.10.sup.-5/.degree. C. and a Young's Modulus of from
about 5.times.10.sup.5 psi to about 7.times.10.sup.5 psi. However,
other polymers are suitable for use as substrate supports. The
substrate support may also be made of a conductive material, such
as aluminum, chromium, nickel, brass and the like. The substrate
support may flexible or rigid, seamed or seamless, and have any
configuration, such as a plate, drum, scroll, belt, and the like.
In particular embodiments of imaging members of the present
disclosure, the substrate is electrically conductive, so that a
conductive layer is not present between the substrate and the
undercoat layer of the present disclosure.
[0058] An optional conductive layer is present when the substrate
is not itself conductive. It may vary in thickness depending on the
optical transparency and flexibility desired for the
electrophotographic imaging member. Accordingly, when a flexible
electrophotographic imaging belt is desired, the thickness of the
conductive layer may be from about 20 Angstrom units to about 750
Angstrom units, and more specifically from about 50 Angstrom units
to about 200 Angstrom units for an optimum combination of
electrical conductivity, flexibility and light transmission. The
conductive layer may be formed on the substrate by any suitable
coating technique, such as a vacuum depositing or sputtering
technique. Typical metals suitable for use as the conductive layer
include aluminum, zirconium, niobium, tantalum, vanadium, hafnium,
titanium, nickel, stainless steel, chromium, tungsten, molybdenum,
and the like.
[0059] An optional adhesive layer may be applied to the undercoat
layer. Any suitable adhesive layer may be utilized. Any adhesive
layer employed should be continuous and, more specifically, have a
dry thickness from about 200 micrometers to about 900 micrometers
and, even more specifically, from about 400 micrometers to about
700 micrometers. Any suitable solvent or solvent mixtures may be
employed to form a coating solution for the adhesive layer. Typical
solvents include tetrahydrofuran, toluene, methylene chloride,
cyclohexanone, and the like, and mixtures thereof. Any other
suitable and conventional technique may be used to mix and
thereafter apply the adhesive layer coating mixture to the hole
blocking layer. Typical application techniques include spraying,
dip coating, roll coating, wire wound rod coating, and the like.
Drying of the deposited coating may be effected by any suitable
conventional technique such as oven drying, infra red radiation
drying, air drying, and the like.
[0060] Any suitable charge generating layer may be applied which
can thereafter be coated over with a contiguous charge transport
layer. The charge generating layer generally comprises a charge
generating material and a film-forming polymer binder resin. Charge
generating materials such as vanadyl phthalocyanine, metal free
phthalocyanine, benzimidazole perylene, amorphous selenium,
trigonal selenium, selenium alloys such as selenium-tellurium,
selenium-tellurium-arsenic, selenium arsenide, and the like and
mixtures thereof may be appropriate because of their sensitivity to
white light. Vanadyl phthalocyanine, metal free phthalocyanine and
tellurium alloys are also useful because these materials provide
the additional benefit of being sensitive to infrared light. Other
charge generating materials include quinacridones, dibromo
anthanthrone pigments, benzimidazole perylene, substituted
2,4-diamino-triazines, polynuclear aromatic quinones, and the like.
Benzimidazole perylene compositions are well known and described,
for example, in U.S. Pat. No. 4,587,189, the entire disclosure
thereof being incorporated herein by reference. Other suitable
charge generating materials known in the art may also be utilized,
if desired. The charge generating materials selected should be
sensitive to activating radiation having a wavelength from about
600 to about 700 nm during the imagewise radiation exposure step in
an electrophotographic imaging process to form an electrostatic
latent image. In specific embodiments, the charge generating
material is hydroxygallium phthalocyanine (OHGaPC) or oxytitanium
phthalocyanine (TiOPC).
[0061] Any suitable inactive film forming polymeric material may be
employed as the binder in the charge generating layer, including
those described, for example, in U.S. Pat. No. 3,121,006, the
entire disclosure thereof being incorporated herein by reference.
Typical organic polymer binders include thermoplastic and
thermosetting resins such as polycarbonates, polyesters,
polyamides, polyurethanes, polystyrenes, polyarylethers,
polyarylsulfones, polybutadienes, polysulfones, polyethersulfones,
polyethylenes, polypropylenes, polyimides, polymethylpentenes,
polyphenylene sulfides, polyvinyl butyral, polyvinyl acetate,
polysiloxanes, polyacrylates, polyvinyl acetals, polyamides,
polyimides, amino resins, phenylene oxide resins, terephthalic acid
resins, epoxy resins, phenolic resins, polystyrene and
acrylonitrile copolymers, polyvinylchloride, vinylchloride and
vinyl acetate copolymers, acrylate copolymers, alkyd resins,
cellulosic film formers, poly(amideimide), styrene-butadiene
copolymers, vinylidenechloride-vinylchloride copolymers,
vinylacetate-vinylidenechloride copolymers, styrene-alkyd resins,
and the like.
[0062] The charge generating material can be present in the polymer
binder composition in various amounts. Generally, from about 5 to
about 90 percent by volume of the charge generating material is
dispersed in about 10 to about 95 percent by volume of the polymer
binder, and more specifically from about 20 to about 50 percent by
volume of the charge generating material is dispersed in about 50
to about 80 percent by volume of the polymer binder.
[0063] The charge generating layer generally ranges in thickness of
from about 0.1 micrometer to about 5 micrometers, and more
specifically has a thickness of from about 0.3 micrometer to about
3 micrometers. The charge generating layer thickness is related to
binder content. Higher polymer binder content compositions
generally require thicker layers for charge generating. Thickness
outside these ranges can be selected in order to provide sufficient
charge generating.
[0064] An optional anti-curl back coating can be applied to the
back side of the substrate support (which is the side opposite the
side bearing the electrically active coating layers) in order to
render flatness. Although the anti-curl back coating may include
any electrically insulating or slightly conductive organic film
forming polymer, it is usually the same polymer as used in the
charge transport layer polymer binder. An anti-curl back coating
from about 7 to about 30 micrometers in thickness is found to be
adequately sufficient for balancing the curl and render imaging
member flatness.
[0065] An electrophotographic imaging member may also include an
optional ground strip layer. The ground strip layer comprises, for
example, conductive particles dispersed in a film forming binder
and may be applied to one edge of the photoreceptor to operatively
connect charge transport layer, charge generating layer, and
conductive layer for electrical continuity during
electrophotographic imaging process. The ground strip layer may
comprise any suitable film forming polymer binder and electrically
conductive particles. The ground strip layer may have a thickness
from about 7 micrometers to about 42 micrometers, and more
specifically from about 14 micrometers to about 23 micrometers.
[0066] An overcoat layer, if desired, may be utilized to provide
imaging member surface protection as well as improve resistance to
abrasion. Overcoat layers are known in the art. Generally, they
serve a function of protecting the charge transport layer from
mechanical wear and exposure to chemical contaminants.
[0067] The imaging member formed may have a rigid drum
configuration or a flexible belt configuration. The belt can be
either seamless or seamed. In this regard, the fabricated
multilayered flexible photoreceptors of the present disclosure may
be cut into rectangular sheets and converted into photoreceptor
belts. The two opposite edges of each photoreceptor cut sheet are
then brought together by overlapping and may be joined by any
suitable means including ultrasonic welding, gluing, taping,
stapling, and pressure and heat fusing to form a continuous imaging
member seamed belt, sleeve, or cylinder. The prepared imaging
member may then be employed in any suitable and conventional
electrophotographic imaging process which utilizes uniform charging
prior to imagewise exposure to activating electromagnetic
radiation. When the imaging surface of an electrophotographic
member is uniformly charged with an electrostatic charge and
imagewise exposed to activating electromagnetic radiation,
conventional positive or reversal development techniques may be
employed to form a marking material image on the imaging surface of
the electrophotographic imaging member of this disclosure. Thus, by
applying a suitable electrical bias and selecting toner having the
appropriate polarity of electrical charge, one may form a toner
image in the charged areas or discharged areas on the imaging
surface of the electrophotographic member of the present
disclosure.
[0068] The present disclosure will further be illustrated in the
following non-limiting working examples, it being understood that
these examples are intended to be illustrative only and that the
disclosure is not intended to be limited to the materials,
conditions, process parameters and the like recited herein. All
proportions are by weight unless otherwise indicated.
EXAMPLES
Comparative Example 1
[0069] An undercoat layer dispersion was prepared by milling 18
grams of TiO.sub.2 (MT-150W, manufactured by Tayca Co., Japan) and
12 grams of a phenolic resin dissolved in 12 grams of a solvent
mixture of xylene and 1-butanol (VARCUM.RTM. 29159, OxyChem. Co.,
phenolic resin was about 50 percent in a 50/50 mixture of
xylene/1-butanol), and a total solid content of about 48 percent in
an attritor mill with about 0.4 to about 0.6 millimeter size
ZrO.sub.2 beads for 6.5 hours, and then filtering with a 20 micron
Nylon filter. A 30 millimeter aluminum drum substrate was then
coated with the aforementioned generated dispersion using known
coating techniques as illustrated herein. After drying at
160.degree. C. for 20 minutes, an undercoat layer of TiO.sub.2 in
the phenolic resin (TiO.sub.2/phenolic resin=60/40 w/w) about 8
microns in thickness was obtained.
[0070] A charge generating layer comprising chlorogallium
phthalocyanine (Type C) was deposited on the above undercoat layer
at a thickness of about 0.2 micron. The charge generating layer
coating dispersion was prepared as follows. 2.7 grams of
chlorogallium phthalocyanine (CIGaPc) Type C pigment were mixed
with 2.3 grams of the polymeric binder (carboxyl modified vinyl
copolymer, VMCH, Dow Chemical Company), 15 grams of n-butyl
acetate, and 30 grams of xylene. The resulting mixture was milled
in an attritor mill with about 200 grams of 1 millimeter Hi-Bea
borosilicate glass beads for about 3 hours. The dispersion mixture
obtained was then filtered through a 20 micron Nylon cloth filter,
and the solids content of the dispersion was diluted to about 6
weight percent.
[0071] Subsequently, a 30 micron charge transport layer was coated
on top of the charge generating layer from a dispersion prepared
from
N,N'-diphenyl-N,N-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine
(5.38 grams), a film forming polymer binder, PCZ-400
[poly(4,4'-dihydroxy-diphenyl-1-1-cyclohexane, M.sub.w=40,000)]
available from Mitsubishi Gas Chemical Company, Ltd. (7.13 grams),
and PTFE POLYFLON.TM. L-2 microparticle (1 gram), available from
Daikin Industries, dissolved/dispersed in a solvent mixture of 20
grams of tetrahydrofuran (THF), and 6.7 grams of toluene through a
CAVIPRO.TM. 300 nanomizer (Five Star Technology, Cleveland, Ohio).
The charge transport layer was dried at about 120.degree. C. for
about 40 minutes.
Example 1
[0072] A photoconductor was prepared by repeating the above process
of Comparative Example 1, except that 0.6 gram of acetyl tributyl
citrate (UNIPLEX.RTM. 84, obtained from Unitex Chemical
Corporation) was added into the undercoat layer dispersion of
Comparative Example 1. A 30 millimeter aluminum drum substrate was
then coated with the aforementioned generated dispersion using
known coating techniques as illustrated herein. After drying at
160.degree. C. for 20 minutes, an undercoat layer of TiO.sub.2 in
the phenolic resin and the citrate (TiO.sub.2/phenolic
resin/citrate=58.8/39.2/2 w/w/w) about 8 microns in thickness was
obtained.
Example 2
[0073] A photoconductor was prepared by repeating the above process
of Comparative Example 1, except that 1.5 gram of acetyl tributyl
citrate (UNIPLEX.RTM. 84, obtained from Unitex Chemical
Corporation) was added into the undercoat layer dispersion of
Comparative Example 1. A 30 millimeter aluminum drum substrate was
then coated with the aforementioned generated dispersion using
known coating techniques as illustrated herein. After drying at
160.degree. C. for 20 minutes, an undercoat layer of TiO.sub.2 in
the phenolic resin and the citrate (TiO.sub.2/phenolic
resin/citrate=57.1/38.1/4.8 w/w/w) about 8 microns in thickness was
obtained.
Example 3
[0074] A photoconductor was prepared by repeating the above process
of Comparative Example 1, except that 3.0 gram of acetyl tributyl
citrate (UNIPLEX.RTM. 84, obtained from Unitex Chemical
Corporation) was added into the undercoat layer dispersion of
Comparative Example 1. A 30 millimeter aluminum drum substrate was
then coated with the aforementioned generated dispersion using
known coating techniques as illustrated herein. After drying at
160.degree. C. for 20 minutes, an undercoat layer of TiO.sub.2 in
the phenolic resin and the citrate (TiO.sub.2/phenolic
resin/citrate=54.5/36.4/9.1 w/w/w) about 8 microns in thickness was
obtained.
Electrical Property Testing
[0075] The above prepared photoconductors of Comparative Example 1,
and Examples 1, 2 and 3 were tested in a scanner set to obtain
photoinduced discharge cycles, sequenced at one charge-erase cycle
followed by one charge-expose-erase cycle, wherein the light
intensity was incrementally increased with cycling to produce a
series of photoinduced discharge characteristic (PIDC) curves from
which the photosensitivity and surface potentials at various
exposure intensities were measured. Additional electrical
characteristics were obtained by a series of charge-erase cycles
with incrementing surface potential to generate several voltages
versus charge density curves. The scanner was equipped with a
scorotron set to a constant voltage charging at various surface
potentials. These four photoconductors were tested at surface
potentials of 700 volts with the exposure light intensity
incrementally increased by regulating a series of neutral density
filters; the exposure light source was a 780 nanometer light
emitting diode. The xerographic simulation was completed in an
environmentally controlled light tight chamber at dry conditions
(10 percent relative humidity and 22.degree. C.).
[0076] The above prepared photoconductors exhibited substantially
similar PIDCs. Thus, incorporation of the citrate in the undercoat
layer did not adversely affect the electrical properties of the
photoconductor.
Ghosting Measurement
[0077] The Comparative Example 1 and Example 3 photoconductors were
acclimated in A zone conditions (85.degree. F. and 80 percent
humidity) for 24 hours before being print tested for A zone
ghosting. Print testing was accomplished in the Xerox Corporation
WorkCentre.TM. Pro C3545 using the K (black toner) station at t=500
print counts. At the CMY stations of the color WorkCentre.TM. Pro
C3545, run-up from t=500 print counts for the photoconductor was
completed. The print for determining ghosting characteristics
includes an X symbol or letter on a half tone image. When the X is
invisible, the ghost level is assigned Grade 0; when X is barely
visible, the ghost level is assigned Grade 1; Grade 2 to Grade 5
refers to the level of visibility of X with Grade 5 meaning a dark
and visible X. Ghosting levels were visually measured against an
empirical scale: the smaller the ghosting grade (absolute value),
the better the print quality. A negative ghosting grade refers to a
negative ghosting. The ghosting results are summarized in Table
1.
[0078] The Comparative Example 1 and Example 3 photoconductors were
also acclimated in J zone conditions (70.degree. F. and 10 percent
humidity) for 24 hours before similarly print tested for J zone
ghosting. The ghosting results are also summarized in Table 1.
Incorporation of the citrate into the undercoat layer reduced the
ghosting by about 1 grade in both A zone and J zone, which was a
better print quality characteristic.
TABLE-US-00001 TABLE 1 A zone ghosting J zone ghosting UCL
composition T = 500 T = 500 Comparative Example 1 (no citrate) -4
-5+ Example 3 (9.1 wt % citrate) -3 -4.5
Adhesion Testing
[0079] The adhesion for Comparative Example 1 and Examples 1, 2,
and 3 between the coating layers and the substrate was tested using
the following protocol. In this adhesion test, the drum was scored
with a razor in a crosshatch pattern with 4-6 mm spacing. A 1''
piece of tape was affixed to the device and then removed to
determine the amount of delamination onto the tape. The results are
included in Table 2. The scale ranges from Grade 1 to Grade 5 where
Grade 1 results in almost no delamination and Grade 5 results in
almost complete delamination.
TABLE-US-00002 TABLE 2 Adhesion Grade Comparative Example 1 (no
citrate) 1.5 Example 1 (2 wt % citrate) 1.5 Example 2 (4.8 wt %
citrate) 1.5 Example 3 (9.1 wt % citrate) 2.0
[0080] Incorporation of the citrate into the undercoat layer
gradually weakened the adhesion between the coating layers and the
substrate. For example, adding about 9.1% of the citrate (Example
3) into the undercoat layer weakened the adhesion by about half a
grade. The adhesion for Examples 1 and 2 was also weakened although
the difference in the weakening effect is not shown from this
specific testing method. However, the difference can be shown from
the following coating layer removal test.
Example 4
[0081] The photoconductors of Comparative Example 1 and Examples 1,
2, and 3 were immersed in a solution of 80 wt %
N-methyl-2-pyrrolidone (NMP), 8 wt % citric acid, and 12 wt % water
at 85.degree. C. for 3 minutes. The coating layer removal was
compared with immersion time, and the immersion time was recorded
in Table 3 when all the coating layers were removed from the
substrate.
TABLE-US-00003 TABLE 3 Immersion time for coating layer removal
Comparative Example 1 (no citrate) After 5 minutes, still lots of
coating layers left Example 1 (2 wt % citrate) 4 minutes Example 2
(4.8 wt % citrate) 3 minutes Example 3 (9.1 wt % citrate) 3
minutes
[0082] Incorporation of the citrate into the undercoat layer
facilitated the coating layer removal. It took about 3 to 4 minutes
to completely remove the coating layers from the substrate for
Examples 1, 2 and 3 (photoconductors with citrate in the undercoat
layer). In contrast, after 5 minutes immersion, there were still
lots of coating layers left on the substrate for the Comparative
Example 1 photoconductor (no citrate in the undercoat layer).
[0083] While particular embodiments have been described,
alternatives, modifications, variations, improvements, and
substantial equivalents that are or may be presently unforeseen may
arise to applicants or other skilled in the art. Accordingly, the
appended claims as filed and as they are amended are intended to
embrace all such alternatives, modifications, variations,
improvements, and substantial equivalents.
* * * * *