Electrophotographic photoreceptors with charge generation by polymer blends

A photoconductive drum of an aluminum substrate and a blend of polyvinylbutyral and one or a blend of phenoxy resin, epoxy novolac resin, and epoxy capped polymers which are derivatives of bisphenol and epichlorohydrin. The blend enhances the electrical properties.

TECHNICAL FIELD 
This invention relates to improved photoconductive elements for 
electrostatic imaging. More specifically, this invention pertains to 
charge generation binders (polymers) of blends with polyvinylbutyral to 
enhance the electrical characteristics, i.e. increased sensitivity, and 
decreased dark decay. This invention seeks improvement in the electrical 
characteristics derived by the use of the binder, rather than increasing 
the pigment or charge transport molecule in the formulation. 
BACKGROUND OF THE INVENTION 
An organic photoconductor typically comprises an anodized layer on a 
conductive subtrate such as aluminum drum or a barrier layer, a charge 
generation layer (CGL) and a charge transport layer (CTL). The charge 
generation layer is made of a pigment, such as metal free or 
metal-phthalocyanine, squaraine, bisazo compound or a combination of a 
bisazo and trisazo compounds. The mechanical integrity to a charge 
generation (CG) layer is often derived from a polymeric support. Various 
polymer binders have been used for this purpose. Some of these polymers 
are polyvinylbutyral, polycarbonates, epoxy resin, polyacrylate, 
polyesters, phenoxy resin, phenolic resins to name a few. In the case of 
phthalocyanines, polyvinylbutyrals (PVBs) have been the polymers of 
choice. This polymer may be used in combination with other polymers. 
Although the patent literature abounds in a number of publications with 
respect to the use of PVB, and a mention of phenoxy resin as a supporting 
binder, no mention is made of the role of the phenoxy resin, or the use of 
blends corresponding to phenoxy, epoxy or epoxy novolac resin with PVB. 
This invention focuses on the improved electrical properties derived from 
the phenoxy resin, epoxy resin or epoxy novolac resins, when used as a 
supporting polymer binder in the charge generation layer. The improved 
electrical characteristics relate to improved dark decay and sensitivity, 
while retaining good adhesion (with respect to PVB) and structural 
integrity. 
Phenoxy resins have been reported to serve as polymer binders for bisazo 
pigments. EP 708 374 A1 (1996) demonstrates the use of a phenoxy resin as 
a binder for a bisazo pigment. The authors refer to some agglomeration in 
some of the dispersion formulation based on the phenoxy resin, but 
attributed this to the combination of the coupler residue and the azo 
pigment. Some of the other patents relating to either a use or a possible 
use of the phenoxy resins as binders with bisazo pigments are JP 03158862 
A (1991), JP 03116152 A (1991) and JP 01198762 A (1989). The Japanese 
patent 03282554 A (1991) demonstrates the use of a phenoxy resin as a 
binder for a metal-free phthalocyanine and using 1,1,2-trichloroethane as 
a solvent. Other patents pertaining to the phthalocyanine based phenoxy 
resin formulations include JP 02280169 A (1990), GB 2 231 166 A (1990), 
U.S. Pat. No. 4,983,483 (1993) to name a few. Limburg et al. (EP 295 126 
A2, 1993 and U.S. Pat. No. 4,818,650, 1987 have discussed the use of a 
polyarylamine phenoxy resin as part of the charge transport layer in the 
preparation of a photoreceptor. The above photoreceptor was shown to 
exhibit improved resistance to cracking during mechanical cycling. Phenoxy 
resin based polymers have also been used as undercoats in the preparation 
of photoconductors (e.g. JP 03136064 A, 1991). 
The use of the phenoxy resin as a binder is hence fairly well known. 
However, it was surprising to note in this invention, that the phenoxy 
resin can be used to improve the electrical characteristics of the 
photoconductor. The use of the phenoxy resin as blends results in improved 
electrical characteristics, without having to increase either the pigment 
or charge transport molecule concentration, which in turn relates to lower 
cost of the resulting photoconductor drum. The use of the polymer in 
formulations investigated in this invention has not been reported in the 
patent literature. The importance of this invention can be extended to the 
use of the phenoxy resins in the preparation of photoconductors required 
for high speed printer applications which would require high 
sensitivities, low dark decays and use in any environmental condition 
(ambient, hot/humid or cold/dry). The dark decay for these formulations 
improve by 5-40%, the change in electricals in various environments is 
usually less than 35 V and the sensitivity measured at most energies are 
improved, in comparisons to photoconductors comprising of PVB as CG binder 
only. 
The inventors found that the use of the phenoxy resins as a pure binder 
results in highly unstable dispersions of the titanyl phthalocyanine and 
hence cannot be used in the coating process of photoconductor drums. 
However, the use of the phenoxy resins as a blend with PVB, results in 
stable dispersions and the resulting photoconductor drums are found to 
exhibit superior electrophotographic properties such as low dark decay's 
and high electrical sensitivity's. 
The use of epoxy novolac resins as a binder polymer in the charge 
generation layer of an electrophotographic photoreceptor is not known in 
patent literature. Epoxy resins have been used in the preparation of 
barrier layers, adhesive layers and charge generation layers. In a similar 
manner, phenolic resins have been shown to improve the adhesion of the CG 
layer to the aluminum core. Epoxy-novolac resins are essentially a 
combination of the epoxy resins and the phenolic resins. The resin system 
can be cross-linked either chemically or thermally. The cross-linked 
resins usually result in enhanced mechanical properties in comparison to 
their precursors. The thermal cross-linking reaction can essentially be 
brought about during the curing of the CG layer. The chemical 
cross-linking may be brought about by the addition of catalysts such as 
titanium alkoxides. The epoxy functionality and the phenolic functionality 
not only impart good mechanical integrity to the charge generation binder, 
but also improved adhesion of the CG layer to the aluminum core. 
Several patents in the literature refer to the epoxy resins as possible in 
binders in the sub-layer, charge generation or charge transport layers. 
For example, U.S. Pat. No. 5,240,801, 1993 lists the epoxy resin as a 
polymer for a protective coat layer. JP 621194257 A, 1987 suggests the use 
of epoxy resin as a binder for an oxazole charge transport molecule. EP 
180 930 A2 (1986) (Mitsubishi Chem. Ind.) lists several binders for CG 
layer of which polyvinylbutyral and epoxy resin are two of them. JP 
56097352 A, 1981 lists binders in a general manner as those derived from 
addition or condensation reactions and refer to the epoxy resins as an 
example. 
DISCLOSURE OF THE INVENTION 
In summary, it may be concluded that: 
a) An electrophotographic photoconductor drum may be prepared using a blend 
of polyvinylbutyral and phenoxy resin, epoxy novolac resins, or epoxy 
resins in the CG formulation or layer by a dip-coating process, followed 
by a charge transport layer coating, with enhanced electrical sensitivity 
and decreaed dark decay of the photoconductor. The charge transport layer 
comprises a resin having a charge transport molecule dispersed therein. 
b) The above resins may be used as blends with polyvinylbutyral (for 
example), at levels of 5-95% by weight of the polymer binder. The CG 
systems thus formed, result in improved electrical characteristics with 
various charge transport molecules namely, benzidines and hydrazones, and 
may be used with other transport molecules such as arylamines. 
c) The dispersions prepared are stable for extended periods and result in 
good coating quality. 
d) The photoconductor drums show good environmental stability with respect 
to their electricals and print quality 
e) The molecular weight of the phenoxy resins may be in the range of 
7,000-16,000 g/mol number average molecular weight. 
f) The epoxy novolac resins may have a number average molecular weight of 
400-1300 g/mol, and may be substituted with groups such as hydrogen, 
methyl etc. 
g) The epoxy resins may have a molecular weight of 3,000-10,000 g/mol 
weight average molecular weight. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
One embodiment of the present invention comprises a photoconductive member 
comprising a conductive substrate, a charge generation layer and a charge 
transport layer on the charge generation layer and having a charge 
transport molecule dispersed therein. Preferably, the charge generation 
layer consists essentially of a blend of oxotitanium phthalocyanine 
pigment, polyvinylbutyral and an epoxy capped polymer which is a 
derivative of bisphenol and epichlorohydrin, wherein the harge generation 
layer has a pigment to binder weight ratio of from 35/65 to 45/55. More 
preferably, the epoxy capped polymer has a formula of: 
##STR1## 
where n is an integer. Preferably, the above epoxy capped polymer has a 
weight average molecular weight of from 4,294 to about 26,869. More 
preferably, the polymer has a molecular weight of from 6,782 to about 
26,869. In another preferred embodiment, the polyvinylbutyral and epoxy 
capped polymer are used in a weight ratio of about 75/25 to about 10/90 of 
polyvinylbutyral to epoxy capped polymer. 
In another embodiment, the present invention comprises a photoconductive 
member comprising a conductive substrate, a charge generation layer and a 
charge transport layer on the charge generation layer and having a charge 
transport molecule dispersed therein. Preferably, the charge generation 
layer consists essentially of a blend of oxotitanium phthalocyanine 
pigment, polyvinylbutyral and an epoxy novolac resin, wherein the charge 
generation layer has a pigment to binder weight ratio of from 35/65 to 
45/55. Preferably, the polyvinylbutyral and epoxy novolac resin are used 
in a weight ratio in a range of about 90/10 to about 25/75 
polyvinylbutyral to epoxy novolac resin. Unless otherwise specifically 
stated, the materials of this specification have the following structure. 
BX-55Z and BM-S polyvinylbutyral (PVB): 
##STR2## 
Number Ave. molecular Wt.: 98,000 g/lmol PHENOXY RESINS 
PKHH, PKHJ, PKHM and PKFE phenoxy resin: 
##STR3## 
where n.about.38-60 Number Ave. Molecular Wt.: 
PKHH: 11,000 g/mol 
PHHJ: 12,000 g/mol 
PKHM: 7,000 g/mol 
PKFE: 16,000 g/mol 
EPOXY NOVOLAC RESINS 
P(GE-F): poly[(phenylene glycidylether)-co-formaldehyde] 
##STR4## 
R.dbd.H or CH.sub.3 where R.dbd.H; resin is P(GE-F) above where 
R--CH.sub.3, resin is poly[(o-cresyl glycidylether)-co-formaldehyde]. 
Number Ave. molecular Wt.: about 600-1270 g/mol 
PC(GE-DCP): poly[phenylene glycidylether-co-dicyclopentadiene] 
##STR5## 
Number Ave. molecular Wt.: about 490 g/mol EPOXY RESINS 
##STR6## 
n=an integer consistent with the molecular weight of the resin Wt. Ave. 
Molecular Weight: 
EPON 1001: 4,294 g/mol 
EPON 1004: 6,782 g/mol 
EPON 1009: 26,869 g/mol 
BENZIDINE: 
N,N.sup.1 -bis(3-methylphenyl)-N,N.sup.1 -bisphenylbenzidine 
##STR7## 
DEH 
##STR8## 
POLYCARBONATE:MAKROLON--5208 polycarbonate 
##STR9## 
APEC 9201 polycarbonate 
##STR10## 
The term "blend" is used in the normal sense of a thorough mixture. 
The phenoxy resins with number average molecular weight, Mn: 7,000-16,000 
g/mol (average molecular weight, Mw: 40,000-80,000) were used as blends 
with polyvinylbutyral (BX-55Z and BM-S, Sekisui Chemical Co.). This work 
pertains to the use of the phenoxy resins (PKHH, PKHJ, PKHM and PKFE; 
Phenoxy Associates, S.C., Phenoxy Resin: Scientific Polymer Products, New 
York) as blends in charge generation formulations. A formulation 
consisting of 45/55 pigment (oxotitanium phthalocyanine) to binder, showed 
improved dark decay and electrical characteristics when the PVB binder was 
suitably blended with the phenoxy resin. The weight ratios used were 
75/25, 25/75 and 10/90 of PVB/phenoxy resin. The dispersions were stable 
for the PVB/phenoxy blends. All data presented below correspond to the use 
of the same transport formulation, namely a polycarbonate (MAKROLON-5208, 
Bayer) and 30% benzidine 
(N,N'-bis(3-methylphenyl)-N,N'-bisphenyl-benzidine) at 20% solids in a 
mixture of tetrahydrofuran and 1,4-dioxane. 
In contrast, the use of phenoxy resin without any PVB as binder for the 
oxotitanium phthalocyanine resulted in an unstable dispersion (phase 
separation). The PVB/phenoxy blends (75/25) resulted in good coating 
quality for the CG layer, whereas the higher phenoxy resin blends (75/25 
phenoxy/PVB) required the drums to be double-dipped to obtain optimum 
optical densities in the CG layer, when coated at 3% solids, although at 
6% solids the CGs required a single-dip. The CG layers were coated with a 
benzidine-polycarbonate transport layer with a cure at 120.degree. C. for 
1 h, to a coat weight of about 20 mg/in.sup.2. The adhesion of the CG 
layer to the aluminum drum core was improved with the higher temperature 
cure, exhibiting similar or improved adhesion of the coatings to the core 
in comparison to the standard BX-55Z based formulations. In comparison to 
the BX-55Z PVB as CG binder, the phenoxy resin blends with BX-55Z showed 
improved electrical characteristics. The dark decay--time data and the 
electrical characteristics for the blends at various cure conditions are 
shown in Tables 1 and 2, respectively. 
TABLE 1 
______________________________________ 
Variation of Dark Decay with Time: BX-55Z/Phenoxy Resins 
(75/25);(45/55) Pigment/Binder 
Dark Decay (V/sec) 
CG BINDER (CURE) 
1 sec 10 sec 30 sec 
60 sec 
______________________________________ 
BX55Z (100C/5 min) 
26 129 219 305 
BX55Z/PKHH (Amb. Cure) 
26 139 267 379 
BX55Z/PKHH (50C/5 min) 
19 72 142 214 
BX55Z/PKHH (100C/5 min) 
22 81 145 212 
BX55Z/PKHJ (Amb. Cure) 
22 80 147 213 
BX55Z/PKHJ (50C/5 min) 
20 73 138 200 
BX55Z/PKHJ (100C/5 min) 
20 85 145 218 
______________________________________ 
TABLE 2 
______________________________________ 
Electrical Characteristics of BX-55Z/Phenoxy Resins (75/25); 
(45/55 Pigment/Binder) 
Charge Voltage 
V.sub.0.23 
CG BINDER (CURE) (-Vo) (-V) 
______________________________________ 
BX-55Z (100C/5 min) 
658 157 
BX-55Z/PKHH (Amb. Cure) 
638 105 
BX-55Z/PKHH (50/5 min) 
643 112 
BX-55Z/PKHH (100C/5 min) 
645 110 
BX-55Z/PKHJ (Amb. Cure) 
643 105 
BX-55Z/PKHJ (50C/5 min) 
645 105 
BX-55Z/PKHJ (100C/5 min) 
645 112 
______________________________________ 
V.sub.0.23 : Voltage at an Energy of 0.23 uJ/cm2 
All phenoxy resin blends had optical density of about 1.30 
In order to test the hypothesis that the phenoxy resin had a role in the 
improved electrical characteristics, a formulation was made such that the 
pigment concentration was decreased, namely, 35% instead of 45%. The 
results were identical to the 45/55 pigment/binder ratio. The 
photoconductor drums exhibited lower dark decays and improved electrical 
characteristics. The dark decay and sensitivities were substantially 
improved for the higher phenoxy resin ratios. The electrical response 
characteristics are shown in Table 3: 
TABLE 3 
______________________________________ 
Electrical Characteristics: BX-55Z/Phenoxy Resins; 
(35/65 Pigment/Binder) 
Charge Voltage 
V.sub.0.23 
CG BINDER (-Vo) (-V) 
______________________________________ 
BX-55Z 658 237 
BX-55Z/PKHH (75/25 
658 188 
BX-55Z/PKHJ (75/25) 
658 180 
BX-55Z/PKHH* (25/75) 
658 122 
BX-55Z/PKHJ* (25/75) 
660 116 
______________________________________ 
*Drums were doubledipped in CG formulation 
All drums had optical density of 1.30-1.40 
V.sub.0.23 : Voltage at an Energy of 0.23 uJ/cm2 
An extension of this work was to study the effect of the phenoxy resin on 
low molecular weight PVB. The resin chosen for this purpose was the BM-S 
PVB (Sekisui Chemical Co., Mn of 48000 g/mol) which has a lower molecular 
weight than the BX-55Z PVB (Mn of 98000 g/mol). The blends prepared were 
the 75/25 and the 25/75 of BM-S/phenoxy resin, respectively. The CG 
dispersions involving the blends were stable and gave good coating 
quality. The dark decay and electrical characteristics were improved, more 
significantly for the drums that were double-dipped in the CG formulation 
(for optimum properties, proper choice of the optical density was 
critical), in comparison to the BM-S standard formulation. As is evident 
from the electrical characteristics in Table 4, the sensitivity of the 
drums are increased if the drums are double-dipped in the CG layer coating 
process, which in turn correspond to higher optical densities. 
TABLE 4 
______________________________________ 
Electrical Characteristics: BM-S/Phenoxy Resins 
(45/55 Pigment/Binder) 
Charge Voltage 
V.sub.0.23 
CG BINDER (-Vo) (-V) 
______________________________________ 
BM-S 658 117 
BM-S/PKHH (75/25) 658 135 
BM-S/PKHJ (75/25 658 142 
BM-S/PKHH* (75/25) 
650 82 
BM-S/PKHJ* (75/25) 
653 85 
BM-S/PKHH (25/75) 658 163 
BM-S/PKHJ (25/75) 658 160 
BM-S/PKHH* (25/75) 
657 85 
BM-S/PKHJ* (25/75) 
657 83 
______________________________________ 
*Drums were doubledipped in CG formulation, optical density of 1.35, 
optical density of all others was 1.20 
V.sub.0.23 : Voltage at an Energy of 0.23 uJ/cm2 
Formulations containing a (bisphenol-TMC-co-bisphenol-A) polycarbonate 
[(BPTMC-co-BPA)PC, APEC 9201, Bayer]-benzidine transport solution were 
coated on a standard CG layer (BX-55Z) and the phenoxy resin/BX-55Z blend, 
and interestingly the phenoxy resin drums exhibited lower dark decays and 
improved electrical behavior. The electrical characteristics for the 
PVB/(bisphenol-TMC-co-bisphenol-A) polycarbonate are shown in Table 5. 
Another significant improvement in the use of the phenoxy resin was the 
limited fluctuation in the electrical characteristics at various 
environmental conditions. 
The drums formulated with the phenoxy resin/PVB blends were subjected to 
different conditions, such as ambient, hot/humid and cold/dry. The 
electrical response stability at different environments is evident in the 
phenoxy resin blends, as seen in Table 5. 
TABLE 5 
______________________________________ 
Electrical Characteristics for the CG/CT binders 
AMBIENT 
(72F/40% COLD/DRY (60F/08% 
RH) RH) 
CG BINDER -V.sub.0 
-V.sub.0.23 
-V.sub.0 
-V.sub.0.23 
______________________________________ 
BX55Z//(BPTMC-co-BPA)PC 
658 185 
BX55Z/PKHH (75/24)// 
662 145 
(BPTMC-co-BPZ)PC 
BX55Z 
(45/55, PIGMENT/BINDER) 
658 192 645 225 
BX55Z/PKHH (25/75) 
647 112 642 140 
BX55Z/PKHJ (25/75) 
647 115 642 152 
BX55Z 658 237 660 282 
(35/65, PIGMENT/BINDER) 
BX66Z/PKHH (25/75) 
658 122 660 155 
______________________________________ 
A significant improvement in the electrical behavior at various 
environments is further manifested in the print quality that one obtains 
for the photoconductor under these environmental conditions. In contrast 
to the standard BX55Z based formulation, the phenoxy resin blends, 
exhibited good isopel optical density (O.D.) and single pel 20 performance 
at ambient, hot/humid and cold/dry conditions. For example while the 
isopel O.D. for BX55Z at ambient, and cold/dry were 0.31 and 0.18, those 
for the phenoxy resin blend (25/75 BX55/PKHH) were 0.62 and 0.32. Print 
quality is usually improved if the isopel O.D. is high and the loss of 
single pel in cold/dry conditions is not observed for the phenoxy resin 
blends. 
The epoxy novolac resins used as blends were poly[(phenylene glycidyl 
ether)-co-formaldehyde] [P(GE-F)] (Mn of.about.605) and poly[(phenylene 
glycidyl ether)-co-dicyclopentadiene] [P(GE-DCP)] (Mn of.about.490) with 
PVB (S-Lec-B [BX-55Z and BM-S], Sekisui Chemical Co.). Formulations 
consisting of 45/55 pigment (oxotitanium phthalocyanine) to binder, showed 
improved dark decay and electrical characteristics when the PVB binder was 
blended with epoxy novolac resin. The blends were prepared at weight 
ratios of 90/10, 75/25, 50/50 and 25/75 of the PVB to the epoxy novolac 
resin. All stable formulations resulted in good coating quality. The CG 
layers involving the above formulations were typically cured at 
100.degree. C. for 5 min. The charge transport (CT) layers coated on the 
CG layers were benzidine-polycarbonate and cured at 120.degree. C. for 1 
h, to a coat weight of about 20 mg/in2. The electrical characteristics of 
drums coated with the above formulations are given in Table 6. 
TABLE 6 
__________________________________________________________________________ 
Electrical Characteristics of Epoxy Novolac Resin CG Blends 
with Benzidine Transport (45% Pigment and 30% Transport 
concentrations) 
Binder Dark 
(Charge Generation 
Optical 
Charge 
Discharge 
Decay 
Back- 
Isopel 
Layer) Environment 
Density 
(-V) 
(-V) (V/sec) 
ground 
O.D. 
__________________________________________________________________________ 
BX-55Z Ambient* 
1.55 
662 192 18 0.45 
0.29 
cold/dry** 
662 225 0.35 
0.18 
BX-55Z/P Ambient 
1.36 
658 147 25 0.61 
0.42 
(GE-DCP) (90/10) 
cold/dry 645 195 1.23 
0.22 
BX-55Z/P Ambient 
1.24 
662 90 21 0.62 
0.56 
(GE-DCP) (75/25) 
cold/dry 663 110 0.32 
0.35 
BX-55Z/P Ambient 
1.38 
662 82 20 0.45 
0.64 
(GE-DCP) (50/50) 
cold/dry 660 102 0.49 
0.37 
BX-55Z/P Ambient 
1.33 
663 100 12 0.37 
0.55 
(GE-DCP) (25/75) 
cold/dry 662 135 0.59 
0.29 
BX-55Z/P Ambient 
1.36 
663 117 34 0.51 
0.57 
(GE-F) (75/25) 
cold/dry 660 137 0.64 
0.33 
BX-55Z/P Ambient 
1.37 
663 97 22 0.40 
0.60 
(GE-F) (50/50) 
cold/dry 662 120 0.49 
0.33 
BX-55Z/P Ambient 
1.35 
663 98 18 0.71 
0.58 
(GE-F) (25/75) 
cold/dry 662 130 0.39 
0.29 
__________________________________________________________________________ 
*Ambient: 72.degree. F./40% Relative Humidity (RH) 
**Cold/Dry: 60.degree. F. /08% RH 
Discharge Voltage corresponds to voltage at energy of 0.23 uJ/cm2 
As is evident from Table 6, the addition of the epoxy novolac resin in the 
CG layer improves the electrical sensitivity and the dark decay. Another 
significant improvement derived from this system, is the stability of the 
photoconductor drum's electricals at different environmental conditions. 
While more often than not, the electricals slow down to a large extent in 
a cold/dry condition (60.degree. F./08% relative humidity), the epoxy 
novolac resin blends show a small variation and result in better print 
quality [background and the isopel optical density (Isopel O.D.)] in 
comparison to the non-epoxy novolac resin blend. In most cases, the 
electrical discharge voltage at an energy of 0.23 uJ/cm2 show a variation 
of about 20-30 V with the change in environment (72.degree. F./40% RH to 
60.degree. F./08% RH), and the photoconductor exhibits better sensitivity 
than the non-epoxy novolac resin drum at ambient condition (72.degree. 
F./40% RH). 
In order to test the theory that the improved electricals were derived from 
the use of the epoxy novolac resin, that resin was blended with a lower 
molecular weight PVB, namely BM-S (Mn of 48000 g/mol). The results were 
identical to the BX-55Z formulation experiment, i.e. improved electrical 
sensitivity and dark decay (Table 7). 
TABLE 7 
__________________________________________________________________________ 
Electrical Characteristics of Epoxy Novolac Resin Based CG with 
Benzidine 
Transport (45% Pigment concentration) 
Optical Dark 
Density 
Charge 
Discharge 
Decay 
Back 
Isopel 
Binder Environment 
(O.D.) 
(-V) 
(-V) (V/sec) 
ground 
O.D. 
__________________________________________________________________________ 
BM-S Ambiemt 
1.21 
658 117 20 0.77 
0.43 
cold/dry 660 187 0.66 
0.23 
BM-S/P (GE-DCP) 
Ambient 
1.29 
662 102 17 0.58 
0.46 
(90/10) cold/dry 662 138 0.53 
0.28 
__________________________________________________________________________ 
It may be argued that the increased sensitivity and decreased dark decay 
are due to the use of a lower molecular weight binder in the CG. The 
advantage derived is that, whereas the epoxy novolac resin as a CG binder 
(100%) results in an unstable dispersion, and the use of a PVB as a CG 
binder results in lower sensitivity, the combination of the polymers 
results in a stable dispersion and optimum electricals. While the use of a 
low molecular weight PVB may result in increased sensitivity (BM-S Vs 
BX-55Z), it is clear that the blend involving the epoxy resin increases 
the sensitivity irrespective of the molecular weight of the PVB binder. 
The use of a low molecular weight PVB often results in CG wash, during the 
CT coating. However, this problem is alleviated by the use of the epoxy 
novolac resin blend. 
To further test the validity of this invention, formulations based on lower 
pigment level namely 25% and 35% were chosen, and photoconductor drums 
formulated. As seen in Tables 8 and 9, the theory that the use of the 
epoxy novolac resin blend in the CG results in improved electrical 
characteristics still holds. 
TABLE 8 
__________________________________________________________________________ 
Electrical Characteristics of Epoxy Novolac Resin Based CG with 
Benzidine 
Transport (35% Pigment concentration) 
Optical Dark 
Density 
Charge 
Discharge 
Decay 
Back 
Isopel 
Binder Environment 
(O.D.) 
(-V) 
(-V) (V/sec) 
ground 
O.D. 
__________________________________________________________________________ 
BM-55Z Ambiemt 
1.4 660 275 70 0.61 
0.29 
60/08 665 310 0.47 
0.20 
BX-55Z/P Ambient 
1.29 
663 115 27 0.12 
0.55 
(GE-DCP) (75/25) 
60/08 665 147 0.48 
0.33 
BX-55Z/P Ambient 
1.29 
665 122 27 0.58 
0.46 
(GE-F) (75/25) 
60/08 665 160 0.53 
0.28 
__________________________________________________________________________ 
TABLE 9 
__________________________________________________________________________ 
Electrical Characteristics of Epoxy Novolac Resin Based CG with 
Benzidine 
Transport (25% Pigment concentration) 
Optical Dark 
Density 
Charge 
Discharge 
Decay 
Back 
Isopel 
Binder Environment 
(O.D.) 
(-V) 
(-V) (V/sec) 
ground 
O.D. 
__________________________________________________________________________ 
BM-55Z Ambiemt 
1.28 
660 277 68 0.62 
0.29 
cold/dry 665 313 0.35 
0.18 
BX-55Z/P Ambient 
1.34 
662 197 60 0.11 
0.41 
(GE-DCP) (75/25) 
cold/dry 665 230 0.47 
0.25 
BX-55Z/P Ambient 
1.38 
663 202 40 0.35 
0.42 
(GE-F) (75/25) 
cold/dry 663 237 0.41 
0.25 
__________________________________________________________________________ 
To further explore the use of the epoxy resin CG, tests were carried out 
with a different charge transport molecule namely 
p-diethylaminobenzaldehyde diphenylhydrazone (DEH). Significant 
improvements in the electrical sensitivity were observed for formulations 
containing the epoxy novolac resin, both at 35% and 45% pigment levels. A 
summary of the results for the DEH system are given in Table 10. It may be 
noted that the DEH drums were not UV cured following the cure of the CT 
layer. 
TABLE 10 
______________________________________ 
Electrical Characteristics of Epoxy Novolac Resin Based CG with DEH 
Transport 
Optical Dis- Dark 
Environ- Density Charge 
charge 
Decay 
Binder ment (O.D.) (-V) (-V) (V/sec) 
______________________________________ 
BX-55Z Ambient 1.4 693 275 23 
(45% Pigment) 
BX-55Z/P Ambient 1.42 692 141 20 
(GE-co-DCP) (90/10) 
BX-55Z/P Ambient 1.49 695 135 15 
(GE-co-F) (90/10) 
BX-55Z Ambient 1.38 695 243 25 
(35% Pigment) 
BX-55Z/P Ambient 1.41 695 162 18 
(GE-co-DCP) (90/10) 
BX-55Z/P Ambient 1.48 697 157 21 
(GE-co-F) (90/10) 
______________________________________ 
The epoxy resins used as blends were EPON 1001, 1004 and 1009 (Shell 
Chemicals ) with polyvinylbutyral (S-Lec-B [BX-55Z], Sekisui Chemical 
Co.). The EPON resins are epoxy capped polymers which are derivations of 
bisphenol and epichlorohydrin having weight average molecular weight of 
4294, 6782, and 26,869 g/mol respectively. Formulations consisting of 
45/55 and 35/65 pigment (oxotitanium phthalocyanine) to binder, showed 
improved dark decay and electrical characteristics when the PVB binder was 
blended with epoxy novolac resin. The blends were prepared at weight 
ratios of, 75/25, 25/75 and 10/90 of the PVB to the epoxy resin. All 
stable formulations resulted in good coating quality. The CG layers 
involving the above formulations were typically cured at 100.degree. C. 
for 5 min. The charge transport (CT) layers coated on the CG layers were 
benzidine-polycarbonate and cured at 120.degree. C. for 1 h, to a coat 
weight of about 20 mg/in2. The electrical characteristics of drums coated 
with the above formulations are given in Table 11. 
TABLE 11 
______________________________________ 
Electrical Characteristics of Epoxy Resin (EPON 1004) CG Blends with 
Benzidine Transport (45% Pigment and 30% Transport concentrations) 
Charge 
CG BINDER Optical Dark Decay 
Voltage 
V.sub.0.23 
(CURE) Density (V/sec) (-V.sub.0) 
(-V) 
______________________________________ 
BX-55Z 1.68 20 698 190 
BX-55Z/EPON 1004 (75/25) 
1.48 14 695 88 
BX-55Z/EPON 1004 (75/25) 
1.35 10 700 132 
BX-55Z/EPON 1004 (25/75) 
1.34 9 699 148 
BX-55Z/EPON 1004 (10/90) 
1.34 9 696 187 
______________________________________ 
V.sub.0.23 : Voltage at an Energy of 0.23 uJ/cm2 
TABLE 12 
______________________________________ 
Electrical Characteristics of Epoxy Resin (EPON 1004) CG Blends with 
Benzidine Transport (35% Pigment and 30% Transport concentrations) 
Charge 
CG BINDER Optical Dark Decay 
Voltage 
V.sub.0.23 
(CURE) Density (V/sec) (-V.sub.0) 
(-V) 
______________________________________ 
BX-55Z 1.29 45 684 237 
BX-55Z/EPON 1004 (75/25) 
1.82 42 686 156 
BX-55Z/EPON 1004 (75/25) 
1.33 23 696 141 
BX-55Z/EPON 1004 (25/75) 
1.61 19 698 81 
BX-55Z/EPON 1004 (25/75) 
1.3 15 695 161 
BX-55Z/EPON 1004 (10/90) 
1.34 13 693 134 
BX-55Z/EPON 1004 (10/90) 
1.23 9 694 194 
______________________________________ 
V.sub.0.23 : Voltage at an Energy of 0.23 uJ/cm2 
It is hence clear from the tables 11 and 12, that the use of BX-55Z/EPON 
blends results in a photoconductor with highly improved electrical 
characteristics of an electrophotographic photoreceptor. The results were 
identical for the use of the PVB/Epoxy resin CG formulations with 
different transports in the charge transport layer, such as 
diethylaminobenzaldehyde diphenylhydrazone (DEH) and 
diphenylaminobenzaldehyde diphenylhydrazone (TPH).

FORMULATION OF PHENOXY RESIN 
COMATIVE EXAMPLE 1 
A charge generation formulation consisting of a 45/55 pigment/binder ratio 
was prepared as follows: 
Oxotitanium phthalocyanine (7.4 g), polyvinylbutyral (BX-55Z, Sekisui 
Chemical Co., 9.00 g) with Potter's glass beads (60 ml) was added to a 
mixture of 2-butanone (50 g) and cyclohexanone (50 g), in an amber glass 
bottle, and agitated in a paint-shaker for 12 h and diluted to about 3% 
solids with 2-butanone (400 g). An anodized aluminum drum was then 
dip-coated with the CG formulation and dried at 100.degree. C. for 5 min. 
The transport layer formulation was prepared from a bisphenol-A 
polycarbonate (MAKROLON-5208, Bayer, 62.30 g), benzidine (26.70 g) in 
tetrahydrofuran (249 g) and 1,4-dioxane (106 g). The CG layer coated drums 
were dip-coated in the CT formulation, dried at 120.degree. C. for 1 h, to 
obtain a coat weight of about 20 mg/in2. The electrical characteristics of 
this drum were: Charge voltage (Vo): -683 V, residual voltage (Vr): -80 V, 
dark decay: 24 V/sec, Voltage at E(0.23 uJ/cm2) of -135 V. 
COMATIVE EXAMPLE 2 
A formulation involving BM-S as the PVB binder at 45/55 pigment binder 
ratio was prepared as follows: 
Oxotitanium phthalocyanine (7.4 g), polyvinylbutyral (BM-S, Sekisui 
Chemical Co., 9.00 g) with Potter's glass beads (60 ml) was added to a 
mixture of 2-butanone (50 g) and cyclohexanone (50 g), in an amber glass 
bottle, milled for 12 h and diluted to about 3% solids with 2-butanone 
(400 g). An anodized aluminum drum was then dip-coated with the CG 
formulation and dried at 100.degree. C. for 5 min. The transport layer 
formulation was prepared from a bisphenol-A polycarbonate (MAKROLON-5208, 
Bayer, 62.30 g), benzidine (26.70 g) in tetrahydrofuran (249 g) and 
1,4-dioxane (106 g). The CG layer coated drums were dip-coated in the CT 
formulation, dried at 120.degree. C. for 1 h, to obtain a coat weight of 
about 20 mg/in2. The electrical characteristics of this drum were: Charge 
voltage (Vo): -689 V, residual voltage (Vr): -60 V, dark decay: 20 V/sec, 
Voltage at E(/0.23 uJ/cm2): -120 V. 
COMATIVE EXAMPLE 3 
A formulation involving BX-55Z as the PVB binder at 35/65 pigment binder 
ratio was prepared as follows: 
Oxotitanium phthalocyanine (4.0 g), polyvinylbutyral (BX-55Z, 8.12 g) with 
Potter's glass beads (60 ml) was added to a mixture of 2-butanone (50 g) 
and cyclohexanone (50 g), in an amber glass bottle, agitated in a 
paint-shaker for 12 h and diluted to about 3% solids with 2-butanone (400 
g). An anodized aluminum drum was then dip-coated with the CG formulation 
and dried at 100.degree. C. for 5 min. The transport layer formulation was 
prepared from a bisphenol-A polycarbonate (MAKROLON-5208, Bayer, 62.30 g), 
benzidine (26.70 g) in tetrahydrofuran (249 g) and 1,4-dioxane (106 g). 
The C/G layer coated drums were dip-coated in the CT formulation, dried at 
120.degree. C. for 1 h, to obtain a coat weight of about 20 mg/in2. The 
electrical characteristics of this drum were: Charge voltage (Vo): -683 V, 
residual voltage (Vr): -140 V, dark decay: 51 V/sec, Voltage at E(0.23 
uJ/cm2): -256 V. 
EXAMPLE 1 
A typical formulation involving a BX-55Z/phenoxy resin (75/25) at 45/55 
pigment/binder ratio was prepared as follows: 
Oxotitanium phthalocyanine (7.4 g), polyvinylbutyral (BX-55Z, 6.820 g), a 
phenoxy resin (PKHH, Phenoxy associates, 2.28 g) with Potter's glass beads 
(60 ml) was added to a mixture of 2-butanone (50 g) and cyclohexanone (50 
g), in an amber glass bottle, agitated in a paint-shaker for 12 h and 
diluted to about 3% solids with 2-butanone (400 g). An anodized aluminum 
drum was then dip-coated with the CG formulation and dried at 100.degree. 
C. for 5 min. The transport layer formulation was prepared from a 
bisphenol-A polycarbonate (MAKROLON-5208, Bayer, 62.30 g), benzidine 
(26.70 g) in tetrahydrofuran (249 g) and 1,4-dioxane (106 g). The CG layer 
coated drums were dip-coated in the CT formulation, dried at 120.degree. 
C. for 1 h, to obtain a coat weight of about 20.9 mg/in2. The electrical 
characteristics of this drum were: Charge voltage (Vo): -645 V, residual 
voltage (Vr): -110 V, dark decay: 22 V/sec, Voltage at E(0.23 uJ/cm2): 
-175 V. 
EXAMPLE 2 
A typical formulation involving a BX-55Z/phenoxy resin (25/75) at 45/55 
pigment/binder ratio was prepared as follows: 
Oxotitanium phthalocyanine (7.4 g), polyvinylbutyral (BX-55Z, 2.28 g), a 
phenoxy resin (PKHH, Phenoxy associates, 6.82 g) with Potter's glass beads 
(60 ml) was added to a mixture of 2-butanone (50 g) and cyclohexanone (50 
g), in an amber glass bottle, agitated in a paint-shaker for 12 h and 
diluted to about 3% solids with 2-butanone (400 g). An anodized aluminum 
drum was then dip-coated with the CG formulation, air-dried for 1 minute 
and dip-coated in the CG layer and dried at 100.degree. C. for 5 min. The 
transport layer formulation was prepared from a bisphenol-A polycarbonate 
(MAKROLON-5208, Bayer, 62.30 g), benzidine (26.70 g) in tetrahydrofuran 
(249 g) and 1,4-dioxane (106 g). The CG layer coated drums were dip-coated 
in the CT formulation, dried at 120.degree. C. for 1 h, to obtain a coat 
weight of about 21 mg/in2. The electrical characteristics of this drum 
were: Charge voltage (Vo): -693 V, residual voltage (Vr): -90 V, dark 
decay: 15 V/sec, Voltage at E(0.23 uJ/cm2): -112 V. 
EXAMPLE 3 
A typical formulation involving a BM-S/phenoxy resin (25/75) at 45/55 
pigment/binder ratio was prepared as follows: 
Oxotitanium phthalocyanine (7.4 g), polyvinylbutyral (BX-55Z, 6.820 g), a 
phenoxy resin (PKHH, Phenoxy associates, 2.28 g) with Potter's glass beads 
(60 ml) was added to a mixture of 2-butanone (50 g) and cyclohexanone (50 
g), in an amber glass bottle, agitated in a paint-shaker for 12 h and 
diluted to about 3% solids with 2-butanone (400 g). An anodized aluminum 
drum was then dip-coated with the CG formulation, dried at room 
temperature for 1 min., dip-coated in the CG layer and dried at 
100.degree. C. for 5 min. The transport layer formulation was prepared 
from a bisphenol-A polycarbonate (MAKROLON-5208, Bayer, 62.30 g), 
benzidine (26.70 g) in tetrahydrofuran (249 g) and 1,4-dioxane (106 g). 
The CG layer coated drums were dip-coated in the CT formulation, dried at 
120.degree. C. for 1 h, to obtain a coat weight of about 19.6 mg/in2. The 
electrical characteristics of this drum were: Charge voltage (Vo): -696 V, 
residual voltage (Vr): -73 V, dark decay: 14 V/sec, Voltage at E(0.23 
uJ/cm2): -133 V. 
PREATION OF EPOXY NOVOLAC BASED FORMULATIONS: 
EXAMPLE 4 
A typical formulation involving a BX-55Z/epoxy novolac resin (75/25) at 
45/55 pigment/binder ratio was prepared as follows: 
Oxotitanium phthalocyanine (7.42 g), polyvinylbutyral (BX-55Z, 6.80 g), an 
epoxy novolac resin (poly[(phenylglycidyl ether)-co-dicyclopentadiene] 
Aldrich Chemical Co., 2.27 g) with Potter's glass beads (60 ml) were added 
to a mixture of 2-butanone (75 g) and cyclohexanone (50 g), in an amber 
glass bottle, agitated in a paint-shaker for 12 h and diluted with 
2-butanone (325 g). An anodized aluminum drum was then dip-coated with the 
CG formulation and dried at 100.degree. C. for 5 min. The transport layer 
formulation was prepared from a bisphenol-A polycarbonate (MAKROLON-5208, 
Bayer, 62.30 g), benzidine (26.70 g) in tetrahydrofuran (249 g) and 
1,4-dioxane (106 g). The CG layer coated drums were dip-coated in the CT 
formulation, dried at 120.degree. C. for 1 h, to obtain a coat weight of 
about 20.5 mg/in2. The electrical characteristics of this drum were: 
Charge voltage (Vo): -662 V, Voltage at E(0.23 uJ/cm2): -90 V and dark 
decay: 25 V/sec, . 
EXAMPLE 5 
A typical formulation involving a BM-S/epoxy novolac resin (75/25) at 45/55 
pigment/binder ratio was prepared as follows: 
Oxotitanium phthalocyanine (7.42 g), polyvinylbutyral (BM-S, 6.80 g), an 
epoxy novolac resin (poly[(phenylglycidyl ether)-co-dicyclopentadiene] 
Aldrich Chemical Co., 2.27 g) with Potter's glass beads (60 ml) were added 
to a mixture of 2-butanone (50 g) and cyclohexanone (75 g), in an amber 
glass bottle, agitated in a paint-shaker for 12 h and diluted with 
2-butanone (325 g). An anodized aluminum drum was then dip-coated with the 
CG formulation, and dried at 100.degree. C. for 5 min. The transport layer 
formulation was prepared from a bisphenol-A polycarbonate (MAKROLON-5208, 
Bayer, 62.30 g), benzidine (26.70 g) in tetrahydrofuran (249 g) and 
1,4-dioxane (106 g). The CG layer coated drums were dip-coated in the CT 
formulation, dried at 120.degree. C. for 1 h, to obtain a coat weight of 
about 20 mg/in2. The electrical characteristics of this drum were: Charge 
voltage (Vo): -662 V, Voltage at E(0.23 uJ/cm2): -102 V and dark decay: 17 
V/sec. 
EXAMPLE 6 
A typical formulation involving a BX-55Z/epoxy novolac resin (25/75) at 
45/55 pigment/binder ratio and DEH transport was prepared as follows: 
Oxotitanium phthalocyanine (9.38 g), polyvinylbutyral (BX-55Z, 8.59 g), an 
epoxy novolac resin (poly[(phenylglycidyl ether)-co-formaldehyde] Aldrich 
Chemical Co., 2.86g ) with Potter's glass beads (60 ml) were added to a 
mixture of 2-butanone (85 g) and cyclohexanone (40 g), in an amber glass 
bottle, agitated in a paint-shaker for 12 h and diluted with 2-butanone 
(275 g). An anodized aluminum drum was then dip-coated with the CG 
formulation, and dried at 100.degree. C. for 5 min. The transport layer 
formulation was prepared from a bisphenol-A polycarbonate (MAKROLON-5208, 
Bayer, 37.6 g), DEH (37.10 g), PE-200 (4.58 g), acetosol yellow (0.68 g) 
in tetrahydrofuran (259.6g) and 1,4-dioxane (111.4 g). The CG layer coated 
drums were dip-coated in the CT formulation, dried at 120.degree. C. for 1 
h, to obtain a coat weight of about 16.1 mg/in2. The electrical 
characteristics of this drum were: Charge voltage (Vo): -695 V, Voltage at 
E(0.23 uJ/cm2): -135 V and dark decay: 15 V/sec, . 
PREATION OF EPOXY RESIN BASED FORMULATIONS: 
EXAMPLE 7 
A typical formulation involving a BX-55Z/epoxy resin (75/25) at 45/55 
pigment/binder ratio was prepared as follows: 
Oxotitanium phthalocyanine (7.0 g), polyvinylbutyral (BX-55Z, 6.82 g), a 
epoxy resin (EPON 1004, Shell Co., 2.28 g) with Potter's glass beads (60 
ml) was added to a mixture of 2-butanone (32 g) and cyclohexanone (32 g), 
in an amber glass bottle, agitated in a paint-shaker for 12 h and diluted 
to about 4.7% solids with 2-butanone (258 g). An anodized aluminum drum 
was then dip-coated with the CG formulation and dried at 100.degree. C. 
for 5 min. The transport layer formulation was prepared from a bisphenol-A 
polycarbonate (MAKROLON-5208, Bayer, 62.30 g), benzidine (26.70 g) in 
tetrahydrofuran (249 g) and 1,4-dioxane (106 g). The CG layer coated drums 
were dip-coated in the CT formulation, dried at 120.degree. C. for 1 h, to 
obtain a coat weight of about 16 mg/in2. The electrical characteristics of 
this drum were: Charge voltage (Vo): -696 V, residual voltage (Vr): -48 V, 
dark decay: 14 V/sec, Voltage at E(0.23 uJ/cm2): -88 V. 
EXAMPLE 8 
A typical formulation involving a BX-55Z/epoxy resin (25/75) at 45/55 
pigment/binder ratio was prepared as follows: 
Oxotitanium phthalocyanine (7.0 g), polyvinylbutyral (BX-55Z, 2.28 g), a 
epoxy resin (EPON 1004, Shell Co., 6.82 g) with Potter's glass beads (60 
ml) was added to a mixture of 2-butanone (32 g) and cyclohexanone (32 g), 
in an amber glass bottle, agitated in a paint-shaker for 12 h and diluted 
to about 4.7% solids with 2-butanone (258 g). An anodized aluminum drum 
was then dip-coated with the CG formulation and dried at 100.degree. C. 
for 5 min. The transport layer formulation was prepared from a bisphenol-A 
polycarbonate (MAKROLON-5208, Bayer, 62.30 g), benzidine (26.70 g) in 
tetrahydrofuran (249 g) and 1,4-dioxane (106 g). The CG layer coated drums 
were dip-coated in the CT formulation, dried at 120.degree. C. for 1 h, to 
obtain a coat weight of about 16 mg/in2. The electrical characteristics of 
this drum were: Charge voltage (Vo): -699 V, residual voltage (Vr): -77 V, 
dark decay: 9 V/sec, Voltage at E(0.23 uJ/cm2): -148 V. 
EXAMPLE 9 
A typical formulation involving a BX-55Z/epoxy resin (75/25) at 35/65 
pigment/binder ratio was prepared as follows: 
Oxotitanium phthalocyanine (5.25 g), polyvinylbutyral (BX-55Z, 7.31 g), a 
epoxy resin (EPON 1004, Shell Co., 2.44 g) with Potter's glass beads (60 
ml) was added to a mixture of 2-butanone (30g) and cyclohexanone (30 g), 
in an amber glass bottle, agitated in a paint-shaker for 12 h and diluted 
to about 5% solids with 2-butanone (240 g). An anodized aluminum drum was 
then dip-coated with the CG formulation, and dried at 100.degree. C. for 5 
min. The transport layer formulation was prepared from a bisphenol-A 
polycarbonate (MAKROLON-5208, Bayer, 62.30 g), benzidine (26.70 g) in 
tetrahydrofuran (249 g) and 1,4-dioxane (106 g). The CG layer coated drums 
were dip-coated in the CT formulation, dried at 120.degree. C. for 1 h, to 
obtain a coat weight of about 24 mg/in2. The electrical characteristics of 
this drum were: Charge voltage (Vo): -696 V, residual voltage (Vr): -80 V, 
dark decay: 23 V/sec, Voltage at E(0.23 uJ/cm2): -141 V. 
EXAMPLE 10 
A typical formulation involving a BX-55Z/epoxy resin (25/75) at 35/65 
pigment/binder ratio was prepared as follows: 
Oxotitanium phthalocyanine (5.25 g), polyvinylbutyral (BX-55Z, 2.44 g), a 
epoxy resin (EPON 1004, Shell Co., 7.31 g) with Potter's glass beads (60 
ml) was added to a mixture of 2-butanone (30g) and cyclohexanone (30 g), 
in an amber glass bottle, agitated in a paint-shaker for 12 h and diluted 
to about 5% solids with 2-butanone (240 g). An anodized aluminum drum was 
then dip-coated with the CG formulation, dried at 100.degree. C. for 5 
min. The transport layer formulation was prepared from a bisphenol-A 
polycarbonate (MAKROLON-5208, Bayer, 62.30 g), benzidine (26.70 g) in 
tetrahydrofuran (249 g) and 1,4-dioxane (106 g). The CG layer coated drums 
were dip-coated in the CT formulation, dried at 120.degree. C. for 1 h, to 
obtain a coat weight of about 24 mg/in2. The electrical characteristics of 
this drum were: Charge voltage (Vo): -698 V, residual voltage (Vr): -65 V, 
dark decay: 19 V/sec, Voltage at E(0.23 uJ/cm2): -81 V. 
Variation from these specific implementations will be apparent and can be 
anticipated.