Process for preparing a phthalocyanine

A process for preparing vanadyl phthalocyanine particles for photoresponsive devices.

BACKGROUND OF THE INVENTION 
This invention relates to an improved process for preparing a 
phthalocyanine composition. More specifically, this invention is directed 
to the reactive formation and treatment of vanadyl phthalocyanine to 
achieve improved electrophotographic properties. 
The formation and development of electrostatic latent images on the imaging 
surface of photoconducttive members by electrostatic means is well known. 
Generally, the method involves the formation of an electrostatic latent 
image on the surface of an electrophotographic plate, referred to in the 
art as a photoreceptor. This photoreceptor usually comprises a conductive 
substrate and one or more layers of photoconductive insulating material. A 
thin barrier layer may be interposed between the substrate and the 
photoconductive layer in order to prevent undesirable charge injection. 
Many different photoconductive members are known, including, for example, a 
homogeneous layer of a single material such as vitreous selenium, or a 
composite layered device containing a dispersion of a photoconductive 
composition. An example of one type of composite photoconductive member is 
described, for example, in U.S. Pat. No. 3,121,006. The composite 
photoconductive member of this patent comprises finely divided particles 
of a photoconductive inorganic compound dispersed in an electrically 
insulating organic resin binder. The photoconductive inorganic compound 
usually comprises zinc oxide particles uniformly dispersed in an 
electrically insulating organic resin binder coated on a paper backing. 
The binder materials disclosed in this patent comprise a material which is 
incapable of transporting for any significant distance injected charge 
carriers generated by the photoconductive particles. The photoconductive 
particles must therefore be in substantially contiguous particle to 
particle contact throughout the layer to permit the charge dissipation 
required for a cyclic operation. The uniform dispersion of photoconductive 
particles requires a relatively high volume concentration of 
photoconductor material, usually about 50 percent by volume, in order to 
obtain sufficient photoconductor particle to particle contact for rapid 
discharge. Specific binder materials disclosed in this patent include, for 
example, polycarbonate resins, polyester resins, polyamide resins, and the 
like. 
Also known are photoreceptor materials comprising inorganic or organic 
materials wherein the charge carrier generating and charge carrier 
transport functions are accomplished by discrete continguous layers. 
Layered photoresponsive devices including those comprising separate 
generating and transport layers are described, for example, in U.S. Pat. 
No. 4,265,990. Additionally, layered photoreceptor materials are disclosed 
in the prior art which include an overcoating layer of an electrically 
insulating polymeric material. Overcoated photoresponsive materials 
containing a hole injecting layer, overcoated with a hole transport layer, 
followed by an overcoating of a photogenerating layer, and an outer 
coating of an insulating organic resin are described, for example, in U.S. 
Pat. No. 4,251,612. Photogenerating layers disclosed in these patents 
include, for example, trigonal selenium and phthalocyanines and transport 
layers including certain diamines. The disclosures of U.S. Pat. Nos. 
4,265,990 and 4,251,612 are incorporated herein by reference in their 
entirety. 
Certain phthalocyanine compositions are useful for incorporation into 
photoresponsive devices to extend the response capability of such devices 
to include visible light as well as infrared illumination. These 
photoresponsive devices can be utilized, for example, in conventional 
electrophotographic copiers as well as in laser printers. Moreover, these 
photoresponsive devices may comprise single or multilayered members 
containing photoconductive materials comprising phthalocyanine 
compositions in a photogenerating layer, between a photogenerating layer 
and a hole transport layer, or between a photogenerating layer and a 
supporting substrate. 
Vanadyl phthalocyanine has been found to be particularly suitable for 
photoresponsive devices. Numerous processes are known for preparing and 
treating vanadyl phthalocyanine. These are described, for example, in U.S. 
Pat. No. 2,155,038 and U.S. Pat. No. 3,825,422 in which phthalonitrile and 
vanadium pentoxide reacted in the absence of a solvent. Various other 
examples are disclosed in U.S. Pat. No. 3,825,422 and U.S. Pat. No. 
4,032,339 in which vanadyl phthalocyanine is prepared by utilizing vanadyl 
trichloride and other co-reactants in the presence of various solvents. 
The use of vanadium trichloride as a reactant for forming vanadyl 
phthalocyanine is less desirable because it is a hydrolytically active 
compound which contributes to instability and the formation of hydrogen 
chloride. 
Phthalocyanines may be treated with sulfuric acid as disclosed, for 
example, in U.S. Pat. No. 2,155,038; U.S. Pat. No. 3,717,493; U.S. Pat. 
No. 3,825,422; U.S. Pat. No. 4,032,339; U.S. Pat. No. 4,076,527; British 
Pat. No. 502,623 (complete specification accepted Mar. 22, 1939) and 
Japanese Patent Application No. 49-43264, published Nov. 20, 1974. 
The particles formed by many of the prior art processes are relatively 
large and less sensitive to light. Thus, longer exposure times are 
required which render the materials unsuitable for high speed 
electrophotographic imaging devices. Moreover, many of the prior art 
processes involve steps which promote the formation of degradation 
products which are difficult to remove in subsequent steps and ultimately 
affect electrical properties of the vanadyl phthalocyanine product. 
Although treatment with an acid facilitates the formation of smaller 
particle sizes, difficulties have been encountered achieving very small 
particle sizes. Moreover, vanadyl phthalocyanine particles cannot simply 
be physically ground down to the appropriate size because of the tendency 
of the grinding processes to form particles having very large particle 
size range distribution including relatively large particles. The 
classification of ground vanadyl phthalocyanine particles is time 
consuming and provides a poor yield. 
As the art of xerography continues to advance, more stringent standards 
need to be met by the electrostatographic imaging apparatus to improve 
performance and to obtain higher quality images. Also desired are layered 
photoresponsive devices which are more responsive to visible light and/or 
infrared illumination for certain laser printing applications. As these 
electrophotographic products become more sophisticated and operate at 
higher speeds, the operating tolerances become extremely stringent and the 
predictability of electrical behavior of components can be particularly 
critical. 
While prior art processes for preparing vanadyl phthalocyanine may be 
suitable for their intended purposes, there continues to be a need for an 
improved process for preparing vanadyl phthalocyanine having predictable 
electrical properties. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of the present invention to provide an improved 
process for preparing vanadyl phthalocyanine compositions. 
It is another object of the present invention to provide an improved 
process for preparing vanadyl phthalocyaine which is consistently 
reproducible. 
It is yet another object of the present invention to provide an improved 
process for preparing vandayl phthalocyanine having a very small average 
particle size. 
It is still another object of the present invention to provide an improved 
process for preparing vanadyl phthalocyanine containing fewer impurities. 
It is yet another object of the present invention to provide an improved 
process for preparing vanadyl phthalocyanine in higher yields. 
It is another object of the present invention to provide an improved 
process for preparing vanadyl phthalocyanine which exhibits higher 
electrophotographic sensitivity. 
It is still another object of the present invention to provide an improved 
process for preparing vanadyl phthalocyanine which imparts lower dark 
decay in photoreceptors. 
It is yet another object of the present invention to provide an improved 
process for preparing vanadyl phthalocyanine which exhibits lower residual 
charge in photoreceptors. 
These and other objects of the present invention are accomplished by a 
providing a process comprising reacting vanadium pentoxide with 
phthalonitrile and an alcohol at least at an exotherm temperature with 
agitation, filtering the resulting mixture to form a reaction product 
pigment cake, washing the reaction product pigment cake at least once with 
a dipolar aprotic solvent to form a treated pigment cake, drying the 
treated pigment cake, leaching with agitation the treated pigment cake 
with a strong acid diluted with water, filtering the resulting mixture to 
form a leached pigment cake, washing the leached pigment cake at least 
once with a strong acid diluted with water to form a washed leached 
pigment cake, washing the leached pigment cake at least once with a 
solvent comprising water to form a water washed leached pigment cake, 
forming a strong base slurry by combining the washed leached pigment cake 
with a strong base diluted with water, heating the strong base slurry with 
agitation, filtering the resulting mixture to form a strong base treated 
pigment cake, forming a solvent slurry by combining the strong base 
treated pigment cake with a dipolar aprotic solvent, heating the solvent 
slurry with agitation, filtering the solvent slurry to obtain a solvent 
treated pigment cake, forming an aqueous slurry by combining the solvent 
treated pigment cake with a solvent comprising water, heating the aqueous 
slurry with agitation, filtering the aqueous slurry to obtain a washed 
pigment cake, drying the washed pigment cake, incrementally dissolving 
with agitation the washed pigment cake in a chilled strong acid to form a 
chilled solution of vanadyl phthalocyanine, incrementally combining with 
agitation the solution with chilled water to form a mixture comprising 
precipitated vanadyl phthalocyanine particles, filtering the resulting 
mixture to obtain a cake of precipitated vanadyl phthalocyanine particles, 
forming an aqueous slurry by combining the cake of precipitated vanadyl 
phthalocyanine particles with a solvent comprising water to form a vanadyl 
phthalocyanine particle water slurry, heating the vanadyl phthalocyanine 
particle water slurry, filtering the resulting mixture to obtain a cake of 
vanadyl phthalocyanine particles, forming an aqueous slurry by combining 
the cake of precipitated vanadyl phthalocyanine particles with a solvent 
comprising water to form a vanadyl phthalocyanine particle water slurry; 
heating the vanadyl phthalocyanine particle water slurry; filtering the 
resulting mixture to obtain a cake of vanadyl phthalocyanine particles; 
forming a water slurry by combining the cake of vanadyl phthalocyanine 
particles with water; filtering the water slurry to form a purified 
pigment cake of vanadyl phthalocyanine; and drying the purified pigment 
cake of vanadyl phthalocyanine. 
Although the improved process of this invention is divided into three 
phases to facilitate description, the phases are interrelated and 
individually and cooperatively contribute to the important reproducible 
electrical characteristics of the final pigment product. The first phase, 
Phase I, relates to the synthesis of crude vanadyl phthalocyanine. 
The starting reactants of the process of this invention comprise vanadium 
pentoxide, phthalonitrile, and ethylene glycol. The mole ratio of 
phthalonitrile to vanadium pentoxide in the reaction mixture is preferably 
between about 10:1 and about 14:1. A larger excess of phthalonitrile leads 
to sacrificial loss of phthalonitrile to side reactions resulting in more 
side product inpurities which must be removed in subsequent process steps. 
As the above molar ratio is decreased to values less than 12.4:1, yields 
decrease based on equivalents of vanadium charged. Therefore, at molar 
ratios of 12.4:1 and higher, all V.sub.2 O.sub.5 charged is converted to 
vanadyl phthalocyanine. 
Any suitable alcohol having two or more hydroxyl groups and a boiling point 
of at least about 180.degree. C. may be employed. A boiling point below 
about 180.degree. C. is normally to be avoided because the alcohol will 
boil before the reaction mixture can reach exotherm temperatures. With 
alcohols that boil at temperatures lower than exotherm maximum 
temperatures, the crude yield of vanadyl phthalocyanine decreases 
significantly. It is very likely that a pressured vessel can be used at 
lower temperatures but the need for such more expensive equipment would be 
wasteful when standard commercial equipment affords nearly quantitative 
yields at moderate temperature and atmospheric pressure. Typical 
polyfunctional alcohols include ethylene glycol, propylene glycol, 
butylene glycol, glycerol and any other mono or polyols having a boiling 
point of at least about 180.degree. C. Optimum yields are achieved with 
ethylene glycol. Ethylene glycol is inexpensive, pure and available in 
bulk. Sufficient alcohol should be employed to dissolve the phthalonitrile 
and to maintain the reaction mixture as a fluid easily agitated throughout 
the reaction. Preferably, sufficient alcohol should be present to achieve 
refluxing of the reaction mixture, to minimize the amount of heat energy 
required to drive the reaction mixture to the exotherm temperature, and to 
prevent unduly high reaction mixture temperatures after the exotherm 
temperature is reached. Unduly high reaction mixture temperatures promote 
greater side reactions which promote the formation of undesirable 
impurities. However, excessive amounts of alcohol should be avoided in 
order to minimize the time and energy requirements to reach exotherm onset 
and for cooling the mixture after the reaction is substantially completed. 
The proportion of alcohol to vanadium pentoxide is preferably between about 
3:1 and about 30:1. Sufficient heat should be supplied to the reaction 
mixture so that the mixture attains the exotherm temperature. The exotherm 
temperature is defined as the maximum temperature attained in the process 
when the batch temperature exceeds the jacket temperature in the heat up 
period. 
It is important that the reaction mixture be agitated during the reaction. 
Vigorous agitation is preferred. Agitation may be accomplished by any 
suitable means such as propeller mixers, magnetic bar mixers, and the 
like. To promote turbulence in the reaction mixture, the reaction vessel 
may contain baffles, irregular interior surfaces, and the like. A typical 
mixing arrangement comprises a 10 gal. Pfaudler Glasteel reactor with H 
baffles and a three-blade propeller stirrer rotated at 100 rpm by a 3.73 
horsepower motor. 
The reaction may be conducted under reduced pressure, atmospheric pressure, 
or super atmospheric pressure. The pressure selected depends on factors 
such as the boiling points of the alcohols employed and the effect of 
pressure on achieving the exotherm temperature. In other words, the 
pressure should not be so low that the alcohol refluxes before the 
reaction mixture attains the exotherm temperature. Moreover, super 
atmospheric pressure may be used with lower boiling point alcohols such as 
amyl alcohol but the pressure should not be so high as to adversely 
reverse the reaction. Generally, reactions at atmospheric pressure are 
preferred to avoid the necessity of special pressurized equipment and to 
minimize energy consumption for conducting the reaction. For example, the 
reactor may merely be fitted with a simple water cooled reflux condenser 
open to the atmosphere of sufficient capacity to condense the solvent 
vapors.

A typical time versus temperature profile for the reaction of this 
invention is illustrated in the drawing. Generally, the reaction may be 
divided into three segments. The temperature of the heating jacket 
surrounding the reactor is represented by a dashed line. The temperature 
of the reaction mixture itself is represented by a solid line. The first 
segment of the reaction ends at about the point where an abrupt increase 
in the slope of the curve occurs. This point is the exotherm onset 
temperature and the maximum temperature attained a short time thereafter 
is the exotherm temperature. The reaction mixture is preferably heated as 
rapidly as practical to the exotherm temperature region to minimize the 
occurrence of side reactions. However, considerable latitude in the rate 
of temperature increase has been observed. As apparent from the drawing, 
the jacket temperature was initially greater than the reaction mixture 
temperature at time 0. Moreover, the temperature of the heating medium in 
the jacket was allowed to level off at about or slightly prior to the 
point in time when the reaction mixture attained the exotherm temperature. 
The temperature of the reaction mixture continued to rise beyond the 
temperature of the jacket due to the heat generated in the reaction 
mixture during the exothermic reaction. 
The next segment of the reaction is a particularly critical period in which 
the temperature of the reaction mixture (batch) must be raised above the 
exotherm onset temperature and must be maintained at the exotherm 
temperature until substantial completion of the reaction or until the 
exotherm abates (batch temperature begins to decrease). 
After substantial completion of the reaction, which is at about 5.55 hours 
in the profile illustrated in the drawing, the application of heat to the 
reaction mixture may be discontinued. This third segment subsequent to the 
reaction phase is not especially critical and considerable latitude in the 
manner in which cooling is effected has been observed. Although an oil 
jacket was employed to heat the reaction mixture, any other suitable 
conventional heating device may be employed. Typical heating means include 
heated oil jackets, electric mantels, heated oil circulating baths and the 
like. Cooling may be effected merely by terminating the addition of heat 
to the reaction vessel. If desired, cooling may be accelerated by any 
suitable conventional means. 
After completion of the reaction, the reaction mixture may be filtered to 
obtain a pigment cake. Filtering may be accomplished by any suitable 
conventional means such as filter cloths and filter paper on ceramic 
filters and the like. If desired, filtering may be accelerated by the use 
of a suitable vacuum means. After filtering to form a first pigment cake, 
the pigment cake is washed with a dipolar aprotic solvent. Any suitable 
dipolar aprotic solvent may be utilized. Typical dipolar aprotic solvents 
include dimethyl sulfoxide, N,N-dimethyl acetamide, 
N-methyl-2-pyrrolidone, sulfolane, N,N-dimethyl formamide, and the like. 
Generally, it is preferred that the dipolar aprotic solvent be pre-warmed 
to enhance removal of impurities in the reaction mixture and to minimize 
the time for removing impurities. It is believed that the use of a dipolar 
aprotic solvent at elevated temperatures causes minor swelling of the 
vanadyl phthalocyanine pigment which promotes more effective removal of 
impurities by the solvent. A solvent temperature of at least about 
80.degree. C. is preferred for rapid removal of impurities. N,N-dimethyl 
formamide is a preferred dipolar aprotic solvent because it is stable at 
80.degree. C. and higher, pure, available in bulk, and less expensive than 
the other dipolar aprotic solvents while having equivalent solvent power 
in removing impurities from the swollen pigment. Washing is usually 
accomplished by applying the dipolar aprotic solvent onto the pigment cake 
supported on the filter. The washing step is carried out at least once but 
may, if desired, be repeated. Moreover, the pigment cake may be 
additionally washed with a suitable solvent such as an alkanol. Typical 
alkanols include ethanol, isopropanol, butanol, and the like. This washing 
step enhances the removal of any pigment imbibed dipolar aprotic solvent 
which is miscible with the alkanol. The alkanol should be miscible or 
partially miscible with water since the filtered pigment cake absorbs 
atmospheric moisture and water miscible alcohols will best remove imbibed 
water. When one or more alkanol washes are employed, pre-warming of the 
alkanol prior to washing is preferred for more effective and more rapid 
removal of alkanol soluble impurities. 
The washed filter cake may optionally be treated with any suitable strong 
base. Typical strong bases include sodium hydroxide, potassium hydroxide, 
and the like. The base is generally employed as a dilute solution. A 
dilute solution of between about 3 percent by weight and about 6 percent 
by weight is preferred. Treatment with a strong base aids in the removal 
of any vanadium pentoxide or other amphoteric vanadium species remaining 
in the filter cake. Treatment with a strong base is typically accomplished 
by forming a slurry with mechanical agitation to form a uniform slurry. A 
typical strong base treatment may be carried out at between about 
70.degree. C. and about 75.degree. C. for about 1 hour. If this optional 
treatment with a base is employed, the resulting slurry is filtered by any 
suitable means such as a conventional vacuum filtration system and 
thereafter washed with pre-warmed deionized water. For reasons of economy 
and impurity solubilities, the slurry should be vacuum filtered while the 
slurry is still hot from the treatment with the base. Washing of the 
filtered pigment cake may be repeated as desired. However, the treatment 
with the base as well as the subsequent filtering and washing steps are 
merely optional and may be omitted if desired. If omitted, higher oven 
drying temperatures may be required to evaporate the higher boiling 
diprotic apolar solvent. 
The pigment cake resulting from the preceeding steps (which may be the cake 
following the dipolar aprotic solvent treatment step because the 
subsequent optional steps were omitted) is dried to remove any of the 
solvents which were utilized to wash the crude pigment. Drying may be 
carried out by any suitable conventional means such as convection air 
ovens, vacuum ovens, and the like. A typical drying technique (after 
strong base slurry and water washes) involves placing the moist pigment 
cake in oven trays in an air convection oven at between about 65.degree. 
C. and about 70.degree. C. for at least about 96 hours or until a constant 
weight is achieved. 
The partially dried pigment may be lightly pulverized by any suitable means 
such as a mortar and pestle, Waring Blender and the like to increase the 
surface area of the dried pigment for more rapid drying. Drying should be 
sufficient to reduce the solvent content to less than about 1 percent by 
weight based on the total weight of the dried pigment. The pulverized 
dried pigment is preferably protected from direct exposure to light during 
the following processing steps. 
The second phase of this invention, Phase II, involves initial purification 
steps including permutoid swelling. Permutoid swelling is the leaching out 
of chemical impurities from the 75 percent sulfuric acid swollen 
gelantinous mass representing a protonated form of vanadyl phthalocyanine. 
The dried pulverized crude pigment is treated with a strong acid. Any 
suitable strong organic or inorganic acid capable of swelling vanadyl 
phthalocyanine pigment and dissolving the impurities therein may be 
employed. Typical strong acids include sulfuric acid, phosphoric acid, 
methane sulfonic acid, and the like. The concentration of the strong acid 
should be between about 70 percent by weight and about 80 percent by 
weight. Concentrations of a strong acid below about 60 percent by weight 
are less effective in removing sufficient impurities from the crude 
pigment. Acid concentrations about 80 percent by weight make for lower 
yields. Sulfuric acid is the preferred strong acid because it is pure and 
inexpensive. Some of the impurities dissolved by the acid include 
phthalimide, phthalic acid, phthalamic acid, and phthaldiamide. The 
pulverized crude dried pigment should be added slowly and incrementally 
with agitation of the chilled acid at about room temperature. The pigment 
is added slowly to assist in maintaining the mixture near room temperature 
to avoid an excessive increase in temperature to levels which may cause 
minor pigment degradation presumably through hydrolytic pathways. The acid 
bath is agitated to obtain all the pigment particles in a swollen 
gelatinous state throughout the addition time period and for 3 hours 
thereafter. This ensures total solvent contact and swelling thereby 
improving the efficiency of the leaching process. The pigment may be left 
in the acid slurry for up to about 20 hours. The acid leached pigment is 
then filtered by conventional filtering means such as those described 
above. The resulting filter cake should be washed with additional fresh 
acid at about room temperature. 
The pigment cake after acid washing is washed with a suitable pre-warmed 
solvent to remove the acid. Preferably, the washing liquid is deionized 
water. However, other more expensive solvents such as alcohols or 
alcohol-water mixtures at room temperature may be employed if desired. For 
reasons of economy, the washing is preferably conducted while the pigment 
cake from the previous filtering step remains on the filter. 
The pigment is mixed with a dilute aqueous base to remove the residual 
acid. Any suitable dilute aqueous base may be employed. Typical aqueous 
bases include sodium hydroxide, ammonium hydroxide, potassium hydroxide, 
and the like. For example, a slurry may be formed with a 4 percent by 
weight solution of sodium hydroxide and water. The slurry may typically be 
agitated by mechanical stirring and heated to between about 70.degree. C. 
and about 75.degree. C. to facilitate removal of residual acid. The slurry 
mixture may, for example, be held at between about 70.degree. C. and about 
75.degree. C. for about 1 hour. Considerable latitude has been observed in 
regard to the degree of agitation, heating, and time of contact between 
the base and the pigment. Slurry is thereafter filtered by any suitable 
conventional means such as those previously described. 
If desired, the filtered pigment may be washed with a suitable liquid such 
as deionized water to remove any impurities remaining in the pigment. 
However, this washing step is optional and may be omitted. 
The pigment cake following washing or following filtering of the slurry (if 
the washing step is omitted) is thereafter formed into a slurry in 
combination with a dipolar aprotic solvent to remove the impurities that 
were not removed during the acid treatment step. The slurry is preferably 
heated to a temperature between about 80.degree. C. and a temperature 
below the boiling point of the dipolar aprotic solvent. Agitation may be 
applied and contact between the pigment particles and the dipolar aprotic 
solvent may take place for about 1 hour. The hot slurry is then filtered. 
This slurry formation and filtering steps may be repeated one or more 
times, if desired. The resulting pigment filter cake may be washed with a 
dipolar aprotic solvent as described previously. If desired, the pigment 
cake may also be washed with a solvent such as deionized water. These 
washing steps with the dipolar aprotic solvent or with the deionized water 
may be repeated one or more times or omitted altogether. 
The pigment cake may thereafter be formed into a slurry with a suitable 
solvent such as deionized water to remove the dipolar aprotic solvent. 
Preferably, the slurry is heated to a temperature between about 70.degree. 
C. and about 75.degree. C. The slurry is typically held at this elevated 
temperature for about 1 hour. The slurry is thereafter filtered by 
conventional means such as described above and dried to reduce the water 
content of the pigment cake to less than about 1 percent by weight water. 
A low water content is important to prevent excessive dilution of the acid 
in the subsequent step. Typically, the pigment can be adequately dried by 
placing the pigment in trays in an air convection oven maintained, for 
example, at between 65.degree. C. and about 70.degree. C. for at least 
about 96 hours. The pigment clumps in the trays after partial drying may 
be lightly pulverized for more rapid drying and more rapid dissolving in 
the subsequent acid purification step. 
The final phase, Phase III, of the process of this invention involves final 
purification steps including acid pasting. Acid pasting requires the 
dissolution of the pigment in greater than or equal to 95 percent sulfuric 
acid, and precipation of said pigment solution to remove impurities and to 
reduce particle size. Highly controlled conditions are required for 
solution and precipitate formation. 
The dried pulverized vanadyl phthalocyanine pigment is next mixed with a 
chilled strong acid. Any suitable strong organic or inorganic acid capable 
of completely dissolving vanadyl phthalocyanine pigment and dissolving the 
impurities therein may be employed. Typical strong acids include sulfuric 
acid, phosphoric acid, methane sulfonic acid, and the like. Sulfuric acid 
is the preferred strong acid because it is pure and inexpensive. The 
concentration of the strong acid is preferably at least 95 percent by 
weight. Concentrations of a strong acid at or below about 93 percent by 
weight caused photoreceptors in which the acid treated vanadyl 
phthalocyanine pigment were used to exhibit unacceptably high dark decay. 
The temperature of the acid is preferably maintained at a temperature 
below about 15.degree. C. although brief temperature spikes as high as, 
for example, 22.degree. C. can be tolerated. However, sustained 
temperatures at about room temperature (about 22.degree. C.) caused 
photoreceptors in which the acid treated vanadyl phthalocyanine pigment 
were used to exhibit unacceptably high dark decay due, apparently to 
impurities that were formed and retained from the sustained elevated 
temperature treatment. Optimum results are achieved when the temperature 
of the acid is maintained at a temperature between about 5.degree. C. and 
about 10.degree. C. The quantity of impurities formed in the solution 
increases with temperature and residence time. The pulverized crude dried 
pigment should be added slowly and incrementally with agitation of the 
acid at a temperature below about 15.degree. C. The pigment is added 
slowly to avoid an excessive increase in temperature exceeding about 
15.degree. C. for any sustained time period. The acid bath is vigorously 
agitated to maintain a more uniform solution temperature and to promote 
more rapid dissolving of the pigment in the acid. The pigment may be left 
in the acid solution for between about 2 hours and about 6 hours. 
Residence times exceeding about 6 hours tends to cause the formation of 
unacceptably large amounts of impurities. Less than about 2 hours may be 
feasible depending upon the amount of acid employed relative to the 
quantity of pigment and the rate of dissolution. Any undissolved pigment, 
for any reason, should not be ice-water quenched in the next step since 
high dark decay devices then result. 
The pigment-acid solution should next be added slowly and incrementally 
with agitation into an ice and water bath. If desired, minor amounts of a 
suitable water miscible acid nonreactive solvent such as alcohols may be 
added to the ice water bath. However the ice water bath should contain 
sufficient water to dissolve impurities from the acid-pigment solution. 
The pigment-acid solution is added slowly to avoid any significant 
increase in bath temperature exceeding about 15.degree. C. for any 
sustained time period and to ensure that a small pigment particle size and 
minimal impurities are formed. Excessively high bath temperatures cause 
unduly rapid hydrolytic breakdown of the pigment, agglomeration of the 
pigment particles formed and trapping of impurities in the pigment 
agglomerates. The acid treated pigment may be introduced into the ice 
water bath in the form of one or more streams to promote more rapid 
dissipation of heat. The introduction should not be so slow as to unduly 
extend the pigment residence time in the strong acid thereby allowing high 
levels of impurities to form prior to quenching in the ice water. A 
typical introduction time is about 1.75-2 hours. Excellent results are 
achieved, for example, with a single stream feed rate of about 150 to 
about 200 ml./min. into a bath containing deionized water containing and 
ice. Preferably the pigment is introduced into the ice water bath at a 
rate sufficient to form particles having an average particle size less 
than about 0.1 micrometer at a bath temperature maintained at less than 
about 15.degree. C. The bath must be vigorously agitated to maintain a 
more uniform bath temperature and to promote more rapid dispersing of the 
pigment in the ice water bath. Any suitable conventional agitation means, 
such as those previously described above, capable of vigorously agitating 
the bath may be employed. To promote turbulence in the reaction mixture, 
the reaction vessel may contain baffles, irregular interior surfaces, and 
the like. Solid particles of ice (part of the 196 lbs.) may periodically 
be added to the bath to ensure that the bath is maintained at a 
temperature less than about 15.degree. C. for any sustained time period. 
However, the ice particles should not be in such quantity that they 
adversely affect proper agitation of the bath. Optimum results are 
achieved when the temperature of the bath is maintained at a temperature 
between about 5.degree. C. and about 10.degree. C. If desired, other 
suitable cooling means such as refrigerated cooling coils submerged in the 
bath may be substituted for or employed in conjuction with the ice 
particles. However, if another suitable cooling source other than 
internally added ice is used, a corresponding volume of cold water should 
be used in place of the ice. The pigment may be left in the ice water bath 
for up to about 0.5 hours and is then filtered by conventional vacuum 
filtering means such as those described above and in the Examples which 
follow. The resulting filter cake was washed on the funnel with prewarmed 
deionized water and was then slurried in 25 gallons of deionized water 
heated to 70.degree.-75.degree. C. for one hour. The hot pigment slurry 
was next vacuum filtered. 
The pigment cake is next formed into a slurry with a concentrated weak base 
or a dilute strong base. Any suitable base may be employed. Typical weak 
bases include ammonum hydroxide, calcium hydroxide, and the like. Typical 
strong bases include potassium hydroxide, sodium hydroxide, and the like. 
Preferably, the slurry is formed with concentrated ammonum hydroxide 
because this base is most capable of extracting impurities from the 
organic pigment. The pigment cake must be formed into a slurry with a 
dilute base with agitation and thereafter filtered at least once in order 
to prevent unacceptable dark decay in the final photreceptor. The first 
slurry is typically heated to about 70.degree. C. and about 75.degree. C. 
and held at this elevated temperature for about 1 hour. 
The pigment cake is thereafter formed into a slurry with deionized water 
and with agitation to remove the base and impurities. The pigment cake 
must be formed into a slurry with water and thereafter filtered at least 
once in order to prevent unacceptable dark decay in the final 
photreceptor. If desired, minor amounts of a suitable water miscible 
nonreactive solvent such as alcohols may be added to the slurry. 
Preferably, the slurry is heated to a temperature between about 70.degree. 
C. and about 75.degree. C. The slurry is typically held at this elevated 
temperature for about 1 hour. The slurry is thereafter vacuum filtered, 
preferably while still hot, by conventional means such as those described 
above and in the working examples below. The steps of forming a pigment 
cake into a slurry with water and thereafter filtering the slurry must be 
carried out a sufficient number of times to reduce the conductivity of the 
filtrate to less than about 10 micromhos. If the conductivity of the 
filtrate is greater than about 10 micromhos, the final photreceptor has 
been found to exhibit unacceptable dark decay. 
The pigment cake may then be dried by any suitable conventional technique. 
The pigment clumps in the trays are preferably pulvurized at least once 
during drying to expose more surface area of the pigment particles. 
Typically, the pigment can be adequately dried by placing the pigment in 
trays in an air convection oven maintained, for example, at between 
65.degree. C. and about 70.degree. C. for at least about 96 hours. 
Additional, more complete drying may be accomplished by conventional 
processes such as drying in a vacuum oven at 65.degree. C.-70.degree. C. 
and a vacuum of about 0.5 mm mercury for about 16 or more hours. The 
pigment may then be bagged and stored in the absence of light. 
The invention will now be described in detail with respect to specific 
preferred embodiments thereof, it being understood that these examples are 
intended to be illustrative only and that the invention is not intended to 
be limited to the materials, conditions, process parameters and the like 
recited herein. All parts and percentages are by weight unless otherwise 
indicated. 
EXAMPLE I 
Phase I: Synthesis of Crude Vanadyl Phthalocyanine Pigment (VOPc) 
Synthesis: A 10 gal glasteel Pfaudler reactor was charged with 23.76 liters 
of ethylene glycol, 829.4 grams vanadium pentoxide and 7257 grams 
phthalonitrile and was agitated at 70 rpm with a propeller mixer. A 
time-temperature profile is indicated for the synthesizing events in the 
following table. The drawing illustrates a corresponding graphic 
description. 
TABLE 
______________________________________ 
Cumulative 
Temperature .degree.F. 
Time (Hours) 
Temperature .degree.C. 
Event 
______________________________________ 
STARTUP 
0-.75 70-90 Charge Reactor and Heat 
21-32 Oil Heater Loop 
HEATUP OR SEGMENT I 
.75-2.65 
90-345 Open Heater Loop to Batch 
32-174 and Heatup to Exotherm 
Onset: at 194.degree. F. (90.degree. C.) Set 
Agitator to 100 RPM 
SEGMENT II 
2.65-3.55 
345-390-345 Exotherm Period 
174-199-174 
and 
3.55-5.55 
345-320 Post Exotherm Period 
174-160 
SEGMENT III 
5.55-6.55 
320-200 Cool Down and Drop 
160-93 Reactor Contents for 
Filtration 
______________________________________ 
A water condenser was adapted to the reactor for the moderate reflux 
occurring during the exotherm period. After the reactor contents cooled to 
90.degree. C.-95.degree. C. (194.degree. F.-203.degree. F.), the hot 
pigment slurry was transferred to a vacuum filter. After suction filtering 
the pigment cake, the latter was washed on an evacuated ceramic funnel 
with prewarmed (80.degree. C.-85.degree. C.) dimethylformamide in 2 gal. 
quantities. A total of four sequential pigment washes with 
dimethylformamide was followed by one prewarmed isopropanol (1.4 gas at 
55.degree. C.) wash. The latter helped remove the higher boiling 
dimethylformamide residues in the pigment cake. 
To a 30 gal. steam jacketed stainless steel tank was added 3447 grams of 
sodium hydroxide and 22.8 gal. (86.3 l) of deionized water to give about a 
4% sodium hydroxide solution. The pigment cake was transferred from the 
ceramic funnel and the resulting alkaline pigment slurry was heated to 
70.degree. C.-75.degree. C. with agitation (400-500 rpm) with a propeller 
mixer and was held in that temperature range for one hour while stirring. 
The pigment slurry was then vacuum filtered and the filter cake was washed 
on a ceramic funnel with 10 gal. of prewarmed (70.degree. C.-75.degree. 
C.) deionized water while maintaining vacuum filtration (pump) conditions. 
The moist pigment cake was transferred to the above described stainless 
steel tank and a hot deionized water slurry (25 gal. of water) was 
prepared under the same conditions as above. After vacuum filtration of 
the pigment slurry, the pigment cake was washed on the funnel with 5 gal. 
of prewarmed (70.degree. C.-75.degree. C.) dieionized water. The moist 
pigment was transferred to drying trays which were placed in an air 
convection oven at 65.degree. C.-70.degree. C. for more than 96 hours. The 
dried crude pigment was lightly pulverized and weighed 4,850 grams (92% 
yield based upon equivalents of vanadium in vanadium pentoxide charged). 
Phase II: Initial Purification: Permutoid Swelling 
In this phase, the crude pigment was leached with 75% sulfuric acid which 
dissolved and removed impurities from the undissolved but solvent swollen 
pigment particles. The impurities were thermally generated in the 
synthesis, probably from the excess phthalonitrile, and were leached out 
as such or were hydrolyzed in the 75% sulfuric acid. In any case, the 
original impurities and hydrolysis by-product impurities were bulk removed 
in this purification process. 
To a 30 gal. polytank, externally cooled with ice and water, was added 
50.16 lbs of ice and then 44.1 l of 96% sulfuric acid. Mechanical 
agitation was begun when enough acid had been added to the ice to give a 
substantial liquid phase. External cooling was continued until the 75% 
sulfuric acid solution reached 22.degree. C. 
The crude vanadyl phthalocyanine, 4850 grams, was added portionwise over 
15-20 minutes to the slowly agitated 75% sulfuric acid solution prepared 
above. The slurry remained at or near room temperature during the addition 
and for 3 hours thereafter while stirring was maintained. The polytank was 
sealed from the atmosphere with a plastic sheet and the pigment acid mass 
was allowed to stand undisturbed overnight (16-20 hrs.) at ambient 
temperature. 
One-third of the pigment acid mass was transferred to the filter and was 
pulled down with vacuum. The pigment paste was washed on the filter cloth 
of the filter with about 4 l of fresh 75% sulfuric acid at room 
temperature. After removing the liquid by suction, the pigment paste was 
combed from the filter cloth and was transferred to another polytank 
containing 6 gal. of deionized water. The second third of the pigment acid 
mass was filtered and transferred in an identical manner. The final third 
was similarly filtered to which was added the previously collected pigment 
and its aqueous medium. In this way, all the pigment was collected on the 
funnel and vacuum filtered. The wet cake was then washed on the filter 
with 6-8 gal. of prewarmed (70.degree. C.-75.degree. C.) deionized water 
while vacuum filtering. 
To the 30 gal. jacketed stainless steel tank was added 2,585 grams of 
sodium hydroxide and 64.34 l of deionized water to give about a 4% alkali 
solution. The above water washed pigment cake was added and the alkaline 
pigment slurry was heated to 70.degree. C.-75.degree. C. with moderate 
mechanical stirring. Stirring and heating were maintained for one hour 
before filtering the hot slurry. The moist pigment cake was next slurried 
with 22 gal. of deionized water in the same container using the same 
conditions and was filtered in the usual manner. The moist pigment on the 
filter cake was next washed with 5 gal. of prewarmed (70.degree. 
C.-75.degree. C.) deionized water. 
Three dimethylformamide pigment slurries were sequentially carried out in 
an 18 gal. jacketed stainless steel tank. The above moist pigment cake and 
8 gal. of dimethylforamide were heated to 80.degree. C. with stirring. 
After one hour at the aforementioned temperature, the pigment slurry was 
vacuum filtered. The procedure described in this paragraph was repeated 
two more times and the final filter cake was washed on the funnel with 
prewarmed (80.degree. C.) dimethylforamide (2.times.4 l) and then with 
prewarmed (70.degree. C.-75.degree. C.) deionized water (2.times.5 gal.). 
Finally, the pigment was slurried with 22 gal. deionized water in the 30 
gal. jacketed stainless steel tank in the usual manner wherein the 
contents were held at 70.degree. C.-75.degree. C. for one hour. After 
vacuum filtration, the moist pigment was air dried on the funnel (4 
hours-6 hours) and was then transferred to drying trays. The pigment was 
dried for at least 96 hours at 65.degree. C.-70.degree. C. after which 
time it was gently pulverized. The yield was 426 grams or 88% of partially 
purified vanadyl phthalocyanine. 
Phase III: Final Purification: Acid Pasting 
In this phase, the partially purified pigment was dissolved in 96% sulfuric 
acid which also dissolved any residual impurities not removed by the above 
leaching process. Subsequent quenching of the pigment acid solution into 
ice water accomplished two tasks. Average particle size was reduced on the 
average from 1 micrometer-2 micrometers to 200 Angstroms-600 Angstroms. 
Moreover, the aqueous acid (about 25% sulfuric acid results when the 
quenching is complete) formed, dissolved away soluble impurities. 
The 96% sulfuric acid (24.5 liters) was chilled to 6.degree. C.-10.degree. 
C. over a period of 1.5 hours-2.0 hours while minimizing the amount of 
atmospheric moisture condensing into the cold acid. The semi-purified 
pigment (2100 grams) was incrementally (about 300 gram portions) added to 
the cold concentrated sulfuric acid over a period of 1.75 hours-2.00 hours 
while maintaining a batch temperature of 6.degree.-15.degree. C. with 
external cooling. A stir rate of at least 100 rpm with a propeller mixer 
was maintained throughout the addition period and for one hour thereafter 
during which time the temperature of the pigment-acid solution was 
10.degree. C.-15.degree. C. 
The cold pigment acid solution was stream fed at an addition rate of 175 
plus or minus 25 ml/min into a 55 gal. polytank containing 10.3 gal. of 
deionized water and sufficient ice to chill the contents of the polytank 
to 5.degree. C.-10.degree. C. The remainder of the original 196 lbs. of 
ice was incrementally added during the pigment acid solution addition 
period. An excess of ice, wherein the vortex was impeded, was avoided and 
the stir rate was maintained at 800 rpm-1000 rpm. The total uninterrupted 
time for the pigment acid solution addition was 2.67 hours-2.83 hours and 
the tank contents remained at 8.degree. C.-12.degree. C. throughout. The 
total residence time of the pigment in the acid was less than 6 hours 
prior to ice water quenching. After stirring the tank contents at 400 
rmp-500 rpm for 0.5 hours beyond the time required to complete the 
addition, the cold dilute acid pigment slurry was vacuum filtered. The 
filtration was slow (overnight) and the yellow filtrate showed no evidence 
of fines. In the morning, the filter cake was washed on the funnel with 
prewarmed (70.degree. C.- 75.degree. C.) deionized water (5.times.2 gal.). 
Residual acid was removed by slurrying the pigment in 25 gal. of deionized 
water heated to 70.degree. C.-75.degree. C. for one hour in a 30 gal. 
jacketed stainless steel tank. The hot pigment water slurry was vacuum 
filtered. 
The following three ammonium hydroxide slurries were prepared to remove 
residual sulfuric acid as ammonium sulfate. The same previously described 
30 gal. vessel was used in the process and the stir rate (400-500 rpm) and 
heating period (one hour) at elevated temperature (70.degree. 
C.-75.degree. C.) were the same. Each slurry was followed by a vacuum 
filtration step. 
First NH.sub.4 OH slurry: 15.5 gal deionized water and 7.8 l conc. NH.sub.4 
OH 
2nd NH.sub.4 OH slurry: 16.8 deionized water and 4.9 l conc. NH.sub.4 OH 
3rd NH.sub.4 OH slurry: 16.8 gal deionized water and 4.9 l conc. NH.sub.4 
OH 
The purpose of the remaining 6 deionized water slurries was to reduce the 
level of ionic species in the pigment particles as measured by 
conductivity in units of micro mhos. An acceptable pigment slurry filtrate 
value of less than about 10 micromhos (at room temperature) must be 
achieved to insure that the pigment was sufficiently free of ionic 
contamination for precision photoreceptors. 
The equipment and conditions described for the ammonium hydroxide slurries 
were maintained. Instead, 22 gal-25 gal. of deionized water was used in 
each slurry and generally 6-8 slurries were required to lower the 
conductivity to less than about 10 micromhos. 
The finally filtered pigment was transferred to trays for convection oven 
drying. The pigment was dried for four days at 60.degree. C.-65.degree. C. 
and any pigment chunks were manually broken and the pigment thereafter 
dried another 24 hours at the same temperature. The pigment was next 
pulverized with a mortar and pestle and drying was resumed in a vacuum 
oven at the same temperature for 16 hours at 0.5 mm Hg. Finally, the 
pigment was bagged and stored in the absence of light. 
EXAMPLE II 
Phase I: Synthesis of Crude Vanadyl Phthalocyanine Pigment (VOPc) 
Synthesis: A 10 gal glasteel Pfaudler reactor was charged with 23.76 liters 
of ethylene glycol, 829.4 grams vanadium pentoxide and 7257 grams 
phthalonitrile and was agitated at 70 rpm with a propeller mixer. A 
time-temperature profile is indicated for the synthesizing events in the 
following table. The drawing illustrates a corresponding graphic 
description. 
TABLE 
______________________________________ 
Cumulative 
Temperature .degree.F. 
Time (Hours) 
Temperature .degree.C. 
Event 
______________________________________ 
STARTUP 
0-.75 70-90 Charge Reactor and Heat 
21-32 Oil Heater Loop 
HEATUP OR SEGMENT I 
.75-2.65 
90-345 Open Heater Loop to Batch 
32-174 and Heatup to Exotherm 
Onset: at 194.degree. F. (90.degree. C.)Set 
Agitator to 100 RPM 
SEGMENT II 
2.65-3.55 
345-390-345 Exotherm Period 
174-199-174 
and 
3.55-5.55 
345-320 Post Exotherm Period 
174-160 
SEGMENT III 
5.55-6.55 
320-200 Cool Down and Drop 
160-93 Reactor Contents for 
Filtration 
______________________________________ 
A water condenser was adapted to the reactor for the moderate reflux 
occurring during the exotherm period. After the reactor contents cooled to 
90.degree. C.-95.degree. C. (194.degree. F.-203.degree.F.), the hot 
pigment slurry was transferred to a vacuum filter. After suction filtering 
the pigment cake, the latter was washed on an evacuated ceramic funnel 
with prewarmed (80.degree. C.-85.degree. C.) dimethylformamide in 2 gal. 
quantities. A total of four sequential pigment washes with 
dimethylformamide was followed by one prewarmed isopropanol (1.4 gal at 
55.degree. C.) wash. The latter helped remove the higher boiling 
dimethylformamide residues in the pigment cake. 
To a 30 gal. steam jacketed stainless steel tank was added 3447 grams of 
sodium hydroxide and 22.8 gal. (86.3 l) of deionized water to give about a 
4% sodium hydroxide solution. The pigment cake was transferred from the 
ceramic funnel and the resulting alkaline pigment slurry was heated to 
70.degree.-75.degree. C. with agitation (400-500 rpm) with a propeller 
mixer and was held in that temperature range for one hour while stirring. 
The pigment slurry was then vacuum filtered. 
Two dimethylformamide pigment slurries were sequentially carried out in an 
18 gal. jacketed stainless steel tank. The above moist pigment cake and 8 
gal. of dimethylforamide were heated to 80.degree. C. with stirring. After 
one hour at the aforementioned temperature, the pigment slurry was vacuum 
filtered. The procedure described in this paragraph was repeated and the 
final filter cake was washed on the funnel with prewarmed (80.degree. C.) 
dimethylforamide (2.times.4 l) and then with prewarmed (70.degree. 
C.-75.degree. C.) deionized water (2.times.5 gal.). 
Finally, the pigment was slurried with 22 gal. deionized water in the 30 
gal. jacketed stainless steel tank in the usual manner wherein the 
contents were held at 70.degree. C.-75.degree. C. for one hour. After 
vacuum filtration, the moist pigment was air dried on the funnel (4 
hours-6 hours) and was then transferred to drying trays. The pigment was 
dried for at least 96 hours at 65.degree. C.-70.degree. C. after which 
time it was gently pulverized. The yield was 426 grams or 88% of partially 
purified vanadyl phthalocyanine. 
Phase II was omitted. 
Phase III: Final Purification: Acid Pasting 
In this phase, the partially purified pigment was dissolved in 96% sulfuric 
acid which also dissolved any residual impurities not removed by the above 
leaching process. Subsequent quenching of the pigment acid solution into 
ice water accomplished two tasks. Average particle size was reduced on the 
average from 1 micrometers-2 micrometers to 200 Angstroms-600 Angstroms. 
Moreover, the aqueous acid (about 25% sulfuric acid results when the 
quenching is complete) formed, dissolved away soluble impurities. 
The 96% sulfuric acid (24.5 liters) was chilled to 6.degree. C.-10.degree. 
C. over a period of 1.5 hours-2.0 hours while minimizing the amount of 
atmospheric moisture condensing into the cold acid. The semi-purified 
pigment (2100 grams) was incrementally (about 300 gram portions) added to 
the cold concentrated sulfuric acid over a period of 1.75 hours-2.00 hours 
while maintaining a batch temperature of 6.degree.-15.degree. C. with 
external cooling. A stir rate of at least 100 rpm with a propeller mixer 
was maintained throughout the addition period and for one hour thereafter 
during which time the temperature of the pigment-acid solution was 
10.degree. C.-15.degree. C. 
The cold pigment acid solution was stream fed at an addition rate of 175 
plus or minus 25 ml/min into a 55 gal. polytank containing 10.3 gal. of 
deionized water and sufficient ice to chill the contents of the polytank 
to 5.degree. C.-10.degree. C. The remainder of the original 196 lbs. of 
ice was incrementally added during the pigment acid solution addition 
period. An excess of ice, wherein the vortex was impeded, was avoided and 
the stir rate was maintained at 800 rpm-1000 rpm. The total uninterrupted 
time for the pigment acid solution addition was 2.67 hours-2.83 hours and 
the tank contents remained at 8.degree. C.-12.degree. C. throughout. The 
total residence time of the pigment in the acid was less than 6 hours 
prior to ice water quenching. After stirring the tank contents at 400 
rpm-500 rpm for 0.5 hours beyond the time required to complete the 
addition, the cold dilute acid pigment slurry was vacuum filtered. The 
filtration was slow (overnight) and the yellow filtrate showed no evidence 
of fines. In the morning, the filter cake was washed on the funnel with 
prewarmed (70.degree. C.-75.degree. C.) deionized water (5.times.2 gal.). 
Residual acid was removed by slurrying the pigment in 25 gal. of deionized 
water heated to 70.degree. C.-75.degree. C. for one hour in a 30 gal. 
jacketed stainless steel tank. The hot pigment water slurry was vacuum 
filtered. 
The following four ammonium hydroxide slurries were prepared to remove 
residual sulfuric acid as ammonium sulfate. The same previously described 
30 gal. vessel was used in the process and the stir rate (400-500 rpm) and 
heating period (one hour) at elevated temperature (70.degree. 
C.-75.degree. C.) were the same. Each slurry was followed by a vacuum 
filtration step. 
First NH.sub.4 OH slurry: 15.5 gal deionized water and 7.8 l conc. NH.sub.4 
OH 
2nd NH.sub.4 OH slurry: 16.8 gal deionized water and 4.9 l conc. NH.sub.4 
OH 
3rd NH.sub.4 OH slurry: 16.8 gal deionized water and 4.9 l conc. NH.sub.4 
OH 
4th NH.sub.4 OH slurry: 16.8 gal deionized water and 4.9 l conc. NH.sub.4 
OH 
The purpose of the remaining 6 deionized water slurries was to reduce the 
level of ionic species in the pigment particles as measured by 
conductivity in units of micro mhos. An acceptable pigment slurry filtrate 
value of less than about 10 micromhos (at room temperature) must be 
achieved to insure that the pigment ws sufficiently free of ionic 
contamination for precision photoreceptors. 
The equipment and conditions described for the ammonium hydroxide slurries 
were maintained. Instead, 22 gal-25 gal. of deionized water was used in 
each slurry and generally 6-8 slurries were required to lower the 
conductivity to less than about 10 micromhos. 
The finally filtered pigment was transferred to trays for convection oven 
drying. The pigment was dried for four days at 60.degree. C.-65.degree. C. 
and any pigment chunks were manually broken and the pigment thereafter 
dried another 24 hours at the same temperature. The pigment was next 
pulverized with a mortar and pestle and drying was resumed in a vacuum 
oven at the same temperature for 16 hours at 0.5 mm Hg. Finally, the 
pigment was bagged and stored in the absence of light. 
EXAMPLE III 
A series of vanadyl phthalocyanine samples prepared with the procedure of 
Example I were studied by the TGA technique to determine their purity. The 
percentages of weight loss for each vanadyl phthalocyanine sample at 
various temperatures were tabulated and shown in the table below. As 
apparent from the Table, all the vanadyl phthalocyanine samples contain a 
small amount of impurities as indicated by the onset of weight loss at low 
temperatures (T less than 105.degree. C.) and the total weight loss at 
400.degree. C. The weight loss below 105.degree. C. is probably due to 
residual water and solvent. Weight loss at 300.degree. C. may be due to 
impurities such as phthalonitrile, phthalic acid, phthalimide, 
phthaldiamide, and phthalamic acid. These organic impurities may affect 
the electrical properties of the photoconductive pigment. Almost all the 
pigments (except Sample 4) were not totally dried as shown by the data of 
onset of weight loss (T less than 170.degree. C.). TGA values beyond 
400.degree. C. have no meaning with respect to impurities because vanadyl 
phthalocyanine itself begins to sublime. The specific procedures and 
equipment for determining the weight loss included a Perkin Elmer 
Thermogravimetric System (Model TGS-2) equipped with an AR-2 Autobalance, 
a microprocessor (System-4) and a Hitachi X-Y recorder was used in this 
Example. Helium was employed as a carrier gas to provide an inert 
atmosphere inside the furnace and the furnace tube. The flow rate of the 
He gas was set at about 60 ml/min. The Thermogravimetric (TGA) instrument 
was calibrated by the microprocessor to ensure accurate temperature 
measurements before the analyses began. A vanadyl phthalocyanine sample 
(about 2-7 mg) was placed in a platinum pan and its weight was accurately 
measured. About 90% of the sample weight was suppressed so that the full 
scale of the chart paper represents 10% of total weight loss. This 
practice allows detection of a very small change in weight loss due to the 
temperature change. For volatile materials other than the pigment, sample 
weight was not suppressed. The experiments were conducted in a programmed 
mode. The sample was allowed to equilibrate at 30.degree. C. for one 
minute and then heated to 500.degree. C. at a rate of 20.degree. C./min. 
The pigment sample was cooled down immediately once it reached 500.degree. 
C. The recorded TGA trace was used to determine % of weight losses at 
various temperatures. The weight loss data at various temperatures up to 
about 450.degree. C. (T less than 450.degree. C.) are quite good and 
reproducible. The weight loss values at greater than 400.degree. C. are 
slightly less accurate because of rapid sublimation of the pigment which 
can vary with its particle size, sample distribution in the holder, 
crystallinity, and sample size. 
TABLE 
______________________________________ 
Thermogravimetric Analysis of Vanadyl Phthalocyanine Samples 
Percent of Weight Loss at Various Temperatures 
Sample 
Pigment Onset of 200.degree. 
250.degree. 
300.degree. 
350.degree. 
400.degree. 
No. I.D. No. Wt. Loss C. C. C. C. C. 
______________________________________ 
1. 15558-63 50.degree. C. 
0.14 0.18 0.22 0.28 0.35 
2. 15558-65 70.degree. C. 
0.14 0.16 0.19 0.23 0.29 
3. 15558-76 190.degree. C. 
0.03 0.07 0.12 0.17 0.24 
4. 15558-89 50.degree. C. 
0.13 0.18 0.25 0.31 0.40 
5. 15558-95 150.degree. C. 
0.06 0.16 0.20 0.29 0.35 
6. 15558-101 
50.degree. C. 
0.12 0.20 0.28 0.35 0.45 
7. 15558-103 
45.degree. C. 
0.11 0.20 0.26 0.31 0.36 
8. 15558-6 75.degree. C. 
0.08 0.13 0.20 0.27 0.36 
9. 20162-8 95.degree. C. 
0.06 0.12 0.19 0.23 0.30 
10. 20162-10 50.degree. C. 
0.12 0.21 0.30 0.38 0.44 
11. 20162-18 65.degree. C. 
0.10 0.20 0.29 0.34 0.40 
12. 20162-20 65.degree. C. 
0.12 0.25 0.33 0.40 0.49 
______________________________________ 
Samples 1 through 12 were found to contain acceptable volatile impurity 
levels of less than about 0.5 percent by weight based on the weight of the 
pigment for use in electrophotographic imaging members. At less than or 
equal to 0.5 weight percent impurity level, dark decay values remain 
acceptable (less than or equal to 50 volts/sec). 
EXAMPLE IV 
The vanadyl phthalocyanine pigment produced by the process of Example I was 
incorporated into a single layer photoreceptor. The photoreceptor was 
prepared in three steps. First the vanadyl phthalocyanine pigment was 
dispersed in a polyester binder polymer dissolved in methylene chloride 
solvent. Second, the dispersion was coated on an aluminum substrate, and 
third, the coating was dried to remove the solvent. In the first step, 
1.77 gms polyester binder polymer (PE-200 from Goodyear Tire & Rubber Co.) 
was weighed on an analytical balance with an accuracy of plus or minus 
0.01 mgm. and added to a 2 oz. amber bottle with a polyseal cap. 21.4 gms 
methylene chloride solvent (reagent grade quality) solvent was next added 
directly to the 2 oz. bottle as it was weighed on a top loading balance 
with an accuracy of plus or minus 10 mgm. This container with the above 
ingredients was placed on a wrist action shaker to dissolve the polymer. 
0.43 gm of vanadyl phthalocyanine pigment was weighed out on the 
analytical balance and added to this solution. 150 gms stainless steel 
shot (1/8 in. #302 grade burnishing balls--Superior Ball Co., 100 
Willington St., Hartford, Conn. 06106) was added to the bottle after 
weighing on the top loading balance. The steel shot had been previously 
washed with methylene chloride to remove residual oils and dried in an 
oven at 100.degree. F. The bottle with these ingredients was then placed 
on the shaker (Cat. No. 5100X Red Devil, Inc., Union, N.J.) for 90 minutes 
to disperse the pigment. The dispersions were allowed to cool to room 
temperature before coating. 
The dispersion as prepared above was coated onto brush-grained aluminum 
(Brush Grained Aluminum Plates Lkk. 10 in..times.16 in., Ron Ink Company, 
Inc., 61 Halstead St., Rochester, N.Y.) using a Gardner Mechanical Drive 
Film Applicator Model AG-3862 (Gardner Laboratory, Inc. Box 5728, 5521 
Landy lane, Bethesda, Md. 20014) with a Bird Film Applicator (Gardner 
Laboratory, Inc. Box 5728, 5521 Landy Lane, Bethesda, Md. 20014). The 
brush-grained aluminum plate was cut to 6 in..times.10 in. and was coated 
in the long direction. The wet film thickness was 3 mils (75 micrometers) 
with a coating width of 3 in. The coating was done in a glove box (Cat. 
No. 50004/5 Labcamco Corp., Kansas City, Mo. 64132) with the gloves 
removed and plastic slit shields installed in their place. The box was 
purged under continuous positive pressure with a flow of dry air to 
maintain a relative humidity of less than 20%. The dispersion was placed 
onto the aluminum plate (previously washed with methylene chloride) in 
front of the Bird Film Applicator using a 3-inch medicine dropper pipett. 
The coated plate was allowed to dry in the dry box for 30 min. Next it was 
placed in a vacuum (Cat. No. 31566 Precision Scientific Co., U.S.A.) oven 
and held at room temperature at a vacuum pressure (DUO Seal Vacuum Pump 
Model 1405 Welch Scientific Co., 7300 N. Linder Ave., Skokie, Ill. of 
about 30 in. of Hg for 1 hour. Then it was heated to 55.degree. C. for 17 
hours. The plate was removed from the oven and allowed to cool to room 
temperature. The thicknesses of the photoreceptor was then measured with 
the Permascope Type EC 8e2Ty (Twin City Testing Corporation, P.O. Box 248, 
Tonawanda, N.Y. 14150). The thickness for the single layer photoreceptor 
was about 10 micrometers. 
Electrical measurements were made on a flat plate scanner. The scanner 
consisted of a motor driven reciprocating belt onto which was placed the 
photoreceptor sample. Because of the flexible belt, the sample is first 
mounted on a thick (50 mm) aluminum palte (5.times.5 cm.sup.2) which fits 
on top of the belt and is normally grounded. The belt and sample are first 
moved about 2 in./sec. under a corotron where the sample is charged 
positively to the corotron. The belt and sample are then moved to an image 
exposure station. The image exposure station comprises a light source, 
filter, electronic shutter and an electrometer. In the image exposure 
position, the surface potential is monitored with a capacitively coupled 
ring probe connected to a Keithley electrometer (Model 610C) (Keithley 
Instruments Inc., 28775 Aurora Road, Cleveland, Ohio 44139) in the coulomb 
mode. The output of the electrometer is displayed on a strip chart 
recorder (HP Model 7402A) (Hewlett Packard Inc.) which is calibrated by 
applying known voltages on an uncoated (bare plate) sample. The dark 
discharge was measured with the shutter closed and the discharge to a 
known light intensity was recorded with the shutter open. A strip chart 
recording of the voltage as a function of time was prepared. The chart 
recorder speed was 125 mm/sec. An initial rise in the voltage was observed 
due to the charged sample moving under the probe. A peak voltage 
(V.sub.DDP) of about 680 volts was observed when the sample stopped. From 
this peak voltage on, the voltage decreased due to dark discharge, 
providing a measure of the dark discharge rate. To measure photodischarge 
the shutter was opened when the peak voltage was attained and the 
photoreceptor exposed to light of constant intensity. The light was 
filtered with first order interference and neutral density filters to give 
a flux of 32 ergs/cm.sup.2 /sec at 597 nm. Discharge did not begin 
immediately but followed an "induction period." The sensitivity of the 
photoreceptor was characterized by two parameters; the maximum discharge 
rate per exposure and the exposure required to reach the maximum rate. 
Since the latter usually occurs when the voltage is half the value of 
V.sub.DDP at time=0, it is measured as the exposure from time=0 to time 
that 1/2 V.sub.DDP is attained. The slope of a line drawn tangent to the 
curve on the strip chart at the maximum discharge, gave a 930 volts-O 
volts=930 volt drop in a time of 0.44 sec. This slope of 930 volts/0.44 
sec=2113 volts/sec divided by the 32 ergs/cm.sup.2 /sec intensity gave a 
sensitivity of 66.1 volts/erg/cm.sup.2. An alternate sensitivity parameter 
was obtained in the following way. From the strip chart, V.sub.DDP =680 
volts, so 1/2 V.sub.DDP =340 volts. Since the exposure time to reach this 
level was 0.59 sec., the energy to obtain 1/2 V.sub.DDP was 0.59 
sec.times.32 ergs/cm.sup.2 sec=18.9 ergs/cm.sup.2. 
EXAMPLE V 
The pigment preparation procedure of Example II was repeated to prepare a 
pigment for a firsrt sample. 
A pigment for a second sample was prepared using the pigment preparation 
procedure of Example II except that room temperature water was used 
instead of ice water in the quench tank. 
A control pigment for a third sample was prepared from vanadium pentoxide 
as described in Example I. For accurate comparisons, the process for 
preparing a control device in this and following Examples was conducted on 
the same days as the other devices being compared to the control device. 
Thus, devices for samples 1 and 2 were prepared on the same day as control 
device 3. The results of the electrical tests of single layer 
photoreceptors prepared from these samples are set forth in the table 
below. 
Single layer photoreceptor devices were prepared from these pigments using 
the procedures and proportions described in Example IV. These 
photoreceptors were tested for electrical properties in the manner 
described in Example IV. The results of the electrical tests are set forth 
in the table below. 
TABLE 
______________________________________ 
Device 
Pigment Dark Decay Device Sensitivity 
Sample No. (volts per sec.) 
E1/2 V.sub.DDP (ergs per cm.sup.2) 
______________________________________ 
1 30 28 
2 20 26 
3 30 24 
______________________________________ 
Generally, dark decays within 10 volts per second of the dark decays 
exhibited by the control are acceptable. However, the photosensitivity 
(Energy 1/2 V.sub.DDP ergs/cm.sup.2) is somewhat less (a larger number 
indicates less photosensitivity) for Samples 1 and 2 compared to the 
control Sample 3. 
EXAMPLE VI 
A pigment for a first sample was prepared as described in Example II. A 
control pigment for a second sample was prepared from vanadium pentoxide 
as described in Example I. 
Single layer photoreceptor devices were prepared from these pigments using 
the procedures and proportions described in Example IV. These 
photoreceptors were tested for electrical properties in the manner 
described in Example IV. The results of the electrical tests are set forth 
in the table below: 
TABLE 
______________________________________ 
Device 
Pigment Dark Decay Device Sensitivity 
Sample No. (volts per sec.) 
E1/2 V.sub.DDP (ergs per cm.sup.2) 
______________________________________ 
1 30 28 
2 20 26 
3 30 24 
______________________________________ 
Generally, dark decays within 10 volts per second of the dark decays 
exhibited by the control are acceptable. However, the photosensitivity 
(Energy 1/2V.sub.DDP ergs/cm.sup.2) is somewhat less (a larger number 
indicates less photosensitivity) for Samples 1 and 2 compared to the 
control Sample 3. 
EXAMPLE VI 
A pigment for a first sample was prepared as described in Example II. A 
control pigment for a second sample was prepared from vanadium pentoxide 
as described in Example I. 
Single layer photoreceptor devices were prepared from these pigments using 
the procedures and proportions described in Example IV. These 
photoreceptors were tested for electrical properties in the manner 
described in Example IV. The results of the electrical tests are set forth 
in the table below: 
TABLE 
______________________________________ 
Device 
Pigment Dark Decay Device Sensitivity 
Sample No. (volts per sec.) 
E1/2 V.sub.DDP (ergs per cm.sup.2) 
______________________________________ 
1 40 24 
2 30 19 
______________________________________ 
Again, the photosensitivity is somewhat less for sample 1 compared to the 
control sample 2. 
EXAMPLE VII 
A pigment for another sample was prepared utilizing the process described 
in Example II except that room temperature water was used instead of ice 
water in the quench tank. A single layer photoreceptor was prepared from 
this pigment using the procedures and proportions described in Example IV. 
This photoreceptor was tested for electrical properties in the manner 
described in Example IV. No charge acceptance of any significance was 
observed. 
EXAMPLE VIII 
A standard three phase pigment preparation procedure as described in 
Example I was employed. However, room temperature water was used instead 
of ice water in the quench tank. In this case, the single layer 
photreceptor device prepared with the resulting pigment using the 
procedures and proportions described in Example IV accepted a charge but 
exhibited very high dark decay of 190,275 volts per second compared to a 
normal acceptable dark decay of 20 to 40 volts. This indicates the 
presence of a significant quantity of impurities trapped in the pigment 
particles. 
EXAMPLE IX 
The pigment preparation procedure of Example I was repeated except that 
only a 28% excess (as compared to a 55% excess) of vanadium pentoxide was 
used in Phase I. The yield was about 79% compared to a normal of 92% to 
99% with 55% excess vanadium pentoxide. In this case, the single layer 
photreceptor device prepared with the resulting pigment using the 
procedures and proportions described in Example IV exhibited a dark decay 
of about 35 volts per second and a E1/2V.sub.DDP (ergs/cm.sup.2) of about 
26. The latter photosensitivity value indicates lower photosensitivity 
versus previously used controls. 
EXAMPLE X 
The pigment preparation procedure of Example I was repeated except that the 
exotherm was thermally starved so that a maximum temperature of only about 
130.degree. C. was attained in Phase I instead of the normal 198.degree. 
C.(or boiling point of ethylene glycol). The yield was only 46% compared 
to the 92% to 99% when the process was repeated with the materials and 
conditions described in Example I. A single layer photreceptor device 
prepared with the resulting thermally starved exotherm pigment using the 
procedures and proportions described in Example IV exhibited a dark decay 
of 30 compared to 35 for the control and the E1/2V.sub.DDP (ergs/cm.sup.2) 
was 27 compared to 21 of the control. Again the photosensivity of this 
sample is considerably lower than the control. 
EXAMPLE XI 
The pigment preparation procedures were repeated except that vanadium 
trichloride was substituted for vanadium pentoxide and Example II was 
thereafter followed. 
A pigment for a second sample was prepared with vanadium trichloride 
substituted for vanadium pentoxide but with standard 2-purification steps 
as in Example I. 
A pigment for a third sample was obtained from the second sample and 
processed in accordance with Phase III of Example I. 
A pigment for a fourth sample was obtained as sample 1. 
A pigment for a fifth sample was obtained from the fourth sample which was 
sublimed and twice processed in accordance with Phase III of Example I. 
A control pigment for a sixth sample was prepared from vanadium pentoxide 
as described in Example I in all three phases. 
Single layer photoreceptor devices were prepared from these pigments using 
the procedures and proportions described in Example IV. These 
photoreceptors were tested for electrical properties in the manner 
described in Example IV. The results of the electrical tests are set forth 
in the table below: 
TABLE 
______________________________________ 
Device 
Pigment Dark Decay Device Sensitivity 
Sample No. (volts per sec.) 
E1/2 V.sub.DDP (ergs per cm.sup.2) 
______________________________________ 
1 20 44 
2 20 32 
3 25 32 
4 20 44 
5 20 34 
6 25 19 
______________________________________ 
Sample 1 compared to the control sample 6 (44 vs. 19) exhibits less than 
half the photosensitivity. As to Samples 2 and 3, the use of the Phase II 
and Phase III steps of Example I improved the photosensitivity from about 
44 to about 32 but this improved photosensitivity is still vastly inferior 
to the device sensitivity of 19 of control pigment 6. 
EXAMPLE XII 
The pigment preparation procedure of Example II was repeated to prepare a 
pigment for a first sample. 
The pigment preparation procedure of Example II was repeated except that 
room temperature water was used instead of ice water in the quench tank. 
A control pigment for a third sample was prepared from vanadium pentoxide 
as described in Example I. 
Single layer photoreceptor devices were prepared from these pigments using 
the procedures and proportions described in Example IV. These 
photoreceptors were tested for electrical properties in the manner 
described in Example IV. The results of the electrical tests are set forth 
in the table below: 
TABLE 
______________________________________ 
Device 
Pigment Dark Decay Device Sensitivity 
Sample No. (volts per sec.) 
E1/2 V.sub.DDP (ergs per cm.sup.2) 
______________________________________ 
1 35 24 
2 35 25 
3 30 19 
______________________________________ 
These results generally demonstrate that photosensitivity decreases when an 
abbreviated pigment preparation process (Example II) is used. 
EXAMPLE XIII 
The pigment preparation procedure of Example II was repeated to prepare a 
pigment for a first sample. 
A control pigment for a second sample was prepared from vanadium pentoxide 
as described in Example I. 
Single layer photoreceptor devices were prepared from these pigments using 
the procedures and proportions described in Example IV. These 
photoreceptors were tested for electrical properties in the manner 
described in Example IV. The results of the electrical tests are set forth 
in the table below: 
TABLE 
______________________________________ 
Device 
Pigment Dark Decay Device Sensitivity 
Sample No. (volts per sec.) 
E1/2 V.sub.DDP (ergs per cm.sup.2) 
______________________________________ 
1 35 18 
2 30 17 
______________________________________ 
These results generally demonstrate that the photosensitivity decrease may 
occasionally be insignificant when using an abreviated pigment preparation 
process (Example II). 
EXAMPLE XIV 
An overcoated photoreceptor drum was prepared by applying, with spraying 
with a Model 21 spray gun (commercially available from Binks Inc.) an 
amine charge transport layer onto a clean aluminum cylinder having a 
diameter of three inches. The spraying was effected in a laminar airflow 
booth designed process with volatile solvents containing an entrance means 
and an exhaust means. This booth also contained a motor driven mandrel 
with the aluminum cylinder mounted thereon. The spray booth was maintained 
at a temperature of 20.degree. C. and a relative humidity of about 40 
percent. 
A charge transport layer was deposited which contained a 4 percent solid 
solution of a mixture of 65 percent by weight of polycarbonate resin 
(Merlon M39N, commercially available from Mobay Chemical Co.) and 35 
percent by weight of 
N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine, This 
mixture was prepared by dissolving a polycarbonate resin in a solution 
containing 60 percent by volume of methylene chloride and 40 percent by 
volume 1,1,2-trichloroethane. The polycarbonate resin was dissolved by 
paint shaking that solution mixture in an amber bottle for one hour and 
thereafter standing about 24 hours at room temperature. 
The resulting solution was then applied to the aluminum cylinder by the 
spray gun followed by drying at 40.degree. C. for 20 minutes and 
160.degree. C. for 60 minutes, the drying being effected in a forced air 
oven. The coating on the aluminum cylinder had a thickness of 15 microns 
and contained 35 percent by weight of the amine and 65 percent by weight 
of the polycarbonate resin. 
This transport layer was then coated with a photogenerating layer 
containing 30 percent by weight vanadyl phthalocyanine dispersed in 70 
percent by weight of a polyester. The photogenerating layer was applied by 
spraying with the Binks Model 21 spray gun described above. 
The photogenerating composition was prepared by mixing 30 percent by weight 
vanadyl phthalocyanine and 70 percent by weight of a polyester (PE-100 
Polyester, commercially available from Goodyear.) This mixture was placed 
in an amber bottle containing in a 60/40 volume ratio of a mixture of 
solvents of methylene chloride and 1,1,2-trichloroethylene. Steel shot 
having a diameter of about 3 millimeters was added to the bottle. The 
contents of the bottle were then mixed on the paint shaker for 24 hours. 
The steel shot was thereafter removed by filtration and sufficient solvent 
was added to achieve a mixture containing 1 percent solids of vanadyl 
phthalocyanine and the polyester. This mixture was then sprayed onto the 
above prepared diamine charge transport layer with the Binks spray gun. 
After spraying, the coated device was dried at 100.degree. C. for 1.25 
hours in a forced air oven to form a photogenerating layer having a dry 
thickness of about 1 micrometer. 
A top ultraviolet absorbing overcoating layer was then applied to the 
photogenerating layer by placing the coated aluminum cylinder containing 
the charge transport layer and photogenerating layer in a vacuum chamber 
and vacuum evaporating on the photogenerating layer an alloy containing 98 
percent by weight of selenium and 2 percent by weight of arsenic. The 
vacuum chamber contained a horizontally rotating motor driven shaft, a 
string of 4 crucibles having a length longer than the aluminum cylinder 
and positioned about 12 inches away from the cylinder. These crucibles 
were loaded with the arsenic-selenium alloy pellets and the vacuum chamber 
was evacuated to a pressure of less than a micro tor. The aluminum 
cylinder was rotated at speeds of about 200 revolutions per minute while 
being treated at 70.degree. C. with radiant heaters. The arsenic selenium 
alloy was evaporated by heating each of the crucibles to 300.degree. C. 
After cooling, the resulting photogenerating layer contained about 2 
percent by weight of arsenic and 98 percent by weight of selenium and a 
thickness of about 1.5 micrometers. 
This device was then positively charged to about 800 volts with a corotron, 
exposed in image configuration to light having a wavelength from about 400 
nanometers to about 800 nanometers. Equipment for testing photoreceptors 
using our improved pigment in the generator layers. Equipment used: Cyclic 
Xerographic Scanner; Photoreceptor Surface Speed: 4 in/sec; Number of 
Cycles Tested (max): 100,000 cycles with cycle up and cycle down 
specification plus or minus 100 volts of Vi=800 volts; Light Intensity: 
Exposure 2.times.10.sup.-5 watts/cm.sup.2, Erase: 2.times.10.sup.-4 
watts/cm.sup.2 ; Sensitivity (E1/2 not used for full device), 25 
ergs/cm.sup.2 ; Dark Decay: less than 50 volts/sec; Residual Voltage: less 
than 50 volts. 
Although the invention has been described with reference to specific 
preferred embodiments, it is not intended to be limited thereto, rather 
those skilled in the art will recognize that variations and modifications 
may be made therein which are within the spirit of the invention and 
within the scope of the claims.