US3897249A - Toners for phthalocyanine photoreceptors - Google Patents

Abstract

Phthalocyanine electrostatographic photoreceptors are subject to cycling fatigue effects when toners containing acidic channel black carbon are used. These fatigue effects are substantially reduced by the use of neutral or alkaline carbon blacks, such as furnace blacks.

Description

United States Patent Mammino et al.

[ 1 July 29, 1975 TONERS FOR PHTHALOCYANINE PHOTORECEPTORS Inventors: Joseph Mammino; Gary L.

Whittaker, both of Penfield, N.Y.

Xerox Corporation, Stamford, Conn.

Filed: Apr. 9, 1973 Appl. No.: 349,491

Assignee:

U.S. Cl 96/1S D; 252/62.1 P Int. Cl G03g 13/08 Field of Search 96/1S D, 1.5; 252/621 P References Cited UNITED STATES PATENTS 1/1965 West et al. 252/621 P Primary Examiner-Norman G. Torchin Assistant Examiner.lohn R. Miller [57] ABSTRACT Phthalocyanine electrostatographic photoreceptors are subject to cycling fatigue effects when toners containing acidic channel black carbon are used. These fatigue effects are substantially reduced by the use of neutral or alkaline carbon blacks, such as furnace blacks.

11 Claims, 3 Drawing Figures TONERS FOR PHTH-ALOCYANINE PHOTORECEPTORS FIELD OF THE INVENTION This invention relates to improvements in toners used with phthalocyanine electrostatographic photoreceptors. In particular, it relates to toners which reduce cycling fatigue effects which have heretofore limited the useful life of such photoreceptors.

BACKGROUND OF THE INVENTION There have been known various methods for the production of images, such as photography, lithography, electrostatography, and the like. In electrostatography, as disclosed, for example, by C. F. Carlson in U.S. Pat. No. 2,297,691, a base plate of relatively low electrical resistance, such as metal, paper, etc., having a photoconductive insulating surface coated thereon, called a photoreceptor is electrostatically charged in the dark. The charged coating is then exposed to a light image. The charges leak off rapidly to the base plate in proportion to the intensity of light to which any given area is exposed. The charges are substantially retained in the non-exposed areas. After such exposure, the coating is contacted with electrostatic solid marking particles referred to as toner. These particles adhere to the areas where the electrostatic charges remain, forming a powder image corresponding to the electrostatic image. This method is further disclosed in U.S. Pat. Nos. 2,659,679, 2,753,308, and 2,788,288. The powder image can be transferred to a sheet of transfer material, resulting in a positive or negative print as the case may be. Alternatively, where the base plate is relatively inexpensive, it may be desirable to fix the powder image directly to the plate itself. A description of electrostatographic processes may be found in a book by Dessauer and Clark, entitled Xerography and Related Processes.

In electrostatography, there are known many photoreceptor materials, some of which function in a reusable system and others which function commercially only in a non-reusable or disposable system. In the reusable system, although many photoconductors have been used or attempted, selenium and materials composed principally of selenium have been most frequently used commercially.

Although selenium has traditionally been the most desirable photoconductor for use in electrostatography, it does have some inherent disadvantages. One of the disadvantages of selenium is that it is not fully panchromatic. A second drawback to the use of selenium is the degree of difficulty encountered when depositing the selenium on a substrate to form an electrostatographic plate.

In U.S. Pat. No. 2,663,636, Arthur Middleton disclosed various methods and means whereby photoconductive insulating material in an insulating resin binder can be formed into an operable electrostatographic plate. In a copending application, Ser. No. 375,191, filed in the United States Patent Office on June 15, 1964, entitled Electrographic Element, now abandoned in favor of U.S. Ser. No. 518,450 filed Jan. 3, 1966 now U.S. Pat. No. 3,816,119the use of phthalocyanine in a resin binder is disclosed as an electrostatographic plate. There are many advantages spelled out in this application especially directed to the use of phthalocyanine in a reusable electrostatographic system. Various metal-free phthalocyanines are disclosed as suitable for use in an electrostatographic plate, as are many binders, both photoconductive and nonphotoconductive.

Metal-free phthalocyanine is known to exist in at least four polymorphic forms, including alpha, beta, gamma, and X-form. X-form has been shown to have unique electrostatographic properties, and is further discussed in a copending application, Ser. No. 375,191, filed in the United States Patent Office on June 15, 1964, now abandoned in favor of U.S. Pat. No. 518,450 filed Jan. 3, 1966 now U.S. Pat. No. 3,816,118. The various forms of metal-free phthalocyanine may easily be distinguished by comparison of their X-ray diffraction patterns and/or infrared spectra (see U.S. Pat. No. 3,357,989.

Methods for preparing metal-freephthalocyanine are disclosed in U.S. Pat. Nos. 3,492,308 and 3,492,309.

Phthalocyanine, also known as tetrabenzotetraazaporphin and tetrabenzoporphyrazine, may be said to be the condensation product of four isoindole groups. Metal-free phthalocyanine has the following general structure:

/ N NH HN i Certain problems, however, have arisen with the use of phthalocyanine photoreceptors. In particular, it has been found that conventional toners often cause changes in the electrical properties of the phthalocyanine plate surface. Furthermore, removal of excess toner is considerably more difficult and this has led to excessive toner build-up after only a few hundred cycles.

It is therefore a principal object of this invention to provide a toner for use with phthalocyanine photoreceptors which will not adversely affect the electrical properties of the phthalocyanine plate.

It is a further object of this invention to provide a toner which will minimize the change in these properties under cycling conditions, i.e., which will reduce fatigue effects. Other objects of this invention will become apparent from the discussion which follows:

SUMMARY OF THE INVENTION The useful life of phthalocyanine photoreceptors is increased and cycling fatigue effects are reduced by employing a toner comprising neutral or alkaline carbon pigments, such as furnace blacks, rather than the acidic channel blacks.

DETAILED DISCUSSION OF THE INVENTION The present invention will become more apparent from the ensuing discussion and drawings wherein:

FIG. 1 is a graphical representation of the variation in D with sensitivity fatigue ratio for phthalocyanine binder plates exposed to a variety of toners relative to unexposed or virgin plates as described in Example I.

FIG. 2 is a graphical representation of the variation in D with the number of copies from the data in Example III; and

FIG. 3 is a graphical representation of the variation in S with the number of prints from the data in Example III.

The use of carbon black pigments in electrostatographic toners is not a new concept. US. Pat. No. 2,753,308 discloses the use of carbon black pigments in the electrostatographic development of vitreous selenium plates. US. Pat. No. 2,914,221 also discloses the use of various carbon black pigments for the electrostatographic development of photoconductive layers of sulfur, selenium, zinc oxide in a resin binder. These patents do not recognize any difference between acidic carbon blacks such as channel blacks and neutral or alkaline carbon blacks such as furnace blacks when used in electrostatographic toners. With respect to selenium photoconductive plates, the difference in the black toner pigments appears to be without any practical significance. Surprisingly, however, with phthalocyanine photoreceptors, it has been found that the use of neutral or alkaline carbon black pigments results in significant enhancement of the useful life of the photoreceptor as compared with the use of acidic blacks.

Any carbon black substance otherwise suitable for use in electrostatographic toners and which has a pH of at least about 7.0 can be used in the practice of this invention. Suitable carbon blacks include the following, most of which are furnace blacks.

The pH of the carbon blacks can be determined by ASTM method D 1512-60.

TABLE I III Product Manufacturer Columbian Carbon Company A series of tests were run on phthalocyanine photoreceptors to determine the comparative performance effects of neutral or alkaline carbon black toners vs. the

acidic toners heretofore used. The properties of interest are charge acceptance, dark discharge, photodischarge characteristics and the nature and magnitude of charges in these properties under cycling conditions, i.e., fatigue effects. Many of these properties, in particular, fatigue associated properties, have been found to change after the plate surface has been subjected to certain toners for a length of time. The amount of change depends upon the particular plate formulation and the type of toner used.

The photodischarge characteristics of phthalocyanine binder plates are more complex than those of the conventional selenium photoconductor; there is an induction period or slow initial discharge rate which is followed by a rapid secondary discharge. Most of the time required for discharge from typical initial potentials of 800 1500 V is in the first 200 or 300 volts of discharge. Conventional methods for determining plate sensitivity, such as initial slope or average discharge rate for to 75% discharge, are therefore not properly descriptive. Accordingly, photodischarge speed as measured here is the reciprocal time required to discharge 200 volts from the initial potential. Sensitivity values measured in this way have shown only slight dependence on parameters such as initial potential and plate thickness, and therefore give a convenient means for comparing different plates or the same plate measured under conditions resulting in different initial potentials. This is quite often the case when comparing a plate in rested and fatigued condition.

The phthalocyanine samples used for these measurements are generally coated on commercial 5-mil aluminum sheet, whose surface has been found to have an excellent blocking interface for phthalocyanine enamels. The samples are taped on a metal drum which is then placed in a cycling scanner for measurements. An electrometer, a charging corotron, and erase lamps are placed at appropriate positions around the drum.

An electrometer with a transparent electrode is used for potential measurements. An enlarger using a tungsten lamp is positioned above the electrometer to give illumination for photodischarge measurements. Corning CSl-69 and CS2-59 filters are used together to isolate a broad band between 650 and 700 millimicrons where phthalocyanine has strong absorption. The intensity at the sample is adjusted by varying the aperture to obtain 1.5 microwatts per cm A speed number, S, is determined, as described above, as the reciprocal time (sec) to discharge the first 200 volts of the accepted potential.

Cycling is accomplished by letting the drum rotate to allow the sample to go through the sequence; charge, potential measurement, photodischarge. The cycle time used is 9 seconds. The corotron voltage is set at +6.5kV and is spaced to give a bare plate current of microamperes. In all cases, the top surface of the plate is charged positively.

Photodischarge and dark discharge measurements are obtained for both a rested and fatigued condition of the plate, i.e. prior to and after cycling. For dark discharge measurements, a plate is considered rested if it has not been subjected to charging for at least one-half hour prior to measurement. For photodischarge measurement, to plate is considered rested if it has not been subjected to charging for 16 hours or more prior to measurement. A plate is considered in a fatigued condition when it has been charge-erase cycled 200 or more times just prior to measurement. For measurement of dark discharge, the plate is allowed to cycle under the electrometer (in the dark) while it discharges, and an average potential value over the complete plate surface is estimated. For photodischarge measurements, the plate is stopped under the electrometer, and the measurement is obtained on a specific area of the plate. The same area is measured when making comparisons between the rested and the fatigued condition.

Dark discharge values are determined as follows: D percent dark discharge in 30 sec. for rested plate. D percent dark discharge in 30 sec. for fatigued plate. D, R percent dark discharge in 9 sec. for rested plate. D percent dark discharge in 9 sec. for fatigued plate. Plate speeds are defined as follows: S speed of rested plate (sec) for initial 200 volt discharge S speed of fatigued plate (sec' for initial 200 volt discharge Generally, plates show a higher speed in the fatigued condition than in the rested condition. This behavior is termed sensitivity fatigue and is defined as the ratio of speed in the fatigued condition to that in the rested condition, i.e.,

Sensitivity Fatigue Ratio S /S EXAMPLE I To determine effects of various carrier/toner combinations on plate electrical properties, a phthalocyanine sample as described above was exposed to the developer in the following way: The phthalocyanine plate was taped on the inside surface of a 16 oz. glass jar.

The carrier particles had an average particle size of about 650 microns.

The toner materials were:

A. Mixture of an acrylic-styrene copolymer, polyvinyl butyral resin, and channel-black carbon at a ratio of 9:1:1.

B. Similar to A except that it contains furnace-black carbon pigment.

C. Similar to A except that it does not contain any carbon black.

D. Similar to A except that it is made from an emulsion and spray dried.

The channel blacks used in the above toners are either Neo Spectra Mark II from Columbian Carbon Company or Supercarbovar from Cabot Corporation. These have pH values of 3 and 5 respectively. The furnace black in toner B is Sterling l 182 from Cabot Corporation with a pH greater than 7.

The phthalocyanine plate used in these experiments consisted of a 6:1 binder/pigment ratio of X- phthalocyanine and EP-89 resin sprayed onto a single large 5-mil aluminum sheet and cured 16 hours at 160C. EP-89 resin is an epoxyphenolic resin made up as follows: 355 g. Epon 1007 (Shell Chemical Co.) at 100% solids-epoxy resin; 200 g. Resyn 5201 (Resyn Corp.) at 75% solids-phenolic resin; 44 g. Uformite F-240 (Rohm & Haas Chem. Co.) at solidsureaformaldehyde resin; and 403 g. Ethyl Cellosolve solvent. From this large plate, small samples were cut to be used with the various carrier/toner combinations.

Electrical properties of two virgin samples (not exposed to developer) and of the samples exposed to the various carrier/toner combinations were measured in the manner described above. Table 11 sets forth the electrical measurements for the various samples.

TABLE 11 Charge Acceptance Sample Carrier/Toner (volts) D D 5 S 5,75,,

1 none (virgin plate) 1300 l3 15 0.68 1.50 2.21 2 none (virgin plate) 1540 9 10 0.68 1.36 2.00 3 carrier A/no toner 1340 9 13 0.69 1.29 1.87 4 carrier A/toner A 1360 11 69 0.84 3.12 3.72 5 carrier A/toner B 1240 10 24 0.79 2.03 2.57 6 carrier A/toncr C 1280 8 19 0.77 1.78 2.31 7 carrier A/toner D 1340 13 76 0.81 2.42 2.99

8 carrier A/no toner (rolled 24 hrs) 1160 14 22 0.84 1.79 2 14 9 carrier A/toner B (rolled 24 hrs) 1420 8 22 0.82 1.97 2.40

10 carrier A/toncr C (rolled 24 hrs) 1440 7 19 0.85 1.74 .05

100cc of carrier mixed with sufficient toner to cover the beads was added to the jar. The jar was tightly covered and rolled at 72 rpm for one hour to tumble the developer vigorously against the sample plate.

After removal of the sample, excess toner was blown off with air. The surface was not wiped or cleaned in any other manner. In general, only a slight toner film adhered to the surface, although near sample edges there was sometimes a substantial toner buildup which had to be removed by wiping. These edges either were trimmed off or not included in electrical measurements.

The carrier used (carrier A) was glass bead carrier particles with an ethyl cellulose coating thereon containing 8% by weight Hansa yellow pigment therein.

Several significant conclusions can be drawn from these results. Dark decay values for the rested plates are quite low in all cases. Speed values for the rested condition do not vary appreciably, although samples 1, 2, and 3 are comparatively low. However, most of this variation can probably be attributed to experimental and measurement errors and sample-to-sample variations rather than to effects due to the toners.

There are significant differences in fatigue properties resulting from contact with different toners goi, S and sensitivity fatigue). The toners can roughly be divided into two groups; those which produce little or no change in fatigue properties and those which produce substantial changes, particularly in D The carrier alone did not show significant interaction, which indicates that the interaction is essentially due to the toners.

To substantiate the validity of grouping into interacting and non-interacting toners, on the basis of these relatively short, though vigorous exposures, samples with the carrier alone and with the non-interacting toners were rolled for 24 hours. No significant increases in fatigue values were seen over those rolledfor 1 hour; in other words, whatever effects were going to take place were complete in the first hours.

The results are presented graphically in FIG. l, which shows changes in Dgop and sensitivity fatigue for the various toners relative to the virgin samples.

Toners which give substantial increase in fatigue properties are:

Toner A Toner D Those which do not are:

Carrier only Toner B Toner C Toners A and D contain channel-black carbon. The

non-interacting toners are known not to contain any channel-black carbon. Toner C is similar to toner A but does not contain any carbon-black pigment. Toner B contains a furnace-black carbon pigment, but is otherwise' similar to toner A. It appears quite clear that channel-black carbon is the interacting element in these toners responsible for producing undesirable fatigue characteristics in the electrical performance of the plates. This is believed to be due to the acidic nature of channel blacks.

EXAMPLE II Confirming measurements were made on three additional phthalocyanine formulations prepared as follows:

Wt. Ratio Binder/ Photoreceptor Formulation Photoreceptor Binder 11 x-phthalocyanine 6: l

Ill x-phthalocyanine These measurements were made using toner A (channel black) and toner B (furnace black) and Carrier A of Example I. A comparison of the results in presented in Table 111 below. It can be seen that all of the phthalocyanine formulations show substantial interaction with toner A and little or no interaction with toner B.

TABLE III Charge Sam- Accepple Carrier/Toner tance* D Dup Sp/SR (volts) 1 l Virgin 1600 7 7 1.8 12 Carrier A/Toner A 1520 5 83 4.6 13 Carrier A/Toner B 1060 3 15 2.4 14 Virgin 1460 8 8 2.0 15 Carrier A/Toner A 1180 9 61 5.0 16 Carrier A/Toner B 1 10 13 1.95 17 Virgin 1400 9 7 1.7 18 Carrier A/Toner A 1440 7 77 high 19 Carrier A/TonerB 1160 13 17 2.16

Variations in charge acceptance are believed to be partially due to plate thickness variations.

EXAMPLE 111 To show the extension of phthalocyanine photoreceptor life by the use of toner with furnace-black carbon, an extended run was made on a Xerox 813 copier. Two drums, X and Y, were coated with a phthalocyanine photoreceptor formulation. Drum X was print tested using toner A (channel-black) with carrier of Example 1. Drum Y was print tested using toner B (furnace black) and carrier A of Example I. With drum Y running up to about 50,000 copies, no significant changes in electrical properties were observed. FIG. 2 shows D vs. number of copies for Drum X using toner A and Drum Y using toner B. FIG. 3 shows a similar plot for S These results confirm the previous observation that electrical degradation does not occur when furnace-black carbon is used.

While various specifics are given in the present application, many modifications and ramifications will occur to those skilled in the art upon a reading of the present disclosure.

What is claimed is:

1. In an electrostatographic reproducing system employing a phthalocyanine photoreceptor and a dry developer comprising a carbon black toner, including the steps of charging said photoconductor, selectively exposing said photoconductor so as to form a latent electrostatic image and developing said photoconductor with said dry developer, the improvement which comprises using a carbon black toner having a pH of at least 7.0 and a carrier in said developing step.

2. The improvement of claim 1 in which the toner is a neutral carbon black.

3. The improvement of claim 1 in which the toner is an alkaline carbon black.

4. The improvement of claim 1 in which the toner is furnace black.

5. A method for reducing cycling fatigue effects on a phthalocyanine electrostatographic photoreceptor, said fatigue effects resulting from contact of said photoreceptors with developer comprising carbon black toner particles during development of electrostatic 1atent images thereon, which method comprises charging said photoreceptor, selectively exposing said photoreceptor and developing said photoreceptor with a dry developer comrpising a carbon black toner having a pH of at least 7.0 and a carrier.

6. The method of claim 5 in which the toner is a neutral carbon black.

7. The method of claim 5 in which the toner is an alkaline carbon black.

3,897,249 9 l 8. The method of claim in which the toner is a furbinder is photoconductive.

black' 11. The method of claim wherein the polymeric 9. The method of claim 5 wherein the photoreceptor is phthalocyanine in a polymeric binder.

10. The method of claim 9 wherein the polymeric 5 binder is polyvinylcarbazole.

.{ UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,897,249

.1 DATED 1 July 29, 1975 lN\/ ENTOR( 1 Joseph Mammino; Gary Whittaker It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, first line of Table I, delete "59" and insert 50.

. Column 3, line 11 of Table I, delete "SC-72" and insert XC-72.

1 Column 3, line 12 of Table I, delete "300" and 1 insert -330.

Column 4-, line 64, delete "to" and insert the--.

Column 5, line 15, delete "D R and insert D Column 6, fifth heading in Table II, delete "D and insert --D Signed and Sealedthis A tlesr:

RUTH'C. MASON Allesring Officer C. MA'RSHALL DANN ('mnmimr'mrur nj'larenrx um/ 'lrurlemurlrs O I T Q QD

Claims (11)

1. IN AN ELECTROSTATOGRAPHIC REPRODUCING SYSTEM EMPLOYING A PHTHALOCYANINE PHOTORECEPTOR AND A DRY DEVELOPER COMPRIING A CARBON BLACK TONER, INCLUDING THE STEPS OF CHANGIING SAID PHOTOCONDUCTOR, SELECTIVELY EXPOSING SAID PHOTOCONDUCTOR SO AS TO FORM A LATENT ELECTROSTATIC IMAGE AND DEVELOPING SAID PHOTOCONDUCTOR WITH SAID DRY DEVELOPER, THE IMPROVEMENT WHICH COMPRISES USING A CARBON BLACK TONER HAVING A PH OF AT LEAST 7.0 AND A CARRIER IN SAID DEVELOPING STEP.

2. The improvement of claim 1 in which the toner is a neutral carbon black.

3. The improvement of claim 1 in which the toner is an alkaline carbon black.

4. The improvement of claim 1 in which the toner is furnace black.

5. A method for reducing cycling fatigue effects on a phthalocyanine electrostatographic photoreceptor, said fatigue effects resulting from contact of said photoreceptors with developer comprising carbon black toner particles during development of electrostatic latent images thereon, which method comprises charging said photoreceptor, selectively exposing said photoreceptor and developing said photoreceptor with a dry developer comrpising a carbon black toner having a pH of at least 7.0 and a carrier.

6. The method of claim 5 in which the toner is a neutral carbon black.

7. The method of claim 5 in which the toner is an alkaline carbon black.

8. The method of claim 5 in which the toner is a furnace black.

9. The method of claim 5 wherein the photoreceptor is phthalocyanine in a polymeric binder.

10. The method of claim 9 wherein the polymeric binder is photoconductive.

11. The method of claim 10 wherein the polymeric binder is polyvinylcarbazole.

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