US 3485624 A
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nited States Patent 3,485,624 PHOTOCONDUCTIVE PROPERTIES OF POLY-N-VINYL CARBAZOLE Roger P. J. G. Thiebaut, Jean-Pierre C. G. Dubosc, and
It has also been found that much more sensitive photoconductive coatings were obtained when crystalline poly- N-vinyl carbazole was used instead of the amorphous polymer. By comparison with the amorphous poly-N-vinyl carbazole, the crystalline polymer shows a T period,
Claude A. L. L. Mercier, Vincennes, 'Frau'ce, assiguors to Eastman Kodak Company, Rochester, N a such as defined hereunder, which is more than twice poration of New Jersey smaller (about 6 to 8 seconds instead of 17 to 20 seconds) No Drawing. Filed June 7, 1966, Ser. N 55 and the practical exposure time, which is also defined f- G03g 5/ 06; Cosf 7/ 16 hereunder, is divided by a still greater factor (4 to 5 CL Z'Ckmns 10 seconds instead of 12 to 30 seconds).
In this specification, the T period is the time required for the potential of a photoconductive layer to ABSTRACT OF THE DISCLOSURE reach of the value of the potential after the initial According to the present in a Substantial charge, when said layer is subjected to an illumination of Crease in Photographic Speed Of PhOtOCOndllctiVe O 15 13,600 1x. The practical exposure time is the minimum ings containing poly-N-vinyl car azole is obta n d by exposure time in seconds, under the same 13,600 lx. heat treatment of such coatings at a temperature in the ill i tion, required to obtain the best possible image range from about I0 about I' a time Without any background fog, with magnetic brush deperiod from about 15 minutes to about 1 hour. velopment. Thus the lowest number indicates the highest photographic speed.
The heat treatment may be conducted as well on coat- This invention relates to electrophotography. More ings comprising either commercial amorphous poly-N- particularly, the invention relates to electrophotographic vinyl carbazole or on crystalline poly-N-vinyl carbazole. elements comprising a photoconductive insulating coat- Examples of commercial amorphous poly-N-vinyl carbaingonasupport. zole are Luvican M-170 or M-710 sold by Badische PolyN-vinyl carbazole is a compound used for its Anilin Soda Fabrik. Crystalline polymers with which photoconductive properties in certain reproduction procwe experimented were synthesized in our laboratory by esses which utilize electrostatic charges. Use of poly-N- the process decsribed in Belgian Patent No. 606,790. vinyl carbazole as an organic photoconductor in electro- With both amorphous and crystalline samples, the results photographic elements is described in numerous literaobtained by heat treatment were quite similar. We prefer ture references, for example, in US. Patent No. 3,037,861, the crystalline materials because they provide better repatented June 5,1962. sistance to degradation by heating. With both types,
An object of the invention is to provide improved elechowever, at the annealing temperatures used, heat detrophotographic elements comprising an annealed photogradation was slight enough to be tolerable. conductive coating containing the organic photocon- The following examples are provided to describe cerductor, poly-N-vinyl carbazole. tain preferred embodiments of the invention.
Another object of the invention is to provide a method for improving the photographic speed of photoconductive EXAMPLE 1 electrically insulating cotaings containing the organic A solution of poly-N-vinyl carbazole in benzene is photoconductor, poly-N-vinyl carbazole. prepared by dissolving 6 gm. Luvican M-170 in 100 ml. According to the present invention, a substantial inbenzene. The solution is coated on an aluminum plate crease in photographic speed of photoconductive coatings and the solvent is evaporated at room temperature in containing poly-N-vinyl carbazole is obtained by heat air, leaving a film of poly-N-vinyl carbazole coated on treatment of such coatings at a temperature in the range the metal support. The coating is electrically insulating from about 250 C. to about 300 C. for a time in the and photoconductive. The coated plate is placed in an range from about 15 minutes to about 1 hour. The higher electric oven in a nitrogen atmosphere and heated to the temperature, the shorter the time. At temperatures annealing temperature; the sample is annealed fora period lower than 250 C., the effect is negligible, whereas at in the range from about 15 minutes to about 1 hour. In temperatures above 300 C. the degradation of the Table 1 are tabulated descriptions of test results obtained polymer is too important for it to be used in a photowith samples prepared as described above and annealed conductive coating. for the times and at the temperatures shown in the table.
TABLE 1 Reduction of charge in darkness, Practical Coating Initial 3 minutes exposure thickness potential (percent time Heat treatment in microns (volts) reduction) Tlio (seconds) None 10 800 10 1. 7 30 15 111111., 250 C..- 10 1,000 33 1. 7 2 mm., 250 0.. 8 650 30 1.4 2 15 min., 275 0. s 600 19 3. 7 5 60111111., 275 C 6 490 28 1.1 1. 4 15 min., 300 c. 0 800 24 1.4 1. 4
3 The test results tabulated in Table 1 were obtained by first dark-adapting each plate for several days and then applying an electrostatic charge by means of corona discharge. The natural charge decay after 3 minutes was observed and recorded. The T 1 no period and the practical 4 may be made within the scope of the invention as described above and as defined in the following claims.
We claim: 1. A method for improving the photographic speed of electrophotographic elements comprising a support and exposure t1me Such as defined above: were also Observed coated thereon a photoconductive electrically insulating and recordedlayer comprising photoconductive poly-N-vinyl carbazole,
EXAMPLE 2 said method comprising the step of annealing said electro- The procedure of Example 1 was repeated, except that photographic element at a temperature in the rangefrom the coating solvent used was a 53/33/14 mixture of mm In the range from mlnutes benzene, methylene chloride and dioxane, with poly-N- t0 1 vinyl carbazole prepared by the process described in the 2. An lmproved electrophotographic element for use aforesaid Belgian Patent No. 606,790. In Table 2 are 1n electrophotography comprising a support and coated tabulated tests results obtained as in Example 1. thereon an annealed, electrically insulating photoconduc- TABLE 2 Reduction of charge in darkness, Practical Coating Initial 3 minutes exposure thickness potential (percent time Heat treatment in microns (volts) reduction) Ti/io (seconds) 13 1,200 12 as 4 10 1, 200 40 0.4 10 1,000 74 0.1 8 1,200 43 0.1, 10 550 78 0.3 10 s50 85 0.2 13 1,000 01 0.4 60 min., 330 0. 12 210 05 3. 5
In the last column of Table 2, the sign indicates tive coating comprising photoconductive poly-N-vinyl that the practical exposure time is too small to be carbazole, said element having been heat-annealed at a measured. temperature in the range from 250300 C. for a time In describing certain preferred embodiments of our inin the range from about 15 minutes to about 1 hour. vention, we have used coatings consisting essentially of poly-N-vinyl carbazole. However, our invention extends References Cited to use of the improvements with poly-N-vinyl carbazole UNITED STATES PATENTS 1n electrophotographic photoconductive coatings which 2 863 6 may also contain other organic polymers in combination g 2 2 Vyverberg et with poly-N-vinyl carbazole. Such coatings are described 19 2 H0631 et in the literature. Our invention further extends to use 1/1969 Inaml at 96 1-6 of the improvements with photoconductive coatings containing photoconductive poly-N-vinyl carbazole with added sensitizers, activators, and the like, of various kinds known and used in the arts relating to organic photoconductive coatings.
It will be understood that modifications and variations GEORGE F. LESMES, Primary Examiner C. E. VAN HORN, Assistant Examiner US. Cl. X.R.