Patent Application
20080020307
A charge generating layer coating dispersion was prepared as follows: 0.60 gram of TiOPc pigment was mixed with 0.113 gram of Iupilon 200 (PC-Z 200) polymer available from Mitsubishi Gas Chemical Corp. and 11.2 grams of tetrahydrofuran in a 30 mL glass bottle containing 70 grams of approximately ⅛ inch stainless steel balls. Four different compositions are made, where each composition is rolled in the roll mill for 2, 4, 6, or 8 hours, respectively. 4 gram of milled pigment dispersion from each bottle was transferred to another bottle and further diluted with a solution of 3 g tetrahydrofuran and 0.19 g of PC-Z200 to form a final coating dispersion to be used for making charge generator layer.
A charge generating layer coating dispersion was prepared according to the procedure described in Comparative Example 1 with the exception that 0.113 g of PC-Z 200 was replaced by 0.113 g PC—OH(PC—OH of the following formula with x=0.25):
Four different compositions were made, where each composition was rolled in the roll mill for 2, 4, 6, or 8 hours, respectively. 4 gram of milled pigment dispersion from each bottle was transferred to another bottle and further diluted with a solution of 3 g tetrahydrofuran and 0.19 g of PC-Z200 to form a final coating dispersion to be used for making charge generator layer.
A charge generating layer coating dispersion was prepared according to the procedure described in Comparative Example 1 with the exception that 0.113 g of PC-Z200 was replaced by 0.113 g polyvinyl butyral (BM-1, Sekisui Co.). Four different compositions are made, where each composition is rolled in the roll mill for 2, 4, 6, or 8 hours, respectively. 4 gram of milled pigment dispersion from each bottle was transferred to another bottle and further diluted with a solution of 3 g tetrahydrofuran and 0.19 g of PC-Z200 to form a final coating dispersion to be used for making charge generator layer.
Imaging member sheets are formed using the charge generating layer coating compositions of Examples 1 and 2 and Comparative Example 1. Each imaging member sheet is formed as follows: Layered photoconductive imaging members were prepared according to the following procedure. The pigment coating dispersion was coated using a Bird's bar (0.00025 inch gap) onto a titanized MYLAR® substrate of 75 microns in thickness, which had a gamma-aminopropyltriethoxy silane layer, 0.1 micron in thickness, thereover, and E.I. DuPont 49,000 polyester adhesive thereon in a thickness of 0.1 micron was used as the base conductive film. Thereafter, the photogenerator layer formed was dried in a forced air oven at 120° C. for 1 minute.
A transport layer solution was prepared by mixing 6.34 grams of N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1-biphenyl-4,4′-diamine, 6.34 grams of polycarbonate resin (available as MAKROLON® 5705 from Bayer A.G.), and 72 grams of methylene chloride. The transport solution was coated onto the above photogenerating layer using a Bird's bar of 5 mil gap. The resulting members were dried at 120° C. in a forced air oven for 1 minute. The final dried thickness of the transport layer was about 29 microns.
The xerographic electrical properties of prepared photoconductive imaging member can be determined by known means, including electrostatically charging the surfaces thereof with a corona discharge source until the surface potentials, as measured by a capacitively coupled probe attached to an electrometer, attained an initial value Vo of about −800 volts. After resting for 0.5 second in the dark, the charged members attained a surface potential of Vddp, dark development potential. Each member was then exposed to light from a filtered Xenon lamp thereby inducing a photodischarge which resulted in a reduction of surface potential to a Vbg value, background potential. The percent of photodischarge was calculated as 100×(Vddp−Vbg)/Vddp. The desired wavelength and energy of the exposed light was determined by the type of filters placed in front of the lamp. The monochromatic light photosensitivity was determined using a narrow band-pass filter. The photosensitivity of the imaging member is usually provided in terms of the amount of exposure energy in ergs/cm2, designated as E1/2, required to achieve 50 percent photodischarge from Vddp to half of its initial value, i.e. from 800 to 400 volts. The higher the photosensitivity, the smaller is the E1/2 value. The device was finally exposed to an erase lamp of appropriate light intensity (200-250 erg/cm2) and any residual potential (Vresidual) was measured. The imaging members were tested with an exposure monochromatic light at a wavelength of 780 nanometers and an erase light with the wavelength of 600 to 850 nanometers.
The Table below includes the electrical performance data for the various imaging members.
From the results, it can be seen that dispersions made with binders containing OH groups demonstrate superior stability as compared to conventional binders. For Example 1 members containing PC—OH, photosensitivity E1/2 value remained fairly constant from 2 to 8 hours of milling. For Example 2 members with BM-1, E1/2 was stable from 2 to 6 hours of milling and increased by 20% at 8 hours. Comparative Example 1 members containing standard PCZ but without hydroxyl polymer, photosensitivity degraded greatly at 6 and 8 hours of milling. E1/2 became three times of initial value at 2 hour milling. Optical measurement also provides additional evidence that the polymorphic stability of high sensitivity TiOPc is greatly enhanced by polymers containing hydroxyl groups as compared to the conventional PCZ binders.
Optical absorption spectra of TiOPc imaging members were obtained using Shimadzu Model UV-1160 spectrophotometer in the wavelength region from 400 to 1000 nm. The variation of optical absorption spectrum with milling time provided some qualitative indication of polymorphic stability of TiOPc dispersion. For example, the shift of absorption peak position, or the change in the absorbance ratio of peak (800 nm)/tail (1000 nm), would indicate a polymorphic change. Example 1 members showed stable optical absorption for all milling times. The absorption peak stayed at 800 nm and the absorbance ratio remained at about 5 in all cases. Comparative Example 1 members prepared from 8 hour milling exhibited absorbance ratio of 2 which was different from the initial ratio of 5 obtained at 2 hour milling.
It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.
