US 3615558 A
Description (OCR text may contain errors)
United States Patent Leonard M. Carreira Webster;
Vsevolod Tulagin, Rochester, both of N.Y. 560,603
June 27, 1966 Oct. 26, 1971 Xerox Corporation Rochester, N.Y.
Continuation-impart of application Ser. No. 384,737, July 23, 1964, now Patent No. 3,384,565
Inventors Appl. No. Filed Patented Assignee PHOTOELECTROPHORETIC IMAGING PROCESS EMPLOYING A FINELY DIVIDED PHTHALOCYANINE PIGMENT 10 Claims, 1 Drawing Fig.
US. Cl 96/88, 96/1 R, 96/1.2,96/1.3, 204/181, 260/314.5
 Int. Cl G030 7/00, BOlk 5/00  Field of Search 96/1, 1.5,
References Cited Primary Examiner-Charles E. Van Horn Attorneys-Stanley Z. Cole and James J. Ralabate ABSTRACT: Phthalocyanine pigments are used as e1ectrica11y photosensitive particles in a photoelectrophoretic imaging system.
PATENTE-DHET 261911 3,615,558
INVENTORS. VSEVOLOD TULAGIN EONARD M. CARREIRA BY z Kb .Qwm
A TTORNE Y5 PHOTOELECTROPHORETIC IMAGING PROCESS This application is a continuation-in-part of application Ser. No. 384,737 filed July 23, 1964 now U.S. Pat. No. 3,384,565 issued May 21, 1968. I
This invention relates in general to imaging methods. More specifically, the invention concerns the use of electrically photosensitive pigments in electrophoretic imaging systems.
There has been recently developed an electrophoretic imaging system capable of producing color images which utilizes photosensitive particles. This process is described in detail and claimed in copending applications now U.S. Pat. No. 3,384,56; 384,681 abandoned in favor of continuing application Ser. No. 655, 03 now U.S. Pat. No. 3,384,566 and A EILPHHALQQXA E.
384,680 abandoned in favor of continuing application Ser.
No. 518,041 now U.S. Pat. No. 3,383,993. In such an imaging system, various colored light absorbing particles are suspended in a nonconductive liquid carrier. The suspension placed between electrodes, subjected to a potential difference and exposed to an image. As these steps are completed, selective particle migration takes place in image configuration, providing a visible image at one or both of the electrodes. An essential component of the system is the suspended particles which must be intensely colored and electrically photosensitive and which apparently undergo a net change in charge polarity upon exposure to activating radiation, through interaction with one of the electrodes. The images are produced in color because mixtures of two or more differently colored sets of particles which are each sensitive only to light of a specific wavelength or narrow range of wavelengths are used. Particles used in this system must have both intense pure colors and be highly photosensitive. The pigments of the prior art often lackthe purity and brilliance of color, the high degree of photosensitivity, and/or periodic table. Also, it is well known that from 1 to 16 of the peripheral hydrogen atoms on the 4 benzene rings of the phthalocyanine molecule may be replaced by halogen atoms and numerous organic and inorganic groups.
Phthalocyanine is known to exist in several different 3 polymorphic forms which may be easily distinguished by comparison of their X-ray diffraction patterns and/or infrared spectra. Also, the color of the pigment varies according to the polymorphic form, the beta form being, in general, greener that the alpha or gamma forms. The alpha, beta and gamma forms of phthalocyanine are described by C. Hammon and M. Starke, inlnvestigation of the Electrical and Thermal-Electric properties of the Modification of Metal-Free Phthalocyanine," Phys. state Vol. 4, 509 (1964).A recently discovered polymorphic form of metal-free phthalocyanine, termed the xform, is described in copending application Ser. No. 505,723, now U.S. Pat. No. 3,357,989 filed Oct. 29, 1965. Several additional polymorphs of metal containing phthalocyanine are known, i.e., R0 -fonn, disclosed in U.S. Pat. No. 3,051,721; delta form described in U.S. Pat. No. 3,160,635 and another delta" form described in U.S. Pat. No. 3,150,150.
Several different forms of phthalocyanine polymers are known, Several of these phthalocyanine containing polymers are described on pages 328-337 of Phthalocyanine Compounds" by F. H. Moser and A.L. Thomas, Rheinhold Publishing Corporation, New York, 1963).
the preferred correlation between the peak spectral response and peak photosensitivity necessary for use in such a system.
it is therefore an object of this invention to provide elecin addition to the unsubstituted phthalocyanine of the above structure, various metal derivatives of phthalocyanine are known in which the two hydrogen atoms in the center of the molecule are replaced by metals from any group of the Of the compositions within the general formula listed above, the unsubstituted, metal-free phthalocyanines in the alpha and x polymorphic forms are preferred for use in an electrophoretic imaging process since they have the highest photosensitivity and most desirable color. The x" crystal form is especially preferred for use in monochromatic imaging since it has substantially panchromatic spectral response. 0n the other hand, the appha-form, or mixtures of the alpha-form with other forms, is preferred for use in ploychromatic imaging since it has the most desirable color and most appropriate spectral response for use in subtractive polychromatic imagmg.
Since the shade or tone of the phthalocyanine and the spectral and photosensitive response varies depending upon the crystal form and the substituents, intermediate values of these variables may be obtained by mixing several of the different phthalocyanines. Any suitable phthalocyanine may be used in the electrophoretic imaging processes of this invention. Typical phthalocyanines including unsubstituted metal-free phthalocyanine, aluminum phthalocyanine, aluminum polychloro phthalocyanine, antimony phthalocyanine, barium phthalocyanine, beryllium phthalocyanine, cadmium hexadecachlorophthalocyanine, cadmium phthalocyanine, calcium phthalocyanine, cerium phthalocyanine, chromium phthalocyanine, cobalt phthalocyanine, cobalt chlorophthalocyanine copper 4-aminophthalocyanine, copper bromochlorophthalocyanine, copper 4-chlorophthalocyanine, copper 4-nitrophthalocyanine, copper phthalocyanine, copper phthalocyanine sulfonate, copper polychlorophthalocyanine, deuteriophthalocyanine, dysprosium phthalocyanine, erbium phthalocyanine europium phthalocyanine, gadolinium phthalocyanine, gallium phthalocyanine, germanium phthalocyanine, hafnium phthalocyanine, halogen substituted phthalocyanine, holmium phthalocyanine, indium phthalocyanine, iron phthalocyanine, phthalocyanine, iron polyhalophthalocyanine, lanthanum phthalocyanine, lead phthalocyanine, lead polychlorophthalocyanine, cobalt hexaphenylphthalocyanine, copper pentaphenylphthalocyanine, lithium phthalocyanine, lutecium phthalocyanine, magnesium phthalocyanine, manganese phthalocyanine, mercury phthalocyanine, molybdenum phthalocyanine, napthalocyanine, neodymium phthalocyanine, nickel phthalocyanine, nickel polyhalophthalocyanine, osmium phthalocyanine, palladium phthalocyanine, palladium chlorophthalocyanine, al- -koxyphthalocyanine, alkylaminophthalocyanine, alkylmer- 'captophthalocyanine, aralkylaminophthalocyanine, aryloxyphthalocyanine, arylemercaptophthalocyanine copper phthalocyanine piperidine, cycloalkylaminophthalocyanine, dialkylaminophthalocyanine, diaralkylaminophthalocyanine, dicycloalkylaminophthalocyanine, hexadecahydrophthalocyanine, imidomethlylphthalocyanine, 1,2 naphthalocyanine, 2,3, naphthalocyanine,octaazaphthalocyanine, sulfur phthalocyanine, tetraazaphthalocyanine, tetra-4-acetylaminophthalocyanine, tetra-4-aminobenzoylphtalocyanine, tetra-4- aminophthalocyanine, tetrachloromethylphthalocyanine, tetradiazophthalocyanine, tetra-4,4 dimethyloctaazapthalocyanine, tetra-4,S-diphenylene-dioxide phthalocyanine, tetra- 4,5-diphenyloctaazaphthalocyanine, tetra-( 6-methylbenzothiazoyl) phthalocyanine, tetra-p-methylphenylaminophthalocyanine, tetra-methylphthalocyanine, tetranaphthotriazolphthalocyanine, tetra-4-naphthalocyanine, tetra-4-nitrophthalocyanine, tetra-peri-naphthylene-4,5-octatazaphthalocyanine, tetra-2,3-phenylenexoide phthalocyanine, tetra-4-phenyloctaazaphthalocyanine, tetraphenylphthalocyanine, tetraphenylphthalocyanine tetracarboxylic acid, tetraphenylphthalocyanine tetrabarium carboxylate, tetraphenylphthalocyanine tetra-calcium carboxylate, tetrapyridyphathalocyanine, tetra-4-trifluoro-methylmercaptophthalocyanine, tetra-4-trifluoromethylphthalocyanine, 4,5- thinonaphthene-octaazaphthalocyanine, platinum phthalocyanine, potassium phthalocyanine, rhodium phthalocyanine, samarium phthalocyanine, silver phthalocyanine, silicone phthalocyanine, sodium phthalocyanine, sulfonated phthalocyanine, thorium phthalocyanine, thulium phthalocyanine, tin chlorophthalocyanine, tin phthalocyanine, titanium phthalocyanine, uranium phthalocyanine, vanadium phthalocyanine, ytterbium phthalocyanine, zinc chlorophthalocyanine, zinc phthalocyanine, Together with, or in lieu of, the above phthalocyanines, any suitable mixture, dimer, trimer, oligomer, polymer, copolymer or mixtures of phthalocyanines may be used, The phthalocyanine may also be in any suitable crystal form. I
The use of the above compositions and electrophoretic imaging will be better understood upon reference to the draw ing which shows schematically and exemplary electrophoretic imaging system.
Referring now to the figure,.t here is seen a transparent electrode generally designated 1 which, in this exemplary instance, is made up of a layer of optically transparent glass 2 overcoated with a thin optically transparent layer 3 of tin oxide, commercially available under the name NESA glass. This electrode will hereafter be referred to as the injecting electrode." Coated on the surface of injecting electrode 1 is a thin layer 4 of finely divided photosensitive particles dispersed in an insulating liquid carrier. The term photosensitive," for the purposes of this application, refers to the properties of a particular which, once attracted to the injecting electrode, will migrate away from it under the influence of an applied electric field when it is exposed to actinic electromagnet radiation. For a detailed theoretical explanation of the apparent mechanism of operation of the invention, see the above-mentioned copending applications Ser. Nos. 384,737; 384.361 and 384,680, the disclosures of which are incorporated herein by reference. Liquid suspension 4 may also contain a sensitizer and/or a binder for the pigment particles which is at least partially soluble in the suspending or carrier liquid as will be explained in greater detail below. Adjacent to the liquid suspension 4 is a second electrode 5, hereinafter called the blocking electrode," which is connected to one side of the potential source 6 through a switch 7. The opposite side of the potential source 6 is connected to the injecting electrode 1 so that when switch 7 is closed, an electric field is applied across the liquid suspension 4 between electrodes 1 and 5. An image projector made up of a light source 8, a transparency 9, and a lens 10 is provided to expose the dispersion 4 to a light image of the original transparency 9 to be reproduced. Electrode 5 is made in the form of a roller having a conductive central core 11 connected to the potential source 6. The core is covered with a layer of a blocking electrode material 12, which. may be I Baryta paper. The pigment suspension is exposed to the image to be reproduced while a potential is applied across the blocking and injecting electrodes by closing switch 7. Roller 5 is caused to roll across the top surface of injecting electrode 1 withswitch 7 closed during the period of image exposure. This light exposure causes exposed pigment particles originally attracted to electrode 1 to migrate through the liquid and adhere to the surface of the blocking electrode, leaving behind a pigment image on the injecting electrode surface which is a duplicate of the original transparency 9. After exposure, the relatively volatile carrier liquid evaporates off, leaving behind the pigment image. This pigment image may then be fixed in place as, for example, by placing a lamination over its top surface or by virtue of a dissolved binder material in the carrier liquid such as parafiin wax or other suitable binder that comes out of solution as the carrier liquid evaporates. About 3 percent to 6 percent by weight of parafiin binder in the carrier has been found to produce good results. The carrier liquid itself may be paraffin wax or other suitable binder. In the alternative, the pigment image remaining on the injecting electrode may be transferred to another surface and fixed thereon. As explained in greater detail below, this system can produce either monochromatic or polychromatic images depending upon the type and number of pigments suspended in the carrier liquid and the color of light to which this suspension is exposed in the process.
Any suitable insulating liquid may be used as the carrier for the pigment particles in the system. Typical carrier liquids are decane, dodecane, N-tetradecane, paraffin, beeswax or other thermoplastic materials, Sohio Odorless Solvent 3440, (a kerosene fraction available from Standard Oil Company of Ohio and lsopar-G, (a long chain saturated aliphatic hydrocarbon available from Humble Oil Company of New Jersey). Good quality images have been produced with voltages ranging from 300 to 500 volts in the apparatus of the figure.
In a monochromatic system, particles of a single composition are dispersed in the carrier liquid and exposed to a blackand-white image. A single color image results, corresponding to conventional black-and-white photography. in a polychromatic system, the particles are selected so that those of different colors respond to different wavelengths in the visible spectrum corresponding to their principal absorption bands. Also, the pigments should be selected so that their spectral response curves do not have substantial overlap, thus allowing for color separation and subtractive multicolor image formation. In a typical multicolor system, the particle dispersion should include cyan colored particles sensitive mainly to red light, magenta particles sensitive mainly to green light and yellow colored particles sensitive mainly to blue light. When mixed together in a carrier liquid, these particles produce a black appearing liquid. When one or more of the particles are caused to migrate from base electrode 1 toward an upper electrode, they leave behind particles which produce a color equivalent to the color of the impinging light. Thus, for example, red light exposure causes the cyan colored pigment to migrate, leaving behind the magneta and yellow pigments which combine to produce red in the final image. In the same manner, blue and green colors are reproduced by removal of yellow and magenta, respectively. When white light impinges upon the mix, all pigments migrate, leaving behind the color of the white or transparent substrate. No exposure leaves behind all pigments which combine to produce a black image. This is an ideal technique of subtractive color imaging in that the particles are not only each composed of a single component but, in addition, they perform the dual functions of final image colorant and photosensitive medium.
It has been found that the compounds of the general formula given above are surprisingly effective when used in either a single or multicolor electrophoretic imaging system. Their good spectral response and high photosensitivity result in dense, brilliant images. The pigments herein disclosed have suprisingly good color separation and image density characteristics.
Any suitable different colored photosensitive pigment particles having the desired spectral responses may be used with the pigments of this invention to fon'n a pigment mix in a carrier liquid for color imaging, From about 2 to about percent pigment by weight have been found to produce good results. The addition of small amounts (generally ranging from 0.5 to 5 percent) of electron donors or acceptors to the suspensions may impart significant increases in system photosensitivity.
The following examples further specifically define the present invention with respect to the use of the compositions of the general formula given above in electrophoretic imaging processes. Parts a percentages are by weight unless otherwise indicated. The examples below are intended to illustrate various preferred embodiments of the electrophoretic imaging process of the present invention.
All of the following examples are carried out in an ap paratus of the general type illustrated in the figure with the imaging mix 4 coated on a NESA glass substrate through which exposure is made. The NESA glass surfaced is connected in series with a switch, a potential source, and the conductive center of a roller having a coating of Baryta paper on its surface. The roller is approximately 2%inches in diameter and is moved across the plate surface at about 4 cm. per second. The plate employed is roughly 4 inches square and is exposed with a light intensity of about 4,000 ft./candles as measured on the uncoated NESA glass surface. Unless otherwise indicated, 8 percent by weight of the indicated pigment and each example is suspended in Sohio Odorless Solvent 3440. All pigments which have a relatively large particle size as received commercially or as synthesized are ground in a ball mill for about 48 hours to produce their size to provide a more stable dispersion which improves resolution of the final image. In examples I -X, the exposure is made with a 3,200 K. lamp through a 0.30 neutral density step wedge filter to measure the sensitivity of the suspensions to white light and then Wratten filters 29, 61 and 47 b are individually superimposed over the light source in separate tests to measure the sensitivity of the suspensions to red, green and blue light respectively.
EXAMPLE] About eight parts of Monarch Green Toner, a polychloro copper phthalocyanine, C. I. No. 74,260, available from Imperial Color and Chemical Company, is suspended in about 100 parts of Sohio Odorless Solvent 3440 The mixtures coated on the NESA glass substrate and a positive potential of about 2,500 volts is imposed on the roller electrode. The plate is exposed in separate runs to white, red, green and blue light as described above. The results are tabulated in table I, below. As can be seen from the table, this pigment is sensitive to red light.
EXAMPLE ll About eight parts of Cyan Blue GTNF, the beta form of copper phthalocyanine, C. I. No. 74160, available from American Cyanamide is suspended in about 100 parts of Sohio Odorless Solvent 3440. The mixture is coated on a N ESA glass substrate and the plate is exposed as in example 1. Here, the potential imposed is +2.500 volts. Sensitivity is indicated in table 1.
EXAMPLE "I About eight parts of Cyan Blue BNF, the alpha form of copper phthalocyanine, C. I. No. 74160, available from American Cyanamide is suspended in about 100 parts of Sohio Odorless Solvent 3440. The mixture is exposed to a stepwedge filter through a color filter while a positive potential of about 2,500 volts is imposed on the roller electrode. As indicated in table 1, this pigment has fairly low sensitivity.
About eight parts of Cyan Blue XR, the alpha form of copper phthalocyanine, available from American Cyanamide is suspended in about 100 parts Sohio Odorless Solvent 3440. This mixture is coated onto four NESA glass substrates, each of which is exposed through a neutral density step-wedge filter and a color filter as described above. In each case, the potential applied is 2,500 volts. As indicated in table I, this pigment has good sensititvity, primarily to red light.
EXAMPLE V About eight parts of Monarch Blue G, copper phthalocyanine, available from Imperial Color and Chemical Company, is suspended in about parts Sohio odorless Solvent 3440. The mixture is coated on several NESA glass substrates and exposure in this instance is 2,500 volts. As shown by table I, this pigment has high sensitivity.
EXAMPLE VI About eight parts of the beta form of metal-free phthalocyanine is suspended in about 100 parts of Sohio Odorless solvent 3440. This pigment is prepared by milling Monolite Fast Blue GS, the alpha form of metal-free phthalocyanine, C. I. No. 74100, available from the Arnold Hofiman Company, in o-dichlorobenzene. The suspension is coated onto N ESA glass substrate and imaging tests are performed as described above. A positive potential of about 2,500 volts is maintained on the roller electrode during exposure. A second set of tests is then run with a negative potential. As is indicated in table I, this pigment has high sensitivity.
EXAMPLE Vll About eight parts of Monolite Fast Blue GS, the alpha form of metal-free phthalocyanine, C. I. No. 74100, available from the Arnold Hoffman Company is suspended in about lOO parts of Sohio Odorless Solvent 3400. The mixture is coated onto NESA glass substrates and imaged as described above. A positive potential of about 2,500 volts is maintained on the roller electrode during imaging. A second set of tests is run with a negative potential. As indicated in table I, this pigment has high sensitivity.
About eight parts of Non-Floc Green Shade Phthalocyanine Blue Lake, benzoated copper phthalocyanine, available from Harmon colors, is suspended in about 100 parts of Sohio Odorless Solvent 3440. The suspension is coated on several NESA glass substrates and images are produced as described above. A positive potential of about 2,500 volts is maintained on the roller electrode during imaging. As'indicated in table I, this pigment has good sensitivity, responding only to red light.
EXAMPLE lX A sample of commercial Monolite Fast Blue GS is heated in an oxygen atmosphere at about 320 C. for about Ix hours. This appears to give the beta form of metal-free phthalocyanine. About eight parts of this pigment is suspended in about 100 parts of Sohio Odorless Solvent 3400. The suspension is coated onto a plurality of NESA glass substrates. A set of imaging tests as described above is performed with the roller electrode held at a positive potential of about 2,500 volts. A second set of imaging tests in then performed with the roller electrode at a negative potential of about 2,500 volts. As indicated in table l, the positive roller potential gives higher sensitivity.
EXAMPLE X About eight parts of the x form of phthalocyanine, prepared as described in copending application Ser. No. 505,723, filed Oct. 29, i965, is suspended in about 100 parts of Sohio Odorless Solvent 3400. Two sets of Nesa glass substrates are coated with the suspension. The first is imaged as described above, while the roller electrode is held at a positive potential of about 2,500 volts. The second set is imaged while the roller electrode is held at a negative potential of about 2,500 volts. As indicated in table I, this form of phthalocyanine has a substantially panchromatic response.
The electrophoretic sensitivity of the pigments to red,
green, blue, and white light is tested according to conventional photographic methods and the results are recorded in table I above. In the table, the first column lists the number of the test example. The second column gives the positive or negative electrical potential applied to the roller electrode in volts. The third through sixth columns give the photographic speed of the various suspensions to blue, green, red and white light respectively in camera stops. The sensitivity is a measure of the exposure necessary to produce a visible image on the NESA surface as determined by the number of step-wedge filter steps of migrated pigment visible on the NESA. Thus, for example, in example I, red light will produce an image at a250f.c. exposure while white light will produce an image at 125 f.c. exposure. As shown by the above table, the tested pigments are primarily sensitive to red light. As discussed above, for polychromatic imaging, it is preferred that cyan pigments be responsive only to red light. On the other hand, as shown by example X, some forms of phthalocyanine are substantially sensitive to all colors of light and would be preferred for use in a monochromatic system.
in each of examples XI-XV below, a suspension including equal amounts of three different pigments is made up by dispersing the pigments in finely divided form in Sohio Odorless Solvent 3400 so that the pigments constitute about 8 percent by weight of the mixture. This mixture may be referred to as a trimix. The mixtures are individually tested by coating them on a NESA glass substrate and exposing them as in example I above, except that a multicolor Kodachrome transparency is interposed between the light source and the NESA plate instead of the neutral density and Wratten filters. Thus, a multicolored image is projected on the suspension as the roller moves across the surface of the coated NESA glass substrate. A Baryta paper blocking electrode is employed and the roller is held at a negative potential of about 2,500 volts with respect to the substrate. The roller is passed over the substrate six times. The roller is cleaned after each pass. The potential application and exposure are both continued during the entire period of the six passes by the roller.
EXAMPLE XI The pigment suspension consists of a magenta pigment, Watchung Red B, the barium salt of l-(4'-methyl-5'- chloroazobenzene-2-sulfonic acid)-2-hydroxy-3-naphthoic acid, C. I. No. 15865, available from E. I. duPont de Nemours & Company; a yellow pigment, Algol yellow GC, C. I. No. 67300, l,2,5,6-di(C,C'-diphenyl)-thiazole-anthraquinone available form General Dyestuffs; and as a cyan pigment, Monolite Fast Blue GS, the alpha form of metal-free phthalocyanine, C. I. No. 74100, available from the Arnold Hoffman Company, This trimix, when exposed to a multicolor image as described above, produces a full color image with good density and excellent color separation.
EXAMPLE XII The pigment suspension consists of a magenta pigment, Bonadur Red B. l-(4'-ethyl-5-chloroazobenzene-2'-sulfonic acid)- 2-hydroxy- 3 -naphthoic acid calcium lake, available fromAmerican Cyanamide; a yellow pigment, N-2"-pyridyl- 8,13-dioxadinaphtholfuran- 6-carboxamide, prepared as described in copending application, Ser. No. 421,281, filed Dec. 28, 1964 and as a cyan pigment, Cyan Blue XR, the alpha form of copper phthalocyanine, C. I. No. 74160, available from American Cyanamide. This trimix is exposed to a multicolor image and produces a full color image of good density and color separation.
EXAMPLE XIII A pigment suspension is prepared consisting of a magenta pigment, Naphthol Red B, l-(2'-methoxy5.'-nitrophenylazo)-2 -hydroxy-3'-nitro-3-naphthanilide, C. I. No. 12355, available from Collway Colors; a yellow pigment, l-cyano-2,3-(3'- nitrol-phthaloyl-7, benzopyrrocoline prepared as described in copending application Ser. No. 445,235, Apr. 2, 1965; and as a cyan pigment, Cyan Blue GTNF, the beta form of copper phthalocyanine, available from Collway Colors. This trimix is exposed to a multicolor image and produces a full color image of satisfactory density and good color separation.
EXAMPLE XVI EXAMPLE XV EXAMPLE XV A pigment suspension is prepared consisting of a magenta pigment, Naphthol Red B, l-(2'-methoxy-5'-nitrophenylazo 2-hydroxy-3"-nitro-3-naphthanilide, C. I. No. 12355; a yellow pigment, l-cyano-2,3-(3'-nitro)-phthaloyl-7,8-benzopyrrocoline; and as a cyan pigment, zinc phthalocyanine. This trimix is exposed to a multicolor image and produces a full color image of satisfactory density and good color separation.
EXAMPLE XVI A pigment suspension is prepared consisting of a magenta pigment Bonadur Red B, l-(4-ethyl-5'-chloroazobenzene-2'- sulfonic acid)-2-hydroxy-3-naphthoic acid calcium lake; a yellow pigment, N-2-pyridyl-8,l3-dioxodinaphtho-(2,l-b;2,3 d)-furan-6-carboxamide; and as a'cyan pigment, the gamma form of metal-free phthalocyanine. This trimix is exposed to a multicolor image and produces a full color image of good density and color separation.
Although specific components and proportions have been described in the above example relating to the use of phthalocyanines in electrophoretic imaging systems, other suitable phthalocyanines, as listed above, may be used with similar results. In addition, other materials may be added to the pigment compositions or to the pigment-carrier suspensions to synergize, enhance or otherwise modify their properties. For example, the pigments or the suspensions may have electrical or dyesensitizers added if desired.
Other modifications and ramifications of the present invention will occur to those skilled in the art upon a reading of the present disclosure. These are intended to be included within the scope of this invention.
What is claimed is:
1. A photoelectrophoretic imaging suspension comprising a substantially insulating carrier liquid having dispersed therein electrically photosensitive particles of at least two colors each of said particles comprising an electrically photosensitive pigment said pigment being both the primary colorant and the primary photosensitive ingredient for the particle, said pigment having a principal light absorption band which substantially coincides with its principal photosensitive response, and wherein the spectral response curve for particles of a single color does not substantially overlap the spectral response curve for particles of a different color, said electrically photosensitive particles of at least one color comprising finely divided phthalocyanine pigments.
2. The imaging suspension of claim 1 wherein said phthalocyanine is a metal-free phthalocyanine.
3. The imaging suspension of claim 1 wherein said phthalocyanine is a metal-free phthalocyanine selected from the group consisting of the alpha polymorphic form of metal-free phthalocyanine, the beta polymorphic form of metal-free phthalocyanine and the X-polymorphic form of metal-free phthalocyanine and mixtures thereof.
4. The imaging suspension of claim l wherein said phthalocyanine is a metal containing phthalocyanine.
5. The imaging suspension of claim 1 wherein said phthalocyanine is a metal containing phthalocyanine selected from the group consisting of copper phthalocyanine, zinc phthalocyanine and mixtures thereof.
6. The method of photoelectrophoretic imaging comprising the steps of:
a. providing a first substantially transparent electrode;
b. providing an imaging suspension comprising electrically photosensitive particles of more than one color dispersed in an insulating carrier liquid each of said particles com prising an electrically photosensitive pigment said pigment being both the primary colorant and the primary photosensitive ingredient for the particle, said pigment i0 having a principal light absorption band which substantially coincides with its principal photosensitive response, and wherein the spectral response curve for particles of a single color does not substantially overlap the spectral response curve for particles of a different color, said electrcially photosensitive particles of at least one color comprising a finely-divided phthalocyanine pigment;
c. providing a second electrode;
d. placing said imaging suspension between said first and second electrodes;
e. applying a potential difference between said first and second electrodes across said imaging suspension; and
f. exposing said imaging suspension to a pattern of activating electromagnetic radiation until an image is formed.
7. The method of claim 6 wherein said phthalocyanine is a metal-free phthalocyanine.
8. The method of claim 6 wherein said phthalocyanine is a metal-free phthalocyanine selected from the group consisting of the alpha polymorphic form of metal-free phthalocyanine, the beta polymorphoric form of metal-free phthalocyanine, the X-polymorphic form of metal-free phthalocyanine and mixtures thereof.
9. The method of claim 6 wherein said phthalocyanine is a metal containing phthalocyanine.
10. The method of claim 6 wherein said phthalocyanine is a metal containing phthalocyanine selected from the group consisting of copper phthalocyanine, zinc phthalocyanine and mixtures thereof.