Патент USA US3041178код для вставки
Stes 1 715: 3,641,168 . ' re‘ Patented “June 26, 19627 1 2 using copolymer coatings are sometimes unsatisfactory? For example, in electrostatic printing processes using‘ liquid developer dispersions such as those described in Metcalf and Wright, op. cit., uneven and inadequate‘ de posit of developer particles on the charged areas of the 3,041,163 . ELECTROSTATIQ PRINTING Henry Wieliclri, Philadelphia, Pa, assignor to Radio Cor poration of America, a corporation of Delaware ' ‘ No Drawing. Filed Sept. 18, 1959, Ser. No. 840,801 , 2 Claims. (Cl. 96-1) coating results. The ?nished print in such a case is de ?cient in intensity and presents a blotchy appearance, . particularly when large areas are developed. This invention relates generally to electrostatic print ing. More particularly, it relates to improved recording elements, and methods of preparing such recording ele ' Accordingly, it is a general object'of this invention to 10 ments for use in electrostatic printing. provide improved electrostatic printing’ on ‘a surface of a photoconductive insulatin‘g'layer which includes a ?lm forming styrenebutadiene copolymer as a major constitu ‘ In the art of electrostatic printing, electrostatic images are produced on the surface of a photoconducting insu ent ‘thereof. ‘ ’ ' It is another object of this invention to‘ provide im lating material. This frequently is accomplished by ?rst producing on the surface a substantially uniform electro 15 proved photoconductive recording elementsand coatings containing a resinous ?lm-forming styrene-butadiene co static charge, as for example, by exposure to -a corona discharge device.‘ Upon exposure to a light image the electrostatic image is produced comprising areas bearing electrostatic charges ‘and 'other areas wherein electro static- charges have been substantially reduced or re polymen. _. , . . ‘ It is a further object of this invention to provide im proved methods of preparing electrophotographic re—‘ cording elements comprising a :backing member coated with a ?nely-divided pho-toconductor dispersed in a moved by the ‘exposureim light. Visible images are pro duced same charge image surface by ‘the electrostatic resinous binder at least a major portion of which is a ?lm-forming styrene-butadiene-copolymer.’ ' ' attraction of ?nely-divided developer particles to that sur It is yet another, object of this invention to provide‘ face. Methods of developing electrostatic images are de scribed in “Electrofax” Direct Electrophotogr'aphic Print 25 improved‘ methods of electrostaticipr-inting on the sur face of a photoconductive layer which includes a resinous ing On Paper, by'C. J. Young and, H. G. Greig, 'RCA Re view,’ December 1954, vol. XV, No. 4. ?lm-forming styrene-butadiene copolymer. > ' So called liquid processes for developing electrostatic images have been proposed inwhich the solid developer The foregoing objects and other advantages are ac Wright consists of ?nely-divided developer particles dis persed in' an insulating‘ liquid. This liquid developer major portion of ?hn-forming styrene-butadiene copolye complished ‘in accordance with this invention which is particles are‘ suspended in an- insulating carrier liquid. 30 based on the ,discovery that pretreatment of photocon ductive coating compositions containing a resinous ?lm-_ A liquid development process is described. by K. A. Met forming styrene-butadiene copolymer with a selectivei calf and R; ‘J. Wright in a paper entitled “Xerography,” solvent provides unusual and unexpected results. The published in‘the Journal vof the Oil and Colour Chemist’s class of coatings or layers which have been found to be Association, November. 1956, vol. 39, No. 11, London,‘ England and in another paper entitled “Liquid Devel 35 improved by such treatment includes those comprising, a ?nely-divided photoconductoi‘ dispersed in a resinous, opers for Xerography” published in the Journal of Scien binder of a ?lm-forming styrene-butadiene copolymer or,‘ ti?c Instruments, February 1955, vol. 32. ' wherein the resinous ‘binder comprises a mixture of a Brie?y, the liquid developer described by Metcalf an mer and a minor portion of another compatible resinous can be‘ flowed over ‘a surface bearing an electrostatic material or wax. ' liquid developer. The liquid developer may also be sprayed or rolled on to the surface. .Deposition of the ' developer particles on the charge image is an example 45 of the phenomenon known asrelectrophoresis or cata phores'is. v_ " v ' ' _ ' , , _ V The selective solvent employed is one having a kauri image, or the surface ‘can be immersed in a tray of 7' ‘ One'type of recording element usable in the fore butanol number of from about 20 to about 40 and which preferably is highly volatile to‘ aid in rapid drying._ The solvent is applied to the surface of the photoconductive layer on the backing member. Application to the surface of the photoconductive layer may be accomplished by‘ immersion,'spraying or washing techniques. Speci?c examples and additional advantages‘are in}v cluded in the detailed description which follows: Photoconductive coatings ‘which can be improved in» going electrostatic printing processes ‘comprises, a back ing member coated with an electrically-insulating photo 50 conductive layer .such as a particulate photoconductive accordance with this invention comprise'lOO'to 900 parts, zinc oxide suspended in a resinous polysiloxane (silicone) by weight, of a ?nely-divided photoconductor dispersed in binder. A coating alsolhas been developed which com about 100 parts, by weight, of binder. The binder corn prises a particulate photoconductive zinc oxide suspended in a'binder of a ?lm-forming resinous styrene-butadiene 55 prises a resinous ?lm-forming styrene-butadiene copoly mer including 60 to 92%, by weight, styrene and _40_ to" copolymer or in ‘a binder mixture comprising a major 8%, by Weight,’ butadienel Such a coating may be pre_-‘ proportion of the copolymer and a minor proportion of pared according to the process disclosed in U.S. Patent’ another insulating resinous material or wax which is 2,611,719, issued to Alvin'M. Borders, or the process de compatible with‘ the copolymer. ‘An important advan tage of coatings containing a styrene-butadiene copolymer 60 scribed in U.S. Patent’2,537,1l'4, issued to A_.E.‘Y_oi.1ng,v is one of cost, resins such-as silicone being much more expensive. 'Although desirable from ‘the standpoint of cost, it has‘ been found that photoconductive coatings containing a styrene'butadiene copolymer are not suitable for all elec 65 trostatic printing applications. I 'When charged with a ‘corona discharge device indgarkness (or with a safe light) ‘ et al. ‘ Example 1 A coating‘ mixture is prepared of the following formu; lation in part by weight. 45 parts photoconductive zinc~oxide ‘(FlorenceGreen‘ Seal 8, marketed by the New Jersey Zinc Sales Co, New; York, New York). I p , _' it hasbeen found that the top voltage _to which such'a 15 ‘parts, by weight, Pliolite S-SD, a high styrene-_ photoconductive coating can be charged is substantially butadiene copolymerv marketed by ‘the Goodyear Tire and less than the top voltage to which a coating containing 70 Rubber Co., Akron,‘ Ohio. silicone can be charged. Since, in many‘ applications, a 1.5 parts plasticizer. high top voltage is a prerequisite, the results obtained 100 parts toluene. 3,041,168 3 4 may be used to provide a ?nal coating thickness of from coating which has been pretreated, unevenness of deposi tion is not noticeable and the density of the image is substantially increased. Additional examples of photoconductive coatings which about 0.0003 to about 0.002 inches. may be prepared in the same manner as Example I and The mixture is milled to a smooth uniform consistency ' and is coated on the surface of a backing member such as, for example, paper. Any conventional coating process The coating is air dried or heat may be used to accelerate the drying step. which may be improved by the application thereto of Once dried, this coating has applied to it, a volatile solvent one of the forernentioned solvents include the follow such as, for example, trichlorotri?uoroethane. Upon mg: evaporation of the volatile solvent from the surface of Example 2 the coating, the recording element is ready for use in 10 Parts electrostatic printing. Florence Green Seal-8 zinc oxide, marketed by the ‘ Any solvent having a kauni-butanol number of from about 20 to about 40 may be applied to the coating to provide improved results. In adition to trichlorotri ?uoro'ethane (kauri-butanol Number 31), speci?c exam New Jersey Zinc Sales Co., New York, NY. ____, 45 Piccopale 100 resin, a methylated para?in resin marketed by the Pennsylvania Industrial Chemical 15 ples include the following: Kauri-butanol No. Petroleum ether ___________________________ __ Pentane __________________________________ __ Isohexane _ ____ __ Hexane' __ ____ __ Iso-octane Octane 6 Rubber Co., Akron, Ohio _________________ __ 25 27.5 _- 30 _ - 32 New York, NY. _________________________ __ 1.5 20 Toluene ____. 100 Example 3 ‘~ 38 Pliolite S-S for producing improved recording elements or, in the alter _ 30 l0 Aroclor 1254, plasticizer marketed by Monsanto Chemical Co., Organic Chemicals Division, St. the electrical properties of the photoconductive coating. native, solvent-treatment may be incorporated in an elec trostatic printing process. It has also been found that duration of treatment is not critical. For example, a recording element prepared as described in Example I may be given a quick dip in 1a quantity of the solvent or it may be immersed therein for several hours without any noticeable difference in results. The solvent-treated recording element may be used for electrostatic printing by any of the methods described ____._ 25 Piccopale 100 resin __________________________ __ It has been found that solvent-treatment as described above produces a substantially permanent improvement in Hence, solvent-treatment may be incorporated in a process Parts Florence Green Seal-8 zinc oxide _____________ __ 125 _ 35.5 __ 9 F-2l Plasticizer, marketed by the National Lead Co., 25 V35 Isoheptane __ Heptane Co., Clairton, Pa. ________________________ __ Pliolite S-SD, marketed by the Goodyear Tire and Louis 7, Missouri ________________________ __ 30 Toluene __________________________________ .._ 1.0 100 Example 4 Parts Florence Green Seal-8 zinc oxide _____________ __ 125 Pliolite S-S __ 25 35 Piccopale 100 resin _ _______________________ __ 5 Aroclor 5460 (a chlorinated polyphenyl resin solu ble in toluene) marketed by Monsanto Chemical Co. __ ____ __ Toluene 20 __________________________________ __ 120 ‘ in the Young and Greig publications or in the Metcalf 40 Example 5 and Wright publications op. cit. By Way of example, the Parts recording element may be placed with its pap er backing on a grounded metal plate and in darkness an electrostatic Florence Green Seal-8 zinc oxide _____________ __ 125 charging device passed over the photoconductive coating to provide a substantially uniform electrostatic charge Pliolite S—5 Toluene thereon. The next step in the process is to discharge selected areas of the charge surface of the recording ele nrent in order to produce an electrostatic image thereon. This may be accomplished by placing a photographic transparency upon the charged surface and exposing it to light through the transparency. Other exposure 1 45 Aroclor 5460 ...l ____________________________ __ 30 20 ________________ ______; ______________ _. 140 Example 7 7 Parts Florence Green Seal-8 zinc oxide ____________ __ 60 5° Pliolite s-s resin ______ _; ___________________ __ 9 Picoopale 100 resin ________________________ __ 6 processes also may be used such as, for example, projec tion and re?ection exposure. Wherever light strikes the F-Zl Plasticizer _________________________ __.__ 0.5 Toluene __________________________________ __ 100 surface of the photooonductive coating, the electrostatic Cellosolve acetate __________________________ __ 5 charge thereon is substantially reduced or removed to 55 Rose‘Bengal (Cl. 779) dissolved in methyl ethyl ketone _ _ _____ __ create a pattern of charges corresponding to the non~ illuminated areas. The electrostatic charge pattern may be converted into a visible image by any of the dry powder techniques de scribed in the Young and Greig publication, or by any Parts 60 Florence Green Seal-8 zinc oxide ______________ __ 150 Pliolite S-S resin ____________ __,_____________ __ of the so-called liquid development techniques described proved performance of the photoconducting coating de-' marketed by Barrett Division, Allied Chemical and Dye ‘Corporation, 40 Rector Street, New York 65 _____ 16 Tricresyl phosphate plasticizer ________________ __ '6, NY. _‘_ ‘ 9 Toluene ’ particles of development material are attracted to the surface than when a photoconductive coating is employed which has been so treated. This e?ect is particularly evident when the electrostatic image is developed by means of liquid processes. In the absence of treatment, the developed image exhibits an insu?ieient density and an uneveness in the deposition of developer material. On the other hand, when one employs a’photoconductive 25 Cumar T-3 a synthetic coumarone indene resin in the Metcalf and Wright publications op. cit. It is dur ing development of the electrostatic image that the im _scribed herein becomes evident. Without treatment of the photoconducting surface with a volatile solvent, fewer 0.24 Example 7 ‘ __ __ __; _______________ __"___ _____________ __ 200 Example 8 70 0 ~ -. Florence Green Seal-8 oxide _____. ____________ __ Parts 45 Pliolite S—5D _________'_.____.__.__. ____________ __ 9 Piccopale 100 _____________________________ __ 6 F~2l plasticizer ____________________________ __ 0.75 75 Toluene .....'> _ _____ 175 3,041,168 It is not known Why coatings containing styrene-buta 6 What is claimed is: diene copolym‘ers are improved as described herein other ‘ 1. In a method of electrostatic printing including the steps of producing a latent electrostatic image on the is greatly enhanced. In actual tests, one sample was surface of a photoconductive insulating material compris found to be capable of being charged to a voltage of 360 ing a ?nely-divided photoconductor suspended in a ?lm volts in darkness, whereas before it was treated with forming binder at least a major portion of which con a solvent it could only be charged up to 160 volts. An sists of a resinous styrene-butadiene copolymer and ap other sample evidenced improvement of from 200 up to plying to said surface a ?nely-divided developer sub 400 volts as a result of solvent treatment. It is known, stance to produce thereon a visible image; the improve however, that pretreatment of a resin prior to the formu 10 ment comprising applying to said surface a solvent the lation of a coating composition does not produce the active element of which is selected from the class con than that the charge storage capability of such coatings same result. Such a test was made by immersing a powder sisting of trichlorotri?uoroethane, petroleum ether, of Pliolite S-SD in trichlorotri?uoroethane for a time pentane, isohexane, hexane, isoheptane, iso-octane, octane, ~ su?ieient for the solvent to thoroughly wet all of the and mixtures thereof, and drying said coating prior to said Pliolite resin. The resin was then dried, dissolved in 15 step of producing said latent electrostatic image. toluene and a photooonductive zinc oxide dispersed there 2. The method of claim 1 wherein said solvent is trichlorotri?uoroethane. in. This mixture was coated on paper following which prints were made thereon with liquid developer disper References Cited in the ?le of this patent sions. It was found that such pretreatment of the resin provided no enhancement of development. It was fur 20 UNITED STATES PATENTS ther ?ound that subsequent immersion of such a coated 2,692,948 Lion ______ __.____'_____ Oct. 26, 1954 paper in trichlorotri?uoroethane or the other solvents de 2,875,054 Griggs et :al. _-_ _______ __,Feb. 24, 1959 scribed herein did enhance development results. No 2,891,911 Mayer et al ___________ __ June 23, 1959 explanation can be given for this phenomenon other than 2,892,709 Myer ______________ __ June 30, 1959 that the solvent treatment of a coated recording element 25 2,904,431 Moncrei?-Yeates __.______ Sept. 15, 1959 must result in some physical reordering of the photo» OTHER REFERENCES conductive surface which may result in an effect equiva lent to providing-a substantially greater surface area Payne: “Organic Coating Technology, vol. 1, page 258. capable of retaining an electrostatic charge. 30 Wiley ‘and Sons, Inc., New York, 1954. '