Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G5/00—Recording members for original recording by exposure, e.g. to light, to heat, to electrons; Manufacture thereof; Selection of materials therefor
  • G03G5/02—Charge-receiving layers
  • G03G5/04—Photoconductive layers; Charge-generation layers or charge-transporting layers; Additives therefor; Binders therefor
  • G03G5/08—Photoconductive layers; Charge-generation layers or charge-transporting layers; Additives therefor; Binders therefor characterised by the photoconductive material being inorganic
  • G03G5/087—Photoconductive layers; Charge-generation layers or charge-transporting layers; Additives therefor; Binders therefor characterised by the photoconductive material being inorganic and being incorporated in an organic bonding material

Definitions

• 96/l.8 X An electrophotographic recording material comprising KUI'Z r X a photoconductive binder layer incorporating 3 2983-220 5/1961 Dalton a] 96/l'8 X mixture of photoconductive zinc oxide particles and Elder Q colourless or white positively chargeable pigment par- 3 607 9/1971 8:51: 5? 96/118 X ticles in a ratio by weight smaller than 50:50 but not 3:634:65 1/1972 Akiyama 96/l.8 x Smaller 3.642.430 2/1972 r e X
• Preferred positively chargeable pigment particles are garmdafth zinc sulphide, barium sulphate, silica or polyethylene ran on 1 partlcles.
• Photoconductive binder type coatings prepared by incorporating a finely divided photoconductor in a binder are well known.
• the zinc oxide Since the zinc oxide has a brilliant white colour it forms an excellent base for contrasting with the developer materials applied to it. Moreover, zinc oxide is relatively less expensive and can be spectrally sensitized by a great variety of dyes. However, as already explained in the United Kingdom patent specification No. 1,256,888 filed June 6, 1968 by Gevaert-Agfa N.V. the positive corona charging of photoconductive zinc oxide binder layers is only of an acceptable level if photoconductive zinc oxide is used that has been treated with a special chemical compound improving its positive chargeability.
• the present invention is based on the discovery that electrophotographic recording materials containing photoconductive zinc oxide can be used for electrophotographic recording purposes including a positive charging by the use in the photoconductive binder type layer of a mixture of photoconductive particles and colourless or white positively chargeable pigment particles in a ratio by weight range being smaller than 50:50 but not smaller than :90.
• Preferred mixtures of dispersed photoconductive zinc oxide and positively chargeable particles are in a ratio by weight range from 30:70 to 40:60.
• the, positively chargeable particles need not to .be photoconductive and that inorganic as well as organic finely divided positively chargeable particles may be used.
• a test has been developed according to the particles involved are dispersed in a ratio of 50 to 95% by weight in an insulating binder having a resistivity of at least 10 ohm.cm and coated on a conductive base forming a layer of 10-30 microns.
• the coated layer is subjected in the dark to a positive corona charging of 6000 V till a maximum voltage level is reached.
• the dark decay is registered e.g. by means of an electrometer with vibrating electrode such as that described by C. J. Young and H. G. Greig, RCA Review (1954) XV, 469, switched to a Bruel & Kjaer Voltage Level Recorder.
• the recording layer in admixture with a suitable insulating binder or binder mixture the recording layer has preferably a resistivity which is approximately between 10 and l0 ohm.crn.
• the recording layer may contain from 50 to 97% by weight of the dispersed particles with respect to the binder material.
• a preferred ratio by weight of binder to dispersed particles is in the range of 1:4 to 1:10 parts.
• Any polymeric or resinous binding agent or mixture of polymeric binding agents already known for use in electrophotographic recording layers containing photoconductive zinc oxide may be used.
• Suitable binding agents have a resistivity that is higher than the inherent resistivity of the photoconductive zinc oxide particles.
• electrically insulating organic resinous binders of the type of polyurethanes, polyesters, polycarbonates, polystyrene, chlorinated rubber, acrylic resin, alkyd resins or vinyl acetate copolymers e.g. vinyl chloride-acetate resin.
• the binder/pig ment layers are coated from an organic solvent or solvent mixture, an emulsion of organic solvents and water or from an aqueous medium.
• Photoconductive coating compositions applied from an aqueous emulsion are described, e.g., in the US. Pat. No. 3,152,895 of Georges H. Tinker, Shu Huai, David Mai and Roger E. Burke issued Oct. 13, 1964.
• Photoconductive coating compositions applied from an alkaline aqueous binder solution are described, e.g. in the United Kingdom patent specification Nos. 1,125,579 and 1,125,580 both filed Oct. 25, 1966 by Gevaert-Agfa NV. and the US. Pat. No. 3,160,503 of Joseph H. Cady issued Dec. 8, 1964.
• the binding agent or binding agent composition has a resistivity that is lower than that of photoconductive zinc oxide grains treated with a compound as described in United Kingdom patent specification Nos. 1,020,504 and 1,020,506 both filed Dec. 29, 1961 by Gevaert Photo- Producten N.V.
• Preferred compounds for treating the photoconductive zinc oxide grains and increasing its dark-resistivity are acid ester derivatives of oxyacids of phosphorus e.g. monoand dibutyl orthophosphate.
• each of R, and R represents hydrogen, an alkyl group including a substituted alkyl group, and aryl group including a substituted aryl group, an acyl group including a substituted acyl group, e.g. an aliphatic acyl group (alcoyl) or substituted aliphatic acyl group, e.g. an acetyl group, or an aromatic acyl group (aroyl), e.g. a benzoyl group, including a substituted aromatic acyl group, or a heterocyclic nucleus including a substituted heterocyclic nucleus, e.g. a pyridine nucleus, or a thiazole nucleus, or R, and R together represent the necessary atoms to close a fused ring or ring system,
• X represents oxygen or imino, and at least one of the nitrogen atoms making part of the ring closed by Z carries a hydrogen atom, that optionally may be replaced by a cation when using the compound in salt form Said compoundsincreasing the dark-resistivity are used in combination with the photoconductive zinc oxide in preferred amounts of 0.01 to 10% by weight.
• any commercially available white zinc oxide prepared e.g. by oxidation of zinc vapour (French process) may be used.
• dyes complementary in colour to the sensitizing agent giving the recording layer an off-white appearance may be applied as described, e.g. in the United Kingdom patent specification No. 1,142,509 filed May 20, 1966 by Gevaert-Agfa N.V.
• both the photoconductive zinc oxide particles and the positively chargeable particles are dispersed homogeneously in a solution containing the dissolved insulating binding agent(s) and the obtained dispersion is applied to an electro-conductive support.
• the coating of the photoconductive layer several techniques may be used, e.g. centrifuging, spraying, brushing, roller coating, dip-coating, knife-coating or extrusion.
• the support for the recording layer preferably has a resistivity that is times as small as that of the dried recording layer in the dark. In general its resistivity is smaller than 10 ohm.cm, but preferably smaller than 10 ohm.cm.
• the supports may be made of metal, resin sheets coated with conductive layers or paper supports that contain conductive substances and/or are coated with conductive interlayers.
• Particularly suitable paper supports are those that have a high impermeability to organic solvents such as glassine paper described in the United Kingdom patent specification No. 995,491 filed Mar. 16, 1962 by Gevaert Photo-Producten N.V.
• Paper sheets that have an insufficient electric conductivity are coated or impregnated with substances enhancing their conductivity, e.g. by means of a conductive polymer overcoat or by means of a metal sheet e.g. aluminium sheet laminated to the paper.
• Substances suited for enhancing the conductivity'of a paper sheet and which can be applied'in the paper mass are hygroscopic compounds and antistatic agents are described, e.g. in the United Kingdom patent specification No. 964,877 filed May 2, 1960 by Gevaert Photo-Producten N.V. and antistatic agents of the polyionic type, e.g. CALGON CONDUCTIVE POLY- MER 261 (registered trade-mark of Calgon Corporation, Inc., Pittsburgh, Pa., USA.) for a solution containing 39.1% by weight of active conductive solids, and which contain a conductive polymer having recurring units of the following type:
• Electrophotographic materials according to the present invention can be used in any of the different techniques known in recording with the aid of photoconductors.
• Recording materials according to the present invention can be used in a recording technique comprising a negative corona charging as well as in a recording technique comprising a positive corona charging.
• EXAMPLE 1 binder composition The average grain size of the photoconductive zinc oxide and the zinc sulphide were 0.l7 micron and 1.8
• the obtained dispersion was dip-coated onto a glassine type paper support having a resistivity of 5.10 ohm.cm at relative humidity and a weight of g per sq.m and dried in a laminar air current drier by conveying air at 40C over the coating at a speed of 2 m per sec.
• the coated layer contained 35 g of pigment per sq.m.
• Column B contains analogously to column A the by weight of zinc sulphide.
• Example 1 was repeated with the difference, however, that the zinc sulphide was replaced by barium sulphate (average grain size 1.7 micron) The obtained results are listed and discussed in Table 2 hereinafter analogously to those in Table 1.
• Example I was repeated with the difference, however, that the zinc sulphide was replaced by silica (average grain size 5 micron).
• a homogeneous mixture containing the following ingredients was prepared in a sand mill:
• ALKYDAL V 15 (trade name) as a 75 by weight solution in toluene 240 ml zinc oxide, type ELECT ROX (trade name) 1,440 kg colloidal silica (average particle size 5 1) 2.160 kg by weight solution of urazole in dimethylformamide 36 ml 1 by weight solution of bromophenol blue in methanol 19 ml 0.5 by weight solution in dimethylformamide of the cyanine sensitizing dye of Example I 22 ml The dispersion was roller-coated in a ratio of 40 g of solids per sq.m. The coated layer was dried in a laminar air current drier. As supported for the coated layer a glassine type paper of 72 g per sq.m being made more conductive with sodium sulphate and calcium chloride was used.
• ALKYDAL L 67 (trade-name of Wegmanriken Bayer AG, Leverkusen, W.-Germany, for a linseed oil (67 by weight) modified alkyd resin) and 500 ccs of white spirit containing 1 l by weight of aromatic compounds are heated at 60C till a clear solution A is obtained. After cooling the solution A to room temperature, 150 g thereof are used as fixing agent for the following dispersion.
• 150 g of said solution are first ground in a ball-mill with 1.5 g of the zinc monotridecyl phosphate. whereupon 30 g of carbon black are added and at least 750 ccs of Shellsol T (trade name).
• the ob tained concentrated developer is diluted with Shellsol T (trade name) in a ratio of 15/1000.
• the developer thus obtained is very stable and yields quite erasure-proof images after evaporation of the solvent from the recording layer.
• a contrasty image having reversed image values with respect to the original was obtained.
• An electrophotographic process for producing selectively positive or negative copies of a given original comprising the steps of: uniformly corona charging a bi-chargeable photoconductive recording material comprising a photoconductive recording layer com prising an electrically insulating binder and dispersed therein a mixture of photoconductive zinc oxide particles and positively chargeable particles of the group consisting of barium sulphate, silica, and polyethylene, the ratio by weight in said layer of the photoconductive zinc oxide particles with respect to said positively chargeable particles ranging from 10:90 to less than 50:50, the recording layer containing the dispersed mixture of particles in a proportion with respect to the binder material of from 50 to 97% by weight, the zinc leaving the charges retained in the non-image aroxide particles having a grain size in the range of 0.1 to eas, and 7 15 micron and the positively chargeable particles 21 developing the exposed sheets by contacting the grain size in the range of to 50 microns, same with toner particles charged with the same said uniform charge having one polarity for positive 5

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• Chemical & Material Sciences (AREA)
• Inorganic Chemistry (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Photoreceptors In Electrophotography (AREA)
• Developing Agents For Electrophotography (AREA)

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Citations (17)

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  • BE BE786207D patent/BE786207A/xx not_active IP Right Cessation
• 1971
  • 1971-07-20 GB GB3404671A patent/GB1392929A/en not_active Expired
• 1972
  • 1972-07-07 IT IT86261/72A patent/IT970897B/it active
  • 1972-07-10 FR FR7225024A patent/FR2146746A5/fr not_active Expired
  • 1972-07-12 CA CA146,953A patent/CA981965A/en not_active Expired
  • 1972-07-18 JP JP7195672A patent/JPS5618948B1/ja active Pending
  • 1972-07-19 DE DE2235408A patent/DE2235408C2/de not_active Expired
  • 1972-07-19 US US273056A patent/US3865587A/en not_active Expired - Lifetime

Patent Citations (17)

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