US3756843A - Method of producing electrophotographic coatings - Google Patents

Method of producing electrophotographic coatings Download PDF

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Publication number
US3756843A
US3756843A US00105988A US3756843DA US3756843A US 3756843 A US3756843 A US 3756843A US 00105988 A US00105988 A US 00105988A US 3756843D A US3756843D A US 3756843DA US 3756843 A US3756843 A US 3756843A
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United States
Prior art keywords
coating
blending
photoconductive
powder
electrophotographic
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Expired - Lifetime
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US00105988A
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English (en)
Inventor
S Honjo
H Miyatuka
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Fujifilm Holdings Corp
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Fuji Photo Film Co Ltd
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    • 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
    • G03G5/05—Organic bonding materials; Methods for coating a substrate with a photoconductive layer; Inert supplements for use in photoconductive layers
    • G03G5/0525—Coating methods

Definitions

  • This invention concerns a process for the production of photoconductive compositions for use in preparing electrophotographic coating.
  • An electrophotographic Coating employed in the typical electrophotographic process which comprises uniform charging, imagewise exposure, and toner development of a photoconductive coating is usually produced by homogeneously dispersing a photoconductive powder such as zinc oxide, cadmium sulfide, or titanium dioxide, in an insulating film-forming binder thorough blending and then coating the mixture on a suitable conductive support.
  • the blending of the photoconductive powder and the resin binder is usually carried outwith the use of ball mill, sand grind mill and other dispersing means.
  • the time for blending is determined by the surface smoothness of the resulting coating formed from the blended mixture. The surface must be sufiiciently smooth so that a toner image obtained shows an acceptable level of uniformity.
  • the inorganic photoconductive powder When the blending is insufiicient, the inorganic photoconductive powder cannot be divided into minute particles having sufiiciently small particle diameters instead a large number of large agglomerates remain which are easily observed in the resulting coating. Such spots due to the agglomerates differ in electrophotographic properties from the surrounding uniform areas, thus bringing about mottles in image density or forming white spots in the developed solid image to noticeably deteriorate image resolution.
  • the time required for blending also depends to a great extent on the particle size of the photoconductive powder involved.
  • zinc oxide having an average particle diameter of 0.5 micron requires at least 6-hour ball milling though this value carries by the diameter of the mill, the size of the balls, and the amount of the zinc oxide charged in the mill. With coarser zinc oxide of more than 1 micron blending for more than 10 hours is necessary.
  • the major factor to determine the surface smoothness is the degree of dispersion of the photoconductive powder in the coating. The more minutely the powder is dispersed, the smoother the surface becomes. It should be noted that ordinary film-forming resin binders are dissolved in toluol or xylol which have poor Wetting power for many inorganic photoconductive powders. Another important factor dominating the light sensitivity of the electrophotographic coating is the ratio of the resin binder to the photoconductor. A higher content of the photoconductive powder is preferable as for light sensitivity.
  • a method is proposed, to attain the present object, in Japanese patent publication No. 13,516/68, which comprises prior to blending zinc oxide and a hinder the zinc oxide is milled in the presence of an organic liquid selected from glycol, glycol ether (monoalkylether) or anhydrous alcohol which readily wet the zinc oxide surface and decompose into minute particles.
  • an organic liquid selected from glycol, glycol ether (monoalkylether) or anhydrous alcohol which readily wet the zinc oxide surface and decompose into minute particles.
  • glycols, glycol ethers (monoalkyl ethers) or alcohols having high boiling points cannot be incorporated in binder formulations which utilize polyisocyanate cornpounds as curing agent for alkyd, epoxyester, or epoxide resins, since hydroxyl-containing solvents will deteriorate the electrophotographic properties of the resulting coatings.
  • resin binders suitable for electrophotographic coating are usually dissolved in nonpolar solvents such as toluol or xylol and insoluble in polar solvents.
  • nonpolar solvents are generally more volatile than glycols or other polar fiuidizing agents mentioned above.
  • a coating mixture containing a photoconductive powder wetted with a polar fiuidizing agent and a binder dissolved in a nonpolar volatile solvent, the nonpolar solvent will evaporate first. As drying proceeds, a point will be reached when the resin binder separates out of the solution due to the change of the solvent composition. The coating thus prepared often exhibits poor mechanical strength and low uniformity.
  • Organic solvents used as fiuidizing agent in the said patent must have a high afiinity with the inorganic photoconductive powders, and those having hydroxyl groups in the molecular structure such as alcohols, and glycol ethers (monoalkylether), are known to remarkably wet the surface of many inorganic photoconductive powders such as zinc oxide, cadmium sulfide, or titanium dioxide. This indicates that the hydroxyl radical has a strong interaction with the surface of these powders.
  • Those accomplishing this object include acetone, methylethyl ketone, diethylketone, isobutyl ketone, methyl-n-propyl ketone, cyclohexanone, benzophenone, or other ketones, pyridine, benzaldehyde, nitrobenzene, ethylenediamine, etc.
  • solvents having a high dielectric constant such as acetone have proved to readily wet the surface of inorganic photoconductive powders, and form a uniform dispersion without causing separation between the solid and liquid phases.
  • the object of the present invention is to disclose a method of producing an electrophotographic coating comprising an inorganic photoconductive powder and an insulating film-forming resin binder suited for liquid development and having a high sensitivity to light as well as an improved surface smoothness.
  • Another object of the present invention is to realize the shortening of the time required for the manufacture of an electrophotographic coating.
  • the above object can be accomplished by treating an inorganic photoconductive powder prior to blending with an insulating film-forming resin binder with an organic solvent having dielectric constant greater than 10 at 20 C. and a high dissolving power and free of hydroxyl group (typical examples are ketones such as acetone, and methylethyl ketone), then blending the binder and the thus treated photoconductive powder in a relatively brief period, obtaining a uniform coating mixture, and coating the mixture on a suitable conductive substrate to form an electrophotographic material.
  • An important advantage of the present method is that it is compatible with a wider variety of resin compositions.
  • the pre-treatment may be carried out by any type of dispersing apparatus such as ball mill, sand mill, or colloid mill, or by an emulsifier such as homogenizer or homoblender.
  • the pre-treatment may be enhanced by incorporating into the pre-treating solvent a resinous material as much as 1-2S% of the weight of the photoconductor involved or a suitable amount of surface-active agent.
  • the time for pretreatment may be about a half to two hours for ball milling, and a half to one hour for homogenizer, though it depends on the amount of photoconductor charge and the average particle diameter thereof.
  • Blending of the pre-treated photoconductor with an insulating film-forming resin binder must be completed and form a uniform dispersion as briefly as possible.
  • an emulsifying apparatus such as homogenizer or homomixer is not suitable, the optimum dispersing condition being around 5 to 10 minutes at 10,000 to 15,000 rpm.
  • an electrophotographic coating results in which the photoconductive powder is finely divided and at the same time does not contact with the resin binder, showing a high sensitivity to light as well as an acceptable smoothness of the surface.
  • spectral sensitizers When spectral sensitizers are to be incorporated in the electrophotographic coating, they may be added either at the pretreatment or blending operation. In the former case, it should be noted the sensitizers are susceptible to mechanochemical effect to lose their sensitivity, and therefore an over-grinding in a ball mill or sand grind mill should be avoided.
  • the preparation for an electrophotographic coating mixture which required blending for 5-6 hours at minimum or overnight in some cases, can be finished in only l-3 hours according to the present invention.
  • the solvents used for pretreatment or wetting of the photoconductive powder need not be removed, but is compatible with many resin formulations since they can dissolve those various materials which are rather difiicult to dissolve in many organic solvents.
  • the advantage of the invention lies in the fact that the resin formulations which employ polyisocyanate compounds as curing agent be used.
  • Resins which can be cured by polyisocyanates and form electrophotographic coatings with excellent properties include alkyd resin, epoxyester resin, vinyl copolymers containing monomer ingredients selected from hydroxyethylacrylate, hydroxyethylmethacrylate, allyl alcohol, hydroxyethylacrylamide.
  • an inorganic photoconductive powder with a rather large mean particle diameter having a high light sensitivity can be used in an electrophotographic coating.
  • zinc oxide having a mean particle diameter greater than 1 micron it requires a relatively long grinding time with a resin binder and when it is dispersed until the mixture gives a smooth surface coating the coating exhibits a sensitivity substantially equal to that given by a coating containing zinc oxide of about 0.5 micron mean diameter.
  • a coating containing the coarse zinc oxide can be obtained which exhibits a higher sensitivity than that containing the fine zinc oxide powder by the factor of 2 to even 4, when one resorts to a blending method such as by means of homogenizer for about 30 minutes.
  • the coating thus prepared possesses an extremely rough surface which is hardly acceptable for practical applications.
  • EXAMPLE I parts by weight of photoconductive zinc oxide commercially available from Sakai Chemical Industries under the trade name Tokugo with a mean particle diameter of 1.98 microns as measures by the permeametry was charged and milled in a. ball mill for together with parts by weight of acetone as the pretreating liquid for about 1 hour. Then 16 parts by weight of styrenated alkyd resin varnish commercially available from Japan Reichhold Chemicals, Inc. under the trade name Styresol 4400 and 11 parts by weight of polyisocyanate compound Desmodur 1 from Bayer Chemische Werke (Germany) were added and the mixture was transferred into a homomixer which was driven for 5-10 minutes at 12,000 r.p.m.
  • the dispersion thus prepared was spread over the metallized surface of polyethyleneterephthalate film with vacuum coated aluminum layer (trade name Metalmy from Toyo Rayon Co.) to give a dry thickness of about 5-6 micorns and dried. The drying was carried out at 50 C. for 16 hours so as to complete the curing of the binder.
  • the dried coating had a uniform surface with a smoothness similar to a' coating from a mixture prepared by griding in a ball mill jar the whole non-volatile ingredients with a suitable amount of solvent for the resin for hours without the pretreatment of the zinc oxide.
  • the sensitivity of each of these three coatings was measured in the following manner. After dark-adaptation over 2 days, a piece of the sample was negatively charged by corona discharge and the dark decay was measured.
  • V ⁇ the potential after irradiation at intensity I for a constant exposure time t sec.
  • V the potential prior to the initiation of irradiation.
  • V the initial potential at the measurement of the dark decay.
  • V designates the initial potential
  • V /V x100% Y represents the dark decay characteristic
  • the third column shows the decay of the potential when the charged sheet is wetted with purified Decalin with a voltmeter measuring probe thereon.
  • the data in the table shows that the coating (a) has a higher sensitivity than (b) has with the difierence of about 0.5 on log scale.
  • the coating (0) exhibits the fastest light speed, it has a quite rough surface. Therefore, only the coating (a) has realized a high sensitivity inherent to the zinc oxide involved not at the expense of other properties such as surface smoothness.
  • EXAMPLE II In this example, the same operations were repeated as in Example I except that the spectral sensitizers comprising 0.02 part by weight of brilliant blue FCF (Color Index No. 42090), 0.04 part by weight of eosine, and 0.05 part by weight of fiuorescein were used which were added prior to pretreatment.
  • the spectral sensitizers comprising 0.02 part by weight of brilliant blue FCF (Color Index No. 42090), 0.04 part by weight of eosine, and 0.05 part by weight of fiuorescein were used which were added prior to pretreatment.
  • EXAMPLE III parts by weight of rutile type titanium dioxide commercially available from Ishihara Sangyo Kaisha under the trade name R-840 and parts by Weight ofmethylethylketone as pretreating liquid were charged in ball mill jar and ground for 1 hour and a half. The mixture obtained was moved together with 40 parts of vinylchloride/vinyl acetate copolymer varnish (45% solid) to a homomixer which was rotated at 12,000 r.p.m. for 510 minutes. The resulting dispersion was coated to form an electrophotographic coating by the same procedures as were described in Example I.
  • the sensitivity of the coating was compared with that of another coating prepared by 15 hours ball milling in the conventional manner.
  • Table III shows a sensitivity increase by the factor of 2 by making use of the invention.
  • EXAMPLE IV This example differed from Example II only in that the formulation for the resin binder was changed to the following:
  • Vinyl copolymer comprising 34% of styrene, 51% of n-butylmethacrylate, and 15% of hydroxyethylmethacrylate; 12 parts by weight Acrylated alkyd resin-3 parts by weight Polyisocyanate (Takenate D102: from Takeda Chemical Industries)7 parts by weight A similar satisfactory result was obtained.
  • a method forming an electrophotographic coating by homogeneously dispersing a finely-divided inorganic photoconductor in an insulating film-forming binder select- TABLE I Voo ao V0 Sensitiv- V0 air, Decalin, ity 10 Surface Preparation of coating mixture V percent percent (It) 35 a smoothness (a) according to the invention, Example I -200 V 94 90 -1. 68 Good. (b) 10 hour ball milling 91 86 -2. 18 Do. (0) 10 minutes blending with homogenizer --210 95 88 -1. 65 Extremely rough.
  • the photoconductive powder is blended with an organic solvent which is free of hydroxyl groups and carboxyl groups in its molecular structure, has a dielectric constant not lower than 10 at 20 C. and can dissolve said film-forming resin binder.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Photoreceptors In Electrophotography (AREA)
  • Paints Or Removers (AREA)
US00105988A 1970-01-12 1971-01-12 Method of producing electrophotographic coatings Expired - Lifetime US3756843A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP45003426A JPS4913028B1 (enrdf_load_stackoverflow) 1970-01-12 1970-01-12

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US3756843A true US3756843A (en) 1973-09-04

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US (1) US3756843A (enrdf_load_stackoverflow)
JP (1) JPS4913028B1 (enrdf_load_stackoverflow)
BE (1) BE761253A (enrdf_load_stackoverflow)
CA (1) CA928586A (enrdf_load_stackoverflow)
DE (1) DE2101067C3 (enrdf_load_stackoverflow)
FR (1) FR2075269A5 (enrdf_load_stackoverflow)
GB (1) GB1334957A (enrdf_load_stackoverflow)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3956526A (en) * 1972-06-26 1976-05-11 Matsushita Electric Industrial Co., Ltd. Method of making a photoconductive layer for an image converting panel
US4251615A (en) * 1975-09-19 1981-02-17 Scm Corporation Viscosity stabilized photoconductive coating material and sheet material using same
US4252883A (en) * 1972-04-28 1981-02-24 Canon Kabushiki Kaisha Process for producing electrophotographic photosensitive member

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4252883A (en) * 1972-04-28 1981-02-24 Canon Kabushiki Kaisha Process for producing electrophotographic photosensitive member
US3956526A (en) * 1972-06-26 1976-05-11 Matsushita Electric Industrial Co., Ltd. Method of making a photoconductive layer for an image converting panel
US4251615A (en) * 1975-09-19 1981-02-17 Scm Corporation Viscosity stabilized photoconductive coating material and sheet material using same

Also Published As

Publication number Publication date
BE761253A (fr) 1971-06-16
CA928586A (en) 1973-06-19
FR2075269A5 (enrdf_load_stackoverflow) 1971-10-08
JPS4913028B1 (enrdf_load_stackoverflow) 1974-03-28
DE2101067B2 (de) 1974-12-19
DE2101067C3 (de) 1975-08-07
DE2101067A1 (de) 1971-07-29
GB1334957A (en) 1973-10-24

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