DE1797099A1 - Electrophotographic process with electrostatic charging of the surface of a photoelectrically conductive insulating layer - Google Patents

Description

PATENTANWXLTI DR. E. WIEGAND DIPL-ING. W. NIEMANN 1 7 Q 7 Π Q Q DR. M. KÖHLER DIPL-ING. C GERNHARDT »/ U / U 5Y MONKS HAMIUIO

55547 ". θοοο monks 15, 16 August 1968

.ilEGIAMME. CARFATENT NUSSLAUMSTIASSf M

826/68 5 / Ln

Shashin movie Kabushiki Kaisha Kanagawa (Japan)

Electrophotographic process β «β electrostatic Charging the surface of a photoelectrically conductive insulating layer.

The invention relates to an electrophotographic Process including charging of a photoelectrically conductive insulating layer by means of friction.

Since electrophotography generally uses electrostatic latent images, it is included herein

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Method for creating a photoelectrically conductive Isolation layer enclosed with a free electrostatic charge. '·

Corona discharge is widely used and it is also a charging method by means of a simple device commonly used in which the surface of a recording layer with a suitable Material is rubbed to make a triboelectric To achieve charging.

One such method is disclosed in U.S. Patent No. 2,297,691 and are additional in addition, a number of patent applications relating to this subject have been published in recent years been.

In der.Untersuchen the composition of electrophotographic photosensitive materials and Beibungs- materials, as well as suitable combinations thereof, it was found that when a photosensitive layer is rubbing, the main component of which is a photoelectrically conductive semiconductor of the n-type, such as. B. photoelectrically conductive zinc oxide, lithium dioxide, etc. dispersed in a binder such as Vinylohlorid-Vinylacetatοopolymerisat, includes, with a üeibunge- '"''■' - ■ material in the triboelectric

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Series in contrast to the photoelectrically conductive Layer on the positive side, a copy of far better quality compared to other combinations can be obtained.

Many suitable insulating binders in connection with the zinc oxide are known and polysiloxane resin, alkyd resin, i ^ -ioxyester, polyacrylic ester, polymethacrylic ester and styrene containing polymers are particularly known. With regard to triboelectric properties, all of these are available Resins are relatively on the positive side and powdery zinc oxide is also extremely on the positive side. Extreme on the positive side, as mentioned above, means that compared to ethyl cellulose (ethoxydated Percentage 47.5 to 49.0%) empirical as typical Example of a positively chargeable resin was chosen, powdered zinc oxide further on the positive side than this stands. Likewise, nitrocellulose can be selected as a typical negatively chargeable resin. Accordingly, the Rubbing a photosensitive layer composed of any of the positively chargeable resins mentioned above exists that are commonly considered typical, and zinc oxide with a suitable friction material, these are positively charged, but when developing this photosensitive layer can in no case

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a "satisfactory visible image can be obtained. It is believed that this is due to the fact that the zinc oxide layer is used as an n-type semiconductor layer reacts and therefore the electrical charges,

even when this layer is charged, immediately disappear. A high density image will be listed below Cases also difficult to obtain. Even when using an insulating material as a carrier material or when applying a relatively thick insulating layer between a conductive substrate and a sensitive one Layer, satisfactory images cannot be obtained. Even if to reduce the leakage effect first an image exposure is applied to a photosensitive layer and then its surface with a Friction material in a liquid developer comprising an insulating liquid as a carrier liquid, is rubbed, a good image cannot be obtained.

In the meantime, vinyl chloride copolymers are known as' negatively chargeable resins, Nitrocellulose, vinylidine chloride copolymers and the like are available. As a result of the Formation of photosensitive layers by dispersing zinc oxide in these layers has been found to be the latter two had low charge acceptance and were difficult to stably handle. · <

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On the other hand, it has been experimentally confirmed that when a photoelectrically conductive insulating layer is rubbed, which consists of vinyl chloride-vinyl acetate copolymer and zinc oxide, with a: friction material, which is strongly on the positive side in the triboelectric series by comparison Extremely high quality image can be obtained, regardless of whether or not such a charging process is g-1 before or after exposure.

The quality of the image obtained by this method differed very favorably from that using a normal corona loading process obtainable and such a satisfactory result could only in the case of the combination of vinyl chloride-vinyl acetate copolymer and zinc oxide or other η-type photoelectrically conductive materials will.

The binder may contain a small amount of a plasticizer, but such a compound tends to stain the surface of the friction material with repeated use and, therefore, its use is avoided whenever possible. With regard to other constituents, polymers with non-migrating properties are desirable. For example, alkyd resins modified with vegetable oil are available,

Epoxy ester resins and alkyds modified with vinyl monomers

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. resins available.

Because -all these components are strongly positively charged they should not be added in excessive amounts will. A composition of 60 parts by weight

Parts by weight of vinyl chloride-vinyl acetate copolymer and 4o / others Ingredients is considered to be the limit of the binder composition. If you carry out a liquid development, it is desirable to first cure the above-mentioned alkyd resins, epoxy ester resins and the like by means of a curing agent in order to improve charge acceptance properties to improve in the liquid.

A vinyl chloride-vinyl acetate copolymer having a content of more than $ 5> and less than 45 wt # acetate is suitable. Polyvinylchloridhomopolymerisat is difficult in many solvents to dissolve while i> acetate also reduce a content of more than 45, the insulating properties and the beneficial triboelectric charging characteristics of polyvinyl chloride.

As carrier materials, those which generally have good conductivity can be used, but it can an insulating base material can also be used in the case of friction after exposure.

Regarding the η-type photoelectrically conductive Materials that can be used in the method according to the invention can be titanium dioxide, zinc oxide, cadmium sulfide, Cadmium sulfide-oadmium carbonate solution and cadmium

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List sulfide-zinc sulfide mixed crystals and the like. Mixtures of these compounds can be used at the same time.

As a triboelectric charging material for a photosensitive material, that which further on the positive side than the photoelectrically conductive layer in the triboelectric Series and has suitable mechanical properties, preferred. Such are velvet cloth, rayon, Wool, tanned leather, nylon cloth and polyurethane sponge are particularly desirable.

In this process, a considerably high surface potential is obtained and therefore the combined use of a development process that guarantees particularly high sensitivity, not always an absolute requirement to obtain an image, that is, a high density image by means of cascade development and magnetic brush development, etc. can be obtained. A picture better Quality can be obtained by means of the liquid development. In this case, if non-polar hydrocarbons or florinated hydrocarbons are used as carrier liquids, the surface charges maintained even in the liquid for a long time, thereby making it possible to produce excellent To get images that only have a slight edge effect

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exhibited. Such properties are superior to the one Properties of the vinyl chloride-vinyl acetate copolymer traced back.

In general, a high resolution image can be obtained by means of the liquid development, but how as is well known, this development process tends to form fog in the background. Accordingly, that can methods set out below as a particularly desirable modification of the method according to the invention be considered. It is doing this the friction between one. Frictional material and a delicate one Layer caused by an insulating liquid. This

Image process can be done before or after / exposure. When using this procedure, the Fog density remarkably decreased. This mechanism can be explained as follows. When forming a thin layer of an insulating liquid on the surface of the photosensitive layer is the adhesion of the toner on the surface of the photosensitive layer due to forces other than electrostatic forces (adsorption attraction, sticking to surface irregularities etc.), remarkable in the subsequent development process decreased. Likewise, if the charge "acceptance a sensitive layer in the insulating liquid

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higher than in the carrier liquid; the developer is, the life of a latent image is extended and the image density is increased due to the existence of a such thin liquid layer is enlarged. In general, the liquid to be used is first a purified, highly insulating, non-polar! liquid and contains the carrier liquid of the developer Resins and other ingredients, whereby the above requirement is met.

The liquid to be applied during the rubbing should be miscible with a subsequently applied developer and should not attack a light-sensitive layer. Typical examples are aliphatic ^, alicyclic and fluorinated hydrocarbons.

The method according to the invention enables extremely easy electrical image transmission (electrography) and creates a compact copying machine and therefore possesses from the technical and economical point of view great value.

Likewise with an electrophotographic

Process in which the photoelectrically conductive layer

on
after image exposure / charging, the method according to the invention, in which charging by means of friction is applied, more advantageously uses than a method

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in which corona discharge is applied, since when the photoelectrically conductive layer before charging

on is exposed and then by means of Oorona discharge / charged If the photoelectrically conductive after-effect is used, usually no sharp images can be obtained.

This phenomenon can be explained as follows.

If you consider the delimitation of an exposed and an unexposed area, the conductivity remains the former is higher while the latter is lower.

Accordingly, when both surfaces are subjected to corona discharge, charges hardly accumulate in the the former area, while the potential of the latter area is quickly consumed.

Furthermore, the corona discharge then becomes a preferred deposition of corona ions on the exposed

on surface cause by the neighboring / charged Face of the same polarity are repelled. Accordingly, the exposed areas recover, the unexposed areas Surfaces are adjacent and which receive a higher concentration of corona ions, faster from a light avoidance than the other exposed areas.

Since such a phenomenon occurs immediately after starting Oorona discharge charging, an image of indistinct sharpness is obtained.

t

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On the other hand, "in the method according to FIG

Invention using frictional charging

Image after exposure, an image without the above

Cons received.

The method according to the invention is explained in more detail below with reference to Beispfe len.

example 1

'A photosensitive layer, the loo parts of a 4 | photoelectrically conductive zinc oxide powder and 25 parts of a vinyl chloride-vinyl acetate copolymer (with a Content of 35 wt .- ^ vinyl acetate) included, was in a Thickness of about 5yu on a conductive one Paper applied. After the dark adaptation of the layer, an image exposure was first carried out by means of a contact exposure applied. Then the photosensitive paper was in a liquid developer which is a paste of a kneaded mixture of phthalocyanine blue pigment and natural resin modified phenol formaldehyde resin in cyclohexane ' dispersed, dipped, and the surface of the photosensitive layer was lightly covered with several times rubbed with a polyurethane sponge. The pigment remained positively charged in the liquid, while that with polyurethane cracked photosensitive layer was negatively charged, whereby an attractive development could be achieved. The picture was quite sharp and had no blurred outlines along the perimeter of the picture as one would see it in the common electrophotographic method of

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Kalmann can observe, and the image density was also very satisfactory.

In another embodiment of the invention the rubbing was carried out in kerosene containing no toner particles, and thereafter the photosensitive one became Put paper in the developer mentioned above.

as a result, a fog density lower than that in the above-mentioned Pail can be obtained could.

Example 2

A photosensitive layer consisting of 50 parts of photoelectrically conductive titanium dioxide, 5o parts of photoelectrically conductive zinc oxide, 27.5 parts of a vinyl chloride-vinyl acetate copolymer (the same as in Example 1), 2.5 parts of an epoxy ester of dehydrated castor oil fatty acid (oil length 4o #) and lo 10000 parts of Rosebengal was applied to a sheet of the same carrier paper as in Example 1 in a thickness of 5 Ai.

Under the conditions of dark adaptation, the surface of the photosensitive layer became several times. Paint rubbed with a piece of cotton velvet cloth and one Image exposure was applied by the projection method. A positive line image was selected as the original. The electrostatic latent image was made using

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a cascade developer containing positively charged toners, with a positive copy of the Originals could be obtained.

Change sifc s could make a copy of excellent Image quality can also be achieved by means of the liquid development.

In an improved embodiment of the invention became a cotton saint cloth impregnated with purified kerosene used to surface the photosensitive layer in the same manner as described above su rub, being after the subsequent exposure and development, a homogeneous image of much lower fog density could be obtained.

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Claims (1)

. Pat ent claims i) Electrophotographic process, which the .electrostatic charging of the surface of a photoelectric conductive insulating layer formed by dispersing photoelectrically conductive powder inorganic materials of the η-type in a binder, the main component of which is a vinyl chloride-vinyl acetate copolymer in the composition ratio of 95: "to 55! 45 parts by weight, was prepared, obei with such a. -. Frictional ?. Material that creates negative charges on the surface of the photoelectrically conductive insulating layer by means of friction, rubbed became. 2. Electrophotographic method according to claim 1, characterized in that the photoelectrically conductive Η-type material made from titanium dioxide, zinc oxide, cadmium sulfide, a mixture of cadmium sulfide and cadmium carbonate and a mixed crystal of cadmium sulfide and zinc sulfide. -3. Electrophotographic process according to claim 1, characterized in that the ... ". Friction * material consists of cotton velvet cloth, rayon cloth, wool, tanned leather, nylon cloth or a polyurethane sponge. 109846 / U67 COPY Γ / 97099 4. Electrophotographic process, which is the electrostatic charging of the surface of a photoelectric conductive insulating layer formed by dispersing photoelectrically conductive powder inorganic materials of the η-type in a binder, the main component of which is a vinyl chloride-vinyl acetate copolymer contains in a composition ratio of 95 J 5 to -55: 45 parts by weight, in the presence of a highly insulating liquid, where · with such a. Friction material that negative charges on the surface of the photoelectrically conductive ». . Insulation layer creates by means of friction, rubbed and has been developed with a liquid developer compatible with the liquid. 5. Electrophotographic method according to claim 4, characterized in that the photoelectrically conductive Η-type material made from titanium dioxide, zinc oxide, cadmium sulfide, a mixture of cadmium sulfide and Cadmium carbonate and a mixed crystal made of cadmium sulfide and zinc sulfide. 6. Electrophotographic method according to claim 4, characterized in that the friction V; ' J._ material consists of cotton velvet cloth, artificial silk cloth, full grain, tanned leather, nylon cloth or a polyurethane sponge » 109846 / US7