US3507693A - Method of producing an electrophotographic plate - Google Patents

Description

United States Patent- 3,507,693 METHOD OF PRODUCING AN ELECTRO- PHOTOGRAPHIC PLATE Yasuo Ueda, 3-32 Kitano-cho, Ikula-ku, Kobe, Hyogo Prefecture, Japan; Akira Takatsu, 3-5-16 Kusatsu-cho, Kusatsu, Siga Prefecture, Japan; and Tatsu Aizawa, 6-34 Kuwagu-cho, Higashisumiyoshi-ku, Osaka, Japan No Drawing. Filed Nov. 13, 1967, Ser. No. 682,509

Int. Cl. Hf US. Cl. 117201 7 Claims ABSTRACT OF THE DISCLOSURE An electrophotographic printing plate including the base of art paper or the like coated with a mixture of citric acid and photoconductive microcrystalline zinc oxide with water and in some cases with ethyl alcohol producing an electrophotographic plate without requiring the use of resins and organic solvents which may be dangerous, the electrophotographic plate being usable with or without charging the plate.

The present invention relates to electrostatic printing and to the plate and the method of producing the electrophotographic plate. More particularly the invention relates to a composition of matter including a photoconductive material which will adhere to an electrophotographic plate base of art paper or other suitable base material and which can be produced economically without employing a resin binder.

Heretofore the methods of producing electrophotographic plates has included mixing a photoconductive material with electrically-insulating plate forming vehicle with a volatile organic solvent, for example by mixing zinc oxide and a silicone resin with toluene thereby producing a form of photoconductive medium that has already been developed by R.C.A. of America. The silicone resin binder is used for keeping a photoconductive coating layer adhesively secured to a base plate and for holding electrons emitted by corona discharge. The use of a volatile organic solvent for the vehicle, however, has several disadvantages particularly that the solvent is expensive and therefore uneconomical and also most organic solvents are inflammable and poisonous thereby presenting a health hazard to factory personnel. Even if water is used as the vehicle a resin binder is relatively expensive.

Accordingly a principle object of this invention is to overcome the above described difiiculties and to provide an improved electrophotographic plate and a method for producing the plate which is economical and can be readily carried out at a minimum of expense.

A further object is to provide a method of producing an electrophotographic plate without employing a resin binder.

A further object is to provide an electrophotographic plate for use in chargeless electrostatic printing.

Briefly the invention provides a method of making an electrophotographic plate by coating a base plate of suitable material with a mixture of a photoconductive material, citric acid, and water and then drying the coating on the base plate. 1

Other and further objects will be apparent as the detailed description proceeds.

"The citric acid and water may be added to the photoconductive material of microcrystalline zinc oxide or the citric acid may be added to the microcrystalline zinc oxide dispersed in water or the water may be added to a mixture comprising the microcrystalline-zinc oxide and citric acid. Also the citric acid may be dissolved in water and added to the microcrystalline zinc oxide.

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An exothermic reaction takes place between zinc oxide and citric acid and it has been found that the photoconductive coating layer of citric acid and zinc oxide adheres firmly to the base plate as a result of the chemical reaction without the use of a particular binder.

It has also been found that the photoconductive coating layer of zinc oxide, citric acid, and water adhere more firmly to the base plate by having ethyl alcohol added thereto and using a small amount of water in the mixture.

The exothermic reaction between citric acid and zinc oxide has the property of causing the coating to adhere firmly to the base plate without requiring the use of an additional binder.

By experiment it has been shown that an electrophotographic plate made according to the present invention can recover from the memory efiect in three to five minutes after exposure to light. The photographic plate of the present invention should be developed within three minutes to produce a visible image by the usual toner used in electrophotographic reproduction. It has been proved by experiment that the electrophotographic plate can recover from the memory efiect (the irradiation effect caused by exposing to light) in 3-5 minutes after exposure, therefore, the electrophotographic plate may be readily used in making reproductions by the electrostatic printing process. The electrophotographic plate of the present invention therefore recovers from the memory effect of irradiation to light in three to five minutes and this may be accomplished by placing the electrophotographic plate in the dark for this period of time. Thereafter, the electrophotographic plate can be exposed to an image pattern of light by any of the usual photographic means including contact with a negative or projection of an image on the electrophotographic plate and the latent image produced thereby can be developed in the usual manner of electrophotography. The present electrophotographic plate is particularly advantageous in the chargeless electrostatic printing process since the image can be formed without requiring the charging of the electrophotographic plate. The toner may be charged before coming in contact with the latent image produced by the light exposure on the photographic plate and this should be done within three minutes before the electrophotographic plate can recover from the memory effect.

The electrophotographic plate of this invention makes it possible to produce visible image thereon with more definition, gloss and fiat than have been obtainable when employing a particular resin binder and a clear visible image can be produced by the chargeless electrostatic printing process.

An organic solvent (e.g. alcohol) mixed with Water, in addition to the citric acid and water may be added to photoconductive zinc oxide in order to accomplish the objects of the invention thereby reducing the milling time required to satisfactorily mix all of the ingredients and the mixture with alcohol can be more easily coated on the base plate regardless of whether the base plate is made of art paper or other suitable materials.

The following examples will serve to illustrate this invention more clearly:

3 EXAMPLE III Grams Microcrystalline zinc oxide 1O Citric acid 2 Water 5 Ethyl alcohol 20 It will be apparent that the coating mixture of each example is applied in a uniform thickness coating to the base thereby producing electrophotographic plates with the coating being of sufiicient thickness such as 5,11. to produce a satisfactory image.

The developed images may be made in accordance with electrostatic printing processes by the use of a charging step, but the charging may be omitted entirely and the developed image produced in Example II is more clear than the image produced in Example I and the image produced by Example III is more clear than the image produced by Example II. The results show that the developed image becomes clearer as the amount of citric acid is increased and the image becomes much clearer by adding organic solvent. It has also been proved by further experiment that the developed image is Worse as the citric acid is increased above 20% of the zinc oxide or the citric acid is decreased to less than 0f the zinc oxide.

It will thus be seen that the coating composition applied to a base and the resulting electrophotographic plate without a particular resin binder is a simple and and economical product.

The developed image on the electrophotographic plate of the present invention has more clarity and definition than has been obtainable with prior art electrophotographic plates and the electrophotographic plate of this invention can be used in chargeless electrostatic printing processes thereby simplifying and reducing the cost of office copying machines where inexperienced personnel are required to make copies of great clarity.

We claim:

1. An electrophotographic plate capable of use in chargeless electrostatic printing with or without charging of the plate comprising a base, a photoconductive coating of zinc oxide, citric acid and water thereon, the citric acid and zinc oxide having reacted to provide the coating.

2. A method of making the printing plate of claim 1 comprising adding citric acid and water to photo-conduc tive zinc oxide producing a chemical action between the citric acid and zinc oxide and coating a base plate with said mixture and drying the coating thereon.

3. A method for producing an electrophotographic plate according to claim 1 comprising adding citric acid, an organic solvent capable of mixing with water and a small amount of water to photoconductive zinc oxide, coating the base plate with the mixture and drying said coating.

4. The invention according to claim 1 in which the zinc oxide and the citric acid are present in the proportion of 10 parts of zinc oxide to approximately 1 to 2 parts of citric acid.

5. The invention according to claim 1 in which the photographic plate is free of other binding materials.

6. The invention according to claim 3 in which the organic solvent is ethyl alcohol.

7. The invention according to claim 2 in which the photoconductive zinc oxide is microcrystalline and present in an amount of approximately 10 parts, the citric acid being present in approximately 1 to 2 parts, water being present in approximately 5 to 25 parts and ethyl alcohol being present in approximately 0 to 20 parts.

References Cited UNITED STATES PATENTS 2,993,787 7/1961 Sugarman 96-1 WILLIAM L. JARVIS, Primary Examiner US. Cl. X.R.