Photoconductive Element And Process Of Preparing Same Using Thermo-shrinkable Material

Abstract

A photosensitive member for electrophotography comprising an endless substrate, a photoconductive layer overlying the substrate and a seamless insulative layer overlying the photoconductive layer, is produced by applying a photoconductive layer to the substrate, loosely encircling such applied photoconductive layer and substrate with a thermally-shrinkable endless resin film and heating the film into continuous contacting relation with the photoconductive layer.

Parent Case Text

This is a continuation of application Ser. No. 828,658 filed May 28, 1969, now abandoned.

Description

This invention relates to a process for producing a photosensitive body for electrophotography and an apparatus for producing the photosensitive body. More particularly, this invention relates to a process for producing an excellent seamless photosensitive member of uniform thickness used for electrophotography, said photosensitive member being composed of a photoconductive layer and an insulating layer provided on a conductive center member and to an apparatus therefor.

In electrophotography, images are produced generally through various stages such as electrostatic latent image formation, developing, fixing, etc., each affected by the photosensitive body which is based on a conductive substrate.

As the photosensitive body, those in flat form and cylindrical shape are already in widespread use. They are, however, selected according to the respective electrophotographic systems to which they are to be applied, and satisfactory results are obtained in accordance with the respective system objects.

There have been introduced hitherto various systems of electrophotography, but we will explain hereunder specifically those systems which are particularly effective.

To a photosensitive body which is composed basically of an electrically conductive layer, a photoconductive layer and an insulating layer, primary charge is applied and then secondary charge or an alternating current corona discharge is applied at the same time as irradiation of an original image is performed, if desired, followed by further entire exposure, so as to form an electrostatic image. After this procedure, the electrostatic latent image is developed, transferred to a specific transfer paper and fixed. In this system, an electrostatic image is not directly formed on the photoconductive layer, unlike in the case of conventional so-called Carlson process, but is formed on the insulating layer which is in close contact with the photoconductive layer. This system is, therefore, characterized not only in protection of the photoconductive body, but also in attainment of clear image of high contrast, as well as in making good transfer onto paper, metal, wood, cloth, etc., since the efficiency of the transfer is very good in this case.

The systems of this type are described in U.S. application Ser. No. 563,899, filed on July 8, 1966 and No. 571,538, filed on Aug. 10, 1966, now abandoned.

For constructing a copier for the formation of electrophotographic images based on the above-mentioned system, it is advantageous that the photosensitive body be in a drum shape and not in the form of a flat plate. That is, it is possible for charge, exposure, developing, transfer and remnant toner cleaning apparatus to be arranged around a photosensitive drum, such that a copier is so constructed as to produce copied images in a rotary system with the different process steps performed one after another, with copying speed increased.

In this case, it is necessary for the structure of the copier that the photosensitive drum be seamless. With seams on the drum, the copier has to be so constructed as to enable it to produce images on the unseamed parts of the drum, disadvantages not presented by a seamless drum.

The photosensitive drums of this seamless type, however, have not been developed practically hitherto, as no adequate manufacturing method has yet been discovered, and only photosensitive plates of flat form are being used today.

The present invention provides photosensitive drums in cylindrical shape, belt form, etc., which are seamless and are composed of the aforesaid different layers, and which are able to act very effectively in the electrophotographic systems described above.

Another object of the present invention is to provide very easy and simple methods for making seamless photosensitive drums.

One more object of the present invention is to provide apparatus for making seamless photosensitive drums.

The present invention further aims at obtaining all advantages of the following explanations, practical examples, etc.

The above and other objects, aspects and advantages will become apparent by reading the following description taken in conjunction with the accompanying drawing, in which:

FIG. 1 is a cross sectional view of an embodiment of a photosensitive body of this invention;

FIG. 2 shows an embodiment of the coating apparatus of this invention;

FIG. 3 shows a thermal shrinking technique;

FIG. 4 schematically illustrates a system for forming a photoconductive layer;

FIGS. 5 and 6 explain the process step of inserting a cylinder member;

FIG. 7 schematically illustrates a method for smoothing the surface of the photosensitive body; and

FIGS. 8 and 9 show an embodiment of the apparatus of this invention.

The photosensitive drum obtained by the present invention is basically composed of a substrate layer 1, photoconductive layer 2 and insulating (insulative) layer 3, as shown in FIG. 1. The substrate layer can be in the form of a conductive layer or an insulating layer, or a combination thereof.

Methods for making such electrophotographic photosensitive drums in general, comprises a first process step of forming a photoconductive layer on the surface of the drum and a second process step of producing an insulating layer thereupon. In this case, the conditions required for the first process step are:

1. to reduce as far as possible the proportion of binder resin in the photoconductive body, so as to improve photoconductivity and to increase sensitivity;

2. to finish the photoconductive layer in specific thickness evenly all over the drum, thus enabling it to receive good images;

3. to make smooth the finish of the surface of the photoconductive layer, so that in the next process step the insulating layer can be formed throughout in specific uniform thickness. With unevenness in the surface of the photoconductive layer, projecting parts on the surface of the photoconductive layer cause thinness and indented parts cause thickness in the insulating layer, thus permitting no uniform finish; and

4. to finish the photoconductive layer sufficiently firm and strong to ensure no change in the thickness and flatness of the photoconductive layer in the process step of producing the insulating layer.

Next, the conditions to be met in the process step of forming the insulating layer are:

1. to finish the insulating layer in specific thickness evenly all over, thus enabling it to receive good images. It is essential for obtaining a better image that the insulating layer be kept as thin and even as possible. It is absolutely essential for this condition to be met that the photoconductive layer be finished smoothly as described above;

2. to finish flat and even the surface of the insulating layer, so that there can be no stain by the adhesion of toner, and also that remnant toner left after the transfer can be cleaned easily;

3. and to finish the insulating layer with enough durability to withstand repeated uses and with chemical resistance, etc.

For satisfying the above various conditions at the same time, it is necessary in general to manufacture the photosensitive drum by the method as described in the following.

The first process step of forming the photoconductive layer can be carried out, for instance, in the following manner. That is, fine powder for the photoconductive body is first dispersed in a binder resin (monomer of epoxy resin) and then this is kneaded thoroughly with a curing agent in order to prepare a mixture in paste form, followed immediately by coating of this paste on the surface of a revolving drum in uniform thickness by means of a doctor blade.

Since the surface of this photoconductive layer cannot be finished flat and even, and exhibits much unevenness, the surface is rubbed until flat and even with a substance of low adhesion, for example, fluorine resin, prior to onset of the curing reaction of epoxy resin and then the said curing reaction of epoxy resin is completed under specific conditions, thus completing preparation of the photoconductive layer. By this method, the unevenness of the surface can be kept below 10 .mu. and a photoconductive layer with a flat and firm surface can thus be produced, and consequently the following process step of forming the insulating layer can be carried out more advantageously.

Next, as to forming the insulating layer, in general this step involves coating and drying a lacquer, but an inevitable obstacle is presented where this method is employed. That is, in the case of producing a photoconductive layer by the method described above or by another coating method, there are formed numerous fine pinholes or uneven parts on the photoconductive layer, and after coating the lacquer thereon, foams may appear in the coated layer and the insulating layer may become uneven in its thickness. Accordingly after completion of such foaming, there may be parts where no insulating layer is present.

In order to remove this disadvantage to some extent, the lacquer is diluted enough for its application in liquid form, thus allowing it to flow more readily into the pinholes or uneven parts and at the same time accelerating the completion of foaming, such that after the completion of foaming, the lacquer around such parts is still able to flow easily and form a flat and even coated layer. When a single coating does not attain thickness after drying, this process step may be repeated as necessary. In this way, however, there may still result disadvantages such as the need for more working, and an increase in dirt adhering to the coated layer between coating and drying.

The present invention aims at excellent methods for the solution of these disadvantageous problems. That is, in the process step of producing the insulating layer, a so-called thermo-shrinkable tube, which is composed of thermoplastic resin of high insulating property (thermoplastic resin in chargeable insulating film form), is loosely encircled over the drum on which the photoconductive layer has been formed, instead of applying a lacquer coat thereto, and by utilization of its thermo-shrinkable property, the surface of the photoconductive layer is covered, so as to build an insulating layer. The thermoshrinkable tube is composed of film of thermoplastic resin and is in form pre-extended circumferentially. When heated and softened, it shrinks to assume its original shape by reducing its diameter. It is possible to make it shrink very easily if it is heated by subjecting it to hot air for a short time or by pouring hot water over it.

When the insulating layer is produced in this way, the surface of the thermo-shrinkable tube pre-formed in flat shape can be made use of as it is, and it is thus possible to manufacture an electrophotosensitive drum which has a level surface superior to the insulating layer produced by the lacquer coating method.

As a result of research conducted to provide apparatus to produce a good insulating layer by practice of this method, it has become evident that apparatus as shown in, for instance, FIG. 2 is useful, and that the method may be practiced generally in the following manner. That is, over the photoconductive layer 2 formed on the surface of the drum 1, the thermo-shrinkable tube 3 is laid, and the whole assembly is moved axially of the drum along the guide prop 15 by making use of wind-up mechanism 14. At the same time, hot air prepared by heating the air from the fan 16 by electric heater 17 is blown onto the surface of the thermo-shrinkable tube, over the whole part thereof within a plane which is perpendicular to the drum axis. Thus, the thermo-shrinkable tube is made to shrink gradually, beginning from its top part, and there is formed by a single operation an insulating layer which completely covers the photoconductive layer. In this case, the mechanism for hot air blowing may alternatively be arranged for movement.

The points that require special care in the practice of this method are two, one being that the thermoshrinkable tube is made to shrink evenly all over and to adhere perfectly onto the photoconductive layer in uniform thickness, and the other being that no foaming is allowed to be involved therein. To completely satisfy these conditions, it is necessary that the hot air be blown evenly all over and that shrinking is made to proceed successively from an end part.

As for the thermo-shrinkable tube to form the insulating layer, it is necessary, in view of the special character of the photosensitive drum, to use a tube which is composed of the thinnest possible film, and in order to make it perform thermal shrinkage evenly circumferentially, it is advisable not to use a thermo-shrinkable tube which is thicker than necessary. Accordingly, it is necessary that air be blown in between the photoconductive layer and the thermo-shrinkable tube, so that the thermo-shrinkable tube is swollen and the distance between the layer and tube is kept equal all over the circumference.

As a result of research conducted to provide the simplest and surest method to obtain uniform heat shrinkage, it has become clear that the simplest and most certain method is to lay the thermo-shrinkable tube, with its one end 18 sealed, over the surface of the photosensitive layer 2 formed on the drum 1 and to dip the whole assembly into hot water 19 gradually, beginning from the end part of the sealed end side, along the guide prop 15, as shown in FIG. 3. In this method, there is merit in that the desired object can be accomplished simply by mechanism to dip the drum and the thermo-shrinkable tube gradually into hot water beginning from the end part.

In order to prevent foaming completely in the shrinkage, heating is by means of an infrared lamp or electric heater instead of heating by blowing hot air and the whole body is placed in a vacuum to perform heat shrinkage. With a vacuum degree higher than about 300 mmHg by mercury column, it is possible to form a light-permeable insulating layer which is entirely free from foams. It is not particularly necessary in this case to heat the thermo-shrinkable tube successively from an end part.

Next, as another different method, we will present a method for coating the photoconductive material beforehand on the insulating film and then providing it on the drum.

The conventional photoconductive materials are all in the form of crystals of large particle size and thus render very difficult making the surface flat and smooth and thus the image produced thereby is not good in quality. The present invention provides improvement in this respect.

In providing a photoconductive layer, the photoconductive substance is dispersed in a binder resin and cured, and the binder resin to be used in this case may be either thermoplastic resin or thermo-setting resin.

First, we will explain about a manufacturing method in which a thermosetting resin is used. A photoconductive material is kneaded well in 5 - 20 percent by weight of the binder resin, and then this photoconductive substance in paste form is coated evenly to a thickness of 50 - 200 .mu. inside the thermo-shrinkable tube film.

An example of this method of coating is shown in FIG. 4. Inside the thermo-shrinkable tube-form film 3 which is held by the roller 21, the spacer 22 is placed facing the film 3, and then cadmium sulphide well mixed and kneaded with the resin 2 is applied to the inside of the tube-form film 3 and the film or metal foil 23 is laid over its surface, and then the coating is made in uniform thickness by rubbing the film 23 with the blade 24. Then, the film 23 is removed. In the case where metal foil is used, it is left in place.

Next, into the tube-form film 3 inside which the photoconductive layer 2 has been formed, the cylinder 25 is inserted as shown in FIG. 5. Then, the thermo-shrinkable tube film is shrunk by heating and the photoconductive layer is adhered compactly to the cylinder 25. After levelling the unevenness that occurred in the photoconductive layer upon the shrinkage of the film 3, it is heated further to cure the binder resin, and thus three different layers, i.e., the highly insulating layer 3, the photoconductive layer 2 and the cylindrical central substrate 25, are combined in a single body. Thus, an electrophotographic photosensitive body in cylindrical form is manufactured. In this case, it is also possible to make it into other optional shapes, for instance, belt form, by removing the central member.

When using thermoplastic resin, 5 - 20 percent by weight of a binder resin is dissolved in a solvent, in which the photoconductive material is dispersed thoroughly, and this is then applied evenly to the inside of the thermo-shrinkable tube film to a thickness of 50 - 200 .mu. by the method shown in FIG. 4. After complete evaporation of the solvent and drying, it is laid over the outside of the cylindrical central member, and then the photoconductive layer is softened by heating and at the same time the thermoshrinkable tube film is made to shrink. Unevenness of the photoconductive layer occurring on this occasion is eliminated in the course of softening of the binder resin and then the resin is hardened by cooling at room temperature. Thus, there is produced an electrophotographic photosensitive body of cylindrical shape comprising three layers, i.e., a highly insulating lyaer, a photoconductive layer and a cylindrical central substrate.

On the other hand, where the photoconductive layer is a coated layer comprising a mixture of dispersed photoconductive material and resin, the layer becomes porous since foams are involved in the mixture, and its surface is uneven and cannot be flat and smooth. Therefore, when lacquer is applied to such surface, the thickness of the insulating layer 3 becomes uneven and also foams float up from the cavities of the photoconductive layer 2, thus causing the formation of cavities in the surface of the insulating layer or pinholes in the insulating layer. It is thus hard to form an insulating layer of uniform thickness and homogeneous quality.

Furthermore, in order to provide print contrast and clearness in use of the photosensitive body on which the surface insulating layer 3 has been formed, it is desirous that the surface insulating layer is made as thin as possible. However, the thinner it becomes, the more conspicuous are the above problems. In addition, it is difficult to render the surface of the insulating layer 3 formed by such lacquer coating method flat and smooth, since it has uneven parts, and the cleaning of remnant toner cannot be readily accomplished. The faults described above are unavoidable in the case of formation of the surface insulating layer by the lacquer coating method. The present invention, therefore, also provides another way to form the surface insulating layer 3, characterized in that the surface insulating layer is produced by covering the photoconductive layer 2 with a tube which is composed of insulating material formed in specific thickness beforehand with an inside diameter large enough for compactly covering the photoconductive layer 2.

As for the tube of insulating material mentioned above, there can be used tubes of various thermoplastic resins which are manufactured by, for instance, the inflation method. By the use of a tube stable in quality, it can be in fixed thickness and also can be uniform in quality and satisfactory in surface flatness and smoothness.

It is a matter of course that the inside diameter of the tube 3 as described above is selected to cover the photoconductive layer 2 compactly, and in the case when its inside diameter is somewhat smaller, this diameter of the tube is made larger by passing through it a mould in conical shape which has its maximum outside diameter larger than th inside diameter of the tube, and then this tube is laid over the photoconductive layer.

In the cylindrical, electrophotographic photosensitive body of the present invention, the surface insulating layer is formed by a separate tube as described above, and hence all of the faults which are found in the above-mentioned method of formation by coating can be eliminated. In addition, it has merit in that when the insulating layer has been harmed or damaged in long use, it can be replaced easily by a new tube.

The present invention further provides other different methods of obtaining a seamless photosensitive body in cylindrical shape. As shown in FIG. 6, the insulating layer 32 is formed by coating, according to necessity, electric insulating lacquer, etc. on the outer surface of the cylindrical body 31 which is made in perfect circular shape by shaving.

A mixture in paste or paint form is prepared by dispersing fine photoconductive powder in a solution of a synthetic resin monomer or a synthetic resin of low polymerization degree and a polymerization accelerator.

Then, this photoconductive material is applied by knife coating or roller coating on the above-mentioned cylindrical body 31 while it is maintained horizontal and rotating. In this case, the coating is made in even thickness all over the circumference by removing surplus portions of the photoconductive body by setting a knife at a proper angle. The photoconductive layer 2 in this case remains in an uncured condition.

Next, it is encircled with a previously produced tube of synthetic resin which is high in electric insulating property and is also of thermosetting nature, and then this is made to shrink with heat and to cover compactly the photoconductive layer 2, thus forming the insulating layer 3.

After the heat shrinkage and covering as described above, the whole cylindrical body is maintained at a specific temperature and the polymerization reaction of the monomer of synthetic resin or the synthetic resin of low polymerization degree in the photoconductive layer 2 is completed.

By the method described above, the photoconductive layer 2 is combined compactly with the electric insulating layer 3, and there is formed a seamless electric insulating layer 3 which is uniform in thickness and has a smooth and flat surface, thus yielding the desired product. This flat and smooth surface is dependent on the flat and smooth surface of the photoconductive layer 2, and therefore, the coating finishing of the photoconductive layer 2 is an important process step. However, since the photoconductive layer 2 immediately after coating is still in uncured and viscous condition as described above, levelling of its surface is quite difficult.

The present inventors made studies and consequently succeeded in levelling the surface by a step of rubbing the surface with a material having low adhesion to the viscous photoconductive layer 2, i.e., by a levelling spatula or roller 34 on the surface of which is provided a substance such as fluorine resin film 33. By this process step, the border between members 2 and 3 is flattened and levelled, so that the surface of the electric insulating layer 3 can be formed fully flat and also in uniform thickness all over.

By having this tube circumferentially extended beforehand (and also somewhat axially) and by utilizing its characteristic of reducing its diameter (and its length also) by assuming its original form upon softening under heating, the photoconductive layer 2 is compactly adhered to the center member. As the means of heating either hot air or hot water is employed. In this thermo-shrinking and covering process, attention should be paid to the following matters:

1. to accomplish shrinkage evenly and in uniform thickness;

2. to take caution to prevent foams from occurring in and between layers 2 and 3; and

3. to prevent scratching of the uncured photoconductive layer 2.

As the means for attending to these matters, effective examples are shown in FIGS. 8 and 9. Therein the shaft 35 is fitted to the cylinder on whose surface the photoconductive layer 2 has been coated, then the shaft 35 is placed in springs 36.sub.1 and 36.sub.2 at both sides of the cylinder 31, and circular plates 37.sub.1 and 37.sub.2 are fixed loosely about the shaft 35. The thermo-shrinkable tube 3.sub.1 is laid over and fixed onto the circular plates 37.sub.1 and 37.sub.2 with the rings 38.sub.1 and 38.sub.2.

The space between members 3.sub.1 and 37.sub.1 and between members 3.sub.1 and 37.sub.2 is rendered air-tight by grease coating, etc.

With the cock 40 open and the ventilation pipe 39 fixed onto the circular plate 37.sub.1, the assembly is placed in a vacuum tank, and when the vacuum tank is evacuated, the space intervening the thermo-shrinkable tube 3.sub.1 and layer 2 is evacuated. As the cock 40 is closed at a certain specific degree of reduced pressure (if located inside the vacuum tank, the cock is closed by remote operation) and the thermo-shrinkable tube 3.sub.1 shrinks under heating by an electric heater placed in the vacuum tank, the tube 3.sub.1 adheres compactly to the photoconductive layer 2 as seen in FIG. 9, and thus the insulating layer 3 is formed.

Upon this thermal shrinkage, axial shrinkage is absorbed by the compression of the springs 36.sub.1 and 36.sub.2. In order to prevent the photoconductive layer 2 from being scratched by the thermo-shrinkable tube 3.sub.1 in its axial shrinkage, it is ideal that the shrinkage occur gradually from the central part of the tube 3.sub.1 to its outer side and also gradually from one end towards the other side. For this purpose, a narrow width electric heater capable of local heating, which can be freely moved by remote control, is located inside the vacuum tank. This is necessary particularly when the photosensitive cylindrical body is very long.

After shrinkage performed as above, air is admitted into the vacuum tank, and then the whole body is taken from the vacuum tank and placed in ambient air. Since the tube 3.sub.1 is further strongly pressed by the atmospheric pressure since its interior is still subjected to vacuum, both the surface insulating layer 3.sub.1 and the photoconductive layer 2 are adhered compactly enough.

There is thus insured ideally compact adhesion and a flat and smooth border. The insulating layer 3 is in uniform thickness all over. It is possible to further improve such compact adhesion by rotating a pressure roller on the surface of the insulating layer 3.

The heat shrinkage in the vacuum described above is performed mainly by the radiant heat. The thermoshrinkable tube 3.sub.1 permits heat to pass through it easily and is thus heated slowly, while the photoconductive cylinder 31 is heated more quickly. Consequently, the photoconductive layer 2 is heated, rapidly advancing the binder resin to its curing reaction, and the photoconductive layer 2 itself gels. Its adhesion to the surface insulating layer 3 is, therefore, reduced, and border flatness may not possibly be maintained. Therefore, a paint containing black inorganic pigment which easily absorbs the heat rays, such as, for example, carbon black, tri-iron tetroxide, and the like is applied previously to the surface of the thermo-shrinkable tube 3.sub.1, and it is removed with a solvent after completion of final product.

Excessive parts of the layer 3.sub.1 are cut off and finally it is put into a bath at constant temperature, so as to complete the polymerization reaction of the binder resin and to thus obtain a final finished product.

For the adhesion of different layers as described above, it is also possible to adhere the photoconductive layer and the insulating film by laying between them an intervening cementing layer.

However, the adhesive generally used in one which is cohesive at room temperature, and hence it is very difficult to affix a thin insulating film onto the surface of photoconductive layer in such a way as to prevent formation of wrinkles and foams. Particularly, in the case when an insulating film in tube form is made to shrink by heat and laminated on drum photoconductive layer by a cohesive bonding agent, thermal shrinkage of the insulating film is always accompanied by local unevenness, and consequently this cohesive bonding agent can act to fix the wrinkles and foams that they formed. A drum in which the wrinkles and foams have formed once, is not good for practical use because elimination of such faults is difficult.

In order to eliminate the aforesaid defects and to manufacture wrinkleless and foamless photosensitive bodies at a high efficiency, so-called hot melting type resin, which is a resin of low softening point may be used.

The resins of hot melting type are resins which are transparent and high in insulating property, having a softening point of approximately 70.degree. - 150.degree.C, such as polyvinyl butyral, polyvinyl acetate, copolymer of vinyl chloride and vinyl acetate, copolymer of vinyl acetate and polyethylene, acrylic resin, rosin, phenol resin, modified phenol resin, maleic resin, modified fumaric resin, dammar gum, and the like. These low softening resins are not cohesive at the room temperature, but when heated up to the above-mentioned temperature by infrared rays, etc., they melt and exhibit their bonding agent characteristics.

In the present invention, the aforesaid resins of low softening point are dissolved in an adequate solvent, and the solution is either applied or sprayed onto the surface of photoconductive layer or the surface of insulating film, followed by drying the evaporation of the solvent. An adhesive layer is thus produced, which does not have the cohesive property of low softening point resins.

Next, with this adhesive layer in between, both the photoconductive layer and the insulating film are laid one above the other, then the adhesive layer is melted by heating and is made to act as a bonding agent, and finally the photoconductive layer and the insulating film are adequately pressed to accomplish their adhesion and lamination.

In other conventional methods, insulating film is adhered directly on the photoconductive layer by using a bonding agent which is cohesive at room temperature. When an insulating film, which is so thin as 20 .mu. or so, is spread over a photoconductive layer, the formation of wrinkles and foams is inevitable. On the contrary, the present invention as explained above, involves laying a photoconductive layer and an insulating layer one above the other with an intervening adhesive layer non-cohesive at room temperature, and to render the adhesive layer cohesive and effective as a bonding agent by heating. It is thus possible to spread a thin insulating film over a photoconductive layer in such a way as to cause neither wrinkles nor foams, and then the agent provides its bond. In addition, this method has merit in that the bonding process can be carried out easily.

This is particularly advantageous for a photosensitive body in a drum form. In this case, a tube form insulating film is bonded on the drum form photoconductive layer by thermal shrinkage, and if a conventional bonding agent which is cohesive at the room temperature is used, local uneven shrinkage, which is unavoidable because of physical phenomena of tube form film, is fixed as it is by the bonding agent, and the formation of correct cylindrical form is difficult. With the above-mentioned other bonding agent used in this case, such local uneven shrinkage described above is still not fixed, since the bonding agent is non-adhesive at the time of thermal shrinkage of the tube form film. As the bonding agent is next melted by heating to exhibit its cohesive properties for bonding, the aforesaid uneven shrinkage is reformed naturally by its internal stress at the time of bonding and thus becomes flat and smooth, eliminating all wrinkles and foams.

As to photoconductive materials to be used for the cylindrical photosensitive bodies manufactured by the different methods mentioned above, it is possible to employ various photoconductive substances which are in general use. As inorganic photoconductive substances, such as, for instance, CdS, CdSe, Se SeTe, ZnO, etc. can be used, and as organic photoconductive substances, such as, for example, those having a heterocyclic ring, those having condensation cycles, those having double bond, those having amino, or nitrole, condensation products, polyvinyl carbazole, vinyl polymer, condensation polymer, etc. can be used. Besides these, other substances which are rendered conductive with light can also be used without limit.

These photoconductive substances can be individually formed into tube or insulating layer directly, for instance, by spattering, etc., or used in form dispersed in binder resin.

As for the binder resins, there may be mentioned, for example, thermoplastic copolymer of vinyl chloride and vinyl acetate, polyvinyl chloride, polyvinyl acetate, cellulose acetate, nitrocellulose, methacryl resin, phenol resin, P.V.A., polyvinyl butyral and the like and thermosetting resins such as epoxy resin, unsaturated polyester resin, and the like.

As to the drums, those in hollow form or hermetically sealed ones can be used. In case of hollow drums, those in endless belt form or in tube form, etc. can also be used. It is also possible to employ drums in polygonal form, etc. in addition to those in cylindrical or tube form.

Further, as to structural materials, metals, nonmetals, alloys thereof, etc. can be used as electroconductive materials, and, for example, wood, paper, resin, cloth, etc. can be used as insulating materials.

These drums or tubes are effective, for example, where insulating material is set on an electroconductive substrate, where an electroconductive substrate is used alone or where an electroconductive material is provided on an insulating base. With respect to insulating materials, inorganic insulating material such as Al.sub.2 0.sub.3, SiO.sub.2, silica glass, TiO.sub.2, BN and the like, as well as organic insulating materials mentioned previously, may be employed. The thermo-shrinkable tube film must be a material which can retain electrostatic charge and is highly insulating, for example, polyester, polyvinyl chloride, polyvinylidene chloride, Teflon, polyethylene, bridged polyethylene, polypropylene, fluorine resin, etc. In this case, light permeability, electric charge retention and other factors are decided relative to another insulating layer which, if desired, is placed between the cylindrical substrate and the photoconductive layer. In such case, at least the tube film or the substrate and the other insulating layer should be light permeable.

Light permeability as mentioned here means such permeability as to permit radiation to permeate to the photoconductive body. That is, if either insulating layer is light permeable, the original image light is projected through its surface, and it is not always necessary that both insulative layers be light permeable.

Examples for practicing the present invention follow.

Example 1

By fully mixing and kneading 40 g. of cadmium sulphide activated by copper, 5 g. of Epikote 815 (product of Shell Petroleum Co.) which is an epoxy resin and 0.6 g. of epoxy resin hardener K 61B (product of Anchor Chemical Co.), a mixture in paste form was obtained. This paste was then applied by a doctor blade to a drum made of aluminum, 15 cm. in diameter and 22 cm. in length, while rotating the drum, to form a coating of 100 .mu. thickness and a photoconductive coating was thus formed. Then, immediately, a film of ethylene tetrafluoride resin was applied to the surface of the photoconductive layer by pressure while rotating the drum and its surface was flattened by rubbing. Then, the whole of this drum was placed in ambient atmosphere at 70.degree.C for 4 hrs. and the epoxy resin was thus hardened. A photoconductive layer was formed thereby.

Next, a thermo-shrinkable tube having an inner diameter of about 15.5 cm. and composed of polyvinyl chloride film of approximately 20 .mu. thickness was laid over the drum, and while applying hot air at about 80.degree.C thereto by the apparatus shown in FIG. 2, the assembly was moved upwardly at a speed of 5 mm. per second and thermal shrinkage was effected. As a result, a polyvinyl chloride film covered the whole surface of the photoconductive layer in uniform thickness of about 25 .mu., thus forming a good light permeable insulating layer, and an electrophotographic photosensitive drum was obtained.

This photosensitive drum was used in, for example, the rotary copier practicing the electrophotographic method disclosed in Japanese Patent Publication No. 23910/1967, and thereby a good copy print was obtained. The sensitivity of the photosensitive drum was as high as 2 - 3 Lux.sec., and the light permeable insulating layer of polyvinyl chloride resin proved durable and adapted for repeated use, and its surface was very flat and smooth.

EXAMPLE 2

Over a photoconductive layer produced on the surface of an electroconductive drum by the same method as in Example 1 above, was laid a thermo-shrinkable tube composed of polyvinyl chloride film, and the assembly was placed in the vacuum of about 50 mm Hg. Next, by an electric heater, this tube was heated over its whole circumference, and the thermo-shrinkable tube shrunk so as to form a light permeable insulating layer. It was thus possible to produce a good light permeable insulating layer which contained enitrely no air foams. In reproduction using this sensitive drum, good images were obtained.

EXAMPLE 3

To provide thermal shrinkage in Example 1 above, the method shown in FIG. 3 was practiced by covering a conductive drum having a photoconductive layer with a thermo-shrinkable tube composed of polyvinyl chloride film, then sealing an end of the tube, and dipping the whole body gradually into hot water at 80.degree.C, beginning from the sealed end of the tube. As a result, there was obtained good even thermal shrinkage, containing no foams. This photosensitive drum also gave very satisfactory reproduction images.

EXAMPLE 4

By mixing and kneading thoroughly 40 g. of cadmium sulphide activated by copper, 5 g. of Acmex R-11 (product of Nihon Gosei Kako Co.) which is an epoxy resin and 1 g. of H-92 (product of Nihon Gosei Kako Co.) which is a hardener for the above epoxy resin, a mixture in homogeneous paste form was prepared. By a doctor blade, this mixture was applied to the surface of aluminum drum, 15 cm. in diameter and 22 cm. length, to a thickness of 80.mu., with the drum rotating. Then, the drum was allowed to stand for 24 hours at room temperature, was then heated for 2 hours in an air drier at 50.degree.C and was finally cooled to form a photoconductive layer.

Next, polyester tube (HS Diafoil manufactured by Mitsubishi Resin Co.), having a folded diameter of 25 cm. (about 16 cm. in diameter) and a thickness of 0.03 mm., was laid over this drum, and an end of the tube was sealed. The assembly was then soaked in hot water at 90.degree.-95.degree.C at a speed of 1 mm. per second, beginning from the sealed end. Thereby, the polyester tube was adhered to the photoconductive layer without introducing any foams inside the tube. After cutting off the excessive portions of the polyester tube at both ends of the drum, the product was used for reproduction in the same way as in Example 1 above, and good reproduction prints were obtained. The sensitivity of the photoconductive drum in this Example was 2 - 3 Lux. sec. and the film formed by the polyester tube was good in light permeability, very tough and strong, and also good in electrical property, thus being adapted for repeated use.

EXAMPLE 5

To epoxy resin (Epikote 815) as binder was added 12 percent by weight of hardener K 61B and the mixture was stirred thoroughly. The resulting mixture was then mixed in and kneaded well with 40 g. of cadmium sulphide. This photoconductive substance (containing 13 percent by weight of CdS) in paste form was next applied evenly, to a thickness of about 100.mu., to the inner side of a thermo-shrinkable tube film (HHS Diafoil, a polyester 15.mu. in thickness), and this was then laid over a cylinder made of aluminum. After shrinkage by heating, the uneven surface of the photoconductive layer was levelled and then the binder was cured. Thus, there was produced a cylindrical electrophotographic photosensitive body comprising three layers. In reproduction using this photosensitive body, it was possible to obtain very satisfactory images.

EXAMPLE 6

Cadmium sulphide was dispersed in a copolymer of vinyl chloride and vinyl acetate as binder, diluted adequately with a thinner such that the copolymer could be 10 percent by weight ratio. This dispersion was then applied, by a sprayer, to the inner side of thermo-shrinkable tube film (HHS Diafoil 15.mu.), to form a film of 100.mu. thickness and, after drying, an aluminum cylinder was inserted in the tube. Since the resin was thermo-plastic, the photoconductive layer was next shrunk by heating. Thereby, the dried photoconductive layer was softened and followed the shrinkage of the film. The surface of the photoconductive layer, which thereby became uneven, was levelled while the resin was in a softened condition. It was then cooled for curing, and there was produced a cylindrical electrophotographic photosensitive body comprising three layers. Very good images were obtained when reproduction was carried out with this photosensitive body.

EXAMPLE 7

Cadmium sulphide (40 g.) was mixed with 5.2 g. of epoxy resin (Epikote 815 plus hardener K 61B), kneaded well and dispersed homogeneously. This dispersion was then applied evenly to a thickness of 80.mu. to the inner side of a polyester film tube, 15 cm. in diameter, by the method shown in FIG. 4, and after curing of the resin, an aluminum cylinder having a cut made thereon was inserted in the tube to form a cylindrical photosensitive body comprising three layers. In testing reproduction by using this sensitive body, it was possible to get good reproduction images.

EXAMPLE 8

By mixing and kneading well 40 g. of CdS with average diameter of 2.mu., which was activated by copper, 20 g. of clear lacquer containing 20 percent solid of copolymer of vinyl chloride and vinyl acetate and 10 cc. of a thinner for the above-mentioned lacquer composed mainly of ketone, a yellow mixture in paint form was prepared. This was then applied to an aluminum cylinder, 20 cm. in diameter and 22 cm. in length, by a knife coating method such that the thickness after drying was 60 - 80.mu., and upon drying, a photoconductive layer was produced. By covering this assembly with polyvinyl chloride resin film, 20.mu. in thickness and about 20 cm. in inner diameter and produced by an inflation method, there was obtained a cylindrical electrophotographic photosensitive body. This photosensitive body was utilized in an electrophotographic copier disclosed in Japanese Patent Publication No. 23910/1967 and good images were obtained. Furthermore, the surface of the insualting layer withstood repeated use for several thousand times and remnant toner was easily removed therefrom.

EXAMPLE 9

By fully mixing 40 g. of zinc oxide, 20 g. of copolymer styrene and butadiene and 40 cc. of xylol by a ball mill and then adding thereto 2 cc. of 1.0 percent ethanol solution of Rose Bengal, a light pink mixture in paint form was prepared. Next, to an aluminum cylinder of the same size as in Example 1 above, epoxy resin lacquer was applied such that after drying, it was in a thickness of about 50.mu.. Upon drying, an insulating layer was produced. The above-mentioned mixture in paint form was applied to this insulating layer such that its thickness after drying was about 60.mu. and upon drying, a photoconductive layer was provided. By then employing a tube made of polyester resin of about 25.mu. thickness and about 20 cm. inner diameter, there was obtained a cylindrical electrophotographic photosensitive body.

In the use of this sensitive body in the same copier as in Example 1 above, it was possible also to obtain good and clear images. The surface insulating layer was durable exhibiting no insulation breakdown, and could be used repetitively.

When the above-mentioned tube of light permeable insulating substance in the present invention was formed by using a thermo-shrinkable tube comprising thermo-plastic resin and this was laid over the photoconductive layer and shrunk by heating, it was possible to make the adhesion still better.

EXAMPLE 10

In place of the polyvinyl resin tube or polyester resin tube referred to in Example 8 above, a slightly larger thermo-shrinkable tube composed of such resins was used for covering, and it was shrunk by pouring thereover hot water at 90.degree.-95.degree. C. By this procedure, the photoconductive layer was covered compactly and a cylindrical electrophotographic sensitive body could be produced. The thickness of the insulating layer formed by shrinkage was approximately 25.mu..

This member also gave good images as in Examples 8 and 9 above.

EXAMPLE 11

A mixture in paste form was prepared by fully mixing 40 g. of cadmium sulphide activated by copper, 5.0 g. of epoxy resin monomer Epikote 815 (product of Shell Petroleum Co.) and 0.6 g. hardener K 61B (product of Anchor Chemical Co.) for said resin.

This was coated on the surface of an aluminum cylinder, 16 cm. in diameter and 22 cm. in length, to a thickness of about 80.mu. by a knife coating method using two knives, and a photoconductive layer was formed.

Next, by means of the apparatus shown in FIG. 8, a thermo-shrinkable tube made of polyester film, about 20.mu. in thickness and 27 cm. in folded diameter (54 cm. circumference and about 17 cm. diameter), was laid over the above-mentioned cylinder and was also fixed to a flange of about 17 cm. diameter. Within about a 10 cm. distance between the cylinder and the flange, a coil spring having a strength of 2 kg/cm was inserted. Next, the assembly was placed in a vacuum tank, the pressure was reduced to about 100mmHg. by a rotary pump, and the cock of an exhaust pipe was closed by means of a rotary solenoid. Upon heating for about 4 minutes in the vacuum tank by a nichrome wire heater of 1 KW. arranged at 1 cm. distance from the thermo-shrinkable tube, the tube shrunk. After the shrinking, the flange compressed the springs and the springs consequently moved about 2 cm. toward the cylinder, respectively.

Then, the cylinder covered with the thermo-shrinkable tube was taken out of the vacuum tank and this cylinder was placed for 3 hours in a constant temperature bath at about 70.degree.C to complete the curing of the epoxy resin. Finally, excessive portions of the thermo-shrinkable tube at both ends of the cylinder were cut off and a cylindrical electrophotographic photosensitive body was obtained. The surface insulating layer formed by the shrinkage of the thermo-shrinkable tube was approximately 25.mu. in thickness.

To this photosensitive body, a corona discharge of (+) 6KV was applied by the same electrophotographic copier as in Example 1 above, and then the image was irradiated thereon while a corona discharge of AC 6KV was simultaneously applied followed by light irradiation all over the surface. Developing was then made with a toner of negative charge. It was possible in this way to obtain images of excellent quality.

In this case, nearly the same good result was obtained by using a direct current corona discharge of (-) 6KV instead of the above-mentioned alternating current corona discharge.

EXAMPLE 12

After the photoconductive layer was formed as in Example 11 above, this cylinder was rotated 120 times per minute (about 100 cm. per second in circumferential speed), and to the surface of the photoconductive layer a Teflon FEP film of 25.mu. thickness (Trade name of a fluorine resin manufactured by Du Pont Co.) was pressed, with its flat and smooth face in contact with the layer surface at slight pressure. The photoconductive layer, still in uncured condition, was thus flattened and smoothened by the rubbing action of the film. This levelled surface was very flat and smooth and also exhibited strong adhesion.

Then, in the same way as in Example 11 above, the shrinkable tube was shrunk to form an insulating layer. As a result, it exhibited very good adhesion, with no foams present between the photoconductive layer and the insulating layer, and there was obtained an excellent cylindrical electrophotographic photosensitive body which provided very good images.

EXAMPLE 13

By mixing thoroughly 40 g. of cadmium sulphide activated by copper, 55 g. of styrene monomer solution of polyester resin, named Ester G-10 (product of Tokyo Koatsu Co., Ltd.), 0.04 g. of methyl ethyl ketone peroxide and 0.03 g. of cobalt naphthenate, a mixture in paste form was prepared.

Subsequently, following the method of Example 11 above, a cylindrical photosensitive body was manufactured. The curing reaction was completed in 2 - 3 hours at room temperature. The photosensitive body thus produced also gave images of good quality.

EXAMPLE 14

Over the surface of the thermo-shrinkable tube referred to in Example 11 above, a paint of good heat absorbing property, which was composed mainly of natural rubber and chlorinated rubber and which also contained 20 - 30 percent of carbon black and tri-iron tetroxide, respectively, was coated. It was possible in this way to get complete shrinkage in about 3 minutes. This black film was later removed with ketone.

EXAMPLE 15

A photoconductive layer, in which CdS was dispersed in epoxy resin, was coated with a 10 percent ethanol solution of polyvinyl butyral (for example, Esleck BM-2 of Sekisui Co.) and dried to form a hot-melt bond layer. By laying it over a polyester film of 25.mu. in thickness, followed by heating and pressing, an electrophotographic photosensitive body in the form of a flat plate was obtained.

Reproducing was carried out by using this electrophotographic photosensitive body in flat plate form in the copier for electrophotography described in Example 1 above, and very good reproduction images were obtained.

EXAMPLE 16

A photoconductive layer was obtained by coating a conductive cylinder with a photoconductive material obtained by dispersing ZnO in silicon resin.

A solution of natural resin modified fumaric resin (for example, 10% MIBK butanol solution of Beccasite 1127 manufactured by Dainippon Ink) was applied to the inside of a thermo-shrinkable tube of polyester, and after drying, it was laid over the cylindrical photoconductive layer. Tying both tube ends, hot water (below 100.degree.C) was poured on it and it shrunk until it adhered compactly onto the cylindrical photoconductive layer.

In this case Beccasite 1127 does not soften with hot water.

After this shrinkage, the insulating layer was adhered jointly by an infrared heater and a pressure roller.

On the surface of this cylindrical electrophotographic photosensitive body, corona discharge of + 6KV was applied and then the image was irradiated while corona discharge of alternating current of 6KV was simultaneously carried out, followed by light irradiation all over the surface. There was obtained a sharp image of high contrast by developing with negative toner according to a known method.

As explained above, the present invention provides excellent manufacturing methods, as well as apparatus for providing a seamless electrophotographic photosensitive drum which has a photoconductive layer incorporating photoconductive material in a resin dispersion on a conductive layer and also has thereon a light permeable insulating layer. This invention therefore can contribute very much to the development of electrophotographic copiers. Further, according to the methods of the present invention, since no solvent whatever is used in the process step of forming the light permeable insulating layer, there can be no degradation of the photoconductive layer even where solvent-soluble resin is used as a binder resin in the photoconductive layer. Thus advantageously, binder resins can be selected from wide ranges. The present invention has further merits in that a light permeable insulating layer, damaged as a result of repeated uses of the sensitive drum, can be replaced easily by other new ones according to the method of the present invention.

Claims

We claim:

1. A method for producing a photosensitive body having a photoconductive layer and an insulative layer overlying said photoconductive layer comprising the steps of:

a. applying to a surface of an endless substrate a mixture including particulate photoconductive material;

b. arranging an endless thermally-shrinkable resin film in loosely encircling relation with said photoconductive material; and

c. heating said film, thereby shrinking said film into contacting relation with said applied photoconductive material.

2. The method claimed in claim 1 wherein said substrate comprises a conductive member.

3. The method claimed in claim 1 wherein said substrate comprises an insulative member.

4. The method claimed in claim 1 wherein said substrate comprises a conductive member overlying an insulative member.

5. The method claimed in claim 1 wherein said resin film comprises polyester resin.

6. The method claimed in claim 1 wherein said heating step is practiced under sub-atmospheric pressure, said photosensitive body being subjected to atmospheric pressure following practice of said heating step.

7. The method claimed in claim 1 wherein said heating step is practiced by applying heated water to said resin film.

8. The method claimed in claim 1 wherein said heating step is practiced by applying heated gas to said resin film.

9. A method of producing a photosensitive body having a photoconductive layer and an insulative layer overlying said photoconductive layer comprising the steps of:

a. applying to the interior surface of a tubular thermally-shrinkable resin film a mixture including particulate photoconductive material;

b. disposing a cylindrical substrate interiorly of said tubular film with said photoconductive material in loosely-encircling relation with said substrate; and

c. heating said film, thereby shrinking said film and disposing said photoconductive material in contacting relation with said substrate.

10. The method claimed in claim 9 wherein said substrate comprises a conductive member.

11. The method claimed in claim 9 wherein said substrate comprises an insulative member.

12. The method claimed in claim 9 wherein said substrate comprises a conductive member overlying an insulative member.

13. The method claimed in claim 9 wherein said substrate comprises an insulative member overlying a conductive member.

14. The method claimed in claim 9 wherein said resin film comprises polyester resin.

15. The method claimed in claim 9 wherein said mixture comprises a dispersion of said photoconductive material in a thermoplastic resin.

16. The method claimed in claim 9 wherein said mixture comprises a dispersion of said photoconductive material in a thermosetting resin.

17. The method claimed in claim 1 including the further step of smoothening the surface of said applied mixture prior to practice of said heating step by rubbing said surface with a member substantially non-adhesive to said mixture.

18. The method claimed in claim 17 wherein said mixture comprises a dispersion of said photoconductive material in a solution of a synthetic resin monomer or a synthetic resin of low polymerization degree and a polymerization accelerator.

19. A method for producing a photosensitive body having a photoconductive layer and an insulative layer overlying said photoconductive layer comprising the steps of:

a. aplying to a surface of an endless substrate a mixture comprising a dispersion of particulate photoconductive material in a solution of a synthetic resin monomer or a synthetic resin of low polymerization degree and a polymerization accelerator;

b. arranging an endless thermally-shrinkable resin film in loosely-encircling relation with said photoconductive material; and

c. heating said film, thereby shrinking said film into contacting relation with said applied photoconductive material,

said arranging and heating steps being practiced prior to completion of polymerization of said synthetic resin.

20. The method claimed in claim 19 wherein said resin film includes a heat-absorbing coating on a surface thereof.

21. The method claimed in claim 10 wherein said resin film comprises polyester resin.

22. The method claimed in claim 1 including the further step, practiced intermediate said applying and arranging steps, of overlaying on said applied mixture a layer comprising a resin rendered adhesive during said heating step.

23. The method claimed in claim 9 including the terminal step of removing said substrate.

24. The method claimed in claim 1 wherein said resin film includes a heat-absorbing coating on a surface thereof.

25. A photosensitive member comprising an endless substrate, a photoconductive layer overlying said substrate and an insulative layer overlying said photoconductive layer, said insulative layer comprising a thermally-shrunk endless film of thermoplastic resin.

26. The photosensitive member claimed in claim 25 wherein said substrate comprises a conductive material.

27. The photosensitive member claimed in claim 25 wherein said substrate comprises an insulative material.

28. The photosensitive member claimed in claim 25 wherein said substrate comprises a conductive layer overlying an insulative layer.

29. The photosensitive member claimed in claim 25 wherein said substrate comprises an insulative layer overlying a conductive layer.

30. The method claimed in claim 1 wherein said substrate comprises an insulative member overlying a conductive member.