GB1587312A - Image holding member e.g.for electrophotography - Google Patents

Description

(54) AN IMAGE HOLDING MEMBER E.G. FOR ELECTROPHOTOGRAPHY (71) We, CANON KABUSHIKI KAISHA, a Japanese company, of 3(W2, 3chome, Shimomaruko, Ohta-ku, Tokyo, Japan, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates tb an image holding member for holding electrostatic latent images and/or toner images, primarily in electrophotography.

Hitherto as an image holding member for use in electrophotography there have been known and used two types of image holding members, one of which is an electrophotographic photosensitive member and the other consists of a group of image holding members other than the electrophotographic photosensitive member. The first mentioned electrophotographic photosensitive member may have a great variety of arrangements designed to suit the electrophotographic process employed.

A typical example of an electrophotographic photosensitive member in use widely has an insulating layer on its surface. This insulating surface layer is provided for the purpose of protecting the photoconductive layer as well as improving the mechanical strength and the dark decay property of the member.

Also, the provision of an insulating surface layer is necessary to make the member usable in a certain particular electrophotographic process. Various representative examples of the photosensitive member provided with such an insulating surface layer and the electrophotographic process in which such a photosensitive member is used, are disclosed, for example, in U.S. Patent No. 2860048 and Japanese Patent Publication Nos. 16429/1966, 15446/1963, 3713/1971, 23910/1967, 19747/1967 and 4121/1961.

When the electrophotographic photosensitive member is subjected to a specific electrophotographic process, an electrostatic latent image is formed thereon which is developed with a toner.

As to the other group of holding members, some representative examples thereof will be described hereinafter.

An electrostatic latent image formed on the electrophotographic photosensitive member having a photoconductive layer by a certain electrophotographic process is usually developed with a toner and then the toner image thus formed is transferred to a suitable recording member such as a sheet of paper. However, in another electrophotographic process as disclosed, for example, in Japanese Patent Publication Nos. 7115/1957, 8204/1957 and 1559/1968, the electrostatic latent image formed on an electrophotographic photosensitive member is at first transferred to an electrostatic latent image holding member, which contains no photoconductive layer, and to which the invention is applicable.

The transferred latent image is developed with a toner and thereafter the toner image is transferred to a recording member. This modified process contributes to an improvement in the life of the electrophotographic photosensitive member.

Further modifications of the electrophotographic process are disclosed, for example, in Japanese Patent Publication Nos. 30320/1970 and 5063/1973 and Japanese Patent Application laid open No. 341/1976. In these modifications there is formed on an electrostatic latent image holding member an electrostatic image corresponding to the electrostatic image formed on an electrophotographic photosensitive member. In the modifications, there is used an electrophotographic photosensitive member in the form of a screen having a plurality of fine openings on which an electrostatic latent image is formed by a specific electrophotographic process.Through the electrostatic latent image formed on the electrophotographic photosensitive member, a corona charging treatment is conducted for the electrostatic latent image holding member so as to form thereon an electrostatic latent image by modulating the ion stream of corona. This image holding member has no photoconductive layer and can be used in this invention. The electrostatic latent image formed on the image holding member is then developed with a toner and the developed image is transferred to a recording member to obtain the final image.

Furthermore there is known such a process according to which a toner image formed on an electrophotographic photosensitive member or an electrostatic latent image holding member is not directly transferred to the recording member, but it is transferred at first to a toner image holding member and then to a recording member on which the toner image transferred from the toner image holding member is fixed. This invention is applicable to any of these members. This process is particularly effective for forming a color image or for carrying out a high speed copying. As the recording member, highly flexible material such as sheet of paper and film is generally used. Therefore, it is somewhat difficult to transfer a tricolor image to such a recording material while maintaining accurate alignment (or registration) of the color components of the image.The process, in which the toner image holding member may be substantially rigid, has an advantage in view of accurate alignment of the color image components. A well aligned color image can be formed by at first transferring the color components of a tricolor image to the rigid toner image holding member and thereafter transferring the toner image to a flexible recording member all at once. Also, by using the process in which a toner image is transferred to a recording member through a toner image holding member, a substantial speed up of copying operation may be attained.

As will be seen from the foregoing, it is very important for an image holding member, which may be an electrophotographic photosensitive member or one of the other members described having no photoconductive layer to have particular electrical characteristics suitable to the electrophotographic process used. Besides, durability and ease of cleaning are other important properties which such an image holding member should have. A high durability is required when the image holding member must be repeatedly used. The cleaning property is indispensable for allowing quick removal of any residual toner adhered to the surface of the image holding member. To obtain a clear and sharp image and also to prevent the associated cleaning means from being damaged, the cleaning property is of critical importance. Various attempts have been made to improve the durability and cleaning property of such image holding members. The provision of a surface layer having excellent durability is one typical solution of the problem. Materials which have been used include vinyl cellulose, ethyl cellulose, acrylic urethane, polyparaxylylene, aluminum oxide and titanium oxide. Also, it is known to overlay a film sheet of polyethylene terephthalate, polyethylene, polypropylene and polystyrene on the photoconductive layer by using a suitable bonding agent or to vapour-deposit an inorganic material such as mica onto the layer. Among them, PTFE, polyethylene, polyethylene terephthalate and vinylidene fluoride resins are useful for forming a surface layer having excellent lubrication, durability and cleaning properties.

However all these materials are in the form of film sheet and therefore they necessitate a high standard bonding technique by which the sheet can be adhered to a photoconductive layer, insulating layer or electrically conductive layer with a suitable bonding agent. This reduces efficiency of production. Furthermore, it is almost impossible to form a seamless surface layer on an image holding member in the shape of drum. With acrylic urethane or epoxy resin or high molecular weight polyesters it may be possible to form a surface layer by coating techniques. But, the surface layer thus formed lacks adequate lubrication, durability and cleaning properties.

Another disadvantage of an image holding member provided with a conventional surface layer is an insufficient moisture resisting property. When the image holding member is used for a long time in an atmosphere of high humidity, the characteristics of the member are adversely affected and therefore the quality of image formed thereon is poor.

Accordingly it is the primary object of the present invention to provide an improved image holding member with improved surface lubrication, durability and cleaning properties and having thereon a surface layer formed as a coating film, and preferably having a good moisture resisting property.

It is another object of the present invention to provide an improved image holding member with such properties which is easy to manufacture.

A further object of the present invention is to provide an improved image holding member which allows the formation of clear and sharp images.

According to the present invention, there is provided a member for holding an electrostatic image and/or toner image, comprising a support which carries a surface layer essentially consisting of at least 75 wit.% of one or both of substances A and B wherein the substance A represents a linear polyester soluble in organic solvents and the substance B represents a polymerization product of a linear isocyanate of the formula:

and a polyol of the formula: HO-(CII2)AOH wherein n is a positive integer from 2 to 20, said polyester having a molecular weight in the range of 5,000 to 50,000.

Embodiments of image holding members used in this invention are hereafter described.

The substances A and B used in the invention have various remarkable advantages and good properties. They are not only excellent in lubrication and moisture resistance but also good insulating materials. The coating film layer formed of them has a high hardness and good adhesion to a photoconductive layer or insulating layer. Also they exhibit a good transparency. Since they enable a surface layer to be formed on any image holding member by a coating process, it is also possible to form a seamless surface layer on an image holding member in the shape of drum.

Owing to the excellent properties of the substances A and B, the image holding member according to the present invention exhibits a very small surface friction resistance and, therefore, the durability of the member is also excellent. It prevents cleaning means from being damaged. The moisture resistance of the image holding member can be remarkedly improved.

The substance A i.e. a linear polyester resin used in the invention may be generally prepared by polycondensation of an organic dibasic acid and a diol.

Examples of organic dibasic acids useful for this purpose are dicarboxylic acids such as adipic acid, phthalic acid, maleic acid, succinic acid and sebacic acid.

Examples of diols useful for this purpose include ethylene glycol, hexamethylenediol-1,6, bisphenol-A, butane diol-1,4, pentadiol-1,5, diethylene glycol and propylene glycol-1,3.

The organic solvent soluble type of linear polyesters used in the invention may be those which are commercially available or those particularly prepared for this purpose. The kind and sort of linear polyester to be employed may vary in accordance with the kind and sort of the photosensitive member then used. In particular, the linear polyesters having a glass transition point of 40"C or above are preferably used. As for the chemical structure, those using one acid and one diol are recommendable. The linear polyester resin has a molecular weight in the range of 5,000 to 50,000. The polyester resins preferably used in the invention have molecular weights in the range of 10,000--40,000.

When a surface layer consisting of, as the essential component, a linear polyester resin is applied to an image holding member, the surface layer may be generally formed by coating a solution of the resin in a suitable organic solvent onto an insulating layer, an electrically conductive layer or photoconductive layer of the member.

When a surface layer consisting essentially of the polymerization product B is applied, a solution containing the diisocyanate and the polyol may be coated onto an insulating layer, electrically conductive layer or photoconductive layer of the member. After coating, the layer is subjected to a polymerizing treatment to form urelhane bonds. To carry out the necessary polymerizing treatment, heat, light, or an electron beam may be used as desired.

The ratio of the polyol to the polymerization product B is preferably 90--98 parts by weight of the polyol to 100 parts by weight of the linear isocyanate.

Since both the polyol and linear isocyanate are soluble in organic solvents, a surface layer can be formed by coating. If desired, the linear isocyanate and the polyol may be preliminarily polymerized to some extent before coating. Here the expression "to some extent" means that the compounds are polymerized to such an extent that the preliminarily and partially polymerized product is still easily soluble in the organic solvent used.

A surface layer essentially consisting of both of the substances A and B may be formed, for example, by preparing a solution containing a linear polyester resin, a linear isocyanate and a polyol, coating the solution onto an insulating layer, photoconductive layer or electrically conductive layer of the member and drying (or hardening) the coating layer.

The polymerization product B, which is produced from the linear isocyanate and the polyol and forms a surface layer, generally has a molecular weight ranging from 10,000 to 60,000 and in particular the range of 15,000--30,000 is preferable.

The thickness of the surface layer may vary in accordance with the particular characteristics required for it. In case that the principal purpose of the provision of such a surface layer is to protect the image holding member as well as to improve its durability and dark decay property, the thickness may be relatively small. When the image holding member is to be used in an electrophotographic member requiring a highly insulating upper layer over a photoconductive layer, a relatively large thickness may be selected for the surface layer. In general, the thickness of a surface layer is in the range of 0.1 to 100 u and more particularly 0.150,.

If desired, some other additional component(s) may be added to the essential component of the surface layer up to a limit of 25 wt.%. Examples of such an additional component include various isocyanates as will be particularly mentioned later in the Examples, silane coupling agents, fatty acid amides, fatty acid metal salts and wax. Silane coupling agent is able to attribute to the improvement of adhesion and hardness of the surface layer according to the invention. Preferable silane coupling agents are those which have vinyl-, epoxy-, methoxy- or ethoxy groups. Such a silane coupling agent can react with terminal groups such as OH, and COOH existing in the resin.

Typical examples of silane coupling agent are given below: ((:H30)3.Si (cri2 I'HCHNH2

(CH3C00)3SiT11=CH2 ( CH30 ) 35iCH=CH2 Fatty acid amides or fatty acid metal salts may attribute to the improvement of image density. Examples of such additive are amides and metal salts of stearic acid an oleic acid.

By the addition of wax, a further improvement of moisture resisting property of the surface layer is attainable. Any commonly used wax including ethylene wax and paraffin wax may be used.

Also, substance A and/or substance B used in forming a surface layer may further contain small amounts of other additional resins, provided the total additives content does not exceed 25 wit.%. Examples of other resin suitable for additives are polyethylene, polyester (e.g. a different type), polypropylene, polystyrene, polyvinyl chloride, polyvinyl acetate, acrylic resin, polycarbonate, silicone resin, fluorine-containing resin, or epoxy resin. These resins are organic insulating materials.Other examples of usable resin as additives are setting (or curing) resins such as urethane resin, acrylic resin and acrylic urethane resin (that is a resin having both of urethane bond and acrylic double bond and obtainable by the reaction among acrylic monomer, isocyanate compound and polyol compound), which may be cross-linked and which serve to improve the hardness of the surface layer according to the invention. Furthermore, by adding a silicone resin to the surface layer, a further improved cleaning property is obtained.

In case that the image holding member according to the invention is an electrophotographic photosensitive member, it is generally manufactured so that the photoconductive layer is sandwiched in between a support and a surface layer.

The support may be made from suitable material such as a metallic sheet of stainless steel, copper, aluminum or tin, paper, sheet, or a resin film.

The photoconductive layer may be formed by vapour-depositing in vacuum a suitable inorganic photosensitive material such as S, Se or PbO, or compounds containing S, Se, Te, As, Sb and/or Pb. When the sputtering method is employed to form the photoconductive layer, it may be formed by making a photoconductive substance with high melting point such as ZnO, CdS, CdSe and TiO2 adhere to a support. If a coating method is employed to form the photoconductive layer, an organic photoconductive material such as polyvinyl carbazole, anthracene and phthalocyanine including those sensitized by adding pigment or Lewis acid and their mixture with an insulating binder may be used. A mixture of an inorganic photoconductive substance such as ZnO, CdS, TiO2 and PbO with an insulating binder also may be used. As the insulating binder, various resins may be used.The thickness of photoconductive layer may be varied in accordance with the type and characteristics of the photoconductive substance then used. Generally speaking, the range of 5-100 ,u and in particular 10--50 u is preferable.

Between the surface layer and the photoconductive layer there may be interposed an additional layer containing neither substance A nor B.

In case that the image holding members of the invention are those which comprise no photoconductive layer, one typical structure of the members comprises a support and a surface layer formed thereon. Another structure comprises a support, an insulating layer made of other material and a surface layer formed on the insulating layer by coating.

Hereinafter the invention will be more fully described by way of examples.

Example 1 200 g of a high purity (99.999V0) Se was weighed and placed on an evaporating dish. With the high purity Se, vapour deposition was carried out for 35 minutes under the conditions of 300"C of evaporating source temperature, 66-680C of substrate (a drum made from aluminum) temperature and lx 10-5 torr of vacuum in the system. Two photosensitive drums were made each of which had a photoconductive layer of film 60 y thick.

To one of the two photoconductive layers thus formed, a surface layer was applied. To form the surface layer on it, the one photoconductive layer was dipped into an immersion liquid bath containing a photosetting (photo curing) type of acrylic urethane resin (trade name: Sonne, manufactured by Kansai Paint Co.

Ltd.). The immersion bath was prepared by diluting the resin with ethanol to a viscosity of 100 cps.

The layer was drawn up from the immersion bath in the direction normal to the liquid level and along the generating line of the drum. Thereafter, it was exposed to the rays of a 4 KW mercury lamp for six minutes to effect photosetting.

A surface layer 0.8 u thick was obtained which is hereinafter referred to as Sample (A).

Another photoconductive layer was dipped into an immersion liquid bath prepared by diluting a mixture (96:4) of a linear polyester (trade name: Vylon, by Toyobo Co., Ltd.) and an isocyanate (Colonate L, by Nippon Polyurethane Co., Ltd. formula specified in last page) with methyl ethyl ketone to a viscosity of 100 cps. Thereafter it was drawn up in the same direction as described above and subjected to a thermosetting treatment by heating it at 700C for 20 minutes. In this manner, a surface layer 0.9 M thick was formed, which is hereinafter referred to as Sample (B).

With each of the Samples (A) and (B), a durability test was carried out in the following manner: The sample was charged by a primary DC charging with positive polarity so that the surface voltage reached the level of 900 V and then imagewise-exposed at an exposure value of 25 lux.sec. Thereafter it was developed with dry developer for magnet brush charged with negative polarity and cleaned with a cleaning blade made of urethane rubber. The cleaning blade had a hardness of 70, a blade angle of 30 retative to the drum and a blade pressure of 1.0 Kg (load).

During the cleaning, Sample (A) generated a tremendous rubbing noise due to the friction between the cleaning blade and the surface layer. After fifty (50) revolutions of the drum, a considerable wear was observed at the edge portion of the blade and also distinct damage was found on the surface layer. At the most heavily damaged portion, the damage reached even the photoconductive layer surface.

In contrast with Sample (A), the drum of Sample (B) continued rotating smoothly with a torque under 0.5 Kg and the image on it could maintain its good quality. Even after forty thousand (40,000) revolutions of the drum, there were scarcely observed breaking at the edge portion of the blade or blade damage to the surface layer.

In the following examples, when the term "the linear polyester" is used without any further specification, it denotes that of Vylon 200 (trade name) (molecular weight 15,000-20,000 prepared from ethylene glycol, butane diol and terephthalic acid).

Example 2 200 g of a high purity (99.9990/,) Se-Te (15 wt.%) alloy was weighed and placed on an evaporating dish. With this alloy, vapour depositing was carried out for forty minutes under the conditions of 320"C of evaporating source temperature, 700C of substrate (aluminum drum plated with Ni) and lx 10-5 torr of vacuum in the system.

Two photosensitive drums were made each of which had a photoconductive layer of film 65 y thick.

To one of the two photoconductive layers thus formed, a surface layer was applied in the following manner. An immersion bath was prepared by diluting a photosetting type of unsaturated polyester resin (that is a non-linear polyester resin; trade name: "UV-CM-103", manufactured by Cashew Co., Ltd. Mol. wt.

about 3000 prepared from ethylene glycol, glycerine, adipic acid and maleic anhydride) with methyl ethyl ketone to a viscosity of 90 cps. The one drum was dipped into the immersion liquid bath thus prepared. Thereafter, in the same manner as in Example 1, it was drawn up from the bath and subjected to a photosetting treatment by irradiation of a 4 KW mercury lamp for six minutes. The above described operation was repeated three times so that a surface layer 30 y thick was formed. This sample is hereinafter referred to as Sample (C).

To the other photoconductive layer, at first a layer 20 u thick was applied by carrying out coating twice the procedure for Sample (C). Then, a surface layer of 10 y thick was overlaid on the 20 p thick layer. To form the surface layer, an immersion bath was used which was prepared by diluting a mixture (95:5 by weight) of the linear polyester and an isocyanate (trade name: "HMDI" (hexamethylene diisocyanate), by Nippon Polyurethane Co., Ltd.) with methyl ethyl ketone as to have the viscosity of 90 cps. Dipping in the immersion bath and drawing up from it were effected in the same manner as in Example 1. Hardening was effected by heating it at 700C for thirty minutes. This sample is referred to as Sample (D1).

Each of samples (C) and (D,) was subjected, in an electrophotographic copying apparatus, to an electrophotographic process comprising the steps of a primary DC charging with negative polarity, a secondary AC discharging simultaneous with imagewise exposure and a whole surface exposure so as to form an electrostatic latent image thereon. After developing the latent image with dry developer for magnet brush charged with positive polarity, the same durability test as that in Example 1 was carried out for Samples (C) and (D1). The results of the test were as follows: Sample (C) generated a tremendous rubbing noise during the test and after sixty (60) revolutions of the drum, the edge portion of the drum was worn out to a ragged edge.

Sample (D,) continued rotating smoothly and maintained the good cleaning feasibility. Even after 30,000 revolutions of the drum, there was observed no change from the original state at the edge portion of the drum and on the surface layer.

Further samples, D2-D11 were prepared by substituting the following materials for the linear polyester and the isocyanate used for Sample D, in this example and tested in the same manner as the above. All of the photosensitive drums of Samples D2 to D" exhibited an excellent durability similar to that of Sample D,. Even after 30,000 revolutions of the drums, neither deterioration of image quality nor reduction in cleaning feasibility was observed. Photosensitive drums D2-D6 were prepared by using a mixture of linear polyesters and isocyanate (trade name: HMDI) (ratio 95:5 by weight) as shown in D2-D6 below.

D2: adipic acid-ethylene glycol polyester (molecular weight: about 25,000) D3: terephthalic acid-ethylene glycol polyester (m.w.: about 38,000) D4: terephthalic acid-adipic acid-ethylene glycol polyester (m.w.: 20,000) D5: terephthalic acid-bisphenol A polyester (m.w.: about 7,500) D6: terephthalic acid-adipic acid-bisphenol A polyester (m.w.: about 30,000) D7: a mixture (95:5, by weight) of the linear polyester (trade name: 49001, by Du Pont mol. wt. about 20,000 prepared from ethylene glycol, hexane diol and terephthalic acid) and a photosetting type of acrylic urethane resin (manufactured by Kansai Paint Co., Ltd.) (setting condition: irradiation of ultraviolet rays with mercury lamp for six minutes) a a mixture (90:5:5, by weight) of the linear polyester resin (by Kansai Paint Co., Ltd.), a photosetting type of acrylic urethane resin and a silicone oil (trade name: SH 157, by Tore Silicone Co., Ltd.) (setting condition: irradiation of ultraviolet rays with mercury lamp for six minutes) D9: the linear polyester 94 parts thermosetting acrylic urethane resin (trade name: Retan, supplied by Kansai Paint Co.) setting condition=700C, 15 min. 6 parts D10: the linear polyester 93 parts thermosetting urethane resin (trade name: Kansai Urethane 500, supplied by Kansai Paint Co., Ltd.) 6 parts silicone oil (trade name: SH 157) 1 part thermosetting condition=80 C, 15 min.

D,1: the linear polyester 95 parts thermosetting acrylic resin (trade name: Acdeck A-810, supplied by Japan Reichhold Chemicals Co., Ltd.) 5 parts setting condition=80 C, 15 min.

Example 3 200 g of a high purity (99.999%) Se was weighed and placed on an evaporating dish. Using it, vapour deposition was carried out for thirty five minutes under the conditions of 300"C of evaporating source temperature, 670C of substrate (aluminum cylinder) and I x 10-5 torr of vacuum in the system. Two photoconductive layers were made each of which had the film thickness of 60 p.

One of the two photoconductive layers was dipped into an immersion liquid bath which was prepared by diluting a photosetting type of acrylic urethane resin (trade name: Sonne, by Kansai Paint Co., Ltd.) with methyl ethyl ketone to a viscosity of 90 cps. After drawing it up from the bath at the rate of 30 mm/min., a setting treatment was carried out by irradiating it for five minutes with a 4 KW mercury lamp so that an insulating layer 10,u thick was formed. The same coating operation was repeated three times so that a surface layer having the thickness of 30 u in total was formed. This sample is referred to as Sample D12.

For the other photoconductive layer, an immersion liquid bath was prepared by diluting a mixture (1.2:1) of a linear isocyanate of the formula:

and a hexamethylene diol of the formula: HO-(CH2)6-OH with methyl ethyl ketone to a viscosity of 90 cps. The photoconductive layer was dipped in the immersion liquid bath and drawn up from it at the rate of 30 mm/min. Then, a thermosetting treatment was carried out at 55"C for twenty minutes so that a layer 10 p thick was formed. This procedure of immersion coating was repeated three times so as to finally form a surface layer 30 thick. This sample is referred to as Sample D13.

Each of Samples D12 and D13 was tested to evaluate the lubricating property.

image forming property and durability thereof. To this end, each the Samples D12 and D13 was used in an electrophotographic process comprising the steps of a primary DC charging with negative polarity, a secondary AC discharging simultaneous with imagewise exposure, a whole surface exposure, a development with a dry positive toner and cleaning. Cleaning was effected with a urethane cleaning blade having the hardness of 70 (blade angle relative to the cylinder was 30 and the blade load was 2.0 Kg).

During the test, Sample D12 generated a loud sliding noise due to the friction between the blade and the surface layer. Its coefficient of friction was found to be 2.60. After fifty (50) revolutions of the drum, considerable wear of the edge portion of the blade as well as a distinct damage on the surface layer were observed, and at the most heavily damaged portion, the surface layer was almost peeling off.

Sample D13 continued rotating smoothly and its coefficient of friction was measured to be 1.05. The quality of image was kept good. Even after forty thousand (40,000) revolutions of the drum, there was not observed any substantial wearing at the edge portion of the blade nor blade damage to the surface layer.

Example 4 200 g of a high purity (99.9990/,) Se-Te (10 wt /") alloy was weighed and placed on an evaporating dish. Using it, vapour deposition was carried out for 40 minutes under the conditions of 320"C of evaporating source temperature, 700C of substrate (aluminum cylinder) and 1x10-5 torr of vacuum in the system. Two photoconductive layers were made each of which had a film thickness of 65 p.

One of the two photoconductive layers was dipped into an immersion liquid bath which was prepared by diluting a photosetting type of unsaturated polyester resin with methyl ethyl ketone to a viscosity of 90 cps. After drawing it up from the bath at the rate of 30 mm/min., a setting treatment was carried out by irradiating it for five minutes with a 4 KW mercury lamp. The same dip coating operation was repeated three times so that a surface layer having the thickness of 30,u in total was formed. This sample is referred to as Sample D14.

For the other photoconductive layer, an immersion liquid bath was prepared by diluting a mixture (2:1) of a linear isocyanate of the formula:

and ethylene glycol of the formula: HO-(CH2-CH2)-OH with methyl ethyl ketone to a viscosity of 90 cps. The photoconductive layer was dipped in the immersion liquid bath and drawn up from it at the rate of 30 mm/min.

Then, a thermosetting treatment was carried out at 550C for thirty minutes so that a layer of 10, thick was formed. This procedure of immersion coating was repeated three times so as to finally form a surface layer 30 p thick. This sample is referred to as Sample D15.

Each of Samples D14 and Dls was tested in the same manner as that of Example 3.

During the test, Sample D14 generated a loud sliding noise due to the friction between the blade and the surface layer and its coefficient of friction was found to be 2.83. After forty (40) revolutions of the drum, considerable wear of the edge portion of the blade as well as a distinct damage on the surface layer were observed.

Sample Dls continued rotating smoothly and its coefficient of friction was measured to be 1.15. The quality of image was good. Even after 35,000 revolutions of the drum, there was not observed any substantial wearing at the edge portion of the blade nor blade damage to the surface layer.

Example 5 200 g of a high purity (99.999%) Se-As (1.0 wt%) alloy was weighed and placed on an evaporating dish. Using the alloy, vapour-depositing was carried out for 40 minutes under the conditions of 315"C of evaporating source temperature, 670C of substrate (aluminum cylinder) temperature and lxl0-5 torr of vacuum in the system so that a photoconductive layer 65 p thick was formed.

The photoconductive layer thus formed was dipped into a liquid bath prepared by diluting a thermosetting acrylic resin (trade name: Pulslac No. 2000, by Chugoku Marine Paints Co., Ltd.) with methyl ethyl ketone to a viscosity of 90 cps.

After drawing up from the bath at the rate of 30 mm/min., a thermosetting treatment was carried out at 500C for thirty minutes. This dipping coating procedure was repeated twice so as to finally produce layer 20 p thick.

Onto the 20 p thick layer, a surface layer 10,u thick was overlaid. The surface layer was applied in the following manner: A mixture (2:0.8:0.1) of

HO-(CH2)12-OH and a silicone oil modified by stearic alcohol was diluted with tetrahydrofuran to a viscosity of 90 cps. The sample described above was dipped in the liquid bath thus prepared and drawn up from it at the rate of 30 mm/min.

Setting was effected by heating it at 550C for'thirty minutes to form a layer of 10 p thick.

The photosensitive drum thus manufactured was tested in the same manner as in Example 3.

The drum continued rotating very smoothly, and it was found that its image resolution and cleaning feasibility were good. Even after 50,000 revolutions of the drum, there was not observed any change in operation from its original state. The edge portion of the cleaning blade and the surface layer were maintained unchanged and undamaged.

Example 6 Onto an aluminum drum, there was coated a layer 50 p thick of CdS dispersion according to the immersion coating method and heated for fifteen minutes at 800 C.

Thereafter, a coating 12 p thick of photosetting acrylic urethane resin (trade name: Sonne, by Kansai Paint Co., Ltd.) was overlaid on the layer. After heating for fifteen minutes at 700C, it was subjected to the irradiation of an 8 KW mercury lamp for ninety sec.

Lastly a surface layer was overlaid on it by using an immersion bath which was prepared by diluting a mixture (ratio 96:4 by weight) of the linear polyester and an isocyanate i.e. ethylene diphenyl isocyanate with methyl ethyl ketone to a viscosity of 90 cps. After drawing up from the immersion bath in the same manner as in Example 1, the coated layer was hardened by heating it at 70"C for thirty minutes.

Thus, a surface layer 12 p thick was formed.

The photosensitive drum obtained in this manner was tested according to the same testing procedure as that in Example 2. During the test, the drum continued rotating smoothly and it was found that the image resolution and cleaning feasibility of the same were very good. Even after 30,000 revolutions of the drum, there was observed neither operational trouble nor damage.

Examples 7-13 Employing the following mixtures as substitute for the mixture of the linear polyester and isocyanate (ethylene diphenyl isocyanate) used in Example 6, various surface layers were formed and tested in the same manner as in Example 6. All of them exhibited good properties and characteristics equivalent to that of Example 6. Example No. Composition of mixture used (percent by weight)

# the linear polyester (92) 7. # metaxylene diisocyanate (6) stearic acid amide (2) the linear polyester (96) 8. # silane coupling agent (4) (trade name: SH6020*, SH6075** by Tore Silicone Co., Ltd.) *(CH30)3Si(CH2)3NHCH2CH2NH2 **(CH3COO)3SiCH=CH2

the linear polyester1 (95) 9. # trans vinylene diisocyanate (4) oleic acid amide or calcium stearate (1) the linear polyester (94) 10. # 2,4-tolylene diisocyanate (4) paraffin wax (m.p.-850C) (2) the linear polyester1 (92) 11. polyethylene terephthalate (3) photosetting acrylic urethane (5) the the linear polyester1 (93) 12. polybutylene terephthalate (3) photosetting polyester (4) the Ithe linear polyester1 13. 5 polyethylene terephthalate (3) N-methyl-2-pyrrolidone (5) (See Example 1) Example 14 A cylindrical aluminum support (200#x500 mm) was dipped in an immersion liquid bath and, after drawing it up from the bath at the rate of 30 mm/min., the drum was subjected to a setting treatment by the irradiation of a 4 KW mercury lamp for five minutes so that a layer 10 p thick was formed. The immersion bath used above was prepared by diluting a photosetting acrylic urethane resin with methyl ethyl ketone to a viscosity of 90 cps.

To the layer thus formed, a second layer 5 p thick was overlaid by repeating the above described dipping operation with only the change that the rate of drawing up was decreased to 23 mm/min. In this manner, a surface layer having the total thickness of 15 p was applied onto the support. This sample is referred to as Sample D16.

To another aluminum support with the same size and the same shape as that of Sample Dlss, there was applied at first a layer 10,u thick of acrylic urethane resin in the same manner as above. Secondly, a surface layer 5 p thick was overlaid on the acrylic urethane layer by using an immersion bath prepared by diluting a mixture (ratio 96:4 by weight) of the linear polyester and an isocyanate (trade name: Colonate L, formula m last page, by Nippon Polyurethane Co., Ltd.) with methyl ethyl ketone to a viscosity of 90 cps. It was drawn up from the immersion bath at the rate of 23 mm/min. and heated for twenty minutes at 800C for setting.

The sample thus prepared is referred to as Sample D17.

Using each of Samples D16 and D1, as an electrostatic latent image holding member, a durability test was carried out respectively in the following manner: The samples were subjected to an electrostatic latent image forming process where an electrostatic latent image was formed thereon by applying a corona discharge modulated by passing through an electrostatic latent image formed on a CdS screen photosensitive member. In this process, dry developer charged with positive polarity and a urethane cleaning blade (hardness: 70, a blade angle relative to the surface layer of Sample: 300, and blade pressure: 2.0 Kg) were used, and the durability regarding developing, transferring and cleaning was evaluated.

The results of the test were as follows: Sample D16 showed a coefficient of friction of 2.70 and produced a loud rubbing noise due to the friction between the cleaning blade and the surface layer.

After fifty revolutions of the drum, there was already observed considerable wear at the blade edge portion and distinct blade damage to the surface.

Sample D17 showed a coefficient of friction of 1.03 and the drum continued rotating very smoothly and continuing to give good images. Even after 40,000 revolutions of the drum there was not observed any wear and tear at the edge portion of the blade. No film forming due to fusion of developer was found.

Substituting the linear polyurethanes as specified below for the above described polyester further samples, Samples D18 and D,, were made and tested in the same manner. They exhibited also good durability and cleaning feasibility equivalent to that of Sample D17.

f linear isocyanate OCN Q eCH243 CO (1) Sample D18: hexamethylene diol (1) linear isocyanate OCN < CH24 > NCO (2) Samples9: HO-(CH2)12-OH (0.8) silicone oil modified by stearic alcohol (0.1) The numerical values in the brackets show composition ratio by weight.

The lubricating property of each of the Samples was measured by using a CdS screen photosensitive member in the following manner.

A photoconductive layer of 30 y thick was attached to a stainless steel network (size of opening: about 50 p) by spray coating. The composition of the photoconductive layer was 70 parts by weight of CdS and 30 parts by weight of silicone resin (trade name: KR-255, supplied by Shinetsu Silicone Co.), and the resulting photosensitive layer was dried at 800C for 15 minutes. Then there was formed an insulating layer of 15 p thick on the photoconductive layer. The insulating layer comprised a silicone resin (trade name: TSR-144, supplied by Toshiba Silicone Co.) containing a curing agent (trade name: CR-15).

A surface of the resulting scree photosensitive member was charged to +450V and subjected to imagewise exposure simultaneously with AC discharging to produce an electrostatic image having -50 V at the light portion and +200 V at the dark portion. The Samples were placed at the stainless steel wire side of the screen photosensitive member, and corona charging was applied to the Sample through the screen photosensitive member. Then the resulting electrostatic image formed on the sample was developed with a toner and the resulting toner image was transferred to a paper with an impressed voltage for transferring of about -6KV and fixed to produce a visible image.

Example 15 On an aluminum drum, a CdS photoconductive layer of 50 p thick was formed, which consisted of 10 parts by weight of vinyl chloride-vinyl acetate copolymer and 90 parts by weight of CdS powder. Further, a layer of 3 p thick of a thermosetting epoxy resin adhesive was applied onto the photoconductive layer and lastly a film 25 p thick of polyethylene terephthalate was overlaid by adhesion on the bonding layer. In this manner, a photosensitive drum was manufactured, which is referred to as photosensitive drum X.

Another photosensitive drum, that is, photosensitive drum Y was manufactured in the same manner as that for the photosensitive drum X, but with the change that instead of polyethylene terephthalate, a layer 25 p thick of the linear polyester resin was overlaid by coating on the epoxy resin layer.

Under conditions of moisture of 60% R.H., an electrostatic latent image was formed on each of the photosensitive drums X and Y according to a conventional electrophotographic process comprising the steps of primary charging with negative polarity, secondary AC discharging simultaneous with imagewise exposure and whole surface exposure.

The formed electrostatic image on either of photosensitive drums X and Y exhibited a high electrostatic contrast of 750 V (dark image portion G3650 V and light image portion 0100 V). The toner image obtained by developing the electrostatic latent image with wet toner also exhibited a high sharpness in either case of X and Y.

The next test was carried out after allowing the photosensitive drums X and Y to stand for twenty hours in an atmosphere of 30"C and 85 " relative humidity. An electrostatic image and a toner image were formed on each of the drums X and Yin the same manner as described above.

The electrostatic image formed on the photosensitive drum X showed a lower electrostatic contrast of 410 V (dark image portion: 0400 V, light image portion: 010 V) and the toner image also lacked sharpness.

The photosensitive drum Y again could produce a good electrostatic latent image having a high electrostatic contrast of 720 V (dark image portion 0630 V, light image portion 090 V). The toner image obtained from the latent image exhibited a high sharpness equal to that of the first test.

Example 16 On an aluminum drum, a CdS photoconductive layer of 50 u thick was formed, which consisted of 10 parts by weight of vinyl chloride-vinyl acetate copolymer and 90 parts by weight of CdS powder. Further, a layer of 3 etc thick of a thermosetting epoxy resin bonding agent was applied onto the photoconductive layer and lastly a film 25,u thick of polypropylene was overlaid by adhesion on the bonding layer. In this manner, a photosensitive drum was manufactured, which is referred as photosensitive drum U.

Another photosensitive drum, that is, photosensitive drum V was manufactured in the same manner as that for the photosensitive drum U, but with the change that instead of polypropylene, a layer of 25 p thick of a linear polyester resin (trade name: B-301, by Kansai Paint Co., Ltd. molecular weight about 6000 prepared from adipic acid and polyethylene glycol was overlaid by coating on the thermosetting epoxy resin layer.

Under the condition of moisture of 60% R.H., an electrostatic latent image was formed on each of the photosensitive drums U and V according to a conventional electrophotographic process comprising the steps of primary charging with negative polarity, secondary AC discharging simultaneous with imagewise exposure and whole surface exposure.

The formed electrostatic image on either of photosensitive drums U and V exhibited a high electrostatic contrast of 750 V (dark image portion 0650 V and light image portion 0100 V). The toner image obtained by developing the electrostatic latent image with wet toner also exhibited a high sharpness in either case of U and V.

The next test was carried out after allowing the photosensitive drums U and V to stand for 25 hours in the atmosphere of 25"C and 90% relative humidity. An electrostatic image and a toner image were formed on each of the drums in the same manner as described above.

The electrostatic image formed on the photosensitive drum U showed a lower electrostatic contrast of 340 V (dark image portion 0340 V, light image portion 0) and the toner image also lacked sharpness.

The photosensitive drum V again produced a good electrostatic latent image having a high electrostatic contrast of 720 V (dark image portion 0630 V, light image portion 090 V). The toner image obtained from the latent image exhibited a high sharpness equal to that of the first test.

Example 17 On an aluminum drum, a CdS photoconductive layer 50 p thick was formed, which consisted of 10 parts by weight of vinyl chloride-vinyl acetate copolymer and 90 parts by weight of CdS powder. Further, on the photoconductive layer a film 25 p thick of epoxy resin (Trade Mark: Epikote, by Shell Chemicals) was overlaid by coating. In this manner, a photosensitive drum was manufactured, which is referred as photosensitive drum S.

Another photosensitive drum, that is, photosensitive drum T was manufactured in the same manner as that for the photosensitive drum S, but with the change that instead of epoxy resin, a layer 25 ,u thick of the linear polyester resin was overlaid by coating on the photoconductive layer.

Under the condition of moisture of 60 /" R.H., an electrostatic latent image was formed on each of the photosensitive drums T and S according to an usual electrophotographic process comprising the steps of primary charging with negative polarity, secondary AC discharging simultaneous with imagewise exposure and whole surface exposure.

The formed electrostatic image on both photosensitive drums S and T exhibited a high electrostatic contrast of 750 V (dark image portion 0650 V, and light image portion 0100 V). The toner image obtained by developing the electrostatic latent image with wet toner also exhibited a high sharpness in either case of S and T.

The next test was carried out after allowing the photosensitive drums S and T to stand for 25 hours in the atmosphere of 30"C and 85% relative humidity. An electrostatic image and a toner image were formed on each of the drums in the same manner as described above.

The electrostatic image formed on the photosensitive drum S showed a lower electrostatic contrast of 360 V (dark image portion 0350 V, light image portion 010 V) and the toner image also lacked sharpness.

The photosensitive drum T again could produce a good electrostatic latent image having a high electrostatic contrast of 710 V (dark image portion 0620 V, light image portion 090 V). The toner image obtained from the latent image exhibited a high sharpness equal to that of the first test.

Using the following materials as substituted for the linear polyester used alone in Sample T, further photosensitive drums P, Q and R were manufactured and tested according to the procedure as described above. All of these drums P, Q and R showed an excellent moisture resisting property equivalent to that of the above described photosensitive drum T.

Photosensitive Drum Composition of material used (part by weight)

the linear polyester resin (80) (P) OCN CH2NCO (10) hexamethylene diol (10) the linear polyester resin (60) (trade name: B-301 (20) OCN - CH2eNCO hexamethylene diol (20) OCN e - CH2eNCO (50) hexamethylene diol (50) Colonate L has the formula:

WHAT WE CLAIM IS: 1. An image-holding member for holding an electrostatic image and/or toner images, comprising a support which carries a surface layer essentially consisting of at least 75 wit.% of one or both of substances A and B wherein the substance A represents a linear polyester soluble in organic solvents and the substance B represents a polymerization product of a linear isocyanate of the formula:

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   negative polarity, secondary AC discharging simultaneous with imagewise exposure and whole surface exposure.

   The formed electrostatic image on both photosensitive drums S and T exhibited a high electrostatic contrast of 750 V (dark image portion 0650 V, and light image portion 0100 V). The toner image obtained by developing the electrostatic latent image with wet toner also exhibited a high sharpness in either case of S and T.

   The next test was carried out after allowing the photosensitive drums S and T to stand for 25 hours in the atmosphere of 30"C and 85% relative humidity. An electrostatic image and a toner image were formed on each of the drums in the same manner as described above.

   The electrostatic image formed on the photosensitive drum S showed a lower electrostatic contrast of 360 V (dark image portion 0350 V, light image portion 010 V) and the toner image also lacked sharpness.

   The photosensitive drum T again could produce a good electrostatic latent image having a high electrostatic contrast of 710 V (dark image portion 0620 V, light image portion 090 V). The toner image obtained from the latent image exhibited a high sharpness equal to that of the first test.

   Using the following materials as substituted for the linear polyester used alone in Sample T, further photosensitive drums P, Q and R were manufactured and tested according to the procedure as described above. All of these drums P, Q and R showed an excellent moisture resisting property equivalent to that of the above described photosensitive drum T.

   Photosensitive Drum Composition of material used (part by weight)

   the linear polyester resin (80) (P) OCN CH2NCO (10) hexamethylene diol (10) the linear polyester resin (60) (trade name: B-301 (20) OCN - CH2eNCO hexamethylene diol (20) OCN e - CH2eNCO (50) hexamethylene diol (50) Colonate L has the formula:

   WHAT WE CLAIM IS: 1.An image-holding member for holding an electrostatic image and/or toner images, comprising a support which carries a surface layer essentially consisting of at least 75 wit.% of one or both of substances A and B wherein the substance A represents a linear polyester soluble in organic solvents and the substance B represents a polymerization product of a linear isocyanate of the formula:

   and a polyol of the formula: HO(CH2)nOH wherein n is a positive integer from 2 to 20, said polyester having a molecular weight in the range of 5,000 to 50,000.
2. 2. An image-holding member as claimed in claim 1 wherein said surface layer contains additionally at least one member selected from isocyanate, silane coupling agents, fatty acid am ides, fatty acid metal salts and wax.
3. 3. An image-holding member as claimed in claim I wherein said surface layer further contains an acrylic urethane resin and/or a silicone resin.
4. 4. An image-holding member as claimed in any preceding claim wherein said surface layer has a thickness ranging from 0.1 to 100 p.
5. 5. An image-holding member as claimed in any preceding claim which comprises a photoconductive layer between the support and the surface layer.
6. 6. An image-holding member substantially as described herein with reference to any one of the Examples.