GB2166370A - Electrostatic recording medium - Google Patents

Abstract

An electrostatic recording medium comprising an electroconductive support in the form of a seamless belt, comprising thermosetting resin binder and electroconductive fine powder dispersed in the binder and a dielectric layer, and a method of manufacturing such a recording medium.

Description

SPECIFICATION Electrostatic recording medium The present invention relates to an electrostatic recording medium and, more particularly, to an electrostatic recording medium which is used repeatedly in a transfer-type electrostatic recording device, has an excellent durability, and comprises a two-layer structure.

An electrostatic recording medium formed by providing an electroconductive layer and a dielectric layer, in sequence, on the surface of an insulating support is heretofore known. In order to form an image by using such an electrostatic recording medium, an image signal voltage sufficient to effect discharge between a recording electrode such as a multistylus electrode and the electroconductive layer of the electrostatic recording medium is applied, while said electrode is in contact with the surface of the dielectric layer, whereby the discharge is effected to form a static charge pattern corresponding to the image, that is, a static latent image on the dielectric layer. The latent image formed in this way is developed in a developing part to form a toner image, which is transferred to and fixed on a transfer sheet such as paper.The recording medium after transfer is cleaned, discharged, and used repeatedly in the subsequent recording processes, in each of which the above cycle is repeated.

It is desirable that such an electrostatic recording medium has a form of an endless belt having a uniform film thickness. A conventional endless belt electrostatic recording medium may be made by forming a sheet-like support into an endless belt, by bonding by heat or an adhesive, and forming an electroconductive layer and a dielectric layer, in sequence, on the support; or by forming a three-layer, sheet-like electrostatic recording medium into an endless belt by heat bonding.

The bonded part of the endless belt thus produced has a disadvantage that the above-mentioned desired uniform film thickness can not be attained, because the bonded part is thicker than the rest of the belt, and large irregularities may be formed on the surface of the recording medium. The medium has also the drawback that the durability of the recording medium is decreased because the above-mentioned bonded part has low mechanical strength.

The production of the conventional endless belt is complicated since two layers, i.e., an electroconductive layer and a dielectric layer, must be formed on the surface of the support layer, by coating.

An object of the present invention is to eliminate the conventional drawbacks described above and, more particularly, to provide a seamless endless belt electrostatic recording medium of high durability.

Another object of the present invention is to provide an electrostatic recording medium whose production process is economically advantageous, by replacing the conventional support layer and the conventional electroconductive layer with an electroconductive support integrally moulded by centrifugal moulding.

According to the present invention there is provided an electrostatic recording medium comprising (1) an electroconductive support in the form of a seamless belt, comprising thermosetting resin biner and electroconductive fine powder dispersed in the binder and (2) a dielectric layer.

According to the present invention there is further provided an electrostatic recording medium wherein the electroconductive support layer comprises from 0.1 to 40 wt. percent electroconductive fine powder and from 60 to 99.9 wt. percent thermosetting resin binder.

Afine powder may be defined as a powder in which the particles have an average size of no more than 1 micron.

An electrostatic recording medium according to the present invention comprises (1) an electroconductive support layer in the form of a seamless belt, comprising a thermosetting resin binder and electroconductive fine powder dispersed in the binder, and (2) a dielectric layer. The electrostatic recording medium of the invention is produced by centrifugally moulding, into a seamless belt, a dispersion of electroconductive fine powder in a thermosetting resin binder and coating thereon a dielectric layer.

The electroconductive support layer comprises from 0.1. to 40 wt.percent of the fine electroconductive particles and 99.9 to 60 wt.percent of the thermosetting resin binder.

By way of example only, the present invention will now be further described, with reference to the accompanying drawing, in which: Figure 1 is a sectional view of one embodiment of the electrostatic recording medium according to the present invention.

In Figure 1, a dielectric layer 2 is provided on a seamless conductive support belt 1 formed by centrifugally moulding a dispersion formed by dispersing a electroconductive fine powder in a thermosetting resin as a binder.

Although the seamless belt containing a fine electroconductive powder of the present invention can be produced by pouring a thermosetting resin solution, containing a fine electroconductive powder dispersed therein, into the inside surface of a cylinder die and centrifugally moulding it by heating, it is preferable that a cured layer of a liquid, curable silicone rubber is formed previously on the inside surface of a cylinder die by centrifugal moulding of said rubber dissolved in a solvent.

The liquid, curable silicone rubbers which can be used include KE 1800A, (trademark) KE 1800B, (trademark) and KE 1800C, (trademark) products of Shintetsu Chemical Industry Co., Ltd. The solvents which can be used for these silicone rubbers include organic solvents, for example, silicone oil, benzene, toluene, and xylene. The thermosetting resins which can be used include those selected from, for example, polyimide resins, polyamide-imide resins, polybenzimidazole resins, and mixtures thereof and suited for the condition of use of a belt. The solvents which can be used for these thermosetting resins include those usually used for these resins, for example, N-methyl-2-pyrrolidone and N,N'-dimethylacetamide.

The fine electroconductive powders which can be used include fine electroconductive powders, for example, carbon black, Ketjen black, stannic oxide, zinc oxide, and cadmium sulfide.

Methods for dispersing these fine powders may be those usually used in the art, for example, dispersion by means of a ball mill, sand mill, or homogenizer, or ultrasonic dispersion.

The substances which can be used in a dielectric layer include organic dielectric substances such as polyester, polycarbonate, polyamide, polyurethane, (meth)acrylic resin, styrene resin, polypropylene, and fluorocarbon resins, and mixtures of powdery inorganic dielectric substances, such as ZnO, TiO2, Awl203, or MgO, comprising no less than 80 wt.percent of particles with a size no greater than 1 micron, with the organic dielectric substances. Methods for forming the dielectric layer may comprise, for example, application of a resin solution of the dielectric substances onto the electroconductive support layer, for example by spraying or bar coating and bonding of a film of these substances onto the support layer.

Because a centrifugally-moulded seamless, electroconductive support belt containing a fine electrocon ductive powder dispersed therein is used, the electrostatic recording medium formed in accordance with the method of the present invention has a uniform film thickness and high durability and can be reduced in size compared with mediums known in the art, because the entire surface of the belt can be utilized as a recording surface. Further, production of such a medium is economically advantageous because the production process is simplified.

Specific embodiments of the present invention will now be described with reference to the following examples, wherein all "parts" are parts by weight.

The tensile strength test was performed according to Standard Test JIS (Japanese Industriai Standard) K 7113 by using a Type 2 test piece with a distance between grips of 80 cm and a testing speed of 10 mm/min.

Example 1 While a cylinder die (inside diameter of 130 mm and length of 500 mm) was being rotated at 1,000 rpm, a mixture of 100 parts of a room temperature-curable silicone rubber (KE 1880A, a product of Shin'etsu Chemica Industry Co., Ltd), 10 parts of a second room temperature-curable silicone rubber (KE 1800B, a product of the same Company), 2 parts of a third room temperature-curable silicone rubber (KE1800C, a product of the same Company), 50 parts of a silicone oil, and 50 parts oftoluene were poured into the cylinder die.The cylinder die was continuously rotated for 10 to 15 minutes to mould the mixture centrifugally on the inside surface of the cylinder die, and was then held in an atmosphere at 140 C for 120 minutes to cure the mixture in the cylinder die to form a cured silicone rubber layer.

The inside diameter of the cured silicone rubber layer was 120.4 mm. While the cylinder die was rotated at 120 rpm, a dispersion formed by dispersing 1.8 g of Ketjen black EC (Trademark, a product of Nippon E.C.

Co., Ltd.) in a mixture of 35 g of a fully aromatic polyimide varnish (a product of Toray industries, Inc.) and 30 g of a solvent (a 50/50 mixture of N-methyl-2-pyrrolidone and N,N'-dimethylacetamide) forthe above varnish (a product of the same Company), by using a ball mill, was poured onto the inside surface of the cured silicone rubber layer. After increasing the speed of rotation of the die to 1,000 rpm, heating was started to gradually raise the temperature of the atmosphere to 120 1 130"C, and the cylinder die was rotated at 1,000 rpm for 30 minutes. The rotation was stopped, and the resulting cylindrical polyimide resin film was released from the cured silicone rubber layer and put on a cylindrical silicone drum, of an outside diameter of 120.4 mm, and heated at 300"C for 30 minutes to complete curing.The seamless belt withdrawn from the silicone drum had a peripheral length of 378 mm, a width of 350 mm, and a thickness of 75 M-m The following dielectric composition was applied to the surface of the above seamless electroconductive support belt by means of a dip coater, and dried to obtain the electrostatic recording medium of the present invention.

[Dielectric Composition] Fluorocarbon resin (Luciflon LF-100 C 100 parts trademark, a product of Asahi Glass Co., Ltd.) Methyl ethyl ketone 80 parts Isocyanate (Colonate EH, trade mark, a product of Nippon 20 parts Polyurethane Co., Ltd.) Table 1 shows the results of the tensile strength test of the electrostatic recording medium of this example.

Table 1 clearly shows that the electrostatic recording medium of this example had a tensile strength nearly equal to that of a 75 thick polyethylene terephthalate film.

Example 2 An electrostatic recording medium was obtained as disclosed in Example 1, but using 2.6 g of carbon black instead of 1.8 g of Ketjen black EC. Table 1 shows the results of the tensile strength test of this electrostatic recording medium.

TABLE 1 Example 1 Example 2 75Wm-thick polyethylene Direction Direction Direction Direction terephthalate of cylinder ofperiphery of cylinder ofperiphery film Yield strength 900 980 970 1140 990 (kg/cm2) Breaking strength 1120 1460 1210 1490 1930 (kg/cm2)

Claims (9)

1. An electrostatic recording medium comprising (1) an electroconductive support in the form of a seamless belt, comprising thermosetting resin binder and electroconductive fine powder dispersed in the binder and (2) a dielectric layer.

2. An electrostatic recording medium as claimed in claim 1, wherein the electroconductive support layer comprises from 0.1 to 40 wt.percent electroconductive fine powder and from 60 to 99.9 wt. percent thermosetting resin binder.

3. An electrostatic recording medium as claimed in claims 1 or 2, wherein the thermosetting resin binder coprises at least one selected from polyimide resins, polyamide-imide resins, and polybenzimidazole resins.

4. An electrostatic recording medium as claimed in any of the preceding claims, wherein the electroconductive fine powder comprises at least one selected from carbon black, Ketjen black, stannic oxide, zinc oxide, and cadmium sulfide.

5. An electrostatic recording medium as claimed in any of the preceding claims, wherein the dielectric layer comprises at least one of polyester, polycarbonate, polyamide, polyurethane, (meth)acrylic resin, styrene resin, polypropylene, and fluorocarbon resins.

6. An electrostatic recording medium as claimed in claim 5, wherein the dielectric layer further comprises at least one of ZnO, TiO2, Al203 and MgO.

7. A process for manufacturing an electrostatic recording medium, which comprises the steps of centrifugally moulding into a seamless belt a dispersion of electroconductive fine powder in a thermosetting resin binder, and coating thereon a dielectric layer.

8. A process for manufacturing an electrostatic recording medium as claimed in claim 7, wherein the dispersion comprises from 0.1 to 40 wt. percent electroconductive fine powder and from 60 to 99.9 wt.

percentthermosetting resin binder.

9. A process for manufacturing an electrostatic recording medium as claimed in either of claims 7 or 8, further comprising forming a cured layer of a silicone rubber on the inside surface of a die by centrifugal moulding, prior to the centrifugal moulding in said die, of the seamless belt.

9. A process for manufacturing an electrostatic recording medium as claimed in either of claims 7 or 8, further comprising forming a cured layer of a silane rubber on the inside surface of a die by centrifugal moulding, prior to the centrifugal moulding in said die, of the seamless belt.

10. A process for manufacturing an electrostatic recording medium as claimed in claim 9, wherein the silicone rubbers are dissolved in a solvent prior to centrifugal moulding and curing.

11. A process for manufacturing an electrostatic recording medium as claimed in claim 10, wherein the solvent used comprises at least one of silicone oil, benzene, toluene, and xylene.

12. An electrostatic recording medium substantially as hereinbefore defined, with reference to the accompanying Examples.

13. A process for manufacturing an electrostatic recording medium, substantially as hereinbefore defined, with reference to the accompanying Example.

Amendments to the claims have been filed, and have the following effect: (a) Claim 9 above has been textually amended.

(b) New or textually amended claims have been filed as follows: