JPS5828575B2 - electrostatic recorder - Google Patents

Description

Detailed Description of the Invention The present invention relates to an electrostatic recording medium that directly converts an electric signal into an electrostatic latent image, and in particular to an electrostatic recording medium that prevents spark discharge during recording, has high resolution, and has a long life. The present invention relates to improvements in conductive layers for the purpose of improving electrical conductivity.

Conventional electrostatic recording media include a dielectric layer on a metal drum, or a conductive layer made of metal such as aluminum, copper, stainless steel, brass, copper iodide, or an organic conductor on a support. It is known that a dielectric layer is deposited thickly and uniformly on top of which a dielectric layer is provided.

However, in an electrostatic recording medium with such a structure, when the discharge voltage is increased to improve image density or the thickness of the dielectric layer is reduced to improve resolution, spark discharge occurs and dielectric breakdown of the dielectric layer occurs. There have been problems in which the image resolution has been reduced.

In order to solve this problem, an intermediate layer exhibiting semiconductivity at least in the thickness direction between the conductive layer and the dielectric layer, for example, a layer with a thickness of several microns to several tens of microns made of a mixture of carbon particles and an organic binder, or , a method of providing an alumina layer of similar thickness is known.

However, even in this case, there is a problem in that the intermediate layer itself causes dielectric breakdown due to the high electric field in the thickness direction and corona deterioration due to repeated discharges.

The inventors of the present invention have carefully studied such dielectric breakdown, resolution reduction, deterioration during long-term use, etc., and have developed a method for applying a specific metal as a conductive layer in the in-plane direction of the surface of an insulating substrate within a certain electrical resistance range. We have discovered that all of these problems can be solved by using conductive fine particle layers that are formed separately and adhered to each other.

We have arrived at the present invention.

That is, the present invention provides an electrostatic recording material comprising an insulating substrate, a conductive layer, and a dielectric layer, in which the dielectric layer contains at least one metal selected from the group consisting of rhodium, palladium, iridium, and platinum. The conductive layer is composed of mutually separated island-like fine particles having an average particle area of 0.01 square microns or less, and is mainly composed of a material, the surface electrical resistivity of the dielectric layer is in the range of 104 ohm to 109 ohm, and the conductive layer Provided is an electrostatic recording medium comprising:

The electrostatic recording medium having such a configuration has the following characteristics.

(1) Materials selected from the group consisting of rhodium, palladium, iridium, and platinum are extremely stable against reactive gas ions such as ozone generated during discharge,
Even in electrostatic recording media that are used repeatedly, stable recording can always be reproduced.

(2) The conductive layer formed by adhering these metals as island-like fine particles separated from each other can be formed so that the mutual conductive particles exhibit electronic conductivity due to tunneling current passing through the substrate, so they can be formed as is. It can be used as a normal electrostatic recording material electrode.

(3) At the same time, the gaps between the island-like fine particles that are separated from each other can exert a kind of capacitor effect, which acts to alleviate sudden voltage application or localized large current flow. .

Furthermore, since this relaxation effect also occurs in a relatively short time, it is possible to sufficiently respond to electrostatic recording at high frequencies.

(4) Furthermore, since the island-shaped conductive fine particles separated from each other are dispersed and arranged only in the in-plane direction of the insulating substrate surface,
The electric field gradually decreases from the recording section to the ground electrode provided at the end of the electrostatic recording medium.

For this reason, compared to conventional electrostatic recording materials that have a semiconductor layer between the conductive layer and the dielectric layer, this technology prevents dielectric breakdown even if a voltage shortage occurs due to corona deterioration of the dielectric layer. can do.

(5) Furthermore, since the conductive layer is preempted by extremely fine, mutually separated particles with an average particle area of 0.01 square microns or less, the charge on the dielectric surface is almost perpendicular to the individual particles. It is possible to prevent the discharge during recording from spreading on the surface of the dielectric layer, and it is possible to obtain high resolution and recording density.

Hereinafter, details of the present invention will be explained based on one embodiment shown in the drawings.

In FIG. 1, 1 indicates an insulating substrate, which is made of an organic polymer,
Among paper, ceramic, glass, etc., those having a surface electrical resistivity of 1010 ohms or more are used.

Among these, organic polymer films and sheets are preferred in terms of flatness, dimensional stability, flexibility, and the like.

Examples of the most preferred organic polymer films used in the present invention include polyethylene terephthalate, polyethylene 2
- Polyesters such as 6-naphthalene dicarboxylate and polyto-4-cyclohexane dimethyl terephthalate, polycarbonate, polystyrene, polymethyl methacrylate, polysulfone, polyphenylene oxide, polyphenylene sulfide, polypropylene, polyamide, polyamideimide, polyimide, etc.

Other copolymers of these or copolymers with others may also be used.

The insulating substrate can be appropriately subjected to pretreatment such as EC treatment, discharge treatment, and undercoating with an insulating paint before forming the conductive layer.

On these insulating substrates, dispersed within the plane of the substrate surface,
A conductive layer 2 is formed of isolated island-shaped conductive fine particles having an average particle area of 0.01 square microns or less.

As the conductive material forming the conductive fine particles, a material mainly containing at least one metal selected from the group consisting of rhodium, palladium, iridium, and platinum is used.

In addition to these metals, it is permissible to mix and add other metals, metal oxides, etc. as appropriate; however, an increase in the amount of the mixture will cause oxidation of the conductive layer and deterioration of the image characteristics of electrostatic recording. It is necessary that the amount be less than 20% by weight, preferably less than 5% by weight.

The surface electrical resistivity of such an island-shaped conductive layer needs to be in the range of 104 ohm to 109 ohm in order to prevent spark discharge and discharge breakdown of the dielectric layer and the conductive layer.
The most preferred range is 105 ohms to 108 ohms.

Note that the surface electrical resistivity is 1C1r for width and length, respectively.
It is a value defined as a physical quantity indicating the surface electrical resistance of a conductive sheet L, and is measured according to the measurement of volume resistivity of JISC2318.

As a method for forming island-shaped conductive fine particles on the surface of the insulating substrate 1, sputtering, vacuum deposition, ion blasting, plating, etc. can be used.

Among these, sputtering is most suitable for uniformly forming surface electrical resistance over a large area.

As the sputtering method, both direct current sputtering and radio frequency sputtering can be used, and all improved sputtering methods such as triode sputtering, quadrupole sputtering, plasma sputtering, magnetron sputtering, etc. can also be used.

In order to make the conductive layer into island-like fine particles separated from each other,
When forming the conductive layer, methods such as increasing the temperature of the surface of the insulating substrate to shrink the conductive layer, or colliding a beam of charged particles such as electrons and ions on the surface of the substrate can be adopted. A method of stretching the substrate in the longitudinal and/or lateral directions, a method of heating the substrate, etc. can also be employed.

In any case, the average particle area of the conductive particles separated from each other is 0.01 square microns or less, most preferably 0.01 square micrometer or less, for the purpose of preventing discharge damage and obtaining an electrostatic recording medium with particularly high resolution. It is necessary that the thickness be less than 0.001 square microns.

The lower limit of the average particle area is not particularly limited, but is preferably 10-5 square microns or more in practice.

In such a configuration, the electrostatic latent image recorded on the surface of the dielectric layer does not spread toward the surface of the dielectric layer, and recording on the order of microns is possible.

The island-like fine particles constituting the conductive layer can be photographed using an electron microscope at a magnification of approximately 300,000 times, and based on this photographed image, an image analyzer computer (Image Analyzer)
The particle area of each particle can be easily and accurately measured using anco (QUANTIMET 720).

The average particle area referred to here is a value defined as the sum of the particle areas of individual particles measured divided by the number of particles measured.

A dielectric layer 3 is formed on the island-shaped conductive fine particle layer.

The dielectric layer 3 is necessary for accumulating charges on the surface during electrostatic recording, and therefore the volume resistivity of the dielectric layer is at least 1012 ohms, preferably 1
It is necessary to set it to 0.014 ohm.cx or more.

Volume resistivity is measured according to JIS C2318.

As the dielectric layer, glass, SiO2, TiO2, Z
Inorganic dielectric materials such as nO1A1□03, BaTiO3,
Organic dielectric materials such as polyester, polycarbonate, polymethyl methacrylate, polyethylene, polypropylene, polyamide, polyimide, polyamideimide, polytetrafluoroethylene, urethane resin, epoxy resin, acrylic acid ester, or inorganic dielectric material powder and organic dielectric material However, it is also possible to use dielectric materials other than these.

As a method for forming the dielectric layer 3, vacuum deposition, sputtering, solution coating, bonding, etc. can be used.

The higher the dielectric constant of the dielectric layer, the higher the surface charge, so it is preferable, and a dielectric constant of 2.0 or more, preferably 2.5 or more is suitable.

On the other hand, the thickness of the dielectric layer is selected according to each application, and is preferably 1% or more from the viewpoint of dielectric breakdown, and preferably 20μ or less from the viewpoint of resolution. It is not necessarily limited to this.

FIG. 2 shows another embodiment based on the present invention.

In the figure, on the back side of the dielectric layer 4 which also serves as an insulating base,
Consisting of rhodium, palladium, iridium, platinum, etc.
A conductive layer 5 of conductive fine particles dispersed in the form of islands in a plane having a surface electrical resistivity of 104 ohms to 109 ohms is directly deposited.

An electrostatic recording medium having such a structure can also be used in the same manner as the electrostatic recording medium shown in FIG.

Electrostatic signals corresponding to the respective electric signals are accumulated and recorded as latent images on the electrostatic recording medium having these structures using needle-like electrodes, knife-like electrodes, or the like.

The recorded electrostatic signal can be reproduced using a detection head, and can also be made into a visible image using toner having the opposite sign to the electrostatic charge.

Such an electrostatic recording medium can be used for facsimile, TV image reproduction,
It can be particularly effectively used in applications where electrostatic recording is performed repeatedly over a long period of time, such as reproduction of TV still images and copy printing.

Examples of the present invention will be described in detail below.

EXAMPLE On an axially stretched polyethylene terephthalate film (thickness 100 μm), platinum with a purity of 99.9% was dispersed in the form of islands on the film surface in the form of fine particles with a surface electrical resistivity of 10.
It was attached by sputtering so that the resistance was 7 ohms.

Sputtering is performed at an argon pressure of 8×1O-2T or
This was carried out by applying a DC voltage of minus 3 KV to the platinum electrode side, setting the discharge current to 0.5 mA/7, and controlling the discharge time in a vacuum apparatus of R.

At this time, in order to make the platinum into fine particles dispersed in the form of islands,
The surface of the film was subjected to 1014 electron bombardments/ca-see.

It was confirmed by measurement using an electron microscope and an image analyzer computer that the obtained platinum conductive layer had a mutually separated island-like structure with an average particle area of 8 x 10-5 square microns.

On the other hand, the following mixed composition was mixed and ground for 24 hours in a ball mill using alumina balls to prepare a uniform dispersion.

Linear saturated polyester resin (Toyobo Co., Ltd. "Vylon" 100 parts by weight #20) Titanium oxide 15 parts by weight Methyl ethyl ketone 300 parts by weight Toluene
200 parts by weight of the dispersion was applied onto the island-shaped conductive layer using a doctor knife coating device until the dry solid content was 4'?
/rrl was coated and dried to form a dielectric layer to obtain an electrostatic recording material.

In an atmosphere of 25° C. and 60% RH, a discharge of 4000 V was applied over the entire surface of the dielectric 1000 times while the film was being transferred using the platinum layer as a counter electrode.
No dielectric breakdown of the dielectric layer occurred.

Further, after this, a development process with toner was performed, and the image density was measured using an optical densitometer (manufactured by Fuji Photo Film ■, densitometer, type P-2), and the image density was found to be 1.8.

Example 2 On the same substrate film used in Example 1, 99.
9% palladium was sputtered in the same manner as in Example 1.

At this time, the surface temperature of the substrate film was controlled at 80°C using an infrared heater, and a conductive layer consisting of palladium particles dispersed in an island shape with an average particle area of 2 x 10-' square microns and a surface electrical resistivity of 106 ohms was obtained. Ta.

A dielectric layer was coated on this conductive layer in the same manner as in Example 1, and a discharge of 3000V was applied for 10 minutes over the entire surface of the dielectric.
Although this was repeated 00 times, no dielectric breakdown occurred in the heavy layer, and the image density after toner development was as good as 1.5.

Example 3 Two-wheel stretched polyethylene terephthalate film (thickness 12μ) and polycarbonate film (thickness 1
2μ) and the purity is 99.2μ) using the same method as in Example 1.
9% palladium was sputtered to obtain substantially uniform conductive layers each having a surface electrical resistivity of 10 ohms.

This was passed through a stretching machine and stretched by 12 to 15% first in the transverse direction and then in the longitudinal direction to generate cracks in the conductive layer and to give a surface electrical resistivity of 105 ohms.

According to electron microscopy, palladium has an average particle area of 8
It was confirmed that the structure had an island-like structure of ×10 −3 square microns.

Using the palladium layer of these films as a counter electrode, a knife-shaped recording electrode was used on the surface of the film not coated with palladium at a frequency of IMHz, with a peak voltage of 50
An AC waveform of 0.0 cm was recorded, and the electrostatic signal on the film surface was reproduced by a detection head.

The film was fixed on a circular turntable with the electrode layer facing down and rotated at 30 revolutions per second.

Changes in the recording signal on the film surface were observed through a synchroscope through a detection head placed opposite the recording electrode.

In either case, there was no dielectric breakdown of the film (recorded waveforms with good reproducibility were observed).

Comparative Example: On an axially stretched polyethylene terephthalate film (thickness 100μ), aluminum with a purity of 99.9% was uniformly deposited using a resistance heating vacuum deposition machine so that the surface electrical resistivity was 1 ohm. did.

It was confirmed using an electron microscope that aluminum was uniformly deposited within the surface.

A dielectric layer was applied and dried on the aluminum of this film by the same method used in Example 1, and the solid content was 4 k.
An electrostatic recording medium having a recording layer of /rtl: was obtained.

Using this, 4000V discharge was performed 500 times in the same manner as in Example 1, but due to the occurrence of spark discharge, 5 pieces/1
Dielectric breakdown of ocr7t occurred.

Furthermore, the image density after toner development was as low as 0.8.

Comparative Example 2 On the aluminum vapor-deposited film used in Comparative Example 1,
A linear polyester resin mixed solution containing 15% by weight of carbon black powder was dried immediately, and the surface electrical resistivity was 107.
A semiconducting interlayer of ohm and 6μ thick was formed.

On top of this, a dielectric layer was formed using the same method as in Example 1. /
An electrostatic recording material was obtained by coating and forming the film so as to have a diameter of m''.

Using this, an attempt was made to perform discharge recording in the same manner as in Example 1, but at a discharge voltage of 2000 V or more, dielectric breakdown of the intermediate conductive layer occurred due to spark discharge.

Example 4 and Comparative Example 3 Platinum, copper, and aluminum each having a purity of 99.9% or more were vacuum-deposited on a biaxially stretched polyethylene terephthalate film (thickness 75 μm) by a method using an electron beam. Using the same stretching machine as in Example 3, an island-shaped conductive layer with a surface electrical resistivity of 105 ohms was obtained.

The average particle area was 4 x 10-3.5 x 10'' 3 x 10-3 square microns for platinum, copper, and aluminum, respectively.

A uniform dispersion of the following mixed composition was coated onto these conductive layers using a doctor knife coater so that the dry solid content was 61/-, and dried to obtain an electrostatic recording material.

Acrylic acid ester methacrylic ester copolymer (Pakotuxu manufactured by Toshi ■), OO weight @ Vr
L) (608 Zinc oxide Toluene Butyl acetate 20 parts by weight 300 parts by weight 300 parts by weight
Electrostatic recording was performed by applying a voltage of 0 V, and then -500
A recording-erase test was carried out many times in which the recorded image was erased by applying a voltage of V. Finally, after applying a voltage of +500 .mu., a development process with toner was performed and the image density was measured using an optical densitometer.

The measurement results of image density are shown in FIG.

In the figure, A shows the case where a platinum electrode is used, B shows the case where copper is used, and C shows the case where aluminum is used.

In the case of platinum, there was almost no decrease in image density even when recording was repeated 10,000 times or more.

In the case of copper and aluminum, the image density decreased when the number of recordings exceeded 100 times.

[Brief explanation of the drawing]

1 and 2 show one embodiment of the invention. FIG. 3 shows a comparison of image densities during repeated recording between electrostatic recording bodies of the present invention and comparative examples. 1: Insulating substrate, 2: Conductive layer made of island-like fine particles, 3:
Dielectric layer, 4: dielectric layer also serving as an insulating substrate, 5: conductive layer made of island-like fine particles.

Claims (1)

[Claims] 1. An electrostatic recording material comprising an insulating substrate, a conductive layer, and a dielectric layer, in which the conductive layer contains rhodium, palladium,
It is made of a material mainly consisting of one or more metals selected from the group consisting of iridium and platinum, and the surface electrical resistivity of the conductive layer is in the range of 104 ohm to 109 ohm, and An electrostatic recording material characterized in that the layer is composed of isolated island-like fine particles having an average particle area of 0.0 square microns or less.