JPH02250060A - Electrostatic recording material - Google Patents

Abstract

PURPOSE:To efficiently suppress dropout of thin lines and occurrence of abnormal dots without lowering record density by using kaoline heat treated in a specified temperature range as a pigment. CONSTITUTION:The kaolin to be used as the pigment is heat treated in the range of 400 - 600 deg.C, preferably, 470 - 550 deg.C the sintering temp. which is very important factor, by feeding kaolin, preferably, kaolinite in a crucible or a rotary kiln or the like for a prescribed time in the temperature range, and controlled to an average particle diameter of 1 - 15mum, preferably, 2 - 8mum, thus permitting dropout of thin lines and occurrence of abnormal dots to be suppressed without lowering recording density.

Description

Detailed Description of the Invention "Field of Industrial Application" The present invention relates to an electrostatic recording medium suitable for an electrostatic recording type electrostatic block using a multi-needle electrode, an electrostatic facsimile, an electrostatic printer, etc. be.

"Conventional technology" Monochrome and color electrostatic recording methods using multi-needle electrodes are
Since it is possible to output wide-width and high-speed recorded images, it has come to be used in a wide range of industrial fields, along with advances in CAD technology such as computer-based design and simulation technology.

By the way, electrostatic recording methods using multi-needle electrodes are capable of high-density recording such as 400 dots/inch in a single row arrangement, but the electrostatic recording media used in these methods have a problem in that the toner after recording is It not only has practical properties such as complete fixation on the surface of the recording medium, high recording density, good writing and stamping properties, and no blocking stains, but also improves fine line recording performance and reduces the number of abnormal dots. It is also necessary to have excellent recording quality.

"Problems to be Solved by the Invention" In particular, the diameter of the recording needle of a high-density electrostatic recording device is approximately 50 μm, compared to approximately 100 μm in the case of a conventional recording density of 200 dots/inch. Since it is extremely small and the discharge area is extremely reduced, line breakage (thin line omission) is likely to occur when drawing a thin line. In addition, abnormal dots that are several times the size of normal dots, which are thought to occur easily, are likely to occur due to the discharge between the needle electrodes, and if the quality of the line drawing is thick, irregularly shaped jagged edges may appear along thin lines. easy.

As a result of intensive research into measures to reduce these thin line omissions and abnormal dots, the present inventors have discovered that spacer pigments incorporated into the dielectric layer play an extremely important role.In particular, when kaolin is used as a pigment, It was found that the occurrence of thin lines and abnormal dots was significantly reduced.

However, kaolin inherently contains adhering water and water of crystallization,
Furthermore, since it has hydroxyl groups on its surface, it has low insulation properties and attenuation of charge, so when added to a dielectric layer, the image density decreases compared to calcium carbonate, which has been commonly used as a spacer pigment. It has become clear that there is a tendency to Therefore, as a result of intensive research to develop an electrostatic recording medium with fewer wire breaks and abnormal dots and a high recording density, we found that when kaolin is fired at a specific temperature range, the recording density does not decrease. We have discovered that the occurrence of thin lines and abnormal dots can be effectively suppressed, and have completed the present invention.

"Means for Solving the Problems" The present invention provides an electrostatic recording material in which a dielectric layer containing an insulating resin and a pigment as main components is provided on an electrically conductive support. This is an electrostatic recording material characterized by using kaolin which has been subjected to firing treatment within a range of 100 to 100%.

"Action J" The kaolin used in the present invention refers to kaolin group minerals such as hallosite, hydrated hallosite, kaolinite, Deckai I., and nacrite, and these may be used alone or in combination. .

Among them, kaolinite is particularly preferably used because it has a remarkable effect of reducing the number of thin lines and the number of abnormal dots.

However, depending on the production area, kaolin may contain quartz as an impurity, and if the amount exceeds 2% by weight, it may cause abnormal dots, so it is recommended to use kaolin with a quartz content of 2% by weight or less. desirable.

The average particle diameter of kaolin is desirably adjusted within a range of about 1 to 15 μm, preferably about 2 to 8 μm.

Kaolin is calcined by placing it in a crucible, rotary kiln, or the like, and subjecting it to a predetermined temperature and time. In the present invention, the firing temperature is particularly important, and is preferably 400 to 600°C, preferably 47°C.
It is necessary to carry out the firing treatment at a temperature range of 0 to 550°C.

Incidentally, if the calcination temperature is less than 400°C, there will be only heavy IN accompanying attached water, but there will be no weight loss due to dehydration of crystallized water, and if the obtained kaolin is left in the atmosphere, it will easily adsorb water. Therefore, the desired recording density improvement effect cannot be obtained. On the other hand, when fired at a temperature exceeding 600° C., a portion of the kaolin is sintered, so that the polishing phenomenon of the recording head becomes noticeable and the number of abnormal dots increases.

Note that since ordinary calcined kaolin is calcined at a temperature of 900°C or higher, it becomes amorphous and does not have a sharp peak in X-ray analysis, but the kaolin calcined at the above-mentioned specific temperature used in the present invention has an A sharp peak is observed in line analysis. In addition, the weight loss of kaolin due to dehydration of crystal water due to firing treatment in the above specific temperature range is 1 to 10
%, the kaolin used in the present invention is considered to be a powder mixture in which some of the interlayer crystallization water has fallen off, but most of it is still retained.

It is thought that the reason why the kaolin subjected to the above-mentioned specific firing treatment contributes to the improvement of the recording density is that the insulating properties of the kaolin are improved. Kaolin contains adhering water in -g, and the specific resistance of its powder is about 10'Ω・1, but when it is dried in an oven at 120°C, it becomes 109Ω・cm.
The specific resistance will be approximately. When this kaolin is used, the effect of improving the recording density is recognized, but if it is left in the atmosphere, it easily returns to its original resistivity, making it impossible to obtain a recording medium that exhibits a stable recording density. However, when fired at a temperature of 400° C. or higher, the specific resistance increases to about 10I0Ω·IJ, and an excellent recording density improvement effect can be obtained. However, even if it is fired at a temperature exceeding 600°C, its resistivity hardly changes any more, and defects due to the occurrence of sintering as described above occur. In addition, since the electrostatic recording material needs to match the characteristics of the electrostatic recording device used, it is desirable to appropriately select and use kaolin having a resistivity suitable for the device.

The blending ratio of the kaolin thus fired into the dielectric layer is generally desirably adjusted within the range of about 3 to 60% by weight, preferably about 5 to 40% by weight of the total solid content of the dielectric layer.

Incidentally, in order to control the glossiness of the surface of the recording medium and to impart writing and sealing properties, a pigment other than calcined kaolin can also be used in combination.

Pigments used for this purpose include graded or light calcium carbonate, amorphous silica, calcined amorphous silica, silica surface-treated with silane treatment, plastic pigments such as polyethylene, polypropylene, and polyacrylonitrile, barium sulfate, Examples include calcined clay, alumina, aluminum hydroxide, clay, magnesium hydroxide, and titanium oxide, among others, surface-treated materials such as graded and light calcium carbonate, amorphous silica, calcined amorphous silica, and silane treatment. Plastic pigments such as silica, polyethylene, polypropylene, and polyacrylonitrile are particularly preferably used because they are effective in reducing gloss and imparting practical properties such as writability and stampability without affecting recording properties. .

In order to maintain the effect of reducing the number of fine lines and abnormal dots, it is desirable that the average particle diameter of the pigment used in combination be smaller than the average particle diameter of the surface-treated kaolin.

It is desirable that the weight ratio of the pigment including such pigments constituting the dielectric layer and the insulating resin is adjusted within the range of about 5:95 to 70:30, preferably about 10:90 to 50:50. If the blending ratio of pigment is less than these ratios,
The gloss on the surface of the recording medium increases to such an extent that it impairs its natural appearance, and conversely, if the amount is too high, the recording density may decrease.

Examples of the insulating resin include methyl acrylate, methyl methacrylate, ethyl acrylate, isobutyl methacrylate, 2-ethylhexyl acrylate, and dimethacrylate.
- Acrylic esters and methacrylic ester copolymers such as ethylhexyl and decyl acrylate, and these with small functional groups such as acrylic acid, methacrylic acid, maleic anhydride, crotonic acid, itaconic acid, acrylonitrile, and methacrylonitrile. Copolymerized polyvinyl acetate, ethylene/vinyl acetate copolymer, phenolic resin, polyester resin, nitrocellulose resin, polystyrene, styrene/acrylic copolymer, styrene/methacrylic acid copolymer, vinylidene fluoride Examples include resin, silicone resin, epoxy resin, urethane resin, and phenol resin.

The dielectric layer is generally prepared using a coating liquid made by dissolving and dispersing an insulating resin or pigment in an organic solvent such as toluene, methyl ethyl ketone, xylene, or isopropyl alcohol using a bar coater, contra coater, gravure coater, curtain coater, champlex coater, roll coater, or the like. It is formed by coating on a conductive support using various coating devices such as a blade coater.

In addition, as the conductive support constituting the electrostatic recording medium, cationic polymer electrolytes such as polyvinylbenzyltrimethylammonium chloride, polydimethylallylammonium chloride, styrene acrylic acid triethylammonium chloride, polystyrene sulfonate, polyacrylic Paper impregnated or coated with a metal semiconductor powder containing impurities such as acid, anionic polymer electrolyte such as polyvinyl phosphate, or zinc oxide, tin oxide, etc., together with a binder, to have a surface resistance of approximately 105 to IO8Ω; Plastic film, synthetic paper, Japanese paper, cloth, etc. are used.

"Examples" Examples of the present invention will be described below, but the present invention is not limited to these Examples. Also, parts in examples are parts by weight.

[Preparation of conductive support] Cationic polymer electrolyte was placed on high-quality paper with a basis weight of 60 g/rd.
Styrene acrylic acid triethylammonium chloride (manufactured by Sanyo Chemical Co., Ltd., Chemistat 7300) was applied at a dry weight of 4 g/% on the surface and 2 g/y on the back surface, and was smoothed to a Bekk smoothness of 700 seconds for conductivity. A sexual support was obtained.

[Preparation of electrostatic recording medium]

A dielectric layer coating solution having the following composition was coated on the above support at a dry weight of 4 g/rrr to obtain an electrostatic recording material.

The coating liquid was prepared by dispersing kaolin in a toluene/MEK (1/1) mixed solvent and then adding and mixing the dielectric layer resin.

Toluene/MEK 200 parts Kaolin calcined according to the following formulation: 35 parts Methyl methacrylate resin 45 parts Normal butyl acrylate resin 20 parts [Examples 1 to 3. Comparative Examples 1 to 3] Kaolin (manufactured by Engelhard, Belvacast) 10
0 parts were placed in a crucible, fired for 2 hours in an electric furnace set at the temperature shown in the table, and then left at room temperature to obtain 6 types of fired kaolin.

Comparative Example 4 An electrostatic recording material was obtained in the same manner except that untreated kaolin was used instead of calcined kaolin.

The following quality evaluation tests were conducted on the seven types of electrostatic recording bodies thus obtained, and the results are listed in the table. That is,
Practical monochrome electrostatic plotter (manufactured by Matsushita Densen Co., Ltd., EP-1
01), and the recording density of the black pattern portion was measured using a Macbeth densitometer. In addition, the number of abnormal dots occurring per meter of the two-dot diagonal line was visually measured. Furthermore, the specific resistance of kaolin was measured by placing a sample in a Teflon block with a hole of 1 cI11 in diameter and applying a pressure of 500 kg/cJ from above and below.

Table [Note] Firing temperature: °C, specific resistance: Ω·cm The fixing properties, curling, and blocking suitability of the electrostatic recording materials obtained in each example were all good.

"Effects" As is clear from the above examples, the electrostatic recording material of the present invention does not deteriorate practical characteristics or recording characteristics.
The recording density was significantly improved, and the recording material was extremely well-balanced in terms of quality.

Claims (1)

[Claims] In an electrostatic recording material in which a dielectric layer mainly composed of an insulating resin and a pigment is provided on a conductive support, 400% of the pigment is used as the pigment.
An electrostatic recording material characterized by using kaolin fired at a temperature range of ~600°C.