JPH02248958A - Electrostatic recording material - Google Patents

Abstract

PURPOSE:To efficiently suppress dropout of thin lines and occurrence of abnormal dots without deteriorating record density by using kaolin surface-treated with styrene as a pigment. CONSTITUTION:The kaolin to be used as the pigment is the surface-treated kaolin, and the kaolin means the minerals of a kaolin family, such as halloysite, hydrated halloysite, kaolinite, dickite, or nacrite, and they are used alone or in a mixture, and since the kaolinite has a remarkable effect of reducing dropout of thin lines and occurrence of abnormal dots among them, it is especially preferable to use the kaolinite, and since this kaoline sometimes contains quartz as impurities according to the areas of origin, and the content of too much silica causes abnormal dots, it is preferred to use the kaolin low in the silica content, thus permitting dropout of thin lines and occurrence of abnormal dots to be reduced without deteriorating image density.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to an electrostatic recording material suitable for an electrostatic recorder 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, in conjunction with advances in CAD technology such as computer-based design and similiar silan 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 about 50 μm, compared to about 1100p in the case of a conventional recording density of 200 dots/inch. Because it is much smaller and the discharge area is extremely reduced, line breakage (thin line dropout) is likely to occur when drawing a thin line, and it is several times that of a normal dot, which is thought to be due to the discharge between the needle electrodes. Abnormal dots of the same size are likely to occur (and if the line drawing quality is thick, irregularly shaped jaggies are likely to occur along thin lines).

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 further intensive research to develop an electrostatic recording medium with fewer wire breaks and abnormal dots and a high recording density, it was found that by treating the surface of kaolin with a specific substance to increase its insulation properties, it was possible to improve the recording density. The present invention was completed based on the discovery that the occurrence of thin lines and abnormal dots can be effectively suppressed without reducing the quality.

"Means for Solving the Problems" The present invention provides an electrostatic recording material in which a dielectric layer mainly composed of an insulating resin and a pigment is provided on a conductive support, in which kaolin surface-treated with styrene is used as the pigment. This is an electrostatic recording material characterized by using.

"Function" The kaolin used in the present invention means kaolin group minerals such as hallosite, hydrated hallosite, kaolinite, defkite, and natalite, and these are 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.

In addition, it is desirable to adjust the average particle diameter of kaolin in the range of about 1 to 15 μm, preferably about 2 to 8 μm.
In addition, kaolin used for ordinary paper coatings may contain organic or inorganic dispersants, but such kaolin has significantly poor reactivity, making it difficult to apply the present invention to recording media. difficult.

To react styrene on the surface of kaolin, reduce the pressure in a desiccator containing styrene monomer, place the kaolin in it so that it does not come into direct contact with the styrene monomer,
Styrene oligomers can be easily generated on the kaolin surface by leaving it at room temperature for several hours or more. In addition, in this method, excess styrene oligomer that has not reacted with the kaolin surface becomes an oil-like substance that precipitates and causes kaolin aggregation, so the obtained kaolin is washed and removed with a large excess of an organic solvent such as toluene. There is a need to.

Another treatment method is to remove the reaction inhibitor present in the styrene monomer by introducing silica gel into the solution to adsorb it, or by distillation or other operations, and then adding kaolin to the resulting styrene monomer solution. There is a method of reacting while stirring.

Although this method also produces excess styrene oligomer,
In this case, since it is obtained as a uniform dispersion system, it can be used as is unless it particularly affects the characteristics of the electrostatic recording medium.

The amount of styrene applied to the kaolin surface is 0.1 to 20 parts by weight, preferably 0.5 to 10 parts by weight, based on 100 parts by weight of kaolin after washing with excess solvent. desirable.

The specific resistance of the powder, which is an indicator of the insulating properties of kaolin, is
It increases in proportion to the amount of styrene treated.

For example, the specific resistance of kaolin under a pressure of 500 kjt/- measured at room temperature is about 10 7 Ω·1, but by treating it with styrene, it is possible to increase the insulation property to about 10 10 Ω·1. However, since the electrostatic recording material needs to match the characteristics of the electrostatic recording device used, kaolin having a resistivity suitable for the device is appropriately selected and used.

The blending ratio of the surface-treated kaolin in 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.

Note that a surface-treated pigment other than kaolin can also be used in combination to control the glossiness of the surface of the recording medium and to impart writing and stamping properties.

Pigments used for this purpose include heavy and 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 pigments including such pigments constituting the dielectric layer and the insulating resin be adjusted within the range of 5:95 to 70:30, preferably 10:90 to so:soΩ. If the blending ratio of the pigment is less than these ratios, the gloss of the surface of the recording medium will increase to the extent that it loses its natural appearance, and if it is too large, 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 small amounts of functional groups such as acrylic acid, methacrylic acid, maleic anhydride, crotonic acid, itaconic acid, acrylonitrile, and methacrylonitrile. Copolymerized copolymer, polyvinyl acetate, ethylene/vinyl acetate copolymer, butyral resin, polyester resin, nitrocellulose resin, polystyrene, styrene/acrylic copolymer, styrene/methacrylic acid copolymer, vinylidene fluoride resin , silicone resin, epoxy resin, urethane resin, phenol resin, etc.

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 Metal semiconductor powder mixed with impurities such as acid, 7-ionic polymer electrolyte such as polyvinyl phosphate, or zinc oxide or tin oxide is impregnated or coated with a binder, and the surface resistance is approximately 10' to 10-Ω. Paper, 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. In addition, parts in the examples are parts by weight.

[Preparation of conductive support]

A cationic polymer electrolyte [styrene acrylate triethylammonium chloride, manufactured by Sanyo Chemical Co., Ltd., Chemistufdoor 300] was applied to the top paper with a basis weight of 60 g/c at a dry weight of 4 g/rd on the surface and 2 g/rd on the back surface, and A conductive support was obtained by smoothing so that the smoothness was 700 seconds.

[Preparation of electrostatic recording medium]

A dielectric layer coating solution having the following composition was coated on the support at a dry weight of 4 g/rd 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 surface treated according to the following formulation: 35 parts Methyl methacrylate resin 45 parts Normal butyl acrylate resin 20 parts [Example 1] 10 parts of styrene monomer was placed in the bottom of a desiccator, and separately kaolin [manufactured by Engelhard, Belba cast〕1
00 parts was placed in a beaker, the pressure was reduced using a water jet pump, and the mixture was left overnight. The obtained kaolin contained 15% by weight of styrene oligomer based on the weight of kaolin, and this was washed and filtered with toluene to obtain kaolin surface-treated with 5% by weight of styrene.

[Example 2] 50 parts of kaolin was added to 200 parts of a styrene monomer solution distilled at 150°C, and stirring was continued for 1 hour to obtain surface-treated kaolin. Note that the obtained kaolin was surface-treated with 10% by weight of styrene based on the weight of kaolin.

[Example 3] After 20 parts of silica gel beads were added to 200 parts of styrene monomer and left for one day and night, 50 parts of kaolin was added and stirring was continued for 1 hour to obtain surface-treated kaolin. Note that the obtained kaolin was surface-treated with 5% by weight of styrene based on the weight of kaolin.

[Comparative Example 1] An electrostatic recording material was obtained in the same manner as in Example 1 except that untreated kaolin was used instead of surface-treated kaolin.

[Comparative Example 2] An electrostatic recording material was obtained in the same manner as in Example 1 except that the styrene oligomer was not washed and filtered with toluene and the obtained kaolin was used as it was.

[Comparative Example 3] In Example 2, the styrene surface treatment time was set to 0.5 hours, and kaolin surface-treated with 0.005% by weight of styrene based on the weight of kaolin was obtained and used. An electrostatic recording medium was obtained in the same manner.

[Comparative Example 4] In the same manner as in Example 2, except that the styrene surface treatment time was changed to 48 hours, kaolin surface-treated with 25% by weight of styrene based on the weight of kaolin was obtained, and this was used. An electrostatic recording medium was obtained.

The following quality evaluation tests were conducted on the seven types of electrostatic recording bodies thus obtained. That is, recording was performed using a practical monochrome electrostatic plotter (manufactured by Matsushita Densen Co., Ltd., EB-101), and the recording density layer of the black pattern portion was measured using a Macbeth density stylus, and the results were as shown in the table below.

Note that the fixing properties, curling, and blocking suitability of the electrostatic recording materials obtained in each example were all good.

[Note] *(1): White spots occur due to aggregation of a material.

*(2): The pigment had a strong tendency to agglomerate, making it impossible to prepare a coating liquid.

"Effect" As is clear from the above examples, the electrostatic recording medium of the present invention has significantly improved recording density without deteriorating practical characteristics or recording characteristics, and has an extremely well-balanced quality. It was a record.

Claims (1)

[Claims] An electrostatic recording material comprising a dielectric layer containing an insulating resin and a pigment as main components on a conductive support, the electrostatic recording material comprising kaolin surface-treated with styrene as the pigment.