JPH05249703A - Electrostatic recording body - Google Patents

Abstract

PURPOSE:To prevent lead edge fogging and a decrease in picture density from occurring by coating a plastic pigment having a specified average grain diameter with a conductive metal oxide semiconductor powder. CONSTITUTION:The pigment is obtained by coating a plastic pigment with a conductive metal semiconductor powder, and the powder of PE, PP, silicone, etc., insoluble in an org. solvent such as toluene, xylene and methyl ethyl ketone dissolving the insulating resin forming a dielectric layer is used as the plastic pigment to be used as a base pigment. A conductive tin oxide, a conductive zinc oxide or a titanium oxide which has been coated with a conductive tin oxide, etc., and calcined is preferably used for the conductive metal oxide semiconductor powder to coat the base pigment. The average grain diameter of the pigment to be incorporated into the dielectric layer of an electrostatic recording body is ordinarily controlled to about 1-15mum or preferably to 2-10mum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic recording body suitable for an electrostatic plotter or printer using multi-needle electrodes.

[0002]

2. Description of the Related Art Generally, in order to obtain a clear image by an electrostatic recording method, the size of a gap between a needle electrode and a dielectric layer of an electrostatic recording medium is controlled within an optimum range estimated from a Paschen's curve. There is a need to. Therefore, an insulating pigment is added as a spacer to the polymer insulating resin that constitutes the dielectric layer,
A method of appropriately controlling voids by contacting a multi-needle electrode with a dielectric layer on which appropriate irregularities are formed is used.

However, in electrostatic plotters and electrostatic printers using multi-needle electrodes, a recording voltage is applied to the multi-needle electrodes to form an electrostatic latent image on the surface of the dielectric layer of the electrostatic recording medium, and then the electrostatic latent image is formed. A visible image is recorded by developing this electrostatic latent image with toner, but when a voltage is applied to the multi-needle electrode, a leakage current of the applied voltage is injected into the developing device, so LEF (lead edge
Tip fogging called the "fog" phenomenon is likely to occur.

Therefore, in an electrostatic recording medium using paper as a support, a method of preventing the LEF phenomenon by conducting a conductive treatment on the back surface of the support and letting leakage current escape in the volume direction of the support is taken. Has been. However, when a recording material treated in this way is recorded in a high humidity environment, the applied pulse may be attenuated without reaching the maximum voltage, resulting in a decrease in recording density.

Further, in an electrostatic recording body using an insulating film as a support, since the support has a very high volume resistance, a part of the conductive layer (usually the end surface of the recording body) is exposed, or A conductive paint such as carbon black is applied to the part to form a ground electrode to prevent the LEF phenomenon. However, it is difficult to control the exposed width of the conductive layer, and the number of manufacturing processes is increased, resulting in poor productivity and high cost.

For this reason, an electrostatic recording body whose dielectric layer is composed of a polymer insulating resin and conductive particles (Japanese Patent Laid-Open No. 61-213).
No. 851 and Japanese Patent Laid-Open No. 2-83547), these proposals have an effect of preventing the LEF phenomenon, but in the case of all-mark recording, scratch-like white in a direction parallel to the recording electrode. Frequent dropouts occur, and the recording density decreases due to insufficient insulation. In addition, when recording for a long time, there is also a drawback that the conductive particles stay on the recording electrode and damage the recording electrode.

[0007]

In view of the above situation, the present inventor has studied the improvement of the LEF phenomenon that occurs in an electrostatic recording medium, and as a result, the LEF phenomenon is a latent image on the surface of the dielectric layer due to air discharge. When the charge is formed, the opposite charge is induced, and as a result, the charge generated in the conductive layer loses its escape and electrostatically attracts the toner to the dielectric layer at the portion of the developing unit that is grounded, thus causing fog. We confirmed that this is a phenomenon that occurs. It was also confirmed that the electric charge generated in the conductive layer can be eliminated by making a trace amount of the conductive particles exist so as to electrically connect the conductive layer and the developing device.

Based on this knowledge, the LEF phenomenon can be efficiently prevented, and the scratch-like white spots that occur at the time of all-mark recording and the reduction in recording density due to insufficient insulation can be eliminated, and even when recording for a longer period of time. As a result of earnest research on an electrostatic recording body in which the recording electrode is not damaged, at least a part of the pigment particles constituting the dielectric layer has a specific average particle diameter coated with a conductive metal oxide semiconductor powder. It was found that the above object can be achieved very efficiently by using the plastic pigment that the present invention has, and the present invention has been completed.

[0009]

The present invention provides an electrostatic recording body having a dielectric layer formed on a conductive support, wherein the dielectric layer contains at least an insulating resin and pigment particles.
In addition, at least a part of the pigment particles is a plastic pigment having an average particle diameter of 2 to 10 μm, which is coated with a conductive metal oxide semiconductor powder, and is an electrostatic recording material.

[0010]

Generally, in order to prevent the LEF phenomenon with a conductive pigment, it is preferable that the conductive pigment penetrates from the conductive layer to the surface of the dielectric layer in the thickness direction of the dielectric layer, but it is effective even if it does not penetrate completely. There is. This is because if the conductive pigment particles contained in the dielectric layer are arranged so as to be connected to the conductive layer, even if an extremely thin dielectric layer film is formed on the conductive pigment particles, Is considered to be a conductive point, and this conductive point is considered to come into contact with a developing device or an earth roll to exert an effect.

The grounding point required to form an escape area for the charges generated in the conductive layer may be present so that a trace amount of the conductive pigment electrically connects the conductive layer and the developing device. for that reason,
For example, in an electrostatic recording medium using a film as a support, it suffices that one conductive pigment is present in 100 mm ^{2 of the} surface of the dielectric layer, and in the present invention, the surface-treated plastic pigment is a lump, It may be an agglomerate, and the effect can be expected even if it is present in a state of covering the surface of the insulating pigment.

In order to prevent the LEF phenomenon, when an inorganic conductive pigment or carbon black having a high Mohs hardness is directly added to the dielectric layer, the dielectric layer resin on the surface of the conductive pigment is peeled off by friction with the recording electrode. As a result, the electrode may be broken due to occurrence of hook-shaped white spots, or because fragments of the conductive pigment are retained in the electrode. However, when the surface of the plastic pigment is coated with the conductive metal oxide semiconductor powder as in the present invention, the amount of the conductive powder present on the surface of the dielectric layer can be controlled to the minimum, so that the It is possible to obtain a desired effect without causing white voids and electrode damage.

The conductive pigment used in the electrostatic recording material of the present invention is a pigment particle obtained by coating the surface of a plastic pigment with a conductive metal semiconductor powder as described above, but as a plastic pigment serving as a mother pigment, A powder of polyethylene, polypropylene, silicon, methyl silicon, tetrafluorocarbon, or the like, which is insoluble in an organic solvent such as toluene, xylene, or methyl ethyl ketone in which the insulating resin forming the dielectric layer is dissolved, is preferably used. Further, as the conductive metal oxide semiconductor powder coated with these mother pigments, impurity semiconductor powder such as conductive tin oxide, conductive zinc oxide, or conductive tin oxide is deposited on the surface and baked. Titanium oxide and the like are preferably used.

Generally, if the average particle size of the pigment particles blended in the dielectric layer of the electrostatic recording medium is too large, it becomes difficult to maintain a proper gap between the surface of the recording medium and the multi-needle electrode, and all marks Since white spots may occur at the time of recording, and conversely, if it is too small, betamura may occur at the time of all mark recording. Therefore, the average particle size of the pigment particles is 1 to 15
It is said that it is desirable to adjust to about μm, preferably about 2 to 10 μm. Even in the plastic pigment coated with the conductive metal semiconductor powder used in the present invention, when the average particle diameter is less than 2 μm, LE
If the effect of preventing the F phenomenon becomes insufficient and conversely exceeds 10 μm, a key-like white spot may occur.
The pigment particles are contained in the dielectric layer as pigment particles having an average particle diameter of 10 μm.

The particle diameter of the conductive metal-semiconductor powder coated on the surface of the plastic pigment is preferably about 1/10 or less of the particle diameter of the mother pigment, preferably 0.01 to 1 μm. Is used. By the way, if the particle size of the conductive metal semiconductor powder is too large, a large number of particles which are not subjected to the coating treatment are generated on the plastic pigment, and not only the effect of preventing the LEF phenomenon is deteriorated,
There is a possibility that the insulation of the dielectric layer may be deteriorated, abnormal dots may be generated, and further problems such as electrode damage may be caused.
Further, the layer of the conductive metal semiconductor powder formed on the surface of the plastic pigment does not need to completely cover the surface of the plastic pigment, and it is sufficient that the conductive path is formed to some extent on the surface. Therefore, the powder specific resistance of the plastic pigment coated with the conductive metal semiconductor powder is 10 ⁸ to 1 at a pressure of 10 kg / m ^2.
It is preferable to perform the treatment so that the resistance is about 0 ¹ Ω · cm.

The method of coating the surface of the plastic pigment with the conductive metal semiconductor powder is not particularly limited, but, for example, when polyethylene powder having a softening point of 95 to 120 ° C. and having softening adhesiveness is used as a mother pigment, This powder and the conductive metal semiconductor powder are added to a dry mixer such as a tumbler type or a stirring blade type and mixed, and then the polyethylene powder is softened to exhibit tackiness.
It can be produced by a method such as heating to about temperature and allowing to cool while stirring. At this time, the outer surface of the polyethylene powder particle is softened or melted, but the inside of the particle is in a transient state in which it is rigid enough to maintain its shape. It is obtained as a powder which is fused and integrated.

In the electrostatic recording material of the present invention, a part or all of the pigment mixed in the dielectric layer is a plastic pigment obtained by coating with the conductive metal semiconductor powder as described above. When the above pigment is used in combination, if the average particle size of the plastic pigment coated with the conductive metal semiconductor powder is smaller than that of the other pigment, the pigment does not act as the conductive point of the charge earth and the effect of preventing the LEF phenomenon is obtained. Therefore, the average particle size of the coated plastic pigment needs to be the same as or larger than that of other pigments.

Other pigments used in combination include, for example, clay, deckite, nacrite, kaolin, aluminum hydroxide, magnesium hydroxide, calcium carbonate, amorphous silica, alumina, calcined clay, calcined kaolin, barium sulfate, titanium oxide, In addition, pigments obtained by subjecting the surface of these pigments to an insulation treatment, and further, a pigment not surface-treated, and the like can be mentioned.

The compounding ratio of the total pigment and the resin including the plastic pigment coated with the conductive metal semiconductor powder compounded in the dielectric layer is generally pigment: resin = 5: 95.
Parts by weight to about 60:40 parts by weight, preferably 15:85
It is adjusted within the range of about 50 to 50:50 parts by weight. When the mixing ratio of the plastic pigment coated with the conductive metal semiconductor powder is low, the coating treatment with the conductive metal semiconductor powder is advanced so that the specific resistance becomes low,
On the contrary, when the mixing ratio is high, the coating treatment with the conductive metal semiconductor powder may be suppressed to a small extent. However, generally, the mixing ratio of the plastic pigment coated with the conductive metal semiconductor powder is 0.1 to 10 of the total solid content of the dielectric layer.
It is preferable that the LEF phenomenon is prevented by adjusting the content to be in the range of about wt%.

In the electrostatic recording medium of the present invention, examples of the highly insulating resin forming the dielectric layer include methyl acrylate, ethyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, methyl methacrylate and methacrylic acid. Acrylic ester copolymers such as isobutyl and 2-ethylhexyl methacrylate, methacrylic acid ester copolymers, vinyl acetate, ethylene-vinyl acetate copolymers,
Butyral resin, polyester resin, nitrocellulose, polystyrene, styrene-acrylic copolymer, styrene-methacrylic acid copolymer, phenol resin and the like can be mentioned.

For the dielectric layer, a dielectric layer forming coating liquid obtained by dissolving and dispersing an insulating resin or a pigment in a suitable organic solvent such as toluene, methyl ethyl ketone, or xylene is generally used, for example, a bar coater, a contra coater, or a gravure It is formed by a method of coating on a conductive support with a suitable coating device such as a coater, a curtain coater, a chanplex coater, a roll coater, and a blade coater.

Examples of the conductive support include cationic polymer electrolytes such as polyvinylbenzyltrimethylammonium chloride, polydimethyldiallylammonium chloride and styreneacrylic acid triethylammonium chloride, polystyrene sulfonate, polyacrylate, polyvinyl. Anionic polyelectrolytes such as phosphates, or metallic semiconductor powders containing impurities such as zinc oxide and tin oxide impregnated or coated,
Paper sheets such as paper, synthetic paper, Japanese paper, etc., whose surface resistance is 10 ⁵ Ω / □ to 10 ⁹ Ω / □ at normal humidity, and whose surface-bedding smoothness is preferably 200 seconds or more, and various synthetic resin films, A cloth, a non-woven cloth, or the like is used, but the dielectric layer of the present invention exerts a remarkable effect of preventing the LEF phenomenon even when a synthetic resin film is used as the support, and thus the synthetic resin film is particularly used as the support. Effective for electrostatic recording media.

[0023]

The present invention will be described in more detail with reference to the following examples, but it goes without saying that the present invention is not limited to these examples. The recording evaluation of the electrostatic recording bodies obtained in Examples and Comparative Examples was performed by the following method, and the results are shown in Table 1.

Recording Density Recording was carried out using a Matsushita Denki Monochrome Plotter [EP-103] under 27 ° C. and 85% RH environmental conditions, and the recording density was measured by a Macbeth densitometer. LEF concentration 23 ° C ・ 25% RH with the same plotter
Recording was performed under environmental conditions, and the fog density between the recording electrode and the developing device at this time was measured with a Macbeth densitometer. Then, the LEF density was obtained by subtracting the blank area density from the fog density. White plot 23 ° C ・ 50% RH with the same plotter
All-mark recording was performed under environmental conditions, and it was determined whether or not there was a key white spot.

Example 1 100 parts by weight of high-density polyethylene powder having a softening point of 96 ° C. and an average particle size of 8.0 μm, and 10 parts by weight of antimony-doped conductive tin oxide powder having an average particle size of 0.4 μm. Was mixed with a tumbler type stirrer, heated to 120 ° C. and held for 1 minute, and then allowed to cool to prepare a polyethylene powder coated with conductive tin oxide. Since the obtained powder contained coarse particles in which polyethylene powders were fused to each other, they were removed by an air classifier.

Next, a surface resistance value of 1 × 10 ⁶ Ω obtained by treating a polyester film having a thickness of 75 μm with a conductive agent containing conductive tin oxide having an average particle diameter of 0.2 μm as a main component.
5 parts by weight of polyethylene powder coated with the conductive tin oxide prepared above on the conductive layer surface of the conductive film of
A solution for forming a dielectric layer having a solid content concentration of 30% prepared by dispersing and mixing 35 parts by weight of calcium carbonate having an average particle diameter of 3.0 μm and 60 parts by weight of a methylmethacrylate resin in a toluene solution is used as a Mayer solution. Dry weight at bar is 3g
The electrostatic recording material was obtained by coating so as to have a thickness of / m ² .

Example 2 Example 2 was repeated except that the average particle size of the high density polyethylene powder coated with the conductive tin oxide powder was changed from 8.0 μm to 5.0 μm. An electrostatic recording material was obtained.

Example 3 The same as Example 1 except that the average particle size of the high density polyethylene powder coated with the conductive tin oxide powder was changed from 8.0 μm to 3.0 μm. An electrostatic recording material was obtained.

Comparative Example 1 The same as Example 1 except that aluminum hydroxide powder having an average particle diameter of 8.0 μm was used in place of the polyethylene powder coated with the conductive tin oxide powder. To obtain an electrostatic recording body.

Comparative Example 2 In Example 2, instead of the polyethylene powder coated with the conductive tin oxide powder, conductive zinc oxide having an average particle diameter of 4.6 μm (KCZ-4 manufactured by Honjo Chemical Co., Ltd.) was used. An electrostatic recording material was obtained in the same manner as in Example 2 except that the above was carried out.

Comparative Example 3 In the same manner as in Example 1, except that the average particle size of the high-density polyethylene powder coated with the conductive tin oxide powder was changed from 8.0 μm to 1.0 μm. An electrostatic recording material was obtained.

Comparative Example 4 In the same manner as in Example 1 except that the average particle size of the high density polyethylene powder coated with the conductive tin oxide powder was changed from 8.0 μm to 12.0 μm. An electrostatic recording material was obtained.

[0033]

[Table 1]

[0034]

As is clear from the results shown in Table 1, the electrostatic recording bodies obtained in the respective examples of the present invention did not cause the LEF phenomenon in the low humidity environment, and in the high humidity environment. It was a recording material having excellent characteristics such as reduction in image density and white spots in the above.

Claims (1)

[Claims] 1. An electrostatic recording body having a dielectric layer formed on a conductive support, wherein the dielectric layer contains at least an insulating resin and pigment particles, and at least a part of the pigment particles comprises: An electrostatic recording material comprising a plastic pigment having an average particle diameter of 2 to 10 μm, which is coated with a conductive metal oxide semiconductor powder.