JPH0764300A - Electrostatic recording material and its production - Google Patents

Abstract

PURPOSE:To prevent selective absorption in a coating liquid for a dielectric layer during the liquid is prepared and to obtain sharp images on an electrostatic recording body produced from the coating liquid in any stage from the initial to the last of one lot by incorporating a oleophilic smectite clay into the dielectric layer. CONSTITUTION:This electrostatic recording body has a dielectric layer containing an insulating resin and pigment particles on a conductive supporting body. The dielectric layer contains oleolphilic smectite clay. More preferably, this oleophilic smectite clay is obtd. by substituting a cation surfactant for exchangeable cation in the smectite. The solid content of the oleophilic smectite clay in the coating liquid to form the inductive material layer is specified to 0.01-10wt.%. This oleophilic smectite clay is produced by the reaction (treatment to give oleophilic property) of smectite clay which is swellable lamellar clay mineral with a cation surfactant or a composite material of a cation surfactant and a nonion surfactant under vigorous stirring.

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 a multi-needle electrode capable of high density recording such as 400 dots / inch, and a manufacturing method thereof.

[0002]

2. Description of the Related Art In an electrostatic plotter or an electrostatic printer using multi-needle electrodes, a recording voltage is applied to the multi-needle electrodes to form an electrostatic latent image on the surface of a dielectric layer of an electrostatic recording medium, and then an electrostatic latent image is formed. A visible image is recorded by developing this electrostatic latent image with toner. Then, in order to obtain a clear image by the electrostatic recording method, it is necessary to control the size of the gap between the needle electrode and the dielectric layer of the electrostatic recording body within the optimum range estimated from the Paschen's curve.
Therefore, an insulating pigment is added as a spacer to the polymer insulating resin that constitutes the dielectric layer, and a method for controlling the voids is performed by bringing the dielectric layer with appropriate irregularities into contact with the needle electrode. ing.

More recently, a recording device capable of high-density recording of 400 dots / inch has been developed, and therefore kaolin or aluminum hydroxide is used in the dielectric layer for the purpose of preventing dot omission that occurs when recording one-dot fine line. Has been proposed (JP-A-62-217251, JP-A-64-32263, JP-A 1-21).
1765).

Certainly, when kaolin or aluminum hydroxide is used as a spacer pigment, the dot omission is improved as compared with the case where calcium carbonate is used, but kaolin and aluminum hydroxide are more insulated than calcium carbonate. Since it is inferior in performance, there is a problem that the recording density is lowered. Further, in order to improve dot omission, it is necessary that particles of kaolin or aluminum hydroxide form convex portions on the surface of the dielectric layer on the surface of the recording material. For that purpose, it has been found that the average particle size of these kaolin and aluminum hydroxide is increased. However, in order to reduce the adverse effect of the decrease in recording density due to the poor insulation of these particles, the amount of kaolin or aluminum hydroxide used should be the minimum amount that does not cause a decrease in recording density. There is a need. Therefore, in addition to these pigments, a method has been proposed in which pigments having a smaller average particle diameter than these pigments are used together with calcium carbonate or the like as a pigment having a small decrease in image density (JP-A-62-2172).
51, JP-A-64-32263). After all,
The dielectric layer of the electrostatic recording body capable of preventing the dot omission that occurs during the recording of 1-dot thin line is a pigment such as kaolin or aluminum hydroxide having a relatively large average particle diameter for forming the surface protrusions. It is formed by a coating material containing a pigment such as calcium carbonate having an average particle diameter smaller than that of, that is, two or more kinds of pigments having different average particle diameters.

[0005]

However, it is impossible to always apply two or more kinds of pigments having different average particle diameters to the conductive support at the same ratio from the initial stage to the final stage of coating as in the preparation of the paint. Although it is possible with a table scale, it is very difficult when mass-producing using a mass-production machine.
A major reason for this is the problem of selective absorption of the paint, in which the pigment having a small particle size is first smeared and then the pigment having a large particle size is smeared. That is, in the initial stage of application, since the dielectric layer is initially formed by the pigment having a small particle size, the gap with the needle electrode is narrow, and the dielectric layer has a high Beck smoothness. A clear image cannot be obtained on the body. When the coating is continued thereafter, the pigment having a large particle size is gradually smeared to form appropriate voids, and an electrostatic recording body capable of obtaining a clear image is produced. However, if you continue smearing for a longer period of time, only the pigment with a large particle size will be smeared,
A wide gap with the needle electrode results in a dielectric layer having a low Beck's smoothness, and a clear image cannot be obtained on the obtained electrostatic recording material.

Such a problem becomes remarkable when two or more kinds of pigments having different average particle diameters are used. However, even when one kind of pigment is used, the particle size distribution of the pigment has a wide range. The occurrence of the above problems due to selective absorption is inevitable. Conventionally, as a method for solving the problem of selective absorption, the paint concentration and the paint viscosity have been increased, and the coating method and the paint supply method have been devised. The current situation is that we have not been able to solve the problem sufficiently.

The present invention solves the above problems and stabilizes even an electrostatic recording material obtained at any time from the initial stage to the final stage of application, in which the phenomenon of selective absorption does not occur during the production thereof. It is an object of the present invention to provide an electrostatic recording body having the above recording characteristics. In view of the present situation, as a result of intensive studies by the present inventors on a method for preventing selective absorption of a paint, by using a lipophilic smectite viscosity, the above problems are effectively solved, and the needle electrode and the dielectric The inventors have completed the present invention by finding that the size of the voids between the layers can be always maintained at a constant size, and that an electrostatic recording body with a clear image can be stably obtained.

[0008]

The electrostatic recording material according to the present invention is an electrostatic recording material in which a dielectric layer containing an insulating resin and pigment particles is formed on a conductive support. It is characterized in that it contains a lipophilic smectite clay. Furthermore, it is preferable that the lipophilic smectite clay is obtained by replacing the exchangeable cation of the smectite clay with a cationic surfactant.

In the method for producing an electrostatic recording material according to the present invention, the solid content of the lipophilic smectite clay contained in the dielectric layer forming coating liquid is 0.01 to 1 in the dielectric layer smearing step.
It is characterized by being 0% by weight.

[0010]

In the present invention, the lipophilic smectite clay contained in the coating liquid for forming the dielectric layer is a swelling layered clay mineral smectite clay which is a cationic surfactant or a cationic surfactant and a nonionic surfactant. It was produced by reacting with a solution of the complex under vigorous stirring (lipophilic treatment). Specifically, the reaction of the lipophilic treatment is to replace the exchangeable cation of the smectite clay with a cationic surfactant. At this time, the amount of the cationic surfactant added to the smectite clay at the time of stirring is at least the saturated equivalent of the cation exchange capacity.

As the cationic surfactant, dimethyldioctadecyl ammonium chloride [(CH ₃ ) ₂ N (H ₃₇ C ₁₈ ) ₂ ] ^+. Cl ^- dimethylbenzil octadecyl ammonium chloride is used.

[0012]

[Chemical 1]

Trimethyloctadecyl ammonium chloride [(CH ₃ ) ₃ NH ₃₇ C ₁₈ ] ^+. Cl ^{− and the} like are used, and stearamide C ₁₇ H ₃₅ CONH _{2 and the} like are used as the nonionic surfactant.

Generally, the affinity for an organic solvent largely depends on the size of the alkyl group of the surfactant used during the lipophilic treatment, and the larger the alkyl group of the surfactant is, the higher the affinity for the nonpolar organic solvent is. The smaller the alkyl group of the surfactant, the higher the affinity for the polar organic solvent. Smectite clay, which is a swellable layered clay mineral that can be used for lipophilic treatment in the present invention, is composed of crystals with a three-layer structure, and various ions having water molecules enter between layers, forming an expansion lattice and stacking. Is irregular. And chemically, the thing containing the following components as a main component can be illustrated.

[0015] 1 montmorillonite _{X 0. 33 (Al 1.} 67 Mg
_{0. 33) Si 4 O 10} (OH) 2 · nH 2 O 2 beidellite _{X 0. 33 (Al 2)} (Al 0.33 Si 3.67) O
_{10 (OH) 2 · nH 2} O 3 nontronite write ^{_{X 0. 33 (Fe 3+ 2}} ) (Al 0.33 Si 3.67)
_{O 10 (OH) 2 · nH} 2 O 4 saponite _{X 0. 33 (Mg 3)} (Al 0.33 Si 3.67) O
_{10 (OH) 2 · nH 2} O 5 iron saponite _{X 0. 33 (Mg, Fe} ) 3 (Al 0.33 S
_{i 3.67) O 10 (OH)} 2 · nH 2 O 6 hectorite _{X 0. 33 (Mg 2.67 Li} 0.33) Si 4 O
_{10 (OH) 2 · nH 2} O 7 sauconite _{X 0. 33 (Mg, Zn} ) 3 (Al 0.33 S
_{i 3.67) O 10 (OH)} 2 · nH 2 O 8 Suchipunsaito _{X 0. 33/2 (Mg 2.97)} Si 4 O 10 (OH) 2
· NH ₂ O 9 Hekutaito _{X 0. 33 (Mg 2.67 Li} 0.33) Si 4 O
₁₀ (OH, F) ₂ · nH ₂ O X is a metal such as K, Na, 1 / 2Ca, 1 / 2Mg, but many of the commercially available products are Na. Further, since X is an exchangeable cation, it has a property of exchanging when another cation is added when dissociated in water. This property is X is N
In the case of a, it appears remarkably. This is considered to be because Na has a weak bonding force between layers and is easily dissociated in water. Therefore, smectite clay in which X is Na is often used for the lipophilic treatment.

A commercial product of a lipophilic smectite clay obtained by subjecting the above smectite clay to a lipophilic treatment is trade name: SA
N, STN (made by Coop Chemical Co., Ltd.), etc. are mentioned. These lipophilic smectite clays are pale yellow or white fine powders, and SAN dissolves in a non-polar organic solvent such as toluene or xylene and exhibits thixotropic properties.
STN is soluble in a polar organic solvent such as methyl ethyl ketone and exhibits thixotropic properties. The reason why these lipophilic smectite clays exhibit thixotropic properties in organic solvents is not always clear, but like the case where smectite clays are dispersed in water, a colloidal state in an organic solvent, that is, a sol is formed, It is presumed that a gel is more likely to be formed as the concentration increases, and that it exhibits thixotropic properties.

The present inventors have incorporated a lipophilic smectite clay into the dielectric layer-forming coating liquid to use two or more kinds of pigments having different average particle diameters, and
Even when only one kind of pigment has a broad particle size distribution, it does not cause selective absorption during application of the coating liquid, and the size of the void between the dielectric layer and the needle electrode of the obtained electrostatic recording medium. The inventors have found that the electrostatic recording medium can be maintained at a constant level and a clear image can be stably obtained, and the present invention has been completed.

In the electrostatic recording material of the present invention, the coating liquid for forming the dielectric layer contains lipophilic smectite clay. The amount of the insulating resin or insulating resin contained in the coating liquid for forming the dielectric layer is used. It is appropriately adjusted depending on the pigment, solvent, etc., and is not particularly limited. However, it is necessary to give consideration to satisfy the following conditions.
That is, considering that it imparts thixotropy to the extent that selective absorption does not occur in the dielectric layer forming coating liquid, the addition amount of the lipophilic smectite clay is 0.01 to 10% by weight relative to the dielectric layer forming coating liquid. %, Preferably 0.1
The range of about 2% by weight is preferable. Incidentally, if it is less than 0.01% by weight, sufficient thixotropy cannot be obtained.
Further, when the content exceeds 10% by weight, the coating material gels, so that the optimum coating viscosity of the coating material by various coaters described later is 10 to 4
The range of 00 cps (20 ° C) cannot be maintained.

The amount of lipophilic smectite clay contained in the dielectric layer is preferably 30% by weight or less, more preferably 10% by weight or less. By the way, 30% by weight
When it exceeds the range, it becomes difficult to maintain the gap between the surface of the recording body and the multi-needle electrode in an appropriate range. The reason for this is that it becomes difficult for the pigment having a large average particle diameter to form a convex portion on the surface of the dielectric layer while maintaining a sufficient distribution density.

However, as described above, if the addition amount of the lipophilic smectite clay is set to 10% by weight or less with respect to the dielectric layer forming coating liquid in consideration of the optimum coating viscosity, naturally,
The amount of lipophilic smectite clay contained in the dielectric layer is below this range. Therefore, such a problem does not occur. Coating Conditions In the electrostatic recording medium of the present invention, examples of the highly insulating resin that constitutes 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 resins, polyester resins, nitrocellulose, polystyrene, styrene-acrylic copolymers Examples thereof include coalesce, styrene-methacrylic acid copolymer, and phenol resin.

Examples of pigments to be incorporated in the dielectric layer include clay, deckite, nacrite, kaolin, aluminum hydroxide, calcium carbonate, calcined clay, amorphous silica, alumina, calcined kaolin, barium sulfate and titanium oxide. , Pigments whose surfaces are insulated, and the like. If the average particle diameter of the pigment is too large, it becomes difficult to maintain the voids between the surface of the recording material and the multi-needle electrode in an appropriate range, and white is used during fill recording (sometimes referred to as all-mark recording). If it is too small, unevenness (white spots) may occur at the time of filling and recording. Therefore, the average particle size is 1 to 15
It is desirable to adjust in the range of about μm, preferably about 2 to 10 μm. The blending ratio of the highly insulating resin and the pigment is appropriately adjusted according to the desired characteristics of the recording material, the type of material used, etc., but generally, the weight ratio of the insulating resin and the pigment is 99: 1 to 1: 1. 30:70, preferably 90:10
It is adjusted in the range of about 40:60.

For the dielectric layer, generally, a coating solution obtained by dissolving and dispersing an insulating resin, a pigment, a lipophilic smectite clay, etc. in a suitable organic solvent such as toluene, methyl ethyl ketone, xylene, etc., for example, a bar coater or a contra coater. , A gravure coater, a curtain coater, a chanplex coater, a roll coater, a blade coater and the like, and a method of coating on a conductive support.

Examples of the conductive support include cationic polymer electrolytes such as polyvinylbenzyltrimethylammonium chloride, polydimethyldiallylammonium chloride, and styreneacrylic acid triethylammonium chloride, or polystyrenesulfonate, polyacrylate, polyvinylphosphate, and the like. Anionic polymer electrolyte or metal oxide semiconductor powder containing impurities such as zinc oxide, tin oxide, etc. is impregnated or applied, and its surface resistance is set to 10 ⁵ to 10 ⁹ Ω at room temperature, and its surface beck smoothness is Papers, synthetic papers, Japanese papers, and various films, cloths, non-woven fabrics, etc., which have been used for 200 seconds or more are used.

[0024]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but of course the present invention is not limited thereto. In addition, unless otherwise indicated, the part and% in an example show a weight part and weight%, respectively. Example 1 (Preparation of conductive support) Chemistat 730, which is a cationic polymer electrolyte, is formed on the surface of woodfree paper having a basis weight of 60 g / m ^2.
0 (manufactured by Sanyo Chemical Industries, Ltd.) 4g / m ² to the surface by dry weight, was applied to a 2 g / m ² on the back surface, dried and smoothed, the conductive support was 500 seconds Bekk smoothness Obtained.

(Preparation of Electrostatic Recording Material) On the surface of the conductive support obtained as described above, a dielectric layer-forming coating solution having the following composition was prepared so as to have a dry weight of 4 g / m ^2. A bar coater was used to apply 1000 m and the product was dried to obtain an electrostatic recording material. Toluene 100 parts Lipophilic smectite clay (trade name "SAN" manufactured by Corp Chemical Co., Ltd.) 2 parts Aluminum hydroxide (average particle size 6 μm) 18 parts Calcium carbonate (average particle size 3 μm) 18 parts Methyl methacrylate resin (solid content 32) %) 230 parts Example 2 An electrostatic recording material was obtained in the same manner as in Example 1 except that the dielectric layer forming coating liquid having the following composition was used. Methyl ethyl ketone 100 parts Lipophilic smectite clay (trade name "STN" Corp Chemical Co., Ltd.) 2 parts Aluminum hydroxide (average particle size 6 μm) 18 parts Calcium carbonate (average particle size 3 μm) 18 parts Methyl methacrylate resin (solid content 32) %) 230 parts Example 3 An electrostatic recording material was obtained in the same manner as in Example 1 except that the dielectric layer forming coating liquid having the following composition was used. Toluene 100 parts Lipophilic smectite clay (trade name "SAN" Corp Chemical Co., Ltd.) 2 parts Calcium carbonate (average particle size 5 μm, coefficient of variation 30% or more) 36 parts Methyl methacrylate resin (solid content 32%) 230 parts

Comparative Example 1 Except that the lipophilic smectite clay (trade name "SAN") was not used in the dielectric layer forming coating liquid of Example 1,
An electrostatic recording material was obtained in the same manner as in Example 1. Comparative Example 2 An electrostatic recording material was obtained in the same manner as in Example 2 except that the lipophilic smectite clay (trade name "STN") was not used in the dielectric layer forming coating liquid of Example 2. Comparative Example 3 An electrostatic recording material was obtained in the same manner as in Example 3 except that the lipophilic smectite clay (trade name "SAN") was not used in the dielectric layer forming coating liquid of Example 3.

In the above examples, the average particle size of each pigment was determined by weight distribution by the Coulter counter method.
The coefficient of variation means a value obtained by dividing the standard deviation by the average diameter (weight average). For each of the six types of electrostatic recording media obtained in this way, at the start of dielectric layer formation (1 m),
The Beck's smoothness of the dielectric layer was measured at three positions, an intermediate time (500 m) and a final time (1000 m), and recorded using a color electrostatic plotter (CE3424: manufactured by Xerox Co., Ltd.). The evaluation after electrostatic recording was performed as follows. The obtained evaluation results are shown in Tables 1 and 2.

(Evaluation Criteria) The sharpness of the image at the filled and recorded portion is visually evaluated as follows. ◯: uniform Δ: unevenness (white spots) in places ×: unevenness (white spots) in the whole area

[0029]

[Table 1]

[0030]

[Table 2]

(Evaluation) In Examples 1 to 3, it was found that stable smoothness was obtained from the initial stage to the final stage of application. On the other hand, in Comparative Examples 1 to 3, it can be seen that the smoothness is high in the initial stage of application, gradually decreases, and considerably decreases in the final stage. Generally, the surface smoothness of the dielectric layer is preferably about 30 seconds, but it is understood that in the comparative example, the smoothness in the preferable range is not obtained at the initial and final stages of the coating.

It can be seen that in Examples 1 to 3, good image sharpness was obtained from the initial stage to the final stage of the application.
On the other hand, in Comparative Examples 1 to 3, much unevenness is seen at the initial stage of application of the liquid. This is because the smoothness is too high. In addition, since the smoothness becomes low at the final stage of application, it is clear that good image sharpness is not obtained.

From Examples 1 and 2, there is no change in the smoothness and sharpness obtained by using the lipophilic smectite clay for the non-polar solvent or the lipophilic smectite clay for the polar solvent. It was It can be seen from Example 3 that the same effect as when two pigments are used can be obtained when one pigment having a large particle size distribution is used.

[0034]

EFFECT OF THE INVENTION A phenomenon in which selective absorption does not occur during the formation of a coating liquid on a dielectric layer, and a clear image can be stably obtained even with an electrostatic recording medium obtained at any of the initial and final stages of coating. An electrostatic recording body having the above recording characteristics and a method for manufacturing the same were obtained.

Claims (3)

[Claims] 1. An electrostatic recording body having a dielectric layer containing an insulating resin and pigment particles formed on a conductive support, wherein the dielectric layer contains a lipophilic smectite clay. Electronic record. 2. The electrostatic recording material according to claim 1, wherein the lipophilic smectite clay is obtained by replacing the exchangeable cations of the smectite clay with a cationic surfactant. 3. The dielectric layer smearing step, wherein the solid content of the lipophilic smectite clay contained in the dielectric layer-forming coating liquid is 0.01 to 10% by weight. Or the method for manufacturing an electrostatic recording body according to 2.