JPH04217261A - Electrostatic recording unit - Google Patents

Abstract

PURPOSE:To obtain an electrostatic recording unit, in which point end fogging is effectively eliminated without causing decrease of recording density, prevention of a void, generation of an abnormal dot, deterioration of fine line reproducibility, damage of a recording head, etc., by improving the electrostatic recording unit of using paper as a supporter. CONSTITUTION:A derivative layer contains at least high molecular insulating resin, pigment grain and a conductive grain. At least one kind of the pigment grain is kaolin or aluminum hydroxide, and a mean grain size of kaolin or aluminum hydroxide is a mean grain size or more of the other pigment grain with a mean grain size of the conductive grain 1/2 times or more the mean grain size of kaolin or aluminum hydroxide and equal or less. Specific resistance under 150kg/cm<2> pressure of the conductive grain is 0.5 to 10000ohm.cm, and a content of the conductive grain is 0.1 to 10wt.% in the derivative layer.

Description

Description: [0001] The present invention relates to an electrostatic recording material suitable for electrostatic plotters and printers using multi-needle electrodes. [0002] Generally, in order to obtain a clear image using an electrostatic recording method, the size of the gap between the needle electrode and the dielectric layer of the electrostatic recording medium is determined by the optimum size estimated from Paschen's curve. It is necessary to control the range. For this reason, an insulating pigment is added as a spacer to the polymeric insulating resin that makes up the dielectric layer.
A method of controlling the air gap is carried out by bringing a needle electrode into contact with a dielectric layer formed with appropriate irregularities. However, in electrostatic plotters and electrostatic printers that use 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 A visible image is recorded by developing this electrostatic latent image with toner. However, when voltage is applied to the multi-needle electrode, the exposure current of the applied voltage is injected into the developing device. Tip fogging, which is called a fog phenomenon, is likely to occur. [0004] For this reason, in electrostatic recording materials using paper as a support, a method of preventing the LEF phenomenon is to apply conductive treatment to the back surface of the support to allow the leakage current to escape in the volume direction of the support. It is being However, when a recording medium treated in this manner is recorded in a high humidity environment, the applied pulse may attenuate before reaching the maximum voltage, resulting in a decrease in recording density. [0005] Furthermore, in electrostatic recording materials using an insulating film as a support, since the support has a very high volume resistivity, it is necessary to expose a part of the conductive layer (usually the end surface of the recording material) or A conductive paint such as carbon black is applied to the area 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 steps is increased, resulting in poor productivity and high costs. [0006] For this reason, an electrostatic recording material (Japanese Patent Laid-Open No. 61-213
No. 851) has been proposed, but in recording media using paper as a support, the effect of preventing the LEF phenomenon is recognized, but abnormal dots that are thought to be caused by discharge between multiple needle electrodes occur frequently, and the In high-density recording (dots per inch), thin line reproducibility deteriorates, scratch-like white spots occur frequently in the direction parallel to the recording electrode, and recording density decreases. Another disadvantage is that the conductive particles remain in the recording electrode, causing damage to the recording electrode. [Problems to be Solved by the Invention] In view of the current situation, the present inventors have investigated the improvement of the LEF phenomenon that occurs in electrostatic recording materials that use paper as a support, and have found that the LEF phenomenon has been improved.
The F phenomenon is when a latent image is formed on the surface of a dielectric layer due to an air discharge, opposite charges are induced, and as a result, the charges generated in the conductive layer have no place to escape, and the part of the developing device that is grounded It was confirmed that this is a phenomenon in which toner is electrostatically attracted to the dielectric layer, causing fog. It has also been confirmed that the electric charge generated in the conductive layer can be eliminated if a trace amount of conductive particles are present so as to electrically connect the conductive layer and the developing device. As a result of further intensive research, it was discovered that a specific amount of pigment particles and specific conductive particles were used in combination with the polymeric insulating resin that constitutes the dielectric layer of an electrostatic recording medium that uses paper as a support. However, if kaolin or aluminum hydroxide having a specific average particle size is used as at least one of the pigment particles, the conductive treatment on the back side of the support can be significantly reduced, and LEF in a low humidity environment can be improved. It is possible to obtain a high-quality electrostatic recording medium that does not cause phenomena or decrease in image density under high humidity environments, and also does not generate abnormal dots, reduce thin line reproducibility, white spots, or damage recording electrodes. This discovery led to the completion of the present invention. Means for Solving the Problems The present invention provides an electrostatic recording material in which a conductive layer and a dielectric layer are sequentially formed on a paper support.
1) the dielectric layer contains at least an insulating polymer resin, pigment particles, and conductive particles, (2) at least one of the pigment particles is kaolin or aluminum hydroxide, and (3) kaolin or water The average particle size of the aluminum oxide is greater than or equal to the average particle size of other pigment particles, and (4) the average particle size of the conductive particles is 1/2 or more and equal to or less than the average particle size of kaolin or aluminum hydroxide. Yes, (5
) The specific resistance of the conductive particles under a pressure of 150 kg/cm2 is 0.5 to 10,000 ohm cm, and (6) the content of the conductive particles is 0.1 to 10% by weight of the dielectric layer. This is an electrostatic recording material characterized by: [Function] Paper supports constituting the electrostatic recording medium of the present invention include cationic polymer electrolytes such as polyvinylbenzyltrimethylammonium chloride, polydimethyldiallylammonium chloride, styrene acrylate triethylammonium chloride, and polystyrene. A conductive layer is formed by impregnating or applying a conductive substance such as anionic polymer electrolyte such as sulfonate, polyacrylate, or polyvinyl phosphate, or metal semiconductor powder containing impurities such as zinc oxide or tin oxide. Paper, synthetic paper, Japanese paper, etc. whose surface resistance value has been adjusted to about 105 to 108 ohms under normal humidity are used, but especially those whose surface smoothness has been adjusted to about 20 ohms are used.
A support that is maintained for 0 seconds or longer is more preferably used. Generally, the dielectric layer is prepared by coating a conductive support with a polymeric insulating resin, a suitable organic solvent such as toluene, methyl ethyl ketone, xylene, isopropyl alcohol, etc.
A method in which a coating liquid prepared by dissolving and dispersing pigment particles, conductive particles, etc. is applied using an appropriate coating device such as a bar coater, contra coater, gravure coater, curtain coater, champlex coater, roll coater, or blade coater. It is formed. As mentioned above, the electrostatic recording material of the present invention has an extremely important feature in the composition of the material constituting the dielectric layer. , ethyl acrylate, acrylic acid 2
- Acrylic acid ester copolymers and methacrylic acid ester copolymers such as ethylhexyl, decyl acrylate, methyl methacrylate, isobutyl methacrylate, and 2-ethylhexyl methacrylate, vinyl acetate, ethylene-vinyl acetate copolymer, butyral resin, Various polymeric insulating resins used in ordinary electrostatic recording materials can be used, such as polyester resin, nitrocellulose, polystyrene, styrene-acrylic copolymer, styrene-methacrylic acid copolymer, and phenol resin. Examples of the pigment particles contained in the dielectric layer include kaolin, aluminum hydroxide, clay, calcined clay, calcined kaolin, calcium carbonate, amorphous silica, alumina, barium sulfate, and titanium oxide. The electrostatic recording material of the present invention contains kaolin or aluminum hydroxide as an essential component, particularly as at least one type of pigment particle. Kaolin in the present invention refers to hallosite,
It refers to kaolin group minerals such as hydrated hallosite, kaolinite, deckite, and nacrite, and also includes kaolin surface-treated with stearic acid, silane, titanate, silicon, etc. Note that kaolin may contain quartz as an impurity, but if the amount exceeds 2% by weight, abnormal dots will occur, so the content of quartz is preferably 2% by weight or less. These various kaolins may be used alone or as a mixture, but among them, kaolinite is particularly preferably used because it has an excellent effect of improving fine wire removal. On the other hand, aluminum hydroxide includes crystalline aluminum hydroxide AL2 O3 .H2 O and A
There are also L2 O3 .3H2 O and the like, and these can be surface-treated in the same way as kaolin to improve their solvent dispersibility and insulation properties. [0016] If the average particle diameter of the pigment particles is too large, it will be difficult to adjust the gap between the surface of the recording medium and the multi-needle electrode, and white spots may occur during all-mark recording.
On the other hand, if the particle size is too small, there is a risk of unevenness occurring when recording all marks, so the average particle size should be 1 to 15 microns.
It is desirable to adjust the thickness preferably to about 2 to 10 microns. In addition, if the average particle size of kaolin or aluminum hydroxide, which is an essential component, is smaller than the average particle size of other pigment particles, the effect of improving fine line reproducibility will decrease, so it is necessary to have an average particle size larger than that of other pigments. It is necessary to selectively use kaolin or aluminum hydroxide. The blending ratio of the insulating polymer resin and the pigment particles is adjusted as appropriate depending on the characteristics of the desired recording medium and the type of material used, but generally the weight ratio of the insulating resin to the pigment particles is 99. :1 to 30:70, preferably 90:1
It is adjusted in a range of about 0 to 50:50. 001
8] In the electrostatic recording material of the present invention, conductive particles are used in combination with the polymeric insulating resin and pigment particles constituting the dielectric layer as an essential component. If the average particle size is smaller than half of the average particle size of kaolin or aluminum hydroxide, the conductive path in the dielectric layer created by the addition of conductive particles will not come into contact with the developer or earth roll, resulting in LEF The effect of preventing the phenomenon will be lost. However, if the average particle size of the conductive particles is larger than the average particle size of kaolin or aluminum hydroxide, white spots may occur or the recording electrode may be damaged. It is necessary to adjust the particle size to a range of 1/2 or more and the same or less, and generally particles of about 1 to 10 microns, preferably about 2 to 10 microns, are used. Furthermore, 150 kg/cm2 of conductive particles
If the resistivity under pressure is less than 0.5 ohm・cm, white spots and a decrease in recording density will occur.
If the particle size is larger than cm, it is necessary to incorporate a large amount of particles in order to obtain a sufficient effect of improving the LEF phenomenon, resulting in a decrease in recording density. Therefore, 1 of the conductive particles
Specific resistance under 50kg/cm2 pressure is 0.5 to 100
It is necessary to adjust within a range of 0.00 ohm/cm. Examples of the conductive particles include conductive tin oxide, conductive zinc oxide, conductive titanium oxide, copper iodide, and composite conductive particles such as titanium oxide with conductive tin oxide formed on the surface. . In addition, carbon black, AL,
Metal particles such as Fe and Cr have too low specific resistance and are therefore unsuitable as the conductive particles of the present invention. In addition, if the amount of conductive particles is less than 0.1% by weight of the dielectric layer, a sufficient effect of improving the LEF phenomenon cannot be obtained, and if it exceeds 10% by weight, white spots and abnormal dots may occur. Since disadvantages such as damage to the electrodes occur, the amount of the conductive particles mixed must be adjusted within the range of 0.1 to 10% by weight of the dielectric layer. [0021] Note that the conductive particles penetrate the dielectric layer,
Since the conductive layer is used to scatter the conductive layer as minute dots on the surface of the recording medium, it is preferable that the conductive layer penetrates from the conductive layer to the surface of the dielectric layer in the thickness direction of the dielectric layer, but does not penetrate completely. Even if the dielectric layer is not connected to the conductive layer, if the dielectric layer is connected to the conductive layer, friction with the recording electrode may peel off the dielectric layer resin on the surface of the conductive particle and cause electrical leakage. A point is formed, and this conductive point contacts the developer and ground roll to achieve the desired effect of the present invention. In order to prevent the LEF phenomenon, conductive particles only need to form a conductive path in the dielectric layer at even one local location. Dielectric layer surface of electrostatic recording material 100mm
It is disclosed that it is sufficient to have one guide path in 2. Therefore, conductive particles may exist in the form of lumps or aggregates, or may exist in a state where they coat the surface of the insulating pigment, but when a voltage is applied to the needle electrode during recording, If conductive particles are present there, white spots,
Since abnormal dots, damage to the electrodes, etc. may occur, it is preferable to minimize the amount of conductive particles incorporated into the dielectric layer as described above. However, unlike the electrostatic recording material of the film support disclosed in the same publication, the electrostatic recording material of the present invention has
Because paper is used as a support, even if the smoothness of the conductive layer formed on the paper sheet is improved as much as possible, the amount used will still be at the level disclosed in the publication due to the waviness and unevenness of the paper sheet. In this case, the effect of the conductive particles is not exhibited at all. Therefore, in the electrostatic recording material of the present invention, conductive particles are blended in a proportion that accounts for 0.1% by weight or more of the dielectric layer as described above, and kaolin is added as pigment particles. Or by using aluminum hydroxide together, abnormal dots that cannot be obtained even when used in combination with other pigments,
This completely prevents the decrease in fine line reproducibility and the occurrence of white spots. The reason why such excellent effects are obtained is not necessarily clear, but even when conductive particles exist between the needle electrodes or directly under the needle electrodes, kaolin and aluminum hydroxide coexist. It is thought that this is because the discharge starting voltage for forming an electrostatic latent image is required to be low, and discharge between the needle electrodes and rapid decrease in the potential of the needle electrodes are prevented. [Example] The present invention will be explained in more detail with reference to Examples below, but the present invention is of course not limited to these. Note that recording evaluation of the electrostatic recording bodies obtained in Examples and Comparative Examples was performed according to the following method. Recording density Monochrome plotter manufactured by Matsushita Densen [EP
-103] under the environmental conditions of 27° C. and 85% RH, and the recorded density was measured. LEF concentration 23℃, 25%RH using the same plotter as above
Recording was performed under the following environmental conditions, and the fog density between the recording electrode and the developing device was measured at this time. [0027] White spots: 23°C, 50% using the same plotter as above.
All-mark recording was performed under RH environmental conditions, and the occurrence of key-shaped white spots was visually evaluated using the following evaluation criteria. 5: Not occurring at all. 3: Occurs partially but is not noticeable. 1: White and clearly generated. Abnormal dot Draw a 2-dot line with the same plotter as above 1
The number of abnormal dots generated per m was counted. Thin line omissions A 2-dot line was drawn using the same plotter as above and the number of thin line omissions occurring per meter was counted. Electrode damage Xerox color electrostatic plotter
CE-3424], and the presence or absence of electrode damage was examined. The following materials were used as various conductive particles, and the average particle diameter was adjusted by air classification. Conductive titanium oxide: Conductive titanium oxide [ET-600W] manufactured by Ishihara Sangyo. Copper iodide: Reagent manufactured by Tokyo Kasei. Conductive zinc oxide: Aluminum oxide was added to zinc oxide powder and fired in the range of 800°C to 1000°C to prepare conductive zinc oxide having a predetermined specific resistance. Examples 1 to 8 Chemistat 6300 (manufactured by Sanyo Chemical Industries), which is a cationic polymer electrolyte, was coated on the back side of high-quality paper with a thickness of 75 microns.
was applied in a dry weight of 0.5 g/m2, and the same was applied on the opposite side in a dry weight of 4 g/m2 to form an intermediate conductive layer. Separately, a 30% by weight toluene solution containing a butyral resin, various pigment particles shown in Table 1, and conductive particles was prepared so that the total solid content was 100 parts by weight, and this solution was poured onto the intermediate conductive layer. A dielectric layer was formed by applying a dry weight of 3 g/m2 using a Mayer bar, and eight types of electrostatic recording materials were manufactured. Recording evaluation of the obtained recording body was carried out by the method described above, and the results are shown in Table 2. [Table 1] [Table 2] [0034] Comparative Examples 1 to 9 Nine types of samples were prepared in the same manner as in the example except that the various pigment particles and conductive particles shown in Table 3 were used. An electrostatic recording medium was manufactured. Comparative Example 10 Chemistat 6300 (manufactured by Sanyo Chemical Industries, Ltd.), which is a cationic polymer electrolyte, was placed on the back side of high-quality paper at a dry weight of 3.0
An electrostatic recording material was produced in the same manner as in Comparative Example 1 except that the coating was applied at a rate of g/m2. Recording evaluations were performed in the same manner on the obtained recording bodies of the 10 types of comparative examples, and the results are listed in Table 4. [Table 3] [Table 4] [Effects of the Invention] As is clear from the results in Tables 2 and 4, the electrostatic recording materials obtained in each example of the present invention had By adopting a dielectric layer with a special structure, the LEF phenomenon occurs in low humidity environments, the image density decreases in high humidity environments,
The occurrence of abnormal dots, decreased fine line reproducibility, white spots, and damage to the recording electrodes were effectively eliminated, and the electrostatic recording material was of high quality.

Claims (1)

[Claims] Claim 1. An electrostatic recording material in which a conductive layer and a dielectric layer are sequentially formed on a paper support, wherein (1) the dielectric layer contains at least an insulating polymer resin, pigment particles, and conductive particles. (2) at least one of the pigment particles is kaolin or aluminum hydroxide; (3) the average particle diameter of the kaolin or aluminum hydroxide is greater than or equal to the average particle diameter of the other pigment particles; (4) The average particle diameter of the conductive particles is 1 of the average particle diameter of kaolin or aluminum hydroxide.
/2 or more and the same or less, (5) 150 of the conductive particles
kg/cm2 Specific resistance under pressure is 0.5 to 10000
(6) An electrostatic recording material characterized in that the content of conductive particles is 0.1 to 10% by weight of the dielectric layer.