JPH0517544B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention relates to an electrostatic recording medium suitable for high-density recording electrostatic facsimiles such as 400 dots/inch, electrostatic printers, electrostatic plotters, and the like. (Prior art) Along with advances in communication technology, electrostatic recording is widely used as a recording method that simultaneously satisfies high-speed recording and high image quality. Examples of this are optical communications and computer output equipment. Examples include fax machines and printers. Especially in recent years, computers are used for designing and drafting.
Electrostatic printers and electrostatic plotters, which are capable of high-density recording, are preferred for outputting drawings such as CAD systems. The multi-needle electrode recording method that is most commonly used in electrostatic recording methods includes single-sided control type and double-sided control type, but in both cases, recording of about 200 dots/inch is mainly used for recording text. There was no particular problem in the generation of discharge itself, probably because the area of each needle electrode was sufficient in terms of density. However, when high-density recording of about 400 dots/inch is performed using conventional electrostatic recording media, mainly for the purpose of recording drawings, when thin lines are drawn, normal discharge does not occur and no recording occurs after the phenomenon occurs. The so-called dot dropout phenomenon occurs, or conversely, depending on the location, the discharge reaches more than 10 times the area of each needle electrode, and abnormally bulged dots appear in the fine line after development. Abnormal dots occur and good records cannot be obtained. In the electrostatic recording method using multi-needle electrodes, it is important to control the smoothness of the dielectric layer of the electrostatic recording medium. Attempts have been made to improve the above-mentioned problems by controlling the distance between the multi-needle electrode and the surface of the recording medium within an appropriate range, but these efforts have not always been satisfactory. Furthermore, an attempt has been made to obtain a good recorded image by applying an electrostatic charge of opposite polarity to the electrostatic charge for recording to the electrostatic recording medium in advance to lower the firing voltage during recording. However, with this method of applying static charge to the recording medium in advance by friction with a styrene resin rod or the like during the manufacturing process of the electrostatic recording medium, it is difficult to uniformly charge the recording medium, and as a result, some areas are insufficiently charged.
There was a drawback that stable and good recorded images could not always be obtained. (Problems to be Solved by the Invention) The present invention provides static recording that does not cause missing dots or abnormal dots in high-density recording such as 400 dots/inch without charging the electrostatic recording medium before recording. The purpose is to provide an electromagnetic recorder. (Means for Solving the Problem) As a result of studying the chemical composition of the pigment used in the dielectric layer and the method of arranging the pigment on the surface of the dielectric layer, the inventors found that aluminum hydroxide or water in the dielectric layer It has been found that excellent recorded images can be obtained when spacers of a specific size are formed using magnesium oxide. The above hydroxides have poor charging properties and tend to reduce the density of recorded images when used, so they have not been used much in the past, and aluminum hydroxide with a small particle size has only been used for the purpose of improving writing properties. It was hot. However, the inventors of the present invention have solved the above problem by forming projections made of aluminum hydroxide or magnesium hydroxide with a thickness of 5 to 15 μm on the dielectric layer as spacers, and have also found that an excellent image can be obtained by using a specific pigment in combination. They have discovered that a high concentration can be obtained, and have completed the present invention. The present invention provides an electrostatic recording material comprising a conductive support and a dielectric layer, wherein the dielectric layer contains a spacer with an equivalent diameter of 5 to 15 μm made of at least one of aluminum hydroxide and magnesium hydroxide, The electrostatic recording material is characterized by containing a pigment having a specific resistance of 10 ⁶ Ωcm or more. (Function) In the present invention, the aluminum hydroxide contained in the dielectric layer includes gel-like, sol-like, and crystalline forms, and crystalline aluminum hydroxide includes Al ₂・O ₃・
H ₂ O and Al ₂ O ₃・3H ₂ O exist, especially Al ₂ O ₃・
3H ₂ O is excellent in the effect of the present invention. Magnesium hydroxide also exists in crystalline form. These may be used alone or in combination, and they may be surface-treated with stearic acid, silane, titanate, silicon, etc. to make them easier to disperse in organic solvents. The effects obtained in the present invention are unique to aluminum hydroxide or magnesium hydroxide, and metal powder, cornstarch, plastic pigment, silica, calcium carbonate, calcined clay, or potassium or iron hydroxides other than aluminum or magnesium. Even if hydroxides of calcium, zinc, etc. are used instead as a spacer, the effect of improving missing dots and abnormal dots cannot be obtained. Furthermore, even if such a pigment is used in combination with aluminum hydroxide or magnesium hydroxide, if the particle size of the aluminum hydroxide or magnesium hydroxide is smaller than that of other pigments and does not function as a main spacer, the present invention may be used. No effect will be obtained. The present invention is characterized in that the dielectric layer contains a spacer having an equivalent diameter of 5 to 15 μ and made of at least one of aluminum hydroxide and magnesium hydroxide. This means that, as shown in Figure 1, protrusions with an equivalent diameter of 5 to 15 μ made of the above hydroxide are used as pigments that have the function of keeping the distance d ₁ between the multi-needle electrode head 1 and the electrostatic recording dielectric layer constant. It means to contain. Furthermore, in this case, the spacer having an equivalent diameter of 5 to 15 .mu.m includes not only the case of aluminum hydroxide or magnesium hydroxide 2 made of a single grain, but also the case of a spacer made of an aggregate 3 of such hydroxide. Even if aluminum hydroxide or magnesium hydroxide 2 with an equivalent diameter of 5 to 15 μm is included, the structure in which the other pigment 4 defines the distance d ₂ between the multineedle electrode head 1 and the dielectric layer (FIG. 2) The effect of the invention cannot be obtained.
Therefore, the equivalent diameter 5 ~ which functions as a spacer
Excellent images can be obtained when the above hydroxide occupies 50% or more, preferably 70% or more of the 15μ projections. In the present invention, it is not necessary that the above-mentioned hydroxide is always present directly under each needle electrode of the multi-needle electrode head, and the above-mentioned hydroxide is not required to be present directly below each needle electrode of the multi-needle electrode head. It is sufficient that the dielectric layer is in contact with the dielectric layer and that the distance between the dielectric layer and the dielectric layer is kept constant. When forming a dielectric layer, if only the above-mentioned hydroxides with an equivalent diameter of less than 5μ are present, discharge will not occur uniformly, resulting in uneven recording density in solid recording, and conversely, if there are many spacers with an equivalent diameter of more than 15μ, The gap between the needle electrode and the dielectric layer is too large, and some spots appear where discharge does not occur, resulting in missing dots. Therefore, there are about 5 to about 9,000 spacers made of the above-mentioned hydroxide (or its aggregates) with an equivalent diameter of 5 to 15 μ per 1 mm ² , and less than 1 extremely large protrusion of 20 μ or more per 1 mm ² . It is desirable to configure it so that If the number of spacers of 5 to 15 μm is small, there will be parts where the distance between the multi-needle electrode and the surface of the dielectric layer cannot be maintained within an appropriate range due to unevenness and waviness of the paper surface. On the other hand, if the amount is too high, the recording density will decrease. However, the equivalent diameter is calculated by the following equation from the projected area s of the protrusion that appears when the surface of the dielectric layer is observed with a scanning electron microscope. If the spacer is made of an aggregate, the projected area is measured using the edges of the entire protrusion as the boundary. Equivalent diameter = 2√ If the amount of the hydroxide compounded is small, it will not be possible to produce a recording medium with a certain surface smoothness unless one with a large particle size and extremely uniform distribution is used. On the other hand, if the amount of the hydroxide is too large, the recording density will decrease, so the amount of the hydroxide to be added is 2% to 60% by weight, preferably 5% to 40% by weight based on the total solid content of the dielectric layer. Prepared between. If the content of the hydroxide is increased in this way, the recording density decreases, so the amount of the hydroxide used is limited.
Therefore, if a dielectric layer is constructed using only the hydroxide as a pigment, the writing properties will be poor and the gloss will be strong, so it is necessary to use a highly insulating pigment in combination. Pigments used in combination include alumina, calcium pyrophosphate, zinc carbonate, barium carbonate, barium sulfate, barium nitrate, barium titanate, lead stearate, potassium sulfate, calcium carbonate, talc, calcium hydroxide, calcined kaolin, amorphous silica, Furthermore, plastic pigments such as polyethylene, epoxy resin, and polyacrylonitrile, and pigments obtained by surface treatment of these with beef tallow, silicone, siloxane, stearic acid, titanate, etc., are also used. Incidentally, when the pigment is surface-treated with the above-mentioned substances, the insulation property can be improved and excellent recording density can be obtained. If the other pigment 4 used in combination acts as a spacer as shown in Figure 2, dots will be missing, so it is preferable to use a pigment that does not contain any particle size of 5μ or more as much as possible, and the average particle size is 4μ or less, preferably 2μ. Use the following: In addition, from the viewpoint of recording density, other pigments used in combination have a specific resistance, which is an indicator of insulation.
It is necessary to select one with a resistance of 10 ⁶ Ω・cm or more. The amount of pigment used in combination is usually 5% based on the total solid content of the dielectric layer.
Prepared between % and 50% by weight. The resin forming the dielectric layer is vinyl acetate,
Ethylene-vinyl acetate copolymer, vinyl chloride, vinyl chloride-vinyl acetate copolymer, vinylidene chloride, polyacrylate, polymethacrylate, butyral resin, polyester, vinylidene fluoride, nitrocellulose, polystyrene, styrene-acrylic copolymer , silicone resin, epoxy resin, vinyl acetate methacrylate resin, styrene butadiene copolymer, vinyl acetate methacrylate ester copolymer, vinyl acetate crotonate ester copolymer, vinylidene chloride vinyl chloride copolymer, vinylidene chloride acrylonitrile copolymer,
Examples include urethane resin, stearylmethacrylchloroprene copolymer, and phenol resin. Among these, from the viewpoint of chargeability and ease of application, it is preferable to use a resin containing methyl methacrylate, styrene, or polyester as a copolymer component or a copolymer thereof as a mixed component. Aluminum hydroxide or magnesium hydroxide is usually dispersed in an organic solvent using a ball mill, an attritor, a high-speed stirrer, etc., but the particle size can also be adjusted at this time. A dispersant or the like may also be used during dispersion. The pigment used in combination is similarly dispersed using a stirrer, and the resin is further dissolved to prepare a paint. The conductive support constituting the electrostatic recording medium may include inorganic salts such as sodium chloride and calcium chloride, cationic salts such as polyvinylbenzyltrimethylammonium chloride, polydimethyldiallylammonium chloride, and styrene acrylate triethylammonium chloride. Impregnation or coating with a polymer electrolyte, anionic polymer electrolyte such as polystyrene sulfonic acid, polyacrylic acid, polyvinyl phosphate, etc., or metal oxide semiconductor powder such as zinc oxide, tin oxide, etc., and increase the surface resistance to 10 ⁵ ~ 10 ⁹ Ω, and the Beck smoothness of its surface is
Paper, plastic film, synthetic paper, Japanese paper, etc. that have been heated for 200 seconds or more are used. (Examples) Examples of the present invention will be described below, but the present invention is not limited only to these Examples.
Further, unless otherwise specified, parts and % in the examples indicate parts by weight and % by weight, respectively. Example 1 Preparation of recording medium: A cationic polymer electrolyte (trade name: Chemistat) was coated on the surface of high-quality paper with a basis weight of 53 g/ ^m2.
6300, manufactured by Sanyo Kasei Co., Ltd.) was coated at an absolute dry weight of 3 g/m ² and on the back surface at a weight of 2 g/m ² to obtain a conductive support. On this conductive support, a dielectric layer paint having the following composition was applied, and the surface was dispersed using an attritor so that the surface smoothness was 100 ± 30 seconds, and the dry weight was 5 g/m ² . The electrostatic recording medium was obtained by coating and drying. Toluene 200 parts Aluminum hydroxide (average particle size 8.0μ; trade name: Hygilite-H32S, manufactured by Showa Denko)
20 parts light calcium carbonate (average particle size 1.27μ, specific resistance
(2.1×10 ⁸ Ω・cm granular pigment) 30 parts Polymethyl methacrylate resin 50 parts When the surface of the recording dielectric layer was observed with an X-ray microanalyzer (EPMA), the distribution of aluminum derived from aluminum hydroxide was large in the SEM image. Compatible with pigments, with an equivalent diameter of 5 to 15μ calculated from the projected area measured from the edge of the protrusion.
average of 5×10 ² aluminum hydroxide per 1 mm ²
observed. Most of the calcium distribution derived from light calcium carbonate observed in EPMA is
Corresponding to the small pigments in SEM images, the dielectric layer of the recording medium was constructed so that aluminum hydroxide functioned as a spacer. Example 2 Preparation of recording material: Magnesium hydroxide (average particle size) was used instead of aluminum hydroxide in Example 1.
A dielectric layer coating material was prepared in the same manner as in Example 1, except that 20 parts of 3.8 μm (trade name: Kiyowa Suimag F, manufactured by Kyowa Kagaku Co., Ltd.) was used as a pigment, and an electrostatic recording medium was constructed. Magnesium hydroxide with an equivalent diameter of 5 to 15 μ is 1 mm ²
An average of 4×10 ² particles were observed per area, indicating that the dielectric layer of the recording medium had a structure in which magnesium hydroxide functioned as a spacer. Example 3 Preparation of recording material: Instead of 30 parts of light calcium carbonate, amorphous silica (average particle size 1.30μ, specific resistance 2.5×
The same procedure as in Example 1 was used except that 65 parts of styrene ^- butyl acrylate copolymer was used instead of 50 parts of polymethyl methacrylate resin. A dielectric layer coating material was prepared, and an electrostatic recording medium was constructed. 1 mm ² of aluminum hydroxide with an equivalent diameter of 5 to 15μ
An average of 5×10 ² particles were observed per unit, indicating that the dielectric layer of the recording medium had a structure in which aluminum hydroxide functioned as a spacer. Comparative Example 1 Preparation of recording medium: Same procedure except that 20 parts of aluminum hydroxide with an average particle size of 1.0 μm (trade name: Hygilite H42, manufactured by Showa Denko K.K.) was used instead of aluminum hydroxide with an average particle size of 8.0 μm. A dielectric layer coating material was dispersed and prepared using an attritor in the same manner as in Example 1, and an electrostatic recording material with a surface Bekk smoothness of 250 seconds after coating was obtained. No spacer with an equivalent diameter of 5 to 15 μm was observed in 1 mm ² . Comparative Example 2 Preparation of recording medium: Except that 20 parts of aluminum hydroxide with an average particle size of 17 μm (trade name: Hygilite H-31, manufactured by Showa Denko K.K.) was used instead of aluminum hydroxide with an average particle size of 8.0 μm. In the same manner as in Example 1, a dielectric layer coating material was dispersed and prepared using an attritor to form an electrostatic recording medium. An average of 8×10 ³ pieces of aluminum hydroxide with an equivalent diameter exceeding 20 μm were found in 1 mm ² and these formed spacers. Comparative Example 3 Preparation of recording medium: Aluminum hydroxide with an average particle size of 1.0μ instead of aluminum hydroxide with an average particle size of 8.0μ (trade name: Hygilite H42, manufactured by Showa Denko)
Light calcium carbonate (average particle size 1.27μ,
An electrostatic recording material was constructed in the same manner as in Example 1, except that heavy calcium carbonate having an average particle size of 5 μm was used instead of the granular pigment having a specific resistance of 2.1×10 ⁸ Ωcm. Observation of EPMA and SEM images revealed that the heavy calcium carbonate in the dielectric layer was larger than the aluminum hydroxide, and that the heavy calcium carbonate served as a spacer. An average of 7×10 ² pieces of heavy calcium carbonate with an equivalent diameter of 5 to 15 μm were confirmed per 1 mm ² . Comparative Example 4 Preparation of recording medium: Light calcium carbonate (average particle size
Same as Example 1 except that zinc hydroxide ball milled to an average particle size of 1μ (specific resistance 3.6×10 ⁵ Ωcm) was used instead of the granular pigment (1.27μ, specific resistance 2.1×10 ⁸ Ωcm). An electrostatic recording medium was constructed. 1 mm ² of aluminum hydroxide with an equivalent diameter of 5 to 15μ
An average of 5×10 ² pieces were confirmed. Comparative Example 5 Preparation of Recording Body: An electrostatic recording body was constructed in the same manner as in Example 1 except that calcium hydroxide (reagent manufactured by Kishida Chemical Co., Ltd.) was used instead of aluminum hydroxide. An average of 7×10 ² pieces of calcium hydroxide with an equivalent diameter of 5 to 15 μm were confirmed per 1 mm ² . Comparative Example 6 Preparation of recording material: 5 parts of amorphous silica (trade name: Thyroid 74, manufactured by Fuji Davison) with an average particle size of 7 μm instead of 20 parts of aluminum hydroxide, and 65 parts of polymethyl methacrylate resin instead of 50 parts. An electrostatic recording medium was constructed in the same manner as in Example 1 except for using the following. Amorphous silica particles with an equivalent diameter of 5 to 15 μm were found on average at 2×10 ² per mm ² . Recording Test Method For each of the electrostatic recording bodies thus constructed, one dot of a thin line was recorded using an electrostatic plotter EP-101 manufactured by Matsushita Densen Co., Ltd. Total length of the obtained thin wire 1
The total length of missing dots per meter and the number of abnormal dots were evaluated. Furthermore, solid recording was performed to evaluate recording density unevenness. The above results are shown in Table 1.

[Table] ×: Significant unevenness in recording density.
(Effects) The electrostatic recording medium of the present invention can be used without going through the step of applying an electrostatic charge of opposite polarity to the electrostatic charge for recording in advance
In high-density electrostatic recording such as dots per inch, it was an excellent electrostatic recording medium that could produce clear images with no missing dots or abnormal dots and no uneven recording density.

[Brief explanation of the drawing]

FIG. 1 shows one embodiment of the present invention, in which aluminum hydroxide or magnesium hydroxide functions as a spacer to define the distance between the dielectric layer and the multineedle electrode head. FIG. 2 shows an electrostatic recording material in which aluminum hydroxide or magnesium hydroxide does not function as a spacer. 1...Multi-needle electrode head, 2...Aluminum hydroxide or magnesium hydroxide, 3...Agglomerate, 4...Other pigments.

Claims (1)

[Claims] 1. An electrostatic recording material consisting of a conductive support and a dielectric layer, wherein the dielectric layer contains a spacer with an equivalent diameter of 5 to 15 μ made of at least one of aluminum hydroxide and magnesium hydroxide, and has a specific resistance. An electrostatic recording material characterized by containing a pigment of 10 ⁶ Ωcm or more.