JPH03167558A - Electrostatic recording body - Google Patents

Abstract

PURPOSE:To obtain an electrostatic storage body with the generation of abnormal dots, flares, etc., reduced and having a high picture density by using kaolin or aluminum hydroxide having a specified average grain diameter as a spacer pigment and also using magnesium hydroxide subjected to hydrophobic surface treatment. CONSTITUTION:A dielectric layer consisting essentially of insulating resin and pigment is formed on a conductive substrate. The kaolin and aluminum hydroxide as the main spacer pigment having 3-15mum average grain diameter are selectively used, and the pigment is arranged in the storage layer to fill the gap between a multi-needle electrode. Furthermore, the magnesium hydroxide pigment subjected to hydrophobic surface treatment is also used. As a result, the recording density is enhanced, the void of dots and generation of abnormal dots and flares are prevented.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an electrostatic recording medium used in electrostatic blotters and color electrostatic plotters, which are high-density recording devices using multi-needle electrodes. be.

(Prior Art) In recent years, with the advancement of communication means, there has been a demand for the development of a recording method capable of outputting high-density recorded images.

The electrostatic recording method is being developed as a recording method that meets this requirement, and because it not only has excellent image quality but also has a fast recording speed, it is widely used in computer output devices, facsimiles, and
It is widely used in various fields such as AD systems or design using computer graphics.

In particular, most electrostatic recording methods using multi-needle electrodes have conventionally had recording densities of 200 dots/inch or less;
Recently, devices with high recording densities such as 400 dots/inch have been developed.

However, with such high-density recording devices, when recording a thin line of one dot, dots may be missing, abnormal dots with a dot area ten times larger than normal dots may occur, or flare may occur around the edges of normal dots. Defects that impair recording quality are likely to occur. Therefore, there is a strong desire to improve these drawbacks, and various proposals have been made.

For example, a method has been proposed in which kaolin and aluminum hydroxide, which have not been used much in the past, are used as spacer pigments in the dielectric layer. (Unexamined Japanese Patent Publication No. 62-2
17251, Japanese Patent Application Laid-Open No. 1-21) 765) It is true that when kaolin or aluminum ξ oxide A is used as a spacer pigment, dot dropout is improved compared to when calcium carbonate or the like is used. Although abnormal dots are also reduced, the flare that occurs around the edges of normal dots is hardly improved. Moreover, since phosphorus and aluminum hydroxide have poorer insulating properties than calcium carbonate, A new difficulty is associated with a decrease in concentration C.

In addition, in order to improve dot dropout, it is desirable to select the uniform particle diameter of kaolin or aluminum hydroxide so that it occupies the highest position on the surface of the recording medium and comes into contact with the recording needle electrode. To this end, the amount of kaolin and argonium hydroxide used should be kept to the minimum level that does not cause a decrease in recording accuracy, and a pigment with a smaller average particle size than this should be used in combination with a pigment that causes less decrease in image density. A method has been proposed.
(Japanese Unexamined Patent Publication No. 62-217251) However, even with such a method, the current situation is that it is still not possible to sufficiently reduce abnormal dots, and moreover, it is not possible to suppress the occurrence of flare.

(Problem M to be Solved by the Invention) In view of the current situation, the inventors of the present invention have conducted intensive studies to solve the above-mentioned drawbacks, and as a result, the present inventors have used kaolin or aluminum hydroxide having a specific average particle size as the main spacer pigment. However, if this is combined with hydrophobically treated magnesium hydroxide, the above drawbacks can be effectively eliminated, and abnormal dots, missing dots, and flare that occur in high-density recording devices such as electrostatic plotters can be eliminated. The present inventors have now completed the present invention by discovering that it is possible to obtain an electrostatic recording material in which the occurrence of electrostatic charges is significantly reduced and the image density is high.

(Means for Solving the Problems) The present invention provides an electrostatic recording material in which a dielectric layer containing an insulating resin and a pigment as main components is formed on a conductive support, in which the pigment has (a) an average particle size of The present invention is an electrostatic recording material characterized by containing at least one member selected from kaolin and aluminum hydroxide having a diameter of 3 to 15 μm, and (b) magnesium hydroxide whose surface has been treated to make it hydrophobic.

(Function) In the present invention, pigment (a
), a specific kaolin or aluminum hydroxide having an average particle diameter in the range of 3 to 15 μm is selectively used. And pigments! a) is arranged in the recording layer so as to define a gap between the multi-needle electrode and the surface of the recording medium.

Incidentally, when the pigment (8) has an average particle diameter of less than 3 μm, the gap between the surface of the recording medium and the multi-needle electrode is too small, resulting in spotty white spots during all-mark recording. Furthermore, if the average particle diameter exceeds 15 μm, the gap between the surface of the recording medium and the multi-needle electrode is too large, resulting in missing dots and white spots due to giant particles.

Kaolin, which constitutes a pigment (al), refers to minerals of the kaolin group such as hallosite, hydrated hallosite, kaolinite, defkite, and natalite, and these may be used alone or as a mixture. It also includes those subjected to hydrophobic treatment using stearic acid, beef tallow, titanium cassoplating agents, aluminum coupling agents, silane coupling agents, etc.

Among the minerals mentioned above, kaolinite is particularly preferably used because it has an excellent effect of improving dot dropouts. Please note that kaolin may contain quartz as an impurity,
If its content exceeds 2%, it may cause abnormal dots to occur, so it is desirable to use kaolin with a low quartz content.

On the other hand, the aluminum hydroxide constituting the pigment (a) is crystalline aluminum hydroxide A1■03.1
{20, AIKO3.3H, O, but similar to kaolin, these can also be surface-treated to improve solvent dispersibility and insulation.

In the present invention, the hydrophobically surface-treated magnesium hydroxide used in combination with the pigment (a) means that the surface of the magnesium hydroxide is treated with, for example, stearic acid, beef tallow, a titanium coupling agent, an aluminum casoplating agent, It is hydrophobized using a silane coupling agent or the like. Among them, higher fatty acids such as stearic acid and beef tallow are 0. 5-2
Magnesium hydroxide treated by weight percent is particularly preferably used because it has high hydrophobicity and provides good image density.

Note that even if amorphous silica or plastic powder is surface-treated in the same manner as magnesium hydroxide and used in combination with pigment (a) instead of magnesium hydroxide, the excellent image density improvement effect obtained in the present invention will not be obtained. I couldn't get it.

By using the specific magnesium hydroxide pigment (b) that has been surface-treated to be hydrophobic as described above in combination with the pigment (a), the occurrence of abnormal dots, missing dots, and flare can be effectively suppressed. b) has an average particle diameter of pigment (a)
If the particle size is larger than the average particle size of kaolin or aluminum hydroxide, missing dots will occur. Therefore, the average particle diameter of magnesium hydroxide constituting pigment (b) is
It is desirable that the pigment (a) be smaller than the pigment (a), and in particular, the pigment (
Particularly preferred is one smaller than a) by 2 μm or more.

By using the above-mentioned specific pigment (b) in combination, the insulation of the dielectric layer is maintained in a desirable range, and as a result, it is possible to record images with a satisfactory recording density, and also prevent abnormal dots and missing dots. , it is possible to obtain an electrostatic recording medium in which the occurrence of flare is effectively suppressed.

In the present invention, the blending ratio of the pigment contained in the dielectric layer is desirably adjusted within the range of 10 to 60% by weight, more preferably 15 to 40% by weight of the total solids of the dielectric layer. If the blending ratio of the pigment is less than 10% by weight of the total solids of the dielectric layer, it will be difficult to maintain the gap between the surface of the recording medium and the multi-needle electrode within a desirable range, and the desired effect of the present invention will not be sufficiently obtained. Furthermore, there is a risk that practical properties may be adversely affected, such as a decrease in blocking resistance and the occurrence of curls. Furthermore, if the amount is so large as to exceed 60% by weight, the insulation properties of the recording layer may deteriorate and good recording density may not be obtained.

The proportion of pigment (a) and pigment (b) used in combination may be adjusted as appropriate depending on the desired characteristics of the recording medium, but at least the proportion of pigment (a) should be 1 to 30% of the total solid content of the dielectric layer. It is desirable to adjust the weight percentage, more preferably within the range of 5 to 20% by weight. Incidentally, if the blending ratio of pigment (a) is less than 1% by weight of the total solid content of the dielectric layer, no improvement effect on missing dots or abnormal dots will be obtained, and if it exceeds 30% by weight, the recording density will decrease. There is a risk of

The blending ratio of pigment (b) is 1% of the total solids of the dielectric layer.
It is preferable to adjust the amount within a range of about 30% by weight, more preferably about 3% to 20% by weight.

In the electrostatic recording material of the present invention, examples of the insulating resin constituting the dielectric layer include methyl acrylate, ethyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, methyl methacrylate, isoptyl methacrylate,
Acrylic esters and methacrylic ester copolymers such as 2-ethylhexyl methacrylate, and acrylic acid, methacrylic acid, maleic anhydride, crotonic acid,
Copolymers made by copolymerizing small amounts of functional groups such as itaconic acid, acrylonitrile, and methacrylonitrile, polyacetic acid M vinyl, ethylene/vinyl acetate copolymers, petitral resins, polyester resins, nitrocellulose resins, polystyrene, styrene・Acrylic copolymer, styrene/methacrylic acid copolymer, vinylidene fluoride resin, silicone resin, epoxy resin, styrene/putadiene copolymer, vinyl acetate/methacrylate copolymer, vinyl acetate/crotonic acid ester copolymer Examples include vinylidene chloride/vinyl chloride copolymer, vinylidene chloride/acrylonitrile copolymer, urethane resin, stearylmethacrylic/chlorobrene copolymer, and phenol resin.

The dielectric layer is generally prepared by dissolving and dispersing an insulating resin or the above-mentioned specific pigments in an organic solvent such as toluene, methyl ethyl ketone, xylene, or isopropyl alcohol. It is formed by coating on a conductive support using various coating devices such as a coater, a Champlex coater, a roll coater, and a blade coater.

Examples of the conductive support constituting the electrostatic recording material include cationic polymer electrolytes such as polyvinylbenzyltrimethylammonium chloride, polydimethylallylammonium chloride, styrene acrylate triethylammonium chloride, polystyrene sulfonate, and polyacrylic acid. Anionic polymer electrolytes such as acid salts and polyvinyl phosphate, or metal semiconductor powders mixed with impurities such as zinc oxide and tin oxide are impregnated or coated with a binder as necessary, and the surface resistance is reduced to 1.
Paper, plastic film, gokai paper, Japanese paper, cloth, etc. with a resistance of about 0.05 to 10.9 ohm 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 represent parts by weight.

Example 1 [Preparation of conductive support] A cationic polymer electrolyte, Chemistat 6300 (manufactured by Sanyo Kayi Co., Ltd.) was applied to the surface side of a 160 g/rd high-quality paper in a dry weight of 4 g/n {, A conductive support was obtained by applying 2 g/bottom to the back side and smoothing the base so that the base smoothness was 200 seconds.

[Preparation of surface-treated magnesium hydroxide] Take 100 parts of magnesium hydroxide whose particle size has been adjusted by classification in a mortar, add 20 parts of a 710% beef tallow hexane solution dropwise while stirring, and then remove the surface of the magnesium hydroxide. was subjected to hydrophobization treatment.

[Preparation of electrostatic recording medium]

An electrostatic recording material was obtained by applying a dielectric layer paint having the following composition on the above conductive support at a dry weight of 4 g/rrf.

Toluene/MEK mixed solvent (1/1) 100 parts Aluminum hydroxide (average particle size 9 μm) 4 parts Surface treatment magnesium hydroxide (average particle size 5.8 μm) 15 parts Methyl methacrylate resin 167 parts (solid content 32%) ) Example 2 Kaolin with an average particle size of 6.5 μm was used instead of argonium hydroxide as the pigment constituting the dielectric layer paint, and the average particle size of the surface-treated magnesium hydroxide was 3 μm.
．． An electrostatic recording material was obtained in the same manner as in Example 1 except that the thickness was 2 μm.

Example 3 An electrostatic recording material was obtained in the same manner as in Example 1 except that a dielectric layer coating having the following composition was used.

Toluene/MEK mixed solvent (1/1) 100 parts Albulkium hydroxide (average particle size 9 μm) 4 parts Surface-treated magnesium hydroxide (average particle size 5.8 μm) 5 parts Surface-treated magnesium hydroxide (average particle size 3 .2 μm) 10 parts Methyl methacrylate resin 167 parts (solid content 32%) Comparative Example I Instead of surface treatment magnesium hydroxide, average particle size 5
．． An electrostatic recording material was obtained in the same manner as in Example 1 except that 3 μm of untreated magnesium hydroxide was used.

Comparative Example 2 Instead of surface treatment magnesium hydroxide, average particle size 5
．． An electrostatic recording material was obtained in the same manner as in Example 2 except that 3 μm of untreated magnesium hydroxide was used.

Comparative Example 3 An electrostatic recording material was obtained in the same manner as in Example 3 except that the average particle diameter of aluminum hydroxide was 4.8 μm.

Comparative Example 4 Instead of surface treatment magnesium hydroxide, average particle size 4
．． An electrostatic recording material was obtained in the same manner as in Example 1 except that 6 μm calcium carbonate was used.

Comparative Example 5 Instead of surface treatment magnesium hydroxide, average particle size 3
．． An electrostatic recording material was obtained in the same manner as in Example 1, except that amorphous silica surface-treated with a 1 μm thick silane coupling agent was used.

Comparative Example 6 An electrostatic recording material was obtained in the same manner as in Example 1 except that a dielectric layer coating having the following composition was used.

Toluene/MEK mixed solvent (1/1) 100 parts Surface treatment magnesium hydroxide (average particle size 5.8 μm) 19 parts Methyl methacrylate resin 167 parts (solid content 32%) The nine types of electrostatic recording materials thus obtained were Images were recorded using an electrostatic blocker (EP-103) manufactured by Matsushita Densen Co., Ltd., and the evaluation results for the images are listed in the table.

Note that the number of missing dots and abnormal dots is expressed as the number of dots generated per 1 m of line. In addition, flare was visually evaluated, and the evaluation criteria were as follows.

○・・・・・・・・・・・・・・・・・・・・・
・・・・・・× [Excellent] [Inferior] (Effect) As is clear from the results in the table, the electrostatic recording materials obtained in each example of the present invention all had a recording density of It was an electrostatic recording medium with high print quality and improved problems with missing dots, abnormal dots, and flare.

table

Claims (2)

[Claims] (1) In an electrostatic recording material in which a dielectric layer mainly composed of an insulating resin and a pigment is formed on a conductive support, the pigment is
An electrostatic recording material characterized in that it contains (a) at least one member selected from kaolin and aluminum hydroxide having an average particle diameter of 3 to 15 μm, and (b) magnesium hydroxide whose surface has been treated to make it hydrophobic. (2) Claim (1) in which the average particle size of magnesium hydroxide is smaller than the average particle size of kaolin or aluminum hydroxide.
) The electrostatic recording medium described in ).