JPS5825242B2 - electrostatic recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrostatic recording medium, and particularly to an electrostatic recording medium that can stably obtain a recorded image of high density even in a low humidity atmosphere.

The electrostatic recording method uses the front side of the recording layer of an electrostatic recording medium, in which a recording layer made of an insulating resin or the like is provided on a conductive-treated support.
An electrostatic latent image is formed on the recording layer by applying a voltage pulse from the back or both sides or by transferring an electrostatic latent image formed on another original plate, and this is developed using colored powder (toner). It is a visualization method and is widely used in facsimiles, printers, etc.

On the other hand, as the amount of information has increased in recent years, facsimile machines using electrostatic recording media have changed from low-speed machines (5-6 minutes/A-4) to medium-speed machines (2-3 minutes/A-4) and high-speed machines (1 minute/A-4). Minutes or less/A
-4), and along with this, the voltage pulse application method has changed from applying full voltage to the pin electrode as in low-speed machines, to applying voltage to the pin electrode and sub electrode or back electrode. The method has changed to a two-part method.

Also, the voltage pulse width is from 500 μsec or more to 50 to 100
μSee is becoming shorter than 20 μsec.

In order to obtain stable recording in response to such increased speeds of facsimile, it is necessary to lower the impedance of the electrostatic recording medium in relation to the response speed.

The conductive support of an electrostatic recording medium is usually said to have an optimum surface electrical resistance value of 106 to 1010 ohm, and is controlled to be within this range. is 101
When the resistance reaches 1 ohm, the recording density begins to decrease, and when the resistance reaches 1012 ohms, no recording occurs at all, or the recording density drops extremely.

As mentioned above, the conductive support of a normal electrostatic recording material has a temperature of 1 at normal humidity.
For example, if it is left in a low humidity environment for a long time, the conductivity of the polymer electrolyte commonly used as a conductive treatment agent is ionic, so the conductivity decreases as the humidity decreases. Coupled with a decrease in the moisture content of the support, the amount of ion dissociation decreases, resulting in a high resistance value.

As a conductive material to replace polymer electrolytes, which have the disadvantage of being easily affected by moisture, there are methods using cuprous iodide powder (Japanese Patent Application Laid-Open No. 159339/1983) and methods using conductive zinc oxide powder ( Japanese Unexamined Patent Publication No. 51-25140) has been proposed, but new drawbacks accompany each improvement, and therefore satisfactory results have not always been obtained.

In other words, cuprous iodide, which is used as a conductive material, is used as an electronically conductive material that has a low specific resistance of 10-1 ohms by containing excess iodine, and is not affected by moisture. Therefore, electrostatic recording materials using this material can obtain recorded images with high density even under low humidity conditions, but when manufacturing electrostatic recording materials, the amount of cuprous iodide applied to the support is small. Because it has a serious defect in that the surface resistance value of the conductive support changes rapidly from 109 ohms to 106 ohms with only a change of about 1.5 y/m, electrostatic recording materials are actually used on an industrial scale. It is extremely difficult to use it as a conductive material.

In addition, conductive zinc oxide requires the use of an organic solvent such as toluene or butanol as a dispersion medium in order to obtain satisfactory conductivity, which is a major drawback in terms of handling, price, etc.

An object of the present invention is to provide an electrostatic recording medium that can stably obtain recorded images with high density even under extremely low humidity conditions such as 20° C. and 10% RH or less.

In particular, it is an object of the present invention to provide an electrostatic recording material which can be easily produced on an industrial scale by improving the above-mentioned drawbacks.

The object of the present invention is to provide an electrostatic recording medium comprising a recording layer mainly made of an insulating resin on a conductive support, in which (a) cuprous iodide, (b) 15
Specific resistance under pressure of 0 kg/crA is 10 to 105
Electronically conductive inorganic pigment powder and (c″
This is achieved by using a support with a conductive layer with M8 adhesive.

In the present invention, we have solved the significant coating amount dependence of the conductivity of the conductive support, which was a serious drawback of cuprous iodide, by using cuprous iodide as an inorganic pigment with specific electronic conductivity. This can be overcome by using them together.

In the present invention, the inorganic pigment powders used in combination with cuprous iodide include clays commonly used in paper coatings;
Kaolin, calcium carbonate, barium sulfate, zinc oxide,
With powder such as titanium oxide, 5 did not have the desired effect, and 15
10 to 105 ohms at a pressure of 0 kg/cnf,
More preferably, it is an electronically conductive inorganic pigment powder having a resistivity of 20 to 1000 ohms, most preferably 50 to 500 ohms.

Such inorganic pigment powders include, for example, AgCL AgI.
, halides such as CuC1, CuBr, TiO2, T
l2O, Al2O3, Ta2o, 5n02, PbO
, oxides such as ZnO, sulfides such as ZnS, InSb, M
g2Si, Zn5b, AlSb, InAs, InSb,
Intermetallic compounds such as AIP, GaP, Inp, Cu (S
CN), 5nZn204, TiZn04.5rTi03
, CaT i 03, S rZ r 03, etc., which have the above-mentioned specific electronic conductivity. In particular, in the present invention, TiO2, Sn02, ZnO, which have the above-mentioned specific electronic conductivity, are used. Preferably used.

When the proportion of such an electronically conductive inorganic pigment in combination with cuprous iodide is less than 30 parts by weight per 100 parts by weight of cuprous iodide, the electrical conductivity of cuprous iodide becomes significantly dependent on the coating amount. could not be improved sufficiently, and on the contrary,
If the weight part is rubbed, the conductivity deteriorates, so in the present invention, the inorganic pigment having the above-mentioned specific electronic conductivity is used in an amount of 30 to 300 parts by weight, more preferably 60 to 300 parts by weight, per 100 parts by weight of cuprous iodide. It is desirable that they be used together in a proportion of 200 parts by weight.

In the present invention, cuprous iodide and electronically conductive inorganic pigment powder include natural polymeric substances such as polyvinyl alcohol, hydroxycellulose, methylcellulose, starch, etc.
Styrene/butadiene copolymer emulsion, vinyl chloride/vinyl acetate copolymer emulsion, styrene/vinyl acetate copolymer emulsion, isobutyne/maleic anhydride copolymer salt, vinyl acetate/crotonate, polyacrylate, etc. It is prepared as a coating liquid by dispersing it in water with a conventional adhesive such as a synthetic resin material.

The content of the adhesive is generally adjusted within the range of 3 to 30 parts by weight based on 100 parts by weight of the combined cuprous iodide and inorganic pigment powder.

The coating liquid thus obtained is treated on a conventional support such as paper or synthetic paper by a conventional method, preferably a coating method, to form a conductive layer at least on the surface in contact with the recording layer.

The amount of coating liquid to be treated is not particularly limited as it varies depending on the type and blending ratio of the inorganic pigment, but it is generally applied on a dry weight basis so that the electrical resistance value of the surface of the conductive layer of the obtained support is 106 to 1010 ohm at normal humidity. It is adjusted in the range of 2 to 12 P/m, preferably 3 to 10 f/m.

In the present invention, coating liquids for forming the recording layer include organic solvents and aqueous dispersion systems, such as vinyl chloride, vinyl acetate, vinyl acecool, vinylitine chloride, ethylene, styrene, butadiene, acrylic ester, and methacrylate. Polymers or copolymers of vinyl monomers such as acid esters, acrylonitrile, acrylic acid, methacrylic acid,
silicone resin, polyester resin, polyurethane resin,
Examples include organic solvent solutions or aqueous dispersions of insulating resins such as alkyd resins and epoxy resins alone or in mixtures, but such coating liquids are used in particular in the electrostatic recording material of the present invention. (It is possible to select and use appropriately from among known insulating resins, and to add auxiliary agents normally contained in coating liquids, such as inorganic pigments, fine polymer particles, starch powder, dyes, etc.) Of course, this is not excluded, and the coating method can be carried out using a conventional coating device.

There are no particular restrictions on the amount of application, but it is generally 2 to 10 f? in terms of dry weight. /m" preferably 4 to 7'f?
/rn: Adjusted within the range.

Conventionally, in an electrostatic recording medium, a conductive layer is provided on the opposite side of the support to the recording layer, if necessary, but a conductive layer can also be provided in the present invention, if necessary.

The conductive layer at this time is not necessarily limited to a specific conductive layer provided under the recording layer of the present invention, and may be a conductive layer made of a common polymer electrolyte.

In the electrostatic recording material of the present invention thus obtained, a recorded image with high density can be stably obtained even under extremely low humidity conditions, and the remarkable coating amount dependence of the conductivity of cuprous iodide is sufficiently improved. Therefore, the electrostatic recording material of the present invention can be easily manufactured on an industrial scale.

The present invention will be explained in more detail below with reference to Examples, but it is of course not limited thereto.

Also, unless otherwise specified, parts and percentages refer to parts by weight and percentages by weight, respectively.

Examples 1 to 6, Comparative Examples 1 to 3 Cuprous iodide powder (
45 parts by weight of nine types of inorganic pigment powders as shown in Table 1, 10 parts of polyvinyl alcohol (trade name: CLAN PVA105, manufactured by CLAN Co., Ltd.)
% aqueous solution and 100 parts by weight of water were mixed and dispersed in a ball mill for 2 hours to prepare a conductive paint.

491/m2 high-quality paper with a dry coating amount of 2 to 10 cm on one side of the coat-in-blond coat. /m'' range, and four types of conductive supports were created.

The obtained 36 types of conductive supports were heated at 20°C and 50% RH.
After the conductive layer was allowed to stand for 24 hours, the surface resistivity of the conductive layer was measured using an insulation resistance meter (Model VE-30, manufactured by Kawaguchi Electric Co., Ltd.).

Figure 1 shows the relationship between the amount of conductive paint applied and the surface resistivity.

As is clear from the results shown in FIG. 1, the surface resistivity of the conductive supports of each Example of the present invention changed much more slowly with changes in the amount of applied conductive paint than in the Comparative Examples.

Examples 7 to 9, Comparative Examples 4 to 6 Cuprous iodide powder (
1 under a pressure of 150 kg/cwt
90 parts by weight of a mixture of ZnO powder (trade name: Conductive Zinc Oxide #20, manufactured by Hakusui Chemical Co., Ltd.) having a specific resistance of 0.00 ohm/I in the proportions shown in Table 2, methylcellulose (trade name: Metrose 5M) -15, 10 (manufactured by Shin-Etsu Chemical Co., Ltd.)
% aqueous solution and 100 parts by weight of water were mixed and dispersed in a ball mill for 2 hours to prepare a conductive paint.

A conductive support was prepared in the same manner as in the previous example except that the paint thus obtained was used, and the surface resistivity was measured in the same manner as shown in FIG.

As is clear from the results shown in FIG. 2, the surface resistivity of the conductive supports of each of the Examples of the present invention changed much more slowly with changes in the amount of applied conductive paint than in the Comparative Examples.

[Characteristics as an electrostatic recording medium]

The 15 types of conductive coating liquids obtained in the above Examples and Comparative Examples were coated on both sides of 491/m' high-quality paper using an air knife coater at a target dry coating amount of 6 fl/m'' per side.
, the other side 27 /, , l and dried to obtain a conductive base paper.

Next, 20 parts of calcium carbonate was added to 400 parts of a 20% methyl ethyl ketone solution of vinyl chloride/vinyl acetate (50:50) copolymer, and the recording layer coating liquid was prepared by thoroughly stirring and dispersing with a mixer. 6 ? /
An electrostatic recording material was manufactured by coating the coated surface with a bar coater and drying it so that the target dry coating amount was 5?/m.

Also, 49'? Polyvinylbenzyltrimethylammonium chloride (trade name: EC
A 15% aqueous solution of R-34 (manufactured by Dow Chemica 1) was prepared at a dry weight of 3? An electrostatic recording material was produced as Comparative Example 7 in the same manner as described above, except that a conductive base paper obtained by coating and drying was used.

The recording properties of the 16 types of electrostatic recording materials obtained in this manner were tested in the following manner.

That is, the electrostatic recording material was left standing in a hot air dryer kept at 55° C. for 30 minutes, so that the moisture content of the recording material was extremely low humidity of 2% or less.

Then, it was installed in a high-speed facsimile machine placed in an atmosphere of 20% RH at 20°C, with a linear density of 817 mm and a pulse width of 12 mm.
Image recording was performed using a magneto toner under the conditions of μsec, pin voltage -500V, and sub voltage +300V.

The density of the obtained image was measured using a Macbeth densitometer (RD-100R).
The reflection density was measured using a mold (manufactured by Macbeth) and the results are listed in Table 3.

As is clear from the results in Table 3, the electrostatic recording materials of each comparative example either do not produce an image at all or have significant variations in image density, whereas the electrostatic recording materials of each example of the present invention are stable. A high-density recorded image was obtained.

[Brief explanation of drawings]

FIGS. 1 and 2 are charts showing the relationship between the amount of conductive paint applied and the surface resistivity.

Claims (1)

[Claims] 1. An electrostatic recording material comprising a recording layer mainly made of an insulating resin on a conductive support, wherein the conductive support has (a
) having a conductive layer containing cuprous iodide, (b) an electronically conductive inorganic pigment powder having a specific resistance of 10 to 105 ohms under a pressure of 150 kg/crA, and me) an adhesive. An electrostatic recording material characterized by: 2. The electrostatic recording material according to claim 1, wherein the electrostatic recording material contains 30 to 300 parts by weight of the electronically conductive inorganic pigment based on 100 parts by weight of cuprous iodide.