JPH0976551A - Image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to always obtain an excellent image even when continuous images are formed by specifying the interval between a recording electrode and the sleeve of a toner carrier and the thickness of a toner layer on the sleeve thin in a direct recording method. SOLUTION: This method for forming an image comprises the steps of disposing a back surface electrode 2 oppositely to a toner carrier, disposing matrix- like recording electrodes 3 between the carrier 1 and the electrode 2, and directly flying toner from the carrier 1 to a recording medium 4 in response to the voltage applying state to the electrodes 3, wherein the interval between the carrier 1 and the electrode 3 at the present position is set to 51 to 80μm. Further, the thickness of the toner layer on the carrier 1 is specified to 10 to 60μm, and the voltage of 300 to 400V is applied to the recording electrode to form the image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method in which a recording electrode and a recording medium such as paper are kept in non-contact with each other and toner is directly ejected from a toner carrier onto the recording medium to form a toner image. .

[0002]

2. Description of the Related Art Conventionally, an electrophotographic apparatus has been generally used as an apparatus for forming a document or a figure on a recording medium. However, in the electrophotographic apparatus, it is necessary to separately provide a means for forming a latent image on the surface of the image carrier and a means for developing the latent image, so that the structure becomes complicated and the size tends to increase.

Therefore, a recording electrode and a back electrode are arranged to face the toner carrier, a recording medium such as paper is conveyed between the recording electrode and the back electrode, and an image signal is fed between the recording electrode and the counter electrode. A direct recording method has been proposed in which a voltage corresponding to is applied to generate an electrostatic force on the toner, and the magnetic toner is ejected from the toner carrier to the recording body according to the voltage application state.

Various methods have been proposed for the direct recording method. As one of them, a recording electrode in which a plurality of conductors are arranged in a matrix is used, and a voltage is applied to each conductor at the same time, so that a magnet roll is formed. A method has been proposed in which the magnetic toner held above is electrostatically ejected from the mesh of the recording electrode and selectively adheres to the surface of the recording body (Japanese Patent Publication Nos. 4-505896 and 4-50589).
No. 9). According to this direct recording method, since a specific recording electrode is used, a high quality image can be obtained.

[0005]

In the above-described direct recording method, the toner is ejected from the toner carrier to the recording body according to the voltage applied to the recording electrode to obtain a toner image. In the direct recording method, the distance between the recording electrode and the sleeve at the developing position is usually 50 μm, a bias voltage of 300 V is applied to the recording electrode, and the toner thickness on the sleeve is regulated to 5 to 100 μm by a doctor blade. ing. However, in the conventional direct recording method, when a large number of sheets are continuously developed, the density of the image is reduced from 1.2 at the beginning to, for example, about 0.2 at the development of about 500 sheets or more, and the image becomes unclear. There was a problem of becoming. According to the research by the present inventor, the image density of an image obtained by the direct recording method is greatly affected by the distance between the recording electrode and the sleeve at the developing position and the thickness of the toner layer on the sleeve conveyed to the developing position. Therefore, the present invention was completed based on this. According to the present invention, by controlling the distance between the recording electrode and the sleeve and the thickness of the toner layer on the sleeve to be thin in the direct recording method, good image density can always be obtained even when a large number of images are continuously formed. The purpose is to do so.

[0006]

SUMMARY OF THE INVENTION According to the present invention, a back electrode is arranged so as to face a toner carrier having a sleeve provided on the outer periphery of a magnet body, and a matrix-shaped recording electrode is provided between the toner carrier and the back electrode. In the image forming method in which the toner is directly ejected from the toner carrier to the recording body between the recording electrode and the back electrode according to the state of voltage application to the recording electrode, the above object is achieved. is there. The distance between the sleeve and the recording electrode at the developing position is 51 to 80 μm.
The thickness of the toner layer on the sleeve is set to 10 to 60 by the regulating member for controlling the thickness of the toner layer on the sleeve.
It is characterized in that an image is formed by applying a voltage of 300 to 400 V to the recording electrode while restricting the thickness to μm. A doctor blade is used as the toner layer thickness regulating member, and the distance between the doctor blade and the sleeve is set to 50 to 150 μm. Alternatively, a contact type blade is used as the toner thickness regulating member, and a pressure of 10 to 250 g / cm ² is applied to the contact type blade on the sleeve side,
The thickness of the toner layer can be easily regulated to 10 to 60 μm. If the pressure is low, toner that is charged with a polarity opposite to the predetermined polarity is likely to be generated (fogging increases), so the pressure is preferably 50 g / cm ² or more, and more preferably 100 g / cm ² or more.

The distance between the sleeve and the recording electrode at the developing position is set to 51 to 80 μm. If it is smaller than 51 μm, the toner on the sleeve may come into contact with the recording electrode and adhere to the recording electrode. If it is larger, the toner easily adheres to the recording electrode when passing through the hole of the recording electrode, and as a result, the hole opening through which the toner of the recording electrode passes becomes smaller and the image density is lowered. The thickness of the toner layer on the sleeve is set to 10 to 60 μm because if it is too thick, a large amount of toner will be ejected to the recording body side, and it will easily adhere to the recording electrode in the middle, and if it is too thin, the image density will decrease. Because it does. In addition, the recording electrode is 300 to 40
The reason why the voltage is regulated to 0V is that a sufficient amount of toner cannot fly at a voltage lower than 300V. Conversely, 40
This is because the fog on the image increases when the voltage exceeds 0V.

The magnetic toner is composed of a binder resin and 20 to 60 wt.
% Magnetic powder, and it is desirable to use a magnetic toner in which a fluidity improver is externally added to toner particles formed by pulverizing and classifying. As the magnetic toner, it is desirable to use a toner having an average particle size of d ₅₀ = 6 to 12 μm. The average particle size of the toner particles is d ₅₀ =
The reason why the thickness is in the range of 6 to 12 μm is that fog is apt to occur when it is smaller than 6, and image density is lowered when it is larger than 12. The magnetic toner has an electric resistance of 10 ¹³ Ω.
・ The absolute value of triboelectric charge is 5 to 40 μc / g at cm or more.
It is preferable to use the same one.

The binder resin as the magnetic toner material used in the present invention may be appropriately set according to the fixing system (see, for example, JP-A-57-97545). As an example, in the case of the heat roll fixing method, a styrene-acrylic copolymer, a styrene-butadiene copolymer, a polyester resin, an epoxy resin and a mixed resin thereof are suitable. As the magnetic powder, an alloy or compound containing an element exhibiting ferromagnetism, such as ferrite, magnetite, and other iron, cobalt, nickel, etc., can be used. Three
Particles of about μm are desirable. The magnetic powder preferably has a coercive force ( _I H _c ) of 0.5 to 500 Oe.

The content of the magnetic powder with respect to 100 parts by weight of the toner particles is appropriately in the range of 20 to 60% by weight. When the content of the magnetic powder is less than 20% by weight, the saturation magnetization of the toner is lowered and the toner is easily detached from the toner carrier, and when it exceeds 60% by weight, the volume resistance of the toner is lowered because the toner itself is conductive. However, the fixability is also poor. Therefore, the preferable content is 20 to 40% by weight. A charge control agent, a fluidizing agent, and a release agent (for example, polyolefins such as polypropylene and polyethylene) can be added to and mixed with the toner particles. A known dye or pigment can be used as the charge control agent. For example, a nigrosine dye having positive triboelectricity resistance and a metal-containing azo dye having negative triboelectricity can be mentioned. The content of this charge control agent is preferably set in the range of 0.1 to 5% by weight in order to obtain the above-mentioned charge amount.

In order to improve the fluidity of the toner particles, silica (SiO ₂ ) or alumina (Al ₂
O ₃ ), inorganic fine powder such as titanium oxide (TiO ₂ ), or lubricant (fluidity improver) typified by a metal salt of stearic acid such as zinc stearate and calcium stearate is externally added. The addition amount is preferably in the range of 0.1 to 3 parts by weight per 100 parts by weight of toner particles. Addition amount is 0.
If it is less than 1 part by weight, the effect is not obtained, and if it exceeds 3 parts by weight, the charging property becomes too high. Also, the method of externally adding is
For example, the toner particles and the additive may be put into a known mixer and stirred for a predetermined time.

In the above image forming method, since the gap between the sleeve and the recording electrode at the developing position is set to 51 to 80 μm, the magnetic toner is hard to adhere to the recording electrode. Further, the thickness of the toner layer on the sleeve is regulated to 10 to 60 μm by the toner thickness regulating member on the sleeve. For this reason, as in the conventional case, an excessive amount of magnetic toner is ejected to the recording body side and adheres to the recording electrode in the middle to reduce the hole opening of the recording electrode, and thereafter, it is difficult for the magnetic toner to pass through the recording electrode. In the present invention, the image density is not lowered when a large number of images are continuously formed.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The image forming method of the present invention is carried out by the direct recording apparatus shown in FIG. Direct recorder
A toner carrier 1 is rotatably provided in a toner layer T via a shaft 6, a back electrode 2 is arranged so as to face the toner carrier 1, and a large number of toner particles are provided between the toner carrier 1 and the back electrode 2. Matrix-shaped recording electrodes 3 having small holes are arranged. A voltage can be applied to the recording electrode 3 so as to correspond to an image to be recorded, and the recording medium 4 such as paper is used.
Is conveyed between the recording electrode 3 and the back electrode 2, and the toner on the toner carrier 1 is made to fly to the recording body 4 to form an image. An iron doctor blade 5 is provided so as to face the toner carrier 1, and the thickness of the toner attached to the toner carrier is regulated to be small.

The toner carrier 1 is made of SUS 30 having an outer diameter of 32 mm.
4 Inside the sleeve 1a, multiple poles (4 in Fig. 1)
A permanent magnet body 1b having a roll shape is arranged, and a DC voltage source is connected between the sleeve 1a and the back electrode 2. Then, the magnetic toner in the toner tank T is attached onto the sleeve 1a, and the magnetic toner is conveyed to the surface facing the recording electrode 3 by the relative rotation of the sleeve 1a and the magnet body 1b. In order to form a good image with the above direct recording device, the sleeve 1a at the developing position is used.
The distance between the recording electrode 3 and the recording electrode 3 is set to 51 to 80 μm, and the thickness of the toner layer on the sleeve 1a is regulated to 10 to 60 μm by the toner layer thickness regulating member on the sleeve 1a. A bias voltage of 400 V is applied to form an image.

When the doctor blade 5 is used as a toner layer thickness regulating member, the doctor blade 5 is used.
The distance between the sleeve 1a and the sleeve 1a is set to 5 to 60 μm. When the contact type blade 7 shown in FIG. 2 is used as the toner layer thickness regulating member, a pressure of 100 g / cm ² is applied to the contact type blade 7 against the sleeve 1a side. The distance between the contact type blade 7 and the sleeve 1a is zero. The direct recording apparatus of FIG. 2 has the same configuration except that the doctor blade 5 in the apparatus of FIG. 1 is replaced by a contact type blade 7.

In the magnetic toner used in the above direct recording apparatus, a fluidity improving agent is externally added to toner particles containing 20 to 60 wt% of magnetic powder in a binder resin. In this embodiment, 67 parts by weight of a polyester resin as a binder resin, 27 parts by weight of magnetite (EPT500 manufactured by Toda Kogyo Co., Ltd.), and 2 parts by weight of polypropylene (Sanyo Kasei TP-32).
And 1 part by weight of charge control agent (Kaya Charge T2 manufactured by Nippon Kayaku
-N) is added and dry-mixed, followed by heating and mixing, followed by cooling,
After solidified, it was pulverized to prepare toner particles. Then, 1 part by weight of SiO ₂ (H2000 manufactured by Wacker) as a fluidity improver was externally added to the obtained toner particles. The magnetic toner thus obtained had an electric resistance of 10 ¹⁴ Ω · cm and a triboelectric charge amount of −25 μc / g.

The above-mentioned triboelectric charge amount was measured by a blow-off triboelectric charge amount measuring device (TB-200 manufactured by Toshiba Chemical Co.) and the magnetic toner and ferrite carrier (Hitachi Metals KBN-
And 100) were adjusted so that the concentration of the magnetic toner was 5% by weight. The magnetic characteristics of the magnetic toner are up to 1 using a vibrating sample magnetometer (VSM-3 manufactured by Toei Industry Co., Ltd.).
The measurement was performed by applying a magnetic field of 0 kOe. The toner particle size is
It was measured with a Coulter Counter Model T-II (manufactured by Coulter Counter). The above electrical resistance is DC4
10 g of a sample is filled in a Teflon (trade name) cylinder having an inner diameter of 3.05 mm with an electric field of kV / cm, and 100 g
It is a value measured by an insulation resistance meter (Yokogawa Hewlett Packard model 4329A) with a load of f applied.

The apparatus was set up as follows for recording with the direct recording apparatus of FIG. 1 using the above magnetic toner.
The recording electrode 3 is provided with a large number of holes through which the toner passes, and the diameter of each hole is made to be 0.2 mm. The distance g ₁ between the recording electrode 3 and the sleeve 1a at the developing position is The thickness h of the toner layer, the doctor gap g ₂ , and the bias voltage V ₁ to the recording electrode were changed as shown in Table 1 below. In addition, Table 1 also shows the same evaluation results for the comparative example. The magnet body 1b of the toner carrier was fixed, the peripheral speed of the sleeve 1a was 300 mm / sec, and plain paper was passed between the back electrode 2 and the recording electrode 3 at a speed of 50 mm / sec. In addition, between the sleeve 1a and the back electrode 2 +
A voltage of 1500 V is applied, the magnetic flux density on the sleeve at the position of the magnetic pole S ₁ facing the doctor blade 5 is set to 700 gauss, and a magnetic toner image is continuously formed on the surface of plain paper, and the fixing temperature is 180 ° C. Pressure (linear pressure) 1
The heat roll fixing can be performed with kg / cm and a nip width of 4.0 mm. Using the magnetic toner in the direct recording apparatus set in this way, 1000 images were obtained under the environmental conditions of temperature 20 ° C. and humidity 40%, and the evaluation results are shown in Table 1. In Table 1, the initial stage evaluated the image obtained on the 50th sheet, and the continuous stage evaluated the image obtained on the 1000th sheet.

[0019]

[Table 1]

From Table 1, the distance g ₁ between the recording electrode 3 and the sleeve 1a, the thickness h of the toner layer at the developing position, the doctor gap g ₂ , and the bias voltage V ₁ to the recording electrode correspond to this embodiment. In this case, the image density is 1.
The result was 28 or more, the density unevenness was 0.05 or less, and there was no fog. However, it can be seen that the images of Comparative Example are not desirable in image density, density unevenness, and fog after continuous printing.

[0021]

According to the image forming method of the present invention, since the gap between the sleeve and the recording electrode at the developing position is set to 51 to 80 μm, it is difficult for the magnetic toner to adhere to the recording electrode.
Also, since the thickness of the toner on the sleeve is regulated to 10 to 60 μm by a doctor blade or the like, an excessive amount of magnetic toner is not ejected from the toner carrier to the recording body side, and an appropriate amount of toner is ejected. You can For this reason, excessive magnetic toner adheres to the recording electrode as in the conventional case, and the hole opening of the recording electrode is made small, and thereafter it is difficult for the magnetic toner to pass through the recording electrode. The image density is not reduced.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an apparatus to which a direct recording method of the present invention is applied.

FIG. 2 is a schematic diagram of an apparatus having another configuration to which the direct recording method of the present invention is applied.

[Explanation of symbols]

 1 toner carrier 2 back electrode 3 recording electrode 5 doctor blade 7 blade

Claims (3)

[Claims] 1. A back electrode is arranged so as to face a toner carrier having a sleeve provided on the outer circumference of a magnet body, and a matrix-shaped recording electrode is arranged between the toner carrier and the back electrode. In an image forming method in which toner is directly sprayed from a toner carrier to a recording body between a recording electrode and a back electrode according to a voltage application state, a distance between a sleeve and a recording electrode at a developing position is 51 to 80 μm. In addition, the toner layer thickness regulating member on the sleeve regulates the thickness of the toner layer on the sleeve to 10 to 60 μm, and a voltage of 300 to 400 V is applied to the recording electrode to form an image. A characteristic image forming method. 2. The image forming method according to claim 1, wherein a doctor blade is used as the toner thickness regulating member, and the distance between the doctor blade and the sleeve is set to 50 to 150 μm. 3. The image forming method according to claim 1, wherein a contact type blade is used as the toner thickness regulating member, and a pressure of 10 to 250 g / cm ² is applied to the contact type blade against the sleeve side. .