JP2003029452A - Magnetic toner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide magnetic toners which are good in developability and are capable of forming MICR magnetic characters of a high recognition rate even when the toners are applied to a nonmagnetic two-component development system and a nonmagnetic one-component development system. SOLUTION: The magnetic toners contain a binder resin and magnetic powder consisting of metal substituted γ-Fe2 O3 .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in electrophotographic method, electrostatic printing method, electrostatic recording method and the like, and in particular, in a magnetic ink character recognition (hereinafter referred to as "MICR") system. The present invention relates to a magnetic toner suitable for forming readable magnetic characters using a non-magnetic one-component developing system or a non-magnetic two-component developing system.

[0002]

2. Description of the Related Art Conventionally, in an image forming method for a printer, a facsimile, etc., to which an electrophotographic method or electrostatic recording is applied, an electrostatic charge image is formed on the surface of a photosensitive drum formed into a cylindrical shape, and then the photosensitive drum is formed. The magnetic developer is attracted to the surface of the sleeve and conveyed by a developing roll including a sleeve which is provided so as to face the sleeve and has a permanent magnet member incorporated therein and is coaxially and rotatably fitted in the permanent magnet member. To do. After that, a method is employed in which a magnetic brush is formed in the developing area and the electrostatic charge image forming surface on the photosensitive drum is rubbed by the magnetic brush to visualize as a toner image. The most general means is to transfer the visualized toner image onto recording paper and then heat fixing.

On the other hand, in recent years, along with the widespread use of image forming apparatuses such as electrophotographic copying machines, the applications thereof have been diversified, and a character printer used for MICR systems has been devised as an application field of electrophotographic printers. Has been done.

This MICR system mainly prints information such as checks, bills, etc. by issuing a bank, amount, account number, etc. using magnetic ink, and efficiently sorts and sorts at a clearing house using a magnetic reader. It was designed to do. In this case, offset printing using magnetic ink has been the mainstream in the past, but as commercial transactions such as personal checks and bills have become more active, small MICR character printing machines (hereinafter referred to as "MICR encoder" Demand) is increasing.

The above-mentioned conventional MICR encoder is mainly an impact printer to which a thermal copying method is applied, but in this case, most of them are single-function machines which print only MICR characters, and are generally used for preparing general documents. It has the drawback of not being available. Therefore, general documents and / or graphics can be printed, and the MIC
It is desired to apply for an electrophotographic printer that can print R characters and that has a good MICR recognition rate.

[0006]

Since MICR printing uses a toner containing a magnetic material, a magnetic one-component developing method using a magnetic one-component developer or a magnetic two-component developer obtained by mixing a magnetic toner and a magnetic carrier is used. The magnetic two-component developing method used is used. The magnetic one-component developing method or the magnetic two-component developing method has a lower charge amount and a lower charging speed than the non-magnetic two-component developing method in which a non-magnetic toner and a magnetic carrier are mixed, and thus high-speed development is difficult. is there. In addition, the specific gravity of the toner is large and the toner consumption amount is large. Therefore, when an MICR toner for a conventional magnetic one-component or magnetic two-component developer is applied to a non-magnetic two-component developing system capable of high-speed development, an attempt to print MICR characters results in a low charge amount. A conventional magnetic substance magnetite for magnetic toner is generally a material having a coercive force of 60 to 400 (Oe) and a residual magnetization of 5 to 30 emu / g. The residual magnetization of MICR toner is 5
22 to 40% by weight in toner because 8 emu / g is required
Must be included. A toner containing such a magnetic powder has a poor triboelectric charge rising characteristic and a low charge amount. In addition, since the toner has magnetism, a sufficient amount of development cannot be obtained due to the magnetic force of the carrier and the magnetic force of the magnet roller. For these reasons, sufficient image density cannot be obtained, and fog also increases. This phenomenon becomes a problem especially under conditions where there is little room for improvement in the amount of development in a high-speed development system. If the content of the magnetic powder in the toner is reduced, the developability is improved, but the recognition rate of the MICR characters obtained is lowered.

On the other hand, it is preferable that the MICR toner for the magnetic one-component developer can be used to perform printing in the non-magnetic developing system. In particular, if printing can be performed by the non-magnetic one-component developing method, it is preferable because the apparatus can be downsized and the speed can be increased. However, if the conventional MICR toner for magnetic one-component developer is used in a non-magnetic one-component developing system capable of high-speed development, the amount of toner charge is reduced due to the magnetic powder contained, and a sufficient image density is obtained. It is not possible to wear it, and the number of coverings increases. Moreover, the transfer efficiency is also reduced. If the content of the magnetic powder in the toner is reduced, the developability is improved, but the recognition rate of the MICR characters obtained is lowered.

An object of the present invention is to solve the above problems and to provide a non-magnetic two-component developing system and a non-magnetic one-component developing system, which has a good developability and a high recognition rate.
An object of the present invention is to provide a magnetic toner capable of forming ICR magnetic characters.

[0009]

DISCLOSURE OF THE INVENTION The inventors of the present invention have studied magnetic powder capable of imparting suitable residual magnetization to MICR toner with a content as small as possible as compared with the conventional one, and as a result, the magnetic powder made of a material having a high residual magnetic flux density Br is obtained. The inventors have found that this can be achieved by employing powder, and have reached the present invention.

That is, the invention of the present application is a magnetic toner containing a binder resin and magnetic powder composed of metal-substituted γ-Fe ₂ O ₃ . Metal-substituted γ-Fe _{2 used in the} present invention
O ₃ is optimum Co _gamma-Fe 2 _{O 3} was replaced with Co. The residual magnetization of metal-substituted γ-Fe ₂ O ₃ is about 25 to 50.
Since the emu / g and coercive force are about 400 to 1000 (Oe), the residual magnetization of the toner of the present invention is 4 to 1 suitable for MICR characters.
The content of the metal-substituted γ-Fe ₂ O ₃ may be 8 to 25% by weight, and preferably about 10 to 20% by weight in order to obtain the range of 0 emu / g. This is about half the content of the conventional magnetic powder described above. For this reason, when the magnetic toner of the present invention is applied to a non-magnetic two-component developing system or a non-magnetic one-component developing system to print MICR characters, a sufficiently high charge amount can be obtained. It is possible to achieve the same developability as when using a magnetic toner. Moreover, the obtained MICR magnetic characters have a high recognition rate.

The magnetic powder preferably has a size of 0.05 to 1 μm. The reason is that the particles are easily dispersed in the toner and the magnetic powder in the toner particles becomes uniform.

When the residual magnetization of the magnetic toner is less than 4 emu / g, the recognition rate (magnetic intensity) of MICR characters is lowered,
If it exceeds emu / g, aggregation of the toner is likely to occur, so that the residual magnetization of the magnetic toner is preferably 4 to 10 emu / g.

The binder resin is styrene-acrylic type,
It is sufficient to select a resin having characteristics suitable for the fixing method such as polyester, epoxy, and phenoxy resin. The fixing method suitable for the present invention is heat roll fixing, flash fixing,
Oven fixing.

In order to improve the affinity with the binder resin and improve the dispersibility in the toner, it is preferable to make the surface of the magnetic powder hydrophobic with a titanate coupling agent or a silane coupling agent.

Wax is added to improve the surface smoothness of the printed surface. Low molecular weight polyethylene, polypropylene, ethylene-propylene copolymer, modified polyethylene, modified polypropylene, Fischer-Tropsch wax, Sazol wax, montanic acid wax, galvana wax and the like can be used. The addition amount is preferably about 1 to 6%. The wax is preferably uniformly dispersed in the toner, and can be dispersed in the binder resin in advance.

The charge control agent is selected according to the polarity of the toner. Chromium azo complex, iron azo complex, salicylic acid metal complex, calixarene and the like are preferable for the negative chargeability, and nigrosine dye and phenylmethane dye are preferable for the positive chargeability.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION To prepare an MICR toner, magnetic powder having a high residual magnetization is required. As described above, the important feature of the present invention is that the magnetic powder contained in the toner has high Br.
This is because magnetic powder composed of metal-substituted γ-Fe ₂ O ₃ was used as the material. Other materials such as hard ferrite high Br material, metal high Br material, hard rare earth magnet material, etc. have the disadvantage that writing cannot be performed by the MICR read head. Further, the metal-based high Br material has a disadvantage that it is easily oxidized and lacks stability.

Co-substituted γ-Fe ₂ O ₃ used in the present invention
An example (two samples) is shown in Table 1. The feature is that Hc and σr are larger than those of magnetite.

[0019]

[Table 1]

Embodiments of the present invention will be described in detail below based on examples. <Image Forming Apparatus> In the examples described below, an image forming apparatus for a non-magnetic one-component developing system having the following configuration was used. The image forming apparatus used in the embodiment has a basic configuration in which a negatively chargeable OPC photosensitive member formed in a drum shape, and a charging device, an exposing device, a developing roll, a transfer charging device, and a cleaner on the peripheral surface thereof. Have a configuration in which they are sequentially arranged to face each other. The developing roll has a conductive shaft connected to a bias voltage source and a conductive elastic layer, and is capable of developing by a contact developing system in a developing area arranged facing the OPC photosensitive member. The developing roller is not provided with magnetic field generating means such as a permanent magnet. In the above configuration, the OPC
The photoconductor does not have to have a drum shape, and may have a belt shape, which is conventionally known.

The surface of the OPC photosensitive member is uniformly charged by a charger while rotating at a constant peripheral speed. As such a charger, a scotron for corona discharge may be used. In addition to corona discharge, roller charging, brush charging, or magnetic brush charging may be used. The charged surface of the OPC photosensitive member is further exposed to an optical image by an exposure device to form an electrostatic latent image on the surface of the OPC photosensitive member. The electrostatic latent image is carried on the surface of the rotating OPC photosensitive member, and is conveyed to the developing area where the developing rolls are opposed to each other. The electrostatic latent image is visualized as a toner image by the magnetic toner of the present invention, which is electrostatically carried on the surface of the developing roll connected to the bias voltage source and conveyed to the developing area.

The magnetic toner used in such a non-magnetic one-component developing system is agitated by an agitator in the toner hopper, first carried on the surface of a rotating replenishing roller, and then, the developing toner is rotated with an adjacent potential difference. It is transferred and carried on the surface of the roll. The magnetic toner carried on the surface of the developing roll is conveyed to the side of the elastic blade pressed against the peripheral surface of the developing roll with a predetermined pressure, and is charged when passing under the elastic blade. The magnetic toner having a predetermined layer thickness, which is charged when the elastic blade passes, is pressed against the surface side of the OPC photoconductor with a predetermined linear pressure to electrostatically adsorb the magnetic toner to the electrostatic latent image to perform contact development. To do. Either one of the OPC photosensitive member and the developing roll is configured to have an elastic surface, and the magnetic toner is appropriately pressed against the electrostatic latent image during the contact development. For example, at least the surface portion of the developing roll is formed of an elastic material such as urethane or EPDM,
It is sufficient to obtain an elastic surface.

The toner image thus formed on the surface of the OPC photosensitive member is further conveyed to a transfer area in which a transfer charger is arranged oppositely. In the transfer area, a material to be transferred such as paper is sent between the transfer charging device and the toner image so that the transfer of the toner image is performed on the back surface of the transfer material from the transfer charging device. The toner image is transferred onto the transfer target material by applying a charge having a polarity opposite to the polarity. A corotron or a roller for corona discharge may be used for the transfer charger. After that, the transfer material to which the toner image has been transferred is sent to a heat roll portion in which a heating roll and a pressure roll are opposed to each other at a predetermined interval, and the toner image is subjected to pressure heat treatment when passing between the heat roll portions. Heat-roll fixing is performed on the material to be transferred. The toner image may be fixed by pressure fixing or oven fixing.

On the other hand, on the surface of the OPC photosensitive member after the transfer of the toner image, the residual developer is removed by a cleaner. In this embodiment, a conventional blade is used as the cleaner so that the magnetic toner remaining on the surface of the OPC photosensitive member without being transferred can be scraped off. Of course, the present invention can be applied to a configuration without such a cleaner.

<Image forming conditions> Using the above image forming apparatus, image formation was carried out under the following conditions. For OPC photoconductor,
A drum-shaped OPC photosensitive member with a diameter of 32 mm is used, and the process speed (VP: also called peripheral speed) is 120 mm / s.
It was rotated at ec, and the surface potential (V0) was set to -480 V by the charging roller. The residual potential (VL) of the surface of the OPC photosensitive member after exposure to a light image was -30V. The developing roll has a diameter (φ) of 25 mm and a volume resistance (R) of 25.
A urethane rubber roll containing a conductive agent and a foaming agent of Ω · cm was used. The developing roller having such elasticity was rotated at a peripheral speed of 130 mm / sec, which was slightly faster than the OPC photosensitive member, and was brought into pressure contact with the OPC photosensitive member through the toner layer at a pressure (linear pressure) of 10 g / cm to perform contact development. . Further, the layer thickness of the magnetic toner layer is regulated to be 0.03 mm by using a stainless steel blade as an elastic blade. Further, for the transfer and fixing of the toner image, a corotron was used as a transfer charger, plain paper was used as the material to be transferred, and heat roll fixing was performed at a fixing temperature of 180 ° C. and a linear pressure of 1 Kg / cm. In the cleaner, the residual toner was removed by bringing a urethane blade into contact with the surface of the OPC photosensitive member after transfer at a linear pressure of 5 g / cm.

<Toner for non-magnetic one-component system>
The magnetic toner of the present invention used in the image forming method based on the non-magnetic one-component developing system having the above-mentioned structure will be described.

Example 1 Polyester resin (Tg 65 ° C., Tm 145 ° C.) 76.5 parts by weight Magnetic powder Co-γ-Fe ₂ O ₃ (A) 17.5 parts by weight Wax (carnauba-based) 1 part by weight Viscole 660P (Sanyo Kasei) 2 parts by weight carbon (Mitsubishi Chemical MA100) 2 parts by weight Charge control agent (Hodogaya Kagaku T77) 1 part by weight The above components are mixed by a Henschel mixer, and then a twin-screw extrusion kneader equipped with a cooling device. Kneading was performed at a set temperature of 130 ° C. After that, cool and crush with a drum breaker,
Further, it was subjected to a Rotoflex coarse crusher. The powder was finely pulverized by a rotor stator type pulverizer T250 type and classified by a microplex classifier T400RS (manufactured by Turbo Kogyo Co., Ltd.) to obtain a powder having the following particle size distribution. D ₅₀ 9.5 μm> 16 μm 2% <5 μm 2% <5 μm Number 10% This powder and the following powder were mixed by a Henschel mixer and subjected to surface treatment, and toner for non-magnetic one-component system of Example 1 Was prepared. 100 parts by weight of the powder Wacker H3004 1 part by weight Titanium oxide (STT30 manufactured by Titanium Industry Co., Ltd.) 0.2 parts by weight Hydrophobic silica (NAX50 manufactured by Nippon Aerosil Co., Ltd.) 0.2 parts by weight

Comparative Example 1 A toner was prepared in the same manner as in Example 1 except that the type and content of magnetic powder were changed. Polyester resin (Tg 65 ° C, Tm 145 ° C) 70 parts by weight Magnetic powder magnetite A 24 parts by weight Wax (carnauba type) 1 part by weight Viscole 660P (Sanyo Kasei) 2 parts by weight Carbon (Mitsubishi Chemical MA100) 2 parts by weight Charge control agent (Hodogaya Kagaku T77) 1 part by weight, that is, the above components were used in the same manner as in Example 1 to prepare a powder and a toner for a non-magnetic one-component system.

MICR printing of 13B font was performed by using the toner of the above type and the image forming apparatus and the image forming conditions having the above-mentioned configuration, and the results are shown in Table 2.

[Table 2]

The values of remanent magnetization shown in Table 2 were obtained by packing the toner in capsules and using a vibration type magnetic measuring device (VSM). The charge amount is the value of the toner on the developing roller and was measured by blow-off TB200. The amount of development is the amount of toner per unit area of a solid black image, and when it is 0.7 or more, it corresponds to an image density of 1.35 or more and is good. The image density is measured by a reflection densitometer (Macbeth RD914) and is preferably 1.35 or more. In order to correctly recognize an MICR font printed by a magnetic reader, it is necessary that the MICR font has an appropriate magnetic reading strength (magnetic strength Signal Strength). The standard of magnetic strength is set in each country and is approximately 100 to 200%, so that the magnetic strength is preferably 120% or more. Comparative Example 1
However, although the residual magnetization of the toner is the same as that of the first embodiment, the charging rise is low because the content of the magnetic powder is high. Therefore, the amount of development is small. As a result, the magnetic strength of MICR characters became insufficient.

Next, another embodiment of the present invention will be described in detail based on examples. In the examples described below, an image forming apparatus for a non-magnetic two-component developing system having the following structure was used. <Developer> A 50φ organic photoconductor was charged to −500 V by a scorotron charger and exposed to −40 V by an LED. 30φ SU with two magnet rolls magnetized to 4 poles so that the developing pole becomes 950G
The S sleeve was blasted to have a surface roughness Rz of 9 μm. A developer was applied on the magnet roller with a gap of 0.6 mm provided by a blade. Process speed 300 mm / s, sleeve peripheral speed ratio 1.
5, at a developing gap of 0.85 mm, -400 to -48
An image containing MICR characters was developed by applying a developing bias of 0V. Transfer was performed by DC + AC using a corotron, and was fixed by a heat roller type fixing device equipped with a halogen lamp.

In the following examples and comparative examples, a developer containing at least a magnetic carrier and toner is carried on a developer carrier having means for generating a magnetic field inside and is supplied to the latent image carrier. An image forming method for developing a latent image on an image carrier, which is carried out by using the above developing device.
Formed magnetic letters.

<Developer for non-magnetic two-component system>
The magnetic toner of the present invention used in the image forming method based on the non-magnetic two-component developing system having the above-mentioned structure will be described.

Example 2 Styrene-acrylic (St-BA) resin (Tg 62 ° C., Tm 137 ° C.) 79 parts by weight Magnetic powder Co-γ-Fe ₂ O ₃ (B) 15 parts by weight Wax (polyethylene) 1 part by weight PP Viscole 550P (Sanyo Kasei) 2 parts by weight carbon (cabot) 2 parts by weight Charge control agent (Hodogaya Chemical TRH) 1 part by weight The above components are mixed by a Henschel mixer and a twin-screw extrusion kneader with a cooling device is added. The mixture was kneaded at a set temperature of 130 ° C. After that, cool and crush with a drum breaker,
Further, it was subjected to a Rotoflex coarse crusher. It was finely pulverized with a jet mill NPK5 type (IDS5 type) and classified with a microplex classifier T400RS (manufactured by Turbo Kogyo Co., Ltd.) to obtain a powder having the following particle size distribution. D ₅₀ 9.8 μm> 16 μm 2% <5 μm 2% <5 μm Number 10% This powder and the following powder were mixed by a Henschel mixer and surface-treated to prepare a toner for a non-magnetic two-component system. 100 parts by weight of the powder Wacker H15 0.6 parts by weight Hydrophobic silica (RX200 manufactured by Nippon Aerosil Co., Ltd.) 0.2 parts by weight

37 to 105 μm as a carrier
(D ₅₀ : 70 μm) magnetite particles were coated with a conductive acrylic / silicone resin, and a coating carrier having an electric resistivity of 5 × 10 ⁴ Ω · cm after 100 V application tap was used. This carrier and the toner were prepared so as to have a toner concentration of 8%, and mixed for 20 minutes with a Turbula mixer to obtain a developer for a non-magnetic two-component system of Example 2.

(Comparative Example 2) A toner was prepared in the same manner as in Example 2 except that the kind and content of the magnetic powder were changed. Styrene-acrylic (St-BA) resin (Tg 62 ° C, Tm 137 ° C) 67 parts by weight Magnetic powder magnetite A + B 27 parts by weight Wax (polyethylene) 1 part by weight PP Viscole 550P (Sanyo Kasei) 2 parts by weight carbon (cabot) 2 parts by weight Charge control agent (Hodogaya Chemical TRH) 1 part by weight That is, a developer for a non-magnetic two-component system of Comparative Example 2 was prepared in the same manner as in Example 2 using the above components.

(Comparative Example 3) A toner was prepared in the same manner as in Example 2 except that the kind and content of the magnetic powder were changed. Styrene-acrylic (St-BA) resin (Tg 62 ° C, Tm 137 ° C) 74 parts by weight Magnetic powder magnetite A + B 20 parts by weight Wax (polyethylene) 1 part by weight PP Viscole 550P (Sanyo Kasei) 2 parts by weight carbon (cabot) 2 parts by weight Charge control agent (Hodogaya Kagaku TRH) 1 part by weight That is, a developer for a non-magnetic two-component system of Comparative Example 3 was prepared in the same manner as in Example 2 using the above components.

MICR printing of 13B font was carried out by using the above-mentioned type of developer and the image forming apparatus and the image forming conditions having the above-mentioned constitutions, and the results are shown in Table 3.

[Table 3]

The fog value shown in Table 3 is expressed by the difference (dE) in hunter whiteness between the white paper before printing and the white background after printing. The smaller this value, the less fog on white background.
It is preferably 5 or less. In Comparative Example 2, although the residual remanent magnetization of the toner is higher than that of Example 2, the charging rise is low because the content of the magnetic powder is high. Therefore, the amount of fogging is large and the amount of development is small. As a result, the magnetic strength of MICR characters became insufficient. In Comparative Example 3, since the content of the magnetic powder was low, the rise of charging was high. Therefore, fog was reduced and the amount of development was increased, resulting in a good image. However, the magnetic remanence of the toner became small, and the magnetic strength of MICR characters became insufficient.

[0040]

From the above results, the magnetic toner having the constitution of the present invention can be applied to the image forming method based on the non-magnetic one-component developing system and the non-magnetic two-component developing system, and has good magnetic strength. And the image density is appropriate,
Moreover, it was confirmed that magnetic characters without fogging could be formed. Therefore, by using the magnetic toner of the present invention, a model to which the non-magnetic one-component developing method and the non-magnetic two-component developing method are applied can be configured as an MICR printer.

Claims (3)

[Claims] 1. A binder resin and a metal-substituted γ-Fe ₂ O
A magnetic toner containing a magnetic powder of ₃ . 2. Metal-substituted γ-Fe_TwoO_ThreeReplace with Co
Coγ-Fe_TwoO _ThreeThe magnetic toner according to claim 1, wherein
-. _3. The content of metal-substituted γ-Fe ₂ O ₃ is 8 to.
The magnetic toner according to claim 1, which is 25% by weight.