JP4074869B2 - MICR toner and image forming method using the same - Google Patents

Description

  The present invention relates to a MICR toner used in a magnetic ink character recognition (MICR) system and an image forming method using the same.

  For example, in order to prevent counterfeiting and alteration of checks, various securities, various tickets, etc., printing identification marks consisting of character strings such as special typeface characters and numbers called MICR font using magnetic ink In addition, there is a magnetic ink character recognition (MICR) system that reads the information with a dedicated reading device to determine whether the check is authentic. In this MICR system, it is possible not only to accurately determine authenticity by reading the identification mark with a dedicated reader, but also because the identification mark is also information of characters and numbers as described above. Unlike codes, it has the advantage that it can be easily and quickly determined by the human eye.

  As a printing method of the identification mark, conventionally, a screen printing method or a gravure printing method using a liquid magnetic ink containing a magnetic material has been generally used.In recent years, as a quicker and simpler printing method, for example, An identification mark can be printed by a laser printer using electrophotography, electrostatic recording method, electrostatic printing method, etc., using a magnetic toner having a structure in which magnetic powder is dispersed in toner particles made of a binder resin. It is being considered.

  In electrophotography, electrostatic recording, electrostatic printing, etc., the surface of the latent image holding member is first uniformly charged by charging means, and then exposed by exposure means such as a semiconductor laser or a light emitting diode. After forming the electrostatic latent image, the electrostatic latent image is developed by a developing unit to be visualized as a toner image. Next, the toner image is transferred onto the surface of a printing medium such as paper by a transfer unit, and then fixed by a fixing unit, thereby completing a series of image forming steps.

  There are various development methods for developing an electrostatic latent image into a toner image. In particular, a magnetic one-component development method is employed as a dry development method using magnetic toner. In the magnetic one-component development method, magnetic toner is supplied while being thinned onto a developer carrying member incorporating a fixed magnet, and then the electrostatic latent image on the latent image holding member is produced by the thinned magnetic toner. Developing the image into a toner image is performed. In addition, as a magnetic one-component development method, there are a development method using a magnetic toner having conductivity and a development method called a magnetic one-component jumping development method using an insulating magnetic toner (see Patent Document 1).

  In the latter, magnetic one-component jumping development method, first, a magnetic toner is composed of a developer carrier that rotates with a built-in fixed magnet, and a magnetic blade that is disposed close to the developer carrier. A thin layer of magnetic toner is formed on the surface of the developer carrier by supplying it to the surface of the developer carrier while being frictionally charged by passing through the gap and holding it by the magnetic force of the built-in fixed magnet. .

Next, a DC bias voltage between the latent image holding body that holds the electrostatic latent image that is opposed to the formed thin layer and that faces the developer and the developer carrying body, or a direct current to the DC By applying a bias voltage in which is superimposed, the charged magnetic toner is ejected from the thin layer onto the surface of the latent image holding member, and the electrostatic latent image is visualized as a toner image.
In this developing method, since the insulating magnetic toner is used, the formed toner image, which is impossible when the conductive magnetic toner is used, is printed on a printed material such as paper using an electric field. It becomes possible to transfer to the surface. In addition, the latent image holding member can be prevented from being destroyed by an electric leak.

  Insulating magnetic toner is easy to be charged, can be sufficiently rubbed with the developer carrier while holding the magnetic toner by magnetic force, and is not in contact with the electrostatic latent image while holding the magnetic toner by magnetic force. Since the electrostatic latent image can be developed in this state, there is an advantage that an image with excellent image quality can be formed by preventing the occurrence of background fogging in which the magnetic toner adheres to the non-printed portion and the blank portion of the formed image. Further, this developing method has an advantage that the developing device can be made very small and have a simple structure as compared with other developing methods such as the two-component developing method.

  As described above, the magnetic toner for MICR system (hereinafter referred to as “MICR toner”) prevents the occurrence of a reading error when the printed identification mark is read by the reading device. In order to improve accuracy, it is required that a certain degree of magnetization remains after printing. Therefore, it is conceivable to increase the residual magnetization of the MICR toner by adding needle-like magnetic powder having a large residual magnetization.

  However, since the acicular magnetic powder has a low dispersibility with respect to the binder resin, it is not easy to uniformly disperse the powder, and the magnetic powder is often present in the toner particles in a state where a large number of magnetic powders are aggregated. This lump causes the toner particles to break easily, and when the toner particles break, there is a problem that a large number of magnetic powders fall out of the lump and the durability of the MICR toner decreases.

  In addition, if the residual magnetization of the MICR toner is too high, the charge amount distribution of the MICR toner in the developing device becomes broader as the image formation is repeated, and the image density of the formed image is lowered or the background fog is reduced. As a result of this, there is a problem that the reading accuracy is lowered. Further, the MICR toner having a high residual magnetization is peeled off from the surface of the printing material by the magnetic force and adheres to the magnetic head of the reading device, thereby causing a reading error and reducing the reading accuracy.

Therefore, in Patent Document 2, as the magnetic powder, the particle shape is needle-shaped, the aspect ratio represented by the ratio of the major axis to the minor axis is 2.0 to 100, the residual magnetization is 24 Am ² / kg or more, 40 Am. ^With respect to the first magnetic powder of ² / kg or less, the particle shape is granular or spherical, the aspect ratio is 1.0 or more and less than 2.0, the residual magnetization is 1 Am ² / kg or more, 24 Am ² / a second magnetic powder in combination is less than kg, a residual magnetization of the MICR toner, exceed 7am ² / kg, it has been described to be adjusted within the range of 20 Am ² / kg.

  Thus, when combining the 1st and 2nd magnetic powder from which the value of a residual magnetization differs, the value of the residual magnetization of both magnetic powder is adjusted, respectively, and the mixture ratio of both magnetic powder is adjusted. Thus, there is an effect that the residual magnetization of the MICR toner can be arbitrarily adjusted within the above range. Further, by reducing the amount of the needle-like first magnetic powder having low dispersibility and using the granular or spherical second magnetic powder that is easier to disperse than the first magnetic powder, The durability of the MICR toner can also be improved by preventing the second two types of magnetic powder from being present in the toner particles in an aggregated state.

  Among the second magnetic powders, those having a granular shape include, for example, a hexahedron (cube, cuboid) shape, which is a convex polyhedron surrounded by six quadrangles, and eight triangles. Polyhedral magnetic powders such as octahedral ones that are convex polyhedrons are known. However, the MICR toner using a polyhedral shape as the second magnetic powder emits charge from the sharp apex of the second magnetic powder exposed on the surface of the toner particles and the sharp ridgeline between adjacent surfaces. As a result, charge leakage is likely to occur.

  In addition, polyhedral magnetic powder is not as good as needle-like ones, but its fluidity is low and its dispersibility with respect to binder resin is not sufficient, so the effect of using it together with needle-like magnetic powder is sufficiently obtained. Absent. That is, since the dispersion state and content of the magnetic powder in the individual toner particles are likely to vary, the ease of charging and the charge amount of the individual MICR toners are also likely to vary.

Therefore, the toner for MICR using a polyhedral toner as the second magnetic powder has a problem that the initial image density is low because the charge amount is difficult to rise quickly and the charge amount itself is low. . In addition, since the toner for MICR easily leaks charged charges, there is a problem that the image density further decreases as image formation is repeated.
As described above, the identification mark for the MICR system is different from a bar code or the like in that it can be discerned by human eyes. However, as described above, the initial image density is low. If the image density is lowered or the image density is further lowered while repeating image formation, this feature cannot be fully utilized. In addition, printers using MICR toner are not exclusively used for printing identification marks for MICR systems. In other cases, it is required that they can also be used for printing ordinary office documents. Will not be enough.

  On the other hand, since the spherical magnetic powder does not have a sharp apex or ridge line and charges are not easily released from the magnetic powder exposed on the surface of the toner particles, charge leakage is unlikely to occur. In addition, the spherical magnetic powder is excellent in fluidity as compared with the polyhedral shape and also excellent in dispersibility in the binder resin, and thus can be easily dispersed uniformly in the binder resin. It is also possible to make the dispersion state and content of the magnetic powder in the toner uniform and to make the ease of charging and the charge amount of each MICR toner uniform. Therefore, according to the MICR toner using a spherical magnetic powder as the second magnetic powder, the initial image density is improved and the image density is not greatly reduced when the image formation is repeated. it can.

However, since the spherical magnetic powder generally has a strong tendency to lower the remanent magnetization as compared with the polyhedral one, even if the remanent magnetization value is within the above-mentioned range, Even if it is used together with the first magnetic powder having a high needle shape, there is a problem that the residual magnetization of the MICR toner is significantly below the above range, and the reading accuracy of the identification mark is greatly reduced.
JP-A-55-18656 (claims, page 11, upper left column, line 23 to page lower left column, line 25, FIG. 8) JP-A-11-327205 (Claim 1, columns 0005 to 0007, columns 0021 to 0024, columns 0028 to 0030, columns 0035 to 0036)

  An object of the present invention is to form a good identification mark that has a high initial image density and that does not significantly decrease the image density even when image formation is repeated, and that is excellent in reading accuracy of the identification mark. An object of the present invention is to provide a toner for MICR that can be used and an image forming method using the same.

In order to solve the above problems, the inventor examined the particle shape of the second magnetic powder. As a result, the second magnetic powder is based on a polyhedron such as an octahedron, which is a convex polyhedron surrounded by eight triangles, and a hexahedron, which is a convex polyhedron surrounded by six squares. It has been found that magnetic powder having a particle shape in which each vertex and ridge line are curved may be used.
That is, the magnetic powder having the above particle shape has a curved shape at the apex and ridge line, and does not have a pointed apex or ridge line that easily discharges charges, so that it is compared with a conventional polyhedral shape. When the toner particles are contained in the toner particles, it is possible to make it difficult for charge leakage to occur. Further, the above magnetic powder is excellent in fluidity and dispersibility in the binder resin, and can be easily dispersed uniformly in the binder resin, and the dispersion state and content of the magnetic powder in individual toner particles. It is possible to prevent the dispersion of the toner, and to uniformize the ease of charging and the charge amount of each MICR toner. Therefore, if the magnetic powder having the above particle shape is used as the second magnetic powder in combination with the first magnetic powder in the form of needles, the initial image density is improved and the image is formed when the image formation is repeated. It is also possible to suppress a significant decrease in concentration.

  Moreover, since the basic shape of the above magnetic powder is a polyhedron, the value of the remanent magnetization of the magnetic powder is substantially the same as that of a normal polyhedron-shaped magnetic powder whose apex and ridge are not curved, so that the toner for MICR It is considered that the reading accuracy of the identification mark can be improved by maintaining the remanent magnetization at a good value. However, as a result of investigation by the inventor, even in the above-described particle shape, when the curvature radius of the curved vertex or ridge is too large, the residual magnetization becomes low as in the spherical shape, and the MICR It was found that the residual magnetization of the toner is lowered and the reading accuracy of the identification mark is lowered.

  Therefore, the inventor studied, for example, that the range of the radius of curvature of the apex and the ridge line formed into a curved surface was determined from the projected image of the magnetic powder photographed using a transmission electron microscope. As a result, the curvature radius of the curved vertices and ridges is too large, the curved surfaces of adjacent vertices and ridges are connected, and there is no portion that can be regarded as a straight line on the outer periphery of the projected image. In addition, while the remanent magnetization is lowered to the same level as that of a spherical one, each of the vertexes and ridgelines of the polyhedron is curved, and the magnetic powder having a portion that can be regarded as a straight line on the outer peripheral portion of the projected image is As initially thought, the remanent magnetization of the MICR toner is set to a good value by making the value of the remanent magnetization of its own substantially the same as that of a polyhedral magnetic powder having a curved vertex or ridge line. It has been found that the accuracy of reading the identification mark can be improved by maintaining it.

  Accordingly, the invention described in claim 1 is a MICR toner for forming an identification mark for a magnetic ink character authentication system, wherein (1) the first magnetic powder having a needle shape and (2 ) For MICR, characterized in that the particle shape is based on a polyhedron, each vertex and ridge line of the polyhedron is a curved surface, and the second magnetic powder has a portion that can be regarded as a straight line on the outer periphery of the projected image. Toner.

  As the second magnetic powder, the particle shape is basically at least one of an octahedron that is a convex polyhedron surrounded by eight triangles and a hexahedron that is a convex polyhedron surrounded by six squares. However, even if the apex and ridge are both curved surfaces, the residual magnetization of the MICR toner is maintained at a good value, and the identification mark reading accuracy is improved. Are preferably used.

Therefore, in the invention according to claim 2, the particle shape of the second magnetic powder is an octahedron that is a convex polyhedron surrounded by eight triangles, and a hexahedron that is a convex polyhedron surrounded by six squares. The MICR toner according to claim 1, wherein the toner is based on at least one of them.
The toner for MICR of the present invention is preferably used in an image forming method using the magnetic one-component jumping development method described above. Further, the MICR toner of the present invention is preferably combined with an amorphous silicon photoreceptor excellent in durability. As described above, since the second magnetic powder is excellent in fluidity and dispersibility with respect to the binder resin, the first and second types of magnetic powder are aggregated in a lump in the toner particles. Therefore, the durability of the MICR toner can be improved. Therefore, by combining such a MICR toner with an amorphous silicon photoconductor, it is possible to achieve maintenance-free and long life of the image forming apparatus.

  Therefore, the invention according to claim 3 is a developer carrying body in which a latent image holding body for holding an electrostatic latent image and a fixed magnet are built and rotated, and a thin layer of MICR toner is formed on the surface thereof. In the state where the thin layer and the latent image holding member are opposed to each other while maintaining a distance from each other, the MICR toner is ejected from the thin layer onto the surface of the latent image holding member. A method for forming an identification mark for a magnetic ink character authentication system on a surface of a printed material, comprising the step of developing the toner image into a toner image, comprising: a MICR toner according to claim 1; An image forming method using an amorphous silicon photoconductor as an image carrier.

<Toner for MICR>
The toner for MICR of the present invention comprises (1) a first magnetic powder having a particle shape of needle shape, and (2) a particle shape based on a polyhedron, each vertex and ridge line of the polyhedron being curved, And a second magnetic powder having a portion that can be regarded as a straight line on an outer peripheral portion of the projected image. Specific examples thereof include a toner particle made of a binder resin containing the above-mentioned two kinds of magnetic powders.

  As the first and second magnetic powders, a metal exhibiting ferromagnetism such as iron, cobalt, nickel, or an alloy thereof, a compound containing these elements, or a ferromagnetic element that does not contain ferromagnetic elements but is subjected to an appropriate heat treatment. An alloy that exhibits ferromagnetism, chromium dioxide, or the like can be used, and ferrite and magnetite are particularly preferable. The magnetite may contain at least one element selected from Mn, Zn, Ni, Cu, Al, Ti, and Si in an amount of 0.1 to 10 atomic% with respect to Fe.

<First magnetic powder>
The reason why the particle shape of the first magnetic powder is limited to the needle shape is as described above. Further, the residual magnetization is preferably 24 Am ² / kg or more and 35 Am ² / kg or less. The reason is as follows.
That is, if the residual magnetization of the first magnetic powder is less than 24 Am ² / kg, the effect of increasing the residual magnetization of the MICR toner by the first magnetic powder may not be obtained. For this reason, the residual magnetization of the MICR toner becomes insufficient, and the reading accuracy of the identification mark formed by the MICR toner may be reduced.

When the residual magnetization exceeds 35 Am ² / kg, the residual magnetization of the MICR toner may become too high despite being combined with the second magnetic powder having a low residual magnetization. For this reason, as the image formation is repeated, the charge distribution of the MICR toner in the developing device becomes broad, resulting in a decrease in the image density of the formed image or the occurrence of background fogging. On the other hand, there is a risk that the accuracy may decrease. Further, the MICR toner having a high residual magnetization is peeled off from the surface of the printing material by the magnetic force and adheres to the magnetic head of the reading device, thereby causing a reading error and reducing the reading accuracy.

In view of improving the reading accuracy of the identification mark by adjusting the residual magnetization of the MICR toner to a more suitable value when combined with the second magnetic powder, the residual magnetization of the first magnetic powder Is particularly preferably 28 to 33 Am ² / kg even within the above range.
Further, in order to adjust the residual magnetization of the first magnetic powder within the above range, the particle shape of the first magnetic powder needs to be needle-shaped. Even if the particle shape is needle-like, if the aspect ratio is less than 2.0, the residual magnetization of the first magnetic powder is less than 24 Am ² / kg, and the first magnetic powder is used for MICR. There is a possibility that the effect of increasing the residual magnetization of the toner cannot be obtained. For this reason, the reading accuracy of the identification mark may be lowered.

The other characteristics of the first magnetic powder are not particularly limited, but the saturation magnetization closely related to the residual magnetization is preferably 75 to 95 Am ² / kg, particularly 80 to 90 Am ² / kg. By changing the type and composition of the magnetic material forming the first magnetic powder and adjusting its saturation magnetization (= spontaneous magnetization, in the case of ferromagnetic material) within this range, it is also closely related to the residual magnetization. Even within the above range, the aspect ratio of the first magnetic powder involved can be set to a range that is easier to adjust.

  Similarly to the saturation magnetization, the coercive force of the first magnetic powder adjusted by the type and composition of the magnetic material forming the magnetic powder forms a good identification mark by a developing method such as a magnetic one-component jumping developing method. In view of maintaining the remanent magnetization of the formed identification mark over a long period of time, it is preferably 0.300 to 0.380 kOe, particularly 0.315 to 0.355 kOe.

Furthermore, the average particle diameter of the first magnetic powder is preferably 0.60 to 0.80 μm, particularly preferably 0.68 to 0.72 μm. If the average particle diameter of the first magnetic powder is less than this range, it is difficult to produce. On the other hand, if it exceeds this range, the dispersibility in the toner may be reduced.
<Second magnetic powder>
The reason why the particle shape of the second magnetic powder is based on a polyhedron, and each vertex and ridge line of the polyhedron is a curved surface and has a portion that can be regarded as a straight line on the outer periphery of the projected image. , As described above. In addition, as the second magnetic powder, the particle shape is an octahedron that is a convex polyhedron surrounded by eight triangles, and a hexahedron that is a convex polyhedron surrounded by six squares (cube, rectangular parallelepiped, etc.). Those based on at least one of them are particularly preferably used. The reason for this is as described above.

  Among these, the second magnetic powder based on the octahedron is based on the octahedron as seen in a photograph (projected image) taken using a transmission electron micrograph (TEM) shown in FIG. The apex and the ridgeline are curved, and there are no sharp vertices or ridgelines that serve as charge discharge points. Also, even if the vertex and ridge line are curved, the radius of curvature is too large, and the curved surfaces of adjacent vertices and ridge lines are connected, and there is no portion that can be regarded as a straight line on the outer periphery of the projected image. As shown in FIG. 1, a portion that can be regarded as a straight line remains on the outer periphery of the projected image, and the feature as an octahedron remains.

The residual magnetization of the second magnetic powder 2Am ² / kg or more, but preferably not more than 12AM ² / kg, the aspect ratio is preferably 1.2 to 1.5. These reasons are as follows.
That is, when the residual magnetization is less than ² Am ² / kg, the residual magnetization of the MICR toner may be too low despite being combined with the first magnetic powder having high residual magnetization. For this reason, the residual magnetization of the MICR toner becomes insufficient, and the reading accuracy of the identification mark formed by the MICR toner may be reduced.

Further, when the residual magnetization exceeds 12 Am ² / kg, there is a possibility that the effect of lowering the residual magnetization of the MICR toner by the second magnetic powder cannot be obtained. For this reason, as the image formation is repeated, the charge distribution of the MICR toner in the developing device becomes broad, resulting in a decrease in the image density of the formed image or the occurrence of background fogging. On the other hand, there is a risk that the accuracy may decrease. Further, the MICR toner having a high residual magnetization is peeled off from the surface of the printing material by the magnetic force and adheres to the magnetic head of the reading device, thereby causing a reading error and reducing the reading accuracy.

Note that, when combined with the first magnetic powder whose residual magnetization is in the above-mentioned preferable range, the residual magnetization of the MICR toner is adjusted to a more preferable value to improve the reading accuracy of the identification mark. Then, it is preferable that the residual magnetization of the second magnetic powder is 4 to 9 Am ² / kg, particularly within the above range.
In order to adjust the residual magnetization of the second magnetic powder within the above range and maintain the effect of the particle shape, the aspect ratio is preferably within the range of 1.2 to 1.5. . That is, when the aspect ratio is less than 1.2, the particle shape of the second magnetic powder approaches a spherical shape, and the residual magnetization is less than 1 Am ² / kg, which is combined with the first magnetic powder having a high residual magnetization. Nevertheless, the residual magnetization of the MICR toner may be too low. For this reason, the reading accuracy of the identification mark may be lowered.

  On the other hand, when the aspect ratio exceeds 1.5, the curvature radius of the curved surface of the vertex and the ridge line of the second magnetic powder becomes small, so that it can hardly be said to be a curved surface. That is, the second magnetic powder approaches a conventional polyhedron that does not have a curved top or ridge, and its fluidity and dispersibility with respect to the binder resin are reduced. Therefore, the second magnetic powder should be used in combination with acicular magnetic powder. There is a risk that the effect of will not be sufficiently obtained. As a result, the dispersion state and content of the magnetic powder in individual toner particles are likely to vary, and there is a possibility that the ease of charging and the charge amount of individual MICR toners are likely to vary. is there. Further, the MICR toner does not easily rise in charge amount, and the charge amount itself becomes low, so that the initial image density may be lowered.

When the aspect ratio exceeds 1.5, the residual magnetization value increases too much and the image density decreases, so that the identification mark reading accuracy decreases.
In addition, in order to make the effect of the shape of the second magnetic powder better, and to adjust the residual magnetization to the above-described more preferable range, the aspect ratio is particularly within the above range, It is preferable that it is 1.3-1.4.

The other characteristics of the second magnetic powder are not particularly limited, but the saturation magnetization is preferably 76 to 90 Am ² / kg, particularly 81 to 85 Am ² / kg. By changing the type and composition of the magnetic material forming the second magnetic powder and adjusting its saturation magnetization (= spontaneous magnetization, in the case of a ferromagnetic material) within this range, it is also closely related to the residual magnetization. Even within the above range, the aspect ratio of the second magnetic powder involved can be set to a range that is easier to adjust.

  Similarly to the saturation magnetization, the coercivity of the second magnetic powder adjusted by the type and composition of the magnetic material forming the magnetic powder forms a good identification mark by a developing method such as a magnetic one-component jumping developing method. In consideration of maintaining the remanent magnetization of the formed identification mark over a long period of time, it is preferably 0.090 to 0.150 kOe, particularly preferably 0.100 to 0.140 kOe.

  Furthermore, the average particle size of the second magnetic powder is preferably 0.05 to 0.5 μm, particularly preferably 0.1 to 0.35 μm. If the average particle diameter of the second magnetic powder is less than this range, the proportion of the second magnetic powder exposed on the surface of the toner particles increases, and charges are released from the exposed magnetic powder, thereby charging the magnetic toner. As a result, the image density may be lowered as a result of the shortage. On the contrary, when this range is exceeded, the ratio of the second magnetic powder exposed to the surface of the toner particles decreases, and the magnetic toner is charged up. As a result, the image density may decrease particularly when image formation is repeated.

The particle shape is basically an octahedron that is a convex polyhedron surrounded by eight triangles, each vertex and ridge line of the octahedron is curved, and has a portion that can be regarded as a straight line at the outer periphery of the projected image. The second magnetic powder made of magnetite can be produced, for example, by the following method.
That is, 26.7 liters of a ferrous sulfate aqueous solution containing 1.5 mol / liter of Fe ²⁺ was added to 25.9 liters of a 3.4N aqueous sodium hydroxide solution prepared in advance in a reaction vessel (relative to Fe ²⁺ (Corresponding to 1.10 equivalents) and heated to 90 ° C. to produce a ferrous salt suspension containing ferrous hydroxide colloid while maintaining the pH at 10.5.

Next, while maintaining the liquid temperature of the suspension at 90 ° C., 100 liters of air is blown in over 80 minutes to cause oxidation reaction until the ferrous salt oxidation reaction rate reaches 60%. .
Next, an aqueous sulfuric acid solution was added to the upper suspension so that the pH was 6.5, and then 100 liters of air was blown in for 50 minutes while maintaining the liquid temperature at 90 ° C. Thus, magnetite particles are generated in the suspension.

  Then, after adding an aqueous sodium hydroxide solution to the suspension containing the magnetite particles so as to have a pH of 10.5, while maintaining the liquid temperature at 90 ° C., air of 100 liters per minute is added. After blowing for a minute, the produced magnetite particles are washed with water by a conventional method, filtered and dried, and then the aggregates of the magnetite particles are pulverized. Then, the second magnetic powder composed of magnetite particles having a particle shape based on an octahedron and having apexes and ridge lines curved and satisfying the above-described characteristics is synthesized.

  Further, the particle shape is basically a hexahedron (mainly a cube) that is a convex polyhedron surrounded by six quadrangles, each vertex and ridge of the hexahedron are curved, and a straight line is formed at the outer periphery of the projected image. The second magnetic powder having magnetizable portions and made of magnetite can be produced, for example, by the method described in JP-A-9-59024. In this patent publication, the above-mentioned magnetic powder is contained in the toner particles together with the first magnetic powder in the form of needles, and the toner is used for forming an identification mark for the MICR system. In this case, there is no description about combining with an amorphous silicon photoconductor.

The residual magnetization of the MICR toner of the present invention containing the first and second magnetic powders is preferably 6 Am ² / kg or more and 10 Am ² / kg or less. The reason is as follows. That is, when the residual magnetization is less than 6 Am ² / kg, there is a possibility that the reading accuracy of the identification mark formed by the MICR toner may be lowered.
On the other hand, when the remanent magnetization exceeds 10 Am ² / kg, as the image formation is repeated, the charge amount distribution of the MICR toner in the developing device becomes broad, and the image density of the formed image decreases, As a result of fogging, the reading accuracy is rather lowered. Further, the MICR toner having a high residual magnetization is peeled off from the surface of the printing material by the magnetic force and adheres to the magnetic head of the reading device, thereby causing a reading error and reducing the reading accuracy. In consideration of improving the accuracy of reading the identification mark, the residual magnetization of the MICR toner is preferably 8 to 10 Am ² / kg, particularly within the above range.

In consideration of adjusting the residual magnetization of the MICR toner within the above range, the first magnetic powder M ₁ and the second magnetic powder M ₂ are represented by a weight ratio M ₁ / M ₂ . It is preferable to mix | blend in the ratio of 70 / 30-40 / 60. When the first magnetic powder is less than this range, the effect of increasing the residual magnetization by the first magnetic powder cannot be obtained, and the residual magnetization of the MICR toner falls below the above range, and the MICR toner There is a possibility that the reading accuracy of the identification mark formed by the lowering may be lowered. Further, when the second magnetic powder is less than the above range, the effect of lowering the residual magnetization of the MICR toner by the second magnetic powder cannot be obtained, and the residual magnetization exceeds the above range. As the image formation is repeated, the charge distribution of the MICR toner in the developing device becomes broader, resulting in a decrease in the image density of the formed image and the occurrence of background fogging. May decrease. Further, the MICR toner having a high residual magnetization is peeled off from the surface of the printing material by the magnetic force and adheres to the magnetic head of the reading device, thereby causing a reading error and reducing the reading accuracy.

  Further, the total ratio of the first and second magnetic powders is preferably 30 to 70% by weight, particularly 30 to 60% by weight, based on the total amount of solids forming the toner. If the total ratio of the first and second magnetic powders is less than this range, the effect of holding a thin layer of MICR toner on the surface of the developer carrier is reduced by the magnetic force of the magnet built in the developer carrier. For this reason, there is a risk that background fogging occurs particularly when image formation is repeated. On the other hand, if the total ratio of both magnetic powders exceeds this range, the effect of holding a thin layer of MICR toner on the surface of the developer carrying member becomes too strong, which may reduce the image density. There is. Further, since the content ratio of the binder resin is relatively reduced, there is a possibility that the durability of the MICR toner may be reduced, or the fixing property to the surface of the printing material such as paper may be reduced.

As the first and second magnetic powders, only one type may be contained in the toner particles, but two or more types of the first magnetic powder satisfying the above conditions and / or the above conditions may be used. You may use together 2 or more types of 2nd magnetic powder to satisfy | fill.
In addition, the aspect ratio of the first and second magnetic powders is expressed as an average value of aspect ratios actually measured for 300 magnetic powders taken in a photograph with a predetermined magnification taken by a transmission electron microscope. To do. In addition, the average particle diameter is expressed by an average value of the Martin diameters (equivalent circle diameters) measured for 300 magnetic powders taken in a photograph with a predetermined magnification taken with a transmission electron microscope.

  The residual magnetization values of the first and second magnetic powders and the MICR toner containing both magnetic powders are determined by applying an external magnetic field of 5 kOe to the magnetic powder or MICR toner to be measured. It is defined by the amount of magnetic memory when is set to zero. Specifically, the residual magnetization is calculated by measuring hysteresis curves of magnetic powder and MICR toner. The saturation magnetization of the first and second magnetic powders, which are closely related to the residual magnetization, depends on the amount of magnetic memory when the magnetic powder to be measured is saturated by applying an external magnetic field of 5 kOe. Shall be defined. Specifically, the saturation magnetization is calculated by measuring the hysteresis curve of the magnetic powder. Furthermore, the coercive force of the first and second magnetic powders is defined by the strength of the magnetic field at which the magnetization becomes zero when a magnetic field opposite to the magnetization is applied to the magnetic powder to be measured. To do.

  Considering that the first and second magnetic powders are well dispersed in the binder resin, a cationic surfactant, an anionic surfactant, an amphoteric surfactant, a titanium coupling agent, and a silane coupling Surface treatment may be performed with a surface treatment agent such as an agent, an aluminum coupling agent, a phenol resin, an epoxy resin, or a urethane resin. The amount of the surface treatment agent used is preferably 0.1 to 100 parts by weight with respect to 100 parts by weight in total of the first and second magnetic powders.

  Of these, silane coupling agents are preferred, and specific compounds thereof include, for example, hexamethyldisilazane, trimethylsilane, trimethylchlorosilane, trimethylethoxysilane, dimethyldichlorosilane, methyltrichlorosilane, allyldimethylchlorosilane, allyl Phenyldichlorosilane, benzyldimethylchlorosilane, bromomethyldimethylchlorosilane, α-chloroethyltrichlorosilane, β-chloroethyltrichlorosilane, chloromethyldimethylchlorosilane, triorganosilyl mercaptan, trimethylsilyl mercaptan, triorganosilyl acrylate, vinyl Dimethylacetoxysilane, dimethyldiethoxysilane, dimethyldimethoxysilane, diphenylethoxysilane, hexamethyldisiloxane 1,3-divinyltetramethyldisiloxane, 1,3-diphenyltetramethyldisiloxane, and the like. Further, dimethylpolysiloxane having 2 to 12 siloxane units in one molecule and having one hydroxyl group bonded to a silicon atom, one for each siloxane unit located at the terminal, can also be used.

<Binder resin>
As the binder resin, for example, polystyrene resin, acrylic resin, polyethylene resin, polypropylene resin, polyvinyl chloride resin, polyester resin, polyamide resin, polyurethane resin, polyvinyl alcohol resin, vinyl ether resin, N -Vinyl-type resin, styrene-butadiene-type resin etc. are mentioned, Polystyrene-type resin and polyester-type resin are especially preferable.

  Examples of the polystyrene resin include a styrene homopolymer, and a binary or ternary or higher copolymer of styrene and another monomer. Other monomers that can be copolymerized with styrene include, for example, p-chlorostyrene; vinyl naphthalene; ethylene unsaturated monoolefins such as ethylene, propylene, butylene, and isobutylene; vinyl chloride, vinyl bromide, and fluoride. Vinyl halides such as vinyl; vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate; methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, dodecyl acrylate, acrylic (Meth) acrylic acid esters such as n-octyl acid, 2-chloroethyl acrylate, phenyl acrylate, methyl α-chloroacrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate; acrylonitrile, methacrylonitrile, acrylic Other acrylic acid derivatives such as vinyl; vinyl ethers such as vinyl methyl ether and vinyl isobutyl ether; vinyl ketones such as vinyl methyl ketone, vinyl ethyl ketone and methyl isopropenyl ketone; N-vinyl pyrrole, N-vinyl carbazole, N- Examples thereof include N-vinyl compounds such as vinyl indole and N-vinyl pyrrolidone. These may be used alone or in combination of two or more with styrene.

  Polystyrene resin improves the fixability when transferring the toner for MICR onto the surface of the printed material and fixing it by heating and pressurizing with fixing means. Specifically, it fixes more firmly at the lowest possible heating temperature. In addition to the fact that the MICR toner adheres to the roller of the fixing unit and prevents the offset from re-adhering to the back surface of the printing material, there are two peaks in the molecular weight distribution. It is preferable to have. Specifically, the weight average molecular weight has a molecular weight distribution peak in the range of weight average molecular weight Mw = 3,000 to 20,000 and Mw = 300,000 to 1,500,000, respectively, and the weight average molecular weight. It is preferable to use a binder resin in which the dispersion of the molecular weight represented by the ratio Mw / Mn between Mw and the number average molecular weight Mn is 10 or more. The molecular weight distribution of the binder resin is prepared in advance by using a standard polystyrene resin as a result of measuring the elution time from the column using a molecular weight distribution measuring device by gel permeation chromatography (GPC) method. It can be determined by checking against a calibration curve.

Examples of the polyester resin include various polyester resins obtained by condensation polymerization or co-condensation polymerization of an alcohol component and a carboxylic acid component. Among these, as the alcohol component, for example, ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-butenediol, Diols such as 1,5-pentanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, 1,6-hexanediol, 1,8-octanediol ;
Bisphenols such as bisphenol A, hydrogenated bisphenol A, polyoxyethylenated bisphenol A, polyoxypropylenated bisphenol A;
Sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentane Triol, glycerin, diglycerin, 2-methylprovantriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, 1,3,5-trihydroxymethylbenzene Examples include alcohols.

As carboxylic acid components, oxalic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, succinic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid , Malonic acid, alkyl succinic acid (n-butyl succinic acid, isobutyl succinic acid, n-octyl succinic acid, n-dodecyl succinic acid, isododecyl succinic acid, etc.), alkenyl succinic acid (n-butenyl succinic acid, isobutenyl succinic acid) Divalent carboxylic acids such as n-octenyl succinic acid, n-dodecenyl succinic acid, isododecenyl succinic acid, etc.];
1,2,4-benzenetricarboxylic acid (trimellitic acid), 1,2,5-benzenetricarboxylic acid, 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,4 -Butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid, tetra (methylenecarboxyl) And trivalent or higher carboxylic acids such as methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, and empole trimer acid.

The softening point of the polyester-based resin is preferably 80 to 150 ° C., considering that it can be satisfactorily fixed on the surface of a printed material such as paper by a heat fixing means used in a normal image forming apparatus, and is preferably 90 to 140 ° C. More preferably, it is ° C.
Part of the binder resin preferably has a crosslinked structure. By introducing a crosslinked structure in part, it is possible to improve the storage stability, form retention, durability, etc. of the MICR toner without deteriorating the fixability. The content of the cross-linked content is preferably 10% by weight or less, particularly 0.1 to 10% by weight, expressed as the gel content (insoluble content) obtained by extracting the binder resin using a Soxhlet extractor. . In order to make a part of the binder resin have a crosslinked structure, a crosslinking agent may be added to crosslink the resin, or a thermosetting resin may be blended.

Examples of the thermosetting resin include epoxy resins such as bisphenol A type epoxy resin, hydrogenated bisphenol A type epoxy resin, novolac type epoxy resin, polyalkylene ether type epoxy resin, cycloaliphatic type epoxy resin, and cyanate resin. 1 type, or 2 or more types.
The glass transition temperature Tg of the binder resin is preferably 50 to 65 ° C, and more preferably 50 to 60 ° C. If the glass transition temperature is less than this range, the toner particles are likely to be fused with each other, and the storage stability may be lowered. Further, since the strength of the resin is low, there is a possibility that the toner adheres to the surface of the latent image holding member and does not leave. On the other hand, when the glass transition temperature exceeds this range, the fixability to the surface of the substrate such as paper may be lowered.

  The glass transition temperature of binder resin can be calculated | required from the change point of specific heat in the endothermic curve measured using the differential scanning calorimeter (DSC), for example. Specifically, for example, a differential scanning calorimeter DSC-6200 manufactured by Seiko Instruments Inc. is used, and 10 mg of a measurement sample is put in an aluminum pan, and an empty aluminum pan is used as a reference, and a measurement temperature range of 25 to 200 ° C. The glass transition temperature of the binder resin can be determined from the change point of specific heat in the endothermic curve obtained by measuring at a temperature increase rate of 10 ° C./min and at normal temperature and normal pressure.

The MICR toner of the present invention may contain various conventionally known additives such as colorants, charge control agents, and waxes. Among these, examples of the colorant include pigments such as carbon black and dyes such as acid violet in order to adjust the color tone. The ratio of the colorant is preferably 1 to 10 parts by weight with respect to 100 parts by weight of the binder resin.
<Charge control agent>
The charge control agent is blended in order to improve the charge level and charge rise characteristics of the MICR toner (an index indicating whether the charge is charged to a constant charge level in a short time), and to improve durability and stability. There are two types of charge control agents, one that is positively charged and the other that is negatively charged, and either one is blended according to the charge polarity of the MICR toner.

  Examples of positively chargeable charge control agents include pyridazine, pyrimidine, pyrazine, orthooxazine, metaoxazine, paraoxazine, orthothiazine, metathiazine, parathiazine, 1,2,3-triazine, 1,2,4-triazine, 1, 3,5-triazine, 1,2,4-oxadiazine, 1,3,4-oxadiazine, 1,2,6-oxadiazine, 1,3,4-thiadiazine, 1,3,5-thiadiazine, 1,2, 3,4-tetrazine, 1,2,4,5-tetrazine, 1,2,3,5-tetrazine, 1,2,4,6-oxatriazine, 1,3,4,5-oxatriazine, phthalazine, Azine compounds such as quinazoline and quinoxaline; Azin Fast Red FC, Azin Fast Red 12BK, Azin Violet BO, Azine Direct dyes composed of sub-zine compounds such as Raun 3G, Azin Light Brown GR, Azin Dark Green BH / C, Azin Deep Black EW, Azin Deep Black 3RL; Nigrosine Compounds such as Nigrosine, Nigrosine Salt, Nigrosine Derivatives; Nigrosine BK , Nigrosine NB, nigrosine Z and other acid dyes; metal salts of naphthenic acid or higher fatty acids; alkoxylated amines; alkylamides; quaternary ammonium salts such as benzylmethylhexyldecylammonium and decyltrimethylammonium chloride 1 type, or 2 or more types. In particular, a nigrosine compound is suitable as a positively chargeable charge control agent because a more rapid charge-up characteristic can be obtained.

  Moreover, as a positively chargeable charge control agent, a resin or oligomer having a quaternary ammonium salt, a resin or oligomer having a carboxylate, a resin or oligomer having a carboxyl group, or the like can be used. Specifically, polystyrene resin having quaternary ammonium salt, acrylic resin having quaternary ammonium salt, styrene-acrylic resin having quaternary ammonium salt, polyester resin having quaternary ammonium salt, carboxylate Polystyrene resin having carboxylate, acrylic resin having carboxylate, styrene-acrylic resin having carboxylate, polyester resin having carboxylate, polystyrene resin having carboxyl group, acrylic resin having carboxyl group 1 type, or 2 or more types, such as a styrene-acrylic resin having a carboxyl group and a polyester resin having a carboxyl group.

  In particular, a styrene-acrylic resin (styrene-acrylic copolymer) having a quaternary ammonium salt, carboxylate or carboxyl group as a functional group can easily adjust the charge amount to a value within a desired range. It is preferable in that it can be performed. Further, acrylic monomers constituting styrene-acrylic resin together with styrene are methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, acrylic acid 2 Examples include (meth) acrylic acid alkyl esters such as ethylhexyl, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, and isobutyl methacrylate.

  Furthermore, as the quaternary ammonium salt compound, a unit derived from a dialkylaminoalkyl (meth) acrylate through a quaternization step is used. Examples of the derived dialkylaminoalkyl (meth) acrylate include di (amino) ethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dipropylaminoethyl (meth) acrylate, dibutylaminoethyl (meth) acrylate and the like ( Lower alkyl) aminoethyl (meth) acrylates; dimethylmethacrylamide; dimethylaminopropylmethacrylamide are preferred. Further, hydroxy group-containing polymerizable monomers such as hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, and N-methylol (meth) acrylamide can be used in combination during polymerization.

  As the negatively chargeable charge control agent, for example, organometallic complexes and chelate compounds are effective, and among them, acetylacetone metal complexes, salicylic acid metal complexes or salts are preferable, and salicylic acid metal complexes or salts are particularly preferable. Among these, examples of the acetylacetone metal complex include aluminum acetylacetonate and iron (II) acetylacetonate. Examples of the salicylic acid-based metal complex or salt include chromium 3,5-di-tert-butylsalicylate.

  The ratio of the charge control agent is 0.5 to 15.0% by weight, particularly 2.0 to 8.0% by weight, particularly 3.0 to 7.0% by weight in the total amount of solids forming the toner. % Is preferred. When the ratio of the charge control agent is less than this range, it is difficult to impart stable charging characteristics to the MICR toner, and there is a possibility that the image density is lowered or the durability is lowered. On the other hand, when the above range is exceeded, the environmental resistance of the MICR toner, in particular, charging failure and image failure under high temperature and high humidity are likely to occur. In addition, since poor dispersion with respect to the binder resin is likely to occur, there is a risk that background fogging may occur, or the charge control agent aggregated without being dispersed may contaminate the photoreceptor.

<wax>
The wax improves the fixability of the MICR toner on the surface of the printed material such as paper, and prevents the offset of the MICR toner from adhering to the fixing roller of the image forming apparatus at the time of fixing. The toner for MICR adhering to the fixing roller or the like is added to improve the image quality, to reattach to the surface of the printing material and to contaminate the image, and to prevent image smearing.

  Examples of the wax include olefin waxes such as polyethylene wax and polypropylene wax; plant waxes such as carnauba wax, rice wax and candelilla wax; mineral waxes such as montan wax; Fischer-Tropsch wax produced by the Tropsch method; petroleum wax such as paraffin wax and microcrystalline wax; ester wax; Teflon (registered trademark) wax, etc. Can be used.

  The ratio of the wax is preferably 1 to 5% by weight in the total amount of solids forming the toner. If the ratio of the wax is less than this range, the effect of improving the offset property of the MICR toner or preventing image smearing may be insufficient. Conversely, if it exceeds this range, the MICR Therefore, the toner for use may be easily fused, and the storage stability may be reduced.

<Manufacture of toner for MICR>
In the MICR toner of the present invention, each of the above components is mixed using a stirring mixer such as a Henschel mixer, then kneaded using a kneader such as an extruder, cooled, and further pulverized. It is manufactured by classification as necessary. Moreover, you may wet-mix said each component.

  As described above, the MICR toner of the present invention thus produced has excellent accuracy in reading with a reading device by using the first and second magnetic powders having different particle shapes in combination. In consideration of the formation of a good identification mark having excellent reading accuracy and high image density, the volume-based center particle size of the toner for MICR is 3 to 15 μm, particularly 5 to 10 μm. Is preferred.

In the toner for MICR of the present invention, the saturation magnetization is preferably 35 to 45 Am ² / kg, particularly 37 to 43 Am ² / kg. By changing the saturation magnetization and blending ratio of the first and second magnetic powders and adjusting the saturation magnetization of the MICR toner within this range, a printer using the MICR toner can be used for normal image formation. When used, the image characteristics, particularly the image density can be stabilized.

  Further, like the saturation magnetization, the coercive force of the MICR toner adjusted by changing the saturation magnetization and blending ratio of the first and second magnetic powders is good by a developing method such as a magnetic one-component jumping developing method. In consideration of forming the identification mark and maintaining the residual magnetization of the formed identification mark satisfactorily over a long period, it is preferably 0.090 to 0.110 kOe, particularly 0.094 to 0.098 kOe.

Further, the surface of the MICR toner of the present invention can be easily removed from the surface of silica (fluidizing agent) for improving fluidity and storage stability, and the surface of the latent image holding member, as in the conventional case. Surface treatment may be carried out with an external additive such as an abrasive such as titanium oxide or aluminum oxide for improving the cleaning performance (usually the average particle size is 1.0 μm or less).
In addition, in order to provide the MICR toner with the chargeability necessary for development by the magnetic one-component jumping development method, the surface is used as an external additive, in particular as a fluidizing agent, with aminosilane, silicone oil, silane series. Surface treatment with coupling agent (hexamethyldisilazane, etc.), titanium coupling agent, etc., and volume resistance value adjusted to 10 ⁵ to 10 ⁹ Ω · cm, especially 10 ⁷ to 10 ⁸ Ω · cm Is preferably used. When an external additive having a volume resistance value within this range is externally added, the durability of the MICR toner can be improved, and in particular, printing characteristics under high humidity conditions that are difficult to be charged can be improved. Specific examples of such fluidizing agents include dry silica that has been introduced with a positively charged polar group (such as an amino group) using a silane coupling agent and has been hydrophobized with silicone oil. Further, as the abrasive, it is preferable to use a conductive abrasive obtained by conducting a conductive treatment on the surface of titanium oxide, aluminum oxide or the like.

  For the surface treatment, it is preferable to dry-mix the MICR toner and the external additive. In particular, in order to prevent the external additive from being embedded in the surface of the toner particles, a Henschel mixer or a Nauter mixer is used. It is preferable to mix them. The ratio of the external additive is preferably 0.1 to 5 parts by weight, particularly 1 to 3 parts by weight with respect to 100 parts by weight of the toner particles. When the ratio of the external additive is less than this range, the fluidity of the MICR toner is lowered and the image density may be lowered. In addition, if it exceeds this range, the durability of the MICR toner may be reduced.

<Image forming method>
In the image forming method of the present invention, a latent image holding body for holding an electrostatic latent image and a fixed magnet are rotated by a magnetic one-component jumping development method, and a thin layer of MICR toner is formed on the surface thereof. The developer carrier is made to face the surface of the latent image carrier from the thin layer in a state where the developer carrier is opposed so that the thin layer and the latent image carrier are not in contact with each other. And forming the identification mark for the magnetic ink character authentication system on the surface of the printing material, and the latent image. An amorphous silicon photosensitive member is used as a holding member.

<Amorphous silicon photoconductor>
As the amorphous silicon photoconductor, for example, photoconductors having various known structures in which an amorphous silicon-based photosensitive layer is provided on the surface of a conductive substrate formed in a predetermined shape such as a drum shape can be used. The amorphous silicon-based photosensitive layer can be formed, for example, by a vapor phase growth method such as a glow discharge decomposition method, a sputtering method, an ECR method, or an evaporation method. In forming the photosensitive layer, H or a halogen element is included. You can also. Further, in order to adjust the characteristics of the photoreceptor, elements such as C, N, and O may be included, or a group 13 element or a group 15 element in the periodic table (long period type) may be included.

Specifically, the photosensitive layer can be formed of various photoconductive materials such as a-SiC, amorphous silicon-based materials such as a-SiC, a-SiO, and a-SiON. In particular, it is preferable to use a-SiC. In that case, the value of x in Si _1-x C _x should be set to 0 <x ≦ 0.5, preferably 0.05 ≦ x ≦ 0.45. . Within this range, the a-SiC layer can have a higher resistance than the a-Si layer while maintaining good carrier transport, and the photosensitivity characteristics of the photoreceptor can be improved. As group 13 elements and group 15 elements, B and P are desirable in that they are excellent in covalent bonding properties, can change semiconductor characteristics sensitively, and can provide excellent photosensitivity.

Furthermore, when the amorphous silicon-based photosensitive layer is formed by laminating a layer region (photoexcitation layer region) having an enhanced function of generating photocarriers and a layer region (carrier transporting layer region) having a function of transporting carriers. Both the photosensitivity and the withstand voltage characteristics of the photoreceptor can be improved. At this time, in order to increase the generation efficiency of the photocarrier in the photoexcitation layer region, among the film formation conditions, (1) the film formation rate is set low, and (2) the dilution rate of the film formation component with H ₂ or He It is preferable to form the film while taking measures such as (3) increasing the amount of the element to be doped to be larger than that of the carrier transport layer region.

The carrier transport layer region mainly has a role of increasing the pressure resistance of the photosensitive layer and smoothly transporting the carriers injected from the photoexcitation layer region to the conductive substrate. Carrier generation is performed by the transmitted light, which contributes to an improvement in photosensitivity of the photoreceptor.
The thickness of the amorphous silicon-based photosensitive layer is preferably a thickness obtained by adding 0.1 to 2.0 μm to the depth of light absorption determined from the absorption coefficient of this layer with respect to light having an exposure wavelength. Further, when the photosensitive layer is formed by laminating the photoexcitation layer region and the carrier transport layer region as described above, it is preferable to set the thickness of the photoexcitation layer region substantially equal to the light absorption depth. .

  A carrier blocking layer is preferably interposed between the photosensitive layer and the conductive substrate. The carrier blocking layer prevents the injection of carriers from the conductive substrate to the photosensitive layer when the surface of the photosensitive member is in contact with the toner while a bias voltage is applied during development, so that the exposed portion and the non-exposed portion are separated. It has a function of improving electrostatic density to improve image density and reducing background fogging. As the carrier blocking layer, inorganic insulating layers formed of a-SiC, a-SiO, a-SiN, a-SiON, a-SiCON, etc., which are insulating, or polyethylene terephthalate, Parylene (registered trademark), It is preferable to use an organic insulating layer formed of polytetrafluoroethylene, polyimide, polyfluoroethylenepropylene, polyurethane, epoxy resin, polyester, polycarbonate, cellulose acetate resin, or the like.

  In addition, the carrier blocking layer is required to have insulating properties, good adhesion to a conductive substrate and an amorphous silicon-based photosensitive layer, and a characteristic that does not cause significant alteration during heating when forming the photosensitive layer. . Considering such characteristics, the carrier blocking layer is preferably formed of a-SiC. In order to make the a-SiC forming the carrier blocking layer insulative, the amount of C contained in the carrier blocking layer may be increased as compared with the photosensitive layer. The thickness of the carrier blocking layer is preferably from 0.01 to 5 [mu] m, more preferably from 0.1 to 3 [mu] m.

  The surface of the photosensitive layer is preferably covered and protected by a surface protective layer made of an organic or inorganic insulating material. Thereby, it is possible to prevent the surface of the photosensitive layer from being oxidized during discharge by a charging means or the like and forming an oxide film that easily adsorbs discharge products and water molecules. In addition, the withstand voltage can be improved, and the wear resistance when repeatedly used can be improved. Among them, it is preferable to use a layer made of an a-Si insulating material such as a-SiC, a-SiN, a-SiO, a-SiCO, or a-SiNO. In particular, it is preferable to use a-SiC.

When a-SiC is used for the surface protective layer, the amount of C contained in the surface protective layer may be increased as compared with the photosensitive layer, as in the case of the carrier blocking layer. Specifically, it is preferable that the x value of Si _1-x C _x is 0.3 ≦ x <1.0, particularly 0.5 ≦ x ≦ 0.95. Further, it is preferable that the dark resistivity of the surface protective layer is 10 ¹³ Ω · cm or more by adjusting the x value of C. When the dark resistivity is 10 ¹³ Ω · cm or more, the photosensitive member has a high ability to maintain an electrostatic latent image because of less potential flow in the surface direction of the surface protective layer, and also has excellent moisture resistance. The effect of suppressing the occurrence of image flow due to water absorption is excellent.

In addition, such a high-resistance surface protective layer prevents the injection of charge due to bias through the toner, enhances the potential contrast between the exposed area and the non-exposed area, and attracts more toner to the surface to attract the toner image. It also has a function of increasing the image density and sufficiently increasing the image density. Moreover, background fogging can also be suppressed. Furthermore, the withstand voltage of the photoreceptor can be increased.
In addition, in the surface protective layer formed of an insulating material other than a-SiC, photocarriers continue to be trapped even after image formation, and there is a possibility that the residual potential cannot be erased reliably in a normal charge removal process. However, the surface protective layer formed of a-SiC effectively blocks positive charges from the surface, but has the property that negative charges from the conductive substrate are relatively easy to pass through. Therefore, the residual potential after image formation is reduced. Further, there is an advantage that the image can be erased effectively by a normal static elimination process and images can be continuously formed.

  Moreover, the surface protective layer formed of a-SiC has good adhesion to an amorphous silicon-based photosensitive layer such as a-SiC, and is excellent in wear resistance, environmental resistance, etc. There is also an advantage that stable image formation can be performed. The surface protective layer formed of a-SiC may form a gradient in the thickness direction in the amount of C in the layer, or may contain elements such as N, O, Ge and the like together with C to provide moisture resistance. It can be further increased.

  The thickness of the surface protective layer is preferably 0.05 to 5 μm, and more preferably 0.1 to 3 μm. If the thickness is less than 0.05 μm, the effect of preventing the above-described oxide film formation, the effect of improving the withstand voltage, or the effect of improving the wear resistance when repeatedly used may not be sufficiently obtained. is there. Further, there is a possibility that the optical carrier cannot be effectively trapped to contribute to the formation of the toner image.

  On the other hand, when the thickness exceeds 5 μm, when a fine charge pattern is formed, the electric field (electric field lines) spreads in the film surface direction in the surface protective layer, resulting in a decrease in resolution, resulting in sufficient resolution. May not be obtained. In addition, since the electric charge remaining on the surface increases and the residual potential becomes high, there is a possibility that problems such as a decrease in image density, background fogging, or a change in image density in repeated use may occur.

The image forming method of the present invention can be carried out in the same manner as in the prior art except that the amorphous silicon photoreceptor and the MICR toner of the present invention are combined. For example, as the developer carrying member, those made of various conventionally known materials can be used, and in particular, those having a ten-point average roughness Rz of 2.0 to 6.0 on the surface thereof are used. It is preferable to do this.
The developer carrying member having a ten-point average roughness Rz less than this range has a surface smoothness that is too high, so that the toner transportability becomes insufficient, and a thin layer having a sufficient thickness is formed on the surface. It cannot be formed, and the image density of the formed image may be reduced.

  On the other hand, a developer carrier having a ten-point average roughness Rz exceeding this range has a surface that is too smooth and has large irregularities. Therefore, a clean thin layer having a uniform thickness and no defects on the surface. Cannot be formed, and the image quality of the formed image may be reduced. Further, among the irregularities on the surface of the developer carrying member, potential leakage to the latent image holding member is likely to occur at the protrusions, and if the leakage occurs, there is a possibility that minute black spots may be formed in the leaked portion of the formed image. is there.

Therefore, the ten-point average roughness Rz of the surface of the developer carrying member is preferably 2.0 to 6.0 μm. The ten-point average roughness Rz of the surface of the developer carrying member can be measured using a surface roughness measuring instrument (for example, Surfcorder SE-30D manufactured by Kosaka Laboratory Ltd.).
The developer carrier can be formed of, for example, aluminum or stainless steel. Among these, examples of the stainless steel include stainless steel classified into SUS303, SUS304, SUS305, SUS316, and the like, and SUS305 is particularly preferable because it is weak in magnetism and easy to process.

(Measurement of aspect ratio and average particle diameter of magnetic powder)
The aspect ratio and average particle diameter of the first and second magnetic powders were measured by the following procedure.
The photograph (magnification 10,000 cups) taken with a transmission electron microscope is further magnified 4 times, the aspect ratio of 300 magnetic powders photographed in the photograph is measured, and the average value is obtained. Of aspect ratio. Further, the Martin diameter (equivalent circle diameter) was measured for the 300 magnetic powders, and the average value thereof was obtained as the average particle diameter of the magnetic powder.

(Measurement of magnetic properties of magnetic powder)
The residual magnetization σr, saturation magnetization σs, and coercive force Hc of the first and second magnetic powders were measured by the following procedure. In addition, the measurement of these magnetic characteristics was performed using the vibration sample type magnetometer [Toei Kogyo Co., Ltd. VSM-C7 type | mold].
A hysteresis curve was measured when an external magnetic field of 5 kOe was applied to the magnetic powder, and then the external magnetic field was reduced to zero, and the residual magnetization σr of the magnetic powder was determined from the amount of magnetic memory. A hysteresis curve was measured when an external magnetic field of 5 kOe was applied and saturated, and the saturation magnetization σs of the magnetic powder was determined from the amount of magnetic memory. Furthermore, when a magnetic field having a direction opposite to the magnetization is applied to the magnetic powder, the strength of the magnetic field at which the magnetization becomes 0 is obtained to obtain the coercive force Hc of the magnetic powder.

Example 1:
(First magnetic powder)
The first magnetic powder is made of magnetite and has a needle shape, an aspect ratio represented by a ratio of major axis to minor axis of 3.57, an average particle diameter of 0.70 μm, and residual magnetization σr. Magnetic powder (manufactured by Toda Kogyo Co., Ltd.) having 32.0 Am ² / kg, saturation magnetization σs of 84.0 Am ² / kg, and coercive force Hc of 0.325 kOe was used.

(Second magnetic powder)
The second magnetic powder is composed of magnetite, and the particle shape is basically a octahedron that is a convex polyhedron surrounded by eight triangles, as shown in FIG. 1, and each vertex and ridge of the octahedron are curved surfaces. And has a portion that can be regarded as a straight line on the outer periphery of the projected image, an aspect ratio of 1.31, an average particle diameter of 0.22 μm, a residual magnetization of 8.82 Am ² / kg, and a saturation magnetization of 83. Magnetic powder (manufactured by Toda Kogyo Co., Ltd.) having 9 Am ² / kg and a coercive force Hc of 0.103 kOe was used.

(Manufacture of MICR toner)
54 parts by weight of styrene-acrylic copolymer resin as a binder resin, 18 parts by weight of first magnetic powder, 22 parts by weight of second magnetic powder, 4 parts by weight of polyethylene wax (manufactured by Sazol), positive charge 2 parts by weight of a quaternary ammonium salt (Bontron P-51 manufactured by Orient Chemical Co., Ltd.) as a control agent was mixed using a Henschel mixer, kneaded using a twin screw extruder, cooled, and then hammered. Coarse pulverization was performed using a mill. Next, after finely pulverizing using a mechanical pulverizer, classification is performed using an airflow classifier, the volume-based center particle diameter is 7 μm, and the particle weight is within the range of 5 to 10 μm. A toner for MICR having a particle size distribution in which weight percent was distributed was produced.

Examples 2-4, Comparative Examples 1-5:
As a 1st magnetic powder, it replaces with what was used in Example 1, and the magnetic powder which has each characteristic shown in following Table 1 [all are Toda Kogyo Co., Ltd.], and also as a 2nd magnetic powder, Instead of the one used in Example 1, the magnetic powder having the characteristics shown in Table 2 below (all manufactured by Toda Kogyo Co., Ltd.) was used in the same manner as in Example 1 except that the same amount was used. A toner for MICR was manufactured. In Tables 1 and 2, the sign of the particle shape column is as follows.

Eight-circle: An octahedron having apexes and ridges that are curved and having a portion that can be regarded as a straight line on the outer periphery of the projected image.
Standing-circle: a cube-like shape having vertices and ridges that are curved and having a portion that can be regarded as a straight line on the outer periphery of the projected image.
Octagon: An octahedron shape whose vertices and ridge lines are not curved. Normal octahedron.

Sphere: Spherical.
Vertical-angle: A cube-like shape whose vertices and edges are not curved. Normal hexahedron.
Needle: Needle-shaped.

<Measurement of magnetic properties of MICR toner>
The residual magnetization Σr, saturation magnetization Σr, and coercive force HC of the MICR toner were determined by the following procedure in the same manner as the residual magnetization σr, saturation magnetization σs, and coercive force Hc of the magnetic powder.
A hysteresis curve was measured when an external magnetic field of 5 kOe was applied to the MICR toner and then the external magnetic field was reduced to zero, and the residual magnetization Σr of the MICR toner was determined from the amount of magnetic memory. Further, a hysteresis curve was measured when saturation was performed by applying an external magnetic field of 5 kOe, and the saturation magnetization Σs of the MICR toner was determined from the amount of magnetic memory. Furthermore, when a magnetic field opposite to the magnetization was applied to the MICR toner, the strength of the magnetic field that caused the magnetization to become zero was obtained and used as the coercive force HC of the MICR toner.

<Real machine test>
Amino group was introduced using aminosilane and 1.0 part by weight of dry silica hydrophobized with silicone oil and 1.4 parts by weight of conductive abrasive subjected to conductive treatment were compared with each of the above examples. In addition to 100 parts by weight of the toner for MICR in the example, a magnetic one-component developer was prepared by mixing using a Henschel mixer.

  Next, this magnetic one-component developer is used in a laser beam printer of a magnetic one-component jumping development system (Ecosys (registered trademark) FS-3750 manufactured by Kyocera Corporation), and the temperature is 20 ° C. and the relative humidity is 65%. The following characteristics were evaluated under RH normal temperature and normal humidity environment. Note that a SUS305 sleeve having a 10-point average roughness Rz of 5.0 μm on the surface was used as the developer holder, and an amorphous silicon photoconductor was used as the latent image holder.

(Image density)
Using the above laser beam printer, after continuous image formation of 50,000 sheets of ISO 4% original and the image density of the first image (initial image) on which the solid black pattern is formed on the surface of plain paper, The image density of the image formed with the solid black pattern (image after durability) was measured using a Macbeth reflection densitometer [RD914 manufactured by Gretag Macbeth Co., Ltd.]. An image density of 1.20 or higher was evaluated as acceptable, and an image density of less than 1.20 was evaluated as unacceptable. The results are shown in Table 3.

Further, in Example 1 and Comparative Example 2, every time continuous images are formed on 5000 ISO 4% originals, the solid black pattern is formed and the image density is measured, and the ISO 4% original is 100,000 sheets. The process was repeated until printing, and the transition of the image density was recorded. The results are shown in FIG.
(Reading accuracy)
Using the above laser beam printer, an image evaluation pattern is formed on the surface of the check paper using MICR font E-13B or all CMC-7 fonts as an MICR system identification mark. The reading rate when the image was passed through a reading device [MICR Qualifier manufactured by Canada RDM Co., Ltd.] was recorded as the initial reading accuracy. In addition, ISO 1004: 1995 “Information Processing—Recognition of Magnetic Ink Characters—Printing when 50,000 sheets of ISO 4% originals were continuously imaged and the same image evaluation pattern was imaged and passed through a reader. The reading rate according to “Specifications” was recorded, and the reading accuracy after durability was recorded. And what read accuracy was in the range of 100 to 200% was evaluated as acceptable, and out of this range was evaluated as unacceptable. The results are shown in Table 3.

  For Example 1 and Comparative Example 2, each time 5000 continuous images of ISO 4% originals are formed, the image evaluation pattern is formed, and the reading rate when passing through the reading device is recorded. The operation was repeated until 100,000 sheets of ISO 4% originals were printed, and the transition of reading accuracy was recorded. The results are shown in FIG.

  From the table, although the particle shape is based on an octahedron, the toner for MICR of Comparative Example 1 using the second magnetic powder having a normal octahedron shape whose apex and ridge lines are not curved, and Although the particle shape is based on a cube, the toner for MICR of Comparative Example 3 using the second magnetic powder having a normal cubic shape whose apex and ridge lines are not curved has both initial image density. In addition, the image density after endurance was further reduced. Further, it was found that the MICR toner of Comparative Example 2 using the second magnetic powder having a spherical particle shape has a remarkably low initial and post-durability reading rate. Furthermore, it was found that the MICR toner of Comparative Example 4 using the second magnetic powder having a needle shape in the particle shape has a remarkably low image density after initial and after durability.

On the other hand, the embodiment using the second magnetic powder whose particle shape is basically an octahedron or a cube and whose apexes and ridges are curved and has a portion that can be regarded as a straight line on the outer periphery of the projected image. It was found that the toners for MICR Nos. 1 to 6 had a high image density after initial and durability, and a high reading rate after initial and durability.
Further, from FIG. 2, the MICR toner of Comparative Example 1 is up and down around 1.30 when the image density is up to 35 million sheets, but from 1.30 when it exceeds 40,000 sheets. In contrast, the MICR toner of Example 1 was found to maintain an image density of 1.30 or more up to 90,000 sheets.

  Further, as shown in FIG. 3, the MICR toner of Comparative Example 1 has a font reading rate of 100% at the time of 50,000 sheets for the E-13B font and 70,000 sheets for the CMC-7 font. On the other hand, it was found that the MICR toner of Example 1 can maintain the reading rate of 100% or more up to 100,000 sheets for both E-13B font and CMC-7 font.

3 is a transmission electron micrograph showing an example of a second magnetic powder used in the MICR toner of the present invention. 6 is a graph showing transition of image density when images are continuously formed using the MICR toners of Example 1 and Comparative Example 2 of the present invention. 6 is a graph showing the transition of the MICR font reading rate when images are continuously formed using the MICR toners of Example 1 and Comparative Example 2;

Claims (3)

  MICR toner for forming an identification mark for magnetic ink character authentication system, comprising: (1) a first magnetic powder having a needle-like particle shape; and (2) a polyhedron whose particle shape is based on a polyhedron. And a second magnetic powder having a curved surface and a portion that can be regarded as a straight line on the outer periphery of the projected image.   The particle shape of the second magnetic powder is based on at least one of an octahedron that is a convex polyhedron surrounded by eight triangles and a hexahedron that is a convex polyhedron surrounded by six quadrilaterals. 1. The toner for MICR as described in 1.   A latent image holding body for holding an electrostatic latent image, a developer carrier on which a thin layer of MICR toner is formed on a surface of the latent image holding body that rotates with a built-in fixed magnet, and a thin layer and a latent image holding body The process of causing the MICR toner to fly from the thin layer onto the surface of the latent image holding member in a state of being opposed to each other so as not to come into contact with the surface, to visualize the electrostatic latent image into a toner image. An image forming method for forming an identification mark for a magnetic ink character authentication system on a surface of a substrate to be printed, comprising: a MICR toner according to claim 1; and an amorphous silicon photoconductor as a latent image holder. An image forming method using the method.