JPH04358164A - Magnetic toner - Google Patents

Abstract

PURPOSE:To provide a magnetic toner having proper magnetic force, capable of accurate recognition of a magnetic reading sign with MICR, hardly causing the exfoliation of a image even by friction with a magnetic head at the time of magnetic reading, having excellent durability and satisfactory environmental stability, not causing image defects such as blur and tailing, hardly wearing a photosensitive material, preventing filming on the photosensitive material and giving a clear image free from fogging. CONSTITUTION:This magnetic toner is composed essentially of a binding resin and magnetic powder. The BET specific surface area of the magnetic powder is 3.5-6.0m<2>/g, the residual magnetization (sigmarm) of the magnetic powder is 7-24, the residual magnetization (sigmart) of the toner is >4.2-7 and the amt. W of the magnetic powder in the toner is 30-70wt.%.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic toner for developing electrostatic images. More specifically, the magnetic toner fixed after printing can be read by a magnetic head, etc.
The present invention also relates to a magnetic toner that prevents printed characters from being rubbed off when read by a magnetic head.

0002

[Prior Art] Currently, there are two types of dry development methods in various electrostatic copying systems that are in practical use: a two-component development method that uses toner and a carrier such as iron powder, and a toner that contains a magnetic material inside without using a carrier. A one-component magnetic toner development method using a toner is known. The development method using one-component magnetic toner does not require an automatic density adjustment device, which is required in a two-component development method, making the developing device more compact, and since there is no carrier contamination, there are no problems such as carrier replacement. No maintenance required. Therefore, it is particularly suitable for small copying machines and printers. However, magnetic toner contains 30 to 70% by weight of magnetic fine powder (hereinafter referred to as magnetic powder), and is essentially a two-component development type toner (generally does not contain magnetic material).
The fixing properties are poor compared to the toner binder, and since the magnetic material is usually hydrophilic, the adhesion with the toner binder is poor. Studies are continuing to improve these problems.

By the way, attempts have been made to use such a one-component magnetic toner development method to very easily create and print documents suitable for magnetic image character recognition, especially personal checks. . Generally, such a method is M
It is called ICR. MICR involves magnetizing an image and reading it out using a magnetic head, and since this involves reading an image printed using liquid magnetic ink, it is not easy to form an image. In this respect, when a one-component magnetic toner development method is used, the machine becomes compact and maintenance becomes easy, so it is thought that efficiency will be greatly improved. However, in the conventional one-component magnetic toner development method, the magnetization of the magnetic toner image forming the image is too weak to be correctly recognized by a MICR reader. Furthermore, M
ICR readers are designed to read liquid-printed images, so magnetic toner images that are simply heat-fused rather than soaked into a fixed image carrier such as paper cannot be processed. , it is required to provide performance not found in conventional magnetic toner images, or to further improve the performance of conventionally used magnetic toners.

[0004] Therefore, in order to increase the magnetization of the magnetic toner image, a method has been considered in which the amount of magnetic toner applied per image is increased to make it readable. In this case, even if the magnetization is sufficient, the amount of magnetic toner is too large and the image becomes distorted or blurred, making it impossible to recognize the symbol correctly. Another possibility is to increase the magnetic content of the magnetic toner particles to increase the magnetic force of the magnetic toner image, but this tends to reduce tribo, and the sharpness of the image is affected, especially under high temperature and high humidity. This causes deterioration in image quality and durability stability, and furthermore, deterioration in fixing performance, so that the image is easily rubbed off by a MICR reader, making it impossible to recognize the symbol. Therefore,
It is conceivable to use a magnetic material with large magnetization itself.

[0005] JP-A-54-20725, JP-A No. 60-20
No. 644 describes a magnetic toner using magnetic powder having a coercive force of 200 Oe or more. The former describes a magnetic toner that can be read out by a magnetic head, and is suitable for high-speed development because it improves the transportability of the magnetic toner. However, since magnetic powder having a coercive force of 300 Oe or more has too large a magnetization, if an appropriate amount is contained, the symbol cannot be recognized by a MICR reader. Furthermore, since both use acicular magnetite, a large amount of magnetic powder is exposed on the surface of the magnetic toner, which causes a problem as it is easily rubbed off by rubbing with the magnetic head.

[0006] Also, Special Publication No. 61-1374, No. 61-
Publication No. 63532 describes granular black ferromagnetic iron oxide particles or equiaxed iron oxide particles having a high coercive force. The shape of the particles is not acicular, but the former has a coercive force of 248 Oe or more, and the latter has a large coercive force of 180 Oe or more, so the magnetization is strong and it is necessary to use an appropriate amount of magnetic powder for one-component magnetic development. If it is contained, it is thought that it will be difficult to recognize the symbol, causing a problem. On the contrary, these high coercive force magnetic powders have strong magnetization, so it is possible to read MICR with less magnetic powder content than conventional magnetic toners, but in the normal one-component magnetic toner development method, residual magnetization Due to the decrease in σγ, conveyance performance deteriorates, making it impossible to obtain stable images. Furthermore, the amount of charge tends to be higher than necessary, which causes problems such as a decrease in image density, especially in low temperature and low humidity environments.

Furthermore, JP-A-58-95748 describes a magnetic toner having a coercive force of 150 to 350 Oe. This magnetic toner has good developability and transferability and can produce high-quality images, but the amount of charge is 151
μc/g or more is required. Particularly under low temperature and low humidity conditions, the amount of charge increases further and the mirroring force with the magnetic toner carrier increases, making it difficult to develop.

Furthermore, Japanese Patent Laid-Open No. 1-219755 discloses that the residual magnetization σγ of the magnetic toner is 3.7-0.11d≦σγ≦6.5-0 with respect to the volume average diameter d of the magnetic toner.
．． A magnetic toner designated as 23d is described. However, such magnetization is insufficient for MICR and cannot accurately recognize symbols.

Furthermore, JP-A-60-26955 discloses that the average particle diameter of the magnetic powder is 1 μm or more, and the BET specific surface area is 0.5 to 3.8 m 2 /g, preferably 0.8 to 3.8 m 2 /g.
A magnetic toner containing magnetic powder specified in a range of 2.5 m2/g is described. However, if the BET specific surface area is small, it has excellent properties with respect to wear resistance, but if the particle size is 1 μm or more, the BET specific surface area is 3.5
If it is less than m2/g, many image quality defects such as trailing and blurring will occur, and when used for MICR, problems such as reading errors will occur.

0010

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. That is, the first object of the present invention is to
An object of the present invention is to provide a magnetic toner that allows accurate magnetic read symbol recognition by CR. A second object of the present invention is to provide a magnetic toner that is difficult to form an image even when rubbed against a magnetic head during magnetic reading. A third object of the present invention is to provide a magnetic toner with excellent durability and stability. A fourth object of the present invention is to provide a magnetic toner with good environmental stability. A fifth object of the present invention is to provide a magnetic toner free from image quality defects such as blur and trailing. A sixth object of the present invention is to provide a magnetic toner that has less abrasion of the sensitive material and does not cause filming on the sensitive material. And the seventh object of the present invention is to
To provide a magnetic toner that exhibits clear images without fogging.

[0011]

[Means for solving the problem] Therefore, the present inventors
As a result of intensive studies, we focused on the BET specific surface area of the magnetic powder, the residual magnetization of the magnetic powder, the residual magnetization of the magnetic toner, and the content of the magnetic powder with respect to the magnetic toner, and by specifying each range to a certain range, the above-mentioned The inventors have discovered that the object of the present invention can be achieved, and have completed the present invention. That is, the feature of the present invention is that in a magnetic toner comprising at least a binder resin and magnetic powder, the BET specific surface area of the magnetic powder is 3.
．． The residual magnetization of the magnetic powder is within a range of greater than 5 m2 /g and less than 6.0 m2 /g, and the residual magnetization of the magnetic powder is σr.
m, the residual magnetization of the magnetic toner is σrt, and the content of the magnetic powder with respect to the magnetic toner is W weight %, the magnetic toner satisfies the following: 4.2<σrt≦7 7≦σrm≦24 30≦W≦70.

The present invention will be explained in detail below. The magnetic toner of the present invention comprises at least a binder resin and magnetic powder. Any known magnetic powder can be used, but preferably, for example, metals such as iron, cobalt, nickel, alloys thereof, Fe3
Examples include metal oxides such as O4, γ-Fe2O3, cobalt-added iron oxide, various ferrites such as MnZn ferrite and NiZn ferrite, magnetite, and hematite. These magnetic powders can be manufactured by known methods. Further, in the present invention, the BET specific surface area of the magnetic powder is greater than 3.5 m2 /g, and is 6.0 m2 /g.
It is necessary to set it within the range of 3.8 m2 /g or less and 5.5 m2 /g or less, especially 4.0 m2 /g or more and 5.0 m2 /g or less. It is preferable. Specific surface area is 3.5m
If it is less than 6.0/g, dispersion into the binder resin will deteriorate, causing image quality defects such as blurring and trailing.
If it is larger than m2/g, the image will be easily scratched off by the MICR reader, making it impossible to recognize the symbol. The residual magnetization σrt range of the magnetic toner is 4.2 to 7 emu/
It must be set in the range of 4.5 to 6.5 g.
It is particularly preferable to set it within the range of emu/g. σrt
However, if it is less than 4.2 emu/g, the magnetization is weak and the symbol cannot be recognized accurately; conversely, if σrt is 7e
If it is larger than mu/g, the magnetization is too strong and it becomes impossible to accurately recognize the symbol. The residual magnetization σrm of the magnetic powder must be set to 7 to 24 emu/g, but the preferable range is 7 to 16 emu/g, and it is particularly preferable to set it to 8 to 14 emu/g. preferable. If σrm is smaller than 7 emu/g, the magnetization is weak and the symbol cannot be recognized accurately. Conversely, if σrm is larger than 24 emu/g, the magnetization is too large, and the influence of the dispersibility of the magnetic powder. , and I still can't recognize the symbols accurately. Furthermore, the content of the magnetic powder relative to the magnetic toner needs to be set within a range of 30 to 70% by weight. Among these, it is preferably set to 30 to 60% by weight, particularly 35 to 55% by weight. If the magnetic powder content is less than 30% by weight, it will be difficult to control the amount of charge, and especially in low temperature and low humidity environments, image density will decrease or uneven development will occur, making it impossible for a reader to read the symbol correctly. On the other hand, if the magnetic powder content is more than 70% by weight, the fixing properties of the magnetic toner deteriorate, and in MICR readers, the image may be rubbed off or
Magnetic powder peels off, making it impossible to accurately recognize symbols.

As the binder resin, any binder resin conventionally used for magnetic toners can be used. Examples include homopolymers or copolymers of one or more vinyl monomers. Typical vinyl monomers include styrene, p-chlorostyrene, vinylnaphthalene, ethylenically unsaturated monoolefins such as ethylene, propylene, butylene, and isobutylene, vinyl chloride, vinyl bromide, vinyl fluoride, and acetic acid. Vinyl, vinyl propionate, vinyl benzoate, vinyl butyrate, vinyl formate, vinyl stearate,
Vinyl esters such as vinyl caproate, such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, dodecyl acrylate, n-octyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, methyl- Ethylenic monocarboxylic acids and their esters such as α-chloroacrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, etc. Ethylenic monocarboxylic acid substitutes such as acrylonitrile, methacrylonitrile, acrylamide, etc., e.g. dimethyl maleate , ethylenic carboxylic acids and their esters such as diethyl maleate, dibutyl maleate, vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, methyl isopropenyl ketone,
For example, vinyl ethers such as vinyl methyl ether, vinyl isobutyl ether, vinyl ethyl ether, etc.
For example, vinylidene halides such as vinylidene chloride and vinylidene chlorfluoride, such as N-vinylpyrrole, N-vinylcarbazole, N-vinylindole,
Examples include N-vinyl compounds such as N-vinylpyrroline.

[0014] Furthermore, various substances can be added to the magnetic toner of the present invention for the purpose of charge control, electric resistance control, etc. For example, fluorine-based surfactants, chromium-based dyes such as chromium salicylate complexes, polymeric acids such as copolymers containing maleic acid as a monomer component, quaternary ammonium salts, azine-based dyes such as nigrosine, and carbon black. etc. can be added.

Furthermore, a mold release agent may be added to improve offset resistance. As the mold release agent, paraffin, polyolefin, etc. having 8 or more carbon atoms are preferable, and for example, paraffin wax, paraffin latex, microcrystalline wax, etc., or polypropylene, etc. can be used.

Furthermore, for the purpose of improving the durability, fluidity, or cleanability of the magnetic toner, fine inorganic powders such as silica, fine organic powders such as fatty acids or their derivatives and metal salts, fine fluororesin powders, etc. can also be added. Although conventionally known methods can be used for manufacturing the magnetic toner, a method using a pulverization method is particularly preferable. That is, this is a method in which a polymer, magnetic powder, colorant, etc. are melt-kneaded using a hot kneader, cooled, and then pulverized and classified to obtain a magnetic toner.

Next, a method for measuring the physical properties of magnetic toner will be described. The BET specific surface area is determined by an adsorption measurement method using N2 gas. In addition, the magnetic properties are V. S. Measurement was performed using the M method with an external magnetic field of 1 KOe. In addition, the particle size of the magnetic toner was measured using a particle size measuring machine TA-II manufactured by Coulter Counter Co., Ltd. with an aperture diameter of 100 μm.

[0018]

[Examples] The present invention will be explained below using Examples.
The present invention is not limited to these. Also,
The magnetic powders used in the Examples and Comparative Examples are those listed in Table 1.

[0019]

[Table 1]

Example 1 Styrene-n-butyl acrylate
48% by weight copolymer (polymerization ratio 72/28, Mw: 175000)
Magnetic powder A
50
Weight% Negative charge control agent

2% by weight of the above materials were mixed into powder using a Henschel mixer, and this was mixed into powder using a two-roll mill at a set temperature of 150°C.
The mixture was heated and kneaded for 5 minutes. After cooling the kneaded material, it was coarsely pulverized and finely pulverized, and then further classified to obtain a classified product having a 50% volume average particle diameter D5011.2 μm. To this, 0.6% by weight of hydrophobic colloidal silica was externally added using a Henschel mixer to obtain a magnetic toner. The residual magnetization σrt of the obtained toner was 5.2 emu/g. This magnetic toner was evaluated using a modified printer, XP-11 manufactured by Fuji Xerox, which was modified by increasing the hopper capacity. The evaluation method in the present invention is shown below. ■Durability: After 6,000 copies were continuously copied, image density, fogging, fine line reproducibility, image quality defects, etc. were evaluated. ■Environmental stability: The same test as in ■ was conducted under different environments: high temperature and high humidity, and low temperature and low humidity. ■ Rate of defective reading by MICR reader The obtained copy sample was passed through NCR675, MICR reader sorter, and the rate of defective reading at that time was determined. Reading was carried out repeatedly using 500 copy samples as one unit, up to 12 units. The results are shown in Table 2.

Example 2 Styrene-n-butyl acrylate
43% by weight copolymer (polymerization ratio 80/20, Mw: 25000)
Magnetic powder B
55% by weight Negative charge control agent
2
5% by weight of the above material by the same manufacturing method as in Example 1.
A classified product with a 0% volume average particle diameter D50 of 10.5 μm was obtained. 0.5% by weight of silica was externally added to this to obtain a magnetic toner. σrt was 5.8 emu/g. This magnetic toner was evaluated in the same manner as in Example 1. Table 2 shows the results.
Shown below.

Example 3 Isophthalic acid, terephthalic acid, ethyl
65% by weight lene glycol, 1,6-hexanediol,
Polyester resin made of trimellitic anhydride
(Mw: 16000) Magnetic powder C

A classified product having a 50% volume average particle diameter D50 of 12 μm was obtained using 35% by weight of the above material by the same manufacturing method as in Example 1. 0.7% by weight of silica was externally added to this to obtain a magnetic toner. σrt was 6.8 emu/g. This magnetic toner was evaluated in the same manner as in Example 1. Table 2 shows the results.
Shown below.

Comparative Example 1 A magnetic toner was prepared in the same manner as in Example 1, except that the magnetic powder in Example 1 was changed to magnetic powder D. The obtained magnetic toner had a 50% volume average particle diameter D50 of 10.6 μm. Moreover, σrt was 4.5 emu/g. This magnetic toner was evaluated in the same manner as in Example 1. The results are shown in Table 2.

Comparative Example 2 A magnetic toner was prepared in the same manner as in Example 1, except that the magnetic powder in Example 1 was changed to magnetic powder E. The obtained magnetic toner had a 50% volume average particle diameter D50 of 11.4 μm. Moreover, σrt was 2.8 emu/g. This magnetic toner was evaluated in the same manner as in Example 1. Table 2 shows the results.
Shown below.

Comparative Example 3 A magnetic toner was prepared in the same manner as in Example 1, except that the magnetic powder in Example 1 was changed to magnetic powder F. The obtained magnetic toner had a 50% volume average particle diameter D50 of 11.0 μm. Moreover, σrt was 2.2 emu/g. This magnetic toner was evaluated in the same manner as in Example 1. Table 2 shows the results.
Shown below.

[0026]

[Table 2]

[0027]

Effects of the Invention According to the magnetic toner of the present invention, (1) magnetic force is appropriate and magnetic read symbol recognition by MICR can be performed accurately. (2) It is difficult to capture an image even when the magnetic head rubs against the magnetic head during magnetic reading. (3) Excellent durability and stability. (4) Good environmental stability. (5) There is no image quality defect such as blur or trailing. (6) There is little abrasion of the photosensitive material and there is no filming on the photosensitive material. (7) Various effects can be obtained, such as a clear image without fog. Therefore, the magnetic toner of the present invention is extremely useful as a magnetic toner in a one-component magnetic toner development system.

Claims (1)

[Claims] 1. A magnetic toner comprising at least a binder resin and a magnetic fine powder, wherein the BET specific surface area of the magnetic powder is greater than 3.5 m2 /g and 6.0 m2 /g.
In addition, when the residual magnetization of the magnetic fine powder is σrm, the residual magnetization of the toner is σrt, and the content of the magnetic fine powder with respect to the toner is W% by weight, 4.2<σrt≦ 7 A magnetic toner characterized in that 7≦σrm≦24 30≦W≦70.