JP2002241133A - Water-soluble magnetic material-dispersed body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new water-soluble magnetic material-dispersed body with which such magnetic information can be printed by using a general purpose ink jet printer as it is without any modification as can be read by a magnetic head, and which has excellent dispersion stability of a magnetic material particle and hardly causes clogging of a nozzle. SOLUTION: The substantially spherical magnetic material particle consisting of the ferrite represented by the formula (1): MO.Fe2O3 (wherein M is a bivalent metal ion) and a salt of a fatty acid as a stabilizer is dispersed in a water-soluble dispersion medium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aqueous magnetic dispersion suitable for use in magnetic inks for ink jet recording.

[0002]

2. Description of the Related Art Conventionally, information recorded in characters, bar codes, and other patterns is read by a magnetic head, so-called magnetic image character recognition [Magnetic Ink Character Recognition].
gnition (MICR)] system is widespread. When recording magnetic information in such a system, it is common to use a magnetic ink ribbon and a dot impact printer. However, there is a problem that a dot impact printer generates a large amount of noise, and a magnetic ink ribbon has a low ink utilization rate, so that the printing cost is high.

Therefore, it has been studied to record magnetic information using an ink-jet printer which has low noise and can print at a required amount by using a required amount of ink so that the printing cost can be kept low. . And, development of an aqueous magnetic ink suitable for it is being conducted.

[0004]

As a method for producing a magnetic ink, a general method for producing a pigment ink in which dry particles of a magnetic material as a main raw material are added to and dispersed in an aqueous dispersion medium is described. It is conceivable to adopt it as is. However, this manufacturing method has a problem that it is not easy to stably disperse particles such as γ · Fe ₂ O ₃ and chromium dioxide generally used as a magnetic material.

In order to improve the dispersion stability of the magnetic particles, it has been considered to add various dispersion stabilizers such as a water-soluble polymer to the aqueous dispersion medium. If sufficient properties are to be ensured, the solid content concentration will inevitably increase. Then, it becomes difficult to suppress the viscosity of the magnetic ink to a low viscosity suitable for use in an ink jet printer, and there is a new problem that clogging or the like of a nozzle is likely to occur.

As a countermeasure, it has been proposed to use an aqueous suspension of magnetic particles synthesized by an aqueous reaction that does not include a drying step to produce an aqueous magnetic dispersion used for magnetic ink and the like ( For example, JP-A-2000-212
498). In other words, a water-soluble compound containing a metal element that is a source of magnetic particles is chemically reacted in a solution with the aqueous dispersion medium to directly generate the magnetic particles in the dispersion medium to form an aqueous suspension. A method has been proposed in which a liquid is synthesized and an aqueous magnetic dispersion is produced using the aqueous suspension.

Most of the magnetic particles in such an aqueous suspension are dispersed in an aqueous dispersion medium in the form of primary particles,
Moreover, since the surface of each particle is hydrophilic, it is considered that the dispersion stability in the magnetic ink is improved. However, magnetic particles synthesized by an aqueous reaction are usually amorphous and cannot be used for magnetic recording due to lack of coercive force. Therefore, the above publication proposes that the magnetic particles be crystalline and have a coercive force.

However, even in the case of the magnetic particles described in the above-mentioned publication, the degree of crystallinity is small or the crystal anisotropy is large as compared with the magnetic particles produced by a normal production method other than the aqueous reaction. Therefore, the residual magnetization and the coercive force are insufficient. Therefore, in the above publication, in order to obtain a print that can be read by a magnetic head, a magnetic field is applied when printing a character or pattern using an ink jet printer, so that the magnetic particles are oriented on the print pattern. Propose that.

However, in order to carry out this method, it is necessary to modify the ink jet printer by adding a device for applying a magnetic field or to newly develop an ink jet printer to which such a device is added.
Therefore, the invention described in the above publication cannot sufficiently achieve the purpose of recording magnetic information at a lower cost than before using a general-purpose inkjet printer as it is. An object of the present invention is to use a general-purpose ink-jet printer as it is without modification, to print magnetic information that can be read sufficiently by a magnetic head, to have excellent dispersion stability of magnetic particles, and to use a nozzle. An object of the present invention is to provide a novel aqueous magnetic dispersion which is less likely to cause clogging and the like.

[0010]

Means for Solving the Problems and Effects of the Invention In order to solve the above-mentioned problems, the present inventors have developed a general method of adding and dispersing dry particles of a magnetic material in an aqueous dispersion medium. In order to improve the dispersion stability of the magnetic particles in the manufactured aqueous magnetic dispersion, each component constituting the dispersion was examined. As a result, regarding the magnetic particles, (a) the particles such as γ-Fe ₂ O ₃ and chromium dioxide described above are acicular, so that the dispersibility in the aqueous dispersion medium is poor, (b) Due to the above shape, clogging in the nozzle is likely to occur. (C) As long as dispersion is performed for a long time to improve dispersibility, needle-like particles are destroyed, resulting in a decrease in residual magnetization and coercive force. It has been found that it becomes impossible to print magnetic information that can be read by a computer.

As for the dispersion stabilizer, when a water-soluble polymer is used, the viscosity of the dispersion increases as described above. As a result, particularly, the ink is heated by a heater provided in the printer head to generate fine bubbles. As a result, when used in a bubble jet (registered trademark) type ink jet printer that discharges a certain amount of ink from a nozzle,
(d) Since bubbles generated due to ink ejection are difficult to disappear, it affects the next ink ejection. (e) If bubbles do not disappear, solidification of the polymer in the thin film part forming the bubbles As a result, the density of the ink was changed due to the occurrence of clogging.As a result, it became clear that clogging in the nozzle was likely to occur, and that (f) the polymer was burned on the surface of the heater, causing so-called kogation. .

Therefore, as a result of further investigation, it was found that the magnetic particles consisted of ferrite represented by the formula (1): MO.Fe ₂ O ₃ (1) (wherein M represents a divalent metal ion). It has been found that the use of magnetic particles that are spherical in nature (hereinafter referred to as "spherical ferrite particles") can solve all of the above-mentioned problems (a) to (c) which have been problems in conventional needle-like particles. did.

That is, since the spherical ferrite particles are substantially spherical, (A) the dispersibility in the aqueous dispersion medium is good, (B) clogging at the nozzle hardly occurs, and (C)
It was found that even if the dispersion was performed for a long time to improve the dispersibility, the shape was hardly changed, and the initial residual magnetization and the coercive force could be maintained. As a result, magnetic information readable by the magnetic head could be printed.

[0014] The "substantially spherical" here means "
A transmission electron micrograph of the magnetic particles was taken, and an image of a predetermined number of sample particles arbitrarily extracted therefrom was actually measured. The ratio h1 / h2 of the major axis h1 and the minor axis h2 of each sample particle, The average value of all sample particles is in the range of 1/1 to 3/1 (preferably 1/1 to 2 /
(Within 1 range). Substantially spherical particles according to the above definition may include spherical particles, spheroids, polyhedrons, irregular particles, and the like.

The present inventors have studied the dispersion stabilizers to be combined with the spherical ferrite particles, mainly on surfactants which do not cause the above-mentioned problems because of their smaller molecular weight than water-soluble polymers. As a result, the inventors have found that the soap fatty acid salt has the best dispersibility with spherical ferrite particles, and have completed the present invention. That is, the aqueous magnetic dispersion of the present invention comprises a ferrite represented by the formula (1): MO.Fe ₂ O ₃ (1) [wherein M represents a divalent metal ion], and is substantially spherical. It is characterized by containing certain magnetic particles (spherical ferrite particles), a fatty acid salt as a dispersion stabilizer, and an aqueous dispersion medium.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below. (Spherical ferrite particles) As spherical ferrite particles,
As described above, ferrite represented by the formula (1): MO.Fe ₂ O ₃ (1) (wherein M represents a divalent metal ion), and a substantially spherical ferrite is used. .
As the spherical ferrite particles, (I) the particle size of the primary particles is sufficiently smaller than the recording wavelength, and the particle size distribution is sharp (in consideration of the suitability of the inkjet ink, The preferred range of the particle size is preferably about 0.01 to 0.2 μm as a number average particle size (if the particle size is smaller than this range, it will be difficult to maintain the coercive force). Magnetic force is 1000O suitable for magnetic recording
e (the preferred range of the coercive force is 100 to 100
(0 Oe), (III) no sintering between particles, (IV)
Magnetic properties do not fluctuate depending on temperature and time,
(V) The residual magnetization is 0.3 emu / g or more (in order to reduce the solid content and facilitate the viscosity reduction of the ink, the larger the residual magnetization, the better). Are preferred.

The spherical ferrite particles satisfying these conditions and having a substantially spherical shape include those represented by the formula (1-1): CoO.Fe ₂ O ₃ (1- Spherical particles of cobalt ferrite represented by 1) (spherical cobalt ferrite particles) are preferably used. (Fatty acid salt) Examples of the fatty acid salt as a dispersion stabilizer include sodium laurate, sodium stearate, sodium oleate and the like, with sodium oleate being particularly preferred.

The spherical ferrite particles and the fatty acid salt are preferably blended in a weight ratio of 2.5: 1 to 5: 1. If the amount of the fatty acid salt is less than this range, the dispersion stability of the spherical ferrite particles may decrease. Conversely, if the amount of the fatty acid salt is larger than this range, the viscosity of the aqueous magnetic dispersion may increase, or excessive fatty acid salt may be precipitated, which may easily cause clogging at the nozzle. (Aqueous dispersion medium) As the aqueous dispersion medium, water is suitably used, and a mixed solvent of water and a water-soluble organic solvent can also be used.

Examples of the water-soluble organic solvent include monohydric alcohols having about 1 to 4 carbon atoms such as methanol and ethanol; ethylene glycol ethers such as ethylene glycol monobutyl ether and diethylene glycol monoethyl ether; propylene glycol and diethylene glycol , Glycerin and the like; and dihydric and trihydric alcohols;

(Aqueous Magnetic Dispersion) When the aqueous magnetic dispersion is used as a magnetic ink for an ink jet printer, the viscosity at the operating temperature of the ink jet printer is preferably 5 mPa · S or less, and preferably 3 mPa · S or less.
It is preferably S or less. If the viscosity is higher than this range, there is a possibility that clogging or the like in the nozzle may easily occur. In order to adjust the viscosity to the above range, the solid content concentration in the aqueous magnetic dispersion may be adjusted. The lower limit of the viscosity is preferably 1.0 mPa · S, which is the viscosity of water. As the viscosity is closer to this value, clogging is less likely to occur.

The dispersed particle diameter of the spherical ferrite particles in the magnetic ink is preferably not more than 0.2 μm in terms of number average particle diameter. If the dispersion particle size is larger than this range, the dispersion stability is reduced, and not only is clogging of the nozzle likely to occur, but also the ejection stability may be reduced. The dispersed particle size can be adjusted not only by the primary particle size of the spherical ferrite particles, but also by the degree of secondary particle generation due to the aggregation of the spherical ferrite particles. In other words, the smaller the degree of generation of secondary particles,
The dispersed particle size can be reduced. Therefore, it is preferable to increase the mixing ratio of the fatty acid salt or lengthen the dispersion time to minimize the degree of secondary particle generation.

The magnetic ink is used to prevent corrosion of the head and maintain the dispersion stability of the spherical ferrite particles.
The pH is preferably from 6 to 10, and particularly preferably from 7 to 9. To adjust the pH within the above range, a pH adjuster may be added to the magnetic ink. pH
Examples of the regulator include organic amines such as diethanolamine and triethanolamine, and hydroxides of alkali metals such as sodium hydroxide and potassium hydroxide.

Further, various kinds of conventionally known additives, such as a fungicide, a surface tension adjusting agent, and the like, may be added to the magnetic ink in an appropriate amount as long as the effects of the present invention are not impaired. The magnetic ink is used in an on-off method such as the bubble jet method described above or the Mach jet method in which a fixed amount of ink is ejected from a nozzle by utilizing deformation of a piezo element.
It can be particularly suitably used for a demand type ink jet printer. In addition, the present invention can be used for a continuous-type ink jet printer that performs printing by forming ink droplets while circulating ink. In any of these cases, it is possible to print magnetic information that can be sufficiently read by a magnetic head by using a general-purpose inkjet printer without modification or the like.

The use of the aqueous magnetic dispersion of the present invention is not limited to magnetic inks, and it can be used, for example, in aqueous inks and paints for ordinary printing by utilizing good dispersion stability. .

[0025]

The present invention will be described below with reference to examples and comparative examples. The cobalt ferrite particles used in Examples 1 to 5 and Comparative Example 1 [average particle diameter of primary particles: 0.015
μm, FCO-2] manufactured by Sakai Chemical Industry Co., Ltd.
When evaluated by the evaluation method (the number of samples is 10) from the image of the transmission electron micrograph described above, the average value of the ratio h1 / h2 of the major axis to the minor axis is 1.3 / 1, which is substantially It was confirmed that the particles were spherical spherical cobalt ferrite particles (FIG. 1).

On the other hand, the γ · Fe ₂ O ₃ used in Comparative Examples 2 and ₃
The particles (average length of primary particles: 0.4 μm) are needle-shaped particles as shown in FIG. 2, and the average value of the ratio h1 / h2 of the major axis to the minor axis determined in the same manner as described above is 6. 2/1.
Further, it was also found that the γ · Fe ₂ O ₃ particles had large variations in length of individual particles. Example 1 An aqueous solution was prepared by dissolving 1.0 g of sodium oleate in 19.0 g of pure water.

Next, 20.0 g of this aqueous solution and spherical cobalt ferrite particles [FCO-2 manufactured by Sakai Chemical Industry Co., Ltd.]
5.0 g together with 30.0 g of zirconia beads were placed in a 37-ml glass bottle. Then, the contents of the glass bottle are removed using a paint shaker.
The mixture was dispersed and mixed for 20 minutes to produce a magnetic ink as an aqueous magnetic dispersion. The blending ratio (weight ratio) of the spherical cobalt ferrite particles and sodium oleate was 5: 1.

Examples 2 to 5 The amounts of sodium oleate and pure water were adjusted as shown in Table 1, and the mixing ratio (weight ratio) of the spherical cobalt ferrite particles and sodium oleate was 6.25: 1 ( Example 2) A magnetic ink was prepared in the same manner as in Example 1 except that 3.125: 1 (Example 3), 2.5: 1 (Example 4) or 2: 1 (Example 5) were used. Manufactured.

Comparative Example 1 A magnetic ink was prepared in the same manner as in Example 1 except that 0.1 g of condensed ammonium naphthalenesulfonate [Roma PWA-40 manufactured by San Nopco Co., Ltd.] was used instead of sodium oleate. Manufactured. Comparative Example 2 The same amount of needle-like γ instead of spherical cobalt ferrite particles
A magnetic ink was produced in the same manner as in Example 3 except that Fe ₂ O ₃ particles were used.

Comparative Example 3 A magnetic ink was produced in the same manner as in Comparative Example 2, except that the dispersion mixing time using a paint shaker was 15 minutes. The following tests were performed on the magnetic inks of the above Examples and Comparative Examples, and the characteristics were evaluated. Dispersion Stability Test Immediately after production, the magnetic ink was centrifuged [FORCE manufactured by Denver Instrument
7], the mixture was centrifuged at 6,000 rpm for 10 minutes, and the state was visually observed. The dispersion stability was evaluated according to the following criteria.

：: No separation of magnetic particles. Extremely good dispersion stability. Δ: Magnetic particles are slightly separated. However, practical level. ×: The magnetic particles were completely separated and settled. Poor dispersion stability. Viscosity measurement The viscosity of the magnetic ink is measured with a viscometer [RE1 manufactured by Toki Sangyo Co., Ltd.
15L viscometer]. Conditions are measurement temperature 2
The temperature was 5 ° C. and the number of revolutions was 60 rpm.

Measurement of dispersed particle size of magnetic particles The dispersed particle size (number average particle size) of the magnetic particles in the magnetic ink is measured using a particle size analyzer [Microtrac UPA150 manufactured by NIKKISO CO., LTD.]. did. Actual machine test (Reading test) Filling the magnetic cartridge with the ink cartridge of a bubble jet type ink jet printer [Deskjet 895Cxi manufactured by Hewlett-Packard Japan Co., Ltd.], and printing E13B characters on plain paper with the ink jet printer attached did. And this character, Atlantic Zeiser (AtlanticZe
iser) using a magnetic reader MINI-QUEST.

：: Readable. ×: Unreadable. (Clogging test) After printing a certain amount of characters using the above-mentioned inkjet printer, take out the ink cartridge, and without capping the nozzle part,
After being left for 7 days at a temperature of 40 ° C. and a relative humidity of 25%, it was mounted on the ink jet printer again. And
Each time the cleaning operation for eliminating clogging is performed once, the above-mentioned reading test is performed, and the number of times of cleaning required until the result becomes ○ (readable) is recorded.
The difficulty of clogging in the nozzle was evaluated according to the following criteria.

○: Reading was possible (○) after 1 to 5 cleanings. Less likely to cause clogging. Δ: Reading was possible (○) after 6 to 10 cleanings. Slightly clogged. ×: Reading is possible unless cleaning is performed 11 times or more (O)
Did not become. Prone to clogging.

Table 1 shows the above results.

[0036]

[Table 1]

From the table, it was found that the magnetic ink of Comparative Example 1 using a dispersion stabilizer other than the fatty acid salt had poor dispersion stability. Therefore, no other tests were performed. Further, printing with the magnetic ink of Comparative Example 2 using needle-like γ · Fe ₂ O ₃ particles could not be read by a magnetic reader. Then, when the state of the particles was observed with a microscope, it was confirmed that the particles, which should have been acicular, were broken.

Further, it was found that the magnetic ink of Comparative Example 3 in which the dispersion time was shortened in order to prevent the destruction of the acicular particles had poor dispersion stability. For this reason, other tests were not performed, but it was predicted that even if the dispersion stability was cleared, clogging in the nozzle was likely to occur, which was not practical. On the other hand, it was found that the magnetic ink of each example using spherical cobalt ferrite particles and sodium oleate as a fatty acid salt had good dispersion stability. Further, it was also confirmed that the printing with the magnetic ink of each of the examples can be read by a magnetic reading device, and that clogging at the nozzle hardly occurs.

Further, comparing the examples, the magnetic ink of Example 2 in which the blending ratio of the spherical cobalt ferrite particles and sodium oleate deviated to the side where the amount of sodium oleate was smaller than 5: 1 was practically used. It was found that the dispersion stability of the spherical cobalt ferrite particles was slightly low, though it was within a range that would be acceptable. On the other hand, the magnetic ink of Example 5 in which the mixing ratio of the above two was out of the range where the amount of sodium oleate was larger than 2.5: 1 was also practically
It was found that the viscosity was slightly increased, though it was within a range (5 mPa · S or less) that would be acceptable.

On the other hand, the compounding ratio of the spherical cobalt ferrite particles and sodium oleate was 2.5: 1 to 1
All of the magnetic inks of Examples 1 to 3 in the range of 5: 1 have extremely good dispersion stability of the spherical cobalt ferrite particles and have a viscosity of 3 mPa · S or less, which is a more preferable range. It was confirmed that it was clear.

[Brief description of the drawings]

FIG. 1 is a transmission electron micrograph showing the state of spherical cobalt ferrite particles used in Examples.

FIG. 2 is a transmission electron micrograph showing a particle state of acicular γ · Fe ₂ O ₃ particles used in a comparative example.

Claims (4)

[Claims] 1. A magnetic particle comprising ferrite represented by the following formula (1): MO.Fe ₂ O ₃ (1) wherein M represents a divalent metal ion, and substantially spherical. An aqueous magnetic dispersion comprising: a fatty acid salt as a dispersion stabilizer; and an aqueous dispersion medium. 2. The aqueous magnetic dispersion according to claim 1, wherein the ferrite is cobalt ferrite. 3. The aqueous magnetic dispersion according to claim 1, wherein the fatty acid salt is sodium oleate. 4. The method according to claim 1, wherein the weight ratio of the magnetic particles to the fatty acid salt is 2.
The aqueous magnetic dispersion according to claim 1, which is blended at a ratio of 5: 1 to 5: 1.