JPH0766887B2 - Thermosetting magnetic fluid - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a thermosetting magnetic fluid that can be suitably used for visualization of a recording pattern on a magnetic disk, a magneto-optical disk, magnetic flaw detection, or the like.

[Conventional technology]

For example, a magnetic fluid is used as a conventional medium for magnetic flaw detection. This is used by coating on the surface of the subject when inspecting the presence or absence of defects in the subject formed of a magnetic material.

When microscopic scratches or foreign matter are present on the surface of the subject or in an extremely shallow place, it is difficult to detect it by simple microscopic examination. However, when a magnetic field is formed in the subject, the magnetic flux leaks at a defective portion of the subject and becomes a non-uniform magnetic field. Then, when magnetic fluid is applied, the applied magnetic fluid is attracted to the leakage magnetic flux portion and rises due to the action force of the non-uniform magnetic field, and shows a pattern different from other portions. The sensitivity is improved as the ferromagnetic fine particles in the magnetic fluid are atomized,
It is known that the accuracy of magnetic flaw detection is improved. However, when the particle size is from submicron to several tens of angstroms, it is not possible to directly observe the particles with a microscope that is usually used, but the above-mentioned magnetic fluid swelling part has a different light reflection state from other parts, so defects The presence of can be clearly observed.

[Problems to be solved by the invention]

However, the magnetic fluid used for the conventional magnetic flaw detection is literally a fluid, and is merely constrained by the leakage magnetic flux of the defective portion, so that the magnetic field of the subject flows at the same time as it flows, and the swelling also disappears. Therefore, when the subject is removed from the magnetic field, the defective portion becomes unclear.

The present invention has been made in view of such conventional problems, and it is possible to fix the magnetic fluid pattern formed according to the pattern of the magnetic flux of the subject and hold it outside the magnetic field. It is intended to provide a magnetic fluid.

[Means for solving problems]

The present invention which achieves the above-mentioned object is a thermosetting magnetic fluid in which a thermosetting resin is mixed and dissolved in a magnetic fluid obtained by dispersing ferromagnetic fine particles having a surfactant adsorbed in a dispersion medium. is there.

Hereinafter, the thermosetting magnetic fluid of the present invention will be described in detail.

Since the dispersion medium of the ferromagnetic fine particles of the present invention is unnecessary after being applied to the subject, it is desirable that the vapor pressure at room temperature is 400 mmHg or less, such as an organic solvent or water that is relatively easily evaporated. The reason for this is that if this value is exceeded, the evaporation rate will be too high, and it will not be possible to apply it uniformly to the subject.

Examples of organic solvents satisfying the conditions include hydrocarbons such as n-pentane, cyclohexane, petroleum ether, petroleum benzine, benzene, xylene, and toluene, halogenated hydrocarbons such as chlorobenzene, dichlorobenzene, and brombenzene, and Alcohols such as methanol, ethanol, n-propanol, n-butanol, isobutanol and benzyl alcohol, and diethyl ether,
Examples include ethers such as diisopropyl ether, aldehydes such as furfural, ketones such as acetone and ethyl methyl ketone, and fatty acids and their derivatives such as acetic acid and acetic anhydride, phenols, fluorocarbons, and silicon.

As the surfactant for stably dispersing the ferromagnetic fine particles in the dispersion medium as described above, for example, C00H group, SO ₃ H group,
It has one or more polar groups such as PO ₃ H groups and has the general formula R—X (R
Is a hydrocarbon group, a fluorocarbon group, a silicon group, X is the unsaturated fatty acid represented by the above polar group) or its salt as a main component, and other known hydrocarbon compounds may be selected.

Further, the surfactant may be selected from compounds represented by the general formula RY (R is a hydrocarbon group and Y is a coupling bond group) such as a silane coupling agent and a titanium coupling agent. In this case, the binding force with the ferromagnetic fine particles is stronger than that of the above-mentioned unsaturated fatty acid surfactant, and a more stable dispersion state can be obtained.

The above-mentioned surfactant, while considering the affinity with the dispersion medium,
Used alone or in combination. That is, when the dispersion medium is water, first of all, an RX type, for example, petroleum sulfonic acid is first used.
When added as a surfactant, the ferromagnetic fine particles are bonded to the polar group X to form a monomolecular layer with the hydrophobic group R facing outward. Then, an R-X type oleic acid, for example, is also added as a second surfactant to form a bimolecular layer by superposing it on the monomolecular layer of the first surfactant. A stable colloidal aqueous solution is obtained by covering the surface of the ferromagnetic fine particles.

When the dispersion medium is an organic solvent, an RX-type or RY-type surfactant is used alone, or an RY-type surfactant is added as a first surfactant, and then Second
Of R-X type is added as a surfactant.

Magnetite colloid obtained by a known wet method can be used as the ferromagnetic fine particles of the present invention. Further, it may be obtained by a so-called wet pulverization method in which magnetite powder is pulverized in water by a ball mill.

Further, it is also possible to use a ferromagnetic oxide such as manganese ferrite, cobalt ferrite other than magnetite, a composite ferrite of these and zinc or nickel, barium ferrite, or a ferromagnetic metal such as iron, cobalt, or a rare earth.

The particle size of the ferromagnetic fine particles of the present invention may be in the range of 0.1 μm to 20 Å used for general magnetic fluids. However, the smaller the particle size of the ferromagnetic fine particles, the higher the accuracy of the magnetic flaw detection and the inspection of the magnetic recording pattern. Therefore, it is preferable to use fine particles as necessary.

The content of the ferromagnetic fine particles of the present invention may be in the range of 1 to 30% by volume ratio that is conventionally generally used, but by using an intermediate medium described later, a higher concentration can be obtained. It is also very easy to do.

When the magnetic fluid is used for magnetic flaw detection, magnetic pattern inspection, or the like, the finer and higher the concentration of the dispersed ferromagnetic fine particles, the more accurate the inspection can be performed. However, in general, the higher the concentration of the ferromagnetic fine particles, the smaller the distance between the particles and the more likely they are to agglomerate.

Therefore, when the magnetic fluid of the present invention requires a particularly high concentration, the first surfactant and a low boiling point solvent such as hexane are added to the ferromagnetic fine particles, and the surface is treated with the surfactant. It is preferable to manufacture it through a step of obtaining an intermediate medium in which the coated ferromagnetic fine particles are dispersed in a low boiling point solvent. If the intermediate medium is placed in, for example, a centrifuge, the poorly dispersible particles therein can be easily separated because the solvent has a low viscosity. Next, by adding the intermediate medium to the dispersion medium to form a mixture and then heating the mixture, the low boiling point solvent is easily evaporated, and a magnetic fluid in which magnetic particles are dispersed can be obtained very stably.

In this step, after separating the particles having poor dispersibility from the intermediate medium, the intermediate medium is heated to evaporate the low boiling point solvent into powder of ferromagnetic fine particles, and then the dispersion medium is added to this powder. Good.

If the magnetic fluid thus obtained is further added with an intermediate medium to evaporate and concentrate the low boiling point solvent, the concentration is extremely high and only fine particles are stably dispersed. A magnetic fluid is obtained.

The thermosetting resin added to the magnetic fluid can be selected from the group of the following synthetic resins in consideration of compatibility with the dispersion medium constituting the magnetic fluid.

Unsaturated polyester resin Orthophthalic acid type, isophthalic acid type, bisphenol type, alicyclic unsaturated fatty acid type, acrylic acid ester type, etc.

Epoxy resin For example, phenolic glycidyl ether type (main materials: bisphenol A, phenol novolac, O-cresol novolac, etc.).

Alcohol-based glycidyl ether type (main materials: polypropylene glycol, hydrogenated bisphenol A).

Glycidyl ester type (main raw material: hexahydrophthalic anhydride, dimer acid).

Glycidylamine type (main ingredients: diaminodiphenylmethane, isocyanuric acid, hydantoin).

Mixed type (main materials: p-aminophenol, p-oxybenzoic acid).

Phenolic resin Urea resin Melamine resin Diallyl phthalate resin Silicone resin Fluorine resin [Function] When the thermosetting magnetic fluid of the present invention is used for, for example, magnetic flaw detection or inspection of a magnetic recording pattern, first, the surface of the subject on which a magnetic field is formed Apply it to. Then, the magnetic fluid is attracted according to the magnetic flux pattern formed by the defective portion of the subject or the magnetic recording, and the magnetic fluid distribution pattern corresponding to the magnetic flux pattern is formed. Then, the thermosetting resin dissolved and contained in the magnetic fluid is cured by heating it in that state by blowing hot air or the like. This allows the magnetic fluid pattern to be fixed.

A specific example of the thermosetting magnetic fluid will be described below along with its manufacturing process.

Example 1 First, 6N NaOHaq was added to an aqueous solution 1 containing 1 mol each of ferrous sulfate and ferric sulfate to adjust the pH to 11 or more, and then 60 ° C.
Aged for 30 minutes to obtain a magnetite colloid (wet method). Thereafter, while maintaining the temperature at 60 ° C., 3N HCl is added to this magnetite slurry to adjust the pH to a value between 2 and 3. 70 g of sodium petroleum sulfonate is added to this magnetite slurry as a first surfactant for stably dispersing colloidal particles, and the mixture is stirred for 30 minutes.

Let it stand, and once the magnetite particles aggregate and settle,
The operation of removing the supernatant, pouring water and further washing with water is repeated several times to remove the electrolyte. After washing with water, transfer the solution to a separating funnel. Next, hexane as a low boiling point solvent is added to the liquid in the funnel, shaken sufficiently, and then allowed to stand to separate water and hexane.

As a result, the magnetite particles migrate into hexane,
An intermediate medium is obtained in which ferromagnetic fine particles whose surface is coated with a surfactant are dispersed in a low boiling point solvent. Next, this intermediate liquid medium was centrifuged at 8000 G for 20 minutes to separate large magnetite particles by sedimentation. The particle size of the ferromagnetic fine particles remaining in the supernatant was 100 to 150Å.

As described above, once a low-viscosity intermediate medium is formed and subjected to centrifugation, it is possible to arbitrarily adjust the particle size distribution of the ferromagnetic fine particles, and particularly there is an advantage that the concentration of fine particles can be increased.

Then, the supernatant was taken out, transferred to a rotary evaporator, and kept at 90 ° C. to remove hexane by evaporation.

1 g of the powdery magnetite fine particles thus obtained was dispersed in 10 g of normal butanol, and 0.45 g of isostearic acid was further added and dissolved as a second surfactant. An equal volume of thermosetting resin (Tamura Seisakusho, SR34G) was added to this solution and mixed by stirring.

Thus, magnetite, which is a fine particle of strong substance, is added to a mixed solution of a normal butanol solution of an organic solvent and a thermosetting resin.
A thermosetting magnetic fluid was obtained which was extremely stably dispersed through the first and second surfactants.

[Example 2] First, a slurry of magnetite colloid was obtained by a wet method similarly to Example 1.

Then, a silane coupling agent (TSC-8185 manufactured by Toshiba Silicone Co., Ltd.) as a first surfactant was added to the slurry.
Is added to the mixture and stirred for 30 minutes.

Thereafter, the same treatment as in Example 1 was carried out, the ferromagnetic fine particles having the surface coated with the first surfactant were passed through an intermediate medium in which a low boiling point solvent was dispersed, and then a normal butanol liquid as a dispersion medium and a heat A thermosetting magnetic fluid was obtained in which the magnetite, which is a fine particle of a strong substance, was extremely stably dispersed in the mixed liquid with the curable resin via the first and second surfactants.

Example 3 First, 6N NaOHaq was added to an aqueous solution 1 containing 1 mol each of ferrous sulfate and ferric sulfate to adjust the pH to 11 or more, and then 60 ° C.
Aged for 30 minutes to obtain a magnetite colloid (wet method). Thereafter, while maintaining the temperature at 60 ° C., 3N HCl is added to this magnetite slurry to adjust the pH to a value between 2 and 3. 70 g of sodium petroleum sulfonate is added to this magnetite slurry as a first surfactant for stably dispersing colloidal particles, and the mixture is stirred for 30 minutes.

Let it stand, and once the magnetite particles aggregate and settle,
The operation of removing the supernatant, pouring water and further washing with water is repeated several times to remove the electrolyte. After washing with water, transfer the solution to a separating funnel. Next, hexane as a low boiling point solvent is added to the liquid in the funnel, shaken sufficiently, and then allowed to stand to separate water and hexane.

As a result, the magnetite particles migrate into hexane,
An intermediate medium is obtained in which ferromagnetic fine particles whose surface is coated with a surfactant are dispersed in a low boiling point solvent. Next, this intermediate liquid medium was centrifuged at 8000 G for 20 minutes to separate large magnetite particles by sedimentation. The particle size of the ferromagnetic fine particles remaining in the supernatant was 100 to 150Å.

As described above, once a low-viscosity intermediate medium is formed and subjected to centrifugation, it is possible to arbitrarily adjust the particle size distribution of the ferromagnetic fine particles, and particularly there is an advantage that the concentration of fine particles can be increased.

Then, the supernatant was taken out, transferred to a rotary evaporator, and kept at 90 ° C. to remove hexane by evaporation.

1 g of the powdery magnetite fine particles thus obtained and 10 ml of an aqueous solution prepared by adding 0.45 g of sodium oleate as a second surfactant are mixed and stirred to disperse the magnetite in the aqueous solution. To this dispersion, 14.7 ml of an aqueous solution containing an alkyd resin (S-695 manufactured by Dainippon Ink and Chemicals, Inc.) was added and dispersed by stirring.

This solution was centrifuged at 8000 G for 20 minutes to remove impurities and prepare a thermosetting magnetic fluid.

Example 4 First, in the same manner as in Example 3, an intermediate medium in which ferromagnetic fine particles whose surface was coated with a surfactant were dispersed in a low boiling point solvent was obtained, and this intermediate medium solution was subjected to a centrifugal force of 8000G. Centrifuge for 20 minutes to settle large magnetite particles,
The supernatant is taken out, transferred to an evaporator and kept at 90 ° C. to remove hexane by evaporation.

1 g of the powdery magnetite fine particles thus obtained is taken and dissolved in a mixed solvent of 15 ml of toluene and 30 ml of hexane and dispersed. To this solution, 15 ml of a toluene melt of a silicone thermosetting resin (KS-841 manufactured by Shin-Etsu Chemical Co., Ltd.) is added and stirred. This was centrifuged at 8000 G for 20 minutes to remove impurities and prepare a thermosetting magnetic fluid.

[Example 5] A magnetic flaw detection test was conducted on steel materials using the thermosetting magnetic fluids obtained in Examples 1 and 2.

As a subject, as schematically shown in FIG. 1, under the surface,
A steel material 2 having a known internal defect 1 having a length of 1 mm and a width of 10 μm was used at a position of several μm.

The subject 2 was previously placed in a magnetic field of an applied magnetic field of 13 K Gauss, and the surface thereof was brush-coated with the thermosetting magnetic fluid 3. Then, due to the action of the leakage magnetic flux 4 generated in the vicinity of the internal defect 1 in the subject 2, the ferromagnetic fine particles are locally concentrated, and the thermosetting magnetic fluid 3 becomes the internal defect 1 as shown in the figure. As a result, the phenomenon of excitement was recognized.

This swelling phenomenon disappeared when the subject 2 was taken out of the magnetic field, and was recognized again when returned to the magnetic field.

Next, the thermosetting magnetic fluid 3 showing a rising state
On the other hand, when hot air having a temperature of about 70 ° C. was blown, the thermosetting magnetic fluid 3 was hardened in about 1 minute, and the state showing the internal defect 1 could be fixed as it was.

By peeling the coating film of the cured thermosetting magnetic fluid 3 from the subject and observing it with a microscope, it was possible to accurately inspect the internal defect state showing a needle-shaped shadow.

〔The invention's effect〕

In the present invention, the thermosetting resin is mixed and dissolved in the magnetic fluid used for the inspection of defects and magnetic recording patterns of the magnetic subject. Therefore, it becomes possible to fix the pattern of the magnetic fluid formed according to the change of the magnetic flux of the subject and hold it outside the magnetic field, which makes a great progress in fields such as magnetic flaw detection and micro inspection of magnetic recording media. be able to.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining the operation of one embodiment of the present invention. 1 is an internal defect, 2 is an object, 3 is a photocurable magnetic fluid, 4
Is the magnetic flux leakage.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location C10M 141/00 9159-4H H01F 1/34 // C10N 40:14

Claims (6)

[Claims] 1. A thermosetting magnetic fluid characterized in that a thermosetting resin is mixed and dissolved in a magnetic fluid obtained by dispersing ferromagnetic fine particles adsorbing a surfactant in a dispersion medium. 2. The thermosetting magnetic fluid according to claim 1, wherein the dispersion medium is an organic solution having a vapor pressure of 20 ° C. and 400 mmHg or less. 3. A dispersion medium comprising water as claimed in claim 1.
A thermosetting magnetic fluid according to the item. 4. The surfactant is represented by the general formula R—X (where R: a hydrocarbon group, a fluorocarbon group or a silicon group, and X: PO ₃ H, COO).
The thermosetting magnetic fluid according to claim 1, which comprises a hydrocarbon compound represented by a polar group such as H, SO ₃ H or a salt thereof. 5. The surfactant is represented by the general formula RY (where R is a hydrocarbon group, a fluorocarbon group or a silicon group, and Y is Si (OR)).
_The thermosetting magnetic fluid according to claim 1, which comprises a coupling agent represented by ₃ , ₃ , SiR ₂ (OR), or the like. 6. The surfactant is represented by the general formula R—X (provided that R is a hydrocarbon group, a fluorocarbon group or a silicon group, X: PO ₃ H, COO).
A hydrocarbon compound represented by a polar group such as H, SO ₃ H or a salt thereof, and a general formula RY (wherein R is a hydrocarbon group, a fluorocarbon group or a silicon group, Y: Si (OR) ₃ , SiR ₂ (OR)
The thermosetting magnetic fluid according to claim 1, which comprises a coupling agent represented by the formula (1) or the like.