JPS63185006A - Heat curing type magnetic fluid - Google Patents

Abstract

PURPOSE:To retain a magnetic fluid pattern formed according to the pattern of the magnetic flux of a detected object even outside a magnetic field by fixing the pattern of the magnetic flux by mixing a heat curing type resin in a magnetic fluid wherein the ferromagnetic material particles adsorbing a surface active agent are dispersed in a dispersion medium. CONSTITUTION:Ferromagnetic material fine particles such as magnetite, manganese ferrite or cobalt ferrite adsorbing a surface active agent wherein the main component is an unsaturated fatty acid which has one or more polar groups such as a COOH group, an SO3H group or a PO3H group and is shown by a general formula R-X (R is a hydrocarbon group, a fluorine carbide group or a silicon group, X is the above-mentioned polar group.) or its acid are stably dispersed in a dispersion medium. An equal heat curing type resin is added to this solution and stirred and mixed. By mixing the heat curing type resin, it becomes possible to fix the pattern of the magnetic fluid formed according to the change of the magnetic flux of a detected object and to hold the pattern of the magnetic fluid outside a magnetic field.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermosetting magnetic fluid that can be suitably used for visualization of recording patterns on magnetic disks, magneto-optical disks, etc., magnetic flaw detection, and the like.

[Conventional technology]

For example, magnetic fluid is used as a medium for conventional magnetic flaw detection. This is used by applying it to the surface of an object made of a magnetic material, such as when inspecting the object for defects.

When there are minute scratches or foreign substances on the surface of the object or in extremely shallow areas, it is difficult to detect them by simple microscopic examination. However, when a magnetic field is applied to the object, magnetic flux leaks at defective locations on the object, resulting in a non-uniform magnetic field. Therefore, when a magnetic fluid is applied, the applied magnetic fluid is attracted to the leakage magnetic flux area and bulges due to the action of the non-uniform magnetic field, creating a pattern different from other areas. It is known that the sensitivity improves as the ferromagnetic particles in the magnetic fluid become finer, and the accuracy of magnetic flaw detection improves.

However, when the particle size is from submicron to several tens of angstroms, it is not possible to directly observe the particle with a commonly used microscope, but since the above-mentioned raised part of the magnetic fluid reflects light differently than other parts, defects can be detected. The existence of can be clearly observed.

[Problem that the invention seeks to solve]

However, the magnetic fluid used in conventional magnetic flaw detection is literally a fluid and is only restrained by the leakage magnetic flux of the defective part, so it flows and the bulge disappears as soon as the magnetic field of the object disappears. Therefore, there is a problem in that when the object to be examined is removed from the magnetic field, the defective part becomes unclear.

This invention was made by focusing on such conventional problems, and it is possible to fix the magnetic fluid pattern formed according to the magnetic flux pattern of the subject and maintain it even outside of the magnetic field. The purpose is to provide magnetic fluids.

[Means for solving problems]

The present invention, which achieves the above object, is a thermosetting magnetic fluid in which a thermosetting resin is mixed with a magnetic fluid made by dispersing fine ferromagnetic particles on which a surfactant is adsorbed in a dispersion medium.

[Effect]

When the thermosetting magnetic fluid of the present invention is used for, for example, magnetic flaw detection or inspection of magnetic recording patterns, it is first applied to the surface of the object to be inspected in which a magnetic field has been formed.

Then, the magnetic fluid is attracted according to the defective part of the object and the magnetic flux patterns formed by magnetic recording, and a distribution pattern of the magnetic fluid corresponding to these magnetic flux patterns is created.

Next, the thermosetting resin 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.

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

Since the dispersion medium for the ferromagnetic fine particles of the present invention is not required after being applied to the subject, it is preferably an organic solvent or water that evaporates relatively easily and has a vapor pressure of 4QQmmHg or less at room temperature. The reason for this is that when this value is exceeded, the evaporation rate is too high and it becomes impossible to uniformly coat the sample on average.

Examples of organic solvents satisfying this condition include hydrocarbons such as n-pentane, cyclohexane, petroleum ether, petroleum benzine, benzene, xylene, and toluene, chlorobenzene, and dichlorobenzene.

Halogenated hydrocarbons such as bromobenzene, alcohols such as methanol, ethanol, n-propanol, n-phthanol, isobutanol, benzyl alcohol, and diethyl ether.

Ethers such as diisopropyl ether, aldehydes such as furfural, ketones such as acetone and ethyl methyl ketone, fatty acids and their derivatives such as acetic acid and acetic anhydride, phenols, and fluorine carbide.

Silicon, etc.

Examples of surfactants for stably dispersing ferromagnetic fine particles in the above-mentioned dispersion medium include C0OH group, 5
An unsaturated fatty acid having one or more polar groups such as an O3H group or a PO3H group and represented by the general formula R-X (R is a hydrocarbon group, a fluorocarbon group, a silicon group, and X is the above polar group) or its It may be selected from those containing salts as a main component and other well-known hydrocarbon compounds.

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

The above-mentioned surfactant should be selected by taking into account its affinity with the dispersion medium, etc.
Used alone or in combination. That is, when the dispersion medium is water, firstly, R-X type petroleum sulfonic acid is first added.
By adding it as a surfactant, the ferromagnetic fine particles and the polar group X bond to form a monomolecular layer with the hydrophobic group R facing outward.

Next, oleic acid of the same type (R- A stable aqueous colloid solution is obtained by covering the surface of the ferromagnetic particles.

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

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

Also, manganese ferrite other than magnetite.

Ferromagnetic oxides such as cobalt ferrite or composite ferrites of these with zinc and nickel, barium ferrite, or ferromagnetic metals such as iron, cobalt, and rare earths can also be used.

The particle size of the ferromagnetic fine particles of the present invention may range from 0.1 μm to 20 μm, which is used for general magnetic fluids. However, the smaller the particle size of the ferromagnetic fine particles, the higher the accuracy of magnetic flaw detection and inspection of magnetic recording patterns, so 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, which is conventionally generally used, but it is possible to achieve an even higher concentration by manufacturing using the intermediate medium described below. It is also extremely easy to make it a reality.

When a magnetic fluid is used for magnetic flaw detection, magnetic pattern inspection, etc., the finer the dispersed ferromagnetic particles are and the higher the concentration, the more precise the inspection can be performed. However, in general, the higher the concentration of ferromagnetic fine particles, the smaller the distance between particles and the easier they are to aggregate, so there is a limit to the improvement of the concentration.

Therefore, when the magnetic fluid of this invention requires a particularly high concentration, a first surfactant and a low boiling point solvent such as hexane are added to the ferromagnetic fine particles, and the surface is coated with the surfactant. It is preferable to produce it through a step of obtaining an intermediate medium in which ferromagnetic fine particles are dispersed in a low boiling point solvent. If the intermediate medium is subjected to, for example, a centrifugal separator, 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 heating the mixture, the low boiling point solvent can be easily evaporated and a magnetic fluid in which magnetic particles are extremely stably dispersed can be obtained.

In the above process, after separating particles with poor dispersibility from an intermediate medium, the intermediate medium is heated to evaporate the low boiling point solvent to form a powder of ferromagnetic fine particles, and then a dispersion medium is added to this powder. You may also do so.

Furthermore, if the magnetic fluid obtained in this way is repeatedly concentrated by adding a new intermediate medium and evaporating the low boiling point solvent, it is possible to obtain an extremely high concentration and to stably disperse only fine particles. A ferrofluid with a high temperature is obtained.

The thermosetting resin added to the magnetic fluid can be selected from the following groups of synthetic resins, taking into consideration its compatibility with the dispersion medium constituting the magnetic fluid.

■ Unsaturated polyester resins such as orthophthalic acid, isophthalic acid, bisphenol, alicyclic unsaturated fatty acid, and acrylic ester.

■ Epoxy resins, such as phenolic glycidyl ether type (main raw materials: bisphenol A, phenol novolac, 〇-talesol novolac, etc.).

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

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

Glycidylamine type (main raw materials: diamino diphenylmethane, isocyanuric acid, hydantoin).

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

■ Phenol resin ■ Urea resin ■ Melamine resin ■ Diaryl phthalate resin ■ Silicone resin ■ Fluorine resin Below, specific examples of thermosetting magnetic fluids will be explained along with their manufacturing process.

[Example 1] First, 6N Na0Haq was added to an aqueous solution IJ containing 1 mole each of ferrous sulfate and ferric sulfate to adjust the pH to 11 or higher, and the mixture was aged at 60°C for 30 minutes to form a magnetite colloid. was obtained (wet method). Afterwards, 3N HCl was added to this magnetite slurry while keeping it at 60°C to adjust the pH to 2.
Adjust between ~3. To this magnetite slurry, 70 g of sodium petroleum sulfonate is added as a first surfactant for stably dispersing colloidal particles, and the mixture is stirred for 30 minutes.

When this is allowed to stand and the magnetite particles aggregate and settle,
Discard the supernatant, pour in water, and repeat the process of rinsing with water several times to remove the electrolyte. After washing with water, transfer the liquid to a separating funnel. Next, hexane is added as a low boiling point solvent to the liquid in the funnel, shaken thoroughly and left to stand to separate water and hexane.

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

In this way, once a low-viscosity intermediate medium is formed and centrifuged, it is possible to arbitrarily adjust the particle size distribution of the ferromagnetic fine particles, and there is an advantage that the concentration of the fine particles can be particularly increased.

Thereafter, the supernatant was taken out, transferred to a rotary evaporator, and kept at 90°C to evaporate hexane.

1 g of the thus obtained powdery magnetite fine particles was taken and dispersed in 10 g of normal butanol, and then 0.45 g of isostearic acid was added as a second surfactant.
g was added and dissolved. To this solution, an equal volume of thermosetting resin (manufactured by Tamura Seisakusho, 5R34G) was added and mixed by stirring.

In this way, fine elastic particles of magnetite were added to the mixture of organic solvent normal butanol and thermosetting resin.
A thermosetting magnetic fluid was obtained which was extremely stably dispersed via the first and second surfactants.

[Example 2] First, a slurry of magnetite colloid was obtained by a wet method in the same manner as in Example 1.

Next, a silane coupling agent (manufactured by Toshiba Silicone ■) was added to the slurry as a first surfactant.

Add 70g of TSC-8185) and stir for 30 minutes.

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

[Example 3] First, 6N Na0Haq was added to an aqueous solution iz containing 1 mol each of ferrous sulfate and ferric sulfate to make the pH 811 or higher, and then aged at 60'C for 30 minutes to form magnetite colloid. obtained (wet method). Thereafter, 3N HCl is added to this magnetite slurry while maintaining the temperature at 60°C to adjust the pH between 2 and 3. In this magnetite slurry,
70 g of sodium petroleum sulfonate is added as a first surfactant for stably dispersing colloidal particles, and the mixture is stirred for 30 minutes.

When this is allowed to stand and the magnetite particles aggregate and settle,
Discard the supernatant, pour in water, and repeat the process of rinsing with water several times to remove the electrolyte. After washing with water, transfer the liquid to a separating funnel. Next, hexane is added as a low boiling point solvent to the liquid in the funnel, shaken thoroughly and left to stand to separate water and hexane.

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

In this way, once a low-viscosity intermediate medium is formed and centrifuged, it is possible to arbitrarily adjust the particle size distribution of the ferromagnetic fine particles, which has the advantage of increasing the concentration of fine particles. .

Thereafter, the supernatant was taken out and transferred to a rotary evaporator, and the hexane was removed by evaporation while maintaining the temperature at 90''C.

1 g of the thus obtained powdered magnetite fine particles and 0.45 sodium oleate as the second surfactant.
Mix and stir 10ml of an aqueous solution in which 100 g of the magnetite was added and dissolved, and the magnetite is dispersed in the aqueous solution. Add alkyd resin (manufactured by Dainippon Ink & Chemicals, S-6) to this dispersion.
Add 14.7 nl of an aqueous solution containing 95) and stir to disperse.

This liquid was centrifuged for 20 minutes with a centrifugal force of 8000 G to remove impurities and produce a thermosetting magnetic fluid.

[Example 4] First, an intermediate medium in which ferromagnetic fine particles whose surfaces were coated with a surfactant were dispersed in a low boiling point solvent was obtained in the same manner as in Example 3, and this intermediate medium liquid was subjected to a centrifugal force of 8000 G. 20 in
Centrifuge for 9 minutes to sediment and separate large magnetite particles, remove the supernatant and transfer it to an evaporator.
Hexane is removed by evaporation while maintaining the temperature at 0°C.

1 g of the thus obtained powdery magnetite fine particles is taken and dissolved and dispersed in a mixed solvent of 1 5 mJ of toluene and 30 ml of hexane. Add this solution to a silicone thermosetting resin (manufactured by Shin-Etsu Chemical Co., Ltd.).

Add 15 ml of toluene melt of MS-841) and stir. This was centrifuged at 8000G centrifugal force for 20 minutes,
By removing impurities, we were able to create 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 the specimen, as schematically shown in Fig. 1, below the surface,
A steel material 2 having a known internal defect 1 with a length of about lam and a width of about 10 μm at several micrometers was used.

This test object 2 was placed in advance in a magnetic field with an applied magnetic field of 13 K GausS, and the thermosetting magnetic fluid 3 was applied with a brush onto its surface. Then, due to the action of the leakage magnetic flux 4 generated in the vicinity directly above the internal defect 1 in the test object 2, the ferromagnetic particles are locally concentrated, and the thermosetting magnetic fluid 3 is applied to the internal defect 1 as shown in the figure. A growing phenomenon was observed.

This swelling phenomenon disappeared when the subject 2 was taken out of the magnetic field, and was observed again when it was returned into the magnetic field.

Next, thermosetting magnetic fluid 3 showing a swelling state
When hot air with a temperature of about 70°C was blown against the
The thermosetting magnetic fluid 3 was cured in about a minute, and the state showing the internal defect 1 could be fixed as it was.

By peeling off the cured coating film of thermosetting magnetic fluid 3 from the test object and observing it with a microscope, it was possible to accurately inspect the state of internal defects showing needle-shaped shadows.

〔Effect of the invention〕

In this invention, a thermosetting resin is mixed into a magnetic fluid used for inspecting defects and magnetic recording patterns in magnetic objects. Therefore, it becomes possible to fix the magnetic fluid pattern that is formed in response to changes in the magnetic flux of the object and hold it outside of the magnetic field, bringing great progress in fields such as magnetic flaw detection and micro-inspection of magnetic recording media. be able to.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram illustrating the operation of an embodiment of the present invention. l is an internal defect, 2 is an object to be inspected, 3 is a photocurable magnetic fluid, 4
is leakage magnetic flux.

Claims (6)

[Claims] (1) A thermosetting magnetic fluid characterized by mixing a thermosetting resin with a magnetic fluid made by dispersing fine ferromagnetic particles adsorbed with 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 400 mmHg or less at 20°C. (3) The thermosetting magnetic fluid according to claim 1, wherein the dispersion medium is water. (4) The surfactant has the general formula R-X (R: hydrocarbon group, fluorocarbon group, or silicon group, X: PO_3H
, a polar group such as COOH, SO_3H, or a salt thereof), the thermosetting magnetic fluid according to claim 1. (5) The surfactant has the general formula RY (where R: hydrocarbon group or fluorocarbon group or silicon group, Y: Si (OR
)_3, SiR_2(OR), etc.) The thermosetting type magnetic fluid according to claim 1, which comprises a coupling agent represented by the following formulas: )_3, SiR_2(OR), etc.). (6) The surfactant has the general formula R-X (where R: hydrocarbon group, fluorocarbon group, or silicon group, X: PO_3H
, COOH, SO_3H, or their salts), and a hydrocarbon compound represented by the general formula RY (however,
R: hydrocarbon group, fluorocarbon group, or silicon group, Y:
The thermosetting magnetic fluid according to claim 1, comprising a coupling agent represented by Si(OR)_3, SiR_2(OR), etc.).