JP3087288B2 - Photocurable magnetic fluid composition - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photocurable magnetic fluid that can be suitably used for visualizing a recording pattern on a magnetic disk, a magneto-optical disk, or the like, or for magnetic flaw detection.

[Conventional technology]

For example, a magnetic fluid is used as a conventional medium for magnetic flaw detection. This is applied to the surface of a test object formed of a magnetic material, for example, when inspecting for the presence or absence of a defect in the test object.

When microscopic scratches or foreign substances are present on the surface or inside of a subject, preferably in a very shallow place, it is difficult to find them by conventional microscopy. However, when a magnetic field is formed on the subject, the magnetic flux leaks at a defect portion of the subject, resulting in a non-uniform magnetic field. Then, when the magnetic fluid is applied, the applied magnetic fluid is attracted to the leaked magnetic flux portion by the action force of the non-uniform magnetic field, and swells. It is known that the finer the ferromagnetic particles in the magnetic fluid, the higher the sensitivity and the higher the accuracy of magnetic flaw detection. However, when the particle diameter is from submicron to about several tens of microns, the particles cannot be directly observed with a commonly used microscope, but the raised portion of the magnetic fluid has a different reflection state of light from the other portions, so that the defect is defective. Can be clarified.

However, the magnetic fluid used in the conventional magnetic flaw detection is literally a fluid, and is merely constrained by the leakage magnetic flux of the defective portion. Therefore, the magnetic fluid of the subject flows as soon as the magnetic field disappears, and the swell disappears. Therefore,
There is a problem that when the subject is removed from the magnetic field, the defective portion becomes unknown.

Therefore, as disclosed in Japanese Patent Application Laid-Open No. 63-150302, the present applicant adds a photocurable resin to a magnetic fluid to apply a magnetic fluid to a subject and then photocures the magnetic fluid. A photocurable magnetic fluid composition in which the defect pattern is prevented from disappearing is proposed.

[Problems to be solved by the invention]

By the way, recording patterns have been miniaturized year by year as the density of magnetic disks and magneto-optical disks increases. Also,
Magnetic flaw detection is also required to visualize finer internal defects, and fixation and visualization of defects of 30 μm or less, particularly 10 μm or less are required.

On the other hand, in the conventional photocurable magnetic fluid composition, in order to sufficiently fix the defect pattern, it is necessary to add a certain amount of a photocuring agent. It has been found that the photocuring agent may have an adverse effect on the dispersion stability of the magnetic particles.

Therefore, after applying the photocurable magnetic fluid to the subject, the dispersion stability of the magnetic particles decreases with time as the concentration of the curing agent increases in the process of evaporating the dispersion medium as the carrier,
Secondary aggregation of the magnetic particles occurs. As a result, photocuring proceeds in a state where the magnetic particles are aggregated.

As described above, despite the recent demand for visualization of minute internal defects, when the aggregation of magnetic particles occurs, there is a limit to forming a clear defect pattern image due to the aggregation. there were. In particular, as the defects become finer, the influence of this aggregation increases.

In order to solve the problem, the present invention can form an image of a sufficiently sharp recording pattern or an image of a defect pattern even when used for an object having a fine recording pattern and / or a minute defect. It is an object of the present invention to provide a photocurable magnetic fluid composition.

[Means for solving the problem]

Therefore, in order to achieve the above object, the present invention provides a photocurable magnetic material in which a photocuring agent is mixed with a magnetic fluid obtained by dispersing ferromagnetic fine particles having a surfactant adsorbed in a dispersion medium. In the fluid composition, the photo-curing agent is RCOR ′
Wherein R and R ′ are aliphatic unsaturated hydrocarbons or aliphatic saturated hydrocarbons, at least one of which is an unsaturated hydrocarbon;
Or, it consists essentially of a polymer.

Preferably, the unsaturated ketone RCOR 'is an alkenyl ketone in which at least one of R and R' is an alkenyl group.

[Action]

The present inventor has examined that, instead of the conventional photocuring agent, RCOR '(R, R' is an aliphatic unsaturated hydrocarbon or an aliphatic saturated hydrocarbon, at least one of which is unsaturated hydrocarbon). The use of a photocuring agent consisting essentially of a monomer and / or polymer of an unsaturated ketone represented by the formula (1), wherein the photocuring composition hardens without adversely affecting the dispersibility of the magnetic particles. It became clear that we could provide.

Hereinafter, the photocurable magnetic fluid composition 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, an organic solvent which is relatively easily evaporated at room temperature is preferable. However, the boiling point under atmospheric pressure is 40 ° C or more and 250
C. or less is desirable. The reason for this is that if the temperature is lower than 40 ° C., the evaporation rate is too high, so that it is impossible to apply uniformly on the test object on average. Further, a dispersion medium that is compatible with the unsaturated ketone as a curing agent is suitably selected.

As a dispersion medium satisfying such conditions, for example,
Hydrocarbons such as hexane, n-octane, cyclohexane, cyclohexanone, petroleum ether, petroleum benzene, benzene, xylene, toluene, and halogenated hydrocarbons such as chloroform, dichlorobenzene, and bromobenzene;
And alcohols such as methanol, ethanol, n-propanol, n-butanol, isobutanol, and benzyl alcohol; ethers such as diisopropyl ether; aldehydes such as furfural; ketones such as acetone and ethyl methyl ketone; and acetic acid and acetic anhydride. Fatty acids and their derivatives and phenols.

As a surfactant (dispersant) for stably dispersing the ferromagnetic fine particles in such a dispersion medium, a surfactant having a high affinity for the dispersion medium is preferable. For example, an anionic surfactant which is a hydrocarbon compound having a polar group such as a carboxyl group, a hydroxyl group or a sulfone group, such as oleic acid or a salt thereof, petroleum sulfonic acid or a salt thereof, and a synthetic sulfonic acid or a salt thereof. Or a non-ionic surfactant such as polyoxyethylene nonylphenyl ether, or an amphoteric surfactant having both a cation portion and an anion portion in the molecular structure such as alkyldiaminoethylglycine. One or more are appropriately selected and used. Or you may use together with the coupling agent described below.

As the dispersant of the present invention, a so-called coupling agent may be used alone or in combination. As the coupling agent, for example, the general formula _{(Y P R) 4-n} SiX n (P is an integer of 1 or more, n represents an integer of 1-3) or R _4-n SiX _{n (n} is 1 to
(An integer of 3). Here, Y in the formula is a vinyl group, an epoxy group, an amino group, a mercapto group or other organic functional groups, and R is a hydrocarbon group such as an alkyl group. X is a hydrolyzable group, for example, a methoxy group (CH ₃ O-) or ethoxy group (C ₂ H ₅ O-) alkoxy group such as a (R'O-).

The alkoxy group of the silane coupling agent is hydrolyzed by water in the aqueous solution, air, or water adsorbed on the surface of the inorganic substance to generate a silanol group (—Si—OH). On the other hand, the ferromagnetic fine particles have -OH groups on their surfaces (M-OH), and a dehydration condensation reaction occurs between the two, and they are chemically bonded by metasiloxane bonds (Si-OM). It is thought to be.

Formula _{(Y P R) 4-n} SiX n (P is an integer of 1 or more, n represents 1
Silane coupling agents represented by 30 integer) is, for example, vinyltriethoxysilane, formula R _4-n silane coupling agent represented by SiX _n (n is an integer of 1 to 3), for example octadecyltriethoxysilane Methoxysilane.

Examples of the coupling agent other than the silane coupling agent include, for example, an aluminum-based coupling agent composed of acetoalkoxyaluminum diisopropylate, which is particularly suitable for non-aqueous systems, a titanate-based coupling agent, and a chromium-based coupling agent. Can be used. These compounds also have, in their molecular structure, an alkoxy group bonded to an -OH group and a portion (e.g., an alkyl acetoacetic acid group) that has an affinity for an organic substance, and have an -OH group on the surface of the ferromagnetic fine particles, which is a hydrophilic solid. It has the function of forming a strong lipophilic film by chemical bonding.

The optimal amount of the coupling agent is such that the surface of the ferromagnetic fine particles is completely covered with a monomolecular film. However, the specific surface area of the ferromagnetic fine particles, the water content, the hydrolyzability of silane, and the film formation state Is determined in consideration of the difference between the two.

It is necessary that the above-mentioned dispersant is contained in an amount capable of dispersing the following ferromagnetic particles, and specifically, it is preferably contained in an amount of 5 to 50% by weight based on the ferromagnetic particles.

As the ferromagnetic fine particles of the present invention, a magnetite colloid obtained by a well-known wet method can be used. Further, a powder obtained by a so-called wet pulverization method in which a magnetite powder is pulverized by a ball mill in water or an organic solvent may be used.

When using a wet grinding method, when using an organic solvent such as hexane in addition to water as the grinding fluid, add a ferromagnetic powder and an amount of a dispersant described below that can form a monolayer on the particle surface. May be ground in a ball mill for several hours or more.

It is also possible to use manganese ferrite other than magnetite, cobalt ferrite, or ferromagnetic oxides such as composite ferrite of these and zinc and nickel, barium ferrite, or ferromagnetic metals such as iron, cobalt, and rare earths, and iron nitride. it can.

Further, as the ferromagnetic fine particles, in addition to those obtained by the above-mentioned wet method or wet pulverization method, those obtained by a dry method can also be used.

The particle diameter of the ferromagnetic fine particles of the present invention may be in the range of 0.1 μm to 20 ° used for general magnetic fluids. However, as the particle size of the ferromagnetic fine particles is smaller, the inspection accuracy of magnetic flaw detection and magnetic recording pattern is improved. 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 20% by volume with respect to the dispersion medium generally used in the related art. Is more suitable.

The curing agent used in the photocurable magnetic fluid composition of the present invention corresponds to a photosensitive polymer containing an unsaturated ketone represented by RCOR 'as a main component. As a result of investigations by the present inventors, a curing agent containing an unsaturated ketone as a main component does not decrease the dispersion stability of ferromagnetic particles, and in the process of evaporating a dispersion medium after applying a photocurable magnetic fluid to a test object. Even if the hardener concentration increases, without lowering the dispersion stability of the ferromagnetic particles,
Therefore, secondary aggregation of ferromagnetic particles can be prevented, and a fine internal defect pattern or recording pattern can be clearly formed.

R and R 'are aliphatic unsaturated hydrocarbons or aliphatic saturated hydrocarbons, at least one of which is an unsaturated hydrocarbon.

As the aliphatic saturated hydrocarbon, those having 1 to 6 carbon atoms, such as methyl, ethyl and propyl, are suitably selected.
These saturated hydrocarbon chains may be branched or linear.

As the aliphatic unsaturated hydrocarbon chain, a linear or branched alkenyl group and / or alkynyl group can be selected. As the alkenyl group, for example, ethenyl (-C = C), 1 to 2- Propenyl [-C = C-
C, -CC = C, -C (C) = C] and having 2 to 6 carbon atoms can be selected. Further, as the alkynyl group, for example, one having 2 to 6 carbon atoms such as ethynyl (-C≡C), 1 to 2 propynyl [-CC-C, -C≡CC] may be selected. it can.

The number of unsaturated bonds is not limited to one, and it does not prevent the presence of a plurality of unsaturated bonds, and a mixture of a double bond and a triple bond may be used as the unsaturated bond. Although the position of these unsaturated bonds is not particularly limited, the present inventor has considered that it is more preferable that the unsaturated bond be located at a position conjugated with the double bond of the carbonyl group (C = O).

Here, specific names of unsaturated ketones (monomers) having a main structure which is a main component of the photocuring agent usable in the present invention will be described.

Methyl vinyl ketone, ethyl vinyl ketone, n-propyl vinyl ketone, isopropyl vinyl ketone, methyl-n-propenyl ketone (ethylideneacetone), ethyl-n-propenyl ketone, methyl isopropenyl ketone (mesityl oxide), ethyl isopropenyl ketone And alkenyl ketones such as divinyl ketone, di-n-propenyl ketone and diisopropenyl ketone, alkynyl ketones such as methylpropynyl ketone, and alkadienyl ketones such as 3,5-hexadien-2-one.

These unsaturated ketones are present in the curing agent in a monomeric state and / or an oligomeric polymer state. These compounds cause a polymerization reaction or a cross-linking reaction particularly at a wavelength in the ultraviolet region (mainly 300 to 400 nm), and are photocured to give the following polymer.

In the photocuring reaction, it is preferable to add a known crosslinking agent and / or a photosensitizer.

In general, in a photocurable magnetic fluid composition, the dispersion stability of ferromagnetic particles is reduced by increasing the content of a known photocuring agent described below, which may be mixed with the composition according to the present invention. Agglomeration tends to increase. On the other hand, when the content of the photocuring agent is reduced, the adhesion strength is reduced, and there is a problem of peeling.
Incidentally, the photo-curing agent consisting essentially of an unsaturated ketone according to the present invention has a higher adhesion strength than known photo-curing agents, and may reduce the dispersion stability of ferromagnetic particles as described above. Absent. Therefore, the photocuring agent comprising the unsaturated ketone can be contained in the magnetic fluid in a range from a low concentration to a relatively high concentration. Specifically, the content is preferably 5 to 40 vol%, particularly preferably 10 to 20 vol%, based on the solvent. In order not to lower the dispersion stability of the ferromagnetic particles, the smaller the content of the curing agent is better,
If the amount is less than 5 vol%, the degree of photocuring is weak and the defect pattern cannot be fixed, and there is a problem that the peeling resistance of the cured magnetic fluid composition is lowered. Also,
If it exceeds 40 vol%, the concentration of the curing agent becomes relatively large, and there is a possibility that the secondary aggregation of the ferromagnetic particles may occur. Further, since the thickness of the adhered film becomes thick, a fine defect pattern becomes unclear due to these factors.

According to the photocurable magnetic fluid composition according to the present invention as described above, the width or length is 30 μm or less, particularly 10 μm
It is possible to fix and visualize a fine recording / defect pattern of m or less.

〔Example〕

 Next, examples of the present invention will be described.

Example 1 Production of Photocurable Magnetic Fluid According to the Present Invention First, 6N NaOHaq was added to an aqueous solution 1 containing 0.3 mol of each of ferrous sulfate and ferric sulfate until the pH became 11 or more. . Thereafter, the mixture was aged at 60 ° C. for 30 minutes to obtain an aqueous suspension of magnetite colloid. Subsequently, the slurry is washed with water at room temperature to remove the electrolyte in the slurry. The above is the step of producing the magnetite colloid by the wet method.

3N HC was added to the magnetite colloid solution thus obtained.
After adding laq to adjust the pH to 3, 40 g of sodium petroleum sulfonate as a surfactant was added thereto, and
, And the surfactant was adsorbed on the surfaces of the magnetite fine particles. Thereafter, the mixture is allowed to stand, and the magnetite fine particles in the liquid are aggregated and settled, and the supernatant is discarded. Further, add fresh water, stir and let stand, and discard the supernatant. This washing was repeated several times to remove the electrolyte in the aqueous solution, followed by filtration, dehydration and drying to obtain powdery magnetite fine particles whose surface was coated with a surfactant.

Next, hexane was added to the magnetite colloid powder as a low-boiling nonpolar solvent and shaken sufficiently to obtain an intermediate medium in which magnetite particles were dispersed in hexane.

Methanol as a low-boiling polar organic solvent is added to the obtained colloid solution, and the particles are once aggregated and precipitated, and the supernatant is discarded. As a result, extra dispersants other than the dispersant adsorbed on the fine particles by a single molecule are removed.

Thereafter, the precipitated fine particles are redispersed in chloroform to obtain an intermediate medium.

The intermediate medium is centrifuged in a centrifuge under a centrifugal force of 8000 G for 20 minutes to precipitate and remove relatively large particles of magnetite dispersed particles having poor dispersibility.
Next, the supernatant in which the magnetite fine particles remaining without precipitation were dispersed was transferred to a rotary evaporator, and the solvent having a low boiling point, that is, chloroform was removed by evaporation at 90 ° C. to obtain lipophilic magnetite fine particles.

6 g of the lipophilic magnetite fine particles thus obtained are redispersed by irradiating 20 ml of a mixed solvent of chloroform and cyclohexanone at a volume ratio of 1: 1 with ultrasonic waves for 20 minutes.

3.9 ml (15vol) at the same time as the solvent (or after redispersion)
% Equivalent) of a methyl isopropenyl ketone having an average molecular weight of about 200,000 (ONNR-20, manufactured by Tokyo Ohka Kogyo Co., Ltd.).

As described above, a photo-curable magnetic fluid containing a photo-curable resin component and dispersed extremely stably was obtained.

Comparative Example 1 Production of Conventional Photocurable Magnetic Fluid Composition 6 g of lipophilic magnetite obtained in the same manner as in Example 1
Is redispersed by irradiating 20 ml of xylene with ultrasonic waves for 20 minutes. 2.6 ml simultaneously with (or after redispersion) xylene (1
(0 vol%) of a curing agent containing a cyclized isoprene (OMR-85, manufactured by Tokyo Ohka Kogyo Co., Ltd.) to obtain a magnetic fluid composition containing a conventional photocuring agent.

(Example 2) A magnetic inspection test of a steel material using the photocurable magnetic fluid composition of Example 1 was performed.

As a test object, as schematically shown in FIG. 1, a steel material 2 having a known internal defect 1 having a length of about 2 mm and a width of about 30 μm at a position 1 μm below the surface was used.

The subject was placed in a magnetic field of 13 K Gauss in advance with an applied magnetic field, and the surface thereof was coated with a photocurable magnetic fluid 3. Then, due to the action of the leakage magnetic flux 4 generated in the subject 2 just above the internal defect 1, the ferromagnetic fine particles are locally concentrated, and the photocurable magnetic fluid 3 is applied to the internal defect 1 as shown in the figure. A phenomenon of swelling along was recognized.

This swelling phenomenon disappeared when the subject 2 was taken out of the magnetic field, and was recognized again when the subject 2 was returned to the inside of the magnetic field. Next, the solvent is removed from the photo-curable magnetic fluid 3 showing a swelling state by a method such as heating and the like and irradiated with ultraviolet rays having a wavelength of about 400 to 500 nm. 3 was cured, and the state showing the internal defect 1 could be fixed as it was. By observing the cured film with a microscope, the state of internal defects showing needle-like shadows could be accurately inspected.

[Example 3] Next, in each of the photocurable magnetic fluid compositions of Example 1 and Comparative Example 1, the concentration of each curing agent was sequentially changed, and Example 2 was performed.
Visualization and fixation of internal defects were performed in the same manner as described above.
Internal defect width is 50 ~ 60μm, 20 ~ 30μm, 5 ~ 10μ respectively
A plurality of the three types of specimens each having m are prepared, and the photocurable magnetic fluid composition according to Example 1 (the composition of the present invention) and the light according to Comparative Example 1 in which the concentration of the curing agent is different for each type of specimen. The curable magnetic fluid composition (comparative composition) was prepared in Example 2 described above.
The coating was performed in the same manner as described above, and the defect pattern was visualized and fixed. Then, the quality of fixing the defect pattern was classified into three stages of ○, Δ, and ×. ○ indicates that a sharp defect pattern was obtained for all the specimens, Δ indicates that the defect pattern for some of the specimens was unclear, and X indicates a defect for all the specimens. Indicates that the pattern has become blurred. The results are shown in Table 1 below.

Further, for a plurality of specimens having a width of 10 μm and other conditions similar to those of the above-described example, the above-described example 1 and comparative example 1 were used.
The photocurable magnetic fluid was applied and cured, and the adhesion strength to the specimen was evaluated by a test (cellotape peel test). The evaluation results were divided into three stages of ○, △, ×, and ○ indicates that no peeling occurred in all the specimens.
Δ indicates that exfoliation occurred in some of the subjects, and X indicates that exfoliation occurred in all of the subjects. The results are shown in Table 2 below.

As can be seen from Table 1, for the composition of the present invention,
Even for a defect having a defect width of 5 to 10 .mu., The defect pattern can be fixed and visualized by setting the concentration of the curing agent to 5 to 20 vol% with respect to the dispersion medium. Table 2 shows that the adhesion strength at this time is almost satisfactory. In contrast, for the comparative example composition, the width of the defect was 5 to 10
The defect pattern of μm can be partially fixed and visualized by setting the concentration of the curing agent to 5 vol%, but the adhesion strength at this time is a value that is almost insignificant as can be seen from Table 2. I have.

When fixing a defect pattern having a width of 20 to 30 μm, the composition of the comparative example requires a minimum hardening agent concentration of 10 vol% in consideration of the adhesion strength shown in Table 2. The defect pattern thus obtained becomes unclear in some objects. On the other hand, in the magnetic fluid composition of Example 1,
In consideration of the adhesion strength in Table 2, when fixing a defect pattern having a width of 20 to 30 μm, a curing agent concentration of at least 5 vol% is required. Is clear.

Therefore, by using the hardening agent of the type of Example 1, it is possible to maintain the peel resistance of the magnetic fluid composition after fixing the defect pattern in a good condition, and to maintain the magnetic fluid composition at 30 μm or less, especially 10 μm.
A fine defect pattern of m or less can be clearly fixed and visualized.

In the embodiment described above, visualization of a defect pattern has been described. However, the same effect can be achieved by applying the present invention to visualization of a fine recording pattern.

〔The invention's effect〕

As described above, according to the photocurable magnetic fluid composition of the present invention, the dispersion stability of the ferromagnetic particles is not reduced,
In addition, since the photocuring agent contains an unsaturated ketone having a relatively high adhesion strength to a subject even at a low concentration, even when used for a subject having a fine recording pattern and / or a defect, the recording can be performed. A sufficiently sharp image of a recording / defect pattern can be formed in a state where the separation resistance of the magnetic fluid composition after fixing the defect pattern is well maintained.

[Brief description of the drawings]

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

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI C08K 5:00 9:04)

Claims (2)

(57) [Claims] 1. A photocurable magnetic fluid composition comprising a magnetic fluid obtained by dispersing ferromagnetic fine particles having a surfactant adsorbed therein in a dispersion medium, and a photocurable agent mixed therein. Is a monomer of an unsaturated ketone represented by RCOR '(R, R' is an aliphatic unsaturated hydrocarbon or an aliphatic saturated hydrocarbon, at least one of which is an unsaturated hydrocarbon) And / or a photocurable ferrofluid composition consisting essentially of a polymer. 2. The photocurable ferrofluid composition according to claim 1, wherein said unsaturated ketone RCOR 'is an alkenyl ketone wherein at least one of R and R' is an alkenyl group. .