JP2536072B2 - Method for evaluating physical properties of surface of particulate material for magnetic recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for evaluating surface physical properties of various particle materials for magnetic recording media used for magnetic recording media such as ferromagnetic powder and abrasives.

[Conventional technology]

Generally, a magnetic recording medium is prepared by dispersing and kneading a ferromagnetic powder in an organic solvent together with additives such as a binder, a dispersant, a circulating agent, and an abrasive on one surface of a non-magnetic support such as a polyester film. The magnetic layer is formed by applying the magnetic layer. This is a so-called coating type magnetic recording medium.

Further, a so-called back coat layer in which conductive carbon black or the like is mixed in a binder is also widely provided on the other surface of the non-magnetic support. This back coat layer is not limited to the above-mentioned coating type magnetic recording medium,
It is also applied to a so-called metal thin film type magnetic recording medium in which a ferromagnetic metal is directly deposited on a non-magnetic support by means such as vacuum deposition to form a magnetic layer.

By the way, the performance of the magnetic recording medium depends not only on the characteristics of the magnetic substance itself, but also on the packing property, orientation property, dispersibility, etc. of the particle material in the magnetic layer or the back coat layer. In such magnetic recording media, it is necessary to know the surface physical properties of various particle materials such as ferromagnetic powder and abrasives used for the magnetic layer and carbon black used for the back coat layer, and Accurate understanding of interactions between agents and other additives is indispensable for improving reproducibility in material development / design or manufacturing process.

From such a viewpoint, evaluation of surface properties of ferromagnetic powders has been attempted by various methods according to the purpose. They are,
For example, various thermochemical methods such as liquid absorption measurement, wetting heat measurement, adsorption heat measurement based on adsorption isotherm, charge zero point measurement by potentiometric titration, surface potential measurement method (electroosmosis method, streaming potential method, sedimentation method) Potential method), or an electrochemical method such as measurement of isoelectric point by electrophoresis method or zeta potential measurement.

[Problems to be Solved by the Invention]

However, each of the above-mentioned methods gives, so to speak, macroscopic information on the average physical properties of the surface, and microscopic information cannot be obtained from it. For example, even if the isoelectric point of a certain particle material is obtained by the electrophoretic method, it is possible to know how strong the acid points and the basic points are distributed in the particle material. I can't. If such a microscopic surface physical property can be understood, it is very effective for improving reproducibility in material design and manufacturing process.

Therefore, an object of the present invention is to provide a method that enables microscopic evaluation of surface physical properties of a particle material for a magnetic recording medium.

[Means for solving the problem]

The present inventors have generally found that the surface of the magnetic recording medium material powder has an acid point or a base point peculiar to the material or generated by adsorption or oxidation of water molecules, and these are Bronsted acid or Bronsted. Focusing on the fact that they act as bases, the inventors have arrived at the present invention by finding a method capable of separately quantifying these by a series of reactions.

That is, the method for evaluating the surface properties of a particle material for a magnetic recording medium according to the first aspect of the present invention comprises contacting a carbonyl compound having an α-hydrogen atom with a particle material used for a magnetic recording medium to form an aldol of the carbonyl compound. The β-hydroxycarbonyl compound produced by the condensation reaction and the α, β-double bond carbonyl compound produced by the dehydration reaction of the β-hydroxycarbonyl compound are analyzed.

Furthermore, the method for evaluating the surface physical properties of the particle material for a magnetic recording medium according to the second aspect of the present invention comprises contacting the β-hydroxycarbonyl compound with the particle material used for the magnetic recording medium, A carbonyl compound having an α hydrogen atom produced by a reverse aldol condensation reaction and an α, β-double bond carbonyl compound produced by a dehydration reaction of the β-hydroxycarbonyl compound are analyzed.

The aldol condensation reaction is a reaction found in an aldehyde or ketone having a hydrogen atom at the α-position. This reaction is represented as follows.

In this formula, R ₁ and R ₂ each represent a hydrogen atom, a hydrocarbon group having a substituent, an unsubstituted hydrocarbon or the like. If R ₂ is a hydrogen atom, the carbonyl compound (I) in the above formula is an aldehyde, and if it is another hydrocarbon group, it is a ketone. In addition, R ₁ and R ₂ may be bonded to each other at the ends to form a cyclic ketone.

According to the above reaction route, first, the carbonyl compound (I) is converted to the β-hydroxycarbonyl compound (II) in the presence of a base catalyst, which is easily dehydrated in the presence of an acid catalyst to form α, β-. Unsaturated carbonyl compound (II
I) is generated. In some cases, the β-hydroxycarbonyl compound (II) and the carbonyl compound (I) are reacted in the presence of a base catalyst to give the carbonyl compound (I).
In some cases, a trimer or a multimer or more thereof is produced.

Here, as typical examples of the compound (I), there are acetaldehyde, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, etc. Among them, acetone is preferable from the viewpoint of analysis.

According to the first aspect of the present invention, the presence of a basic point is prevented by the formation of the β-hydroxycarbonyl compound (II) when the particle material and the carbonyl compound (I) are brought into contact with each other.
It is possible to know the existence of acid sites by the production of unsaturated carbonyl compound (III), and it is also possible to know the standard of the abundance ratio of base sites and acid sites by the production ratio of these two compounds. However, since this method undergoes a catalytic action by the base point, a particle material having only the acid point without the base point,
Alternatively, it cannot be applied to a particle material having a large excess of acid sites compared to basic sites. In addition, the carbonyl compound (I)
Since the pathway from the β-hydroxycarbonyl compound (II) to the β-hydroxycarbonyl compound (II) is a reversible reaction, it is necessary to use the carbonyl compound (I) in a large excess in order to completely proceed the catalytic action by the base site.

Further, according to the second aspect of the present invention, the particulate material and β-
The presence of a basic point due to the formation of the carbonyl compound (I) when the hydroxycarbonyl compound (III) is contacted,
It is possible to know the existence of an acid site by the production of the α, β-unsaturated carbonyl compound (III), and it is also possible to know the standard of the abundance ratio of the base site and the acid site by the production ratio of these two compounds. The particle material to which this method can be applied is not limited as in the case of the first invention.

The particle materials for magnetic recording media to which the present invention can be applied are roughly classified into ferromagnetic particles, polishing powder and other added particles.

Examples of the ferromagnetic particles include ferromagnetic iron oxide particles, ferromagnetic chromium dioxide particles, ferromagnetic alloy particles, hexagonal barium ferrite fine particles, metal carbides and metal nitrides.

As the above-mentioned ferromagnetic iron oxide particles, when expressed by the general formula FeO _x , the value of x is in the range of 1.33 ≦ x ≦ 1.50, that is, maghemite (γ-Fe ₂ O ₃ , x = 1.50), magnetite ( Fe ₃ O ₄ ,, x = 1.33), and their solid solutions (FeO _x , 1.
33 <x <1.50). Further, a material in which cobalt is doped or adhered to these ferromagnetic iron oxides for the purpose of improving coercive force is also included.

The ferromagnetic chromium dioxide includes a material to which at least one kind of metal element such as Ru, Sn, Te, Sb, Fe, Ti, V, Mn is added for the purpose of improving coercive force.

As the ferromagnetic alloy particles, Fe, Co, Ni, Fe-Co, Fe-
Ni, Fe-Co-Ni, Co-Ni, Fe-Co-B, Fe-Co-Cr-B, Mn-B
Examples thereof include i, Mn-Al, Fe-Co-V and the like. Further, metal elements such as Al, Si, Ti, Cr, Mn, Cu and Zn may be added to these for the purpose of improving various characteristics.

Examples of the polishing powder include alumina, chromium oxide, silicon carbide, corundum, diamond, garnet, and emery (main components: corundum and magnetite).

Further, other added particles include polymer gel particles such as epoxy resin, polystyrene resin, benzoguanamine-formaldehyde condensation resin, etc., contact black, channel black, roll black, disk black, furnace black, thermal black added to the back coat layer. , Various carbon black such as lamp black, CaCo ₃ powder, BaSO ₄ powder, ZnO powder, α-Fe ₂ O ₃ powder,
Inorganic pigments such as TiO ₂ powder, Al ₂ O ₃ powder and Cr ₂ O ₃ powder can be used.

The aldol condensation reaction between these particle materials and a carbonyl compound having an α hydrogen atom can be carried out in a gas phase system or a liquid phase system.

The product of the aldol condensation reaction can be analyzed by various qualitative quantitative analysis methods such as gas chromatography (GC), GC / mass spectrometry, liquid chromatography, and high performance liquid chromatography.

[Action]

Considering the case of using acetone as the carbonyl compound having an α hydrogen atom, the aldol condensation reaction is explained as follows.

First, of the two molecules of acetone, one of the hydrogen atoms at the α-position is extracted as a proton by the catalytic action of the base point existing on the surface of the magnetic recording medium particle material. Next, the generated anion reacts nucleophilically with the carbonyl carbon of the other acetone to produce diacetone alcohol. Next, this diacetone alcohol is dehydrated by the catalytic action of the acid sites present on the surface of the magnetic recording medium particle material.
It becomes a mesityl oxide stabilized by resonance of -C = C-C = O type. The above reaction is expressed as follows.

As is clear from the above reaction mechanism, according to the evaluation method of the present invention, the products corresponding to the catalytic action of the base points and the acid points of the magnetic recording medium particle material are obtained.
Therefore, for example, even if the material is determined to have the same isoelectric point by the conventional evaluation method, microscopically, how strong the base point and the acid point are in equilibrium. Differences may become apparent.

Basic points and acid points are considered to act as adsorption points for other material particles. For example, base points and acid points existing on the surface of the ferromagnetic powder act as adsorption points for various additives such as a kneading agent, a dispersant, and a polishing agent. Therefore, based on the information obtained by applying the present invention, it is possible to improve the characteristics such as dispersibility and surface property by appropriately selecting the combination of various particle materials used for the magnetic paint and the back coat layer paint. Is possible.

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described based on experimental examples.

In this example, various magnetic powders were selected as the particle material for the magnetic recording medium, and their basic points and acid points were experimentally evaluated. First, the magnetic powder A used in Table 1
Or magnetic powder J is mentioned.

Example 1 In this example, the magnetic powder A to the magnetic powder J shown in Table 1 were reacted with acetone, and diacetone alcohol produced by the catalytic action of the base site and mesityl oxide produced by the catalytic action of the acid site. Is analyzed.

First, 0.5 to 1 g of each magnetic powder shown in Table 1 and 40 g of acetone were weighed in an Erlenmeyer flask with a stopper having a volume of 100 ml, sealed, and ultrasonically dispersed. Then add 25 ± 0 to the Erlenmeyer flask.
It was shaken for 15 to 20 hours in a constant temperature water bath adjusted to 05 ° C. About 2 ml of the obtained dispersion system was put into a 2 ml glass syringe equipped with a disposable membrane filter, and extrusion filtration was performed to obtain a transparent filtrate. The filtrate was analyzed by gas chromatography. The analysis was carried out using a Shimadzu gas chromatograph GC-8A equipped with a 3 m long PEG-20 column and a hydrogen flame ionization detector, and a nitrogen gas flow rate of 40
The conditions were ml / min and temperature 180 ° C.

A typical gas chromatogram obtained by such an analysis method is shown in FIG. In this figure, the vertical axis represents the relative peak height, and the horizontal axis represents the retention time (minutes). Retention time
The peak at 0.83 minutes is unreacted acetone, the peak at 3.05 minutes is diacetone alcohol corresponding to the dimerized compound by the aldol condensation reaction of acetone by the catalytic action of the base point, and the peak at 1.63 minutes is diacetone alcohol is acid. Mesityl oxide produced by dehydration due to the catalytic action of spots,
The peak at 8.34 minutes is 4,6-dihydroxy-4,6-dimethyl-2-heptanone (corresponding to a trimer of acetone) generated by diacetone alcohol further undergoing an aldol condensation reaction with acetone. The identification of each of these compounds was performed based on the comparison with the retention time of the standard substance and the mass spectrum.

Example 2 In this example, the magnetic powder A to the magnetic powder J shown in Table 1 were reacted with diacetone alcohol to form acetone produced by the catalytic action of the base site and mesityl oxide produced by the catalytic action of the acid site. Is analyzed.

The experiment was performed according to the method described in Example 1 except that the water temperature in the constant temperature water tank was 30.0 ± 0.05 ° C.

The results of Examples 1 and 2 are summarized in Table 2 above.

According to the method for evaluating surface physical properties according to the present invention, it is possible to evaluate microscopic surface physical properties that cannot be grasped by conventional methods. For example, the present inventors have previously reported that Bulletin of Chemical Society of Japan (Bull.Chem.Soc.Jpn.) Vol. 53, No. 9, page 2683 (1986), γ-Fe. ₂ O ₃ has been announced to be more acidic overall than α-Fe ₂ O ₃ . However, when looking at the amount of diacetone alcohol or the amount of acetone produced, which is an index of the height of the basic site activity in Table 2, γ-Fe ₂ O
The basic site activity of ₃ (magnetic powder B) is rather higher than that of α-Fe ₂ O ₃ (magnetic powder D). On the other hand, looking at the amount of mesityl oxide produced, which is an index of high acid site activity, γ-Fe ₂ O ₃
The acid site activity of (magnetic powder B) is α-Fe ₂ O ₃ (magnetic powder D).
Higher than that. In other words, both γ-Fe ₂ O ₃ have high base-site activity and high acid-site activity, and as a whole, α-Fe ₂ O _3
It can be concluded that the reason why it is more acidic than ₂ O ₃ is that the acid site activity of γ-Fe ₂ O ₃ exceeds the base site activity.

It should be noted that, when looking at Table 2, the values in Example 2 were generally higher than those in Example 1, and this is considered to be due to the equilibrium constant of each elementary reaction. Furthermore, even if the acid point and the base point are not detected by the method of Example 1, such as magnetic powder A, magnetic powder C, or magnetic powder G, they may be detected by the method of Example 2, so the evaluation method is It is preferable to select appropriately according to the physical properties of the magnetic powder.

〔The invention's effect〕

As is clear from the above description, according to the evaluation method of the present invention, it is possible to microscopically evaluate the surface physical properties of the particulate material for a magnetic recording medium, as compared with the prior art. As a result, it becomes possible to know in detail the interaction of various particle materials with the solvent, the affinity between the particle materials, etc., and the reproducibility during material design and manufacturing is improved. Particularly in recent years, various polar groups have been introduced into additives such as binders for the purpose of improving various properties such as dispersibility and surface properties. It is extremely effective in understanding the interaction between the base point and the acid point.

Further, as another application of the evaluation method according to the present invention, deterioration diagnosis of a ketone solvent when preparing a magnetic paint can be considered. The ketone-based solvent is likely to be polymerized by aldol condensation as the material particles such as magnetic powder are dispersed. The thus-polymerized ketone-based solvent is hard to evaporate during the coating / drying process of the magnetic paint or the back coat layer paint, and remains in the magnetic layer to exert an adverse effect. By applying the evaluation method of the present invention, it becomes possible to discover the deterioration of the ketone solvent and avoid the above-mentioned adverse effects.

As yet another application, it is possible to evaluate the case where the aldol condensation of a ketone solvent is positively used. For example, it is disclosed in JP-A-62-248128 that condensation products of cyclic ketones have a lubricating effect. Therefore, when cyclohexanone is used as a solvent in the preparation of magnetic paints and the material particles are dispersed and the progress of the aldol condensation reaction is confirmed by the evaluation method of the present invention, the lubricant can be separated by selecting an appropriate degree of condensation. It is possible to obtain a magnetic paint or the like that exhibits lubricity without being mixed with.

[Brief description of drawings]

FIG. 1 is a typical gas chromatogram when the present invention is applied to magnetic powder.

Claims (2)

(57) [Claims] 1. A β-hydroxycarbonyl compound produced by an aldol condensation reaction of the above carbonyl compound by bringing a carbonyl compound having an α hydrogen atom into contact with a particle material used for a magnetic recording medium, and the β-hydroxycarbonyl compound. Α, β produced by the dehydration reaction of
-A method for evaluating surface physical properties of a particle material for a magnetic recording medium, characterized by analyzing a double bond carbonyl compound. 2. A β-hydroxycarbonyl compound and a particle material used for a magnetic recording medium are brought into contact with each other, and a carbonyl compound having an α-hydrogen atom produced by a reverse aldol condensation reaction of the β-hydroxycarbonyl compound and the β-hydroxycarbonyl compound. A method for evaluating the surface properties of a particle material for a magnetic recording medium, which comprises analyzing an α, β-double bond carbonyl compound produced by a dehydration reaction of a hydroxycarbonyl compound.