JPH0568009B2 - - Google Patents

Description

[Detailed description of the invention]

B. Field of Industrial Application The present invention relates to magnetic recording media, such as magnetic tapes, magnetic disks, magnetic cards, and the like. B. Prior art For example, in magnetic recording media such as magnetic tape, Co
Deposited γ-Fe ₂ O ₃ has been used as a magnetic powder, but this has low residual magnetic flux density (Br) and saturation magnetization (σs).
There are problems in that the output is low due to a small amount of light, and the electrical conductivity is insufficient, and the hiding power is also poor (high light transmittance). Therefore, the magnetic layer cannot be made very thin, which is disadvantageous for making magnetic tapes thinner and longer.Moreover, adding a large amount of carbon black or the like to improve electrical conductivity and hiding power may cause a decrease in output. arise. For this reason, for example, for video tapes for long-term recording using Co-coated γ-Fe ₂ O ₃ magnetic powder, the standard is a total thickness of 12 to 16 μm, a light transmittance of 0.1% or less, and a thickness of the magnetic layer. It is said that at least about 4 μm is required. Therefore, recently, metal (iron or iron alloy) magnetic powder, which has high Br, high σs, and has excellent electrical conductivity and moderating power, has been considered and put into practical use as acicular magnetic powder especially for video tapes. . However, although metal magnetic powder has these characteristics, it has poor oxidation resistance, low hardness, and inevitably contains Al ₂ O ₃ in the magnetic layer.
It is necessary to add an abrasive material such as Moreover,
Metal magnetic powder has a large coercive force (Hc), so it is easy to record.
Erasability is difficult, and Hc is less than 1100 Oe (especially
(900 Oe or less), the particle size of the acicular powder cannot be made very small. A magnetic recording medium using such acicular metal powder cannot obtain a sufficiently low noise level for, for example, video use. As a solution to these drawbacks of metal magnetic powders, magnetic powders made of iron nitride (iron nitride) have been proposed in "Technical Report of the Institute of Electronics and Communication Engineers," Vo1.81, No.274, 1-6.
This method has been proposed in Page, '82 and Japanese Unexamined Patent Publication No. 57-26101. For example, Fe ₄ N magnetic powder has a large audio output, is superior in stability, hardness, and Hc distribution compared to metal magnetic powder, and has a larger σs (larger output) than Co-coated γ-Fe ₂ O ₃ . It is. As described above, iron nitride is worthy of attention as a magnetic powder for magnetic recording media, but the fact is that the required performance when applied to magnetic recording media has not been sufficiently studied with the above-mentioned known technology. It is. In particular, the use of lecithin as a dispersant for iron nitride magnetic powder is shown in the above-mentioned Japanese Patent Application Laid-Open No. 57-26101, but such a dispersant improves the surface properties of the magnetic layer and enables high-density recording. It is insufficient to perform dispersion to cope with this problem. Moreover, when lecithin is used, the problem of easily staining the calender roll during supercalendering for surface finishing cannot be avoided. C. Objective of the Invention An object of the present invention is to provide a magnetic recording medium that exhibits excellent surface properties, improved dispersibility of magnetic powder, and excellent S/N ratio and productivity. D. Structure of the invention and its effects That is, the magnetic recording medium according to the present invention is a magnetic recording medium comprising a magnetic powder, a surfactant, and a fatty acid ester in a coating film, wherein the magnetic powder is made of iron nitride. Or an iron alloy nitride is used, and the BET value is 35 m ² /g or more or more specific surface area, and the surfactant is an anionic surfactant having a carboxyl residue or a phosphoric acid residue. and the fatty acid ester has 6 carbon atoms.
It is an ester of the above aliphatic carboxylic acid and an aliphatic alcohol having 1 or more carbon atoms, and the total amount of the anionic surfactant and fatty acid ester is 1 to 10 parts by weight based on 100 parts by weight of the magnetic powder. ,and,
It is characterized in that the weight ratio of anionic surfactant to fatty acid ester is 20:1 to 1:5. According to the present invention, since iron nitride and/or iron alloy nitride is used as the magnetic material of the magnetic layer,
The inherent features of nitrides (i.e. Hc distribution, high Br,
In addition to exhibiting high σs, stability, high hardness, etc., it is also possible to realize a practical or useful configuration as a magnetic recording medium by specifying the above-mentioned physical and magnetic property conditions according to the present invention. Making the magnetic material finer (increasing the specific surface area) is the S/N
This is an important factor for improving the ratio. However, when using conventional metal magnetic powder, it is necessary to miniaturize it to a size sufficient for use in, for example, video tapes.
If it is refined so that it exhibits a specific surface area of 35 m ² /g or more in terms of BET value, Hc will become too high.
On the other hand, since the iron nitride or iron alloy nitride of the present invention has a nitride structure, even if the iron nitride or iron alloy nitride has a fine BET specific surface area of 35 m ² /g or more like metal magnetic powder, Hc can be lowered. and,
If Hc can be lowered to less than 1000 Oe, an inexpensive ferrite head can be used as a magnetic head. Moreover, if the BET specific surface area is set to a fine one of 35 m ² /g or more, an improvement in S/N can be expected. Moreover, according to the present invention, since the magnetic layer containing the magnetic material contains an anionic surfactant and a fatty acid ester, the dispersibility of the magnetic material is improved compared to the conventional case of using lecithin. It was found that a magnetic layer with good surface properties could be obtained. In addition, the anionic surfactant and fatty acid ester used in the present invention have the property of being less likely to bleed out compared to when lecithin is used, which reduces staining of calender rolls during calendering and improves productivity. Sexuality also improves. The content or content ratio of the above two components used to achieve these remarkable effects is 100% of the magnetic powder.
It is important that the total amount of anionic surfactant and fatty acid ester per part by weight is 1 to 10 parts by weight, and preferably 1.5 to 8 parts by weight.
Further, it is important that the blending ratio of anionic surfactant and fatty acid ester is 20:1 to 1:5 by weight, and preferably 15:1 to 1:3. It is important that the anionic surfactant used in the present invention has at least one of a carboxylic acid residue (carboxyl residue) and a phosphoric acid residue. Those having a carboxylic acid residue can be broadly classified into the following two types (1) and (2), which are preferably used. (1) Higher fatty acids having 14 or more carbon atoms (either saturated or unsaturated) and their salts. For example, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, linolenic acid, linoleic acid, oleic acid, behenic acid, caprylic acid, and their salts with alkali metals, alkaline earth metals, amino acids, ammonia, etc. . (2) an unsaturated aliphatic hydrocarbon having a double bond;
Copolymers with compounds having carboxylic acid residues (carboxyl residues) and salts thereof. Examples of the unsaturated aliphatic hydrocarbons include:
Isobutylene, 2,3-dimethyl-1-butene, 2,3,-dimethyl-1-pentene, isooctene (diisobutylene), isododecene,
Isononen et al. Examples of the above-mentioned compounds having carboxylic acid residues include maleic anhydride, acrylic acid, methacrylic acid, areic acid substituted with a methyl group, and combinations of these with alkali metals, alkaline earth metals, amines, and ammonia. salt etc. In addition, as an anionic surfactant having a phosphoric acid residue,

[C] (However, M is a hydrogen atom or an alkali metal atom,
R is a hydrocarbon residue, and X is -OM or -OR. ) Phosphate esters represented by these are preferred. More preferred are at least one of the following two types or a mixture thereof.

[ka]

[C] (However, R' is an aliphatic hydrocarbon residue with 2 to 20 carbon atoms,
n is an integer from 1 to 20. ) In addition to the above, usable anionic surfactants are listed below. Higher alcohol sulfate ester: R ² −OSO ₃ M Liquid fatty oil sulfate ester: R ² (OSO ₃ M)
COOR ³ Sulfuric acid esters of aliphatic amines and amides: R ² CONHR ³ CH ₂ OSO ₃ M Sulfonic acid salts of dibasic fatty acid esters:

[C] Fatty acid amidosulfonic acids:
R ² CONR ³ CH ₂ CH ₂ SO ₃ M Alkylaryl sulfonic acids:

[ka]

[ka]

(However, in the above, R ² and R ³ are aliphatic hydrocarbon residues, and M is a hydrogen atom or an atomic group that forms a salt with an alkali metal, alkaline earth metal, amines, or ammonia. ) Furthermore, as the fatty acid ester used in the present invention, it is important to use an ester of an aliphatic carboxylic acid having 6 or more carbon atoms and an aliphatic alcohol having 1 or more carbon atoms. Usable fatty acid esters include butyl stearate, methyl myristate, isocetyl stearate, ethyl palmitate, octyl myristate, butyl isostearate, and the like. Further, the above-mentioned anionic surfactant and/or fatty acid ester may be used to pre-surface-treat the nonmagnetic material, may be kneaded together with the magnetic material, binder resin, etc., or may be used on the magnetic layer. May be overcoated. Further, the magnetic material used in the present invention is mainly composed of iron or an iron alloy (e.g., iron-nickel, iron-cobalt), but may also contain a small amount of other elements (e.g., phosphorus). . In the magnetic recording medium according to the present invention, polyurethane can be used as a binder resin for the magnetic layer, which can be synthesized by reacting a polyol with a polyisocyanate. In addition, if a cellulose resin and/or a vinyl chloride copolymer is also included as a binder resin together with the above polyurethane, the dispersibility of the magnetic powder will be improved when applied to the magnetic layer, and its mechanical strength will be increased. increase However, if the cellulose resin and/or vinyl chloride copolymer alone is used, the layer may become too hard, but this can be prevented by containing polyurethane. Furthermore, phenoxy resin can also be used as a binder resin component. FIG. 1 shows a magnetic recording medium, for example a magnetic tape, according to the present invention, in which a subbing layer 2 (this layer may not be provided if necessary) and a magnetic layer 3 are provided on a support 1. Laminated. Based on the present invention, the magnetic layer 3 contains the above-mentioned iron nitride magnetic powder and dispersant. As the binder resin for the magnetic layer, in addition to the binder resins described above, a mixture of this binder resin and a thermoplastic resin, a thermosetting resin, a reactive resin, or an electron beam curable resin may be used. The total amount of binder resin used in the present invention is desirably 5 to 50 parts by weight per 100 parts by weight of magnetic powder from the viewpoint of recording density, strength, etc. Furthermore, in order to improve the durability of the magnetic recording medium, various hardening agents can be contained in the magnetic layer.
For example, isocyanate can be contained. For magnetic recording media, such as magnetic tapes, a magnetic paint is prepared by mixing and dispersing magnetic powder, a binder resin, and various additives in an organic solvent, and after adding an aromatic isocyanate and/or aliphatic isocyanate, this is coated on a support ( (e.g. polyester film), dry if necessary, calender treatment,
Manufactured through slitting. It is preferable to use an aromatic isocyanate and an aliphatic isocyanate together in order to maintain the physical properties of the magnetic coating material so that it is easy to apply and to improve the physical properties of the magnetic layer formed. The paint used to form the magnetic layer may contain known additives such as dispersants, lubricants, abrasives, and other antistatic agents, if necessary. The surface of the support opposite to the side on which the magnetic layer is provided has a second layer for the purpose of preventing static electricity, preventing transfer, improving running properties, etc.
As shown in the figure, so-called backcoat 4
It is better to apply As a coating method for coating the magnetic coating material onto the support to form a magnetic layer, air doctor coating, blade coating, reverse roll coating, etc. can be used, and other methods are also possible. The magnetic layer coated on the support by such a method is optionally treated to orient the magnetic powder in the layer, and then the formed magnetic layer is dried. Further, if necessary, the magnetic recording medium is manufactured by subjecting it to surface smoothing processing or cutting it into a desired shape. Hereinafter, the present invention will be explained with reference to specific examples. The components, proportions, order of operations, etc. shown below may be changed in various ways without departing from the spirit of the invention. In addition, all "parts" in the following examples represent "parts by weight." Examples 1 to 3 Iron powder was heated to 400 ml in a mixed gas of NH ₃ and H ₂ (3:1).
By heat-treating at ℃ for 4 hours, iron nitride (composition: γ-Fe ₄ N, BET value: 40 m ² /g) magnetic powder was obtained. Then, the components shown in Table 1 below were charged into a ball mill and dispersed. After filtering this magnetic paint with a 1 μm filter, 5 parts of polyfunctional isocyanate was added, and the mixture was coated on a support using a reverse roll coater and superimposed. It was calendered and slit into 1/2 inch width to make video tapes (corresponding to the numbers of each Example and Comparative Example). However, the numbers after the second column of Table 1 represent parts by weight, and "actual" after the second column represents an example, and "ratio" represents a comparative example.

[Table] When the characteristics of the videotape shown in Table 1 above were measured, the results shown in Table 2 below were obtained. The measurement method was as follows. RF output: 4MHz playback output was measured. Lumi S/N: Recorded and played back on a VHS video deck and measured using a Shibasoku Color Video Noise Meter 925C. Glossiness: Measured using a commercially available gloss meter.

[Table] Based on the results, based on the present invention, if iron nitride magnetic powder is used as a magnetic material and an anionic surfactant and fatty acid ester are used together, not only the surface properties (glossiness) of the magnetic layer but also the It can be seen that the S/N ratio and output are significantly improved.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views of a portion of each magnetic recording medium according to an embodiment of the present invention. In addition, in the symbols shown in the drawings, 1...support body, 3...magnetic layer.

Claims (1)

[Claims] 1. A magnetic recording medium containing magnetic powder, a surfactant, and a fatty acid ester in a coating film, wherein the magnetic powder is made of iron nitride or iron alloy nitride, The BET value has a specific surface area of 35 m ² /g or more, the surfactant is an anionic surfactant having a carboxyl residue or a phosphoric acid residue, and the fatty acid ester has a carbon atom It is an ester of an aliphatic carboxylic acid having a number of 6 or more and an aliphatic alcohol having a carbon number of 1 or more, and the total amount of the anionic surfactant and fatty acid ester is 1 to 10 parts by weight per 100 parts by weight of magnetic powder. A magnetic recording medium characterized in that the ratio of anionic surfactant to fatty acid ester is 20:1 to 1:5 by weight.