JP2007265487A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium having excellent dispersion properties, coating film smoothness, electromagnetic transducing characteristics and running durability. <P>SOLUTION: The magnetic recording medium has at least one magnetic layer formed by dispersing ferromagnetic fine powder in a binder on a non-magnetic supporting body, wherein the ferromagnetic fine powder has granular or rotational elliptical particle shapes and is iron nitride based magnetic powder of 5 to 50 nm in particle diameter, the binder contains a polyurethane resin obtained by using a polyol, a diol having a short chain of ≤500 in a wight average molecular weight and an organic diisocyanate, wherein the diol having the short chain has an alicyclic and polycyclic structure and/or a spiro structure, and the concentration of the alicyclic, and the ratio of polycyclic structure and the spiro structure to the concentration of a urethane group is 1.0 to 2.0. A non-magnetic layer having non-magnetic powder dispersed in a binder may be formed between the non-magnetic supporting body and the magnetic layer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a magnetic recording medium in which one or more magnetic layers formed by dispersing ferromagnetic fine powder and a binder are provided on a nonmagnetic support, and has excellent electromagnetic conversion characteristics and durability. About.

Magnetic recording technology enables other recordings such as the ability to repeatedly use media, the ease of digitizing signals, the construction of a system in combination with peripheral devices, and the simple modification of signals. Since it has excellent features not found in the system, it has been widely used in various fields including video, audio, and computer applications.
In general, in response to the demand for high-density recording on magnetic recording media for computers and the like, further improvement in electromagnetic conversion characteristics is required, and it is important to make ferromagnetic powder fine particles, super smooth the surface of the media, etc. Become.

  In order to improve the smoothness of the coating film, etc., the support has a magnetic layer in which acicular ferromagnets or flat magnetic bodies are dispersed in a binder containing a polyurethane resin having a bridged hydrocarbon structure or a spiro structure. A magnetic recording medium is disclosed (see Patent Document 1).

In making magnetic particles fine, recent magnetic materials use ferromagnetic metal powders or ferromagnetic hexagonal ferrite fine powders of 0.1 μm or less.
Larger saturation magnetization and improved electromagnetic conversion characteristics are desired with respect to particle size. Iron and nitrogen at least as constituent elements, at least one element of aluminum, silicon, or rare earth element, and at least an Fe ₁₆ N ₂ phase, wherein the nitrogen content relative to iron is 1.0 to 20.0 There is disclosed a magnetic recording medium in which a magnetic layer containing a granular or elliptical magnetic powder with an average particle size of 5 to 30 nm and a binder is provided on a nonmagnetic support (patent) Reference 2).
However, although a fine iron nitride magnetic material is used, there is a problem that the dispersibility of the magnetic material is insufficient and sufficient electromagnetic conversion characteristics cannot be obtained.

JP 2005-129150 A JP 2005-310857 A

  The problem to be solved by the present invention is to provide a magnetic recording medium excellent in dispersibility, coating film smoothness, electromagnetic conversion characteristics and running durability.

The problem to be solved by the present invention has been achieved by the invention described in the following (1) and (2) and (3) which is an embodiment thereof.
(1) A magnetic recording medium having at least one magnetic layer in which ferromagnetic fine powder is dispersed in a binder on a magnetic support, wherein the ferromagnetic fine powder has a granular or spheroidal particle shape. a, 5 to 50 nm particle size, saturation magnetization is iron nitride-based magnetic powder ^{50~150emu / g (50~150A · m 2} / kg), the binder is a polyol, a weight average molecular weight of 500 or less short A polyurethane resin obtained using a chain diol and an organic polyisocyanate, wherein the short-chain diol is a diol having an alicyclic polycyclic structure and / or a spiro structure, the alicyclic polycyclic structure and the diol A magnetic recording medium wherein the concentration of the spiro structure is present at a ratio of 1.0 to 2.0 with respect to the urethane group concentration;
(2) having at least one nonmagnetic layer in which at least one nonmagnetic fine powder is dispersed in a binder (1) on a nonmagnetic support, and binding the ferromagnetic fine powder on the nonmagnetic layer. In the magnetic recording medium having at least one magnetic layer dispersed in the agent (2), the ferromagnetic fine powder has a granular or spheroidal particle shape, a particle diameter of 5 to 50 nm, and a saturation magnetization of 50. ~ 150 emu / g (50 ~ 150 A · m ² / kg) iron nitride magnetic powder, at least binder (2) is obtained using polyol, short chain diol having a weight average molecular weight of 500 or less, and organic polyisocyanate The short-chain diol is a diol having an alicyclic polycyclic structure and / or a spiro structure, and the concentration of the alicyclic polycyclic structure and the spiro structure is relative to the concentration of the urethane group. 1.0 ~ The magnetic recording medium characterized in that present in a proportion of 2.0,
(3) The magnetism according to (1) or (2), wherein the alicyclic polycyclic structure or the spiro structure includes at least one structure selected from the group consisting of the following (1) to (3): recoding media.

  According to the present invention, as a result of being able to smooth the interface between the coating film surface and the foreign coating film, electromagnetic recording characteristics and repeated running durability are improved, and magnetic recording in which durability deterioration after storage is reduced The medium could be obtained.

The magnetic recording medium of the present invention is a magnetic recording medium having at least one magnetic layer in which a ferromagnetic fine powder is dispersed in a binder on a nonmagnetic support, and the ferromagnetic fine powder is granular or rotated. It is an iron nitride magnetic powder having an elliptical particle shape, a particle diameter of 5 to 50 nm, and a saturation magnetization of 50 to 150 emu / g (50 to 150 A · m ² / kg), and the binder has a weight average molecular weight. A polyurethane resin obtained using a short chain diol of 500 or less and an organic diisocyanate, wherein the short chain diol is a diol having an alicyclic polycyclic structure or a spiro structure, and the alicyclic polycyclic structure and The spiro structure has a concentration of 1.0 to 2.0 with respect to the urethane group concentration.

The magnetic recording medium of the present invention is presumed to have been technically improved based on the following actions. However, the truth of this estimation does not affect the patentability of the present invention.
As a conventional technique using a polyurethane having a polycyclic structure such as a spiro structure or an alicyclic polycyclic structure, a fine particle metal, and a hexagonal barium ferrite magnetic substance, as disclosed in Patent Document 1, a spiro structure is used as a polyurethane structure of polyurethane. In addition to having a structure and an alicyclic polycyclic structure, a short chain diol used as a chain extender and an organic diisocyanate component have the same structure. Unlike the magnetic material of the present application, the magnetic material used in Patent Document 1 has a needle shape or a flat plate shape, so that it is difficult to finely fill the magnetic layer with the magnetic material, and the number of magnetic particles per unit volume is increased. The electromagnetic conversion characteristics were insufficient.
Similar to Patent Document 1, the use of alicyclic polycyclic diols such as tricyclodecane dimethanol and spiroglycol as short-chain diols and diisocyanate components enables the formation of a bulky polycyclic skeleton in the vicinity of the urethane bond. Since it can be introduced, it has the effect of sterically hindering the association of urethane groups in the solution. In other words, although it has the effect of increasing the solubility of polyurethane in the solvent and it is possible to improve the dispersibility of the ferromagnetic fine powder, in the case of a magnetic material having a needle shape or a flat shape, the upper magnetic layer and the lower nonmagnetic layer When applying the layers at the same time and orienting the upper magnetic body, the magnetic body rotates due to the magnetic field, causing disturbance at the interface between the upper and lower layers, which is disadvantageous for improving the electromagnetic conversion characteristics. .

When the granular or spheroid magnetic material used in the present invention is used, mixing at the upper and lower layer interfaces due to orientation becomes difficult to occur, but the needle-like ratio is small, and the magnetic material close to a sphere is less likely to be fluidly oriented and coated. When shearing by the coater is released, the upper magnetic body settles at the lower layer liquid interface, causing mixing at the upper and lower layer interfaces, resulting in a problem that a uniform interface and thus sufficient electromagnetic characteristics cannot be obtained.
Therefore, a uniform interface is ensured after using an iron nitride magnetic powder having an elliptical particle shape with a particle diameter of 5 to 50 nm and a saturation magnetization of 50 to 150 emu / g (50 to 150 A · m ² / kg). As a result of diligent research aiming to achieve this, by introducing a bulky polycyclic skeleton at a specific ratio in the vicinity of the urethane bond of the above polyurethane, the thixotropic property of the magnetic layer dispersion is properly controlled and shear is released. However, it was found that mixing at the upper and lower layer interfaces did not occur and a uniform interface could be formed.

  Specific means for achieving the above regulations include the size of the powder contained in the upper magnetic layer, the saturation magnetization, the concentration of urethane groups contained in the polyurethane resin, and the spiro skeleton and oil that have the action of preventing the association of urethane groups. The concentration of the polycyclic structure such as a cyclic bridged hydrocarbon skeleton is defined and controlled so that no mixed region is generated in the upper and lower layers. In general, soft aggregates having a three-dimensional network structure formed by applying shear are loosened, and the binder solution trapped between the aggregates contributes to the flow and causes a decrease in viscosity. In the present invention, it has been found that by controlling the above factors, soft aggregates can be formed while ensuring appropriate dispersibility of the magnetic material, and the fluidity of the binder solution can be ensured. It is thought that the structure of the bulky polycyclic skeleton introduced in the vicinity of the urethane bond of polyurethane and the ratio between the urethane groups were suppressed, and the dispersibility of the magnetic substance and the fluidity of the binder solution could be controlled. As other factors related to thixotropy, as for the dispersed magnetic powder, the properties of the powder surface (pH, loss on heating, etc.), etc., regarding the binder, (1) molecular weight, (2) type of functional group As for the solvent, (1) type (polarity, etc.), (2) binder solubility, (3) solvent prescription amount, water content, etc. are mentioned.

In addition, the polyurethane having such a structure can increase Tg, and also has an effect of being excellent in coating film durability at high temperatures. In particular, when a fine magnetic material is used, durability cannot be ensured because a sufficient mechanical strength of the magnetic layer coating film cannot be secured with the conventional binder, but there is also an effect of using the binder of the present application.
This is considered to be due to the fact that the above-mentioned magnetic substance was highly dispersed and the strength was improved by having a polycyclic skeleton.

I. Magnetic Layer The magnetic recording medium of the present invention has at least one magnetic layer in which ferromagnetic fine powder is dispersed in a binder on a nonmagnetic support.
When the magnetic recording medium of the present invention has the nonmagnetic layer and the magnetic layer on the nonmagnetic support in this order, at least the binder (2) of the magnetic layer, preferably the binder (2) of the magnetic layer and the nonmagnetic layer. The binder (1) of the magnetic layer contains the following polyurethane.

1) Binder (2) preferably Binder (1) and Binder (2)
The binder (2) used in the present invention, preferably the binder (1) and the binder (2) contains a polyurethane resin obtained by reacting a polyol and a polyisocyanate.
In the present invention, “polyol” refers to a compound or a group of compounds having two or more hydroxyl groups in the molecule. The polyol used in the present invention is preferably two or more compounds having two hydroxyl groups in the molecule.

The “alicyclic polycyclic structure” means a structure having a plurality of alicyclic structures shared by two or more carbon atoms. Among the alicyclic polycyclic structures, those having a bridged hydrocarbon structure in which three or more alicyclic structures are shared by two or more carbon atoms are preferable. “Spiro structure” refers to a structure in which a plurality of rings share one carbon atom.
The bridged hydrocarbon structure or spiro structure is preferably at least one structure selected from the group consisting of formulas (1) to (3).

(1) Method of introducing a bridged hydrocarbon structure or spiro structure into a polyurethane resin The method of introducing an alicyclic polycyclic structure, preferably a bridged hydrocarbon structure or a spiro structure, into a polyurethane resin is as follows. Things can be raised.
The alicyclic polycyclic structure and the spiro skeleton are as described above, and the introduction of these structures into the polyurethane can be introduced as a short-chain diol component or an organic diisocyanate component used as a chain extender.

The molecular weight of the polyol is preferably 400 to 5,000.
(1-1) Examples of the polyol include a polyester polyol, a polyether polyol, and a polycarbonate polyol.

Examples of the short-chain diol having a bridged hydrocarbon structure include the following compounds.
Bicyclo [1.1.0] butanediol, bicyclo [1.1.1] pentanediol, bicyclo [2.1.0] pentanediol, bicyclo [2.1.1] hexanediol, bicyclo [3 .1.0] hexanediol, bicyclo [2.2.1] heptanediol, bicyclo [3.2.0] heptanediol, bicyclo [3.1.1] heptanediol, bicyclo [2.2.2] Octanediol, bicyclo [3.2.1] octanediol, bicyclo [4.2.0] octanediol, bicyclo [5.2.0] nonanediol, bicyclo [3.3.1] nonanediol, bicyclo [3 3.2] Decanediol, bicyclo [4.2.2] decanediol, bicyclo [43.3] dodecanediol, bicyclo [3.3.3] undecandio Le,

Bicyclo [1.1.0] butanedimethanol, bicyclo [1.1.1] pentanedimethanol, bicyclo [2.1.0] pentanedimethanol, bicyclo [2.1.1] hexanedimethanol, bicyclo [ 3.1.0] Hexanedimethanol, bicyclo [2.2.1] heptanedimethanol, bicyclo [3.2.0] heptanedimethanol, bicyclo [3.1.1] heptanedimethanol, bicyclo [2. 2.2] Octanedimethanol, bicyclo [3.2.1] octanedimethanol, bicyclo [4.2.0] octanedimethanol, bicyclo [5.2.0] nonanedimethanol, bicyclo [3.3. 1] Nonanedimethanol, bicyclo [3.3.2] decandimethanol, bicyclo [4.2.2] decandimethanol, bicyclo [4.3 3] dodecane dimethanol, bicyclo [3.3.3] undecane methanol, tricyclo [2.2.1.0] heptane-diol, tricyclo [5.2.1.0 ^{2, 6]} decane diol, tricyclo [4 2.1.2 ^7,9 ] undecanediol, tricyclo [5.4.0.0 ^2,9 ] undecanediol, tricyclo [5.3.1.1] dodecanediol, tricyclo [4.4.1. 1] dodecanediol, tricyclo [7.3.2.0 ^5,13] tetradecane diol, tricyclo [5.5.1.0 ^3,11] tridecane diol, tricyclo [2.2.1.0] Heputanji methanol, tricyclo [5.2.1.0 ^2,6] decane methanol, tricyclo [4.2.1.2 ^7,9] undecane methanol, tricyclo [5.4.0.0 ^2,9] undecane Methanol, tricyclo [5.3.1.1] dodecane dimethanol, tricyclo [4.4.1.1] dodecane dimethanol, tricyclo [7.3.2.0 ^5,13] tetra decane dimethanol, tricyclo [5 .5.1.0 ^3,11] birds de Kanji methanol.

Specific examples of the short chain diol having a spiro structure include the following compounds.
Spiro [3.4] octanedimethanol, spiro [3.4] heptanedimethanol, spiro [3.4] decandimethanol, dispiro [5.1.7.2] heptadecandimethanol, cyclopentanespirocyclobutane Examples include methanol, cyclohexane spirocyclopentanedimethanol, spirobicyclohexanedimethanol, bis (1,1-dimethyl-2-hydroxyethyl) -2,4,8,10-tetraoxaspiro [5.5] undecane. Among these, bis (1,1-dimethyl-2-hydroxyethyl) -2,4,8,10-tetraoxaspiro [5.5] undecane.

The polyol having a bridged hydrocarbon structure or a spiro structure, a polyester polyol with a tricyclo [5.2.1.0 ^2,6] decanedimethanol, tricyclo [5.2.1.0 ^{2, 6]} de Polyether polyol using a polyether polyol of a propylene oxide adduct of candimethanol and tricyclo [5.2.1.0 ^2,6 ] decanedimethanol is preferred.

  A known dibasic acid can be used as the dibasic acid component of the polyester polyol. Examples of the dibasic acid include isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, malonic acid, glutaric acid, pimelic acid, and suberic acid. Among these, isophthalic acid, succinic acid, adipic acid, and sebacic acid are preferable.

A known short chain diol may be copolymerized with the polyether polyol or polycarbonate polyol.
The following can be illustrated as a short chain diol which can be used together.
Aliphatic linear diols such as 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol;
2,2-dimethyl-1,3-propanediol, 3,3-dimethyl-1,5-pentanediol, 2-methyl-2-ethyl-1,3-propanediol, 3-methyl-3-ethyl-1 , 5-pentanediol, 2-methyl-2-propyl-1,3-propanediol, 3-methyl-3-propyl-1,5-pentanediol, 2-methyl-2-butyl-1,3-propanediol 3-methyl-3-butyl-1,5-pentanediol, 2,2-diethyl-1,3-propanediol, 3,3-diethyl-1,5-pentanediol, 2-ethyl-2-butyl- 1,3-propanediol, 3-ethyl-3-butyl-1,5-pentanediol, 2-ethyl-2-propyl-1,3-propanediol, 3-ethyl-3-propyl-1,5- Nthanediol, 2,2-dibutyl-1,3-propanediol, 3,3-dibutyl-1,5-pentanediol, 2,2-dipropyl-1,3-propanediol, 3,3-dipropyl-1, 5-pentanediol, 2-butyl-2-propyl-1,3-propanediol, 3-butyl-3-propyl-1,5-pentanediol, 2-ethyl-1,3-propanediol, 2-propyl- 1,3-propanediol, 2-butyl-1,3-propanediol, 3-ethyl-1,5-pentanediol, 3-propyl-1,5-pentanediol, 3-butyl-1,5-pentanediol 3-octyl-1,5-pentanediol, 3-myristyl-1,5-pentanediol, 3-stearyl-1,5-pentanediol, 2-ethyl -1,6-hexanediol, 2-propyl-1,6-hexanediol, 2-butyl-1,6-hexanediol, 5-ethyl-1,9-nonanediol, 5-propyl-1,9-nonane An aliphatic diol having a branched side chain such as diol and 5-butyl-1,9-nonanediol;
Diols having a ring structure such as bisphenol A and hydrogenated bisphenol A.
The short chain diol used in combination is preferably one having a molecular weight of less than 400.

(1-2) Chain extender by alicyclic polycyclic structure, preferably short chain diol having bridged hydrocarbon structure or spiro structure The above-mentioned short chain diol having bridged hydrocarbon structure or spiro structure is chain extender You may use as.
Preferred are tricyclo [2.2.1.0] heptanedimethanol, tricyclo [5.2.1.0 ^2,6 ] decanedimethanol, bicyclo [3.3.2] decanedimethanol, bicyclo [4. 2.2] decanedimethanol, spiro [3,4] decanedimethanol, bis (1,1-dimethyl-2-hydroxyethyl) -2,4,8,10-tetraoxaspiro [5,5] undecane. Particularly preferably, tricyclo [5.2.1.0 ^2,6 ] decandimethanol, bis (1,1-dimethyl-2-hydroxyethyl) -2,4,8,10-tetraoxaspiro [5,5] An example is undecane.

(1-3) Diisocyanate having a bridged hydrocarbon structure or spiro structure Examples of the diisocyanate having a bridged hydrocarbon structure or a spiro structure include tricyclo [2.2.1.0] heptane diisocyanate and tricyclo [5.2.1. .0 ^2,6] decane diisocyanate, tricyclo [4.2.1.2 ^7,9] undecane diisocyanate, tricyclo [5.4.0.0 ^2,9] undecane diisocyanate - door, tricyclo [5.3 .1.1] dodecane diisocyanate, tricyclo [4.4.1.1] dodecane diisocyanate, tricyclo [7.3.2.0 ^5,13] tetradecane diisocyanate, tricyclo [5.5.1.0 ^3,11] Tridecane diisocyanate, norbornene diisocyanate, spiro [3,4] octane diisocyanate, spiro Examples include [3,4] heptane diisocyanate, spiro [3,4] decane diisocyanate, dispiro [5,1,7,2] heptadecane diisocyanate, cyclopentane spirocyclobutane diisocyanate, cyclohexane spirocyclopentane diisocyanate, spirobicyclohexane diisocyanate. it can. Preferably, tricyclo [5.2.1.0 ^2,6 ] decane diisocyanate and norbornene diisocyanate can be used.

  The urethane resin used in the present invention can be produced by polyadding the above polyol, polyisocyanate, and, if necessary, a chain extender in the presence of a tin compound as a catalyst.

(2) The content of the bridged hydrocarbon structure or spiro structure in the polyurethane The content of the bridged hydrocarbon structure or spiro structure in the polyurethane is preferably 1 to 5.5 mmol / g. The concentration of the skeleton is present at a ratio of 1.0 to 2.0 with respect to the urethane group concentration. If the amount is less than the above range, the effect of suppressing the association between urethane groups is insufficient, the dispersibility and interface fluctuation are deteriorated, and the durability is not sufficient. Even if it exceeds the said range, smoothness will fall.

(3) Diisocyanate As the diisocyanate component used in combination with a polyol having a bridged hydrocarbon structure or a spiro structure and a short-chain diol, known ones are used. TDI (tolylene diisocyanate), MDI (diphenylmethane diisocyanate), p-phenylene diisocyanate, o-phenylene diisocyanate, m-phenylene diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, isophorone diisocyanate and the like are preferable.

(4) Urethane group concentration The urethane group concentration in the polyurethane is preferably 2.0 mmol / g to 6.0 mmol / g, and more preferably 2.5 mmol / g to 5.5 mmol / g.
If it is in the above range, the glass transition temperature (Tg) of the coating film does not decrease, so the durability is good. Further, since the solvent solubility can be ensured, the dispersibility does not decrease. If the dispersibility is not lowered, a polyol can be contained, which is advantageous in terms of synthesis such as easy molecular weight control.

(5) Weight average molecular weight The weight average molecular weight of the polyurethane resin used in the present invention is preferably 40,000 to 100,000, more preferably 50,000 to 90,000. In the above range, the coating film strength does not decrease, and the durability is good. Moreover, since the solubility to a solvent does not fall, dispersibility becomes favorable.

(6) Glass transition temperature The glass transition temperature (Tg) of the polyurethane resin used in the present invention is preferably 40 to 200 ° C, more preferably 70 to 180 ° C, and further preferably 80 to 170 ° C. Within the above range, the coating strength at high temperature does not decrease, and durability and storage stability are improved. Moreover, the calendar moldability is good and the electromagnetic conversion characteristics are good.

(7) Polar group in polyurethane The polyurethane resin used in the present invention may contain a polar group. As the polar group, —SO ₃ M, —OSO ₃ M, —PO ₃ M ₂ , and —COOM are preferable. Among this, -SO ₃ M, -OSO ₃ M is more preferable. M represents a hydrogen atom or a monovalent cation. Examples of monovalent cations include alkali metals and ammonium. The polar group is preferably contained in the polyurethane resin in an amount of 1 × 10 ⁻⁵ eq / g to 2 × 10 ⁻⁴ eq / g. When the content of the polar group is within the above range, the adsorption to the magnetic material and the solubility in the solvent are sufficient, and the dispersibility is good.

(8) Hydroxyl group in polyurethane The polyurethane resin used in the present invention may contain a hydroxyl group (OH group). 2-20 are preferable per molecule, and 3-15 are more preferable. When the number of OH groups is in the above range, the reactivity with the isocyanate curing agent is improved, so the coating film strength and durability are improved, and the solubility in the solvent is improved, so the dispersibility is good. Become.

2) Ferromagnetic fine powder The ferromagnetic fine powder used in the magnetic recording medium of the present invention is preferably iron nitride particles. The iron nitride particles desirably include at least an Fe ₁₆ N ₂ phase, and preferably do not include other iron nitride phases. This is because the crystal magnetic anisotropy of iron nitride (Fe ₄ N or Fe ₃ N phase) is about 1 × 10 ⁵ erg / cc, whereas the Fe ₁₆ N ₂ phase is 2 to 7 × 10 ⁶ erg / cc. This is because it has a high magnetocrystalline anisotropy of cc. Thereby, a high coercive force can be maintained even when the particles are made fine.
This high magnetocrystalline anisotropy results from the crystal structure of the Fe ₁₆ N ₂ phase. The crystal structure is a body-centered tetragonal system in which N atoms regularly enter the Fe interstitial positions of Fe, and the strain when N atoms enter the lattice is considered to be the cause of high crystal magnetic anisotropy. . The easy axis of magnetization of the Fe ₁₆ N ₂ phase is the C axis extended by nitriding.

The shape of the particles containing the Fe ₁₆ N ₂ phase is preferably granular or spheroid. More preferably, it is spherical. This is because one of three equivalent directions of cubic α-Fe is selected by nitriding and becomes the c-axis (magnetization easy axis). Therefore, if the particle shape is acicular, the easy magnetization axis is the minor axis. This is because particles in the direction and the major axis direction are mixed, which is not preferable. The average value of the major axis length / minor axis length ratio is preferably 1 to 2, more preferably 1 to 1.5, with the maximum diameter of one particle being the major axis length and the smallest diameter being the minor axis length. What is described as particle size represents the major axis length.

The particle size of the Fe ₁₆ N ₂ phase, which is a magnetic material, is 5 to 50 nm, preferably 5 to 20 nm. This is because as the particle size becomes smaller, the influence of thermal fluctuation becomes larger, and it becomes superparamagnetic and becomes unsuitable for a magnetic recording medium. Also, because of the magnetic viscosity, the coercive force at the time of high-speed recording with a head increases, making it difficult to record. On the other hand, if the particle size is large, the saturation magnetization cannot be reduced, so that the coercive force during recording becomes too high, making it difficult to record. Further, when the particle size is large, the particle noise when the magnetic recording medium is obtained becomes high.
The particle size distribution is preferably monodisperse. This is because, in general, monodispersion reduces the medium noise. The coefficient of variation of the particle size is preferably 20% or less (1 to 20%), more preferably 15% or less (2 to 15%), and further preferably 10% or less (2 to 10%). .
In the present invention, the “particle size variation coefficient” means a value obtained by calculating a standard deviation of the particle size distribution at the equivalent circle diameter and dividing this by the average particle size. The “composition variation coefficient” means a value obtained by calculating a standard deviation of the composition distribution of the alloy nanoparticles and dividing this by the average composition in the same manner as the particle diameter variation coefficient. In the present invention, these values are multiplied by 100 to display%.

  The particle size and the coefficient of variation of the particle size are determined by placing a diluted alloy nanoparticle on a Cu200 mesh with a carbon film and drying it, and shooting a negative photographed with a TEM (JEOL 1200EX) at a magnification of 100,000. It can be calculated from the arithmetic average particle diameter measured with (Carl Zeiss KS-300).

In the particles containing the Fe ₁₆ N ₂ phase, the content of nitrogen with respect to iron is preferably 1.0 to 20.0 at%, more preferably 5.0 to 18.0 at%, more preferably 8.0 to 15. It is more preferably 0 at%. This is because if the amount of nitrogen is too small, the amount of Fe ₁₆ N ₂ phase formed decreases, the increase in coercive force is caused by strain due to nitriding, and the amount of nitrogen decreases, the coercive force decreases. This is because if the amount of nitrogen is too large, the Fe ₁₆ N ₂ phase is a metastable phase and therefore decomposes into other nitrides that are stable phases, resulting in excessive reduction in saturation magnetization.

This is because the fine Fe ₁₆ N ₂ phase has poor oxidation stability and there is a concern that it will ignite if there is no surface compound phase. Therefore, a core / shell structure having a surface compound layer made of an oxide, nitride, or carbide is preferable. From the viewpoint of oxidation stability, the surface compound layer is preferably an oxide.
The surface compound layer can be formed by gradually oxidizing the Fe ₁₆ N ₂ phase, but a surface compound layer containing a rare earth element or at least one element selected from boron, silicon, aluminum, and phosphorus is used. It is preferable.
The thickness of the surface compound layer is preferably 1 to 5 nm. If the thickness is less than 1 nm, the oxidation stability is poor. If the thickness is more than 5 nm, the proportion of the surface compound layer in the magnetic powder increases, and as the particle size decreases, an appropriate saturation magnetization cannot be maintained. Because.
As for the composition of the surface compound layer, the total content of rare earth elements or boron, silicon, aluminum and phosphorus with respect to iron is preferably 0.1 to 40.0 at%, more preferably 1.0 to 30.0 at%, and more preferably Is preferably 3.0 to 25.0 at%. If the amount of these elements is too small, it becomes difficult to form the surface compound layer, not only the magnetic anisotropy of the magnetic powder is reduced, but also the oxidation stability is poor. Moreover, when there are too many of these elements, the saturation magnetization will fall excessively easily.

The saturation magnetization of the Fe ₁₆ N ₂ phase is preferably 50 emu / g to 150 emu / g (50 to 150 A · m ² / kg). This is because if the saturation magnetization is high, the coercive force at the time of recording increases, and recording with the recording head becomes impossible. Also, in reproduction, even if the saturation magnetization is increased, the MR head is saturated and an improvement in output cannot be expected. On the other hand, if it is too low, the reproduction output becomes low, which is not preferable.

The magnetic powder preferably has a BET specific surface area of 40 to 100 m ² / g. This is because when the BET specific surface area is too small, the particle size increases, and when applied to a magnetic recording medium, the particulate noise increases, the surface smoothness of the magnetic layer decreases, and the reproduction output tends to decrease.
Further, if the BET specific surface area is too large, particles containing the Fe ₁₆ N ₂ phase are likely to aggregate, and it is difficult to obtain a uniform dispersion and it is difficult to obtain a smooth surface.

(Synthesis of α-Fe)
A method for producing particles containing the Fe ₁₆ N ₂ phase will be described. The Fe ₁₆ N ₂ phase is obtained by nitriding α-Fe. In order to obtain α-Fe, there are a method of reducing iron-based oxide or hydroxide (for example, hematite, magnetite, goethite, etc.) in the gas phase and a method of synthesizing in the liquid phase. First, a method for reducing in the gas phase will be described. The average particle size of the iron-based oxide or hydroxide is not particularly limited, but normally it is preferably about 5 to 100 nm. If the particle size is too small, inter-particle sintering is likely to occur during the reduction treatment, and if the particle size is too large, the reduction treatment tends to be heterogeneous, making it difficult to control the particle size and magnetic properties.

Therefore, a rare earth element or a compound containing at least one element selected from boron, silicon, aluminum, phosphorus and the like is deposited on iron-based oxide or hydroxide to prevent sintering. Is preferred. The rare earth element is deposited by dispersing a starting material in an alkali or acid aqueous solution, dissolving a salt of the rare earth element in this, and adding a hydroxide or hydrate containing the rare earth element to the raw material powder by a neutralization reaction or the like. It can be performed by precipitation. When depositing a compound containing at least one element selected from boron, silicon, aluminum, phosphorus, etc., these compounds are dissolved in a solution in which the raw material powder is immersed and deposited by adsorption, The deposition is carried out by precipitation.
A rare earth element and at least one element selected from boron, silicon, aluminum, phosphorus, and the like may be simultaneously or alternately deposited on the hydroxide or hydrate. Moreover, in order to perform these deposition processes efficiently, it is also preferable to mix additives, such as a reducing agent, a pH buffer agent, and a particle size control agent.

Next, the hydroxide or hydrate on which the compound was deposited was heated in a reducing gas stream. As the reducing gas, hydrogen gas or carbon monoxide gas can be used. Hydrogen which becomes H ₂ O after the treatment is preferably used from the viewpoint of environmental suitability.
The reduction temperature is preferably 250 to 600 ° C. More preferably, it is 300-500 degreeC. In this temperature range, the reduction temperature proceeds sufficiently and particle sintering can be prevented.

  A method of synthesizing α-Fe in the liquid phase is preferably used as a method for avoiding the sintering of the particles in the gas phase reduction. As a method for producing iron nanoparticles, when classified by the precipitation method, an alcohol reduction method using a primary alcohol, a secondary alcohol, a tertiary alcohol, a polyol reduction method using a divalent or trivalent polyhydric alcohol, a thermal decomposition method Ultrasonic decomposition method and strong reducing agent reduction method are known. Further, the production method is classified into a reaction system, and a polymer existence method, a high boiling point solvent method, a normal micelle method, a reverse micelle method, and the like are known.

First, the reverse micelle method that is easy to control the particle size and easily obtain a monodispersed fraction and is preferably used in the present invention will be described.
<Reverse micelle synthesis method of iron nanoparticles>
Next, the manufacturing method of the alloy nanoparticle of this invention is demonstrated.
The alloy nanoparticles of the present invention comprise a reduction step in which a reverse micelle solution (I) containing one or more metal compounds and a reverse micelle solution (II) containing a reducing agent are mixed and subjected to a reduction treatment, as necessary. It can be manufactured by an aging step in which an aging treatment is performed after the reduction treatment. By this production method, iron nanoparticles are produced. Hereinafter, each step will be described.

(Reduction process)
First, a reverse micelle solution (I) is prepared by mixing a water-insoluble organic solvent containing a surfactant and an aqueous solution containing one or more metal compounds. The reverse micelle solution (I) contains an iron salt used to form iron nanoparticles.

  An oil-soluble surfactant is used as the surfactant. Specifically, sulfonate type (for example, aerosol OT (manufactured by Wako Pure Chemical Industries), quaternary ammonium salt type (for example, cetyltrimethylammonium bromide), ether type (for example, pentaethylene glycol dodecyl ether) and the like can be mentioned. It is done.

Preferable water-insoluble organic solvents for dissolving the surfactant are alkanes and ethers. The alkane is preferably an alkane having 7 to 12 carbon atoms. Specific examples include heptane, octane, nonane, decane, undecane, and dodecane. On the other hand, the ether is preferably diethyl ether, dipropyl ether, or dibutyl ether.
The addition amount of the surfactant in the water-insoluble organic solvent is preferably 20 to 200 g / l.

  Metal compounds contained in an aqueous solution of a metal compound include nitrates, sulfates, hydrochlorides, acetates, metal complex hydrogen acids with chloride ions as ligands, and metal complex potassiums with chloride ions as ligands. Examples include salts, sodium salts of metal complexes having chloride ions as ligands, and ammonium salts of metal complexes having oxalate ions as ligands, and these can be arbitrarily selected and used in the production method of the present invention. can do.

  The concentration of each metal compound aqueous solution as a metal compound is preferably 0.1 to 2,000 μmol / ml, and more preferably 1 to 500 μmol / ml.

It is preferable to add a chelating agent to the aqueous metal compound solution so that the resulting particles have a uniform composition. Specifically, DHEG (dihydroxyethylglycine), IDA (iminodiacetic acid), NTP (nitrilotripropionic acid), HIDA (dihydroxyethyliminodiacetic acid), EDDP (ethylenediamine dipropionic acid dihydrochloride), BAPTA It is preferable to use (diaminophenylethylene glycol tetraacetic acid tetrapotassium salt hydrate) or the like as a chelating agent. The chelate stability constant (log K) is preferably 10 or less.
The addition amount of the chelating agent is preferably 0.1 to 10 mol, and more preferably 0.3 to 3 mol, per 1 mol of the metal compound.

  Next, a reverse micelle solution (II) containing a reducing agent is prepared. The reverse micelle solution (II) can be prepared by mixing a water-insoluble organic solvent containing a surfactant and an aqueous reducing agent solution. When two or more reducing agents are used, they may be mixed together to form a reverse micelle solution (II), but in consideration of the stability and workability of the solution, each is separately mixed in a water-insoluble organic solvent. Thus, it is preferable to prepare them as separate reverse micelle solutions ((II ′), (II ″), etc.) and to use them by appropriately mixing them.

Examples of the reducing agent aqueous solution include alcohols; polyalcohols; H ₂ ; HCHO, S ₂ O ₆ ²⁻ , H ₂ PO ₂ ⁻ , BH ₄ ⁻ , N ₂ H ₅ ⁺ , H ₂ PO ₃ ^{− and the} like and water. These reducing agents are preferably used alone or in combination of two or more.
The amount of the reducing agent in the aqueous solution is preferably 3 to 50 mol with respect to 1 mol of the metal salt.

  Examples of the surfactant and non-aqueous organic solvent used in the reverse micelle solution (II) include those used in the reverse micelle solution (I).

  The mass ratio of water and surfactant (water / surfactant) contained in each of the reverse micelle solutions (I) and (II) is preferably 20 or less. If the mass ratio is 20 or less, precipitation is unlikely to occur and uniform particles can be obtained. The mass ratio is more preferably 15 or less, and further preferably 0.5 to 10.

  The mass ratio of water and surfactant in the reverse micelle solutions (I) and (II) may be the same or different, but the mass ratio is preferably the same in order to make the system uniform.

The reverse micelle solutions (I) and (II) prepared as described above are mixed. The mixing method is not particularly limited, but it is preferable to add and mix the reverse micelle solution (II) while stirring the reverse micelle solution (I) in consideration of the reduction uniformity. . After the mixing is completed, the reduction reaction is allowed to proceed, and the temperature at that time is a constant temperature in the range of -5 to 30 ° C. If the reduction temperature is −5 ° C. or higher, the reduction reaction can be made uniform without condensation of the aqueous phase, and if it is 30 ° C. or lower, aggregation or precipitation is unlikely to occur and the system is stabilized. Can do. A preferable reduction temperature is 0 to 25 ° C, and more preferably 5 to 25 ° C.
Here, the “constant temperature” means that the temperature is in a range of T ± 3 ° C. when the set temperature is T (° C.). Even in such a case, the upper limit and the lower limit of the T are in the range of the reduction temperature (−5 to 30 ° C.).

  The time for the reduction reaction needs to be appropriately set depending on the amounts of the reverse micelle solutions (I) and (II), but is preferably 1 to 30 minutes, and more preferably 5 to 20 minutes.

Since the reduction reaction has a great influence on the monodispersity of the particle size distribution of the alloy, it is preferable to carry out the reduction reaction while stirring as fast as possible (for example, about 3000 rpm or more).
A preferred stirring device is a stirring device having a high shearing force. Specifically, the stirring blade basically has a turbine-type or paddle-type structure, and a sharp blade is attached to the end of the blade or a position in contact with the blade. It is a stirring device that has a structure and rotates blades with a motor. Specifically, devices such as a dissolver (manufactured by Special Machine Industries), an omni mixer (manufactured by Yamato Kagaku), and a homogenizer (manufactured by SMT) are useful. By using these apparatuses, monodisperse nanoparticles can be synthesized as a stable dispersion.

  After the reaction of the reverse micelle solutions (I) and (II), at least one dispersant having 1 to 3 amino groups or carboxy groups is added in an amount of 0.001 to 10 per mole of alloy nanoparticles to be prepared. It is preferable to add a molar amount. If the addition amount of a dispersing agent is 0.001-10 mol, the monodispersity of an alloy nanoparticle can be improved more and aggregation will not occur.

The dispersant is preferably an organic compound having a group that adsorbs to the surface of the alloy nanoparticles. Specifically, it has 1 to 3 amino groups, carboxy groups, sulfonic acid groups or sulfinic acid groups, and these can be used alone or in combination.
As structural formulas, R—NH ₂ , H ₂ N—R—NH ₂ , H ₂ N—R (NH ₂ ) —NH ₂ , R—COOH, HOCO—R—COOH, HOCO—R (COOH) —COOH , R—SO ₃ H, HOSO ₂ —R—SO ₃ H, HOSO ₂ —R (SO ₃ H) —SO ₃ H, R—SO ₂ H, HOSO—R—SO ₂ H, HOSO—R (SO ₂ H) a compound represented by -SO ₂ H, R in the formula is a hydrocarbon residue of a straight, branched or cyclic, saturated or unsaturated.

A particularly preferred compound as a dispersant is oleic acid. Oleic acid is a well-known surfactant in colloidal stabilization and is used to protect iron nanoparticles. The relatively long chain of oleic acid gives an important steric hindrance that counteracts the strong magnetic interaction between particles (oleic acid has 18 carbon chains, about 2 nm in length (about 20 angstroms), double bond 1). Oleic acid is preferred because it is an inexpensive natural resource that can be easily obtained from, for example, olive oil. In addition, oleylamine derived from oleic acid is a useful dispersant like oleic acid.
In addition, similar long-chain carboxylic acids such as erucic acid and linoleic acid can be used similarly to oleic acid (for example, long-chain organic acids having 8 to 22 carbon atoms can be used alone or in combination). .

  The addition timing of the dispersant is not particularly limited, but is preferably between immediately after the reduction reaction and the start of the following aging step. By adding such a dispersant, iron nanoparticles that are more monodispersed and have no aggregation can be obtained.

(Aging process)
The production method of the present invention includes an aging step of raising the temperature of the solution after the reaction to the aging temperature after the reduction reaction is completed.
The aging temperature is preferably a constant temperature between 30 and 90 ° C., and the temperature is suitably higher than the temperature of the reduction reaction. The aging time is preferably 5 to 180 minutes. When the aging temperature and the aging time are within the above ranges, aggregation and precipitation hardly occur, the reaction is completed, and the composition can be made constant. More preferable aging temperature and aging time are 40 to 80 ° C. and 10 to 150 minutes, and further preferable aging temperature and aging time are 40 to 70 ° C. and 20 to 120 minutes.

  Here, the “constant temperature” is synonymous with the temperature of the reduction reaction (where “reduction temperature” is the “aging temperature”), but in particular, the range of the above aging temperature (30 It is preferably 5 ° C. or higher, more preferably 10 ° C. or higher, than the temperature of the reduction reaction. By increasing the temperature by 5 ° C. or more, a composition as prescribed can be obtained.

  In the aging step as described above, iron nanoparticles having a desired particle size can be produced by appropriately adjusting the stirring speed at the temperature during aging.

After the aging, the solution after aging is washed with a mixed solution of water and a primary alcohol, and then subjected to a precipitation treatment with a primary alcohol to generate a precipitate. It is preferable to provide a washing / dispersing step for dispersing with a solvent. By providing such a cleaning / dispersing step, impurities can be removed, and the coating property when forming the magnetic layer of the magnetic recording medium can be further improved.
The washing and dispersion are performed at least once, preferably twice or more each.

  The primary alcohol used for washing is not particularly limited, but methanol, ethanol, and the like are preferable. The volume mixing ratio of water and primary alcohol (water / primary alcohol) is preferably in the range of 10/1 to 2/1, and more preferably in the range of 5/1 to 3/1. When the ratio of water is high, the surfactant may be difficult to remove, and conversely, when the ratio of primary alcohol is high, aggregation may occur.

  Nanoparticles can be stably prepared by the presence of a protective colloid when reducing or thermally depositing iron. For thermal precipitation, a method is known in which iron carbonyl is thermally decomposed to obtain iron. It is preferable to use a polymer or a surfactant as the protective colloid. Examples of the polymer include polyvinyl alcohol (PVA), poly N-vinyl-2pyrrolidone (PVP), gelatin and the like. Of these, PVP is particularly preferable. The molecular weight is preferably 20,000 to 60,000, more preferably 30,000 to 50,000. The amount of the polymer is preferably 0.1 to 10 times the mass of the hard magnetic nanoparticles to be produced, and more preferably 0.1 to 5 times.

The surfactant preferably used as the protective colloid preferably contains an “organic stabilizer” which is a long-chain organic compound represented by the general formula: R—X. R in the above general formula is a “tail group” which is a linear or branched hydrocarbon or fluorocarbon chain and usually contains 8 to 22 carbon atoms. X in the above general formula is a “head group” which is a moiety (X) that provides a specific chemical bond to the nanoparticle surface, and is a sulfinate (—SOOH), sulfonate (—SO ₂ OH), phosphinate ( -POOH), phosphonate (-OPO (OH) ₂ ), carboxylate, and thiol are preferred.

Examples of the organic stabilizer include sulfonic acids (R—SO ₂ OH), sulfinic acids (R—SOOH), phosphinic acids (R ₂ POOH), phosphonic acids (R—OPO (OH) ₂ ), carboxylic acids (R— COOH) and thiols (R-SH) are preferred. Of these, oleic acid is particularly preferred.

  Oleic acid is a well-known surfactant in colloidal stabilization and is suitable for protecting iron-based nanoparticles. Oleic acid has 18 carbon chains, and its length is ˜20 angstroms (˜2 nm). In addition, oleic acid is not aliphatic and has one double bond. And the relatively long chain of oleic acid provides an important steric hindrance that counteracts the strong magnetic interactions between the particles. Similar long chain carboxylic acids such as erucic acid and linoleic acid have been used as well as oleic acid (for example, long chain organic acids having between 8 and 22 carbon atoms can be used alone or in combination) Oleic acid is particularly preferred because it is an inexpensive natural resource (such as olive oil) that is readily available.

  The combination of phosphine and organic stabilizer (such as triorganophosphine / acid) can provide excellent control over particle growth and stabilization. Didecyl ether and didodecyl ether can also be used, but phenyl ether or n-octyl ether is preferably used as a solvent because of its low cost and high boiling point.

  The reaction is preferably performed at a temperature in the range of 80 ° C. to 360 ° C., more preferably 80 ° C. to 240 ° C., depending on the required nanoparticles and the boiling point of the solvent. If the temperature is lower than this temperature range, the particles may not grow. If the temperature is above this range, the particles may grow uncontrolled and increase the production of undesirable by-products.

  In order to increase the particle size, it is preferable to use a seed crystal method. At this time, since there is a concern about oxidation of the seed crystal iron particles, it is preferable to previously hydrotreat the particles.

  It is preferable to remove the salts from the solution after the synthesis of the iron nanoparticles from the viewpoint of improving the dispersion stability of the nanoparticles. For desalting, there is a method in which alcohol is added excessively to cause light agglomeration, and natural sedimentation or centrifugal sedimentation is performed to remove salts together with the supernatant. However, in such a method, aggregation is likely to occur, so an ultrafiltration method is adopted. It is preferable.

(Nitriding treatment)
Prior to the nitriding treatment, when there is a concern about the oxidation of the iron nanoparticles, reduction treatment in a mixed gas stream of hydrogen or hydrogen and an inert gas (H ₂ , Ar, He, etc.) can be performed. In this case, when the temperature is too high, the particles are fused, which is not desirable, and when the temperature is low, the particles are not sufficiently reduced. Therefore, as temperature, 200 to 300 degreeC is preferable, More preferably, it is 250 to 300 degreeC.

The Fe ₁₆ N ₂ phase can be obtained by heating the iron nanoparticles in a nitrogen-containing gas stream.
Nitrogen gas, nitrogen + hydrogen mixed gas, ammonia gas, etc. can be used as the nitriding gas, but ammonia gas is convenient for use.
The nitriding treatment in the NH ₃ atmosphere is performed in an ammonia (NH ₃ ) gas stream or a mixed gas stream containing ammonia gas (for example, any one or more of argon, hydrogen, nitrogen, and ammonia gas). The mixed gas is preferably used in a relatively low temperature range of 100 to 250 ° C. When the nitriding temperature increases, it becomes difficult to obtain the Fe ₁₆ N ₂ phase. On the other hand, if it is too low, the progress of Fe ₁₆ N ₂ phase generation tends to be slow. These gases are preferably of high purity (5N or more) or oxygen content of several ppm or less.
A temperature range of 100 to 250 ° C. and a range of 0.5 to 48 hours are industrially preferable, and the treatment time depends on the particle size, but the treatment is preferably performed for 0.5 to 24 hours.

In such nitriding treatment, it is desirable to select the nitriding treatment conditions so that the content of nitrogen with respect to iron in the obtained magnetic powder is 1.0 to 20 atomic%. If the amount of nitrogen is too small, the amount of Fe ₁₆ N ₂ produced is small and the effect of improving the coercive force is reduced. If the amount of nitrogen is too large, an Fe ₄ N or Fe ₃ N phase or the like is likely to be formed, the coercive force is rather lowered, and the saturation magnetization is likely to be excessively lowered.

(Oxide film)
In order to form an oxide film, the above-mentioned thickness is obtained by treatment at a temperature of 0 to 100 ° C. for 1 to 10 hours in an atmosphere of an inert gas (N ₂ , Ar, He, Ne, etc.) having an oxygen concentration of 1 to 5%. The oxide film can be formed.

In order to deposit a rare earth element, particles containing mainly Fe ₁₆ N ₂ are usually obtained by dispersing a starting material in an aqueous solution of an alkali or acid, dissolving a salt of the rare earth element therein, and performing a neutralization reaction or the like. In this case, hydroxides and hydrates containing rare earth elements may be precipitated.

Further, to dissolve the silicon and aluminum further compound composed of elements such as boron or phosphorus necessary, this was immersed particles comprising Fe ₁₆ N ₂ mainly the Fe ₁₆ N ₂ to mainly containing particles Thus, silicon or aluminum may be deposited. In order to perform these deposition processes efficiently, additives such as a reducing agent, a pH buffering agent, and a particle size controlling agent may be mixed.
As these deposition treatments, a rare earth element and silicon, aluminum or the like may be deposited simultaneously or alternately.

3) Other components Additives can be added to the magnetic layer in the present invention as required. Examples of the additive include an abrasive, a lubricant, a dispersant / dispersion aid, an antifungal agent, an antistatic agent, an antioxidant, a solvent, and carbon black.
Examples of these additives include molybdenum disulfide, tungsten disulfide, graphite, boron nitride, graphite fluoride, silicone oil, silicone having a polar group, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester, Polyolefin, polyglycol, polyphenyl ether, phenylphosphonic acid, benzylphosphonic acid group, phenethylphosphonic acid, α-methylbenzylphosphonic acid, 1-methyl-1-phenethylphosphonic acid, diphenylmethylphosphonic acid, biphenylphosphonic acid, benzylphenylphosphon Acid, α-cumylphosphonic acid, toluylphosphonic acid, xylylphosphonic acid, ethylphenylphosphonic acid, cumenylphosphonic acid, propylphenylphosphonic acid, butylphenylphosphonic acid, heptyl Aromatic ring-containing organic phosphonic acids such as phenylphosphonic acid, octylphenylphosphonic acid, nonylphenylphosphonic acid and alkali metal salts thereof, octylphosphonic acid, 2-ethylhexylphosphonic acid, isooctylphosphonic acid, isononylphosphonic acid, isodecyl Alkylphosphonic acids such as phosphonic acid, isoundecylphosphonic acid, isododecylphosphonic acid, isohexadecylphosphonic acid, isooctadecylphosphonic acid, isoeicosylphosphonic acid and alkali metal salts thereof, phenyl phosphate, benzyl phosphate, phosphorus Phenethyl phosphate, α-methylbenzyl phosphate, 1-methyl-1-phenethyl phosphate, diphenylmethyl phosphate, biphenyl phosphate, benzylphenyl phosphate, α-cumyl phosphate, toluyl phosphate, xylyl phosphate, phosphate Ethylphenyl, Aromatic phosphates such as cumenyl phosphate, propylphenyl phosphate, butylphenyl phosphate, heptylphenyl phosphate, octylphenyl phosphate, nonylphenyl phosphate, and alkali metal salts thereof, octyl phosphate, 2-ethylhexyl phosphate , Isooctyl phosphate, isononyl phosphate, isodecyl phosphate, isoundecyl phosphate, isododecyl phosphate, isohexadecyl phosphate, isooctadecyl phosphate, isoeicosyl phosphate, and alkali metal salts thereof, alkylsulfonic acid Esters and alkali metal salts thereof, fluorine-containing alkyl sulfates and alkali metal salts thereof, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, butyl stearate, oleic acid, linoleic acid, linolenic acid, Elai Monobasic fatty acids which may contain or be branched, such as acid and erucic acid, or a metal salt thereof, or butyl stearate, octyl stearate, amyl stearate, stearic acid It is branched even if it contains an unsaturated bond having 10 to 24 carbon atoms such as isooctyl, octyl myristate, butyl laurate, butoxyethyl stearate, anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate A monobasic fatty acid that may be included and a 1 to 6-valent alcohol that may be branched or include an unsaturated bond having 2 to 22 carbon atoms, or a branched chain that includes an unsaturated bond having 12 to 22 carbon atoms. Alkoxy alcohols or monoalkyl ethers of alkylene oxide polymers Mono-fatty acid esters composed of one or Re, di-fatty acid esters or polyvalent fatty acid esters, fatty acid amides having 2 to 22 carbon atoms, and aliphatic amines having 8 to 22 carbon atoms can be used. In addition to the above hydrocarbon groups, alkyl groups, aryl groups, and aralkyl groups substituted with nitro groups and groups other than hydrocarbon groups such as halogen-containing hydrocarbons such as F, Cl, Br, CF ₃ , CCl ₃ , and CBr ₃ You may have something.

  In addition, nonionic surfactants such as alkylene oxide, glycerin, glycidol, and alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphonium or sulfoniums, etc. Amphoteric interfaces such as cationic surfactants, anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, and sulfate ester groups, amino acids, aminosulfonic acids, sulfuric or phosphate esters of aminoalcohols, and alkylbetaines An activator or the like can also be used. These surfactants are described in detail in “Surfactant Handbook” (published by Sangyo Tosho Co., Ltd.).

The dispersant, lubricant, and the like are not necessarily pure, and may contain impurities such as isomers, unreacted materials, side reaction products, decomposition products, and oxides in addition to the main components. These impurities are preferably 30% by weight or less, more preferably 10% by weight or less.
Specific examples of these additives include, for example, manufactured by NOF Corporation: NAA-102, castor oil hardened fatty acid, NAA-42, cation SA, Naimine L-201, Nonion E-208, Anon BF, Anon LG, Takemoto Oil and fat: FAL-205, FAL-123, Shin Nippon Chemical Co., Ltd .: NJ Lube OL, Shin-Etsu Chemical: TA-3, Lion Armor: Armide P, Lion: Duomin TDO, Nisshin Oil : BA-41G, Sanyo Kasei Co., Ltd .: Profan 2012E, New Pole PE61, Ionette MS-400, and the like.

  Known organic solvents can be used in the magnetic layer of the present invention. The organic solvent is an arbitrary ratio of ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone and tetrahydrofuran, alcohols such as methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol and methylcyclohexanol. , Esters such as methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycol acetate, glycol ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, benzene, toluene, xylene, cresol, chlorobenzene, etc. Aromatic hydrocarbons, methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin Chlorinated hydrocarbons such as dichlorobenzene, N, N- dimethylformamide, may be used hexane.

  These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted materials, side reaction products, decomposition products, oxides, and moisture in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less. The organic solvent used in the present invention is preferably the same in the magnetic layer and the nonmagnetic layer. The amount added may be changed. Use a solvent with high surface tension (such as cyclohexanone or dioxane) in the nonmagnetic layer to increase the coating stability. Specifically, the arithmetic average value of the upper layer solvent composition may not fall below the arithmetic average value of the nonmagnetic layer solvent composition. It is essential. In order to improve dispersibility, it is preferable that the polarity is somewhat strong, and it is preferable that 50% or more of a solvent having a dielectric constant of 15 or more is included in the solvent composition. Moreover, it is preferable that a solubility parameter is 8-11.

  These dispersants, lubricants, and surfactants used in the magnetic layer of the present invention can be properly used in the magnetic layer and the nonmagnetic layer described later as needed. For example, of course, the dispersant is not limited to the example shown here, but the dispersant has a property of adsorbing or binding with a polar group, and in the magnetic layer, mainly on the surface of the ferromagnetic powder, as will be described later. In the nonmagnetic layer, it is presumed that the organophosphorus compound adsorbed or bonded to the surface of the nonmagnetic powder mainly by the polar group and once adsorbed is difficult to desorb from the surface of metal or metal compound. Accordingly, the surface of the ferromagnetic powder of the present invention or the nonmagnetic powder surface described later is in a state of being coated with an alkyl group, an aromatic group, etc., so the affinity of the ferromagnetic powder or nonmagnetic powder for the binder resin component And the dispersion stability of the ferromagnetic powder or non-magnetic powder is also improved. In addition, since it exists in a free state as a lubricant, the non-magnetic layer and the magnetic layer use fatty acids with different melting points to control the bleeding to the surface, and use esters with different boiling points and polarities to bleed to the surface. It is conceivable that the stability of coating is improved by controlling the amount of the surfactant, and the lubricating effect is improved by increasing the amount of lubricant added in the nonmagnetic layer. All or a part of the additives used in the present invention may be added in any step during the production of the coating solution for the magnetic layer or nonmagnetic layer. For example, when mixing with a ferromagnetic powder before the kneading step, when adding at a kneading step with a ferromagnetic powder, a binder and a solvent, when adding at a dispersing step, when adding after dispersing, when adding just before coating, etc. There is.

II. Nonmagnetic Layer The magnetic recording medium of the present invention may have at least one nonmagnetic layer in which a nonmagnetic powder is dispersed in the binder (2) between the nonmagnetic support and the magnetic layer.
The binder (2) includes a polyurethane resin obtained by using a short-chain diol having a weight average molecular weight of 500 or less and an organic diisocyanate as in the above-mentioned binder (1). A diol having a cyclic structure or a spiro structure, wherein the concentration of the alicyclic polycyclic structure, preferably a bridged hydrocarbon structure and the spiro structure is 1.0 to 2.0 with respect to the urethane group concentration Is preferably present.
The nonmagnetic powder used for the nonmagnetic layer may be an inorganic substance or an organic substance. Moreover, you may mix carbon black with a nonmagnetic powder as needed with a nonmagnetic layer.

For the nonmagnetic layer, magnetic powder may be used as long as the nonmagnetic layer is substantially nonmagnetic, but it is preferable to use nonmagnetic powder.
The nonmagnetic powder that can be used in the nonmagnetic layer may be an inorganic substance or an organic substance. Carbon black or the like can also be used. Examples of the inorganic substance include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides.

Specifically, titanium oxide such as titanium dioxide, cerium oxide, tin oxide, tungsten oxide, ZnO, ZrO ₂ , SiO ₂ , Cr ₂ O ₃ , α-alumina, β-alumina having an α conversion of 90 to 100%, γ-alumina, α-iron oxide, goethite, corundum, silicon nitride, titanium carbide, magnesium oxide, boron nitride, molybdenum disulfide, copper oxide, MgCO ₃ , CaCO ₃ , BaCO ₃ , SrCO ₃ , BaSO ₄ , silicon carbide Titanium carbide or the like is used alone or in combination of two or more. Preferable are α-iron oxide and titanium oxide.

The shape of the nonmagnetic powder may be any of acicular, spherical, polyhedral and plate shapes.
The crystallite size of the nonmagnetic powder is preferably 4 nm to 1 μm, and more preferably 40 to 100 nm. A crystallite size in the range of 4 nm to 1 μm is preferred because it does not become difficult to disperse and has a suitable surface roughness.
The average particle size of these non-magnetic powders is preferably 5 nm to 2 μm. However, if necessary, non-magnetic powders having different average particle sizes may be combined, or even a single non-magnetic powder may have a wide particle size distribution. It can also have an effect. The average particle size of the particularly preferred nonmagnetic powder is 10 to 200 nm. The range of 5 nm to 2 μm is preferable because the dispersion is good and the surface roughness is suitable.

The specific surface area of the non-magnetic powder is preferably 1 to 100 m ² / g, more preferably 5 to 70 m ² / g, and still more preferably 10 to 65 m ² / g. A specific surface area in the range of 1 to 100 m ² / g is preferred because it has a suitable surface roughness and can be dispersed with a desired amount of binder.
The oil absorption using dibutyl phthalate (DBP) is preferably 5 to 100 ml / 100 g, more preferably 10 to 80 ml / 100 g, and still more preferably 20 to 60 ml / 100 g.
The specific gravity is preferably 1 to 12, more preferably 3 to 6. The tap density is preferably 0.05 to 2 g / ml, more preferably 0.2 to 1.5 g / ml. When the tap density is in the range of 0.05 to 2 g / ml, there are few particles to be scattered, the operation is easy, and there is a tendency that it is difficult to adhere to the apparatus.

The pH of the nonmagnetic powder is preferably 2 to 11, but the pH is particularly preferably between 6 and 9. When the pH is in the range of 2 to 11, the friction coefficient does not increase due to high temperature, high humidity, or liberation of fatty acids.
The water content of the nonmagnetic powder is preferably 0.1 to 5% by weight, more preferably 0.2 to 3% by weight, and still more preferably 0.3 to 1.5% by weight. A water content in the range of 0.1 to 5% by weight is preferable because the dispersion is good and the viscosity of the paint after dispersion is stable.
The ignition loss is preferably 20% by weight or less, and the ignition loss is preferably small.

When the nonmagnetic powder is an inorganic powder, the Mohs hardness is preferably 4-10. If the Mohs hardness is in the range of 4 to 10, durability can be ensured. The nonmagnetic powder has a stearic acid adsorption amount of 1 to 20 μmol / m ² , more preferably ² to 15 μmol / m ² .
The heat of wetting of the nonmagnetic powder into water at 25 ° C. is preferably in the range of ^{20 to} 60 μJ / cm ² (200 to 600 erg / cm ² ). Moreover, the solvent which exists in the range of this heat of wetting can be used.
The amount of water molecules on the surface at 100 to 400 ° C. is suitably 1 to 10 / 100Å. The pH of the isoelectric point in water is preferably between 3 and 9.

The surface of these nonmagnetic powders is preferably surface-treated with Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , SnO ₂ , Sb ₂ O ₃ and ZnO. Particularly preferred for dispersibility are Al ₂ O ₃ , SiO ₂ , TiO ₂ , and ZrO ₂ , but more preferred are Al ₂ O ₃ , SiO ₂ , and ZrO ₂ . These may be used in combination or may be used alone. Further, a surface-treated layer co-precipitated according to the purpose may be used, or a method of treating the surface layer with silica after first treating with alumina, or vice versa may be employed. The surface treatment layer may be a porous layer depending on the purpose, but it is generally preferable that the surface treatment layer is homogeneous and dense.

  Specific examples of the non-magnetic powder used in the non-magnetic layer of the present invention include, for example, Showa Denko Nanotite, Sumitomo Chemical HIT-100, ZA-G1, Toda Kogyo DPN-250, DPN-250BX, DPN-245, DPN-270BX, DPB-550BX, DPN-550RX, Ishihara Sangyo Titanium oxide TTO-51B, TTO-55A, TTO-55B, TTO-55C, TTO-55S, TTO-55D, SN-100, MJ -7, α-iron oxide E270, E271, E300, STT-4D, STT-30D, STT-30, STT-65C manufactured by Titanium Industry, MT-100S, MT-100T, MT-150W, MT-500B manufactured by Teika T-600B, T-100F, T-500HD, etc. are mentioned. FINEX-25, BF-1, BF-10, BF-20, ST-M, Dowa Mining DEFIC-Y, DEFIC-R, Nippon Aerosil AS2BM, TiO2P25, Ube Industries 100A, 500A, Titanium Industry Y-LOP manufactured and what baked it are mentioned. Particularly preferred nonmagnetic powders are titanium dioxide and α-iron oxide.

Carbon black can be mixed in the nonmagnetic layer together with nonmagnetic powder to lower the surface electrical resistance, reduce the light transmittance, and obtain the desired μ Vickers hardness. Μ Vickers hardness of the nonmagnetic layer is normally 25 to 60 kg / mm ^2, preferably in order to adjust the head contact, and a 30 to 50 kg / mm ^2, using a thin film hardness meter (manufactured by NEC Corporation HMA-400) Measurement can be made using a diamond triangular pyramid needle with a ridge angle of 80 degrees and a tip radius of 0.1 μm at the tip of the indenter. It is standardized that the light transmittance is generally 3% or less for absorption of infrared rays having a wavelength of about 900 nm, for example, 0.8% or less for a VHS magnetic tape. For this purpose, rubber furnace, rubber thermal, color black, acetylene black and the like can be used.

Non specific surface area of the carbon black used in the magnetic layer is 100 to 500 m ² / g, preferably 150~400m ² / g, DBP oil absorption of the present invention are 20 to 400 ml / 100 g, preferably 30 to 200 ml / 100 g . The particle size of carbon black is 5 to 80 nm, preferably 10 to 50 nm, and more preferably 10 to 40 nm. Carbon black preferably has a pH of 2 to 10, a water content of 0.1 to 10%, and a tap density of 0.1 to 1 g / ml.

  Specific examples of carbon black that can be used in the non-magnetic layer of the present invention include BLACKPEARLS 2000, 1300, 1000, 900, 800, 880, 700, VULCAN XC-72, manufactured by Mitsubishi Kasei Kogyo Co., Ltd. 3050B, # 3150B, # 3250B, # 3750B, # 3950B, # 950, # 650B, # 970B, # 850B, MA-600, Columbia Carbon Corporation CONDUCTEX SC, RAVEN8800, 8000, 7000, 5750, 5250, 3500, 2100 2000, 1800, 1500, 1255, 1250, Ketjen Black EC manufactured by Akzo Corporation, and the like.

  Carbon black may be surface-treated with a dispersant, or may be grafted with a resin, or may be obtained by graphitizing a part of the surface. Moreover, before adding carbon black to a coating material, you may disperse | distribute with a binder beforehand. These carbon blacks can be used in a range not exceeding 50% by weight and not exceeding 40% of the total weight of the nonmagnetic layer with respect to the inorganic powder. These carbon blacks can be used alone or in combination. The carbon black that can be used in the nonmagnetic layer of the present invention can be referred to, for example, “Carbon Black Handbook” edited by Carbon Black Association.

  Further, an organic powder can be added to the nonmagnetic layer according to the purpose. Examples of such organic powder include acrylic styrene resin powder, benzoguanamine resin powder, melamine resin powder, and phthalocyanine pigment, but polyolefin resin powder, polyester resin powder, polyamide resin powder, polyimide resin, and the like. Resin powder and polyfluorinated ethylene resin can also be used. As the production method, those described in JP-A Nos. 62-18564 and 60-255827 can be used.

  As the binder resin, lubricant, dispersant, additive, solvent, dispersion method and the like of the nonmagnetic layer, those of the magnetic layer can be applied. In particular, with respect to the binder resin amount, type, additive, and dispersant addition amount and type, known techniques relating to the magnetic layer can be applied.

III. Nonmagnetic Supports Examples of the nonmagnetic support that can be used in the present invention include known ones such as biaxially stretched polyethylene terephthalate, polyethylene naphthalate, polyamide, polyamideimide, and aromatic polyamide. Among these, polyethylene terephthalate, polyethylene naphthalate, and polyamide are preferable.
These supports may be subjected in advance to corona discharge, plasma treatment, easy adhesion treatment, heat treatment and the like. The surface roughness of the nonmagnetic support that can be used in the present invention is preferably a center average roughness Ra of 3 to 10 nm at a cutoff value of 0.25 mm.

IV. Smoothing layer The magnetic recording medium of the present invention may be provided with a smoothing layer. The smoothing layer is a layer for embedding protrusions on the surface of the nonmagnetic support. In the case of a magnetic recording medium in which a magnetic layer is provided on the nonmagnetic support, the nonmagnetic support is provided between the nonmagnetic support and the magnetic layer. In the case of a magnetic recording medium in which a nonmagnetic layer and a magnetic layer are provided in this order on a support, it is provided between the nonmagnetic support and the nonmagnetic layer.
The smoothing layer can be formed by curing a radiation curable compound by radiation irradiation. The radiation curable compound refers to a compound having a property of starting to polymerize or crosslink when irradiated with radiation such as ultraviolet rays or an electron beam, to be polymerized and cured.

V. Backcoat layer Generally, magnetic tape for computer data recording is strongly required to have repeated running characteristics as compared with video tape and audio tape. In order to maintain such high storage stability, a backcoat layer can be provided on the surface of the nonmagnetic support opposite to the surface on which the nonmagnetic layer and the magnetic layer are provided. The coating material for the back coat layer disperses a particle component such as an abrasive and an antistatic agent and a binder in an organic solvent. Various inorganic pigments and carbon black can be used as the particulate component. Moreover, as a binder, resin, such as a nitrocellulose, a phenoxy resin, a vinyl chloride resin, a polyurethane, can be used individually or in mixture, for example.

VI. Layer Structure In the structure of the magnetic recording medium used in the present invention, the preferable thickness after drying of the nonmagnetic support is 3 to 80 μm. In the case where an undercoat layer is provided between the nonmagnetic support and the nonmagnetic layer or the magnetic layer, the thickness of the undercoat layer after drying is 0.01 to 0.8 μm, preferably 0.02 to 0.8 mm. 6 μm. Moreover, the thickness after drying of the backcoat layer provided on the surface opposite to the surface on which the nonmagnetic layer and the magnetic layer of the nonmagnetic support are provided is 0.1 to 1.0 μm, preferably 0. .2 to 0.8 μm.

<< Magnetic recording medium >>
Examples of the magnetic recording medium include magnetic tapes such as video tapes and computer tapes; magnetic disks such as floppy (registered trademark) disks and hard disks.

A magnetic layer can be formed by coating a layer mainly composed of Fe ₁₆ N ₂ particles on the support. As a method of coating on the support, air doctor coat, blade coat, rod coat, extrusion coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, kiss coat, cast coat, spray coat Spin coating or the like can be used.

  The thickness of the magnetic layer to be formed depends on the type of magnetic recording medium to be applied, but is preferably 4 nm to 1 μm, and more preferably 4 nm to 100 nm.

  The magnetic recording medium of the present invention may have other layers as needed in addition to the magnetic layer. For example, in the case of a disk, it is preferable to further provide a magnetic layer or a nonmagnetic layer on the opposite surface of the magnetic layer. In the case of a tape, it is preferable to provide a back layer on the surface of the insoluble support opposite to the magnetic layer.

  In addition, by forming a very thin protective film on the magnetic layer, the wear resistance is improved, and a lubricant is applied on the protective film to increase slipperiness, thereby providing sufficient reliability. It can be a magnetic recording medium.

  As a material of the protective film, oxides such as silica, alumina, titania, zirconia, cobalt oxide and nickel oxide; nitrides such as titanium nitride, silicon nitride and boron nitride; carbides such as silicon carbide, chromium carbide and boron carbide; Examples of the carbon include carbon and carbon such as graphite and amorphous carbon, and particularly preferable is a hard amorphous carbon generally called diamond-like carbon.

A carbon protective film made of carbon is suitable as a material for the protective film because it has a very thin film thickness and sufficient wear resistance, and hardly causes seizure on the sliding member.
As a method for forming a carbon protective film, sputtering is generally used for hard disks, but many methods using plasma CVD with a higher film formation rate have been proposed for products that require continuous film formation such as video tape. ing. Therefore, it is preferable to apply these methods.
Among them, it has been reported that the plasma injection CVD (PI-CVD) method has a very high film formation rate, and the obtained carbon protective film is hard and has a good quality protective film with few pinholes (for example, JP-A-61-61). No. 130487, JP-A 63-279426, JP-A 3-113824, etc.).

The carbon protective film preferably has a Vickers hardness of 1000 kg / mm ² or more, and more preferably 2000 kg / mm ² or more. The crystal structure is preferably an amorphous structure and non-conductive.
When a diamond-like carbon (diamond-like carbon) film is used as the carbon protective film, this structure can be confirmed by Raman light spectroscopic analysis. That is, when a diamond-like carbon film is measured, it can be confirmed by detecting a peak at 1520 to 1560 cm ⁻¹ . When the structure of the carbon film deviates from the diamond-like structure, the peak detected by Raman light spectroscopic analysis deviates from the above range, and the hardness as a protective film also decreases.

  As the carbon raw material for forming this carbon protective film, it is preferable to use carbon-containing compounds such as alkanes such as methane, ethane, propane, and butane; alkenes such as ethylene and propylene; and alkynes such as acetylene. Further, a carrier gas such as argon or an additive gas such as hydrogen or nitrogen for improving the film quality can be added as necessary.

When the carbon protective film is thick, the electromagnetic conversion characteristics are deteriorated and the adhesion to the magnetic layer is deteriorated. When the carbon protective film is thin, the wear resistance is insufficient. Accordingly, the film thickness is preferably 2.5 to 20 nm, and more preferably 5 to 10 nm.
In order to improve the adhesion between the protective film and the magnetic layer serving as the substrate, it is preferable to etch the surface of the magnetic layer with an inert gas in advance or to modify the surface by exposure to a reactive gas plasma such as oxygen. .

  The magnetic layer may have a multilayer structure in order to improve electromagnetic conversion characteristics, or may have a known nonmagnetic underlayer or intermediate layer under the magnetic layer. In order to improve running durability and corrosion resistance, it is preferable to apply a lubricant or an antirust agent on the magnetic layer or protective film as described above. As the lubricant to be added, known hydrocarbon lubricants, fluorine lubricants, extreme pressure additives and the like can be used.

  Examples of hydrocarbon lubricants include carboxylic acids such as stearic acid and oleic acid; esters such as butyl stearate; sulfonic acids such as octadecyl sulfonic acid; phosphate esters such as monooctadecyl phosphate; stearyl alcohol and oleyl alcohol. And the like; carboxylic acid amides such as stearamide; amines such as stearylamine; and the like.

Examples of the fluorine-based lubricant include a lubricant in which part or all of the alkyl group of the hydrocarbon-based lubricant is substituted with a fluoroalkyl group or a perfluoropolyether group.
Examples of perfluoropolyether groups include perfluoromethylene oxide polymer, perfluoroethylene oxide polymer, perfluoro-n-propylene oxide polymer (CF ₂ CF ₂ CF ₂ O) _n , perfluoroisopropylene oxide polymer (CF (CF ₃ ) CF ₂ O) _n or a copolymer thereof.

In addition, a compound having a polar functional group such as a hydroxyl group, an ester group, or a carboxyl group at the terminal or in the molecule of the alkyl group of the hydrocarbon-based lubricant is preferable because of its high effect of reducing frictional force.
Further, the molecular weight is 500 to 5,000, preferably 1,000 to 3,000. If it is less than 500, volatility is high and lubricity may be low. On the other hand, if it exceeds 5,000, the viscosity becomes high, so that the slider and the disk are likely to be attracted, and it may be liable to cause a travel stop or a head crash. Specifically, this perfluoropolyether is commercially available under trade names such as FOMBLIN manufactured by Augmond and KRYTOX manufactured by DuPont.

  Examples of extreme pressure additives include phosphate esters such as trilauryl phosphate; phosphites such as trilauryl phosphite; thiophosphites and thiophosphates such as trilauryl trithiophosphite; dibenzyl disulfide; And sulfur-based extreme pressure agents such as

  The lubricants may be used alone or in combination. As a method for applying these lubricants on the magnetic layer or the protective film, the lubricant is dissolved in an organic solvent and applied by a wire bar method, a gravure method, a spin coating method, a dip coating method, or a vacuum deposition method. Can be attached.

  Examples of rust inhibitors include nitrogen-containing heterocycles such as benzotriazole, benzimidazole, purine, and pyrimidine, and derivatives in which an alkyl side chain is introduced into the mother nucleus; benzothiazole, 2-mercapton benzothiazole, tetrazaindene And nitrogen- and sulfur-containing heterocycles such as ring compounds and thiouracil compounds and derivatives thereof.

As described above, when the magnetic recording medium is a magnetic tape or the like, a backcoat layer (backing layer) may be provided on the surface of the nonmagnetic support on which the magnetic layer is not formed. The back coat layer is formed by applying a back coat layer forming paint in which particulate components such as abrasives and antistatic agents and a binder are dispersed in a known organic solvent on the surface of the nonmagnetic support on which the magnetic layer is not formed. It is a layer provided.
Various inorganic pigments and carbon black can be used as the particulate component, and resins such as nitrocellulose, phenoxy resin, vinyl chloride resin, and polyurethane can be used alone or in combination as binders. .
A known adhesive layer may be provided on the surface on which the alloy particle-containing liquid is applied and on the surface on which the backcoat layer is formed.

The magnetic recording medium manufactured as described above has a surface centerline average roughness of preferably 0.1 to 5 nm, more preferably 1 to 4 nm, at a cutoff value of 0.25 mm. This is because it is preferable for the magnetic recording medium for high-density recording to have a surface having extremely excellent smoothness.
As a method for obtaining such a surface, there is a method in which a calender treatment is performed after the magnetic layer is formed. Moreover, you may perform a varnish process.

  The obtained magnetic recording medium can be used by appropriately punching with a punching machine or cutting to a desired size using a cutting machine or the like.

  Hereinafter, the present invention will be described more specifically with reference to examples. It should be noted that the components, ratios, operations, order, and the like shown here can be changed without departing from the spirit of the present invention, and should not be limited to the following examples. Further, “parts” in the examples represents parts by weight unless otherwise specified.

<Measurement method>
(1) Smoothness of coating film Using a Nanoscope II manufactured by Digital Instrument Co., Ltd. Relative when the number of protrusions of 10 nm or more was obtained by scanning the range of 30 μm × 30 μm with a tunnel current of 10 nA and a bias current of 400 mV, which was 10 Indicated by value.
(2) Average value Δd of fluctuation of upper layer thickness d
The cross section of the tape was photographed with a transmission electron microscope (TEM) (magnification of 20,000 times), and obtained from the following formula.
Δd = (Δd1 + Δd2 +... + Δdm) / m (m = 10 to 20)
The values are shown as relative values when Comparative Example 1 is 10.
(3) Electromagnetic conversion characteristics A 4.7 MHz single frequency signal was recorded with an optimum recording current using a DDS3 drive, and the reproduction output was measured. The reproduction output of Comparative Example 1 is shown as a relative value with 0 dB.

(4) Sus stain resistance The tape is brought into contact with the guide pole made of sus used in the DDS3 drive under the environment of 40 ° C and 80% of the tape, and a load of 100g (T1) is applied, so that it becomes 14mm / sec. Tape damage after repeated sliding to 5,000 passes while applying tension (T2) was evaluated according to the following rank.
Excellent: Some scratches are seen, but there are more parts without scratches.
Good: There are more flawed parts than flawless parts.
Bad: The magnetic layer is completely peeled off.

(5) Preservability Tapes stored for 60 days in a 60 ° C. and 90% RH environment are brought into contact with a guide pole used in a DDS3 drive under a 40 ° C. and 80% RH environment, and a load of 50 g (T1) is applied. The tension (T2) was applied so as to be 14 mm / sec, and the friction coefficient of the magnetic surface against the guide pole was obtained from the tension T2 / T1.
The measurement was repeated up to 500 passes, and the friction coefficient of the 500th pass when the friction coefficient of the first pass was 1 was determined.
The dirt on the guide pole after the measurement was observed with a differential interference optical microscope and evaluated according to the following rank.
Excellent: No stains are seen.
Good: Dirt is seen, but there are more areas without dirt.
Defect: There are more areas with dirt than areas without dirt.

<Polyurethane synthesis example>
The polyol and chain extender having the composition shown in Table 1 were dissolved in a nitrogen stream at 60 ° C. in a vessel equipped with a reflux condenser and a stirrer and previously substituted with nitrogen so that a 30% cyclohexanone solution was obtained. Next, 60 ppm of dibutyltin dilaurate was added as a catalyst and further dissolved for 15 minutes. Furthermore, the organic diisocyanate shown in Table 1 was added and reacted by heating at 90 ° C. for 6 hours to obtain polyurethane resin solutions AK.
The weight average molecular weight of the obtained polyurethane is shown in Table 1.
The weight average molecular weight of the polyurethane was determined in terms of standard polystyrene using a DMF solvent.

  The chain extenders, organic diisocyanates and polyol compositions used in Table 1 are as shown in Tables 2 and 3.

The magnetic powder 1 used in the following examples was prepared as follows.
The following operation was performed in high purity N ₂ gas.
Triammonium iron oxalate (Fe (NH ₄ ) ₃ (C ₂ O ₄ ) ₃ ) (manufactured by Wako Pure Chemical Industries, Ltd.) was dissolved in an aqueous solution of metal salt dissolved in 24 ml of H ₂ O (deoxygenated). An alkane solution prepared by dissolving 5 ml of OT in 80 ml of decane was added and mixed to prepare a reverse micelle solution (I).
NaBH ₄ (manufactured by Wako Pure Chemical Industries, Ltd.) 0.57 g of H ₂ O (deoxygenated) dissolved in 12 ml of reducing agent aqueous solution, aerosol OT (manufactured by Wako Pure Chemical Industries, Ltd.) in 2.5 ml decane (manufactured by Wako Pure Chemical Industries, Ltd.) An alkane solution dissolved in 40 ml was added and mixed to prepare a reverse micelle solution (II).
The reverse micelle solution (II) was instantaneously added to the reverse micelle solution (I) while stirring the reverse micelle solution (I) at a high temperature with an omni mixer (manufactured by Yamato Kagaku) at a temperature of 22 ° C. Five minutes after the completion of the addition, the stirring was changed to magnetic stirrer and the temperature was raised to 40 ° C., followed by aging for 120 minutes. After cooling to room temperature, 2 ml of oleic acid (manufactured by Wako Pure Chemical Industries) was added and mixed.
In order to destroy the micelles, a mixed solution of 200 ml of H ₂ O (deoxygenated) and 200 ml of methanol was added to separate into an aqueous phase and an oil phase. A state in which the metal nanoparticles were dispersed on the oil phase side was obtained. The oil phase side was washed 5 times with 600 ml of H ₂ O + 200 ml of methanol. Thereafter, 1300 ml of methanol was added to cause flocculation of the alloy nanoparticles and to precipitate them. The supernatant was removed, and 20 ml of heptane (manufactured by Wako Pure Chemical Industries, Ltd.) was added for redispersion, followed by precipitation by adding 100 ml of methanol. This was repeated twice, and finally 5 ml of heptane (manufactured by Wako Pure Chemical Industries, Ltd.) was added to obtain an iron nanoparticle dispersion having a particle size of 13 nm.
The iron nanoparticle dispersion was vacuum degassed to obtain an iron nanoparticle dispersion dispersed in a dispersion aid (oleic acid, oleylamine).
Thereafter, reduction treatment was performed at 280 ° C. for 1 h in an H ₂ air current, and nitriding treatment was performed in a mixed gas flow of NH ₃ 100 cc / min and Ar 50 cc / min at 130 ° C. for 24 hours.
Thereafter, the temperature was returned to room temperature, and deoxidation treatment was carried out by maintaining at 25 ° C. for 5 hours in an atmosphere of 1% O _{2 and} 99% N ₂ .
An iron nitride-based magnetic powder having a granular shape, a particle diameter of 13 nm, and a saturation magnetization of 90 emu / g (90 A · m ² / kg) was obtained.

An example of a magnetic recording medium having a single magnetic layer on a nonmagnetic support will be described.
<Example 1>
(Preparation of magnetic paint)
In the following formulation, “parts” indicates “parts by weight”.
100 parts of granular ferromagnetic powder (Hc 211 kA / m, particle size 13 nm, σs 90 emu / g (90 A · m ² / kg)) was pulverized for 10 minutes with an open kneader, then 20 parts of polyurethane resin solution A (solid content), 60 parts of cyclohexanone Kneaded for 60 minutes, and then 2 parts of abrasive (Al ₂ O ₃ , particle size 0.3 μm) 2 parts carbon black (particle size 40 μm) 2 parts methyl ethyl ketone / toluene = 1/200 parts were added and dispersed in a sand mill for 120 minutes. . To this was added 2 parts of butyl stearate, 1 part of stearic acid, 50 parts of methyl ethyl ketone, and the mixture was further stirred and mixed for 20 minutes, followed by filtration using a filter having an average pore size of 1 μm to prepare a magnetic coating material.

(Production of magnetic tape)
Next, a sulfonic acid-containing polyester resin as an adhesive layer was applied to the surface of a polyethylene terephthalate support having a thickness of 7 μm using a coil bar so that the thickness after drying was 0.1 μm.
Next, the obtained magnetic coating material was applied using a reverse roll so that the thickness after drying was 1.0 μm. A magnetic roll is applied to a non-magnetic support on which a magnetic paint is undried and a magnetic orientation is applied with a 5,000 gauss Co magnet and a 4,000 gauss solenoid magnet. -Calendering by combining metal roll-metal roll-metal roll-metal roll-metal roll (speed 100 m / min, linear pressure 300 kg / cm, temperature 90 ° C), then slit to 3.8 mm width and magnetic A tape was prepared.

<Examples 2-8 and Comparative Examples 1-3>
Magnetic tapes of Examples 2 to 8 and Comparative Examples 1 to 3 were produced in the same manner as in Example 1 except that the polyurethane resin A was changed to that shown in Table 4.

  Table 4 shows the types of polyurethane used in Examples and Comparative Examples, and the evaluation results of the produced magnetic tape.

An example of a magnetic recording medium having one nonmagnetic layer on a nonmagnetic support and further having one magnetic layer thereon will be described.
<Example 9>
As the magnetic coating for the upper layer, the same magnetic coating as in Example 1 was used.
Preparation of nonmagnetic coating for lower layer α-Fe ₂ O ₃ (average particle size 0.15 μm, S _BET 52 m ² / g, surface-treated Al ₂ O ₃ , SiO ₂ , pH 6.5 to 8.0) 85 parts A compound obtained by pulverizing with an open kneader for 10 minutes and then adding hydroxyethyl sulfonate sodium salt to a copolymer of vinyl chloride / vinyl acetate / glycidyl methacrylate = 86/9/5 (SO ₃ Na = 6 × 10 ⁻⁵ eq / G, epoxy = 10 ⁻³ eq / g, Mw 30,000) is kneaded with 7.5 parts of polyurethane resin A 10 parts (solid content) and 60 parts of cyclohexanone for 60 minutes, and then methyl ethyl ketone / cyclohexanone = 6/4 200 Part was added and dispersed in a sand mill for 120 minutes. To this was added 2 parts of butyl stearate, 1 part of stearic acid, 50 parts of methyl ethyl ketone, and the mixture was further stirred and mixed for 20 minutes, followed by filtration using a filter having an average pore diameter of 1 μm to prepare a lower layer coating material.

Next, a sulfonic acid-containing polyester resin as an adhesive layer was applied to the surface of a polyethylene terephthalate support having a thickness of 7 μm using a coil bar so that the thickness after drying was 0.1 μm.
Next, the obtained coating for the lower layer was applied so that the dry film thickness was 1.5 μm, and immediately after the application, using a reverse roll so that the thickness after drying the upper layer magnetic paint was 0.1 μm. Simultaneous multilayer coating was applied. The magnetic coating is applied to the nonmagnetic support with the magnetic coating undried with a 5,000 gauss Co magnet and a 4,000 gauss solenoid magnet. A calendar treatment by a combination of metal roll-metal roll-metal roll-metal roll-metal roll was performed at a speed of 100 m / min, a linear pressure of 300 kg / cm, and a temperature of 90.degree. Thereafter, a back layer having a thickness of 0.3 μm was applied to the other support surface using a coating liquid having the following back layer formulation. A tape for digital recording was produced by slitting to a width of 3.8 mm.

Back layer formulation Kneaded product (1)
Carbon black BP-800 Cabot 100 parts Nitrocellulose (Asahi Kasei Corporation RS1 / 2) 30 parts Polyurethane resin A 100 parts Dispersant Copper oleate 5 parts Copper phthalocyanine 5 parts Precipitated barium sulfate 5 parts Methyl ethyl ketone 500 parts Toluene 500 Part After pre-kneading the above with a roll mill,
Kneaded product (2)
100 parts of carbon black (S _BET : 8.5 m ² / g, average particle size: 270 nm, DBP oil absorption: 36 ml / 100 g, pH: 10)
Polyurethane resin A 100 parts Methyl ethyl ketone 300 parts Toluene 300 parts were kneaded.

The kneaded product (1) and the same (2) were dispersed with a sand grinder. After the dispersion was completed, the following was added to obtain a coating solution for a back layer.
Polyester resin (Toyobo Byron 300) 5 parts Polyisocyanate (Nihon Polyurethane Coronate L) 5 parts

(Comparative Example 4)
A magnetic tape was produced in the same manner as in Example 9 except that the polyurethane resin of the upper magnetic layer and the lower nonmagnetic layer was changed to that shown in Comparative Example 1.

As is clear from the results in Table 4, the magnetic tape of the present invention has a small surface roughness, little interface fluctuation in the multilayer structure, a small coefficient of friction after 500 passes, good guide bar contamination, and reproduction output. Is also big.

Claims (3)

A magnetic recording medium having at least one magnetic layer in which a ferromagnetic fine powder is dispersed in a binder on a magnetic support,
The ferromagnetic fine powder is an iron nitride magnetic powder having a granular or spheroidal particle shape, a particle diameter of 5 to 50 nm, and a saturation magnetization of 50 to 150 emu / g.
The binder includes a polyurethane resin obtained by using a polyol, a short chain diol having a weight average molecular weight of 500 or less, and an organic polyisocyanate, and the short chain diol has an alicyclic polycyclic structure and / or a spiro structure. A magnetic recording medium, wherein the concentration of the alicyclic polycyclic structure and the spiro structure is present at a ratio of 1.0 to 2.0 with respect to the urethane group concentration. On the nonmagnetic support, it has at least one nonmagnetic layer in which at least one nonmagnetic fine powder is dispersed in the binder (1), and the ferromagnetic fine powder is bonded onto the nonmagnetic layer by a binder ( 2) In a magnetic recording medium having at least one magnetic layer dispersed therein,
The ferromagnetic fine powder is an iron nitride magnetic powder having a granular or spheroidal particle shape, a particle diameter of 5 to 50 nm, and a saturation magnetization of 50 to 150 emu / g.
At least the binder (2) includes a polyurethane resin obtained by using a polyol, a short-chain diol having a weight average molecular weight of 500 or less, and an organic polyisocyanate, and the short-chain diol has an alicyclic polycyclic structure and / or a spiro structure. A magnetic recording medium, wherein the concentration of the alicyclic polycyclic structure and the spiro structure is present at a ratio of 1.0 to 2.0 with respect to the urethane group concentration. The magnetic recording medium according to claim 1 or 2, wherein the alicyclic polycyclic structure or the spiro structure comprises at least one structure selected from the group consisting of the following (1) to (3).