JP2009099240A - Method for manufacturing magnetic recording medium, and magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a magnetic recording medium and a magnetic recording medium which has excellent electromagnetic conversion characteristics and prevents contamination on a head. <P>SOLUTION: The method for manufacturing a magnetic recording medium includes a step of forming a magnetic layer by applying application liquid for forming the magnetic layer onto a non-magnetic substrate and drying it. The application liquid for forming the magnetic layer contains at least a compound having at least one of a carboxyl group and/or a hydroxyl group per molecule, together with prescribed ferromagnetic powder and a binder. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a magnetic recording medium and a magnetic recording medium, and more specifically, a method for manufacturing a magnetic recording medium capable of manufacturing a magnetic recording medium capable of achieving both excellent electromagnetic conversion characteristics and suppression of head contamination, and The present invention relates to a magnetic recording medium.

  In recent years, means for transmitting information at a high speed have remarkably developed, and it has become possible to transfer images and data having enormous information. Along with the improvement of this data transfer technique, recording and reproducing devices and recording media for recording, reproducing and storing information are required to have higher density recording.

In order to obtain good electromagnetic conversion characteristics in a high-density recording region, it is known that it is effective to use fine magnetic particles and to disperse the fine magnetic materials to a high degree to improve the smoothness of the magnetic layer surface. ing. For example, in Patent Document 1, by increasing the amount of the polar group of the binder to a specific range, and further controlling the water content of the magnetic powder to a specific range, the binding property of the binder to the magnetic material is increased, It has been proposed to increase the dispersibility by preventing aggregation between bodies.
Japanese Patent Laid-Open No. 2003-132931

  However, as a result of the study by the present inventors, in a magnetic recording medium in which the surface property of the magnetic layer is increased by using a binder having an increased amount of polar groups by the method described in Patent Document 1, the dispersion of the magnetic material is reduced. As a result, the surface property of the obtained magnetic layer was improved, and good electromagnetic conversion characteristics could be obtained. However, it was revealed that head contamination occurred significantly during running. Head contamination is desired to be reduced because it causes increased noise and reduced head life.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for manufacturing a magnetic recording medium and a magnetic recording medium that can achieve both excellent electromagnetic conversion characteristics and suppression of head contamination.

As a result of repeated studies to achieve the above object, the present inventors speculated that the presence of a low molecular component derived from a binder having an increased amount of polar groups on the surface of the magnetic layer may cause head staining. did. In addition, it is considered that as the surface smoothness of the magnetic layer increases, the contact area between the running head and the magnetic layer increases, and the ratio of the low molecular components present on the surface of the magnetic layer to the head increases.
Based on the above findings, the present inventors first use a relatively high molecular weight binder as a binder to be added to the magnetic layer as a means for reducing low molecular components present in the surface layer of the magnetic layer. I examined that. However, as a result of the study by the present inventors, when a large amount of polar group is introduced for improving dispersibility, a low molecular component is still present on the surface of the magnetic layer even though a high molecular weight binder is used. Became clear. The reason for this is that the binder that has increased the adsorptivity to the magnetic material by introducing a large amount of polar groups comes into contact with the active sites on the surface of the magnetic material, so that the polymer chain is cleaved by hydrolysis or the like. It was thought that the low molecular component was liberated as a result.
As a result of further investigation based on the above knowledge, the present inventors have determined that the water content of the ferromagnetic powder is within a specific range, together with the high molecular weight binder into which a large amount of polar groups have been introduced, and the carboxyl group and / or By forming the magnetic layer using a compound having at least one hydroxyl group in one molecule, the dispersibility of the magnetic layer can be improved while suppressing the cutting of the polymer binder, thereby improving the excellent electromagnetic properties. The inventors have found that a magnetic recording medium having conversion characteristics and suppressing head contamination can be obtained, and the present invention has been completed.

That is, the above object was achieved by the following means.
[1] A method for producing a magnetic recording medium comprising a step of forming a magnetic layer by applying and drying a magnetic layer forming coating solution on a nonmagnetic support,
The method for producing a magnetic recording medium, wherein the magnetic layer forming coating solution contains the following component A, component B, and component C.
Component A: ferromagnetic powder having an average particle size in the range of 10 to 40 nm and a water content of 0.3 to 3.0% by mass;
Component B :( _{b) -SO 3 M, -OSO 3 M} , -PO (OM) 2, -OPO (OM) 2, and COOM (where, M is a hydrogen atom, an alkali metal or ammonium) A binder containing 0.2 to 0.7 meq / g of at least one polar group selected from the group and having a mass average molecular weight in the range of 20,000 to 200,000, and / or (b)- CONR ¹ R ² , —NR ¹ R ² , and —N ⁺ R ¹ R ² R ³ (wherein R ¹ , R ² and R ³ each independently represents a hydrogen atom or an alkyl group) A binder containing 0.5 to 5 meq / g of at least one polar group selected from: and having a mass average molecular weight in the range of 20,000 to 200,000;
Component C: A compound having at least one carboxyl group and / or hydroxyl group in one molecule.
[2] The component B is mixed with the coating solution for forming the magnetic layer by mixing the component A, the component B and the component C at the same time, or the mixture obtained by mixing the component A and the component C. The method for producing a magnetic recording medium according to [1], comprising the step of:
[3] the component B, _{(b) -SO 3 M, -OSO 3 M} , -PO (OM) 2, -OPO (OM) 2, and COOM (where, M is a hydrogen atom, an alkali metal or ammonium A binder containing at least one polar group selected from the group consisting of 0.2 to 0.7 meq / g and having a mass average molecular weight in the range of 20,000 to 200,000 [1 ] Or the method for producing a magnetic recording medium according to [2].
[4] The method for producing a magnetic recording medium according to any one of [1] to [3], wherein the compound having at least one carboxyl group and / or hydroxyl group in a molecule is a cyclic compound.
[5] The method for producing a magnetic recording medium according to [4], wherein the cyclic compound is at least one selected from the group consisting of an alicyclic compound, an aromatic compound, and a heterocyclic compound.
[6] The production of the magnetic recording medium according to [4] or [5], wherein the cyclic structure contained in the cyclic compound is at least one selected from the group consisting of a cyclohexane ring, a benzene ring, a pyridine ring and a naphthalene ring. Method.
[7] The method for manufacturing a magnetic recording medium according to any one of [1] to [6], wherein the ferromagnetic powder is a hexagonal ferrite powder.
[8] The method for producing a magnetic recording medium according to any one of [1] to [7], wherein the binder is a polyurethane resin.
[9] The method for producing a magnetic recording medium according to any one of [1] to [8], wherein a magnetic recording medium having a center line average roughness on the surface of the magnetic layer in the range of 1.0 to 3.0 nm is produced. .
[10] A magnetic recording medium having a magnetic layer containing a ferromagnetic powder and a binder on a nonmagnetic support, which is produced by the production method according to any one of [1] to [8]. A magnetic recording medium.
[11] The magnetic recording medium according to [10], wherein the center line average roughness of the surface of the magnetic layer is in the range of 1.0 to 3.0 nm.

  According to the present invention, it is possible to provide a magnetic recording medium manufacturing method and a magnetic recording medium capable of manufacturing a magnetic recording medium for high density recording that achieves both excellent electromagnetic conversion characteristics and suppression of head contamination. .

The method for producing a magnetic recording medium of the present invention relates to a method for producing a magnetic recording medium comprising a step of forming a magnetic layer by applying and drying a coating solution for forming a magnetic layer on a nonmagnetic support. The magnetic layer forming coating solution contains the following component A, component B, and component C.
Component A: ferromagnetic powder having an average particle size in the range of 10 to 40 nm and a water content of 0.3 to 3.0% by mass;
Component B :( _{b) -SO 3 M, -OSO 3 M} , -PO (OM) 2, -OPO (OM) 2, and COOM (where, M is a hydrogen atom, an alkali metal or ammonium) A binder containing 0.2 to 0.7 meq / g of at least one polar group selected from the group and having a mass average molecular weight in the range of 20,000 to 200,000, and / or (b)- CONR ¹ R ² , —NR ¹ R ² , and —N ⁺ R ¹ R ² R ³ (wherein R ¹ , R ² and R ³ each independently represents a hydrogen atom or an alkyl group) A binder containing 0.5 to 5 meq / g of at least one polar group selected from: and having a mass average molecular weight in the range of 20,000 to 200,000;
Component C: A compound having at least one carboxyl group and / or hydroxyl group in one molecule.
In the method for producing a magnetic recording medium of the present invention, the magnetic layer surface smoothness is obtained by using, as the ferromagnetic powder, a fine particle magnetic material (component A) having an average particle size in the range of 10 to 40 nm together with components B and C. As a result, a magnetic recording medium having excellent electromagnetic characteristics can be obtained. More specifically, in order to increase the adsorptivity of the binder to the magnetic material and improve the dispersibility, a predetermined amount of the polar group is introduced into the magnetic layer binder, and the moisture content of the ferromagnetic powder is set to a predetermined amount. To do. Thereby, the dispersibility of the ferromagnetic powder is improved, and the surface smoothness of the magnetic layer can be improved. On that basis, a relatively high molecular weight binder having a mass average molecular weight of 20,000 to 200,000 is contained in the magnetic layer together with the compound, so that the running head stains in the smooth magnetic layer can be prevented. Can be suppressed. The reason is considered to be the following two points.
(1) Even if a binder that is not adsorbed on the magnetic substance and is released is present on the surface layer of the magnetic layer, the binder has a relatively high molecular weight, so that it does not easily adhere to the head and does not cause head contamination. Conceivable.
(2) It is considered that the reason why low molecular components derived from the binder are generated is that the binder is hydrolyzed when the binder contacts the active sites on the surface of the magnetic material. As described above, a binder having a relatively large amount of polar groups introduced therein has a high adsorptivity to a magnetic substance, and therefore has a high ratio of contact between the active site on the surface of the magnetic layer and the binder. On the other hand, since the compound (component C) has a high adsorptivity with the magnetic material, it is considered that when used as a magnetic layer component, it adheres to the surface of the magnetic material and deactivates the active sites on the surface of the magnetic layer. Thereby, it is guessed that the production | generation of the low molecular component by the cutting | disconnection of a polymer chain by hydrolysis etc. of a binder can be suppressed.
Below, the manufacturing method of the magnetic recording medium of this invention is demonstrated in detail.

Component C
The coating solution for forming a magnetic layer contains at least one compound (component C) having at least one carboxyl group and / or hydroxyl group in one molecule. In order to improve the dispersibility of the ferromagnetic powder, it is necessary to prevent aggregation of the magnetic materials. In order to prevent aggregation between the magnetic bodies, it is necessary to adsorb the binder on the surface of the magnetic body. At this time, by further adsorbing a compound having at least one carboxyl group and / or hydroxyl group in one molecule with the magnetic material, aggregation of the magnetic materials can be prevented and dispersibility between the magnetic materials can be improved. . Furthermore, a compound containing a carboxyl group and / or a hydroxyl group has a high adsorptivity with a magnetic substance and can function as a so-called surface modifier for the magnetic substance. Thereby, it can suppress that the low molecular component derived from the component B produces | generates abundantly by contact with ferromagnetic powder (component A) and binder (component B).

  The said compound can also have only any one of a carboxyl group or a hydroxyl group, and can also have both. The number of the substituents per molecule of the compound is at least one, preferably 1 to 5, and more preferably 1 to 3.

  The compound (so-called surface modifier) may be a cyclic compound or a chain compound as long as it has at least one carboxyl group and / or hydroxyl group in one molecule. A compound is preferred.

  The cyclic structure of the cyclic compound may be an aliphatic ring, an aromatic ring, or a heterocyclic ring. That is, the cyclic compound includes at least one selected from the group consisting of alicyclic compounds, aromatic compounds, and heterocyclic compounds. The cyclic structure may be a single ring or a condensed ring. Moreover, 1 type or 2 types or more may be sufficient as the cyclic structure contained in 1 molecule, and the structure where the cyclic structure of a different kind was connected by the coupling group may be sufficient. For example, the cyclic structure contained in the cyclic compound is preferably at least one selected from the group consisting of a cyclohexane ring, a benzene ring, a pyridine ring and a naphthalene ring.

  When the cyclic compound is an alicyclic compound, the included cyclic structure is, for example, an aliphatic ring which may be condensed having 5 to 30 carbon atoms, and preferably a condensed ring having 5 to 10 carbon atoms. An aliphatic ring that may be used, more preferably a cyclohexane ring.

  When the cyclic compound is an aromatic compound, the aromatic ring contained is preferably a 5-membered ring, a 6-membered ring or a 7-membered ring or a condensed ring, preferably a 5-membered ring or 6-membered ring. A ring is more preferable, and a 6-membered ring is more preferable. Specific examples include a benzene ring, a naphthalene ring, an anthracene ring, and a phenanthrene ring, and among them, a benzene ring and a naphthalene ring are preferable.

  When the cyclic compound is a heterocyclic compound, examples of the hetero atom contained in the heterocyclic ring include a nitrogen atom, an oxygen atom, and a sulfur atom, and a nitrogen atom is preferable. The heterocycle has, for example, 1 to 30 carbon atoms, preferably 1 to 20 carbon atoms, and particularly preferably 1 to 12 carbon atoms. Specific examples of the heterocyclic ring include a pyrrole ring, a pyrazole ring, an imidazole ring, a pyridine ring, a furan ring, a thiophene ring, an oxazole ring, a thiazole ring, and a benzo condensed ring and a heterocyclic condensed ring thereof. As the heterocyclic ring, a pyridine ring is preferable.

  The cyclic compound may have a substituent other than a carboxyl group and a hydroxyl group. Examples of the substituent include a halogen atom (a fluorine atom, a chlorine atom, a bromine atom, an iodine atom), a cyano group, a nitro group, an alkyl group having 1 to 16 carbon atoms, an alkenyl group having 1 to 16 carbon atoms, and a carbon atom. An alkynyl group having 2 to 16 carbon atoms, an alkyl group substituted with a halogen atom having 1 to 16 carbon atoms, an alkoxy group having 1 to 16 carbon atoms, an acyl group having 2 to 16 carbon atoms, and 1 to 16 carbon atoms An alkylthio group having 2 to 16 carbon atoms, an alkoxycarbonyl group having 2 to 16 carbon atoms, a carbamoyl group, a carbamoyl group substituted with an alkyl group having 2 to 16 carbon atoms, and 2 to 16 carbon atoms. Of the acylamino group. The substituent is preferably a halogen atom, a cyano group, an alkyl group having 1 to 6 carbon atoms, or an alkyl group substituted with a halogen atom having 1 to 6 carbon atoms, and a halogen atom or an alkyl having 1 to 4 carbon atoms. Group, an alkyl group substituted with a halogen atom having 1 to 4 carbon atoms is more preferable, and particularly a halogen atom, an alkyl group having 1 to 3 carbon atoms, and a trifluoromethyl group can be exemplified.

  Specific examples of the cyclic compound include 1-naphthoic acid, catechol, phenol, phthalic acid, 4-tert-butylphenol, 4-tert-butylbenzoic acid, 4-butylphenol, 4-hydroxypyridine, and cyclohexanecarboxylic acid. Preferably, it is catechol or 1-naphthoic acid, more preferably 1-naphthoic acid.

  The component C can be easily synthesized by a known method, and some are available as commercial products.

  The content of the component C in the magnetic layer can be appropriately set, but is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 10 parts by weight, more preferably 100 parts by weight of the ferromagnetic powder. Preferably, it is 1-8 mass parts. By making content of component C below the upper limit of the said range, it can suppress that a film | membrane plasticizes and can suppress that film | membrane peeling arises. On the other hand, by making the content of component C equal to or higher than the lower limit of the above range, head contamination can be further suppressed.

Binder (component B)
The binder (component B) contained in the magnetic layer forming coating solution is (i) -SO ₃ M, -OSO ₃ M, -PO (OM) ₂ , -OPO (OM) ₂ , and COOM (where, M represents a hydrogen atom, an alkali metal or ammonium) and contains at least one polar group selected from the group consisting of 0.2 to 0.7 meq / g and a mass average molecular weight of 20,000 to 200,000 A range of binders and / or (b) -CONR ¹ R ² , —NR ¹ R ² , and —N ⁺ R ¹ R ² R ^3, where R ¹ , R ² and R ³ are each Independently represents a hydrogen atom or an alkyl group) at least one polar group selected from the group consisting of 0.5 to 5 meq / g and has a mass average molecular weight in the range of 20,000 to 200,000. Contains a binder. That is, the binder may satisfy either (a) or (b), or both. The binder preferably satisfies at least (A), and more preferably (A). As the polar group (a), those having any of —SO ₃ M, —OSO ₃ M, —PO (OM) ₂ , and —COOM are preferable. Here, the alkyl group is preferably an alkyl group having 1 to 18 carbon atoms, and may have a linear structure or a branched structure. The content of the polar group in (a) is 0.2 to 0.7 meq / g, preferably 0.25 to 0.6 meq / g, more preferably 0.3 to 0.5 meq / g. . Moreover, content of the polar group in said (b) is 0.5-5 meq / g, Preferably it is 1-4 meq / g, More preferably, it is 1.5-3.5 meq / g. When the content of the polar group is out of the above range, it is difficult to obtain a magnetic layer with improved dispersibility of the magnetic material and excellent surface smoothness. The polar group may be included alone or in combination of two or more. The polar group contents in the above (a) and (b) are the total amount when plural kinds of polar groups are contained. The polar group can be introduced into the binder in a desired amount by, for example, addition polymerization or copolymerization.

  The binder has a weight average molecular weight in the range of 20,000 to 200,000. When the mass average molecular weight is less than 20,000, head contamination occurs remarkably. This is presumably because there are many low molecular components in the surface layer portion of the magnetic layer. On the other hand, when the mass average molecular weight exceeds 200,000, dispersibility is lowered and it is difficult to obtain good electromagnetic characteristics. The mass average molecular weight is preferably 30,000 to 180,000, more preferably 50,000 to 150,000.

  The structure of the binder is not particularly limited as long as it satisfies the above-mentioned (A) and / or (B) and has a mass average molecular weight within the above-mentioned range. A plastic resin, a thermosetting resin, a reactive resin, a polymer thereof, a mixture, or the like can be used. Examples include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal, There are polymers or copolymers containing vinyl ether as a structural unit, polyurethane resins, and various rubber resins. Thermosetting resins or reactive resins include phenolic resins, epoxy resins, polyurethane curable resins, urea resins, melamine resins, alkyd resins, acrylic reactive resins, formaldehyde resins, silicone resins, epoxy-polyamide resins, polyester resins. And a mixture of an isocyanate prepolymer, a mixture of a polyester polyol and a polyisocyanate, a mixture of a polyurethane and a polyisocyanate, and the like. These resins are described in detail in “Plastic Handbook” published by Asakura Shoten. It is also possible to use a known electron beam curable resin for each layer. These examples and their production methods are described in detail in JP-A No. 62-256219. The above resins can be used alone or in combination, and among them, those containing a polyurethane resin are preferable. For example, a combination of at least one selected from vinyl chloride resin, vinyl chloride vinyl acetate copolymer, vinyl chloride vinyl acetate vinyl alcohol copolymer, vinyl chloride vinyl acetate vinyl maleic anhydride copolymer and polyurethane resin, or What combined polyisocyanate can be mentioned suitably. The production method of the present invention can effectively suppress head contamination particularly in a magnetic recording medium using a polyurethane resin.

  As the structure of the polyurethane resin, known structures such as polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane, and polycaprolactone polyurethane can be used.

  The binder can be synthesized by a known method. Alternatively, commercially available products can be used as they are or after introducing a desired amount of polar groups.

  As will be described later, the magnetic recording medium produced by the production method of the present invention can also have a nonmagnetic layer containing a nonmagnetic powder and a binder between the magnetic layer and the nonmagnetic support. Examples of binders that can be used in the nonmagnetic layer include binders that can be used in the magnetic layer. Moreover, the binder normally used for a magnetic layer can also be used.

In the magnetic layer and the nonmagnetic layer, the binder can be used in a range of, for example, 5 to 50% by mass, preferably 10 to 30% by mass with respect to the nonmagnetic powder or the ferromagnetic powder. It is preferable to use a combination of 5 to 30% by mass when using a vinyl chloride resin, 2 to 20% by mass when using a polyurethane resin, and 2 to 20% by mass of polyisocyanate. However, for example, when head corrosion occurs due to a small amount of dechlorination, it is possible to use only polyurethane or only polyurethane and isocyanate. The glass transition temperature in the case of using a polyurethane -50 to 150 ° C., preferably from 0 ° C. to 100 ° C., elongation at break from 100 to 2,000% breaking stress 0.05~10kg / mm ² (0.49~98MPa), The yield point is preferably 0.05 to 10 kg / mm ² (0.49 to 98 MPa).

  Examples of polyisocyanates include tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, triphenylmethane triisocyanate and the like. Moreover, the product of these isocyanates and polyalcohol, the polyisocyanate produced | generated by condensation of isocyanate, etc. can be used. Commercially available product names of these isocyanates include Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate MR, Millionate MTL, Takeda Pharmaceutical Taketake D-102, Takenate D-110N, There are Takenate D-200, Takenate D-202, Sumitomo Bayer's Death Module L, Death Module IL, Death Module N, Death Module HL, etc., either alone or by utilizing the difference in curing reactivity. Each layer can be used in the above combination.

As explained above, the reason why the head dirt can be reduced by using the component C is that the use of the high molecular weight binder (binder) and the component C deactivates the active sites on the surface of the magnetic layer, By preventing the generation of low molecular components due to hydrolysis or the like, it is considered that the amount of low molecular components that can cause head contamination in the surface layer of the magnetic layer can be reduced. The mass average molecular weight of the binder (resin component) can be measured by the following method.
(Method for measuring mass average molecular weight of resin component)
The binder is evaluated by gel permeation chromatography (GPC). The mass average molecular weight is a value obtained by standard polystyrene conversion using a dimethylformamide (DMF) solvent as the mass average molecular weight of the resin component.

Magnetic Layer Surface Roughness The surface roughness of the magnetic layer of the magnetic recording medium produced by the method for producing a magnetic recording medium of the present invention is in the range of 1.0 to 3.0 nm as the center line average roughness. preferable. When the center line average roughness of the magnetic layer is 3.0 nm or less, better electromagnetic conversion characteristics can be obtained, and when it is 1.0 nm or more, stable running is increased. Further, the center line average roughness of the magnetic layer is preferably 1.5 to 3.0 nm, and more preferably 1.5 to 2.5 nm. By using a coating solution for forming a magnetic layer containing the components A, B and C, a magnetic layer having excellent surface smoothness can be formed. Further, the particle size of the ferromagnetic powder, the dispersion of the coating solution for the magnetic layer The surface smoothness of the magnetic layer can also be controlled by adjusting conditions, calendar conditions, adjusting the amount of filler in the nonmagnetic support, using an undercoat layer for smoothing, and the like.

Ferromagnetic powder (component A)
As the ferromagnetic powder (component A) contained in the coating solution for forming the magnetic layer, hexagonal ferrite powder and ferromagnetic metal powder can be used, and hexagonal ferrite powder can be more preferably used. When the length of the signal recording area is close to the size of the magnetic material included in the magnetic layer, a clear magnetization transition state cannot be created, and thus recording becomes substantially impossible. For this reason, the magnetic material size should be reduced as the recording wavelength is shortened. In the present invention, in order to obtain excellent electromagnetic conversion characteristics, a ferromagnetic powder having an average particle size of 10 to 40 nm is used. When the average particle size is less than 10 nm, it is difficult to disperse the particles individually. This means that it becomes difficult to coat individual magnetic bodies with a binder. Since the surface of several agglomerated magnetic bodies is coated with a binder, there are those that do not have a binder between the magnetic bodies, and the coupling between the magnetic bodies is weakened. It is considered that the coating strength is lowered. When the average particle size exceeds 40 nm, it is difficult to obtain good electromagnetic characteristics. The average particle size is preferably 15 to 40 nm, more preferably 15 to 30 nm.

The average particle size of the ferromagnetic powder can be measured by the following method.
The ferromagnetic powder is photographed with a transmission electron microscope H-9000, manufactured by Hitachi, at a photographing magnification of 100,000, and printed on a photographic paper so that the total magnification is 500,000 times to obtain a particle photograph. The target magnetic material is selected from the particle photograph, the outline of the powder is traced with a digitizer, and the particle size is measured with the image analysis software KS-400 manufactured by Carl Zeiss. Measure the size of 500 particles. The average particle size measured by the above method is defined as the average particle size of the ferromagnetic powder.

In the present invention, the size of the powder such as a magnetic material (hereinafter referred to as “powder size”) is (1) the shape of the powder is needle-like, spindle-like, or column-like (however, the height is the bottom surface). In the case of larger than the maximum major axis, etc., it is represented by the length of the major axis constituting the powder, that is, the major axis length, and (2) the shape of the powder is plate-shaped or columnar (however, the thickness or height is (Smaller than the maximum major axis of the plate surface or the bottom surface), and (3) the shape of the powder is spherical, polyhedral, unspecified, etc. When the major axis constituting the body cannot be specified, it is represented by the equivalent circle diameter. The equivalent circle diameter is a value obtained by a circle projection method.
The average powder size of the powder is an arithmetic average of the above powder sizes, and is obtained by carrying out the measurement as described above for 500 primary particles. Primary particles refer to an independent powder without aggregation.

The average acicular ratio of the powder is determined by measuring the short axis length of the powder in the above measurement, that is, the short axis length, and calculating the arithmetic average of the values of (long axis length / short axis length) of each powder. Point to. Here, the minor axis length is defined by the above powder size in the case of (1), the length of the minor axis constituting the powder, and in the case of (2), the thickness or height is defined respectively. In the case of (3), since there is no distinction between the major axis and the minor axis, (major axis length / minor axis length) is regarded as 1 for convenience.
When the shape of the powder is specific, for example, in the case of the definition (1) of the powder size, the average powder size is referred to as an average major axis length, and in the case of the definition (2), the average powder size Is called the average plate diameter, and the arithmetic average of (maximum major axis / thickness to height) is called the average plate ratio. In the case of definition (3), the average powder size is referred to as an average diameter (also referred to as an average particle diameter or an average particle diameter). In powder size measurement, the standard deviation / average value expressed as a percentage is defined as the coefficient of variation.

The water content of the ferromagnetic powder contained in the coating liquid for forming a magnetic layer used in the method for producing a magnetic recording medium of the present invention is 0.3 to 3% by mass, preferably 0.5 to 1.5% by mass, More preferably, it is 0.8-1.5 mass%. When the moisture content is in the above range, the adsorption of the binder (component B) containing a predetermined amount of polar groups to the magnetic material is optimized and the dispersibility is improved, so that magnetic recording exhibiting high S / N. A medium can be obtained. If the water content of the ferromagnetic powder is less than 0.3% by mass, the binder is not sufficiently adsorbed and the dispersibility is lowered, which is not preferable. When the water content exceeds 3% by mass, the reaction between the curing agent such as polyisocyanate and the binder in the coating solution for forming the magnetic layer proceeds excessively, and the viscosity of the coating solution for forming the magnetic layer is preferably increased. Absent. The moisture content can be adjusted by drying and humidification after the production of the magnetic material. The moisture content can be measured by the Karl Fischer method. The following method can be used as a method for measuring the moisture content by the Karl Fischer method.
Vaporizer temperature was set to 120 ° C., carrier gas (N ₂ ) was flowed at a flow rate of 300 ml / min, about 300 mg of sample was precisely weighed, and a trace moisture meter with a vaporizer (VA-05) manufactured by Mitsubishi Chemical Corporation ( The moisture content of the sample is calculated from the absolute moisture content obtained using CA-05) by the following formula.
Moisture content (%) = A / (10 × S)
However, A: Amount of water (μg), S: Amount of sample (mg).

  Examples of the ferromagnetic powder contained in the coating solution for forming the magnetic layer include ferromagnetic metal powder and hexagonal ferrite powder.

(i) Hexagonal ferrite powder The hexagonal ferrite powder includes, for example, barium ferrite, strontium ferrite, lead ferrite, calcium ferrite, and their substitutes such as Co. More specifically, magnetoplumbite type barium ferrite and strontium ferrite, magnetoplumbite type ferrite whose particle surface is coated with spinel, and magnetoplumbite type barium ferrite and strontium ferrite partially containing a spinel phase, etc. Is mentioned. In addition to predetermined atoms, Al, Si, S, Sc, Ti, V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, Ba, Ta, W, Re, Au, Hg , Pb, Bi, La, Ce, Pr, Nd, P, Co, Mn, Zn, Ni, Sr, B, Ge, and Nb may be included. In general, elements such as Co—Zn, Co—Ti, Co—Ti—Zr, Co—Ti—Zn, Ni—Ti—Zn, Nb—Zn—Co, Sb—Zn—Co, and Nb—Zn are added. Things can be used. Some raw materials and production methods contain specific impurities.

  A hexagonal ferrite powder having an average plate diameter of 10 to 40 nm is used. Preferably it is 15-40 nm, More preferably, it is the range of 15-30 nm.

The average plate ratio [arithmetic average of (plate diameter / plate thickness)] of the hexagonal ferrite is preferably 1-15, and more preferably 1-7. When the average plate ratio is 1 to 15, sufficient orientation can be obtained while maintaining high filling properties in the magnetic layer, and noise increase due to stacking between particles can be suppressed. Further, the specific surface area (S _BET ) by the BET method within the above particle size range is preferably 40 m ² / g or more, more preferably 40 to 200 m ² / g, and 60 to 100 m ² / g. Is most preferred.

  The distribution of the particle plate diameter and plate thickness of the hexagonal ferrite powder is generally preferably as narrow as possible. As described above, the particle plate diameter and plate thickness can be measured by randomly measuring, for example, 500 particles from a particle TEM photograph. In many cases, the distribution of the particle plate diameter and plate thickness is not a normal distribution, but when calculated and expressed as a standard deviation with respect to the average size, σ / average size = 0.1 to 1.0. In order to sharpen the particle size distribution, in general, the particle generation reaction system is made as uniform as possible, and the generated particles are subjected to a distribution improving process. For example, a method of selectively dissolving ultrafine particles in an acid solution is also known.

In general, a hexagonal ferrite powder having a coercive force (Hc) of about 143.3 to 318.5 kA / m (1800 to 4000 Oe) can be produced. The coercive force (Hc) of the hexagonal ferrite powder is preferably 167.2 to 294.5 kA / m (2100 to 3700 Oe), more preferably 199.0 to 278.6 kA / m (2500 to 3500 Oe).
The coercive force (Hc) can be controlled by the particle size (plate diameter / plate thickness), the type and amount of the contained element, the substitution site of the element, the particle generation reaction conditions, and the like.

The φm of the magnetic layer can also be controlled by the saturation magnetization (σs) of the hexagonal ferrite powder. In general, the saturation magnetization (σs) is preferably higher, but tends to be smaller as the particles become finer. In the present invention, it is preferable to select the saturation magnetization (σs) of the hexagonal ferrite powder in consideration of the desired φm, and specifically, the range is 30 to 80 A · m ² / kg (emu / g). It is preferable. In order to improve the saturation magnetization (σs), it is well known to combine spinel ferrite with magnetoplumbite ferrite, and to select the type and amount of contained elements. It is also possible to use W-type hexagonal ferrite. When dispersing the magnetic material, the surface of the magnetic material particles is also treated with a material suitable for the dispersion medium and polymer described later. The pH of the magnetic material is also important for dispersion. Usually, about 4 to 12 has optimum values depending on the dispersion medium and the polymer, but generally about 6 to 11 is selected from the chemical stability and storage stability of the medium. Since the moisture contained in the magnetic material also affects the dispersion, the present invention uses a ferromagnetic powder having a moisture content in the above range.

The hexagonal ferrite powder is manufactured by mixing (1) barium oxide / iron oxide / metal oxide replacing iron and boron oxide as a glass forming substance so as to have a desired ferrite composition, and then melting and quenching. A glass crystallization method for obtaining a barium ferrite crystal powder by re-heating treatment after being reheated, and (2) neutralizing the barium ferrite composition metal salt solution with an alkali to produce a by-product Hydrothermal reaction method to obtain barium ferrite crystal powder by liquid phase heating at 100 ° C. or higher after removal of water, (3) neutralization of barium ferrite composition metal salt solution with alkali, by-product There is a coprecipitation method in which the product is removed, dried, treated at 1100 ° C. or lower, and pulverized to obtain a barium ferrite crystal powder, but the present invention does not select a production method. The hexagonal ferrite powder may be subjected to surface treatment with Al, Si, P, or an oxide thereof as required. The amount thereof is, for example, 0.1 to 10% by mass with respect to the ferromagnetic powder, and surface treatment is preferable because adsorption of a lubricant such as a fatty acid is 100 mg / m ² or less. The hexagonal ferrite powder may contain soluble inorganic ions such as Na, Ca, Fe, Ni, and Sr. Although it is preferable that these are essentially not present, if they are 200 ppm or less, they do not particularly affect the characteristics.

(iii) Ferromagnetic metal powder The ferromagnetic metal powder used for the magnetic layer is not particularly limited, but it is preferable to use a ferromagnetic metal powder containing α-Fe as a main component. These ferromagnetic metal powders include Al, Si, S, Sc, Ca, Ti, V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, Ba, other than predetermined atoms. Atoms such as Ta, W, Re, Au, Hg, Pb, Bi, La, Ce, Pr, Nd, P, Co, Mn, Zn, Ni, Sr, and B may be included. In particular, at least one of Al, Si, Ca, Y, Ba, La, Nd, Co, Ni, and B is preferably included in addition to α-Fe, and further includes at least one of Co, Y, and Al. preferable. The Co content is preferably 0 atom% or more and 40 atom% or less, more preferably 15 atom% or more and 35 atom% or less, more preferably 20 atom% or more and 35 atom% or less with respect to Fe. The Y content is preferably from 1.5 atomic percent to 12 atomic percent, more preferably from 3 atomic percent to 10 atomic percent, and particularly preferably from 4 atomic percent to 9 atomic percent. Al is preferably from 1.5 atomic percent to 12 atomic percent, more preferably from 3 atomic percent to 10 atomic percent, and even more preferably from 4 atomic percent to 9 atomic percent.

  These ferromagnetic metal powders may be previously treated with a dispersant, a lubricant, a surfactant, an antistatic agent or the like, which will be described later. Specifically, Japanese Patent Publication No. 44-14090, Japanese Patent Publication No. 45-18372, Japanese Patent Publication No. 47-22062, Japanese Patent Publication No. 47-22513, Japanese Patent Publication No. 46-28466, Japanese Patent Publication No. 46-38755. No. 47, No. 47-4286, No. 47-12422, No. 47-17284, No. 47-18509, No. 47-18573, No. 39-10307 No. 46-39639, U.S. Pat. Nos. 3,026,215, 3,031,341, 3,100,194, 3,342,005 and 3,389,014.

  The ferromagnetic metal powder may contain a small amount of hydroxide or oxide. As the ferromagnetic metal powder, those obtained by known production methods can be used, and the following methods can be mentioned. A method of reducing a complex organic acid salt (mainly oxalate) with a reducing gas such as hydrogen, a method of reducing iron oxide with a reducing gas such as hydrogen to obtain Fe or Fe-Co particles, a metal carbonyl compound A method of thermal decomposition, a method of reducing by adding a reducing agent such as sodium borohydride, hypophosphite or hydrazine to an aqueous solution of a ferromagnetic metal, a metal is evaporated in a low-pressure inert gas, and a fine powder is obtained. How to get. The ferromagnetic metal powder obtained in this manner is a known gradual oxidation treatment, that is, a method of drying after immersing in an organic solvent, an oxygen-containing gas is sent after immersing in an organic solvent, and an oxide film is formed on the surface. Either a drying method or a method of forming an oxide film on the surface by adjusting the partial pressure of oxygen gas and inert gas without using an organic solvent can be applied.

The specific surface area by BET method of the ferromagnetic metal powder employed in the magnetic layer is preferably 45~100m ² / g, more preferably 50-80 m ² / g. If it is 45 m ² / g or more, low noise is obtained, and if it is 100 m ² / g or less, good surface properties can be obtained.
The crystallite size of the ferromagnetic metal powder is preferably 40 to 180 mm, more preferably 40 to 150 mm, and still more preferably 40 to 110 mm. The average major axis length (average particle size) of the ferromagnetic metal powder is 10 to 50 nm, preferably 10 to 40 nm, and more preferably 15 to 30 nm. The acicular ratio of the ferromagnetic metal powder is preferably 3 or more and 15 or less, and more preferably 3 or more and 12 or less. Σs of the ferromagnetic metal powder is preferably from 80~180A · m ² / kg, more preferably 80~150A · m ² / kg, and more preferably from 80~120A · m ² / kg. The coercive force of the ferromagnetic metal powder is preferably 2000 to 3500 Oe (160 to 280 kA / m), more preferably 2200 to 3000 Oe (176 to 240 kA / m).

As described above, the moisture content of the ferromagnetic metal powder is 0.3 to 3% by mass. It is preferable to optimize the moisture content of the ferromagnetic metal powder depending on the type of the binder. The pH of the ferromagnetic metal powder is preferably optimized depending on the combination with the binder used. The range can be 4-12, preferably 6-10. The ferromagnetic metal powder may be surface-treated with Al, Si, P, or an oxide thereof as required. The amount thereof can be 0.1 to 10% with respect to the ferromagnetic metal powder, and the surface treatment is preferable because the adsorption amount of a lubricant such as a fatty acid is 100 mg / m ² or less. The ferromagnetic metal powder may contain inorganic ions such as soluble Na, Ca, Fe, Ni, and Sr. Although it is preferable that these are essentially not present, if they are 200 ppm or less, they hardly affect the characteristics. The ferromagnetic metal powder used in the present invention preferably has fewer vacancies, and its value is 20% by volume or less, more preferably 5% by volume or less. As for the shape, any of needle shape, rice grain shape, or spindle shape may be used as long as the above-mentioned characteristics regarding the particle size are satisfied. The SFD of the ferromagnetic metal powder itself is preferably small and is preferably 0.8 or less. It is preferable to reduce the Hc distribution of the ferromagnetic metal powder. When the SFD is 0.8 or less, the electromagnetic conversion characteristics are good, the output is high, the magnetization reversal is sharp, and the peak shift is small, which is suitable for high density digital magnetic recording. In order to reduce the distribution of Hc, there are methods such as improving the particle size distribution of getite in the ferromagnetic metal powder and preventing sintering.

  In the production method of the present invention, a binder, a lubricant, a dispersant, an additive, a solvent, a dispersion method and the like used for forming a magnetic layer, a nonmagnetic layer, and an optional back layer of the magnetic recording medium. As for, known techniques related to them can be applied as appropriate. In particular, known techniques relating to the amount and type of binder, the amount of additive added, and type can be applied.

Additives can be added to the coating liquid for forming the magnetic layer as necessary. Examples of the additive include an abrasive, a lubricant, 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, phenethylphosphonic acid, α-methylbenzylphosphonic acid, 1-methyl-1-phenethylphosphonic acid, diphenylmethylphosphonic acid, biphenylphosphonic acid, benzylphenylphosphonic acid , Α-cumylphosphonic acid, toluylphosphonic acid, xylylphosphonic acid, ethylphenylphosphonic acid, cumenylphosphonic acid, propylphenylphosphonic acid, butylphenylphosphonic acid, heptylph Aromatic ring-containing organic phosphonic acids such as enylphosphonic acid, octylphenylphosphonic acid, nonylphenylphosphonic acid and their alkali metal salts, octylphosphonic acid, 2-ethylhexylphosphonic acid, isooctylphosphonic acid, isononylphosphonic acid, isodecylphosphonic acid Acids, isoundecyl phosphonic acid, isododecyl phosphonic acid, isohexadecyl phosphonic acid, isooctadecyl phosphonic acid, isoeicosyl phosphonic acid, alkylphosphonic acids and alkali metal salts thereof, phenyl phosphate, benzyl phosphate, phosphoric acid Phenethyl, α-methylbenzyl phosphate, 1-methyl-1-phenethyl phosphate, diphenylmethyl phosphate, biphenyl phosphate, benzylphenyl phosphate, α-cumyl phosphate, toluyl phosphate, xylyl phosphate, ethyl phosphate Phenyl Aromatic phosphates such as cumenyl phosphate, propylphenyl phosphate, butylphenyl phosphate, heptylphenyl phosphate, octylphenyl phosphate, nonylphenyl phosphate, and alkali metal salts thereof, octyl phosphate, 2-phosphate Alkyl phosphates such as ethylhexyl, isooctyl phosphate, isononyl phosphate, isodecyl phosphate, isoundecyl phosphate, isododecyl phosphate, isohexadecyl phosphate, isooctadecyl phosphate, isoeicosyl phosphate, and alkali metal salts thereof, alkyl sulfones 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 , Monobasic fatty acids which may contain or be branched, such as elaidic acid and erucic acid, and their metal salts, or butyl stearate, octyl stearate, amyl stearate, stearin One or more unsaturated bonds having 10 to 24 carbon atoms such as isooctyl acid, octyl myristate, butyl laurate, butoxyethyl stearate, anhydrosorbitan monostearate, anhydrosorbitan tristearate, etc. A basic fatty acid and a 1 to 6-valent alcohol which may contain or be branched with an unsaturated bond having 2 to 22 carbon atoms, an alkoxy alcohol which may contain or be branched with an unsaturated bond with 12 to 22 carbon atoms, or A module comprising any one of monoalkyl ethers of alkylene oxide polymer Fatty acid esters, difatty 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.

  Also, nonionic surfactants such as alkylene oxide, glycerin, glycidol, and alkylphenol ethylene oxide adducts, and cationic surfactants such as cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, phosphonium or sulfoniums Agents, anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, sulfate ester group, amino acids, aminosulfonic acids, sulfuric acid or phosphate esters of amino alcohol, amphoteric surfactants such as alkylbetaine type, etc. Can be used. These surfactants are described in detail in “Surfactant Handbook” (published by Sangyo Tosho Co., Ltd.).

  The above-mentioned lubricant, antistatic agent and the like are not necessarily pure and may contain impurities such as isomers, unreacted materials, side reaction products, decomposition products, oxides, etc. in addition to the main components. These impurities are preferably 30% by mass or less, more preferably 10% by mass or less.

  Specific examples of these additives include, for example, NAF-102, castor oil hardened fatty acid, NAA-42, cation SA, Naimine L-201, Nonion E-208, Anon BF, Anon LG, Takemoto, manufactured by NOF Corporation. Oil and fat: FAL-205, FAL-123, Shin Nippon Chemical Co., Ltd .: NJ Lube OL, Shin-Etsu Chemical Co., Ltd .: TA-3, Lion Corporation: Armido P, Lion Corporation: Duomin TDO, Nisshin Oilio Co., Ltd .: BA-41G, Sanyo Kasei Co., Ltd .: Profan 2012E, New Pole PE61, Ionette MS-400, etc. are mentioned.

Dispersant The aforementioned compound (component C) can function as a dispersant. In the present invention, the compound (component C) can also be added to the coating solution for forming a nonmagnetic layer. Furthermore, in this invention, the other compound which has a dispersibility improvement effect with the said compound can also be used together. The dispersant that can be used in combination is preferably at least one selected from the group consisting of alicyclic compounds, aromatic compounds, and heterocyclic compounds. Among the cyclic compounds other than Component C and Component C, compounds that can be added as dispersants include, for example, phenol, benzoic acid, cyclohexanol, cyclohexanecarboxylic acid, 1-naphthoic acid, catechol, and structural isomers thereof, phthalates Acid, and its structural isomer, cyclohexanedicarboxylic acid, and its structural isomer, 4-tert-butylphenol, and its structural isomer, 4-butylphenol, and its structural isomer, 4-hydroxypyridine, and its structural isomer 4-tert-butylbenzoic acid and its structural isomers, niacin and the like.

Carbon black can be added to the magnetic layer as necessary. Examples of carbon black that can be used in the magnetic layer include rubber furnace, rubber thermal, color black, and acetylene black. Specific surface area is 5 to 500 m ² / g, DBP oil absorption is 10 to 400 ml / 100 g, particle size is 5 to 300 nm, pH is 2 to 10, moisture content is 0.1 to 10%, tap density is 0.1 to 1 g / ml is preferred.

  As specific examples of carbon black, BLACKPEARLS 2000, 1300, 1000, 900, 905, 800, 700, VULCAN XC-72, manufactured by Cabot Corporation, # 80, # 60, # 55, # 50, #, manufactured by Asahi Carbon Co., Ltd. 35, Mitsubishi Chemical Corporation # 2400B, # 2300, # 900, # 1000, # 30, # 40, # 10B, Colombian Carbon Corporation CONDUCTEX SC, RAVEN150, 50, 40, 15, RAVEN-MT-P, Ketjen・ Ketjen Black EC manufactured by Black International, etc. Carbon black may be surface-treated with a dispersant, or may be used after being grafted with a resin, or may be obtained by graphitizing a part of the surface. Carbon black may be dispersed with a binder in advance before being added to the magnetic layer coating solution. These carbon blacks can be used alone or in combination. When using carbon black, it is preferable to use 0.1-30 mass% with respect to the mass of a ferromagnetic powder. Carbon black functions to prevent the magnetic layer from being charged, reduce the coefficient of friction, impart light-shielding properties, and improve the film strength. These differ depending on the carbon black used. Therefore, these carbon blacks used in the present invention have different types, amounts, and combinations in the magnetic layer and the non-magnetic layer, and are based on the above-mentioned characteristics such as particle size, oil absorption, conductivity, pH, etc. Of course, it is possible to use them properly according to the purpose, but rather they should be optimized in each layer. Carbon black that can be used in the magnetic layer can be referred to, for example, “Carbon Black Handbook” edited by Carbon Black Association.

As abrasives , α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, silicon carbide titanium carbide, titanium oxide, silicon dioxide, nitriding Known materials having a Mohs hardness of 6 or more, such as boron, can be used alone or in combination. Moreover, you may use the composite_body | complex (what surface-treated the abrasive | polishing agent with the other abrasive | polishing agent) of these abrasive | polishing agents. These abrasives may contain compounds or elements other than the main component, but the effect is not affected if the main component is 90% or more. The particle size of these abrasives is preferably from 0.01 to 2 [mu] m, and in particular, the narrower particle size distribution is preferable in order to improve electromagnetic conversion characteristics. Further, in order to improve the durability, it is possible to combine abrasives having different particle sizes as necessary, or to obtain the same effect by widening the particle size distribution even with a single abrasive. The tap density is preferably 0.3 to ² g / cc, the water content is preferably 0.1 to 5%, the pH is 2 to 11, and the specific surface area is preferably 1 to 30 m ² / g. The shape of the abrasive may be any of acicular, spherical, dice, and plate shapes, but those having a corner in a part of the shape are preferable because of high abrasiveness. Specifically, AKP-12, AKP-15, AKP-20, AKP-30, AKP-50, HIT-20, HIT-30, HIT-55, HIT-60, HIT-70, HIT- manufactured by Sumitomo Chemical Co., Ltd. 80, HIT-100, ERC-DBM, HP-DBM, HPS-DBM manufactured by Reynolds, WA10000 manufactured by Fujimi Abrasives, UB20 manufactured by Uemura Kogyo Co., Ltd., G-5 manufactured by Nippon Chemical Industry Co., Ltd., Chromex U2, U1, Toda Kogyo TF100, TF140, Ibiden Beta Random Ultra Fine, Showa Mining B-3, and the like. These abrasives can be added to the nonmagnetic layer as required. By adding to the nonmagnetic layer, the surface shape can be controlled, and the protruding state of the abrasive can be controlled. The particle size and amount of the abrasive added to these magnetic and nonmagnetic layers should of course be set to optimum values.

  Known organic solvents can be used. As the organic solvent, specifically, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, tetrahydrofuran, etc., methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol, in any ratio Alcohols such as 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 , Aromatic hydrocarbons such as cresol, chlorobenzene, methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethyl Nkuroruhidorin, 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% by mass or less, more preferably 10% by mass 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 non-magnetic layers with high surface tension solvents (cyclohexanone, dioxane, etc.) to increase 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 the dispersibility, it is preferable that the polarity is somewhat strong, and it is preferable that 50% by mass or more of the 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 present invention can be properly used in the magnetic layer and further in 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 metal powder and nonmagnetic. In the layer, it is presumed that the cyclic compound adsorbed or bonded mainly to the surface of the nonmagnetic powder with the polar group, for example, is difficult to desorb from the surface of the metal or metal compound once adsorbed. Therefore, the surface of the ferromagnetic metal powder or nonmagnetic powder is covered with an alicyclic ring, aromatic ring, heterocyclic ring, etc., so the affinity of the ferromagnetic metal powder or nonmagnetic powder for the binder component And the dispersion stability of the ferromagnetic metal powder or nonmagnetic powder can be improved. In addition, since the lubricant exists in a free state, fatty acids with different melting points are used in the nonmagnetic layer and magnetic layer to control the bleeding to the surface, and leaching to the surface using esters with different boiling points and polarities. It is conceivable to improve the coating stability by controlling the amount of the surfactant, to improve the lubrication effect by increasing the additive amount of the lubricant 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 liquid 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.

Non-magnetic layer Next, detailed contents regarding the non-magnetic layer will be described. In the production method of the present invention, the magnetic layer may be formed by directly applying and drying the magnetic layer forming coating solution on the nonmagnetic support. However, the nonmagnetic layer forming coating solution may be formed on the nonmagnetic support. After coating, a magnetic recording medium having a nonmagnetic layer and a magnetic layer in this order on a nonmagnetic support can be obtained by applying and drying a coating solution for forming a magnetic layer. The coating solution for forming a nonmagnetic layer contains a nonmagnetic powder and a binder, and can optionally contain additives. The nonmagnetic powder that can be used in the coating solution for forming 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 , Ca
CO ₃ , BaCO ₃ , SrCO ₃ , BaSO ₄ , silicon carbide, titanium carbide and the like can be used alone or in combination of two or more. Preferred 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 500 nm, more preferably 40 to 100 nm. If the crystallite size is in the range of 4 nm to 500 nm, it is preferable because dispersion does not become difficult and it has a suitable surface roughness. The average particle size of these non-magnetic powders is preferably 5 nm to 500 nm. However, if necessary, non-magnetic powders having different average particle sizes may be combined, or 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 500 nm is preferable because the dispersion is good and the surface roughness is suitable.

The specific surface area of the nonmagnetic powder is, for example, 1 to 150 m ² / g, preferably 20 to 120 m ² / g, and more preferably 50 to 100 m ² / g. A specific surface area in the range of 1 to 150 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, for example, 5 to 100 ml / 100 g, preferably 10 to 80 ml / 100 g, and more preferably 20 to 60 ml / 100 g. The specific gravity is, for example, 1 to 12, preferably 3 to 6. The tap density is, for example, 0.05 to 2 g / ml, 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 non-magnetic powder is preferably 2 to 11, and particularly preferably 6 to 9. When the pH is in the range of 2 to 11, it is possible to prevent the friction coefficient from increasing due to high temperature, high humidity, or liberation of fatty acids. The water content of the nonmagnetic powder is, for example, 0.1 to 5% by mass, preferably 0.2 to 3% by mass, and more preferably 0.3 to 1.5% by mass. A water content in the range of 0.1 to 5% by mass is preferable because the dispersion is good and the viscosity of the paint after dispersion is stable. The ignition loss is preferably 20% by mass 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 stearic acid adsorption amount of the nonmagnetic powder is preferably 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 200 to 600 erg / cm ² (200 to 600 mJ / m 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. It is preferable that Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , SnO ₂ , Sb ₂ O ₃ and ZnO are present on the surface of these nonmagnetic powders by surface treatment. 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 nonmagnetic powder used in the coating solution for forming the nonmagnetic layer 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, and the like. 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 the thing which baked it are mentioned. Particularly preferred nonmagnetic powders are titanium dioxide and α-iron oxide.

In the coating liquid for forming the nonmagnetic layer, carbon black can be mixed together with the nonmagnetic powder to lower the surface electrical resistance, reduce the light transmittance, and obtain a desired micro Vickers hardness. The micro-Vickers hardness of the nonmagnetic layer is generally 25~60kg / mm ² (245~588MPa), preferably in order to adjust the head contact, a 30~50kg / mm ² (294~490MPa), thin film hardness meter ( Using a HMA-400 manufactured by NEC, measurement can be performed using a diamond triangular pyramid needle having a ridge angle of 80 degrees and a tip radius of 0.1 μm at the tip of the indenter. For details, refer to Realize Co., Ltd. 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.

The specific surface area of carbon black employed in the nonmagnetic layer coating solution, for example 100 to 500 m ² / g, preferably from 150 to 400 m ² / g, DBP oil absorption, for example, 20 to 400 ml / 100 g, preferably 30 to 200 ml / 100 g. The particle size of carbon black is, for example, 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 for the coating liquid for forming the nonmagnetic layer include BLACKPEARLS 2000, 1300, 1000, 900, 800, 880, 700, VULCAN XC-72, manufactured by Mitsubishi Chemical Corporation, manufactured by Cabot Corporation. 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, and Ketjen Black EC manufactured by Ketjen Black International.

  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 mass with respect to the inorganic powder and in a range not exceeding 40% of the total mass of the nonmagnetic layer. 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.

  In addition, an organic powder may be added to the coating solution for forming 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.

  The binder, lubricant, dispersant, additive, solvent, dispersion method and the like used in the coating solution for forming the nonmagnetic layer can be those of the magnetic layer. In particular, known techniques relating to the magnetic layer can be applied to the amount of binder, type, additive, and amount of dispersant added, and type.

Nonmagnetic support In the present invention, the nonmagnetic support includes polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamideimide, polysulfone, aromatic polyamide, polybenzo Known films such as oxazole can be used. It is preferable to use a support having a glass transition temperature of 100 ° C. or higher, and it is particularly preferable to use a high-strength support such as polyethylene naphthalate or aramid. Moreover, in order to change the surface roughness of a magnetic surface and a base surface as needed, the laminated type support body as shown by Unexamined-Japanese-Patent No. 3-224127 can also be used. These supports may be subjected in advance to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment, and the like.

As the non-magnetic support, the center surface average surface roughness (Ra) measured with a light interference type surface roughness meter HD-2000 manufactured by WYKO is 8.0 nm or less, preferably 4.0 nm or less, more preferably 2. It is preferable to use one having a thickness of 0 nm or less. These supports preferably have not only a small center plane average surface roughness (Ra) but also no coarse protrusions of 0.5 μm or more. The surface roughness shape is freely controlled by the size and amount of filler added to the support as required. Examples of these fillers include organic fine powders such as acrylic, in addition to oxides and carbonates such as Ca, Si, and Ti. The maximum height Rmax of the support is 1 μm or less, the ten-point average roughness Rz is 0.5 μm or less, the center surface mountain height Rp is 0.5 μm or less, the center surface valley depth Rv is 0.5 μm or less, and the center surface area ratio Sr is preferably 10% or more and 90% or less, and the average wavelength λa is preferably 5 μm or more and 300 μm or less. In order to obtain the desired electromagnetic conversion characteristics and durability, the surface protrusion distribution of these supports can be arbitrarily controlled by fillers, each having a size of 0.01 μm to 1 μm, 0 pieces per 0.1 mm ² Can be controlled in the range of 2,000 to 2,000.

The F-5 value of the support used in the present invention is preferably 5 to 50 kg / mm ² (49 to 490 MPa). The heat shrinkage rate of the support at 100 ° C. for 30 minutes is preferably 3% or less, more preferably 1.5% or less, and the heat shrinkage rate at 80 ° C. for 30 minutes is preferably 1% or less, more preferably 0. .5% or less. Breaking strength 5~100kg / mm ² (49~980MPa), it is preferred that each elastic modulus is 100~2000kg / mm ² (0.98~19.6GPa). The temperature expansion coefficient is preferably 10 ⁻⁴ to 10 ⁻⁸ / ° C., more preferably 10 ⁻⁵ to 10 ⁻⁶ / ° C. The humidity expansion coefficient is preferably 10 ⁻⁴ / RH% or less, more preferably 10 ⁻⁵ / RH% or less. These thermal characteristics, dimensional characteristics, and mechanical strength characteristics are preferably substantially equal with a difference within 10% in each in-plane direction of the support.

  In the method for producing a magnetic recording medium of the present invention, an undercoat layer may be provided. By providing the undercoat layer, the adhesive force between the support and the magnetic layer or the nonmagnetic layer can be improved. As an undercoat layer for improving adhesion, a polyester resin soluble in a solvent can be used. As will be described later, a smoothing layer can be provided as an undercoat layer.

Layer structure The thickness structure of the magnetic recording medium produced by the method for producing a magnetic recording medium of the present invention is such that the thickness of the nonmagnetic support is preferably 3 to 80 μm, more preferably 3 to 50 μm, and particularly preferably 3 to 10 μm. is there. When an undercoat layer is provided between the nonmagnetic support and the nonmagnetic layer or the magnetic layer, the thickness of the undercoat layer is, for example, 0.01 to 0.8 μm, preferably 0.02 to 0.6 μm.

In addition, an intermediate layer for smoothing can be provided between the support and the nonmagnetic layer or magnetic layer, and between the support and the backcoat layer. For example, the surface of the nonmagnetic support contains a polymer. Apply and dry the applied coating solution, or apply a coating solution containing a compound having a radiation curable functional group in the molecule (radiation curable compound), and then irradiate with radiation to cure the coating solution Can be formed.
The number average molecular weight of the radiation curable compound is preferably in the range of 200 to 2,000. When the molecular weight is within this range, the molecular weight is relatively low, so that the coating film is easy to flow in the calendar process, has high moldability, and a smooth coating film can be formed.
Preferred as the radiation curable compound is a bifunctional acrylate compound having a molecular weight of 200 to 2000, and more preferred are acrylics such as bisphenol A, bisphenol F, hydrogenated bisphenol A, hydrogenated bisphenol F, and these alkylene oxide adducts. Acid and methacrylic acid are added.

The radiation curable compound may be used in combination with a polymer-type binder. Examples of the binder used in combination include conventionally known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof. When ultraviolet rays are used as radiation, it is preferable to use a polymerization initiator in combination. As the polymerization initiator, known radical photopolymerization initiators, cationic photopolymerization initiators, photoamine generators, and the like can be used.
The radiation curable compound can also be used for the nonmagnetic layer.

  The thickness of the magnetic layer is optimized according to the saturation magnetization amount, head gap length, and recording signal band of the magnetic head to be used, but is generally 10 to 150 nm, preferably 20 to 120 nm, and more preferably. Is 30 to 100 nm, particularly preferably 30 to 80 nm. Further, the thickness variation rate (σ / δ) of the magnetic layer is preferably within ± 50%, and more preferably within ± 30%. There may be at least one magnetic layer, and the magnetic layer may be separated into two or more layers having different magnetic characteristics, and a configuration related to a known multilayer magnetic layer can be applied.

  The thickness of the nonmagnetic layer is, for example, 0.1 to 3.0 μm, preferably 0.2 to 2.0 μm, and more preferably 0.3 to 1.5 μm. The non-magnetic layer of the magnetic recording medium of the present invention exhibits its effect if it is substantially non-magnetic. For example, even if it contains a small amount of magnetic material as an impurity or intentionally, This shows the effect of the invention and can be regarded as substantially the same configuration as the magnetic recording medium of the invention. Note that “substantially the same” means that the residual magnetic flux density of the nonmagnetic layer is 10 mT or less or the coercive force is 7.96 kA / m (100 Oe) or less, and preferably has no residual magnetic flux density and coercive force. Means.

Back Coat Layer According to the method for producing a magnetic recording medium of the present invention, a magnetic recording medium having a back coat layer on the surface opposite to the surface having the magnetic layer of the nonmagnetic support can be formed. The back coat layer preferably contains carbon black and inorganic powder. For the binder and various additives, the formulation of the magnetic layer and the nonmagnetic layer can be applied. It is particularly preferable to apply the prescription for the nonmagnetic layer. The thickness of the back coat layer is preferably 0.9 μm or less, and more preferably 0.1 to 0.7 μm.

  Details of preferable physical properties and the like of the magnetic recording medium manufactured by the manufacturing method of the present invention are as described later for the magnetic recording medium of the present invention.

  In the following, specific embodiments of detailed procedures will be described with respect to the method for producing a magnetic recording medium of the present invention.

  The coating liquid for forming a magnetic layer used in the production method of the present invention contains the component A, component B and component C. Details thereof are as described above. Further, the surface on which the magnetic layer forming coating solution is applied is not necessarily the surface of the nonmagnetic support. For example, when manufacturing a magnetic recording medium having a nonmagnetic layer, the surface is applied directly or indirectly on the nonmagnetic layer. be able to.

  The process for producing a coating liquid for forming the magnetic layer, nonmagnetic layer or back layer comprises at least a kneading process, a dispersing process, and a mixing process provided before and after these processes as necessary. Each process may be divided into two or more stages. All raw materials such as ferromagnetic powder, non-magnetic powder, binder, carbon black, abrasive, antistatic agent, lubricant, and solvent used in the present invention may be added at the beginning or during any step. In addition, individual raw materials may be added in two or more steps. For example, polyurethane may be divided and added in a kneading step, a dispersing step, and a mixing step for adjusting the viscosity after dispersion. In order to achieve the object of the present invention, a conventional known manufacturing technique can be used as a partial process. In the kneading step, it is preferable to use a kneading force such as an open kneader, a continuous kneader, a pressure kneader, or an extruder. Details of these kneading treatments are described in JP-A-1-106338 and JP-A-1-79274. Further, glass beads can be used to disperse the magnetic layer coating solution, nonmagnetic layer coating solution or back layer coating solution. Such glass beads are preferably zirconia beads, titania beads, and steel beads, which are high specific gravity dispersion media. The particle diameter and filling rate of these dispersion media are optimized. A well-known thing can be used for a disperser.

In order to effectively obtain the addition effect of the compound (component C), it is preferable that the component C is present when the ferromagnetic powder and the binder are in contact with each other. This is to avoid contact of the binder with the ferromagnetic powder surface before component C adheres to the ferromagnetic powder surface. Therefore, the coating liquid for forming the magnetic layer is prepared by mixing the above-mentioned component A (ferromagnetic powder), component B (binder), and component C (cyclic compound) at the same time, or combining component A and component C. It is preferable to prepare by mixing the component B into the mixture obtained by mixing. In addition, it is more preferable to prepare by mixing Component B into a mixture obtained by mixing Component A and Component C. First, by mixing the component A and the component C, the component C is more adsorbed on the surface of the ferromagnetic powder, and the generation of a low molecular component derived from the binder can be suppressed.
Specifically, component A, component B and component C are preferably mixed by the following method.
(1) Component A and component C are previously dispersed in a dry process for about 15 to 30 minutes, and then added to an organic solvent. Component B may be added simultaneously with the dispersion, or may be added after the dispersion is added.
(2) Component A and component C are dispersed in an organic solvent for about 15 to 30 minutes and then dried. The dried mixture is appropriately pulverized and added to an organic solvent. Component B may be added simultaneously with the mixture or after the mixture is added.
(3) After component A and component C are dispersed in an organic solvent for about 15 to 30 minutes. Add component B.
(4) Components A, B and C are simultaneously added and dispersed in an organic solvent.

  In the manufacturing process of the magnetic recording medium, for example, a nonmagnetic layer coating liquid is applied to the surface of a nonmagnetic support under running so as to have a predetermined film thickness, and then a nonmagnetic layer is formed thereon. Then, the magnetic layer is formed by applying the magnetic layer so that the magnetic layer coating solution has a predetermined thickness. A plurality of magnetic layer coating solutions may be applied sequentially or simultaneously, and a nonmagnetic layer coating solution and a magnetic layer coating solution may be applied sequentially or simultaneously. The coating machine for applying the magnetic layer coating liquid or the nonmagnetic layer coating liquid includes air doctor coat, blade coat, rod coat, extrusion coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure A coat, a kiss coat, a cast coat, a spray coat, a spin coat, etc. can be used. As for these, for example, “Latest Coating Technology” (May 31, 1983) issued by General Technology Center Co., Ltd. can be referred to.

  In the case of a magnetic tape, the magnetic layer coating liquid coating layer may be subjected to magnetic field orientation treatment using a cobalt magnet or solenoid on the ferromagnetic powder contained in the magnetic layer coating liquid coating layer. In the case of a disk, a sufficiently isotropic orientation may be obtained even without non-orientation without using an orientation device, but known random methods such as alternately arranging cobalt magnets obliquely and applying an alternating magnetic field with a solenoid. It is preferable to use an alignment device. In the case of a ferromagnetic metal powder, the isotropic orientation is generally preferably in-plane two-dimensional random, but can also be three-dimensional random with a vertical component. Further, isotropic magnetic characteristics can be imparted in the circumferential direction by using a well-known method such as a counter-polarized magnet and making it vertically oriented. In particular, when performing high density recording, vertical alignment is preferable. Moreover, circumferential orientation can also be achieved using spin coating.

  It is preferable that the drying position of the coating film can be controlled by controlling the temperature, air volume, and coating speed of the drying air, the coating speed is preferably 20 m / min to 1000 m / min, and the temperature of the drying air is preferably 60 ° C. or higher. . Moreover, moderate preliminary drying can also be performed before entering a magnet zone.

The coating raw material thus obtained can be once wound up by a take-up roll, then unwound from the take-up roll, and then subjected to a calendar process.
For the calendar process, for example, a super calendar roll or the like can be used. Calendering improves surface smoothness and eliminates voids generated by solvent removal during drying and improves the filling rate of the ferromagnetic powder in the magnetic layer. Obtainable. The step of calendering is preferably performed while changing the calendering conditions according to the smoothness of the surface of the coating raw material.

  The surface smoothness of the coating raw material can be achieved by controlling the calender roll temperature, the calender roll speed, and the calender roll tension. In consideration of the characteristics of the coating type medium, it is preferable to control the calender roll pressure and the calender roll temperature. By decreasing the calender roll pressure or lowering the calender roll temperature, the surface smoothness of the final product is lowered. Conversely, increasing the calender roll pressure or the calender roll temperature increases the surface smoothness of the final product.

  Apart from this, the magnetic recording medium obtained after the calendering process can be thermo-processed to allow thermosetting to proceed. Such thermo treatment may be appropriately determined depending on the formulation of the magnetic layer coating solution, and is, for example, 35 to 100 ° C, and preferably 50 to 80 ° C. The thermo treatment time is 12 to 72 hours, preferably 24 to 48 hours.

  As the calender roll, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, polyamideimide or the like can be used. Moreover, it can also process with a metal roll.

  As the calendering conditions, the temperature of the calender roll can be set in the range of, for example, 60 to 100 ° C., preferably in the range of 70 to 100 ° C., and particularly preferably in the range of 80 to 100 ° C. It is in the range of 500 kg / cm (98 to 490 kN / m), preferably in the range of 200 to 450 kg / cm (196 to 441 kN / m), particularly preferably in the range of 300 to 400 kg / cm (294 to 392 kN / m). It can be. Moreover, in order to improve the smoothness of the magnetic layer surface, the nonmagnetic layer surface can be calendered. The calendar treatment for the nonmagnetic layer is also preferably performed under the above conditions.

  The obtained magnetic recording medium can be cut into a desired size using a cutting machine or the like. The cutting machine is not particularly limited, but is preferably provided with a plurality of pairs of rotating upper blades (male blades) and lower blades (female blades). The slitting speed, the engagement depth, and the upper blade (male blade) are appropriately selected. The peripheral speed ratio (upper blade peripheral speed / lower blade peripheral speed) of the blade and the lower blade (female blade), the continuous use time of the slit blade, and the like can be selected.

Furthermore, the present invention relates to a magnetic recording medium having a magnetic layer containing a ferromagnetic powder and a binder on a nonmagnetic support. The magnetic recording medium of the present invention is manufactured by the above-described method for manufacturing a magnetic recording medium of the present invention. Details of each component and preferred physical properties of each layer included in the magnetic recording medium of the present invention are as described above.
Hereinafter, physical characteristics of the magnetic recording medium of the present invention will be described.

[Physical properties]
The coercive force (Hc) of the magnetic layer is preferably 143.2 to 318.3 kA / m (1800 to 4000 Oe), more preferably 159.2 to 278.5 kA / m (2000 to 3500 Oe). The coercive force distribution is preferably narrow, and SFD and SFDr are 0.8 or less, more preferably 0.5 or less.

The friction coefficient with respect to the head of the magnetic recording medium of the present invention is, for example, 0.50 or less, preferably 0.3 or less, in the temperature range of −10 to 40 ° C. and humidity of 0 to 95%. The surface resistivity is preferably 10 ⁴ to 10 ⁸ Ω / sq of the magnetic surface, and the charging position is preferably within −500 V to +500 V. The elastic modulus at 0.5% elongation of the magnetic layer is preferably 0.98 to 19.6 GPa (100 to 2000 kg / mm ² ) in each in-plane direction, and the breaking strength is preferably 98 to 686 MPa (10 to 70 kg). / Mm ² ), the elastic modulus of the magnetic recording medium is preferably 0.98 to 14.7 GPa (100 to 1500 kg / mm ² ) in each in-plane direction, and the residual spread is preferably 0.5% or less, 100 ° C. The thermal shrinkage at any of the following temperatures is preferably 1% or less, more preferably 0.5% or less, and most preferably 0.1% or less.

The glass transition temperature of the magnetic layer (the maximum point of the loss elastic modulus of the dynamic viscoelasticity measurement measured at 110 Hz by a dynamic viscoelasticity measuring device (for example, Leo Vibron)) is preferably 50 to 180 ° C., and that of the nonmagnetic layer is 0-180 degreeC is preferable. The loss elastic modulus is preferably in the range of 1 × 10 ⁷ to 8 × 10 ⁸ Pa (1 × 10 ⁸ to 8 × 10 ⁹ dyne / cm ² ), and the loss tangent is preferably 0.2 or less. If the loss tangent is too large, adhesion failure is likely to occur. These thermal characteristics and mechanical characteristics are preferably almost equal within 10% in each in-plane direction of the medium.

The residual solvent contained in the magnetic layer is preferably 100 mg / m ² or less, more preferably 10 mg / m ² or less. The porosity of the coating layer is preferably 40% by volume or less, more preferably 30% by volume or less for both the nonmagnetic layer and the magnetic layer. The porosity is preferably small in order to achieve high output, but it may be better to ensure a certain value depending on the purpose. For example, in the case of a disk medium in which repeated use is important, a larger void ratio is often preferable for running durability.

  In the magnetic recording medium of the present invention, these physical characteristics can be changed between the nonmagnetic layer and the magnetic layer according to the purpose. For example, the elastic modulus of the magnetic layer can be increased to improve running durability, and at the same time, the elastic modulus of the nonmagnetic layer can be made lower than that of the magnetic layer to improve the contact of the magnetic recording medium with the head.

  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 means parts by mass unless otherwise indicated.

[Example 1]
Magnetic layer coating solution component A) Hexagonal barium ferrite powder 100 parts Composition excluding oxygen (molar ratio): Ba / Fe / Co / Zn = 1/9 / 0.2 / 1
Hc: 176 kA / m (2200 Oe), average plate diameter: 20 nm, average plate ratio: 3
BET specific surface area: 65 m ² / g
σs: 49 A · m ² / kg (49 emu / g)
pH: 7
Component B) Polyurethane resin 17 parts Branched side chain-containing polyester polyol / diphenylmethane diisocyanate,
-SO ³ Na = 0.35meq / g
Component C) Cyclic compound (1-naphthoic acid) 5 parts α-alumina (particle size 0.15 μm) 5 parts Diamond powder (average particle diameter 60 nm) 1 part Carbon black (average particle diameter 20 nm) 1 part Cyclohexanone 110 parts Methyl ethyl ketone 100 parts Toluene 100 parts Butyl stearate 2 parts Stearic acid 1 part

Nonmagnetic layer coating solution Nonmagnetic inorganic powder 85 parts α-iron oxide Surface treatment layer: Al ₂ O ₃ , SiO ₂
Average long axis length 0.15μm
Average needle ratio: 7
Specific surface area by BET method 52m ² / g
PH8
Carbon black 15 parts Vinyl chloride copolymer 10 parts (MR110 manufactured by Nippon Zeon Co., Ltd.)
10 parts of polyurethane resin Branched side chain-containing polyester polyol / diphenylmethane diisocyanate,
-SO ₃ Na = 0.2meq / g
Phenylphosphonic acid 3 parts Cyclohexanone 140 parts Methyl ethyl ketone 170 parts Butyl stearate 2 parts Stearic acid 1 part

Backcoat layer coating solution 100 parts of fine carbon black powder (Capr BPr800, average particle size: 17 nm)
Coarse carbon black powder 10 parts (manufactured by Kerncarb, thermal black, average particle size: 270 nm)
α-alumina (hard inorganic powder)
Average particle size: 200 nm, Mohs hardness: 9
Nitrocellulose resin 140 parts Polyurethane resin 15 parts Polyester resin 5 parts Dispersant: Copper oleate 5 parts
Copper phthalocyanine 5 parts
5 parts of barium sulfate (BF-1 manufactured by Sakai Chemical Industry Co., Ltd., average particle size: 50 nm, Mohs hardness 3)
Methyl ethyl ketone 1200 parts Butyl acetate 300 parts Toluene 600 parts

About said nonmagnetic layer coating liquid, after kneading | mixing each component with an open kneader, it was disperse | distributed using the sand mill. To the obtained dispersion, 5 parts of polyisocyanate (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) was added, 40 parts of methyl ethyl ketone and cyclohexanone mixed solvent were added, mixed and stirred, and then filtered using a filter having a pore size of 1 μm. Thus, a nonmagnetic layer coating solution was prepared.
For the magnetic layer coating solution, hexagonal ferrite powder and 1-naphthoic acid were dispersed in a dry process for 15 minutes, and this dispersion was kneaded with the above magnetic layer components with an open kneader, and then dispersed using a sand mill. . Add 3 parts of polyisocyanate (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) to the resulting dispersion, add 40 parts of methyl ethyl ketone and cyclohexanone mixed solvent, mix and stir, and then filter using a filter having a pore size of 1 μm. Thus, a magnetic layer coating solution was prepared.
For the backcoat layer coating solution, the above components were kneaded with a continuous kneader and then dispersed using a sand mill. To the obtained dispersion, 40 parts of polyisocyanate (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) and 1000 parts of methyl ethyl ketone were added and stirred, followed by filtration using a filter having a pore size of 1 μm.

  The obtained nonmagnetic layer coating solution and magnetic layer coating solution are further dried so that the nonmagnetic layer has a thickness of 1.5 μm after drying and the magnetic layer has a thickness of 0.10 μm after drying. A multi-layer coating was performed on a 7 μm thick support (polyethylene terephthalate subjected to biaxial stretching) so that the total thickness of the tape was 8.6 μm and dried. Thereafter, the back coat layer was applied on the surface opposite to the magnetic layer surface so as to have a thickness of 0.5 μm after drying.

  After that, calendering was performed at a speed of 100 m / min, a linear pressure of 350 kg / cm (343 kN / m), and a temperature of 80 ° C. with a seven-stage calendar composed only of metal rolls, and the obtained roll was heated at 50 ° C. for 48 hours. Processed. Next, a magnetic tape was prepared by slitting to 1/2 inch width.

[Examples 2-5, 14, 15, 23-25, Comparative Examples 1, 5, 6, 9, 10]
The polyurethane resin contained in the magnetic layer coating solution and the nonmagnetic layer coating solution was changed in the same manner as in Example 1 except that the polyurethane resin having the mass average molecular weight, polar base type and polar group amount shown in Table 1 was changed. A magnetic tape was prepared.

[Examples 6 to 13, 16 to 20, Comparative Example 2]
A magnetic tape was produced in the same manner as in Example 1 except that the component C contained in the magnetic layer coating solution and / or the amount added was changed as shown in Table 1.

[Examples 21 and 22]
A magnetic tape was produced in the same manner as in Example 1 except that the hexagonal ferrite contained in the magnetic layer coating solution was changed to one having an average plate diameter shown in Table 1.

[Example 28]
The hexagonal ferrite powder contained in the magnetic layer coating solution is changed to a ferromagnetic metal powder having an average major axis length shown in Table 1, and the compound shown in Table 1 is used as Component C. While the non-magnetic layer is still wet, it is oriented and dried by a cobalt magnet having a magnetic force of 0.3T (3000G) and a solenoid having a magnetic force of 0.15T (1500G) (simultaneous multi-layer coating), and then back A magnetic tape was produced in the same manner as in Example 1 except that the coat layer was applied to a thickness of 0.5 μm after drying.

[Example 29]
A magnetic tape was produced in the same manner as in Example 1 except that the hexagonal ferrite powder, the binder and 1-naphthoic acid were simultaneously dispersed during the preparation of the magnetic layer coating solution.

[Comparative Example 3]
A magnetic tape was produced in the same manner as in Example 1 except that Component C was not added to the magnetic layer coating solution.

[Comparative Example 4]
The polyurethane resin contained in the magnetic layer coating solution and the nonmagnetic layer coating solution was changed to a polyurethane resin having the mass average molecular weight, polar group type and polar group amount shown in Table 1, and component C was not added. A magnetic tape was produced in the same manner as in Example 1.

[Comparative Examples 7 and 8]
A magnetic tape was produced in the same manner as in Example 1 except that the hexagonal ferrite contained in the magnetic layer coating solution was changed to one having an average plate diameter shown in Table 1.

[Examples 26 and 27, Comparative Examples 11 and 12]
A magnetic tape was produced in the same manner as in Example 1 except that the hexagonal ferrite contained in the magnetic layer coating solution was changed to one having a moisture content shown in Table 1.

1. Magnetic layer surface roughness Measured under the following conditions.
Equipment: Nanoscope III manufactured by Veeco Japan
Mode: Contact mode Measurement range: 40 μm square Scan line: 512 * 512
Scan speed: 2Hz
Scan direction: medium longitudinal direction S / N
(Driving method)
One roll at a running speed of 6 m / s, a back tension of 0.7 N, and a tape / head angle (1/2 of the wrap angle) of 10 degrees while winding / unwinding the tape between reels using a magnetic tape tester. An 800 m tape sample was run.
A linear head was used to record and reproduce a signal of 19.0 MHz (linear recording density 160 KFC I) while running the tape sample by the “running method” described above. The reproduction signal was input to Advantest Corporation: R3361C, the peak signal of 19.0 MHz was output as a signal (S), and the integrated noise (N) in the range of 1 MHz to 37.7 MHz excluding 19.0 MHz ± 0.3 MHz was measured. The ratio was defined as SNR. If it is 20 dB or more, it can be determined that the electromagnetic conversion characteristics are good.
3. Head dirt The tape sample was run for 500 m by the above "running method". The head after running was observed with an optical microscope to evaluate head contamination. The image of the head observed with an optical microscope was taken into a PC and binarized. (The head was observed at a magnification of 50) The area ratio of dirt to the tape sliding surface of the head was 0 to 5%, ◯ was 5 to 15%, and 15 or more was x.

Evaluation Results In Examples 1 to 29, a smooth magnetic layer could be obtained, and the electromagnetic conversion characteristics were also good. Moreover, although the magnetic layer surface property was high, no head contamination was observed.
On the other hand, in Comparative Example 1 using a binder that does not contain a predetermined polar group, the surface of the magnetic layer was rough and good electromagnetic conversion characteristics could not be obtained.
In Comparative Example 2 in which a cyclic compound (aniline) having neither a carboxyl group nor a hydroxyl group was used as the surface modifier instead of the compound having a carboxyl group and / or a hydroxyl group, the magnetic layer was insufficiently dispersed and the surface of the magnetic layer was smooth. As a result, the electromagnetic conversion characteristics deteriorated.
In Comparative Example 3 where no surface modifier was added, head contamination occurred. This is presumably because the binder was cut by contact with the magnetic substance and many low molecular components were present on the surface of the magnetic layer.
In Comparative Examples 4 and 5 in which the amount of the polar group of the binder was small, the magnetic layer surface was rough and the electromagnetic conversion characteristics deteriorated. On the other hand, in Comparative Example 6 in which the amount of the polar group of the binder was excessive, the electromagnetic conversion characteristics deteriorated.
In Comparative Example 7, since the particle size of the ferromagnetic powder was too small, as described above, the coupling between the magnetic materials was weakened and the coating strength of the magnetic layer was reduced, so that the S / N could not be evaluated. Film peeling occurred. On the other hand, in the comparative example 8 in which the particle size of the ferromagnetic powder was too large, the electromagnetic conversion characteristics deteriorated.
In Comparative Example 9 in which the mass average molecular weight of the binder was small, head contamination occurred. This is presumably due to the presence of many low molecular components on the surface of the magnetic layer.
Further, in Comparative Example 10 using a binder having a mass average molecular weight exceeding 200,000, the magnetic layer was not sufficiently dispersed and the electromagnetic conversion characteristics were deteriorated.
In Comparative Example 11, the moisture content of the magnetic material was small, the magnetic layer surface was rough, and the electromagnetic conversion characteristics deteriorated. This is presumably because the binder could not be sufficiently adsorbed to the magnetic material. In Comparative Example 12 in which the moisture content of the magnetic material was excessive, the magnetic layer surface was rough and the electromagnetic conversion characteristics deteriorated. This is presumably because the surface of the magnetic layer became rough because the water content was high, and the reaction with the polyisocyanate in the magnetic paint proceeded.

  The magnetic recording medium of the present invention is suitable as a magnetic recording medium for high density recording.

Claims (11)

A method for producing a magnetic recording medium comprising a step of forming a magnetic layer by coating and drying a coating solution for forming a magnetic layer on a nonmagnetic support,
The method for producing a magnetic recording medium, wherein the magnetic layer forming coating solution contains the following component A, component B, and component C.
Component A: ferromagnetic powder having an average particle size in the range of 10 to 40 nm and a water content of 0.3 to 3.0% by mass;
Component B :( _{b) -SO 3 M, -OSO 3 M} , -PO (OM) 2, -OPO (OM) 2, and COOM (where, M is a hydrogen atom, an alkali metal or ammonium) A binder containing 0.2 to 0.7 meq / g of at least one polar group selected from the group and having a mass average molecular weight in the range of 20,000 to 200,000, and / or (b)- CONR ¹ R ² , —NR ¹ R ² , and —N ⁺ R ¹ R ² R ³ (wherein R ¹ , R ² and R ³ each independently represents a hydrogen atom or an alkyl group) A binder containing 0.5 to 5 meq / g of at least one polar group selected from: and having a mass average molecular weight in the range of 20,000 to 200,000;
Component C: A compound having at least one carboxyl group and / or hydroxyl group in one molecule.   The magnetic layer forming coating solution is prepared by mixing component A, component B, and component C simultaneously, or by mixing component B with a mixture obtained by mixing component A and component C. The method of manufacturing a magnetic recording medium according to claim 1, comprising: Wherein component B, _{(b) -SO 3 M, -OSO 3 M} , -PO (OM) 2, -OPO (OM) 2, and COOM (where, M represents a hydrogen atom, an alkali metal or ammonium) 3. A binder containing at least one polar group selected from the group consisting of 0.2 to 0.7 meq / g and having a mass average molecular weight in the range of 20,000 to 200,000. A method for producing the magnetic recording medium according to 1.   The method for producing a magnetic recording medium according to claim 1, wherein the compound having at least one carboxyl group and / or hydroxyl group in a molecule is a cyclic compound.   The method for producing a magnetic recording medium according to claim 4, wherein the cyclic compound is at least one selected from the group consisting of an alicyclic compound, an aromatic compound, and a heterocyclic compound.   6. The method of manufacturing a magnetic recording medium according to claim 4, wherein the cyclic structure contained in the cyclic compound is at least one selected from the group consisting of a cyclohexane ring, a benzene ring, a pyridine ring, and a naphthalene ring.   The method for manufacturing a magnetic recording medium according to claim 1, wherein the ferromagnetic powder is a hexagonal ferrite powder.   The method for manufacturing a magnetic recording medium according to claim 1, wherein the binder is a polyurethane resin.   The method for producing a magnetic recording medium according to claim 1, wherein a magnetic recording medium having a center line average roughness on the surface of the magnetic layer in the range of 1.0 to 3.0 nm is produced.   A magnetic recording medium having a magnetic layer containing a ferromagnetic powder and a binder on a nonmagnetic support, wherein the magnetic recording is produced by the production method according to any one of claims 1 to 8. Medium. The magnetic recording medium according to claim 10, wherein the center line average roughness of the surface of the magnetic layer is in the range of 1.0 to 3.0 nm.