JP2016071926A - Magnetic recording medium and coating composition for magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide new means for achieving enhanced dispersibility of a ferromagnetic powder and also enhanced durability of a magnetic layer in a magnetic recording medium.SOLUTION: The magnetic recording medium comprises a magnetic layer comprising a ferromagnetic powder and a binder on a nonmagnetic support, and further comprises a compound expressed by the following general formula (1) in the magnetic layer. A coating composition for magnetic recording medium comprises a compound expressed by the following general formula (1), a ferromagnetic powder, a binder, and a solvent. In the general formula (1), X represents -O-, -S-, or -NR-; each of R and Rindependently represents a hydrogen atom or a monovalent substituent; L represents a divalent connecting group; Z represents an n-valent partial structure comprising at least one group selected from the group consisting of carboxyl groups and carboxylate groups; m represents an integer of 2 or more; and n represents an integer of 1 or more. The general formula (1) is shown in the figure below.SELECTED DRAWING: None

Description

  The present invention relates to a magnetic recording medium and a coating composition for a magnetic recording medium.

  A coating-type magnetic recording medium (hereinafter also simply referred to as “magnetic recording medium”) is usually prepared by applying a coating composition containing a binder together with a ferromagnetic powder directly on a nonmagnetic support or other nonmagnetic layer or the like. It is produced by coating indirectly through the above layer and applying a curing treatment such as heating and light irradiation as necessary to form a magnetic layer.

  Conventionally, in a coating type magnetic recording medium, a binder has played an important role in improving the dispersibility of the ferromagnetic powder and improving the durability of the magnetic layer. Therefore, various studies have been made on binders (for example, see Patent Document 1 as an example).

JP 2004-67941 A

  For improving the dispersibility of the ferromagnetic powder, as described in Patent Document 1, a polar group such as a sulfonate group is introduced into the binder. The polar group is introduced into the binder in order to increase the dispersibility by efficiently adsorbing the binder on the surface of the ferromagnetic powder. However, as described in paragraph 0026 of Patent Document 1, introduction of an excessive amount of polar groups tends to lower the dispersibility of the ferromagnetic powder. Accordingly, it has become difficult to sufficiently improve the dispersibility of the ferromagnetic powder by introducing a polar group into the binder.

  For improving the durability of the magnetic layer, it has been studied to use a resin having high mechanical properties as a binder for the magnetic layer. In this regard, Patent Document 1 proposes to use a predetermined copolymer component such as an aromatic polyisocyanate in order to increase the urethane group concentration in order to improve the mechanical properties of the polyurethane resin used as a binder for the magnetic layer. Has been. However, as described in paragraph 0025 of Patent Document 1, as the urethane group concentration of the resin used as the binder is increased, the mechanical properties of the resin can be increased, but the solubility is decreased. The dispersibility of the magnetic powder tends to decrease. Therefore, paragraph 0025 of Patent Document 1 describes that the urethane group concentration should be within a range in which the dispersibility of the ferromagnetic powder can be maintained satisfactorily.

On the other hand, in recent years, magnetic layers are required to have even better durability. This is because the demanded performance of the market is becoming more sophisticated and the ferromagnetic powder is finely divided. For example, demand performance in the market in recent years includes high durability capable of continuous running for a longer period of time and with higher reliability than in the past. Further, since the magnetic force per bit becomes weaker as the ferromagnetic powder becomes finer, the read head and the surface of the magnetic recording medium (magnetic layer) tend to be closer to read information from such a bit. It is in. Therefore, in recent years, the contact frequency between the read head and the surface of the magnetic recording medium (magnetic layer) has increased. Therefore, magnetic recording media have been used in a state where the surface of the magnetic layer is more susceptible to scratches than in the past.
In order to improve the durability of the magnetic layer, it is conceivable to improve the mechanical properties of the resin used as the binder for the magnetic layer as has been studied. However, as described above, the dispersibility of the ferromagnetic powder tends to decrease as the mechanical properties of the binder are increased to improve the durability of the magnetic layer. That is, it has become difficult to achieve a further improvement in the durability of the magnetic layer, which has been required in recent years, together with an improvement in the dispersibility of the ferromagnetic powder, by using a conventional binder.

  Therefore, an object of the present invention is to provide a new means for achieving both improvement of the dispersibility of the ferromagnetic powder and improvement of the durability of the magnetic layer in the magnetic recording medium.

  As a result of intensive studies to achieve the above object, the present inventors have used a compound represented by the following general formula (1) as a magnetic layer component together with a ferromagnetic powder and a binder, thereby producing a ferromagnetic powder. It has been newly found that it is possible to improve both the dispersibility of the magnetic layer and the durability of the magnetic layer.

(In the general formula (1), X represents —O—, —S— or —NR ¹ —, R and R ¹ each independently represent a hydrogen atom or a monovalent substituent, and L represents a divalent group. Represents a linking group, Z represents an n-valent partial structure having at least one group selected from the group consisting of a carboxyl group and a carboxyl base (hereinafter also referred to as “carboxyl (salt) group”); (The above integer is represented, and n represents an integer of 1 or more.)

The following is a guess by the present inventors and does not limit the present invention at all, but the present inventors are able to achieve both improved dispersibility and improved durability with the above compounds. Is considered as follows.
The compound represented by the general formula (1) has a structure (polyester chain) represented by-((C = O) -LO) m-. The present inventors consider that this structure may contribute to imparting moderate easiness to the magnetic layer (coating film). More specifically, simply increasing the strength of the magnetic layer is considered to make the magnetic layer brittle and easy to break. However, the above-mentioned compound imparts moderate stretchability to the magnetic layer. The present inventors speculate that it may contribute to the improvement.
As for the improvement of dispersibility, the carboxyl (salt) group contained in the Z portion serves as an adsorbing part on the particle surface of the ferromagnetic powder, whereby the compound represented by the general formula (1) is efficiently incorporated into the ferromagnetic powder. It is thought that the reason why the above-mentioned compound can improve the dispersibility of the ferromagnetic powder is that the polyester chain has a steric hindrance effect and can prevent aggregation of the particles of the ferromagnetic powder after the adsorption. .
The present invention has been completed based on the above findings.

One aspect of the present invention is a magnetic recording medium having a magnetic layer containing a ferromagnetic powder and a binder on a nonmagnetic support,
A magnetic recording medium further comprising a compound represented by the general formula (1) in the magnetic layer;
About.

A further aspect of the invention provides:
A compound represented by the above general formula (1);
Ferromagnetic powder,
A binder,
A solvent,
A coating composition for magnetic recording media,
About.

  In one aspect, in general formula (1), L represents an alkylene group.

  In one aspect, in general formula (1), X represents -O-.

  In one aspect, in general formula (1), Z represents a reactive residue of a carboxylic acid anhydride. Carboxylic anhydride is a compound having a partial structure represented by-(C = O) -O- (C = O)-. In the carboxylic acid anhydride, the partial structure serves as a reaction site, and the oxygen atom of-((C = O) -LO) m- in the general formula (1) and Z are bonded to a carbonyl bond (-( Bonding via C = O)-) results in a carboxyl (salt) group. The partial structure thus formed is a reaction residue of carboxylic anhydride. In one embodiment, the carboxylic acid anhydride is a tetracarboxylic acid anhydride. Details will be described later.

  In one embodiment, the compound represented by the general formula (1) has a weight average molecular weight in the range of 1,000 or more and less than 20,000.

  In one aspect, the average particle size of the ferromagnetic powder is in the range of 10-50 nm.

  In one aspect, the compound represented by the general formula (1) is contained in the magnetic layer or magnetic recording medium coating composition in an amount of 0.5 to 50.0 parts by mass per 100.0 parts by mass of the ferromagnetic powder.

  According to the present invention, it is possible to improve both the dispersibility of the ferromagnetic powder and the durability of the magnetic layer.

A magnetic recording medium according to one embodiment of the present invention is a magnetic recording medium having a magnetic layer containing a ferromagnetic powder and a binder on a nonmagnetic support, and the magnetic layer is represented by the general formula (1). Further comprising a compound.
The compound contained in the magnetic layer of the magnetic recording medium can contribute to improving the dispersibility of the ferromagnetic powder. Furthermore, the magnetic layer containing the above compound can exhibit excellent durability (more specifically, excellent scratch resistance that is difficult to be scratched).

The coating composition for magnetic recording media according to one embodiment of the present invention includes a compound represented by the general formula (1), a ferromagnetic powder, a binder, and a solvent.
The magnetic recording medium coating composition is used as a magnetic layer forming coating solution for forming a magnetic layer of a magnetic recording medium according to one embodiment of the present invention or for preparing a magnetic layer forming coating solution. be able to.

  Hereinafter, the magnetic recording medium and the coating composition for magnetic recording medium (hereinafter also referred to as “composition”) will be described in more detail.

  In the present invention, unless otherwise specified, the described group may have a substituent or may be unsubstituted. When a group has a substituent, examples of the substituent include an alkyl group (for example, an alkyl group having 1 to 6 carbon atoms), a hydroxy group, an alkoxy group (for example, an alkoxy group having 1 to 6 carbon atoms), and a halogen atom (for example, fluorine Atom, chlorine atom, bromine atom), cyano group, amino group, nitro group, acyl group, carboxyl (salt) group, and the like. In addition, the “carbon number” of the group having a substituent means the carbon number of a portion not including the substituent.

<Compound represented by the general formula (1)>
(Details of general formula (1))
General formula (1) is as follows.

(In the general formula (1), X represents —O—, —S— or —NR ¹ —, R and R ¹ each independently represent a hydrogen atom or a monovalent substituent, and L represents a divalent group. Represents a linking group, Z represents an n-valent partial structure having at least one group (carboxyl (salt) group) selected from the group consisting of a carboxyl group and a carboxyl base, m represents an integer of 2 or more, and n represents Represents an integer of 1 or more.)

  In general formula (1), L includes m × n. Further, n each of R and X is included. When a plurality of Ls are included in the general formula (1), the plurality of Ls may be the same or different. The same applies to R and X.

In General Formula (1), X represents —O—, —S—, or —NR ¹ —, and R ¹ represents a hydrogen atom or a monovalent substituent. Examples of the monovalent substituent include the above-mentioned substituents, preferably an alkyl group, more preferably an alkyl group having 1 to 6 carbon atoms, and still more preferably a methyl group or an ethyl group. More preferably, R ¹ is a hydrogen atom. X preferably represents -O-.

R represents a hydrogen atom or a monovalent substituent. R preferably represents a monovalent substituent. Examples of the monovalent substituent represented by R include a monovalent group such as a linear or branched alkyl group, aryl group, heteroaryl group, alicyclic group, non-aromatic heterocyclic group, and the above-described one. Examples include a structure in which a divalent linking group is linked to a valent group. Examples of the divalent linking group include —C (═O) —O—, —O—, —C (═O) —NR ¹⁰ — (R ¹⁰ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. One or two or more selected from the group consisting of: -O-C (= O) -NH-, a phenylene group, an alkylene group having 1 to 30 carbon atoms, and an alkenylene group having 2 to 30 carbon atoms. A divalent linking group composed of a combination can be exemplified. Specific examples of the monovalent substituent represented by R include the following structures. In the following structure, * represents a bonding position with X. However, the present invention is not limited to the following specific examples.

  In general formula (1), L represents a divalent linking group. Examples of the divalent linking group include an alkylene group which may be a linear, branched or cyclic structure, an alkenylene group which may be a linear, branched or cyclic structure, -C (= O)-, -O-, Mention may be made of a divalent linking group composed of one or a combination of two or more selected from the group consisting of an arylene group and a halogen atom. More specifically, an alkylene group having 1 to 12 carbon atoms which may be a linear, branched or cyclic structure, an alkenylene group having 1 to 6 carbon atoms which may be a linear, branched or cyclic structure, -C (= Examples thereof include a divalent linking group composed of one or a combination of two or more selected from O)-, -O-, a phenylene group, and a halogen atom. Said divalent linking group preferably consists of 1 to 10 carbon atoms, 0 to 10 oxygen atoms, 0 to 10 halogen atoms and 1 to 30 hydrogen atoms. It is a divalent linking group. Specific examples are an alkylene group and the following structure. In the following structures, * indicates a bonding position with another structure. However, the present invention is not limited to the following specific examples.

  L is preferably an alkylene group, more preferably an alkylene group having 1 to 12 carbon atoms, more preferably an alkylene group having 1 to 5 carbon atoms, more preferably an unsubstituted alkylene having 1 to 5 carbon atoms. It is a group.

  Z represents an n-valent partial structure having at least one group (carboxyl (salt) group) selected from the group consisting of a carboxyl group and a carboxyl base. The carboxyl base is a salt form of a carboxyl group (—COOH), and means a salt in which M represents a cation such as an alkali metal ion in —COOM.

  The number of carboxyl (salt) groups contained in Z is at least one per Z, preferably 2 or more, and more preferably 2 to 4.

  Z may include one or more of a linear structure, a branched structure, and a cyclic structure. From the viewpoint of ease of synthesis and the like, preferably Z is a reaction residue of carboxylic anhydride. For example, the following structure is mentioned as a specific example. In the following structures, * indicates a bonding position with another structure. However, the present invention is not limited to the following specific examples.

  By synthesizing the compound represented by the general formula (1) using a carboxylic acid anhydride having one of the partial structures-(C = O) -O- (C = O)-described above. The compound represented by the general formula (1) having the monovalent reaction residue can be obtained, and the compound represented by the general formula (1) having the divalent reaction residue can be obtained by using the compound having two. Can be obtained. The same applies to the compound represented by the general formula (1) having the above-mentioned trivalent or higher reactive residue. As described above, n is an integer of 1 or more, for example, an integer in the range of 1 to 4, preferably an integer in the range of 2 to 4.

  As the carboxylic acid anhydride, for example, by using a tetracarboxylic acid anhydride, a compound represented by the general formula (1) with n = 2 can be obtained. The tetracarboxylic acid anhydride is a carboxylic acid anhydride having two partial structures in one molecule by dehydration condensation of each two carboxyl groups in a compound having four carboxyl groups in one molecule. In general formula (1), a compound in which Z represents a reactive residue of tetracarboxylic anhydride is preferable from the viewpoint of further improving the dispersibility of the ferromagnetic powder and the durability of the magnetic layer. Examples of the tetracarboxylic acid anhydride include various tetracarboxylic acid anhydrides such as aliphatic tetracarboxylic acid anhydrides, aromatic tetracarboxylic acid anhydrides, and polycyclic tetracarboxylic acid anhydrides.

  Examples of the aliphatic tetracarboxylic acid anhydride include meso-butane-1,2,3,4-tetracarboxylic dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,3 -Dimethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 2,3,5-tricarboxycyclopentylacetic acid dianhydride, 2,3,5,6-tetracarboxycyclohexane dianhydride, 2,3,5,6-tetracarboxynorbornane dianhydride, 3,5,6-tricarboxynorbornane-2-acetic acid dianhydride, 2,3 , 4,5-tetrahydrofurantetracarboxylic dianhydride, 5- (2,5-dioxotetrahydrofuryl) -3-methyl-3-cyclohexene-1,2-dicarboxylic acid Anhydride, bicyclo [2,2,2] - oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride, can be mentioned ethylenediaminetetraacetic acid dianhydride and the like.

  Examples of the aromatic tetracarboxylic acid anhydride include pyromellitic dianhydride, ethylene glycol ditrimellitic anhydride ester, propylene glycol ditrimellitic anhydride ester, butylene glycol ditrimellitic anhydride ester, 3,3 ′ , 4,4′-benzophenone tetracarboxylic dianhydride, 2,2 ′, 3,3′-benzophenone tetracarboxylic dianhydride, 3,3 ′, 4,4′-biphenylsulfone tetracarboxylic dianhydride 2,2 ′, 3,3′-biphenylsulfonetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride 3,3 ′, 4,4′-biphenyl ether tetracarboxylic dianhydride, 3,3 ′, 4,4′-dimethyldiphe Rusilanetetracarboxylic dianhydride, 3,3 ′, 4,4′-tetraphenylsilanetetracarboxylic dianhydride, 1,2,3,4-furantetracarboxylic dianhydride, 4,4′- Bis (3,4-dicarboxyphenoxy) diphenyl sulfide dianhydride, 4,4′-bis (3,4-dicarboxyphenoxy) diphenylsulfone dianhydride, 4,4′-bis (3,4-dicarboxy) Phenoxy) diphenylpropane dianhydride, 3,3 ′, 4,4′-perfluoroisopropylidene diphthalic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, bis (phthal Acid) phenylphosphine oxide dianhydride, p-phenylene-bis (triphenylphthalic acid) dianhydride, M-phenylene-bis (triphenylphthalic acid) dianhydride, (Triphenylphthalic acid) -4,4′-diphenyl ether dianhydride, bis (triphenylphthalic acid) -4,4′-diphenylmethane dianhydride, 9,9-bis (3,4-dicarboxyphenyl) Fluorene dianhydride, 9,9-bis [4- (3,4-dicarboxyphenoxy) phenyl] fluorene dianhydride, and the like can be given.

  Examples of the polycyclic tetracarboxylic acid anhydride include 3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalene succinic dianhydride, 3,4-dicarboxy-1,2, Examples include 3,4-tetrahydro-6-methyl-1-naphthalene succinic dianhydride.

  In general formula (1), m represents an integer of 2 or more. As described above, the compound represented by the general formula (1) has a structure (polyester chain) represented by-((C = O) -LO) m-, which improves dispersibility and durability. It is thought that it contributes to. From these viewpoints, m is preferably an integer in the range of 5 to 200, more preferably an integer in the range of 5 to 100, and still more preferably an integer in the range of 5 to 60.

(Weight average molecular weight)
The compound represented by the general formula (1) only needs to have the above structure, and the molecular weight is not limited. Preferably, the compound represented by the general formula (1) has a weight average molecular weight of 1,000 or more and less than 20,000. The weight average molecular weight is generally lower than that of a binder used for a magnetic layer. A compound having such a weight average molecular weight is considered to contribute to further improving the durability of the magnetic layer by exerting a plasticizer-like action. From this point, the weight average molecular weight of the compound represented by the general formula (1) is more preferably 12,000 or less, and more preferably 10,000 or less. Moreover, the compound represented by General formula (1) is 1,000 or more, for example, it is preferable that it is 1,500 or more, and it is more preferable that it is 2,000 or more. In addition, the weight average molecular weight in this invention shall mean the value measured by gel permeation chromatography (GPC) and calculated | required by standard polystyrene conversion. The weight average molecular weight shown in the below-mentioned Example is the value calculated | required by converting into standard polystyrene the value measured on condition of the following using GPC. In addition, the weight average molecular weight of a mixture of two or more structural isomers means the weight average molecular weight of two or more structural isomers contained in the mixture.
GPC device: HLC-8220 (manufactured by Tosoh)
Guard column: TSK guard column Super HZM-H
Column: TSKgel Super HZ 2000, TSKgel Super HZ 4000, TSKgel Super HZ-M (manufactured by Tosoh, 4.6 mm (inner diameter) × 15.0 cm, three kinds of columns connected in series)
Eluent: Tetrahydrofuran (THF), containing stabilizer (2,6-di-t-butyl-4-methylphenol) Eluent flow rate: 0.35 mL / min Column temperature: 40 ° C
Inlet temperature: 40 ° C
Refractive index (RI) measurement temperature: 40 ° C
Sample concentration: 0.3% by weight
Sample injection volume: 10 μL

  Specific examples of the compound include various compounds shown in Examples described later.

(Synthesis method)
The compound represented by the general formula (1) described above can be synthesized by a known method. As an example of the synthesis method, for example, a method in which a carboxylic acid anhydride and a compound represented by the following general formula (2) are subjected to a reaction such as a ring-opening addition reaction can be exemplified. In general formula (2), R, X, L, and m are respectively synonymous with general formula (1). A represents a hydrogen atom, an alkali metal atom or a quaternary ammonium base, preferably a hydrogen atom.

  The reaction between the carboxylic acid anhydride and the compound represented by the general formula (2) is, for example, when butanetetracarboxylic acid anhydride is used, 0.4 to 0.5 mol of hydroxyl group per equivalent. Mix butanetetracarboxylic anhydride in a proportion and heat for about 3 to 12 hours in the presence of no solvent, if necessary, an organic solvent having a boiling point of 50 ° C. or higher, and a reaction catalyst such as a tertiary amine or an inorganic base. It is carried out by stirring. Even when other carboxylic acid anhydrides are used, the reaction between the carboxylic acid anhydride and the compound represented by the general formula (2) is performed according to the above reaction conditions or according to known reaction conditions. be able to.

  After the above reaction, a post-process such as purification may be performed as necessary.

  Moreover, the compound represented by General formula (2) may use a commercial item, and can also be obtained by a well-known polyester synthesis method. For example, examples of the polyester synthesis method include ring-opening polymerization of lactone. Examples of the lactone include ε-caprolactone, δ-caprolactone, β-propiolactone, γ-butyrolactone, δ-valerolactone, γ-valerolactone, enanthlactone, β-butyrolactone, γ-hexanolactone, and γ-octalactone. Examples include nolactone, δ-hexalanolactone, δ-octanolactone, δ-dodecanolactone, α-methyl-γ-butyrolactone, and lactide. The lactide may be L-form or D-form. In polyester synthesis, only one kind of lactone may be used, or two or more kinds of different structures may be used. As the lactone, ε-caprolactone, lactide or δ-valerolactone is preferable from the viewpoint of reactivity and availability. However, it is not limited to these, and any lactone may be used as long as the polyester can be obtained by ring-opening polymerization.

As the nucleophile for ring-opening polymerization of lactone, alcohol, thiol, amine and the like can be used. One nucleophilic reagent may be used, or two or more nucleophiles may be mixed and used.
For example, when alcohol is used, when the alcohol is represented by R ² OH, the R ² O- moiety may be present as the RX- moiety in the structure represented by the general formula (1). Here, X represents -O-.
When using a thiol, when the thiol is represented by R ² SH, the R ² S- moiety may exist as an RX- moiety in the structure represented by the general formula (1). Here, X represents -S-.
When an amine is used, when the amine is represented by RR ¹ NH, the RR ¹ N- moiety may exist as the RX- moiety in the structure represented by the general formula (1). Here, X represents —NR ¹ —. R and R ¹ are respectively synonymous with the general formula (1).

  However, the compound represented by the general formula (2) is not limited to a polyester-derived structure obtained by ring-opening polymerization of lactone, and is a known polyester synthesis method, for example, polyvalent carboxylic acid and polyvalent It can also be a structure derived from polyester obtained by polycondensation with alcohol, polycondensation of hydroxycarboxylic acid, or the like.

  The synthesis method described above is an example and does not limit the present invention. As long as the compound represented by the general formula (1) can be synthesized, a known synthesis method can be used without any limitation. The synthesized reaction product can be used as it is or after purification by a known method as necessary to form a magnetic layer.

  The compound represented by the general formula (1) described above is contained in the magnetic layer of the magnetic recording medium together with the ferromagnetic powder and the binder. The composition according to one embodiment of the present invention includes a ferromagnetic powder, a binder, and a solvent. The said compound may use only 1 type and may use 2 or more types from which a structure differs. Moreover, you may use the compound represented by General formula (1) as a mixture of 2 or more types of structural isomers. For example, when two or more structural isomers are obtained by the synthesis reaction of the compound represented by the general formula (1), such a mixture can also be used for the preparation of the composition according to one embodiment of the present invention. When using 2 or more types together, content described below shall mean the total content of the compound used together. This also applies to the content of each component described later. The content of the compound represented by the general formula (1) is 0.5 parts by mass or more per 100.0 parts by mass of the ferromagnetic powder, from the viewpoint of improving the dispersibility of the ferromagnetic powder and the durability of the magnetic layer. It is preferable that it is 1.0 mass part or more. On the other hand, in order to improve the recording density, it is preferable to increase the filling rate of the ferromagnetic powder in the magnetic layer. In this respect, it is preferable to relatively reduce the content of components other than the ferromagnetic powder. From the above viewpoint, the content of the compound is preferably 50.0 parts by mass or less, more preferably 40.0 parts by mass or less, with respect to 100.0 parts by mass of the ferromagnetic powder. More preferably, it is 0 parts by mass or less.

<Binder>
As the binder contained in the magnetic recording medium and the composition according to one embodiment of the present invention, various resins usually used as a binder for a coating type magnetic recording medium can be used without any limitation. For example, polyurethane resin, polyester resin, polyamide resin, vinyl chloride resin, acrylic resin copolymerized with styrene, acrylonitrile, methyl methacrylate, cellulose resin such as nitrocellulose, epoxy resin, phenoxy resin, polyvinyl acetal, A single resin or a mixture of a plurality of resins can be used from polyvinyl alkylal resins such as polyvinyl butyral. Among these, a polyurethane resin, an acrylic resin, a cellulose resin, and a vinyl chloride resin are preferable, and a polyurethane resin and a vinyl chloride resin are more preferable. These resins can also be used as a binder in the nonmagnetic layer described later.
JP, 2010-24113, A paragraphs 0028-0031 can be referred to for the above binder. The binder content can be, for example, in the range of 5.0 to 50.0 parts by mass, preferably in the range of 10.0 to 30.0 parts by mass with respect to 100.0 parts by mass of the ferromagnetic powder.

  As described above, the compound represented by the general formula (1) is preferably a compound having a lower molecular weight than a resin that is usually used as a binder. The present inventors presume that such a compound exerting a plasticizer action on the binder can contribute to further improvement of the durability of the magnetic layer. The weight average molecular weight of the binder is preferably in the range of 20,000 to 120,000, more preferably in the range of 30,000 to 100,000, still more preferably in the range of 30,000 to 60,000. is there.

<Ferromagnetic powder>
The ferromagnetic powder preferably has an average particle size of 50 nm or less. A ferromagnetic powder having an average particle size of 50 nm or less is a ferromagnetic powder that can cope with high-density recording that has been demanded in recent years, but it is not easy to disperse highly. On the other hand, when used in combination with the compound represented by the general formula (1), it is possible to improve the dispersibility of the ferromagnetic powder having an average particle size of 50 nm or less. From the viewpoint of the stability of magnetization, the average particle size is preferably 10 nm or more, and more preferably 20 nm or more.

The average particle size of the ferromagnetic powder is a value measured by the following method using a transmission electron microscope.
The ferromagnetic powder is photographed at a photographing magnification of 100,000 using a transmission electron microscope and printed on a photographic paper so that the total magnification is 500,000 times to obtain a photograph of particles constituting the ferromagnetic powder. The target particle is selected from the photograph of the obtained particle, the outline of the particle is traced with a digitizer, and the size of the particle (primary particle) is measured. Primary particles refer to independent particles without agglomeration.
The above measurements are performed on 500 randomly extracted particles. The arithmetic average of the particle sizes of the 500 particles thus obtained is defined as the average particle size of the ferromagnetic powder. As the transmission electron microscope, for example, Hitachi transmission electron microscope H-9000 type can be used. The particle size can be measured using known image analysis software, for example, image analysis software KS-400 manufactured by Carl Zeiss.
In the present invention, the average particle size of the powder refers to the average particle size obtained by the above method. The average particle size shown in the examples described later was measured using a Hitachi transmission electron microscope H-9000 type as a transmission electron microscope and Carl Zeiss image analysis software KS-400 as image analysis software.

  As a method for collecting sample powder such as ferromagnetic powder from the magnetic layer for particle size measurement, for example, the method described in paragraph 0015 of JP2011-048878A can be employed.

In the present invention, the size of the particles constituting the powder such as ferromagnetic powder (hereinafter referred to as “particle size”) is the shape of the particles observed in the above particle photograph,
(1) In the case of needle shape, spindle shape, columnar shape (however, the height is larger than the maximum major axis of the bottom surface), it is represented by the length of the major axis constituting the particle, that is, the major axis length,
(2) In the case of a plate or column (however, the thickness or height is smaller than the maximum major axis of the plate surface or bottom surface), it is represented by the maximum major axis of the plate surface or bottom surface,
(3) In the case of a spherical shape, a polyhedral shape, an unspecified shape, etc., and the major axis constituting the particle cannot be specified from the shape, it is represented by an equivalent circle diameter. The equivalent circle diameter is a value obtained by a circle projection method.

The average acicular ratio of the powder is determined by measuring the length of the minor axis of the particle, that is, the minor axis length in the above measurement, and obtaining the value of (major axis length / minor axis length) of each particle. Refers to the arithmetic average of the values obtained for the particles. Here, the short axis length refers to the length of the short axis constituting the particle in the case of (1) in the definition of the particle size, and the thickness or the height in the case of (2), 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.
And when the shape of the particle is specific, for example, in the case of definition (1) of the above particle size, the average particle size is the average major axis length, and in the case of definition (2), the average particle size is the average plate diameter. The average plate ratio is an arithmetic average of (maximum major axis / thickness or height). In the case of the same definition (3), the average particle size is an average diameter (also referred to as an average particle diameter or an average particle diameter).

  Preferable specific examples of the ferromagnetic powder include hexagonal ferrite powder. With respect to the size of the hexagonal ferrite powder, the average plate diameter is preferably 10 nm or more and 50 nm or less, and more preferably 20 nm or more and 50 nm or less, from the viewpoint of high density recording and magnetization stability. For details of the hexagonal ferrite powder, paragraphs 0134 to 0136 of JP2011-216149A can be referred to, for example.

  Preferable specific examples of the ferromagnetic powder include a ferromagnetic metal powder. Regarding the size of the ferromagnetic metal powder, the average major axis length is preferably 10 nm or more and 50 nm or less, and more preferably 20 nm or more and 50 nm or less, from the viewpoint of high density recording and magnetization stability. As for the details of the ferromagnetic metal powder, paragraphs 0137 to 0141 of JP2011-216149A can be referred to, for example.

  The content (filling rate) of the ferromagnetic powder in the magnetic layer is preferably in the range of 50 to 90% by mass, more preferably in the range of 60 to 90% by mass. A high filling factor is preferable from the viewpoint of improving the recording density.

<Solvent>
The composition according to one embodiment of the present invention includes the compound represented by the general formula (1) described above, the ferromagnetic powder, and the binder in a solvent. Examples of the solvent include organic solvents generally used for producing a coating type magnetic recording medium. 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, methylcyclohexanol, etc. at an arbitrary ratio Alcohols, methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycol acetates such as glycol acetate, glycol dimethyl ether, glycol monoethyl ether, dioxane and other glycol ethers, benzene, toluene, xylene, cresol, chlorobenzene Aromatic hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin Chlorinated hydrocarbons such as dichlorobenzene, N, N- dimethylformamide, may be used hexane. Among these, it is preferable to use an organic solvent containing a ketone (ketone-based organic solvent) from the viewpoint of the solubility of the binder usually used in magnetic recording media and the adsorption of the binder to the surface of the ferromagnetic powder. .

  The organic solvent is not necessarily 100% pure, and may contain impurities such as isomers, unreacted materials, by-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. In order to improve dispersibility, it is preferable that the polarity is strong to some extent, and it is preferable that 50% by mass or more of a solvent having a dielectric constant of 15 or more is included in the solvent composition. Moreover, it is preferable that a solubility parameter is 8-11. The amount of the solvent in the magnetic recording medium coating composition according to one embodiment of the present invention is not particularly limited, and can be the same as the coating liquid for forming a magnetic layer of a normal coating type magnetic recording medium.

<Other ingredients>
In addition to the various components described above, an additive can be added to the composition according to one embodiment of the present invention as necessary. Examples of additives include abrasives, lubricants, dispersants / dispersing aids, antifungal agents, antistatic agents, antioxidants, carbon black and the like, which are commonly used for forming coated magnetic recording media. Can do. As the additive, commercially available products can be appropriately selected and used according to desired properties. Note that in the composition according to one embodiment of the present invention, the compound represented by the general formula (1) can function as a dispersant.

  Moreover, the said composition can also contain a well-known hardening | curing agent. A magnetic layer formed using a coating solution for forming a magnetic layer containing a curing agent usually contains a reaction product in which a binder and a curing agent are cross-linked. The use of a curing agent is preferable for increasing the strength of the magnetic layer. From the viewpoint of crosslinking reactivity and the like, polyisocyanate is preferable as the curing agent. JP, 2011-216149, A paragraphs 0124-0125 can be referred to for the details of polyisocyanate. The curing agent is, for example, 0 to 80.0 parts by mass with respect to 100.0 parts by mass of the binder in the coating liquid for forming the magnetic layer, and preferably 50.0 to 80.0 from the viewpoint of improving the strength of the magnetic layer. It can be added and used in an amount of parts by mass.

  The composition can be prepared by adding and mixing the various components described above simultaneously or sequentially in any order. The method for preparing the composition is not particularly limited, and any known technique relating to the preparation of a coating solution for forming a magnetic layer of a coating type magnetic recording medium can be applied without any limitation.

<Configuration and manufacturing process of magnetic recording medium>
Hereinafter, the configuration and manufacturing process of the magnetic recording medium will be described in more detail.

(Magnetic layer)
For the magnetic layer, the coating solution for forming the magnetic layer is applied directly to the surface of the nonmagnetic support or the surface of another layer such as a nonmagnetic layer provided on the nonmagnetic support and dried. It can be formed by performing a treatment such as heating. The various components contained in the magnetic layer and the composition that can be used to form the magnetic layer are as described above.

(Nonmagnetic layer)
Next, the nonmagnetic layer will be described.
The magnetic recording medium may have a nonmagnetic layer containing a nonmagnetic powder and a binder between the nonmagnetic support and the magnetic layer. The nonmagnetic powder that can be used in the nonmagnetic layer may be an inorganic substance or an organic substance. Carbon black or the like can also be used. Examples of the inorganic substance include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. These nonmagnetic powders are available as commercial products, and can also be produced by a known method. The details can be referred to paragraphs 0146 to 0150 of JP2011-216149A.

  As the binder, lubricant, dispersant, additive, solvent, dispersion method and the like of the nonmagnetic layer, those of the magnetic layer can be applied. 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. Further, carbon black or organic powder can be added to the nonmagnetic layer. For example, JP 2010-24113 A, paragraphs 0040 to 0042 can be referred to.

(Non-magnetic support)
Next, the nonmagnetic support will be described. Examples of the nonmagnetic support include known ones such as biaxially stretched polyethylene terephthalate, polyethylene naphthalate, polyamide, polyamideimide, and aromatic polyamide. Among these, polyethylene terephthalate, polyethylene naphthalate, and polyamide are preferable.
These supports may be subjected in advance to corona discharge, plasma treatment, easy adhesion treatment, heat treatment and the like.

(Layer structure)
Regarding the thickness of the nonmagnetic support and each layer in the magnetic recording medium, the thickness of the nonmagnetic support is preferably 3 to 80 μm. 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 nm to 150 nm, preferably 20 nm to 120 nm, and more preferably. Is 30 nm to 100 nm. 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 0.1 to 2.0 μm, and more preferably 0.1 to 1.5 μm. The nonmagnetic layer of the magnetic recording medium according to the present invention includes a substantially nonmagnetic layer containing a small amount of ferromagnetic powder together with the nonmagnetic powder, for example, as impurities or intentionally. . Here, the substantially nonmagnetic layer means that the residual magnetic flux density of this layer is 10 mT or less, the coercive force is 7.96 kA / m (100 Oe) or less, or the residual magnetic flux density is 10 mT or less. And a layer having a coercive force of 7.96 kA / m (100 Oe) or less. The nonmagnetic layer preferably has no residual magnetic flux density and coercive force.

(Back coat layer)
The magnetic recording medium can also have a backcoat layer on the surface opposite to the surface having the magnetic layer of the nonmagnetic support. The back coat layer preferably contains carbon black and inorganic powder. For the binder and various additives for forming the backcoat layer, the formulation of the magnetic layer and the nonmagnetic layer can be applied. The thickness of the back coat layer is preferably 0.9 μm or less, and more preferably 0.1 to 0.7 μm.

(Manufacturing process)
The process for producing a coating solution for forming a magnetic layer, a nonmagnetic layer or a backcoat layer usually 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. Ferromagnetic powder used in the present invention, compound represented by general formula (1), non-magnetic powder, binder, carbon black, abrasive, antistatic agent, lubricant, solvent, etc. Alternatively, it may be added in the middle. 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 or other beads can be used to disperse the coating solution for forming the magnetic layer, the coating solution for forming the nonmagnetic layer, or the coating solution for forming the backcoat layer. As such dispersed beads, zirconia beads, titania beads, and steel beads, which are dispersed beads having a high specific gravity, are suitable. The particle diameter and packing rate of these dispersed beads are optimized and used. A well-known thing can be used for a disperser. For details of the method of manufacturing the magnetic recording medium, reference can be made, for example, to paragraphs 0051 to 0057 of JP2010-24113A. In addition, as described in JP 2012-74097 A, paragraph 0055, a heat treatment can be performed separately from the drying step and the calendar treatment, if necessary.

  The magnetic recording medium according to one embodiment of the present invention described above can achieve both improvement in the dispersibility of the ferromagnetic powder and improvement in the durability of the magnetic layer. Moreover, the coating composition for magnetic recording media according to one embodiment of the present invention can be suitably used for the formation of such a magnetic layer.

EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to the aspect shown in an Example. Unless otherwise specified, “part” and “%” described below are based on mass.
Moreover, the following weight average molecular weight was measured by GPC on the measurement conditions described previously, and it calculated | required as a polystyrene conversion value.
It was confirmed by ¹ H-NMR (nuclear magnetic resonance), GPC, and acid value measurement that the target compound was obtained by the following synthesis method. The acid value was measured according to JIS K 2501 (2003).

<Precursor synthesis example>
(Synthesis Example 1) Synthesis of Precursor 1 Into a 500 mL three-necked flask, 197.2 g of ε-caprolactone and 15.0 g of 2-ethyl-1-hexanol were introduced and stirred and dissolved while blowing nitrogen. Monobutyltin oxide 0.1g was added and it heated at 100 degreeC. After 8 hours, it was confirmed by gas chromatography that the raw material had disappeared, and then cooled to room temperature to obtain 200 g of solid precursor 1 (the following structure).

(Synthesis Example 2) Synthesis of Precursor 2 Into a 500 mL three-necked flask, 197.2 g of ε-caprolactone and 18.9 g of methyltriglycol were introduced, and dissolved by stirring at 80 ° C. while blowing nitrogen. Monobutyltin oxide 0.1g was added and it heated at 100 degreeC. After 8 hours, it was confirmed by gas chromatography that the raw material had disappeared, and then cooled to room temperature to obtain 200 g of solid precursor 2 (the following structure).

(Synthesis Example 3) Synthesis of Precursor 3 Into a 500 mL three-necked flask, 197.2 g of ε-caprolactone and 12.5 g of benzyl alcohol were introduced, and dissolved by stirring at 80 ° C. while blowing nitrogen. Monobutyltin oxide 0.1g was added and it heated at 100 degreeC. After 8 hours, it was confirmed by gas chromatography that the raw material had disappeared, and then cooled to room temperature to obtain 200 g of solid precursor 3 (the following structure).

(Synthesis Example 4) Synthesis of Precursor 4 Into a 500 mL three-necked flask, 197.2 g of ε-caprolactone and 27.2 g of diethylene glycol monobenzyl ether were introduced and dissolved with stirring while blowing nitrogen. Monobutyltin oxide 0.1g was added and it heated at 100 degreeC. After 8 hours, it was confirmed by gas chromatography that the raw material had disappeared, and then cooled to room temperature to obtain 210 g of solid precursor 4 (the following structure).

(Synthesis Example 5) Synthesis of Precursor 5 Into a 500 mL three-necked flask, 197.2 g of ε-caprolactone and 18.2 g of 4- (2-hydroxyethyl) morpholine were introduced and dissolved while stirring while blowing nitrogen. Monobutyltin oxide 0.1g was added and it heated at 100 degreeC. After 8 hours, it was confirmed by gas chromatography that the raw material had disappeared, and then cooled to room temperature to obtain 200 g of solid precursor 5 (the following structure).

<Synthesis Example of Compound Represented by General Formula (1)>
(Synthesis Example 6) Synthesis of Reaction Product 1 40.0 g of Precursor 1 was introduced into a 200 mL three-necked flask and dissolved by stirring at 80 ° C. while blowing nitrogen. 2.2 g of meso-butane-1,2,3,4-tetracarboxylic dianhydride was added and heated to 110 ° C. After 5 hours, it was confirmed by ¹ H-NMR that the raw material had disappeared, and then cooled to room temperature to obtain 38 g of a solid reaction product 1 (mixture of the following structural isomers).

(Synthesis Example 7) Synthesis of Reaction Product 2 Synthesis was performed in the same manner as in Synthesis Example 6 except that 2.2 g of butanetetracarboxylic acid anhydride was changed to 2.4 g of pyromellitic dianhydride in Synthesis Example 6. As a result, 38 g of a solid reaction product 2 (mixture of the following structural isomers) was obtained.

(Synthesis Example 8) Synthesis of Reaction Product 3 Except that, in Synthesis Example 6, butanetetracarboxylic anhydride 2.2 g was changed to 2,3,6,7-naphthalenetetracarboxylic dianhydride 3.0 g. Synthesis was performed in the same manner as in Synthesis Example 6 to obtain 39 g of a solid reaction product 3 (mixture of the following structural isomers).

(Synthesis Example 9) Synthesis of Reaction Product 4 Synthesis was performed in the same manner as in Synthesis Example 6 except that 2.2 g of butanetetracarboxylic acid anhydride was changed to 2.8 g of ethylenediaminetetraacetic acid dianhydride in Synthesis Example 6. As a result, 39 g of a solid reaction product 4 (compound having the following structure) was obtained.

(Synthesis Example 10) Synthesis of Reaction Product 5 Except that 2.2 g of butanetetracarboxylic anhydride was changed to 3.6 g of 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride in Synthesis Example 6. Was synthesized in the same manner as in Synthesis Example 6 to obtain 40 g of a solid reaction product 5 (mixture of the following structural isomers).

(Synthesis Example 11) Synthesis of Reaction Product 6 In Synthesis Example 6, 2.2 g of butanetetracarboxylic anhydride was converted to 5- (2,5-dioxotetrahydrofuryl) -3-methyl-3-cyclohexene-1,2. -Synthesis was performed in the same manner as in Synthesis Example 6 except that the amount was changed to 2.9 g of dicarboxylic dianhydride, to obtain 40 g of a solid reaction product 6 (mixture of the following structural isomers).

(Synthesis Example 12) Synthesis of Reaction Product 7 A synthesis was performed in the same manner as in Synthesis Example 6 except that Precursor 1 (40.0 g) was changed to Precursor 2 (40.7 g) in Synthesis Example 6, and the solid was synthesized. 38 g of a reaction product 7 (a mixture of the following structural isomers) was obtained.

(Synthesis Example 13) Synthesis of Reaction Product 8 A synthesis was performed in the same manner as in Synthesis Example 6 except that Precursor 1 (40.0 g) in Synthesis Example 6 was changed to Precursor 3 (39.5 g). 37 g of a reaction product 8 (a mixture of the following structural isomers) was obtained.

(Synthesis Example 14) Synthesis of Reaction Product 9 A synthesis was performed in the same manner as in Synthesis Example 6 except that Precursor 1 (40.0 g) in Synthesis Example 6 was changed to Precursor 4 (42.3 g). 38 g of a reaction product 9 (a mixture of the following structural isomers) was obtained.

(Synthesis Example 15) Synthesis of Reaction Product 10 The synthesis was performed in the same manner as in Synthesis Example 6 except that Precursor 1 (40.0 g) was changed to Precursor 5 (40.5 g) in Synthesis Example 6, and the solid was synthesized. 37 g of a reaction product 10 (a mixture of the following structural isomers) was obtained.

(Synthesis Example 16) Synthesis of Reaction Product 11 As in Synthesis Example 6, except that 2.2 g of butanetetracarboxylic acid anhydride was changed to 3.4 g of 4,4′-oxydiphthalic acid anhydride in Synthesis Example 6. Synthesis was performed to obtain 38 g of a solid reaction product 11 (mixture of the following structural isomers).

(Synthesis Example 17) Synthesis of Reaction Product 12 Synthesis Example 6 is the same as Synthesis Example 6 except that 2.2 g of butanetetracarboxylic anhydride is changed to 4.0 g of 4,4′-sulfonyldiphthalic anhydride. Synthesis was conducted in the same manner to obtain 39 g of solid compound 12 (mixture of the following structural isomers).

(Synthesis Example 18) Synthesis of Reaction Product 13 Except that, in Synthesis Example 6, butanetetracarboxylic anhydride 2.2 g was changed to 4,4 ′-(hexafluoroisopropylidene) diphthalic anhydride 4.9 g. Synthesis was carried out in the same manner as in Synthesis Example 6 to obtain 40 g of a solid reaction product 13 (mixture of the following structural isomers).

Table 1 shows measured values and theoretical values of the acid values of the reaction products obtained in Synthesis Examples 6 to 18. The acid value is the number of milligrams (mg) of potassium hydroxide (KOH) required to neutralize acidic components contained in 1 g of a sample, as defined in JIS K 2501 (2003). In Synthesis Examples 6 to 18, a compound having the above structure having two carboxyl groups at Z in the general formula (1) is generated from one molecule of tetracarboxylic acid anhydride. Therefore, the theoretical value of the acid value is “molecular weight of KOH × tetracarboxylic anhydride amount used in each synthesis example (unit: mmol) / total mass of precursor and tetracarboxylic anhydride used in each synthesis example ( Unit: g) ”.
As shown in Table 1, since there was no significant difference between the actual value and the theoretical value of the acid value, almost the total amount in the reaction product was the compound represented by the general formula (1) having the above structure. It can be confirmed that there is.

<Preparation of coating composition for magnetic recording medium (coating liquid for forming magnetic layer)>
(Prescription of composition)
Ferromagnetic tabular hexagonal ferrite powder: 100.0 parts Composition excluding oxygen (molar ratio): Ba / Fe / Co / Zn = 1/9 / 0.2 / 1
Hc: 160 kA / m (2000 Oe)
Average plate diameter: 20nm
Average plate ratio: 2.7
BET (Brunauer-Emmett-Teller) specific surface area: 60 m ² / g
σs: 46 A · m ² / kg (46 emu / g)
Reaction product obtained in any of Synthesis Examples 6 to 18 (see Table 2): 10.0 parts Polyurethane resin (Byron (registered trademark) UR4800 manufactured by Toyobo Co., Ltd., functional group: SO ₃ Na, functional group concentration : 70 eq / t, weight average molecular weight 70,000): 4.0 parts Vinyl chloride resin (MR104 manufactured by Kaneka Corporation, weight average molecular weight 5,5000): 10.0 parts α-Al ₂ O ₃ (average particle size 0. 1 μm): 8.0 parts Carbon black (average particle size: 0.08 μm): 0.5 parts Cyclohexanone: 110.0 parts

(Preparation of composition)
Each of the above components was kneaded with an open kneader and then dispersed using a sand mill. The following components were added to the resulting dispersion and stirred, followed by sonication and filtration using a filter having an average pore size of 1 μm to obtain a coating composition for magnetic recording media.
Butyl stearate: 1.5 parts Stearic acid: 0.5 parts Stearic acid amide 0.2 parts Methyl ethyl ketone: 50.0 parts Cyclohexanone: 50.0 parts Toluene: 3.0 parts Polyisocyanate compound (Coronate manufactured by Nippon Polyurethane Industry Co., Ltd.) 3041): 2.5 parts

<Evaluation of dispersibility>
0.5 mL of the composition prepared above was taken out and diluted with a mixed solution of methyl ethyl ketone (MEK) / cyclohexanone = 6/4 (volume ratio) 25 times to prepare a dispersion for evaluation. The transmittance of this dispersion at a wavelength of 450 nm was measured using UV-3600 manufactured by Shimadzu Corporation and evaluated according to the following evaluation criteria. The lower the dispersibility is, the more the ferromagnetic powder is aggregated or settled in the liquid, and the higher the transmittance of the liquid (supernatant liquid). Therefore, the lower the transmittance, the better the dispersibility.
A: Transmittance is 0 to 5.0%
B: The transmittance is 5.1% or more

<Durability evaluation>
(Preparation of film for durability evaluation)
Reaction product obtained in any of Synthesis Examples 6 to 18 (see Table 2): 10.0 parts Polyurethane resin: (Byron (registered trademark) UR4800 manufactured by Toyobo Co., Ltd.): 4.0 parts A mixture obtained by mixing 10.0 parts of vinyl chloride resin (MR104 manufactured by Kaneka Corporation) was cooled to 10 ° C. or lower. To the mixed solution after cooling, 5.0 parts by mass of a polyisocyanate (Coronate 3041 manufactured by Nippon Polyurethane Industry Co., Ltd.) (solid content 2.5 parts, toluene 1.25 parts, methyl ethyl ketone (2-butanone) 1.25 parts). After the addition, cyclohexanone was added and dissolved so that the solid content was 22%.
The composition for film preparation prepared by the above method was applied to a base film (Torelina (registered trademark) film 3000 manufactured by Toray Industries, Inc.) using a doctor blade having a gap of 300 μm, and vacuum-dried at 140 ° C. for 30 minutes. did. The obtained dried film was cooled to room temperature, and then annealed at 100 ° C. for 2 days. After the annealed film was cooled to room temperature, the base film was peeled off to obtain a film for durability evaluation.

(Durability evaluation)
-Measurement of breaking energy-
The obtained film for durability evaluation was cut out to have a width of 6.35 mm and a distance between chucks of 50 mm. Set the distance between chucks of the Toyo Seiki Strograph (TOYOSEIKI STROGRAPH V1-C) to 50 mm, place the cut film sample, conduct a film tensile test at a test speed of 50 mm / min, and increase the elongation during the test. And the stress was measured.
The load obtained when the film broke (kgf) was taken as the breaking load, and the value obtained by the calculation of the obtained breaking load / film cross-sectional area (μm ² ) × 9.8 was the breaking stress (MPa) and the elongation at break The rate was determined as the elongation at break.
The breaking energy is obtained as an integral value of a region where the intersection of breaking elongation and breaking stress is the end point of the elongation-stress curve obtained by taking the measured elongation on the horizontal axis and the stress on the vertical axis.
Higher breaking energy means higher film strength and better durability.

<Production and evaluation of magnetic tape>
(Preparation of coating solution for nonmagnetic layer formation)
Nonmagnetic powder (αFe ₂ O ₃ hematite): 80.0 parts
Average particle size (average major axis length) 0.15 μm
Specific surface area by BET method 52m ² / g
pH 6
Tap density 0.8
DBP (dibutyl phthalate) oil absorption 27-38g / 100g
Surface treatment agent Al ₂ O ₃ , SiO ₂
Carbon black: 20.0 parts
Average particle size 0.020μm
DBP oil absorption 80ml / 100g
pH 8.0
Specific surface area by BET method: 250 m ² / g
Volatile content: 1.5%
Polyurethane resin: 19.0 parts Branched side chain-containing polyester polyol / diphenylmethane diisocyanate system —SO ₃ Na = 100 eq / ton
Methyl ethyl ketone: 150.0 parts Cyclohexanone: 150.0 parts

  The above components were kneaded using an open kneader and then dispersed using a sand mill. The following components were added to the obtained dispersion and stirred, followed by filtration using a filter having an average pore size of 1 μm to prepare a coating solution for forming a nonmagnetic layer.

Butyl stearate: 1.5 parts Stearic acid: 1.0 part Methyl ethyl ketone: 50.0 parts Cyclohexanone: 50.0 parts Toluene: 3.0 parts Polyisocyanate compound (Coronate 3041 manufactured by Nippon Polyurethane Industry Co., Ltd.): 5.0 parts

(Preparation of coating solution for backcoat layer formation)
Carbon black (average particle size 40 nm): 85.0 parts Carbon black (average particle size 100 nm): 3.0 parts Nitrocellulose: 28.0 parts Polyurethane resin: 58.0 parts Copper phthalocyanine-based dispersant: 2.5 parts Nippon Run 2301 (manufactured by Nippon Polyurethane Industry Co., Ltd.): 0.5 part Methyl isobutyl ketone: 0.3 part Methyl ethyl ketone: 860.0 part Toluene: 240.0 parts

The above components are pre-kneaded with a roll mill and then dispersed with a sand mill, and 4.0 parts of a polyester resin (Byron 500 manufactured by Toyobo Co., Ltd.), 14.0 parts of a polyisocyanate compound (Coronate 3041 manufactured by Nippon Polyurethane Industry Co., Ltd.), α-Al 5.0 parts of ₂ O ₃ (manufactured by Sumitomo Chemical Co., Ltd.) was added, followed by stirring and filtration to prepare a coating solution for forming a backcoat layer.

(Production of magnetic tape)
Both surfaces of a polyethylene naphthalate support (thickness 5 μm, center line surface roughness 1 nm on the magnetic layer forming side surface) were subjected to corona discharge treatment.
The non-magnetic layer-forming coating solution is applied to one surface of the polyethylene naphthalate support so that the thickness after drying is 1.0 μm, and immediately after that, the thickness of the magnetic layer is formed thereon. The coating solution for forming the magnetic layer was simultaneously applied in a multi-layer so that the thickness was 100 nm. While both layers were in a wet state, they were subjected to orientation treatment by a cobalt magnet having a magnetic force of 0.5T (5000G) and a solenoid having a magnetic force of 0.4T (4000G), followed by a drying treatment.
Thereafter, the back coating layer forming coating solution was applied to the other surface of the polyethylene naphthalate support so that the thickness after drying was 0.5 μm. Next, a seven-stage calendar composed of metal rolls was used to process at a temperature of 100 ° C. and a speed of 80 m / min, and slit to a width of 1/2 inch (0.0127 meter) to produce a magnetic tape.

<Scratch resistance test>
For the scratch resistance test on the magnetic layer surface of the magnetic tape, an automatic frictional wear analyzer (Triboster TS501: manufactured by Kyowa Interface Science Co., Ltd.) using a horizontal linear reciprocating sliding method was used. Contact: diameter 3 mmΦ, ball load: 3 g, speed : 3 mm / second, number of measurements: 10 reciprocations. The surface of the magnetic layer after the test was observed with an optical microscope (magnification: 100 to 500 times), and scratch resistance was evaluated according to the following evaluation criteria.
A: No scratches are observed on the surface of the magnetic layer B: Small scratches are observed on the surface of the magnetic layer C: Deep scratches are observed on the surface of the magnetic layer, and scraped components are deposited on the surface of the magnetic layer

  The results are shown in Table 2.

As shown in Table 2, the dispersibility of the ferromagnetic powder could be improved by the compound represented by the general formula (1). Further, in the magnetic tape of the example having the magnetic layer containing the compound represented by the general formula (1), the magnetic layer showed excellent scratch resistance. From the values of breaking energy, breaking stress, and breaking elongation shown in Table 2, it can be confirmed that in the examples, the ease of elongation (breaking elongation) is greatly improved as compared with the comparative example. From this, it is considered that the compound represented by the general formula (1) contributed to improving the durability (scratch resistance) of the magnetic layer by imparting moderate easiness to elongation to the magnetic layer.
From the above results, according to the present invention, it was confirmed that both the improvement of the dispersibility of the ferromagnetic powder and the improvement of the durability of the magnetic layer can be achieved.

<Production and evaluation of magnetic tape>
(Production of magnetic tapes of Examples 14 to 16)
Magnetic tapes of Examples 14 to 16 were produced in the same manner as in the above Examples, except that the following coating solution (coating composition) for forming a magnetic layer containing a ferromagnetic metal powder was used.

-Preparation of coating solution (coating composition) for forming magnetic layer containing ferromagnetic metal powder-
Ferromagnetic metal powder: 100.0 parts Composition Fe / Co = 100/25
Hc 195 kA / m (2450 Oe)
Specific surface area by BET method 65m ² / g
Surface treatment agent Al ₂ O ₃ , SiO ₂ , Y ₂ O ₃
Average particle size (average major axis length) 45nm
Average needle ratio 5
σs 110 A · m ² / kg (110 emu / g)
Reaction product obtained in synthesis example (see Table 3): 10.0 parts Polyurethane-based resin: (Byron (registered trademark) UR4800 manufactured by Toyobo Co., Ltd., functional group: SO ₃ Na, functional group concentration: 70 eq / t) : 5.0 parts Vinyl chloride resin (MR104 manufactured by Kaneka Corporation): 10.0 parts Methyl ethyl ketone: 150.0 parts Cyclohexanone: 150.0 parts Abrasive: α-Al ₂ O ₃ Mohs hardness 9 (average particle size 0.1 μm) ): 15.0 parts Carbon black (average particle size 0.08 μm): 0.5 parts

About said coating liquid, after kneading | mixing each component with an open kneader, it was disperse | distributed using the sand mill. The following components were added to the resulting dispersion and stirred, followed by sonication and filtration using a filter having an average pore size of 1 μm to prepare a coating solution for forming a magnetic layer.
Butyl stearate: 1.5 parts Stearic acid: 0.5 parts Stearic acid amide 0.2 parts Methyl ethyl ketone: 50.0 parts Cyclohexanone: 50.0 parts Toluene: 3.0 parts Polyisocyanate compound (Coronate manufactured by Nippon Polyurethane Industry Co., Ltd.) 3041): 5.0 parts

  The following evaluation was implemented about the magnetic tape of Examples 14-16 and the magnetic tape of the above-mentioned Examples 1-3. The results are shown in Table 3.

<Average surface roughness of tape>
Using an atomic force microscope (AFM: NANOSCOPE III manufactured by DIGITAL INSTRUMENT), an area of 40 μm × 40 μm was measured on the magnetic layer surface in the contact mode, and the centerline average surface roughness (Ra) was measured.

<Electromagnetic conversion characteristics: S / N (Signal-to-Noise) ratio>
Using an IBM LTO-Gen4 (Linear Tape-Open-Generation 4) drive, a signal with a recording track width of 11.5 μm, a playback track width of 5.3 μm, a linear recording density of 172 kfci and 86 kfci is recorded, and the playback signal is spectrumd Frequency analysis was performed by an analyzer, and the ratio of the carrier signal output during 172 kfci signal recording to the integrated noise of the entire spectrum band during 86 kfci signal recording was taken as the S / N ratio. Fujifilm LTO-Gen4 tape was used as a reference tape. The S / N ratio of the reference tape was 0.0 dB, and the S / N ratio of each tape was obtained as a relative value. If the S / N ratio is 1.0 dB or more, it is determined that the ferromagnetic powder having the average particle size has excellent dispersibility in the magnetic layer (as a result, excellent electromagnetic conversion characteristics are obtained). Can do.

<Running durability (scraping of magnetic layer surface)>
When recording information on the magnetic tape and reproducing the recorded information, the surface of the magnetic layer of the magnetic tape and the magnetic head usually slide. The surface of the magnetic layer being scraped and adhered to the magnetic head due to this sliding causes a decrease in running durability. Therefore, the running durability of the magnetic tape was evaluated by the following method.
The magnetic tape is passed at an angle of 150 degrees so that the surface of the magnetic layer is in contact with the edge of a prismatic bar made of Al ₂ O ₃ / TiC having a cross section of 7 mm × 7 mm, and the length is 100 m under the conditions of a load of 100 g and a speed of 6 m per second. Was slid for one pass. The edge part of the prismatic bar after sliding was observed with a microscope, and the adhesion state of the deposit (the magnetic layer surface scraped by sliding) adhered to the edge part of the prismatic bar by the sliding was evaluated. Evaluation was made into sensory evaluation and evaluated in 10 steps. 10 has few deposits and 1 has the most deposits. If the evaluation value is 8 or more, it can be determined that there are few deposits (scratching of the magnetic layer surface) and the running durability is good.

  The present invention is useful in the field of manufacturing high-density magnetic recording media such as high-capacity backup tapes.

Claims (19)

A magnetic recording medium having a magnetic layer comprising a ferromagnetic powder and a binder on a nonmagnetic support,
A magnetic recording medium further comprising a compound represented by the following general formula (1) in the magnetic layer;
In the general formula (1), X represents —O—, —S— or —NR ¹ —, R and R ¹ each independently represent a hydrogen atom or a monovalent substituent, and L represents a divalent linkage. Represents a group, Z represents an n-valent partial structure having at least one group selected from the group consisting of a carboxyl group and a carboxyl base, m represents an integer of 2 or more, and n represents an integer of 1 or more. The magnetic recording medium according to claim 1, wherein L in the general formula (1) represents an alkylene group. The magnetic recording medium according to claim 1, wherein X in the general formula (1) represents —O—. The magnetic recording medium according to claim 1, wherein Z in the general formula (1) represents a reaction residue of a carboxylic acid anhydride. 5. The magnetic recording medium according to claim 1, wherein Z in the general formula (1) represents a reaction residue of tetracarboxylic anhydride. 6. The magnetic recording medium according to claim 1, wherein the compound represented by the general formula (1) has a weight average molecular weight in a range of 1,000 or more and less than 20,000. The magnetic recording medium according to claim 1, wherein the ferromagnetic powder has an average particle size in a range of 10 to 50 nm. The magnetic recording medium according to claim 1, wherein the compound is contained in an amount of 0.5 to 50.0 parts by mass per 100.0 parts by mass of the ferromagnetic powder. The magnetic recording medium according to claim 1, wherein the binder is selected from the group consisting of a polyurethane resin and a vinyl chloride resin. A compound represented by the following general formula (1):
Ferromagnetic powder,
A binder,
A solvent,
A coating composition for magnetic recording media comprising:
In the general formula (1), X represents —O—, —S— or —NR ¹ —, R and R ¹ each independently represent a hydrogen atom or a monovalent substituent, and L represents a divalent linkage. Represents a group, Z represents an n-valent partial structure having at least one group selected from the group consisting of a carboxyl group and a carboxyl base, m represents an integer of 2 or more, and n represents an integer of 1 or more. The coating composition for magnetic recording media according to claim 10, wherein L in the general formula (1) represents an alkylene group. The coating composition for magnetic recording media according to claim 10 or 11, wherein X in the general formula (1) represents -O-. The coating composition for magnetic recording media according to any one of claims 10 to 12, wherein Z in the general formula (1) represents a reaction residue of a carboxylic acid anhydride. The coating composition for magnetic recording media according to any one of claims 10 to 13, wherein Z in the general formula (1) represents a reaction residue of a tetracarboxylic acid anhydride. The coating composition for magnetic recording media according to any one of claims 10 to 14, wherein the compound represented by the general formula (1) has a weight average molecular weight in the range of 1,000 or more and less than 20,000. The coating composition for a magnetic recording medium according to any one of claims 10 to 15, wherein the binder has a weight average molecular weight in the range of 20,000 to 120,000. 17. The coating composition for a magnetic recording medium according to claim 10, wherein the ferromagnetic powder has an average particle size in a range of 10 to 50 nm. The coating composition for magnetic recording media according to any one of claims 10 to 17, comprising 0.5 to 50.0 parts by mass of the compound per 100.0 parts by mass of the ferromagnetic powder. The coating composition for a magnetic recording medium according to any one of claims 10 to 18, wherein the binder is selected from the group consisting of a polyurethane resin and a vinyl chloride resin.