Magnetic recording medium, magnetic tape cartridge, magnetic recording and playback device, and polymer

Abstract

The present invention provides a magnetic recording medium that exhibits a low coefficient of friction after repeated use. [Solution] A magnetic recording medium having a non-magnetic support and a magnetic layer containing ferromagnetic powder contains one or more polymers selected from the group consisting of polymers containing at least one structural unit represented by formulas S-1 and S-2, and polymers containing at least one structural unit represented by a predetermined formula, in the portion of the non-magnetic support on the magnetic layer side. TIFF2026049820000016.tif60170

Description

[Technical Field]

[0001] The present invention relates to a magnetic recording medium, a magnetic tape cartridge, a magnetic recording and playback device, and a polymer. [Background technology]

[0002] Magnetic recording media are generally manufactured by forming a magnetic layer containing ferromagnetic powder on a non-magnetic support (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 4070147 specification [Patent Document 2] Japanese Patent Publication No. 2000-11359 [Overview of the project] [Problems that the invention aims to solve]

[0004] Recording data onto a magnetic recording medium and reproducing recorded data are typically performed by moving the magnetic recording medium within a magnetic recording and reproduction device, causing the magnetic layer surface of the recording medium to come into contact with and slide against a magnetic head. From the viewpoint of running stability, it is desirable that the coefficient of friction during sliding between the magnetic layer surface and the magnetic head is low, even when the magnetic recording medium is repeatedly moved.

[0005] One aspect of the present invention aims to provide a magnetic recording medium that can exhibit a low coefficient of friction after repeated operation. [Means for solving the problem]

[0006] The present inventors have intensively studied to provide a magnetic recording medium that can exhibit a low coefficient of friction even after repeated running. As a result, the present inventors have newly found that a magnetic recording medium containing the following polymers in a portion on the magnetic layer side of a non-magnetic support (details will be described later) can exhibit a low coefficient of friction after repeated running.

[0007] That is, one aspect of the present invention is as follows. [1] A magnetic recording medium having a non-magnetic support and a magnetic layer containing ferromagnetic powder, wherein a portion on the magnetic layer side of the non-magnetic support contains at least a polymer P containing a structural unit represented by the following formula (S-1) and a structural unit represented by the following formula (S-2), and at least a polymer Q containing a structural unit represented by the following formula (S-3) and a structural unit represented by the following formula (S-4), a magnetic recording medium containing one or more polymers selected from the group consisting of; [Chemical formula] In formula (S-1), R represents a monovalent aromatic group or a monovalent hydrocarbon group having 6 or more carbon atoms, and L 1 represents a single bond or a divalent group; In formula (S-2), R 2 represents a monovalent polar group, and L 2 represents a single bond or a divalent group; [Chemical formula] In formula (S-3), R 3 represents a monovalent aromatic group or a monovalent hydrocarbon group having 6 or more carbon atoms, and L 3 represents a single bond or a divalent group, and R 11 represents an alkyl group; In formula (S-4), R 4 represents a monovalent polar group, and L 4 represents a single bond or a divalent group, and R 12 represents an alkyl group. [2] The portion on the magnetic layer side of the non-magnetic support contains polymer P, and In the above equation (S-1), R 1 The magnetic recording medium described in [1] represents a monovalent aromatic group or a monovalent hydrocarbon group having 8 to 50 carbon atoms. [3] In the above equation (S-2), R 2 The magnetic recording medium according to [1] or [2], wherein -COOH, -SO3H, -NH2, -OH, -C(O)NH2, -NHC(O)NH2, or epoxy group. [4] In the above equation (S-2), R 2 A magnetic recording medium as described in any of [1] to [3], where -COOH, -SO3H, -NH2, -OH, -C(O)NH2, or -NHC(O)NH2. [5] The polymer P contains more than 30 mol% of the constituent unit represented by formula (S-1) based on 100 mol% of all constituent units contained in the polymer, as described in any of [1] to [4]. [6] The portion of the non-magnetic support on the magnetic layer side contains polymer Q, In the above equation (S-3), R 3 The magnetic recording medium described in any of [1] to [5] represents a monovalent aromatic group or a monovalent hydrocarbon group having 8 to 50 carbon atoms. [7] In the above equation (S-4), R 4 A magnetic recording medium according to any one of [1] to [6], where -COOH, -SO3H, -NH2, -OH, -C(O)NH2, -NHC(O)NH2, or epoxy group. [8] In the above equation (S-4), R 4 A magnetic recording medium as described in any of [1] to [7], where -COOH, -SO3H, -NH2, -OH, -C(O)NH2, or -NHC(O)NH2. [9] The polymer Q contains more than 30 mol% of the constituent unit represented by formula (S-3) based on 100 mol% of all constituent units contained in the polymer, as described in any of [1] to [8].

[10] A magnetic recording medium according to any one of [1] to [9], further comprising one or more fatty acid compounds selected from the group consisting of fatty acids, fatty acid esters, and fatty acid amides on the magnetic layer side of the non-magnetic support.

[11] A magnetic recording medium according to any one of [1] to

[10] , further comprising a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer.

[12] A magnetic recording medium according to any one of [1] to

[11] , further comprising a back coat layer containing non-magnetic powder on the surface side of the non-magnetic support opposite to the surface side having the magnetic layer.

[13] A magnetic recording medium described in any of [1] to

[12] , which is a magnetic tape.

[14] The portion of the non-magnetic support on the magnetic layer side further contains one or more fatty acid compounds selected from the group consisting of fatty acids, fatty acid esters, and fatty acid amides, A non-magnetic layer containing non-magnetic powder is further provided between the above non-magnetic support and the above magnetic layer. The non-magnetic support has a back coat layer containing non-magnetic powder on the surface side opposite to the surface side having the magnetic layer, and A magnetic recording medium, as described in [6], which is a magnetic tape.

[15] The portion of the non-magnetic support on the magnetic layer side further contains one or more fatty acid compounds selected from the group consisting of fatty acids, fatty acid esters, and fatty acid amides, A non-magnetic layer containing non-magnetic powder is further provided between the above non-magnetic support and the above magnetic layer. The non-magnetic support has a back coat layer containing non-magnetic powder on the surface side opposite to the surface side having the magnetic layer, and A magnetic recording medium, as described in [9], which is a magnetic tape. A magnetic tape cartridge containing the magnetic tape described in any of

[16] ,

[13] , or

[15] . A magnetic recording and playback device containing a magnetic recording medium as described in any of

[17] [1] to

[15] .

[18] Polymer P comprising at least one constituent unit represented by the following formula (S-1) and one constituent unit represented by the following formula (S-2); [ka] In formula (S-1), R 1 represents a monovalent aromatic group or a monovalent hydrocarbon group having 6 or more carbon atoms, L 1represents a single bond or a divalent group; In formula (S-2), R 2 represents a monovalent polar group, L 2 represents a single bond or a divalent group.

[19] Polymer Q comprising at least one constituent unit represented by the following formula (S-3) and one constituent unit represented by the following formula (S-4); [ka] In formula (S-3), R 3 represents a monovalent aromatic group or a monovalent hydrocarbon group having 6 or more carbon atoms, L 3 represents a single bond or a divalent group, R 11 represents an alkyl group; In formula (S-4), R 4 represents a monovalent polar group, L 4 represents a single bond or a divalent group, R 12 represents an alkyl group. [Effects of the Invention]

[0008] According to one aspect of the present invention, a magnetic recording medium that exhibits a low coefficient of friction after repeated operation can be provided. Furthermore, according to one aspect of the present invention, a magnetic tape cartridge and a magnetic recording and playback device including the above-mentioned magnetic recording medium can be provided. Moreover, according to one aspect of the present invention, a novel polymer can be provided. [Modes for carrying out the invention]

[0009] [Magnetic recording medium] One aspect of the present invention relates to a magnetic recording medium having a non-magnetic support and a magnetic layer containing ferromagnetic powder. The magnetic recording medium contains one or more polymers selected from the group consisting of polymer P and polymer Q in the portion of the non-magnetic support that is on the magnetic layer side.

[0010] In the present invention and this specification, "the portion on the magnetic layer side of the non-magnetic support" refers to the magnetic layer in the case of a magnetic recording medium having a magnetic layer directly on a non-magnetic support, and to the magnetic layer and / or non-magnetic layer in the case of a magnetic recording medium having a non-magnetic layer between the non-magnetic support and the magnetic layer, as described later. "The portion on the magnetic layer side of the non-magnetic support" is also simply referred to as "the portion on the magnetic layer side." The presence of a certain component on the magnetic layer side surface of a magnetic recording medium is also included in the inclusion of that component in the magnetic layer side portion. In the present invention and this specification, "the surface of the magnetic layer" is synonymous with the magnetic layer side surface of a magnetic recording medium.

[0011] The above magnetic recording medium contains one or more polymers selected from the group consisting of polymer P and polymer Q in the magnetic layer portion. Each polymer P and polymer Q is thought to be able to function as a lubricant for the magnetic recording medium. The inventors believe that the ability of the polymers to function as lubricants for the magnetic recording medium and thereby impart lubricity to the magnetic layer surface contributes to the magnetic recording medium exhibiting a low coefficient of friction after repeated operation. Specifically, in polymer P, the constituent unit R represented by formula (S-1) 1 It is presumed that this part contributes to providing lubricity to the magnetic layer surface. Furthermore, the R of the constituent unit represented by formula (S-2) 2 It is presumed that the part can function as an adsorption functional group adsorbed onto the particle surface of the ferromagnetic powder. Furthermore, the R of the constituent unit represented by formula (S-2) 2 The inventors believe that the adsorption of polymer P onto the particle surface of ferromagnetic powder in certain parts contributes to improving the film strength of the magnetic layer. Similarly, in polymer Q, the constituent unit R represented by formula (S-3) 3 It is presumed that this part contributes to providing lubricity to the magnetic layer surface. Furthermore, the R of the constituent unit represented by formula (S-4) 4 It is presumed that the part can function as an adsorption functional group adsorbed onto the particle surface of the ferromagnetic powder. Furthermore, the R of the constituent unit represented by formula (S-4) 4 The inventors believe that the adsorption of polymer Q onto the particle surface of ferromagnetic powder in certain areas contributes to improving the film strength of the magnetic layer. For example, it is thought that at least a portion of the polymer contained in the magnetic layer can be present on the surface of the magnetic layer. Furthermore, the inventors speculate that the polymer contained inside the magnetic layer can be present on the surface of the magnetic layer by moving to the surface of the magnetic layer during sliding with the magnetic head, etc. Also, the polymer may be contained in the non-magnetic layer described later, and it is thought that the polymer contained in the non-magnetic layer can move to the magnetic layer and then move to the surface of the magnetic layer and be present on the surface of the magnetic layer. However, the above is merely speculation and does not limit the present invention. Furthermore, the present invention is not limited by other speculations described herein.

[0012] The magnetic recording medium described above will be explained in more detail below.

[0013] <Polymer P> Polymer P has at least one structural unit represented by formula (S-1) and one structural unit represented by formula (S-2). Polymer P has "-SiO" in its main chain. 3 / 2 Because it has the characteristic "-", it can be called a polyorganosilsesquioxane.

[0014] Polymer P may contain constituent units represented by formula (S-1) with the same or different structures. 1 and L 1 Each part may be the same or different in the constituent units represented by multiple formulas (S-1). Furthermore, polymer P may contain constituent units represented by formulas (S-2) that have the same or different structures. 2 and L 2 Each part may be the same or different in the constituent units represented by multiple formulas (S-2). Each of the two ends of each constituent unit is bonded to another constituent unit or to a terminal group of polymer P.

[0015] The constituent units represented by formula (S-1) and formula (S-2) will be described below in order. In the present invention and this specification, unless otherwise specified, the groups described may be unsubstituted or substituted. If a group has a substituent, examples of substituents include alkyl groups (e.g., alkyl groups having 1 to 6 carbon atoms), hydroxyl groups, alkoxy groups (e.g., alkoxy groups having 1 to 6 carbon atoms), cyano groups, amino groups, nitro groups, acyl groups, carboxyl groups, etc. Furthermore, for groups having a substituent, "number of carbon atoms" refers to the number of carbon atoms in the portion that does not contain the substituent. Furthermore, in the present invention and this specification, unless otherwise specified, "alkyl group," "alkylene group," and "hydrocarbon group" include the linear, branched, and cyclic forms of each group, respectively.

[0016] (Constituent units represented by formula (S-1))

[0017] [ka]

[0018] In formula (S-1), R 1 This represents a monovalent aromatic group or a monovalent hydrocarbon group having 6 or more carbon atoms.

[0019] R 1 The aromatic ring contained in the monovalent aromatic group represented by may be a monocyclic ring, a fused ring, or a bridging ring. 1 A monovalent aromatic group represented by R has, in one form, no heteroatoms as atoms constituting the aromatic ring, and in another form, one or more heteroatoms (e.g., oxygen, nitrogen, sulfur) as atoms constituting the aromatic ring. Preferred aromatic rings included in the above aromatic group are benzene rings, naphthalene rings, fluorene rings, furan rings, thiophene rings, pyrrole rings, oxazole rings, thiazole rings, imidazole rings, triazole rings, pyridine rings, pyrimidine rings, pyrazine rings, and indole rings, with substituted or unsubstituted benzene rings being more preferred. That is, in one form, R 1 The monovalent aromatic group represented by can be a substituted or unsubstituted phenyl group.

[0020] R 1 The monovalent hydrocarbon group having 6 or more carbon atoms represented by can be a linear hydrocarbon group, a branched hydrocarbon group, or a cyclic hydrocarbon group. The cyclic hydrocarbon group is preferably a monocyclic hydrocarbon group and preferably does not have a cyclic structure corresponding to a fused ring structure and / or a crosslinked ring structure. Also, R 1 The monovalent hydrocarbon group having 6 or more carbon atoms represented by can be a saturated hydrocarbon group or an unsaturated hydrocarbon group, and is preferably a saturated hydrocarbon group.

[0021] R 1 The number of carbon atoms in the monovalent hydrocarbon group represented by is 6 or more, preferably 7 or more, and more preferably 8 or more, 9 or more, 10 or more, 11 or more, 12 or more, 13 or more, 14 or more, and 15 or more, in that order. On the other hand, from the viewpoint of solubility, R 1 The number of carbon atoms in the monovalent hydrocarbon group represented by is preferably 50 or less, more preferably 28 or less, and still more preferably 24 or less, and 22 or less. 1 The monovalent hydrocarbon group represented is preferably a linear hydrocarbon group or a branched hydrocarbon group, and more preferably a linear alkyl group or a branched alkyl group. When an alkyl group is linear, in addition to the low surface energy effect brought about by hydrophobicity, alkyl groups tend to aggregate with each other and orient towards the interface, R 1 A linear alkyl group is more preferably represented as the monovalent hydrocarbon group.

[0022] In equation (S-1), L 1 L represents a single bond or a divalent group. 1 If it is a single bond, R 1 It is directly bonded to the Si (silicon atoms) of the main chain.

[0023] L 1 The divalent group represented by R 1It is a linking group that connects the main chain's Si (silicon atom). Examples of divalent linking groups include divalent linking groups selected from the group consisting of ester groups (-C(=O)O-), carbonyl groups (-C(=O)-), oxygen atoms (-O-), sulfur atoms (-S-), -NH-, alkylene groups, arylene groups, aryleneoxy groups (-Ar-O-: Ar represents the arylene group, the same applies below), and arylenealkylene groups (-Ar-R-: R represents the alkylene group), as well as divalent groups consisting of two or more combinations of the above divalent linking groups. In one form, L 1 The divalent linking group that can be represented by can be an alkylene group; a divalent group consisting of a combination of one or more (e.g., one or two) alkylene groups and an oxygen atom; or a divalent group consisting of a combination of one or more (e.g., one or two) alkylene groups, a divalent group represented by -NH- and a carbonyl group. The above arylene group and the arylene group represented by Ar can preferably be an arylene group having 6 to 20 carbon atoms. The above alkylene group and the alkylene group represented by R can preferably be a linear or branched alkylene group having 1 to 10 carbon atoms.

[0024] From the viewpoint of friction reduction, the content of the constituent unit represented by formula (S-1) in polymer P is preferably more than 30 mol% relative to 100 mol% of the total constituent units contained in this polymer, and is more preferably 35 mol% or more, 40 mol% or more, 45 mol% or more, and 50 mol% or more, in that order. On the other hand, since polymer P contains at least the constituent unit represented by formula (S-2) along with the constituent unit represented by formula (S-1), the content of the constituent unit represented by formula (S-1) in polymer P is less than 100 mol% relative to 100 mol% of the total constituent units contained in this polymer, and can be, for example, 99 mol% or less, 95 mol% or less, 90 mol% or less, or 85 mol% or less.

[0025] The content of various constituent units in a polymer can be measured by known methods, or it can be calculated from the molar ratio of the polymerization components (generally called "monomers") used in the synthesis of the polymer. For example, for a polymer synthesized using two polymerization components (components A and B) in a molar ratio of component A:component B = 80:20, the content of constituent units derived from component A can be calculated as 80 mol% and the content of constituent units derived from component B can be calculated as 20 mol%, relative to the total 100 mol% of constituent units constituting the polymer.

[0026] (Constituent units represented by formula (S-2))

[0027] [ka]

[0028] In formula (S-2), L 2 L represents a single bond or a divalent group. 2 If it is a single bond, R 2 It is directly bonded to the Si (silicon atom) of the main chain. 2 The divalent group represented by R 2 It is a linking group that connects the main chain's Si (silicon atoms). 2 For details on the divalent group represented by L 1 You can refer to the previous description regarding the divalent linking group represented by .

[0029] In formula (S-2), R 2 represents a monovalent polar group. In the present invention and this specification, "polar group" means a group selected from the group consisting of acidic groups, basic groups, and hydrogen bonding groups.

[0030] In the present invention and this specification, "acidic group" means a group that falls under at least one of the following (1) and (2). (1) H in water or a solvent containing water (hereinafter referred to as "aqueous solvent") + A group that releases and can dissociate into an anion. (2) A group that corresponds to a Lewis acid (i.e., an electron pair acceptor) in the definition of Lewis acids and bases. R2 When represents an acidic group, such an acidic group is not particularly limited as long as it is a group that falls under at least one of (1) and (2) above. 2 Examples of acidic groups that can be represented by this include carboxyl groups (-COOH), sulfonic acid groups (-SO3H), phosphate groups (-OP(=O)(OH)2), phosphonic acid groups (-P(=O)(OH)2), and boronic acid groups (-B(OH)2).

[0031] In the present invention and this specification, "basic group" means a group that falls under at least one of the following (3) and (4). (3) Dissociable into cations in water or aqueous solvents or H + A group that accepts a cation and becomes a cation. (4) A group that corresponds to a Lewis base (i.e., an electron pair donor) in Lewis's definition of acids and bases. R 2 When represents a basic group, such basic group is not particularly limited as long as it is a group that falls under at least one of (3) and (4) above. 2 Examples of basic groups that can be represented by this include amino groups, guanidyl groups, amidyl groups, and imidazoyl groups, and from the viewpoint of further improving adsorption, amino groups are preferred. The amino group may be an unsubstituted amino group (-NH2) or a substituted amino group. Furthermore, the substituent that substitutes a hydrogen atom in the substituted amino group can be, for example, a linear, branched, or cyclic alkyl group having 1 to 10 carbon atoms.

[0032] In the present invention and this specification, "hydrogen bonding group" means a group that can interact via a hydrogen atom. 2 When represents a hydrogen bonding group, such a hydrogen bonding group is not particularly limited as long as it is a group that fits the above definition. Examples of hydrogen bonding groups include hydroxyl groups (-OH), amide groups (-C(O)NH2), urea groups (-NHC(O)NH2), and cyclic ether groups such as epoxy groups.

[0033] From the perspective of further improving adsorption, R2 It is preferable that -COOH, -SO3H, -NH2, -OH, -C(O)NH2, -NHC(O)NH2, or epoxy group represent -COOH, -SO3H, -NH2, -OH, -C(O)NH2, or -NHC(O)NH2.

[0034] The content of the constituent unit represented by formula (S-2) in polymer P is greater than 0 mol% relative to 100 mol% of the total constituent units contained in this polymer. From the viewpoint of further improving the adsorption of polymer P to the particle surface of ferromagnetic powder, it is preferably 1 mol% or more, and more preferably in the order of 3 mol% or more, 5 mol% or more, 10 mol% or more, and 15 mol% or more. In addition, the content of the constituent unit represented by formula (S-2) in polymer P can be, for example, less than 70 mol%, 65 mol% or less, 60 mol% or less, or 55 mol% or less relative to 100 mol% of the total constituent units contained in this polymer.

[0035] The constituent units contained in polymer P may, in one form, consist only of one or more constituent units represented by formula (S-1) and one or more constituent units represented by formula (S-2), while in another form, it may contain one or more constituent units that do not fall under formulas (S-1) and (S-2). An example of a constituent unit that does not fall under formulas (S-1) and (S-2) is R 1 Except that the part is a hydrocarbon group having 1 to 5 carbon atoms, other structural units similar to those in formula (S-1) can be given as examples. For such structural units, R 1 Except for the number of carbon atoms in the part, the previous description regarding formula (S-1) can be referred to. The total content of the constituent units represented by formula (S-1) and formula (S-2) relative to 100 mol% of all constituent units contained in polymer P can be, for example, 50 mol% or more and 100 mol% or less, or 60 mol% or more and 100 mol% or less.

[0036] Polymer P is a copolymer because it has constituent units represented by formula (S-1) and constituent units represented by formula (S-2). "Constituent units" are also generally called "repeating units." In polymer P, multiple constituent units represented by formula (S-1) may exist consecutively or discontinuously. Similarly, multiple constituent units represented by formula (S-2) may exist consecutively or discontinuously. That is, the copolymerization form of polymer P is not particularly limited and can be any copolymerization form (e.g., random copolymerization, alternating copolymerization, block copolymerization, or graft copolymerization).

[0037] <Polymer Q> Polymer Q has at least the constituent units represented by formula (S-3) and the constituent units represented by formula (S-4). Since polymer Q has "-SiO-" in its main chain, it can be called a polyorganosilicone.

[0038] Polymer Q may contain constituent units represented by formula (S-3) with the same or different structures. 3 , R 11 and L 3 Each part may be the same or different in the constituent units represented by multiple formulas (S-3). Furthermore, polymer Q may contain constituent units represented by formulas (S-4) that have the same or different structures. 4 , R 12 and L 4 Each part may be the same or different in the constituent units represented by multiple formulas (S-4). Each of the two ends of each constituent unit is bonded to another constituent unit or to a terminal group of polymer Q.

[0039] The constituent units represented by equation (S-3) and equation (S-4) will be explained in order below.

[0040] (Constituent units represented by formula (S-3))

[0041] [ka]

[0042] In formula (S-3), R 3 This represents a monovalent aromatic group or a monovalent hydrocarbon group having 6 or more carbon atoms.

[0043] R 3 For monovalent aromatic groups represented by , the R in formula (S-1) 1 As previously described, this refers to the monovalent aromatic group represented by .

[0044] R 3 For monovalent hydrocarbon groups with 6 or more carbon atoms represented by (S-1), the R in formula (S-1) 1 As previously described, monovalent hydrocarbon groups with 6 or more carbon atoms are represented by .

[0045] R 3 The number of carbon atoms in the monovalent hydrocarbon group represented by is 6 or more, preferably 7 or more, and more preferably 8 or more, 9 or more, 10 or more, 11 or more, 12 or more, 13 or more, 14 or more, and 15 or more, in that order. On the other hand, from the viewpoint of solubility, R 3 The number of carbon atoms in the monovalent hydrocarbon group represented by is preferably 50 or less, more preferably 28 or less, and still more preferably 24 or less, and 22 or less. 3 The monovalent hydrocarbon group represented is preferably a linear hydrocarbon group or a branched hydrocarbon group, and more preferably a linear alkyl group or a branched alkyl group. When an alkyl group is linear, in addition to the low surface energy effect brought about by hydrophobicity, alkyl groups tend to aggregate with each other and orient towards the interface, R 3 A linear alkyl group is more preferably represented as the monovalent hydrocarbon group.

[0046] R 11 The alkyl group represented by can be a linear alkyl group or a branched alkyl group, and is preferably a linear alkyl group. 11 The number of carbon atoms in the alkyl group represented by can be 1 or more, and is preferably 3 or less or 2 or less.

[0047] From the perspective of friction reduction, the content rate of the structural unit represented by formula (S-3) in polymer Q is preferably more than 30 mol% with respect to 100 mol% of all the structural units contained in this polymer, more preferably 35 mol% or more, 40 mol% or more, 50 mol% or more, 55 mol% or more, 60 mol% or more, 65 mol% or more, 70 mol% or more, 75 mol% or more in this order. On the other hand, since polymer Q contains at least the structural unit represented by formula (S-4) together with the structural unit represented by formula (S-3), the content rate of the structural unit represented by formula (S-3) in polymer P is less than 100 mol% with respect to 100 mol% of all the structural units contained in this polymer, and can be, for example, 99 mol% or less, 95 mol% or less, 90 mol% or less, or 85 mol% or less.

[0048] In formula (S-3), L 3 represents a single bond or a divalent group. When L 3 is a single bond, R 3 is directly bonded to the Si (silicon atom) in the main chain. The divalent group represented by L 3 is a linking group that links R 3 and the Si (silicon atom) in the main chain. Regarding the divalent group represented by L 3 , it is as described above for the divalent group represented by L 1 in formula (S-1).

[0049] (Structural unit represented by formula (S-4)) "

[0050]

Chemical formula

[0051] " In formula (S-4), L 4 represents a single bond or a divalent group. When L 4 is a single bond, R 4 is directly bonded to the Si (silicon atom) in the main chain. The divalent group represented by L 4 is a linking group that links R 4 and the Si (silicon atom) in the main chain. Regarding the details of the divalent group represented by L 4 , it is as described above for L in formula (S-1).1 You can refer to the previous description regarding the divalent linking group represented by .

[0052] In formula (S-4), R 4 R represents a monovalent polar group. 4 For monovalent polar groups represented by , the R in formula (S-2) 2 You can refer to the previous description regarding the monovalent polar group represented by . From the viewpoint of further improving adsorption, R 4 It is preferable that -COOH, -SO3H, -NH2, -OH, -C(O)NH2, -NHC(O)NH2, or epoxy group represent -COOH, -SO3H, -NH2, -OH, -C(O)NH2, or -NHC(O)NH2.

[0053] In one form, R 4 When represents a hydrogen bonding group, such a hydrogen bonding group can be a hydrogen bonding group other than a hydroxyl group (-OH), and can be, for example, an amide group (-C(O)NH2), a urea group (-NHC(O)NH2), or a cyclic ether group such as an epoxy group.

[0054] The content of the constituent unit represented by formula (S-4) in polymer Q is greater than 0 mol% relative to 100 mol% of the total constituent units contained in this polymer. From the viewpoint of further improving the adsorption of polymer Q to the particle surface of ferromagnetic powder, it is preferably 1 mol% or more, and more preferably in the order of 3 mol% or more, 5 mol% or more, 10 mol% or more, 15 mol% or more, and 20 mol% or more. In addition, the content of the constituent unit represented by formula (S-4) in polymer Q can be, for example, 40 mol% or less, 35 mol% or less, or 30 mol% or less relative to 100 mol% of the total constituent units contained in this polymer.

[0055] In one form, the constituent units contained in polymer Q may consist only of one or more constituent units represented by formula (S-3) and one or more constituent units represented by formula (S-4), while in another form, it may contain one or more constituent units that do not fall under formulas (S-3) and (S-4). An example of a constituent unit that does not fall under formulas (S-3) and (S-4) is R3 Except that the part is a hydrocarbon group having 1 to 5 carbon atoms, other structural units similar to those in formula (S-3) can be given as examples. For such structural units, R 3 Except for the number of carbon atoms in the part, the previous description regarding formula (S-1) can be referred to. The total content of the constituent units represented by formula (S-3) and formula (S-4) relative to 100 mol% of all constituent units contained in polymer Q can be, for example, 50 mol% or more and 100 mol% or less, or 60 mol% or more and 100 mol% or less.

[0056] Polymer Q is a copolymer because it has constituent units represented by formula (S-3) and formula (S-4). In polymer Q, the multiple constituent units represented by formula (S-3) may exist consecutively or discontinuously. Similarly, the multiple constituent units represented by formula (S-4) may exist consecutively or discontinuously. That is, the copolymerization form of polymer Q is not particularly limited and can be any copolymerization form (e.g., random copolymerization, alternating copolymerization, block copolymerization, or graft copolymerization).

[0057] In one embodiment, polymer P may include the constituent units represented by formula (S-1) and formula (S-2), as well as the constituent units represented by formula (S-3) and / or formula (S-4). Also in one embodiment, polymer Q may include the constituent units represented by formula (S-3) and formula (S-4), as well as the constituent units represented by formula (S-1) and / or formula (S-2). Furthermore, in one embodiment, the polymer may include the constituent units represented by formula (S-1), formula (S-2), formula (S-3), and formula (S-4). Such polymer corresponds to polymer P and also to polymer Q.

[0058] <Method for synthesizing polymers> Polymers P and Q can be synthesized by known methods. For synthesis methods, please refer to the examples section below. The compounds used as polymerization components for synthesizing each polymer are commercially available or can be synthesized by known methods.

[0059] <Weight-average molecular weight of polymers> The larger the weight-average molecular weight of polymers P and Q, the higher the R content in one molecule of polymer P. 1 The density of the part and R in one molecule of polymerization Q 3 The density of the part tends to be high. As mentioned earlier, R 1 Part and R 3 This part is presumed to contribute to friction reduction. From the viewpoint of increasing the density, the weight-average molecular weight of polymer P and polymer Q is preferably 500 or more, and more preferably 800 or more, 1000 or more, 1500 or more, and 2000 or more, in that order. On the other hand, from the viewpoint of minimizing changes in the surface shape of the magnetic layer before and after repeated operation, the weight-average molecular weight of polymer P and polymer Q is preferably 30,000 or less, and more preferably 25,000 or less, 20,000 or less, 15,000 or less, and 10,000 or less, in that order. Minimizing changes in the surface shape of the magnetic layer before and after repeated operation is desirable from the viewpoint of suppressing the deterioration of the magnetic recording medium's performance after repeated operation.

[0060] In the present invention and this specification, weight-average molecular weight refers to the value obtained by measuring by gel permeation chromatography (GPC) and converting it to standard polystyrene.

[0061] <Polymer content> For example, a magnetic layer or magnetic layer-forming composition may contain 0.1 parts by mass or more, preferably 0.5 parts by mass or more, of one or more polymers selected from the group consisting of polymer P and polymer Q, per 100.0 parts by mass of ferromagnetic powder. The content of the polymer in the magnetic layer or magnetic layer-forming composition may be, for example, 50.0 parts by mass or less, 40.0 parts by mass or less, 30.0 parts by mass or less, 20.0 parts by mass or less, 10.0 parts by mass or less, 5.0 parts by mass or less, or 3.0 parts by mass or less, per 100 parts by mass of ferromagnetic powder. The polymer contained in the magnetic layer or magnetic layer-forming composition may be only one type or two or more types. If two or more types are included, the above content is the total content of those two or more types. If the non-magnetic layer and the composition for forming the non-magnetic layer contain the above polymer, the above description can be applied to the content of the above polymer in the non-magnetic layer and the composition for forming the non-magnetic layer by replacing the ferromagnetic powder with the non-magnetic powder.

[0062] Specific examples of polymer P include polymers P-1 to P-8 shown in the Examples section below. Specific examples of polymer Q include polymers Q-1 to Q-7 shown in the Examples section below. However, the present invention is not limited to these examples.

[0063] The magnetic layer and other components of the above-mentioned magnetic recording medium will be described in more detail below. <Magnetic layer> (Ferromagnetic powder) The magnetic layer contains ferromagnetic powder. As the ferromagnetic powder contained in the magnetic layer, one or more known ferromagnetic powders used in the magnetic layers of various magnetic recording media can be used in combination. Using ferromagnetic powder with a small average particle size is preferable from the viewpoint of improving recording density. From this viewpoint, the average particle size of the ferromagnetic powder is preferably 50 nm or less, more preferably 45 nm or less, even more preferably 40 nm or less, even more preferably 35 nm or less, even more preferably 30 nm or less, even more preferably 25 nm or less, and still even more preferably 20 nm or less. On the other hand, from the viewpoint of magnetization stability, the average particle size of the ferromagnetic powder is preferably 5 nm or more, more preferably 8 nm or more, even more preferably 10 nm or more, even more preferably 15 nm or more, and even more preferably 20 nm or more.

[0064] Hexagonal ferrite powder A preferred example of ferromagnetic powder is hexagonal ferrite powder. For details on hexagonal ferrite powder, see, for example, paragraphs 0012 to 0030 of Japanese Patent Publication No. 2011-225417, paragraphs 0134 to 0136 of Japanese Patent Publication No. 2011-216149, paragraphs 0013 to 0030 of Japanese Patent Publication No. 2012-204726, and paragraphs 0029 to 0084 of Japanese Patent Publication No. 2015-127985.

[0065] In the present invention and this specification, "hexagonal ferrite powder" refers to a ferromagnetic powder in which a hexagonal ferrite crystal structure is detected as the main phase by X-ray diffraction analysis. The main phase refers to the structure to which the highest intensity diffraction peak in the X-ray diffraction spectrum obtained by X-ray diffraction analysis belongs. For example, if the highest intensity diffraction peak in the X-ray diffraction spectrum obtained by X-ray diffraction analysis is attributed to the hexagonal ferrite crystal structure, it shall be determined that the hexagonal ferrite crystal structure has been detected as the main phase. If only a single structure is detected by X-ray diffraction analysis, this detected structure shall be considered the main phase. The hexagonal ferrite crystal structure contains at least iron atoms, divalent metal atoms, and oxygen atoms as constituent atoms. Divalent metal atoms are metal atoms that can become divalent cations as ions, and examples include strontium atoms, barium atoms, alkaline earth metal atoms such as calcium atoms, and lead atoms. In the present invention and this specification, hexagonal strontium ferrite powder refers to powder in which the main divalent metal atom contained is strontium, and hexagonal barium ferrite powder refers to powder in which the main divalent metal atom contained is barium. The main divalent metal atom refers to the divalent metal atom that accounts for the largest proportion on an atomic percentage basis among the divalent metal atoms contained in the powder. However, rare earth atoms are not included in the above divalent metal atoms. In the present invention and this specification, "rare earth atoms" are selected from the group consisting of scandium atoms (Sc), yttrium atoms (Y), and lanthanide atoms. Lanthanide atoms are selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0066] Below, we will describe hexagonal strontium ferrite powder, a form of hexagonal ferrite powder, in more detail.

[0067] The activation volume of the hexagonal strontium ferrite powder is preferably 800 to 1500 nm. 3 The activation volume is within the range described above. Finely milled hexagonal strontium ferrite powder exhibiting an activation volume within this range is suitable for the fabrication of magnetic recording media that exhibit excellent electromagnetic conversion properties. The activation volume of the hexagonal strontium ferrite powder is preferably 800 nm. 3 That's all, for example, 850nm 3 It can also be the above. Furthermore, from the viewpoint of further improving electromagnetic conversion characteristics, the activation volume of hexagonal strontium ferrite powder is 1400 nm. 3 The following is more preferable: 1300nm 3 It is even more preferable that the following occur: 1200 nm 3 It is even more preferable that the following conditions be met: 1100 nm 3 The following is even more preferable.

[0068] "Activation volume" is a unit of magnetization reversal and an indicator of the magnetic size of a particle. The activation volume and the anisotropy constant Ku described herein and below are values ​​obtained from the following relationship between Hc and activation volume V, measured using a vibrating sample type magnetometer at magnetic field sweep speeds of 3 minutes and 30 minutes in the coercivity Hc measurement section (measurement temperature: 23℃±1℃). Note that the unit of the anisotropy constant Ku is 1erg / cc = 1.0 × 10⁻⁶. -1 J / m 3 That is the case. Hc=2Ku / Ms{1-[(kT / KuV)ln(At / 0.693)] 1 / 2} [In the above formula, Ku: anisotropy constant (unit: J / m 3 ), Ms: Saturation magnetization (unit: kA / m), k: Boltzmann constant, T: Absolute temperature (unit: K), V: Activation volume (unit: cm) 3 ), A: Spin precession frequency (unit: s) -1 ), t: magnetic field reversal time (unit: s)]

[0069] As an indicator of reducing thermal fluctuations, or in other words, improving thermal stability, the anisotropy constant Ku can be cited. The hexagonal strontium ferrite powder is preferably 1.8 × 10⁻⁶ 5 J / m 3 It can have a Ku of the above, and more preferably 2.0 × 10 5 J / m 3 It can have a Ku content of the above. Also, the Ku content of hexagonal strontium ferrite powder is, for example, 2.5 × 10⁻⁶. 5 J / m 3 The following values ​​are possible. However, since a higher Ku value is preferable as it indicates higher thermal stability, the values ​​are not limited to those exemplified above.

[0070] Hexagonal strontium ferrite powder may or may not contain rare earth atoms. When hexagonal strontium ferrite powder contains rare earth atoms, it is preferable that the rare earth atoms are present at a concentration of 0.5 to 5.0 atomic percent (bulk concentration) per 100 atomic percent of iron atoms. In one embodiment, hexagonal strontium ferrite powder containing rare earth atoms may exhibit a segregation of rare earth atoms in the surface layer. In the present invention and this specification, "rare earth atom surface layer segregation" means that the rare earth atom content relative to 100% of iron atoms in a solution obtained by partially dissolving hexagonal strontium ferrite powder with acid (hereinafter referred to as "rare earth atom surface layer content" or simply "surface layer content" with respect to rare earth atoms) is different from the rare earth atom content relative to 100% of iron atoms in a solution obtained by completely dissolving hexagonal strontium ferrite powder with acid (hereinafter referred to as "rare earth atom bulk content" or simply "bulk content" with respect to rare earth atoms), Rare earth atom surface content / Rare earth atom bulk content > 1.0 This means that the ratio is satisfied. The rare earth atom content of hexagonal strontium ferrite powder described later is synonymous with the rare earth atom bulk content. In contrast, partial dissolution using acid dissolves the surface layer of the particles constituting the hexagonal strontium ferrite powder, so the rare earth atom content in the solution obtained by partial dissolution is the rare earth atom content in the surface layer of the particles constituting the hexagonal strontium ferrite powder. When the rare earth atom surface layer content satisfies the ratio "rare earth atom surface layer content / rare earth atom bulk content > 1.0", it means that in the particles constituting the hexagonal strontium ferrite powder, rare earth atoms are concentrated in the surface layer (i.e., there are more of them in the surface layer than in the interior). In this invention and specification, the surface layer means a part of the region extending from the surface to the interior of the particles constituting the hexagonal strontium ferrite powder.

[0071] When hexagonal strontium ferrite powder contains rare earth atoms, the rare earth atom content (bulk content) is preferably in the range of 0.5 to 5.0 atomic percent relative to 100 atomic percent of iron atoms. It is believed that containing rare earth atoms at the bulk content within the above range, and having the rare earth atoms unevenly distributed on the surface of the particles constituting the hexagonal strontium ferrite powder, contributes to suppressing the decrease in regeneration output during repeated regeneration. This is presumed to be because the anisotropy constant Ku can be increased by containing rare earth atoms at the bulk content within the above range, and having the rare earth atoms unevenly distributed on the surface of the particles constituting the hexagonal strontium ferrite powder. The higher the value of the anisotropy constant Ku, the more it is possible to suppress the occurrence of a phenomenon called thermal fluctuation (in other words, to improve thermal stability). By suppressing the occurrence of thermal fluctuation, the decrease in regeneration output during repeated regeneration can be suppressed. It is hypothesized that the uneven distribution of rare earth atoms on the surface of hexagonal strontium ferrite powder particles contributes to stabilizing the spin of iron (Fe) sites within the crystal lattice of the surface layer, thereby increasing the anisotropy constant Ku. Furthermore, it is presumed that using hexagonal strontium ferrite powder with a rare-earth atom uneven distribution on the surface as the ferromagnetic powder for the magnetic layer contributes to suppressing wear on the magnetic layer surface due to sliding with the magnetic head. In other words, it is presumed that hexagonal strontium ferrite powder with a rare-earth atom uneven distribution on the surface may also contribute to improving the running durability of the magnetic recording medium. This is presumed to be because the uneven distribution of rare-earth atoms on the surface of the particles constituting the hexagonal strontium ferrite powder contributes to improved interaction between the particle surface and organic substances (e.g., binders and / or additives) contained in the magnetic layer, resulting in improved strength of the magnetic layer. From the viewpoint of further suppressing the decrease in regeneration output during repeated regeneration and / or further improving running durability, the rare earth atom content (bulk content) is more preferably in the range of 0.5 to 4.5 atomic percent, even more preferably in the range of 1.0 to 4.5 atomic percent, and even more preferably in the range of 1.5 to 4.5 atomic percent.

[0072] The bulk content mentioned above is the content obtained by completely dissolving the hexagonal strontium ferrite powder. In this invention and specification, unless otherwise specified, the content of atoms refers to the bulk content obtained by completely dissolving the hexagonal strontium ferrite powder. The hexagonal strontium ferrite powder containing rare earth atoms may contain only one type of rare earth atom, or it may contain two or more types of rare earth atoms. When it contains two or more types of rare earth atoms, the bulk content mentioned above is determined for the sum of the two or more types of rare earth atoms. This also applies to other components in this invention and specification. That is, unless otherwise specified, a certain component may be used alone, or two or more types may be used. When two or more types are used, the content or content refers to the sum of the two or more types.

[0073] When hexagonal strontium ferrite powder contains rare earth atoms, the rare earth atoms included may be one or more of the rare earth atoms. From the viewpoint of further suppressing the decrease in regeneration output during repeated regeneration, preferred rare earth atoms include neodymium atoms, samarium atoms, yttrium atoms, and dysprosium atoms, with neodymium atoms, samarium atoms, and yttrium atoms being more preferred, and neodymium atoms being even more preferred.

[0074] In hexagonal strontium ferrite powder having a rare-earth atom surface segregation, the rare-earth atoms only need to be segregated in the surface layer of the particles constituting the hexagonal strontium ferrite powder, and the degree of segregation is not limited. For example, in hexagonal strontium ferrite powder having a rare-earth atom surface segregation, the ratio of the rare-earth atom surface content obtained by partial dissolution under the dissolution conditions described later to the rare-earth atom bulk content obtained by total dissolution under the dissolution conditions described later, "surface content / bulk content," is greater than 1.0 and can be 1.5 or greater. A "surface content / bulk content" greater than 1.0 means that in the particles constituting the hexagonal strontium ferrite powder, rare-earth atoms are segregated in the surface layer (i.e., there are more of them in the surface layer than in the interior). Furthermore, the ratio of the surface content of rare earth atoms obtained by partial dissolution under the dissolution conditions described later to the bulk content of rare earth atoms obtained by total dissolution under the dissolution conditions described later, "surface content / bulk content," can be, for example, 10.0 or less, 9.0 or less, 8.0 or less, 7.0 or less, 6.0 or less, 5.0 or less, or 4.0 or less. However, in hexagonal strontium ferrite powder having a rare earth atom surface distribution bias, the rare earth atoms only need to be biased towards the surface of the particles constituting the hexagonal strontium ferrite powder, and the above "surface content / bulk content" is not limited to the upper or lower limits exemplified.

[0075] The partial and total dissolution of hexagonal strontium ferrite powder is described below. For hexagonal strontium ferrite powder existing as a powder, the sample powders to be partially and completely dissolved are taken from the same lot of powder. On the other hand, for hexagonal strontium ferrite powder contained in the magnetic layer of a magnetic recording medium, a portion of the hexagonal strontium ferrite powder extracted from the magnetic layer is subjected to partial dissolution, and another portion is subjected to total dissolution. The extraction of hexagonal strontium ferrite powder from the magnetic layer can be carried out, for example, by the method described in paragraph 0032 of Japanese Patent Application Publication No. 2015-91747. Partial dissolution, as described above, refers to a state where the hexagonal strontium ferrite powder is dissolved to the extent that residual particles can be visually confirmed in the liquid at the end of the dissolution process. For example, partial dissolution can dissolve 10 to 20% by mass of the particles constituting the hexagonal strontium ferrite powder, with the total particles being 100% by mass. On the other hand, total dissolution, as described above, refers to a state where the hexagonal strontium ferrite powder is dissolved to the extent that no residual particles can be visually confirmed in the liquid at the end of the dissolution process. The above-mentioned partial dissolution and surface layer content measurement are performed, for example, by the following method. However, the dissolution conditions such as the amount of sample powder described below are examples only, and any dissolution conditions that enable partial and total dissolution can be arbitrarily adopted. A container (e.g., a beaker) containing 12 mg of sample powder and 10 mL of 1 mol / L hydrochloric acid is held on a hot plate at a set temperature of 70°C for 1 hour. The resulting solution is filtered through a 0.1 μm membrane filter. Elemental analysis of the resulting filtrate is performed using an inductively coupled plasma (ICP) analyzer. In this way, the surface content of rare earth atoms relative to 100% iron atoms can be determined. If multiple types of rare earth atoms are detected by elemental analysis, the total content of all rare earth atoms is taken as the surface content. This is also the case when measuring bulk content. On the other hand, the measurement of total dissolution and bulk content is performed, for example, by the following method. A container (e.g., a beaker) containing 12 mg of sample powder and 10 mL of 4 mol / L hydrochloric acid is held on a hot plate at a set temperature of 80°C for 3 hours. Afterward, the bulk content relative to 100 atomic percent of iron can be determined by performing the same procedure as described above for partial dissolution and surface layer content measurement.

[0076] From the perspective of increasing the playback output when reproducing data recorded on a magnetic recording medium, it is desirable for the mass magnetization σs of the ferromagnetic powder contained in the magnetic recording medium to be high. In this regard, hexagonal strontium ferrite powder containing rare earth atoms but lacking surface segregation of rare earth atoms tended to have a significantly lower σs compared to hexagonal strontium ferrite powder that does not contain rare earth atoms. In contrast, hexagonal strontium ferrite powder having surface segregation of rare earth atoms is considered preferable in order to suppress such a large decrease in σs. In one embodiment, the σs of hexagonal strontium ferrite powder is 45 A·m 2 It can be 47 A·m or more / kg. 2 It can also be more than / kg. On the other hand, σs is 80 A·m from the viewpoint of noise reduction. 2 Preferably less than / kg, at 60 A·m 2 It is more preferable that it be less than or equal to / kg. σs can be measured using a known measuring device capable of measuring magnetic properties, such as a vibrating sample magnetometer. In the present invention and this specification, unless otherwise specified, the mass magnetization σs is the value measured at a magnetic field strength of 1194 kA / m (15 kOe).

[0077] Regarding the constituent atom content (bulk content) of hexagonal strontium ferrite powder, the strontium atom content can be in the range of, for example, 2.0 to 15.0 atomic percent relative to 100 atomic percent of iron atoms. In one embodiment, hexagonal strontium ferrite powder may contain only strontium atoms as the divalent metal atom. In another embodiment, hexagonal strontium ferrite powder may contain one or more other divalent metal atoms in addition to strontium atoms. For example, it may contain barium atoms and / or calcium atoms. When other divalent metal atoms besides strontium atoms are included, the barium atom content and calcium atom content in the hexagonal strontium ferrite powder can be in the range of, for example, 0.05 to 5.0 atomic percent relative to 100 atomic percent of iron atoms.

[0078] The known crystal structures of hexagonal ferrite include magnetoplumbite (also called "M-type"), W-type, Y-type, and Z-type. Hexagonal strontium ferrite powder may have any of these crystal structures. The crystal structure can be confirmed by X-ray diffraction analysis. Hexagonal strontium ferrite powder may show a single crystal structure or two or more crystal structures by X-ray diffraction analysis. For example, in one embodiment, hexagonal strontium ferrite powder may show only the M-type crystal structure by X-ray diffraction analysis. For example, M-type hexagonal ferrite is AFe 12 O 19It is represented by the following compositional formula. Here, A represents a divalent metal atom, and if the hexagonal strontium ferrite powder is of type M, A is either only a strontium atom (Sr), or if A contains multiple divalent metal atoms, then as described above, strontium atoms (Sr) make up the largest proportion on an atomic percentage basis. The divalent metal atom content of hexagonal strontium ferrite powder is usually determined by the type of crystal structure of the hexagonal ferrite and is not particularly limited. The same applies to the iron atom content and oxygen atom content. Hexagonal strontium ferrite powder contains at least iron atoms, strontium atoms and oxygen atoms, and may also contain rare earth atoms. Furthermore, hexagonal strontium ferrite powder may or may not contain atoms other than these atoms. As an example, hexagonal strontium ferrite powder may contain aluminum atoms (Al). The aluminum atom content can be, for example, 0.5 to 10.0 atomic percent relative to 100 atomic percent of iron atoms. From the viewpoint of further suppressing the decrease in regeneration output during repeated regeneration, the hexagonal strontium ferrite powder contains iron atoms, strontium atoms, oxygen atoms, and rare earth atoms, and the content of atoms other than these atoms is preferably 10.0 atomic percent or less, more preferably in the range of 0 to 5.0 atomic percent, and may even be 0 atomic percent, relative to 100 atomic percent of iron atoms. That is, in one embodiment, the hexagonal strontium ferrite powder does not need to contain atoms other than iron atoms, strontium atoms, oxygen atoms, and rare earth atoms. The above content expressed in atomic percent is obtained by converting the content of each atom (unit: mass%) obtained by completely dissolving the hexagonal strontium ferrite powder into an atomic percent value using the atomic weight of each atom. Furthermore, in the present invention and this specification, "does not contain" for a certain atom means that the content measured by an ICP analyzer after complete dissolution is 0 mass%. The detection limit of an ICP analyzer is typically 0.01 ppm (parts per million) or less by mass. The term "does not contain" above is used to include the presence of substances in amounts below the detection limit of the ICP analyzer.Hexagonal strontium ferrite powder can, in one form, be bismuth-free (Bi).

[0079] metal powder A preferred specific example of ferromagnetic powder is ferromagnetic metal powder. For details on ferromagnetic metal powder, see, for example, paragraphs 0137-0141 of Japanese Patent Publication No. 2011-216149 and paragraphs 0009-0023 of Japanese Patent Publication No. 2005-251351.

[0080] ε-Iron oxide powder A preferred specific example of a ferromagnetic powder is ε-iron oxide powder. In the present invention and this specification, "ε-iron oxide powder" refers to a ferromagnetic powder in which the crystalline structure of ε-iron oxide is detected as the main phase by X-ray diffraction analysis. For example, if the highest intensity diffraction peak in the X-ray diffraction spectrum obtained by X-ray diffraction analysis is attributed to the crystalline structure of ε-iron oxide, it is determined that the crystalline structure of ε-iron oxide has been detected as the main phase. Methods for producing ε-iron oxide powder include methods from goethite and the reverse micelle method. All of the above production methods are publicly known. Furthermore, for methods for producing ε-iron oxide powder in which some of the Fe is substituted with substitution atoms such as Ga, Co, Ti, Al, and Rh, see, for example, J. Jpn. Soc. Powder Metallurgy Vol. 61 Supplement, No. S1, pp. S280-S284, J. Mater. Chem. C, 2013, 1, pp. 5200-5206, etc. However, the method for producing ε-iron oxide powder that can be used as ferromagnetic powder in the magnetic layer of the magnetic recording medium described above is not limited to the method described herein.

[0081] The activation volume of ε-iron oxide powder is preferably 300 to 1500 nm. 3 The activation volume is within the range described above. Micronized ε-iron oxide powder exhibiting the above activation volume range is suitable for the fabrication of magnetic recording media that exhibit excellent electromagnetic conversion properties. The activation volume of the ε-iron oxide powder is preferably 300 nm. 3 That's all, for example, 500nm3 It can also be the above. Furthermore, from the viewpoint of further improving electromagnetic conversion characteristics, the activation volume of ε-iron oxide powder is 1400 nm. 3 The following is more preferable: 1300nm 3 It is even more preferable that the following occur: 1200 nm 3 It is even more preferable that the following conditions be met: 1100 nm 3 The following is even more preferable.

[0082] The anisotropy constant Ku can be cited as an indicator of the reduction of thermal fluctuations, or in other words, the improvement of thermal stability. The ε-iron oxide powder is preferably 3.0 × 10 4 J / m 3 It can have a Ku of the above, and more preferably 8.0 × 10 4 J / m 3 It can have the above amount of Ku. Also, the amount of Ku in ε-iron oxide powder is, for example, 3.0 × 10⁻⁶. 5 J / m 3 The following values ​​are possible. However, a higher Ku value indicates higher thermal stability and is therefore preferable, so the values ​​are not limited to those exemplified above.

[0083] From the perspective of increasing the playback output when reproducing data recorded on a magnetic recording medium, it is desirable for the mass magnetization σs of the ferromagnetic powder contained in the magnetic recording medium to be high. In this regard, in one embodiment, the σs of ε-iron oxide powder is 8 A·m 2 It can be 12A·m or more / kg. 2 It can also be more than / kg. On the other hand, the σs of ε-iron oxide powder is 40 A·m from the viewpoint of noise reduction. 2 Preferably less than / kg, 35A·m 2 It is more preferable that the amount be less than or equal to / kg.

[0084] In the present invention and this specification, unless otherwise specified, the average particle size of various powders such as ferromagnetic powders shall be the value measured using a transmission electron microscope by the following method. The powder is photographed using a transmission electron microscope at a magnification of 100,000x, and the resulting image is printed on photographic paper or displayed on a screen to obtain a total magnification of 500,000x, thereby obtaining a photograph of the particles that make up the powder. From the obtained photographs of the particles, the target particles are selected, and their contours are traced with a digitizer to measure the size of the particles (primary particles). Primary particles are defined as independent particles that do not aggregate. The above measurements are performed on 500 randomly selected particles. The arithmetic mean of the particle sizes of these 500 particles is taken as the average particle size of the powder. As the transmission electron microscope, for example, a Hitachi H-9000 transmission electron microscope can be used. The particle size can be measured using known image analysis software, for example, Carl Zeiss KS-400 image analysis software. Unless otherwise specified, the average particle sizes described in the Examples section below are values ​​measured using a Hitachi H-9000 transmission electron microscope and Carl Zeiss KS-400 image analysis software. In the present invention and this specification, "powder" means a collection of multiple particles. For example, ferromagnetic powder means a collection of multiple ferromagnetic particles. Furthermore, a collection of multiple particles is not limited to a form in which the particles constituting the collection are in direct contact, but also includes forms in which binders, additives, etc., described later, are interposed between the particles. The word "particle" is sometimes used to refer to powder.

[0085] As a method for collecting sample powder from a magnetic recording medium for particle size measurement, for example, the method described in paragraph 0015 of Japanese Patent Application Publication No. 2011-048878 can be employed.

[0086] In the present invention and this specification, unless otherwise specified, the size of the particles constituting the powder (particle size) is determined by the shape of the particles observed in the above particle photograph. (1) In the case of needle-shaped, spindle-shaped, columnar (however, the height is greater than the longest diameter of the base), etc., the length of the long axis constituting the particle is expressed as the long axis length, (2) In the case of a plate or columnar shape (provided that the thickness or height is less than the longest diameter of the plate or base), it shall be expressed by the longest diameter of the plate or base. (3) If the shape is spherical, polyhedral, or of an unspecified shape, and the major axis constituting the particle cannot be determined from the shape, it shall be represented by the equivalent diameter of a circle. The equivalent diameter of a circle refers to the diameter obtained by the circular projection method.

[0087] Furthermore, the average needle-shape ratio of the powder refers to the arithmetic mean of the values ​​obtained for the 500 particles by measuring the length of the short axis of each particle, i.e., the short axis length, in the above measurement, and determining the (long axis length / short axis length) value for each particle. Here, unless otherwise specified, the short axis length refers to the length of the short axis constituting the particle in the above definition of particle size (1), the thickness or height in the case of (2), and in the case of (3), since there is no distinction between the long axis and the short axis, (long axis length / short axis length) is considered to be 1 for convenience. Unless otherwise specified, when the particle shape is specific, for example, in the case of definition (1) above, 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. In the case of definition (3), the average particle size is the average diameter (also called the average particle size or average particle diameter).

[0088] The content (filling rate) of ferromagnetic powder in the magnetic layer is preferably in the range of 50 to 90% by mass, and more preferably in the range of 60 to 90% by mass, relative to the total mass of the magnetic layer. The magnetic layer contains ferromagnetic powder, may contain a binder, and may optionally contain one or more further additives. A high filling rate of ferromagnetic powder in the magnetic layer is preferable from the viewpoint of improving recording density.

[0089] (Binder, curing agent) The above magnetic recording medium can be a coated magnetic recording medium, and the magnetic layer may contain a binder. The binder is one or more resins. Various resins commonly used as binders for coated magnetic recording media can be used as the binder. For example, as the binder, a resin selected from polyurethane resin, polyester resin, polyamide resin, vinyl chloride resin, acrylic resin copolymerized with styrene, acrylonitrile, methyl methacrylate, etc., cellulose resin such as nitrocellulose, epoxy resin, phenoxy resin, polyvinyl acetal, polyvinyl alkylal resin such as polyvinyl butyral can be used alone or in mixture of multiple resins. Among these, polyurethane resin, acrylic resin, cellulose resin, and vinyl chloride resin are preferred. These resins may be homopolymers or copolymers. These resins can also be used as binders in the non-magnetic layer and / or back coat layer described later. For more information on the above binders, see paragraphs 0028 to 0031 of Japanese Patent Application Publication No. 2010-24113. The binder content of the magnetic layer can be, for example, 1.0 to 30.0 parts by mass per 100.0 parts by mass of ferromagnetic powder. The average molecular weight of the resin used as a binder can be, for example, 10,000 to 200,000 as a weight-average molecular weight. Unless otherwise specified, the weight-average molecular weights described in the Examples section below were measured by gel permeation chromatography (GPC) under the following measurement conditions and are values ​​obtained on a standard polystyrene basis. The binder can be used in an amount of, for example, 1.0 to 30.0 parts by mass per 100.0 parts by mass of ferromagnetic powder. GPC device: HLC-8120 (manufactured by Tosoh Corporation) Column: TSK gel Multipore HXL-M (manufactured by Tosoh Corporation, 7.8mm ID (Inner Diameter) × 30.0cm) Eluent: Tetrahydrofuran (THF)

[0090] Furthermore, a curing agent can be used together with a resin that can be used as a binder. In one form, the curing agent can be a thermosetting compound, which is a compound that undergoes a curing reaction (crosslinking reaction) by heating, and in another form, it can be a photocurable compound, which undergoes a curing reaction (crosslinking reaction) by light irradiation. As the curing reaction progresses during the magnetic layer formation process, at least a portion of the curing agent may be included in the magnetic layer in a state where it has reacted (crosslinked) with other components such as the binder. This also applies to layers formed using a composition that contains a curing agent when the composition used to form other layers contains a curing agent. Preferred curing agents are thermosetting compounds, and polyisocyanates are preferred. For details on polyisocyanates, refer to paragraphs 0124 to 0125 of Japanese Patent Application Publication No. 2011-216149. The curing agent content of the magnetic layer forming composition can be, for example, 0 to 80.0 parts by mass per 100.0 parts by mass of the binder, and from the viewpoint of improving the strength of the magnetic layer, it can be 50.0 to 80.0 parts by mass.

[0091] (Additives) The magnetic layer may contain one or more additives as needed. An example of an additive is the curing agent mentioned above. Other additives that can be included in the magnetic layer include non-magnetic powders, lubricants, dispersants, dispersion aids, antifungal agents, antistatic agents, antioxidants, etc. For dispersants, see paragraphs 0061 and 0071 of Japanese Patent Application Publication No. 2012-133837. Dispersants may also be added to the composition for forming the non-magnetic layer. For dispersants that can be added to the composition for forming the non-magnetic layer, see paragraph 0061 of Japanese Patent Application Publication No. 2012-133837. Other non-magnetic powders that can be included in the magnetic layer include non-magnetic powders that can function as abrasives, and non-magnetic powders that can function as protrusion-forming agents that form appropriately protruding protrusions on the surface of the magnetic layer. Examples of abrasives include powders of alumina (Al2O3), silicon carbide, boron carbide (B4C), TiC, chromium oxide (Cr2O3), cerium oxide, zirconium oxide (ZrO2), iron oxide, and diamond, which are commonly used as abrasives for magnetic layers. Among these, alumina such as α-alumina, silicon carbide, and diamond powder are preferred. The abrasive content of the magnetic layer is preferably 1.0 to 20.0 parts by mass, more preferably 3.0 to 15.0 parts by mass, and even more preferably 4.0 to 10.0 parts by mass, per 100.0 parts by mass of ferromagnetic powder. The average particle size of the abrasive is, for example, in the range of 30 to 300 nm, and preferably in the range of 50 to 200 nm. Examples of protrusion-forming agents include carbon black and colloidal particles. The content of the protrusion-forming agent in the magnetic layer is preferably 0.1 to 10.0 parts by mass, more preferably 0.1 to 5.0 parts by mass, and even more preferably 0.5 to 5.0 parts by mass, per 100.0 parts by mass of ferromagnetic powder. The average particle size of the colloidal particles is preferably in the range of 90 to 200 nm, and more preferably in the range of 100 to 150 nm. The average particle size of the carbon black is preferably in the range of 5 to 200 nm, and more preferably in the range of 10 to 150 nm. In addition, known additives such as various polymers described in paragraphs 0030 to 0080 of Japanese Patent Application Publication No. 2016-051493 can also be used as additives.

[0092] In one embodiment, the magnetic recording medium may contain one or more fatty acid compounds selected from the group consisting of fatty acids, fatty acid esters, and fatty acid amides in the portion on the magnetic layer side of the non-magnetic support. The fatty acid compounds can function as lubricants. The portion on the magnetic layer side may contain only one fatty acid compound selected from the group consisting of fatty acids, fatty acid esters, and fatty acid amides, or it may contain two or more. Furthermore, it may contain only one type of fatty acid or two or more types of fatty acids. The same applies to fatty acid esters and fatty acid amides. Examples of fatty acids include lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, behenic acid, erucic acid, and elaidic acid, with stearic acid, myristic acid, and palmitic acid being preferred, and stearic acid being more preferred. The fatty acids may also be included in the magnetic layer in the form of salts such as metal salts. Examples of fatty acid esters include esters of the various fatty acids listed above. Specific examples include butyl myristate, butyl palmitate, butyl stearate, neopentyl glycol dioleate, sorbitan monostearate, sorbitan distearate, sorbitan tristearate, oleyl oleate, isocetyl stearate, isotridecyl stearate, octyl stearate, isooctyl stearate, amyl stearate, and butoxyethyl stearate. Examples of fatty acid amides include the amides of the various fatty acids listed above. Specific examples include lauric acid amide, myristic acid amide, palmitic acid amide, and stearic acid amide. With regard to fatty acids and fatty acid derivatives (amides, esters, etc.), it is preferable that the fatty acid-derived portion of the fatty acid derivative has a structure similar to or the same as the fatty acid used in combination. For example, when using stearic acid as the fatty acid, it is preferable to use stearic acid amide and / or stearic acid ester in combination. A magnetic recording medium containing one or more fatty acid compounds selected from the group consisting of fatty acids, fatty acid esters, and fatty acid amides in the magnetic layer portion can, in one embodiment, be manufactured by forming a magnetic layer using a magnetic layer-forming composition containing one or more of the above fatty acid compounds. Alternatively, in one embodiment, a magnetic recording medium containing one or more of the above fatty acid compounds in the magnetic layer portion can be manufactured by forming a non-magnetic layer using a non-magnetic layer-forming composition containing one or more of the above fatty acid compounds. Alternatively, in one embodiment, a magnetic recording medium containing one or more of the above fatty acid compounds in the magnetic layer portion can be manufactured by forming a non-magnetic layer using a non-magnetic layer-forming composition containing one or more of the above fatty acid compounds, and forming a magnetic layer using a magnetic layer-forming composition containing one or more of the above fatty acid compounds. The non-magnetic layer can hold and supply components that can function as lubricants, such as fatty acids, fatty acid esters, and fatty acid amides, to the magnetic layer. The lubricants such as fatty acids, fatty acid esters, and fatty acid amides contained in the non-magnetic layer may migrate to the magnetic layer and be present in the magnetic layer. The fatty acid content in the magnetic layer or magnetic layer forming composition is, for example, 0 to 3.0 parts by mass, preferably 0.5 to 3.0 parts by mass, per 100.0 parts by mass of ferromagnetic powder. The fatty acid ester content in the magnetic layer or magnetic layer forming composition is, for example, 0 to 10.0 parts by mass, preferably 0.5 to 7.0 parts by mass, per 100.0 parts by mass of ferromagnetic powder. The content of fatty acid amide in the magnetic layer or magnetic layer forming composition is, for example, 0 to 1.0 parts by mass per 100.0 parts by mass of ferromagnetic powder, preferably 0.1 to 1.0 parts by mass. Regarding the content of fatty acids, fatty acid esters, and fatty acid amides in the non-magnetic layer or composition for forming a non-magnetic layer, the above description can be applied by replacing the ferromagnetic powder with the non-magnetic powder. Regarding the mixing ratio of the polymer and the fatty acid compound in a magnetic layer or a composition for forming a magnetic layer, with the total amount (by mass) of the polymer and the fatty acid compound being 100% by mass, the ratio of the fatty acid compound can be 10% by mass or more, 15% by mass or more, 20% by mass or more, 25% by mass or more, 30% by mass or more, or 40% by mass or more, and can also be 90% by mass or less, 80% by mass or less, 70% by mass or less, or 60% by mass or less. The above points also apply to the mixing ratio of the polymer and the fatty acid compound in a non-magnetic layer or a composition for forming a non-magnetic layer.

[0093] The magnetic layer described above can be provided directly on the surface of a non-magnetic support, or indirectly via a non-magnetic layer.

[0094] <Nonmagnetic layer> Next, the non-magnetic layer will be described. The magnetic recording medium may have a magnetic layer directly on the surface of a non-magnetic support, or it may have a magnetic layer on the surface of a non-magnetic support via a non-magnetic layer containing non-magnetic powder. The non-magnetic powder used in the non-magnetic layer may be inorganic or organic powder. Carbon black can also be used. Examples of inorganic powders include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. These non-magnetic powders are commercially available and can also be manufactured by known methods. For details, see paragraphs 0146 to 0150 of Japanese Patent Application Publication No. 2011-216149. For carbon black that can be used in the non-magnetic layer, see paragraphs 0040 to 0041 of Japanese Patent Application Publication No. 2010-24113. The content (filling rate) of non-magnetic powder in the non-magnetic layer is preferably in the range of 50 to 90% by mass, and more preferably in the range of 60 to 90% by mass, relative to the total mass of the non-magnetic layer.

[0095] The non-magnetic layer may be a layer containing non-magnetic powder and a binder, and may further contain one or more additives. Regarding other details of the binder, additives, etc., of the non-magnetic layer, known technologies relating to non-magnetic layers can be applied. Furthermore, regarding, for example, the type and content of the binder, the type and content of the additives, known technologies relating to magnetic layers can also be applied.

[0096] In the present invention and this specification, the non-magnetic layer includes a substantially non-magnetic layer containing a small amount of ferromagnetic powder, for example as an impurity or intentionally, along with the non-magnetic powder. Here, a substantially non-magnetic layer means a layer in which the remanent magnetic flux density is 10 mT or less, the coercivity is 100 Oe or less, or the remanent magnetic flux density is 10 mT or less and the coercivity is 100 Oe or less. 1 [kOe] = 10 6 The magnetic field density is 4π [A / m]. It is preferable that the non-magnetic layer does not have residual magnetic flux density or coercivity.

[0097] <Nonmagnetic support> Next, we will describe non-magnetic supports (hereinafter also simply referred to as "supports"). Known non-magnetic supports include biaxially oriented polyethylene terephthalate, polyethylene naphthalate, polyamide, polyamide-imide, and aromatic polyamide. Among these, polyethylene terephthalate, polyethylene naphthalate, and polyamide are preferred. These supports may be subjected to pre-treatment such as corona discharge, plasma treatment, easy adhesion treatment, or heat treatment.

[0098] <Backcoat layer> The above magnetic recording medium may also have a back coat layer containing non-magnetic powder on the surface side opposite to the surface side having the magnetic layer of the non-magnetic support. Preferably, the back coat layer contains either or both carbon black and inorganic powder. The back coat layer may be a layer containing non-magnetic powder and a binder, and may further contain one or more additives. With regard to the binder and various additives that may be optionally included in the back coat layer, known technology relating to back coat layers can be applied, as can known technology relating to the formulation of magnetic layers and / or non-magnetic layers. For example, paragraphs 0018 to 0020 of Japanese Patent Application Publication No. 2006-331625 and lines 65 to 38 of column 5 of U.S. Patent No. 7,029,774 can be referenced with respect to the back coat layer.

[0099] <Various thicknesses> The thickness of the non-magnetic support is, for example, 3.0 to 80.0 μm, preferably 3.0 to 20.0 μm, more preferably 3.0 to 10.0 μm, and even more preferably 3.0 to 6.0 μm.

[0100] The thickness of the magnetic layer can be optimized according to the saturation magnetization of the magnetic head used, the head gap length, the bandwidth of the recording signal, etc. From the viewpoint of high-density recording, the thickness of the magnetic layer is preferably 10 nm to 150 nm, more preferably 20 nm to 120 nm, and even more preferably 30 nm to 100 nm. At least one magnetic layer is sufficient, and the magnetic layer may be separated into two or more layers having different magnetic properties, and known multilayer magnetic layer configurations can be applied. When separated into two or more layers, the thickness of the magnetic layer is the total thickness of these layers.

[0101] The thickness of the non-magnetic 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.

[0102] The thickness of the backcoat layer is preferably 0.9 μm or less, and more preferably in the range of 0.1 to 0.7 μm.

[0103] The thickness of each layer and non-magnetic support of a magnetic recording medium can be determined by known film thickness measurement methods. For example, a cross-section in the thickness direction of the magnetic recording medium can be exposed using a known method such as an ion beam or microtome, and then the exposed cross-section can be observed using a scanning electron microscope or a transmission electron microscope. Various thicknesses can be determined as the arithmetic mean of the thickness obtained at any one location in the cross-sectional observation, or the thickness obtained at two or more randomly selected locations (e.g., two locations). Alternatively, the thickness of each layer may be determined as the design thickness calculated from the manufacturing conditions.

[0104] <Contact angle> In one embodiment, the contact angle with water measured on the surface of the magnetic layer of the magnetic recording medium can be 90° or more. The inventors believe that this contact angle can serve as an indicator of the amount of polymer present in the magnetic layer portion. Furthermore, the inventors believe that including the polymer in the magnetic layer portion in an amount that results in a contact angle of 90° or more is preferable for further reducing the coefficient of friction after repeated running.

[0105] In the present invention and this specification, the contact angle with water measured on the surface of the magnetic layer is determined by the following method. In the present invention and this specification, "surface of the magnetic layer" is synonymous with the magnetic layer side surface of the magnetic recording medium.

[0106] (Measurement of contact angle) The contact angle is determined by dropping water onto the measurement points on the magnetic layer surface of the magnetic recording medium under measurement conditions of an ambient temperature of 20°C and relative humidity of 25%, and using the θ / 2 method. An example of the measurement conditions will be described later in the Examples section. Six locations are randomly selected on the magnetic layer surface, and the contact angle is measured at each of the six locations. The arithmetic mean of these six measurements is taken as the contact angle with respect to water measured on the surface of the magnetic layer of the magnetic recording medium under measurement.

[0107] The contact angle of the magnetic recording medium described above is preferably 90° or more, and may be 95° or more or 100° or more. From the viewpoint of maintaining the strength of the magnetic layer, the contact angle of the magnetic recording medium described above is preferably 120° or less, more preferably 115° or less, and even more preferably 110° or less. The unit of angle "°" is also written as degree.

[0108] The contact angle of the magnetic recording medium can be controlled, for example, by the amount of the polymer used in the manufacture of the magnetic recording medium.

[0109] <Method for manufacturing magnetic recording media> The process of preparing compositions for forming a magnetic layer, and optionally a non-magnetic layer and a back coat layer, typically includes at least a kneading step, a dispersion step, and mixing steps provided before and after these steps as needed. Each individual step may be divided into two or more stages. Components used in the preparation of each layer-forming composition may be added at the beginning or in the middle of any of the steps. Alternatively, individual raw materials may be added in two or more steps. Known techniques can be used to prepare each layer-forming composition. In the kneading step, it is preferable to use a kneader with strong kneading force, such as an open kneader, continuous kneader, pressure kneader, or extruder. Details of these kneading processes are described in Japanese Patent Publication No. 1-106338 and Japanese Patent Publication No. 1-79274. Furthermore, in order to disperse each layer-forming composition, one or more dispersion beads selected from the group consisting of glass beads and other dispersion beads can be used as a dispersion medium. Suitable dispersion beads include high-density dispersion beads such as zirconia beads, titania beads, and steel beads. The particle size (bead diameter) and packing density of these dispersed beads can be optimized for use. Known dispersers can be used. Each layer-forming composition may be filtered by a known method before being subjected to the coating process. Filtration can be performed, for example, by filter filtration. As filters used for filtration, for example, filters with a pore size of 0.01 to 3 μm (e.g., glass fiber filters, polypropylene filters, etc.) can be used.

[0110] The magnetic layer can be formed by directly applying the magnetic layer-forming composition onto the surface of a non-magnetic support, or by sequentially or simultaneously applying it in multiple layers with the non-magnetic layer-forming composition. The back coat layer can be formed by applying the back coat-forming composition onto the surface of the non-magnetic support opposite to the surface on which the magnetic layer is provided (or subsequently provided).

[0111] After the coating process, various treatments such as drying, magnetic layer orientation, and surface smoothing (calendar treatment) can be performed. Known techniques can be applied to the coating process and various treatments; for example, paragraphs 0051 to 0057 of Japanese Patent Application Publication No. 2010-24113 can be referenced. For example, vertical orientation can be performed as the orientation treatment. Vertical orientation can be performed by known methods such as using opposing magnets. In the orientation zone, the drying speed of the coated layer can be controlled by the temperature and airflow of the drying air and / or the transport speed of the magnetic recording medium in the orientation zone. Alternatively, the coated layer may be pre-dried before being transported to the orientation zone.

[0112] As described above, a servo pattern can be formed on the magnetic recording medium by known methods to enable tracking control of the magnetic head in a magnetic recording and playback device, control of the travel speed of the magnetic recording medium, and so on. "Formation of a servo pattern" can also be referred to as "recording of a servo signal." The magnetic recording medium may be a tape-shaped magnetic recording medium (magnetic tape) or a disk-shaped magnetic recording medium (magnetic disk). Below, the formation of a servo pattern will be explained using a magnetic tape as an example.

[0113] Servo patterns are typically formed along the longitudinal direction of the magnetic tape. Examples of control methods that utilize servo signals (servo control) include timing-based servo (TBS), amplitude servo, and frequency servo.

[0114] As indicated in ECMA (European Computer Manufacturers Association)-319, magnetic tapes conforming to the LTO (Linear Tape-Open) standard (commonly called "LTO tapes") employ a timing-based servo system. In this timing-based servo system, the servo pattern is composed of multiple pairs of non-parallel magnetic stripes (also called "servo stripes") arranged continuously along the longitudinal direction of the magnetic tape. The reason the servo pattern is composed of pairs of non-parallel magnetic stripes is to inform the servo signal reading element of its position as it passes over the servo pattern. Specifically, the pair of magnetic stripes is formed so that the spacing between them changes continuously along the width direction of the magnetic tape, and the servo signal reading element can determine the relative position between the servo pattern and the servo signal reading element by reading this spacing. This relative position information enables the tracking of data tracks. For this purpose, multiple servo tracks are usually set up on the servo pattern along the width direction of the magnetic tape.

[0115] A servo band consists of servo signals that run continuously along the longitudinal direction of the magnetic tape. Typically, multiple servo bands are provided on a magnetic tape. For example, in an LTO tape, there are five. The area between two adjacent servo bands is called the data band. A data band consists of multiple data tracks, each corresponding to a specific servo track.

[0116] In one embodiment, as shown in Japanese Patent Publication No. 2004-318983, each servo band has embedded information indicating the servo band number (also called "servo band ID (identification)" or "UDIM (Unique DataBand Identification Method) information"). This servo band ID is recorded by shifting a specific pair of servo stripes within a servo band so that its position is displaced relative to the longitudinal direction of the magnetic tape. Specifically, the method of shifting a specific pair of servo stripes is changed for each servo band. As a result, the recorded servo band ID is unique for each servo band, so that a servo band can be uniquely identified by reading it with a servo signal reading element.

[0117] Furthermore, one method for uniquely identifying a servo band is the staggered method, as described in ECMA-319. In this staggered method, a group of non-parallel magnetic stripes (servo stripes) arranged continuously along the longitudinal direction of the magnetic tape are recorded in a manner that shifts each servo band along the longitudinal direction of the magnetic tape. Since the combination of this shift between adjacent servo bands is unique across the entire magnetic tape, it is possible to uniquely identify a servo band when reading the servo pattern with two servo signal reading elements.

[0118] Furthermore, each servo band typically contains embedded information indicating its position along the longitudinal direction of the magnetic tape (also known as "LPOS (Longitudinal Position) information"), as described in ECMA-319. This LPOS information, like the UDIM information, is recorded by shifting the positions of a pair of servo stripes along the longitudinal direction of the magnetic tape. However, unlike the UDIM information, the same signal is recorded for each servo band in this LPOS information.

[0119] It is also possible to embed information other than the UDIM and LPOS information mentioned above into the servo bands. In this case, the embedded information may be different for each servo band, like the UDIM information, or it may be common to all servo bands, like the LPOS information. Furthermore, methods other than those described above can be used to embed information in the servo bands. For example, a predetermined code may be recorded by thinning out a predetermined pair from a group of servo stripes.

[0120] The servo pattern forming head is called a servo light head. The servo light head has a pair of gaps corresponding to the pair of magnetic stripes, for each servo band. Typically, a core and a coil are connected to each pair of gaps, and by supplying current pulses to the coils, the magnetic field generated in the core can create a leakage magnetic field in the pair of gaps. When forming a servo pattern, the servo pattern can be formed by inputting current pulses while running a magnetic tape over the servo light head, thereby transferring the magnetic pattern corresponding to the pair of gaps onto the magnetic tape. The width of each gap can be set appropriately according to the density of the servo pattern to be formed. For example, the width of each gap can be set to 1 μm or less, 1 to 10 μm, 10 μm or more, etc.

[0121] Before forming a servo pattern on a magnetic tape, it is usually demagnetized (erased). This erasing process can be performed by applying a uniform magnetic field to the magnetic tape using a DC or AC magnet. There are two types of erasing: DC (Direct Current) erasing and AC (Alternating Current) erasing. AC erasing is performed by gradually reducing the strength of the magnetic field while reversing the direction of the magnetic field applied to the magnetic tape. On the other hand, DC erasing is performed by applying a unidirectional magnetic field to the magnetic tape. There are two further methods of DC erasing. The first method is horizontal DC erasing, which applies a unidirectional magnetic field along the longitudinal direction of the magnetic tape. The second method is vertical DC erasing, which applies a unidirectional magnetic field along the thickness direction of the magnetic tape. The erasing process may be performed on the entire magnetic tape or on each servo band of the magnetic tape.

[0122] The direction of the magnetic field of the formed servo pattern is determined according to the direction of the erase. For example, when a magnetic tape is horizontally DC erased, the servo pattern is formed such that the direction of the magnetic field is opposite to the direction of the erase. This makes it possible to increase the output of the servo signal obtained by reading the servo pattern. As shown in Japanese Patent Application Publication No. 2012-53940, when a magnetic pattern using the above gap is transferred to a vertically DC erased magnetic tape, the servo signal obtained by reading the formed servo pattern is in the shape of a single-pole pulse. On the other hand, when a magnetic pattern using the above gap is transferred to a horizontally DC erased magnetic tape, the servo signal obtained by reading the formed servo pattern is in the shape of a double-pole pulse.

[0123] [Magnetic tape cartridge] One aspect of the present invention relates to a magnetic tape cartridge including the tape-shaped magnetic recording medium (i.e., magnetic tape).

[0124] Details of the magnetic tape included in the above magnetic tape cartridge are as described above.

[0125] In a magnetic tape cartridge, the magnetic tape is generally housed inside the cartridge body, wound onto a reel. The reel is rotatably mounted inside the cartridge body. Two types of magnetic tape cartridges are widely used: single-reel cartridges, which have one reel inside the cartridge body, and double-reel cartridges, which have two reels inside the cartridge body. When a single-reel magnetic tape cartridge is mounted in a magnetic recording / reproduction device for recording and / or reproducing data onto magnetic tape, the magnetic tape is pulled out from the cartridge and wound onto the reel on the magnetic recording / reproduction device side. A magnetic head is positioned in the magnetic tape transport path from the magnetic tape cartridge to the take-up reel. The magnetic tape is fed and wound between the reel on the magnetic tape cartridge side (supply reel) and the reel on the magnetic recording / reproduction device side (take-up reel). During this time, the magnetic head and the surface of the magnetic layer of the magnetic tape come into contact and slide against each other, enabling data recording and / or reproduction. In contrast, a dual-reel magnetic tape cartridge has both a supply reel and a take-up reel housed inside the magnetic tape cartridge. The magnetic tape cartridge may be either a single-reel or dual-reel type. The magnetic tape cartridge may contain a magnetic tape according to one aspect of the present invention, and prior art may be applied for other aspects.

[0126] [Magnetic recording and playback device] One aspect of the present invention relates to a magnetic recording and playback apparatus including the above-mentioned magnetic recording medium.

[0127] In the present invention and this specification, "magnetic recording and reproduction device" means a device capable of recording data onto a magnetic recording medium and reproducing data recorded on a magnetic recording medium, or at least one of the latter. Such a device is generally called a drive. The magnetic recording and reproduction device may be, for example, a sliding type magnetic recording and reproduction device. A sliding type magnetic recording and reproduction device is a device in which the surface of the magnetic layer and the magnetic head come into contact and slide when recording data onto a magnetic recording medium and / or reproducing recorded data. For example, the magnetic recording and reproduction device may include a magnetic tape cartridge that can be detachably attached.

[0128] The above magnetic recording and playback device may include a magnetic head. The magnetic head may be a recording head capable of recording data onto a magnetic recording medium, or a playback head capable of playing back data recorded on the magnetic recording medium. In one embodiment, the above magnetic recording and playback device may include both a recording head and a playback head as separate magnetic heads. In another embodiment, the magnetic head included in the above magnetic recording and playback device may have a configuration in which both an element for recording data (recording element) and an element for playing back data (playback element) are provided on a single magnetic head. Hereinafter, the elements for recording data and the elements for playing back data will be collectively referred to as "data elements". As the playback head, a magnetic head (MR head) that includes a magnetoresistive (MR) element as a playback element capable of sensitively reading data recorded on a magnetic recording medium is preferred. As the MR head, various known MR heads such as AMR (Anisotropic Magnetoresistive) heads, GMR (Giant Magnetoresistive) heads, and TMR (Tunnel Magnetoresistive) heads can be used. Furthermore, the magnetic head that records and / or reproduces data may include a servo signal reading element. Alternatively, a magnetic head equipped with a servo signal reading element (servo head) may be included in the magnetic recording and / or reproduction device as a separate head from the magnetic head that records and / or reproduces data. For example, a magnetic head that records and / or reproduces recorded data (hereinafter also referred to as the "recording and reproduction head") may include two servo signal reading elements, and each of the two servo signal reading elements may simultaneously read two adjacent servo bands. One or more data elements may be placed between the two servo signal reading elements.

[0129] In the above-described magnetic recording and reproduction apparatus, recording data onto a magnetic recording medium and / or reproducing data recorded on a magnetic recording medium can be performed, for example, by bringing the magnetic head into contact with the magnetic layer surface of the magnetic recording medium and sliding it. The above-described magnetic recording and reproduction apparatus may include a magnetic recording medium according to one aspect of the present invention, and prior art may be applied for other aspects.

[0130] For example, when recording data and / or playing back recorded data, tracking using servo signals is performed first. That is, by making a servo signal reading element follow a predetermined servo track, the data element is controlled to pass over the target data track. The movement of the data track is achieved by changing the servo track read by the servo signal reading element in the tape width direction. Furthermore, the recording / playback head can also record and / or play back data on other data bands. In this case, the servo signal reading element can be moved to a predetermined servo band using the UDIM information described above, and tracking for that servo band can be started.

[0131] [polymer] One aspect of the present invention relates to polymers P and Q. Details of polymers P and Q are as described above. In one embodiment, polymers P and Q may be compounds that do not contain fluorine atoms as constituent atoms of the compound.

[0132] Another aspect of the present invention is: One or more constituent units selected from the group consisting of constituent units represented by formula (S-1) and constituent units represented by formula (S-3), One or more constituent units selected from the group consisting of constituent units represented by formula (S-2) and constituent units represented by formula (S-4), A polymer containing at least Regarding this matter, the various constituent units contained in such polymers are as described above, and for further details, please refer to the previous descriptions concerning polymers P and Q. [Examples]

[0133] An embodiment of the present invention will be described below based on examples. However, the present invention is not limited to the embodiments shown in the examples. Unless otherwise specified, the "parts" and "%" mentioned below refer to "parts by mass" and "mass%", respectively. "eq" is equivalent and is a unit that cannot be converted to SI units. Furthermore, unless otherwise specified, the following processes and operations were carried out in an environment with a temperature of 20-25°C and a relative humidity of 40-60%. The room temperature was in the range of 20-25°C.

[0134] [Ferromagnetic powder] In the examples and comparative examples, the following hexagonal strontium ferrite was used as the ferromagnetic powder.

[0135] 1707g of SrCO3, 687g of H3BO3, 1120g of Fe2O3, 45g of Al(OH)3, 24g of BaCO3, 13g of CaCO3, and 235g of Nd2O3 were weighed out and mixed in a mixer to obtain a raw material mixture. The obtained raw material mixture was melted in a platinum crucible at a melting temperature of 1390°C. While stirring the molten material, the outlet at the bottom of the platinum crucible was heated, and the molten material was dispensed in a rod shape at approximately 6 g / second. The dispensed material was rolled and rapidly cooled using water-cooled twin rollers to produce an amorphous body. 280g of the prepared amorphous material was placed in an electric furnace and heated to 635°C (crystallization temperature) at a heating rate of 3.5°C / min. The temperature was maintained at this temperature for 5 hours to precipitate (crystallize) hexagonal strontium ferrite particles. Next, the crystalline material obtained above, containing hexagonal strontium ferrite particles, was coarsely ground in a mortar. 1000g of 1mm particle size zirconia beads and 800mL of 1% aqueous acetic acid solution were added to a glass bottle containing this ground material, and the mixture was dispersed in a paint shaker for 3 hours. After that, the resulting dispersion was separated from the beads and placed in a stainless steel beaker. The dispersion was allowed to stand at a liquid temperature of 100°C for 3 hours to dissolve the glass components, then precipitated using a centrifuge, washed by repeated decantation, and dried in a heating furnace at a furnace temperature of 110°C for 6 hours to obtain hexagonal strontium ferrite powder. The average particle size of the hexagonal strontium ferrite powder obtained above was 18 nm, and the activation volume was 902 nm. 3 The anisotropy constant Ku is 2.2 × 10⁻⁶. 5 J / m 3 , mass magnetization σs is 49A m 2 It was / kg. A sample powder of 12 mg was taken from the hexagonal strontium ferrite powder obtained above, and the elemental analysis of the filtrate obtained by partially dissolving this sample powder under the dissolution conditions exemplified earlier was performed using an ICP analyzer to determine the surface layer content of neodymium atoms. Separately, 12 mg of sample powder was taken from the hexagonal strontium ferrite powder obtained above, and the elemental analysis of the filtrate obtained by completely dissolving this sample powder under the dissolution conditions exemplified earlier was performed using an ICP analyzer to determine the bulk content of neodymium atoms. The neodymium atom content (bulk content) relative to 100 atomic percent of iron atoms in the hexagonal strontium ferrite powder obtained above was 2.9 atomic percent. Furthermore, the neodymium atom content in the surface layer was 8.0 atomic percent. The ratio of surface layer content to bulk content, "surface layer content / bulk content," was 2.8, confirming that neodymium atoms were concentrated in the surface layer of the particles.

[0136] The hexagonal ferrite crystal structure of the powder obtained above was confirmed by scanning with CuKα rays at a voltage of 45kV and intensity of 40mA, and measuring the X-ray diffraction pattern under the following conditions (X-ray diffraction analysis). The powder obtained above showed a magnetoplumbite-type (M-type) hexagonal ferrite crystal structure. Furthermore, the crystalline phase detected by X-ray diffraction analysis was a single phase of the magnetoplumbite type. PANalytical X'Pert Pro diffractometer, PIXcel detector Soller slit for incident and diffracted beams: 0.017 radians Fixed angle of dispersion slit: 1 / 4 degree Mask: 10mm Scatter prevention slit: 1 / 4 degree Measurement mode: Continuous Measurement time per step: 3 seconds Measurement speed: 0.017 degrees per second Measurement step: 0.05 degrees

[0137] The activation volume and anisotropy constant Ku of the hexagonal strontium ferrite powders described above were determined for each ferromagnetic powder using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.) and the method described above. Furthermore, the mass magnetization σs was measured using a vibrating sample type magnetometer (manufactured by Toei Kogyo Co., Ltd.) at a magnetic field strength of 1194 kA / m (15 kOe).

[0138] [Synthesis of polymer P-1] In a 500 mL three-necked flask, 50 mmol (18.73 g) of octadecyltrimethoxysilane, 35 mmol (4.77 g) of trimethoxymethylsilane, 15 mmol (2.69 g) of aminopropyltrimethoxysilane, and 39 mL of MEK (methyl ethyl ketone) were mixed and stirred. 20 mL of 0.05 N (normal) aqueous potassium hydroxide solution was added, and the mixture was heated to 60 °C for a polycondensation reaction to be carried out for 6 hours. After cooling, the reaction mixture was cooled, 60 mL of heptane was added, and the organic layer was extracted. The organic layer was washed twice sequentially with 39 mL of pure water, and then concentrated under conditions of 35 mmHg pressure and 40 °C. The product was re-slurred with acetone, filtered, and dried to obtain the polymer (polyorganosylsesquioxane) P-1.

[0139] [Synthesis of polymer P-2] In a 200 mL three-necked flask, 4 g of polymer P-1, 3.6 g of succinic anhydride, and 45 mL of THF (tetrahydrofuran) were mixed and the mixture was heated to 60 °C. 6.0 g of DBU (1,8-diazabicyclo[5,2,0]-7-undecene) was added and the mixture was stirred for 4 hours. After the reaction, the mixture was cooled to room temperature, 44 mL of 1 N hydrochloric acid aqueous solution was added, and the mixture was stirred for 1 hour. 45 mL of heptane was added, and the organic layer was extracted. The organic layer was washed twice sequentially with 45 mL of pure water, and then concentrated under conditions of 35 mmHg pressure and 40 °C. The product was re-slurred with acetone, filtered, and dried to obtain polymer (polyorganosylsesquioxane) P-2.

[0140] [Synthesis of polymers P-3 to P-8, synthesis of polymer R-1] The synthesis was carried out in the same manner as P-1, with changes to the type and / or amount of polymerization components used.

[0141] [Synthesis of Polymer Q-1] In a 500 mL three-necked flask, 37.5 mmol (13.45 g) of octadecylmethyldimethoxysilane, 12.5 mmol (2.04 g) of aminopropylmethyldimethoxysilane, and 100 mL of THF were mixed and stirred. 15 mL of 1N hydrochloric acid aqueous solution was added, and the mixture was heated to 50°C and the reaction was carried out for 6 hours. After the reaction mixture was cooled, 100 mL of heptane was added, and the organic layer was extracted. The organic layer was washed twice sequentially with 50 mL of pure water, and then concentrated under conditions of 35 mmHg pressure and 40°C. In a 100 mL three-necked flask, 1.25 g of the product and 5 g of toluene were mixed, and 2 μL of 50% cesium hydroxide aqueous solution was added, and the mixture was reacted at 120°C for 6 hours. After the reaction, the mixture was cooled, 10 μL of 0.01 N hydrochloric acid aqueous solution was added, and the mixture was washed twice sequentially with 10 mL of pure water. Finally, it was dried at a pressure of 35 mmHg and a temperature of 50°C to obtain polymer (polyorganosilicone) Q-1.

[0142] [Synthesis of Polymer Q-2] In a 100 mL three-necked flask, 9.07 g of polymer Q-1, 0.86 g of succinic anhydride, 21.5 mL of toluene, and 0.1 g of N,N-dimethylaminopyridine were mixed and the mixture was heated to 60°C. The mixture was stirred for 6 hours. After the reaction, the mixture was cooled to room temperature, 30 mL of 1N hydrochloric acid aqueous solution was added, and the mixture was stirred for 1 hour. 100 mL of heptane was added, and the organic layer was extracted. The organic layer was washed twice sequentially with 10 mL of pure water, and then concentrated under conditions of 35 mmHg pressure and 50°C. The product was re-slurred with acetone, filtered, and dried to obtain polymer (polyorganosilicone) Q-2.

[0143] [Synthesis of polymers Q-3 to Q-7, synthesis of polymer R-2] The synthesis was carried out in the same manner as Q-1, with changes to the type and / or amount of polymerization components used.

[0144] For each synthesized polymer, GPC measurements were performed under the following conditions, and the weight-average molecular weight was determined using standard polystyrene equivalents. Measuring device: Product name "TOSOH EcoSEC HCL-8320GPC", manufactured by Tosoh Corporation. Columns: Tosoh Corporation TOSOH TSKgel Guardcolumn SuperHZ-L, Super HZM-H, Super HZ4000, Super HZ2000 Measurement temperature: 40℃ Eluent: Tetrahydrofuran (THF) Sample concentration 0.1-0.2% by mass Flow rate: 0.35mL / min Detectors: RI (Refractive Index) detector, UV-VIS (Ultraviolet-Visible Absorption) detector (254nm) Molecular weight: on a standard polystyrene basis

[0145] The constituent units contained in each polymer synthesized above are shown below. In the following, the number in the lower right corner of each constituent unit represents the content of that constituent unit relative to 100 mol% of the total constituent units contained in that polymer.

[0146] [ka]

[0147] [Example 1] <Preparation of composition for forming a magnetic layer> The following components were kneaded in an open kneader, and then dispersed using a sand mill to obtain a dispersion. Ferromagnetic powder: 100.0 parts Additive A: 10.0 parts Polyurethane resin: (Byron® UR4800, manufactured by Toyobo Co., Ltd., functional group: SO3Na, functional group concentration: 70 eq / ton): 4.0 parts Polyvinyl chloride resin (Kaneka Corporation MR104): 10.0 parts Methyl ethyl ketone: 150.0 parts Cyclohexanone: 150.0 parts α-Al2O3 (average particle size: 100 nm): 6.0 parts Carbon black (average particle size: 20nm): 0.7 parts

[0148] The additive A described above is a polymer synthesized by the method described in paragraphs 0115 to 0123 of Japanese Patent Publication No. 2016-051493.

[0149] The dispersion obtained above was mixed with the following components, then subjected to sonication, and filtered using a filter with a pore size of 1 μm to prepare a composition for forming a magnetic layer. Polymer (see Table 1): See Table 1 Stearic acid: 0.5 parts Butyl stearate: 1.5 parts Stearic acid amide: 0.3 parts Methyl ethyl ketone: 110.0 parts Cyclohexanone: 110.0 parts Polyisocyanate compound (Colonate 3041, manufactured by Tosoh Corporation): 3.0 parts

[0150] <Preparation of composition for forming a non-magnetic layer> The following components were kneaded in an open kneader and then dispersed using a sand mill to obtain a dispersion. The obtained dispersion was filtered using a filter with a pore size of 1 μm to prepare a composition for forming a non-magnetic layer. Carbon Black: 100.0 parts DBP (Dibutyl phthalate) oil absorption: 100mL / 100g pH:8 BET (Brunauer-Emmett-Teller) specific surface area: 250m 2 / g Volatile content: 1.5% Polyurethane resin (Byron UR4800, manufactured by Toyobo Co., Ltd., functional group: SO3Na, functional group concentration: 70 eq / ton): 20.0 parts Vinyl chloride resin (functional group: OSO3K, functional group concentration: 70 eq / ton): 30.0 parts Trioctylamine: 4.0 parts Cyclohexanone: 140.0 parts Methyl ethyl ketone: 170.0 parts Stearic acid amide: 0.3 parts Toluene: 3.0 parts Polyisocyanate compound (Colonate 3041, manufactured by Tosoh Corporation): 5.0 parts

[0151] <Preparation of composition for forming backcoat layer> The following components were pre-mixed in a roll mill and then dispersed in a sand mill. To the resulting dispersion, 4.0 parts of polyester resin (Byron 500, manufactured by Toyobo Co., Ltd.), 14.0 parts of polyisocyanate compound (Coronate 3041, manufactured by Tosoh Corporation), and 5.0 parts of α-Al2O3 (manufactured by Sumitomo Chemical Co., Ltd.) were added, stirred, and then filtered to prepare a composition for forming a backcoat layer. Carbon black (average particle size: 40nm): 85.0 parts Carbon black (average particle size: 100nm): 3.0 parts Nitrocellulose: 28.0 parts Polyurethane resin: 58.0 parts Copper phthalocyanine dispersant: 2.5 parts Nipponran 2301 (manufactured by Tosoh Corporation): 0.5 parts Methyl isobutyl ketone: 0.3 parts Methyl ethyl ketone: 860.0 parts Toluene: 240.0 parts

[0152] <Manufacturing of magnetic recording media (magnetic tape)> Corona discharge treatment was applied to both surfaces of a biaxially oriented polyethylene naphthalate support with a thickness of 5.0 μm. On one surface of the polyethylene naphthalate support described above, a composition for forming a non-magnetic layer was applied so that the thickness of the non-magnetic layer after drying was 1.0 μm. Immediately thereafter, a composition for forming a magnetic layer was simultaneously applied on top of it so that the thickness of the magnetic layer after drying was 100 nm. While both layers were still wet, they were subjected to vertical orientation treatment using a cobalt magnet with a magnetic force of 0.5 T (Tesla) and a solenoid with a magnetic force of 0.4 T, followed by a drying treatment. Subsequently, a composition for forming a back coat layer was applied to the other surface of the polyethylene naphthalate support described above so that the thickness of the back coat layer after drying was 0.5 μm. Then, calendering was performed using a 7-stage calender consisting of metal rolls at a calender roll surface temperature of 100°C and a speed of 80 m / min. After that, magnetic tape was produced by slitting to a width of 1 / 2 inch (1 inch = 0.0254 meters).

[0153] [Examples 2-18, Comparative Examples 1 and 2] A magnetic tape was prepared using the method described for Example 1, except that the items shown in Table 1 below were changed as shown in Table 1.

[0154] [Evaluation Method] <Contact angle> For each magnetic tape in the examples and comparative examples, the contact angle was determined using the method described above. Specifically, the contact angle was determined using the following method. Sample pieces were cut from each magnetic tape in the examples and comparative examples. The contact angle with respect to water was measured on the magnetic layer surface of the sample piece using a contact angle measuring instrument (DropMaster700, manufactured by Kyowa Interface Science Co., Ltd.) according to the following method. The contact angle was measured in an ambient temperature of 20°C and a relative humidity of 25%. The sample piece described above was placed on a microscope slide so that the backcoat layer surface was in contact with the slide glass surface. 2.0 μL of measurement liquid (water) was dropped onto the surface of the sample piece (magnetic layer surface), and after visually confirming that the dropped liquid had formed a stable droplet, the droplet image was analyzed using FAMAS, the contact angle analysis software attached to the contact angle measuring instrument, and the contact angle between the sample piece and the droplet was measured. The contact angle was calculated using the θ / 2 method. Six locations were randomly selected on the magnetic layer surface, and the contact angle was measured at each of the six locations. The arithmetic mean of these six measurements was taken as the contact angle of the magnetic tape being measured. Method: Droplet method (θ / 2 method) Droplet recognition: automatic Droplet detection line (distance from needle tip): 50 dots Algorithm: Automatic Image Mode: Frame Threshold level: Automatic

[0155] The measured contact angles were ranked according to the following evaluation criteria. For magnetic tapes ranked A, the contact angle was between 95° and 110°. (Evaluation Criteria) A: Contact angle of 95° or more B: Contact angle between 90° and less than 95° C: Contact angle less than 90°

[0156] <Friction> The frictional properties of each magnetic tape in the examples and comparative examples were evaluated by the following method. Under controlled ambient temperature of 13°C and relative humidity of 80%, a magnetic head removed from an IBM LTO(registered trademark) G7 (Linear Tape-Open Generation 7) drive was attached to the tape transport system. A 20m long magnetic tape was repeatedly run at 4.0m / second (10,000 cycles) while applying a tension of 0.6N (Newtons), with the tape being fed from the feed roll and wound onto the take-up roll. In the first cycle of running and the 10,000th cycle of running, the frictional force applied to the magnetic head during running was measured using a strain gauge, and the friction coefficient μ value was obtained from the measured frictional force. The friction coefficient after repeated running was evaluated based on the following evaluation criteria from the measured μ value. Evaluation result A or B is preferable, and A is most preferable. (Evaluation criteria) A: The μ value is less than 0.08 B: The μ value is 0.08 or more and 0.12 or less C: The μ value exceeds 0.12

[0157] <Abrasion resistance> For each magnetic tape of the examples and comparative examples, the abrasion resistance was evaluated by the following method. In an environment with an ambient temperature of 23°C and a relative humidity of 10%, an alumina ball with a diameter of 4 mm was repeatedly run 20 times with a load of 20 g on the magnetic layer surface of each magnetic tape. The magnetic layer surface after running was observed with an optical microscope (magnification: 200 times), and the abrasion resistance was evaluated according to the following evaluation criteria. (Evaluation criteria) A: No scratches are confirmed on the magnetic layer surface in the field of view of the optical microscope B: Scratches are confirmed at 1 to 5 locations or less on the magnetic layer surface in the field of view of the optical microscope C: Scratches are confirmed at 6 or more locations on the magnetic layer surface in the field of view of the optical microscope

[0158] <Reduction rate of protrusions (evaluation of surface shape change of magnetic layer before and after repeated running)> For each magnetic tape of the examples and comparative examples, the number of protrusions with a height of 5 nm or more on the magnetic layer surface was determined by the following method for the non-run magnetic tape and the magnetic tape after repeated running in the above environment, respectively. The number of protrusions with a height of 5 nm or more can be determined by measurement using an atomic force microscope (AFM). Specifically, in the planar image of the magnetic layer surface obtained by AFM, a plane where the volume of the convex and concave components in the measurement area is equal is defined as the reference plane, and the number of protrusions with a height of 5 nm or more is determined from this reference plane. Note that among the protrusions with a height of 5 nm or more present in the measurement area, there may be protrusions that are partially within the measurement area and partially outside of it. When determining the number of protrusions, such protrusions should also be included in the measurement. The measurement area for AFM measurements is a 5 μm square (5 μm × 5 μm) region on the surface of the magnetic layer. Measurements are performed at three different measurement areas on the surface of the magnetic layer (n=3). The number of protrusions with a height of 5 nm or more is determined by the arithmetic mean of the three values ​​obtained from these measurements. The following measurement conditions are adopted for AFM. An AFM (Veeco Nanoscope 4) in tapping mode will be used to measure a 5μm square (5μm x 5μm) area on the surface of the magnetic layer of a magnetic tape. A BRUKER RTESP-300 probe will be used, with a resolution of 512 pixels x 512 pixels and a scan speed of 341 seconds to measure one screen (512 pixels x 512 pixels). The surface shape change of the magnetic layer before and after repeated operation was evaluated based on the protrusion reduction rate calculated using the following formula, according to the evaluation criteria below. A smaller protrusion reduction rate indicates that the surface shape change of the magnetic layer before and after repeated operation is suppressed. Protrusion reduction rate (%) = [(Number of protrusions found on unrunned magnetic tape) - (Number of protrusions found on magnetic tape after repeated runs) / (Number of protrusions found on unrunned magnetic tape)] × 100 (Evaluation Criteria) A: Protrusion reduction rate is 40% or less B: Protrusion reduction rate is between 40% and less than 70% C: Protrusion reduction rate is 70% or more

[0159] The results are shown in Table 1 (Tables 1-1 and 1-2).

[0160] [Table 1-1]

[0161] [Table 1-2]

[0162] The results shown in Table 1 confirm that the magnetic tapes of Examples 1 to 18 have a low coefficient of friction after repeated use. Furthermore, the results shown in Table 1 also confirm that the magnetic tapes of Examples 1 to 18 have excellent scratch resistance. [Industrial applicability]

[0163] One aspect of the present invention is useful in the field of high-density magnetic recording media.

Claims

1. A magnetic recording medium having a non-magnetic support and a magnetic layer containing ferromagnetic powder, In the portion of the non-magnetic support on the magnetic layer side, A polymer P comprising at least one constituent unit represented by the following formula (S-1) and one constituent unit represented by the following formula (S-2), and Polymer Q comprising at least one constituent unit represented by the following formula (S-3) and one constituent unit represented by the following formula (S-4), A magnetic recording medium comprising one or more polymers selected from the group consisting of the following; 【Chemistry 1】 In formula (S-1), R １ L represents a monovalent aromatic group or a monovalent hydrocarbon group having 6 or more carbon atoms. １ represents a single bond or a divalent group; In formula (S-2), R ２ represents a monovalent polar group, L ２ represents a single bond or a divalent group; 【Chemistry 2】 In formula (S-3), R ３ L represents a monovalent aromatic group or a monovalent hydrocarbon group having 6 or more carbon atoms. ３ represents a single bond or a divalent group, R １１ represents an alkyl group; In formula (S-4), R ４ represents a monovalent polar group, and L ４ represents a single bond or a divalent group, and R １２ represents an alkyl group.

2. The portion of the non-magnetic support on the magnetic layer side contains polymer P, and In the above formula (S-1), R １ The magnetic recording medium according to claim 1, wherein is a monovalent aromatic group or a monovalent hydrocarbon group having 8 to 50 carbon atoms.

3. In the above formula (S-2), R ２ -COOH, -SO ３ H, -NH ２ , -OH, -C(O)NH ２ , -NHC(O)NH ２ The magnetic recording medium according to claim 2, or representing an epoxy group.

4. In the above formula (S-2), R ２ -COOH, -SO ３ H, -NH ２ , -OH, -C(O)NH ２ or -NHC(O)NH ２ A magnetic recording medium according to claim 2, which represents the magnetic recording medium described in claim 2.

5. The magnetic recording medium according to claim 4, wherein polymer P contains more than 30 mol% of a constituent unit represented by formula (S-1) based on 100 mol% of all constituent units contained in the polymer.

6. The portion of the non-magnetic support on the magnetic layer side contains polymer Q, and In the above formula (S-3), R ３ The magnetic recording medium according to claim 1, wherein is a monovalent aromatic group or a monovalent hydrocarbon group having 8 to 50 carbon atoms.

7. In the above formula (S-4), R ４ -COOH, -SO ３ H, -NH ２ , -OH, -C(O)NH ２ , -NHC(O)NH ２ The magnetic recording medium according to claim 6, or representing an epoxy group.

8. In the above formula (S-4), R ４ -COOH, -SO ３ H, -NH ２ , -OH, -C(O)NH ２ or -NHC(O)NH ２ A magnetic recording medium according to claim 6, representing the above.

9. The magnetic recording medium according to claim 8, wherein polymer Q contains more than 30 mol% of a constituent unit represented by formula (S-3) based on 100 mol% of all constituent units contained in the polymer.

10. The magnetic recording medium according to claim 1, further comprising one or more fatty acid compounds selected from the group consisting of fatty acids, fatty acid esters, and fatty acid amides in the portion of the non-magnetic support that is on the magnetic layer side.

11. The magnetic recording medium according to claim 1, further comprising a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer.

12. The magnetic recording medium according to claim 1, further comprising a back coat layer containing non-magnetic powder on the surface side of the non-magnetic support opposite to the surface side having the magnetic layer.

13. The magnetic recording medium according to claim 1, wherein it is a magnetic tape.

14. The portion of the non-magnetic support on the magnetic layer side further contains one or more fatty acid compounds selected from the group consisting of fatty acids, fatty acid esters, and fatty acid amides. The non-magnetic support and the magnetic layer further comprise a non-magnetic layer containing non-magnetic powder. The non-magnetic support further has a back coat layer containing non-magnetic powder on the surface side opposite to the surface side having the magnetic layer, and The magnetic recording medium according to claim 6, wherein it is a magnetic tape.

15. The portion of the non-magnetic support on the magnetic layer side further contains one or more fatty acid compounds selected from the group consisting of fatty acids, fatty acid esters, and fatty acid amides. The non-magnetic support and the magnetic layer further comprise a non-magnetic layer containing non-magnetic powder. The non-magnetic support further has a back coat layer containing non-magnetic powder on the surface side opposite to the surface side having the magnetic layer, and The magnetic recording medium according to claim 9, wherein it is a magnetic tape.

16. A magnetic tape cartridge comprising the magnetic tape described in any one of claims 13 to 15.

17. A magnetic recording and regeneration apparatus including a magnetic recording medium according to any one of claims 1 to 15.

18. Polymer P comprising at least one constituent unit represented by the following formula (S-1) and one constituent unit represented by the following formula (S-2); 【Transformation 3】 In formula (S-1), R １ L represents a monovalent aromatic group or a monovalent hydrocarbon group having 6 or more carbon atoms. １ represents a single bond or a divalent group; In formula (S-2), R ２ represents a monovalent polar group, L ２ represents a single bond or a divalent group.

19. Polymer Q comprising at least the constituent units represented by the following formula (S-3) and the constituent units represented by the following formula (S-4); 【Chemistry 4】 In formula (S-3), R ３ L represents a monovalent aromatic group or a monovalent hydrocarbon group having 6 or more carbon atoms. ３ represents a single bond or a divalent group, R １１ represents an alkyl group; In formula (S-4), R ４ represents a monovalent polar group, L ４ represents a single bond or a divalent group, R １２ represents an alkyl group.

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